Reinforced Plastics Handbook, Third Edition

Reinforced Plastics Handbook Third edition Donald V. Rosato PlasticSource, Concord, MA, USA

Dominick V. Rosatot Chatham, MA, USA

UK USA JAPAN

Elsevier Ltd, The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK Elsevier Inc, 360 Park Avenue South, New York, NY 10010-1710, USA Elsevier Japan, Tsunashima Building Annex, 3-20-12 Yushima, Bunkyo-ku, Tokyo 113, Japan

9 2004 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic tape, mechanical, photocopying, recording or otherwise, without permission in writing from the publishers. First edition 1994 Second edition 1998

British Library Cataloguing in Publication Data Rosato, Donald V. (Donald Vincent), 1947Reinforced plastics handbook.- 3rd ed. 1. Reinforced plastics- Handbooks, manuals, etc. I. Title II. Rosato, Dominick V. III. Murphy, John, 1934 May 23668.4'94 ISBN 1 8561 74506 No responsibility is assumed by the Publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein. Published by Elsevier Advanced Technology, The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK Tel: +44(0) 1865 843000 Fax: +44(0) 1865 843971 Typeset by Land & Unwin (Data Sciences) Ltd, Bugbrooke Printed and bound in Great Britain by MPG Books Ltd, Bodmin, Cornwall

Contents

Preface and Acknowledgement About the Authors Abbreviations Chapter 1

Chapter 2

INTRODUCTION Overview Commodity and Engineering Plastics Performances Composites Advantages and Limitations Responsibility Commensurate with Ability REINFORCEMENTS

Overview Glass Fibers Long Fibers In-Line Compounding Aspect Ratios Woven Constructions Nonwoven Constructions Glass for Special Reinforcements Glass, Silica, Quartz Fibers Glass Characteristics Glass fiber types Nylon Fibers Polyester Fibers Polyethylene Fibers Hybrid fibers

xv

xix xxi 1

1 14 14 16 18 23 24 24 28 33 34 37 37 37 38 41 41 44 55 55 56 57

iv Contents

Chapter 3

Other Fibers and Reinforcements Overview Natural Fibers Mineral Fibers Forms of Reinforcements Three-Dimensional Reinforcements Surface Tissues Conductive Nonwovens High Performance Reinforcements Aramid Fibers Carbon Fibers Graphite Fibers Boron Fibers Silica Fibers Quartz Fibers Fiber/Filament Characteristics Reinforcement Fabrics and Forms

57 57 59 63 65 65 65 66 68 68 71 75 77 80 80 80 97

PLASTICS Family of Plastics Definitions Thermoplastics Crystalline Plastics Amorphous Plastics Liquid Crystal Polymers Molding Processes Thermoplastic Types Acetals Nylons Polyarylates Polycarbonates Polyesters, TP Polyethylenes Polypropylenes Polystyrenes Polyvinyl Chlorides High Performance Thermoplastics Thermoset Plastics Thermoset Plastic Types Epoxies Phenolics Polyesters, TS Vinyl Esters

109 109 112 113 114 114 115 116 117 117 117 121 121 122 123 124 125 126 126 133 136 136 137 139 148

Contents v

Chapter 4

High Performance Thermoset Resins Specialty Thermoset Resins Crosslinked Plastics Natural Resins Compounding and Alloying Surface Waviness/Low Shrink Profile Concentrates Fillers Additives Recycling Overview Analyzing Materials Detailed Analyses Recycling Technologies Reinforced Thermosets Reinforced Thermoplastics Applications Definitions Value Analysis of Recycling Potential Chemistry of Plastics Thermoset Plastics Thermoplastics Molecular Structures/Property/Processes Viscosities: Newtonian & Non-Newtonian Rheology and Viscoelasticity Viscoelasticity Polymer Structure Viscoelasticity Behaviors Summary

151 154 157 158 158 159 159 159 161 171 171 174 176 180 184 189 190 192 193 193 194 195 199 201 201 203 2O5 208 210

C O M P O U N D CONSTRUCTIONS Overview Compounding Materials Prepregs Sheet Molding Compounds, Thermosets Low Pressure Molding Compounds VE Molding Compounds Sheet Molding Compounds, Thermoplastics Glass Mat Thermoplastics Powder Impregnations Commingled Glass/Thermoplastics Filaments Hot Compaction Technology Bulk Molding Compounds, Thermosets

212 212 214 216 221 229 229 230 231 234 236 236 238

vi Contents

Chapter 5

Bulk Molding Compounds, Thermoplastics Laminar Composites Molding Compounds Factors for Compounding Compounding Basics

242 243 244 247 248

FABRICATING PROCESSES

254 254 261 263 263 269 270 270 271 275 280 280 282 282 283 283 285 287 290 291 292 293 293 293 300 300 301 301 302 303 304 307 307 309 309 310 311

Overview Fabricating Startup and Shutdown Reinforced Thermoplastics Curing Systems Mold Release Processing & Patience Reinforcement Patterns Preform Processes Compression Moldings Compression Transfer Moldings Cold Press Moldings Hot Press Moldings Flexible Plunger Moldings Flexible Bag Moldings Laminates Hand Lay-ups Bag Moldings Vacuum Bag Moldings Vacuum Bag Molding and Pressures Autoclave Moldings Autoclave Press Claves Wet Lay-Ups Spray-Ups Bag Molding Hinterspritzen Contact Moldings Squeeze Moldings Soluble Core Moldings Lost-Wax Moldings Marco Processes Reinforced Resin Transfer Moldings Equipment Mixing Technologies Improvement of Resin Flow and Injection Improved Process Controls Feeding and Cleaning Preform Systems

Contents vii

Automations RTM Melt Resin Filling Monitoring Bladder Molding with RRTM Advanced RTM RTM Molding with Phenolics RTM Molding with Epoxies Autoclave to VARTM Case Histories Infusion Molding SCRIMP Process Injection Moldings Molding Reinforced Thermoplastics Injection-Compression Moldings Vacuum-Assisted Resin Injection Moldings Overmoldings D-LIFT Extruder/Injection Processes Pushtrusion/Injection Processes Injection Molding ZMC Liquid Injection Moldings Pulsed Moldings Pultrusions Continuous Laminations Other techniques Extrusions Pushtrusion/Extrusion Processes Pulsed Melts Thermoformings Reinforced Reaction Injection Moldings RIM Infusion Technology Polyurethane Processes Rotational Moldings Blow Moldings Foams Foamed Reservoir Moldings Syntactic Cellular Plastics Centrifugal Moldings Encapsulations Castings Stampings Cold Formings Comoform Cold Moldings Filament Windings Tape Windings

311 313 314 315 316 317 317 319 320 323 325 329 330 330 331 334 335 336 336 338 340 342 343 345 347 348 348 350 351 352 357 361 364 366 367 367 367 368 369 370 371 371 383

viii Contents

Fabricating RP Tanks Processing, Equipment, Products Filament Winding Terms Calendering Powder Metallurgy Processing Fundamentals Melt Flow Analysis Processing and Thermal Interface Process Control Processing Window Process Control and Patience Processing and Moisture Drying Operations Machines Not Alike Plasticator Melting Operation Screw Mixing Screw Wear Wear Resistant Barrel Barrel Heating & Cooling Method Purging Tools Overview Contact Molds Autoclave Molds Cold Press Molds (low pressure) Resin Transfer Molds Filament Winding Molds Injection and Compression Molds Mold Design for RRIM Assembly/Joining/Finishing Joining, Fastening Adhesive Bonding Joints and Adhesives Consolidations Paintings, Surface Finishing Washing Equipment Solvent Recovery Systems Troubleshooting Repairs Energy Upgrading Plant FALLO Approach

383 385 390 395 397 398 398 399 399 403 406 406 407 408 409 409 413 414 414 415 417 418 418 425 429 429 429 431 433 451 453 459 461 464 465 466 470 470 470 475 476 477

480

Contents ix

Chapter 6

Chapter 7

MARKETS/PRODUCTS Overview Buildings and Constructions Bathtubs Walkways/Bridges/Fences Roofs Infrastructures Plastics Lumber Pallets Heat Resistant Column Transportation Design Concepts Automobiles Buses Trucks Tanks Hopper Rail Car Tanks Highway Tanks Corrosion-Resistant Tanks Underground Storage Tanks Rocket Motor Tanks Cryogenic Fuel Tanks Marine Boats Underwater Hulls Windmills Overview Underwater Blades Fabrication Appliances, Electrical/Electronic Consumer and Other Products Aerospace Aircraft Turbine Engine Fan Blades All Plastic Airplanes Wright Brothers Flying Machine Replica Atmospheric Flights Chemical Propulsion Exhausts

483

DESIGNS

613

Overview Practical and Engineering Approaches Increase Properties

613 620 622

483 485 490 490 491 494 499 501 501 502 5O3 513 528 529 53O 53O 535 536 537 543 543 543 544 554 554 554 557 558 559 561 564 564 585 586 592 593 602

x Contents

Formabilities Surface Stresses and Deformations Design Approaches Design Foundations Theory of Elasticities and Materials Reinforced Plastic Performances Design Detractor and Constrain Design Analysis Processes Design Accuracies Design Failure Theory Design and Product Liabilities Stress-Strain Behaviors Rigidities (EIs) Hysteresis Effects Vibration Suppression" Isolation and Damping Poisson's Ratios Tolerances/Shrinkages Stress Whitening Static Stresses Tensile Stress-Strains Flexural Stress-Strains Compressive Stress-Strains Shear Stress-Strains Residual Stresses Dynamic Stresses Creep and Fatigue Tests Dynamic/Static Mechanical Behaviors Impacts Frictions Rain Erosions Directional Properties Orientation Terms Heterogeneous/Homogeneous/ Anisotropic Properties Facts and Myths- RP Behavior Orientation of Reinforcement Anisotropic RP Design Shapes Bars Columns Euler's Formula Torsional Bars

624 625 626 634 642 643 646 646 651 651 652 652 653 653 655 657 658 660 662 664 670 672 674 675 675 675 689 691 692 694 696 698 700 701 701 701 703 704 704 705

708

Contents xi

Filament Windings Netting Analyses Pressure Hull Structures Springs Leaf Springs Cantilever Springs Torsional Beam Springs Special Springs Sandwiches Design Approaches Optimizing Structures Stiffnesses and Bucklings Structural Foams Finite Element Analyses Constant Stress Applications Prototypes Need for Prototyping Prototype Products Prototype Techniques Prototype Testing and Evaluation Computer-Aided Designs Computer-Integrated Manufacturing Tolerances Computers and People Protect Designs Acceptable Risks Safety Factors Chapter 8

ENGINEERING ANALYSIS

Overview Stress- Strain Analyses Basic Design Theories Fiber Strength Theories Fiber Geometry on Strengths Stress-Strain: Metal and Plastic Metal Design Spheres Tanks Pipes Thermoplastic Pipes RP Pipes Commodity and Custom Pipes

709 710 713 719 720 725 726 727

729 730 737

738 740 744 744 745 745 746 748 754 755 757

758 758 760 761 761 765 765 766 766 768 769 770 771 772 773 775 775 776

785

xii Contents

Chapter 9

Beams Theories RP Beams Ribs Reinforced Foamed Plastic Cylinders and Ribs Plates RP Isotropic Plates RP Non-Isotropic Plates Hybrid RP Plates

789 791 792 795 799 803 804 809 809 814

SELECTING PLASTIC AND PROCESS Overview Influencing Factors Performances/Behaviors Additives Chemical Resistance Color Crazing/Cracking Electricity Electric/Electronic Flame Resistance Impact Odor/Taste Permeability Radiation Temperature Resistance Weathering Moisture Variabilites Testing and Selection Nondestructive Tests Nondestructive Evaluation Experimental Stress Analysis Testing Against Trouble Testing Procedures Computer Software Programs Statistics Software Design via Internet Summation on Selection Materials

817 817 824 826 831 841 841 843 843 843 843 846 846 846 847 847 853 853 855 857 859 861 864 867 869 872 874 874 875 876 877

Contents xiii

Processes Designs Detailed RP Data Sheets

903 926 940

Chapter 10 SUMMARY Overview Global Business Fortunes New Reinforcement Technology Plastic Raw Materials Molding RPs with Profits Predicting Performances Design Verifications Design Demands Costings Technical Cost Models Safety Reinforced Plastic Successes Developments Micromechanics Nanotechnology Successes Fuel Cell's Bipolar Plates Future Product Developments Innovations

997 997 1002 1003 1004 1005 1010 1011 1012 1012 1015 1017 1018 1023 1026 1027 1028 1030 1031 1032

Chapter 11 CONVERSIONS

1035

BIBLIOGRAPHY

1043

INDEX

1051

This Page Intentionally Left Blank

Preface a nd Acknowledgement

The text is organized and written with useful information in the World of Reinforced Plastics to provide a source and reference guide for fabricator, mold maker, material supplier, engineer, maintenance person, accountant, plant manager, testing and quality control individual, cost estimator, sales and marketing personnel, new venture type, buyer, user, educator/trainer, workshop leader, librarian/information provider, lawyer, consultant, and others. It will be useful for those using reinforced plastic (RP) composites as well as those contemplating their use. People with different interests will gain knowledge by focusing on a subject and interrelate across subjects that they have or do not have familiarity. Information and data presented includes some important history, detailed up dates, and what is ahead. As explained throughout this book, this type of understanding is required in order to be successful in the design, prototype, and manufacture of the many different, marketable, fabricated products worldwide. This approach provides potential innovations concerning materials of construction, fabricating techniques, improved products performance to cost, and designing new products. The book provides an understanding that is concise, practical, and comprehensive and that goes from "A-to-Z" on the subject of RP. Its concise information for either the technical or the non-technical reader goes from interrelating and understanding basic factors starting with the materials of construction and plastics melt flow behavior during processing. This third edition has been written to update the subject of reinforced plastics in the World of Reinforced Plastics. By updating the book, there have been changes with extensive additions to over 75% of the 2nd Edition's content. Many examples are provided of processing

xvi Preface and Acknowledgement different plastics and relating them to critical factors that range from product designs-to-meeting performance requirements-to-reducing costs-to-zero defect targets. More information that is basic has been added concerning present and future developments, resulting in the book being more useful for a long time to come. Detailed explanations and interpretation of individual subject matters (3000 plus) are provided using many figures and tables. Information ranges from basic design principles to designs of different size fabricated products by different processes. Throughout the book, there is extensive information on problems and solutions as well as extensive cross-referencing on its many different subjects. This book continues to represent the encyclopedia on RP. Even though the worldwide industry literally encompasses many hundreds of beneficial computer software programs, this book introduces these programs (ranging from operational training to product design to fabricating to marketing). However, no one or series of software programs can provide the details obtained and the extent of information contained in this single source book with its extensive cross references. It is important to recognize that a major cost in the production of RP products, ranging from the design concept to the finished molded product, is that of the materials of construction. They range from 40 to 90% of the total product cost. Thus, it is important to understand how best to use the materials based on the appropriate design approach and processing technique. Design is interdisciplinary. It calls for the ability to recognize situations in which certain techniques may be used and to develop problem-solving methods to fit specific design requirements. Many different examples are presented concerning problems with solutions that may develop in different design approaches, fabricating techniques, etc., up to the final product in use. In the manufacture of products, there is always a challenge to utilize advanced techniques, such as understanding the different plastic melt flow behaviors, operational monitoring and control systems, testing and quality control, and so on. However, these techniques are only helpful if the basic operations of fabricating are understood and characterized, to ensure the elimination or significant reduction of potential problems. What makes this book unique is that the reader will have a useful reference of pertinent information readily available as summarized in the Table of Contents and Index. As past book reviewers have commented, the information contained in this book is of value to even the most experienced designers and engineers, and provides a firm basis for the beginner. The intent is to provide a complete review of all aspects of

Preface and Acknowledgement xvii the RP process that goes from the practical to the theoretical and from the elementary to the advanced. This book can provide people, not familiar with RP, an understanding of how to fabricate products in order to obtain its benefits and advantages. It also provides information on the usual costly pitfalls or problems that can develop, resulting in poor product performances or failures. Accompanying the problems are solutions. It will enhance the intuitive skills of those people who are already working in plastics. From a pragmatic standpoint, any theoretical aspect that is presented has been prepared so that it is understood and useful to all. The theorist, for example, will gain an insight into the limitations that exist relative to other materials such as steel, wood, and so on. Based on over a half century of worldwide production of all kinds of low to high performance RP products, they can be processed successfully, meeting high quality, consistency, and profitability. As reviewed in this book, one can apply the correct performance factors based on an intelligent understanding of the subject. This book has been prepared with the awareness that its usefulness will depend on its simplicity and its ability to provide essential information. With the authors experience gained in working in the RP industry worldwide and in John Murphy's work in preparing the 1st and 2nd editions, we are able to provide a useful book. The book meets the criteria of providing a uniquely useful, practical reference work. The material properties information and data presented are provided as comparative guides; readers can obtain the latest information from material suppliers, industry software, a n d / o r as reviewed in this book's Bibliography section. Our focus in the book is to present, interpret, analyze, and interrelate the basic elements of RP to processing plastic products. As explained in this book, even though there are many reinforcements and plastic materials worldwide, selecting the right reinforcement/plastic requires applying certain factors such as defining all product performance requirements, properly setting up or controlling the RP process to be used, and intelligently preparing a material specification purchase document and work order to produce the product. Extensive selection information is provided. With all types of plastics that include primarily RPs, an opportunity will always exist to optimize its use, since new and useful developments in materials, processing, and design continually are on the horizon requiring updates. Examples of these RP developments are in this book, providing past to future trends in the World of Reinforced Plastics.

xviii Preface and Acknowledgement Recognize that with the many varying properties of the different RPs, there are those that meet high performance requirements such as long time creep resistance, fatigue endurance, toughness, and so on. Conversely, there are RPs that is volume and low cost driven in their use. As explained in this book, each of the different materials requires their specific RP processing procedures. Patents or trademarks may cover information presented. No authorization to utilize these patents or trademarks is given or implied; they are discussed for information purposes only. The use of general descriptive names, proprietary names, trade names, commercial designations, or the like does not in any way imply that they may be used freely. While information presented represents useful information that can be studied or analyzed and is believed to be true and accurate, neither the authors nor the publisher can accept any legal responsibility for any errors, omissions, inaccuracies, or other factors. In preparing this book and ensuring its completeness and the correctness of the subjects reviewed, use was made of the authors worldwide personal, industrial, and teaching experiences that total over 100 years, as well as worldwide information from industry (personal contacts, conferences, books, articles, etc.) and trade associations. The Rosatos 2004

Acknowledgement As the reinforced plastic industry worldwide continues to grow and expand its capabilities material wise, process wise, design wise, and product wise, so does the literature. This Third Edition of the Reinforced Plastics book and the Reinforced Plastics magazine published by Elsevier Advanced Technology provides important information. This Third Edition is a tribute to John Murphy for the excellent work presented in the First and Second issues. Following Murphy's work the Rosatos' continue to provide updates and information on what is ahead.

About the Authors

Donald V. Rosato has extensive technical and marketing plastic industry business experience from laboratory, testing, through production to marketing, having worked for Northrop Grumman, Owens-Illinois, DuPont/Conoco, Hoechst Celanese, and Borg Warner/G.E. Plastics. He has written extensively, developed numerous patents within the polymer related industries, is a participating member of many trade and industry groups (Plastics Institute of America, Plastics Pioneers Association, Society of Plastics Engineers, Society of Plastics Institute, etc.), and currently is involved in these areas with PlastiSource, Inc., and Plastics FALLO. He received a BS in Chemistry from Boston College; MBA at Northeastern University; M.S. Plastics Engineering from University of Massachusetts Lowell (Lowell Technological Institute); Plastics Engineer of Society of the Plastics Engineers and Ph.D. Business Administration at University of California, Berkeley. Dominick V. Rosato since 1939 has been involved worldwide principally with plastics from designing through fabricating through marketing products. They have been used on and in land, ocean/water, and air/space. Products in many different markets worldwide ranged from toys to electronic devices to transportation vehicles to aircraft to space vehicles products. Experience includes Air Force Materials Laboratory (Head Plastics R&D), Raymark (Chief Engineer), Ingersoll-Rand (International Marketing Manager), and worldwide lecturing. He is a past director of seminars and in-plant programs and adjunct professor at University Massachusetts Lowell, Rhode Island School of Design, and the Open University (UK). He has received various prestigious awards from USA and international associations, societies (SPE Fellows, etc.), publications, companies, and National Academy of Science (materials advisory board). He is a member of the Plastics Hall of Fame. He received American Society of Mechanical

xx About the Authors

Engineers recognition for advanced engineering design with plastics. He is a senior member of the Institute of Electrical and Electronics Engineers and licensed professional engineer of Massachusetts. He was involved in the first all plastics airplane (1944/RP sandwich structure). He worked with thousands of plastics plants worldwide, prepared over 2,000 technical and marketing papers, articles, and presentations and has published 28 books with major contributions in over 45 other books. He received a BS in Mechanical Engineering from Drexel University with continuing education at Yale, Ohio State, and University of Pennsylvania.

Abbreviations

AAM ABL ABC abs. ABS AC AC ACA ACC ACCS ACG ACMA ACN ACTC ADC adh. AEC AF AF AFML AFRP A1 AMBA ANFI ANSI ANTEC APC APPR

American Architectural Manufacturers Allegheny Ballistic Laboratory acrylonitrile-butadiene-styrene acetal (see POM) absolute acrylonitrile- butadiene-styrene advanced composite alternating current Automotive Composites Alliance Automotive composites Consortium advanced composite construction system Advanced Composites Group American Composites Manufacturers Association acrylonitrile Advanced Composite Technology Consortium allyl diglycol carbonate (also see CR-39) adhesive acrylonitrile-ethylene-styrene Air Force aramid fiber Air Force Materials Laboratory aramid fiber reinforced plastic aluminum American Mold Builders Association Assoc. of the Nonwoven Fabrics Industry American National Standards Institute Annual Technical Conference (SPE) American Plastics Council, unit of American Chemistry Council Assoc. of Postconsumer Plastic Recyclers

xxii Abbreviations

ARMI ARP ASA ASA ASM ASME ASTM atm B

bbl Be BeCu BF BM BM BMC BO

bpd BPF BPO BS BSI Btu Buna Butyl C C C C CAD CAE CAM CAT cal CAR CAT CBA CCA CCPIA CCV CEO CF CFA

Assoc. of Rotational Molders International advanced reinforced plastics acrylic-styrene-acrylonitrile American Standard Association advanced stitching machine American Society of Mechanical Engineers American Society for Testing and Materials atmosphere boron barrel beryllium beryllium copper boron fiber bag molding blow molding bulk molding compound biaxial-oriented barrels per day British Plastics Federation Benzoyl peroxide British Standard British Standard Institute British thermal unit polybutadiene butyl rubber carbon Celsius Centigrade (preference Celsius) composite computer-aided design computer-aided engineering computer-aided manufacture computer-aided testing calorie (see also C) carbon fiber computer-aided testing chemical blowing agent cellular cellulose acetate China Plastics Processing Industry Assoc. Composite Concept Vehicle chief executive officer carbon fiber chemical foaming agent

Abbreviations xxiii

CFC cfm CFRP CFRTP cg CLTE cm

CM CNC CO CO2 cP CP CPE CPET CPVC Cr CR CR-39 CRP CSM CU

Cu 3-D D 3-D DIN DMC DMC-12 DN DNA DOD DSQ DV DVR DVR DVR E EC EEC E-glass EI EMI

chlorofluorocarbon cubic foot per minute carbon fiber reinforced plastics continuous fiber reinforced thermoplastics center of gravity coefficient of linear thermal expansion centimeter compression molding computer numerical control carbon monoxide carbon dioxide centipoise Canadian Plastics chlorinated polyethylene chlorinated polyethylene terephthalate chlorinated polyvinyl chloride chromium compression ratio diethylene glycol bis-allyl carbonate carbon reinforced plastics continuous strand mat cubic copper three dimension diameter three-dimensional Deutsches Institut fur Normung (German Standard) dough molding compound DeLorean motor car (plastic body) Deutscher Normenausschus deoxyribonucleic acid Department of Defense German Society for Quality design verification design value resource Dominick Vincent Rosato Donald Vincent Rosato modulus of elasticity (Young's modulus) European Community European Economic Community glass fiber modulus (times) moment of inertia (stiffness) electromagnetic interference

xxiv Abbreviations

EP EPA EPS ER EUROMAP EVAL F F FALLO FDA FEA FP FPL fpm FRP FRTP FRTS ft FW g G G gal GDP GF GFRP GLARE GM GM GMRP GMT GNP GP gpd gpm GR GS GSP h H2 HDBK HDPE

epoxy Environmental Protection Agency expandable polystyrene epoxy resin European Committee of Machine Manufacturers for the Rubber & Plastics Industries (Zurich, Swiz.) ethylene-vinyl alcohol copolymer (or EVOH) force Fahrenheit F_ollow ALL Opportunities Food & Drug Administration finite element analysis fluoroplastic Forrest Products Laboratory feet per minute fiber glass reinforced plastic fiber reinforced thermoplastic fiber reinforced thermoset foot filament winding gram giga ( 106) torsional modulus gallon gross domestic product (see also GNP) glass fiber glass fiber reinforced plastic GLAss fiber-REinforced aluminum General Motors glass mat glass mat reinforced thermoplastic glass mat thermoplastic gross national product (GDP replaced GNP in US 1993) general purpose grams per denier gallons per minute glass reinforced glass sphere Generalized System of Preferences hour hydrogen handbook high density polyethylene (also PE-HD)

Abbreviations xxv

HDT

H20 hp HRc Hz I

IDSA IM IM IMM in.

I/o J IF IIS JIT

jsw lv K K

I
L lb LCTE LDPE LF LFP LLDPE LMDPE LPE m m m mg M M

~mm MA MAD MD MDAFRPCA

heat distortion temperature water horsepower hardness Rockwell cone Hertz (cycles) moment of inertia Industrial Designers Society of America infusion molding injection molding injection molding machine inch input/output joule jute fiber Japanese Industrial Standard just-in-time Japan Steel Works joint venture Kelvin Kunststoffe (plastic in German) kilogram length liter pound linear coefficient of thermal expansion low density polyethylene (also PE-LD) long fiber long fiber prepreg linear low density polyethylene (also PE-LLD) linear medium density polyethylene linear polyethylene matrix metallocene (catalyst) meter milligram mega million micrometer (see also pm) Manufacturers Alliance molding area diagram machine direction Material Development Alliance of the FRP Composites Industry

xxvi Abbreviations

MDPE MEK MF mg Mg MI mike mil ml mm MM mol.wt. MPa MPA MPF mph Msi MT MVD MW MWD N2 NA NAM NBR NBS

NC NDT NEAT NEN NFPA NIBS nm NPCM NPE NR NTMA 02 03 OEM OSHA

medium density polyethylene (also PE-MD) methyl ethyl ketone melamine formaldehyde milligram magnesium melt index microinch ( 10 -6 in.) milliinch/one-thousand of inch (10 -6 in.) milliliter millimeter billion molecular weight mega-Pascal Massachusetts Plastics Alliance melamine-phenol-formaldehyde miles per hour million pounds per square inch (psi x 106) metric ton molding volume diagram molecular weight molecular weight distribution nitrogen not available National Association of Manufacturers nitrile-butadiene rubber National Bureau of Standards (since 1980s renamed National Institute of Standards & Technology or NIST) numerical control nondestructive testing nothing else added to it Dutch standard National Fire Protection Association National Institute of Building Sciences nanometer National Plastics Center & Museum National Plastics Exhibition (SPI) natural rubber (polyisoprene) National Tooling and Machining Association oxygen ozone original equipment manufacturer Occupational Safety & Health Administration

Abbreviations xxvii

%vol %wt P P P Pa PA PAE PAEK PAI PAK PAM PAM PAN Pb PBA PBI PC PC PC PC PE PE PEEK PEEKK PEK PEKEKK PEKK PEKK PET PETG PEX PF Phr pi PI PI PIA PLTA POM PP ppb pph

percentage by volume (prefer vol%) percentage by weight (prefer wt%) load poise pressure Pascal polyamide (nylon) polyarylether polyaryletherketone polyamide-imide polyester alkyd modified acrylic fiber polyacrylamide polyacrylonitrile lead physical blowing agent polybenzimidazole personal computer polycarbonate printed circuit process control polyethylene polythene polyetheretherketone polyetheretherketoneketone polyetherketone polyetherketoneetherketoneketone polyaryletherketoneetherketone polyetherketoneketone polyethylene terephthalate polyethylene terephthalate glycol cross-linked polyethylene (or XLPE) phenol formaldehyde (phenolic) parts per hundred = 3.141593 isoprene rubber polyimide Plastics Institute of America Plastic Lumber Trade Association polyacetal polypropylene parts per billion parts per hour

xxviii Abbreviations

ppm ppm PPS PS psi psia PTFE PU PUR PVA PVAB PVAL PVF pVT

Qc QPL R R R

R&D radome RF RFI RFI r.h. RIM RM ROI RP

RP/C RP/CI RPMP rps RRIM RTM RTP RTS S

SAE SAMPE SF SG

parts per million parts per minute polyphenylene sulfide polystyrene pounds per square inch pounds per square inch, absolute polytetrafluoroethylene (TFE) polyurethane (PUR) polyurethane (PU) polyvinyl acetate polyvinyl acetal butyral polyvinyl alcohol (PVOH) polyvinyl fluoride pressure-volume-temperature (also P-V-T or pvT) quality control qualified products list Rankin Reynold's number Rockwell (hardness) research & development radar dome radio frequency radio frequency interference resin film infusion relative humidity reaction injection molding rotational molding return on investment reinforced plastic reinforced plastics/composites reinforced plastics/Composites Institute (SPI) reinforced plastic Marco process revolutions per second reinforced reaction injection molding resin transfer molding reinforced thermoplastic reinforced thermoset second Society of Automotive Engineers Society for the Advancement of Material and Process Engineering safety factor specific gravity

Abbreviations xxix

SMC SMCAA SME SPE SPI SRIM S-S STD T Tg Tm Ts

T/C TD TDI Tg three-D TM TM TP Ts TS two-D TX ~ain. lam UD UF UHMPE UHMWPE UL UN UP URP UV V VEM VF VIP VOC vol

sheet molding compound Sheet Molding Compound Automotive Alliance Society of Manufacturing Engineers Society of the Plastics Engineers Society of the Plastics Industry structural reaction injection molding stress-strain standard temperature glass transition temperature melt temperature tensile strength thermocouple transverse direction toluene isocyanate glass transition temperature 3-dimensional (3-D) trademark transfer molding thermoplastic temperature, softening thermoset 2-dimensional (2-D) thixotropic microinch micron/micrometer (see also Mm) unidirectional urea formaldehyde ultrahigh modulus polyethylene ultrahigh molecular weight polyethylene (or PE-UHMW) Underwriters Laboratories United Nations unsaturated polyester (TS) unreinforced plastics ultraviolet volt viscoelastic material vulcanized fiber vacuum infusion process volatile organic compound volume

x x x Abbreviations

vol% VS.

WF wt

wt% WYSIWYG XL XLPE Y-axis yr Z-axis ZMC Ziegler-Natta Z-twist

percentage by volume; if % alone is used, it usually identifies wt% versus woven fabric weight percentage by weight; if % alone is used, it usually identifies wt% what you see is what you get crosslinked crosslinked polyethylene axis in the plane perpendicular to X-axis year axis normal to the plane of the X-Y axes low viscosity molding compound Z-N (ZN) twisting fiber direction

Introduction

Overview It would be difficult to imagine the modern world without unreinforced (URPs) and reinforced plastics (RPs). Today they are an integral part of everyone's life-style, with products varying from commonplace domestic to sophisticated scientific products. In fact, many of the technical wonders we take for granted would be impossible without these versatile and economical materials. Information and presented data includes some important history, detailed dates, and what is ahead. As explained throughout this book, this type of understanding is required in order to be successful in the design, prototype, and manufacture of the many different, marketable, fabricated RP products worldwide. This approach provides potential innovations concerning materials of construction, fabricating techniques, improved products performance to cost, and designing new products. RPs is a separate major and important segment in the plastic industry worldwide. Industry continues to go through a major evolution in RP structural and semi-structural products meeting performance and cost requirements in different markets particularly since the 1940s. Many different RPs are used, each with their own capabilities process-wise and performance-wise. RPs have been developed to produce exceptionally strong materials that perform in different environments (Figure 1.1 and Table 1.1). The RP products normally contain from 10 to 40 wt% of a plastic (usually called resin) matrix, although in some cases, plastic content may go as high as 60% or more (Tables 1.2 and 1.3). In the past, the RP industry has grown about 6.5% annually or about twice the growth rate of USA economy. During this period gross domestic product (GDP/USA consumer represents two-thirds of GDP) tripled,

2 Reinforced Plastics Handbook ~:)

100

x

90

~

7o

~----

COMPOSITE & ENGINEERED PLASTICS

.1

t

5O

a -J .I

40

>"

3o

--.

2O

Z W F-

10

.I

TYPICALSTEEL

COMMODITY PLASTICS

0 -100

0 100 200 300 400 500 600 700 800 9 0 0 1 0 0 0

9 9 1500

TEMPERATURE, F ~

Figure 1.1 Guide on strength vs. temperature of plastics and steel (courtesy of Plastics FALLO)

Table 1.1 Mechanical and physical properties of materials Specific Gravity

Modules of Elasticity

Plastics Reinforced Plastics Wood Steel Aluminum Concrete

Plastics Reinforced Plastics Wood Steel Aluminum Concrete-Stone 0

2

4

6

8

10 I I 100

Strength

0.0

Plastics Reinforced Plastics Wood Steel Aluminum

40 i

20 I 200

50 x 10 e psi

I

300 GPa

Thermal Conductivity 0.5 I

1.0 I

W/m" K

Plastic Foams II Reinforced Plastics II

Wood I Brick I

Glass II Concrete

Concrete 50

I

I

500

100

1150

I

I 200 x 10 3 psi

0

2

4

6

8

10

1000 MPa

Continuous Service Temperature Thermal Expansion

0 Reinforced Plastics WoodChars Alluminum Copper Alloys

steel

Concrete S0 i7-S 100 1~)5i 150x1061n./in.~ I I 100 200unVm~

200 I

400 I

~ 600 I

800 I

1000 I

1800

Table 1.2 Propertiesof RP thermoplastic resins with different amounts of different fibers

Resin Nylon-6,6 Un rein forced 30o/0 glass fibers 30% carbon fibers 40% mineral filler 40% glass-mineral Polypropylene Unreinforced 30% glass fibers 30o/0 glass fibers chemically coupled 40% mica 400/o talc Polycarbonate Un rein forced 30o/0 glass fibers 30% carbon fibers 5% stainless steel Polyesters 30O/o glass fibers (PBT) 30% glass fibers (PET)

Specific gravity

Tensile strength, MPa

Tensile modulus, GPa

1.14 1.39 1.28 1.50 1.49

83 172 227 92 124

2.9 9.0 20.7 5.5 7.6

0.9 1.13 1.13

34 52 83

1.4 5.5 5.9

1.23 1.25

31 29

4.8 3.1

1.20 1.43 1.33 1.27

65 131 152 68

2.4 9.0 17.2 3.1

1.51 1.56

121 158

6.9 8.7

Elongation, O/o 60 4 3 3 3

Flexure/ strength, M Pa

Flexural modulus, GPa

Izod impact notched, Jim

Deflection temperature under load, C

119 248 324 155 207

2.8 9.0 20.7 7.2 9.7

53 107 85 48 64

90 252 263 249 246

11 2.5 2.3

65 110

1.6 4.1 5.5

51 64 107

53 137 151

4 4

48 48

4.1 3.1

37 27

96 76

93 138 220 110

2.3 7.6 15.2 3.1

801 e 160 107 69

132 143 149 146

200 234

8.7 9.1

96 107

206 224

7 2.5 1.8 5 4 3

,,...,.

0 r

c m o

0

4~ m ,

a. Table 1.3 Propertiesof TS polyester RPs with different amounts of glass fiber

a,1 Ill

m ,

Glass Fiber (wt %) Property Specific gravity Specific volume m3/mg x 10-1~ Tensile strength MPa Tensile elongation (O/o) Flexural strength MPa Flexural modulus GPa Compressive strength MPa Heat deflection temperature at ~ Thermal expansion mm/mmK x 10s Water absorption, 24 h (O/o] Mold shrinkage

0

10

20

30

40

50

60

1.14 24.3 8.8 12 83 60 15 103. 4.0 28 4.9 33.8 150 4.5 8.1 1.6 15

1.21 22.9 8.3 13 90 3.5 20 138 6.0 .41 13 89.6 470 1.6 2.9 1.1 6.5

1.28 21.6 7.8 19 131 3.5 29 200. 9.0 .62 23 158.6 475 1.4 2.5 0.9 5

1.37 20.1 7.3 25 172 3.0 34 234. 13 .90 27 186.2 485 1.3 2.3 0.9 4.0

1.46 19.0 6.9 31 214 2.5 42 290. 16 1.10 28 193.1 5OO 1.2 2.2 0.6 3.5

1.57 17.6 6.4 32 221 2.5 46 317. 22 1.52 29 200.0 5OO 1.0 1.8 0.5 3.0

1.70 16.3 5.9 33 228 1.5 5O 345 28 1.93 3O 206.9 5O0 0.9 1.6 0.4 2.0

9,1

=i D., 0" 0 0

1

9I n t r o d u c t i o n

steel consumption doubled, aluminum consumption tripled, and RP shipments grew 15 times (Chapter 6). RP growth unfortunately follows economic recessions such as the last that started during 2001. Important developments have occurred and continue to occur in USA, UK, Germany, Italy, England, Sweden, Japan, and other countries. Throughout this book, examples of past, present and future developments arc reviewed. The past developments continue to provide the basis for present and future developments. For example, in England, the British Standard Institute issued a code for storage tanks and vessels in 1973. It used relatively simple formulas for stresses under service loads and for RP design. These methods could be developed for vehicle components. A significant research effort at the British National Physical Laboratory developed design-analysis methods for anisotropic materials at an intermediate level between a standard formula and full computer analysis. This work concentrated on rectangular plates under various support and loading conditions, and could be applied to RP panel structures that contain components of an approximately rectangular shape such as a car door. Results reported at that time-included work on design procedures for RP plates under flexural loading, on optimum design of laminated glass fiber RP (GFRP) materials, and on an interactive minicomputer program for plate design analysis. During 1941, USA produced bulletins HDBK ANC-17 on reinforced plastics and HDBK ANC-23 on sandwich constructions that included RPs. Based on this type information the all RP sandwich monique constructed airplane was designed and built by the USA Air Force. It flew during 1944. This advanced RP technology of 1944 was demonstrated in the fabricating (hand-lay-up bag and autoclave molding) of this two-seater glass fiber/TS polyester airplane. Later, Grumman built 50 of this type of airplane under A.F. contract (Chapter 6). The term RP refers to composite combinations of resin and reinforcing materials that provide significant property a n d / o r cost improvements than the individual components that can produce products. To be structurally effective, there must be a strong adhesive bond between the resin and reinforcement. Reinforcements usually come in continuous or chopped fiber forms as in woven and nonwoven fabrics. Both thermoplastic (TP) and thermoset (TS) resins are used in RPs (Chapter 3). At least 90 wt% of all RPs use glass fiber (E-type) materials (Chapter 2). At least 55 wt% of all RPs use TPs even with their relatively lower properties compared to reinforced TSs (RTSs). Practically all reinforced TPs (RTPs) with short or long glass fibers arc injection molded at very fast processing cycles; producing

5

Table 1.4 Comparing mechanical properties of glass fiber/thermoset and thermoplastic RPs with different metals

Reinforced plastics (selected)

Glass fiber % Specific gravity Tensile strength MPa 103 psi Tensile modulus GPa 106 psi Elongation % Flexural strength MPa 103 psi Flexural modulus GPa 106 psi Compressive strength MPa 103 psi Izod impedance J/m Ft-I b/i n Hardness Rockwell 1Barcol hardness;2Brinell hardness.

UPSMC

UP hand lay-up

PA66 30% glass

30 1.85

30 1.37

30 1.48

40 1.64

7.75

7.86

8.03

82.8 12.00

86.25 12.50

158.7 23.00

151.8 22.00

448.5 65.00

331.2 48.00

207 30.00 22.0

207 30.00 37.0

1173 1.70 <1.0

6.9 1.00 1.3

179.4 26.00

193.2 28.00

11.04 1.60 165.6 24.00

5.175 0.75 151.8 22.00

854.4 694.2-801 16.00 13-15 681 507

8.28 1.20 1.9

HSLA Cold roll

14.145 2.05 3.0

241.5 35.00

255.3 37.00

5.52 0.80

13.11 1.90

Low carbon Cold roll

m . ,

Magnesium

Aluminum

Steel PPS 40% glass

t,D =I Zinc

Diecast

Diecast

Diecast

2.74

2.82

1.83

6.59

552.0 80.00

338.1 49.00

331.2 48.00

227.7 33.00

282.9 41.00

193.2 28.00 40.0

70.38 10.20 23.0

71.07 10.30 2.5

448.5 65.00 3.0

75.21 10.90 10.0

331.2 48.00

277.7 33.00

6.9 1.00

Stainless

Wrought

s"

r

es

m,o Ill

"!-

137 68.6

182.85 26.50

144.9 21.00

422.5 65.00

331.2 48.00

552 80.00

338.1 49.00

117.48 2.20 M-95

80.1 1.50 R123

B-80

B-50

B-88

R-80

852

852

822

:3 0" 0 0

1

9I n t r o d u c t i o n

high performance products used in different environments Table 1.4 introduce RP properties. Higher performing fibers that arc used include organic and inorganic high performance glass (other than the usual E-glass), aramid, carbon, graphite, and boron (Table 1.5). Other fibers used to meet different performance requirements and/or costs include natural (cotton, sisal, jute and other cellulosics), synthetic (nylon, polyester, acetate, rayon). When more than one fiber is used, the reinforcement is termed a hybrid. Table 1,5 Comparison of commonly used reinforcing fibers

Fiber/grade

Carbon HT Carbon IM Carbon HM Carbon UHM Aramid LM Aramid HM Aramid UHM E-glass R-glass Quartz glass Aluminum Titanium Steel (bulk) Steel (extruded) Steel (stainless)

Density {g cm -3)

Tensile strength (mPo}

Flexuro l modulus (GPo)

Specific modulus (Mm)

1.8 1.8 1.8 2.0 1.45 1.45 1.47 2.5 2.5 2.2 2.8 4.5 7.8 7.8 7.9

3500 5300 3500 2000 3600 3100 3400 2400 3450 3700 400 930 620 2410 1450

160-270 270-325 325-440 440+ 60 120 180 69 86 69 72 110 207 207 197

90-150 150-180 180-240 200+ 40 80 120 27 34 31 26 24 26 26 25

Also available arc whisker reinforcements with exceptional high performances (Chapter 2). Also used arc non-fibrous materials, such as steel wire (Table 1.6), and surface-treated mineral fillers that include mica platelets, talc, fibrous and finely divided minerals, glass flakes, and hollow and/or solid glass micro spheres. Lightweight expanded materials, such as sheets of reinforced foam or honeycomb, arc used as cores in sandwich structures (Chapter 7). Based on contents of an RP other terms are used to identify an RP. Examples include glass fiber reinforced plastic (GFRP), aramid fiber reinforced plastic (AFRP), carbon fiber reinforced plastic (CFRP), graphite fiber reinforced plastic (GFRP), boron fiber reinforced plastic (BFRP), etc.

7

8 Reinforced Plastics Handbook Table 1,6 Relative weights vs. equal tensile strength for different materials based on 100% for steel structures

Relotive weight

(%) Steel Aluminum E-glass fiber RP Carbon fiber RP (C:FRP) High strength CFRP Aramid fiber RP (AFRP) High strength AFRP S-glass fiber RP

100 65 38 29 8 26 8 8

The mechanical properties of the RPs are largely determined by the type of reinforcement, its form, and positioning (orientation) (Chapter 7). A high content of fibrous reinforcement produces a high tensile strength (which increases with the length of the fiber), but does not necessarily confer higher rigidity. A high mineral content in the plastic may give high rigidity but relatively poor tensile strength. A combination of the two is often used but, to improve the bonding between the various components, it may also be necessary to introduce a sizing or processing aid. The balance between resin and reinforcement (known as the resin/reinforcement ratio) is a major factor determining the properties of an RP structure. Both RTSs and RTPs can be characterized as high performance engineering plastics, competing with engineering unreinforccd plastics. When comparing processability of RTSs and RTPs, the RTPs are usually easier to process and permit faster molding cycles. RPs can also be characterized by their ability to be molded into either extremely small to extremely large structurally loaded shapes well beyond the basic capabilities of other materials or processes at little or no pressure. In addition to shape and size, different RPs posses other characteristics that make them very desirable in designing engineering products. The other characteristics include lightweight, high strength and modulus, directional properties (Figure 1.2), high strength-toweight ratio, creep and fatigue endurance, high dielectric strength, corrosion resistance, long term durability, ease of fabrication, simplified installation, aesthetic appeal, cost reduction, and the potential to be combined with many other useful qualities.

1

9I n t r o d u c t i o n

Figure 1.2 Directional properties of reinforced plastics

The form the RP takes, as with URPs, is determined by the product requirements. It has no inherent form of its own so it must be shaped. This provides an opportunity to select the most efficient forms for the application. Shape can help to overcome limitations that may exist in using a lower-cost material with low stiffness. As an example, underground fuel tanks can include ribs to provide added strength and stiffness to the RP orientation in order to meet required stresses at the lowest weight and production cost.

9

10 Reinforced Plastics Handbook

The formability of these products usually leads to one-piece consolidation of constructed products to eliminate joints, fasteners, seals, and other costly or potential joining problems. As an example, formed building RP fascia panels eliminate many fastenings and seals. Examples of design characteristics, gained by using RP materials to produce RP products, are reviewed in this book. RPs, also called plastic composites or composites, are tailor-made materials that provide the designer, fabricator, equipment manufacturer, and consumer engineered flexibility to meet different environments and create different shapes (Table 1.7). They can sweep away the designer's frequent crippling necessity to restrict performance requirements of designs to traditional monolithic materials. The objective of an RP is to combine similar or dissimilar materials in order to develop specific properties related to desired characteristics. They can be designed to provide practically any variety of characteristic. For this reason, practically all industries use them. Economical, efficient, and sophisticated parts are made, ranging from toys to bridges to preserving historic buildings, to reentry insulation shields to miniature printed circuits to missiles/ rockets. Table 1.7 Examplesof different composite systems Matrix Material

Reinforcementmaterial

Examplesof properties modified

Thermoset plastic, Thermoplastic

Glass, aramid, carbon, graphite, whisker, metal, etc.

Mechanical strength, wear resistance, elevated temperature resistance, energy absorption, thermal stability

Metal

Metal, ceramic, carbon, glass fiber, etc.

Elevated temperature strength, thermal stability, etc.

Ceramic

Metallic and ceramic particles and fibers

Elevated temperature strength, chemical resistance, thermal resistance, etc.

It is acknowledged that these RP materials used to fabricate different products have not come close to realizing their full potential in a multitude of applications (Chapter 10). They could be both more efficient and cost effective. Meanwhile they are used widely and successfully. Utilizing the laws of physics, chemistry, and mechanics, theoretical values can be determined for different materials. For steel, aluminum, and glass, the theoretical and actual experimental values are practically the same, whereas plastics have the important potential of

1

9I n t r o d u c t i o n

reaching values that are far superior to those of other materials. Their structural properties together with lightweight are demonstrated by their use in aircraft, boats, water skis, surfboards, boat docks, and the list goes on used in underwater, on land, to space. The electrical insulation property of RPs results in their effective use in electrical and electronic housings, printed circuit boards, hardware for the electrical utility industry, shatterproof fight globes, cherry picker boom with 'people bucket' for high voltage wire electrical lines, ladders, etc. RP components and pole-line hardware have contributed greatly to the aims of beautifying and providing safety in the electric utility industry. In addition to their excellent dielectric properties, RPs provide necessary strength with reduced silhouette and weight. The corrosion resistant, smooth, hard surfaces also resist the embedment of contaminants. Since at least the 1940s utility companies have used components that include pole-top pins, adjustable tension braces, guy-strain insulators, line spacers, insulator pins, upsweeps, double-insulator standoff brackets, switch control rods, hot sticks, and switchgear components. Thermal insulation properties are typically used in motor transport, refrigerator railroad cars, and unwrapped (uninsulated) process vessels and piping. The ability of RPs to be formed into complex shapes and irregular contours is demonstrated in a variety of products (aircraft parts, boats, chairs, public transportation vehicles, automotive parts, truck bodies and components, park benches, truck and railcar hoppers, etc.). Successful corrosion resistant applications are extensive. For many years, they have included chemical processing piping, fume collection hoods, scrubbing towers, handling equipment in the electroplating industry, and stack liners inside chimneys. A specific example of the latter is an installation in Utah that used 600 metric tons of glass fiber roving reinforcement with a TS polyester matrix. Double liners were installed inside a 207.8 m high reinforced concrete chimney. Filament wound field-fabricated sections were 13.7 m long with an 8.5 m diameter. Thirty-six sections were installed. These types of liners have been used since the 1970s. Many RP water-filtration systems are found throughout the world. Different designs are used depending on the particular filtration system used, i.e., very large and deep RP tanks have circulating and stirring arms, etc. An example of a large closed-designed water filtration system is glass fiber/TS polyester RP. It is 6.1 m (20 ft) diameter by 9.8 m (32 ft) high and was low-pressure molded. It was shipped in one assembled and bonded structure by water barge to its destination.

11

12 Reinforced Plastics Handbook

High strength-to-weight ratios have been demonstrated in primary and secondary structures and components of aircraft, rocket engine cases, large underground and overground storage tanks, portable oxygen tanks for fire fighters, etc. Weather resistance is another necessary property of decorative panels for residential and commercial buildings, patio roofs, highway signs, protective shields in transcontinental communication systems, aircraft and ground radomes, antennas, etc. Other RP products include shipping pallets, organic fiber RP filtration membranes, wall panels that absorb the impact of bullets, waterfront piers/pilings, and aerial booms. Since the 1940s, the aeronautical and aerospace technologies have soared, with all types of RPs playing major roles in both pragmatic improvements and dramatic advances. RPs lightweight and durability provide savings on fuel consumption and the ability to stand up to stress (creep, fatigue, etc.) and varied environments. The Chevrolet Corvette was one of the first major applications of RPs in the automotive field (USA 1953). The body was made of short Eglass fibers with TS-polyester RP molded largely by the low-pressure hand lay-up and matched die molding (Chapter 5). The list of accepted applications could continue endlessly covering products used for all industries and people of all ages. Each product contributes to the worldwide plastic industry's technical growth. Information on production of products is reviewed throughout this book. Designing different products demonstrated a variety of performances RPs provide such as a range of static to dynamic loads (Table 1.8), aesthetics, environments, recycling, shapes, assemblies or joining, etc. These performances are reviewed in this book (Chapters 6, 7, 8, etc.). In order for the designer to be successful, it is important that all the product performance requirements be obtained and understood. This does not always occur. Once the requirements are obtained including time schedules and quantity needed, the designer can proceed to determine if an RP is required, the material of construction to be used, and the manufacturing process to be utilized. The designer should know possible shaping limitations based on materials and process to be used and if the shape can be determined based on the best design or engineering approach. There are different designs and engineering basic and practical approaches reviewed in this book (Figure 1.3). Others are available in different design textbooks that are included in the Bibliography section.

1 Introduction 9 13 Table 1.8 Static and dynamic loads (courtesy of Plastics FALLO)

LOAD STATIC

DYNAMIC CREEP THERMAL !

IMPACT SLOW TO FAST

I TRANSIENT FATIGUE

TENSILE FLEXURE

MATERIAL

PRODUCT

PRODUCT MARKETING

PERFORMANCE

COMPETmON

STRUCTURAL

1

CIC/QA/SPC -"

r ~

-

ENVIROMENT

LEGAL

AGENCY ~

> R&DLAB

~

OTHERS

",,, //

MATERIALS~"

> MANUFACTURING

SUPPUERS Figure 1.3 Examples of factors that influence the design challenge (courtesy of Plastics FALLO)

14 Reinforced Plastics Handbook

As reviewed in this book, designing products range from using simple to complex approaches. However and fortunately, people we know did not have to design the human body. The human body is the most complex structure ever "designed" with its so-called 2,000 parts (with certain parts being replaced with plastics) and having recirculating all the blood in the body every 20 minutes, pumping it through 60,000 miles of blood vessels, etc. Thus, the designer of the human body had to be extremely creative; some of us know who designed the human body.

Commodity and Engineering Plastics Of the URPs, about 90 wt% of all plastics can be classified as commodity plastics (CPs), the others being engineering plastics (EPs). The EPs such as polycarbonate (PC) representing at least 50wt% of all EPs; others include nylon, acetal, etc. EPs include most reinforced plastics. The EPs are characterized by improved performance in higher mechanical properties, better heat resistance, and so forth when compared to CPs. The EPs demand a higher price. Just over a half century ago, the price per pound was at 20r and above; at the turn of the century it started at $1.00, and now higher. When CPs with certain reinforcements and/or alloys with other plastics are prepared, they become EPs. Performances

All TP or TS matrix property can be improved or changed to meet varying requirements by using reinforcements. Typical thermoplastics used include TP polyesters, polyethylenes (PEs), nylons (polyamides/ PAs), polycarbonates (PCs), TP polyurethanes (PURs), acrylics (PMMAs), acetals (polyoxymethylenes/POMs), polypropylencs (PPs), acrylonitrile butadienes (ABSs), and fluorinated ethylene propylenes (FEPs). The thermoset plastics include TS polyesters (unsaturated polyesters), epoxies (EPs), TS polyurethanes (PURs), diallyl phthalates (DAPs), phenolics (phenol formaldehydes/PFs), silicones (Sis), and melamine formaldehydes (MFs). RTSs predominate for the high performance applications with RTPs fabricating more products. The RTPs continue to expand in the electronic, automotive, aircraft, underground pipe, appliance, camera, and many other products. Fiber strengths have raised to the degree that 2-D and 3-D RPs can be used producing very high strength and stiff RP products having long service lives. RPs can be classified according to their behavior or performance that varies widely and depends on time, temperature,

1

9I n t r o d u c t i o n

environment, and cost. The environment involves all kinds of conditions such as amount and type of loads, weather conditions, chemical resistances, and many more. Directly influencing behaviors or performances of RPs involve factors such as type of reinforcement, type of plastic, and process used (Chapter 2, 3, and 5). These parameters are also influenced by how the product is designed. Examples of design performances of RPs follow with more details in the other Chapters:

Thermal Expansion URPs generally have much higher coefficients of linear thermal expansion (CLTE) than conventional metal, wood, concrete, and other materials. CLTEs also vary significantly with temperature changes. There is RPs that does not have these characteristics. With certain types and forms of fillers, such as graphite, RPs can eliminate CLTE or actually shrink when the temperature increases.

Ductility Substantial yielding can occur in response to loading beyond the ductility limit of approximate proportionality of most stress-to-strain in URPs. This action is referred to as ductility. Most RPs does not exhibit such behavior. However, the absence of ductility does not necessarily result in brittleness or lack of flexibility. For example, glass fiber-TS polyester RPs do not exhibit ductility in their stress-strain behavior, yet they are not brittle, have good flexibility, and do not shatter upon impact (Chapter 7). The RPs do not shatter upon impact like sheet glass. TS plastic matrix is brittle when unreinforced. However, with the addition of glass or other fibers in any orientation except parallel, unidirectional, the fibers arrest crack propagation. This RP construction results in toughness and the ability to absorb a high amount of energy. Because of the generally high ratio of strength to stiffness of RPs, energy absorption is accomplished by high elastic deflection prior to failure. Thus, ductility has been a major factor promoting the use of RPs in many different applications since the 1940s. Some unreinforced TPs such as polycarbonate (PC) and polyethylene (PE) do yield with ductility prior to failure, exhibiting similar stress-strain behavior to mild steel.

Toughness The generally low-specific gravity and high strength of reinforcement fibers such as glass, aramid, carbon, and graphite can provide additional benefits of toughness. For example, the toughness of these fibers allows them to be molded into very thin constructions. Each fiber has special characteristics. For instance, compared to other fiber reinforcements,

15

16 Reinforced Plastics Handbook

aramid fibers can increase wear resistance with exceptionally high strength or modulus to weight.

Tolerance~Shrinkage RTPs and RTSs combined with all types of reinforcements a n d / o r fillers are generally much more suitable for meeting and retaining fight dimensional tolerances than are URPs. As an example for injection molded products, they can be held to extremely close tolerances of less than a thousandth of an inch (0.0025 cm) or effectively down to zero (0.0%). Achievable tolerances range from 5% for 0.020 in. (0.05 cm), to 1% for 0.500 in. (1.27 cm), to 1/2%for 1.000 in. (2.54 cm), to 1/4%for 5.000 in. (12.70 cm), and so on. Some URPs change dimensions and~or shrink immediately after fabrication or within a day to a month due to material relaxation and changes in temperature, humidity, and~or load application. RPs can significantly reduce or even eliminate this dimensional change after fabrication. When comparing tolerances and shrinkage behaviors of RTSs and RTPs there is a significant difference. Working with crystalline RTPs can be yet more complicated if the fabricator does not understand their behavior. Crystalline plastics generally have different rates of shrinkage in the longitudinal, melt flow direction, and transverse directions. In turn, these directional shrinkages can vary significantly due to changes in processes such as during injection molding (IM). Tolerance and shrinkage behaviors are influenced by factors such as injection pressure, melt heat, mold heat, and part thickness with shape. The amorphous type materials can be easier to balance (Chapter 3).

Composites As reviewed a composite is a combination of two or more materials with properties that the components do not have by themselves. They are made to behave as a single material. Nature made the first composite in living things. Wood is a composite of cellulose fibers held together with a matrix of lignin. Most sedimentary rocks are composites of particles bonded together by natural cement; and many metallic alloys are composites of several quite different constituents. On a macro scale, these are all homogeneous materials. There are steel reinforced concrete, medical pills, and more. Included is RPs. The term composite started to be used in the RP industry during the 1940s. The Society of the Plastics Industry (SPI) during the 1940s

1

9I n t r o d u c t i o n

started the Low pressure Industries Division and shortly there after was called the Reinforced Plastics Division with energetic Charlic Condit at the helm of this growing industry for the SPI. D. V. Rosato during 1950, as a Board Member of the Reinforced Plastics Division of SPI, was finally successful at expanding the name of the Division to Reinforced Plastics/Composite Division (1954). The original product was only glass fiber-TS polyester plastic RPs. In the mean time, other reinforcements and plastics were being used; thus the name change. Other name changes have been made such as the Composites Institute of SPI (1988), etc. It is now a more powerful and useful organization for the RP industry called the American Composites Manufacturers Association (ACMA). Its president is Richard Morrision (Morrision Fiber Glass Co., Ohio, USA). Recognize that composites identify literally many thousands of different material combinations not containing plastics. There arc: aggregate-cement matrix (concrete] aluminum film-plastic matrix asbestos fiber-concrete matrix carbon-carbon matrix carbon fiber-carbon matrix cellulose fiber-lignin/silica matrix ceramic fiber-matrix ceramic {CMC] ceramic fiber-metal matrix ceramic-metal matrix (cermet) concrete-plastic matrix, fibrous-ceramic matrix fibrous-metal matrix fibrous-plastic matrix flexible reinforced plastic glass ceramic-amorphous glass matrix laminar-layers of different metals laminar-layer of glass-plastic {safety glass] laminar-layer of reinforced plastic

laminar-layers of unreinforced plastic metal fiber-metal matrix metal matrix composite (MMC) microsphere glass-plastic matrix {syntactic] particle-ceramic matrix particle-metal matrix particle-plastic matrix potassium nitrate-charcoal-sulfur matrix (blasting powder] plastic adhesive bonding metal-to-metal plastic-coated fabric plastic-plastic (coextruded coinjection, laminated] silver-copper-mercury matrix {dental amalgram) steel-rod-concrete matrix whisker-metal matrix whisker-plastic matrix wood-plastic matrix, reinforced plastic

and thousands more that do not include plastics. At the atomic level, all elements arc composites of nuclei and electrons. At the crystalline and molecular level, materials are composites of different atoms. In addition, at successively larger scales, materials may become new types of composites, or they may appear to be homogeneous. In this review, RPs is considered to be combinations of materials differing in composition or form on a macro scale. However, all of the

17

18 Reinforced Plastics Handbook constituents in the plastic composite retain their identifies and do not dissolve or otherwise completely merge into each other. This definition is not entirely precise, and it includes some materials often not considered composites. Furthermore, some combinations may be thought of as composite structures rather than composite materials. The dividing line is not sharp, and differences of opinion do exist. Thus the name composite literally identifies many thousands of different combinations with very few that include the use of plastics. In using the term composites when plastics are involved the more appropriate term is plastic composite. However, the more descriptive and popularly used worldwide term is reinforced plastic (RP).

Advantages and Limitations As a construction material, RPs provides practically unlimited benefits to the fabrication of products, but unfortunately, as with other materials, no one specific RP exhibits all these positive characteristics. The successful application of their strengths and an understanding of their weaknesses (limitations) will allow producing useful products. With any material, (plastic, steel, etc.) products fail not because of its disadvantage(s). They failed because someone did not perform their material and process selection in the proper manner a n d / o r incorrectly processed the material (Chapter 9). There is a wide variation in properties among the many commercially available materials classified as RPs. They now represent an important, highly versatile group of engineering materials. Like steel, wood, and other materials, specific groups of RPs can be characterized as having certain properties. As with other materials, for every advantage cited for a certain material, a corresponding disadvantage can probably be found in another. Many RPs that are extensively used worldwide are typically not as strong or as stiff as metals and they may be prone to dimensional changes especially under load or heat. Regardless they are used extensively instead of metals because their performances meet product requirements. There are RPs that meet dimensional tight requirements (includes those that meet zero change), dimensional stability, and are stronger or stiffer based on product shape than other materials including steel. In most cases, a basic beam structure can be used in the design of parts. Conventional designs with other materials are based on single rectangular shapes or box beams because generally, in timber and in steel, they are produced as standard shapes. Their use in RP

1

9I n t r o d u c t i o n

components is often accompanied by a wasteful use of material, as in large steel sections. Using RP, the hollow channel such as I- and Tshapes designed with generous radii (and other basic plastic flow considerations during processing) rather than sharp comers, are more efficient on a weight basis. They use less material that might cause a high second moment of inertia. The moment of inertia of such simple sections possibly causing stresses and deflections is a matter of basic calculations using very simple theories (Chapters 7 and 8). Such non-rectangular sections are common in many RP or unreinforced plastic components. Channels, T-sections, and hollow corner pillars are found in crates and stacking containers, and inverted U-sections and cantilevers that are common in parts such as street lamp housings to aircraft structural parts. Where such latitude exists in designing shapes, as is found in RP materials, designs using large amounts of materials are not necessarily the best, nor do they give the best mechanical and physical performance per unit weight of material. For example, sometimes quite minute amounts of material judiciously placed in, as an example, an injectionmolded crate can make an important difference in the behavior of crates when stacked. Processing any plastics, reinforced or unreinforced, into curved panels is relatively easy and inexpensive. Panels fit the structural theory that curved shaped can be stiffer to bend than flat shapes of the same weight. However, to withstand external pressure, a square section component will usually be heavier than one that is circular and of the same volume. Both single- and double-curvature designs are widely used to ensure a more effective use of RP materials. An example of single curvature in a structural element is the RP translucent corrugated roofing panel that is inherently much stiffer than material of the same volume used as a flat sheet. The stiffness of corrugated panels under loading conditions can be calculated. To improve stiffness further, the corrugated panels can sometimes be slightly curved along the length of the corrugations. Double-curved shells can take the form of special domes, be saddle shaped, or use hyperbolic shapes, as featured in architectural design textbooks. These shapes can be made similar in modular forms molded with RP, thereby providing an efficient structural shape with a higher buckling resistance than special shapes of comparative curvature and thickness. Structural benefits are derived from using RP-faced sandwich designs in different shapes. In addition to shape and size, RPs often possess characteristics that

19

20 Reinforced Plastics Handbook

make them desirable from a design engineering approach, such as cost reduction, ease of fabrication, simplified installation, weight reduction, aesthetic appeal, and the potential to be combined with many other useful qualifies. Cost reduction is reviewed throughout this book. The form the RP takes is determined by the designer's conception or product requirements. It has no inherent form of its own so it must be shaped. This provides an opportunity to select the most efficient forms for the application. Shape can help to overcome limitations that may exist in using a lower-cost material with low stiffness. Tanks and vessels are shaped and fibbed to provide added strength and stiffness to oriented RPs in order to meet required stresses at the lowest cost. Their shape is selected for greatest efficiency. Enclosures of all types can be shaped to meet the requirements of its contents. Where electrical properties, particularly high resistivity are important, such as in insulating hangers for high-voltage electrical lines, RPs can be a logical choice compared to glass and other materials. When minimal strength requirements are to be met, URPs may be adequate. In contrast to the high electrical resistivity of most plastics, graphite fibers, and other fiber materials can provide electrically conductive RP materials. The generally low-specific gravity and high strength of reinforcement fibers such as glass, aramid, carbon, and graphite can provide other benefits. For example, the toughness of these fibers allows them to be molded into very thin constructions. Each have special characteristics, i.e., aramid fibers have increased wear resistance. Information on fiber reinforcements are reviewed in Chapter 2. Industry has learned that the high cost of corrosion in manufacturing can be reduced significantly using well-designed and well-applied RPs. There are a number of factors that have a marked influence on the service life of RP equipment that is used in corrosion service environments. These are: 1. the type of matrix plastic 2. the type of reinforcement 3. the sequence of fabrication of layers 4. the controlled distribution of plastic and reinforcement within the laminate 5. the proper design of the laminate to meet the stress requirements of the structure 6. well-controlled fabrication techniques to assure adequate cure (TS) of the plastic system and minimize faults such as voids and pinholes,

1

7.

9I n t r o d u c t i o n

frequently applying a protective surface plastic layer ranging from 10 to 15 mils in thickness.

The importance of the fabrication technique cannot be adequately stressed. In an appropriate application, a well-prepared RP laminate utilizing the proper materials will guarantee satisfactory performance. Laminates or structures containing the correct plastic matrix and reinforcement combination, but made poorly, will generally not meet expectations. Plastic matrices are largely immune to the electrochemical corrosion to which metals are often susceptible. Consequently, they can frequently be used profitably to contain water and corrosive chemicals that would attack metals (such as chemical tanks, water treatment plants, and piping to handle drainage, sewage, and water supplies). Plastics are subject to attack by some aggressive fluids and chemicals. However, not all plastics are attacked by the same materials. It is generally possible, therefore, to select a plastic matrix to meet a particular condition. Some plastics, such as high-density polyethylene (HDPE), are immune to almost any commonly found solvents. A few such as polytetrafluoroethylene (PTFE) are immune to almost any corrosive conditions. Tolerances should not be specified fighter than necessary for economical production. However, after production starts, the target is to mold as 'fight' as possible to be more profitable by using less material, reducing molding cycle time which results in lower fabrication cost. Serviceability limits are considered to determine performance of the product when subjected to service loads and environments. Service conditions represent those maximum or limiting conditions that are expected in service. Examples of serviceability limits that should be considered in the design of RPs include residual deformation, buckling or wrinkling, deflection and deformation, thermal stress and strain, crazing, and weeping. All plastics can be destroyed by fire, like other organic structural materials such as wood. Some burn readily, others slowly and with difficulty. There are those that do not support combustion upon removal of the flame. The URPs and RPs can be rated in standard codes for varying degrees of combustibility, but none is completely resistant to fire. In certain applications, such as aircraft and transportation vehicles, codes specify a time period prior to flame developing. Since fuel, oxygen, and heat are needed for fire, attempts to reduce the flammability of URPs and RPs center upon suppressing one or more of

21

22 Reinforced Plastics Handbook

these factors. The two most common approaches are the incorporation of flame-retardant functional groups in the molecular structure, and the use of additives. Frequently, both of these approaches operate in combination with reactive combustion promoting free radicals given off during combustion. Additives operate in several ways. The mineral types are resistant to fire and absorb heat. Because they are likely to be good heat conductors, they carry heat rapidly away from local hot spots, thus preventing or delaying the possibility of temperatures rising to the ignition point. There is hydrated alumina whose evaporation retards the raising of temperature until the water evaporates. Some chemical formulation additives, such as aromatics, sometimes form char in cellular forms that insulate the substrate against heat and access by oxygen, thus reducing the chance of fire. In addition, other additives and fillers are used to influence the degree of flammability. Smoke and other volatile combustion products may be as important as, or more important than flame. Gases may be completely innocuous, such as water and carbon dioxide generated by hydrocarbons which burn in sufficient oxygen. When oxygen is deficient, toxic carbon monoxide may be generated with organic plastics and other organic materials used extensively. Depending upon their chemical structure, gases may be noxious or toxic, and dense smoke may not be generated. Some of the most effective flame suppressants promote the formation of smoke. Thus, the designer may have to make a choice between flame and smoke. Sometimes the most effective fire retardants diminish the durability of the plastic matrices when the product is exposed to the outdoors. Again, it may be necessary to make a choice between requirements. Highly favorable conditions such as less density, strength through shape, good thermal insulation, a high degree of mechanical dampening, high resistance to corrosion and chemical attack, and exceptional electric resistance exist for certain plastics. There are also those that will deteriorate when exposed to sunlight, weather, or ultraviolet light, but then there are those that resist such deterioration. For room-temperature applications, most metals can be considered truly elastic. When stresses beyond the yield point are permitted in the design permanent deformation is considered a function only of applied load and can be determined directly from the usual static a n d / o r dynamic tensile stress-strain diagram. The behavior of most plastics is much more dependent on time of application of the load, history of loading, current and past temperature cycles, and environmental

1

9I n t r o d u c t i o n

conditions. This dependency relates to temperature, time, and load. Ignorance of these conditions has resulted in the appearance on the market of plastic products that were improperly designed (Chapter 7).

Responsibility Commensurate with Ability Recognize that people have certain capabilities; the USA law says that people have equal rights (so it reads that we were all equal since 1776) but some interrupt it to mean equal capabilities. So it has been said via Sun Tzu, The Art of War, about 500 Bc that now the method of employing people is to use the avaricious and the stupid, the wise and the brave, and to give responsibilities to each in situations that suit the person. Do not charge people to do what they cannot do. Select them and give them responsibilities commensurate with their abilities. People meet an endless succession of challenges in the workplace, at home, and elsewhere. Since this book concerns reinforced plastics, the target is to have qualified people with the willingness to get things done in the World of Reinforced Plastics. These types of people provide strength in the World of RP technology that provides company profits both financially and product performances. This technology is explained throughout this book.

23

Reinforcements

Overview Many combinations of reinforcements and plastics are used by the plastic industry to affect a diversity of performance and cost characteristics. These may be in layered form, as in typical thermoset (TS) polyester impregnated glass fiber mat, fabric and melamine-phenolic impregnated paper sheets, or molding compound form such as in glass fiber or cotton-filled/TS polyester, phenolic, urea, or nylon RPs. Inline compounds are prepared by injection molding or extruding with short and long glass (and other) fibers. As an example, chopped glass fibers (rovings, etc.) can be fed into an injection-molding machine or a single to twin-screw extruder where principally TP is melted and bonded to the fibers providing an excellent mix. All these resulting plastic RPs have many properties superior to the component materials (Chapter 4). Reinforcements can significantly improve the structural characteristics of a TP or TS plastics. They are available in continuous forms and chopped forms having different lengths, or discontinuous in form (whiskers, flakes, spheres, etc.) to meet different properties and/or processing methods. Glass fiber represents the major material used in RPs worldwide. Others provide higher structural performances, etc. The reinforcements can allow the RP materials to be tailored to the design, or the design tailored to the material (Figures 2.1 and 2.2 and Tables 2.1 to 2.3). The large-production reinforcing fibers used today are glass, cotton, cellulosic fiber, sisal, jute, and nylon. Specialty reinforcing fibers are carbon, graphite, boron, aramid, whiskers, and steel. They all offer wide variations in properties, weight, and cost.

2 . Reinforcements 25

Figure 2, I Comparison of specific strength vs. specific modulus of RPs. Specific properties are normalized by RP density (Pa or N/m 3 divided by kg/m 3) Epoxy

60% c a d ~

Steel

S.esl

I~polly

~en

Aluminum

Epoxy Epoxy

Su~in

Figure 2,2 Tensile stress-strain curves for different fiber/epoxy and aluminum and steel materials

Fibers in RPs are primarily used to reinforce a resin by transferring the stress under an applied load from the weaker resin matrix to the much stronger fiber. Plastics provide valuable and versatile materials for use as matrices, but other materials, such as metals, ceramics, and cements, are

Table 2.1

Properties of synthetic and natural-inorganic or organic and metallic fibers

Fiber Synthetic-Inorganic Conventional glass (Type €1 Beryllium glass Quartz (fused silica) Carbon Aluminum silicate Graohite Rock wool Natural-inorganic asbestos Metals and refractories Steel Aluminum Tungsten Ta nta I u rn MoI ybden u m Magnesium Synthetic-organic FI uorocar bon Polyester Acrylic Polya rnide Cellulose acetate Regen era ted ce IiuI ose [rayon] Natural organic Cotton Sisal Wool

sp. GI:

length, in.

Diameter, P.

Tensile strength 1 0 3 , psi

Modulus o f elasticity x 10-6,PSI

Heat resistance, "F

Coeffof linear expansion 2.8 6 5-7 1-3 1-8

2.6

-e b

5-15

400

10.5

2.6 2.2 1.8 2.7 3.9 1.6

-0. b

5-15 8-10 1-100 2-20

280 100-350 20 100-600

12-20 10-25 1-4 2-1 5

6OOc 1500d 1500d 35OOc 6200e 3300d

to 4

2-30

2-20

-

6764'

0.6-4

2.2 2.8

up to 4

1-22

2800d

2-6

2.5

up to 4

1-3

0.02

100-200

2770d

20-25

1-25 4-20 20 5 5-20 6-1 5

200-400 60-90 200 70-90

20-30 10 58 28 42

2920e 1212e 61 50e 5390e 4700e 1200e

8-10 17-20 4.5 6.6 5.4 8-20

20 10-25 10-25 10-40 11-44 10-40

47 100 50 70- 120 25 30-105

17 19 28

50- 100 120 29

7.8 2.8 19.3 16.6 10.2 1.8

-0,b

-0.4

up to 10 UD

-o,b -0. b

up to 1 up to 0.5 up to 0.5 -0, b

2.2 1.4 1.2 1.1 1.3 1.5 1.6 1.3 1.3

up to 2 up to 24 UD to 15

Filament DStaple 'Softens dDecomposes 'Melts Tublimes Wsed up to this temperature

40

6

0.4 -

-

525' 480e 450e 480e 500e 400d 2759 21 29 21 29

i

?

8 P I ! b vl

9

2

I a a

P

U 0 0

x

eN

o

c-

~5

o

o

c-

o

x

r

Table 2.2 Examples of mechanical properties of unidirectional RPs ~

Transverse compressive strength MPa [Ksi) ~

o

~

lnplane shear strength MPa (Ksi)

0

0 I'~

0

0 ~

0

0 qo

.~,

0 O0

0

0 o'~

00

0 I'~

LO

co

0

~

0 I~

LO

0

co

~

0 r'.-

Lr~

0 00

0 0

LO

,--~

0 0

LO

,--

C~l ,~.~ ~ .

o

0

~. W ~. o

0

O eO

0

O cO

0

O O

0

O ~--

0

o

O cN

0

o o '~- c o

O CO

620 (90) 280 (40) 3310 (480) 1380 (200) 1380 (200) 760 (110) 280 (40) 280 (40) 0

O CO

0

O LC~

O O OU

1520 (220) 3530 (510) 1380 (200) 900 (130) 900 (130)

40 (7) 30 (4.3) 70 (10) 41 (6) 41 (6) 41 (6) 20 (3) 20 (3)

0 Q/

~'~'~

O O OU

LO C'q

O CO c~

LO C~I

O CO ~

0 ~

O CW ~

LO C'q

O ~cN

1.0 LO C'xl C'q

qO

O ~C'~

'~" CO

1020 (150) 1240 (180) 1240 (180)

Axial compressive strength MPa (Ksi)

~

o

Transverse tensile strength MPa (Ksi)

O C~ O

0

d o o d o d o d

00 C~I

cO

~-

qO

(9")

cO

~:

CO

OU

r~.

~-

c~

OU

co

~-

0.28 0.34 0.25 0.25 0.25 0.20 0.25 0.25

Axial tensile strength MPa [Ksi)

N~

.tll

Poisson's Ratio 0

r,D

O

5.5 (0.8) 2.1 (0.3) 4.8 (0.7) 4.1 (0.6) 4.1 (0.6) 4.1 (0.6) 4.1 (0.6) 4.1 (0.6)

"B.~

~

~-

0

~

_o

O

0

~

c4

0

.~ ~._

OU

0

~

~

r~

0 _o

~-

c'0

_o

c ~ m ~ ~ v

o

0

o

~

2 (1.8) 5.5 (0.8) 19 (2.7) 10 (1.5) 10 (1.5) 9 (1.3) 9 (1.3) 9 (1.3)

~-

45 (6.5) 76 (11) 210 (30) 145 (21) 170 (25) 310 (45) 480 (70) 480 (70)

cN

E-glass Aramid Boron SM carbon (PAN) UHS carbon (PAN) UHM carbon (PAN) UHM carbon (pitch) UHK carbon (pitch)

~

L~

Transverse modulus GPa [Msi)

E

Fiber

Axial modulus GPa (Msi)

lnplane shear modulus GPa (Msi)

140 (20) 140 (20) 280 (40) 170 (25) 170 (25) 170 (25) 100 (15) 100 (15)

70 (10) 60 (9) 90 (13) 80 (12) 80 (12) 80 (12) 41 (6) 41 (6)

2-Reinforcements 27

28 Reinforced Plastics Handbook Table 2.3 Cost comparison of type fibers and mechanical properties (glass cost = 100)

Structural requirement

Compressive strength Tensile strength Tensile modulus

E-glass

Carbon (1997)

Carbon (2000)

Weight Cost

Weight Cost

Weight Cost

1000 1000 1000

1.00 1.00 1.00

419 267 147

6.91 4.40 3.14

419 267 147

2.88 1.84 1.30

Source: Reinforced Plastics

also used as matrices for fibrous reinforcement composites. For an efficient RP under stress, the elongation of the fiber must be less, and its stiffness modulus higher, than that of the matrix. Stress transfer along the all-important fiber/matrix interface can be improved by use of sizings, binders, or special coupling agents. The diameter of the fiber also plays an important part in maximizing stress transfer. Smaller diameters give a greater surface area of fiber per unit weight, to aid stress transfer in a given reinforcement context.

Glass Fibers Glass fibers, the most widely used at over 90% of all reinforcements with TSs or TPs matrixes, arc available in many forms for producing different commercial and industrial products. They also include parts in aircraft to space vehicles, and surface water to underwater vehicles. The older and still most popular form is E-glass. Other forms of glass fiber are used that meet different requirement such as S-glass that produces higher strength properties. Materials in the form of fibers are often vastly stronger than the same materials in bulk form. Glass fibers, for example may develop tensile strength of 7 MPa (1,000,000 psi) or more under laboratory conditions, and commercial fibers attain strengths of 2,800 to 4.8 MPa (400,000 to 700,000 psi), whereas massive plate glass breaks at stresses of about 7 MPa (1000 psi). The same is true of many other materials whether organic, metallic, or ceramic. Compression wise there are plate glasses that are the strongest of any material (steel, etc.) however very weak under other loads. Acceptance and use of nonwoven fabrics as reinforcement of structural plastics continues to increase. Theoretically only with nonwoven fiber

2 . Reinforcements 29

sheet structures can the full potential of fiber strength be realized. Great advances have been made in developing new fibers and plastics, in new chemical finishes given to the fiber, in methods of bonding the fiber to the plastic, and in mechanical processing methods. Nonwoven fabrics are inherently better able to take advantage of these developments than are woven products. Strength of commercial RPs is far below any theoretical strength. Ordinary glass fibers are three times stronger and stiffer for their weight than steel. Nonwoven glass fiber structures usually have strength about 40 to 50% below that of woven fabric lay-ups. In special constructions, properly treated fibers have produced products as strong as the woven product, better in some cases. RPs are usually applied as laminates of several layers. Many variables are important in determining the performance of the finished product. Some of the important ones arc orientation of plies of the laminate, type of plastic, fiber-plastic ratio, type or types of fibers, and directional orientation of fibers (Chapter 7). Nonwoven fabrics are fibrous sheets made without spinning, weaving, or knitting. They include felts, bonded short to long fiber fabrics, and papers. The interlocking of fibers is achieved by a combination of mechanical work, chemical action, moisture, and heat by either textile or paper malting processes. Still stronger and stiffer forms of fibrous materials are the unidirectional crystals called whiskers. Under favorable conditions, crystal-forming materials will crystallize as extremely fine filamentous single crystals a few microns in diameter and virtually free of the imperfections found in ordinary crystals. Whiskers are far stronger and stiffer than the same material in bulk form. To date their use is limited principally due to special handling requirement during fabrication into RPs and cost. Fine filaments or fibers by themselves have limited engineering use. They need support to hold them in place in a structure or device. This is accomplished by embedding the fibers in a continuous supporting matrix (plastic) sufficiently rigid to hold its shape, to prevent buclding and collapse of the fibers, and to transmit stress from fiber to fiber. The matrix may be, and usually is, considerably weaker, of lower elastic modulus, and of lower density than the fibers. By itself, it would not withstand high stresses. When fibers and matrix are combined into a plastic composite, a synergistic effect occurs; combination of high strength, rigidity, and toughness frequently emerges that far exceed the properties in the individual constituents. Glass fibers are a family of short (staple, chopped, milled), long chopped, or continuous fiber reinforcement, used widely with both TSs

30 Reinforced Plastics Handbook

and TPs for increased strength, dimensional stability, thermal stability, corrosion resistance, dielectric properties, etc. (Figures 2.3 and 2.4). ~IL

HIGHER

~

1

GER

JCONCENTRATIONI / / MORE ~ / ORIENTATI~~

~

~

~

BETTER T FIBERS ~~176 -<--.~-X/~.o~,E.

r~ ~

~

JlP FIBERS

,

,

0.01

O. I

I.O

IO

FIBERLENGTHS(mm)

Figure 2.3 Short to long fibers influence properties of RPs Flexural modulus, million psi

4.

3-

0 t~5~ 0 IdOl

(~0J0

0 c55~ O (4o)

c401D

,- .,,-.,o.,,..,., -,,

Long-fiber compounds

P" Ops' O"y'~

% Gloss shown in porenlheses I

2

3

4

5

I

i

10

notched Izod Impact Strength, (ft-lb/in.)

Figure 2.4 Mechanical properties of short and long fiber/thermoplastic compounds (BMCs)

Glass fibers have high tensile strength combined with low extensibility (3.5%), giving exceptional tensile, compression and impact properties, with a relatively high modulus of elasticity and good bend strength. It also has high temperature resistance and low moisture pick-up, giving good dimensional stability and weather resistance. Finally, low moisture

2

9R e i n f o r c e m e n t s

absorption makes it possible to produce moldings with good electrical properties that do not deteriorate, even under adverse weather conditions. However proper bond between fiber and resin matrix has to exist otherwise properties of the RP will be significantly reduced or destroyed with the migration of moisture between the fiber and resin. The fiber also exhibits virtually elastic behavior. It will stretch uniformly under stress to its breaking point without yielding and, on removal of the tensile load short of breaking point, the fiber will return to its original length. This lack of hysteresis (which is not found in conventional metal and organic fibers), together with high mechanical strength, makes it possible for glass fiber to store and release large amounts of energy without loss. If protected against abrasion, this capability, together with dynamic fatigue resistance is put to effective use in applications such as springs for automobiles, trucks, trailers and furniture. The fibers are made by the melt drawing of various grades or types to be reviewed (electrical, chemical, high tensile strength, etc.) of glass and are comprised of strands of filaments that can be further processed by size reduction, twisting, or weaving into fabrics or mats (Figure 2.5). The fiber is produced by blending the raw materials (sand, kaolin, limestone and colemanite) and feeding the mix into a batch oven heated to about 1600C. The liquid glass flows into channels and the fibers are drawn through electrically heated bushings, each of which can produce thousands of filaments of 10-24 pm diameters. The filaments are coated with size, to ensure cohesion and protect them from abrasion (also providing properties essential for subsequent processing operations). Finally, the wet fiber is dried and processed into its finished form. To be effective, the reinforcement must form a strong adhesive bond with the plastics; for certain reinforcements special cleaning, sizing, coupling agents, finishing, etc. treatments are used to improve bond. They are often surface modified to provide a special property such as electrical conductivity (by coating with nickel, etc.). Also used alone or in conjunction with fiber surface treatments are bonding additives in the plastic to promote good adhesion of the fiber to the plastic. Different types of reinforcement construction are used to meet different RP properties a n d / o r simplify reinforcement layup fabricating processes to meet design performance shape requirements. They include woven, nonwoven, rovings, prcforms, and others. These different constructions are used to provide different processing and directional properties.

31

32 Reinforced Plastics Handbook

Quarryproducts

Glasscompound

I

'

$ Production

Furnace vvv99~vtvtv~9~vwvvv~9~999~9~vtvgvvvvvv~vQvvvvvvvv'v~

F

Drawing

,, Molten glass

Bushing

~VVgVV~gVVVWgVV~gVVgVVg~VgVVt99VgVVV~V~Vv~ iqPVVVVVVV~VV~VV~V~VVVV~999VVVVgVVgVg~VVVVVVg~ iVV~VVVg~gggggVVVVVgVVV~

Filaments, E~5 to 24l~m Sizing Basicfiber linearweight2.5to 4800tex .~o,, j ~ ~ a t c h

Bins S

ElevatingTracks

~ / ; . ,~ . ~n~ BatchMelting ' ~/_ k J ~ t c h Mixer J , / ~ i~..~ and GlassRefinring ~ ~, . ~ ( ~'/ ~ ~ B . a t c_ . . ~_ ~ ~ ~ Batch ran s ~~r "DayTank" ' Reheating Raw Materials

/ /

/ /

/

I ! Coffector ~ Car

Weighing Hoppers and AutomaticRecording Scales

I I "1~

Marble Formingc~r ~ o , , Inspection ~v.oo~na

STAPLE FIBER PROCESS

J i Sliver Winding on Tubes

~

Marbles

n

I ElectricFurnace n Bushing r'\Steam~ Apron

III!11 . ~ , ~~.~ LubricantSpray ~'~ DryingTorch

~~.~~"Revolving Drum Sliver to Drafting and Twisting to Form Yarns I

~

CONTINUOUS FILAMENT PROCESS

arbles ElectricFurnace Bushing

ilament Forming atheri:fgF~lndmL:bricating

~ High-Speed Winder

Strands to

Yarns

Throwing Department to Form Yarns

To Weaving and Textile Fabrication - or Direct to Wire and Cable Manufacturers

Figure 2 . 5 Condensed and detailed schematics for production of glass fiber

Cullet Can

2. Reinforcements 33 Manufacturers are moving to a policy of making a product of identical specification available anywhere in the world, from a platform of a common technology. There is also an industry-wide initiative to convert the standards for glass from classification by composition to classification by properties.

Long Fibers In production of injection molding compounds, some amount of mechanical work occurs. If proper equipment is not used, fiber reinforcement is inevitably broken up into very short lengths. Because of this situation, TP molding compounds can contain very short lengths of fiber (typically 0.3 mm). The mechanical properties of the compound are closely related to the length of the reinforcing fiber. With the proper equipment, longer fibers are retained if not complete lengths retained. In an ideal nylon 6 / 6 compound reinforced with 50 wt% glass fiber and with all fibers aligned along the length of the molding, the flexural and tensile moduli increase rapidly as the fiber length is increased from 0.1 mm to 2.0 mm. These are produced, not by classical physical mixing, but by a process analogous to the TS resin pultrusion process, with internal lubrication additives to counteract the chopping effect of injection molding plasticizing screw action (Chapter 5). However, with the proper injection molding technology (Ingersoll-Rand IMPCO machine, etc.) used since at least the 1970s, RTPs can be processed retaining long fiber lengths. Notched Izod impact strength tests have been conducted on the effect of fiber length in a nylon 6 / 6 compound reinforced with 50 wt% glass fiber. It shows that impact strength of reinforced TPs (RTPs) increases significantly, as fiber length is increased. Similar effects have been measured with other fibers, such as aramid and carbon, and with other matrices, such as polypropylene and polyphenylenc sulphide. The theory has shown that an improvement of some 50% in mechanical properties should be produced by increasing fiber length from 0.3 mm to 2 mm. Several producers and specialist compounders of TPs have long fiber technology using nylons, polypropylenes, TP polyesters, and polyphenylene sulphide (PPS). As an example LNP Engineering Plastics, USA has been publishing results of tests that include a selection of die-cast metals compared with a 60 wt% long glass fiber reinforced nylon 6 / 6 compound (Verton RF700-12EM). The conclusion was that (for moisture-conditioned samples) with a density lower than metals, with the exception of certain

34 Reinforced Plastics Handbook magnesium alloys, a long fiber-reinforced nylon 6 / 6 compound shows reasonable tensile strength, high impact, and good elongation. Flexural modulus, however, is low. When values are calculated relative to density, the specific tensile strength of the nylon compound exceeds all alloys tested and the modulus is a little below that of the zinc alloys (Zamak). Shear strength values are close to those of magnesium and aluminum and about twice those of Zamak. Specific impact favors nylon 6 / 6 by a factor of nearly seven compared with Zamak, and 30 compared with aluminum. With long fiberglass reinforcement, the mechanical values of the nylon compound are less influenced by temperature. The effect is seen particularly at low temperatures, where impact strength falls by only 5% at --40C, where Zamak alloys fall from about 60 Joules at room temperature to 5 Joules a t - 2 0 C . At elevated temperatures (120-170C), the performance of nylon is at least comparable with that of most of the die-cast alloys. Compared with short fiber reinforced TPs, resistance to creep is outstanding, up to 140C. The LNP report concludes that long fiber TPs offer a viable alternative to metals in many structural applications, at temperatures up to 175C. Of the long fiber RTPs, polypropylene is the most interesting due to the relatively low cost of the matrix material. A typical range is in the form of 15 mm (0.59 in) chips with 20-50 wt% glass content. Properties include high dimensional stability, low warping, good surface finish and elimination of the usual effects of shrinkage. The compound offers high impact, especially a t - 2 0 C to + 30C (-4F to + 86F) and is free of ductile fracture (shatter). Stability at elevated temperature is good: a 40% long glass fiber compound withstands 150C (300F) under 1.8 MPa loading. Long-fiber nylon 11 and 12 (30/50 wt% glass fiber) shows up to 200% improvement in impact, dimensional stability, good surface appearance, low moisture content and improved abrasion resistance. Table 2.4 provides short- and long-glass fiber/nylon 6 / 6 RPs properties at elevated temperatures.

In-Line Compounding Automobile underbody shields of glass fiber filled polypropylcne (PP) produced on an unusually elaborate, multi-step system for direct molding of long fiber thermoplastics with in-line compounding. Sources at machine builder Dieffenbacher GmbH & Co. in Germany reported this was its most complex installation ever for auto-parts production. The system was delivered to Menzolit-Fibron GmbH of

2 . Reinforcements 35 Table 2.4 Exampleof short- and long-glass fiber/nylon 6/6 RPs properties at elevated temperatures Short fiber Property

300/o

Long fiber

50%

30%

50%

13.8 7.8 14.3 5.27

14.3 5.3 17.4 5.50

19.2 5.6 23.7 8.90

7.3 9.5 7.4 4.80

7.8 6.2 8.9 5.19

8.3 6.8 10.0 7.51

At 300~

Tensile strength (103 psi) Elongation (%) Flexural strength (103 psi) Flexural modulus (105 psi)

12.8 9.3 13.8 4.64 At 400~

Tensile strength (10 3 psi) Elongation{O/o) Flexural strength (103 psi) Flexural modulus (10s psi]

6.3 8.6 6.9 3.96

Data on long-fiber glass-reinforced grades are for Verton compounds * To convert psi to pascals (Pa), multiply 6.895 x 103

Bretten, Germany, and on start up fabricated parts for the Volkswagen Golf, AudiA3, and other cars. The plant starts with twin-screw compounding of PP and glass fiber to produce a hot sheet, which is robotically transferred to a vertical compression press of 3300 tons. The fast-stroke press has automatic parallelism control. Another robot transfers parts to a l l0-ton press that punches out attachment holes in the parts. Finally a third robot transfers parts to a machine that inserts hole reinforcements and inspects the parts. With double tools, the line can produce two parts every 22 s. Dieffenbacher reports the line is designed to operate on cycles as short as 20 sec. A single supervisory computer oversees the entire process. A barcode printer records critical process data for each molding cycle on each part. (Contact Tel: 519-979-6937, www.dieffenbacher.com)

Long Aligned Discontinuous Fiber Technology LDF (long discontinuous fiber) technology is a proprietary technology, employing reinforcement of long aligned discontinuous fibers, including carbon, aramid, or glass. In high-performance TP matrices, such as the polyether ketone group of materials [polyetheretherketone (PEEK), etc.], aligned, discontinuous fibers provide a drawable feature that can

36 Reinforced Plastics Handbook

overcome some of the thermoforming limitations encountered with continuous fiber systems (Table 2.5). Fabrication processes such as stretch forming and press forming can be used. The technology is claimed to be cost-effective in manufacture of complex shape parts of aerospace structures. Composites demonstrate excellent mechanical properties comparable with those of continuous fibre-reinforced products. Table 2.5 LDFtechnology applied to aramid/PEEKreinforced thermoplastics

Property Tensile: Strength (0~ Modulus (0~ Strength (90 ~ Modulus (90 ~ Compressive: Strength (0~ Flexural: Strength (0~ Modulus {0~ Shear: Inplane strength Inplane modulus Short beam shear strength

Unit

LDFtechnology

Continuousfiber

MPa GPa MPa GPa

1100 725 21 6.2

1240 76 18 5.5

MPa

269

255

MPa GPa

656 63

760 64

MPa GPa MPa

64 2.1 55

55 2.1 55

QBT Technology An advanced reinforcements system identifies QBT. It is the name for a biaxial thermoplastic (PA, PBT, PET, PP/PPS, PE1, APC-2, Radel), carbon, aramid, and glass pre-impregnated tape. It is unidirectional, interlaced in biaxial form, in continuous lengths and very large width (up to 10 ft). It maintains and improved properties of unidirectional cross-ply laminates, giving the benefit of unidirectional tape in larger and more easily processed formats. It is claimed to be first real alternative to a woven composites compromise, with good drape.

Pushtrusion/Injection Molding Processes The Pushtrusion direct inline process for molding small to large products is accomplished by compounding and injection molding (IM) in a single operation long and/or short fibers from continuous fiber reinforcements. Details are reviewed in Chapter 5 Injection Molding.

Pushtrusion/Extrusion Processes The Pushtrusion direct inline process for extruding small to large profile products is accomplished by an in-line, single operation compounding

2

Reinforcements 9 37

extruder and injection molding (IM) of long a n d / o r short fibers from continuous fiber reinforcements. Details are reviewed in Chapter 5 Extrusion. Aspect Ratios

Aspect ratio of fibers is applicable to RPs. It is the ratio of length to diameter ( L / D ) of a fiber (also the ratio of the major to minor axis lengths of a material such as a particle). In RPs fiber L / D will have a direct influence on the RP performance. High values of 5 to 10 provide for good reinforcements. Lining up and overlapping fibers (disks, etc.) takes advantage of directional properties. Theoretically, with proper layup the highest performance RPs (using fibers such as glass, graphite a n d / o r boron) could be obtained when compared to other materials. These ratios can be used in determining the effect of dispersed additive fibers a n d / o r particles on the viscosity of a fluid/melt and in turn on the performance of the compound based on L / D ratios. Woven Constructions

Woven reinforcement material constructed is by interlacing fibers, yarns, or filaments to form such fabric patterns as basket, plain, harness, satin, leno weaves, scrim, etc. These different weaving patterns are used to provide different processing a n d / o r directional properties. There are filling threads that represent threads in the so-called machine direction; warp threads represent those in the transverse direction or at 90 ~ to the filling threads. Nonwoven Constructions

There are certain types of so-called nonwovcn fabric that are directly formed from short or long chopped fibers as well as continuous filaments that may be in circular or other patterns. They are produced by loosely compressing together fibers, yarns, rovings, etc. with or without a scrim cloth carrier; assembled by mechanical, resin, chemical, thermal, a n d / o r solvent methods. Products of this type include melted and spun-bonded fabrics. The nonwoven spun-bonded integrates the spinning, lay-down, consolidation, and bonding of continuous filaments to form fabrics. Felt is the term used to describe nonwoven compressed fabrics, mats, and bats prepared from staple fibers without spinning, weaving, or knitting; made up of fibers interlocked mechanically. A fibrous material extensively used in RPs is the mat constructions. It consists of different randomly and uniformly oriented products:

38 Reinforced Plastics Handbook 1

chopped fibers with or without carrier fibers or binder plastics

2

short fibers with or without a carrier fabric

3

swirled filaments loosely held together with a plastic binder

4

chopped or short fiber with long fibers included in any desired pattern to provided addition mechanical properties in specific directions

5

chopped or long fibers included in any desired pattern to provided maximum mechanical properties for mats in specific directions;

and so on. There are reinforcement preform constructions. A preform is a method of making chopped fiber mats of complex shapes that are to be used as reinforcements in different RP molding fabricating processes (hand layup, injection, etc.). Oriented fiber patterns can be incorporated in the preforms (Chapter 5). When conventional flat mats are used, they may tear, wrinkle, or give uneven glass distribution when producing complex shapes. To alleviate this problem, it is necessary to take great care in tailoring the mat and in placing it properly in or on the mold cavity. Otherwise, mats may cause poor products or poor production rates. Preforms are used to overcome these problems. They are slightly more expensive for short production runs. However, they are used when mats are considered impractical, or a relatively high production run exists that offset the higher cost.

Glass for Special Reinforcements Special types of glass fiber for specific processes (Chapters 4 and 5), such as sheet molding compound (SMC), pultrusion, and reinforcement of thermoplastics, is a marked trend in current development. Examples follow:

For SMC, a needled mat reinforcement from PPG (MatVantage SMC) reduces overall system costs while providing compounders with a product with higher level of uniformity, using expertise in producing needled mat for glass mat thermoplastics. As a prefabricated needled glass fiber mat, it removes a number of subsidiary systems from manufacture of SMC, and the removal of roving adds the benefit of eliminating fuzz and fly issues, strand entanglement problems, and chopper investment and maintenance. It allows reinforcement levels of up to 50 wt%, which could support the use of SMC in structural applications such as bumper beams.

2 . Reinforcements 39

Owens Coming has also developing a structural pigmentable sheetmolding compound roving for general purpose and semi-structural applications. Also for SMC (and described as the next generation of reinforcement) is Roving 23C from Vetrotex. It is easily chopped with good fiber distribution, fast wet-through, wet-out, and generating low fuzz and fly. It is particularly suited to molding of automobile doors, wings, boot lids, spoilers, cross-car beams and other components.

For wet lay-up, resin transfer molding (RTM) and SCRIMP molding processes, a stitched mat which combines some of the advantages of mat and woven roving (Fabmat from Fiber Glass Industries, USA) improves consistency, enabling processors to maintain good control of laminate weight and thickness. It can be formed to tight radii without any tendency to spring back and, with rapid wetting out, can reduce molding cycle times.

For pultrusion, a heavier roving from Owens Corning (366 high rex type 30) cuts costs. It has a nominal weight of 9600 tex, doubling the weight of any previously available single end roving, so that the product requires less than half the number of ends to produce a part of equal glass content.

Flexible knitted reinforcement for complex shapes Syncoflex (from Syncoglas), provides a regular strength distribution across the whole surface (virtually equal values in all directions). The reinforcement has many holes allowing quick and thorough wetting out.

For TPs, improved chopped strand glass fiber grades for reinforcement of nylon and TP polyester (PET) are from PPG Industries, in response to the increasing use of glass fiber-reinforced thermoplastic RPs, in automotive components especially. They include:

Type 3660 chopped strand, for use with hydrolysis-resistant nylon 66 compounds, aimed particularly at glass-reinforced nylons for radiator and other under-bonnet automotive applications. It has improved elongation and toughness after exposure to ethylene glycol engine coolant, giving up to 10-30% higher impact resistance in impact-modified compounds.

Type 3563 chopped strand arises from a breakthrough in sizing, giving 50% better resistance to generation of fuzz during transit, while superior strand integrity allows the fiber to be conveyed horizontally for more than 130 m in a dense-phase conveying system. It is suitable for PET grades including glass filled, glass/mineral (where a 20% improvement in impact is claimed), and high-glass

40 Reinforced Plastics Handbook

content, flame-retardant, and impact-modified. The novel sizing chemistry also makes it a candidate for polymer blends and alloys containing compatibilizers.

High strength and brilliant whiteness is provided by PPG glass fiber reinforcement with PE Maxichop 3298 chopped strand uses new sizing chemistry that gives color control during compounding and molding. By maintaining whiteness during processing, the amount of white pigment required is substantially reduced, allowing mechanical properties to be maintained.

Fiber-directed preforms development, where new glass fiber reinforcements have been designed specifically for liquid RP molding applications such as resin transfer molding (RTM) with TS polyesters. A new E-glass roving gives fast wet-out with TS polyester, vinyl ester, epoxy, phenolic, urethane, and furan resin systems, due to low sizing content. Low loss on ignition means that there is not an excessive amount of sizing to be broken down by the styrene in the resin.

Fiber reinforcement ofpolypropylene (PP) has attracted a number of developments, both for injection molding compounds and for glass mat TP products. For molding compounds, a new range of fiber products for homopolymer and chemically coupled PP has been introduced by Owens Corning under the name Cratec 146A chopped strand. It aims to enhance the properties of the RP and improve its whiteness, while maintaining a good balance of cost and performance. In chemically coupled PP RPs, it is possible to improve properties with the same or a lower amount of coupling agent. Glass fiber in both 14 and 17 micron diameters is available (but the company's research so far shows little difference between them in PP compounds).

Other new forms of glass reinforcement (from Chomarat) include Rovimat (woven roving/chopped fiber fabric), Aramat (glass/ aramid hybrid), Diagonap (muhiaxial fabric for isotropic strength where required, such as in windmill blades) and Rovicore (woven fabric/chopped fiber fabric for closed molding). Rovicore is a sandwich of chopped strand or woven mat with a core layer of large diameter unidirectional glass fibers that can easily be stretched around shapes, to eliminate preforming. A modification is Rovicore mat, a nonwoven core of large diameter fibers in the sandwiched construction without chemical binder or woven mat, the whole sandwich mechanically stitched together. It has high deformability and a surface veil gives good finish, while the molded part has good

2

Reinforcements 9 41

stiffness from the sandwich structure. It is particularly suitable for RTM and vacuum molding. Glass, Silica, Quartz Fibers

The term high silica is used to describe any high-purity glass. For use in RPs, it is at least 95% pure silicon dioxide (SiO2) produced by a leaching process; glass fiber, with a silica content of 65%, is subjected to a hot-acid treatment that removes virtually all the impurities while leaving the silica in tact. High silica fibers and fabrics are flexible materials that are similar in appearance as conventional E-glass fibers. Quartz, somewhat similar to glass and high silica, has 99.95% SiO2. High silica and quartz are both used in a wide variety of similar products. The selection of what type to use is generally dictated by a combination of performance requirements, manufacturing needs, and cost. Quartz has about five times the tensile strength of high silica and both have similar thermal characteristics. The major difference is the higher melt viscosity of quartz because of its higher silica content. Both do not melt and vaporize until a temperature exceeds 3000F (1649C). At continuous temperature in excess of 1800F (982C), both forms will begin to denitrify into a crystallized form known as cristobalite. This conversion tends to stiffen the materials, but causes no change in their physical form. Their products can be heated to 2000F (1093C) and rapidly quench in water without any apparent change.

Glass Characteristics In designing fibrous-RPs it is necessary to take into account the combined actions of the fiber and the plastic. At times, the combination can be considered homogeneous; in many cases, homogeneity cannot be assumed. Information on glass fiber compositions, behaviors, properties, and terminology follows: Glass, borate A glass in which the essential glass former is boron oxide instead of silica Glass chopper A chopper gun cuts long glass fibers into strands and shorter fibers to be used as reinforcements in preforms, spray, etc. Glass cloth Woven glass fiber material. Glass collet The drive wheel that pulls glass fibers from the bushing/spinneret; a forming tube is placed on the collet and a package of strand is wound upon the tube.

42 Reinforced Plastics Handbook

Glass composition Glass is an inorganic product of fusion that has cooled to a rigid condition without crystallizing. Glass is typically hard and relatively brittle, and has a conchoidal fracture. It contains the most abundant elements of the earth that is sand. Although basically a ceramic product, glass is an amorphous inorganic plastic. Glass is always used in its elastic range; below its glass transition temperature (Tg). Most glass is based on the silicate system and is made from the three major constituents of silica (SiO), lime (CaCO3), and sodium carbonate (NaCO3). Various oxides are added to tailor the glass to meet specific requirements. Families of glass include sodalime (most common: windows, bottles, drinking glasses, etc.), borosilicate (thermal and chemical shock resistance), lead-alkali (optical applications, better electrical), alumino-silicate (high operating heat), silica (formable), and fused silica (high properties; expensive). Glass, continuous Also called long glass fiber, continuous strand roving, continuous roving, or continuous glass roving. They are strands of filaments (rovings) that can be twisted and used alone or in many different configurations for use in reinforcing plastics and elastomers. Glass devitrification Formation of crystals (seeds) in a glass melt, usually occurring when the melt is too cold. These crystals can appear as defects in glass fibers. Glass devitrified Glass with controlled crystallization. Glass fiber Also called glass fiber and Owens-Corning trade name Fiberglas TM. Glass fibers represent the major material used in RPs. They are a family of short (staple, chopped, milled) or continuous fiber reinforcement, used widely with both TSs and TPs for increased strength, dimensional stability, thermal stability, corrosion resistance, dielectric properties, etc. Available in different forms such as mat, fabric, roving, etc. The fibers are made by the melt drawing of various grades (electrical, chemical, high tensile strength, etc.) of glass and are comprised of strands of filaments (rovings) that can be further processed by size reduction, twisting, or weaving into fabrics or mats. They are often surface modified with coupling agents to improve bonding with plastic matrix and/or to impart special properties such as electrical conductivity (by coating with nickel). Glass fiber, bare It is glass fiber from which the sizing or finish have been removed. It is also the glass fibers prior to the application of sizing or finishing.

2 . Reinforcements 43

Glass fiber, bilobe Fibers of non-round cross section are prepared by different methods in various geometries. The shapes provide a different fiber packing. Glass fiber b i n d e r / s i z i n g coupling agent This treatment is used on different types of fibers to provide meeting their specific requirements such as bonding capabilities a n d / o r protection of fibers. A major requirement for these agents involves treating glass fibers. Continuous glass fiber (as well as other fiber) strands intended for weaving are treated at their forming bushing during their manufacture with starch-oil binders. These binders protect the fibers from damage by lubrication during their formation and such subsequent textile operations as twisting, plying, and weaving. Usually they are satisfactory when used with TPs but are not compatible with most TSs. The hydrophilic character of the binders allows moisture to penetrate the glass-plastic interface, which leads to degradation of TS-RPs in wet and humid environments. Binder is removed via heat treatment before being used with these plastics. This is accomplished by exposing the reinforcing material (fabric, etc.) to carefully controlled time-temperature cycles. To protect the weak heatcleaned fibers, chemical sizing coupling agents are used such as methacrylic chromic chloride complex, organosilanes, etc. Glass fiber bushing The spinneret platinum unit through which molten glass is drawn in making glass filament. Glass fiber cheese A supply of glass fiber wound into a cylindrical mass. Glass fiber chopped Fiber glass can be cut to deferent lengths of fibers or produced into short fibers. Their length can range from milled to any short length with the usual about 1/8 to 2 in. (3.2 to 50 mm) or to long lengths of 2 to 5 in. (5 to 12.7 cm) for use in molded RP products. See Glass fiber milled. Glass fiber, continuous Also called long glass fiber, continuous strand roving, continuous roving, or continuous glass roving. They are strands of filaments (rovings) that can be twisted and used alone or in many different configurations for use in reinforcing plastics and elastomers.. Glass fiber diameter The industry standard provides for the RP industry letter designations that range from about 1.5 to 5.1 x 10 -4 in (3.8 to 13 l~m). Glass fiber forming package A single glass strand gathered on a thinwall paper or plastic tube to be used in manufacture.

44 Reinforced Plastics Handbook

Glass fiber milled Also called milled glass filler. Usually produced by hammer milling equipment continuous glass ends into very short fibers ranging from 1/64to 1/4 in. (0.40 to 6.35 mm). They produce lower stiffness and strength than chopped fiber, but controlling heat distortion and improving surface finish. Use includes alone or as an additive in liquid component mixing/injection processes such as reinforced reaction injection molding (RRIM) of polyurethanes (Chapter 5). Used also as anti-crazing reinforcing fillers for plastics and adhesives. Because of fiber-length and lightness, they can cause dust and irritation in the production shop and should only be handled in closed systems. Glass fiber production Both continuous and staple fibers are manufactured by the same basic process up until fiber drawing. Temperature of glass melt and actual production method vary depending on glass composition; generally about 1260C (2300F) with melts extruding through platinum multi-opening bushings (spinnerets). Two principal manufacturing processes are used namely the glass marble (batch) method or the direct melt method. See Glass Fibers in this chapter. Glass fiber slug A particle of glass sometimes taking the form of a glass bead, which is imperfection in glass fibers. Glass fiber tempered Glass with surface compressive stresses induced by heat treatment, resulting in toughened glass. Glass fiber texturizing For special applications, fibers are subjected to a jet of air impinging on their surfaces, which causes random controlled breakage or fluffing of their surfaces. Although mechanical damage occurs weakening the fibers, its bulkiness allows greater plastic absorption.

Glass fiber types A-glass (alkali): the original type, a high alkali-content material, with a chemical composition similar to that of window glass; it has been largely replaced by other forms. C-glass (chemical): a grade with improved resistance to chemical attack, mainly used for surface tissue.

D-glass (dielectric): particularly good dielectric characteristics and used mainly in the electronics industry. E-glass (electrical): a calcium-alumino-borosilicate composition, low in alkali content and stronger than A-glass. This is regarded as the

2

9R e i n f o r c e m e n t s

pioneer type and is usually specified for reinforcement of plastics, unless operating stresses are relatively low (Ta Hanser 2.16 p70++). It has good tensile and compressive strength and stiffness, good electrical properties and relatively low cost, but impact resistance is relatively poor. Although E-glass fiber is widely used for its high strength/cost ratio, glass generally is not totally inert in chemically corrosive environments and many design codes require a corrosion barrier or liner to be incorporated in a laminate, to protect the structural integrity of the glass-reinforced substrate. This usually consists of a resin-rich layer supported by C-glass, or an organic fiber veil such as polyester or acrylic, to act as an impermeable protective layer. Sustained stresses and corrosive attack by strong acids or alkalis act synergistically, gradually deteriorating E-glass fibers (Table 2.6 and 2.7). Table 2.6

Mechanical properties of E-, S-, and (3- glass fiber RPs

Physical properties Tensile strength (psi) at 80~ at 500~ at IO00~ Modulus of elasticity, x 106 psi at 80~ Density (grams/cm3) at 80~ Coefficient of thermal expansion -linear (F) Coefficient of thermal ConductivityBtu-in. hours-square feet-~ Specific heat (bulk glass) at 80~ at 500~ at IO00~ Index of refraction at 80~ Dielectric constant at 104 cycles at 101~cycles Dissipation factor at 104 cycles at 10 l~ cycles Volume resistivity (Ohms/cc) at 72~ at 1320~ at 1600~ at 2300~

Electrical 'E'

High temperature, 'S'-glass

500,000 430,000 250,000

650,000 610,000 353,000

450,000

10.5 2.55

12.33 2.49

2.49

2.8 x 10-6

-

4.0 x 10-6

6-6.4

-

7-7.3

0.185 0.244 0.275 1.547

1.523

0.188 0.52 0.290 1.54

6.4-6.5 6.1-6.4

5.6

7.2-7.5 6.8-6.9

0.001-0.002 0.005-0.006

-

0.008-0.009 0.010-0.013

2 - 5 x 1012 107 105 102

-

-

Chemical 'C'

-

-

45

Table 2.7

Thermal and electric properties of E-glass fiber RPs

Coefficient of linear

Heo t deflection Plostic A05

Acetal

Nylon-6 Nylon-6,6

Gloss-fiber content, w t '70

Polyester, thermoplastic Polyethylene

cm/cmPC, D 696

Maximum temp,

Water absorption,

Volume resistivity,

strength dry,

continuous use, "C

24 h, %, 17570

cm,

V/pm,

R 257

D 749

shrinkage, cm/cm, R955

77 82 82 110

0.3 0.3 0.2 0.22

1015

17.7 18.3 18.9 20.0 18.9 16.5 16.1 20.9 19.7 19.7 17.3

0.003 0.002 0.002 0.006

4.1 3.8 3.1 5.2 4.3 3.1 2.7 2.7 2.3 2.2 3.2 2.3 2.5

127

0.2

30 10 30 30

98 99 100 124 163 196 204 246 252 199 138 143 213

93 110 107 127 110 127 132 121

1.8 1.3 1.o 0.9 0.2 0.14 0.12 0.06

10 30

110 124

5.4 3.8

82 93

0.08 0.06

10 20 30 10 30 15 30 13

30 Nylon-6,12 Polycarbonate

temp a t 1.7 MPan, "C, D 648

thermal expansion,

Dielectric

10'6 10'6 10'4 1014 10'5

10'5 10'6 10'6 10'3 1015

Mold

0.005 0.007

0.004

10'6

I8.9 23.6

0.007 0.004 0.004 0.005 0.003 0.003

10'6 10'6

26.8 24.0

0.005 0.003

1015

2 . Reinforcements 47

E - C R glass (corrosion-resistant): developed to meet the demand for improvement in long-term resistance to chemicals. The resistance to acid corrosion is significantly better than that of E-glass although its composition does not differ greatly, the main difference being that it does not contain boron oxide. It is listed (in ASTM D578 and ISO 2078) for improved resistance to acidic corrosion and, under DIN 1259, is classified as aluminum-lime-silicate glass, which is particularly designed for reinforcement of plastics, submitted to acidic environments. Grades of this glass have Lloyds approval and are certified to meet the Boeing BMS-8-79 specification. The slightly higher density of E-CR glass is not a serious factor, as the diameter ranges are within the tolerances of traditional E-glass. A slightly higher refractive index may give E-CR glass laminates a slightly more yellowish tint, but this is barely distinguishable. The moduli and stiffness of laminates made with E- and E-CR glass are identical. Tensile, flexural and shear strengths are generally equal or slightly higher with E-CR. The long-term behavior (tension-creep in air) is also identical. R- and S-glass: have a different chemical composition, giving a higher tensile strength and modulus and better-wet strength retention. Rglass is the type produced in Europe and S-glass in the USA: their properties are broadly similar and the density is the same as E-glass. They were developed to meet demand for higher technical performance from the aerospace and defense industries. They have smaller filament diameters that increase the surface area, so improving inter-laminar strength and wet-out properties. Advantex-glass: A replacement for E-glass with the properties of ECRglass is available from Owens Corning under the name Advantex. It combines the electrical and mechanical properties of the current industry standard, E-glass, with the higher heat resistance and acid corrosion properties of ECR-glass glass fibers. It is based on a new boron-free formulation developed by the company, which minimizes production of air pollutants during the manufacturing process (and so contributes to meeting increasingly strict environmental standards without the need to resort to cosily control systems). It is available in the form of both continuous filament and chopped strand. At the time of writing, some 10% of Owens Corning capacity has been converted to the new glass. ZenTron glass: Claimed to be the strongest glass fiber yet is ZenTron developed by Owens Corning. This combines a revolutionary glass composition with Type 30 single end technology and offers 15-20%

48 Reinforced Plastics Handbook

higher tensile strength than standard glass and 50% improvement in impact resistance. It is compatible with epoxy and vinyl ester systems because of unique coating chemistry, and offers excellent adhesion. The impregnated tensile strength is quoted as 3789.5 MPa and intralaminar shear strength is over 68.9 MPa. Glass fiber wear Tooling (molds, dies, cutters, etc.) will wear when processing glass fibers. As an example, wear in screw melting plasticators generally causes an increase in the clearance between screw flight and barrel. It often occurs toward the end of the compression section. This type of wear is more likely to occur when the screw has a high compression ratio. Regardless of where this erosion of metal occurs, the plasticators melting capacity is reduced. If the wear is serious enough it will effect the process so that products are exiting at a slower rate or more likely a lower quality product at the end of the line. The mechanism that causes wear include abrasive wear due to glass, etc. (galling), adhesive wear (metal to metal contact under high stress), laminar wear (thin outer layers of metal interface wear), surface-fatigue wear (micro- or macroscopic separation from the surfaces), and corrosion wear (chemical reaction and mechanical attack of the sliding surfaces. Glass filament A form of glass that has been drawn to a small diameter and extreme length. Most filaments are less than 0.005 in. (0.013 cm) in diameter. Glass filament liquid temperature The maximum temperature at which equilibrium exists between the molten glass during its manufacture and its primary crystalline phase. Glass filler These are a widely used family of fillers in the form of beads, hollow spheres, flakes, milled particles. They increase dimensional stability, mechanical strength, chemical resistance, moisture resistance, and thermal stability of the plastic matrix. Glass flake Thin, irregular shaped flakes of glass used as non-fibrous reinforcements. They are used especially in resin-based coatings, to reduce permeability to moisture, vapors, and solvents. Also used in reaction molded polyurethanes to improve molded product surface finish. Methods of application have in the past involved mixing the flake with resin and other fillers and either spraying or trowelling the mix onto the lay-up. This had the disadvantage of losing control over quality and orientation of the glass, leading to inconsistent properties across the surface, and between moldings. A more controlled method of use is to use flake glass in the form of a surfacing veil, together with corrosion resistant fiber. When applied

2-Reinforcements 49

as a surfacing veil, the flakes are mainly parallel to the surface of the lay-up. Glass former Oxide that forms glass easy and contributes to the network of silica glass when added to it. Glass forming package A single glass strand gathered on a thin-wall paper or plastic tube to be used in manufacture. Glass form For reinforcement of plastics, glass fiber is available in continuous and discontinuous forms, for use as roving, bonded mats, or a wide variety of woven or knitted textile forms (Table 2.8). An increasing amount of glass fiber is supplied as continuous roving, which is chopped into small lengths in resin mixing and spraying units, for fiber-directed pre-forming. Using roving rather than continuous strand mat has an important economic benefit, because the glass costs less and there is less waste. A key advantage of the fiber-directed preform process is the ability to change the geometry of the reinforcement strands simply by changing the input. Impact strength increases as the roving strand geometry becomes coarser, while tensile and flexural strengths are only minimally affected. An important area of current development is the design of 3-D fabrics and other forms, which will either provide bulk a n d / o r lend themselves easily to the shape of a require molding without the need for expensive pre-forming stages. Table 2.8 Typical propertiesof moldings with various glass reinforcement forms

Property Glass content Specific gravity Tensile strength Compressive strength Bend strength Modulus in bend Impact strength: Izod (unnotched) Coefficient of linear thermal expansion Thermal conductivity

Unit Olo

Woven cloth

Chopped strand met

Continuous roving

MPa MPa MPa GPa kJlm 2

55 1.7 300 250 400 15 150

30 1.4 100 150 150 7 75

70 1.9 800 350 1000 40 250

x 10-6 per ~

12

30

10

W/mK

0.28

0.2

0.29

50 Reinforced Plastics Handbook

Glass liquidus temperature Maximum temperature at which equilibrium exists between molten glass and its primary crystalline phase. Glass marble Small spheres of glass used for melting and subsequently drawing into glass fibers. Glass production Both continuous and staple fibers are manufactured by the same basic process up until fiber drawing. Temperature of glass melt and actual production method vary depending on glass composition; generally about 1260C (2300F) with melts extruding through platinum multi-opening bushings (spinnerets). Two principal manufacturing processes are used namely the glass marble (batch) method or the direct melt method. Glass roving They are bundled glass filament strands supplied in cylindrical packages (called cheeses), classified by the number of strands in the bunch (such as 6 to 150 end rovings). This is the lowest cost form of glass fiber reinforcement. It can be used to give very high strength in the direction of the fiber. Extensively used in filament winding of hollow symmetrical structures, such as pipes, tanks or high-pressure containers. It is increasingly used in spray deposition techniques, where it is chopped at the point of molding to give isotropic orientation. Different forms are available.

Bulked continuous roving can include loops in both the axial and transverse direction

Gun roving is continuous roving processed in chopper/spray gun: the process offers good lay-down without falling or sliding from the mold, fast wet-out and wet-through to aid roll-out, and air removal adaptability to different gun and transfer systems, together with good laminate properties. Unidirectional roving cloth (orientated) is a variation of woven roving where the fibers are arranged to provide greater strength in a specific direction or directions (such as by using heavier roving for the warp and lighter for the weft/Chapter 7). Woven roving can be supplied in a variety of weights and types for use where both strength and bulk are needed. Woven roving is a fabric that can be heavier or lighter according to number and density of strands. It is difficult to produce a good surface finish with woven' roving alone and inter-laminar cohesion between layers is not good. It is often used in conjunction with chopped strand mat to give bulk and additional strength. Densities are measured in weight per unit area. Fibers are usually arranged at right angles to

2

each other or in other positions so that their uniform and well-balanced strength (dcscribed pcrties/Chapter 7). Woven roving (continuous heavy drapeable fabric) offers rapid wet-out of and fast build-up of strength, with rigidity and finished product.

9R e i n f o r c e m e n t s

orientation gives a as directional proroving woven into fabric in the mold smoothness in the

Woven raving mat A ply of woven roving is joined with a chemical binder to a layer of chopped strand mat (CSM). It forms strong drapeable reinforcement that combines the strengths of bidirectional and multi-directional orientations. It is laborsaving in pattern cutting, giving reduced laminate build-up time and excellent conformability to the shape of thc mold, making a light, strong, smooth laminate, with high stiffness plus impact strength, and excellent appearance on the visible surface. Glass slug A particle of glass sometimes taking the form of a glass bead, which is imperfection in glass fibers. Glass sphere Spheres, in addition, called beads, are uses as fillers and reinforcements. They are available in different forms and a wide range of dimensions (5 to 1000 ~tm). Their smooth shapes reduce abrasive and viscosity effects.

Salid sphere Microscopic solid glass spheres addcd to an RP compound gives smoothness, hardness, and excellent chemical resistance. The spheres lower the viscosity of most resin mix systems. They act as miniature ball bearings to improve flow. They can be used in combination with fibcrs and other particle shapes such as flakes, reducing product dcfccts. Precise geometry allows even dispersion, close pacldng and easy wetting out in the compound, for high filler loadings. High loadings add significantly to the dimensional stability of finished products, by reducing shrinkage and improving part flatness. High loadings can increase flexural modulus, abrasion resistance, surface hardness, and improve stress distribution. Better stress distribution is given by spherically shaped particles: the stress pattern around the particle is regular and predictable, with fewer localized stress concentrations. With conventional fibre reinforcement, shrinkage is generally very low along the fibre but very high across it, so that the dimensional stability of the molded part is dependent on flow. The non-directional orientation of spheres, however, gives a more uniform shrinkage rate throughout the part and the isotropic nature of spheres results in more predictable manufacturing quality. Specially formulated coupling agents are incorporated in the coatings

51

52 Reinforced Plastics Handbook

on spheres, designed for optimum performance in specific resin systems, applied in molecular layers to obtain maximum sphere/ resin interfacial bonding (Table 2.9). Table 2.0 Improved properties with coated glass solid sphere-filled nylon 6/6 compounds

Flexural strength Flexural modulus Tensile strength Heat distortion temperature

psi dry wet psi x I0 s dry wet psi dry wet ~ @ 264 psi

Fiber-reinforced Solidglass spheres

Unfilled

(40%by weight)

14,300 8,900 3.2 1.7 9,400 8,000 75

14,200 8,700 4.9 2.7 7,100 5,500 127

13,000 12,100 5.4 3.1 11,100 9,400 126

Note: Samples were conditioned 16 h in water at 50~ prior to testing.

The blow molding (BM) process can take advantage of improving melt flow with spheres (Chapter 5). Elongational flow is one of the main processing criteria and plastics, which in their elongational viscosity exhibit strong strain hardening thus tend to have good processability by BM. A team at Yamagata University, Japan has studied the effect of glass beads in a high-density polyethylene (HDPE) compound for BM. A high molecular weight HDPE was examined, both unfilled and reinforced with untreated glass beads of 18 mm diameter and 2.6 specific gravity. Modulus increased with glass bead content at both low and high frequencies and it was shown that Trouton's law (that, for homogeneous plastics/polymers, elongational viscosity in the strain rate independent region is very close to three times the shear viscosity) holds good for RP systems as well as for the virgin material. Strain hardening has an anomalous dependency on strain rate, and is more marked at lower strain rate. In composites, strain rate dependence of strain hardening is similar to that of virgin HDPE. The hardening phenomenon appears at large strain and is generally believed to be caused by elastic behavior of elongated polymer chains. The glass beads suppress the large deformation of matrix polymer chains around them (which may possibly be one of the causes of the suppression of chain hardening by the glass beads). In BM, it is important for the parison to be able to resist drawdown and, since this occurs slowly, it can be expected that a compound

2 . Reinforcements 53

with a strong strain hardening at low rates of strain (as exhibited by the RPs tested) will have good processability (reference my BM book).

Hollow sphere Hollow microscopic spheres of a chemically stable soda lime borosilicate glass are used in plastics compounds, for reinforcement and weight reduction of both TSs and TPs. They have a density of about one-fifth that of most solid spheres or resin. For an equal weight, hollow spheres occupy about five times the volume of the resin, resulting in reducing the cost and weight of a compound. They can also produce/improve other useful properties, such as resistance to impact and thermal shock, and the surface finishing characteristics. They can be used in formulations for sprayup and casting, and in molding compounds. In SMC or BMC compounds, weight can be reduced by up to 30% (to 1.3 g / c m 3 or less). A typical range runs from very low density (0.125 g / c m 3) with moderate pressure strength (17 bar) to moderate density (0.60 g / c m 3) with high-pressure strength (690 bar). Other grades include 8 pm diameter boro-silicate spheres, which are white in color and can be used at injection molding pressures. The density of a typical range is 1.1 g / c m 3 (mineral fillers have a density of 2.4-2.9). On an equal volume basis, the amount of a typical hollow glass sphere grade compounded on weight addition would be (1.1/2.5) x 100 or 44% by weight. If a compound calls for 40% by weight of mineral filler, then 17.6% (44% of 40) by weight should be added, to get the same volume loading. The spheres are moderately alkaline and prolonged exposure may irritate the respiratory tract. In dusty environments, it is recommended to use a NIOSH-approved mask or respirator. Safety data sheets are available from suppliers. Hollow spheres also produce opacity and whiteness, allowing titanium dioxide to be replaced. Weight reductions of 20-25% can be achieved compared with mineral-filled polymers.

Syntactic sphere core Syntactic cellular core plastics are also called RP syntactic foam or syntactic foam. An RP compound made by mixing hollow microspheres of glass, epoxy, phenolic, etc. into a fluid plastic with its additives and curing agents. It forms a moldable, curable, lightweight mass, as opposed to foamed plastics in which its cells are formed by gas bubbles, etc. A syntactic core material made of a 120C curing epoxy film adhesive filled with glass micro spheres and supplied with a lightweight carrier scrim is also available. In the uncured state, the material is in

54 Reinforced Plastics Handbook

1 and 1.5 mm thick sheet-form, pliable at room temperature with respective surface weights of 570 g / m 2 and 855 g / m 2. In use, it is taken from cold storage (it will store for up to six months a t - 1 8 C in sealed polyethylene bags) and allowed to reach room temperature. It is then trimmed to the required shape. The release paper is removed from one side, the trimmed sheet is positioned and the other release paper is removed. Gel time is 13 rain at 120C (248F), curing is one hour at the same temperature, using a heat up rate of 2C (3.6P) per minute. The cured material has a density of 0.57 g / c m 3.

Expandable microsphereThermoplastic microspheres are droplets of liquid hydrocarbon encapsulated in a shell of a thermoplastic polymer. When exposed to heat, the shell softens and the hydrocarbon gasifies, and the microsphere expands from, typically, 12 to 40 pm and the density drops from 1000 to 30-40 k g / m 3. The microspheres can be used either as a form of blowing agent, or may be supplied in expanded form for use as a lightweight filler. The activating temperature of mold and material is 100C (212F). The expansion creates an internal force in the molding compound, which is maintained until gel or cure takes place. This results in reduction of surface defects, voids and hollow parts. It will also reduce resin shrinkage while a syntactic foam core is established. Parts containing hollow microspheres can be deflashed and trimmed more easily and with less work. They are also easier to grind, drill, tap, and thread with increased holding power, which can be attributed to the syntactic foam, which will exhibit compression/ rebound properties. When a resin or heavy filler is replaced with the microspheres, most physical properties are reduced, based on constant volume (lower density). Stiffness is reduced, due to the resilient characteristics. Strength/weight ratio, fatigue, stress and resilience can offer useful product enhancement, with relatively small additions. The pre-expanded form can be used with open or closed mold applications. At moderate pressure of 7-14 bar (100-200 psi) the expanded spheres are compressed, increasing the volume of liquid displaced through the system. When pressure is released, the spheres regain their original volume, increasing viscosity and reducing density. In the cured matrix, the microspheres retain their resilient properties, and are able to compensate stress from curing as well as differential thermal expansion in the composite. They also improve matrix resilience by absorbing energy without suffering permanent set and

2 . Reinforcements 55

reduce fatigue by allowing movement of the matrix in combination with good adhesion to the resin, so reducing crack formation. There are phenolic-based prepregs in which glass fiber is continuously impregnated with a binder, a water-based phenolic resin, and unexpanded microspheres. When the water is dried, it either puts the resin into a semi-cured stage allowing the microspheres to be expanded (producing a thick low-density prepreg) or left unexpanded (for expansion during the molding process). The product is a syntactic foamed or foamable phenolic-based material, of 100-1000 k g / m 3 density, which can be molded to various shapes, offering useful mechanical properties, and a good level of flame retardancy and low smoke evolution. Applications are in high-speed railway trains (3 k g / m 2 laminated prepreg is used in ceilings), automobile interiors (800 g / m 2 x 4 mm thick material meets requirements for headliners), etc. Glass strand It is a primary bundle of continuous filaments combined in a single compact unit without the usual twist of a fiber. These filaments that number usually 51, 102, or 204, are gathered together during the fiber forming operation. The filament strand end is the group of filaments at an end. Filament strand integrity is the degree to which the applied sizing holds the individual filaments making a strand or end together. Glass strand is normally measured by the number of 100 yards in 1 lb weight (for example, a 130 s count contains 13,000 yards per pound weight or the number of grams per kilometer, under the international unit rex. Tex is a unit for expressing linear density equal to the mass of weight in grams of 1000 m of strand, fiber, filament, yarn, or other textile strand.

Nylon Fibers Also called aramid fibers. See H i g h Performance Reinforcements, Aramid Fibers in this chapter.

Polyester Fibers TP polyester offers a low density, high tenacity fiber with good impact resistance but low modulus. It is used in areas where high stiffness is not required, but where low cost, lightweight, and high impact or

56 Reinforced Plastics Handbook

abrasion resistance are important. Polyester is used mainly in surface tissue for laminates, but also offers high impact resistance, good chemical resistance and good abrasion resistance. The advantages of polyester are that it does not use binders that have to be dissolved in the resin matrix, has high conformability and excellent strength/weight ratio. As a surfacing material, the fiber is easy to sand. Fabrics are half the weight of the equivalent glass, with excellent energy absorption, chemical resistance, and dielectric/electrical insulating properties. Lloyd's Register of Shipping and the American Bureau of Shipping internationally certify them. Continuous needle-punched nonwoven polyester fabrics have been developed specifically for the fiber-RPs industry and are designed to saturate easily with all resin systems. Individual grades are used as a surface layer, to reduce print-through of the gel coat, as a superior bedding substrate for thick cores and reinforcing materials, or as a core to increase structural thickness and stiffness. Polyester fiber mats can also reduce laminate density, reducing total weight and can be used with, or as a replacement for, glass fiber in sheet molding compounds (SMCs). The same impact and density advantages are obtained in resin transfer moldings (RTMs). A polyester surfacing veil is also designed for the outer layer for filament winding. It uses specially modified spun laced polyester, 0.076 mm (0.003 in) thick, which is very smooth and flat. Typical applications include print blocker, thin core, core bedding, and toughening layer in marine applications; surfacing veil, thin core, and exterior abrasion-resistant layer in pultrusion and compression molding; corrosion barrier in anti-corrosion applications, and as thin core and surfacing veil in panels.

Polyethylene Fibers Very low-density fiber can be produced from ultra-high molecular weight polyethylene (UHMWPE), offering strengths which (for the density of the fiber) are among the highest to be found anywhere. It is made up of aligned polymer chains with high elongation and good impact resistance. However, although the fiber has remarkable properties, its low modulus and ultimate tensile strength and the relatively high cost of treating the surface to improve the fiber/matrix bond mean that PE fiber is not often used in RP structures. The specific gravity is very low, at 0.97 (aramid is 1.44, polyester 1.38). It is 35% stronger than aramid and has a high energy/break ratio, giving

2 . Reinforcements 57

remarkable ballistic properties. It exhibits impact energy absorption in RPs 20 times that of glass, aramid, graphite, and also has excellent vibration damping. The melting point is 147C (300F). Possible applications for composites include boat hulls, sports equipment, radomes, and structural components, pressure vessels, aerospace and industrial.

Hybrid Fibers There are inter-ply hybrid RPs that have two or more fiber reinforcements embedded in the plastic matrix. They have evolved as a logical sequel to conventional single-fiber RPs. Hybrids provide unique combinations of performance features to meet different and competing requirements in a more cost effective way. This cost advantage has been found principally in using glass fibers with the more expensive fibers, since the 1950s. For example, regarding the cost of hybrid RPs, high modulus graphiteresin is about 60 times more expensive than E-glass laminates. Intermediate graphite modulus-resin is about 36 times more expensive. Aramid-resin is about 8 times as costly. Thus, when performance standards of hybrid RPs can be met, cost advantages occur. An almost unlimited field of possibilities continues to exist with the combination of different fibers as hybrids that, with an appropriate resin matrix, can most closely fill a specific closely identified application. In most cases, however, this is a matter for specialists, backed by an exhaustive database of fiber forms and properties. A typical example of an off-the-shelf hybrid is a boron/graphite prepreg, composed of small diameter graphite fibers dispersed between 76-100 pm diameter boron fibers, in an epoxy matrix, to 70-80 wt% total fiber content. This prepreg provides properties superior to RPs based on either fiber. The flexural stiffness and strength is twice that of carbon and 40% higher than boron. Intralaminar shear strength also exceeds carbon and boron. The resin matrix can be a toughened epoxy or a polyimide.

Other Fibers and Reinforcements Overview

Other reinforcing fibers, of less commercial importance at the present time, include asbestos, ceramic fibers, silicon carbide fibers, whisker

58 Reinforced Plastics Handbook

fibers, natural fibers, and mineral fibers. See Fiber/Filament Characteristics that includes more information on different fibers. Asbestos Fibers They have been used extensively in the past in many different applications including RPs. The fibers offer advantages such as excellent/high strength and stiffness, good rigidity, chemical resistance, and particularly fire resistance. However its use has ceased in all but closely controlled applications, following realization of the health hazards associated with it. Ceramic Fibers They posses unique wear and corrosion resistance, and high temperature stability. They consist of approximately 50 wt% alumina and 50% silica with traces of other inorganic materials. The fibers are made by atomizing a molten ceramic stream using high-pressure air or spinning wheels; also use chemical vapor deposition, melt drawing, and special extrusion processes. Although glass fibers are also ceramic material, they are not generally categorized as ceramic fiber; they are called glass fibers. Silicon Carbide Fibers A reinforcing fiber with high strength and modulus with 2.7 density. Primary purpose for this development was for the reinforcement of metal matrix and ceramic matrix composite structures used in advanced aerospace applications by the military. SiC fibers were developed to replace boron fibers in these RPs, where boron had its drawbacks; principally degradation of mechanical properties at temperatures greater than 540C (1000F) and very high cost. Whisker Fibers Whiskers are metallic and nonmetallic single crystals (micrometer size diameters) of ultrahigh strength and modulus. Their extremely high performances (high melting points, resistance to oxidation, low weights, etc.) are attributed to their near perfect crystal structure, chemically pure nature, and fine diameters that minimize defects (Figure 2.6). They exhibit a much higher resistance to fracture (toughness) than other types of reinforcing fibers. Many different materials have been used (literally hundreds) with diameters ranging from 1 to 25 ~am (40 to 980 lain.) and having aspect ratios between 100 to 15,000. Processes used to manufacture whiskers include growing them by condensation from supersaturated vapor, from chemical solution, and by electrodeposition. Because of their extremely high costs and not easy to process with present technology, use has been in specialty applications such as aerospace, medical/dental, etc. Matrices include plastics, ceramics, and metals.

2 . Reinforcements 59

Figure 2.6 Range of properties for different materials including glass fiber and whisker reinforced plastics

Natural Fibers

They are usually derived from vegetable matter and since the Ford Model T automobile (1903) continues to receive increasing attention worldwide, where there is a strong urge to use materials that are thought to be friendlier to the environment. There is growing interest in the possible use of natural fibers in RPs, not only in the developing countries that produce them, but also in the industrialized countries, where some believe they might help in solving recycling problems. However, they do not match the performance and consistency offered by existing reinforcement materials (such as glass). Natural fibers may well have to be treated with coatings that may militate against easy recycling of the base fiber. Mcrcedes-Benz (among other companies) has studied many materials and is using animal hair and fibers made from flax, sisal, coconut, and cotton, in upholstery, door panels and rear shelves of its cars. The company is looking to replace glass fiber with natural fiber alternatives, but has found it difficult. Not only arc natural materials usually sensitive to temperature, but they also tend to absorb water and often exhibit extreme variation in quality that is not good for an automobile manufacturer. For over a century results of studies and evaluations of the different natural fibers continue not to be practical for use in the RP industry.

60 Reinforced Plastics Handbook

As well as biodegradability, the advantages of natural fibers include low density and cost, better damage tolerance in RPs, and high specific strength to stiffness. These advantages make natural fibers interesting for applications with low load requirements. On the negative side, however, there continues to be basic problems of degradation by moisture, poor surface adhesion to hydrophobic resins, and susceptibility to fungal and insect attack. As reviewed properties can be improved by treatment of the fibers, one obvious route being to reduce the water absorption, which has a direct effect on physical performance such as tensile properties.

Flax Fibers It is reported to be able to withstand the same tensile force as ramie, and can out-perform glass fiber on a weight-for-weight basis. However, to counter the other drawbacks of natural reinforcements, various forms of resin matrix are being studied. Polyurethane, processing at low temperatures, is promising. Another development approach is with TPs such as PP , using an extrusion/compression molding technique developed by DaimlerBenz at Ulm (Chapter 5). Hemp Fibers Environmental considerations (including clean production and reduced skin irritation when handling at the workplace) were key factors in the decision by Ford UK to investigate the use of hemp (Cannabis Sativa) in place of glass fiber for reinforcement of some components on the Transit van. Hemcore Ltd processes the hemp (which is grown under close government scrutiny, although the strain has negligible narcotic content) in conjunction with J E Plant Fibres as a needle-punched mat, Hempmat 250. Ford is using hemp fibers as a replacement for chopped strand glass mat in the parcel shelf for the high roof model of the Transit. It is molded by resin injection molding (RTM). Depending on results, the auto company sees a wide range of components in both vans and cars using hemp as the reinforcement. The hemp is grown free of pesticides and is separated by a completely mechanical process. In the molding shop, it is said to have lower skin irritability than glass fiber. However, the environmental advantages are really a bonus for Ford, which has also identified significant savings in both cost and weight. The mat is also being tested as a core material for thick RPs. Results to date point to properties superior to standard core products, suggesting that there might be significant cost-saving as well as increased stiffness. B IP Plastics Ltd is testing a short chopped hemp fiber as reinforcement for TS polyester compounds for injection and compression molding.

2

9R e i n f o r c e m e n t s

Hemcore does not see the product as meeting every application need of the fiber-RPs industry, but it considers that the fiber could find some price/performance gaps. No yield figures have yet been published, but it is possible that, in common with other natural fibers, a very large area of land will be needed to produce viable quantifies.

Jute Fibers This is one of the most important natural fibers. It is produced in India, Bangladesh, Thailand, Vietnam, and other countries. It contains 56-64 wt% cellulose, 29-25% hemicellulose, 11-14% lignin, and a small proportion of fats, pectin, ash, and waxes. Application of jute fiber in RPs with matrices of TS resins such as unsaturated polyester or vinyl ester resins has been widely studied. To date the poor adhesion to hydrophobic TPs, such as polyethylene and polypropylene, has to date limited application in TPs. Jute fiber (JF) has been popular since the start of this century, principally as a filler and as a reinforcement with TP matrices. These low-cost natural fibers consist mainly of cellulose and hemicellulose chains running parallel to the fiber direction and lignin. High performance, average unidirectional-oriented tensile strength (Ts) is 500 MPa, elastic modulus (E) is 40 GPa, and elongation is 1.7%. Other fiber properties are density 1.45 and weight 0.21 g / m . Testing of JFRPs has been conducted using polypropylene (PP) film (T~ at 17 MPa, E at 0.7 GPa, and 100% elongation). Prepregs were made by pressing unidirectional-oriented layers of JFs between PP films. No fiber pretreatment was used. Eight layers of prepregs were compression molded (at 190C and 20 MPa) to produce test specimens. One series was unidirectional and another isotropic ( 0 ~ 1 7 6 45~176176 +45~176176 JFRPs had a density of 1.11 with fiber content of 50 wt% (40 vol %). Unidirectional and isotropic properties were Ts of 140 and 50 MPa, E of 13.2 and 5.7 GPa, and elongation Ts yield of 2.7 and 3.0%, respectively. In comparison to the unidirectional Ts at 0 ~ of 140 MPa, the 10 ~ was 70 MPa, and 45 ~ or less it was 10 MPa. With the isotropic RPs, Ts in all directions was 50 MPa. No brittle behavior occurred during testing. When the tensile yield strain is exceeded (for unidirectional RPs), about 50% of Ts remains at 5% elongation and about 20% at 8% elongation (Table 2.10). Work on production of RPs from jute fiber by hot press molding with TP films (at Ho Chi Mihn City University of Technology, Polymer Research Centre, Vietnam) has shown that they have a potential use in replacement of wood and also glass fiber RPs, provided that the high water absorption and poor interfacial adhesion can be eliminated. A

61

62 Reinforced Plastics Handbook Table 2.10 Jute fiber (40 wt%) isotropic lay-up RPtensile properties with thermoplastics

Matrix

Fiber

LDPE

Untreated fiber NaOH-treated fiber Cardanol-treated fiber Untreated fiber NaOH-treated fiber Cardanol-treated fiber Untreated fiber NaOH-treated fiber Cardahal-treated fiber

HDPE

PP

Tensile strength (MPa)

Tensile modulus (GPa)

94 101 114 126 128 142 148 152 172

5.25 5.28 5.74 7.86 7.92 8.39 11.45 11.59 12.15

Flexural Flexural strength modulus

(MPa)

(GPa)

19 22 28 43 47 56 73 74 82

1.16 1.22 1.27 2.81 2.97 3.22 3.13 3.25 3.86

Source: Polymers Et Polymer Composites.

number of chemical treatments can be used, including those used with glass fibers that are silane coupling agents, polyisocyanate, vinyl monomer linkages, or compatibilizers. A particularly promising route is to treat the fiber with a phenolic resin based on cardanol formaldehyde (CF). This is a natural alkyl-phenol, in which the methylol groups are able to react with the hydroxyl groups of the cellulose, while the long C-15 alkyl group of cardanol facilitates the formation of an adhesive bond with non-polar TPs. It is concluded that Jute fiber thermoplastic RPs can bear comparison with glass fiber RPs. However, the best solution may well be a combination of treated jute with glass.

Ramie Fibers It is derived from a 2.5 m high Chinese relative of the common stinging nettle (more correctly known as Boehmeria Nivea). It yields fibers that are almost as resistant to tearing as glass and has been evaluated in the past by different organizations. Recently Daimler-Benz Aerospace specialists in Bremen are studying it as a possible replacement for glass in interior fittings of the Airbus, where it also satisfies a crucial requirement in that it is fireproof. Processing the ramie fiber proved a problem until the team in Bremen found the right technology in Switzerland (with a manufacturer of cheesecloth). Sisal Fibers A white fiber produced from the leaves of the agave plant found in Central America, West Indies, and Africa. Used primarily for at least half of the 20th century as cordage, binder twine, RPs, etc. When

2-Reinforcements 63

chopped, it is used as a low cost filler. This natural fiber is used in some bulk (dough) molding compounds and more with phenolic matrices than with TS polyesters or epoxies. Soya Bean/Cellulose Fibers These fibers form a range of materials also claimed to be a viable alternative to glass fiber in RPs. The basis is waste cellulosic fibers bound with soy protein/phenolic binder systems. The fibers have been developed by United Soybean Board (USB) under the name Proteinol Composites and can be formed into extruded shapes and compression molded sheets and can be nailed, sawed and machined. The cellulosic fibers are essentially wastes from agricultural crops, forest products, and paper. Future development will turn on growing understanding of the chemistry of soy proteins. Improvements are being sought in moisture resistance, fiber/binder compatibility, and processing efficiency. Mineral Fibers

The mineral fillers are a large subclass of inorganic fillers comprised of ground rocks as well as natural, refined, or synthetic minerals. Commodity minerals are relatively inexpensive and are used mostly as additive extenders. Other fillers, so-called specialty minerals, are usually the reinforcing types. There are also inherently small particle size fillers such as talc and surface chemically modified fillers. The inert filler are those added to plastics to alter the properties of a product through physical rather than chemical means. Wollaston i te Fibers These fibers played a key role in the development of a prototype automobile wing molded in reinforced reaction injection molded (RRIM) polyurethane which can resist temperatures of up to 190C (Tremin 939-100 USST wollastonite fiber from Quarzwerke GmbH, Frechen, Germany). In the PU RP, it produced a wing with surface quality similar to that of sheet metal, while permitting wall thicknesses as low as 2.5 mm in series production. It was claimed to be interesting to the automotive industry, which requires plastics materials for bodywork panels that can be coated inexpensively in an on-line f~shing process, using a cathodic electrodeposition primer. Temperatures of around 190C level are encountered during cathodic electrodeposition priming and it is important that plastics panels should be able to resist this without requiring separate assembly. Intumescent Graphite Fibers A range of graphite-based mineral fiber stabilized flexible mats, which can be incorporated in a laminate and Technical Fiber Products

64 Reinforced Plastics Handbook

(Technofire), UK, have developed give intumescent performance in the event of fire. The thermally active constituent is exfoliating graphite, which increases its volume considerably in fire conditions, leaving a stable insulating layer of mineral fibers. The material starts activation at 190C, developing a peak expansion pressure of about 1.5 kgf/cm 2 at about 400C. The average expansion ratio is 9:1. The mat is available in standard sizes in 1.5, 1.8, 3.0, and 4.0 mm thickness: non-standard thicknesses between 0.5 and 5.0 mm can be supplied. Mica

Mica is a generic name to describe a group of complex hydrous potassium aluminate silicate materials, differing in chemical composition, but sharing a unique laminar crystalline structure. In nature, mica develops in a book-like form. The individual platelets can be delaminated into very thin high aspect ratio particles that are tough and flexible. Of the commercially important forms, muscovite and phlogopite are used as reinforcements for plastics. Mainly used in TPs, mica reinforcement improves the tensile and flexural strength and flexural modulus. Heat distortion temperature is increased and the coefficient of linear thermal expansion is reduced. Shrinkage and creep are significantly reduced, and warpage is virtually eliminated. Chemical resistance is high and permeability is reduced. Mica can also help to produce a Class A surface finish (Table 2.11). Table 2. I I

Effect of various reinforcements with 40 wt% polypropylene

Tensile strength (psi)

Flexural modulus (kpsi)

Notched Izod (ft-lb/in)

HDT (264 psi ~

Shrinkage (%)

100% PP

4580

240

2.90

150

2.3

Calcium carbonate

3250

430

0.41

157

1.5

Glass: flake 1/64

3370

710

0.43

183

0.6

Glass: milled 1/8

3580

670

0.42

200

0.4

Type

Mica, HiMod-360

4435

1110

0.39

238

0.8

Mica, L-135

3710

1010

0.46

244

0.8

Silica

3090

380

0.51

154

1.5

Talc

4220

660

0.44

181

1.1

Wo IIasto n ire

3690

740

0.41

190

0.6

Source: Franklin Industrial Minerals

Because of the flexibility and softness of mica, injection molding and extrusion is possible with very little change in particle size (whereas

2

Reinforcements 9 65

milled glass fiber, glass flake, and wollastonite tend to break during processing) and there is less wear on equipment than with other minerals. To avoid size reduction, however, these materials should be processed under low shear conditions, and material of larger particle size should be added to an extruder through a side feeder at a stage after the resin has been softened. In PP compounds (which is the main use of mica in TP reinforcement), the mechanical and thermal properties are considerably enhanced by modifying the PP with a maleic anhydride compatibilizer, which improves adhesion. Test results suggest that the improvement continues with increasing amounts of maleic anhydride.

Forms of Reinforcements The available forms of reinforcement follow terminology and technology borrowed from the textile industry. The basic forms described throughout this chapter and other chapters for glass and other fibers including hybrid mixtures are summarized in this chapter. They are continuous filament, woven fabrics, nonwoven fabrics, knitted fabrics, braids, and tapes. Three-Dimensional Reinforcements

The introduction of what is a 2-D (two-dimensional) fiber reinforcement into a molding that is intended to have 3-D produces a conflict. Depending on the shape of the intended product, and the molding technology employed, the fiber reinforcement will be in the form of short or long chopped filaments/strands, mats made of random chopped strands, or woven fabrics of varying density. Woven and nonwoven fabrics can be also used to improve surface qualities such as appearance, impact resistance, abrasion and chemical resistance. To improve the distribution and orientation of fibers in a 3-D molding, there have been produced machine-made 3-D arrangements of fiber that offer better drape in a mold. Surface Tissues

Nonwoven surfacing fabrics are used, with special gel coats, to give RPs additional resistance to abrasion and corrosion, optically smooth surface, and stability under load. They have been used for over a half century, meeting extreme fluctuations in temperature, chemically aggressive substances, mechanical stresses, high UV radiation, and

66 Reinforced Plastics Handbook

high-pressure loads. They are based on textile glass fibers (C-, E- and E-CR-glass), polyacrylonitrile, and TP polyester. Standard weights range from 14 to 40 g / m 2 and special products from 18 to 60 g / m 2. There arc grades suitable for all types of RP processes. Special products are printable or electroconductive. Overlay mats and surfacing tissues are widely used to produce a highquality surface to RPs. These are thin tissues of staple fiber with a binder that wets out rapidly and are designed to absorb a high percentage of resin, to produce a resin-rich surface (or to cover a coarse pattern of chopped strand mat on the inner surface of a contact molding). Nonwoven tissues for surfacing veil are available in glass, TP polyester, carbon, and aramid fiber. Conductive Nonwovens

Nickel-coated carbon fiber nonwovens offer very high electrical conductivity (Table 2.12). They are used for many applications such as in shielding, panel heaters, aircraft lightning strike protection, electromagnetic interference/radio frequency interference ( E M I / R F I ) shielding and layers in de-icing systems, automotive E M I / R F I shielding and seat heaters, architectural anti-surveillance systems and anti-icing systems, and industrial conductive tapes and resistive heating. They can be used alone or mixed with other fibers. A nonwoven mat of smooth flexible aluminum coated oriented glass fibers, Metafil, has been developed by Tracor Aerospace and BGF Industries, USA, for electrically or thermally conductive applications, such as parabolic dish antennae. It is compatible with most resin systems and processing is said to be similar to uncoated glass mat, but cost is lower than other conductive materials. University of Maryland physicists have found that semiconducting carbon nanotubes have the highest "mobility" of any known material at room temperature. Mobility refers to how well a semiconductor conducts electricity. A semiconducting transistor made from a single carbon nanotube showed mobility more than 70 times greater than the silicon used today in computer chips. The researchers had to grow extremely long carbon nanotubcs, up to 0.3 mm in length, and had to place metal wires precisely on each end of a single tube to make the measurements. The technology holds promise as a replacement for silicon chips, if production and substrate issues can be resolved. Semiconductors arc just one of many potential applications of singlewall carbon nanotubes, which include use as RPs.

Table 2,12 Typical properties of conductive fiber reinforced thermoplastics

Specific gravity

Tensile modulus, GPa (Mpsi)

Notched Izod impact strength, Jim (6.4ram bar) (ft-lb/in. ( 7/4"bar)

Surface resistivity, ohms/sq.

Shielding effectiveness db attenuation @ lOSMHz, 6.4mm (7/8") thick.

Base polymer

Reinforcement, wt. %

PC

ASTM 5% Stainless steel

D792 1.28

D638 4.83

D256 80.1

D257 102

ES7 40

PA 6/6

5% Stainless steel

1.22

42.7

102

40

PPS

15% Carbon fiber nickel, coated

1.45

20

15O/oCarbon fiber nickel, coated

1.20

101

55

PPS

400/0 Carbon fiber

1.49

102

30

PA 6/6

500/0 Carbon fiber

1.38

32.0 (0.6) 37.4 (0.7) 80.1 (1.5) 106

103

PA 6/6

101

50

PA 6/6

400/0 Carbon fiber

1.33

102

40

PA 6/6

30% Carbon fiber

1.28

4.41 (0.64) 6.89 (1.00) 7.58 (1.10) 30.30 (4.40) 34.5 (5.00 29.3 (4.10) 20.7 (3.00) 15.9 (2.30)

102

30

PC

300/0 Carbon fiber

1.38

(0.70)

(1.5) (0.8)

(2.0)

118 (2.2) 107 (2.0) 96.1

(1,8)

102

I'D m,

"-h 0

40

I'D

3

I'D Ill

68 Reinforced Plastics Handbook

High Performance Reinforcements Aramid Fibers

Aramid fiber (AF) is the generic name for the organic aromatic polyamide fibers. It has a long chain synthetic polyamides (nylon) in which over 85 wt% of the amide linkages are attached directly to two aromatic rings. DuPont's trade name is Kevlar TM. They have excellent properties such as high strength, modulus of elasticity, lightweight, impact resistance, abrasion resistance, creep-rupture characteristics, and chemical and mechanical stability over a wide temperature range (Table 2.13). Their use includes RPs, high performance fabrics (boat sails, bulletproof vests, etc.), medical devices, etc. AFs have low density/high tensile strength and are produced by spinning liquid crystal polymer, usually as filament yarns, rovings or chopped fibers. They have a characteristic of bright golden yellow color. All grades are particularly good in resistance to high impact; lower modulus grades are widely used in anti-ballistic applications. The compressive strength, however, is unexceptional and only equivalent to that of glass fiber RPs. Applications are not restricted to the obviously high performance sector. In fact, a large part of the business of aramid fibers is in combinations with other reinforcements as hybrids, giving predictable properties precisely where they are required. For example, the PH11 Hovercraft boat was designed with a hull of aramid/glass hybrid/TS polyester RP to give a wear- and impact-resistant surface with high tensile strength and limiting bending in the horizontal direction. The gangways were an aramid/glass RP and, around the propeller, an aerodynamic tunnel of aramid/epoxy was used to increase thrust, stop flying parts (in the event of the propeller fracturing), and ensure a rigid construction, preventing contact between propeller and tunnel in starting and stopping. Aramid fiber is also used in production of reinforced thermoplastics (RTPs), as commingled yarns or a hybrid yarn or fabric, suitable for high drapability and coping with very sharp fillet radii, and in specialty tires. A significant development is a technique for pulping or fibrillation that greatly increases the surface area of short-length fibers of para-aramid, and renders them suitable for reinforcement of plastics and elastomers. A typical staple fiber will have a surface area of about 0.1 m2/g, but the compounding process increases this to 7-9 m2/g, so increasing the area available for adhesion to the matrix plastic. The bond achieved will

Table 2.1 3 Properties of aramid fiber/thermoplastic RPs

Base resin Nylon 616 Nylon 616 Nylon 6 Polyester (PBT) Polycarbonate

Specific gravity D 792

Mold shrinkage [in./in.) D 955

1.19 (1.14) 1.29 1.19 (1.14) 1.33 (1.31) 1.23 (1.20)

0.008

0.90

(0.016) 0.008 0.008 (0.016) 0.013 (0.020) 0.005 (0.006)

(1.50) 0.6 1.o

water absorption, 24hr. (%) D 570

(1.8) 0.06 (0.08) 0.1 2 (0.15)

Tensile

Flexural

strength Id psi IMP4

modulus 106psi

D 638 14.5 100.0 (11.8) 81.4 (13.5) 93.1 13.0 89.6 (11.8) 81.4

9.5 65 (8.5) 59 11.0 75.8 (9.0)62

[GPai D 790 0.64 (4.4) (0.41) (2.8) 0.55 (3.8) 0.58 (4.0) (0.40) (2.8) 0.60 (4.1) (0.34) (2.3) 0.54 (3.7) (0.33) (2.3)

Impact Strength, lzod Iff.-I b.lin.1Thermu l #etched Unnotched D256 D256 6.7

8.5 9.0 9.0 -

Deflection expansion temperuture, [7R5in./in. -"fl 264 psi "F D 696 YC) D 648 2.4 (4.5)

3.1 3.0 (4.6) 3.0

(5.3)

11

3.0

(601

(3.71

450 (232)

(170) 465 390 t167) 380 (130) 280 (265)

(76.7) 1240)

1199) [75) [193) [54.4) (138) (129)

N

",,4

o

Table 2.1 4 Examplesof different carbon fibers

Type T300 T3OOJ T4OOH T700S T8OOH TIOOOG M35J M40J M46J M50J M55J M60J M30S M40

No. of filaments per tow

Tensile strength ksi

MPa

kgf/mm 2

msi

GPa

kgf/mm 2

1,000-12,000 3,000-12,000 3,000-6,000 12,000-24,000 b 6,000-12,000 12,000 6,000-12,000 6,000-12,000 6,000-12,000 6,000 6,000 3,000-6,000 18,000 1,000-12,000

514 611 640 711 796 924 683 640 611 597 583 555 797 398

3530 4210 4410 4900 5490 6370 4700 4410 4210 4120 4020 3820 5490 2740

360 430 450 500 560 650 480 450 430 420 410 390 560 280

33.4 33.4 36.3 33.4 42.7 42.7 49.8 54.7 63.3 69.0 78.2 85.3 42.7 56.9

230 230 250 230 294 294 343 377 436 475 540 588 294 392

23,500 23,500 25,500 23,500 30,000 30,000 35,000 38,500 44,500 48,500 55,000 60,000 30,000 40,000

a Measured using the impregnated strand test method bT700S - 24,000 is temporary value, subject to change. This information can be used just for material selection purpose Source:Toray Industries Inc.

Tensile modulusa

'-h

0

Elongation 0/0

Mass per unit length Tex [g/lO00 m)

Density

1.5 1.8 1.8 2.1 1.9 2.2 1.4 1.2 1.0 0.8 0.8 0.7 1.9 0.7

66-800 198-800 198-396 800-1650 223-445 485 225-450 225-450 223-445 216 218 100-200 745 61-728

1.76 1.78 1.8O 1.8O 1.81 1.80 1.75 1.77 1.84 1.88 1.91 1.94 1.73 1.81

g/cm~

"1"

0 0

2

9R e i n f o r c e m e n t s

improve properties of the compound, particularly abrasion resistance. High strength/low weight, mechanical stiffness and resistance to thermal and chemical attack are other advantages. The development has been commercialized (by DuPont) as a masterbatch for elastomers used in applications for power transmission beltings, hoses, tire beads and tread areas, beatings, packings, and seals. With advances in technology, there is cooperation between some manufacturers on product and process development of higher-performance aramid fibers. Different production processes use different solvent systems, making it possible to modify product properties by changing the basic polymer composition with additives a n d / o r fillers. Techniques for production of 3-D structures of high tenacity aramid fiber have also been developed, offering excellent fatigue resistance to abrasion, flexure, and stretching. One such system is on a wire frame basis, with mechanized frame building, and it is proposed as reinforcement for concrete pillars and other structures. As well as the strength of the fiber, this application exploits the high chemical resistance of aramid to acids, alkalis, and cement.

Carbon Fibers Various organizations worldwide have been involved in developing carbon fibers (CFs). A few of these organizations are reviewed as well as performances of carbon fibers (Table 2.14). Carbon fibers based on rayon (cellulose) were first investigated during 1880 in USA. It was during this year that Thomas Edison and Joseph Swan first patented the incandescent electric lamp (after years of trial and error with literally thousands of materials). The filaments that he used in the lamp were made of carbon and had been produced by pyrolyzing natural and regenerated cellulose fibers. The carbon filaments themselves were very fragile. However, the invention of the tungsten filament overtook this development. Initial modern carbon fiber development occurred during 1944-1960 in the research and development Materials Laboratory of the WrightPatterson Air Force Base (WPAFB), Dayton, OH, USA. The UK Royal Aircraft Establishment developed carbon fiber-RPs in the late 1950s. During this period carbon fiber produced from cotton and viscose rayon fabrics were principally used in military applications such as rocket nozzle cones and ablative surface panels on outer space vehicles (other fibers were also used). Barnaby-Cheney and National Carbon manufactured a small amount of carbon fiber from these fibers. Starting during 1951 new ablative plastics were developed in Materials Laboratory, WPAFB; they are materials that absorbs heat, while part of

71

72 Reinforced Plastics Handbook

it is being consumed by heat through a decomposition process that takes place near its surface when exposed to excessive heat. Their use is to prevent heat build-up under the ablative material. An example is the initial use of asbestos fibers/phenolic RPs used as ablative materials on the nose cones and exhaust cones on rockets and missiles. Other materials were latter used that included carbon fiber-phenolic RP. These materials are exposed to a temperature of 1650C (3000F) for a time of less than a second. It is the surface material on a reentry into the earth's atmosphere from outer space of a rocket or space vehicle that is subjected to the high heat when entering the earth's atmosphere (D. V. Rosato involved in R&D, preparing compound, and fabrication of nose cones, etc.) Sohes and Abbot of USA during 1955 developed processes for converting both natural cellulose and rayon into fibrous carbon. Essentially the carbon fibers were produced by heat-treating the precursors to temperatures about 1,000C (1,832F) in inert atmosphere. Fiber tensile strengths were as high as 40 ksi (275 MPa). Union Carbide, USA, begins production of carbon fiber cloths, felts, yarns, and battings using rayon fibers as the precursor material during 1959. Carbon fibers were batch processed by heat-treating the rayon in an inert atmosphere at about 900C (1652F), subsequently carbonizing the fibers at temperatures generally over 2,500C (4,532F). Tensile strength of fibers is 48 to 130 Ksi (300 to 900 MPa). Use included reinforcing plastics. During 1961 A Shindo, of the Japanese Government Industrial Research Institute, Osaka, produced carbon fiber from polyacrylonitrile fiber, and started the development of PAN type-high performance carbon fiber. In 1967, Rolls Royce, UK, experienced an unsuccessful project to use carbon fiber (CF) fan blades in jet engines. Problem was due primarily to the RP's coefficient of thermal excessive expansion that occurred during the heating operations causing blades to expand. The heated rotating blades would contact its enclosed peripheral wall and in turn cause engine failure. Prior work during 1944 and 1953-1954 on RP jet engine blades had a similar problem. Work was done at Air Force R&D Laboratory with D. V. Rosato involved in design, fabricating, and testing RPs blades. This unsuccessful program was caused by not being able to restrict expansion of the RP blades using different fibers and resins available at that time. RP blades for aircraft jet engines are being designed now by NASA, USA. They are essentially hollow with an internal rib structure. These

2

9R e i n f o r c e m e n t s

rib like vents direct, mix, and control airflow more effectively and reduce thermal expansion that reduces the amount of energy needed to turn the blades and cuts back on heat and noise. Most engine noise actually comes from wind turbulence that collides with the nacelle. By directing air out the back of the fan blades, the noise can be reduced by a factor of two. By drawing more air into the blades, engine efficiency is improved by 20%. There also exist embedded elastic dampening materials in the blades, which minimizes vibrations and expansions to improve resiliency, etc. Because the blade is lighter and experiences lower centrifugal forces further enhanced the blade's durability occurs. Small-scale wind tunnel tests show they last 10 to 15 times longer than any existing blade. The No. I maintenance task is the constant process of taking engines apart to check the blades. These new blades should lend themselves to more efficient production techniques. If you use titanium, you need to buy a big block of it and machine it down to size, wasting a lot of material. As reported, this is very time consuming, and one has to worry about thermal warping. The RP allows for mass production. It is fabricated into a mold, making the process more precise and ensuring the blades are identical. NASA will test the new blades in large-scale wind tunnels at the NASA Glenn Research Center in Cleveland. Today, high cost carbon fiber alone and in hybrid form (Table 2.15) is widely used in high performance applications were performance to cost advantages exist. Depending on the manufacturing method the types of fiber available range from amorphous carbon to crystalline graphite. Its stiffness or modulus of elasticity can range from less than that of glass to three times that of steel; the most widely used types have a modulus of 230-392 GPa. The fiber is available as short-length fibers, twisted and non-twisted yarns, continuous filament and tows. A fiber tow is an untwisted bundle of continuous filaments, usually referring to any synthetic fibers. As an example, a tow designated as 140 K has 140,000 filaments. CFs arc the predominant high strength, high modulus fiber used in the manufacturer of advanced RPs products. They can be made by the pyrolytic degradation of a fibrous organic precursor. Most CFs arc obtained by the pyrolysis of polyacrylonitrilc (PAN); this old basic technology subjects the PAN to temperatures up to 1080F (2000C). Other methods include pyrolysis of cellulose (rayon) and acrylic fibers, burning-off binder from the pitch precursor, and growing single crystals (whiskers) via thermal cracking of hydrocarbon gas. CFs are essentially crystalline carbon (graphite) having high mechanical and physical performances in reinforcements. Their benefits also extend to

73

74 Reinforced Plastics Handbook Table 2.1 5 Properties of unidirectional carbonlaramid hybrid/epoxy RPs

Ratio of carbon / aramid fibers 0/100 50/50 75/25 100/0

Ratioof aramid/ carbon 100/0 50/50 25/75 0/100

Specific gravity

Tensile modulus, 106psi

1.35 1.51 1.56 1.60

11.2 15.7 17.4 21.1

Stress at 0.02% offset, 103 psi Compression

Flexure

26.4 59.9 68.8 98.4

49.2 120 181 233

Dynamic flexure strength, 103 psi

Impact energy,

63 82 82 99

48 44 34 28

ft.-lb./in. 2

high thermal stability, electrical conductivity, chemical resistance wear resistance, and relatively low weight. MEC (London U.K. and Shanghai, China), an international engineering services company, was awarded a $25 million contract by China Worldbest Group Co. Ltd. (Changzhou, China) to engineer and construct a polyacrylonitrile (PAN) and carbon fiber production plant in Bengbu, a city in Anhui province, located in eastern mainland China. The plant will be the first combined polyacrylonitrile and carbon fiber manufacturing facility built in China. The operation will include production of PAN precursor, which then will be converted into carbon fiber tow at the same location. The plant will house all the facilities necessary for raw material preparation and storage, batch polymerization processing (conversion of acrylonitrile monomer into polyacrylonitrile), the spinning of the polymerizcd product into yarn, all further processing and drying necessary to form the PAN precursor, collection of the precursor on bobbins, and the final pyrolization process that forms the carbon fiber product. Project completion is scheduled for February 2005. China Worldbest Group is China's largest textile/pharmaceutical group, with 50,000 employees working in 34 subsidiaries and affiliates in China and elsewhere in the world.

2

9Reinforcements 7 5

In the ongoing search for a lower-cost carbon fiber precursor, researchers from Virginia Tech's Materials Research Institute (MRI) and Clemson University have worked over the past three years, with Department of Energy funding, to develop cheaper, more environmentally friendly materials. During laboratory-scale trials, the team has developed acrylic fibers that can be spun directly from the melt, from 100% solids and without the addition of solvents. Elimination of solvents cuts processing costs and avoids hazardous waste handling. In addition, by adding a molecular component to the polymer that reacts with ultraviolet (UV) light, the group hopes to use photo crosslinking and UV energy to cut fiber carbonization time down to one or two hours. It is expensive to process material for 10 or more hours at very high temperatures. If the process can be successfully scaled up, lowercost carbon fiber may be the result. R&D is being conducted on a new generation of carbon fibers. See Chapter 10 Nanotechnology Successes for details concerning the potential of this new generation carbon fibers. Graphite Fibers

Graphite is a relatively soft, black material that is naturally occurring. It is made synthetically via graphitization principally to produce graphite fibers for high performance RPs. It is a crystalline allotropic form of carbon. This allotropic structure exists as a substance, especially an element, in two or more physical states such as crystal and graphite. Graphitization is the formation of graphite-like material from organic compounds by pyrolyization. Pyrolysis is the technology of decomposing organic materials at high temperatures where chemical change is brought about by the action of heat occurring during carbonization. An intermediate phase in the formation of carbon from a pitch precursor is called mesophase. This is a liquid crystal phase in the form of microspheres which upon prolonged heating above 400C (750F) coalesce, solidify, and form regions of extended order. Heating above 2000C (3630F), forms graphite structures. Fiber properties relate to degree of heat. The process of pyrolyization occurs in an inert atmosphere at temperatures in excess of 2000C (3630F), usually as high as 2480C (4500F), and sometimes as high as 9750C (5400F), converting carbon to its crystalline allotropic form. Temperature depends on precursor and final properties desired. These carbon fibers develop higher modulus of elasticity and the product is usually identified as graphite fiber. During pyrolysis, molecules containing oxygen, hydrogen, and

76 Reinforced Plastics Handbook

nitrogen are driven from the precursor fibers, leaving continuous chains of carbon. The terms graphite and carbon are often used interchangeably, though they differ. The basic differences lie in the temperature at which the fibers are made and heat-treated, in the amount of elemental carbon produced, and mechanical properties. Carbon fiber is produced by controlled oxidization and carbonization of fiber-form precursors. The usual precursors are cellulose, polyacrylonitrile (PAN), lignin, and pitch, of which PAN is most commonly used as it has high carbon content. Oxidization and carbonization at temperatures of up to 2600C (4500F) produces a high-strength fiber, and graphitization by increasing the temperature to 3000C (5500F) produces a high modulus graphite fiber. They assay at more than 99% elemental carbon. As reviewed, this heat chemically changes the fiber yielding high strength/weight and high stiffness/weight fibers. Resistance to fatigue and creep is high and the fiber has good resistance to wear, together with properties of vibration damping, thermal stability and high longterm resistance to corrosion. As it is carbon, the fiber also imparts electrical conductivity and it is permeable to X-rays. Surface treatment and sizing is used to improve bonding and handleability. The latest types of fiber also offer lower fuzz and greater spreadability. The resulting fiber is stronger than steel, lighter than aluminum, and stiffer than titanium. Carbon fiber (CF) can also be produced from a pitch precursor, but the elongation of these fibers tends to be low. Pitch is the high molecular weight residue from the destructive distillation of petroleum and coal products. The usual grades of fiber (indicated by their initials) are high strain (HS), low modulus (LM), high modulus (HM), ultra high modulus (UHM), high strength (HT), and intermediate grades, such as intermediate modulus (IM). The most common form is a high tensile strength fiber, produced by most suppliers. CFs offers the highest specific stiffness and very high strength in both tension and compression. Their impact strength is lower than that of glass or aramid fibers, and carbon is often combined with these to form hybrid materials. Examples of performance in TP matrix with carbon or graphite fibers include the use of epoxy and nylon (PA). Nylon 6 (DuPont) with a 30 wt% fiber content will increase flexural strength by about three times, and flexural stiffness may be raised by a factor of seven. Electrical properties, friction behavior and wear resistance may also be improved. The electrical applications largely fall into two categories: to impart conductivity and prevent build-up of electrostatic discharge (which may

2 . Reinforcements 77

cause short circuits or explosions when handling hazardous materials), and to screen components from electromagnetic interference. For engineering applications, frictional and wear properties are very good in comparison with non-reinforced or glass fiber-reinforced compounds. Unreinforced nylon has static and dynamic friction coefficients about 25% and 40% higher than those of a carbon-reinforced PA 6, while the abrasion factor is ten times higher. Combined with the higher thermal conductivity of carbon-reinforced compounds, this produces higher pv values. These are a measure of the heat generated by parts sliding in contact with each other (p = bearing pressure, v = sliding velocity). Graphite or carbon fiber is supplied as a continuous or as a chopped fiber. Continuous fiber can be combined with virtually all thermoset and thermoplastic resin systems and is used for weaving, braiding, prepreg manufacture and filament winding. Chopped fibers can be used in molding compounds for compression and injection molding, giving parts with high resistance to corrosion, creep and fatigue, with high strength and stiffness (Tables 2.16 and 17). Boron Fibers

Boron fibers (BFs) were the first high strength, high modulus fiber to be produced. They are produced by chemical vapor deposition from a gaseous mixture of hydrogen (H2) and boron trichloride (BCI3) on primarily an electrically heated tungsten substrate of 0.5 rail (12.5 pro) diameters. The resulting amorphous boron has excellent properties, but the process is very costly. The final filament diameter is 4 mil (100 ~am), 5.6 mil (140 pm), or 8 mil (200 }am) in descending order of production quantifies; however, both small and large diameters have been produced in experimental quantities. Performance wise, they have exceptionally high tensile strength and modulus of elasticity with a relatively low density. High and uniform modulus and tensile strength are attainable [modulus of 380-400 GPa (55-58 x 106 psi) and tensile strengths of 3.5-3.65 GPa (500,000-530,000 psi)]. There are lower-cost fibers but they are not as consistent or high performance. Upper temperature limit in an oxidizing atmosphere is 250C (480F). This high cost material usually has a matrix of expensive high performance epoxy plastic. This was the first of the high strength, high modulus fibers to be produced; U.S. Air Force Materials Laboratory, Dayton, OH was very influential in its development during the early 1950s. Use includes aerospace structural parts, tennis rackets, fishing rods, golf clubs, etc.

',,4 r, m ,

Table 2.16 Examplesof graphite fiber/thermoset and thermoplastic RPs

Grephite-epoxy Property

Unidirectional laminate Longitudinal (0~ properties Tensile strength Tensile modulus of elasticity Compressive strength Compressive modulus of elasticity Flexural strength Flexural modulus of elasticity Interlaminar shear strength (short beam) Transverse (90 ~) properties Tensile strength Tensile modulus of elasticity RC = resin content by weight VC = void content by volume

Units

22~ {72~

277~ {350~

ml

t'1)

Graphite-epoxy RC = 29-33% VC = I. 7-2.40/0 22~ (72~

177~ {350~

Graphite-polyimide RC = 350/0 VC= 00/0 22~ (72~

177~ {350~

Graph ite-polyimide RC= 27.5-31o/o VC= 0~ 22~ (72~

177~ (350~

Graphite-polysulfone RC = 33-34o/o VC= 0-1.9O/o 22~176

117~176

I/I m, I/I

,-r

a" 0 0

Ksi(MPa)

218 (1502)

208 (1433)

197.7 (1362) 141.7 (976)

156.7 (1080) 152.2 (1049)

203.3 (1401) 187.4 (1291)

187.9 (1295) 179.1 (1234)

Msi(GPa) Ksi(MPa)

26.3 (181) 218 (1502)

28.5 (196) 206 (1419)

20.3 (140) 19.3 (133) 157.4 (1084) 148.1 (1020)

20.25 (140) 19.56 (135) 180.0 (1240) 120.0 (827)

18.3 (126) 18.9 (130) 206.1 (1420) 164.6 (1134)

16.3 (112) 102.1 (703)

Msi(GPa) Ksi(MPa) Msi(GPa)

23.0 (158) 247 (1702) -

22.5 (155) 196 (1350) -

19.8 (136) 25.0 (172) 200.7 (1383) 96.4 (664) 17.77 (122) 16.29 (112)

18.2(125) 20.5(141) 204.0 (1406) 179.1 (1234) 16.89 (116) 18.43 (127)

18.7 (129) 224.4(1546) 18.4 (127)

17.3 (119) 18.5 (127) 191.5 (1319) 135.2 (932) 17.8(123) 20.0(138)

Ksi(MPa)

15.9 (110)

8.9 (61)

Ksi(MPa) Msi(GPa)

3.85 (26.5) 1.50 (10.3)

14.8 (102)

12.69 (87.4)

7.18 (49.5)

2.89 (19.9)

4.9 (33.8)

3.7 (25.5)

2.82 (19.4)

1.78 (12.3)

1.3 (9.0)

1.05 (7.2)

1.50 (10.3)

19.1 (132) 178.8 (1232) 17.3 (119)

11.6 (79.9)

17.5 (121) 90.2 (621)

8.4 (57.9)

13.62 (93.8)

9.79 (67.5)

2.97 (20.5)

5.37 (37)

3.81 (26.3)

5.02 (34.6)

5.39 (39.1)

1.15 (7.9)

1.39 (9.6)

1.09 (7.5)

1.15 (7.9)

1.07 (7.37)

10.2 (70.3)

2-Reinforcements 79 Table 2.17

Properties of carbon and graphite fabriclthermoset resin RPs

Material composition Density, Ib/ft 3

EpoxyEpoxy Phenolic (330/o), Phenolic (31O/o), novolac (370/0), novolac (350/0) carbon graphite carbon graphite fabric (670/o) fabric (690/0) fabric (63O/o) fabric (650/0) 84

89

85

85

75~

21,600

12,900

18,500

10,100

350~

19,250

12,325

2,620

3,820

75~

2,450

680

4,000

1,000

350~

230

574

160

100

75~

3.50

1.58

2.63

2.16

350~

2.80

1.70

0.64

0.58

Tensile strength, psi Parallel

Perpendicular

Tensile elastic modulus, million psi, Parallel

Perpendicular 75~

2.39

0.81

1.46

1.13

350~

-

0.48

0.09

0.14

75~

1.08

0.97

1.15

0.77

350~

1.14

1.10

0.67

0.47

Tensile elongation at failure, % Parallel

Perpendicular 75~ 350~ Shear strength, psi Parallel 75~ 350~ Compressive strength, psi Compressive elastic modulus, million psi Flexural strength, psi Flexural elastic modulus, million psi Hardness, Barcol Specific heat, Btu/Ib-~

0.10

0.11

0.29

0.10

0.32

0.16

0.19

0.10

4,000 3,230 35,000

1,820 1,590 10,800

16,700

2,600 1,500 -

1.57

1.29

1.19

-

30,000 2.4

23,000 1.9

16,000 0.93

-

73

52

-

-

0.24

0.26

-

-

Thermal conductivity, Btulhrlft3-~ Para Ilel

0.82

1.30

0.59

1.50

Perpendicular

0.27

0.80

0.35

0.66

Thermal expansion coefficient, 10-6 in./in./~ Parallel

3.8

2.4

7.5

7.0

Perpendicular

8.5

9.0

60.0

53.0

0.8

0.8

0.8

0.8

Emittance

All properties are parallel to the fabric warp unless otherwise noted.

80 Reinforced Plastics Handbook Silica Fibers

Silica fibers are smooth-surfaced, glasslike fibers, with a nearly round cross section. They are spun from silicon dioxide, which may be pure or contain a small amount of other materials. Silica fibers can be produced indirectly from glass filaments from which all constituents other than silica have been removed, or through spinning a viscous filament that contains a high amount of silica. The organic materials are burned away, leaving a porous silica filament. Silica fibers are principally used in chemical engineering, high temperature electrical insulation, and high temperature thermal insulation. Quartz Fibers

Quartz fibers are made from natural quartz crystals by softening quartz rods in an oxy-hydrogen flame and drawing rods into filaments. Because high purity quartz crystals are rare, the cost of quartz fibers is considerable higher than that of glass fiber and high silica fibers. Quartz filaments have assumed a role as high-temperature resistant fibers, and are produced in considerable quantities for high temperature and corrosion-resistant applications. They are widely used as filtration and insulation materials at temperatures above those of mineral silicate fibers. Quartz and silica fiber RPs are used in jet aircrafts, rocket nozzles, nose cones, and reentry heat shields for spacecraft. Quartz fiber tensile strength at room temperature is 130 x 103 psi (896 MPa) and at 204C (400F) is 99 x 103 psi (682 MPa). Tensile modulus at room temperature is 10 x 106 psi (6.89 GPa). High silica (s.g. 1.74) and quartz (s.g. 2.2) fibers have higher strengthto-weight ratios than most other high temperature materials. Mso, quartz has about 5 times the tensile strength of high silica. Both types of fibers are almost perfectly elastic and their elongation at break is about 1%.

Fiber/Filament Characteristics Information on fibers applicable to different materials of construction and use that relates to compositions, surface treatments, performances, processing, and terminology follows: Fiber Fiber is a general term used to refer to filamentary materials. Often it is used synonymously with filament, monofilament, whisker, and yarn. It is any material in a form such that it has a

2

9R e i n f o r c e m e n t s

minimum length of at least 100 times its diameter. Diameters are usually 0.004 to 0.005 in. (0.10 to 0.13 mm). Fibers can be continuous or reduced to short lengths (discontinuous) where the industry lists less than as having a specific length such as 0.125 in (3.2 mm). A filament is the smallest unit of a fibrous material and usually not used alone. They are the basic units formed during manufacture that are gathered into strands of fiber. Their diameters are less than 0.001 in. (0.025 mm). Its denier also identifies the fineness of a fiber. Fiber, abaca The plant Musa textiles provides 6 to 12 ft (1.8 to 3.6 m) long fiber bundles used in the manufacture of ropes, cables, and RPs. Fiber, acrylic Filaments made from any long chain synthetic plastic containing 85 wt% or more acrylonitrile. Fiber, alumina-silica Amorphous structure with excellent resistance to all chemicals except hydrochloric acid, phosphoric acid, and concentrated alkalis. Tensile strength is 400,000 psi (2,000 MPa), modulus of elasticity 16 million psi (110 GPa), upper temperature limit in oxidizing atmosphere at 1,470F (800C), noncombustible, low heat conductivity, and thermal shock resistance. Fiber, aramid See Aramid Fibers previously reviewed in this chapter. Fiber, areal weight The weight of fiber reinforcement per unit area (width x length) of tape or fabric. Fiber attenuation The process for making thin or slender. It applies to the formation of fiber from molten glass. Fiber biconstituent A hybrid or composite fiber comprising a dispersion of fibrils of one synthetic plastic within and parallel to the longitudinal axis of another; also a construction of plastic and metal or alloy filaments. Fiber binder See Glass Characteristics, Glass fiber b i n d e r / s i z i n g coupling agent in this chapter. Fiber bobbin Sometimes also called a package. It is the smallest production unit of yarn or roving, including its appropriate (usually cardboard or plastic tube) support. Fiber, boron See Aramid Fibers previously reviewed in this chapter. Fiber braided/directional Weaving fibers into a tubular shape. As an example, A&P Technology, Cincinnati, OH, specializes in developing braided reinforcements using a variety of material types, braid forms, and braid architectures for applications ranging from prostheses to

81

82 Reinforced Plastics Handbook

airframe structures to hockey sticks to boat hulls. Their braided reinforcements allow the molder to optimize fiber architectures better than conventional fabric reinforcements, while enabling an easy method of manufacture. Standard reinforcements include carbon, Kevlar, and glass fiber sleevings, broadgoods, and tapes, and its most recent additions are Bimax TM biaxial fabric, Trimax TM triaxial broadgoods and Zero TM unidirectional carbon fabrics. Bimax biaxials are constructed to provide the molder with a _+45~ fiber orientation fabric that does not need to be cut, stitched, or manipulated. Its design makes it highly drapeable and conformable, which reduces processing time and cost by making the lay-up process easy and consistent. Fine hot melt yarns are incorporated in the axial direction to enable better handling. Zero unidirectional carbon fiber fabric was originally developed for Lockheed Martin's F-22 air fighter program. Designers at Lockheed were looking for a unidirectional fabric with increased compression values and to meet these needs, A&P designed a nonwoven unidirectional reinforcement. Since it is nonwoven there is little crimp in the individual yarns, which increases the fabric's compression values. In the Spring of 2003, intermediate modulus Zero fabrics were qualified for applications on the F-22, which involved testing against a baseline of unidirectional prepreg and dry fabric lay-up. In all areas, including compression, Zero outperformed the baseline. It has since been specified for use throughout the airframe where it will replace other dry unidirectional fabrics a n d / o r prepregs. Zero's use is not restricted to high cost aerospace applications as A&P designed the fabric to provide affordable but superior performance. It can be used in a wide range of RP molding processes including resin transfer molding (RTM), vacuum assisted RTM (VARTM), resin film infusion, and hand lay-up (Chapter 5). Fiber breakout Fiber separation or break on surface plies at drilled or machine edges. Fiber bridging Reinforcing fiber that bridges an inside radius that is caused by shrinkage stresses around such a radius during curing. Fiber bristle A generic term for a short stiff, coarse fiber. Fiber bundle Identifies a collection of essentially parallel fibers or filaments. Fiber, buttress A type of thread used for transmitting load in only one direction. It has the efficiency of the square thread and the strength of the V-thread.

2" Reinforcements 83

Fiber capillarity action The attraction between molecules, similar to surface tension, which results in the rise of a liquid in fibers, as could occur in RPs, etc. Fiber, carbon See Aramid Fibers previously reviewed in this chapter. Fiber, carbon stabilization During forming, it is the process used to render the carbon fiber precursor infusible prior to carbonization. Fiber carding A process of untangling and partially straightening fibers, such as cotton and asbestos, by passing them between two closely spaced surfaces which are moving at different speeds, and at least one of which is covered with sharp points. Carding machine converts a tangled mass of fibers to a filmy web. Use includes reinforcements in reinforcing plastics. Fiber, cellulose acetate Acetyl derivative of cellulose. Triacetate designation can be used when not less than 92% of the cellulose groups are acetylated. Fiber, ceramic See Other Fibers and Reinforcements in this chapter. Fiber count The number of warp fiber/yarn (ends) and filling fiber/yarn (picks) per inch. Cross section or thickness of fiber, yarn or roving expressed as denier. See Fiber decitex. Fiber creel A spool, along with its supporting structure, that holds the required number of fibers or roving balls for supply packages in a desired position for unwinding into the next processing step such as weaving, braiding, filament winding, RP fabrication, etc. Fiber crimp The formations. It light pressure. unit length, or of the crimp.

waviness of a fiber or fabric responsible for void determines the capacity of fibers to cohere under Measure either by the number of crimps, waves per the percent increase in extent of the fiber on removal

Fiber decitex Also called dtex or (deci)tex. This is a property unique to the fiber industry to describe fineness (and conversely the cross sectional area) of a filament, yarn, rope, etc. It is defined as the weighting of 10,000 m of the material. One decitex-- 0.9 denier. Fiber denier It is a unit of weight expressing the size or coarseness but particularly the fineness of a continuous fiber or yarn. The weight in grams of 9000 m (30,000 ft) is one denier. The lower the deniers, the finer the fiber, yarn, etc. One denier equals about 40 micron. Sheer women's hosiery usually runs 10 to 15 denier. Commercial work of 12 to 15 denier fiber is usually generated.

84 Reinforced Plastics Handbook

Fiber desizing Process of eliminating sizing from gray or greige goods before applying special finishes or bleaches. Also removing lubricant size following weaving of a cloth. Fiber directional property See Chapter 7. Fiber drawing Fiber with a certain amount of orientation imparted by the drawing process when the fibers are formed. Result is significant increase in strength and other properties. Fiber end It is an individual fiber, thread, roving, yarn, or cord. In fabric, an end is a warp yarn, running the length of the fabric. A strand of roving consisting of a given number of filaments gathered. The group of filaments is considered an end or strand prior to twisting. Fiber, felt A fibrous material made up of interlocking fibers by mechanical or chemical action, moisture, a n d / o r heat. They can be made of many different fibers, including glass, cotton, nylon, etc. Fiber fibrillation Production of fiber from film. Fiber finish The surface treatment applied to processed fibers, particularly glass fibers. Fiber f'mish, satin Type of finish having a satin or velvety appearance that is midway glossy (or bright) and mat. It behaves as a diffuse reflector that is lustrous but not mirror-like. Fiber, flax Natural fiber obtained from the inner bark of the flax plant. Use includes as filler and in producing of high strength reinforced or laminated plastics. Fiber float A warp or filling fiber that lies on top of the opposite series of yarn for a distance of several fibers. Fiber flock Very short fibers used as fillers in plastic materials that can improve processing, properties, a n d / o r reduce cost. Reducing fibers to these fragments is by cutting, tearing, or grinding producing different forms that include entangled fibers, small bead size, or usually broken fibers. Fiber flocking Also called flock spraying. It is a method of coating by spraying finely dispersed fibers or powders by pneumatic or electrostatic means on adhesive coated surface producing a velvety surface. Another method takes preheated parts that are dropped into a bed of fibers or powders. Fibers used include nylon, rayon, cotton, or TP polyester. It provides an attractive/decorative surface, sound absorber, etc.

2-Reinforcements 85

Fiber fuzz Accumulation of short, broken filaments after passing strands, yarns, rovings, etc. over a contact point. Fiber, graphite See Aramid Fibers previously reviewed in this chapter. Fiber, hollow These plastic fibers can produce high bulk, low-density fabrics. Other fiber configurations can be produced such as trilobal cross section. Annular dies are used to produce the desired hollow cross section shape. Fiber spinning methods used are: (1) wet from a plastic solution into a liquid coagulant, (2) dry from a plastic solution in a volatile solvent with an evaporative column, and (3) conventional melt systems. Fiber, hybrid Two or more different types of fibers are used to provide different RP performances. Fiber, inorganic Fibers used in RPs, etc. include glass (different types), aluminum silicate, beryllium glass, carbon, ceramic, graphite, and quartz (fused silica). Fiber, jute See Jute Fibers previously reviewed in this chapter. Fiber, Kevlar See Aramid Fiber previously reviewed in this chapter. Fiber kink Also called curl yarns, looped yarn, or snarl in a fiber. In fabric, a short length of yarn that has spontaneously doubled back on itself to form a loop. It can be a type of a waviness occurring as interior edges, not to be confused with the more abrupt departures as ridges or surface marks. Fiber length, critical Minimum fiber length required for shear loading to its ultimate strength by the matrix. Fiber linter Short, fuzzy fibers that adhere to the cotton seed after ginning. Use includes in rayon manufacture, as fillers for plastics, as a base for the manufacture of cellulosic plastics etc. Fiber manufacturer Originator of commercially produced glass fibers Owens Corning is a world leader in building materials systems and RP solutions. Founded in 1938 by Owens Illinois and Dow Coming, the company had sales of $4.8 billion in 2001 and employs approximately 19,000 people worldwide. Additional information is available on Owens Corning's Web site at www.owenscorning.com or by calling the company's line 1-800-GETPINK. Fiber mat A fibrous material used in RPs; consists of randomly and uniformly oriented: (1) chopped fibers with or without cartier fibers or binder plastics; (2) short fibers with or without a cartier fabric; (3) swirled filaments loosely held together with a plastic binder; (4)

86 Reinforced Plastics Handbook

chopped or short fiber with long fibers included in any desired pattern to provided addition mechanical properties in specific directions; and so on. They are produced in flat and curved blanket sheets, tape forms, etc. for use in the different RP processes. Fiber mat, needled A mat felted together in a needle loom with or without a cartier. Fiber mat veil An ultra-thin mat similar to a surface mat, often composed of organic fibers as well as glass fibers (Table 2.18). Fiber material, plastic Different TPs are used to produce fibers. The more important production wise materials are PP, nylon 66, polyester, and PETP; other plastics are also used. Each plastic family has different grades to provide different properties during and after being processed. Their plastic fiber structures have different levels of molecular organizations with each relating to certain aspects of fiber behaviors and properties. As an example, their organochemical structure defines the chemical composition and molecular structure. This molecular structure is directly related to the fibers chemical properties, dye ability, moisture sorption, swelling characteristics, and indirectly related to all physical properties. The physical properties of fibers are influenced by the processing techniques used on-line where factors from melt conditions to windup speed. However, they are strongly influenced by the plastic morphology. All plastic fibers that are useful in textile applications are usually semicrystalline (usually referred to as crystalline), irreversibly in an oriented pattern. Fiber, metallic Manufactured fiber used in RPs includes metal, plasticcoated metal, metal-coated plastic, or a core completely covered by metal. Included are steel, aluminum, magnesium, and tungsten. The latest steel reinforcement (Hardwire TM 3S and 3SX) from Hardwire, of Pocomoke, MD, USA, provides a significantly greater flexural strength and modulus with ductility than its previous products. The new steel cords grades have been specially designed by Hardwire in partnership with cord manufacturer Goodyear. The fibers can either be used as reinforcement in their own right or together with other fibers such as glass or carbon to produce fiber RP structures that fail in a ductile manner rather than catastrophically. They can be used with various resin systems including TS polyester, vinyl ester, modified acrylic, urethane and epoxy. It permits fabricating RP boats that dent instead of tear open, concrete repairs that survive fire and earthquakes, pressure vessels, pipe that exhibit no long-term creep or stress rupture, and wind turbine blades that are lower in weight, faster to make and lower in cost.

2 . Reinforcements 87 Table 2.18 Characteristics and applications of nonwoven surfacing veils Type

Physical data

Characteristics

Applications

Aramid: para-aramid, 2.8 Pa strength, 70 GPa modulus; chopped staple or fibrid (pulp)

10-150 glm 2 Tensile strength: up to 8 Nlmm 2 Density: 80 kg/mm 3

Improved impact resistance Smooth finish Good wear resistance Can be blended with conductive fiber Superior temperature resistance

Aerospace: adhesive carriers Automotive: improved stone impact resistance Defence: radar cross section Recreation: skis, snow and surf boards, surf boards, canoes Industrial: substrata for friction products; wear resistance for high-speed rolls Electrical: printed circuit boards

Carbon: PAN-based, 200 or 250 GPa modulus 3-25 mm fiber length

8-200 glm 2 Tensile strength: up to 20 Nlmm 2 Density: 80 kg/mm 3

Integral electrical conductivity Corrosionresistance Improved strength, stiffness, surface finish

Chemical vessels and pipework: electrical grounding, improved corrosion resistance; spark lasting tank liners Computer cases: high strength, integral EMI/RFI shielding Electronics Fuel cells Sports goods Pultrusion: increased hoop strength, better surface finish

Glass: C-glass (chemical resistance) E-glass (electrical properties)

10-200 glm 2 Tensile strength: up to 12 Nlmm 2 Density: 140 kg/mm 3

Improved impact, wear resistance Can be blended with conductive fiber to reduce static discharge Reduced weight and cost with less paint and resin can prevent galvanic corrosion by separating dissimilar conductive materials Superior temperature resistance

Aerospace:interior surface finishing Defence: blended with conductive fiber to reduce radar cross section RecreationIndustrial: C-glass improves corrosion resistance; better wear resistance; blended with conductive fiber to reduce static discharge Electronics: printed circuit cards

Polyester

10-100 g/m 2 Tensile strength: up to 10 N/mm 2 Density: 120 kg/mm 3

Improved impact, wear resistance Electrical transparency Superior drape to glass surfacing Opacitylwhiteness Good acid resistance

Aerospace: adhesive carriers surfacing layer for radomes Defence: blended with conductive fiber to reduce radar cross section Recreation: smooth complex shapes; screen printable Industrial: reaction vessels, double curvature; flexible laminates

Source: Based on data from Technical Fibre Products

88 Reinforced Plastics Handbook

Its improved stiffness, strength, and ductility is targeted to enable fabricators in molding extremely strong parts like conventional RPs yet act more like metal. Working with the US Navy as the testing partner, Hardwire and Goodyear worked on material, configuration, surface chemistry, and production machinery developments to achieve the desired performances (website: www.hardwirellc.com).

Fiber, micro- Fiber whose individual filaments are less than 1.0 denier or 1.0 tex. They are four times finer than the average human hair; at least three times finer than cotton fiber; and finer than natural silk. They are TP polyester spun and oriented to produce incredibly lightweight, durable, and water resistance.

Fiber, nylon See Aramid Fibers previously reviewed in this chapter. Fiber, nanotube See Chapter 10 Nanotechnology Successes. Fiber, one-ended A fiber so short in length it appears that it only has one end. Examples include very short length milled glass fibers and asbestos fibers.

Fiber orientation See Chapter 7 Directional Properties. Fiber optics Fiber optics may be defined as the guidance of electromagnetic radiation along transparent dielectric hair-thin glass fibers. More specifically, the guidance usually involves the mechanism known as total internal reflection. If the fibers are of dimensions comparable to the wavelength of light, the fiber will act as a waveguide to conduct the radiation in discrete modes. Glass fibers with extruded plastic coating, usually PE, are used. A fine-drawn silica (glass) fiber or filament of exceptional purity and specific optical properties (refractive index) that transmits laser light impulses almost instantaneously with high fidelity is used.

Fiber, other They include natural/vegetable, sisal, asbestos, ramie, flax, soya bean/cellulose, and hemp types.

Fiber pattern The pattern formed by the fibrous strands. Fiber pencil A rod-like assemblage of fibers in close packed parallel orientation of generally uniform diameter that can be fiberized readily.

Fiber pick Also called fill, woof, or weft. An individual filling yarn running the width of a woven fabric at right angles to the warp.

Fiber, polybenzimidazole High strength, heat resistance fiber made from polybenzimidazole plastic

Fiber, polyethylene terephthalate Plastic fiber identified as XTC.

2 . Reinforcements 89

Fibers processing Thermoplastic fibers or filaments can be produced by screw extruders. They are manufactured using the three common methods of melt spinning, dry spinning, and wet spinning. There are many variations and combinations of these basic processes. Other types of fiber-forming processes include: (1) reaction spinning; (2) dispersion, emulsion, and suspension spinning; (3) fusion-melt spinning; (4) phase-separation spinning; and (5) gel spinning. The processes force molten plastic by an extruder and/or gear pump through fine holes in a spinneret (or spinaret) die. In turn they are immediately stretched or drawn (oriented), cooled, and collected at the end of the line. During this process, they may be subjected to other operations such as: (1) thermal setting and thermal relaxation processes to provide dimensional stability; (2) twisting and interlacing to provide cohesion of the filaments with or without sizings; (3) texturing; and (4) crimping and cutting to provide staple products. Speeds of certain lines using the melt and dry spinning processes can go from 6,600 to 13,000 ft/min (2,000 to 4,000 m/min). Numerous techniques for producing fibers without using the spinneret have been used. They include centrifugal spinning, electrostatic spinning, tack spinning, and solid-state extrusion (SSE). The SSE process extrudes through a capillary remoter with a conical die; the processing temperature is close to the melting point of the plastic. In the manufacture of fibers a relatively isotropic plastic with properties similar in all directions converts into an orthotropic plastic where most of the plastics strength is in the direction of the fiber axis. This desirable effect provides a certain degree of fiber strength in their longitudinal direction, but usually not enough. So the fibers arc made stronger by stretch-orientation during or after processing. These spinning lines can include a variety of operations useful for the fibers different applications. A finish can be applied after cooling in-line. Rather than keeping them straight, texturing techniques are used. Texturing introduces crimp, whereby the straight filaments are given a twisted, coiled, or randomly kinked structure. A yarn made up of these filaments is softer and more open in structure; it is more pleasing to the touch. Finishes are used to improve the processing and handling of fibers. The finishing mix can include a lubricant. Fiber processing development Unusual plastic fibers such as polyolefin fibers are produced by a spurted or melt-blown spinning technique. A variety of directly formed nonwovens with excellent filtration characteristics is produced. Original development was by

90 Reinforced Plastics Handbook

Exxon Corp. that produced very fine, sub-micrometer filaments. Pulp like olefin fibers are produced by a high-pressure spurting process developed by Hercules, Inc. and Solvay, Inc. A high modulus commercial PE fiber with properties approaching those of aramid and graphite fibers is prepared by gel spinning. Higher tensile strengths are also available from gel spinning or fibrillar crystal growth. Fiber processing filtration Many processes require a plastic melt free of contaminates larger than a specific size. The fiber processors usually filter down to 5 micron particle size to protect the melt spinning machines from filament breaks. The fiber process typically operates at very high speeds. A filament break at this speed is costly to both the product quality and the process efficiency. The media used for filtration has included sand packs, wire screens, sintered metal powder sheets, and sintered metal fiber sheets. There are also different sandwich combinations such as wire screens and sintered metal fiber sheets that in theory provided the best properties of each component. With a gear pump running clearance can be as low as 0.00025 in. (0.006 ram) about its periphery and on either side of the metering gear. Any slight burr, nick, or particle of any "foreign" matter will cause scoring and possible seizure of the pump. Recognize that 0.001 in. (0.025 ram) equals 25 microns, so filtration down to just the pump has to be down to 6 microns or less. Fiber processing, solid-state extrusion SSE is a means for the deformation and evaluation of uniaxial molecular chain orientation and product extension for a wide range of plastics. Developments produced HDPE drawn into fibers with some of highest specific tensile moduli and strengths. A two-step drawing process is used for the preparation of polyoxyethylene, PP, and PE fibers. The plastic is first drawn to their natural draw ratio at a fast rate and subsequently slowly super-drawn at a temperature that depends on the crystalline dispersion temperature. A highly oriented extrudate can be obtained by extruding through a capillary rheometer with a conical die at temperatures close to the melting point. Initial work led to the development of transparent and fibrous linear PE extrudates. These were obtained by extruding H D P E from the molten state [55 to 58F (132 to 136C)] above a critical shear rate in a capillary rheometer and through a conical die. This procedure was subsequently modified by processing HDPE exclusively in the solid state where the plastic is semicrystalline before extruding through the die. This modification produced continuous transparent fibers with moduli in the range of 4,400 to 10,200 psi (30 to 70 MPa).

2

9R e i n f o r c e m e n t s

Fiber processing, spinning The processes principally used are wet spinning, dry spinning, and melt spinning. The plastic and ingredients (such as primarily stabilizers, pigments, and rheological modifiers) are fed into a screw extruder. The gear pump accurately meters melt through a filter pack of graded sand or porous metal and a spinneret. The multihole spinneret represents the die. Upon leaving the spinneret, the molten filaments pass at very high speed usually vertically downwards into water a n d / o r a counter current of air where they are cooled and solidified. At the same time, after leaving the spinneret, they are stretched to the desired diameter. Finish can be applied prior to the fiber reaching the end of the line where it is wound on bobbins or other windup rolls. To obtain the required high performance properties, reheating and drawing orient the fibers. This operation is usually a separate operation since it requires much higher linear speeds than melt spinning. The slit-film or film-to-fiber technology produces a substantial volume of polypropylene (PP) fibers. Cutting or slitting the film produces fibers. Stretching before or after the cutting process orients the fiber. Also used is mechanical or chemo-mechanical fibrillation. In this procedure film is created to be anisotropy by stretching before fibrillation. This is the phenomenon wherein filament or fiber shows evidence of basic fibrous structure or fibrillar crystalline nature. It occurs by a longitudinal opening up of the filament under rapid load with excessive tensile or shearing stresses. Separate fibrils can then often be seen in the main filament trunk. The whitening of the plastic when unduly strained at room temperature is a manifestation of fibrillation. Applications for this product are primarily for carpet backing, rope, and cordage. Fiber processing, spinning, dry In dry spinning a plastic solution is extruded (metering pumped) through a spinneret. The filaments exit the spinneret through a gas-heated cabinet where the solvent is rapidly removed from the plastic filaments. The suitable solvent is filtered and recovered for further use in-line. Filaments end up at the driven haul-off roll. Fiber processing, spinning, gel Basically the world's strongest commercial fiber, the polyethylene fiber strength is increased by 30% via gel spinning, 15 times stronger than steel, and twice as strong as aramid fiber. It uses ultrahigh molecular weight PE (patented by DSM High Performance Fibers, Heerlen, Netherlands). In this process, U H M W P E molecules are dissolved in a volatile solvent. By cooling and solvent removal, a gel-like fiber is spun from this solution. It is then subjected to a drawing-orienting operation. In

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the gel-like fiber, the molecules lie folded in crystals that are at fight angles to the fiber length. In the drawing process, these molecules are tipped over so they unfold in longitudinal direction, which is what gives the fiber its high strength. Fiber processing, spinning, jet For most purposes this process is similar to fiber spinning. Hot gas jet spinning uses a directed blast or jet of hot gas to pull molten plastic from a die lip and extending it into fine fibers. Fiber processing, spinning, raw nucleation The mechanism by which stress-induced crystallization is initiated usually during fiber spinning or hot drawing. Fiber processing, spinning, reaction A liquid polymer is extruded through a spinneret plate and encounters a chain extending crosslinking component producing a filament. Fiber processing, spinning, solution Process is a used to produce high modulus polyethylene fibers; fibers are called extended-chain PE (ECPE). Fibers have tensile strengths of 3.75 to 5.60 x 10 s psi (2890 to 3860 MPa) and moduli of 15 to 30 x 106 psi (103 to 207 MPa). In this process, a high molecular weight PE is used. The process begins with the dissolution in a suitable solvent of a polymer of about 1 to 5 million molecular weight. The solution serves to disentangle the polymer chains, a key step in achieving an extended chain polymer structure. The solution must be fairly dilute but viscous enough to be spun using conventional spinning equipment. The cooling of the extrudate leads to the formation of a fiber that can be continuously dried to remove the solvent or latter extracted by an appropriate solvent. The fibers are generally post-drawn or stretched oriented. Fiber processing, spinning, wet In this process, also called reaction spinning, a plastic solution is extruded from a spinneret and immersed into a spin bath tank containing a circulating non-solvent solution that coagulates (precipitates) the plastic filaments. Both the solution and the precipitation stages involve chemical reactions. After passing through the spin bath tank, they are washed prior to the windup. Conventional wet spinning has the slowest line speed compared to the other lines. However, since it permits very short distances between the holes in the spinneret face, a single spinneret may carry a very large number of holes. With this single spinneret, high production rates can still be obtained. Fiber property Different grades of each fiber exist so that properties can change. Typical tensile strength values in lb/in 3 ( g / c m 3) are:

2 . Reinforcements 93

aramid 90.4 (2.55) and E-glass 159.0 (2.55). Their modulus of elasticity in 106 psi (104 MPa) are: aramid 27 (18.6), E-glass 10 (6.9), and S-glass 12 (8.6). Fiber, quartz See Q u a r t z Fibers previously reviewed in this chapter. Fiber, ramie A strong natural fiber of vegetable origin, sometimes used as a filler or reinforcing material providing high shock resistance and strength. Fiber, rayon The generic term for fibers, staples, and continuous filament yarns composed of regenerated cellulose but also frequently used to describe fibers obtained from cellulose acetate or cellulose triacetate. Rayon fibers are similar in chemical structure to natural cellulose fibers (cotton) except that the synthetic fiber contains short plastic units. Most rayon is made using the viscose process. Fiber, rayon viscose A regenerated cellulosic fiber made by treating wood pulp with caustic soda, and with carbon disulfide to form cellulose xanthate that is then dissolved in a weak caustic solution. It is from the latter that extrusion and coagulation forms the fiber. Fiber reinforced plastic FRP is a term that is usually used as a generic term for all fiber RPs, regardless of process and type of fiber. Fiber, silk A natural fiber secreted as a continuous filament by the silkworm. Fiber skein A continuous fiber, filament, strand, yarn, or roving wound up to some measurable length and usually used to measure various mechanical and physical properties. Fiber sliver A number of staple or continuous filament fibers aligned in a continuous strand without twist. Fiber, spandex Elastomeric fibers are principally made from segmented polyurethanes (spandex) and polyisoprene (natural rubber). The elastomeric fibers consist of plastics with a main glass transition temperature (Tg) well below room temperature. This criterion excludes some fibers with elastic properties. The fibers are produced primarily using dry spinning and wet spinning with a few producers using melts spinning. For the natural rubber, a latex mixture is continuously forced through a capillary tube into an acid bath, where it is coagulated; the thread-like coagulum is pulled from the bath followed simultaneously with washing, drying, and curing. Fiber, spider silk These DuPont fibers, on an equal weight basis, are stronger than steel. They are also very elastic and tough. Their combination of strength and stretch makes the energy-to-break very

94 Reinforced Plastics Handbook

high. These biosynthetic plastics provide a very broad range of mechanical properties. Fiber spinneret The spinneret (or spinnaret) is a type of die principally used in fiber manufacture. It is usually a metal plate with many small holes (or oval, etc.) through which a melt is pulled a n d / o r forced. They enable extrusion of filaments of one denier or less. Conventional spinneret orifices are circular and produce a fiber that is round in cross section. They can contain from about 50 to 110 very small holes. A special characteristic of their design is that the melt in a discharge section of a relatively small area is distributed to a large circle of spinnerets. Because of the smaller distance in the entry region of the distributor, dead spaces are avoided, and the greater distance between the exits orifices make for easier threading. Precision machining of the orifices is required in order to avoid differences in thickness between the filaments being pulled. Note that the volumetric discharge from a cylindrical die increases with the fourth power of the diameter. An error of 10% in diameter will cause a 47% error in output. Because these differences in spinneret heads cannot be balanced out by adjusting the individual filament haul-off speeds, the diameter of the monofilament is altered by 21%. Fiber spool Holder for fibers. Fiber, staple Staple fibers are made up of a very large number of discontinuous, randomly oriented, individual fibers normally shipped in a box or bale. The fibers can be obtained by cutting continuous filament into 1/2 to 2 in. (12.7 to 50 mm) lengths and 1 to 5 denier or manufactured directly into desired lengths. They are usually subjected to a series of processes, culminating in textile spinning to yarn and are processed like natural fibers, such as wool and cotton, with which they can be blended. Fiber, straw A fibrous, cellulosic component of certain plants (wheat, rice, etc.). Its fibers are 1 to 1.5 mm long, similar to those of hardwoods. Straw can be used as filler in plastics. Its main use is preparing a pulp by the alkaline process to yield specialty papers of high quality. Use of straw for conventional papermaking in USA is of limited importance due to the abundance of pulpwood. Fiber s t r e s s , m a s s Force per unit mass per unit length in grams per linear denier. Used the same way as force per unit area. Fiber stretch, cold Pulling operation with little or no heat on fibers to increase tensile strength. Fiber tenacity Also called breaking strength. The term generally used

2 . Reinforcements 95

in yarn manufacture and textile engineering to denote the strength of a yarn or a filament for its given size. Numerically it is the grams (of breaking force) per denier unit of yarn or filament size (gpd). The yarn is usually pulled at the rate of 5 c m / m . Tenacity equals breaking strength (g) divided by denier. Fiber tex A unit for expressing linear density equal to the mass of weight in grams of 1000 m of fiber, filament, yarn, or other textile strand. Fiber t o w The precursor of staple fibers is tow, which consists of large numbers of roughly parallel, continuous filaments. They are converted by cutting or breaking into staple fibers or directly into slivers, intermediate stages between staple fibers and yarns. In the latter case, the filaments remain parallel. Fiber, textile Fibers or filaments that can be processed into yarn or made into a fabric by interlacing in a variety of methods, including weaving, knitting, and braiding. These forms of textile are used with plastics to fabricate parts such as high strength tubes/pipes, electrical and medical devices, etc. Fiber t o w An untwisted bundle of continuous filaments, usually referring to fabricated fibers. As an example, a tow designated as 140 K has 140,000 filaments. Fiber t u r n per inch Tpi is a measure of the amount of twist produced in a fiber, yarn, roving, etc. during its processing. Fiber tracer A fiber or yarn added to a prepreg for verifying fiber alignment, in the case of woven materials for distinguishing warp fibers from fill fibers, etc. Fiber twist In the yarn or other textile strand, it is the spiral turns about its axis per unit of length. Twist may be expressed as turns per inch (tpi). The letters S and Z indicated the direction of the twist, in reference to whether the direction conforms to the middle-section slope of the particular letter. A yarn or strand has what is known as an "S" twist if when held in a vertical position, the spirals conform in slope to the central position of the letter S. It has a "Z" twist if the spirals conform in slope to the central portion of the letter Z. Strands that are simply twisted (greater than 1 turn/in, or 40 t u r n s / m ) will kink, corkscrew, a n d / o r unravel because of their twist is only in one direction. The plying operation normally eliminated this problem. For example, single yarns having a "Z" twist are plied with an "S" twist, thus resulting in a balanced yarn. Depending on the twisting and plying operations, different yarn strengths,

96 Reinforced Plastics Handbook

diameter, and flexibility can be obtained. This action provides the different shaped and handling fabrics that are used to meet different performance requirements of plastic materials such as coated fabrics, RPs, pultrusions, etc. Fiber, V Fiber with its leading flank intersecting with flowing flank of adjacent fiber at the fiber root. Fiber, vegetable Different vegetable fibers are used in RPs, etc. They include: (1) seed-hair-cotton, kapok, milkweed floss; (2) bast-flax, hemp, jute, ramie; and (3) leaf-abaca, sisal. Fiber, vulcanized There are natural plastics such as gutta percha and shellac; the synthetics include many such as nylon and phenolics. There has been, patented in 1871, one that seems to be between the two and is known as vulcanized fiber which is processed regenerated cellulose fibers, viscose rayon, etc. In the past, this material was popular but now it is almost obsolete. Fiber wadding A loose cohering mass of fibers in sheet or lap form. Fiber warp Identifies the yarn running lengthwise in a woven fabric. Also a group of yarns in long lengths and approximately parallel, put on beams or warp reels for further textile processing including weaving, knitting, dyeing, etc. Filament A single, thread-like fiber or a number of these fibers put together. A variety of fiber characterized by extreme length, which permits their use in yarn with little or no twist and usually without the spinning operation required for fibers. As an example, it is a form of glass that has been drawn to a small diameter and extreme length. Most filaments are less than 0.005 in. (0.013 cm) in diameter. Filament greige Also called gray goods. It is any filament, fiber, yarn, fabric, etc. before finishing, sizing, dyeing, etc. Filament lay Length of twist produced by stranding filaments, such as fibers, wires, or rovings; angle that such filaments make with the axes of the strand during a stranding operation. The length of twist of a filament is usually measured as the distance parallel to the axis of the strand between successive turns of filaments. Filament, mono- Mso called monofill. A monofilament is a single filament of relatively indefinite length. They are generally produced by extrusion. Filament, multi- A continuous thread comprising of several individual monofilaments.

2 . Reinforcements 97

Filament shoe A device for gathering the numerous filaments into a strand in glass fiber forming. Filament sliver A number of staple or continuous filament fibers aligned in a continuous strand without twist. Filament strand A primary bundle of continuos filaments combined in a single compact unit without twist. These filaments, usually 51, 102, or 204, are gathered together in their forming operation. Filament strand end The group of filaments is considered an end. Filament strand integrity The degree to which the individual filaments making a strand or end are held together by the applied sizing. Filament, virgin An individual filament, which has not been in contact with any other fiber or any other hard material. Finish The surface treatment applied to processed fibers, particularly glass fibers. Finish, satin Type of finish having a satin or velvety appearance that is midway glossy (or bright) and mat. It behaves as a diffuse reflector that is lustrous but not mirror-like. Flax Natural fiber obtained from the inner bark of the flax plant. Use includes as filler and in producing of high strength reinforced or laminated plastics. Float A warp or filling fiber that lies on top of the opposite series of yarn for a distance of several fibers. Flock Very short fibers used as fillers in plastic materials that can improve processing/properties a n d / o r reduce cost. Reducing fibers to fragments makes them by cutting, tearing, or grinding producing different forms that include entangled fibers, small bead size, or usually broken fibers. Fuzz Accumulation of short, broken filaments after passing strands, yarns, rovings, etc. over a contact point.

Reinforcement Fabrics and Forms Fabric identifies any woven, nonwoven, knitted, felted, bonded, braided, knotted, three-dimensional (3-D), chopped mat, etc, textile material used to fabricate RP products. Information on fabrics applicable to different materials of construction and uses that relates to

98 Reinforced Plastics Handbook

compositions, surface terminology follows:

treatments,

performances,

processing,

and

Batt Term used to describe felts. They are nonwoven compressed fabrics, mats, and bats prepared from staple fibers without spinning, weaving, or knitting; made up of fibers interlocked mechanically. Bias Fabric consisting of warp and fill fibers at an angle to the length of the fabric. Bias cut Cutting material at 450 from the weave pattern. Bonded A web of fibers held together by an adhesive medium that does not form a continuous film. Braids Is used to give high strength three-dimensional (3-D) reinforcement, incorporating more than one type of fiber, if required. Conventional woven fabrics are limited to providing reinforcement at orthogonal orientations, but many reinforced plastics structures are loaded in non-orthogonal fashion. Woven fabrics are, therefore, not necessarily mechanically efficient. Braids offer the designer an opportunity to specify a nonorthogonal reinforcement, but 2-D laminated braided structures have inherent weakness in the out-of-plane direction, analogous to 2-D woven structures. Therefore, there has been development of 3D braided preforms, the first step being so-called track-and-column braids, where most of the reinforcement is out of the plane of the general loading. However, these types might not withstand the same degree of in-plane loading as a 2-D braided preform, while the production equipment does not easily allow introduction of axial yarn reinforcement as is a common feature of 2-D constructions. An important variant has been introduced: multilayer interlock braiding, with interlocking contiguous layers of braid, offering the possibility of a varying amount of axial yarns (or none) and a costeffective production method. The interlocking yarns are mainly in the plane of the braided structure and thus do not significantly compromise in-plane properties of RPs. Energy absorption and residual compression strength after impact is higher than for comparable conventionally braided materials such as carbon/epoxy RPs. Multilayer interlocked braids can be produced in tubular or solid configuration. Broad good Fiber woven into fabric usually 50 in. (1.27 ram) wide. It can be impregnated with plastic and is usually furnished in rolls of 50 to 300 lb (25 to 140 kg).

2 . Reinforcements 99

Burlap A coarse, loose woven fabric made from jute or similar fiber. Used in low cost, low performance laminated or RPs. Canvas A closely woven cloth of flax, hemp, or cotton, which is sometimes used in industrial laminated plastics. It usually represents fabric weighing more than 4 o z / y d 2 (0.14 kg/m2). C o u n t In fabric, it is the number (count units) of warp fibers (ends) and filling fibers (picks) per unit of length (cm or in). Cowoven A fabric woven with two different types of fibers in individual yarns. For example, TP fibers woven side by side with glass fibers. Crimp Cloth woven with about equal corrugations in both the warp and fill. Desizing The process of eliminating sizing, which is generally starch, from gray goods prior to applying special finishes or bleaches for fibers such as glass or cotton. Drape The ability of a fabric weave to conform to a contoured surface. Elastic Fabric made from an elastomer either alone or in combination with other textile materials. At room temperature, it will stretch under tension and will return quickly to its original dimensions and shape when tension is removed. Fabric, closed molding Multicore Saint-Gobain Technical Fabrics (SGTF) has a new fabric for use in closed mold processes such as resin transfer molding (RTM), pressure and vacuum injection molding, infusion molding, and compression molding. The fabric Multicore | consists of stitched on both sides of a synthetic core. The outer layers give the fabric its strength while the core facilitates resin flow through a part. Advantages of using the product are said to include: good conformability; fast wet-out; quicker processing; compatibility with most resins; and excellent surface finish. The fabric is available in a number of weights that allow selection of a single product for varying cavity thicknesses. This also reduces cutting and installation labor and material scrap. Fabric, d o s e d molding O C | FlowTex TM Owens Corning Composite Solutions business launched its latest fabric reinforcement during the 2003 October's boatbuilding exhibition in Florida, USA. With emissions standards forcing many boat builders to change from traditional open molding techniques to cleaner, closed mold processes, OC has produced OC | FlowTcx TM fabrics that can help the transition to be smooth and cost effective. Since closed molding processes are automatically MACT clean air compliant (Chapter 3),

100 Reinforced Plastics Handbook

many manufacturers are looking at ways to replace at least a portion of their open mold processes. At first glance, a switch can appear to be capital-intensive, so changeovers in the industry have been slow. FlowTex fabrics can enable boat builders (and others) who do not have the resources, but want to convert to a closed molding process, to do so in an economical way. The fabric's unidirectional fibers are constructed in a way that increases resin flow during molding, and wet-out is up to 40% faster than with other products. So that molders don not have to modify their existing laminate designs, the fabrics are based on traditional knitted fabric technology and have comparable properties. Channels are built into the fabric structure to ensure a fast, even resin distribution. The faster flow rate can lead to higher production and mold turnover and because there is no need for local resin distribution media, the fabric can potentially decrease molding costs. A continuous filament mat version of the fabric is said to offer even faster surface flow. Fabric, cut Distributor Composites One Co. highlights its Kit Concepts, a new service that provides manufacturers with prepackaged glass fiber material cut to size and nested in the order needed, saving the manufacturer labor-intensive cutting and loading time. The pre-cut glass fiber is said to be ideal for customers using closed mold processes such as RTM and closed cavity bag molding. Each kit contains material cut exactly to the customer's patterns and computer aided design (CAD) drawings. Cut material is then packed together in a single kit, in the order that it is used in the manufacturing process. Fabric, gray Also called greige goods. It is any fabric, yarn, fiber, etc. before finishing, sizing, dyeing, etc. Fabric, OC Owens Corning introduces innovative fabrics for use in closed molding, a process being increasingly utilized in the marine industry. OC Molding Mat Fabrics are unique in that they combine the infusion capability of traditional molding mat with the structural stability and visual quality associated with knitted OC TM Knytex | fiber fabrics. Designed for use in various closed molding processes including resin transfer molding (RTM) and vacuum infusion, OC Molding Mat Fabrics are a composite reinforcement comprised of a non-woven synthetic core, stitch-bonded between two layers of binder free chopped glass fiber, a n d / o r continuous reinforcement, including a surfacing veil. The combination of these materials results in highly conformable reinforcement fabrics that boast high

2

resin permeability, capabilities.

fast wet-out

and

variable

9R e i n f o r c e m e n t s

part

thickness

OC Molding Mat Fabrics bring numerous benefits to the marine industry. More structurally sound than traditional molding mat, OC Knytex fabrics offer greater stability. The flexibility and versatility of the product enables it to better accommodate boat design, thereby creating new opportunities for marine designers. Additionally, OC Molding Mat Fabrics impart a surface on finished parts that is superior to traditional woven and knitted reinforcements, and their unique composition provides for reduced processing time and increased ease of handling. Combined with the corrosion advantages of OC Advantex | glass fibers, the fabrics are a unique reinforcement. These fabrics are well suited for use in closed molding applications. They allow reduction in both the kit cutting time and the part loading time, by combining all layers of a laminate into one stack. As the marine industry is moving into closed molding, it needs to rethink the laminate composition and move away from a layer-bylayer approach. Fabric, three-dimensional See Three-Dimensional Reinforcements in this chapter. Fill Also called weft or woof. It is the transverse threads or fibers in a woven fabric; those fibers running perpendicular to the warp. Filler Pieces of chopped cloth or other fabric to improve properties a n d / o r reduce cost. Fill face That side of a woven fabric on which the greatest number of yarns is perpendicular to the selvage. Fourdrinier The machine most widely used for papermaking. Includes use of plastic fibers to produce "plastic" papers or nonwoven fabrics. Gigg A machine for raising a nap on fabrics. Glassine A thin, transparent, and very flexible paper obtained by excessive beating of wood pulp. It may contain an admixture such as urea-formaldehyde plastic to improve strength. G o u t Foreign matter, usually lint or waste fibers, woven in a fabric by accident. Gray Also called greige goods. It is any fabric, yarn, fiber, etc. before finishing, sizing, dyeing, etc. Hand The softness of fabric as determined by a touch, subject to the persons judgment.

