Specialist yarn and fabric structures
© Woodhead Publishing Limited, 2011
The Textile Institute and Woodhead Publishing The Textile Institute is a unique organisation in textiles, clothing and footwear. Incorporated in England by a Royal Charter granted in 1925, the Institute has individual and corporate members in over 90 countries. The aim of the Institute is to facilitate learning, recognise achievement, reward excellence and disseminate information within the global textiles, clothing and footwear industries. Historically, The Textile Institute has published books of interest to its members and the textile industry. To maintain this policy, the Institute has entered into partnership with Woodhead Publishing Limited to ensure that Institute members and the textile industry continue to have access to high-calibre titles on textile science and technology. Most Woodhead titles on textiles are now published in collaboration with The Textile Institute. Through this arrangement, the Institute provides an Editorial Board that advises Woodhead on appropriate titles for future publication and suggests possible editors and authors for these books. Each book published under this arrangement carries the Institute’s logo. Woodhead books published in collaboration with The Textile Institute are offered to Textile Institute members at a substantial discount. These books, together with those published by The Textile Institute that are still in print, are offered on the Woodhead website at: www.woodheadpublishing.com. Textile Institute books still in print are also available directly from the Institute’s website at: www.textileinstitutebooks.com. A list of Woodhead books on textile science and technology, most of which have been published in collaboration with The Textile Institute, can be found towards the end of the contents pages.
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Woodhead Publishing Series in Textiles: Number 123
Specialist yarn and fabric structures Developments and applications Edited by R. H. Gong
Oxford
Cambridge
Philadelphia
New Delhi
© Woodhead Publishing Limited, 2011
Published by Woodhead Publishing Limited in association with The Textile Institute Woodhead Publishing Limited, 80 High Street, Sawston, Cambridge CB22 3HJ, UK www.woodheadpublishing.com Woodhead Publishing, 1518 Walnut Street, Suite 1100, Philadelphia, PA 19102-3406, USA Woodhead Publishing India Private Limited, G-2, Vardaan House, 7/28 Ansari Road, Daryaganj, New Delhi – 110002, India www.woodheadpublishingindia.com First published 2011, Woodhead Publishing Limited © Woodhead Publishing Limited, 2011 The authors have asserted their moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publisher cannot assume responsibility for the validity of all materials. Neither the authors nor the publisher, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing Limited. The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing Limited for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. Library of Congress Control Number: 2011935506 ISBN 978-1-84569-757-0 (print) ISBN 978-0-85709-393-6 (online) ISSN 2042-0803 Woodhead Publishing Series in Textiles (print) ISSN 2042-0811 Woodhead Publishing Series in Textiles (online) The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp which is processed using acid-free and elemental chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. Typeset by RefineCatch Limited, Bungay, Suffolk Printed by TJI Digital, Padstow, Cornwall, UK
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Contents
Contributor contact details Woodhead Publishing Series in Textiles 1
Compound yarns
xi xiii 1
T. CHEN, Soochow University, China
1.1 1.2 1.3 1.4 1.5 1.6 1.7 2
Introduction Types of compound yarns Production methods for compound yarns Applications of compound yarns Future trends in compound yarns Sources of further information and advice References
1 1 5 13 14 19 19
Developments in hybrid yarns
21
H. R. MANKODI, M. S. University of Baroda, India
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 3
Introduction Types of hybrid yarns and their development Basic structures and properties of hybrid yarns Production methods for hybrid yarns Applications of hybrid yarns Future trends in hybrid yarns Acknowledgements References
21 22 24 26 49 52 53 54
Developments in rope structures and technology
56
J. W. S. HEARLE, University of Manchester, UK
3.1 3.2 3.3 3.4 3.5
Introduction New fibres Laid ropes Braided ropes Low-twist ropes
56 57 59 60 63 v
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vi
Contents
3.6 3.7 3.8 3.9 3.10
Manufacturing technology Terminations Uses of ropes Conclusions References
65 69 71 74 74
Developments in fancy yarns
75
4
R. WRIGHT, Racheland Designs, UK
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 5
Introduction to fancy yarns Historical development Types of fancy yarns and their development Production methods for fancy yarns Applications for fancy yarns Future trends in fancy yarns Sources of further information and advice Bibliography
75 76 78 87 104 106 107 108
Developments in 3D knitted structures
109
Z. GUO, Zhongyuan University of Technology, China
5.1 5.2 5.3 5.4 5.5 6
Introduction to 3D knitted structures Multiaxial warp-knitted fabrics Space fabrics (or sandwich fabrics) Fully-fashioned 3D knitted fabrics (or near-net-shaped knitted fabrics) Bibliography
109 109 112
Developments in leno-weave fabrics
118
116 116
Y. CHEN, Soochow University, China
6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 7
Introduction to leno-weave fabrics The structure of leno-weave fabrics Fabrics with leno-weave The production of leno-weave fabrics Properties of leno-weave fabrics Applications of leno-weave fabrics Future trends in leno-weave fabrics Sources of further information and advice References
118 119 123 125 133 134 136 140 140
Developments in triaxial woven fabrics
141
T. TYLER, Consultant, UK
7.1 7.2 7.3 7.4
Introduction Basic patterns A history of triaxial woven fabrics Classification
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141 141 144 148
Contents
7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 8
vii
Variations Properties Advantages Applications Aesthetics Manufacturing Future trends Sources of further information and advice References
148 152 153 154 157 158 160 161 161
Interwoven fabrics and their applications
164
X. CHEN, University of Manchester, UK
8.1 8.2 8.3 8.4 8.5 8.6 9
Introduction Structure and design Properties and applications Future trends Sources of further information and advice References
164 168 185 186 186 187
Pile carpets
188
G. H. CRAWSHAW, formerly of the IWS Interior Textiles Group, UK
9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 9.10 9.11 9.12 9.13 9.14 9.15 9.16 10
Market background Environmental considerations Pile fibres Pile yarns Tufting Backing materials, back-coating and laminating Wireloom weaving Face-to-face weaving Axminster weaving Needling Other methods of manufacture Coloration Chemical and other treatments Textile sports surfaces Sources of further information and advice References
188 190 192 196 198 205 207 208 211 213 214 215 216 217 220 220
Developments in Jacquard woven fabrics
223
A. M. SEYAM, North Carolina State University, USA
10.1 10.2 10.3
Introduction to Jacquard woven fabrics Jacquard construction Converting artwork to woven Jacquard patterns
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224 229 241
viii
Contents
10.4 10.5 10.6 10.7
Recent developments in Jacquard systems Patterns in Jacquard woven fabrics Applications of Jacquard woven fabrics Relationship between structures and properties of Jacquard woven fabrics Future trends in Jacquard woven fabrics Sources of further information and advice References
257 259 262 262
Developments in 3D nonwovens
264
10.8 10.9 10.10 11
242 249 254
R. H. GONG, University of Manchester, UK
11.1 11.2 11.3 11.4 11.5 12
Introduction High-bulk flat nonwovens Shaped 3D nonwovens Future trends References
264 266 273 284 284
Flocked fabrics and structures
287
Y. K. KIM, University of Massachusetts Dartmouth, USA
12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 12.9 12.10 12.11 12.12 13
Introduction The theory of fiber coating Flock fibers and preparation Flocking substrates Adhesives for flocking Flocking processes Testing and quality assurance New developments in the application of flocked fabrics and structures Conclusions and future trends Sources of further information and advice Acknowledgements References
287 290 297 300 301 303 308 311 314 315 315 316
Knotted fabrics
318
L. PHILPOTT, International Guild of Knot Tyers Pacific Americas branch, USA
13.1 13.2 13.3 13.4 13.5 13.6 13.7
Introduction Types of knotted fabrics Production methods for knotted fabrics Applications for knotted fabrics Future trends for knotted fabrics Sources of further information and advice References
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318 321 326 329 331 331 332
Contents
14
Developments in braided fabrics
ix
333
P. POTLURI and S. NAWAZ, University of Manchester, UK
14.1 14.2 14.3 14.4 14.5 14.6 14.7
Introduction Braiding Classifying braids The geometry of the braided structure Applications of braided fabrics Future trends in braided fabrics References
333 334 338 344 347 351 353
Index
355
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Contributor contact details
(* = main contact)
Editor and Chapter 11
Chapter 3
R. H. Gong Textiles and Paper School of Materials University of Manchester Manchester M13 9PL UK
J. W. S. Hearle The Old Vicarage Mellor Stockport SK6 5LX UK
Email:
[email protected]
Chapter 1 T. Chen College of Textile and Clothing Engineering National Engineering Laboratory for Modern Silk Soochow University 178 East Ganjiang Road Suzhou Jiangsu 215021 China Email:
[email protected]
Email:
[email protected]
Chapter 4 R. M. Wright Racheland Designs UK Email:
[email protected]
Chapter 5 Z. Guo College of Textiles Zhongyuan University of Technology 41 Middle Zhongyuan Road Zhengzhou 450007 China Email:
[email protected]
Chapter 2 H. R. Mankodi Department of Textile Engineering Faculty of Technology and Engineering M.S. University of Baroda Kalabhavan Vadodara 390001 Gujarat India Email:
[email protected]
Chapter 6 Y. Chen College of Textile and Clothing Engineering Soochow University 178 East Ganjiang Road Suzhou Jiangsu 215021 China Email:
[email protected]
xi © Woodhead Publishing Limited, 2011
xii
Contributor contact details
Chapter 7
Chapter 12
T. Tyler 62 Ashton Road Bristol BS3 2EQ UK
Y. K. Kim Department of Bioengineering University of Massachusetts Dartmouth 285 Old Westport Road North Dartmouth MA 02747 USA
Email:
[email protected]
Chapter 8 X. Chen School of Materials University of Manchester Manchester M13 9PL UK Email:
[email protected]
Chapter 9 G. H. Crawshaw Flat 5, Chapel House Wells Road Ilkley West Yorkshire LS29 9JD
Email:
[email protected]
Chapter 13 L. Philpott 3646 Gaviota Avenue Long Beach CA 90807 USA Email:
[email protected]
Chapter 14
Email:
[email protected]
Chapter 10 A. M. Seyam College of Textiles North Carolina State University Raleigh NC 27513-8301 USA
P. Potluri* and S. Nawaz Textile Composites Group School of Materials University of Manchester Manchester M13 9PL UK Email:
[email protected]
Email:
[email protected]
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1 Compound yarns T. CHEN, Soochow University, China
Abstract: Compound yarns (core-spun yarns) have attractive development prospects because compound yarns combine the advantages of both core and wrapping fibres. This chapter will introduce compound yarns. It first reviews types of compound yarns – elastomer core, polyester core and worsted core. It then describes production methods for compound yarns – conventional ring spinning systems and the Siro spinning system. Finally applications and future trends for compound yarns are discussed. Key words: compound yarn, core-spun yarn, yarn types, ring spinning, Siro spinning.
1.1
Introduction
With the rise in living standards, consumers have been paying more attention to the functionalities and diversifications of textile products, and the diversity of yarn types is expected to increase. Nowadays, new raw materials and new technologies continue to come up, among which compound yarns (core-spun yarns) have attractive development prospects because compound yarns combine the advantages of both core and wrapping fibres. Compound spinning technologies are beneficial both to the improvement of spinning technology and to changes in structures, styles and properties. In this chapter, compound yarns will be introduced. In Section 1.2, types of compound yarns will be given, including elastomer core, polyester core and worsted core. In Section 1.3, production methods for compound yarns will be described, including the conventional ring spinning systems and the Siro spinning system. In Section 1.4, applications of compound yarns will be shown with examples. In Section 1.5, future trends for compound yarns will be discussed.
1.2
Types of compound yarns
Compound yarns (core-spun yarns) are yarns that have a central core with a second layer or sheath of fibres wrapped around it. The filament or strand of fibres confined mainly on the yarn axis is named as the ‘core filament’ or ‘core yarn’. Fibres wrapped around the core are called the ‘wrapping fibres’. There is a distinct boundary between the core and the wrapping. However, the core and wrapping integrate tightly so that fibres will not strip or slip during processing or use. The core and wrapping may either be of the same fibre type, or two different types (or more) may be used. Furthermore, one part may be of filament fibres while the 1 © Woodhead Publishing Limited, 2011
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Specialist yarn and fabric structures
other is of staple fibres; or both parts may be of either filament or staple fibres. According to the fibre type used, compound yarns can be divided into elastomer core, polyester core and worsted core.
1.2.1 Compound yarns with elastomer core Elastomers are elastic, rubberlike substances. All elastomers are characterized by extremely high elongation – at least 200%, and frequently between 500 and 800% – and excellent elastic recovery. The point of introducing elastomers into yarn manufacturing is to achieve elastomeric yarns or stretch yarns. The most widely used elastomeric fibre, as the core of compound yarns, is polyurethane fibre. Polyurethane fibre is defined as a synthetic fibre in which the fibre-forming substance is a long-chain synthetic polymer comprised of at least 85% segmented polyurethane. Polyurethane fibre is known as ‘spandex’ in the USA, whereas fibre manufacturers in Western Europe prefer the name ‘elastane fibre’ (EL). Polyurethane fibre was developed by the Bayer Company in the 1930s. Plans for volume production and the trade name Lycra were announced by the DuPont Company in late 1959 (Wang et al., 2004). One of the most common types of core-spun yarns is the elastomer core-spun yarn, which involves a core of elastomeric fibre such as polyurethane fibre with a covering of staple fibres. Figure 1.1 shows the longitudinal morphology of a polyurethane core-spun yarn. It can be found from Fig. 1.1 that polyurethane core-spun yarn has the same appearance as the wrapping staple fibres. The core
1.1 Longitudinal morphology of a polyurethane core-spun yarn.
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filament is wrapped closely in the staple fibres. Both the core filament and the wrapping staple fibres have the same twist. Because the wrapping staple fibres migrate around the core filament during the spinning process, the core filament is unexposed even when the core-spun yarn is under tension. The wrapping staple fibres (cotton, wool and other natural fibres) give the polyurethane core-spun yarn good moisture absorption and hand. The yarn has excellent elastic recovery that can be altered up to 20% according to different end uses, which is far beyond the elasticity of the wrapping staple fibres. Since the core filament is unexposed, the yarn is easily dyed, even with deep colours. Because polyurethane fibre is a low-strength high-extension type fibre, it destroys the cohesion among the staple fibres, and so the strength of the core-spun yarn decreases. Therefore, using polyurethane fibre makes no contribution to the yarn strength. And with higher polyurethane fibre content, the yarn strength will decrease. In general, the strength of the polyurethane core-spun yarn is about 80~90% of that of wrapping staple fibre yarn with the same specifications (Davies, 1997). When the core-spun yarn is under tension, the wrapping staple fibres break first; the core-spun yarn is only as strong as the wrapping staple fibres. So when the core-spun yarn has the same specifications as the yarn formed by the wrapping staple fibres, the strength of the core-spun yarn is lower.