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Impregnated A fabric in which the interstices between yarns are completely filled with the impregnating compound throughout the thickness of the fabric, as distinguished from sized or coated fabrics where these interstices are not completely filled. Knitted This woven fabric has an interlacing (interloping) yarn or thread in a series of connecting loops with needles. This is a rather compact woven construction. Knitted textiles Knitted fiber reinforcement textiles can give properties more precisely tailored to the application, plus improvements in processing. These multi-axial reinforcement textiles differs from conventional materials in that flat straight fiber assemblies are knitted and cross-stitched with fine high-strength resin-compatible yarn with all needlework carried out between individual fiber assemblies, to prevent fiber damage. Layer-fiber orientations are often at + 45 ~ and -45 ~ and angles may be set as required between 30 ~ and 60 ~. This helps to achieve the required directional and multidirectional strengths, yet gives a drapability tailored to the individual application, which is particularly important in resin transfer molding and other fabricating processes. Unlike woven reinforcement, however, the resulting textile is virtually flat, without the risk of fraying when cut and laid up. It can be more uniformly wetted out without resort to excessive resin and the resulting finish is superior, without weave pattern or wash-up of fibers to the surface of the laminate. The Norwegian naval authorities, initially for construction of minehunters and minesweepers, have approved an advanced multiaxial range of textile reinforcement. Among the first civil applications was the hull of the 35 m luxury yacht Moonraker (which was designed to be the fastest large yacht in the world, utilizing the weight saving, strength and structural integrity of the knitted reinforcement). Mats This is a form of glass fiber reinforcement. Supplied in roll form, it is a mat of cuffed continuous or random chopped strand held together by a light binder. Popular is the chopped strand mat (CSM) that offers uniformity of weight, improved drape ability, exceptionally fast wet-out, easy workout of entrapped air, and good surface finish. It is used to fabricate different products by different processes such as open contact molding and closed press molding, and for production of sheet (Chapter 5). The nature of the binder is important. For contact molding it must be readily soluble to facilitate rapid wetting-out and conform to the mold contours. For

2

9R e i n f o r c e m e n t s

press molding it should be less soluble, to avoid the possibility of the mat being pulled apart as the mold closes. For translucent sheet production, the binder should dissolve completely in the resin, to avoid blemishes. The length of the chopped strand usually ranges from 1/8 in. (3.2 mm) to 2 in. (50 mm) and the quality of mat is expressed as weight per unit area, ranging from 300 g / m 2 (10 o z / f t 2) to 750 g / m 2 (2.5 oz/ft2). Moldings made from CSM/TS polyester resin may have 30-60% of the tensile strength of a laminate made of woven glass cloth but have exceptionally good inter-laminar cohesion and impact strength. On a weight basis, CSM is considerably less expensive and has now largely replaced cloth except where very high strength is needed, justifying the additional cost. Mechanical fabrics Identifies nonwoven fabric. Naps Little lumps of tangled fibers or small thickened places found in fabric or yarn. Nesting Also called nested cloth. Placing plies of fabric so that the fibers of one ply lie in the valleys between the fibers of the adjacent ply developing laminated constructions Nonwovens The textile and paper industries are based on the two oldest (wet and dry) processes. Manufacturers of nonwovens for plastics draw on both. With the wet, there are basically two types namely the Fourdrinier and cylinder machine types that have been modified. In addition, two basic types exist for the process; formation of the web and application of the bonding agent or system where mechanical carding of fibers is used. The particular equipment and method of operation to be used, with their many modifications, is influenced by desired requirements such as mechanical properties, softness, surface condition, tenacity, etc. There are certain types of so-called nonwoven fabric that are directly formed from short or chopped fiber as well as continuous filaments. They are produced by loosely compressing together fibers, yarns, rovings, etc. with or without a scrim cloth carrier; assembled by mechanical, chemical, thermal, or solvent methods. Products of this type include melted and spun-bonded fabrics. N o n w o v e n flash-spuns Flash-spinning is a radical departure from the conventional melt spinning methods to produce nonwoven fabrics. In flash-spinning a 10-15 wt% solution of, for example HDPE in trichlorofluoromethane or methylene chloride. It is heated to 200C (392F) and pressurized to at least 4500 kPa (650 psi). This pressurized vessel is connected to a spinneret containing a single

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104 Reinforced Plastics Handbook

hole. When the pressurized solution is permitted to expand rapidly through the single hole, the low boiling solvent is instantaneously flashed off, leaving a 3-D film-fibril nonwoven network referred to as a plexifilament. This process with precise conditioning can result in film thickness is 4 lum. Nonwoven mechanicals The general paper product processed through Fourdrinier cylinder wet machines is very dense, so the saturation with plastics is very difficult. Saturability is improved by reducing paper thickness, including plastics in the pulp mix, using foaming or dispensing agents in the pulp, air-blowing paper during drying, or increasing hole diameters or porosity in wire screen or felt carriers used in the processing. In the dry process sheets are formed by mechanical carding of fibers, air-laying system, or air-floatation system. The techniques provide latitude in orientation fibers including continuous swirl fiber patterns, fibers can be roughly parallel in the machine direction, or other patterns such as orthotropic and isotropic lay-ups. Nonwoven melt-blown These fibers are composed of discontinuous filaments and are smaller than those of spun-bonded fabrics. Fibers produced are very fine with a typical diameter of 3 lum. Most commercial products are made of polyester or high melt-flow polypropylene plastic. Nonwoven spun These fabrics include spun-bonded, flash-spun, meltblown, and mechanical nonwoven swirl. They are used in durable and disposable products that include interlining-interfacing (apparel), carpet backing, geotextile, roofing, industrial filtration media, surgical apparel, medical dressing, and diaper. Nonwoven spun-bonded They are distinguished from other nonwoven fabrics by a one-step operation that provides a complete chemical to fabric route. The process integrates the spinning, laydown, consolidation, and bonding of continuous filaments to form fabrics. Its largest growth area is disposable diaper cover stock. Reinforced plastics, advanced The advanced RP (AR~) refers to a plastic matrix reinforced with very high strength, high modulus fibers that include carbon, graphite, aramid, boron, and S-glass. They can be at least 50 times stronger and 25 to 150 times stiffer than the matrix. ARPs can have a low density (1 to 3 g/cm3), high strength (3 to 7 GPa) and high modulus (60 to 600 GPa). Scrim A low cost reinforcing nonwoven fabric made from continuous filament yarn in an open-mesh construction. Used includes surfacing RPs to produce a smooth surface. Mso used as a carrier of adhesives for use in secondary bonding of RPs, etc.

2

9R e i n f o r c e m e n t s

Selvage That edge of a woven fabric that runs parallel to the direction of the warp threads. Sheer A fabric that is transparently thin or diaphanous. Uses include as overlayer for plastic protection or provide decorative effects. Tyvek DuPont's trade name for a spun bonded, tough, strong H D P E fiber sheet product. Its use includes mailing envelopes (protects contents, etc.), medical devices, wrapping around buildings to completely seal off cracks and seams to prevent drafts and cut airflow penetration between the outside and inside (allows moisture to escape from the walls, eliminating or minimizing the prospect of harmful condensation damage), etc. Vent cloth Also called breather cloth. A layer or layers of open weave cloth used to provide a path for vacuum to reach the area over the RP being cured during fabrication so that plastic volatiles and air can be removed. This action also provides a means of applying pressure to the complete RP. Warp It is the yarn running lengthwise in a woven fabric. Also identifies a group of yarns in long lengths and approximately parallel, put on beams or warp reels for further textile processing including weaving, knitting, dyeing, etc. Warp face Fabric side that has the greatest number of yarns that are parallel to the selvage. Weave The particular manner in which a fabric is formed by interlacing yarns. Weft The threads of a woven structure that can run across the fabric from selvedge to selvedge at right angles to the warp threads. Woven Glass woven cloth is produced by conventional textile methods in virtually any variation (Figure 2.7). Thinner cloths make laminates of very high tensile strength and modulus, but generally poor inter-laminar cohesion and tend to be less economical than heavier fabrics, on a basis of weight. The tensile strength offered by woven fabrics is often far higher than is actually needed, and care should be taken not to over design or over specify. Standard types of weave include: Basket weave Two or more warp fibers go over and under two or

more filing fibers in a repeat pattern. This weave is less stable than the plain weave but produces a flatter and stronger fabric. It is also a more pliable fabric and will conform more readily to simple contours. It maintains a

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106 Reinforced Plastics Handbook

Figure 2~

Examples of types of weaves: (a) plain, (b) twill, (c) satin, (d) unidirectional, (e) gauze, {f] bidirectional deformable pattern, and {g) knit

certain degree of porosity without lack of too m u c h firmness but not as m u c h as the plain weave. Bias weave Consists of warp and fill fibers at an angle to the length of the fabric. Bidirectional deformable pattern weave Any crimp in the threads is eliminated. The threads are arranged in plies placed at 90 ~ to each other and b o u n d together by a thin thread, representing less than 10% of the total. Cowoven weave Two different types of fibers in individual yarns, such as thermoplastic fibers woven side by side with glass fibers. Crowfoot weave It is a three-by-one weave, that is, a filling thread floats over three warp threads and then under one. This type fabric looks different on one side than the other. Fabrics with this weave are popular since they are more pliable than either the plain or basket weave. It is easier to form around curves and provide 3-D forming. Eight-harness satin weave It is a seven-by-one weave where a filling thread floats over seven warp threads and then under one. Like a crowfoot weave, it looks different on one side from the other side. This weave is more pliable than others are and is especially adaptable to forming around the more complex shapes. Four-harness satin weave Also called crowfoot satin because the weaving pattern resembles the imprint of a crow's foot. It is a

2 . Reinforcements 107

three-by-one weave. The filling thread floats over three warp threads and then under one thread. The two sides of this fabric have different appearances. As with other satin weaves, it provides some flexibility to form around shapes. This is an example of a special weave pattern where two warp threads are taken around the weft threads, to the right and left alternately. A wide variety of fabrics can be held together more or less closely by points (gauze weave) with plain links. These patterns produce a decorative effect used mainly in veils.

G a u z e weave

Also called geosynthetic. Geotextiles, as well as geonets, geogrids, and geomembranes, represent a major market for plastics. They appear in all manners of civil works, from roads to canals, from landfills to landscaping. They often prove more cost-effective than nature and other man-made products. The primary plastics are polyester, nylon, PP, and HDPE filaments. The fabrics are made in both woven and nonwoven varieties. The former are characterized by high-tensile, high modulus, and lowelongation traits; the latter by high-permeability and highelongation. There are those impregnated with plastic to eliminate permeation of water and other liquids.

Geotextile weave

Also known as unidirectional fabrics and non-woven roving are made by gathering continuous roving into unidirectional two-layer (biaxial) or three-layer (triaxial) orientation and knitting them together with plastic thread. The result is higher tensile strength, reduced laminate weight and thickness, easy wet-out and good mould conformability, with minimal pattern print-through.

K n i t weave

A locking-type weave in which two or more warp threads cross over each other and interlace with one or more filling threads. It is used primarily to prevent the shifting of fibers in open-weave fabrics.

Leno weave

Open weave that resembles a leno. It uses a system of interlacing that draws a group of threads together and leaves a space between one group and the next group. The warp threads do not actually cross each other as in a real leno and, therefore, no special attachments are required for the loom. Used when a high strength is required and the fabric is to remain porous.

Leno mock weave

Also called woof or weft count. It is an individual filling yarn running the width of a woven fabric at right angles

Pick c o u n t weave

108 Reinforced Plastics Handbook

to the warp. Call out is the number of filling yarns per inch (cm) of woven fabric. P l a i n weave (linen weave): the weft thread passes successively

above and then below each warp thread, and then inversely in the following pass. It is a one-by-one weave where one filling thread floats over one warp thread providing bidirectional strength properties. weave The warp and weft threads are crossed in a programmed order and frequency to obtain a flat appearance. As a result, one side of the fabric has more warp threads, while the back appears to consist mainly of weft threads. The higher the satin number (7 satin, 8 satin), the higher the count of warp and weft threads. Satin weaves allow production of fabrics with high mass per unit of surface area, and good drapability over molds. Different satin patterns are used. See Eight-harness satin and four-harness satin.

Satin

T w i l l weave A basic weave characterized by a diagonal rib or twill

line. Each end floats over at least two consecutive picks, allowing a greater number of yarns per unit area than in a plain weave, while not losing a great deal of fabric stability. This pattern has better drapability than either plain or basket weaves.

U n i d i r e c t i o n a l weave The

number of threads is considerably higher in one direction than in the other (unidirectional warp fabric or unidirectional weft fabric). The threads are parallel and simply held together.

Woven, shuttle m a r k A fine filling line caused by damage to a group of warp yarns by weaving shuttle abrasion.

Plastics

Family of Plastics There are different plastic matrixes (also called resin matrixes) used in RPs that provide different properties and processing procedures in fabricated products. Plastics are a family of materials such as ceramics and metals. Within this family of plastics about 30 wt% of them are RPs; the others are referred to as unreinforced plastics (URPs). Factually, the quantity of RPs could be debatable since it depends on defining when a plastic is an URP; they can include additives that can be used not as a reinforcement. As shown in Figure 3.1 the amount of resin in RPs influences properties.

................. Actual - - - - - - Theoretical

""'-.......

0 el

pjj.~'P

_=

. . . .

I

..........

0

! 100

Resin content, wt

Figure 3,1

Effect of matrix content on strength (F) or elastic moduli (E) of reinforced plastics

The family of plastics is classified several ways. The two major classifications are thermoplastics (TPs) and thermosets (TSs). Over 90wt% of all plastics used are TPs. The TPs and TSs in turn are classified as commodity or engineering plastics (CP and EP). Commodities such as polyethylenes (PEs), polyvinyl chlorides (PVCs), polypropylenes (PPs),

1 10 Reinforced Plastics Handbook

and polystyrenes (PSs) account for over two-thirds of plastic sales worldwide. Engineering plastics are characterized with meeting higher a n d / o r improved performances such as heat resistance, impact strength, chemical resistance, and the ability to be molded to highprecision standards. Examples are polycarbonate (PC representing at least 50wt% of all EPs), nylon, acetal, etc. Most of the thermoset plastics, as well as reinforced thermoplastics (RTPs) and reinforced thermoset (RTSs) plastics, are of the engineering type. Historically, as more competition and/or production occur for certain engineering plastics, their costs go down and they become commodity plastics. Half a century ago, the dividing line coastwise was about $0.20/1b; more recently became above $1.00/lb. There are different types of plastics that are usually identified by their composition and/or performance. As an example, there are polymers that identify a material that is a pure material. They are NEAT polymers that identify materials with Nothing Else Added To (Table 3.1). They are very rarely used. When additives, fillers, and/or reinforcement are included in the polymer it is called a plastic. A virgin plastic is one that has not been subjected to any fabricating process. It can be said that all plastics in order to be processed and meet product requirements contain additives, fillers, and/or reinforcements. Table 3.1 Polypropylene NEAT and filled flexural modulus of elasticity data

NEAT plastic 40wt% glass fiber 40wt% talc

180,000 psi ( 1.240 M Pa) 1,100,000 psi (7,600 MPa) 575,000 psi

The terms plastic, polymer, resin, elastomer, and RP are somewhat synonymous. Plastic and resin are interchangeable. Worldwide the term preferred is plastic for URP and resin for RP. Polymer denotes the basic material. Whereas plastic pertains to polymers or resins (as well as elastomers, RPs, etc.) containing additives, fillers, and/or reinforcements. An elastomer is a rubber like material (natural or synthetic). RPs (also called plastic composites) are plastics with reinforcing additives such as fibers and whiskers, added principally to increase the product's mechanical properties. Plastic materials to be processed are in the form of pellets, granules, flakes, powders, flocks, liquids, etc. Of the 35,000 types available, worldwide about 200 basic types or families are commercially recognized with less than 20 that are popularly used. Examples of these

3

9Plastics

plastics are shown in Table 3.2. Recognize that a basic type of plastic (PE, PC, nylon, polyester, epoxy, etc.) are compounded with many different additives, fillers, a n d / o r reinforcements to meet different performance requirements. Thus one basic plastic can have thousands of compounded formulations. Table 3.2 Examplesof major plastic families Acetal (POM) Acrylics Polyacrylonitrile (PAN) Polymcthylmethacrylate (PMMA) Acrylonitrile butadiene styrene (ABS) Alkyd Allyls Diallylisophthalate(DAIP) Diallylphthalate(DAP) Aminos Melamine formaldehyde(MF) Urea formaldehyde(UF) Cellulosics Celluloseacetate (CA) Cellulose acetate butyrate (CAB) Cellulose acetate propionate (CAP) Cellulose nitrate Ethyl cellulose (EC) Chlorinated polyether Epoxy (EP) Ethylene vinylacetate (EVA) Ethylene vinyl alcohol (EVOH) Fluorocarbons Fluorinated ethylene propylene (FEP) Polytetrafluoroethylene (PTFE) Polyvinyl fluoride (PVF) Polyvinylidenefluoride (PVDF) lonomer Ketone Liquid crystal polymer (LCP) Aromatic copolyester (TP polyester) Melamine formaldehyde (MF) Nylon (Polyamide) (PA) Parylene Phenolic Phenol formaldehyde (PF) Polyamide (nylon) (PA) Polyamide-imide (PAl) Polyarylethers Polyaryletherketone (PAEK) Polyaryl suifone (PAS) Polyarylate (PAR) Polycarbonate (PC) Polyesters Saturated polyester(TS polyester) Thermoplastic polyesters Polybutylcne terephthalate (PBT) Polyethylene terephthalate (PET) Unsaturated polyester (TS polyester)

Polyetherketone(PEK) Polyetheretherketone(PEEK) Polyetherimide(PEI) Polyimide(PI) ThermoplasticPI Thermoset PI Polymethylmethacrylate(acrylic)(PMMA) Polyolefins(PO) ChlorinatedPE (CPE) Cross-linkedPE (XLPE) High-densityPE (HDPE) Ionomer LinearLDPE ('LLDPE) Low-densityPE (LDPE) Polyallomer Polybutylene(PB) Polyethylene (PE) Polypropylene (PP) Ultra-high-molecular weight PE (OHMWPE) Polyurethane (PUR) Silicone (SI) Styrenes Acrylic styrene acrylonitrile (ASA) Acrylonitrile butadiene styrene (ABS General-purpose PS (GPPS) High-impact PS (HIPS) Polystyrene (PS) Styrene acrylonitrile (SAN) Styrene butadiene (SB) Sulfones Polyether sulfone (PES) Polyphenyl sulfone (PPS) Polysulfone(PSU) Urea formaldehyde (UF) Vinyls ChlorinatedPVC (CPVC) Polyvinylacetate(PVAc) Polyvinylalcohol(PVA) Polyvinylbutyrate(PVB) Polyvinylchloride(PVC) Polyvinylidenechloride(PVDC) Polyvinylidenefluoride(PVF)

111

1 12 Reinforced Plastics Handbook

Within these 20 popular plastics, there are five major families of thermoplastics that consume about two-thirds of all thermoplastics. They are the low density polyethylenes (LDPEs), high density polyethylenes (HDPEs), polypropylenes (PPs), polystyrenes (PSs), and polyvinyl chlorides (PVCs). Definitions

The term plastic comes from the Greek word "to form." It identifies many different plastic materials based on their polymer (plastic) structure to meet different requirements. They include those used as the plastic matrix in RPs. Practically all plastics at some stage in their fabrication (manufacture) can be formed into simple to extremely complex shapes that can range from being extremely flexible too extremely strong (Figure 3.2). The use of a virtually endless array of additives, fillers, and reinforcements permits compounding the base polymers, imparting specific performance qualifies to the processable plastics.

1

10 Elastic Limit Percent

1--100

Figure :3.2 Toughnessbehaviors of materials There are terms that overlap and interfere with each other such as TPs arc cured during processing. Cure occurs only with TSs or when a TP is converted to a TS plastic. The term curing TPs occurred since at the beginning of the 20th century because the term curing was used for TSs. At that time TSs represented practical all the plastic used worldwide. Thus, TPs took on the incorrect term curing even though there is no chemical reaction or curing action.

3

9Plastics 1 1 3

The term plastic is not a definitive one. Metals, for instance, are also permanently deformable and therefore have a plastic behavior. How else could roll aluminum be made into foil for kitchen use, or tungsten wire be drawn into a filament for an incandescent fight bulb, or a 90 ton ingot of steel be forged into a rotor for a generator. Likewise the different glasses, which contain compounds of metals and nonmetals, can be permanently shaped at high temperatures. These cousins to polymers and plastics are not considered plastics within the plastic industry.

Thermoplastics There are crystalline and amorphous thermoplastics (TPs). During processing they soften and upon cooling harden into products that are capable of being repeatedly softened by reheating with their morphology (molecular structure) being crystalline or amorphous. Their softening temperatures vary. An analogy would be a block of ice that can be softened (turned back to a liquid), poured into any shape mold or die, and then cooled to become a solid again. This cycle repeats. During the heating cycle care must be taken to avoid degrading or decomposition. With some TPs no change or practically no significant property changes occur. However some may have significant changes. In classifying TPs, there are two distinct molecular structures (which largely dictate the properties and characteristics): crystalline and amorphous (Table 3.3). Table 3.3 Examplesof crystalline and amorphousthermoplastics

Crystalline

Amorphous

Acetal

Polycarbonate

Nylon

Modified PPO

Best property balance Stiffest unreinforced thermoplastic Low friction

High melting point High elongation Toughest thermoplastic Absorbs moisture

Polyester(glass-reinforced)

High stiffness Lowest creep Excellent electrical properties

Good impact resistance Transparent Good electrical properties Hydrolytic stability Good impact resistance Good electrical properties

114 Reinforced Plastics Handbook Crystalline Plastics They are TPs that have a highly ordered molecular structure with sharp melt points. They do not therefore soften gradually as the temperature increases but tend to remain hard until a given quantity of heat has been absorbed, at which point they rapidly change to a low viscosity melt (Table 3.4). The mechanical properties are greatly influenced by this melt flow action. They are anisotropic in flow, shrinking less in the direction of flow than transverse to it. They have very good chemical resistance. Reinforcement produces a substantial improvement in heat distortion temperature, and useful levels of strength and stiffness can be retained well beyond the load-bearing capabilities of unreinforced types above the glass transition temperature (Tg). Conventional and high performances crystalline include polyethylene (PE), polypropylene (PP), polyphenylene sulphide (PPS), polyetheretherketone (PEEK), polythalamide (PPA) and TP polyimide (TPI). Table 3.4 Crystallinethermoplastic melt temperatures Plastic

Low Density Polyethylene High Density Polyethylene Polypropylene Nylon 6 Nylon 66 Polyester Polyarylamide Polytetrafluoroethylene

~

116 130 175 215 260 260 400 330

~

240 266 347 419 500 500 755 626

Crystalline behavior identifies its morphology; that is the study of the physical form or structure of a material. They are usually translucent or opaque and generally have higher softening points than the amorphous plastics. They can be made transparent with chemical modification. Since commercially perfect crystalline polymers are not produced, they are identified technically as semicrystalline TPs. The crystalline TPs normally have up to 80% crystalline structure and the rest is amorphous.

Amorphous Plastics The amorphous plastic is the term used that means formless describing a TP having no crystalline plastic structure. They form no pattern whereby their structure tends to form like spaghetti with their molecules going in all different directions. They have a randomly ordered molecular

3

Plastics 9 1 15

structure, without a sharp melt point, softening gradually as the temperature rises. The materials change viscosity on heating, but are seldom as easy flowing as crystallines. If they are rigid they may be brittle unless modified with certain additives. They are isotropic in flow (Chapter 7 Directional Properties), shrinking uniformly both in the flow direction and transverse to it. Consequently, they tend to show lower mold shrinkage and are less prone to warping than crystallines. Amorphous TPs tend to lose strength rapidly above their glass transition temperature (Tg). They are usually glassy and transparent such as polystyrene (PS) and polymethyl methacrylate (PMMA). High performance amorphous plastics include polysulphone (PSU), polyethersulphone (PES), polyarylsulphone (PAS) and polyetherimide (PEI). Liquid Crystal Polymers

TPs that exhibit self-reinforcing properties during processing are liquid crystal polymers (LCPs). Chemically part of the wide polyester family, they are resins that, under certain processing conditions, can set up an internal molecular reinforcing structure, which can be further enhanced by conventional reinforcements. They are self-reinforcing TPs with molecules that are rod like structures in parallel arrays (Table 3.5). LCP's densely packed fibrous polymer chains result in high performance plastics. Unlike many high-temperature TPs, LCPs have a low melt viscosity and are thus more easily processed resulting in faster cycle times than those with a high melt viscosity thus reducing processing costs.

Table 3.5 Propertiesof a glass-reinforced LCP (DuPont Zenite LCP 3130L).

Property

Units

Testmethod

Value

Glass content Stress at break Strain at break Flexural modulus Flexural strength Izod impact (notched) Heat deflection temp.

% MPa O/o MPa MPa kJ/m2 ~

ISO 527-1/2 ISO 527-1/2 ISO 178 ISO 178 ISO 18011A ISO 75

30 143 1.8 12,300 172 26.4 227

Source: DuPont.

They have the lowest warpage and shrinkage of all the TPs. When they are injection molded or extruded, their molecules align into long, rigid chains that in turn align in the direction of flow and thus act like reinforcing fibers giving LCPs both very high strength and stiffness.

1 16 Reinforced Plastics Handbook Result is high strength-to-weight at extreme temperatures, excellent mechanical property retention after exposure to weathering and radiation, good dielectric strength as well as arc resistance and dimensional stability, low coefficient of thermal expansion, excellent stability in boiling water, excellent flame resistance, and easy processability. Their resistance to hightemperature flexural creep is excellent, as are their fracture-toughness characteristics. This family of different LCPs resists most chemicals. Another rod like TP is self-reinforcing polymers (SRPs) that has exceptional high performance properties but very difficult to process. Unlike LCPs they are amorphous, isotropic, and transparent. Research on SRPs was sponsored during the 1960s by Wright-Patterson Air Force Base, Dayton, OH. Molding Processes TPs during processing are normally in the amorphous state with no definite order of molecular chains. If TPs that normally crystallize are not be properly quenched (when hot melt is cooled to solidify the plastic) the result is an amorphous or partially amorphous solid state usually resulting in inferior properties. Compared to crystalline types, amorphous polymers undergo only small volumetric changes when melting or solidifying during processing. This action influences the degree of dimensional tolerance that can be met after the heating/ cooling process. As symmetrical molecules approach within a critical distance during melt processing, crystals begin to form in the areas where they are the most densely packed. A crystallized area is stiffer and stronger; a noncrystallized (amorphous) area is tougher and more flexible. With increased crystallinity, other effects occur. As an example, with polyethylene (crystalline) there is increased resistance to creep. In general, crystalline types of plastics are more difficult (but controllable) to process, requiting more precise control during fabrication, have higher melting temperatures, and tend to shrink and warp more than amorphous types. They have a relatively sharp melting point. That is, they do not soften gradually with increasing temperature but remain hard until a given quantity of heat has been absorbed, then change rapidly into a low-viscosity liquid. If the correct amount of heat is not applied properly during processing, product performance can be drastically reduced and/or an increase in processing cost occurs. Different processing conditions influence the performance of these plastics. For example, the effects of time are similar to those of temperature in the sense that any given plastic has a preferred or

3

9Plastics 1 1 7

equilibrium structure in which it would prefer to arrange itself time wise. However, it is prevented from doing so instantaneously or at least on short notice. If given enough time, the molecules will rearrange themselves into their preferred pattern. Proper heating time causes this action to occur sooner. Otherwise with a fast action severe shrinkage property changes could occur in all directions in the processed plastic products. This characteristic morphology of plastics can be identified by tests. It provides excellent control as soon as material is received in the plant, during processing, and after fabrication.

Thermoplastic Types TPs offer a wide range of matrix materials for reinforcement by fibers, flakes, beads, or particulate materials such as talc and mica. They bring the great advantage that they are more easily molded in massproduction quantifies (such as injection molding) than are reinforced thermosets (RTSs). Reinforcement will improve the stiffness of the compound and increase its service temperature. Fiber and compounding technology permits high contents of long-length fiber used in injection molding, compression molding, stamping, pultrusion, and tape layering or winding. Most types of TPs can readily be compounded with reinforcing materials. Among the fibers, glass is the main reinforcement (Table 3.6). Examples of these TPs follow. Acetals

Acetal or polyacetal (POM) also described as polyformaldehyde or polyoxymethylene, is an engineering thermoplastic often linked with polyamide (nylon), for its similar general appearance and properties and its use with polyamides in intermeshing URP and RP gear systems, etc. These crystalline plastics have exceptional resistance to abrasion, heat, chemicals, and solvents. With a low coefficient of surface friction, it is especially useful for mechanical products such as gears, pawls, latches, cams, cranks, plumbing parts, etc. It has high strength and stiffness, plus excellent creep and fatigue life, and (relatively) high service temperature. Different formulations are available to meet different requirements. RP grades with glass, aramid, and other fibers are used, aimed at specialist products. Nylons

With a favorable cost structure and ease in compounding, nylon [polyamide (PA)] is extensively used as RTPs, using mainly glass fiber,

Table 3 . 6 Examples of unreinforced and reinforced thermoplastic processing conditions

Material

Symbol

Density [g/cm3]

Shrinkage

[~

Mold temperature

[~

[%]

280-320 300-330 260-290 260-290 240-260 250-270 350-390 350-400

80-100 100-120 140 140 60-8O 60-8O 120-150 120-150

0.8 0.15-0.55 1.2-2.0 1.2-2.0 1.5-2.5 0.3-1.2 1.1 .0.2-1

240-260 270-290 260-290 280-310 210-250 210-250 330-380

70-120 70-120 70-120 70-120 40-80 40-80 230

0.5-2.2 0.3-1 0.5-2.5 0.5-1.5 0.5-1.5 0.5-1.5

370

> 150

0.2

360-420 330-380

340-425 360-390 120-160 110-180

65-175 140-190 1.1 0.7

0.4-0.7 0.2-0.5

Glass fiber content [%]

Average specific heat [kJ/(kg x K)]

10-30

1.3 1.1

Processing temperature

Polycarbonate Polycarbonate-GR Poly(ethylene terephthalate) Poly(ethylene terephthalate)-GR Poly(butylene terephthalate) Poly(butylene terephthalate)-GR Polyetheretherketone Polyetheretherketone-G R

PC PC-GR PET PET-GR PBT PBT-GR PEEK PEEK-GR

1.2 1.42 1.37 1.5-1.53 1.3 1.52-1.57 1.32 1.49

Polyamide 6 (nylon-6) Polyamide 6-GR Polyamide 66 (nylon-66) Polyamide 66-GR Polyamide 11 Polyamide 12 Polyamide-imide

PA 6 PA 6-GR PA 66 PA 66-GR PA 11 PA 12 PAl

1.14 1.36-1.65 1.15 1.20-1.65 1.03-1.05 1.01-1.04 1.4

Poly(phenylene sulfide)

PPS

1.64

Poly(etherimide) Poly(ether sulfone) Polyether ketone Polysulfone

PEI PES PEK PSU

1.27 1.6 1.3 1.24

Polyurethane

PUR

1.2

1.85

195-230

20-40

0.9

Phenol-formaldehyde resin Melamine-formaldehyde resin Melamine/phenol-formaldehyde resin Unsaturated polyester Epoxy, epoxide

PF MF MPF UP EP

1.4 1.5 1.6 2.0-2.1 1.9

1.3 1.3 1.1 0.9 1.7-1.9

60-80 70-80 60-80 40-60 ca. 70

170-190 150-165

1.2 1.2-2 0.8-1.8 0.5-0.8 0.2

20-30 30-50 30 30-50 30-35

1.8 1.26-1.7 1.7 1.4 2.4 1.2 _

40 30 .....

30-80

160-180 150-170

160-170

S~

m

m ,

-r 0 "

o o

T a b l e 3 . 6 continued

Material

Symbol

Density [g/cm3]

Glass fiber content [%]

Average specificheat [kJ/[kg x K)]

Processing temperature [~

Mold temperature [~

Shrinkage [%]

Polystyrene Styrene-butadiene Styre ne-a crylo n it ri le Acryl o n itri Ie- b utad ie ne-styre ne Acrylonitrile-styrene-acrylate

PS SB SAN ABS ASA

1.05 1.05 1.08 1.06 1.07

1.3 1.21 1.3 1.4 1.3

180-280 170-260 180- 270 210- 275 230-260

10-40 5-75 50-80 50-90 40-90

0.3-0.6 0.5-0.6 0.5-0.7 0.4-0.7 0.4-0.6

Low-density polyethylene High-density polyethylene Polypropylene Polypropylene-G R Polyisobutylene Poly(4-methyl pen tene- 1)

LDPE HDPE PP PP-GR PIB PM P

0.954 0.92 0.917 1.15 0.93 0.83

2.0-2.1 2.3-2.5 0.84-2.5 1.1 - 1.35 -

160-260 260-300 250-270 260-280 150-200 280- 310

50-70 30-70 50-75 50-80 50-80 70

1.5-5.0 1.5-3.0 1.0-2.5 0.5-1.2 1.5- 3.0

Poly (vinyl chloride) Poly (vinyl chloride) Poly (vinylidene flouride) Polytetra flou roethylene

PVC soft PVC rigid PVDF PTFE

1.38 1.38 1.2 2.12-2.17

0.85 0.83-0.92 O.12

170-200 180-210 250-270 320-360

15-20 30-50 90-100 200-230

<0.5 ~0.5 3-6 3.5-6.0

Poly(methyl methacrylate)

PMMA

1.18

1.46

210-240

50-70

O.1-0.8

Polyoxymethylene, polyacetal Poly(phenylene oxide) Poly(phenylene oxide)-GR

POM PPO PPO-GR

1.42 1.06 1.27

1.47-1.5 1.45 1.3

200-210 250-300 280-300

>90 80-100 80-100

1.9-2.3 0.5-0.7 >0.7

Cellulose acetate Cellulose acetate butyrate Cellulose propionate

CA CAB CP

1.27-1.3 1.17-1.22 1.19-1.23

1.3-1.7 1.3-1.7 1.7

180-230 180-230 180-230

50-80 50-80 50-80

0.5 0.5 0.5

30

30

=~,

m, Ill

I,O

120 Reinforced Plastics Handbook

but also mineral reinforcements and high performance fibers (carbon fiber, etc.). The number of carbon atoms in the monomer differentiates the various nylon types: 6, 6 / 6 are the main types, but there are also 6 / 9 , 6/10, and 6/12. Specialty grades include 11, 12 and 4/6. Each has specialty performances. Nylons are generally a very tough material, with excellent all-round chemical resistance. Heat resistance varies with the molecular count. It is most commonly reinforced with glass fiber, either short or long fiber lengths, in injection molding pellets, adding significantly to mechanical properties. Addition of glass fiber, however, tends to reduce the impact strength of the compound and an elastomeric component is often included to compensate. High fiber loadings are possible, giving particularly good heat resistance. Materials in the nylon family have relatively high moisture absorption, meaning that they require drying before molding. Dimensional stability and tolerances can be affected by moisture pickup in the first few days of service, reaching equilibrium at about 2.7 wt% moisture content in air at 50% relative humidity and about 9-10% in water. Carbon fiber-reinforced PAs may be used for conductive and electrical shielding applications where high mechanical properties are also required, and for applications requiring a measure of internal lubrication, slip and good wear-resistance. Mineral-reinforced PA (with talc or mica) offers very good dimensional stability, and low shrinkage and warpage. Using lower-cost intermediates, glass-reinforced PA 6 / 6 can compete effectively with engineering resins such as PPS, PA 46, PA 6, and the aromatic nylons. Prepregs for RTPs, using a PA 12 powder coating combined with woven webs of glass/carbon and aramid are manufactured. They, and laminates made from them, are characterized by low weight and high chemical resistance. They can be molded as a secondary stage and can be combined with carboxylated rubbers without the use of coupling agents or adhesives. Nylon 6 / 6 is the most widely used, followed by nylon 6, with similar properties except that it absorbs moisture more rapidly and its melting point is 21C (70F) lower. In addition, its lower processing temperature and less crystalline structure result in lower mold shrinkage. Nylon 6 / 6 has the lowest permeability by gasoline and mineral oil of all the nylons. The 6 / 1 0 and 6 / 1 2 types are used where lower moisture absorption and better dimensional stability are needed. Nylons 11 and 12 have better dimensional stability and electrical properties than the others because they absorb less moisture. These more expensive types also are compounded with plasticizers to increase their flexibility and ductility.

3

9Plastics 121

With nylon, toughening and technology advancements super tough nylons became available. Their notched lzod impact values are over 10 J / m (20 ft-lb/in), and they fail in a ductile manner. A new class of semi-aromatic, high- temperature nylons and their compounds has been introduced (Japan's Kuraray Co. Ltd.)called Genestar PA9T. They compete in cost-performance with nylons 6 / 6 and 4 / 6 , other high temperature nylons and polyphthalamides, PPS, and LCP. PA9T is reported as a poly 1,9-nonamethylene terephthalamide. It is described as unique because it is a homopolymer, has semi-aromatic cores, and has a longer (nine-carbon) hydrocarbon chain structure than other high temperature nylons, which are based on PA6T (six-carbon) structures. There are liquid castable monomers that polymerize and become solid at atmospheric pressure. From these nylons complex products several inches thick and weighing hundreds of pounds can be cast with and without reinforcements. Another castable liquid monomer is a moldable transparent material. This amorphous type offers better chemical resistance than other TPs that are transparent. Polyarylates

PARs are aromatic polyesters (amorphous aromatic TP polyester) with a structure similar to that of polycarbonate (PC), which is also reflected in their physical properties. They are tough materials, with good processing characteristics, high heat distortion temperatures, and good resistance to weathering. A related group is polyester carbonates (PEC), or polyarylcarbonates, which are true copolymers (not to be confused with blends of polycarbonate and polyester). They exhibit an excellent balance of properties such as stiffness, UV resistance, combustion resistance, high heat-distortion temperature, low notch sensitivity, and good electrical insulating values. Uses include for solar glazing, safety equipment, electrical hardware, transportation components, and in the construction industry. They are used primarily in electronic/electrical and automotive applications. Polyearbonates

PCs is one of the strongest of TPs, with good overall heat resistance, excellent electrical properties, tough, heat and flame resistant, dimensional stabile, with stands boiling water, and environmentally-friendly. Moreover, they are transparent and resistant to a variety of chemicals (though not to organic solvents). They also have good dimensional stability, moisture pick-up is low and there is good resistance to creep. Outdoor exposure

122 Reinforced Plastics Handbook can cause some discoloration and embrittlement, but this is corrected by additives. Glass-reinforced PCs offer very high tensile strength and modulus, high impact strength, and other properties. Creep resistance, which is already excellent throughout a broad temperature range, can be further improved by a factor of two to three when PC is reinforced with glass fibers. Polyesters, TP The popular thermoplastic polyesters are polybutylene terephthalate (PBT) and polyethylene terephthalate (PET). TP polyesters are in a family of polyesters that has widely varying and important range of properties. There are the two major groups of the TPs (with comparatively high melting points) and the TSs (which are usually typified by a crosslinked structure). TP polyesters are often called saturated polyesters to distinguish them from unsaturated polyesters that are the TSs. Overall the TP polyesters have properties similar to those of nylons, but offering lower moisture absorption and therefore better dimensional stability. The key practical difference between them is in speed of crystallization during processing (which establishes the optimum mechanical properties). PBT shows high speed of crystallization and can give fast molding cycles even at low mold temperatures (65-85C). PET does not reach its optimum properties until the level of crystallinity is raised by special processing and/or the molecules are oriented. For molding to technical component standards, it must be modified to achieve the rate of crystallization at the low temperatures needed for fast cycles. PET matrix in a glass fiber mat TP sheet molding material is produced. A 40 wt% glass-reinforced PET was used by Chrysler for the four exterior body panels of its experimental Compact Concept car (with the comment that it would be possible to produce the resin matrix by chemically recycling waste drinking bottles). Commercially the PBTs are used widely in electrical/electronics applications, for housings, covers and base plates, and for applications involving relatively high heat. For PET, with its more applications where orientation is used to stabilize the melt, for injection/stretch molded bottles for carbonated drinks and for high-performance film for packaging, magnetized tapes, and optical materials. It is injection molded with reinforcements such as glass fiber, provides for useful products, especially for electrical components. Moldings show very good stability and resistance to warpage. PBT is used as a matrix material for RPs, with its crystallization offering high rigidity and tensile strength, low polarity giving high dimensional

3-Plastics 123 stability even at high atmospheric humidities, and a terephthalic acid component giving high thermal stability. Properties are significantly improved by the addition of glass fiber (for example, a 50 wt% fiber addition will boost rigidity and strength to 19,000 MPa), making PBT a potential candidate in applications which have hitherto the province of metals. Despite optimum processing conditions, however, addition of glass fiber to PBTs results in loss of good surface appearance (often described as the glass fiber effect). Technology has been developed by BASF that allows high (up to 50%) reinforcement loadings, without loss of high surface finish when molded, for production of new all-plastics automotive windscreen wiper systems. The key is to modify the crystallization behavior of the matrix PBT, using copolymers to make the whole system more amorphous. This effect is especially pronounced where the lowest temperatures occur during molding, such as the surface of the molding tool. Molding with high glass fiber content and a high surface appearance can be produced. Applications include all-plastic windscreen wiper systems, where it has been possible to integrate parts and reduce the complexity of the component (and eliminate the need for painting), with 30% and 50% glass-reinforced PBTs. Other potential applications include housings for door mirrors and headlamps. Another significant improvement has been made by blending 20 wt% glass fiber (GF) PBT with acrylonitrile-styrcne-acrylate copolymcr (ASA), giving a major improvement in warpage properties and other advantages. The PBT component contributes good mechanical properties and processability while the ASA, due to its amorphous character, is characterized by extremely low warpage. Scanning electron micrographs of the polymer phase show that incorporation of compatibilizers produces a homogeneous dispersion of ASA in the partially crystalline PBT matrix. Warpage, which is normally a problem in crystalline materials, is significantly improved; flow is also improved, giving shorter molding cycles and density is also reduced compared with a standard 20% GF PBT grade, resulting in a cost-saving.

Polyethylenes Also called polythene. Representing the largest used plastic with very little using reinforcements, PEs are of the olefin family with many different formulations [US consumption HDPE 42 wt%, LLDPE 27%, LDPE 20%, EVA 4%, others (VLDPE, MDPE, UHMWPE, etc.) 7%]. By far the largest volumes of these unreinforced materials go into film

124 Reinforced Plastics Handbook for packaging and many other applications. PE is one of the most versatile of plastics. In common usage these translucent, wax-like plastics have no less than 85% ethylene and no less than 95% total olefins. These TPs can be cross-linked by irradiation or chemically resulting in TSs with improved strength and dielectric properties. PEs comes in a range of densities, of which those relevant to RPs are low density PE (LDPE) and high density PE (HDPE). PE is rarely encountered as a matrix for RPs, though it forms a useful neutral carrier for specialty concentrates and master batches, for pigments, conductive/ antistatic compounds, and other specialties. Recent work, however, has produced high-performance PE fibers that are targeted to have a useful role to play in the future, as reinforcing materials (Chapter 2). Polypropylenes PP, by virtue of its increasing value as an injection moldable material with capability of offering useful relatively low cost engineering properties, is now the second most important RTP, in volume terms, after reinforced nylon, and it could possibly overtake this group. Particularly for the automotive and appliance industries (and in reinforced structural foam compounds) PP compounds reinforced with glass fiber, talc or mica are widely used. To make it possible to bond glass fiber to a PP matrix, special chemical coupling materials and technologies have been developed. Long-fiber and continuous fiber reinforcement technology with PP produce molding materials with higher tensile strength and semi-finished materials such as sheet and tape which arc beginning to find applications, mainly in structural parts. Both glass- and mineral-reinforced PPs appear to have greatest potential in the automotive industry, the former for lightweight structural parts such as bumper supports, where the mass-production advantage of injection molding can be utilized, and the latter for many general applications such as interior components, where acrylonitrile-butadienestyrene (ABS) is being partly displaced. A growing advantage of reinforced PP is its facility for recycling, and many producers now have programs to take back used or scrapped parts for recovery and reprocessing. An interesting new material is syntactic TP foam with high thermal insulation properties. It is based on a PP matrix incorporating small hollow glass microsphercs containing inert gases offering good insulating sheath for pipelines conveying hot oil f}om distant wells (Chapter 2). The advanced RP offers a combination of lighmess in weight with high compressive strength and can be formed rapidly into pipeline sheaths.

3. Plastics 125 PP production technology controls the geometry of the molecule by means of sophisticated catalysts, such as metallocenes. While greatly improving the productivity of the process (and minimizing residues that have to be removed from the polymer during production), these highyield catalysts provide a range of PP types, from flexible/elastic to tough/rigid. They are well suited for RPs and to alloying with other plastics, to produce engineering (or at least 'engineered') TPs with improved physical properties, on what is basically an inexpensive PP backbone. Polystyrenes PSs is high volume worldwide consumed plastic principally unreinforced. It is used in many different formulations. PS is noted for its sparkling clarity, hardness, low water absorption, extreme ease of processing general purpose PS (GPPS), excellent colorability, dimensional stability, and relatively low cost. This amorphous TP often competes favorably with higher-priced plastics. It is available in a wide range of grades for all types of processes. In its basic crystal PS form it is brittle, with low heat and chemical resistance, poor weather resistance. High impact PS (HIPS) is made with butadiene modifiers that provide significant improvements in impact strength and elongation over crystal polystyrene, accompanied by a loss of transparency and little other property improvement. Modifications available to the basic GPPS include grades for high heat and for various degrees of impact resistance. There are ignition-resistant polystyrenes (IRPSs). Some examples of members in the PS family are compounds of ABS, SAN, and SMA (styrene maleic anhydride). The structural characteristics of these copolymers are similar, but the SMA has the highest heat resistance. Although it is technically possible to add glass fiber to PSs and styrene copolymers (ABS, etc.), there has been little commercial interest to date, due to the relative cost of additional reinforcement against the limited improvement in performance.

Acrylonitrile-Butadiene-Styrenes Popularly used ABS is an amorphous terpolymer composed of acrylonitrile, butadiene, and styrene. These materials are processed by most methods including injection molding, extruding, and thermoforming. They provide a tough, hard, not brittle, rigid plastic with good chemical, electrical and weathering characteristics, low water absorption, resistance to hot-and-cold water cycles, good dimensional stability, high abrasion resistance, and some grades are easily electroplated. Often considered as a modified PS since its properties resemble PS, except that its

126 Reinforced Plastics Handbook impact strength is much higher. There is only limited use of reinforced grades.

Styrene Maleic Anhydrides SMA is a copolymer of styrene and acrylonitrile, offering good chemical resistance, good impact strength, and high heat distortion temperature, putting it more firmly in the sector of engineering TPs. It competes with PP-glass mat TP particularly when using modified styrene maleic anhydride polymer (mSMA). With injection molding, manufacturer DSM reports cost savings of 15-20% against press-molded PP-RP, for an automobile front fascia. On an annual production of 300,000 moldings, it concludes: investment in molding lines is lower than with RP stamping because of shorter cycle times with injection molding, reject rates are considerably lower, material losses are lower, and by far labor costs are lower. Per part, the average cost was calculated at Dutch guilders (NLG) 31.7 for mSMA compared with NLG 39.1 for PP-RP on 50,000 parts, and NLG 30.1 compared with NLG 37.6, on 300,000 parts per year. For equal stiffness, average wall thickness of the mSMA part was 2.6 mm, compared with 4.2 mm for the equivalent PP-RP part, and both moldings weigh the same, at 4.1 kg.

Polyvinyl Chlorides PVC is one of the major standard plastics. It possesses exceptional flexibility in formulation and processing producing flexible to rigid plastics. Rigid PVC, so-called poor man's engineering plastic, has a wide range of properties for use in different products. It has not been generally seen as a candidate for reinforcement (although in a great many of its applications it forms the matrix for RP products, such as reinforced hose, conveyor belting and heavy-duty fabrics). For processing, it must be compounded with stabilizers and lubricants. A rigid glass fiber-reinforced PVC extrusion compound by Solvay replaced the metal in side-protection strips on the Opel Astra car. The compound was coextruded together with a flexible PVC compound. The compound provided a low coefficient of linear thermal expansion (2.5 x 10 -5 K-1) and good adhesion to the car body. Recycling was facilitated, because the two compounds were compatible and there was no metal insert.

High Performance Thermoplastics While the heat stability of the so-called engineering TPs may be adequate for a large number of general-purpose applications, clearly

3 . Plastics 127

there is a place for materials that, while retaining the processing advantages of TPs, raise the heat stability ceiling. For ease of classification, this level may be taken as a continuous operating temperature of above 180C (356F). Addition of reinforcement raises this level. A group of TPs with performance above this level is characterized also by good mechanical properties and particularly good flammability performance (self-extinguishing, low smoke emission when burning). They can all be reinforced, with glass, carbon, or other higher performance fibers, and are often used in this way Tables 3.7 and 3.8). Examples of these materials follow: Polyetherimides PEIs is amorphous and transparent amber in color, giving high temperature resistance, rigidity, and impact strength. Good long-term creep resistance makes it an alternative to metals in some structural applications. It offers particularly good flammability performance, rated UL V-O at thicknesses as low as 0.010 in. It meets FAA standards for aircraft interiors, and is also useful for medical/pharmaceutical applications and in high-heat electrical,/ electronics components. Reinforced forms include glass- and carbon-fiber versions, and PE1 can itself be drawn into a fiber for use as a reinforcing material. Polyimides The first so-called high-heat-resistant TPs were the PIs family of some of the most heat- and fire-resistant plastics known. They are available in both TPs and TSs. Moldings and laminates are generally based on TSs, though some are made from TPs. PIs are available as laminates and in various shapes, as molded parts, stock shapes, and plastics in powders and solutions. Porous PI parts are also available. Uses include critical engineering parts in aerospace, automotive, and electronics components subject to high heat, and in corrosive environments. Generally, the compounds that are the most difficult to fabricate are also the ones that have the highest heat resistance. They have a density of 1.41 to 1.43, tensile strength of 12,000 psi at 73F, and an elongation of 6.8% at that same temperature. They have a low coefficient of expansion. PIs retain a significant portion of their room temperature mechanical properties f r o m - 2 4 0 to 315C (-400 to + 600F) in air. The service temperature for the intermittent exposure of PIs can range from cryogenic to as high as 480C (900F). Their deformation under a 28 MPa (4.000 psi) load is less than 0.05% at room temperature for 24 hours. Glass fiber reinforced PIs retain 70% of their flexural strength and modulus at 250C (480F). Creep is almost nonexistent, even at high temperatures.

m o

e~

Table 3.7 Comparison of high performance reinforced thermoplastics with 40 wt% glass fiber

m

Polyphenylene Polyether sulphide etherketone Polyphthalamide

Polyimide

Polysulphone

Polyethersulphone/ polyarylsulphone

198

290

274

482

374

435

Continuous use temperature

400-450

400-450

400-450

500-550

300-340

350-400

Heat distortion temperature

500

550

530

640

365

415

Tensile strength

26,000

28,000

36,000

27,500

19,000

23,000

Tensile modulus

2.6

2.6

2.5

2.4

1.7

2.0

Tensile elongation

1.6

2.5

2.0

2.0

1.7

1.5

Flexural strength

37,000

41,000

50,000

37,000

25,000

31,000

Flexural modulus

2.0

1.8

2.3

1.8

1.4

1.6

Glass transition temperature

(Tg)

Impact strength

1.7

2.3

2.2

2.2

1.6

2.0

Specific gravity

1.65

1.61

1.53

1.57

1.56

1.68

.

.

Source: RTPCo.

.

.

.

.

.

.

.

Ill

Polyetherimide 415

Liquid crystal polymer

350-400

400-500

31,000

15,000

500-600

2.0

2.7

43,000

20,000

1.0

1.6

2.3

1.59

1.70

2.1

. . . . . . . . . . . .

"I" :3 0. O" 0

0

410

2.5

Itt

1.2

Table 3,8 Comparison of high performance unreinforced and reinforced thermoplastics

Unreinforced Unit

Polyether sulphone

Polyether imide

Reinforced with 30O/oshort glass fiber Poly-phenylene sulphide

Melting point Glass transition temperature

~ ~ ~ ~

220 428

340 640 215 419

277 531 190 374

Heat distortion temperature UL rating continuous use Tensile strength Flexural Modulus Izod impact strength

~ ~ ~ ~ MPa psi x 103 GPa psi x 106 J/m ft Ib/in

205 401 180 356 85 12.3 2.6 0.37 90 1.68

200 392 170 338 105 15.2 3.0 0.43 50 0.93

135 275 220 428 75 10.8 4.2 0.60 16 0.29

Polyether sulphone

215 419 180 356 160 23.2 10 1.45 90 1.68

Polyether Poly-phenylene im ide sulphide

210 410 180 356 160 23.2 10 1.45 100 1.87

260 500 180 356 135 19.5 11 1.59 22 0.41

m,,. IJl

I,o

130 Reinforced Plastics Handbook

These materials have good wear resistance and a low coefficient of friction, both of which are factors that can be further improved by including additives like PTFE. Self-lubricating parts containing graphite powders have flexural strengths above 69 MPa (10,000 psi.) Their electrical properties are also outstanding over wide temperature and humidity ranges. They are unaffected by exposure to dilute acids, aromatic and aliphatic hydrocarbons, esters, alcohols, hydraulic fluids, Jp-4 fuel, and kerosene. They are, however, attacked by dilute alkalis and concentrated inorganic acids. PIs show good radiation resistance, and retain useful properties after absorbing radiation doses as high as 6.000 megarads. Polyimide laminates curing conditions are 200 psi at 370C for 1 h. Laminates have shown 25% strength retention after 1000 h at 315C. The resins do lose considerable strength in air at service temperatures above 315C. PIs are essentially nonfusible and difficult to fabricate by conventional shaping processes. Parts are fabricated by techniques ranging from powder metallurgy methods to modifications of conventional injection, transfer, compression, and extrusion that include ram instead of screw plastication (Chapter 5). Polyketones PK are crystalline engineering TPs that provide high performing thermal [240-245C (465-475F)], mechanical, chemical, and electrical properties. They are self-extinguishing, with low smoke emission on burning, and hydrolytic stability. They are used in a variety of products with and without reinforcement for the electrical, automotive, aerospace, chemical, and oil industries. They compete for applications with ceramics, glass, metals, thermoset plastics, and heat-tolerant and chemical resistant engineering thermoplastics such as polysulfone, polyimide, polycarbonate, fluoropolymer, and some nylons. The family of PKs, also called polyaryletherketones (PAEKs), consists of polyetheretherketone (PEEK), polyetheretherketoneketone (PEEKK), polyetherketone (PEK), and polyetherketoneetherketone-ketone (PEKEKK). They share similar molecular structures based upon repeating ether and ketone groups in various ratios. Cost of the resins is high but, in RPs with high-performance fibers, there are many applications in the aerospace and defense industries, electrical and atomic installations, and industrial and electronics products. Compounds for injection molding are available, but the major area of application is with thermoplastic prepreg materials, using mats, fabrics and/or continuous fiber.

3

9Plastics

Polyphenylenes The polyphenylcne-based thermoplastics family includes polyphenylcne ether (PPE), polyphenylene oxide (PPO), and polyphenylene sulphide (PPS). They have been one of the most successful groups introduced in the medium/higher range of cost/performance, with good heat stability and particularly good flammability properties. PPEs compounds are characterized by outstanding dimensional

stability, low water absorption in the engineering TPs, broad temperature ranges, excellent mechanical and thermal properties from -46 to 121C (-50 to 250F), and excellent dielectric characteristics over a wide range of frequencies and temperatures. Several injection molded and extrusion grades arc rated UL 94 V-1 or V - O including the glass fiber reinforced compounds. Because of their hydrolytic stability, both at room and elevated temperatures, blended parts in PPE can be repeatedly steam sterilized with no significant change in their properties. When exposed to aqueous environments their dimensional changes are low and predictable. PPEs resistance to acid bases and detergents are excellent. However, it is attacked by many halogenated or aromatic hydrocarbons. Foamable grades have service temperature ratings of up to 96C (205F) in 1/4 in. sections. PPOs was developed in the 1960s but proved very difficult to process until the development of technology to compound it with other polymers, such as polystyrene. Subsequently, as modified PPO, it has become a key engineering TP, largely complementary to ABS. It has good mechanical properties, with good resistance to heat and excellent dimensional stability. Electrical properties are also excellent. Resistance to chemicals is good, but not all-round. It is also known as PPE. Grades with glass and other fiber reinforcements are available. PPSs is one of the more successful of the medium/higher performance TP matrices for RPs. It has high heat resistance, with good strength and stiffness, good mold ability, good electrical properties, and outstanding resistance to chemicals. It is also inherently flame retardant. It is available as standard short and long fiber-reinforced granules, for injection molding, or as compression and extruded sheets reinforced with glass or carbon mat or woven fabrics. The latter form exhibit five to seven times the impact strength of conventional short-fiber granules, absorbing some 10-20 times more energy from impact, which is retained from -40 to 260C (-40 to 500F). Mat-reinforced PPS materials show a metal-like fatigue limit. Creep resistance is excellent.

131

132 Reinforced Plastics Handbook

The chemical resistance of PPS is excellent. It has no known organic solvents at temperatures below 204C (400F) and RPs are not affected by most solvents, lubricants and chemical environments found in oil production, aircraft, and automotive operations (where it is finding an increasing number of applications). Carbonreinforced RPs are also resistant to many strong oxidizing inorganic acids used in the chemical process industry. PPS is inherently flame-resistant, under a range of circumstances. The base resin has an oxygen index of 44 and, without additives, PPS compounds have received an UL rating of V - 0 / S V under the UL 94 test (meaning that they are quickly self-extinguishing and non-dripping). RPs burn with difficulty when exposed to flame and are extinguished immediately the flame is removed. PPS also shows low smoke emission and low toxic gas generation, rating a Number One in the 1977 NASA study of relative fire safety of TPs. PPS RPs also pass the OSU fire safety test required by FAA for materials for use in aircraft interiors. The UL temperature index is 200-240C (392-464F); the highest rating of any RTPs. Good (at least 75%) retention of tensile and impact properties and 55% retention of flexural strength is achieved at 204C (400F) by both carbon and glass-reinforced RPs. The carbon fiber RP also show excellent electromagnetic interference (EMI) and radio frequency interference (RFI) shielding characteristics, without use of additives. High performance injection molding compounds can give attenuation values of 60-70 dB; RPs for stamping, laminates and thermoforming can reach 90-100 dB and above. PPS is available as advanced RPs based on both glass and carbon, with long fibre technology. RPs with glass or carbon mat, are supplied as stampable sheet up to 30 in. wide x 70 mils thick (typical fiber content is 40 wt%, but this can be varied) or reinforced with satin weave glass or carbon fabric, for processing by lamination or thermoforming. Sheets are in 30 in. widths x 0.012 in. thickness. Typical fiber content is 40-60%. PPS RPs are also available as premolded stampable sheet, bar stock, and flat slab stock for machining; preconsolidated laminates of the satin woven fabric RPs are available in 8-ply thicknesses. Polysulphones The polysulphone family of polysulphone (PSU) and polyether sulphone (PES) is a TP based on sulphone derivatives, aiming at high heat-stability. PSU originated in the discovery of a method of producing high molecular weight aromatic polyethers,

3

9Plastics

and the resulting patent is the source of all subsequent commercial processes for derivatives such as polyarylether sulphone and polyarylether ketones. PSUs is characterized by high thermal and oxidative resistance, with high mechanical strength. They are used especially for electrical and electronic applications and for components for medical equipment. PESs is one of the highest-temperature engineering TPs, with a continuous service rating (UL) of 180C (356F). It is selfextinguishing and, when it does burn, it produces little smoke. It finds applications in reinforced and unreinforced compounds in aircraft interiors, medical equipment, household goods and electrical/ electronic components. Blends with polyarylsulphone (PAS) can replace metals, glass, or ceramics in many applications.

Thermoset Plastics When processing thermosets (TSs) heat is applied making them flowable. At a higher temperature they solidify and become infusible and insoluble. Cured TSs cannot be resoftened with heat. Its curing cycle is like boiling an egg that has turned from a liquid to a solid and cannot be converted back to a liquid. They undergo a crosslinking chemical reaction of its molecules by the action of heat and usually pressure (exothermic reaction), oxidation, radiation, a n d / o r other means often in the presence of curing agents and catalysts. In general, with their tightly crosslinked structures there are TSs that resist very high temperatures and provide greater dimensional stability and strength than do most TPs. They are normally used in the liquid state and solidify and harden on curing. With some resins it is possible to part-cure and then hold the prepreg in what is termed the B-stage, for the cure to be completed at a later time (Chapter 4). Cure A-B-C stages for TS polyester and other resins identifies their cure cycle where A-stage is uncured, B-stage is partially cured, and C-stage is fully cured (Figure 3.3). Typical B-stage is TS molding compounds and prepregs, which in turn are processed to produce C-stage fully, cured plastic material products. Different testing procedures used to determine the degree of cure or hardness of the plastics. A very simple, fast, and useful test used since at least the 1940s is the Barcol hardness tester (ASTM C 581). Its values serve as an indication of degree of cure with high values indicating thorough cure and low values indicating incomplete cure. Barcol values will vary from one resin

133

134 Reinforced Plastics Handbook

system to another and will depend on the type and number of surface (veil, etc.) layers. Generally, a well fabricated, well cured laminate will have a minimum Barcol reading of 30.

~,

~

CONSTANT

~ "

Or)

o o

Or) > U..I

! ! !

! I !

I !

I !

MELTING

CROSS LINKING

TIME Figure 3.3 Thermoset A-B-C: stages from melt to solidification

TSs offer high thermal stability, good rigidity and hardness, and resistance to creep. It also means that, once cured, the resin and its RP cannot be reprocessed, except by methods of chemical breakdown. For practical purposes, as it has been done for a century, cured TS resins can be recycled most effectively if ground to fine particles. Then they can be incorporated into TSs and TPs, as cost-effective fillers. TSs has little use as pure resin, but requires addition of other chemicals to render them processable. For RPs, the compounds usually comprise a resin system [with curing agents (catalysts), hardeners, inhibitors, plasticizers] and fillers a n d / o r reinforcement. The resin system provides the binder, to a large extent dictating the cost, properties, dimensional stability, heat, chemical resistance, and basic flammability. The reinforcement influences primarily the effect of tensile strength and toughness. Once a thermoset is compounded for processing, it has a pot life that is also called working life. When the thermoset, has been mixed or compounded with a catalyst, its pot life is the time remaining in a usable condition. It is measured at room temperature or the temperature to be encountered. This term should not be confused with shelf life. Special fillers and additives can influence mechanical properties, especially for improvement in dimensional stability, but they are mainly used to confer specific properties such as flame retardancy, ultraviolet (UV) stability, or electrical conductivity (Table 3.9).

3 . Plastics 135 Table 3,9 Characteristicsand limitations of thermoset RPs Resin t y p e

Characteristics

Limitations

Epoxy

Excellent composite properties Very good chemical resistance Good thermal properties Very good electrical properties Low shrinkage on curing Can be B-staged (prepreg)

Long cure cycles Best properties obtained only with cure at elevated temperature Skin sensitizer

Phenolic

Very good thermal properties Good fire properties (self-extinguishing) B-stage possible Good electrical properties

Color limitation Alkali resistance Contact with foodstuffs

Polyester

Wide choice of resins - easy use Cure at room temperature and elevated temperature Very good composite properties Good chemical resistance Good electrical properties

Emission of styrene Shrinkage on curing Flammability No B-stage possible

Polyimide and Excellentthermal properties polyamide-imide Good composite properties Good electrical properties Good fire properties

Restricted choice of color Arc resistance Acid and alkali resistance

Polyurethane

Good composite properties Very good chemical resistance Very high toughness {impact} Good abrasion resistance

Nature of isocyanate curing agents Color Anhydrous curing No B-stage

Silicone

Very good thermal properties Excellent chemical resistance Very good electrical properties Resistant to hydrolysis and oxidation Good fire properties (self-extinguishing) Non toxic

Lack of adhesion Long cure cycles Can only be cured at elevated temperature

Vinyl ester

Good fatigue resistance Excellent composite properties Very good chemical resistance Good toughness

Emission of styrene Shrinkage on curing Flammability No B-stage

136 Reinforced Plastics Handbook

Thermoset Plastic Types TSs, like TPs, offer a wide range of matrix materials for reinforcement by fibers, flakes, beads, or particulate materials such as talc and mica. They are compounded with reinforcing materials. Among the fibers, glass is the main reinforcement. Examples of these TPs follow: Epoxies They generally provide the highest performance of all TSs. Epoxy resins are characterized by their very high strength (tension, compression, flexural, etc. loadings), very low shrinkages, hard, superior adhesion to other materials, very good electrical properties and chemical resistance, low absorption of moisture, etc. After the TS, (unsaturated) polyester resins, epoxies are the most widely used TS in RPs, complementing them at the higher end of performance. Due to the superior properties of epoxies, they are frequently used with high performance fiber reinforcement, such as carbon, and with high concentrations of glass fiber. Epoxies are versatile resin systems, offering particularly excellent resistance to corrosion (to solvents, alkalis and some acids), high strength/weight ratio, dimensional stability and adhesion properties. They are linear polymers produced by condensing epichlorhydrin with bisphenol A. Other formulations are glycidyl esters (for vacuum impregnation, lamination and casting), glycidyl ethers of novolac resins, and brominated resins. They differ from TS polyesters and vinyl esters because they do not contain any volatile monomer component. Different resins are produced by varying the ratios of the components. The resins are relatively high in viscosity, so that they are usually molded at temperatures in the region 50-100C (120-212F), or dissolved in an inert solvent to reduce viscosity to a point at which lamination at room temperature becomes possible. Curing agents (catalysts, hardeners and/or accelerators) are used, either acting by catalytic action or directly reacting with the resin. With correct additives, they can exhibit outstanding resistance to heat [some up to 290C (550F)] and electrical insulation properties. They can be either liquid or solid in form and can be formulated to cure either at room temperature or with the aid of heat. Heat curing is the more common for situations where maximum performance is required. Epoxies generally cure more slowly than other TSs. They are often used in contact molding, for tooling and pipefitting. A major use is for filament winding. Applications are particularly in aerospace and defense, chemical plant, high-performance components

3

9Plastics 1 3 7

of automobiles, and different industrial structures (circuit boards, tooling surfaces for metals, etc.). Another major use, with or without reinforcement, is as surface-coating materials where they combine toughness, flexibility, adhesion, and chemical resistance to a degree unmatched by almost any other plastic. Phenolics

Phenolics (produced by reacting phenol with formaldehyde/PF) have been the low-cost workhorse since 1907 in the electrical and other industries. They were the original major commercially viable synthetic TS plastic materials. They have low creep, excellent dimensional stability, good water and chemical resistance, heat resistant [up to 150C (300F)], and good weatherability. Fire, smoke, and toxicity properties are particularly good. Phenolic resins are inherently brittle, giving poor impact performance but by adding material such as siloxanc and glass fibers impact significantly increases. Molded black or brown opaque handles for cookware have been familiar applications. Also used as a caramel colored impregnating plastics for wood or cloth laminates, and (with reinforcement) for brake linings and many under-the-hood automotive electrical components since the 1940s. Standard phenolics usually have wood flour filler. Phenolics are formulated with one- or two-stage curing systems. In general, one-stage plastics arc slightly more critical to process. They have a time to temperature to viscosity behavior that has to be followed. Compounds from these resins have been produced with glass, natural, and other fibers since the 1940s (Table 3.10). Principally compression, transfer, and injection molding process them. There are phenolics when processed that release water and others that do not release water. As is typical of many TSs, they are postcured to obtain maximum performance. Table 3.10 Properties of chopped glass fibers reinforced phenolics and TS polyester resins Property Glass content (% wt} Compressive strength (MPa) In-plane shear strength (MPa) Short beam shear strength {MPa) Flexural strength: 16:1 {GPa) Flexural modulus: 16:1 (GPa) Flexural strength: 32:1 (GPa) Flexural modulus: 32:1 (GPa}

ASTM test D-695 D-3846 D-2344 D-790 D-790 D-790 D-790

Note: original values in Imperial units, converted to SI. Source: SPI 48th Annual Conference

Phenolic 76-77 641 39 4-5.5 1.12 45 1.21 48

Polyester 73-74517 41.4 48.3 1.06 48 1.15 5O

138 Reinforced Plastics Handbook

They offer an advantage compared with TS polyesters: a degree of good inherent resistance to heat and combustion. Compared to most other RTSs they have lower mechanical properties. Gradually their use in the past (1907-1930s) almost disappeared because new plastics were developed that out performed them even based on costs. With new developments in preparing phenolics, specialty applications have been developing. Without modification or additive, the typical oxygen index of a low glass content laminate (35 wt%) is higher than 55%, a figure which can be matched by only a few other materials, even when highly loaded with flame-retardant additives (Table 3.11 and 3.12). The resins do not readily ignite, and have no auto-propagation of flame, very low emission of smoke and toxic fumes, low heat release, and no release of flammable vapor. They are claimed to be the only organic construction material capable of meeting the demands of many international fire standards, except where non-combustibility is specified. Table 3.11 Fire performance of phenolic/glass fiber RP compounds

Fire properties measured Test

Flame spread

BS 476 Part 7 Cone calorimeter

Class 1

IMO surface flammability A 16IRes. 653 NT Fire 004

PASS: Bulkhead wall Et ceiling linings

Smoke dynamic

Toxic gases

SEA 182 m2/kg Qe 50 kW/m 2

Light absorption <2% full deft Ao ON <1.0 Ao OFF <1 Category 1 Dm NF 55 F91 Ds 1.5 min 5 4 min 25 Smoke index 4

3 m cube smoke test BS 7853 NBS smoke box ASTM E 662 ATS 1000.001

NES 711 NES 713 NF F 16-101 Brandschacht ASTM E 162 ASTM E 84

Smoke cumulative

M1 B 1 (indicative) FE Index 2 FS Index 5-10

PASS

Unpainted < 5

Notes: (a} Test specimens3 mm thick, 35% wt glass; (b] increasing glasscontent or laminate thickness will further improve the fire properties; (c] unlessotherwise indicated, performanceapplies to unpainted or painted composites.

3

9Plastics 1 3 9

Table 3.1 2 Fire performance of phenolic/glass fiber RP compounds (ignitability/heat) Fire properties measured

Test

Ignitability

Oxygen index ASTM D2863 NES 714 BS 2782 Method 14 Temperature index Small flame {Bunsen) Cone calorimeter IMO surface flammability A 16IRes.653

>55%

NT Fire 004 BS476 Part 6 OSU calorimeter

Ignitability direct flame

Rate of heat release

Effective heat of combustion

Total heat released

>420~

UL 94 V-O

PASS: Bulkhead, wall and ceiling linings

128 kW/m2 Qe 50 kW/m2 PASS: Bulkhead, wall and ceiling linings < Curve 1 i<6 /<12 26 kW/m2 painted

PASS: Bulkhead, wall and ceiling linings

39 kW/m2 painted

Polyesters, TS

Thermoset (unsaturated) polyester resins (UP) are the most widely used TS matrices for RPs, spanning the whole range of fabricating from basic hand lay-up to complex mechanized molding processes (Table 3.13 and 3.14). This family of polyesters has widely varying and important range of properties. There are the two major groups of the TPs (with comparatively high melting points) and the TSs (which are usually typified by a crosslinked structure). TP polyesters are often called saturated polyesters to distinguish them from unsaturated polyesters that are the TSs. The term TS polyester covers a very large chemical family, of which the unsaturated resins (covering orthophthalic, isophthalic, vinyl esters, and blends) form the largest single group of fiber reinforced TSs (RTSs). Polyesters offer a good balance of mechanical, electrical and chemicalresistance properties, at relatively low cost (Table 3.15). They also have good dimensional stability and are relatively easy to handle. They are

140 Reinforced Plastics Handbook Table 3.13 Examples of properties based on processes for E-glass fiber/TS polyester RPs Composite Hand lay-up/spray-up Bulk molding compound Sheet molding compound Mat/preform-structural Mat/perform-low shrink High-glasssheet molding com pou nds* XMC-3 composite (lengthwise) Pultrusion (lengthwise)

Tensile strength, psi x 103 (MPa)

Flexuralstrength, psi x 103 (MPa)

Flexuralmodulus, psi x 106(GPa)

10.0 3.0 10.0 15.0 10.5 19.5

17.0 10.0 22.0 30.0 24.0 36.0

1.0 1.6 1.5 1.3 1.1 1.9

(68.9) (20.7) (68.9) (103.4) (72.4) (134.4)

75 (517) 30.0 (206.8)

(117.2) (68.9) (151.7) (206.8) (165.5) (248.2)

125 (862) 30.0 (206.8)

(6.9) (11.0) (10.3) (9.0) (7.6) (13.1)

5.5 (37.9) 2.5 (17.2)

* Minimum averages for a range of high-strength compounds

Table 3.14 Characteristics and use of glass fiber/TS polyester RPs Polyester

Characteristics

Named by characteristic of cured resin General purpose Rigid moldings, craze resistant Flexible resins and semirigid resins

Tough, good impact resistance, high flexural strength, low flexural modulus

Light stable and weather resistant Chemical resistant

Resistant to weather and ultra-violet degradation Highest chemical resistance of polyester group, excellent acid resistance, fair in alkalies Self-extinguishing, rigid

Flame resistant High-heat distortion Electrical

Service up to 500~ rigid Fast cure, good hot strength, good electrical properties

Typical Uses Trays, boats, tanks, boxes, luggage, seating vibration damping: machine covers and guards, safety helmets, electronic parts encapsulation, gel coats, patching compounds, auto bodies, boats Structural panels, skylighting, glazing Corrosio n- resista nt, applications such as pipes, tanks, ducts, fume stacks Building panels (interior], electrical components, fuel tanks Aircraft parts Where good electrical properties are required

Named by processing characteristics Hot strength Low exotherm Extended pot life Air dry Thixotropic

Fast rate of cure, "hot" moldings easily removed from die Void-free thick laminates, low heat generated during cure Void-free and uniform, long flow time in mold before gel Cures tack free at room temperature Resists flow or drainage when applied to vertical surfaces

Containers, trays, housings Encapsulating electronic components, electrical premix parts- switchgear Large complex moldings Pools, boats, tanks

Boats, pools, tank linings

3

9Plastics

usually manufactured by reacting together dihydric alcohols (glycols) and dibasic organic acids, either or both of which contain a doublebonded pair of carbon atoms. Table 3 . 1 5 Glass fiber/TS polyester properties compared to metals and timber

Unit

Polyesterlaminates

Mild steel

Duralumin

g/m 3 MPa GPa MPa

roving cloth mat 70o/0 55Olo 30% 1.9 1.7 1.4 800 300 100 30 15 7 400 200 70

7.8 310 200 40

2.8 450 70 150

Glass reinforcement Density Tensile strength Tensile modulus Specific strength

Douglas fir Hickory

0.5 75 13 150

0.8 150 15 200

By elimination of water between the acids and glycols, ester linkages are formed, producing a long chain molecule comprising alternate acid and glycol units. It is possible to regulate the ratio of saturated/unsaturated dibasic acid, allowing incorporation of crosslinkage sites (unsaturation or carbon-carbon double bonds) at regular intervals along the chain. The polymer chain is dissolved in a reactive organic solvent usually styrene monomer. Others used include diallyl phthalate, methyl methacrylate, and vinyl toluene. The type of acid and glycol used will influence other properties such as resistance to chemicals or flame. Polyesters are therefore classified according to the material used in their manufacture (orthophthalic, isophthalic, iso-NPG, bisphenol, etc.). Processing will largely determine the length of polymer chain; other influential factors arc monomer content and filler addition. The polymer is dissolved in styrene or a monomer containing vinyl unsaturated. With heat and a chemically activated free radical initiation, the polyester and the reactive diluent crosslink to form a 3-D nonmehing network. The reaction occurs at 170-200C (338-390F), with components in roughly equal molecular ratio and water eliminated. The polyester is then dissolved in stabilized comonomers. Protected from light, the resin has a shelf life of about six months. Thirty percent styrene usually serves as comonomer solvent. In response to growing unease about the presence of styrene vapor at the workplace, lowstyrene emission types have been introduced in recent years. Polyester resins are cured by organic peroxides that initiate a free radical copolymerization reaction. This can occur at room temperature, under heat [60-90C (140-194F) or by UV or visible light radiation. The possibility of cold-curing polyester resins from the liquid state is one of

141

142 Reinforced Plastics Handbook

the key reasons for widespread use of these systems for large structures. The catalyst system comprises organic peroxides (initators) which are activated by accelerators or promoters. An accelerator can assist the speed of cure; it must not be mixed with the catalyst, but can be added in advance to the UP resin. Cold curing may require post-curing/ conditioning at up to 20C (68F) for one or two weeks. Accelerators come in a broad variety of formulations, making them useful in both low and high temperature processes, as well as room temperature and heat assisted curing. Additives are used to reduce or increase viscosity, adjust filler loading, reduce volatilization of monomer, add strength, and counteract shrinkage. Pigments are available to add color and ultraviolet absorbers can be added to improve resistance to sunlight/outdoor exposure. The resin begins to cure as soon as the initiator is added, the speed of the reaction depending on temperature, resin composition, and catalyst reactivity. The curing reaction generates its own heat (exotherm) and it may often be necessary to pay special attention to this heat build-up in fabricating the part, use of cooling and control of the rate of the reaction, and to avoid irreversible damage to the RP during the process. Polyesters can be used on their own, in applications such as casting and encapsulation/potting and in pastes and concretes. Their largest field of application, however, is in RPs, where glass fiber in different forms is the main type of reinforcement, offering a cost/performance profile that complements that of the resin (Table 3.16). By choice of the chemical constituents, the properties of the resin can readily be tailored to specific applications, influencing such properties as: heat resistance, resistance to hydrolysis, impact strength, flexibility, light refraction, electrical properties, and flammability (self-extinguishing) properties. There are many variations of resin on the market, adapted to different applications. The characteristic data for classification are: viscosity, gel time at 25C (77F), reactivity at 80C (176F) and maximum temperature. Standard These resins are usually based on orthophthalic acid and can be attacked by chlorinated hydrocarbons, some solvents, alkali solutions and concentrated and oxidizing acids. The heat deformation temperature is approximately 70C (160F).

Resins based on dicyclopentadiene (DCPD) offer better wettability of fillers and better prevention of print-through than conventional unsaturated polyesters, making them particularly suitable for appearance parts in transportation and marine applications. Polyesters based on DCPD require special chemical competence on the part of the fabricator, but

3

Table 3.16

9Plastics

Comparing RP properties of TS polyester with different forms of glass fibers Type of reinforcement None

Typical glass content (%) Tensile strength (MPA} Tensile modulus (GPa) Flexural strength (MPa) Flexural modulus (GPa)(psi) Compressive strength (MPa)(psi) Coefficient linear thermal expansion (I0-6/K) Density (kg/dm 3)

Chopped roving a

85 4.2 120 4.0 _e

30 100 7.7 180 7.0 200

110 1.2

30 1.4

Roving fabric ~

Bidir. fabric c

Unidir. fabric d

Unidir. roving

50 270 16 300 15 160

65 460 22 600 21 310

65 680 34 900 32 _e

75 1150 42 1300 40 e

20 1.65

15 1.75

10 1.75

8 2.0

aFiber length: 50 mm. bTwill weave;warp = weft. cStyle 7581; silane-sized yarns. dWarp/weft ratio: 10; silane-sized yarns. eNo reliable test method.

can reduce manufacturing costs by allowing the use of lower-cost glycols. They also offer lower shrinkage and low styrene emissions. Reduction in emission of styrene is one of the main lines of current development, to comply with current or expected national and regional regulations covering safety in the workplace. The normal method is to include a wax-based additive that forms a blanket over the resin when it is rolled out and curing, sealing the surface and restricting evaporation of free styrene. This may also affect inter-laminar adhesion and alternative approaches seek to develop resins with inherently low styrene emissions. A range of polyester resins from BIP offers a unique blend of toughness and flexibility with a high level of temperature resistance, for applications particularly in puhrusion. Named Flexitough, the resins can be formulated in various grades from isopththalic to orthophthalic, and to customer requirements. They mold and cure as conventional polyesters. In the context of the demand to extend the scope of recycling, Alpha/ Owens Corning has resins using recycled terephthalic acid, produced from PET bottle scrap. Chem ical-Res#ta n t/Corrosion -Resista n t

In common with most plastics, polyester resins have good all-round resistance to chemical attack and corrosion, but all significant conditions must be known before a particular resin is specified. Improved corrosionresistance is usually based on iso- or terephthalic acid and neopentyl glycol, giving good mechanical properties. These resins are also suitable for gel coats that are continuously stressed with warm water (such as

143

144 Reinforced Plastics Handbook

baths and bathing pools). Table 3.17 provides examples were RPs are used in corrosion resistant products. Table 3.17 Reinforcedplasticcorrosion resistantproducts Industry

Process

Reinforcement

Oilfield pipes Fume handling ducts

Filament winding Spray-up/hand lay-up

Roving Epoxy Gun roving Polyester Vinyl Chopped strand ester mat Woven roving Roving Gun roving Polyester

Underground gasoline Centrifugalcasting tanks Spray-up Pump bodies/impellers PRM Sucker rods

Pultrusion

Continuous strand roving Roving

Resin

PolyesterVinyl ester Polyester Vinyl ester

Flame-Retardant Polyester resins can be rendered flame-retardant or self-extinguishing to a greater or less degree, by use of special additives, brominated or highly chlorinated (HET acids) acid components, and antimony trioxide. Smokeless low-viscosity resins are filled with special aluminum hydroxide, up to 1:1.8 ratio. There are S M C / B M C formulations using technology allowing a very high loading of aluminum trihydrate, removing the need for halogen or phosphorus flame retardant additives and giving limiting oxygen index of 100.

There is considerable continuous development of improved flameretardant additives to give better performance and easier processing. As national and international regulations coveting flame-retardant materials are steadily tightened (and are increasingly seeking to control smoke and by-products that may be evolved during combustion) new flameretardant chemicals and resin formulations are being developed. Gel Coats Specialized polyester resins are commonly used in processes such as hand lay-up and spray-up, to provide an attractive and weather-resistant surface finish to molded parts. These gel coats are sprayed onto the mold before the reinforcement is introduced. In addition to their cosmetic function, gel coats can also provide the RP surface with resistance to impact and abrasion. There is also anti-bacterial additive technology to gel coats, especially for applications such as baths and

3-Plastics 145

sanitary ware, food manufacturing, and preparation equipment and marine structures.

TS Polyester Solvents-MACT For the past decades those processing TS polyester plastics have had to reduce its styrene, acetone, and other volatile organic compound (VOC) emission into the atmosphere. Boat builders are directly involved as new USA Environmental Protection Agency (EPA) regulations are issued that involve HAPs (harmful air pollutants) and MACT (Maximum Achievable Control Technology) that are under the CAAA (Clean Air Act Amendments). To reduce solvent emission different approaches have been used that includes polyesters with less styrene content and enclosing the fabricating process so that solvents are not released into the atmosphere. Process wise vacuum systems have been used since at least the 1940s that have become popularly known as infusion systems (Chapter 5 ). Worldwide resin suppliers and fabricators have been taking action to reduce volatiles. One of many companies switching to low-styrene emission (LSE) resins is USA powerboat builder Baja Marine. Having made its move before MACT requirements for low emissions of hazardous air pollutants (HAP) started to be enforced, Baja now uses products containing 25-30% styrene compared with around 40% for standard products. It reports no problems with the materials used; generalpurpose DCPD-modified orthophthallic polyester for bulk laminating and vinyl ester for skin coats. Thanks to good results achieved, the company has not had to adopt styrene suppressants or zero-VOC alternatives such as polyurethanes. Baja has incorporated non-atomizing spray equipment into its get coating processes, replacing high-volume/ tow-pressure spray guns and flow coating equipment previously used. Ashland Specialty Chemical Company has expanded its range of low styrene resins particularly to help boat builders meet EPA Maximum Achievable Control Technology (MACT) standards. Aroguard LSO is claimed to be the first 100% orthophthalic marine resin to contain less than 35% styrene and volatile organic compounds (VOC). It is designed as a premium low-styrene product that can be seamlessly integrated into manufacturing operations without adding alternative monomers, changing equipment or compromising product performance. Other additions in the Aroguard range are Aroguard 35 and Aroguard 45, which are 100% vinyl ester resins containing 35% and 45% styrene, respectively. Aroguard 35 INF is an infusible marine product. Developments have also been made in the company's AME and Aropol resin lines. AME marine resins are used to construct high performance

146 Reinforced Plastics Handbook

marine laminates requiting high strength, impact resistance and corrosion resistance. A closed molding process that is claimed virtually to eliminate all styrene emission to the atmosphere has been developed by the USA fabricator Molded Fiber Glass Co, Union City, OH, USA. It is progressively being introduced throughout its own manufacturing plant. Few details have been released about the process, but its name, VACRIM, suggests that it combines vacuum and resin injection. The process produces a finished surface on both sides of the part, with better surface consistency, and significantly reduces rejects due to porosity. The company also claims it is more flexible in size of part produced, with lower costs per part, lower tooling costs and wider choice of material. An environmental advantage is that the glass fiber is contained within the working area, making for a cleaner workplace. Target has been to develop solvent-free resins and eliminate the use of acetone. EPA estimates nationwide annual compliance costs to the points system summarized in Table 3.18 of $14 million for existing USA plants. It allows various materials and methods to be compared in terms of their emissions. The MACT model point values are in units of lbs of HAP per ton of resin or gel coat. Point values shown are for vapor-surpassed resins applied manually, mechanically, or by filament winding/centrifugal casting are applicable for unfilled resin systems only. Refer to EPA for more information.

Solvent Recovery Systems Recovery of expensive solvents is an attractive proposition, and there is a range of equipment suited to various requirements. Units employ a simple distillation process to restore waste solvents, removing contaminants introduced during production processes, such as solvents, paints, resins, oils, pigments, inks, and grease. Vacuum distillation systems (with integral vacuum pump and more robust construction) are designed for recovering solvents with higher boiling points and thermally unstable solvents, such as halogenated and acetate solvents, reducing boiling point, cycle time and power consumption by up to 20%. When the contaminated solvent is placed in the unit and distillation temperature set, the process is automatic, requiring no supervision, restoring 90-97% of the solvent to its original condition. The residue is easily removed and in most cases can be legally disposed of as ordinary waste. Distillation does not affect the solvent and can be repeated as often as necessary. It is also possible to extract selectively a single solvent from a mixed solution.

Table 3.1 8 EPA MACT model point values’ ~

HAP con tent (Yo by wt.)

26.0 27.0 28.0 29.0 30.0 31.0 32.0 33.0 34.0 35.0 36.0 37.0 38.0 39.0 40.0 41 .O 42.0 43.0 44.0 45.0 50.0

Manual resin opplicotion (Hand lay-uplbucket Et tool opplicotion) Non-vopor Vapor Vacuum suppressed suppressedZ bogging3

43 47 51 55 60 64 69 74 79 85 90 96 102 108 114 121 128 135 142 149 189

28 31 33 38 39 42 45 48 52 55 59 62 66 70 74 79 83 87 92 97 123

24 26 28 30 33 35 38 41 44 47 50 53 56 59 63 66 70 74 78 82 104

~

~

~

_

_

Mechanical resin application Atomized application Non-atomized application Non-vapor Vapor Vocuum Non-vapor Vopor Vocuum suppressed suppressed2 bagging3 suppressed suppressed2 bagging3

74 81 89 96 107 117 127 137 149 160 173 185 199 213 227 243 258 275 292 309 407

48 53 58 64 70 78 82 89 97 104 112 121 129 138 148 158 168 179 190 201 285

41 45 49 54 59 64 70 76 82 88 95 102 109 117 125 133 142 151 160 1 70 224

43 47 51 55 60 64 69 74 79 85 90 95 102 108 114 121 128 135 142 149 189

28 31 33 38 39 42 45 48 52 55 59 62 66 70 74 79 83 87 92 97 123

24 26 28 30 33 35 38 41 44 47 50 53 58 59 63 66 70 74 78 82 104

_

_

~

filament winding/ centrifugal casting Non-vapor Vapor suppressed suppressed2

88 93 97 102 106 111 116 120 125 130 135 139 144 149 154 159 164 169 170 180 206

57 60 63 66 69 72 75 78 81 84 87 91 94 97 100 104 107 110 113 117 134

Gel-coat applico tion Atomised applications

194 208 222 238 253 2 69 286 303 320 338 356 375 394 41 4 434 454 475 496 51 8 541 658

NotcThis table is indicative only and should not be used as a basis for current calculations. Refer to the EPA for the latest information and point values.

3 . Plastics 1 4 7

1: MACT Model point values are in units o f lbs o f HAP per ton o f resin or gel-coat. 2 , The MACT Model point values shown for vapor-suppressed resins applied manually, mechanically or by filament winding/centrifugal casting, are applicable for unfilled resin systems only. For filled resin systems, the non vapor-suppressed point values should be used whether or not the resin contains a vapor-suppressant. Point values shown for vapor-suppressed resins assume a 35% reduction in emissions when such resins are used in an unfilled resin system. Point values for a vapor-suppressed resin used t o comply with a MACT standard would be obtained from an equation that uses results of a laboratory test conducted on that resin system. 3: Point values shown for applications with vacuum bagging assumed that the use of vacuum bagging reduced HAP emissions by 45% when the bag and vacuum were applied to the mould immediately after the application o f the resin and no roll-out o f the applied resin occurred.

148 Reinforced Plastics Handbook

Basic units have at least capacities of 13, 24, 54 and 99 liters (2.8, 5.2, 11.8 and 21.7 gallons), operating at temperatures from 40 to 280C (104-536F), with a cycle time of 3-6 h. An air-cooled design collects the dirty solvent in a removable stainless/steel tank, with disposable plastics liners manufactured to withstand temperatures up to 200C (390F), removing the need to scrape out the tank after each cycle. It has four basic elements: removable evaporator tank (serving also as a closed collection vessel to transport dirty solvent from the point of use to the recycling system); boiler with electric heating elements heating a diathermic oil bath in which the evaporator is immersed; air-cooled condenser (cheaper to run than water-cooled or refrigerated systems); and electrical control panel and enclosure. Sizes range from 16 to 150 liters, operating at up to 180C (350F), with an output ranging from 5 to 35 liters/h. Agitated distillation systems can handle heavily contaminated solvents which tend to polymerize when heated, scraping the sides of the tank, chopping any solids and keeping them moving to prevent any build-up on the tank sides as well as to ensure uniform heating (by induction through the walls of the boiling tank). The residue is a dry powdery substance resembling a dry concrete mix, which can easily be disposed of by means of a built-in crane and tipping trolley. Vinyl Esters

These VE stiff and tough unsaturated thermoset plastics are cured by both peroxide catalyzed addition polymerization of vinyl groups and anhydride crosslinking of hydroxyl groups at room or elevated temperatures. Cured bisphenol-A vinyl esters are characterized by chemical resistance; epoxy novolac vinyl esters by solvent and heat resistance; flame retardant, and all types in general are tough and flexible in a wide range. Major use is as the matrix in glass and other fiber RPs. They provide exceptional high strength properties in highly corrosive or chemical environments when compared to other commercial RP matrices such as TS polyesters. Popular processes used include filament winding, transfer molding, pultrusion coating, and laminating. Uses include structural composites, sheet molding compounds, and chemical apparatus. VE resins combine the best features of both polyester and epoxy resins, with few compromises. Strength is similar to epoxies, but the resins are less expensive and easier to handle. They are characterized by high RP strength and outstanding resistance to aggressive media (including both acids and alkalis) at high temperatures. They also possess good resistance to impact and fatigue and have low permeability to water, so

3

9Plastics

reducing blistering. Electrical and thermal insulation properties are also excellent. Compatibility and bond strength to glass, graphite and aramid fibers is good. They differ from the conventional bisphenol polyester resins, having unsaturation only at the end of the chain and not in the repeat units, and containing fewer ester linkages. This gives the improved chemical resistance, while terminal double bonds give a tougher and more resilient resin structure. Epoxy based VE offer particularly good chemical resistance at elevated temperatures. Rubber-modified epoxy VE have increased adhesive strength, with superior resistance to abrasion and severe mechanical stress, while providing greater toughness and elongation. VE may also be chemically modified, to give specific but more limited properties, at a lower price. VE are styrene soluble, giving a low viscosity. They are processed in a similar manner to TS polyester resins, using peroxide catalysts and cobalt accelerators, often boosted by the addition of dimethylaniline. Not all brands of peroxide give the same results, so specific advice on suitable curing systems should be obtained from the resin supplier. Hot-cure systems based on benzoyl peroxide or tertiary-butyl peroxybenzoate are used. To achieve maximum temperature resistance, a high temperature post-cure is necessary, in hot air or radiant heat. Recommended conditions range from 16 h at 66C (150F) to 2 h at 121C (250F). The most common applications are chemical-resistant equipment, tanks and pipes, and structural automobile parts. Resins can also be formulated for SMC and BMC systems, with excellent specific properties, such as dimensional stability, heat resistance, and resistance to oil. Low-Emission Resins

As with TS polyester resins, the VE resin is diluted with 30-50% styrene, to give usable consistency and, during fabrication, part of the styrene evaporates into the workplace atmosphere. Low styrene emission (LSE) resins are used (Table 3.19). Traditionally, the route is to introduce a wax-based additive, which seals the surface as soon as lamination is completed, so preventing evaporation, but this technique can also reduce the effectiveness of the bonding between layers, leading to possible delamination. Other additives and stabilisers are therefore used, using similar technology to that developed with TS polyesters, but large quantities must be used with vinyl esters that may impair the corrosion-resistant properties of these resins (which is one of the main reasons why they are used). Producers have therefore developed special additives. A typical solution is a version of a bisphenol-A epoxy VE, developed in

149

1 50 Reinforced Plastics Handbook Table 3.19 Typical properties of vinyl ester standard and low styrene emission (LSE) resins

Physical properties

Standard resin

LSEversion

25 22

25 22

172 7.8 2.2

193 7.8 2.5

115 8.6 1.5

124 8.7 1.7

Inter-laminar shear strength (MPa): 1 laminate 8 layers 1 laminate 2 x 4 layers Flexural properties: Strength (MPa) Modulus (GPa) Strain (%) Tensile properties: Strength (MPa) Modulus (GPa) Strain (%)

parallel with a low-emission version of a high performance novolac epoxy VE, both of which use individual variations of wax-based technology. The resins command a price premium of about 10% over non-LSE grades (Table 3.20). Table 3,20

Typical properties of modified vinyl ester laminates

Unit

Versatile, F l a m e economic retardant

Romeretordant

Thixotropic Thixotropic

Flexural strength

psi x 103

30.1

22.7

26.6-30.0

30.5

Flexural modulus

psi x 105

10.4

11.9

10.5-10.9

10.3

10.6

Tensile strength

psi x 103

22.9

23.6

17.0-19.4

22.5

23.2

15.2

15.5

15.6-17.2

15.5

15.3

1.8

1.7

1.6-2.2

1.8

Tensile modulus

psi x 10s

Tensile elongation

%

Barcol hardness

934-1

43

50

42-48

43

30.7

1.7 46

Note: Laminate construction = VeillmatlmatlWRImatlWRImat[veil = 1.0 mil C-glass; mat = 1.5 oz/ft2; WR = 24 oz/ft2: glass content = 40O/o). Room temperature curing of the system can be accomplished with: Catalyst range - 50% MEKP: 0.75-2.50/h. Promoter range - 20%, Cobalt: 0.10-0.25/h. Activator range - DMA: 0-0.25/h. Source:Interplastic.

In line with new resins on the horizon, Alpha/Owens Corning has for open-mold fabrication two flame retardant (an epoxy VE and a proprietary GP resin) marketed under the name Firepel. Also available is isophthalic polyester suitable for containing petroleum fuels and a VE engineered for high impact resistance, both meeting the increasingly stringent US fire safety regulations, ASTM-84 flame spread. Adding a

3

Plastics 9 1 51

small percentage of antimony trioxide enables a Class 1 rating to be achieved. New grades of molding compounds have also been introduced for automobile headlamp reflectors, to meet the specification ECE 20.02 for halogen lamps, and also for low smoke to meet transport requirements and the Channel Tunnel NFF 16-101 specification.

Epoxy Vinyl Esters These plastics used in RPs can withstand many of the world's most aggressive chemical environments. Different formulated epoxies permit meeting exceptional corrosion resistance, different performance such as the ability to withstand exothermic stresses that are built up during curing, used in different temperature ranges, low burning rate, and limited oxygen index. High Performance Thermoset Resins

Polyimides The first so-called high-heat-resistant TPs were the PIs, a family of some of the most heat- and fire-resistant plastics known. They are available in both TPs and TSs. Moldings and RPs are generally based on TSs, though some are made from TPs. PIs are available as RP laminates and in various shapes, as molded parts, stock shapes, and plastics in powders and solutions. Porous PI parts are also available. Uses include critical engineering parts in aerospace, automotive and electronics components subject to high heat, and in corrosive environments. Parts include coated glass fabrics. Generally, the compounds that are the most difficult to fabricate are also the ones that have the highest heat resistance. PIs are high performance TSs, notably with very high heat resistance [up to 540C (1000F) for short periods] and good stability at elevated temperatures. However, to obtain this, they have to be molded at about 300C (570F) with post-cure at 400C (750F). They also have good impact, tensile strength and modulus, and dimensional stability, as well as inherent resistance to combustion. Applications include aircraft engine and electrical components, and chip carriers for integrated circuits. These materials have good wear resistance and a low coefficient of friction, both of which are factors that can be further improved by including additives like PTFE. Self-lubricating parts containing graphite powders have flexural strengths above 69 MPa (10,000 psi.) Their electrical properties are also outstanding over wide temperature and humidity ranges. They are unaffected by exposure to dilute acids, aromatic and aliphatic hydrocarbons, esters, alcohols, hydraulic fluids, JP-4 fuel, and kerosene. They are, however, attacked by dilute alkalis and concentrated inorganic acids.

152 Reinforced Plastics Handbook

PIs show good radiation resistance, and retain useful properties after absorbing radiation doses as high as 6.000 megarads. Polyimide laminates curing conditions are 200 psi at 370C for 1 h. Laminates have shown 25% strength retention after 1000 h at 315C. The resins do lose considerable strength in air at service temperatures above 315C. Typical properties include tensile strength, 24,000 psi; modulus, 415,000 psi; elongation, 65%. Polyimide is difficult to process by conventional means. Parts are fabricated by techniques ranging from powder metallurgy methods to modifications of conventional injection, transfer, compression, and extrusion that include ram instead of screw plastication (Chapter 5). Since PIs are essentially nonfusible and difficult to fabricate by conventional shaping processes. As an example DuPont with its Kapton has employed special processes, including a high temperature-pressure procedure similar to that used in powder metallurgy, to fabricate its PI into finished parts (called Vespel). This process is useful for producing parts for low friction, high temperature applications.

Polyimide Powders Special PI powders with" desirable melt flow behavior and properties are formed in reaction vessels, without grinding (NASA Langley Research Center, 1994). Crystalline PIs that have controlled molecular weights can be synthesized in a process that yields the PIs in powder form. They exhibit transparent crystallinity that gives rise to melt flow of a high degree at processing temperatures of about 300 to 350C (572 to 662F) that are slightly above their melt temperatures. They are commercially attractive for processes such as extrusion, injection and compression molding of complex shaped parts, adhesive bonds, and deposition onto reinforcing fibers for subsequent hot pressing into PI-matrix/fiber reinforced plastics.

Polyurethanes Polyurethanes (PU or PUR) and polyureas are classified as TS resins, but their chemistry is so flexible that they can be formulated different ways. There are moldable solid and expanded TSs, with (RPUR) or without reinforcement, flexible and rigid foams, elastomers and thermoplastic molding compounds. As RPs they are important in reinforced reaction injection molding (RRIM) (Chapter 5) and are also available as reinforced thermoplastic molding compounds. A variant on the process employs a structural preform of the reinforcement that is placed in the mold cavity and is called structural reaction injection molding (SRIM).

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9Plastics

PURs are noted for their high impact strength, toughness and excellent resistance to abrasion. They bond well with reinforcements (one of the main applications of PURs is as adhesives) and offer very good resistance to chemicals. These resins are based on the reaction of di-isocyanates with polyols (polyesters or polyethers) which are hydroxy-terminated. A wide range of variants can be produced by adjusting the molecular structure. The resins must be cured under anhydrous conditions and the reaction can be very rapid. For processing, the two components, isocyanate and polyol are separately stored and prepared and then brought together in a mixing/dispensing head from which they are injected into a closed mold. The process is similar to resin injection molding. Other components, such as chopped reinforcement, fillers and other materials can be introduced into the mixing head and the whole compound can then be injected, with a cycle time usually measured in low numbers of minutes. A reasonably high quality of surface finish can be achieved (depending on mold cavity quality) and a form of in-mold coating system can also be employed to achieve Class A finishes. RPURs can also be formulated for use as SMC type materials, foamed panels, and filament winding. The RIM process operates at low pressure, allowing inexpensive materials to be used for molds, and the mixing/ injection head is usually flushed out between injection cycles. Because of the need for accurate dosing, and the speed and sensitivity of the reaction, the process is often controlled by computer. RRIM is used increasingly for medium/large automobile parts, such as external body panels (where the general toughness of the material makes it an interesting candidate for damage-prone panels such as front fenders). In RPs applications, PUR is a TS resin and cannot be directly recycled as a molding material. Scrapped parts can, however, be reground in much the same way as the technologies developed for TS polyester SMCs, and there has been considerable development of chemical recycling processes, by which the P U R is separate into its original base chemicals, for re-formulation as new PUR. Silicones They are based on silicon (as opposed to the usual carbon make-up of plastics). Typical values for structural systems are semi-organic compounds, with chains of alternate silicon and oxygen atoms. They are noted for their excellent long-term heat-resistance, with low water absorption, very good electrical properties and good weatherability

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154 Reinforced Plastics Handbook over a wide range of temperatures. Silicones are used mainly where flame-retardant properties are required, and often form part of a prepreg formulation. They are crosslinked by heating with a catalyst such as cobalt naphthenate, zinc octoate or an amine such as triethanolamine. In the plastics industry, the most common form is as an elastomer formed from liquid components. Rigid silicones can be formulated on polysiloxane resins, giving high thermal stability of over 250C (500F).

Specialty Thermoset Resins There is also a wide range of TS resins for specialty uses.

Alkyds Used both in liquid and molding compound: as liquids, ~alkyds are fatty acid modified polyesters mainly for paints, and as compounds, they are dry polyesters, usually crosslinked with a diallyl phthalate monomer, for electrical applications. They have good moldability, short cure time, and good heat-stable electrical performance up to 250-300F. The form for molding is as granule or putty, and the ~resins, which mold at low pressures, are particularly suitable for molding with delicate complex inserts. Molding compounds usually have mineral fillers and can be reinforced with glass or synthetic fibers~ in.both short and long fiber lengths.

Allyls There are two major allyl plastics, diallyl phthalate (DAP) and diallyl isophthalate (DAIP). Both 0f these are widely used in fiber R P forms. The allyl plastics are usually compression or transfer molded performing well in automated equipment (Chapter 5). They retain their physical and electrical characteristics under prolonged exposure to severe environmental conditions. They have high heat and moisture resistance, excellent electrical performance, good chemical resistance, dimensional stability, and low creep. These plastics are used where they provide environmental resistances. The best known of this group is diallyl phthalate (DAP), a relatively high-priced molding material, with very good dimensional stability and high insulation resistance which is retained at high temperature and after exposure to moisture [150-177C (300-350F)]. A variation, diallyl isophthalate (DAIP), offers a higher heat-resistance [177-230C (350-450F)]. Applications are mainly in electrical and electronics components. Prepreg forms can be used for molding RP parts.

Bismaleimides Bismaleimides are resins with characteristics similar to those of epoxies, but with higher temperature resistance [204-232C (400-450F)]. They

3

9Plastics

are produced by reacting maleic anhydride with a diamine such as methylene diamine. Their main uses are in manufacture of printed circuit boards, heat-resistant coatings, and in RP structures for military aircraft and aerospace applications.

Furanes Furane resins are produced by self-condensation of furfuryl alcohol with furfural. They offer possibly the best chemical resistance of any thermosetting resin in non-oxidizing conditions, and have excellent resistance to solvents. However, they also require acidic catalysts that give a complication in processing. Melamines These resins possess high hardness, good pigmentation potential and good electrical properties. Molding grades are usually filled with alpha cellulose, but glass reinforced compounds are available for certain electrical applications. Melamines are used mainly for high-pressure molding, as the surface skin of decorative and industrial laminates, exhibiting good hardness, strong arc and abrasion resistance but only fair dimensional stability. The main applications are house wares and tableware, and some electrical components. Polyetheramides PEAR is a TS originally discovered by Ashland Chemical. It has 50% higher modulus and tensile strength than epoxy and five times the toughness. It has better thermo-oxidative stability than bismaleimide (BMI) and samples have shown no weight-loss after 3800 h testing at about 176C. The resin has good adhesion to glass and carbon fibers and shows a lower coefficient of thermal expansion than epoxies and most plastics. As a matrix resin in a carbon composite, PEAR is said to surpass epoxy (Hercules/Hexcel 3501-6) by 48% in tensile, compression, hot/wet, compression-after-impact, and other fiber-dominated properties. Shear strength (matrix-dominated property) is reported at 50% higher than epoxy at room temperature and up to 80% higher under hot-wet conditions. Flammability and smoke release are low, about 45% and 25% lower, respectively, than epoxy. PEAR could be a credible competitor to phenolics, also being easier to process and giving superior mechanical properties. The resin does not release volatiles during curing (giving few problems with voids) and the exotherm is five to six times lower than conventional two-part epoxy systems (allowing thicker parts to be fabricated). This, with low viscosity, also makes it suitable for molding by resin transfer (RTM). Generally, components can be molded by

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processes similar to those used for epoxy, with much the same cure cycle. PETI-5

Phenyl-ethynyl terminated imide, fifth formulation is a high temperature resin developed by NASA's Langley Research Center for the next generation of high-speed civil transport (HSCT) aircraft. Selected for the advanced airframe of the proposed Mach 2.4 aircraft that would require plastic matrices to be able to withstand temperatures of up to about 177C for 60,000 flying hours, over an aircraft life span of 25 years. It can be used to within 50C of its glass transition point Tg of 270C and is up to 30 times tougher than standard epoxies. Resistance to microcracking is good, with little degradation from thermal cycling. A sample PETI/carbon RP survived the 'open hole' compression test (which is a particularly hard test to assess damage tolerance). Processing requires autoclave curing at 370C and 1400 kPa, which is costly and difficult, but further development and volume production are expected to reduce costs. Four companies are licensed to use the technology: Culver City Composites, Cytec Engineering Materials, Fiberite, and Imitec. P M R - 15

PMR-15 is a polyimide resin containing methylene dianiline (MDA), which is difficult to process. It is the accepted baseline matrix resin for high temperature (320C) applications in jet engines. A solventless resin, with similar thermal and mechanical performance, but containing no known carcinogenic or mutagenic compounds, has been developed by Foster Miller Inc. It is a modified version of the NASA-Lewis AMB-21 resin system, but with improved glass transition temperature (344C) and thermo-oxidative stability. Where the traditional high temperature polyimides such as PMR-15 and AMB-21 typically have minimum viscosities of around 2000 cPs at temperatures up to 210C, the Foster Miller resin has a viscosity of about 300 cPs at 110-150C, with good pot life. It can be processed by RTM, and flat panels have been molded by conventional techniques without the use of solvents. Foster Miller has linked with Cyclopss Corporation, Salt Lake City, USA to commercialize the system and a joint company, Pyrogonn LLC, will control the process patents and work to extend the system into new markets. H y b r i d Resins

With growing understanding of the chemistry and a wider choice of components, manufacturers are increasingly introducing hybrid resins (made of two or more polymer components). The most common

3 . Plastics 157

hybrid is a polyester/polyurethane two-component system. The A component comprises isocyanates and additives and the B component is a low molecular weight unsaturated polyester with additives. The isocyanate reacts with a polyol to develop a very high molecular weight linear polymer; a monomer such as styrene reacts with the unsaturated portion of the polyol to add strength and stiffness, creating a crosslinked network. VE polyurethane resins have mechanical properties similar or superior to those of conventional VE and epoxies. Characteristics include a heat distortion temperature of 120C (248F). Ultimate elongation of an unreinforced molding compound without fillers is 5.5%; tensile strength is 80 MPa and flexural strength 150 MPa. The resins can be custom-formulated. Applications include customized automobile parts, recreational vehicles, outdoor equipment, tubs/showers and electrical parts. The resins are suitable for standard molding processes: some were specifically developed for pultrusion, RIM, foam, adhesive, and polymer concrete applications. Crosslinked Plastics

Certain TPs can readily be converted to TSs providing improved a n d / o r different properties. Crosslinking is an irreversible change that goes through a chemical reaction. Cure is usually accomplished by the addition of curing (crosslinldng) agents with or without heat and pressure. Crosslinking improves resistance to thermal degradation of physical properties and improves resistance to cracking effects by liquids and other harsh environments, as well as resistance to creep and cold flow, among other effects. Prime interest has been with aliphatic polymers such as the olefins that include the polyethylenes and polypropylenes; also popular are polyvinyl chloride. The crosslinked PE, identified as XLPE or PEX, is recognized as a standard within the industry. Use includes electrical cable coverings, cellular materials (foams), rotationally molded articles, and piping. High-intensity radiation from electron beams or UV (ultraviolet) sources has been used to initiate polymerization in TS systems of oligomers capped with reactive methacrylate (acrylic) groups or isocyanates. Using this crosslinking polymerization technique, films with low shrinkage and high adhesion properties have been used in such applications as pressure-sensitive adhesives, glass coatings, and dental enamels.

158 Reinforced Plastics Handbook

Natural Resins Development of resins based on naturally occurring products, such as agricultural products, is being actively pursued by a number of organizations throughout the world, in response to ecological demands and as a further outlet for surplus agricultural produce. A parallel development approach seeks to meet a perceived need for polymeric materials that are genuinely biodegradable (usually in compost, in the presence of moisture, over a period of several months). The latter is aimed at TP compounds, with properties similar to PE or PP, for applications in agriculture/horticulture and (possibly) packaging. On present evidence, these biodegradable materials do not appear to have much that is relevant to RPs. However, there has been some interesting work in the USA on soybean, as a potential source of TS binder resins. These resins are being developed by the United Soybean Board, St Louis, Missouri, USA, under the name Proteinol. They are made from various waste cellulosic fibers tightly bound with various soy protein/phenolic binder systems. Fillers can be agricultural crop wastes such as wheat straw, corn, bagasse, kenaf, or hemp, forest waste products such as wood fibers, shavings, sawdust or chips, and shredded newsprint, de-inked office paper, and other recycled products. Extruded and compression molded shapes are being produced, which can be nailed, drilled, sawn, routed, sanded, painted and stained.

Compounding and Alloying Practically all plastics are compounded with other products (additives, fillers, reinforcements, etc.) to provide many different properties a n d / or processing capabilities. It includes mechanical mixing/blending. They do not normally depend on chemical bonds, but do often require special compatibilizers. Mechanical compounding is extensively used worldwide. Using a post-reactor technique, plastics can be compounded by alloying or blending polymers in addition to using additives such as colorants, flame-retardants, plasticizers, biocides, heat or light stabilizers, lubricants, fillers, reinforcements, and/or many more. With combinations of two or more polymers synergistic property improvements beyond those that are purely additive in effect develop. Among the techniques used to combine dissimilar polymers are crosslinking to form what are called interpenetrating networks (IPNs), grafting to improve the compatibility

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Plastics 9 159

of the plastics, and reactive polymerization where molecular structure changes occur. Surface Waviness/Low Shrink Profile

Refers to low profile RP surfaces. These are special TS polyester compounds for RPs that are combinations of thermoset and thermoplastic materials. Although the term low profile and low-shrink are sometimes used interchangeably, there is a difference. Low-shrink contain up to 30wt% TP, while low-profile contain from 30-50wt% TP. Low-shrink offers minimum surface waviness on molded parts, as low as 25 lum (1 mil) per in mold shrinkage; whereas low-profile offers no surface waviness of 0-12.7 lum (0-0.5 in) per in mold shrinkage. Concentrates

Available are concentrates of high strength reinforcement encapsulating glass fiber in a resin by conventional fabricating techniques. In Japan there is development of concentrates produced in the polymerization reactor producing polymers and is being tested by automotive manufacturers. The reinforcing concentrate is 80 wt% milled glass fiber in a styrene acrylonitrile (SAN) carrier. The concentrate is introduced directly into the polymerization reactor and the polymer matrix is thus literally polymerized around the fibers, as opposed to incorporation at a later compounding stage using conventional compounding technique. Fiber integrity and matrix/fiber adhesion are both higher, while the health hazards of handling loose glass fibers are also alleviated. According to reports, in an ABS polymer, the reinforcement produces 35% higher flexural strength, 47% higher tensile strength, and 50% higher notched Izod impact strength than reinforced compounds produced by conventional compounding methods. Leading Japanese car manufacturers are said to be using instrument panel substrates containing the concentrate, and it has also been used in USA made cars, where the SAN concentrate was let down in styrene maleic anhydride (SMA) resin to a 20% glass level. It is reported that the concentrate can be used in production of ABS and other engineering resins such as polyamides, polycarbonates and polyesters. Fillers

Fillers also called extenders are used in large quantities to provide some degree of improvements in properties. Properties include strength and stiffness of RPs. Fillers added to plastics alters the properties through

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physical rather than chemical means; they are inert. They include alumina (aluminum oxide), calcium carbonate, dolomite [a double carbonate of lime and magnesia filler having the formula (CaCO3) (MgCO3)], calcium silicate, cellulose flock, cotton (different forms), short glass fiber, glass beads, glass microspheres (solid or hollow), plastic microspheres (solid, hollow with or without encapsulated gas), graphite, iron oxide powder, mica, quartz, sisal, silicon carbide, titanium oxide, and tungsten carbide (Tables 3.21 and 3.22). A few of these fillers are reviewed in Chapter 2. Choice of filler varies and depends largely upon the requirements of the end item, type of material in the RP, and/or method of fabrication. Table 3.21 Thermosets Alkyds Diallyl phthalate Epoxy Phenolic Polyester Melamine Urea Silicone Urethane

Table 3.22

Example of fillers used in thermoset reinforced plastics

Calcium Carbon Cotton Glass Glass Alumina carbonate black Clay flock bubbles fibers Graphite Mica Quartz Talc X X X X

X X

X X X X X

X

X X X X

X X X X X

X

X X X

X

X X X X

X X X

X X X X X X X X

X X X X

X X X

X

X

X

X

X X

X X

Effect of reinforcements and fillers on thermoplastics

Reinforcements Amorphous + Can more than double tensile strength + Can increase flexural modulus four-fold + Raise HDTa slightly + Toughen brittle resins; embrittle tough resins + Can provide 1000 cm resistivity + Reduceshrinkage - Reduce melt flow Raisecost -

Fillers + +

Lower tensile strength Can more than double flexural modulus RaiseHDTa slightly embrittle resins + Can impart special properties, eg, lubricity, conductivity, flame retardance + Reduceand balance shrinkage - Reducemelt flow + Can lower cost -

Crystalline + Can more than triple tensile strength + Can increase flexural modulus seven-fold + Can nearly triple HDTa + Toughen brittle resins; embrittle tough resins + Can provide 1 s resistivity + Reduceshrinkage Causedistortion - Reducemelt flow Raisecost -

-

a Heat-deflectiontemperature

+ +

Lower tensile strength Can more than triple flexural modulus RaiseHDTa slightly embrittle resins + Can impart special properties, eg, lubricity, conductivity, magnetic properties, flame retardance + Reduceshrinkage Reducedistortion - Reducemelt flow + Can lower cost

-

-

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9Plastics 1 61

In addition to strength and stiffness, fillers offer a variety of other benefits. They include reduced cost, shrinkage reduction, exothermic heat reduction, thermal expansion coefficient reduction, improved heat resistance, slightly improved heat conductivity, improved surface appearance, reduced porosity, improved wet strength, reduced crazing, improved fabrication mobility, increased viscosity, improved abrasion resistance, hardness, and/or impact strength. Fillers also can have disadvantages. They may limit the method of fabrication, inhibit cure of certain plastics, and shorten pot life of the plastics. The particles are usually small, in contrast to those of reinforcements.

Filler vs. Unfilled Compound Cost~Property Fillers use includes reducing the cost of materials of construction. Simply adding filler to a plastic does not automatically assure savings. The density and cost of both the filler and plastic play an important role in determining the savings compared to unfilled. As an example, by adding 30 wt% of mineral filler like talc to medium-impact polystyrene [specific gravity (s.g.) 2.5 to 3.1] reduces the amount of plastic by only 15%. However, if low density filler like wood flour [specific gravity (S.G.0 0.5; other types range from 0.2 to 1.5) is used in the same weight percentage, the S.G. of a part is reduced to 0.79. Plastic content saving of 47 wt% occurs compared to unfilled material.

High Loading An example of the performance of special additives are titanate coupling agents. They permit high filler loadings, significantly reduce viscosity, and can be used with many mineral types of filler to improve flow and various mechanical properties. Wide use in applications with calcium carbonate fillers, where silanes alone are not applicable. They serve as molecular bridges between inorganic fillers and organic plastics. The reaction with the free protons at the inorganic interface results in monomolecular layers of organo-functionality joining the organic and inorganic elements together. Additives

Overview An additive is a substance compounded into a plastic to modify its characteristics. They are physically dispersed in a plastic matrix without affecting significantly the molecular structure of the plastic. In thermoset plastic additives such as crosslinking, catalyst, and other agents do purposely affect their structure. Additives are normally classified according to their specific functions rather than a chemical basis. While some additives have broad applications and are adaptable to many TPs

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and TS plastics, others are used exclusively with specific plastics. Of all the additives used, the highest-volume additives used are modifiers followed with property extenders and processing aids. The pace of developments in additives continues unabated. Unfortunately, there is no one ideal additive since each of the infinite number of end uses will call for a particular set of characteristic, including diverging properties. Recognize that, like a sea-saw, improvements in one property can lead to deterioration in others. In addition, the effectiveness of compounding additives depends also on the correct procedure of incorporation into the plastic matrix. The compatibility and diffusibility of additives is normally assessed from experience or by trial and error. The basic theories and knowledge of solution thermodynamics may be used to determine potential compatibility. The theories of their behaviors do exist so that they can be used in the preliminary concepts to meet specific performances. Examples of classifications are: assist processing (processing stabilizers, processing aids and flow promoters, internal and/or external lubricants, thixotropic agents); modify the bulk mechanical properties (plasticizers or flexibilizers, reinforcing agents, toughening agents); 3

reduce formulation costs (diluents and extenders, particle fillers); surface properties modifiers (antistatic agents, slip additives, antiwear additives, anti-block additives, adhesion promoters);

5

optical properties modifiers (pigments and dyes, nucleating agents);

6

anti-aging additives (anti-oxidants, UV stabilizers, fungicides); and

7

others (blowing agents, flame retardants).

Examples of only a few additives are reviewed:

Ultraviolet Stabilizers RP structures that are placed outdoors may experience surface chalking and/or discoloration. This chalking and/or discoloration is a surface phenomenon only and should not be detrimental to properly fabricated products. As example TS polyesters are inherently more ultraviolet (UV) stable than vinyl ester resins and the addition of UV stabilizers to the outermost resin layer may reduce UV degradation. Thixotropes Commonly called fumed silicas, they are used to thicken resin and reduce drainage. Resins with these additives are used in hand lay-up and spray-up applications on vertical surfaces.

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9Plastics

Polyester resins can be purchased with fumed silica already in, the resin and fumed silica can be added to vinyl esters by the customer. To insure uniform dispersion, fumed silica should be thoroughly mixed into the resin using a high shear dissolver or equivalent.

Antimony Oxides Certain plastics such as cured TS polyester and vinyl ester resins will burn if provided with a sufficient amount of heat and oxygen. However, certain resins are flame retardant due to the addition of halogens that improve the flame-retardant properties over non-halogenated resins. With most flame-retardant resins, adding antimony trioxide or antimony pentoxide can increase the degree of flame retardancy of the resin. Antimony acts as a synergist and reacts with the halogen to greatly improve the resin's flame retardant properties. The addition of antimony to nonhalogenated resins does not make the resin flame retardant, but instead acts only as filler. (The literature available on flammability characteristics, test procedures, ratings, and additives is extensive.) Alumina Trihydrates Alumina trihydrate is used to improve flame retardancy and reduce smoke emissions of specific resin systems. It is a fine, white filler material which, when added in the proper amount, can improve flame retardancy of halogenated or nonhalogenated resin systems. When a properly filled RP is exposed to fire, it decomposes into water and anhydrous alumina. The water cools the RP thus slowing the rate of decomposition or burning.

Antimony Trioxides vs. Antimony Oxides Alumina trihydrate differs from antimony trioxide. As an example, antimony trioxide is effective only with halogenated resin systems and is used in small percentages. Alumina trihydrate can be effective with both halogenated and non-halogenated resin systems but much higher filler loadings are required to achieve the desired flame retardance. Consequently, alumina trihydrate can not be used directly in place of antimony trioxide. The addition of high levels of alumina trihydrate can produce a higher viscosity system and reduce the physical properties of the RP.

Types and Functions A wide variety of additives is used with both TS and TP to adjust the handling and processing properties, achieve a specific property, or, simply, to add bulk and reduce cost without impairing the properties of the resin. Cost-reduction is not always the end-result. Apart from reinforcement (see Chapter 2), additives for both TS and TP are generally in the form of particles or liquids, or combinations of the two. Generally, the particles influence the mechanical properties, while the

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liquids are reactant components. Colorants can take the form of powders, pastes or liquids. For particulate additives, the term filler is still widely used (reflecting the original and continuing need to add bulk to the mix to reduce the cost). An important aspect of the development of even low-cost additive fillers, however, is surface treatment of particles to aid bonding to the matrix and offer positive mechanical advantages as well as sheer bulk. Once an additive has been selected, other factors must also be considered. Within each family, there are types and grades that impart differing properties due to variations in coarseness, impurity level, and method of preparation. The chemistry of additives is often extremely complex and the choice of materials can be bewildering to anyone but a specialist. Nevertheless, it is important for designers, engineers, and processors to have some overall familiarity with additives and their technology. Storage and handling of some of additives also calls for great care, as some of the materials are classified as fire a n d / o r explosion hazards and can also be hazardous to the health of people working with them. The mix ratios need to be accurate, to obtain optimum properties (and to keep down costs). Originally (inheriting the practice from the rubber industry a century ago), the plastics processing sector has purchased resins and additives separately and mixed its own compounds. However, the growing sophistication of compounds (especially reinforced materials), together with the need for special investment in separate handling of additives and market demand for reproducible performance, have created a specialist industry sector that is devoted to the production of compounds. This has occurred mainly in TPs but the use of ready-made compounds is growing rapidly in TSs. With RTPs, the technical difficulty of mixing the plastic matrix with reinforcement such as glass fiber has made it standard practice for materials suppliers to offer a reinforced molding compound that is ready formulated with all the necessary ingredients, with the possible exception of pigment. A ready-made RTP in sheet form is also available, known as glass mat thermoplastic (GMT). Only in the case of PVC, and for some other large-volume production, is it normal now for the processor to carry out any significant amount of in-plant mixing of TP compounds. However, with color concentrates and compact, clean, and reliable metering/dosing systems that are mounted on the molding machine itself, there is a growing tendency for TP processors to return to in-plant coloring, holding stocks of

3

9Plastics

natural-color material, and coloring as required, so saving on inventory costs.

With RTSs, however, where the resin is liquid and requires curing, inhouse mixing is the norm, especially in the hand and spray lay-up sector, and in many press-molding and resin transfer molding operations. Resin suppliers now offer resins formulated and possibly pigmented to meet a set specification, but it still requires the processor to add the reinforcement and initiate the curing reaction. In larger-volume production there has been a marked trend in recent years to put on the market pre-combined systems, of resin, additives and reinforcement, which simply require forming to shape and initiating the cure (usually by compression or injection molding). These compounds are known as preimpregnated materials (prepregs) and may be in various forms, according to the type of molding required. The most commonly-used are compounds in a bulk form [bulk molding compound (BMC)] and in sheet form [sheet molding compound (SMC) ]. There are many variations within each group (Chapter 4).

Incorporating Additives The amount of additive by weight that can be incorporated in a resin depends on the particle size, density, and oil absorption properties. The viscosity is often directly influenced by additive content. Porous high oil absorption fillers (such as diatomaceous silicas) and chopped glass can greatly increase the viscosity of a resin system at low loadings of only 1-50 phr (parts per hundred). Medium-weight granular fillers, such as powdered aluminum and alumina, may be used at loadings of up to 200 phr. The non-porous lower oil absorption fillers, such as aluminum oxide, silica and calcium carbonates, can be incorporated at levels of 700-800 phr without making the formulation unworkable. Loadings can be increased by adding a diluent, but this may not always be desirable, as the diluent may detract from other desired properties. Organo titanates can be added to improve filler wetting, enabling higher loadings at the same viscosity. Fine particles are easier to incorporate and there are fewer tendencies for them to settle. Coarse and heavy fillers will settle and cake on standing, but this may be countered by adding lightweight fillers such as the colloidal silica compounds.

Properties Influenced by Additives In addition to what has been reviewed a summation is presented. All fillers will increase the viscosity of resins; most fillers also influence the gel time. Gelation is normally retarded, but alumina and some types of china clay have the reverse effect. It is difficult to predict the precise

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166 Reinforced Plastics Handbook

effect on gel time of particular filler and this should be determined by trial and error in each case. Fillers also reduce the volumetric shrinkage of resins when curing, as well as peak exothermic temperature and are therefore sometimes used in castings. They may also be used to make the resin thixotropic, for contact molding on vertical or inclined surfaces. Powdered mineral fillers tend to increase compressive strength, hardness and modulus of the compound. However, when used in large amounts, there is a considerable reduction in bending strength. Fibrous fillers are used to increase tensile and impact strength. Surface properties of moldings can be improved by use of a suitable powdered mineral in the gelcoat only. Powdered quartz or zircon in the gelcoat can improve hardness and abrasion resistance. Properties that may be selectively altered by use of fillers include: 9 pot life and exotherm" pot life can be increased and exotherm reduced, because fillers reduce the concentration of reactants and function as better heat conductors than the resin matrix. Commonlyused fillers for this arc silica, calcium carbonate, alumina, lithium aluminum silicate and powdered metals 9 stability (thermal): the properties of many polymers (especially thermoplastics) are strongly influenced by exposure to heat, not only during service life but also during proccssing, when overheating can cause deterioration or failure to build up the designed strength. On the other hand, it is sometimes desirable to process at a higher temperature, to permit the use of specific polymers and other additive systems. Stabilizing additives are used to improve the proccssability of the compound and enlarge the processing window. They also can be employed to increase the heat-stability of the product. Heat stabilizers usually act by countering or absorbing the products of oxidation of the polymer, caused by heat 9 stability (ultra-violet/sunlight): exposure to ultra-violet light is a well-known cause of oxidation of many polymer systems, both TS and TP, leading to loss of mechanical properties and deterioration in appearance. This has obvious implications for outdoor applications. Stabilizers can be added to counteract this effect, either by screening out harmful radiation, or by absorbing or converting the by-products of oxidation. Pigments can also playa useful role, and there is considerable scope in balancing a pigment and stabilizer to achieve the best results 9 thermal shock resistance: part of the resin can be replaced with a material which does not change significantly with variation of

3 . Plastics 167

temperature, with the result that resistance to thermal shock is increased and coefficient of thermal expansion is reduced. Typical such fillers are clay, alumina, wood flour, sawdust and mica. When bonding with metals, powdered metals in the resin mix will help to bring the thermal expansion closer to that of the metals, so reducing differential stress mechanical strength: tensile, flexural, impact and compressive strength: mechanical properties such as tensile and flexural strength are mainly affected by reinforcements but the addition of these materials (especially glass fiber) may also create a more brittle compound (as with reinforced polyamides), and an elastomeric modifier may often be added to counter this tendency. Elastomeric additives are also widely used to improve impact strength, especially at sub-zero temperatures. Mineral fillers can improve compressive strength (Table 3.23). Table 3,23 Effect of fillers on nylon 6/6 RPs

Glass fiber, by weight Mineral filler (kaolin) Glass spheres

40 0 0

25 15 0

0 40 0

0 0 40

Specific gravity Tensile strength MPa (Kpsi) Flex modulus GPa (Kpsi) Izod impact, notched (6.4 mm) Jim (ft-lb/in. 3) Relative cost by volume

1.46 214 (31) 11.0 (1600) 139 (2.6) 1.00

1.47 138 (20) 10.0 (1450) 43 (0.8) 0.98

1.49 103 (15) 6.6 (950) 43 (0.8) 0.85

1.44 97 (14) 5.2 (750) 53 (1.0) 0.92

Source: LNPEngineeringPlastics,Inc.

flame retardancy: this is a key growth area for additives, as reinforced plastics are increasingly employed in sensitive applications, such as building and construction, automobile and public transport, aircraft and electrical electronic products, where there is some risk of fire or smoldering. A number of chemical compounds have been used and are being developed for use in plastics compounds, to prevent or retard ignition, or to reduce the spread of flame. An important aspect is also the reduction or elimination of by-products of combustion, particularly dangerous or unpleasant fumes, and smoke. In the past, halogenated (especially chlorinated)

168 Reinforced Plastics Handbook

compounds have proved effective as flame-retardants, but these tend to release by-products and are being phased out. Nonhalogenated compounds, phosphorus and other compounds are widely used, and there is growing understanding and use of compounds which have synergistic actions on each other electrical conductivity, arc or tracking resistance: most plastics are inherently electrical insulators but, in some applications, it may be necessary to make them conductive to a greater or lesser degree. At the lowest, it is to reduce the poor ability of plastics to dissipate charges of static electricity. This may be useful to eliminate dustattraction in food-contact applications, or to eliminate the risk of sparks in medical and hazardous industrial applications. At the highest, it is possible to produce low-wattage plastics heating elements, such as aircraft deicing strips and industrial process heaters. Static can be reduced by adding lubricants and additives materials that bloom to the surface after molding. Conductivity can also be improved by adding materials such as carbon black, carbon fibers, steel fibers, aluminum platelets, glass flakes coated with nickel, mica coated with nickel, and fine whiskers of metals. The effect of such additives on the other physical characteristics of the product must also be taken into account self-lubricating properties: additives such as graphite, molybdenum disulphide and fluoropolymer compounds are widely used as lubricants, to reduce friction in moving parts such as gearwheels and slide/slip bearing surfaces. Waxes are also used as lubricants, to improve the flow of the molding compound, but especially to migrate to the surface of a molding compound, to act as a release agent shrinkage: Any filler will decrease shrinkage: the most commonlyused fillers are silica, clay, calcium carbonate, alumina talc, powdered metals and lithium aluminum silicate. Low-shrink or lowprofile additives are used in TS systems such as sheet and BMCs to minimize shrinkage during and after molding, and improve the surface appearance of a molding machinability and abrasion resistance: These additives make the system harder and more easily cut or machined. Typical fillers for this include powdered metals, wood flour, calcium carbonate, sawdust, clay and talc. Resistance to abrasion may be improved by the addition of elastomers or polyurethanes.

Selection of Additives When selecting an additive, it is important to take into account also the potential side-effects it may have on other properties. In most cases, the

3

9Plastics

pot life and exotherm of the resin system will be reduced by addition of fillers, because they reduce the concentration of reactants and act as better heat conductors than the resin. In some cases, the cost of the system will be reduced (but at a potential penalty in other directions), and mechanical properties are sensitive to addition of other materials (Table 3.24). Proprietary additives are used. As an example, using a proprietary additive change to its material formulation, Trex Co.'s new deck board product has enhanced mold and mildew resistant properties,. The extruder company also introduced several other products at the builders trade show (2004 International Builders' Show in Las Vegas, NV) including Accents, a line of wood composite deck and railing products with a wood-grain texture offered in deep tan, grey, and reddish brown colors. Its traditional deck boards, with a smoother surface, will be marketed as Origins. On the railing side of its business, the company is marketing a system known as Trex Express intended to encourage more contractors to offer decking matching railings. The system includes an extruded PVC jig with spacers that facilitate the set up the rail system. Using the tool, contractors can install railing at 5-6 minutes per 6-foot section, including bracket alignment, baluster spacing, and post and baluster leveling. The tool also includes a hole locator for different joist sizes (National Assoc. Home Builders, 1201 15th St., NW, Washington, DC 20005-2800; telephone: 201-266-8181; e-mail: [email protected]).

Current Lines of Development A main line of development continuing today is multifunctional additives, such as fillers, which are treated to provide also a degree of reinforcement. For example, calcium carbonate improves surface gloss of PVC, talc is added to PP to improve stiffness and heat stability. An essential aspect is the compatibility with the resin matrix and there is intense development of surface-modification technology, to render fillers of all types more acceptable to the matrix. A major line of development is to meet increasingly strict regulations for health and safety, both in the workplace and in public use. This particularly affects flame retardant additives (where concern has been expressed about possible escape of flame-retardant components during storage, under heat and flame and in recycling) and pigments (where legislation has centered on use of heavy metals in pigment formulations, possibly creating hazards in disposal of the product).

169

o I'D .--,

Table 3.24 Typical effect of additives on properties

Desired effect

Improvement in: Thermal conductivity

Additive type

Cost reduction Exotherm Thermal conductivity Heat deflection temperature Machinability Abrasion resistance Impact strength Tensile strength Flexural strength Compressive strength Dielectric constant Thixotropy

"1

Calcium carbonate calcium silicate powdered aluminum or copper

Machinability Alumina flint powder carborundum silica molybdenum

Abrasion resistance

Impact strength

Electrical conductivity

Thixotropic response

Chopped glass

Mica silica powdered or flaked glass

Metallic fillers or alumina

Colloidal silica Bentonite clay

disulphide +

+

+

+

+

+

+

+

+

+

+

K e y - D e c r e a s e + increase; = essentially no effect.

+

+ +

+

+

+

+ + + + +

+

+

+

+ +

Ill IJl

-T" oo o

3

9Plastics 1 7 1

Recycling Overview

From latest work, it is clear that all types of plastics can be recycled to some extent, by some process. It is equally clear, however, that no one method gives a universal answer, and a sensible recycling policy (for any material) will probably involve different approaches. This leads on to a general policy regarding use of materials, where there is growing support for a cascade philosophy, in which materials have a high-grade first use, followed (possibly) by a lower-grade second use, after which they may be disposed of by safe incineration with recovery of energy, thus giving a three-fold benefit. Overall incineration with recovery of energy as well as aiding incineration of non-plastic materials. With RPs, which is necessarily linked with products with medium or long-term service life, from automobiles and appliances to building and structural engineering, the turn-round may extend over many years, but is equally valid, in the final analysis. Analysis is the key word. It is important in any planning of a product and providing for recycling it, to use as a basis a life-cycle analysis, covering the impact on the environment of everything, from production of the raw material and processing/fabrication, through the useful lifetime of the product and on to the method of recovery or disposal. Governments worldwide are generating information for such a database, which will greatly assist designers and manufacturers, in setting a policy for product development and materials utilization. They include fabricating scrap, pre-consumer, and post-consumer plastics. In North America about 51/4 billion pounds are recycled with total recycling capacity at 71/8 billion pounds of all plastics (flexible, soft, or hard plastics; unreinforced to reinforced; and so on). Different systems are used for different materials and products based on type of plastic matrix, thickness, degree of hardness, etc. They include mechanical granulators, hammer mills, energy recovery systems (energy thermal reclamations), chemical recycling systems, and others. Granulators are predominantly used. There are different sizes and types of granulators used that process thin to thick RPs. If large and thick RPs is to be granulated, two or more granulators are used to gradually reduce their size so that the minimum damage will occur to the fibers and ensure that overheating is minimized particularly with RTPs. A cascading action occurs by granulating the thick scrap and next granulator further reduces the output from the first granulator.

172 Reinforced Plastics Handbook

When granulating RTPs or RTSs, their fiber lengths are reduced. This fiber reduction will reduce property performance (Tables 3.25-327). The reduction is related to original lengths, degree of uniformity in cut lengths, type of resin, etc. Processability of all the recycled materials (TPs, RTPs, TSs, or RTSs) will also be influenced and that can affect quality control. The actual amount of negative influence on processing the recycled material depends on the method of granulation (such as overheating particularly TPs during the cutting action, amount (if any) of microscopic metal from the cutting metal blades, and size as well as shape of granulated material (such as fine to coarse, powdered to shredded, with or without fuzz, degree of uniformity, etc. )/target for uniformity. These influences are also applicable with the virgin liquid compounded or solid materials that affect the processability during fabrication of the RP by the different processes. Properties are also influenced by the degree of mixing/compounding as shown in Figure 3.4. Table 3.25 Propertiesof recycled glass reinforced phenolic

40% resin + 60o/0regrind

50o/0resin + 500/oregrind

1.45 245

1.43 263

1.40 273

1.61 230

100 2.05 7.8

102 1.98 8.6

83 2.03 6.0

110 3.60 8.0

Density (g/cm 3) Compressive strength (MPa) Flexural strength (MPa) Notched izod (Id/m 2) Unnotched izod (kJ/m2)

600/0resin + Typicalproperties 40% regrind of virgin material

Table 3.26 Propertiesof increased glass content recycled reinforced polypropylene resin

Tensile Sample Control (300/0 glass) Recycled (300/0 glass) + 2.5% glass + 5.0% glass + 7.5% glass + 10.0% glass

Flexural

Stress Modulus Elongation Stress Modulus (MPa) (MPa) (O/o) (MPa) (MPa)

IZOD impact Notched Unnotched (J/M) (J/M)

76.5

6405

2.31

121.7

7239

101

400

62.5

5798

2.45

97.6

4888

73

314

67.2 70.3 73.8 75.8

6260 6964 7377 8067

2.36 2.13 2.08 1.87

101.5 108.8 112.2 117.4

5460 6101 6722 8169

81 82 85 83

317 302 305 281

3-Plastics 173 Table 3.27 Propertiesof recycled30 wtO/oglass/polypropylenerepeatedlymolded Tensile Sample

Flexural

IZODimpact

Stress Modulus Elongation Stress Modulus Notched Unnotched Glasslength (MPa) (MPa) (%) (MPa) (MPa) (J/m) (j/m) (microns)

Control Recycled

80.0 69.6

6688 6329

2.19 2.28

126.6 108.4

7562 6749

103 80

421 321

361 329

Recycled

63.5

6026

2.29

100.0

6308

74

292

305

Recycled

55.9

5461

2.47

89.8

5557

64

253

280

Recycled

52.0

5261

2.50

86.1

5288

60

241

271

lx

2x

3x

4x

1

MachineWear

~

k

._=

io O.

~'~-/O Dry blend i

e"

Increasedmixing-- Mechanicalwork

Figure 3,4 The better the compoundingthe better the performanceof RPs

When RPs is granulated, its processability and performance when rcprocessed into any product is insignificantly or significantly reduced. Thus, it is important to evaluate what the properties of the recycled material provide. The size reduction and uniformity exerts a substantial influence on the quality of the recycled RPs. When recycled RPs is nonuniform in size and is processed with or without virgin plastics, it is subject to operating in a larger fabricating process window (Chapter 5). Figure 3.5 shows how regrind levels (wt%) with virgin plastic mix effect the mechanical properties of certain formulations of injection molded plastics after the first and a number of times recycled, respectively. Since scrap can be a mixture ranging from fine dust to large irregular chunks of different shapes, thicknesses, etc., it is important to use a granulator that provides the most uniformity and the least heat and mechanical damage to the scrap. Material having this range of size when granulating will influence product performances where critical requirements exist. The material influences the processing characteristics that in turn affect the product's performances and costs.

174 Reinforced Plastics Handbook

10o

i

95-1

I .C

'

,

~

"~

m,. 0 e-

85 --] 80 ....

"l"

lie Sire

I

60

._= lg

u~

"6-6 (U U

C

100

fll

95

25

90

40

r

E

85 8O

1st

2rid

3rd

6O 4th

Numberof timesmolded

Figure 3.5

Examples of the effect of recycling RPs more than once through a granulator where the mix of virgin RP is with wtO/oof regrind

As reviewed overheating is a cause of damage particularly with RTPs during the cutting action of the granulator. For heat sensitive RTPs to eliminate any heat damage cryogenic granulating is used. A granulator that handles soft plastics will not work well when granulating hard plastic. One that handles thin plastic is not the proper type to handle thick plastics size and shape. There are different approaches to eliminate overheating, particularly when granulating heat sensitive RTPs. One method is to expose the scrap to cryogenic temperature. The low temperature freezing action on plastics can keep them from overheating during granulating. It can also aid to separate plastics or different materials, etc. Cryogenic cleaning uses liquid nitrogen a t - 2 0 0 F (-93C) to freeze material, which is hurled by high-speed vanes against a steel impact plate. This action pulverizes any unwanted frozen material such as glue a n d / o r releases labels. When required metal detectors, aspirators, hot water float/sink tanks, etc. are used.

Analyzing Materials If possible the goal is to significantly reduce or eliminate any trim, scrap, rejected products, etc. in an industrial plant because it has already cost money and time to go through a fabricating process. Recycled scrap handling and granulating just adds more money and time. Also it usually requires resetting the process to handle it alone (or in most

3 . Plastics 175

cases even when blending with virgin material and/or additives) because it usually does not have uniform particle sizes, shapes, and melt flow characteristics because it was overheated during the cutting action of a granulator, etc. Keeping the scrap before/after granulating clean is an important requirement. Methods used for handling mixed material parts include: selective collection of parts (selective picking by IR spectroscopic identification, light optical identification, geometrical identification by hand), separation of granulates and ground stock (floating-settling trough or separating column, liquid cyclone, wind sifting, floatation, electrostatic separation, extraction, melt separation), degradation (pyrolysis, reduced oxygen incineration, hydrolysis, methanalysis, glycolysis, hydrogenation), material recycling inconsistent with plastics characteristics (building and construction aggregates, soil improving additives), processing in a mixed phase (physical compatibility improved, cross-linking, fine dispersion), and energy recycling (refuse and waste incineration, energy recycling of the pyrolysis products). When required different approaches are used to improve performances or properties of mixed plastics such as: additives, fillers, and/or reinforcements (use specific types such as processing agent, talc, short glass fibers), 2

active interlayers (cross-linking, molecular wetting), and dispersing and diffusing (fine grinding, enlarging molecular penetration via melt shearing).

Different methods are used to recycle materials to provide plastics with a continuing life. Method used is influenced by factors such as quantity involved, weight involved, size and shape, costs, continued availability of material, etc. Solid waste volume reduction is an important consideration. It is the decreasing of the volume of solid waste through compaction or incineration. A 50 to 80% reduction is possible through compaction; 90 to 98% through incineration. In the recycling industry there are fines. They are the pieces that are substantially smaller than the bulk of the regrind that fall through the granulator screen. Fines are bigger than dust but smaller than regrind.

176 Reinforced Plastics Handbook Too many fines can cause feeding and processing problems. There are also longs. They are oversized raw material that can result from loose or broken granulating screens.

Detailed Analyses

Checklistfor Recycling Consider the following: Can the product, or any part of it, have a secondary use, without significant change? If so, what measures will assist acceptability for a secondary use? -

by the consumer: (as a storage container, garden utensil, plaything) by the manufacturer (in-plant shipment).

H o w / w h e r e will the product arrive for disposal? -

with other identical products (e.g. telephone handsets, carbreaking yard) with mixed products (e.g. municipal dump).

What happens to the product during use? -

-

-

-

wear? degradation (e.g. by heat)? contamination (e.g. by chemicals/oil)? which parts? will this affect recycling, down-grade value of material recovered? can the affected parts be readily detached, for separate disposal?

What is the value of each material used/largest part(s)? -

-

that are the most-used materials/largest parts? can they be extracted? how will the product be dismantled- now?

9 H o w can the most useful parts be removed more easily for reprocessing? (e.g: automobile bumpers, dashboards; computer housings, furniture) 9 H o w could it better be dismantled- in the future? -

what steps can be taken (in material specification or part design) to exploit the recycling potential of large parts/large amounts of compatible materials?

9 Is it worth it? -

is there any economic benefit in changing design or specification? what is the cost of the material used? how can any recovered material be re-used or re-sold?

3 . Plastics 177

Are there any financial or legal obligations to recycle? - is recycling mandatory? Is it subsidized? Is there any value in establishing a system for collection/disposal? - has a genuine recycling scheme any implications or benefits for marketing or price setting?

Waste Minimization It is a good discipline to use only the minimum of material. The call for recycling simply reinforces this rule: minimize the amount of material entering the waste stream. Design the product to be re-used in the same form: - as a re-usable product, re-tillable container - for a second use: as container (for shopping, household, gardening). minimize use of material" - look to using compatible materials; - exercise good control of resin amounts metered, thicknesses of laminates - look also at use of intrinsically reinforced thermoplastics (LCPs) or with synthetic fibre reinforcement; some fillers can have a toxic effect (heavy metal additives, pigments, obsolete flameretardant chemicals) and should be avoided. minimize the volume of material: use computer-aided design to optimize: consult specialists if in doubt use minimum sections and ribbing to achieve strength. - other methods of reducing material volume are: molding in structural foam plastics using a sandwich layer of foam, or recycled material coring-out thick sections by use of gas-assisted molding technology.

-

-

Materials suppliers a n d / o r molders and mold makers should be consulted for detailed advice about how to use these techniques. reduce the waste caused in processing. Thermoplastic waste produced in-plant, from flash, off cut and trim, and rejects moldings, can usually be fed straight back into the process, since it is one material, of known source and in a clean state. Problems arise when the waste is non-homogeneous or when non-compatible materials have been included (such as products with metal inserts or reinforcement, or-which have been painted). Thermosetting flash and trim can be pulverized and re-used as a filler, but anything in design or tooling to reduce or eliminate flash would be valuable.

178 Reinforced Plastics Handbook

The molder/processor will naturally do what is possible to reduce scrap, but consideration at the design stage will certainly help. Processing residues should be minimized, especially sprues and runners in injection molding: 9 are they correctly dimensioned? 9 is it feasible to use temperature-controlled runners (which hold the melt in a suitable state for the next shot)? 9 where scrap is necessary, is it easy for the molder/processor to remove and reprocess it? 9 can it be incorporated in the product (by direct mixing with the virgin compound, or by introducing a core layer of factory scrap)? 9 is any additional cost justified?

Select Compatible Materials The presence of other materials in the compound, particularly fillers and reinforcements, may limit the options in re-formulating any recycled material. It would be prohibitively expensive to remove additives, and the new compound must therefore contain them. Glass fiber presents no difficulty. In TSs, it may be ground with the matrix material; while in TPs (apart from possible abrasive effect on recompounding equipment); it simply goes to make up a new glass reinforced compound. In all cases of direct material recycling, however, there is likely to be some loss on mechanical properties (up to about 20%), which can be offset in the new compound by adding new material a n d / o r corrective additives. Not all types of TPs are compatible with each other and it makes sense to work, if possible, with types that are from the same family or are compatible with each other. This removes the need t o dismantle a product into all its component parts for recycling and so reduces the cost of recycling. Moreover, a large number of small parts, in different materials, may well be unnecessary design.

Integration of Parts The mold ability of plastics can often be exploited to eliminate the need for additional parts, such as fasteners. Additional functions can be incorporated in the one molding, and (with experience) separate components can be integrated, as in an increasing number of applications in automobile engineering. Parts made of the same TP can be assembled by welding, avoiding the use of other materials such as adhesives or mechanical fasteners. These will call for special detailing in the design of the mating surfaces.

3

9Plastics

Problem Materials Some commonly used materials, especially from assembly and finishing processes, can also produce problems at the recycling stage. The most obvious are: 9 Metal inserts. Since the molded product will be chopped or ground up, any metal in it can cause contamination a n d / o r damage to the size-reducing machinery. Soft metals are to be preferred. Plastics inserts are also available. 9 Bonding/painting systems using solvents. Solvent systems are being phased out on health and safety grounds. Many paints will produce contaminating flakes in recycling. Specialist advice should be sought. 9 Pigments/printing inks using heavy metals. Inks can also be a contaminant, especially in heavily-printed components. Trials and advice are needed, to establish the best balance between effectiveness and environmental loading.

Easy Collection The economics of recycling plastics depend heavily on availability at one place of large volumes of waste (if possible, clean and uniform material). Is there anything in the product that could cause injury or damage? 9 Set up/integrate with a positive recycling system 9 use material identification systems (code, tracer additives, magnetic inserts).

Facilitate Identification~Sorting It is relatively easy to separate plastics from other materials, manually (visually) and mechanically (by specific gravity). Problems can arise if it is valuable to separate the individual plastics thereafter. Methods of identifying/separating plastics are under active development: 9 labeling (using a bar code, or agreed symbols) 9 always using one type of plastic for a specific product (but this could lead to fossilization of material specifications) 9 use of trace additives or infra-red analysis (important work is being done in this area). A set of agreed symbols, to be molded into the plastic, or stamped or printed on it, to indicate the type of material, has been introduced in the USA and is being adopted in Europe. A German DIN specification has been published, for identification of plastics parts with particular reference to their material content (DIN 54840 Kunststoffe; Kennzeichnung von Kunststoffteilen).

179

180 Reinforced Plastics Handbook

Designfor EasyDismantling This means designing without compromise of the original function/ safety. The first question is: Why must the product be dismantled at all? 9 because it forms part of a larger assembly? 9 because of different materials? because of valuable inserts? 9 because of valuable contents? If it is agreed that it must be dismantled for disposal, actions taken at the design stage may help later on. Essentially, designing for easy dismantling is a contradiction: to design a product which can readily be dismounted and taken to pieces, but will not do this accidentally during its useful life. The following points should be reviewed: 9 accessibility of joints, modular construction 9 with larger parts, or where there are valuable internal parts (such as motors or instruments), it should be considered whether to make covers or housings reopenable, or to provide predetermined break areas 9 identify areas/elements that will be badly worn or contaminated, and provide for easy replacement, limited contamination and easy identification and separation, so that they can be eliminated from further processing.

Recycling Technologies To meet the call for materials that can be recycled after their main use, so reducing the pressure on resources and the environment, a great many studies have been launched on how best to recycle RPs. As a result, technologies to deal with all types have been developed (at least some to pilot stage), based on the following: Recycling as new plastics materials. TP matrices can be re-melted and re-compounded, with some possible loss of mechanical properties due to thermal degradation of the matrix and breakage of the fiber reinforcement into shorter lengths. On the other hand, TSs have been crosslinked and therefore cannot be re-melted, but can be ground to fine powder that is an effective filler in new compounds Recycling as feedstock or as fuel: both thermoplastics and thermosets can be broken down by chemical and thermal means to produce basic chemicals, for reuse in polymerization or other chemical

3

9Plastics

processes, or to produce fuel oils to replace conventional fuel oils in industrial and heating processes Recycling as energy: because of their high calorific value, all types of plastics can readily be incinerated in efficient plants which can harness the thermal energy liberated; the resulting ash is a safe and compact landfill. Experience to date has shown that a more serious consideration is the cost of collection and preparation of scrapped plastics moldings because, by their very nature, they are not (yet) brought together in one central place for scrapping, but tend to be distributed widely. In addition, in recycling processes in which the material is recovered and directly reprocessed as a new compound in the same family, it is important to have a uniform homogenous input of waste material. Extraneous matter (including some other plastics) can add considerably to costs, as it must be separated and extracted, to produce a clean stream. The incoming waste must be not only be of adequate volume and uniform type, but it must also be clean, as dirt and contaminants such as oil, grease, paint and printing ink can also cause complications in reprocessing. Moves are being made both by resin manufacturers and major users of RPs to set up recycling loops, by which specific parts are collected or taken back, to be fed into a recycling stream. Reinforced plastics feature in some of these studies, especially in the automotive industry. It is obvious, however, that the logistical problem is likely to remain one of the most severe challenges to effective recycling of plastics, failing some form of levy or tax (as is beginning to be introduced in packaging) to compensate for the extra costs.

Chemical Recycling A good many of the problems identified with mechanical recycling can be overcome or bypassed by subjecting the incoming waste to chemical or thermal processes. Depending on the type of material it can be broken down to its basic constituents, or to a form of crude oil, which can be used as a substitute or extender for industrial fuel oil. These processes are ideal for handling large volumes of material, and are less sensitive to mixed types of plastics and to degree of contamination. On the other hand, the cost window is that much lower, as costs are incurred in collection, handling and processing waste plastics, to meet a price level for the resulting feedstock that is competitive with the new feedstock (from which the waste materials were originally produced). Chemical recycling is potentially very interesting, but it is no panacea, and (saving a massive increase in prices of new materials) it would inevitably have to be subsidized. The basic chemical technologies are:

181

182 Reinforced Plastics Handbook

pyrolysis: treatment under vacuum to break down molecules, producing hydrocarbons in gas- or liquid-form, for processing in a refinery

9 hydrogenation: heating in the presence of hydrogen, to crack polymer chains to hydrocarbon oil, for processing in a refinery

gasification: heating in the presence of air/oxygen, producing gas for use in chemical production or in blast furnaces

chemolysi~, breakdown of plastics only as far as their monomer constituents, for re-polymerization. While the chemolysis approach is suitable for certain materials, more severe technologies such as pyrolysis or hydrocracking are needed to return thermoplastics to a useful feedstock. This aims at conversion of the waste to acceptable forms that can be used further upstream, in a petrochemical or refinery operation. A process to convert plastics waste to naphtha has also been tested in Japan. A volume reduction machine is used to dissolve plastics wastes into waste oil, reducing the volume of waste. The solution is then processed to naphtha in a 5000 tonnes/year plant. As well as direct incineration of plastics waste, under clean and efficient conditions, there has been some research into conversion into fuel oil, by chemical methods. The Veba Combi-Cracking (VCC) process produces synthetic crude oil under liquid phase hydration. In trials, 100 tonnes of mixed and contaminated plastics waste from normal domestic sources was hydrated to high quality oil, similar to that used as a source for diesel fuel. With metal-free granular material, costs were estimated at about DM 500/tonne. The process has also been used with polyurethane waste, producing oil that can be mixed with new oil (but costing over twice). A process has also been developed in Japan for turning waste plastic into petroleum products such as gasoline, fuel oil, and kerosene. The fuel recovered is believed to be cheaper than gasoline derived from traditional petroleum refining. It can recover 600 ml of high-grade gasoline and 200 ml of both fuel oil and kerosene from 1 kg of plastic, using a special synthetic zeolite catalyst. The process works best with the polyolefin-type materials, such as polyethylene and polypropylene, but can tolerate a mixture of plastics, including PVC. The waste plastics is pulverized, extruded, mixed, and then thermally degraded, and the decomposed mixture is gasified by heating to 400C. The gas is fed into a catalytic cracking unit at around 330C.

3

9Plastics

Recycling as Energy Since plastic matrix materials are overwhelmingly composed of hydrocarbon molecules, they have a high calorific value (usually put as about the same as fuel oil), which can be utilized by efficient incineration (Table 3.28). It is vital, however, that the incineration process should be efficient, and carried out at a high temperature, in a plant with an effective fume-cleansing system, to prevent any hazardous or unpleasant emissions. The same goes, however, for incineration of any material. With adequate investment and modern technology, however, it is easy to see considerable development in the future of waste-to-energy plants, and of plants producing refuse-derived fuel (RDF). Table 3.28

Calorific value of different materials

Type

Value (MJ/kg)

Wood

20.5

Paper

15.5-18.5

Heating oil

42.0-46.0

Coal

21.0-32.6

Plastics: - polyethylene

46.0

- polypropylene

46.0

- polystyrene

41.0

- PVC

20.0

- polyester

18.8-30.1

- polyurethane

23.8-31.0

Incineration and, to a lesser extent, RDF processing, can have less stringent requirements for type and state of waste input, but there is still some need for sorting to eliminate potentially hazardous materials. A waste-to-energy plant, operating at over 400,000 t/year, is often capable of generating over 500 k W / h of electrical power for every tonne of municipal solid waste. If all Europe's waste were handled this way, it is estimated that 3-4% of domestic electric power could be generated from waste (Table 3.29). If the incineration is efficient, plastics are claimed to produce no more serious emissions than incineration of any other material. For example, dioxins can be produced by inefficient incineration of many different materials, and there is no evidence that combustion of PVC makes any significant addition to acidic emissions. Modern computer-controlled furnaces ensure steady operating temperatures above 850C (1560F), giving high levels of total combustion. Studies show that at least two

183

184 Reinforced Plastics Handbook Table 3.29

Energy content of plastics in MJ/kg

Energy Electricity Feedstocks for plastics: - naphtha

-isobutylene

- ethylene (for polyethylene) - propylene (for polypropylene) - butadiene (for polystyrene and ABS) - formaldehyde (for thermosetting resins) - urea (for urea/formaldehyde) - phenol (for phenol/formaldehyde) - vinyl chloride (for PVC) - styrene (for polystyrene and ABS) - acrylonitrile (for ABS) Glass fiber (for reinforced plastics)

3.2 7.35 47 75 63 61 69

45 23 67 45 77 79 50

seconds exposure at this temperature is necessary to promote not only efficient conversion of almost all carbon content to carbon dioxide but also to minimize the emission of dioxins. Combined with modern combustion gas cleaning systems, this reduces emissions to levels meeting the most stringent environmental regulations and conforming to latest legislation. Reinforced Thermosets

There continues the growing worldwide demand for recycling TS polyester/glass fiber RPs in different marketable products such as automobile parts. A pilot plant for recycling RTS parts (as, for example, SMC automobile bumpers) was set up in Europe by FRP molders and some materials producers under the auspices of ERCOM. The starting point was the realization that the hammer mill process used for size reduction of the parts not only grinds the resin to powder but tends to split along the line of the fiber, leaving it intact. After grinding, the powder and fiber can be separated for re-use. The recyclate is suitable for production of new parts as well as use as filler a n d / o r reinforcement material. Parts containing up to 60 wt% recyclate have been tested, suggesting that properties of strength, surface quality and paintability are nearly as good as in new parts, and up to 25% recyclate can be incorporated without significant loss of properties. Clean SMC and BMC parts are suitable; moldings with other materials need to be separated.

3

9Plastics

In the USA, having demonstrated that SMC can be recycled and material can be used in new SMC parts, Phoenix Fiberglass Inc was obliged to close down in mid-1996, due to lack of demand for the reclaimed materials. The company (backed by Owens Corning) pioneered a process by which high-value glass fibers were separated from scrap RPs, allowing scrap to be reused instead of being sent to landfill. Over 20 US automotive components contain recycled SMC from in-plant and post-consumer scrap, using the material as a 6-25 wt% replacement for calcium carbonate (which makes up about 50% of the raw material of SMC). A similar mechanical process has been developed in Japan by Takeda Chemical Industry Co., using a combination of granulator and hammer mill crusher. The resulting powder is used as filler in place of calcium carbonate, controlling the after-effect of the curing agent. SMCs using 10-20 wt% recyclate have 5% lower specific gravity than standard SMC and good properties and have been used successfully by Toyota for automotive parts. E R C O M runs a mobile shredder unit that will visit plants or collection points of member companies to size-reduce scrap parts on site and so reduce transport costs. It then ships the compacted material to a central fractioning plant at Rastatt, Germany where, with a 30 t / d a y facility, it produces a range of active fillers and fibrous reinforcement material for sale back to SMC producers and other users. Primary SMC products have been developed containing up to 25% recyclate without loss in properties. Several have already been approved by the automotive industry for commercial use and product testing continues as a high priority to demonstrate consistent quality for recyclate material, SMC product, and finished molding. To meet automotive demand for parts with high gloss Class A finish, E R C O M has to resort to heavy grinding of the recovered material, which is expensive and degrades the length of fiber to a point where mechanical properties are so poor as to be indistinguishable from cheap fillers. The cascade effect is therefore in play, rather than the closed loop. E R C O M notes that the most valuable component of recovered SMC is, in fact, the glass, at a value of DM 1.98-2.10/kg. The project has demonstrated that up to 25% hammer mill regrind can be reused in S M C / B M C formulations without significantly affecting properties: the cost is 5% higher by weight but about 7% lower by volume due to the lower density of the recyclate. Up to 8% of virgin fiber can also be replaced, and the fines and milled fiber from the process could also be used as an additive in TPs, or as a medium for blast-removal of paint.

185

186 Reinforced Plastics Handbook

By mid-1996, ERCOM Composite Recycling GmbH had mechanically recycled over 1 million SMC parts. Production scrap accounted for 750,000 parts and post consumer scraps 250,000 (from the Mercedes Recycling System MeRSy, BMW repair shops and Deutsche Telekom dismantling plants). As a result, over 2 million parts containing recyclate were put back into service in automobiles, including spare wheel well (Audi: 320,000), noise barrier shield (VW: 250,000), truck bumpers and front end panels (Mercedes Benz: 600,000), sunroof frames (350,000), and other components (450,000). Studies carried out so far indicate that the particle size is critical in determining the new compounds in which the recyclate can be used, and the most effective percentage of recyclate. For commonly-used SMC/BMC compounds, it is possible to use up to 25% regrind, if the fraction coded RC are used (Tables 3.30 and 3.31). Mechanical properties are essentially unchanged up to a regrind content of about 15% by weight. Table 3.32 provides data for a low-profile HSMC system (curing with virtually no shrinkage, by addition of a socalled high polymer component). The lower density of the regrind compared with a conventional filler gives a weight reduction of 8-12% (density of chalk = 2.7 g / c m 3, density of regrind = approximately 1.8 g/cm3). Additives to improve the wetting and dispersibility of the regrind will give better paste viscosity and homogeneity, improving the physical and surface properties of the compound. An SMC formulation containing 25% regrind modified with a suitable agent will meet automotive industry requirements for incorporation of recycled material, while maintaining the original properties. Phenolic molding scrap is accepted back by some producers for re-use as filler in new compounds. Similarly, amino plastics (urea and melamine) present no problems in disposal or re-use when ground up. Molders have reused as much as 20 wt% ground scrap with virgin molding compounds in injection molding and those who have adopted the technique have found it an effective method for recycling in-house scrap, but for sub-surface parts only. There is no single method for treating polyurethane (PUR) waste, due to the different quantifies, qualifies, mixes, and cleanliness. It is estimated that some 125,000 t of RIM polyurethane is used worldwide, 85% in automotive parts, mainly in bumper fascias. Current technologies for physical recycling of PURs are mainly directed towards flexible and rigid foams, but systems have also been developed for recycling reinforced reaction injection molded (RRIM) PURs, on the

3 . Plastics 187 Table 3.30 Classification of regrind fractions in particle recycling

Powder

Fiber

Fractions type

RC

RC

RM

RG

SMC/BMC Thermoplastic compounds Laminate

++

++ + +

++ ++ +

++

++

++

RC = SMC Base, RM = medium glass concentration, RG = high glass concentration.

Table 3.31 Formulations and performances of 25 wt% regrind with addition of a wetting agent for sheet molding compound

Form. 1

Form.2

(Marshall FBX200) UP resin 1 (including shrink control) UP resin 2 (including shrink control) Wetting agent (BYK-W 996) Styrene TBPB Zinc stearate CaCO3 - 5.5/_/m C a C O 3 - 10 pm Regrind MgO paste Glass, 25 mm % (w/w) Viscosity (Pa-s) without MgO Shrinkage (%) Short-term waviness (Wt) a Long-term waviness (Ws)a Tensile strength (MPa)(approx) Flexural strength (MPa) (approx)

100 2 5 1.5 4.0

100 1

60 90 3 31 41 0.1 227 240 120 220

220

Form. 3

Form.4

(ERCOMRC1000) 50 50 2 5 1.5 4.0 60

1.5 4.0

90 3.0 32 44.2 -0.02 257 415 80 180

3 24 22 0.1 191 289 100 210

50 50 2 1.5 4.0 220

2.5 22 25.5 -0.03 273 448 75

160

aDiffracto-measured by Akzo-Nobel in Deventer, NL. Source: BYK Chemie.

Table 3.32 Use of reground material in a low-profile SMC compound

Property Density (g/m 3) Bending strength (N/mm 2) Bending E-modulus (kN/mm 2) Impact strength (Id/mm 2)

Content of regrind by weight (%) 0% 1.9 194 9.3 102

10% 1.8 200 9.5 107

15O/o

20O/o

25O/o

1.72 209 9.1 112

1.62 186 7.6 97

1.58 172 7.8 91

188 Reinforced Plastics Handbook

same lines as for TS polyester SMC. Mechanical processes involve granulating or flaking and re-molding with a suitable binder and recent development in Europe and USA enables solids to be fed directly to the foam mixing head (Chapter 5). There are also technologies for splitting PURs back into the original chemical components. Regrind/powdering involves grinding the polyurethane material to a very fine powder (50-200 micron/0.05-0.2 mm) by means of a tworoll mill (for flexible foam) or impact disc mill (for glass-reinforced RIM parts). This is then mixed with the polyol component and used to make new products. The mixture has been used successfully in new RIM automotive parts. Up to 10% rcgrind, reduced t o - 8 0 mesh, can be included without impairing original part quality (Table 3.33). Additional cost is involved, but it is estimated that total material costs, for example, for an 11 Ib fascia are about US $1.00 lower than with all-virgin material. Table 3.33 Propertiesof products incorporating recycled polyurethane

Type Rebonded foam (typical values) Regrind/powder: 0% by weight 10% by weight Amine extended RIM: original painted original unpainted comp. m. painted comp. m. unpainted Glycol extended RIM: original comp. m. RRIM polyurethane: 0% wt glycosate 10% wt glycosate 20% wt glycosate Alcoholysis recycled polyurethane: 100% new system polyol system polyol + 25% recyclate

Tensile strength kPa

Elongation at break O/o

4-20 (10%) 5-50 (250/0) 15-150 (50%)

40-150

40-90

1.18 1.20

59 63

28 24.6

160 133

900 836

1260 1220 1260 1260

68 67 66.5 65-67

25 26 23 25

120 130 70 120

1100 1300 700 700

1030 1200

55 67

23 33

204 143

600 613

1.22 1.23 1.22

69 66 66

27 25 25

125 100 107

62(A)

4.1 N/mm2 441

<6

60(A]

5.2 N/mm2 400

<1

Density kg/m 3

Hardness Shore D

60-200

Flexural modulus N/mm 2

3

Plastics 9 189

Structural reaction injection molded (SRIM) sandwich panel composites incorporating recycled RR]M granulate have been developed in Europe, comprising two layers of glass reinforcement on either side of a core layer of granulated RR~M. The filling can be composed of either painted or unpainted material and can be preformed to shape before resin injection. The panels are reported to have approximately 50% better flexural stiffness as a feature of their sandwich construction, while retaining the tensile properties of previous SRIM panels with similar reinforcement. They utilize approximately 30% recycled material. The new composite could be used for a broad range of automotive applications, such as interior trim panels, dashboard support systems, load floors, and other lightweight semi-structural parts. RIM and RR]M PURs are ground to fine particles (0.5 mm or less) and subjected to high pressure and heat, by compression molding: glycolextended compositions, molded at the optimum temperature of 195C (380F), can actually have mechanical properties superior to those of new material. The technique has been tried successfully both with production trim from PUR processing (usually high-quality material) and PUPs recovered from scrapped vehicles. It is being used on a commercial scale by BMW. Polyurethanes also lend themselves to chemical recycling processes. Pyrolysis subjects PURs to very high temperatures, under conditions in which they are broken down to liquid and gaseous hydrocarbons. Hydrolysis produces derivatives of the original PURs. GM and Ford have been involved in this development. Reinforced Thermoplastics

The main RTPs are nylons and polypropylenes, both as granules for molding and as glass mat TPs (GMT). Other glass-reinforced TP, particularly PET, PBT, PC and PPS, are steadily increasing in use. The value of the compounds is relatively high, encouraging some effort to recycle them. The overall use of RTPs remains relatively small, while the applications are necessarily technical and may be difficult to separate from other materials. In principle, there is no real problem in recycling RTPs as new molding compounds in themselves, or as additions to virgin materials. The process of re-compounding, however, has the effect of breaking the fiber reinforcement to shorter lengths. This means that, in effect, the fiber becomes particulate filler and, without other compensation, the mechanical properties of the recycled compound arc lower than those

190 Reinforced Plastics Handbook of the original material. Recycled compounds made of conventional glass fiber RTPs need the addition of new fiber, to up-grade the mechanical properties. Recycled long-fiber RTPs, however, will downgrade in recycling to exhibit properties similar to those of compounds reinforced with conventional short length fiber; the long fibers are reduced in length during granulation. Addition of glass fiber reinforcement provides a means to upgrading the properties of an unreinforced TP recyclate, with the aid of suitable coupling agents or compatibilizers. Dow Automotive Materials and Services Group's glass reinforced PC/ABS 8209 blend with 25 wt% post consumer recyclate is called Retain. It was developed to meet the enhanced toughness criteria of the glass-reinforced instrument panel market. The recycle content will come from a range of finished goods. It is claimed to meet or exceed all performance standards for existing materials-of-choice for glassreinforced retainers. With comparable shrink rate, it can replace currently-used glass-filled materials without modification to tooling. Recycled PET grades that do not require painting have been developed by AlliedSignal Plastics. The TP polyester resins (trade-named PaintPree Petra) are produced with 100% recycled PET and mold with superior surface appearance, excellent processability, and cost-savings. Applications include automotive parts, furniture, lawn and garden tools, and power tools. Built-in consistent color matches remove the need to paint the products after molding. Chemical technologies have been developed for nylons and PET, by which the plastics are reduced to their basic chemical constituents, for reuse in whatever process is most effective. Work on these processes is still in an early stage, but it appears that the presence of reinforcement (such as glass) would not adversely affect the process, and would become a by-product.

Applications As reviewed different RP products have been fabricated incorporating all recycled or recycled/virgin. What follows concerns railroad ties. Worldwide other applications exist.

Recycled Railroad Ties Different applications in recycling RP materials have been developed and put to use. Developments in the use of recycled plastics continue to be on the horizon. An example is from Polywood Inc. Edison, N.J that uses mixed recycled plastics to make fiber-reinforced structural profiles for railroad ties, I-beams, and decks. What is unusual is that it does not

3

9Plastics

add any fiber reinforcements but creates them inside the profiles during the extrusion process. Polywood did not invent this process. In the late 1980s, a PhD student at Rutgers University in Piscataway, NJ discovered that extruding incompatible blends of polystyrene and polyethylene in the fight proportions creates a co-continuous blend of matrix plastic reinforced with intertwined fibers. This in-situ RP can have astonishing high compressive strength. Mixing 20 to 35wt% of a high-melt-strength PS with curbside recycled H D P E produces this effect. Rutgers patented its immiscible plastic-blend extrusion process and tried to commercialize it in cooperation with a company that later became U.S. Plastic Lumber. However, by the late 1990s, that relationship had ended in litigation. James Kerstein, an entrepreneur, heard about the process. He raised capital and bought used equipment to make plastic lumber. He obtained a broad, exclusive license on Rutgers' technology for the life of the patent, which extends to 2011. He also received an interest-free loan of $250,000 from the New Jersey Commission for Science and Technology and invested it in more R&D at Rutgers to qualify the P S / P E RP for railroad ties. The new company, Polywood eventually patented its use of the unfilled P S / P E RP for railroad ties and has patents pending on other applications. Polywood can make 35 million lb/yr of P E / P S RPs. After testing by six research institutes, Polywood's RR ties were qualified in the year 2000 by the Chicago Transit Authority for embedded and elevated track. The CTA has since installed the ties in 10 to 15 miles of track. P S / P E ties behave differently from wood. When new wood ties are installed in a rail bed of crushed rock, trains passing over the ties press the ties into the rock, creating dents that lock the ties in place. Plastic ties, however, do not dent so readily. Plywood embosses the sides and bottom of its ties with dimples to give the rocks a grip. Oddly, the mechanical properties of Polywood's ties have been shown to improve over time. Compressive modulus for a Polywood tie is 2600 psi when new and 3100 psi after 20 years' simulated aging. New wood ties start at 3200 psi and drop to 1000 psi after aging. Ties are made by compounding PS and H D P E in-line with two types of intrusion molding. Its original intrusion lines are two Davis-Standard extruders, piped and manifolded to fill molds for different parts at the same time. Polywood later added two carousel intrusion molding lines from A.R.T. in Belgium. These fill closed molds at 400 to 500 l b / h and rotate them into a cooling-water tank. Newer lines incorporate systems

191

192 Reinforced Plastics Handbook

such as continuous compounding and fabricating profiles that are cooled in a 6 ft calibrator with water and glycol fluid at 30F to freeze the profile surface rapidly. This gives the ties excellent stiffness. The profile then goes through two 30 ft water-spray cooling tanks separated by 5 ft air gaps. Next, the profile surface is reheated and embossed with dimples. Finally, the profile is cut and immersed in a water tank to cool for a couple of hours. The core is slightly foamed, which keeps spikes from splitting the ties later. Use is made of two formulations: one high in PS and stiffer because it has a higher fiber content, the other high in H D P E and less rigid, used in industrial pallets and decking. The H D P E matrix plastic melts at a lower temperature than the PS, so the PS is still solid but above its glass-transition temperature. That causes the PS to be pulled into interlocking fibers with a mean diameter of about 15 microns and aspect ratio of at least 8: 1, according to Rutgers' patent (U.S. No. 5,298,214). Definitions

When discussing many subjects it is important that they be properly identified by definitions such is the case in recycling. Different definitions exist to meet different industry and commercial requirements. ASTM defines a recycled plastics as those plastics composed of postconsumer material and recovered material only, or both, that may or may not have been subjected to additional processing steps of the types used to make products such as recycled regrind, or processed or reconstituted plastics. The industry scrap includes what is commonly referred to as trim or regrind in plastic production, is not considered recycled material. Recycling commingled plastics are plastics not sorted by type in a waste system. The unsorted plastics is combined or blended into one harmonious material. Post-consumer material identifies those products generated by a business or consumer that have served their intended end uses. They have been separated or diverted from solid waste for the purposes of collection, recycling, and disposition. Post-consumer plastic color-measurement technology control is used in recycling of post-consumer plastics (PCPs). As the demand increased for consistent natural and other colors of particularly recycled PET and H D P E , the need for standardization and codification of color measurement based on analytical data continued to be critical. In the past the human eye was the only means of determining color quality. Samples

3

Plastics 9 193

were graded A, B, or C and judgment calls were the standard of the day. However, today's recycled plastic customers and fabricators have very specific color needs that must be met. Visual standards are not satisfactory so standardization and codifying provides credibility and professionalism to an increasingly sophisticated industry. Colorimetric instruments provide benchmarks of quality in recycled clear and colored PCPs. The calorimeter is also used to meet other requirements such as determining the most effective cleaning agents for PCPs. Because it is primarily dirt that gives recycled plastic an unattractive appearance, the portable colorimeter was a real boom in determining the dirt levels of raw materials during the recycling process. These measurements provide early data on PCP appearance prior to pelletizing. Value Analysis of Recycling Potential

A value analysis should be made, to determine how much of the product, or which sections of it, can effectively be recovered. As noted already, the decision may not be wholly on economic grounds. Other non-market factors, such as legislation and image/good-will may also have to be considered. Overall, however, is the fact that, almost irrespective of the value of the materials recovered, the time and therefore the cost of dismantling will usually be disproportionate. Consideration should be given to incinerate rather than recycle when certain materials provide no benefit to the environment particularly cost wise.

Chemistry of Plastics Chemistry is a science that deals with the composition, structure, and properties of substances and the transformations they undergo. Its value and importance continue to permit an endless growth of new plastics with improved fabricating and product performances. Examples of stages in plastic manufacturing follows:

Basic chemicals Petroleum is converted to petrochemicals such as ethylene, benzene, propylene, and Acetylene. Monomers Petrochemicals plus other chemicals is converted into monomers such as styrene, ethylene, propylene, vinyl chloride, and acrylonitrile. Polymerization One or more monomers are polymerized to form polymers or copolymers such as polyethylene, polystyrene, polyvinyl chloride, and polypropylene.

194 Reinforced Plastics Handbook

Compounding Additives,

fillers, a n d / o r reinforcements are mixed with polymers (referred to as plastics) providing different properties a n d / o r different fabricating methods for plastics. Hundreds of different materials are used such as heat stabilizers, color pigments, antioxidants, inhibitors, and fire retardants.

Processing Plastics

are formed into different shapes such as sheets, films, pipes, buckets, primary and secondary structures (boats, cars, airplanes, bridges, etc.), toys, housings, and many thousand more products. Basically heat and pressure are used to shape these products that usually are in finished form. Processes used include extrusion, injection molding, blow molding, thermoforming, compression molding, spraying, rotational molding, reaction injection molding, and filament winding.

Finishing In

certain applications a finishing step is required on the fabricated part such as printing, bonding, machining, etc.

Polymers, the basic ingredients in plastics, is defined as high molecular weight organic chemical compounds, synthetic or natural substances consisting of molecules characterized by the repetition of one or more types of monomeric units (Figure 3.6). A repeated small unit, the mer, such as ethylene, butadiene, or glucose, can represent its structure. Practically all of these polymers use certain types of material to perform properly during fabrication a n d / o r in service. Thermoset Plastics

As reviewed TSs and TPs melt behaviors, differ. With TSs a catalyst is used to provide for their solidification. Catalysis is a substance that changes the rate of a chemical reaction without itself undergoing permanent change in composition or becoming a part of the molecular structure of a product. It markedly speeds up the cure of a compound when added in minor quantity, compared to the amounts of primary reactants. There rarely exist as a single polymerization process in which certain accelerating regulating and modifying ingredients arc not used with great advantage even though they might be present only in very small quantities. In the early years of producing plastics, when there did not yet exist a well founded understanding of the mechanism of polymerization processes, the action of these ingredients and additives so much resembled the phenomenon of normal catalysis that the name catalyst was used for them. With the development in the theory of polymerization reactions, it became evident that in most cases the role of these materials during the formation of macromolecules do not fall

3. Plastics 195

Figure 3.6

Overview of the plastic industries from source to products that includes plastics and fabrication processes (courtesy of Plastics FALLO)

in the domain of the classical definitions of the word catalysis or catalyst. However, since the misnomer is now well established and such correct expressions as initiator, transfer agent, terminator or telomer, crosslinking agent, accelerator, curing agent, hardener, inhibitor, or promoter are frequently used interchangeably with the general term catalyst.

Thermoplastics Generally no chemical change occurs in TPs as in TSs. Knowledge of the chemistry of TPs can be used to understand the performance of RTP designed products. With TSs the chemistry differs since they crosslink. Chemistry is the science that deals with the composition, structure, properties, and transformations of substances. It provides the theory of organic chemistry, in particular, our understanding of the mechanisms of reactions of carbon (C) compounds (Figure 3.7). The polymer in plastics undergo some primary processing such as distillation, cracking, or solvent extraction to produce ethylene (C2H4),

196 Reinforced Plastics Handbook

Figure 3.7 Exampleof differences in the processing temperature of crystalline and amorphous TPs

propylene (C3H6) , or benzene (C6H6) that are precursors to plastics. Chemical composition of plastics is basically organic polymers that are very large molecules composed of connecting chains of carbon (C) items generally connected to hydrogen atom elements (H) and often also oxygen (O), nitrogen (N), chlorine (C1), fluorine (F), and sulfur (S). Thus, while polymers form the structural backbone of plastics, they are rarely used in pure form. In almost all polymers other useful and important materials (reinforcements, additives, and/or fillers) are added producing plastics to modify and optimize properties for each desired process and/or product performance application. A polymer is a large molecule built up by a repetition of small simple chemical units. These large molecules are formed by the reaction of a monomer. For example, the monomer for the plastic polyvinyl chloride (PVC) is vinyl chloride. When the vinyl chloride monomer is subjected to heat and pressure it undergoes a process called polymerization: the joining together of many small molecules in repeat units to make a very large molecule. Structural representations of the monomer repeat unit and polymer are shown below. H H

H el Repeat unit

H H H C|H

H el Polymer chain

H

3 . Plastics 197

The number of repeat units in PVC may range from 800 to 1600 that in turn produces different polymers. In some cases a polymer molecule will have a linear configuration, much as a chain is built up from its links. In other cases the molecules are branched or interconnected to form 3-D networks. The particular configuration, which is a function of the plastic materials and manufacturing process involved, largely determines the properties of the finished plastic article. Even though monomers are generally quite reactive (polymerizable), they usually require the addition of catalysts, initiators, pH control, heat, a n d / o r vacuum to speed and control the polymerization reaction that will result in optimizing the manufacturing process and final product. When pure monomers can be converted directly to pure polymers, it is called the process of bulk polymerization, but often it is more convenient to run the polymerization reaction in an organic solvent (solution polymerization), in a water emulsion (emulsion polymerization), or as organic droplets dispersed in water (suspension polymerization). Often choose of catalyst systems exert precise control over the structure of the polymers they form. They are referred to as stereospecific systems. There are relatively many different catalysts that are usually used for specific chemical reactions. Types include Ziegler-Natta Catalyst (Z-N), metallocene, and others including their combinations. These different systems arc available and used worldwide from different companies. The chemical and physical characteristics of plastics are derived from the four factors of chemical structure, form, arrangement, and size of the polymer. As an example, the chemical structure influences density. Chemical structure refers to the types of atoms and the way they are joined to one another. The form of the molecules, their size and disposition within the material, influences mechanical behavior. It is possible to deliberately vary the crystal state in order to vary hardness or softness, toughness or brittleness, resistance to temperature, and so on. The chemical structure and nature of plastics have a significant relationship both to properties and the ways they can be processed, designed, or otherwise translated into a finished product (Figures 3.8 and 3.9). Morphology is the study of the physical form or structure of a material (thermoplastics crystallinity or amorphous); the physical molecular structures of a polymer or in turn a plastic. As a result of these structures in production of plastics, processing the plastics into products, and product designs, great differences are found in mechanical and other properties as well as processing plastics.

198 Reinforced Plastics Handbook .... GLASSY

STAGES ....

TRANSITION

r t~5In O

9 9

MELT FLOW

RUBBERY 9 9

qp-

>'4-

o

0

o

Im m

I-

e e o

,<3..I ILl U.

0

~

~

.J i

01,,

6O

o o e 9

9

80

100

140

120

|

160

TEMPERATURE (Oc)

Figure 3.8

Example of TP melt stages vs. temperature

450 -"

I I I I

STALLINE

I-< tL

"i

~

o

o

ul

.J 0 0 IE

I 0.450

AMORPHOUS i

-100

Figure 3.9

I

0

G

l

~

i

CROSS-LINKED I

100

Dynamic mechanical properties of plastics vs. temperature

i

200

,

3

9Plastics 1 9 9

Knowledge of molecular size and flexibility explains how individual molecules behave when completely isolated. However, such isolated molecules are encountered only in theoretical studies of dilute solutions. In practice, molecules always occur in a mass, and the behavior of each individual molecule is very greatly affected by its intermolecular relationships to adjacent molecules in the mass. Molecular Structures/Property/Processes

Three basic molecular structure or properties affect processing performances (flow conditions, etc.) that in turn affect product performances (strength, dimensional stability, etc.). They are: 1

mass or density (d),

2

molecular weight (MW), and

3

molecular weight distribution (MWD)

In crystalline plastics, such as PE, density has a direct effect on properties such as stiffness and permeability to gases and liquids. Changes in density may also affect some mechanical properties. One method of defining plastics melt behavior and property performance is to use information concerning their molecular weight (MW), a reference to the plastic molecules' weight and size. MW is the sum of the atomic weights of all the atoms in a molecule. It represents a measure of the chain length for the molecules that make up the polymer. Atomic weight is the relative mass of an atom of any element based on a scale in which a specific carbon atom (carbon-12) is assigned a mass value of 12. The polymerized polymer contains molecules having many different chain lengths. For some products, the resulting distribution of molecular weights can be calculated statistically and illustrated by the standard form of frequency distribution. The term apparent density of a material is sometime used. It is the weight in air of a unit volume of material including voids usually inherent in the material. Also used is the term bulk density that is commonly used for compounds or materials such as molding powders, pellets, or flakes. Bulk density is the ratio of the weight of the compound to its volume of a solid material including voids. MW of plastics influences their properties. As an example with increasing MW, properties increase for abrasion resistance, brittleness, chemical resistance, elongation, hardness, melt viscosity, tensile strength, modulus, toughness, and yield strength. Decreases occur for adhesion, melt index, and solubility.

200 Reinforced Plastics Handbook

Adequate MW is a fundamental requirement to meet desired properties of plastics. With MW differences of incoming material, the fabricated product performance can be altered. The more the difference, the more dramatic change occurs in the product. MW refers to the average weight of plastics that is always composed of different weight molecules. It is a convenient term that recognizes the fact that all polymeric materials comprise a mixture of different polymers of differing molecular weights. These differences are important to the processor, who uses the molecular weight distribution (MWD) to evaluate materials. A narrow MWD enhances the performance of plastic products. Wide MWD permits easier processing. The processing and property characteristics of plastics are partly a function of the MWD that may vary widely, even among plastics of identical composition, density, average molecular weight, and melt index (Figure 3.10). NARROW MWD

t

z O i.m rr I-rE) I:1 m

WIDE MWD

._i 0 LOW

Figure 3.10

INCREASING MOLECULAR WEIGHT WIDTH

HIGH

Examples of narrow and wide molecular weight distributions

Melt index (MI) or melt flow rates is dependent on the MWD. With MWD differences of incoming material the fabricated performances can be altered requiring resetting process controls (Table 3.34). The more the difference, the more dramatic changes that can occur in the products. MI tests are used to detect degradation in products. MI has a reciprocal relationship to melt viscosity. This relationship of MW to MFR is an inverse one; as one drops, the other increases or visa-versa.

3

Plastics 9 201

Table 3.34 Examplesof melt index for different processes Process

MI ronge

Injection Molding Rotational Molding Coating Extrusion Film Extrusion Profile extrusion Blow molding

5-100 5-20 0.1-1 0.5-6 0.1-1 0.1-1

Viscosities" Newtonian Et Non-Newtonian The resistance of melt flow exhibited within a body of material identifies its viscosity. It relates to plastic melt flow that in turn relates to the processing behavior of plastic. During melt flow internal friction occurs when one layer of fluid is caused to move in relationship to another layer. Ordinary viscosity is the internal friction or resistance of a plastic to flow. It is the constant ratio of shearing stress to the rate of shear. Shearing is the motion of a fluid, layer by layer, like the movement of a deck of cards. When plastics flow through straight tubes or channels they are sheared and the viscosity expresses their resistance. A method to measure melt flow is by the melt index (MI) [also called melt flow index (MFI)]. It is an inverse measure of viscosity. High MI implies low viscosity and low MI means high viscosity. Plastics are shear thinning, which means that their resistance to flow decreases as the shear rate increases. This is due to molecular alignments in the direction of flow and disentanglements. There is Newtonian and Non-Newtonian viscosity. With Newtonian viscosity the ratio of shearing stress to the shearing strain is constant such as theoretically water. In non-Newtonian behavior, which is the case for plastics, the ratio varies with the shearing stress (Figure 3.11). Such ratios are often called the apparent viscosities at the corresponding shearing stresses. Viscosity is measured in terms of flow in Pa.s, with water as the base standard value of 1.0. The higher the number, the less flow. Different plastics have different viscosities. Rheology and Viscoelasticity They are a phenomenon of time-dependent in addition to elastic and deformation (or recovery) in response to load. This property possessed by all plastics (primarily thermoplastics) to some degree, highlights that

202 Reinforced Plastics Handbook

Newtonian Non-Plastic ....

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.

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.

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.

.................... ..~~Non.Newton ~

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Non-plastic (Newtonian) and plastic (non-Newtonian) melt flow behavior (courtesy of Plastics FALLO}

while plastics have solid-like characteristics such as elasticity, strength, and form-stability, they also have liquid-like characteristics such as flow depending on time, temperature, rate, and amount of loading. Thus, plastics arc said to be viscoelastic. As an introduction to viscoelasticity the mechanical behavior of these viscoelastic plastics is dominated by such phenomena as tensile strength, elongation at break, stiffness, and rupture energy, which are often the controlling factors in a design. The viscous attributes of plastic melt flow are also important considerations in the fabrication of plastic products. When discussing melt flow the subject of rheology or flow of matter is involved. It is concerned with the response of plastic melts to mechanical force. An understanding of rheology and the ability to measure rheological properties such as molecular weight and melt flow is necessary before flow behavior can be controlled during processing. Such control is essential for the fabrication of plastic materials to meet product performance requirements. With plastics there are two types of deformation or flow; viscous, in which the energy causing the deformation is dissipated, and elastic, in which that energy is stored. The combination produces viscoelastic

3 . Plastics 203

plastics. Not only are there two classes of deformation, there are also two modes in which deformation can be produced: simple shear and simple tension. The actual action during melting, as in the usual screw plasticator is extremely complex, with all types of shear-tension combinations. Together with engineering design, deformation determines the pumping efficiency of a screw plasticator and controls the relationship between output rate and pressure drop through a die system or into a mold. There is a different flow behavior of plastic when compared to water. The volume of a so-called Newtonian fluid, such as water, when pushed through an opening is directly proportional to the pressure applied following a straight line (flow vs. pressure). The flow rate of a nonNewtonian fluid such as plastics when pushed through an opening increases more rapidly than the applied pressure resulting in a curved line. Different plastics have their own flow rates so that their nonNewtonian curves are different. This property of viscoelasticity is possessed by all plastics to some degree, dictates that while plastics have solid-like characteristics, they also have liquid-like characteristics. This mechanical behavior is important to understand. It is the mechanical behavior in which the relationships between stress and strain are time dependent for plastic, as opposed to the classical elastic behavior of steel in which deformation and recovery both occur instantaneously on application and removal of stress.

Viscoelasticity Viscoelasticity is a very important behavior to understand for the designer. It is the relationship of stress with elastic strain in a plastic. The response to stress of all plastic structures is viscoelastic, meaning that it takes time for the strain to accommodate the applied stress field. Viscoelasticity can be viewed as a mechanical behavior in which the relationships between stress and strain are time dependent that may be extremely short or long, as opposed to the classical elastic behavior in which deformation and recovery both occur instantaneously on application and removal of stress, respectively (Figure 3.12). The time constants for this response will vary with the specific characteristics of a type plastic and processing technique. In the rigid section of a plastic the response time is usually on the order of microseconds to milliseconds. With resilient, rubber sections of the structure the response time can be long such as from tenths of a second

2 0 4 Reinforced Plastics Handbook

B C

A

1

0

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~

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Instantaneous loading produces immediate strain (top curve). Viscoelastic deformation (or creep} gradually occurs with sustained load. Instantaneous elastic recovery occurs when load is removed. Viscoelastic recovery gradually occurs; where no permanent deformation (D') with a permanent deformation (D"- D'. Any permanent deformation is related to type plastic, amount and rate of loading, and fabricating procedure. Instantaneous loading produces immediate strain {bottom curve). With strain maintained gradual elastic relaxation occurs. Instantaneous deformation occurs when load is removed. Viscoelastic deformation gradually occurs as residual stresses are relieved. Any permanent deformation is related to type plastic, amount and rate of loading, and fabricating procedure.

Figure 3.12

Highlighting load-time/viscoelasticity of plastics: (1) stress-strain-time in creep and (2) strain-stress-time in stress relaxation

to seconds. This difference in response time is the cause of failure under rapid loading for certain plastics. By stressing a viscoelastic plastic material there are three deformation behaviors to be observed. They are an initial elastic response, followed by a time-dependent delayed elasticity that may also be fully recoverable, and the last observation is a viscous, non-recoverable, flow component. Most

3. Plastics 205 plastic containing systems (solid plastics, melts, gels, dilute, and concentrated solutions) exhibit viscoelastic behavior due to the long-chain nature of the constituent basic polymer molecules (Chapter 1). This viscoelastic behavior influences different properties such as brittleness. To understand why the possibility for brittle failure does exist for certain plastics when the response under high-speed stressing is transferred from resilient regions of a plastic, an analysis of the response of the two types of components in the structure is necessary. The elastomeric regions, which stay soft and rubbery at room temperature, will have a very low elastomeric modulus and a very large extension to failure. The rigid, virtually crosslinked regions, which harden together into a crystalline region on cooling, will be brittle and have very high moduli and very low extension to failure, usually from 1 to 10%. If the stress rate is a small fraction of the normal response time for the rubbery regions, they will not be able to strain quickly enough to accommodate the applied stress. As a consequence, for the brittle type plastics, virtually crosslinked regions take a large amount of the stress, and since they have limited elongation, they fail. The apparent effect is that of a high stretch, rubbery material undergoing brittle failure at an elongation that is a small fraction of the possible values. A fluid, which although exhibits predominantly viscous flow behavior, also exhibits some elastic recovery of the deformation on release of the stress. The term viscoelastic is reserved for solids showing both elastic and viscous behavior. Most plastic systems, both melts and solutions, are viscoelastic due to the molecules becoming oriented due to the shear action of the fluid, but regaining their equilibrium randomly coiled configuration on release of the stress. Elastic effects are developed during processing such as in die swell, melt fracture, and frozen-in orientation.

Polymer Structure The viscoelastic deviations from ideal elasticity or purely viscous flow depend on both the experimental conditions (particularly melt temperature with its four temperature regions and magnitudes and rates of application of stress or strain). They also depend on the basic polymer structure particularly molecular weight (MW), molecular weight distribution (MWD), crystallinity, crosslinking, and branching.

High MW glassypolymer An amorphous polymer well below its glass transition temperature (Tg) value where very few chain melt flow motions are possible so the material tends to behave elastically, with a very low value for the creep

206 Reinforced Plastics Handbook

compliance of about 10 -9 Pa -1. When well above the Tg value (for an elastomer polymer) the creep compliance is about 10 -4 Pa q , since considerable segmental rotation can occur. The intermediate temperature region that corresponds to the region of the Tg value, is referred to as the viscoelastic region, the leathery region, or the transition zone. Well above the Tg value is the region of rubbery flow followed by the region of viscous flow. In this last region flow occurs owing to the possibility of slippage of whole polymer molecular chains occurring by means of coordinated segmental jumps. Melt Characteristics Melt strength of plastic occurs during its processing molten state. It is an engineering measure of the extensional viscosity and is defined as the maximum tension that can be applied to the melt without breaking. Linear plastics such as LLDPE, HDPE, and PP generally have poor melt strength. The reason is that in extension the linear chains slide by without becoming entangled. However, branched plastics like LDPE exhibit higher melt strength and elongation viscosity because the long branches become entangled.

Melt temperature (Tm) refers to a plastic when it melts or softens and begins to have flow tendency. It provides recommendation for processing temperature to be used and related to tolerance and shrinkage behavior of molded products. In a hypothetical characterization, a perfectly free or relative free melt in consistency temperature wise, pressure wise, mixture wise, etc. is referred to as the absolute melt temperature. This condition does not exist during processing but with the passing of time with improvement developments in plastic and processing and testing equipment the melt mix becomes more uniform. Trying to measure the melt temperature could be deceiving. As an example, an extruded extrudate with a room temperature pyrometer probe will often give a false reading because when the cold probe is inserted, it becomes sheathed with the plastic that has been cooled by the probe. A more effective method is by using what some call the 3 0 / 3 0 method. One simple raises the temperature of the probe about 30F (15C) above the melt temperature and then keep the probe surrounded with hot melt for 30 s. The easiest way to preheat the probe is to place the probe on, near, or in a hole in the die. By preheating above the anticipated temperature, just prior to inserting it into the melt, then it requires the probe to actually be cooled by the melt. The lowest temperature reached will be the stock temperature. It

3 . Plastics 207

also helps to move the probe around in the melt to have the probe more quickly reach a state of equilibrium. To be more accurate, repeat the procedure. A computerized control system is used to vibrate melt during processing, monitoring viscosity, and to control their microstructure. Vibration is created through hydraulic pumps and servo-valves. In a mold, the melt can be oriented in three directions. Results include increases in tensile strength and modulus of elasticity, melt transition temperature, eliminate knit line and warping, etc. With extruders, it can reduce barrel friction so that the melt temperature can be reduced at least 20C. The action permits pelletizing at lower temperature allowing the use of organic stabilizers and colors that degrade at higher temperatures. (patent by Solomat Partners of Stamford, CT, USA).

Glass Transition Temperatures Also called glass-rubber transition. Identified as Tg. Basically this important characteristic is the reversible change in phase of a plastic from a viscous or rubbery state to a brittle glassy state. Tg is the point below which thermoplastic behaves like glass but very strong and rigid. Above this temperature it is not as strong or rigid as glass, but neither is it brittle. At Tg the plastic's volume or length increases and above it, properties decrease.. The amorphous TPs have a more definite Tg when compared to crystalline plastics. It is usually reported as a single value. However, it occurs over a temperature range and is kinetic in nature (Table 3.35 and Figures 3.13 and 3.14). Table 3,35 Rangeof Tgfor different thermoplastics Plastic Polyethylene Po lyp r o pyl e n e Polybutylene Polystyrene Polycarbonate Polyvinyl Chloride Polyvinyl Fluoride Polyvinylidene Chloride Polyaceta I Nylon 6 Polyester Polytetrafl uoroethylene Silicone

~

~

- 120 - 22 -25 95 150 85 -20 -20 -80 50 110 - 115 -120

- 184 -6 - 13 203 302 185 -4 -4 - 112 122 230 - 175 -184

208 Reinforced Plastics Handbook

T

-1t(.9 z I.U ._1

I I I I

rg TEMPERATURE Figure 3 . 1 3 Thermoplastic volume or length changes at Tg

r

~

STARTS SOLID

AMORPHOUS Rmmmm ~ ~

]g

Tm

TEMPERATURE

Figure 3.14

hange of amorphous and crystalline thermoplastic's volumes at Tg and Tm

Viscoelasticity Behaviors There is linear and nonlinear viscoelasticity. The simplest type of viscoelastic behavior is linear viscoelasticity. This type of rheology behavior occurs when the deformation is sufficiently mild that the molecules of a plastic are disturbed from their equilibrium configuration and entanglement state to a negligible extent. Since the deformations that occur during plastic processing are neither very small nor very slow, any theory of linear viscoelasticity to date is of very little use in processing modeling. Its principal utility is as a method for characterizing

3 . Plastics 209

the molecules in their equilibrium state. An example is in the comparison of different plastics during quality control. In the case of oscillatory shear experiments, for example, the strain amplitude must usually be low. For large and more rapid deformations, the linear theory has not been validated. The response to an imposed deformation depends on (1) the size of the deformation, (2) the rate of deformation, and (3) the kinematics of the deformation. Nonlinear viscoelasticity is the behavior in which the relationship of stress, strain, and time are not linear so that the ratios of stress to strain are dependent on the value of stress. (The Boltzmann superposition principle does not hold). Such behavior is very common in plastic systems, non-linearity being found especially at high strains or in crystalline plastics.

Relaxation/Creep Analysis Theories have been developed regarding linear viscoelasticity as it applies to static stress relaxation. This theory is not valid in nonlinear regions. It is applicable when plastic is stressed below some limiting stress (about half the short-time yield stress for URPs); small strains are at any time almost linearly proportional to the imposed stresses. When the assumption is made that a time wise linear relationship exists between stress and strain, using models it can be shown that the stress at any time in a plastic held at a constant strain (relaxation test) can be determined.

RP Stiffness-Viscoelasticity The stiffness response of RPs can be identified as viscoelasticity. RPs is nearly elastic in behavior and tends to reduce the importance of the time-dependent component of viscoelastic behavior. Also, the stiffness of fiber reinforcements and the usual TS resin matrices are less sensitive to temperature change than most URPs. The stiffness of both the fibers and the matrices are frequently more stable on exposure to solvents, oils, and greases than TPs although for certain composites water, acids, bases, and some strong solvents still may alter stiffness properties significantly. Stiffness properties of RPs are used (as with other materials) for the usual purpose of estimating stresses and strains in a structural design, and to predict buckling capacity under compressive loads. Also, stiffness properties of individual pries of a layered "flat plate approach" may be used for the calculation of overall stiffness and strength properties. The relationship between stress and strain of unreinforced or RPs varies from viscous to elastic. Most RPs, particularly RTSs are intermediate between viscous and elastic. The type of plastic, stress, strain, time, temperature, and environment all influence the degree of their viscoelasticity.

210 Reinforced Plastics Handbook

Creep and Stress Relaxation Properties of URPs are strongly dependent on temperature and time. This is also true, to a lesser degree, for RPs, particularly RTSs, compared with other materials, such as steel. This strong dependence of properties on temperature and how fast the material is deformed, based on a time scale, is a result of the viscoelastic nature of plastics. Consequently, it is important in practice to know how the product is likely to be loaded with respect to time. In structural design, it is important to distinguish between various modes in the product. The behavior of any material in tension, for example, is different from its behavior in shear, as with plastics, metals, concrete, etc. For viscoelastic materials such as plastics, the history of deformation also has an effect on the response of the material, since viscoelastic materials have time- and temperature-dependent material properties.

Summary A combination of viscous and elastic properties in a plastic exists with the relative contribution of each being dependent on time, temperature, stress, and strain rate. It relates to the mechanical behavior of plastics in which there is a time and temperature dependent relationship between stress and strain. A material having this property is considered to combine the features of a perfectly elastic solid and a perfect fluid; representing the combination of elastic and viscous behavior of plastics. In the plastic, strain increases with longer loading times and higher temperatures. It is a phenomenon of time-dependent, in addition to elastic, deformation (or recovery) in response to load. This property possessed by all plastics to some degree, dictates that while plastics have solid-like characteristics such as elasticity, strength, and form-stability, they also have liquid-like characteristics such as flow depending on time, temperature, rate, and amount of loading. These basic characteristics highlight: (a)

simplified deformation vs. time behavior,

(b) stress-strain deformation vs. time, and (c)

stress-strain deformation vs. time (stress-relaxation).

A constitutive relationship between stress and strain describing viscoelastic behavior will have terms involving strain rate as well as stress and strain. If there is direct proportionality between the terms then the behavior is that of linear viscoelasticity described by a linear differential

3

9Plastics 2 1 1

equation. Plastics may exhibit linearity but usually only at low strains. More commonly complex non-linear viscoelastic behavior is observed. Thus viscoelasticity is characterized by dependencies on temperature and time, the complexities of which may be considerably simplified by the time-temperature superposition principle. Similarly the response to successively loadings can be simply represented using the applied Boltzmann superposition principle. Experimentally viscoelasticity is characterized by creep compliance quantified by creep compliance (for example), stress relaxation (quantified by stress relaxation modulus), and by dynamic mechanical response. The general design criteria applicable to plastics are the same as those for metals at elevated temperature; that is, design is based on (1) a deformation limit, and (2) a stress limit (for stress-rupture failure). There are cases where weight is a limiting factor and other cases where short-term properties arc important. In computing ordinary short-term characteristics of plastics, the standard stress analysis formulas may be used. For predicting creep and stress-rupture behavior, the method will vary according to circumstances. In viscoelastic materials, relaxation data can be used to predict creep deformations. In other cases the rate theory may be used.

Compound Constructions Overview Reinforcements can be in continuous forms (fibers, filaments, woven or non-woven fabrics, tapes, rovings, etc.), chopped forms having different lengths, or discontinuous in form (flakes, spheres, etc.). The reinforcements can allow the RP compounds to be tailored to the design, or the design tailored to the material. Fibers usually are treated to binder/sizing coupling agent treatments to maximize their performances. This treatment is used on different types of fibers (glass, etc.) to provide meeting their specific requirements such as bonding capabilities and, very important particularly for glass, protection of fibers. A major requirement for these agents involves the proper handling of the glass fibers during their treatment. Continuous fiber strands intended for weaving are usually treated at their forming bushing during their manufacture with starch-oil binders. Protect the fibers from damage is by a binder lubrication during their formation and such subsequent textile operations as twisting, plying, and weaving. Usually they are satisfactory when used with certain thermoplastics (TPs) but are not compatible with thermoset (TS) plastics. As an example, the hydrophilic character of the binders allows moisture to penetrate the glass-plastic interface, which leads to degradation of RTPs or RTSs in wet and humid environments. The binder is removed prior to applying sizing agents via heat treatment before being used with these plastics. This is accomplished by exposing the reinforcing material (fiber, fabric, etc.) to carefully controlled time-temperature cycles. To protect the weak heat-cleaned fibers, chemical sizing coupling agents are used such as methacrylic chromic chloride complex, organosilanes, etc. Review of the different

4-Compound Constructions 213 types of reinforcements is provided in Chapter 2. Review on the plastics used is included in Chapter 3. Because of the need to achieve a very good interfacial contact between reinforcement and the resin matrix (and to simplify in-plant processing operations), there continues to be a growing trend towards supplying reinforcement already impregnated with resin such as prepregs. These are available in the form of woven a n d / o r continuous fiber reinforcement impregnated with liquid resin, and also as braided structures and tapes, for precise placement of reinforcement. They rely on resin systems that permit a part-cure (B-stage), leaving the resin still flexible, so that the prepreg material can be placed in a mold or wound round a mandrel and then finally cured. Prepregs, in the strict sense of the term, are therefore limited to certain resin systems and are usually employed in higher-performance materials. An alternative form, which has been used very widely for almost a half century, is sheet molding compound (SMC) and bulk molding compound (BMC), which are fully-formulated materials ready for molding by compression or injection, mainly based on TS polyesters and glass fibers (Table 4.1). Table 4,1 Examplesof E-glass construction used in TS polyester RPs Bulk Sheet Chopped Molding Molding Strand Woven Unidirectional Unidirectional Compound Compound Mat Roving Axial Transverse Glass content

20

30

30

50

70

70

Tensile

9 (1.3)

13 (1.9)

7.7 (1.1) 16 (2.3)

42 (6.1)

12 (1.7)

Tensile strength MPa (Ksi)

45 (6.5)

85 (12)

95 (14) 250 (36) 750 (110)

(wt 0/4 Modulus GPa (Msi)

50 (7)

There are also TP equivalents, such as high performance carbon/PEEK tapes, in which continuous filament and matrix have been closely combined by a form of pultrusion process and require only placing in position (often by winding or layering) and heating, to fuse the TP matrix. Technology extending the principle to continuous filament and PP matrices is also available.

214 Reinforced Plastics Handbook A further variation is to bring both the reinforcement and TP matrix together in the form of fibers, which are then readily combined (described as commingled), giving an improved interfacial bond. Advanced forms of these are based on biaxial TPs in the form of fibers (such as PA, PBT, PET, PP/PPS, PEI, APC-2, or PSU), with carbon, aramid, and glass pre-impregnated tape. The prepreg is unidirectional and interlaced in a biaxial form in continuous lengths. They have various widths (such as up to 3.04 m / 1 0 ft). Overall, the material maintains and improves the properties of unidirectional cross-ply laminates, giving the benefit of unidirectional tape in larger and more easily processed formats. With very good drape characteristics, it is claimed to be the first real alternative to the compromise often necessary with woven RPs. Analogous also to TS SMCs and BMCs are TP molding compounds in sheet form, known as glass mat thermoplastics (GMTs), and compounded into standard granules for injection molding and extrusion. Most TPs are capable of combination with reinforcement. The main types used commercially are PA and PP.

Compounding Materials Important to their success includes the preparation of the resin compound to be used with the reinforcements. The additives a n d / o r fillers to be used and mixed is usually done by computer controlled electronic weighing scales that supply precise amounts of each ingredient to a high intensity mixer. In producing bulk molding compounds (BMCs) the still-dry, free-flowing blend can be charged through a feed hopper where it is screw fed into a continuous mixer such as an extruder a n d / o r kneader. Under the action of a mixer's reciprocating screw in the confined volume of the mixer chamber, the blend begins to flux or masticate into the required plastic state. Usually the next step is to force it out of the barrel of the mixing chamber through a die producing the compound. The compound can exit as a continuous thick rope or be chopped into small baseball size buns. This hot material may be passed through a two-roll mill. The (usual) parallel rolls have extremely flat surfaces and rotate at slightly different speeds depending on the plastic being processed. Products such as sheet molding compounds (SMCs) and BMCs are usually manufactured by a two-stage process, in which resin, fillers and other additives are first mixed to a paste and then combined with fiber reinforcement, according to the required form of compound. For continuous production of SMC, the paste is thickened and metered by

4 . Compound Constructions 21 5

doctor blade onto two moving carrier films. Glass fiber roving is chopped continuously and distributed over one of the paste-loaded films and the second film is then led over the first and consolidated by rollers to a sandwich, impregnating the glass fiber. Formulation of S M C / B M C compounds is a very sophisticated balance of many ingredients to enhance specific properties a n d / o r act synergistically with other components. Most S M C / B M C formulations have three main elements: binder, filler and fiber reinforcement, from a choice of ingredients such as: unsaturated polyester resin, monomer, catalyst, inhibitor, fillers, TP anti-shrinkage additives, flame-retardant, thickener, release agent, and glass fiber reinforcement. The TS polyester resins themselves are usually highly reactive thicken able types, based on an isophthalic or orthophthalic acid. TP-modified polyesters are also used. The monomer is usually styrene. Catalysts used in molding compounds are inactive at room temperature and are activated during the molding operation, at 120-160~ (248-320~ A hardener for S M C / B M C has to give a rapid (but not too rapid) cure, or pre-curing and pre-gelling will produce incomplete flow in the more complex tools. A very rapid catalyst will also reduce shelf life of the compound. An inhibitor is added to delay the cure so that, even when using rapid peroxides, good stability can be achieved. The selection of filler has a basic influence on the surface finish of the molded part, and an even greater effect on mechanical and electrical properties, as well as on chemical resistance and flammability. The most common fillers include calcium carbonate, dolomite, china clay and aluminum trihydrate (6). Fillers usually improve the flow of the compound, and its impact strength and stiffness, provided that the content of filler is kept down to acceptable limits. Linear coefficient of thermal expansion (LCTE), shrink resistance, and flame retardancy also benefit from higher filler content. A negative effect is an increase in density, but the cost of the compound may be correspondingly lower. When very large quantities of filler are used, surface-treated grades are usually preferred, which are normally silane-treated to reduce viscosity of the compound and improve mechanical properties by providing better adhesion to the matrix. Most polyesters exhibit shrinkage during curing by 5-9% of their volume, but the high filler content of S M C / B M C tends to reduce this to about 0.15% in standard formulae. Lower shrinkage is obtained by introducing high molecular weight TPs as additives. These swell during curing, under the influence of the exothermic heat, and so offset the shrinkage of the matrix resin. Such formulations are usually described as

216 Reinforced Plastics Handbook

low profile, and exhibit less than 0.05% shrinkage (and may even expand). Good flame-retardancy is achieved by using aluminum trihydrate (A12)3 x 3H20) that releases water at relatively low temperatures. Thickening agents such as alkaline earth metal oxides or hydroxides are added to increase the viscosity of the resin and so prevent separation of resin and solids during molding and to improve handling properties before fabrication. Internal release agents based on metal stearates are the most commonly used, acting at molding temperatures above 130~ (266~ Glass fiber reinforcement is usually continuous roving cut to lengths of 250-500 mm (1-2 in.) for SMCs and 3-12 mm for BMCs. By incorporating higher performance fibers, such as carbon, boron, aramid, or polyester, strengths exceeding those of the highest grades of steel have been obtained.

Prepregs Resin pre-impregnated reinforcements or prepregs are usually TS polyester hot liquid melt with or without a solvent impregnated around reinforcements. They can be stored in a cool location for use at a latter time either in-house or to deliver to a fabricator. TS polyester/glass fiber reinforcement prepregs have been in use since the 1940s and continue to be used throughout the industry. More recently developed are TP prepregs. Prepregs are used to mold different products. Different forms of reinforcements are used (nonwoven mat, woven fabric, braided, preform, roving, etc.). The TS catalyzed compounded resin is impregnated into the continuous reinforcement and partially cured to a tack-free state in the B-stage (Chapter 3). The impregnated liquid resin provides for precise placement of reinforcement. The reinforcement can be predesigned to meet performance shape requirements. The molder uses the prepreg in a compression mold or other molding process that will allow the required temperature (low to high) and pressure (low to high) conditions to be met, based on how the resin was compounded. With proper storage condition of temperature [ at least about 21 ~ (70~ ], their shelf life can be controlled lasting at least 6 months. Techniques for locating and orienting them onto a molding surface, in accordance with the RP design pattern, are adapted to the tack and drape characteristics of the prepreg. The woven fabrics make possible

4

Compound 9 Constructions 2 1 7

use of sewn stitches, staples, or clamps. Usually, the lay-ups are enlarged to provide allowances for trimming after the RP has been cured. Sometimes they are draped over male forms with weighted edges to draw the lay-ups snugly onto the molding surface prior to final cure. Very often, successful lay-ups depend on the operators' skills to innovate. Prepregs have advantages over resin wet lay-up fabrication systems (Chapter 5). The wet lay-up places the reinforcement in a mold cavity followed with literally pouring resin over the reinforcement. Resin or a gel coating can be applied to the mold surface prior to placement of the reinforcement to provide an improved molded part surface. The main advantages of prepregs over wet lay-up fabrication are: 9 factory-made accurately pre-catalyzed resin 9 accurate control over resin/fabric ratio 9 lower end resin contents are possible; saving excess weight of resin 9 generally higher mechanical properties (since it is not necessary to resort to the low viscosity, lower performance components are needed for hand lamination) 9 cleaner materials with no resin mixing; resin systems used are generally of a viscosity high enough not to transfer to hands and clothing 9 TS epoxy resins when used are free of styrene eliminating environmental problems arising with TS polyesters, and 9 elevated cure temperatures employed mean that the materials react slowly at room temperature and have typical working times of up to 8 weeks. Reinforcing fabrics made from glass, carbon, aramid, and other fibers are supplied, ready impregnated with a resin in solvent (Tables 4.2 and 4.3). With their higher viscosity, the resin systems used in prepregs have usually been incorporated by dissolving the catalyzed system in a solvent and passing the fabric through a resin bath, removing excess resin, and then passing through an oven to evaporate the solvent and take the resin to the B-stage (the intermediate stage of cure) (Figure 4.1). The prepreg is then cooled to prevent further onset of cure and wound into rolls with a release paper or film. The usual resin content is about 30 wt%. This method is now falling from favor, on environmental grounds. A second hot melt method is becoming more popular, in which the viscosity is reduced for a short time at an elevated temperature and the fiber or fabric is impregnated with the liquid under pressure.

m,

s~ e,~

ISI

Table 4.2 Propertiesand applications of some typical prepregs

-r-

Aramid/ epoxy

Carbon/epoxy Reinforcement

Balanced fabrics

Unidirectional fiber

Unit weight Tensile modulus Flexural strength Fiber volume Properties/ applications

345 241 69 148 690 2130 62 62 Structural high temperature: aerospace industry

Balanced fabrics 345 69 690 62

e~

Glass/epoxy

Unidirectional fiber

Unbalanced fabrics

Balanced fabrics

Unbalanced fabrics

241 130 2000 62 Structural: advanced industry

340 32 535 49 Structural: high toughness

517 26 430 44 Structural: advanced industry

306 36 732 48 Structural: sporting goods

0 0

Table 4.3

Guideline properties of advanced RP prepregs

Cure temperature Cure time Cure type a Application temperature Shelf life c Properties and applications

Epoxies

Phenolics

Polyim ides

Polyesters

Siloxira ne

80-180~ 175-360~ 10-240 min a, p, v -40 to 175~ -40 to 350~ 6-30/6-7 Good electrical, chemical resistant: aerospace, helicopter blades, etc.

90-160 200-320 15-120 a, c, p, v -55 to 80 b -70 to 200 15/6 Flame-resistant, low smoke: aircraft interior parts

150-360 300-700 up to 1080 a, c, p, v 260-360 500-675 5-10/6-12 High temperature: electrical, engine parts, fairings

120-150 250-300 20-90 a, p, v 70-120 160-250 14-30/6 Good mechanical, self-extinguishing airframe parts, electrical

150-230 300-450 check supplier a, c, v 205 400 30/9 Tough, easy processing: missiles, engine parts, radomes

4~ 0

a Cure types are indicated as: a = autoclave, c = compression molding, p = press, v = vacuum bag.

3

b High temperature grades up to 260~176

o c-

c Shelf life is given as: days @ 23~

@ - 18~

Source: Condensed from data of AIK-Advanced Composites GmbH.

o Ill

e,, o

220 Reinforced Plastics Handbook

Figure 4.1 Basicproduction system for prepreg materials

Application of prepreg fabrics includes aerospace components, printed circuit boards, etc. Pre-impregnated continuous rovings and tapes are sometimes used for filament winding, with epoxy or special types of TS polyester resin. A new prepreg manufacturing process for RPs, using electrostatic deposition technology, applies resin in powder form to fibers or fabrics, via an electrostatic fluidized bed. The powders adhere to the reinforcement that is then heated on the same machine, lowering resin viscosity sufficiently to wet out the fibers. The technology eliminates use of solvents in resins, and processing speeds are increased, it is claimed, translating into lower energy usage. Conventional prepregs require curing at 120-180~ calling for expensive high temperature ovens or autoclaves, with tooling also able to withstand such temperatures. High process pressures are needed for good consolidation and the low flow characteristics limit the weight of materials that can be impregnated by the resin, leading to use of more layers and increased cost, particularly when making thick laminates for large structures. One-off moldings tend to be uneconomical. For large (especially one-off; only one layer of prepreg is used) structural applications, such as large boat hulls, prepregs curing at lower temperatures and pressures are used. Curing at 75~ and with high flow characteristics, can be used with either lightweight unidirectional materials and heavyweight woven and muhiaxial fabrics, up to 1600 g / m 2, with low-cost wooden tooling. They can include sandwich cores

4-Compound Constructions 221 such as PVC foam or RP honeycomb cores. This lay-up has been used for construction of many boat hulls, up to 30 m long. Other advances have since been made, in both resin chemistry and prepreg manufacturing techniques. A unique high performance epoxy prepreg that can be stored at ambient temperatures for at least a year is available from Thiokol Corp, Brigham City, Utah. It is available in a variety of fibers, from E-glass to high modulus carbon, in both tow and woven fabric. Resin content, flow during cure, and tack levels can be modified to suit the process requirements. The prepregs were originally produced by Thiokol to withstand the severe internal pressures to which RP rocket motor cases are subjected and are used in the company's Castor 120 booster. They are also used cost-competitive commercial applications.

Sheet Molding Compounds,Thermosets Sheet molding compounds (SMC) is a ready-to-mold material representing a special form of a prepreg. From the original development of the thin or single-ply prepregs, the thicker SMC was developed. SMC is a ready-to-mold material representing a special form of a prepreg. It is usually a glass fiber-reinforced TS polyester resin compound in sheet form (Table 4.4). Other popular constructions use different TS resins such as epoxies with different reinforcements such as carbon fibers (Table 4.5). Table 4.4 Properties of glass fiber mat RPs with different types of TS polyesters

Phthalic laminating Isophthalic corrosionresin resistant resin Property Glass fiber mat, O/o

Casting Laminate

Casting Laminate

Vinyl ester resin Casting Laminate

0

30

0

30

0

30

Flexural strength, MPaa

82

172

90

193

103

190

Flexural modulus,

4137

5517

4827

6206

4482

6896

MPaa Tensile strength, MPaa Tensile Modulus,

41

89

62

103

82

124

4482

4827

4482

8275

5172

8275

MPaa Tensile elongation, O/o Heat-distortion temperature, ~

1.8 70

1.4 150

2.1 100

1.6 >200

4.5 110

1.8 >200

n ,

a.

Table 4.5 Comparing properties of glass and carbon fiber sheet molding compounds .

.

.

.

.

.

.

ASTM classification

.

.

Unit

.

Heat-resistan t

High-strength

High-glass/epoxy

Carbon fiber/epoxy Ill .,...

Reinforcement content Specific gravity Tensile strength Tensile modulus Flexural strength Flexural modulus Compressive strength Compressive modulus Shear modulus Barcol hardness Water absorption Molding shrinkage Flammability Coefficient of linear thermal expansion

Source:Premix.

Olo D 792 D 638 D 638 D 790 D 790 D 695 D 695 D 4065 D 2583 D 570 D 955

MPa GPa GPa GPa MPa GPa GPa Olo mm/mm ISO 3795 TMA ~

50 1.82 194 18.7 311 15.2 173 54 60 O.15 0.001 self-extinguishing 15x 10-6

1.9 330 26.1 610 21.3 280 18.6

63 1.82 35,000 psi 66,000 psi 2.6 x 106 psi

0.08 0.001 in/in

55 1.45 43,000 psi 10.1 x 106 psi 90,000 psi 5.0 x 106 psi 40,000 psi 4.6 x 106 psi

0.001 in/in

1.5 x I061~

-10" o o

4. Compound Constructions 223

The sheet can be rolled into coils during continuous processing. SMC is basically made by mixing and metering the compound, feeding the glass fiber reinforcement, wetting out the glass fibers, rolling up the sheet, and allowing the material to mature. A plastic film usually polyethylene covering separates the layers to enable coiling and to prevent contamination, sticking, and monomer evaporation. This film is removed before the SMC is charged into a mold such as matched-die molding or compression molding. Depending on product performance requirements, the SMC consists of additional ingredients such as low-profile additives, cure initiators, thickeners, and mold-release agents. They are used to enhance the performance a n d / o r processing of the material. Glass fibers are usually chopped into lengths of 12 mm (0.5 in.) to at least 50 mm (2 in.) however longer fibers arc also used. The amount can vary from 25 to 50 wt%. The usual ratio is based on performance requirements, processability, and cost considerations. SMC can be formulated in-house or by compounders to meet performance requirements of a particular application such as tensile properties or Class A surface finish. Varying the type and percentage of the composition will result in variations in mechanical properties and processability. Before SMC can be used for molding, it must age or mature. This maturation time is required to allow the relatively low-viscosity resin to thicken chemically. The thickened SMC is easier to handle and prevents the resin paste from being squeezed out of the glass fiber sheet during processing. Typically, SMC requires about three to five days reaching the desired molding viscosity. SMC is a chemically thickened TS polyester resin, manufactured as a continuous mat of (usually) glass, resin, filler and additives as necessary, from which blanks can be cut and loaded into a press for molding. This is the standard material, widely used for low and high pressure molding of medium to large products and offering almost boundless potential in mass-production manufacturing of products with superior finish and excellent mechanical properties. Different methods arc used to produce SMCs that provide different properties and performances (Figures 4.2 and 4.3). SMC primarily consists of TS polyester resin, glass fiber reinforcement, and filler. Additional ingredients, such as low-profile additives, cure initiators, thickeners, and mold release agents are used to enhance the performance or processing of the material. As with any material, such as metallics and plastics, SMC can be formulated in-house or by compounders to meet performance requirements of a particular application such as tensile properties or Class A surface finish.

224 Reinforced Plastics Handbook

Figure 4.2 Different SMC production lines; {a] only chopped fibers, (b) chopped fiber with continuous fiber {s), and {c) chopped fiber with continuous fibers cut to meet part form

Figure 4.3

More details schematic of SMC manufacturing line that includes continuous fibers

4. Compound Constructions 225 In addition to the number of different materials that can be combined, there are also different forms and proportions of each material. Glass fibers are usually chopped into lengths of 12 mm (0.5 in.) to at least 50 mm (2 in.). The amount can vary from 25-50 wt%. The usual ratio is based on performance requirements and processability versus cost. Varying the type and percentage of the composition will result in variations in mechanical properties and processability. SMC is made by mixing and metering the compound, feeding the glassroving reinforcement, wetting out the glass fibers, masticate by a device such as a corrugated chain link compaction belts, rolling up the sheet, and allowing the material to mature. Sheets can also include continuous fibers to provide engineering-designed properties. Fibers can be included in many different directions. Typical data for SMC are in Table 4.6. Table 4,6 Comparesproperties of SMC short (R25) and long (RSO)glass fiber with steel

Property

SMC R25

SMC RSO

Steel SAE 1008

Tensile Strength MPa (psi x 10 E03)

65-90 (9.4-13.0)

124-204 (18-29.6)

330.7 (47.9)

Tensile Modulus GPa (psi x E06)

10-12.5 (1.2-1.8)

12.2-19.1 (1.8-2.8)

206.7 (30.0)

Flexural Strength MPa (psi x 10 E03)

155-200 (22.4-29.0)

248-380 (36.0-55.1)

n/a

Flexural Modulus GPa (psi x 10 E06)

8.5-14.0 (1.2-2.0)

11.6-16.4 (1.7-2.4)

n/a

Notched IZOD J/m (ft Ibs/in.)