1.2.2 Compound yarns with polyester core Polyester was the second synthetic fibre type to be developed (1941) and is now by far the most widely used synthetic fibre, due to a balance of properties that gives it great versatility, and a less expensive manufacturing process compared with nylon. Polyester has good strength and abrasion resistance compared with nylon and also takes a permanent heat set – all ‘first-class’ fibre properties from the point of view of performance. Further characteristics that make polyester more popular than nylon are good resilience (the nearest to wool of any chemical fibre) and high modulus: these mean that it is springy and can recover well from strain, yet resists stretching better than nylon. Polyester also conducts moisture away from the skin better than nylon, dries faster, and is suppler in cold conditions. The compound yarns with the polyester core are manufactured precisely to create their high strength and shrink-proof qualities (Sawhney and Folk, 1992). The longitudinal morphology of polyester core-spun yarn is similar to that of polyurethane core-spun yarn. Figure 1.2 is a schematic diagram of a cross-section of a polyester core-spun yarn. As the figure illustrates, the cross-section of the polyester core-spun yarn is not quite circular and the core filaments are not always in the geometrical centre of the yarn. Because of fibre migration during twisting, a few core filaments migrate to the sheath and some wrapping staple fibres migrate to the core. However, these minor migrations will not affect the appearance or wearing properties of core-spun yarn.
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Specialist yarn and fabric structures
1.2 Schematic diagram of the cross-section of a polyester core-spun yarn.
The wrapping fibres can be cotton, wool, rayon, Tencel, Modal, or other fibres. The core-spun yarns combine the advantages of a polyester (core) such as high strength, large elongation rate, limited unevenness and easy care with such advantages of natural or man-made staple (wrapping) fibres as moisture regain, heat retention, softness, comfort, pilling resistance and antistatic. And the weavability of core-spun yarns is better than that of filaments. A reasonable configuration of the ratios of core and wrapping fibres will lower material and production costs.
1.2.3 Compound yarns with worsted core Nowadays, the development trend of woollen textiles is towards finer and lighter fabrics. The use of new yarn structures provides an effective solution. A compound yarn with a worsted core is one of the new yarn structures. Worsted core spinning can break through the count limit of the traditional wool spinning process by changing the yarn structure to achieve finer and lighter wool fabrics. Worsted core spinning uses a filament yarn and a wool roving, which are fed separately and kept a fixed distance from the nip of the front drafting roller, and they make up a triangular zone that is twisted together to form worsted core-spun yarn (Dong, 2004). Figure 1.3 shows the cross-section of a worsted core-spun yarn. As can be seen, the cross-section is roughly circular. The wool fibre strand is wrapped in filaments with circular or curved shapes. There are few migrations between wool fibres and filaments. The reason is as follows. Before convergence, there are some twists in both the wool fibre strand and filaments, separately. Twists in the wool fibre strand filaments follow the same direction as twists in the core-spun yarn, but are less tight than in the core-spun yarn. When arriving at the convergence point, the wool
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1.3 Cross-section of a worsted core-spun yarn.
fibre strand and filaments are twisted again. Since they have already been twisted quite a few times, two different components can be found in the core-spun yarn. Compared with worsted yarns with the same specifications, worsted core-spun yarns have the following advantages: 1. Because filaments wrap the worsted core, the yarn is noticeably less uneven and has fewer defects than worsted yarns. The yarn is less hairy than worsted yarns. The yarn surface is brighter and cleaner. 2. Because of the added filaments, the strength and elongation rate of the yarn increase substantially and are much greater than those of worsted yarns. 3. As the spinning tension decreases, the yarn becomes easier to spin, and the endbreaking rate decreases notably, which benefits the spinning and winding speeds. 4. Because worsted core-spun yarns have a smaller yarn diameter than worsted yarns with the same specifications, gaps between yarns on the fabric are large, which noticeably improves the air permeability of the fabric. 5. Because of the simultaneous twisting of the wool fibre strand and filaments and the effects of the mechanical properties of filaments, the stiffness and elasticity of core-spun yarns increase accordingly. The fabric produced has good wrinkle resistance, which enhances the crisp handling of the product.
1.3
Production methods for compound yarns
Several methods can produce compound yarns (core-spun yarns). The basic difference among these methods is how the core and wrapping fibres are combined. The conventional ring spinning system and the Siro spinning system are most widely used.
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Specialist yarn and fabric structures
1.3.1 The conventional ring spinning system The conventional ring spinning system is a yarn spinning system by which a filament (usually an elastic filament under tension) is covered with a sheath of staple fibres. Upon the release of tension, the sheath fibres are pulled into a closer formation. The resultant yarn becomes stretchable, depending on the tension of the core filament. Conventional ring spinning is a means of producing stretch yarns for both knitted and woven fabrics. For example, a spandex core (as little as 1%) can be completely covered by the nonstretch staple fibre that is spun around it. The resultant stretch fabric has all the characteristics of the predominant fibre, with the added advantage of stretch and recovery (Tortora and Merkel, 1996).
The technological process of conventional ring spinning for compound yarns The technological process of conventional ring spinning for compound yarns is shown in Fig. 1.4. To spin compound yarns, a feeding device for the core filament
1.4 The technological process of conventional ring spinning for compound yarns.
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(or core yarn) must be installed on the ring spinning machine. The core filament (or core yarn) passes the yarn guide and is fed directly into the front roller, while the wrapping fibre strand passes the back, middle and front roller successively. Finally the wrapping fibre strand meets the core filament (or core yarn) in the front nip. They pass the yarn carrier and are twisted and wound by the combined action of ring and traveller. After the wrapping fibre strand leaves the front nip, tension on the strand will decrease. However, tension on the core filament (or core yarn) is always high from the front roller to the winding position. Therefore, the fibre strand wraps around the core filament (or core yarn) and a compound yarn is produced. There are two types of feeding device for the core filament (or core yarn): a positive feeding device and a negative feeding device (Liu and Zhang, 2008). When using a negative feeding device, a tubular package is often employed. The core filament is unwound straight along the radial direction, or from the head end of the package. This device has a simple structure and does not need a driving mechanism, which is applicable to such rigid filaments as polyester, etc. However, a tension controller should be installed to prevent the fluctuation of tension during unwinding. When using a positive feeding device, a cylindrical package is often utilized. The filament is unwound from the package driven by a couple of feed rolls. A specific drafting ratio is necessary from the feed rolls to the front roller. Therefore, a drafting assembly is usually required in this system, which positively controls the drafting ratio of the filament. The wrapping fibre strand and core filament are separately drafted by the original and newly installed drafting assembly and meet each other in the front nip. This system is applicable to elastomeric filaments such as polyurethane, etc. The key to producing elastomeric core-spun yarns is properly controlling the feeding of elastomeric filaments. Elastomeric filaments such as polyurethane fibre have a high elongation rate and a small initial modulus. The core filament meets the wrapping fibres in the front roller and both of them enter the twisting zone. After twisting, the wrapping fibres wrap closely around the core filament. Upon leaving the front roller, the core filament will shrink because of the removal of the external force. The extensibility of elastomeric core-spun yarn is attributed mainly to the straightening of the flexural wrapping fibres. The stability of the drafting of the core filament directly influences the stability of formation of the yarn. After leaving the front roller, the core filament (or core yarn) and wrapping fibres are twisted by a strong torsion; fibre ends are prone to protrude from the yarn surface and thus hairiness is formed. The spinning tension results in frequent migrations of wrapping fibres running at different parallels to the yarn axis. Therefore, the forces acting upon the wrapping fibre are unbalanced during drawing. The feeding position depends upon the direction of twist so as to obtain a better wrapping effect.
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The forming conditions of compound yarns There are two conditions for forming compound yarns: 1. The spinning tension of the core filament (or core yarn) must be higher than that of the wrapping fibres. 2. The delivery speed of the wrapping fibres must be higher than that of the core filament (or core yarn). That is to say, there must be a tension difference and speed difference between the core filament (or core yarn) and wrapping fibres. Because the wrapping fibres rotate around the core filament (or core yarn) during spinning, the elongation of the wrapping fibres will be greater than that of the core filament (or core yarn) within the same length of the core-spun yarn, which requires a speed difference between the wrapping fibres and core filament (or core yarn), i.e. the wrapping fibres run faster than the core filament (or core yarn). A high spinning tension will prevent the wrapping fibres from rotating around the core filament (or core yarn). Hence, the spinning tension of the wrapping fibres should be lower than that of the core filament (or core yarn). Factors influencing the wrapping effect The wrapping effect is an important quality index of core-spun yarn. Factors influencing the wrapping effect include tension, percentage of the core filament (or core yarn) and twist. Tension of the core filament The tension of the core filament (or core yarn) has a great influence upon the wrapping effect. At high tension, the core filament leaves the front roller very slowly. However, the wrapping fibres leave the front roller with a constant speed. Therefore, the wrapping fibres wrap the core filament too frequently, which will result in slugs on the core-spun yarn. If the tension exceeds the breaking strength of the core filament, the core filament will break. But the wrapping fibres do not break and the spinning process goes on. As a result, the core filament is not wrapped properly and long or short segments of wrapping fibre yarn will form. So the tension of the core filament should not be too high. At low tension, the core filament leaves the front roller very quickly. The speed difference between the core filament and wrapping fibres is too small to meet the requirement of wrapping, which results in inadequate wrapping around the core filament, and the core will be exposed. Therefore, the tension of the core filament must be moderate to achieve an ideal wrapping effect. When using a moderate tension, the core filament is in the centre of the yarn and the yarn is called a core type. When using low tension, the core filament is off-centre and the yarn is called an ‘excentral type’ or a ‘bare core type’.
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Percentage of the core filament The percentage of the core filament is the mass of the core filament as a percentage of the mass of the core-spun yarn. If this percentage is low, it will cause too much wrapping and thus a decrease in the yarn strength. A high percentage will cause the core filament to be exposed, and weaken the wrapping effect. Twist A strong twist in the core filament will increase its strength and abrasion resistance, and thereby provides a good foundation for spinning a core-spun yarn. A strong twist of the wrapping fibre strand favours proper wrapping, whereas too strong a twist will cause yarn breakage. Therefore, the yarn twist must be determined reasonably so as to achieve an ideal wrapping effect with few yarn breakages. The traveller should be selected taking the linear density of the core-spun yarn into account. A relatively large yarn path and thin arched path section are preferred. Because the balloon tension of the core filament increases during spinning and the balloon shape becomes more convex, the weight of the traveller should be greater than for pure cotton yarns with the same linear density. The operation of the spinning machine will also influence the wrapping effect. A machine that operates well keeps the core filament and wrapping fibres in a proper and reasonable relative position, which is a premise for producing good-quality core-spun yarns.
1.3.2 The Siro spinning system The Siro spinning technique was first developed by the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia, in cooperation with the International Wool Secretariat (IWS) in the 1970s. In 1988, the Zinser Corporation began to apply the Siro spinning technique, and it has gained a respectable share of the worsted market. The technological process of Siro spinning The technological process of Siro spinning is shown in Fig. 1.5. The rovings are fed into a ring frame with separators to ensure that each roving is drafted individually. The two strands emerging from the drafting system twist together into a single yarn. The yarn is called Sirospun yarn. The principle of Siro spinning is illustrated in Fig. 1.6. The advantages of the Siro spinning technique are as follows: the ring spinning frame can be easily modified; the structure of the Sirospun yarn is similar to that of plied yarn; and the yarn has more abrasion resistance and is less hairy.
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1.5 The technological process of Siro spinning.
A conventional ring spinning machine can be easily modified into a Siro spinning machine. The main alterations are as follows: 1. The creel is altered to add one more roving. The spindle space and roving building are determined by the type of spinning machine. The two twistless rovings on the same bobbin must be fed at different phase positions. 2. Yarn guides with a single groove are changed for those with a double groove, with moderate pitches of grooves. 3. The groove width of the middle leather roller increases from 18 mm to 24 mm on wool spinning machines with a slip draft. 4. A break-out device (BOD) is installed between the front roller and yarn guide. When a strand breaks, the break-out device can break another strand automatically to avoid the production of a single yarn. The break-out device should have high sensitivity and excellent stability (Mao et al., 2006). Effects of the spinning parameters on yarn properties Spinning parameters influencing the yarn properties include strand spacing, the front zone condenser and the convergence guide.
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1.6 The principle of Siro spinning.
Strand spacing Strand spacing is the most important parameter in ordinary two-strand spinning. As the strand-spacing increases, the length of the individual strands above the convergence point increases, and therefore the total amount of twist increases due to random changes in the twist equilibrium. However, once the convergence point is far enough below the front nip to allow the fibre ends to be thrown out from the strands, it can be expected that a further increase in strand spacing will not cause a major increase in the number of fibres being trapped by this mode. With more strand spacing, the yarn hairiness decreases. When the strand spacing increases to a certain level, the yarn hairiness reaches the minimum, because the level of strand-twist that can be generated is small, and it is likely that the yarn formation mode of fibre-trapping is dominant in this initial decrease in hairiness. The abrasion resistance of yarn appears to increase almost linearly with strand spacing. The linear increase suggests that the strand-twist is also making a contribution to this change in abrasion resistance. There is also a suggestion that a small increase in the tenacity and elongation of yarn results from the increase in strand spacing. However, these are not large enough to affect the weaving performance significantly. The increase of the strand spacing favours more twisting of each strand. Fibres are twisted into the yarn closely and can hardly slip. Therefore, the yarn tenacity increases; yarn hairiness decreases; and compactness of the yarn increases. With
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the initial increase of the strand spacing, the doubling effect caused by leaving the two strands from the front nips results in greater yarn evenness. However, a further increase in strand spacing will reduce the control of each strand and thus reduce the yarn’s evenness. When compared with a single yarn of the same linear density and twist multiplier, Sirospun yarn is superior in tenacity, evenness, hairiness and abrasion resistance. Comparing conventional two-fold yarn with Sirospun yarn shows that the two-fold yarn is more abrasion resistant, but more hairy. Both abrasion resistance and hairiness are important properties determining weavability, and the two-strand yarn generally performs as two-fold yarns. The optimum gauge of strand spacing is determined mainly by fibre length. The optimum gauge is 14~18 mm for Sirospun wool and ramie yarns and 6~12 mm for Sirospun cotton yarns. Front zone condenser In conventional spinning, front-zone condensers will reduce surface hairs by condensing the fibres so that they are more readily picked up by the rotating strand. In two-strand spinning, this action might, however, reduce the number of fibres available for trapping by the yarn formation mode. Provided that yarn hairiness without the condenser is not excessive, the condenser appears to have no effect on tenacity, elongation or abrasion resistance. These results are typical for general observations, which show that the presence of a front-zone condenser slightly reduces hairiness on the spinning bobbin but this improvement is generally lost during the winding. Convergence guide For convergence guides placed just above the natural convergence point of the strands, a small decrease in hairiness is generally observed when measurements are made straight off the spinning bobbin. No effect is observed on either abrasion resistance or tenacity. Traveller number The traveller number (which describes the traveller’s weight) is relative to the yarn linear density and spindle speed. All influence the spinning tension, and thus the height of the twist triangle. The effect of the traveller number in Siro spinning is in accordance with that in conventional ring spinning. As there are two strands leaving the front nips in Siro spinning, the traveller number in Siro spinning may be a little smaller than in conventional ring spinning of yarns with the same linear density. Moreover, selection of the traveller number must ensure a higher spinning tension than the working tension of the break-out device; or else the break-out device cannot start, and loses effectiveness.
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Twist multiplier The effects of the twist multiplier on the properties of Sirospun yarns resemble those on conventional ring-spun yarns. A large twist multiplier will yield high tenacity and elongation rate and less hairiness in the yarn. The twist multiplier also influences the twists on each strand. The larger the twist multiplier, the stronger the twist on each strand will be, the more closely fibres will entangle, and the less the hairiness. Because twist is difficult to propagate through the convergence point, the twist multiplier of Sirospun yarns should be moderately greater than that of conventional ring-spun yarns with the same linear density in order to ensure a sufficient twist on each strand. Drafting ratio and linear density of roving The high tenacity and evenness of Sirospun yarn can be attributed to its compactness. Utilizing finer roving and smaller drafting ratios can reduce the scattering of the strand during drafting, which will result in compact yarn structures. However, the same performance cannot be observed in conventional ring spinning. Therefore, a moderate decrease in the roving tex and drafting ratio will produce a more even and more compact yarn.
1.4
Applications of compound yarns
By effectively integrating the advantages of both core and wrapping fibres, compound yarns are produced with excellent combination properties and can be applied to many fields like apparel, decorative and industrial textiles with both civil and military uses. The following paragraphs describe some examples. Compound yarns with a polyurethane core and wrapping fibres of cotton, wool, silk, ramie, viscose, Modal or Tencel are elastomeric compound yarns, which can be used to produce elastic fabrics with such characteristics as comfort, breathability, and a good fit as well as being aesthetically pleasing. These fabrics can be woven or knitted. Woven fabrics can have plain, twill, satin or figure weaves. Shell fabrics include denim, corduroy, poplin, khaki, velour, and so on. The end products are shirts, coats, underwear, sports wear, swimwear, stockings, gloves, elastic bands, medical bandages, fire hoses, conveyor belts and tents. Compound yarns with a polyester core and wrapping cotton fibres can produce sewing threads with a high tenacity and abrasion resistance and low shrinkage that are suitable for high-speed sewing (Sawhney and Ruppenicker, 1997). The yarns are also antistatic and even high temperatures will not melt them easily. Compound yarns with a polyester core and wrapping fibres of cotton or viscose are burnt-out core-spun yarns. The fabrics produced have a semi-transparent surface and patterns with a three-dimensional effect that can be used in decorative fabrics like curtains, tablecloths and bedcovers.
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Compound yarns with a polyester core and wrapping fibres of bamboo pulp, coloured cotton or coloured chemical fibres can make good use of such superior features as a soft hand, breathability, perspiration and the visual effects of wrapping fibres. Compound yarns with a polyester core and wrapping antibacterial fibres can produce underwear, socks and hygienics textiles. Compound yarns with a worsted core have a good wrapping effect, low hairiness, good evenness, good elasticity and strong covering power that can produce light and thin fabrics. The end products may be shirts, tailored trousers and tailored suits. Mercerized wool fibres are spun with difficulty, purely because of their low strength and poor cohesion. However, compound yarns with a worsted core of mercerized wool are easily spun. And the heat resistance and dimensional stability of the products have been improved. The fabrics have a full handle, like velvet (Wang and Zhang, 2007). These compound yarns can replace yarns made of super-fine wool fibres to produce light and thin fabrics with a low material cost.
1.5
Future trends in compound yarns
The market demand for compound yarns is continuing to increase. Now compound yarns are manufactured on more than ten million spindles of spinning machines all over the world and two to three hundred thousand spindles are expected to be added every year. Future trends for compound yarns will concentrate on developments in raw materials, technologies and products.
1.5.1 Developments in raw materials As far as the raw materials are concerned, besides conventional fibres, more and more new regenerated fibres (soybean protein fibre, polyactic fibre and so on), specialty fibres, functional fibres and high-performance fibres will be employed to spin compound yarn. The yarns and fabrics produced will have attractive functionalities, hands or styles. Combining such conventional core filaments as polyurethane and polyester with other differential fibres is a further development. For example, Dupont Company developed Lycra 3D by combining polyurethane with a superfine fibre named Tactel. The Spantel series developed by Kuraray are also combinations of polyurethane with various other fibres.
1.5.2 Rotor spinning of compound yarns As for the spinning technologies, the application of the rotor spinning technique in the production of compound yarns is worth noting. The principle is shown in Fig. 1.7. The core filament enters the rotor through an axial hollow spindle. The wrapping staple fibres are carded by the opening roller and transported into the condensing groove of the rotor. The high-speed rotation of the rotor results in the wrapping of the core filament by the staple fibres. Finally the compound yarn
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1.7 The principle of rotor spinning for compound yarns.
is drawn off by the delivery roller and wound onto a bobbin. It is easy to modify a conventional rotor spinning machine into a core rotor spinning machine. The main alterations include adding a hollow spindle and an unwinding device for the filament while the design features and spinning functions of the conventional rotor spinning are maintained. Conventional rotor-spun yarns can also be spun with this equipment as long as the filament is not fed into the spindle. Rotor-spun compound yarns have such advantages as large strength, good evenness, structure stability, structure diversification and less hairiness. The process flow of rotor-spun compound yarns is shorter than that of ring-spun–compound yarns, and the productivity is higher. Therefore, the rotor spinning technique for compound yarns has high processing reliability and productive capacity. Combining staple fibres with filaments overcomes the weakness of conventional rotor-spun yarns because the filament will not be twisted and contributes significantly to increasing the yarn’s strength. The evenness of rotor-spun compound yarns is superior to that of ring-spun compound yarns because of the high power of the doubling effect during fibre condensing. Rotor-spun compound yarns are less hairy than ring-spun compound yarns while their bulkiness is higher. The removal of roving and winding decreases the production cost greatly. Rotor-spun compound yarns can be wound into larger packages than ring-spun compound yarns, which will increase the unwinding length in any following processes, thus reducing endbreakages. Rotor-spun compound yarns also have good material adaptability. The
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staple fibres may be cotton or synthetic. The core filament may be a conventional elastic filament or an unconventional filament such as glass fibre, metal fibre, etc. Industrializing the production of rotor-spun compound yarns will greatly increase the output of these yarns, and meet market demands.
1.5.3 Air-jet spinning of compound yarns Air-jet spinning is one of the new spinning techniques that can produce core-spun yarns. This process employs an air-jet to rotate the fibre strands and twist them into a yarn. The twisters are two air nozzles with several orifices. The yarn is formed during the rotation of the fibre strands, which is generated by an air-jet inside the nozzles without any high-speed rotating elements. The spinning speed can reach up to 300 m/min. It can spin blended yarns of polyester and cotton or chemical staple fibres. The technological process of air-jet spinning compound yarns is illustrated in Fig. 1.8. A feeding device for the core filament is installed on the air-jet spinning
1.8 The technological process of air-jet spinning for compound yarns.
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machine. The core filament is released from the feeding device, passes the tension device and filament guide, and is fed directly into the front roller. The wrapping fibre strand (roving or sliver) goes through the drafting assembly. After leaving the front nip, the wrapping fibre strand enters the air nozzles along with the core filament to form a compound yarn. The principle of air-jet spinning for compound yarns is as follows. The wrapping staple fibre strand and core filament leave the front nip and come into the first nozzle. Some free edge fibres are separated from the wrapping fibre strand by the airflow of the first nozzle. Simultaneously, these edge fibres wrap around the yarn core (core filament and other wrapping fibres), which is twisted by the airflow, and initial wrapping is realized. Because the air-jet inside the second nozzle rotates in the opposite direction to that inside the first nozzle and the intensity of the air-jet inside the second nozzle is greater than inside the first nozzle, the yarn core is untwisted after entering the second nozzle. However, because the wrapping direction of the free edge fibres is opposite to the false twist direction of the yarn core, the free edge fibres are more tightly wrapped around the yarn core; thus final wrapping is achieved and an air-jet compound yarn is produced. The air-jet compound yarns may have a core of polyester, polyamide, polyurethane, glass fibre or carbon fibre. Figure 1.9 illustrates the structure of the air-jet compound yarns, which have the following features: 1. The core, which is especially fragile under torsion load, is not twisted and is free from damage, maintaining the strength of the yarn.
1.9 The structure of air-jet compound yarns.
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2. The core tends to move into the centre of the yarn and wrapping fibres are firmly rooted in the core, which prevents exposure of the core when stretched.
1.5.4 Friction spinning of compound yarns Another new spinning technique – friction spinning – can also produce compound yarns. Friction spinning utilizes a combination of mechanical and aerodynamic methods, which sucks and collects fibres on the perforated drums wherein a suction slot is fixed. The perforated drums rotate and rub the fibres into a rubbing twisted yarn with the aid of the drum friction forces. The friction spinning machine for producing compound yarns has two fibre supply devices, as shown in Fig. 1.10. The first device is drafting unit 1, which drafts the wrapping staple fibres. The second device (drafting unit 2) consists of a four-roller double-apron drafting system. The sliver drafted through drafting unit 2 becomes staple fibre strands that are fed into the wedge-shaped area of two perforated drums in the horizontal direction. Or a filament can be inserted directly into the wedge-shaped area of the two perforated drums instead of the staple fibre strands from drafting unit 2. When the perforated drums rotate, the core staple fibres or filament and the wrapping staple fibres added vertically from drafting unit 1 will be rubbed and twisted
1.10 The technological process of friction spinning for compound yarns.
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together into a compound yarn. Owing to the gradations of components and twists, friction spinning can produce diversified compound yarns by utilizing different cores, different wrapping fibres and different colours. The wrapping effect of friction spun compound yarn is also excellent.
1.5.5 Product developments Consumers are more and more interested in knitted fabrics because of such advantages as good fit and softness. Application of compound yarns in knitting is also a development direction. For example, compound yarns with a polyurethane core and wrapping nylon fibres can produce the middle and outer layers of threelayered thermal underwear of good elasticity. Another example is a compound yarn with a worsted core and wrapping nylon fibres, which can produce knitted sweaters of high strength, low pilling, colourfastness, good drapability, a bright surface, soft hand and elegant style. The third example is a compound yarn with a polyester core and wrapping spun silks. The polyester core and wrapping spun silks provide the compound yarn with strength and comfort, respectively. The fabric has a gentle and elegant appearance and will not stick to the skin. Other examples are compound yarns of cotton/polyester/cashmere, acrylic/cotton/rabbit hair, acrylic/Tencel/cotton knitting yarns, and so on.
1.6
Sources of further information and advice
To learn more about compound yarns, please refer to the following books: Lawrence, C. A. (2010), Advances in Yarn Spinning Technology, Cambridge UK, Woodhead Publishing Ltd. Lawrence, C. A. (2003), Fundamentals of Staple Yarn Manufacture, Boca Raton, CRC Press LLC. Lord, P. R. (2003), Handbook of Yarn Production: Technology, Science and Economics, Cambridge UK, Woodhead Publishing Ltd and CRC Press LLC. Wang, S. and Yu, X. (2007), New Textile Yarns, Shanghai, Donghua University Press.
1.7
References
Davies, S. (1997), ‘Focus on stretch yarns’, Knit Int, 104, 58. Dong, W. (2004), ‘New techniques of ring spinning used for woolen yarn systems’, Wool Textile J, (5), 44–46. Liu, R. and Zhang, W. (2008), ‘Spinning of core-spun yarn’, China Textile Leader, (10), 70–73. Mao, L., Xing, M. and Dou, Y. (2006), ‘Spinning mechanism and applications of Siro spinning’, Adv Textile Tech, (3), 17–18. Sawhney, A. P. S. and Folk, C. L. (1992), ‘Improved method of producing cotton-covered polyester staple-core yam on a ring spinning frame’, Textile Res J, 62, 21–25. Sawhney, A. P. S. and Ruppenicker, G. F. (1997), ‘Special purpose fabrics made with corespun yams’, Indian J Fibre & Textile Res, 22, 246–254.
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Tortora, P. G. and Merkel, R. S. (1996), Fairchild’s Dictionary of Textiles (Seventh Edition), New York, Fairchild Publications. Wang, H. and Zhang, G. (2007), ‘Introduction to the technology and products of worsted core-spun yarn’, Wool Textile J, (2), 41. Wang, S., Dang, M. and Zhang, H. (2004), ‘The study on the processing and performance of polyurethane fiber yarn’, China Textile Leader, (4), 49–59.
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2 Developments in hybrid yarns H. R. MANKODI, M. S. University of Baroda, India
Abstract: Hybrid yarns are engineered yarns, in which various materials are combined in one strand to create different structures based on the performance requirements of the final product. The chapter describes different production methods, both those developed by modifying conventional methods as well as entirely new methods for creating new structures and properties in hybrid yarns. The conventional methods are modified to incorporate high-performance textile materials like glass, carbon, and conductive materials into natural or synthetic material, principally for performance apparel and non-apparel applications; some methods have been especially developed to produce hybrid yarns for textile preforms used in thermoplastic composites for industrial applications. Key words: hybrid yarn, high performance, commingling, reinforcing, matrix.
2.1
Introduction
Hybrid yarns are an ‘engineered material’, a term encompassing a range of materials that can be designed according to technical functional requirements for a specific use, other than just covering the body or looking fashionable. To achieve various levels of technical performance in various types of products, different types of fibers, yarns and fabrics may be engineered to meet the specific requirements of each application. These hybrid yarns are manufactured using modified conventional techniques or newly developed methods. This allows the material scientist to meet new challenges by extending this technology to other materials to create advanced engineering structures. Hybrid yarns consist of highperformance materials like glass, carbon, kevlar, basalt (reinforcing materials), conductive materials, elastomeric materials, and natural or synthetic materials like cotton, jute, polyester, nylon, polypropylene (matrix materials), and so on. Owing to new designs and developments in manufacturing technology there is direct control over fiber placement, and various structures can be created through a combination of different forms of materials. Thus a hybrid yarn can meet its end use requirements. Hybrid yarns with core-sheath structures produced by a modified process are used in protective clothing, elastomeric yarns are used in stretch fabrics and conductive yarns in intelligent fabrics for apparel and nonapparel applications. With regard to the industrial applications of hybrid yarns, thermoplastic composites are becoming increasingly widely accepted as substitute materials for metals. Hybrid yarns are widely used in preform structures required in textile 21 © Woodhead Publishing Limited, 2011
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composites. Some methods such as commingling, schappe and KEMAFIL techniques are especially designed to produce hybrid yarns for thermoplastic composites. In the thermoplastic composite used for perform structures, when heat is applied the thermoplastic component melts and is subsequently converted into a composite by a consolidation process. A homogeneous distribution of reinforcement and matrix reduces the mass transfer distance. This produces a lightweight material with superior mechanical properties, suitable for various applications including the aerospace, automotive and marine sectors, as well as sporting goods and electronic industries (Alagirusamy et al. 2006).