500-1000 (9.4-18.7)

725-1360 (13.5-25.4)

n/a

Specific Gravity

1.8-2.0

1.85-2.15

7.86

Coefficient of Expansion m/m. (3 x 10 E06 (in/in. F x 10 E06)

12-14 (6.7-7.8)

13-17 (7.2-9.5)

12.1 (6.7)

All ingredients, except the glass, are mixed together to form a resin paste. The paste is transferred to a doctor box where it is deposited onto a moving carrier film passing directly beneath. The doctor box controls the

226 Reinforced Plastics Handbook

amount of the paste applied. Simultaneously, glass fiber rovings are fed into a rotary chopper above the paste-covered cartier film. The fibers arc chopped to required length by adjusting chopper blades and are dropped onto the paste. The fibers are deposited randomly, but can also be oriented slightly parallel to the direction of the film travel (machine direction). The amount of glass deposited is controlled by the speed of the rotary chopper and the speed of the carrier film. View (c) in Figure 4.2 is a schematic of an off-line production process, when required, to cut directional-type SMCs. This action permits the sheet to conform to a specific mold contour during processing, significantly reducing or eliminating unwanted 'wrinkles' during lay-up and permitting molding with the least, if any, excess flash. Downstream from the chopping operation, a second carrier film is coated with the paste and is laid, resin side down, on top of the chopped glass. This stage of the process creates a resin paste and glass fiber sandwich construction that is then sent through a series of offset compaction rollers where the fibers are wetted out with the resin paste and excess air is squeezed out of the sheet. The final SMC is put on a storage roll or bi-folded into a bin. In this store condition, the roll or bin is wrapped with a barrier film to avoid styrene evaporation. The usual size is about 4 mm thick by 120 cm wide. The length is determined by the molder preference for handling. The SMC's resin paste has a viscosity of about 20,000 to 40,000 cp when in the doctor box (the consistency of molasses or honey). Before SMC can be used for molding, it must age or mature. This maturation time is required to allow the relatively low-viscosity resin to thicken chemically. The thickened SMC is easier to handle and prevents the paste from being squeezed out of the glass fiber sheet during fabrication. Typically, SMC requires about three to five days reaching the desired molding viscosity. After maturing, it reaches about 20-30 million cp which is a consistency similar to leather. The continuous mat can be of different sizes depending on available equipment size. It can be approximately 1 m wide x 3 mm thick. Typically, it has 20-25 wt% glass, with 25 mm (1 in.) length fibers distributed randomly. Strength can be increased by increasing fiber content, increasing fiber length, a n d / o r incorporating local oriented reinforcement such as continuous fibers in different directions. By careful combination of certain unsaturated polyesters, with additives, high polymer components, viscosity reducing additives, and alumina trihydrate (ATH) grades it has been possible to formulate SMCs with very high filler contents. Variations include the following types:

4 . Compound Constructions 227

9 LP-SMC (low profile SMC): A compound with shrinkage of less than 0.05% volume, used especially for automobile bodywork panels. 9

LS-SMC (low-shrink SMC): Slightly higher shrinkage than LPSMC, but less than 1 vol%. It usually comprises pigmentable TP polyester mixtures particularly when making thick laminates for large structures.

9 H M C (high modulus compound): A high-strength RP, with glass fiber content of 50-60 wt% 9 XMC (cross-wound molding compound): Glass fiber content can be up to 80 wt%. 9 R-D-O-C-SMC: Structural versions of SMC in which the fiber is random direction-oriented continuous type, using a combination of various fiber lengths and directions. S M C / C / R (continuous/ random) has a total glass fiber content of 50-60 wt% and glass distribution ranging from C30/R20 wt% to C60/R5 wt%. 9

Low-pressure SMC: Low-pressure sheet molding compounds can present problems due to difficulty in controlling the chemical thickening process at low viscosity levels, and achieving a dry, tackfree easily handled compound without any resin separation. New technology from Union Carbide is claimed to overcome this, offering wide process latitude for thickener control, with dry easily handled compounds of stable viscosity.

9 SMC LITE: Compounding technology, giving lower density RPs and using low-pressure resins, has been developed by various organizations. Low-pressure/low-temperature SMC has been developed by Premix Inc., in the course of its development of a complete low pressure molding system. Another is Ashland Chemical, in conjunction with Nero Plastics and Kenworth Truck Co. With a density of 1.6-1.65 g / c m 3, compared with the usual 1.88-1.9 g / c m 3, SMC LITE produces parts of lighter weight without sacrifice of surface quality. The resins used can be compounded and molded at reduced pressure, allowing lower-cost tooling and presses to be used. As an example, a Class A side air deflector for a truck was molded at lower pressure with weightsaving, producing cost-savings from a reduction in cycle time and minimized post finishing. 9 Melamine sheet molding compound: Developed by DSM and Perstorp, is under the name Remel, as a dry sheet for compression molding, for applications especially in the electrical, public transport, domestic appliance, and sanitary ware industries. It complies with all recognized industrial fire test standards without need for halogen additives. With a limiting oxygen index of 95%, the V-O standard in

228 Reinforced Plastics Handbook

the Underwriters' Laboratory (UL) 94 flammability test is reached at only 0.25 mm, and the material is certified M1/F1 in the French Epiradiator Test and B1 under DIN 4102. The glass reinforcement content is relatively low, at 20 wt%, but stiffness and impact strength are high (with a modulus about 50% higher than glass reinforced TS polyester and 3-4 times higher than RTPs). Heat distortion temperature is 300~ at 1.8 MPa and continuous service temperature is 170-190~ Molding conditions are similar to those for TS polyester SMC. The recommended mold temperature is about 145~ and pressure is 5-8 MPa. High-performance sheet molding compound: Includes highglass/epoxy and carbon fiber/epoxy SMCs that have been developed by Premix primarily for military and aerospace structural applications. Flame-retardant SMC formulations no longer tend to be based on additives such as halogen or phosphorus compounds, but with fillers such as chalk powder or, for much better results, alumina trihydrate (ATH). The specific flame retardant effect of ATH is obtained by the release, at the elevated temperatures of a fire, of large amounts of chemically bound water of crystallization; in effect, it is a built-in sprinkler system. This process is extremely endothermic, so making a significant improvement in properties such as flammability and flame spread. These ready to use molding compounds combine resin, reinforcement, mineral fillers, and various additives as required, controlling cure, shrinkage and other properties. The main resin used is, predominantly, TS polyester (unsaturated polyester) resin, with others being used such as epoxies and vinyl esters. Similarly, the main reinforcement is, predominantly, glass fiber, but fibers offering higher performance are added where specific properties are needed. The compounds are usually made by resin suppliers or specialist formulators but, for large demand, many molders produce their own in-house. Broadly, they provide a very wide range of possible forms and specialties. For large (especially one-off single SMC sheet) structural applications, such as large boat hulls, SMCs curing at lower temperatures and pressures are used. A typical curing system is Ampreg 75, developed by SP Systems. Curing at 75C and with high flow characteristics, this can be used with both lightweight unidirectional materials and heavyweight woven and multi axial fabrics, up to 1600 g / m 2, with low-cost wooden tooling and with or without PVC foam cores. It has been used for construction of many boat hulls, up to 30 m long. Other advances have since been made in both resin chemistry and SMC manufacturing techniques.

4. CompoundConstructions 229 Low Pressure Molding Compounds SMC is, in the opinion of some, not fulfilling its true potential, partly because of the reliance on a chemical thickening process that is not fully controllable, placing the material at a disadvantage against alternative materials because of the difficulty in achieving consistent and reliable parts. One approach has been in using a physical thickening process, which allows consistent production, immediate use, reproduceable moldings and significantly lower molding pressure. The material is known as low pressure molding compound (LPMC). There are claims to have same properties as SMC but are molded at lower (700-3500 kPa) pressure, enabling use of less-expensive tooling (30-120% cheaper), allowing shorter runs, with a wider processing window, and easier handling. An early commercial application of the material was for an air intake for a truck, previously molded by R T M / o p e n mold. Weighing just over 1 kg and measuring 432 mm x 242 mm, with four bosses with moldedin threaded inserts on the reverse side (calling for four times the average sectional thickness), the part was molded by the LPMC process on a cycle time of just under four minutes, giving 120 parts per eight-hour shift, with reported cost savings of 60%. A second part, a sun visor, was also switched to LPMC, with considerable savings in postmolding finishing work, producing reported savings of US $14/part (equaling US $112,000 in the first year). A similar LPMC was developed to meet the requirements of a sports car builder. Comparable properties of compounds (respectively, LPMC, low profile RTM and a typical SMC) are given in Table 4.7.

VE Molding Compounds Thicken VE (vinyl ester) grades have been developed to offer specific improved properties in compression molding compounds, with a view particularly to under-bonnet automobile applications. As well as dynamic, mechanical, and physical properties, they provide good glass wet-out properties, excellent process ability, durability, and resistance to high temperatures. They are available with or without a TP shrinkage control additive. Compounds are available formulated on epoxy novolac-based resins and bisphenol epoxies. The latest bisphenol-A compounds offer high mechanical properties at a cost saving, in comparison with novolacs. Especially at glass contents of over 35 wt%, VE SMC offers advantages over isopolyester SMC. Under stress, S M C / B M C parts with low glass content show initiation at a higher elongation (2.2%) than equivalent

230 Reinforced Plastics Handbook Table 4.7 Low pressuremolding compound compared with resin transfer molding and sheet molding compound

Low-profile resin transfer molding

Typicalsheet molding compound 1-3

5-10 0.5-1.0 0.5-1.5 8.5-19.0

1-3 1-2 0.5-1.5 2-4 10-20 0.5-1.0 0.5-1.5 15.5-33.0

1-2 0.5-1.0 0.5-1.5 3.1-8.0

26 74.0 7.5 136.0 6.1 900

26 98 9.9 199.0 8.1 1250

28 72.3 10.0 149.9 6.6 1155

40+ 90 45-55 0.7

40+ 65 45-55 0.7

40+ 150 85-95 0.12

LPMC Molding cycle Tool preparation (min) Set perform Close mold Injection Gelation Demolding part Open mold Total cycle time (estimated) Mechanical properties Glass content (%) Tensile strength (MPa) Tensile modulus (GPa) Flexural strength (MPa) Flexural modulus (GPa) Izod impact unnotched (J/M) General properties Barcol hardness (24 h) Molding temperature (~ Loria (surface finish) rating Water absorption (%)

1-3 1-2 0.5-1.5

0.1-0.5

polyesters (0.9%). Heat distortion temperature is about 145~ (293~ and retention of mechanical properties at elevated temperature is superior to both polyester SMC.

Sheet Molding Compounds,Thermoplastics Thermoplastic RPs (RTPs), even with their relatively lower fabricated properties when compared to thermoset RPs (RTSs) are used in about 55 wt% of all RP parts. Included in these RTPs are thermoplastics SMC providing advantages processing wise and/or performance wise when compared to TS SMCs. By far the majority of RTPs are bulk-molding compounds (to be reviewed) that are primarily injection molded with very fast cycles using glass fiber producing highly automated and high performance parts.

4. Compound Constructions 231 Glass Mat Thermoplastics GMTs is a form of molding material, analogous to TS resin SMC that have been available for over at least four decades. They offer the processor a factory-made TP prepreg material that can be molded simply and effectively in a press, at high rates of production. Since the matrix resin is TP, the GMT needs to bc heated for molding, while the pressmolding stage can be seen as similar to stamping sheet metal. These materials have usually been identified as stampable materials. With preheating of GMT blanks in an oven prior to loading them into the stamping press it is possible to rationalize the molding cycle and achieve high production rates (cycle times of 20-50 s are possible); moldings have good flow properties to fill relatively intricate molds. Since the material is in sheet form, it is more suited to molding of shell- or dish shaped components, with little change in sectional thickness. Thicker sections, including areas incorporating molded-in metal inserts, can be built up by placing additional blanks in the press. The efficiency with which the sheet can be cut to produce blanks with minimum wastage is a key feature in GMT molding (though, since it is a TP matrix, it is possible easily to re-use/recycle off-cut material). It also lends itself to automation, placing the hot blanks in the open press by robot. There are several ways in that GMT materials can be manufactured, with various forms of reinforcement providing different properties (Table 4.8 and Figure 4.4). Continuous strand mats impregnated with a TP melt have only limited flow capabilities and cannot be used for deep-draw moldings, products with variations in wall thickness, or with ribs or bosses. Better flow properties are obtained when the sheet is reinforced with needled mats, which arc usually produced as part of the main production process. Needling of swirled continuous strands or long-length chopped rovings entangles the fibers and provides stretchability. As with SMCs the impregnation or wetting-out of the fibrous reinforcement with a resin is all-important and, since the resin is a TP, used in solid form, it is not so easy. The mats can be impregnated with TP resin by combining with an extruded sheet of the resin as it is extruded, and passing the mix through a double-belt press for consolidation and compaction. If the extruded sheet is cooled, it will require preheating prior to combining with the mat. A GMT material called SymaLITE offers 20% to 50% better mechanical properties than other GMT materials. Its first commercial use was in underbody panels formed by processor Seeber Systemtechnik (Worms,

232 Reinforced Plastics Handbook Table 4.8 Typicalpropertiesof long and short glass mat with 30 wtOlothermoplastics Long fiber grades (< 50 mm)

Density Tensile strength Tensile modulus Flexural strength Flexural modulus Charpy impact (unnotched) Coefficient of linear thermal expansion Heat distortion temperature

Short fiber grades (< 50 mm, wt process)

Unit

PP

PET

PA

PP

PET

kg/dm 3 MPa GPa MPa GPa kJ/m2

1.12 80 5.2 120 5.5 85

1.60 105 8.0 220 8.3 80

1.35 95 7.6 220 9.8 70

1.15 75 5.2 120 5.2 20

1.55 115 6.5 170 6.5 35

1/K

30

~

150 302

155 311

220 428

~

24 245 473

215 419

Figure 4,4 Basicsystem for production of glass mat thermoplastics

Germany) for the 5- and 6-Series sedans from BMW. Supplied by Quadrant Plastics Composites (QPC), Lenzburg, Switzerland, the material-made of commingled PP fibers with 20% to 60 wt% glass-fiber content could also see substantial use in noise-absorption panels and other large, semi structural automotive parts that require high rigidity and/or noise absorption. Additionally, QPC continues work on matching SymaLITE as a structural backside with aluminum or plastic sheet for parts that meet Class A surface requirements.

4. Compound Constructions 233 Processors of GMT can use low-pressure (less than 0.2 MPa) molding systems, such as stamping or thermoforming machinery, to form parts. Heat in the mold causes flattened glass fibers to return to their original 3-D shape. The expansion of the glass fibers, and thus the thickness of the parts, can be controlled via the alignment of the molds. The material's improved mechanical performance over competing TPsbased GMTs makes it a viable alternative to metals and TS plastics based RPs for large horizontal parts, until now off limits to TPs. A direct competitor is SuperLite GMT, supplied since 1999 by Azdel (headquarters' Shelby, NC, USA), a 5 0 / 5 0 joint venture of glass fiber supplier PPG and engineering TPs supplier GE Plastics. Azdel markets its material for many of the same applications as QPC now hopes to, and in the last two years has doubled SuperLite capacity at its Lynchburg, VA site. Demand for the product is growing at a pace that may soon justify European production. Like the QPC material, low molding pressures are used, and cycle times typically arc less than one minute. Differences in the materials stem from their production, with SuperLite made in a slurry process during which short (13mm) glass fibers and PP powder are mixed in an aqueous solution and then deposited onto a porous bed to drain liquid. SymaLITE is made in a dry process with long (up to 75mm) glass and TP fibers mixed to form a homogeneous, high-loft fleece, which is then needled. These fleeces are heated above the melt temperature of the matrix and then consolidated online to a solid laminate.

Stampable Sheets Stampable sheets of this type (such as Azdel) have high flow capabilities and can fill intricate molds, incorporating ribs, bosses, and thickness variations. Before molding, the pre-cut blanks are heated to just below their processing temperature, so that they can be formed immediately when placed in the press. Other processes are used for manufacturing GMT materials such as producing glass fiber simple to complex shaped preforms (Chapter 5). Continuous rovings, tapes and fabrics impregnated with TPs can be resin impregnated. They can be molded by thermoforming, or by tape laying or fiber placement, or by shaping the heated material by drawing it through a die (Chapter 5). TPs and reinforcement can be combined by solution coating, or by commingling of TPs and reinforcement yarns. Which method is finally selected depends largely on the materials involved. Not all TPs can form stable melts of sufficiently low viscosity; some cannot be obtained in powdered form and not all can be dissolved in solvent. Commingling calls for the TP to be available in a yarn form, which is not always possible.

234 Reinforced Plastics Handbook Stampable GMTs include advanced reinforced thermoplastics (ARTPs) that have been developed by a number of fabricators and companies. Applications include aircraft and automotive components such as control surfaces, nose ribs, rudder trailing edges, floor panels, cabin fitments such as galleys and closets, partitions and closets, brackets, profile covers, exterior fairings, sandwich floor panels, and auto oil pans (Table 4.9). These high performances TP RPs can readily compete with TS prepreg materials in various applications. Table 4.9 Thermal properties of thermoplastics for aircraft interiors

Tg(~ Crystallinity (%) T process (~

PAS

PPS

PEI

PEKK

260 0 330-340

85 30-35 330-340

217 0 340-350

156 O- 10 320-340

Source: Ten CateAdvanced Composites.

Powder Impregnations Impregnation of the reinforcement with TP in powder form provides other methods of combining the resin matrix with the fiber reinforcement. The processes are newer and are thought to be potentially more versatile, with the possibility also that they might accept recycled material. One such process uses glass fiber in 12 mm lengths • 11 pm diameter and powdered PP, deposited on a porous flexible web. The standard density is 1000g/m 2. The material is processed by hot air at 200-250~ (390-480P) temperature in 10-40 s (2-10 layers). Properties are claimed to be superior. Several possibilities exist as matrix resins with most using PP, treated with coupling agents to improve the bond with the glass fiber mat. Other resins include nylons, TP polyesters (both PBT and PET), PE, and blends of PPO and PC/PBT. Several powder-based processes arc used (Table 4.10). An example is a low-cost plant for manufacturing TP prepregs using powdered deposition is a coating line developed by Electrostatic Technology Inc (E-Preg). It can apply dry powers quickly and safely to aramid, carbon, and glass fiber tow and fabric, eliminating the need for solvents. The powder particles are fluidized by ionized air passed through a porous plate at the base of the coater and, as they are charged, they repel each other, forming a cloud. When the substrate is passed through the coater, the charged particles uniformly coat the material, being more

4 . Compound Constructions 235

attracted to exposed areas than coated areas. Coating thickness and deposition rate is controlled by the amount of voltage applied in the air ionization process. The coated substrate is then passed into an oven, to melt and flow the powder. The coating chamber has a slight negative pressure, to prevent powder from escaping and contaminating air in the factory. Any airborne powder is returned to the handling system, for recycling. Virtually all the powder purchased is applied. This coating procedure has been used to coat different materials including conventional plastics. Table 4.10 Powder impregnation lines for GMT production Research institute

Spreadingdevice

Powder coating unit

Stabilising unit

LTC,Switzerland Porcher Textile/ Enichem FIT

Venturi slot tunnel Pins

Fluidizedbed Fluidized bed

NASA Langley Research Center

Pneumatic tow spreader

NASA Langley Research Center

Pneumatic tow spreader

Georgia Institute of Technology

Air jet, spreads tow 2 cm wide

Clemson University

Spreadingbars

Technical University, Berlin

Polishedsteel pins

University of Akron

Venturi slot tunnel

Virginia Polytechnic Institute/State University Michigan State University

Venturi slot tunnel

Bubble bed feeder delivers powder to fluidized bed Powder curtain (two runs, inverting the tow) Fluidized bed with electrostatically charged powder Powder extruder sprinkles powder onto tow Aqueous powder dispersion followed by optical tow width adjustment Electrostatic powder coating gun distributes powder onto an earthed carbon fiber tow Powderdeposited on moistened carbon fibers Pretreatment tank to modify fiber surface for better adhesion

Oven Polymer sheath enclosing powdercoated tow Oven, Vmcontrolled by measuring electric capacity of tow Oven

Unknown

Source: Universityof Newcastle-upon-Tyne/Polymers~t PolymerComposites.

Oven DC heating Drying oven followed by powder fusing oven Electrostatic charges, radiation/ convection oven Oven: eliminates moisture and fuses particles in place Heater or oven

236 Reinforced Plastics Handbook Commingled Glass/Thermoplastics Filaments Vetrotex has developed a novel approach to the problem of effectively combining glass fiber with a TP matrix, under the name Twintex. This is a roving and fabric, made up of commingled E-glass and TP filaments (either PP or PET), that can be processed by heating to a temperature above the melting point of the TP and applying pressure and heat [180-230~ (360-450~ It is suitable for press molding, filament winding, and pultrusion, and for local reinforcement of PP GMTs. When compared with TS SMC and TP GMT, the TP matrix gives good impact resistance, while the PET matrix version offers mechanical properties in bending that are superior to those of PE and PP grades, and are particularly suitable for structural parts (Table 4.11). Processing can be by filament winding, using consolidation rolling and heating at the mandrel, or by pultrusion, with a pre-heating unit and a hot die, feeding into a cold die (Chapter 5). A take-off to pultrusion is roll forming, using the hot deformability of the material and the forming capability of successive die sets. Fabric and sheet can be preheated with existing equipment and thermoformed, by stamping or by vacuum molding. Co-molding with GMT can combine the mechanical properties of a fabric reinforcement structure, control over fiber placement, and positioning the reinforcement in amount and orientation to suit the design of the product with the advantage of a flowable material. For stamping, relatively low pressures (5-40 atm) and cycle times of up to 1 min are sufficient.

Hot Compaction Technology While one solution to producing very stiff and strong products is to incorporate fibers in a resin matrix up to a fiber volume fraction of about 65 wt%, another technology, based on heating and compacting fibers drawn from the same TP material, can be performed. This procedure has been used to fabricate different products such as plastic packaging PP and PE papers and boards. Hot compaction of high modulus TP fibers produces a very highstrength lightweight RP. Oriented plastic fibers arc compacted inside a mold at a temperature sufficiently high to allow them to coalcsce, without significant loss of mechanical properties. The process has been shown to work with oriented polyolefin fibers, and self-reinforced materials with good properties can also be made using chopped fiber, woven mat or multi-filament yarn. Compacting a number of layers of a

Table 4.11 Comparative properties of commingled glass/TPfilaments

Property

Unit

PP 6O 7/7 balance weave

Glass content (weight) Glass content (volume) Tensile strength (ISO 527) Tensile modulus Flexural strength Flexural modulus Elongation Comp. strength (ISO 8515) Shear strength (ISO 14130) Impact: Charpy unnotched Impact: Izod notched Heat distortion temperature Theoretical density

% % MPa

60 35 350

75 50 420

65 5O 440

60 35 500/180

75 50 700

MPa MPa MPa % MPa

15 280 13 2.5 140

21 340 17.5 2.5 160

25 6O0 23 3.25 410

24/8 380/160 18/6.1 2.5/3.6 230/100

38 400 32 2.0 170

MPa

22.5

22.5

43

24/15

22.5

300 10

300/90 11/3

Source:Vetrotex.

Id/m 2 J/cm 3 kJ/m 2 ~ g/cm 3

220 8 220 159 1.50

PP 75 1/1

PET65 I/I balanced weave

PP604/1

PP 75 unidirectional

300 10 159 1.75

257 1.95

159 1.50

445 15 159 1.75

TRE/PP

SMC

49 20 95

45 35 160

6 150 6

14 300 15

4~

80 70

115 100

0 3

"C3

o

:3 o C

o :3 P~

238 Reinforced Plastics Handbook

woven mat of high-modulus PE fibers has produced an RP with a flexural modulus in all directions of about 11 GPa. H o t compaction technology (compacting TP fibers under heat) is also being studied by resin producers and educational institutions (includes Vantage Polymers, University of Leeds, etc.). Oriented PE fibers are now available with a specific strength greater than that of steel and other fibers, such as aramid. By selectively melting a small proportion of the fiber surfaces, it may be possible to utilize more fully the properties of such high-strength fibers. On cooling, the melt binds the fibers together. In a typical manufacturing process, the fibers are packed together in parallel in matched metal molds, in a heated press at fixed temperature. Pressure is applied to prevent the fiber from shrinking and losing orientation and, after a period, pressure is increased so that the spaces between the fibers arc completely filled with melt. Compaction is complete and the fibers are mainly still circular in cross-section. It is possible to find an optimum balance between stiffness and strength: the stiffness rises as air is removed and then falls at high temperature as the original fiber is destroyed. Transverse strength, however, rises continually with temperature as the fibers are successively melted. Choice of temperature allows the proportion of the two phases, fiber and melt, to be controlled. High modulus melt-spun PE from Hoechst Celanese' Certran has a modulus of about 40 GPa (common unreinforced engineering TPs have a modulus in the range 2.3 to 3 GPa) showed a longitudinal modulus of 37 GPa for unidirectional fiber and 110 MPa longitudinal strength, a transverse modulus of 3.9 GPa and transverse strength 28 MPa. The process continues to be applied to all melt-spun fibers. Other fiber configurations include chopped fibers, woven cloth, and laminates of unidirectional fibers. The process allows a light tough and highly stiff RP to be manufactured using only one phase of the material, which has considerable advantages over two-component RPs.

Bulk Molding Compounds,Thermosets Bulk molding compounds (BMC) are mixtures usually of short glass fibers, plastic, and additives similar to the SMC compound. This dough mixture, with the consistency of modeling clay, can be produced in bulk form or extruded in rope-like form for easy handling. The extrudate type is called a "log" that is cut to specific lengths such as 0.3 m (1 ft).

4. Compound Constructions 239

BMC is commercially available in different combinations of resins, predominantly TS polyesters, additives, and reinforcements. They meet a wide variety of end-use requirements in high-volume applications where fine finish, good dimensional stability, part complexity, and good overall mechanical properties are important. The most popular method of molding BMCs is compression. They can also be injection molded in much the same way as other RTS compounds using ram, ram-screw, and, certainly BMC mixes, conventional reciprocating screw plasticators. From the original dough-like form, it was earlier termed doughmolding compound (DMC) and the name is still often used, but there are now many different forms of the same basic molding compound. It is chemically thickened with 15-25 wt% of glass fiber, usually cut to lengths of 6-25 mm. The filler content is often higher than SMC and glass fiber content lower. The mechanical characteristics are therefore generally not as high as SMC (Tables 4.12 and 4.13) Molding parameters are analogous to SMC, as are design and type of mold. Tables 4.12 Comparative properties of TS polyester molding compounds (28 wt% glass fiber)

Property

Unit

Specific gravity Tensile strength Flexural strength Flexural modulus Izon notched impact strength Water absorption 24 h Barcol hardness

+ 0.05 psi psi psi 106 ft Ib/in 23~176

Sheet molding Bulkmolding Thickmolding compound compound compound (SMC) (BMC) (TMC) 1.85 9,000 25,700 1.5 15 0.25 50 +

1.85 6,000 18,600 1.4 7 0.25 50 +

1.85 10,500 26,700 1.55 18 0.25 50 +

There are BMCs that have good resistance to heat and flammability and, for specific applications, there are grades with reduced flammability, arc resistance, low profile, and cosmetic appearance. There are also special grades for encapsulation, wear resistance, low smoke, electrical conductivity and cooking ware. Shrinkage can be 0.15% (medium), 0.05% (low) and less (Nil). The lowest shrinkage grades are usually not so readily pigmentable. BMC is manufactured by feeding the paste premix into a Z-blade mixer, where chopped glass fiber is added and mixed in until it is thoroughly distributed (Figure 4.5). The resulting dough is either

o m,

ih 0

"0

Tables 4,13

TS polyester molding compounds compared with other engineering materials

Ill

Ill

Property

Unit

BMC

LP-SMC

SMC/C/D/C

Spraylaminate GF-ABS

Steel

Aluminum

"I"

Density Glass content Flexural strength Flexural modulus Tensile strength Tensile elongation Tensile modulus Compressive strength Impact strength Coefficient thermal expansion Oxygen index

glcm 3 Olo N/mm 2 N/mm 2 N/mm 2 Olo N/mm 2 N/mm 2 kJlm 2 CI0 -6 %

1.8-1.9 ~20 70-100 9-12 25-40 0.35-0.5 13-17 160-190 7-15 15-21 23-40

1.7-1.9 ~27 160-190 8-10 70-90 1.3-1.5 10-12 190-210 35-60 15-21 23-40

1.8-1.9 ~60 600-800 20-30 400-600 1.9-3.0 30-40 500/200

1.4-1.5 30-35 130-140 6.5-7.5 70-80 1.5-1.6 7.5-8.5 150-160 70-80 25-30 19-20

7.8-7.9

2.7-2.8

a" 0 0

250-450 210 250-450 20-60 210 300

140- 240 60 100-200 5-12 60 100

12

24

0.9-1.9 23-24

1.25-1.38 20-40 160-170 6-10 75-110 4-6 80-150

4. Compound Constructions 241 extruded in sausage-like shape, or formed into large lumps, and then packed in diffusion-air fight foil. Variations of BMC include:

Measuring/weighing1

ventilationl

FinishedBMC Figure 4,5 Basicproduction system for bulk molding compound (BMC) C I C (continuously impregnated compound): The batch production process is replaced with a continuous process, for larger volumes with more consistent properties D M C (dough molding compound): this is basically the same as BMC but usually without a thickener. L P / L S - B M C : BMCs to which TPs components have been added, to give molding with minimal shrinkage, without cracks or porosity. On a standard test, such as 48 h at 100~ (212~ zero shrinkage is recorded and 0 . 1 % post-shrinkage at 160~ (320~ Thermal expansion is also low compared with other plastics. The operating temperature window is -40~ to 160~ (-40 to 320~ for long periods without serious permanent loss of properties. Brief exposure to higher temperatures is also possible, with heat distortion temperature (HDT) at 1.8 MPa in the region 230-250~ (446-480~ Grades are available with oxygen index ratings from 22% to above 50%, without loss in moldability or mechanical performance. Compounds are also available to UL 94 yellow card approval, to V - O and in some cases 5 V standards at typical design thicknesses of 3.5 mm to 1.5 ram. T M C (thick molding compound): Thickened long-fiber BMC in sheet form, up to 50 turn thick (Figure 4.6).

242 Reinforced Plastics Handbook

Figure 4.6 Basic production systems for thick molding compound (TMC) (left), and continuously impregnated compound (CIC)

ZMC: A molding compound similar to BMC but with considerably longer fibers. ZMC is a complete manufacturing system embracing the molding compound, injection molding machine, and mold, permitting parts with properties superior to conventional BMC and high quality surface finish. Molding temperature is about 160~ (320~ and injection pressure 150-200 bars. Molds are made from high compressive strength steel. NMC (nodular molding compound): A BMC in pellet form for easier handling in molding, but giving lower mechanical strength due to its shorter fiber length.

Bulk Molding Compounds,Thermoplastics Thermoplastics offer a wide range of matrix materials for reinforcement by fibers, flakes, beads, or particulate materials such as talc and mica. Different TPs types and construction (crystalline, amorphous, blended, etc.) are used to meet different processing conditions and/or molded performances (Chapter 3). They bring the great advantage that they are more easily molded in mass-production quantifies [by injection molding (IM)/Chapter 5] than are reinforced thermosets (RTSs). IM machines are available to process short as well as long glass fibers with high fiber content. Reinforcements improve unreinforced TPs (URPs) molded product performances such as strength and stiffness, increase its service temperature, reduce thermal expansion, improve toughness, and improved cost-effectiveness. Most types of TPs can readily be compounded with reinforcing materials that include different forms of glass fibers and high

4. Compound Constructions 243

performance fibers such as carbon fibers. Among the fibers, glass is the main reinforcement. Mineral reinforcement, using high-grade materials, which are treated to bond with the resin matrix (as opposed to use of low-grade minerals as fillers, to reduce compound cost), is also standard practice. Talc and mica are commonly used.

Laminar Composites Combining layers of materials into a laminated is an ancient art, as illustrated by Egyptian plywood, Damascus and Samurai swords, and medieval armor. There are many reasons for laminating; among them are superior strength, often combined with toughness, resistance to wear or corrosion, decoration, thermal or acoustical isolation, color and light transmission, shapes and sizes not otherwise available, controlled distortion, minimum weight, and many others. As an example, automobile or window glass by itself is hard and durable but brittle, and upon impact may shatter into lethal shards. Polyvinyl butyral (PVB) by itself is a tough but limp and easily scratched plastic material unsuitable for window panels. When it is laminated between two sheets of glass a RP results in which the tough plastic layer (PVB), firmly bonded to the glass, prevents the shards from flying when the sheet is struck. Safety glass is thus a composite laminate having properties unattainable by the constituents alone while offering the most valuable characteristics of each. This product has been produced since the early 1930s. For over a century, some RP laminates have become as familiar as to be practically household words. Among them are the RPs consisting of layers of heavy strong Kraft paper impregnated with phenolic resins. The resulting sheet is serviceable for many mechanical and electrical purposes. When combined with a melamine formaldehyde saturated decorative overlay sheet, a familiar decorative sheet is obtained that is widely used for counters, furniture, and wall coveting. Paper of three types are in common use: Kraft paper (high strength when compared to other papers), alpha paper (electrical use), and rag paper (low moisture pickup with good machinability). For heavy-duty purposes such as bearings, tough strong fabrics like cotton duck are substituted for the paper. Fabric-based laminates may be further modified with graphite, fluorocarbons, or other low friction materials to provide low-friction RP beatings requiting no lubricant. Many different RP laminates continue to be produced and used in different markets (principal circuit boards, etc.).

2 4 4 Reinforced Plastics Handbook

Molding Compounds Figure 4.7 provides information on compounding equipment vs. liquid viscosity of the compound. In addition to BMCs many TPs and TSs are compounded with some type of additive, filler, reinforcement, and/or plastic blend with reinforcements that are short to long chopped fibers or milled glass fibers. Commercial compounds arc available in several forms: pellets for injection molding or extrusion, unidirectional tape for filament winding and similar applications, sheets for stamping and compression molding, bulk compounds for compression molding, etc. Reinforcements significantly improve or modify mechanical properties with some additives providing improve or modify mechanical properties. The workhorses of the RTP industry are nylon and ABS with glass fiber (Figures 4.8 and 4.9). Nonfibrous reinforcements are also employed as reinforcements and fillers. They result in increased tensile strength and deflection temperature, but usually with TPs decrease impact resistance. Nonfibrous reinforcements are included when fabricating with exceptional flatness. The nonfibrous include mica, glass beads, and minerals such as wollastonite (talc, calcium carbonate, and kaolin are considered fillers). Like fibrous reinforcements, the nonfibrous reinforcements can be processed by many different technologies. There are also flexible RP compounds. These RTP elastomeric materials provide special engineered products such as bushings, conveyor belts, mechanical belts, high temperature or chemical resistant suits, wire and cable insulation, and architectural designed shapes. The workhorse of the RTS industry is TS polyester (also called polyester-TS) with glass fiber. The fiber reinforcement may be in the form of chopped fibers, porous nonwoven mats, woven fabrics, or continuous fibers. The combination of plastics and reinforcements results in versatile materials with unusual characteristics. The reinforcement adds strength and toughness to inherent weather resistance, moldability, and colorability. Thus RTSs are used because of their increased tensile, flexural, torsional, and impact strengths; increased modulus of elasticity; increased creep resistance; reduced coefficient of thermal expansion; increased thermal conductivity; and, in many cases, lower costs. Other TSs used includes epoxy, phenolic, melamine and urea formaldehyde, silicone, and polyurethane-TS. They may be formulated to produce a range of materials from soft flexible elastomers to tough solids. For structural RP applications, the rigid material is of principal

4

106

Extruders Banbury mixers Roll mills

Ko-Neaders Sigma mixers Other high-shear devices

Modified paddles:

Anchors Helical ribbons Helical screws

10s >= .

Paddles~~~-~.~,~

104

m

o

Turbi n~ ~ ~ ~ " ~ . ~ . ~ . ~ . ~

>

.

Compound 9 Constructions 2 4 5

m

__J

103

Propellers at 1.750 rpm or turbines

102

Propellers at 1,150 rpm or turbines

101

104

10 102 103 Mixing-tank volume, gal

1

Figure 4.7

Propellers at 420 rpm or turbines

Examples and performances of compounding equipment

~ Glass fibres

~

Polymer

Gravimetric

weight feeder

()

Vacuum

Granulator

^

Figure 4.8

^

RTP

pellets

Example for producing thermoplastic bulk molding compounds via an extruder {courtesy of FTP Co.)

246 Reinforced Plastics Handbook

Figure 4.9 Popularlyused for compounding are ribbon mixer and Banbury mixer

4. Compound Constructions 247

interest. They include outstanding wear and abrasion resistance with low coefficients of friction properties. Examples include truck wheels, wear plates, liners for equipment handling abrasive materials, and pump impellers.

Factors for Compounding Modern compounding, especially for engineered plastics, may require the addition of a complex range of materials, each with its own characteristics. The sequence in which these arc introduced into the compounder (usually in the hopper or along an extruder plasticator barrel/screw) is fundamentally important. Additives, fillers, and/or reinforcements with their weight and volume, are usually brought in first, but the latest technology, in which polymerization or crosslinking takes place in the extruder, may alter the sequence. When compounding there may often be an adhesion problem between a nonpolar plastic matrix and additive, filler, and/or reinforcement. It is essential to obtain perfect wetting/coating of the particles by the matrix before it can meet its performance requirement. The size and geometry of the particles influence the case with which it can be compounded and the bond strength with the other components. Surface energy influences the polymer/filler interaction, and hence the mechanical properties, particularly of polar plastics. The surface energy of fillers is not measurable directly. High surface energies produce dispersion problems, reducing mechanical properties, but surface energy may be improved to some extent by surface coating. To assist in obtaining a good dispersion of filler/reinforcement in a compound, it may be useful to employ a dispersing agent (reference Murphy). Typical are phosphoric esters of fatty alcohols, used to improve dispersion of alkaline fillers and pigments in TPs, including polyolefins, polystyrenes, and plastisols. The additive can be introduced before the filler is added or can be premixed with the filler. In polypropylene, it is claimed that calcium carbonate loadings can be increased to 70wt% without significant change in mechanical properties, while Charpy impact strength is improved by better dispersion. An aggregate of calcium carbonate with a multiple surface coating allows calcium carbonate to be added directly to TPs during processing. The granulated product can be mixed easily with the TP and fed directly into the extrusion compounding machine. Redispersion is very good. It can be used with all TPs, and in all processes. Dosing ranges from 2 to 15wt%. Abrasion can be serious when using glass fiber reinforcements and mineral fillers. Fillers with alpha-quartz components

248 Reinforced Plastics Handbook have by far high abrasion rate, but heavy and tabular spars and dolomite also show high abrasion compared with some calcium carbonates. The measurement value usually cited is the Mohs hardness scale, but this is not a decisive indicator.

Aggregation of Filters A continuing problem with particulate fillers is that they often will not flow smoothly, but tend to aggregate, leading to irregular distribution of the particles in a compound, with attendant processing problems, poor surface quality, and reduction in mechanical properties. Research has shown that aggregation is determined by the relative magnitude of attractive and separating forces, the most important factors influencing the homogeneity of RPs being the size of the particles, their surface tension, and the shear forces acting on them during homogenization. The extent of aggregation is always determined by the relative magnitude of the forces attracting and separating. In RPs, the most important attractive force is adhesion, while hydrodynamic forces (such as shear) lead to separation of particles. The size and surface tension of the particles strongly influence aggregation. Although the specific surface area tends to give a good indication of the aggregation tendency of filler, the particle size distribution is more important, since individual particles tend to interact with each other. The results obtained also indicate that the properties of the powder and the suspension may yield valuable indirect information about aggregation. The extent of aggregation may be reduced by nonreactive surface treatment and increased shear. Compounding Basics The use of a virtually endless array of materials permits compounding from the raw material suppliers to the fabricators imparting specific qualifies to the basic raw materials (polymers) and expanding opportunities for plastics. Compounding relies on the polymerization chemistry to mechanical mixing to combine a base polymer with modifiers, additives, and other plastics to develop new plastics. Clearly, these many combinations are endless so that new materials are always on the horizon to meet new industry requirements. Examples of these new compounds are two new grades of high heat connector materials introduced by LNP Engineering Plastics, Div. GE Plastics. They have been designed to resist thermal challenges of infrared reflow soldering, offer shrinkage characteristics of widely used thermoplastic polyesters for easy replacement, and are formulated with a halogen-free, flame-retardant package that can be used in ecological

4. Compound Constructions 249

label applications. These glass fiber reinforced plastic (RP) grades, Thermocomp HT Solder UF-1006 RP, and Thermocomp HT Solder ZF-1006 RP, are targeted to replace lower temperature materials used in lead-free solderable connector applications in the computer peripherals, telecommunications, and data communications industries. The ecological impact of printed wiring board manufacturing is coming under increased international scrutiny. Rapid advances in technology mean a large number of electronic devices (cell phones, computers, printers, and other peripherals) are rendered obsolete each year. Incineration or land filling of nonrecycled waste from these devices can potentially cause lead, a major component of conventional solder, contaminate groundwater. Traditional use of halogenated flameretardants, while effective at suppressing the spread of fire, can release toxic, corrosive gases when burned. These risks have resulted in a variety of global legislation that favor lead-free soldering and use of halogen-free flame-retardants. The two new Thermocomp HT Solder compounds feature a matrix of resin blends and 30 wt% glass fiber. The former is based on polyphthalamide resin (PPA), while the latter is a matrix of modified polyphenylene ether (PPE). Both grades offer high heat distortion temperatures of 260C+, excellent dimensional stability, and excellent flame retardancy. Compounding to change and improve the physical and mechanical properties of plastics makes use of a wide variety of materials as reviewed throughout this book. The major and large market for these materials, such as additives, fillers, and reinforcements, continues to expand as the demand for reducing the cost of plastics, plastics to function in wider or extreme markets, and under stricter regulatory regimes continue to expand. Additives They are substances compounded into a plastic to modify its characteristics. They are basically physically dispersed in a plastic matrix without affecting significantly the molecular structure of the TPs. In TS plastics, additives such as crosslinldng; catalyst; and other agents do purposely affect their structure. They are classified according to their specific functions rather than a chemical basis. While some additives have broad applications and are adaptable to many TPs and TS plastics, others are used exclusively with specific plastics (Chapter 3). Examples of classifications are:

1

assist processing (processing stabilizers, processing aids and flow promoters, internal a n d / o r external lubricants, thixotropic agents, etc.)

250 Reinforced Plastics Handbook

modify the bulk mechanical properties (plasticizers or flexibilizers, reinforcing agents, toughening agents, etc.) reduce formulation costs (diluents and extenders, particle fillers, etc.) surface properties modifiers (antistatic agents, slip additives, antiwear additives, anti-block additives, adhesion promoters, etc.) optical properties modifiers (colorants, pigments, dyes, nucleating agents, etc.) anti-aging additives (anti-oxidants, UV stabilizers, fungicides, etc.) and 7

others (blowing agents, flame retardants, etc.)

Examples of only a few additives are carbon black, carnauba wax, coconut shell, coke dust, macerated filler, shell flour, vermiculite, and wax. Many additives, especially those that are conductive may affect electrical properties. Most plastics, which are poor conductors of current, build up a charge of static electricity. Antistatic agents can be used to attract moisture, reducing the likelihood of a spark or discharge. Fillers These low cost fillers, also called extenders, with their many different inert substances (organic and inorganic with low to high molecular weights) are added to plastics principally to reduce costs. They may also improve processing and physical and mechanical properties, particularly hardness, thermal insulation and stiffness. The particles are usually small, in contrast to those of reinforcements.

The mineral fillers are a large subclass of inorganic fillers comprised of ground rocks as well as natural, refined, or synthetic minerals. Commodity minerals are relatively inexpensive and are used mostly as additive extenders. Other fillers, so-called specialty minerals, are usually the reinforcing types. There are also inherently small particle size fillers such as talc and surface chemically modified fillers. The inert filler are those added to plastics to alter the properties of a product through physical rather than chemical means. Examples of a few are alpha cellulose, ash, calcium carbide, calcium carbonate, carborundum, channel black, china clay, coral, coke dust, diatomaceous earth, dolomite [double carbonate of lime and magnesia filler having the formula (CaCO3) and (MgCO3)], ferrite, flint, fuller's earth, glass spheres, hemp, keratin, lampblack, leather-dust, macerate

4. Compound Constructions 251

filler, magnesium carbonate, milled glass, mica, pumice, quartz, sawdust, talc, vermiculite, volcano dust, and wood flour. Importance of fillers is highlighted by the Single Buoy Moorings of Monaco (www.singlebuoy.com) a major supplier of floating production, storage, and off loading systems (FPSO), has turned to polyetheretherketone (PTFE) filled Victrex| plastic to overcome the corrosion problems of bronze components. The plastic bearings and thrust washers in the mooring systems, driving chains, and swivels provide an extended service life (of at least 10 years), significant weight reduction (making them easier to handle), and excellent load beating capabilities. Many of the mooring bearings and thrust washers are large, up to 50 cm (19.7 in.) in diameter. Corrosion resistance in subsea environments is of prime importance, as FPSO's are constructed in open water to facilitate mooring tankers at offshore oil and gas exploration stations without jetties and breakwaters. Unlike bronze components, which can develop severe galvanic corrosion, PEEK beatings and thrust washers provide longterm corrosion resistance and superior wear resistance. PEEK compound requires no external lubrication, another key advantage in this application. Bronze bearings and thrust washers are subject to premature wear and reduced service life should they run dry. (Victrex plc, Victrex Tech. Ctr., Hillhouse Int'l., Thornton Cleveleys, Lancashire FY5 4QD, UK; Phone: +44-1253-897700; URL: www. victrex.com).

Reinforcements They are strong, usually inert materials bound into a plastic to improve its properties such as strength, stiffness/modulus of elasticity, impact resistance, reduce dimensional shrinkage, etc. They include fiber and other forms of material. There are inorganic and organic fibers that have the usual diameters ranging from about one to over 100 micrometers. Properties differ for the different types, diameters, shapes and lengths. Their properties range from very low to very high values. To be effective, the reinforcement must form a strong adhesive bond with the plastic; for certain reinforcements special cleaning, sizing, finishing, etc. treatments are used to improve the bond. Types of reinforcements include fibers of glass, carbon, graphite, boron, nylon, polyethylene, polypropylene, cotton, sisal, asbestos, metals, whiskers, etc. Other types and forms of reinforcements include whiskers, bamboo fibers, burlap fibers, carbon blacks, platelet forms (includes mica, glass, and aluminum), and hemp fibers (Chapter 2).

252 Reinforced Plastics Handbook

Mixing General theory of mixing usually considers a non-random or segregated mass of at least two components and their deformation by a laminar or shearing deformation process. The object of the sheafing is to mix the mass in such a way that samples taken from the mass exhibit minimal variations, ultimately tending to be zero. The three basic principles are: 1

interfacial area between different components must be greatly increased to decrease striation thickness,

2

elements of the interface must be distributed uniformly, and

3

ratio of mix within any unit or the whole is the same.

A mixture can be described in terms of the statistical deviation of a suitable number of samples from a mean, the sample sizes being dependent upon some length, volume, or area characteristics of the mixture or its properties. Types of mixtures and methods of evaluation range from simple to complex systems. There i s the usual dispersive a n d / o r distributive mixing.

Dispersive Mixing It is the mixing of a fluid/plastic melts with a solid/unmelted plastic that exhibits a yield point. It involves the final melting of a plastic or breaking down an additive such as a pigment in the manufacture of a color concentrate. Distributive Mixing Distributive mixing is the commingling of two fluid/plastic melts so that the scale of fluid separation reduces to where another process (diffusion or a chemical reaction) can occur. The mixing is in a laminar flow regime that is characteristic of NEAT plastics (Chapter 3). It is distinguished by the deformation of the fluid interfaces as a result of the applied shear strain. Distributive mixing relates the amount of interfacial area growth to the fluid strain rate, as distinguished from dispersive mixing, that is a function of the magnitude of the stress. The latter accomplishes droplet and agglomerate breakup; the former is the distribution of those components. As an example, it is aimed at achieving thermal and color uniformity where no solids breakdown is required. Mixing Evaluation There are many variables of mixing and the scantiness of criteria for measuring mixing effectiveness exists. Types of mixtures and methods of evaluation range from simple to complex systems. A mixture can be described in terms of the statistical deviation of a suitable number of samples from a mean, the sample sizes being dependent upon some

4 . Compound Constructions 253

length, volume, or area characteristics of the mixture or its properties. For example if color is imparted by adding pigment and homogeneity is measured by visual impression, the characteristic length is the resolving power of the eye, say 0.001 in. A completely mixed compound exhibits pigment streaks no greater than 0,001 in. However, the color value for any given series of samples would appear uniform to a spectrophotometer that integrates over a 1 in. diameter circle even if the streaks were 0.1 in. thick. Likewise, the intensity of color difference between streaks would affect the resolving power of the eye, or spectrophotometcr, and thus the characteristic length. The means of measuring arc varied. In commercial practice, inspection of color homogeneity, streaks or spots of unmixed filler or plastic is visual. Frequently changes in properties, such as tensile strength, modulus, or density arc used to evaluate degree of mixing.

Fabricating Processes Overview Many factors are important in making reinforced plastics (RPs) the success it has worldwide. One of these factors involves the use of the availability of different fabricating processes. All processes fit into an overall scheme that requires interaction and proper control of different operations. Factors such as good engineering product design and selecting the appropriate plastic are very important but only represent pieces of the "pie." Philosophical many different ingredients blend together to produce profitable products. Fabricating is one of the important main ingredients. In addition to fabricating in-house, there is fabricating outsourcing that also requires controls. It is also called contract manufacttt~g or professional services. This term originally was coined to mean buying rather than making parts. Now it encompasses the much broader concept of using outside organizations to replace people, including entire departments and processes, such as data processing, telemarketing, and customer services. Different fabricating processes and materials of construction are employed to produce RP products (fibers and reinforcing additives) that represent about 20 wt% of all plastic products produced worldwide. Injection molding consumes over 75 wt% of all RP materials with practically all of it being RTPs. The processes range in fabricating pressures from zero (contact), through moderate, to relatively high pressure [2,000 to 30,000 psi (14 to 207 MPa)], at temperatures based on the TS or TP plastic's requirements that range from room temperature and higher (Figure 5.1). Equipment may be of simple construction/low cost with labor costs high to rather expensive specialized computer control sophisticated equipment with very low labor costs for the different processes. Depending on their size,

5

9Fabricating

Processes 255

equipment can process small to large parts (Figure 5.2) Each process provide capabilities such as meeting production quantity (small to large), performance requirements, proper ratio of reinforcement to matrix, fiber orientation, reliability/quality control, surface finish, and so forth versus cost (equipment, labor, utilities, etc.). HEAT RISE AT MOLD GATE

MOLD HEAT

I

HEAT

I TEMPI

TS

HEAT RISE I . ~ 1

AT

DUE TO NOZZLE

SCREW

I

l,Sr'

AVl

BARREL TEMR MOLD

COOL

i I

~.........PLASTICIZING -

TP

~ I*-----CURE TIME .....................

C C'Ej

Figure 5.1 Processing temperatures for TS and TP materials Product size r ..... Large part over lsq ft over 5 Ibs

!

! Over250~ thermosets

Low pressure Lamination Filament winding Compression High-pressure Lamination Post form Adhesive bond Machine Pultrusion

Figure 5,2

I

Thermoforin ! Foam I Heat seal I Weld I Rotoform I Blow mold I Adhesive bond I Structural | Foam | Rim I

"!

Iu~

I

I

i

~igh-vl~_ el Compression Transfer Injection Lamination Pultrusion

Guide to product size vs. process

I

[Less than 250~ 1 It_herm~ lastics |

Over 250~ thermosets

Under 250~ 1 hermoplastics I

,,,I

1

Small part f~ less than lsq over 5 Ibs

I

I

]

I

!

I

lL~ :v~

!

! [High-volume]

Casting Machining Low pressure Lay-up Post form Spray-up Resin transfer

1

Injection Blow m o l d Thermoform Extrusion Rotoform Rim

[Low-volume 1

!

Machine Thermoform Compression Casting Rotoform Foam Adhesive bond

256 Reinforced Plastics Handbook

The plastic may be either reinforced TSs (RTSs) or reinforced TPs (RTPs). The RTSs were the first major plastics to be adapted to this technology. The largest consumption of RTPs is processed by different methods such as injection molding, rotationally molding, or extruded on conventional equipment. There are even RTP sheets that can be "cold" stamped into shape using matching metal molds that form the products. It is called cold stamping because the molds are kept at or slightly above room temperature. The sheets, however, must be pre-heated. Designing good products requires some familiarity with processing methods as summarized in Figure 5.3. Based on process to be used, different wall thickness ranges and tolerances exist. Different unreinforced plastics (URPs) and reinforced plastics (RPs) processed meet different shrinkage rates (Chapter 7). The different processes can have different processing capabilities (Chapter 9). Until the designer becomes familiar with processing, a qualified fabricator must be taken into the designer's confidence early in development. The fabricator and mold or die designer should advise the product designer on material behavior and how to simplify the design in order to simplify processing and reducing cost. Understanding only one process and in particular just a certain narrow aspect of it should not restrict the designer. As an example, it is possible to place reinforcement precisely where it will give of its best properties. With closed molding processes, it is important to understand that the compound, whether thermoset (TS) or thermoplastic (TP), must flow inside the mold, usually under the effects of heat and pressure. While flowing, it will tend to align the reinforcement fiber in the direction of the flow, especially with granular TP molding compounds. In the original design of the product, consideration should be taken of the positioning of the material blanks in the mold. When compression molding, bulk molding compound (BMC) and sheet molding compound (SMC), stamping compounds, or injection molding RTP and RTS compounds, ensure that the material flows in such a way as to gain the optimum alignment of the fiber. It is also important to remember that, while the compound is flowing in the mold, it is also undergoing other changes. It could be crosslinking (TSs), or simple cooling (TPs). Anything in the design or mold construction that obstructs the flow will also tend to imbalance curing or cooling, producing molded-in stress, which will usually exhibit itself as warpage. With proper process control, these type problems are eliminated or tolerated. The pre-mixed molding materials contain randomly arranged fibers. They give properties approximately equal in all directions though with

COMPONENTS Hydraulics.

(Pum~. Va~,,N.Cyund~,. Nozzkm

9P i s s , )

PRIMARY MACHINERY . . . . .

<

injection Molding Machimm

<.

,

Shutoff Valves Gas InjecUon Equipment Quickmold-Claml~ng Systems

UPSTREAM AUXILIARY EQUIPMENT Bulk Material Processing Loaders Feeders Blenders Dryers Kneaders Magnetic Sepuators Prslormers 4 Screw Type) Pmheatars (Hlglt F ~

l

' 'COMPONENTS

'

Process Measurement Screws Biemstallic Barrels & Liners Instruments & Controls Heaters & Heating Elements Motors & Drives On-line InspeclJon Devices

COMPONENTS Parison Control

Figure 5.3

,

PRIMARY MACHINERY ,

Extnaders

"

Thermoform|ng Compression Molding Trsnsfer PmsNe Pu#rualon Rotational Molding

MOLDS AND MOLD PARTS

l

Hot Runner Systems Cold Runner Syatems

DOWNSTREAM AUXILIARY EQUIPMENT . . . . Mold Heating & Cooling Part Conveyors Robotk:a

J I

j

DOWNSTREAM AUXILIARY EQUIPMENT

PRIMARY MACHINERY Blow Molding Machines

.

..

Gauge Inspection Pelletizers I Oicers Cut off Equipment Vacuum Sizing Equipment Takeoff equipment

<

OFF LINE EQUIPMENT

Welders Cleaning Ovens & Baths Printing & Stamping Equipment Assembly Equipment Testing Inspection Equipment

Sllttars

DOWNSTREAM AUXILIAF~ EQUIPMENT

"T'I

Melf Index Rheoer~ers Iml~cf

Fihration Gear Pumps Oies Feed 8locks Static Mixers Continuous Conveyors

Ts~lle

Wetgl~t Eiecfrical t~luea

Scrap Recovery - Granulators 0e freshets

F l o w c h a r t in f a b r i c a t i n g m a c h i n e r y ( c o u r t e s y o f A d a p t i v e I n s t r u m e n t s

(.11

Corp.)

0"

"O -.! 0 1'3 r~ i/I i/i r~ i/i (31 ..j

258 Reinforced Plastics Handbook

some sensitivity to the plastic melt flow direction. These are termed isotropic, usually with isotropy only in one plane (planar). Where a laminate is stacked using different types and forms of reinforcement, the directional properties of each can be harnessed to their best advantage. In addition to using processes specifically designed for over a half century worldwide the more commonly used processes for unreinforced RPs (URPs) also process RPs. They include injection molding (IM), extrusion (EX), thermoforming (TF), foaming, calendering, coating, casting, reaction injection molding (RIM), rotational molding (RM), compression molding (CM), transfer molding (TM), reaction injection molding, rotational molding, and others that include hand lay-up, Marco process, resin transfer molding, and others are to be reviewed. Since glass fibers are extensively used, specifically during IM, the glass fibers will cause wear of metal molds during processing such as plasticating screw/barrels and molds or dies. Using appropriate metals that can provide a degree of extending their operating time can reduce this wear. Be aware that wear will occur and gradually reduce your efficiency in maximizing the performance of the equipment. Cost for replacing or repairing eroded equipment parts has always been included in the cost of operating equipment. Popularly used basic processes each having many modifications so that there are literally hundreds of processes used. The ways in which plastics can be processed into useful products tend to be as varied as the plastics themselves. However only a few basic processes are used worldwide for most of the products produced. If an extruder can be use to produce products it has definite operating and economical advantages compared to IM. It requires detailed process control. IM requires more sophisticated process control to fabricate many thousands of different complex and intricate products. Product markets for IM arc extensive with little to date using extruders. While the processes differ, there arc elements common to many of them. In the majority of cases, TP compounds in the form of pellets, granules, flake, and powder, are melted by heat so they can flow. Pressure is often involved in forcing the molten plastic into a mold cavity or through a die and cooling must be provided to allow the molten plastic to harden. With TSs, heat and pressure also are most often used, only in this case, higher heat (rather than cooling) serves to cure or harden the TS plastic, under pressure, in the mold. When liquid TPs or TSs plastics incorporate certain additives, heat a n d / o r pressure need not necessarily be used. Common features of the different

5

9Fabricating Processes 2 5 9

processes fit into a flow pattern to fabricate products. These features follow a pattern such as what follows:

(a)

Mixing and melting: This stage takes the plastic compound and in turn produces a homogeneous melt. This is often carried cut in screw plasticators, mixer, or other compounders, where melting takes place because of heat conducted through a barrel wall a n d / o r heat generated in the plastic by the action of shear via a screw or mixing blades. Homogeneity is called for at the end of this stage, not only in terms of material but also in respect to temperature. Equipment and RP material development continues to improve and control melts.

(b) Tooling:

When processing plastics some type of tooling is required. These tools include molds and dies for shaping and fabricating products. They have some type of female a n d / o r male cavity into or through which a molten or melted compound moves usually under heat and pressure. They are used in processing many different materials to form desired shapes and sizes. They can comprise of many moving parts requiring high quality metals and precision machining. Some molds and dies cost more than the primary processing machinery with the usual approaching half the cost of the primary machine.

(c)

Melt transport and shaping: In a screw plasticator that melts material the next step would be to build up an adequate pressure in the plasticator so that it will produce the desired shape to be fabricated. In an injection molding process pressure is applied to force the melt into a mold that defines the product shape in three dimensions. In an extruder, the die (that initiates the shape) can vary from a simple cylindrical shape to a complex crosshead profile shape.

(a) Forming and stamping: Processes

such as compression molding and thermoforming can produce different shaped products.

(c) Casting:

With screw plasticator or other systems the melt permits castings in an open or closed mold.

(f)

Non-screw plasticating: Reactive mixing provides the melted compound, such as in reaction injection molding, to produce the plastic.

(g) Finishing:

The final stage after a process fabricates a product usually does not require secondary operations. However, there are products that may require annealing, sintering, coating, assembly, decoration, etc.

260 Reinforced Plastics Handbook

Understanding, controlling, and measuring the plastic melt flow behavior of plastics during processing is important. It relates to a plastic that can be fabricated into a useful product. The target is to provide the necessary homogeneous-uniformly-heated melt during processing to have the melt operate completely stable and working in equilibrium. Unfortunately, the perfect melt does not exit. Fortunately with the passing of time where improvements in the plastics and equipment uniformity continues to occur, melt consistency and melt flow behavior continues to improve simplifying the art of processing. An important factor for the processor is obtaining the best processing temperature for the plastics used. A guide is obtained from experience and/or the material producer. The set-up person determines the best process control conditions (usually requires certain temperature, pressure, and time profiles) for the plastic being processed. Recognize that if the same plastic is used with a different machine (with identical operating specifications) the probability is that new control settings will be required for each machine. Reason is that, like the material, machines have variables that are controllable within certain limits that permit meeting the designed product requirements including costs. The secondary operations fabricating methods include the broad categories of assembling, machining, cutting, sewing, sealing, and forming. Target is not to have secondary operations eliminating extra time and cost. However, there are exceptions where, due to quantity or other factors, advantages occur in time and cost. The machining techniques used are quite common to metal, wood, and other industries requiring modifications to handle conditions such as the brittleness of glass fibers and the meltable or heat sensitive RPs. Plastic shapes can be turned into products by such methods as grinding, turning on a lathe, sawing, reaming, milling, routing, drilling, and tapping. The cutting, sewing, and sealing involve obtaining product pattern by hand, in die-cutting presses, or by automatic methods. The pieces are then put together using assembly techniques such as sewing, heat bonding, welding, high frequency vibration, or ultrasonic sealing depending on the type plastic used. Different techniques are used with certain RPs that can only use certain techniques. When a technique is used for URP, due to the heat transfer condition of glass fibers the RP may not bond or minimize bondability. There are post-finished forming methods that can be used such as postembossing with textures and letterpress, gravure, or screening can print them. Rigid plastic parts can be painted or they can be given a metallic surface by such techniques as mctallizing, barrel plating, or electro-

5

9Fabricating Processes 2 6 1

plating. Another popular method is hot stamping, in which heat, pressure, and dwell time are used to transfer color or design from a cartier film to the plastic part. However, secondary operations can be performed during fabrication to reduce fabricating time a n d / o r costs. Popular is the in-mold decorating that involves the incorporation of a printed foil or other material onto a plastic product during molding so that it becomes an integral part of the product; it can be located under the surface or inside the product. There are applications where the foil provides structural integrity thus reducing the more costly amount of plastic to be used in the products. Each process provide capabilities such as meeting production quantity (small to large quantities and shapes), performance requirements, proper ratio of reinforcement to matrix, fiber orientation, reliability/ quality control, surface finish, materials used, quantity, tolerance, time schedule, and so forth versus cost (equipment, labor, utilities, etc.). There are products when only one process can be used but there can be applications where different processes can be used.

Fabricating Startup and Shutdown Primer and secondary (Table 5.1) equipment manufacturers have procedures for startup and shutdown that provides an initial guide. The actual procedures to follow depend on a number of existing variables that include type of RP being processed and available controls. Information here provides some basic information. Machine operation takes place in three stages. The first stage covers the running of a machine and its peripheral equipment. The next involves setting processing conditions to a prescribed number of parameters for a specific RP, with a specific tool (mold, die, etc.) in a specific processing line; to meet product performance requirements. The final stage is devoted to problem solving and fine-tuning of the complete line that leads to meeting performance requirements at the lowest cost. A successful operation requires close attention to many details, such as quality and flow of feed material(s), a heat profile adequate to melt but not degrade the RP. Processors must also become familiar with troubleshooting guides that are available from equipment manufacturers. There are fabricating turnkey operations. They are complete fabrication lines or systems with upstream and downstream equipment. Controls interface all the equipment in-line from raw material delivery to the end of the line handling the product for in-plant storage or shipment out of the plant. Target is always to reduce fabricating time in order to reduce cost. However, there are the right and wrong ways. Properly setting up

262 Reinforced Plastics Handbook

Table 5.1 Examplesof auxiliary and secondaryequipment Adhesive applicator Bonding Chemical etching Cutting Die cutting Dryer Dust-recovery Flash removal Freezer/cooler Granulator Heater Joining Knitting Labeling Leak detector Machining Material handling Metal treating Metering/feeding material Mold extractor Mold heat/chiller control Oven Pelletizer/dicer Plating

Polishing Printing/marking Process control for individual or all equipment Pulverizing/grinding Quick mold change Recycling system Robotic handling Router Saw Screen changer Screw/barrel backup Sensor/monitor control Software Solvent recovery Solvent treatment Testing/instrumentation Trimming Vacuum debulking Vacuum storage Water-jet cutting Welding Others

the process controls for the equipment and material being used provides the right way. Recognize that there are equipment and material variables that exist and are controllable. Competitiveness built around an obsession for the customer should ultimately be the primary focus in a distribution or manufacturing strategy. The best approach is, therefore, to identify opportunities to improve effectiveness and reduce the costs of the manufacturing and distribution systems, both of which will benefit the customer and, thus, the manufacturer. One opportunity is to consolidate distribution centers worldwide. Another opportunity is to adopt a world-class manufacturing (WCM) approach to fabricating processes. Philosophies and methodologies such as just-in-time (lIT) fabricating to total quality management (TQM) can be applied to cut operating costs and improve quality levels, customer service, and return on manageable assets.

5 Fabricating 9 Processes 263 Reinforced Thermoplastics Fabricating RTPs is mainly by injection molding. There is glass mat TPs molded by pre-heating and stamping, tape layering with TP preimpregnated reinforcement is carried out by a variation of filament winding, pultrusion can be used to produce TP rod/profiles with continuous filament reinforcement, and so on as reviewed in this chapter. RTPs are being used increasingly in all sectors of engineering design, for high performances such as mechanical properties, electrical insulation, lighmess in weight and good resistance to chemicals and corrosion, and/or together with excellent moldability at fast production rates such as by injection molding. Examples of resins used include the nylon family (polyamide/PA), polypropylene (PP), polystyrene, and polyethylene. There continues to be growing applications for the higher-performance RTPs, such as polyphenylene sulphide (PPS) and polysulphone (PSU). Use is made of many other TPs (Chapter 3). High-performance RTPs, which are increasingly used in aircraft and transportation components and in the field of general engineering products, use different molding technology to accommodate the advanced reinforcement structure. Examples include a complex notebook computer case that was one of a number of exercises produced by Composites Horizons Inc., Covina, California (CHI), in response to a request from IBM to design a lightweight mass-producible case. It would have been difficult to injection mold a component with wall thiclmess less than about 1.8 mm (0.070 in) and IBM's baseline design in aluminum was 1.27 mm (0.050 in) thick. C H I created a design using woven continuous carbon fiber in a nylon 12 matrix, at 60 vol% fiber, which gave high thermal conductivity (Table 5.2). The fiber was laid in a 0 / 9 0 ~ arrangement: the additional use of 45 ~ laid fiber was considered unnecessary, and it would have created problems with re-use of off cut waste. The wall thickness of the finished case was 0.89 mm (0.035 in) and its weight was 33% lower than the baseline aluminum design. The thinner wall also offered about 5% more internal volume for an external envelope of the same size. For mass-production of the case, C H I selected a woven carbon fabric powder impregnated with nylon (by Electrostatic Technology Inc.), press-molded in a high-speed fabricating process.

Curing Systems The process of curing TSs is by means of a change in their molecular structure, in which, under certain circumstances, the individual

264 Reinforced Plastics Handbook Table .5.2 Design study: a lightweight computer case press-molded in nylon 12/carbon fiber

Aluminum

(baseline)

Nylon 12/ woven carbon

Nylon66/ short carbon

Nylon66/ log carbona

Epoxy SMC/1-in carbona

Flexural modulus {psi)

10 m

8m

1.5 m

3.5 m

5m

Specific stiffness {in]

100 m

133.3 m

30 m

70 m

83.3 m

Weight (g)

400

290

356

- at 200 MHz

82

55

- a t 1 GHz

95

50

55

33

-

20

9.5

18

EMI shielding (db)

- at 8 GHz Notched Izod (ft Ib/in)

2.4

Source: ElectrostaticTechnology Inc. aThesedesigns were considered unproducible, due to the intricacies of the part.

molecular chains can be made to link up in an irregular fashion, forming a solid infusible network. This is called curing and it will happen, in time, by normal processes (in fact, it was this phenomenon that first attracted the interest of researchers a century ago). For industrial purposes, curing (or crosslinking) is activated by means of special chemicals, heat, or irradiation. The chemistry involved in curing is complex, and the names of the various chemicals are very complex. It will be useful, however, if the engineer or processor is at least familiar with the basic mechanism by which these materials operate, and the overall trade-off effect which often occurs, as one additive improves properties in one direction but may reduce them in another. Standard curing systems are based on two catalyst groups. Several different terms are used in the industry to cover these curing agents: catalyst (not technically accurate, but widely used) and hardener or initiator. There are activators (also called promoters or accelerators) that are used to speed up and enhance the cure. Inhibitors (also known as retarders) perform the opposite function and are used to extend the curing time.

Curing Agents for TS PolyesterSystems TS polyester resins, major and important resin matrix in the RP industry are usually cured by the addition of special chemicals that decompose to free radicals, so offering a simple technique that can easily be controlled, with regard to rate and length of cure. Polyester

5

9Fabricating Processes 2 6 5

resins can also be cured by heat or irradiation and the technology has been used that cure under the effect of ultra-violet. The usual chemical curing agent is organic peroxide, which decomposes under the influence of heat. A wide range of organic peroxides is available, for various thermal stability requirements, from compounds that decompose rapidly to free radicals at ambient temperature to those active only at higher temperatures. The former are not normally used for curing unsaturated polyester resins. More often used are peroxides stable at ambient temperature and decomposing at 50-150C (122302F), but this is not sufficiently active at ambient to cure the resin. Reducing agents such as tertiary aromatic amines, heavy metal salts of cobalt, vanadium, iron, and similar materials are used to accelerate decomposition. Compounds that prevent undue polymerization of the resin are called inhibitors, typically monohydric or polyhydric phenols and some quinones. They are added during fabrication of the resin to ensure storage stability. These can prolong pot life of a resin system containing peroxide and accelerator, particularly with cobalt systems. Inhibitors can also influence the ratio of cure to gel time, as they mainly prolong gel time. Paratertiary butylcatehol extends gel time and pot life at room temperature and at elevated temperatures; 2.6-ditertiary butylparacresol is used with B PO/amine systems, to give lower peak exothcrm and gradual cure. Use of accelerators to aid curing is the most popular method. Curing can occur at below 100C (212F) with organic peroxides combined with accelerators or pro-accelerated resins. Post curing at 80-120C (176248F) is normally required. The normal curing system is ketone peroxide (based on either methyl ethyl ketone, cyclohexanone or acetyl acetone) with cobalt octoate or naphthenate. Alternatively, diactyl peroxides such as benzoyl peroxide are accelerated with diethylaniline, dimethylaniline and dimethyl p-toluidcne. Amine acceleration gives a fast curing cycle but can produce tackiness in thin layers and very strong discoloration during ageing. Ketone peroxide with cobalt acceleration therefore forms the most popular curing system. There are also: dimethylaniline with dibcnzoyl peroxide at room temperature (for normal/long gel times); dimethylparatoluidine (for very short gel times); cobalt octoatc (mainly used with ketone peroxides for polyesters at room and elevated temperatures); cobalt/amine very high reactivity with ketone peroxides for very fast cure (for example polymer concrete); and vanadium special for ketone peroxide,

266 Reinforced Plastics Handbook

hydroperoxide, and peroxy esters, giving short gel times and very high cure speed.

Curing Without Accelerators Without use of accelerators, external heat is required, making a system suitable for mechanical processes, such as hot press molding and continuous impregnation of sheet and profile. Temperatures in the range 120-160C (248-320F) are used to cure in a short cycle; accelerators offer no advantage as the rate of cure depends on thermal decomposition of the peroxide, and typical cycle times are 1-10 min. Usually a combination of long shelf life of the uncured compound with short curing cycle is required, calling for adequate thermal and chemical stability. Organic peroxides for high temperatures are peresters and perkctals. Low initiation temperature with adequate curing performance is given by dimyristyl peroxy dicarbonate or methyl isobutyl ketone peroxides (in the latter case limiting shelf life to a few hours). Combinations of peroxides can be used. The more active types reduce initiation temperature while more stable types give a better degree of cure.

Selecting a Curing System A number of factors must be considered, in descending order of importance: processing conditions: - high-output production batch or continuous process with/without external heat - molds closed or open to air - required shelf life of activated compound: i m m e d i a t e / d a y s / weeks/months possibility of using resin + peroxide and resin + accelerator as separate - components in a two-pot system; -

-

type and size of finished product: thick-walled castings or thermally-insulated moldings, which can reach a peak exotherm of over 200C (392F), producing cracks from internal stress or shrinkage, can be molded better with lessactive curing systems surface coatings (with no exotherm and slow cure with possible air inhibition) can better use very active curing systems - where color is important, accelerators must be kept to a minimum; amines are not suitable, ketone peroxides/metal salts are preferable. -

-

type of resin and other ingredients: gel time is stated at 20C (68F). To achieve fast cure under practical conditions, curing temperature should be at least 20C above the critical temperature.

5

9Fabricating Processes 2 6 7

Table 5.3 provides information on when and where to use curing systems. It provides details on the curing systems as well as accelerators, and inhibitors. The information relates to curing processes to fabricating processes. Table 5,3 Curing systems for TS polyesters regarding when and where to use them Type~form

Main characteristics

Process

Ketone peroxides for cobalt curing at ambient temperatures Methyl ethyl ketone peroxide: -liquid high activity

-liquid low activity

-liquid super activity Acetyl acetone peroxide: -liquid normal activity

-liquid low activity -liquid low activity

Cyclo hexanone peroxide: -liquid normal activity -liquid high activity

Standard for all resins including bisphenol and vinyl esters; relatively short gel times moderate heat evolution little internal stress. Versatile type for all resins particularly vinyl esters; relatively long gel times short mold release times; good for large parts and/or use in hot countries. Special for buttons/button sheets

ABcDEf

Versatile type for ortho- or isophthalicbased resins; relatively short cure time strong heat evolution; suitable for thin-wall moldings. Special for thick-wall moldings; variable gel times reduced peak exotherm short mold release times. Special for very thick-wall moldings; relatively long gel times little heat acceptable mold release times.

aBCdFG

Versatile type for nearly all resins; variable gel times moderate heat little stress; suitable for large or thick-wall moldings. Versatile type for nearly all resins (also vinyl esters); variable gel times relatively short mold release times reasonable mold release factor

AcDEG

abdef

ABCDEG abe

abCE

Benzoyl peroxides for amine curing at ambient temperatures Dibenzoyl peroxide: - 50% powder with phthalate - 50O/osuspension - 40% suspension

Rapidly dissolving in all resins incl. bisphenol A and vinyl ester; variable gel times, strong heat evolution, short release times; no accelerator needed above 70-80~ (158-176~ Pourable/pumpable suspension dissolves rapidly; curing performance as above Pourable/pumable suspension dissolves rapidly; special type for easy dosing/ metering; curing performance as above

abcg

abcG abcG

268

Reinforced Plastics Handbook Table 5,3 continued Type~form

Main characteristics

Process

Organic peroxidesfor curing at 60-120~ (140-248~ Dimyristyl peroxy dicarbonate: technically pure flakes

Special type for curing above 50~ but only with more thermally stable peroxides; suitable for all resin types

Methyl isobutyl ketone peroxide: liquid normal activity

Versatile type for curing above 55~ poss. with more thermally stable peroxides and/or cobalt accelerators; suitable for all resin types

ef

Tertiary butyl peroxy 2-ethylhexanoate: technically pure liquid

Versatile type for curing above 70~ poss. with more thermally stable peroxides and/or cobalt accelerators; suitable for all resin types

fgh

Dibenzoyl peroxide: 50Olo powder with phthalate

Versatile type for curing above 70~ poss. with more thermally stable peroxides and/or amine accelerators; suitable for all resin types

fg

Cumene hydroperoxide: 80% liquid

Special type for curing above 80~ with cobalt accelerators

1,1-Di(tert. butylperoxy) trimethyl cyclohexane: liquid high activity 50% solution in aliphatics

Versatile type for curing above 80~ Quickset in range 120-150~ for hot-press molding SMC or BMC; can be accelerated by promoters. Special for SMC/BMC at 130-160~ without accelerator; not sensitive to fillers pigments and promoters

FGH gh

1,1-Di(tert. butylperoxy) cyclohexane: 50% solution in aliphatics

Standard type for SMC/BMC at 130-160~ without accelerator; not sensitive to fillers pigments and promoters

gH

Tertiary butyl peroxy benxoate: technically pure liquid

Standard type for SM(3/BM(3at 130-160~ can be accelerated by promoters; sensitive to some fillers and pigments (e.g. carbon black). Standard for granulated molding compounds at 130-160~ without accelerator; can easily be mixed in as free-flowing powder

HI

50% powder with chalk

Tertiary butyl cumyl peroxide: technically pure liquid

Special for SMC/BM(3with deep flow at 130-160~ not sensitive to fillers pigments and promoters

1,3-Di(tertiary butylperoxy isopropyl) benzene: technically pure flakes

Special for granulated molding compounds at 140-170~ without accelerator; not sensitive to fillers pigments and promoters; also available as 40% powder with chalk

hi

5

Type/form

9Fabricatin 9

Main characteristics

Processes Process

Accelerators Standard for ortho or isophthalic acid resins with ketone peroxides or peresters gel and cure times vary according to peroxide 20-100~ Special for large batches or high usage can be diluted performance as for above

ABCDefg

Cobalt octoate/dimethyl aniline: liquid mixture in phthalate

Special for bisphenol A or vinyl esters with ketone peroxides or peresters short gel/cure times 10-100~

abcdEG

Dimethyl-p-toluidine: 10% solution in phthalate

For short gel/cure times with dibenzoyl peroxide suitable for all resins 10-100~

acG

Dimethyl aniline: 10% solution in phthalate

For medium gel/cure times with dibenzoyl peroxide suitable for all resins 15-100~

abcG

Diethyl aniline: 10% solution in phthalate

For long gel/cure times with dibenzoyl peroxide suitable for all resins 15-100~

abcg

Di(tert. Butyl}p-cresol techn, pure powder 40O/o solution in xylene (SETA flash point ~30)

Prolongs (up to weeks/months) shelf life - gel time of resin + peroxide - at ambient temperature effect on cure times diminishes with rise in temperature efficient with many types of resin and peroxide

fgHI

Tert. butyl catechol techn, pure powder 10O/o solution in styrene (SETA flash point ~31}

Prolongs (up to many hours) pot life - gel time of resin + (ketone) peroxide + (cobalt) accelerator- at ambient temperature mold release factor improved also efficient at elevated temperatures

acdefghi

Cobalt octoate: -in phthalate with 1O/ocobalt -in xylene with 6-10% cobalt

ABCDefg

Inhibitors

Key to processes: A or a = hand lay-up; B or b = spray lay-up; C or c = injection/vacuum molding; D or d = centrifugal casting; E or e = filament winding; F or f = continuous impregnation; G or g = wet press molding; H or h = hot press molding (SMC/BMC); I or i = hot press molding {granular molding compound) [capital letter =very suitable; small letter = suitable).

Mold Release Mold release agents are generally necessary with RTS resins. These are film-forming coatings that are applied to the mold, but there are also

269

270 Reinforced Plastics Handbook internal mold release agents that can be incorporated as additives in the gel coat or in the molding material itself. Types are available for open and closed molding, TS polyester and epoxy resin transfer molding, casting slab stock, pultrusion, etc. Internal release agents are usually preferred for injection molding RTPs. During processing, the additive migrates to the surface to form a releasing film. In all cases, it is advisable to check the compatibility with the resin, to ensure that there is no detrimental effect to its properties. Liquid mold release provides a flesh coating of wax at each application without causing wax build-up, avoiding the need to take a mold out of production for de-waxing. Paste wax uses pure canauba wax and no silicones. There are durable visible film with non-volatile organic content (such as Sealproof, from Zyvax), offering superior adhesion to gelcoat, RP, and as well as metal and wood. When coated with a proprietary release agent (such as Watershield) it provides multiple releases and reduces downtime due to cleaning. For mold preparation and cleaning, longwearing release films can be applied. A typical system is a semi-permanent agent that polymerizes on the mold surface; grades for cure at ambient and oven temperatures are available. Flange waxes are designed for release of moldings from the flange/edge areas of the mold; they can be applied easily (by cloth or sponge, brush or spatula) and remain smooth and wet during the molding process. Mold sealer is a basecoat for all types of release agents. If a silicone release agent is used, be aware of certain situations. If the fabricated product is to be printed, decorated, bonded, etc. the bond or proper bond probably will not occur. It probably will interfere if electrical connections are to be made on its surface.

Processing and Patience The starmp of fabricating lines usually requires changing equipment settings. When making processing changes, allow enough time to achieve a steady state in the complete line before collecting data. It may be important to change one processing parameter at a time. As an example with one change such as temperature zone setting, or other process control parameter, allow time to achieve a steady state prior to collecting data.

Reinforcement Patterns To process RPs different reinforcement patterns can be used that range from chopped to long fibers, woven to nonwoven, preform to com-

5

Fabricating 9 Processes 271

pounds, and so on. In the past most of the activity in using different patterns has been with TSs and in particular with TS polyester resins. The pattern chosen is dependent on performance required by the fabricated RP product and usually also by the process to be used. Chapter 2 provides information on different types of fibers and other reinforcements used. A general introduction has been provided concerning preforms. However since preforms continue to play an important part in the RP industry since the 1940s additional information is to be presented. As an example, prcforms were used during the 1940s and 1950s with compression molding and the Marco infusion processes. It used pressure, vacuum, or a combination of pressure/vacuum systems that in turn provided proper disposal of styrene monomers and other gases. Preform Processes

As time passed since the 1940s, significant improvements occurred processing wise, equipment wise, plastic wise, and cost wise. This is a method of making chopped fiber mats of complex shapes that are to be used as reinforcements in different RP molding fabricating processes rather than conventional fiat mats that may tear, wrinkle, or give uneven glass distribution when producing 3-D or complex shapes. Most of the reinforcement used is glass fiber rovings. They are desirable where the product to be molded is deep or very complex shapewise. Oriented patterns can be incorporated with continuous fibers in the preforms to develop required directional properties. Different methods are used with each having many different modifications. They include a plenum chamber, directed fiber, and water slurry. Continuous rovings are fed into a cutter and after being cut to the desired lengths, fall into a plenum chamber perforated screen where the air is exhausted from under the screen. A plastic binder of usually up to 5 wt% is applied and is later cured (Figure 5.4). As the glass falls into the plenum chamber, the airflow pattern and baffles inside the screen control its distribution. Preform screen rotates and sometimes tilted to ensure maximizing uniform deposits of the roving. With the directed fiber system strands are blown onto a rotating preform screen from a flexible hose. Roving is directed into a chopper where airflow moves it to a preform screen. Use can be made of a vertical or horizontal rotating turntable. This process requires a rather high degree of skill on the part of the operator; however, automated robots are used to provide a controlled system producing quality preforms (Figures 5.5 and 5.6). With water slurry, chopped strands are in water (take-off used by the paper pulp industry for centuries). It produces intricate shaped preforms

272 Reinforced Plastics Handbook

Figure 5.4 Flow of glass fiber rovings traveling through a plenum machine

Figure 5,5 Schematicof the direct preform process

5

9Fabricating Processes 2 7 3

I i

Pos 1

Figure 5.6

Schematic of the direct preform process spraying two molds

that are tough and self-supporting. Bonding together the preform can use cellulose fibers a n d / o r bonding resins. Where maximum strength is not required, the cellulose content can be sufficiently high to reduce cost. The fibers can be dyed during the slurry process (Figure 5.7). Important to being successful is manufacturing the screen. Different shapes can be used to meet different product designs. Recognize that cylindrical preforms are easier and less cosily to produce than box-like sections. In addition, it is important to recognize that during the rotation of a cylindrical part, the fibrous glass will flow uniformly onto the screen because most sections move at a uniform linear rate. With a rectangular section, it is difficult because the comers rotate in a wider circle than do the center sections and because the airflow is lowest at the comers. Contouring the box shape can improve reinforcement distribution. Preform screens are usually made from 16-gauge perforated material with 1/8 in. holes on 3/16 in. centers. This produces about 40% open area. For some operations, a more open area is required. Perforation patterns are also used to develop specifically designed reinforcement directional properties. The screen is usually designed so that the outside contour is identical with the contour of the mating half of the mold. A screen, which is not of the correct size, will cause a great deal of difficulty in

2 7 4 Reinforced Plastics Handbook

Figure 5.7 Flow of glass fiber rovings traveling through a water slurry machine the molding operation. If the screen is too small, the preform will tear during the molding. If too large, wrinkling and overlapping of the preform will result. The preform is usually heavy on the flat top and light on the edges and comers. Internal baffles may be added in the preform screen to control the airflow, thus giving a uniform deposition of glass. The exact area of the baffle usually has to be worked out on a trial-and-error basis until experience is developed. Close cooperation with the preform-machine manufacturer is helpful. When molding a product with a variable wall thickness, it is possible to vary the thickness of the preform. This is usually accomplished by baffling. Another approach that can be used is to completely block off areas where no fiber is desired. This action saves material that would otherwise be trimmed off and probably discarded. It has also proven practical to combine two or more preforms into one molded part. This technique is very useful where the thickness of the molded part prohibits the collection of the preform in one piece. Also prepared is mat preforming. It is the usual flat fiber mat that is formed into a shape usually using a set of matched dies (often made of fiber reinforced epoxy). A mat is cut to the correct dimensions and

5

9Fabricating Processes 2 7 5

placed over the male half of the mold. Using an infrared device, heat is then applied to the mat and the female half of the mold is lowered. The shaped mat must be cooled before removal from the tool. The resulting preform approximates the shape of the final part to be molded.

CompressionMoldings CM is the most common method of forming TS plastic products. Until the advent of injection molding, it was the most important of plastic processes. CM is the compressing of a material into a desired shape by application of heat and pressure to the material in a mold cavity (Table 5.4). Pressure is usually at 7 to 14 MPa (1000 to 2000 psi). Some RTSs may require low pressures down to 345 kPa (50 psi) or even just contact (zero pressure). The majority of TS compounds are heated to about 150 to 200C (302 to 392F) for optimum cure; but can go as high as 650C (1200F) for the very high performing resins (Figures 5.8 and 5.9). Table 5.4 Examplesof the effect of preheating and part depth of phenolic parts on compression molding pressure(psi)

Depth of molding (in.) 0-3/4

114-11/2 2 3 4

Conventional phenolic Dielectric Not preheat preheated 1,000-2,000 1,250-2,500 1,500-3,000 1,750-3,500 2,000-4,000

3,000 3,700 4,400 5,100 5,800

Low-pressurephenolic Dielectric Not preheat preheated 350 450 550 650 750

1,000 1,250 1,500 1,750 2,000

A force is also required to open the mold that is usually much less (20% of clamp) than the clamping force. One has to ensure that available opening clamping pressure is available. Usually this requirement is not a problem. Clamping predominantly use hydraulic systems. Also becoming popular are all electric drive systems a n d / o r with hydraulic/electrical hybrid systems. The actual mechanical mechanisms range from toggle to straight ram systems. Each of these different systems has their individual advantages. Mold cavities can be filled separately with reinforcement and resin. The reinforcement can be in loose form or as a preform. Very popular is the use of RTS sheet molding compound (SMC) or bulk molding

276 Reinforced Plastics Handbook

Figure 5.8 Various configurations of compression molding presses

5

9Fabricating Processes 2 7 7

Figure 5.9 Exampleof land locations in a split-wedge mold

compound (BMC) (Figures 5.10 and 5.11) (Chapter 4). Also used are RTP sheets and compounds. With TSs CM can use preheated material (dielectric heater, etc.) that is placed in a heated mold cavity providing a uniform heat through the compound and reducing cycle time during molding. The mold is closed under pressure causing the material to flow and completely fill the cavity. Based on how the RTS compounds are prepared they can be processed at low or high pressures. Chemical crosslinking occurs solidifying the TS molding material. The closed mold shapes the material usually by heat and pressure. With special additives, the TS material can cure at room temperature. It would have a time limit (pot life) prior to curing and hardening. Based on the compounds preparation sufficient time is allowed to store and

Figure 5.10 Compressionmolding sheet molding compound (SMC)

Figure 5.11 Compressionmolding bulk molding compound (BMC)

278 Reinforced Plastics Handbook

handle the compound prior to its chemical reaction curing action occurs.

Figure 5.12

A 400 ton compression press with 18 platens

The mold is fastened on the platens. These platens usually include a mold-mounting pattern of bolt holes or "T" slots; standard pattern is recommended by SPI. Platens range from the usual parallel design to other configurations meeting different requirements. The parallel type can include one or more "floating" platens located between the stationary and normal moveable platens resulting in two or more daylight openings where two or more molds or flat laminates can be used simultaneously during one machine operating cycle (Figure 5.12). The other designs include shuttle (molds in which usually two, or more, are moved so that one mold is positioned to receive material and then moves to the press permitting another mold to receive material with this cycle repeating; result is to permit insert molding, reduce molding cycle, etc.), rotary or carousal system, and "book" opening or tilting press (Figure 5.13).

With certain plastic compounds mold breathing is required. This action is also called mold bumping, dwell pause, dwell, gassing, and degassing. It is a pause or repeated pauses in the application of mold pressure using plastics that gives off gases during the heating process; also to remove any entrapped air. This on-off-on pressure action occurs in parts of a second just prior to having the mold completely closed to allow the escape of gas a n d / o r air. Application is with many TS plastics, vulcanization of reinforced TS elastomers, and any material that releases gases. Use is made of CM charging tray; also called loading tray. It is a tray designed to charge simultaneously with material all the mold cavities of

5

9Fabricating Processes 2 7 9

Figure 5~13 Book opening large compression press a multi-impression mold. The device can operate by using a tray with openings where the material is placed (manually or usually automatically) and in turn a withdrawing sliding bottom tray that initially closes the openings and slides exposing openings matching the top tray so material drops into the cavities.

280 Reinforced Plastics Handbook Applying vacuum in a mold cavity can be very beneficial in molding plastics particularly when using low clamping pressures. Press can include a vacuum chamber around or within the mold providing removal of air and other gases from the cavity(s) and safely disposing them. CM is a matched die molding system that can be broadly defined as a process in which the loading a n d / o r closing of the mold causes the molding material to conform to the desired configuration in the mold cavity and in which cure (RTS) or cool (RTP) takes place while material is contained in the mold. The process includes cold press molding and resin transfer molding (RTM). The threshold of medium series production lies between 1000 and 10,000 parts per year, above which the molder may have to consider changing to injection molding or low-pressure molding, to speed up the production rate and achieve two smooth surfaces, while retaining a degree of freedom in terms of shape and size. Changes continue to be made in molding compounds for use in compression molding. As an example is Owens Corning's future technology, dubbed SS2. It assumes that SMC will always be somewhat porous if it is manufactured using current techniques. The firm is developing a different means of placing an SMC charge in a tool so that the charge's surface stays on the surface. The reinforcing material and other additives stay in the middle of the charge after molding rather than being squeezed out, as occurs during standard compression molding.

Compression Transfer Moldings Also called transfer molding not to be confused with the more popular resin transfer molding system to be reviewed. It is a method of compression molding principally RTSs. The plastic is first softened by heat and pressure in a transfer chamber (pot) and then forced by the chamber ram at high pressure through suitable sprues, runners, a n d / o r gates into a closed mold to produce the molded part or parts using two or more cavities (Figures 5.14 and 5.15). Usually dielectrically preheated circular preforms are fed into the pot.

Cold Press Moldings Cold press molding represent compression molding that involves only a moderate investment in equipment and using a lower-powered press than with large series processes. Molds can be made from RP materials rather than from high-quality steel. The reinforcement is generally mat which can be preformed if necessary; fabric can also be used. Molds can be at ambient temperature or heated to 80C (176F). Cold press

5

9Fabricating Processes 2 8 1

Figure 5.15 Screwtransfer where RP

Figure .5.14 Schematic of transfer press

travels from hopper, through screw plasticator, to pot, and into the mold cavities

molding uses a low pressure of 1-5 k g / c m 2 on the projected area of the molding and is suitable for small batches with good surface finish. Matched male and female molds are employed, in a vertical press, giving good surfaces to both sides of the molding and a higher degree of dimensional and quality consistency than is usually obtained from hand lay-up operations. The molds are prepared and a release agent is applied. The reinforcement (usually tailored to size and shape) is then laid in the open mold and a charge of liquid catalyzed resin is poured over the lay-up. The mold is then closed, to allow cure to take place. When cured, the mold is opened and the part removed automatically. It may well be moved to a simple jig to hold the shape while allowing the full cure to take place (meaning that de-molding can take place at an earlier stage). Unheated molds can be used, which can be produced relatively inexpensively from special reinforced/filled epoxy resin compounds (backed if necessary with a material such as concrete). Since this technique relies on the normal exothermic curing reaction of the resin, a low-pressure press can be used, employing the power of the press only to raise and lower the mold-half, while using mechanical clamps to secure the mold halves during curing. Cold press molding is simple, low cost and effective but requires lengthy molding cycles (usually measured in hours).

282 Reinforced Plastics Handbook Hot Press Moldings The matched die hot press molding process identifies compression molding. It can be greatly speeded up to molding cycles measured in seconds to minutes (depending on part thickness). Use is made of heated molds produced in high grade mold-steel, on a high-pressure hydraulic press. The molds are cleaned and treated with release agent as necessary (agents that last for several cycles are available) and the reinforcement and resin are laid up as for cold press molding. When the molding cycle is complete, the press opens and the molded part is removed and, if required, trimmed. It is probably moved to a jig for post-cure. This is normally carried out in a vertical press (compression molding), which is also convenient for loading inserts into the molding tool. High-pressure hot press compression molding is the highest-volume method for compression molding RPs parts, usually reaching an economic output at.a level of about 10,000 parts/yea. To facilitate shop floor working, prepared combinations of resin, reinforcement, and additives (prepregs) are increasingly used, for easy handling and reduction in press-loading times. The most widely used are known as bulk molding compound (BMC) and sheet molding compound (SMC). For this matched-die compression molding, metal molds are used, which are considerably more expensive than plastic molds because of the high pressures and high mold temperature.

Flexible Plunger Moldings This process is a take-off from compression molding that uses solid material male and female matching mold halves. This unique process uses a precision-made, solid shaped heated cavity and a flexible plunger that is usually made of hard rubber or polyurethane. This two-part system can be mounted in a press. Rather excellent product qualities are possible at fairly low production rates. The reinforcement is positioned in the cavity and the liquid TS resin is poured on it. Also used are prepregs, BMC, and SMC. The plug is forced into the cavity and the product is cured. The plunger is somewhat deeper and narrower than the cavity. It is tapered in such a manner that contact occurs first in the lowest part of the mold. Ultimate pressure usually used are up to 400 to 700 kPa (58 to 100 psi) in the plunger causes the contact area to expand radially toward the rim of the cavity, thereby forcing the resin and air ahead of it through the reinforcement with the target of developing a void free product.

5 Fabricating 9 Processes 283 The pressure conforms to irregularities in the lay-up, permits wall thickness to be varied within reasonable limits, and makes a good surface possible only against a metal mold surface. The fact that the heat can be applied only from the cavity side leads to longer cure cycles. This factor tends to produce resin richness, and consequently greater smoothness on the side of the solid mold surface. Flexible Bag Moldings An air inflated-pressurized flexible-type envelope can replace the plunger. This process provides higher glass content and decreases chance of voids. Limitations include extensive trimming and only one good surface. Laminates This refers to many different fabricated RP processes such as contact/ low to high-pressure laminates, and continuous laminations. It usually identifies flat or curved panels using high pressure rather than contact or low pressure. It is a product made by bonding together two or more layers of laminate materials. The usual resins are TS such as epoxies, phenolics, melamines, and TS polyesters. A modification of this process uses TPs. The type of materials can be endless depending on market requirements. Included are one or more combinations of different woven a n d / o r nonwoven fabrics, aluminum, steel, paper, plastic film, paper, etc. High-pressure laminates generally use pre-loaded (prepreg) RP sheets in a hot mold at pressures in excess of 7 MPa (1000 psi) (Table 5.5). Compression multi platen presses are used; up to at least 30 platens producing the flat (also curved) sheets at high production rates. Laminates are molded between each platen simultaneously. Automatic systems can be used to feed material simultaneously between each platen opening and in turn after curing and the multiple platens open cured products are automatically removed. The contact or low-pressure laminates use prepregs that cure at low pressures such as TS polyester resins. Depending on the resin formulation just contact pressure is only required such as using hand-operated rollers. The usual highest pressure that identifies low-pressure laminates is at 350 kPa (50 psi). In industry, for almost a century these laminates are used for their electrical properties, impact strength, wearing qualifies, chemical resistance, decorative panels, or other characteristics depending on laminate construction used with or without a surfacing material. They are used for printed circuit boards, electrical insulation, decorative

2 8 4 Reinforced Plastics Handbook Table 5,5 High-pressurereinforcedTSlaminatesusing different resins

Reinforcement

E

0

~

-~

-~

~

m

Resin type

Production form

Phenol formaldehyde

Sheet Tube Rod Molded-macerated Molded-laminated

Melamine formaldehyde

Sheet Tube Rod Molded-macerated Molded-laminated

Polyester

Sheet Tube Rod Molded-macerated Molded-laminated

Epoxy

Sheet Tube Rod Molded-macerated Molded-laminated

Silicone

Sheet Tube Rod Molded-macerated Molded-laminated

"~-

t/~

panels, mechanical paneling, etc. The major change in the process about a half century ago was making the operation completely automatic that significantly reduced labor cost.

5 • Fabricating Processes 2 8 5

Hand Lay-Ups This is the oldest and in many ways, the simplest and most versatile process for producing RP products. Overall, this open molding is a low cost process that has different names such as open, contact, bag, or infusion molding where slight differences or overlaps may exist between them. Different market uses at times develop different processing names. However, it is usually slow and is usually very labored intense. There are also automated systems for relatively high production runs that significantly improve lay up procedure, reduce labor lay-up, fabricating time, and cost. See information concerning "Layout of fabric reinforcement" in Chapter 6 Aerospace, All Plastic Airplanes. The non automated process consists of hand tailoring and placing one or more layers of usually fibrous reinforcements (random oriented mat, woven roving, fabric, etc.) on a mold and followed with saturating the reinforcement layers with a liquid plastic (usually TS polyester) (Figure 5.16). Usually it is required to coat the mold cavity with a parting agent. Gel coatings with or without very thin woven or mat glass fiber scrim reinforcement are also applied to provide smooth and attractive surfaces. Molds can be made of inexpensive metal, plaster, RP, wood, etc.

Figure 5.16 Contactmolding by hand lay-up

Depending on the resin preparation, the material in or around a mold can be cured with or without heat, and commonly without pressure. Curing needs include room temperature, heat sources, bag (BagM),

a" r e-i

Ill 1-4Ill -I",1 el 0" 0 0

Figure 5,17

Aut0mated-integrated RP vacuum hand lay-up process that uses TS polyester prepreg sheets

5

Fabricating 9 Processes 287

vacuum bags, pressure bags, autoclaves, etc. An alternative is to use prepreg and sheet molding compound (Chapter 4), but in this case, heat is applied with low pressure via an impermeable sheet over the material. This process can produce compact structures that meet tight thickness tolerance. Generally, the process only requires low-cost equipment that is not automated. However, automated systems have been used. Figure 5.17 shows Grumman's automated-integrated hand lay-up system. It uses TS prepreg sheet material. Automation includes cutting and providing the layout of the cut prepreg in a mold. In turn, the designed RP assembly is delivered to a curing station such as an oven or autoclave. This process can be recommended for prototype products, products with production runs that require thickness fight tolerance control, and molding complex products that require high strength and reliability. The size of the product that can be made is limited by the size of the curing oven. However, outdoor UV via outdoor sunlight curing or room temperature curing plastic systems permits practically unlimited product size. Alternate curing methods are used that include induction, infusion, dielectric microwave, xenon, UV, electron beam, or gamma radiation. The general process of hand molding can be subdivided into specific molding methods such as those that follow. The terms of some of these methods as well as others reviewed here overlap the same technology; the different terms are derived from different sections of the RP industry during different periods since 1940. Bag Moldings

Process applies an impermeable tailored flexible bag (parting film, elastomer, etc.) over an uncured thermoset RP product located in a mold cavity (male or female), sealing the edges (bagging), and introducing a vacuum a n d / o r compressed air pressure (or water) and heat around the bag. It provides a means of evacuating air and other gases as pressure is applied. Hand operated serrated rollers arc usually used to squeeze out voids, air, etc. This high labor technique can produce compact structures that meet tight thicl~ess tolerance simulating injection molded products. This technique is also applied with other RP fabricating processes. Since the 1940s this process has been used in fabricating high performance structural parts, particularly for large parts, for military and commercial components, bridge components, containers, machine housings and covers, sports car bodies and components, and boat hulls and components.

288 Reinforced Plastics Handbook

The mold (usually female, such as a boat hull or tank) is cleaned, prepared, and sealed (Figure 5.18). Where it is of single curvature only, it may be possible to use a plastic film as a solid release agent but usually the mold is coated with a release agent and a gel coat. Surfacing tissue (of fine glass fiber reinforcement) can be applied, to produce a good smooth surface, before the main reinforcement (usually in the form of chopped strand glass mat) is laid in place, trimming the pieces to size and adding additional local reinforcement as necessary. Liquid catalyzed resin (mixed with pigments and such additives as are needed) is then carefully poured over the reinforcement. This lay out is then covered with a flexible bag and the whole assembly is worked over with handrollers (serrated), to ensure even distribution of the resin and (most important) effective wetting-out of the reinforcement. The objective throughout is to ensure a good bond between resin and reinforcement, eliminating all voids and air bubbles (as these will impair the physical properties of the final molding).

Figure 5.18

Glass fiber swirl mat/TS polyester RP hand lay up boat shell

5

9Fabricating Processes 2 8 9

Core materials such as rigid foam, balsa wood, or honeycomb may be added during the reinforcement lay up. Inserts, such as metal fittings or reinforcements can also be incorporated and virtually encapsulated in resin and reinforcement. Finally, the completed lay-up in its mold is moved to a separate area for curing, which may take several hours or may be speeded up by controlled heating, in an oven, under infra-red sources, etc. When finally cured, the molding is removed from the mold (in many cases, the mold may itself be dismantled, to facilitate de-molding, especially where reverse curvature is involved). The molding can be trimmed, finished and fitted out as necessary. A number of moldings can be bonded to each other.

Advantages: 9 relatively low investment cost for equipment and tooling 9 great flexibility in part shape and laminate design 9 wide range of physical properties, according to type of resin and amount and type of reinforcement 9 relatively inexpensive materials.

Disadvantages: 9 threatened by government regulations (volatiles, worker exposure, hazardous waste) 9 difficulty of quality control, due to dependence on the skill and expertise of individual laminators 9 relatively slow production/high labor cost one molded controlled surface only.

Equipment required: 9 laminating brushes 9 brush cleaners/renovators 9 metal rollers: paddle roller 2-6 in width x 5/8-1.75 in diameter; disc roller (for removing air from awkward areas): 3 ribs x 1.5 in diameter laminating rollers, with extra pile/long hair/short hair for applying resin/gelcoat. The limitations improvements.

of lay-up

have

led

to

development

of many

290 Reinforced Plastics Handbook Vacuum Bag Moldings This process also called just bag molding, is the conventional bag molding, hand lay-up, or spray-up that is allowed to cure without the use of external pressure. For many applications, this is sufficient, but maximum consolidation may not be reached. There can be some porosity; fibers may not fit closely into internal corners with sharp radii but tend to spring back. Resin-rich a n d / o r resin-starved areas may occur because of draining, even with thixotropic agents. With moderate pressure, these defects or limitations can be overcome with an improvement in mechanical properties. One way to apply such moderate pressure is to enclose the wet-liquid resin material and mold in a flexible membrane or bag, and draw a vacuum inside the enclosure (Table 5.6). Atmospheric pressure on the outside then presses the bag or membrane uniformly against the wet lay-up. An effective pressure of 10 to 14 psi (69-283 kPa) is applied to the product. Air is mechanically worked out of the lay-up by hand usually using serrated rollers. The vacuum directly helps to remove air in the wet lay-up via techniques such as using bleeder channels within the bag (using material such as jute, glass wool, etc.) to aid in the removing of air and permit drainage of any excess resin. This layup is than exposed to heat using an oven, heat lamp, or other device. Table 5.6 Dimensions of typical disposable vacuum consolidation materials.

Type

Width (mm)

Breather/bleed fabrics

1550

Roll Thickness length (m) (mm)

Surfoce mass (g/m2)

Moximum operoting temperature (~

5

100

150

205

10

50

340

205

-

160

Perforated release films

(rigid) 122

0.025

183

(elastic)

0.025

183

-

260

Vacuum bag film

3400

0.050

50-250

-

205

3

15

-

100

Tacky tape

1.2

Vacuum bag film is usually a polypropylene film, modified to resist elevated temperatures. The elastic nature of the film offers high formability and resistance to puncture, also permitting the film to be stretched over complex molds without need for a large number of tucks and folds, so improving the efficiency of the vacuum. The film is suitable for use with prepreg and wet lay-up laminating systems in an autoclave.

5

Fabricating 9 Processes 291

9 Breather~bleed fabric is a 5 mm or 10 mm thick uncompressed felt of temperature-resistant synthetic fibers, treated with mold release. The material has good drapability, allowing use with large and complicated mold patterns. It can be used also as a bleed fabric to absorb excess resin from wet lay-ups. 9 Perforated release films are made from modified polypropylene and can be rigid (recommended for use on flat or uncomplicated mold surfaces) or elastic (thin and stretchable, for large complex molds without need for tucks and folds). The films have good mechanical properties and performance at elevated temperature and are naturally self-releasing, treated on one side to assist adhesion to the breather fabric or a protective film. 9 Tacky tape is a butyl-based vacuum bag sealant giving high elasticity and tenacity. It has exceptional sealant properties, eliminating the risk of imperfect seals often found in the initial phases of vacuum bag application, so improving the vacuum efficiency and reducing labor. It is suitable for polyester, vinyl ester, and epoxy laminating systems.

Vacuum Bag Moldings and Pressures To maximize properties in the product higher pressure is needed in the conventional vacuum bag system. A second envelope can be placed around the whole assemblage. Air under pressure is admitted between the inner bag and the outer envelope after the initial vacuum cycle is completed (Figure 5.19). In addition to air, application of pressure can be by steam or water that forces the bag against the product to apply pressure while the product cures. Still higher uniform pressures can be obtained by placing the vacuum assemblage in an autoclave. By this technique, an initial vacuum may or may not be employed. Result in using an autoclave is ensuring development of maximum molded product performances. Using this combination of vacuum and pressure bags results in ease of air or gas removal and higher pressures resulting in more dcnsification.

Figure 5.19

Schematic of vacuum bag molding

292 Reinforced Plastics Handbook Autoclave Moldings As a further improvement on the hand lay-up, vacuum bag, spray-up processes, and other processes it is possible to insert the laid-up molds (depending on size) into special bags, which are then evacuated a n d / o r placed in an autoclave for cure under controlled (steam) heat and pressure. This vacuum consolidation method produces high-quality moldings, with complete exclusion of air bubbles and improvement to the inner surface of the molding. The controlled curing conditions also improve quality and consistency and allow high performance resin systems to be used, while opening the way to a more rapid cure with faster turn-round of molds. This technique is widely used for higherperformance moldings, such as for aircraft and aerospace applications. Vacuum bag molding is a modification of hand lay-up, in which the layup is completed and placed inside a bag made of flexible film, and all edges are sealed. The bag is then evacuated, so that the pressure eliminates voids in the laminate, forcing excess air and resin from the mold. By increasing external pressure, a higher glass concentration can be obtained, as well as better adhesion between the layers/plies of laminate. Some items for the process can be disposable. Some of the different RP processes are used in conjunction with the use of an autoclave oven (Figure 5.20). Hot air or steam pressures of 0.36 to 1380 MPa (50 to 200 psi) is used. The higher pressure will yield denser products. If still higher pressures are required (avoid this approach unless you have consider the danger of extremely high pressures), a hydroclave may be used, employing water pressures as high as 70 MPa (10,150 psi). The bag must be well sealed to prevent infiltration of high-pressure air, steam, and/or water into the molded product. In all these approaches, the fluid pressure adjusts to irregularities in the lay-up and remains effective during all phases of the resin cure, even though the resin may shrink. Use of this process includes seamless containers, tanks, pipes, etc.

~

essure line

Part

ool Steam coils

AUTOCLAVE

Figure 5.20 Schematic of hand lay-up bag molding in an autoclave

5 Fabricating 9 Processes 293 Autoclave Press Claves

This process simulates conventional autoclave by using the platens of a press to seal the ends of open chamber. It provides both the force required to prevent loss of the pressurized medium and the heat required to cure the RP inside. Wet Lay-Ups

This method is sometimes combined with bag molding to enhance the properties. This procedure can be called bag molding. Because it is difficult to wet out dry fibers with too little resin, initial volumetric fraction ratios of resin to fiber are seldom less than 2:1. On a weight basis the ratio is about 1:1. Liquid catalyzed resin is hand-worked or automatically worked into the fibers to ensure wet-out of fibers and reduce or eliminate entrapped air. Glass fiber/TS polyester RPs (GRP) remains a major focus in the boat business. Crafts are still being laid up in open molds by traditional manual wet lay-up using chopped strand mat (CSM). Requiring only modest start-up investment, this accessible, entry-level technology is used for thousands of working and leisure craft annually. GRP craft range from 7 ft dinghy/tenders to plastic minehunters in service with leading navies. As an example glass RP boats in use are visually almost indistinguishable from traditional, but more expensive, wooden craft. Slightly higher tech is the Raptor Sportier, an advanced personal watercraft (PWC) produced in North America. Although hand laid in glass fiber molds and room temperature cured, the all-glass prototype incorporates 00/90 ~ woven fabric and stitched triaxial reinforcement as well as chopped strand mat. Hull cavities are filled with two-part polyurethane foam for buoyancy and noise reduction. Conyplex in the Netherlands, like many series production boatbuilders uses glass fiber constructions, including in its latest Contest 44 and 50 yachts, to achieve easily driven hulls of modest displacement. Performance of its new-generation boats is further enhanced by wing keels, an RP wet lay-up appendage. The company has been transitioning to resin injection molding techniques.

Spray-Ups The mold is prepared as for hand lay-up but the resin and reinforcement are applied either by spray gun, which can be operated manually or by robot. This gives a more reproducible process, with greater control over the amount of each material that is deposited, opening the way to complete automation. The process has been a popular system

2 9 4 Reinforced Plastics Handbook

with RP production for over half century. Many different fabricated products have been made by spraying. Included has been using the reinforced spray-up as non-structural and structural supports to solid materials (Figure 5.21).

Figure 5.21 Thermoformed plastic, used as the female mold, is backed up with sprayed RP

With time passing significant new developments occur particularly in the spraying equipment. An air spray gun includes a roller cutter that chops usually glass fiber rovings to a controlled short length before being blown in a random pattern onto a surface of the mold (Figure 5.22). Suppliers of spray-up equipment continue to produce cleaner, reduced styrene emissions (as low as 2.2%), higher capacity, more

Figure 5.22

Contact molding by spray-up

5

9Fabricating Processes 2 9 5

uniform spray pattern, and more versatile. Types and performances of spray guns are many such as external or internal mixing gun, distributive/turbulent mixing gun, air atomized, airless, etc. As the fibers leave the spray gun simultaneously, the gun sprays the usual catalyzed TS polyester plastic. The chopped fibers can be plastic coated as they exit the gun's nozzle (Figure 5.23). The resulting, rather fluffy, RP mass is consolidated with serrated rollers to squeeze out air and reduce or eliminate voids; automatic equipment is also used. A closed mold with appropriate temperature and pressure produce products.

Figure 5.23 Various methods of spraying

If required alternate layers of sprayed fibers with layers of woven roving or other fabric construction can be included during the spraying cycle.

296 Reinforced Plastics Handbook

It is possible to deposit several layers until the desired thickness is obtained. The quality of the part will depend directly on the efficiency of impregnation and removal of entrapped air. When the required thickness has been built up, the lay-up is worked over manually as with hand lay-up. This method is used both in-plant and out of doors, for work such as on-site application of reinforced corrosion-proof coatings to chemical and similar plant. The fact that resin and reinforcement are in spray form makes it essential that the operatives use protective clothing, including face-masks, to protect them from volatile chemicals, particularly vapor from styrene (which is used as a solvent). Regulations governing emission of styrene at the workplace are being progressively tightened worldwide, by EPA and OSHA in the USA, and by national authorities in Europe. Selection of suitable spray guns is important, to ensure that chopping and mixing of the components is effective and that operation is safe and comfortable. Although cost of this equipment is relatively low compared with costs of material, labor, and overheads, correct selection of equipment is still vital. For example, assuming a daily use of two barrels of resin (1000 lb), ten boxes of glass (500 lb) and two gallons of catalyst (15 lb), with a standard resin/glass/catalyst lay-up mix of 6 6 / 3 3 / 1 wt%, annual material costs can be calculated as US $342,372, suggesting that cutting costs on equipment is a false economy if it does not produce more effective use of materials (cost here are subject to change). Typical spray-up systems draw the resin from the manufacturer's drum by positive displacement double-acting pump, filtering through a fine mesh screen with control devices to ensure steady even flow. Catalyst is similarly pumped, with pressurized air in the catalyst accumulator to exert back pressure against the pump. The ratio of catalyst to resin can be adjusted at the pump, typically from 0.75% to 3% _+0.1%. Glass strands are threaded through ceramic-coated eyes to the chopper and the chopped glass is dispersed evenly throughout the resin fan and carried to the mold surface, with very little trapped air, requiring little rollout. Spray guns are available for gelcoat, chopper, saturator and flow coater, at outputs of 3.6-9 kg (8-20 lb)/min resin, 1.8 kg (41b)/min glass two-strand chopper, or 1.1 kg (2.61b)/min one-strand chopper, giving a total laminate deposition of 5.4 kg (12 lb)/min with two strands. Air consumption is 9-10 ft3/min. For higher volumes, four- and six-strand choppers are also available, dispensing 17-19 kg/min resin and 33% glass content.

5

9Fabricating Processes 2 9 7

Spray guns provide the following: 9 easy start-up with accuracy and repeatability, with a precision proportioning system fitted to a 12:1 ratio positive displacement resin pump. This has a rack and pinion drive for smooth linear motion, eliminating use of unequal forces and requiring only an easy dial setting to program catalyst delivery between 0.5 and 3.5% 9 continuous adjustability of catalyst mixing ratio between 0.16 and 2.5% with a resin roller impregnator 9 some equipment allows the same gun to be used for spraying, wetout, flow coaters, chopping, resin transfer molding and roller attachments, in a range of internal mix applicators with an airoperated pistol machined from 6061 aluminum stock. Attached to the gun body is a series of modular plates allowing the fabricator to select the type of nozzle outlet 9 linear columns of resin can form the spray pattern, at significantly lower atomization levels. The nozzle can be used as a chopper as well as for simple resin wet-out, using a patented air-assist containment system to increase resin/catalyst transfer efficiency and is an external mix design. As well as reinforcement, different spray systems have been developed to handle other materials at the same time: 9 granite gel coat can be sprayed directly from the shipping container with a special system, with automatic recirculation modes delivering a fast and predictable spray pattern. Adjustable disperse air control gives a uniform dispersion of granules at very low pressure 9 metal flake can be sprayed with an airless air-assisted system. The flake can be applied separately or together with a gel coat (the former gives better reflectivity). Airless air-assisted spraying reduces overspray with savings of up to 50%. Dry fillers and extenders can also be sprayed 9 reground laminate, from recycling processes, can also be fed into some types of spray nozzles, acting as a filler with good mechanical properties in the lay-up.

Airless internal mixing A patented hydraulic injection system is claimed to provide a truly airless internal mixing method. As well as ensuring thorough blending of materials, reducing waste and contributing to strength of the laminate, it also significantly reduces styrene emissions. The system relies on a positive displacement pump and uses low-pressure hydraulic atomization to break the resin into large droplets after mixing, which improve saturation of roving by their stronger penetration than smaller droplets.

298 Reinforced Plastics Handbook

It is automated by a four-axis bridge robot, which can be set in motion just by pressing a few buttons. Graphical software is used to enter the coordinates and the four-axis design allows efficient spraying of threedimensional molds up to 9 m (29.5 ft) wide. A further development incorporates a mechanically blended foam unit, to automate foam applications. A low-pressure glass fiber polyester spray plant also gives low styrene emission and little mist formation. Resin and hardener are mixed and an automatic pump delivers safe exact proportions of peroxide from original containers, no peroxide being dispersed in the air. The German Technical Monitoring Service has confirmed an emission of only 5 ppm and low-pressure equipment with internal mixing also ensures that no peroxide is freely dispersed into the air. For spray lay-up with low emission, it is claimed that external equipment can over-atomize resin and catalyst, but an internal mix system operating at lower pressure creates a 0 larger particle size which has less surface area exposed to atmosphere where styrene can flash. The flow-chop nozzle (from Venus-Gusmer) is designed to carry glass with no atomization of raw resin, catalyst or mixed material, in an overall design claimed to disperse glass throughout the resin pattern with minimal loss of glass.

Turbulent Mixing Hydraulic injection also reduces air entrapment, so that roll-out can be quicker, giving a laminate with improved properties. The units are designed for medium production rates of 1.8 kg (4 lb)/min. Systems using external mixing simply combine resin and catalyst within the spray pattern, but inclusion of a device to improve mixing (such as a turbulent mixer) improves performance of equipment. The design fits inside the gun head, to mix catalysts and resin thoroughly, using a continuous spiral groove with many cross-cuts, creating a 235 mm (9.25 in.) mixing path to ensure a complete blend. Again, airless mixing permits low-pressure atomization, which greatly reduces styrene fume emission and cuts down waste.

Distributive Mixing Distributive mixing enhances airless internal blending by pre-mixing catalyst and resin before they pass through the turbulent mixing device, giving further all-round improvements in quality and economy.

Foaming Polyester Using compressed gas instead of chemicals to foam polyester resins can reduce control problems and heat reactions. Mechanically blended foam processing systems use a non-reacting additive pre-mixed into the resin

5

9Fabricating Processes 2 9 9

before the gas is introduced. Compressed gas does not normally have a lasting foaming effect and the resin bubbles immediately begin to burst, but the additive sustains them until cured, also working to produce a uniform size and shape of bubble. The process can be used to foam a wide variety of resins, with foam density dependent on the gas used. Relatively large cells provide good compressive strength. Foam layers can be sandwiched between polyester/glass laminate skins, giving better bond strength. In chop and spray applications, the fiber sprayed with foam need no roll-out, offering savings when the unit is used with robot automation. A wheel-mounted range of pressure-feed dispensing roller machines (by applicator) blends compressed gas with a special polyester resin to create a foamed material with good impact resistance and compressive strength. Good working conditions with minimum styrene emission are claimed. No roll-out is needed after spray-up application, saving labour time and sandwich constructions can be made on one step, without waiting for layers to cure. A new dispensing unit uses patented Double Flow Technology to give an accurate catalyst dosage with good mixing with the resin. A pneumatically-operated trigger on the shaft gives individual adjustment and there is only one part in the solvent pump. The output is 1.8 to 6 kg (3.9-13 lb/min). A similar design is also used for a gel coater unit.

Ancillary Equipmentfor Spraying Ancillary equipment for spray-up work includes: 9 automatic gun/robot arm mounting, with variable volume accessories 9

wall-mounted systems

9 flow coater nozzle (eliminating atomisation and significantly reducing over spray) 9 air-assisted nozzle (for pattern-shaping of internally mixed catalyst and resin and optimizing the mix design) 9 catalyst alarm (to monitor catalyst flow, rather than pressure) 9 air purge attachment (to inject air through the mixing tube while flushing and providing extra turbulence to move thick fillers during clean out) 9 resin roller dispenser attachments (instead of spraying, these dispense the mix internally through small holes in the roller) 9 air motor shut-off(safety override) valve 9 nitrogen accumulator charge system floor and ceiling mount booms.

300 Reinforced Plastics Handbook Bag Molding Hinterspritzen This patented process allows virgin or recycled RPs such as PP and P C / A B S to thermally bond with the backing of multilayer PP based fabrics providing good elasticity. This one-step molding technique provides a low cost approach for in-mold fabric lamination that range from simple to complex shapes.

Contact Moldings Also called open molding or contact (very low) pressure molding. It is a process for molding RPs in which the reinforcement and TS polyester resin are placed in a mold cavity. Depending on plastic used cure is either at room temperature using a catalyst-promoter system or by heating in an oven without pressure or using very little (contact) pressure. Contact molding gave rise to bag molding, hand lay-up or open-mold, and lowpressure molding. It has played a significant role in molding RPs. It is difficult to surpass if a few products are to be made at the lowest cost. The process relates to what was reviewed for Bag Molding. Resin lamination should n o t be carried out at a temperature of less than 20C (68F). A catalyzed/promoted resin is heat-sensitive and catalyst levels should be adjusted to varying temperature as recommended by the manufacturer. With resin laminating, where space is limited, mold preparation such as releasing and gelcoating can be done in a tent made of polyethylene film (which can also be used as a warm area for curing resins in cold weather). When working with TS resins, hot water, soap, and an eyewash system should always be available. Styrene vapor is heavier than air, so ventilation or extraction equipment should take off vapor from the lowest part of the mold, or the lowest level of the molding area. Air bubbles in a laminate reduce strength and may impair corrosion resistance. To minimize air bubbles, the following are recommended: 9 Avoid violent mixing, which can mix air into the r e s i n - but ensure that the catalyst is mixed in thoroughly. 9 Apply resin to the mandrels first, then apply the glass and roll it into the resin. Air bubble problems are inevitable when resin is applied to dry glass. 9 Roll the laminate from the centre, out to the edges, firmly but not too hard. Excessive pressure can fracture any existing bubbles and make them more difficult to remove. 9 Eliminate all the bubbles from one ply before starting on the next. 9 Thoroughly clean the rollers between uses.

5 Fabricating 9 Processes 301 Useful materials and equipment include a range of toggle mold clamps such as the following: 9 hold-down vertical: 100-1200 lb 9 hold-down horizontal: 60-750 lb 9 flush mount: 300-700 lb 9 pull action: 375 lb 9 straight line: 300-2500 lb 9 squeeze action: 2 0 0 - 7 0 0 lb. As well as the materials and molds, resin lamination of all types needs a broad back-up of equipment for application and materials for cleaning. Many suppliers offer the full range and give useful comprehensive advice: 9 drum carriages 9 buckets, pots (polyethylene) 9 knives, scissors, snips 9 tapes/rules 9 laminating brushes. Styrene monomer is used as a thinner and can also be used for cleaning wax buildup from molds. Paraffin wax solution is an organic solvent that can be added to the final layer of a laminate to prevent stickiness; up to 2% by weight can be added. Details on styrene monomer use are given in Chapter 3 Thermoset Plastics, TS Polyester Solvents.

Squeeze Moldings This method is a take off between resin transfer molding (RTM) and hand lay-up. The reinforcement and a room temperature curing TS polyester resin are put into a mold. In turn, the mold is put into an air pressure bag where the resin is slowly forced through the reinforcement in the mold cavity at low pressures of about 30 to 75 psi (200 to 500 kPa). The RP is cured at room temperature in unheated molds. It is a slow process so one or a few products per day is usually molded.

Soluble Core Moldings This technology is also called fusible core molding, soluble core technology (SCT), lost-wax molding, loss core molding, etc. This technique is a take off and similar to the lost wax molding process used

302 Reinforced Plastics Handbook during the ancient Egyptian times fabricating jewelry. In this process, a core is usually molded of a low-melting-point eutectic alloy (zinc, tin, etc.), water-soluble TP, wax formation, etc. During core installation, it can be supported by the mold core pins, spiders, etc. The core is inserted in a mold (IM, CM, casting, etc.) and plastic injected or located around the core. When plastic has solidified and is removed from the mold, the core is removed by melting at a temperature below the plastic melting point through an existing opening or will require drilling a hole in the RP. Cores of metal alloys have been used in production of automobile air intake manifolds, pump and valve housings, etc. In a typical application, lightweight RP cylinders, said to be about half the weight of aluminum equivalents, are molded on fusible cores (which have themselves been cast in GRP mold). The core molds reduce tooling costs by up to 90% and mold-making time by several days, making it viable to produce single-piece RP components. Prototype high-pressure cylinders have been produced, using the technique. The cores are cast in a split GRP mold, using a bismuth-based alloy, formulated to flow freely and reproduce closely the contours of the mold. When the core has been cast, an uncured RP material shell is placed over it and cured. When the RP shell is cured, the alloy is melted out at 137C (278F), producing a single-piece RP cylinder, with an accurately dimensioned interior. The melted alloy is recovered and recycled. Alloys with melting points up to 250C (480F) are available, meaning that the technique is flexible enough to be applied to a range of RPs curing and molding at relatively high temperatures. Cylinders of up to 5-liters capacity can be produced with the present technology, to withstand pressures of up to four times the design rating.

Lost-Wax Moldings When this soluble fusible core molding technique was first used to fabricate structural supports it involved a rectangular bar of wax wrapped with RPs (such as glass fiber/TS polyester resin) (Figure 5.24). After the RP is cured (bag molding, oven, autoclave, etc.) in a restricted two part mold to keep the rectangular shape, the wax is removed at low heat by drilling a hole or removing the ends. The result is very high strength RP rectangular channel. Its shape can be rectangular, round, curved, etc. This process was used during 1944 to fabricate the first all plastic airplane. This lost wax process was used with bag molding the RP sandwich monocoque construction fuselage, wings, etc.

5

Figure .5.24

9Fabricating Processes 3 0 3

Lost wax process fabricated a high strength RP structural box beam

Marco Processes During the 1940s to 1960s, this matched mold and bag molding process was used extensively to fabricate many different RP products. It was the forerunner for resin transfer molding (RTM), infusion molding, and other RP processes. Reinforcements are laid up in any desired pattern as in BagM and RTM in a mold cavity. Low cost matched molds (wood, etc.) confine the reinforcement. In this initial process, a horizontal open mold trough at the molds parting line surrounds the usual two-part mold. An opening (hole) usually in the center of the top mold halvc provides liquid catalyzed resin to flow under controlled pressure into thc mold cavity (Figurc 5.25). The plastic melt flows into the cavity to encapsulate completely and wetting the reinforcement. With proper wet-out of fibers, voids are eliminated and excellent bond of fiber to resin occurred. The resin exits into the mold's trough; the trough has controllable restrictions that aids in dispersing the resin in the cavity. In addition, vents are located in the mold located where resin is not properly covering the reinforcement or the last areas of the mold to be filled. When the mold has filled, the vents and the resin inlet(s) are closed. This mold was either not enclosed or enclosed in a sealed box, etc. When enclosed gases, etc. were released they were trapped and disposed. This relatively closed mold method when first used was the forerunner of the resin transfer molding (RTM) and the different infusion processes. Other approaches were incorporated in the Marco process that included a vacuum applied in the opening with resin flowing from the trough (reversing the melt flow), vacuum via the trough with resin flowing from the opening entrance in the top mold half, push-pull

304 Reinforced Plastics Handbook

Figure .5.25 Use is made of vacuum, pressure, or pressure-vacuum in the Marco process

action on the resin where pressure and suction was applied in the center hole with limited and controlled vent and trough openings, and reverse of the push-pull action so it takes place from a restricted trough with limited and controlled mold opening (or openings). The Marco process was engineered with different shape and size resin drainage channeled ribs and vents to control melt flow through and around fibers. With the vacuum system, it was a takeoff of vacuum bag molding with or without pressures.

Reinforced Resin Transfer Moldings Reinforced resin transfer molding (RRTM) is also identified as just resin transfer molding (RIM). It is a closed mold, low-pressure process in which a preplaced dry reinforcement fiber construction (such as woven and nonwoven fabric or a fiber preform) with or without decorative surface material is impregnated with a liquid plastic through an opening in the center area of a mold (Figures 5.26 and 5.27). The resin at about 100 to 200 psi (0.69 to 1.38 MPa), possible as low as 50 psi (0.3 MPa) pressure [and possibly assisted by vacuum (VARTM)])moves through the reinforcement located in the mold cavity. The air inside the cavity is displaced by the advancing resin front, and escapes through vents located at the high points or the last areas of the mold to be filled. When the mold has filled, the vents and the resin inlet(s) are closed. After curing via room temperature hardeners a n d / o r heat, the part is removed. This process provides a rather simple approach to molding designed RP parts in relatively low-cost molds (using low pressure), and the molds are manufactured in a short time. It can also incorporate

5

9Fabricating Processes 3 0 5

vacuum to assist resin flow; with VARTM the process is called infusion molding. This type of action could be identified as a take-off to the Marco process.

Figure 5.26 Description of the reinforced resin transfer molding fabricating system

Figure 5.27 Cut away example of a mold used for resin transfer molding mold

306 Reinforced Plastics Handbook

RTM was described May 1957 (at the BPF Reinforced Plastics Conference), in a paper on work dating from 1954 at Bristol Aircraft, Filton, UK. It is basically a liquid resin version of compression transfer molding; a process in which a charge of compound is placed in a transfer pot and is injected into a closed mold, usually by a plunger system. The method allows the compound to be suitably prepared melt and then transferred fast and accurately into the mold, in which the required reinforcement has already been placed, in suitable form. Essentially, the RTM fabricator places a preform in the mold, which is then closed. The catalyzed resin system is then pumped into the mold, impregnating the reinforcement. Heat can be applied to the mold to shorten the cure-time and the finished part is then removed. Drawbacks of the system in the past have been the manual lay-down of reinforcement, high-energy consumption, need for ventilation, and difficulty of demolding. There was no control over fiber orientation and the lay-up required separate surface veil. Past developments have gone a long way to rectify these drawbacks, but it remains vital to maintain accurate control over the process, if consistent specifications (such as acceptable surface finish) are to be achieved. Control and monitoring systems have been developed, so that RTM is an important process for molding RP parts to high levels of quality and reproduceability. Operating at low pressure, it uses lower-cost machinery and molds than compression or compression transfer systems. It offers an economic means of medium volume production of high quality parts. For example, for production of automobile components up to 30,000 per year RTM is preferred over compression molding with SMC because of lower capital investment (about 10% and 20% of the cost of a typical SMC compression molding plant) and versatility in component design. Components of large surface area (up to 2.5 m 2) can often be more economically produced in low-pressure RTM because of the lower tooling cost and low tonnage presses (both SMC and sheet steel require higher pressures for molding/stamping). RTM is competing over autoclave molding for production of high performance aerospace and sporting components, using advanced materials such as epoxy resins and carbon fiber reinforcement, with accurate fiber placement systems, to mold (for example) RP propeller blades. It is also frequently used in production of sandwich (such as foam core) structures, where high molding pressures could damage or dislodge the core. Novel smart core molding technology is now applied to RTM, for production of 8.5 m long rotor blades for wind power generators. Compared with hand and spray lay-up, the RTM process also offers an

5 Fabricating 9 Processes 307 environmentally preferable option, with better quality assurance and lower process economics. It has demonstrated an ability to accommodate foam cores, precise thickness changes, inserts and different fiber styles, all integrated simultaneously. The trend is now towards perfecting catalyst injection as the preferred route, with machines metering and mixing over a wide ratio, up to 200: 1. Experience has shown (not for the first time) that it is not satisfactory to convert equipment from another process. Converted spray meter mix machines, for example, can give poor control over mix ratios and backpressure in RTM and specialized machines now favored. These give higher output with low nozzle pressure, pump speed control, precise catalyzed mix start-up, automatic predetermining of shot volume control, gel timers, automatic shutdown and clean out, recirculation systems to and from the mixing head, and process data acquisition. Mold design has also proved to be a key factor to its success. Automatic mold clamping systems with built-in manipulators and low-cost pneumatic presses have also assisted the development of RTM. Equipment Equipment wise five processes are available: manual, braiding, knitting, thermoforming continuous strand mat, and directed fiber preforming. The last two are most applicable to large-size industrial parts. Continuous strand mat is better for medium/small series where investment of robot preforming cannot be justified, but price differential between rovings and continuous strand mat, plus scrap rate (less than 2%) makes directed fiber a very economical way of producing preforms for high volume applications, especially when the part involves deep draw or complex geometry. RTM is capable of many variations, and significant modifications have been introduced in recent years, testifying to the commercial attractiveness of the process. The technology depends on: preparation of the resins to be injected, controlled injection with regulation of the cycle and a tracing/copying system by which each phase of the operation is recorded. Until recently, development has been inhibited by the lack of efficient cost-effective preforming technology and over-long cycle times. The latest developments have centered on mixing, resin flow, process control, feeding, etc. Mixing Technologies The basic mixing head technology developed for polyurethane components can be applied also to RTM for other reactive chemicals. A typical metering system today can handle TS polyesters, epoxies and

308 Reinforced Plastics Handbook

acrylics, using impingement high-pressure mixing in a self-cleaning head not requiring solvents for rinsing, giving an output of 100--400 cm3/s at ratios from 100:1 to 100:2.5, for an injected weight of up to 40 kg (88 lb). Cylinder metering is used (with advantages in processing filled and abrasive resins); with common oil tank feeding two pumps for resin cylinder and mixing head accumulator and catalyst cylinder. Twocomponent reactive resin blending is possible with metering to +_2%, at 25-2000 cc/min, in a volumetric ratio range of 1:1 to 40:1 (Table 5.7). Table 5.7 Equipment selection chart for resin transfer molding Polyester Medium to large size parts High volume hydrajectors 5:1 Power ratio

10:1

Power ratio

Small to medium size parts

Epoxy Advanced composite

Standard volume hydrajectors

No or medium filler loading

Re:~in transfer ram

Two component resin/hardner

11-4.7:1 mix ratio

5-50 Ib/min

Higherfiller loading 4:1

Power ratio

7:1

Power ratio 8:1 Power ratio

No or medium filler loading

2:1-11:1 mix ratio

I EPo21

1 1-8:1

Higher filler loading

mix ratio Higher fiberglass content

I EPo, I

Low flow

A Wolfangel design runs four components, at 40 kg/min output, metering and mixing resin, peroxide, accelerator and inhibitor on-line, so making it possible to fill a large tool in one minute. Compared with a pre-mix arrangement, an on-line mixing system also guarantees fresh resin, which gives better flow through the glass fiber pack. A user is claimed to have achieved a timesaving of nearly 50% in molding large vacuum-assisted components.

5 Fabricating 9 Processes 309 Improvement of Resin Flow and Injection Irregular flow and pressure during the mold-filling sequence can cause waviness, dry patches and overloading. Since many advanced RTM resins arc solid or highly viscous at room temperature (and therefore all machine hardware must be thoroughly heated), a compact injection machine needs to have custom-fitted heated mantles on the reservoirs, pumps, fittings and mixers to eliminate any cold spots. The heating capability is from ambient to 150C (300F) and insulation ensures that, even when operating at over 100C (212F), the exterior is only warm to the touch. A modern machine is kept to 760 x 1000 mm (2.5 x 3.30 ft) floor space. One or two components can be injected, maintaining pre-programmed pressures of between 140 and 2050 MPa: the ratios are from 1:1 to 150:1, flow rates up to 1500 cm3/min and flow rate and injection pressure are both controlled. A dosing unit suitable for all flowable two-component materials is available, adjustable to any required mixing ratio, with pneumatic drive operated by push-button. Further development for RTM makes it possible to produce high quality moldings at high volume: designed to overcome problems with resin flow and wetting out of reinforcements, all injection parameters can be controlled by programmable logic control (PLC), allowing optimization both of flow and pressure within the actual mold. A low-pressure injection system, with 4:1 ratio pump at 9.5 liters/min output, is available, with a stainless steel catalyst delivery pump offering rates of 0.5 to 4.5%. The injection gun has a single moving valve, which shifts when the gun is activated. The system includes complete loop recirculation, air logic maintaining consistent static and dynamic pressure, and a stroke counter located at the injection gun. Low-cost injection systems have been developed for RTM systems. The Spartan and VR-2 units, respectively, inject TS polyester and vinyl ester systems with a catalyst content ranging from 0.5-4.5% and can handle closer ratio mixes, as for epoxy or hybrid systems. The two can be combined in a single unit (VR-3).

Improved Process Controls Available is a programmable logic-controlled machine for a one-stroke machine with no pulsing of resin flow and full control of all filling parameters. It uses hydraulically driven and computer-controlled delivery cylinders, with the catalyst cylinder mechanically connected to the material cylinder, for accurate and complete dosage of the components. The system

310 Reinforced Plastics Handbook allows for pre-setting of all mold-filling parameters and control of all aspects of injection. A catalyst flow monitoring and alarm system demonstrates outstanding sensitivity over the whole range of flows in meter mix machines, for RTM and also for spray and dispensing machines. Various options offered include a miniaturized light-emitting diode bar display repeater, for remote mixing head mounting, and an enlarged wall-molded catalyst flow indicator. The unit is designed to fit to any meter mix machine and is an inexpensive solution to the problem of accurate monitoring of catalyst flow. Another monitoring system, which can be retrofitted to a range of makes of machine, can measure catalyst flow rates down to 6 m l / m i n (equivalent to 0.5% catalyst) pumped with the resin at an output lower than 1 liter/rain. It has two electronic flow indicators, 100 mm scale meter, and 10-element light-emitting diode (LED) display. With a controlled flow-pressure module, an accurate RTM unit (from Magnum Industries, USA) allows the user to select exact fluid pressures, for high flow rates eliminating pressure differentials and surges during pumping. A minimum of moving parts gives quick easy flushing at low and high pressures. The catalyst level can be held to an accuracy of within 0.1%. The Megaject Mark II injection system, from Plastech TT, offers facilities such as pre-setting the amount of catalyzed resin to be injected (pre-determining counter), pre-setting safe nozzle pressure (mold pressure guard), catalyst flow sensor and auto-stop (Catal), and automatic valve and controller (autosprue).

Feeding and Cleaning An industry-standard programmable logic control has been added to a RTM valve, which allows a single pump to feed ten stations and can give remote flushing without removing the gun from the mold. The control works in concert with the computer-controlled process monitor, operated by remote keypad and, in combination, greatly improves and facilitates the RTM process. A connector developed by Wolfangel leaves a clean injection port every time, avoiding the need to clean or clear the port after every molding. The system uses pneumatic tubes similar to fire hoses in size and construction to apply a uniform clamping force over the whole molding tool (which is a continual problem with conventional clamping systems), while permitting rapid opening and closing.

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Preform Systems

The Swedish company Fiberteknik AB has developed VARIM, using Aplicator's P-4 robot preforming system and RI-10 injection machine to give a fast and economic net preform production, using a pair of perforated screens of the same shape as the molding tool. A computer controlled robot with a chopper forms a veil by spraying glass fiber filaments onto the screen and air is sucked through to hold the glass in place. Chopped or continuous strands are then sprayed onto the veil, either randomly distributed or oriented to meet performance specifications and a powder binder is sprayed with the glass. The lower part of the screen is then moved into the press and the upper part is applied to compress the preform, using hot air to melt the binder. The cycle time depends on the maneuverability of the robot, preforms area, part complexity, and required glass load. The maximum capacity for the chopper is in the range of 3 kg/min but, on complicated shapes and narrow corners, the robot must work more slowly to deposit the glass evenly. Time required to consolidate the fibers is very short (less than 30 s), irrespective of surface area and glass load. Automations

Added to an RTM line is automation that gives advantages in production, reduction of materials wastage, and increase in part consistency. Ongoing R&D programs by several manufacturers are converting it from a slow labor-intensive process into an industrial system for production of high-volume parts for the automotive industry. Among the first results are: a fully-automated RTM system, from preforming to injection stage; two new preforming processes and development of a new one-stroke pump, and mold inlet valve and sealing/filling system. The automated system is based on a robot with several glass fiber delivery systems, including glass fiber choppers. Typically, with three glass fiber delivery systems, the first delivers glass fibers for the surface veil (a low-tex direct roving opened up into single filaments, chopped and transported pneumatically to the nozzle). The main chopper produces 25-125 mm strand lengths and a powdered binder is combined with the glass fiber in pneumatic tubing (a device attached to the nozzle also permits orientation of the fibers in the desired direction). The third glass fiber system delivers continuous fibers, metered and delivered through a pipe by a speed-controlled motor; an electronically controlled knife cuts the roving when required at two speeds, the higher for making loops of continuous fibers, the lower for straight

312 Reinforced Plastics Handbook

oriented fibers robot placed in desired direction. A mold carrier with preform screens completes the system. A production line package from Matrasur (the RTM Concept), which is designed to optimize throughput and maximize control, with guaranteed quality, allowing precise costings to be set and ensuring adherence to environmental constraints. It features a volumetric injection system with double action constant flow and low pressure. Technology is used for a uniform mix and for manipulating and closing molds. A gun permanently fixed to the mold gives automatic injection and flushing. To reduce costs, a glass mat can be laid in the molds instead of using a preform. The system is able to produce two to three parts per hour per mold, with gelcoat (approximately 24 parts per day), regardless of size. Without gelcoat the rate increases to 5-6 parts per hour. Magnum Venus Products (MVP) simplified the RTM process with its comprehensive line of systems and services-PrecisionTECH TM RTM. This concept covers the entire process, from initial consultation, through to training of staff. To start with, MVP offers consultation on the design of the customer's specific system, even designing a turnkey line for larger operations. With the design completed, MVP will build the part-specific TransPRO T M Preform and TechLock TM Clamp system. For automation, the OptiLogic TM Control and Uniport TM Injection Sprue can be incorporated. A diverse range of pumping systems is available, from basic to high-volume systems. Once the system is built, MVP offers training on the process and equipment to the customer's staff. A fully-automated RTM plant, for high consistency and reduced costs, is producing at 20,000 parts/year at Sisteme Compositi SpA, Frosinone, Italy. A smart control system comprises a mathematic model simulating the rheology and kinetics of the resin system, a sensor for temperature, pressure and degree of polymerization, data acquisition, and software for real-time comparison between predicted and experimental data and servomechanisms. Resin and gelcoat systems are stored in separate rooms in thermostatic tanks under pressure to prevent solvent evaporation, stirred continuously by pneumatic motors and with levels controlled by load cells. Resin is transferred by hydraulic pump and ge 1coat by pneumatic pump giving a feed to a specific robot. The pump control is based on precise and controlled pressure balance between resin/catalyst and gelcoat/catalyst ratios. A resin injection gun was developed to interface with the injection gate valves, with an anti-dripping system. Molds are opened automatically when the sensors measure a preset degree of polymerization, reducing cycle times. Five hydraulic hoists on the five parallel molding lines

5 Fabricating 9 Processes 313 instead of molding presses control tool movements, simplifying operations. A comparative cost study between hand lay-up, SMC, and smart RTM for production of class A Euroclass 380 bus body panels, showed a specific mono-skin structure body panel weighing 5 kg showed material costs were similar for hand lay-up and RTM and about 30% lower than SMC. Although a single hand lay-up tool was 85% lower than an RTM tool, this was offset by the need for many more tools to match a life cycle of nearly 3000 parts, and RTM tooling costs were 50% lower than for SMC. Labor time per cycle was three minutes both for RTM and SMC, compared with 60 minutes for hand lay-up. The investment amortization time was fixed at seven years.

RTM Melt Resin Filling Monitoring Monitoring the flow of resin during the RTM process is important to producing consistent quality moldings. A SMART weave sensing system developed by the US Army Research Laboratory can provide mold-filling data by making in process measurements at multiple locations inside the mold, to provide a map of the mold filling process. The technology has been licensed to Micromet Instruments Inc, to develop a commercial product. It depends on the fact that the presence of resin at any point in a mold can be detected by measuring the dielectric properties of the medium between two electrodes at that point. If no resin is present, conductance will be very low, rising as resin is introduced. Multiple sets of electrodes throughout the mold can therefore present an accurate picture of how the resin is flowing. Dielectric measurements have been used since the 1940s to monitor the cure of TS resins that used imbedded sensors, etc. The equipment (parallel plate or interdigitated comb electrodes) could not be used in the numbers required for all-over flow monitoring. The SMART weave system is based on a sensor grid of electrically conductive filaments crossing in non-intersecting planes to produce a sensing gap between them. Typically, this can be produced by placing the filaments on opposite sides of layers of preform, or by weaving them into the preform. The filaments can be low in cost (such as metal-clad aramid and graphite tow fibers, or bare metal wires, glass fiber insulated thermocouple wire or copper tape) and they offer a large number of sensing nodes for a relatively low number of connections. The user, as required, can configure the geometry of the grid. Since the grid forms a permanent part of the molding, there are also opportunities for monitoring the health of the structure (such as gross damage detection and moisture

314 Reinforced Plastics Handbook absorption) throughout its service life. An electronic package and a computer running a Lab VIEW software program monitor the signals from the sensing nodes. This system has been used in development on the lower hull and crew capsule of the US Army's Composite Armored Vehicle and the Northrop-Grumman Advanced Technology Transit Bus. Research is continuing at the US Army Research Laboratory and the University of Delaware Centre for Composite Materials.

Bladder Molding with RRTM Developed by the Institute of Plastics Processing (IKV), Aachen, Germany is combining bladder molding with RRTM. It makes possible to produce hollow components with complex geometry. The normal bladder process involves winding prepregs around an inflatable bladder, which is then placed in a heated mold cavity. The mold is then closed and the bladder is inflated. To overcome the disadvantage of the stickiness and poor drapability of the prepregs, the process can be combined with RRTM (which does not rely on prepregs). Dry textiles as necessary are placed around the inflatable bladder and preformed in the mold, prior to injection of the resin to impregnate the reinforcement. A tubular sprue system has proved its worth for molding hollow components. Key process parameters are" resin temperature during injection, mold temperature, injection pressure or resin volume flow, bladder pressure during injection, and bladder pressure during curing (Figure 5.28).

Figure 5.28

Bladder molding combined with RTM for fabrication of hollow structural fiber reinforced components (courtesy of IKV, Aachen, Germany)

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Fabricating 9 Processes 31 5

Different materials can be used for bladders, giving larger, equal, or smaller diameter than the largest diameter of the hollow component. These can be fixed (polyolefins) or flexible (silicones) and an auxiliary core can be used to pre-drapc the reinforcement. It is possible to match the possible variations to each specific molding project. IKV tested a number of options in transparent (polymethyl methacrylate) molds, looking also at lost core systems, in which the bladder or core remains in the hollow molding, and possibilities of automation. As opposed to the relatively thick silicone bladders that have to be removed from the component, thinner bladders may remain inside without negative effect on mechanical properties. Thin unstretched tubular polyamide films appear to offer best drapability and, at an air pressure of 0.5 MPa, they could expand into the edges of the component. Good results were obtained with these with braided glass fiber textile tubes, with the following process parameters: 9 preforming with auxiliary cores (such as plastic foams) 9 inflating the bladder at 0.7 MP A air pressure, for draping the textile 9 resin injection at 0.2 MPa pressure, for impregnation of the reinforcement increasing air pressure to 1.1 MPa after closing the venting channel, for consolidation of the impregnated reinforcement. The system can be automated by designing a pneumatic piston-based bladder-sealing unit to replace the time-consuming manual system used at present. Reduction in manual work (mainly in inserting, fixing and sealing the bladder) can save up to 30% of the total cycle time, and pneumatic coupling of both process steps, closing the pneumatic pistons and inflating the bladder, can produce a further reduction. Beyond this, IKV concludes that the most effective way of further reducing cycle time is to use quicker-acting resin matrix systems (since curing accounts for about 45% of the cycle time at present). Advanced RTM

Dow-United Technologies Composite Products Inc (Dow-UT), Wallingford, Connecticut, developed an advanced resin transfer molding (AdvRTM) process for production of complex and flightcritical airframe and engine structures in RPs. The process has been further developed to improve the quality of RP aerospace components substantially at the point where two or more sections are molded together. A patented technique of shaped unidirectional fiber preforms

31 6 Reinforced Plastics Handbook involves molding unidirectional carbon fiber pre-treated with resin into the three-dimensional shapes required to fill the gaps between sections of RP components. Previously the sections could not be molded as a single piece without problems such as risk of excessive resin build-up at the junction, making the joint unable to withstand high stress loads.

RTM Molding with Phenolics What has been reviewed principally involves TS polyesters. RTM with phenolic resin has also been used by companies such as Kobe Steel. These resins generally offer better fire/smoke/toxicity properties and reduced weight, but arc more brittle and are more difficult to mold by RTM to give acceptable color and surface finish (Table 5.8). An RP mold, made of glass fiber/polyester with a special vinyl ester gelcoat for prolonged service life, heated to 50C during molding was used. It was possible to mold a shell within 15 min floor-to-floor cycle time with the aid of a tool allowing faster prcforming. Table 5,8 Mechanical properties of RTM reinforced plastics (railway carriage seat shells)in phenolic and acrylic resin Properties

Phenolic

Acrylic a

Flexural modulus (GPa) Flexural strength (MPa) Tensile modulus (GPa) Tensile strength (MPa) Notched Izod impact (kJ/m2) Charpy-flat impact (kJ/m 2) Barcol hardness NFF- 16-101 UL 94 Viscosity (mPa s @ 30~ Injection pressure (bar) Mold fill time (sec) Mold temperature (~ Post cure Porosity (%) Vf(%) Specific gravity

23.57 (0.48) 588.50 (3.60) 14.81 (0.80) 254.90 (28.80) 242.5 (32.5) 47.54 (4.68) 35 M 1/F1 V-O 300 3 23 60 4 h @ 60~ 4 30 1.57

22.37 (0.62) 491.30 (27.20) 14.91 (0.51) 292.35 (11.3) 268.8 (29.5) 50.26 (4.73) 43 M2/F1 V-O 550 3 43 40 2.5 32 1.81

a70 phr FSTfiller loading Source: KobeSteel

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RTM Molding with Epoxies

Artificial limbs have been an application of RTM, demonstrating higher performance capabilities. For lower weight and better fatigue performance, carbon fiber-reinforced epoxy was used in preference to cast aluminum in the manufacture of the artificial intelligent prosthesis frame, housing a microprocessor-controlled pneumatic and hydraulic module for a lower-limb artificial prosthesis manufactured by NABCO, Japan, and Blatchford, UK. The frame has a weight limit of 200 g and had to pass a number of tests, maintaining its performance at temperatures from -40 to 100C. The RP leg module flame was designed with computer-aided systems. Finite element analysis was used to determine the reinforcement pattern, and a special epoxy with amine curing was formulated. The reinforcement fabric was wrapped on a sacrificial mandrel/core and placed in an aluminum mold at 80C (176F) and the epoxy resin mixture, preheated to 45C (113F), was injected using minimal pressure to avoid displacing the fiber/mandrel insert. The part was demolded in 15 min, followed by removal of the mandrel and deflashing. Manufacturing cost was almost 50% of the cost using autoclaving. Autoclave to VARTM Autoclave curing is important to the RP industry, particularly for the aerospace RP industry. Very few RP processes can match the consistent part quality and attainable high fiber volume of prepreg laminates cured in an autoclave. However, hand lay-up processes dominates autoclave including those with automated cutting tools and laser placement systems driven by computer-aided design (CAD) programs minimize part-to-part variations and reduce labor costs. Fiber placement brings the autoclave process even closer to complete automation. However, autoclave processing remains expensive, especially for mediumto large-size production runs with low cycle times compared to most other processes. Capital cost is high, fiber placement equipment is usually even more expensive, maintenance, and operating expenses tend to be higher than for ovens, presses, and similar equipment. With military budgets under increasing pressure, engineers have looked for alternative processing methods that can reduce costs while maintaining the high performance of autoclave-cured components. Within the last few years, liquid composite molding (LCM) technologies have advanced to the point where they can provide that alternative. LCM processes involve the injection of a liquid resin into a dry fiber preform,

318 Reinforced Plastics Handbook

and include resin transfer molding (RTM) and vacuum-assisted RTM (VARTM). As reviewed in conventional RTM, the preform is placed into a closed, matched tool and resin is injected under pressure about 100 to 200 psi (0.69 to 1.38 MPa). Early RTM processes lacked the consistency needed for aerospace components, in both dimensional tolerances and mechanical properties. Fiber volume fractions were significantly lower than the 60 to 65 wt% typical of prepregs. Problems with predicting flow fronts as well as flaws that were introduced into the preform when closing the matched metal molds often led to high void contents and dry spots. Improvements in both materials and processes have made RTM a viable option for aerospace manufacturing. However, it normally takes 10 to 15 years for a new technology to become accepted in the aerospace industry. Use of RTM began about 1998 when Lockheed Martin (Fort Worth, Texas, U.S.A.) selected RTM for many of the F / A - 2 2 Raptor's structural components. RPs comprise approximately 27 wt% of the F / A - 2 2 ' s structural weight (24% TS and 3% TP). RTM accounts for more than 400 parts, made with epoxy resins. The wing's sine wave spars were probably the first structural application of RTM composites in an aircraft. For a vertical tail on another Lockheed Martin aircraft, the RTM process reduced the part count from 13 to one, eliminated almost 1,000 fasteners, and reduced manufacturing costs by more than 60%. Unfortunately a general lack of material properties databases has slowed the adoption of RTM in the aerospace industry. Most large companies spend several years and tens or even hundreds of thousands of dollars qualifying RPs for structural applications. Using prequalified materials produces a significant savings in development cost and time. RP manufacturers like VSC, though, are seeing a willingness to develop databases for RTM materials. Since the RTM process is more complex than autoclave curing, it is more difficult to develop a general qualification methodology. With prepregs, the material manufacturer mixes the resin and impregnates the tape or fabric under highly controlled conditions. Once a material is qualified, the end user just has to demonstrate site equivalency of its manufacturing process. With RTM, however, both the resin mix and the resin content are more variable. In particular, the final resin content depends on maintaining a good flow front. Still, it is possible to develop general allowables for RTM systems. As of October 2001, a general method for qualifying braided RTM systems was prepared. The methodology has been used to qualify RTM parts made with a PR250

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resin (Cytec Engineered Materials Inc., Tempe, Ariz., U.S.A.) and an AS4 carbon fiber (Hexcel Corp., Dublin, Calif., U.S.A.) braid produced by A&P Technology Inc. (Cincinnati, Ohio, U.S.A.). High cost of tooling has limited the adoption of RTM. Although the price is competitive with autoclave tools, autoclave programs can usually get by with a single set of tooling for both development and production. With RTM the resin flow front (and hence the part quality) is highly dependent on the tooling geometry. Often it is necessary to build one or more sets of prototype tools, to develop and test the process, before the production tooling can be built. Although prototype tooling is less expensive than production tooling, it is not that inexpensive that it can be considered expendable. Case Histories

Resin/glass spoilers for about 30% of the Ford Fiesta models sold in Europe have been molded by RTM resulting in an output of 1000 per day by molder Sotira, France. The highest volume from the company previously was 500 parts/day for the Citroen XM spoiler. A three-cavity mold is used to produce the spoiler, which weighs 1.3 kg (about half the weight of the same part on the previous model), and has a Class A surface finish matching the body color. The production uses Sotira's patented Injection Compression System, which is a modification of standard RTM, on a production line, which cost FFr 5 million. The spoiler is molded on a low density (110 k g / m 3) polyurethane foam core, sanded to give good adhesion and fitted with aluminum plates for mounting inserts. This is encased in two pieces of Vetrotex U750-375 glass mat and two layers of surface veil in a preform mold, and the preforms are loaded into the three cavities of the chromed steel mold, with the addition of a second surface veil. A special Matrasur injection machine at the mold-parting line, at about 200 tonnes pressure, injects a low-profile zero-shrink polyester resin sequentially. Where conventional tools would use vents to exhaust air during injection, the Sotira process incorporates a compression chamber for air expansion, ensuring that all air is evacuated from the cavities, in turn eliminating porosity. Injection takes 8 s per cavity, curing takes 2.8 rain and total cycle time is less than 4 min. Bonnets for mini excavators manufactured by Kobe Steel, Japan, are molded by RTM using a modified acrylic resin and glass fiber fabric. The 850 mm wide x 420 mm high component has double curvature and is molded with a glass fiber strand preform with surface mat on the outer surface, preformed with an organic binder. The resin system contains 100

320 Reinforced Plastics Handbook

phr calcium carbonate, pigment, and flow modifying agents to achieve a good surface finish with a thin gelcoat layer. The resin formulation was modified to reduce the molding cycle to less than 30 min, improving the mechanical and thermal performance and surface finish. The mold was a nickel shell heated to 60C, with the mold halves mounted on a hydraulic frame, and the resin was injected using a VenusGusmer on-line mixing RTM machine at 3 bar injection pressure. The fill time and resin cure time were 2 and 10 min, respectively. Railway carriage interior components molded by RTM have been developed by Kobe Steel Europe with Transintech, UK, and Compin, France. A lightweight (5 kg) seat back shell with high static load and absorption capacity is molded in a modified acrylic resin (from Ashland) with a filler combination to achieve low fire, smoke and toxicity (FST) properties (which is easy to mold by RTM, with little effect on mechanical properties). A combination of glass fiber-based fabrics of _+45~ non-crimp (936 g/m 2) with unidirectional reinforcement and continuous filament mat (450 g / m 2) is used.

Infusion Molding This is a take off from vacuum associated RP processes. Infusion molding is the relative modern technology used to identify and streamline different RP processes such as vacuum bag molding technologies. Infusion refers to the introduction of a media into a substance identifying the application of a vacuum that moves a plastic melt through a fibrous construction. Examples of processes are Seemen Composites Resin Infusion Manufacturing Process (SCRIMP), resin transfer molding (RTM) vacuum-assisted resin injection (VARI), vacuum-assisted resin transfer molding (VARTM), resin infusion under flexible tooling (RIFT), old Marco molding, and others. One way or another vacuum infusion has been used since at least the late 1940s continually providing improvements in the fabricating processes. They involve using a mold surface or cavity that is covered with reinforcements and sealed. A vacuum is drawn on the space between the mold and the seal containing the reinforcements, and a liquid resin is allowed to infiltrate the reinforcements directly or via channels to obtain wet out of all fibers. The resin flows through the reinforcements and cures/solidifies to form the finished RP. Low-cost RP tooling can be used and environmental emissions arc controlled within this closed process. Any fumes that develop during the fabrication process can be

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9Fabricating Processes 3 2 1

contained, disposed quickly, and safe. Large high reinforcement content structural RP parts can be produced to make parts such as small to large boat hulls, bridge structures, housings, and windmill blades. Savings occur due to the use of less materials, improved and desired smooth finish, etc. Very active in using infusion molding is the boat industry worldwide since they have contaminating processes such as wet lay-ups. Boat builders want lower weight, faster vessels, and the processes that produce them to be more efficient, and cleaner. These issues are leading a growing interest in closed molding techniques such as compression moldings. Faced by the thrust of current legislation (MACT, OSHA etc) which logically disapproves of the wet lay-up/open mold technology that has served the industry for over a half a century, boat builders are exposed between various alternatives (Chapter 3). These include prepregs and its semi-preg resin film infusion (RFI) derivative; or one of several resin infusion processes. Compression or injection molding provides molding operations into closed molds that have include enclosures providing vacuum infusion. Present day developments include Lotus for production of car bodies, the female mold half is first coated with a gelcoat and dry reinforcement (mainly continuous filament mat and some woven roving) and P U R foam formers are placed on it. The foam inserts have previously been wrapped in continuous filament mat to create a stiff torsion box on each side. The inner male mold, with an airtight peripheral seal, is then placed over the loaded mold and bolted in place and resin is then drawn evenly into the mold by vacuum. The entire process is complete in several minutes for small panels and approximately one hour for upper/lower body shell halves. Released from the mold, the halves are joined with epoxy structural adhesive on an overlapping joint along the waistline of the car. The joint is reinforced in certain areas by over bonding with glass fiber cloth. The body, a one-piece molded floor-pan and the chassis are then bolted together, creating structure with almost double the torsional stiffness of the basic backbone chassis. Warship builder Vosper Thornycroft, initially a SCRIMP licensee, subsequently developed its own method for single-shot infusion of up to 30 laminate plies, including heavy shipbuilding fabrics, and complex structures with inserts, cores, stiffeners and fasteners. Since vacuum bags are used for consolidation rather than precision matched tooling, set-up costs are modest and labor is said to be halved compared with hand lay-up.

322 Reinforced Plastics Handbook

Large spars are fabricated. An 86 ft unstayed carbon fiber mast built by Composites Engineering for Ocean Planet, a yacht built by Schooner Creek Boat Works for an American owner, utilizes an infusion resin and hardener specialty formulated by MAS Epoxies. For the best in high volume fraction, low-void quality, autoclaved prepreg construction is used. New Zealand builder Southern Ocean Marine utilized both prepreg and wet preg in building Mike Golding's latest Owen/Clarke designed Open 60 in carbon/Nomex sandwich. The rotating carbon wing mast was also manufactured using carbon prepreg. Prepregs based, for example, on Hexcel Composites M10 and SP's SE84 resin system, both of which can be cured in the mid 80C, Hexcel's 75C curing M34 and other similar products, are making prepreg technology more accessible. A lead adopter, at least among production boat builders, of new resin film infusion materials is the French company Poncin Yachts, which offers hulls laid up in SP Systems Resin Infusion Technology (SPRINT) material. The company could equally have chosen Hexcel Composites HexFit, or another of the several semi- preg products now available on the market. An interesting experiment was carried out by Julian Spooner, technical manager at the Advanced Composites Manufacturing Centre in Plymouth, UK, compared infusion and prepreg manufacture directly by molding the two hulls of a catamaran using the two methods. The first hull was manufactured from SE84 carbon prepreg and Nomex honeycomb core. Outer and inner sldns and core were laid up separately and the laminate was vacuum consolidated and cured in ovens built around the mold prior to each cure cycle. The second hull was produced by single-shot resin infusion of carbon/aramid inner and outer skins over a Baltek SuperLite balsa core. The resin used was Sicomin SR 8100 epoxy. The laminate was cured at room temperature, and then postcured at an average 100C after the hull was &molded. The hulls are part of a full-scale comparative manufacturing study. Structural stiffness, weight, manufacturing time, and production cost will be assessed for each produced item. A laboratory study of specific structural performance for the different laminates will complete the comparison. Resin infusion is likely to emerge as offering a combination advantages attractive to marine fabricators (and others) contemplating a transition from open molding. Early, unofficial, indications suggest that resin infusion is likely to emerge as offering a combination of structural,

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Fabricating 9 Processes 3 2 3

manufacturing, and cost advantages attractive to marine fabricators contemplating a transition route from conventional open molding. At the upper end of the glass technology scale, GRP is the basis for Sandown class mine hunters built by Vosper Thornycroft for the UK Royal Navy using a proprietary infusion process. A number of navies have selected FRP for the structures of mine countermeasures vessels since it provides immunity to magnetic influence mines. SCRIMP Proeess

The Secman Composites Resin Infusion Process (SCRIMP) is a gasassist resin transfer molding patented process. This resin infusion molding process is a vacuum resin molding technique patented by Seeman Composites, USA, arising from an attempt to develop an environmentally friendly alternative to open molding. The technique is based on use of a distribution medium (knitted mesh fabric incorporating a network of resin distribution channels) which is incorporated in the laminate lay-up, which is molded by the vacuum bag method. The medium is placed on both sides of the fiber pack (on one side only, for thin laminates), to ensure that thorough wetting out is achieved quickly. A resin-permeable peel ply is placed between the distribution layer and the part being molded, so that the mesh, together with excess resin, can be removed and disposed of afterwards. The system has proved itself for thick, large-area laminated structures, from flat to highly contoured. Refractory and metal/organic fabrics can also be laid into the laminate, enabling it to resist passage of fire. Some organizations, however, challenge the basic novelty of the system, citing other techniques for incorporating resin distribution and questioning the need to remove and dispose of the distributor. There was the Marco process of the 1940s-1960s that included laying down glass fiber reinforcement constructions with resin channels in a vacuum bag and in turn applying a vacuum placing TS polyester in the reinforcement followed with its cure. Bofors, Sweden, uses penetrations in the fiber cloth to speed up resin flow and Fibrelite, UK, injects resin through gaps and channels in the cores of sandwich RPs, to produce manhole covers. Scott Bader and DSM Resins have developed a texturized embossed film to act as a resin distributor. The process allows panels measuring several meters in each dimension to be infused with resin quickly and thoroughly, to give more rapid and consistent production. It can be controlled more closely than openmold wet lay-up, giving parts of higher consistency and reproducibility. Structures, which are both thick and complex, can be impregnated and

324 Rein%reed Plastics Handbook

(if the resin flow is controlled so that the advancing wave front penetrates all parts at the same rate) structures incorporating cores, inserts, stiffeners, and fasteners can be infused in the one shot. Generally, the larger the part, the better the economics. Set-up costs are said to be modest and labor savings can be up to 509/0 of hand lay-up costs. There appears a consensus that it has a good future in styrenefree volume production of moldings with large relatively planar surfaces. From the technical viewpoint, users comment that low viscosity resins are preferred, with longer than normal working time and low cxotherm. A dry fiber pack basis for a boat hull can be infused in about 30 rain and cured at ambient temperature. Diluents in the resin may have some effect on quality. It is unlikely that the mechanical properties will compare with those of a prepreg curing at 60C (140F) and above, meaning that it will be hard to achieve the strength requirements of (for example) the aircraft industry, but they may well meet the requirements of boat builders who do not need the level offered by prepregs. The process has been licensed to some 30 organizations worldwide. The UK shipbuilder Vosper Thornycroft uses it for molding large bulkhead panels for minehunters and believes that laminates can be developed to meet stringent new regulations, such as the latest International Marine Organization (IMO) code (which some have feared would spell the end of TS polyesters in fabrication of primary marine structures). SCRIMP has been shown to be able to produce consistently high quality parts, including high-end military minesweepers, pleasure boats, windmill blades, marine fenders and piling, a 14.6 m (48 ft) all-RP flatbed trailer, utility poles for transmission lines, small temporary bridges. Lockheed has also used it for carbon fiber laminates. A noteworthy application was an insulated railcar, molded in two parts, with a 5-tonne body (fabricated from Dow's Derakane vinyl ester with Vetrotex E-glass fiber and Dow polyurethane (PUR) foam core for insulation, molded on a segmented FRP tool). In USA, SCRIMP fabricated large RP products such as a transportation bus weighs about 10,000 kg (22,000 lb) that is 3200 kg (7000 lb) lighter than steel units are. It fabricates a trial 75 ft high integrated mast structure for an amphibious warfare vessel. The RP structure, made up of infused panels, encloses and supports the forest of antennas visible on a normal warship, in a weatherproof, electro-magnetically tuned m a s t / housing.

5

9Fabricating Processes 3 2 5

Canada's West Bay Son Ship Yachts recently transitioned its RP production from open-mold spray-up processes to a vacuum infusion processes. Infusion with glass offered a clean, low emissions way to make better parts and saving on labor and materials. Two years of research into different methods and materials preceded the decision to change from open molded isophthalic polyester/glass to vacuum bagged vinyl ester/glass for its 58-107 ft RP yachts. With growing confidence, infusion progressed from small panels and stringers through bulkheads to full hulls (the first was infused during 2003), and then to decks. Stronger parts with a higher glass-to-resin ratio developed. It is estimated that weight savings of up to 30% occurs for the boat hulls that in turn permits higher speeds.

Injection Moldings The process of IM is used for reinforced TPs (RTPs); however, it is principally used for (URTPs) and some TSs. IM machines (IMMs) represent over half of all the primary plastic fabricating machines in the world processing all types of plastics and plastic compounds; representing just a USA multibillion-dollar business. Figure 5.29 is a simplified version of IM machine (IMM) where plastic flows from hopper, through plasticator (screw-barrel), to mold cavity. The IMMs used for molding RTPs are a take off the same system as in molding UTPs. Temperatures/pressures differ, as does the design of the screw. Unlike UTPs that just melt in the plasticator and solidify in the cooled mold, the TSs melt in the plasticator and cure to a harden state in the mold that operates at a higher temperature than in the plasticator. Over 50 wt% of all glass fiber RTPs go through IMMs. The RP TS compounds that are thick and pasty (BMC, etc.) are processed through ram IMMs as well as screw IMMs (Figures 5.30 and 5.31). Both short and long glass and other fibers are injection molded. They require special designed screws in their plasticators. They generally use reciprocating screw IMMs. Also used is two-stage IMMs design that includes replacing a preloader with a single or twin-screw extruder. This widely used process in the plastic industry is essentially a process in which a charge of material is fed from a hopper into a cylinder, from which it is injected under pressure into a mold, through a nozzle on the machine, a sprue and (usually) runner system in the mold. From the runner it goes through a gate, into the cavity of the mold. It is ideally suited to processing of TP compounds but, because of the efficiency of

326 Reinforced Plastics Handbook

Figure 5 . 2 9 Schematic of IMM with reciprocating screw melting system (hydraulic operation shown/also used is electrical or hybrid systems)

Figure 5.30

Schematics of ram and screw injection molding machine with a preloader usually providing heat to the RP compound

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9Fabricating Processes 3 2 7

Figure 5,31 Examplesof different injection molding machine plasticators the process and its ability to produce large numbers of threedimensional moldings to a high (in some cases very high) degree of precision, TS compounds are also processed. IMMs with the proper screw designs process short or long fiber reinforced compounds. As an example with a suitable machine and

328 Reinforced Plastics Handbook

tooling, designated ZMC (low viscosity molding compound), for many years has been used in the production of complete rear doors for some European hatchback designs of passenger car. These are molded as an inner and an outer shell, which are then bonded together with a resin adhesive. Compared with compression molding, IM offers a number of advantages. It is a natural closed molding system, producing parts with good finishes on both sides, and is automatic and highly cost-efficient. It produces reproducible moldings, to constant weight and identical properties, and will produce parts not prone to porosity (which can be further guaranteed by introducing a vacuum during the injection stage in the mold cavity, to evacuate gases and air occlusions). This action also speeds up the injection speed, giving in turn a better surface and shorter cycle time. In the past, the main criticism of IM of RTPs or RTSs has been the relatively low mechanical strength of the molded product, compared with the theoretical strength of the components. This was due to reducing fiber length. Screws cut fibers during its plastication in the plasticator (identifies the screw in the barrel), which damages the strength-producing fibrous reinforcement. Older injection molding technology (up to 50 years ago) only employed a plunger method that did not damage fibers, but the main line of development has long been to use screws to move the compound along the barrel of the machine because they improved the melting action resulting in a more uniform melt and shorter cycle time. As experience of the materials has developed, design of the screw is of paramount importance and it has been possible to adapt screw designs to more efficient processing of glass fiber RTP and RTS compounds. This allows the machinery manufacturers to offer (in principle) one basic machine body which can be adapted to processing RTPs and RTSs as well as the more popular unreinforced TP, simply by changing the design of screw. Nevertheless, plasticizing glass fiber-reinforced compounds has a strong abrasive effect on the screw, and various grades and treatments have been developed to give this component a longer life. Alongside the economic importance of injection molding have grown up sub-industries concerned with more efficient control of the whole molding process (by use of microprocessor systems) and robot external handling of parts, including placing of inserts before molding and removal of parts after molding. The advent of robots for part-removal has many implications, since it is relatively simple to have the robot present the part to other equipment

5. Fabricating Processes 329 for, when required, deflashing, trimming, addition of inserts and printing, as well as to optical and weighing inspection systems, for control of quality (dimensions, weight, etc.) at the machine.

Molding Reinforced Thermoplastics Different TPs are IM. Low-pressure [17-140 bars (250-2000 psi)] can be used making it easy to fabricate small to relatively large moldings (limited based on size of IMMs). The optimum pressure is usually 70 bar (1000 psi). Total cycle time is most significantly affected by section thickness. The following conditions are examples of the molding cycle: mold temperature 120-160C (248-320F), barrel temperature 20-60C (68-140F), injection pressure (as noted above), and injection time 0.5-6.0 s. Details on IM TPs are provided in the literature. RTPs can be IM with virtually the same equipment as is standard for other forms of UTPs injection molding. The exception is that, although the reinforcement (such as glass fiber) has been treated with special lubricants prior to compounding, it may still have some abrasive effect on the critical metal parts of the injection system, particularly the screw and barrel (plasticator). For molding operations involving continual or frequent use of reinforced compounds, it may well be better to use dedicated machines. In any case, care should be taken to ensure that the screw and barrel are suitably hardened (and attention is paid to wear during the normal maintenance schedule): With continuous use, (24 h every day) plasticator could wear in six months if special plasticators are not used and would require maintenance, etc. to maximize fabricating performance. It is also important to ensure that the compound is stored according to manufacturers' recommendations, and to check the moisture content before injection. In operation, compounds fed into a hopper on the machine, from which it is drawn by gravity into the heated barrel, where they are melted (plasticized) by a rotating screw. The screw also has an intermittent reciprocating movement, so that it acts as a plunger, to inject the melt into a closed mold. The whole molding cycle is precisely timed, with accurate metering of the shot-weight, exact control of movement and a programmed profile of injection and hold-on pressures. As well as continuous development of machine design and especially machine control systems, there has been considerable development of molds. These may be quite simple or very sophisticated, with multiple cavities, moving parts. Since the molding of RTPs is essentially a question of the control of heat transfer, advanced temperature control systems are frequently used, which can repay their additional cost by

330 Reinforced Plastics Handbook reducing the molding cycle. At the production rates of injection molding, a few second reductions from the cycle can make a large difference in monthly or annual production costs. Particularly sophisticated tooling is used for major application for RTPs such as automobile air intake manifolds. These large (1.5-3 kg) moldings, in glass fiber/reinforced nylon, are IM on fusible metal cores, which are subsequently melted out, or are molded as two mirror images, which are then ultrasonically welded together.

Injection-Compression Moldings Also called ICM, coining, and injection stamping. ICM is a variant of injection molding. The essential difference lies in the manner in which the RTP thermal contraction in the mold cavity that occurs during cooling (shrinkage) is compensated. With conventional injection molding, the reduction in material volume in the cavity due to thermal contraction is compensated by forcing in more melt during the pressureholding phase. By contrast, with ICM, a compression mold design is used where male plug fits into a female cavity rather than the usual flat surface parting line mold halves for 1M (Figure 5.32). The melt is injected into the cavity as a short shot thereby not filling the cavity. The melt in the cavity is literally stress-free; it is litcrally poured into the cavity. Prior to receiving melt, the mold is slightly opened so that a closed cavity exists; the male and female parts are engaged so the cavity is closed. After the melt is injected, the mold automatically closes producing a relatively even melt flow. Upon controlled closing, a uniform pressure is applied to the melt. Sufficient pressure is applied to provide a molded product without stresses easily meeting and repeating very close tolerance measurements.

Vacuum-Assisted Resin Injection Moldings This process has been used since the 1940s to provide better control of the molding cycle to fabricate parts that are more precise. Those that used it were Bell Laboratories (USA) and D. V. Rosato. This technology is to combine IM of the compound with a complete or partial vacuum in the mold cavity, to facilitate the impregnation of the reinforcement. The vacuum injection process requires a perfect seal around the edge of the mold. Development included applying vacuum from the hopper, through the plasticator, and into the mold. It has very little interest.

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9Fabricating Processes 3 3 1

Figure 5.32 Exampleof mold action during injection-compression (courtesyof Plastic FALLO)

Overmoldings Also called two-shot injection molding, in-mold assembly, two-color rotary or two-color shuttle. Two materials are molded so that the first molded shot is over-molded by the second molded shot; first molded part is positioned so the second material can be molded around, over, sections, or through it. The two materials can be the same or different and they can be molded to bond together or not bond together. If materials are not compatible, the materials will not bond so that a product such as a universal or ball-and-socket joint can be molded in one operation. If they are compatible, controlling the processing temperature can eliminate bonding. A temperature drop at the contact surfaces can occur in relation to the second hot melt shot to prevent the bond. An example is shown in Figure 5.33. This three IM part universal joint is all molded from the same RP (glass fiber/nylon 6 / 6 molding

332 Reinforced Plastics Handbook

compound) producing extremely flat and snug fit mating surfaces that do not bond since mold temperature control was properly set: (a)

assembled universal joint with inserted bearings and part of mold

(b)

prototype mold for center part, and

(c)

view of the complete universal join being removed from mold cavity; the center cube with bearings was molded in its own mold, it was put into a different mold that molded one U arm, and the cube with its one arm was put into this prototype mold resulting in the complete universal joint.

Figure 5.33 Precision IM of universal joint; RP molded of glass fiber/nylon 6/6 molding compound

In addition to universal joints, other examples of this type product using this technique include many such as inner-door panels for automobiles where woven or nonwoven textiles are placed in a mold and the melt is injected. In-mold labeling is another application that goes beyond just a printed message. Individual labels or continuous film can be indexed in the mold at the beginning of each cycle. Besides printing on the film, the film can serve many other functions (increasing impact, toughen plastic, etc.), or the film can contain additives and stabilizers to protect the surface of the molded product.

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9Fabricating Processes 3 3 3

Also molded are unreinforced or RP to metal hybrids. Plastic-metal hybrids are replacing all-steel structures in automotive front end modules at an accelerated rate. Technical approaches to hybrids are multiplying as more resin suppliers develop alternatives to the overmolding method first established by Bayer. Tier One automotive part suppliers, while tight-lipped on their plans, are also working on proprietary hybrid concepts. Hybrid moldings, which combine thin-wall steel stampings and glass fiber RTPs into integrated load-bearing parts, have appeared on a dozen new car and truck platforms in 2004, doubling North American usage. This action opens the floodgates for other load-bearing automotive parts reports Paul Platte, Bayer Polymers' director of automotive marketing and industry innovation. As examples, he cites instrument panel and bumper crossbeams, door modules, and tailgates. Non-automotive applications, from appliance housings to bicycle frames, are also emerging. Hybrid conversion in front-end modules has been led by Bayer, whose patented injection over-molding method has been used by Volkswagen, Audi, Nissan, and Ford since 1996. Ten new platforms, including several light trucks, are used in North America through mid-2004. Mso aboard are alternative hybrid systems developed by Rhodia Engineering Polymers, Dow Automotive, and BASF Performance Polymers. It is reported that hybrid systems face stiff competition from directcompounded, long-fiber polypropylene RPs in semi-structural loadbearing automotive uses. Ml-plastic RPs have greater potential for weight and cost reduction than do hybrids, while both approaches increase parts consolidation and foster functional integration. As alI-RP approaches continue to improve, hybrids seem to be carving out a niche in higher performance applications. Hybrid solutions are potentially aided by more stringent side-impact regulations in USA and a mind-set among automotive engineers favoring metal inclusion in load-bearing subassemblies. Bayer's hybrid system exploits the fact that increased side support in open section, V-shaped steel stampings significantly boosts their loadbearing strength. Metal inserts with flared through-holes are stamped, put in an injection mold and over-molded with 30 wt% short-glass reinforced nylon 6 to create a cross-ribbed supporting structure. The metal and nylon are joined by nylon melt penetrating through-holes to form rivets that provide mechanical interlocks. Because an injection press opens in one direction, Bayer's system initially limited cross-rib geometry to just two dimensions. Bayer says tooling side actions now open the way for multi-directional ribbing designs.

334 Reinforced Plastics Handbook Bayer's hybrid structures have an open section, yet the flexural, axial, and torsional strengths match those of many closed-section, box-like structures. Their approach can thin-wall and lightweight metal stampings 40% to 60% and yet deliver excellent load-bearing strength. Payoffs are evident in the Audi A6 front end module and Ford Focus grille-opening reinforcement, which boast weight and cost savings of at least 10%. A recent refinement is in-mold assembly of hybrids. Two or more metal stampings are robotically placed in the mold with holes aligned, and then they are over-molded into one piece with nylon. This approach will reduce the assembly costs of front ends, door modules, and window regulators. Certain applications of over-molding are not restricted to a low pressure. Two-shot molding is an example where a plastic is molded into a shape, then placed in another cavity before a second plastic is injected. The first plastic injected serves as a solid mold wall for the second cavity. Keys for a computer keyboard, knobs, and other items are often molded this way to provide information that does not fade or wear away with use. Many variations exist, including molding an elastomer over a rigid plastic, and molding a frame around a lens or optical window. Each step in over-molding is essentially the standard molding process even though the integral structure might resemble a product molded by coinjection molding.

D-LIFT Extruder/Injection Processes A hybrid of twin-screw compounding extruder and injection molding is proving its commercial viability for molding structural automotive parts of direct-compounded long fiber thermoplastic (D-LFT) composites. The latest proof is the front-end cartier of the 2003 Volkswagen Golf V, injection molded of 30 wt% long glass filled polypropylene by RKT Kunststoffe, part of Aksys Group, in Kongen, Germany. This 7.5 lb part is the third commercial application of the IMC (injection molding compounding) process of machine builder Krauss-Maffei (USA office is in Florence, KY). This system piggybacks a twin-screw compounding extruder on top of an injection machine with a. special accumulator and a plunger injector. The accumulator allows the extruder to run continuously to produce more homogeneous melt quality than with conventional start-and-stop plasticating. The extruder takes in continuous glass roving and c u t s it while wetting it with already molten resin. As compared with conventional injection molding of long fiber pellets, this process saves one heat history on the

5

9Fabricating Processes 3 3 5

resin and subjects the glass fiber to less shear, preserving fiber length. IMC is also more suitable for heat-sensitive materials such as natural fibers. The machine system includes material handling and gravimetric feeding systems. It has a plasticating capacity of more than 5000 l b / h r of PP or HDPE. The largest press in commercial operation is 2000 metric tons, though KM has a 2700 ton in its own laboratory. Krauss-Maffei has delivered 10 of these IMC systems to European molders and two more to European university laboratories. Two more are on order for RKT plants in Germany and Mexico. One system is used in the USA for a non-automotive application. The VW front-end carrier is molded on a 1300-ton press. The first commercial use of IMC was to produce the front-end carrier for the Citroen C3, introduced in late 2001. The second application came early last year, a similar part for the Peugeot 307 (tel: ????6.06-283-0200, www.kraussmaffei.com). Pushtrusion/Injection Processes

The patented Pushtrusion direct inline process for molding small to large products is accomplished by compounding and injection molding (IM) in a single operation long a n d / o r short fiber from continuous fiber reinforcements. Inventor Ronald Hawley in 2001 patented the Pushtrusion process that can pull glass fiber from supply creels at rates as high as 600 feet per minute. Equipment maker Milacron Inc. is manufacturing the machine and retrofitting IM machines under a nonexclusive equipment license from PlastiComp Inc. of LaCreseent, MN, USA. Dow Automotive of Auburn Hills, MI is a nonexclusive resin supplier with development capability. They will use the process to complement Dow technology being transitioned from Europe. Owens Corning of Toledo, O H will provide product development expertise and will serve as the exclusive supplier of glass fiber rovings to Pushtrusion molders. The modular Pushtrusion process pulls standard, continuous length fiber from supply creels at rates of 400-600 feet per minute, embeds the fibers into molten resin under high pressure, uses a chopper for cutting and maintains material temperature through an entrainment die. This pliable mixture moves through a nozzle directly into the IM machine's (IMM's) plasticator where the screw action, under pressure, completes the melting action providing proper bond of fibers to resin. This approach of a single melt minimizes fiber degradation; process eliminates usual wear on screws and barrels from the resin-glass fiber mix. The Pushtrusion process can be applied in other technology. See in this chapter Pushtrusion/Extrusion Processes.

336 Reinforced Plastics Handbook Injection Molding ZMC Injection molding is most suitable for large series production of RTS compounds because of the possibility of automating the process and attaining high production rates, and in particular ZMC (low viscosity molding compound) compounds that provide developing a total manufacturing system (molding material/press/mold/finishing line), for parts with properties superior to conventional bulk molding compounds (BMCs) and a high quality surface finish. Application has been for the two-part rear door of the Citroen BX saloon. The molding temperature is about 160C (310F) and injection pressure 150-200 bars. Molds are made from high compressive strength steel. IMMs for TS polyester molding compounds can have either a flighted screw or a solid injection piston and are of modular design, allowing quick and effective change of injection unit from screw to piston. A unique aspect of one design is an automatic feed unit in three capacities of 100, 350 and 650 liters.

Liquid Injection Moldings Also could be called LIM, liquid molding, or reaction injection molding (RIM). This LIM process, which has been in use since at least the 1940s, involves proportioning, mixing, and dispensing two liquid TS plastic formulations via two plungers; one contains the basic plastic with or without reinforcements (fibers, flakes, additives, etc.) and the other a catalyst system to active the plastic. This compound is directly injected into a closed mold. It can be used for encapsulating electrical and electronic devices, decorative ornaments, medical devices, auto parts, etc. It differs to reaction injection molding (RIM) where it uses a mechanical mixing rather than a high-pressure impingement mixer. Flushing the mix at the end of a run is easily handled automatically (Figures 5.34 and 5.35). Plastics used include silicones, acrylics, etc. To avoid liquid injection hardware from becoming plugged with plastics, consider using a springloaded pin type nozzle. The spring loading allows you to set the pressure so that it is higher than the pressure inside the extruder barrel, thus keeping the port clean and open. Development at the Advanced Materials Intelligent Processing Centre (AMIPC) of the University of Delaware, set up in the USA with funding from the Office of Naval Research is a project called liquid molding technologies. It potentially offers lower costs for molding URPs and RPs. The Centre is working on virtual manufacturing,

(,n "11 o"

w~ ,-I1

0

Figure 5.34

Example of a more accurate mixing of components for liquid injection casting via a moving wedge technique W W

338 Reinforced Plastics Handbook

resin-hardener mixing chamber

mixing motor drive

casting in mold cavity ram injector clamp

resin and hardner proportioning chamber

Figure 5.35 Example of a liquid injection molding casting process laboratory-scale evaluation and prototype development. Virtual manufacturing uses computer simulations to identify ideal processing parameters based on liquid injection molding simulation (LIMS) that is a computer-aided mold design tool developed by a team at the University of Delaware. The information gained from this will be used to develop a laboratory scale validation unit at the University of Delaware's Centre for Composite Materials, including evaluation and integration of on-line sensors. Previous research has shown that thermography techniques can be used to detect voids and other inconsistencies in RPs, and thermal imaging is seen as having high potential as an external sensor in RTM. In the third phase, the laboratory-scale intelligent manufacturing cell will be scaled up for production of an actual prototype at Boeing's facility at St. Louis.

Pulsed Moldings Various processes are reported to provide a means to pulsate the IM melt to improve performance of the molded parts. Scol/'i l4~

Scorirn Moldings British Technology Group tradename Scorirn is for the process of creating dynamics to molten plastics inside a mold cavity (or in extrusion from a die) to improve melt flow. Purpose of the

5

9Fabricating Processes 3 3 9

Scorim process is to eliminate what they report as problems for IM RTPs. There is the tendency of reinforcing fibers to align with the direction of flow, as the molten plastic passes at high pressure through a gate and then fills the mold cavity. There is the difficulty of molding thick sections without also producing sink marks caused by differential shrinkage. Subjecting the melt to pressure pulsing during the injection and hold-on stages can produce better results under both situations. A shear-controlled orientation system of molding (and extrusion), which gives much greater control over the distribution and alignment of fibers in processing RTPs, has been patented. It is believed to be the only system that offers complete control and management of the melt during the entire freezing phase. Fitted to standard plasticizing units, Scorim provides multiple feeds for the melt flow and independently controlled pistons in the melt channels. Once the cavities have been filled in the normal manner, the system is activated at the hold-on pressure stage. Pulsing of the pistons generates shear in the melt as it solidifies, optimizing homogeneity and eliminating internal welds. Where fibrous reinforcements and fillers are involved, the shear also tends to orientate the fiber and resin matrix, further improving the properties of the finished molding.

Liquid CrystalPolymers A pulsed molding process for LCP was developed by Klockner Ferromatik, using two opposed injection units, either in tandem or in sequence, to produce distinct orientation of the opposing melt streams in the cavity, while also allowing a flow-through and eliminating weld lines. The maximum attainable tensile strength is influenced not only by the type of sprue system but also by the number of pulsing cycles, the cooling gradient of the melt in the mold and the length of the stroke. Tensile strength of the LCP was increased from about 228 N / m m 2 to 298.5 N / m m 2 (or about 150% of the 207 N / m m 2 claimed by the manufacturer of the plastic). At the same time, up to 250% increase in notched impact strength was achieved, due to orientations in the core layer running parallel to the flow direction. It was used commercially for the production of window flames for the European Airbus A-340, following a study that indicated that IM parts were increasingly important in reducing unnecessary weight in aircraft. However, using most types of IM TPs introduced also the question of flame and smoke generation. This led to interest in LCPs as an effective combination of high performance mechanical strength and fire resistance and replacement of the aluminum die-formed part on the Airbus with moldings in LCP saved 50 kg.

340 Reinforced Plastics Handbook

Pultrusions This is a process that is dedicated to just continuously processing RPs that usually have a constant cross sectional shape from profiles to flat panels (I-, U-, H-, flat panel, corrugated panel, and other shapes). The reinforcing fibers are pulled through a plastic (usually TS however, TP are also used) liquid impregnation bath through rollers, etc. and then through a shaping die followed with a curing action (Figure 5.36). There are also systems where no plastic bath is used and the plastic is impregnated in the die that is a take-off in extruding wire and cable providing a very controlled impregnation.

Figure 5.36 Schematicexamplesof the pultrusion process

This process can produces products that meet very high structural requirements, high weight-to-strength performances, electrical requirements, etc. The material most commonly used is TS polyester with glass fiber. Other TS plastics, such as epoxy and polyurethane are used where their improved properties are needed. When required fiber material in mat or woven form is added for cross-ply properties.

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9Fabricating Processes 3 4 1

In contrast to extrusion, in this process a combination of liquid resin and continuous fibers (or combined with short fibers) is pulled continuously through a heated die of the shape required for continuous profiles. Extruder pushes the material. Glass content typically ranges from 25 to 75 wt% for sheet and shapes, and at least 75% for rods. In this process, continuous fiber reinforcement usually in the form of roving or mat/roving is drawn through a resin bath to coat each fiber with specially formulated resin mixture (Chapter 2). The resinimpregnated fibers are then assembled by a forming guide and pulled through a heated die in which shaping and compacting them and initiating the cure. The rate of reaction is controlled by the catalyst in the mix and by the arrangement of heating and cooling zones in the die. Curing is at 120-150C (250-300F), and mirror-polish machined steel, generally chromium-plated, is used for the die. High frequency (HF) or ultra- high frequency (UHF) pre-heating of the reinforcement may also be used, linked with the curing by the heated die. The profile is pulled through the die at a constant speed, for continuous production. The cured product is rigid, and the downstream equipment will include a cutting saw and stacking device. The process is suitable for complex hollow or solid profiles with high mechanical properties. Profiles have a high ratio of reinforcement to resin, and the fiber is orientated in the length direction, giving units of very high tensile strength. Typical applications of pultruded products are extensive and serve many different industries: 9 electrical: lift-truck booms, ladder components, third rail cover, cable trays, lighting poles, pole line hardware 9

anti-corrosion: grating, mist eliminators, sucker rods, troughs, pipe, sub-structure beams

9 construction: all-composite buildings, frames, window frames, roof supports, patio doors, trim, roof deck panels 9 transport: roll-doors, bus panel components, interior trim, display panels, drive shafts, luggage rack, dunnage bars. Development in equipment continues. As an example, a line of low-cost pultrusion machines with electromechanical controls, eliminating high maintenance costs and minimizing noise, has been developed by Composites Machines Co, Salt Lake City, USA. The advanced technology pultrusion (A TP) line comprises three series: 9 Model a up to 50 mm x 25 mm profiles, 450 kg pull force, with simple electromechanical control and formed wheel pullers

342 Reinforced Plastics Handbook

9 Model /3 up to 200 mm x 100 mm profiles, 2268 kg pull force, caterpillar pullers for higher pulling forces and larger profiles 9 Model 6 up to 610 mm x 250 mm, 2268-9072 kg pulling force, reciprocating pullers with linear roller beating ways, ball screw drive and brushless servo motors giving high precision in closed-loop pulling and reciprocating synchronization. MMFG, the largest pultruder in the USA, is progressively replacing its open bath wet-out with multi-stage pre-die injectors. The direct die injectors that are currently available, while significantly reducing styrene emissions, often give inadequate wet-out of roving, producing parts with poor mechanical properties. The MMFG pre-die concept is claimed to reduce emissions by over 90% without and loss of properties. Line speed increases of 30-40% are also being sought. Special machines include one for pultruding plate up to 1.2 m wide. Another machine can produce 610 mm I-beams, and foam-filled building panels are produced on a Pulstar reciprocating machine with the foam functioning as the mandrel. A current research and development project is production of large glass and carbon fiber reinforced phenolic I-beam. Continuous Laminations

Continuous fabricating between layers of film is used for continuous production of sheet, both colored and translucent, in flat or profiled (such as corrugated) configuration. Catalyzed polyester resin is metered onto a carrier film using a doctor blade and glass fiber (now usually 25 mm length) is cut from rovings and deposited on the resin. An alternative (but more expensive) material is chopped strand mat. A 28 wt% glass content is typical. After impregnation, optimized by pressure rollers or flaps, a second film is applied to the upper face and the whole lay-up is passed through a nip roller. Figure 5.37 is a schematic of a continuous production of

Figure 5.37 Continuous production of profiled sheet line

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9Fabricating

Processes 3 4 3

profiled sheet, forming the profile transversely with twin forming belts inside the curing oven. An alternative method is to form longitudinal profiles in the green stage, before the sheet enters the oven. The laminate usually passes over a heated surface (typically 60C) to introduce heat at an early stage, maximize line speed and reduce internal distorting stresses, also reducing resin viscosity and so aiding wetting-out. The sandwich then passes over preformers, molds as necessary, to produce corrugations or other profiles, and passes through a curing oven at 80-120C. As the continuous sheet leaves the cure chamber it is edge-trimmed and cut to desired length. As well as acting as a conveyor and release agent, the two layers of film also ensures that both surfaces are, smooth. Choice of cartier film offers two alternatives: a relatively high-cost film, which can be re-used several times, or a lower-cost film that can be left adhering to the surface of the sheet, as a protection in transit. The process can also be used for production of simple open profiles without sharp angles. A gelcoat can be incorporated as necessary, applied 100 pm thick to the carrier film. Thin gauge film (19 lam) is used once; thicker gauge (38 pm) is reused (some manufacturers are known to reuse 5-6 times). The line speed at an average product weight of 1 k g / m 2 x 0.5 mm thick is up to 24 m/rain: for 4 k g / m 2 x 3.0 mm the speed is 5-10 m/min. Some techniques for manufacture of heavy-duty sheet for packaging and tarpaulins for construction, agriculture and transport, have involved pultruding (also laminating for long production runs). They can include sandwiching a reinforcing fiber web between layers of sheet. Reinforced PVC sheet is produced similarly by pultrusion (also calendering for long production runs). Reinforced hose is produced by braiding the fiber reinforcement construction through a pultrusion die (also extrusion for long production runs). Other techniques Different TP pultrusion processes are used. As an example Thermoplastic Pultrusion Technologies (TPT), Yorktown, VA, USA, uses a hot-melt injection process for pultruding RP thermoplastic. Unlike TS pultruded profiles, TP profiles can be postformed and reshaped. Higher continuous use temperatures are possible with some TP matrices, and line speeds are faster with raw materials usually costing less. The TPT process and apparatus consist of a creel, fiber heating unit, resin feeder (which may also include an extruder), impregnation

3 4 4 Reinforced Plastics Handbook

chamber with resin flow control mechanism, resin metering and profile die, cooling mechanism, and pulling mechanism. The process can combine conventional glass fiber roving, aramid, or carbon fiber tows with TPs, most commonly polyethylene terephthalate (PET) and nylon (polyamide/PA). Other plastics used include polyphenylene sulphide (PPS), styrene-maleic anhydride (SMA), highdensity polyethylene (HDPE), and polypropylene (PP). The TPs can take the form of pellets, chips, chunks, or shreds, and as the process uses hot-melt injection, no solvents or two-part systems are involved. Additives such as colorants and fillers can be used as required. The process achieves excellent fiber wet-out and allows the use of recycled TPs as well as virgin plastics. Fiber wetting is often a major problem with hot-melt TP pultrusions because TPs have a much higher viscosity than TSs at typical processing temperatures. Outside coatings of most TPs can be applied in-line while pultruding, by using an extruder. Many applications exist including round and flat profiles for tension cables, high strength rivets, bolts, bicycle spokes, reinforcement cables for erosion control revetments, and straps for transporting heavy construction materials. Production of prepreg, rods, and ribbons, reinforcement bars for concrete, tool handles and high fiber weight long fiber pellets are fabricated. Dow has developed a pultrusion simulation modeling (PSM) service designed to help fabricators achieve higher levels of productivity and reliability. Process variables such as pull speed, part and die temperature, heater output and pulling force can affect the quality of pultruded components. The PSM tool allows fabricators to predict processing performance for specific applications, and is accurate to within 10% of actual performance. The tool has been validated in customer trials and allows the pultrusion process to be optimized quickly. Without effective modeling, it could take several weeks to a month to optimize a process, not to mention all of the accompanying scrap or waste material. Using this state-of-the-art and unique modeling technology, one can optimize the process within a week and have a lot of confidence in the processing performance that one gets before ever running a pultruder. A technical service engineer can run PSM tool from a laptop or any standard computer platform on site. Dow is using the tool as part of a technical support service and to develop new pultrusion resins that will be faster and easier to process.

5

9Fabricating Processes 3 4 5

Extrusions While injection molding is the largest process in the plastics industry in terms of number of plastic fabricating machines operating, extrusion of TPs is by far the largest in terms of volume of material processed. The vast majority of this material, however, is film, sheet, and profile such as pipe, practically all of which is unreinforced. However, there are film, sheet and profiles, such as thermoplastic polyurethanes (TPU) as thin as 5 mills, that are bonded in layers with glass, polycarbonate, fiber glass fabrics, paper, and other substrates to produce high-strength laminates with anti-ballistic properties, together with the ability to allow for new architectural features (backing for automotive foam-in-place seating, athletic equipment, computer keyboard covers, building panels, etc.). Other thermoplastics are used such as thermoplastic polyesters, polyvinyl chlorides, copolyamides, and polyolefins with each plastic composite providing different requirements ranging from high impact resistance to reducing costs. The extruder, that offers the advantages of a completely versatile processing technique, is unsurpassed in economic importance by any other process. It is to be used whenever the opportunity exists such as fabricating RP lumber. This continuously operating process, with its relatively low cost of operation, is predominant in the manufacture of shapes such as profiles, sheets, tapes, filaments, pipes, wire and cable coatings, rods, in-line postforming, and others. The basic processing concept is similar to that of injection molding (IM) in that material passes from a hopper into a plasticating cylinder in which it is melted and pushed forward by the movement of a screw. The screw compresses, melts, and homogenizes the material. When the melt reaches the end of the cylinder it precedes through a die that has an opening, the shape of the product to be produced. Practically only TPs go through extruders with some of TP containing reinforcement such as glass fiber. A limited amount of unreinforced or reinforced TSs is extruded. In extrusion, plastic material is first loaded into hopper using upstream equipment that provides the proper mix of ingredients to be processes. This mixture is fed into a long heating chamber (plasticator) through which it is moved by the action of a continuously revolving screw. At the end of this plasticator the molten plastic is forced/pushed through an orifice (opening) in a die with the relative shape desired in the finished product. As the extrudate (plastic melt) exits the die, it is fed downstream onto a pulling and cooling device such as multiple rotating rolls, conveyor belt with air blower, or water tank with puller.

346 Reinforced Plastics Handbook

Important to the RP industry is the use of multi-screw extruders (two or more screws in a barrel). Multi-screw extruders are primarily used for compounding plastic materials. A major, large market for RP molding compounds prepared by extruders is RTPs. Different designs of multiscrew extruders are used to produce compounds based on the plastic being processed and the products to be fabricated. At times, their benefits can overlap, so the type to be used would depend on cost factors, such as cost to produce a quality product, cost of equipment, cost of maintenance, etc. Latest in extruder design has 12-screws. Worldwide being used for in-line mixing/compounding (also reactive extrusion, devolatization, and fabricating specialty products such as fuel cells) is at present 14 extruders that use 12-screws. They are called ring extruders (REs), because 12 screws are set up in a circle around a fixed core. Each screw has a 30 mm diameter with length-to-diameter ( L / D ) ratio is 32-1. Its design passes the plastic from one screw to the next, around the circle providing less shear for gentle melt processing of heat- and shear-sensitive materials like thermoplastic, elastomers, or highly filled materials. Machine was developed by ExtriCom GabH of Lauffen, Germany (company used to be called BIach Verfahrenstechnik GmbH). Century, based in Traverse City, Mich., has the rights to manufacture, sell, and service the RE machines in North and South America. Century introduced the 12-screw machine to the USA at The 2000 NPE show. Its first extruder was sold to an undisclosed USA customer that is running a highly filled plastic (85wt% filled) that requires a high level of devolatization and dispersion (Asmut Kahns, Century business advisor). Eventually more markets will develop using RTPs so forward planning recognizes some basics in their operations. Size of the die orifice initially controls the thickness, width, and shape of any extruded product dimension. It is usually oversized to allow for the drawing and shrinkage that occur during conveyor pulling and cooling operations. The rate of takeoff also has significant influences on dimensions and shapes. This action, called drawdown, can also influence keeping the melt extrudate straight and properly shaped, as well as permitting size adjustments. Drawdown ratio is the ratio of orifice die size at the exit to the final product size. With RPs when compared to URPs the drawdown ratio is significantly reduced if not eliminated. A major difference between extrusion and IM is that the extruder processes plastics at a lower pressure and operates continuously. Its pressure usually ranges from 200 to 1,500 psi (1.4 to 10.3 MPa) and could go 5,000 or possibly 10,000 psi (34.5 or 69 MPa). In IM, pressures go from 2,000 to 30,000 psi (13.8 to 206.7 MPa). However,

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Fabricating 9 Processes 3 4 7

the most important difference is that the IM melt is not continuous; it experiences repeatable abrupt changes when the melt is forced into a mold cavity; during injection the screw melting action is usually not operating. With these significant differences, it is actually easier to theorize about the extrusion melt behavior, as many more are required in IM. In turn more controls are required when IM. Good-quality plastic extrusions require homogeneity in terms of the melt-heat profile and mix, accurate and sustained flow rates, good die design, and accurately controlled downstream equipment for cooling and handling the product. Four principal factors determine a good die design: internal flow length, streamlining, construction materials, and heat control profile. Heat profiles are preset via tight controls that incorporate cooling systems in addition to electric heater bands. Barrels external surfaces can include the use of forced air a n d / o r water jackets to aid in controlling the melt temperature. In some machines, a water bubbler channel is located within the screw. Pushtrusion/Extrusion Processes

The Pushtrusion technology is applied to extrusion. It can be apply to different fabricating processes providing the capability of processing/ compounding long fibers (glass, etc.). As reviewed in this chapter's section under the heading Pushtrusion/Injection Molding Processes, it is applied to preparing compounding long glass fibers and other size and type fibers. PlastiComp Inc., LaCreseent, MN provides its Pushtrusion brand technology into the profile extrusion market through an agreement with GaMra Composites Inc. This technology, that provides in-line compounding of glass RP materials, provides GaMra with cost savings of 50% on RP polypropylene profiles. Previous efforts to use highly loaded glass fiber fillings in profile extrusion had only limited success because of the cost involved. Pushtrusion is giving the fabricator a real benefit in the savings obtained from doing the compounding right in the extrusion line. The process now is drawing extrusion interest not only because of cost savings, but also because of its ability to reduce the thermal expansion rates of products such as lineals by as much as 90%. Pushtrusion is being used to make products such as window components and railing systems for the building and construction market. Initially, it had been used with PP, ABS. PlastiComp is under way to adapt it to PVC and higher performing engineering resins. In the long fiber RP markets applying Pushtrusion to profile extrusion, as in injection molding requires only a little modification. Technically,

348 Reinforced Plastics Handbook

profile extrusion is an easier process for Pushtrusion because it is a continuous process, unlike molding, which is a sequential process. Pulsed Melts

Various processes are reported to provide a means to pulsate the melt to improve performance of the extruded product. An example is the Scorim process reviewed in the Injection Molding section in this chapter. A variation in the IM process has been applied to production of reinforced extruded TP pipe. This has been a center of interest, on the argument that a predictable orientation of fiber would considerably increase the pressure resistance of the pipe, without the need to increase wallthickness (on the analogy of winding a TS resin pipe with continuous filament). The Scorim process combines the extrusion of a fiberreinforced compound with pressure pulsing around the periphery of the die, which appears to have the effect of orientating the reinforcement.

Thermoformings Thermoforming consists of uniformly heating TP sheet to its softening temperature that is usually URP. However, RPs can be used; they have limited use. The heated flexible TP sheet or film is forced by vacuum and/or pressure against the contours of a mold. Force is applied by mechanical means (tools, plugs, solid molds, etc.) or by pneumatic means (differentials in air pressure created by pulling a vacuum between plastic and mold or using the pressures of compressed air to force the sheet against the mold). Almost any TP can be thermoformed. However, certain types make it easier to meet certain forming requirements such as deeper draws without tearing or excessive thinning in areas such as corners, a n d / o r stabilizing of uniaxial or biaxial deformation stresses. Ease of thermoorming depends on stock material's thickness tolerance and forming characteristics. This ease of forming is influenced by factors such as to minimize the variation of the sheet thickness so that a uniform heat occurs in the sheet material thicknesswise, ability of the plastic to retain uniform and specific heat gradients across its surface and thickness, elimination or minimizing pinholes in the plastic, and stabilizing of uniaxial or biaxial deformation. Many forming techniques are used. Each has different capabilities depending on factors such as formed product size, thickness, shape, type plastic, a n d / o r quantity (Figure 5.38). Mold geometry with their

5

9Fabricating Processes 3 4 9

Figure 5.38 Examplesof thermoforming methods different complex shapes vs. type of plastic material being processed will influence choice of process. Thermoforming is a fast, low-cost method of producing essentially shell-shapes, but suffers from the need to have a relatively large trim area around the forming. Little has been done to date to utilize this process for reinforced materials, because of the lack of suitably reinforced sheet and the problems of fiber thinning that must necessarily arise when the two-dimensional sheet is drawn over the three-dimensional mold. A form of thermoforming is used; however, with high performance TP/fabric prepreg sheet (especially where the forming is required in one plane only, or where there is relatively shallow depth of draw, as with some dish-shaped panels used on aircraft. A combination of matched molding and thermoforming has been found successful with some high-performance parts. The material (fabric-reinforced PPS laminate) is heated to 316C (600P) in an infrared oven and then rapidly transferred to the mold. A seal is made

350 Reinforced Plastics Handbook

between the laminate and the periphery of the mold and vacuum is applied, drawing the hot laminate to conform to the mold surface. The mold can be heated or used at ambient temperature, depending on mold design and final application. Parts up to 660-950 mm (2-3 feet) x 1.22 mm (0.048 in) thick can be formed in a matter of seconds. Thermoforming can also be used, to some extent, for preforming reinforced TP foam cores for laminating with TS resins. The Advance RP process (developed by Advance USA, East Haddam, CT, USA) is an adaptation of thermoforming for production of RPs. In the recent pass various organizations thermoformed b-stage RTS sheet (sheet molding compound/Chapter 3). Different shapes were formed that include boat hulls.

Reinforced Reaction Injection Moldings There is reinforced reaction injection molding (RRIM) and reaction injection molding (RIM) (Figure 5.39). These process predominantly uses TS polyurethane (PUR) plastics both reinforced and unreinforced types. Others include nylon, TS polyester, and epoxy that are reinforced and unreinforced types. PUPs offer a large range of product performance properties. As an example PUR has a modulus of elasticity in bending of 200 to 1400 MPa (29,000 to 203,000 psi) and heat resistance in the range of 90 to 200C (122 to 392F). The higher values are obtained when glass fiber reinforces the PUR (also with nylon, etc.). In addition to RRIM there is structural RIM (SKIM) that identifies fabricating higher strength structural parts. Very large and very thick RRIM or SKIM products can be molded with or without reinforcements using fast cycles. When compared to injection molding (IM) that processes a plastic compound, RIM uses two liquid PUR chemical monomer components (polyol and isocyanate) that are mixed to produce the polymer (plastic). Additives such as catalysts, surfactants, fillers, reinforcements, a n d / o r blowing agents are also incorporated in the reactive system that produces the basic polymer. Their purpose is to propagate the reaction and form a finished product possessing the desired properties (Table 5.9). Mixing is by a rapid impingement in a chamber (under high pressure in a specially designed mixing head) at relatively low temperatures before being injected into a closed mold cavity at low pressure. An exothermic chemical reaction occurs during mixing and in the cavity requiring less energy than the conventional IM system. Polymerization of the

5

Fabricatin 9 9 Processes 351

Figure 5.:39 Exampleof typical polyurethane RIM processes (courtesy of Bayer] monomer mixture in the mold allows for the custom formulation of material properties and kinetics to suit a particular product application. RIM Infusion Technology

The reinforcement can be included during mixing of the two liquid monomer components or put into the mold cavity followed with injecting the polymer mix in the closed mold. This system provides another infusion technology as explained earlier in this chapter. RRIM is a process to consider at least for molding large and/or thick products. With RRIM technology cycle times of 2 min and less have been achieved in production for molding large and thick [10 cm (3.9 in.)] products. It is less competitive for small products. Capital requirements for RIM processing equipment are rather low when compared with injection molding equipment (includes mold) that would be necessary to mold products of similar large size.

352 Reinforced Plastics Handbook Table 5.9 RRIM and injection molding processing conditions compared for large surface production parts

Plastic temperature, ~ (~ Plastic viscosity, Pa, s Injection pressure, bar {psi} Injection time, s Mold cavity pressure, bar {psi} Gates Clamping force, t Mold temperature, ~ {~ Time in mold, s Annealing Wall/thickness ratio Part thickness, typcal maximum, cm {in.} Shrinkage, % Unreinforced Reinforce-glass parallel to fiber vertical to fiber Inserts Sink marks around metal inserts Mold prototype, months Mold alterations

PUR-RIM

Injection molding

40-60 (50-140) 0.5-1.5 100-200 {1,450-2,900}

200-300 {392-572} 100-1,000 700-800 (10,100-11,600}

05.-1.5

5-8

10-30 (145-430}

300-700 (4,400-10,200}

1 80-400 50-70 {122-158)

2-10 2,500-10,000 50-80 (122-176)

20-30

30-80

30 min. @ 120~ (248~ 1/0.8 10 (3.9}

Rarely 1/0.3 1 (0.04)

1.30-1.60

0.75-2.00

0.25 1.20

0.20 0.40

Easy Practically none 3-5 {epoxy) Cost-effective

Costly Distinct 9-12 (steel) Costly

Polyurethane Processes Details on reinforced reaction injection molding (RRIM) using TS polyurethane (PUR). Two-component P U R mixtures, in which a polyol and isocyanate are brought together and a fast reaction takes place to produce a solid compound with useful properties lend themselves well to molding with reinforcement. This can be a flat or preformed mat placed in the mold, or a chopped reinforcement introduced into the stream of components in the mixing head. The two components (polyol and isocyanate) which are reacted together to produce a P U R are brought together in a mixing head, into which it is also possible to add other components, such as mineral fillers (or ground-up recycled resin/glass moldings, acting as a filler). Because of the fast reaction of the polyurethane system components, the ingredients are mixed very rapidly and then injected under pressure into a closed mold, in which a preform or other fiber lay up has been placed.

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9Fabricating Processes 3 5 3

Depending on the size and geometry of the part, it is also possible to feed fiber reinforcement in continuous roving form into the mixing head, where it is chopped and mixed with the liquid reacting components and the whole mix is then injected (Figure 5.40).

Figure 5.40

Schematic of reinforced RIM with (a) continuous reinforcement chopped in the mixing head (RRIM] and (b] mat reinforcement placed in the mold (SRIM)

3 5 4 Reinforced Plastics Handbook

A combination of chopped roving and preform may also be used. The use of PUR gives a wide range of properties, extending towards elastomeric (for parts such as automobile fenders or bumper beams) and introduces cellular/foam forms. SRIM is a reinforced PUR molding process in which the fiber reinforcement is in the form of a mat, which is usually preformed and laid into the mold before the polyurethane mix is injected from the mixing heads. Since it uses the reinforcement in the form of a mat, it offers better structural properties, but also suffers from the disadvantage of requiring a preform. Experience has demonstrated that this stage can be integrated into the molding process and is not a serious drawback to commercial production (Table 5.10). Table 5.10 RTM,SRIM and thermoplastic injection molding processescompared Materiels

Temperature (oC) Materials Mold Material viscosity (Pa s) Pot life/cream life (s) Molding pressure (bar) Mold clamping (tonnes) per 1 m 2 surface area Equipment cost (US $ x 103)

RTM

S-RIM

TIMa

Mainly room temp - 40 Room temp - 80

40-60

180-400

70-100 0.1-1

50- 200 102-105

2-20 100-200

300-1500

100 hundreds

3000 thousands

0.1-1 120-1000 0.9-6.0 20 tens

aThermoplasticinjection molding. Source: ReinforcedPlastics.

Development of the process has been rapid and in many different directions, aiming primarily at improving the cycle time, introducing internal release agents (to eliminate lengthy mold cleaning between cycles), and allowing other materials to be included in the mix. Computer control has made a major difference, because of the need for split-second control over mixing time and ratios, with the possibility of integrating with peripheral systems such as robot demolding, finishing and take-off, on the lines of the technology now developed for injection molding of TPs. Important developments have also been made in the ability to introduce finely ground-recycled material into the mixing head and use it as filler with positive properties. Low density reinforced reaction molded polyurethane (LD-RRIM) is claimed to simplify production of interior automobile components,

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9Fabricating Processes 3 5 5

especially complex parts such as door panels. Dow's Spectrim RL system is used for many of the interior parts of the Dodge Viper GTS Coupe, by Chrysler and Prince Co. Different textures and materials can readily be incorporated, allowing for deep draw designs, while retaining one-piece construction. The technology was developed with Strapazzini Auto, Italy.

Long Fiber Technology As with all RPs, the length of reinforcing fiber in PUR systems plays a significant role in the strength of the molded part. Typically, fibers are hammer-milled and are up to 400 pm long, enabling them to pass through a mixing head and be poured into the mold. Even where high volume fractions of 20% or more are achieved, the additional strength gained from fiber which is, in practical terms, little more than a powder, is only limited. For high strength, longer fibers are needed, and therefore other methods of incorporating them have been developed. The first such method was structural reaction injection molding (SRIM), as described above, in which the fiber reinforcement is in the form of a mat, which is usually preformed and laid into the mold before the polyurethane mix is injected from the mixing heads. This, however, introduces the additional operation of preforming the reinforcement, so adding to cost.

Long Fiber Injection Processes Alternative technologies have been developed for introducing long fibers (in the range 15-100 mm length) into the injection stream at some stage and avoiding the cost and delay of preforming: 9 Long fiber injection (LFI) of PUR, developed by the German companies KraussMaffei (machinery) and Elastogran (processing): the fiber is introduced inside the mixing head 9 Fipur-Tec, developed by Bayer: chopped glass fibers are sprayed into the PU resin just downstream of the mixing head. For long fiber injection (LFI), an existing high-pressure head is modified to include a cutter and fiber delivery nozzle, to cut and meter the glass fiber directly at the mixing head. Glass fiber is used in the lessexpensive form of rope (roving), which is fed straight from a spool to a cutter. The cut fibers are fed at high speed into the hollow within the annular liquid pipe formed by the reaction mix issuing from the mixer discharge. The kinetic energy promotes effective wetting out, enabling fibers up to 100 mm long to be processed. The fiber is introduced into the resin stream as late as possible, to minimize abrasion wear and need for frequent replacement of components. The polyol component can contain a significant proportion of recycled material, or up to 80%

356 Reinforced Plastics Handbook

natural raw material. The mix is sprayed into a metal mold that is then closed. High pressure exerted on the reacting mix produces very good resin/fiber bonding. The process can be controlled by automatic closed-loop systems: for example, concentration of fiber is varied by controlling the speed of the cutter. Integrated cutter, mix, and spray heads, controlled by robot, can inject rapidly into the mold and so contribute to short molding cycles. Hydraulic piston-based metering pumps are used in preference to rotary pumps, which can be prone to clogging. After each shot, a separate cleaning piston removes the last traces of the reaction mix from the head. Data for the LFI process suggest that high-strength components can be produced, offering lower weight and higher dimensional stability than SRIM moldings. With the fight fiber concentration, moldings as thin as 1.5 mm can be produced, giving a strength equivalent to 3 mm thick SRIM, while being substantially lighter. Savings in materials and weight are claimed to be up to 40% less than with SRIM. Since it is possible with this process to distribute the fibers more evenly across the whole cross section of the part, and to wet them out more thoroughly, it is possible to achieve high strength with relatively thin sections. Moldings are also almost free from warpage and remain dimensionally stable over a wide range of temperatures. Basic parts are lighter and more dimensionally stable than SRIM equivalents, with only slightly lower mechanical properties. At higher densities (such as 1000 g/m3), the mechanical properties are equal or better. Trials (mainly with automobile components manufacturers) have suggested that, compared with SRIM, LFI can give 20% lower glass fiber cost, with glass waste of 3-5% (compared with 30% when a preform is used) and 2-3 mm wall thickness (compared with 3-4 mm). On a pilot application, a PU metering unit with a robot controlled mixing head was able to fill three or more average molds in succession. With a demolding time of about 3 min, two operators could produce 45 or more parts per hour, including time for cleaning molds and handling demolded parts. Calculations suggest that the faster cycles and lower glass cost could reduce unit cost by 15-20%. Standard SRIM metering equipment and mold tools can be used. The investment for a complete plant, however, would be in the region of DM 1 million. On the other hand, with large investment in SKIM, the older process will be hard to displace, while many designers believe that, with directed fiber preforms and very high volume fractions, SRIM may still have the edge where high mechanical performance is required.

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Developed by Bayer, the Fipur-Tec system claims much the same advantages as the LFI process, but with the advantage that a special glass cutter shoots fibers into the P U R stream just outside and downstream of the mixing head. This avoids possible mechanical damage to the fiber, so that the full reinforcing properties of the fiber can be delivered to the molded part. It also avoids possible clogging problems. Krauss-Maffei is said to be studying a similar modification to its LFI process. The Hennecke MX head produces a wide (60 mm) rectangular P U R stream, giving a consistent distribution of random oriented fibers.

Rotational Moldings This method, like blow molding, is used to make hollow one-piece parts. RM consists of charging a measured amount of TP without or with chopped fiber reinforcements (RRM) into a warm mold cavity that is rotated in an oven about two axes. In the oven, the heat penetrates the mold, causing the plastic, if it is in powder form, to become tacky and adhere to the mold female cavity surface, or if it is in liquid form, to start to gel on the mold cavity surface. Since the molds continue to rotate during the heating cycle, the plastic will gradually become distributed on the mold cavity walls through gravitational force. As the cycle continues, the plastic melts completely, forming a homogeneous layer of molten plastic. After cooling, the molds are opened and the parts removed (Figures 5.41-5.43). RRM can produce uniform wall thicknesses even when the product has a deep draw from the parting line or small radii. The liquid or powdered plastic used in this process flows freely into corners or other deep draws upon the mold being rotated and is melted/fused by heat passing through the mold's wall. This process is particularly cost-effective for small production runs and very large product sizes. Figures 5.44 and 5.45 provide examples of reinforced and unreinforced products that range from polyethylene small beach ball to chopped glass fiber cross-linked polyethylene (XLPE) 22,500 gallon large tank. This size tank with 11/2 in. wall thickness uses a triple XLPE charge with the first about a 2,500 lb charge, and the following two each at 1,500 lb. The molds are not subjected to pressure during molding, so they can be made relatively inexpensively out of thin sheet metal. The molds may also be made from lightweight cast aluminum and electroformed nickel,

358 Reinforced Plastics Handbook

Figure 5.41 Rotational molding's four basic stations (courtesy of The Queen's University, Belfast)

Figure 5,42 Rotational molding of the two axes is at 7:1 for this product (courtesy of Plastics FALLO)

Figure 5.43 Rotational molding of a three station/two axis carousel RM machine

5

Figure 5.44 Examplesof RM recreational products

Fabricating 9 Processes 3 5 9

360 Reinforced Plastics Handbook

Figure 5.45 Example of large tank that is RM both of them light in weight and low in cost. Large rotational machines can be built economically because they use inexpensive gas-fired or hot air ovens with the lightweight mold-rotating equipment. There are rock 'n' roll rotational machines. They are designed for long length to small diameter ratio. An example of a machine is one designed for large-diameter; heavy technical parts located in the Molding Co. plant in Farmington, MO. It has a loading station and an unloading station. Operators stand on a platform about 5 feet above the floor. The mold swings back and forth with the oven while the mold turns. This machine built by Ferry Industries Inc., Stow, Ohio is also called a rocking oven machine, the rockin' press. It pivots at the center and swings 45 degrees in both directions, oven, molds and all. Traditional carousel rotomolders mount the mold on arms that cycle through a fixed oven. But to make very long, cylindrical shapes, such as a kayak, the rock, 'n' roll style is preferred. Making that shape of parts with a fixed oven would require a huge oven, and lots of wasted space. Most kayaks are made at dedicated kayak factories, so it is unusual for a custom molder like Molding Co. to get into rock 'n' roll molding. However, the big Ferry press can make industrial parts and things a lot bigger and heavier than a kayak. The Rotospeed rocking oven machine can make parts measuring as large as 24 feet by 10 feet. It is robust enough to carry 9,000 pounds of combined mold and part weight. Molding Co. bought the machine to

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9Fabricating Processes 3 6 1

make parts measuring 23 feet long, 4 feet and 8 feet wide. To fit the big machine into the plant, the company had to bring in heavy equipment and dig a pit 18 feet deep by 13 feet wide. The machine is a sophisticated piece of equipment. All the different motions on this machine are computer controlled. You can stop any of the variables at this machine, at any time, and control speeds. Every motion is adjustable. The operator can freeze the swinging motion at any point and keep rotating the molds, to build up thicker walls in strategic areas of the part. Different colors can be added during the operation. The amount of control gives a huge flexibility as far as the type of parts and the uniqueness of parts that can be molded.

Blow Moldings BM can be divided into three major processing categories: extruded BM (EBM) with continuous or intermittent melt (called a parison) from an extruder and which principally uses an unsupported parison (Figure 5.46),

Figure 5,46

Schematicof the extrusion BM process

injection BM (IBM) with noncontinuous melt (called a preform) from an injection molding machine and which principally uses a preform supported by a metal core pin (Figure 5.47), and

362 Reinforced Plastics Handbook

Figure 5.47 Schematicof the injection BM process

stretched/oriented EBM and IBM to obtain bioriented products providing significantly improved performance-to-cost advantages. These BM processes offer different advantages in producing different types of products based on the plastics to be used, performance requirements, production quantity, and costs. Practically all the plastic used is unreinforced TPs (Figure 5.48). Some parts have been blown using milled and short glass fiber reinforcements (Figure 5.49).

Figure 5.48 Examplesof complex BM products

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9Fabricating Processes 3 6 3

Figure 5.49 Milled glass fiber/ polyethylene blow molded water floatation wheels

The BM lines have an extruder with a die or an injection mold to form the parison or preform, respectively. In turn, the hot parison or preform is located in a mold. Air pressure through a pin-type device will expand the parison or preform to fit snugly inside their respective mold cavities. Blow molded products are cooled via the water cooling systems within mold channels. After cooling, the parts arc removed from their respective molds. Increased attention has been paid to the technology influencing the use of reinforcement in the BM compounds. Elongational flow is one of the main processing criteria and plastics which in their clongational viscosity exhibit strong strain-hardening thus tend to have good process ability by BM. A team at Yamagata University, Japan has studied the effect of glass spheres in a high-density polyethylene compound for BM (Chapter 2 Glass Characteristics, Glass sphere regarding melt flow). A high molecular weight HDPE (as used for automobile fuel tanks, and many other applications) was examined, both unfilled and reinforced with glass spheres of 18 mm diameter and 2.6 specific gravity. Storage modulus and loss modulus increased with glass bead content at both low and high frequencies and it was shown that Trouton's law (that, for homogeneous plastics, elongational viscosity in the strain rate independent region is very close to three times the shear viscosity) holds good for RP systems as well as for the virgin plastics. Strain hardening has an anomalous dependency on strain rate, and is more marked at lower strain rate. In RPs, strain rate dependence of

3 6 4 Reinforced Plastics Handbook

strain hardening is similar to that of virgin HDPE. The hardening phenomenon appears at large strain and is generally believed to be caused by elastic behavior of elongated polymer chains. The glass beads suppress the large deformation of matrix polymer chains around them (which may possibly be one of the causes of the suppression of chain hardening by the glass beads). In B M, it is important for the parison to be able to resist draw down and, since this occurs slowly, it can be expected that a compound with a strong strain hardening at low rates of strain (as exhibited by the RPs tested) will have good BM processability.