2.2
Types of hybrid yarns and their development
The development of new types of technical yarns started after 1995. Before this, yarn was developed and modified only according to the aesthetic and tactile properties of apparel fabrics. Technical textiles have opened up new horizons for functional yarns, as well as new technological developments. The journey of yarn manufacturing started over 200 years ago with mule spinning in 1779, followed by the commercialization of ring spinning in 1828. Rotor spinning, initially known as open end spinning, was developed in 1963 in Czechoslovakia and started the third generation of the new spinning process. With advancements in man-made spinning technology, research was started into the modification of synthetic fibers to replace natural fibers. During the fourth stage of development, filament surface characteristics were modified and new yarn structures were developed, such as air-interlaced, bulk and crimped yarns, etc. Technical textile development has increased the demand for new processes and modifications with the aim of producing a fifth generation of yarns such as specialty yarns, technical yarns, hybrid yarns, etc. for high-performance requirements. Technical yarns need more functional properties in order to meet the technical requirements of the final products. Various means of producing technical hybrid yarns have been developed: modifying old techniques, creating new processes and developing modified yarn structures and yarn coatings. In addition, some special types of yarns like hybrid yarns, conductive yarns, novel yarns, plasma-treated yarns and technical sewing threads have been developed in the last few years. The generations of yarn development are given in Table 2.1. Hybrid yarns were developed by incorporating a functional material such as elastomeric materials, conductive materials, glass, Kevlar, carbon, etc. as the core in core-spun yarns; more recently they have been adapted for specific application in thermoplastic composites, by combining reinforcing filaments with thermoplastic matrix filaments to produce ready-made yarns using newly developed dedicated systems. The possible combinations of yarns in the production of hybrid yarns using different methods are given in Table 2.2.
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Table 2.1 Developments in yarns Generation
Development in yarns
Years
First generation Second generation
Short staple spinning: ring-spun yarns. Long staple spinning, Filament spinning: long staple yarns, mono filaments, multi filaments. New spinning process, Textured yarns: rotor yarns, friction-spun yarns, air vortex, air-textured yarns. Modified spinning system: core-spun yarns, specialty yarns, fancy yarns, elasto yarns, etc. Newly developed process: technical yarns, hybrid yarns, novel yarns, plasma-treated yarns, conductive yarns and nano filament yarns.
1760–1850 1830–1960
Third generation Fourth generation Fifth generation
1960–1990 1990–2000 2000 onwards
Table 2.2 Different types of hybrid yarns Production method New method
1 2 3 4 5
Type of yarn
Structure
Modified conventional method
Conventional Hybrid yarns yarns
Ring spinning Rotor spinning D REF spinning Wrap spinning Air-jet texturing
S S S SF, FF F,FF F,FF Fh
SSh, SFh, SC, SE SSh, SFh, SC,SE SSh, SFh, SC, SE SFh, FFh, SC, SE FFh, FC, FE
6 7 8
Commingling Parallel winding Stretch break
FFh, FE FFh SFh
9
KEMAFIL technology
FFh
10 Schappe technology
ShF
Twisted, core-spun Wrapped, core-spun Wrapped, core-spun Core–sheath Interlaced loop, core–sheath Nip, pleated Side by side Stretch-break fiber plus filament core Knitted sheath plus filament core Stretch break fiber plus wrapped filament
Notes: S = spun yarn, F = filament yarn, SS = spun–spun, FF = filament–filament, C = conductive material, E = elastomeric material, Sh = high-performance fiber, Fh = high-performance filament.
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2.3
Basic structures and properties of hybrid yarns
The basic structures of hybrid yarns can be divided into three categories based on different forms that are combined and on the properties of the material: 1. Staple fiber (S) and high-performance staple fiber (Sh) 2. Staple fiber (S or Sh) and filaments (F or Fh) 3. Filament (F) and high-performance filament (Fh). The basic possible yarn combinations for producing hybrid yarns are given in Fig. 2.1. The structures and properties of hybrid yarns depend also upon the method of manufacturing, the combination of fibers, filaments and yarns, and the position of the components of the yarn. The mechanical properties of staple yarns depend not only on the constituent fibers, but also on the yarn structure as characterized by the geometric arrangement of the fibers in the yarn. Staple fiber yarns, filament yarns and performance materials do not share the same properties and structures, causing differences between conventional yarns and hybrid yarns, where the most challenging aspect is to combine two dissimilar materials in a single yarn. As
2.1 Basic structures of hybrid yarns.
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hybrid yarns are designed to meet functional requirements, the final properties of any hybrid yarn depend on the properties of the functional component and its position in the yarn structure. Table 2.3 gives different structures of hybrid yarns produced by different manufacturing processes.
Table 2.3 Hybrid yarn structures based on production method Hybrid yarn structure
Position of performance filaments Performance filaments in core and covered spun fibers in twisted form
Ring core-spun yarn (RS) Performance filaments in core and covered spun fibers in wrapped form
Rotor core-spun yarn (R0S) Parallel arrangement of performance filaments in core and covered spun fibers
DREF core-spun yarn (DF) Parallel laid fibers in core and covered by performance filaments
Wrap yarn (WS) Thermoplastic filament and performance filaments are interlaced forming loop structure
Air-jet textured yarn (AT) Thermoplastic filaments and performance filaments in mingled form
Commingled (COM) Parallel arrangement of performance filaments and thermoplastic filaments
Parallel winding (SBS) (Continued overleaf )
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Table 2.3 Continued Hybrid yarn structure
Position of performance filaments Stretched break thermoplastic filaments covered by performance filaments
Stretch break (SB) Parallel arrangement of thermoplastic filaments surrounded by parallel performance filaments in the core, sheath in continuous filament in knitted form Kemafil technology (KEM) Mixture of discontinuous performance material and fibers surrounded by thermoplastic filaments Schappe technology (SCH) Note: Perfomance fiber of filaments (reinforcement) Spun fiber or continuous filament (matrix)
2.4
Production methods for hybrid yarns
Normally, spun yarns are produced on any of the conventional or new spinning systems. Various types of specialty yarns are also made on the existing spinning machines. Specialty hybrid yarns with core-sheath structures, bi-component materials, hybrid yarns consisting of reinforcing material, and so on, are able to impart technical properties like elasticity, electrical properties and resilience in yarns. Core-spun yarns can be manufactured by various spinning methods like ring spinning, rotor spinning, air-jet spinning and friction spinning by the incorporation of special attachments in a conventional spinning system. The new systems have been developed in order to achieve a homogeneous mix of reinforcing and thermoplastic matrix material in filament form, known as hybrid yarns, for use in thermoplastic composites. The main objective of this system is to mix two dissimilar materials, where the reinforcing material provides the backbone structure (preform) to the composite, and the matrix material melts and is impregnated into the composite structure. A great deal of research is currently underway in order to produce hybrid yarns commercially, as well as to understand the behavior of different reinforcing materials, with the aim of standardizing the process.
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2.4.1 Ring spinning The ring-spinning process is close to 200 years old. In the last few years a series of developments has taken place, as existing systems have been modified to combine staple yarns with different filaments, conductive yarns, elastomeric materials and high-performance materials such as glass, carbon and Kevlar in order to obtain hybrid yarns for performance requirements. Generally the performance filaments are inserted into the core, which contributes to the strength of the yarn. This is then surrounded by staple fibers as a sheath for aesthetic purposes. The production of core-spun yarns has been successfully carried out by many spinning systems, with each system having its own unique features. Conventional ring spinning is simple and economical but the positioning of the core in the center of the yarn is difficult and major strip-back problems may arise during later stages of the process, leading to twisting of the core filaments. The same system is used to produce core-spun conductive yarns on a ring-spinning system. Thin metal wire is used as the core and cotton fiber is used as the sheath. A schematic representation of the feeding of the core and the drafted staple fiber sheath into the yarn is shown in Fig. 2.2. The yarn formation is achieved by
2.2 Conventional ring spinning core-spun system (Chellamani and Chattopadhyay, 1999: 3).
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conventional ring spinning and by the traveler method of twist insertion (Chellamani and Chattopadhyay, 1999). The Southern Regional Research Center (SRRC) has developed a core-spinning system, which is shown in Fig. 2.3. The SRRC core-spinning system consists of a central core of a particular filament or staple fiber and the core material is coaxially and almost entirely wrapped with cotton or other staple fibers. This process gives a high degree of coherence between the constituent fibers. The same system was also developed with slight modifications as shown in Fig. 2.4, where two roving feeds are drafted on both sides of the core. The flame retardant-treated ARS corespun cotton yarn allowed the creation of fabrics with the desired level of fire resistance, greater than that provided by FR-treated 100% cotton yarn. Many other methods have also been developed such as the core twin-spinning system and the composite electrostatic spinning system, among others, but these have not yet been commercialized (Rameshkumar and Anbumani, 2008b). Rieter and Suessen have both developed commercial core-spun systems that are fed with two roving feeds, and thus provide a further reduction in hairiness as well as displaying some of the attributes of a two-fold structure. Additionally, several manufacturers have demonstrated the possibility of incorporating elastomers into the yarn through the use of a retro-feed arrangement as shown in Fig. 2.5. The alternative approach of using mechanical compaction was shown by LMW on its LR 63, which uses Switzerland-based Rotorcraft’s Rotorcraft Compact Spinning (RoCoS) system, demonstrating the potential of the RoCoS
2.3 SRRC core wrap spinning system (Rameshkumar and Anbumani, 2008b).
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2.4 ARC spinning system (Alagirusamy et al. 2006: 5).
2.5 Retro-feed for ring spinning system.
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system for spinning double roving yarns and incorporating a core yarn such as an elastomer (James and Roe, 2007). The process variables that affect the properties of core-spun yarn are the coresheath ratio, pre-tension applied to the core material, spinning draft, the number of roving feeds and twist. Two-roving feeding (with the filament at the center of the roving yarns) provides better core positioning and control during spinning, influencing the structures, properties and performance of core-spun yarns (Babaarslan and Osman, 2001). Elasto core yarns consisting of an elastomer core are covered with staple fibers during the ring-spinning process. The advantage of this feed over other production processes is that the sensitive filament is completely wrapped by staple fibers. The elastomer is protected against mechanical stress and the yarn usually comprises between 3 and 10% elastomer. The range of applications extends from classic yarn for sportswear and underwear to outer garments and fashion items (Oerlikon, 2009). By combining the core-spun and siro-spun processes, directly weavable, twofold elasto siro-spun yarns are produced on the ring-spinning machine as shown in Fig. 2.6. To produce elastomeric spin-twisted yarns, two roving feeds of staple fiber material are drafted in parallel in the drafting zone. The elastomeric material is then introduced in the front pair of drafting rollers. Yarn production, twisting
2.6 Elasto yarn by combined core-spun and siro-spun processes (Oerlikon, 2009).
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and insertion of the elastomeric material thus take place in a single step in the process. The outstanding features of this yarn are its high strength, low level of hairiness, smooth surface and round yarn cross-section. Elasto siro-spun yarns are used in high-quality outerwear. The major advantages of these yarns include a doubling of production in ring-spinning and winding processes, reduced energy and air-conditioning costs. In addition, the process is made considerably simpler by the elimination of the twisting process.
2.4.2 Rotor spinning Nield and Ali have developed a technique in a rotor-spinning machine for producing core-spun yarn as shown in Fig. 2.7. Twist efficiency and pre-tension of filament are the influencing factors in core spinning. In order to increase the contact area between yarn arm and doffing tube (for increased twist efficiency), a copper flange was soldered to the inner end of the doffing tube. The doffing tube was mounted on a ball bearing, and rotated by a separate drive in the opposite direction to the rotation of the rotor, with a speed ratio of 1:9. The rotating doffing tube inserts a false twist and pushes the twist back to the peel-off point. The rotation of the rotor wraps the yarn arm around the continuous filament core. The main advantage of this process is that the core is not twisted. It is more economical to produce coarse core-spun yarns with a rotor machine than with a ring-spinning system (Rameshkumar and Anbumani, 2008). The research carried out on hybrid yarns created by combining staple fibers and filament yarns is useful for improving the structure and properties of the yarn. Research into the new modified open-end rotor spinning has shown that it is able to produce hybrid yarns as shown in Fig. 2.8. The characteristics of hybrid yarns and means of production of novel yarns depend on the yarn formation technique,
2.7 Core-spun yarn by rotor-spinning process (Chellamani and Chattopadhyay, 1999: 7).
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2.8 Core-spun yarn by modified rotor-spinning process (Alagirusamy et al., 2006: 6).
filament overfeed and the twisting mechanism of rotor spinning. The structure and tensile properties of the yarn, as well as any irregularities, depend on the filament overfeed. A change in the filament overfeed has been shown to affect the geometric disposition of the filament yarn in the hybrid yarn, which in turn results in irregularities and changes in the tensile properties of the yarn. The level and structure of the twist are very important characteristics of all yarns: the fiber twist angle of the strand in a hybrid yarn is smaller than that of a rotor spun single yarn with the same spinning conditions. A comparative analysis of three typical hybrid yarns can be carried out by combining staple fibers with filament yarns with different twist angles and by varying filament over-feed: these three types are rotor core spun (RCS), rotor folded spun (RFS), and rotor wrapped spun (RWS) (Pouresfandiari et al., 2002; Matsumoto et al., 2002). A similar method also employed involves incorporating a metal wire into the yarn as a core. A rotor then wraps the wire with staple fibers: the core filament that passes through the center of the rotor is surrounded by a spiral ring of fibers, producing metallic yarns with a fiber cover. This new type of rotor-wrapping twister is used to produce novel hybrid yarns comprising a stainless steel filament, polypropylene nonwoven tape and a reinforced filament. These are then woven into fabrics and converted into laminates (Lin and Lou, 2003). The BD 340 filea® rotor-spinning machine produces an Elasto rotor yarn. This machine is characterized by its flexibility, facilitating the production of both standard rotor yarns and incorporating elastomeric yarn combination rotor yarns. The yarn counts range between 20 and 100 tex. These yarns are used in special fabric constructions for work wear or elasticated bed linen, although applications for finished textile products, which are limited as yet, will be steadily expanded in the future.
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2.4.3 DREF spinning The development of DREF core-spun yarns has opened up a new range of yarns, including hybrid yarns, high-performance cover yarns, and sewing threads used for technical textiles and in apparel due to their exceptional strength, outstanding abrasion resistance, consistent performance in sewing operations, adequate elasticity for stretch requirements, excellent resistance to perspiration, and ideal wash and wear performance. The stages of development of the friction-spinning machine known as DREF began in 1973, and six models have been developed to date:
• • • • • •
DREF 1 developed in 1973 by Dr Fehrer A.G. of Austria DREF 2 exhibited in 1975 at the Institute of Trade Mark Attorneys (ITMA) exhibition DREF 3 came onto the market in 1981 DREF 5 developed by Schalafhorst, Suessen and Fehrer, Inc. DREF 2000 demonstrated at ITMA in 1999 DREF 3000 displayed at ITMA in 2003.