Foams A generic term for flexible to rigid materials containing many cells (open, closed, or both) dispersed throughout the material. Foamed products, whether TPs or TSs with and without reinforcements, have been a large part and special category within the plastics industry. They are known by different names such as cellular plastics, expanded plastic foams, structural plastic foams, low-pressure foams injection molding, high-pressure foams injection molding, and just plastic foams. It is a plastic whose apparent density is decreased by the presence of numerous empty cells throughout the mass. The manufacture of foam plastic products cuts across most of the processing techniques fabricating RP parts. The foams can include milled, to short and long cut glass fiber reinforcements in their mix. Foams can be fabricated during extrusion, injection molding (Figure 5.50), blow molding, casting, calendering, coating, rotational molding, spraying (Figure 5.51), etc. Typical requirements in such instances will include blowing agents in the plastic. Blowing agents, also called foaming agents are used for the production of plastic foams. Depending on the basic plastic and process, different blowing agents arc used to produce gas and thus to generate cells or gas pockets in the plastics. Various controls to accommodate the foaming action are used. They are divided into the two broad groups of physical blowing agents (PBAs) and chemical blowing agents (CBAs). The compressed gases often used are nitrogen or carbon dioxide. These gases are included into a plastic melt to form a cellular structure. The volatile liquids arc usually aliphatic hydrocarbons, which may be halogcnated, and include materials such as carbon dioxide, pcntane, hexane, methyl chloride, etc. Polychlorofluorocarbons were formerly

Figure 5.50

Schematic of foam reciprocating injection molding machine for low pressure

lJ1 -rl o" r

m ,

a,1 m o

0 t'3 qJl

Figure 5,51

Liquid (left), froth (center), and spray polyurethane foaming processes

t'1) (.~ 03

Cn

366 Reinforced Plastics Handbook used but they have now been phased out due to the reported environmental problems. Different types are available because certain plastics can only use a specific type. There are some techniques unique to foamed plastics. It is possible to use spray guns or mixing metering machines to mix the liquid ingredients with additives and reinforcements together and direct them into a mold cavity. The mixed ingredients with their chemical blowing reaction start to foam after leaving the dispensing equipment. There is a unique technology of molding structural foam, foams with integral solid skins, and a cellular core resulting in a high strength-toweight ratio. When processing structural foams, several techniques are used with most related to injection molding and extrusion. Uses range from water floatation devices to high performance structural components.

Foamed Reservoir Moldings Also known as elastic reservoir molding, this process creates a sandwich of plastic-impregnated, open-celled, flexible polyurethane foam between the face layers of fibrous reinforcements. When this plastic RP is placed in a heated mold and squeezed, the foam is compressed, forcing the plastic and air outward and into the reinforcement. The elastic foam exerts sufficient pressure to force the plastic-impregnated reinforcement into contact with the mold surface (Figure 5.52).

Figure 5.52 Foamed reservoir molding

5

Fabricating 9 Processes 3 6 7

Syntactic Cellular Plastics

Also called RP syntactic foam or syntactic foam. An RP compound made by mixing hollow microspheres of glass, epoxy, phenolic, etc. into a fluid TS plastic with its additives and curing agents. It forms a moldable, curable, lightweight mass, as opposed to foamed plastics in which its cells are formed by gas bubbles, etc. Use includes water floatation apparatus.

Centrifugal Moldings Centrifugal fabrication has been in use since the 1940s. It is suited to the production of hollow parts such as pipes with two smooth faces. Fiber reinforcement (usually roving chopped during the process) and TS or TP resin are sprayed onto the inside of a mandrel rotating at high speed and the centrifugal force pushes the resin outwards, impregnating the reinforcement (Figure 5.53). Predominately used is TS plastics. The process is generally used to produce cylindrical parts (such as pipes, tanks, vats and silos) but it is increasingly used to produce slightly tapered poles (such as telegraph and street lighting posts). A device to prevent air entrapment needs to be incorporated into the mechanism.

Figure 5.53 Schematic of centrifugal casting of reinforced plastics

Eneapsulations Also called conformal coating. It encloses a product in a closed envelope of plastic unreinforced or reinforced by immersing the product (solenoids, ornament, sensors, motor components, integrated

368 Reinforced Plastics Handbook

circuits, and other articles.) in an unheated or heated plastic. Different processes can be used that range from casting to injection molding. Casting permits applying different techniques. As an example, half or part of the casting can gel. The product such as an ornament is placed on the gelled plastic followed with the final pouring of the plastic without or with chopped fiber reinforcements. The typical TP RP encapsulation process is an insert injection molding or liquid injection molding operation. The insert, a coil or an integrated circuit, for example, is placed in a mold equipped with either fixed spider type supports, retractable pins, or other features to support it when molten material is injected. This technique with insert molding is a clean, repeatable process that lends itself to automation and cellular manufacturing, and fits well with total quality management (TQM). With off-the-shelf process controls and systematic production methods, manufacturers can deliver repeatable, high-quality products that come out of the tool ready for assembly. The products generally do not require costly trimming or deflashing, as do many TS encapsulated products when using processes such as compression molding. Although horizontal clamp injection molding equipment can be used for encapsulation, vertical-clamp machines allow easier insert placement and greater insert stability during mold clamping movement. For highvolume production, a vertical machine with a shuttle or rotary table is highly efficient. For example, a two-station table fitted with two lower mold halves allows molding at one station while an operator or robot unloads finished products and loads inserts at the other shuttle station.

Castings Some TPs and TSs begin as liquids that can be cast and polymerized into solids. In the process, various ornamental or utilitarian objects can be embedded in the plastic with out or with fiber reinforcements as reviewed for the encapsulation process. By definition, casting applies to the formation of an object by pouring a fluid plastic solution into an open mold where it completes its solidification. Casting can also lead to the formation of sheet, made by pouring the liquid compound onto a moving belt or by precipitation in a chemical bath. Casting differs from many of the other techniques described in this book in that it generally does not involve pressure or vacuum casting, although certain materials and complex products may require one or the other.

5

9Fabricating Processes 3 6 9

Stampings In the stamping process, usually a reinforced TP sheet material is precut to the required sizes. The precut sheet is preheated in an oven, the heat depending on the TP used (such as PP or nylon, where the heat can range upward from 270 to 315C (520 to 600F). Dielectric heat is usually used to ensure that the heat is quick and, most important, to provide uniform heating through the thickness and across the sheet. After heating, the sheet is quickly formed into the desired shape in cooler matched-metal dies, that can use conventional stamping presses or SMC type compression presses. Reinforced TS plastic B-stage sheet material can be used with its required heating cycle (Chapter 3). However, the most popular is to use TP sheets. Stamping is potentially a highly productive process capable of forming complex shapes with the retention of the fiber orientation in particular locations as required (Figure 5.54). Figure 5.55 compares stamping of Azdel (Chapter 4 Glass Mat Thermoplastics) with other processes. The process can he adapted to a wide variety of configurations, from small components to large box-shaped housings and from fiat panels to thick, heavily ribbed parts.

Figure 5.54 Processing sequence for compression stamping glass fiber reinforced thermoplastic sheets

370 Reinforced Plastics Handbook

I

150

125 -

300

Thermoplastic stamping

1 O0 --

_

250

-

200

-150

75-

ection molding

50-

~

.

~, Thermoset compression molding (SMC)

-

100

Structural foam

._.._..._-50

25Parts

per hour at 80% lob

efficiency

'

1

I

I'"

I

~"

I

I

' 1

Parts per shift per year, thousands

20 40 60 80 100 120 140 160 Part cycle time. seconds

Figure 5.55 Stampingcomparedto other processes

Cold Formings This process is similar to the hot-forming stamping process. It is a process of changing the shape of a TS or TP sheet or billet in the solid phase through plastic (permanent) deformation with the use of pressure dies. The deformation usually occurs with the material at room temperature. However, it also includes forming at a higher temperature or warm forming, but much below the plastic melt temperature, and lower than those used in thermoforming or hot stamping (Figure 5.56).

Figure 5.56 Coldforming

5

Fabricating 9 Processes 371

Different forms of glass fiber/TS plastics are used with or without special surface coatings such as gel coatings. Materials are compounded with controlled pot life so that they start their cure reaction after being placed in the mold cavity. For room temperature cure, cure occurs by an exothermic chemical reaction that heats the RP. Pressures are moderate at about 20 to 50 psi (140 to 350 kPa). Molds can be made of inexpensive metal, plaster, RP, wood, etc. Comoform Cold Moldings

This is another version of cold forming by utilizing a thermoformed plastic skin too impart an excellent surface and other characteristics (for weather resistance, etc.) to a cold-molded thermoset RP. For example, a TP sheet is placed in a matched mold cavity with an RP uncured material placed against the sheet. The mold is closed and the fast, room temperature curing resin system hardens. The finished product has a smooth TP-formed sheet backed-up with RP.

Filament Windings Also called FW. Produces high strength and lightweight products that consist of two RP ingredients that are the reinforcement and a plastic matrix. The plastic is usually a TS material. The process uses a continuous reinforcement (glass, carbon, graphite, PP, wire, and other materials in filament, yarn, tape, etc. forms) either previously impregnated (prepreg) or impregnated at the machine with a plastic matrix that is placed on a revolving (removable) mandrel followed with curing. Reinforcements have set pattern lay-ups to meet performance requirements; target is to have them stressed based on performance requirements of the molded part (Figure 5.57).

Figure 5.57

Schematic of the filament winding process

,m,,

a"

D,1

Ill r-I,,

:!:: 0" 0 0

Figure 5,58 Early 20th century tape wrapping patent of a tube-making machine by H0ganas-Billesh01ms A. B., Sweden

5

9Fabricating Processes 3 7 3

The use of circumferential wrappings to increase the bursting strength of certain structures is not new. Historically, wire and tape (Figure 5.58) wrappings have been used to prevent bursting of cannon barrels and to wrap two-part wooden pipes both to increase the bursting strength and to hold the two parts together so that a leakproof cylinder is formed. Use of filamentary structures for applications requiring ultimate structural performance is rather recent (1940s) and unique (Tables 5.11 and 5.12). Table 5,11 Filamentwound structures for commercial and industrial applications Railway tank cars Storage tanks: acids, alkalies, water, oil, salts, etc. High-voltage switch gears Electrical containers Propellers High-pressure bottles Decorative building supports Containers for engines, batteries, etc. Buoys Valves Aircraft tanks Aircraft under-carriage Aircraft structures Fishing rods Round nose boat Boat masts Lamp poles Golf clubs Race track railing Auto bodies Drive shafts Air brake cylinder Heating ducts Acid filters Recoil-less rifle barrel Pontoons Motor housing Computer housings Marker buoys Laundry tubs Ventilator housings Rifle barrel Dairy cases Auto and truck springs Circuit breaker rupture pots Cartop boats Electroplating jigs

Irrigation pipes Salt water disposal pipes Underground water pipe Oil well tubes Ladders Extension arms for telephone trucks Textile bobbins Weather rockets Gas bottle-mines Structural tubing Insulating tubes Electrical conduit Chemical pipe Pulp and paper mill pipe Water heating tanks Pipe fittings and elbows Truck-mounted booms Highway stanchions Capacitor jackets and spacers Coil forms Electronic waveguides Printed circuit forms Electric motor rotors, binding bands Circuit breaker housing High-voltage insulators Rectifier spacers Antenna/dishes Rotating armatures-DC motors DC commutator Fan housing High voltage fuse tubes Floating ducts Automotive parts Tank trucks Light poles Brassiere supports Looms

3 7 4 Reinforced Plastics Handbook Table 5.12 Filamentwound structures for aerospace,hydrospace,and military applications Rocket motor cases Rocket motor insulators Solid propellent motor liners Nose cones for space fairings Rocket nose cones (2) Rocket nozzle liners Jato motor APU turbine cases High-pressure bottles {gas or liquid] Vacuum cylinders Torpedo launching tubes Rocket launcher tubes Flame thrower tubes Missile landing spikes Deep space satellite structures Radomes Igniter baskets Wing dip tanks Helicopter rotor blades Thermistors Missile shipping cylinders Boat ventilator cowlings

Liquid rocket thrust chamber Rocket exit cones Chemical rockets Chemical tanks Sounding rocket tubes Tactical bombardment rockets Tent poles Heat shields Artillery shell shipping grommet Artillery round-protective cones Submarine fluid pipes Submarine tanks and containers Submarine ventilation pipes Submarine hulls Underwater buoys Cryogenic vessels Electronic packages Submarine fairwaters Sonar domes Engine cowlings Fuse cases Torpedo cases and launchers

Frequently used is some form of glass: continuous filaments roving, yarn, or tape. The glass filaments, in what ever form, are encased in a plastic matrix, either wetted out immediately before winding (wet process) or impregnated ahead of time (preimpregnated process). The plastic fundamentally contains the reinforcement, holding it in place, sealing it from mechanical damage, and protecting it from environmental deterioration, Reinforcement-matrix combination is wound continuously on a form or mandrel whose shape corresponds to the inner structure of the part being fabricated. After curing of the matrix, the form may be discarded or it may be used as an integral part of the structural item. Reinforcements have set pattern lay-ups to mcct performance requirements (Table 5.13 and Figures 5.59 and 5.62). Target is to have them uniformly stressed. Figures 5.61 provides the relationship of RP density vs. percent glass fiber by weight or volume that can be related to the compacting action that occurs when FW. In winding cylindrical pressure vessels, tanks, or rocket motors, two winding angles are generally used (Figure 5.63). One angle is determined by the problem of winding the dome integrally with the cylinder. Its magnitude is a function of the geometry of the dome. These

Table 5.13 Different filament winding patterns meet different performance requirements Type of winding

Considerations

Machinery required

Hoop or circumferential

High winding angle. Complete coverage of mandrel each pass of carriage. Reversal of carriage can be made at any time without affecting pattern.

Simple equipment. Even a lathe will suffice.

Helix with wide ribbon

Complete coverage of mandrel each pass of carriage. Reversal of carriage can be made at any time without affecting pattern.

Simple equipment with provision for wide selection of accurate ratios of carriage-to-mandrel speeds. Powerful machine and many spools of fiber required for large mandrel.

Helix with narrow ribbon and medium or high angle

Multiple passes of carriage necessary to cover mandrel. Programmed relationship between carriage motion and mandrel rotation necessary. Reversal of carriage must be timed precisely with mandrel rotation. Dwell at each end of carriage stroke may be necessary to correctly position fibers and prevent slippage.

Precise helical winding machine required. Ratio of carriage motion to mandrel rotation must be adjustable in very small increments. Relationship of carriage to mandrel positions must be held in selected program without error through carriage reversals and dwells. Relationship between carriage position and mandrel rotation must be progressive so that pattern will progress.

Helix with low winding angle

Fibers positioned around end of mandrel close to support shaft. Characteristics of "helix with narrow ribbon" apply. Fibers tend to go slack and loop on reversal of carriage. Fibers tend to group from ribbon into rope during carriage reversal. Mandrel turns so slowly that extremely long delay occurs at each end of carriage stroke and speed-up of mandrel at each end of carriage stroke is highly desirable to shorten winding time.

Similar machinery required as for "helix with narrow ribbon." Take-up device for slack fibers is necessary if cross-feed on carriage is not used. Cross-feed on carriage is required for very low winding angles. Programmed rotating eye can be used to keep ribbon in fiat band at carriage reversal. Mandrel speed-up device must be programmed exactly with carriage motion or pattern will be lost. Polar wrap machine can be used for narrow ribbons with winding angle below about 15 ~ without take-up device or mandrel speed-up being required,

t.n "TI

o"

o LII

continued td~

Table 5.13 continued

0")

Type of winding

Considerations

Machinery required

Zero or longitudinal

Mandrel must remain motionless during pass of carriage and then rotate a precise amount near 180 ~ while carriage dwells. Fibers must be held close to support shaft during mandrel motion or fibers will slip.

Precise mandrel indexing required. Simple two-position cross feed on carriage sufficient. Vertical mandrel machine and pressure follower for ribbon sometimes required to preserve ribbon integrity.

.

m

,

m

~

~

-ILow angle wrap. Fibers may be placed at different distances from centers at each end when geodesic (nonslipping) path does not have to be followed.

Polar wrap machine with swinging fiber delivery arm desirable for high-speed winding. Helical machine with programmed cross-feed will wind polar wraps more slowly.

Cone

General considerations same as for helical winding except that carriage motion is not uniform.

Programmed non-linear carriage motion required. Other machine requirements same as for helical winding.

Simple spherical

Planar windings at a particular angle result in a heavy build-up of fibers at ends of wrap. For more uniform strength, successive windings at higher angles are required.

Sine wave motion of carriage is required for carriage with no cross-feed. At low angles of wind, cross-feed is necessary because carriage travel becomes excessive. Polar wrap machine may be used if range of axis inclination is large enough.

Polar wrap

oo o

Simple ovaloid

Similar to simple spherical winding but with different carriage or cross-feed motion.

Helical machine with programmed carriage or cross-fee. Polar wrap machine can be used where geodesic (nonslipping) path is in a plane.

True spherical

Path of fibers programmed to give uniform wall thickness and strength to all areas on sphere.

Special machine best approach. Otherwise complex programming of all motions of helical machine required.

Miscellaneous

For successful filament winding, it must be possible to hand-wind with no sideways slipping of fibers on mandels surface.

Machine to reproduce motions of hand winding. Programmed motions in several axes may be required.

O" m

,

t'3

t~3 o t'D

t~

378

Reinforced Plastics Handbook

Figure 5.59

Schematic of an RP composite S-2 glass fiber/burn resistant phenolic adhesive prepreg and aluminum metal lay-up (adhesive by Cytee, formerly American Cyanamid, Havre de Grace, MD)includes use on the Airbus A380 fuselage providing directional properties

l

Winding position ~1

Shift right

[•1

1

3

I

Winding position #2

I

Shift left 1

2

Winding position #3

Shift right

i-

:f Winding position #1, start second cycle

Figure 5.60

E

3 Rotate ~I

Box winding machine with position changes of clamp tooling

5

0.09

/ 0.08 ~

range

u

/

J7

0.07

/

/

/

c

/

/

/

/

0.06

/

/

/

/

/ /

J

/

/ /

0.04

/

,4

Practical

d

0.05

/

//

Fabricating 9 Processes 3 7 9

/ /

I

I

I

I

I,

I

I

20 40 60 80 Per cent glass by weight or volume

I

Figure 5,61 Filament winding density vs. percent glass by weight or volume

I

100

Figure 5,62 Fiber arrangements and

property behavior (courtesy of Plastics FALLO)

Figure 5.63 Helical filament winding

windings also pick up the longitudinal stresses. The other windings are circumferential or 90 ~ to the axes of the case and provide hoop strength for the cylindrical section. It is possible to wind domes with a single polar port integrally with a cylinder comparatively easily without the necessity of cutting filaments. Cutting is obviously not desirable, since it interrupts the continuity of

3 8 0 Reinforced Plastics Handbook

the orthotropic material. The usual procedure in winding multiported domes is to add interlaminate reinforcements during the winding operation where the ports are to be located. It is possible to wind integrally most of the bodies of revolution, such as spheres, oblate spheres, and torroids. Each application, however, requires a study to insure that the winding geometry satisfies the membrane forces induced by the configuration being wound. FW can be carried out on specially designed automatic machines. Precise control of the winding pattern and direction of the filaments are required for maximum strength, which can be achieved only with controlled machine operation. The equipment in use permits the fabrication of parts in accordance with properly designed parameters so that the reinforced filamentous wetting system is in complete balance and optimal strength is obtained. The maximum strength is achieved when filaments in tension carry all major stresses. Under proper design and controlled fabrication, hoop tensile strengths of filament wound items can be achieved of over 3,500 MPa (508,000 psi), although strength of 1,500 MPa (218,000 psi) is more frequently achieved. Since this fabrication technique allows production of strong, lightweight parts, it has proved particularly useful for components of structures of commercial and industrial usefulness and for aerospace, hydrospace, and military applications. Both the reinforcement and the matrix can be tailor-made to satisfy almost any property demand. This aid in widening the applicability of FW to the production of almost any item wherein the strength to weight ratio is important. FW is used in different shapes such as the usual circular and elliptical shape to produce rectangular shapes. FW structures present certain problems because of the lack of ductility in the glass reinforcement. These can be partially solved by proper design and fabrication procedures. Reinforcements other than glass can be used to obtain good ductility, but some of these have lower temperature strength and characteristics. Proper construction constitutes a well-proved means of utilizing an intrinsically nonductile reinforcement to obtain a high degree of confidence in the structural integrity of the end product. Since glass has high strength and is a relatively low-cost product, glass filaments arc still the major reinforcing materials. Other filaments for applications requiring properties such as higher temperatures or greater stiffness include quartz, carbon, graphite, ceramics, and metals alone or in combinations that include glass fibers. A further difficulty with the basic materials is that they do not lend themselves readily to simple concepts and to simple comparisons. The

5

9Fabricating Processes 3 8 1

matrix components are essentially the same plastics as those used for conventional RP laminates. Epoxy plastics are more widely used than others are, although phenolics and silicones give structures with higher temperature properties. TS polyesters are used for many commercial structures in which cost is a problem and high temperatures do not prevail. For certain FW vessels, the low modulus of elasticity of the glass-plastic material is a serious disadvantage. Only moderate improvements in modulus of elasticity by modifications in glass composition or in processing tend to be feasible. Any significant improvement in modulus of elasticity requires changes in the glass composition. There are effective additives to the glass to increase its modulus without proportional increase in density such as beryllium oxide. Interlaminar shear constitutes possible limitations on FW parts. Mthough the absence of interweaving (such as fabrics) boosts tensile strength by eliminating cross flaying, shear strength is limited by the bonding of the reinforcement to the plastic. In conventional woven cloth laminates, the high points of one layer tend to interlock with the low points of adjacent layers. This results in strengthening of the RP against shear failure. Compared to other plastics or matrices epoxy gives better interlaminar shear because of its inherently better bonding. By proper design, the low values of interlaminar shear can be minimized. FW structures have lower ultimate bearing strengths than conventional laminates, for they are more rigid and less ductile. Accordingly, they have less ability to absorb stress concentrations around holes and "cutouts." The original higher tensile strength permits allowable design stresses under these conditions. Since cutting, drilling, or grooving for attachments or access openings reduces the high mechanical strength of filament wound structures, proper design is necessary. Damaging machining operations are to be avoided after final curing of the part. Destructive "cut-outs" or attachment holes are to be eliminated by incorporating the use of premolded plastic or metal inserts into the designs. Techniques cannot be used for every structural element. The shape of the part must permit removal of the winding mandrel after final curing. Reversed curvatures should be eliminated whenever possible, since it is difficult to wind them and hold the filaments under tension. In order to meet this problem, fusible, expandable, and multiparty mandrels are often required. The cost of FW parts is low only when volume production is achievable. Manufacturing processes should be mechanized and completely

382 Reinforced Plastics Handbook

automated to obtain, by extensive and careful tooling, the close tolerances which are required in filament wound structures to meet highstrength but low-cost objectives (Figure 5.64). Precision winders with carefully selected mandrels and speed controls, special curing ovens, and matched grinders are required. It takes time to develop this equipment, and a high initial investment is necessary. Once the original tooling cost has been amortized, the unit cost of individual filament wound parts becomes relatively low, since the basic materials have a low cost.

Figure 5.64

Schematics of "racetrack" filament winding machines. Top view shows a schematic of a machine built to fabricate 150,000 gal rocket motor tanks; other view is machine in action

5 Fabricating 9 Processes 383 This racetrack filament wound tank was fabricated by the Rucker Co. for Aerojet-Gencral (1966). It measured 6.7 m (22 ft) high, 18.3 m (60 ft) wide, 38.1 m (125 ft) long that weighed 32 ton, of all RP. Just the mandrel for this FW machine weighed 100 ton all of metal. Total weight of the steel-constructed machine was 200 ton. The tank contained about 251 million km (158 million miles) of glass fiber, used 8 ton of textile creel containing 60 spools of glass fiber moving up to 7.24 k m / h (41/2 mph), and took three weeks to manufacture the epoxyglass fiber RP tank in the Todd shipyard in Los Angeles, California.

Tape Windings Tape windings or layering is a technique developed for production of high-performance laminates, using either TS or TP RPs. A preimpregnatcd (prepreg) material, in which resin and reinforcement have been combined under factory conditions (to give more reliable mix ratios), is used (Chapter 4). It is in the form of a continuous tape, which is applied to the surface of the mold or former. With TS resin matrices, this can be consolidated by roller during its heat cure cycle. With TP resin matrices, heat is also applied, fusing the matrix as the tape is applied. New equipment has made tape placement within reach of small shops. This process offers a method of producing more predictable laminated structures, for high performance applications. Prepreg tapes are mainly made of the higher performance materials, such as epoxy/carbon or PEEK/carbon. This system can also be used in filament winding. For TP tapes, a TP welding head has been developed, in conjunction with a hot gas torch. This uses the latter as a heat source to melt the prepreg tow prior to lying down and consolidation with the pressure roller. It does not rely on tension and can therefore be used for concave surfaces. Winding speeds of more than 0.15 m (6 in.)/s has been achieved with graphite/PEEK prepregs.

Fabricating RP Tanks Classical stress analysis proves that hoop stress (stress trying to push out the ends of the tank) is twice that of longitudinal stress. To build a tank of conventional materials (steel, aluminum, etc.) requires the designer to use sufficient materials to resist the hoop stresses that result in unused strength in the longitudinal direction. In RP, however, the designer specifies a laminate that has twice as many fibers in the hoop direction as in the longitudinal direction.

3 8 4 Reinforced Plastics Handbook

Consider a tank 0.9 m (3 ft) in diameter and 1.8 m (6 ft) long with semi-spherical ends. Such a tank's stress calculations (excluding the weight of both the products contained in it and the support for the tank) are represented by the formulas: s = p d / 2 t for the hoop stress

and: s = p d / 4 t for the end and longitudinal stresses where s = stress, p = pressure, d = diameter, and t = thickness.

Tensile stresses are critical in tank design. The designer assumes the pressure in this application will not exceed 100 psi (700 Pa) and selects a safety factor of 5. The stress must be known so that the thickness can be determined. The stress or the strength of the final laminate is derived from the makeup and proportions of the resin, rnat, and continuous fibers in the RP material. Representative panels must be made and tested, with the developed tensile stress values then used in the formula Thus, the calculated tank thickness and method of lay-up or construction can be determined based on: th

=

p d / 2 5 h or th

=

1 0 0 x 3 x 12 20 x 103 2x 5

= pd/45h

where: th

=

0.450 in.

tt = th =

1/2 th = 0.225 in. {or the same; thickness with half the load or stress) hoop thickness

tt

longitudinal thickness

=

sh =

hoop stress

st

longitudinal stress

=

5h =

20 x 103 psi (140 MPa)

safety factor = 5 p = 100 psi (700 Pa) d = 3ft (0.9m)

If the stress values had been developed from a laminate of alternating plies of woven roving and mat, the lay-up plan would include sufficient plies to make 1 cm (0.40 in.) or about four plies of woven roving and three plies of 460 g / m 2 (11/2 oz) mat. However, the laminate would be too strong axially. To achieve a laminate with 2 to 1 hoop to axial strength, one would have to carefully specify the fibers in those two right angle directions, or filament wind the tank so that the vector sum of the helical wraps would give a value of 2 (hoop) and 1 (axial), or wrap of approximately 54 ~ from the axial.

5 Fabricating 9 Processes 385

Another alternative would be to select a special fabric whose weave is 2 to 1, wrap to fill, and circumferentially wrap the cylindrical sections to the proper thickness, thus getting the required hoop and axial strengths with no extra, unnecessary strength in the axial (longitudinal) direction, as would inevitably be the case with a homogeneous metal tank. As can be seen from the above, the design of RP products, while essentially similar to conventional design, does differ in that the materials are combined when the product is manufactured. The RP designer must consider how the load-bearing fibers are placed and ensure that they stay in the proper position during fabrication. Processing, Equipment, Products

Filament winding is a technique used to produce high performance hollow symmetrical products. A mandrel of the required shape is rotated on its axis (usually horizontally, but depending on the size and shape of the object to be produced). When fully wound with resinwetted or prepreg reinforcement, the TS resin lay-up is cured, on or off the mandrel. An equivalent process for TPs uses a form of TP prepreg (usually in tape form) which is similarly wound, but is consolidated by heat during the winding process without the need for curing. The first recorded use of filament winding was for lightweight RP hoops for the Manhattan Project in 1954 (which later became the basis for Naval Ordnance Laboratory (NOL) rings used for tension and shear tests). Dick Young of M W Kellogg Co had explored its potential in the mid-1940s and built the first dedicated machine; Dick prepared the first patents on FW; D. V. Rosato performed some work with Dick on rocket motor cases. The first filament wound product as such was the nozzle for the X248 rocket motor unit, produced in 1948, using the E-glass with an epoxy resin system for higher temperature capability. The first commercial filament winding machines were designed and made by McClean Anderson in 1960s. (Brandt) Goldsworthy Engineering designed and built the first six-axis machine for US Army Aviation Systems Command in 1965, which was delivered to Boeing Vertol, Pennsylvania, USA, for production of helicopter blades. The 1980 Beech Stars hip had a filament-wound fuselage. In the early 1980s, automobile drive shafts looked to have a big future, but the growth of this application was largely negated by the development of front wheel drive. Filament winding has potential for compressed natural gas (CNG) bottles as an alternate fuel for automotive truck and bus. Bottles in production measure 3 m x 250-300 mm diameter and are certified by US Dept of Transportation. Lampposts up to 46 m long have also been

386 Reinforced Plastics Handbook

made. D. V. Rosato during 1947-1951 conducted an R&D project for a large CNG company to determine the feasibility of replacing steel tanks with RP FW tanks. Result was that technically FW was superior but cost was excessively high. By the 1970s, FW tanks containing oxygen were approved and used by fire fighters replacing their steel tanks used for breathing; major advantage was the FW lighter weight. The process is capable of great flexibility in type, mix, density and direction of winding, and is used in particular for production of vessels required to withstand high pressures. The pattern of winding also lends itself to computerization. In many cases the reinforcement consists of a band of several rovings; the band may be positioned perpendicular to the axis of the mandrel (circumferential winding) or inclined at an angle relative to the axis (helical winding). High glass contents (60-75%) are obtained, producing parts with very good mechanical properties, for applications demanding rigidity. Pre-impregnated roving facilitates production of parts with very high glass content (80%). FW parts will have only one smooth face. Almost any continuous reinforcement can be used. The most commonly used is glass, both E and S, but carbon and aramid fibers are also used, and quartz, boron, ceramics and metal wire and strip have all been successfully applied. Latest developments include adaptation of the process for asymmetrical products. Suitable resins include TS polyesters, epoxies, bismaleimides, polyimides, silicones, phenolics and thermoplastics. Fibers are usually wound either encapsulated in a B-staged resin (prepreg winding) or with dry fiber which is impregnated with resin during the winding process (wet winding). In some cases, the part is wound dry and then the entire part is impregnated under pressure. Wet winding has the advantage of using the lowest cost materials, with long storage life and less frequent compaction cycles during winding, using a low viscosity resin to coat the fiber completely. The prepreg systems tend to produce parts with more consistent resin content and can often be wound faster because the fiber is already wetted-out. Prepreg fibers also minimize slippage during winding because of their tacky nature and require less consolidating time after winding, and allow a wide range of resin systems to be used. On-site TP winding requires heat and pressure to consolidate the RE; heat sources include lasers, infrared and quartz lamps, induction heating shoes and hot gas torches. The consolidation pressure can be applied either by fiber tension or by mechanical devices. On-site winding is being used in the USA for reinforcement and refurbishment of structures such as

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9Fabricating Processes 3 8 7

concrete supports for highways, to increase their resistance to earthquake shocks. Proper design of the mandrel or tooling is essential to produce high quality parts. It must maintain dimensional accuracy and avoid excessive residual stresses during the cure stage, and it can be very long, inviting problems of sag. If it is to be removed, it must be designed to minimize fiber damage during extraction of the part. Some mandrel types include plaster, sand/polyvinyl alcohol, sand/sodium silicate, water-soluble salts, eutectic salts, low melt metals, collapsible and solid metals, composites, inflatables, and molded TPs. The primary classes of FW are hoop, polar, and helical. The simplest is hoop or circumferential winding, in which fibers are wound approximately normal to the mandrel axis of rotation with the fiber payout head advancing one band width for each revolution of the spindle. Hoop winding is usually combined with helical winding in more complex parts. Polar or tumble machines are used for parts wound using a planar winding path (such as for a short closed-end pressure vessel). These machines normally have the mandrel mounted vertically, over which a rotating arm wraps fiber onto the mandrel. For smaller parts, tumble machines can be used to rotate the part about a fixed arm. Helical winding machines give greatest flexibility and are most common. There is a wide variety of machinery and control systems and these machines can be used to wind from simplest to most complex shapes. Mechanically controlled helical winders are the simplest and least expensive, winding parts that require sinusoidal motion of the fiber payout eye at both ends of the part with constant carriage lead through the part. Programming is usually by changing the gear ratio between spindle and carriage drive, and the horizontal carriage drive chain length. Servo-controlled helical winders provide greatest versatility, with one or more axes under servo control. The number of axes used and the method of controlling them depends on the economics and needs of the process, ranging from simple two-axis to machinery with eight or more servo controlled axes. Computerized servo control gives the greatest versatility with easy development of program and machine set-up. Very complex parts can also be wound. Better control can be obtained by defining the entire process, which will then be automatically executed by the machine, making for a more reproducible product. Automatic logging can be used to document the process and monitor quality.

388 Reinforced Plastics Handbook

Auxiliary process control allows external devices to be controlled during winding, allowing further automation. The winding pattern can turn simple devices on and off or activate smart devices that can interact with the winding process. Fiber tension can be controlled and varied automatically during winding. Application software allows most winding patterns to be generated numerically and then fine-tuned if necessary, using the robotic teaching capabilities of the machine. Analysis capabilities allow finite element models to be created from the winding patterns, and the process can be simulated and the projected RP analyzed early in the design stage, without having to do the initial winding. Typical equipment is computer-controlled and offers facility for both chop-hoop and helical winding. Helical winding is preferred where additional axial strength is required (such as, for example, suspended pipes or tanks) without using unidirectional tape as used in chop-hoop winding. The latter method is, however, a very efficient and economical means of producing large-diameter pipes and tanks, and for pipes that are to be joined with an O-ring type of bell-and-spigot joint. The systems can include many options: surface veil, chopped liners, sprayed resin systems, hoop winding strands, helical winding strands, resin bath, unidirectional tape, woven roving tape, pigmented resin surfaces, wax-resin surfaces, gel coats, BPO catalyst, epoxy resins, vinyl ester resins, filled resin systems, abrasive resin systems, polyester foam, syntactic foam, and charting film. Racetrack and Other Winders

Because of the great flexibility of the process, it is possible to offer a great many options in machine dimensions (the size and sheer bulk of the product being the limiting factor). For example, very large diameter ducting for fume scrubbers now being fitted to electrical power stations is FW (in some cases, with a temporary production unit constructed on site), while other machines can produce tanks up to 7.3 m diameter and 15 m length (24 x 50 ft). A wide variety of machinery is available, including simple lathe-like hoop winders, polar and tumble machines, ring winders, racetrack winders, robotic arm helical winders, vertical and horizontal helical and special purpose machines. Sizes range from small tabletop machines, for laboratory R&D work, to giants (Figure 5.64). FW technology is also being used for production of blanks for high performance products outside the hollow cylinder geometry. Springs for motor vehicle suspension elements are produced by filament winding and then cut, while a carbon/epoxy I-beam has also been produced on a small machine, producing a tube on a cylindrical mandrel

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9Fabricating Processes 3 8 9

which was then loaded in the uncured state into a die and pressmolded. A considerable amount of development of engineering structures can be expected in these directions, where the FW machine is used as a means of producing a high density/high-precision lay-up. Developments in FW include large vehicle bodies (by Schindler Waggon) and the company is investigating whether its technology can be used for economic production of other large structures such as bus bodies, insulated or double-shell containers, passenger bridges for airports or shelters. Internacional de Composites SA, Toledo, Spain is also investigating buses. The design for the interior is a series of filament wound rings, joined together with further filament wound elements. Different core sections, open or closed can be used, with diverse exterior geometry. Any element not containing concave geometry can be wound, it is claimed. During the 1950s-1970s various USA organizations (commercial and military) built FW box shaped low cost housings. A CNC control system with brushless motors has been used by specialist processors to re-engineer a filament tube-winding machine for fast, accurate and consistent performance. The control made the unit capable of distributing resin-impregnated fibers evenly around the rotating mandrel at programmable feed rates of 60 m / m i n irrespective of the pitch of the filament. The vertical machine produce tubes up to 3 m finished length and 760 mm inside diameter. Usually the mandrel must be spun uniformly and the FW around it, placing limitations on the design, and even symmetrical RP structures generally have to be joined by the same mechanical fasteners as are used for metal. Another system, however, attaches to any commercially available robot arm and is based on a unique fixed mandrel system. An integrated computer graphics simulation package allows complex winding processes to be tried and proved at the workstation and downloaded when proved. Speed and repeatability offers production quantities. The material payout is a direct function of the speed and position of the winder (not the mandrel), giving precise tension, so that it is actually possible to tie structural components together into integrated assemblies. A collapsible mandrel for FW is used to make a 9.8 m long x 1880 mm diameter glass-reinforced graphite/epoxy rocket motor case. A unique collapsing design curls in on itself to allow easy part removal without use of rams or winches that may damage the product. Mandrels are constructed over a series of rolled tings, each ring individually finished by a special grinding machine producing close tolerances. After grinding, the mandrel is skinned with sheet metal and painted.

390 Reinforced Plastics Handbook Filament Winding Terms ABL bottle The ABL (Allegeny Ballistic Laboratory) is an internal pressure vessel used to determine the quality and properties of the filament winding material in a vessel. Angle Winding angle is the angular measured in degrees between the direction parallel to the filaments and an established reference. It is usually the centerline through the polar bosses, that is, the axis of rotation. Axial Filament parallel or at a small angle to the rotational axis (0 helix angle). Balanced Winding pattern so designed that the stresses in all fibers/filaments are equal. Biaxial Winding in which the helical band is laid in sequence, side by side, with cross-over of the fibers eliminated.

Bladder/liner An elastomeric (barrier) lining for the containment of hydroproof and hydroburst pressurization medium during curing. When a protective inside liner is required, the properly bonded bladder remains in the FW structure. Bleedout The excess liquid plastic that migrates to the surface of a winding. Butt wrap Tape wrapped around the mandrel in an edge-to-edge condition. Cake forming The collection (package) of glass fiber strands on a mandrel during the forming or winding operation. Circuit One complete traverse of the fiber feed mechanism of a filament winding machine. Circumferential Filaments are essentially perpendicular to the axis of rotation. Closure In filament winding, it is the complete coverage of a mandrel with fiber. When the last tape circuit that completes the mandrel coverage is laid down adjacent to the first without gaps or overlaps, the winding pattern is said to have closed. Directional property See Chapter 7 Directional Properties Displacement angle The advancement distance of the winding reinforcement on the equator after one complete circuit. D o f f The act of removing a full package such as a roving ball from a winding machine.

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9Fabricating Processes 3 9 1

Doily Planar RP applied to a local area between windings to provide extra strength where a cutout such as a port opening is to be included. D o m e The spherical or elliptical shell ends of a FW container. D o u b l e r A local area with extra reinforcement, wound generally with the part, or wound separately and fastened to the part. D r y w i n d i n g A term used to describe FW using impregnated roving as differentiated from wet winding. Dwell In filament winding, the time that the transverse mechanism is stationary while the mandrel continues to rotate to the appropriate point for the traverse to begin a new pass. E q u a t o r junction Also called the tangent line or point. It is the line in a tank that describes the junction of the cylindrical portion with the end of the dome. Filament w i n d i n g radius Radius of a cylindrical surface of a mandrel that meets the inside surface of the bend during bending. With free or semi-guided bends to 180 ~ in which a shim or block is used, the radius of bend is one-half the thickness of the shim or block. Filament w i n d i n g tape Unidirectional prepreg tapes are used for laying or around a mold in filament winding. Filament w i n d i n g tape laying Tape is laid side by side or overlapped to form a structure. Filament winding, tension The amount of tension on the reinforcement as it makes contact with the mandrel; target is to have the required tension uniformly applied to all reinforcements. Filament w i n d i n g test A parallel filament wound tensile hoop test specimen of a specific diameter such as 15 cm (developed by Bob Bennett at Naval Ordnance Laboratory during the 1950s) provides a simple means to conduct mechanical tests. Filament winding, wet w i n d i n g A term used to describe the process of winding unimpregnated roving directed toward a mandrel where the reinforcements are impregnated with plastic just prior to contacting the mandrel. Gap 1 It is the space between successive windings in which they are usually intended to lay flat next to each other. 2 It is the separations between fibers within a filament winding band. 3 Distance between adjacent plies in lay-up of unidirectional tape materials.

392 Reinforced Plastics Handbook

Geodesic isotensoid It has a constant stress level in any given surface at all points in its path. Filament wound plastic structures are extensively used. Geodesic-isotensoid c o n t o u r Dome contour on a pressure vessel in which the filaments are placed on geodesic paths so that they exhibit uniform tensions throughout their lengths under pressure loading; this design produces a pressure container with the combination of providing the highest pressure loading for the lightest weight. The term geodesic is the shortest distance between two points on a surface; major principal use is in designing load-bearing structures that includes the use of RPs. Geodesic-ovaloid Contour for end domes where the fibers form a geodesic line; the shortest distance between two points on a surface of revolution. The forces exerted by the filaments are proportional to meet hoop and mechanical stresses at any point. Helical p a t h Filament band advances along a helical path, but not necessarily at a constant angle except when winding a cylinder.

Knuckle area Also called Y-joint. It is the area of transition between sections of different geometry such as where the skirt joins the cylinder of a pressure vessel. Lap The amount of overlap between successive windings usually intended to minimize gapping. Lattice p a t t e r n It is a pattern with a fixed arrangement of open voids.

Longs Low-angle or longitudinal windings. L o o p strength tenacity The tenacity or loop strength value obtained by pulling two loops against each other that can cause the fibrous (particularly glass) material to be cut a n d / o r crushed. Mandrel In filament winding, the form that is usually cylindrical onto which preimpregnated reinforcements are wound. Muticircuit Requires more than one wrapping circuit before the band repeats by laying adjacent to the first band. N e t t i n g analysis The analysis assumes that all stresses induced in the RP structure are carried entirely by the filaments and the strength of the plastic is neglected. Also assumes that the filaments possess no bending or shearing stiffness and carry only the axial tensile loads. P a t t e r n Different patterns are used to meet different performance requirements. Names of patterns include hoop or circumferential, helix narrow or wide ribbon, helix low angle, zero or longitudinal, polar wrap, simple or true spherical, and ovaloid.

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9Fabricating Processes 3 9 3

Planar The winding path lies on a plane that intersects the winding surface. Planar helix FW domes where the filament path lies on a plane that intersects the dome while a helical path over the cylindrical section is connected to the dome paths. Polar Winding in which the filament path passes tangent to the polar opening at one end of the chamber and tangent to the opposite side of the polar opening at the other end. It is a one-circuit pattern that is inherent in the system. Pole piece Basically a winding in which the filaments do not lie in an even pattern. The supporting part of the mandrel is usually on one side of the axes of rotation.

Prepreg and bag molding Used to obtain special high performance RP products requiring special fiber patterns a n d / o r high fiber volume content such as 65%. These prepregs can be cut to the required shape and fitted in a mold. R a n d o m pattern Winding with no fixed pattern. If a large number of circuits are required for the pattern to repeat, a random pattern approached can be used.

Reverse helical pattern As the fiber delivery arm traverses one circuit, a continuous helix is laid down, reversing direction at the polar ends, in contrast to biaxial, compact, or sequential winding. The fibers cross each other at definite equators, the number depending on the helix angle. The minimum region of crossover is three. Roving The term roving is used to designate a collection of bundles of continuous filaments/fibers, usually glass fibers, either untwisted strands or twisted yarns. Rovings can be lightly twisted; their degree of twisting and format depends on their use. As an example for filament winding they are generally wound as bands or tapes with little twist as possible. Roving ball The supply package offered to the filament winder (and others) consisting of a number of ends or strands wound onto a length of cardboard tube to a given outside diameter. Usually designated by either fiber weight or length in yards. Spool is sometimes used to identify the roving ball, however, the preferred term is roving ball. Roving ball d o f f To remove a finished package (roving ball, twister tube, forming cake, etc.) from a spindle. Roving band A collection of strands or ends which act together as a band or ribbon.

3 9 4 Reinforced Plastics Handbook

Roving catenary A measure of difference in length of the strands in a specified length of roving caused by unequal tension. The tendency with some strands in a taut, horizontal roving to sag more than others which in turn can effect the properties of the fabricated part. Roving cloth A coarse textile fabric woven from rovings. Roving, collimated Made using a process permitting parallel winding so that the strands are more parallel than in standard roving. Roving cord It is the central member of an assembly. Includes all types threads, twine, and rope produced by twisting fibers together. Roving end A strand of roving consisting of a given number of filaments gathered together. Roving end count An exact number of ends supplied on a ball or roving. Roving fiber tension even Process whereby each end of roving is kept in the same degree of tension as the other ends making up a ball of roving. Roving fuzz A measure of broken filaments in a strand or roving. Roving integrity Degree of bond between strands in a roving. Roving knuckle The point at the end of a way-wound roving ball where the roving reverses its axial direction. Roving open top package A term used to describe a roving package in a carton which has no top. Roving ribbonization A phenomenon occurring in a finished roving on which the individual strands have been "blocked" or bonded together to give a ribbon of strands; describes the degree of bonding together of the strands of roving which make up the roving band. Roving, spun A heavy low-cost glass, aramid, etc. fiber strand consisting of filaments that are continuous but doubled back on themselves. Roving strand count The number of warp fiber/yarn (ends) and filling fiber/yarn (picks) per inch. Cross section or thickness of fiber, yarn or roving expressed as denier or decitex. Roving, textile A form of fibrous glass having less twist than is present in a yarn. As a fibrous glass reinforcement, it means strands of continuous fibers wound into a cylindrical spool. Usually 60 strands, or ends are used. For staple fibers, roving is used to designate one or more slivers with a very small amount of twist and thus indicates an intermediate stage between liver and yarn.

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Roving tow The precursor of staple fibers is tow, which consists of large numbers of roughly parallel, continuous filaments. They are converted by cutting or breaking into staple fibers or directly into a slivers, intermediate stages between staple fibers and yarns. In the latter case, the filaments remain parallel. Roving twist, balanced An arrangement of twists in a combination of two or more strands that do not kink or twist when the yarn produced is held in the form of an open loop. For example, single S twist fiber plied with a Z fiber results in "balancing" the fibers. The amount of twist with plying provides many different combinations useful in different applications. Filament yarns can exist in an almost twistless form, but this is not the case for staple fiber yarns. Single-circuit pattern Filament path makes a complete traverse of the chamber/mandrel, after which the following traverse lies immediately adjacent to the previous one. Slip angle pattern Angle at which a tensioned fiber will slide off the filament wound dome. If the difference between the wind angle and the geodesic angle is less than the slip angle, the fiber will not slide off the dome. Slip angles for different fiber-plastic systems vary and must be determined experimentally. Winding pattern The total number of individual circuits required for a winding path to begin repeating by laying down immediately adjacent to the initial circuit.

Calendering The calendering process is used in the production of plastic products. It converts plastic into a melt and then passes the paste like mass through roll nips of a series of heated and rotating speed-controlled rolls into webs of specific thickness and width. The web may be polished or embossed, either rigid or flexible. At the low cost side these lines can start a $ million (USA). A line, probably the largest in the world processing PVC sheet, built by Kleinewefers Kunststoffanlagen GmbH, Munich, Germany, cost $33 million (1999). It is a 5-roll using L-type configuration. They have 3500 mm roll-face widths and 770 mm diameters with an output rate at 4000 kg/h. Calendering in the manufacture and surface finishing of plastic products, such as URP sheets and films, plastic impregnated nonwovens, and woven fabrics sheets and films, requires roll systems to meet stringent control of their nip pressure requirements. In this respect, products of

396 Reinforced Plastics Handbook

uniform quality and thickness, with defined properties, call for an adjustable nip a n d / o r controllability of the nip pressure. Control across the full roll width is achieved by various methods such as: suitable compensation of the deflection of a pair of rolls, mechanical-geometrical compensation such as roll bending, axis crossing and crowning of the rolls, and hydraulic compensation systems. Bowl deflection can occur. It is the distortion suffered by calender rolls resulting from the pressure of the plastic running between them. If not corrected the deflection produces a sheet or film thicker in the middle than the edges. The calender was developed over a century ago to produce natural rubber products. With the developments of TPs, these multimilliondollar extremely heavy calender lines started using TPs and more recently process principally much more TP materials. The calender consists essentially of a system of large diameter heated precision rolls whose function is to convert high viscosity plastic melt into film, sheet, or coating substrates. The equipment can be arranged in a number of ways with different combinations available to provide different specific advantages to meet different product requirements. Automatic thickness profile process control is used via computer, microprocessor control. The calendering configuration of rolls may consist of two to at least seven rolls. The number of rolls and their arrangement characterizes them. Examples of the layout of the rolls are the true "L", conventional inverted "L", reverse fed inverted "L", "I", "Z", and so on. The most popular are the four-roll inverted "L" and "Z" rolls. The "Z" calenders have the advantage of lower heat loss in the sheet or film because of the melts shorter travel and the machines simpler construction. They are simpler to construct because they need less compensation for roll bending. This compensation occurs because there are no more than two rolls in any vertical direction as opposed to three rolls in a four roll inverted "L" calender and so on. The nip is the radial distance or "V" formed between rolls on a line of centers. In-going safety devices in the nip areas are built into these machines. They protect the hands of operators. An emergency stop device is placed in an accessible location on the upstream side. If a problem develops, the machines immediately stop. Variations in these multimillion-dollar calender lines are dictated by the very high forces exerted on the rolls to squeeze the plastic melt into thin film or sheet web constructions. High forces at least up to 6000 psi (41 MPa) could (if rolls were not properly designed and installed) bend or deflect the rolls, producing gauge variations such as a web thicker in

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the middle than at the edges. During calendering, particularly film, rollseparating forces in the final nip may be as high as 6000 psi. This potential problem is counteracted by different methods that include the following: crowned rolls, which have a greater diameter in the middle than the edged crossing the rolls slightly (rather than having them truly parallel), thus increasing the nip opening at both ends of the roll; and roll bending, where a bending moment is applied to the end of each roll by having a second beating on each roll neck, which is then loaded by a hydraulic cylinder. Controls are used to perform any roll bending and crossing of the rolls.

Powder Metallurgy There are plastics that are essentially nonfusible and difficult to fabricate by conventional shaping processes. Parts molded from these plastics are fabricated by techniques ranging from powder metallurgy methods to modifications of conventional injection, transfer, compression, and extrusion that include ram instead of screw plastication. An example is polyimide (PI) plastic. Since PIs are essentially nonfusible and difficult to fabricate by conventional shaping processes. As an example DuPont with its Kapton TM has employed special processes, including a high temperature-pressure procedure similar to that used in powder metallurgy, to fabricate its PI into finished parts (called VespelTM). This process is useful for producing parts for low friction, high temperature applications. Powder metallurgy involves the atomization of liquid metals that is compacted in a mold by the sintering process to produce a solid part. Sintering identifies the forming in a mold of parts from fusible metal or plastic powders. The process involves holding the pressed powder (such as PTFE, UHMWPE, and nylon) at a temperature just below its melting point for a prescribed period based on the plastic used. Powdered particles are fused (sintered) together, but the mass as a whole does not melt. This solid-state diffusion results in the absence of a separate bonding phase. After being withdrawn, it is heated to a higher temperature to completely fuse the sintered material. This process is accompanied by increased properties such as strength, ductility, and density.

398 Reinforced Plastics Handbook There is the isotactic molding system, also called isotactic pressing or hot isotactic pressing (HIP). It is the compressing or pressing of powder material (plastic, etc.) under a gas or liquid so the pressure is transmitted equally in all directions. Examples include autoclave, sintering, injection-compression molding, elastomeric mold using hydrostatic pressure, and underwater, sintering.

Processing Fundamentals While the processes differ, there are elements common to many of them. In the majority of cases, TP are melted by heat so they can flow. Pressure is often involved in forcing the molten plastic in a mold cavity or through a die and cooling must be provided to allow the molten plastic to harden. With TSs, heat and pressure also are most often used, only in this case, higher heat (rather than cooling) serves to cure or solidify the TS plastic, usually under pressure.

Melt Flow Analysis Measuring melt flow is important for two reasons. First, it provides a means for determining whether a plastic can be formed into a useful product such as completely fill a mold cavity, a usable extruded extrudate, provide mixing action in a screw, meet product thickness requirements, etc. Second, the flow is an indication of whether its final properties will be consistent with those required by the product. The target is to provide the necessary homogeneous melt during processing to have the melt operate completely stable and working in equilibrium. In practice, even though with the developments that has occurred in the past and continues this perfect homogeneous stable situation is never achieved and there are variables that continually affect the output. If the process is analyzed one can decide that two types of variables affect the quality and output rate. They can be identified as: 1

the variables of the machine's design and manufacture and the operating or dynamic variables, which control how the machine is run.

Software provides simulation of the desired process and comparison with reality. The purpose of flow analysis is to gain a comprehensive understanding of the melt flow filling process based on process controls. The most sophisticated computer models provide detailed information concerning the influence of filling conditions on the

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Fabricating 9 Processes 399

distribution of flow patterns as well as flow vectors, shear stresses, frozen skin, temperatures and pressures, and other variables. The less sophisticated programs that model fewer variables are also available. From these data, conclusions can be drawn regarding tolerances, as well as part quality in terms of factors such as strength and appearance. Processing and Thermal Interface

Different plastic characteristics influence processing and properties of plastic products. Important are glass transition temperature (Tg) and melt temperature (Tm) (Chapter 3). The Tg relates to temperature characteristics of plastics that influence the plastic's processability. It is the reversible change in phase of a plastic from a viscous or rubbery state to a brittle glassy state. Below Tg thermoplastic behaves like glass and is very strong and rigid. Above this temperature, it is not as strong or rigid as glass, nor is it brittle as glass. At and above Tg the plastic's volume or length increases more rapidly and rigidity and strength decrease. Most noticeable is a reduction that can occur by a factor of 1,000 in stiffness. The amorphous TPs have a more definite Tg when compared to crystalline TPs. Even with variation, it is usually reported as a single value. The Tg generally occurs over a relatively narrow temperature range. Crystalline plastics have specific melt temperatures (Tm) or melting points. Amorphous plastics do not. They have softening ranges that are small in volume when solidification of the melt occurs or when the solid softens and becomes a fluid type melt. They start softening as soon as the heat cycle starts. Regardless, a melting temperature is reported usually representing the average in the softening range (Chapter 3). The T m is dependent on the processing pressure and the time under heat, particularly during a slow temperature change for relatively thick melts during processing. In addition, if the T m is t o o low, the melt's viscosity will be high and more costly power required for processing it. If the viscosity is too high, degradation will occur. There is the correct processing window used for the different plastics.

Process Control In the past because melts have different properties and there were many ways to control processes, compared to what has happened, it was difficult to interrelate them. Detailed factual predictions of final output were rather difficult to arrive prior to prototyping, fabricating, or

400 Reinforced Plastics Handbook

having prior experience. Research and hands-on operation have been directed mainly at explaining the behavior of melts like with other materials (steel, glass, and so on). Modern equipment and process controls (PCs) continue to overcome some of this unpredictability. Processes and equipment are designed to take advantage of the novel properties of plastics rather than to overcome them. Figures 5.65 and 5.66 provide examples of process controls (PCs) used on injection molding machines (IMMs) and molds. Extensive R&D has been performed producing programmers for IMMs because they represent over 50% of all machines sold worldwide. To date other processes have available PCs that usually monitor and control just a few parameters when compared to IMM PCs. When required, PC automation improves process efficiency, product quality, and reduces fabricating cost. Regardless of the PC available or used, the molder setting up the process uses a systematic approach that should be outlined. Once the system is operating, the processor methodically makes one change at a time to set up the most efficient operation. Many devices are available for PC, such as pressure and temperature sensors, actuators, or computer programs, which can be used by the molder. These devices can be connected with the automation apparatus and integrated into a procedure. To the designer, a model is a quantitative abstraction of a physical process in which the description of the process is represented by the solution to a set of mathematical equations. The model equations represent the behavior of the real process to the extent that the equations embody an accurate description of the underlying physical and chemical phenomena of processing. The mathematical formulation enables the model to be used for a variety of purposes, including design, control, and exploration of operating strategies. The effect of changes in process variables can be inferred from the model response without excessive experimentation. Mathematical models are used for these purposes in the plastic/ chemical, petrochemical, and other industries. Computer-aided design (CAD), computer-aided manufacturing (CAM) are use in product designs and product manufacturing operations. The essential elements of any model of a physical process are threefold: the geometry, the relevant laws of physical conservation (momentum, mass, and energy), and the specific constitutive relations (see the Software section in Chapter 9). The manufacturing processes offer great flexibility for creating a wide range of RP products. Recent years have seen a growth in PCs software

NozzleMeltTemperature Mold Temperature RunnerTemperature ~ B a r

Heat Cycle Time

Fill Time

BoostPressure BoostFlow BackPressure BackPressureBuildUpTime BackPressureBuildUp Rate

Peak Plastic Pressure Average Hold Pressure

HoldPressure HoldPressureBuildupTime HoldPressureBuildup Rate ~

Average Back Pressure(

Figure 5,65

Pressure Heats

Regrind Reinforcements

Material

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MeltViscosity' Melt Compressibility

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Examples of basic process controls for injection molding machines Q

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Figure 5.66 Exampleof mold operation controls

5

Fabricating 9 Processes 4 0 3

programs to serve the needs of processors. These tools provide a contribution to the past rules of thumb with analyses based on sound theoretical principles, and combine the benefits of ease of use with the speed of the computer. This approach results in cost-effectiveness when applied to a large number of problems. This type of development is on going so improved methods are always forthcoming. In general, these analysis tools fall under the domain of computer-aided engineering (CAE). However, analysis tools in no way replace skill or education in the basics of RP materials properties, mold design, or processing. Analyses can only supplement knowledge and improve productivity and accuracy. In CAE, a design or process is proposed as the first step. The designer or engineer then constructs a model for the specific design using a prescribed method. The computer rapidly evaluates the results of both the input conditions and the model. The output conditions are listed by the computer, and the designer or engineer evaluates the consistency of the results with experience and determines modifications to meet performance requirements and in turn can provide a guide to setting up the PC. Processing Window

Regardless of the type of controls available, the processor setting up a machine uses a systematic approach based on experience or that should be outlined in the machine a n d / o r control manuals. It is a defined area or volume in a processing system's PC pattern. This window for a specific plastic part can vary significantly if changes are made in its design and the fabricating equipment used. Note that a major cause for problems with any process is not of poor product design but instead that the processes operated outside of their required operating window. Once the machine is operating, the processor methodically makes one change at a time, to determine the result for each change. It provides a range of processing conditions such as melt temperature, pressure, shear rate, etc. within which a specific plastic can be fabricated providing acceptable and optimum properties. Windows such as a molding area diagram (MAD) and molding volume diagram (MVD) can be used during injection molding. The same approach can be applied to the other processes (compression molding, resin transfer molding, filament winding, extrusion, blow molding, etc.). By plotting at least injection pressure (ram pressure) with mold temperature, a molding area diagram (MAD) will provide the best combination of pressure and mold temperature necessary to produce

4 0 4 Reinforced Plastics Handbook

quality parts (Figure 5.67). Developing this 2-D MAD approach ends up with a dramatic and easily comprehensive visual aid in analyzing these variables. Within the diagram area, all parts meet performance requirements, however rejects could occur at the edges since material and machine capability are not perfect; variability exist (Chapter 9). Other controllable parameters can be added to target for improved quality such as melt temperatures (in the plasticator, nozzle, and in the cavity), rate of injection, etc.

.e r

E E n-

T Short shot area

Mold temperature Figure 5.67 Molding area diagram processing window concept

After a 3-D molding volume diagram (MVD) is constructed, it can be analyzed to find the best process settings of three combinations evaluated during start-up such as melt temperature, mold temperature, and injection or ram pressure (Figure 5.68). This type of procedure can be used in setting up, as an example, a complicated molded IM product. As shown in Figure 5.69 IMM control settings involve melt temperature, mold cavity filling speed, shot size, melt pressure packing, etc. With proper control, high quality parts are fabricated. The term PC is often used when machine control is actually performed. As the knowledge base of the fundamentals of the fabricating process continues to grow and understand, the control approach is moving

5

Figure 5.68

9Fabricating Processes 4 0 5

Molding volume diagram processing window concept

PROCESS ANALYSIS

...... V V V ......

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Example of setting process controls for a melt going from an IM plasticator into the mold cavity

away from press control and closer to real process control where material response is monitored and then moderated or even managed.

406 Reinforced Plastics Handbook The fabricator should note that changes in process parameters, such as injection rate, could have dramatic effects on moldings, especially mechanical properties, meeting tolerances, and surface properties. Process Control and Patience As reviewed when making processing changes, have patience by allowing enough time to achieve a steady state in the complete fabricating line before collecting data. It may be important to change one processing parameter at a time. As an example with one change such as extruder screw speed, temperature zone setting, cooling roll speed, blown film internal air pressure, or another parameter, allow four time constants to achieve a steady state prior to collecting data.

Processing and Moisture Recognize that properties of designed products can vary, in fact can be destructive, with improper processing control such as melt temperature profile, pressure profile, and time in the melted stage (Figures 5.705.72). An important condition that influences properties is moisture contamination in the plastic to be processed. There arc the hygroscopic plastics (PET, etc.) that are capable of retaining absorbed and adsorbed atmospheric moisture within the plastics. The non-hygroscopic plastics (PS, etc.) absorb moisture only on the surface. In the past when troubleshooting, plastic's reduced performance was 90% of the time due to the damaging effect of moisture because it was improperly dried prior to processing. Now it could be at 50%. 100 Tensile

Strength

,

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I

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Strain, %

Figure

5 . 7 0 Example of moisture effect on glass fiber/PET RPs

Figure 5,71 Effect of moisture on tensile behavior of reinforced nylon 6 (33 wt% glass fiber) at elevated temperature

5

Fabricating 9 Processes 4 0 7

300 11 D, 250

a~ 2o0 C

0

I . i

w C Qa

15o lOO 50 0 0.0%

0,6%

1.2%

1.8%

2.4%

3.0%

Moisture, %

Figure 5.72 Impact of temperature and moisture on tensile strength reinforced nylon 6 (33 wtO/oglass fiber)

All plastics, to some degree, are influenced by the amount of moisture or water they contain before processing. With minimal amounts in many plastics, mechanical, physical, electrical, aesthetic, and other properties may be affected, or may be of no consequence. However, there are certain plastics that, when compounded with certain additives such as color, could have devastating results. Day-to-night temperature changes are an example of how moisture contamination can be a source of problems if not adequately eliminated when plastic materials are exposed to the air. Moisture contamination can have an accumulative effect. The critical moisture content that is the average material moisture content at the end of the constant-rate drying period is a function of material properties, the constant-rate of drying, and particle size. Although it is sometimes possible to select a suitable drying method simply by evaluating variables such as humidifies and temperatures when removing unbound moisture, many plastic drying processes do not involve removal of bound moisture retained in capillaries among fine particles or moisture actually dissolved in the plastic. Measuring drying-rate behavior under control conditions best identifies these mechanisms. A change in material handling method or any operating variable, such as heating rate, may affect mass transfer. Drying Operations

When drying at ambient temperature and 50% relative humidity, the vapor pressure of water outside a plastic is greater than within. Moisture migrates into the plastic, increasing its moisture content until a state of

408 Reinforced Plastics Handbook

equilibrium exists inside and outside the plastic. However, conditions are very different inside a drying hopper (etc.) with controlled environment. At a temperature of 170C (350F) and -40C (-40F) dew point, the vapor pressure of the water inside the plastic is much greater than the vapor pressure of the water in the surrounding area. Result is moisture migrates out of the plastic and into the surrounding air stream, where it is carried away to the desiccant bed of the dryer or some other device. Target is to keep moisture content at a designated low level, particularly for hygroscopic plastics where moisture is collected internal. They have to be carefully dried prior to processing. Usually the moisture content is >0.02 wt%. In practice, a drying heat 30C below the softening heat has proved successful in preventing caking of the plastic in a dryer. Drying time varies in the range of 2 to 6 h, depending on moisture content. As a rule of thumb, the drying air should have a dew point o f - 3 4 C (-30F) and the capability of being heated up to 121C (250F). It takes about 1 ft 3 min -1 of plastic processed when using a desiccant dryer. The non-hygroscopic plastics collect Drying this surface moisture can be warm air over the material. Moisture warm air resulting in dry air. The processing can be destructive.

moisture only on the surface. accomplished by simply passing leaves the plastic in favor of the amount of water is limited or

Determine from the material supplier a n d / o r experience the plastic's moisture content limit. Also important is to determine which procedure will be used in determining water content. They include equipment such as weighing, drying, a n d / o r re-weighing. These procedures have definite limitations based on the plastic to be dried. Fast automatic analyzers, suitable for use with a wide variety of plastic systems, are available that provide quick and accurate data for obtaining the in-plant moisture control of plastics.

Machines Not Alike Just like people, not all machines may be created equal. Recognize that identical machine models, including auxiliary equipment, built and delivered with consecutive serial numbers to the same site can perform so differently as to make some completely unacceptable by the customer, assuming they were installed properly.

5

Fabricating 9 Processes 4 0 9

Plasticator Melting Operation The RP processing methods that process well over 50wt% of all plastics is injection molding. This process as well as a few others uses a plasticator to melt plastics. It is a very important component in a melting process with its usual barrel and screw (or screws). If factors such as the proper screw design a n d / o r barrel heat profile are not used correctly fabricated products may not meet or maximize their performance and very important not provide for low cost parts. Plasticators have a wide operating range to meet different performance requirements of all the different plastic compounds processed. Its rotating drive system can be via a hydraulic a n d / o r electrical motor. Electrical motors tend to increase melt processing efficiency that in turn increases production rate. It has a wide operating range to meet different performance requirements of all the different plastics processed. Important is to obtain maximum throughput with as close to a perfect melt quality. It is an endless target due to the limits a n d / o r variabilities that exist of the plastics, machines, and controls. Since the start of using screw plasticators and with time passing definite improvements have been occurring in the melt quality. This action continues because advancements tend to be endless in applying advanced screw designs and the changing melting characteristics of plastic compounds. Screw

Figure 5.73 provides an introduction to the performance of a plasticator where the screw usually has a 17.6 degree flight helical angle. There are the following three main parts (zones) of a screw:

Figure ,5.73 Nomenclature of an injection screw (courtesy of Spirex Corp.)

410 Reinforced Plastics Handbook

1

Feed Zone: This is the part of the screw that picks up the plastic compound at the feed opening (throat) plus an additional portion downstream. Many screws, particularly for extruders, have an initial constant lead and depth section, all of which is considered the feed section. This section can be welded onto the barrel or a separate part bolted onto the upstream end of the barrel. The feed section is usually jacked for fluid heating a n d / o r cooling.

2

Transition~Melting Zone: It is .-the section, also called the compression zone, of a screw between the feed zone and metering zone in which the flight depth decreases in the direction of discharge. In this zone the plastics starts in both solid and molten state with target to have all molten upon leaving this zone.

3

Metering Zone: This section is a relatively shallow portion of the screw at the discharge e n d with a constant depth and lead usually having the melt moves 3 or 4 runs of the flight length.

Many different screw designs are available to meet the desired performance for the different plastics and RP being processed. The features common to all screw plasticators are screw(s) with matching barrel(s) that have at least one hopper/feeder (usually two hopper/feeder for RPs) in-take entrance for plastics/reinforcements, and one discharge port/exiting of the melt. The essential factor in their "pumping" process is the interaction between the rotating flights of the screw and the stationary barrel wall. If the plastic compound is to be mixed and conveyed at all, its friction must be low at the screw surface but high at the barrel wall. If this basic criterion is not met the material may rotate with the screw without moving at all in the axial direction and out through the mold/die. The clearance between the screw and barrel is usually extremely small. The difference in the diameters of the screw and barrel bore (diametrical clearance) are more commonly one-half the diametrical clearance that is referred to as the radial clearance. In the output zone, both screw and barrel surfaces are usually covered with the melt, and external forces between the melt and the screwchannel walls has no influence except when processing extremely high viscosity materials such as rigid PVC (polyvinyl chloride) and U H M W P E (ultra high molecular weight polyethylene). The flow of the melt in the output section is affected by the coefficient of internal friction (viscosity) particularly when the mold/die offers a high resistance to the flow of the melt. The constantly turning screw augers the plastic compound through the heated barrel where it is heated to a proper temperature profile and blended into a homogeneous melt. The rotation causes forward transport. It is the major contributor to heating the plastic compound

5

9Fabricating Processes 4 1 1

via the plastic's shearing action once the initial barrel heat startup occurs. The primary purpose for using a screw is to take advantage of its mixing action. Theoretically speaking, the motion of the screw should keep any difference in melt temperature to a minimum. It should also permit materials and colors to be blended better with the result that a more uniform melt is delivered to the mold/die. The designs of the screw is important for obtaining the desired mixing and melt properties as well as output rate and temperature tolerance on melt. Generally, most machines use a single, constant-pitch, meteringtype screw for handling the majority of plastic compounds. A straight compression-type screw or metering screws with special tips (heads) is used to process heat-sensitive TPs or most TPs. The helix angle affects the conveying and the amount of mixing in the channel. Experience has shown that a helix that advances one turn per nominal screw diameter gives excellent results. This corresponds to an angle of 17.8 degree that has been universally adopted. The land width is usually 10% of the diameter. The radial flight clearance is the clearance between the screw flight and the barrel. It is specified considering the following effects: 9 Amount of leakage flow over the flights 9 Temperature rise in the clearance. The heat is generated in shearing the plastic. The amount of heat generated is related to the screw speed, the design of screw and the material 9 The scraping ability of the flights in cleaning the barrel 9 The eccentricity of the screw and the barrel 9 Manufacturing costs. The length of the screw is the axial length of the righted section. An important criterion of a screw design is the ratio of the length over the diameter of the barrel ( L / D ) . As reviewed, a screw has three sections: feed, melting (transition), and metering. The feed section that is at the back end of the screw can occupy from zero to 75% of the screw length. Its length essentially depends upon how much heat has to be added to the plastic compound in order to melt it. The pellet or powder are generally fed by gravity into this section and are conveyed some distance down the barrel, during which time they become soft. Both conduction and mechanical friction accomplish heating. The melting (transition) section is the area where the softened plastic compound is transformed into a continuous melt. It can occupy

412 Reinforced Plastics Handbook

anywhere from 5% to 50% of the screw length. This compression zone has to be sufficiently long to make sure that the entire plastic compound is melted. The straight compression-type screw is one having no feed or metering sections. In the metering section, the plastic compound is smeared and sheared to give a melt having a relatively uniform composition and temperature for delivery to the mold/die. As high shear action will tend to increase the melt's temperature, the length of the metering zone is dependent upon the plastics heat sensitivity and the amount of mixing required. For heat-sensitive materials, practically no metering zone can be tolerated. For other plastics, it averages out at about 20 to 25% of the total screw length. Both the feed and the metering sections have a constant cross section. However, the depth of the flight for the feed zone is greater than that in the metering zone. The screw compression ratio or C / R relates to the compression that occurs on the plastic compound in the transition (or compression) section; it is the ratio of the volume at the start of the feed section divided by the volume in the metering section (determined by dividing the screw feed depth by the screw metering depth). The C / R should be high enough to compress the low bulk unmelted plastic compound into a solid melt without air pockets. A low ratio will tend to entrap air pockets. High percentages of regrinds, powders, and other low bulk materials are usually processed by a high C / R . A high C / R can over pump the metering section. A common misconception about C / R is that engineering and heat sensitive plastics should use a low C / R . This is true only if it is decreased by deepening the metering section, and not having a more shallow feed section. The problem of overheating is more related to channel depths and shear rates than to C / R . As an example, a high C / R in polyolcfins can cause melt blocks in the transition section, leading to rapid wear of the screw a n d / o r barrel. For TSs the C / R is usually one so that accidental over heating does not occur and cause the plastic compound to solidify in the barrel. Their barrels are usually heated using a liquid medium so that very accurate control of the melt occurs with no overriding the maximum melt heat. With overheating TS melt solidifies. If it solidifies, the C / R of one also permits ease of removal by just "unscrewing" it from the screw. C / R ratio of one's is also used for TPs when the rheology so requires. Fixed screw speed, pitch, diameter, and depth of the channels relate to output. A deep-channel screw is much more sensitive to pressure changes than a shallow channel. In the lower pressure range, a deep

5

Fabricating 9 Processes 4 1 3

channel will mean more output; however, the reverse is true at high pressures. Shallower channels tend to give better mixing and flow patterns. The flow pattern in the screw flights changes with the backpressure. The flow of a particle in the flights with open discharge and in the blocked flow there is a similar circulatory motion between the flights, and no forward motion because the open end is closed. There is the greatest mixing when the flow is blocked. The importance of this flow concept is that it shows that the more blocked the flow, the better the mixing in the screw. The higher the pressure the greater the pressure flow and the lower the output. In injection molding, this pressure corresponds to the backpressure setting of the machine. This is the reason that color dispersion is improved and homogeneity increased by raising the backpressure. Often warpage and shrinkage problems can be overcome in this manner. In our high technological world, the art of screw design is still dominated by experienced trial and error approaches providing the exact capabilities of the screws for a particular plastic compound operating under specific conditions. Screw design technology is considered to be empirical a n d / o r secretive, however scientific approaches to screw designs based on an analytical melting model can be used. Available are computer models that play a very important role that are based on proper data input and, very important, experience of the person with a set up similar to the one being studied. When new materials are developed or improvements in old materials are required, one must go to the laboratory to obtain rheological and thermal properties before computer-modeling mixing can be performed effectively. Production rate of an acceptable melt from a screw is its most important function. It is often limited by its melting capacity. The melting capacity of the screw depends on the plastic compound properties, the processing conditions, and the particular geometry of the screw. Once the melting capacity is predicted, the screw can be designed to match the melting capacity. Mixing

The action of mixing plastic compound can be distributive a n d / o r dispersive. They are not physically separated. In dispersive mixing, there will always be distributive mixing. However, the reverse is not always true. In distributive mixing, there can be dispersive mixing only if there is a component exhibiting a yield stress and if the stresses acting on this component exceed the yield stress.

414 Reinforced Plastics Handbook

In order for a dispersive mixing device to be efficient, the mixing section should have a region where the plastic compound is subjected to high stresses. It also has a high stress region that should be deigned so that exposure to high stresses occurs only for a short time, and all fluid elements should experience the same high stress level to accomplish uniform mixing. In addition, they should follow the general rules for mixing of minimum pressure drop in the mixing section, streamline flow, complete barrel surface wiping action, and easy to manufacturing the mixing section. As reviewed concerning screw types, these dynamic mixers are used to improve screw performance. Static mixers are sometimes also inserted at the end of the plasticator. Proof of their success is shown by their extensive use worldwide. Each type of mixer offers its own advantages and limitations. Where practical they should not be located in a region where the melt viscosity is not too low. With some of these installations because they may have to operate at a lower speed to avoid problems such as surging, independently driven mixers can be used so machines can operate at optimum speed. Other benefits of independently driven mixers involving feeding capability and performance occur. For example, metering pumps can inject with precision liquid additives directly into the mixer. Screw Wear

When injection molding, extruding, blow molding, etc. short or long glass fiber reinforced compounds there will be steel wearing of the plasticator screw/barrel, particularly the screw, usually within six months operating 24 hours per day. Steel wear also occurs in the molds runner and gate systems and cavities. Wear is associated with reducing the performance of molded products a n d / o r increasing cost to mold. Special screw designs and materials of construction have been used to process glass fiber RTPs and RTSs most efficiently. Wear Resistant Barrel

As it is easier to replace a screw than a barrel, the barrel is made harder than the screw. Barrel and screw assembly operates in an aggressive environment that can cause gradually or severe wear problems. To improve the wear resistance of the barrel, it may be modified, or lined. Modification may be by nitriding or ion implantation but these treatments are not as good as lining. Lining is done with a wear resistant alloy. This wear resistant layer may be cast in during barrel manufacture or the liner may be inserted subsequently or for rebuilding a worn

5 Fabricating 9 Processes 415 barrel. These bimetallic barrels are usually used when abrasive compounds are being processed. The increasing use of plastics with abrasive fillers and reinforcements created a demand for an even more abrasion resistant barrel than the standard i r o n / b o r o n type. The use of glass fiber reinforced compounds for injection molding has been the single most important factor since a fabricator would be lucky if they could reach 6 months of continuous operation. This need has been successfully answered by the development of liner materials containing metallic carbides such as tungsten carbide and titanium carbide extending their life. Barrel Heating and Cooling Method Heat to soften the plastic compound is supplied in two ways: by external barrel heating and internal frictional forces brought about on the plastic compound due to the action of the metal screw in the metal barrel. The amount of such frictional heat supplied in the plasticator is appreciable. In many extrusion operations, it represents most of the total heat supplied to the plastic. To provide temperature control, the barrel is divided into zones. Each of these zones is fitted with its own external heating/cooling system. The smallest machine will have three zones and larger machines may have twelve. A temperature sensor and associated equipment, usually a microprocessor-based controller for each of the zones developing a temperature profile to provide the best melt. Target for these controllers is to measure the melt temperatures that are important rather than the cylinder temperatures. There are three principal methods of barrel heating: electrical, fluid, and steam. Electrical heating can cover a much larger temperature range. It is clean, relatively inexpensive, and efficient. The heaters are generally placed around and along the barrel, grouped in zones. Each zone is usually controlled independently, so the desired temperature profile can be maintained along the barrel. Electrical heating is generally preferred because it is the most convenient, responds rapidly, easiest to adjust, easy to clean, requires a minimum of maintenance, covers a much larger temperature range, and is generally the least expensive in terms of initial investments. Fluid heating, such as the use of heated oil, allows an even temperature over the entire heat-transfer area, avoiding local overheating. If the same heat-transfer fluid is used for cooling, an even reduction in temperature can be achieved. The maximum operating temperature of most fluids is relatively low for processing TPs, generally below 250C

4 1 6 Reinforced Plastics Handbook

(482F). With its even temperature, the required fluid heating is desirable with TS plastics so that no accidental overheating occurs to chemically react and solidify in the barrel. Steam heating was used in the past, particularly when processing natural rubber. Now it is rarely used. Steam is a good heat-transfer fluid because of its high specific heat capacity, but it is difficult to obtain steam to the temperatures required for TP processing of 200C (392F) or greater. The cooling of barrels is an important aspect. The target is to minimize any cooling and, where practical, to eliminate it. In a sense, cooling is a waste of money. Any amount of cooling reduces the energy efficiency of the process, because cooling directly translates into lost energy; it contributes to machine's power requirement. If a machine requires a substantial amount of cooling, when compared to other machines, it is usually a strong indication of overheating the plastic, improper process control, improper screw design, excessive L / D , a n d / o r incorrect choice of plasticator. Cooling is usually required with forced-air blowers mounted underneath the barrel. The external surface of the heaters or the spacers between the heaters is often made with cooling ribs to increase the heat-transfer area. The design using fibbed surfaces will have a larger cooling area than flat surface, result is significantly increases cooling efficiency. Forced air is not required with small diameter extruders because their barrel surface area is rather large compared to the channel/rib volume, providing a relatively large amount of radiant heat losses. Fluid cooling is used when substantial or intensive cooling is required. Mr-cooling is rather gentle because its heat-transfer rates are rather small compared to water-cooling. However, it does have the advantage in that, when the air-cooling is turned on, the change in temperature occurs gradually. Water cooling produces rapid and steep change; a requirement in certain operations for processing certain RPs. This faster action requires much more accurate control and is more difficult to handle without proper control equipment. The larger barrels are often liquid cooled, using cored channels to circulate the cooling medium because they require intense cooling action (feed-throats also use water-cooling). However if not properly controlled, problems could develop. If the water temperature exceeds its boiling point, evaporation can occur resulting in poor cooling control. The water system is an effective way to extract heat, but can cause a sudden increase in cooling rate resulting in a nonlinear control problem; resulting in more difficulty to regulate temperature. Nevertheless, the

5

Fabricating 9 Processes 4 1 7

water cooling approach is used very successfully with adequate installation and adequate control and startup procedures. IMMs for processing TS resins and rubbers (that are TSs) control the barrel temperature most of the time indirectly with an external heat exchanger. It is operated by a liquid heat-transfer medium such as oil or brine. Curing of the plastic or rubber compound occurs in the mold cavity(s) by the application of higher heat than what exists in their barrel melt. A chemical crosslinking action occurs with the additional heat resulting in the solidification of the TS materials. Depending on the IMM operation capability as well as type plastic compound being processed, the melt passing from the plasticator through the nozzle may also require heat control. This action is usually required when processing certain heat sensitive plastics a n d / o r if a long nozzle is used. Purging

Purging is an important t o o l to permit color changes, remove contaminants such as black specks, and plastic compound adhering to screws and barrels. At the end of a production run, the plasticator may have to be cleared of all its plastics in the barrel/screw to eliminate barrel/screw corrosion. This action consumes substantial nonproductive amounts of plastics, labor, and machine time. It is sometimes necessary to run hundreds of pounds of plastic compound to clean out the last traces of a dark color before changing to a lighter one; if a choice exists, process the light color first. Sometimes there is no choice but to pull the screw for a thorough cleaning. Purging material include the use of certain plastics to chemical purging compounds. Popular is the use of ground/cracked cast acrylic and PEbased (typically bottle grade HDPE) plastics. Others are used for certain plastics and machines. Cast acrylic, which does not melt completely, is suitable for virtually any plastic. PE-based compounds containing abrasive and release agents have been used to purge the softer plastics such as other polyolefins, polystyrenes, and certain PVCs. These types of purging agents' function by mechanically pushing and scouring residue out of the plasticator (Table 5.14). The chemical purging compounds are generally used when major processing problems develop. However to eliminate the major problems with their associated machinery downtimes, regularly scheduled purgings prevent problems and can yield operational benefits. With the proper use of these purging agents' helps to reduce reject rates significantly. The schedule depends on factors such as plastic compound

41 8 Reinforced Plastics Handbook

Table 5.14 Examplesof purging agents when changing plastic compound in a plasticator Material to be purged

Recommendedpurging agent

Cast acrylic, polystyrene Polystyrene, low-melt-index HDPE,cast acrylic Next material to be run Polystyrene, low-melt-index HDPE,cast acrylic Cast acrylic or polycarbonate regrind; follow with polycarbonate regrind; do not purge with ABS or nylon Polystyrene; avoid any contact with PVC Acetal Polystyrene, low-melt-index, HDPE,cast acrylic Engineering resins Cast acrylic, followed by polyethylene Fluoropolymers Cast acrylic, followed by polyethylene Polyphenylene sulfide Reground polycarbonate, extrusion-grade PP Polysulfone Reground polycarbonate, extrusion-grade PP Polysulfone/ABS General-purpose polystyrene, cast acrylic PPO Material of similar composition without catalyst Thermoset polyester Filled and reinforced materials Cast acrylic Immediate purging with natural, non-flame-retardant Flame-retardant compounds resin, mixed with 1% sodium stearate HDPE Polyolefins Cast acrylic Polystyrene Polystyrene, general-purpose, ABS, cast acrylic PVC

ABS Nylon PBT polyester PET polyester Polycarbonate

being processed, size and plasticator operational settings with its time schedule that it is in use. Repeated equipment shutdowns and startups are the most common cause of degraded plastic build-up. Purging compound producers can recommend the time schedule to be used in order to minimize down time and increase profits.

Tools Overview Tools include molds, dies, mandrel, jigs, fixtures, punch dies, etc. for fabricating and shaping parts. These terms are virtually synonymous in the sense that they have female or negative cavity through which a molten plastic compound moves usually under heat and pressure or they are used in other operations such cutting dies or stamping plastic sheet dies, etc. Tool is the term that identifies all these devices particularly used to identify molds (Table 5.15). Molds represent an

Table 5,15 Guide for tools used in different processes I Tool to be made I I

I Processes I I

I Injection I

Hi vol

I I Steel (machine hobbed ) electro form Et back-up

I

I

I Extrusi~ I IB'ow molding I

I

I

lo vol

Hi vol

Cast al I Mach.AI I Kirksite I Filled epoxy

Steel

]

I Hi vol

I AI

I BeCu

Lo Ivol

I AI

I Plaster

I I Electroform Epoxy-

Et back-up fiberglass

I

I

I

I

IT,hermoforming I

I Comp. e{ trans I

Hi ~ol

I Steel

(mach hobbed)

I

I

Lo vol

I AI I Electroform

I

Hi

Lo

I AI

I Wood I Plaster

I IRotoform I

I

Hi vol

I Cast al

I Electroform

I

ICaslingl

I

Electroformed

I Sheet

Spraylmetal

Lo vol

I

metal

Dipped metal

I I Plastic I

~t back-up Filled

lepoxy

Silicone

Filled epoxy

IRml Steel Cast aI Mehanite Filled epoxy

Elastomer

I En~p I

Foam process {not struct)

Rein/f plastics

Plaster

Plastic

Dip metal

AI

Plastic (tp or ts)

I

I I Plastic I Electroform I Sprayed metal AI

I

I I Wood I Steel I Electroform I Sprayed metal I Elastomer

"1"1 o-

I

Elastomer ul

o

420 Reinforced Plastics Handbook

important part in fabricating the different RP products using the different fabricating processes. Molds arc used in many RP processes with many of the molds having common assembly and operating parts with the target to have tool's cavity designed to form desired final shapes and sizes. A mold can be an unsophisticated low cost to highly sophisticated expensive piece of machinery. It can comprise of a single to many parts requiring high quality metals and precision machining. To capitalize on its advantages, the mold may incorporate many cavities, adding further to its complexity. Many molds, particularly for injection molding and compression molding, have been preengineered as standardized products that can be used to include cavities, different runner systems, cooling lines, unscrewing mechanisms, etc. A die is a device, usually of steel, having an orifice (opening) with a specific shape or design geometry that it imparts to an RP melt such as the extrudate pushed from a pultruder or extrudate pumped form an extruder. The function of the die is to control the shape of the extrudate. The important word is control. In order to do this, the extruder must deliver melted plastic to the die targeted to be an ideal mix at a constant rate, temperature, and pressure. Measurement of these variables is desired and usually careful performed. A mold, particularly for injection molding and compression molding, or die, particularly for pultrusion and extrusion, is a controllable complex mechanical device that must also be an efficient heat exchanger. If not properly designed, handled, and maintained, it will not be an efficient operating device. Hot melt, under pressure, moves rapidly through them. In order to solidify the hot melt, water or some other media circulates in the mold or die to remove heat from RTPs or heat is used with RTSs. All kinds of actions can be used to operate the mold such as sliders and unscrewing mechanisms or die with melt pressure and directional channels. CAD and CAE programs are available that can aid in mold and die design and in setting up the complete fabricating process. These programs include melt flow to part solidification and the meeting of performance requirements. There are variable conditions during processing that influence part performance. Of paramount importance in injection molds is gate location(s) and controlling the cavity(s) fill rate or pattern. The proper fill helps eliminate part warpage, shrinkage, and other problems. In the practical world of mold design, there arc many instances where tradeoffs must be made in order to achieve a successful overall design. As an example, while naturally balanced runner system are certainly desirable,

5

9Fabricating Processes 4 2 1

they may lead to problems in mold cooling or increased cost due to excessive runner-to-part weights. Available are software flow analysis guides allowing successful designs of runners to balance for pressure, temperature, rate of flow, etc. Design of a die includes: 1

minimize head and tooling interior volumes to limit stagnation areas and residence time;

2

streamline flow through the die, with low approach angles in tapered transition sections; and

3

polish and plate interior surfaces for minimum drag and optimum surface finish on the extrudate.

Basically, the die provides the means to "spread" the plastic being processed/plasticated under pressure to the desired width and thickness in a controllable, uniform manner. In turn, this extrudate is delivered from the die (targeted with uniform velocity and uniform density lengthwise and crosswise) to takeoff equipment in order to produce a shaped product (rods, sheet, pipe, profile, etc.). Depending on material, molding process, and the anticipated number of parts-off, molds and tools for RPs can be made of (in ascending order of production numbers) RPs themselves, alloys, aluminum, or chromed steel (Tables 5.16-5.18). The general characteristics and use of each are as follows: 1

Steel molds made from machined steel are especially suitable for mass-produced parts. Their high cost is written off over long production runs giving a piece-part which can be very economical, both in injection molding of RTPs and RTSs and high-pressure compression molding of RTSs. Commonly used is P20 steel, a high grade of forged tool steel relatively free of defects and is a prehardened steel. It can be textured or polished to almost any desired finish and is a tough mold material. H - 1 3 is usually the next most popular mold steel used. Stainless steel, such as 420 SS, is the best choice for optimum polishing and corrosion resistance. The mold can be equipped with moving parts and elaborate automated ejection systems, which can make the relatively large capital investment more attractive by further reducing the molding cycle and producing parts that require little or no finishing. Steel molds may also be required to counter the abrasive effect of glass fiber.

2

Aluminum offers lighter weight, better heat conductivity than steel and lower machining costs and is a mold-making material for low-

Table 5,16 Exampleof tool materials arranged in order of hardness Suitable for

Material Class

Suitable for

m

Thermoplastics glass-filled

Prototype injection molds TP resins

High-pressure thermosets Phenolics Ureas Diallylls Melamines Alkyds

Low-pressure thermosets SMC BMC

Structural f foams

Casting

Ill m,

Carbides Steel, nitriding Steel, carburizing Steel, water-hardening Steel, oil-hardening Steel, air-hardening Nickel, cobalt alloy Steel, prehardened 44 Rc Beryllium, copper Steel, prehardened 28 Rc Aluminum bronze Steel, low alloy ~t carbon Kirksite (zinc alloy) Aluminum, alloy Brass Sprayed metal Epoxy, metal-filled Silicone, rubber

Ill

"1" :3

O" 0 0 ~--

Thermoplastics unfilled Blow molds

Vacuumforming sheets TP resins

Table 5,17

Performances of plastic molds vs. type of molding

Molding

Materials

-

-

Compression molding

Hot press

Cold press - - ~

-

-

Stamping

Filament winding

Injection molding

RLM

I

Flexural modulus x 103kg/mm 3

Impact strength

Heat resistance (HDT18.6)~

Paintability by baking [74o- 75ooc)

Weight ratio 1 [Equiflextural modulus)

Moldability

Cost2 (Mold cost) 3 O (O)

Polyester + GF (SMC)

1

o~A

>200

@

0.65

O~A

Polyester + GF (BMC)

1.1

1`

1'

@

0.6

f

Polyester + GF (High-strength SMC)

1.6~4.2

@

1`

Polyester + GF (Resin injection)

0.8

O

150~200

A~x

0.62

A

PP + GF or sawdust. paper pulp (AZDEL, etc.)

0.6

@

160

-

0.5

@

A~O (O)

Nylon + GFEF (ST)(, etc.)

0.8

@

215

O

?

@

A (O)

Epoxy + CF (CFRP)

15

O

>200

-

0.2

A

PP + GF, talc (EPDM) AS + GF

0.6~0.4

1`

120~105

-

0.5

O

PBT or nylon + GF

1.2~1.4

1`

205~215

@~O

0.5

?

Foamed styrene or ABS (+ GF)

2.4~2.5

O~A

80 (100)

@

-

0.4~0.5

t O (O) @ (@)

Polyester + GF (Hand lay-up)

Urethane + GF (RRIM)

0.1~0.2

0.4,,,0.6 A~x

Note: I. Ratio based on sheet metal weight as I" 2. Relativecomparison for 400-500 kg; 3. Mold cost for sheet metal. Symbols: @ Excellent; O Good; A Fair; x No good

O~A

A,,,x (O) @ (-) A (O) O (O) A (@~O)

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4 2 4 Reinforced Plastics Handbook

Table 5.18 Examplesof machining Machining method

Purpose of machining operation

Cutting with a single-point tool with a multiple-point tool

Turning, planing, shaping Milling, drilling, reaming, threading, engraving

Cutting off with a saw by the aid of abrasives shearing by the aid of heat Finishing by the aid of abrasives

Hack sawing, band sawing, circular sawing Bonding abrasives: abrasive cutting off, diamond cutting off Loose abrasives: blasting: ultrasonic cutting off Shearing, nibbling Friction cutting off, electrical heated wire cutting off Bonded abrasives: grinding, abrasive belt grinding Loose abrasives: barreling, blasting, buffing

Types of parts

Kinds of machining methods used

Bearing, roller Button Cam Dial and scale Gear Liner and brake lining Pipe and rod Plate (ceiling, panel) Tape (mainly for PTFE)

Turning, milling, drilling, shaping Turning, drilling Turning, copy turning Engraving, sand blasting Turning, milling, gear shaving, broaching Cutting off, shaping, planing, milling Cutting off, turning, threading Cutting off, drilling, tapping Peeling

Purpose of machining operation

Typesof machining used

Compression, transfer, injection and blow molding

Degating deflashing, polishing

Extrusion Laminating

Cut lengths of extrudate Cut sheets to size, deflashing edges Polish cut edges, trim parts to size

Cutting off, buffing, tumbling, filing, sanding Cutting off Cutting off

Processing method

Vacuum forming

Cutting off, sanding, filing

5

Fabricating 9 Processes 4 2 5

pressure work. It may not be suitable for long runs or some RP systems. Zinc alloy (kirksite) high-quality molds can be made from cast zinc alloys, offering good non-porous surfaces but are relatively heavy, with lower heat conductivity than aluminum, requiring closely spaced cooling channels. Nickel shells are particularly good for high-quality surface reproduction, with good hardness and good release properties. For structural rigidity, shells will normally require backing with a steel or aluminum frame, or a suitable casting material. Cooling lines can be attached or plated on the rear of the shell before backing. Epoxy/reinforced can be used for molds for open (contact), and low-pressure cold-press molding. Epoxy molds have poor temperature control and tend to be fragile. Compounding with a metal filling improves heat conductivity but, in general, epoxy molds should only be used for short runs or for prototype parts, when quality is not the key criterion, but cost and flexibility are paramount. Contact Molds

Molds for hand lay-up (as well as others such as spray-up, contact molding, thermoforming, and casting) are usually made of TS polyester or epoxy shell set in a cradle made of a material such as steel angle. They can usually be made in-house, on a model of the product that could be made from an inexpensive material that can be shaped or sculpted, such as plaster, balsa wood, or expanded polystyrene, sealed and coated with a release agent. Low-cost molds for contact and low-pressure molding can be made from reinforced TS polyester or epoxy compounds with glass fiber a n d / or mineral filler reinforcement. These constructions have also been used to make prototype molds for compression and injection molding, with the advantages that they can be produced quicldy and at low cost (often in-house) and can readily be modified. Latest technology uses blocks of resin-based compounds that can be machined by computerized instructions, for production of prototype molds. Epoxy prepreg tapes, with carbon, glass, or aramid reinforcement, have been used for production of tooling. They require an initial cure at 20-80C (68-176F) and offer a maximum service temperature of at least 200C (392F) in air. A low-temperature cure means very low residual stress levels. Low-temperature master models can be used directly without

426 Reinforced Plastics Handbook

intermediate molding stages, giving improved accuracy in tooling and high quality/long-life tools. High-quality cast aluminum tooling as an alternative to all-RP tooling is also used, without the high cost of electroforming. A ceramic matrix material offers improvements in mold-building, eliminating print-through, enabling a mold to be built without steel reinforcement and reducing weight by up to 75%. A patented mold closure system, using plates built on the mold on which wedges slide to close the halves, knocked into place and knocked out by hammer, as needed, is also available. For contact molding, only one mold-half is needed, which can be either male or female, depending on which face is required to be smooth (Figure 5.74). Almost any material of sufficient rigidity can be used such as those reviewed for making the mold with the most common method being glass fiber-reinforced TS polyester.

Figure 5.74 Construction of plaster pattern mold for contact molding A good mold made of RP will produce hundreds of moldings, with a minimum amount of maintenance. It consists of a shell, reinforced as necessary, often mounted on a light timber or metal flame. Once a suitable master pattern has been prepared, it is possible to produce many RP molds from it, easily and at low cost, using the contact molding process (but in reverse). Patterns can be made from timber or metal, or using plaster on a timber framework. They must be accurately

5

9Fabricating Processes 4 2 7

finished and well polished, to give a smooth mold surface. Plaster and other porous materials must be sealed with a solution of shellac or cellulose acetate, before waxing and polishing. Gel coats should be about 0.6 mm thick; thicker than is usual for a finished molding, but allowing for any rubbing down which may be necessary during the lifetime of the mold. If it is intended to use the mold many times, over a long period, it is a good precaution to make it of a heat-resistant resin, to give a harder tougher surface, with better overall stability. Molds can be reinforced with external ribbing, using cores on an open metal profile, plastic piping, or foamed plastics (Figure 5.75). These should be added when the laminate itself is sufficiently cured, to avoid the danger that contraction of the resin around the ribs may distort the laminate itself, and so leave an impression on the mold surface.

Figure 5 . 7 5 Design and lamination of ribs to reinforce a contact mold

With larger contact molds, it may also be necessary to design to split the mold, to facilitate demolding of the part (Figure 5.76). This calls for inclusion of flanges, which are reinforced with continuous roving on the sharp corners, where areas of unreinforced resin are particularly prone to damage. When the resin is fully cured, the flanges should be trimmed to about 75 mm (approximately 3 in). To avoid damage and ensure long life, the flanges should be about 50% thicker than the mold shell itself and metal plates should be incorp-

428 Reinforced Plastics Handbook

Figure 5.76

Construction of the flange for split molds

orated along their length to spread the load of the mold-clamping bolts which should be placed at intervals of about 150 mm (6.25 in). An automated pattern construction for the marine industry pioneered by Mollicam, Florida, USA, uses five-axis computer controlled milling machines to generate exact complex shapes for all sizes of glass fiber RPs tooling. The equipment can machine up to 9.75 x 3 x 1.8 m (32 x 10 x 6 feet) as a single unit, with easy combination of multiple units for larger sizes. Recent projects have exceeded 18.3 m (60 feet) in length. Advantages claimed include: time saving: a typical 6 m (20 ft) hull can be CNC machined in less than 40 hours and, with full five-axis machining, hand finishing is minimal 9 accuracy: tolerances ofless than 0.4 mm ( 1 / 6 4 in) can be achieved relative to the computer model 9 symmetry: tool paths are developed for one side of the hull and a mirror image is computer generated. New and unique methods have also been developed to produce a superior plug, machined with an outer seamless shell of high-density plastic foam, which is strong but light for easy handling, and evenly absorbs heat generated in the mold-making process. High-temperature processing of high performance resins, at up to 475C (800F) temperature and up to 2.76 MPa (400 psi) pressure is provided by CareMold, a system developed by Composites Horizons Inc., USA. It uses proprietary expendable mandrel material and permits

5. Fabricating Processes 429 casting at room temperature or high temperature breakaway tooling for complex stiffeners and shapes.

Autoclave Molds Molds for autoclaving must be more substantial and can carry more detail. Depending on molding requirements and conditions, they can be produced by electroforming nickel. To cure large parts size restrictions and availability of autoclaves and ovens can occur. Additional heat is obtained by incorporating electrical heating elements in the molds.

Cold Press Molds (low pressure) Soft tools will usually comprise a shell of reinforced epoxy tooling compound, backed or reinforced (depending on size) with concrete or other dimensionally stable material. They take about 6-8 weeks to make and have a life of about 2000 components. Costs, amortized over this number, usually amount to around 2% of product value. As an alternative, electroformed nickel tools can be used, costing about three to five times more, but giving a lifetime output of about ten times (20,000 components).

Resin Transfer Molds Mold design has proved to be a key factor in successful development of resin transfer molding (RTM). The guidelines given for mold design are in general valid, but advice should also be sought from suppliers. For RTM, the accuracy of cavity thickness dimensions is critical. Good mold seals are essential. A fight 45 ~ pinch-off is inadequate, and usually it is better to use a double seal configuration, to allow an optional vacuum-assist system during injection. Automatic mold clamping systems with built-in manipulators and low-cost pneumatic presses have all assisted RTM development. A mold-making system is used for the RTM process using TS polyesterbased materials. Molds have already been used for three years and are reported to show good surface despite 5000-6000 demoldings, while involving minimum capital outlay and giving a shortened lead-time. Electroformed nickel shell tooling can be useful for high quality/ medium volume (such as RTM). FET Engineering, Kentucky, USA, has a die spot press allowing both halves of the tool to be placed outside the press with both cavities in the up position, allowing work on the tool while registration of both halves is maintained. Helisys rapid prototype machine and SNK digitizer have been installed. Vapor

430 Reinforced Plastics Handbook

deposition development allows production of uniform nickel tools much faster than currently allowed by electroform technology. RP tooling has been developed over the past ten years, less costly than nickel shell tooling, allowing RTM to be used for smaller production runs but, with rapid turn-round and high temperatures, conventional gel coats and resin systems can quickly fail. The Durabuild range (from Hawkeye, USA) was initially based on air-cure TS polyester putties, primers, and high-gloss coatings used for repair and resurfacing, including high-gloss, heat distortion temperature up to 150C (302F), low porosity, and good impact resistant surface. If the mold is structurally stable, resurfacing will last as long as the original. Molds have been known to give good production for several years. Wolfangel GmbH, Germany, has a process that can make a mold in three days (compared with usual two weeks). First, laminating layers are laid on the tooling gel applied to the normal pattern, using virtually zero-shrinkage TS polyester, three or four layers of hand-lay TS polyester/glass fiber. The gel/laminate is then allowed to cure (one day). On the second day, a heavy deposit of chopped glass/polyester is sprayed on the back of the laminate and consolidated using a special resin allowing build-up to 15 mm (0.6 in) without exotherm problems. Finally, a lightweight plastic concrete is spray-applied, building the tool and adding additional rigidity, up to 50 mm (2 in) thick non-sagging. The TS polyester-based mix is based on a Reichhold tooling resin, mixed with equal parts of alumina trihydrate, with low exotherm chemistry, allowing a high build in a single shot. It also incorporates a core material such as end-grain balsa, to simplify the shape of the back of the mold and further increase stiffness without a weight penalty. A further spray/chop layer is then consolidated to the final back of the tool and once the mold is cured, the steel supporting frame can be attached to fittings laminated into the tool. Wolfangel developed this system for its own RTM production. The largest part so far reported is a 100 m 2 mold made up as follows: 9 mold gel coat 9 styrene-resistant buffer 3 mm 9 tooling resin spray/chop laminate 5 mm 9 balsa wood core 10 mm 9 resin spray/chop laminate 5 mm 9 balsa wood core 10 mm 9 resin spray/chop laminate 7 mm.

5

Fabricatincj 9 Processes 431

Because of the reduced pressure, molds for low-pressure molding can be either larger or made with less expensive materials. USA molder Modern Tooling, with back up from Alpha Owens Corning, has adapted metal-working technology from the aerospace industry to reduce machining costs in mold-making, eliminating many of the steps in the process. A large mold can be made in half the usual time. Filament Winding Molds

The mandrel (mold) on which filament-wound products are produced is essentially fight, but solid, in construction and (usually) near cylindrical. The most common product is pipe, when the mandrel can be made simply of aluminum sheet on a lightweight framework. RP can also be used. An important aspect of the mandrel is that it must be possible to extract it easily from the wound lay up, after curing. This may mean use of a tapered or collapsible mandrel (Figure 5.77), or even a sacrificial mandrel (made possibly of plaster) which is broken up inside the cured product.

Figure 5,77 Basic configuration of a mandrel for filament winding, and the principle of a collapsing mandrel

Cylindrical mandrels are available from specialist suppliers, to order, across a complete range of sizes from typically 610 mm (2 ft) diameter

4~

a~ e,t ill e.,i. r IJI

:I: e-t 0 0

Figure 5.78

Examples of injection molding mold layouts, configurations, and actions

5 Fabricating 9 Processes 433

to 3600 mm (12 ft), constructed over a series of roller tings, each individually ground to produce a perfect surface. After grinding, the mandrel is skinned with sheet metal and then painted. It is also possible to obtain mandrels constructed with special infrared curing elements along the surface, to encourage efficient heat-penetration of the laminate and economical use of power. Injection and Compression Molds

Mechanically, the tools for molding TSs and TPs have some similarity. Historically, TSs have been compression molded, using vertical presses, while TPs have been injection molded, predominantly using a horizontal press configuration (Figure 5.78) with molds viewed alone in a vertical position (Figures 5.79 and 5.80). Since at least the 1950s, the injection molding process has been molding TSs. A vertical press lay out is sometimes used for molding TPs, especially where metal inserts are involved (as in electrical/electronics work). In both cases, the molding tool comprises two matching halves (male and female), with guide pins to ensure exact mating and ejector pins to ease removal of the molded part (Tables 5.19 and 5.20).

Figure 5.79 Sequenceof mold operations Whereas in compression molding, the charge of material is loaded into the open mold, an injection-molding tool incorporates an enclosed system for feeding the material into the tool and distributing it evenly. This is usually done through a gate, which is positioned to give the best balance of feed to all parts of the mold cavity. For larger or more

4 3 4 Reinforced Plastics Handbook 1. Back plate 2. Backplate 5.4, SupportC~176176 3.

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8. Ejectorback plate 9. Locatingring 10.. Locating ring 11 Locating guide pillar 12. Stripper rod 13. Ejector coupling rod 14. Heated Locatingnozzle guide bush "15. 16. Stripper rod guide bush 17: Ejector bush 18. Thermal insulating plate 19. fElectrical O r nozzelhservice e a connector t e d box 21.20"Centering dowel 22. Cap screw 23. Cap screw 24. Cap screw 25. Cap screw 26. Cap screw 27. Cap screw 28. Cap screw 29. Cap screw 30. Cap screw 31. Cap screw 32. Cap screw 33. Ejector coupling rod connector 34. Ball catch 35. Ejector pin 36. Ejector stop button 37. Support pillar 38. Spring washer 39. Spring washer 40. O-ring seal 41. Water channel service coupling 42. Water channel sealing plug 43. Cooling water spiral core 44. O-ring seal 45. O-ring seal 46. Pressure sensor 47. Core insert block 48. Cavity insert block 49. Stripper bar 50. Side action 51. Cam

Description of mold shown in previous figure

complex molds, there may be a number of gates, which are linked together in the mold by runners. Figure 5.81 is a schematic of a compression mold. Figure 5.82 shows positive, flash, and scmipositive molds. They provide different methods of processing RPs to meet different part performance requirements. Air is entrapped and/or gases are formed during processing requiting vents at the parting lines; an example is shown in Figure 5.83. The essential difference between tools for TSs and TPs is that, whereas the TS compound must be made to cure/solidify in the mold (and so the mold is heated), the TP compound is already molten and must be "frozen" (and so the mold is cooled).

5

Table 5ol 9 __......

.

9Fabricating Processes 4 3 5

Mold quotation guide prepared by the Society of the Plastics Industry

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THE MOt,DMAKERS OIVtSlON

THE SOCIETY O F THE PLASTICS INDUSTRY, INC.

3150 9 Des P|lines Avwnutl (Rivet Rolidl, O~ls Pillnel. lU. 80018. Tlittahoml: 3t2t297,6150

TO .

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FROM

QUOTE NO. DATE DELIVERY REQ

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. . . . Gentlemen: Please submit your quotation for a mold as per following specifications and drawings: COMPANY NAME Name 1. BIP No. Rev. No, No, C av. of 2. . . . . BtP No. Ray. No .............. No, Cav, Partts 3. _ _ .., BIP No. . . . . Rev. No . . . . No, Cav. No. of Cavities: Design Charges: Prk~: I~llvery:

Type of Mold: O Injection Mold Construction O Standard D 3 PlBte 0 Stripper [3 Hot Runner 0 Insulated Runner [3 Other (Specify)

O Compression O Transfer O Other (specify) Material Special Features _ O Leader Pins & Bushings in K,O. Bar Cavities Cores 0 Spring Loaded K.O. Bar [3 Tool Steel D 0 Inserts Molded in Place O Beryl. Copper D (3 Spring Loaded Plate O Steel Stnktngs O 0 Knockout Bar on Statlona~ Side O Olher (Specify) _ [] Accelerated' K.O, O Positive K.O. Return Pleas Mold.Bead Steel 0 Hyd, Operated K.O. Bar Clamp Tons 0 gl D Parting Line Locks Make/Model 0#2 0 Double Ejection 0r O Other :(Specify) . . . . . . . . Finish Hardness Cooling Cavities Cores CavitlN " Cores Cavities: Core [3 SPF.JSPI O 0 Hardened O O Inserts O O MiLch.Finish O 0 Pre.Hard O Retainer Plates O O Chrome Plate O O Other (Specify) _ _ O Other Plates O O Texture O O Bubblers O ElatiOn O Other (Specify) , .. O Other(Specify) _ Cavities ....... Coles Side Action O K.O. Pins 0 Cavities . . . . Cores E] Blade ~ 0 , 0 Angle Pin C O Edge 0 Steers 0 ~] Hydraulic Cyl. t::) O Center Spree 0 Stdpper 0 Air Cyl. O O SutPGete 0 Air 0 O Positive Lock O O Pin Point [3 .Special Lifts 0 O Cam O 0 Unscrewing (Auto) 0 O Other(Specify)_ D K.O. Activated Spring Ld, O 0 Removable Inserts (Hand) 0 O Other (Specify) [] 0 Other (specify) Design.by:.. 0 Moldmaker 0 Customer Type of Design: 0 DelaI!ed Design. [3 Layout Only O Mounted by Moldmaker Ltmlt Switches: O Supplied by Engraving: 0 Yes 0 NO ApproxlmMe Mold $1m= He|loll b i l l I ~ 0 Moldmaker O Customer DupllclllinO O u l i |)~ OMoldmaker [:)Customer Mold Function Try.Out .By:. O Moldmaker O Customer Tooling Mochdts or Muter/s.By: O Moldmaker O Customer Trj-Out.Matedal Supplied.By: O Moldmaker L'] Customer Terms subject to Purchase Agfeemerd. This quotation holds for 30 days. Special Instructions:

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T-he PriCes quoted me on the buiS'O! Piece part print, models or designs submitted or suPPiled..~10uld there-be shy change In the final design, prices are subject to change. By .

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Table 5 , 2 0 Time guide to manufacture a mold" number of columns represent weeks

i ~,3,,,~,~,,,8 i ' 'I ' lIl I Design

Elapsed time varies I

Design product Decide on quantity

Approve preliminary

I Select molding machine

Order steel

Screen candidate vendors

I Issue quote request Review quotes Review mold concepts Finalize product drawing Place order Release drawing place order

Stage 3: Development

91011 i~ 13 I, i, i~ i, 1819 ~0 ~I ~ ~3 ~ , ~

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Preliminary mold design

i Decide number of cavities Set mold specifications

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Stage I Quotation

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Reviewand approve

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Figure 5.82 Example of mold types (a) positive compression mold, (b) flash compression mold, and (c) semipositive compression mold W ,,,,a

438 Reinforced Plastics Handbook

Figure 5,83

Example of vent locations in a compression mold processing reinforced thermoset plastics

An RP system for mold-making for compression, resin transfer molding (RTM), resin injection molding (RIM), thermoforming, and contact molding has been developed by Lenox Polymers, USA, using highperformance polymers with metals and fibers, producing a material which can withstand temperatures of over 300C (570F). It is claimed to reduce automobile tooting costs by at least 50%. A major supplier is reported to have funded a $100,000 program to manufacture automobile door interior panels in plastics, first parts from which have been delivered. A few considerations are listed to help understand what is needed in designing molds for injection molding. Even though there are many factors to be considered that include its operation, designing the mold is not complex. What is needed is a thorough understanding of the requirements of the literature.

mold backing plate A plate used to support cavity blocks, guide pins, bushings, and similar mold parts. mold, balanced A mold is laid out/designed with runner(s) and cavity(s) spaced and sized for uniform melt flow, fill, and packing pressure throughout the system. mold base Assembly of, usually steel, plates that holds or retains the cavity(s). mold bottom plate Part of the mold contains the heel radius and push ups (ejection mechanism). It is used to join the lower section of the mold to the platen. mold cam bar The stationary angled bar or rod used to mechanically operate the slides on a mold for side action core pulls. mold cavity Also called die or tool. The space between matched molds that encloses the molded part. It is the depression in the mold that

5

9Fabricating Processes 4 3 9

forms the outer surface of the molded part. There can be single or multiple cavities in one mold.

mold cavity chase Enclosure of any shape, used to shrink-fit parts of a mold cavity in place, to prevent spreading or distortion in hobbing. In addition, to enclose an assembly of two or more parts of a split cavity block.

mold cavity, compression The male cavity is designed as a plug that fits into the female cavity so that the mold action during closing provides a hydraulic pressure loading. The tight fitting male plug literally acts as a hydraulic ram.

mold cavity debossed Depressed or indented lettering or designs in the cavity producing bossed impressions on the molded part.

mold cavity draft Also called draft in the direction of the mold. On most molded parts, there are features that must be cut into the surface of the mold perpendicular to the molding parting line. To properly release the part from the tool, parts usually include a taper. The amount of mold draft required will depend on factors such as type plastic being processed, processing conditions, surface finish, etc. As an example, a highly polished surface will require less than an unpolished mold. Any surface texture will increase the draft at least 1 ~ per side for every 0.001in. (0.003 cm) depth of texture. Special mold cavity surface action can be used. With elastomeric material, it is possible with its rubber condition, that ejection does not require the required draft.

mold cavity, duplicate plate Removable plate that retains cavities; used where two-plate operation is necessary for loading inserts.

mold cavity etched To treat the surface with an acid, leaving relief to form the desired design texture on the molded part.

mold cavity ejector Different mechanical means are used to eject or remove the molded part from the cavity.

mold cavity, female The indented half of a mold designed to receive the male half.

mold cavitygrit blasting Steel grit or sand are blown onto the wall cavity to produce a rough surface. This surface treatment may be required to permit air in leaving the mold during molding a n d / o r provide a desired surface finish on the part.

mold cavity hobbing Forming single or multiple mold cavities by forcing a hob into relatively soft steel blank. Hobbing is a technique where a master model in hardened steel is used to sink the shape of the cavity into a heated mild steel such as beryllium copper. The hob is

4 4 0 Reinforced Plastics Handbook

larger than the finished plastic molded part because after hobbing, the metal shrinks during cooling.

mold cavity honing Using a fine grained whetstone or equivalent to obtain precise accuracy to the surface finish.

mold cavity, male Also called plunger. The extended half of a mold designed to match the female half.

mold cavity register Angle faces on the mold that match when the mold halves are closed, to ensure their correct alignment.

mold cavity retainer plate They hold the inserted cavities in a mold. These plates are at the mold parting line and usually contain the guide pins and bushings that line up the two halves of the mold.

mold cavity, split Cavity made in sections. mold cavity, split-ring A mold in which a split cavity block is assembled in a chase to permit the forming of undercuts in a molded part. The part along with the molded part(s) is ejected from the mold and then separated.

mold cavity surface The surface of the mold cavity that faces and reproduces its surface condition on a molded part. A significant advantage of the molding processes is the fact that surface polish and textures arc molded into the part. No secondary surface-finishing operations are required unless special finishes are required such as plating, hot stamping, etc. High gloss finishes, dull, matte, textured, etc. (as well as their combinations) surfaces on parts are feasible.

mold cavity unit Cavity insert(s) designed for quick interchangeability with other cavity insert(s).

mold cavity venting Basically shallow channel(s) or minute hole(s) in the cavity a n d / o r in the mold parting line to allow air and other gases that may form during processing escape.

mold chase An enclosure of any shape used to: (1) shrink fit of a mold cavity in place, (2) prevent spreading or distortion in hobbing, or (3) enclose an assembly of two or more parts of a split block.

mold design Keep the design as simple as possible (Figure 5.84). molding cold slug The first plastic melt to enter an injection molding machine cold runner mold; so called because in passing through the spruc orifice it is cooled below the effective molding temperature. Usually a well in the runner system is used to unload this cold slug.

molding cold slug well The space or cut-out in the runner system (such as opposite the sprue travel of the melt in the mold) to trap the cold slug so that it does enter the cavity.

5

9Fabricating Processes 4 4 1

OPENING PARTING LINE

SIDE VIEW OF PART

..........

~

PARTING LINE

PARTING LINE

LINE

Figure 5.84

Examples of simplifying mold construction to produce openings without side action movements.

molding, dished A term used to describe a depression in a molded surface.

molding, double-shot A method for producing 2-color or 2-different plastics in a part using an I M M with two plasticators. The part molded first becomes an insert for the second shot. Other processes can be used such as injection blow molding and compression molding.

molding dwell Time between when the injection screw ram action is fully forward holding pressure on the plastic in the cavity and the time the ram action retracts.

molding, film insert FIM starts with a cut film that is decorated a n d / o r labeling, thermoformed to shape, and then insert in the mold.

molding flash line A raised line evident on the surface of a molding and formed at the junction of the mold faces such as at the parting line after the removal of the excess flash. It is usually removed by highspeed buffing or grinding.

molding pressure Pressure maintained on the melt after the cavity is filled until the gate freeze-off allowing the complete transformation to a solid state.

442 Reinforced Plastics Handbook

molding pressure pad A metallic reinforcing device designed to absorb pressure on the land areas of the mold when the mold is closed.

molding pressure required It is the unit pressure applied to the molding material in the mold cavity such as during injection molding. Mold material of construction is to support this pressure without the mold cavity moved. The area is calculated from the projected area taken at fight angles under pressure during complete closing of the mold, including areas of runners that solidify. The unit pressure is calculated by dividing the total force applied by this projected area. It is expressed in psi (Pa). To determine pressure required for a specific material the melt pressure used is based on experience a n d / o r from the material supplier. The pressure is multiplied by the projected area. Result is the total clamping pressure required. To ensure proper pressure is applied, consider using a safety factor (SF) of having available another 10% more pressure. With experience, this SF can be reduced or even eliminated.

molding, rotary Also called rotary press. Refers to a type of injection molding, blow molding, compression molding, etc. utilizing a plurality of mold cavities mounted on a rotating platen or table. This process is not to be confused with rotational molding.

molding shrinkage It is the difference in dimensions between a plastic molding and the mold cavity in which it was molded, both being at room temperature when measured, expressed in./in. (cm/cm). Shrinkage usually occurs in the mold while it is solidifying or curing; however, certain plastics may take up to 24 hours before it has completed its shrinkage. In designing a product and its mold, it is extremely important to make allowance for shrinkage.

mold knife edge Describes a projection from the mold surface that has a narrow included angle. They are undesirable because they are susceptible to breakage under molding pressures.

mold land Describes the area of those faces of a closed mold which come into contact with one another.

mold leader pin and bushing Also called guide pins. Pins, usually four, maintain the proper alignment of the male plug and female cavity as the mold closes. One of the pins is not symmetrical placed so that the mold halves can only be aligned one way eliminating misalignment. Hardened steel pins fit closely into hardened steel bushings.

mold life For any mold, the term mold life refers to the number of acceptable parts that can be produced in a particular mold. There are molds that run a few hundreds to many millions. Design and construction that relates to cost of a mold depends on the lifetime required.

5

9Fabricating Processes 4 4 3

mold locating ring Also called register ring. It serves to align the nozzle of an injection cylinder with the entrance of the mold's sprue bushing.

mold locking ring A slotted plate which locks the parts of a mold together while the material is being injected or placed.

mold, loosepunch Male part of the mold when it functions in such a way that it remains attached to the molding when the press opens and molding removed. It is commonly used for moldings possessing threads or undercuts, when the punch cannot be removed from the molding merely by opening the press.

mold manifold It is a runner system in a mold that has its own heating a n d / o r cooling insulated section to control the melt and be ready for injection into the cavity.

mold parting line Also called cutoff or spew. A line established on a 3-D model from which a mold is to be prepared, to indicate where the mold is to be split into two halves (sections) representing where they meet on closing (Figure 5.85).

Figure 5.85

Example of molding with or without parting line on threads

4 4 4 Reinforced Plastics Handbook

mold pillar support The general construction of a mold base usually incorporates an ejection housing. If the span in the housing is long, the forces during molding can cause a sizable deflection in the plates that are supported by the ejector housing causing flashing, etc. To overcome this problem, pillar supports are included so that deflection does not occur.

mold pin Different pins are used that include dowel pin, ejector pin, leader pin, return pin, side draw pin, and sprue draw pin.

mold, preengineered Standardized mold components have been available at least since 1943. They provide for exceptional quality control on materials used, quick delivery, interchangeability, and lower cost. These available preengineered molds and mold parts provide high quality manufacturing techniques that result in consistent quality and reduced mold cost. The different manufacturers of these preengineered mold bases and components provide similar but also different products. The variations can provide unique and different approaches to meeting complex product designs. A major advantage to the molder is saving time and money should a component ever need replacement. Most often, these components serve the function of the mold and are not designed for use as plastic-forming mold members.

mold pressure pad Reinforcement of hardened steel distributed around the dead/open area in the faces of a mold to help the mold land absorb the final pressure of closing without collapsing.

mold runner A mold manifold runner system involves all the sprues, runners, and gates through which melt flows from the nozzle of an injection molding machine (the pot of a transfer molding machine, etc.) through the mold and into the mold cavity(s). There are primary, secondary, and tertiary (sometimes more) runners to provide melt flow into one or more cavities. Their diameters are based on the melt flow requirements of the plastic being processed that are easy to determine.

mold runner, balanced Exists in a multicavity mold when the runners linear distances of the melt flow from the sprue to the cavity gates is the same.

mold runner, cold (for thermoplastic) Mold in which the melt within the mold [sprue to gate(s)] solidifies by the cooling action of the mold requiring their removal and usually recycled.

mold runner, cold (for thermoset plastic) Mold in which the melt within the mold [sprue to gate(s)] is cooled in the mold maintaining its free melt flowing characteristic so that the next shot starts from the

5

9Fabricating Processes 4 4 5

gate(s) rather than the nozzle. The cavity and core plates are heated to solidify the plastic but the runner system is kept insulated from the cooler manifold section. This action eliminates TS scrap that is similar to a hot runner system for TPs.

mold runner, hot (for thermoplastic) Mold in which the melt within the mold [sprue to gate(s)] are insulated from the chilled cavity(s) and core(s). They remain hot producing no scrap and the next shot starts from the gate(s) rather than the nozzle.

mold runner, hot (for thermoset plastic) Mold in which the melt within the mold [sprue to gate(s)] are hot as in the cavity(s) and core(s); all solidify by the heating action. The solid sprue to gate(s) can be recycled at least as filler.

mold runner, insulated Mold has oversized runner passages formed in a conventional cold runner for certain TPs. The passages heated mold runner system are of sufficient diameter that, conditions of operation, an insulated surface occurs on the melt runner wall with hot melt flowing in the center runner(s). The next shot starts from the gate(s).

in the under plastic of the

mold, runnerless Identifies a TP hot runner or a TS cold runner even t h o u g h runners are used.

mold side action Mold operates at an angle to the normal open-closed action permitting the removal of a part that would not clear a cavity or core; may have a pin to core a hole that has to be withdrawn prior to opening the mold.

mold, single impression A mold with only one cavity. mold, split-ring Also called split mold. Mold in which a split-cavity block is assembled in a chase to permit forming of undercuts in a m o l d e d part. These parts are ejected from the m o l d and then separated from the part.

mold sprue Also called stalk. Feed opening in a mold that is directing melt into the mold from an I M M nozzle.

mold sprue bushing A part of the mold which provides an interface between the injection molding machine nozzle and runner system in the mold.

mold spewgroove The groove in a mold that permits the escape of excess or surplus plastics.

mold, stack Also called three-plate mold. Rather than the usual twoplate to handle a single mold, there is a third or intermediate movable plate. It makes possible center or offset gating of each cavities on two levels. Thus, it is a two level m o l d or two sets of

4 4 6 Reinforced Plastics Handbook

cavities stacked one on top of the other for molding more parts per cycle. These molds generally use a hot runner manifold located in the center plate (platen). There are also four-stack molds in use.

mold standard and practice The SPI continually updates its publication on designing plastic molded parts entitled Standards and Practices of Plastics Molders. It is useful to designers, purchasing agents, custom molders, processors, etc. Details presented include engineering and technical guidelines commonly used by molders for injection, compression, and transfer molding processes; lists tolerance specifications for plastic materials in metric and English units; and a glossary of terms. It reviews important commercial and administrative practices for purchasers to consider when specifying and purchasing molded parts. These customs of the trade include mold type, safety considerations, maintenance requirements, contract obligations, charges and costs, inspection limitations, storage, disposals, proper packing and shipping, and claims for defects. mold stripper-plate Plate that strips a molded part(s) from a cavity with or without air support. mold undercut Reverse or negative draft such as a protuberance or indentation in a mold molding a rigid plastic, necessitating inserts or a split mold for removal of the part; if a flexible mold can be used, it will provide for the rigid part ejection. Molding a flexible plastic with a slight undercut usually can be ejected intact. mold venting, water transfer This technique is based on negative pressure coolant technology. Mold coolant is being pulled; not the more conventional way of pushing under water pressure but having a negative pressure. This system permits venting into the water via the mold knockout pins, difficult locations in a cavity (such as long, thin cores) that entraps air during molding, etc. They require that the pin or cavity (through a porous metal media) run through the water line. Coolant does not leak into the cavity because it is under atmospheric pressure. In an emergency, it could eliminate water leak in a cracked mold that extends into the water line. mold water channel Channels, through which water circulates to cold the melt in the cavity, are designed to properly extract heat. mold yoke In a large single cavity mold, the entire cavity and core plates usually form the mold cavity. In a smaller and multicavity mold, core and cavity blocks (inserts) are mounted on or in the various plates of the mold base. When various components are mounted in the plates, the plates are called a yoke.

5

9Fabricating Processes 4 4 7

Mold Temperature Controls Correct control of mold temperature is fundamental to producing good quality moldings and achieving economic molding cycles. Reinforced compounds have a faster rate of cooling than unreinforced and the mold must allow for adequate cooling to take advantage of this facility. Poor cooling results in rising mold temperatures and longer cycle times, but inadequate heating can produce voids, shorts, and poor surface finish. Cooling and heating channels should also be located directly in mold inserts and cores, if the design permits it. Good temperature control over all areas of the tool is recommended and correctly placed cartridge heaters used in conjunction with thermocouples and efficient controllers give an ideal system. Mold heating can be by any of the conventional methods, but direct conduction from platens is probably the easiest and most versatile. Conventional methods of production of heat are by oil or electricity. It is standard operating procedure to heat the female tool about 10C higher than the male half, as an added precaution against tool lock-up. This also facilitates removal of the part from the tool.

Hardening~Platings In all cases, tools (especially the cavity areas that form the molded product) have to withstand high working temperatures without distortion and resist the abrasive characteristics of the molding compound (and general abuse in handling), while giving an expected life of up to several hundred thousand moldings. For strength, toughness and hard-wearing surface, tool cavities should be made from a good grade of tool steel. The exact composition depends on several factors, such as tool size, tool life expectancy, and surface finish requirements. For steel when correctly hardened (typically at 800C) and tempered at 200C, a hardness of Rockwell C52-58 would be expected. Where additional skin hardness is needed (as on sliding surfaces of the tool) it is possible to harden by flame or vacuum treatment, but any subsequent grinding (which may be carried on final assembly of the tool) will easily remove the surface and expose the softer substrate, which will be very prone to wear. It is normal toolroom practice to polish the tool cavities and, when samples have been accepted by the customer, to chromium plate all cavity and flash surfaces of the tool. Chromium plating, which normally has a thickness of 0.005 ram, is recommended because: 9 high gloss is imparted to the molded part

448 Reinforced Plastics Handbook

9 ejection and extraction of the molding is facilitated, especially when molding deep-drawn parts 9 core pins and thread formers (which are subject to considerable wear) can be replated as soon as any appreciable wear is detected. Ion implantation can also be used as an alternative to (or in addition to) chromium plating, to increase tool life. For sheet molding compound (SMC) auto body parts, surface finish is critical. A quality of 1200 SPI (international polishing standard) is demanded, with no undulations, orange peel, punctures, stains, or holes. Optical quality control is implemented using light beams. Rough and semi-finished machining is done with three-dimensional milling, finishing by spark erosion and chrome plating. Thermoregulation is critical: no temperature difference greater than 5C is acceptable on any of the molding surfaces. Steel molds are usually employed for high volume applications. RPs can be used for medium/low volume. Standard Mold Parts By rationalizing design and production requirements, it is possible to make use of the very wide range of ready-made standard mold components on the market. These include standard die sets, guide pins, bushes, ejector pins, cartridge heaters, and runner systems, so that in many cases it may be possible to build up the entire tool from standard components, with only the cavity/cavities produced to order. This simplifies and speeds up tool production, while keeping costs to a minimum; also ensures use of the best steels, etc. With multi-cavity tools, it may also be possible to advance the finishing of only one cavity, for proving the tool and production of sample moldings, before incurring the cost of the other cavities.

There has been some development work (in Japan) on using or blanking off individual cavities to adjust to varying production requirements, and combining different but balanced cavities in the same tool, for completely flexible production. Clearances TS polyester molding compounds require very close pinch-off clearances, so it is possible to develop high hydrostatic pressures (which is desirable in all moldings). The locating or guide strips should be plentiful and substantial, or the tool halves may become misaligned. The material must be under compression up to the final stop, so nip lines must be long and with very small clearance. Shear edges should be avoided and tools designed with a very thin vertical flash. Where the design cannot accommodate this type of flash, semi-horizontal pinchoff must be used.

5

9Fabricating Processes 4 4 9

Electroformed Molds Electroformed molds are produced by a process derived from standard electroplating. The metal (usually nickel) is first dissolved and then reassembled electrolytically around a model. By this means a very dense non-porous metal shell is formed, exactly conforming to the threedimensional contours of the model and, at the same time, able to reproduce fine surface detail, such as textures or engraving. After forming, the shell (which may be up to 10 mm thick) is removed from the model and engineered into a finished mold by various methods, according to the molding process in which it will be used. Electroformed molds are subject to interaction of temperature and pressure they can be used in the following cases: 9 any process where combined working temperatures and pressures do not exceed 6 bars and 100C (212F) 9 where no cavity pressure is involved, in any process involving temperatures up to 300C (570F) 9 at ambient temperature, in any process with pressure up to 60 bars. Other advantages include: 9 large size: a typical maximum is 12.2 m x 1.8 m x 3.05 m 9 significantly lower cost, compared with machined tools 9 surface qualities: satin, polished, textured, leather grained, without large additional cost; 9 non-porous hard surface: 200--400 VPN, on request 9 good thermal conductivity: 0.22 cal/cm s/C, giving rapid warm-up and fast curing. For RPs, electroformed molds are mainly useful for autoclave molding and for closed matched die molding (cold press, low-pressure hot press, resin injection, resin transfer, low-pressure phenolic molding, and resin casting) as well as for reinforced reaction injection molding (RRIM). Prototyping can also use this technique for mold-making.

Mold~Platen Insulations Since injection molding and compression molding machines operates with heated molds, efficient thermal insulation on the mold and platen can make an important contribution to reduction of operating costs, by improved energy efficiency and temperature control. A number of materials are in use that includes specially engineered glass fiberreinforced TS polyester RP, which gives a good balance of high resistance to heat, high compressive strength, and low thermal conductivity, with

4 5 0 Reinforced Plastics Handbook

low moisture absorption, resistance to oils and other fluids, durability and good machinability. With possibly a considerable investment in the cost of a mold, it is important to maintain it properly. This means (obviously) storage where it will not be exposed to extremes of temperature or humidity, or to physical damage. Wear and tear on the tool during its lifetime will normally be all-too visible in terms of moldings with poorer finish or reduced tolerances. Not so visible is the wear on components such as guide pins. At regular intervals during the lifetime of the tool, it is particularly important to check guide pins for wear and platens for parallelism, as accurate location of the male half into the female half is clearly of paramount importance.

Heat Transfer Fluids Many of the molding processes for RPs employ heat transfer fluids to control the heating of molds. When a continuous supply of fresh air comes into intimate contact with the heat transfer fluid (as when there is constant tool changeover), significant oxidation occurs. Chemically, the result is that some molecules in the fluid are converted to organic acids. In practical terms, the fluid becomes thicker, darker, and more odorous, while heat transfer capability drops dramatically. There are heat transfer fluids (such as Paratherm OR) that resist oxidation and also offer increased thermal efficiency, significantly higher flash and fire points and longer service life. Precise uniform temperature control to 316C (600F) is provided, in dosed-loop systems where the heat transfer fluids are more than occasionally exposed to air. Typical performance characteristics are: 9 optimum use range: 49-316C (150-600F) 9 maximum recommended film temperature: 338C (650F) 9 flash point (coc: ASTM D 92): 190C (370F) 9 fire point (coc: ASTM D 92): 210C (410F) 9 auto ignition (ASTM D 2155): 373C (710F).

Mold Cost/Maintenance Molds in general are very expensive with the major cost principally in machine building labor. The proper choice of materials of construction for the cavity, core, and other components is paramount to quality, performance, and longevity (number of parts to be processed) of a mold. Add good machinability of component metal parts, material that will accept the desired finish (polished, textured, etc.), ability to transfer heat rapidly and evenly, capability of sustained production without constant maintenance, etc. Using low cost material to meet high

5

Fabricating 9 Processes 451

performance requirements will compromise mold integrity. As an example, the cost of the cavity and core materials, for more than 90% of the molds, is less than 5% of the total mold cost. Thus, it does not make sense to compromise mold integrity to save a few dollars; use the best material for the application. Molds require very careful handling when in use and storage. Any protruding parts should be protected against damage in transfer. The mold surfaces, especially cavities and cores, should be covered with a protective, easy to remove, coating against surface corrosion when the mold is not operating. For special protection, vacuum containers are used after the mold is properly dried. Records should be kept to ensure required maintenance is accomplished on a regular time schedule. Mold Design for RRIM

Edge gating is recommended for molds for RIM, except with structural RP, which should be center gated to prevent the glass mat from moving (Figure 5.86). The mixture should enter the mold cavity as a laminar stream. Air entrapment, which happens with incorrect mold-filling, is the largest single cause of defective moldings. For RRIM materials, where back pressure is most likely, the most simple and cheapest type of gating is direct fill, center-gated. Flow lengths are minimized and there is uniform flow in all directions. The mixing head attaches directly to the mold wall, creating an airtight seal and minimizing leakage. A selfcleaning mixing head mounted flush in the cavity wall also minimizes waste material from the gating (Figure 5.87). Disadvantages of direct fill are the possibility of causing blemishes opposite the entry point, because the material makes a 90 ~ turn over a sharp edge (which can cause bubbles or scarring). The mixture will be free of bubbles only if the wall thickness at the entry point is less than one-eighth of the diameter of the entry area. If the mixing head cannot be flush-mounted, the sprue should be as short as possible, to allow mold release to be sprayed into the sprue cavity. Short fiber-reinforced systems are particularly vulnerable to formation of weld lines because the fibers tend to align with the direction of the flow. When flow fronts join, there is no fiber crossover or homogeneity, and the problem is intensified with faster reaction and gelling times. To minimize this, consider locating the gate closest to the largest obstruction to the flow. Computerized moldflow analysis can help predict where problems may occur. In structural molding, the glass mat should fill the entire mold cavity leaving no empty areas between mat and mold wall. The mat therefore

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Figure 5.86

Examples of RIM mold configuration (courtesy of Bayer)

5. Fabricating Processes 453

Figure 5.87

Gating and runner systems demonstrating melt flow in RIM molds (courtesy of Bayer)

should be slightly oversized and the mold should have a (renewable) steel shear edge to cut away any glass fiber overhang, a pocket to hold the excess and a mold seal external to the shear edge. Glass fiber can erode softer metal, so it is advisable to use steel to make molds for structural RIM SRIM). Typical molding pressures are 100 psi for rigid solid RIM systems and 200 psi for SRIM.

Asse m b ly/Joi n i ng/Fi n ish i ng Different methods arc used for assembling, joining, or finishing RP to RP products as well as RP to other materials. It is important to both

4 5 4 Reinforced Plastics Handbook

designer and end-user that the techniques, advantages, and limitations of these methods be understood so that intelligent choices can be made. As an example, different materials that include RP-to-RP and RP-tometal could have different thermal expansions and could cause failure of the assembly. Parts to be assembled for RTP include for high volume production solvent bonding, adhesive bonding, ultrasonic welding, hot tool welding, electromagnetic and induction bonding, and dielectric heat welding; RTP include for low volume production gas welding, adhesive bonding, ultrasonic tool welding, hot tool welding, and spin welding. RTSs include for high volume production molded-in inserts, mechanical fasteners, adhesive bonds, and electromagnetic and induction heating of adhesives; RTSs include for low volume production adhesive bonding and mechanical fastening. To complete the secondary finishing work on certain parts after they arc fabricated such as decorating, deflashing, buffing, tapping, degating, machining, etc. RP moldings can be finished with all the techniques familiar in other branches of plastics. Due to the reinforcement content and the high flow of the resin, TS moldings often require trimming after they come off the mold. Depending on the process and materials, this can be achieved simply with a sharp knife, rasp, and abrasive paper or it may call for mechanized systems (Figure 5.88). Sensible investment in tool design and manufacture, and good maintenance should (ideally) remove the need to trim compression and injection molded parts. However, this is not always the case, and flash removal systems can be employed in which the moldings are tumbled with mildly abrasive materials such as nutshells. Reground TS material may itself be used effectively in such systems for finishing/buffing moldings. After curing and removal from the mold, TS RPs continues to mature and will benefit from being kept for about two weeks at normal ambient temperature. This maturing process can be speeded up by a period of post-cure at a higher temperature. Three hours at 80C (176F) is ideal, but this may not be practicable for larger moldings, when a lower temperature over a longer time will be suitable, such as overnight at about 40-60C (104-140F). For best results, the molding should then be allowed to stabilize at room temperature for a day or two after post-curing and, to prevent warping during this period, it may be a good policy to place a large molding in a simple jig while it fully cures. When working with TS resins, it is essential that the resin be fully cured before any finishing operations are carried out.

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ii

456 Reinforced Plastics Handbook

Large and complex TP moldings should be rested on jigs for a time after they come out of the press. It is good practice to think in terms of robot aided demolding for such parts, for safety, speed, and quality. This may also permit moldings to be demolded before they have cooled (so shortening the molding cycle). Certain TPs such as nylon moldings may require annealing after molding, to achieve their full mechanical strength. Consult the resin supplier for detailed advice. Practically any TS RP molding has to be trimmed, machined (Table 5.21), and finished in some way, before it is finally put into service. Most of these operations are standard common sense and should not present difficulty to the fabricator, but some points differ from normal workshop practice. Considerable time can be saved if the RP can be trimmed while the resin is still in a green stage; when it has not yet fully hardened and is still in the mold. This can be done with a sharp trimming knife held at right angles to the RP, or with scissors, but taking great care not to disturb or distort the lay-up. It is often possible to design the edge of the mold to serve also as a trimming guide, suitably reinforcing it for this purpose. After trimming, the molding can be left in the mold to develop its full cure and, when fully cured, the trimmed edge can be finally finished with a fine file, glass-paper or wet and dry abrasive paper. TP moldings should not require trimming but, because of the fiber content in the molding compound, it may have been necessary to design the mold with a relatively large gate, so that moldings must be demolded with sprues and runners still attached. These can easily be removed with a sharp knife and should be placed in a separate bin, for granulating and feeding back into the machine hopper. The mold can be designed to remove gates during the molding cycle. Stamped glass mat thermoplastic (GMT) parts will also require trimming, which (due to volume of production) can usually be automated by robot or similar system. Saws, hand, jig-saw, or circular saws may be needed for trimming thicker moldings, both in TSs and TPs, where the trim is more than 1 mm thick. Precautions must be taken to protect workers against dust, with adequate extraction systems and wearing of masks. Robot or robot-assisted systems are being increasingly introduced into RP molding, at all levels of production, assembly and finishing. Where some processors prefer to specify such equipment separately, and adapt it themselves to their own production needs. Primary machinery

Table 5.21 Guideto machining

Phenolic laminates Molded thermosets

Feed (in./rev)

Front Clearance (o)

0.005 to

12 to 15

Speed (ft/minute)

Blade (teeth/in.)

Cutting Speed (ft/minute)

1500 to

2 to 11 (skip

600

7,500

tooth)

2,000 to

8 to 20

250 to 800

0.010

3 to 10

300to

0.004 to

500

0.008

4 to 9 (skip

300to

0.004 to

6,000 Glass filled laminates

300 to 400

0.005 to

2,000 to 6,000

tooth)

500

0.010

Acetal, Polypropylene,

3,000 to

4 to 9 (skip

500 to

0.004 to

Rigid PVC

6,000

tooth)

1,000

0.010

4,000 to

4 to 11

300to

0.008 to

1,000

0.024

100 to

0.005 to

500

0.010

300to

0.002 to

11,000 Acrylics

5,000 to

4 to 12

10,000 Polystyrene

2,500 to

10 to 24

Top Rake

Speed 1/8in. diem. (rev/minute)

Speed 1/2in. diem. (rev/minute)

Speed 1 in. diem. (rev/minute)

Routing Speed (rev/minute)

Milling Speed (ft/minute)

Oto30

8,000

2,000

700

18,000 to

4,000 to

0.010

Polyethylene, PTFE

Nylon

Drilling

Turning

Sawing

24,000

6,000 4,000 to

15

0 to 15

8,000

1,500

600

18,000to 24,000

6,000

0 to 15

15 to -5

1,000

500

300

18,00 to

150 to

26,000

40O

18 to 30

Oto-5

1,000

5OO

300

15,000 to

800 to

24,000

1,500

18 to 30

Oto-10

1,200

800

500

15,000 to

800 to

24,000

1,500

15 to 22

Oto-5

5,000

1,000

500

15,000 to

600 to

24,000

900

15,000 to

700 to

24,000

1,200

300

12,000 to

15 to 20 15

Oto-5 0

6,000

1,000 1,500

600 700

400 to

gl

-I1

a,1 C~"

/,) m

,

m,,,

4,000

1,000

0.008

24,000

1,000 o

',,4

458 Reinforced Plastics Handbook

manufacturers integrate robots complete production system.

into

their machinery,

offering a

Robotic systems for loading and demolding presses are in widespread use, to optimize production efficiency. Machines are available either from the molding press manufacturers, or direct from the equipment manufacturers (for processors who prefer to assemble their own production systems). Essentially robot systems operate on three or more axes, using electrical, servo, or pneumatic drives, for fast positive action and need to be specified according to the load to be carried and distance to be traveled. Systems use robot control with learning ability, by which the device is programmed by 'walking it through' the sequence of operations. Control of the device can usually be integrated with the control system of the press. Design of the gripper system (by which the robot device holds the molding) depends on the configuration of the molding itself (and it may be a good idea to incorporate in the product design features to aid robot handling). In many cases, the gripper arrangement can be customized in-plant by the processor. Fully cured RP are not easy materials to cut or machine, since glass fiber tends to blunt most ordinary steel tools. An additional complication is the size of many RPs, making it difficult to take the work to the machine. Portable hand tools are often used for this work, and portable reciprocating electric saws have proved themselves for trimming and shaping, especially where high-grade blades are used. Where possible, abrasive discs or wheels are recommended for cutting. Carbide-tipped steel tools should be employed for all other machining operations. Available have been the proper tools for trimming, shaping, drilling, cutting, etc. Workers operating such equipment should be provided with suitable respiratory protection, as recommended by manufacturers. RPs are not homogeneous, and can be vulnerable to delamination. The work should, therefore, be firmly supported or clamped as close as possible to the cutting line. Where a large run of moldings is to be produced, it will save time and effort if cutting/trimming jigs are also produced. Water is not recommended as a lubricant or coolant, except where there are facilities for thoroughly drying the laminate afterwards. Overheating must be avoided. Waterjet cutting systems, which can readily be robotized, are used for cutting and trimming parts such as panels, on a production line basis. Holes of up to 10 mm (0.4 in) diameter can be drilled with carbidetipped twist drills. Above this size, cutters are recommended rather than drills. Cracking can be avoided by using as little pressure as possible and

5

Fabricating 9 Processes 4 5 9

by starting the drilling on the good (gelcoat) side. When drilling, they should be backed with hardwood to prevent the drill breaking through and producing ragged edges. Where the production justifies it, investment in CNC-controlled routing machines makes it possible to machine very large moldings and reduces the time required to deftash and finish a typical component (such as going from 40 min to less than seven). The machines have an in-built teach-and-learn capability. Two basic types of abrasive paper are normally used for fairing and finishing. The more coarse type of sanding uses aluminum oxide production paper, supplied on the roll and cut to length for use with boards or mechanical sanders. Wet or dry silicon carbide paper, which can be used wet (with water as lubricant) or dry, is always used for final finishing of coatings. The paper is usually cut and used with a rubber hand-held sanding pad. Table 5.22 is a guide to recommended grades of abrasive paper for use in different stages of fairing (note that the lower the grade number, the larger the grit particle size and the lower the density of the cutting particles). Table 5.22 Gradesand types of abrasive paper for fairing and finishing

Surface

Typeof sanding

Production paper grade

Wet or dry grade

Expoxy filler or wood

General rough fairing Fine fairing Finishing (wood only) Surface preparation Fine surface fairing

40-60 80-100 120-180

Not used Rarely used 180-220

120-180 80-120

180 120-180

Very fine surface fairing Keying for finish coats Very fine surface fairing and keying

180 Not used Not used

180-220 280-320 280-320

Polyester gelcoat High build epoxy surfacer/undercoat Polyurethane undercoats Polyurethane finish coats

Joining, Fastening

Mechanical joints to assemble RP moldings to each other or to other components usually employ metal inserts or fixtures (also used are RP and URP types), which are molded into the product. With o p e n / contact molding, this can readily be organized within the scope of the molding cycle. For press molding of both TSs and TPs, it can often be a

4 6 0 Reinforced Plastics Handbook

time-consuming and costly operation (as, for example, in molding electrical or electronics components, where many fine contacts must be inserted into a molding tool). For insert work, a vertical configuration press is usually employed, and it is increasingly possible (and cost effective) to robotize this operation. Where inserts must be loaded by hand, however, it is important to pay close attention to safety precautions for working with an open mold and working with hot metals. In some cases with TPs it is possible to insert metal fittings, such as bushes, into the molded component, using friction or ultrasonic methods of insertion, and fusing the TP around the metal insert. With RTP compounds, this may create undesirable stresses, however, and advice should be sought from the material supplier. Other useful techniques with TPs include hot staking, where the plastic is deformed around a metal part (such as a plate), to secure it in place. Methods of applying range from electrically heated irons to hot air systems, and will depend on the degree of complexity of the part, the number of hot stakes to produce and the required speed of production. TP components can also be welded for assembly, using hot-plate or ultrasonic systems, or by spinning two matching circular parts to weld the surfaces by friction. The technique employed will, largely, be dictated by the type of TP involved. Information, as a guide, follows where a welding process is followed by (a) equipment cost, (b) tooling cost, (c) typical output rates, (d) normal economic production quantities, and (e) general remarks:

Hot-gay (a) very high, (b) low (holding fixture only), (c) 0.3 to 1.5 m (12 to 60 in) of weld seam per minute, (d) very low, and (e) manual operation.

Hot-plate: (a) moderately low to high, (b) moderate to high, (c) about 120 parts/h/fixture cavity, (d) medium to high, and (e) setup time 1 h or less.

Induction: (a) low to moderate, (b) low, (c) about 900 parts/h, manually loaded, (d) high, and (e) setup time 1 h or less.

Spin: (a) moderate, (b) moderate, (c) about 640 parts/h, manually loaded, (d) high, and (e) setup time 1/2 h, mechanization possible.

Ultrasonic: (a) moderately low to high, (b) moderate to high, (c) about 1000 parts/h, manually loaded, (d) high, and (e) automatic operation desired.

Vibration: (a) moderate, (b) moderate, (c) about 240 parts/h from single cavity, manually loaded, (d) medium to high, and (e) setup time 10 min., multiple cavities and mechanized loading possible.

5

Fabricating 9 Processes 461

In this, and in other aspects of secondary assembly and finishing, it is well worthwhile to take into account the requirements for handling and manipulating in the original design of the parts. Adhesive Bonding

An adhesive is a substance made principally from TP and TS plastics (also vegetable, animal by-products, silicates, etc.) which applied, as an intermediate is capable of holding material together by surface attachment. Mechanism of adhesion (adherence) is the phenomenon in which interfacial forces hold surfaces together. Adhesion may be by molecular attraction, mechanical, electrostatic, or solvent depending upon whether it results from interlocking action, from the attraction of electrical charges, from valence forces, or solvent action, respectively. Advances in the use of TP and TS plastic adhesives have made possible the adhesive bonding of RP structural and nonstructural parts in appliances, automobile, aircraft, medical devices, and so on. Adhesives with strengths higher than some metals are used (epoxy, etc.). The wealth of adhesive technologies that are available could make adhesive selection a task if one does use the proper approach such as determining specifically what performance requirements are needed (as with any selection procedure). The best adhesive for an application MI1 depend on processing considerations and meeting the performance requirements. Tables 5.23 and 5.24 provide information on types and use of adhesives. Table 5.23 General comparison of adhesives used with plastics and coatings Bond properties

Standard epoxies

Two-part polyurethanes a

Methcrylates [Plexus}

Silicones

Cyanoacrylates

Shear strength

Poor-fair

Good-excellent

Excellent

Poor-fair

Excellent

Peel strength and flexibility

Poor-fair

Good-excellent

Excellent

Goodexcellent

Fair-good

Impact resistance

Poor-fair

Good-excellent

Excellent

Goodexcellent

Poor-fair

Temperature resistance

Fair-good

Fair-good

Excellent

Goodexcellent

Fair-good

Moisture resistance

Poor-fair

Good-excellent

Excellent

Fair-good

Gap filling

Fair-good

Good-excellent

Excellent

Excellent

Poor-fair

Cure speed

Fair-good

Poor-fair

Excellent

Poor-fair

Excellent

aUsuallyrequiresa primer. Source: ITW Plexus

462 Reinforced Plastics Handbook Table 5 . 2 4 Basic types of adhesives used with reinforced plastics Adhesive system

Curing temp

Adhesion

Resistance to water

Gap filling

Main uses

Ureaformaldehyde

Room temp

Fair

Poor

Fair

Used mainly for interior grades of plywood

Resorcinol

Room temp

Good

Good

Fair

Used for large laminated structures where high clamping pressures can be achieved

Phenolic

Usually elevated temp

Good

Good

Fair

Used for marine-grade plywood; similar to resorcinol {has good heat and fire performance]

Polyester

Room temp

Fair: will bond well only to part-cured polyester

Fair/good

Excellent

Used for laminating with fiber (FRP) and for bonding 'green' FRP moldings

Epoxy

Room t e m p

Excellent with most substrates

Excellent

Excellent

Used for highperformance lamination and for bonding to wood and aluminum

Two-part methacrylate adhesives offer good structural bonding properties with TS laminates and composites, including SMC/BMC, phenolic and flame retardant resins, vinyl esters, and epoxies (Table 5.25). A typical range can be mixed and dispensed using hand-held cartridge dispensers, or with automated meter mix equipment. There are adhesives having good gap-filling characteristics and thixotropic formulations that can be used on vertical or inverted surfaces without sagging, curing on their own at room temperature. Robotized dispensing of a high-quality bead of two-component structural adhesives (epoxy, polyurethane, acrylic) is possible with servo-powered equipment. Positive displacement pumps control the mix ratio and flow of low to high viscosity adhesives and sealants. There are solvent adhesive, also called solvent fusion. They provide a method of joining two TP types by application of a solvent to soften the part surfaces. Types have to be those that solvent will attack.

5

9Fabricating Processes 4 6 3

Table 5 . 2 5 Two-part methacrylate adhesives designed for structural bonding

Times (rain) at 22~ Type

Description

Color

Working

Fixture

MA300 MA310 MA320 MA3940 MA3940LH A0420 AO420FS MA425 MA550 MA920 MA922 MA925

All purpose adhesive Difficult to bond plastics General purpose Excellentlow temperature Fastersetting version of MA 3940 All purpose adhesive All purpose adhesive - very fast curing All purpose adhesive White, UV stable Low odor Low odor Low odor

Cream Cream Off-white Off-white Blue 0ff-white Blue Blue White Blue Blue Blue

4-6 15-18 8-12 12-15 4-5 4-6 1-2 30-35 40-45 4-6 17-24 30-35

12-15 3O-35 25-30 25-3O 8-10 15-18 3-4 80-90 70-75 15-18 35-40 80-90

Source: ITW Plexus.

Softening the plastic increases the movement of the plastic chains, allowing them to intermingle at the joint interface. Adhesion occurs after solvent evaporation. Solvent application must be carefully controlled for optimal joint strength and to avoid damage to the part. With time the solvent can penetrate the plastic with damage occurring immediately or latter when in service. Solvent solutions that attack TPs are also used to determine the amount of undesirable "frozen stress" existing in parts. There are different solventless adhesive systems. An example from Liquid Control LTD., UK is their successful Liquid Control Compact Twinflow | meter, mix, and dispensing machine. This compact, variable ratio meter, mix, and dispense machine consistently delivers a supply of two part adhesives. This machine processing, as an example, polyurethane laminating adhesive to their laminator is capable of supporting line speeds in excess of 1000 ft/min on laminating webs of up to 50 in. wide. The Compact Twinflow is gravity fed from a four-drum rack eliminating the need for on board reservoirs and the transfer pumps required to keep them replenished. Level sensors between the top and bottom drums provide an "empty" signal when it is time to change to a fresh drum. In the meantime, the supply of material is uninterrupted since the bottom drum maintains a supply of material during the changeover. Additional confidence in the quality of product is delivered through the EnGarde ratio monitoring and flow rate system provided as an

4 6 4 Reinforced Plastics Handbook

accessory by Liquid Control. In line flow meters constantly monitor the fluid streams and report not only ratio but provide material consumption information for each production run. Phasing lights enable the operator to detect and adjust the equipment for any lead/lag conditions that may occur due to variations in flow characteristics of the two materials.

Joints and Adhesives The basic types of joint can be used with either bonded or mechanical fastening, but there are special requirements when using mechanical fasteners with tapered thickness plates. The simplest design (unsupported single lap) is the weakest; the most complex (stepped-lap joint) is the strongest (Figures 5.89 and 5.90). .

9

r

~

_. .

.

-1 .

, .

,,

~-

.

I

''

r.

.

.

.

.

.

.

.

.

.

,

i

, ,

,

_

'i

~ l i

,,

.

i

,

. ,,

.

, Tapered

3

l

Single strap or butt joint .

.

,

u.

'

,

'

i

.

'~

iJI

]

Unsupported single lap joint |

,

.

Double strap joint

Double i

..

,

u

......

~'~

strap joint

,

,,,

.

,

I

Stepped lap joint

Tapered single lap joint ,, ,,I l:'iJ

Double lap joint

Figure 5 . 8 9

,,, ",'

, J

1_..

' ,,,, Scarf joint

/

Basic types of joint

The purpose of a joint is to transfer load, which will create differential stress between the components as well as in the joining medium, whether fasteners or adhesive. Figure 5.91 has diagrams that illustrate the basic mechanisms that identify (a) single cover butt joint, (b) adhesive in shear (c) fastener in shear, and (d) bending of plates at ends of a joint. In many RPs, the most convenient joint will be a bonded type (possibly produced during the lay-up process), and the geometry is therefore very influential. The weakest joints are those where failure is limited by inter-laminar failure of the adherend, or peel of the adhesive. Next strongest are those where the load is limited by the shear strength of the adhesive. The strongest designs will fail outside the joint area, at a load equivalent to the strength of the adherend. Selection of adhesives depends on many requirements, particularly the nature of the materials to be bonded, the function of the bond,

5

9Fabricating Processes 4 6 5

Bad

Good IIII

I 1

I

I____ I Figure 5.90 Examplesof good and bad joint configurations production conditions, and the expected performance of the finished product. Consolidations

Onc-piccc RP components replace multiple parts previously made both from RPs and from metals or other materials including unreinforced plastics. The motivations for the design and the challenges for fabricating

466

Reinforced Plastics Handbook (a)

i

B

x,,,,~ , ,

.,

y

[

c

,r/x,

I

I

I

y

I

x

,A

I----~

y

(b) 4 - - ~

~- ......

,! .....'5'.,'.~.i..,:'.,~ ............................ ....... 9 J " ........

'

"

]

~-'-~

I,

(c) ,

,<7"..

....

,.

(d) x

x

x

Figure 5.91

Basic m e c h a n i s m s of l o a d - t r a n s f e r in joints

can differ as much as do the end products. A common incentive for part consolidation is cost. RPs frequently earn their way onto a project not just for their properties, but because reduction of part count makes it possible to mold and assemble what would otherwise be a much more expensive multi-part structure at or near the cost expected for parts made with competing materials. Yet a great deal of design and engineering innovation may be required before those benefits can be reaped. Painting, Surface Finishing

Where the molding is to be painted, it is a good precaution to avoid using waxes or silicone release agents in the first place, or use these only as a primary release agent. Primers with particularly good adhesion to RP surfaces are offered by several paint manufacturers and, for a durable surface, it is advisable to use them. They can be applied without previous abrading, if the surface is clean and dry. When normal paint primers are used, it is advisable, however, to rub down the surface with a fine abrasive, to obtain good keying. Most paint systems can be used on RPs. For stoving finishes, the molding should be post-cured at 80C before the finish is applied: airdrying finishes can usually be applied without post-curing. Most cellulose finishes are also suitable, but with these, it is particularly important to ensure that the resin has fully cured, to prevent the solvents attacking any uncured resin.

5

9F a b r i c a t i n g

Processes

In the early 1980s, the automotive industry in the USA began using inmold coating (IMC) technology for SMC bodywork panels, using primers to eliminate pinholes, improve the surface finish and improve the grit resistance of the paint range (Table 5.26). The IMC process applies a coating of primer lacquer of about 0.1 mm thickness to the relatively rough surface of a molding during pressing. Taking advantage of the need to open the press slightly during curing to allow venting, a special lacquer is injected at this point and the mold is re-closed with electronic/hydraulic control of the parallel motion. Table 5 . 2 6 Guide for coatings vs. properties

E E

~

~ ~ . ~ ~ ~ ~ ' ~ ' ~ '~~ ~

~~

~

E

0

Hardness

2

1

2

2

2

3

1

2

2

2

2

2

2

2

2

2

1

Adhesion

2

1

2

1

1

2

1

1

1

2

2

2

2

2

2

1

1

Flexibility

3

2

2

1

1

1

2

2

2

3

3

2

1

1

1

1

1

Mar resistance

2

2

2

2

3

3

1

2

1

2

2

2

3

3

2

2

Gloss (85 units

1

1

2

2

3

4

1

2

1

1

1

1

4

4

4

4

2

Fabricability after aging 4

1

2

1

1

1

3

2

2

3

3

2

1

1

1

1

1

plus 60 ~ Humidity resistance

2

1

1

1

1

1

1

1

1

2

2

1

1

1

1

1

1

Grease and oil

2

2

2

1

1

1

1

2

2

2

2

2

1

1

1

1

1

3

2

3

2

1

1

1

2

2

2

2

2

1

1

1

1

1

2

2

2

2

1

1

1

2

2

2

2

2

1

1

1

1

1

2

2

3

2

2

2

4

4

2

1

1

1

1

1

1

2

1

3

3

3

3

3

3

4

4

2

2

2

2

1

1

1 4

1

resistance General chemical resistance General corrosion resistance (industrial atmospheres) Exterior durability (pigment) Exterior durability (clear films) Ratings" 1 = excellent, 2 = good, 3 = fair, 4 = poor

467

468 Reinforced Plastics Handbook

While the process was found to offer significant advantages, such as manufacturing versatility, fast color-change, and use of near-zero volatile organic compounds (VOC), there were also some drawbacks. These are particularly entrapment of air, need for a sophisticated system to adjust parallelism on the mold halves, difficulty of coating vertical surfaces, and increased cycle time and limitation of possible locations for the ejector system. In 1985, a USA paint manufacturer introduced a high-pressure injection molding IMC process (HPIP). It was based on injection of the coating into a closed mold at 300--400 bars pressure, before the SMC was fully polymerized. At this stage, the compound is still compressible, allowing the coating to flow between it and the mold. The technology overcomes the objections to conventional IMC and is used today worldwide (Table 5.27). Table 5.27 Typical physical properties of a decorative in-mold topcoat Property

Test

Gloss 600

Almond

White

ASTM D523

87

91

Pencil hardness Barcol hardness

ASTM D3363 ASTM D2583

3H 94

3H 95

Color fastness 200 h Xenon arc Stain resistance Wear/cleanability 10,000 cycles

ANSi Z124.1

dE 1.0

dE = 0.75

dE = 1.0

ANSI Z124.1 ANSI Z124.1

50 First cleaning 50/0 2nd cleaning 20/0

37 1.8%, 1.2%

34 0.9% 0.1%

ANSI Z124.1 ANSI Z124.1

repairable dE = 1.5 no blister

repairable dE = 1.0 no blister

repairable dE = 1.5 no blister

dE = 1.5

dE = 1.5

dE = 1.5

no blister

no blister*

no blister*

No cracks,

No cracks,

No cracks,

no chips

no chips

no chips

Chemical resistance Water resistance: 100 h @ 150oF 100 h @ 212~ Point impact 20 in

ANSI Z124.1

Specification

Note: with certain SMCsthereare occasionallya few small blisters.

The IMC must flow and polymerize at the same temperature as the SMC (150C) or BMC (up to 170C), in 15-60 s. The formulation is an unsaturated (TS) polyester resin requiring addition of an organic peroxide before use. At ambient temperature, it has a pot life of about five days. IMCs used by the automotive industry are usually employed as conductive or non-conductive primers, for subsequent painting with a

5

9Fabricating Processes 4 6 9

conventional topcoat. The sanitary, electrical, garden furniture, leisure, and other industries also use IMCs as finishing coats. Using formulations based on TS polyesters or polyurethanes, the highpressure closed mold system can be used with SMCs/BMCs, RIM and RRIM polyurethanes, RTM, and also injection molded TP parts. The basic concept has been extended to injection molded TPs and has been developed jointly by a coatings manufacturer, machinery manufacturer, and an automotive group. It involves phased injection into the mold of two components, the molding material itself, and a special pigmented coating formulation based on powder coating technology, using computer-aided mold design with existing two-component molding technology to produce a molding with automotive class A finish direct from the mold. The coating meets the growing demand for more compatible materials for recycling. Even the best quality isophthalic gelcoats can be subject to loss of gloss and yellowing, eventually exhibiting a chalky and stained surface, particularly on boat decks. Osmosis is a further problem. Water ingresses between gelcoat and RP creating pressure and the unreinforced gelcoat layer gives slightly, showing as blisters. A novel in-mold coating, Crystic Protec, from Scott Bader, uses a new polymer backbone. The gelcoat is formulated to resist sunlight and yellowing and, to counter osmosis, it uses the concept of chemically matching the gelcoat and RP resin, giving a measured water uptake 24% less than the best isophthalic gelcoat. For producing a high-quality finish on compression molded parts, Ferro developed a premold coating in powder form which melts rapidly on coming into contact with the heated ld surface [130-160C (266-320F)], but the inner surface remains unreacted until contact with the molding compound, when it bonds chemically to form an integral laminate. Post-finishing is unnecessary and release agents are not required, even with low profile SMC. Chemical and physical properties are excellent and the coating has a high Barcol hardness, resisting damage during handling, even when hot. It can be applied by conventional manual or automatic powder spray equipment. A range of colors and decorative effects is available. In can be used particularly in sanitary ware, automotive and exterior applications. When a colored gel coat has been used and subsequent painting is not required, the release agent should first be thoroughly washed off. The molding can then be buffed or polished with any of the normal cutting compounds. If the product it is not to be painted, extra care should be taken to ensure that all trace of release agent is removed. Release agents

470 Reinforced Plastics Handbook based on polyvinyl alcohol can easily be washed off with detergent and plenty of warm water. There may be difficulty in removing any wax or silicone release agent still adhering, and it may be necessary to use wet or dry abrasive paper to remove these release agents.

Washing Equipment Equipment for washing RP tools and equipment takes a variety of forms, depending on size and volume requirements. A typical system is based on manual washing stations, with or without solvent bath, for small-scale washing of brushes, rollers and guns, which can be located close to the workplace and connected to existing extraction systems or to portable activated carbon filter units. A closed chamber can be loaded via a foot-operated flip-up lid and solvent fed by gravity from holding tanks, draining to a waste tank below, which can be transferred to a solvent recovery unit. For safe efficient cleaning of larger items there are washing booths with fume hoods, which can be connected to extraction systems and drain solvent to portable containers for recovery. The washing process can be speeded up by a rotary machine or fully automated, with a washing tunnel. Rotary machines, using a horizontally rotating basket in which the components are loaded, will handle items from 38 to 78 cm diameter x 50-58 cm height x 25-40 kg weight. Tunnels (which are suited mainly to washing printing ink from silk screens and litho/flexo ink trays) employ a traveling longitudinal spray nozzle, directed at a 45 ~ angle to the object being washed automatically reversing after completing a pass.

Solvent RecoverySystems Recovery of expensive solvents is an attractive proposition, and there is a range of equipment suited to various requirements. Details are presented in Chapter 3 Polyesters, TS, TS Polyester Solvents.

Troubleshooting Processing of RP is an art of detail. The more you pay attention to details, the fewer problems/faults develop in the process. If it has been running, it will continue running well unless a change occurs. Correct the problem and do not compensate. It may not be an easy task, but understanding what you have equipment wise, material wise, processing wise, environment wise, a n d / o r people wise can help. In order to understand potential problems/faults and solutions of fabrication, it is

5

9F a b r i c a t i n 9 Processes

helpful to consider the relationships that are directly related to machine capabilities and variables, plastics processing variables, and product performance. The following Tables 5.28-5.31 list typical problems/ faults and solution/corrective measures. Much more information is available in the literature usually associated with specific processes (see Bibliography). Table 5.28 Troubleshooting thermoset RPs Problem

Possible cause

Solution

Nonfills

Air entrapment

Additional air vents and/or vacuum required Adjust resin mix to lengthen time cycle

Gel and/or resin time too short Excessive thickness variation

Improper clamping and/ or layup

Check weight and layup and/or check clamping mechanisms such as alignment of platens, etc.

Blistering

Demolded too soon Improper catalytic action

Extend molding cycle Check resin mix for accurate catalyst content and dispersion

Extended curing cycle

Improper catalytic action

Check equipment, if used, for proper catalyst metering Remix resin and contents; agitate mix to provide even dispersion

Table 5 . 2 9 Problem/fault vs. solution/correction of injection molded glass fiberlTPs Fault

Priority order for remedies a

b

c

d

e

f

7

27

30

34

3

4

Brittleness

27

26

34

4

25

Excessive flash

30

10

29

2

6

Gas burns

30

3

27

21

2

7

Oversized part

30

29

28

27

17

33

23

Poor surface finish

17

14

15

23

9

2

7

Poor weld lines

Blisters

g

h

7

17

32

7

28

27

i

12

30

j

k

I

16

14

13

17

8

3

21

30

1

15

23

Short shots

8

14

15

21

23

9

17

18

19

20

Silver streaking

7

15

27

4

34

18

26

30

Sink marks

14

13

30

18

19

20

22

8

31

11

12

Undersized part

12

13

31

23

16

9

8

15

17

18

19

Voids

14

13

30

18

19

20

22

17

31

8

7

5

14

17

31

32

1

27

28

11

24

Warping

3

471

Table 5 . 3 0 Problem/fault vs. solution/correction of glass fiber/TS polyester reinforced plastic

Fault

Appearance

Wrinkling

Cause Attack on the gelcoat by solvent from monomer in the laminating resin due to undercure of gelcoat. Can be corrected by ensuring that the resin formulation is correct the gelcoat not too thin and temperature and humidity controlled keeping the mold away from moving air (especially warm air}. If the workshop has hot air blowers they should be directed away from the molds. Temperatures below 16~ (commonly due to storage of containers outdoors overnight) will drastically affect gel time; high humidity moisture condensation and damp release film also retard cure also check catalyst concentration and grade of polyether ketone peroxide (activity may vary)

Gel coat cures too slowly

Pinholing

el)

Small bubbles of air trapped in the gelcoat before gelling also when resin is too viscous or toohigh filler content or when gelcoat wets release agent imperfectly.

Poor adhesion of gelcoat

Flaking of gelcoat in handling blister local surface undulations when viewed obliquely

Can be caused by imperfect consolidation of the laminate contamination of gelcoat before glass fiber is laid up or (more frequently} gelcoat left too long to cure.

Spotting

Small spots all over gelcoat surface

Usually due to inaccurate dispensing of one ingredient of the resin formulation.

Striations

Color waves over surface

Flotation of color paste most common when color used is a mixture of more than one paste; remedied by thorough mixing or using different paste

Fiber pattern

Pattern of fiber reinforcement is visible through gelcoat or prominent on surface

Usually when gelcoat is too thin or reinforcement is laid up and rolled before gelcoat has hardened sufficiently or molding demolded too early. Does not usually affect performance but can be unsightly.

'Fish eyes'

Patches of pale color (usually up to 6 mm diameter)

Can occur on very highly polished mold especially when using silicone-modified waxes gelcoat 'de-wets' from certain areas leaving thin spots. Can also occur in long straight lines following brush application strokes. Rarely encountered when liquid release agent is correctly applied.

m

,

Ill

,-r

0" 0 0

Table 5 , 3 0

continued

Fault

Appearance

Blisters

Crazing

Cause Usually indicates delamination/trapped air or solvent; over large area can also indicate undercured resin {and may take six months after molding to show). Can also form when subjected to excessive radiant heat during cure. Often caused by using liquid rather than paste catalyst. Below-surface blister probably due to imperfect wetting of fiber from allowing insufficient time for mat to absorb resin {can usually be detected by inspection on demolding).

Hair-cracks in surface; poor surface gloss

Can happen immediately after manufacture or may take some months to develop. Generally associated with resin-rich areas due to unsuitable resin or formulation in gelcoat; common cause is adding styrene monomer to gelcoat. Or gelcoat may be too hard relative to its thickness (harder the gelcoat more resilient must be the resin). When occurring some months after exposure to weathering crazing can be due to undercure too much filler or too flexible resin.

Star cracking

Over-thick gelcoat occurs when laminate receives reverse impact" gelcoat should never be more than 0.4 mm (0.016 in} thick.

Internal dry patches

Trying to impregnate more than one layer of mat at a time; presence of dry patches can be confirmed by tapping surface with a coin.

Poor wetting of mat

Reverse side has unglazed appearance

Not enough resin used in laying-up or lay-up not properly consolidated reverse side will appear 'glazed' if fibers are correctly coated.

Leaching

Loss of resin in weathering leaving fibers exposed

This is a serious fault. Either the resin has not been properly cured or an unsuitable resin has been used.

Yellowing

Slight yellowing after exposure to sunlight

Can be marked with white or translucent laminates. Surface phenomenon due to absorption of ultraviolet (UV) radiation; does not affect mechanical properties. Most resins contain UV stabilizers to reduce rate of yellowing; high resin content discolors less rapidly than high glass content (75% resin in sheet will make yellowing negligible).

(,n -i-1 o-

m,,,

"0

0 Ill

w

4 7 4 Reinforced Plastics Handbook Table 5.31 Examplesof computer software information generated and typical problems it can solve

Cooling Analysis Mold surface Temperature Freeze time Coolant temperature and flow rate Metal temperature

Part quality: even cooling prevents distortion Minimizes cycle time. Optimizes coolant: can eliminate need to chill coolant. Cooling efficiency: ensures optimum circuit design.

WarpageAnalysis Warped shape Single variant Warpage shape

Tendency to warp. Indicates fundamental causes of warpage.

FIowAnalysis Fill pattern

Pressure distribution Temperature

Shear stress distribution

Shear rate cooling time Flow-angle packing pressure volumetric shrinkage

Weld line position. Air trap position. Position of vents. Overpacking: excessive costly part weight. Overpacking: warpage due to differential shrinkage. Underflow: structural weaknesses. Clamp force required. Overpacking: ribs, etc. sticking in mold. Poor surface finish. Weak weld lines. Distortion due to differential cooling. Quality of part: tendency to distort. Quality of part: tendency to crack. Cycle time: low stresses permit hotter demold temperature. Avoids degradation of material. Shows tendency to distort due to uneven cooling. Quality of part: molecular orientation. Under/overpack to poor packing. Dimensional variations due to poor packing.

Fabricating products involves conversion processes that may be described as an art. Like all arts they have a basis in science and one of the short routes to processing improvement is a study of the relevant sciences (as reviewed throughout this book that range from the different plastic melt behaviors to fabricating all size and shape products to meet different performance requirements.

5

9Fabricating Processes 4 7 5

Repairs

RP may need to be repaired to rectify faults occurring during production, or to repair damage in service. Most fabricating faults can readily be dealt with at the trimming/finishing stage, where materials and equipment are available. When repair involves RTPs the fact that TPs can easily be heated and melted can simplify the procedure. Simple patchwork is performed with ease. If there is a catastrophic failure of the reinforcement, repair is probably difficult or impossible. Examples of repair procedures are highlighted in Figure 5.92. Edgeschamfered

Damagedarea . cut out

I~'";';"~"-".:,E;';:.'.';'.".7~ J ~

Damagedarea repaired

l.':':.,_':.'.,:'.~'.'.":.'.::;.'..i

Undamaged J laminate

/

Temporary

mould

Rib laminatedoverrepair

~,~,~ ~,,-'~~;.-;~-.;;-.;;;~;--.~..--~"~'~ "~'i' l.'.v':::-':i::'-:".'.T.-',,,'.l

Laminate

Temporarymould

Figure 5.92 Two methodsfor repairing damagedfiber reinforced plastics

With RTSs, any loose resin and reinforcement should be removed and the affected area cleaned and dried. It may be useful to roughen surrounding areas, to obtain better adhesion. For superficial damage (to gelcoat only), apply catalyzed/activated resin to the damaged area and allow to set/solidify. Film, such as transparent cellulose, tape or TP polyester, may be used to keep the resin in position and impart a smooth surface finish. Apply a thicker film of resin than usual, to allow for shrinkage. When the repair patch has fully hardened, dress the resin back to the correct contour of the molding. Where damage goes beyond the surface, resin and reinforcement should be laid up overlapping the edges to give good adhesion over a wide area. If the laminate is fractured, the whole of the damaged area

476 Reinforced Plastics Handbook

can be cut away and the inside edge of the aperture chamfered to make it larger on the gelcoat side than on the reverse. The surrounding area should be roughened to obtain good adhesion. Where the surface area is large, a temporary mold should be built up on the exterior surface, release agent applied and left to dry. For smaller holes, a piece of cellulose or polyester film can be fixed over the hole with adhesive tape, to act both as mold and release agent. The literature provides repair techniques ideas for RPs. As an example with very extensive damage, the best solution, if feasible, is to consider replacing the molding in its original mold and repair it in the mold. Where a strengthening rib can be added, a different repair method can be used. The hole is chamfered to be larger on the inside than on the gelcoat side and the actual repair is carried out as described above, but it need be no thicker than the laminate. One or more reinforcing ribs are then laminated over the area, overlapping as far as possible.

Energy When examining energy consumed or lost, the equipment used in the complete production line as well as the plastic is involved. Regarding electric energy, 1998 was the year that the USA government-subsidy stopped. Cost of energy started to doubled and tripled setting market forces in motion that makes more energy-efficient all-electric equipment desirable. As an example, an injection molder facing a mandatory energy cutback realizes 2 or 3 all electric IMMs could run on the same power as it takes to run one.hydraulic machine of the same size. As the electric injection machines become larger, more energy advantage over hydraulics exists. Here is one of many examples where RP provides for energy savings. Table 5.32 illustrates the total energy saving and increase in fuel economy obtained by designing a single component front-end grille opening panel of SMC to replace a multi-component metal assembly on a production car. It replaced many metal stamping, machining, and fastening operations, as well as the associated dies and fixtures that eliminated the replacement of 16 steel and die cast parts with a single RP molding. The data in the table assume a vehicle life of 9.2 years. When discussing energy the target is usually to reduce consumption and thus reduce cost of fabricating. Regardless of action, being taken it may appear that the cost of energy continually increases as any savings occur in the workplace, at home, etc. In the mean time energy shortages

5

9Fabricating Processes 4 7 7

Table 5.32 Energysavings and fuel economy Front-end panel

Metol

20 (9.07) Zinc die cast and stamped steel, weight, Ib (kg) 400,000 (157.24) BTU/finished part (hp-hours/finished part] Fuel economy increase, % Fuel saving, gal (1)

RP

9 (4.08)

200,000 (78.62)

0.2

13 (49.205)

Source: Ford Motor Co.

continually occur. Interesting with all the political movements worldwide, their appears insufficient action to meet the International Energy Agency report that the global population presently at 6.3 billion will increase requiting worldwide energy demand to increase 25% by 2015.

Upgrading Plant When a plastic fabricator considers updating a fabricating facility with a state-of-the-art operation the usual operating factors already in use require reviews and up dates such as material handling and services (electric power, water cooling, etc.) to machine safety operations. Estimating cost and site location are two initial pitfalls that must be avoided. One can over-estimate difficulties or underestimate challenges with results ranging from expensive too disastrous financial situations. However, these problems can be avoided by assembling a qualified high-quality team that includes an architect, facility contractor, and if needed a consulting engineer that has experience with plastics manufacturing plants. Regarding choosing the correct site is often the most critical decision in the process. This action contains various variables such as make sure there is adequate access to power and water. Consider what combination of highway and rail access will work best for receiving raw materials and shipping products. Check local zoning laws such as permitting silos or cooling towers. Determine if the local labor supply is adequate for the type of people required. Select a site that permits future expansion. Design the building so that expansion can be accomplished without interrupting production. Wiring and piping systems should be designed with expansion possibilities. More loading dock space should be planned. Parking area must be easy to enlarge. New venting and air conditioning technology can help reduce operating costs significantly.

478 Reinforced Plastics Handbook

All types of RP molding should be carried out in a controlled environment. This is essential where TS polyester resins are being processed and there may be risk of over-exposure to styrene emissions, and is advisable also when working with TPs, because of heat build-up from machines, the effect of sudden drops in temperature (as, for example, when doors are left open), and the removal of fumes. With the more mechanized molding processes, adequate space is obviously necessary, and special attention must be paid to safety precautions and guarding. The apparent simplicity of hand lay-up or sprayup should not lead one into thinking that generous space here is not equally essential. The ideal for all work is a large, airy, solid factory building, free from draughts, and with a controlled temperature of 20-25C. Precise machine alignment reduces wear and tear, minimizes downtime, and reduces flashing such as for alignment of injection molding machines. Cleanliness and good housekeeping are, similarly, the watchwords for all types of plastics molding. It is good practice to introduce a flow-line layout: firstly, because it is logical, and second because it separates the various stages of production (material preparation/molding/assembly/ finishing), preventing dust and contamination from one affecting another. Working with TS resins, this is particularly important. It is also worth remembering that, as work progresses from one stage to the next, so also does the value of the product increase. Damage/failure at a late stage is much more costly. Effective quality control should be interposed between critical stages, where it is practicable to introduce feedback loops to correct any rejects. Examples of plant layouts for various RP operations are shown in Figures 5.93 and 5.94. No RP plant in the world can rival Boeing's 22,000 m 2 (237,000 ft 2) Composites Center of Excellence at Seattle, Washington, USA, which makes parts for military and civil aircraft, including the B-2 stealth bomber, which is the world's largest application of s in aerospace engineering to date. The upper and lower skin panels of the wing are thought to be the largest single-piece aircraft RP structure yet made. The outboard wing sections are effectively flying fuel tanks, each 20 m (65.6 ft) long, with a total wingspan of 52 m (170 ft). Included in the equipment in Seattle are five computerized tape laminating machines capable of producing parts up to 36.5 m (120 ft) long and 6 m (20 ft) wide from coordinates taken direct from production data. A channel laminator is used for very long reinforced plastics

5

9Fabricating Processes 4 7 9

Figure 5.93 Casting production line for filled TS polyester molding

Figure 5.94 A resin transfer molding (RTM) plant stiffeners and high-speed water-jet cutting systems and precise five-axis milling machines refine parts to microscopic tolerances. Also installed are the world's two largest autoclaves, 27.4 m (90 ft) long x 7.6 m (25 ft) in diameter. Another interesting operation, in addition to many worldwide is a fullyautomated RTM plant, for high consistency and reduced costs, is

4 8 0 Reinforced Plastics Handbook

producing at 20,000 parts/year at Sisteme Compositi SpA, Frosinone, Italy. Details have been provided in above section entitled Reinforced Resin Transfer Moldings, Automations.

FALLO Approach Conditions that are important in making plastic products the success it has worldwide are summarized in Figure 5.95. All designs, processes, and materials fit into the overall FALLO (Follow ALL Opportunities) approach flow chart that produces products meeting required performance and cost requirements. Designers and processors to produce qualified products at the lowest cost eliminating or significantly reducing troubleshooting fabricated products have used the basic concept of the FALLO approach. This approach makes one aware that many steps are involved to be successful, all of which must be coordinated and interrelated. It starts with the design that involves specifying the plastic and specifying the manufacturing process. The specific process (compression molding, resin transfer molding, injection molding, and so forth) is an important part of the overall scheme. The FALLO approach diagram consists of: Designing a product to meet performance and manufacturing requirements at the lowest cost; 2

Specifying the proper plastic material that performance requirements after being processed;

3

Specifying the complete equipment line by:

meets

product

(a)

designing the tool (die, mold) "around" the product,

(b)

putting the "proper performing" fabricating process "around" the tool,

(c)

setting up auxiliary equipment (up-stream to down-stream) to "match" the operation of the complete line,

(d) setting up the required "complete controls" (such as testing, quality control, troubleshooting, maintenance, data recording, etc.) to target in meeting "zero defects"; Purchasing and properly warehousing plastic materials and maintaining equipment. Using this type of approach leads to maximizing product's profitability. If processing is to be contracted, ensure that the proper equipment is

THE COMPLETE PROCESSING OPERATION ... THE FALLO APPROACH I

I, I-" I

I

Figure 5.95

I

I Individual CONTROLfor each operation, from software to hardware I

I SOFTWAREOPERATION I I-" I I I I PRODUCT I PERFORMANCE I REQUIREMENTS I based on market I requirements I I I use VALUE PRODUCT I ANALYSIS CONCEPT I approach to meet I performance to I cost requirements I I I Select I SELECT PLASTIC PROCESS I material I I I FALLO I Follow ALL Opportunities I I I

L.,

PRODUCT DEVELOPMENT

MANUFACTURING OPERATION Integrate all individual operations that produce parts

I

BASIC PROCESSINGMACHINE

SOFTWARE OPERATION I I i

I

I

AL

I I I I I I I

operator, conveyor, robot, etc. Secondary operation packaging, etc.

MOLDED PRODUCT ~ ! - ~ ready for I delivery I I I

Set up PREVENTATIVEMAINTENANCE

I I

I I I I I I I I I

Set up TESTING/QUALITYCONTROL- Characterize properties: mechanical, physical, chemical, thermal, etc. - - - ~ 1

I I

I Set up practical, useful TROUBLESHOOTINGGUIDE based ____~J on 'causes ~ remedies' of potential 'faults'

!

I

GOODMANUFACTURINGPRACTICE

FALLO approach includes going from material to fabricated product (courtesy of Plastics FALLO)

Immediately after the product is in production take the next important step. Reevaluate and target the product to be produced at a lower cost. Use the FALLOapproach by reexamining the parameters going from the product design through production. Examples of potential cost reductions include: (1) redesign product with thinner walls to reduce production cost, etc. (2) reduce cost by using less plastic, change to a more expensive plastic that reduces processing cost etc. (3) modify process control to reduce production costs, etc, and, (4] other parameters reviewed in this publication

IF YOU DO NOTTAKETHIS ACTION - someone else WILL TAKETHE ACTION

v I .v - I I I ._1 v I I I I I I I I I I I I I I I I I I I I I I I I I I

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482 Reinforced Plastics Handbook

available and used. This interrelationship is different from that of most other materials, where the designer is usually limited to using specific prefabricated forms that are bonded, welded, bent, and so on. Summary of Figure 5.95 is that acceptable products will be produced. It highlights the flow pattern to be successful and profitable. Recognize that this action provides meeting the phrase of first to market with a new product capture 80% of market share.

M a rkets/Prod u ets

Overview Throughout this book, different subjects are reviewed that pertain to reinforced plastic (RP) products. This chapter provides additional information on RP products and marketing aspects effecting RP products. The gradual growth of the total USA plastic [RP and URP (unreinforced plastic)] industry for over a century has been spectacular evolving into today's routine to sophisticated high performance products (parts). Examples of these products are in building and construction (34 wt%), transportation (33%), sports and appliances (14%), electrical and electronic (10%), and others (9%). Use is made of thermoplastic (TP) and thermoset (TS) plastic matrixes. Plastics data source, such as the Society of Plastics Industry's (SPI's) suite of economic studies and statistics, provide current, comprehensive data, and analysis of the domestic and international trade markets for USA plastic materials, processing, machinery, and moldmaking industries that follows the ups and downs of the overall local and worldwide economy (www.plasticsdatasource.org or tel. 800.541.0736). During the most recent economy downturn SPI reported plastics total USA industry shipments for year 2000 was $420.9 billion and 2002 was $393.2 billion. The year 2002 included 37% plastic products, 21% upstream impact products, 20% captive plastic products (products from activities such as auto assembly and milk bottling are not classified by the government or most economists as being part of the plastic industry), 11% plastic materials, 10% captive plastic products, and 1% molds for plastics fabrication. SPI also reports that the top ten plastics processing states for year 2002 were in billions of sales dollars: $13.8

4 8 4 Reinforced Plastics Handbook

California, $11.2 Ohio, $10.1 Texas, $9.8 Illinois, $9.4 Michigan, $8.3 Pennsylvania, $7.3 Indiana, $5.5 Wisconsin, $4.9 North Carolina, and $4.9 New Jersey. These totaled for 2002 at $143.9 compared to $151.6 during year 2000. During the latest economy downturn that started during 2001, unlike its usual behavior home building and new construction remained steady. USA industry suffers from a competitive disadvantage because USA manufacturers have relatively high tax rates and pay more for health care, according to a new study by the National Association of Manufacturers (NAM) and the Manufacturers Alliance (MA). The study determined that the USA industry generally is competitive against other developed countries, but it calls for changes to help combat a 22% premium that USA industry shoulders for things like benefits and litigation. Efforts by other industrialized nations to cut their corporate tax rates in the past five years have left the USA and its 40% rate the second highest, trailing only Japan. This report is the first comprehensive look at how USA manufacturing costs stack up with other countries in USA dollars per hour (year 2002): $29.77 Germany, 25.77 France, 24.30 USA, 23.14 UK, 22.67 South Korea, 22.46 Canada, 16.64 Japan, 12.85 Taiwan, 6.19 Mexico, and 3.50 China. Plastic products (includes RPs) is ranked as the 4th largest USA manufacturing industry with motor vehicles in 1st place, petroleum refining in 2ed place, and automotive parts in 3ed place. Plastic is followed by computers and their peripherals, meat products, drugs, aircraft and parts, industrial organic chemicals, blast furnace and basic steel products, beverages, communications equipment, commercial printing, fabricated structural metal products, grain mill products, and dairy products (in 16th place). At the end of the industry listings are plastic materials and synthetics in 24th place and ending in the 25th ranldng is the paper mills. Total plastics consumption yearly worldwide is estimated at 399.5 billion lb (200 million ton). In USA about 106.9 billion lb is consumed with about 90% are thermoplastics (TPs) and 10% thermoset (TS) plastics. USA and Europe consumption's are each about 27% of the world total with Japan, China, Australia, and the Pacific RIM countries accounting for 20%, central and South America 10%, India and Southwest Asia 8%, and Africa, Middle East, and rest of the world (ROW) 8% (Chapter 3). Of the total plastic industry, RPs consuming about 18 wt% or 19.2 billion lb. Of the RPs 18%, at least 82% (15.7 billion lb) represents injection molded products using different type fiber, powder (includes

6-Markets/Products 485 fibers with one end/milled fibers), and flake reinforcements. Fibers include glass, cotton, cellulosic sisal, flax, jute, polypropylene, polyethylene, and nylon with by far most being milled, short, and/or long glass fibers (Chapters 3 and 5). Remaining 3.5 billion lb represents products other than those IM. RP products have gone worldwide into the deep ocean waters, on land, and into the air including landing on the moon and in spacecraft. Major markets are aerospace, appliances/business machines, building/ construction, consumer, corrosion, electrical/electronic, marine, and transportation. Practically all markets worldwide use RPs. Examples of the thousands of products or parts include electrical and electronic devices, pipes/tubes, furniture, automobiles, boats, toys and games, recreations, sports, appliances, water filters, corrosion resistant containers, windmill blades, gas filters, liners, papers, missiles and rockets, farm equipment, USA postal service handling equipment, toilet and water conservation devices, bearings, gears, and so on with new developments always on the horizon. Very high performance RPs for over a half century has been required in specialty applications. As an example the first Delta IV Heavy Launch Vehicle was successfully rolled out and erected in preparation for its summer 2004 launch. The Delta IV is the newest and largest of Boeing's Delta family of expendable launch vehicles. The Delta IV's carbon fiber/epoxy sandwich structure, including interstages, heat shield, nose cone, and payload fairings is produced by Alliant Techsystems Inc., Edina, Minn., USA.

Buildings and Constructions This industry consumes at least 20 wt% of all plastics (includes RPs) produced. It is the second-largest consumer of plastics following packaging. This amount of plastics only represents about 5% of all materials that industry consumes. URPs and RPs will eventually significantly expand in this market. Its real growth will occur when plastic performance is understood by the building industry (meeting their specifications, etc.) and more important when the price is fight in order to compete with other materials. There are many applications of structural and nonstructural plastics being used in the building and construction industry worldwide. Plastic use continues to expand in homes. One application that has not received much consideration yet in USA is the Homeland Security Act's requirement for strengthened, blast-hardened critical structures, for which carbon fiber is, so far, the only qualified material, according to GHL Inc., USA (Figures 6.1-6.3).

O0 03 t'i} n,,

,,m, Ijl

,-r

O" 0 0~ - -

Figure 6.1

Schematic of different plastics in a house

6. Markets/Products 487

Figure 6,2 All-plastic GE house in Pittsfield, MA (courtesy of GE)

Figure 6.3 Carbon fiber reinforced plastic bridge (Herning, Denmark) components resulted in significant savings in maintenance costs

Engineering RP ideas using unconventional approaches to building houses have evolved since at least the 1940s from commercial and military groups. As an example during 1957 one of the first all RP house was the Monsanto House of the Future erected in Disneyland, CA, USA (Figures 6.4 and 6.5). The key structural components were four 16 ft (4.9 m) U-shaped cantilever (monocoque box girders) RP designs by MIT. Different plastics were used throughout the house including

488 Reinforced Plastics Handbook

different plastic sandwich panels. When this house was to be removed in 1977 to provide a different scene (a main attraction for two decades), it had suffered almost no change in deflection. It was estimated to have been subjected to winds, earthquakes, subjected to families using it to the equivalent of centuries based on all the people that passed through it, etc. Destruction by conventional techniques (wrecking ball, etc.) was impossible without first cutting sections, etc.

Figure 6.4 Monsanto house in Disneyland,CA, USA

The present and growing large market for plastics in building and construction is principally due to its suitability in different internal and external environments. The versatility of different plastics to exist in different environments permits the ability for plastics to be maintenance-free when compared to the more conventional and older materials such as wood. As the saying goes if wood did not have its excellent record of performances and costs for many centuries, based on present laws and regulations they could not be used. They burn, rot, etc. Regardless it would be ridiculous not to use wood. The different plastics inherently have superior properties such as high strength and stiffness, durability, insulation, cosmetics, etc. so eventually their use in building and construction will expand particularly as they become more economical.

6-Markets/Products 489

Figure 6,5 Schematic of Monsanto's cantilever type structure of House of the future

490 Reinforced Plastics Handbook Bathtubs The USA Commerce Department report on the tub-shower business. In 2001, the U.S. construction industry made wholesale shipments of approximately 4.5 million conventional bathtubs, 700,000 whirlpooltype bathtubs, one million shower stalls, and 250,000 hot tubs. RPs account for about two-thirds of the bathtubs and 80-90% of the other tub-shower components. The government does not identify whether units are consumed in new housing or remodeling but, knowing that 56% of new homes in 2001 had 2.5 or more bathrooms, leads one to some rough estimating that perhaps 20-30% of all tub-showers are used for aftermarket replacement and remodeling projects. RP predominantly used was glass fiber/TS polyester.

Walkways/Bridges/Fences Since the 1940s, RP simple to complex suspended and or partially to fully supported walkways, bridges, fences, and other construction products have been built. They have performed as required for many decades. Early work by the USA army engineers using these different products were built and put to use permitting moving soldiers to heavy military tanks. Included were RP sprayed on the ground as walkways to aircraft landing strips. As an example, a large RP truss structure has been designed and installed to support one end of an 850 m long floating walkway on a river in Brisbane, Australia. The truss was developed by the University of Southern Queensland's Fibre Composites Design and Development (FCDD) Centre of Excellence. It measures 18 m long and 2.5 m deep with a 1 m cutout in the middle to accommodate another part of the walkway. A number of horizontal, vertical, and diagonal glass fiber reinforced isophthalic pultruded profiles are held together with stainless steel pins to create the structure. At the joints, the pultruded members are reinforced locally using solid glass fiber RP inserts. A 0.5 mm thick epoxy coating painted on the entire structure provides extra protection against corrosion. The truss is partially submerged in salt water and is expected to be used by up to 20,000 pedestrians and cyclists per day. RPs was chosen over traditional materials to provide the necessary durability and corrosion resistance. The structure is said to cost about a third of an equivalent steel truss, with its low weight (5 tonnes) making construction and installation much easier than if metal had been used. Assembly took place at FCDD's facility in Toowoomba before the completed truss was transported by truck to the site 150 km away.

6

9Markets/Products 4 9 1

Once in position, the truss sits between 12 concrete pontoons, with the structures tied together with a number of 20 mm and 30 mm diameter stainless steel through-rods. (website: www.fcdd.com.au). Hardcore Composites' fabrication of wind fairings for the New York City Metropolitan Bridge and Tunnel Authority's Bronx-Whitestone Bridge earned The Dow Chemical Co's 2003 Americas Fabricator Excellence Awards (FEA). The RP wind fairings replaced 7400 ft (2.2 km) of heavy steel trusses. Hardcore used vacuum assisted resin transfer molding (VARTM) and Dow's Derakane 8084 epoxy vinyl ester resin to fabricate the fairings. The Derakane was chosen because it has the chemical resistance required to withstand the harsh conditions on top of the bridge, but it is also lightweight and two to three times as strong as other resins. This means that the wind fairings are very durable, offering a longer service life and, reducing long-term maintenance costs. Dow reports that to date this project represents the largest use of structural RPs in the world, requiring 890,000 lb (400 tonnes) of FRP to complete the project. RP fencing is considered better than metal. Prestige TM Series ornamental RP fencing is said to look like wrought iron fencing but is more durable and virtually maintenance-free. Prestige fence posts, rails, and pickets are manufactured from Saint-Gobain Vetrotex's Twintex | a 75 wt% glass fiber, 25% chemically coupled, heat- and light-stabilized polypropylene based concentrate. Prestige fencing is 60% stronger than aluminum, and at lower load stress levels it is slightly more flexible than aluminum, absorbing impacts better. At higher stress loads it becomes more rigid than aluminum, which means it can better withstand heavier impacts such as fallen tree limbs and the occasional climber. The RP also gives Prestige fencing a fade-resistant, matte finish. Roofs

The following example provides information on designing of plastic structural products to take static loads. It will be a structural problem common to a number of different structures to show how the different structural requirements will affect the choice designers have to make. The design problem will be a roof section that may be used for anything from a work shed, to a house, to a vehicle, or even to a simple weather shelter. The analysis begins with a definition of the function that a roof performs. A roof is the overhead product of a structure intended to

492 Reinforced Plastics Handbook

protect the occupants a n d / o r contents of the structure from the outside environment. It involves rain, snow, wind, sun, falling objects, hurricanes, and the other elements that make up the outside or surrounding environment. In order to perform this function the roof must be capable of supporting its own weight and the weight of snow or any other possible accumulations on the roof. It must be resistant to wind loads that are quite severe in some regions. The roof must also support loads imposed by people walking on it, usually for maintenance. In some instances the roof may double as a deck and the traffic may be constant. The roof must be able to shed water that falls on it, although it need not be waterproof in the sense of being a waterproof membrane structure. The roof surface is exposed to sun, wind and driven debris and must be resistant to erosion by the action of sunlight and the abrasive action of wind driven debris. In most cases the roof is insulated thermally to prevent heat loss in cold weather and heat input during warm weather. Obviously, not all roof requirements apply to all roof situations, but most of them do so you can set up your own requirements. The major load applied to a roof is the static load of the roof structure itself. Since roofs come in a wide variety of types, the self-load will depend on the basic roof design. The simplest is the corrugated RP panel structure. This type of structural element is widely used for roofs on industrial buildings to admit daylight, porch and patio roofs, shelter roofs such as those used at bus stops, and a variety of similar applications. Variations of this simple roof are used for roof sections on transportation vehicles such as buses and trains. Since this section is one of the easier ones on which to describe loading conditions, it will be used to illustrate the design procedure. Other roof sections such as the domes, arches, geodesics, and paraboloids involve complicated stress analysis and the results would not be particularly useful in a general analysis of a static structure. The corrugated materials are available in sheets which vary from 4 ft x 8 ft to as large as 10 ft x 20 ft. A typical material is 0.100 in. thick with 2 in. corrugations, and a corrugation depth of 1 in. The RP material from which they are made is glass fiber mat as the reinforcement and weather-resistant TS polyester plastic. In general, the sheet material is nailed or screwed to wooden supports (could be pultruded RP supports if the price was fight) at proper intervals. In some cases the roof section is made in one piece with spars of TS polyester-glass material molded into the product to provide the stiffening support needed. In this case the only requirement for installation involves anchoring the edge of the section to the structure.

6. Markets/Products 493 This type of design problem is somewhat different from others in that the unit is made from standardized sections that have specific physical properties and are available in only a limited number of thicknesses and configurations. The design problem now consists of trying the available materials in the structure with the supports that can be used and then determining if the material will perform. The self load is easily determined from the weight of the materials. The snow load is a design value available from experience obtained in the area where the structure is to be used. Similarly, the maximum wind load and people load can be determined from experience factors that are generally known. The problem is worked out using several different sheet types and different support spacings in an environment that would be typical of a city in the Midwestern part of the USA. The indicated solution is that the material selected will take the required loads without severe sagging for a 15 year period with no danger that the structure will collapse due to excessive stress on the material. If a standard material had not been suitable, it would have been possible to use one specifically molded for the application, or by the use of several layers of the material. One typical way in which excessive loading for a single section is handled is to bond two layers of the corrugated panel together with the corrugations crossed. This results in a very stiff section capable of substantially greater weight bearing than a single sheet and it will meet the necessary requirements. The double sheet material also provides significant thermal insulation because of the trapped air space between the sheets particularly if they are edged sealed. The roof section was designed to meet the static load requirements. However, it is necessary to consider transient loads such as people walking on the roof and fluctuating wind loads. The localized loads represented by people walldng on the roof can be solved by assuming concentrated loads at various locations and by doing a short time solution to the bending problem and the extreme fiber stress condition. The local bearing loads and the localized shear should also be examined since they may cause possible local damage to the structure. Stresses from varying winds are general alternating stress loads and occur over wide areas of the structure. When the wind changes direction, the stress frequently changes direction, and the tendency is for the roof to lift away from the structure. The main point of stress caused by the wind is at the anchorage points of the roof to the rest of the structure. They should be designed to take lifting forces as well as bearing forces; the lower the angle of roof, the less wind lifting force. Proper anchorage of the support structure to the ground is also essential. Local fire and building codes impose additional restrictions.

494 Reinforced Plastics Handbook

A large area of plastics, such as described here, has a substantial change in dimension with temperature. Surprisingly, very few of the traditional building materials, including wood, have significant expansion under normal temperature shifts. The RP materials generally are not a problem since they have low thermal coefficients of expansion and the corrugated shape tends to flex and accommodate the changes caused by heating and cooling. In the case of materials such as vinyl siding, the expansion factor becomes significant and is an important consideration in the fastening system. The effects of the environment on the performance of the material must be considered. Using the initial physical properties of the materials, the structure is sound. Exposure to weather, which includes water and sunlight, has a significant effect on the physical properties of the materials and this must be taken into account in the design. This type data is available from the reliable panel producers. Let us assume that there is a 50% or more drop in the physical properties in 5 years; actually far less. This can be due to surface damage and to changes in the bulk of the material. In general, this type of loss of physical properties levels off to a low rate of deterioration in suitable materials so that any potential failure can be anticipated. This loss of properties can be compensated for by increasing the strength requirements by a suitable factor of safety, probably about three in this case, and by using a protective coating on the sheet material to minimize the effects of weathering. The preferred type of coating would be a fluorocarbon material that has the best resistance to sunlight and other weathering factors of all of the plastics. If this type of surfacing is used, the material will retain its surface integrity for at least 20 years. The example of the roof structure represents the simplest type of problem in static loading in that the loads are clearly long term and well defined. Creep effects can be easily predicted and the structure can be designed with a sufficiently large safety factor to avoid the probability of failure (Chapter 7). Infrastructures

RPs continue their use during the past half century in civil infrastructure such as in highway structures within the USA and worldwide primarily due to their high strength and stiffness to weight ratios and their design flexibility for specific structural characteristics. In addition, the serviceability and functional service life of an RP structure such as a bridge may be greater than those built using conventional structural materials. Investigators continue to develop its environmental durability data. Freeze-thaw durability is one such environmental condition.

6. Markets/Products 495 A work targeted specifically to civil infrastructure application has reported mechanical data on freeze-thaw tests conducted on isophthalic polyester and vinyl ester pultruded/glass fiber RPs (Chapter 3). Specimens were aged in accordance with ASTM C666 (namely, 40F to OF followed by a hold at OF and a ramp up to 40F followed by a hold) while submerged in 2% sodium chloride and water. Specimens were removed after every 50 cycles and tested in ASTM 3-point flexure mode. The results clearly indicated a reduction in flexure strength and modulus after 300 cycles. One of the first reports highlighted the importance of cracks in the matrix and fiber-matrix interface as being the cause of the damage in RP materials. When these cracks form beyond a certain critical size and density, they coalesce to form macroscopic matrix cracks which tends to increase the diffusion of water into the system. Water can then condense within these cracks resulting in crack propagation as well the formation of micro and macro level ply delamination during the expansion of water undergoing a liquid-solid phase transition. In Kevlar fabric laminates subjected to two-hour temperature cycles f r o m - 2 0 F to 125F, ultimate tensile strength of the laminate was found to decrease by 23% after 360 cycles and by 63% after 1170 cycles. When differential scanning calorimetry (DSC) was used to identify the nature and presence of freezable water for each constituent material within an E-glass/vinyl ester RP, i.e., matrix, and interphase (via an assembled RP). Thawing heat flow measurements taken for a single cycle (-150C to +50C, 5 C / m i n ) on saturated, NEAT (Chapter 1), unreinforced vinyl ester resin samples indicated no thawing endotherm and thus the absence of freezable water. This was attributed to the fact that water would reside in the free volume of the resin. Since this free volume size is on the order of about 6 to 20 A., it indicates that these voids will be thermodynamically too small for water to freeze. Heat flow measurements taken for an E-glass/vinyl ester RP with the same cycle parameters clearly indicated a melt endotherm a t - 6 . 8 C thus indicating the presence of small voids at the interphase region within the RP and potential susceptibility t o freeze-thaw degradation. Cyclic DSC cycling (-18C to +4C, 5C/rain) of an E-glass/vinyl ester RP displayed a shift up in the thaw endotherm as cycling progressed, indicative of freeze-thaw damage via increased void size. It seems unlikely that water can freeze in limited void system of a NEAT plastic (Chapter 3), but the crack dimensions in an RP system appear are large enough to facilitate the freezability of water. The following review concerns both saturated and dry fiber RP samples that will be placed in an accelerated freeze-thaw environment and

496 Reinforced Plastics Handbook

tested for mechanical property degradation, changes in crack density, and moisture uptake at specified intervals to assess damage. A group of saturated controls will be held at a constant temperature above freezing and will be tested in the same manner as the freeze-thaw samples. All samples are pultruded glass reinforced cross-ply ( 0 / 9 0 ) laminates with plastic matrix materials.

Pultruded Materials All materials were pultruded using an open resin impregnation bath (Chapter 5). During pultrusion both pull force and die temperature were monitored at all times and allowed to reach steady state before any material was considered usable. Three different matrix resins were used in this study: a toughened vinyl ester, an untoughened vinyl ester, and an epoxy. Two different fiber layups were used designated by the letters "L" and "P". The vinyl ester laminates were pultruded with the "L" lay-up while the epoxy laminate employed the "P" lay-up in order to prevent scaling problems in the epoxy resin system. From the batch of pultruded material, 510 samples were cut to 25.4 mm by 177.8 mm (1 in. by 7 in.) from the larger as-received panels using an abrasive wet saw. Special care was taken to align all saw cuts with the principal material directions with the long direction corresponding to pull direction. All laminates were nominally 4 mm (0.160 in.) thick. After the cutting operation, the edges of each sample were wet sanded smooth with 400-grit abrasive paper and blown dry with compressed air. All samples destined for saturation were edge coated with an oven cured two-part epoxy to prevent moisture infusion through cut edges.

Tests and Analyses Ultimate tensile strength, stiffness, and strain-to-failure were determined quasi-statically for each class of as-received material in accordance with ASTM D 3039 Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials using a deflection rate of 2.5 ram/rain (0.10 in./min). A total of thirty samples were tested, ten of each material type. In addition, two samples of each material were set aside for crack density analysis using x-ray and optical microscopy techniques. A total of 324 samples were fully saturated in a 65C (149F) water bath with moisture uptake measured throughout the saturation process. Weight measurements were taken hourly on the first day the samples were placed in the saturation tank, every three hours on the second day, every four hours the third day, every six hours the fourth day, and once everyday thereafter. The samples reached saturation within 45 days.

6

9Markets/Products

The freeze-thaw conditioning parameters chosen for this study were based on ASTM C 666 Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing. This test protocol calls for a ramp down from 4.4C (40F) t o - 1 7 . 8 C (OF) followed by a hold at -17.8C (OF), a ramp up to 4.4C (40F) and a hold a t - 1 7 . 8 C (OF). There may be a minimum of 4.8 and a maximum of 12 conditioning cycles per day with 75% of the cycle time set aside for freezing and 25% for thawing. Two high performance cascading refrigeration freeze-thaw conditioning chambers were used to achieve a ten cycle per day rate. A series of trays were fabricated to hold each sample in accordance with ASTM C 666, namely to surround the samples with between 0.8 mm ( 1 / 3 2 in.) to 3.2 mm ( 1 / 8 in.) of water. Additional design goals for the trays were to minimize the volume of water and maximize convective heat transfer with the air inside chamber. Each tray can hold eight samples and every other slot were machined all the way through to allow airflow vertically through the trays. A second type of tray were also fabricated to allow the application of four point bending loads to each sample capable of causing 0.55% strain at the centerline on the surface of the tension face. This strain level was chosen because it is beyond the knee in the stress-strain curve for each material in this study and it likely opens up cracks that might be large enough to allow additional freezing to take place. This tray can also hold up to eight samples. Three levels of freeze-thaw exposure were included in this study: 100, 300, and 500 cycles. A set of control samples were also placed in a constant 4.4C (40F) bath for the duration of each freeze-thaw exposure level. Similar to the as-received testing regime, ultimate tensile strength, stiffness, and strain-to-failure were determined quasi-statically in accordance with ASTM D 3039 for each class of material after saturation. A total of thirty samples were tested, ten of each material type. In addition, two samples of each material were set aside for crack density analysis using x-ray and optical microscopy techniques. Similar mechanical testing and crack density analyses were performed at each of the three specified freeze-thaw conditioning levels for both unloaded and loaded samples in each of the general conditioning categories, i.e., saturated freeze-thaw (144 samples), saturated constant temperature (144 samples), and dry freeze-thaw (144 samples).

Crack Density Analyses Crack density was assessed using non-destructive acousto-ultrasonic (AU) techniques with confirmation by optical microscopy. AU is an

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498 Reinforced Plastics Handbook

ultrasonic NDT technique useful for quantifying small, distributed changes not easily detected with traditional ultrasonic techniques. It returns results related to the ability of the interrogated material to transfer mechanical energy. In this setup, the transducers are spaced in a manner (typically, far apart) so that there is no direct or minimally reflected energy transmission between them and the primary transmission is by plate wave propagation. AU results are calculated from the energy spectral distribution of the AU signal by moment analysis. The most useful AU parameters tend to be the area under the stress-strain curve and the centroidal frequency (ratio of the first and zero moments). The area is directly related to the amount of energy transfer along the specimen. Shifts in the centroidal frequency also indicate changes in the materials ability to propagate particular modes. Typically, the spectral content of the AU signal has several relatively discrete frequency peaks with a few dominant ones. Each peak corresponds to a different mode or order of plate wave propagation. The modes were typically categorized as symmetric (extensional) and anti-symmetric (flexural). The order of a particular mode indicated the complexity of that type of deformation. Since each peak represents energy propagating with a different type of deformation, it possibly can be sensitive to different types of degradation. AU samples were taken from the general sample population and have already been base-lined for as-received and post-saturation conditions. For optical microscopy, representative sections of material were cut, potted, and polished for each post-conditioning group and examined using an inverted optical microscope. Though this initial study some data was reported. Strength for the toughened vinyl ester was 389 MPa in the as-received condition vs. 237 MPa for the post-saturation condition. Likewise, for the untoughened vinyl ester, strengths were 432 MPa vs. 240 MPa. For the epoxy, strengths were 424 MPa versus 237 MPa. Stiffness for the toughened vinyl ester was 19.9 GPa in the as-received state v. 22.1GPa for the post-saturation condition. Stiffness for the untoughened vinyl ester was 23.9 GPa for both conditions. For the epoxy, stiffness was 26.2 GPa versus 25.6 GPa. Strain-to-failure for the toughened vinyl ester was 2.49% in the asreceived condition versus 1.26% for the post-saturation condition. For the untoughened vinyl ester, strain-to-failure was 2.58% vs. 1.36% and for the epoxy, 2.29% vs. 1.20%. Strength and strain-to-failure were approximately 50% lower after saturation for all three materials. Stiffness effectively remained unchanged.

6. Markets/Products 499 The moisture content at saturation was 0.70% for the toughened vinyl ester samples, 0.74% for the untoughened vinyl ester samples, and 0.84% for the epoxy samples. Because of this, the moisture aging experiment had to be terminated after 45 days at which point the heaters were turned off and the tank was allowed to equilibrate to room temperature. Conclusions It is virtually impossible to freeze water in a highly crosslinked amorphous plastic. This is in part due to geometric space constraints in addition to hydrogen bonding that further impedes the process. In the RP system however, the crack dimensions are large enough to facilitate the freezability of water. It is believe that this is the mechanism of freezing and the associated volume increase during the transition leads to the propagation of cracks and the accumulation of damage.

Plastics Lumber Plastic lumber is recycled plastics processed such as commingled plastic, polyethylene plastic, and polypropylene plastic. To improve their performances different developments have been used such as specialty additives (lubricants, deoxidizers, etc.). An example is by adding as low as 10 wt% of short glass fiber to these recycled plastics can double their strength. Other fibers used include hemp, flax, and sisal. They are principally extruded; other processes are used such as injection and compression molding, to produce products competitive to wood lumber on land and in the water. Compression molding allows for a deep-molded grain and a much more dense board. The density also helps the product resist moisture absorption and improves weatherability. Mixed recycled plastic lumber bridge decks, boat docks, doors, floors, furniture, windows, fences, pallets, etc. are product examples in service. Plastic lumber would be maintenance-free for at least half a century, as opposed to 15 years for treated wood and 5 years for untreated wood. Extensive use is made in applying plastics in wood to improve their structural and decorative properties. Different forms/profiles of plastic/wood are used. Extruded profiles can contain at least 70 wt%, some up to 90%, wood content and produce wood-like appearance. Proper drying of the wood is required since it is hygroscopic otherwise burning can occur and properties are reduced. These products compete in different markets particularly the building and construction market and where water is located like a boating dock. It is entering the $8 billion USA residential siding market that is now at least half vinyl.

500 Reinforced Plastics Handbook

There are compregs. They are compressed plastic impregnated wood usually referring to wood assembly veneer layers and other wood-plastic impregnated combinations. There is also compressed wood that is also called densified wood or laminated wood. It is wood that has been subjected to high compression pressure to increase its density with plastics. Laminated wood is a high-pressure bonded wood product composed of layers of wood with plastic such as phenolic as the laminating agent. Compreg or impregnated wood-plastic was produced in the early part of the 20th century after phenolic was developed (1909). Plastic loaded wood (impregnated) resulted in significant increased performance for the wood such as higher mechanical properties, hardness, etc. In addition, gains with longer life, rot resistance, etc. Originally most of the plastics used were phenolics. By the 1950s other plastics were used that includes acrylic and vinyls. For certain applications vinyl polymerization was an improvement over phenolic condensation polymerization that would leave by-products such as water that had to be removed. Dry wood is used with the impregnating of the plastics after the wood is evacuated of air using a vacuum. The wood is put into a bath of plastic solution. The soaking period, like the evacuation period, depends on the type and structure of wood. Curing of plastics is usually by a radiation rather than regular polymerization reactions. Compressed wood is also called densified wood or laminated wood. It is wood that has been subjected to high compression pressure to increase its density with or without plastics. It is usually supplied in the form of a laminate in which plastics have been incorporated by drying the wood and using a vacuum. Laminated wood is a high-pressure bonded wood product composed of layers of wood with plastic such as phenolic as the laminating agent. There are wood composition boards that refer to a product that is usually made by reducing wood to small particles and re-forming into a rigid board. Bonding is by adhesion developed from the natural adhesive action of the wood substance and/or through addition of various binders such as different plastics (phenolic, etc.) to meet different structural and environment performance requirements. Plastic lumber scored a major commercial breakthrough during 1999 with Home Depot Inc. to stock products from USA Plastic Lumber Co., Boca Raton, F1 (USA's largest maker of recycled plastic lumber made mostly from HDPE milk jugs and shampoo bottles). Home Depot is the world's largest home-improvement retail chain. Also aboard in USA stocking Boca's lumber were the nation's second (Loewes) and third (Menard) largest home-improvement retailers

6

Markets/Products 9 501

Rising consumer awareness of alternative decking materials is translating into manufacturing expansions as highlighted at the halls of the Las Vegas Convention Center were decked out with boards made of 100% plastic or RP composites during the International Builders' Show, held January 2004. Product acceptance is being pushed along by factors including the Environmental Protection Agency's phase-out of arsenic-treated lumber, and the desire of consumers to make the most of outdoor living space. This action of using plastic lumber all started decades ago with vinyl fencing, taking business away from wood fencing. Following this action, decking came aboard. The Freedonia Group Inc., Cleveland, OH, reported that in USA during year 2002 plastic composite decking represented 9% with 91% wood of a total 4,873 million board feet. They expect that during year 2007 plastic composite decking will represent 17% with 83% wood of a total 5,460 million board feet. Pallets

In the industrialized countries there are almost more pallets then people. USA has about 1.6 billion with Europe at least 0.5 billion. Virtually all are wood. Since at least the 1950s various organizations have fabricated URP and RP pallets. Major problem has been to produces pallets meeting performances at costs competitive to wood. Gradually slight market penetration has occurred particularly where special requirements exist in favor of plastics with its superior performances and cost advantages. Underwriter's Laboratories (UL) during 2001 developed a standard for pallets. The new UL 2335 was created to classify plastic pallets to meet requirements of the recently revised National Fire Protection Assoc. standard NFPA 13. That change allows plastic pallets to be treated like wood pallets if test data indicate that the burning characteristics of the plastic pallets are equal or better than wood (UL telephone 847-6641508). Heat Resistant Column

RL Industries won a Dow FEA (Fabricator Excellence Awards) award, for the fabrication of a high temperature, dual-laminate FRP chemical absorber column for Rubicon Inc in Geismar, Louisiana, USA. The column needed to work in temperatures greater than 250F (120C). RL Industries fabricated the column using a combination of hand lay-up and filament winding with Dow's Derakane 470HT-400 epoxy vinyl

502 Reinforced Plastics Handbook

ester resin, which combines maximum chemical resistance with high temperature performance.

Transportation URP and RP play a very important role in the vital areas of transportation technology by providing special design considerations, process freedom, novel opportunities, economy, aesthetics, durability, corrosion resistance, lightweight, fuel savings, recyclability, safety, and so on. As an example designs include lightweight and low cost principally injection molded TP car body to totally eliminate metal structure to support the body panels including combining component parts (Figure 6.6). There is the recently designed Human Transporter by Segway LLC, Manchester, NH with its exterior PC/PBT film fimsh, 20 wt% glass fiber/PPE/PA RP molded wheels, PC/ABS RP molded control shaft, etc. Skydivers with their RP glass or carbon fiber helmets now use non-circular high strength nylon fiber parachutes that include harness and hardware.

Figure 6.6 Graphite fiber RP automobile (courtesy of Ford Co.) Practically all types of plastics are used (literally from seats to the outside shells), and in many cases required in all methods of transportation; such as, automotive, railroad, buses, trucks, trailers, boats, submarines,

6. Markets/Products 503 aircraft and space vehicles. A major reason for its use is resistance to corrosion. Other reasons pertain to many different inherent characteristics that range from attractiveness to durability, mechanical strength or toughness to quick mass production techniques, light-weight, etc. In USA RP consumption in automobiles represents the largest market. It accounts for 32 wt% of the total demand.

Design Concepts URPs and RPs are extensively used in all types of transportation vehicles providing aesthetics to structural performances. To assure the structural integrity/durability and cost effectiveness of RP structural components for vehicles requires careful consideration of numerous factors during the design. These factors generally include: 1 service load environment (loads, temperatures, moisture time); 2 types of RPs (conventional, advanced, hybrid); 3 constituent materials (glass fibers, graphite fibers, aramid fibers, epoxies, polyesters, etc.); 4 environment effects on material properties (temperature, moisture. fatigue, creep, strain rate); 5 fabrication process; 6 quality control; 7 attachments; 8 structural analysis methods to validate the design concept with respect to previously established design criteria; 9 unique test methods to characterize the RP selected; 10 simulated and full component testing to verify that the component has been fabricated as designed; and 11 attendant costs of ad these factors. RPs takes advantage of the fibers directional properties. They have evolved as a logical sequel to conventional RPs particular since at least the 1940s and to intraply hybrids, lntraply hybrid RPs have unique features that can be used to meet diverse and competing design requirements in a more cost-effective way than either advanced or conventional RPs. Some of the specific advantages of intraply hybrids over others are balanced strength and stiffness, balanced bending and membrane mechanical properties, balanced thermal distortion stability, reduced weight a n d / or cost, improved fatigue resistance, reduced notch sensitivity, improved fracture toughness a n d / o r crack-arresting properties, and improved impact resistance. By using intraply hybrids, it is possible to obtain a

504 Reinforced Plastics Handbook

viable compromise between mechanical properties and cost to meet specified design requirements. Structural mechanics analyses arc used to determined design variables such as displacements, forces, vibrations, buckling loads, and dynamic responses, including application of corresponding special areas of structural mechanics for simple structural elements. General purpose finite element programs such as NASTRAN arc used for the structural analysis of complex structural shapes, large structures made from simple structural elements, And structural parts made from combinations of simple elements such as bars, rods and plates. Plastic composite mechanics in conjunction with structural mechanics can be used to derive explicit equations for the structural response of simple structural elements. These explicit expressions can then be used to perform parametric studies (sensitivity analyses) to assess the influence of the hybridization ratio on structural response. For example the structural response (behavior variables) equations for maximum deflection, buckling load and frequency of a simply supported beam made from intraply hybrids are summarized in Figure 6.7 Flexural modulus is used to dcterminc the maximum deflection, buckling load, and frequency of a simple supported beam made from intraply hybrids.

P

L_ I-

PCR"~ ~

_1 -T-

-I

-'- --"~-~~'= "~"" PCR i-

-1

4,EFI 4, pc, § Vsc( .%1

PCR" y "

~'

+,

/.1)

Un'lmr)2~. 2~112 +V ~SC ~] 112 + VSC(P~c Figure 6.7 Loadsrelatedto flexuralmodulus The notation in these and further equations are as follows: a~, a2

B'cl,k B'c2, k

Correlation coefficients for longitudinal compressive stength. Buckling limit (buckling behaviour constraint) due to loading condition k. Strength limit (strength behaviour constraint) due to loading condition k.

6-Markets/Products 505 B'c3, k

Interply delamination limit (delamination constraint) due to loading condition k. Flexural modulus. EF Ef11, Ef22 Longitudinal and transverse fiber moduli Emil, Era22 In situ matrix longitudinal and transverse moduli. Modulus primary composite. Epc Modulus secondary composite. Esc Fiber shear modulus. Gf12 Matrix shear modulus. em12 Hj Matrix interply layer effect. / Moment of inertia. Correlation coefficients in the combined-stress failure criterion; Ke12~13 cz, [3 = Tor C denoting stress direction. Fibre volume ratio. Void volume ratio. K-- I, 2, 3, denotes loading condition index. k Length. f Number of plies. N Inplane loads - x and y directions corresponding to k. NxkNyk P Load. Buckling load. Per Buckling load of reference composite. Pcro Fiber tensile strength. 5# Strength primary composite. Strength secondary composite. Volume fraction secondary composite. Panel cost units per unit area. W ,&#" Correlation coefficients in composite micromechanics to predict ply elastic behaviour. Interply delamination factor. ~del Displacement. 6 Displacement of reference composite. 60 ~moc, S, T In situ allowable matrix strain for compression, shear and tension. Ply angle measured from x-axis. 0 Fiber Poisson's ratio, numerical subscripts denote direction. 13f Matrix Poisson's ratio, numerical subscripts denote direction. I)m Frequency of the nth vibration mode. CO~] Frequency of the nth vibration mode of the reference composite. COqo

The equations are first expressed in terms of Ef, the equivalent flexural modulus, and then in terms of the moduli of the constituent composites (Epc and Esc) and the secondary composite volume ratio (Vsc). These equations were used to generate the parametric nondimensional plots shown in Figures 6.8-6.10. The nondimensionalized structural response is plotted versus the hybridizing ratio Vsc for four different intraply hybrid systems. These

506 Reinforced Plastics Handbook 4 --

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6-Markets/Products 507 figures show that small amounts of secondary composite (V~c<0.2) have negligible effect on the structural response. However, small amounts of primary composite (Vsc >0.8) have a substantial effect on the structural response. A parametric plot of Izod-type, impact energy density is illustrated in Figure 6.11. This parametric plot shows also negligible effects for small hybridizing ratios (V~c <0.2) and substantial effects for hybridizing ratios (Vsc >0.2).

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The parametric curves in Figures 6.8 to 6.11 can be used individually to select hybridization ratios to satisfy a particular design requirement or they may be used jointly to satisfy two or more design requirements simultaneously, for example, frequency and impact resistance. Comparable plots can be generated for other structural components, such as plates or shells. Also plots can be developed for other behavior variables (local deformation, stress concentration, and stress intensity factors) and/or other design variables, (different composite systems).This procedure can be formalized and embedded within a structural synthesis capability to permit optimum designs of intraply hybrid composites based on constituent fibers and matrices. Low-cost, stiff, lightweight structural panels can be made by embedding strips of advanced unidirectional composite (UDC) in selected locations in inexpensive random composites. For example, advanced composite strips from high modulus graphite/resin, intermediate graphite modulus/resin, and Keviar-49 DuPont resin can be embedded in planar random E-glass/resin composite. Schematics showing two possible locations of advanced UDC strips in a random composite are shown in Figure 6.12 to illustrate the concept. It is important to note that the embedded

508 Reinforced Plastics Handbook

strips do not increase either the thickness or the weight of the composite. However, the strips increase the cost.

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It is important that the amount, type and location of the strip reinforcement be used judiciously. The determination of all of these is part of the design and analysis procedures. These procedures would require RP mechanics and advanced analyses methods such as finite element. The reason is that these components are designed to meet several adverse design requirements simultaneously. Henceforth, planar random RP with advanced composite strips will be called strip hybrids. Here, the discussion is limited to some design guidelines inferred from several structural responses obtained by using finite clement structural analysis. Structural responses of panel's structural components can be used to provide design guidelines for sizing and designing strip hybrids for aircraft engine nacelle, windmill blades and auto body applications. Several examples are described below to illustrate the procedure. The displacement and base material stress of the strip hybrids for the concentrated load, the buckling load, and the lowest natural frequency are plotted versus reinforcing strip modulus in Figure 6.13. As can be seen the displacement and stress and the lowest natural frequency vary nonlinearly with reinforcing strip modulus while the buckling load varies linearly. These figures can be used to select reinforcing strip moduli for sizing strip hybrids to meet several specific design requirements. These figures are restricted to square fixed-end panels with 20% strip reinforcement by volume. For designing more general panels, suitable graphical data has to be generated. The maximum vibratory stress in the base material of the strip hybrids due to periodic excitations with three different frequencies is plotted versus reinforcing strip modulus in Figure 6.14. The maximum vibratory stress in the base material varies nonlinearly and decreases

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rapidly with reinforcing strip modulus to about 103 GPa (15 x 106 psi). It decreases mildly beyond this modulus. The significant point here is that the modulus of the reinforcing strips should be about 103 GPa (18 x 1 0 6 psi) to minimize vibratory stresses (since they may cause fatigue failures) for the strip hybrids considered. For more general strip hybrids, graphical data with different percentage reinforcement and different boundary conditions are required.

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! 35

509

510 Reinforced Plastics Handbook

The maximum dynamic stress in the base material of the strip hybrids due to an impulsive load is plotted in Figure 6.15 vs. reinforcing strip modulus for two cases: (1) undamped and (2) with 0.009% of critical damping. The points to be noted from this figure arc: (a) the dynamic displacement varies nonlincarly with reinforcing strip modulus and (b) the damping is much more effective in strip hybrids with reinforcing strip moduli less than 103 GPa (15 x 106 psi). Corresponding displacements arc shown in Figure 6.16. The behavior of the dynamic displacements is similar to that of the stress as would be expected.

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6

9Markets/Products

The previous discussion and the conclusions derived there from were based on panels of equal thickness. Structural responses for panels with different thicknesses can be obtained from the corresponding responses in Figure 6.15 as follows (let t = panel thickness): The displacement due to a concentrated static load varies inversely with t 3 and the stress varies inversely with t 2. 2

The buckling load varies directly with t 3.

3

The natural vibration frequencies vary directly with t.

No simple relationships exist for scaling the displacement and stress due to periodic excitation or impulsive loading. Also, all of the above responses vary inversely with the square of the panel edge dimension. Responses for square panels with different edge dimensions but with all edges fixed can be scaled from the corresponding curve in Figure 6.13. The significance of the scaling discussed above is that the curves in Figure 6.13 can be used directly to size square strip hybrids for preliminary design purposes. The effects of a multitude of parameters, inherent in composites, on the structural response a n d / o r performance of composite structures, a n d / or structural components are difficult to assess in general. These parameters include several fiber properties (transverse and shear moduli), in situ matrix properties, empirical or correlation factors used in the micromechanical, equations, stress allowables (strengths), processing variables, and perturbations of applied loading conditions. The difficulty in assessing the effects of these parameters on composite structural response arises from the fact that each parameter cannot be isolated and its effects measured independently of the others. Of course, the effects of single loading conditions can be measured independently. However, small perturbations of several sets of combined design loading conditions are not easily assessed by measurement. An alternate approach to assess the effects of this multitude of parameters is the use of optimum design (structural synthesis) concepts and procedures. In this approach the design of a composite structure is cast as a mathematical programming problem. The weight or cost of the structure is the objective (merit) function that is minimized subject to a given set of conditions. These conditions may include loading conditions, design variables that are allowed to vary during the design (such as fiber type, ply angle and number of plies), constraints on response (behavior) variables (such as allowable stress, displacements, buckling loads, frequencies, etc.) and variables that are assumed to remain constant (preassigned parameters) during the design.

51 1

512 Reinforced Plastics Handbook

The preassigned parameters may include fiber volume ratio, void ratio, transverse and shear fiber properties, in situ matrix properties, empirical or correlation factors, structure size and design loads. Once the optimum design for a given structural component has been obtained, the effects of the various preassigned design parameters on the optimum design are determined using sensitivity analyses. Each parameter is perturbed about its preassigned value and the structural component is re-optimized. Any changes in the optimum design are a direct measure of the effects of the parameter being perturbed. This provides a formal approach to quantitatively assess the effects of the numerous parameters mentioned previously on the optimum design of a structural component and to identify which of the parameters studied have significant effects on the optimum design of the structural component of interest. The sensitivity analysis results to be described subsequently were obtained using the angle plied composite panel and loading conditions as shown in Figure 6.17. ,/

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Sensitivity analyses are carried out to answer, for example, the following questions: What is the influence of the preassigned filament elastic properties on the composite optimum design? What is the influence of the various empirical factors/correlation coefficients on the composite optimum design? Which of the preassigned parameters should be treated with care or as design variables for the multilayered-filamentary composite? What is the influence of applied load perturbations on the composite optimum design?

6

9Markets/Products 5 1 3

The load system for the standard case consisted of three distinct load conditions as specified in Figure 6.17. The panel used is 20 in. x 16 in. made from an [(+0)n]s. angle plied laminate. The influence of the various preassigned parameters and the applied loads on optimum designs are assessed by sensitivity analyses. The sensitivity analyses consist of perturbing the preassigned parameters individually by some fixed percentage of that value which was used in a reference (standard) case. The results obtained were compared to the standard case for comparison and assessment of their effects. Introductory approaches have been described to formally evaluate design concepts for select structural components made from composites including intraply hybrid composites and strip hybrids. These approaches consist of structural analysis methods coupled with composite micromechanics, finite element analysis in conjunction with composite mechanics, and sensitivity analyses using structural optimization. Specific cases described include: Hybridizing ratio effects on the structural response (displacement, buckling, periodic excitation and impact) of a simply supported beam made from intraply hybrid composite. Strip modulus effects on the structural response of a panel made from strip hybrid composite and subjected to static and dynamic loading conditions. Various constituent material properties, fabrication processes and loading conditions effects on the optimum design of a panel subject to three different sets of biaxial in-plane loading conditions. Automobiles

RPs continue to make impressive inroads in automobiles. General Motors Corp., Detroit, MI via Plastics News (Feb. 23, 2004) compared the materials used per vehicle in North America during 1977 and 2003. Weight percentage was ferrous at 71.4 (1977) and 52.6 (2003), h i g h / medium-strength steel at 3.4 and 16.3, aluminum at 2.6 and 8.3, plastics and reinforced plastics at 4.6 and 7.6, and others at 18 and 20.2. The pounds per vehicle was high/medium-strength steel at about 130 (1977) and 375 (2003), aluminum at 175 and 250, plastics and reinforced plastics at 100 and 275. Intake manifolds, camshafts, and engine blocks are just a few such parts under development for tomorrow's cars. The plastic auto engine has been a reality since the debut of the Polimotor in 1980, with its subsequent success as a power plant in racing cars.

514 Reinforced Plastics Handbook

Both RP strength and appearance qualities continue to be new designs in the latest models. The Smart Roadster roof module has a glossy, pigmented surfacing film backed up with long fiber polyurethane RP in an innovative example of in-mold film decorating. In a BMW underbody closure compression molded glass mat thermoplastic (GMT) material made from a blend of chopped glass and polypropylene fibers was used. A VW Golf front-end carrier demonstrated the commercial viability of in-line compounding long glass polypropylene in a twinscrew extruder piggybacked on an injection machine. Glass filled/phenolic RPs, namely SMCs and BMCs was used in the Powertrain category. Also aboard were a carbon-fiber Corvette hood and Nissan driveshaft. There are body interior parts that did nothing to improve appearance, strength, or weight. Rather, it was the fulfillment of an engineer's dream. A material substitution cut costs 43% without any changes to product design, tooling, or assembly methods. RP components continue to find more use in the OEM and replacement field. They include such items as primary structural supports, fenders, hoods, etc. Most of the RP used is SMC (Chapter 4). The continued development of improved primer surfacing for the RPs will undoubtedly increase the use of RPs in bodies and components. Large components and entire auto bodies have been designed and built indicating what may lie in the future for RPs. In areas where volume is limited and the number of models is increased, the tooling advantages of plastics become evident. There was a new design approach for the use of plastics in the auto construction was used on the DeLorean DMC-12 car that was designed and built (1967). Process used was principally the elastic recovery molding (ERM); also called foamed reservoir molding (FRM) that included glass fiber reinforcements. It consisted of fabricating a sandwich of plastic-impregnated in opencelled flexible P U R foam between the face layers of fibrous reinforcements. When heated in a mold and squeezed, the foam is compressed, forcing the plastic and air outward and into the reinforcement contacting the mold cavity. Unfortunately the car never took off into the market. At present, there is an increasing number of special, medium volume cars in production and others under consideration extending the use of RPs. Over the last few years, the injection-molded bulk molding compound (BMC/Chapter 4) hatchback program of Citroen has developed to a two-part design using an outer skin for class A surface and an inner panel providing mechanical properties, injected from a single port on the parting line (which produces fewer weld lines, no need for a cold

6

9Markets/Products

channel in the mold and easier mold machining). Both moldings are adhesively bonded together and coated with a conductive primer. The flow length, however, measures about 2 m (6.56 ft) which produced its own problems. The latest version, for the Xantia, is a three-part design. Chrysler specified a modified polymethyl methacrylate (PMMA) laminating resin for the body panels of the high-performance sports car, the 400 bhp 10 cylinder Dodge Viper, which went on sale in January 1992. The transition from styling to production took only three years. The decision to use glass fiber reinforced PMMA resin, molded by resin transfer, was a fundamental departure from established Chrysler practice, where previously all main exterior bodywork had been in sheet metal. However, at expected sales of 3000 a year and a unit price of about $50,000, sheet metal would not have been viable and the annual volume was too low to justify injection or compression molded plastics. Chrysler used glass-reinforced polyethylene terephthalate (PET) fenders for its main 1990s family saloons, the LH range, from 1993 model year, saving around 3.17 kg (7 lb) per car and up to 80% tooling costs. They are painted on-car and are claimed to be the first plastics parts to go through the E-coat (with temperatures up to 200~ meeting the requirement for electrophoretic coating of the whole car body and allowing the plastics components to withstand the temperature necessary for the steel parts. However, Chrysler proposed to injection-mold bodywork panels for its planned Composite Compact Vehicle, which weighs 544 kg and register a fuel economy of 4.7 liters/100 km. Mming to design a vehicle which is as easy to assemble as a toy, the body is envisaged as four large moldings, in glass reinforced PET, bonded with adhesive, produced on a gas-assisted 8200 ton clamp molding machine. The target cost of the composite was $3.3/kg, which the company compared with carbon fiber ($22/kg), polyester SMC, and polyurethane structural (with glass mat) reaction injection molding (SKIM) ( $ 1 1 - 1 3 / k g ) and steel (less than $0.90/kg). Carbon fiber RPs are showing up (2004) on a spectrum of concept cars and prototypes at auto shows, both on predictable vehicles, high-end super sports cars, and the unexpected, including a roadster concept aimed at selling for less than $20,000. Whether any of the dream cars actually make it into production with the RP still on board is hard to predict, but the number of vehicles rolling out show an increasing interest in the material. Many people continue to examine these vehicles. Resin and fiber suppliers, RP experts, universities and automakers themselves are researching ways to make carbon fiber a more

51 5

51 6 Reinforced Plastics Handbook

economical alternative. The attraction is easy to understand since it relates to high strength and low weight of the material make it possible to fine-tune structural systems. There is some prestige that goes along so certain people are willing to pay for performance and prestige. Prestige comes into play on two major concept cars that debuted at the 2004 Detroit show. The Chrysler division of DaimlerChrysler AG stormed onto the stage with the ME Four-Twelve sports car, that would sell for well in excess of $100,000 if produced. The car goes from zero to 60 mph in 2.9 seconds. Designers wanted this car to be as rigid and as light as possible. Carbon fiber and aluminum make up the Four-Twelve's body, while carbon fiber is used as the frame for the seat structure. Chrysler was looking at a cheaper prospect with the Dodge Slingshot concept. Based on DaimlerChrysler's European-made Smart roadster, which uses thermoplastic and standard RP for its body. The Slingshot also would have a plastic exterior, but the dream is to take it to carbon fiber. In the case of the Slingshot, carbon fiber would lend its light weight to a vehicle measuring in at 1,800 pounds that develops 45 miles per gal in fuel usage. Any possible future vehicle probably would not keep with the high-cost, high technology RP, since the automaker wants to sell it for less than $20,000. Price remains a problem for carbon fiber's wide acceptance. The Ford Motor Co. may have found a place for carbon fiber in the seat structures of the high-end Shelby Cobra concept vehicle, and while it is being used in limited editions of GM's Corvette and the Chrysler Dodge Viper, it is expected that it will take time for the material to go into other vehicles. What is occurring is a continual, gradual increase in carbon-fiber use. What was thought to be the world's largest yet surface-finished molded sandwich panel is being produced in Germany: an 8 m 2 (86 ft 2) polyester roof for the camper version of the Volkswagen T4 van. A push-up California design, it was molded in tools based on epoxy resin. Following trial molds with epoxy tools, Westfalia opted for twin counter-molds faced with nickel alloy on an epoxy/silica sand backing mix (which offered superior compression strength at temperatures in the 60-70C range). In production, the twin counter-molds are mounted on a sliding table and operated alternately with the mold, allowing one roof panel to cure while materials for the next are laid up on the other. Nissan reduced the weight of the front panel of its low-production Fairlady Z model by 30% by replacing a standard class A SMC with a lightweight grade: density of 1.3, against 1.85 g / c m 3, with no increase

6

9Markets/Products

in material costs. A high-pressure in-mold coating gives a class A surface with good paintability. SMC also offers a cost-saving potential against steel in two-part closures, such as tailgates and bonnets. Studies by USA car manufacturers suggest that it is cost competitive on high-volume cars, at up to 200,000 a year. Other studies indicate that SMC has a clear advantage up to 150,000 cars a year and is competitive with steel up to 350,000 units. There are additional benefits such as weight reduction, freedom of styling and improved acoustic behavior. Production and marketing requirements in North America have tended to favor the use of glass-reinforced. A design for a high-back automobile safety seat, molded in carbon fiber and engineering TPs, won the UK's 1990 Plastics on the Road design competition. The winners were a team of industrial design students from the Istituto Europeo di Design, Milan, Italy. Incorporating an integral safety harness, it used pneumatics to cushion bumps and shocks. Driver and passenger seat shells for the BMW 3-Series arc in production in polypropylene GMT, following two years' use of this material for seat shells and rests for the BMW 8-Series. Computer-aided design and computer aided engineering techniques were employed. As well as good structural properties, the GMT parts are suitable for recycling (by re-pressing or by grinding and re-formulating as molding granules) and can also be incinerated with energy recovery at the end of the recycling chain. Corvettes

The facility of hand lay-up of TS polyester/glass fiber laminates led to early use in construction of bodywork for special car models requiring only limited production, such as sports and racing cars, leading to development of the all fiber glass reinforced plastic (FRP) monocoque body. The first car in the world to have an aI1-FRP body was the 1953 Chevrolet Corvette (fabricated by Morrision Fiber Glass Co., Ohio, USA); just over a half century ago General Motors Corp.'s Corvette sports car made its debut. Over 40 years later, the Corvette illustrated the development of technology, with nearly 100 kg (220 lb) of RPs, the main changes being the introduction of SMC and the use of recycled material in low-density inner panels. The original 1953 production run was 300 hand-built cars: the 1992 Corvette production was 24,000. Its makers continue to make improvements on how best to produce it that includes doing more with the tooling and finishes. For the sixthgeneration Chevrolet Corvette, this is debuting at the 2004 North American International Auto Show in Detroit that means tweaking the

517

518 Reinforced Plastics Handbook

molding process to create better fit to the RP body panels. Launch of the 2005 model is an important milestone for the Detroit automaker since Corvette is a consistent icon as well as one of the most desired American-made vehicles on the road. Its introduction was a highlight of the auto show. The vehicle has been a hallmark for the plastics industry throughout its history, made of glass fiber/TS polyester RP from its first models. The new version retains a sheet molding compound outer body as well as an RP flooring. The carmaker and its suppliers also are using techniques developed for the 2003 launch of Corvette's sister sports car, the Cadillac XLR. To create a fighter fit and crisper lines, workers on the XLR carefully shifted freshly molded panels onto a special fixture to prevent warping or distortions. Result was to obtain a higher level of surface perfection than in the past. Higher-technology materials may not be part of the new standard Corvette, but plans are under way for special-edition vehicles. Carbon fiber RPs is being used on 2004 Z06 Commemorative Edition Corvettes. GM's two concept cars at the 2004 auto show also shared a body heritage with the Corvette, with both the Saturn Curve and Chevrolet Nomad using glass fiber/TS polyester RPs for their sports car bodies. The concept models were built on a new rear-wheel-drive sports car platform, called the Kappa architecture. The automaker built that platform for the future Pontiac Solstice, that began as a concept car in 2001 and will hit the roads within 2005.

Bumpers RPs for bumpers are used in USA, whereas in Europe the mass market to date is primarily in unreinforced injection molded TPs, with RPs used mainly for larger structures and bumper support systems, especially on export models. Front and rear bumper impact beams of some General Motors models are made of 60 wt% glass vinyl ester sheet molding compound, reinforced with a chopped and continuous strand glass fiber giving strength in all directions, replacing steel and withstanding 8 k m / h pendulum and impact testing on the 1700-1800 kg cars. The beams have been designed to aid reduction in number of parts, cutting assembly time from 33.7 to 14.5 min. They weigh 6.4 kg (14 lb) with 4-8 mm wall thickness and are molded on a standard compression molding machine. In Europe, the 5 kg recyclable front bumper beam for the Mercedes S range is produced in series quantifies in a special grade of polypropylene GMT. To withstand impact up to 4 k m / h without damage to itself or the car chassis a Mercedes internal requirement, approximating to USA

6

9Markets/Products

standards, the GMT has directional glass fiber reinforcement. One part of the fiber is laid unidirectionally, lengthwise across the bumper and random fibers give consistent distribution of the TP matrix in the flow regions. The front and back layers are GMT with horizontally laid fibers about 1800 mm (70 in) long. The part is molded in a fully automatic plant, heating the blanks to over 200C, placing them in the press by robot and molding at about 1700 ton of pressure. The beam gains further absorption strength from four polyurethane core units, with three items behind and one in front. Finally, the structure is clad with a shell of reinforced reaction injection molding (RRIM), using a glass fiber reinforced paintable polyurethane (PUR) system. Integrated front ends in polypropylene GMT stampings of SMC were adopted by many automobile manufacturers. Replacing a conventional metal stamping comprising 15-20 pieces and weighing more than 6 kg, they integrate functions such as attachment for cooling fans, radiator, headlamps, bonnet locking device and a metal crossbeam, making the part lighter and more cost effective. The unit is preassembled with all these components, including the front grille and bumper fascia and the complete sub-assembly is finally assembled to the car after the engine has been installed. The approach has been proved in the USA, by Ford (in SMC) and in Europe, by VW (in GMT). Glass manufacturer Vetrotex estimated that some 25% of European vehicles have some form of integrated front-end concept, of which about 30% are produced in RPs. French manufacturers have been particularly to the forefront, including Renault (RI9, Laguna and Safrane), Peugeot (205, 306 and 605), and Citroen (AX and Xantia). By the year 2000 50% of European cars were integrated front-end systems and 63% of these were in RPs. SMC/BMC have a good chance in such applications, in which up to 20 other components can be brought together on one molded supporting framework which can also play a structural role in the car bodywork. The need is for good engineering properties and heat resistance, with moldability and lightness. Steel is a competitor, as also are glass-reinforced polypropylene (PP) or nylon and PP glass mat thermoplastics (GMT) but, the more work the part is required to do, the more likely it is to be made in SMC/BMC. German automotive suppliers of front-end modules Hella KG Hueck and Co. (Lippstadt, Germany) and Behr GmbH (Stuttgart, Germany) already are major players through their joint venture with Hella-Behr Fahrzeugsysteme GmbH. France's Plastic Ommum SA (Levallois, France) is joining this business arrangement as of year 2004. This threeway joint venture will launch a 350 million euros ($440.4 million) in annual sales, strengthen Hella and Behr's existing capabilities and

519

520 Reinforced Plastics Handbook

provides for more expansion in the modules. The new company would be based in Lippstadt with a dedicated research and development center at Plastic Omnium's office in Lyon, France. It would launch with 550 employees in eight production sites in Germany, Czech Republic, Slovakia, Spain, Mexico and South Korea, making an estimated 1.25 million modules in 2004 and a predicted output climbing to 2 million/year during 2005 and 2006. Different module designs are manufactured having different definitions. Some North American suppliers use it to refer to bumper systems completed with painted fascia, energy absorption, and lighting. A full module produced in Europe is different, reflecting a change in manufacturing at the auto assembly plant. A typical module Hella-Behr now produces for Volkswagen AG and other auto makers includes the entire front vehicle structure and multiple parts from the radiator forward, including cooling, lighting, hoses and connectors, hood latch assemblies and wiring. North American automakers do not use the complete systems as widely as their European counterparts do because they would have to change their assembly architecture Vehicles made with the modules are open on the front end through manufacturing, with the module carrying the tie bars that unite the frame. The typical USA-based auto plant is designed to build the car around a complete frame from the start of the line. Future proposals to expand the systems in Europe would add the bumper beam and painted fascia to those parts, increasing the value of the overall system. Each company is a leader in its respective businesses. Plastic Omnium brings talent into the venture, while also strengthening Hella-Behr's capabilities in existing modules through its expertise in the structural plastics used in the carrier that holds all of the individual components. Hella-Behr has a lot of experience on how to design and develop the carrier. With Plastic Omnium, the German companies will have access to proprietary technology, since the French firm already has expertise with long glass fiber RPs in both thermoplastics and thermoset materials.

Window Regulators Innovative design by North American Body and Glass Division of Dura Automotive Systems Inc., Rochester Hills, MI during 2003 launched production during 2004 of a new plastic window regulator system. The basic window regulator, which is used to raise and lower the glass in an auto door, was developed in the 1920s as two pieces of steel, liberally coated in grease and operated with a hand crank to work like a pair of scissors.

6

9M a r k e t s / P r o d u c t s

A drum and cable system has become more popular with wider use of powered window systems, but still require heavy steel components, grease, and expensive and fragile cable systems. The old designs with grease solves the problems with lubrication, however it catches a lot of sand, grit, and dust and makes it a mess. When temperatures drop, the greasy mess does not permit ease of the window operation. The new basic design uses interlocking gears directly driving along a thermoplastic rack, outperformed the existing standard. This RP glass-filled nylon track and gears have integrated lubrication, eliminating the need for grease. It is 2 lb lighter than a drum and cable system, capable of saving 8-12 lb per vehicle. It is more efficient, requiring fewer volts, which can make a difference for automakers looking to package more electrical options with the same battery. It performs better in all weather conditions and requires less space in the door. Very important, it is easier and less expensive to manufacture, requiring only three to five assembly steps and 20-30% less in up-front investments. Dura featured this new design system at the Society of Automotive Engineers 2004 World Congress March 8-11 in Detroit. Batteries

The combination gasoline and electric motor systems making up the new hybrid range of vehicles hitting the roads are drawing increased interest from drivers, carmakers, and the plastic (including RPs for fuel cells as reviewed in Chapter 10) industry. They must package several cubic feet of batteries. Early on, carmakers were packaging them in metal, but that is moving forward into plastics now; they could be all plastic. The first commercial consumer hybrid systems introduced by Japanese automakers Toyota Motor Corp, and Honda Motor Co. in 2000 relied on in-house battery and electric motor developments. Ford Motor Co. took its first hybrid to the market during the summer of 2004, a gas-electric version of the Escape SUV. With North American automakers joining the interest in the vehicles, suppliers of existing standard batteries, like JCI, with an auto unit based in Plymouth, MI, are moving toward production of battery modules for hybrids that may occur by 2006 or 2007 in autos. JCI's automotive unit is in talks with a cross-section of automakers for future products. Its European battery unit, under the Varta name, already makes systems for hybrid buses. Hybrids fuel up on standard gasoline used in an internal combustion vehicle, but also have a supplemental electric motor that taps into batteries that store energy created during vehicle use, such as when brakes are applied. Those batteries, currently nickel hydride, arc

521

522 Reinforced Plastics Handbook

expected to shift to lithium ion eventually, hold about 4 volts of electricity per cell. Hybrids need between 144 volts and 350 volts, so the battery modules can be sizable, measuring 2 to 4 ft in width and length and a few inches in depth. The second generation of Toyota's power system in the Prius won notice from car buyers and industry watchers in 2003. Honda has hybrid power available with its Insight and a version of the Civic. Following on their heels arc new offerings from a cross-range of vehicles. Toyota's Lexus brand will introduce a hybrid sport utility vehicle later 2004, the RX:400H, and will focus on hybrid technology in advertising. In March, 2001 BP announced that it had joined a project with DaimlerChrysler, First Bus, Transport for London, UK, and the Energy Saving Trust to introduce three hydrogen fuel cell buses to England in year 2003. BP built and managed the infrastructure to supply hydrogen to the vehicles. The fuel cell engines work by producing electricity when hydrogen (H2) reacts with oxygen (02) to form water, a process more efficient than the internal combustion engine. This energy drives an electric motor that generates no local emissions. The H2 can be produced from a number of sources, including natural gas and oil, but in the case of the fuel cell buses 40% of it will be produced from renewable energies. Each bus will have a range of 400 km (250 mile). As well as London, nine other European cities are set to join the twoyear program. This 2001 project was one of at least five different potential technologies that may emerge this decade. As well as fuel cells, where hydrogen is only one of the potential fuel sources, other possibilities exist. They include liquefied petroleum gas and compressed natural gas for internal combustion engines; advanced direct-injection gasoline and diesel engines; hybrids that comprise an electric battery motor and a gasoline or diesel engine; and for limited range, purely electrically motored cars. An update as of 2004 of buses in the UK has this radical transport project supported by B P that could be a vital breath of fresh air for inner city travel in London. Commuters taking the number 25 from Ilford to Oxford Street can say goodbye to the noisy rattle and choking fumes that are usually associated with London's roads if they are fortunate enough to catch one of the three hydrogen-powered buses that have been trialed on the route since 14 January. The buses have none of the vibration and noise of traditional diesel because they are powered by electricity, produced when hydrogen is combined in a fuel

6. Markets/Products 523 cell with oxygen to become water that is the buses' only emission. The $1 million buses are now specially-built versions of the single-decker Mercedes Benz Citaro, used in most European cities. They are part of Clean Urban Transport for Europe, a Europe-wide two-year pilot project to test hydrogen as a viable alternative fuel. BP is acting as fuel provider in five of the nine cities taking part. Recognize that what might look commercial by 2005 may not be competitive during 2010. The winning emergent technologies have to be market-developed activities. As reported, it goes through three phases namely: 1

making it possible;

2

integrating it back into the vehicle; and

3

then creating a commercial infrastructure that makes the vehicle a commercial option to buy.

With fuel cells, for instance, they are currently between phases two and three. Other Parts Leaf springs for some passenger cars and trucks have been developed in RPs, using unidirectional glass fibers and special resins. These were also be used in a major German research project on a Mercedes Benz transporter and, on customer request, MAN installed two of the springs in heavy loading trucks, thus achieving a weight-saving of some 150 kg on each truck.

One of the most significant applications for RPs in automobiles in recent years has been the development of air intake manifolds. These are injection molded in 30-35% glass fiber-reinforced nylon 6 or 6 / 6 , either in one part, using fusible metal cores to produce the complex internal air channels, or as two mirror halves that are then welded together. The parts are up to 50% lighter than their metal counterparts and contribute to improved engine efficiency and better emissions, by providing a way to optimizing the flow and mixture of air. Latest developments are moving to integrating other components, with positive cost savings. It is estimated that about 40-45% of all new models are using plastic manifolds, with more in the future. The original development was by Porsche, in 1972, but the massproduction breakthrough was by Ford Europe, molded with fusible core technology by Dunlop Automotive in the UK (subsequently taken over by Siemens). Ford's interest dates back to the 1970s, when it developed a manifold compression molded in TS polyester BMC, but

524 Reinforced Plastics Handbook

this was overtaken by the development of TPs. In particular, USA manufacturers have actively taken up the technology and Japanese companies have also taken up plastics manifolds. The market will probably split evenly between fusible core and two-part welding, depending on the complexity of the part and the required production numbers. Fusible core molding is costly and requires dedicated investment in a production cell that includes not only the injection molding machine but also a complete loop for molding, inserting, melting out, and recycling the low melting point metal alloy. This makes it economical for long production runs of the more complex designs. For more flexible production, where the design is relatively simple, the economic solution is to mold in two parts that are then welded together. Nylon type 6 / 6 tends to be used for fusible core moldings and type 6 gives better properties for welding, but manufacturers have developed special grades that cross over this distinction. A variation, developed by Bayer and Mercedes, brings together more than two parts that are vibration welded at 120-240 Hz frequency, in multi shell technology. Other molding techniques have been studied, particularly molding with sliding cores and a variation of blow molding. Fiber-RP s, both TS and TP, are also used for the oil sump and rocker covers of automobile engines, both in the USA and Europe. Dimensional stability is a major problem, however. In a recent development, Rover UK specified mineral-reinforced nylon for cam valve covers for its K8 1.1 and 1.4 engines, in the Metro and 200 Series, specifying good mechanical properties at 120C, acceptable creep at 140C, excellent resistance to hot engine oil and low distortion/low tolerance moldings. The same, larger, parts on trucks in the USA are specified in vinyl ester. Pedal clusters are also injection molded in glass-reinforced nylon, replacing steel, with weight-saving and simplified manufacture. Clutch and accelerator pedals are in plastics but there is more caution about the brake pedal. Ford is typical in replacing steel with 33% glassreinforced nylon 6 (Allied Signal Capron 8233) for a C-channel floor pedal, molded by Comcord Technologies. The pedal completed two million cycles at 18 kg loading without incident, passing 113 kg loading requirements a t - 20 to + 70C. Assembly weight and number of parts are both reduced by 50%, with 10% cost saving. Special applications for RPs include lightweight armor for police cars are being investigated as a potential application for Dyneema, DSM's high-strength polyethylene (PE) fiber. A special ballistic yarn SK66, thought to be suitable on grounds of high energy absorption and low weight, is being tested for door and seat armoring on 50 Volvo 440

6. Markets/Products 525 police cars in major cities in the Netherlands. A key advantage is that, unlike steel armor, the lightweight PE armor does not require any structural changes to the car. The system used by the Dutch police is to the German class 1 standard, meaning that it is an effective shield against 90% of all ballistic threats against police forces in Europe. Typical arm our weighs only 1.7 kg (door) and 2.3 kg (seat), amounting to only about 8 kg additional weight. It can be mounted virtually invisibly. The shields are made by pressing binder-impregnated fabrics of Dyneema SK66 into the required form. Special requirement for Class A finish on preimpregnated material such as SMC is to being used on some of DaimierChysler's 2004 coupe models. It is in response to the reliance by today's vehicles on electronic systems that communicate via satellite and electromagnetic waves. Modern cars need several antennae, and for styling and design reasons these are, where possible, hidden beneath a body panel section. However, an all-metal body needs external antennae since electromagnetic waves cannot penetrate sheet metal. Designs exists of all-in-one metal/plastic antennae modules. An upper class car is now equipped with an average of ten antennae, and the figure will rise as car makers introduce systems for monitoring and automatically regulating the distance from the vehicle in front, and install warning sensors to avoid collisions when reversing. The antennae have generally been spread over the entire body shell, a challenge for designers because the area near the antenna has to be suitably designed to guarantee optimum rcccption. The antenna modulc in Volvo's XC90 SUV, developed by Johnson Controls and Volvo, demonstrates a way round the problem. The module accommodates all the antennae and relevant receivers (radio, TV, GPS) in one unit. It is made of steel and Durethan| BM 130 H2.0 polyamide supplied by Bayer MaterialScience AG, Leverkusen, Germany, manufactured using the plastic/metal hybrid technology already established for the series production of vehicle front-ends. RPs is also used in this type design. The antenna module weighs 1.8 kg and is located under a plastic cover on the rear of the roof of the off road vehicle. The antennae are integrated into a film that forms part of the plastic cover so as not to impair their performance. The backing for the film, which extends almost across the entire width of the vehicle, and various fixing elements are also made of polyamide. The receivers, such as the F M / A M , Digital Audio Broadcasting (DAB) and TV tuners, are screwed to the metal support of the hybrid construction. This compact module design with its high level of integration obviates the need for a large number of cables.

526 Reinforced Plastics Handbook

SMC is transparent to electromagnetic waves and is said to offer additional benefits such as lower systems costs compared with metal over the same production volumes. SMC also offers dimensional stability, stiffness, low weight, and high temperature resistance to enable online painting. To ensure a consistent product quality, DaimlerChrysler teamed up with molder Peguform, SMC manufacturer, molder MenzolitFibron, and resin supplier DSM Composite Resins in a quality improvement and consistency program called CCC (compound, characterization, consistency). The goal is guaranteed product consistency across all levels of the supply chain from raw material to the Class A painted part. The European Alliance for SMC reports that since the introduction of the CCC project during 2001, scrap and rework rates have been substantially reduced and many process improvements have been implemented. The changes introduced range from raw material analysis and tightening of tolerances to improvements in mold heating and materials handling practices. A Cadillac hood assembly includes a complex-shaped SMC inner panel that is bonded to an SMC outer panel. The outer panel has a Class A finish. The hood surface has a four-sided, tapered design and includes steel hinges, brackets and the hood latch. Here is an example where SMC has the ability to create high style, lower vehicle weight, reduce tooling costs and resist corrosion and denting. The new Cadillac ZLR attracted sports car enthusiasts. The vehicle's hood is compression molded from SMC by ThyssenKrupp Budd Company, of Troy, Michigan, USA. The SMCs used are based on AOC resins. HiPer Technology Inc., Armada, MI. has new carbon fiber/nylon RP wheels that came during 2004. The company has an exclusive use agreement with DuPont Co. of Wilmington, DE. for DuPont's patented carbon fiber material. HiPer's goal is to provide products designed to replace those currently made in aluminum. They are offering a new ATV wheel for professional circuit racers, a micro-sprint car wheel, a junior dragster motorcycle wheel, and a motocross wheel. The ATV production is now 30,000 wheels a year. Products expected 2005 include baseball and softball bats, a 15 inch automotive spare tire, and wheels for golf cart, marine trailers, and mountain bikes. The RP is lighter than aluminum, 2.7 times stronger than aluminum, and five times tougher than aluminum. You can beat it with a sledge hammer with no damage. Thomas A. Darnell, 33, the president and founder of HiPer, worked as project manager for Ford Light Truck Development for Automotive

6. Markets/Products 527 Molding Co. of Warren, MI, and later for Plastech Engineered Products Inc., Dearborn, MI. Darnell worked with DuPont to develop the material used in the energy-absorbing, impact-resistant wheels, and shared the patents with DuPont. DuPont has assigned the patents to HiPer. North America's first high-volume thermoplastic (RP) valve cover made its debut on the 2004 Chrysler Town and Country, Dodge Caravan and Grand Caravan with 3.3 and 3.8 liter V6 engines. The valve cover, manufactured by Bruss Sealing Systems (Bruss North America, 4405 Baldwin Rd., Orion, MI48359) from DuPont Minion mineral reinforced nylon, reduces weight by more than 65% and cuts cost significantly compared to metal. The innovative thermoplastic valve cover also delivers benefits through integrated functionality: an integrated air/oil separator significantly reduces the amount of oil pulled into the engine to reduce environmental impact; an integrated Positive Crankcase Ventilation (PCV) valve housing helps reduce evaporative emissions and ensures the PCV system stays secure. A global team from Chrysler Group, Bruss, and DuPont Engineering Polymers ensured this program went from CAD drawing to commercial launch in just under 22 weeks. The rapid development ensured the benefits of thermoplastics were delivered in the current vehicle model year. The valve cover is made of a specially formulated grade of glass/ mineral reinforced Minion that delivers a balance of stiffness, strength, dimensional stability, and warpage resistance to meet stringent requirements for the application. Switching to thermoplastics made it possible to eliminate the cosily e-coating process along with several secondary machining steps. The Minion runners and scrap from the injection molding manufacturing process are melt recycled. The USA plastic industry is looking to expand its plastic under the car hood, trying to convince North American automakers to use reinforced thermoplastics (RTPs) in valve covers in place of the existing metal components. Just over 50% of the autos made in Western Europe use RTPs for the covers, but in North America metal is the material of choice with 37wt% being thermoset. About 15wt% of global Market use glass and mineral filled nylon. The switch may not be easy or sudden, but the change is beginning to occur. It is expected to take the same route the intake manifold did in that the RTPs was a longtime coming but now it is accepted everywhere. The North American RTPs usage number is expected to climb to 4% by 2006. DaimlerChrysler AG is backing the first high-volume use of RTPs for valve covers with its decision to use DuPont's Minion

528 Reinforced Plastics Handbook

reinforced nylon on sixcylinder versions of its 2004 Chrysler Town and Country, Caravan and Grand Caravan minivans. Buses

Buses and public transport in general, offer wide opportunities for the use of RPs. Unreinforced plastics (URPS) and reinforced plastics (RPs) have been used in different types of buses. In the world of buses during year 2000 Brunswick Technologies (Brunswick, ME) fabricated the socalled CompoBus. Its design incorporates oriented glass fiber satin woven tri-axial fabrics with TS polyester plastics in its chassis and body. Delphi Automotive Systems, Woodridge, IL and Hendrickson Innovations International developed and manufactured a plastic composite (glass/ carbon fiber hybrid reinforcement) for use in the medium and heavy duty truck and bus markets. When compared to metals they are lighter and more impact resistant, require less mounting hardware, and designed to conduct 50% less vibration. The facility of small volume production in RPs by hand lay-up led quickly to the use of these materials for van and truck bodies. Today, however, numbers have built up to justify press-molding many panels in SMC. Lighter weight and improved aerodynamics (reducing fuel costs), with lower maintenance, reduction in noise and overall improvement in comfort have been the reasons. While it is difficult for RPs to match the economics and flexibility of metal sheet for flat bodywork panels, they become interesting as soon as curvature, contouring or any additional function is introduced. RPs also lend themselves to production of special vehicle bodies, including sandwich-structure insulated bodies for refrigerated transport and very high performance filament wound tanks for oil, gasoline and chemicals tankers. Insulated containers are also a strong candidate for the SCRIMP resin infusion molding process. This Seeman Composites Resin Infusion Process (SCRIMP) has been used to manufacture corrosion resistance bus shells (Chapter 5). North America Bus Industries (NABI) of Anniston, AL uses glass fiberpolyester plastic material from TPI Composites of Warren, RI. These new buses weigh about 10,000 kg (22,000 lb) that is 3200 kg (7000 lb) lighter than steel units. Lighter weight results in reduced axial loads, brake wear, etc. and improved fuel efficiency. Schindler Waggon, Switzerland, is studying using its large-scale filament winding technology for bus bodies, insulated and double-shell

6. Markets/Products 529 containers and passenger bridges for airports and shelters. Internacional de Composites SA, Toledo, Spain is also investigating composite bus and coach bodies, based on a series of filament wound rings joined elements that are also filament wound. Different cross-sections can be used, both open and closed, and it is possible to wind and element which does not contain external concave geometry. The majority of frames are rectangular box beams or square frames. TS polyester resin and E-glass are used, with local use of carbon fiber to improve the structure. Mechanical properties are reported to be excellent.

Trucks Use of P,_Ps in trucks goes back to the early days when plastics were produced and throughout past years. Here is a brief introduction to RP applications. During 1946 to 1950 DVR designed and fabricated for Strick Trailers, Philadelphia, PA. 32 to 40 ft. long RP floors, side panels, translucent roofs, aeronautical over-the-cabin structures, etc. Practically all products were made of RPs (glass fiber-TS polyester plastic) providing lighter weight trucks, streamlining frontal area, insulator for refrigerator trucks, and lower product costs. The lighter weight products permitted trailers to carry heavier loads, conserve fuel, refrigerated trucks traveled longer distance (due to improved heat insulation), etc. Different plastics continued to be used in the different truck applications to meet a static and dynamic load that includes high vibration loads. Continued use is in the 4x4 pickup truck 100 lb boxes using thermoformed thermoplastic PEs and for the tougher requirements resin transfer molded SMC. A series of trucks using sheet molding compounds (SMC/Chapter 4) for at least part of the bed, began with the introduction of the 2005 Tacoma X-Runner by Toyota Motor Corp. They were introduced during the February 2004 Chicago Auto Show. Production on the 2005 Tacomas began late 2004. ThyssenI~upp Automotive AG's plastics division, formerly called Budd Co. has built a plant in Tijuana, Mexico, to make these inner truck beds for Toyota from SMCs. Toyota's adoption of SMC marked an expansion of RPs in pickup beds. Ford Motor Co. of Dearborn, Mich., uses SMC for the bed of its Explorer Sport Trac. General Motors Corp. uses mostly reinforced reaction injection molding (RIM/Chapter 5) for the beds of its Chevrolet Avalanche and Escalade EXT trucks.

530 Reinforced Plastics Handbook

Tanks Extensive use is made in using commercial and engineering plastics to fabricate all tank sizes and shapes used in the transportation industry as well as many other industries (agriculture, chemical storage, filtration, etc.). The processes in other chapters review fabricating tanks and containers using different types of URPs and RPS (Chapter 5).

Hopper Rail Car Tanks In the past (1973) a severe shortage of railroad covered hopper cars for the transportation of grain developed. Cargill, Inc. provided a contract to Structural Composites, Inc. for determine feasibility studies on the potential of using RP in the design and fabrication of these cars. Test results showed structural deficient existed. By 1978 an acceptable design resulted fabricating the Glasshopper (registered name). It was used in rail service March 1981. Cargill Inc., Southern Pacific Transportation Co., and ACF Industries, Inc. (Figure 6.18). It was larger and lighter in weight than the conventional steel covered hopper car resulting in being able to deliver more commodities per fuel dollar. Other advantages included corrosion resistance, and lower maintenance costs.

Figure 6.18

RP railroad covered hopper car

6

9M a r k e t s / P r o d u c t s

The first to be built was Glasshopper I. It successfully passed all of the required American Association of Railroads (AAR) tests including the 454,000 kg (1,000,000 lb) static end compression test and the 568,000 kg (1,250,000 lb) coupler force impact test in the laboratory, and then successfully completed a round trip between St. Louis, MO and Oakland, CA [9700 km (6000 mile)]. From outward appearance, the RP designs were very similar to the standard ACF steel-covered hopper car. The first RP prototype, Glasshopper 1 that was in grain service, had four compartments. The car had a total capacity of 142 m 3 (5000 ft 3) and an overall length of about 16 m (53 ft). Its basic specifications are shown in Table 6.1. Table 6.1 Glasshopper 1 basic specifications Length inside Length over end sills Length over strikers Length over coupler pulling face Length over running boards Length between truck centres Extreme width Height, rail to top of running boards Height, rail to bottom of outlet Extreme height, rail to top of hatch bumper Number of discharge outlets Roof hatch opening, continuous Curve negotiability, uncoupled Cubic capacity Tare weight Gross rail load AAR clearance diagram

50 ft 31/2 in 51 ft 55/8 in 52 ft 11 in 55 ft 61/2 in 53 ft 7/8 in 42 ft 3 in 10 ft 8 in 15 ft 1 27/32 in 12 in 15 f t 6 i n 4 20 in x 44 ft 73/4 in 150 ft 500 ft 3 59,000 Ib 263,000 Ib Plate 'C'

The second prototype car Glasshopper 11 that was latter put into service had three compartments. The tare weight of the second car was 24,600 kg (54,200 lb), which was 4000 kg (8800 lb) lighter than a standard steel car weight of 28,600 kg (63,000 lb). Construction details for Glasshopper I consist of a filament wound (FW) RP car body, RP/balsawood core sandwich panel bulkheads and slope sheets, steel side sills and shear plates, steel bolster webs, and RP hatch covers. Standard running gear and safety appliances were utilized, as were standard gravity outlets. Several changes in construction details

531

532

R e i n f o r c e d Plastics H a n d b o o k

such as the use of single laminate slope sheets were made in the design of Glasshopper 11 to reduce weight and manufacturing costs. Table 6.2 shows the weight percentages of steel or RP materials. A significant amount (30 wt%) of the RP car structure is fabricated using RP materials. By subtracting the trucks steel weight, the remaining structure is RP. This construction allows the significant weight reduction to be possible. Finite element analysis (FEA) modeling was used throughout the design stages of the program to aid the structural analysis effort. The structural response in both static and dynamic loading conditions was characterized prior to initiation of the car construction. Table 6.2 Glasshopper 1 component weight summary

Component

Moteriol

Weight Ibs

Car body Sandwich panels Wide flange beams Stiffeners Top sill Roof/side angles Adhesive/bonding strip Hatches Outlets End arrangement Side sills Running boards/safety appln. Brake system Misc. hardware Trucks

R)

R~

RD R~ R~ R~ R~ R~

Steel Steel Steel Steel Steel Steel Steel Total weight

6800 4410 640 2910 46O 510 1070 860 1800 9640 4420 1650 1570 1060 21200 59000

Componentweight x 100 Totol weight 11.5 7.5 1.1 4.9 0.8 0.9 1.8 1.5 3.0 16.3 7.5 2.8 2.7 1.8 35.9 100.0

2 RPcomponentpercentages= 30 Steel componentpercentages= 70

FW process was used to fabricate both Glasshopper car bodies. It was determined that this process afforded the best mechanical properties for the lowest cost. Fabricating processes exist that can be highly automated which would help towards having RP-covered hopper cars compete economically with conventional steel-covered hopper cars in the marketplace.

6. Markets/Products 533 Resin matrix material system chosen for fabrication of the car bodies was a proprietary (TS) isophthalic polyester resin system developed by Cargill specifically for the Glasshopper project. PPG, Certain Teed, and OCF supplied the reinforcement of E-glass rovings. Both OCF 450 and 675 yield glass was used successfully in conjunction with the Cargill resin during FW operation. To provide adequate mechanical properties in the directions required to withstand the externally applied service loads, the FW apparatus was programmed to provide the multi-axial filament directional orientation capability. Secondary bonding operations involving the attachment of stiffeners, etc., for the first RP car, used Hysol's epoxy adhesive (EA 919). This same adhesive was used in joints where both bonding and bolting with mechanical fasteners were employed. Lord Corp.'s acrylic adhesive system (TS 3929-70) was used successfully for Glasshopper 11. Hat section stiffeners and wide flange beams were fabricated using the hand lay-up and pultrusion processes, respectively. The material used in the construction of the hat stiffeners included 1/2 oz mat, 24 oz woven rovings, 221/2 oz unidirectional fabric, and the isophthalic polyester resin. Pultrusions were purchased finished, and were fabricated using standard pultrusion processes. In order to demonstrate structural adequacy, Glasshopper 1 was tested in the ACF test laboratory located in St. Charles, MO. The test program was designed to show that the car meets and exceeds all requirements as specified by the AAR. Both static and dynamic tests were included in the testing. To determine the car's structural response under various applied loading conditions, Glasshopper 1 was instrumented with a total of 224 strain gauges, located at various areas determined through structural analysis to be of greatest importance and to provide maximum information. Glasshopper 11, instrumented with 310 strain gauges, successfully completed the test program in 1983. A series of six different static tests were successfully passed by Glasshopper 1, including end compression, draft, vertical coupler-up, vertical coupler-down, coupler shank, and torsional jacking. The end compression test consisted of "squeezing" the car, while empty, with a hydraulic ram until a coupler force of 1,000,000 lb was measured. The draft test was conducted on the loaded car (105.9 tons) and consisted of pulling on the coupler until a force of 630,000 lb was experimentally observed. The remaining static tests were all conducted on the loaded car and involved using calibrated hydraulic rams to: Jack the car upward with a vertical force of 22,700 kg (50,000 lb) applied at the coupler pulling face.

534 Reinforced Plastics Handbook

Jack the car downward with a vertical force of 22,700 kg (50,000 Ib) applied at the coupler pulling face. Lift the car free of the truck bolster by jacking at the coupler shank, a vertical force of 50,400 kg (111,000 lb) was required. Lift the car free of the truck bolster by jacking at the lifting lug/jacking pad assembly to verify torsional rigidity and stability, a vertical force of 31,780 kg (70,000 Ib) was required. An analysis of test results show the experimentally observed strains to be very close to those predicted using FEA techniques and "hand" calculations. This fact made it possible to use these techniques to further optimize the Glasshopper 11 design. After successfully passing all required static tests, Glasshopper 1 was subjected to a series of impact tests. For these tests, the car that was fully loaded, was pulled by cable up an inclined ramp and released to impact another fully loaded standing car that had its brakes released. Velocity of the car at impact was controlled by its height on the ramp at the time of release. Car's velocity was incrementally increased until an experimentally measured coupler force of 113,500 kg (250,000 lb) was developed during the impact. Velocity of 14.9 k m / h (9.24 m / h ) was required to obtain the AAR specified load. It is noted that this velocity is significantly higher than the velocity required to reach the specified force with conventional steel covered hopper cars, which is about 12.1 k m / h (7.5 m/h). Glasshopper 1, with modified bulkhead joints, successfully passed the AAR impact test required and was subsequently prepared for the extended road test. Following completion of laboratory testing, Glasshopper 1 was tested over a 9700 km (6000 m) route on the Southern Pacific system. Fully loaded car with 9,600 kg (211,000 lb) made the trip from St. Charles, MO to Oakland, CA and back to Houston, TX. The car was unloaded at the Cargill export grain terminal in the Houston area and then returned empty to the facility in St. Charles, MO. The car was accompanied on the trip by the fully instrumented ACF test car used for data acquisition that monitored key strain gauges and load cells throughout the trip. All test results and visual observations showed the car performed well, and as predicted. During certain segments of the testing, speeds of 113 k m / h (70 m / h ) were reached with no dynamic problems (flutter, hunting, etc.) being observed. It was determined that two major advantages of the RP covered hopper rail car are its tare weight and its corrosion resistance. As a result of its significantly lower weight and large size, the car is capable of carrying

6. Markets/Products 535 more payload per fuel dollar. This fact is extremely important in today's conditions of escalating and high-fuelled prices. Glasshopper is able to carry many highly corrosive commodities (salts, potash, fertilizer, ore, etc.) without the need for expensive linings and with significantly reduced car maintenance costs. Also, the car's service lifetime would be greatly extended in these severe service environments. Other advantages include the potential to eliminate painting requirements, reduced labor costs in manufacturing, lower center of gravity in the unloaded condition, ability to easily adapt to internal pressure designs, and rapid production changeover to alternate capacity cars.

Highway Tanks RP tanks on firm/above ground have been holding corrosive materials safely since the 1940s. The same technology, with some enhancements material wise and design wise, has been applied to over-the-road highway tankers. As an example tankers fabricated by Comptank Corp., Bothwell, Ontario, Canada are on the road in the USA and Canada since 1998 carrying a wide range of corrosive and hazardous liquids (Figure 6.19). These RP tank trailers are coded 312 for hauling corrosive and hazardous materials; special designed models haul acids or other corrosive chemicals; they unload by pressure, vacuum, or gravity.

Figure 6.19

Plastic tank trailer safely transports corrosive and hazardous materials on the highway

536 Reinforced Plastics Handbook

The tankers are filament wound using E-glass rovings with TS polyester resin (Reichhold Atlac 4010 AC) and surfacing veil. RP moldings are integrated parts of the shell that is usually 15.88 mm (0.625 in.) thick. These parts include external rings/ribs, covers for steel rollover guards, spill dam, catwalk, hose trays, etc. Corrosion-Resistant Tanks

As reviewed throughout this book part of the wide acceptance of plastics is from their relative compatibility to chemicals, particularly to moisture, as compared to that of other materials. Because plastics are largely immune to the electrochemical corrosion to which metals are susceptible, they can frequently be used in transportation and other markets successfully to contain water and corrosive chemicals that would attack metals. RP fabricators also have a major market for tanks as well as pipes, grating, and a variety of other structures used to withstand corrosive working environments that serve industrial customers. Plastics are often used in corrosive environments for chemical tanks, water treatment plants, and piping to handle drainage, sewage, and water supply. Structural shapes for use under corrosive conditions often take advantage of the design capability and properties of RPs. Glass fiber TS polyester RP water filtration tank is shown in Figure 6.20. It is 20 ft diameter, 32 ft high structure made in sections by a low-pressure RP fabricating method. This bonded, assembled tank was shipped on a water barge to its destination. Structural shapes such as this tank for use under corrosive conditions often takes advantage of the properties of RPs and other plastics.

Figure 6.20 Large water filtration tank with 6 ft opening

6

Markets/Products 9 537

However, certain plastics are subject to attack by aggressive fluids and chemicals, although the same media attacks not all plastics. It is thus most practical to select a plastic to meet a particular design performance condition. For example, some plastics like H D P E are immune to almost all commonly found solvents. Polytetrafluoroethylene (PTFE) in particular is noted principally for its resistance to practically all-chemical substances. It includes what has been generally identified as the most inert material known worldwide. It is important to recognize that all materials will have problems in certain environments, whether they are plastics, metals, aluminum, or something else. For example, the corrosion of metal surfaces has a damaging effect on both the static and dynamic strength properties of metals because it ultimately creates a reduced cross-section that can lead to eventual failure. The combined effect of corrosion and stress on strength characteristics is called stress corrosion. When the load is variable, the combination of corrosion and the varying stress is called corrosion fatigue. This problem can be controlled in several ways. One is to select the best material, such as stainless steel, a copper alloy, or titanium. Another is to use a nonmetallic protective coating of plastic. Certain systems like plating can reduce fatigue strength. Shot peening rather then plating seems to produce much greater improvement, but shot peening, plating, and then baldng can bring the fatigue limit to a point lower even than that of the base metal. The point in this review is that all materials have their limitations and must be critically analyzed if no prior experience exists upon which to draw. Underground Storage Tanks

Glass fiber-TS polyester RP (GFRP) underground tanks for storing gasoline and other materials used in transportation have been in use worldwide since the 1950s (Figure 6.21). Experience with them initiated many tank standards. RPs provided much longer life than their steel counterparts. In fact, steel tanks previously had no "real life" or no requirement standards until the RPs entered the market. It has been estimated that more than 200,000 GFRP tanks were installed in the USA from 1960-1990. A previous study by the Steel Tank Institute (Lake Zurich, IL) reported 61% were of steel and 39% of GFRP. At present, at least 50% of all tanks are GFRP. This RP vs. steel debate escalated when the EPA gave service stations and fleet refueling areas 10 years to remove steel tanks that leaked. Historically a Chicago service station documented the long life of RPs. A May 1963 installations remained leak tight and structurally sound

538 Reinforced Plastics Handbook

Figure 6.21 Underground glass fiber/TS polyester filament wound RP gasoline storage tank

when unearthed in May 1988. After testing the vessel, engineers buried it at another gas station. This tank was one of sixty developed by Amoco Chemical Co. It was fabricated in two semi-cylinder sections of glass fiber woven roving and chopped strand mat impregnated by an unsaturated isophthalic TS-polyester resin selected for its superior resistance to acids, alkalis, aromatics, solvents, and hydrocarbons. Two sections were bonded to each other and to end caps with RP lap joints. Today, the tanks are fabricated by using chopped glass fiber mixed with the isophthalic resin. This mixture is dropped from above onto a rotating steel mandrel. The glass-resin mix is sprayed to make the end caps. Demand for this type of petroleum storage tank has grown rapidly as environmental regulations have become more stringent. Marina installation has taken advantage of these RP tanks. They permit for boat owners to purchase gasoline at the pier. Before they were installed,

6-Markets/Products 539 gasoline either had to be carried to the marina or purchased elsewhere, because of corrosive conditions underground for metal or other tanks, particularly ones next to salt water. Standards require that today's underground tanks must last thirty or more years without undue maintenance. To meet these criteria, they must be able to maintain structural integrity and resist the corrosive effects of soil and gasoline, including gasoline that has been contaminated by moisture and soil. The tank just mentioned that was removed in 1991 met these requirements, but two steel tanks unearthed from the same site at that time failed to meet them. One was dusted with white metal oxide and the other showed signs of corrosion at the weld line. Rust had weakened this joint so much that it could be scraped away with a pocketlmife. Tests and evaluations were conducted on the RP tank that had been in the ground for 25 years; tests were also conducted on similarly constructed tanks unearthed at 51 and 71 years that showed the RP tanks could more than meet the service requirements. Table 6.3 provides factual, useful data from these tests. Table 6.3 Unearthed underground gasoline storage tank data Test results Age at testing Property

5.5 years

Z5 years

25.0 years

Buried-excavated Flexural strength:

1/7/65-8/21/70 19,500 134

4/4/64-10/24/71 24,200 167

5/15/63-5/11/88 22,400 154

Flexural modulus: Tensile strength: Tensile modulus: Tensile elongation: Notched Izod impact strength:

Psi MPa Psi

MPa Psi MPa Psi MPa O/o

ft.-lb./in

Jim

725 x 103

795 x 103

4,992 10,700 74 1,160 x 103 7,260 1.11

5,482 13,600 94 1,053 x 103 8,000 1.25

9.7 518

11.0 587

635 x 103

4,378 10,500 72 1,107 x 103

7,630 1.13 14.1 753

Prior to the development of the GFRP tanks, no standards were required for buried tanks such as loads or loading conditions, minimum depths of earth cover, or structural safety factors were available. At that

540 Reinforced Plastics Handbook

time, sizes were 22,704 to 45,408 liter (6,000 to 12,000 gal), with a nominal width and height of 2.44 m (8 ft) for truck shipments to local gasoline stations. Standards have developed listing requirements for stored fluid type, environmental resistance, minimum earth cover, ground water submerged limits, and surface wheel load over tank. Increasing acceptance of buried GFRP tanks has widened the size range from 2,081 to 181,632 liter (550 to at least 48,000 gal) and the range in typical diameters from about 1.22 to 3.35 m (4 ft to at least 11 ft). The tank configuration is cylindrical, in order to provide the required design volumes within the established envelope of heights and widths. Length ranges are from 5.5 to 11 m (18 to 36 ft); they are well within practical truck shipment limits. A circular shape is required to support the substantial internal and external fluid and earth pressures with good structural efficiency. Other considerations in selection of an efficient configuration are used. With a vertical axis, tank underlay requires that much less land area than with axis horizontal, but very deep excavation is required where expensive ledge or ground water conditions will frequently be encountered. Both internal and external pressures are large, requiring a substantial increase in wall thickness and rib stiffness, compared with a horizontally-placed tank. With axis horizontal, maximum external and internal pressures do not vary with size (length), and can be resisted with economically feasible wall thickness and rib proportions. Tanks underlay a larger ground area. Uniform bedding is more difficult to attain. Hemispherical shells, low-rise dished-shaped heads and flat plate closures were all considered. Hemispherical shells were found structurally very efficient because of good buckling resistances under external fluid and earth pressure, good strength under internal pressure, no requirement for edge ring, and low discontinuity stresses at the junction with the cylinder. Flat end closures result in excessive deflections and large edge bending moments on the cylinder. Sandwich construction could be used to improve structural efficiency of flat ends. Sandwich wall construction was also investigated for attaining necessary buckling resistance of spherical shell end closures and found to be feasible but less cost effective. Use of rib stiffening was required. It was found necessary to stiffen the cylindrical shell against buckling under external pressure from ground water and dimpling from local earth pressure due to surface wheel loads. Sandwich wall construction was investigated as an alternative to use of stiffening ribs and found to be feasible but less cost effective. Shape-wise, a hollow trapezoid provides efficient bending strength and stiffness, a wide base for proper spacing of cylinder shell support against

6

Markets/Products 9

local buckling, and a narrower top to resist local buckling with high circumferential flange forces. Figure 6.22 provides a design concept for a tank with hollow trapezoidal ribbing.

0.3

0.28" SO-

Shop .,--9 Splice (Overwr I:) f.Typical Rib a/l/Detail A

F h o l d down straps with guides

W[_. _ . . . , . _ .

~ "'"w'7, , ' " "1~U _

"

_

. =

-;,-

77

i i

I

!

,,L.,, ,,.o. 2"_,

1'-3" . ].

21 '-8" L.2V=" ,~_2"_,

Detail A

4'-0"

(3FRP Laminates Tank Wall: .28" Spray-up 125" 9 Mat Woven Roving Rib: Top: .12" Filament Winding 125" 9 Mat Woven Roving

Sides: .25" Mat Woven Roving Feet: .125" Mat Woven Roving .060" Filament Winding

125" 9 Mat Woven Roving

Bottom: .125" Mat Woven Roving

added over entire rib for 3'-6" length centered on invert 9

Figure 6.22 Example of a design for 10,000 gal gasoline RP storage tank

Base width and clear spacing between ribs are established to minimize the number of ribs while providing adequate local buckling resistance for a cylinder wall of approximately the minimum practical shell thickness. Clear spacing must also be sufficient to permit installation of sleeves or nozzles for fill pipes and vents between ribs. The RPs selected for detailed consideration is designed to provide both structural and liquid-sealing qualifies. For example, a smooth liquid tight inner surface is obtained with a resin rich surface layer reinforced with glass filament surfacing veil. It is backed up by a 3.2 mm (1/8 in.) thick liquid seal layer of chopped glass/polyester spray-up. Discontinuous fibers are provided to avoid a continuous path for liquid migration into and along the reinforcement. Additional thickness for structural purposes is provided, either by adding more chopped fiber

541

542 Reinforced Plastics Handbook

reinforced spray-up, or by filament winding. An outer resin rich surface layer is reinforced with a surfacing veil. A silica sand filler may be used of bulk, improved compressive stiffness and economy. Minimum practical total RP thickness is established as 4.8 m m (3/16 in.) for the combined spray-up liquid seal and filament wound structural layers and 6.4 mm (1/4 in.) for an all-chopped fiber spray-up laminate with sand filler. The choice for any construction is made on the basis of comparative design thickness, weight, and fabrication costs. The allchopped fiber reinforced construction using somewhat greater wall thickness than the composite filament wound-chopped fiber wall is determined to provide the lowest tank cost; filament winding provides lower weight. The National Petroleum News Survey, as of the first quarter of 2002 reported that the USA had 170,678 retail gasoline underground storage tank outlets, down from 187,892 at year-end 1987. Total sales of gasoline have grown modestly resulting in average sales volume per outlet increasing. Size and ownership of many stations have changed over the last decade and new, larger-scale facilities are replacing the traditional owner-operated service stations. The wholesale tank replacement business of the 1990's is over and was replaced by more modest growth paralleling the growth rate of GDP and vehicle miles. Adding some new approaches to this segment have been new hyper-market entrants in the gasoline retailing business like Wal-Mart and Lowe's. Another important corrosion segment is the chemical processing industry (CPI), a mature and cyclical, industry that produces 70,000 chemical substances, many of which need protection or require protection for employees handling them. Industrial production of chemicals was expected to grow 4.5% in 2003, according to most recent forecast. Capital spending in 2000 (latest available year) was $31.2 billion, according to the American Chemistry Council. While this total number appears large, chemical producers suffer from the same restrictions on spending as most USA businesses in this economic down cycle. Oilfield activity has benefited from relatively high prices of crude oil in 2001 to 2003 but that has not translated into more exploration nor any more production of plastics such as RP down-hole pipe, line pipe, or sucker rods for the oil patch. Crude prices peaked in 2000 and drilling rig activity declined along with pricing since then. Industrial production indices for this business have been flat through 2002, and 2003 show more of the same. New investments declined about 8% in 2003 and expect the same decline in 2004. The price for West Texas Intermediate was $26 per barrel late in 2002 and ranged from $25-26 per barrel in 2003.

6. Markets/Products 543 Rocket Motor Tanks Very small to large filament wound cases have been fabricated for use on rockets and missiles. As an example, a racetrack filament winding RP fabricating technique was used to fabricate a very large tank (rocket motor case) for NASA. See Chapter 5 Filament Windings, Racetrack and Other Winders.

Cryogenic Fuel Tanks NASA's $5.3 million contract (year 2003) to Northrop Grumman, USA provides continued developing and refining manufacturing processes for constructing large-scale reinforced plastic (RP) cryogenic fuel tanks. One half of a 3.2 m diameter, reusable fuel tank will be fabricated. The manufacturing process will involve a cost saving process that eliminates the need for autoclave curing. Current launch vehicles use single-use, aluminium tanks for storing cryogenic fuels. The RP multiple use tank will weigh 20-30% less than an aluminium tank of the same size. For a given payload. Weight reductions will result in about an 8% decrease in vehicle acquisition costs and a 6% decrease in operational costs.

Marine From boats (ships) to submarines to mining the sea floor, certain URPs and RPs can survive the sea environment. The sea can bc considered more hostile than that on earth or in space. For water surface vehicles, many different plastics have been used in designs in successful products in both fresh and more hostile seawater. Plastic boats have been designed and fabricated since at least the 1940s. Anyone can now observe that practically all boats, at least up to 9 m (30 ft) are made from RPs that are usually hand lay-up moldings from glass rovings, chopper glass spray-ups, a n d / o r glass fiber mats with TS polyester resin matrices. Because of the excellent performance of many plastics in flesh and seawater, they have been used in practically all-structural and nonstructural applications from ropes to tanks to all kinds of instrument containers. Statistics on full year 2002 wholesale shipments of new boats activity was down about 5% compared to the prior year. Industry spokespeople report that consumer confidence and discretionary spending was affected by the events of September 11, 2001 Twin Tower disaster that carried over into 2002 boat sales. The weak state of the economy also compelled many buyers to defer buying-decisions. As expected, various categories of boats fared differently. Outboard boats seemed to be

544 Reinforced Plastics Handbook

holding their own quite well while personal watercraft and jet drive boats continued their declines and were down about 15%. Inboard cruisers recorded their first decline since 1996 (estimated at 11%) and sterndrives were expected to be down 5%. The 2003 boat sales ranging from flat to +5% following the economy situation. Consumer confidence, job creation, and growth in disposable income are relevant indicators of boat buying sentiment. Boats

By far the most important application of RP in marine structures, particularly with respect to volume consumed, has been in boat construction (Table 6.4). This has occurred in both civilian and military markets. Growth continues where it already dominates the small boats with the larger boat market growing. Materials of construction are reviewed in Tables 6.5-6.7. The Mirabella V, to date the largest RP vessel and largest single-masted sailing yacht yet built, was launched in late November 2003 by VT Shipbuilding (formerly Vosper Thornycroft of Portchester, U.K.). The 75m (244 ft) long super-yacht was designed by Ron Holland from Kinsale, County Cork, Ireland and engineered by High Modulus Europe Ltd. Of Hamble, Hampshire, U.K. VT's sister company VT Halmatic built the ship's 90m (292 ft) high carbon fiber mast, the world's tallest RP mast. Its sandwich construction hull and deck were hand laid up and vacuum bagged in disposable open female molds made with wood (medium density fiberboard) with steel backup structures. Duratec mold surfacing material, supplied by Hawkeye Industries Inc., Marietta, Ga., USA, was used to prepare the mold surface, which was treated with an inexpensive wipe-on wax mold release. A vinyl ester primer gel formed the gel coat. Use was made of non-styrenated vinyl ester to avoid pinholes. Stitched multiaxial E-glass materials, supplied by SaintGobain BTI of Andover, Rants, U.K., reinforced with several plies of aramid fiber were wet out with vinyl ester resin from Reichhold of Research Triangle Park, N.C., USA to form the hull skins. Core material was Airex closed-cell foam from Alcan Airex of Sins, Switzerland, with a higher density used below the water line. The 50 mm (2 in.) thick foam was too thick to thermoform, so VT created tongue-in-groove foam planks that were fitted together to form the sandwich core. In order to provide sufficient stiffness to support working and entertainment areas as well as to resist the high longitudinal bending

6. Markets/Products 545 Table 6.4 Material choice/design considerationsfor boat hulls Resin

Phenolic Epoxy Vinyl ester Polyester

Fiber

Carbon: Unidirectionals Cloths Aramid: Unidirectionals Cloths Glass: Unidirectionals Biaxals Multiaxials CSM/combination mats

Core material

Dynamic loading: high strain rate foam Hot climate/dark color hull: crosslinked foam Balsawood/cedar Flame retardant: honeycomb

Flame-retardant properties/available in prepreg format/requires temperature cure Good mechanical properties/available in prepreg format/requires temperature cure/use with any fiber CSM possible required at bond lines/osmosis problems reduced compared with polyester Most inexpensive resin/CSM required between layers/osmosis concern/avoid high performance fibers Used for shells of high performance race craft and stiffening of internal structure Used on all weight critical components not directly exposed to impacts Used mainly on racing sailboats Used to increase penetration resistance and toughness Avoid female mould construction with unidirectionals

Reduce the number of layers and hence the construction time Avoid high modulus thin skins with low densities/care with high processing temperatures Avoid high processing temperatures

High compressive strength/temperature stable/poor shear elongation properties Excellent shear strength/density. Can be expensive

Source: RoyalInstitutionof NavalArchitects,UK.

forces of the very long hull, the upper deck has carbon/vinyl ester skins over a foam core. The deck is built up at rigging attachment points and reinforced with additional unidirectional carbon fiber to carry stress around openings. All internal decks, tanks, and interior bulkheads were vacuum-infused as large, flat glass/vinyl ester, foam cored sandwich panels, then cut to shape by hand and installed. The disposable mold

546 Reinforced Plastics Handbook Table 6.5 Mechanical properties of various laminate constructions

Unit

Single skin CSM/WR polyester

Single skin aramid/ glass epoxy

SandwichSandwich oramid/ carbon/ Strip Fromed glass aramid wood/ aluminum Framed epoxy epoxy epoxy alloy steel

Density

kg/m 3 1900

1300

1400

2010

1800

1350

1450

Fiber weight

%

52

46

47

60

58

50

58

0~ strength

MPa

352

360

424

1050

1090

1000

1133

0 ~Tensile

GPa

13.46

21.97

31.38

55.0

67.0

70.0

100.0

O/o

2.7

1.7

1.4

3.3

2.3

1.8

1.28

MPa

242

75

122

350

360

200

380

GPa

12.99

16.27

19.07

47.0

57.0

50.0

80.0

900 Tensile strength

MPa

283

310

389

39

39

37

42

900 Tensile modulus

GPa

11.70

18.57

32.98

6.0

6.0

5.7

5.9

900

MPa

242

75

122

100

95

90

95

GPa

12.99

14.05

19.07

9.0

10.0

9.0

11.0

Shear strength

MPa

55

38

50

55

55

40

58

Shear

MPa

5.0

5.0

5.0

4.7

4.75

2.57

4.8

fraction %

modulus Ultimate strain 0o Compressive strength 0o Compressive modulus

Compressive strength 900 Compressive modulus

modulus

Source:SPSystems

6 . Markets/Products T a b l e 6 . 6 Effect of thickness of laminate on strength

7/8-3/16 in (psi)

7/4 in (psi)

9,000

Minimum ultimate tensile strength

5/76 in (psi)

12,000

3/8 in and over (psi)

13,500

15,000

Minimum flexural strength

16,000

19,000

20,000

22,000

Minimum flexural modulus

700,000

800,000

900,000

1,000,000

T a b l e 6 . 7 Possible construction for a 20 m powerboat hull, giving equivalent strength

Single Single skin Sandwich Skin aramid/ aramid/ CSM/WR glass glass Polyester epoxy epoxy

Sandwich carbon/ Strip Framed aramid wood aluminum Framed e p o x y epoxy alloy steel

Weight

***

**

.

.

.

.

Stiffness

*

**

.

.

.

.

Abrasion/indent

*

**

****

**

** .

**

** .

. .

.

.

.

.

.

.

.

.

.

. .

. .

.

.

. .

.

.

resistance Low-velocity

.

.

.

.

.

.

.

.

impact: ult. safety from puncture High-velocity

.

.

.

.

.

.

i m p a c t ballistic projectiles Ease of repair

****

***

.

Ease of

***

****

****

.

.

.

. ***

.

.

. *

.

.

. **

. *

maintenance

Key: *Poor, **fair,***good,****excellent, *****outstanding. Source: SP Systems.

was disassembled once fabrication was complete, leaving the hull in position for launching. The huge, hollow mast was fabricated in five internally heated female molds. Stitched unidirectional carbon/epoxy prepreg from Cytec Engineered Materials Inc. of Wrexham Clwyd, U.K. was hand laid up to form the two back sections and the three front sections. Cure was controlled by a computer that monitored the mold heating system to prevent excessive exotherm heat. The five cured sections were bonded

547

548 Reinforced Plastics Handbook

together with an epoxy adhesive. Maximum mast laminate thickness is 40 mm (1.5 in.), to support the 3,400 m 2 (35,912 ft 2) (about an acre) of sail. In 1972, the British launched the world's largest (at that time) RP ship. The H.M.S. Wilton was 46.7 m (153 ft). It became the forerunner of a new class of minehunters that involved other countries (Netherlands, Belgium, Germany, France, Italy, USA, and others). The British program followed with 45.8 to 61 m (100-200 ft) RP minesweepers. The U.S. Navy pioneered in glass-TS polyester RP (hand lay-up) large boat construction with the production of an 8.5 m (28 ft) hull in 1947. RP Navy boats (in the USA and other countries) range from 3.7 m (12 ft) to over 30.5 m (100 ft). Small boat construction was initiated during 1944 at the Philadelphia Navy Yard, Materials Laboratory (D. V. Rosado involved; unfortunately the first vacuum bag molded 15 ft boat gradually sank due to unsatisfactory cure cycle but thereafter none sunk). Untraditional hull design by the U.S. Navy upgraded its minehunter fleet (1991) with a successful ship design based on using glass fiber glass/TS polyester resin. The glass-to-plastic ratio was 1:1. This "Osprey" class minehunter was designed and built by Interimarine S.P.A. of Sarzana, Italy (Figures 6.23 and 6.24). Unlike traditional ships, the new minehunter class does not have longitudinal or transverse framing inside the hull. It has a one piece RP super structure. The design and material combine to provide enough strength and resiliency to withstand underwater explosions. The hull that is not stiffened is engineered to deform elastically as it absorbs the shock waves of a detonated mine. Judicious design simplifies inspection and maintenance from within the structure. The hand lay-up molding process was used, with 98wt% of the structure via a semiautomated lay-up process. Each mat layer was unrolled and sent through an impregnation liquid plastic bath. Up to six layers were laid-up, wet-on-wet, as a package. A crane laid the wet lay-up along a path in the ship's huge female stainless steel mold. Decks, similarly fabricated, were form-fitted to the hull and bolted in place. Not all the RPs was hand lay-ups. Storage tanks for fuel and water used the filament winding process, etc. The ship's RP hull was up to 17.8 cm (7 in) thick in the thickest sections. No core materials were used. Final outfitting with gear and equipment resulted in a 55 m (188 ft) long warship that holds a crew of 44 people. In addition to their use in boat hull construction, RPs has been used in a variety of shipboard structures (internal and external). RPs was used generally to save weight a n d / o r to eliminate corrosion problems

6. Markets/Products 549

Figure 6.23 us Navy's all RP minehunter" view of hull

Figure 6~

us Navy's all RP minehunter; view of deck

550 Reinforced Plastics Handbook

inherent in the use of aluminum and steel or other metallic constructions. Applications included masts, booms, spinnaker poles, deckhouses, bridge housings, radio rooms, storage tanks (potable water, fuel, etc.), ventilation ducts, piping systems, reefer boxes, hatch covers, sonar domes, radomes, floats, buoys, small safety boats, and more. Much more history exists on RP boats/ships in the literature. Aramid, though trailing glass and carbon as a choice for marine composite reinforcement, is favored where resilience is required. Kevlar (DuPont) canoes, for example, are a popular alternative to rotarymolded plastic types and aramid has stood up well to tough, round-theworld duty on Volvo Ocean 60 sailboats. Barracuda Technologies in Brazil chose aramid in designing the hulls for a Hobie 21 beach catamaran intended to sail from Cape Horn to Antarctica. With possible encounters with ice in mind, engineers specified skins of 220 g / m 2 woven aramid cloth sandwiching a core of 10 mm DLAB Divinycell polyvinyl chloride (PVC) structural foam. A 900 g / m 2 glass/aramid stitched fabric (Saint-Gobain BTI) provides extra ice protection below the waterline. Unidirectional aramid/E-glass tape (SP) further reinforces the forward 1 m portion of each hull. A low-viscosity epoxy resin formulated by Barracuda was used in infusing the hulls by vacuumassisted resin transfer molding (VARTM). This aramid-based hybrid construction shaved 70 kg from the weight of standard Hobie cat hulls. Low weight was a particular requirement for a high-speed dash across one of the world's stormiest ocean tracts, between weather windows. Cross beams are of DivinyceH core inside carbon composite skins. Hull-beam attachment points are carbon reinforced. US company Hylas Offshore Yachts uses Twaron aramid, combined with glass, in the hulls and decks of luxury yachts, particularly its latest 54 and 66 ft models. The aramid adds resilience, helping to secure a light structure that can, nevertheless, withstand the rigors of ocean going. In Europe, French builder Catana had resistance to collision damage in mind in selecting Twaron for its latest Catana 52 catamarans. A composite sandwich structure on these yachts incorporates aramid in the outer hull laminates, as well as triaxial glass fiber. Various cores, including PVC foam and balsa, used in the sandwich are 20-40 mm thick, according to purpose and location. Shaped foam core is used below the waterline, though where the hull bottoms could take the ground, the laminate is solid. Weight saving carbon/honeycomb bulkheads are bonded into the hulls while they are still in the mold. Plastic use in boat construction is in both civilian and military boats [28 to 247 ft. (8.5 to 75 m)]. Hulls with non-traditional structural shapes

6

9M a r k e t s / P r o d u c t s

do not have longitudinal or transverse flaming inside the hull. Growth continues where it has been dominating in the small boats and continues with the longer boats. Big boats in the past were up to 188 ft long have been designed and built in different countries (USA, UK, Russia, etc.). Figure 6.25 shows a 247 ft being built. In practically all of these boats low-pressure RP molding fabrication techniques were used.

Figure 6.25 The 247 ft long Mirabella Vunder under construction (courtesy of RP magazine and Julian Hickman)

Material Trends GRPs has been used to build boats in production since the 1940s and now dominate the boatbuilding world. Preliminary work occurred during the 1940s. They provided monocoque structures that are smooth and hydro/aerodynamic as welt as aesthetically pleasing. GRPs are being challenged by other materials that include light, corrosionresistant steels and marine-grade aluminum as well as more advanced fiber FRPs, and by environmentally-driven legislative pressures. Additionally, its maritime reputation has suffered with the awareness that, like any other boatbuilding material, it is subject to degenerative attack by water.

What makes RPs desirable is that plastics can be modified chemically to meet different property requirements. Unfortunately, these requirements are not always compatible. For example, modifications used to cut

551

552 Reinforced Plastics Handbook

emissions of hazardous air pollutants (HAPS) can reduce resistance to hydrolysis, the mechanism behind that insidious enemy of marine GRP, osmotic blistering. At a time when failure to meet Maximum Achievable Control Technology (MACT) limits in the USA and similar limits elsewhere could put companies out of business, the drive for low styrene emissions (LSE) and other pollutants may take precedence over properties like blister resistance, weatherability, and processability (Chapter 3). Glass reinforcement has also moved on since the standard alumina borosilicate E-glass first used in the 1950s. Improved thermal, electrical and mechanical characteristics available with S/R/T, E-CR, S-, R-, T-, and other grades have been combined with sizings and surface modifications designed to produce a stronger fiber/resin interface (Chapter 2). Chopped strand mats (CSMs) and rovings for spray-up have been joined by continuous fiber forms such as knitted, woven or braided fabrics, enabling fibers to be oriented in particular directions. This has led to glass technical textiles moving alongside, and in some cases displacing, textiles of higher-specification fibers such as aramid. Companies with a strong glass focus like Owens Coming, PPG Industries, Ahlstrom and Saint Gobain Vetrotex have between them significantly improved the glass performance. Aromatic polyamide or aramid is an extremely tough fiber that has become most familiar to boaters in characteristic yellow sails, but is also used in boat hulls and rigging. Though not as strong as carbon (specific strength about two thirds), it is (unlike glass or carbon) extremely resilient with good impact resistance. In a collision, sport rigid inflatable boats (RIBs), personal watercraft, canoes, and other small vessels made from Kevlar or Twaron (DuPont and Akzo Nobel trade names) are as likely to bounce as break. With its low weight, aramid competes with rotary-molded plastic in performance canoes, used either alone or in glass or carbon hybrids. In larger craft, although the material is often specified for outer skins to confer damage tolerance, there is perhaps greater merit in utilizing its high tensile strength for inner skins especially in sandwich construction. Inner skins see greater tension loadings due to the pressure of water outside the hull or on external impact. Carbon has attracted a dedicated following among owners willing to pay a premium for performance. An advantage is its specific strength (strength per weight) in tension that is up to 1.5 times that of constructional steel and specific stiffness (Young's modulus per weight). It is about three times that of most metals. It was first used as black RPs by aerospace engineers followed by the marine community. Extremely

6. Markets/Products 553 thin, light, and rigid hulls were a hallmark of the America's Cup yachts that performed in New Zealand (2002 year), while carbon has for some time been a material of choice for performance masts. Other structures made possible by carbon RPs include radical figs, such as the AeroRig (an entire m a s t / b o o m and sails assembly that rotates as one around a pivot point on deck) and unstayed masts. Such innovations avoid the major disadvantage of conventional rigs that masts are strongly loaded in compression by tensioning wires that are, in effect, trying to push the mast through the bottom of the boat. Analogies can be made with a bow and arrow. Carbon's strength and stiffness also make innovative winged and canting keels practical (the latter can be rotated round a pivot to vary their angle to the hull). Racing and cruising powerboat design has similarly benefited from the material's possibilities. Brodrene Aa, based in Hyen, western Norway, has made a breakthrough in the use of carbon fabrics in commercial ferries. The company is experienced in the construction of high speed boats made from carbon fiber such as the Moonraker, the world's fastest luxury yacht with a top speed of 67.6 knots. Recently it has turned its attention to the producing a cost effective carbon composite vessel. Using multiaxial fabrics produced by Devoid AMT AS, Langevag, Norway, over a core material, Brodrene has produced the Rygerkatt. This boat is designed for use as a passenger ferry and will make an average of 200 stops a day, carrying up to 62 passengers. Industrial design company Harreide Designmill has given the boat its distinctive look. Carbon fiber was used to reduce the weight of the boat so that it will use less fuel. This makes the use of carbon fiber (previously the exclusive territory of luxury yachts, racing boats, and military ships) economical by greatly reducing operating costs over the life of the vessel. At 18.5 m (60 ft) long, 7.5 m (24 It, 6 inches) wide, the boat weighs just 27 tonnes. The use of carbon fibers has resulted in a structural weight reduction of 40% over traditional materials. With the increased strength and reduced weight achieved by using multiaxial fabrics the boat has a top speed of 29 knots and an operational speed of 24.9 knots. At normal operating speeds the ferry requires 5.90 liters of fuel per nautical mile. The commercial series was launched with the Ryger Doktoren an ambulance boat with a top speed of 44 l~ots. This model combines great maneuverability with high speeds. The successes of this vessel led to the construction of the Rygerkatt ferry. A representative of the high-tech marine market, Sydney's (Australia) leading yacht manufacturer, McConaghy's, reported that changes in

554 Reinforced Plastics Handbook

processing along with changes in design tools arc driving the highperformance yacht market. Once described as "standing under the shower tearing up $100 bills," today ocean racing enthusiasts ride on hulls virtually designed and built in an environment of increasing sophistication. In the past three years (2002-2004) each major project at McConaghy's has involved improvements in materials, processing, and design, such as specialized vacuum infusion processing. The company recently built the 90 ft long, 135 ft high all-carbon-fiber Alfa Romeo and others, like the new 98 ft Wild Thing out of Hart Marine (Mornington, Melbourne). These boats are definitely large, elite applications of advanced composites. Though high specifications and, perversely, high prices have fed the fashionable desire for carbon in premium markets, continued fails in carbon prices could extend the material's market base. Producers (notably Zoltek) that have developed production routes based on alternative cheaply sourced acrylic precursors believe that breaching the psychological $5/lb barrier would transform carbon's prospects. So far price levels of some $7/lb are about the best that can be obtained. Underwater Hulls

Information on underwater hulls is reviewed in Chapter 7 Filament Windings, Pressure Hull Structures.

Windmills Overview

Use of RP energy rotor blades continues to expand worldwide. During 2001 worldwide it was estimated billion dollars worth of wind energy rotor blades were in use. These blades, up to 45 m (148 ft) long in the case of some of the new offshore installations, used about 55,000 ton of materials, most of which are glass fiber reinforced plastic (GFRP). It was determined that only RPs could deliver the combination of strength, stiffness, low weight, damage resistance, durability and low maintenance that today's larger blades must exhibit. Producing RP blades, which account for about a fifth of the total cost of a turbine installation, is becoming a considerable industry in its own fight. This industry has expressed a great willingness to invest and undertake R&D projects. During 2000 saw a dip in the growth rate for the global wind market to 26%, from 37% in 1999. This was largely because of a hiatus in the

6-Markets/Products 555 USA, where just 53 megawatts (MW) of new capacity were added of a world 3500 MW. Fortunately, this was partly compensated by European growth rates of up to 40% and investment that broadly held up in other regions. With its limited land area, Denmark is leading moves towards offshore wind exploitation, a sector in which the economics favor very large turbines and blades. Small facilities erected at Vindeby in the Baltic and near Jutland in the early 1990s were the world's first offshore wind farms of any sort. The first large offshore wind farm in Europe was at Middelgrunden, near Copenhagen, where twenty 2 MW turbines provide the power. Turbines of up to 5 MW are offshore, with Denmark and Germany being lead adopters. Such turbines required large advanced blades in which carbon RP is needed to confer the required stiffness. In the Netherlands, providing all 400,000 kWh of electrical power for a conference center at the Hague from wind and solar sources during recent climate change negotiations constituted a symbolic statement supporting this important international event. One of the world's largest wind plants was recently completed near Naples in southern Italy. Under a $260 million contract, the Italian Vento Power Corp and the Tomen Corp of Japan erected 282 Vestas 600 kW turbines, power from which is sold to Italian state utility ENEL. Finance has been arranged, with 23 participating banks, for new wind farms totaling 283 MW planned for southern Italy and Sardinia. Shell could be on the brink of a massive windfall in Nigeria in which the oil giant triples its production from the West African country. In a move that kicks off Shell Wind Energy's European commercial wind operations, the company will purchase a 40% stake of the La Muela Wind Park in northeast Spain from TXU Europe Energy Trading B.V. Muela comprises 132 N E G - M I C O N 750-kilowatt wind turbines, split into two 49.5 megawatt wind parks located 15 kilometers southwest of the city of Zaragoza. To determine potential wind sources for wind farms in New Mexico and South Dakota, USA, two 82 m carbon fiber RP meteorological measurement towers are to be used. These guyed towers, built by IsoTruss Structures of Brigham City, Utah, USA, will measure wind resources at the hub height of a number of large, megawatt-size wind turbines. Compared with the steel towers often used, the carbon fiber structure is easier to transport and can be delivered and assembled at a significantly lower cost. Global Energy Concepts of Dayton, OH, USA is using carbon fiber prepreg for large wind blades for the Vestas' 90 m long blade. This

556 Reinforced Plastics Handbook

company has an order for ten 65 ft long production drilling riser joints for the Magnolia Platform in the Gulf of Mexico. Different parts of the USA are gradually evaluating the potential of developing RP energy rotor blades such as off the shores of Cape Cod, Massachusetts. About 25% of the USA has enough wind power to generate electricity at the cost of natural gas or coal-fired plants. Wind power accounts for less than 1% of the nation's energy supply, while coal and natural gas generate about two-thirds of the electricity. A study by Stanford University, California, USA, researchers measured wind speeds that hit turbines perched at the equivalent of a 20-storey building. Because wind is, intermittent wind power farms in locations with high wind speeds could be linked into energy networks that may provide a reliable and abundant source of electric power. The mill, Mohawk Paper Mills in Cohoes, NY located near the banks of the Hudson River, began purchasing nonpolluting wind power, malting it one of the first paper mills in the USA to use wind power for manufacturing operations. There interest was due to wind turbines being cost-effective renewable energy technology, produced electricity with zero fuel and zero pollution. Mohawk purchases wind energy from Community Energy, Inc., a marketer of emission-free wind energy in the Eastern USA. The wind energy for the Cohoes facility comes from New York State's largest wind farm near Syracuse. The project uses state-of-the-art 1.5megawatt (MW) wind turbines. The wind turbine power Mohawk is using translates into 4-million kilowatt hours of power, enough for 12,000 tons of paper production. Community Energy officials said this move would help remove more than 6.1 million pounds of carbon dioxide from the air; the equivalent of taldng more than 300 cars off the road each year. These wind plants use many wind turbines, often assembled on a large singe wind site called a wind farm, to produce electricity. In Germany the wind is overtake water as the most important sustainable source of electricity. Just around one hundred twenty years ago, Germany commissioned the first hydroelectric plants, and water was the most important green source of electricity in Germany. However, 2002, wind blew away water as the most important sustainable source of electricity. At the end of September 2002 year, there were 14,467 wind turbines with a capacity of 13,404 MW installed in Germany. The 2002 wind-based electricity generation in Germany was about 25 billion kilowatt hours or for the first time more than the hydroelectric plants can achieve.

6. Markets/Products 557 The use of RP materials in turbine blades used to generate electricity from wind is one of the more exciting, new developments in the USA RP industry. The USA pioneered much of the early development and first installations in the 1970s, but commercial efforts languished in subsequent years. Wind turbine designs continued to make efficiency gains in the 1990s and Denmark, Germany, Spain and other European countries accelerated their adoption of wind energy encouraged by government support of renewable energy. According to estimates from early 2002, Germany is now the world leader in installed wind energy with approximately 8,000 MW of capacity. Spain has 3,000 MW, Denmark has 2,500 MW, and the United. States is around 4,000 MW India, Brazil and China have progressive wind energy programs, as do other countries. Driving demand is the fact that the cost to produce electricity using wind turbines dropped from 34-38 cents per kwh in the 1970s to around 4 cents per kwh today. That compares well with natural gasgenerated electricity at 3-5 cents and coal at 2-4 cents. Plus wind energy produces no environmental side effects. Globally, the business has been growing more than 30%/yr during the past five years. This worldwide growth rate will slow down but is likely to remain in the double-digit growth range for several more years.

Underwater Blades A prototype power station featuring RP blades is running in a northern Norway strait. Hammerfest Strom's 120 tonne submerged turbine uses similar principles to a wind turbine, with 10 m long glass reinforced plastic (GRP) blades capturing the energy of tidal currents. The installation is located in a narrow strait where the current speed is both fast and uniform. Unlike wind energy, tidal currents are highly predictable, repeating themselves in known cycles. This simplifies plant design as the loads subjected to the components are known to a high level of accuracy. Currents generally flow in only two directions, unless the strait is very wide. This means the nacelle of the turbine can remain in a fixed position, with only the blades rotating with the reversing current (pitch control) to capture the maximum energy. Access is much more of a challenge than for wind turbines, and therefore the turbines are built with a modular design allowing critical components to be lifted out of the water for maintenance or repair. The plant generates 700,000 kWh of power per year, which is enough electricity for 35 homes. (Website: www.e-tidevannsenergi.com).

558 Reinforced Plastics Handbook Fabrication

Wind turbine blades represent one of the success stories for the RP industry with increasing market demand for longer blades. This has caused designers to incorporate carbon fibers adding stiffness, while blade manufacturers are moving away from wet lay-up processes to ensure that the several tonnes of materials that make up a blade can be processed safely and quickly. As a result the raw materials have changed from wet-lay up systems to prepregs and both wet and dry infusion materials (Chapters 4 and 5). Within this rapidly altering environment, there is the need to continually reduce costs and increase output. As final refinements are made to the process and materials, the focus switches to the mold as a means to deliver further improvements. At present blade molds incorporate several common features as follows: 1

two or three robust blade mold shells fabricated from RP materials, often formed over a male plug of the blade shape

2

structural steel framework to support each mold shell during blade processing

3

mechanical closing mechanism to bring the blade mold shells together to form the blade shape

4 5

heating system to cure the blade; and several ancillary systems and features specific to the blade manufacturing process, including vacuum and a resin delivery system.

Because of their size, these molds are often stand-alone equipment packages and as such need to be sufficiently robust to permit repeated daily process cycles with the minimum of maintenance downtime. They must offer the blade manufacturer the means to reliably produce blades with the minimum number of operators in the shortest possible time. Benefits gained with proper designed blades include: reduced mold height to eliminate cumbersome platforms around the molds; improved speed and safety of mold closing mechanisms; accurate blade shape and blade edge tolerances; and all electrical, vacuum, and other services within the structural framework. All of these elements contribute to minimize the blade manufacturing and finishing time permitting the blade manufacturer to reduce costs while meeting targets for blade output. The high quality and robust design of these blade molds ensures minimum downtime and maximum output both of which serve to reduce costs. As blades become longer, the molds themselves obviously will become larger and heavier. The molds will be required to process a larger

6. Markets/Products 559 quantity of materials in an increasingly rapid cycle time. Such molds will need to permit a variety of blades to be produced with the minimum downtime. The molds will need to process a larger quantity of materials in an increasingly rapid cycle time. To achieve this target the mold maker will offer improvements such as: 1 2

automation for safe materials handling, improved processing and fast demolding delivery of one-shot manufacturing processes to increase output and eliminate finishing

3

modular design permitting blade alternatives by only changing parts of the mold

4

smart molds that are self monitoring both for blade processing and for maintenance purposes; and elevated temperature performance for more rapid cure of the blade.

5

Appliances, Electrical/Electronic Both TS and TP compounds have many applications in electrical appliances and electronics products, both as internal components and as external housings (Figure 6.26). The choice between the two groups of materials depends largely on size and service temperature. Processes used are primarily injection molding and compression molding.

Figure 6.2G An iron includes the use of RPs

560 Reinforced Plastics Handbook

Polyester bulk molding compounds (BMCs) are widely used for large electrical switchgear moldings, and the latest types of low-shrink high impact BMCs are used for the housings of power tools and small kitchen appliances that must meet severe impact standards and may also have to resist heat. A long-established application of TSs is for printed circuit boards (PCBs), and the trend towards 3-D molded PCBs; also are TPs. High performance PCBs use glass fiber constructions where the others use paper, wood fibers, etc. Pultruded profiles are ideal for electrical trunking, conduit, and high voltage line insulators where outdoor environmental conditions are likely to be harsh (for impact, chemicals, moisture, and heat). Using a special grade of polyester molding compound, a Belgian lighting manufacturer has replaced metal components for an emergency lighting unit for hospitals, offices and public places. It now uses two injection moldings in TS polyester molding compound, one of which has a special white coating and acts as a reflector, withstanding a working temperature of 100C. The compound has UL flammability approval to V-0 at 1.5 mm thickness. A special low-smoke sheet molding compound (SMC) is used for highperformance electrical housings used in the channel tunnel and in the Eurostar train. Combining good electrical properties with exceptionally high fire retardancy and low smoke without use of halogens, the molding forms part of a larger module, the common block that converts power flow to the train motors. Filament-wound RPs are increasingly replacing ceramics for insulators for transformers and high-voltage switchgear, insulating and supporting tubes in high-voltage test equipment and switch rods in power switchgear. They do not shatter in the event of an internal explosion and offer more reliable performance in earthquake-risk areas. Typical are epoxy resin/glass tubes with silicone rubber shielding, as produced by Isola, Germany, using CNC winding machines. Production to close tolerances reduced the need for subsequent machining. Low mass and high stiffness are other advantages in dynamic switchgear applications, using aramid fiber where it was necessary to achieve the stiffness. Tensile breaking load of a switch rod of 36 mm inner diameter and 3 mm wall thickness is more than 100 kN and density of aramid-RPs is only 65% of that of glass. GEC Alsthom is using a void-free filament winding process to produce insulating linings for end-bells of large two-pole 1000 MW generators. This replaces phenolic/asbestos-lined woven glass fiber molded by

6

9Markets/Products

vacuum bag, giving a more resilient medium to counter the greater forces of very large generators. The technique is based on vacuum treatment of the glass and resin before wet filament winding. The wound element is gelled and step cured on the mandrel. By careful attention to processing conditions, the final product is transparent, confirming voidfreedom. Interlaminar shear strength can be increased by up to 35% over conventional GRP and increase in glass content from 55% to 75% by weight gives a much higher compressive modulus. A new plastic pulley, a cost effective replacement of a cast aluminum counterpart, is now used in all Hotpoint washing machines. The injection molded pulley, made of DuPont glass fiber reinforced Zytel nylon resin offers lower part cost vs. casting, without compromise in mechanical properties. The pulley was designed and manufactured by Rolinx Plastics Co. Ltd., UK, in conjunction with appliance maker Merloni UK. Most domestic washing machines use a pulley to transmit torque from the motor to spin the washing machine inner drum. Rolinx saw an opportunity to replace the cast aluminum pulley with a reinforced nylon resin, a mechanically stiff plastic used to make reliable, highperformance and cost-effective components and systems. Dimensions of the Zytel replacement part needed to remain identical to the aluminum one, while the center boss section had to withstand a compressive force of 105 Newton (N). At the same time the pulley was required to withstand a belt tension of over 300 N and operating temperatures of 70C and above, with noise levels not permitted to be greater than the aluminum variant. Finite element and mold flow injection analyses confirmed that the Zytel part offered the most mechanically sound option. Additional physical testing, involving the continuous running of the washing machine for the duration of the machine's 'lifetime' confirmed the analytical data (Rolinx Plastics Co. Ltd., Ledson Rd., Wythenshawe, Manchester, UK; telephone: +44161-610-6400; fax: +44-161-610-6474; e-mail: enquires@rolinx, co.uk).

Consumer and Other Products In this chapter and throughout this book different RP products have been presented that only provide an introduction to the many produced during the past half century. New products tend to always be on the horizon. Zoltek Companies Inc. (St. Louis, Mo., U.S.A.) receive a 1 million lb order for its commercial grade fiber tow, the largest single order the

561

562 Reinforced Plastics Handbook

company has received for that fiber type (2003). Two additional orders also were announced totaling 800,000 lb. The customers are sporting goods manufacturers in China and Taiwan. The large-scale orders are expected to generate up to $10 million in revenue through the end of calendar year 2004. RP high technology has been in the sports and leisure markets, in the shape of advanced materials that were originally developed for aerospace applications. Carbon fiber-RPs is used for fishing rods, pole vault pools, golf clubs, tennis racquets, kayaks, and others. In these products, justification was based on their ability to provide considerable improvement in operational efficiency (Table 6.8). Table 6.8 Examplesof reinforced plastic leisure and sport products Industry

Process

Reinforcement

Resin

Fishing rods Golf club shafts Snowmobile hoods golf carts Snow skis water skis RV bodies

Pultrusion

Roving Roving Gun roving

Polyester Vinyl ester Polyester Vinyl ester Polyester

Pultrusion Spray-up

Low pressure compression Woven roving roving Spray-up Gun roving Continuous lamination Panel roving

Polyester

The global market for sports and recreation products has been stagnant during the last few years. This fact has been blamed on a number of causes however, the Sporting' Goods Manufacturers Association International (SGMAI) reports that the electronics and entertainment industries are providing the chief competition for leisure dollars. For example, the movie and home electronics industries in the USA each grew 21% in sales, while wholesale sporting goods and accessories dropped 2% in 2001. The increased popularity of these indoor, sedentary activities may continue to cause a decline in the number of people who only occasionally participate in sport or exercise activities. According to SGMAI, a large portion of sporting goods production has moved to Asian countries to take advantage of lower manufacturing costs. USA exports of sports and recreation equipment decreased substantially during 2002. Exports of golf clubs, fishing rods, tennis and other racquets, water skis, and arrows all declined in both sales value and volume, some losing up to 52% compared to 2001. However, there are opportunities for smaller volume applications for RPs such as

6-Markets/Products 563 hockey sticks and baseball bats continue to grow within the sports in terms of participation and consumption of RPs, making up for losses experienced in other applications. Developed during 1960s was a form of composite armor that uses glass ceramic files bonded to an aramid fiber reinforced multi-ply laminate. A projectile rapidly dissipates its kinetic energy in destroying the ceramic layer and any remaining energy is absorbed as the laminate is deformed to contain the broken fragments of the projectile completely. It can deflect high-velocity rifle rounds at about half the weight of conventional steel armor. The system has been developed for the C-130 Hercules aircraft, where it is fitted to the cockpit floor and sides and the crew seats, giving protection against high-velocity small arms fire. A liquid oxygen (LOX) converter situated in the nose wheel bay is also protected. The overall thickness of the composite armor is 14.5 mm (0.57 in.); the typical weight is 26.4 k g / m 2 (5.4 Ib/ft2). The Hercules armor comprises 83 panels coveting 14.8 m 2 (160 ft 2) of the flight deck and LOX unit, with a total weight of 392 kg (864 lb). Panels can be quickly applied or replaced by ground support staff. Fire-resistant storage boxes and crates, to meet the requirements of the German VdS (Association of Indemnity Assurance Companies) are molded in an especially developed TS polyester sheet molding compound (by DSM-BASF Structural Resins, in association with BYK Chemic, Martinswerke, Mitras Kunststoffe and Wientjes). They have been classified by VdS as class VI (nonflammable packaging), according to the guidelines for sprinkler systems- a classification previously held only by sheet metal containers. The crates measure 500 x 390 x 280 mm and are compatible with all commonly used transport systems and existing crates with regard to dimensions and stackability. The surface resistance of the sheet-molded compound (SMC) can be adapted to meet requirements for storage of parts sensitive to electrostatic charges, and the crates can easily be cleaned with common agents and processes. A unique system for restoring wooden poles, used throughout the USA for supporting utilities such as telegraph wires, is to wrap deteriorating or mechanically damaged poles with alternating layers of glass fiber fabric and phenolic resin. This gives them outstanding strength and fire resistance, with a significant extension of service life. Poles are usually treated with creosote and pentachlorophenol for preservation. Once treated, they are considered hazardous waste in some states, so costly disposal methods must be used. M1 told, it can cost up to $10,000 for each pole replacement. Glass-fiber reinforced has been solving the problem of many agricultural corrosive environmental parts. As examples are mudguards

564 Reinforced Plastics Handbook

on machinery carrying mud from fields on to roads, for crop-sprayer, and chemical sprayers. Different RPs is used in furniture. An example is SMC used in the office furniture sector. One of the world's largest suppliers of office furniture continues to mold nearly 50% of its output of office chairs in SMC instead of conventional wood or steel. Use is also made for chair backs and seat shells, where it finds the material sufficiently stiff and dimensionally accurate. The SMC used is A graded, giving class 2 fire retardancy, meeting British Standard 5459 level S for continuous loading service. Production of SMC chairs is about 2000 units a week: cost-savings arise from reduced costs of tooling and assembly, as well as the elimination of the need for painting. Paper industry producers are generating additional demand for corrosion products due to environmental projects required by the socalled "Cluster Rule" published by EPA in 1998. MACT regulations have been very slow in coming but phases for compliance fall due by 2006. Due to the massive scale of some of these facilities, potential sales of plastics such as RP materials could be on the up swing.

Aerospace Plastics use is rather extensive in primary and secondary aeronautical structures that include aircraft, helicopters, balloons, to missiles space structures. Lightweight durable plastics and high performance RPs save on fuel while resisting all kinds of static and dynamic loads (creep, fatigue, impact, etc.) in different and extreme environments. The chief challenge to the plastics industry is not in pounds of plastics needed but rather in the translation of plastic development technology into production line expertise. The aerospace industry is geared to pay high prices for plastics with exceptional properties; as high as hundreds of dollars per pound with up to ten-fold cost increases for fabricated products plus additional dollars to conduct continual testing and evaluation to insure safety of aircraft operation. Aircraft

Starting in the past, RPs continue to expand their use in aircraft. These RP materials have been used in primary and secondary components. Table 5.5 (p. 284) includes some of the applications. Figures 6.276.29 and Table 6.9 provide information on the growth of primary structural use of RPs.

6 . Markets/Products Figure 6.27 Historical trend with plastic composites (RPs)

Figure 6.28 RP composites implementations

ACAP LEAR FAN 2100 lf'~' -BUSINESSJETS

HELICOPTERS

~

r

LANDINGGEAR,

50I

~. 40

~

! O~E'EOPMENTJ

o~o 30 m

1C

ADV FIGHTER

1PRODucTION'1

i APPLICATION|

z

~,<

2o

~ FUSELAGES WINGS "~.~

10

FLAPS

0 1950

' ~ .~.~ , ,, .

.

1960

.

.

.

/

/

I

.oI_ / L I 2001 j 0

/

f

./

~

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NACELLES

SECONDARY

,.A,.' COMME.C,AL, ST.UCTU.E

_

_ ~

~ P R I M A R Y

~

1:.15 F-16

STRUCTURE 1:-18 LEARAVIA (MAINLY MILITARY) AV-8B I

'80 '81 '82 '83 '84 '85 '86 '87 '88 '89

CALENDAR YEAR

I

I

1990

2000

Figure 6.29 USA RP composites aerospace airframe primary and secondary structure production

1000

/ L e~176 /

t

1970 1980 FISCALYEAR

1200I ADVANCED COMPOSITE AIRFRAME PRODUCTION, KLBIYR FLY AWAY WT

COMMERCIAL TRANSPORTS

565

566 Reinforced Plastics Handbook

Table 6.9 Examplesof RP in aerospace

Material

Application

Chopped glass/polyester

Molded secondary components, substitution for metal castings, electrical housings, and parts. Chopped E-glass/epoxy Complex electrical components, leading and trailing edges, and highly loaded complex shapes. Primary and secondary structure for subsonic E-glass fabric/epoxy aircraft, ducts, housings, bulkheads, intake manifolds, helicopter blades, radomes, etc. (Probably the most versatile material) High temperature resistant applications; high E-glass fabric/polyimide energy radomes, engine fairings. Higher strength application; rotor blades, wing E-glass - unidirectional/epoxy tapes components for smaller aircraft. Stiffer and stronger than E-glass for more critical S-glass- unidirectional tape/epoxy applications. E- and S-glass, filament wound/epoxy Radomes, high pressure tanks. Same as above for higher temperature use. E- and S-glass, filament wound/ polyimide Structural application for higher stiffness and Graphite/epoxy fatigue resistance; suitable for most higher loaded structural parts. Boron/epoxy Same as above, but limited to shapes with simple curvature. Used for high speed aircraft for high temperature Graphite/polyimide resistance. Aramid (Kelvar)/epoxy Higher efficiency radomes, high impact resistance, lower weight. Excellent for helicopters and ITL-aircraft. Many Glasslgraphitelaramidlboronlepoxy combinations of fibers may produce a better part hybrids than individual fibers alone.

Figure 6.30 provides a comparison between advanced RPs and metallic specific tensile strengths. Here, the strengths of the RPs used are realistic working stress levels for multidimensional laminates as they would be used for wing or stabilizer covers. It also shows that RPs can be very hole-sensitive relative to metals that can be corrected or compensated for with proper RP designs. However, this problem is offset by far less sensitivity to tension fatigue. Their effectiveness in compression applications is shown in Figure 6.31 where the low density significantly reduces panel weight but, in contrast to metals,

6. Markets/Products 567 2.0

~- ........

1.5 SPECIFIC TENSILE 1.0 STRENGTH.

Flip

Gr/Ep 5116 HOLES ~ . . - - -

Ti

/Ep 5/16 HOLES

. -

.5

., . . AI

--

GLASS/EPOXY

KEVLAPIIEPOXY - -

0

1930

BIEp NO HOLES

_....,.~~"-

ir

106 IN.

GrlEp NO HOLES

-

. . . . . .

STEEL \

-

-

GLASS/POLYESTER

- - -

I

1940

SPRUCE

!

I

1950

I

1960

I

1970

I

1980

I

1990

2000

YEAR OF INTRODUCTION

Figure 6.30 Specific tensile strength (strength/specific gravity) of different materials kg/m 2 m

LB/IN. 2 IN.

300-]_ .01

AI 2024-T3

Ti+ 6AI-6V-2Sn

PANEL WEIGHT W/b

1

" / j ~ ~ , , , , ~

0

~

0

0

/

5

2

0

8

)

~

LB/IN.

1000

0

B/Ep (AVCO 5505l

I

2000 l

10

|

3000

4000

I I

I

20

6000 I

30

I

MN/m_

STRUCTURAL INDEX Nx/b

m

Figure 6,31 Comparing aircraft compression panelweights of different materials

compression fatigue and low ener~Ampact damage become design considerations. In the past, RP components were commonly designed with a safety factor of 5 times the ultimate strength, such as the 1944 all plastic airplane. In the meantime, significant improvements in materials of construction and quality control during processing with sophisticated design analysis via computers have been developed. Safety factors have

568 Reinforced Plastics Handbook

been reduced for certain structural parts having values such as 1.2 or less. The result has been to reduce the weight and cost of components. Although the general parameters for optimizing airplanes arc well known, their relative importance is permanently changing, and diverging cost development redefines design criteria and "cost-efficiency". In the field of structural design the cost of fuel, and consequently the demand of the operators for the best fuel-efficient aircraft, has pushed the development activities and their components in the direction of advanced RPs. Where even if the RP component may cost more than that of aluminum or other material, its weight savings can significantly reduce fuel consumption; thus, cost-efficiency results. Fuel efficiency is a function of the aircraft's power plant, aerodynamics, and structural efficiency. With military aircraft, flight distance is gained is an important gain. Producing airplanes at lower costs is another aspect of advanced RP structural applications. In many cases, the carbon and aramid fiber RP components compare favorably with the cost of conventional component structures, in spite of the rather high material costs. An important aspect here is the possible simplification of the design. For example, the complicated leg fairing of the Airbus was replaced by a simple all-RP sandwich (honeycomb core) panel reinforced by two RP beams. Besides a weight savings of about 30%, the production hours were reduced by 27%. The technology of RPs reached a level of maturity which led to its use on stabilizers for practically all USA fighter aircraft since 1970 (F-14, F-15, F-16, YF-17, F-18, etc.), and these parts are generally giving long-fife, trouble-free service. Fighter wing covers (F-18 is an example) and the covers and substructures of a V/STOL attack aircraft (A V-8B) are made from graphite/epoxy advanced composite material (Figure 6.32). The unconventional and revolutionary LearAvia Lear Fan 2100 twin turboprop set a trend for business aircraft with the use of graphite and aramid/epoxy for all primary and secondary structures with the exception of the landing gear (Figure 6.33). The single engine Smith Prop-Jet also used graphite/epoxy for its wing, fuselage, and tail. The latest generation of large commercial aircraft [Boeing 757, 767, 757, and 777 (Figure 6.34)] uses advanced RPs extensively for such secondary structural parts as ailerons, rudders, and spoilers. The RP technology's current level of maturity and experience makes it a strong candidate for a large proportion of the airframes of future commercial and military aircraft. Extensive usage of advanced composites has been committed to production on the Boeing aircraft family of the 757, 767, and 737. The history of Boeing's use of RPs is well documented. Applications include secondary exterior structure with functional and decorative internal

6. Markets/Products 569

Figure 6.32 RP applications in the AV-8B airplane

Figure 6,33 RP applications in the LearAvia Lear Fan 2100 twin turboprop airplane

components. The application of RP materials to Boeing is not new. An RP fabrication facility existed in the 1920s using cellulose fibers from spruce lumber in a lignin binder matrix and linen fabric coated with dope. As these early composite materials were replaced by aluminum, the industry has now gone through a full-scale materials and process evolution. Now the advanced fiber RPs has been replacing aluminum in a number of aircraft applications. The first of the fiber-RP materials to be used on Boeing commercial airplanes was the glass fiber/epoxy composition. Boeing has an extensive

570 Reinforced Plastics Handbook 9GRAPHITE/KEVLAR EPOXY 91900 LB TOTAL WEIGHT

BOEING 757 9COMPOSITE COMPONENTS NOSE LANDING GEAR DOORS MAIN LANDING GEAR DOORS RUDDER ELEVATORS SPOI LE RS AILERONS WING TO BODY FAIRINGS ENGINE STRUT FAIRINGS FLAP TRACK FAIRINGS NACELLE COMPONENTS (TOTAL WEIGHT OF SIMILAR PARTS ON BOEING 767 IS 2860 LB)

Figure 6.34 RPapplications in the Boeing 757 airplane

and very successful experience base with this material. The first Boeing commercial jet transport, the 707, used glass fiber RP components, and usage increased with each succeeding model through the 747. Most of these applications were lightly loaded components such as fairings and interior components. Even with the extensive exterior surface area involved, the 747 has only approximately 1% structural weight of glass/ epoxy RPs, aluminum at 81%, steel at 13%, titanium at 4%, and other materials at 1%. Boeing is now developing their twin-aisle 7E7 commercial passenger jetliner, a plane designed to lower operating costs sharply. It is targeted to cost less than $8 billion. It is targeted to compete with the low cost successful Airbus jets. Airbus undercuts Boeing by as much as 15%. Boeing expects that the 7E7 will be attractively priced and still generate a 10% profit margin. With the performance to weight advantages of carbon fiber the 200 to 250 passenger Boeing 7E7 high speed jet (mach 0.85) light weight commercial airplane will have the majority of its primary structure (wings, fuselage, etc.) made of carbon RPs. Result will be that more than 50% of the aircraft's structural weight will be RPs. This program alone will consume about 25 ton (55,000 lb) of carbon fiber RPs on each aircraft, translating to about 1,450 ton (4 million lb) per year, based on production of five aircraft per month.

6. Markets/Products 571

It will use 15 to 20% less fuel when compared to other wide-body airplanes. Production will begin 2005. First flight is expected in 2007 with certification, delivery, and entry into service 2008. To get there, Boeing is rewriting the way it does business. While they devise the 7E7s basic outlines, an unprecedented amount of detail work is being farmed out, especially to Japanese companies. For the first time, Mitsubishi, Kawasaki, and Fuji, which helped build the 777, have been invited to design and produce the fuselage and wings. Boeing is taking this step in part to get Japan Airlines and All Nippon Airways to launch the 7E7. But Boeing also expects the Japanese government to provide money to local suppliers to help fund the development. In the mid-1960s, design studies started at Boeing for the structural application of advanced RPs. At that time, boron filament was considered the most promising reinforcing material. As studies, component fabrication, and testing continued, it became increasingly clear that graphite or carbon fiber would be the predominant high strength, high modulus material used because of economic and other practical considerations. Up to 50% of all home built airplanes today are made with RPs. Commercial airplanes have at least 5wt% (some projections have been at 10 wt%) unreinforced and RPs. Certain past to future military airplanes, contain up to 60 wt% plastics used in primary and secondary structures). Other airplanes take advantage of plastics performances such as the McDonald-Douglas AV-8B Harrier with over 26 % of this aircraft's weight using carbon fiber-epoxy RPs; other plastics also used (Figure 6.35). Examples of plastic used in other aircraft are shown in Figures 6.36-6.38. The use of RPs in successful secondary structures occurred during the early 1940s. A major product designed and fabricated (E-glass fiber/TS polyester resin) were radomes that have continued to be used (Figure 6.39). Figure 6.40 radome configurations show effects on radar waves emanating from the radar reflector or antenna through the RP material (meeting fight thickness requirements of the glass fiber/TS polyester laminated structure) so that the waves are properly focused in the required direction. This is basically the same setup as when optical waves are transmitted through a transparent medium so as not to cause visual distortion (Figure 6.40). Small to large ground radomes using RP spherical and other shapes are used. Figure 6.42 shows the use of RPs in the more modem Boeing 767 airplane that has been in service for a long time. In this commercial airplane use is made of RP and URP. In this view G = graphite, K =

572 Reinforced Plastics Handbook

Figure 6.35 View of the McDonald-DouglasAV-88 Harrier combat aircraft using carbon-epoxy RPs

Figure 6.36 AirbusA-320 componentsof RPs

6

9M a r k e t s / P r o d u c t s

Figure 6,37 Examplesof RPs in the de Havilland Dash-8 only on exterior

Figure 6~

Large RP rotating radome on top of the Grumman Hawkeye airplane; airplane also contains RP components

573

574 Reinforced Plastics Handbook

Figure 6 . 3 9 Exampleof an RP radome with a rain erosion coated surface that is located on the front of the airplane Radome ~

Streamlined-radome L [ Original wave

Original

An'enna~jS~"

/

T

directi,ion Lobe direc

Reflected wave - / Antenna

1 9,

Original wave .../

Figure 6 . 4 0

j

"~-el:le~ewave

Radar waves emanating through a radome

6

9M a r k e t s / P r o d u c t s

Figure 6.41 Ground antenna protected by a 150 ft diameter RP radome

Kevlar (DuPont's aramid), and F-fiber glass. During the past half century, other airplanes have included RPs, including all RP airplanes. Figure 6.43 highlights RP parts on the Boeing 777 that include improved damage resistance and damage tolerance; parts that have been redesigned for simple, bolted, or bonded repairs; weight savings; and corrosion and fatigue resistance.

Figure 6 . 4 2 Examplesof RP on commercial aircraft such as the Boeing 767 in use for many decades

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576 Reinforced Plastics Handbook

Figure 6,43 Examplesof reinforced plastic parts on Boeing 777 The first 14 m (46 ft) tall vertical tail fin, for the Boeing 777 airliner was one of the first major uses of RPs for primary structures in a USA commercial aircraft, and saves about 450 kg (992 lb) compared with a comparable metal fin. RPs will represent about 9% of the structural weight of the 7 7 7 - more than ten times the use of RPs in thc 757 and 767 jets. Other structural composite parts include horizontal tail stabilizers, control surfaces, engine cowlings, landing gear and nose radome. Non-structural applications include the interior and systems ducting. The trend is to expand the use of plastics, particularly RPs. The past, present, and what arc ahead innovations in aircraft target for faster, smoother flights. They have given rise to more new plastic developments and have kept the plastics industry profits at a higher level than any other major market principally since they can meet different structural-to-weight to environmental conditions. Virtually all plastics have received the benefit of the aircraft industry's uplifting influence. The use of optically transparent plastics in windshield canopies and other glazing areas is another example of their functional use. Low K-

6

9M a r k e t s / P r o d u c t s

factor of urethane foam, silicone and polyimide require them in the different thermal environments. Adhesives have made it possible to make lighter metal structures without the use of rivets that give nonhomogeneous stresses and interfere with surface smoothness. Innovations range from individual parts to the complete plane. There is the armored flight deck door to help secure flight decks. The one-inch thick door includes an RP sandwich structure using a phenolic honeycomb core between phenolic-glass fiber laminated facing sheets. New on the drawing board is the preliminary Lockheed Martin's F-35, the Joint Strike Fighter (JSF), plane with extensive use of RPs. This $19 billion system-development and demonstration phase extends to year 2012 with initial flights in 2005. Included are thick composite wings to help carry the physical load in this multifunction aircraft, which is targeted for a broad international market. On its outside it uses low observable of the stealth plane. The program uses more primary structural composites and less titanium than recent designed and built fighter airplanes. Composites account for about 36wt% of the proposed structural weight. Of the total, graphite fiber-epoxy RPs represents about 32% with glass fiber- and graphite fiber-bismaleimide make up 2% each. By comparison, composites make up about 30% of the structural weight of the Air Force's B-2 bomber, 26% of the Air Force's nextgeneration F-22 fighter, and 18% of the Navy's upgraded F / A - 1 8 E / F . The RPs will be fabricated to close-tolerance composite components. When these parts are assembled to the aluminum substructure, they will be a perfect fit. In the monocoque construction, thick, heavy composite skins carry more of the total load than in other fighters by unitizing the skins. This approach minimizes the number of seams on the aircraft. With this design the interior frame uses one-half as much substructure as exists on the F-22. What has been happening is the development in use of RP in aerospace, with the breakthrough to major structural components. In multi-role combat aircraft there is widespread use of RPs, including wings, tail, and most of the fuselage, almost all of the visible airframe structure of which is RPs. Carbon fiber RPs arc used for the front fuselage, wings, fin, control surfaces, doors, engine covers, and much of the landing gear; aramid RPs for wing fillets, tail fairing and nose radome. The European fighter aircraft (EF A) will have substantial use of RP, and would have been some 30% heavier with a conventional metal structure. Necessarily, the culture of commercial aviation is driven by safety-first philosophy, which has to ensure that nothing can go on an aircraft until it is fully characterized RPs, with their inherent high variability, have

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578 Reinforced Plastics Handbook

not always fitted well into that culture. The pioneering use of glass and carbon fiber for fin and wing box structures in the European A TR series regional turboprops remains pioneering: few airframe manufacturers have to date followed this example for larger aircraft. The largest manufacturers, Boeing, McDonnell-Douglas and Airbus Industrie are gradually adopting RPS for primary airframes. The European Airbus has been more progressive, but much of the growing content remains in secondary and tertiary structures such as appendages, doors/hatches, floors and control surfaces. Airbus, will need greater RP capacity, based on their two new programs. The A380 double-deck passenger jet is using RPs in many new applications, such as the flap track beams, floor beams, the resin film infusion (RFI) rear bulkhead, and much of the center wing box. For much of its fuselage and for the leading edge on the vertical stabilizer, the aircraft will feature GLARE (GLAss fiber-REinforced aluminum) panels, multilayered laminates built up with glass fiber/epoxy and aluminum sheet. GLARE is in the vanguard of advanced composites, using three different materials to achieve a unique set of properties. No simple RP can match GLARE's impact resistance (or enable airlines to continue to have shiny fuselages) The future of RPs will certainly lie with optimizing different combinations of fibers, plastics, ceramic, and metallic materials in ways that will only be limited by imaginations. Although the A380 will use a lower proportion of RPs than the 7E7 and fewer will be built, it will still require more than 1,000 ton (2.2 million lb) of RP per year. Another program at Airbus is the A400M military transport aircraft. The aircraft will be able to carry a greater proportion of its weight due to the extensive use of RPs, which will make up 35 to 40% of the latter's structural weight. RP components will include not only the usual RP stabilizers and moveable wing components, but the main wing box as well as the first application of RPs on a wing of this size. These three Boeing and Airbus programs alone will use more than 3,000 ton (6.6 million lb) of RPs per year. This compares with current RP structures capacity in civil aircraft, which has been estimated at just over 2,000 ton (4.4 million lb) a year, most of which will still be required, as the aircraft that the new programs will replace use very small amounts of RPs. Airbus has targeted to match Boeing's 7E7 materials technology leap, launching a new aircraft of its own with an RP wing and fuselage. There are many indications from the program's research into RPs for fuselage, center wing box, and wing that Airbus is preparing to do just that. Question is whether Airbus will build an RP mid-sized, twin aisle to

6

9Markets/Products

rival Boeing's new aircraft or go for a smaller, high-tech single aisle aircraft. For the RP industry, it makes little difference. The total quantity of material used is a function of the number of aircraft and the weight of RPs on each plane. The quantities required will be similar. For the main use of RPs in structures, one has to turn to the defense industry. There are major RP structures in the US Stealth bomber, including wings, aft body and other components, produced at Boeing's 22,000 m 2 Composites Center of Excellence at Seattle, Washington. Mso made there are the wings, aft body and other components of the F-22 air superiority fighter; advanced new folding wings for the US Navy's cartier-borne A-6 Intruder strike jet; lightweight primary and secondary tail structure for advanced technology Boeing 777 widebody twin-jet; and most of the structure of the Condor high-altitude long-endurance HALE aircraft. The B-2 represents the world's largest application of RPs in aerospace engineering to date; the upper and lower skin panels of the wing are thought to be the largest single-piece aircraft RP structure yet made. The outboard wing sections are effectively flying fuel tanks, each of 20 m length, with a total wingspan of 52 m (170.5 ft). The aft center section includes a weapons delivery system for nearly 20 tonnes of munitions, twice the capacity of the B-52. Boeing has a raked wing design for the stretched B767-400, with carbon fiber skins over metal spars, saving 1000 kg over previous metal winglets, and is considering composite spars as the next stage. Boeing is also pursuing RP fuselage and wing structures, which were being separately studied by it and McDonnell-Douglas prior to their merger, under a $130 million NASA-funded Advanced Composites and Technology (ACT) program, aiming at 25% weight-saving and 20% cost-saving compared with conventional aluminum structures. A sewing technology for RPs, developed by NASA and Boeing (and based on traditional methods) could make aircraft wings based on aluminum a thing of the past. The airframe manufacturer has invested $6 million in the development by Ingersoll Milling Machine, Illinois, of a 28 m long advanced stitching machine (ASM), which can produce 12.3 x 2.5 m wing panels by stitching together up to 20 layers of carbon fiber/resin RPs, to a total thickness of over 30 mm. The process replaces riveting with metals. In practical terms this can eliminate the need for some 80,000 mechanical metal fasteners in the panel sizes under study. The result is that a full-scale aircraft wing could be manufactured, not only 25% lighter in weight but also 20% less expensive.

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580 Reinforced Plastics Handbook

The ASM is controlled by an overhead gantry, with computers and lasers to position stitches along 38 axes of motion. Four heads stitch 36 mm thick fabric at 3200 stitches/min and braided stiffeners are then sewn on to give greater strength. Finally, the panels are treated with an epoxy film adhesive and autoclaved. High-performance RTPs have moved out of prototypes into commercialscale production and are out-performing RTSs for certain aircraft applications. Glass/polyether imide (PE1) stamp-formed components are used in commercial helicopter interiors, where they give mechanical performance equal to RTSs, particularly phenolics, but offer significantly lower heat release. Airworthiness Notice 61 specifies that, using the modified Ohio State University test rig, figures of 6 5 / 6 5 should be achieved (total positive heat release over the first two minutes of exposure for each of three or more samples must not exceed 65 kW mins/m2). Phenolic systems usually average about 5 4 / 5 5 , which is dangerously close to the limit when painted. A decorated monolithic glass/PE1 panel, however, has given results of 13/17, offering a valuable safety margin. Techniques such as stamp forming, a method similar to stamping of sheet metal, have been developed. The Bell/Boeing V22 Osprey flit-rotor aircraft uses carbon fiberreinforced polyether etherketone (PEEK) for doors and housings of the engine air particle separator and for fuel vent tanks (Figure 6.44). TP polyimide (TPI) forms the basis for an injection-molded spline adapter in the drive train which tilts the rotors. Costs were reduced some 22%. The parts were developed by RTP Company with Bell Helicopter and molder RAM Inc., Texas. The tanks are molded by the lost core process. Business aircraft made from RPs include the mainly glass fiber Chichester Miles Leopard (UK) and the Raytheon Permier 1 six-seater, notable for a largely filament-wound carbon-epoxy/honeycomb/ carbon-epoxy fuselage. A hybrid light jet aircraft was developed in the

Figure 6.44 A range of RPs is used for components of the Osprey tiltrotor aircraft

6

9Markets/Products

USA by Raytheon, following the success of its all composite turboprop, Starship. Called Premier 1, the business jet has an all RP fuselage with metal alloy wing. The carbon fiber/epoxy honeycomb fuselage is produced by computer-controlled automated machines, which are quicker than the hand lay-up used for the Starship. The cabin is reported to be 178 mm higher and 203 mm wider than competitors. The construction saves weight and is stronger than aluminum. Westland, the UK helicopter manufacturer, which is also a leading molder of RP aerospace structures, is molding main wing flaps for the MD-11 civil airliner. Measuring some 5 m and 10 m (16.4 ft and 32.8 ft) long, the flaps are made of advanced technology RPs, incorporating carbon fiber-reinforced epoxy top and bottom skins bonded to a methacrylic foam core, the only metallic components being goose-neck attachments to the flap track mechanism of the aircraft. The design and construction was selected to be significantly lighter than conventional metal vanes, improving damage tolerance and giving better interchangeability, validated by experience in service. Phenolic RPs is used. In the cargo hold of the Jetstream 41, the lining material is a self-extinguishing glass fiber/phenolic laminate, giving also durability and lightweight with low smoke and toxic emissions. Fiber RPs is used for the interior surfaces of the 4.8 m 3 size (170 ft 3) baggage area. Contract awards for military RPs continued to proliferate. GKN Aerospace Services of Farnam, Surrey, UK recently was awarded an approximately $4 million contract to supply the control surfaces and edges package, including tool design and production, for the 14 flying and 8 ground test aircraft being built during the F-35 Joint Strike Fighter's System Development and Demonstration (SDD) phase. The carbon/bismaleimide RP details require very close manufacturing tolerances, due to the stealthy nature of the aircraft. Other F-35 work was awarded recently to GKN's subsidiary in Australia, which will support Northrop Grumman in the design, analysis and manufacture of F-35 center fuselage parts. GKN Australia is one of 19 Australian firms that will be involved in the F-35 program. GKN Aerospace also has received a contract from Sikorsky Aircraft Co., USA to develop and manufacture side skin panels for the RAH-66 Comanche military helicopter. The contract initially calls for 42 cored RP test panels for material qualification and three actual 3-ft by 4-ft forward side panels. Sikorsky has the option to extend the contract to include 73 actual production panel sets, for a total value of $1.5 million.

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582 Reinforced Plastics Handbook

Boeing has announced that itsAH-64 Apache Longbow helicopter will receive a new RP main rotor blade, manufactured by the company's Mesa, Ariz. facility. The blade, with a more efficient airfoil shape and higher overall twist rate, provides improved hover and forward flight performance. Made with S-2 glass fiber and carbon fiber with epoxy resin, the new blade has a much simpler design than the original and costs less to manufacture. The original blade had four spars and was difficult to fabricate. The new blade, although it is hand laid up, has a single spar and a simpler design, still meets ballistic requirements and lasts longer. The new blade fits all existing AH-64s and will be part of the 269 new aircraft to be manufactured and delivered through the year 2006. Boeing will award this work to a outside contract manufacturer. Hitco Carbon Composites Inc. of Gardena, CA., USA has won a fouryear contract to build vapor barrier assemblies for 60 Boeing C-17 aircraft. The autoclaved, foam-cored glass fiber/epoxy panel assemblies measure 6.5 m long by 5.5 m wide (21 ft by 18 ft) with compound curvature, designed to prevent fuel and fuel vapors from the main fuel tanks from penetrating the plane's cargo area. The Boeing 7E7 and Airbus A380 as well as the growing military applications, such as unmanned aerial vehicles, are using more carbon fiber. Designs are targeted for low-cost ways to incorporate carbon fiber into parts, using puhrusion, carbon fiber sheet molding compound (SMC), and automated manufacturing methods. One application that has not received much consideration yet in USA is the Homeland Security Act's requirement for strengthened, blast-hardened critical structures, for which carbon fiber is, so far, the only qualified material, according to GHL Inc. Interestingly enough, the prognosticators believe that aside from the traditional aerospace and recreational arenas, the biggest growth area will be industrial applications. Boeing Co. announced an end-of-year blockbuster award from the U.S. Navy for the production of an additional 210 F / A - 1 8 ElF Super Hornet aircraft. The multi-year contract is valued at $8.6 billion. An additional $1 billion is earmarked for design and development of an upgraded F / A 1 8 - G version that will carry more weaponry and electronics. Forty-two planes will be purchased each year from 2005 through 2009. Boeing's Super Hornet program in St. Louis has already produced 170 of the tactical aircraft, which are roughly 20% RPs. Boeing builds the forward fuselage and wings and performs final assembly while parmer Northrop Grumman supplies the center and aft fuselage. Commercial small airplane business jet segment appears to be booming. Honda Motor Co. entered the market with its new experimental

6. Markets/Products 583

compact jet, featuring an all-carbon fiber RP fuselage and fuel-efficient Honda-developed HFl18 jet engine. The plane recently completed a successful flight test. Meanwhile work continues at Adam Aircraft, Englewood, CO., on the A700 small business jet, with first deliveries expected in late 2004. The A700's airframe is a carbon fiber/epoxy and honeycomb sandwich construction, powered by two Williams International FJ33 fanjet engines. FAA certification is expected. Carbon fiber RPs have played a key role in commercial and military aircraft for the Antonov Aeronautical Scientific/Technical Complex located in Kiev, Ukraine. RPs have been used in aircraft designs since the early 1970s. Over the company's history, a large number of its aircraft designs have been manufactured, including the AN-225 sixengine jet transport, the largest aircraft on record. A team of Antonov engineers initially began designing and manufacturing RP components to replace noncritical metallic parts such as doors, trim tabs, and panels, but in the few years that followed, comparative performance tests convinced the company that RPs could meet design specifications, so they were put into production. In 1975, the AN-72 model carried approximately 980 kg/2,156 lb of glass fiber RP in the belly fairing, engine nacelles, radome, and other areas. The AN-124 super heavyweight model, the world's largest series production aircraft, incorporated RP parts throughout the airframe for a total of 5,500 kg/12,100 lb. The experience accumulated during their first stage opened the way for the transfer from low-stressed and medium stressed RP structural components to highly loaded structures. In the late 1980s, design work began on the AN-70 transport model. They made the decision to develop RP torsion boxes for the tail structure. An analysis of RP designs used by other aircraft OEMs for highly loaded structures demonstrated that all showed, to some degree, the influence of more traditional metallic designs. Antonov designers wanted a completely new design concept to fully exploit the unique properties of RPs, while eliminating stress concentrators, minimizing the potential for impact damage and making production as straightforward and automated as possible. Their concept was a torsion box structure for the vertical and horizontal stabilizers. They reduced the number of parts to be joined, and rejected, to the extent possible, the use of mechanical fasteners to eliminate stress concentrator sources of RPs. The design for the 10m/32.5 ft high vertical stabilizer and the two 7m/22.75 ft long horizontal stabilizer torsion boxes essentially involved tape-wound, hollow rectangular spar

584 Reinforced Plastics Handbook

sections with spar caps (five in the vertical stabilizer and four in the horizontal stabilizer), molded with each other and covered with a core and outer skins to form a sandwich structure. The walls of the hollow spars and the outer sandwich skins, loaded primarily in shear, are designed with a high percentage of 45 ~ fibers. The unconventional sandwich core consists not of honeycomb, but 15 m m / 0 . 6 inch square continuous carbon fiber prepreg tubing wound with 45 ~ prepreg tape bonded to the spars and oriented chord-wise (parallel to the airflow, or front to back). Spar caps were made mainly with unidirectional prepreg tape. Root and tip ends of the spar caps were reinforced and the parts are attached to the fuselage with metallic fittings at a flange joint. Structural strength analysis showed that the deformation of the integral structure under load differed considerably from the deformation of a traditional ribbed and riveted structure, which required a new approach for stress and strain analysis. Analytical tools and an in-house software program were developed to allow accurate strain analysis and optimum use of the RP material for this unusual design. A major challenge for developing the RP torsion boxes was manufacture. Automation was obviously preferred, given the parts as well as their critical structural function. Tape winder, by PROGRESS Production Assoc. (Savelovo, Russia), was winding parts as large as 2.5 m / 8 . 1 ft in diameter and up 39 ft in length.

design for size of the developed capable of to 12 m /

A matched set of tapered rectangular winding mandrels for the spars was designed from glass fiber, based on the similarity of its linear coefficient of thermal expansion (GTE) characteristics with the GTE characteristics of carbon. One kit of five mandrels was fabricated for the vertical stabilizer, and a second kit of four mandrels was made for the horizontal stabilizer. For the small, square tubing used as core, a cable braider was used to wind prepreg tape over long, hollow mandrels made with extruded PVG and silicon rubber. Selected materials included unidirectional carbon fiber/epoxy prepreg tape, 0.08 mm/0.003-inch thick and 10mm/0.4inch or 2 0 m m / 0 . 8 inch wide, used for the skins, spar webs and the tubular cores. Thicker 0.24 mm/0.009-inch (240 to 265 g m / m 2) carbon/epoxy tapes were used for the spar caps. The 130C (265F) cure epoxy was selected for its long out-time (three to four months). The ARGON facility (Balakovo, Russia) was the material supplier. All materials were certified by the AllRussian Aviation Materials Research Institute (VIAM, Moscow, Russia).

6. Markets/Products 585 Turbine Engine Fan Blades Developments of aircraft RP turbine intake engine blades that started during the early 1940s may now reach an important stage in its development. Major problem that caused destruction of engines in the past has been to control the expansion of the blades that become heated during engine operation. The next generation of turbine fan blades should significantly improve safety and reliability, reduce noise, and lower maintenance and fuel costs for commercial and military planes because engineers will probably craft them from carbon fiber RP composites. Initial feasibility tests by University of California at San Diego (UCSD) structural engineers, NASA, and the U.S. Air Force show these carbon composite fan blades are superior to the metallic, titanium blades currently used. Turbine fan blades play a critical role in overall functionality of an airplane. They connect to the turbine engine located in the nacelle, a large chamber that contains wind flow to generate more power. These usually 6 ft long blades create high wind velocity and 80% of the plane's thrust. It is reported that the leading cause of engine failure is damaged fan blades. Failure may occur from the ingestion of external objects, such as birds, or it may be related to material defects. If it is a metallic blade and it breaks, it can tear through the nacelle as well as the fuselage and damage fuel lines and control systems. When this happens, the safety of the aircraft and its passengers is threatened, and the likelihood of a plane crash increases. In contrast, if an RP blade breaks, it simply crumbles to bits and does not pose a threat to the structure of the plane. However, breakage is less likely because composite materials arc tougher and lighter than metallic blades and exhibit better fatigue characteristics. A multiengine plane can shut down an engine and continue to fly if a blade is lost and no other damage has occurred. A composite blade disintegrates into many small pieces because it is really just brittle graphite fibers held together in a plastic. A titanium blade, however, will fail at the blade root, causing large, 4- to 6-foot blades to fly through the air. As designed, the RP blades are essentially hollow with an internal rib structure. These rib like vents direct, mix, and control airflow more effectively which reduces the amount of energy needed to turn the blades and cuts back on noise. Most engine noise actually comes from wind turbulence that collides with the nacelle. By directing air out the back of the fan blades, the noise can be reduced by a factor of two. And by drawing more air into the blades, engine efficiency is improved by 20%.

586 Reinforced Plastics Handbook There also exists an embedded elastic dampening material in the blades, which minimizes vibrations to improve resiliency. Because the blade is lighter and experiences lower centrifugal force further enhanced the blade's durability occurs. Small-scale wind tunnel tests show they last 10 to 15 times longer than any existing blade. The No. 1 maintenance task is the constant process of taking engines apart to check the blades. These new blades should lend themselves to more efficient production techniques. If you use titanium, you need to buy a big block of it and machine it down to size, wasting a lot of material. As reported, this is very time consuming, and one has to worry about thermal warping. The RP allows for mass production. It is fabricated into a mold, making the process more precise and ensuring the blades are identical. NASA will test the new blades in large-scale wind tunnels at the NASA Glenn Research Center in Cleveland. If successful, they could see installation by year 2004.

All Plastic Airplanes A historical event occurred during 1944 at U. S. Air Force, WrightPatterson AF Base, Dayton, O H with a successful all-plastic airplane (primary and secondary structures) during its first flight. The BT-19 aircraft was designed, fabricated, and flight-tested in the laboratories of WPAFB using RPs (glass fiber/TS polyester surface skins hand lay-up that included the use of the lost-wax process (Chapter 5) sandwich constructions (Chapter 7) for the fabrication of monocoque fuselage, wings, vertical stabilizer, etc. The sandwich (cellular acetate foamed core) constructions provide meeting the static and dynamic loads that the aircraft encountered in flight and on the ground. (D. V. Rosato worked on the development and fabrication of this airplane.) This project was conducted in case the aluminum that was used to build airplanes became unavailable (plants destroyed) or capacity limited. The wooden airplane, the Spruce Goose built by Howard Hughes was also a contender for replacing aircraft aluminum. Extensive material testing was conducted to obtain new engineering data applicable to the loads the sandwich structures would encounter; data was extrapolated for long time periods). Short term creep and fatigue tests conducted proved to be exceptionally satisfactory. Latter 50 of this type aircraft were built by Grumman Aircraft that also resulted in more than satisfactory technically performance going through different maneuvers. Figure 6.45 shows the first flight of the all plastic airplane. In order to develop and maximize load performances required in the aircraft structures, glass fabric reinforcement/TS polyester resin sandwich

6-Markets/Products 587

Figure 6.45

Flight test of the first all reinforced plastic airplane

laminated construction (with varying thickness) was oriented in the required patterns (Chapter 7). Figure 6.46 shows is an example of the fabric layout pattern for the wing structure. Figure 6.47 is a view of a section of the wing after fabrication and ready far attachments, etc. The fabricated monocoque sandwich fuselage structure is shown in Figure 6.48.

Figure 6.46

Layout of fabric reinforcement designed to meet structural requirements

In addition to this all RP airplane being built and flown, their have been other planes built and flown with parts or complete structures that used RPs and URPs. Examples follow:

588 Reinforced Plastics Handbook

Figure 6.47

View of RP fabricated monocoque sandwich aircraft wing

Figure 6.48 View of RP fabricated monocoque sandwich fuselage structure

1934 Fibrous sheet material, such as paper, is used together with a heat-hardened phenolic condensation product and a layer of vulcanized rubber bonded to the material to minimize sound transmission. It gives desired flexibility for airplane cabin construction. Developed by H. Swan and S. Higgins USA. 1937 In Germany, airplane builders use polyester to bond wooden subassemblies. 1939 Germany builds ME-109 airplane wings with polyester resin developed from Ellis's patent.

6. Markets/Products 589

1942 J. F. Dryer, USA, develops a luminous material suitable for use in instrument boards of automobiles, airplanes, etc., made by adding fluorescent dye to a urea-formaldehyde varnish and impregnating the fabric body sheet with it. 1943 Prepreg wood (plastic-impregnated reinforced wood) used to construct airplane propellers. 1944 Army Air Force (latter the Air Force), Dayton, OH, USA issues Technical Reports on the BT-15 airplane that was made of RP. An example is the report entitled Molded Glass Fiber Sandwich Fuselage for BT-15 Airplane issued 8 November. 1944 Helicopters are being designed using glass fiber-TS polyester primary and secondary structures, including rotor blades. 1950 A. Dreyling and C. W. Johnson, Du Pont, USA, patent an airplane fabric which is pre-doped with an aqueous emulsion of a cellulose derivative, dried, and then mounted on the airframe and doped again. 1955 Taylor Craft Model 20 airplane uses RP wings, engine cowlings, doors, seats, fuel tanks, instrument panels, and fuselage skins from nose to fin trailing edges. 1960 Leo Windecker (dentist) builds the Windecker Eagle airplane. The Windecker aI1-RP airplane, after seven years (1967) of development, is successfully flight tested. It is the first plastic composite to receive USA FAA certification. This glass fiber-epoxy (Dow plastic and construction) plane has a monocoque fuselage. 1974 Upper aft carbon/epoxy rudder program begins on the DC-10 airplane by McDonald Douglas Aircraft Co., CA, USA, 1981 The Solar Challenger aircraft on 7 July flew. It was a lightweight sun-powered airplane that made aviation history by flying from France to England [370 km (230 miles in 5 h and 23 min.). Its 16,128 wing-mounted solar cells powered an all plastic lightweight plane 98 kg (217 lb)]. It used DuPont's Kevlar aramid fiber reinforced plastic structures, Mylar shrunk polyester film outboard skins, Delrin acetal control pulleys, Zytel ST supertough nylon landing gear wheel, etc. 1984 Beech's (USA) Starship, an all plastic RP composite, lightweight business turboprop airplane, successfully completes its proof-ofconcept flight. 1984 The twin-turboprop Aviek 400 aircraft promotes the use of advanced plastic composites. 1984 Five sets of plastic composite horizontal stabilizers are installed on the Boeing aircraft 737.

590 Reinforced Plastics Handbook

1986 Burt Rutan and Jeanna Yeager, USA, designed and built the Voyager. This twin-boomed airplane using advanced RP composites is the first to fly around the world without refueling. 2003 The small airplane business jet segment appears to be booming. Honda Motor Co. entered the market with its new experimental compact jet, featuring an all-carbon fiber RP fuselage and fuelefficient Honda-developed HFl18 jet engine. The plane recently completed a successful flight test. Meanwhile work continues at Adam Aircraft, Englewood, CO., on the A700 small business jet, with first deliveries expected in late 2004. The A700's airframe is a carbon fiber/epoxy and honeycomb sandwich construction, powered by two Williams International FJ33 fanjet engines. FAA certification is expected. 2003 With the performance to weight advantages of carbon fiber the 200 to 250 passenger Boeing 7e7 high speed jet (mach 0.85) light weight commercial airplane will have the majority of its primary structure (wings, fuselage, etc.) made of carbon RPs. It will use 15 to 20% less fuel when compared to other wide-body airplanes. Production will begin 2005. First flight is expected in 2007 with certification, delivery, and entry into service 2008. The crash of American Airlines Flight 587 in November 2001 briefly threatened growing public acceptance of RP structures, when newspaper accounts suggested that faulty carbon fiber/epoxy laminates in its vertical tail fin might have caused the Airbus A300 to go down. The ongoing investigation exonerated RPs with the aircraft industry moving ahead with new designs, featuring more composites than ever before. Observers look for an upturned in late 2004 or 2005 of carbon reinforced composites. Boeing and Airbus are using more carbon fiber on their new models, and older models take on more carbon as they get updated. Innovative aerospace fabricators push the carbon-fiber envelope with new, low-cost advanced RPs such as pultruded key parts on the Airbus A380. The huge Airbus A380 will carry 30 metric tons/66,000 lb of structural composites; 16% of its airframe weight. 2003 Many subcontractors supply Boeing and Airbus Industrie. An example is Mitsubishi Rayon Co. Ltd.. Tokyo, Japan. They were selected as an Airbus A380 supplier of unidirectional and woven carbon fiber prepregs, incorporating two types of carbon fiber (medium-elasticity and high-strength fiber). Materials will be produced both in Japan and by the company's affiliate Structit SA, Vert le Petit, France. Airbus expects to complete materials certification by the end of 2004.

6

9M a r k e t s / P r o d u c t s

2003 FACC AG (Ried, Austria) fabricated a demonstration RP replacement part for a highly stressed aluminum spoiler center fitting on the Airbus A340-600. It used a low-viscosity epoxy resin in the resin transfer molding (RTM) process because the part's complex shape would be difficult to produce consistently and costeffectively with hand lay-up. 2003 Contract awards for military RPs continued to proliferate. GKN Aerospace Services of Farnam, Surrey, UK recently was awarded an approximately $4 million contract to supply the control surfaces and edges package, including tool design and production, for the 14 flying and 8 ground test aircraft being built during the F-35 Joint Strike Fighter's System Development and Demonstration (SDD) phase. The carbon/bismaleimide RP details require very close manufacturing tolerances, due to the stealthy nature of the aircraft. Other F-35 work was awarded recently to GKN's subsidiary in Australia, which will support Northrop Grumman in the design, analysis and manufacture of F-35 center fuselage parts. GKN Australia is one of 19 Australian firms that will be involved in the F-35 program. GKN Aerospace also has received a contract from Sikorsky Aircraft Co., USA to develop and manufacture side skin panels for the RAH-66 Comanche military helicopter. The contract initially calls for 42 cored RP test panels for material qualification and three actual 3 ft by 4 ft forward side panels. Sikorsky has the option to extend the contract to include 73 actual production panel sets, for a total value of $1.5 million. Boeing has announced that its A H - 6 4 Apache Longbow helicopter will receive a new RP main rotor blade, manufactured by the company's Mesa, Ariz. facility. The blade, with a more efficient airfoil shape and higher overall twist rate, provides improved hover and forward flight performance. Made with S-2 glass fiber and carbon fiber with epoxy resin, the new blade has a much simpler design than the original and costs less to manufacture. The original blade had four spars and was difficult to fabricate. The new blade, although it is hand laid up, has a single spar and a simpler design, still meets ballistic requirements and lasts longer. The new blade fits all existing AH-64s and will be part of the 269 new aircraft to be manufactured and delivered through the year 2006. Boeing will award this work to a outside contract manufacturer. Hitco Carbon Composites Inc. of Gardena, CA., USA has won a four-year contract to build vapor barrier assemblies for 60 Boeing C-17 aircraft. The autoclaved, foam-cored glass fiber/epoxy panel

591

592 Reinforced Plastics Handbook assemblies measure 6.5 m long by 5.5 rn wide (21 ft by 18 ft) with compound curvature, designed to prevent fuel and fuel vapors from the main fuel tanks from penetrating the plane's cargo area. 2003 The latest version of the A H - 6 4 Apache helicopter has improved structurally to carry more weaponry and payload. RP structures makes the rotor blades with a filament-wound fiberglass spar that is combined with aramid core material and titanium forgings in a metal-bonding process. 2003 Utah State University, Logan, Utah, U.S.A. was one of several groups who took on the challenge of creating a replica of the original Wright Brothers' flying machine, which first took to the air 100 years ago, on Dec. 17, 1903. The Utah State creation, while a replica of the historic aircraft, was constructed with a number of RP materials, which the Utah group claims would have been the basics available to the Wright Brothers had they conceived their design today.

Wright Brothers Flying Machine Replica Utah State University, Logan, Utah, U.S.A. was one of several groups who took on the challenge of creating a replica of the original Wright Brothers' flying machine, which first took to the air 100 years ago, on Dec. 17, 1903. The Utah State creation, while a replica of the historic aircraft, was constructed with a number of RP materials, which the Utah group claims would have been the basics available to the Wright Brothers had they conceived their design today. The USU Wright Flyer replica made its maiden flight in March 2003, in Utah, and then traveled in September to Dayton, Ohio where it was displayed at the SAMPE Technical Conference (Figure 6.49). The aircraft and the USU team were featured in a December History Channel special commemorating the flight anniversary. The tubular spars that support the two 40 ft long wings were filament wound by ATK Thiokol Propulsion (Brigham City, Utah, U.S.A.) using T C R Composites (Ogden, Utah, U.S.A.) c a r b o n / e p o x y tow prepreg material. Fitted over the spars were evenly spaced 0.5 in. (12.5 ram) thick ribs made of Rohacell polymethacrylimide (PMI) foam (supplied by Degussa Performance Plastics, Darmstadt, Germany) with aramid/epoxy face skins. The aramid was needed to give the foam some additional strength for torsional loads. Other RP components included the struts that connect the two wings and the wings' leading and trailing edges. All RP materials were donated

6. Markets/Products 593

Figure 6.49

Wright Brothers flying machine replica with Donald V. Rosato (right) and Dominick V. Rosato at the controls

by suppliers, including Patterned Fiber Composites Inc., Lindon, Utah, U.S.A. and Hexcel Composites, Dublin, Calif., U.S.A., in addition to those mentioned above. Majority of the fabrication and assembly was accomplished by USU flight technology students.

Atmospheric Flights During the past decades, progress in aeronautics and astronautics has been remarkable because people have learned to master the difficult feat of hypervelocity flight. A variety of manned and unmanned aircraft have been developed for faster transportation from one point on earth to another. Similarly, aerospace vehicles have been constructed for further exploration of the vast depths of space and the neighboring planets in the solar system. RPs has found numerous uses in specialty areas (ablation, insulation, etc.) such as hypersonic atmospheric flight and chemical propulsion exhaust systems. The particular RP employed in these applications is based on the inherent properties of the material or the ability to combine it with another component material to obtain a balance of properties uncommon to either component. Plastics have been development for uses in very high temperature environments. It has been demonstrated that RPs are suitable for

594 Reinforced Plastics Handbook

thermally protecting structures during intense rocket and missile propulsion heating. This discovery became one of the greatest achievements of modern times, because it essentially initially eliminated the thermal barrier to hypersonic atmospheric flight as well as many of the internal heating problems associated with chemical propulsion systems. Modern supersonic aircraft experience appreciable heating. This incident flux is accommodated by the use of an insulated metallic structure, which provides a near balance between the incident thermal pulse and the heat dissipated by surface radiation. The result is that only a small amount of heat has to be absorbed by mechanisms other than radiation. With speeds increasing (8,000 fps), heating increases to a point where some added form of thermal protection is necessary to prevent thermo structural failure. Hypervelocity vehicles transcending through a planetary atmosphere also encounter gas-dynamic heating. The magnitude of heating is very large, however, and the heating period is much shorter. This latter type of thermal problem is frequently referred to as the reentry heating problem, and it posed one of the most difficult engineering problems of the twentieth century. A vehicle entering the earth's atmosphere at 25,000 fps has a kinetic energy equivalent to 12,500 Btu/lb of vehicle mass. Assuming the vehicle weighs a ton, it possesses a thermal energy equivalent to 25,000,000 Btu. This magnitude of energy greatly exceeds that required too completely vaporize the entire vehicle. Fortunately, only a very small fraction of the kinetic energy converted to heat reaches the body while the remainder is dissipated in the gas surrounding the vehicle. Materials performance during hypersonic atmospheric flight depends upon certain environmental parameters. These thermal, mechanical, and chemical variables differ greatly in magnitude and with body position. In general, they are concerned with temperatures from about 2,000 to over 20,000F (1,100 to 11,000C), gas enthalpies up to 40,000 Btu/lb, convective/radiative heating from 10 to over 10,000 Btu/ft2/see. The stagnation pressures is less than 1 to over 100 arm., surface shear stresses up to about 900 psf, heating times from a few to several thousand seconds, and gaseous vapor compositions involving molecular, dissociated, and ionized species. To operate in these extreme conditions ablative materials can be used (Table 6.10). Mechanical Parameters Structures traveling at very high velocities are adversely influenced by many mechanical aspects of the environment, which may include external and internal pressure forces, gasdynamic shear, solid and liquid

6-Markets/Products 595 Table 6.10 RPs and other high temperature performance materials (courtesy of Plastics FALLO)

Ablative Plastics

Elastomer

Ceramic

Metal

Polytetrafluoroethylene

Silicone rubber filled with microspheres and reinforced with a plastic honeycomb

Porous oxide (silica) matrix infiltrated with phenolic resin

Porous refractory (tungsten infiltrated with a low melting point metal {silver)

Epoxy-polyamide resin with a powdered oxide filler

Polybutadiene-acrylonitrile elastomer modified phenolic resin with a subliming powder

Porous filament wound composite of oxide fibers and an inorganic adhesive, impregnated with an organic resin

Hot-pressed refractory metal containing an oxide filler

Hot pressed oxide, carbide, or nitride in a metal honeycomb

Phenolic resin with an organic (nylon), inorganic (silica), or refractory (carbon) reinforcement Precharred epoxy impregnated with a noncharring resin

Major property Of interest

Type of plastics

Ablative

Phenol-formaldehyde

Charring resin for rocket nozzle

Chemical resistance

Fluorosilicone

Seals, gaskets, hose linings for liquid fuels

Cryogenic

Polyurethane

Insulative foam for cryogenic tankage

Adhesion

Epoxy

Bonding reinforcements on external surface of combustion chamber

Dielectric

Silicone

Wire and cable electrical insulation

Elastomeric

Polyb utad ie ne-a cryl o n it ri le

Soil propellant binder

Propulsion system application

Power transmission

Diesters

Hydraulic fluid

Specific strength

epoxy-novolac

Resin matrix for filament wound motor case

Thermally nonconductive

Polyamide

Resin modifier for plastic thrust chamber

Absorptivity :emissivity ratio

Alkyd silicone

Thermal control coating

Gelling agent

Polyvinyl chloride

Thixotrophic liquid propellant

596 Reinforced Plastics Handbook

impact, mechanical and acoustical vibration, and inertial and dynamic forces. The general effect is to cause destruction of a material or premature failure before it has accomplished its intended purpose. Chemical Parameters At subsonic velocity flight, the environment is essentially composed of rigid, rotating diatomic molecules. The energy of these molecules is distributed among five degrees of freedom (equipartition of energy theorem), and a kinetic energy corresponding to its microscopic relative velocity. In the supersonic regime, however, air is in vibration excitation as a result of the energy imparted to it. At even higher speeds of the hypervelocity regime, the molecules are heated to a level at which they dissociate and ionize. These processes occur first for oxygen and then for nitrogen. Thermal Protection Systems The design of vehicles for hypersonic atmospheric flight represents a compromise between the intended mission, the thermo structural aspects of the environment, the rate and magnitude of vehicle deceleration permitted, and the amount of lift necessary for flight control and landing at a predetermined point on some planet. The heating problem associated with high performance vehicles has been solved by a variety of design techniques. These include radiative cooling, heat sinks, transpiration cooling, ablation, and combinations thereof. Each thermal protective scheme is applicable to a particular portion of the flight regime, with reduced efficiency or no utility at other flight conditions. Ablation Materials The ablation technique can be used to handle the intense heating and extremely high temperatures encountered. Surface material is physically removed or a temperature-sensitive component of a composite is preferentially removed. The injected vapors alter the chemical composition, transport properties, and temperature profile of the boundary layer, thus reducing the heat transfer to the material surface. At high ablation rates, the heat transfer to the surface may be only 15% of the thermal flux to a non-ablating surface. This approach can absorb up to tens of thousands of Btu's of heat. The ablation action dissipates material through chemical reactions, phase changes, surface radiation and boundary layer cooling of the ablator (Figure 6.50). The heating rate temperature of an ablative system is no limit. The total heat load limits it. Even with this limit the versatility of ablation has permitted it to be used on hypervelocity atmospheric vehicles.

6. Markets/Products 597 Glass Droplets

CONVECTION RADIATION GAS-PHASE COMBUSTION SURFACE COMBUSTION RERADIATION TRANSPIRATION < COOLING CHEMICAL REACTIONS-" BOUNDARY LAYER COOLING

Figure 6~50 Schematic shows ablation energy exchange action of an RP material No single, universally acceptable ablative material has been developed. Nevertheless, the interdisciplinary efforts of materials scientists and engineers have resulted in obtaining a wide variety of ablative compositions and constructions. These thermally protective materials have been arbitrarily categorized by their matrix composition. During ablation its surface material is physically removed. The injected vapors alter the chemical composition, transport properties, and temperature profile of the boundary layer, thus reducing the beat transfer to the material surface. At high ablation rates, the heat transfer to the surface may be only 15% of the thermal flux to a non-ablating surface. Up to tens of thousands of Btu's of heat can be absorbed, dissipated and blocked per pound of ablative material through the sensible heat capacity, chemical reactions, phase changes, surface radiation and boundary layer cooling of the ablator. R P Plastics Plastic-base RPs, which employ an organic matrix, are a

widely used class of ablative heat protective materials. They respond to a hyper-thermal environment in a variety of ways, such as depolymerization-vaporization (polytetrafluoroethylene), pyrolysisvaporization (phenolic, epoxy), and decomposition-melting-vaporization (nylon fiber RP). The principal advantages of plastic-base ablators are their high heat shielding capability and low thermal conductivity. The major limitations are high erosion rates during exposure to very high gas-dynamic shear forces and, limited capability to accommodate very

598 Reinforced Plastics Handbook

high heat loads. Most TS plastics and highly crosslinked plastics (especially those with aromatic ring structures) form a hard surface residue of porous carbon. Elastomers Another major class of plastic ablators is elastomeric-base materials and particularly silicones. During ablation, they thermally decompose by such processes as depolymerization, pyrolysis, and vaporization. The silicone elastomers provide low thermal conductivity, high thermal efficiency at low to moderate heat fluxes, low temperature properties, elongation of several hundred percent at failure, oxidative resistance, low density, and compatibility with other structural substrate materials. Elastomeric materials are generally limited by the amount or structural quality of the char formed during ablation, which restricts their use to hyperthermal environments of relatively low mechanical forces. Ceramics Ceramic-base ablators constitute another class of heat shielding materials. They generally have high thermal efficiency, but this capability is difficult to realize because of their susceptibility to thermal stress failure. During thermal shock, the material may crack extensively and fail catastrophically. Placing the ceramic in a metal honeycomb tends to alleviate this problem by restricting any cracks to the outer walls of the cell structure.

Porous ceramics per se are potential ablative-insulative materials, but by plastic impregnation, their ablative characteristics are greatly improved. Specifically, the resin component increases the composite strength and thermal shock resistance, decreases the thermal conductivity, and permits higher environmental temperatures to be tolerated without exceeding the melting or decomposition temperature of the ceramic. Typical compositions of porous ceramics include silica, zirconium, alumina, magnesia, carbides, borides, and suicides. They are prepared by such processes as hot pressing, isostatic pressing, slip casting, pyrolysis of organic inclusions, and chemical bonding. Suitable plastic infiltrants include the phenolics, epoxies, acrylics, polystyrenes, and others. Of the numerous combinations available, phenolic resin impregnated porous silica composite has found the greatest use. The principal limitations of this material (like other internally ablating composites) are a reduced thermal efficiency with exposure time, or loss of molten surface material by the shearing action of the high temperature aerodynamic stream. Metals Metal-base ablators are a fourth major class of thermal protection materials. The most common type of ablator is a porous refractory skeleton containing a lower melting point metallic infiltrant.

6. Markets/Products 599

Tungsten matrices with up to 80% porosity are generally employed. Fiber felting or cold pressing powder followed by sintering prepares them. The porous matrix is then infiltrated with such metals as copper or silver using high pressures, high vacuum, or a combination of both. The resultant composite has high strength, good thermal shock resistance, and can be easily machined. Its low thermal efficiency (about 1,500 Btu/lb), high density, and high thermal conductivity tend to restrict its use to intensely heated areas where the original configuration of the matrix must be maintained.

Material Properties The properties and characteristics of ablative composites are greatly influenced by the presence of a plastic component. The inherently wide range of material properties available in these plastic containing composites has led to broad use in a variety of entry thermal protection systems.

Comparative Performances The capability of various types of ablative materials for insulating entry vehicles has been reviewed. The more refractory materials like graphite and infiltrated tungsten dissipate a considerable amount of heat by radiation, but their inherently high thermal conductivities introduce severe insulation problems. The charring plastics are also capable of reaching very high surface temperatures, but their ability to restrict the internal transfer of heat is significantly better. Ceramic-base ablators operate at intermediate surface temperatures. The plastic impregnated porous ceramics provide better insulation than the bulk ceramics, until the organic material is expended. The subliming plastics operate at relatively low ablative surface temperatures, and hence are inefficient in disposing of heat by surface radiative cooling. The low density elastomeric and plastic composites combine the desirable charring attribute of the aromatic polymers with the insulative characteristic of the subliming plastics. They are thus very effective in environments comprising low to moderate heating rates and long heating times.

Entry Simulations Tests There are different entry simulation testing equipment to evaluate plastic materials. The utility of polymeric materials for hypersonic atmospheric flight applications is determined by a series of sequential evaluations. Initial screening of candidate materials is carried out in the laboratory, using the high temperature apparatuses. The performance data obtained is then analyzed collectively to determine both the mechanism and magnitude of thermo-chemical degradation at high temperatures. Plastics exhibiting promising properties

6 0 0 Reinforced Plastics Handbook

and characteristics are subsequently screened in small, subsonic air are jets to identify their unique ablative characteristics and limitations, type of entry environment in which the material will most likely best perform, need for additional specialized testing, and other factors which could influence the nature and rate of subsequent developmental efforts. Plastic materials receiving the highest overall rating are then evaluated in other ground simulation facilities. The wind tunnel is most frequently employed for this purpose. Perfect simulation is impossible, however, and thus the choice of facility is dictated by the importance of closely simulating either the thermal, chemical, or mechanical aspects of the entry environment. Subsequent specialized testing is then carried out to determine the importance of environmental parameters not closely simulated in the previous evaluation work. Finally, the plastic material is flown in the actual service environment to prove its heat shielding effectiveness, confirm previous theoretical prediction of material behavior, and to provide a sound basis for the selection and design of heat shields for operational flight vehicles. The selection of an appropriate ground test facility for ablative characterization of plastic and composite materials requires consideration of a large number of factors. These include: the environmental conditions desired and ability to generate them simultaneously, degree of control over the environmental parameters and ability to vary them individually, uniformity and reproducibility of the test medium, ability to accurately calibrate the test medium, and the available testing time and area. Numerous ground base facilities have been developed for materials characterization. The more widely used facilities have been reviewed, together with their capability to simulate various flight velocity-altitude (enthalpy-pressure equivalent) conditions. Each facility is characterized by its capability to generate a high temperature fluid stream, differing in static and impact pressure, temperature and enthalpy, velocity, species concentration., energy states, and heat and mass transfer.

Entry Environmental Affects The mechanism and magnitude of ablation of plastics is a strong function of the individual thermal, mechanical and chemical parameters of the entry environment. While it is difficult and often impossible to independently study the particular influence of each parameter, some of the more important material-environment interactions have been identified.

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Gas Enthalpies The ablative efficiency of all plastics increases with gas enthalpy. This is due to the transpiration cooling effect of the newly formed pyrolytic species and to increase surface emission caused by higher surface temperatures. Gaseous products formed by material ablation are injected into the hot boundary layer. In diffusing through this high temperature region, they absorb heat by sensible temperature rise. The boundary layer is thus increased in thickness, and its original enthalpy or temperature is lowered. Consequently, less heat is transferred from the environment to the ablating surface.

Intense Convective Heatings The subsonic air arc heater is widely employed to ablatively screen plastic materials for potential entry heat shielding applications. The chemical composition and structure of the polymer exerted the greatest influence on the ability of the composite to accommodate intense heating and to impede the flow of heat into the specimen. Cold wall heats of ablation values ranged between 7700 and 13,800 Btu/lb. The best performance was obtained with the heterocyclic polyimide and polybenzimidazole and the aromatic polyphenylene resins, all of which exceed the heat of ablation for the widely used phenol formaldehyde (phenolic) resin. The superior charring characteristics of these polymers contributed greatly to their high heats of ablation. The various plastic materials, with their inherently low thermal conductivities, greatly restricted the flow of heat from the surface region into the specimen substrate. The stable char forming polymers and those capable of producing an appreciable amount of pyrolytic gaseous species provided the best insulative characteristics. Both polyphenylene and phosphonitrilic chloride polymers exhibited significantly lower back wall temperatures during ablation, as compared to the phenolic resin composites. Surface temperatures of the composite materials were within a 4290 to 5350F range, and apparently controlled by the ratio of vaporized: retained molten surface on the specimen. Surface emittance values varied appreciably, i.e., between 0.19 and 0.62. The higher emittance values were either due to a thin surface layer of silica (high emission from the subsurface char, or an appreciable amount of polymer carbon particles in the molten silica layer). The ablative characteristics of the carbon fabric RP composites were significantly different from that containing silica reinforcement. The carbon reinforced composites had higher heats of ablation, poorer

602 Reinforced Plastics Handbook

insulative characteristics, higher surface temperatures, higher surface emittance values, and higher surface re-radiation. Plastics that yielded a structurally sound char of high surface emittance possessed the highest heats of ablation. These included many of the heterocyclic and aromatic polymers, like the polyirnides and modified phenolics. The poorer char forming polymers, like epoxy novolacs, had a higher ablation rate, and consequently, lower heat of ablation. Poor dimensional stability during ablation was obtained with the semiorganic phosphonitrilic chloride polymer. With respect to the insulative characteristics, the high char yielding polymers performed the best. Polyphenylene, polybenzimidazole, and polyimide-containing composites provided about 50% more insulation than the conventional phenolic resin. The poor insulative characteristic of the phosphonitrilic chloride composite was apparently due to its high rate of ablation during exposure. With respect to surface temperature and emittance, the type of polymer in the composite had little effect.

Summary The outstanding performance of plastics in providing thermal protection for hypersonic atmospheric vehicles, and the broad base of knowledge concerning ablative technology could mistakenly give the impression that the reentry problem has been solved. Moreover, one may have the false impression that only minor improvements will be made in future ablative materials. Nothing could be further from the truth. New types of ablative plastics are required to accommodate the ever increasing severity of the entry environments, to keep pace with new and improved vehicle missions and designs, and to provide satisfactory performance in new service environments. Chemical Propulsion Exhausts

Plastics with their wide range of properties and characteristics have found numerous uses in chemical propulsion systems. The particular plastic employed in these applications is based on the inherent properties of the plastic or the ability to combine it with another component material to obtain a balance of properties uncommon to either component. Various propulsion systems have been developed over the years, which are dependent upon chemical, mechanical, electrical, nuclear, and solar means for accelerating the working fluid by high temperatures. Only chemical propulsion will be further discussed, and in particular, that associated with liquid, solid, and hybrid motors and engines. These motors and engines are uniquely different from other chemical

6. Markets/Products 603 propulsion systems in that they carry on board the necessary propellants, as contrasted to jet engines that rely on atmospheric oxygen for combustion of the fuel. The basic purpose of a propulsion system is to convert the thermal energy of a chemical reaction into useful kinetic energy by directing the flow of the resultant products. In other words, the propulsion system is to provide thrust for the movement of a vehicle. Expulsion of material is the essence of thrust production and without material to expel no thrust can be produced, regardless of how much energy is available. The amount of thrust generated is equal to the rate of propellant consumption multiplied by the exhaust gas velocity. In order to maximize the exhaust velocity, it is necessary to have the combustion process take place at the highest possible temperature and pressure. Energy is released in the process, with a major fraction appearing as thermal (heat) energy. The amount of heat released is the difference value in bond energies of the newly formed reaction products and those of the precursory reactants. The reaction products are usually energetic, and characterized as being thermally reactive, chemically corrosive, and mechanically erosive. Yet, they must be contained and controlled in order to achieve the desired magnitude and direction of thrust. The development of engineering materials, which can accommodate the hyper-environmental conditions of chemical propulsion thus, constitutes a very difficult problem. The combustion process is carried out in a thrust chamber or a motor case, and the reaction products are momentarily contained therein. The newly formed species are heterogeneous in composition and involve a wide variety of low molecular weight products. The temperature of these products is generally high, and it ranges from about 2000F in gas generators to well over 8000F in advanced liquid propellant engines. The combustion products leave the chamber and are directed and expanded in a nozzle to obtain velocities from about 5,000 to 14,000 R/see. The mass rate of flow through the nozzle will generally vary from less than 1 lb/see-in, 2 in small liquid space engines to more than 6 lb/see-in. 2 in solid and liquid propellant engines. The firing period may last from a few seconds as in tactical missiles, and range upwards to over 20 min as in spacecraft engines. Since the flow is highly turbulent and the temperature level of the reaction products and the local pressure are numerically great, heat may be transferred at a high rate to the walls of the combustion chamber, nozzle, and adjacent parts. With an increase in firing time, heat protection becomes more important and ultimately approaches the critical stage. It then becomes necessary to thermally protect or cool the

604 Reinforced Plastics Handbook

exposed parts. High-performance materials and cooling techniques are thus necessary to accommodate the hyper-environmental conditions associated with rocket engines and motors. Ablation Processes

Since 1950, plastics have been seriously considered and under development for used in very high temperature environments. By 1954, it was demonstrated that plastic materials were suitable for thermally protecting structures during intense propulsion heating. This discovery became one of the greatest achievements of modern times, because it essentially initially eliminated the "thermal barrier" to hypersonic atmospheric flight as well as many of the internal heating problems associated with chemical propulsion systems. Plastics in the form of rigid TSs, flexible elastomers and TPs, and semi rigid elastomer-modified TS materials have thus acquired a new function in the engineering world, namely, that of providing thermal protection. As reviewed this mode of heat protection is now known as the "ablation" or "ablative" process, and the functional materials employed are commonly referred to as "ablators." While significant progress has been made in understanding the complex nature of materials ablation, many of the subtle aspects continue to elude the researcher. Nevertheless, the ablation process for a fiber RP or elastomeric RP will be described for the purpose of illustration. At the onset of heating, energy is absorbed at the exposed surface and then conducted internally. The rate of heat penetration is dependent upon the surface temperature (driving force), and it is diffusion limited by the inherent properties of organic materials. The containment of heat in the surface region causes its surface temperature to rise rapidly. The net heat flux to the material surface is thus decreased continuously as the surface temperature value moves toward the radiation equilibrium temperature. Eventually the material is heated sufficiently to generate volatiles, which have varying compositions such as water, residual diluents, or low molecular weight polymers. At higher temperatures, the plastic begins to soften and it may physically slump. Thermal agitation eventually becomes severe enough to split side groups off the polymer backbone, and finally the chemical bonds in the backbone structure arc ruptured. The polymer is thus undergoing pyrolysis, which continues over a broad temperature range. The organic component of the composite is degraded into numerous gaseous products of varying molecular weights, such as water vapor, carbon monoxide, carbon dioxide, hydrogen, methane, ethylene, acetylene, and other unsaturated and saturated hydrocarbon fragments.

6. Markets/Products 605 These pyrolytic species are injected into the adjacent hot boundary layer, and they effectively lower the enthalpy (heat content) of the environment. In this manner, less heat is convected to the ablating surface. TP and elastomeric plastics tend to thermally degrade into simple monomeric units with the formation of considerable liquid and a lesser amount of gaseous species. Little or no solid residue generally remains on the ablating surface. On the contrary, most TS and highly crosslinked polymers (especially those with aromatic ring structures) form a hard surface residue of porous carbon. The amount of char formed depends upon such factors as the carbon-hydrogen ratio present in the original polymer structure, degree of crosslinldng and tendency to further crosslink during heating, presence of foreign elements like the halogens, asymmetry and aromaticity of the polymer structure, degree of vapor pyrolysis of the ablative hydrocarbon species percolating through the char layer, and type of elemental bonding. With the formation of a carbonaceous layer, the primary region of pyrolysis gradually shifts from the surface to a substrate zone beneath the char layer. The newly formed char structure is attached to the virgin substrate material and remains thereon for at least a short period of time. Meanwhile, its refractory nature serves to protect the temperaturesensitive substrate from the environment. Gaseous products formed in the substrate pass through the porous char layer, undergo partial vapor phase cracking, and deposit pyrolytic carbon (or graphite) onto the walls of the pores. As the organic polymer or its residual char are removed by the ablative aspects of the hypcr-environment, the reinforcing fibers or particle fillers are left exposed and unsupported. If vitreous in composition, they undergo melting. The resultant molten material covers the surface as liquid droplets, irregular globules, or a thin film. Continued addition of heat to the surface causes the melt to be vaporized. A fraction of the melt may be splattered by internal pressure forces, or sloughed away when acted upon by external pressure and shear forces of the dynamic environment. These reactions and products are favored at given temperature levels. For example, silicone carbide is formed at temperatures up to about 2800F. At higher temperatures, equilibrium mixtures of metallic silicon and silicon monoxide gas are favored. The summation of all of these reactions is a tremendous potential for absorbing heat. Naturally, only a fraction of these endothermic reactions actually take place in any given ablation situation. The objective, then, is to control the materials

606 Reinforced Plastics Handbook

variables so as to maximize the heat absorbed and dissipated by any given material. From a thermo-physical point of view, ablation may be defined as an orderly heat and mass transfer process in which a large amount of thermal energy is expended by sacrificial loss of surface region material. The heat input from the environment is absorbed, dissipated, blocked, and generated by numerous mechanisms. These are:

(a) heat conduction into the material substrate and storage by its effective heat capacity, (b) material phase changes, heat absorption by gases in the substrate as they percolate to the surface, (d) convection of heat in a surface liquid layer, if one exists, (e) transpiration of gases from the ablating surface into the boundary layer with attendant heat absorption, (t) surface and bulk radiation, and (g) endothermic and exothermic chemical reactions. These energy absorption processes take place automatically and simultaneously. It is apparent, then, that the performance of an ablative plastic is achieved in a manner quite unlike that for heat-resistant plastics. Ablators depend upon various degradative reactions to absorb, dissipate, and block a copious amount of heat. On the contrary, heat-resistant plastics must essentially remain intact during high temperature exposure to retain a significant fraction of their room-temperature properties.

Liquid Propulsions Liquid propellant engines have been used for many years to propel aircraft, guided missiles, rockets, research devices, and other types of vehicles. They have provided thrust levels ranging from a few ounces for altitude control to several hundred thousand pounds for the earth launching of vehicles. Liquid propulsion is characterized by its high state of development, relatively complicated systems design, capability for repeated operation, long firing times, and of course the propellants employed. Their use has been based on a number of selection criteria, such as the operational mission, performance required, reliability, minimum weight, logistics, economics, availability, maintainability, mobility, and others. Ablative cooling has been used in a number of liquid propellant engines. The materials employed are generally of an oriented fiber reinforced resin,

6. Markets/Products 607

and they are used in direct contact with the exhaust products. A thin layer of elastomeric material may also be used to insulate the outer structure from the inner ablating plastic. Fibrous oxides and in particular silica and quartz have consistently shown superior performance in oxidizing environments. This desirable performance has been attributed to their inherently high heat absorbing capability. By realizing a significant fraction of the theoretical heat absorption, high ablative cooling is insured. Another reason for the desirable performance of silica fibers is their ability to reinforce the char layer, and form a viscous melt during intense heating. This molten layer covers the thermally degrading resin surface, and acts as an oxidative barrier for the charred residue. In fluorine environments, however, oxide reinforcement experience increased vaporization. Carbon and graphite reinforcements exhibit greater chemical inertness in fluorine-containing products of combustion, and thus have been used exclusively. With respect to resins, only the high char yielding phenolics and epoxy novolacs have been employed. Ablative plastics have certain limitations in the liquid propellant exhaust environments. Their service life is time dependent, and varies with the firing time to about the one-half power. Firing times in excess of 310 s have been obtained, however, with a low thrust (150 lb) and low chamber pressure (130 psia) engine. At lower chamber pressures, engine operations up to about 1980 s have been achieved. Ablative plastic composites are generally not used in the throat region of liquid propellant engines, unless the total erosion can be maintained at 5% or less at the end of the firing period. Very high mass-flow rates of exhaust products, extremely long firing times, and small diameter nozzle throat regions tend to decrease the attractiveness of ablative plastic cooling. Ablators are somewhat sensitive to the propellant injector performance. Poorly designed injectors have been noted to cause recirculation hot spots at the chamber wall, which resulted in a nonpredictable, nonuniform, and excessive localized erosion. Some residual thrust may also be encountered in liquid propellant engines that utilize ablative cooling. During engine cool down, gaseous products may be formed by continued resin vaporization in the hot char layer. With respect to the high thrust engines of launch vehicles, ablative materials have only been used sparingly. The frequent need for proof testing, availability of cryogenic propellants for cooling, and the previously mentioned long firing durations and high mass-flow rates of exhaust products tend to favor other forms of cooling. Ablative plastic chambers have been built and successfully used on liquid engines having small to moderately high thrust levels.

608 Reinforced Plastics Handbook

Solid Propellants The evolution of propulsion for ordnance purposes, weapon delivery systems, ballistic and space vehicles, and scientific exploration suggests an ever-increasing role for solid propellant motors. Unlike the previously discussed liquid propellants, the solid rocket fuels are characterized by their obvious solid phase propellants, lower specific impulse (about 8 to 20% less), higher densities, fixed fuel oxidizer ratios, and higher costs. Motors employing the solid propellants exhibit certain performance traits, which include simplicity, compactness, safety, instant firing readiness, short developmental times, reduced developmental costs, greater reliability, shorter firing times, .storability, ease of maintenance, and a passive thermal protection system. Other motor characteristics that were once exclusive to liquid propellant engines, such as throttling and restarting, have been achieved in certain rocket engines. A solid propellant is a mixture of an oxidizing and a reducing material that can coexist in the solid state at ordinary temperatures. It is generally composed of three elements, the oxidizer, fuel or binder, and various additives.

Materials of Construction Rocket motors are constructed of composite materials with each component material performing a specific function depending on its location. This type of construction is optimum, since the environmental conditions and hence the materials requirements vary greatly with motor position. The forward bulkhead of the motor case is exposed to stagnant but hot gases, and thus must be lined with an insulative material. The modulus of this insulator is sufficiently low so as to transmit the chamber pressure into the external structural member. Insulators that are brittle tend to crack during the initial pressurization, with possible catastrophic burn-through of the motor case wall. Insulators are composed of an elastomer-modified charring resin (like a copolymer of butadieneacrylonitrile and phenolic) with various reinforcements a n d / o r low conductivity fillers. The bulkhead insulator is generally premolded in segments and then adhesively (plastic) bonded in place. In the cylindrical portion of the motor, a liner material is required to prevent corrosion of the structural case during storage and overheating during motor firing. Since the liner must transmit the chamber pressure forces into the structural case, it must posse flexibility, an elongation greater than the propellant, and high tensile strength. Optimum performance also requires that it have a low thermal conductivity, some

6. Markets/Products 609 erosion resistance, low density consistent with ablative and mechanical properties, low gas permeability, good bonding characteristics, compatibility with the propellant and the case, and a resistance to longtime aging effects. This demanding combination of requirements along with a need for ease of fabrication and low cost are difficult (if not impossible) to achieve in a single material. By far, the plastic elastomers have been found to be most suitable. They are flexible and have elongations up to several hundred percent. As a result, they will follow (without cracking or bond separation) the shrinkage of a solid propellant during curing as well as the compressive loading during motor firing. The liner material is frequently very similar to that employed as the propellant binder, and is generally composed of a nitrile, urethane, butyl, or polysulfide rubber. To these elastomeric polymers are added various particulate and fibrous matter, such as powders of boric oxide, potassium oxalate, silica, alumina, carbon, or phenolic, and long fibers of asbestos, silica, or possibly carbon. These liners are applied to the motor case by conventional spray or centrifugal sling methods, or by hand rolling solid sheets to the interior of the case. In the aft end of the motor case, sidewall insulation is necessary in those areas exposed throughout the motor firing and those locations left exposed by recession of the propellant grain front. The materials used in these areas must have performance capabilities similar to the insulator in the forward bulkhead, except improved erosion resistance is required because of the moving gas stream. In general, the sidewall insulator is composed of an clastomer-resin copolymer or charring rubber reinforced with various fibrous compositions. The external case of the rocket motor supports the mechanically and thermally induced stresses, which are due to internal gas pressure, vibration, acceleration, thrust vector control, and differential thermal expansion of component materials. To accommodate these factors, the structural material should have high strength, adequate modulus, and resistance to buckling. Either a continuous glass filament wound epoxy plastic or a high temperature metal (steel, titanium, or aluminum) case serves as the exterior structural member. Material requirements become more demanding as the gases move into the aft bulkhead section of the nozzle. Increased material rigidity, resistance to erosion and thermal insulations is required. Some degree of surface recession is permitted, since its influence on thrust is small. The aft bulkhead insulator is usually composed of a material similar to that employed in the case sidewall. Both elastomer-modificd TS resins and heavily loaded rubber compositors have been employed with success.

610 Reinforced Plastics Handbook

The divergent entrance cone of the nozzle must exhibit even greater erosion resistance because it is redirecting the propellant gases at a relatively steep angle. Refractories like metals, ceramics, and graphites are unsuitable for use in this section because of certain property limitations, and the configuration and size of the part. Instead, ablative plastic composites, which form a surface char and possibly a viscous melt during heating , appear to be optimum. They are composed of either phenolic or epoxy resins reinforced with fibers or fibrous constructions of asbestos, glass, silica, quartz, carbon, or graphite. The latter material in the form of a woven fabric or tape impregnated with phenolic resin has shown exceptionally good performance. Undoubtedly, the most critical materials requirements are those of the nozzle throat. Its configuration and dimensions must remain essentially unchanged throughout motor firing to insure constant chamber pressure and thrust conditions. Small diameter (5 in. or less) throats generally require the use of steel, molybdenum, tungsten, a high density graphite wit or without an oxide coating, a metal carbide, a highly crystalline pyrolytic graphite, or a metal infiltrated porous refractory. Nozzle throat inserts of molybdenum and steel are most frequently used for short duration firings, while bulk graphite is much better for longer duration operations. When it is critical to maintain throat dimensions, a metal (like silver) infiltrated porous refractory (such as tungsten) is employed. M1 of these materials are heavy, however, and they possess certain other limitations. Molybdenum and tungsten are inherently brittle below their ductile-to-brittle transition temperatures. Graphites and carbides are brittle because their crystallographic structures preclude plastic flow at low temperatures. Moreover, the carbides are sensitive to thermal shock. The use of thermally conductive throat materials necessitates the addition of an insulative backup material. An example of this type of construction is a phenolic-asbestos fiber (PSI 150 type; R-M) insulator molded around a graphite throat insert. The insulator should have a high thermal stability, little or no gasification at temperature, high strength, medium to low density, high heat capacity, and moderate thermal conductivity. Asbestos and silica fiber reinforced phenolics have many of these attributes, and thus have been used in virtually every application. Resin gasification at high temperatures presents a potential problem, and when encountered, a thin layer of fibrous oxide insulation is placed between the throat and the backup material. Ablative plastics are also used in the throat region of solid propellant motors when the firing duration is short, the chamber pressure is relatively low, or the throat diameter is quite large.

6

9Markets/Products

Ablative plastics are also employed in the divergent exit cone region. The material adjacent to the throat insert must have a high erosion resistance. It is therefore composed of graphite or carbon fabric reinforced phenolic resin backed up with an insulative phenolic-silica fabric laminate. The exit cone is usually prepared by a tape wrapping operation. Reinforcing fibers are oriented normal to the nozzle centerline or canted downstream (shingle lay-up). In the smaller nozzles, compression molded parts are generally adequate. Diced fabric (one-half inch impregnated fabric squares) or chopped fibers are compacted by means of match metal molding, autoclaving, or hydroclaving. Since the thermal severity of the exhaust stream decreases with distance from the nozzle throat, ablative materials having a good balance of insulative and erosion characteristics are employed. These materials are of a phenolic resin composition with silica, glass, or asbestos fibrous reinforcements. The fabrication process used is identical to that previously noted for the forward exit cone section, but in some cases, may involve, a filament wound plastic (Chapter 5). Jet vanes and tabs are sometimes employed in solid rocketry for thrust vector control. They are normally located behind the nozzle and protrude into the exhaust stream. Their basic purpose is to provide directional control at low missile speeds following launch, and at very high altitudes where air vanes become less effective. They offer the advantages of being reliable, simple in design, low in cost, and produce less than 1% thrust loss. Since the jet vanes and tabs are subjected to highly erosive environmental conditions, their service lives are generally short. Nevertheless, RPs have been found suitable for use in certain solid propellant motors. For other designs, alloys of tungsten and molybdenum are more promising. Structural parts and control accessories in the aft region of a solid propellant motor may be overheated by thermal radiation from the exhaust gases and nozzle, recirculation of the combustion products, and after burning of the fuel rich gases. This basic heating problem was solved by the use of heat barriers in the aft end of the motor. They are generally constructed of a rigid plastic sandwich material overcoated with a metallic reflective film or an elastomeric coating. Heat barriers in the region of movable or gimballed nozzles require both flexibility and thermal protection, and for these areas, asbestos blankets coated with an elastomeric material have proven to be adequate. In addition to the ablative materials employed in the primary propulsion systems, specialty purpose ablators are also required in the launching area of rocket motors. During ignition and takeoff of the solid propelled vehicle, the launch equipment may be immersed in the

611

612 Reinforced Plastics Handbook

exhaust plume for up to 5 s. Severe damage by heat and blast may result unless suitable thermal protection is afforded to the exposed areas. A number of ablative elastomeric coatings have been developed which exhibit a high degree of transient thermal protection, good adhesive properties, permanence characteristics, and case of application. Millions of dollars of cables, hoses, umbilical cords, piping, electronic equipment, etc., have been saved from destruction by use of these coatings.

Designs

Overview Designing RP products follows what can be considered the logical approach in designing with any material. Table 7.1 presents the flow pattern in product design. Reinforced plastics (RPs) and unreinforced plastics (URPs) offer the opportunity to optimize plastic designs by focusing on material composition as well as product structural geometry to meet different product requirements (Figures 7.1 and 7.2). The minimum volume of plastic that will satisfy the structural, functional, appearance, and moldbility requirements of an application is usually the best choice. This is in sharp contrast to machining operations, where one starts with a solid block of material and machines away only until what one needs to make the part function remains. The term "design" has many connotations. Essentially, it is the process of devising a product that fulfills as completely as possible the total requirements of the user, and at the same time satisfies the needs of the fabricator in terms of cost-effectiveness (return on investment). The efficient use of the best available material and production process should be the goal of every design effort; includes tool design. Product design is as much an art as a science. Design guidelines for RPs have existed for over a century producing many thousands of parts meeting service requirements, including those requiring long fife. Basically, design is the mechanism whereby a requirement is converted to a meaningful plan (Table 7.2). Based on experiences different design approaches can produce products that are more efficient. For example, shape must be considered for a house to stand up to the forces of a catastrophic hurricane. Low pitch roofs are less vulnerable than steeper roofs because the same aero-

614 Reinforced Plastics Handbook Table 7,I Product concept feasibility study

Flow chart for designing a product from concept to fabricating the product

Set up requirements Apply available experience Conceptual product layout

Study shape, dimensions, structural loads, environments, government/industry, etc. Target quantity, cost and production schedule Manual approach

Apply design creativity

Computer approach

Formulate plan Geometric drawings or graphic analysis Initial design analysis Engineering analysis

Dimensions ~ tolerances

Structural integrity

Static Dynamic

Finite element modelling Physical integrity

Environment Minimum weight/cost Aesthetics, etc.

Fabrication analysis

Material selection Process selection Cost analysis

Melt flow analysis Shrinkage analysis Tool thermal analysis Cycle time Tool part selection Provide detailed individual orthotropic drawings

Set up safety factors to meet product functions

Material Process/equipment/tools Product service performance Plant personnel capability

Release tooling (mold/die) for manufacture Set up processing specifications Plant layout Develop manufacturing Manufacturing processing specifications Plant personnel capability evaluation Document good manufacturing practice (GMP) procedure _ _ Update plant personnel training Develop production cost models Documentation for management to ensure meeting delivery schedules and profitability

Product release

Mechanical simulation

Mold/die design Finalize design

Implement production

Solid Wire Surface

Image manipulation

Data bases and/or available information Standard parts Nonstandard parts

Equipment Material handling Automation/robotics Preventative maintenance Safety procedures Machine operations Troubleshooting guide Testing/q ua lity con trol

Ensure product quality Finalize testing/quality control Product output schedule Accounting schedule Purchasing schedule Inventory schedule

Ensure meeting all product functions Conduct value analysis (VA)

After start of production, analyze complete design [again) to change design/production/safety factors in order to reduce costs

7

9Designs 6 1 5

Figure 7.1 Examplesof shapes to increasestiffness

Figure 7.2 Exampleof a design where thin wall with ribbing supports high edge loading

dynamic factors than make an airplane fly can lift the roof off a house. If such a design is to be used, then the roof has to be properly attached to the building structure (as delineated in textbooks and local a n d / o r federal building specifications, depending on location). Air pressure remains the same in the horizontal direction under the roof. However, on top of the roof surface air pressure drops. This difference in air pressure can cause the roof to lift off. Generally, if the roof pitch is less than 30 ~ from the horizontal, it tends to deflect winds better than gable designs. Gabled roofs should be braced (joined) behind the trusses at both ends and the ends of the trusses along the outside walls should be attached to the tops of the wall at all points, with hurricane straps.

616 Reinforced Plastics Handbook Table 7.2 Basic design guide

Design

Sub-objective

Requirernents

Develop functional and performance requirements that have to be met

Determine size and shape

Time schedule Aesthetics and marketing Shipping Available space Weight Standardization Strength and stiffness criteria Flexibility Process limitations

Structural requirements

Loads Static ~t dynamic (that includes what follows) Dead - Own weight Live - People Furniture - Water - Snow - Others Wind Impact Handling and shipping product Temperature fatigue exposures -

Nonstructural requirements

Service environment: Corrosion resistance Moisture Aging Moisture Temperature Fire safety Incombustibility Flame spread rate Toxic gases Fuel content Product safety Light transmission Aesthetics Surface coating Thermal insulation Moisture and vapor penetration Electrical insulation Others

Cost

Examine economics for successful competition with similar products in conventional materials Consider total effect of new design on end product costs: materials, tooling, finishing, assembly, warehousing and inventory, quality control, packaging and shipping, and installation

7

Design

Preliminary design

9Designs 61 7

Sub-objective

Requirements

Establish production and marketing requirements

Number of identical pieces (quantity] Minimum and maximum probable production rates Available plant Market locations Shipping costs Method of marketing Cost restrictions imposed by competing products or technology

Size and configuration

Consider end use and limitations of suitable plastics, efficient manufacturing processes, requirements for sufficient strength and stiffness with efficient use of materials, and cost

Select plastics

Satisfy structural requirements with favorable cost ratios Satisfy nonstructural criteria with acceptable compromises and trade-offs where necessary Is efficient fabrication process available?

Select manufacturing process

Provide required size and configuration Tooling and plant capital costs to be appropriate for number of pieces and rate of production Compatible with available plant and marketing plan Provides required structural properties and quality control

Establish design criteria for trial materials selected

Determine suitable allowable design strengths and stiffness, taking into account type and duration of load, service environments, process effects, quality expectations, etc.

Proportion component for specific configuration and thickness

Determine trial shape of plates, shells, and ribs, depth of ribs and sandwiches, and wall thicknesses to meet strength, deflection, and stability criteria Review economics and suitability

Develop significant details

Determine concept and principal details for shop and field connections, penetrations, and other subparts (if required) continued

618 Reinforced Plastics Handbook Tabte 7.2 Continued

Design

Sub-objective

Requirements

Examine preliminary design

Evaluate preliminary design

Review economics and suitability of materials and process based on preliminary proportions Consider overall compatibility and practicality of all materials and parts in component as a system

Review performance and functional requirements

Determine if all original performance requirements are feasible within economic objectives, or whether compromises and trade-offs should be considered

Optimize design to reduce cost or satisfy functional and performance requirements

General configuration Configuration proportions such as rib depths, shell radii, fillet radii, etc. Material thickness Material alternatives-consider additives to tailor properties Process alternatives

Perform structural analysis of acceptable accuracy

Determine structural response-stresses, support reactions, deflections, and stability based on a structural analysis of acceptable accuracy. Determine acceptable accuracy based on economic value.

Prepare engineering drawings

Design and fabrication drawings

Prepare specifications

Materials requirements and standards Fabrications requirements and standards Shipping and handling

Prepare manuals

Periodic maintenance Service and environment conditions Repair procedures

Prepare prototype for structural test

Develop test program to evaluate components

Revise design, if required

Correct design and detail problems if any Modify materials or process

Develop final design

Develop prototype if required

7

9Designs 6 1 9

In structural applications for RPs, which generally include those in which the product has to resist substantial static a n d / o r dynamic loads, it may appear that one of the problem design areas for many unreinforced plastics (URPs) is their low modulus of elasticity. Since shape integrity under load is a major consideration for structural products, low modulus type plastic products are designed shapewise for efficient use of the material to afford maximum stiffness and overcome their low modulus. These type plastics and products represent most of the plastic products produced worldwide. Design analysis is required to convert applied loads and other external constraints into stress and strain distributions within the product, and to calculate associated deformations. The nature and complexity of these calculations is influenced strongly by the geometric shape of the component. It is most convenient if the component approximates to some simple idealized form, such as a plate or shell (for example a body panel), a beam or tube (for example a chassis member or bumper), or a combination of idealized forms (for example a box structure). In these cases, standard design formulae can be provided into which appropriate parameters can be substituted for a particular application. There are many more cases where the component shape does not approximate to a simple standard form (for example a wheel, pump housing, or complex manifold) or where a more detailed analysis is required for part of a product (for example the area of a hole, boss, or attachment point). In these cases, the geometry complicates the design analysis and it may be necessary to carry out a direct analysis, possibly using finite element analysis. Analyses are presented in this section using different shapes including product sizes. Product size is limited to available equipment that can handle the size and pressure as well as other processing requirements such as the product thickness. Also involved are factors such as packaging and shipment to the customer. The ability to achieve specific shapes and design details is dependent on the way the process operates. Generally the lower the process pressure, the larger the product that can be produced. With most labor-intensive fabricating methods, such as RP hand lay-up with thermoset plastic (TS) plastic, slow process curing reaction time of the plastic can be used so that there is virtually no limit on size (Chapter 5). A general guide to practical processing thickness limitations based on heat transfer capability through plastics is in inches: injection molding 0.02 to 0.5; extrusion 0.001 to 1.0; blow molding 0.003 to 0.2; thermoforming 0.002 to 1.0; compression molding 0.05 to 4.0; and

620 Reinforced Plastics Handbook foam injection molding 0.1 to 5.0. However with the proper process controls on materials and equipment, products are produced that range below and above these figures. Success with plastics, or any other material for that matter, is directly related to observing design details. For example, something as simple as a stiffening rib is different for an injection molded or structural foam product, even though both may be molded from the same plastic (Table 7.3). However, a stiffening rib that is to be molded in a low-mold-shrink, amorphous TP will differ from a high-mold-shrinkage, crystalline TP rib, even though both plastics are injection molded (Chapter 3). Ribs molded in RP have their own distinct requirements. Hollow stiffening ribs of the type produced by thermoforming, blow, or rotational molding have the same function, but they are designed to be totally different shapewise. Table 7.3 Property examples of ribs using different materials

Property Thickness (in.) E (psi) I(in. 4) E x I (rigidity) Weight (Ibs.)

Steel

Solid plastic

Structural foam

0.040 3 x 107 0.000064 1,920 3.24

0.182 3.2 x 105 0.006 1,920 1.98

0.196 2.56 x 105 0.0075 1,920 1.78

Preparing a complete list of design constraints is a crucial first step in the design; failure to take this step can lead to costly errors. For example, a designer might have an expensive injection mold prepared, designed for a specific material's shrink value to meet specific product dimensions, only to discover belatedly that the initial material chosen did not meet some overlooked design requirement or constraint. The designer may have the difficult if not impossible task of finding an RP or URP that does meet all the design constraints, including the important appropriate shrink value for the existing mold cavity(s) otherwise expensive mold modifications may be required, if not replacing the complete mold.

Practical and Engineering Approaches RP products can often be designed and fabricated with very little or no stress analysis. Many parts, particularly URPs, are volume-tilting products that carry only small stresses and only require a "practical approach" (Table 7.4). There is a cost disadvantage in performing any analysis

7

9Designs 6 2 1

when it is not needed. The designer or engineer's experience is required in determining the level of equation evaluation. Even when stresses are critical, there are usually other aspects of design that also must be considered.

Table 7.4 Flowdiagramfor a practicalor engineeringapproach ,

.....

[ PERFORMANCEREQUIREMENTS ! Establish criteria

APPROACH

APPROACH

.">.. [ JMATERIAL , SELECTION

f

,,

How to I PROPERTI select I

,

u

t

-

"'"---'1

]

I I I I I I I I

II ~

'

'

IDEAL CHOICE/COMPROMISE

The designer may not be able to reduce stresses by just increasing the part thickness, because thick walls can cause internal stresses during molding that can result in severe distortions and dimensional instability of the RPs (or other materials). The experienced RP designer will recognize and respect the restrictions that are caused by molding a n d / or joining components when adjusting section areas to control stresses; often curved shapes, ribs, etc., can be used. Unfortunately, there are conditions to accept, or restrictions on the use of many handbook equations for RPs and other materials, so it is important that the user be aware of the methods used to obtain them. The term engineering equations refers primarily to those in handbooks and texts by which stress analysis can be accomplished. They can be adjusted to meet product performance for RPs and other materials; this is similar to reviewing definitions in the ASTM terms, where two or more may be given and the user determines which best suits the design situation. The restrictions applied to the change of the classical stress results should be recognized when used in design or analysis. RP parts may exhibit deviations rendering the handbook equations invalid without some modification. Without experience, this approach has risks, so the results should be compared to experimental observations, prototyping evaluations, a n d / o r other validating data.

622 Reinforced Plastics Handbook As an example, designing load-beating products involves selecting suitable materials and specifying the molded shape. An important aspect of shape is its effect on internal stress. With proper fabricating procedures, as the cross-sectional areas are increased for a given load, the stresses are reduced. Design is concerned with the determination of stresses for a given or hypothetical shape, and the subsequent adjustment of the shape, until the stresses are neither so high as to risk failure nor so low as to result in extra use of material that becomes wasted. The basic/simplified equations can be very restricted because of idealizations made in their deviations with regard to the simplicity of any material and the kinematics of the displacements. They are usually used in cases of intermediate difficulty, such as those for which some numerical guidance on internal stress is needed, or when the inherent simplicity of the part or the lack of any need for high precision indicates that relatively elementary analysis approaches are used. Stress analysis involves using the description of part geometry, applied loads and displacements, and material properties to obtain numerical expressions for internal stresses as a function of position in the part. When using these elementary equations, they are a useful first approach, even for those cases where more general treatments are used, such as the finite element or finite difference analyses (FEAs or FDAs) that is used as the next approach. Unfortunately, computational analysis can sometime allow the designer to avoid understanding the real nature of the problem. Many have learned that computer solutions with different materials must be checked carefully for their degree of logic or reason. The elementary analyses, however, do provide one of the most efficient means of verifying computational methods, as they allow a computer solution to be checked against a solution that is known to be correct.

Increase Properties There are different techniques that have been used for over a century to increase properties such as the modulus of elasticity (E) and moment of inertia (/) of products. Orientation or the use of fillers a n d / o r reinforcements such as RPs can be used. There is also the popular and extensively used approach of using geometrical design shapes that makes the best use of materials to improve stiffness even for those that have a low modulus. Structural shapes that arc applicable to all materials include shells, sandwich structures, and folded plate structures (Table 7.5). These widely used shapes employed include other shapes such as dimple sheet surfaces. They improve the flexural stiffness in one or more directions.

7

Table 7.5

9Designs 6 2 3

Examplesof moment of inertia

Moment of inertia I (cm 4)

Section

Ix= lbh3 12

ll! r x

ly=

--b-

\\

i x = ly = Iz =

x

~

b3h 12

1

!

a4

12

z

1= 1 7rr4 = 1 ~d 4 4 64

X

I = 1 ~(R 4 - r4) = 1 ~(D 4 - d 4) 4 64

Y ix = 1 7ra3b 4 ly=

1 ~ab 3

b Y

1 ~ . (A3B - a3b) I x = -~ ly= B

17r. 4

(AB3-ab3)

ix = 1__ (BH 3 - bh 3) 12 B

I3

]3

-

ix = 1 (BH 3 - bh 3) 12

~

B-'~

T

In each example, displacing material from the neutral plane makes the improvement in flexural stiffness. This increases the EI product that is the geometry material index that determines resistance to flexure. The EI theory applies to all materials (plastics, metals, wood, etc.). It is the elementary mechanical engineering theory that demonstrates some shapes resist deformation from external loads.

624 Reinforced Plastics Handbook

This phenomenon stems from the basic physical fact that deformation in beam or sheet sections depends upon the mathematical product of the E and I, commonly expressed as El. This theory has been applied to many different plastic constructions including solid to different sandwich structures. In the case of RPs, emphasis is on the way RPs can be used in these structures and why they arc preferred over other materials. In many cases RPs can lend themselves to a particular field of application only in the form of a sophisticated lightweight stiff structure and the requirements are such that the structure must be of RP. In other instances, the economics of fabrication and erection of a RP lightweight structure and the intrinsic appearance and other desirable properties make it preferable to other materials. Formabilities

Formability into almost any conceivable shape is one of plastics' design advantages. It is important for designers to appreciate this important characteristic. Both the materials and different ways to manufacture products provide this rather endless capability. Shape, which can be almost infinitely varied in the early design stage, is capable for a given volume of materials to provide a whole spectrum of strength properties, especially in the most desirable areas of stiffness and bending resistance. With shell structures, materials can be either single or double curved via the different fabricating processes. There are different design approaches to consider as reviewed in this book and different engineering textbooks concerning specific products. They range from designing an open top cubical box to a complex shape such as an aircraft wing structure. Other examples include the advantage of basic beam structures as well as hollow channel, I-shape, T-shape, etc. They are used to provide more efficient strength-to-weight products and so forth. While this construction may not be as efficient as the sandwich panel, it does have the advantage that it can be molded, pultruded, extruded, etc. directly in the required configuration at a low cost and the relative proportions be designed to meet the flexural, etc. requirements. One of the potential limitations is that generally it imparts increased stiffness in one direction much more than in the other. However processing techniques can be used to develop bidirectional or any other directional properties such as combining pultrusion or extrusion with filament winding. In most cases, plastic products can take advantage of a basic beam structure in their design. Hollow-channel, I-, T-shapes, and cantilever

7

Designs 9 625

beams designed with generous radii (and other basic plastic flow considerations) rather than sharp corners are more efficient on a weight basis in plastics because they use less material, thus provide a high moment of inertia, etc. The moments of inertia of such simple sections, and hence their stresses and deflections, can be easily calculated, using simple engineering equations. Surface Stresses and Deformations

It can be said that the design of a product involves analytical, empirical, a n d / o r experimental techniques to predict and thus control mechanical stresses. Strength is the ability of a material to bear both static (sustained) and dynamic (time-varying) loads without significant permanent deformation. Many non-ferrous materials suffer permanent deformation under sustained loads (creep). Ductile materials withstand dynamic loads better than brittle materials that may fracture under sudden load application. As reviewed, materials such as RPs can exhibit changes in material properties over a certain temperature range encountered by a product. There are examples where control of deflection or deformation during service may be required. Such structural elements are designed for stiffness to control deflection but must be checked to assure that strength criteria are reached. A product can be viewed as a collection of individual elements interconnected to achieve an overall systems function. Each element may be individually modeled; however, the model becomes complex when the elements are interconnected. The static or dynamic response of one element becomes the input or forcing function for elements adjacent or mounted to it. An example is the concept of mechanical impedance that applies to dynamic environments and refers to the reaction between a structural element or component and its mounting points over a range of excitation frequencies. The reaction force at the structural interface or mounting point is a function of the resonance response of an element and may have an amplifying or damping effect on the mounting structure, depending on the spectrum of the excitation. Mechanical impedance design involves control of element resonance and structure resonance, providing compatible impedance for interconnected structural and component elements. As an example view a 3-D product that has a balanced system of forces acting on it,/'1 through F5 in Figure 7.2, such that the product is at rest. A product subjected to external forces develops internal forces to transfer and distribute the external load. Imagine that the product in Figure 7.3 is cut at an arbitrary cross-section and one part removed.

626 Reinforced Plastics Handbook F~

\ CUT

Fs

FORCE VECTORS o

F1

"-"

F4

P

!

S

F4 Figure 7.3 Exampleof stresses in a product

To keep the body at rest there must be a system of forces acting on the cut surface to balance the external forces. These same systems of forces exist within the uncut body and are called stresses. Stresses must be described with both a magnitude and a direction. Consider an arbitrary point, P, on the cut surface in the figure where the stress, S, is as indicated. For analysis, it is more convenient to resolve the stress, S, into two stress components. One acts perpendicular to the surface and is called a normal or direct stress, ~. The second stress acts parallel to the surface and is called a shear stress, r.

Design Approaches Product design starts by one visualizing a certain material, makes approximate calculations to see if the contemplated idea is practical to meet requirements that includes cost, and, if the answer is favorable, proceeds to collect detailed data on a range of materials that may be considered for the new product. The application of appropriate data to p r o d u c t design can mean the difference between the success and failure of manufactured products made from any material. The available plastic test data requires an understanding and proper interpretation before an attempt can be made to apply t h e m to the product design. Details on designing a product can follow a flow pattern as shown in Table 7.6.

Table 7.6 Productdesignflow pattern

i ................

..................

111

_

,

..........

i

I

|

I fill

,

PRODUCT DESIGN "k Flow Pattern * i

9

,,, _

,,

,

,

,,,

iiii

I

i

ii

II

____

I I I

I

J

Project Team Feasabili~ Study

I

--.

Optimize& Document

Optimize Design

l

Produc~on i

II iiii Ii

r ii

i

Preliminary Design Analysis

Product Release

~ _

i

ii

~J

FALLO FOLLOW ALL OPI:::~RTUNIT1ES

l =

Continued

LO

ha ~J

O~ !%1 00

TabJe 7.6

Continued

PROJECTTEAM FEASIBILITYSTUDY ii

I .

.

.

.

i

.

.

.

.

I

.

.

.

.

.

.

.

.

i,

k

,,,

,r ,

J

f-) tl) -o

.

t-h i, f~ -r

.

Identify

"

Specific Functions

i

i Apply available experience

i

i i

_l, ,,,

........

,,,,

Dimensions, structural loads, ElOV't/Industr~ standards, service environments, etc.

. _

....

Manual Approach quantity, cost and production scheduile iii

i

i

il

il

i ,,

,, ,, ,,

=

!

,

II

,

1

Computer Approach

I .........

i i n.

J ill, I

I

!

i

i lliHi

L"i

L

~'Apply Design' "

F.ed..LO FOLLOWALL OPPORTUNITIES

..... Creativity

oo o

P R E U M I N A R Y DESIGN ANALYSIS

FORMULATE PlAN GEOME~IC OR E~:IAPHIC

ENGINEERING ANALYSIS

DRAWINI~

ANL~YSIS

D I M ~

&

TOLERANCES

B11:IL~nJRAL

FABRICATION ANALYSIS;

INTEGRITY

IMAGE MAMPULATION

ENVIRONMENT

SELECTION

MINIMUM WEIGHT~

.JM~4.YSIS AES3HETICS ETC. ' i

,

PROCESS !

~T ~

I

i

9OLID

i

~.IRFAIP.~

|ll

i

- " WIRE

i

r

1 I,

i

i

MECHANICAL SIMULATION

RNITE ELEMENT MOOEUNG

1 FALLO FOLLOWALL OPPORTUNITIES

STATIC

,

I

l

.,4

DYNAMIC i Ill ,,...

L~ Continued

9

Ill

03 I%1 r.D

03 O

Table 7.6 Continued

t'1) ,=,=,

O~,M,ZE ~OES,GN" "!

:3 '-h O .,,r r fl) "qD i 9.1 U,t ,,,,,,,

SETUP ~M:ETY FACTOI:~ TO MEEI" PRO[XICT RJNC'IIOhB

_._L_ PROVIDE i~ET/MLED/ I~i~LJAL ORTHOTI:IORC DRAWING8

~1111111 ~.

I/t

--r9.1 :3 o" o o

i

TOOL T H ~ AN~YgS

TOOLP~T ~ELECTION

r

MELT FLOW ANALYBS

ii

ii

..... ..... MATERIAL

,

SHRINKAt~ ANALYSIS

CYCLE TIME

TOOLS

STANDA.qo PARTS

FALLO FOLLOW ALL ORPORTUNITIES

|

i

9 SERVICE R E m O ~

i

NON STANDARD PARTS

.

ill

~ E L CAPABILITY

,

,

Z

=t

I -1

L~9 su6!sac! L9

ffl

rtl

Z

or-"

~~

o

o

,

,

0

......

1

1

....................

~

m il

~

' i'

...... .....

0"~ W

Table 7.6 Continued i

ii iii

iiii iiiiii

[

i

iii

i

m,

i

OPTIMIZE & DOCUMENT REPRODUCTION !

mmllnlllll u iii

i'I I'D O. "O g.1

iii

II

"r"

UPDATE PLANT PERSONNEL TRAINING

II

DOCUMENT GOOD MAdMUFACTIJRING PRACTICE (GMP) PROCEDURE

ENSURE PRODUCT QUAUTY

!

i

! H ,, ,,

i

,

FINAUZE TESTING & QUAUTY CONTROL

II FALLO FOLLOWALL OPPORTUNITIES

DEVELOP" PRODUCTION COST MODELS

PRODUCT OUTPUT SCHEDULE I ACCOUNTING SCHEDULE I PURCHASING SCHEDULE [ INVENTORY SCHEDULE

I i

DOCUMENTATION FOR MANAGEMENT TO ENSURE MEETING DEUVERY SCHEDULES AND PROFITABIUTY

o. O" O O

!

0 D UCT

. . . . . . . . . . . . . . . .R . . . . .E . . . . L. . . E. . .A .

I

I ,

i

II IIII III

I

I II

i

ii i i

....

ii

I

,, ,,, ,, i,

J i

i i

,,

I

I II

i

,

SET UP VALUE ANALYSIS (VA)

ill

,

, i

i i

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I

ill ii

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ENSURE MEETING ALL PRODUCT FUNCTIONS ....

E

S

II

i i i ii

i, i

i !

i

ii

Jl ]1 i i

i i ii

AFTER START OF PRODUCTION, ANALYZE COMPLETE DESIGN (AGAIN) TO CHANGE DESIGN/PRODUCTION/SAFETY FACTORS IN ORDER TO REDUCE COSTS ,,

L

i

,,,,

,

i, H

i

,

,

ii,

:3 W W

634 Reinforced Plastics Handbook There are three important sources of data and information on RPs. Obtain data from products your organization previously fabricated; there is the data sheet compiled by a manufacturer of the material and derived from tests conducted in accordance with standardized specifications. If suppliers' data were to be applied without a complete analysis of the test data for each property, the result could prove costly and embarrassing. Final source is preparing your own test specimens and conducting your own tests. Either one or both specimen preparation and test evaluation could be conducted by an outside source. If the fabricator prepares the specimens a duplicate of the fabricating process to be used will be produced or as close to the process as possible. The amount and degree of testing is usually related to factors such as (1) if a prototype is to be prepared and tested and (2) product requirement such as safety. The nature of RPs is such that an oversight of even a small detail in its properties or the method by which they were derived could result in problems and product failure. Once it is recognized that there are certain reservations with some of the properties given on some data sheets, it becomes obvious that it is very important for the designer to have a good understanding of these properties. Thus the designer can interpret the test results in order to make the proper evaluation in selecting a material for a specific product.

Design Foundations The target of the integration of technological or non-technological subject material in an effective and efficient manner is greatly enhanced by having a visible operational structure ranging from field service studies to analysis by computers. Some type of visibility is a crucial factor in bringing about integration. Visibility helps everyone find out what people are doing and why. With this approach design may be construed as having a central foundation of activities, all of which are imperative for any design. This foundation includes product conceptual design, design specification, detail design, manufacture, and sales. All design starts, or should start, with a need that, when satisfied, will fit into an existing market or create a market of its own. From the statement of the need of a specification, or equivalent, must be formulated for the product to be designed. Once this is established, it acts as the envelope that includes all the subsequent stages in the design. It becomes the theoretical control for the total design activity, because it places the boundaries on the subsequent design approaches.

7

9Designs 6 3 5

Use is made of the optimization theory and its application to problems arising in engineering that follows by determining the material and fabricating process to be used. The theory is a body of mathematical results and numerical methods for finding and identifying the best candidate from a collection of alternatives without having to specify and evaluate all possible alternatives. The process of optimization lies at the root of engineering, since the classical function of the engineer is to design new, better, more efficient, and less expensive products, as well as to devise plans and procedures for the improved operation of existing products. Result of the R&D performed in the field of RPs since the 1940s have resulted in significant improvement in their performance. Examples are shown in Figures 7.4 and 7.5.

---- Ratiotnnsile ~ (psi) to density (Ibs,/cu. In.) x 10# - - - - Ratio tensile modules of elasticity (psi) ~odensity (IbsJcu. In.) x 106

1~P"

~Numinum 1910 Figure

1920 7.4

m

1930

1930

1930

1960

1970

1980

1990

Epo"y 60% c l r l x ~

Steel

El)only 0am

Numi~

Epoxy 30'X, Sore Epoxy

Strain

Figure

/

/

m

Past to future tensile properties of RPs, steel, and aluminum

Stress

/

7 . 5 Tensile stress-strain curves for different materials

2OOO

2010

636 Reinforced Plastics Handbook

To optimize this approach the boundaries of the engineering system are necessary in order to apply the mathematical results and numerical techniques of the optimization theory to engineering problems. For purposes of analysis, they serve to isolate the system from its surroundings, because all interactions between the system and its surroundings are assumed fixed/frozen at selected, representative levels. However, since interactions and complications always exist, the act of defining the system boundaries is required in the process of approximating the real system. It also requires defining the quantitative criterion on the basis of which candidates will be ranked to determine the best approach. Included will be the selection system variables that will be used to characterize or identify candidates, and to define a model that will express the manner in which the variables are related. Use is made of the optimization methods to determine the best condition without actually testing all possible conditions comes with a modest level of mathematics and at the cost of performing repetitive numerical calculations using clearly defined logical procedures or algorithms implemented on computers. This RP activity constitutes the process of formulating the engineering optimization problem. Good problem formulation is the key to the success of an optimization study and is to a large degree an art. This knowledge is gained through practice and the study of successful applications. It is based on the knowledge and experience of the strengths, weaknesses, and peculiarities of the techniques provided by optimization theory. Unfortunately at times this approach may result in that the initial choice of performance boundary/requirements is too restrictive. In order to analyze a given engineering system fully it may be necessary to expand the performance boundaries to include other sub-performance systems that strongly affect the operation of the model under study. As an example, a manufacturer finishes products that are mounted on an assembly line and decorate. In an initial study of the secondary decorating operation one may consider it separate from the rest of the assembly fine. However, one may find that the optimal batch size and method of attachment sequence are strongly influenced by the operation of the RP fabrication department that produces the fabricated products (as an example problems of contaminated surface and other detriments in the product could interfere with applying the decoration). Required is selecting an approach to determine a criterion on the basis of which the performance requirements or design of the system can be evaluated resulting in the most appropriate design or set of operating conditions can be identified. In many engineering applications this criterion concerns economics. In turn one has to define economics such

7

9Designs 6 3 7

as total capital cost, annual cost, annual net profit, return on investment, cost to benefit ratio, or net present worth. There are criterions that involve some technology factors such as plastic material to be used, fabricating process to be used, minimum production time, number of products, maximum production rate, minimum energy utilization, minimum weight, and safety. This review shows what the veteran plastic designer knows that plastic products are often stiffness critical, whereas metal products are usually strength critical. Consequently, metal products are often made stiffer than required by their service conditions, to avoid failure, whereas plastic products are often made stronger than necessary, for adequate stiffness.

Temperature/Time Behavior To design successful RP products meeting factors such as quality requirements, consistency, designated life, and profitability what is needed is understanding and applying the behavior of plastics such as the important factors of service load, temperature, and time at temperature load in optimizing the design. When compared to other materials such as steel and certain other metals their data are rather constant, at least in the temperature range in which plastics are used. The same computations are used, when the design engineer is accustomed to working with metals in order to obtain a plastic product with sufficient strength and deformation under a given load that must not exceed a definite limit for proper performance. One will probably include safety factors of 1.5 to 2 or even more if not to familiar when designing with RPs. That means the designer initially does not utilize the full strength of the material a n d / o r significantly increases product cost (safety factor reviewed at the end of this chapter). The physical and mechanical properties of RPs, including URPs, have some significant difference from those of familiar metallic materials. Consequently in the past those not familiar with designing RP or URP products may have had less confidence in plastics and in their own ability to design with them. Thus, plastic material selection and optimization was confined to the familiar steel materials approach resulting in overdesign, or failures that may have occurred in service. A skilled designer blends knowledge of materials, an understanding of manufacturing processes, and imagination of new or innovative designs. It is the prediction of performance in its broadest sense, including all the characteristics and properties of materials that are essential and relate to the processing of the plastic. To the designer, an example of a

638 Reinforced Plastics Handbook

strict definition of a design property could be one that permits calculating of product dimensions from a stress analysis. Such properties obviously are the most desirable upon which to base material selections. These correlative properties, together with those that can be used in design equations, generally are called engineering properties. They encompass a variety of stress situations over and above the basic static strength and rigidity, such as impact, fatigue, high and low temperature capability, flammability, chemical resistance, and arc resistance. Recognize that there are many stresses that cannot be accurately analyzed in RPs, URPs, metals, aluminum, etc. Thus one relies on properties that correlate with performance requirements. Where the product has critical performance requirements, such as ensuring safety to people, production prototypes will have to be exposed to the requirements it is to meet in service. Loads on a fabricated product can produce different types of stresses within the material. There are basically static loads (tensile, modulus, flexural, compression, shear, etc.) and dynamic loads (creep, fatigue torsion, rapid loading, etc.). The magnitude of these stresses depends on many factors such as applied forces/loads, angle of loads, rate and point of application of each load, geometry of the structure, manner in which the structure is supported, and time at temperature. The behavior of the material in response to these induced stresses determines the performance of the structure. The behavior of materials (RPs, URPs, steels, etc.) under dynamic loads is important in certain mechanical analyses of design problems. Unfortunately, sometimes the engineering design is based on the static loading properties of the material rather than dynamic properties. Quite often this means over-design at best or incorrect design resulting in failure of the product in the worst case. Failure analysis can be related to potential crack growth behavior to prevent fracture. Fracture is a crack-dominated failure mode. For fracture to occur, a crack must somehow be created, then initiate, and finally propagates. The prevention of any of these events will prevent fracture. Cracks can be considered elastic discontinuities that can come from a variety of sources such as internal voids or dirt, a n d / o r surface scratch, embrittlement, or weld line. Cracks can be consequences of faulty design, poor processing, a n d / o r poor handling of raw material, assuming material arrived clean (Figure 7.6). The nature and complexity of applied loads as well as the shape requires the usual engineering calculations. For a simple engineering form like a plate, beam, or box structure the standard design formulas can be used

7

Fiber buckles

Fiber breaks

9Designs 6 3 9

I

Slot/crack

Crock propagation

Adjoining fibers buckles

Adjoining fibers break

I

Crack propagates

Fracture

f Reduced cross section Open surfaces still support during compression half of loading

Fails during tensile half of loading

Figure 7.6 Schematicsof crack propagation in reinforced plastics

with appropriate parameters relating to the factors of short- and longtime loadings, creep, fatigue, impact, etc. and applying the viscoelastic plastic material behavior (Chapter 3). In a product load analysis the structure as a whole and each of its elements together are in a state of equilibrium. These forces could deform the product due to internal stresses of varying types and magnitudes. This action could be immediate or to some timetemperature period based on its viscoelastic behavior and underestimating potential internal stresses. To overcome this situation different approaches are use, as explained in the engineering books. An example is when the cross-sectional area of a product increases for a given load, the internal stresses are reduced, so make it thicker. Design is concerned with determining the stresses for a given shape and

640 Reinforced Plastics Handbook

subsequently adjusting the shape until the stresses are neither high enough to risk fracture nor low enough to suggest that material is being wasted (cosily). With the more complex shapes the component's geometry complicates the design analysis for RPs (and other materials) and may make it necessary to carry out a direct analysis, possibly using finite element analysis (FEA) followed with prototype testing. When structural components arc to be designed using RPs it must be remembered that the standard engineering equations that arc available (Figures 7.7 and 7.8) have been derived under the assumptions that (1) the strains arc small, (2) the modulus is constant, (3) the strains are independent of the loading rate or history and arc immediately reversible, (4) the material is isotropic, and (5) the material behaves in the same way in tension and compression.

4 F

~ , j ~

F(totalload)

,,,4--------- L

(at/oad) [at load)

/ o l

FL.

(at center)

o =

y =

FL= 48EI

(at center)

y =

4Z

(at support)

a - FL

(at load)

y =

FL

8Z 5FL=

384EI

Y

Z FL= 3El

(at supports)

o = FL 8Z

(at load)

y, =

FL=

192EI

I

F (total load)

1

f

Y

(at support)

a - FL 2Z

(at supports)

o =

(at support)

y =

(at center)

y =

FL= 8El

Figure 7.7 Engineeringequations (no= neutral axis)

FL 12Z FL=

384EI

7 A ,. ncl~ 4

f

C= d

2

9Designs 641

c..o 2

I - b__~ ~

b*-b

,2

I-

. t)

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n~ 84

Z= ~

Z-

6

T

hi-

c.~_

do

c-

2

. t)

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~.._~ 32

do

-;-

I .

#do".

~)

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~cl.4 . ~)

A

4.h~

# .tx~.h~(b.t) f2

Z .

bd: . h.yb . t)

s

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+

c ..~ 2 I -

Z:

I

~///~~//na/~

c - d -

2stP+M,

~'1

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/

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c

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tcl§ 3

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h

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f

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6d

t)

na

c.b-

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- --2A-~

j ,

c), Z..#_. c Z"-

I b-c

Figure 7,8 Beamequations

These equations cannot be used indiscriminately. Each case must be considered on its merits, with account being taken of the plastic behavior in time under load, mode of deformation, static and/or dynamic loads, service temperature, fabrication method, environment, and others. The traditional engineering equations arc derived using the relationship that stress equals modulus time's strain, where the modulus

642 Reinforced Plastics Handbook is a constant. The moduli of many URPs are generally not a constant, but most RPs approach a constant. However, as reviewed throughout this book one has to at least take into account the temperature-time effect.