The principle behind friction spinning is the contact between the completely opened fiber strand and the rotating drum, with the open end of yarn rolled by the frictional contact of the two drums as shown in Fig. 2.9(a) and 2.9(b). This system can incorporate any type of high-performance filament in order to produce hybrid
2.9 DREF friction spinning system: (a) DREF II (Alagirusamy et al., 2006: 7). (Continued overleaf)
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2.9 Continued (b) DREF III (Chellamani and Chattopadhyay, 1999: 10).
2.10 Core (glass) spun (polypropylene) DREF yarn cross-section (Mankodi, 2007).
yarns. Figure 2.10 shows a cross-sectional view of a glass core covered with a polypropylene fiber hybrid yarn for thermoplastic composites. DREF 3 is also used for glass, carbon and aramide to produce thermoplastic hybrid yarns for composites; and it gives good results with a metallic core. DREF 2000 and 3000, as shown in Fig. 2.11(a) and 2.11(b), are especially designed to produce hybrid yarns for use in composites, carpet backing, heat-proof fabric with a glass core, cut-resistant fabric with a kevlar core and high temperature-resistant fabrics with a glass or carbon core. These hybrid yarns are used for home textiles, in hotels and
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2.11 New DREF friction spinning system: (a) DREF 2000, (b) DREF 3000 (DREF Corporation SDN BHD).
hospitals, for camping equipment, in the military and in the automotive industry, as well as for covers made entirely from waste material or virgin fibers.
2.4.4 Wrap spinning The concept of wrapping a filament over a staple fiber core began with wrap spinning. A roving or sliver feedstock is drafted in a three-, four- or five-roller
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drafting arrangement, and the fiber strand that is delivered runs through a hollow spindle without receiving a true twist. In order to impart strength to the strand before it falls apart, continuous filaments are wound around the strand from the drafting arrangement. This thread comes from a small and rapidly rotating bobbin mounted on the hollow spindle as shown in Fig. 2.12. Withdrawal rollers lead the resulting wrap yarn to a winding device. The wrap yarn consists of two components: one twist-free staple fiber component in the yarn core and a filament wound around the core. These yarns are used mainly for making home textiles, automotive textiles, outerwear, carpet yarns, etc. Filament–filament wrapping can be similarly achieved through the use of the hollow spindle technique as shown in Fig. 2.13. The hollow spindle unit was developed in order to produce conductive thermoplastic hybrid yarns consisting of a glass core and a copper wire, which is passed through the center of the hollow spindle and then moves upward through the device. The principle behind the hollow spindle wrapping technique is that the core yarn passes through the bottom of the hollow spindle and the double flange bobbin with wrap yarn is mounted on the spindle as shown in Fig. 2.14. As the spindle rotates, the filament is unwound from the double flange bobbin and binds the core yarn by spiral wraps. The
2.12 Wrap-spinning process (Mankodi, 2007).
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2.13 Wrap yarn by the hollow spindle process (Mankodi, 2007).
required number of wraps in the yarn can be obtained by controlling the spindle speed and yarn take-up speed. The hollow spindle wrapping technique is mainly used to produce zari yarns, elastomeric yarns and other cover yarns in which the core component determines the technical properties of the yarn and the sheath component covering the core gives the yarn its aesthetic value. This process is also known as the covering process. Hybrid yarns can be produced by combining the matrix and reinforcing material using the hollow spindle wrapping technique. Hybrid yarns for industrial applications are produced mainly by combining thermoplastic yarn with a reinforcing material such as glass and carbon. Conductive materials can be incorporated into hybrid yarns for protective or shielding applications. This type of hybrid yarn improves weavability as well as knitting performance as compared to the direct use of glass or carbon yarns for preform. The machine consists of a
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2.14 Hollow spindle unit attachment (Mankodi, 2007).
feeding unit, a hollow spindle unit and a winding unit, and can be adjusted for the required number of wraps per meter in the yarn. Fig. 2.15 shows a cross-sectional view of a hybrid yarn. The covering of a core yarn by twisting and retwisting is achieved through a new technique called ‘direct twist covering’. This method produces two types of hybrid yarns: one is single (S) twist (similar to the hollow spindle wrapping method) and the other is double (SZ) twist. In the fiber twist technique, it is possible to adjust the thermoplastic fiber and glass fiber composition by controlling fiber and twist number. In the single twist method, twisting thermoplastic fiber around the reinforcement fiber in an ‘S’ twist produces a hybrid yarn. On the other hand, in the double twist method a hybrid yarn is produced by twisting thermoplastic fiber around the reinforcement fiber in both ‘S’ and ‘Z’ twists (Agteks, 2005).
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2.15 Core (glass filament)/wrap (polypropylene filament) hollow spindle yarn cross-section (Mankodi, 2007).
2.4.5 Air-jet texturing Air-jet texturing is a well-established filament yarn processing technology that was first used more than half a century ago. There is much debate in the literature about various aspects of the process, such as the mechanism of loop formation, the role of water in air texturing and the influence of material and process variables on air-textured yarn structure. The principle of the air-jet texturing process and the structure of the air-textured yarn are demonstrated in Fig. 2.16. In this process, supply yarn is overfed in the turbulent zone where compressed air is directed mainly parallel to the yarn path, resulting in longitudinal shifting of the filaments
2.16 Principle of the air-jet texturing process.
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together with the formation of filament loops. The heart of the air-jet texturing process is the air nozzle. The purpose of the nozzle is to create a supersonic, turbulent and non-uniform flow to entangle or blend the filaments, forming them into loops to produce stable textured yarns. Some texturing nozzles have impact elements of different sizes and shapes at the exit of the nozzle, aiming to improve the process stability and quality of the textured yarns (Alagirusamy et al. 2006). In recent years a great deal of research has been carried out to produce hybrid yarns through this process, for use in commercialized products like elastomeric yarns, glass filament texturing and high-performance yarns. Air-jet texturing is a purely mechanical process and can be used to combine reinforcing and matrixforming filaments. In the case of air-jet texturing or commingling (as described in the next section), the three factors that play the most important roles are the crosssection of the fiber, the drag force and the bending behavior of the filament. The reinforcing material, such as glass, and the thermoplastic matrix filament, such as PET and PP, have a different cross-sectional area and different torsional and bending behavior, which prove difficult to combine. The carbon filament is difficult to texture due to very poor loop strength, high stiffness (high initial modulus) and also due to its ability to resist the perpendicular force that acts on it during the process. The same is true of glass but due to low modulus and better loop strength compared to carbon, glass can more easily be combined with other thermoplastic materials. The existing texturing machines have been modified, with some commercial machines also developed by companies in order to investigate and further the airtexturing technology for glass fiber roving feeds as shown in Fig. 2.17(a). The machines have the following modifications:
• • • •
New types of air texturing nozzles Multiple glass fiber roving feeds Simple threading through the machines to minimize damage to fibers Devices to ‘loosen’ the fibers, which can stick together due to sizing.
The texturing technology has been developed to a stage where it is possible to air-texture glass fiber roving up to a size of 600 tex together with thermoplastic fibers. The quality of the textured yarn depends heavily on both the type and amount of sizing on the glass fibers. Glass filament yarns and roving feeds are difficult to handle during textile processing as a result of their low bending and transversal compression strength. Improperly designed friction and deflection areas lead to filament damage, thus reducing the mechanical properties of the composite material. The main focus of the modifications is on optimizing the yarn line from the bobbins to the texturing zone; thus the basic requirements for the manufacture of glass–PP hybrid yarns can be achieved. Commercially available air nozzles suitable for the texturing process are shown in Fig. 2.17 (b).
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2.17 Air-jet texturing: (a) hybrid yarn texturing machine, (b) two nozzles: (i) Hema jet LB 341, (ii) Hema jet EO 52.
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2.4.6 Commingling Commingling is a process involving two or more continuous multifilament yarns, the filaments of which have been intermixed without adding twist or otherwise disturbing the parallel relationship of the combined filaments. The yarns used are normally a reinforcing yarn, such as graphite or glass, and a thermoplastic matrix yarn. The first commercial commingling process was developed by Saint-Gobain Vetrotex with the trade name Twintex®. This process was developed to mix glass and polypropylene at melt spinning stage in order to produce hybrid yarns for thermoplastic composites. Twintex® is unique and produces ready-to-use commingled hybrid yarns from a thermoplastic matrix yarn and glass reinforcing yarn designed with high mechanical properties such as an excellent stiffness:weight ratio, and superior impact properties, as well as efficient and environmentally friendly processing conditions and recyclability. Twintex® products are made of commingled E-glass and thermoplastic filaments. Direct roving is the base material for the whole Twintex® product line, and can be provided with a polypropylene (PP) matrix and most recently with a co-polyester resin (PET) matrix. Today the co-polyester thermoplastic matrix is mainly produced by the Twintex® Roving R with 70% glass loading in weight. Figure 2.18 shows a crosssection of commingled yarn. The manufacturing process of Twintex® is a patented process and is shown in Fig. 2.19. The mixing of polypropylene and glass after they emerge from the spinneret provides a homogeneous mixing of two dissimilar materials at the spinning stage. The parameters influencing the selection of materials for use are glass fiber orientation, thickness ratio, and stiffness of each material. Yarns produced in this way are widely employed in the automobile industry due to their unique advantages such as lower cost, design freedom, functional integration, noise absorption, crashworthiness, corrosion resistance and recyclability (Owens Corning Twintex® R PP, 2008).
2.18 Twintex® commingled yarn cross-section (Owens Corning Twintex® R PP, 2008).
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2.19 Twintex® process (Owens Corning Twintex® R PP, 2008).
Attempts to mix reinforcing and thermoplastic material in filament form using the air-interlacing process have also been carried out. This concept of air interlacing or mingling was developed as a replacement for twisting and sizing with the aim of improving weavability. Later on, the same principle was also used to mix two different-colored filaments to achieve different color effects and to produce hybrid yarns with an elastomeric component covered by continuous filaments or staple fiber yarns. The basic principle of the mingling process when applied to two or more dissimilar yarns to form a single strand of yarn can be defined as commingling. In the commingling process, rapidly moving air in an air nozzle generates entanglements in and among the filaments, as shown in Fig. 2.20. Cohesive forces between the fibers and filaments are essential to hold the fiber and filaments bundled together to form a flexible structure such as textile yarn. When a loose bundle of filaments are instantaneously subjected to the effect of a turbulent perpendicular cold air-jet, the air flow opens up the filaments, while in the immediate vicinity of the opened-up section, and the filaments are intertwined and mingled with each other to form a compact section. The basic filament structure does not change either physically or chemically, but the position of filaments is altered. Commingled yarn consists of blended combinations of reinforcing filament yarn and thermoplastic yarn. A homogeneous distribution of the reinforcement and matrix yarns would reduce the mass transfer distance of the matrix during processing, which would in turn lead to a fast and complete impregnation of the reinforcement filaments. In combination with the developments in textile structures, the use of commingled yarns significantly improves the mechanical properties of the resultant composite parts. Several patents have been filed for the
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2.20 Principle of the commingling process (Mankodi, 2007).
commingling of high-performance and matrix-forming filaments for composites and other applications. Processing parameters and the selection of the nozzle both play an important role in the distribution and opening of the filament. A new type of commingling machine has been developed, and the effect of various processing parameters on the characteristics of commingled hybrid yarns, including air pressure, over-feed and take-up speed, has been studied, leading to optimization of the parameters. A new type of machine was developed as shown in Fig 2.21, by combining two methods, namely commingling and the hollow spindle technique, in order to obtain different hybrid yarn structures using one single machine. The three different structures produced are shown in Fig. 2.22(a) and 2.22(b).
2.4.7 Parallel winding The term ‘parallel winding’ as used in textile processes does not simply mean the positioning of filaments side-by-side to create hybrid structures. Hybrid yarns manufactured by parallel winding, also called tape winding or the side-by-side technique, are especially employed in thermoplastic composites, similarly to the use of friction winding for thermoset composites. In this process, the continuous reinforcing filaments and thermoplastic filaments are assembled in the form of a tape. This sheet passes through the heating chamber, the temperature of which is set at the softening temperature of thermoplastic yarns. The sheet emerges in tape form, runs through the laying head and is wound on a mandrel. Once in the heating zone, the pressure roller applies pressure on the outer surface of the mandrel. The hot air nozzle (set to melting temperature) melts the thermoplastic material and consolidation takes place. In this process, lay-down, melting and consolidation are all achieved in one single step. Figure 2.23 shows a flow chart of the parallel winding process (Debalme et al., 2003).
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2.21 Commingling machine for hybrid yarn (Mankodi, 2007).
2.4.8 Stretch breaking Stretch breaking is the process of making spun yarn from high-strength, highmodulus hybrid yarns by feeding one or two tows of high-modulus materials such as carbon or glass. The process is similar to the stretch break process used for converting filaments into staples as shown in Fig. 2.24. The ratio of reinforcement to matrix can vary but the amount of reinforcement fiber should preferably be 40 to 75% by volume. The average fiber length can vary but should ideally be 6 inches in length with random overlap distribution. In the
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2.22 Commingled yarn cross-section: (a) glass/polypropylene, (b) glass/polypropylene mingled core and polypropylene wrapping (Mankodi, 2007).
process a sliver of stretch broken fiber is mixed with tow or with a yarn of continuous thermoplastic filament in the tensioning zone, causing the filament to break randomly, producing a hybrid yarn. Heating causes melting of the thermoplastic matrix material and a composite is formed (Armiger et al. 1989, Hendrix et al. 2007).
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2.23 Flow chart showing parallel winding of hybrid yarns.
2.24 The stretch break process.
2.4.9 KEMAFIL technology The Saxon Textile Research Institute in Chemnitz, Germany, has developed KEMAFIL technology for geo-textiles. This is a turning thread technique. By means of mechanically interlacing yarns into a knitted structure, linear textiles are produced. KEMAFIL machines as shown in Fig. 2.25(a) are circular knitting machines operating with loppers that are arranged around a guide bar and produce a tubular knitted structure, which can cover any type of core yarn. In this type of hybrid yarn, parallel reinforcing filaments surround a parallel arrangement of matrix fibers. The entire structure of matrix and reinforcing filaments is placed in the core with a sheath
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2.25 KEMAFIL technology: (a) machine, (b) hybrid yarn structures (SL-Spezialnähmaschinenbau Limbach GmbH & Co. KG).
of matrix fibers acting as the skin. The structures of hybrid yarns produced by the KEMAFIL technique are shown in Fig. 2.25(b). Kemafil Machine Model 3602 is used for products such as rope-like technical cords and packing seals. The shroud can be composed of a wide variety of core materials such as threads, linen threads, wires, foils, fleeces, or of combinations involving glass, wool, aramide, carbon fibers, fiber volumes, pressure oil hoses, pipes or textile wastes (Alagirusamy et al. 2006, SL-Spezialnähmaschinenbau Limbach GmbH & Co. KG).