Theory of Elasticities and Materials Engineering wise for RPs there are basic approaches of theory of elasticity and strength of materials. In most engineering problems, both methods assume homogeneous, isotropic solid, linearly elastic material. A very important requirement for both approaches is that equilibrium of loads/forces be satisfied. These conditions being met to a reasonable degree, one would expect the elasticity solution to be superior to the strength of materials. Theories exist that provide a unifying principle that explains a body of facts and the laws that is based on those facts. Strength of material refers to the structural engineering analysis of a part to determine its strength properties. There is also the important empirical approach that is based on experience and observations rather than theory. The basic optimization design theory can be related to the systematic activity necessary, from the identification of the market/user need, to the selling of the successful product to satisfy that need. It is an activity that encompasses product, process, people, and organization. No fine line separates the theory of elasticity from the strength of materials method. The value of one approach over the other depends on the particular application regardless of what material is used (plastic, metal, etc.). In most design or engineering problems, both methods assume homogeneous, isotropic, linearly elastic material. Both methods require that equilibrium of force be satisfied. To determine a 3-D stress distribution using the theory of elasticity, six stress-strain equations and six strain-displacement equations can be used in addition to three equilibrium equations. The unknowns, six stress components and three displacements, may be found for given loading and boundary conditions. If the problem is formulated in such a way that the displacements are not explicitly included, it is necessary to establish compatibility of strains; that is, one must show the material to be continuous in a stressed and unstressed state. An alternative problem formulation assumes a state of stress that satisfies equilibrium of forces and corresponds to the loading and boundary conditions. Compatibility of strains is not necessarily satisfied. The strength of materials approach solves problems that would be very unwieldy using elasticity methods. Because the stress distribution is assumed beforehand, it is apparent that the latter approach would be meaningless if one were required to find the stress concentration due to a hole in a tension

7

Designs 9 643

member or for any problem where one would have no rational basis for assuming a certain distribution. Where the theory of elasticity results in a tractable formulation, the solution is accurate to the degree described in the loading and boundary conditions, and to the degree to which the material approaches the assumed ideal of an homogeneous, isotropic solid. Under these conditions, the elasticity solution would be expected to be superior to the strength of materials approach. However, the strength of materials method may be favorable when an assumed stress distribution accurately portrays the system due to factors such as local yielding. The above review pertains too many, but not all metals, as some have directional properties (nonisotropic) such as drawn steel. In this case, the theory of elasticity is used. With RPs that is isotropic and nonhomogeneous, the same is applied. In fact, recognizing the imperfection of certain metals during processing, this method is still used, using a higher design safety factor. This approach can also be used with RPs to provide some guidelines for the strength of materials approach. Reinforced Plastic Performances

RPs offers certain important structural and other performance requirements. These requirements provide the designer great flexibility and provide freedom practically not possible with most other materials. However, it requires a greater understanding of the interrelations to take full advantage of RPs. It is important to understand that RPs has an extremely wide range of properties, structural responses, product performance characteristics, product shapes, manufacturing processes, and influence on product performances. The usual approach is that the designer is involved in "making the material." RP designed products have often performed better than expected, despite the use of less sophisticated fabricating tools in their design. Depending on construction and orientation of stress relative to reinforcement, it may not be necessary to provide extensive data on time-dependent stiffness properties since their effects may be small and can frequently be considered by rule of thumb using established practical design simplified approaches. When time dependent strength properties are required, creep, fatigue, and other data are used most effectively. The arrangement and the interaction of the usual stiff, strong fibers dominate the behavior of RPs with the less stiff, weaker plastic matrix [thermoset (TS) or thermoplastic (TP)]. A major advantage is that directional properties can be maximized in products by locating fibers

644 Reinforced Plastics Handbook

that maximize mechanical (Chapters 2 and 5).

performances

in

different

directions

When compared to URPs, the analysis and design of RPs is simpler in some respects and more complicated in others. Simplifications are possible since the stress-strain behavior of RPs is frequently linear to failure and they are less time-dependent. For high performance applications, they have their first damage occurring at stresses just below their high ultimate strength properties. They are also much less temperature-dependent, particularly RTSs (reinforced TSs). When constructed from any number and arrangement of RP plies, the stiffness and strength property variations may become much more complex for the novice. Like other materials, there arc similarities in that the first damage that occurs at stresses just below ultimate strength. Any review that these type complications cause unsolvable problems is incorrect. Reason being that an RP can be properly designed, fabricated, and evaluated to take into account any possible variations; just as with other materials. The variations may be insignificant or significant. In either case, the designer will use the required values and apply them to an appropriate safety factor; similar approach is used with other materials. The designer has a variety of alternatives to choose from regarding the kind, form, amount of reinforcement to use (Figure 7.9), and the process vs. requirements.

Figure 7~9

Properties of reinforced plastics based on type and amount of reinforcement

With the many different fiber types and forms available, practically any performance requirement can be met and molded into any shape. However they have to be understood regarding their advantages and limitations. As an example there are fiber bundles in lower cost woven rovings that are convoluted or kinked as the bulky rovings conform to

7

9Designs 6 4 5

the square weave pattern (Chapter 2). Kinks produce repetitive variations in the direction of reinforcement with some sacrifice in properties. Kinks can also induce high local stresses and early failure as the fibers try to straighten within the matrix under a tensile load. Kinks also encourage local buckling of fiber bundles in compression and reduce compressive strength. These effects are particularly noticeable in tests with woven roving in which the weave results in large-scale reinforcement. Fiber content can be measured in percent by weight of the fiber portion (wt%). However, it is also reported in percent by volume (vol%) to reflect better the structural role of the fiber that is related to volume (or area) rather than to weight. When content is only in percent, it usually refers to wt%. As shown in Figure 7.10 they can be isotropic, orthotropic, etc. Basic behaviors of combining actions of plastics and reinforcements have

Figure 7.10

Fiber directional arrangements and property behavior (courtesy of Plastics FALLO)

646 Reinforced Plastics Handbook been developed and used successfully. As an example, conventional plain woven fabrics that are generally directional in the 0 ~ and 90 ~ angles contribute to the highest mechanical strength at those angles. The rotation of alternate layers of fabric to a layup of 0 ~ + 45 ~ 90 ~ and -45 ~ alignment reduces maximum properties in the primary directions, but increases in the + 45 ~ and -45 ~ directions. Different fabric and/or individual fiber patterns are used to develop different property performances in the plain of the molded RPs. Examples are shown in Figure 7.11. These woven fabric patterns can include basket, bias, cowoven, crowfoot, knitted, leno, satin (four-harness satin, eightharness satin, etc.), and twill (Chapter 2). For almost a century many different RP products have been designed, fabricated, and successfully operated in service worldwide. They range from small to large products such as small electric insulators for high voltage cable lines to large 250 ft diameter deep antenna parabolic reflectors to high performance aircraft, boats, and spacecrafts. RPs have been used in all types of buildings, transportation vehicles, different designed bridges, road surfacing such as aircraft landing strips and roads, mining equipment, water purification and other very corrosive environmental equipment, all types of electrical/electronic devices, etc.

Design Detractor and Constrain Designing good products (profiles, moldings, etc.) requires knowledge of RPs that includes their advantages and disadvantages also some familiarity with the processing methods. Until the designer becomes familiar with processing, a fabricator must be taken into the designer's confidence early in the development stage and consulted frequently during those early days. The fabricator and the mold or die designer should advise the product designer on RP materials behavior and how to simplify the design to permit easier processability. Although there is no limit theoretically to the shapes that can be created, practical considerations must be met such as available processing equipment and cost. These relate not only to the part design, but also the mold or die design, since they must be considered as one entity in the total creation of a usable, economically feasible part.

Design Analysis Processes The nature of design analysis obviously depends on having productperformance requirements. The product's level of technical sophistication and the consequent level of analysis that can be justified costwise basically control these requirements. The analysis also depends on the

7

9Designs 6 4 7

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A. Properties of style 181 glass fabric; parallel lay-up with 60 wt% glass content B. Properties of style 143 glass fabric; parallel lay-up with 65 wt% glass content C. Properties of style 143 glass fabric; plied at 0 ~ 90 o with 65 wt% glass content D. Properties of style 143 glass fabric; plied at 0 ~ 45 ~ 90 ~ 135 o with 65 wt% glass content E. Properties of chopped glass strand mat; parallel lay-up with 40 wt% glass content

648 Reinforced Plastics Handbook

design criteria for a particular product. If the design is strength limited, to avoid component failure or damage, or to satisfy safety requirements, it is possible to confine the design analysis simply to a stress analysis. However, if a plastic product is stiffness limited, to avoid excessive deformation from buckling, a full stress-strain analysis will likely be required. Even though many potential factors can influence a design analysis, each application fortunately usually involves only a few factors. For example, RTPs' properties are dominated by the viscoelasticity (Chapter 3) relevant to the applied load. Anisotropy usually dominates the behavior of long-fiber RPs and so on. The design analysis processes for metals, URPs, and RPs are essentially the same, however, due to a certain degree of differences; they sometimes appear to be drastically different. Experience of design analysis can be misleading if applied without consideration to RPs behaviors and processes. The design analysis process is composed essentially of the three main steps" (a)

assessment of stress and strain levels in the proposed design;

(b) comparison of critical stress and/or deformation values with

design criteria to ensure that the proposed design will satisfy product requirements and materials limitations; and

(c)

modification of the proposed design to obtain optimum satisfaction of product requirement.

For metallic materials, component design is usually strength limited so that the design criteria in step (b) are often defined in terms of materials strength values, that is, in terms of a maximum permissible stress. Even when the design criterion is avoidance of plastic flow, rather than avoidance of material failure, the criterion is specified by the limiting yield stress. In these cases, step (a) is only required to provide an analysis of the stress distribution in the component, and the strain and deformation distributions are of little practical interest. These conclusions are a consequence of the relatively high stiffness of metals, and the principal exception is the deformation of thin sections that may lead to buckling. A further simplification can often arise if the stress analysis problem required in step (a) is statistically determinate. In particular, this requires that the externally applied constraints (or boundary conditions) can all be expressed in the form of applied loads and not in terms of imposed relative displacements. The stress distribution depends on the applied loads and on the component geometry, but not on the material stiffness

7

9Designs 6 4 9

properties. Thus, it is identical for all materials, whether they be elastic, rigid, or any other form, provided only that the material is sufficiently stiff for satisfaction of the assumption that the applied loads can be considered to be applied to the undeformed, rather than deformed, component geometry. Thus, for metallic materials in many idealized practical situations, the design process is simplified to a stress (but not strain or displacement) analysis followed by comparison and optimization with critical stress values. When the problem is not statistically determinate, the stress analysis requires specification of material stiffness values, but the associated strain and deformation values are usually not required. Since the material behavior is usually represented adequately by linear isotropic elasticity, the stress analysis can be limited to that form, and there are many standard formulae available to aid the designer. For URPs, the emphasis is somewhat different. Due to their relatively low stiffness, component deformations under load may be much higher than for metals and the design criteria in step (b) are often defined in terms of maximum acceptable deflections. Thus, for example, a metal panel subjected to a transverse load may be limited by the stresses leading to yield and to a permanent dent. Whereas a URPs panel may be limited by a maximum acceptable transverse deflection even though the panel may recover without permanent damage upon removal of the loads. Even when the design is limited by material failure it is usual to specify the materials criterion in terms of a critical failure strain rather than a failure stress. Thus, it is evident that strain and deformation play a much more important role for URP than they do for metals. As a consequence, step (a) is usually required to provide a full stress/strain/ deformation analysis and, because of the viscoelastic nature of plastics, this can pose a more difficult problem than for metals. A particular distinction between the mechanical behaviors of metals and plastics (URPs and RPs) is explained in order to avoid a possible confusion that could have arisen from the preliminary review. A typical stress-strain curve for a metal exhibits a linear elastic region followed by yield at the yield stress, plastic flow, and ultimately failures at the failure stress. Yield and failure occur at corresponding strains, and one could define yield and failure in terms of these critical strains. This is not common practice because it is simpler in many cases to restrict step (a) to a stress analysis alone. By comparison, it may appear strange that it was stated that plastics failure criteria are usually defined in terms of a critical strain (rather than stress) and, by comparison with the metals case, switching back from strain to stress may appear to be a minor operation.

650 Reinforced Plastics Handbook

Explanation of this apparent fallacy depends on recognition of the fact that stress and strain are not as intimately related for URPs as they are for RPs and metals. This is demonstrated by a set of stress-strain curves for typical URPs where their loading rates increase. This emphasizes that the stress-strain curve for URPs is not unique, but depends on the loading type, that is, also on time, frequency, or rate. For example, the stress-strain curves obtained at different loading rates and for metals these curves would essentially coincident. However, the behavior of plastics can be very different at low and high rates, and there is no unique relation between stress and strain since this depends also on the loading rate. It is evident that characterization of failure through a unique failure strain cannot be valid in general, but it can be a good approximation in certain classes of situations such as, for example, at high rates or under creep conditions. For RPs, the emphasis and difficulty in the design analysis depends on the nature of the RPs. For a thermoplastic reinforced (RTP) with short fibers, the viscoelastic nature of the matrix remains an important factor, and the discussion given above for URPs is relevant. In addition, there may be a significant degree of anisotropy a n d / o r inhomogeneity due to processing that could further complicate the analysis. For TSs reinforced (RTS) with short fibers (for example, BMC) their may be only a low level of viscoelasticity, anisotropy, and inhomogeneity, and metals-type design analysis may be a reasonable approximation. However, RTSs with long fibers can have a high degree of anisotropy (depends on lay up of reinforcement), and this must be taken into account in the design analysis. When TPs are reinforced with long fibers there may be significant anisotropy and viscoelasticity, and this creates a potentially complex design analysis situation. In all cases, RPs failure characteristics may be specified in terms of a critical strain, and this requires the design analysis to be performed for stress and strain. Long-fiber materials can often be tailored to the product requirements, and therefore materials design analysis and component design analysis interacts strongly. If the component design analysis is statistically determinate (stresses independent of materials properties) then this can be carried out first, and then the material can be designed to carry the stresses in the most efficient manner. However, if the analysis is not statistically determinate, then the component stresses depend on material anisotropy, and material and product design have to be carried out and optimized at the same time. This is also the case if component shape is regarded as one of the variable design parameters. In summary, it can be seen that RPs and URPs design analysis follows the same three steps (a) to (c) as that for metals, but as reviewed there

7 Designs 9 651 are some differences of emphasis and difficulty. In particular, step (a) is usually more substantial for the newer materials, partly because a full stress/strain/deformation analysis is required and partly because of the need to take account of viscoelasticity, inhomogeneity, a n d / o r anisotropy. For long fiber materials, the component design analysis may need to contain an associated material design analysis.

Design Accuracies Also called deviation, it is a concept of exactness. When applied to a method, it denotes the extent to which bias is absent; when applied to a measured value, it denotes the extent to which both bias and random error are absent. Accuracy can refer to freedom from making errors or conformity to a standard. A fabricating system can be very "precise" and have poor accuracy. Manufacturing target of consistent, repeatable fabrication requires more than fight mechanical equipment standards, fight plastic material standards, and precise instruments with fastintegrated control response. However, these conditions can go a long way to meeting the target. What has to be included is calibrating instruments to fixed standards. To achieve accuracy the pressure, temperature, speed, and other control parameters must be calibrated to traceable standards. By measuring against known standards, the accuracy of the measurements can be determined. There can be parameters that cannot be quantified so these will contribute to the variability and limit the accuracy that can be obtained. Variations in molecular weight, pellet size, virgin/recycled mixes, etc. can affect the process. Unfortunately, these variations are not often recognized or easily identified.

Design Failure Theory In many cases, a product fails when the material begins to yield "plastically". In a few cases, one may tolerate a small dimensional change and permit a static load that exceeds the yield strength. Actual fracture at the ultimate strength of the material would then constitute failure. The criterion for failure may be based on normal or shear stress in either case. Modes of failure include excessive elastic deflection or buckling. The actual failure mechanism may be quite complicated; each failure theory is only an attempt to explain the failure mechanism for a given class of materials. In each case a safety factor is employed. However, with proper part design, these failures are eliminated or can be permitted since part performance is met.

652 Reinforced Plastics Handbook There are different design failure theories such as the Griffith theory. It expresses the strength of a material in terms of crack length and fracture surface energy. Brittle fracture is based on the idea that the presence of cracks determines the brittle strength and crack propagation occurs. It results in fracture rate of decreased elastically stored energy that at least equals the rate of formation of the fracture surface energy due to the creation of new surfaces.

Design and Product Liabilities In designing a product, equipment, testing procedure, etc. factors to consider include top management support; product liability recognized by design, production, and other people involved; include all possible safety devices; communicate and document with customer or buyer regarding any potential problems, hazards, etc.; if outside source used for parts check their safety programs with documentation; have a system to collect history of the same or similar part; and when sold get "feedback" on performance and problems with recall system.

Stress-Strain Behaviors The information presented throughout this book is used in different loading equations. As an example stress-strain (S-S) data may guide the designer in the initial selection of a material. Such data also permit a designer to specify design stresses or strains either safely within the proportional/elastic limit of the material. However for certain products such as a vessel that is being designed to fail at a specified internal pressure, the designer may choose to use the tensile yield stress of the material in the design calculations. Designers of most structures specify material stresses and strains well within the proportional/elastic limit. Where required (with no or limited experience on a particular type product material wise a n d / o r process wise) this practice builds in a margin of safety to accommodate the effects of improper material processing conditions a n d / o r unforeseen loads and environmental factors. This practice also allows the designer to use design equations based on the assumptions of small deformation and purely elastic material behavior. Other important properties derived from S-S data that are used include modulus of elasticity and tensile strength.

7 Designs 9 653 Rigidities (EIs) Tensile modulus of elasticity (E) is one of the two factors that determine the stiffness or rigidity (E/) of structures comprised of a material (RPs, etc.). The other is the moment of inertia (/) of the appropriate cross section, a purely geometric property of the structure. Table 7.5 provides examples of moment of inertia. In identical products, the higher the modulus of elasticity of the material, the greater the rigidity and doubling the modulus of elasticity doubles the rigidity of the product. The greater the rigidity of a structure, the more force must be applied to produce a given deformation. It is appropriate to use E to determine the short-term rigidity of structures subjected to elongation, bending, or compression. It may be more appropriate to use the flexural modulus to determine the shortterm rigidity of structures subjected to bending, particularly if the material comprising the structure is non-homogeneous, as foamed or fiber-reinforced materials tend to be. In addition, if a reliable compressive modulus of elasticity is available, it can be used to determine short-term compressive rigidity, particularly if the material comprising a structure is fiber-reinforced.

Hysteresis Effects Hysteresis relates to the relation of the initial load applied to a material and its recovery rate when the load is released. There can be a time lapse that depends on the nature of the material and the magnitude of the stresses involved particularly RTPs. This behavior is typically nonlinear and history dependent. This incomplete recovery of strain in a material subjected to a stress during its unloading cycle is due to energy consumption. Upon unloading, complete recovery of energy does not occur. During a static text this phenomenon is called elastic hysteresis; for vibratory stresses it is called damping. The area of this hysteresis loop, representing the energy dissipated per cycle, is a measure of the damping properties of the material. Under vibratory conditions the energy dissipated varies approximately as the cube of the stress (Figure 7.12). This energy is converted from mechanical to frictional energy (heat). It can represent the difference in a measurement signal for a given process property value when approached first from a zero load and then from a flail scale. They provide examples of recovery to near zero strain. It shows that material can withstand stress beyond its proportional limit for a short time, resulting in different degrees of the hysteresis effect.

654

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Figure 7.12 Hysteresisrecovery effects (above) and hysteresis loop related to cyclic loading The hysteresis heating failure occurs more commonly in TP type members subject to dynamic loads. An example is a plastic gear. With the gear teeth under load once per revolution, it is subjected to a bending load that transmits the power from one gear to another. Another example is a link that is used to move a paper sheet in a copier or in an accounting machine from one operation to the next. The load may be simple tensile or compressive stresses, but more commonly it is a bending load.

7 Designs 9 655 Vibration Suppression: Isolation and Damping Vibration occurs in any structure that moves or has moving parts. The effects of vibration range from minor annoyance, such as noise in an automobile, to significant damage to the structure or its contents. The simplest way to design around vibration problems is to make the structure more rugged so that it can withstand the vibration without damage. This approach, however, always adds weight to the structure and cost. It often cannot be applied to certain delicate instruments or other sensitive payloads. For example, while it is possible to build an electronics package that can survive the vibration environment of a space launch vehicle, designing a mirror that can withstand the same conditions is a much greater challenge. An alternative approach is to suppress the vibration, reducing its magnitude and thereby minimizing its effects. CSA Engineering (CSA, Mountain View, CA., USA) specializes in designing and building vibration suppression systems for aerospace and industrial applications. The company uses two main approaches to vibration suppression: isolation and damping. Neither eliminates vibration, but both reduce the vibration at frequencies where the structure is most susceptible to damage. Isolation is mainly used to counteract higher frequency vibrations. Special mounts are installed, which prevent the vibration from either moving across certain parts of the structure, isolating individual components, such as instruments, or isolating a vibration source, such as a motor or pump. Damping systems do not isolate the structure from the vibration source, but instead reduce the magnitude of the vibration within the structure. There is damping technologies that are passive and active. In passive systems, vibrations are diverted into special materials or structural components that dissipate the vibration energy as heat. In active systems, an electronic system monitors the response of the structure to vibration, and actuators then move the structure in opposition to the vibration, effectively canceling it out. Active systems can achieve greater performance and control than passive systems, but are much more expensive, take up more space, and require power. Structures vibrate when an applied force varies with time, Cyclic force repeatedly peaks and drops off; the time between peaks is the frequency. Although the dynamic force may not follow a smooth curve with a simple frequency, most forces can be viewed as combinations of sinusoidal cyclic forces and different frequencies. Likewise, the dynamics of a structure can be characterized by discrete resonant frequencies, or modes, each with its own unique shape. Structures react to the entire spectrum of applied force frequencies, but the response to the resonant

656 Reinforced Plastics Handbook

components of the force will be amplified. Suppression systems lower the overall response, but most often, the main goal is to remove the resonant peaks. Resonant responses can lead to many problems, including high dynamic stresses, excessive dynamic motions, and early fatigue failures. Minimizing these effects enables the structure to be fighter. Vibration may cause a stationary object to move out of position or alignment, which would prevent certain instruments, such as optical systems, from operating properly at all. In a design one has to identify the mode(s) to suppress. It usually requires a special type of finite element analysis (FEA), called modal analysis. At CSA detailed FE models use MSC.Nastran (MSC.Software, Santa Aria, CA., USA), running on dual processor HP/Linux machines. Dynamic models typically require less detail than static stress models in order to accurately capture the modal shapes. FE results show the vibrations as strain energy; identifying regions of high strain energy shows where vibration suppression methods should be applied. Damping treatments can be applied directly to the areas of highest strain energy, making them an efficient suppression method, but care must be taken to maintain strength and stiffness requirements. Damping works by putting the strain energy into a system or material that can transform the motion into heat. CSA uses several damping techniques, but it is particularly known for its expertise in using viscoelastic materials (VEMs) (Chapter 3). Adhesives and elastomer-like materials are common VEMs used in damping applications. VEMs reduce the vibration amplitude and peak dynamic stresses; they also delay the reaction to input forces, resulting in a time or phase difference between the peak in the input force and the peak in strain energy. Mathematically, the viscoelastic material is represented by a complex stiffness function. It includes a stiffness component or shear modulus, and a loss modulus or loss factor, which describes the energy loss and phase difference. For any given material, the complex stiffness function varies with both frequency and temperature; VEMs get stiffer as frequency increases, and the loss factor peaks over material-specific temperature and frequency ranges. Because VEMs work by converting motion into heat, they must be free to move. This means that VEMs have a very low stiffness compared to RPs or metals. Used improperly, they can reduce the overall stiffness of the structure. One way to overcome this problem is to bond the VEMs on the face of the RP. The idea is to place the VEM far away from the neutral axis (center) of bending so the strains in the VEM are larger than in the structure. This allows dissipating strain energy while adding significant stiffness to the structure.

7

9Designs 6 5 7

Viscoelastic layers convert strain energy into heat, suppressing the harmful effects; viscoelastic damping systems reduce overall vibration response and remove resonant peaks. Co-curing viscoelastic materials (adhesives, etc.) with RPs reduces the space required by damping suppression systems and cuts manufacturing costs. FEA coupled with materials databases enables selection of materials with optimum damping properties. Poisson's Ratios

Poisson's ratio is a required constant in engineering analysis for determining the stress and deflection properties of materials (RPs, URPs, metals, etc.). It is a constant for determining the stress and deflection properties of structures such as beams, plates, shells, and rotating discs. With plastics when temperature changes, the magnitude of stresses and strains, and the direction of loading all have their effects on Poisson's ratio. However, these factors usually do not alter the typical range of values enough to affect most practical calculations, where this constant is frequently of only secondary importance. The application of Poisson's ratio is frequently required in the design of structures that are markedly 2-D or 3-D, rather than 1-D like a beam. For example, it is needed to calculate the so-called plate constant for flat plates that will be subjected to bending loads in use. The higher Poisson's ratio, the greater the plate constant and the more rigid the plate. When a material is stretched, its cross-sectional area changes as well as its length. Poisson's ratio (v) is the constant relating these changes in dimensions. It is defines as the ratio of the change in lateral width per unit width to change in axial length per unit length caused by the axial stretching or stressing of a material. It is the ratio of transverse strain to the corresponding axial strain below the tensile proportional limits. For plastics the ratio falls within the range of 0 to 0.5. With a 0 ration there is no reduction in diameter or contraction laterally during the elongation but would undergo a reduction in density. A value of 0.5 would indicate that the specimen's volume would remain constant during elongation or as the diameter decreases such as with elastomeric or rubbery material. RTPs range is usually from about 0.1 to 0.4, URPs about 0.2 to 0.4, and natural rubber is at 0.5 (Table 7.7). In mathematical terms, Poisson's ratio is the diameter of the test specimen before and after elongation divided by the length of the specimen before and after elongation. Poisson's ratio will have more than one value if the material is not isotropic.

658 Reinforced Plastics Handbook Table 7.7 Examples of Poisson's ratios Material

Ratio

Aluminum Carbon steel Rubber Rigid thermoplastics NEAT RP Rigid thermosets NEAT RP

0.33 0.30 0.50 0.20-0.40 0.20-0.40 0.20-0.40 O.2O-O.4O

To lera n ces/S h ri n kages

The RTSs (also TS) plastics are usually more suitable to meet fight tolerances than RTPs (also TPs). With amorphous and crystalline RTPs, they can be more complicated tolerancewise if the fabricator does not understand their behavior (Chapter 3). Crystalline plastics generally have different rates of shrinkage in the longitudinal (melt flow direction) and transverse directions when it is injection molded (IM). TPs with reinforcements significantly permit meeting fighter tolerances than those unreinforced thermoplastics (UTPs). Shrinkage changes can occur at different rates in different directions for RTPs, particularly UTPs. These directional shrinkages can vary significantly due to changes in processes such as during IM. Activity is influenced by factors such as injection pressure, melt heat, mold heat, and part thickness as well as shape. The amorphous type melt flow can be easier to balance. Shrinkage is caused by a volumetric change in a material, particularly RTP, as it cools from a molten to a solid form. Shrinkage is not a single event since it can occur over a period of time for certain plastics, particularly TPs. Most of it happens in the mold, but it can continue for up to 24 to 48 hr after molding. This so-called post-mold shrinkage may require a product to be constrained in a cooling fixture to eliminate warpage. Additional shrinkage can occur principally with RTPs when annealing or exposure to high service temperatures that relieves frozenin stress during fabrication. The main considerations in mold design affecting product shrinkage are to provide, for instance, with IM of RTPs, mold cavity shape to allow

7

9Designs 6 5 9

for shrinkage and adequate cooling, proper cooling rate, proper gate size and location, and structural rigidity. Of these three, cooling conditions is the most critical, especially for crystalline TPs. A number of the computer-aided flow simulation programs offer modules designed to forecast product shrinkage (and, to a limited degree, warpage) from the interplay of RP or URP and mold temperatures, cavity pressures, molded part stress, and other variables in mold-fill analysis. The predicted shrinkage values in various areas of the product should be used as the basis for sizing the mold cavity, either by manual input or feed-through to a mold-dimensioning program. All the programs can successfully predict a certain degree of shrinkage. Experience provides useful information. Target is to consider providing an initial cavity on the smaller size so if a molded part is too small all that is required is machining the cavity to enlarge the cavity. To meet tolerances or shrinkages (as with other materials), more is needed to be applied than simple arithmetic. An important requirement is that someone such as the product moldmaker be familiar with plastics behavior and, particularly, its fabrication method. Of course, with experience in a product equal or similar, as with other materials, setting tolerances and shrinkages is automatic. TSs has a much lower shrinkage than TPs. The TSs is also easier to control shrinkage; however, TPs are controllable. When comparing the shrinkage behaviors of URPs with RPs, there is much less shrinkage with RPs. Thus with RPs, tolerances and shrinkages are significantly reduced or eliminated and provide more reliability in ease of repeatability than URPs. TS matrix with all type of reinforcements a n d / o r fillers generally are more suitable to meet fight dimensional tolerances. For example with injection molded products they can be held to extremely close tolerances of less than a thousand of an inch (0.0025 cm) or down to zero (0.0%) such as when using graphite powder fillers. Tolerances that can be met commercially go from 5% for 0.020 in. (0.05 cm) thick, to 1% for 0.500 in. (1.27 cm), to 1/2% for 1.000 in. (2.54 cm), to 1/4% for 5.000 in. (12.70 cm), etc. With a small amount of blowing agent, such as 5 wt%, shrinkage can usually be eliminated or practically eliminated with practically no change in density (Chapter 5 FOAMS). Tolerances should not be specified tighter than necessary for economical production. However, after production starts, the target is to mold as 'fight' as possible to be more profitable by using less material a n d / o r reducing molding cycle time which result in lower fabrication cost. As reviewed there are unreinforced molded plastics

660 Reinforced Plastics Handbook that change dimensions (shrink) immediately after or in a day or a month due to material relaxation and changes in temperature, humidity, a n d / o r load application. RPs can significantly reduce or even eliminate this dimensional change after molding. Using any calculated shrinkage approach provides a guide in simple shapes. For other shapes, some critical key dimensions of the product will, more often than not, not be as predictable from the shrink allowance, particularly if the product is long, complex shape, or tightly toleranced. This situation also exists with other materials when new shaped products are to be produced (steel, aluminum, etc.). Determining shrinkage involves more than just applying the appropriate correction factor from a material's data sheet. Experience and data sheets provide guides (Figures 7.13 and 7.14) (Chapter 9). 20.0

16.0

E

~

\

12.0

8.0

Nylon6 / 6 ~ , ~

r~

4.0

0

5

in

15

20

25

30

35

40

Glass fiber, w t %

Figure 7.13

Thermoplasticcompounds mold shrinkage vs. glass fiber content

Stress Whitening Also called crazing. It is the appearance of white regions in a material when it is stressed. Stress whitening or crazing is damage that can occur when an RP but particularly an unreinforced TP, is stretched near its yield point. Means to eliminate this damage can be used that includes fillers such as milled glass fibers/resin as a gel coating. The surface takes on a whitish appearance in regions that are under high stress. It is

7 3.0

U n r e i n f o r c ~ gradml

Unreinforced nvton 6 (3% moisture)

~. 2.0

~'~ ~

t 2

I 4

Wall thickness, mm

1.5

Unreinforced PST Un rei n forced pol v~:arbonate

1.0

0

9Designs 6 6 1

I 6

. . . . . . . . .

4 1.0

~ I~

.z ,,,.

Glass reinforced nylon 6 (3% moisture) reinforced PST

0.5

~

2

Figure 7.14

30% glass reinforced polycagoonate

4 6 Wall thickness, mm

Mold shrinkage vs. wall thickness comparisons of thermoset plastic compounds

usually associated with yielding. For practical purposes, stress whiting is the result of the formation of microcracks or crazes that is a form of damage. Crazes are not basically true fractures because they contain strings of highly oriented plastic that connect the two surfaces of the crack. These fibrils arc surrounded by air voids. Because they are filled with highly oriented fibrils, crazes are capable of carrying stress, unlike true fractures. As a result, a heavily crazed part can carry significant stress even though the part may appear fractured. It is important to note that crazes, microcracking, and stress whitening represent irreversible first damage to a material that could ultimately cause failure. This damage usually lowers the impact strength and other properties. In the total design evaluation, the formation of stress cracking or crazing damage should be a criterion for failure based on the stress applied.

662 Reinforced Plastics Handbook

Static Stresses This section reviews the static property aspects that relate to short-term loads (Figure 7.15 and Table 7.8). As reviewed with RTPs the TPs being viscoelastic respond to induced stress by two mechanisms" viscous flow and elastic deformation occurs. Viscous flow ultimately dissipates the applied mechanical energy as frictional heat and results in permanent material deformation. Elastic deformation stores the applied mechanical energy as completely recoverable material deformation. The extent to which one or the other of these mechanisms dominates the overall response of the material is determined by the temperature and by the duration and magnitude of the stress or strain. The higher the temperature, the most freedom of movement of the individual plastic molecules that comprise the TP and the more easily viscous flow can occur with lower mechanical performances. Reinforcements in TPs significantly reduce this situation compared to UTPs.

!

i TENSILE ---

,o,o ] Ii

I

O =lC ---CREEP

MODULUS ---

---FATIGUE

FLEXURAL ---

"--TORSION

COMPRESSIVE --SHEAR ---

TORSION --OTHERS ---

I

---RAPID --MOTION

"--COMBINED

STRESSES

---OTHERS

Figure 7. 1,5 Examplesof stresses due to loads (courtesy of Plastics FALLO)

With the longer duration of material stress or strain, the more time for viscous flow to occur that results in the likelihood of viscous flow and significant permanent deformation. As an example when a RTP product is loaded or deformed beyond a certain point, it yields and immediate or eventually fails. Conversely, as the temperature or the duration or

Table 7.8 Examples o f static mechanical properties o f unidirectional fiber/epoxy RPs

Fiber

Axial Modulus GPa [Msi)

Transverse Modulus GPa [Msi)

lnplane Shear Modulus GPa [ M i )

Poisson 5 Ratio

Axial Tensile Strength MPa [Ksi)

E-glass Aramid Boron SM carbon (PAN) UHS carbon (PAN) U H M carbon (PAN) U H M carbon (pitch) UHK carbon (pitch)

45 (6.5) 76 (11) 210 (30) 145 (21) 170 (25) 310 (45) 480 (70) 480 (70)

12 (1.8) 5.5 (0.8) 19 (2.7) 10 (1.5) 10 (1.5) 9 (1.3) 9 (1.3) 9 (1.3)

5.5 (0.8) 2.1 (0.3) 4.8 (0.7) 4.1 (0.6) 4.1 (0.6) 4.1 (0.6) 4.1 (0.6) 4.1 (0.6)

0.28 0.34 0.25 0.25 0.25 0.20 0.25 0.25

1020 (150) 1240 (180) 1240 (180) 1520 (220) 3530 (510) 1380 (200) 900 (1 30) 900 (1 30)

Transverse Tensile Strength MPa [Ksi]

Axial Compressive Strength MPa (Ksi)

Transverse Compressive Strength MPa (Ksi)

lnplane Shear Strength MPa [Ksi]

620 (90) 280 (40) 3310 (480) 1380 (200) 1380 (200) 760 (110) 280 (40) 280 (40)

140 (20) 140 (20) 280 (40) 170 (25) 170 (25) 170 (25) 100 (15) 100 (15)

70 (10) 60 (9) 90 (13) 80 (12) 80 (12) 80 (12) 41 (6) 41 (6)

664

Reinforced

Plastics Handbook

magnitude of material stress or strain decreases, viscous flow becomes less likely and less significant as a contributor to the overall response of the material; and the essentially instantaneous elastic deformation mechanism becomes predominant. Changing the temperature or the strain rate of a RTP may have a considerable effect on its observed stress-strain behavior (Figure 7.16). At lower temperatures or higher strain rates, the stress-strain curve of a TP may exhibit a steeper initial slope and a higher yield stress. In the extreme, the stress-strain curve may show the minor deviation from initial linearity and the lower failure strain characteristic of a brittle material. 10 lo

-- , l day and more .

--1

io s

~ 3

10 6 10 4 10 2

=o o

10 o

10 -2

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10-4 10 -6

10-1o 10-12

7.16

~ooI ! !1,

~

-'

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l! !1

;

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I

I I

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Figure

I I

! j 10 -10

I , 10 -8

sta~testing

I i ~ 10 -6

i III l I I!

sec.to 1.o ~.

i _Rap!d ! ! loading !

I

I

!111 I ! t11! x ! I ! ~ 10 .4 10 -2 10 0 Strain rate, in./in./sec.

! I

I

I !! ~ 10 2

"

~, Disc., etc.

---

"~Mach.--

nmpact I I 10 4

I /

! ,! 10 s

Comparison of different loading rates for different methods of testing (Courtesy of Plastics FALLO)

At higher temperatures or lower strain rates, the stress-strain curve of the same material may exhibit a more gradual initial slope and a lower yield stress, as well as the drastic deviation from initial linearity and the higher failure strain characteristic of a ductile material. There are a number of different modes of stress-strain that must be taken into account by the designer. They include tensile stress-strain, flexural stress-strain, compression stress-strain, torsional stress-strain, a n d / o r shear stress-strain (Table 7.9). Tensile

Stress-Strains

In obtaining tensile stress-strain (S-S) engineering data, as well as other data, the rate of testing directly influences results. The test rate or the

7

9Designs 6 6 5

Table 7,0 Torsional deformation and shear stress formulas F o r m u l a for K in 0 -

Shape

O

K

m

TL n KO

F o r m u l a for S h e a r Stress

16T

rd' 32

rd 3

r

i 6Td

K ~= 1/32r(d 4 -- dl 4)

~r(d ~ - dz 4)

K

"- 2/3 ~rt 3 r

wa3b t K a s ~ a2 + b 2

m r

G ~

K

-

rasXbl3

asffi~+-bi2

[(I

+

q)4

_

GI

v]

b-

K - b4~/~ 8O

O

K -

-

2T tab 2

Ol

bz

watbl2[(I

2T -}. q)4 -- l]

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T

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2.69b4

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3T 2 r r t ~-

_

~

(3a +

b4

t.Sb)T

a~-b2 J.---o---~

tit

bxxxxx\xN1 T-"

at: + btz -

K -- 0.140664

t2-" -

ts 'z

9~

4.8T

.o-~----

t--~--4

speed at which the movable cross-member of a testing machine moves in relation to the fixed cross-member influences the property of material. The speed of such tests is typically reported in cm/min. (in./ min.). An increase in strain rate typically results in an increase yield point and ultimate strength.

666 Reinforced Plastics Handbook

An extensively used and important performance of any material in mechanical engineering is its tensile stress-strain curve (ASTM D 638). It is obtained by measuring the continuous elongation (strain) in a test sample as it is stretched by an increasing pull (stress) resulting in a S-S curve. It defines several useful qualities that include the tensile strength, modulus (modulus of elasticity) or stiffness (initial straight-line slope of the curve following Hooke's law and reported as Young's modulus), yield stress, and the length of the elongation at the break point (Figure 7.17). (Modulus of elasticity is also called modulus, Young's modulus, coefficient of elasticity, or E. As Hooke's law states, it is the ratio of stress to strain; documented mathematically during 1678 by Robert Hooke, England. Prior to that year this engineering behavior was understood and put to use since the Roman Empire and prior to the pre-Christian era that in particular includes the Chinese Era.) TENSION

30

ULTIMATE TENSILE STRENGTH

--

F~ 2 9 0 0 0 ..... 6 . Et " ~ - " I~16 " , . o , x ,u ps,

~

~ lO t

0

I 0.000

0.008

0.016

]..

0.024

e---STRAIN, INCHES PER INCH

COMPRESSION

z5 c~

\

~2o

\

~.__ ULTIMATE COMPRESSION STRENGTH

(L

Ec. F.j.c. 25,. ~ . 9 .012

u~ 10

0

0.000

0.OO8

--

I

0.016

,

2.08 x 106 psi

I

0.024

e',- STRAIN, INCHES PER INCH

Figure 7.17

Examples

of tensile and compression stress-strain curves for reinforced plastics

Stress is the force on a material divided by the cross sectional area over which it initially acts (engineering stress). When stress is calculated on the actual cross section at the time of the observed failure instead of the

7

9Designs 6 6 7

original cross sectional area it is called true stress. The engineering stress is reported and used practically all the time. The units of strain are meter per meter ( m / m ) or inch per inch (in./in.). Since strain is often regarded as dimensionless, strain measurements are typically expressed as a percentage. Tensile strength is the maximum tensile stress sustained by a specimen during a tension test. When a maximum stress occurs at its yield point, where the curve deviates from the straight line of the S-S curve, it is designated as tensile strength at yield. When the maximum stress occurs at a break, it is its tensile strength at break. The ultimate tensile strength is usually measured in megapascals (MPa) or pounds per square inch (psi). As an example, tensile strength can range from under 20 MPa (3000 psi) to about 75 MPa (11,000 psi) for URPs to more than 350 MPa (50,000 psi) for RTPs. On an S-S curve, there can be a location at which an increase in strain occurs without any increase in stress. This represents the yield point that is also called yield strength or tensile strength at yield. The yield point can also be identified as the proportional limit; it is the greatest stress at which the plastic is capable of sustaining an applied load without deviating from the straight line of an S-S curve. Some materials may not have a yield point. Yield strength can in such cases be established by choosing a stress level beyond the material's elastic limit. The yield strength is generally established by constructing a line to the curve where S-S is proportional at a specific offset strain, usually at 0.2% (Figure 7.18). Per ASTM testing the stress at the point of intersection of the line with the S-S curve is its yield strength at 0.2% offset.

Yield point

Tensile

(proportio~ //

strength yield

strength

Stress cn Q,I L

" I/ V

AStrain 1

0.2%

.

Strain

Figure 7,18 Selecting a usable yield point and offset strain

668 Reinforced Plastics Handbook

The area under the S-S curve is usually proportional to the energy required to break the specimen that in turn can be related to the toughness of a plastic (Figure 7.19). There are types, particularly the RTSs that are very hard, strong, and tough, even though their area under the stress-strain curve is extremely small.

T u~

Strain

Strain TOUGH MATERIALS

T1

T r

Strain

Strain BRITTLE MATERIALS

Figure 7.19 Areas under the tensile stress-strain curves relate to toughness except for reinforced thermoset plastics

The elastic limit identifies a material at its greatest stress at which it is capable of sustaining an applied load without any permanent strain remaining, once stress is completely released. With RPs the modulus that is the initial tangent to the S-S curve does not change significantly with the strain rate. The softer TPs, such as general purpose polyolefins, the initial modulus is independent of the strain rate. The significant time-dependent effects associated with such materials, and the practical difficulties of obtaining a true initial tangent modulus near the origin of a nonlinear S-S curve, render it difficult to resolve the true elastic modulus of the softer TPs in respect to actual data.

Modulus of Elasticities Many RPs and URPs have a definite tensile modulus of elasticity (E) where deformation is directly proportional to their loads below the proportional limits. Since stress is proportional to load and strain to

7

Designs 9 669

deformation, stress is proportional to strain. Figure 7.20 shows this relationship based on the slope of the stress-strain curve. The left curve is where the S-S straight line identifies a modulus and a secant modulus based at a specific strain rate at point C, which could be the usual 1% strain. Bottom curve secant moduli of different plastics are based on a 85% of the initial tangent modulus. Slope represents tangent modulus - - - , , , , ~ / , , ~

9 f

/~=.=.

~-SIope represents secant modulus at strain C'

o'}

~rtional limit

r

CO

A'

,

,,

Strain

C'

,, r

Tangent modulus

~

85% secant modulus

P

O3

i/ '' /

Strain Figure 7.20 Examplesof tangent moduli and secant moduli

670 Reinforced Plastics Handbook There are plastics such as unreinforced commodity TPs that have no straight region on the S-S curve or the straight region of this curve is too difficult to locate. The secant modulus is used. It is the ratio of stress to the corresponding strain at any specific point on the S-S curve. It is the line from the initial S-S curve to a selected point C on the stress-strain curve based on an angle such as 85% or a vertical line such as at the usual 1% strain. With RPs there can be two or three moduli. Their S-S curve starts with a straight line that results in its highest E, followed by another straight line with a lower E, and so forth. To be conservative providing a high safety factor the lowest E is used in a design however the highest E is used in certain designs where experience has proved success. Interesting straight-line correlations exist of the tensile modulus of elasticity to specific gravity of different materials (Figure 7.21). In this figure, the modulus/specific gravity of RPs with its high performing fibers (graphite, aramid, carbon, etc.) continues to increase in the upward direction.

40x

.~

o

._.L",30

E 8

--

~

,,, 20--'=:'~:E 0

1

1 0 - I ~ J 0

Figure 7,21

0

Spruce I 2

eel

/'ntan~um

Aluminum. Reinforced plastics ,

.

! 4

Specific

I

~ . 6 gravity

I 8

Modulus vs. specific gravity ratio for different materials follows a straight line

Flexural Stress-Strains Flexural stress-strain testing according to ASTM D 790 determines the load necessary to generate a given level of strain on a specimen typically using a three-point load. Testing is performed at specified constant rate of crosshead movement based on material being tested. A solid plastic is usually at 0.05 in./min., foamed plastic at 0 . 1 in./min., etc. Using these

7

9Designs 6 7 1

relationships, the flexural strength (also called the modulus of rupture) and the flexural modulus of elasticity can be determined. Example of flexural modulus of elasticity for URP [true virgin polymer since it does not contain additives, fillers, etc.; a Nothing Else Added To (NEAT) polymer] compared to talc and glass fiber RPs (Table 7.10). Table 7o10 Flexural modulus of elasticity for URP and RPs

UNREINFORCEDPLASTICS Polypropylene neat plastic REINFORCEDPLASTICS Polypropylene plastic/40 wtO/otalc Polypropylene plastic/40 wtO/oshort glass fiber

180,000 psi 575,000 psi 1,100,000 psi

A flexural specimen is not in a state of uniform stress on the specimen. When a simply supported specimen is loaded, the side of the material opposite the loading undergoes the greatest tensile loading. The side of the material being loaded experiences compressive stress (Figure 7.22). These stresses decrease linearly toward the center of the sample. Theoretically, the center is a plane, called the neutral axis that experiences no stress.

COMPRESSIVE STRESS

TENSILE STRESS

Figure 7.22 Tensile-compressive loading occurs on a flexural specimen

In the flexural test the tensile and compressive yield stresses of a RP or URP may cause the stress distribution within the test specimen to become very asymmetric at high strain levels. This change causes the neutral axis to move from the center of the specimen toward the surface that is in compression. This effect, along with specimen anisotropy due to processing, may cause the shape of the S-S curve obtained in flexure to differ significantly from that of the normal S-S curve.

672 Reinforced Plastics Handbook The S-S behavior of plastics in flexure generally follows that of tension and compression tests for RPs. The flexural E tends to be the average between the tension and compression Es. The flexural yield point follows that observed in tension. For the standard ASTM flexural strengths most plastics are higher than their ultimate tensile strengths, but may be either higher or lower than compressive strengths. Since most plastics exhibit some yielding or nonlinearity in their tensile S-S curve, there is a shift from triangular stress distribution toward rectangular distribution when the product is subject to bending. This behavior with plastics is similar to that when designing in steel and also for ultimate design strength in concrete. Shifts in the neutral axis resulting from differences in the yield strain and post-yield behavior in tension and compression usually affect the correlation between the modulus of rupture and the uniaxial strength results. The modulus of rupture reflects in part nonlinearities in stress distribution caused by plastification or viscoelastic nonlinearities in the cross-section. Plastics such as short-fiber RPs with fairly linear S-S curves to failure usually display moduli of rupture values that are higher than the tensile strength obtained in uniaxial tests; wood behaves much the same way. Qualitatively, this can be explained from statistically considering flaws and fractures and the fracture energy available in flexural samples under a constant rate of deflection as compared to tensile samples under the same load conditions. These differences become less as the thickness of the bending specimen increases, as would be expected by examining statistical considerations. The cantilever beam is another flexural test that is used to evaluate different plastics (RPs, etc.) and structures such as beam designs. It is used in creep and fatigue testing and for conducting testing in different environments where the cantilever test specimen under load is exposed to chemicals, moisture, etc.

Compressive Stress-Strains A test specimen under loading conditions located between the two flat, parallel faces of a testing machine is compressed at a specified rate (ASTM D 695). Stress and strain are computed from the measured compression test, and these are plotted as a compressive S-S curve for the material at the temperature and strain rate employed for the test. Procedures in compression testing are similar to those in tensile testing. However in compression testing particular care must be taken to specify the specimen's dimensions and relate test results to these dimensions. If

7

9Designs 6 7 3

a sample is too long and narrow buckling may cause premature failure resulting in inaccurate compression test results. Buckling can be avoided by examining different size specimens or using external supports on the specimen sides. An ideal consideration is a test specimen with a square cross-section and a longitudinal dimension twice as long as a side of the cross-section. At high stress levels, compressive strain is usually less than tensile strain. Unlike tensile loading, which usually results in failure, stressing in compression produces a slow, indefimte yielding that seldom leads to failure of an RP. Where a compressive failure does occur, the designer should determine the material's strength by dividing the maximum load the sample supported by its initial cross-sectional area. When the material does not exhibit a distinct maximum load prior to failure, the designer should report the strength at a given level of strain that is usually at 10%. The compression specimen's ends usually do not remain rigid. They tend to spread out or flower at its ends. Test results arc usually very scattered requiring close examination as to what the results mean in reference to the behavior of the test specimens. Different clamping devices (support plates on the specimen sides, etc.) are used to eliminate the flowering action that could provide inaccurate readings that in turn influence results by usually making them stronger. The majority of tests to evaluate the characteristics of RPs are performed in tension a n d / o r flexure because compression data could be misleading. The result is that compressive stress-strain behavior of many RPs is not well described. Generally, the behavior in compression is different from that in tension, but the S-S response in compression is usually close enough to that of tension so that possible differences can be neglected (Figure 7.23). COMPRESSIVE

TENSILE

0

s _

0

STRAIN

Figure 7.23

0 0

Stress-strain tensile and compressive response tends to be similar

674 Reinforced Plastics Handbook The compressive strength of a URP or a mat-based RTP laminate is usually greater than its tensile strength (unidirectional fiber RTP is usually slightly lower than its tensile strength). However, this is not generally true for RTSs. Different results are obtained with different plastics. As an example the compression testing of foamed plastics provides the designer with the useful recovery rate. A compression test result for rigid foamed insulating polyurethane (3.9 l b / f t 3) resulted in almost one-half of its total strain recovered in one week. Shear Stress-Strains Shear deformation occurs in structural elements such as those subjected to torsional loads and in short beams subjected to transverse loads. Shear S-S data can be generated by twisting (applying torque) to a specimen at a specified rate while measuring the angle of twist between the ends of the specimen and the torque load exerted by the specimen on the testing machine (ASTM D 732). Maximum shear stress at the surface of the specimen can be computed from the measured torque that is the maximum shear strain from the measured angle of twist. The shear mode involves the application of a load to a material specimen in such a way that cubic volume elements of the material comprising the specimen become distorted, their volume remaining constant, but with opposite faces sliding sideways with respect to each other. Basically, shearing stresses are tangential stresses that act parallel to the planes they stress. The shearing force in a beam provides shearing stresses on both the vertical and horizontal planes within the beam. The two vertical stresses must be equal in magnitude and opposite in direction to ensure vertical equilibrium. However, under the action of those two stresses alone the element would rotate. Torsion Stress-Strains Shear modulus can be determined by a static torsion test or by a dynamic test using primarily a torsional pendulum (ASTM D 2236). Also used is an oscillatory rheometer test. The torsional pendulum is applicable to virtually all plastics and uses a simple specimen readily fabricated by all commercial fabricating processes or easily cut from fabricated part. The moduli of elasticity, G for shear and E for tension, are ratios of stress to strain as measured within the proportional limits of the material. Thus the modulus is really a measure of the rigidity for shear of a material or its stiffness in tension and compression. For shear or torsion, the modulus analogous to that for tension is called the shear modulus or the modulus of rigidity, or sometimes the transverse modulus.

7 Designs 9 675

Direct Load Shear Strengths Unlike the methods for tensile, flexural, or compressive testing, the typical procedure used for determining shear properties is intended only to determine the shear strength. It is not the shear modulus of a material that will be subjected to the usual type of direct loading (ASTM D 732). When analyzing plastics in a pure shear situation or when the maximum shear stress is being calculated in a complex stress environment, shear strength equal to half the tensile strength or that from shear tests is generally used, whichever is less.

Residual Stresses It is the stress existing in a body at rest, in equilibrium, at uniform temperature, and not subjected to external forces. Often caused by the stresses remaining in a plastic part as a result of thermal a n d / o r mechanical treatment in fabricating parts. Usually they are not a problem in the finished product. However, with excess stresses, the product could be damaged quickly or after in service from a short to long time depending on amount of stress and the environmental conditions around the product.

Dynamic Stresses For certain products long time dynamic (creep, fatigue, impact, etc.) mechanical load performances in different environments are required. Dynamic loading in the present context is taken to include deformation rates above those achieved on the standard laboratory-testing machine (commonly designated as static or quasi-static just reviewed). These slower tests may encounter minimal time-dependent effects, such as creep and stress-relaxation, and therefore are in a sense dynamic. Thus the terms static and dynamic can be overlapping.

Creep and Fatigue Tests Two of the most important types of long-term material behavior are more specifically creep and fatigue. Whereas S-S behavior usually occurs in less than one or two hours, creep and stress relaxation may continue over the entire life of the structure such as 100,000 hours or more (per ASTM procedures). In many applications, intermittent or dynamic loads arise over much shorter time scales. Examples of such products include chair seats, panels that vibrate and transmit noise, engine mounts and other anti-

676

Reinforced Plastics Handbook

vibration products, and road surface-induced loads carried to wheels and suspension systems of a vehicle. Plastics' relevant properties in this regard are material stiffness and internal damping, the latter of which can often be used to advantage in design. Both properties depend on the frequency of the applied loads or vibrations, a dependence that must be allowed for in the design analysis. The possibility of fatigue damage and failure must also be considered. Mechanical loads on a structure induce stresses within the material. The magnitudes of these stresses depends on many factors, including forces, angle of loads, rate and point of application of each load, geometry of the structure, manner in which that structure is supported, and time at temperature. The behavior of the material in response to these induced stresses determines the performance of the structure (Figures 7.24 to 7.30 and Tables 7.11 and 7.12).

827 "A

t.

:S

Tension

689

= u)

551-" E

:3

_s :i

413 -"

1

276

102

10

....

!

..... !

103

104

!

I

105

I

106

107

Number of Cycles to Failure, N

Figure 7.24

Carbon fiber-epoxy RPs fatigue data

10a

cycles

,.,

Percentof Ultimate Static Strengtt',

107

100

80

60 40 2O Steel

4130

Aluminum 2024-T3

Aluminum 7075-T6

Boror~' Epoxy

Glass Fiber Epoxy

Glass Fiber Epoxy

" E . . . . . . "S'

Figure 7.25

Cafoon Fiber; Epoxy ('Thomel 300)

Aramid Fiber/ Epoxy (Kevlar 49)

High performance fatigue properties of RPs and other materials

Carbon Fiber; Epoxy (HTS)

0---

7

2O0

Maximum Tensile Stress (MPa)

"s ---O-

LongGlass PP ShortGlass PP

---X--~-

ShortGlass Nylon 616 LongGlass PPA

Long Glass Nylon 6/6

150

9 Better long fiber fatigue behavior at Intermediate cycles. 9Similar fatigue behavior at high cycles.

100,

I 0

9Designs 6 7 7

;

100

"I

101

'"h"l

10 =

'' .... I ' J ' " ' l '' ....I ' " ' " l " ' " J " l

103 104 10a 10e

9Polyphthalamide~ Nylon 6/6> Polypropylene

'""

107 10s

Cycles to Failure 1~0

,

,

m

"o'--O--

LongGlass PP Short Glass PP

--](-

Long Glass Nylon 6/6 Short Glass Nylon 6/6

~

100-

Maximum Flexural Stress (MPa)

G l s s s PPA

9Superior long glass fiexural fatigue behavior at all cycles

50-

9Polyphthalamide Nylon 6/6> Polypropylene 0,

104

10 3

102

10e

lC

Cycles to Failure

Figure 7.26

Fatigue endurance of reinforced thermoplastics (A) tensile and (B) flexural (courtesy of LNP) 100

50 '|'.,,----- Glass fiber (initial) t- " ' " Aramid. (initial) 40

ci.

E

.E x r

I

z 8o

'"

j

mi-. 03

~

30

E~

~

i .....

i,9

....

GRAPHITE 60

.

.J

2o

i1

40

o lz

10

RBERG~SS

,,,

Glass fiber

rr Lu 0_[

0

10 3

I 10 4

I 10 s

I 10 6

101

107

Cycles to failure

Figure 7.27

~

lexural fatigue data of woven glass fiber roving/epoxy RPs

| 11

102

I

I II

I

I III

1

I II

10a 104 10s CYCLES TO FAILURE

I

I

II

I

106

Figure 7,28; Fatigue data of 181 glass fiber fabriclTS polyester (fiberglass), steel, graphite fiber fabric/epoxy, and aluminum

I II

10 7

678

Reinforced

Plastics Handbook

Table 7,11 Reinforced thermoplastic short glass and carbon fiber (by weight) compounds fatigue data

Stress at Failure [psi) Cycles to Failure

Fiber Type and Content(O/o) Glass

Carbon

104

105

106

107

SAN

30

-

8,500

7,500

6,500

5,500

Styrene

30

-

8,000

7,000

6,000

5,000

40

-

9,500

7,750

6,500

5,500

20

-

9,000

6,000

5,200

5,000

30 40

-

12,500 14,500

7,000 8,750

5,500 6,100

5,350 6,000

3,500 6,100

Base Resin

Polycarbonate

ETFE copolymer Polysulfone Polyethersulfone

30

-

4,500

3,600

3,500

-

30

9,000

6,300

6,100

30

-

14,000

6,500

5,000

40

-

16,000

7,750

6,000

4,500 5,500

30

-

16,000

7,500

6,000

5,000

40

-

19,000

8,500

7,600

6,200

-

30

22,000

10,000

8,000

6,700

Acetal copolymer

30

-

9,000

7,000

7,000

7,000

Polypropylene

30

-

5,500

4,500

4,500

4,500

Polyphenylene sulfide

-

30

13,000

9,700

9,500

9,500

Nylon 6*

30

-

7,000

6,000

5,750

5,750

Nylon 6/10"

30

-

6,800

5,750

5,600

40

-

8,000

7,000

7,000

5,500 7,000

Nylon 6/6

40

-

6,500 10,500

5,900 9,300

5,300 9,100

5,200 9,100

Nylon 6/6*

-

-

3,400

3,200

3,100

3,100

30

-

8,000

6,500

6,000

5,900

40

-

9,000

7,300

7,000

7,000

-

30 40 -

13,000 15,000 6,400

10,500 10,300 4,400

8,000 8,800 3,900

8,000 8,500 3,700

-

30 Polyester (PBT) Modified PPO PEEK

30

-

11,000

7,200

5,600

5,100

-

30

13,000

9,200

7,400

6,500

30

-

7,200

5,800

4,900

4,750

-

30

18,000

17,500

17,500

17,500

7

9Designs 6 7 9

Increasing e,,.es s

L..

Log time

ISOMETRIC STRESS VS LOG TIME

..

ISOCHRONOUS STRESS VS STRAIN

% Increasing Stra>

I

~

~

Log time

Figure 7,29

,,

J

.,,

Increasing" Time Strain

Examples of different formatted creep vs. log time curves (courtesy of Bayer)

1.00

Unreinforced nylon "q'-'-6/6, 1.250 psi

'

glass !i ber/nylon6/6.5.000ps i

0.75

. / 4 0 % glass fit~qnylon 6/6, 5,000 psi ........ _____,,---

~ 0.5o r

9

~

"~'30% glass fiber/nylon 6/6.2,500 psi

~.~'~"'"~~

~!, Figure 7,30

glass bead/nylon 6/6, 1,250 psi

~rne~)

iir ......

i:~'

Reinforcement and filler inverse effect on flexural creep rate (courtesy of LNP)

680 Reinforced Plastics Handbook Table 7.1 2

Examples of flexural glass and carbon fiber, by weight, reinforced thermoplastics creep data

Base Resin

Fiber Content Stress (Yo) (psi)

Strain (010) Hours 10

100

Apparent Modulus (103 psi)" Hours 1,000

10

100

1,000

Glass- Fiber-Rei nforced Cornposites

ABS

20 40

SAN

20

30 40

Polystyrene

20

40

2,500 5,000 5,000 10,000

0.263 0.520 0.290 0.585

0.288 0.607 0.302 0.61 5

0.325 0.643 0.332 0.660

951 962 1,724 1,709

868 824 1,656 1,626

769 778 1,506 1,515

2,500 5,000 10,000 5,000 10,000

0.277 0.455 0.9 10 0.367 0.558

0.239 0.478 0.956 0.389 0.600

0.271 0.540 1.086 0.402 0.642

1,101 1,099 1,099 1,362 1,792

1,046 1,046 1,046 1,285 1,667

923 926 921 1,244 1,558

2,500 5,000 10,000 5,000 10,000

0.273 0.519 1.090 0.280 0.570

0.301 0.550 1.205 0.290 0.630

0.338 0.585 1.350 0.300 0.690

916 963 917 1,786 1,754

831 909 830 1,724 1,587

740 855 741 1,667 1,449

Polycarbonate

20 30 40

5,000 5,000 5,000 10,000

0.618 0.451 0.312 0.620

0.628 0.462 0.319 0.700

0.654 0.466 0.322 0.710

809 1,109 1,603 1,613

796 1,082 1,567 1,429

764 1,073 1,553 1,408

Polyet he ri m ide

20 40

5,000 5,000 10,000

0.512 0.275 0.554

0.551 0.299 0.559

0.580 0.31 5 0.631

976 1,818 1,805

907 1,672 1,669

862 1,587 1,585

PoIyet hy I e ne

20

2,500

0.796

0.894

0.936

314

280

267

Polysulfone

30 40

5,000 5,000 10,000

0.362 0.290 0.590

0.439 0.340 0.670

0.453 0.340 0.680

1,381 1,724 1,694

1,139 1,471 1,492

1,104 1,471 1,471

Polyacetal

30

1,250 2,500 5,000 5,000 10,000

0.159 0.278 0.546 0.380 0.640

0.182 0.320 0.629 0.480 0.800

0.190 0.337 0.670 0.520 0.860

786 899 916 1,316 1,562

687 781 795 1,042 1,250

658 742 746 961 1,163

40

PoIy propyIene

30 40

5,000 5,000

0.410 0.680

0.460 0.940

0.480 1.130

610 735

543 532

421 442

Polypheny Iene sulfide Nylon 6

30

2,500 5,000

0.190 0.350

0.190 0.350

0.190 0.350

1,316 1,429

1,316 1,429

1,316 1,429

20 30

5,000 5,000 10,000

0.890 0.750 1.533

1.070 0.800 1.892

1.090 0.830 1.933

562 667 652

467 625 528

459 602 517

7 . Designs 681 Nylon 6/10

40

Nylon 616

60 30 40

60 Polyurethane High-impact nylon Polyester (PBl

40 30

30 40

Amorphous nylon 30 Polyester elastomer

30

Polyphenylene oxide

30

5,000 10,000 5,000 2,500 5,000 2,500 5,000 10,000 5,000 10,000 2,500 1,250 2,500 5,000 2,500 5,000 5,000 10,000 2,500 5,000 1,250 2,500 5,000 2,500 5,000

0.550 1.320 0.280 0.340 0.434 0.298 0.380 0.800 0.250 0.560 0.375 0.270 0.482 1.369 0.210 0.41 6 0.278 0.590 0.248 0.640 0.365 0.448 1.460 0.255 0.51 8

0.640 1.450 0.340 0.470 0.617 0.391 0.514 0.960 0.320 0.630 0.481 0.290 0.534 1.719 0.241 0.478 0.284 0.630 0.275 0.678 0.397 0.496 1.550 0.277 0.548

0.680 1.490 0.360 0.490 0.662 0.391 0.528 0.990 0.350 0.640 0.500 0.330 0.679 2.018 0.252 0.502 0.298 0.640 0.324 0.757 0.411 0.538 1.660 0.314 0.625

909 756 1,785 735 1,152 839 1,316 1,250 2,000 1,786 667 463 519 365 ,190 ,202 1,799 1,695 1,008 781 342 558 342 980 965

781 690 1,471 532 810 639 973 1,041 1,563 1,587 520 431 468 291 1,037 1,046 1,761 1,587 909 737 315 504 322 902 912

735 671 1,389 510 755 639 947 1,010 1,429 1,562 500 379 368 248 992 996 1,678 1,562 772 660 304 465 301 796 800

940 1,089 1,253 1,284 2,232 2,092 3,205 2,941 1,064 1,066 1,488 1,330 1,880 1,968 2,273 2,232

880 1,044 1,190 1,219 1,984 2,000 2,976 2,941 1,020 1,030 1,287 1,282 1,785 1,945 2,232 2,058

Carbon-Fiber-Reinforced Composites

Polycarbonate

30

2,500 5,000

Polyet h er imide

20

PoIysu Ifo ne

30

PoIy phe ny I en e sulfide

30

Nylon 6

30

Nylon 616

30

5,000 10,000 2,500 5,000 2,500 5,000 2,500 5,000 2,500 5,000 2,500 5,000 2,500 5,000

40 Polyester (PBT)

30

0.120 0.240 0.367 0.721 0.098 0.224 0.070 0.168 0.221 0.443 0.140 0.334 0.112 0.240 0.084 0.196

0.128 0.251 0.399 0.779 0.112 0.239 0.078 0.170 0.235 0.467 0.168 0.376 0.133 0.254 0.110 0.224

0.129 0.260 0.420 0.820 0.126 0.250 0.084 0.170 0.245 0.485 0.194 0.390 0.140 0.257 0.112 0.243

954 1,104 1,362 1,387 2,551 2,232 3,571 2,976 1,131 1,128 1,786 1,497 2,232 2,083 2,976 2,551

682 Reinforced Plastics Handbook

Designing With Creep Data Creep data can be very useful to the designer. In the interest of sound design-procedure, the necessary long-term creep information should be obtained on the perspective specific RP, under the conditions of product usage. In addition to the creep data, a stress-strain diagram under similar conditions should be obtained. The combined information will provide the basis for calculating the predictability of the plastic performance. The factors that affect being able to design with creep data include a number of considerations. First, the strain readings of a creep test can be more accessible to a designer if they are presented as a creep modulus. In a viscoelastic, material (Chapter 3) the strain continues to increase with time while the stress level remains constant. Since the creep modulus equals stress divided by strain, one thus has the appearance of a changing modulus. Second, the creep modulus, also known as the apparent modulus or viscous modulus when graphed on log-log paper, is normally a straight line and lends itself to extrapolation for longer periods of time. The apparent modulus should be differentiated from the modulus given in the data sheets, which is an instantaneous or static value derived from the testing machine, per ASTM D 638. Third, creep data application is generally limited to the identical material, temperature use, stress level, atmospheric conditions, and type of test (that is tensile, flexural, or compressive) with a tolerance of _+ 10%. Only rarely do product requirement conditions coincide with those of a test or, for that matter, are creep data available for all the grades of materials that may be selected by a designer. In such cases a creep test of relatively short duration, say 1,000 hours, can be instigated, and the information be extrapolated to long-term needs. In evaluating plastics it should be noted that reinforced TPs and TSs display a much higher resistance to creep than do URPs. Finally, there have been numerous attempts to develop formulas that could be used to predict creep information under varying usage conditions. In practically all cases the suggestions have been made that the calculated data be verified by actual test performance. Furthermore, numerous factors have been introduced to apply such data to reliable predictions of product behavior.

Creep and Stress Relaxations As reviewed, viscoelasticity can be related to designing (Chapter 3). In general, this is tractable only if the mechanical behavior is linear, although methods for nonlinear behavior

7

9Designs 6 8 3

have been developed. For example, creep under constant stress relates to applications that are statically obtained and for which the applied loads are constant in time. Here the controlling equations for stress and strain analysis are identical with those for an elastic material, except that material properties are functions of time under load (creep). If the design analysis problem for an elastic material has a specific solution, such as a design equation, then the solution for the viscoelastic material is obtained by replacing the elastic modulus by the creep modulus. In the absence of a specific solution such as a complex component shape, a numerical solution may have to be derived and this must include the material time dependence. In principle, this is straightforward, particularly if use is made of the corresponding principle relating elastic and viscoelastic solutions. However, in practice the numerical calculations may be complex and possibly impractical (as reviewed, judgment is often used). Creep performance may be inferred from the solution of simpler, desired product geometry, or a simple model of creep properties may be used. However, any such model must adequately represent the creep properties of the material, as with models for metals where creep contained in FEA software may not be adequate for plastics, particularly unreinforced TPs. Metals creep is usually approximated by its secondary (constant rate) component, whereas plastics creep is essentially primary creep (decreasing creep rate), one consequence of which is that creep strain for metals is usually plotted against time, but for plastics it is plotted against log time. Stress relaxation under constant strain has been reviewed. It relates to applications which are kinematically evaluated and for which applied displacements are constant in time. Examples are bolted joints or plastics subjected to a mismatch-fit into a much stiffer structure or having a different coefficient of thermal expansion.

Time-Dependent Loads There may be plastic components that are subjected to applied loads or displacements that vary with time. Material and component performance may be a complex interaction between creep and stress relaxation loadings. Where precise equations exist for the corresponding elastic problem, the viscoelastic solutions can be obtained simply by replacing elastic moduli in the equation by time-dependent creep or stress relaxation moduli. This psuedo-elastic approximation has been used. The corresponding results for intermittent loading over relatively long time intervals are reasonably easy to handle in practical design analysis. However, fatigue loads, involving many load reversals and operating over short time scales,

684 Reinforced Plastics Handbook

would be difficult to determine by the creep loading mechanism. It can be approximated by a dynamic form.

Isometric and Isochronous Graphs Creep curves are a common method of displaying the interdependence of stress-strain-time. However, there are other methods that may also be useful in particular applications, specifically isometric and isochronous graphs. An isometric graph is obtained by taking a constant strain section through the creep curves and replotting this as stress versus time. It is an indication of the relaxation of stress in the plastic when strain is kept constant. These data are often used as a good approximation of stress relaxation in a plastic. In addition, if the vertical (stress) axis is divided by the strain, one obtains a graph of the modulus against time. These graphs provide a good illustration of the time-dependent variation of the modulus (Figure 7.29). An isochronous graph may be obtained by taking a constant time section through the creep curves and then plotting stress versus strain. It can also be obtained experimentally by performing a series of brief creep and recovery tests on a plastic. In this procedure, a stress is applied to a plastic test piece and the strain is recorded after a specified time, typically 100 s. The stress is then removed and the plastic allowed to recover, normally for a period of 4 (4 x 100 s). A larger stress is then applied to the same specimen, after recording the strain at the 100 s. time period; then this stress is removed and the material allowed recovering. This procedure is repeated until enough points have been obtained to let an isochronous graph to be plotted. Isochronous data are usually presented in log-log scales. One reason for doing so is that on linear scales any slight, but possibly important, nonlinearity between stress and strain may go unnoticed. Whereas the use of log-log scales will usually produce a relatively straight-line graph, the slope of this gives an indication of the linearity of the material. If the material is perfectly linear, the slope will be at 45 degrees, but if it is nonlinear the slope will be less than 45 degrees. Isochronous graphs are particularly valuable when obtained experimentally, because they are less time consuming and require less specimen preparation than creep curves. Such graphs at several time intervals can also be used to build up creep curves and indicate areas where the main experimental creep program could be most profitable. They are also popular as means of evaluating deformational behavior, because their method of data presentation is similar to the conventional tensile test data.

7

9Designs 6 8 5

Designing with Fatigue Data Fatigue is the phenomenon of having materials under cyclic loads at levels of stress below their static yield strength. Fatigue data are used so the designer can predict the performance of a material under cyclic loads. The fatigue test, analogous to static long-term creep tests, provides information on the failure of materials under repeated stresses. This fatigue behavior is by no means a new problem. The term was applied to the failure of a wooden mast by hoisting too many sails too often in the pre-Christian era. Under a repeated applied cyclic load, fatigue cracks begin somewhere in the specimen and extend during the cycling. Eventually the crack will expand to such an extent that the remaining material can no longer support the stress, at which point the product will fail suddenly. However, failure for different service conditions may be defined differently than just as the separation of two parts. ASTM D 671 defines failure as occurring also when the elastic modulus has decreased to 70% of its original value. The failure effect is generally a loss of toughness, lowered impact strength, and lowered tensile elongation. Failure includes the melting of any part of a specimen, excessive change of dimensions or the warping of the part, and the crazing, cracking, or formation of internal voids or deformation markings. These types of defects all may seriously affect performance strength. URPs are susceptible to brittle crack-growth fractures as a result of cyclic stresses in much the same way as metals. In addition, because of their high damping and low thermal conductivity, TPs are prone to thermal softening if the cyclic stress or cyclic rate is high. Fatigue data are normally presented as a plot of the stress (S) versus the number of cycle's (N) that cause failure at that stress; the data plotted defined as an S-N curve. The use of an S-N curve is to establish fatigue endurance limit strength. The curve asymptotically approaches a parallel to the abscissa, thus indicating the endurance limit as the value that will produce failure. Below this limit the material is less susceptible to fatigue failure (Figure 7.31). The fatigue behavior of a material is normally measured in a flexural but also in a tensile mode. Specimens may be deliberately cracked or notched prior to testing, to localize fatigue damage and permit measuring the crack-propagation rate. In constant-deflection amplitude testing a specimen is repeatedly bent to a specific outer surface strain level. The number of cycles to failure is then recorded. In constant flexural load amplitude, testing a bending load is repeatedly applied to the specimen.

686 Reinforced Plastics Handbook

t NUMBER OF CYCLES TO FAILURE

Figure 7.31

Typical S-N fatigue curve

This load causes a specified outer-surface stress level. The number of cycles to failure is then recorded. Both modes of flexural fatigue testing can be related to the performance of real structures, one to those that are flexed repeatedly to a constant deflection and the other to those that are repeatedly flexed with a constant load. Since fatigue cracks often start at a random surface imperfection, considerable scatter occurs in fatigue data, increasing with the increasing lifetime wherever crack initiation occupies most of the fatigue life of a specimen. When a line of the best fit is drawn from the available data points on an S-N curve, this represents the mean life expected at any given stress level or the stress that would cause, say, 50% of the product failures in a given number of cycles. If sufficient data are available, much more information can be provided when different curves for various percentages of failure are plotted. Where such data are available, reasonable design criteria would be based on some probability for failure, depending on how critical the effects of failure occur. If a large, expensive repair of a complex mechanism would result from the fatigue failure of one product, then a 10 or even 1% probability of failure would be a more likely design criterion than the 50% suggested above. The fatigue strength of most unreinforced TPs is about 20 to 30% of the ultimate tensile strength determined in the short-term test but higher for RTPs. It decreases with increases in temperature and stresscycle frequency and with the presence of stress concentration peaks, as in notched components. ASTM Special Technical Publication No. 91 discusses in detail the important ramifications to be considered in the various statistical aspects of fatigue testing. Most often, the fatigue curves as well as the tabulated values of endurance strengths and endurance limits are based on the 50% probability curve. As a result, designers do not resort to using scatter-band

7

9Designs 6 8 7

curves unless they are involved with a design that takes a statistical approach. The designer requiring information on the highest order of reliability should always contact the plastic manufacturer or run tests.

Heat Generation Since TPs are viscoelastic (Chapter 3), there is the potential for having a large amount of internal friction generated within the plastics during mechanical deformation, as in fatigue. This action involves the accumulation of hysteretic energy generated during each loading cycle. Examples of products that behave in this manner include coil or leaf springs. Because this energy is dissipated mainly in the form of heat, the material experiences an associated temperature increase. When heating takes place the dynamic modulus decreases, which results in a greater degree of heat generation under conditions of constant stress. The greater the loss modulus of the material, the greater the amount of heat generated that can be dissipated. Plastics for fatigue applications can therefore have low losses. If the URP's surface area is insufficient to permit the heat to be dissipated, the specimen will become hot enough to soften and melt. The possibility of adversely affecting its mechanical properties by heat generation during cyclic loading must therefore always be considered. The heat generated during cyclic loading can be calculated from the loss modulus or loss tangent of the plastics. The rate dependence of fatigue strength demands careful consideration of the potential for heat buildup in both the fatigue test and in service. Generally, since the buildup is a function of the viscous component of the material, the materials that tend toward viscous behavior will also display sensitivity to cyclic load frequency. Thus, TPs, particularly the crystalline polymers like polyethylene that are above their glasstransition temperatures, are expected to be more sensitive to the cyclic load rate, and highly crosslinked plastics or glass fiber reinforced TS plastics are much less sensitive to the frequency of load.

Reinforced Plastics In common with metals and URPs, RPs also is susceptible to fatigue. However, they provide high performance when compared to URPs and many other materials. If the matrix is a TP, there is a possibility of thermal softening failures at high stresses or high frequencies. However, in general the presence of fibers reduces the hysteretic heating effect, with a reduced tendency toward thermal softening failures. When conditions are chosen to avoid thermal softening, the normal fatigue process takes places as a progressive weakening of the material from crack initiation and propagation.

688 Reinforced Plastics Handbook

Plastics reinforced with carbon, graphite, boron, and aramid are stiffer than the glass reinforced plastics (GRP) and are less vulnerable to fatigue (Chapter 2). In short fiber, GRPs cracks tend to develop easily in the matrix, particularly at the interface close to the ends of the fibers. It is not uncommon for cracks to propagate through a TP matrix and destroy the material's integrity before fracturing of the fabricated product occurs. With short fiber RPs fatigue life can be prolonged if the fiber aspect ratio of its length to its diameter is large, such as at least a factor of five, with ten or better for maximum performance. In most GRPs, debonding can occur after even a small number of cycles, even at modest levels. If the material is translucent, the buildup of fatigue damage can be observed. The first signs (for example, with glass fiber/TS polyester) are that the material becomes opaque each time the load is applied. Subsequently, the opacity becomes permanent and more pronounced, as can occur in corrugated RP translucent roofing panels. Eventually, plastic cracks will become visible, but the product will still be capable of bearing the applied load until localized intense damage causes separation in the component. However, the first appearance of matrix cracks may cause sufficient concern, whether for safety or aesthetic reasons, to limit the useful life of the product. Unlike most other materials, GRPs give visual warning of their fatigue failure. Since GRPs can tend not to exhibit a fatigue limit, it is necessary to design for a specific endurance, with safety factors in the region of three to four being commonly used. Higher fatigue performance is achieved when the data are for tensile loading, with zero mean stress. In other modes of loading, such as flexural, compression, or torsion, the fatigue behavior can be worse than that in tension due to potential abrasion action between fibers if debonding of fiber and matrix occurs. This is generally thought to be caused by the setting up of shear stresses in sections of the matrix that are unprotected by some method such as having properly aligned fibers that can be applied in certain designs. Another technique, which has been used successfully in products such as high-performance RP aircraft wing structures, incorporates a very thin, high-heat-resistant film such as Mylar between layers of glass fibers. With GRPs this construction significantly reduces the selfdestructive action of glass-to-glass abrasion and significantly increases the fatigue endurance limit. The basic rules to providing fatigue endurance can be summarized. Fiber reinforcement provides significant improvements in fatigue with carbon fibers and graphite and aramid fibers being higher than glass fibers. The effects of moisture in the service environment should also be considered, whenever hygroscopic plastics such as nylon, PCs, and

7

Designs 9 689

others are to be used. For service involving a large number of fatigue cycles in TPs, crystalline-types offer the potential of more predictable results than those based on amorphous types, because the crystalline ones usually have definite fatigue endurance (Chapter 3). In addition, for optimum fatigue life in service involving both high-stress and fatigue loading, the reinforced high-temperature performance plastics such as PEEK, PES, and PI are recommended. Dynamic/Static Mechanical Behaviors

Mechanical tests measure the response or deformation of a material to periodic or varying forces. Generally an applied force and its resulting deformation both vary sinusoidally with time. From such tests it is possible to obtain simultaneously an elastic modulus and mechanical damping, the latter of which gives the amount of energy dissipated as heat during the deformation of the material. Description of material behavior is basic to all designing applications. Many of the problems that develop may be treated entirely within the framework of plastic's viscoelastic material response. While even these problems may become quite complex because of geometrical and loading conditions, linearity, reversibility, and rate independence generally applicable to elastic material description certainly eases the task of the analyst for dynamic and static loads that include conditions such as creep, fatigue, and impact. Many plastic products seen in everyday life are not required to undergo sophisticated design analysis because they are not required to withstand high static a n d / o r dynamic loads. However, one is increasingly confronted with practical problems that involve material response that is inelastic, hysteretic, and rate dependent combined with loading which is transient in nature. These problems include structural response to moving or impulsive loads, all the areas of ballistics (internal, external, and terminal), contact stresses under high speed operations, high speed fabricating processes, shock attenuation structures, seismic wave propagation, and many others of equal importance. From past problems it became evident that the physical or mathematical description of the behavior of materials necessary to produce realistic solutions did not exist. Since at least the 1940s, there has been considerable effort expended toward the generation of both experimental data on the dynamic and static mechanical response of materials (steel, RP, URP, etc.) as well as the formulation of realistic constitutive theories. Interesting is that metals are unique under both dynamic and static loads that can be cited as outstanding cases. The mechanical engineer

690 Reinforced Plastics Handbook

and the metallurgical engineer have both found these materials to be most attractive to study. When compared to plastics, they are easier to handle for analysis. However there is a great deal that is still not understood about metals, even in the voluminous scientific literature available. The importance of RPs and URPs has been growing steadily, resulting in more dynamic mechanical behavior data becoming available since 1940; unfortunately there is always more required. Summarization of all material behaviors can be by classifications. They include: 1

creep, and relaxation behavior with a primary load environment of high or moderate temperatures;

2

fatigue, viscoelastic, and elastic range vibration or impact;

3

fluidlike flow, as a solid to a gas, which is a very high velocity or hypervelocity impact; and

4

crack propagation and environmental embrittlement, as well as ductile and brittle fractures.

Dynamic Loadings Design analysis problems can fall into one of two situations that relate to small and large deformations. Small amplitude deformations associated with product vibration or noise transmission can also be a source of fatigue failure. Linear viscoelastic behavior results in designs that differ from the corresponding elastic analysis in two respects. The material moduli have to be determined at the frequency of vibration; this may be one of the unknowns of the design analysis. With the other difference, the moduli appear in the analysis as complex quantifies where the imaginary part corresponds to the materials' damping characteristics. When the elastic analysis has a specific solution, generation of the viscoelastic solution is straightforward. However, if the elastic analysis employs a computer solution into which elastic modulus data must be substituted, then the corresponding viscoelastic solution is not straightforward due to complex and frequency dependent forms of the moduli. Such an analysis requires special consideration and the use of appropriate designer/engineering capabilities. Design analysis problems with large deformation and strains often require nonlinear design analyses. Component design is difficult due to nonlinear mechanical behavior, component geometry, and loading conditions, and to frequency dependence and material damping. Some of the original work in this area has shown that the first three factors can be analyzed using FEA and a nonlinear elastic model of material behavior. However, inclusion of viscoelastic effects would greatly

7

9Designs 6 9 1

complicate the numerical analysis, and would require the development of an adequate nonlinear viscoelastic model. Progress in this area has been ongoing principally from various internal organizations. There are components that are subjected to a combination of compression and shear, large and small deformations, and static and dynamic loads; the latter may occur over a range of frequencies. Without previous data, a combination of theory and testing is usually employed to model the stiffness and damping properties of the candidate materials with respect to these parameters. The model has a relatively simple form, reducing the amount of testing required for new materials data, and can be used to analyze small amplitude (linear) vibrations that are superimposed on an existing large static deformation. Analysis of large amplitude vibrations would be much more complex.

Impacts Impact loading analysis may take the form of design against impact damage requiring an analysis under high-rate loading or design for acceptable energy absorption, or a comVELOCITY, FT./SEC. bination of the two (Figure 7.32). Impact resistance of a structure is defined 1,000 -- FIRED PROJECTILE as its ability to absorb and dissipate the ~" --BATTED BASEBALL energy delivered to it during relatively , high-speed collisions with other objects --PITCHED BASEBALL without sustaining damage that would . ~ 100 --FOOTBALL HELMET damage its intended performance. --TEN-FOOT FALL .!

_ _

To determine whether failure will occur the acceptable energy absorption case requires an analysis of the stress-strain distribution during the impact loading followed by comparison with materials impact failure data. Whenever a product is loaded rapidly, it is subjected to impact loading. Any product that is moving has kinetic energy. When this motion is somehow stopped because of a collision, its energy must be dissipated. The ability of a plastic product to absorb energy is determined by such factors as its shape, size, thickness, type of material, method of processing, and environmental condi-

_ _

i,: ::~ ~:::~ ~.~ ,: ~ ~

--IZOD IMPACT TEST

9

,

,

--REFRIGERATOR DOOR-SLAM

-HOUSE DOOR-SLAM

'

. . . . .

, i .il i:i 0.1

;~,;~ -- CONVENTIONALTENSILESTRENGTH :'! ,:: .~ 0.01 - Figure 7.32 Rapidloading velocity

692 Reinforced Plastics Handbook

tions of temperature, moisture, a n d / o r others. Temperature conditions affect impact strength. The impact strength of URPs is reduced drastically at low temperatures however, the RPs provide significant improvement in impact strength at low temperature. From a design approach several design features affect impact resistance. For example, rigidizing elements such as ribs may decrease a part's impact resistance, while less-rigid sections may absorb more impact energy without damage by deflecting elastically. Dead sharp corners or notches subjected to tensile loads during impact may decrease the impact resistance of a product by acting as stress concentrators, whereas generous radii in these areas may distribute the tensile load and enhance the impact resistance. This factor is particularly important for products comprised of materials whose intrinsic impact resistance is a strong function of a notch radius. An impact resistance that decreases drasticaUy with notch radius characterizes such notch sensitive materials. Wall thickness may also affect impact resistance. Some materials have a critical thickness above that the intrinsic impact resistance decreases dramatically. There are different methods used to determine the impact resistance of plastics. They include pendulum methods (Izod, Charpy, tensile impact, falling dart, Gardner, Dynatup, etc.) and instrumented techniques. Impact strengths of plastics are widely reported, these properties have no particular design value. However, they are important, because they can be used to provide an initial comparison of the relative responses of materials. With limitations, the impact value of a material can broadly separate those that can withstand shock loading from those that are poor in this response. The results provide guidelines that will be more meaningful and empirical to the designer. To eliminate broad generalizations, the target is to conduct impact tests on the final product.

Frictions Friction is the opposing force that develops when two surfaces move relative to each other. Basically, there are two frictional properties exhibited by any surface; static friction and kinetic friction. The ranges of friction properties are rather extensive. Frictional properties of plastics are important in applications such as machine products and in sliding applications such as belting and structural units such as sliding doors. In friction applications suggested as well as in many others, there are important areas that concern their design approach. It starts in plastic selection and modification to provide either high or low friction as required by the application. There is also determining

7. Designs 693 the required geometry to supply the frictional force level needed by controlling contact area and surface quality to provide friction level. A controlling factor limiting any particular friction force application is heat dissipation. This is true if the application of the friction loads is either a continuous process or a repetitive process with a high duty cycle. The use of cooling structures either incorporated into the products or by the use of external cooling devices such as coolants or airflow should be a design consideration. For successful design the heat generated by the friction must be dissipated as fast as it is generated to avoid product overheating and failure. The relationship between the normal force and the friction force is used to define the coefficient of static friction. Coefficient of friction is the ratio of the force that is required to start the friction motion of one surface against another to the force acting perpendicular to the two surfaces in contact. Friction coefficients will vary for a particular plastic from the value just as motion starts to the value it attains in motion. The coefficient depends on the surface of the material, whether rough or smooth. These variations and others make it necessary to do careful testing for an application that relies on the friction characteristics of plastics. Once the friction characteristics are defined, however, they are stable for a particular material fabricated in a prescribed method. The molecular level characteristics that create friction forces are the intermolecular attraction forces of adhesion. If the two materials that make up the sliding surfaces in contact have a high degree of attraction for each other, the coefficient of friction is high. This effect is modified by surface conditions and the mechanical properties of the materials. If the material is rough there is a mechanical locking interaction that adds to the friction effect. Sliding under these conditions actually breaks off material and the shear strength of the material is an important factor in the friction properties. If the surface is polished smooth the governing factor induced by the surface conditions is the amount of area in contact between the surfaces. In a condition of large area contact and good adhesion, the coefficient of friction is high since there is intimate surface contact. It is possible by the addition of surface materials that have high adhesion to increase the coefficient of friction. If one or both of the contacting surfaces have a low compression modulus it is possible to make intimate contact between the surfaces that will lead to high friction forces in the case of plastics having good adhesion. It can add to the friction forces in another way. The displacement of material in front of the moving object adds a mechanical element to the friction forces.

694 Reinforced Plastics Handbook

In regard to surface contamination, if the surface is covered with a material that prevents the adhesive forces from acting, the coefficient is reduced. If the material is a liquid, which has low shear viscosity, the condition exists of lubricated sliding where the characteristics of the liquid control the friction rather than the surface friction characteristics of the plastics. The use of plastics for gears and beatings is the area in which friction characteristics have been examined most carefully. As an example highly polar plastic such as nylons and the TP polyesters have, as a result of the surface forces on the material, relatively low adhesion for themselves and such sliding surfaces as steel. Laminated plastics (RPs) make excellent gears and beatings. The typical coefficient of friction for such materials is 0.1 to 0.2. When they are injection molded (IM) the skin formed when the plastic cools against the mold tends to be harder and smoother than a cut surface so that the molded product exhibit lower sliding friction and are excellent for this type of application. Good design for this type of application is to make the surfaces as smooth as possible without making them glass smooth which tends to increase the intimacy of contact and to increase the friction above that of a fine surface. To reduce friction lubricants are available that will lower the friction and help to remove heat. Mixing of slightly incompatible additive materials such as silicone oil into an IM plastic is used. After IM the additive migrates to the surface of the product and acts as a renewable source of lubricant for the product. In the case of beatings it is carried still further by making the beating plastic porous and filling it with a lubricating material in a manner similar to sintered metal bearings, graphite, and molybdenum sulfide are also incorporated as solid lubricants. Fillers/reinforcements can be used to increase the thermal conductivity of the material such as glass and metal fibers or spheres. The filter can be a material like PTFE (polytetrafluoroethylene) plastic that has a much lower coefficient of friction and the surface exposed material will reduce the friction.

Rain Erosions As has been reported since the 1940s, when one walks through a gentle spring rain one seldom considers that raindrops can be small destructive "bullets" when they strike high-speed aircraft. These rapid loaded bulletlike raindrops can erode paint coatings, plastic products, and even

7

9Designs 6 9 5

steel, magnesium or aluminum leading edges to such an extent that the surfaces may appear to have been sandblasted. Even the structural integrity of the aircraft may be affected after several hours of flight through rain. Also affected are commercial aircraft, missiles, and highspeed vehicles on the ground, spacecraft before and after a flight when rain is encountered and even buildings or structures that undergo highspeed rainstorms. Critical situations can exist in flight vehicles, since flight performance can be affected to the extent that a vehicle can be destroyed. First reports on rain erosion on aircraft were first reported during WW II when the B-29 bomber was flying over the Pacific Ocean. Aerodynamic shaped RP radar radome wing-type shaped structure on the B-29 was flying at a so called (at that time) high-speed was completely destroyed by rain erosion (D. V. Rosato was a flight engineer on B-29 and worked on this B-29 rain erosion problem). These "Eagle Wing" radome all-weather bomber airplanes were than capable of only flying at a high speed of up to 400 mph. The aerodynamic RP (woven glass fabric/TS polyester) leading edges of the eagle wings and nose radomes were particularly susceptible to this form of degradation and destruction. The problem continues to exist as can be seen on the front of commercial and military airplanes with their black neoprene protective coated RP radomes; the paint coating over the rain erosion elastomeric plastic erodes and then is repainted prior to the catastrophic damage of the rain erosion elastomeric coating. Extensive flight tests conducted to determine the severity of the rain erosion were carried out during 1944. They established that aluminum and RP leading edges of airfoil shapes exhibited serious erosion after exposure to rainfall of only moderate intensity. Inasmuch as this problem originally arose with military aircraft, the U.S. Air Force initiated research studies at the Wright-Patterson Development Center's Materials Laboratory in Dayton, Ohio (D.V. Rosato department directly involved; a physicist actually developed the theory of rain erosion impact damage that still applies). It resulted in applying an elastomeric neoprene coating adhesively bonded to RP radomes. The usual 5 mil coating of elastomeric material used literally bounces off raindrops, even from a supersonic airplane traveling through rain. Even though a slight loss (1%/mil of coating) of radar transmission occurred it was better than losing 100% when the radome was destroyed. To determine the type of physical properties materials used in this environment should have, it is necessary to examine the mechanics of the impact of the particulate matter on the surfaces. The high kinetic energy of the droplet is dissipated by shattering the drop, by indenting

696 Reinforced Plastics Handbook

the surface, and by frictional heating effects. The loading rate is high as in impact and impulse loading, but it is neither as localized as the impact load nor as generalized as the impulse load. Material that can dissipate the locally high stresses through the bulk of the material will respond well under this type of load. The plastic should not exhibit brittle behavior at high loading rates. In addition, it should exhibit a fairly high hysteresis level that would have the effect of dissipating the sharp mechanical impulse loads as heat. The material will develop heat due to the stress under cyclical load. Materials used are the elastomeric plastics used in the products or as a coating on products.

Directional Properties RPs behavior is dominated by the arrangement and the interaction of the stiff, strong reinforcing fibers with the less stiff, weaker plastic matrix. The fiber arrangement determines the behavior of RPs where a major advantage is that directional properties can be maximized. Arrangements include the use of woven with different weaves and nonwoven with different lengths and forms (Chapter 2). Figure 7.33 provides examples relating directional properties to processes. Figure 7.34 provides schematics highlighting the ability to position reinforcements where required.

Figure 7.33 Guide to relating directional properties to processes

7

Schematic representation of laminate lay-ups

Modulus of elasticity of various fibre composites

Effect of fibre orientation in the composite part Figure 7.34 Schematicshighlighting the positioning of reinforcements

9Designs 6 9 7

698 Reinforced Plastics Handbook

Design theories of combining actions of plastics and reinforcement arrangements have been developed and used successfully for about a century. Theories are available to predict overall behavior based on the properties of fiber and matrix. In a practical design approach, the behavior can use the original approach analogous to that used in wood for centuries where individual fiber properties are neglected; only the gross properties, measured at various directions relative to the grain, are considered. This was the initial design evaluation approach used during the 1940s (D. V. Rosato started designing via the previous wood industry knowledge of understanding and using its directional properties). The behavior of RPs is dominated by the arrangement and the interaction of the stiff, strong fibers with the less stiff, weaker plastic matrix. A major advantage is the fact that directional properties can be maximized. They can be isotropic, bidirectional, orthotropic, etc. Woven fabrics that are generally directional in the 0 ~ and 90 ~ angles contribute to the mechanical strength at those angles. The rotation of alternate layers of fabric to a lay-up of 0 ~ + 45 ~ 90 ~ and -45 ~ alignment reduces maximum properties in the primary directions, but increases in the + 45 ~ and -45 ~ directions. Different fabric weaves patterns a n d / o r individual fiber patterns are used to develop different property performances.

Orientation Terms Orientation terms of RP directional properties include the following: Abscissas The horizontal direction in a diagram or curve. Anisotropic Exhibiting different properties when tested along axes in different directions. Balanced In a material where they have equal properties in the warp and filled directions; also called the machine (warp) and transverse (filled) directions Biaxial Also called bi-directional property. Material with their two major axis (horizontal and vertical at 900 to each other) having the highest properties; they could be equal as in a balanced material. Coordinated Reference coordinate system used to describe the properties in the direction of the principal axes (x and y). Crosswise 1. Also called bidirectional or cross-plied laminate. Materials are oriented at 0 ~ and 90 ~ only providing equal highest strengths only in those directions; designated high strength directional properties in the lengthwise direction and at fight angle to the lengthwise direction (transverse direction). 2. It can refer to the cross-themachine direction of a material/product.

7

9Designs 6 9 9

Isotropic Having uniform properties in all directions in the plane of the material (x-y directions). Isotropic, non- Anisotropic is one in which the properties are different in the different directions along the flat plane. It exhibits different properties in response to stresses applied along axes in different directions. Isotropic transversely Material exhibits a special case of orthotropy in which the properties are identical in two orthotropic (or a single plane) dimensions but not the third. Having identical properties in both transverse but not in the longitudinal direction. Machine or lengthwise Refers to product output in the machine direction; 90 ~ to the transverse direction. Materials such as sheet being extruded or RP being pultruded, basically are exiting in the machine inline direction where the direction follows the flow of the plastic from the die. At 90 ~ to this direction is the transverse or crosswise direction. O r d i n a t e The vertical direction in a diagram. O r i e n t e d Applies to the different directional properties that can exist in a material such as reinforced plastic construction. O r t h o t r o p i c Having three mutually perpendicular x-y-z planes of elastic symmetry. Parallel Layers of materials such as oriented film or fabric that are all aligned and stacked in the same position as they were on their respective roll. Planar Lying essentially in a single plane. Quadraxially A four directional layer. Quasi-isotropic The material approximate an isotropic construction by orientation of plies in several or more directions. R h o m b o h e d r a l Having three equal axes with the included angles equal to each other but not equal to 90 ~. Symmetrical It has a stacking sequence of plies below its midplane and is a mirror image of the stacking sequence above the midplane. Tetragonal Having three mutually perpendicular axes; two equal in length and unequal to the third axis. Transverse Also called crosswise direction. Refers to product output at 90 ~ to the machine direction. Materials such as flat sheet, film, or pipe being extruded basically are exiting in the machine inline direction with the transverse at 90 ~ to this direction.

700 Reinforced Plastics Handbook Uniaxial load Condition where a material is stressed in only one direction along the axis or centerline of a component part. Uniaxial state of stress State of stress in which two of the principle stresses are zero. Unidirectional A material where all the strength are substantially all oriented in one direction. U n s y m m e t r i c a l Structure having an arbitrary stacking sequence without midplane symmetry.

Heterogeneous/Homogeneous/Anisotropic Properties Heterogeneous identifies an RP that has properties that vary so that the composition varies from section to section in a heterogeneous mass that has uniform properties. For design purposes, many heterogeneous materials are treated as homogeneous (uniform). This is because a reasonably small sample of material cut from anywhere in the body has the same properties as the body. An unfilled (unreinforced) TP is an example of this type of material. The designer must be aware that as the degree of anisotropy increases the number of constants or moduli required describing the material increases. With isotropic construction one could use the usual independent constants to describe the mechanical response of materials, namely, Young's modulus and Poisson's ratio. RPs are either constructed from a single layer or built up from multiple layers. The properties of each layer are usually orthotropic, which is a special case of anisotropy. Fibers that remain straight in the single layer are desired. However, with many fabrics, they are woven into configurations that kink the fiber bundles severely. Such fabric constructions may be very practical since they drape better over doubly-warped molds than do fabrics that contain predominantly straight fibers. There are fiber bundles in lower cost woven roving that are convoluted or kinked as the bulky rovings conform to a square weave pattern. Kinks produce repetitive variations in the direction of reinforcement with some sacrifice in properties. Kinks can also induce high local stresses and early failure as the fibers try to straighten within the matrix under a tensile load. Kinks also encourage local buckling of fiber bundles in compression and reduce compressive strength. These effects are particularly noticeable in tests with woven roving, in which the weave results in large-scale convolutions. Regardless, extensive use of fabrics is made based on their capabilities. Examples of properties for different E-

7 Designs 9 701 glass fabric constructions and lay-ups with TS polyester plastic moldings have been reviewed in section Design Approaches.

Facts and Myths- RP Behavior It is a fact that the designed directional properties of the nonhomogeneous RPs is to the advantage of a designer when products require directional properties. Therefore, the literature, speakers, and certain designers have stopped stating that one cannot design with RPs and that one can only design with isotropic materials. It is easier to design with "real" isotropic materials that have "real" equal properties in all directions. Molded, URP parts can be isotropic or, depending on how they are processed, can have some orientation because of flow velocity gradients that exist during the melt processing operation. In addition, it is not necessary to state that RPs is assumed to be homogeneous; they are obviously nonhomogeneous (inhomogeneous) but can be prepared close to being homogeneous.

Orientation of Reinforcement The behavior of RPs is dominated by the arrangement and the interaction of the stiff, strong fibers with the less stiff, weaker plastic matrix. The features of the structure and the construction determine the behavior of RPs that is important to the designer. A major advantage is the fact that directional properties can be maximized. They can be isotropic, orthotropic, etc. Basic design theories of combining actions of plastics and reinforcements have been developed and used successfully. Different fabric a n d / o r individual fiber patterns are used to develop different property performances. A microscopic view of an RP reveals groups of fibers surrounded by the matrix. For example, glass fibers at about 0.01 mm (4 x 10 .4 in.) in diameter may comprise from 10 to 90 wt% of the area of a given crosssection. Theories are available to predict overall behavior based on the properties of fiber and resin constituents (Chapter 8). In a practical design approach, the behavior can use the original approach analogous to that used in wood, where individual fiber properties are neglected; only the gross properties, measured at various directions relative to the grain, are considered. This was one of the initial evaluation approaches used during the 1940s.

Anisotropic RP Design RP methods of design analysis differ from those of traditional materials due to:

702

Reinforced Plastics Handbook

(a) the need to take account of isotropy in the component analysis and (b) the need to include material design. Extension of linear isotropic elastic analysis to allow for anisotropy is treated in some standard texts. The range of standard formulae is much more restricted than that for isotropic materials. Some computer software use FEA that include the use of anisotropic elements, so that anisotropic analyses can be used. However, it requires materials data. Thus, although the procedures for isotropic and anisotropic materials are the same, the latter may be limited by available formulae. However, material nonlinearity is less likely to be encountered with RP materials (Figure 7.35). a .......... d f

,

,

~ , s.i~.~t..~r.al stool

-] .....

Cor bonlepoxy

I

I//// 0

..

I

.I

I

2

3

Strain (%)

Figure 7.35

Examples of stress/strain curves for unidirectional RPs and metals

Another factor of anisotropic design analysis is greater dependence of stress distributions on materials properties. For isotropic materials, whether elastic, viscoelastic, etc., static values often result in stress fields which are independent of material stiffness properties. In part, this is due to the fact that Poisson's ratio is the only material parameter appearing in the compatibility equations for stress. This parameter does not vary widely between materials. However, the compatibility equations in stress for anisotropic materials depend on ratios of Young's moduli for different material axes, and this can introduce a strong dependence of stress on material stiffness. This approach can be used in component design, but the product and material design analysis become more closely related. For fixed component geometry, changes in proposed material stiffness properties result in modifications in the way in which loads are carried

7

9Designs 7 0 3

as stresses within the component, and these stresses must be related to the material strength properties. Material design is normally associated with long-fiber RP because of the greater ability to control fiber placement during fabrication. The initial material and product designs with successful solutions usually depend on the designer's judgment and experience rather than on a well-defined rational procedure. New RP designers require the proper backup designers or proper education in designing with RPs that is available from various sources worldwide.

Shapes In addition to what has been reviewed in meeting structural shapes, analyses of product shapes also includes factors such as the size of available processing equipment. The ability to achieve specific shapes and design details is dependent on the way the process operates and plastics to be processed. Generally the lower the process pressure, the larger the product that can be produced. With most labor-intensive fabricating methods, such as RP hand lay-up there is virtually no limit on size (Chapter 5). Based on the usual data on metals, they are considered much stiffer and stronger than plastics. This initial evaluation could eliminate the use of plastics in many potential applications, but in practice it is recognized by those familiar with the behavior of plastics (RPs or URPs) that it is the stiffness and strength of the product that is important, not its material properties. An important requirement concerns meeting dimensional tolerances of shaped products. Reported are different shrinkages for different RPs per standard tests that may have a relation to the designed product. The probability is that experience with prototyping will only provide the true shrinkage conditions of the shaped products. Minimum shrink values are included in the design of tools such as mold cavities and die openings so that if the processed material does not meet required dimensions all that is required is to cut the metal in the tool. If the reverse occurs expensive tool modifications may be required, if not replacing the complete tool. Fortunately, there are occasions where changes in process control during fabrication can be used to produce the required dimensional product.

704 Reinforced Plastics Handbook

Bars Basically a bar identifies shapes such as a column under axial compression and a structure under torsional stress when it is held fast at one end. Columns A column can be identified as having an unbraced length greater than about eight or ten times the least dimension of its cross section. Because of its length, it is impossible to hold a column in a straight line under a load; a slight sidewise bending always occurs, causing flexural stresses in addition to the compressive stresses induced directly by the load. The lateral deflection will be in a direction perpendicular to that axis of the cross section about which the moment of inertia is the least. Thus in a complex shape such an H-column it will bend in a direction perpendicular to its major axis. In a square shape it will bend perpendicular to its two major axes. With a tubular shape it is likely to bend in any direction. The radius of gyration of a column section with respect to a given axis is equal to the square root of the quotient of the moment of inertia with respect to that axis, divided by the area of the section, that is:

k=q . A!=k where I is the moment of inertia and A is the sectional area. Unless otherwise mentioned, an axis through the center of gravity of the section is the axis considered. As in beams, the moment of inertia is an important factor in the ability of the column to resist bending, but for purposes of computation it is more convenient to use the radius of gyration. The length of a column is the distance between points unsupported against lateral deflection. The slenderness ratio is the length e divided by the least radius of gyration k. Various conditions may exist at the ends of columns that usually are divided into four classes. 1

Columns with round ends; the bearing at either end has perfect freedom of motion, as there would be with a ball-and-socket joint at each end.

2

Columns with hinged ends; they have perfect freedom of motion at the ends in one plane, as in compression members in bridge trusses where loads are transmitted through endpins.

7

Designs 9 705

Columns with flat ends; the bearing surface is normal to the axis of the column and of sufficient area to give at least partial fix to the ends of the columns against lateral deflection. Columns with fixed ends; the ends are rigidly secured, so that under any load the tangent to the elastic curve at the ends will be parallel to the axis in its original position. Tests prove that columns with fixed ends are stronger than columns with flat, hinged, or round ends, and that columns with round ends are weaker than any of the other types. Columns with hinged ends are equivalent to those with round ends in the plane in which they have movement; columns with flat ends have a value intermediate between those with fixed ends and those with round ends. Usually columns have one end fixed and one end hinged, or some other combination. Their relative values may be taken as intermediate between those represented by the condition at either end. The extent to which strength is increased by fixing the ends depends on the length of column; fixed ends have a greater effect on long columns than on short ones. There is no exact theoretical formula that gives the strength of a column of any length under an axial load. Different formulas involving the use of empirical coefficients have been deduced, however, and they give results that are consistent with the results of tests. These formulas include the popular Euler's formula, different eccentric formulas, crossbend formulas, wood and timber column formulas, and general principle formulas. Euler's Formula

The Euler's formula developed by Leonard Euler (Swiss mathematician, 1707 to 1783) is used in product designs and also in designs using columns in molds and dies that process plastic. Euler's formula assumes that the failure of a column is due solely to the stresses induced by sidewise bending. This assumption is not true for short columns that fail mainly by direct compression, nor is it true for columns of medium length. The failure in such cases is by a combination of direct compression and bending. Column formulas are found in most machine and tooling hand books as well as strength of materials textbooks. Euler first published this critical-load formula for columns in year 1759. For slender columns it is usually expressed in the following form: F

=

m~2EI I2

=

m~2EA (Ilk) 2

706

Reinforced Plastics Handbook

where F = Collapsing load on the column in pounds, I = length of the column in inches, A = area of the section in square inches, k = least radius of gyration, which = I/A, E = modulus of elasticity, I - the least moment of inertia of the section, m = a constant depending on the end conditions of the column. Euler's formula is strictly applicable to long and slender columns, for which the buckling action predominates over the direct compression action and thus makes no allowance for compressive stress. The slenderness ratio is defined as the ratio of length 13to the radius of gyration k, represented as e/k. When the slenderness ratio exceeds a value of 100 for a strong slim column, failure by buckling can be expected. Columns of stiffer and more brittle materials will buckle at lower slenderness ratios. The constant factor m in Euler's critical-load formula clearly shows that the failure of a column depends on the configuration of the column ends. The basic four types with their respective m are: 1

Both ends pivoted or hinged (m = 1)

2

One end fixed and the other free (m

3

One end fixed and, the other pivoted (m = 2)

4

Both ends fixed (m = 4)

= 1/4)

Table 7.13 shows cross sections of the three common slender column configurations. Formulas for each respective moment of inertia I and radius of gyration k are given. With the above formulas buckling force F can be calculated for a column configuration. Table 7.14 lists values of slim ratios (1/k) for small-nominal-diameter column lengths. Table 7,13

Moments of inertia and radii of gyration MOMENT OF INERTIA I riD'

nr ~

'64 = T ~'~t r

--

F~-4

bh 3 12

nO 4 128

nr ~ =

T

= k

m D. - - mr

4

I1

..,.....

~~

RADIUS OF GYRATION

,

2 = 0.289h

D 5.66

Most failures with the slender columns occur because the slenderness ratio exceeds 100. The prudent designer devises ways to reduce or limit the slenderness ratio.

7

9Designs 7 0 7

Table 7 . 1 4 Slendernessratio Ilk of round columns

Diameter (in.) Column length (in.)

0.031

0.047

0.0625

0.078

0.083

0.125

O. 1875

1.0

128

85

64

51

43

32

21

1.5

192

128

96

77

64

48

32 37

1.75

224

149

112

90

75

56

2.0

256

171

128

102

85

64

43

2.25

288

192

144

115

96

72

48

2.5

320

213

160

128

107

80

53

3.0

384

256

192

154

128

96

64

3.25

416

277

206

166

139

104

69

In the following formula P = axial load; f = length of column; I = least moment of inertia; k = least radius of gyration; E = modulus of elasticity; y = lateral deflection, at any point along a larger column, that is caused by load P. If a column has round ends, so that the bending is not restrained, the equation of its elastic curve is: d2y

El dx2 = - P y

When the origin of the coordinate axes is at the top of the column, the positive direction of x being taken downward and the positive direction of y in the direction of the deflection. Integrating the above expression twice and determining the constants of integration give: p

=

s

E! /2

which is Euler's formula for long columns. The factor s is a constant depending on the condition of the ends. For round ends s 1; for fixed ends s = 4; for one end round and the other fixed s 2.05. P is the load at which, if a slight deflection is produced, the column will not return to its original position. If P is decreased, the column will approach its original position, but if P is increased, the deflection will increase until the column fails by bending. For columns with value off/k less than about 150, Euler's formula gives results distinctly higher than those observed in tests. Euler's formula is used for long members and as a basis for the analysis of the stresses in some types of structural parts. It always gives an ultimate and never an allowable load.

708 Reinforced Plastics Handbook Torsional Bars A bar is under torsional stress when it is held fast at one end, and a force acts at the other end to twist the bar. In a round bar (Figure 7.36) with a constant force acting, the straight line ab becomes the helix ad, and a radial line in the cross-section, oh, moves to the position ad. The angle bad remains constant while the angle hod increases with the length of the bar. Each cross section of the bar tends to shear off the one adjacent to it, and in any cross section the shearing stress at any point is normal to a radial line drawn through the point. Within the shearing proportional limit, a radial line of the cross section remains straight after the twisting force has been applied, and the unit shearing stress at any point is proportional to its distance from the axis.

aM,,

!

Figure 7 . 3 6 Round bar subject to torsion stress

The twisting moment, T, is equal to the product of the resultant, P, of the twisting forces, multiplied by its distance from the axis, p. Resisting moment, T~, in torsion, is equal to the sum of the moments of the unit sheafing stresses acting along a cross section with respect to the axis of the bar. If dA is an elementary area of the section at a distance of z units from the axis of a circular shaft, and c is the distance from the axis to the outside of the cross section where the unit shearing stress is T, then the unit sheafing stress acting on dA is ('rz/c) dA, its moment with respect to the axis is (xz2/c) dA, and the sum of all the moments of the unit shearing stresses on the cross section is f ('rz2/c) dA. In this expression the factor fz 2 dA is the polar moment of inertia of the section with respect to the axis. Denoting this by J, the resisting moment may be written "cJ/c. The polar moment of inertia of a surface about an axis through its center of gravity and perpendicular to the surface is the sum of the

7

9Designs 7 0 9

products obtained by multiplying each elementary area by the square of its distance from the center of gravity of its surface; it is equal to the sum of the moments of inertia taken with respect to two axes in the plane of the surface at fight angles to each other passing through the center of gravity section of a round shaft. The analysis of torsional sheafing stress distribution along noncircular cross sections of bars under torsion is complex. By drawing two lines at fight angles through the center of gravity of a section before twisting, and observing the angular distortion after twisting, it as been found from many experiments that in noncircular sections the sheafing unit stresses are not proportional to their distances from the axis. Thus in a rectangular bar there is no shearing stress at the comers of the sections, and the stress at the middle of the wide side is greater than at the middle of the narrow side. In an elliptical bar the sheafing stress is greater along the flat side than at the round side. It has been found by tests as well as by mathematical analysis that the torsional resistance of a section, made up of a number of rectangular parts, is approximately equal to the sum of the resistances of the separate parts. It is on this basis that nearly all the formulas for noncircular sections have been developed. For example, the torsional resistance of an I-beam is approximately equal to the sum of the torsional resistances of the web and the outstanding flanges. In an I-beam in torsion the maximum shearing stress will occur at the middle of the side of the web, except where the flanges are thicker than the web, and then the maximum stress will be at the midpoint of the width of the flange. Reentrant angles, as those in I-beams and channels, are always a source of weakness in members subjected to torsion. The ultimate/failure strength in torsion, the outer fibers of a section are the first to shear, and the rupture extends toward the axis as the twisting is continued. The torsion formula for round shafts has no theoretical basis after the shearing stresses on the outer fibers exceed the proportional limit, as the stresses along the section then are no longer proportional to their distances from the axis. It is convenient, however, to compare the torsional strength of various materials by using the formula to compute values of x at which rupture takes place.

Filament Windings Filament winding (FW) shapes are principally circular (cylinders, pipes, tubing, etc.) or enclosed vessel (storage tanks, oxygen tanks, etc.). They

710 Reinforced Plastics Handbook produce spherical, conical, and geodesic shapes. The fabricating process permits tightly controlled fiber netting orientation and exceptional quality control in different fiber-plastic matrix ratios required by design (Chapter 5). Structures can be fabricated into shapes such as rectangular or square beams or boxes, longitudinal leaf or coil springs, etc. Filaments can be set up in a part to meet different design stresses. There are two basic patterns used by industry to produce FW structures, namely, circumferential winding and helical winding. Each winding pattern can be used alone or in various combinations in order to meet different structural requirements. The circumferential winding pattern involves the circumferential winding at about a 90 ~ angle with the axis of rotation interspersed with longitudinal reinforcements. Maximum strength is obtainable in the hoop direction. This type of pattern generally does not permit winding of slopes over 20 ~ when using a wet winding reinforcement or 30 ~ when using a dry winding process. It also does not result in the most efficient structure when end closures are required. With end closures a n d / o r steep slopes, a combination of helical and circumferential winding is used. With helical winding, the reinforcements are applied at any angle from 25 ~ to 85 ~ to the axis of rotation. No longitudinal filament need be applied because low-winding angles provide the desired longitudinal strength as well as the hoop strength. By varying the angle of winding, many different ratios of hoop to longitudinal strengths can be obtained. Two different techniques of applying the reinforcements in helical windings are used by industry. One technique is the application of only one complete revolution around the mandrel from end to end. The other technique involves a multi-circuit winding procedure that permits a greater degree of flexibility of wrapping and length of cylinder.

Netting Analyses Continuous reinforced filaments should be used to develop an efficient high-strength to low-weight FW structure. Structural properties are derived primarily from the arrangement of continuous reinforcements in a netting analysis system in which the forces, owing to internal pressure, are resisted only by pure tension in the filaments (applicable to internal-pressure systems). There is the closed-end cylinder structure that provides for balanced netting of reinforcements. Although the cylinder and the ends require two distinctly different netting systems, they may be integrally fabricated. The structure consists of a system of low helix angle windings carrying the longitudinal forces in the cylinder shell and forming integral end

7

9Designs 71 1

closures that retain their own polar fittings. Circular windings are also applied to this cylindrical portion of the vessel, yielding a balanced netting system. Such a netting arrangement is said to be balanced when the membrane generated contains the appropriate combination of filament orientations to balance exactly the combination of loadings imposed. The girth load of the cylindrical shell is generally two times the axial load. The helical system is so designed that its longitudinal strength is exactly equal to the pressure requirement. Such a low-angle helical system has limited girth strength. The circular windings are required in order to carry the balance of the girth load. The end dome design contains no circular windings since the profile is designed to accommodate the netting system generated by the terminal windings of the helical pattern. It is termed an ovaloid: that is, it is the surface of revolution whose geometry is such that fiber stress is uniform throughout and there is no secondary bending when the entire internal pressure is resisted by the netting system. There is the ovaloid netting system that is the natural result of the reversal of helical windings over the end of the vessel. The windings become thicker as they converge near the polar fittings. In order to resist internal pressure by constant filament tension only, the radius of curvature must increase in this region. It can also be equal to one half the cylinder radius when the helix angle a = 0 ~ and equal to the cylinder radius when a -- 45 ~ The profile will also be affected by the presence of an external axial force. In the application of bidirectional patterns, the end domes can be formed by fibers that are laid down in polar winding patterns. The best geometrical shape of the dome is an oblated hemispheroid. Theoretically, the allowable stress level in the two perpendicular directions should be identical. However, the efficiency of the longitudinal fibers is less than that of the circumferential fibers. It is possible to estimate an optimum or length-to-diameter ratio of a cylindrical case for a given volume. The filament-wound sphere design structure provides another example of a balanced netting analysis system (Chapter 5). It is simpler in some respects than the closed-end cylinder. The sphere must be constructed by winding large circles omni-directionally and by uniform distribution over the surface of the sphere. In practice, distribution is limited so that a small polar zone is left open to accommodate a connecting fitting. The netting pattern required generates a membrane in which the strength is uniform in all directions. The simplest form of such a membrane would have its structural fibers running in one direction and

712 Reinforced Plastics Handbook

the other half at right angles to this pattern. This layup results in the strength of the spherical membrane being one-half of the strength of a consolidated parallel fiber system. The oblated spheroid design structure relates to special spherical shapes. Practical design parameters have shown that the sphere is the best geometric shape when compared to a cylinder for obtaining the most efficient strength-to-weight pressure vessel. The fiber RPs is the best basic constituents. Certain modifications of the spherical shape can improve the efficiency of the vessel. One modification involves designing the winding pattern of the fibers so that unidirectional loading can be maintained. In this type of structure, it is generally assumed that the fibers are under equal tension. This type of structure is identified as an isotensoid (Figure 7.37). The geometry of this modified sphere is called oblated spheroid, ovaloid, or ellipsoid.

Figure 7.37

One view shows isotensoid pattern of only fibers. Other view is the completely fabricated vessel (fabricated by D. V. Rosato)

The term isotensoid identifies a pressure vessel consisting entirely of filaments that are loaded to identical stress levels. The head shape of an isotensoid is given by an elliptical integral, which can most readily be solved by a computer. Its only parameter is the ratio of central opening to vessel diameter. This ratio determines the variation of the angle of winding for the pressure vessel. During pressurization the vessel is under uniform strain; consequently, no bending stresses or discontinuity stresses are induced. A short polar axis and a larger perpendicular equatorial diameter characterize the vessel. The fibers are oriented in the general direction of a polar axis. Their angle with this axis depends on the size of the pole

7

9Designs 7 1 3

openings (end closures). For glass fiber-TS polyester RP vessels levels of 200,000 psi (1.4 GPa) can be obtained. The toroidal design structure is a pressure vessel made with two sets of filaments symmetrically arranged with respect to the meridians. The meet two basic requirements: static equilibrium at each point, which determines the angle between the two filaments, and stability of the filaments on the surface, which requires the filaments to follow geodesic paths on the surface. When the equation of the surface is given, these two requirements are generally incompatible. One way to reconcile the correct angularity of the filaments (equilibrium) with the correct paths of the filaments (stability) is to take some freedom in determining the geometry of the surface.

Pressure Hull Structures R&D programs have been conducted for deep submergence hulls. Materials of construction are usually limited to certain type's steel, aluminum, titanium, glass, fiber RPs, and others (Figures 7.38 and 7.39). There is a factor relating material's strength-to-weight characteristics to a geometric configuration for a specified design depth. The ratio showing the weight of the pressure hull to the weight of the seawater displaced by the submerged hull is the factor referred to as the weight displacement ( W / D ) ratio. The submergence materials show the variation of the collapse depth of spherical hulls with the weight displacement of these materials. All these materials, initially, would permit building the hull of a rescue vehicle operating at 1800 m (6000 ft) with a collapse depth of 2700 m (9000 ft). 0

STEEL

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w

30,000

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0.2

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714 Reinforced Plastics Handbook

Figure 7,39

Effect of a pressure-hull and floatation system on vehicle weight

For a search vehicle operating at 6000 m (20,000 ft) with collapse depth of 9000 m (30,000 ft), the only materials that appear suitable are glass and RP. Metals potential do not have sufficient strength-to-weight values. One of the advantages of glass is its high compressive strength; however, one of its major drawbacks is its lack of toughness. Another serious problem is the difficulty of designing and building suitable penetrations and hatches in a glass hull. A solution could be filament winding RP around the glass or using a tough plastic skin. These glass problems show that the RP hull is very attractive on weight-displacement ratio, strength-weight ratio, and for its fabrication capability. By using the higher modulus and lower weight advanced designed fibers (aramid, graphite, etc.) additional gains will occur. The depth limitations of various hull materials in near-perfect spheres superimposed the familiar distribution curve of ocean depths. To place materials in their proper perspective, the common factor relating their strength-to-weight characteristics to a geometric configuration for a specified design depth is the ratio showing the weight of the pressure hull to the weight of the seawater displaced by the submerged hull, a factor referred to as the weight displacement (W/D) ratio. The portions the vehicles above the depth distribution curve correspond to hulls

7

9Designs 71 5

having a 0.5 W / D ratio; portion beneath showing the depth attainable by heavier hulls with a 0.7 W / D . The ratio of 0.5 and 0.7 is not arbitrary, as it may appear, for small vehicles can normally be designed with W / D ratios of 0.5 or less, and vehicle displacements can become large as their W / D approach 0.7. Using these values permits making meaningful comparisons of the depth potential for various hull materials. An examination of data reveals that for all the metallic pressure-hull materials taken into consideration, the best results would permit operation to a depth of about 18,288 m (20,000 ft) only at the expense of increased displacement. The RPs (those just with glass fiber/TS polyester resin) and glass would permit operation to 20,000 ft or more with minimum displacement vehicles (Figure 7.40).

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Design approach in analyzing use of different materials in an underwater s t r u c t u r e includes only use of glass fiber/TS polyester RP

Complex problems develop when designing hulls. Under varying submergence depths there can be significant movement and working of the hull structure, resulting in movement and working of the attached piping and equipment foundation. These deflections, however slight, set up high stresses in the attached members. The extent of such strain loads must be considered in designing attached components. Structural Details This review concerns the structural behavior of filament wound RP cylinders. Test specimens of thick-walled, unstiffened cylinders with the

716 Reinforced Plastics Handbook

ends restrained by metallic end-closure plates to prevent premature instability failure were prepared. They developed compressive strengths from 1 to 1.2 x 103 MPa (150 to 170 x 103 psi) and an effective modulus of 0.04 x 106 MPa ( 5 x 106 psi) when subjected to hydrostatic pressure loading. These cylinders were filament wound from S-glass roving preimpregnated with an epoxy resin. Similar strength levels have also been realized with flat-specimen tests of 2:1 orthogonal laminates under unidirectional compressive loading (Naval Ship Engineering Center). In realistic pressure hull structures, a stiffening system has to be incorporated into a cylindrically shaped hull to prevent premature instability failure and thereby to assist in utilizing the high-strength properties available in the material. When GRP (glass-reinforced plastics) cylinders were stiffened by ring frames, lower strength levels were observed as a result of localized bending and sheafing stresses induced by the ring frames. Shear failure occurred in the cylindrical shell at the toe of the frame. The importance of considering the shear sensitivity of GRP material can be illustrated by the test results of two identical models in which one of the models incorporated generous fillets at the toe of the frame. Basic dimensions of both models were identical: shell thickness = 0.388 in.; internal diameter = 6.0 in.; frame spacing = 1.544 in.; frame depth = 0.542 in.; flame width = 0.271 in.; number of internal frames - 19. By including the fillets in the structure, the weight-displacement ( W / D ) ratio was increased from 0.524 to 0.544. The model without fillets failed at a pressure of 85 MPa (12,300 psi), whereas the model with fillets failed at a pressure of 111 MPa (16,100 psi); weight-displacement ratio 0.544. The higher collapse pressure of the latter model more than offset the increase in weight of 4% that resulted from incorporating fillets into the hull structure. However, affective strength levels of only 792 to 828 MPa (115,000 to 120,000 psi) were developed. Failures were directly related to the interlaminar shear strength of the material. A concept offering high instability resistance and reducing shear and bonding is the sandwich cylinder with a uniform core of syntactic foam (Chapter 5). Tests have demonstrated that shells of this type can develop stress levels of 1,103 MPa (160,000 psi) in the GRP facings. However, only a marginal increase in static-strength performance over the ring-stiffened cylinders has been achieved because of the relatively low strength-to-weight characteristics of the foam. The simplest method of reducing shearing and bending stresses is to use an unstiffened cylinder. Development of lower density, hollow fiber,

7

9Designs 7 1 7

glass-RP s has made this concept practical for hulls having a collapse depth of or exceeding 10,700 m (35,000 ft), provided that the overall length of the cylinder is four diameters or less. The increase in thickness of the cylinder afforded by the lighter weight, hollow fibers more than offsets the loss of stability due to lower elastic modulus of the RP material. In addition, because of the lower rigidity of the hollow fibers, better compatibility exists between the glass reinforcement and the resin binder. Little or no static strength-weight advantage has been found for the hollow glass cylinder over the ring stiffened cylinder. However, improved cyclic performance and simpler fabrication procedures are anticipated. Still another potential method for alleviating the stiffener problem in cylindrical hulls is to use fibers with a higher modulus than glass fibers. Higher modulus RPs would inherently give rise to hull structures with higher resistance against the instability modes of failure. Lighter frames would be required. Thus, shear and bending stresses would be reduced, and higher structural strength could be obtained. Higher modulus fibers would also lead to more efficient utilization of RP materials for sandwich hull structures. The structures would be more stable and thus less core material would be required. Also, due to the substantial difference between moduli of the facing and core materials, less load would be transmitted to the low-strength core. Calculations indicate that a cylinder with a W / D ratio of 0.44 and made of carbon-filament-RPs with an effective RP modulus of 0.1 MPa (15 x 105 psi) would not require a stiffening system. With this W / D ratio an unstiffened cylinder of semi-infinite length would have an elastic buckling depth exceeding 21,300 m (70,000 ft). At a depth of 12,200 m (40,000 ft) a RP stress of 690 MPa (100,000 psi) would be developed. Present problems with high-modulus, carbon-fiber RPs have been the inability of laminates to take high-compressive stresses. It is recognized that glass-fiber reinforcement can be replaced by superior fiber materials offering high improvements over the upper limit of properties in GRP. As an example the carbon fibers modulus ranges from 0.17 x 106 to 0.34 MPa (25 x 106 to 50 x 106 psi) and tensile strength at 2,760 MPa (400,000 psi). Densities of RPs made from these fibers would only be less than 75% of the weight of GRP. Studies with filament-wound cylinders have been extended to investigation of design details that arise in realistic pressure hulls such as closures, openings, and joints. The entire pressure hull was designed to obtain a collapse depth of 9,150 m (30,000 ft) and to sustain 10,000 excursions to a depth of 4,575 m (15,000 ft) without loss in overall

718 Reinforced Plastics Handbook

strength. The basic ring-stiffened cylinder had a W / D ratio of 52%. It represented the lightest weight hull obtained that satisfied the strength requirements. The stiffening tings were relatively lightweight and in conjunction with the shell provided adequate resistance to premature failure due to overall instability. The ring flame utilized only 19% of the material in the region representing efficient hull design. In the region of the cylindrical hull opening, a thicker shell, larger frames, and greater frame spacing were used. The latter geometry, representing a W / D ratio of 62% and less efficiency, was selected to provide sufficient space for an opening in the shell without interfering with the adjacent frames. The shell was of Sglass filaments; the frames were of the same type of material but utilized a different fiber distribution. The end closures consisted of S-glass cloth lay-ups with a RP strength of 413 MPa (60,000 psi) and were fabricated by a vacuum-bag molding process (Chapter 5). Closures were attached to the cylindrical hull by adhesive-bonded lap joints. A disconnectable transverse joint was incorporated in the cylindrical hull to provide a means of access for equipment and machinery. The openings into the pressure hull, both in the cylindrical section and the closure, were reinforced by 17-4 PH stainless steel fittings designed to carry in-plane shell loads about the opening in both compression and bending. Light flanges were provided to locally support the cut-fiber ends of the shell and thereby to assist in the transfer of highcompressive beating loads into the fitting. One model was tested to failure under static loading. The static model collapsed at a pressure of 83 MPa (12,000 psi). Two other models were subjected to 10,000 cycles to a pressure of 46 MPa (6,700 psi) and then were tested to failure under static loading, resulting in collapse pressures of 76 MPa ( 11,000 psi). It appears that the incorporation of design details is feasible if proper design procedures are employed and adequate sealing methods are utilized in the test. However, weight penalties are imposed on the overall pressure hull due to, the addition of structural details. It was reviewed that the basic ring-stiffened cylinder has a W / D ratio of 0.52; the overall pressure hull, however, has a W / D ratio of 0.65. It is apparent that in order to achieve efficient pressure hulls, attention must be given to concepts and approaches to obtain lightweight, watertight closures, joints, and penetrations.

7

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9Designs 7 1 9

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There is a difference when comparing the URP or RP to metal spring shape designs. With metals shape options are the usual torsion bar, helical coil, and flat-shaped leaf spring. The TPs and TSs (URPs) can be fabricated into a variety of shapes to meet different product requirements. An example is TP spring actions with a dual action shape (Figure 7.41). This injection molded stapler illustrating spring design with the body and curved spring section molded in a single part. When the stapler is depressed, the outer curved shape is in tension and the fibbed center section is put into compression. When the pressure is released, the tension and compression forces are in turn released and the stapler returns to its original position.

Figure 7.41 TP Delrin acetal plastic molded stapler {courtesy of DuPont)

Other TPs are used to fabricate springs. Acetal plastic has been used as a direct replacement for conventional metal springs as well providing the capability to use different spring designs such as in zigzag springs, uncoil springs, cord locks with molded-in springs, snap fits, etc. A special application is where TP replaced a metal pump in a PVC plastic bag containing blood. The plastic spring hand-operating pump did not contaminate the blood. RP leaf springs have the potential in the replacements for steel springs. These unidirectional filament wound fiber RPs have been used in trucks and automotive suspension applications. Their use in aircraft landing systems dates back to the early 1940s taking advantage of weight savings, corrosion-resistance, and performances. The 1988 GM-10 (Pontiac Grand Prix, Oldsmobile Cutlass, Buick Regal and Chevrolet Lumina) has a rear transverse RP glass/epoxy leaf spring. This represents the first RP application on a high volume platform vehicle. Over half a million springs were sold each year on this particular model.

720 Reinforced Plastics Handbook Because of the material's high specific strain energy storage capability as compared to steel, a direct replacement of multileaf steel springs by monoleaf RP springs can be justified on a weight-saving basis. The design advantage of these springs is to fabricate spring leaves having continuously variable widths and thicknesses along their length. These leaf springs serve multiple functions, thereby providing a consolidation of parts and simplification of suspension systems. One distinction between steel and plastic is that complete knowledge of shear stresses is not important in a steel part undergoing flexure, whereas with RP design shear stresses, rather than normal stress components, usually control the design. Spring design has been documented in various SAE and ASTM-STP design manuals. They provide the equations for evaluating design parameters that are derived from geometric and material considerations. However, none of this currently available literature is directly relevant to the problem of design and design evaluation regarding RP structures. The design of any RP product is unique because the stress conditions within a given structure depend on its manufacturing methods, not just its shape. Programs have therefore been developed on the basis of the strain balance within the spring to enable suitable design criteria to be met. Stress levels were then calculated, after which the design and manufacture of RP springs became feasible.

Leaf Springs RP leaf springs constructed of unidirectional glass fibers in a matrix, such as epoxy resin, have been recognized as a viable replacement for steel springs in truck and automotive suspension applications. Because of the material's high specific strain energy storage capability compared with steel, direct replacement of multi-leaf steel springs by mono-leaf RP springs is justifiable on a weight saving basis. Other advantages of RP springs accrue from the ability to design and fabricate a spring leaf having continuously variable width and/or thickness along its length. Such design features can lead to new suspension arrangements in which the RP leaf spring will serve multiple functions thereby providing part consolidation and simplification of the suspension system. The spring configuration and material of construction should be selected to maximize the strain energy storage capacity per unit mass without exceeding stress levels consistent with reliable, long life operation. Elastic strain energy must be computed relative to a particular stress state. For simplicity, two materials arc compare, steel and unidirectional glass fibers in an epoxy matrix having a volume fraction of 0.5 for the stress

7

9Designs 7 2 1

state of uniaxial tension. If a long bar of either material is loaded axially the strain energy stored per unit volume of material is given by U = (6212E} (in-lb/in 3)

where 6A is the allowable tensile stress and E is Young's modulus for the material. In Table 7.15 the appropriate E for each material has been used and a conservative value selected for 6A. On a volume basis the RP is about twice as efficient as steel in storing energy; on a weight basis it is about eight times as efficient. Table 7.1 5 Glass fiber-epoxy RP leaf spring design

Material

OA[k$0

U{Ib/in 2)

U/w* (in}

Steel Glass/epoxy

90 60

135 325

470 4880

w = specific weight

The RP has an advantage because it is an anisotropic material that is correctly designed for this application whereas steel is isotropic. Under a different loading condition (such as torsion) the results would be reversed unless the RP were redesigned for that condition. The above results are applicable to the leaf spring being reviewed because the principal stress component in the spring will be a normal stress along the length of the spring that is the natural direction for fiber orientation. In addition to the influence of material type on elastic energy storage, it is also important to consider spring configuration. The most efficient configuration (although not very practical as a spring) is the uniform bar in uniaxial tension because the stresses are completely homogeneous. If the elastic energy storage efficiency is defined as the energy stored per unit volume, then the tensile bar has an efficiency of 100%. On that basis a helical spring made of uniform round wire would have an efficiency of 32% (the highest of any practical spring configuration) while a leaf spring of uniform rectangular cross section would be only 11% efficient. The low efficiency of this latter configuration is due to stress gradients through the thickness (zero at the mid-surface and maximum at the upper and lower surfaces) as well as along the length (maximum at midspan and zero at the tips). Recognition of this latter contribution to inefficiency led to development of so-called constant strength beams that for a cantilever of constant thickness dictate geometry of triangular plan-form. Such a spring would have an energy storage efficiency of 33%. A practical embodiment of this principle is the multi-leaf spring of

722 Reinforced Plastics Handbook

constant thickness, but decreasing length plates, which for a typical five leaf configuration would have an efficiency of about 22%. More sophisticated steel springs involving variable leaf thickness bring improvements of energy storage efficiency, but are expensive since the leaves must be forged rather than cut from constant thickness plate. However, a spring leaf molded of the RP can have both thickness and width variations along its length. For instance, a practical RP spring configuration having a constant cross-sectional area and appropriately changing thickness and width will have an energy storage efficiency of 22%. This approaches the efficiency of a tapered multi-leaf configuration and is accomplished with a material whose inherent energy storage efficiency is eight times better than steel. In this design, the dimensions of the spring are chosen in such a way that the maximum bending stresses (due to vertical loads) are uniform along the central portion of the spring. This method of selection of the spring dimensions allows the unidirectional long fiber RP material to be used most effectively. Consequently, the amount of material needed for the construction of the spring is reduced and the maximum bending stresses are evenly distributed along the length of the spring. Thus, the maximum design stress in the spring can be reduced without paying a penalty for an increase in the weight of the spring. Two design equations are given in the following using the concepts described above. Design formulas have been developed for RP springs.

Automotive and Truck Leaf Springs During the early 1990s the National Composite Center (NCC), Kettering, OH, USA began efforts to forge a new chapter in the leaf spring history. In 2001 NCC plucked this key technology from being shelved by automotive systems supplier Delphi Corp, helped launch a new business and attract the attention of a world-class distributor. The distributorship provides a previously missing link by opening marketing and sales channels that will help move RP leaf springs into mainstream applications for the automotive and heavy-duty truck markets. To better understand the impact NCC's contributions will have on filament winding technology, it is important to look at some of the factors that have influenced its development. The Inland Division of General Motors (GM), which has since become part of Delphi, first delved into RP spring development in 1963. Based in Dayton, Ohio, the company ran a four-year program producing 150 quarter and semielliptic springs. Although the program demonstrated the material's advantages, inability to find a suitable market eventually caused the project to be discontinued. The company revisited its RP spring program

7

9Designs 7 2 3

in 1977 when the transportation industry's interest in fuel economy and mass reduction justified renewing development activity. The industry was looking for a cost effective RP spring with minimum mass capable of resisting corrosion and possessing a high degree of durability. Following lengthy experimentation with a variety of reinforcement and resin candidates, a material combining epoxy resin and unidirectional glass fiber was found to meet market requirements. Delphi called the new material Liteflex| The material possesses high elastic strain properties making it ideal for use as a spring. The process used to produce RP leaf springs involves filament winding resin-impregnated glass fiber rovings over an open mold, and compression molding with heat to cure to a final shape (Chapter 5). Once molded, the spring is machined to allow attachment of the cushions a n d / o r brackets needed to connect the spring to a vehicle or suspension module. Delphi first introduced Liteflex as a rear suspension RP spring for the 1981 Corvette. The 3.6 kg mono leaf transverse spring replaced a 19 kg ten-leaf steel spring delivering a mass reduction of 80%. By 1984, new Corvette models were sporting Liteflex RP springs on both front and rear suspensions. The following year the RP leaf spring made its first appearance on a truck application with GM's Astro Van. It was also the first time the spring was used in a longitudinal configuration. In 1986, Liteflex springs were introduced on rear suspensions of frontwheel drive luxury passenger cars in a constant width, transverse mounted configuration. By 1989 Delphi's annual production rate of RP springs had exceeded one million parts. The early '90s saw a departure from passenger vehicles, as new RP spring applications focused on heavy-duty tractors and trailers. The heavy-duty truck market posed perhaps the most challenging and dramatic use of RP springs. Traditional steel leaf springs had long been considered a replacement part for semi-tractor trailers. The lighter weight, more durable RP springs offered an attractive material choice over the more conventional steel springs. However, to gain market acceptance, the new RP product would need to be a direct retrofit for the steel spring. Width, thickness and length of the RP spring were also key design considerations. Another design challenge involved packaging constraints. For each of these applications, Liteflex springs promised the potential for improved durability, fide, isolation and packaging. Nevertheless, lack of proper distribution channels and the higher cost of the manufacturing process kept the technology from expanding. During

724 Reinforced Plastics Handbook

2000 Delphi's strategic business plan took it in a direction that no longer included its RP springs product line so the company decided to have the intellectual property evaluated. Because Delphi's springs were manufactured with RP material, NCC was selected to participate in the evaluation process. This step led to NCC identifying an opportunity to retain important technology for Dayton. NCC's ability to identify the fight partners and lead negotiations resulted in the purchase of Delphi's RP spring business and its Liteflex trademark. In turn, NCC licensed the Liteflex trademark and intellectual properties to Dayton-based entrepreneur John Prikkel to help him launch a new business. In addition to normal bank financing from National City Bank and gap financing through CityWide Development Corp, funds for the venture were also provided by the Ohio Department of Development (ODOD). In 2001, NCC held a special press conference to introduce Liteflex LLC to local, national and international business communities. The fledgling company began working to grow its RP spring business from the select niche markets previously carved out and leverage it into a much broader application for the automotive and medium- to heavy-duty truck industries. Market potential for the springs was identified by Delphi's research data that showed RP springs for North America's heavy-duty truck industry comprising only 2% of the market; steel held 38% and air suspension systems 60%. NCC's unique partnership with Liteflex retained a revenue stream from the licensing agreement. However, the Center also provided the company with key support services including design development and application. "By teaming with an organization like NCC, a small startup gains the advantage of finding out about opportunities like filament winding technology that they would otherwise never hear about," said Lou Luedtke, president and CEO of NCC. Innovative partnering also gives a relatively unknown entity the credibility and clout they need to secure an audience with critical decision makers. In 2003 Liteflex announced a second strategic joint partnership with ArvinMeritor's Commercial Vehicle Systems Worldwide Suspension Systems business. ArvinMeritor Inc is a $7 billion global supplier of a broad range of integrated systems, modules and components to the motor vehicle industry. The joint venture is expected to double Liteflex's volume of heavy-duty truck springs over the next two years. In addition to RP springs, ArvinMeritor and Liteflex will develop integrated RP suspension systems that meet the heavy-duty truck, trailer and specialty markets' needs for improved tiding suspensions that are also lighter weight. Several new systems are forth coming. The commercialization trail NCC followed to ultimately link Liteflex with

7

Designs 9 725

Arvin Meritor has also fostered a companion project as well. The trio will work to develop suspension components designed with NCC's patented process Litecast TM. This unique casting technology permits metal to be die cast directly to the RP insert to form a suspension link's end attachment. Litecast causes controlled vaporization of the outer resin layer, leaving metal interlocked with the fibers to create a mechanical bond that eliminates end attachment failure. Litecast suspension link assemblies for mediumto heavy-duty trucks offer a weight saving over steel of at least 50% and 10-15% over forged aluminum. Litecast is the only process on the market able to eliminate adhesive bond failure. The technology also eliminates the need for secondary mechanical fastening systems that add cost and reduce the strength of RP parts. For Liteflex and its RP spring business, teaming with ArvinMeritor allows the smaller company to take advantage of ArvinMeritor's engineering and sales expertise, world-class distribution channels and ability to integrate with original equipment manufacturers (OEMs)' designs. NCC will continue in its R&D role by investigating innovative methods to reduce the cost of the RP spring manufacturing process even further while working to link filament winding technology to applications for other commercial markets. (NCC, 2000 Composite Drive, Kettering, O H 45420, USA; tel: 1 937 297 9450; fax: 1 937 297 9440; e-mail: [email protected]; website: www.co.mpositecenter.org). Cantilever Springs

The cantilever spring (URP or RPs) can be employed to provide a simple format from a design standpoint. Cantilever springs, which absorb energy by bending, may be treated as beams, with their deflections and stresses being calculated as short-term beam-bending stresses. The calculations arrived at for multiple-cantilever springs (that is, two or more beams joined in a zigzag configuration, as in Figure 7.42 are similar to, but may not be as accurate as, those for a single-beam spring. A zigzag configuration may be seen as a number of separate beams each with one end fixed. The top beam is loaded (F) either along its entire length or at a fixed point. This load gives rise to deflection y at its free end and moment M at the fixed end. The second beam is then loaded by moment M (upward) and load F (the effective portion of load F, as determined by the various angles) at its free end. This moment results in deflection Y2 at the free end and moment M2 at the fixed end (that is, the free end of the next beam). The third beam is then loaded by M2 (downward) and force F2 (the effective portion of F1), and so on.

726 Reinforced Plastics Handbook Load on multiple spring

t T Y

T T Figure 7.42 Multiple-cantilever zigzag beam spring (courtesy of Plastics FALLO) The total deflection, y, is the sum of the deflections of the individual beams. The bending stress, deflection, and moment at each point can be calculated by using standard equations. To reduce stress concentration, all corners should be fully radiused. This type of spring is often favored because of its greater design flexibility over the singlebeam spring. The relative lengths, angles, and cross-sectional areas can be varied to give the desired spring rate Fly in the available space. Thus, the total energy stored in a cantilever spring is equal to: Ec = 1/2 Fy

where F = total load in lb, y = deflection in., and E, = energy absorbed by the cantilever spring, in-lbs.

Torsional Beam Springs There are torsional beam springs that absorb energy by twisting through an angle 0 (Figure 7.43) and may thus be treated as a shaft in torsion. A shaft subject to torque is generally considered to have failed when the strength of the material in shear is exceeded. For a torsional load the shear strength used in design should be the published value or one half the tensile strength, whichever is less. The maximum shear stress on a shaft in torsion is given by the following equation:

7

Designs 9 727

Figure 7.43 Exampleof a shaft under torque

where T - applied torque in in-lb, c = the distance from the center of the shaft to the location on the outer surface of shaft where the maximum shear stress occurs, in. and J = the polar moment of inertia, in. 4 (Table 7.5). The angular rotation of the shaft is caused by torque is given by: O=

TL/GJ

where L = length of shaft, in., G = shear modulus, psi = El2 (1 + v), E = tensile modulus of elasticity, psi, and v = Poisson's ratio. The energy absorbed by a torsional spring deflected through angle 0 equals: Et= 1/2M0 x 0

where Mo = the torque required for deflection 0 at the free end of the spring, in-lb.

Special Springs As RP leaf springs find more applications, innovations in design and fabrication will follow. As an example, certain processes are limited to producing springs having the same cross-sectional area from end to end. This leads to an efficient utilization of material in the energy storage sense. However, satisfying the requirement that the spring become increasingly thinner towards the tips can present a difficulty in that the spring width at the tip may exceed space limitations in some applications. In that case, it will be necessary to cut the spring to an allowable width after fabrication. There are special processes such as basic filament winding that can fabricate these type structures. A similar post-molding machining operation is required to produce variable thickness/constant width springs. In both instances, end-to-

728 Reinforced Plastics Handbook

end continuity of the fibers is lost by trimming the width. This is of particular significance near the upper and lower faces of the spring that are subject to the highest levels of tensile and compressive normal stresses. A practical compromise solution is illustrated in Figure 7.44. Here excess material is forced out of a mid-thickness region during molding that maintains continuity of fibers in the highly stressed upper and lower face regions. A further advantage is that a natural cutoff edge is produced. The design of such a feature into the mold must be done carefully so that the molding pressure (desirable for void-free parts) can be maintained.

Figure 7,44 Spring with a practical loading solution

An area of importance is that of attaching the spring to the vehicle. Since the RP spring is a highly anisotropic part especially designed as a flexural element, attachments involving holes or poorly distributed clamping loads may be detrimental. For example, central clamping of the spring with U bolts to an axle saddle will produce local strains transverse to the fibers that in combination with transverse strains due to normal bending may result in local failure in the plastic matrix. The use of a hole for a locating bolt in the highly stressed central clamped region should also be avoided. Load transfer from the tips of the RP spring to the vehicle is particularly difficult if it is via transverse bushings to a hanger bracket or shackles since the bushing axis is perpendicular to all the reinforced fibers. One favorable design is shown in Figure 7.45. It utilizes a molded random fiber RP bracket that is bonded to the spring. Load transfer into this part from the spring occurs gradually along the bonded region and results in shear stresses that arc conservative for the adhesive as well as both RP parts.

7

9Designs 7 2 9

Figure 7~45 Spring has a bonded bracket

Sandwiches A sandwich structure is composed of two skins and a core material. The same or different materials are combined in the form of sandwich construction (Figure 7.46). They can be used in products with an irregular distribution of the different materials, and in the form of large structures or sub-structures. Overall load-carrying capabilities depend on average local sandwich properties, but materials failure criteria depend on local detailed stress and strain distributions. Design analysis procedures for sandwich materials composed of linear elastic constituents are well developed. In principle, sandwich materials can be analyzed as RP structures, but incorporation of viscoelastic properties will be subject to the limitations discussed throughout this book.

Load

Face

Honeycomb co, e V

Figure 7.46

Bondonrmaterial

~ m o | e t ~ J saJ'~Jw~ch structure

Honeycomb core sandwich structure {courtesy of Plastics FALLO]

730 Reinforced Plastics Handbook Structures and sub-structures composed of a number of different components and/or materials, including traditional materials, obey the same principles of design analysis. Stresses, strains, and displacements within individual components must be related through the characteristics (anisotropy, viscoelasticity, etc.) relevant to the particular material, and loads and displacements must be compatible at component interfaces. Thus, each individual component or sub-component must be treated. Load and support conditions for individual components depend on the complete structure (or system) analysis, and are unknown to be determined in that analysis. For example, if a plastic panel is mounted into a much more rigid structure, then its support conditions can be specified with acceptable accuracy. However, if the surrounding structure has comparable flexibility to the panel, then the interface conditions will depend on the flexural analysis of the complete structure. In a more localized context, structural stiffness may be achieved by fibbing and relevant analyses may be carried out using available design formulae (usually for elastic behavior) or finite element analysis, but necessary anisotropy or viscoelasticity complicate the analysis, often beyond the ability of the design analyst.

Design Approaches A structural sandwich is a specially shaped product of a RP in which two thin facings of relatively stiff, hard, dense, strong material is bonded to a relatively thick core material. With this geometry and relationship of mechanical properties, facings are subjected to almost all the stresses in transverse bending or axial loading. The geometry of the arrangement provides for high stiffness combined with lightness, because the stiff facings are at a maximum distance from the neutral axis, similar to the flanges of an I-beam. Overall load-carrying capabilities depend on average local sandwich properties, but material failure criteria depend on local detailed stress and strain distributions. Design analysis procedures and fabricating procedures for sandwich materials composed of linear elastic constituents are well developed and reported in the literature. In principle, sandwich materials can be analyzed as RPs. The usual objective of a sandwich design is to save weight, increase stiffness, and use less expensive materials, or a combination of these factors. Sometimes, other objectives are also involved such as reducing tooling and other costs, achieving smooth or aerodynamic smoothness, reducing reflected noise, or increasing durability under exposure to acoustic energy. The designers consider factors such as getting the loads in, getting the loads out, and attaching small or large load-carrying

7

9Designs 7 3 1

members under constraints of deflection, contour, weight, and cost. To design properly, it is important to understand the fabrication sequence and methods, use of the correct materials of construction, the important influence of bond between facing materials and core, and to allow a safety factor that will be required on original, new developments. Use of sandwich panels are extensively used in building and, construction, aircraft, containers, etc. The primary function of the face sheets is to provide the required bending and in-plane shear stiffness, and to carry the axial, bending, and in-plane shear loading (Chapter 8 BEAMS). In high-performance structures, facings most commonly chosen are RPs (usually prepreg), URPs, aluminum, titanium, or stainless steel. The primary function of a core in structural sandwich parts is that of stabilizing the facings and carrying most of the shear loads through the thickness (Tables 7.16 to 7.24). In order to perform this task efficiently, the core must be as rigid and as light as possible, and must deliver uniformly predictable properties in the environment and meet performance requirements. Several different materials are used such as plastic foam, honeycomb [using RP, film (plastic, aluminum, paper, etc.), balsa wood, etc. Different fabricating processes are used. These include bag molding, compression molding, reinforced reaction rejection molding (RRIM), filament winding, corotational molding, etc.

Table 7.16 Properties and relative cost of structural sandwich cores

Core material

Density (kg/m3)

Shear strength (MN/m 2)

Compressive strength Relative cost (MN/m 2) {for equal thickness}

PVC foam PVC foam End-grain balsa End-grain balsa Aluminum honeycomb Aluminum honeycomb Phenolic honeycomb Phenolic honeycomb Shell GRP core (estimate)

75 190-200 100 180 26 160 29 130 250

0.8 2.7-3.7 1.4 2.5 0.5/0.:] 8.2/4.2 0.9/0.6 5.2/3.6 6.5

1.1 3.7-4.0 6.0 13.0 0.3 14.0 0.9 8.5 15.8/5.2 a

aFiguresshow adjacentcore unit websworking as one and working independently. Source: Shell International Trading.

1.0 0.6 1.7 > 1.7 0.5-0.8

W bo r m

Table 7.17 Examples of rigid plastic foam properties

,

o

r

...........

Property Density, lb./ft. 3 (kg/m3) Tensile strength, psi

ASTM Test

Phenolic ................ Foamed in Syntactic Place Castable

D 1623

2-5 (32-80) 20-54

D 1621

22-85

(MPa)

Comprcssitm strength at 11)% dellcction, psi (MPa)

(0.15-0.59)

Thermal conductivity BTU/in./hr.-ft.A ~ (W/mK)

D 2326

Continuous at 300 225 (149) 0.20-0.22

Coefficient of linear expansion, 10-6 in./in.-~

D 696

(0.29-0.032) 5

Maximum service temperature dry, ~ (~

Polyvinyl Chloride Phenylene Polyethylene Rigid Oxide MediumClosed Foamable Polycarbonate Density Foam Cell Resin

tel Polystyrene Molded

Extruded

2.0 (32) 42-68 (0.29-0.47) 25-40

2-5 (32-80) 180-200 (1.24-1.38) 100-180 at 5% (0.69-1.24)

(0.48-1.90)

165-175 (74-79) 0.17-0.21

200-250 (93-121) 0.15-0.21

8,(XX)-

5O (800) 3,300 (22.7) 5,500

50 (8OO) 5,500 (37.9) 7,500

5.5-7.0 (88-112) 110-210 (0.76-1,45) 2-18

(55.1-89.6)

(37.9)

(51.7)

(0.0.14-0.12) (0.17-0.28)

200 (93.3)

270 (132)

38

25

50-60 (800-960) 10(K) (6.89)

2-4 (32-~) 1,~ (6.89)

13,(XX)

275 (135) 1.0

2.0

(0.14) 100

(0.29) 40-60

180-200 (82-93) 0.32-0.34

(0.046-0.049)

Polyurethane Rigid Closed Cell

1.65-175 (74-79) 0.23

(0.033) 30-40

4-8 (64-130) 90-290 (0.62-2.00) 70-275

(0.024-0.030) (0.022-0.030) 30-40 40

-IO" O O

Table 7.1 8 Propertiesof 1/4"thick thermoplastic structural foam (20% weight reduction)

Property S|~cilic graviiy l)ctl~iioa

.b7

,70

.85

405 346

167 1t 2

189 176

194 187

4.5 9,9 t0

5+2 1,960

9 t ,8~

4.5 2,3~

79,~

14 I, 160

245,~

I ,(X20,~

80~400

2~,321

275,000

l|.3~ V-0

2.800 HB

3,447 HB

V-0

Polycarbonate

Thermoplastic Polyester

~60

.86

,85

.90

! .2

129.6 93.5

187 t 72

205 | 80

280 2~

i2 1,310

4.9 3,900

3.8 3,4~

2 6,100

2,5~,~

235,~

300,~

•,028,~

2,11~,~

261 ,IX~

357,~

4~400 V-0

V-OISV

5,200

5,2L~ V-0/SV

ASTM-D-?92

~ p~i ASTM-D-792 ~F@264 p~i

Iti~i,t fi,'

High Impact Polystyrime w/FR

ABS

Method of Testing

Unit

High Impact Polystyrene

Modified Polyphere ylene Oxide

High Density Polyethylene

Polypropylene

lr162

ilitdct toltd C~ilicieni of

Ihcfril~l

expatt~i~Jn Tensile

T.~n,~,ilc t"ll~ulut Flixur~t

modulus

Compressive stlcntlllt (10% dcformaiioa) Conlt~tlibitiiy r~iing

in~lin.i~ • i0 -~

ASTM-D-696 ASTM- D-638 ASTM-D-638

psi

ASTM-D-7~

ASTM.-D-.695 UL :Sia~id~rd 94"

120,0(K)

l,~0

~J r I/I

I/I

~J W

734 Reinforced Plastics Handbook Table 7.19 Averagepropertiesof rigid and contourableend-grain balsa core materials Property

Units

Density

kg/m 3 Ib/ft 3 W/m-~ Btu-in/h-ft2-~ MPa psi MPa psi MPa psi MPa psi GPa kpsi in/in~ tangential radial longitudinal

Thermal conductivity Tensile strength Shear strength Shear modulus Compressive strength Compressive modulus Linear coefficient of thermal expansion

Rigid and contourable sheet

100-250 6.5-15.5 0.0509-0.0890 0.353-0.617 6.90-23.7 1000-3440 1.85-4.94 268-717 108-312 15,600-45,300 6.52-26.6 945-3850 2.24-7.72 325-1120 10.5 x 10 -6 7.0 x 10 -6 1.7 x 10-6

Source:BaltekCorporation.

Table 7.20 Propertiesof Cell structural phenolicfoam

Compressive strength Flexural strength Tensile strength Thermal conductivity X Linear coefficient of thermal expansion Moisture properties Smoke generation and toxic gas emission Punking Source:Acell Italia.

Standard

Unit

80

120

150

200

UNI 6350

kg/cm2

6.1

7.0

8.2

10.0

UNI 7031

kg/cm 2

4.3

5.0

6.1

8.0

UNI 8071

kg/cm 2

4.2

4.9

5.6

6.0

UNI 7745

0.035

0.037

0.039 0.044

BS 4371, p 3

kcal/ mh~ m/m~

-6 20/40

20/40

20/40

20/40

DIN 52615

p

50

70

90

110

ATS 1000.001 aero-nautical, NF F16-101 railway

passed M1F1

passed passed passed M1F1 M1F1 M1 F1

BS 5946

passed

passed passed passed

7

9Designs 7 3 5

Table 7,21 Typical values of rigid polyurethane foam cores

Apparent density Compressive strength Shear strength E-modulus in compression Shear elongation at break Impact strength Thermal conductivity Maximum operating temperature Water absorption (7d)

Test

Unit

Value

ISO 845 ASTM D 1622 ISO 844 ASTM D 1621 ISO 1922 ASTM C 273 DIN 53 457 ASTM D 1621 ISO 1922 DIN 53 453

kg/m 3 Ib/ft 3 N/mm 2 psi N/mm 2 psi N/mm 2 psi O/o kJ/m 2 ft Ib/in 2 W/mk BTU in/ft2h~ ~ ~ Vol.O/o

60 3.7 0.42 61 0.41 59 20 2900 30 0.9 0.4 0.030 0.208 150 300 2.3

ISO 2581 ASTM C 177

DIN 53 428

Table 7,22 Typical properties of plastic microsphere-cored laminates

Laminate thickness Weight Specific gravity Proportion balsa core a Proportion glass fiber b Flexural stiffness per inch width Apparent flexural modulus Flexural strength Bending moment at failure Tensile modulus Tensile strength Number of layers

Units

A

B

C

D

E

inch Ibf/ft 2 Ib/ft 3 % % Ibf in 2 psi x 104 psi x 104 Ibf in psi x 104 psi x 103

0.36 1.84 61.3 54 20 2946 74.6 2.0 17.31 55 6.59 5

0.31 1.43 56.3 64 17 1593 66.1 1.79 11.01 45.1 5.30 3

0.31 1.66 64.4 51 24 2495 102 2.39 14.99 69.3 9.0 5

0.32 1.72 63.8 49 21 2168 77.8 2.09 14.33 60.7 7.33 5

0.29 2.15 89.4 0 30 1840 91.4 2.47 13.54 110.3 13.8 7

aFiretCorematXW: % relativeto laminatethickness. bO/o relativeto laminateweight. Source:BaltekCorporation.

736 Reinforced Plastics Handbook Table 7 . 2 3 Typical properties of high performance thermoplastic foam cores

Property

Testmethod

Unit

Cross-linked foam:low density

Cross-linked foam:high density

PEI/PES foam

Apparent nominal

ISO 845

kg/m 3

4O-8O

100-200

8O

density

D1621

Ib/ft 3

2.5-5.0

6.25-12.5

Compressive

ISO 844

N/mm 2

0.5-1.4

2.0-4.6

5.0 0.75

strength Tensile strength

D1621 DIN 53455

psi N/mm 2 psi

70-200

290-667

110

0.5-1.9 75-230

2.6-6.0 340-870

Flexural

DIN 53455

N/mm 2

1.9

strength Shear

276

ISO 1922

psi N/mm 2

0.4-1.2

1.6-3.5

0.9

strength E-modulus,

(3 273 DIN 53457

psi N/mm 2

60-160

220-508

130

26-75

110-223

45

compression E-modulus,

D621 DIN 53457

psi N/mm 2

DIN 53457

psi N/ram 2

15,950-32,346 80-188 12,300-27,270

6530

tensile E-modulus,

3900-10,850 29-57 4200-9700

ASTM

psi N/mm 2

modulus Shearing at break Impact strength

(3 ISO 1922 DIN 53453

psi O/o kJim 2 ft Ib/in 2

Thermal conductivity

DIN 5261 (3 177

W/m K BTU in/ft2hoF

0.029-0.033 0.19-0.23

0.038-0.042 0.25-0.27

52 7540 18 2610 30 1.6 0.4 0.035 0.23

Max. operating temperature

DIN 53445

~ ~

65-75 149-167

80 176

190 375

flexural Shear

Sheet dimensions:

12-30 1750-4600 10-30 0.2-0.9 0.007-0.29

38-77 5450-11,170 30-31 1.4-4.0 0.33-1.01

(depending on color)"

width (mm + 10)

760-1330

length (mm + 10) thickness (mm + 0.5)

1025-2850 5/8-10/77

Note: PEI/PESfoam has also passedthe following fire performance specifications: Aircraft: Burn length FAR 25 852/ATS 1000 Smoke density FAR 25 853(a) Toxicity FAR 25 853(a-I) Heat release FAR 25 853(a-I): HRR,HR Railway: DIN 5510 Flammability $4 Smoke density SR2 Drip test ST2 NF 16-101/P92-501 Flammability M 1 Smoke density and toxicity F1

1350 2700 5/10-50/70

7

Designs 9 737

Table 7.24 Comparative material and laminating costs (DM) Balsa sandwich

PVCsandwich

5pherecore 5BC laminate

Balsa (I 5 mm)

35.00

PVC (15 mm)

50.00

UP resin (2.6 kg) Laminate (6 mm) Total

7.8 33.00

UP resin (2.2 kg) Laminate (7 mm)

6.60 38.50

Spherecore

30.00

(15 mm)

75.80

95.10

UP resin (6.0 kg) Laminate (5 mm)

18.00 27.50 75.50

Note: Basedon a resin cost of DM 31kgand laminatecost of DM 5.501kg.

There is also the so-called structural foam (SF) that is also called integral skin foaming or reaction injection molding. It can overlap in lower performance use with the significantly larger market of the more conventional sandwich. Up until the 1980s in the U.S., the RIM and SF processes were kept separate. Combining them in the marketplace was to aid in market penetration. During the 1930s to 1960s, liquid injection molding (LIM) was the popular name for what later became RIM and SF. SF is characterized as a plastic structure with a nearly uniform density foam core and integral near-solid skins (facings). When these structures are used in load-bearing applications, the foam bulk density is typically 50 to 90% of the plastic's unfoamed bulk density. Most SF products (90wt%) are made from different TPs, principally PS, PE, PVC, and ABS. Polyurethane is the primary TS plastic. Unfilled and reinforced SFs represent about 70% of the products. The principal method of processing (75%) is modified low-pressure injection molding. Extrusion and RIM account for about 10% each. Optimizing Structures

In a sandwich design, overall proportions of structures can be established to produce an optimization of face thickness and core depth that provides the necessary overall strength and stiffness requirements for minimum cost of materials, weight of components, or other desired objectives. Competing materials should be evaluated on the basis of optimized sandwich section properties that take into account both the structural properties and the relative costs of the core and facing materials in each combination under consideration. For each combination of materials being investigated, thickness of both facings and core

738 Reinforced Plastics Handbook should be determined to result in a minimum cost of a sandwich design that provides structural and other functional requirements. Sandwich configurations are used in small to large shapes. They generally are more efficient for large components that require significant bending strength a n d / o r stiffness. Examples of these include roofs, wall and floor panels, large shell components that are subject to compressive buckling, boat hulls, truck and car bodies, and cargo containers. Frequently, sandwich constructions also provide an efficient solution for multiple functional requirements such as structural strength and stiffness combined with good thermal insulation, or good buoyancy for flotation. In principle, sandwich materials can be analyzed as RP structures. Structures and sub-structures composed of a number of different components a n d / o r materials, including traditional materials, obey the same principles of design analysis. Stresses, strains, and displacements within individual components must be related through the characteristics (anisotropy, viscoelasticity, etc.) relevant to the particular material; also loads and displacements must be compatible at component interfaces. Thus, each individual component or sub-component must be treated using the relevant methods. Load and support conditions for individual components depend on the complete structure (or system) analysis. For example, if a panel is mounted into a much more rigid structure, then its support conditions can be specified with acceptable accuracy. However, if the surrounding structure has comparable flexibility to the panel, then the interface conditions will depend on the flexural analysis of the complete structure. In a more localized context, structural stiffness may be achieved by ribbing, and relevant analyses may be carried out using available design formulae (usually for elastic behavior) or finite element analysis. But necessary anisotropy or viscoelasticity complicate the analysis, often beyond the ability of the design analyst.

Stiffnesses and Bucklings The primary structural role of the face/core interface in sandwich construction is to transfer transverse shear stresses between faces and core. This condition stabilizes the faces against rupture or buckling away from the core. It also carries loads normally applied to the panel surface. They resist transverse shear and normal compressive and tensile stress resultants. For the most part, the faces and core that contain all plastics can be connected during a wet lay-up molding or, thereafter, by adhesive bonding. In some special cases, such as in a truss-core pipe,

7

9Designs 7 3 9

faces and core are formed together during the extrusion process, resulting in an integral homogeneous bond/connection between the components. Fasteners are seldom used to connect faces and core because they may allow erratic shear slippage between faces and core or buckling of the faces between fasteners. In addition, they may compromise other attributes such as waterproofing integrity and appearance. For RP-faced sandwich structures the design approaches includes both the unique characteristics introduced by sandwich construction and the special behavior introduced by RP materials. The overall stiffness provided by the interaction of the faces, the core, and their interfaces must be sufficient to meet deflection and deformation limits set for the structures. Overall stiffness of the sandwich component is also a key consideration in design for general instability of elements in compression (Figure 7.47).

Figure 7.47 Examplesof buckling modes in sandwich construction

With most typical sandwich constructions, the faces provide primary stiffness under in-plane shear stress resultants (Nxy), direct stress resultants (Nx, Ny), and bending stress resultants (Mx, My) (Figure 7.48). Also as important, the adhesive and the core provide primary stiffness under normal direct stress resultants (Nz), and transverse shear stress resultants (Q~, Qy). Resistance to twisting moments (Txz, Tyz) that is important in certain plate configurations, is improved by the faces. Capacity of faces is designed not to be limited by either material strength or resistance to local buckling. The stiffness of the face and core elements of a sandwich RP must be sufficient to preclude local buckling of the faces. Local crippling occurs when the two faces buckle in the same mode (anti-symmetric). Local wrinkling occurs when either or both faces buckle locally and independently of each other. Local buckling can occur under either axial compression or bending compression. Resistance to local buckling is

740 Reinforced Plastics Handbook

Figure 7.48

Coordinatesystem and stress resultants

developed by an interaction between face and core that depends upon the stiffness of each. Structural Foams

With the structural foam (SF) construction, large and complicated parts usually require more critical structural evaluation to allow better prediction of their load-bearing capabilities under both static and dynamic conditions. Thus, predictions require careful analysis of the structural foam's cross-section. The RP cross-section of an SF part contains an ideal distribution of material, with a solid skin and a foamed core. The manufacturing process distributes a thick, almost impervious solid skin that is in the range of 25% of overall wall thickness at the extreme locations from the neutral axis (Figure 7.49). These are the regions where the maximum compressive and tensile stresses occur in bending. The simple supported beam has a load applied centrally. The upper skin goes into compression while the lower one goes into tension, and a uniform bending curve will develop. However, this happens only if the shear rigidity or shear modulus of the cellular core is sufficiently high. If this is not the case, both skins will deflect as independent members, thus eliminating the load-beating capability of the RP structure.

7

Figure 7,49

9Designs 7 4 1

Loadapplied to a structural foam sandwich

The fact that the cellular core provides resistance against shear and buckling stresses implies an ideal density for given foam wall thickness (Figure 7.50). This optimum thickness is critically important in designing complex stressed parts.

Figure 7.50 Core thickness vs. density impact strength

When the SF cross-section is analyzed, its RP nature still results in a twofold increase in rigidity, compared to an equivalent amount of solid plastic, since rigidity is a cubic function of wall thickness (Figure 7.51).

Figure 7~51 Sandwich and solid material construction

742 Reinforced Plastics Handbook This increased rigidity allows large structural parts to be designed with only minimal distortion and deflection when stressed within the recommended values for a particular foamable plastic. Depending on the required analysis, the m o m e n t of inertia can be evaluated three ways. First approach is where the cross-section is considered to be solid material (without a core). M o m e n t of inertia (Ix) is then equal to: Ix = b h 3 / 1 2

where b = width and h = height. This commonly used approach provides acceptable accuracy when the load-beating requirements are minimal. An example is the case of simple stresses or when time and cost constraints prevent analysis that is more exact. The second approach ignores the strength contribution of the core and assumes that the two outer skins provide all the rigidity (Figure 7.52). The equivalent moment of inertia is then equal to:

--T V////////////,/////,d L

I-

Figure 7 , 5 2

b

.

.

.

.

_!

-I

_1

I

Sandwich cross-section with and without a core

Ix = b(h 3 - h3/12)

This formula results in conservative accuracy, since the core does not contribute to the stress-absorbing function. It also adds a built-in safety factor to a loaded beam or plate element when safety is a concern. A third method is to convert the structural foam cross-section to an equivalent I-beam section of solid resin material (Figure 7.53). The m o m e n t of inertia is then formulated as: Ix = [ bh 3 - (b - b 7)(h - 2

tx)3]/12

where b] = b(Ec)/(Es), Ec = modulus of core, Es = modulus of skin, ts = skin thickness h] = core height

7

-[

, ....

I-

Figure 7.S3

-I

~

~,

9Designs 7 4 3

~//~~/~/~~~m I....[II

l

l [--

b

-1

Sandwich and I-beam cross-sections

This approach may be necessary where operating conditions require stringent load-beating capabilities without resorting to overdesign and thus unnecessary costs. Such as analysis produces maximum accuracy and would, therefore, be suitable for finite element analysis (FEA) on complex parts (Chapter 19). However, the one difficulty with this method is that the core modulus and the as-molded variations in skin thicknesses cannot be accurately measured. The following review relates to the performance of sandwich constructions such as those with RP skins and honeycomb core. For an isotropic material with a modulus of elasticity (E), the bending stiffness factor (E/) of a rectangular beam b wide and b deep is:

El= E(bha/12) In the rectangular structural sandwich with the same dimensions just given whose facings and core have moduli of elasticity Ef and Ec, respectively, and a core thickness c, the bending stiffness factor E1 is: El = {Epol #2)( h 3 - c a) +

(Ec6112) ca

This equation is exact if the facings arc of equal thickness, and approximate if they are not, but the approximation is close if the facings are thin relative to the core. If, as is usually the case, E~ is much smaller than Eft the last term in the equation can be ignored. For asymmetrical sandwiches with different materials or different thicknesses in their facings or both, the more general equation for E1 may be used. In many isotropic materials, the shear modulus G is high compared to the elastic modulus E, and the shear distortion of a transversely loaded beam is so small that it can be neglected in calculating deflection. In a structural sandwich the core shear modulus G, is usually so much smaller than Efof

744 Reinforced Plastics Handbook the facings that the shear distortion of the core may be large and therefore contribute significantly to the deflection of a transversely loaded beam. The total deflection of a beam is thus composed of two factors: the deflection caused by the bending moment alone, and the deflection caused by shear, that is, 6-- ~Jm+ 6s where 6 = total deflection, ~Jm = moment deflection, and 6~-- shear deflection. Under transverse loading, bending moment deflection is proportional to the load and the cube of the span and inversely proportional to the stiffness factor, El. Additional information is in the literature.

Finite Element Analyses This is the most commonly used method for designing fiber RP parts. Specific calculation modules arc offered by some companies, which are able to take into account the characteristic features of fiber RPs (anisotropy, etc.). The type of software available, however, may restrict use of this method. The preconditions for use of specific programs (orthotropy, symmetry to the central plane, two-dimensional stress, etc.) must be established from case to case. Information required for determination of mechanical properties may not always be readily available, but can be calculated from the respective properties of the individual components, fiber, and matrix, on a theoretical basis. If this is not possible, the data required should be determined by means of destructive mechanical tests. After making the calculations, results must be analyzed. For fiber RP parts, special failure hypotheses have been developed, distinguished by type of load (static or dynamic), evaluation of failure type (failure of fiber, matrix, or interface) and preference given to either high strength or maximum strain. As with failure hypotheses for conventional materials, it should be possible to make a comparison between multi axial loading conditions and reference values obtained from uniaxial tests. Finally, the design of the part should be evaluated and the wide range of materials and fiber arrangements, impossible to use a purely theoretical approach and therefore to make physical prototypes (to be reviewed) them to relevant tests (Chapter 9).

assessed. With it is virtually it is advisable and to subject

Constant Stress Applications For constant stress applications, the isochronous stress-strain curve can be used with standard equations by choosing the appropriate "effective

7

Designs 9 745

modulus" considering the range of stresses in the application. This requires engineering judgment where higher stressed parts would typically be analyzed with a lower "effective modulus." The use of this modulus based on the maximum stress in the part should provide a conservative estimate of the time and temperature dependent deflection of the part. When the isochronous stress-strain curve is highly nonlinear or the part geometry is complex, fimte-element structural analysis techniques can be used. Then, the complete nonlinear, isochronous stress-strain curve can be used in a nonlinear finite-element analysis or a linear effective modulus can be used in a linear analysis.

Prototypes Need for Prototyping

Physical prototyping can save time and money. The process of manufacturing a prototype part and testing it under simulated end-use conditions increases the likelihood that the part will meet customer quality requirements, improves time to market, and minimizes the risk to investments in production tooling. The goal is to expose and correct functional shortcomings of the design, evaluating part geometry, material, and fabrication method (including mold flow effects). Prototyping can determine something as simple as whether the entire mold can be easily filled or something as fundamental as whether the material is capable of meeting the application requirements. Prototyping is a worthwhile investment for all but the most elementary of designs. To some degree, computer simulation techniques provide reliable prediction of fiber orientation, polymer orientation, and weld line location. Certain fabricating processes, such as injection molding, can significantly reduce performances or destroy a molded product if a weld line exists in a critical area subjected to loads. A weld line, also called weld mark, flow line, or striate, is a potential defect when two melt flow fronts meet during the filling of an injection mold with chopped fibers and do not properly blend. This action can also occur during extrusion through a die, etc. Under the poorest processing conditions, literally a space could exist. Finite element analysis (FEA) also offers some guidance to design optimization before prototyping. Nevertheless, until these simulation techniques are proven accurate and reproducible for the design in question, judgment and prototyping will be the primary tools for optimizing a design. It may be necessary to repeat prototype part

746 Reinforced Plastics Handbook production, testing, and design modification several times to arrive at the optimum material and geometry. This is needed because judgment is often incomplete and some times incorrect, so that the initial design may produce a part with inadequate properties. In addition, each prototype phase may have a different purpose and require a different approach. In many cases, it is more effective to examine specific property aspects of a component in the early prototype phases, and then simulate actual service later in the evolution of the design. The quickest and economic prototyping process depends on a number of factors, primarily the following: 9 experience of the design engineer, 9 sophistication and precision of the design tools available and the complexity of the design, 9 number of parts to be produced and size of the investment in production of materials and tooling, once the design is finalized, 9 potential cost of a failure to the end user, and 9 intended service life and durability of the product. These factors need to be considered when choosing which properties to examine most carefully and the required confidence level.

Prototype Products For products made of RP, it is possible to manufacture a 3-D model (for appearance, styling and space filling) by any standard technique, such as molding from clay, construction from wood, or machining/ fabrication from solid plastics, such as nylons a n d / o r acrylics. A useful benefit of working with acrylics is that it is possible to make a model that is transparent, which may prove useful in deciding and checking details of assembly and fits. A fundamental question, however, is how to produce a series of prototypes that can be realistically tested, before any major commitment is made to series production. Much depends on the information that is required from the test program (mechanical/load beating properties, heat stability, chemical resistance, etc.). With RPs it is virtually impossible to produce such a prototype without using some form of molding (especially if more than one is required). However, reinforced TS resin products lend themselves to a range of molding processes, from one to literally thousands. This makes it possible to match fairly closely the actual system that will be used in production. It is also possible to produce one-off or a very low volume by one process (which will give certain basic test data), then advancing to small-volume production (to obtain more refined data).

7

9Designs 7 4 7

One must decide whether to make a model of the part or to skip this stage and to attempt actual prototype production with original designed geometry and material. A model part may use a material that behaves like the design material, but does not necessarily have the same exact dimensions as the final design. Next, the part is subjected to an environment, for example, load, heat, or chemical attack that simulates some or all aspects of the application. The choice of prototype technique is best determined by assessing what properties of the product are unknown at the time. What is of greatest interest: stiffness, yield load, or heat distortion temperature? This will help to determine the simplest and least expensive prototyping technique. Techniques for creation of a physical prototype product include the following: 9 injection or compression molding with a low-cost mold, 9 machining from a block of similar material, 9 assembly, for example, by adhesive bonding, of standard shapes, hand-lay-up of a model material, and 9 thermoforming of sheet and other standard shapes. Short fiber RPs are not homogeneous (properties vary from local point to point) nor are they isotropic (properties vary with direction of measurement). Some of the above methods will not reproduce the flow patterns that occur during production molding, so they cannot be used to study properties that are dependent on fiber orientation, such as modulus, yield stress, or stresses induced by shrinkage. In addition, prototypes made from slab or bar stock are based on extrusion grades of the polymers involved, which usually have higher molecular weight than injection molding grades. This, in turn, will often cause the prototype to exhibit better impact strength, creep resistance, and chemical resistance than the molded product. These differences are particularly pronounced with crystalline plastics such as nylon, acetal, and polypropylene. Even the smaller differences observed with amorphous plastics such as polycarbonate and modified polyphenylene ether (PPE) may be critical to a given application. Machining removes the "skin" (often resin-rich) from prototypes parts, introducing further deviation from the production versions. Consequently, injection molding with a low-cost mold is the most reliable technique in designs based on short fiber RPs. Note, however, that prototype molds still introduce another variable: cooling rate. The less similar the cooling rate of the material inside the prototype mold vs. inside the production mold, the less realistic the

748 Reinforced Plastics Handbook fiber orientation-dominated properties of the prototype part will be. This is due to the dependence of skin and core flow effects on cooling rate. The two different types of flow produce markedly different fiber orientations, and their relative thicknesses strongly affect the in-plane properties of molded products. Therefore, the thermal conductivity and the heat capacity of material used for the prototype mold should approximate that of the material used for the production mold (which is usually steel). The economic compromise for a prototype mold material is often aluminum or epoxy filled with aluminum powder. The latter material has a thermal conductivity approaching that of solid aluminum, which is nearly five times that of mold grade steel (and therefore introduces a variant into the prototype process). Either material can be machined into the correct cavity shape; filled epoxy has the additional capability to be cast around a part form. Once the physical prototype is created, it can be subjected to tests and evaluated under some or all aspects of the application environment. Mechanical, chemical, microstructural, electrical, visual, frictional, and combustive properties are usually relevant in some combination. Testing may also be divided into two categories: simulation testing in the laboratory, and service testing where the prototype is placed in actual use. Laboratory testing is more economical where environmental conditions are not complicated by coupling (such as high moisture and temperature accompanying mechanical stress) in the application.

Prototype Techniques Prototype tools, where small quantities (perhaps of 50-100 moldings) are needed for test and evaluation, can be made of materials such as mild steel, aluminum, or epoxy resin tooling compounds. The tool life is limited and there is no long-term alternative to having a correct production tool manufactured. Two quite different prototypes are needed today: 9 for checking styling and geometry, particularly the fit of a component into a larger assembly. This can be a one-off, sculpted in clay, carved in wood, or machined from a block of transparent plastic or soft metal. 9 for testing under real-life conditions of production and use, giving not only further data on geometry but also information on performance (often highlighting aspects which could not have been foreseen in the original design).

7

9Designs 7 4 9

Specialists, such as the UK Warwick Manufacturing Group and the German Fraunhofer Institute for Production Technology and Automation, identify three areas where rapid prototyping is now paying off: 9 proving the design of the part before any metal is cut 9 building working models of complex tools, to ensure that the moving parts operate correctly 9 producing prototypes in realistic quantities for field testing. There are at least 30 different techniques for rapid prototyping, and each has its own niche. Basically, there are two approaches: either remove material or add it. Removing material is the older technology: carving a block of soft metal or plastic such as transparent acrylic. Nevertheless, the carving (or machining) can also be integrated with design data from the computer and some recent developments demonstrate that it can be achieved very quickly. A range of tooling blocks by Advanced Composites Group includes epoxy products with low coefficients of thermal expansion and compatibility with epoxy based laminating systems. It includes blocks for hand carving, for styling where CNC facilities are not available, and for large master models, where it might be beneficial to use a lower cost/ lower mass core block. All blocks can sustain full autoclave pressure over a wide range of temperatures. Polyurethane board can include a low density foam block for applications from styling models to cutter path verification, and styling. Low density master models from which vacuum-consolidated RP tools and components can be produced. Lite System Ltd (LSL), Newfoundland, Canada, has developed a lowvolume mold-making process, using molds direct milled by CNC output from a blank of a substrate coated with a millable medium on the tool face. Using an RP substrate helps keep costs down, creating relatively lightweight mold. The approach minimizes the amount of heavy or expensive milling needed, reducing the number of roughing passes required. Weight will be less than a solid plug milled from the same material, but probably more than a comparable glass fiber mold. Direct milled molds make the advantages of CNC-milled tools available for small volume or one-off production, eliminating the master to save time and labor costs. The method was used to make a wind tunnel for a USA helicopter test program. LSL has also developed Magnum Ceramics Composites, allowing it to mill a plug or master mold and spray up a production tool with ceramic

750 Reinforced Plastics Handbook

composite, giving costs very close to direct milling of a female tool (which is very complex). Low Temperature Milling (LTM) prepregs are also used in prototype tooling. The McDonnell Douglas/NASA X36 tail-less fighter agility research aircraft (unveiled in March 1996) used the LTM 10 (from UK Advanced Composites Group) prepreg for fuselage skins and air inlet/ diffuser sub-assembly, for its ability to cure at 30--40C under vacuum pressure only. Sealed chipboard masters were used to mold LTM prepreg tool skins, supported on a plywood frame. LTM prepregs allow the fabricator to mold direct from the master model, without needing to go through a wet lay-up intermediate stage. A wide range of cure temperatures means accurate tools can be made from a master in almost any material, without needing to allow for expansion or shrinkage. Resins have a Tg (Chapter 3) above 200C and can be used to process high temperature curing epoxy and other aerospace resins. High-speed machining by Japanese companies has developed highspeed machining. Research at Kanazawa University shows that there is little heat build-up and barely any work hardening during high-speed milling. In most cases, the temperature of the work piece does not increase by more than 3C above ambient. The implication is that thinwall sections can be produced, pre-hardened or difficult materials can be cut and intricate patterns can be followed. Yamazaki Machinery subsidiary Mazak Machine Tools has demonstrated how high-speed machining can produce finishes comparable with surface grinding. On HRc 55 tool steels, with coated carbide tooling and with spindle speeds of up to 25,000 revs/min, finishing feed rates of up to 5 m / m i n and roughing feed rates of up to 8 m / m i n , much (if not all) the time spent on hand finishing can be eliminated. Examples of time savings include the forging die for an automotive connecting rod (reduced from 50 h work to less than 20) and, at the other end of the scale, a die for vacuum forming chocolate box trays (reduced from 20 h to just two). Vacuum castings, the more basic processes, such as vacuum casting in silicone molds, also have their place and a range of gun-applied TS polyurethane resins introduced by Axson, France, avoids the need even for the casting machine. Martello Design has developed a polyurethane injection process, Thin-RIM, complementary to its existing vacuum casting method, which allows features and wall sections down to 0.5 mm to be produced. A stage further is the use of low-melting point alloys. Mining and Chemical Products, UK (MCP) has specialized in development of metal

7

9Designs 7 5 1

alloys which melt at low temperature and has continued into complementary plastics systems, with the necessary equipment. Molds for injection molding have been made in one-twelfth of the normal time, with costs down to 10-33 % of conventional levels, ready for molding in a week or less. The process also allows direct use of 3-D models from stereolithography and other rapid prototyping processes as spray-on patterns. Vacuum casting with low melting point alloys is also used. The prototype component is used as a master for a silicone rubber mold for a vacuum-casting machine. Typical is a bench-mounted system from MCP, capable of taking molds up to 400 mm x 400 mm x 320 mm, delivering a shot of up to 800 g in any one of a number of special MCP two-part resins. In conventional mold-making technology standard parts are used for prototype development, and mold-makers have developed simple but valuable systems for building up a mold this way. For example, Protoform, Germany, has developed a system using aluminum building blocks and Nissei, Japan, has developed a multi-impression mold block which allows one cavity to be produced and run in molding trials, before the user is committed to producing the whole mold. Adding material is a newer technology. Current prototyping methods seek to integrate data from a computer with a model-making process such as applying layers of plastic, paper, or wax. The most interesting approaches are bound up with developments in liquid plastics resins and systems to cure them. The stereolithographic (STL) method works with photo-curing polymers, using a laser beam to trace the contours of the 3-D shape on the surface of a bath of liquid polymer, shading the relevant sections. Teijin Seiki, Japan, has developed an acrylic-urethane resin and demonstrated that a mold can be made by STL which can be used to produce over 20 prototypes of the desired product and in the actual resin which will be used for commercial production. Selective laser sintering (SLS) uses a powdered starting material. DTM Corporation, USA, provides superior accuracy and faster production for its Sinterstation 2000 system, which accepts output from industrystandard CAD packages to create soft tooling in polycarbonate or nylon. DTM also claims that direct production of metal tooling can also be achieved with its system, using a special metal powder to produce precision metal parts in a single working cycle, without the timeconsuming detour via master model and follow-up work. The mechanical properties of these sintered metal components are comparable with those of aluminum.

752 Reinforced Plastics Handbook

Other techniques include solid ground curing (SGC), laminated object manufacturing (LaM) and fused deposition modeling (FDM). The latest technology brings mold-making right into the design office (Table 7.25). Literally, a desktop operation is multi-jet modeling (MJM) from 3D Systems, USA, which links with a CAD network but employs 3-D ink-jet printing technology to spray molten TP, and produce a model in about 4: h. Table 7.26 provides examples of specialist suppliers of products and services. Table 7 . 2 5 Rapid prototyping processes Manufacturer

Process name

Material ~ structure generation

3D Systems Inc., Valencia, CA, USA

Stereo lithography Apparatus (SLA)

Photopolymer system; point-by-point irradiation with a HeCd resp. an argon ion laser

CMET,Japan

Solid Object UV Plotter (SOUP)

Photopolymer system; point-by-point irradiation with an argon ion laser

SONY-Japan Synthetic Rubber, Tokyo, Japan

Solid Creater

Photopolymer system; point-by-point irradiation with an argon ion laser

SPARX, Molndal, Sweden

Hot Plot

Self-adhesive film; cutting of the films layer by layer with a thermal electrode

Stratasys Inc., Minneapolis, Wl, USA

Fused Deposition Modelling (FDM)

Thermoplastic filaments (PA, etc.} as well as wax; melting the plastic in a mini extruder

Light Sculpting Inc, Milwaukee, Wl, USA

LSI

Photopolymer system;irradiation of the entire surface with a UV lamp

Mitsui Engr' [-t Shipbuilding Ltd., Tokyo, Japan

COLAMM

Photopolymer system; point-by-point irradiation with a HeCd laser

Cubital Ltd., Herzlia, Israel

Solider 5600

Photopolymer system;irradiation of the entire surface with a UV lamp

DTM Corp., Austin, TX, USA

Sinterstation 2000

Powderized thermoplastics (PA, PC), wax; local melting of the powderized plastic by laser energy

DuPont license to Teijin Seiki,Tokyo, Japan

SOMOS

Photopolymer system; point-by-point irradiation with an argon ion laser

EOS GmbH, Plaegg/ Munich, Germany

STEREOS

Photopolymer system; point-by-point irradiation with an argon ion laser

Helisys Inc., Torrence, CA, USA

Laminated Object Manufacturing (LOM)

Self-adhesive paper and plastic films; cutting of the films layer by layer with a C02 laser beam

7

9Designs 7 5 3

Table 7 . 2 6 Suppliers of tooling products and services Supplier

Product

Advanced Composites Group, UK

Tooling blocks, ancillaries, prepregs, support structures

Australian Fibreglass Supplies, Australia

Tooling gel-coats, ISO NPG polyester for mold laminating, surfacing primers for plug work, mold release systems, waxes, polishes

Brookhouse Patterns, UK

Tooling manufacture, especially for aerospace industry

Donsea Composite, Malaysia

Mold- and pattern-making services

Farecla Products, UK

Finishing compounds for plugs and molds

FET Engineering Inc., USA

Nickel shell tooling

FICI, USA

Parting waxes, mold cleaners, mold glazes

Finish Care Products, USA

Polymer release agents, wax removers, finishing compounds for removal of sanding marks, cutting compounds, surfacing agents (incl. styrene-free grades)

Flex-O-Therm, The Netherlands

CNC-milled patterns, epoxy molds for RTM, pressing and injection molding, prototypes and 3-D visualizations, hydraulic/pneumatic auxiliary machines

Form-Rite Plastics, Australia

Form-Core for stiffening laminates

Franklynn Industries, USA

Water-based release coating

Hawkeye Industries, USA

Marine interior finishes, in-mold surfacing primers for post-painted parts, surfacing plaster plugs and models

Hawk International Distributors, UK

Polyester coatings, tooling gel-coats, finishing systems, mold releases

LSL, Canada

Low volume and prototype molds

Metra, France

Steel molds

MCP- Mining ~ Chemical Products, UK

Low melting point alloys for tooling for plastics molding and resin forming; small machinery

Multistation, France

Rapid prototyping

Plastech Tr, UK

Mold manufacture, training, tooling materials and ancillaries, high temperature core materials, heating and sensor equipment Flexible mold materials and rigid castings resins for composites, incl. silicone and urethane mold components

Polytek Development, USA Rawlson, UK

Consultancy services on product design, pattern-making, tool-making

RW Roll Wolfangel, Germany

Low-cost, rapid RTM tooling

Swancor Industrial, China

Vinyl ester resins for mold-making

Wela, Germany

Heatable laminating molds with Technotex space fabrics

Source: Reinforced Plastics.

754 Reinforced Plastics Handbook Summarizing this subject since the late 1980s, RP has evolved from a tool for making factory molds and dies to a low-volume technique for making finished parts, and even consumer product prototypes. One type of RP machine turns computer models into functional parts by creating thin layer upon layer of powdered metal or plastic, fusing each layer into a solid. This so-called sintering is done by scanning a laser back and forth within the part's often-intricate outline. However, with most such machines, it takes hours to build a large 3-D shape. Behrokh Khoshnevis, a professor of industrial and systems engineering at the University of Southern California, reported on his better idea. Instead of sintering a layer by scanning it with a laser beam, his system quickly fuses the whole layer under an oven-like electric or gas heater. The powder outside the part's outline does not solidify because it gets treated in advance with a special liquid. Khoshnevis says his patented approach can polish off each layer in less than 15 seconds. In addition, it does not need a laser, which can cost tens of thousands of dollars.

Prototype Testing and Evaluation Testing allows isolation of the individual parameters, a useful feature if the application involves a complex and varied environment or if the behavior of the prototype is not predictable. Accelerated simulation of in-service conditions is often feasible by applying environmental factors that are most influential in product lifetime, such as stresses, strains, temperature, and humidity fluctuations; sunlight exposure; and attack by solvents. Several years of service can be simulated in the laboratory in just a few days but requires close attention to validity. For example, mechanical stresses can be applied in a shorter amount of time or at higher values than will occur in service, but only if such foreshortening does not invalidate the test. Applying stresses at a greater rate is valid if the increased rate will not cause a different response in the material due to effects such as self-heating or reduced severity of chemical attack. Using higher stresses than the real application may cause creep, crack initiation, or fracture that would not occur at lower stresses over a longer time and must therefore usually not be attempted. Temperature or humidity fluctuations can be accelerated only to the point of maintaining uniform penetration that is likely in the end use environment. If creep or vibration is expected in service, time-temperature superposition may often be applied to accelerate laboratory testing. This technique mathematically predicts the material's response in service, based on laboratory characterization of the material over a

7

9Designs 7 5 5

range of temperatures (but at low strains). The prototype can then be tested at a lower temperature or rate of stress that will occur in service, and the effect of the same stress applied over a much longer time or the effect of vibration at a higher frequency may be predicted. Service testing, or field trial, includes all aspects of the application environment, notably those that may be unforeseen by the designer, and other variables such as the compounding effects of stress and temperature. For example, vibration may cause self-heating (resulting in altered mechanical properties) that was never anticipated by the designer. These same factors also complicate failure analysis, sometimes to the point that laboratory testing is also needed to establish the cause of part failure. If service testing will require weeks (or months) of data gathering, it is best reserved for cases where environmental conditions are unpredictable or failure analysis should be uncomplicated. These techniques are also useful for production proving during the first runs and for failure analysis if the production design fails to perform in the application.

Computer-Aided Designs .....

i

84

.

i

The computer continues to provide the engineer with the means to simplify and more accurately develop a design timewise and costwise. It provides a better understanding of the operating requirements for a product design, resulting in maximizing the design efficiency in meeting product requirements. The computer is able to convert a design into a fabricated product providing a faster manufacturing startup. Other benefits resulting from the computer technology include ease of developing and applying new innovative design ideas; fewer errors in drawings; good communications with the fabricator; improved manufacturing accuracy; and a faster response to market demand. Many of the individual tasks within the overall design process can be performed using a computer. As each of these tasks is made more efficient, the efficiency of the overall process increases as well. The computer is suited to aid the designer by incorporating customer inputs, problem definitions, evaluations, and final product designs. An example is from Composites Design Analysis (CODA), developed by the UK National Physical Laboratory, that is a Windows-based software

756 Reinforced Plastics Handbook

package to aid engineers in selection of materials and designs for RP parts, allowing new materials and prototype products to be developed. The software may be used for various processing technologies, including hand lay-up, injection molding, pultrusion, and autoclaved prepregs. What may be considered a disadvantage of resin transfer molding (RTM) is said to be its restricted visibility, making it impossible to intervene or check for errors arising during injection. The process can be simulated by a computer program developed by TNO Institute for Industrial Technology, Delft, the Netherlands. The program makes it possible to analyze the RTM process and determine the most accurate positioning of reinforcement and resin. The number and position of resin injection points can be selected, eliminating the need for a series of pre-production runs before correct conditions are obtained. Material SA's Cadwind program for filament winding is one of the longest established programs. It uses the strength requirements for the component to calculate the fiber lay-up on the mandrel, automatically generating the part program for any winding machine. It can also predict laminate thickness, part weight, fiber consumption and production time. It can also calculate structures for elbow or T-joints, permitting automatic production of these shapes. Use and positioning of fiber is optimized, with possible cost savings of up to 30%, and 40% reduction in production time. It can calculate any desired winding pattern and generate the corresponding part program for any winding machine. It offers more flexibility with greater user friendliness and a module structure to meet needs of users. A post processor permits conversion of externally calculated or experimentally generated windings into a part program. Wind for Windows has been developed by Delft University of Technology, The Netherlands. It uses a numerical approach to all elements of filament winding simulation and pattern generation, firstly creating a numerical model of the mandrel with a 3-D modeler. This comprises small triangles forming a fully enclosed surface. The pattern generation engine uses information from the surface of the model, with information from the user, to perform a simulation. When the winding pattern has been completed, post processing is used to reformat the data for the winding machine. Computer-aided design (CAD) uses the mathematical and graphicprocessing power of the computer to assist the engineer in the creation, modification, analysis, and display of designs. Many factors have contributed to CAD technology becoming a necessary tool in the engineering world, such as the computer's speed at processing complex

7

Designs 9 757

equations and managing technical databases. CAD combines the characteristics of designer and computer that are best applicable to the design process. There is also the combination of human creativity with computer technology that provides the design efficiency that has made CAD such a popular design tool. CAD is often thought of simply as computeraided drafting and its use as an electronic drawing board is a powerful tool in itself. The functions of a CAD system extend far beyond its ability to represent and manipulate graphics. Geometric modeling, engineering analysis, simulation, and communication of the design information can also be performed using CAD. For many decades CAD has allowed the designer to bypass much of the manual drafting and analysis that was previously required, making the design process flow more smoothly and much more efficiently. It is helpful to understand the general product development process as a step-wise process. However, in today's engineering environment, the steps outlined have become consolidated into a more streamlined approach called concurrent engineering. This approach enables teams to work concurrently by providing common ground for interrelated product development tasks. Product information can be easily communicated among all development processes: design, manufacturing, marketing, management, and supplier networks. Concurrent engineering recognizes that fewer alterations result in less time and money spent in moving from design concept to manufacture and from manufacturing to market. The related processes of computer-aided engineering (CAE), computer-aided manufacturing (CAM), computer-aided assembly (CAA), computeraided testing (CAT), and other computer-aided systems have become integral parts of the concurrent engineering design approach. Design for manufacturing and assembly methods use cross-disciplinary input from a variety of sources (design engineers, manufacturing engineers, materials and equipment suppliers, and shop floor personnel) to facilitate the efficient design of a product that can be manufactured, assembled, and marketed in the shortest possible period of time. Computer-Integrated Manufacturing

CIM is a computer or a system of computers that coordinates different (parts or all) stages of manufacturing through troubleshooting, which will enable the manufacturer to custom design products efficiently and economically. All equipment and processes that have an effect on productivity, quality control, etc. will be monitored and controlled by a

758 Reinforced Plastics Handbook central computer. The CIM addresses different functional aspects of plant operations that have an impact on productivity and quality.

Tolerances Computer programs developed since the 1980s continually improve and have made it possible to aid in modeling the complex interactions of the many processing factors that include RP properties and behaviors, geometry of the part, tool making quality applied to manufacture of dies or molds, and very important the processing conditions and fluctuations inherent in the equipment and materials.

Computers and People Computers have their place but most important is the person involved with proper knowledge in using and understanding its hardware and software in order to operate them efficiently. The computer basically supports rather routine tasks of embodiment and detailed operation rather than the human creative activities of conceptual human operation. Recognize that if the computer can do the job of a designer, fabricator, and others there is no need for these people. The computer is another tool for the designer, fabricator, and others to use. It makes it easier if one is knowledgeable on the computer's software capability in specific areas of interest such as designing simple to complex shapes, product design of combining parts, material data evaluation, mold design, die design, finite element analysis, etc. By using the computer tools properly, the results are a much higher level of product designing and processing that will result in no myths. A variety of useful techniques continue to be available via software that includes: Acrobat'. Software to render the output of any software package into a neutral form, devised by the Adobe Corp., so that it can be viewed without the software that created the output. Notes:. Forms-based e-mail and database software useful to create shared databases over a wide area network and create workflow applications. EDI: Electronic data interchange, a host of formats standardized by various interest groups under ANSI to exchange commercial information of different types among companies who wish to do business with each other electronically.

Web: The Internet de facto standard, consisting of a transport protocol called HM, a document format description standard called HTML, and a variety of graphic and video standards, so that users can access linked multimedia documents placed on Web servers from anywhere

7

9Designs 7 5 9

in the world. Currently, there are many application packages, such as databases and spreadsheets that are readily accessible using the Web interface, without extra work. PDM: Product Data Management Systems that store information about products, their decomposition structure, and revision history, in order to support a company's manufacturing, inventory control, maintenance, and other technical activities. DMS: Document-management systems that perform much the same as PDMS for the more general class of documents occurring in a company. Also enables fast retrieval by indexes, keywords, document types, and even text search. ISS: An information-sharing system that constructs a model of the information lying in different databases, builds gateways to each of them, and provides a single system image to external users who wish to access data from any of the constituent databases.

Examples of different websites that provide important services include: Reinforced Plastics: www.reinforcedplastics.com Elsevier/RP provides information and answers to questions concerning RPs data, latest research, buyer's guide, etc. I B M Patents Website: http://www.patents.IBM.com The IBM Intellectual Property Network (IPN) has evolved into a premier Website for searching, viewing, and analyzing patent documents. The IPN provides you with free access to a wide variety of data collections and patent information. Federal Web Locator: http://www.infoctr.edu/fwl/ The Federal Web Locator is a service provided by the Center for Information Law and Policy and is intended to be the one stop shopping point for federal government information on the World Wide Web. This site is hosted by the Information Center at Chicago-Kent College of Law, Illinois Institute of Technology. M A A C K Business Services:. A Maack & Scheidl Partnership CH-8804 Au/near Zfirich, Switzerland te1:+41-1-781 3040, Fax:+41-1-781 1569, http://www.MBSpolymer.com. Plastics technology and marketing business service, which organizes global conferences, and edits a range of reports and studies, which focus on important worldwide aspects of polymer research, development, production, and end uses. Provides updates on plastic costs, pricing, forecast, supply/demand, and analysis. Identified early in the cycle are trends in production, products and market segments.

760 Reinforced Plastics Handbook

Material Safety Data Sheets (MSDS): http://www.msdssearch.com/ MSDSSEARCH.COM, Inc., is a National MSDS Repository, providing FREE access to over 1,000,000 Material Safety Data Sheets; the largest centralized reference source available on the Internet. MSDSSEARCH.COM is dedicated to providing the most comprehensive single source of information related to the document known as a Material Safety Data Sheet (MSDS). MSDS SEARCH serves as the conduit between users of MSDSs and any reliable supplier. MSDSSEARCH.COM provides access to 350K MSDSs from over 1600 manufacturers, 700K MSDSs from public access databases, links to MSDS software, services, training and product providers, links to Government MSDS information, an MSDS discussion forum where you can ask questions, and supplies MSDSs directly from manufacturers via search engine.

The Canadian Center for Occupational Health and Safety: CCOHS, 250 Main Street East, Hamilton ON L8N 1H6 Canada, tel: 1-800263-8466 (toll free in Canada only)/1-905-572-4400, Fax: 1-905572-4500, http://www.ccohs.ca/products/databases/msds.html. Promotes a safe and healthy working environment by providing information and advice about occupational health and safety.

Protect Designs Five different methods of protecting your design exist in USA. Each is weighed according to its advantages and disadvantages based on specific needs. They are: contracts/other party agrees not to make, use, etc. without designer's permission; 2

copyrights/protection exists upon creation of design; trade dress/protection when design is either inherently distinctive or has become distinctive; utility patents/protects the functional and structural features of a product; and design patents/protect the ornamental appearance of a product without regard to how it functions.

7

9Designs 7 6 1

Acceptable Risks Many risks people are subjected to can cause health problems or death. Precautions should be taken based on what is practical, logical, and useful. However, those involved in laws and regulations, as well as the public and, particularly, the news media, should recognize that there is Acceptable Risk. This is the concept that has developed in connection with toxic substances, food additives, air and water pollution, fire and related environmental concerns, and so on. It can be defined as a level of risk at which a seriously adverse result is highly unlikely to occur but it cannot be proven whether or not there is 100% safety. In these cases, it means living with the reasonable assurance of safety and acceptable uncertainty. This concept will always exist. Note the use of automobiles, aircrafts, boats, lawnmowers, food, medicine, water, and the air we breathe. Practically all elements around us encompass some level of uncertainty. Otherwise, life as we know it would not exist. Many products and environmental factors are not perfect and never will be perfect. The goal is to approach perfection in a zero-risk society. No product is without risk; failure to recognize this factor may put excessive emphasis on achieving an important goal while drawing precious resources away from product development and approval. A major result of this goal is the excessive waste of money that the public either directly or indirectly pays for. The target or goal should be to attain a proper balance between risks and benefit using realistic factors and not the public-political "panic" approach. People are exposed to many risks. Some pose a greater threat than others do. The following data concern the probability over a lifetime of premature death per 100,000 people: 290 hit by a car while being a pedestrian, 200 tobacco smoke, 75 diagnostic X-ray, 75 bicycling, 16 passengers in a car, 7 Miami/2'qew Orleans drinking water, 3 lightning, 3, hurricane, and 2 fire.

Safety Factors A safety factor (SF) or factor of safety (FS) (also called factor of ignorance) is used with plastics or other materials (metals, aluminum, etc.) to provide for the uncertainties associated with any design, particularly when a new product is involved with no direct historical performance record. SF equals ultimate strength/maximum working stress. There are no hard and fast rules to follow in setting a SF. The most basic consideration is the consequences of failure. In addition to the basic uncertainties of graphic design, a designer may also have to consider additional conditions such as:

762 Reinforced Plastics Handbook

1 variations in material property data (data in a table is the average and does not represent the minimum required in a design); 2

variation in material performance;

3

effect of size in stating material strength properties;

4

type of loading (static, dynamic, etc.);

5

effect of process (stress concentrations, residual stress, etc.); and

6

overall concern of human safety.

RP moldings and, particularly, large structures are often required to work in critical conditions, where failure could have serious consequences. It is good practice in all design to include a factor of safety, which should be based on a reliable knowledge of the material and the operating conditions. Much information of value can be obtained from testing both of the materials and then the product in use. For most applications, this is indispensable. It is important also to be practical in testing, recognizing that figures for specimens produced under laboratory conditions may well be significantly better than for actual parts produced under production conditions (Table 7.27). Statistical analysis, using as many test results as possible, can establish the value of the ultimate stress. The maximum working stress (design stress) may be established by an industry code of practice. Failing this, the designer must decide on a value for F (factor of safety F -- ultimate stress/maximum working stress), bearing in mind the following considerations. The SF usually used based on experience is 1.5 to 2.5, as is commonly used with metals. Improper use of a SF usually results in a needless waste of material or even product failure. Designers unfamiliar with plastic products can use the suggested preliminary safety factor guidelines in Table 7.28 that provide for extreme safety; intended for preliminary design analysis only. Low range values represent applications where failure is not critical. The higher values apply where failure is critical. Any product designed with these guidelines in mind should conduct tests on the products themselves to relate the guidelines to actual performance. With more experience, more-appropriate values will be developed targeting to use 1.5 to 2.5. After field service of the preliminary designed products has been obtained, action should be taken to consider reducing your SF in order to reduce costs. Realistic SFs are based on personal (or others) experience. The SFs can be related to the probable consequences of failure. To ensure no failure

7

9Designs 7 6 3

Table 7.2 7 Exampleof setting up safety factors for RPs

Requirement

Service conditions

Safety factor

Nature of loading Minimum value of F

Static short-term loads Static long-term loads Variable/changing loads Repeated loads Fatigue or load-reversal Impact loads- repeated The less-accurate the estimation the higher must be the value of F Where stress analysis is not possible and/or gross approximations are used a higher value of Fmust be applied Reduction in mechanical properties by the environment is possible. This means using a high value of For using a value of ultimate stress in the known environment in any calculation If failure of the material can harm personnel or damage equipment or be in any way serious a high value of F must be used

2 4 4 6 6 10 Use a high value

Accuracy of estimation of working loads Possibility and accuracy of stress analysis Range of properties given by the proposed molding process

Consequences of failure

Use a high value

Use a high value

Use a high value

Table 7.28 Guide for safety factors

Typeof load

Safety factor

Static short-term loads Static long-term loads Repeated loads Variable changing loads Fatigue loads Impact loads

I to 2 to 5 to 4 to 5 to 10 to

2.5 5 15 10 15 15

where a product could be damaging to a person (etc.) prototype tests should be run at their most extreme service operating conditions. For instance, the maximum working load should be applied at the maximum temperature and in the presence of any chemicals that might be encountered in the end use. Impact loading should be applied at the lowest temperature expected, including what occurs during shipping

764 Reinforced Plastics Handbook

and assembly. The effects of variations in plastic lots and manufacturing conditions must also be considered. In product design there has always been the desire to use less of any material, because the result is usually a lower-cost product. On the other side of the issue is the use of more material to provide for a higher design safety factor beyond what is required. Thus, unfortunately, there are designs using more material than needed, particularly when using RPs. It is inexperience in designing with RPs that causes this problem. Many designers lack the knowledge of at least relating a material's performance to the processing variables that directly influence SFs and the amount of an RP to be used. With the flexibility that exists in designing with RPs, there are different approaches that may be used to reduce part weight, such as applying different shapes like internal ribbing, corrugations, sandwich structures, and orienting or prestrctching. A designer sometimes has an opportunity to use a material that provides no problem in the solid-waste stream or to use a design that lets lowercost recycled plastics be used. In fact, blends of virgin (not previously processed) plastics with recycled plastics could permit the meeting of required product performance requirements. This approach has been used for the past century. However, the designer must take into account the possible lower performances that will occur with recycled plastics (Chapter 3 ). The recycled plastic could have a degree of different contaminants that would eliminate its use in certain devices or products, such as in medicine, electronics, and packaging. However, in certain applications there are designs that permit their use such as three-layer cocxtruded, coinjected, or laminated structures having the contaminated plastic as the center layer, isolated by clean plastics around it. Another method of reducing the quantity of plastics that has been used in certain products is to use engineered plastics with higher performance than the lower-cost commodity plastics. When applicable, this approach permits using less material to compensate for its higher cost. With a thinner-walled construction there could also be additional cost savings, since less processing heat, pressure, and fabricating time cycle is required.

Engineering Analysis Overview The following information applies the elements of design theory applicable to reinforced plastics (RPs). Fibrous RPs differs from most other engineering materials because they combine two essentially different materials, fibers and plastic (resin), into a single material. In this, they are somewhat analogous to reinforced concrete that combines concrete and steel rods, but in RPs, the fibers are generally much more evenly distributed throughout the mass and the ratio of fibers to resin is much higher than the ratio of steel to concrete. In their design, it is necessary to take into account the combined action of fiber and resin. Sometimes the combination can be considered to be homogeneous and, therefore, to be similar to engineering materials like metal but in other cases, homogeneity cannot be assumed and it is necessary to take into account the fact that two widely dissimilar materials have been combined into a single unit. In designing these RPs, certain important assumptions are made. The first and most fundamental is that the two materials act together and that the stretching, compression, and twisting of fibers and of resin under load is the same, that is, the strains in fiber and resin are equal. This assumption implies that a good bond exists between fiber and resin to prevent slippage between them and to prevent wrinkling of the fiber. The second major assumption is that the material is elastic, that is, strains are directly proportional to the stresses applied, and when a load is removed, the deformation disappears. More or less implicit in the theory of materials of this type is the assumption that all of the fibers are straight and unstressed or that the initial stresses in the individual fibers are essentially equal. In practice it

766 Reinforced Plastics Handbook is very unlikely that this is true. It is to be expected, therefore, that as the load is increased some fibers reach their breaking points first. As they fail their loads are transferred to other yet unbroken fibers, with the consequence that failure is caused by the successive breaking of fibers rather than by the simultaneous breaking of all of them. The effect is to reduce the overall strength and to reduce the allowable working stresses accordingly, but the design theory is otherwise largely unaffected as long as essentially elastic behavior occurs. The development of higher working stresses is, therefore, largely a question of devising fabrication techniques to make the fibers work together to obtain maximum strength. Design theory shows that the values of a number of elastic constants must be known in addition to the strength properties of the fibers, resin, and their combination. Reasonable assumptions are made in carrying out designs. In the examples used, more or less arbitrary values of elastic constants and strength values have been chosen to illustrate the theory. Any other values could be used. As more experience is gained in the design of these materials, and as more complete experimental data are forthcoming, the design procedures will no doubt be modified. This review can be related to the effects of environment.

Stress-Strain Analyses Any material when stressed stretches or is deformed. If the fiber and resin in RPs are firmly bonded together, the deformation is the same in both. For efficient structural behavior, high strength fibers are employed, but these must be more unyielding than the resin, therefore for a given deformation or strain, a higher stress is developed in the fiber than in the resin. If the stress to strain relationships of fiber and resin are known from their stress-strain diagrams, the stresses developed in each for a given strain can be computed, and their combined action determined.

Basic Design Theories In designing RPs, as reviewed certain important assumptions are made so that two materials act together and the stretching, compression, twisting of fibers and of plastics under load is the same that is, the strains in fiber and plastic are equal. Another assumption is that the RP is elastic, that is, strains are directly proportional to the stress applied, and when a load is removed, the deformation disappears. In engineering terms, the material obeys Hooke's Law (Hooke's law states, it

8

9Engineering Analysis 7 6 7

is the ratio of stress to strain). This assumption is a close approximation to the actual behavior in direct stress below the proportional limit, particularly in tension, where the fibers are stiff and elastic in the Hookean sense and carry essentially all of the stress. The assumption is probably less valid in shear where the resin carries a substantial portion of the stress. The resin may undergo plastic flow leading to creep or to relaxation of stress, especially when stresses are high (Chapter 7). In this analysis, it is assumed that all the glass fibers are straight; however, it is unlikely that this is true, particularly with fabrics. In practice, the load is increased with fibers not necessarily failing at the same time. Values of a number of elastic constants must be known in addition to strength properties of the resins, fibers, and combinations. In this analysis, arbitrary values are used that are low for elastic constants and strength values. Any values can be used; here the theory is illustrated. Any material, when stressed, stretches or is otherwise deformed. If the fiber and plastic are firmly bonded together, the deformation is the same. Since the fiber is more unyielding, a higher stress is developed in the glass than the plastic. If the stress-strain relationships of fiber and plastic are known, the stresses developed in each for a given strain can be computed and their combined action determined. Figure 8.1 stressstrain (S-S) diagrams provide the basis for this analysis; it provides related data such as strengths and modulus.

I

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3.0

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l

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Figure 8.1 Analysis of RPs stress-strain curves (courtesy of Plastics FALLO)

768 Reinforced Plastics Handbook These stress-strain diagrams curve A, typical of glass, shows that stress and strain are very nearly directly proportional to each other to the breaking point. Stiffness, or modulus of elasticity, as measured by the ratio of stress to strain, is high. Curve B represents a hard resin. Stress is directly proportional to strain when both are low, but stress gradually levels off as strain increases. Stiffness, or modulus of elasticity, is much lower than that of glass. The tangent measures it to the curve, usually at the origin. Curve C represents a softer resin intermediate between the hard resin and the very soft plastics. Stress and strain are again directly proportional at low levels, but not when the strains become large. Modulus of elasticity, as measured by the tangent to the curve, is lower than for the hard resin. These stress-strain diagrams may be applied, for example, in the investigation of a rod in which half the total volume is glass fiber and half is resin. If the glass fibers are laid parallel to the axis of the rod, at any cross section, half of the total cross-sectional area is glass and half is resin. If the rod is stretched 0.5%, the glass is stressed at an intensity of 345 MPa (50,000 psi) and the resin, if resin B, at 52 MPa (7500 psi), or if resin C, at 17 MPa (2500 psi). If, for example, the rod has a total cross section of one-half square inch, the glass is one-quarter square inch, and the total stress in the glass is 1/4 times 50,000 or 5,675 kg (12,500 lb). Similarly, the stress in the resin, if resin B, is 850 kg (1875 lb), and in resin C is 280 kg (625 lb). The load required to stretch the rod made with resin B is therefore the sum of the stresses in glass and resin, or 6,526 kg (14,375 lb). Similarly, for a rod utilizing resin C, the load is 5,960 kg (13,125 lb). The average stress on the one-half square inch cross section is therefore 198 MPa (28,750 psi) or 180 MPa (26,250 psi), respectively. An analogous line of reasoning shows that at a strain of 1.25% the stress intensity in the glass is 860 MPa (125,000 psi), and in resins B and C it is 87 and 31 MPa (12,600 and 4,500 psi), respectively. The corresponding loads on rods made with resins B and C are 237 and 223 MPa (34,400 and 32,375 lb), respectively.

Fiber Strength Theories The deformation and strength of filamentary structures subjected to combined loading can be theoretically predicted using experimentally determined intrinsic stiffness and strength of the individual constituent layers. In order to have an integrated material and structure design, the gross properties as functions of the micromechanical parameters represent an important issue on the continuing and expanding use of RPs. It has been established, in both theory and experiment, that four principal

8

Engineering 9 Analysis 769

elastic moduli and three principal strengths govern the deformation and strength of unidirectional fiber RPs. With the aid of a yield condition, the initial failure of filamentary structures can be predicted. After the initial failure, the structure may carry additional loads. An analysis of a partially failed or degraded structure can be used to predict the ultimate deformation and strength. With an understanding of the gross behavior of a filamentary structure, a proper assessment of the mechanical and geometric properties of the constituent materials is possible. In particular, the use of fiber strength, the binding resin matrix, and the interface may be placed in a perspective based on the results of a mathematical analysis. They provide accurate guidelines for the design of RPs. A better understanding exists of the elastic stiffness of filamentary materials than of the strengths. The generalized Hooke's law is usually accepted as the governing equation of the linear elastic deformation of RP materials. The simultaneous or sequential modes of deformation and fracture are difficult to describe from the phenomenological standpoint. In general, a strength theory on one criterion will not be sufficient to cover the entire range of failure modes of RP. In addition, fabrication variables and test methods are also known to introduce uncertainties in strength data that makes the verification of theories more difficult. A macroscopic theory of strength is based on a phenomenological approach. No direct reference to the mode of deformation and fracture is made. Essentially, this approach employs the mathematical theories of elasticity and tries to establish a yield or failure criterion. Among the most popular strength theories are those based on maximum stress, maximum strain, and maximum work. Fiber Geometry on Strengths

Various investigators have developed mathematical means for determining the efficiency of glass-fiber RPs. In order to analyze the effect of fiber geometry on strength, the fundamental mechanics of RP theory is reviewed. Relationships have been derived to relate the load distribution in an RP to the properties of the individual materials. The derivations are based on the following: 1

stress is proportional to the strain in both materials; fiber-resin bond is efficient, so that fiber and resin are strained an equal amount under load; fibers are straight, continuous, and aligned with the axis of the applied load; and

770 Reinforced Plastics Handbook material components have isotropic and homogeneous directional properties (Chapter 7). Stress-Strain" Metal and Plastic An explanation is reviewed regarding a particular distinction between the mechanical behaviors of metals and unreinforced reinforced plastics (URPs). The typical stress/strain curve for metal exhibits a linear elastic region followed by yield at the yield stress, plastic flow, and ultimately failure at the failure stress [reinforced thermosets (RTSs) have similar behavior]. Yield and failure occur at corresponding strains. Thus, yield and failure can be called the critical strains. However, it is easier in many products to restrict factor to a stress analysis alone. By comparison, it may appear unjustified to state that plastic failure criteria are usually defined in terms of critical strain (rather than stress), and, by comparison with metal, going from strain to stress may appear to be a limited analysis. This apparent error depends on recognition of the fact that stresses and strains are not as intimately related for URPs as they are for metals. This action is demonstrated by reviewing stress/ strain curves for typical URPs material. This highlights that stress/strain curves for these types of plastics are not unique, but depend on the loading conditions such as time, frequency, a n d / o r rate. Stress/strain curves obtained at different loading rates for metals would be essentially similar. However, the behavior of URPs can be very different at low- and high rates of testing; there is no unique relationship between stress and strain since this also depends on the loading rate. It is evident from examining curves that characterization of failure through a unique failure strain cannot be valid, in general. However, it can be a good approximation in certain analyses, such as at high rates or under creep conditions. For RPs, the emphases and difficulty in the design analysis depends on the type of RP. For a reinforced thermoplastic (RTP) with short fibers, the viscoelastic behavior of the TP matrix is important. In addition, there may be a significant degree of anisotropy a n d / o r homogeneity due to processing which could further complicate the analysis if the designer does not understand the influence of processing. (Recognize that with RPs, a material is being produced; metals and other materials do not require the designer to manufacture the material.) For RTSs with short fibers, such as bulk molding compounds (BMCs), there may be only a low level of viscoelasticity, anisotropy, and inhomogeneity (Chapter 4). However, these RPs with the TS resin

8

9Engineering Analysis 771

matrices and long fibers can have a high degree of anisotropy that is taken into account in the design analysis. When TPs are reinforced with long fibers, there may be significant anisotropy and viscoelasticity resulting in a possible complex design analysis. Regardless, in all cases, RP failure characteristics may be specified in terms of a critical strain. This requires the design analysis to be performed on the actual or simulated processing condition for stress and strain. Having processing knowledge and experience in related testing is very useful in these types of analyses. Long-fiber RPs can often be tailored to the product requirements; materials design and product design analyses interact strongly. If the product design analysis is statically determined (stresses independent of materials properties) then this analysis is carried out first. The next step is designing the RP to carry the stresses. However, if the analysis is not statically determinate, then the component stresses depend on material isotropy, and material and product design have to be carried out and optimized simultaneously. This is also the case if shape is regarded as one of the variable design parameters. Thus, URPs and RPs design analysis follows the same three factors as that for metals, but there are some differences. In particular, factor is usually more substantial for the materials partly because a full-scale stress/strain/deformation analysis is required and partly because of the need to take account of viscoelasticity, nonhomogeneity, and/or anisotropy directional properties. For long-fiber RPs, the component design analysis may need to contain the associated material design analysis.

Metal Design The mechanical behavior of metals in service can often be assumed to be that of a linear, isotropic, and elastic solid. Thus, design analysis can be based on classical "strength of materials" theory extensively reviewed in textbooks and literature. Practically, results may be used in the form of standard formulae, or design charts for a selected class of applications. Such uses are most appropriate to components of simple geometric shapes for which standard solutions exist, or for more shapes that are complex where they can possibly be used for initial approximate design calculations. For the more complex, and shapes that do not exist, the solution of the applicable elasticity equations may require some form of numerical procedure, such as finite element analysis (FEA) or finite difference analysis (FDA). If design analysis involves frequent consideration of similar problems, then the burden on the designer can be reduced by generating a set of solutions presented as a set of design charts. An alternative is to

772 Reinforced Plastics Handbook

provide a method in the form of a computer program for which the design analyst requires minimal familiarity with the design method. However, in critical situations, there may be no alternative to a detailed FEA with evaluation of the manufactured product to ensure meeting performance requirements. Under appropriate conditions, metal design involves plasticity, creep, and geometric nonlinearity. These topics are treated in standard texts and have been put into computer software. However, such complexities are necessarily modeled in a simple technical format.

Spheres Circumferential load in the wall of all the spheres under internal pressure is equal to the pressure times the internal cross-sectional area, and the hoop stress, using the previous engineering assumption, is found to be: fh = pd/at

where 3~ = circumferential load, p thickness.

=

pressure, d

=

diameter, and t

=

It will readily be seen that no matter which section is chosen, provided the plane of the section passes through the center of the sphere, the condition will be the same, and it can be said that the hoop stress will be the same in all directions based on outside radius (R) and inside radius (r). When it is assumed that: ( R2 - r 2) =

27

~rt

it is determined that for wall thicknesses up to approximately 3 inches, the error is negligible. It can also be determined that the percent of error decreases as the inside radius/thickness ratio r/t increases. Table 8.1 provides size vs. weight of RP spheres. For a sphere with the stresses uniform in all directions, it follows that the fibers require equal orientation in all directions. The problem of orientation resolves itself purely into one of practical application of the fibers. In the cylinder, the fibers are specifically oriented to meet any condition of stressing. The simplest method of doing this is to employ a single helical pattern. Theory shows that this is highly sensitive to variations in the longitudinal hoop-stress ratio and also the accuracy of the angle wound.

8

9Engineering Analysis 7 7 3

Table 8,1 Data for 3000 psi glass fiber-epoxy spheres

Copocity, cubic inches

Outside diometer, inches

Nom in o l weight, pounds

Moxim u m weight, pounds

Overo ll length, inches

5O IO0 2OO 3OO 4OO 5OO 65O 88O 1 070 1 325 1 575 1 8O0 2,500 3,200

51/4

1.50 2.50 4.44 6.25 8.06 9.87 12.56 16.00 20.06 24.50 28.75 32.75 44.81 56.50

1.60 2.63 4.62 6.56 8.48 10.35 13.18 16.80 21.07 25.73 30.15 34.42 47.06 59.32

55/8 615/16 81/2 95/8 109/16 115/16 125/16 133/8 143/8 157/16 161/4 1615/16 187/8

61/2 81/8

91/4 101/8 1015/16 1115/16 131/16 14 151/8 157/8 165/8 181/2 20

207/16

The addition of pure hoop windings to the helix gives a theoretical gain in stability with no loss of strength or efficiency. In order to develop the most satisfactory orientation, the winding is performed so those two different helix angles are used.

Tanks Classical engineering stress analysis shows that hoop stress (stress trying to push out the ends of the tank) is twice that of longitudinal stress. To build a tank of conventional materials (steel, aluminum, etc.) requires the designer to use sufficient materials to resist the hoop stresses that results in unused strength in the longitudinal direction. In RP, however, the designer specifies a laminate that has twice as many fibers in the hoop direction as in the longitudinal direction. An example is a tank 0.9 m (3 ft) in diameter (d) and 1.8 m (6 ft) long with semi-spherical ends. Such a tank's stress (s) calculations (excluding the weight of both the product contained in it, and the support for the tank) are represented by the formulas: 5 = pd/2t for the hoop stress

and"

7 7 4 Reinforced Plastics Handbook 5 = pd/4t

for the end and longitudinal stresses

Tensile stresses are critical in tank design. The designer can assume the pressure (p) in this application will not exceed 100 psi (700 Pa) and selects a safety factor of 5. The stress must be known so that the thickness (t) can be determined. The stress or the strength of the final laminate is derived from the makeup and proportions of the resin, mat, and continuous fibers in the RP material. Representative panels must be made and tested, with the developed tensile stress values then used in the formula Thus, the calculated tank thickness and method of lay-up or construction can be determined based on: th =

p d / 2 s h or t h = p d / 4 s h

where th =

100x3 2x

tl

=

112

x 12

200 x 103

th

5 =

= 0.450 in.

0.225 in. (or the same thickness with half the load or stress)

th = hoop thickness tl =

longitudinal thickness

sl = Sh = safety p = d =

longitudinal stress 20 x 103 psi (140 MPa) factor = 5 100 psi (700 Pa) 3ft(O.9m)

Sh = hoop stress

If the stress values had been developed from a laminate of alternating plies of woven roving and mat, the lay-up plan would include sufficient plies to make 1 cm (0.40 in.) or about four plies of woven roving and three plies of 460 g / m 2 (11/2 oz) mat. However, the laminate would be too strong axially. To achieve a laminate with 2 to 1 hoop to axial strength, one would have to carefully specify the fibers in those two right angle directions, or filament wind the tank so that the vector sum of the helical wraps would give a value of 2 (hoop) and 1 (axial), or wrap of approximately 54 ~ from the axial. Another alternative would be to select a special fabric whose weave is 2 to 1, wrap to fill, and circumferentially wrap the cylindrical sections to the proper thickness, thus getting the required hoop and axial strengths with no extra, unnecessary strength in the axial (longitudinal) direction, as would inevitably be the case with a homogeneous metal tank. As can be seen from the above, the design of RP products, while essentially similar to conventional design, does differ in that the materials

8 Engineering 9 Analysis 775 are combined when the product is manufactured. The RP designer must consider how the load-bearing fibers are placed and ensure that they stay in the proper position during fabrication.

Pipes Thermoplastic Pipes Extensive amount of URP pipe is used worldwide to move different types of liquids, gases, and solids. With the different properties of plastics (such as corrosion resistance, toughness, and strength), pipes can be fabricated to handle practically any type of material. A major and important market for URPs is in producing pipe (tube) for use such as on the ground, underground, in water, and electrical conduits. Figure 8.2 provides a method to determine pipe thickness subjected to uniform internal pressure P using the standard engineered thin-walltube hoop-stress equation. View (a) provides an equation that is approximately accurate for t (d/10). However when the wall thickness increases the error becomes large. It is useful in determining an approximate wall thickness, even when condition t (d/lO) is not met. View (b) provides an equation for the maximum hoop stress that occurs on the surface of the inside wall of the pipe. After the thin-wall stress equation is applied, the thick-wall stress equation can be used to verify the design.

(a)

(b)

HOOP STFI

Figure 8.2

Pipe wall thickness determination based on internal pressure

Pipe's exceptional growth in what was a very competitive market is the result of its outstanding performances to costs (includes handling and installation). The total USA pipe market has been in the order of $5 billion per year. About 10 billion pounds of plastics are consumed with

776 Reinforced Plastics Handbook

72wt% of PVC, 23% HDPE, and others that include LDPE, LLDPE, chlorinated PVC, XLPE (PEX), ABS, and PP. Plastic pipe represents about 30% of the dollar share compared to other materials (iron/steel at 45%, copper at 12%, concrete at 8%, aluminum at 4%, etc.). While any plastic material, irrespective of its chemical composition and character, may be made into pipe or tubing, by far the greatest amount of pipe is made from thermoplastics (TPs) that are adaptable to extrusion processes (Chapter 5). Specialty pipe is made in small amounts from TS materials such as phenolic and polyester, but very large of commercial pipe is made from polyethylene, polyvinyl chloride, acrylonitrile butadiene copolymers, and acrylonitrile butadiene styrene types of alloys. Specialty tubing in relatively small amounts is made of acrylates and acrylate copolymers, as well as other transparent materials (Chapter 3). In general, plastic pipe offers advantages over metal pipe because of its resistance to widely varying conditions of environment, lightweight, relatively low cost, ease and economy of installation, self-insulating characteristics, minimum solid deposit tendency, and/or low frictional losses. They provide internal pressure retention capability. RP Pipes

An important product even though it represents a smaller portion of the market is reinforced TS (RTS) plastic; also called reinforced thermoset resin (RTR) according to ASTM standards. Its major material construction is glass fiber with TS polyester plastic that uses fabricating methods ranging from bag molding to filament winding (Chapter 5). These RTR pipes provide high load performance both internally and externally. There is large diameter filament-wound pipes (RTRs) used and accepted in underground burial because they provide conditions such as corrosion resistance and installation-cost savings. Pipe design equations have been used that specifically provide useful information to meet internal and/or external pressure loads. More recently finite element analysis (FEA) has been used to design RP pipes and other structural products. These design approaches utilize performance standards based upon internal pressures and pipes' stiffness. Other requirements must be met such as longitudinal effects of internal pressure, temperature gradients, and pipe bridging. When compared to steel pipes there are similarities and dissimilarities. They both differ from concrete pipe which is a rigid pipe that cannot tolerate bending or deflection to the same extent as RTR and steel pipe. The following review provides information on the design approach and

8

9Engineering Analysis 7 7 7

results of tests conducted on these type pipes (rigid RTR, rigid steel, and flexible concrete). They were buried in trenches under 25 ft of the same dirt and subjected to actual load testing. Specific pressures varied from installation to installation, but the relationship in the way these pipes react to the same burial condition generally remains constants. As shown in Figure 8.3 the load on the surface of the rigid pipe (concrete) is higher at the crown and is transmitted through the pipe directly to the bed of the trench in which the pipe rests and using some side support. The RTR or steel flexible conduit deflects under covering load of earth. This deflection transfers portions of the load to the surrounding envelope of soil that increases the strength of the flexible conduit. Analyzing the type and consolidation of backfill materials is to be considered an integral part of the design process. Because less of a load on the trench bed occurs the trench requires less bedding bearing strength reduce the installed cost. 26 psi Computed

41 = 54.7% 26

26

4,

14 psi

ilil_Iklllll 12 psi i l ~

~11112 psi

t

4.1 psi

t

14 psi

Figure 8.3 Loading (26 psi) rigid concrete pipe (left)and flexible plastic pipe Steel pipe is considered a homogeneous isotropic material (equally strong in both hoop and longitudinal directions) where RTR is an anisotropic material (different strength in both the hoop and longitudinal directions). These directional behavior results in the modulus of elasticity (E) to be equal in all directions for steel and not equal for RTR (Figure 8.4). The RTR pipe structure is shown in Figure 8.5 where the glass fibers arc filament wounded at a helix angle that is at 55 ~ to 65 ~ to the horizontal to maximize hoop and longitudinal stress efficiency. Glass fiber content is at a minimum of 45wt%. An internal corrosion resistant leak proof barrier liner is usually included that is not included in the stress analysis.

778 Reinforced Plastics Handbook EH

EL=E H EL~ E H

EH

Figure 8.4 Directional modulus of elasticity properties of relatively homogeneous isotropic steel pipe {left)and anisotropic RTR pipe

Resin

External Postcoat

Strength Longitudinal Strength Hoop

Structural

Pipe wall Internal Lin~ Cross Section

Figure 8,5

PrescribedWind Angle

Cross-section of filament wound lay up of the RTR pipe

Required is to design a pipe wall structure of sufficient stiffness and strength to meet the combined loads that the pipe will experience in long time service. One design is a straight wall pipe in which the wall thickness controls the stiffness of the pipe. Another way is to design a rib-wall pipe on which reinforcement ribs of a specific shape and dimension arc wound around the circumference of the pipe at precisely designed intervals. As to be reviewed (RIB section) the advantage of a rib wall pipe is that the wall thickness of the pipe can be reduced (also reducing costs) while maintaining or even increasing its overall strength-

8

9Engineering Analysis 7 7 9

to-weight ratio (Figure 8.6). With difficult underwater installations exist a rib-wall pipe design should be considered. RTR Pipe Wall Structures

Straight Wall

Rib Wall

Figure 8.6 Pipe structure with and without ribs Maximum allowable pipe deflection should be no more than 5% using the Figure 8.7 equation where AX = deflection. This value is the standard of the pipe industry for steel conduit and pipe (AWWA M-11, ASTM, and ASME). Deflection relates to pipe stiffness (El), pipe radius, external loads that will be imposed on the pipe, both the dead load of the dirt overburden as well as the live loads such as wheel and rail traffic, modulus of soil reaction, differential soil stress, bedding shape, and type of backfill.

xo,o

_

dl

Maximum 5% Deflection [AXmax ~ SO/o)

by AWWA M-11, ASTM,and ASME

Figure 8.7

Pipe deflection equation

To meet the designed deflection of no more than 5% the pipe wall structure could be either a straight wall pipe with a thickness of about 1.3 cm (0.50 in.) or a rib wall pipe that provides the same stiffness. It has to be determined if the wall structure selected is of sufficient stiffness to resist the buckling pressures of burial or superimposed longitudinal loads. The ASME Standard of a 4 / 1 safety factor on

780 Reinforced Plastics Handbook

critical buckling is used based on many years of field experience. To calculate the stiffness or wall thickness capable of meeting that design criterion one must know what anticipated external loads would occur (Figure 8.8).

l.e-el

Vmeuum L o a d

Figure 8.8

-" j,

"-~

Confined Media

Soil

Buckling analysis based on conditions such as dead loads, effects of possible flooding, and the vacuum load it is expected to carry

As reviewed the strength of RTR pipe in its longitudinal and hoop directions are not equal. Before a final wall structure can be selected, it is necessary to conduct a combined strain analysis in both the longitudinal and hoop directions of the RTR pipe. This analysis will consider longitudinal direction and the hoop direction, material's allowable strain, thermal contraction strains, internal pressure, and pipe's ability to bridge soft spots in the trench's bedding. These values are determinable through standard ASTM tests such as hydrostatic testing, parallel plate loading, coupon test, and accelerated aging tests (Figure 8.9).

Hydrostatic Testing

Parallel Plate Testing

-I:::::3m

Flexural

Figure 8.9

Coupon Testing

I

Tensile

Schematics of tests using strain gauges to obtain stress-strain curves

Stress-strain (S-S) analysis of the materials provides important information. The tensile S-S curve (Figure 8.10) for steel-pipe material

8

9Engineering Analysis 781

identifies its yield point that is used as the basis in their design. Beyond this static loaded yield, point (Chapter 7) the steel will enter into the range of plastic deformation that would lead to a total collapse of the pipe. The allowable design strain used is about two thirds of the yield point. 120

Stress/Strain Curve Mild Steel Pipe

100 90 80

Stress 70 o x 103 PSI 60

SO 40 30 20

~ *--Oesign Value at 213rd Yield Modulus of Elasticity 30(10)~ PSi

10 F 0

Figure 8.10

1000

2000

3000 4000

6000 8000

10,000

Strain x (10)-6 in./in.

Mild steel's tensile stress-strain curve

RTR pipe designers also use a S-S curve but instead of a yield point, they use the point of first crack (empirical weep point) as shown in Figure 8.11. Either the ASTM hydrostatic or coupon test determines it. The weep point is the point at which the RTR matrix (resin) becomes excessively strained so that minute fractures begin to appear in the structural wall. At this point it is probable that in time even a more 100 90

Stress/Strain Curve

80

RTR Pipe

70 Stress O0 (~ x 10 3 PSI SO

/

40

Hoop

10

,

Normal ~ Dqmlgn Slnlin

Slmin to let Crack or

Empirical Weep Point (0.009 in./in.)

Longltudlrml Dlreotlon /5'000 ~10,000 lS,000 ' ~ . Tmrmkmt Strain Deellln StnDin ~ x (10)-6 in./in.

Figure 8.11 RTR'stensile stress-strain curves

20,000

782 Reinforced Plastics Handbook

elastic liner on the inner wall will be damaged and allow water or other liquid to weep through the wall. Even with this situation, as is the case with the yield point of steel pipe, reaching the weep point is not catastrophic. It will continue to withstand additional load before it reaches the point of ultimate strain and failure. By using a more substantial, stronger liner the weep point will be extended on the S-S curve. The filament-wound pipe weep point is less than 0.009 in./in. The design is at a strain of 0.0018 in./in, providing a 5 to 1 safety factor. For transient design conditions a strain of 0.0030 in./in, is used providing a 3 to 1 safety factor. Stress or strain analysis in the longitudinal and hoop directions is conducted with strain usually used, since it is easily and accurately measured using strain gauges, whereas stresses have to be calculated. From a practical standpoint both the longitudinal and the hoop analysis determine the minimum structural wall thickness of the pipe. However, since the longitudinal strength of RTR pipe is less than it is in the hoop direction, the longitudinal analysis is first conducted that considers the effects of internal pressure, expected temperature gradients, and ability of the pipe to bridge voids in the bedding. Analyzing these factors requires that several equations be superimposed, one on another. All these longitudinal design conditions can be solved simultaneously; the usual approach is to examine each individually. Poisson's ratio can have an influence since a longitudinal load could exist (Chapter 7). The Poisson's effect must be considered when designing long or short length of pipe. This effect occurs when an open-ended cylinder is subjected to internal pressure. As the diameter of the cylinder expands, it also shortens longitudinally. Since in a buffed pipe movement is resisted by the surrounding soil, a tensile load is produced within the pipe. The internal longitudinal pressure load in the pipe is independent of the length of the pipe. Several equations can be used to calculate the result of Poisson's effect on the pipe in the longitudinal direction in terms of stress or strain. Equation provides a solution for a straight run of pipe in terms of strain. However, where there is a change in direction by pipe bends and thrust blocks are eliminated through the use of harness-welded joints, a different analysis is necessary. Longitudinal load imposed on either side of an elbow is high. This increased load is the result of internal pressure, temperature gradient, a n d / o r change in momentum of the fluid. Because of this increased load, the pipe joint and elbow thickness may have to be increased to avoid overstraining. The equation shown in Figure 8.12 calculates the longitudinal strain in pipe at the elbow. The

8

9Engineering Analysis 7 8 3

effects of internal pressure, temperature gradient, and change in momentum of the fluid have been combined into this equation. r

"t=

IF t

Where:

Ft

[1-CosO]

E,A

Ft = Total thrust F~ = Pressure ~ Temperature § Change in momentum 11'd2 P .QpV F: = ~ * O'L,A A : l'fdt

OL ' :

Figure 8.12

89 ATELOC

Equation for an elbow's longitudinal tensile strain

The extent of the tensile forces imposed on the pipe because of cooling is to be determined. Temperature gradient produces the longitudinal tensile load. With an open-ended cylinder cooling, it attempts to shorten longitudinally. The resistance of the surrounding soil then imposes a tensile load. Any temperature change in the surrounding soil or medium that the pipe may be carrying also can produce a tensile load. Engineeringwise the effects of temperature gradient on a pipe can be determined in terms of strain. Longitudinal analysis includes examining bridging if it occurs where the bedding grade's elevation or the trench bed's bearing strength varies, when a pipe projects from a headwall, or in all subaqueous installations. Design of the pipe includes making it strong enough to support the weight of its contents, itself, and its overburden while spanning a void of two pipe diameters (Figure 8.13). Ground Level

J

t

Earth

Figure 8.13

2 diameters

Example of a longitudinal tensile load on pipe

When a pipe provides a support the normal practice is to solve all equations simultaneously, then determine the minimum wall thickness that has strains equal to or less than the allowable design strain. The

784 Reinforced Plastics Handbook

result is obtaining the minimum structural wall thickness. This approach provides the designer with a minimum wall thickness on which to base the ultimate choice of pipe configuration. As an example, there is the situation of the combined longitudinal analysis requiting a minimum of% in. (1.59 cm) wall thickness when the deflection analysis requires a 1/2 in. (1.27 cm) wall, and the buckling analysis requires a 3/4 in. (1.9 cm) wall. As reviewed the thickness was the 3/4 in. wall. However, with the longitudinal analysis a % in. wall is enough to handle the longitudinal strains likely to be encountered. In deciding which wall thickness, or what pipe configuration (straight wall or fibbed wall) is to be used, economic considerations are involved. The designer would most likely choose the 3/4 in. straight wall pipe if the design analysis was complete, but it is not since there still remains strain analysis in the hoop direction. Required is to determine if the combined loads of internal pressure and diametrical bending deflection will exceed the allowable design strain. Figure 8.14 (left) shows deflection Ax with only external load. Deflection with external load and internal pressure is shown in Figure 8.14 (fight).

.kt] l ]'$.1,1 Lt/I III

,

Ax

|1 Ax

'It' ,It,

'9,

Figure 8.14

Jill 11

~

t

"e

11 11

Strain analysis in the hoop direction with different loading conditions

There was a tendency in the past to overlook designing of joints. The performance of the whole piping system is directly related to the performance of the joints rather than just as an internal pressure-seal pipe. Examples of joints are bell-and-spigot joints with an elastomeric seal or weld overlay joints designed with the required stiffness and longitudinal strength (Figure 8.15). The bell type permits rapid assembly of a piping system offering an installation cost advantage. It should be able to rotate at least two degrees without a loss of flexibility. The weld type is used to eliminate the need for costly thrust blocks (Figure 8.16).

8 Engineering 9 Analysis 785

Figure 8,15 Pipe fittings using bell-and-spigot joints

Figure 8,16 External and internal weld joints

Commodity and Custom Pipes Glass reinforced plastic (GRP) piping is the material of choice for handling corrosive fluids and is especially suitable when corrosive external conditions exist. Corrosive external conditions are typically caused by corrosive soils or by chemical fumes. In some cases, corrosive external conditions govern the selection of materials. As an example GRP pipe was used for a project requiring many kilometers of large diameter pipe because of the very corrosive soil conditions. The conveyed fluid for this project was flesh water, which is only mildly corrosive, but the external soil conditions were highly corrosive. GRP pipe was the clear choice in terms of external corrosion resistance, weight, ease of installation and price. GRP pipe can be generally categorized as commodity pipe and custom pipe. Both types of pipe have relative merits and fit into different niches within the GRP pipe market. Commodity pipe is made in select sizes up to about 48 in. (but normally 36 in. is the limit). Custom-engineered pipe can be made in virtually any size. Pipe 12 ft in diameter is not uncommon. Commodity pipe is produced in large quantities and the properties are typically fixed in terms of the reinforcement lay up, the liner thickness, the structural thickness, and the resin system. Commodity pipe is designed to suit the mass production process and issues such as resin type and liner thickness are selected to satisfy the commodity market. Commodity pipe is generally lower in cost than custom pipe due to

786 Reinforced Plastics Handbook

mass production and commodity pipe is often an off the shelf' product, resulting in shorter delivery lead times. Custom pipe is custom engineered and custom fabricated for the particular corrosive environment and mechanical and thermal loading. Essential design variables considered during the design of custom pipe are pressure, vacuum, peak temperature, differential temperature, coefficients of expansion, support span, burial conditions (for underground pipe), liner thickness, and resin system(s). An example of what can happed if the correct pipe is not used relates to a large power plant in the southern part of the USA which some years ago suffered a multi-million dollar loss because commodity GRP pipe had been used without proper attention to the essential design variables listed above. Properly engineered and fabricated custom GRP pipe would have performed very well in this service. In this particular power plant, GRP pipe has been blacklisted, which is unfortunate for the GRP industry as a whole. The engineers at the power plant understand that the failures were not due to the use of GRP but to the use of the incorrect GRP product. However, the company management issued a blanket ban against GRP pipe because of the large monetary loses, preventing the engineering department from specifying GRP pipe of any type. The power plant engineers expressed regret that this had occurred and said it will take years to get the ban lifted. They fully understand that customengineered pipe would have performed successfully for many years. Commodity pipe is typically manufactured either by filament winding or centrifugal casting (Chapter 5). In the case of centrifugal casting, glass fibers are chopped and mixed by various means with resin, and centrifugal force is used to keep the pipe against the inside of the mold until the resin solidifies (TP) or cures (TS). For buried pipe, some manufacturers mix sand into the matrix. Sand is a low cost material that builds up the pipe thickness and reduces cost. Centrifugally cast pipe properties are highly resin dependent due to the short fiber lengths, so the long-term properties are significantly lower than long-term properties of custom-engineered pipe. In addition, the strength and stiffness of short-fiber pipe is more sensitive to temperature. The wall thickness is relatively high because the material strength is relatively low. In the case of sand-filled pipe, mechanical strength is very low but wall thickness high because pipe stiffness is proportional to thickness cubed and linear with modulus. It is important to note there are many ways to do filament winding and the resultant properties can vary greatly. Commodity pipe is typically wound at 5 5 ~ (as measured from the pipe axis). Many have been led to

8

9Engineering Analysis 7 8 7

believe 55 ~ is the optimum wind angle for GRP pipe, but this assertion is a half-truth. An angle of 55 ~ is optimum only for pipe subjected to biaxial pressure and manufactured only with single angle helical filament winding reinforcement. A ring joint pipe with thrust blocks is subjected only to hoop pressure while locked joint capped pipe is subjected to biaxial pressure loading. Other winding methods and reinforcement schemes will result in pipe with significantly improved properties over 55 ~ filament wound pipe. However, for commodity pipe, these superior winding techniques are not practical for mass production. The hoop and axial strengths of 55 ~ pipe are dependent to a large degree on the shear strength of the resin. This explains the large ratio of short term to longterm strengths. Long term burst is typically about one-third the shortterm burst pressure because of the resin dependent properties. Another consideration is that winding at 55 ~ is difficult for larger pipe and relatively slow. The carriage speed required for 55 ~ is about four times faster than required for typical custom-engineered pipe. When the carriage speeds become high, the mandrel speed and material application speeds have to be reduced. Turn-around-zones on larger pipe are problematic at 55 ~ in terms of band slippage and the large thickness. Pipe wound at 55 ~ as compared to 65 ~ will result in 4-5 wt% (of the total material weight) extra waste and 25-30% extra winding time. When pipe is wound at high angles, the reduction in waste and improvements in wind time become even more significant. As reviewed, the mechanical properties of centrifugally molded pipe and 55 ~ filament wound pipe are much more resin dependent than typical custom engineered pipe. With centrifugally cast pipe, the tensile properties are very resin dependent because the fibers are chopped into relatively short lengths. It is subjected to creep and time-loss of mechanical properties. In addition, resin properties drop radically with temperature especially near the glass transition temperature. With 55 ~ filament wound pipe, the mechanical properties are a function of the shear strength and stiffness of the resin. The small angles with respect to the axis create a 'scissor' action between the layers that puts the resin in shear. Like tensile properties, resin shear properties are subject to creep and a loss of strength and stiffness at elevated temperatures. The properties of well-designed custom pipe are much more glass dependent than resin dependent. Glass fibers are not subject to creep and, for temperatures up to 200C (the upper limit for GRP pipe), glass fibers do not lose strength or stiffness. By custom designing the pipe laminate, superior axial strength and stiffness can be achieved. This can be used to advantage to increase

788 Reinforced Plastics Handbook

support spans thus reducing costs associated with pipe supports. Custom-engineered pipe can also be designed to be more tolerant of the localized stresses caused by pipe supports. This can be accomplished by the design of the laminate and by the addition of special reinforcements in support regions. Stiffeners are often a very cost effective way to handle load conditions which cause the pipe to buckle and collapse. Examples are vacuum loading, soil loading and traffic loading. Commodity pipe can rarely, if ever, be purchased with stiffeners. However, custom-engineered pipe can be designed and fabricated with stiffeners, taking advantage of the cost savings and better performance that can be realized with stiffeners. The stiffener laminate, the stiffener size, and the stiffener spacing can all be 'fine tuned' for the most efficient and cost effective design. The corrosion liner in commodity pipe is typically fixed and relatively thin as compared to custom pipe. The corrosion liner of commodity pipe is typically 1.25 mm or less. The corrosion liner of custom pipe is determined by the corrosive environment and is typically 2.5 mm or more. Depending on the performance requirements, some commodity pipe has no corrosion barrier at all. With some exception, commodity pipe is made with epoxy resin. Epoxy, while having good properties for mechanical strength and for the commodity-manufacturing environment, is inferior to vinyl ester in terms of corrosion resistance. Custom-engineered pipe can be made with a wide range of resins, including fire retardant vinyl esters, epoxy vinyl esters, isophthalic polyesters, halogenated polyesters, etc. This allows custom pipe to handle a wide range of chemical services at competitive prices. Dual resin systems are possible with custom pipe but not possible for commodity pipe. For example, vinyl ester can be used for the corrosion liner and a fire retardant vinyl ester can be used for the structure. This optimizes the performance of the pipe. The best mechanical properties are found in properly engineered custom pipe. By using large wind angles and axial unidirectional glass, the long-term hoop and axial strengths are significantly higher than either 55 ~ filament wound or centrifugally cast pipe. In addition, the properties are much more a function of the glass reinforcement than the resin. Hence, the pipe properties are much less a function of time under load, cyclic loading, and temperature. The higher and more stable mechanical properties of properly engineered custom pipe typically results in higher design factors. The design factor for commodity pipe is typically 3.0 for internal pressure while it typically ranges from 7 to 10 for custom engineered pipe. Higher design factors result in pipe with greater

8

9Engineering Analysis 7 8 9

tolerance of upset conditions and pipe with a longer mechanical service life. Combined with the typically greater liner thicknesses, customengineered pipe can be expected to have a much longer and more reliable service life. Typically, the only advantages of commodity pipe over custom-engineered pipe are cost savings and off-the-shelf availability. In some cases, the cost savings are realized with custom engineered and fabricated pipe. For mildly corrosive applications where mechanical loading is not severe, commodity pipe is a good choice. However, for corrosion applications where chemical environment, temperature, temperature differential, coefficient of expansion, resin compatibility, available sizes, etc. are important factors, custom engineered and fabricated pipe is the appropriate choice.

Beams A beam is a bar or structural member subjected to transverse loads that tend to bend it. Any structural members act as a beam if external transverse forces induce bending. A simple beam is a horizontal member that rests on two supports at the ends of the beam. All parts between the supports have free movement in a vertical plane under the influence of vertical loads. A fixed beam, constrained beam, or restrained beam is rigidly fixed at both ends or rigidly fixed at one end and simply supported at the other. A continuous beam is a member resting on more than two supports. A cantilever beam is a member with one end projecting beyond the point of support, free to move in a vertical plane under the influence of vertical loads placed between the free end and the support. When a simple beam bends under its own weight, the plastic or fibers in a plastic on the upper or concave side is shortened with the stress acting on them is compression. The fibers on the under or convex side are lengthened, and the stress acting on them is tension. In addition, shear exists along each cross section, the intensity of which is greatest along the sections at the two supports and zero at the middle section. When a cantilever beam bends under its own weight, the fibers on the upper or convex side are lengthened under tensile stresses. The fibers on the under or concave side are shortened under compressive stresses, the shear is greatest along the section at the support, and zero at the free end. The neutral surface is that horizontal section between the concave and convex surfaces of a loaded beam, where there is no change in the

790 Reinforced Plastics Handbook

length of the fibers and no tensile or compressive stresses acting upon them. The neutral axis is the trace of the neutral surface on any cross section of a beam. The elastic curve of a beam is the curve formed by the intersection of the neutral surface with the side of the beam, it being assumed that the longitudinal stresses on the fibers are within the elastic limit. The reactions, or upward pressures at the points of support, are computed by applying certain conditions necessary for equilibrium of a system of vertical forces in the same plane. They are: 1

the algebraic sum of all vertical forces must equal zero; that is, the sum of the reactions equals the sum of the downward loads, and

2

the algebraic sum of the moments of all the vertical forces must equal zero.

Condition (1) applies to cantilever beams and to simple beams uniformly loaded, or with equal concentrated loads placed at equal distances from the center of the beam. In the cantilever beam, the reaction is the sum of all the vertical forces acting downward, comprising the weight of the beam and the superposed loads. In the simple beam each reaction is equal to one-half the total load, consisting of the weight of the beam and the superposed loads. Condition (2) applies to a simple beam not uniformly loaded. The reactions are computed separately, by determining the moment of the several loads about each support. The sum of the moments of the load around one support is equal to the moment of the reaction of the other support around the first support. The fundamental laws for the stresses at any cross-section of a beam in equilibrium are: 1

sum of the horizontal tensile stresses equal sum of horizontal compressive stresses,

2

resisting shear equal vertical shear, and

3

resisting moment equal bending moment.

Bending moment at any cross-section of a beam is the algebraic sum of the moments of the external forces acting on either side of the section. It is positive when it causes the beam to bend convex downward, hence causing compression in upper fibers and tension in lower fibers of the beam. When the bending moment is determined from the forces that lie to the left of the section, it is positive if they act in a clockwise direction; if determined from forces on the fight side, it is positive if they act in a counterclockwise direction. If the moments of upward

8

Engineering 9 Analysis 791

forces are given positive signs, and the moments of downward forces are given negative signs, the bending moment will always have the correct sign, whether determined from the right or left side. The bending moment should be determined for the side for which the calculation will be the simplest. The deflection of a beam as computed by the ordinary formulas is that due to flexural stresses only. The deflection in honeycomb (Chapter 7 Sandwiches) and short beams due to vertical shear can be high, and should always be checked. Because of the nonuniform distribution of the shear over the cross section of the beam, computing the deflection due to shear by exact methods is difficult. It may be approximated by: Ys = M/AEs

where Ys = deflection, inch, due to shear; M = bending moment, lb-in, at the section where the deflection is calculated; A = area of cross section of beam, square inches; and Es = modulus of elasticity in shear, psi. For a rectangular section, the ratio of deflection due to shear to the deflection due to bending, will be less than 5% if the depth of the beam is less than one-eighth of the length. In designing a beam the procedure is: 1

compute reactions;

2

determine position of the dangerous section and the bending moment at that section;

3

divide the maximum bending moment (lb-in) by the allowable unit stress (psi) to obtain the minimum value of the section modulus; and

4

select a beam section with a section modulus equal to or slightly greater than the section modulus required.

Theories

Theorywise in simple beam bending a number of assumptions must be made. They are 1

the beam is initially straight, unstressed, and symmetrical;

2

its proportional limit is not exceeded;

3

the Young's modulus for the material is the same in both tension and compression; and

792

R e i n f o r c e d Plastics H a n d b o o k

all deflections are small, so that planar cross- sections remain planar before and after bending. The maximum stress occurs at the surface of the beam farthest from the neutral surface, as given by the following equation" o = Mc/I = M/Z

where M = bending moment in in./lbs., c = distance from the neutral axis to the outer surface where the maximum stress occurs in inches, I = moment of inertia in in. 4, and Z = I / c , the section modulus in in. 3. This theoretical approach concerns a geometric property. It is not to be confused with the modulus of the material, which is a material property I, c, Z ( C h a p t e r 7). RP B e a m s

The following exercise concerns glass fiber/TS polyester RP beams. They may be homogeneous, isotropic, or nonisotropic depending on their structure. Mat reinforced plates may be considered essentially isotropic and the usual engineering formulas may be applied. RP/nonisotropic structures require suitable modified formulas but otherwise the procedures for computing bending stresses, stiffness, and bending shear stresses are essentially the same as for isotropic materials. Considering two beams of identical overall dimensions, one isotropic and the other non-isotropic may bring out the differences and similarities. Two such cross-sections are laminated of same materials and laminated of different materials. Two such cross-sections are shown in Figure 8.17, views (a) and (b). For each cross-section, it is necessary to know the stiffness factor EI to compute deflection, the section modulus to compute bending stresses, and the static moments of portions of the cross-section to compute shear stresses. For isotropic materials (a) the neutral axis of a rectangular cross-section is at mid-depths, and the familiar formulas are: Moment of inertia I = bd~ ~ , Stiffness factor = El 12 I

bd 2

Section modulus . . . . y 6

for outermost fiber

6M

Bending stress - o = M

- ~

for outermost fiber

VQ 3V Shear stress~ = ~ = bl 2bd

for maximum shear at the neutral axis

8 b

b

A, E

Aa B3 A4 E4 As Es

Neutral axis

d/~"

9Engineering Analysis 7 9 3

Cb)

1.00~'

,F

i" d3 d4

io

z

"axis

wL ~-

IO"

(d)

. ~[w -

"i

+ "! t

f

(c)

E~ -E, -E,-E,-E~--

Figure 8.1 7

5.0 X 3.0 x 1.OX 5.0 X 3.0 X

I(P psi lOe psi 106 psi 10" psi 106 psi

,9= 25,(X10 ,9= 5,(XM) l ~ i a4 - " 40,000 l ~ i a , = ~,IX)O ~fi

Cross-section of: (a)isotropic; (b) reinforced plastic beam made of layers of different materials (c) reinforced plastic beam having properties indicated, (d) simple beam carrying a load

For RPs the neutral axis is not necessarily at mid-depth of a rectangular section, and it must first be found. Neutral a x i s x =

~--~EiAixi XEiAi

in which Ei, Ai, xi are the modulus of elasticity, cross-sectional area (bdi); and distance from some reference line, such as the bottom of the cross-section, to the center of gravity of any particular layer. Stiffness Factor =

~,EI= Eili

in which Ei and Ii are, for any particular layer, the modulus of elasticity and the moment of inertia about the neutral axis. Bending stress o =

MEvy/EI

in which y is the distance from the neutral axis to any point, and Ey is the modulus of elasticity of the layer at that point. The maximum bending stress does not necessarily occur at the outermost (top or bottom) fiber, as it does in isotropic materials. Shear stress 1: =

VQ'/bEI

in which V is the total shear on the cross-section, i: is the shear stress intensity along some horizontal plane, and Q ' is the weighted statically

794 Reinforced Plastics Handbook

moment EiAiy' about the neutral axis of the portion of the cross-section between the horizontal plane in question and the outer edge (top or bottom) of the cross-section. An example of the foregoing is an RP beam [Figure 8.17 (c)] made up of five layers having three different moduli of elasticity, and three different strengths. The neutral axis, found by applying the neutral axis x equation, is 0.415 in from the bottom of the cross-section. Distances from the neutral axis to the centers of the individual layers are computed, and the stiffness factor E1 calculated. This is found to be: El = ~,Eil i = O. 174 x 106 Ib-in 2

Bending stresses are next computed for the top and bottom edges of the cross-section and for the outer edge of each layer, that is, the edge of each layer farther from the neutral axis. From these, the bending moment the cross-section is capable of carrying can be computed. This is most simply done by applying a bending moment M of one in-lb and computing the unit bending stresses. These unit-bending stresses multiplied by the strengths of the individual layers give a series of calculated resisting moments, the smallest of which is the maximum bending moment the beam is capable of carrying without exceeding the strength of any portion of the cross-section. For a unit bending moment M = 1 in-lb, % = Eyy/EI

Plane

y

Ey

a-a b-b c-c d-d

0.385" 0.185" 0.085" 0.115" 0.315" 0.415"

5 3 1 1 5 3

e-e

f-f

oy/in-lb x x x x x x

106 106 106 106 106 106

o

oy/in-lb

=

M

11.1 psi 40,000/11.1 = 3,600 in-lb 3.19 psi 25,000/3.19 = 7,800 in-lb 0.49 psi 5,000/0.49 = 10,200 in-lb

0.66 psi 5,000/0.66 = 9.07 psi 40,000/9.07 = 7.16 psi 25,000/7.16 =

7,600 in-lb 4,400 in-lb 3,500 in-lb

The smallest value is 3,500 in-lb. If, for example, the beam were a simple beam carrying a load W on a 10-inch span, the bending moment at the center of the span would be WL/4. Setting this equal to 3,500 in-lb gives the load Was 1,400 lb. Shear V is W/2 or 700 lb. Using this value, the shear stress intensity at various horizontal planes in the beam may be computed by means of the shear stress equation. For planes b-b, c-c, and d-d, for example:

8 Plane b-b c-c d_d

9Engineering Analysis 7 9 5

EiAi

y'

Q'

"r

1 { 1 2

0.2 x 5 x 106 0.2 x 5 x 106 +0.1 x 3 x 106

0.285" 0.285} 0.135

0.285 x 106 06 0.326 x 1

1150 psi 1315psi

{ 4 5

0.2 x 5 x 106 +0.1 x 3 x 10 6

0.215} 0.365

06 0.324 x 1

1310 psi

Layers

These would be the critical planes because they represent planes between layers of different materials, and consequently the resin alone would largely carry the stress. The shear stress at the neutral axis would be slightly higher and might or might not represent the critical plane, depending upon the structure of the material in the third layer. As is true of all theory respecting laminates such as these, certain assumptions are implicit in the equations given. One of these is that sections plane before bending remains plane after bending; another is that stress at any point can be found by multiplying strain by the corresponding modulus of elasticity. These assumptions may be reasonably valid in the range of working stresses if these in turn lie on the straightline portions of their stress-strain curves. Modulus of rupture figures calculated on this basis is probably more or less meaningless. Depth and form factors may also enter into the picture. For example, there is evidence to indicate that in rectangular cross-sections the resisting moment is not proportional to the square of the depth but is more nearly proportional to the 1.89 power of the depth.

Ribs When discussion problems in minimizing or increasing load-bearing requirements in wall thickness, ribbing is recommended if it is determined that space exist for adding ribs (Figure 8.18 and Table 8.2). If there is sufficient space, the use of ribs is a practical, economic means of increasing the structural integrity of plastic products without creating thick walls. With thinner walls that use ribs when feasible, a major cost saving could develop since processing them reduces processing time and provides more heat uniformity during processing.

796

Reinforced Plastics Handbook

Table 8.2 Analyzing rib and cross-section designs

Geometry

t'--~

Crosssection area, square inches (mm2)

Mximum stress, psi (mPa)

Maximum deflection, inches (mm)

0.0600 (38.7)

6,800 (46.9)

0.694 (17.6)

0.0615 (39.7)

2,258 (15.6)

0.026 (0.66)

0.1793 (115.7)

2,258 (15.6)

0.026 (0.66)

fi_L

r.~./////~...;i

OBIGIIVAL SECTION 0.060

e~i

..... T,

T

.457

..... L Aluminum E = 10.3 I

=

Zinc • 106

E = 2.0 x

0.0049

El = 5.08 x Area Wt/in

I 104

= 0.283 = 0.446

Plastic-PC

in. oz.

=

0.0254

E1 = 5.08 Area Wt/in

I0

\

E =

I = 0.0424

x I0

4

E1 = 5.08 Area

= 0.489 = 2.01

1.2 x I0 ~

oz

Wt/in

x 10

4

= 0.170 = 0.149

oz

Figure 8.18 Comparing a rib design strength wise and weight wise with other materials

8

9Engineering Analysis 7 9 7

Mthough the use of ribs gives the designer great latitude in efficiently tailoring the structural response of a plastic product, fibbing can result in warping and appearance problems. In general, modifying the process a n d / o r redesigning the product eliminate problems. What would be a very complex operation in sheet metal is an attractive option in plastic because the fabrication method permits incorporation of ribs during processing. Ribbing increases part section modulus with minimum weight increase. Table 8.3 Case 6 is indicative of ribbing's mechanical and weight effectiveness showing how the addition of a 1/4 in. wide x 1/2 in. high rib to a 2 in. x 1/4 in. base section provides an increase of 646% in the moment of inertia while adding only 25% to the weight. In most cases, ribbing can be very simply and easily incorporated with minimal weight addition and without a penalty in molding cost. Table 8,3 Examples of ways in using ribs to increase rigidity and reduce weight

Case

Shape

1

-

2

3

4

5

6

Change i_

[...1_'_ I--- ~'-i ;~ :-~i~ ..... ~_~-'~

' i ~

Base

Moment of Inertia

Increase in I

Increase in Weight

Ratio I Wt.

.0026

Double Height

.0208

7000/0

100O/o

7

Add 1/8" WX 1/4" H Rib

.0048

850/0

6.25%

14

Add 1/4" wx 1/4" H Rib

.0064

146O/o

12.5O/o

12

.0118

354%

12.5%

28

.0194

6460/0

250/0

26

Add 1/8" WX 1/2" H Rib

Add 1/4" wx 1/2" H Rib

Handbooks reviewing Stress and Deflections in Beams and Moments of Inertia provide information such as the moment of inertia and

798 Reinforced Plastics Handbook Table 8,4 Structural shapes {ribs, etc.) processed by different methods {courtesy of Owens Corning Fiberglas) Compression molding Sheet Bulk molding molding Preform compound compound molding __

tt

Minimum inside radius, in. (ram)

n

Injection molding (thermoplastics)

Cold press molding

I a

i n

41#

Spray-up and hand lay-up

(1.59)

(1.59)

(3.18)

(1.59)

(6.35)

(6.35)

Yes

Yes

Yes

~s

No

Large

Trimmed in mold

Yes

Yes

~s

No

Yes

No

Core pull & slides

Yes

Yes

No

~s

No

No

Undercuts

Yes

Yes

No

Yes

No

Yes

Molded-in holes

Minimum recommended draft, in./'

Parallel ~

~

~

~/Perpendk:ular

88 to 6" (6.35-152 mm) depth: 1~ to 3" 6" (152 mm) depth and over:.3~ or as required

Minimum practical thickness, in. (mm)

0.05~' (1.3)

Maximum practical thickness, in. (mm)

(25.4)

Normal thickness variation,in.(mm)

Maximum thickness buildup, heavy buildup and increased cycle

o.06e' (1_5)

0.03~' (0.76)

0.35(0.89)

0.08~' (2.0)

0.06~' (1.5)

(25.4)

1"

0.250' (6.35)

0.500' (12.7)

0_500"

(12.7)

No limit

~:0.005

~-0.005

~:0.008

~:o.oos

4-0.01~,

~.oa(y'

(4=0.1)

(4-0.1)

(4=0.2)

(4-0.1)

(+0.25)

(4=0.51)

2-to-1

As req'd.

2-to-1

As req'd.

I"

As req'd. As req'd.

max.

max.

Corrugated sections

~s

~s

~s

~s

Yes

Yes

Metal inserts

Yes

Yes

Not recommended

Yes

No

Yes

Bosses

Yes

Yes

Yes

Yes

Not recommended

Yes

..Ribs

As req'd.

Yes

Not

Yes

Molded-in labels

~s

~s

~s

Raised numbers

~s

~s

Finished surfaces (reproduces mold surface)

Two

Two

Not

recommended

Yes

No

~s

~s

~s

~s

~s

~s

Two

Two

Two

One

recommended

8

9Engineering Analysis 7 9 9

resistance to deflection that expresses the resistance to stress by the section modulus. By finding a cross section with the two equivalent factors, one ensures equal or better performance. The moment of inertia can be changed substantially by adding ribs and other shapes such as gussets as well as their combinations. There are available basic engineering rib-design guidelines. The most general approach is to make the rib thickness at its base minimum to one-half the adjacent wall's thickness. With ribs opposite appearance areas, the width should be kept as thin as possible. In areas where structure is more important than appearance, or with very low shrinkage materials, ribs are often 75% or even 100% of the outside wall's thickness. A goal in rib design is to prevent the formation of a heavy mass of material that can result in a sink, void, distortion, long cycle time, or any combination of these problems. Calculations for engineered proportions/locations of ribs and their cross-sectional shapes are available so that no additional plastic is used. Table 8.4 provides examples of different shapes, including fibbing, applicable to processing RPs. Over designing with more plastics then required could promote high stresses affecting the parts loading capacity. Lengthy equations for the moment of inertia and for deflection and stress are normally required to determine the effect of ribs on stress. There are also nondimensional curves developed to allow quick determination of proper rib proportions and a corresponding program for a pocket calculator or computer will allow for obtaining greater precision when required.

Reinforced Foamed Plastic Frequently cases arise in which ribs are used to reinforce plastic (RP) plates such as in tanks, boat hulls, bridges, floors, etc. The design of ribbed plates such as these is somewhat analogous to reinforced concrete and T-beam design. In view (a) of Figure 8.19, for example, a construction is shown consisting of a plate composed of balanced fabric RP 0.15 in. thick and mat RP 0.05 in. thick, combined with a rib, making a structure whose overall depth is 1.500 in. The rib is formed of a cellular material such as foamed plastic, plus a cluster of resin-bonded parallel fibers such as roving, at the bottom. The mat is carried around the rib and serves to tie the rib and plate together. The plate and rib form a T-beam. The principal design problem is to determine how much of the plate can be considered to be acting as a

800

Reinforced Plastics Handbook

0:!:r

,.,po-o

/

"l ! ~ ! /Lo.eo'Jl

0.05 "--,1 I -

'*l

.

r 9

~, ~

9

"-"'7_ 0.20"

J. . . .

_.

~-;,~ ^..

T-

kO'

5

:

o,,,.

~ t| ,,I / 1.on5"1 / I .

.....

2 39 3 o ~

, ~ .

_~

.

I

Strain

d;,,,;~.,io,

(b) E I =3

0.0.5"

/-"

"

t

....

/

A!

-11~

;o:___.1 o.,,,. (-) "

.

~ ~J

-

/,

,

:;

~

.

,

|

r 1

179

J

.285

i

1

1'

50.000 psi

s,,.. (c) d;slribution 0"! = 2 0 . 0 0 0

psi

(T2 =

psi

5,000 psi

0":3 = 50,000 Psi

A 2 = 4.2 x 0.05 = 0.21 in. 2 E 2 = 1 x 10 6

.

,

~ i

5 x 0.15 = 0.75 ;n. 2 x 10 6

I---

fill,,

psi

A:I = 0.2 x b.8 = 0 . 1 6

in. 2

E 3 = $ x 10 6 psi

Figure 8 . 1 9

Cross-section

o f a rib a p p l i e d

to a plate

flange with the rib, that is, the magnitude of b in Figure 8.19(a). For purposes of illustration, b is taken as 5 in. If the T-beam is loaded in bending so as to induce compression at the top and tension at the bottom, the balanced fabric and the mat will be in compression at the top, and the roving and mat will be in tension at the bottom. Because the roving is much stronger than the mat, it is evident that the mat adjacent to it will break before the roving reaches its maximum stress. That is if the roving were stressed 50,000 psi the adjacent mat would be stressed 10,000 psi, which is double its strength. Consequently, in finding the neutral axis and computing the strength of the crosssection, the mat is neglected on the tension side. Above the neutral axis the mat is in compression, but in order to simplify the computations, only the mat in the flange of the T is considered. The foamed plastic has such a low modulus of elasticity and such low strength that it contributes little to either the stiffness or the bending strength of the T beam. It must, however, be stiff enough to prevent buckling or wrinkling of the mat or the roving. The active elements of the T-beam are therefore as shown in Figure 8.19(b). The flange consists of balanced fabric 5.000 in. wide and 0.150 in. thick plus mat 4.200 in. wide and 0.050 in. thick. The web

8

9E n g i n e e r i n g Analysis 8 0 1

consists of the bundle of roving 0.800 in. wide and 0.200 in. thick. By the application of the appropriate equation, the neutral axis is found to be 1.105 in. from the bottom, or 1.055 in. above the lower edge of the roving. The basic assumptions discussed in the introduction imply that when this beam is bent, strains at any point in both tension and compression are proportional to the distance from the neutral axis, and that stress is equal to strain multiplied by modulus of elasticity. If, for example, the stress in the lower-most roving fiber is 50,000 psi, the stress in the topmost fiber of the flange is 11,250 psi. Similarly, the stresses in the upper edge of the bundle of rovings, at the lower edge of the balanced fabric, and at the upper and lower edges of the balanced fabric, and at the upper and lower edges of the mat in the flange are as shown in Figure 8.19(c). These are all less than the corresponding values of c% ~2, and ~3 listed. The internal resisting moment, or resistance to outside bending forces, can be found by computing the total resultant compression C1 in the balanced fabric, total resultant compression C2 in the mat, finding the distances 12/1 and/2/2 between the lines of action of these two resultants and the line of action of the total resultant tension T in the roving, computing the values C1/2/1 and C2lZ12,and adding. Resultant C1 acts at the centroid of the trapezoidal stress area la, resultant C2 at the centroid of area 2a, and resultant T at the centroid of area 3a. Solving for these centroids, the distance /5/1 is found to be 1.285 in. and distance 12/2is 1.179 in. These are the internal moment arms of the two resultant compressive forces C1 and C2. C1

[(11250 + 7000)/2][5.000

=

C2 = [(2330 + 1850)/2][4.200

x 0.150]

=

x 0.05]

=

Total C =

6840 Ib 440 Ib 7280

A check on the accuracy of the computations is afforded by the fact that Tmust equal C. T = [(40,600 + 50,000)12][0.800

x 0.200]

= 7250 Ib

The initial resisting moment is Cll211+ C2~2: Cl1~ 1 = C202

=

6840 x 1.285 = 8790 in-lb 440 x 1.179 = 520

Mres =

9310 in-lb

Evidently, if the mat in the flange had been left out of the computation (C2E12), the error in the calculated result would have been approximately 5 percent. Omitting the mat in the rib between the flange and the neutral axis affected the result much less.

802

Reinforced Plastics Handbook

If a shear force is imposed on the rib, two critical planes of internal shear stress occur, one at the neutral axis and one at the plane between the mat and the fabric in the flange. Shear stresses are computed, -~.=

Q! bEI

For example, suppose the T-beam is 30 in. long (L) and carries a uniformly distributed load W. Then M = wL/8 = 9310 in-lb and 147= 2500 lb. The maximum shear Vis half the total load or 1250 lb. At the neutral axis the statistical moment Q ' is the weighted moment of the flange or of the roving about the neutral axis; El, is the stiffness factor of flange plus roving; and b is the total thickness of the mat at the neutral axis plus the effective thickness of the cellular filler. This effective thickness may be computed in accordance with the principles set forth on combined action. If, for example, the shear modulus of the cellular core is i/is the shear modulus of the mat-reinforced material, the effective width of the core is 0 . 8 / 1 5 or 0.053 in. The total effective width of the mat and the care at the neutral axis is therefore 0.05 + 0.05 + 0.053 = 0 . 1 53 in. The computed value of Q ' is 0.725 x 106 lb-in, and the value of El is 0.968 x 106 psi. The shear stress intensity in the mat at the neutral axis is: ~rm =

1250 x 0.725 0.153 x 0.968

= 6100

psi

The shear stress i n t e n s i t y in the cellular core is

Tc = 6100/15 = 410 psi

If either ~7~ or T~ is excessive it is necessary to increase the rib thickness at the neutral axis, probably by increasing the thickness of the mat. Properties of the cellular core may not be known well enough or may be too low to warrant inclusion with the mat in calculating shear. If the core is not included, the thiclcness at the neutral axis is that of the mat alone, or 0.10 in. The shear stress Vm then becomes 9400 psi instead of 6100 psi. At the interface between mat and fabric in the flange of the T-beam, the value of Q" is that of the fabric alone. This is found to be 0.720 x 106 psi. The width b is 4.2 in. (neglecting the width of the cellular core). Therefore: ~: =

1250 x 0.720 4.2 x 0.968

= 220

psi

8

9Engineering Analysis 8 0 3

In all probability the shear stress intensity is actually higher adjacent to the rib, and lower near the outer ends of the flange, but in any event it is not likely to be excessive.

Cylinders and Ribs Plastics provides an easy fabricating means to producing cylindrical monocoque constructions without and with ribs such as has been done in different applications that include toys and pipes to automotive bodies, motor trucks, railroad cars, aircraft fuselages and wings, and houses. Its construction is one in which the outer coveting "skin" carries all or a major part of the stresses. The structure can integrate its body and chassis into a single structure. Unreinforced a n d / o r RPs are used. Consider a cylinder (pipe) of inside radius r, outside radius R, and length L containing a fluid under pressure p. The circumferential or hoopwise load in the wall (t = thickness) is proportional to the pressure times radius = pr, and the hoop stress: fh = h o o p w i s e l o a d / c r o s s s e c t i o n a l area =

pr/t or

=

pd/2t

similarly, the longitudinal stress:

fl = pd/4t assuming

Jr ( R 2 - r 2) -

27Jrrt for a thin-walled tube.

This condition of the hoop stress being twice the longitudinal stress is normal for a cylinder under internal pressure forces only. The load in pounds acts on the tube at a distance from one end and a bending moment M is introduced. This produces a bending stress in the wall of the cylinder of:

f6= My/I where y = R and I= moment of inertia. For a cylinder with outside diameter (D) and inside diameter (d): l= ~ (04- d4)/64 in. 4

This stress must then be considered in addition to the longitudinal stress already presented because of internal pressure. If the end closures are in the form of flat plates, bending stresses due to the internal pressure are introduced as:

Fb =

1.25

(pr2/tf)

where te = thickness of end.

804 Reinforced Plastics Handbook

This necessitates the wall of a flat disc-type end being extremely thick compared with a hemispherical end which is found to be the most efficient shape where the stress in the wall is"

pd/4t Figure 8.20 compares the thicknesses and corresponding volumes of the two types of ends for varying values of r (assuming p = 2,000 psi and ultimate stress in the wall material of 100,000 psi). 1.8

1.6

------

, Flat end Hemispherical end

400

1.4 523 cu. in.

300

~, 1.2

.c u c

.c u

.c_.

.u

1.0

.o u

8.2 cu. in.

c

.u_ N 0.8

2OO E

0.6 125.8 cu. in. 0.4

/ 0.2

0

2

4

/

/

/

/

I00

/

2 cu. in.

6 8 Radius, inches

10

12

F i g u r e 8 . 2 0 Cylinder comparison of thickness for a flat end and a hemispherical end

The volume of the flat end is found to be approximately four times the volume of the hemispherical end for any given radius of tube, resulting in increased weight and material cost. Other end shapes such as ellipse will have a volume of weight somewhere between the two, depending on the actual shape chosen.

Plates Methods for the design analysis in the past for plastics were base on models of material behavior relevant to traditional metals, as for

8

9Engineering Analysis 8 0 5

example elasticity and plastic yield. These principles were embodied in design formulas, design sheets and charts, and in the modern techniques such as those of computer-aided designs (CAD) using finite element analysis (FEA). Design analyst was required only to supply appropriate elastic or plastic constants for the material, and not question the validity of the design methods. Traditional design analysis is thus based on accepted methods and familiar materials, and as a result many designers have little, if any, experience with such other materials as plastics (URPs or RPs), wood, and glass. Using this approach it is both tempting and common practice for certain designers to treat plastics as though they were traditional materials such as steel and to apply familiar design methods with what seem appropriate materials constants. It must be admitted that this pragmatic approach does often yield acceptable results. However, it should also be recognized that the mechanical characteristics of plastics are different from those of metals, and the validity of this pragmatic approach is often fortuitous and usually uncertain. It would be more acceptable for the design analysis to be based on methods developed specifically for the materials, but this action will require the designer of metals to accept new ideas. Obviously, this acceptance becomes easier to the degree that the newer methods are presented as far as possible in the form of limitations or modifications to the existing methods discussed in this book. Table 8.5 provides examples of formulas for flat plates. In this table all dimensions are in inches and all logarithms are to the base e (log~ x = 2.3026 lOgl0 x). Symbols are identified as follows-W = total applied load, lb; w = unit applied load, psi; t = thickness of plate, in.; o = stress at plate surface, psi; y = vertical deflection of plate from original position, in.; E = modulus of elasticity, psi; m = reciprocal of Poisson's ratio; g = any given point on the surface of plate; r = distance of q from the center of a circular plate. Positive sign for o refers to tension at upper surface and equal compression at lower surface; negative o is the reverse condition. Positive sign for y concerns upward deflection, negative y is downward deflection, Subscripts r, t, a, and b for o refer to radial direction, tangential direction, dimension direction (a), and dimensional direction (b), respectively. Based on the usual data on metals, they are much stiffer and stronger than plastics. This initial evaluation could eliminate the use of plastics in many potential applications, but in practice it is recognized by those familiar with the behavior of plastics that it is the stiffness and strength of the product that is important, not its material properties.

806 Reinforced Plastics Handbook

Table 8,5

Examples of handbook's stress and deflection engineering formulas for flat plates

~'~rlf~ll OF L O A D

FORMULAS

FOR 8TRF..88 AND D,qn,zenoN

&~D SUPPORT , ,,,

Outer edges flied. At q, r < ro: Uniform load over eoncentric circular arm ofradius ro.

3W

cri --" -- ~

[

,IV [ ( = . l . i )

~lW(mI - I) " -16rEtail ''''-'T"

i

-

a +(re+l)

r~

lo a + ( m + l ) r~ ki

E

--

,']

(3re+l)

ro' r'] ~ -- ( - "1- 3) 4---toz

(8r I + 4tol) log a _ 2rZroz + . _ _ 3rol ro ~ a roi

*'

l

At q, r > re: W - u.wr/

" , = - ~ - ~ ,iW E (m+l) l ~ -ai+ ( m §- 2 4 7mro' u l - - - ~ - ~ ,w

At center: rr " or/-- -- ~ 3W rL

3W(ms - !)

max llt = -- ~ 16rSm~

Uniform load on oo~me~fzi 9circular r i ~ of radius ro.

At l, r < ro:

,,[

rr=~i=--~ I

Ill

re

ro'

]

~d

,it I + ~ 0 1 -J

-- max ~r when ro < 0.588a

_ ~o t ]

)]

,o, (re+l)( 21Og--ro4--~--I =maxawhenr
., _ _ ~3w [(.+

ra

(m 4- l)'log o_.. 4. (m 4- I) r~ E ~ l -- 4roi log a ro

]

2r~ro ai i

(&rt 4- 41"ol) leg a,

ro

to'

L. ' (I + roi~a./ - 3.(.'-2.,.~, 1) F~ -~. (a i - r l) - ( rl + re l) log a_ + ( ri - ro')]

At q, r > re:

ffi

leg-a+(m ~ 4 - 1 )- ~ ',o' i - -I ( m - -rI ) ~

E (m+l)

3W(mi _ I ) [ ~ i i &rlm~ l

i---

r

,) ( 2 ~ 7= +,o'~ ~i/+("-

r~ - ( m - I )

"-~L(m+i)

,. _

,o'

,,<., -,.,.~_.____~,[ >~' (,

~.]

i)-~-

r~ - 2]

+ -~'~
;]

At center:

3 w ( m. i -"l I) [ ~ (ai - r~ - r~ l~

~At inner edge:

3w [.~2(=+ t) tog a~ +(m - t)]

ported. Uniform eden. Y'--

concenirio ~,lenear outer edge. Uniform k i d i l o i i concentric cirde heir inner

ed~

*M inner ed~:

3W(~s - I) ~rEmil I

,---

[(a2 - bt)(3m+ I) + -

(re+l)

'

-

~l~'('+') ( l~i ;)']

(m--I)(a i-b

l)

--

8 Outer edges tixecl. At center: 3W(m + I) Uniform load over Or = fit =' -8z.l~ t entire eurfae~ At g: W = wwa ~ fit" " ~ - ~3w

EOm+

-3W(m t;I = ' ' ' ' 16,rEmtt --''---~--

max It " --

l)~_

9Engineering Analysis 807

3W(m s -- l)a I I&rBmSt I

3w E<,,,+$) ~_ c,,,+ i) ]

(m+ n)]

1) I-(a 2 - r")= -]

L a'" J

At q, r < r0: Outer edges sup ~ r t e & Uniform to' -- (3m -l- I) r ' ~ ~r = -- ~3W E m -[- (m -!- I) log aro---- (m -- I) ~-~ load over concentric circular area of radius ro. a - (m - I) ~-~ to' - (m + 3) 4-ro r' ~ 3 . , = - ~ 3 w E m + (m + 1) log-to r' a 2(m -- I)ro2(a * -- r ~) 4a ~ -- 5to ~ -I- --- -- (Sr~ ~- 4to 2) log -- -ro t ro (m + I)a ~ 8m(a= - r t) "]

3W(m ~ -- i) It = - - ' -I~rEm~t ''--T"

At q, r > ro: 3W [

<,r - - ~--x~ i

W = wnr0J

at----~ r(~ r o

It

-

--

(m

3iV [

a ro t ro2"] -t- I) log-r - (m - !) ~a-i + (m - I) ~-~.j

a ro t (m--l)-I-(m-t-I)log-r--(m--I)~--(m--

3W(m 2 - l) E(12m -F 4)(a= - r t) " -I&rEm2t -----T -m-+ i

ro 2-] I)~r=.j

2(m - I)ro=(a= - r 2) --

( m -I-

l)a t

-- (Srt + 4ret) log a ] At center: max.,

=.,

= - ~ -3W ~

E m + (m + I) log a_ _ (m - 1) ~rot'] -tj ro

3]V(m t - !)E(12~n 4-4)a t a__ . - ( 7 . : + 3)ro t ' ] max It ffi -- ' ' -16~rEmtt ---'--F ---t- ] -- 4to: log re m -t- 1 _! CxP.cox~R F ~ T P~Tr.s Outer edges s u p

ported. Uniform load on concentric

cireulsr r i ~

At q, r < r0: max ~ ffi ~, - - ~

~r

[~

a (m - l) + (~ + ,) log ~o

(m_

|)r0']

of

radius to. ~'--

3W(m 2 - I) [ ( 3 m + I)(a 2 - r ~) _ (r ~ + ro~) log a + (r= - ro 2) " -2- z' 'E- 'm' ~~' 2(m + I) ro (m -- i)ro2(a 2 -- r 2) 1 2(m -~" I)a 2 .]

At q, 9 > ro: 3W [

r %

(m-l-I)

9

log--]--(m--r

ro ~

3W [ a fi!-- - - ~ - ~ ( m - - l)-~-(m-J-I) | o g - - - ( m - - r

11 =

3~(.'

- ,) [ o .

" - 2rEm=t'~'-"-" ~

ro 2-]

I) 2r2 - - (m -- I) ~ - ~ . j

ro2

I)~--

+ ,)c.' - .') _ , . , + . o . ) , o ~

~ ' n ~ "1)

ro 2"] ( m - - I) ~--~j ~

r --

(- - ,).o'(.' -

2(m -t- I)a s

~]

The proper approach is to consider the application in which a material is used such as in panels with identical dimensions with the service requirements of stiffness and strength in flexure. Their flexural stiffnesses and strengths depend directly on the respective material's modulus and strength. Other factors arc similar such as no significantly different Poisson ratios. The different panel properties relative to stiffness and strength arc shown in Figure 8.21. The metal panels arc stiffer and stronger than the plastic ones because the panels with equal dimensions that use equal volumes of materials.

808

Reinforced Plastics Handbook

Steel

A 200Aiuminium r ~ ~ E I ~

GRP

e,e

z

oLIJ

400

E

2oo

100

eq

z

~_

Figure 8.21 Open bar illustrations represent stiffness and shaded illustrations represent strength with panels having the same dimensions

By using the lower densities of plastics, it allows them to be used in thicker sections than metals. This approach significantly influences the panel's stiffnesses and strengths. With equal weights and therefore different thickness (t) the panels are loaded in flexure. Their stiffnesses depend on (Et 3) and their strength on (o~2) where E and o are the material's modulus and its strength. For panels of equal weight their relative stiffnesses are governed by (E/s s) and their relative strengths by (c~/s2) where s denotes specific gravity. As shown in Figure 8.22, the plastics now are much more favorable. Thus the designer has the opportunity to balance out the requirements for stiffness, strength, and weight saving.

GRP E 4

e,q

z O WI

A|urntnlum

e,t

.~~ PP

v

,,'n

--

lOO

E

50

~'

2

Figure 8.22 Open bar illustrations represent stiffness and shaded illustrations represent strength with panels having the equal weights.

Recognize that it is easy to misinterpret property data and not properly analyze the merits of plastics. No general conclusions should be drawn on the relative merits of various materials based on this description alone. In comparing materials a designer can easily obtain different useful data. As an example the GRP panel has 2.4 times the thickness of a steel panel for the same flexural stiffness. It has 3.6 times its flexural strength and only half its weight. The tensile strength of the GRP panel would be 50% greater than that of the steel panel, but its tensile stiffness is only 17% that of the steel panel.

8

9Engineering Analysis 8 0 9

Similar remarks could be made with respect to various materials' costs and energy contents, which can also be specified per unit of volume or weight. General statements about energy content or cost per unit of stiffness or strength, as well as other factors, should be treated with caution and applied only where relevant. If these factors are to be treated properly, they too must relate to final product values that include the method of fabrication, expected lifetime, repair record, and in-service use.

RP Isotropic Plates Fibrous reinforced plates, flat or curved, is commonly made with mat, fabrics, and parallel filaments, either alone or in combination. Mat is usually used for good strength at minimum cost, fabrics for high strength, and parallel filaments for maximum strength in some particular direction. Because the fibers in mat are randomly oriented, mat-reinforced materials have essentially the same strength and elastic properties in all directions in the plane of the plate, that is, they are essentially isotropic in the plane. Consequently, the usual engineering theories and design methods employed for isotropic engineering materials may be applied. It is only necessary to know strength, modulus of elasticity, shearing modulus, and Poisson's ratio of the combined mat and resin. These can be obtained from standard stress-strain measurements made on specimens of the particular combination of fiber and plastic under consideration.

RP Non-lsotropic Plates In fabric and roving-reinforced materials, the strength and elastic properties are different in different directions; they are not isotropic. The usually engineering equations must be modified, because fabrics are woven with yams at right angles (warp and fill directions), a single layer of fabric has two major directions that are longitudinal (warp) and transverse (fill) at right angles to each other. This orthotropic structure can also be called aeolotropic (fight-angled directions). Parallel strands of fiber, as in a single layer of roving or unidirectional plates, are also orthotropic with the two principle axes at right-angles. Multi-layer plates, in which layers of fabric or of rovings are laid-up parallel or perpendicular to each other are also orthotropic. If the same number of strands or yams is found in each principal direction (balanced construction), the strength and elastic properties are the same in those directions but not at the intermediate angles. If they are different in the

810

Reinforced

Plastics Handbook

two principal directions (unbalanced construction), the strength and elastic properties are different in those directions as well as at all intermediate angles. In the foregoing review the direction perpendicular to the plane of the plate has been neglected because the plate is assumed thin and the stresses are assumed to be applied in the plane of the plate rather than perpendicular to it. This assumption, which considerably simplifies the theory, carries through all of the following review. However, it is true that properties perpendicular to the plane of the plate are undoubtedly different than in the plane, and in thick plates this difference has to be taken into account, particularly when stresses are not planar. This summation is not true if 3-D fabrics are used. For isotropic materials, such as mat RPs, if E is the modulus in any direction, the E1 at any angle to this direction is the same, so the ratio is:

El~E= unity Poisson's ratio v is similarly a constant in all directions and the shearing modulus (G) is: G= EI2 x (1 +v)

If v, for example, is 0.3, G/E = 0.385 at all angles. These relations are shown in Figure 8.23. ,,,

I

I

I

I

i

I

I

I

70

80

,

I

I

,

1.00 0.90 - 0.80-0.70 - 0.60-0.50 -

1

G/E =

0.40-

2(1+u)' It

0.30 0.20 0.10 0

0

I

10

I

20

I

30

I

40

I,

50

!

60

I

!

!

90

!

100

Degrees

Figure 8~

Modulus of elasticity, shear modulus, and Poisson's ratio for isotropic RPs such as glass fiber/TS polyester mat RPs

8

9Engineering Analysis 81 1

The following familiar relationships between direct stress c~ and strain e, and shearing stress 1: and strain ),, hold: e = e/E }' = "dG

A transverse strain (contraction or dilation) sT is caused by o equal to" 's = VE

For orthotropic materials, such as fabric and roving-reinforced construction, EL anti ET are the elastic moduli in the longitudinal (L) and transverse (T) directions, GLT is the shearing modulus associated with these directions, and VLTiS the Poisson's ratio giving the transverse strain caused by a stress in the longitudinal direction, and VTL is Poisson's ratio giving the longitudinal strain caused by a stress in the transverse direction. The modulus at any intermediate angle is El, and if a/ is a stress applied in the 1-direction at an angle c~ with the longitudinal direction (top of Figure 8.24), the stress ~1, causes a strain el or: 81 = CT1/EI

in which E1 may be found from: I

I

I

I

I

,r~

I

I

I

I

1.00 - 0.50 - 0.40 - 0.30 - 0.20 -0.10 :0 - -0.10

0.90 0.80 0.70 0.60 "U

= 0.50 M i~ 0.40 0.30 0.20

0.1o

!

o Angle a

Figure 8.24

Elastic constants of unbalanced orthotropic material

812 Reinforced Plastics Handbook EL

EL ET

1

_--= cos4ot + --_ sin4a +

E7

-

4

E L _ 2 VLT sin22a GLT

This relationship is plotted as E]IEL in Figure 8.24, in which 0 ~ corresponds to the longitudinal direction and 90 ~ to the transverse direction. A transverse strain e2 is caused by c~] or: E,2 = -V12E 1

in which:

EL EL sin22~ } GL'~T

1 + 2Vtr + ~ -

Unlike isotropic materials, stress c~], when applied at any angle except 0 ~ and 90 ~ causes shear distortion and the shear strain }'12 is found

from" ~/12 = -m l (Yl/EL

in which: ml =Isin2cz

VLT + EL ET

[

1 EL 2 EGT

cos2ot

1 + 2VLT+

EL

EL

ET

GLT

A shearing stress ~r]2applied in the 1-2 direction causes a shear strain v]2 or:

V12 = "E12/G12

in which: GL._.[. T = GLT G72 EL [

EL

1 + 2VLT+---~T

[1 + 2VLT + EL ET

[

EL COS22~ } GLT

This relationship is plotted as G]2/'GLT. Unlike isotropic materials, stress "g12 causes a strain e] in the 1-direction or: S 1 = -m 1 "E12/EL

and a strain e2 in the 2-direction or: e2 =-m2 v~2/EL in which"

f [

m 2 = sin2(~ ~ VLT+

EL

I

ET

2 GLT

sin2cz

1 + 2VLT+

The two values of Poisson's ratio are related:

VLT/VTL=EJET

EL ET

GLr

8

9E n g i n e e r i n g Analysis 8 1 3

In plotting Figure 8.24, the following values are used: EL= 5,000,O00-psi Er- 500,O00-psi GET = 550,O00-psi VLT = VO~ = 0 . 4 5 0

VTL -- V90 ~ = 0 . 0 4 5

These values, for example, might correspond to a roving-reinforced panel employing an intermediate TS polyester plastic. When the orthotropic material is balanced, the longitudinal and transverse properties are the same, that is, EL= Er and vLr = vT~. The properties are symmetrical about the 45 ~ angle, as shown in Figure 8.25 in which the following values were used:

EL = VLT =

Er = 3,000,000

GLr =

psi

500,000 psi

VTL =

0.20

I

I

I

I~

I

I

I

I

I

OlzlOLr

+0"80F m

+2.00

F

y,/ \

--0.20 ff o.600

-o.40

0.400

-0 .6 0

I,,

+ 1.00

//

-0.80

-1.00 ~I

0

Figure 8.25

10

!

20

!

30

!

40

!

I

50 60 Angle a

,!

70

!

80

,!

90

I

100

Elastic constants of balanced orthotropic material" constants and angles have the same meanings as previous figure

814 Reinforced Plastics Handbook

These values might correspond, for example, to a square-weave or symmetrical satin-weave fabric-reinforced construction. As an example in the application of the foregoing equations, the tensile stress ~/, acting on the small plate at the top is 10,000 psi, the shear stress x12 is 4000 psi, and the angle ~ is 30 ~ Then from Figure 8.25: ET/EL = 0.367, or

G72/GLT=

0.81,

or

v72 = - 0 . 0 2 8 6

Then strains caused by e7 E'2

= =

E~

=

0.367 x

G12 =

0.81

m~

4.66

c~]

=

5,000,000

=

1,830,000 psi

550,000

=

4 4 5 , 0 0 0 psi

x

m2 =

4.98

are:

0 , 0 0 0 / 1 , 8 3 0 , 0 0 0 = 5.45 x 103 - ( - 0 . 0 2 8 6 ) 5.45 x 10 -3 = 0.16 x 10 -3

v72 = - 4 . 6 6 x 1 0 , 0 0 0 / 5 , 0 0 0 , 0 0 0 = -9.32

x 10 -3

and strains caused by "r]2 are: v72 = 4,000/550,000 = 7.28 x 10-3 e7 E'2

= - 4 . 6 6 x 4 , 0 0 0 / 5 , 0 0 0 , 0 0 0 = -3.73 x 10 -3 --'-

- 4 . 9 8 x 4 , 0 0 0 / 5 , 0 0 0 , 0 0 0 = - 3 . 9 8 x 10 -3

Total strains, therefore, are: V12

--

e7

=

1.72 x 10 -3

~e 2

"-

3.82 x 10 -3

- 2 . 0 4 x 10 -3

Problems involving Figure 8 . 2 5 can be resolved in an analogous manner. It must be kept in mind that equations are valid and useful if the fibers and plastics behave together in accordance with the assumptions upon which their derivation is based. If only the values of EI, ET, G~T, and vLT are available, the intermediate values of Eb G~2, v]2, and the values of m] and m2 can be estimated by means of these equations.

Hybrid RP Plates Fibrous reinforced plates in practice are often made up of several layers, and the individual layers may be of different construction, such as mat, fabric, or roving. Furthermore, the various layers may be oriented at different angles with respect to each other in order to provide the best combination to resist some particular loading condition. Outside loads or stresses applied to a RP plate of this type result in internal stresses that are different in the individual layers. External direct stresses may result not only in internal direct stresses but in internal shear stresses and external shear stresses may result in internal direct stresses as well as internal shear stresses.

8

Engineering 9 Analysis 81 5

Figure 8.26 depicts a small RP plate made up of materials a and b having principal longitudinal and transverse directions L a and Ta, and Lb and Tb, respectively. Several layers of each are present but their total thicknesses are ta and tb, respectively, and the overall thickness is t. Outside stresses ~1, ~2, and T12 are applied in the I and 2 directions, as shown. The I-direction makes an angle a with La3 and a reverse angle/3 with Lb. The angle a is considered to be positive and the angle /3 negative. 0"1

1

~,

t-->

>~ T12

llll fill

!

bx

I11i

a2

r

,iI 3

>o'2

T.

al

I I 2

~ = ta~ + t,, 2 + t.3 tb =

0"1

tb~ +

tb2

t - - ta + tb

Figure 8.26 Composite panel with layers aand bof different orthotropic materials oriented at arbitrary angles a and ,6 with respect to applied stresses ~r7, 6r2, and ~:72.

The internal stresses CTla, CT2a, and "u12a and cqo, o2b, and T12b in the individual layers can be found by observing that the sums of the internal stresses in the I and 2 directions must equal the external stresses in these directions, and that the strains must be the same in all layers. The application of the foregoing expressions may be illustrated by a cylindrical pressure vessel as shown in Figure 8.27(a). The wall of this vessel, having an external radius of 5 in., and wall thickness of 0.20 in., may be considered to be a thin plate. It is subjected to an internal pressure of 800 psi. the circumferential stress ~1 and the longitudinal stress c~2 in the wall are calculated: c~7 = pro/t = 19,200 psi c~2 = p r o / 2 t = 9,600 psi

The stresses acting on a small part of the wall are therefore as shown in Figure 8.27(a).

816 Reinforced Plastics Handbook

1

(rl - 19 200 psi

p = 800 psi rt = 5.00 in. ro = 4.80 in.

(.)

tatb

t 19,200 psi

'1

"-->" 9600 psi

9600 psi "<'-"

t ''~176 "

"

1

t

T = 25.000 in.

9 =

=

9600 psi-<--- J r12 = 920 psi

9600

~

19,200 psi

.........

J

> (r~ = 9600 psi

] " P r = 19,200 psi

0 20

,o.

19,200 psi (3)

. r

90"

1

19,200 psi (2)

.

(b) T = 25,000 in.

,.

o lo;..~

30" ps,

19,200 psi (1)

1

' L/ . . . . t. . '"'~176 " psi

r = 19,200 psi

920 psi ~

t:~

~'0"01 \~"

2 ~ 19,200 psi

"~/'

L0.20i~ "

Figure 8.27 Fibrous glass-reinforced plastic thin-wall cylinder" (a) internal pressure alone and (b) internal pressure plus twisting moment

Selecting Plastic and Process

Overview This Chapter provides a summary concerning the selection procedures. Within each chapter in this book, detailed information on their respective subjects are presented. In presenting the information and data, comparisons are made that provide important information for selection for the process, material of construction (reinforcement, resin, additive, a n d / or filler), and product design approach. Additional data is provided here particularly at the end of this chapter. Many materials, fabricating processes, and design approaches are employed. Which design, material, and process to use depends on factors such as performance requirements of product, materials of construction properties and their availability, process capability and availability, quantity of products, cost of material and process, and time schedule to deriver product(s) to customer. Some processes can be used with different kinds of RPs or a certain process can only be used with specific RPs. Plastic material selection for many materials (plastics, metals, etc.) can be a highly complex process if not properly approached particularly when using recycled plastics. Its methodology ranges from a high degree of subjective intuition in some areas to a high degree of sophistication in other areas. It runs the gamut from highly systematic value engineering or failure analysis of toys to aerospace products. In order to arrive at the optimum material for a given use with some degree of efficiency and reliability, a systematic planned approach (obviously) has to be used that identifies and lists the product requirements with all the steps required to produce and deliver the products; a few examples of plans have been reviewed in this book. The requirements include factors such as aesthetics, tolerances, fabricating

818 Reinforced Plastics Handbook

process to be used, surface fil~sh, length of service, storing or shipping, and so on. Setting up requirements can be complex and may not include all requirements if one is not familiar with the material and/or process. Throughout this book are different requirements identified for materials, processes, and designs that can be used as guides in setting up requirements, for certain materials and/or processes there could be a requirement that perhaps was overlooked or considered not to be important. Available are different publications, seminars, and software that can be helpful. The reinforcing and plastics material properties information and data presented in this book are provided as comparative guides. Readers can obtain the latest specific information from resin suppliers and/or software listing properties of these materials recognizing that a specific material usually has many modifications to meet different properties a n d / o r processing requirements. Also new developments in materials are always on the horizon requiting updates. This selection includes size or shape of reinforcement (such as continuous or chopped fibers, fabric weave, preforms, etc.) (Chapter 2) and plastic form (such as liquids, pellets, flakes, powder, etc.) (Chapter 3). There are those requiting prepregs, bulk molding compounds, sheet molding compounds, etc. (Chapter 4). Different considerations are to be used such as certain processes require certain forms of materials to operate efficiently at the lowest costs (Chapter 5). Of the total worldwide 35,000 different plastics (URPs), there could be a few thousands that could be used in RPs. Of those, a couple hundred may be important with probably a dozen principally used (Chapter 3). With so many available plastic types, it is best to recognize that they fit into systematic groups and subgroups of categories or classifications that can be used in selection procedure. Examples of these are thermoplastics (TPs), thermosets (TSs), foams, elastomers, electrically conductive and nonconductive, weather and/or environmental resistant, chemical resistant, high performance properties (strength, stiffness, wear resistant, etc.), as well as by performance, environments and products, or applications. In spite of the diversity of plastic materials, the basic principle of their construction is always the same. Certain parts of the plastic material industry organizations and companies provide there own groupings that significantly simplifies the selection procedure. It is unfortunate that plastics (URP and RP) do not have all the advantages and none of the disadvantages of other materials but often overlooked is the fact that there are no materials that do not suffer from some disadvantages or limitations. The faults of materials known and utilized for hundreds of years are often overlooked; the faults of the new materials (URP and RP) are often overemphasized.

9

Selecting 9 Plastic and Process 8 1 9

As examples, steel is attacked by the elements of fire [1500 to 2500F (815 to 1370C) ]. They immediately loose all their strength, modulus of elasticity, etc. resulting in catastrophic failures of buildings, etc. Common protective practice includes the use of coatings (plastic, cement, etc.) and then forgetting their susceptibility to attack is all too prevalent. Wood and concrete are useful materials yet who has not seen a rotted board (wood on fire, etc.) and cracked concrete. Regardless this lack of perfection does not mean that no steel, wood, or concrete should be used. The same reasoning should apply to plastics. In many respects, the gains made with plastics (URPs and RPs) in a short span of time far outdistance the advances made in these other technologies. As reviewed steel support, beams fail in a fire. To significantly extend the life of structural beams hardwood (thicker than steel, etc.) can be used; thus, people can escape even though the wood slowly burns. The more useful and reliable structural beams would be using RPs that meet structural performance requirements with even a much more extended supporting life than wood. To date these RPs are not used in this type of fire environment primarily because of their high cost. Even though the range of RPs continues to be large and the levels of their properties so varied that in any proposed application only a few of the many available will be suitable. A compromise among properties, manufacturing process, and cost generally determines the material of construction. Selecting an RP is very similar to selecting a metal. Even within one class, RPs differs because of varying formulations, just as steel compositions vary (tool steel, stainless steel, etc.). For many applications, RPs has superseded metal, wood, glass, natural fibers, etc. Many developments in the electronics and transportation industries and in packaging and domestic goods have been made possible and economically feasible by the availability of suitable RPs. Thus comes the question of whether to use an RP and if so, which one. As a general rule, until experience is developed, it is considered desirable to examine the properties of three or more materials before making a final choice. Material suppliers should be asked to participate in type and grade selection so that their experience is part of the input. The technology of manufacturing RP materials, as with other materials (steel, wood, etc.) results in that the same RP compounds (or individual components) supplied from various sources will generally not deliver the same results in a product. As a matter of record, individual suppliers furnish their product under a batch number, so that any variation can be tied down to the exact condition of the raw-material production. Taking into account manufacturing tolerances of the RPs, plus variables

820 Reinforced Plastics Handbook

of equipment and procedure, it becomes apparent that checking several types of materials from the same a n d / o r from different sources is an important part of material selection. Experience has proven that the so-called interchangeable grades of materials have to be evaluated carefully as to their affect on the quality and performance of a product. Another important consideration as far as equivalent grade of material is concerned is its processing characteristics. There can be large differences in properties of a product and test data if the processability features vary from grade to grade. It must always be remembered that test data have been obtained from simple and easy to process shapes and do not necessarily reflect results in complex product configurations. This situation is similar to those encountered with other materials (steel, wood, glass, etc.). Most RPs is used to produce products because they have desirable mechanical properties at an economical cost (Tables 9.1 and 9.2). For this reason, their mechanical properties may be considered the most important of all the physical, chemical, electrical, and other considerations for most applications. Thus, everyone designing with such materials needs at least some elementary knowledge of their mechanical behavior and how they can be modified by the numerous structural geometric shape factors that can be in RPs (Chapter 7). Tabte 9.1 Mold costs, output, and life expectancy

Process Hand lay-up Low pressure press SMC molding

Mold cost (UK s

Daily output

Life of mould

350 4,500 40,000

3 30 80

200 15,000 100,000

Selection via computerized databases is clearly a more viable method, and this process is described later in this chapter and else where in this book. The authors have assumed that the reader has some idea of which properties the application will need. If this is not the case and the reader finds it initially difficult to select which material properties are important, then it may be more useful to read Chapter 7 on design and then return to this chapter. Chapter 7 addresses the relationship of properties to design requirements in some detail. One must also consider whether the application will require that the material to be used meet a specific customer's (commercial or government) specification, such as whether an Underwriters Laboratory (UL) listing is required, or possibly FDA or USP compliance. These considerations will help at least to narrow the range of potential materials.

9

Selecting 9 Plastic and Process 8 2 1

Table 9,2 Examplesof economic comparison of structural foam molding, injection molding, and sheet molding compound

Production considerations

Structuralf o a m

Injectionmolding

Sheet molding compound

Typical minimum number of parts a vendor is likely to quote on for a single setup

250 {using multiple nozzle equip, with tools from other sources designed for the same polymer and ganged on the platen)

1,000to 1,500

500

Relative tooling cost, single cavity

Lowest. Machined 20 percent more. aluminum may be Hardened-steel viable, depending tooling on quantity required

20 percent to 25 percent more. Compressionmolding steel tools

Average cycle times for consistent part reproduction

2 to 3 minutes (I14 in. nominal wall thickness)

40 to 50 seconds

1112to 3 minutes

Is a multiple-cavity tooling approach possible to reduce piece costs?

Yes

Yes. Depends on size and configuration, although rapid cycle time may eliminate the need

Not necessarily. Secondary operations may be too costly and material flow too difficult.

Are secondary operations required except to remove sprue?

No

No

Yes, e.g., removing material where a "window" is required (often done within the molding cycle)

Range of materials that can be molded

Similar to thermoplastic injection molding

Unlimited; cost depends on performance requirements

Limited; higher cost

Finishing costs for good cosmetic appearance

40 to 60 cents per sq. ft. of surface {depending on surface-swirl conditions)

None, if integrally None, if secondary colored; 10-20 cents operations such as per sq. ft. if painted trimming are not required. Otherwise 20 to 30 cents per sq. ft. of surface

Recognize that the final actual properties of a processed RP for an application are directly related to how the RPs is processed. If process controls are not properly set up, followed, and continually rechecked to

822 Reinforced Plastics Handbook

insure meeting part performance requirements, products could be improperly processed. This quality control requirement on processing RPs applies to all products. In spite of what has been achieved so far, the industry continues to surmount the hurdles of systematic advanced processing development. The industry must not regard the present state of processing as the last word in progress. On the contrary, the great possibilities in development, many of which are dormant, must be recognized and opened up by close cooperation between theorists and technologists. Specialty processes have been developed over the past century and continue to be developed. Included are those that have different names for the same process. The different names are used for diversified reasons that include: 1

used in different industries that have their method of identifying a process based on their market requirements,

2

an old process that may be basically the same or slightly modified requiring a more modern name,

3

promoting new ideas requiting a name to symbolize a new generation, and so on.

There are also overlapping of terms such as molds, dies, and tools and also terms such as molding, embedding, casting, potting, etc. There are continuous and noncontinuous extrusion processing methods. Injection molding includes gas injection, insert molding, micromolding, etc. This situation does not cause a problem or should not affect anyone's thinking when examining processes. As one may recognize throughout the world and particularly in the industrialized nations, one might say that there are words or situations that could have more than one meaning. The important message here is that it may be important for you to be very specific when describing a process (also materials, designs, and so on). When analyzing processes to produce all types of products, at least 65wt% of all RPs require some type of specialized compounding. They principally go through compounding extruders, usually twin-screw extruders (Chapter 5), before going through equipment such as injection and compression molding machines as well as single screw extruders to produce products. There are exceptions where IM and EX can prepare the compound and produce the product. This type of action usually requires large market consumption of the products. Improved understanding and control of materials and fabricating processes have significantly increased product performances and reduced

9

Selecting 9 Plastic and Process 8 2 3

their variability resulting in good to excellent return on investments (ROIs). RP processes permit the fabrication of products whose manufacturing would be very cosily or difficult if not impossible in other materials. Processors must routinely keep up to date on developments with the more useful RPs and acquire additional information on how to process them. The emphasis throughout this book has been that it is not difficult to design and fabricate with RPs and to produce many different sizes and shapes of RTP and RTS commodities and engineering plastics. Process selection can take place before material selection, when a range of materials may be available, or made first to meet certain performance requirements such as size and only then have the applicable process or processes chosen. Usually, in the latter situation only one process can be used to provide the best performance-to-cost advantages. A particular design group may have its own in-house processing capabilities. Unfortunately, some operations use just whatever equipment is available. This situation could be very unprofitable, limit profitability, or restrict product performance. It is important to recognize that the fabrication process can markedly influence all aspects of product performance, particularly cost. Overall, the critical phase of product development is the concept selection phase. During this period, the array of design ideas are narrowed down to one concept that one or the design team predicts will best meet product user requirements. This phase offers the team the most freedom to choose one design path over another. However, little objective data are available to evaluate the alternative paths, so the design process can be influenced as much by office politics and costs as by engineering considerations. This phase can be when brilliant products are conceived, or when fundamental flaws are designed into the product. These flaws delay the schedule by months, yet are never satisfactorily resolved, because they are inherent in the concept itself. The most frustrating types of product flaws are those that could have easily been avoided had a little more thought gone into the original concept. Much of a product's success is dependent on this concept phase, yet the output from this phase can vary from exceptional to barely functional. Some product development teams seem to consistently produce good designs and then there are others. The performance of the development team ultimately depends on the design skills of the individuals involved.

824 Reinforced Plastics Handbook

Influencing Factors Design guidelines for RP and URP have existed for over a century producing literally millions of parts meeting all kinds of service requirements that include those subjected to static and dynamic loads requiring long life. The basic information involved in designing with RPs concerns the load, temperature, time, and environment. Analyzing how a material is expected to perform with respect to other requirements can include mechanical space available, electrical, and chemical requirements combined with time and temperature could become essential to the selection process. The designer translates product requirements into material properties. Characteristics and properties of materials that correlate with known performances are referred to as engineering properties. They include such properties as tensile strength and modulus of elasticity, impact, hardness, chemical resistance, flammability, stress crack resistance, and temperature tolerance. Other important considerations encompass such factors as optical clarity, gloss, UV stability, and weatherability (Chapter 7). In evaluating and comparing specific RPs to meet these requirements past experience and/or the material suppliers are sources of information. It is important to ensure that when making comparisons the data is available where the tests were performed using similar procedures. Where information or data may not be available some type of testing can be performed by the designer's organization, outside laboratory (many around), and/or possible the material supplier if it warrants their participation (technical wise and/or potential cost wise). If little is known about the product or cannot be related to similar products product testing is usually required. Updating testing centers is an endless process. As an example productivity at Bayer MaterialScience AG's Thermoplastics Testing Center (TTC) has been significantly increased by automation of processes. TTC now offers all its external and internal customers one-stop service, which, in addition to 200 different tests for thermoplastics, also covers the production of granules and test pieces. The new very versatile center has a complete production line, which enables the compounding of ABS and its blends, PC and industrial thermoplastics in quantifies of 1.3-100 kilograms. Test piece production is carried out using fully automated injection molding machines. 100 different injection molds are available for virtually every testing procedure in accordance with ISO, UL, and CAMPUS. The TTC carries out applicable tests for all major plastics applications, with standard thermoplastics such as PE and PP being just as welcome as high-performance thermoplastics.

9. Selecting Plastic and Process 825

The key to the excellent service at the TTC is Bayer's very versatile systematic automated testing center (Bayer MaterialScience AG, Gebaeude R33, 47812 Krefeld-Uerdingen, Germany; Fax: +49-2151885210; e-mail: [email protected]). Additionally, the use of robots and state-of-the-art machinery contributes to precision and good test reproducibility. In accordance with I S O / I E C 17025, the TTC has the expertise to carry out selected physical-technological tests on plastics, as confirmed by the German Accreditation System for Testing. The accreditation also includes the compounding of thermoplastics and injection molding of test parts. In addition, the world's foremost and largest testing organization, UL, has issued the center with a quality certificate for fire, aging, weathering and electrical tests. When required RPs permit a greater amount of structural design freedom than any other material (Chapters 7 and 8). Products can be small or large, simple or complex shapes, rigid or flexible, solid or hollow, tough or brittle, transparent or opaque, black or virtually any color, chemical resistant or biodegradable, etc. Materials can be blended to achieve different desired properties. The final product performance is affected by interrelating the RP with its design, material, and processing method. The designer's knowledge of all these variables can profoundly affect the ultimate success or failure of a consumer or industrial product. For these reasons, design is spoken of as having to be appropriate to the materials of its construction, its methods of manufacture, and the loads (stresses/strains) involved in the product's environment. Where all these aspects can be closely interwoven, RPs is able to solve design problems efficiently in ways that are economically advantageous. It is important to recognize that these characteristics of RPs exist. This book starting with Chapter 1 provides their characteristics and behavior. Evaluating processes should take into consideration factors such as eliminating problems that include insufficient compaction and consolidation before plastic solidification (TPs) or cure (TSs) occurs before air pockets develop, incomplete or uncontrollable wet-out and encapsulation of the fibers, a n d / o r insufficient fiber or uniform fiber content. These deficiencies lead to loss of strength and stiffness and susceptibility to deterioration by water and aggressive agents. Heat control may not be adequate particularly for crystalline TPs or it may be too rapid (Chapter 3 ). In some applications the designer or fabricator will not have the ability to choose freely from all the design, material, and process alternatives. For example, a design is often heavily constrained by the need to fit an

826 Reinforced Plastics Handbook

existing assembly, and the material and process may be determined largely by the need to use existing material and fabricating facilities. The geometric symmetry of a product can influence process selection. Both shape and design details are heavily process related. The ability to mold fibs, for example, may depend on material flow during a process or on the flowability of a plastic reinforced with fibers. The ability to produce hollow shapes depends on the ability to use removable cores, including air, fusible or soluble solids, and even sand. Hollow shapes can also be produced using cores that remain in the product, such as foam inserts in RTM or metal inserts in IM. A process's pressure and the available equipment can limit product size, whereas the ability to achieve specific shape and design detail is dependent on the way the process operates. Generally, the lower the processing pressure, the larger the product that can be produced. With most laborintensive methods, such as hand lay-up, slow-reacting TSs can be used and there is virtually no limit on size. There may be a requirement for surface fimsh, molded-in color, textured surface, or other conditions the RP is to meet. Surface finish can be an important consideration. The different processes may be able to provide only one surface to be smooth or both sides are smooth. Important that smooth be identified since it has many meanings to different people. Surface fil~sh can be more than just a cosmetic standard. It also affects product quality, mold cost, and delivery time. Different organizations have developed standards on surface finishes. An example is from Society of Plastics Engineers/Society of Plastics Industries. The standards range from a No. 1 mirror finish to a No. 6 grit blast fimsh. A mold finish comparison kit consisting of six hardened tool steel pieces and associated molded pieces is available through SPE/SPI.

Performances/Behaviors Any attempt to compare RP with other conventional materials (metal, wood, glass, etc.) on a straight property-for-property or a straight costfor-cost basis is doomed to failure from the very start. There are just too many different types of grades and formulations grouped under the overall heading of RP, just as there are a wide variety of grades grouped under the category of metal or wood to make any such comparisons valid. About all one can be certain of is the fact that the technology of RPs has become so sophisticated that plastics are virtually the most versatile group of materials available to industry today. It is interesting to note

9

Selecting 9 Plastic and Process 8 2 7

how fast such sophistication has taken place. Almost a century ago, the rule of thumb was that RTSs could not go much over 200C (392F) in service and RTPs could not go over 55C (131F). In the mean time, many new plastics developed such as the TP polyimides that will retain properties at temperatures up to 400C (750F). Moreover, the aerospace industry has a group of materials known as ablative plastics (based on reinforced phenolics) that can take over l l 0 0 C (2000F) for short periods of time (less than a s). In the past, it was generally accepted that plastics could not compete with other materials as loadbearing elements. Nevertheless, that was before engineering designs were properly applied; RP structures are used in buildings, bridges, aircraft, boats, wind turbine blades, furniture, and so on. The plastics material properties information and data presented in this chapter provide comparative guides. As reviewed in Chapters 2 and 3 plastics can be modified to meet all kinds of properties, performances, and processes by compounding, alloying, etc. Figure 9.1 provides a simplified summary in a pie section representing the properties of plastics. Literally each of the plastics can be modified to almost exist in any position within the pie section. TOUGH

ACETAL PHENOLIC

NYLON

ABS

POLYETHYLENE

EPOXY POLYSTYRENE DAP

POLYPROPYLENE

BRITTLE

Figure 9,1 With modifications each of these plastics can be moved into literally any position in the pie section meeting different requirements

There are many industry plastic classification systems such as ASTM D 4000 (Tables 9.3 to 9.7). There is also ISO-1043 and others to meet different industry requirements. They provide a way to identify plastics for purchasing, quality control, etc. Plastics are classified according to their origin and method of synthesis as well as fitting into systematic group categories such as plastic material type, modulus, nonrigid, semirigid, and

828 Reinforced Plastics Handbook Table 9 . 3 Classification of plastics (ASTM D 4000) 0

1

2

3

4

5

6

7

Group

Broad

Specific

Reinforce-

% Rein-

Table

Cell Requirements

Suffix

generic

I

ment

forcement

type

I Group class grade I

I I

x x x x x

I

Physical properties 0 = One digit for expanded group, as needed. 1 = Two or more letters identify the generic family based on abbreviations D 1600. 2 = Three digits identify the specific chemical group, the modification or use class, and the grade by viscosity or level of modification. A basic property table will provide property values. 3 = One letter indicates reinforcement type. 4 = Two digits indicate percent of reinforcement. 5 = One letter refers to a cell table listing of physical specifications and test methods. 6 = Five digits refer to the specific physical parameters listed in the cell table. 7 = Suffix code indicates special requirements based on the application and identifies special tests.

Table 9.4 Symbols for the families of plastics

Standard Symbol

PlasticFamily Name

ABS AMMA ASA CA CAB CAP CE CF CMC CN CP CPE CS CTA CTFE DAP EC EEA EMA EP EPD EPM ETFE EVA FEP FF IPS

Acrylnitrile/butadiene/styrene Acrylonitrile/methylmethacrylate Acrylonitrile/styrene/acrylate Cellulose acetate Cellulose acetate butyrate Cellulose acetate propionate Cellulose plastics, general Cresol formaldehyde Carboxymethyl cellulose Cellulose nitrate Cellulose propionate Chlorinated polyethylene Casein Cellulose triacetate Polymonochlorotrifluoroethylene Poly(diallylphthalate) Ethyl cellulose Ethylene/ethyl acrylate Ethylene/methacrylic acid Epoxy, epoxide Ethylene/propylene/diene Ethylene/propylene polymer Ethylene-tetrafluoroethylene copolymer Ethylene/vinyl acetate Perfluoro (ethylene-propylene) copolymer Furan formaldehyde Impact styrene

ASTM Standard

D_ D 706 D 707

D 1562

Suggested Reference Cell Tables for Materials without an ASTM Standard Unfilled

Filled

E E E E H E

D D H

E

D

F H E

H D

H E F F H

H D

F

D

H

F (see PS)

H

H

9 . Selecting Plastic and Process 829 MF PA PAl PARA

Melamine-formaldehyde Polyamide (nylon) Polya m ide-i m ide Polyaryl amide

D 4066

H

H

G

G

T a b l e 9 , 5 Additive, filler, and reinforcement symbols with tolerances

Symbol

Material

Tolerance

Carbon and graphite fiber-reinforced Glass-reinforced Lubricants (i.e., TFE, graphite, silicone, and molybdenum disulfide) Mineral-reinforced Reinforced-combinations, mixtures of reinforcements or other fillers, reinforcements

+2 percentage points _+2 percentage points by agreement between the supplier and user +2 percentage points +3 percentage points {based on the total reinforcement]

Table 9.6 Example of an ASTM D 4000 cell table Symbol

Characteristic Color (unless otherwise shown by suffix, color is understood to be natural] Second letter: A = does not have to match a standard; B = must match standard Three-digit number: 001 = color and standard number on drawing; 002 = color on drawing Not assigned Melting point, softening point Second letter: A = ASTM D 789 {Fisher-Johns]; B = ASTM D 1525 Rate A (Vicar); C = ASTM D 1525 Rate B {Vicar); D = ASTM D 3418 {transition temperature DSC/DTA); E = ASTM D 2116 (Fisher-Johns high temperature) Three-digit number = minimum value ~ Deformation under load Second letter: A = ASTM D 621, Method A; B = ASTM D 621, Method B First digit: 1 = total deformation; 2 = recovery Second and third digit x factor of 0.1 (deformation) = % minimum 1 {recovery] Electrical Second letter: A = dielectric strength (short-time], ASTM D 149; Three-digit number x factor of 0.1 = kV/mm, minimum B = dielectric strength (step by step), ASTM D 149; Three-digit number x factor of 0.1 = kV/mm, minimum D = dielectric constant at 1 MHz, ASTM D 150, maximum; Three-digit number x factor of 0.1 = value E = dissipation factor at 1 MHz, ASTM D 150, maximum; Three-digit number x factor of 0.0001 = value F = arc resistance, ASTM D 495, minimum; Three-digit number = value [Other methods under review, ASTM D 257 and D 1531] Flammability (Note 1) Second letter: A = ASTM D 635 (burning rate], 000 = to be specified by user, B = ASTM D 2863 {oxygen index) Three-digit number = value O/o,maximum

Q

r

r "o

Table 9.7 Example of the data developed based on using ASTM D 4000 a

m o

Order Number

z

Cell Limits

Designation Property

0

1

2

3

4

9,1

5

6

7

8

1

Tensile strength, ASTM D 638, MPa, minimum b

Unspecified

15

40

65

85

110

135

160

185

Specify value

2

Flexural modulus, ASTM D 790, MPa, minimum b

Unspecified

600

3,500

6,500

10,000

13,000

16,000

19,000

22,000

Specify value

3

Izod impact, ASTM D 256, J/m, minimum c

Unspecified

15

30

50

135

270

425

670

950

Specify value

4

Deflection temperature, A S T M

Unspecified

130

160

200

230

260

300

330

360

Specify value

5

To be determined

Unspecified

-

D 648 (1,820 kPa), ~ minimum

a Other cell tables are in D 4000. b M Pa x 145 = psi. c j/m x 18.73 x 10-3 = ft Ibf/in.

D. O" O o

9

Selecting 9 Plastic and Process 831

What follows is a simplified but practical material-selection approach (from LNP). This type of "longhand" system has been used for almost a half century during which time it became a basis in computerized software for material selection databases. One starts by selecting the design criteria as well as potential plastics of interest and incorporating them into a table format (Table 9.8) and check off only the major criteria across the worksheet. Follow by setting up a comparison of the performance requirements for the potential plastics being considered (Table 9.9) and transfer the bold-faced numerical rating in each selected criteria column to the worktable. Add these numbers across the worktable to determine the plastic group with the lowest-point subtotals that will be the best plastic for a given application on a performance basis. Finally add in the cost factor and total it to find the plastic group with the lowest number that results the best choice based on a cost-performance evaluation. Follow by determining the specific plastic within the plastic group selected. The plastic with the lowest final total will be the best for the application on a cost-performance basis. Tables 9.10 and 9.11 are examples in the plastic selection of a chain saw and pump. Additives

A wide variety of additives is used with both TS and TP resins to adjust the handling, processing, property, and/or simply to add bulk and reduce cost without impairing the properties of RPs. Cost-reduction is not always the end-result. Apart from reinforcement, additives for these resins are generally in the form of particles or liquids, or combinations of the two, such as pastes (Chapters 3 and 4). Generally, the particles influence the mechanical properties, while the liquids are reactant components. Colorants can take the form of powders, pastes or liquids. In addition to what follows in this section more follows in his chapter and throughout this book. For particulate additives, the term filler is still widely used (reflecting the original and continuing need to add bulk to the mix to reduce the cost). An important aspect of the development of even low-cost additive fillers, however, is surface treatment of particles to aid bonding to the matrix and offer positive mechanical advantages as well as sheer bulk. Once an additive has been selected, other factors must also be considered. Within each family, there are types and grades that impart differing properties due to variations in coarseness, uniformity of sizes and shapes of solid materials, impurity level, and method of preparation. The mix ratios need to be accurate, to obtain optimum properties (also

Table 9.8 Worktable format related to requirements Material Characteristics

Strength and Stiffness

Short-Term Heat Toughness Resistance

Long-Term Heat Resistance

I~) Environmental Resistance

Dimensional Accuracy in Molding

Dimensional Stability

cDesign riteria ~ ....

Resin Groups Styrenics ABS SAN Polystyrene

Olefins Polyethylene Polypropylene Other Crystalline Resins Nylons 6 616 6/10,6/12 Polyester Polyacetal Arylates Modified PPO Polycarbonate Polysulfone Polyethersulfone High Temp. Resins PPS Polyamide-imide Fluorocarbons FEP ETFE Ratings: l-most desirable;6-1eastdesirable. Largenumbers indicate group classification,small numbersthe specific resinswithin that group.

Wear and Frictional Properties

Point Subtotal

Cost

Point Total

,,,,, o

a" RI

i'I)

o.. a,1 ljl m ,

-r oo o

0 e-

ll# _0

ccm 0 0

l--

II#

II#

._m

o

co .4...o

d

c-

II#

C~ c-

0 .-c-

~o

"4~

.~_ _

.~_

c

.o_ ..o

0

~--

E~ 123

~ ~.; 0

c.__

c"-~_ -s

i:5<

c-~.r

"~

~.r c--

E u'~ ~

~ c--

c" O

L.LI

~

~

E

c-o

~

~-~

-3 o h--

c--

.~

~

c--

-r

E

o

c--

c-

g_~

CD

u')

rC

~')

_.c

m~c ~ a _ a _

i1# c-

t._

o

~

~

9

,~t-

QA c"

~ r~

"5-

E ~:~a_o

o

Li_ W

w

uq o E i

m --o

..o

b-

d~

m r~

m --o

....1 ~J ..o

E c-

.~_ "o .c_ m

o

c. o_

un

c

..o E

.,..., m

m

.~_

m cm

.c_ c-

._c

.1.-,

o

1:5_

Selecting 9 Plastic and Process 8 3 3

c,')

>- >-

,--- r,~

o~

-~ ~

h = a - ~

Table 9.10 Nylon 6 or 6/6 provides the best choice for a gasoline-powered chain saw

~

Material Characteristics

Resin Groups Styrenics ABS

Design

Strength Short-Term and Heat Stiffness Toughness Resistance

Criteria

SAN

Polystyrene

Polyethylene Polypropylene

Arylates Modified PPO Polycarbonate Polysulfone Polyethersulfone

X

X

X

X

3

6

6

6

Dimensional Accuracy in Molding

Dimensional Stability

Wear and Frictional Properties

~=

Point Subtotal

Cost

Point Total

21

2

23

s~

Ill

-l-

a-

Olefins

Other Crystalline Resins Nylons 6 6/6 6/10, 6/12 Polyester Polyacetal

Long-Term Heat Environmental Resistance Resistance

4

5

2

1 3 4 5

1

2

3 1 4 5

1

4

2

1 3 2 5

2

3

s

4 3 2 1

16 11 8 9 10 12 16

17 13

2 4 1 1

~2 11

11 14 13 17

3

2

3

13

High Temp. Resins PPS Polyamide-imide

2

4

1

9

14

Fluorocarbons FEP ETFE

6

2

2

11

17

4

17

0 o

Table 9.11 PPS provides the best choice for the impeller used in a chemical-handling pump Material Characteristics

Strength Short-Term and Heat Stiffness Toughness Resistance

Design Criteria

Long-Term Heat Environmental Resistance Resistance

Dimensional Accuracyin Molding

Dimensional Stability

Wear and Frictional Properties

Point Subtotal

Cost

Point Total

X

X

X

X

3

6

6

6

21

23

Olefins Polyethylene Polypropylene

5

4

5

3

17

18

Other Crystalline Resins Nylons 6 6/6 6/10, 6/12 Polyester Polyacetal

1

2

4

4

11

14

Resin Groups Styrenics ABS SAN Polystyrene

I'D r i

Arylates Modified PPO Polycarbonate Polysulfone Polyethersulfone High Temp. Resins PPS Polyamide-imide Fluorocarbons FEP ETFE

1,0

i

3

3

3

5

18

14

i

Ill i

1

22

2 1

1 2

2 1

1 1

1

2

2 1

6 10

1

25

11

16

i

,

i I

o ~3

W

836 Reinforced Plastics Handbook

to keep down costs). The chemistry of additives is often extremely complex and the choice of materials can be bewildering to anyone but a specialist. Nevertheless, it is important for designers, engineers, and processors to have some overall familiarity with additives and their technology. The mix ratios need to be accurate, to obtain optimum properties (also to keep down costs). Storage and handling of some of additives calls for great care, as some of the materials are classified as fire a n d / o r explosion hazards and can be hazardous to the health of people working with them. Originally (inheriting the practice from the rubber industry), the plastics processing sector has purchased resins and additives separately and mixed its own compounds. However, the growing sophistication of RP compounds, together with the need for special investment in separate handling of additives and market demand for reproducible performance, have created a specialist industry sector which is devoted to the production of RP compounds. This has occurred mainly in TPs but the use of ready-made compounds is growing rapidly in TSs also. With many RTPs, the technical difficulty of mixing the plastic matrix with reinforcement such as glass fiber has made it standard practice for materials suppliers to offer a reinforced molding compound that is ready formulated with all the necessary ingredients, with the possible exception of pigment. Ready made/resin impregnated resins RTP in sheet form is also available such as glass mat TP (Chapter 4). Only in the case of PVC, and for some other large-volume production, is it normal now for the processor to carry out any significant amount of in-plant mixing of RTPs. Nevertheless, with the development of color concentrates and compact, clean, and reliable weight metering/ dosing systems, which can be mounted on the molding, machine, there is a growing tendency for RTP processors to return to in-plant coloring, holding stocks of natural-color material and coloring as required, so saving on inventory costs. With RTSs, however, where the resin is usually liquid and requires curing, in-house mixing is used, especially in the hand and spray lay-up sector, and in many press molding and resin transfer molding operations. Once mixed they have a limited pot life prior to hardening. Resin suppliers now offer resins formulated and possibly pigmented to meet a set specification including pot life. Pot life is also called working life. When the thermoset has been mixed or compounded with a catalyst, its pot life is the time remaining in a usable condition. It is measured at room temperature or the temperature to be encountered. This term should not be confused with shelf life.

9

Selecting 9 Plastic and Process 8 3 7

In larger-volume production, preimpregnated sheet compounds are used. The fabricator forms the sheet compound to shape and initiates the cure. These compounds are known as prepregs (preimpregnated materials), SMCs (sheet molding compounds), and BMC (bulk molding compounds). There are many variations within each group (Chapter 4).

Selection of Additives When selecting an additive, it is important to take into account also the potential side-effects it may have on other properties. In most cases, the pot life and exotherm of the resin system will be reduced by addition of fillers, because they reduce the concentration of reactants and act as better heat conductors than the resin. In some cases, the cost of the system will be reduced (but at a penalty in other directions such as mechanical properties that can influence performance of the fabricated product).

Incorporating Additives The amount of additive by weight (identified as wt%) which can be incorporated in a resin depends on the particle size, density and oil absorption properties. The viscosity is often directly influenced by additive content. Porous high oil absorption fillers (such as diatomaceous silicas) and chopped glass can greatly increase the viscosity of a resin system at low loadings of only 1-50 phr (parts/hundred). Medium-weight granular fillers, such as powdered aluminum and alumina, may be used at loadings of up to 200 phr. The non-porous lower oil absorption fillers, such as aluminum oxide, silica and calcium carbonates, can be incorporated at levels of 700-800 phr without making the formulation unworkable. Loadings can be increased by adding a diluent, but this may not always be desirable, as the diluent may detract from other desired properties. Organo titanates can be added to improve filler wetting, enabling higher loadings at the same viscosity. Fine particles are easier to incorporate and there are fewer tendencies for them to settle. Coarse and heavy fillers will settle and cake on standing, but this may be countered by adding lightweight fillers such as the colloidal silica compounds.

Properties Influenced by Fillers and Additives All fillers will increase the viscosity of resins; most fillers also influence the gel time. Gelation is normally retarded, but alumina and some types of china clay have the reverse effect. It is difficult to predict the precise effect on gel time of particular filler and this should be determined by experiment in each case. Fillers also reduce the volumetric shrinkage of resins when curing, as well as peak exothermic temperature. Fillers such as silica may also be used to make the resin thixotropic, for contact molding on vertical or inclined surfaces. Thixotropic is a

838 Reinforced Plastics Handbook

characteristic of material undergoing flow deformation where viscosity increases drastically when the force inducing the flow is removed. The material is gel-like at rest but fluid when agitated such as during molding. They lose viscosity under stress. Liquids containing suspended solids are likely to be thixotropic. They have high static shear strength with low dynamic shear strength at the same time. As an example, these materials provide the capability to be applied on a vertical wall and through quick curing action remain in its position during curing such as aBMC. Powdered mineral fillers tend to increase compressive strength, hardness and modulus of the compound. However, when used in large amounts, there is a considerable reduction in bending strength. Fibrous fillers are used to increase tensile and impact strength. Surface properties of moldings can be improved by use of a suitable powdered mineral in the gelcoat only. Powdered quartz or zircon in the gel coat can improve hardness and abrasion resistance. Properties, which may be selectively altered by use of fillers, include:

Pot life and exotherm: Pot life can be increased and exotherm reduced, because fillers reduce the concentration of reactants and function as better heat conductors than the resin matrix. Commonly-used fillers for this are silica, calcium carbonate, alumina, lithium aluminum silicate, and powdered metals. Stability (thermal): The properties of many resins (especially TPs) are strongly influenced by exposure to heat, not only during service life but also during processing, when over-heating can cause deterioration or failure to build up the designed strength. On the other hand, it is sometimes desirable to process at a higher temperature, to permit the use of specific resins and other additive systems. Heat stabilizing additives are used to improve the processability of the compound and enlarge the processing window. They also can be employed to increase the heat-stability of the product. Heat stabilizers usually act by countering or absorbing the products of oxidation.

Stability (ultra-violet/sunlight): Exposure to ultra-violet light is a well-known cause of oxidation of many resin systems, both TS and TP, leading to loss of mechanical properties and deterioration in appearance. This has obvious implications for outdoor applications. Stabilizers can be added to counteract this effect, either by screening out harmful radiation, by absorbing, or converting the by-products of oxidation. Pigments can also play a useful role, and there is considerable scope in balancing a pigment and stabilizer to achieve the best results.

9

Selecting 9 Plastic and Process 8 3 9

Thermal shock resistance: Part of the resin can be replaced with a material that does not change significantly with variation of temperature, with the result, that resistance to thermal shock is increased and coefficient of thermal expansion is reduced. Typical such fillers are clay, alumina, wood flour, sawdust and mica. When bonding with metals, powdered metals in the resin mix will help to bring the thermal expansion closer to that of the metals, so reducing differential stress.

Mechanical strength: tensile, flexural, impact and compressive strength: Mechanical properties such as tensile and flexural strength are mainly affected by reinforcements but the addition of these materials (especially glass fiber) may also create a more brittle compound (as with reinforced polyamides), and an elastomeric modifier may often be added to counter this tendency. Elastomeric additives are also widely used to improve impact strength, especially at subzero temperatures. Mineral fillers can improve compressive strength.

Flame retardanc~ This is a key growth area for additives, as RPs are increasingly employed in sensitive applications, such as building and construction, automobile and public transport, aircraft and electrical electronic products, where there is some risk of fire or smoldering. A number of chemical compounds have been used and are being developed for use in resins compounds, to prevent, retard ignition, or to reduce the spread of flame. An important aspect is also the reduction or elimination of by-products of combustion, particularly dangerous or unpleasant fumes, and smoke. In the past, halogenated (especially chlorinated) compounds have proved effective as flame-retardants, but these tend to release by-products and are being phased out. Non-halogenated compounds, phosphorus and other compounds are widely used, and there is growing understanding and use of compounds that have synergistic actions on each other. Examples of specialty compounds are from Custom Films Div., PolyOne Corp., St. Louis, MO. They introduced CoverWise, a product line of engineered films for commercial and residential interiors. The line provides architects/designers with new solutions to meet stringent indoor air quality standards for wall coverings, flooring, window shades, and other interior applications. The line features two new products, CoverWise Olefm Film and CoverWise Green Vinyl. CoverWise Olefm Film is produced with an olefinbased polymer and does not contain plasticizers. The film is flame retardant and meets the Class A flame rating based on ASTM E-84 testing. Unlike traditional olefin based products, CoverWise Olefm

840 Reinforced Plastics Handbook

Film does not drip when exposed to flame. Its first commercial application by Lcn-Tcx Corp. won a Gold Best in Show Award at the 2003 NeoCon World's Trade Fair. CoverWisr Green Vinyl is formulated without heavy metals (lead, chromium, nickel, mercury and cadmium). It has lower VOC emissions and less odor than traditional vinyl. It is also available at a lower cost than many other 'green' alternatives.

9 Electrical conductivity, arc or tracking resistance: Most resins are inherently electrical insulators but, in some applications, it may be necessary to make them conductive to a greater or lesser degree. At the lowest, it is to reduce the poor ability of plastics to dissipate charges of static electricity. This may be useful to eliminate dustattraction in food-contact applications, or to eliminate the risk of sparks in medical and hazardous industrial applications. At the highest, it is possible to produce low-wattage plastics heating elements, such as aircraft deicing strips and industrial process heaters. Static can be reduced by adding lubricants and additives materials that bloom to the surface after molding. Conductivity can also be improved by adding materials such as carbon black or fine whiskers of metals. The effect of such additives on the other physical characteristics of the product must also be taken into account. 9 Self-lubricating properties:. Additives such as graphite, molybdenum disulphide and fluoropolymer compounds are widely used as lubricants, to reduce friction in moving parts such as gearwheels and slide/slip bearing surfaces. Waxes are also used as lubricants, to improve the flow of the molding compound, but especially to migrate to the surface of a molding compound, to act as a release agent. 9 Shrinkage: Any filler will decrease shrinkage: the most commonlyused fillers are silica, clay, calcium carbonate, alumina talc, powdered metals, and lithium aluminum silicate. Low-shrink or low-profile additives are used in TS systems such as SMCs and BMCs to minimize shrinkage during and after molding, and improve the surface appearance of a molding. 9 Machinability and abrasion resistance: These additives make the resin harder and more easily cut or machined. Typical fillers for this include powdered metals, wood flour, calcium carbonate, sawdust, clay, and talc. Resistance to abrasion may be improved by the addition of elastomers or polyurethanes. Lines of Development A main line of development today is multifunctional additives, such as fillers that are treated to provide also a degree of reinforcement. For

9

Selecting 9 Plastic and Process 841

example, calcium carbonate improves surface gloss of PVC and talc is added to PP to improve stiffness and heat stability. An essential aspect is the compatibility with the resin matrix and there is intense development of surface-modification technology, to render fillers of all types more acceptable to the matrix. Another major line of development is to meet increasingly strict regulations for health and safety, both in the workplace and in public use. This particularly affects flame retardant additives (where concern has been expressed about possible escape of flame-retardant components during storage, under heat and flame and in recycling, and pigments. Chemical Resistance

Most plastic producers have developed long-term data for commonly used chemicals. Some plastics like HDPE are immune to almost all commonly found solvents. PTFE (polytetrafluoroethylene) in particular is noted principally for its resistance to practically all-chemical substances. It has been generally identified as the most inert material known worldwide. Others exhibiting good chemical resistance are all of the fluorocarbon plastics, ethylpentene, polyolefins, some phenolics, and diallyl phthalate compounds. Chlorinated polyether is formulated particularly for products requiring good chemical resistance. Additives such as fillers, plasticizers, stabilizers, colorants, and catalysts can increase the chemical resistance of unfilled plastics. Table 9.12 provides chemical resistant loss in tensile strength and flexural strain of glass fiber/TP (wt%) RPs where E = excellent (0 to 3%), A = Acceptable (3 to 10%), F = fair (10 to 2 5%), X = unacceptable (<2 5%), and bold face at 0.2 5 % flexural strain. Careful tests should be made under actual use conditions in final selection studies and ensure using the required amount and proper blending of fillers, etc. Extensive and important data compilation is available worldwide concerning the chemical resistance on the properties and characteristics of reinforced TPs (RTPs) and unreinforced TPs (URTPs), reinforced TSs (RTSs) and unreinforced thermosets (URTSs), as well as reinforced and unreinforced elastomers.

Color Color has always been an important component of the URP and RP aesthetic value. In the beginning, putting color into plastics justified its cost by eliminating, in many cases, the need to paint a fabricated part. This is no longer sufficient. Today, color stylists seek to exploit the entire appearance experience to help create a desired product image.

842 Reinforced Plastics Handbook

Table 9.12 Chemical resistant loss in tensile strength and flexural strain of glass fiber/thermoplastic (wtO/o) (courtesy of LNP)

Polymer

ETFE

FEP

Nylon66

PBT

PPS

PES

PSF

Glass Content

20

20

50

40

40

40

40

7 days at 23~ HC1, 10O/o H2S04, 10O/o Water NH4OH, 10O/o Ethylene Glycol Toluene Trichloroethylene

E,E F,F E,E E,E E,E F,F E,E

E,E A,F E,E E,E E,E E,E E,E

F,X F,F F,F F,X A,F E,E E,A

A,A F,X F,F X,X A,A F,F F,F

E,E F,F E,E E,E A,A A,F F,X

A,A A,F E,E A,F E,E F,X F,F

A,F A,F E,A F,F E,E X,X X,X

3 days at 82~ HC1, 10O/o H2504, 10O/o Water NH4OH, 10O/o Ethylene Glycol Toluene Trichloroethylene

E,E E,E E,E E,E E,E F,F F,F

A,A F,F E,E E,E F,F F,F F,X

X,X X,X X,X X,X X,X A,A A,F

X,X X,X X,X X,X X,X X,X X,X

A,F X,X A,F E,A A,F F,F X,X

A,F A,F A,F F,F E,A F,X X,X

F,F F,F F,F F,F A,F X,X X,X

1 day at 149~ HC1, 10% H2504, 10O/o Water NH4OH, 10O/o Ethylene Glycol Toluene Trichloroethylene

F,F X,X F,F X,X F,X F,F X,X

F,F X,X F,F F,F F,F F,X X,X

X,X X,X X,X X,X X,X F,F F,F

X,X X,X X,X X,X X,X X,X X,X

X,F X,X X,X F,X F,X X,X X,X

X,X X,X F,X F,X F,X X,X X,X

X,X X,X X,X X,X X,X X,X X,X

Source: Data courtesy of LNP Engineering Plastics, Inc.

Package design has been an interactive process: stylists demanding more from the technology, and, at the same time, advances in plastics coloring technology stirring creative and innovative approaches. A way in which the plastic industry has created more value when required is by making plastic look more like the traditional materials they replaced: glass, aluminum, wood, stone, metal, etc. The industry has responded with special effects colorants to give plastic the luster and iridescence of pearl, the rich sheen of gold and silver, or natural appearance of wood, stone, or leather.

9 Selecting 9 Plastic and Process 843

There are pigment and dye colorants. Pigments are defined as colorants that do not dissolve in the plastic matrix of interest. The dyes are colorants that do go into solution. Different colorants are used to meet different requirements ranging from surface to transmission conditions. Urea, melamine, polycarbonate, polyphenylene oxide, polysulfone, polypropylene, diallyl phthalate, and phenolics are examples of plastics used in the temperature range above 200F (93C) for good color stability. Most TPs will be suitable below this range. Special colors have been produced for specific products. Crazi n g/era cki ng

Many UTPs will craze or crack under certain environmental conditions, and products, which are highly stressed mechanically, must be checked very carefully with RTPS potentially reducing this condition. Polypropylene, ionomer, chlorinated polyether, phenoxy, EVA, and linear polyethylene offer greater freedom from stress crazing than some other TPs. Solvents may crack parts held under stress. TSs can be used for parts under continuous loads without crazing/cracking. Elasticity

If the RP product requires flexibility, the choice is limited to plastics such as EVA, ionomer, polyethylene, vinyl, polypropylene, fluorocarbon, silicone, polyurethane, plastisols, acetal, nylon, natural rubber, or some of the rigid plastics that have limited flexibility in thin sections; e.g., thin laminations are quite flexible. Electric/Electron ic

RPs and their properties are extensively used and extremely important in this market. Applicable data has been presented throughout this book. What follows provides additional information on RPs (Tables 9.13 and 9.14). Flame Resistance

The Underwriters' ruling on the use of self-extinguishing RPs for contact-carrying members and many other components introduces critical material selection problems. All TSs are self-extinguishing. Nylon, polyphenylene oxide, polysulfone, polycarbonate, vinyl, chlorinated polyether, chlorotrifluoroethylene, vinylidene fluoride, and fluorocarbon are TP examples that may be suitable for applications requiring self-

844 Reinforced Plastics Handbook Table 9.13

Class

Examples of electrical properties for RPs

Material types Phenolic resin - glass fiber b Epoxy resin - glass fiber

Continuous Limited dose service for sealing temperature properties range

(rad)

(oF)

10 lo

-423 to SO0

Preferred for general use in interior

5 x 109

-423 to 250

and exterior structural applications a

Modified epoxy- phenolicglass fiber (heat resistant

Remarks

particularly where moderate to high 5 x 109

temperatures and radiation exposures

epoxy)

are encountered; excellent mechanical strength properties and good stability to vacuum and UV radiation

Polyester resin - glass fiber

109

-423 to 250

Not preferred for general primary

Melamine resin - glass fiber

109

-423 to 500

structural use because of lower

Silicone resin - glass fiber

109

-423 to 500

Triallylcyanurate resin (TAC)-

strength properties, and slightly poorer stability to the space environment;

glass fiber (heat resistant

recommended for external or internal

polyester)

electrical applications where optimum dielectric properties are required (e.g., radomes) particularly at moderate to high temperatures and moderate radiation exposures

III

Phenolic, polyester, epoxy resins and modifications filled or reinforced with organic fibers {e.g., Dacron and Orlon)

108

-100 to 250

Not recommended for structural applications but may be used in certain non-structural internal applications such as dielectrics. These materials may be used instead of l and II only under exceptional circumstances, after thorough review of design and environment application. Relatively low mechanical strength properties and temperature and radiation stability. Good vacuum and dimensional stability. Good electrical properties

a Many combinations of resins and reinforcement types and weaves available for specific structural applications. Directional strength properties can be varied from unidirectional to orthotropic by choice of reinforcement type and laminate fabrication method. bOther fibrous inorganic reinforcements, e.g., Refrasil quartz or asbestos; should be equally suitable for use in space but data lacking to support recommending them. These reinforcements are generally used for more specialized applications such as thermal insulation, ablation, etc., where mechanical strength properties are secondary to heat resistance.

extinguishing properties. Cellulose acetate and ABS are also available with these properties. Glass reinforcement improves these materials considerably.

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846 Reinforced Plastics Handbook Impact Although impact strength of URPs and RPs is widely reported, the properties have no particular design values and can be used only to compare relative response of materials. Even this comparison is not completely valid because it does not solely reflect the capacity of the material to withstand shock loading, but can pick up discriminatory response to notch sensitivity. A better value is impact tensile, but unfortunately, this property is not generally reported. The impact value, with this limitation, can broadly separate those, which can withstand shock loading versus those, which are poor in this response. Therefore, only broad generalizations can be obtained on these values. However, RP products tend to have outstanding impact properties. Comparative tests on sections of similar size that are molded in accordance with the proposed product must be tested to determine the impact performance of a plastics material. The laminated plastics, glassfilled epoxy, melamine, and phenolic are outstanding in impact strength. Polycarbonate, nylon, and ultrahigh molecular weight PE are examples of having outstanding impact strength (Table 9.15). Table 9.15 Charpy impact test results of square woven fabric using hybrid fibers/nylon RPs

Rotio of oromida/ corbon~

Dynomic flexure strength, 103 psi

Impoct energy,

100/0 50/50 25/75 0/100

63 82 82 99

48 44 34 28

ft.-Ib.fin. 2

Odor/Taste Many different plastics, particularly URPs, are used in food packaging and refrigerating conditions. TPs that are odor- and taste-free include polyethylene, polystyrene, styrene-acrylonitrile, acrylic, ABS, polysulfone, EVA, polyphenylene oxide, and many others. TS melamine and urea compounds are suitable for this service. FDA approvals are available for many plastics.

Permeability Certain plastics are impervious to different materials that are used as interlayers in RPs. However, there are those that have certain poor

9

Selecting 9 Plastic and Process 847

permeability properties. As an example, polyethylene will pass wintergreen, hydrocarbons, and many other chemicals. It is used in certain cases for the separation of gases since it will pass one and block another. Chlorotrifluoroethylene and vinylidene fluoride, vinylidcne chloride, polypropylene, EVA, and phenoxy merit special study. Extensive data compilation is available concerning permeability properties and characteristics of plastics and elastomers. The basic physical characteristics of these materials are generally well defined by resin manufacturers. The permeation of gases and vapors through thin films is dependent on the molecular size, shape, wettability and soundness of the fabricated membrane. Since permeation in well-made products is a molecular transport phenomenon, it is affected by orientation, degree of crystallinity and temperature. Attempts have been made to relate permeation rates through thin films to absorption of thicker films, sheets, pipe, etc. This has been generally unsuccessful. Thicker films and sheets represent an average set of properties obtainable from many thin films produced under a variety of conditions. To produce a thin film representative of this average is not practical. Radiation

In general, rigid plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics. Examples of materials, which will respond satisfactorily in the range of 101~ and 1011 erg per gram, are fluoroplastics, glass fiber-filled phenolics, certain epoxies, polyurethane, polystyrene, mineral-filled polyesters, silicone, and furane resins. The next group of resins in order of radiation resistance includes polyethylene, melamine, urea formaldehyde resins, unfilled phenolic, and silicone resins. Those materials, which have poor radiation resistance, include methyl methacrylate, unfilled polyesters, cellulosics, polyamides, and fluorocarbons (Tables 9.16 and 9.17). Temperature Resistance

Thermal considerations will quickly eliminate certain materials. For products operating above 450F (232C), the silicones, polyimides, fluoroplastics, hydrocarbons, methylpentene cold mold, or glass-bonded mica are examples of plastics that may be required. A few of the organic resin-bonded inorganic fibers such as bonded ceramic wool perform well in this field. Epoxy, diallyl phthalate, and phenolic-bonded glass fibers may be satisfactory in the 450 to 550F (232 to 288C) range. Between 250 and 450F (121 and 232C), glass or mineral-filled phenolics, melamine, alkyd, silicone, nylon, polyphenylene oxide,

4~

Table 9.1 6 Mechanical properties of glass fabriclTS polyester RPs exposed to various intensities of near UV radiation in a vacuum

Material Polyester (P-43)

Epoxy (Epon 815)

Phenolic (91 -LD)

Ultraviolet in tensity b (W/cm 2) 0 0.036 0.054 0.072 0.090 0.108 0 0.036 0.054 0.072 0.090 0.108 0 0.036 0.054 0.072 0.090 0.108

Exposure time (hr)

Maximum temperature reached [~

Weight loss c (O/o)

125 125 25 3 3

250 290 325 338 442

0.7 1.1 2.5 3.6 5.1

125 125 25 3 3

270 300 335 342 448

0.5 0.8 1.7 2.1 2.3

125 125 25 3 3

275 320 350 402 460

0.5 1.2 1.3 1.6 1.5

a Pressure range during exposures: 7.1 x 10-s (at highest intensity] to 6.0 x 10-6 torr. b Wavelength range: 2000-4200 ~, {0.0164 W/cm2 = 1 sun in this wavelength range]. cSpecimens exposed to high vacuum at 70~ for 1000 hr had negligible weight loss (< 0.1%). d Average of four specimens.

Average d ultimate flexure strength (psi)

Average a flexu ra l modulus (106 psi)

Average a compressive strength (psi)

A verag ea compressive modulus (106 psi)

59,300 61,800 64,400 50,100 24,200

2.4 2.6 2.8 2.5

40,900 47,300 51,900 40,80O 39,900

3.1 3.1 3.2 3.1 3.1

84,400 84,700 84,000 57,600 39,800

3.8 3.8 3.8 3.5

53,900 48,400 51,300 43,800 44,200

3.5 3.5 3.5 3.4 3.4

68,900 61,700 56,700 49,500 57,100

3.6 3.6 3.5 3.0 3.2

44,800 39,400 39,300 31,500 32,600

3.5 3.5 3.5 3.4 3.4

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9

Selecting 9 Plastic and Process 8 4 9

Table 9.17 Properties of glass fiber fabriclTS polyester RPs after irradiation at elevated temperatures

Resin type Silicone ~

Heat-resistant epoxy b

Phenolic b

Test Flexure

Compression

Flexure

Exposure Temperature (rad) (~

Exposure Ultimate time strength (hr) (psi)

None 8.3 x 107

Room Room

None 200

None 2.1 x 107

500 500

50 50

None 4.15 x 107

500 500

100 100

None

500

200

8.3 x 107 None 8.3 x 107

500 Room Room

200 None 200

None 2.1 x 107

500 500

50 50

None 4.15 x 107 None 8.3 x 107 None 8.3 x 107

500 500 500 500 Room Room

100 100 200 200 None 200

None 2.1 x 107

500 500

50 50

None 4.15 x 107 None 8.3 x 107

500 500 500 500

100 100 200 200

31 760 31 460 12 390 13 625 13,410 11 720 14,060 9 860 46,680 46,660 3,705 3 780 4,090 5,490 4,720 6,360 84,525 84,040 27,300 55,020 17 660 47,015 12,330 15,645

Flexural modulus (106 psi) 3.06 2.94 1.90 2.0 2.0 2.0 2.0 1.9

4.22 4.35 3.14 3.46 2.62 3.61 2.13 2.41

a 181 glassfabric (112finish). b 181 glassfabric (Volan-Afinish).

polysulfone, polycarbonate, methylpentene, fluorocarbon, polypropylenc, and diallyl phthalate can be evaluated; the addition of glass fillers to the TPs can raise the useful temperature range as much as 100F (212C) and at the same time shorten the molding cycle. In the 0 to 212F (-18 to 100C) range, a broad selection of materials is available. Low temperature considerations may eliminate many of the TPs. Polyphenylene oxide can be used at temperatures as low as -273F (-170C). TS materials exhibit minimum embritdement at low temperatures. Different plastics behave differently when exposed to temperatures; most plastic can take greater heat than humans can or buildings can take. Some cannot take boiling water and others operate at 150C (300F) with a

Table 9.18

Properties of thermoset RPs at ambient and elevated temperatures

Room temperature tensile strength [ 103psi)

Room temperature compressive strength ( 103psi)

Ultimate flexural strength (103psi) At room temperature

After 30-day water immersion

01 0

Flexural modulus (103 psi)

At 300~

At 500oF

At room temperature

At 300~

At 500~

40-60 58-63 60-65 44

8-11 25 47

3600-3800 3200-3400 4000-4200 5000

2900-3300 2700 3700-3900 3700

3200

23

5300

40 47- 52 65

3000 4800 4300 2600 3700

s~ e,~

Fabric Laminates

Epoxy-glass Bisphenol A Novalac Peracetic acid Bisphenol A and high-modulus glass High-temperature epoxy and high-modulus glass Phenolic-glass Standard grade Heat- resistant Silane-modified Phenolic-leached glass Phenolic-quartz Polyesters Styrene-modified TAC-modified Styrene-modified and high-modulus glass Silicone-glass

Filamen t- Wound Structures

Epoxy-g lass Epoxy and high-tensile glass Mil P-27327 (proposed)

Molding Compounds

Phenolic-glass Phenolic-lea ched-g lass Phenolic-asbestos Silicone-glass Polyester-g lass

50 42 57-59 64

55 57 49-53 61

85-89 85-90 85-90 90

55

59

86

50 65 46 14 35

35 48 51 24

50 86 80 25 68

50-55 59

40-45 51 52

50-75 65 59

64 59 49

30 43

24 30

41

29

50

36

23

270 285 200

70

271

50

220

10 8.5 9 4.5 9.5

35 36 24 16 29.5

20 14 24 14 19

65-80 76

52 73

78 65 20 37

-1"-

o-

3000

4OOO 3500 2600 3400

3000 3300-3600 3500 2600 3200

3300 3000 4200

2500 2000

2000 1800

21

2900

2400

2200

180

7000

6800

6800

3300 3000 2000 2100 1400

1100 910

1400 500 910

50

245 210

200 16.4 6 12.7

15 6 6.7

mo ISI

o o

9

Selecting 9 Plastic and Process 8 5 1

few up to 540C (1000F). The flexible (elastomer) plastics at room temperature become less flexible as they are cooled finally become brittle at a certain low temperature. Then there are plastics that reach 1370C (2500F) with exposures in fractions of a second. An excellent test if a plastic can take heat is put in your automobile trunk or a railroad boxcar where temperatures can reach 55C (130F). Important to understand that there is a temperature transition in plastics; also called ductile-to-brittle transition temperature. It is temperature at which the properties of a material change. Depending on the material, the transition change may or may not be reversible. A few of other characteristics are presented. The plastic softening range temperature is the temperature at which a plastic is sufficiently soft to be distorted easily. A number of tests exist (ASTM) and the temperatures arrived at may vary according to the particular test method. Softening range is sometimes erroneously referred to as the softening point. Temperature stability identifies the percent change usually in tensile strength or in percent elongation as measured at a specified temperature and compared to values obtained at the standard conditions of testing. Temperature can influence shortand long-time static and dynamic mechanical properties, aesthetics, dimensions, electronic properties, and other characteristics. The socalled high-temperature types can take various degrees of continuous use above 149C and there are plastics that reach at least 538C (1,000F). Examples of temperature influence on plastics are provided in Table 9.18 and Figures 9.2 to 9.4. Figure 9.2 includes RP with glass fiber contain at 30 wt%; higher temperatures obtained by using fiber reinforcements such as boron, carbon, graphite, and aramid.

F -1000--g50-900-850-

Polyimide/Graphite - 0 0 0 -750-

Polyimide/Glass - 7 0 0 Silicone

Fluoroplastics/Glass Polyetherketoneketone(PEEK)/Graphite - 6 5 0 -

Liquid Crystal/Polymer - 6 0 0 Polyester TS/Glass Epoxy/Glass - 5 5 0 Nylon/Glass Allyl/Glass -500-

Cyanates

Silicones/Glass Polybenzimidazole (PBI) Bismaleimide

(BMI)/Carbon

Polyimide/Glass

Polyetherketone/Glass Bismaleimide (BMI)/Glass

Polyketone/Glass

Polyetheretherketone(PEEK)/Glas~ Polyphenylene Sulfide/Glass Polyimide Polamide-lmide/Glass Phenol-Formaldehyde

CyanateEster/Glass

Polysulfone/Glass PolyaromaticTP-EpoxyTS/Glass PolyethyleneTerephthalate/Glass Silicon-Polycarbonate/Glass Polyethersulfone/Glass Polyarylsulfone/Glass Polyurea/Glass Polysulfone - 3 5 0 - Polyester TP/Glass ; Polymethylpentene -" - PolycarbonateCopolymer Polyethylene/Glass --300- Polypropylene/Glass

TS Polyester/Glass - 4 5 0 Polyetherimide/Glass _ _ Polybutadiene/Glass Silicone --400Melamine-Formaldehyde --

Epoxy PBT L 2 5 0 Polyester TS Polyester TP i

Polycarbonate ABS/Glass Polyurethane/Glass

With a temperature change the Vinyl/Glass short-term static strength, the Polyurethane 200 SAN elastic modulus, and the elongation behavior of a material will be Figure 9.2 URP and RP heat deflection similar for it's tensile, compressive, temperature under 10adper ASTM flexural, and shear properties. A D 648 (courtesyof Plastics FALL0)

852 Reinforced Plastics Handbook

Figure 9,3

Temperature-time guides retaining 50% plastic properties; with reinforcements properties increase (courtesy of Plastics FALLO) AMORPHOUS

t

UNFILLED REINFORCED

CRYSTALLINE

~ E D REN IFORCED

::3 ,.,J :::> c3 0

O=MELT

TEMPERA TURE

"=

r

Figure 9.4 Glass fiber/nylon RP modulus behavior with increase in temperature (heat deflection temperature under load per ASTM D 648) (courtesy of Bayer)

material's strength and modulus will decrease and its elongation increase with increasing temperature at constant strain. Curves for creep isochronous stress and isometric stress are usually p r o d u c e d from measurements at a fixed temperature. Complete sets of these curves are sometimes available at temperatures other than the ambient. It is c o m m o n , for instance, to find creep rupture or apparent

9

Selecting 9 Plastic and Process 8 5 3

modulus curves plotted against log time, with temperature parameter.

as

a

These curves suggest that it would be reasonable to estimate moduli at somewhat longer times than the data available from the lower temperatures. However, a set of creep-rupture curves from various temperatures would suggest that projecting the lowest-temperature curves to longer times as a straight line could produce a dangerously high prediction of rupture strength, so this approach is not recommended (Chapter 7). As previously reviewed one advantage of conducting complete creeprupture testing at elevated temperatures is that although such testing for endurance requires long times, the strength levels of the plastic at different temperatures can be developed in a relatively short time, usually just 1,000 to 2,000 h. The Underwriters Laboratories and other such organizations have employed such a system for many years. Testing different impact properties at various temperatures produces a plot that looks very much like an elongation vs. temperature curve. As temperatures drop significantly below the ambient temperatures, most TPs lose much of their room-temperature impact strength. A few, however, are on the lower, almost horizontal portion of the curve at room temperature and thus show only a gradual decrease in impact properties with decreases in temperature. One major exception is provided by the glass fiber RPs, which have relatively high Izod impact values, down to at least - 4 0 C (-40F). The S-N (fatigue) curves for TPs at various temperatures show a decrease in strength values with increases in temperature. However the TSs, specifically the TS RPs, in comparison can have very low losses in strength.

Weathering Many plastics have short lives when exposed to outdoor conditions. RPs, particularly glass fiber RPs) can be destroyed if not properly fabricated to eliminate seepage of water between fibers and resin. The better materials to weatherability include acrylic, chlorotrifluorethylene, vinylidene fluoride, chlorinated polyether, black linear polyethylene, TS polyester, epoxy, alkyd, and phenolic (Table 9.19). Some of these plastics have successfully performed outdoors for over a half-century. Black materials are best for outdoor service. Some of the styrene copolymers are suitable for certain outdoor uses. Moisture

For high moisture applications, polyphenylene oxide, polysulfone, acrylic, butyrate, diallyl phthalate, glass-bonded mica, mineral-filled

854 Reinforced Plastics Handbook

Figure 9,5 Compressivestrength of 1/8 in. thick glass fabric laminated flat RPs exposed to outdoor weathering tested at 23(Z(73F) Table 9, I 9 Flexural modulus of glass fiber/TS polyester exposed to different weathering/environment elements

Flexural modulus (106psi) Test conditions Atmospheric pressure and room temperature Low pressure (10-6 torr) at room temperature Low pressure (10-6 torr), ultraviolet (0.036 W/cm 2) and moderate temperature {250~ Atmospheric pressure, ultraviolet (0.036 W/cm 2) and moderate temperature (250oF) Atmospheric pressure, ultraviolet (0.036 W/cm 2) and room temperature Low pressure (10-6 torr} and moderate temperature (250~ Atmospheric pressure and moderate temperature (250oF)

Polyester

Epoxy Phenolic

4.67 4.67 3.84

3.54 3.54 2.14

4.17 4.17 3.94

3.38

2.00

3.86

3.75

3.54

3.68

3.61

2.38

3.96

3.75

2.25

3.81

9

Selecting 9 Plastic and Process 8 5 5

phenolic, chlorotrifluoroethylene, vinylidene, chlorinated polyether chloride, vinylidene fluoride, and the fluorocarbons should be sarisfactory. Diallyl phthalate, polysulfone, and polyphenylene oxide have performed well with moisture/steam on one side and air on the other (a troublesome combination), and they also will withstand repeated steam autoclaving. Long-term studies of the effect of water have disclosed that chlorinated polyether gives outstanding performance. Impact styrene plus 25 wt% graphite and high density polyethylene with 15% graphite give long-term performance in water. The effect of having excess moisture manifests itself in various ways, depending on the process being employed. The common result is a loss in both mechanical and physical properties for hygroscopic (tending to absorb moisture; capable of adsorbing and retaining atmospheric moisture) and nonhygroscopic (collect moisture only on the surface) plastics. During injection molding splays, nozzle drool between controlled shot-size, sinks, and other losses may occur. The effects during extrusion can include gels, trails of gas bubbles in the extrudate, arrowheads, waveforms, surging, lack of size control, and poor appearance. See Chapter 5 Processing and Moisture.

Variabilities There is continuous progress concerning reducing the existing RP material and processing equipment variabilities (as there are for steel and other materials). Target is always to improve their manufacturing and process control capabilities. However, they still exist. To ensure minimizing material and process variables different tests and setting limits on performances are important. Even set within limits, processing the materials could result in inferior products. As an example, the material specification from a supplier will provide an available minimum to maximum value such as molecular weight distribution (MWD). It is determined that when material arrives all on the maximum side it produces acceptable products. However, when all the material arrives on the minimum side process control may have to be changed in order to produce acceptable products. In order to judge performance capabilities that exist within the controlled variabilities, there must be a reference set up to measure performance. As an example, the injection mold cavity pressure profile is a parameter that is easily influenced by variations in the materials. Injection molding related to this parameter are four groups of controls that when put together influences the processing profile:

856 Reinforced Plastics Handbook

1

melt viscosity and fill rate,

2

boost time,

3

pack and hold pressures, and

4

recovery ofplasticator.

Thus, material variations may be directly related to the cavity pressure variation (Chapter 5). Even though equipment operations have understandable but controllable variables that influence processing, the usual most uncontrollable variable in the process can be the RP material. A specific RP will have a range of performances. However, more significant, is the degree of properly compounding or blending by the manufacturer, converter, or in-house by the fabricator is important. Most additives, fillers, a n d / o r reinforcements when not properly compounded will significantly influence processability and molded product performances. A very important factor that should not be overlooked by a designer, processor, analyst, statistician, etc. is that most conventional and commercial tabulated material data and plots, such as tensile strength, are average or mean values. They would imply a 50% survival rate when the material value below the mean processes unacceptable products. Target is to obtain some level of reliability that will account for material variations and other variations that can occur during the product design to processing the RP products. In addition to material variables, there are variables in equipment hardware and controls that cause processing variabilities. They include factors such as accuracy of machining component equipment parts, method and degree of accuracy during the assembly of component parts, temperature/pressure control capability particularly when interrelated with time and heat transfer uniformity in metal components such as those used in molds and dies. These variables are controllable within limits to produce useful and cost efficient products. What is important to appreciate is that during the past many decades' improvements in equipment, as in RP materials, have made exceptional strides in significantly reducing operating variabilities or limitations. This action will continue into the future since there is a rather endless improvement in performance of steels and other materials and methods of controlling such as fuzzy control. Growth is occurring in applying fuzzy logic that in 1981 was based on the idea to mimic the control actions of the human operator.

9

Selecting 9 Plastic and Process 8 5 7

Testing and Selection Testing provides a means for material and molded product selection (evaluating product designs and comparing the evaluation). They yield basic information about RPs, its properties relative to another RP, its quality with reference to standards, and applied to designing with plastics. They are usually destructive tests but there are also nondestructive tests (NDTs). Most of all, it is essential for determining the performance of materials to be processed and of the finished products. Testing refers to the determination by technical means properties and performances. This action, when possible, should involve application of established scientific principles and procedures. It requires specifying what requirements are to be met. Many different tests that can be conducted relate to practically any requirement. Many different tests are provided and explained in different specifications and standards by different organizations (Table 9.20). Table 9 . 2 0 Organizations involved in specifications, regulations, and standards ASTM. American Society for Testing and Materials. UL. Underwriters Laboratories. ISO. International Organization for Standardization. DIN. Deutsches Instut, Normung. ACS. American Chemical Society. ANSI. American National Standards Institute. ASCE. American Society of Chemical Engineers. ASM. American Society of Metals. ASME. American Society of Mechanical Engineers. BMI. Battele Memorial Institute. BSI. British Standards Institute. CPSC. Consumer Product Safety Commission. CSA. Canadian Standards Association. DOD. Department of Defense. DOSISS. Department of Defense Index Et Specifications Et Standards. DOT. Department of Transportation. EIA. Electronic Industry Association. EPA. Environmental Protection Agency. FMRC. Factory Mutual Research Corporation. FDA. Food and Drug Administration. FTC. Federal Trade Commission. IAPMO. International Association of Plumbing Et Mechanical Officials.

IEC. International Electrotechincal Commission. IEEE. Institute of Electrical and Electronic Engineers. ISA. Instrument Society of America. JIS. Japanese Industrial Standards. NADC. Naval Air Development. NACE. National Association of Corrosion Engineers. NAHB. National Association of Home Builders. NEMA. National Electrical Manufacturers' Association. NFPA. National Fire Protection Association. NIST. National Institute of Standards ec Technology {previously the national Bureau of Standards]. NIOSH. National Institute for Occupational Safety ~ Health. OSHA. Occupational Safety ec Health Administration. PLASTEC. Plastics Technical Evaluation Center. PPI. Plastics Pipe Institute. OPL. Qualified Products List. SAE. Society of Automotive Engineers. SPE. Society of Plastics Engineers. SPI. Society of the Plastics Industry. TAPPI. Technical Association of the Pulp and Paper Industry.

858 Reinforced Plastics Handbook

Choosing and testing an RP when only a few existed that could be used for specific products would prove relatively simple, but the variety has proliferated. However, a few basic tests, such as a tensile mechanical test, will help determine which material is best to meet the performance requirements of a product (Chapter 7). At times, a complex test may be required. The test or tests to be used will depend on the product's performance requirements. Examples of tests with their capabilities and limitations will be reviewed. Understanding and proper applications of the many different destructive and NDTs tests can be an endless project. However, they are essential for determining the performance of materials to be processed and of the finished fabricated products. Testing requires specifying what requirements are to be met. To ensure quality control material suppliers and developers routinely measure such properties as molecular weight and its distribution, stereochemistry, crystallinity and crystalline lattice geometry, and detailed fracture characteristics (Chapter 3). They use specialized tests such as gel permeation chromatography, wide- and narrow-angle X-ray diffraction, scanning electron microscopy, and high-temperature pressurized solvent reaction tests to develop new polymers and plastics applications. A different type of evaluation is the potential of a material that comes in contact with a medical patient to cause or incite the growth of malignant cells (that is, its carcinogenicity). It is among the issues addressed in the set of biocompatibility standards and tests developed as part 3 of ISO-10993 standard that pertain to genotoxicity, carcinogenicity, and reproductive toxicity. It describes carcinogenicity testing as a means to determine the tumorigenic potential of devices, materials, a n d / o r extracts to either a single or multiple exposures over a period of the total life span of the test animal. The circumstance under which such an investigation may be required is given in part 1 of ISO-10993. The primary purposes of testing related to shock and vibration are to verify and characterize the dynamic response of the product to a dynamic environment and to demonstrate that the final design will withstand the test environment specified for the product under evaluation. Basic characterization testing is usually performed on an electrodynamic vibration machine with the unit under test hardmounted to a vibration fixture that has no resonance in the pass band of the excitation spectrum. The test input is a low-displacement-level sinusoid that is slowly varied in frequency (swept) over the frequency range of interest. Sine sweep testing produces a history of the response (displacement or acceleration) at selected points on the equipment to

9

sinusoidal excitation displacements.

over the

tested

Selecting 9 Plastic and Process 8 5 9

excitation

frequencies

and

Caution is advised when using a hard-mount vibration fixture, as the fixture is very stiff and capable of injecting more energy into a test specimen at specimen resonance than would be experienced in service. For this reason, the test-input signal should be of low amplitude. In service, the reaction of a less stiff mounting structure to the specimen at specimen resonance would significantly reduce the energy injected into the specimen. If a specimen response history is known prior to testing, the test system may be set to control input levels to reproduce the response history as measured by a control accelerometer placed at the location on the test specimen where the field vibration history was measured. Vibration-test information is used to aid in adjusting the design to avoid unfavorable responses to service excitation, such as the occurrence of coupled resonance. It is a component having a resonance frequency coincident with the resonance frequency of its supporting structure, or structure having a significant resonance that coincides with the frequency of an input shock spectrum. Individual components are often tested to determine and document the excitation levels and frequencies at which they do not perform. This type of testing is fundamental to both shock and vibration design. For more complex vibration-service input spectra, such as multiple sinusoidal or random vibration spectra, additional testing is performed, using the more complex input waveform on product elements to gain assurance that the responses thereof are predictable. The final test exposes the equipment to specified vibration frequencies, levels, and duration, which may vary by axis of excitation and may be combined with other variables such as temperature, humidity, and altitude environments. Nondestructive Tests

N D T examines material without destroying or impairing its ultimate usefiflness. It does not distort the specimen or product and provides useful data. N D T allows suppositions about the shape, severity, extent, distribution, and location of such internal and subsurface residual stresses; defects such as voids, shrinkage, cracks, etc. Test methods include acoustic emission, radiography, IR spectroscopy, x-ray spectroscopy, magnetic resonance spectroscopy, ultrasonic, liquid penetrant, photoelastic stress analysis, vision system, holography, electrical analysis, magnetic flux field, manual tapping, microwave, and birefringencc (Table 9.21). To determine the strength and endurance of a material under stress, it is necessary to characterize its mechanical behavior. Moduli, strain,

oo Q

Table 9.21 Examplesof nondestructive test methods

Method

Typical Flaws Detected

TypicalApplication

Advantages

Disadvantages

Radiography

Voids, porosity, inclusions, and cracks

Castings, forgings, weldments, and structural assemblies

Detects internal flaws useful on a wide variety of geometric shapes; portable; provides a permanent record

High cost; insensitive to thin laminar flaws, such as tight fatigue cracks and delaminations; potential health hazard

Liquid penetrants

Eddy current testing

Cracks, gouges, porosity, laps, and seams open to a surface

Castings, forgings, weldments, and components subject to fatigue or stress-corrosion cracking

Inexpensive easy to apply portable easily interpreted

Flaw must be open to an accessible surface, level of detectability operatordependent

Cracks, and variations in alloy composition or heat treatment, wall thickness, dimensions

Tubing, local regions of sheet metal, alloy sorting, and coating thickness measurement

Moderate cost, readily automated portable

Detects flaws that change in conductivity of metals; shallow penetration; geometry-sensitive

Castings, forgings, and extrusions

Simple; inexpensive detects shallow subsurface flaws as well as surface flaws

Useful for ferromagnetic materials only; surface preparation required, irrelevant indications often occur; operator-dependent

Magnetic particles Cracks, laps, voids, porosity and inclusions

Thermal testing

Voids or disbands in both metallic and nonmetallic materials, location of hot or cold spots in thermally active assemblies

Laminated structures, honeycomb, and electronic circuit boards

Produces a thermal image that is easily interpreted

Difficult to control surface emissivity poor discrimination

Ultrasonic testing

Cracks, voids, porosity, inclusions and delaminations and lack of bonding between dissimilar materials

Composites, forgings, castings, and weldments and pipes

Excellent depth penetration good sensitivity and resolution can provide permanent record

Requires acoustic coupling to component; slow; interpretation is often difficult

a"

Ill m, IJI

-Ta" o o

9

Selecting 9 Plastic and Process 861

strength, toughness, etc. can be measured microscopically in addition to conventional destructive testing methods. These parameters are useful for design and material selection. They have to be understood as to applying their mechanisms of deformation and fracture because of the viscoelastic behavior of plastics. The fracture behavior of materials, especially microscopically brittle materials, is governed by the microscopic mechanisms operating in a heterogeneous zone at the crack tip or stress raising flow. In order to supplement micro-mechanical investigations and advance knowledge of the fracture process, micro-mechanical measurements in the deformation zone are required to determine local stresses and strains. In RTPs craze zones can develop that are important microscopic features around a crack tip governing strength behavior. Plastics fracture is preceded by the formation of a craze zone that is a wedge shaped region spanned by oriented micro-fibrils. Methods of craze zone measurements include optical emission spectroscopy, diffraction techniques, scanning electron microscope, and transmission electron microscopy. Conditioning procedures of test specimens and products are important in order to obtain reliable, comparable, and repeatable data within the same or different testing laboratories. Procedures are described in various specifications or standards such as having a standard laboratory atmosphere [50 _+ 2% relative humidity, 73.4 _+ 1.8F (23 _+ 1C)] with adequate air circulation around all specimens. The reason for this type or other conditioning is due to the fact the temperature and moisture content of plastics affects different properties. Nondestructive Evaluation

The following sections review laboratory NDE, microscopy, and experimental stress analysis methods, which the engineer can use to obtain information about the presence and severity of flaws developed by test or parts when they are subjected to sustain mechanical loading. NDE methods have the advantage that they cause no harm to the specimen; thus the same part can be nondestructively retested or subsequently tested destructively. However, NDE only reveals the location and severity of flaws. The experimenter must judge the importance of each particular flaw. Some times, the importance of a defect is obvious (harmless, or likely to shorten service lifetime, or likely to cause catastrophic failure); otherwise, experimental stress analysis will quantify the severity of the flaw. The defects that arc relevant to the strength of short/long fiber RPs are as follows:

Table 9 . 2 2 Examples of defects detected by NDT methods

Defects

X-ray

Unbond

9

Delamination

9

Neutron

Gamma ray

9

Damaged filaments

9

Variation in resin Variation in thickness

Sonic

Microwave

Penetrant

n

~

m

,

--r-

::3 s 0" 0 0

Undercure Fiber misalignment

Ultrasonic

Temperature differential

Heat, photosensitive agent

9

9

9 9

9

Variation in density

9

9

Voids

9

9

Porosity

9

9

Fracture

9

9

Contamination

9

Moisture

9

9 9

9 . Selecting Plastic and Process 863

9 surface cracks (due to excessive rate of cooling, for example), 9 weld lines (where two plastic flow fronts converge while molding), 9 areas of undesirable fiber concentration (due to undispersed fiber clumps or resin-rich areas), 9 areas of undesirable fiber orientation (such as predominant orientation transverse to the direction of maximum stress, or random orientation where alignment is preferred), and 9 excessive porosity or visible voids (gas bubbles). Materials such as RPs may contain some flaws, which may or may not be a cause for concern. Flaws that grow under operating stresses can lead to structural or component failure, whereas other flaws may present no safety or operating hazards. NDE provides a means for detecting, locating, and characterizing flaws, while the component or structure is in service. NDE methods include vision system, acoustic emission, radiography, microscopy, thermography, infrared spectroscopy, X-ray spectroscopy, Xradiography using metal-coated fibers or tracers, nuclear magnetic resonance spectroscopy, ultrasonic, fluorescent dye penetration/liquid penetrant, photo elastic stress analysis, holography, electrical NDT, magnetic flux field, manual tapping, microwave, and birefringence. Examples of defects detected by various NDT methods are given in Table 9.22. Selection of the NDE method(s) depends on the specific type of material, the type of defect/flaw to be analyzed, the environment of the evaluation, the effectiveness of the evaluation method, the size and thickness of the product, and other factors. The selection should also include the economic consequences of structural failure. However, there are always increasing demands for more accurate characterization of the size and shape of defects that may require available advanced techniques and procedures, and may involve the use of more than one method. It is usually appropriate to begin any evaluation with a microscopic examination (micrography) of the part's structure at a failure point, at the surface, and of several key cross-sections. Using typical magnification scales of 40x to 200x, sliced and carefully polished sections will reveal fiber orientation, porosity, cracking, and crazing. Thus the experimenter may evaluate a product design after fabrication, but before physical testing (to detect any obvious problem areas), as well as after, as an aid in failure analysis. In some design situations, the locations of critical areas of stress are obvious. Proper mold design and choice of part geometry should ensure adequate strength in these areas, but microscopic observation of the

864 Reinforced Plastics Handbook fiber orientation and plastic flows is a prudent precaution. Micrography is typically cheaper than physical testing, often the most cost-effective way to determine the next step early in a product program. Microscopic examination is more often beneficial when examining a part after physical testing. For example, a region that suffered unexpected cracking or complete loss of mechanical integrity may show inappropriate fiber orientation or voids formed during molding. As another example, chemical attack may cause damage in the form of matrix crazing. This insidious damage is most easily detected with micrography. One should examine from one to ten or more locations in a product part. Each location may require one or more sections. Each section is obtained by cutting a small block of material from the part. This is usually accomplished with carbide or diamond saw. The specimen is then embedded in a cylinder of resin for handling convenience. Micrography specimen is then polished until its appearance is adequately smooth under microscopic examination. The smallest remaining scratches should be at least five times smaller than the smallest feature of interest. This will ensure that details, such as crazing, are not obscured or go undetected. Approximate specimen preparation equipment costs range from $2000 to $20,000, while microscope costs are anywhere from $2000 to $40,000. The higher costs are associated with the ability to observe increasingly fine details, stereo viewing, photographic capability, etc.

Experimental Stress Analysis The greatest uncertainty of a design is often whether it will withstand mechanical loads and displacements. Examining critical areas of high stress or strain is most precisely quantified using experimental stress analysis methods. All but the most complex experimental stress analysis techniques are limited to measurement of strain on the surface of the product. The surface is often where stresses are greatest, for example when twisting or bending are present, so most analysis techniques apply. When required, through-the-thickness data may be obtained by "slicing" the product and analyzing the slices separately. The analysis methods are divided into "local" and "filll-field" categories. A local analysis reveals strain only at a point, while a flail-field analysis reveals strain at all points (a strain field). If the important localized stress points are not easily identified, then a technique that gives a flail strain field is far more useful. Precise full-field methods are generally more expensive and time consuming.

9

Selecting 9 Plastic and Process 8 6 5

Common techniques for experimental stress analysis are as follows, in descending order of the resolution and quantity of data they yield: 9 full-field 9 holographic interferometry 9 speckle interferometry (full-field type) 9 photoelastic stress analysis 9 Moire interferometry 9 crackle lacquer coating 9 adhesively bonded strain gages 9 speckle interferometry (single or dual spot type) O 9 optical extensometry (video or laser-based) An inexpensive initial evaluation may be accomplished by placing a crackle-lacquer-coated part under typical environmental loads. After observing the result, the engineer can select from among the above techniques to develop more information. Holographic interferometry measures displacements optically by reflecting light (often a laser source) first off an undeformed product and then off a mechanically deformed one. By superimposing the images as a holograph, fines of equal displacement appear on the product because of interference between laser light reflected by the separate images. The result is a "map" of the displacement field where displacement magnitude and direction are known at every point. Areas of high stress concentration are highlighted by closely spaced interference lines. The displacements can subsequently be transformed into strains and then stresses by computer software. The holograph may be recorded on film, video tape, or a computer. This may be done several times by loading the product incrementally. Holography can accurately and quantitatively measure static and dynamic displacements. Sensitivity is very high, but measurements are time consuming and expensive. Full-field speckle interferometry is similar to holographic interferometry except that the speckles are observed on the specimen surface by illuminating it with laser light or by establishing an optically speckled surface (for example by painting it). Photoelastic stress analysis is a powerful full-field technique where a product part is first covered with a thin film of special, transparent plastic. The layer must be bonded on with a reflective adhesive. The part is then deformed under static conditions and illuminated with polarized light. Viewing the part with a special polarizing optic system

866 Reinforced Plastics Handbook

will visually display lines of equal displacement. The strain field may also be recorded on film or video tape. As with holographic interferometry, the displacement must be transformed to strains and stresses. The method produces accurate, quantitative results. Furthermore, the apparatus is moderately priced at approximately $15,000. Moire interferometry is accomplished by first bonding a clear plastic film, marked with closely spaced lines, to the specimen. A second sheet, similarly marked, is then placed over the first but without bonding or electrostatic coupling. During incremental static loading, the bonded layer deforms while the second, unbonded layer, does not. Consequently, some lines will super-impose while others overlap (the so-called Moire effect). Lines of equal displacement appear which can be photographed or transformed to strains and stresses. The technique is inexpensive (less than $1000 for equipment and materials), but limited in application because significant curvature can not be accommodated. Crackle lacquer coating entails painting the product with a brittle lacquer, then incrementally deforming the part. The lacquer cracks at a known strain and the lacquer will develop easily observed regions of dense cracks when the failure strain of the lacquer is developed during incremental loading. The cracks are perpendicular to the direction of strain, thus providing information on the direction of maximum stress. Such lacquers are commercially available with failure strains from 0.0005 to 0.0008 cm/cm, as determined by temperature and humidity conditions. This technique is inexpensive (about $1000 in equipment and materials) but produces limited information: it only indicates the location and approximate magnitude of stress concentrations. Furthermore, if lacquer cracks appear below routine service loads, an appropriate modification of the design may not be obvious because the relationship between the loading across the entire part and local strains is probably not linear. Crackle lacquer coating analysis, however, is useful for screening evaluations (such as proof loading where it is determined whether the product can sustain a typical service load) or determining suitable placement of strain gauges on parts with complex geometry. The popular adhesively bonded resistance strain gauges provide an accurate, sensitive means of measuring strain at a point. They can be as small as 0.2 by 0.1 7 cm with a gauge length of 0.02 cm, and in rosette configuration can measure strain in two perpendicular directions. With proper attention to technique, one can obtain resolutions of 1 or 2 c m / c m , and record strain from static to 20 kHz transient conditions. Accuracy is typically 4% of the measured strain but can be better than 1% with special procedures. Standard gauges may be used at temperatures

9

Selecting 9 Plastic and Process 867

f r o m - 2 7 0 to +290 C and up to 0.025 c m / c m strain. The apparatus is not expensive (about $3000), but some skill is required to adhesively bond the gauges to the part and make solder connections without causing damage to the gauge or the part. Strain gauges measure inplane strains on surfaces even with curvature as high as 0.03 cm of radius. Strain gauges cannot be feasibly placed over the entire surface of a product, so key points of high stress must be identified before instrumenting the product with gauges. In many cases, these critical areas are easily identified by judgment. Note that similar gauges may be used for sensing surface temperature at a point. This is most useful for product localized heat transfer. Single- or dual-spot speckle interferometry measures motion past a point without the need of physical contact. Using dual spots makes it possible to measure relative displacement by calculating the difference between the motions. Resolution is very high and motions of a wide range of rates may be observed. The product must have a diffuse reflecting surface; it may be necessary to apply an appropriate coating if the product does not already have suitable surface reflectivity. Laser speckle interferometers cost approximately $50,000 and have the disadvantage that only one point is monitored per interferometer. They are most useful in specialized product analyses where high loading rates, high heating rates, or delicate parts are involved. Optical extensometry measures relative displacement of two marks or targets. The resolution and rate of measurement depends on optics and the image algorithm. A basic type of optical extensometry is simple photography, but dedicated electronics and a computer will yield higher resolution and real time data handling. Like speckle interferometry, the noncontacting nature of optical extensometry is particularly suited to tests with temperature fluctuations and delicate parts. Testing Against Trouble

As RPs (and URPs) continues to grow into more diverse applications, testing must adapt to meet new demands. Important in targeting to reduce or eliminate trouble is to set up troubleshooting guides for materials, fabricating products, molded products, plant operation, and so on. As the applications have grown so has the potential for costly field failures. Testing and troubleshooting are understandably more cost effective than finding design or material flaws in the field, particularly in our litigious society. Troubleshooting guides are available from your suppliers and from the literature. Table 9.23 introduces troubleshooting a glass fiber/TS polyester RP injection molding fabricating process.

868 Reinforced Plastics Handbook Table 9.2:3 Troubleshooting RP process Problem

Possible cause

Solution

Nonfills

Air entrapment

Additional air vents and/or vacuum required Adjust plastic mix to lengthen time cycle

Gel and/or plastic time too short Excessive thickness variation

Improper clamping and/ or lay-up

Check weight and lay-up and/or check clamping mechanisms such as alignment of platens

Blistering

Demolded too soon Improper catalytic action

Extend molding cycle Check plastic mix for accurate catalyst content and dispersion

Extended curing cycle

Improper catalytic action

Check equipment, if used, for proper catalyst metering Remix plastic and contents: agitate mix to provide even dispersion

The changing business environment means that most large OEM's now outsource functions that they would normally have retained within their own operations, including some design, assembly, and testing of complete assemblies. Suppliers are now seen as partners and the testing laboratory is a key function. A part supplier today has to perform in a full service role. The testing lab has been integrated into the design process and plays a big role in qualifying and providing test data to validate actual performance. Traditional tensile, compression, and flexural tests are being supplemented by newer and more exacting requirements that include much more action in formability, instrumented impact, pressure, thermal environment simulation, and fatigue and fracture testing that can provide product life prediction. Data from these exhaustive tests are fed back to designers using finite element analysis and to customers as proof of quality. Failure analysis is another key role of the lab to study warranty returns and identify root causes of problems. There are many new industry and customer-specific test methods that must be applied. Many lab managers indicate they never do the same test twice in a month, but have to adapt to changing needs. Software plays a big role in the ability of the lab to quickly change over test methods and data analysis. These

9

Selecting 9 Plastic and Process 8 6 9

factors have created demands for new, more capable testing systems and software from a full-service supplier capable of global support. The total cost is a key issue since the labor and other costs of testing and the use of the test results will far exceed initial equipment costs. The implications of flawed test results, resulting in over-designed products, field failures, warrantee costs, and customer dissatisfaction, overshadow the cost of acquiring equipment to get proper data. The down stream impacts of a less costly, poor quality material, flawed manufacturing process, or design error greatly exceeds the investment of updating lab equipment. Combined with the labor savings of changing test methods, the uses of newer software-based test systems greatly enhance the laboratory's capability. Testing Procedures

In this book many examples of test results have been presented. They all follow the American Society for Testing for Materials (ASTM) and International Organization for Standardization (ISO) unless otherwise noted. For those desiring information on conducting and evaluating tests just contact these organizations. Internet provides a valuable tool for those involved in keeping up to date on standards and testing. ASTM is a worldwide organization that started in the 19th century with headquarters now in West Conshohocken, Penna. (suburb of Philadelphia), USA. It is recognized as a world authority on standards for testing all types of materials that includes plastics. Their annual books of ASTM Standards contain more than seven thousand standards published in sixty-six volumes that include different materials and products. There are four volumes specifically on plastics: 08.01-Plastics I; 08.02-Plastics II; 08.03-Plastics III, and 08.04-Plastic Pipe and Building Products. Other volumes include information on plastics and reinforced plastics (RPs). The complete ASTM index is listed under different categories for the different products, types of tests (by environment, chemical resistance, etc.), statistical analyses of different test data, and so on. ASTM International's Committee D30 on Composites held a joint meeting with the MIL-17 Composite Materials Handbook committee in Charleston, S.C. in late October, 2003 hosting attendees from Germany, Canada, Israel, UK, France, and Spain to increase international participation in D30 standards development. D30 currently has members from 15 countries, plus non-member tech specialists from eight more. D. V. Rosato during the early 1940s was involved in developing MIL-17 (and also MIL-23 on sandwich structures) and

870 Reinforced Plastics Handbook

latter for many decades was involved in up dating different ASTM D standards as well as new standards such as ASTM D 4000. There are different worldwide industry organizations all providing industries voluntary information for the preparation and/or updating testing procedures, specifications, standards, and/or certifications (Table 9.20). They provide updated information to meet different requirements such as aiding processors in controlling product quality, meet safety requirements, etc. In addition to ASTM examples of other important organizations include Underwriters Laboratories (UL), International Organization for Standardization (ISO), Deutsches Instut, Normung (DIN), and Japanese Industrial Standards. Note that previously issued test procedures and standards arc subject to change and being updated periodically. ASTM issues annual publications that include all their changes. In USA there is a government worldwide testing directory that lists that reviews all kinds of testing capabilities including plastics. The National Voluntary Accreditation Program (NVLAP) endorses them. The directory is available from NIST, NVLAP Directory, A124 Building, Gaithersburg, MD 20899. Information on a few of these organizations is presented. ISO is the English abbreviation of the worldwide International Organization for Standardization founded 1946 and headquartered in Geneva, Switzerland. It provides the important mission of promoting the development of a very extensive amount of international standards and the activities that demonstrate compliance with the standards. The following standards define their quality system requirements for firms with varying scope of business requirements. ISO-9000 and ISO-9004 are guidelines that provide insight and interpretation of the requirements of the three main standards ISO-9001 (quality system in design/development to servicing ISO-9002), ISO-9002 (quality system for quality assurance in production and installation), and ISO-9003 (quality system for quality insurance in final inspection and testing). These standards outline easy to understand procedures in meeting their requirements. As an example, ISO-9004 certification involves quality management and quality system element supplier guideline to help determine which elements are addressed by each standard in the series. ISO-10993 standard concerns material biocompatibility testing and occupies a central position in the safety assessment programs for different products. Through the use of such tests, fabricators are able to select materials and manufacturing processes that contribute to the creation of products that are safe for people to use. However, manufacturers and others often fine themselves challenged when they attempt to discover how to develop an appropriate biocompatible testing

9

Selecting 9 Plastic and Process 8 7 1

program. Included in this ISO, with its different parts, is a practical guide to designing sub-chronic and chronic systemic toxicity tests. This ISO cites ASTM document F 1439-92 entitled Performance of Life Time Bioassay for Tumorigenic Potential of Implanted materials. IS0-14000 certification is the first international standard for environmental-quality management. It is not a compliance standard; it consists of voluntary guidelines for constructing a management system from start to finish ensuring setting and meeting objectives for environmental compliance. Plant certification will provide evidence of proactive environmental management and will reduce their exposure to lawsuits and regulatory problems. ISO-14001 is an international, voluntary standard that specifies the minimum elements for an effective environmental management system (EMS). It was published in 1996 by the International Organization for Standardization and adopted as the USA national EMS standard by the American National Standards Institute (ANSI). While third-party registration is not mandated by this voluntary standard, some companies have found independent assessment to be a marketing advantage. In addition, some large companies have mandated third party registration as proof of conformance to the standard. UL is an example of an approval laboratory that industry and the government depends on its exceptionally qualified performance. It identifies a product which has been produced under UL's classification and follow-up service and which bears authorized classification marking of UL as the manufacturer's declaration that the product complies with UL's requirements. The UL's Laboratory Factory Inspection involves visits by a UL's representative to a factory or other facility. Purpose of conducting the examination a n d / o r tests of products is to ensure compliance with UL approved requirement. The examination is the means that shows how the manufacturer exercises its operation to determine compliance with the UL's requirements. On the subject of appliance safety the UL have published more than 450 safety standards to assess the hazards associated with manufacturing appliances. These standards represent basic design requirements for various categories of products covered by the organization. For example, under UL's Component Plastics Program a material is tested under standardized, uniform conditions to provide preliminary information as to a material's strong and potentially weak characteristics. The UL's plastics program is divided into two phases. The first develops information on a material's long- and short-term properties. The second phase uses these data to screen out and indicate a material's

872 Reinforced Plastics Handbook

strong and weak characteristics. For example, manufacturers and safety engineers can analyze the possible hazardous effects of potentially weak characteristics, using UL standard 746C. Products manufactured using concepts in UL Standard 746D provide quick verification of material identification, along with the assurance that acceptable blending or simple compounding operations are used that would not increase the risk of fire, electrical shock, or personal injury. The Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances (UL 94) has methods for determining whether a material will extinguish, or burn and propagate flame. The UL Standard for Polymeric Materials-Short Term Property Evaluations is a series of small-scale tests used as a basis for comparing the mechanical, electrical, thermal, and resistance-to-ignition characteristics of materials. It is the general consensus within the worldwide "fire community" that the only proper way to evaluate the fire safety of products is to conduct full-scale tests or complete fire-risk assessments. Most of these tests were extracted from procedures developed by the American Society for Testing and Materials (ASTM) and the International Electrotechnical Commission (IEC). Because they are time tested, they provide generally accepted methods to evaluate a given property. Where there were no universally accepted methods the UL developed its own.

Computer Software Programs The use of computer software RP programs in design, RP property data, processing fabrication, troubleshooting, and related fields is widespread. It is increasingly important to keep up to date continually with the nature and prospects of new software technologies. Advances in computer technology have made designers quite sophisticated. Mathematical models are used to study stress and strain as well as processing techniques. Computers can apply detailed charts to controlling processes. With all the engineering aids, basic design is intuitive. When a designer is called to design a product to perform certain functions, the concept of the mechanism that will do the job is arrived at by calling on experience and trying different approaches via the computer. Once the design is established and drawings are made, the designer must arrive at the materials of construction. The material selection phase of design, like the concept phase, is based upon accumulated knowledge via literature searches a n d / o r personal design experiences with performance of materials in previous

9

Selecting 9 Plastic and Process 8 7 3

applications. This experience can be obtained directly or indirectly via experience from others. However, the designer must have a basic understanding of the RP material systems and call upon this knowledge to make the material selection otherwise that person is subject to developing problems. Knowledge-based computer selection software systems are available as aids in the selection process, but they can be dangerous if the user does not understand the first principles of the RP material systems that one is using; what the RP properties mean and how they apply to factors such as directional properties with creep, static, and dynamic loads, and so on. Mathematically speaking, stress analysis is a boundary value field problem in which a set of differential equations must be solved, subject to a number of constraints. It is possible to outline the general nature of the problem by means of simple examples that contain most of the concepts used in structures that are more complicated. These types of examples illustrate what is sometimes called elementary or direct approach to stress analysis, which is the approach used in developing many of the stress equations listed in mechanical engineering design handbooks or textbooks. Although both designing and testing have sophisticated software to assist the designer, in the past these areas have remained largely isolated from one another. However, increases in hardware power and availability of special software linked these two disciplines. Programs are available allowing design to take advantage of test data so that testing can benefit design data. Software to link designing and testing comes from several sources. Some vendors of computer-aided design (CAD) software offer test data analysis modules so that information can be easily exchanged and compared. In addition, suppliers of finite element analysis (FEA) and modal-analysis software create ways to use other data in their programs. Modal-testing software typically will allow designers to test prototype changes in a computer, once the original prototyping is done. A computer solution could take as little as 30 seconds, whereas modifying an actual physical prototype might take as long as a week. In a computer-aided testing (CAT) system, the computer is actively involved in testing that takes place in all stages of product development from design to producing the product. It includes factors such as quality control, statistical analysis, and so on. An advantage for CAT is that sensors measuring the characteristics of the prototype or the finished product can exercise the product model to improve its accuracy, or to identify design modifications. In this way, testing

874 Reinforced Plastics Handbook

integrates design and fabrication into development process.

an

ongoing self-correcting

Statistics

Testing, quality control, and statistics can all be integrated. Computers make statistics a more flexible tool and help prevent "cookbooks" (the blind application of the same standard techniques no matter what problem exists). A statistical perspective can be a simple route to substantially increase productivity, quality, and profit. Statistics is concerned with design of efficient experiments and with the transformation of data into information, in other words, by asking good questions and getting good answers. For most people, statistics conjures up endless tables of uninteresting numbers. However, modem statistics have very practical applications and, thanks to computers, is no dreary science of numbercrunching drudgery. Statistical methods should be applied to decision-making at all stages of production that go from incoming materials to outgoing molded products. For example, statistics can help with forecasting; a problem managers face every day: Should raw materials by ordered? Should marketing and advertising techniques be changed? The data used to make these decisions represent random variation as well as real changes. Software

There are many plastic materials. They include thousands for RPs with some being RTSs but most being RTPs. So just reviewing what is available in a relatively small grouping of a specific type such as RPs as well as the constant proliferation of up dated and new types could be considered mind-boggling. With a logical approach, i.e., design wise, engineering wise, production wise, etc., it can become practical. However, for individuals or organizations, it would probably be impossible to manually keep up to date, even for the "veteran". Manual searching (of the past) that, initially, will do the job at a lower cost, becomes phenomenal and expensive. On-line computerized databases cut through this information overload by organizing materials (properties, processing, availability, updated cost, storage conditions, etc.) into a manageable format. These programs not only significantly reduce acquisition time but also add options, such as updates on what is new and those no longer available, etc. Selection of computer hardware should be one of the last steps in the purchase of any computer system. The software provides instructions for the hardware, and without the proper software, the most impressive

9

Selecting 9 Plastic and Process 8 7 5

hardware specifications are meaningless. One would first choose the "correct" software, and then select the appropriate computer that is compatible with the software. An example of software is COFATE (Composite Fabrication Technology Evaluation) from the Composite Materials and Structure Center of Michigan State University. It helps processors narrow the field for choosing from 16 processes: RTM, RIM, structural or reinforced RIM (SRIM or RR1M), prepreg/autoclave cure, hand layup, spray-up, pressure molding, vacuum bag, filament winding, automated tape lay-up autoclave, injection molding, transfer molding, compression molding, blow molding, extrusion, and pultrusion. The system offers a problem-solving computer format known as "structural pattern matching," which helps match the most suitable processing choices to specific part applications. More information on software is in Chapter 7. Design via Internet

As Tom Rodak (Commerx, Inc.) reported in today's time-constrained workplace, you can spend a great deal of valuable time trying to find the information you need to make product design decisions. Unfortunately, not many have the luxury of time. Unforgiving deadlines and customer demands make the ability to find information quickly a necessity. Over the past few years, the Internet has rapidly evolved as an ideal tool for locating this needed data. However, with the incredible vastness of the Internet, knowing where to go is key to success. Currently, a growing number of sites cater to the needs of product designers and engineers. From materials selection and design software to educational programs and article archives, the Internet can provide a great deal of information at the click of a mouse. The Plastics Network from Commerx, Inc. (www. plasticsnet.com) features a Sourcing Center that allows users to search for specific plastics related products and services. The site, which provides secure online ordering, enables users to compare vendors of similar products and services to get the best value. Regarding materials selection there are a number of company-specific sites on the Internet that allow you to search product lines by brand name, intended application, and properties. These include: GE Plastics (www.plasticsnet.com/ge), Bayer Corporation (www.polymers-usa. bayer.com), BASF (www.basf.com), Polymerland (www.polymerland. com), and M.A. Hanna (www.plasticsnet.com/mahanna). When searching for materials from a multiple number of vendors, there are several online material databases to visit. Some offer free access to

876 Reinforced Plastics Handbook

information, while others require a fee for their information. Some of these include: IDES (idesinc.com), and PLASPEC (www2.plaspec.

corn). In addition, the Material Engineering Center at Dow Plastics offers its PAMS (Processes and Materials Selection) system on the Internet to help designers match material and fabrication requirements with product and economic requirements (www. plasticsnot.com/moc). Regarding supplier and product selection in addition to materials selection, there are several sites that allow users to locate and interact with suppliers of products and services. Some of these sites support online ordering as well. Devclopages (www.developages.com) allows users to locate companies that can assist with all areas of product development from design and prototyping through sales and logistics. Regarding articles, educational information, and Networking in addition to sourcing vendors and selecting materials, the Internet makes it easy to locate article archives, register for educational programs, and network with other professionals. Many industry trade associations have Web sites that provide a number of resources for designers. For example, the Web site of the PD3 (Product Design and Development Division) of the Society of Plastics Engineers (www-pd3.org) contains a Design Forum or chat area where users can discuss design challenges and exchange advice. They also provide a schedule of educational programs and links to helpful design articles. The IDSA (industrial Designers Society of America) (wwwidsa.org) provides similar links, as well as opportunities to locate reference materials, job openings, and suppliers.

Summation on selection Comparison information and data (ASTM unless otherwise listed) regarding materials, processes, and designs as well as detailed RP data sheets-TS and detailed RP data sheets-TPs follows. In addition to what follows, comparison information has been presented in this chapter and throughout this book. The information provides guides in the selection procedure. Information has been presented so that selection can be of direct or indirect use.

9 . Selecting Plastic and Process 8 7 7 Materials

Table 9.24 Property guide for unreinforced and reinforced thermoplastics and thermosets vs. metals

PHENOLIC

T

H a

O

S

E

T S

T H E

R

~'I

-~

POLYESTER

EPOXY

~ I

12 UNFILLED

('m J L_

I0 UNFILLED 7 MINERAL

1~ L===I III -

MeLAM,Ne; i ,

! C S M E

T

A

L

S

PSi X t o -~

I O0 I

ff

Z20 ~ i

240 i

260 i

I

, II 60 GLASS I I I

I IiilI 2 4 0

GL~S (FW)

l:S

CELLULOSE

S,UCONE r - - ' oMINERAL UN,,L-,O

30 G~ss

L-

POLYIMIDE . ~ ' , i =

Io UNFILLED

%

ACETAL

; m

IO UNFILLED

~ . ~ 18 GLASS NYLON . / ' m 9 UNFILLED

POLYPROPYLENE

T

I

cE~.~os=

UREA ~ ~

O

L

'

80 a

IO GLASS

POLYCARBONATE ~ m m

A S

60 i

" AsBestos zo GLAss

~.m

M

P

STREN~3TH ,

20 40 .... I a 7.5 UNFILLED 7 MINERAL

' . , . ~ ,o GLAss

E

M

TENSILE

0 I

~ . ~f I i

32 GLASS

II UNFILLED

~ 2 2 GLASS 5 1o U N FSILLALSESD

POLYSULFONE .,,r,mi 1o UNFILLED ~ . ~ 20 GLASS PVC

./'I

'7' UNFILLED

~ . ~ IS GLASS ABS j ' I 7 UNFILLED -'~.~

16 GLASS

SAN . ~ I _ . ~ l o POLYESTER ALUMINUM ZINC DIE CAST BRASS TITANIUM MAGNESIUM DIE CAST GRAY IRON LOW CARBON STEEL

./'I

8 GLASS

8 UNFILLED

~,.mmi

~

UNFILLED 18 GLASS

2

~ ~

4 22 14 I I00

-

2B

I

_ 40

140

continued

878 Reinforced Plastics Handbook Table 9,24 continued

o PHENOLIC

T H E R M 0 S E T S T H E

R

M 0

P L A S T I C S

M E T A L S

9

I

5

MODULUS,PSI IO

I

~'m t.O UNFILLED -~ i.5 MINERAL L ~ z.5 GLASS

I

X I 0 -6

15

?.o

i-

25

3O

!

i

1

POLYESTER r ' = O,5 UNFILLED ~m 1.5 ASeESTOS L ~ Z.5 GLASS m 0.5 UNFILLED EPOXY L ~ .

3.s GLASS 9 GLASS ( FW )

MELAMINE ~'m=-i.o CELLULOSE L ~ 2.4.. GLASS UREA ( m ; 1.5 CELLULOSE SILICONE ( ~

Z.S GLASS

POLYIMIOE " ~L,i l 0.7 UNFILLED ACETAL ~"!! 0.5 UNFILLED L ~ 1.5 GI.J~SS NYLON ( ~ 1 ~ 4 UNFILLED 2.0 GLASS POLYCARBONATE ~" S o.+ UNFILLED Lm 1.5 GLASS POLYPROPYLENE ~'1. 0.1 UNFILLED L i l 0.8 GLA.~ POLYSULFONE J " n 0.4 UNFILLED 1.5 GLASS ~ PVC r'il. 0.4. UNFILLED ~.m 1.9 GLASS ADS f u 0,4 UNFILLED ~=m. I.O GLASS

+A,,,

(:..? ;, UNFILLED ~

POLYESTER (~m~.41.5UNFILLED GLASS ALUMINUM ZINC DIE CAST BRASS TITANIUM MAGNESIUM DIE CAST GRAY IRON LOW CARBON STEEL STAINLESS STEEL

ii

_ IO

~li~mlllmlmml

14.

_6.5 18

-- 30 II

I

I

_28

9 Table

9.24 continued

PHENOLIC

T H E R M 0 S E T S

I

Z

I

I

l

t~

~

EPOXY j

L L

-

~

7

8

9

i

|

i

UNFILLED 92.0 MINERAL 1.9 GLASS

1.4 UNFILLED

NYLON

{

i.6 GLASS I.I UNFILLED I _. 1.7 GLASS I.Z_I.sUNFILLEDGLASS

B

POLYCARBONATE{mmmlml

0

POLYPROPYLENE ~

M E T A L S

I

%

M

P L A S T I C S

6

I

1.5 CELLULOSE

I"amBiBm I.Z (

5

|

1.5 CELLULCSE Z.O GLASS

tit t

\ ,

4

I

I.Z UNFILLED .1.8 MINERAL 1.8 GLASS I 2.1 GLASS ( F W )

MELAMINE ~._

SILICONE

3

1.2 UNFILLED t.B ASBESTOS I 1.8 GLASS

~

UREA-

SPECIFIC GRAVITY

1.3 UNFILLED 1.4 MINERAL GLASS

.....

m

m

R

0

POLYESTER

POLYIMIOE

E

Selecting 9 Plastic and Process 8 7 9

POLYSULFONE PVC SAN

~ ~

L

J'L~ ' ;

~.

; l ~ l l l L ~

~

,.

ALUMINUM

1.4 UNFILLED 1.6 GLASS 1.3 GLASS I.I UNFILLED 1.4 GLASS 1.3 UNFILLED _ 1.5 GLASS

II

ZINC DIE CAST BRASS

STAINLESS STEEL

I.s GLASS

~

POLYESTER ~

TITANIUM MAGNESIUM DIE CAST GRAY IRON LOW CARBON STEEL

0.9 UNFILLED I.P. GLASS 1.2 UNFILLED

IIII III

?..8 I

I

6.5 I

8.5

4.~ IIIII I

__ 1.8

II

II II

h

II

7.1 HI

7.8 LI

_7.9

880 Reinforced Plastics Handbook Table 9~

Properties of thermoset and thermoplastic/glass fiber RPs (SMCs, BMCs, etc.) and unreinforced thermoplastics

Material Glass-fiber-reinforced thermosets (RTS)

Polyester SMC, compression Polyester SMC, compression

PolyesterSMC,compression

Polyester BMC, compression Polyester BMC, injection Epoxy filament wound Polyester, pultruded Polyurethane, milled fibers (RRIM) Polyurethane, flaked glass (RRIM) Polyester spraying/lay-up Polyester, woven roving, lay-up Glass-fiber-reinforced thermoplastics (RTP)

Unreinforced thermoplastics (TP)

Acetal resin Nylon 6/6 Polycarbonate Polypropylene Poly(propylene sulfide) Acrylonitrile-butadiene-styrene terpolymer (ABS) Poly(phenylene oxide] (PPO) Styrene-acrylonitrile copolymer (SAN) Poly{butylene terephthalate) Poly(ethylene terephthalate) Acetal resin Nylon 6/6 Polycarbonate Polyproplylene Poly(phenylene sulfide) Acrylonitrile-butadiene-styrene terpolymer (ABS) Poly(phenylene oxide)(PPO) Styrene-acrylonitrile (SAN) Poly(butylene terephthalate) Poly(ethylene terephthalate)

Glass fiber, Wt.%

Specific gravity

Thermal coefficient of expansion

30.0 20.0 50.0 22.0 22.0 80.0 55.0 13.0

D792 1.85 1.78 2.00 1.82 1.82 2.08 1.69 1.07

D696

23.0

1.17

53.1

30.0 50.0

1.37 1.64

12.0 4.0

25.0 30.0 10.0 20.0 40.0 20.0

1.61 1.48 1.26 1.04 1.64 1.22

4.7 1.8 1.8 2.4 1.1 2.1

20.0 20.0

1.21 1.22

2.0 2.1

30.0 30.0

1.52 1.56 1.41

1.4 1.7 4.7

1.13 1.20 0.89 1.30 1.03

4.5 3.7 3.8 3.2 68.0

1.10 1.05 1.31 1.34

36.0 4.5 6.8 6.7

9.4 6.6 6.6 2.0 5.0 78.0

-

9 Selecting Plastic and Process 88 1

Heat deflection at 7.8Mfa, CO Pfl

Thermal conductivity, (Wlm K) (BTU in/hr.ft.2 ~ f l

Specific

heat,

J/h K)

C177 200+ 200+ 200+ 260 260 200+

8.37 8.37 1.77 6.92

(58.1) (58.1) (12.3) (48.0)

1.26 1.26 1.26 1.26 1.26 0.96 1.17

29

Tensile strength, #Pa (psi) D638 83 36.5 158 41.3 33.5 552 2 07 19.3

(1 2,000) (5,300) (22,900) (5,990) (4,860) (80,000) (30,000)

Tensile modulus, G h (kip/in.*) D638 11.7 11.7 15.7 12.1 10.5 27.6 17.2

(1,700) (1,700) (2,280) (1,750) (1,520) (4,000) (2,490)

(2,800)

30.4

(4,410)

86.2 255

(12,500) (37,000)

6.9 15.5

(1,000) (2,250)

128 159 83 45 152 76

(1 8,600)

(6,500) (22,000) ( 11,000)

8.6 8.3 5.2 3.7 14.1 6.2

(1,250) (1,2001 (750) (540) (2,050) (900)

2.60

(1 8.0)

1.30

161 254 141 132 266 99

2.60 7.97 14.5 3.47 2.42

(1 8.0) (55.3) (100.6) (24.1) (16.8)

1.26 1.21

143 102

6.57 4.54

(45.6) (33.6)

0.84-1.67

100 100

(14,500) (1 4,500)

6.3 8.6

(910) (1,250)

213 216 110

12.1 11.2 2.80

(84.0) (77.7) (19.4)

0.46

131 145 81

(19,000) (21,000) (11,700)

8.3 9.0 2.6

(1,200) (1,300) (380)

75 132 46-60 135 93-104

2.94 2.34 2.10 2.89 1.61

(20.4) (16.21 (1 4.6) (20.1I (11.2)

1.26 1.26 1.88

79 66 34 66 41

(11,400)

(9,600) (4,900) (9,600) (5,900)

2.8 2.3 0.7 3.3 2.1

(400) (330) (100) (480) (300)

0.84-1.36 1.38

54 66 57 59

(7,800) (9,6001 (8,300) (8,600)

2.6 2.8 1.9 2.8

(380) (400) (280) (400)

200+ 200+

100 104 50-85 38-41

(11.0) 1.59 (8.40) 1.21 1.76-2.89 (12.2-20.1) 1.51 (10.5)

1.05

1.46

1.42

(23,100) (1 2,000)

continued

882 Reinforced Plastics Handbook Table 9.25 Continued Material Glass-fiber-reinforced thermosets (RTS)

Glass-fiber-reinforced thermoplastics (RTP)

Unreinforced thermoplastics (TP)

Elongation % Polyester SMC, compression Polyester SMC, compression Polyester SMC, compression Polyester BMC, compression Polyester BMC, injection Epoxy filament wound Polyester, pultruded Polyurethane, milled fibers (RRIM) Polyurethane, flaked glass (RRIM) Polyester spraying/lay-up Polyester, woven roving, lay-up Acetal resin Nylon 616 Polycarbonate Polypropylene Poly(phenylene sulfide) Acrylo n itri le-b uta die ne-styre ne terpolymer (ABS) Poly(phenylene oxide)(PPO) Styrene-acrylonitrile copolymer (SAN) Poly(butylene terephthalate) Poly(ethylene terephthalate) Acetal resin Nylon 6/6 Polycarbonate Polypropylene Poly(phenylene sulfide) Acrylon itri le-buta die ne-styre ne terpolymer (ABS) Poly(phenylene oxide)(PPO) Styrene-acrylonitrile (SAN) Poly(butylene terephthalate) Poly(ethylene terephthalate)

Flexural modulus, GPa (kip/in 2) D 638 <1.0 0.4 1.7 0.5 0.5 1.6 140.0

D 79O 11.0 9.7 13.8 10.9 9.9 34.5 11.0 0.26-0.37

(1,600) (1,400) (2,000) (1,580) (1,400) (5,000) (1,600) (38-54)

38.9

1.0

(145)

1.3 1.6

5.2 15.5

(7,500) (2,250)

3.0 1.9 9.0 3.0 3.0 2.0

7.6 5.5 4.1 3.6 13.1 6.0

(1,100)

5.0 1.8

5.2 7.6

(1,000)

4.0 6.6 30.0

8.1 8.6 2.7

(1,200) (1,250) (390)

(800) (600)

(520) (1,900)

(870)

(750)

60.0 110.0 200.0 1.0 5.0

2.9 2.3 0.9-1.4 3.8 2.4-2.8

(420) (330) (130-200) (550) (350-400)

50.0 0.5 50.0 50.0

2.3-2.8 3.8 2.3-2.8 2.4-3.1

(330-400) (550) (330-440) (350-450)

9

Compressive strength, MPa (psi)

Impact strength Izod at 22~ Jim

D 695 166 (24,100) 159 (23,100) 221 (32,000) 138 (20,000)

D 256 854 438 1,036 227 154 2,400 1,335

310 (45,000) 207 (30,000)

Selecting 9 Plastic and Process 8 8 3

Water absorption in 24 hr. O/o

Mold shrinkage, O/o

D 785 Barcol 68 Barcol 68 Barr 68 Barcol 68 Barcol 68 M98 Barcol 50 Shore D 65-75

D 57O 0.25 O.10 0.50 0.20 0.20 0.50 0.75

D 955

Barcol 50 Barcol 50

1.30 0.50

Hardness

0.002 0.001 0.004 0.008

112 152 (22,000) 186 (27,000)

690-800 1,760

117 (17,000) 183 (26,500) 97 (14,000) 172 (24,900) 145 (21,000) 97 (14,000)

96 117 107 59 80 64

M97 M95 M80 R103 R123 R107

O.29 O.5O 0.14 0.05 O.01 0.30

O.OO4 0.OO2 0.005 0.003 0.0O2 0.002

121 (17,500) 121 (17,500)

96 59

R107 R122

0.24 0.06

0.003 0.002

124 (18,000) 172 (24,900) 90 (13,000)

96 96 32

Rl18 R120 Rl19

0.06 0.05 0.3-1.9

0.003 0.003 0.005

R120, M83 M70 R50-96 R123 R107-115

1.0-1.3 O.15 0.03 <.02 0.20-0.45

0.008 0.005-0.007 0.029 0.007 0.004-0.009

Rl15 M80-85 M68-78 M94-101

0.07 0.20-0.35 0.08-0.09 O.1-0.2

0.005-0.007 0.005-0.007 0.015-0.020 0.02-0.025

103 (14,900) 86 (12,500) 24 (3,500) 110 (16,000) 69 (10,000)

43 854 50-1,000 <27 160-320

83 (12,000) 97 (14,000) 59 (8,500) 76(11,000)

270 16-24 43 13-35

4~

Table 9 . 2 6 Trade-offs in TPs and RTPs

m .

a"

Sacrifice [from base resin)

il

Desired modification

How achieved

Amorphous

Crystalline

Comments

Increased tensile strength

Glass fibers Carbon fibers Fibrous materials

Ductility, cost Ductility, cost

Ductility, cost Ductility, cost Ductility

Glass fibers are the most cost effective way of gaining tensile strength. Carbon fibers are more expensive, fibrous minerals are least expensive but only slightly reinforcing. Reinforcement makes brittle resins tougher and embrittles tough resins. Fibrous minerals are not commonly used in amorphous resins.

Increased flexural modulus

Glass fibers Carbon fibers Rigid minerals

Ductility, cost Ductility, cost Ductility

Ductility, cost Ductility, cost Ductility

Any additive more rigid than the base resin produces a more rigid composite. Particulate fillers severely degrade impact strength.

Flame resistance

FR additive

Ductility, tensile strength, cost

Ductility, tensile strength, cost

FR additives interfere with the mechanical integrity of the polymer and often require reinforcement to salvage strength. They also narrow the molding latitude of the base resin. Some can cause mold corrosion.

Increased Heat-deflection temperature (HDT)

Glass fibers Carbon fibers Fibrous minerals

Ductility, cost Ductility, cost

Ductility, cost Ductility, cost Ductility

When reinforced, crystalline polymers yield much greater increases in HDT than do amorphous resins. As with tensile strength, fibrous minerals increase HDT only slightly. Fillers do not increase HDT.

Warpage resistance

5 to 10Ologlass fibers 5 to 10Olocarbon fibers Particulate fillers

Cost Cost Ductility, cost tensile strength

Amorphous polymers are inherently nonwarping molding resins. Only occasionally are fillers such as milled glass or glass beads added to amorphous materials, because they reduce shrinkage anisotropically. Addition of fibers tends to balance the difference between inflow and cross-flow shrinkage usually found in crystalline polymers. When a particulate is used to reduce and balance shrinkage, some fiber is needed to offset degradation.

Ductility, cost tensile strength

,.,.,..

,...,. Ill

"1" o-

o o ~.-

Sacrifice (from base resin) Desired modification

How achieved

Amorphous

Crystalline

Comments

Reduced mold shrinkage (increased mold-tosize capability)

Glass fibers Carbon fibers Fillers

Ductility, c o s t Ductility, c o s t Tensile strength, ductility, cost

Ductility, cost Ductility, cost Tensilestrength, ductility, cost

Reinforcement reduces shrinkage far more than fillers do. Fillers help balance shrinkage, however, because they replace shrinking polymer. The sharp shrinkage reduction in reinforced crystalline resins can often lead to warpage. The best'mold-tosize' composites are reinforced amorphous composites.

Reduced coefficient of friction

PTFE Silicone MoSe Graphite

t

Reduced wear

Glass fibers Carbon fibers Lubricating additives

Electrical conductivity

Carbon fibers Carbon powders

Cost

Cost

These fillers are soft and do not dramatically affect mechanical properties. PTFEloadings commonly range from 5 to 20%; the others are usually 5% or less. Higher loadings can cause mechanical degradation. The subject of plastic wear is extremely complex and should be discussed with a composite supplier.

Ductility, cost Tensile strength, ductility, cost

Ductility, cost Tensile strength, ductility, cost

Resistivities of I to I00,000 ohm-cm can be achieved and are proportional to cost. Various carbon fibers and powders are available with wide variations in conductivity yields in composites.

~D Uq f~ m.

m. a,1 Q..

0

00

Table 9.27 General properties of thermoset RPs

Reinforcing material Polyester Glass cloth Glass mat Asbestos Paper Cotton cloth Epoxy Glass cloth Glass mat Paper Phenolic Glass cloth Glass mat Asbestos Paper Cotton cloth Nylon cloth Silicone Glass cloth Asbestos cloth

m .

Tensile Strength modulus

s"

Heat resistance continuous, oF

Arc resistance,

5-30 2-10 2-8 1-2 1-4

300-350 300-350 300-450 220-250 230-250

60-120 120-180 100-140 28-75 70-85

Izod impact strength, ft-lb/in. notch

l9 I

106psi

Compressive strength, 103 psi

Flexuml strength, 103 psi

30-70 20-25 3O-6O 6-14 7-9

1-3 1/2-2 1-3 1/2-11/2 1/2-11/2

25-50 15-50 30-50 20-25 23-24

40-90 25-40 50-7O 13-28 13-18

1.9-2.0 1.8-2.0 1.4-1.5

20-60 14-30 10-19

2-4 1-3 1/2-1

50-70 30-38 20-28

7O- 100 20-26 19-24

11-26 8-15 1/2-1

330-500 330-500 260-300

100-110 110-125 30-100

1.8-2.0 1.7-1.9 1.7-1.9 1.3-1.4 1.3-1.4 1.1-1.2

40-60 5-20 40-65 8-20 7-16 5-10

1-3 2-5 1-2 1/2-11/2 1/4-1/2

35-40 17-26 45-55 20-40 30-44 28-36

65-95 10-60 50-90 10-30 14-30 9-22

10-35 8-16 1-6 1/3-1 1/2- 3 2-4

350-500 350-500 350-600 225-250 225-250 150-165

20-130 400-150 120-200 Tracks Tracks Tracks

1.6-1.9 1.7-1.8

10-35 10-25

1-2 1-2

25-46 40-50

10-38 12-20

5-13 6-9

400-700 450-730

150-250 150-300

Specific gravity

103psi

1.5-2.1 1.3-2.3 1.6-1.9 1.2-1.5 1.2-1.4

e~

sec.

,-r oo o

rl rY"

o

E i_ co

Q_ o !._ C~5

cCO

r~

r~ r~

r,.O

O

O

O

oo

9

r,-,.

LO O~

~--

9 CO ~'-I

oo

r...o ao

'm'~

o.

C.O ~'--

@

,--C~

q

'~" ~--

~

O '~-

,---

O ','-'-

~

~.. ~

I'~

LO C~I

,~

O0 ~-

@

~

o

~

~

04

~

~

'~-

,-

LO

~

C'~

~

,-

OO

.,r

9Selecting Plastic and Process 8 8 7

c~ c-

~

~

~

~.

c": --....0

--

O

c

,---

~, oq. ~

I.~

OO

,--"

d

,..__ ~.

r~

.d

"~-

~

q

r<

~

Lr~

C',,!

r.-O O

--" 9

~.

~

~

C',,I O

O

od r-,, u6 o .

O0

,'--

q.-

aq. ' -

r...O ,---

O

~,..d

C'xl

C',,I

c~

E "-O

~ c-

~

O

Lr~

L.O

CO

~

rd

CO

C",,I C",,I O0

ro

,---

OO

O

co 0

~

~

~ 0

o0 ,_: ~

c~

,.._

I'~

CO

,---

L~

o

OO

o ~ co ---9

~

~

co r6

o,....,.d CO

o

~

r...O O'~

o CO

O

~

0

eo

O

O

c-

~_ 8 ,:,.., ~

CO

Table 9 . 2 9 Properties of thermoplastic RPs with glass and other fibers

Base polymer

Fiber, % by weight

PA 6/6

Glass

PC

PP

Tensile strength MPa (Kpsi) 30

"Long" glass*

30

Glass

20

Carbon

20

Carbon (pitch)

20

Aramid

20

Nickel coated carbon Glass

20

Carbon

20

Aramid

20

Stainless steel

10

Glass

40

Glass (chem. coupled)

40

Asbestos (anthophylite)

40

20

186 (27) 193 (28) 131 (19) 193 (28) 90 (13) 103 (15) 103 (15) 110 (16) 131 (19) 83 (12) 76 (11) 76 (11) 103 (15) 35 (5)

Compressive strength MPa (Kpsi) 186 (27) 193 (28) 159 (23) 172 (25) 138 (20) 110 (16) 131 (19) 76 (11) 69 (10) 69 (10) 41 (6)

Tensile modulus GPa [Kpsi)

Deflection temperature ~ @ 1.82MPa (~ @ 264 p s i )

Notched Izod impact strength J/m [6.4 mm thick] (ft-lb/in. (1~4in.))

8.96 (1,300) 10.00 (1,450) 5.86 (850) 16.50 (2,400) 10.30 (1,500) 4.83 (700) 9.65 (1,400) 5.86 (850) 13.79 (2,000) 4.07 (590) 3.79 (550) 6.89 (1,000) 6.89 (1,000) 4.48 (650)

254 (190) 255 (491) 254 (490) 256 (492) 232 (450) 249 (480) 241 (465) 149 (300) 149 (300) 138 (280) 141 (285) 149 (300) 154 (310) 96 (205)

Note Glass fiber is E-glass, carbon fiber is PAN, unless noted otherwise. Fiber lengths before processing are ~ 6mm (114in.)length (* is 13mm (112in.).

a~

gravity

Approximate relative volumetric cost

112 (2.1) 182 (3.4) 64 (1.2) 59 (1.1) 32 (0.6) 53 (1.0} 43

1.37

1.0

182 (3.4) 107 (2.0) 43 (O.8) 85 (1.6) 96 (1.8) 107 (2.0) 27

(0.8)

(o.s)

Specific

,,,,,,,,

a,1 Ill

B. Ill

1.37

1.0

-r,

1.20

0.9

1.23

3.1

o-" o o

1.24

3.0

1.28

4.3

1.25

5.0

1.34

1.0

1.28

2.5

1.25

5.0

1.35

2.0

1.22

1.0

1.22

1.1

1.24

NA

~

~

~

o

.

~

~ .._.

~i

"--~

--~

--~

.o .

b,-~ b - ~ b o

~

.

~

0"~

o

--~

cz

~

~

.o

0

o

~

.~

--~

--~

Z

~

~

~

~

.._..

.~

~o 0

r~

K~

~

~

~

~ ~~ o~

~

~

O0

cz

o

~

~

~

I./'1

4::,

b

O~

~

~

~

--

0"~

m

z~~ ,-t.

-o

~

~

m

~

I

Lo

I

~

~

O0

F'D

--

0

~--. ~

-'~

m

~ "-o Lr~

b-,

~

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~

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"~ ~o ~_.

~

~

~

~

.--~

"~_ ~o".--~~.-.--,.-. oo ~ T'" ~'~ ~

~

~ ~ ~ ~ ~ ~ ~ ~

~

-I~

~

"--" r~ .._..

-~

~

~

~

o

I

~

"-o

f3

~

~__ ~o .

~

b ~ o -,

0

I~

O~

~

~

~

o~

..--. . ~

b

O0

o~

b

.

~

.

~

.