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2.4.10 Schappe technology Schappe technology was established in the late nineteenth century, based on silk yarn spinning techniques. In the twentieth century, further developments were made based on stretch breaking techniques for synthetic fibers. Today Schappe techniques have applied this same technology to the spinning of the latest generation of advanced technical hybrid fibers. Schappe technology is based on the use of long fibers to obtain yarns that are more bulky and of higher tenacity. Stretch breaking, the first step of the process (see section 2.4.8), consists of transforming the continuous filaments into a top of long fibers. This technique removes the weak points of the fibers and improves their characteristics by increasing their tenacity and spinnability. Technical yarns are composed of a wide range of products. They are designed to fulfill the highest requirements in a large number of industrial fields such as thermal protection, fire resistance and cut resistance for personal protective equipment, technical sewing threads, packing and composites.
2.5
Applications of hybrid yarns
The applications of hybrid yarns include apparel, non-apparel and industrial products. The properties and composition of hybrid yarns are determined by the requirements of the end product and by the fabric (preform) structures.
2.5.1 Apparel Thanks to hybrid yarns, apparel fabrics can now be intelligent, protective and fireresistant, as well as offering many other functional properties. Core-spun elastomeric materials were used traditionally in knits for hosiery, underwear or swimwear. Thanks to their variable and specifically adaptable properties, new material blends and optimized production processes, they have become established in many new areas of application. They are used in sportswear, leisure garments and children’s wear, in functional clothing (fashionable denim garments or work wear), and in high-quality outerwear (shirts, blouses, suits). These materials have, among many other attributes, superb dimensional stability, durable elasticity, good stability under load, wear resistance, simple care and above all a high level of wear comfort, making them suitable for a wide variety of functions, and giving rise to a highly dynamic market. Some of the applications are shown in Fig. 2.26. Annual growth rates of approximately 10% on average have been observed in recent years and are also predicted for the future. It is estimated that around 50% of clothing now contains some form of elastane material (Oerlikon, 2009). Conductive hybrid yarns are also widely used in e-jackets, intelligent fabrics, fabric sensors, actuators, and so on. The washable wearable electronics produced from conductive core hybrid yarns are employed in niche applications like sportswear, defense uniforms, protective clothing, etc. So apparel fabrics
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2.26 Hybrid yarns in apparel applications.
are now able to offer protection and communication, as well as being both intelligent and fashionable, thanks to the multitude of applications for hybrid yarns.
2.5.2 Non-apparel The market for DREF yarn is increasing due to the wide range of possible applications. There are a number of non-apparel applications of hybrid yarns as shown in Fig. 2.27 and listed below:
• •
Blankets for home textiles, hotels, hospitals, camping, military uses, etc. Cleaning rags and mops from cotton waste and various waste-blends
2.27 Hybrid yarns in non-apparel applications.
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• • • • • •
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Decorative and upholstery fabrics Secondary carpet backing for tufting carpets and filler yarns for carpet wefts Flame retardants for the aviation and contract business range, cut-resistant textiles (e.g. protective gloves, mail-bags, seat covers) Outdoor textiles (e.g. chair and deck-chair coverings) Filter cartridges for liquid filtration Asbestos substitutes (e.g. heavy protective clothing and gloves, gaskets, packaging, clutch and brake linings, flame retardant fabrics, etc.).
2.5.3 Industrial applications Hybrid yarns are generally used as a reinforcing component for making thermoplastic composites. There is a growing interest in applications of thermoplastic composites in ever broader areas, including for sports and in the automotive industry. Thermoplastic materials are used in various industrial applications as listed in Table 2.4, including aerospace, automotive, defense, construction, rail, sports, medical, oil/gas, energy and irrigation. The main factors influencing the use of hybrid yarns in automotive applications are cost reduction, weight reduction and recyclability. The cost of composite molded parts is becoming increasingly competitive for applications such as bumper beams, floor, under-body shields and so on. Thermoplastic composites are also used in a number of other industrial applications that can afford to use a
Table 2.4 Industrial applications of hybrid yarns Serial no. Sector 1
2
3
4
5
Applications
Building and construction Window frames and components; cladding – exterior horizontal and vertical; door frames and components; ducting; roofline products: shingles, roof tiles, etc. Interiors/internal finishes Interior panels, decorative profiles; office furniture; kitchen cabinets; shelving; worktops; blinds, shutters; skirting boards; railings, etc. Automotive Door and head liners; ducting; interior panels; rear shelves; spare tire covers; truck floors, etc. Garden and outdoor Decking; fencing and fence posts; garden furniture; shelters and sheds; park benches; playground equipment; playground surfaces, etc. Industrial/infrastructure Industrial flooring; railings; marine pilings/ bulkheads; railway sleepers, etc.
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premium product with a long life cycle. The important end uses of thermoplastic composites in aircraft applications are in access panels and doors, engine cowlings, movable wing surfaces such as elevators, rudders and spoilers. Aircraft floor panels are made through thermo folding whereby the laminate is locally heated and folded. This process provides durable products at low cost for such applications. Composites have been used in the rail industry for many years in such applications as seating, walls, ceilings, platforms, interior doors, window panels, side frames, front structures, etc. The driving forces for the use of polymer matrix composites in transportation includes cost reduction, reduced weight, excellent mechanical properties, durability, noise/vibration dampening, aesthetics, dent resistance, corrosion resistance and dimensional stability. So far, thermoplastics have not been used in rail applications as widely as in automotive and aerospace applications, but considerable market growth is expected in this area.
2.6
Future trends in hybrid yarns
Advances in products and processes are taking place at a very quick rate. Many areas have yet to be fully explored, and extensive research is required to develop new yarn structures and process technologies and to replace and modify existing products and processes. Some areas of potential future development are highlighted below. One area of future research is to develop the technology to produce hybrid yarns with different structures using a single machine. A commingling machine has been developed that combines the processes of a mingling hollow spindle in a single machine (section 2.4.6). These techniques have high market potential due to the flexibility of the process and their ability to produce different varieties of hybrid yarns as per functional requirements. Some other techniques have also been reported, such as the combination of air-jet texturing with twisting. The other upcoming area with potential for future development is nanofibre technology. Electro spinning is widely used to produce nanofibres from the synthetic, natural or composite polymer systems used in medical filtration applications. Attempts have been made to produce commingled yarns with a nanostructured glass surface and polypropylene filaments for effective composite properties. Developing commingled yarn technologies and understanding the fundamental interface nanostructures of reinforcement and thermoplastic filaments are of significant current interest. Recently, extensive different studies using carbon nanotube reinforcements in polymer composites have reported limited improvements in their bulk mechanical properties compared with traditional fiber reinforced composites. The effective use of nanotube mechanical properties in composites is a longstanding problem, despite their huge promise, due to issues such as dispersion, alignment, and interfacial strength. The most
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significant opportunity for nanotubes in composites lies in the use of unique online hybrid yarns through simultaneous sizing with single-wall carbon nanotubes (SWNTs) in order to optimize the fiber/matrix interface properties. The selection of the processing route for online spinning of hybrid yarns is based on the sizing/finish application and nano surface structuring using this online process at high speeds. The influence of different sizing and processing conditions of the hybrid yarns on the mechanical composite properties has been studied (Mäder, 2007). The electro-spinning technique is also used to manufacture nanostructured yarns, mainly carbon nanotube yarns, due to their technical application in electronic textiles, ballistic protection fabric and tissue engineering including artificial muscles. Studies have discussed the use of single-needle electro spinning to coat nanofibers onto monofilament arrays, followed by twisting to achieve balanced hybrid yarn structures for improved cohesion. These types of hybrid yarns have tuneable mechanical properties and high porosity, making them suitable for artificial tendon or ligament scaffolds (Zhou et al. 2010). Biodegradable, intelligent material and smart material are the unique polymeric materials or hi-tech fibres that are combined with natural fibre to make hybrid materials more economical and functional. Conventional materials can be preserved but also made more functional, thanks to hybrid yarns. Hybrid yarns created using new technologies, such as plasma-coated yarns, FR yarns, and nanofibre hybrid yarns are among the areas in need of further research for the development of commercialized products. Further applications for hybrid yarns require hybrid technology to become more widely accepted in the marketplace. Today the development of new technical textile products requires an integrated approach. Such an approach is necessary in developing any commercial product or process to meet market requirements, but the environmental implications of using and applying the product should not be forgotten.
2.7
Acknowledgements
The content of this chapter deals with developments in hybrid yarns. My research work on the effects of processing parameters on the commingling behavior of glass/polypropylene hybrid yarns was carried out at the M.S. University of Baroda, India. The earlier information available on hybrid yarns was principally focused on their use in thermoplastic composites. This chapter was developed with the help of several leading manufacturers of hybrid yarns. My sincere acknowledgement to Owens Corning Composite Materials, Oerlikon Textile GmbH & Co. KG, DREF Corporation SDN BHD and SL-Spezialnähmaschinenbau Limbach GmbH & Co. KG for their quick responses and help in allowing me to reproduce material.
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I am grateful to The Textile Institute, UK, and SITRA, Coimbatore, for their permission to use their publications in order to provide more detailed information in the chapter. I would like to acknowledge all the authors of articles, books or patents mentioned in the references who directly or indirectly helped me to complete my work. My special thanks to Mr Devel Vasavada, Department of Textile Engineering, M.S. University of Baroda, for his valuable suggestions. Finally, I wish to express my gratitude to Dr R. H. Gong for giving me the opportunity to share my knowledge with a global readership.
2.8
References
Agteks (2005), Redefinition of twisting, http://www.agteks.com. Alagirusamy R., Fangueiro R., Ogale V. and Padaki N. (2006), ‘Hybrid yarns preforming for thermoplastic composite’, Textile Progress, 38(4). Armiger T. E., Edison D. H., Lauterbach H. G., Layton J. R., Okine R. K. (1989), Composites of stretch broken aligned fiber carbon and glass reinforced resin, US Patent 4 856 147, August 15. Babaarslan and Osman. (2001), ’Method of producing a polyester/viscose core spun yarn containing spandex using modified ring frame’, Textile Research Journal, 71940, 367–371. Chellamani K. P. and Chattopadhyay D. (1999), Yarns and Technical Textiles, SITRA, Coimbatore. Debalme J.-P., Voiron J., Cividino, A. (2003), Method for making hollow solid generated by rotation, US Patent 6 605 171 B, August 12. Hendrix J. E., Hamrick D. H., Edwards H. B. (2007), High-strength spun yarn produced from continuous high-modules filaments and process for making same, US Patent 7 188 462 B2, March 13. James B. and Roe B. (2007), ITMA technology, http://www.textileworldasia.com. Lauke B., Bunzel U., Schneider K. (1998), ‘Effect of hybrid yarn structure on the delamination behavior of thermoplastic composites’, Composites: Part A, 29A: 1397–1409. Lin J. H. and Lou C. W. (2003), ‘Electrical properties of laminates made from a new fabric with pp/stainless steel commingled yarn’, Textile Research Journal, 73(4), 322–326. Mäder E., Rothe C., Gao S. L. (2007), ‘Commingled yarns of surface nano-structured glass and polypropylene filaments for effective composite properties’, J Mat Sci, 42, 8062–8070. Mankodi H. (2007), ‘Effect of processing parameter on commingling behavior of glass/ polypropylene hybrid yarns’, PhD Thesis, M.S. University of Baroda. Matsumoto Y.-I., Saito H., Sakaguchi A, Toriumi K., Nishimatsu T. et al. (2002), ‘Twisting mechanisms of open-end rotor spun hybrid yarns’, Textile Research Journal, 735. Oerlikon: Saurer Total Solutions (2009), Elasto, http//www.orlikontextile.com Owens Corning (2008), Twintex® R PP product manual.
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Pouresfandiari F., Fushimi S., Sakaguchi A., Saito H., Toriumi K. et al. (2002), ‘Spinning condition and characteristics of open-end rotor spun hybrid yarns’, Textile Research Journal, 72(1) 61–70. Rameshkumar C. and Anbumani N. (2008), ‘DREF spinning: A platform for hi-tech textiles’, http://www.fiber2fashion.com. Rameshkumar C. and Anbumani N. (2008), ‘Production and properties of core-spun yarns’, http://www.fiber2fashion.com. Zhou F.-L., Gong R.-H., Porat I. (2010), ‘Nano-coated hybrid yarns using electro spinning’, Surface and Coatings Technology, 204, 3459–3463.
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3 Developments in rope structures and technology J. W. S. HEARLE, University of Manchester, UK
Abstract: For thousands of years, short fibres had to be twisted into yarns and strands to form ropes. The situation changed around 1950, when continuous filament nylon yarns meant that low-twist ropes could be made. Later, polyolefins, polyester, aramid and HMPE (high modulus polyethylene) yarns became available. New rope constructions, including single- and double-braid ropes, Parafil, parallel-strand, and wire-rope types, have been developed. The discontinuous operation of constructing a ropewalk has been replaced by new continuous machinery. New splices and mechanical terminations have been developed. More demanding uses have appeared: for example, deepwater moorings, where extensive study has shown that polyester ropes are most suitable. Traditional uses have become more specialised: in sailing and mountaineering, a range of different ropes is now available that suits different technical and economic needs. Key words: synthetic fibres, low-twist ropes, rope machinery, terminations, rope uses.
3.1
Introduction
3.1.1 The history of ropes Ropes and cords are one-dimensional fibre assemblies. They are used in tension, which means that they are straight when free, unless their weight causes a catenary effect, and follow curved paths round guides. The technology of the production and use of three-strand ropes is shown in paintings and carvings from 5000 years ago. A papyrus rope dating from 500 BC was found 65 years ago in a cave on the banks of the Nile. This technology was not challenged until the 1950s. The dominant materials were the hard plant fibres, sisal, manila hemp and henequen, and the soft plant fibres, jute, cotton, flax and hemp. These are all fibres of limited length, so that twist was needed to generate the transverse forces that result in the frictional forces that allow stress transfer from one fibre to its neighbours. Three-strand ropes were produced on ropewalks, which might be several hundred metres long. As shown in Fig. 3.1, the action took place in three stages: three sets of rope yarns were pulled in; they were twisted into strands; the strands were twisted together to form the rope. The range of products was small. Similar ropes were used for different purposes. There was a range of sizes and, for example, cotton ropes were softer than sisal ropes. Twist levels varied little. There were some four-strand ropes. Braiding was limited to small cords. 56 © Woodhead Publishing Limited, 2011
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3.1 Rope construction on a ropewalk.
3.1.2 Post-1950 developments The major changes after 1950, which will be described in this chapter, result from four causes:
• • • •
New materials: the introduction of continuous filament yarns New machinery and control technology Design for use: specialist ropes for specialist markets Some new demanding uses.
3.2
New fibres
3.2.1 Continuous filament yarns Continuous filament yarns do not need twist to transmit stress from one fibre to another. In principle a tow of parallel filaments would support a load. In practice, the tow would not be easy to handle. The filaments would spread out, could
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become entangled or snag on neighbouring objects. Some structure is needed to give a coherent rope but, whereas in staple fibre ropes a substantial level of twist is needed to generate a self-locking structure and more to maximise strength, in continuous filament structures maximum strength is achieved at the low level needed to give support to weak places in filaments. This was an opportunity for rope-makers to exploit with new low-twist structures. The first cellulosic continuous filament yarns, rayon and acetate, did not impact on the rope industry, though high-tenacity viscose became important in tyre cords. The low wet strength may have been a contributory factor.