~

~~~~5~~~~o

O0

~

"~

~

O~

~

~

m

o

O0

r

~

Lr~

~

a

~y ""*

tm

4

b~

~

w~

b~

b~

F

0

r~

0

3

~'D

0

0

Q_

L~'.

0 -0 ~'D

"-0

0

C~

I#1

O0 O0

Ill lit

0 ~3 r'D

f~

,,,,,,,

,,,,,,

I,'4-

r

r 0

Table 9.31 Properties of unidirectional RP graphite, boron, and aramidlepoxy RPs m

Property Gross area stress W/D = 6 No holes Tension Longitudinal Transverse Compression** Longitudinal Transverse Interlaminar shear Strengths, ksi (MPa) with holes Tensionf Longitudinal Transverse Compression **Jr Longitudinal Transverse Bearing, D/t>2.0 Moduli, MSI (GPa) Longitudinal Transverse In-plane shear Interlaminar shearf (Ell - E22) Major Poisson's ratio Coefficient of thermal expansion, in./in.~ (m/m/~ Longitudinal Transverse Average cured layer thickness, in. (mm) Density, Ib/in. 3 (g/cm 3)

Symbol

Graphite/Epoxy AS- 1/3501-5A T300/N5208 (Hercules) (Narmco)

Gy70/Hye 1534 (Celanese)

Boron/Epoxy Aramid/Epoxy Avco 5505* Kevlar 49/Ce3305 (Avco) (DuPont)

~u P2u

169 (1165) 6 (41)

169 (1165) 4 (30)

90 (621) 2 (13.8)

165 {1138) 10 (73)

168 (1158) 1.6 (11.0)

F~u F2u

F/Ls

162 (1116) 25 (172) 7 (49)

141 (972) 20 (138) 14 (98)

90 (621) 28 (193) 4 (27.6)

480 (3309) 40 (276) 7 (48)

40(276) 12.1 (83) 10(69)

F~u F2u

76 (524) 3 (22)

76 (524) 2 (14)

21 (145) 1 (6.9)

80 (551) 5 (34)

95 (655)

Fllu F2u

76 (524) 12 (86) 66 (455)

76 (524) 10 (69) 66 (455)

21 (145) 14 (96.5) 66 (455)

185 (1275) 12 (83) 140 (965)

30 (207) 6.1 (42) 22 (152)

Ell E22 G12 Ell 1712

Gz

18.50 (127.6) 1.60 (11.0) 0.65 (4.5) 0.104 (0.72) 16.90 (116.6) 0.25

22.0 (151.7) 1.50 (10.3) 0.52 (3.6) 0.14 (1.0) 20.50 (141.4) 0.25

42 (289.6) 1 (6.9) 0.7 (4.8) >0.08 (0.55) 41 (282) 0.25

30.3 (208.9) 2.8 (19.3) 0.72 (5.0) 0.25 (1.72) 27.5 (189.6) 0.25

11.9 (82) 0.6 (4) 0.4(2.8) >0.04 (0.28) 11.3 (78) 0.25

O['11 cz22 t" p

0.25 (0.45) 15.20 (27.4) 0.00525 (0.133) 0.055 (1.52)

0.30 (0.54) 11.0 (19.8) 0.00525 (0.133) 0.055(1.52)

-0.58 (1.04) 16.5 (29.7) 0.0055 (0.140) 0.061 (1.69)

2.5 (4.5) 13.0 (23.4) 0.00525 (0.133) 0.075 (2.07)

-2.0 (-3.6) 32.0 (57.6) 0.00716 (0.181) 0.048 (1.32)

Fbru

0.8 (55)

* In hybrids ** Laminate compression strength cannot exceedGz f 5116-in. (7.9-mm) diameter holes.Strength/diameter correction is (0.6 + 5(DolD)- 0.1(DolD)2),where Do= 5116in. (7.9 mm) and D = actual hole diameter (0.625 < DolD< 2.50) Grossarea stress, W/D = 6

,

a" t'1)

D,.

"0 &} m

,

-r D. o" o o

9 Table 9.32

Nominal notch length, in.

Selecting 9 Plastic and Process 891

Damage propagation of aramid and E-glass fiber RPs using tensile-notched test specimen

Net failure stress, 103 lb./in. 2 Aramid a

Stress concentration factor K

E-glass ~

Aramid

% initial strength retained

E-glass .

.

Aramid

E-glass

84.3

0

35.4

31.3

.

0.25

33.5

26.4

1.06

1.19

. 94.6

0.50

31.3

22.7

1.13

1.38

88.4

72.5

1.00

30.0

21.3

1.18

1.47

84.7

68.1

a - Style 1350 woven roving of Du Pont's Kevlar 49 aramid on either side of 1.5 oz./ft, glass CSM. Resin: Reichhold's 33-072 polyester. b - 24 oz./yd.2 glass fiber WR on either side of 1.5 oz./ft.2 glass CSM. Resin: Reichhold's 33-072 polyester.

Table 9.33 Tensile properties of biaxially oriented PTFEsheeting unreinforced and reinforced

35% Graphite filled Granular PTFE

Biaxially Oriented 25% Glass Fiber Filled fine Powder PTFE

35% Glass Fiber Filled Granular PTFE

-40 32.8

-54 8.6

-40 32

-54 10.9

85

15

6

48

8

23 35.6 450

23 16.8 130

23 6.7 4

23 18.1 280

23 7.6 79 100

Biaxially Oriented Unfilled

Biaxially Oriented 40% Graphite Filled Fine PowderedPTFE

Temperature ~ Tensile Strength MPa

-40 56.8

Break Elongation O/o Temperature ~ Tensile Strength MPa Break Elongation % Temperature ~

100

100

100

100

Tensile Strength MPa

19.3

9.8

4

9. I

3.7

Break Elongation %

380

77

5

240

144

Temperature ~

260

260

260

260

260

Tensile Strength MPa

9

4.9

1.8

3.2

1.5

Break Elongation %

340

42

11

200

108

O0 ~D

Table 9.34 Tensile and impact properties of RPs and URPsbased on type resin

m.

:3

-i,i o

MECHANICALPROPERTIES

I HIGHTENSILESTRENGTH > S x 10 3 psi

I

I

,,,

LOWTENSILESTRENGTH < 5 x 10 3 psi

GLASSREINFORCED > 15x 10 3 psi

STANDARDAND NON-GLASSFILLED > lOx 10 3 psi

Polyester-TS Alkyd Vinyl Ester Nylon (including aromatics) Thermoplastic Polyesters Polycarbonates/AIIoys Polysulfones Polystyrene/Copolymers Epoxy ABS Polyacetal Phenolic Polyimides Melamine

Thermoset Polyester Alkyd Vinyl Ester Nylon {including Aromatics) Polyimides Polyamide-imides {including Aromatics) Polysulfones Polystyrene/Copolymers Epoxy Polyphenylene Sulfide Phenolic Ureas PVC [-t Copolymers

I IMPACTSTRENGTH

<5ft-lbs/in. of notch

Thermoplastic Elastomers Polymethyl pentene Polybutylene Furan Silicone Polyethylene ~t Copolymers Cellulosics Polyurethane PVC ec Copolymers FIuoroplastic/copolymers Polypropylene Phenolic ABS Epoxy Polystyrene Thermoplastic Polyesters Polyamide-imides Polyimides Alkyd Vinyl Ester

Polybutylenes Thermoplastic Elastomers Fluoroplastics Nylons Polyethylene ~ Copolymers Polyurethane PVC Copolymers Epoxy Thermosetting Polyesters Alkyds Vinyl Esters Polypropylene Polycarbonate Melamines Phenolic Polyimide Allyls ABS Glass-reinforced Silicone Polystyrene Copolymers

Ill ,,,.. Ill

,-r, :3

O" 0 0~--

Table 9 . 3 5

Coefficients of thermal expansion for parallel glass fiber thermoset RPs

Coefficient of thermal expansion

Resin type Epoxy-phenolic Silicone (MIL-R-25506) Phenolic a (MIL-R-9299) Polyester b (MIL-R-7575) Triallyl cyanurate polyester (MIL-R-25402) Epoxy (MIL-R-9300)

Temperature, ~

Parallel to warp, 106 in. per in.

- 100 to 200

4.8

5.0

5.0

10.0

300 to 600

2.8

2.5

4.5

6.3

- 1 0 0 to 100

4.0

5.0

5.0

38.0

100 to 600

3.0

3.0

3.0

80.0

- 100 to 200

6.0

5.8

6.4

11.1

300 to 600

3.2

2.9

3.0

6.2

- 1 0 0 to 100

7.8

9.3

8.5

19.1

200 to 400

1.4

2.3

1.3

237.6

Perpendicular to warp, 106 in. per in.

45 o to warp, 106 in. per in.

Through thickness, 106 in. per in.

- 100 to 200

5.5

5.2

5.2

11.0

r'D

3 50 to 600

3.6

3.9

3.6

12.0

r-k

- 100 to 200

5.5

6.7

6.7

300 to 600

3.3

1.5

2.3

t~

Ill

a Averageof data from laminates made with 181 fabric and two mats b Averageof data from laminates made with several styles of fabric (116, 112, 181 and 143) o ~3

1,0 W

Table 9 . 3 6

Properties of wear resistance short fiber RPs

, n ,

Coefficient of friction

Base polymer

Reinforcement lubricant, wt. %

POM

None 30% Glass fiber 30Olo Glass fiber + 15% PTFE 20OloCarbon fiber

Nylon 6/6

None 30Olo Glass fiber 30% Glass fiber + 15Olo PTFE 30Olo Glass fiber + 15Olo PTFE+ 2OloSilicone 3OOloCarbon fiber 50OioGlass fiber + 5% MoS2 20% Aramid fiber

Wear factor @ 23oC, 10-8 cm3min./m/kg/h (@ 73~ 10-70in.3min/ft/Ib/hr) 77 (65) 290 (245) 237 (200) 47 (4O) 237

(2oo) 89 (75) 19 (16)

(@ 73~ psi, 50 fpm))

Dynamic @ 23~ (276 KPa, 15.2 m/min) ((psi-fpm) @ 73~ 100 fpm)

0.14

0.21

0.25

0.34

0.2

0.28

0.11

0.14

0.20

0.28

0.25

0.31

Static @ 23oC(276 KPa)

0.19

0.26

11

0.12

0.14

24 (20) 89 (75) 73 (62)

0.16

0.20

0.24

0.31

0.22

0.25

(9]

Limiting PV (Kpa-m/s x 10-3) @ 23~ and 30.5 m/min ((psi-fpm) @ 73~ 100 fpm) 51 (3,500)

256 (17,500) 292 (20,000) 37 (2,500) 146 (10,000) 292 (20,000) 292 (20,000) 394 (27,000) 219 (15,000)

S" I'D

Deflection temperature ~ @ 1.82Mpa (~ @ 264 psi) 110 (230) 163 (325) 160 (320) 160 (320) 104 (220) 254

{490) 254 (495) 257 (495) 254 (490) 254 (490) 249 (480)

Water absorption % in 24 h 0.22 0.60 0.27 0.50 1.50 0.09 0.50 0.45 0.50 0.80 0.65

Ill

r-I,, i , -r,

:3 O"

0 0

Base polymer

Reinforcement lubricant, wt. %

PPS

None

Wear factor @ 23oC, 10-8cm3min./m/kg/h (@ 73~ 10-1oin.3minlft/Ib/hr)

30% Glass fiber

640 (540) 28 (24) 89 (75) 190 (160) 5,925 (5,000) 12

30% Carbon fiber

7

0.11

0.20

403 (340) 213 (180) 41 (35) 356 (300)

0.32

0.37

0.30

0.34

400/0 Glass fiber 30% Glass fiber + 30% PTFE 20~ Carbon fiber ETFE

TPU

None

(lo) (6)

None 30% Glass fiber 30% Glass fiber + 15% PTFE

Phenolic

Coefficient of friction Dynamic @ Static@ 23~ (276 KPo, 23~ [276 KPa) 15.2 m/min) (@ 73~ psi, ((psi-fpm) @ 50 fpm)) 73~ 100 fpm)

40% (z-Cellulose fiber 10O/oPTFE

Source: LNP Engineering Plastics, Inc.

+

0.30

0.24

0.38

0.29

0.13

0.15

0.23

0.20

Limiting PV

(Kpa-m/sx

Deflection temperature ~ @ 1.82Mpa [~ @ 264 psi)

44 (3,000) 234 (16,000)

138 (280) 263

(35,000) 292 (20,000)

0.05

0.40

_

0.17

0.18

_

0.20

0.25 (0.16)

70-~)

@ 23~ and 30.5 m/rain ((psi-fpm) @ 73~ 100 fpm)

22

(1,500) 146

(10,000} 511 (35,000)

(505) 26O (500) 263

(5o5) 71 (16o] 238 (46o) 241 (465) 32

(90) 171

(340) 85 (185) 163 (325)

Water absorption %in24h 0.05 0.02 0.03 0.04 0.02 0.02

f,D

0.02

I'D i,.,i

0.40 0.25

i-.Ii.i

i.i.

i-.IiIii

0.35 0.70

o

896 Reinforced Plastics Handbook Table 9.37 Plasticgear (a) safe bending stress (psi), (b) tooth form examplesof Y factors, and (c) service factors

(a)

Plastics Type

Unfilled

ABS Acetal Nylon Polyca rbonate Polyester Polyurethane

3,000 5,000 6,000 6,000 3,500 2,500

(b)

Safe Stress

Glass-filled 6,000 7,000 12,000 9,000 8,000

Numberof Teeth

147/2-deg Involute or Cycloidal

20-deg Full Depth Involute

20-deg Stub Tooth Involute

20-deg Internal Full Depth Pinion Gear

12 13 14 15 16 17 18 19 20 21 22 24 26 28 30 50 100 150 300 Rack

0.210 0.220 0.226 0.236 0.242 0.251 0.261 0.273 0.283 0.289 0.292 0.298 0.307 0.314 0.320 0.352 0.371 0.377 0.383 0.390

0.245 0.261 0.276 0.289 0.259 0.302 0.308 0.314 0.320 0.327 0.330 0.336 0.346 0.352 0.358 0.480 0.446 0.459 0.471 0.484

0.311 0.324 0.339 0.348 0.361 0.367 0.377 0.386 0.393 0.399 0.405 0.415 0.424 0.430 0.437 0.474 0.506 0.518 0.534 0.550

0.327 0.327 0.330 0.330 0.333 0.342 0.349 0.358 0.364 0.371 0.374 0.383 0.393 0.399 0.405 0.437 0.462 0.468 0.478 ...

8-10 hr/day

24 hr/day

Intermittent 3 hr/day

Occasional 1/2hr/day

1.00 1.25 1.5 1.75

1.25 1.5 1.75 2.00

, ,

0.691 0.679 0.613 0.565 0.550 0.534 . , ,

(c) Type of load

Steady Light shock Medium shock Heavy shock

0.80 1.00 1.25 1.5

0.50 0.80 1.00 1.25

Table 9 . 3 8 Different fibers mechanical and cost used in RPsa

Property Diameter, lam Density, glcm 3 Tensile strength, GPae Tensile modulus, GPae Thermal Expansion, 10-6/~ Thermal conductivity, W/(mK) Cost ratiog

E-glass 3 -20d 2.54 2.4 72.4

1.86 1

Kevlar 49

S-glass

HS~graphite

HMc graphite

9 2.49 4.5 85.5

6-8 1.7-1.8 3-4.5 234-253 -o.5(a) f 7(r) f 8-25(a) f

7-9 1.85 2.4 345-52O -1.2(a) f 12(r) f 105(a) f

12.1 1.44 3.5 59 -2(a) f

11.9 1.44 3.6 124 -2{a) f

58(r) f

59(r) f

60-100

200-650

20

3.1 33

2.55 30

Kevlar 29

Boron, W core 100, 140, 200 2.65, 2.45, 2.38 3.6 386-400 5.4 2.7 300-450

(,o

a Data only for certain fibers b High strength c High modulus

m ,

d Example of roving sizes are 9, 10, 13 lam e To convert GPa to psi, multiply by 145,000 f

(a) = axial; (r) = radial

g One is lowest cost

m . ,

o ~3

CO ~D

l,o

TabJe 9.39 Examples of various types of E-glass fiber reinforcement costs and applications Type of structure

Form

Precursor

We~lhts range

Dimensions range

Cost FactoP

End-use application

Continuous strand

Yarn Continuous roving Spun roving

Twistedsingle ends Untwisted multistrands

176,400 yds./lb, to 200yds./lb.

0.0026" diam. to 0.055" diam.

1-2-1/2

Filament winding Production of other reinforcements Pultrusion products Preforms Open mold Laminates Bag molding Open mold Laminates Compression molding Bag molding Preforms and molding compounds Injection molding Open mold Coining Resin transfer molding Laminates Bag molding Foam molding Stampable Reinforcements of gel coats Special surface effects in laminates

Looped single ends Cloth fabrics

1 oz. to 40 oz./sq, yd.

0.0010 to 0.045"

Continuous roving Spun strand roving Staple yard

15 oz. to 27 oz./sq, yd.

0.027 to 0.048" thick

2-3-1/2

Various lengths from 1/4" to over 4" Choppedstrand or continuous swirl

Continuous filament strands or spun strands Choppedstrands or continuous strands

Not applicable

Various lengths

1-1-1/2

3/4 oz. to 3 oz./sq, ft. Mechanically bonded 2 oz. to 10 oz./sq, ft.

Not representative unless compressed

1-1/2-2-1/2

Decorativeoverlay surfacing veils

Monofilaments

Generally less than 1.oz./sq. ft

0.010 to 0.030" thick

5-6

Various s t y l e s of weave

Yarn-continuous

Woven roving fabrics

Various s t y l e s of weave

Chopped strands

Reinforcing m a t s

Surfacing m a t s

Cost factor 1 indicates lowest cost, while 10 shows highest cost on S/lb. basis

3-1/2-6-1/2

.-i,i o

"o i

B , Ill

-I--

o" o o

9

Selecting 9 Plastic and Process 8 9 9

Table 9.40 Thermal properties of different fibers used in RPs

Property

E-glass

Carbon

Mean fiber diameter, 10-17 (0.39-0.67) 7 (0.27) p (mils) Therm. Cond., 7.0 60 BTU- i n.lh r.-ft. 2 (I .0) (8.6) (W/m. K) Specific Heat @ 70oF, 0.192 0.17 BTU/Ib./~ (803) (710) (J/Kg- K) Coefficient of thermal exp., 10-6 in./in./oF (10-6 cm/cm ~ Longitudinal 1.6 (2.9) -0.55 (-0.99) Transverse 4.0 (7.2) 9.32 (16.8) Surface energy, ergs/cm 2 31.0 53.0

HM Carbon

Aramid

8 (0.31)

12 (0.47)

97 (I 4)

3.5 (0.50)

0.17 (710)

0.34 (1400)

-0.28 (-0.50) - (1.8) -

-1.1 (-2.0) 33.0 (59.4) 41.0

Table 9.41 Tensile properties of different materials including 40 wtO/oglass fiber/TS polyester RP

Property Tensile modulus (EJ 106 GN/m 2 (psi) Tensile strength (a) 103 MN/m 2 (psi) Specific gravity (S)

Aluminum

Mild steel

70 (10) 400 (58) 2.7

210 (30) 450 (65) 7.8

Glass-fiber reinforced Polypropylene plastics

PP)

IGRP)

1.5 (0.21) 40 (5.8) 0.9

15 (2.2) 280 (40.5) 1.6

0 0 I'D ...,o

Table 9.42 Propertiesof wood, steel, concrete, brick masonry, aluminum, cast iron, and plate glass

I'D

Strength (psi) (MPa) (Yield values except where noted) Material Wood (dry)parallel-to-grain Douglas fir Redwood Southern pine

2 2 3

Tension

Compression

Shear

6,000 (41.4) 6,500 (44.8) 8,500 (58.6)

3,500 (24.1) 4,500 (31.0) 5,000 (34.5)

500 (3.45) 450 (3.10) 600 (4.14)

1,700 (11.7) 1,300 (8.96) 1,700 (11.7)

36,000 (248) -

20,000 (138)

29,000 (200) 25,000 (172)

3,500 3,500 4,500 30,000 85,000 36,000

180 130 300 18,000 25,000

3,500 2,100 4,500 10,000 25,000 10,000

Steel

Mild, low-carbon Cable, high strength Concrete Stone Structural, lightweight Brick masonry Aluminum, structural Iron, cast Glass, plate

Modulus of Elasticity (E) KS/ (eRa)

Coefficient of Thermal Expansion (oF-') [10-6)

36,000 (248) 275,000 (1,896) 200 150 300 30,000 20,000 10,000

(1.38) (1.03) (2.07) (207) (138) (69.0)

(24.1) (24.1) (31.0) (207) (586) (248)

(1.24) (0.80) (2.07) (124) (172)

(24.1) (14.5) (31.0) (69.0) (172) (69.0)

6.5 6.5 5.5 5.5 3.4 12.8 6 4.5

.,.,,.

e-I" m .

-Ie,~

0" 0 0

9

Selecting 9 Plastic and Process 901

35.000 I 30.000 25.000 ..,..

u~

20,000 Useable Range

15,000

10,000

, - - - - - / 73 F

/!

II

,,ooo/ 0

! 1%

2%

3%

Strain (in./in.)

Figure 9.6

Tensile stress-strain curves at different temperatures

4 .--.-

SPECIFIC STRENGTH

I x

SPECIFIC MODULUS

~x

aS

CARBON/

EPOXY

Figure 9.7

GLASS/

EPOXY

,1

WOOD

ALUMINUM

STEEL

Specific properties (strength and modulus + specific gravity] of RPs, wood, aluminum, and steel

r O f~ ~0 tl) =,,..

~' Materia'; I properties 1

111 I.i.,Chemical I Composition Microstructure Phases Grain size Corrosion resistance Inclusions

Metals

Composition Fillers Crys-tallinity Molecular weight Flammability Spatial configuration Chemical resistance

Plastics

I

Figure 9,8

Ceramics

Composition Porosity Grain size Binder Corrosion resistance

Composites

Composition (matrix/reinforcement) Matrix/reinforcement bond Volume fraction reinforcement Reinforcement nature Corrosion resistance

11

f3 I

LPi~Ysical......]

i

Melting ~oint Thermal Magnetic Electrical Optical Acoustic Gravimetric

Guide to various material properties of different materials

I'"" Mechanical

1

l

.....

I~

I

i

Tensile properties Toughness Ductility Fatigue Hardness Creep resistance

Available shapes Available sizes Available surface texture Manufacturing tolerances

Tensile properties Heat distortion Compression strength PV Limit Toughness

Manufacturing tolerances Stability Available sizes

Tensile properties Compression strength Fracture toughness Hardness

Available shapes Available sizes Manufacturing tolerances Available surface rex ture

Tensile properties Compression strength Fracture toughness Creep resistance

Available shapes Available sizes Manufacturing tolerances Stability

=O I/t ,-F m. f3 "1" Or" O

O

Table 9.43 Guide to RP process selection

0

I Reinforced plastics part to be processed (thermoset) I

r

I

I Large part

(over 3x5 ft)

(under 3x5 ft)

I

Strength predominant

I

Spray up

I

I

Vacuum bag Filament winding

I

I

Contact

Autoclave

I

I

Resin transfer

I

Cost predominant

I iLowl

Strength predominant

L

I,!wl

I M~diu~ I I Hbh I

Spray up

Contact I Vacuum bag I Resin transfer

I I

Pultrusion

Pressure bag

I

I

Pressurebag I Autoclave I Matched tool

I

Bmc ~t premix* I Resin transfer

I

Contact

I

Spray up

I

Pultrusion

I

I

I~owl

l"ig h I

Pressure bag

Contact

Pressure bag

Filament winding

Autoclave I Matched tooling

I

Matched tool

I

Mat preforms

I Medium I I Smcmat preform

I

I I

Vacuum bag

I

Spray up

* Bmc, premix preforms and prepregsall matched tool compression molding

I I

I

Simp,e I I

Mat

I

Fabric prepregs I Compression

I

l"i! h I I

Fabric prepregs

I

Matched tool

I

Injection ~D

I

Shape

I Complex I

Autoclave

Fabric* prepregs I Matchedtool

I Low I

I

Volume

I

Smcmat* preform I Continuous lamination

I

Injection

Shape

Filament winding

I

I

Pultrusion

I

Cost predominant

I L~I I I M~d~u~ I I" ,lh I

I

I

I'D

I Small part

,,,,,.

Volume

I

I C~ 'ex I I

I

I,owl I

I

I

:3 t~

I

Ill

I"~ h I

Preform

Preform

Compression

Premix

Mat

Injection

I I

I

I

I

Injection

Preforms

Matched tooling

Continuous lamination

I

,,,,,,

I

o q3 r,D Q

t,D 0

,m,~

Table 9 . 4 4

Overview of RP properties and processes

"0

Thermal Conductivity

Process

Reinforcement wt%

Spray

30-50glasspolyester Compression 15-30 glassSMC Compression 25-50 glass matpolyester Filament 30-80glasswinding epoxy Pultrusion 40-80 glass matpolyester Pultrusion Pultrusion

Pultrusion

30-50 glass matpolyester 30-55 glass mat and rovingvinyl ester resin 30-55 glass mat and rovingpolyester resin

Tensile Strength

Tensile Modulus

MPa

ksi

GPa

106psi

60-120

9-18

5.5-12

0.8-1.8

55-140

8-20

11-17

1.6-2.5

Flexural Strength

Compressive Strength

Impact Strength

ksi

MPa

ksi

J/m

ft. II~f/ft

W/m . K

Btu . in./h ft 2. ~

110-190

16-28

100-170

15-25

210-640

48-144

0.17-0.23

1.2-1.6

120-210

18-30

100-210

15-30

430-1150

96-264

0.19-0.25

MPa

Isi m =

Heat Distortion a t I. 8 MPa ~

~

Dielectric Strength kV/cm

kV/in.

175-205 350-400

80-160

200-400

1.3-1.7

205-260 400-500

120-180 300-450

170-210 25-30 550-1700 80-250

6.2-14 0.9-2.0 28-62 4.0-9.0

70-280 690-1850

10-40 100-270

100-210 310-480

15-30 45-70

530-1050 2150-3200

120-240 480-720

0.19-0.26 0.27-0.33

1.3-1.8 1.9-2.3

175-205 350-400 175-205 350-400

120-240 300-600 120-160 300-400

410-1050

60-150

28-41

4.0-6.0

690-1050 100-150

210-480

30-70

2400-3200

540-720

0.27-0.33

1.9-2.3

205-260 400-500

80-160

200-400

80-210

12-30

6.9-17

1.0-2.5

170-210

25-30

210-340

30-50

530-1350

120-300

0.22-0.27 1.5-1.85

95-150

200-300

80-120

200-300

70-280

10-40

6.9-21

1.0-3.0

100-280

15-40

140-340 20-50

270-1600

60-360

0.22-0.33

1.5-2.3

175-230 350-450

80-130

200-325

50-240

7-35

5.5-17 0.8-2.5

70-210

10-30

100-280

210-1350

48-300

0.22-0.33

1.5-2.3

175-205 350-400

80-120

200-300

15-40

-lOr"

0 0

Table 9.45 General information compares processes to properties of URPs and glass fiber RPs Material family

Cold Structural Injection Compression Transfer Casting Molding Coating F o a m Extrusion Laminating

ABS Acetal Acrylic Allyl ASA Cellulosic Epoxy Fluoroplastic Melamineformaldehyde Nylon Phenol-formaldehyde Poly (amide-imide) Polyarylether Polybutadiene Polycarbonate Polyester (TP} Polyester-fiberglass

X X X

Polyethylene Polyimide Polyphenylene oxide Polyphenylene sulphide Polypropylene Polystyrene Polysulfone Polyurethane (TS](TP) SAN Silicone Styrene butadiene Urea formaldehyde Vinyl

X X X X

(TS)

X X X X X X X X X X X

X X X X X X X

X

X

X X X

X X X

X X

X X

X X

X X

X X

(,o

X X X(TP) X

X

X

X

X X X

X

X X

X X

X X

X X

Dip RP and Sheet Molding Filament Slush Blow Rotational Forming FRP

X

X X X X(TP) X X X

m

,

,,I,1,,

Ill =i "0 o ~3

0

r 0

Table 9.46 General information relating RP materials properties to processes Thermosets

Properties

Processes

Polyesters Properties shown also apply to some polyesters formulated for thermoplastic processing by injection molding

Simplest, most versatile, economical and most widely used family of resins, having good electrical properties, good chemical resistance, especially to acids

Compression molding Filament winding Hand lay-up Mat molding Pressure bag molding Continuous pultrusion Injection molding Spray-up Centrifugal casting Cold molding Comoform Encapsulation

Epoxies

Excellent mechanical properties, dimensional stability, chemical resistance {especially alkalis), low water absorption, self-extinguishing (when halogenated), low shrinkage, good abrasion resistance, very good adhesion properties

Compression molding Filament winding Hand lay-up Continuous pultrusion Encapsulation Centrifugal casting

Phenolics

Good acid resistance, good electrical properties (except arc resistance), high heat resistance

Compression molding Continuous laminating

Silicones

Highest heat resistance, low water absorption, excellent dielectric properties, high arc resistance

Compression molding Injection molding Encapsulation

Melamines

Good heat resistance, high impact strength

Compression molding

Diallyl phthalate

Good electrical insulation, low water absorption

Compression molding

a" "1

Ill m.

-ie,~ a"

0 0

Thermoplastics

Properties

Processes

Polystyrene

Low cost, moderate heat distortion, good dimensional stability, good stiffness, impact strength

Injection molding Continuous laminating

Nylon

High heat distortion, low water absorption, low elongation, good impact strength, good tensile and flexural strength

Injection molding Blow molding Rotational molding

Polycarbonate

Self-extinguishing, high dielectric strength, high mechanical properties

Injection molding

Styrene-acrylo-nitrile

Good solvent resistance, good long-term strength, good appearance

Acrylics

Good gloss, water resistance, optical clarity, and color; excellent electrical properties

Injection molding Injection molding Vacuum forming Compression molding Continuous laminating

Vinyls

Excellent weatherability, superior electrical properties, excellent moisture and chemical resistance, self-extinguishing

Injection molding Continuous laminating Rotational molding

Acetals

Very high tensile strength and stiffness, exceptional dimensional stability, high chemical and abrasion resistance, no known room temperature solvent

Injection molding

Polyethylene

Good toughness, light weight, low cost, good flexibility, good chemical resistance can be "welded"

Injection molding Rotational molding Blow molding

Fluorocarbons

Very high heat and chemical resistance, nonburning, lowest coefficient of friction, high dimensional stability

Injection molding Encapsulation Continuous pultrusion

Polyphenylene oxide modified

Very tough engineering plastic, superior dimensional stability, low moisture absorption, excellent chemical resistance

Injection molding

Polypropylene

Excellent resistance to stress or flex cracking, very light weight, hard, scratch-resistant surface, can be electroplated good chemical and heat resistance; exceptional impact strength; good optical qualities Good transparency, high mechanical properties, heat resistance, electrical properties at high temperatures; can be electroptated

Injection molding Continuous laminating Rotational molding

Polysulfone

Injection molding

C,O

m,

et

o

t~

Q ~4

908

Reinforced Plastics Handbook

Table 9,47 Comparisonof closed molding techniques Vacuum molding/RTM L i g h t - usually composite tooling

For:

9Often used as an 'entry level' process but possible to scale up to high volume production {>2,000 per annum) 9Tooling significantly cheaper than RTM (approx 40% saving) with the possibility of using existing 'open' tooling as starting point 9Tooling can be manufactured in-house with the appropriate training 9Short tooling lead times 9Light weight tooling poses less handling problems 9Very 'scalable' with large structures (>20 m2) being achievable

Against: 9Laminate thickness control less precise than RTM 9Relatively labor intensive and difficult to automate RTM - composite tooling For. 9Relatively short lead times and tooling can be manufactured in house with the appropriate training 9Automation is possible, with good control over process variables 9Rigid tooling allows faster injection and thus shorter cycle times 9Tooling can be produced from a conventional 'pattern' without the need for CAD data

Agoinst: 9Tool life must be carefully balanced against cost 9Tool manufacture must be carefully controlled at all stages 9Tooling must be meticulously maintained to achieve maximum life RTM - metal tooling

For:

9Tool life - very high production numbers possible (> 10,000) 9Balance between tool cost and tool life can render metal significantly cheaper than composite if production numbers are suitable 9Tooling can be cut directly from CAD data without the need for a 'pattern' 9Very fine detail/surface finishes are achievable 9High temperature, pressure and abrasion resistance are inherent features 9Certain shapes can actually be cheaper to produce in metal than as a composite structure

Against: 9Larger structures can be prohibitively expensive either to machine or simply in material cost 9Specialist expertise needed to avoid costly mistakes 9Weight, tool handling infrastructure can add significant cost

Table 9 . 4 8 Molding comparison of resin transfer, open (spray and hand), and compression (mat and sheet)

CompressionMolding

OpenMolding Resin TransferMolding Mold construction

Pressure

FRPI- spray metal, cast aluminum: gusket seal, air vents, self-sealing injection port Pressure feed pumping equipment req'd: mold halves clamped (methods range from clamp frame to pressure pod)

High shear type Continuous strand m a t , preform, woven roving

Part trim equipment Generally expected mold life {parts)

Met-Preform

Hand Lay-up

3,000

I- FRP= Fiberglassreinforced plastics CourtesyOwners-ComingCorps.

SheetMolding Compound

FRP

FRP,spray metal cast aluminum, pinch (land)

Metal, shear edge

High grade steel shear edge

None

Lows pressure press, capable for 50 psi (hydraulic or pneumatic mechanical); resin dispensing equipment not req'd but recommended

Hydraulic press, normal range of 100-500 psi (0.69-3.05 MPa)

Hydraulic:as high as 2,000 psi (138 MPa)

Heated normal range of 225-325~ (107-163~ High shear type

Heated normal rangeof 275-350~ (135-177~

Room temperature

Cure system Resin compounding equipment Reinforcement

Spray-up

Not needed Continuous Chopped strand mat, woven roving roving, cloth Yes 1,000

Continuous strand mat, preform, woven roving

3,000

Continuous strand Continuous roving mat, preform, (specific orentations woven roving for higher strength} With optimum shear edges, minor trimming only 150.000+ 150.000+

1.0 IJl

l-l-

Ill Be

:3

o ~3

0

910 Reinforced Plastics Handbook Table 9.49 Molding comparison of compression and transfer Charecteristic

Compression

Transfer

Molding temperature

I. One step closures: 350-450~ 2. Others: 290-390~

290-360oF

Pressure via clamp

1.2,000-10,000 psi (3,000 optimum on part) 2. Add 700 psi for each inch of part depth

1. Plunger ram at 6,000-10,000 psi 2. Clamping ram having minimum tonnage of 750/0of load applied by plunger ram on mold

Pressure in cavity

Equal to clamp pressure

Very low to maximum of 1,000 psi

Breathing the mold

Frequently used to eliminate gas and reduce cure time

1. Neither practical nor necessary 2. Accomplished by proper venting

Cure time {time pressure is being applied on mold)

30-300 s but will vary with mass of material, thickness of part, and preheating

45-90 s but will vary with part geometry

Use of inserts

Limited because inserts may be lifted out of position or deformed by closing

Unlimited but complicated; inserts readily accommodated

Tolerances on finished products

1. Fair to good: depends on mold construction and direction of molding 2. Flash = poorest, positive = best, semipositive = intermediate

Good: close tolerances are easier to hold

Shrinkage

Least

1. Greater than compression 2. Shrinkage across line of flow is less than with line of flow

9

Selecting 9 Plastic and Process 911

Table 9 . 5 0 Molding comparison of resin transfer, SMC, and injection

Process

Process operation: Production requirement, annual units per press Capital investment Labor cost Skill requirements Finishing Product: Complexity Size Tolerance Surface appearance Voids/wrinkles Reproducibility Cores/inserts Material usage: Raw material, cost

Handlinglapplying

Waste Scrap Reinforcement flexibility Mold: Initial cost Cycle life Preparation Maintenance

RTM

SMC Compression

Injection

5,000-10,000

50,000

50,000

Moderate High Considerable Trim flash, etc.

High Moderate Very low Very little

High Moderate Lowest Very little

Very complex Very large parts Good Gel coated Occasional Skill-dependent Possible

Moderate Big flat parts Very good Very good Rarely Very good Very difficult

Greatest Moderate Very good Very good Least Excellent Possible

Lowest Skill dependent Up to 3 percent Skill dependent Yes

Highest Easy Very low Cuts reusable No

High Automatic Sprues, runners Low No

Moderate 3,000-4,000 parts In factory In factory

Very high Very high Years Years Special mold-making shops Special machine shops

Table 9.51 Molding comparison of stamp steel, compression, resin transfer, injection, and stamped aluminum

Part consolidation Comparable mass Corrosion resistance Resistance to minor impact Tooling cost Raw material cost Stiffness Linear thermal Heat deflection temperature

Stamped Compression steel molded SMC R R I M

Injection molded Stamped thermoplastics aluminum

Baseline Excellent 100% 75% Baseline S u p e r i o r

Very g o o d 75% Superior

Excellent 70% Superior

Baseline

Better

Best

Better

Fair 75% Slight improvement Poor

100% 100% 100% 100% N/A

40% 300% 6% 100%-130% Baseline

60o/o 600% 1% 600%-1000% Poor

60o/o 600% 2% 600%-1000% Poor

100O/o 400% 30% 170%-200% N/A

"This table usedsteel as a standard by which all other processesare compared

912 Reinforced Plastics Handbook Table 9 . 5 2

Molding comparison of PUR-reaction injection and injection

PUR-RIM Plastic temperature, ~ Plastic viscosity, Pa s9 Injection pressure, bar Injection time, s Mold cavity pressure, bar Gates Clamping force, t Mold temperature, ~ Time in mold, s Annealing Wall/thickness ratio Part thickness, typical maximum cm Shrinkage, O/o Unreinforced Reinforced - glass parallel to fiber vertical to fiber Inserts Sink marks around metal inserts Mold prototype, months Mold alterations

Injection molding

40-60 0.5-1.5 100-200 0.5-1.5 10-30 1 80-400 50-70 20-30 30 min. @ 120 ~ 1/0.8 10

200-300 100-1,000 700-800 5-8 300-700 2-10 2,500-10,000 50-80 30-80 Rarely 1/0.3 1

1.30-1.60

0.75-2.00

0.25 1.20 Easy Practically none 3-5 (epoxy) Cost-effective

0.20 0.40 Costly Distinct 9-12 (steel) Costly

Tabte 9 . 5 3 Molding comparison of blow, thermoforming, and rotational

Factor Typical product volume range (cm3) Plastics available Feedstock Raw material preparation cost Reinforcing fibers Mold materials Mold pressure Mold cost Wall thickness tolerance Wall thickness uniformity Inserts Orientation in part Residual stress Part detailing In-mold graphics c:ycle time Labor intensive

Blow Molding

Thermo Forming

Rotational Molding

101-106

5x 10~

limited pellets none yes steel/aluminum <1 MPa high 10%-20% tends to be nonuniform feasible high moderate very good yes fast no

broad sheet up to +100O/o yes aluminum <0.3 MPa moderate 10%-20% tends to be nonuniform no very high high good, with pressure possible fast moderate

106

101-108 limited powder/liquid up to 100% yes, very difficult steel/aluminum <0.1 MPa moderate 10%-20% uniformity possible yes none low adequate yes slow yes

Table 9.54

Molding comparison of foaming vs. other processes

Foam vs. sheet metal

Foam vs. die casting

1. Fabrication economy: less assembly time; tighter dimensional tolerances; increased product integrity; less final product-inspection time 2. Fewer parts required for assembly 3. Dent resistance 4. Elimination of oil canning 5. Greater design freedom 6. Better sound damping 7. Reduced damage from shipping 8. Reduced tooling costs for complex configuration

1. Much lower tooling costs 2. Longer tool life, lower maintenance 3. No trim dies required 4. Lighter weight 5. Higher impact resistance 6. Better sound damping 7. Better strength-to-weight 8. Better impact resistance

1. Smaller variety of finishes available, such as chrome or baked enamel 2. No R.F.I. and grounding capabilities 3. Harder to retrofit to frame or skins 4. Thicker wall 5. Higher tool costs than with brakeforming

1. No heat sink capabilities 2. No R.F.I. and grounding capabilities 3. Fewer available finishes for cosmetic appearance 4. Higher finishing costs 5. Thicker walls 6. Possible internal voids

50+*

15 to 30

* Even with limited quantities

f Depending on unit volume and part size

Foam vs. sheet molding compound Advantages 1. Uniform physical properties throughout the part 2. Warping and sink marks reduced or eliminated 3. No resin-rich areas to cause configuration problems 4. Higher impact resistance 5. Greater inherent structural capabilities 6. Lower shipping costs 7. Large parts more economical 8. Lower tooling costs 9. Better sound damping

Limitations 1. Increased finishing costs (surface swirl) 2. Heat distortion 3. Thicker wall 4. Lower physical properties 5. Possible internal voids

Foam vs. hand lay-up fiSerglass

Foam vs. injection molding

1. 2. 3. 4. 5. 6. 7.

(Many process similarities exist} 1. Flexibility for functional engineering 2. Better low- to mediumvolume economics 3. Lower tooling costs 4. Better large-part capability 5. Better sound damping 6. Lower internal stresses 7. Sink marks reduced or eliminated 8. Inherent structural strength

More consistent part reproduction Lower labor Simplified assembly Better dimensional stability More design freedom More uniform physical properties Better sound damping

f,D

1. More prone to heat distortion 2. Poorer economies of part size vs. quantity 3. Thicker walls 4. Higher tooling costs

Potential Savings from Structural Foams (in %) Up to 30 50+

1. Poorer surface finish 2. Application of cosmetic detail for appearance parts 3. Longer cycle time 4. Thicker walls 5. Poorer high-volume economics 6. Less equipment available for various shot sizes

15 to 20-1-

,,m 9

Ill m ,

o Ilq

r

r

Tabte 9~55 Exampleof wall thickness ranges and tolerances for RP products vs. processes Thickness rangea Molding method

Minimum, mm (in.)

Maximum, mm (in.)

s" Maximum practica61e 6uildup within individual port

Hand layup Sprayup Vacuum bag molding Cold-press molding Casting, electrical Casting, marble

1.5 (0.060) 1.5 (0.060) 1.5 (0.060) 1.5 (0.060) 3 (0.125) 10 (0.375)

30(1.2) 13 (0.5) 6.3 (0.25) 6.3 (0.25) 115 (4.5) 25(1)

EMC molding Matched-die molding: SMC Pressure bag molding Centrifugal casting

1.5 (0.060) 1.5 (0.060) 3(0.125) 2.5 (0.100)

25(1) 25(1) 6.3 (0.25) 450/0 of diameter

No limit; use cores No limit; use many cores No limit; over 3 cores possible 3-13mm (1/8-1/2in.) 3-115mm (1/8-41/2 in.) 10-13mm 19-25mm (3/8-1/2in 3/4-1in.) Min. to max. possible Min. to max. possible 2:1 variation possible + 50/0 of diameter

Filament winding Pultrusion

1.5 (0.060) 1.5 (0.060)

25(1) 40(1.6)

Pipe, none; tanks, 31 around ports None

Continuous laminating Injection molding Rotational molding Cold stamping

0.5 (0.020) 0.9 (0.035) 1.3 (0.050) 1.5 (0.060)

6.3 (0.25) 13 (0.5) 13 (0.5) 6.3-13 (0.25-0.50)

None Min. to max. possible 21 variation possible 31 possible as required

r

Normal thickness tolerance, mm (in.)

~3

+0.5 (0.020) +0.5 (0.020) +0.25 (0.010) +0.5 (0.020) +0.4 (0.015) +0.8 (0.031)

IsI

+0.13 (0.005) +0.13 (0.005) 0.25 (0.010) +0.4mm for 150mm diameter (0.015in. for 6in. diameter) +0.8mm for 750mm diameter (O.030in. for 30in. diameter) Pipe, +50/0; tanks, +l.5mm (O.060in.) 1.5mm, +O.025mm (1/16 in. +O.O01in.) 40mm, +0.5mm (11/2in. +O.020in.) +lOwtO/o +0.13 (0.005) +50/0 +6.5wtO/o for flat +6.0wt% parts

a Thickness may be varied within parts, but it may cause prolonged cure times, slower production rates, and warpage. If possible, the thickness should be held uniform throughout a part

mo

-r

Q.1

o" o o

9 Table 9 . 5 6

Selecting 9 Plastic and Process 9 1 5

Wall thickness tolerance guide for thermoset plastic moldings

Minimum Thickness in.(mm) Alkyd - glass filled Alkyd - mineral filled Diallyl phthalate Epoxy - glass filled Melamine - cellulose filled Urea - cellulose filled Phenolic - general purpose Phenolic- glass filled Phenolic- fabric filled Silicone glass Polyester premix

0.040 0.040 0.040 0.030 0.035 0.035 0.050 0.030 0.062 0.050 0.040

(1.0) (1.0) (1.0) (0.76) (0.89) (0.89) (1.3) (0.76) (1.6) (1.3) (I.0)

Average thicknessin.(mm)

Maximum thicknessin.(mm)

O. 125 (3.2) 0.187 (4.7) 0.187 (4.7) 0.125 (3.2) 0.100 (2.5) 0.100 (2.5) 0.125 (3.2) 0.093 (2.4) 0.187 (4.7) 0.125 (3.2) 0.070 (1.8)

0.500 0.375 0.375 1.000 0.187 0.187 1.000 0.750 0.375 0.250 1.000

(13) (9.5) (9.5) (25.4) (4.7) (4.7) (25.4) (19) (9.5) (6.4) (25.4)

Table 9 , 5 7 Guide to dimensional tolerances for Classes A, B, and C RP products

Dimension, mm (in.)

0-25 25-100 100-200 200-400 400-800 800-1600 1600-3200

(0-1) (1-4) (4-8) (8-16) (16-32) (32-64) (64-128)

Class A (fine tolerance), mm (in.) +0.12 +0.2 +0.25 +0.4 +0.8 +1.3 +2.5

(+0.005) (+0.008) (+0.010) (+0.016) (+0.030) (+0.050) (+0.100)

Class B Class C (normal tolerance), (coarse tolerance), mm (in.) mm (in.) +0.25 +0.4 +0.5 +0.8 +1.3 +2.5 +5.0

(+0.010) (+0.016) (+0.020] (+0.030) (+0.050) (+0.100) (+0.200)

+0.4 (+0.016) +0.5 (+0.020) +0.8 (+0.030 +1.3 (+0.050) +2.0 (+0.080) +3.8 (+0.150) +7.0 (+0.280)

ClassAtolerances apply to parts compression molded with precision matched-metal molds, BMC,SMC and preform are included ClassB tolerances apply to parts press molded with somewhat less precise metal molds. Cold-press molding, casting, centrifugal casting, rotational molding, and cold stamping can apply to this classification when molding is done with a high degree of care BMC,SMC and preform compression molding can apply to this classification if extra care is not used. ClassCapplies to hand layup, sprayup,vacuum bag, and other methods using molds made of RP/Cmaterial. It applies to parts that would be covered by Class B when they are not molded with a high degree of care.

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Selecting 9 Plastic and Process 91 7

Table 9 , 5 9 Comparing unreinforced and reinforced thermoplastic mold shrinkage rates per ASTM D 955

Avg. rate per ASTM D 955 Material ABS Unreinforced 30Ologlass fiber Acetal, copolymer Unreinforced 30% glass fiber HDPE, homo Unreinforced 30Oioglass fiber Nylon 6 Unreinforced 30% glass fiber Nylon 6/6 Unreinforced 15Ologlass fiber + 25% mineral 15% glass fiber + 25% beads 30% glass fiber PBT polyester Un reinforced 30Ologlass fiber Polycarbonate Unreinforced 10Ologlass fiber 30Oioglass fiber Polyether sulfone Unreinforced 30% glass fiber Polyether-etherketone Unreinforced 30Oioglass fiber Polyetherimide Unreinforced 30Ologlass fiber Polyphenylene oxide/PS alloy Unreinforced 30% glass fiber Polyphenylene sulfide Unreinforced 40% glass fiber Polypropylene, homo Unreinforced 30% glass fiber Polystyrene Unreinforced 30% glass fiber

0.125 in. (3.18 mm)

0.250 in. (6.35 mm)

0.004 0.001

0.007 0.0015

0.017 0.003

0.021 N/A

0.015 0.003

0.030 0.004

0.013 0.0035

0.016 0.0045

0.016 0.006 0.006 0.005

0.022 0.008 0.008 0.0055

0.012 0.003

0.018 0.0045

0.005 0.003 0.001

0.007 0.004 0.002

0.006 0.002

0.007 0.003

0.011 0.002

0.013 0.003

0.005 0.002

0.007 0.004

0.005 0.001

0.008 0.002

0.011

0.004

0.015 0.0035

0.025 0.004

0.004 0.005

0.006 0.001

91 8 Reinforced Plastics Handbook Table 9 . 6 0 Detail guides for limits and tolerances of RP vs. Processes

Factor limiting maximum size of product Maximum size, m2 Shape limitations U.S. production volume, articles per year Production cycle time Glass, O/o Strength orientation Strength Wall thickness, mm Minimum Maximum Tolera nce Variations Minimum draft to 15 cm depth over 15 cm depth Minimum inside radius Ribs Bosses Undercuts Holes Parallel Perpendicular Built-in cross Metal inserts Metal edge stiffeners Surface finish Number of finished surfaces Quality of surface Gel-coat surface Surfacing mat Combination with thermoplastic linear Trim in mold Molded-in labels Raised numbers Translucency Tool cost Capital equipment cost

Resin transfer molding

Injection molding

Pultrusion

Reinforced reactioninjection molding

Machine size

Machine size

Materials

Metering equipment

9.3 Moldable 1,000-20,000

9.3 Moldable 50,000-1,000,000

29 Round, rectangular 3,050m

4.6 Moldable 15,000-100,000

10-20 min 15-25 Random Low-medium

15 s to 15 min 20-40 Random Low

10-30 min 30-75 Highly oriented High

1-2 min 5-25 With flow Low

0.76 25

0.76 13-25

Uniform

Uniform

1.6 13 0.3 + 25 Uniform

2.0 13 +0.05 Uniform

10 10 1/2 part depth

10 lo+ 1/2 part depth

0-20 0-20 1.5 mm

1-30 3~ 1/2 part depth

Yes Yes Possible

Yes Yes Possible

No No No

Yes Yes Yes

Yes Yes Yes Yes Yes

Yes Yes Yes Yes Yes

No No No No No

Yes Yes Yes Yes Yes

all

2

2

2

Excellent Yes Yes

Excellent Yes Yes Yes

Fair to good No No No

Excellent No No No

No Yes Yes Yes High High

No Yes Yes Yes High High

No No No No Low Low

Yes No Yes No Low-medium Low-medium

9

Hand lay-up, spraying

Filament winding

Mold size; transport

Selecting 9 Plastic and Process 9 1 9

SMC

BMC

Preform molding

Winding machine

Press rating and size

Press rating and size

Pressrating and size

280 None 1,000

93 Surface of revolution 1,000

4.6 Moldable 103-106

4.6 Moldable 103-106

18.6 Moldable 103-106

3 min to 24 h 20-35 Random Medium

5 min 65-90 Highly oriented Very high

1.5-5 min 15-35 Random Low-medium

1.5-5 min 15-35 Random Low-medium

1.5-5 min 24-45 Random Medium-high

0.76 >38 +0.5 As desired

0.3 50 +0.3 As desired

0.8 6.4 +0.2 Uniform desirable < 3:1

1.5 25 +0.1 As desired

0.8 6.4 +0.1 Uniform desirable -=2 : 1

0-2 o 0-2 o 6.3mm

3o 3o+ 3.1 mm

1-3 o 3~ 1.5mm

1-3 o 3o+ 1.5mm

1-3 o 3~ 3.1 mm

Yes Yes Avoid

No No No

Yes Yes Avoid

Yes Yes No

Not recommended Not recommended No

Yes Yes Possible Yes Yes

Yes

Yes Undesirable Possible Yes No

Yes Undesirable Possible Yes No

Not recommended Undesirable Possible Not recommended Yes

Possible Yes No

All Excellent Yes Yes Yes

Excellent Yes Yes Yes

Very good No No No

Excellent No No No

Very good Yes Yes No

No Yes Yes Yes Low Low

Yes Yes

Yes Difficult Yes No High High

Yes Difficult Yes No High High

Yes Difficult Yes Yes Medium High

Yes Low Low

920 Reinforced Plastics Handbook Table 9.61 Economic comparison of structural foam molding, injection molding, and compression SMC molding

Production Considerations

Structural Foam

InjectionMolding

Sheet Molding Compound

Typical minimum number of parts a vendor is likely to quote on for a single setup

250 {using multiple nozzle equip, with tools from other sources designed for the same polymer and ganged on the platen)

1,000 tO 1,500

500

Relative tooling cost, single cavity

Lowest. Machined aluminum may be variable, depending on quantity required

20 percent more. Hardened-steel tooling

20 percent to 25 percent more. Compression-molding steel tools

Average cycle times for consistent part reproduction

2 to 3 minutes (I14in. nominal wall thickness)

40 to 50 seconds

1112to 3 minutes

Is a multiple-cavity tooling approach possible to reduce piece costs?

Yes

Yes. Depends on size and configuration, although rapid cycle time may eliminate the need

Not necessarily. Secondary operations may be too costly and material flow too difficult

Are secondary operations required except to remove sprue?

No

No

Yes, e.g., removing material where a "window" is required (often done within the molding cycle)

Range of materials that can be molded

Similar to thermoplastic injection molding

Unlimited; cost depends on performance requirements

Limited; higher cost

Finishing costs for good cosmetic appearance

40 to 60 cents per sq. ft. of surface (depending on surface-swirl conditions)

None, if integrally colored; 10-20 cents per sq. ft. if painted

None, if secondary operations such as trimming are not required. Otherwise 20 to 30 cents per sq. ft. of surface

Table 9.62 Properties to cost of RP processes and materials

Molding

Materials

m

Compression molding

Hot press

Cold p r e s s - ~

Stamping - - ~

I RLM

Heat resistance (HDT18.6)~

(74o- 75oo0

Weight ratio 7 {Equiflextural modulus)

Moldability

Paintabilityby baking

1

O~A

>200

|

0.65

o~A

Polyester + GF (BMC)

1.1

1'

1'

@

0.6

I'

Polyester + GF (High-strength SMC)

1.6~4.2

@

1'

Polyester + GF (Resin injection)

0.8

0

150~200

A~x

0.62

A

0.6

|

160

-

0.5

|

0.8

|

215

15

0

> 200

Cost2 (Mold cost) 3

0

(o) t 0

0.4~0.5

(o) |

(|

Polyester + GF (Hand lay-up) PP + GF or sawdust, paper pulp (AZDEL, etc.)

Epoxy + CF (CFRP)

Injection molding

Impact strength

Polyester + GF (SMC)

Nylon + GFTF (STX, etc.) Filament winding

Flexural modulus x 103kg/mm 3

PP + GF, talc (EPDM) AS + GF

0.6,,,0.4

PBT or nylon + GF

1.2~1.4

1'

205~215

Foamed styrene or ABS (+ GF)

2.4~2.5

O~A

80 (100)

|

-

Urethane + GF (RRIM)

0.1~0.2

1'

120~105

o

t

|

-

0.2

A

-

|

0.5

0.5

0

f

(o)

(,0

A

(o)

A~x

(o) @

(-) A

r-lm

,

-o

,,,m

Ill

(o) 0

0.4~0.6 A~x

A~O

(o) o~A

A

(|

-o o VI

Note: I. Ratio basedon sheet metal weight as I 2. Relative comparison for 400-500 kg; 3. Mold cost for sheet metal. Symbols: @ Excellent- 0 Good; A Fair x No good

t,O

922 Reinforced Plastics Handbook Table 9.63 Examplesof limitations of different processes Process

Limitations*

Blow molding

Limited to hollow or tubular parts; wall thickness and tolerances difficult to control; principally used with thermoplastics

Calendering

Limited to sheet materials; very thin films are not possible

Casting

Limited to simple shapes; uneconomical at high volume production rates

Centrifugal casting

Limited to simple curvatures in single-axis rotation; low production rates

Coating

Economics dependent on close tolerance control

Coining

This injection-compression process produces high pressure, stress-free precision parts

Cold-pressure molding

Limited tosimple shapes and few materials

Compression molding

For intricate parts containing undercuts, side draws, small holes, delicate inserts

Encapsulation

Low volume process subject to inherent limitations on materials, which can lead to product defects

Extrusion molding

Limited to sections of uniform cross section; principally used with thermoplastics

Filament winding

Limited to shapes of positive curvature; openings and holes can reduce strength if not properly designed

Injection molding

High initial tool and die costs; not economical for small runs

Laminating

High tool and die costs; limited to simple shapes and cross section profiles

Matched-die molding

High mold and equipment costs; parts often require extensive surface finishing

Pultrusion

Close tolerance control requires care; unidirectional strength

Resin transfer molding

Low mold costs, low pressure molding, two good surfaces providing quick manufacture of wood molds and producing rather complicated small and particularly large parts to rather tight tolerances

Rotational molding

Limited to hollow parts; low production rates; principally used with thermoplastics

Slush molding

Limited to hollow parts; low production rates; limited choice of materials; principally used with thermoplastics

Thermoforming

Limited to simple parts; high scrap; limited choice of materials; principally used with thermoplastics

Transfer molding

High mold cost; high material loss in sprues and runners; and size of products limited

Wet lay-up or contact molding

Not economical for large volume production; uniformity of resin distribution difficult to control; only one good surface; limited to simple shapes

* Theseare general comments;there are manyexceptions basedon availableor new equipmentdeveloped to meet specific processing and performance requirements

Table 9.62 Properties to cost of RP processes and materials

Molding

Materials

m

Compression molding

Hot press

Cold p r e s s - ~

Stamping - - ~

I RLM

Heat resistance (HDT18.6)~

(74o- 75oo0

Weight ratio 7 {Equiflextural modulus)

Moldability

Paintabilityby baking

1

O~A

>200

|

0.65

o~A

Polyester + GF (BMC)

1.1

1'

1'

@

0.6

I'

Polyester + GF (High-strength SMC)

1.6~4.2

@

1'

Polyester + GF (Resin injection)

0.8

0

150~200

A~x

0.62

A

0.6

|

160

-

0.5

|

0.8

|

215

15

0

> 200

Cost2 (Mold cost) 3

0

(o) t 0

0.4~0.5

(o) |

(|

Polyester + GF (Hand lay-up) PP + GF or sawdust, paper pulp (AZDEL, etc.)

Epoxy + CF (CFRP)

Injection molding

Impact strength

Polyester + GF (SMC)

Nylon + GFTF (STX, etc.) Filament winding

Flexural modulus x 103kg/mm 3

PP + GF, talc (EPDM) AS + GF

0.6,,,0.4

PBT or nylon + GF

1.2~1.4

1'

205~215

Foamed styrene or ABS (+ GF)

2.4~2.5

O~A

80 (100)

|

-

Urethane + GF (RRIM)

0.1~0.2

1'

120~105

o

t

|

-

0.2

A

-

|

0.5

0.5

0

f

(o)

(,0

A

(o)

A~x

(o) @

(-) A

r-lm

,

-o

,,,m

Ill

(o) 0

0.4~0.6 A~x

A~O

(o) o~A

A

(|

-o o VI

Note: I. Ratio basedon sheet metal weight as I 2. Relative comparison for 400-500 kg; 3. Mold cost for sheet metal. Symbols: @ Excellent- 0 Good; A Fair x No good

t,O

r 4~

Table 9~65

Guide to process selection based on product size m..

a"

PARTTO BE FORMED

I

I

LARGE PART

SMALL PART LESSTHAN 1 SQ FT LESSTHAN 5 LB

OVER 1SQFT OVER 5 LBS

I OVER 250~

I

I

I

I

LONG LENGTHS

LOW-PRESSURE LAMINATION FILAMENT WINDING COMPRESSION HIGH-PRESSURE LAMINATION POST FORM ADHESIVE BOND MACHINE PULTRUSION

I

THERMOFORM FOAM HEAT SEAL WELD ROTOFORM BLOW MOLD ADHESIVE BOND STRUCTURAL FOAM RIM

I

I EXTRUDE

I

LOW-VOLUME

HIGH-VOLUME

CASTING MACHINING LOW-PRESSURE LAY-UP POST FORM SPRAY-UP RESIN TRANSFER

COMPRESSION TRANSFER INJECTION LAMINATION PULTRUSION

c-

>- .-.ix

Blow Molding

C3_

Injection Molding

E 0

Compression

4.-., c13 o_

Thermoforming Extrusion

I -'~

0

Large

Small Part Size

el" 0 0

LESSTHAN 250~ THERMOPLASTICS

THERMOSETS

I

LARGE AREA

=3=

OVER 250~ F

UNDER 250~ THERMOPLASTICS

THERMOSETS

,,,.,. I/I

I

HIGH-VOLUME

I

INJECTION BLOW MOLD THERMOFORM EXTRUSION ROTOFORM RIM

I

LOW-VOLUME

I

MACHINE THERMOFORM COMPRESSION CASTING ROTOFORM FOAM ADHESIVE BOND

9

Selecting 9 Plastic and Process 9 2 5

Table 9.66 Guide to mold costs in various materials, relative to machined steel molds

Material and technique Steel, machined Aluminum, machined Nickel steel, electro- or vapor-deposited Aluminum, cast Kirksite, cast Zinc, sprayed metal Epoxy, cast (prototyping only)

Relative cost (%) 100 80 70 60 60 40 30

926 Reinforced Plastics Handbook Designs Table 9.67

Examples of processing methods as a function of part design

Process Thermoplastics Injection Injection compression Hollow injection Foam injection Sandwich molding Compression Stamping Extrusion Blow molding Twin-sheet forming Twin-sheet stamping Thermoforming Filament winding Rotational casting Thermosetting Compression Powder Sheet molding compound Cold-press molding Hot-press molding High-strength and sheet molding compound Prepreg Vacuum bag Hand lay-up Injection Powder Bulk molding compound ZMC Stamping Reaction injection molding Resin transfer molding, or resinject High-speed resin transfer molding, or fast resinject Foam polyurethane Reinforced foam Filament winding Pultrusion

Ribs

Vertical B o n e s walls

Spherical Box shape sections

Slides/ cores

Weldable

Y Y Y Y Y Y N Y N N N N Y N

Y Y Y Y Y Y N N N N N N N N

Y N Y Y Y Y N N/A Y Y N Y Y Y

N N N N N N N N Y Y N N Y Y

N N Y Y N N N Y Y Y Y N Y N

Y Y Y Y Y Y N N Y N N Y N N

Y Y Y Y Y Y Y Y Y Y Y Y Y Y

Y Y N N Y

Y Y Y Y Y

Y Y Y Y Y

N N N N N

N N N N N

Y Y N N

N N N N N

N N N

N Y Y

Y Y Y

N N N

N Y Y

N N N

N N N

Y Y Y N Y Y

Y Y Y N Y N

Y Y Y Y N Y

N N N N N N

N N N N Y Y

Y Y Y N N N

N N N N Y N

Y

N

Y

N

Y

N

N

Y Y Y Y

Y Y N N

Y Y Y N/A

Y N Y N

Y Y Y Y

N N N N

N N N N

Note: Y,yes; N, no; N/A, not applicable

Varying Good crossfinish, both sides section

9

9Selecting Plastic and Process 9 2 7

Table 9.68 Design recommendations for selecting an RP process Contact molding, spray-up

Pressure bag

Filament winding

Continuous pultrusion

1/8 N/R** Yes Yes No 0.010 (0.25) 3 (76.2) +0.010 (+0.25) As desired

N/A* N/A Yes N/A No 0.037 (0.94)

Minimum inside, radius, in. Molded-in holes Trimmed-in mold Built-in cores Undercuts Minimum practical thickness, in. (mm) Maximum practical thickness, in. (mm) Normal thickness variation, in. (mm) Maximum buildup of thickness Corrugated sections

1/4 Large No Yes Yes 0.060 (1.5) 0.50 (13) +0.020 (+0.51) As desired

1/2 Large No Yes Yes 0.060 (1.5) 1 (25.4) +0.020 (+0.51) As desired

Yes

Yes

Metal inserts Surfacing mat Limiting size factor

Yes Yes Mold size

Metal edge stiffeners Bosses Fins Molded-in labels Raised numbers Gel coat surface Shape limitations

Yes Yes Yes Yes Yes Yes None

Translucency Finished surfaces Strength orientation

Yes One Random

Random Typical glass percent by weight

Random 30-45

Note:*N/A Not applicable **N/R Not recommended

1

(25.4) +0.005 (+0.1) N/A

Matched die Premix/ molding with molding preform or compound mat 1/32 Yes Yes Yes Yes 0.060

(1.s) 1

(25.4) +0.002

(_+o.o5)

As desired

Circumferential only Yes Yes Yes Yes Bag size Lathe bed length and swing N/R Yes N/R No Yes No Yes Yes Yes No Yes Yes Flexibility Surfaceof of the bag revolution Yes Yes One One Orientation of ply

No Yes No Yes N/R Yes Yes No No Yes No No Constant Moldable cross-section Yes No Two Two Dependson wind

45-60

30-60

50-75

In longitudinal Yes direction No Yes Yes No Pull capacity Press capacity

25

1/8 Yes Yes Yes No 0.030 (0.76) 0.25 (6.4) +0.008 (+0.02) 2 to 1 maximum Yes Yes Yes Press dimensions Yes Yes N/R Yes Yes Yes Moldable Yes Two Directional 30

Table 9~G9

r

Basic overall processing methods as a function of part design

m i ,

Process

Part design

Blow molding

Casting

Compression Extrusion

Major shape characteristics

Hollow bodies

Simple configurations

Moldable in one plane

Limiting size factor Maximum thickness, in. (mm) Minimum inside radius, in. (mm) Minimum draft (deg.) Minimum thickness, in. (mm) Th reads Undercuts Inserts Built-in cores 3 Molded-in holes Bosses Fins or ribs Molded-in designs and nos. Surface finish 7 Overall dimensional tolerance (in./in., plus or minus)

Material >0.25 (6.4) 0.125 (3.18) 0 0.01 (0.25) Yes Yes Yes Yes Yes Yes Yes Yes

Material None

1-2 0.01

Filament winding

Injection

Matched die molding

Rotational

Thermoforming

Transfer compression

Wet lay-up (contact molding)

Simple configurations

Moldable in one plane

Equipment 6 (150) 0.01-0.125 (0.25-3.18) 1 0.01-0.125 (0.25-3.18) Yes NR2 Yes Yes Yes Yes Yes Yes

Mold size 0.5 (12.7) 0.25 (6.4) 0 0.06 (1.5) No Yes Yes Yes Yes Yes Yes Yes

1-2 0.001

4-5 0.02

Moldable in one plane

Hollow bodies

0.01-0.125 (0.25-3.18) 0-1 0.01-0.125 (0.25-3.18) Yes Yes1 Yes Yes Yes Yes Yes Yes

Structure with surfaces of revolution Equipment 3 (76) 0.125 (3.18) 2-3 0.015 (0.38) No NR2 Yes Yes Yes No No5 No

Few limitations

Equipment 0.5 (12.7) 0.125 (3.18) >1 0.01-0.125 (0.25-3.18) Yes NR2 Yes No Yes Yes Yes Yes

Constant cross section profile Material 6 (150) 0.01-0.125 (0.25-3.18) NR2 0.001 (0.02) No Yes Yes Yes Yes4 Yes Yes No

Equipment 6 (150) 0.01-0.125 (0.25-3.18) <1 0.005 (0.1) Yes Yes1 Yes Yes Yes Yes Yes Yes

Equipment 2 (51) 0.06 (1.5) 1 0.03 (0.8) No NR2 Yes Yes Yes Yes No 6 Yes

Material 0.5 (12.7) 0.01-0.125 (0.25-3.18) 1 0.02 (0.5) Yes Yes1 Yes Yes Yes Yes Yes Yes

Moldable in one plane Material 3 (76) 0.125 (3.18) 1 0.002 (0.05) No Yes1 N R2 Yes No Yes Yes Yes

2 0.001

1-2 0.001

1-2 0.005

5 0.005

1 0.001

4-5 0.005

2-3 0.01

1-3 0.01

1 Special mold required 2 Not recommended 3 Only flexible material 4 Only direction of extrusion 5 Possible with special techniques 6 Fusing premix/yes 7 Rated 1 to 5 (1 = very smooth, 5 = rough)

r

Ill in, ISI

"I" :3

O" 0 0~--

9

Selecting 9 Plastic and Process 9 2 9

Table 9 . 7 0 Basic processing (bag, flexible plunger, vacuum injection, matched die, and compression} methods as a function of part design

Design factor

Bag molding

Flexible plunger molding

Vacuum injection molding

Matched die molding

Comp. molding

Min. inside radius Molded-in holes Undercuts Min. draft

Large Yes 50

No SIig ht 10

No N/R 3~

Yes No 10

Yes N/R 10

+

_+

+

__+

+

Yes No N/R P Yes Yes Yes

N/R Yes N/R P No Yes Yes

Yes Yes N/R N/R P No N/R Yes

Yes P Yes Yes P

Yes Yes No Yes Yes Yes No Yes

Min. thickness Max. practical thickness Normal thickness variation, inches Corrugated sections Metal inserts Surfacing mat Metal edge stiffening Bosses Fins Molded-in labels Raised numbers or letters

P- Possible N/R - Not recommendedat presenttime

Yes Yes

930 Reinforced Plastics Handbook Table 9.71

Basic processing (resin transfer, spray, hand lay-up, mat/preform compression, and SMC: compression ) methods as a function of part design

Designparameter Minimum inside radius, in. (mm) Molded-in holes In-mold trimming Core pull and slides Undercuts Minimum recommended draft Minimum practical thickness, in. (mm) Maximum practical thickness, in. (mm) Normal thickness variation, in. (mm) Maximum thickness buildup, heavy buildup (ratio) Corrugated sections Metal inserts Bosses Ribs Hat section Raised numbers Finished surfaces

Resin transfer molding

Sprayup

Hand layup

Mat/preform SMC

1/4 (6.35)

1/4 (6.35)

1/4 (6.35)

1/4 (6.35)

No No Difficult Difficult 2-3 ~

Large No Difficult Difficult 0~

Large No Difficult Difficult 0~

0.080 (2.0) 0.500 (12.7) +0.010 (+0.25) 2:1

0.060 (1.5) No limit

0.060 (1.5) No limit

Yes Yes Yes Yes No Yes No Yes 1/4 in. to 6in. depth, 1-3 o 6in. depth, 30 or as required 0.030 0.0,50 (0.76) (1.3) 0.500 1 (12.7) (25.4)

+0.020 (+0.50) Any

+0.020 (+0.50) Any

+0.008

+0.005

(+0.2) 2:1

(+0.1) Any

Yes Yes Difficult Difficult Yes Yes 2

Yes Yes Yes No Yes Yes 1

Yes Yes Yes No Yes Yes 1

Yes Yes Difficult Yes Difficult Yes 2

Yes Yes Yes Yes No Yes 2

1/16 (1.59)

9 Table 9 . 7 2

Selecting 9 Plastic and Process 9 3 1

Basic processing (resin transfer, injection, pultrusion, and reaction injection) methods as a function of part design

Factor limiting maximum size of product Maximum size, m2 Shape limitations U.S. production volume, articles per year Production cycle time Glass, % Strength orientation Strength Wall thickness, mm Minimum Maximum Tolerance Variations Minimum draft to 15 cm depth over 15 cm depth Minimum inside radius Ribs Bosses Undercuts Holes Parallel Perpendicular Built-in cores Metal inserts Metal edge stiffeners Surface finish Number of finished surfaces Quality of surface Gel-coat surface Surfacing mat Combination with thermoplastic liner Trim in mold Molded-in labels Raised numbers Translucency Tool cost Capital equipment cost

Resin transfer molding

Injection molding Pultrusion

Reinforced reactioninjection molding

Machine size

Machine s i z e

Materials

9.3 Moldable 1,000-20,000

Metering equipment 9.3 29 4.6 Moldable Round, rectangular Moldable 50,000-1,000,000 3,050 m 15,000-100,000

10-20 min 15-25 Random Low-medium

15 s to 15 min 20-40 Random Low

10-30 min 30-75 Highly oriented High

1-2 min 5-25 With flow Low

0.76 25

0.76 13-25

Uniform

Uniform

1.6 13 0.3+25 Uniform

2.0 13 +0.05 Uniform

1o 1o 1/2 part depth Yes Yes Possible

1~ 1o+ 1/2 part dept Yes Yes Possible

0-20 0-20 1.5 m m No No No

1-3 ~ 3~ 1/2 part depth Yes Yes Yes

Yes Yes Yes Yes Yes

Yes Yes Yes Yes Yes

No No No No No

Yes Yes Yes Yes Yes

all

2

2

2

Excellent Yes Yes

Excellent Yes Yes Yes

Fair to good No No No

Excellent No No No

No Yes Yes Yes High High

No Yes Yes Yes High High

No No No No Low Low

Yes No Yes No Low-medium Low-medium

tad ;xl ,,.,.,.

s" Table 9,73 Economicand design factors for RPs

Molding process Hand lay-up Vacuum bag Pressure bag Spray-up Filament winding Pultrusion SMC Centrifugal Continuous laminate Resin injection Injection Shell coating Pre-mix (BMC) * 10 equals highest; 1 equals lowest

Equipment cost

Rate of production

Molded part strength

Importanceof operator's skill

Part complexity possible

Part reproducibility

1 2 3 4 6 7 10 9 10 3 10 9 9

3 2 1 4 6 9 8 7 10 2 10 4 8

3 4 6 3 10 9 7 8 5 3 6 3 7

10 10 6 10 2 2 4 3 2 7 2 5 4

9 9 7 8 4 2 9 3 1 7

1 3 4 1 9 10 10 6 10 8 10 9 10

10 7 8

Ill m~ Ill

-1-oo o

9 Table 9 , 7 4

Selecting 9 Plastic and Process 9 3 3

Guide to decorating selection PARTTO BE DECORATED

I

SURFACE PREPARATION

I

I

I

I

I I

SURFACE COATING

INTEGRALCOATING

I

COLOR CONCENTRATES

TUMBLING

SANDBLAST

PAINTING

WHEELABRATOR

PLASMA ETCH

DYE APPLICATION

IN RESIN

HAND FILING

SOLVENT ETCH

METALLIZATION

LIQUID ADDED AT

MACHINING

CHEMICAL ETCH

by VACUUMand

PRESSOR EXTRUDER

ELECTROPLATING

COLOR MIX IN

SILK SCREENTRANSFER

TUMBLE BARREL

HOT STAMPING

and EMBOSSING DECALS IN-MOLD DECORATION

Table 9,75 Example of decision factors to be considered based on decorating technique used Direct

Decision factors

screen printing

Pad printing

Hot stamping

Heet transfer

Image size and limitations

Any size

7 by 14 inches is usual; 10 by 20 opt.

Roll-on can apply 12 by 24 inches

Roll-on can apply 12 by 24 inches

Resolution of detail

Medium

Fine to medium

Medium

Fine

Arc limits

360 ~

1000 3600 special wrap

900 (reciprocal) 3600 special wrap

900 (reciprocal) 3600 special wrap

Opacity

Good

Poor; multiple prints fair

Good

Good for screen; fair for gravure

Wet or dry process

Wet

Wet

Dry

Dry

Operator learning

Hours to days

Hours to days

Minutes to hours

Minutes to hours

Operator skill level

Semiskilled

Semiskilled

Unskilled

Unskilled

Part changeover

Minutes to hours

Minutes to hours

Secondsto minutes

Seconds to minutes

Cost of inks, foils, transfers

Inks - not costsensitive to size or color

Inks - not costsensitive to size or color

Foils - costsensitive to size; linear increase for addl. colors

Transfers - costsensitive to size; not as sensitive to addl. colors

CU rye

Table 9 , 7 6

l,o w 4~

Guide to printing and decorating systems

The Process

How it Works

Equipment

Applications

Effect

Painting, conventional spray

Paint's sprayed by air or airless gun(s) for functional or decorative coatings. Especially good for large areas, uneven surfaces, or relief designs Masking used to achieve special effects. Charged particles are sprayed on electronically conductive parts; process gives high paint utilization; more expensive than conventional spray. Paint is applied conventionally, then paint is wiped off. Paint is either totally removed, remaining only in recessed areas, or is partially removed for special effects such as woodgraining. Raised surfaces can be painted without masking. Special effects like stripes

Spray guns, spray booths, mask washers often required; conveying and drying apparatus needed for high production.

Can be used on all materials (some require surface treatment).

Solids, multicolor, overall or partial decoration, special effects such as woodgraining possible.

Electrostatic spray

Wiping

Roller coating

Screen printing

Ink is applied to part through a finely woven screen. Screen is masked in areas that will not be painted. Economical means for decorating flat or curved surfaces, especially in relatively short runs.

a" r

m,

Spray gun, high-voltage power supply; pumps; dryers. Pre-treating station for parts (coated or preheated to make conductive). Standard spray-paint setup with a wipe station following. For low production, wipe can be manual. Very high-speed, automated equipment available.

All plastics can be decorated. Some work, not much, being done on powder coating of plastics.

Generally for one-color, overall coating.

Can be used for most materials. Products range from medical containers to furniture

One color per pass; multicolors achieved in multistation units

Roller applicator, either manual or automatic. Special paint feed system required for automatic work. Dryers

Can be used for most materials

Generally one-color painting, though multicolor possible with side-by-side rollers

Screens, fixture, squeegee, conveyorized press setup (for any kind of volume). Dryers. Manual screen printing possible, for very low-volume items

Most materials. Widely used for bottles; also finds big applications in areas such as TV and computer dials

Single or multiple colors (one station per color)

ill

-r

:3 O"

o o

The Process

How it Works

Equipment

Applications

Effect

Hot stamping

Involves transferring coating from a flexible foil to the part by pressure and heat. Impression is made by metal or silicone die. Process is dry.

Rotary or reciprocating hotstamp press; dies. High-speed equipment handles up to 6,000 parts/h.

Heat transfers

Similar to hot stamp but preprinted coating (with a release paper backing) is applied to part by heat and pressure.

Ranges from relatively simple to highly automated with multiple stations for, say, front and back decoration.

Metallics, wood grains or multicolor, depending on foil. Foil can be specially formulated (for example, chemical resistance) Multicolor or single color; metallics (not as good as hot stamp).

Electroplating

Gives a functional metallic finish (matte or shiny) via electrodeposition process.

Metallizing vacuum

Depositing, in a vacuum, a thin layer of vaporized metal (generally aluminum] on a surface prepared by a base coat.

Preplate etch and rinse tanks; Koroseal-lined tanks for plating steps; preplating and plating chemicals; automated systems available. Metallizer, base, and topcoating equipment (spray, dip, or flow], metallizing racks.

Most thermoplastics can be printed; some thermosets. Handles flat, concave, or convex surfaces, including round or tubular shapes Can handle most thermoplastics. A big application area is bottles. Handles flat, concave, or cylindrical surfaces Can handle special plating grades of ABS, PP, polysulfone, filled Noryl, filled polyesters, some nylons.

Cathode sputtering

Uniform metallic coatings by using electrodes

Discharge systems, to provide close control of metal buildup

Deposition of a metallic finish by chemical reaction of water-based solutions.

Activator, water-clean and applicator guns; spray booths, top- and base-coating equipment if required

Spray

Most plastics, especially PS, acrylic, phenolics, PC, unplasticized PVC. Decorative finishes (for example, on toys], or functional (for example, as a conductive coating]. High-temperature materials. Uniform, precise coatings for applications such as microminiature circuits. Most plastics. For decorative items

Very durable metallic finishes.

Metallic finish, generally silver but can be others (for example, gold, copper]

Metallic finish. Silver and copper generally used. Also gold, platinum, palladium.

(.o

Ill m,

Metallic (silver and bronze) o

continued

c.D w

w

Table 9 . 7 6

Continued

The Process

How it Works

Equipment

Applications

Effect

Tamp printing

Special process using a soft transfer pad to pick up image from etched plate and tamp it onto a part.

All plastics. Specially recommended for oddshaped or delicate parts (for example, drinking cups, dolls' eyes}.

Single- or multicolor, one printing station per color.

Most plastics, especially polyolefins and melamines. For parts in which decoration must withstand extremely high wear. Most plastics. Used on such areas as coding pipe and extruded profiles. Most plastics. Used in applications such as coding pipe.

Single- or multicolor decoration.

In-the-mold decorating

Film or foil inserted in mold is transferred to molten plastics as it enters the mold. Decoration becomes integral part of product.

Metal plate, squeegee to remove excess ink, conical-shaped transfer pad, indexing device to move parts into printing area, dryers, depending on type of operation. Automatic or manual feed system for the transfers. Static charge may be required to hold foil in mold.

Flexography

Printing of a surface directly from a rubber or other synthetic plate.

Manual, semiautomatic, or automatic press; dryers.

Offset printing

Roll-transfer method of decorating. In most cases, less expensive than other multicolor printing methods.

Valley printing

Uses embossing rollers to print in depressed area of a product.

Labeling

From simple paper labels to multicolor decals and new preprinted plastic sleeve labels.

Ranges from low-cost hand presses to very expensive automated units. Drying, destaticizers, feeding devices. Embosser with inking attachment or special package system. Equipment runs the gamut from hand dispensers to relatively high-speed machines

Used largely with PVC, PE for such areas as floor tiles, upholstery. Can be used on all plastics. Used mostly for containers and price marking.

s" e~ .,..,. Ill n,.

-r

Single- or multicolor. Multicolor print or decoration Generally two-color maximum All sorts of colors and types.

0" 0 0

Table 9 . 7 7 Guide to in-mold decorating systems

Engraved mold

Inmold label

Inserted nameplates

Two-shot molding

Applique

Electrostatic

Economics

Aesthetics

In Mold Decorating Product Design Chemistry

Manufacturing

Comments

Unit cost low

Limited

Unrestricted

No extra operations

Best for simple lettering and texture

Labor cost: low Investment moderate Unit cost high Labor cost: high Investment none to moderate Unit cost: high Labor cost high Investment: moderate Unit cost: high Labor cost high Investment: moderate to high Unit cost: high Labor cost: high Investment: moderate to high Unit cost: low to moderate Labor cost: low Investment: moderate to high

Not critical Good durability

Unlimited

Somewhat restricted

Critical

Good durability Partially limited

Restricted

Not critical Good durability

Limited

Somewhat restricted

Not critical

Longer molding cycles Good for thermoplastics and thermosets. Automatic loading equipment becoming available Longer molding cycles Allows three-dimensional as well as special effects Two molding operations

Good durability Somewhat limited

Unrestricted

Not critical

Good when maximum abrasion resistance is necessary

~3 r-h

Hand operation

Allows unusual effects

Good durability Limited

Somewhat restricted

Critical Moderate to good durability

~D

t~

-o

~3

Dry process, no tool contact with product

Q. o r3

continued

Ltl

r,D f~

Table 9 . 7 7 Continued m

Flexographic

Hand painting Heat transfer

Hot stamping

Labeling

Metallizing

Economics

Aesthetics

In Mold Decorating Product Design Chemistry

Manufacturing

Comments

Unit cost: low Labor cost: low Investment: moderate to high Unit cots: high Labor cost: high Investment: low Unit cost: low to moderate Labor cost: low to moderate Investment: low to moderate Unit cost: low Labor cost: low to moderate Investment: low to moderate Unit cost; low to moderate Labor cost: low to moderate Investment: low to high

Somewhat limited

Restricted

Automates well

Wet process, tool contacts product. Sometimes requires top coat

Unit cost: moderate to high Labor cost: moderate to high Investment: High

Critical

s~

Moderate durability Somewhat limited Unlimited

Unrestricted

Critical

Somewhat restricted

Good durability Critical

Hand operation Requires little floor space

Good durability Limited

Somewhat restricted

Critical

Limited

Somewhat restricted Lesscritical

Somewhat restricted

Moderate to good durability Critical

Good durability

Wet process, tool contacts product Dry process, tool contacts product Multicolor graphics

Requires little floor space

Good durability Unlimited

,

Dry process, tool contacts product Produces bright metallics

Adaptable to many situations

Dry process, no tool contact with product at times Multicolor graphics

Requires special technological know-how

Wet and dry process, no tool contact with product Produces bright metallics

e,~

Ill Ill

"1o"

o o

Nameplates

Offset

Offset intaglio

Silk screening Spray

Woodgraining

Economics

Aesthetics

In Mold Decorating Product Design Chemistry

Unit cost: high Labor cost: moderate to high Investment: low to moderate Unit cost: low Labor cost; moderate Investment: high

Unlimited

Somewhat restricted

Unit cost low Labor costs moderate Investment moderate

Limited

Unit cost: moderate Labor cost: moderate Investment: moderate Unit cost: moderate Labor cost: moderate Investment: moderate to high Unit cost: high Labor cost: high Investment: moderate to

Lesscritical

Manufacturing

Comments

Adaptable to many situations

Dry process, tool contacts product

Good durability Restricted

Critical

Unrestricted

Moderate to good durability Critical

Somewhat limited

Somewhat restricted

Moderate to good durability Critical

Limited

Unrestricted

Good durability Critical

Unlimited

Good durability Specialized high

Specialized

Critical

Multicolor graphics Automates well

Wet process, tool contacts product Multicolor graphics

Requires little floor space

Wet process, tool contacts product New process

Flexible operation

Wet process, tool contacts product

Requires much floor space

Wet process, no tool contact with product

Mostly hand-operated

Wet process, tool contacts products

Good durability

~D

.,i,

:3

r~ Q. ,i I

o ISI

W

940 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 941

942 Reinforced Plastics Handbook

9. Selecting Plastic and Process 943

944 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 4 5

946 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 4 7

948 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 4 9

950 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 951

952 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 5 3

954 Reinforced Plastics Handbook

9

Notes: Hardness = Barcol 50

Selecting 9 Plastic and Process 9 5 5

956 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 5 7

958 Reinforced Plastics Handbook

9

Notes: Recommended molding conditions are: temperature: 140-160~

Selecting 9 Plastic and Process 9 5 9

molding pressure: 80 bars; curing time" 14-22 s/m m.

960 Reinforced Plastics Handbook

Notes: Thick molding compound (TMC) hardness = >Barcol 50.

9. Selecting Plastic and Process 961

962 Reinforced Plastics Handbook

Notes: Hardness = Barcol 68.

9

Selecting 9 Plastic and Process 9 6 3

Notes: Low profile SMCs can give LORIAwaviness index reading of about 50:1.5-2.0 long waviness by Daimler BenzlBASF method IX = 10-100 mm).

9 6 4 Reinforced Plastics Handbook

Notes: Recommended molding conditions are: temperature: 140-160os molding pressure: 80 bars; curing time: 18-28 slm. m.

9

Notes: Recommended molding conditions are" Molding temperature: 140-160~

Curing time: 19-40 sec/m, m.

Selecting 9 Plastic and Process 9 6 5

Molding pressure: 80 bars;

966 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 6 7

Notes: Data is based on novolac and bisphenoI-A resins Poisson's Ratio is stated as 0.33 for all grades Heat distortion temperature of unreinforced resins is 130-155~ (266-311~

968 Reinforced Plastics Handbook

9 Table 9 . 7 9 Detailed data on thermoplastic RPs

Selecting 9 Plastic and Process 9 6 9

970 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 7 1

Notes: Where two sets of figures are given, they indicate: Dry as Molded (DAM)/50Olo RH x 23oC.

972 Reinforced Plastics Handbook

Notes: Where two sets of figures are given, they indicate: Dry as Molded (DAM)/50% RH x 23~

9

Selecting 9 Plastic and Process 9 7 3

Notes: Where two sets of figures are given, they indicate: Dry as Molded (DAM)I50OloRH x 23oC*(3harpy notched impact

strength.

974 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 7 5

976 Reinforced Plastics Handbook

9 . Selecting Plastic and Process 977

*% water absorption at saturation

978 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 7 9

D. oo o

-r

ttl

"o m. 9.1 r-4.... r~

rJ ~D

,~[

~D

co o

9

Selecting 9 Plastic and Process 981

982 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 8 3

984 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 8 5

986 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 8 7

988 Reinforced Plastics Handbook

9. Selecting Plastic and Process 989

990 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 991

Notes: Melt temperature: 180-220~ (endless mat)" 190-220~ (other types). Mold temperature: 20-70~ (endless mat);

40-90~ (other types). Molding pressure: 50-150 bar (endless mat), 50-200 bar (20o/oneedled mat), 100-200 {30% needled mat).

992 Reinforced Plastics Handbook

Notes: Melt temperature: 190-220o(3. Mold temperature: 40-90~

Molding pressure: 100-300 bar.

9

Selecting 9 Plastic and Process 9 9 3

994 Reinforced Plastics Handbook

9

Selecting 9 Plastic and Process 9 9 5

996 Reinforced Plastics Handbook

Notes: All values measured at 3.18 mm thickness.

"l (]-

Summary

Overview From the initial development of all types of plastics and particularly since the last half of the 20th century one can say it was extremely spectacular based on its growth rate but more important on how they have helped people and industries worldwide. The plastic industry (includes RPs consuming about 20 wt%) is a worldwide multi-billion dollar business (Figures 10.1 and 10.2). Exciting discoveries and inventions continue to give the world of plastic products vitality. In a society that never stands still, plastics are vital components in its increased mobility. 1,000,000

' ""

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10

~ PEClALT ~$TOM ,~Er~

1960 1970 1980

COM = ~ S r r E s

'

1990 2000 2010 2020

YEAR

Figure 10~

Estimated plastic consumption through year 2020 includes reinforced plastics

I

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PLASTIC INDUSTRY GUIDE ............................

....

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

SERVICES .

.

.

.

.

.

.

.

.

m,

.

.

.

.

.

.

.

Consultants - D e s i g n e r s - Process Engineering - ISO - Education- Legal - Accounting - Financial - Marketing - Advertising

RESIN SUPPLIERS Acetal - Acryllcs ABS - Alkyds Cellulosics Diallyl Phthalates Epoxies Fluoropolymers Melamine Nitrile Resins Nylon Phenolics Polyamide - Imide Polycarbonate Polyester Polyethylene Polyimides Polypropylene Polystyrene Polyurethanes PVC Silicones Urea

Extruders Injection Molding Machines Blow Molding Compresion Presses Transter Presses Thermoforming Machines Molds Dies Auxiliary Equipment Liquid Depensing Systems Impregnators Plotters Test & Measurements Components Process Control Equipment

DISTRIBUTORS

L--I~

COMPOUNDERS

.

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t

P u b l i s h i n g - Training

i

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I OTHER PLANT & EQUIPMENT

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DECORATING

ASSEMBLY

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PROCESSORS ' -

~Custom :I C.a_p,tive: i: t

ADDITIVES Accelerators Antioxidants Antistats Blowing agents Colorants Fillers Flame Retartants Ir~hibitors Lubricants Plasticizers Stabilizers

1

MACHINERY SUPPLIERS

a~

- Injection M o l d i n g Extrusion B l o w Molding Blown / Cast Film Coaters Rotational M o l d i n g Pultrusion Thermoforming Calendering Compression Molding Reaction Molding , Transfer M o l d i n g

I.

Figure 10.2 Overview of the worldwide plastics industry (courtesy of Adaptive Instruments Corp.)

JI

&

EXAMPLES OF PRODUCTS

l

1 o..nm n, i

Appliances Transportation - Auto Packaging Building and Construction Computers - Electronics - Electrical Telecommunication Medical- Health Care Adhesive - Coatings Furniture Industrial Machinery Fast Foods Consumer & Institutional Products Recreation / Toys Rope & Cordage Textile - Synthetic Fibers

Ill ,,,,,,i f3 I/t

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10

10,000

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I

1,000

-

-

-

I

I "1

-

9S u m m a r y

I ---r

. . . . I I

1960

1970

1980

1990

YEAR

Figure 10.:3 Volume of

plastic and steel worldwide crossed about year 1983 (courtesy of Plastics

FALLO)

Plastics have surpassed steel on a volume basis about 1983 (Figure 10.3) and by the start of this century plastics surpassed steel on a weight basis (Figure 10.4). Plastics and a few other materials as shown in Figure 10.4 represent about 10 wt% of all materials consumed worldwide. The two major and important materials consumed are wood and construction or nonmetallic earthen (stone, clay, concrete, glass, etc.). Volume wise wood and construction materials each approach about 70 billion ft 3 (2 billion m3). Each represents about 45% of the total consumption of all materials. The remaining 10% include other materials with plastics being the largest. Plastic materials and products cover the entire 1 xl06 I I

i

I I

i

s~!

I I

I

I

I I

200 x 103

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10 x 10 s I 1 x 103 1930

1940

1950

1960

1970

I

1940

1990

2000

Year

Figure 10,4 Weight FALLO)

of plastic and steel worldwide crossed about year 2000 (courtesy of Plastics

999

1000 Reinforced Plastics Handbook

spectrum of the world's economy, so that their fortunes are not tied to any particular business segment. Designers are in a good position to benefit in a wide variety of markets: building and construction, electronics and electrical, furniture, apparel, appliances, agriculture, housewares, luggage, transportation, medicine and health care, recreation, and so on. A continuous flow of new materials (Figure 10.5), new processing technologies, and product design approaches has led the industry into profitable applications unknown or not possible in the past. What is ahead will be even more spectacular based on the continuous new development programs in materials, processes, and design approaches that are always on the horizon to meet the continuing new worldwide industry product challenges. New re.~,forcement)

10'

/ 55%

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A,'etai " ' ' y 30% glass-re,nforced

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~~, _Nylon

i0.1 1900 1920 Yi~ar

1940 1960 1980 2000

Figure 10.5 Examplesof plastic property developments

For over a decade what has been happening in USA, as has occurred worldwide, is consolidations within the plastics industry (includes RP) particularly materials and equipment. S. M. Bernard and J. E. Hoffman of the Robert Baird & Co., Chicago, USA, reports a major consolidation that will ultimately result in an industry with fewer competitors that are significantly larger, have greater capabilities, and are more global in focus. Plastics mergers and acquisitions (M&A) have been relatively active. During year 2002 there were 198 completed mergers and acquisitions in USA. The current wave of consolidation is being driven by a number of key industry trends that will continue to shape the competitive landscape. Included is increasing importance of size, scale, and low-cost positioning; globalization; pursuit of more attractive product categories, end

10

9S u m m a r y

markets, customer bases and product/process capabilities; challenging competitive, capacity, pricing, and input cost conditions; increasing foreign competition; increasing importance of low-cost/foreign manufacturing capabilities; technological change; and increased customer demand for comprehensive services and solutions. Since 1993, there have been a total of 6,149 global plastics M&A transactions announced with 2,455 having disclosed values aggregating $282.4 billion. In the USA there have been a total of 1,849 transactions announced with 765 having disclosed values aggregating $103.1 billion. In the future plastics will continue to contribute significantly worldwide towards a sustainable economy. They will continue to provide a vital role in people's daily lives. As the world's population increases plastics, as usual, will meet new developing challenges by providing solutions without compromising the needs of future generations. With all this action, global consumption of plastics, with its continuing new developments in plastic materials and processing, will continue to rise. Accompanying this action will be the continued advancement of technology in the "art" of producing plastic products. Plastics (URPs and RPs) are one of the most important business sectors providing significant contributions to the economy and standard of living across all sectors worldwide. Technically Figure 10.6 highlights how just one factor of RPs, namely modulus of elasticity tends to have constant weight as the modulus increase.

i........... ] . . . . . . . . . ~'

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8

10

Figure 10.6 Modulus of different materials can be related to their specific gravities with RPs providing an interesting behavior

1001

1002 Reinforced Plastics Handbook Global Business Fortunes

The following is an abstract from professor of management Karl Moore, McGill University, Montreal, Canada article in B P global publication, December 2003, that is applicable in the plastic ad other industries. It reviews that present day fortunes favors global business as it did in ancient times. Spanning every corner of the known world, Roman businesses had more in common with today's multinationals than one might imagine, reports Karl Moore. The Roman Empire had the first known world economy stretching west to China to east about 2,000 years ago. Real business firms operated in that environment. Roman managers did business in brick making, pottery, and shipbuilding across cultures from Italy to Gaul, Germany, the Near East, and even India. They faced the challenges of multiculmral workforces, often investmentand profit-threatening external environments filled with pirates and other dangers, as well as formidable competitors like the merchant princes of Carthage. Today's global firms sound familiar and resemble these pioneer companies of Roman citizens like Publius Sestius, Terentius Hispo and the Domitii family, but they have evolved far beyond them in many ways. Their challenges were far smaller and simpler than those now facing multinationals. The single greatest theoretical advantage of being a global firm is the increased learning resulting from activities spread around the globe. Innovation is one of the key drivers of the new economy. This is an area where leading firms are looking for competitive advantage and are experimenting to learn how to deliver on this promise. Firms that operate in only one or two markets have limited learning opportunities. Most ancient firms were in that category. Successful global firms today learn from multiple, diverse environments, and use that learning to beat their non-global competitors. Learning from global environment is appealing, but few companies live up to it. As late as the 1980s many multinationals were ethnocentric (one group/one race as being superior). Some still are today, insisting employees had to be citizens of the firm's home country. Today, this is frowned upon as failing to take advantage of clever, talented employees worldwide. By this action, the company is the loser. There are multinationals that have more employees outside their home country than within. One thinks of Finland's Nokia, Canada's Nortel, or USA's Ingersoll-Rand. When a firm adopts a global strategy it must, almost by definition, centralize some of its activities, traditionally in the home country of the firm. However, increasingly, some insightful firms question why the home country. Some leading firms are turning to

10

Summary 9 1003

dispersed centralization. Companies have very good reasons to shape global strategy in their home markets. They are often among the most demanding markets in the world, with an ample supply of educated, experienced people to draw upon. However, consider locating the global head office for some product lines and business sectors in the country of an important subsidiary. There are two critical advantages of this approach. First, it provides exciting career opportunities for employees from those countries without having to relocate. Secondly, it allows the firm to tap into global learning from diverse locations. There exist very real tensions between realizing global economies of scale and yet keeping the entrepreneurial, close to the market attitude. Target is to accomplish cost savings. This calls for a centralized, one-firm approach. Meanwhile the multinational has to be free enough to response to market shifts. Required is decision making to be made close to the action and important is for junior people be involved early in their career. This is a tough thing to get fight and most firms swing back and forth on it over time. New Reinforcement Technology

An example of many new developments occurring worldwide is a novel approach to increase strength of reinforcements. Involved via a Japanese development is encapsulating glass fiber during the manufacture/ polymerization of a polymer. The polymerization reactor produces RPs. Development started with a reinforcing concentrate of 80 wt% milled glass fiber in a styrene/acrylonitrile (SAN) carrier. The concentrate is introduced directly into the polymerization reactor that manufactures the polymer (Chapter 3). The polymer matrix is thus literally polymerized around the fibers, as opposed to incorporation at a later compounding stage. Fiber integrity and matrix/fiber adhesion are both higher. Another gain is that the potential health hazards of handling loose glass fibers are also alleviated. According to reports, in an ABS polymer, the reinforcement produces 35% higher flexural strength, 47% higher tensile strength, and 50% higher notched Izod impact strength than RPs produced by conventional fabricating methods. Leading Japanese car manufacturers are said to be using instrument panel substrates containing the concentrate, and it has also been used in USA-made cars, where the SAN concentrate was let down in styrene maleic anhydride (SMA) resin to a 20% glass level. It is reported that the concentrate can be used in production of ABS and other engineering resins such as polyamides, polycarbonates, and polyesters.

1004 Reinforced Plastics Handbook Plastic Raw Materials

Raw materials are the precursor of a processed (virgin) plastic that combines with additives, fillers, a n d / o r reinforcements to become a plastic matrix in RPs. The source is principally petroleum. Others include natural gas, coal, and agriculture products. Agricultural products are used; they are continually studied and targeted to develop a major raw material source and one of the latest concerns corn. Cornfields that dot the countryside may some day not only provide food, but also be a huge supplier of fuel. That is because researchers are developing a biorefinery that uses corn or other renewable resources rather than traditional petrochemicals to produce fuels and chemicals. A $7.7 million cooperative R&D agreement between the U.S. Department of Energy's National Renewable Energy laboratory (NREL) and DuPont calls for the two to develop, build, and test a biorefinery pilot process that will make fuels and chemicals from the entire corn plant including the fibrous material in the stalks, husks, and leaves, and the starchy material in the kernels. The agreement is part of the larger $38 million DuPont-led consortium known as the Integrated Corn based Bio products Refinery (ICBR) project. ICBR, includes DuPont, NREL, Diversa Michigan State, and Deere & Co. picked up $19 million in matching funds from the Department of Energy year 2003 to design and demonstrate the feasibility and practicality of alternative energy and renewable resource technology. The initiative will develop the world's first biorefinery, capable of producing a range of products' from plant-material feedstock. Several biorefineries currently produce a range of products mainly from starchrich or protein-rich biomass, while other biorefineries start with a variety of vegetable oils. The scarcity of nonrenewable resources amplifies the need to develop sustainable science-based solutions. Operating like a conventional refinery, the ICBR will make use of the entire corn plant. Purified sugars from the corn kernel will be the primary source of value-added chemicals, while researchers will convert the remainder of the corn plant, commonly called "the stover," into fuel-grade ethanol and electrical power. One of those value-added chemicals could be 1,3 propanediol (PDO), the key building block for DuPont Sorona, the company's newest polymer platform, used in applications such as plastic, textile apparel, carpeting, and packaging.

10

Summary 9 1005

Molding RPs with Profits What has made RPs profitable has been reviewed throughout this book. The following is just a summation on their behaviors that continues to make them profitable. The RP industry is comprised of mature technology. Improved understanding and control of processes have increased fiber/resin mechanical properties and reduced variability. Fiber strength has risen to the degree that out-of-plane reinforcement (3-D) can be employed -without jeopardizing in-plane strengths, producing very high strength and stiff RP products with long service life. Thermoplastic RPs (RTPs), with their relatively lower performance properties, represents the major material used when compared to thermoset RPs (RTS). More RTPs fabricated products are produced than RTSs. Over 50 wt% of all RPs processed are RTPs that are injection molded using highly automated systems operating at very fast molding cycles. The combination of most fibers and resin matrices produce materials that are quite tough, indeed much tougher than either alone. This synergism is achieved by a combination of mechanisms that tend to keep cracks small, isolated, and blunted, which dissipates energy. These mechanisms, based in part on the heterogeneity of RP, constitute another difference from structural metals. Toughness in advanced RPs is achieved without the large-scale "plastic" flow seen in tough metals. RPs can be characterized in many different ways, such as those with high impact and fatigue properties. As impact types, characterization can only provide (as with other materials) a qualitative guide to materials selection. Testing for tensile stress-strain and strength properties over a range of high test rates with areas under the S-S (stressstrain) curves, are potential methods for estimating potential relative toughness. Fatigue characterization can be presented in several forms. An example compares fatigue strength for notched and unnotched conditions, at various ratios of maximum to minimum stress, which is useful in structural design. Depending on specific construction and orientation of stress relative t o reinforcement, it may not be necessary to provide extensive data on time-dependent stiffness properties since time-dependent effects may be small and can frequently be considered by a rule of thumb or a "practical" design approach. Behavior under off-axes must always be considered, however. Time-dependent strength properties must always be considered as well. Many RP products have had super life spans of many decades. Included have been products that have been subjected to different dynamic loads in many different environments at very low temperature in very corrosive environments to high temperatures.

0 0 0")

Table 10ol

Examples of the more conventional reinforced plastics

I'D m

,

Glass fiber and quartz composites

Property Physical Specific gravity Density, Ib/cu. in. Rockwell hardness (M) Barcol hardness Water absorption - 24 hr, % Mechanical at room temp. at 0 ~to warp Tensile strength, KSI ult MPa ult Tensile modulus, MSI GPa Flexural strength, KSI ult MPa ult Compressive strength, KSI ult MPault Shear strength Interlaminar, KSI (Short beam), MPa Bearing strength, KSI M Pa 13od impact str, ft-lb/in, o/notch J/cm Poisson's ratio

BMC mat/ polyester 15-25% glass

SMC mat/ polyester 30-40% glass

Glass fabric polyester

Glass fabric epoxy

Filament wound epoxy

Nonwoven epoxy unidirectional

I'D

Nonwoven epoxy xplied

Glass fabric polyimide

Glass fabric menolil

Glass fabric silicone

Quartz fabric epoxy

S-Glass unidirectional epoxy

e~

"0 Ill m, Ill

"l" 1.65-1.78 0.055 95 45-50 1.8

1.7 0.062 100-110 50-60 1.7

1.7-1.8 0.062 110 6O 0.6

1.8-1.9 0.O65 105-120 55-60 0.20-0.30

1.9-2.2 0.O7-0.08 115-120 6O 0.4-1.0

10.0 69 1.6 11 15 103 20 138

20-25 138-172 1.7-1.9 12-13 20-25 138-172 25-28 172-193

44 3O3 2.4-3.O 17-21 31 214 40 276

55-75 379-517 3.4-3.8 23-26 75-95 517-654 50-60 345-413

15O-20O

2.0 13.8 25 172 8-12 4.3-6.4 O.11

2.5-4.0 17.2-27.6 30-36 207-248 12-16 6.4-8.5 O.11

3.5 24.0 33-43 227-296 14-18 7.5-9.6 0.11-0.12

4.0 27.6 38-46 262-317 30 16 0.12-0.16

0.07 -0.08 110-120 6O 0.3 -0.5

1.9-2.1 O.07-0.08 110-120 6O 0.3-0.5

2.05 0.08 110-120 75

4.5-7.5 31-52 90-200 620-1380 45-80 310-551

160 1112 5.3 37 165 1147 90 626

75 521 3.5 24 120 834 75 521

27 186 60 32 0.1-0.3

3.8 26.4 30-40 207-276 60 32 0.1-0.3

3.0 20.9

1030-1380

1.9-2.1

0.065 100 60-74 0.5

1.7-1.9 0.065 IO0 60-7O 0.08-0.12

1.73-1.80 0.062

50-82 345-565 2.8-4.2 20-29 75-100 517-695 58-80 475-550

50-60 345-413 2.5-3.5 17-24 60-70 413-482 40-45 276-310

30-40 2O7-276 2.7 19 33 227 29 200

79 545 2.8-3.1 19-22 99 68O 66.4 458

3.8 26.4

2.5 17.2 50 345 8-15 4.3 -8.0

0.8 5.5 34 234

1.73

1.92

0.069

7O

215 1480 7.1 49 220 1520 95 660 9.0-11 63-76

e'~ 0" 0 0

10

Summary 9 1007

Elastic constants and strength properties needed for the characterization of directional behavior can be used. The number of constants needed depends primarily on the complexity of the construction, that is, whether it is isotropic, planar isotropic, or orthotropic. With these stiffness constants known, the directional stiffness properties can be calculated using textbook equations. Perhaps the most controversial aspect of fiber reinforced plastics (FRPs) is that of their exact strengths. Much has been said about FRP being "stronger than steel". There are many types of steels; there are many combinations of RPs. Broad-sweeping comparisons cannot be truly accurate; they are merely approximations. Some forms of RP are stronger than some forms of steel, but other forms are not. However, these "other" RPs can easily compete with the properties of the weaker steels that are extensively used. The stronger and stiffer fibers available provide exceptional "advanced" high performance RPs. Tables 10.1 and 10.2 provide examples of properties with different resin matrices, different fibers, and different fiber formations (fabrics, mats, unidirectional); more details on different properties are given throughout this book. There are structural materials, including the high performance steels and aluminums, which have yield strengths, lower than their ultimate strengths. This does not usually hold true with many RPs (depending on fiber pattern formation and directional orientation). The yield and ultimate strength can almost be identical, so that in these cases they are usually considered one and the same; however, there is a small separation. While metals are designed to the yield (or below), RPs are not designed to the yield or ultimate strength. Metals have a safety factor by only going to yield without having failures. However, with RPs, a safety factor has to be included to eliminate failure. In terms of yielding, as reviewed in this book, RPs behaves like wood materials. In fact, when designing with glass fiber/TS polyester RPs during the 1940s to produce different products (including an all-RP airplane), the approach used was based on knowledge gained by the past wood designers (D. V. Rosato used this approach). The fibrous structures of wood, with their different directional lay-ups and their design approach and equations, were applicable to RPs. The wood industry had been using a fibrous material design approach for a long time with many high-performance structures that have endured for long times. Those equations were included in the preparation of the start of the first design manuals on RPs.

0 0

Table 10.2 Examples of the more advanced reinforced plastics m ,

Advanced or high performance composites

Property

Boron/epoxy unidirectional

Graphite/epoxy int. modulus

Graphite/epoxy high modulus

Graphite/ polyimide int. modulus

Graphite~epoxy woven

Aramid/epoxy non- woven

Aramid/epoxy woven

Physical Specific gravity Density, Ib/cu. in.

KSI MPa Tensile modulus, MSI GPa Flexural strength, KSI MPa Compressive strength, KSI MPa Shear strength Interlaminar, (short beam), KSI MPa Bearing strength, KSI MPa 13od impact str, ft-lb/in, o/notch Jlcm Poisson's ratio

,,,m,

"1"

2.01 0.073

1.60 0.056

1.56 0.058

1.60 0.056

1.59 0.06

1.35 0.05

1.33 0.049

:3

O" 0 0

Mechanical at room temp. at 0 ~ to warp-parallel plied Tensile strength,

Ill

200 1380 30 207 260 1790 353 2430 13 90

0.21

220-250 1520-1720 20-30 138-207 240-270 1650-1860 213-230 1470-1580

113-208 783-1435 30-47 207-324 90-230 620-1600 90-102 620-703

8-16 55-110

3.5-8 24-55

28 15 0.045

0.199

160-200 1100-1380 17 117 220-230 1520-1580 100 690 16 110

85-90 586-620 10.2 70.3 122-150 841-1034 34-4O 235-276

183 1260 11.2-11.9 77-82 90 625 12 83

8-9 55-62 100-143 689-988

4.2-7.1 28-49

0.077

48 26 0.31

75 517 4.5 31 50 345

8

55

Advanced or high performance composites

Property

Boron/epoxy unidirectional

Graphite/epoxy int. modulus

0.17-0.21 0.02-0.03 2.3 4.14

6-10 0.86-1.44

Graphite/epoxy high modulus

Graphite/ polyimide int. modulus

Graphite/epoxy woven

Aramid/epoxy non-woven

Aramid/epoxy woven

Thermal Thermal conductivity, Btu in.lhrlsq ftl~ W/m/~ Thermal expansion, in/in/~ x 10-6 m/ml~ x 10-6

3.22 0.46 - 0.2-0.3 - 0.36-0.54

28-35 4.03-5.04

1.49 0.21 0 0

Heat distortion, 264 psi ~ oC Maximum oper. Temp, ~ ~

350 177

350 177

Specific heat, Btu/Ib/~

350 177

700 371

350 177

350 177

86 @ F 593@ 177~ 82 @ 350~ 566@ 177~ 10.3 @ 350~ 71.0 @ 177~

55 @ 350~ 382 @ 177~

350 177

0.I 7

Mechanical at elev. Temp Tensile strength @ temp KSI MPa

168 @ 375~ 1170 @ 191~

220 @ 350~ 1380@ 191~

Flexural strength at temp KSI MPa Tensile modulus at temp MSI GPa

220 @ 1520 @ 26 @ 179 @

190 @ 350~ 1310@ 191~ 16 @ 350~ 110 @ 191~

375~ 191~ 375~ 191~

115 @ 350~ 793 @ 177~

30 @ 350~ 207 @ 177~

150@ 350~ 1030@ 177~ 180 @ 350~ 1240@ 177~ 19 @ 350~ 131 @ 177~

Q e,,,, 3 3

Q Q

1010 Reinforced Plastics Handbook

Predicting Performances Avoiding nonstructural or structural failure can depend in part on the ability to predict performance of materials. When required designers have developed sophisticated computer methods for calculating stresses in complex structures using different materials. These computational methods have replaced the oversimplified models of materials behavior relied upon previously. The result is early comprehensive analysis of the effects of temperature, loading rate, environment, and material defects on structural reliability. This information is supported by stress-strain behavior data collected in actual materials evaluations. With computers, the finite element analysis (Chapter 7) method has greatly enhanced the capability of the structural analyst to calculate displacement, strain, and stress values in complicated plastic structures subjected to arbitrary loading conditions. Nondestructive testing (NDT) can be used to assess a component or structure during its operational lifetime. Radiography, ultrasonics, eddy currents, acoustic emissions, and other methods are used to detect and monitor flaws that develop during operation. The selection of the evaluation method(s) depends on the specific type of RP, the environment of the evaluation, the effectiveness of the evaluation method, the size of the structure, the fabricating process to be used, and the economic consequences of structural failure. Conventional evaluation methods are often adequate for baseline and acceptance inspections. However, there are increasing demands for more accurate characterization of the size and shape of defects that may require advanced techniques and procedures and involve the use of several methods (Chapter 9). Designing a good product requires a knowledge of plastics that includes their advantages and disadvantages (limitations) with some familiarity of the processing methods (Chapters 1 and 5). Until the designer becomes familiar with processing, a fabricator must be taken into the designer's confidence early in the development stage and consulted frequently during those early days. The fabricator and the mold or die designer should advise the product designer on plastic materials behavior and how to simplify the design to permit easier processability. As with other materials, for every advantage cited, a corresponding disadvantage can probably be found (Figure 10.7). Probably (hopefully) the disadvantage has no influence in your project; but best to find the disadvantage.

I0

9Summary I 01 1

Figure 10.7 With gain possible loss not originally predicted in the design

Design Verifications DV refers to the series of procedures used by the product development group to ensure that a product design output meets its design input. It focuses primarily on the end of the product development cycle. It is routinely understood to mean a thorough prototype testing of the final product to ensure that it is acceptable for shipment to the customers. In the context of design control, however, DV starts when a product's specification or standard has been established and is an on-going process. The net result of DV is to conform with a high degree of accuracy that the final product meets performance requirements and is safe and effective. According to standards established by ISO-9000, DV should include at least two of the following measures: (a) holding and recording design reviews, (b) undertaking qualification tests and demonstrations, (c) carrying out alternative calculations, and (d) comparing a new design with a similar, proven design.

1012 Reinforced Plastics Handbook

Design Demands It can be said that the challenge of design is to make existing products obsolete or at least offer significant improvements. Despite this level of activity, there are always new fields of industry to explore. Plastics meet this challenge and will continue to change the shape of business rapidly. Today's plastics (URPs and RPs) tend to do more and overall cost less, which is why in many cases they came into use in the first place. Tomorrow's requirements will be still more demanding, but with sound design plastics will satisfy those demands, resulting in not only new processes and materials but improvements in existing processing and materials.

Costings Important to recognize that a major cost in the production of RPs, going from the design concept to the finished product, are materials of construction. They can range from 40 to 90% of the total cost. Thus, it is important to understand how best to use the materials based on their design and processing requirements. An important criterion is to understand and properly apply the interrelations of design requirements with materials of construction and fabricating methods. RPs has some mechanical, formability, and other characteristics that differ from other materials (unreinforced plastics, steel, aluminum, wood, etc.). It is a fact that RPs have not come near to realizing their great potential in a multitude of applications usually due to cost limitations that particularly involves the use of expensive fiber reinforcements (graphite, carbon, etc.). A major cost advantage for fabricating plastic products has been and will continue to be their usual relatively low processing cost. In production, cost to fabricate usually represents about 5% (maximum 10%) of total cost. Even though fabricating costs are low there tends to always be the capability to reduce fabricating costs with the start of production (Figure 10.8). It is a popular misconception that plastic matrices are cheap materials; they are not. There are low cost types (commodity types) but there are also the more expensive types (engineering types) (Chapter 3). Important that one recognizes that it is economically possible to process with a more expensive plastic because it provides for a lower processing cost. By far the real advantage to using RPs to produce many low-cost products is their low weight with their low processing costs.

10

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Different approaches are used to estimate molded part cost. Material cost is almost straightforward. However, processing costs can significantly vary as summarized in Tables 10.3 and 10.4. A reasonable costing procedure is presented using Figure 10.9 to show the best options in fabricating hand lay-up or spray-up products. It is based on a five-step procedure prepared by the Owens Coming Fiberglas Corp. This five-step system involves the following: Choice of material system: (a) percentage of glass fiber by weight, (b) type of fabrication (hand lay-up or spray-up), and (c) unfilled or filled system. Material components and laminate weight factor: using the above information and Tables 10.4 orl0.5 is used to fill in the horizontal blocks in Figure 10.9.

1013

1014 Reinforced Plastics Handbook Table 10.3 Unfilled RP systems Fiberglass reinforcement content (% by weight) Laminate weight (Ibs./ft2 @ 0.100" thickness) Resin weight (Ibs./ft2 @ 0.100" thickness) Fiberglass reinforcement weight (ounces/ft 2 @ 0.100" thickness) Approximate laminate specific gravity

15

20

25

30

35

40

45

50

60

55

0.65 0.67 0 . 6 9 0.71 0 . 7 4 0 . 7 6 0 . 7 9 0.82 0.86

0.89

0.55 0.53 0 . 5 2 0 . 5 0 0.48 0 . 4 6 0 . 4 4 0.41

0.39

0.36

1.55 2.14 2 . 7 6 3.42 4.13 4 . 8 9 5.71 6.59 7.54

8.57

1.25 1.28 1.33 1.37 1.42 1.47 1.53 1.59 1.65

1.72

Table 10,4 Filled RP systems

One part resin to one part hydrated alumina (by weight) Fiberglass reinforcement content (% by weight) Laminate weight (Ibs./ft 2 @ 0.100" thickness) Resin weight (Ibs./ft 2 @ 0.100" thickness} Filler weight (Ibs./ft 2 @ 0.100" thickness) Fiberglass reinforcement weight (ounces/ft 2 @ 0.100" thickness) Approximate laminate specific gravity

15

16

18

20

22

24

25

0.86

0.86

0.87

0.88

0.89

0.90

0.36

0.36

0.36

0.35

0.34

0.34

0.34

0.36

0.36

0.36

0.35

0.34

0.34

0.34

2.06

2.20

2.50

2.80

3.11

3.43

3.58

1.65

1.66

1.67

1.69

1.70

1.72

1.72

Part geometry: based upon your particular part, fill in the horizontal blocks. Material cost: based on present materials costs, fill in the vertical blocks. Proceed from left to right in Figure 10.9 to calculate component costs, part cost, and the approximate finished weight of the part. The following information pertains to the Figure worksheet"

10.9 costing

Always input values as shown in the parentheses above the blocks, i.e., where 4 0 r = 40r

10

Figure 10.9

Summary 9 1015

Costing worksheet for hand lay-up or spray-up RP products

2

Arrows drawn between blocks indicate information is duplicated; and

3

Efficiencies should be estimated based on molder's experience.

Identification of the costs associated with a part produced by hand layup or spray-up is similar to most other manufacturing products. Once it has been determined that a process satisfies the part design requirements, a logical sequence of contributing cost factors can be identified. A flow diagram will key the thought process to include the relevant cost factors. Process items (for the TS polyester resin matrix) such as a catalyst, solvents for gun flushing, etc., have not been included. In addition, part cost must be appropriately adjusted by finished part efficiency at molding. Technical Cost Models

TCM has been developed as a method for analyzing the economics of alternative manufacturing processes without the prohibitive economic

1016 Reinforced Plastics Handbook burden of trial-and-error innovation and process optimization. Its approach to estimating cost is not dependent on the intuition of costestimating individuals. It follows the conventional process modeling that ranges from design to process variables during fabrication. T C M takes all the details for each of the functions that go into designing to fabricating to delivery to the customer such as summarized in Figure 10.10. T C M provides the means to coordinate cost estimates with processing knowledge. Included are the critical assumptions (processing rates, energy used, materials consumed, scrap, equipment wear, etc.) that can be made to interact in a consistent, logical, and accurate flamework of economic analysis, producing cost estimates under a wide range of conditions.

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T C M can establish direct comparisons between processes. In turn it determines the plastic process that is best for the production of a product without extensive expenditures of capital and time. It also determines the ultimate performance of a particular process, as well as identifying the limiting process steps and parameters.

lO.Summary 1017 Each of the elements that contribute to the total cost is estimated individually. These individual estimates are derived from basic principles and the manufacturing process. This reduces the complex problem of cost analysis to a series of simpler estimating problems and brings processing expertise rather than intuition to bear on solving these problems. By this approach in dividing cost into its contributing elements it takes into account that some cost elements depend upon the number of products produced annually, whereas others do not. For example, the cost contribution of the plastic is the same regardless of the number of items produced, unless the material price is discounted because of high volume. It allows for the per-piece cost of tooling that will vary with changes in production volume. These types of cost elements, which are called the variable and fixed costs, respectively, create a natural division of the elements of manufacturing product cost. The technical cost analysis should be viewed as a philosophy, not road map. The important tenets of this philosophy are that: 1

Primary and secondary processes contribute to the cost of a finished component.

2

The total cost of a process is made up of many contributing elements.

3

These elements can be classified as either fixed or variable, depending on whether they are effected by changes in the production volume.

4

Each element can be analyzed to establish the factors and nature of the relationships that affect its value.

5

Total cost can be estimated from the sum of the elements of cost for each contributing process.

One advantage of the above philosophy over simpler cost-estimating techniques is that estimates obtained in this manner provide not only a total cost, but also quickly an understanding of the contribution of each element. This information can be used to direct efforts at cost reduction, or it can be used to perform sensitivity analyses, answering questions such as what if one of the elements should change?

Safety Plastics as well as practically everything around us logically continue to be involved in safety aspects. They fit into individual and overall safety programs. As an example recent data suggests that by 2020 road traffic

1018 Reinforced Plastics Handbook

accidents will rank third behind heart disease and major depression of death and disability across the world. By comparison war will be number eight with AIDS at number 10. Road crashes now result in 1.2 million deaths and 15 million injuries worldwide every year. They are the biggest cause of premature death for men and the fifth most cause for women. All types of plastics, including RPs requires following safety rules and regulations. They include from storing to handling materials to fabricating equipment to products. An example concerning materials is the monomer styrene used in TS polyester. Processing with the styrene monomer requires that precautions have to be taken to ensure the proper removal and handling of this toxic material. Legal limits in the workplace have been set up by regulations. Suppliers and fabricators continue to target in the reduction of styrene monomer quickly, effectively, and economically as well as using fabricating methods meeting regulations restricting styrene contamination in the atmosphere (Chapter 3). In addition, other resins require proper precautions in handling them. Processing equipment has standard procedures to operate and meet safety requirements. Safety information and standards are available from various sources that include the equipment suppliers, Society of Plastics Industry (SPI), and American National Standards Institute (ANSI). For the past century we have observed increasing activity on the part of manufacturers to upgrade safety in fabricating plants. Examples of safety features are many and differ for the different equipment in the lines. Safety interlocks ensure that equipment will not operate until certain precautions have been taken. Safety machine lockout procedures are set up for action to be taken in proper lockout of the machine's operation such as electrical and mechanical circuits. There are preloaded pressure bolts around dies, pressure rupture disks on barrels, and so on. The operating environment is continuously upgraded with reduced sound and noise in the operating areas.

Reinforced Plastic Successes Many RP successes continue to occur worldwide. A few have been reviewed in this book. There are more on the horizon that focus on design (Table 10.5). The extent to which RPs are used in any industry in the future will depend in part upon the continued creativity approach (Table 10.6), proper presentation (data, etc.) of new materials (Figure 10.11), and total R&D activity carried on by material producers, equipment manufacturers, processors, fabricators, and users ~in their

10

Summary 9 1019

desire to broaden the scope of plastic applications both performance wise and cost wise. Table 10,5 Focusing on design BASICDESIGNAPPROACH

TECHNOLOGYDESIGNDEVELOPMENT

Product and process measures are instituted after the development process is complete.

Product and process measures are implemented throughout development as the basis for continuous improvement of product design and process efficiency.

Internal personnel are recruited and trained for each product

External experts are recruited to address speciality areas internal personnel focus on key technology areas. Risk discipline required, reduction methods such as concurrent development and prototyping are encouraged.

Requirements changes are experienced throughout the project as new requirements are added and schedule slips occur.

Requirements are managed to accommodate target schedules, and new requirements and requirements changes are evaluated based on schedule impact.

Manufacturability is a key focus throughout the development Manufacturability is addressed process and manufacturing equipment is validated in parallel once the product design is fomalized and ready for production. with product design. Management focuses on tracking project risks that may Management focuses on tracking of project deliverables as a measure impact schedule, as well as ensuring that deliverables are completed on schedule. of project progress. Proprietary interfaces are developed to restrict access.

Standard interfaces are supported to provide increased interoperability with other devices that can support a diverse range of related functionality.

New requirements focus on enhancing existing products and addressing competitor capabilities.

New requirements include customer requests as well as new functionality that is based on a prediction of evolving technological capabilities.

Product quality is evaluated based on the results of final product testing.

Product quality is based on success of incremental design and product reviews, and incremental tests, as well as final product tests.

Testing is defined as the final phase Testing activities are addressed throughout development, including an emphasis on development of validation test of the development process. procedures as soon as the requirements are defined to provide early test capabilities. Product reliability is based on the results of validation tests on selected components.

Product reliability is designed into the product using techniques ........and as predicted based on test results and models.

1 0 2 0 Reinforced Plastics Handbook Table 10.6 Basicapproaches to successful creativity 1.

Problem solving in designing and fabricating through to production, like with business and personnel problems, generally requires a systematic approach with creativity.

2.

If practical rather small changes should be made and time allotted to monitor the reaction or result.

3.

With whatever time is available, patience and persistence is required.

4.

When the problem is particularly difficult or limited time exists, consider a new and imaginative approach using techniques that classically generate creativity ideas.

5.

Generate as many ideas as possible that are even remotely related to the problem.

6.

During the idea-generating phase, it is of critical importance to be totally positive. No ideas are bad.

7.

Evaluation comes at a later time so do not attempt to provide creativity and evaluation at the same time. It could be damaging to your creative approach.

8.

Look for quantity of ideas an not quality at this point. All ideas are good with the best becoming obvious later.

9.

If possible relate the problem to another situation and look for a similar solution. This approach can stimulate creative thinking toward other ideas.

10.

Try humor so do not be afraid to become ridiculous about the problem. It is better than becoming upset or crying.

11.

Next step is to evaluate all the ideas. Consider categorizing the list. Add new thoughts, select the best and try them. So after you take all this action and nothing satisfactory occurs, rather than give up, look for that real creative solution. It is out there.

12.

You may be to close to the problem (Set away from the trees and look a the forest. Climb up one of the tall trees and look at what has happened from a different perspective.

13.

Use your creativity talents, but again, be positive. This positive action will make you be successful. You have creatively worked through the frustration and negativism that problems seem to generate.

14.

Your increasingly creative input will generate future opportunities.

Logically the material producers provide the bulk of such research expenditure themselves and the rest by the equipment and additive industries that do more than the processors and fabricators. Important to growth, as in other categories such as computers, has been government

10

Figure 10.11

Summary 9 1021

Skill of the sa.lesperson may be required to sell a real novel and useful designed product

and in particular the military (particularly during a war to the present hot or cold wars). Projects in basic and applied research as well as new applications material wise and equipment wise have been extensive. Their work in turn significantly expands into the industrial industry and marketable products. In fact, their R&D variety of programs from 1940 has provided what may be said as extremely important in the consumption of RPs. After meeting government and particularly military requirements, they provide the basics to significantly expand the technology into commercial and industrial products worldwide. They include all types of RPs, computer hardware and software, communication systems (satellite, Internet, Fax, wireless telephones, etc.), medical procedures and devices, machining materials (URPs, RPs, metals, etc.), highway transportation control via computer programs, aircraft, ships, packaging bar coding and radio coding, and so on. Manufacturers need to continually update their traditional design methods in order to keep pace with rapidly evolving technologies and an increasingly demanding worldwide marketplace. Consumers demand products that are increasingly faster, easier to use, and lower in cost. An example of increasing demand continues to expand in China that will continue its manufacturing boom. General Motors will boost their plant capacity 50% by 2006. GM currently builds 510,000 vehicles and plans to raise its total in China to 766,000 vehicles by 2006. GM will add production lines at its main Shanghai plant and another in the southern region of Guangxi.

1022 Reinforced Plastics Handbook

Compared to other material-based industries, RPs have enjoyed an overall average impressive growth rate since their inception over a century ago, but particularly since about 1940 (Figure 10.12). The product-design and product-material communities were quick to recognize the design freedom and great versatility that materials and processing techniques afforded. Recognizing a growing marketing opportunity worldwide, international plastics material suppliers started an endless cycle of developing new and improved materials to meet continually new design needs. Processing machinery builders worldwide then responded with improved equipment (Figure 10.13) and very new processes, as conventional tool shops everywhere expanded their capabilities to include mold and die manufacturing for the plastics industry. 2o

PLASTICS

io%/YR- s

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Figure 10,12

I oo

150 2oo YEARS

:.

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When growth rate of different materials are made, reinforced and unreinforced plastic stands out (courtesy of Plastic FALL0)

1

Figure I0,13

You cannot expect a 20 year old machine to compete with a machine built to today's standards

10

Summary 9 1023

The plastic manufacturers and compounders usually provide the material for the processor who converts the plastic materials into finished products; certain fabricators compound their own materials. The basic principle involved consists of partially melting the plastics mass by the application of heat and compressing of the softened plastic into the desired shape by the use of molds, dies, rolls, etc. Finally, the shaped hot plastic is solidified, either simply by chilling in the case of the TPs heating or through further polymerization heat called the "cure stage" in the case of TS plastics (Chapter 3). Many reinforced plastic businesses have been in operation and continue to operate and be profitable. As an example M. C. Gill Corp., CA. is the oldest, continuously operating RP business in the world; continues to operate the manufacturer of RPs. Life for the M. C. Gill Corp. started as Peerless Plastic Products in 1945. The company is also the world's largest manufacturer of original RP equipment and replacement baggage compartment liners for commercial and freighter aircraft. During 2003 Merwyn Gill founder and leader of M.C. Gill Corp. at age 92 was still raring to go. He just contributed $7 million to the University of Southern California for a Center for Composite Materials. Developments

In the early days of the development of fiber RPs for use in aircraft/ aerospace vehicles, there were considerably fewer choices available to the designer of materials, fabrication techniques, and design concepts than there are today. During 1940s and early 1950s, the predominant reinforcement was glass fiber in fabric form, the principal resin matrix was TS polyester, and the most often-used fabrication procedure was vacuum bag molding and resin transfer molding or off shoots of these processes. Designs of RP military parts, other than radomes, were generally used as substitutes for previously used metal parts. Most parts were made either of parallel or cross-laminated fabrics, which in some cases resulted in superfluous reinforcement in certain directions. At that time, the number of combinations of fabrics and plastics popular for designers, although significant, was still small enough that most of the design data needed could be obtained experimentally. The limited number of variables, especially types and forms of reinforcements was conducive to the development of RP technology primarily through empiricism. The lack of a strong scientific foundation for this technology resulted in materials that were not always optimally structured. A principal structural deficiency of glass fabric (E-glass) RPs was their low modulus of elasticity. Development of new, higher modulus fibers,

1024 Reinforced Plastics Handbook

such as carbon, graphite, boron, and beryllium provided reinforcements with several times the modulus of elasticity of glass fibers with densities as low as or lower than glass; strength was close to that of glass fibers. In addition to having new chemical types of fibers available, new options appeared in fiber diameter, fiber length, and the grouping of filaments into strands, roving, and yam. These new types and forms of fiber provided the industry with more freedom to select the most appropriate type of fiber reinforcement for a given application. Newly developed, high modulus plastics, such as cycloaliphatic epoxies and new-generation high-temperature plastics, such as polybenzimidazole and nylon plastics, offer another degree of freedom in terms of material matrix selection. The new advanced fibers and plastics were being combined in unidirectional preimpregnated form, such as yarn, tape, and sheet material. The availability of such unidirectional prepreg material permitted precise orientation of each ply in an RP at any desired angle. This allowed the structural designer to specify the appropriate orientation of each ply in an RP that gave maximum structural efficiency for a given application. This apparent abundance of fiches with regard to newly improved constituent materials for RPs, and new or more versatile physical constructions of RPs could, however, have some potential pitfalls that were recognized and investigated at an early stage. For example, the new fibers and matrix materials must fimction in an integrated manner to resist externally applied loads, where the load is transferred from fiber to fiber through the matrix and through fiber-matrix interface. For the matrix to transfer the load it must have sufficiently high cohesive shear strength and it must provide sufficient high interfacial shear strength through chemical a n d / o r mechanical adhesion. Both the matrix cohesive shear strength and the interfacial shear strength must be adequate for the anticipated service conditions of the RP (Figure 10.14). These service conditions usually included high humidity and sometimes-elevated temperature, both of which could reduce the interfacial shear strength largely or at a faster rate than the matrix cohesive shear strength. For this reason, the fiber-matrix interface was, in many cases, the weak link in the load transfer mechanism within a fiber RP. It had, therefore, been found to be prudent to investigate the nature of this interface in order to provide fundamental scientific information leading to improved load transfer characteristics at the fiber-matrix interface, thus resulting in more structural efficiency. There are two principal theories on how load transfer between fibers is achieved in fiber RPs where they either operate alone or together

10

Summary 9 1025

Figure 10o 14 Examplesof directional characteristics of RPs under in-plane shear stress

(Chapter 8). One is the mechanical bonding, friction, or shrink-fit theory. This theory states that during solidification of the plastic, the plastic shrinks around the fiber with sufficient force to provide frictional resistance to movement of the fiber through the cured/solidified plastics. The second is the chemical coupling theory. According to this theory, certain functional groups in the plastic chemically react with the reinforcement surface to form a chemical bond, or a separate chemical agent is used, one part of which reacts with the reinforcement surface, and another part of which reacts with, or is compatible with the plastic matrix. With glass fibers, organosilanes were generally used as chemical coupling agents. It was theorized that the silane part of the organosilane reacts with Si-OH groups on the glass fiber surface to form Si-O-Si

1026 Reinforced Plastics Handbook

bonds. The organic part of the silane is expected to react with, or be compatible with, the specific functionality of the plastic matrix being used. For example, the silane used with unsaturated polyesters (TS polyester) would have double-bond functionality, while the silanes used with epoxies would have the amino or hydroxy functionality. The nature of the fiber surface, not only in its manufactured state, but also as it exists during the various processing and RP fabrication operations, plays an important role in establishing the fiber-matrix interracial conditions in the fabricated RP. The fundamental work investigating interfacial phenomena in fiber RP materials has been divided into two broad categories. One addresses the chemical and physical compatibility of the plastic matrix (in its uncured state/for TSs) with the fiber surface. The other is concerned with factors affecting the degradation of the fiber-matrix interface after it is formed and subsequently exposed to potentially adverse environments such as high humidity or elevated temperature. This type work has expanded in producing modern day new capabilities for RPs. Throughout the past century, new RP compounds continue to be developed and used. Available have been concentrates of high strength reinforcement encapsulating glass fiber in a resin by conventional fabricating techniques. As reviewed, in Japan there is development of concentrates produced in the polymerization reactor producing polymers and is being tested by automotive manufacturers. The reinforcing concentrate can be up to 80 wt% milled glass fiber in a styrene acrylonitrile (SAN) carrier. Micromechanics

Development concerning the interface aspects of RPs is oriented toward providing the designer with RP materials that arc physically and structurally sound initially, and that retain this structural integrity under various adverse service and environmental conditions. Once the interfacial fiber-matrix bond strength is known quantitatively, together with the mechanical properties of the fiber and plastic matrix, and the relative percentages and geometrical distribution, it should be possible to predict analytically the mechanical properties of the RP. Fundamental investigations into the mechanical properties of RP constituents and into the gross mechanical properties of RPs have been termed micromechanics to indicate that the part of the RP under investigation is usually only a microscopically small part of the total RP. One of the principal goals of micro mechanics research is to develop analytical techniques for predicting elastic constants, stress-strain

10

Summary 9 1027

behavior, and the ultimate strength of RPs. Such tools enable designers to analytically compare the mechanical properties of RPs with those of other candidate materials for various applications. Using such techniques, the structural efficiency of fabricated RPs can be determined by comparing experimentally measured mechanical properties with analytically predicted properties. Selected RPs as a particular structural component, micromechanics analyses, together with classic mechanics theory, should provide a means for predicting optimum fiber orientations and material thicknesses for specific load conditions. In addition to the analytical, predictive type of micromechanics research, there is also a significant amount of experimental micromechanics research that has been done, i.e., determination of stress concentration at fiber ends and crossovers, investigations of deformation and fracture modes, and crack propagation studies. Such work helps the analyst in establishing realistic assumptions of material behavior and in comparing observed mechanical behavior with predicted behavior. Reasonably accurate analytical methods have been established for predicting elastic constants of a unidirectional RP. Using laminated plate and shell theory (macromechanics), the elastic constants of multidirectional RPs are derived from the elastic constants of the unidirectional layer (Chapter 8). In addition to the work on prediction of elastic constants, work has been done in predicting strength of multidirectional RPs based on experimentally determined strengths of unidirectional RPs. Nanotechnology Successes

An interesting novel RP development that differs from what has been occurring involves special nanotechnology used to reinforce plastics. The Business Communications Co., Inc., Norwalk, CT reported that total worldwide sales during 2003 of plastic nanocomposites were $90.8 million with about 78% thermoplastic and 22% thermoset. By 2008 sales should reach $211 million with about 90% thermoplastic and 10% thermoset. Carbon nanotubes can be used. It is a spin-off of the research leading to the award of the 1996 Nobel Prize to Robert F. Curl, Harold W. Kroto, and Richard E. Smalley. Carbon nanotubes are sheets of carbon atoms rolled up into tiny hollow cylinders. With diameters measured in nanometers (nm) and up to a millimeter (mm) long, carbon nanotubes (CNT) have unusual structural and conducting properties: These make them potentially very useful for many applications. For example, CNT

1028 Reinforced Plastics Handbook use in flat panel computer and television displays is nearing commercialization. CNTs have many unique properties, which make them an attractive component of lightweight yet very strong RPs. Nanocomposites with carbon nanotubes have been an area of considerable R&D ever since the excellent electrical and mechanical properties of carbon nanotubes were demonstrated. However, attempts to prepare carbon nanotubc RPs often result in phase separation of the CNT and polymer phases causing premature material failure. Researchers at Nomadic Inc. and Oklahoma State University developed a layer-by-layer (LBL) assembly process that permits preparing polyelectrolyte/CNT RP with a CNT loading greater than 50 wt%. The excellent mechanical properties of these materials can be improved further by additional chemical action; crosslinking of the CNT and polymer phases and by parallel alignment of the CNTs. The LBL method has been used to prepare various types of RPs. The integration of nanofibers into textile RP structures may create the next generation of super carbon fiber. Continuous spinning of RP fibers containing CNTs can produce fibers with toughness, the capability to absorb energy, more than four times that of spider silk and 17 times that of the aramid. Researchers at the University of Texas Dallas (UTD) and Trinity College, Dublin, Ireland, have reported that these fibers have twice the stiffness and strength, and 20 times the toughness, of the same weight and length steel wire. According to Dr. Ray H. Baughman, Robert A. Welch Professor of Chemistry and director of the UTD NanoTech Institute, possible applications of these continuous reinforced fibers includes using carbon nanotubes to reinforce PAN could produce a new generation of carbon fibers (Chapter 2). Commercial carbon fibers produced from polyacrylonitrile (PAN) appear to have reached their performance limit. There are other reinforced nanofibers being examined.

Fuel Cell's Bipolar Plates Fuel cells, despite being in the embryonic stage of development, are viewed as potentially as a huge market for unreinforced and particularly reinforced plastics. During 1839 William Grove, USA, developed the concept of the fuel cell in which electricity and water are generated from the oxidation/reduction of hydrogen and oxygen. Major R&D activities in fuel cells started about 1960 because of the space exploration program. Hence, it is not that the fuel cell per se is an emerging technology, but it is the desire to make fuel cells affordable for use in automobiles that is driving new research. The result would be

10

Summary 9 1029

clean, hydrogen-powered batteries for automobiles. The critical phases of this program consist of developing cost-effective durable fuel cells and hydrogen storage technology. There are numerous opportunities for the use of plastics (URPs and RPs), sealants, and adhesives. In fact, the only cost-effective solutions for developing the desired technology will come from the plastic materials (Chapter 6 Automobiles,

Batteries). A fuel cell is a device that converts chemical energy from a fuel directly to electrical energy. The basic operating principle of a PEM (polymer electrolyte membrane) fuel cell has Hydrogen (fuel) being fed into the channels of a plate. As H2 passes through the catalyst layer, protons are created, which are transmitted by the proton exchange membrane, while the electrons are conducted through the endplate. The protons then react with oxygen and electrons, which have conducted through an external circuit on the other side of the membrane to complete the reduction reaction forming water. Typically at present, the voltage produced from one cell is about 0.7 V, which is, of course, not sufficient for most applications.Thus, the fuel cells are stacked, and the end plates then become both the anode and cathode, and are therefore called bipolar plates. Bipolar plate materials have historically been metals coated with corrosion-resistant layers or graphite with a seal treatment (to lower the gas permeability). In recent years, major efforts have been made for developing RP bipolar plates. The new plates usually have molded-in gas flow channels so that they can be fabricated rapidly and costeffectively. However, the cost of bipolar plates ($10/plate with 400 cm 2) today is still too high to be applied to automotive and other civil power applications, and the conductivity is marginal. Graphite is one of the traditional materials used for making bipolar plates; the gas-flow channels on the plate are cut by machining. The graphite plates have good conductivity, chemical compatibility, and corrosion resistance. The problem is the complexity and the cost of the graphite and machining of the bipolar plates. The raw graphite has to be made by a high-temperature sintering/graphitization process that takes several weeks and results in some porosity and distortion of the material. Then the raw graphite is cut into slabs, vacuum-impregnated with resin filler for gas-tightness, and ground and polished. Other bipolar plates in development include carbon/carbon (graphitization of slurry mixture of carbon fibers) and phenolic resin. There is the polymer matrix RO bipolar plate; uses both thermoset (TS) and thermoplastic (TP) as binders to conductive fillers such as graphite and metal coated graphite. Parts are compression or injection molded.

1030 Reinforced Plastics Handbook

Work continues by different organizations using different resins and compounds in the RP bipolar plates such as sulfonated copolymers, vinyl ester, phenolic, and fluoropolymer to provide high conductivity and mechanical properties without carbonization and/or graphitization resulting in lower cost. Latest commercial developments use highly conductive RP compounds for key components because they offer a cost-effective alternative that meets demanding chemical, electrical, mechanical, and physical requirements.

Future A very important development occurring is the RP industry moving gradually away from its origins towards more mechanized and efficient manufacturing processes. Markets are developing that require this development. Simple contact molding (hand, spray, etc.) is becoming less and less desirable for products in these markets. Influencing this move is the environmental concerns about emissions within and from the workplace (Chapters 3 and 5). Most important, RPs are increasingly competing with more conventional materials in high specification applications, which demands more sophisticated, efficient, and better controlled manufacturing processes using closed molds. Examples of processes include resin transfer molding (RTM) and vacuum assisted RTM (VARTM). These closed mold processes provide meeting emission issues usually associated with contact molding and lend themselves to automation, opening the way to high volume production of sophisticated RP products with precisely controlled thicknesses and fiber placement. However, this step-up from very lowtech contact molding methods to more sophisticated techniques can create confusion for many RP fabricators. Successful management and use of sound engineering principles of this transition is required in order to be successful. A continuous flow of new materials, new processing technologies, and product design approaches has led the industry into applications unknown or not possible in the past. What is ahead will be even more spectacular based on the continuous new development programs in materials, processes, design approaches, and innovations that are always on the horizon to meet the continuing new worldwide industry product challenges. Included is the fact that there is always a growing need in many areas to find alternatives to heavy structures. The modern lightweight RPs continues to be used in applications where they provide savings in raw materials, energy, and/or installation costs.

10

Summary 9 1031

A skilled designer blends knowledge of RPs, an understanding of manufacturing processes, and imagination of new or innovative designs. Recognizing the limits of design with traditional materials is the first step in exploring the possibilities for innovative design with RPs. Some designers operate by creating only the stylish outer appearance, allowing basic engineers to work within that outside envelope. This approach is used very successfully such as in certain products or parts for furniture, etc. There are also the combination of designing appearance with engineering so that the stylish product incorporates the best combination with ease of processing when using a specific RP, simplify assembly, provide capability of repair, streamlining quality control, and/or other conditions. The stylish envelope that eventually emerges will be a logical and aesthetic answer to the design challenge. Product Developments

Only a few recent product developments will be reviewed. There are by far many more which have all kinds of significant aid and importance to people worldwide.

World's Largest Wind Blades German wind turbine company REpower Systems AG has joining forces with Denmark's LM Glasfiber to develop an RP blade for REpower's SM turbine, a 5 MW machine with a rotor diameter of over 125 m. It will be the largest blade in the world in series production. From 1978 to 2001 LM fabricated over 60,000 RP blades of smaller sizes for wind farms.

Bridge Infrastructures and RPs Use of RPs to support deteriorating bridges has been on going and expected to significantly expand. The Road Information Program (TRIP), non-profit transportation research group in Washington, DC reported that 1 in 4 USA's major heavily traveled bridges is deficient and in need of repair or replacement. Due to significant deterioration 14% are structural deficient.

RP Commercial Airplane With the performance to weight advantages of carbon fiber the 200 to 250 passenger Boeing 7e7 high speed jet (mach 0.85) light weight commercial airplane will have the majority of its primary structure (wings, fuselage, etc.) made of carbon RPs. It will use 15 to 20% less fuel when compared to other wide-body airplanes. Production will begin 2005. First flight is expected in 2007 with certification, delivery, and entry into service 2008.

1032 Reinforced Plastics Handbook

Airbus Super-Jumbo RP Wing Parts GKN Aerospace Services/Cowes, UK is fabricating wing trailing edge panels for the new (present count) 350-seat A380 Airbus. It will be made from glass and carbon fiber RPs using GKN's resin fusion process. Self-Healing RPs The University of Illinois developed a technology for repairing hairline cracks in RPs by embedding microcapsules containing monomers corresponding to the plastic matrix. Innovations

RPs is currently one of the most innovative and rapidly expanding fields of engineering worldwide. The Infrastructure Composites Report' 2001 published by Composites Worldwide predicted that globally, the use of composites (RPs) will grow by more than 525% between 2000 and 2010. Through the laws of physics, chemistry, and mechanics, in 1944 theoretical data was determined for different fiber materials. These are compared to the present actual values in Table 10.7. With steel, aluminum, and glass the theoretical and actual experimental performance values are practically the same, whereas for polyethylene, polypropylene, nylon, and other plastics they are far apart; that is significantly higher. They have the continued important potential of reaching values that are far superior to the present values. When polyethylene was first produced during the late 1930s, physicists in England, USA, and Germany predicted a tremendous potential for it. At that time, the properties of PEs were much lower than those presently available. Specific PEs such as LDPE, HDPE, UHMWPE, etc. have been developed, with higher product performance requirements, out of the original general-purpose PE. One of many examples of a future process development has been introduced. It will use laser and microwave plasticators, fiber-optics monitoring, quiet electromagnetic drives, voice-activated controls, permit quick plastic changes without purging, eliminate hoppers by storing plastics in modular tanks on the machine's bed and feeding by vacuum pumps behind the plasticators, and more innovations. Features to be gained include more energy savings, increase process efficiencies, and simplify controls so that the IMMs will be easier to operate, and improve and provide repeatability of melts. This program called Mother Project was started in 1999 and targeted to be completed by 2017. Studies are being conducted by MIR, S.p.A, Italy in cooperation with the Univ. of Turin's Plasturgy Dept.; USA agent MIR USA, Leominster, MA.

10

Summary 9 1033

Table I0,7 Comparison of theoretically possible and actual experimental values for fiber properties of various materials

Modulus of elasticity

Tensile strength

Experimental

Typeof material

Theoretical, Fiber, N/m m2 N/m m2 (psi) (psi)

Polyethylene

300,000

Polypropylene

(43,500) 50,000

Polyamide 66

(7,250) 160,000

Glass

(23,200) 80,000

Steel

(11,600) 210,000

Aluminum

(30,400) 76,000 (11,000)

100,000 (33%) (14,500) 20,000 (400/0) (2,900) 5,000 (3%) (725) 80,000 (100%) (11,600) 210,000 (100%) (30,400) 76,000 (100%) (11,000)

Normal polymer, N/m m2 (psi) 1 000 (0.330/0) (145) 1 600 (3.2%) (232) 2,000 (1.3%) (290) 70,000 (87.5%) (10,100) 210,000 (100%) (30,400) 76,000 (100%) (11,000)

Experimental Theorectical, Fiber N/m m2 N/m m2 (psi) (psi) 27,000 (3,900) 16,000 (2,300) 27,000 (3,900) 11 000 (1,600) 21 000 (3,050) 7,600 (1,100)

Normal polymer, N/m m2 (psi)

1,500 30 (5.50/0) (0.1O/o) (218) (4.4) 1,300 38 (8.1%) (0.24%) (189) (5.5) 1,700 50 (6.3%) (0.18%) (246) (7.2) 4,000 55 (36%) (0.5%)

(580)

(8.0)

4,000 1,400 (19%) (6.67%) (580) (203) 800 600 (10.5O/o) (7.89%) (116) (87)

* For the experimentalvaluesthe percentageof the theorecticallycalculatedvalues is given in parentheses, as (47)

Summarization can be made as to what has been occurring in the World of Reinforced and Unreinforced Plastics. It can be said that no other materials have had such a lasting impact on virtually all spheres of life. What is more interesting and important with these plastics is the endless new development in all facets going from plastic materials-to-equipmentto-designing-to-fabricated products-to-markets (Figure 10.15). They have successfully conquered broad sections of virtually all spheres of life demonstrating dynamic development from their infancy to futuristic, highly specialized, high-tech applications. No industry is more future oriented than the plastic industry continual growth material wise, process wise, and product wise.

1034 Reinforced Plastics Handbook New

Product% Fabrication TechnologyUpdate (k MARKETS ~ APPROACH bricaating~Analysis FeasibilityStucly

MARKETABLE PRODUCTS

T d

LEADS

T

R&D

GOOD BUSINESS & VIANUFACTURING PRACTICES

T d

Rec Engineering Molding Injection Evaluation / . x x Blow -/~ k Molecular ~ \ Compression Selecting MaterialProc / ~ x / / ~ / ~^~StructureSR&oL~ Rein_._._forced Plastics Evaluate 9 I / RheoloLgy'~MOrphOlOgy ~"~ ExtrusionF~l'dlm Detractors- / ~ Constraints I~ "Properties )~ I :~.',: ThermoformL'~ ~-. I Pipe CostAnalysis / ; ~ " 9~ Compounding ~ r"~mow I Coating Alloys ~ Blends ~ IEtc" Etc. Etc.

Figure 10.15

Reinforced plastic growth related to tree growth

T

GOOD ENGINEERING DESIGN

"1"1

Conversions

T a b l e 11.1 Basic conversion factors

To convert from:

To:

Multiply by:

m/m or in/in MPa Ib/in 2 GPa Ib/in 2 MV/m V/O.O01 in

0.01 m/m or in/in Ibf/in 2 MPa Ibf/in 2 GPa V/O.O01 in MV/m

100 145.3 0.00688 145.3 x 103 0.00688 x 10-3 25.4 0.0394

Pressures or Stress

Ib/in2(psi) Ib/ft 2 g/cm 2 bar atm

Volume

6,8948 Pa 27.8803 Pa 98.0665 Pa 1 x 105 Pa 1.01 x 105 Pa

in 3 ft 3

0.0071 0.1129 1.3558 9.8067 1 x 10-7

Ib s/in 2

Torque oz. in lb. in lb. ft kg.m dyne. cm

0.0254 m 0.3048 m 0.9144 m 2.54 x 10-5 m 2.54 x 10-8 m 1 x 10-6m

Mass OZ

Ib T(Iong,2240 Ib) T(metric) T(short,2000 lb)

gal (US) L

m3 m3 m3 m3 m3

Viscosity

N-m N-m N.m N.m N.m

Length in ft yd mil pin pm

OZ

1.6 x 10-5 0.0283 2.9573 0.0038 0.0010

P

Flow oz

Ib kg dyne

Density

oz/in 3 Ib/in 3 Ib/ft 3

Temperature 0.0288 0.4536 1,016 1,000 907

kg kg kg kg kg

6,894 Pa.s O.100 Pa.s

C= F= K= K=

(5/9)(F- 32) (9/5)C + 32 C + 273.15 F + 459.67

0.2780 4.4482 9.0867 1 x 10-5

N N N N

1,730 kg/m 3 27,689 kg/m 3 16,018 kg/m 3

1036 Reinforced Plastics Handbook Table 11.2

SI units and deviations

Quantity

Special name Symbol m2

Area

Recognized units

Multiples in use

Relations

a (are)

dm 2

1 a = 102 m 2

ha (hectare)

cm 2

1 ha = 104 m 2

mm 2 m3

Volume

litre

dm 3

1 litre = 1 dm 3

cm 3 mm 3 Mass

kg

tonne

Mgg

1 tonne = 1 Mg

Mg pg Linear density

kg/m

Density

kg/m 3

1 tex = 10-6 kg/m

tex

= 1 g/km kg/dm 3 g/cm 3 min minute

Time

h hour d day Frequency

Hertz

Hz

Velocity

-

m/s

Acceleration

g

m/s 2

Force

Newton

N

Pressu re

Pascal

Pa

1 Hz =

1Is

1 km/h = 1/3.6 m/s

km/h

km/h

ba r

MPa

1 bar = 105 Pa

GPa

1 Pa = 1 N/m 2

1 N = 1 kg m/s 2

mbar Stress

Pascal

Energy work

Joule

Pa N/m 2

N/tex

MPa N/mm 2

1 N/tex = 1 N km/g

eV kW h

kJ

1J=lNm

1 MPa = 1 N/mm 2 =lWs

Quantity of heat

1 kW h = 3.6 MJ Power Viscosity

Watt

W

kW

lW=

Pa s

mPa s

1 Pa s = 1 N s/m 2

oc

Celsius temperature Linear expansion

K-1

coefficient Thermal

W/(m K)

conductivity Heat transfer coefficient

W/(m 2 K)

1J./s

11 Table 11.3

9C o n v e r s i o n s

Conversions of USA measurements to metric units

US units

Metric

SI units

Length: 1 foot fit) 1 inch (in) 1 thou

0.3049 m 2.54 cm 0.0254 mm

25.4 mm

Area: 1 square yard 1 square foot 1 square inch

0.8361 m 2 0.0929 m 2 6.451 cm 2

Volume: 1 cubic yard 1 cubic foot 1 cubic inch

0.7645 m 3 0.0283 m 3 16.387 cm 3

Liquid: 1 gallon (UK) 1 fluid ounce

4.5459 litres 28.4130 cm 3

Weight: 1 ton 1 pound (Ib) 1 ounce (oz)

1.10160 tonnes 0.4536 kg 28.349 g

Fo rce: 1 Ibf 1 Ibf/in 2 (psi}

0.457 kgf 0.0703 kgf/cm 2

4.4482 N 6.8948 kN/m 2

Density: 1 Ib/ft 3 1 Ib/in 3

16.018 kg/m 3 27.68 g/cm 3

27.68 Mg/m 3

Thermal:
(1.8 x ~ + 32 251.996 gcal 0.00413 Cal cm/cm 2 s ~

645.16 mm 2

028.317 dm 3

4.5459 dm 3

1.0550 O.1442 W/m ~

1037

1 0 3 8 Reinforced Plastics Handbook Table 11.4 Conversions of metric units to USA measurements

Metric units

US

Length: 1 meter (m) 1 centimeter (cm) 1 millimeter (mm)

3.2808 feet 0.3937 in 0.03937 in

Area: 1 square meter 1 square centimeter

Volume: 1 cubic meter 1 cubic centimeter

Sl units

1.1959 yards 2 10.7639 feet 2 0.1550 in 2

1.3079 yards 3 35.3147 feet 3 0.061 in 3

Liquid: 1 litre 1 cubic centimeter

0.2199 gallons (UK) 0.0353 fluid ounces

Weight: 1 tonne (te) 1 kilogramme (kg) 1 gramme (g)

0.9842 tons 2.2046 Ib 0.0353 oz

l dm

Foroe:

1 kgf lkgf/cm 2

Density: 1 kg/m 3 1 g/cm 3 Thermal: ~ 1 Cal cm/cm 2 S ~163

2.2046 Ibf 14.2233 Ibf/in 2

9.8066 N 98.0665 kN/m 2

0.0624 Ib/ft 3 0.0361 Ib/in 3

(~

32)/1.8

241.9 Btu in/ft 2 h ~

418.68 Wm/m 2 ~

Table 11.5

Temperatureconversions

- 2 1 0 to 0 C. OF

F.

C.

1 to 25

!

I

I1

]:

,

C.

F..

- 1 3 4 " -Z10 -zoo -129 -190 -123 -180 -118 -170 -112

-34~ " -17.2

-loo

-3ss

-16.7

-292

-16.1 -15.6

-274

-310

28 to 50

P. C•,.o• 1 2

33.8

C.

C. or

3.33

!

F.

F.

24

78.8

i

||__

C.

132.8 134.6 136.4 138.2 140.0

61 62

,Ls

31

0.56

33 34

"87.8 ' 13.3 89.6 13.9 91.4 14.4 98.~ 15.0

51.8 ..... 2.22 53.6 2.78 55.4 3.33 57.2 3.89 59.0 4.44

34 37 38 39 40

"96.8 " 16.1 98.6 18.7 100.4 1Y.2 102.2 17.8 104.0 18.3

,+o., " - +.oo

41 42

-256 .... -14.4

.

,,s.,

7 8

46.4

52 53 54 SS

123.8 125.6 127.4 129.2 131.0

-150

-238 -13.9 - 2 2 0 ! -13.3

-140

.

I

-166 -148 -130

~

J-11.2 -11.1 -10.6

32

1.11 1.67

35

95.0

....

, ,!l

+

- 76 - 58 - 40

- 51.1i - 60 - 45.6 - SO - 40.0 - 40

8.89 ' I , ' 8.33 17 - 7.78 18

-

- 22 - 7.22 19 - 4 , - 6.67 20

- 34.4 - 30 - 28.9 - 20

. ,|

- 23.3 - 10 J - 17.8 0

,.

0

50.0

11 12 13 -112 i -10.0 14 - 94 - 9.44 IS

- 73.3 - 1 0 0 - 67.8 - 90 80 62.2 70 56.'7i

"

1~o _ 48.2

-13o-2~-12.8 -184 +! - 1 2 2 84.4 - 1 2 o

- 78,~ - 1 1 0

44.6

14

- 6.11 - 5.56 5.00 2~

32

:i~

~

4.44 &89

62.6 64.4 66.2 68.0

5.56 6.11 6.67 7.22

71.6 73.4 75.2 7%0

,|

18.9

60

63

%

414 4.5

44 48

105.8 107.6 109.4! 111.2 i ll&O

21.1

70

,,

,.s

~,7

7,

48 49

1 1 8 . 4 1 22.8 120.2 23.3 122.0 ~ 23.9

43

8.33 8.89 9.44 10.0

15.6

SO

II

|i

19.4

20.0 20.6

68

73 74

75

,a

11o 14o 284 t 193 13o ,302 i, ISS

C.

54 6O 66

27.2 27.8

81 82

!77.8 179.6 18i.4 183.2 185.0

71 77 82 88 93

leo 17o 18o 194 zoo

320

~oi

4oo

338 356 374 39'/

210 216 ~1 22"/

410

440

186.8i . . . . 99

21o

,to ~ .z 413 2SS

,so 460

428 446 464

470 480 49O

28.9 29.4

1't0.6

Is

" ~o.o30.6 31.1 31.7 32.2

188.6! 100 190.4 i 104 192.2 110 194.0 114

87

P,

195.8 1 2 1 197.6 127 199.4 132 201.2 138 208.0 i+ i43

91

92

159.8

35.&

N i 204.8 97 ! 208.6 98 208.4

36.1 36.7 37.2 37.8

49

93 94

95

210.2 100 +212.0 ,

I

!

12o 13o

2 4 8 ! 182 266 i 188

212 22O 23O 24O

~o

F. ___ 662 680 898 '716

370

338~ 420

430

27O 28O ~0

5'72 ~L 590 6O8 i;211 644 ..... at

752 7'70 788 806 824

288 i m 293 299 MO MO 304 310

842 860 878

316 321 327 332 338

6OO 610 62O 63O 640

343 349 354 360 366

eSO ~ 1 2 0 2 1220 NO 670 1 2 3 8 68O 1256 800 1274

371

70O ~1292 710 1310 720 1328 730 1 3 4 6 740 1864

896

914

482 "~: 500 518 538 554

24o

149 3 0 0 154 310 160 320 lee 33O 171 34O

243 249 254

491 Co 750 ,,, I C . or F. C. F. '" ' " _.. 5OO 932 260 268 95O S10 968 $20 271 53O 986 54O 1004

i!

I

C. or F.

172.4 174.2 176.0

77

79 SO

33.3 33.9 34.4 35.0

167.0

F.

78

!i

.J

C. or I;'.

i..8

152.8 154.4 156.2 156.0

161.6 163.4 165.2

. . . . .

71

15o8 " ~ 2 8

~7

It:

24.4 25.0 25.8 26.1 26.7

28.8

143.6 145.41 147.2 149.0

::

C. ii

is,

-107 -I01 - 95.~ 90.0

,

F.

C. ,!

341 to 490

I01 to 340

! ~.

5~ 57 58 59

o..

-15.0

C . or iF. S1

27 28 29 30

37.4 39.2 41.0

9 .i,

I!

10.8 80.6 ! I I . I 82.4 91.7 84.2 12.2 86.0 i 12.8

- 2.78 - 2.22 - 1.67 - 1.11

35.6

3 4 S

'76 to I00

51 to 75

t:

137'7 382

388

393 J

" 399

INTERPOLATION

aT he numbers in boldface type refer to the temperature either in (le~.rees Centigrade or Fahrenheit. If converting from de~ees Fahrenheit to ~legrees'Cenfigrade the equlvalent tem perat, re will be found in the left column, while if converting from de~rees Centigrade to degrees Fahrenheit, the answer will be'J'ound in the column on the right.

~

1040 1058 1078 1094 1112 1130 1148 1166

I 1184

780 L 1882

FACTOP~q

9 - ~ (*C) + 32 5

"C = w (~ --

32)

J

1.II2

] l

1.67 ~2Z

z.7s

3 ~

s

3.6 J 3.89

7

12.~

5.4 J 4.44 5.09

8 S

i4.4 16.2

9.0 I 5.56

]0

___I

18.0 o

~ -40

0

32

98.6

140

80 J 120

i,l,l,l,l,l,l,i,l,l,i,i,l I" I ' I I f '

~

-40

-20

0

20

I' 40

160 ! ' 60

80

212 200

1

240

l,i ' I'l'l I00

280

i,lll 120

140

320

~

:3 < /'I) "5 .m., O :3

'1 160

~

O r

1040 Reinforced Plastics Handbook Table 11.6 Surface area and volume

Surface area Triangle Right angled triangle

Equilateral triangle

Trapezium

..~c

a/ h~

Volume

!bxh 2

lbxc 2 la2.~/4

d

1 (b + d) x h

b

bxh

Parallelogram

b,~. axh

Rhomb

Rectangle

Square

Circle Sector

.a

al ~ ia ~~~ !a

O

<~r

=2r

axb

/l:r2 / l ~ d 2 4 OC

36"0 x xr 2

!~xaxb 4 Ellipse 6a 2

a2

2~rh + 2~r 2

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1042 Reinforced Plastics Handbook Table 11.7 Continued * The number of grams per cubic centimeter is the same as the specific gravity. For example, if the specific gravity is 1.47, that substance has a density of 1.47 gms/cm 3 Factor used in converting to ounces per cubic inch = specific gravity multiplied by 0.5778 Factor used in converting to grams per cubic inch = specific gravity multiplied by 16.387 To compute: Specific gravity - multiply pounds per cubic foot by .01604 Pounds per cubic foot - multiply specific gravity by 62.4 Pounds per cubic inch - multiply specific gravity by .0361 One ounce equals 28.3495 gms One gram equals 0.3527 93 oz

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Bibliography

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1046 Reinforced Plastics Handbook ISO Standards Handbook-Statistical Methods for Quality Control, 4th edn., ASTM, 1995. Jaguar Adopts Long Fiber Technology, RP, May 2003. Keates, J., Designing it Right the First Time, 1M, Feb. 2001. Kent, R., Cost management in processing, Rapra, 2002. Kutz, M., Handbook of Materials Selection, Wiley, 2002. Lauzon, M., Wood-fiber Uses Moving Beyond Decking, PN, Jun. 10, 2002. Lubin, G., Handbook of Composites, VNR, 1982. Lubin, G. and D. V. Rosato, Application of Reinforced Plastics, 4h International RP Conference, British Plastics Federation, London, UK. Nov. 25-27. 1964. MacNeil, R., The U.S. Composites Market: 2003 and Beyond, Composite Fabrication, Jan. 2003. Mamzic, C. L., Statistical Process Control, ISA, 1995. Mapleston, P., Compounds are Conductive or Not as Necessary, MP, Mar. 2003. Mapleston, P., New Rigid-Rod Polymer Jumps to Market, MP, Nov. 2003. Mapleston, P., Plastics are Primed for Big Push in Auto Exteriors, MP, Jul. 2002. Market Data Book, PN, Dec. 30, Annual. Marsh, G., Big, Bold Boating, RP, Oct. 2003. Marsh, G., Composite Cutting Considerations, RP, Nov. 2002. Marsh, G., Filling the Front-Line Training Gap, RP, Apr. 2002. Marsh, G., Flying High with the Self-Build Movement, RP, Jan. 2002. Marsh, G., Laminators Take Cover, RP, Oct. 2003. Marsh, G., MACT: A More Restrictive World for Boat Builders, RP, Jan. 2002. Marsh, G., Material Trends for FRP Boats, RP, Oct. 2003. Marsh, G., Wright Brothers Legacy Flying High; Composites and Aircraft, Reinforced Plastics, Apr. 2003. Materials Data, PE, Apr. 2002. McConnell, V. P., Composites and the Fuel Cell Revolution, RP, Jan. 2002. McConnell, W. K., Ten Fundamentals of Thermoforming, SPE, 2002. Miel, R., Composites' Fans Try To Curb Costs, PN, Jan. 26, 2004. Miel, R., Splashy New Corvette Still Supporting Plastics, PN, Jan. 12, 2004. Moalli, J., Plastics Failure: Analysis and Prevention, PDL, 2001. Moore, S., Innovative Reactive Extrusion Technologies bring Added Value to Recycled Plastics, MP, Jan. 2000. Moore, S., Stereolithography Advances with Desktop System-Performance Resins, MP, June 2003. Mordfin, L., Handbook of Reference Data for Nondestructive Testing, ASTM, 2002. Murphy, J., Additives for Plastics Handbook, 2nd Edition, Elsevier, 2003. Murphy, J., Reinforced Plastics Handbook, 2nd Edition, Elsevier Advanced Technology, 1998. Naitove, M., Editorial, PRT, Dec. 2003. New Generation DMA (dynamic mechanical analysis), PE, June 2003.

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Index

abaca fiber 81 ablation cold wall heats 601 definition 606 energy exchange 597 liquid propellant systems 607 mechanisms 606 processes, chemical propulsion systems 604-6 ablative efficiency, gas enthalpies 601 ablative materials 596-9 carbon fabric RP composites 601-2 comparative performances 599 properties 599 ablative plastics limitations 607 solid propellant systems 611 ablators ceramic-base 598 elastomeric-base 598 metal-base 598-9 plastic-base 597-8 specialty purpose 611 abrasion resistance 840 additives 168 abrasive paper 459 accelerators 265,269 acceptable risks 761 acetals 117 acousto-ultrasonic (AU) techniques 497-8 acrylic fiber 81 acrylic resins, data sheets 940 acrylonitrile-butadiene-styrene (ABS) 124-6, 159,844, 969, 1003

acrylonitrile-styrene-acrylate copolymer (ASA) 123 additives 22, 161-9,249-50, 831-41 abrasion resistance 168 chemistry of 836 classification 161-2,249-50 current lines of development 169 effects on properties 170 elastomeric 839 electrical conductivity 840 flame retardancy 138,167-8,839 incorporation 165,837 machinability 168 multifunctional 840-1 overview 161-3 particulate 164, 831 properties influenced by 165-8,837 proprietary 169 selection of 168-9, 837 self-lubricating properties 168,840 special 161 specialist industry 164 stabilizing 166 storage and handling 164, 836 symbols 829 types and functions 163-5 wetting and dispersibility 186 see also specific types adhesion, intermolecular attraction forces of 693 adhesive bonding 461-4, 738 adhesively bonded resistance strain gauges 866 adhesives 461-4, 577 selection 464-5

1052 Index adhesives c o n t i n u e d solventless 463 two-part 463 Advanced Materials Intelligent Processing Centre (AMIPC) 336-7 advanced RP (ARP) 104 advanced stitching machine (ASM) 579-80 Advantex-glass 47 aerospace applications 12, 380, 564-612, 1023 airframe production 565 chemical parameters 596 entry environmental effects 600 entry simulations tests 599 examples of RP 566 mechanical parameters 594-6 reentry heating problem 594 supersonic aircraft 594 thermal protection systems 596 see also aircraft and specific applications aerospace components 339, 478 aerospace construction 302 aerospace manufacturing, RTM 318 A-glass 44 air intake manifold 523 aircraft 564-84, 1023, 1031-2 all-plastic 586-8 business aircraft 580, 582-3 compression panel weights of different materials 567 examples (1934-2003) 587-92 fighter aircraft 568 innovations 577 interiors 234 rain erosion 694-5 RP applications 569 specific tensile strength (strength/specific gravity) of different materials 567 see also aerospace applications alkyds 154 all-plastic airplanes 586-92 alloying 158-69 allyls 154 alumina trihydrate (ATH) 163,226 alumina-silica fiber 81 aluminum modulus of elasticity 1033 properties 900 specific properties 901 stamping 911

tensile properties 899 tensile strength 1033 aluminum coated oriented glass fibers 66 aluminum oxide production paper 459 aluminum trihydrate 216 AMB-21 156 AME marine resins 145 American Bureau of Shipping 56 American National Standards Institute (ANSI) 871, 1018 American Society for Testing for Materials (ASTM) 869-70, 872 see also ASTM amorphous polymer 205 amorphous reinforcements 160 amorphous thermoplastics 113-14, 399 change in volume with temperature 208 processing temperature 196 anisotropic materials, design 701-3 anisotropic properties 700-1 anisotropy 7 7 0 annealing 456 antennae 575 modules 525-6 antimony oxides 163 antimony trioxides 163 apparent density 199 aramid fiber 68-71,550 aramid fiber reinforced plastic (AFRP) 7 damage propagation 891 aramid fiber/thermoplastic RPs 69 ARGON facility 584 Aroguard LSO 145 aromatic polyamide 552 Aropol resins 145 Arvin/Meritor Commercial Vehicle Systems WorldWide Supension Systems 724 asbestos fibers 58 aspect ratio 37 assembly 453-70 flexibility 923 ASTM D 955 917 ASTM D 3039 496-7 ASTM D 4000 827-30, 870 cell table 829 classification of plastics 828 data developed based on 830 atmospheric flights 593-602 autoclave curing, VARTM 317-19

Index 1053 autoclave moldings 292 autoclave molds 429 autoclave press claves 293 automation 368, 1030 pattern construction 428 automotive applications 12, 302,319, 321,333-4, 455,468-9, 502, 513-28 Corvette models 723 miscellaneous parts 523-8 Bag Molding Hinterspritzen 300 bag moldings 287-9, 393 advantages 289 core materials 289 disadvantages 289 equipment required 289 see also vacuum bag moldings ballistic yarn SK66 524 Banbury mixer 246 bars 704-9 basket weave 105-6 bathtubs 490 batt 98 batteries 521-3 beams 789-95 bending 789, 791-2 cantilever 789-90 deflection 791 design 791 equations 641 maximum stress 792 neutral axis 790, 793,801 neutral surface 789 rectangular section 791 stiffness factor 793-4 stresses in 790 bearings, friction charactistics 694 Bell/Boeing V22 Osprey flit-rotor aircraft 580 bending moment 790-2 bending moment deflection 744 bending stiffness factor 743 bending stresses 716, 792-4 benzoyl peroxides 267 bias 98 bias weave 106 biaxial TPs 214 biaxially oriented PTFE sheeting unreinforced and reinforced, tensile properties of 891

bidirectional deformable pattern weave 106 bidirectional patterns 711 bimax biaxials 82 binder lubrication 212 binder/sizing coupling agent treatments 212 biorefinery 1004 bipolar plate materials 1029-30 bismaleimides 154-5 bladder molding with RRTM 314-15 blow molding (BM) 52, 361-4, 912 complex products 362 blowing agents 364 BMW 3-Series 517 BMW 8-Series 517 boatbuilding 293,321-2,324-5,544-54 material trends 551-4 Boeing 210 F/A-18 ElF Super Hornet aircraft 582 Boeing aircraft 568-71,575-6, 579, 582, 591, 1031 bonded fibers 98 bonding, secondary operations 533 book-opening (or tilting) press 278 boron fiber reinforced plastice (BFRP) 7 boron fibers 77 boron/graphite prepreg 57 box winding machine 378 braids 98 branching 205 breather/bleed fabric 291 breather cloth 105 brick masonry, properties 900 bridge construction 487, 490, 1031 broad good fiber 98 buckling analysis 780 buckling load 506 building and construction industry 485-502 bulk molding compounds (BMC) 165, 184-6, 213-16, 282, 514, 560, 770 compression molding 2 7 5 - 7 thermoplastics 242-3,245 thermosets 238-42 basic production system 241 variations 241 bumpers 518-20 burlap 99 buses 528-9 business aircraft 580, 582-3

1054 Index CAAAs (clean air act amendments) 145 Cadillac ZLR sports car 526 Cadwind program for filament winding 756 calcium carbonate 247 calender, development 396 calender lines, variations in 396 calendering 395-6 configuration of rolls 396 crossing the rolls 397 crowned rolls 397 roll bending 397 camper 516 canoes 550, 552 cantilever beam flexural test 672 cantilever springs 725-6 canvas 99 carbon/aramid hybrid/epoxy RPs 74 carbon fabric RP composites, ablative materials 601-2 carbon fabric/thermoset resin RPs 79 carbon fabrics 553 carbon fiber 71-7, 552-4, 1028, 1031 examples 70 new generation 75 stabilization 83 carbon fiber/epoxy, fatigue 676 carbon fiber/epoxy honeycomb fuselage 581 carbon fiber nonwovens, nickel-coated 66 carbon fiber/nylon RP, wheels 526 carbon fiber prepreg for wind blades 555 carbon fiber reinforced composites, creep data 681 carbon fiber reinforced plastic (CFRP) 7, 515 carbon nanotubes 66, 1027-8 cast iron, properties 900 casting 259, 368 production 479 catalysts, types 197 catamarans 550 cellular core, shear stress intensity in 802 cellular manufacturing 368 cellulose 844 cellulose acetate fiber 83 cellulose fibers 63 center of gravity 709 centrifugal fabrication 367 centrifugal moldings 367 ceramic fibers 58

ceramics 598 properties guide 902 C-glass 44 mechanical properties 45 char forming polymers 602 chemical blowing agents (CBAs) 364 chemical characteristics of plastics 197 chemical coupling theory 1025 chemical-handling pump, impeller for 835 chemical processing industry (CPI) 542 chemical properties 902 chemical propulsion systems 602-12 ablation processes 604-6 combustion process 603 reactions and products 605 chemical resistance 841-2 chemistry of plastics 193-203 chemolysis 182 Chevrolet Corvette 12 chop-hoop winding 388 chopped fiber glass 43 chopped glass fiber reinforced phenolics 137-8 chopped strand 39 chopped strand mat (CSM) 102 CIC (continuously impregnated compound) 241 circular windings 711 circumferential winding 710 clamp tooling 378 cleanliness and good housekeeping 478 closed-end cylinder structure 710 closed molding 256,469, 1030 comparison of techniques 908 closed molding fabric 99 closed molding OC FlowTex fabric 99 Cluster Rule 564 CNC-controlled routing machines 459 coach bodies 529 coatings vs. properties 467 coefficient of linear thermal expansion (CLTE) 15 coefficient of thermal expansion 749 parallel glass fiber thermoset RPs 893 COFATE software 875 coil springs 687 cold formings 370-1 cold moldings, comoform 371 cold press moldings 280-1 color 841-3

Index 1055 columns 704-5 end conditions 704-6 formulas 705 long 707 slender 705-6 strength of 705 combustion 21 combustion products 22 commingled glass/thermoplastics filaments 236 properties of 237 commodity plastics 14-16, 109 ductility 15 performances 14-16 shrinkage 16 thermal expansion 15 tolerances 16 toughness 15-16 comoform, cold moldings 371 compatible materials, recycling 178 component design 690 composites material combinations 17 overview 16-23 properties 10, 902 use of term 16-17 Composites Design Analysis (CODA) 755-6 compound constructions 212-53 compounding 158-69, 194 basic principles 248-53 equipment 245 factors for 247-8 materials 214-15 use to change and improve physical and mechanical properties 249 compregs 500 compression mold flash 437 positive 437 semi-positive 437 vent locations 438 compression molding 275-84, 909-10 BMC 275-7 charging tray (loading tray) 278-9 effect of preheating and part depth of phenolic parts 275 press configurations 276 SMC 275-7, 920 compression molds 433-8 manufacture time guide 436

multi-cavity semi-positive 437 compression press 278 compression stamping, glass fiber reinforced thermoplastic sheets 369 compression strength 167 compression stress-strain 672-4 compression stress-strain curves 666, 672 compression stress-strain response 673 compression transfer moldings 280 computer hardware, selection 874 computer-aided assembly (CAA) 757 computer-aided design (CAD) 317, 400, 755-7, 805,873 application 757 benefits of 755 function of 756-7 people role in 758 techniques available 758-60 computer-aided engineering (CAE) 403, 757 computer-aided flow simulation programs 659 computer-aided manufacturing (CAM) 400, 757 computer-aided testing (CAT) 757, 873 computer-controlled automated machines 581 computer-integrated manufacturing (CIM) 757-8 computer software, use in troubleshooting 474 computer software programs 872-6 computerized databases 874 selection via 820 computerized tape laminating machines 478 concentrates 159 concept selection phase 823 concrete limitations 819 properties 900 conditioning procedures of test specimens 861 conductive compounds 993-5 conductive fiber reinforced thermoplastics 67 conductive nonwovens 66 conformal coating 367 consolidations 465-6 constant stress applications 744-5 consumer and other products 561-4

1056 Index contact molding 300-1 air bubbles 300 back-up of equipment and materials for cleaning 301 by hand lay-up 285 by spray-up 294 useful materials and equipment 301 contact pressure molding 300 contaminants in recycled plastic 764 continuous fiber reinforcement, pultrusions 341 continuous laminations 283,342-3 continuous roving 353 control variables 856 conversions 1035-42 Conyplex 293 coordinate system 740 corrosion resistance in subsea environments 251 corrosion resistant applications 11 corrosion resistant products 144 corrosion resistant tanks 536-7 corrosion service environments 20-1 corrosive conditions 21 corrosive materials, tanks for 535 corrugated sheets 492-3 Corvettes 517-18 cost comparison of fibers and mechanical properties 28 cost estimates 1013, 1017 cost factors 1013 cost reduction 20 costing manufacturing products 1013 costing worksheet 1014-15 costs 1012-17 cowoven fabric 99 cowoven weave 106 crack density analyses 497-9 crack-dominated failure mode 638 crack growth behavior 638 crack propagation, schematics of 639 crackle lacquer coating 866 crazing/cracking 660-1,843 creep 210, 675-91 constant stress 683 overview 675-6 stress-strain-time in 204 vs. log time curves 679 creep analysis 209 creep curves 684

creep data carbon-fiber-reinforced composites 681 design 682 glass-fiber-reinforced composites 680-1 creep isochronous stress and isometric stress 852-3 creep performance 683 crimp 99 crosslinked plastics 157 crosslinked polyethylene (XLPE) 357 crosslinking 205 cross-wound molding compound (XMC) 227 crowfoot weave 106 crystalline plastics 199 crystalline reinforcements 160 crystalline thermoplastics 113-14, 399 change in volume with temperature 208 common types 114 melt temperatures 114 processing temperature 196 crystallinity 205 curing autoclave moldings 292 system selection factors 266-7 systems 263-7 TS polyesters 267 TS resins 454 without accelerators 266 curing agents for TS polyester resins 264-6 custom pipe, mechanical properties 788 cut fabric 100 cutting 260 cyclic loading 654 cylinders and ribs 803-4 sandwich 716 cylindrical hulls, stiffener problem 717 cyrogenic fuel tanks 543 damping 653,655-7 debonding, GRPs 688 decoration decision factors based on technique used 933 in-mold 937-9 selection guide 933 deformation 625-30 modes 203 types 202 vs. time behavior 210

Index 1057 de Havilland Dash-8 573 delamination 458 DeLorean DMC- 12 car 514 densified wood 500 design 613-764 accuracy 651 and fabricating processes 256 and performance 12 anisotropic materials 701-3 approaches 14, 613,620-2,626-52 basic approach 1019 basic guide 616-18 constraints 620, 646 control 1011 creep data 682 criteria 211 demands 1012 details 620 detractions 646 documentation 632 engineering analysis 765-6 engineering approach 20,620-2 flow diagrams 621 equations 622 factors influencing 13,652 failure theory 651-2 fatigue data 685-7 feasibility study 628 flexibility 923 flow chart 614 flow patterns 627-33 foundations 634-42 guidelines 824 impact resistance 692 integration 634 lightweight computer case press-molded in nylon 12/carbon fiber 264 load-bearing products 622 material selection 764 metal 771-2 of RP products 385 optimization 630, 745 overview 613-26 preliminary analysis 629 processing methods as function of 926 protection methods 760 recommendations for process selection 927 recycling 180 requirements 1010 sources of data and information 634

stiffness increase 615 stress 762 structural components 640 techniques to increase properties 622-4 technology design development 1019 theories 698 basic 766-8 theory 766 thickness limitations 619-20 thin wall with ribbing to support high edge loading 615 transportation 503-13 updating 1021 use of term 613 verifications (DV) 1011 via Internet 875 viscoelasticity 682 see also experimental stress analysis design analysis 619, 770 anisotropic 702 comparison with metals 650-6 dynamic loadings 690-1 nonlinear 690 plates 804-9 processes 646-51 steps involved 648 desizing process 99 deterioration 22 developments 1023-6 D-glass 44 diallyl isophthalate (DAIP) 154 diallyl phthalate (DAP) 154 dicyclopentadiene (DCPD) 142, 145 dielectric properties 11,854 dies design 421 use of term 420 differential scanning calorimetry (DSC) 495 dimensional properties 902 dimensional tolerances for Classes A, B, and C RP products 915 direct stress 626 directional characteristics 1025 directional load shear strengths 675 directional modulus of pipe 778 directional properties 8-9,696-8 facts and myths 701 orientation terms 698-700 relating to processes 696

1058 Index D-LIFT extruder/injection processes 334-5 Dodge Slingshot 516 Double Flow Technology 299 double-curved shells 19 dough molding compound (DMC) 241 drape 99 drilling 458-9 dry infusion 558 dry winding 391 drying operations 407-8 ductility 380 CPs 15 EPs 15 dynamic loads 13,638 design analysis 690-1 dynamic mechanical properties of plastics vs. temperature 198 dynamic stresses 675-91 E-CR glass 47 effective modulus 744-5 E-glass 28, 44 construction in TS polyesters 213 costs and applications 898 damage propagation 891 electrical properties 46 mechanical properties 45 thermal properties 46 E-glass fiber/TS polyester RPs, properties based on processes 140 eight-harness satin weave 106 elastic constants 1007, 1026-7 elastic deformation 662 elastic fabric 99 elastic flow 202 elastic limit 667-8 elastic recovery molding (ERM) 514 elasticity 843 elastomers, use of term 110 electrical appliances 559-61 electrical components 460 electrical conductivity 168 additives 840 electrical insulation properties 11 electrical properties 20, 843 glass fibers 31 electroformed molds 449 electroformed nickel shell tooling 429 electromagnetic interference (EMI) 132 electronic appliances 559-61

electronic components 460 electronic properties 843 embedded elastic dampening material 586 encapsulations 367-8 energy absorption 606, 691 energy consumption 476-7 energy content of plastics 184 energy saving 477 EnGarde ratio monitoring 463-4 engineering analysis 765-816 overview 765-72 engineering equations 640 engineering materials 18 engineering plastics 14-16, 109-10 ductility 15 performances 14-16 shrinkage 16 thermal expansion 15 tolerances 16 toughness 15-16 engineering systems, boundaries of 636 environmental concerns 1030 environmental conditions 22-3 see also weathering environmental effects 494, 695 environmental management system (EMS) 871 environmental projects 564 epoxies 136-7 RTM 17 epoxy advanced performance laminates 949 epoxy/glass, data sheets 941-2 epoxy novolacs 602 epoxy prepreg tapes, with carbon, glass, or aramid reinforcement 425 epoxy/unidirectional reinforcement, data sheets 943-6 epoxy vinyl esters 151 epoxy/woven reinforcement data sheet 948 flammability/electrical properties 947 equipment variables 856 equivalent flexural modulus 505 ERCOM 184-6 Euler's formula 705-7 European Airbus A320 572 European Airbus A340 339 European Airbus A380 378,578, 1032 European Airbus A400M 578 European fighter aircraft (EF A) 577

Index 1059 exotherm 838 expandable microsphere 54-5 experimental stress analysis 864-7 techniques 865 extenders 159 external shear stresses 814 extruded BM (EBM) 361 extruder design 346 extrusion 36-7, 345-8 fabric count 99 fabric reinforcement 587, 814 fabricating processes 21,254-482 auxiliary equipment 262 commonly used processes 258 cost reduction 262 flow chart 257 high-performance RTPs 263 overview 254-70 processing changes 270 reinforced thermoplastics 263 secondary equipment 262 secondary operations 260-1 shutdown 261-2 startup 261-2 troubleshooting 474 turnkey operations 261-2 world-class manufacturing (WCM) approach 262 see also specific process, materials, and applications fabrics, use of term 97-8 failure see product failure FALLO approach 480-2 fastening 459-61 fatigue 675-91 carbon fiber-epoxy 676 overview 675-6 reinforced plastics 687-9 reinforcements 688 fatigue cracks 686 fatigue curves 686 fatigue data design 685-7 reinforced thermoplastic short glass and carbon fiber compounds 678 reinforcements 6 7 7 fatigue endurance 6 7 7 basic rules 688-9 fatigue properties, high performance 676 fatigue strength 686-7

faults see troubleshooting fences 490-1 ferries 553 fiber areal weight 81 attenuation 81 biconstituent 81 braided/directional 81-2 breakout 82 bridging 82 bristle 82 bundle 82 buttress 82 capillarity action 83 carding 83 characteristics 80-96 content measurement 645 cost 897 cost comparison and mechanical properties 28 decitex 83 denier 83 desizing 84 directional arrangements and property behavior 645 felt 84 fibrillation 84 geometry effect on strengths 769-70 high performance 216 hollow 85 hybrid 85 lay-up directional patterns 648 length 85 linter 85 manufacture 85 mechanical properties 28 new types and forms 1024 one-ended 88 orientation 697 plastic 86 properties 92-3,897, 1032 strength theories 768-9 tenacity 94-5 thermal properties 899 use of term 80-1 fiber bobbin 81 fiber composites, modulus of elasticity 697 fiber count 83 fiber creel 83 fiber crimp 83

1060 Index fiber-directed preforms 40 fiber drawing 84 fiber end 84 fiber finish 84 fiber float 84 fiber flock 84 fiber fuzz 85 fiber kink 85 fiber mat 85 needled 86 fiber mat veil 86 fiber optics 88 fiber pattern 88 fiber pencil 88 fiber pick 88 fiber processing 89 development 89-90 see also specific processes fiber reinforced plastics (FRPs) 93, 1023 strength properties 1007 fiber reinforcement comparison of commonly used fibers 7 cost comparison of fibers and mechanical properties 28 properties of synthetic and naturalinorganic or organic and metallic fibers 26 see also reinforcement and specific types of reinforcement fiber skein 93 fiber sliver 93 fiber spool 94 fiber stress, mass 94 fiber stretch, cold 94 fiber tex 95 fiber tow 95,561-2 fiber tracer 95 fiber turn per inch (Tpi) 95 fiber twist 95 fiber wadding 96 fiber warp 96 field trials 755 filament 96 filament greige 96 filament lay 96 filament shoe 97 filament silver 97 filament strand 97 filament strand end 97 filament strand integrity 97

filament winding 371-95,531,536, 560, 709-18,786 aerospace, hydrospace, and military applications 374 application software 388 applications 388-9 auxiliary process control 388 Cadwind program 756 circumferential wrappings 373 CNC control system 389 collapsible mandrel 389 commercial and industrial applications 373, 380 computerized servo control 387-8 continuous reinforcement 386 cost 381-2 current and future developments 389 density vs. percent glass by weight or volume 379 design limitations 389 early development 385 equipment 385-9 fiber arrangements and property behavior 379 helical 379 high glass content parts 386 high-pressure vessels 386 interlaminar shear 381 limitations 381 low modulus of elasticity 381 mandrel/tooling design 387, 431 matrix components 381 molds 431-3 on-site TP winding 386 performance requirements 375-7 potential applications 385-6 primary classes 387 processing 385-9 products 385-9 racetrack machines 382-3 radius 391 schematic 371 simulation 756 structural details 715-18 system options 388 tape laying 391 technology 528-9 tension 391 terminology 390-5 test 391

Index 1061 filament winding c o n t i n u e d tooling 382 ultimate bearing strengths 381 filament winding machines 385 filament winding tape 391 filament-wound cylinders 717 filament-wound lay up 778 filament-wound pipe 776, 787 weep point 782 fill 101 fill face 101 fillers 1 0 1 , 1 5 9 - 6 1 , 2 5 0 - 1 , 6 2 2 benefits of 159-61 current lines of development 169 effect on gel time 166 effect on nylon 6 / 6 167 effect on thermoplastics 160 powdered mineral 838 properties influenced by 837 properties that may be selectively altered 166 selection 215 shrinkage 168 symbols 829 use in thermoset reinforced plastics 160 use of term 831 vs. unfilled compound cost/property 161 film insert molding (FIM) 441 filters, aggregation 248 filtration 90 fines 175-6 finishing 194, 259,453-70 finite difference analysis (FDA) 622,771 finite element analysis (FEA) 622,640, 657, 690, 744-5,771-2, 805, 1010 finite element programs 504 Fipur-Tec system 357 fire performance of phenolic/glass fiber RP compounds 138-9 fire resistance 21 fire-resistant storage boxes and crates 563 flame resistance 843-4 flame-retardancy 216, 249 additives 138, 167-8,839 flame-retardant functional groups 22 flame-retardant polyesters 144 flammability 21-2, 845 flax fiber 60, 84, 97 flexible bag moldings 283_ flexible knitted reinforcement 39

flexible plunger moldings 282-3 flexible RP compounds 244 flexural creep rate, reinforcement and filler inverse effect 679 flexural fatigue data, woven glass fiber roving/epoxy RPs 6 7 7 flexural modulus 504 flexural strength 167, 672 flexural stress-strains 670-2 float 97 flock 97 flow behavior 202-3 flow-chart for designer to customer 1016 flow rate system 463-4 foam reciprocating injection molding machine 365 foamed reservoir molding (FRM) 366, 514 foaming agents 364 foams 364-7 cell structural phenolic foam 734 high performance thermoplastic cores 736 manufacture 364 polyurethane cores 735 properties of thermoplastic structural foam 733 reinforced plastic 799-803 rigid plastic properties 732 vs. die casting 913 vs. hand lay-up fiberglass 913 vs. injection molding 913 vs. sheet metal 913 vs. sheet molding compound 913 see also structural foams Ford Motor Co. 516 formability 10, 624-5 design approaches 624-5 forming 259 post-finished 260-1 four-harness satin weave 106-7 Fourdrinier machine 101 fracture prevention 638 freeze-thaw durability 494 freeze-thaw environment 495-7 friction 692-4 coefficient of 693-4 definition 692 friction force 693 frictional energy 653 frictional heating effects 696

1062 Index fuel cells 1028-30 basic operating principle 1029 fuel economy 477 furanes 155 furniture 564 fused deposition modeling (FDM) 752 fusible core molding 301 fusible core technology 523 fuzz 97 gas enthalpies, ablative efficiency 601 gasification 182 gasoline RP storage tank 541 gauze weave 107 gear safe bending stress 896 gear tooth form 896 gears, friction charactistics 694 gel coatings 144, 285,297, 427, 469 choice of carrier film 343 Genestar PA9T 121 geodesic isotensoid 392 geodesic ovaloid 392 geometric symmetry 826 geotextile weave 107 Germany, wind-based electricity generation 556 gigg 101 GKN Aerospace Services 581,591 GLARE (GLAss fiber-REinforced aluminum) 578 glass ceramic tiles 563 glass chopper 41 glass cloth 41 glass collet 41 glass fabric, structural deficiency 1023 glass fiber 28-41 aluminum coated oriented 66 bare 42 bilobe 43 binder/sizing coupling agent 43 borate 41 brilliant whiteness 40 bushing 43 characteristics 41-55 cheese 43 classification by properties 33 composition 42 continuous 42-3 devitrification 42 diameter 43 elastic behavior 31

electrical properties 31 forming package 43 high-purity 41 high-strength 40 in TS polyester 4 in-line compounding 34-7 liquidus temperature 50 long fibers 33-4 mechanical properties 30-1 milled 44 modulus of elasticity 1033 overview 28-33 production 31-2, 44, 50 properties 59 short to long fibers influence on properties 30 special reinforcements 38-41 tempered 44 tensile strength 1033 texturizing 44 types 29-30, 42, 44-8 wear 48 glass fiber/epoxy RP leaf spring 721 glass fiber/epoxy spheres 773 glass fiber fabric/TS polyester RPs 849 glass fiber mat RPs 221 glass fiber/nylon 6 / 6 molding compound 332 glass fiber/nylon RP 852 glass fiber/PET RPs 406 glass fiber reinforced composites, creep data 680-1 glass fiber reinforced LCP 115 glass fiber reinforced plastic (GFRP) 7 processes/properties 905 tensile properties 899 glass fiber reinforced thermoplastic sheets, compression stamping 369 glass fiber reinforced thermoplastics (RTP), properties 880-3 glass fiber reinforced thermosets (RTS), properties 880-3 glass fiber rovings traveling through plenum machine 272 traveling through water slurry machine 274 glass fiber slug 44 glass fiber swirl mat/TS polyester RP hand lay up boat shell 288

Index 1063 glass fiber/TS, comparison of mechanical properties with metals 6 glass fiber/TS polyester, properties compared to metals and timber 141 glass fiber/TS polyester reinforced plastic 293,537-42 characteristics and use 140 troubleshooting 472-3 glass filament 48,374 liquid temperature 48 glass filler 48 glass flake 48-9 glass form 49 glass former 49 glass forming package 49 glass marble 50 glass mat thermoplastic (GMT) 164, 214, 231-4, 517, 519,991-2 production 232 properties of long and short 232 stamping 456 SymaLITE 231, 233 glass/polyether imide (PEI) 580 glass/polypropylene, recycled 173 glass reinforced phenolic, recycled 172 glass reinforcement lack of ductility 380 new forms 40-1 glass roving 50-1 glass slug 51 glass spheres 51-5,363 glass strand 55 glass transition temperature 205,207, 399 glass woven cloth 105 Glasshopper I and II rail car tanks 531-5 glassine 101 glazing 576 gout 101 granite gel coat 297 granulators 171-4 graphite-based mineral fiber 63-4 graphite bipolar plates 1029 graphite fabric/thermoset resin RPs 79 graphite fiber 7 5 - 7 graphite fiber reinforced plastic (GFRP) 7, 323 graphite fiber/thermoset and thermoplastic RPs 78 graphite/PEEK prepregs 383 gray fabric 100-1

gripper system design 458 Grumman Hawkeye airplane 573 guide pins 442 hand 101 hand lay-up 285-302, 548 automated-integrated RP vacuum process 286-7 comparative cost study 313 contact molding 285 non-automated process 285 overview 285-7 products 1013, 1015 RTM 313 terminology 285 see also specific methods HAPs (harmful air pollutants) 145-6, 552 hazardous materials, tanks for 535 health and safety 169,761 heat dissipation 687 heat generation 687 heat-resistant column 501-2 heat stabilizers 166 heat transfer fluids 450 heaW metals 179 helical winding 387-8,710 helicopters 581-2, 591-2 hemispherical shells 540 hemp fibers 60 heterogeneous properties 700-1 high density polyethylene (HDPE) 52, 90, 112, 124, 206, 344, 364, 1032 high frequency pre-heating 341 high modulus compound (HMC) 227 high molecular weight glassy polymer 205-6 high performance carbon/PEEK tapes 213 high performance resins, high temperature processing of 428 high performance thermoplastics, unreinforced and reinforced 128-9, 580 high pressure closed mold system 469 high pressure injection molding IMC process (HPIP) 468 high silica fibers 41 high temperature environments 593-4 high temperature performance materials 595 highway tanks 535-6

1064 Index hollow channels 19 hollow sphere 53 holographic interferometry 865 homogeneous properties 700-1 honeycomb core 743 honeycomb core sandwich structure 729 hood assembly 526 Hooke's law 666, 766 hoop stress 383, 772-3,803 hoop winding 387 hopper rail car tanks 530-5 horizontal clamp injection molding equipment 368 hot compaction technology 236-8 hot isotactic pressing (HIP) 398 hot press moldings 282 hot staking 460 house-building 486-9 hull materials, depth limitations 714 hull structures 547-50, 553 design 548,715 stiffening system 716 hulls deep submergence 713 material choice/design considerations 545 humidity fluctuations 754 hybrid construction 550 hybrid fibers 57 hybrid moldings 333 hybrid resins 156-7 hybrid structures 334 hybrid systems 505-6 hybrid vehicles 521 hybridizing ratio 505-7, 513 hydraulic piston-based metering pumps 356 hydrogenation 182 hydrolysis 189 hypervelocity flight 593 hypervelocity vehicles 594 hysteresis effects 653-4 hysteresis heating failure 654 hysteresis level 696 hysteresis loop 654 IDES 876 IDSA 876 ignition-resistant polystyrenes (IRPSs) 125 impact energy 507

impact loading analysis 691-2 impact properties, RPs and URPs based on type of resin 892 impact resistance design 692 determination methods 692 impact strength 167, 846 impeller for chemical-handling pump 835 impregnated fabric 102 incineration 171,182-3 Infrastructure Composites Report 2001 1032 infrastructures 494-9 infusion molding 320-5 prepregs 322 inhibitors 265,269 inhomogeneity 770 initial resisting moment 801 injection blow moldings (IBM) 361-2 injection-compression, mold action during 331 injection-compression moldings (ICM) 330 injection-compression system 319 injection molded glass fiber/TPs, troubleshooting 471 injection molding 36-7, 325-39,433-8, 911-12,920 controls 855-6 criticism of 328 design considerations 438-46 economic comparison 821 economic importance 328 large surface production parts 352 mold layouts, configurations, and actions 432 mold manufacture time guide 436 reinforced thermoplastics 329-30 screw design 328 tooling 330 ZMC 336 injection molding compounds 33 injection molding machines (IMMs) 325-7, 336, 1032 and barrel temperature 417 process controls 400-1 in-mold assembly 334 in-mold coating (IMC) technology 335, 467-8 in-mold decorating systems 937-9 in-mold topcoat, physical properties 468

Index 1065 innovations 1032-3 inorganic fiber 85 Institute of Plastics Processing (IKV) 314 instrument calibration 651 insulating linings 560 Integrated Corn based Bio products Refinery (ICBR) 1004 integrated front and rear trimming and punching line 455 integration of parts 178 interchangeable material grades 820 interfacial shear strength 1024 internal friction 687 internal resisting moment 801 internal shear stresses 814 International Electrotechnical Commission (IEC) 872 International Marine Organization (IMO) 324 International Organization for Standardization 871 Internet design via 875 materials selection via 875 interpenetrating networks (IPNs) 158 intraply hybrid composite beams 506 intumescent graphite fibers 63-4 ISO-9000 870, 1011 ISO-9001 870 ISO-9002 870 ISO-9004 870 ISO-10993 858,870 ISO-14000 871 ISO-14001 871 isochronous data 684 isochronous graphs 684 isochronous stress-strain curve 744 isocyanate 352 isometric graphs 684 isophthalic corrosion-resistant resin 221 isotactic molding system 398 isotactic pressing 398 isotensoid pattern 712 isotropic materials 743 joining 453-70 Joint Strike Fighter (JSF) 577, 581 joints basic types 464

bell-and-spigot 784-5 design 784-5 good and bad configurations 465 load-transfer in 466 just-in-time (JIT) fabricating 262 jute fiber 61-2 isotropic lay-up RP, tensile properties with thermoplastics 62 ketone peroxides 267 Kevlar 550 knit weave 107 knitted fabric 102 knitted textiles 102 laboratory testing 748,754 laminar composites 243 laminated object manufacturing (LaM) 752 laminated wood 500 laminates 2 9 , 2 8 3 - 4 , 4 5 8 effect of thickness on strength 547 high-pressure 283 high-pressure reinforced TS 284 lay-ups 697 low-pressure 283 mechanical properties 546 microsphere-cored 735 properties 283 theory 795 uses 283-4 land locations in split-wedge mold 277 launch vehicles 607 LDF (long discontinuous fiber) technology 35-6 LDPE 112, 124, 1032 leaf springs 523,687, 719-25 automotive 722-5 configuration 720-1 glass fiber-epoxy RP 721 material of construction 720-1 trucks 722-5 LearAvia Lear Fan 2100 twin turbo turboprop airplane 568-9 leisure products 562 leno mock weave 107 leno weave 107 lightweight armor for police cars 524-5 linear coefficient of thermal expansion (LCTE) 215 liquid composite molding (LCM) 317

1066 Index liquid crystal polymers (LCPs) 115,339, 996 glass-reinforced 115 liquid injection molding (LIM) 336, 737 development 336 plastics used 336 liquid injection molding simulation (LIMS) 338 liquid oxygen (LOX) converter 563 liquid propellant systems 606-7 ablation 607 Lite System Ltd (LSL) 749 Liteflex rear suspension R~ spring 723-4 LLDPE 206 Lloyd's Register of Shipping 56 load analysis 639 load-time/viscoelasticity 204 load-transfer between fibers 1024-5 in joints 466 loading history 22 loading rates for different methods of testing 664 Lockheed Martin F-35 aircraft 577 long aligned discontinuous fiber technology 35-6 long fiber injection (LFI) 355 long fiber materials 650 long fiber reinforced compounds 985-90 long fiber technology 355 longitudinal analysis in pipe 783 longitudinal strain in pipe 782-3 longitudinal stress 803 longitudinal tensile load on pipe 783 loss core molding 301 lost-wax molding 301-3 lost-wax process 303 low density reinforced reaction molded polyurethane (LD-RRIM) 354-5 low melting point alloys 750-1 low pressure molding compound (LPMC) 229-30 low pressure SMC 227 low profile SMC 227 low shrink profile 159 low shrink SMC 227 low styrene emission (LSE) resins 145, 149 low temperature milling (LTM) 750 LP/LS-BMC 241 lubricants 694

McDonald-Douglas AV-8B Harrier airplane 569, 571-2 machinability 840 additives 168 machining 424, 456-8 high-speed 750 macromechanics 1027 macroscopic theory of strength 769 MACT (maximum achievable control technology) 145-7, 552 Magnum Ceramics Composites 749 Magnum Venus Products (MVP) 312 mandrels 431,584 Manhattan Project 385 manufacturing analysis 631 manufacturing processes, mechanized 1030 Marco molding 320 Marco processes 303-4 marine industry 428,543-54 see also specific applications markets 483-612 overview 483-5 see also specific markets and products mass (or density) 199-200 masts 547-8 mat 102 mat preforming 274-5 mat reinforcement 353 material behavior 689,826-55 classifications 690 material performance 826-55 material properties guide 902 material properties information and data 827 material selection 817-996 approach targeted to obtain best choice 833 influencing factors 824-6 overview 817-23 summation 876 testing as means of 857-72 variabilities 855-6 via Internet 875 material suppliers, involvement of 819 materials testing 762, 857-72 mathematical models 400 matrix 21, 29 cohesive shear strength 1024 matrix content, effect on strength or elastic moduli 109

Index 1067 matrix materials 10 Maximum Achievable Control Technology (MACT) 145-7, 552 maximum impulse displacement 510 maximum impulse stress 510 Mazak Machine Tools 750 mechanical behavior dynamic/static 689-91 of metals and plastics 649 mechanical bonding 1025 mechanical compounding 158 mechanical energy 653,662 mechanical fabrics 103 mechanical properties 2,637, 902 comparison of glass fiber/thermoset and thermoplastic RPs with metals 6 cost comparison of fibers and 28 custom pipe 788 determination of 744 effect of additives 839 glass fabric/TS polyester RPs 848 laminate constructions 546 pipe 7 8 7 reinforced plastics 820, 1026 role of reinforcement 8 short and long fiber/thermoplastic compounds 30 unidirectional fiber/epoxy RPs 663 unidirectional RPs 27 mechanical strength 167 mechanical testing 496-7, 689 mechanized molding processes 478 Megaject Mark II injection system 310 melamine 155 melamine sheet molding compound 227 melt characteristics 206-7 melt flow analysis 398-9 melt flow behavior 260 Newtonian and non-Newtonian 202 melt flow rates 200 melt index (MI) 200-1 melt orientation 207 melt temperature 206, 399 melt transport 259 melting 259 metal design 771-2 metal fittings 460 metal flake 297 metal inserts 179, 333,459 metallic fiber 86

metals mechanical behavior 771 properties guide 902 methacrylate adhesives 462-3 methylene dianiline (MDA) 156 metric units 1037-8 mica 64 microfibers 88 micromechanics 1026-7 microscopic examination 864 mild steel stress-strain curve 781 tensile properties 899 milled glass fber/polyethylene blow molded water flotation wheels 363 milling machine, five-axis computercontrolled 428 minehunter 549 mineral fibers 63-5 Mining and Chemical Products (MCP) 750 Mirabella V sailing yacht 544, 551 mixing 259, 413-14 basic principles 252 dispersive 252 distributive 252 evaluation 252-3 see also resin transfer molding (RTM); spray-ups MMFG 342 modulus of elasticity 622-3,653,666, 668-70, 801,810, 1023-4 fiber composites 697 vs. specific gravity 1001 modulus of rupture 795 Moire interferometry 866 moisture applications 853-5 moisture contamination 406-8 accumulative effect 407 moisture content limit 408 target level 408 moisture control 408 moisture effect 406 on tensile behavior of reinforced nylon 6 406-7 mold action during injection-compression 331 mold backing plate 438 mold base 438 mold bottom plate 438

1068 Index mold breathing 278 mold cam bar 438 mold cavity 275,438-40 vacuum in 280 mold clearances 448 mold construction, openings 441 mold costs .450-1 output, and life expectancy 820 relative to machined steel molds 925 mold design, RRIM 451-3 mold knife edge 442 mold land 442 mold leader pin and bushing 442 mold life 442 mold locating ring 443 mold locking ring 443 mold maintenance 450-1 mold manifold 443 mold operation controls 402 mold operation sequence 433-4 mold parting line 443 mold pillar support 444 mold pin 444 mold/platen insulations 449-50 mold pressure pad 444 mold quotation guide 435 mold release agent 269-70,469-70 mold runner 444-5 mold side action 445 mold spew groove 445 mold sprue 445 mold stripper-plate 446 mold undercut 446 mold venting 446 mold water channel 446 mold yoke 446 molding cold slug 440 dished 441 double-shot 441 molding area diagram (MAD) 403-5 molding compounds 214, 228,244-53 low pressure 229 see also specific types and applications molding dwell 441 molding flash line 441 molding materials, pre-mixed 256-8 molding pressure 441-2 molding process 116-17 closed 146 economic and design factors 932

molding shrinkage 442 molding volume diagram (MVD) 403-5 molds 418-20 aluminum 421-5 autoclave 429 balanced 438 ceramic matrix 426 cold press 429 complex 434 contact 425-9 epoxy/reinforced 425 filament winding 431-3 function 420 heat-resistant resin 427 importance factors 420 loose punch 443 low-cost 425 low-pressure 429,431 matched male and female 281 materials 421 plastic 423 pre-engineered 444 prototype 7 4 7 reinforced with external ribbing 427 single impression 445 split 428 split ring 445 stack 445 standard parts 448 steel 421 temperature controls 447 three-plate 445-6 use of term 418-20 uses 420 zinc alloy 425 molecular structure 22 property and processes 199-222 molecular weight (MW) 199-200, 205 molecular weight distribution (MWD) 199-200, 205 narrow and wide 200 moment of inertia 622-3,653,706, 742, 792 monofilament 96 monomers 193 morphology 197 Mother Project 1032 moving wedge technique 337 multifilament 96 multi-jet modeling (MJM) 752

Index 1069 nanocomposites 1028 nanofibers 1028 nanotechnology 1027-8 naphtha, waste conversion to 182 naps 103 National Composite Center (NCC) 722, 724 National Petroleum New Survey 542 natural fibers 59-63 natural resins 158 NEAT plastic 495 NEAT polymer 110, 671 nesting 103 netting analyses 710-13 nickel-coated carbon fiber nonwovens 66 nickel shells 425 Nissan Fairlady Z 516 nodular molding compound (NMC) 242 nondestructive evaluation (NDE) 861-4 defects detected by 861-3 selection of method(s) 863 nondestructive testing (NDT) 497-8, 859-61, 1010 defects detected by 862 nonfibrous reinforcements 244 non-rectangular sections 19 non-screw plasticating 259 nonwoven constructions 37-8 nonwoven fabrics 28-9 nonwoven flash-spuns 103-4 nonwoven mechanicals 104 nonwoven melt-blown fibers 104 nonwoven processing 103 nonwoven spun-bonded fabrics 104 nonwoven spun fabrics 104 nonwoven surfacing veils 87 nonwoven tissues 66 nonwovens, conductive 66 nylon 6 834, 971 nylon 6 / 6 120, 834 long glass fiber reinforced 33-4 reinforced with glass fiber 33 nylon 6/12 120 nylon 11 120 long fiber reinforced 34 nylon 12 120 long fiber reinforced 34 nylon 12/carbon fiber design study 264 nylon 66 972 modulus of elasticity 1033 tensile strength 1033

nylon fibers 55 nylons 117-21,344, 985-6, 1032 effect of fillers on 167 mineral reinforced 973 semi-aromatic high-temperature 121 oblate spheres 380 oblated spheroid design structure 712 OC fabric 100-1 odor/taste 846 oil sump covers 524 oilfield applications 542 open molding 300, 909 operating costs 477 optical extensometry 867 optically transparent plastics 576 optimization process 635-6 optimization theory 635-6 organic matrix 597 organic peroxides 268 organosilanes 1025-6 orientation reinforcement 701 terminology 698-700 orthotropic material 811,813, 815 ovaloid netting system 711 overheating, elimination 174 overlay mats 66 overmoldings 331-4 Owens Coming Fiberglas Corp. 1013 package design 842 painting 466-70 painting decorating system guide 934-6 pallets 501 panels, properties of 807-8 paper industry 564 parallel glass fiber thermoset RPs, coefficients of thermal expansion 893 paratertiary butylcatehol 265 particle recycling, regrind fractions in 187 pedal clusters 524 PEM (polymer electrolyte membrane) fuel cell 1029 perforated release films 291 performance boundary 636 performance prediction 637, 1010 performance requirements 636, 643-4 permeability properties 846-7 personal watercraft (PWC) 293 PETI-5 156

1070 Index petroleum products from waste plastic 182 petroleum storage tank 538 phenolic general performance laminates 95O phenolic/glass fiber RP compounds, fire performance of 138-9 phenolic molding scrap 186 phenolics 137-9 chopped glass fiber reinforced 137-8 reinforced plastics 581 RTM 316 special laminates 951-2 photoelastic stress analysis 865-6 phthalic laminating resin 221 physical blowing agents (PBAs) 364 physical characteristics of plastics 197 physical properties 2,637, 902 pick count weave 107-8 pigments/printing inks 179 pipe 775-89 commodity 785-6, 788-9 compared to steel pipes 776 corrosion liner 788 custom-engineered 786-9 deflection 779 directional modulus 778 flexible plastic 777 laminate 787-8 longitudinal analysis 783 longitudinal strain in 782-3 longitudinal tensile load 783 mechanical properties 787 minimum structural wall thickness 784 reinforced plastic 776-85 rib-wall 779 rigid 777 rigid concrete 777 ring joint 787 stiffeners 788 stiffness 779 strength in longitudinal and hoop directions 780 thermoplastic 775-6 underwater installations 779 wall thickness determination 775 see also filament-wound pipe plain weave 108 plant layouts 478 plant upgrading 477-80 PLASPEC 876

plastic fiber 86 plastic lumber 499-501 plastic-metal hybrids 333 plasticator barrel 410,414 barrel heating and cooling method 415-17 barrel temperature control 415 liquid-cooled barrels 416 melting operation 409-18 screw 409-13 compression ratio (C/R) 412 deep-channel 412-13 design 411,413 feed zone 410 flights 411 flow pattern in flights 413 helix angle 411 length 411-12 metering zone 410 nomenclature 409 primary purpose 411 production rate 413 speed, pitch, diameter, and depth of channels 412 transition/melting zone 410-12 wear 414 wear-resistant barrel 414-15 plastics chemical characteristics 197 classification 109, 827 definitions 112 family(ies) 109-211 future 1001 growth rate 1022 output statistics by volume 999 output statistics by weight 999 overview 997-1004 physical characteristics 197 properties developments 1000 properties guide 902 selection procedures 817-996 overview 817-23 statistics 997 strength vs. temperature 2 symbols 828 use of term 110, 113 plastics industry competitive disadvantage 484 consolidation 1000 future 1030-3

Index 1071 plastics industry c o n t i n u e d global business fortunes 1002-3 growth 483 guide 998 multinationals 1002 new materials 1000 overview 195 statistics 483-5 worldwide 998 Plastics Network from Commerx, Inc. 875 plate glass, properties 900 plates 804-9 design analysis 804-9 hybrid 814-16 isotropic 809 non-isotropic 809-14 stress and deflection engineering formulas 806 plenum machine, glass fiber rovings traveling through 272 PMR-15 156 Poisson's effect 782 Poisson's ratio 657-8,782, 807, 810-12 polar machines 387 polar moment of inertia 708-9 polar winding 393 police cars, lightweight armor for 524-5 polyacetal (POM) 117, 970, 986 polyacrylonitrile (PAN) 1028 polyamide see nylon(s) polyarylates (PARs) 121 polyaryletherketones (PAEKs) 130 polybenzimadazole fiber 88 polybutylene terephthalate (PBT) 122-3 polycarbonates (PCs) 121-2,974, 989 polychlorofluorocarbons 364-5 polyester fibers 55-6 polyester molding compounds 239-40 polyester/glass, laminates 958 polyesters 987 basic properties 953-4 BMCs 960 BMCs- special grades 959,961 flame-retardant 144 formulated 955-7 PBT 975 PET 976 shrinkage during curing 215 SMCs 962-3 SMCs - special grades 964-5

thermoplastic 122-3 thermosets 137-48,244, 430 chemical-resistant/corrosion-resistant 143-4 curing agents for 264-6 curing systems for 267 prepreg sheets 286-7 sheets, prepregs 286-7 standard 142-3 with different amounts of glass fiber 4 with different forms of glass fibers 143 polyether compounds 977 polyether ketones/aramid 978 polyether ketones/carbon 979 polyether sulphone (PES) 132-3 polyetheramides (PEAR) 155 polyetheretherketone (PEEK) 35, 130, 251 polyetheretherketoneketone (PEEKK) 130 polyetherimides (PEIs) 127 polyetherketone (PEK) 130 polyetherketonetherketone-ketone (PEKEKK) 130 polyethylene fibers 56-7 polyethylene terephthalate (PET) 88, 122, 344, 515 polyethylenes 109, 123-4, 1032 crosslinked 157 modulus of elasticity 1033 tensile strength 1033 polyimide powders 152 polyimides 127-30, 151-2 processing 397 polyketones (PK) 130 polymerization 193 polymerization reactor 1003 polymers definition 194 structure 205-6 use of term 110, 196 polymethyl methacrylate (PMMA) 515 polyol 352 polyphenylene 131,980-1 polyphenylene ether (PPE) 131 polyphenylene oxide (PPO) 131 polyphenylene sulfide (PPS) 131-2, 344, 835,989 polypropylene (PP) 34, 109, 112, 124-5, 206, 344, 982,988, 1032 compounds 65

1072 Index polypropylene (PP) c o n t i n u e d effect of reinforcement 64 fiber reinforcement 40 fibers 91 glass mat thermoplastics (GMT) 517 modulus of elasticity 1033 NEAT and filled flexural modulus of elasticity 110 reinforced, recycled 172 tensile properties 899 tensile strength 1033 polystyrene (PS) 110, 112, 125,983 polysulphones (PSU) 132-3,984 polytetrafluoroethylene (PTFE) 537 polyureas 152 polyurethane (PU/PUR) 152-3, 189 board 749 foam cores 735 foaming processes 365 reaction injection molding 912 recycling 188 reinforced 152-3,966 RIM process 351 RRIM 352-7 thermoplastic 345 waste 186 polyvinyl chloride (PVC) 109, 112, 126, 146, 836 post-consumer plastics (PCPs), recycling 192-3 post-curing 265 post-finished forming methods 260-1 post-finishing 469 pot life 838 and exotherm 166 powder impregnations 234-5 powder metallurgy 397-8 powerboat hull 547 preform processes 271-5 direct 272-3 RTM 311,318 spraying two molds 273 preform screens 273 preimpregnated material 525 premold coating 469 prepregs 213,216-21,393,558 advantages over resin wet lay-up fabrication 217 applications 220 basic production system 220 curing 220

graphite/PEEK 383 guideline properties 219 high performance epoxy 221 infusion molding 322 properties and applications 218 structural applications 220-1 techniques for locating and orienting 216-17 TS polyester sheets 286-7 unidirectional 214 uses 216 winding 386 press molding 459-60 pressure-feed dispensing roller machines 299 pressure hull structures 713-18 pressure vessels 712-13 stresses acting on wall 815 printed circuit boards (PCBs) 560 manufacture and ecological impact 249 problem solving 1020 process controls 399-406 injection molding machines (IMMs) 400-1 parameter changes 406 setting 405 process development 1032 process evaluation 825 process limitations 922 process selection 817-996 based on product size 924 design recommendations 927 guide 903 influencing factors 824-6 overview 817-23 summation 876 variabilities 855-6 processing 19, 194 processing equipment, safety requirements 1018 processing methods as function of part design 928-31 processing temperature 255,260 processing window 403-6 product design see design product development 823, 1011, 1031-2 product dimensions from stress analysis 638 product failure 634 analysis 638,868 characterization 650

Index 1073 product failure c o n t i n u e d criterion 651-2 hypotheses 744 modes 651-2 types 744 product information 757 product liabilities 652 product performance requirements 12 product release 633 product requirements 9, 18,824 worktable format related to 832 product size limitation 826 vs. process 255 product testing 762 products 483-612 miscellaneous 485 overview 483-5 see also specific markets and products profiled sheet line 342-3 profitability 1005-7 1,3-propanediol (PDO) 1004 prototyping 703,745-55 choice of technique 747 current methods 751 economic compromise 748 factors affecting process selection 746 need for 745-6 products 746-8 rapid 749, 752 techniques 748-54 test conditions 763 testing and evaluation 640, 754-5 3-D model 746 variable cooling rate 747-8 public transport 528-9 pulsed melts 348 pulsed moldings 338-9 pultrusion process 39, 340-4 advanced technology 341-2 applications 341,344 continuous fiber reinforcement 341 equipment 341 heavy-duty sheet 343 materials 496-7 profiles 560 schematic examples 340 TPs 343-4 pultrusion simulation modeling (PSM) service 344

purging 417 compounds 417 material 417 purging agents 417-18 Pushtrusion direct inline process 36 Pushtrusion/injection processes 335 Pushtrusion technology 347-8 pyrolysis 182, 189 QBT technology 36 Quadrant Plastics Composites (QPC) 232 quality control 478,858 quartz fibers 41, 80 quartz filaments 80 racetrack winders 388 radiation resistance 847-9 radio frequency interference (RFI) 132 radius of gyration 704, 706 radome 571,574-5 railroad ties, recycling 190-2 railway carriage interior components, RTM 320 rain erosion 694-6 ramie fiber 62, 93 Raptor Sportjet 293 raw materials 1004 rayon fiber 93 rayon viscose fiber 93 R&D 635, 1004, 1018, 1021 RDF processing 183 R-D-O-C-SMC 227 reaction injection molding (RIM) 189, 336, 350-1 infusion technology 351 melt flow 453 mold configuration 452 mold gating and runner systems 453 polyurethane processes 351 ready made/resin impregnated resins 836 recreation products 562 recycling 171-93 analyzing materials 174-6 as energy 181, 183 as feedstock or fuel 180-1 as new plastics materials 180 checklist 176-9 chemical 181-2, 189 commingled plastics 192 compatible materials 178 definitions 192-3

1 0 7 4 Index recycling continued design for easy dismantling 180 economics 179, 181 identification/sorting of materials 179 life-cycle analysis 171 mechanical 181 more than once 174 overview 171-4 polyurethane 188 post-consumer plastics (PCPs) 192-3 problem materials 179 railroad ties 190-2 reinforced polypropylene resin 172 reinforced thermoplastics 189-90 RTS parts 184 technologies 180-4 value analysis 193 refuse-derived fuel (RDF) 183 regrind fractions in particle recycling 187 regrind/powdering 188 reground laminate 297 regulations 857 reinforced plastic molding compound 164 reinforced plastic moldings, finishing 454 reinforced plastics advanced 1008-9 advantages 18-23 businesses 1023 characterization 8, 1005 conventional 1006 development world wide 5 filled systems 1014 growth rate 1022 implementations 565 interface aspects 1026 limitations 18-23 materials properties/processes 906-7 mechanical properties 1026 new developments 1034 overview 1-14 performances 18 processes and materials, properties and costs 921 properties and processes overview 904 properties based on type and amount of reinforcement 644 specific properties 901 success factors 1018-19 unfilled systems 1014 use of term 5, 17-18

vs. processes, limits and tolerances 918-19 reinforced reaction injection molding (RIM) 186, 189,911 cycle times 351 large surface production parts 352 mold design 451-3 TS polyurethane (PUR) 352-7 reinforced reaction injection molding (RRIM) 152-3, 350-1 reinforced resin transfer molding (RRTM) 304-20 bladder molding with 314-15 description of system 305 mold used for 305 reinforced rotational molding (RRM) 357 reinforced thermoplastics 110, 339, 527, 836 applications 190-2 characterization 8 property guide 877-9 ready made/resin impregnated resins 836 recycling 189-90 trade-offs 884-5 reinforced thermosets 110, 165,184-9, 836 characterization 8 reinforcement 24-108,251,622 adhesive bond 31 construction types 31 fabrics 217 fatigue data 677 forms 65-6, 97-108, 212 high performance 68-80 materials 10 new technology 1003 orientation 701 overview 5, 24-8 patterns 270-5 positioning 697 properties based on type and amount of 644 role of 24-5 in mechanical properties 8 symbols 829 three-dimensional 65 types 24, 251 relative weights vs. equal tensile strength for materials 8 repairs 475-6

Index 1075 residual stresses 675 resin, use of term 110 resin/glass spoilers 319 resin infusion under flexible tooling (RIFT) 320 resin injection gun 312 resin injection molding (RIM) 60 resin lamination 300-1 resin transfer molding (RTM) 39-40, 56, 100, 155,303-20, 4 2 9 , 4 7 9 , 9 0 9 , 9 1 1 , 1030 advanced (AdvRTM) 315-16 aerospace manufacturing 318 automation 311-13 case histories 319-20 cleaning 310 comparative cost study 313 computer simulation 756 dielectric measurements 313 epoxies 317 equipment 307 equipment selection chart 308 feeding 310 hand lay-up 313 improved process controls 309-10 improvement of resin flow and injection 309 mechanical properties of reinforced plastics (railway carriage seat shells) 316 melt resin filling monitoring 313-14 mixing technologies 307-8 monitoring and alarm systems 310 phenolics 316 preforms 311, 318 railway carriage interior components 216, 320 tooling 319 vacuum-assisted see VARTM return on investments (ROIs) 823 R-glass 47 rheology 201-3 ribbon mixer 246 ribs 795-9 and cylinders 803-4 applied to plate 800 design analysis 796 design guidelines 799 design strength wise and weight wise 796 engineered proportions/locations 799

over designing 799 reinforced plastics 799 shear force on 802 stiffening 540, 620 structural shapes 798 ways of using 7 9 7 rigid inflatable boats (RIBs) 552 rigidity 653 ring-stiffened cylinder 716, 718 Road Information Program (TRIP) 1031 robots 328,456-8,462 rocker covers 524 rocket motors launching 611-12 materials of construction 608-12 materials requirements 609-10 tanks 543 rocking oven machine 360 roofs 491-4 design 613-15 gabled 615 room-temperature applications 22 rotary molding 442 rotational moldings (RM) 357-61,912 basic stations 358 large tank 360 recreational products 359 rock 'n' roll machines 360 Rotospeed rocking oven machine 360 rovings 801 terminology 393-5 safety 1017-18 safety factors 761-4, 1007 conditions affecting 761-2 guide for 763 range of values 762 setting up 763 safety information and standards 1018 safety requirements, processing equipment 1018 safety rules and regulations 1018 safety seat 517 sandwich structures 540, 544, 729-44 asymmetrical 743 balsa core materials 734 buckling modes 739 bucklings 738-40 comparative material and laminating costs 7 3 7 core properties and cost 731

1076 Index sandwich structures continued cylinder 716 design approaches 730-7 fabricating processes 731 load and support conditions 738 local buckling 739 local crippling 739 materials analysis 738 monocoque aircraft wing 588 monocoque fuselage structure 587-8 optimization 737-8 overview 729-30 performance 743 primary function of core 731 primary function of face sheets 731 RP-faced 739 stiffnesses 738-40 transverse loading 744 see also foams satin finish 97 satin weave 108 Scorim process 338-9, 348 scrap handling and granulating 174-6 scrap reduction 178 screw transfer 281 scrim 104 SCRIMP process 39, 320-1,323-5, 528 sealing 260 search vehicle 714 secant modulus 669 secondary operations 533,923 section modulus 792 Seemen Composites Resin Infusion Manufacturing Process (SCRIMP) see SCRIMP process selective laser sintering (SLS) 751 self-healing RPs 1032 self-heating 755 self-lubricating properties, additives 168, 84O self-reinforcing polymers (SRPs) 116 selvedge 105 semiconductors 66 sensitivity analysis 512 service life, factors influencing 20-1 service testing 755 serviceability limits 21 sewing 260 S-glass 28, 47 mechanical properties 45

shape and shaping 9, 11, 19,259,703 dimensional tolerances 703 shear modulus 674, 743, 810 shear strength 1024 shear stress 626, 716, 792-4, 802 formulas 665 shear stress intensity 802 adjacent to rib 803 in cellular core 802 shear stress-strains 674-5 sheer fabric 105 sheet molding compounds (SMCs) 38-9, 56, 153, 165, 184-8,213-16, 228, 282,469, 514, 516-17, 525-6, 529, 560, 564, 582, 911 comparative cost study 313 comparison of glass and carbon fiber 222 compression molding 2 7 5 - 7 , 911 economic comparison 821 high-performance 228 LITE 227 manufacture 224-6 production lines 224 short and long glass fiber 225 thermoplastics 230-8 thermosets 221-30 short-term loads 662 shrinkage 658-60, 703, 840 CPs 16 EPs 16 fillers 168 vs. glass fiber content 660 vs. wall thickness 661 shrinkage rates 917 shuttle mark 108 SI units and deviations 1036 Sikorsky Aircraft Co. 581 silanes 1025-6 silica fibers 80 silicon carbide fibers 58 paper 459 silicones 153-4 silk fiber 93 Single Buoy Moorings 251 sintered metal components 751 sintering process 397 sisal fibers 62-3 site selection 477 slenderness ratio 706-7

Index 1077 smoke resistance 22 Society of Plastics Engineers 826 Society of the Plastics Industry (SPI) 16-17, 435,826, 1018 solid ground curing (SGC) 752 solid propellant systems 608 ablative plastics 611 structural parts and control accessories 611 solid-state diffusion 397 solid-state extrusion 90 soluble core moldings 301-2 cores of metal alloys 302 soluble core technology (SCT) 301 solvent adhesives 462 solvent recovery systems 146-8,470 solvent systems 179 soya bean/cellulose fibers 63 spandex fiber 93 speciality compounds 822, 839--40 speciality thermoset resins 154-7 specialty processes 822 specific gravity 20, 1041-2 specific gravity ratio 670 specific modulus 901 specific strength 901 vs. specific modulus 25 specifications 857 speckle interferometry 865 single- or dual-spot 867 spheres 380, 714, 772-3 circumferential load in wall 772 filament-wound 711 glass fiber-epoxy 773 inside radius/thickness ratio 772 spider silk fiber 93-4 spinneret 91, 94 spinning 91-2 dry 91 gel 91-2 jet 92 raw nucleation 92 reaction 92 solution 92 wet 92 split-wedge mold, land locations in 277 sport products 562 spray guns applications 296-7 selection 296

spray-ups 293-9 air-aspirated mixing 295 airless internal mixing 297-8 ancillary equipment 299 contact molding by 294 distributive mixing 298 equipment 294-5 external mixing 295 foaming polyester 298-9 low pressure, airless, internal mixing 295 new developments 294-5 products 1013, 1015 turbulent mixing 298 various methods of spraying 295 springs 719-28 design 720 Liteflex 723-4 special designs 727-8 SPRINT 322 square weave pattern 645 squeeze moldings 301 stabilizers 166 stable char forming polymers 601 stamping 259, 369-71,580 aluminum 911 compared to other processes 370 glass mat thermoplastic (GMT) parts 233-4, 456 steel 911 standards 857 staple fibers 94 static loads 13,638 static stress 662-75 statistical analysis 762, 874 steel limitations 819 modulus of elasticity 1033 output statistics by volume 999 output statistics by weight 999 properties 900 specific properties 901 stamping 911 strength vs. temperature 2 tensile strength 1033 stereolithographic (STL) method 751 stiffening ribs 540, 620 stiffness critical products 637 stiffness properties 209 stiffness response 209 strain analysis 782 in hoop direction 784

1078 Index strain gauges 780, 866-7 strain hardening 52, 363-4 strain rate 664-5 strain-stress-time in stress relaxation 204 straw fiber 94 strength of materials 642-3,771 strength-to-weight ratio 12 strength vs. temperature plastics 2 steel 2 stress definition 666-7 due to load 662 in beams 790 magnitude and direction 626 stress analysis 782, 873 product dimensions from 638 stress-elastic strain relationship 203 stress relaxation 209-10, 683 strain-stress-time in 204 stress resultants 739-40, 801 stressstrain analysis 766, 780 stress-strain behavior 652-61, 1026-7 stress-strain curve 669-71,767, 780 area under 668 comparison of metal and plastics 770 mild steel 781 unidirectional RPs and metals 702 stress-strain-deformation analysis 771 stress-strain deformation vs. time 210 stress-strain diagrams 768 stress-strain modes 664 stress-strain-time in creep 204 interdependence 684 stress whitening 660-1 strip hybrids 508-10 plates 509 strip modulus 509, 513 structural components, design 640 structural foam molding 920 economic comparison 821 structural foams (SF) 737, 740-4 cellular core 741 construction 740 core thickness vs. density impact strength 741 design approaches 742-3 load applied to sandwich 741

sandwich cross-section with and without core 742 sandwich vs. solid material construction 741 structural integrity 923 structural materials 1007 structural mechanics analyses 504 structural reaction injection molding (SRIM) 152, 189, 353-6 structural synthesis 512 styrene acrylonitrile (SAN) 159, 1003, 1026 styrene emissions 478,552 styrene-maleic anhydride (SMA) 126, 159, 344 SuperLite GMT 233 surface area and volume 1040 surface contamination 694 surface finish, standards 826 surface finishing 466-70 surface stresses 625-30 surface tissues 65-6 surface waviness/low shrink profile 159 SymaLITE GMT material 231,233 syntactic cellular plastics 367 syntactic sphere core 53-4 tacky tape 291 tangent modulus 669 tanks 530-43,773-5 fabrication 383-5 tensile stresses 384, 774-5 see also specific types and applications tape windings 383, 584 tape wrapping patent of tube-making machine 372 T-beam, design 799-800, 802 technical cost analysis, important tenets of 1017 technical cost models (TCM) 1015-17 temperature controls, mold 447 temperature conversions 1039 temperature effects 664 on tensile strength of reinforced nylon 6 407 temperature fluctuations 754 temperature resistance 847-53 temperature stability 851 temperature/time behavior 637-42 temperature-time guides 852 temperature transition 851

Index 1079 tensile-compressive loading 671 tensile properties 899 biaxially oriented PTFE sheeting unreinforced and reinforced 891 RPs and URPs based on type of resin 892 RPs, steel, and aluminum 635 tensile strength 167, 667 tensile stress, tanks 384, 774-5 tensile stress-strain curve 25,635,666, 672, 781 vs. temperatures 901 tensile stress-strain response 673 tensile stress-strains 664-70 test specimens, conditioning procedures 861 testing and troubleshooting 867-9 applications 858 as means of material selection 857-72 primary purposes 858 procedures 869-72 see also specific types and applications textile fibers 95 thawing heat flow measurements 495 theory of elasticity 642-3 thermal conductivity 694 thermal expansion CPs 15 EPs 15 thermal insulation properties 11 thermal interface 399 thermal properties 847-53,899 thermal shock resistance 166-8,839 thermal stability 166, 838 thermoforming 348-50, 912 thermoplastic polyurethanes (TPU) 345 thermoplastics 109, 1005 chemistry 195-9 classification 113-17 comparison of mechanical properties with metals 6 cost 889 Delrin acetal plastic molded stapler 719 examples of unreinforced and reinforced processing conditions 118-19 general properties 887 high performance 126-33 melt stages vs. temperature 198 molding compounds 33 overview 113-17 processing fundamentals 398-9

properties 888-9 thermal properties 234 trade-offs 884-5 types 117-33 use of term 112 waste 177 with different amounts of different fibers 3 Thermoplastics Testing Center (TTC) 824-5 thermoset polyester, with different amounts of glass fiber 4 thermosets 109, 1005 A-B-C stages from melt to solidification 133-4 characteristics 135 chemistry 194-5 curing 454 data sheets 940-96 general properties 886 high performance resins 151-4 limitations of 135 maturing process 454 overview 133-5 processing fundamentals 398-9 property guide 8 7 7 - 9 troubleshooting 471 types 136-57 use of term 112 thermosetting flash and trim 177 thick molding compound (TMC) 241 thin-wall cylinder, internal pressure on 816 thixotropes 162-3,837-8 three-dimensional reinforcements 65 time-dependent loads 683-4 titanate coupling agents 161 tolerances 21,658-60 CPs 16 EPs 16 tooling 259 tooling blocks 749 tooling costs 923 tooling products and services 753 tools 418-53 guide for different processes 419 hardening/platings 447 materials 421 in order of hardness 422 overview 418-25 use of term 418

1080 Index toroidal design structure 713 torque 727 torroids 380 torsion, ultimate/failure strength 709 torsional bars 708-9 torsional beam springs 726-7 torsional deformation 665 torsional load 726 torsional resistance 709 torsional shearing stress distribution analysis 709 torsional springs, energy absorbed 727 torsional stress 708 torsional stress-strains 674 total quality management (TQM) 262, 368 toughness CPs 15-16 EPs 15-16 tracking resistance 168 transfer molding 910 transfer press 281 translucent corrugated roofing panel 19 transportation 502-43 design concepts 503-13 transverse shear stresses 738 transverse strain 811-12 Trex Express 169 trimming 456 troubleshooting 470-6 and testing 867-9 computer software use in 474 fabricating 474 glass fiber/TS polyester reinforced plastic 472-3 injection molded glass fiber/TPs 471 RP process 868 thermoset RPs 471 trucks 529 truss structures 490-1 tube-making machine, tape wrapping patent 372 tumble machines 387 turbine blades materials 557 underwater 557 turbine engine fan blades 585-6 Twaron aramid 550 twill weave 108 twisting forces 708 twisting moment 708

two-shot molding 331,334 Tyvek 105 UL 94 872 UL laboratory 871-2 UL standard 746C 872 UL standard 746D 872 ultimate strength 1007, 1027 ultimate stress 762 ultimate tensile strength 667 ultra-high frequency (UHF) pre-heating 341 ultra-high molecular weight polyethylene (UHMWPE) 56, 1032 ultravio;et radiation 848 ultraviolet stabilizers 162 ultraviolet/sunlight stability 166, 838 underground storage tanks 537-42 underwater structures 715 underwater turbine blades 557 uniaxial load 700 uniaxial state of stress 700 unidirectional composite (UDC) 507 unidirectional fiber/epoxy RPs, mechanical properties 663 unidirectional loading 712 unidirectional material 700 unidirectional preimpregnated form 1024 unidirectional prepreg material 1024 unidirectional RPs graphite, boron, and aramid/epoxy 890 mechanical properties 27 processes/properties 905 unidirectional RPs and metals, stress-strain curves for 702 unidirectional weave 108 universal joint, precision IM 332 unreinforced thermoplastics, properties 877-83 unsaturated resins 139 unsymmetrical structure 700 updating testing centers 824 upgrading plant 477-80 USA measurements 1037-8 V fiber 96 VACRIM 146 vacuum bag film 290-1 vacuum bag moldings 290-3 combination of vacuum and pressure 291

Index 1081 vacuum bag moldings c o n t i n u e d pressures 291 schematic 291 vacuum bag replacement 291 vacuum-assisted resin injection moldings 330 vacuum-assisted resin injection (VARI) 320 vacuum-assisted resin transfer molding see VARTM vacuum casting 750-1 vacuum consolidation 292 materials 290 value analysis, recycling 193 valve covers 527 variabilities in material and processing equipment 855-6 VARTM 3 0 4 - 5 , 3 2 0 , 4 9 1 , 5 5 0 , 1030 autoclave curing 317-19 preform system 311 Veba Combi-Cracking (VCC) process 182 vegetable fibers 96 vent cloth 105 vertical-clamp machines 368 very low density fiber 56 vibration 755 suppression, isolation and damping 655-7 vibration tests 859 vinyl ester 148-51,221,967 laminate properties 150 molding compounds 229-30 polyurethane resins 157 properties 150 SMCs 968 virgin filament 97 viscoelastic behavior 690 viscoelastic materials 656-7 viscoelastic plastics 202-3 viscoelasticity 201-11,662,687, 770 characterization 211 design 682 linear and nonlinear 208-10 use of term 203 viscosity 201 Newtonian and non-Newtonian 201 viscous flow 202,205,662 volatile organic compounds (VOCs) 145, 468 Vosper Thornycroft 321,323-4 vulcanized fiber 96

walkways 490-1 wall thickness ranges and tolerances 914-16 warp 105 warp face 105 warping 454 washing equipment 470 washing machines, plastic pulley 561 waste minimization 177-8 water filtration systems 11 water filtration tank 536 water slurry machine, glass fiber rovings traveling through 274 wear resistance of short fiber RPs 894-5 weathering 853 weave 105 types 106 weft 105 weight displacement (W/D) ratio 713-15,717-18 weld joints, external and internal 785 welding processes 460-1 wet infusion 558 wet lay-ups 39,293 wet winding 386, 391 wheels, carbon fiber/nylon RP 526 whiskers 7, 29, 58 range of properties 59 wind-based electricity generation, Germany 556 wind blades 554-9, 1031 wind farms 554-9 wind sources for 555 Wind for Windows 756 wind sources for wind farms 555 wind stresses 493 wind tunnel 600 wind turbine blades, fabrication 558-9 wind turbine power 556 winding angles 374 windmills 554-9 window regulators 520-1 windshield canopies 576 Wolfangel GmbH 430 wollastonite fiber 63 wood

limitations 819 properties 900 specific properties 901 wood composition boards 500

1082 Index wood-plastic 500 wood pole restoration 563 woven glass fiber roving/epoxy RPs, flexural fatigue data 677 woven reinforcement 37 Wright Brothers flying machine replica 592-3 XMC (cross-wound molding compound) 227

yachts 550 yield point 667 yield strength 667, 1007 Young's modulus s e e modulus of elasticity ZenTron glass 47-8 zero-risk society 761 zero unidirectional carbon fiber fabric 82 ZMC molding compound 242,328,336