3.2.2 Nylon Nylon, which became available in 1938, was soon used in small cords and in larger ropes in the 1950s. In ropes, it has moderately high strength, comparatively low modulus and high extension, high work of rupture and good elastic recovery. This makes it ideal when high-energy absorption is required. A weakness is poor abrasion resistance when wet.
3.2.3 Olefins Polyethylene and polypropylene were introduced into ropes next. Their properties are not as good as nylon, particularly in poorer recovery, but they are extensively used at the cheaper end of the market.
3.2.4 Polyester Polyester, which was available before polypropylene, was a later entrant to the rope market, but is now a major player with a good combination of properties for many uses. The modulus is higher than nylon and the fibres do not suffer from poor wet abrasion and have a high resistance to axial compression fatigue.
3.2.5 High-performance fibres The high-performance fibres, aramids (Kevlar, Twaron, Technora), high-modulus polyethylene (Spectra, Dyneema), aromatic polyester (Vectran), PBO (Zylon), became available in the last quarter of the twentieth century. These are highstrength, high-modulus, low-extension fibres. To varying extents, they suffer from axial compression fatigue, which occurs when one component of a rope goes into compression. TTI and Noble Denton (1999) recommend a guidance design limit for cycles in compression of 2000 for aramid, 40 000 for HMPE and 100 000 for polyester. HMPE is prone to creep and creep rupture.
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Laid ropes
3.3.1 Three-strand ropes As shown in Fig. 3.2, a three-strand rope is a multi-level structure. The first level is a textile yarn; this is then usually twisted into a three-ply yarn and a number of these are combined into a rope yarn. Many rope yarns are then twisted into strands and the strands are twisted into ropes. The old ropewalks were replaced by continuously operating machines. Although this was an important change in manufacturing, the resulting rope structure, shown in Fig. 3.3, was unchanged. Three-strand ropes remain the dominant form for most purposes. The differences in price and performance reflect the fibre content.
3.3.2 Other laid ropes There is a limited production of four-strand ropes in which three strands surround a central strand. The ropes are rather similar to three-strand ropes. Six-strand ropes are made by tightly laying six strands round a central strand. They are used in sizes up to 80 mm on mooring winches for large vessels.
3.2 The many levels of structure in a three-strand rope.
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3.3 Three-strand rope.
3.4
Braided ropes
3.4.1 Overview Modern braided ropes are made on large braiding machines. Because, except in the old solid braids used in sash cords, halter cords and people control in theatres, strands go round in opposing directions and can be opposed in their twist constructions, it is usually possible to make braided ropes that are torque-free under tension, which is not possible with most twisted ropes. A long lay-length means that the obliquity angle is low and so there is little reduction in strength and modulus. A disadvantage is that the structure is then very loose, which can lead to snagging. The rope can be firmed up by coating with an adherent or enclosing in a jacket. The variety of available fibres, which may be used in combinations such as polyester/polypropylene, the different types of braid and the range of specifications for each type mean that the rope-maker now has the opportunity to produce a wide range of different braided ropes. Apart from optimising performance and cost for a given end-use, companies are limited by their machinery. Customers must therefore search for companies that can best suit their needs, if necessary taking advice from expert consultants.
3.4.2 Eight-strand plaited ropes A plait is a specific type of braid. In an eight-strand plaited rope, the carriers move as four sets of pairs, with the strands moving from the centre to the outside of the rope. As shown in Fig. 3.4, the strands that move clockwise (Z-direction) along the rope have a right (S) lay and those that move anti-clockwise (S-direction) along the rope have a left (Z) lay. This means that the rope yarns on the outside lie parallel to the rope axis.
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3.4 Eight-strand plaited rope.
Eight-strand plaited ropes are made up to 160 mm in diameter. They have good strength conversion with a long lay and good abrasion resistance.
3.4.3 Single hollow braid ropes The difference in a hollow braid from a plaited rope is that the carriers do not cross the centre but circle round in opposite directions in a maypole fashion. This means that there is a hollow at the centre, though in practice this may collapse to a negligible size. The carriers run singly in an eight-strand rope and not in pairs as in the plaited rope. With more carriers, the strands may run singly or in pairs. The interlacing may be plain or twill. The structure of a twelve-strand rope is shown in Fig. 3.5. A sixteen-strand rope has a larger hole in the centre and tends to collapse into a flattened form. Hollow braided ropes generally have somewhat higher strength and less stretch than laid or plaited ropes but are more prone to internal abrasion damage. They
3.5 Twelve-strand rope.
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can be made in unlimited lengths. Carriers are initially supplied with varying lengths of strand. When one runs out, it can be replaced by one with a new supply. An overlap length is formed between the two strands with minimal disturbance of rope dimensions.
3.4.4 Double-braid or braid-on-braid ropes In double-braid ropes, Fig. 3.6, the load is carried roughly equally between a core braid and an outer braid. The core is usually braided with eight or twelve carriers, with increasing numbers of strands per carrier for larger ropes. The cover will have more carriers, typically 16 for small ropes and 32 for large ropes, again with more than one strand per carrier. The core is produced with a long pitch, which maximises strength conversion. Since it is within the cover, looseness does not matter and snagging cannot occur. The outer braid is made in a tighter construction with the yarns at a higher angle to the axis of the rope. This means the core tends to pick up load faster. The use of a nylon core and a polyester cover tends to equalise the loading and the polyester improves abrasion resistance. A variant is the use of a polypropylene core; the polypropylene creeps (actually it is more stress relaxation) more than polyester, which tends to equalise loading.
3.4.5 Braided rope with jacket In a variant braid-on-braid a core of a high-modulus, high-tenacity fibre, such as aramid or HMPE, is designed to carry most of the load and a polyester jacket protects it from external abrasion. This type of rope is suited to applications needing high strength and low extension.
3.6 Double-braid rope.
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Low-twist ropes
3.5.1 Advantages and disadvantages of low twist In the simplest model of yarn mechanics, strength and resistance to extension fall off with the mean value of cos4θ, where θ is the angle between the fibre axis and the yarn or rope axis. There are some corrections in more detailed models, but the trend is clear. For staple yarns with fibres of limited length, this obliquity term must be multiplied by a term that accounts for slip at the fibre ends. The effect is lower with high-friction, high-transverse forces generated by twist, longer fibres and finer fibres. Below a critical level, there is little resistance to slippage; beyond this, at higher twist levels, the structure becomes self-locking but continues to increase in strength until the reduction due to obliquity has a greater effect than further resistance to slip. With continuous filament yarns, only the obliquity term has to be taken into account. There is a small rise in strength from zero angle to about 7°, as mutual support overcomes the effect of weak places. There is therefore a clear advantage in terms of strength and resistance to extension in keeping twist levels low. The difficulty is that a zero-twist bundle, and to a lesser extent a low-twist bundle, are not controlled and can become entangled and snagged. As continuous filament yarns have moved into the rope industry, efforts to deal with this problem have been made.
3.5.2 Parafil rope The first completely new rope type was developed by ICI in the 1960s. A collection of polyester yarns was fed through an extruder and coated with a plastic cover. Parafil ropes are now produced by Linear Composites Ltd with high-tenacity polyester and aramid cores and various plastic covers. When well made, the yarns are straight, which maximises strength. As shown in Fig. 3.7, the yarn bundles are usually wrapped to avoid disturbance of the yarns during extrusion. Parafil ropes do not bend easily and so they are best suited to straight line, static
3.7 Parafil rope.
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uses. An early application was in guy ropes for aerial masts, but there are now many more uses.
3.5.3 Parallel-strand ropes A slightly later development was the parallel-strand rope, in which a low-twist core of a number of sub-ropes or strands is encased in a braided jacket of fibres that resist abrasion. Figure 3.8 is an example in which the core consists of threestrand laid ropes. Half would have S-twist and half Z-twist, so that the rope would be torque balanced. In order to show the geometry in a reasonable width of diagram, the helix angle is higher than would be used in practice, when the pitch of the twist would be much longer. The jacket is fairly thin. There are at least two other options: the sub-ropes could be braided with a long braid pitch; the core could consist of a collection of ply yarns, half S-twisted and half Z twisted. An advantage of this technology is that it is easy to make very long lengths. Miles of the small sub-ropes can be made on small machines and then fed into the final braiding operation. Since the core is thin, a considerable length of yarn can be stored on the carriers. The strength conversion efficiency from yarn to rope can be 80 to 85% compared with 45 to 60% for conventional laid or braided ropes. Fatigue life under cyclic loading is excellent. Very large ropes with break loads up to 1500 tonnes or more can be made and used for deepwater moorings.
3.5.4 Kernmantle ropes The above two types of rope are made in large sizes. Kernmantle ropes are directed to markets for smaller ropes, 4 to 11 mm in diameter. Their core or kern may consist of parallel textile yarns (with modern interlacing, there is not even low twist), S- and Z-twisted yarns or laid sub-ropes, and long pitch braids. The jacket or mantle is very
3.8 Parallel-strand rope.
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thin and made of many strands of fine twisted textile yarns, which are usually multi-coloured. Typically, there might be 32 carriers each carrying two yarns. ‘Static’ kernmantle ropes, which are used for rescue work and other applications not requiring high-energy absorption, have low extension, 5% or less at 10% of break load. ‘Dynamic ‘kernmantle’ ropes, which must survive a stated number of fall arrests, e.g. a 7-fall or 10-fall rope, are more extensible. A drop of 80 kg through 2.5 m should result in an elongation of 6.5% to 7.5%. The light weight and ease of handling are features favoured by sportsmen and rescue workers. The jacket can become worn, but this is easily visible and is not a problem with responsible use.
3.5.5 Wire-rope constructions Wire ropes have always been made in a different structure to fibre ropes and largescale machinery existed to make long lengths of large ropes, such as the cables used to support suspension bridges. It was found that this technology could be adopted to provide good strength conversion efficiency (up to 85%) with high modulus fibres, such as aramids, but was later found to work with polyester. The basic principle of a wire rope structure is that a central core is surrounded by layers, starting with six strands and increasing by six in each layer. The core runs straight and, because it tends to pick up load faster, may be of a different material. Since the layers are added separately, the outer layers can all have the same helix angle, in contrast to normal textile twisting, which has constant pitch and increasing helix angle from centre to surface. The terminology omits to count the core, so there are six-strand, 18-strand, etc., ropes. In order to secure a compact rope, the size of strands in outer layers may vary. Individual strands may be jacketed and the whole rope enclosed in a braided cover. Wire rope constructions are inherently subject to the development of torque under tension, but by reversing the lay directions a 36-strand rope can be virtually torque free, since there are 18 strands in the outer layer and 18 in the two inner layers. A six strand rope is shown in Fig. 3.9 and some other types in Fig. 3.10.
3.6
Manufacturing technology
3.6.1 New machinery and new routes Production of a ropewalk was traditionally slow and labour-intensive. By the 1950s, ropewalks had become obsolescent. Advances in engineering led to machines for continuous production. New machinery was introduced for new rope structures. The sequence of rope production is shown in Fig. 3.11. The early stages of twisting yarns from staple fibre spinners or, in the new technology, from the synthetic fibre manufacturers, into heavier rope yarns follow normal textile practice and take advantage of the improvements in textile machinery. Two-forone twisting was widely adopted.
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3.9 Six-strand wire rope construction.
3.10 Other wire rope constructions.
3.11 Production sequence for three-strand ropes.
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It is in the later stages, from rope yarns to strands and from strands to laid or braided ropes, that machines were designed specifically for the rope industry. Back twist is an issue. If yarn or strand is taken off a static supply package and twisted into the new assembly, the twist in the component will change. In more advanced machines, this can be countered by allowing the supply package to rotate to make up for the change of twist.
3.6.2 Strand production For continuous strand production, a number of packages of rope are mounted on a rotating frame and fed to a take-up drum. There are two configurations. In a tubular strander, Fig. 3.12, the packages are all in line. The yarns pass through guides on the frame, but the packages are free to rotate, which gives a 100% back twist. Brakes control the yarn tension, but this can be uneven as yarns at the back pass over more guides. Tubular braiders run at 500 to 1000 revs/min. In a planetary strander, Fig. 3.13, the packages are spaced round the central axis. They run at 10 to 100 revs/min.
3.6.3 Three- (and four-) strand ropes A separate rope machine would feed strands to a rotating take-up. However modern practice is to use an integral rope-making machine, Fig. 3.14. The first section of the machine has three (or four) rotating stranders. Instead of the strands being wound up, they are fed to the second section, which contains a
3.12 Tubular strander.
3.13 Planetary strander.
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3.14 Integral rope-making machine.
take-up package mounted on a rotating frame. Both sections adopt two-for-one twisting.
3.6.4 Braided ropes Small braiding machines have been around since the early days of the industrial revolution. The advance has been to scale these up, so that the carriers can carry large packages of yarn. Depending on the type of braid, there may be a small number of very large strand carriers or a larger number of somewhat smaller carriers. The carriage tracks may spread out over an area as much as 4 m in diameter. In order to maintain a suitable angle to the braid point and add a take-up package, the height may reach 4 m. The forces involved will be large, so the machine needs a heavyweight construction. The type of braid is determined by the routes selected for the carriers and when the transfers occur. Two examples are shown in Fig. 3.15. It is usually necessary to re-wind from the strander package to the carrier package and essential when there are two strands per carrier. For braid-on-braid ropes, the core braid is first made and then fed as a core in a second braiding operation. In a similar way, the core components of parallelstrand or kernmantle ropes are fed into the centre of the braider, which forms the jacket.
3.6.5 Parafil ropes The manufacture of Parafil ropes is completely different to other types of rope manufacture. Typically a tow of polyester or aramid yarns provides the load bearing part of the rope. This bundle is fed into a plastics extruder in such a way that the yarns become encased in plastic.
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3.15 Braid paths.
3.6.6 Post-production treatments As shown above, jackets are an essential feature of some rope types. However, any rope can be supplied with a braided jacket if it is needed to protect against abrasion or make for better handling. An alternative is to apply a plastic, usually polyurethane, coating. This can be sprayed on by hand. The strength of HMPE ropes can be enhanced by hot-stretching the rope or strands under a low tension at around 120°C.
3.7
Terminations
3.7.1 Knots A rope is only as effective as the way it is fastened to the rest of the system. Knots are a traditional method and are still the best solution in many cases.
3.7.2 Splices Splicing is another old method, which can be used to form an eye that can be placed over a hook or thimble, to join two lengths of rope together without the bulk of a knot, or to join two ends of the same rope to make a circular grommet. The essential principle of an eye splice in a three-strand rope is that the strands are unwound from the end of the rope and then inserted between the strands at the base of the eye. Similar principles apply to the joining of two rope ends. The free ends of strands may be progressively reduced in size in order to avoid an abrupt large change in rope thickness. Making a good splice requires considerable skill. Experts have devised splices to suit the various types of braided and low-twist ropes and to splice fibre ropes to wire ropes. McKenna et al. (2004) report that double-braid ropes did not achieve popularity until a splicing method had been developed. The splice shown in Fig. 3.16 is the most complex of splices. The core and cover are separated and the core shortened. The core and cover are then reassembled, crossing over in opposite directions. Detailed instructions on such features as the location of the crossover point are given in splicing manuals.
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3.16 Splice in a double braid rope.
3.7.3 Mechanical terminations Splicing is not an option for parallel yarn ropes and they are too stiff to make good knots. A solution is a barrel-and-spike termination as shown in Fig. 3.17. The rope is pulled through the barrel and the jacket is cut off leaving a length of the core yarns. The rope is then pulled back into the barrel and the yarns are spread out round the circumference of the barrel. A spike is inserted to hold them in place, with transverse forces large enough to prevent slippage. The geometry is such that pressure increases as tension increases. Sometime grooves or teeth are included to increase the grip. The lugs at the top of the termination have holes to allow connection to the rest of the system. In order to secure a good grip the length must be large enough and the forces involved are large. This means that barreland-spike terminations are much larger than eye splice terminations.
3.7.4 Socketed terminations In another type of termination the strands are separated and the yarns spread out within a conical socket. A thermo-setting resin, such as polyester or epoxy, is then poured in and cured.
3.17 Barrel-and-spike termination.
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3.7.5 External grips A simple way of securing the end of a rope is to grip it, for example by hand. Various forms of external clamp can be used. This technique is particularly useful when combined with a bollard. After a few turns round the bollard, the tension needed to hold the rope is small and can be achieved by pressing the rope into a cleat. This is a useful technique when the securing of the rope is temporary, for example in tying up a boat at a quayside or fixing the sails of a yacht on the port or starboard sides.
3.8
Uses of ropes
3.8.1 Diversity and specialisation McKenna et al. (2004) list 48 uses of rope and that list is probably not complete. As recently as the 1950s, the range of ropes was small. Nearly all were three-strand ropes made of a limited range of natural fibres, such as sisal, hemp and cotton. There were bulk users in shipping, fishing, agriculture, trucking and so on. The yachtsman or the mountain climber would go to the same store and pick from the same small selection of ropes. Now there is a wider range of commodity ropes supplemented by high-priced ropes for special purposes. The climber and the sailor will choose different ropes for different purposes and at the Olympic level may even change ropes between races. For demanding applications, there is a greater emphasis on design for use. An oil company spending a million dollars or more on mooring ropes for an off-shore oil-rig will need to be assured that the ropes will perform in the required way and will last for a substantial number of years. The competitive yachtsman will want to choose ropes that will optimise performance.
3.8.2 Deepwater mooring The most detailed evaluation of ropes has been for offshore oil production. This covered both experimental studies and computer modelling. One driving force was the US Navy, who had a plan to build a large floating military base and airstrip. Unfortunately, when it was not needed, construction did not have priority and when it would have been of real value, it was too late to build it. The urgent need in the 1980s was for moorings for oil rigs in deep water. A joint industry study was set up with technical input from Noble Denton marine consultants and Tension Technology International rope consultants. Up to 500 m depth, steel ropes or chain are suitable for mooring. Beyond 1000 m, steel is too heavy. Fibre ropes needed to be evaluated to see which types were suitable and how they would perform. The main criteria to be satisfied are: (1) the rope should not be exposed to tensions above a safe limit; (2) the elongation of the rope should not allow for
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more than a specified offset from the rest position; (3) there should be no significant deterioration of rope performance over a 20-year period of use. Many of the participants in the study thought that high-performance fibres would prove to be needed, but it turned out that polyester ropes had the best balance of properties. A high-modulus rope is not suitable because the tensions generated as the rig is displaced by wave, wind and current action are too great. A large number of cyclic loading tests were carried out for millions of cycles. The potential failure mechanisms are creep rupture, which is usually the final cause of failure when the contribution of most filaments has been lost for other reasons, external and internal abrasion, and axial compression fatigue. Polyester withstands all these mechanisms well. Marine engineers have developed mooring analysis programmes for steel moorings, in order to predict the behaviour of the rig and the forces involved in sequences of environmental conditions. There is a problem in applying these to fibre ropes. Firstly, the system mechanics are different. In contrast to the straight tension of fibre ropes, the restoring forces in steel moorings are generated by the weight of the rope in the catenary. This is relatively easy to calculate because the linear density of the rope is a simple, well-known quantity. Secondly, fibre ropes suffer a period of irreversible extension as the rope tightens up under the first loading cycles. Thirdly the tensile properties of polyester fibres are non-linear, follow different load-extension paths dependent on previous history and are timedependent. It was necessary to develop test procedures that would provide values of modulus appropriate to the circumstances of use. The work of the joint industry study culminated in Deepwater Fibre Moorings: An Engineers’ Design Guide (TTI and Noble Denton, 1999). More joint industry studies looked at other issues. Apart from its particular significance, this work is a prototype for a change of culture in the textile industry, replacing the old craft approach by a quantitative engineering approach, which is expected by engineering customers.
3.8.3 Sailing In the old days, yachtsmen would have gone into a marine store and bought threestrand ropes, which were made of fibres like hemp or cotton and which were used for a great variety of purposes. Rope-makers now provide a range of different ropes designed to meet different needs. For example, Gleistein produce 11 types of rope in 10 mm diameter for sheets, which control the boom, and halyards, which hold up the sails. Figure 3.18 shows the range of extensibilities. There is a more limited selection at 3, 5, 20 and 24 mm diameter. Ropes also have to be selected for backstays, topping lifts, pole uphaul, fore guy and roller reefing line. Similar comments could be made about mountaineering ropes, arborist ropes or ropes for use on barges.
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3.18 Load-elongation curves for yachting ropes from Gleistein.
3.8.4 Two unusual uses A Kevlar rope was suspended between 8500- and 6000-foot mountain tops, which were thee miles apart in the White Sands Missile Range in New Mexico. This was the longest span in the world. It was used as a rail to support a target, with a plan for the target to run at speeds up to 1000 mph. This is used to test ground-to-air missiles.
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At the other extreme, ropes are used in farming mussels. With the right choice of rope, mussels will attach themselves to the rope, which can be hauled up when the mussels are ready to be harvested.
3.9
Conclusions
A comprehensive account of rope technology is given by McKenna et al. (2004). The upsurge in advances in the second half of the twentieth century with the advent of synthetic fibres, the building of large integrated rope-making machines and the exploitation of continuous filament yarns in new low-twist rope structures is unlikely to continue. Developments are likely to be more incremental variations in the rope types now being made. For example, the use of combinations of different fibre types may increase. One advance would be a greater use of computer-aided design and calculations of performance properties. However, like most of the textile industry, with its thousands of years of craft experience, practical expertise and intuition on how a system will behave, rope manufacturers are reluctant to switch to new ways of working.
3.10
References
H. A. McKenna, J. W. S. Hearle and N. O’Hear (2004), Handbook of Fibre Rope Technology, Woodhead Publishing, Cambridge, England. TTI and Noble Denton (1999), Deepwater Fibre Moorings: An Engineers’ Design Guide, Oilfield Publications Ltd, Ledbury, England.
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4 Developments in fancy yarns R. WRIGHT, Racheland Designs, UK
Abstract: An overview of basic fancy yarn structures, together with the methods used for producing them. Recent developments in manufacturing are described. There have been changes in the final market for these goods, which affect not only the manufacturing routes but also the yarns themselves. Key words: fancy yarns, novelty yarns, bouclé, chainette, chenille, metal thread.
4.1
Introduction to fancy yarns
The term ‘fancy yarns’ may be taken to cover all fancy and novelty effects, while ‘fancy doubled yarns’ covers yarn and fibre effects. Colour effects and effects based on metallic components are also available. While some are important for the embellishment of plain fabrics, many are used with great success as components in ‘fancy fabrics’ or as design elements within an otherwise simple fabric structure. This chapter provides a short overview of the basic fancy yarn structures, and a discussion of how they are made. Once this groundwork is laid, it then describes new production techniques and changes in the yarns produced for various markets.
4.1.1 Yarn structures The basic structure of a fancy doubled yarn consists of ‘core’ threads, an ‘effect material’, and a ‘binder’ which, as the name suggests, ensures that the entire structure holds together. The introduction of an individual, variable speed drive for each feed roller extends the range of effects available to include fibre as well as yarn feeds. Such a modification allows changes in roller speed, and thus in the draft, and thus in the build-up or reduction of the effect, at certain points on the yarn. Further fibre effects may be created by the introduction of additional fibre material prior to or during spinning or by varying the feed rate of the fibre material during spinning. In developing an understanding of yarn structures and types, there is no substitute for handling yarns and analysing their structure and form. It is a valuable exercise to create a private collection of interesting yarns, and their use in fabrics. The more easily discovered features might include, for example: 75 © Woodhead Publishing Limited, 2011
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Specialist yarn and fabric structures Count Fibre or fibres used Basic structure (is the yarn a slub, bouclé, chenille, chainette, or a yarn involving several fancy effect yarns . . .?) Number of component threads Purpose of each component thread (is it a core, effect, binder . . .?) Intended use for the yarn itself (knit, weave, embellishment . . .?).
4.1.2 Yarn properties There is still much potential for research to discover the physical properties of the different types of yarn, depending on the machinery used to make them or the particular structures involved. In particular, the properties that might be of interest specifically to commercial users of fancy yarns include strength, wear resistance, flexibility, comfort, stretch properties, and suitability for a particular manufacturing or dyeing process. Other potentially useful and interesting research might cover, for example, the effect of the production rate upon the behaviour of the yarn in further processing, the potential for the inclusion of lycra to improve stretch properties or the details of changes in handle resulting from different means of production for each structure. Since superficially similar yarns may now be produced by several different processes, it behoves the user to select a yarn produced in the fashion that best suits the processing it will subsequently receive.
4.2
Historical development
For the greater part of the textile industry’s very long history, its various technological advances have been primarily concerned with producing plain round yarns ever more perfectly and speedily. The extensive range of decorative elements available for the majority of that period has resulted from the introduction of colour and pattern, rather than from the yarn itself. Thus the technological advances seen in earlier times related to the creation of fabrics, and then to the application of pattern to those fabrics through printing and other embellishment. The fancy yarn may even have had its beginnings in the work of those early weavers, who would occasionally combine the threads they used in different ways as they were weaving, to produce a wide variety of colourful and textural effects. In spite of difficulties relating to the huge amount of information in a variety of fields and subject areas that is involved in publishing the results of excavation, archaeologists have been able to push back our horizon of textile knowledge, thanks to some fortunate accidents of environment that have led to the preservation of textile materials, otherwise rarely discovered within the archaeological record (Wilson, 2001). Still more information can be expected, as publication catches up with excavation. Some examples have been found which allow us to deduce that
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the early artisans were able to envisage the textural variations in fabric and then spin the yarns that they needed to create the textures and patterns that they planned (Wayland Barber, 1999). It has been relatively easy to find evidence for metallic threads. These were most often made of thin strips of metal wrapped around a core of silk or linen, or in some cases they might be fine threads or wires produced by wire-drawers. An example of such a thread was found in a Roman burial in London during the late 1990s (Barham, 2000). Metal threads have been used by many cultures throughout history – the Egyptians and Babylonians are known to have had metal threads by 2000 BC. It is thought that the ancient Chinese and Indians knew techniques for making and working with metal threads even earlier than that. In ancient times, gold threads were also made by applying fine gold leaf to parchment, cutting the parchment into thin strips and then wrapping that around the core. This metallic thread was not very durable and therefore not well thought of, but it was a relatively inexpensive way of achieving the effect (Lemon, 1987). There was considerable use of metallic yarns of this type in fabrics for ceremonial and ritual garments throughout much of history, throughout the world. The expense of the raw materials has ensured that whereas weaving and spinning, until the industrial revolution, could be domestic activities, the making of metal threads has always had to be an organised craft composed of a few skilled artisans (Glover, 1978). The Elizabethans, and their contemporaries throughout Europe, made considerable use of fine gold and silver threads in embroidery and lace making. Recent research into metal threads used for embroidery and embellishment in the sixteenth and seventeenth centuries has led to the re-creation of some of those threads. Originally intended for use in the Plimoth Jacket Project, a reproduction of a particular garment (the Margaret Laton jacket, now in the Victoria and Albert Museum), such threads are now being manufactured in small quantities, both for modern embroiderers to enjoy and for further use in historical research (WilsonNguyen, ‘The Embroiderer’s Story’ blog). Although there is evidence of their use for this purpose much earlier in Arab countries (von Folsach and Bernsted, 1993), in Europe the metallic threads found an extension to their use in the eighteenth century when they began to be included in the designs of silks for apparel. By that time, there seem to have been four basic types of thread whose definitions were universally accepted, the ‘plain’ (filé) thread, the ‘frost’ (frisé) thread (both wrapped around a core), the ‘plate’ (flattened wire), and the ‘clinçon’ (plate wrapped around a frost thread – in effect, a metallic fancy doubled yarn). In addition, the plate, being based upon a drawn metal wire, was capable of many variations. It could be passed through rollers to flatten it and broaden it to varying degrees, or even to apply some texture to the surface. ‘Spangles’ were produced by cutting coils of wire longitudinally and then flattening the resultant curls of metal individually, which creates a different shape and effect to the modern method of stamping sequins out of sheets of foil, and even requires different means of attachment to the fabric being embellished.
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Also in the eighteenth century, a material then named ‘floss silk’ became widely used in ornamentation. This material consists of bundles of silk filaments tied across the main strand of silk thread, an effect somewhat reminiscent of chenille. The chenille itself may even be the earliest true fancy doubled yarn to have been developed. It is mentioned – although as a thread for embroidery – in Art of the Embroiderer published in 1770 (de Saint-Aubin, facsimile edition, 1983), and there are examples of its use for this purpose in many museums and costume collections. It was not until the late nineteenth century that the range of fancy doubled yarns available today began to be developed, and with it, an increasing profusion of machinery intended to create specific effects. This in turn meant that the quantities that could be produced were increased, making it possible to use the yarns to create fabrics, rather than simply to embellish them. Then in the late twentieth and early twenty-first centuries, as electronic process control became increasingly prevalent as well as more flexible, reliable and useful, it became easier to produce variable, and varying, effects while maintaining a consistent level of quality. When we realise how difficult it is to detect, by eye, faults in a fancy yarn, and especially in a fabric incorporating fancy yarns, the importance of this particular development becomes clear.
4.3
Types of fancy yarns and their development
4.3.1 The structure and formation of fancy yarns Fancy yarns may be categorised according to their basic morphology. Marls, spirals and gimps are relatively straightforward structures and may be produced on ordinary doubling frames or the ring spinning system. Gimp yarns require a binder and are therefore produced in two stages on the ring spinning system. Snarl, loop and bouclé yarns are more exaggerated effects that require specialised feed systems. They may be produced using modified ring spindle systems, hollow spindle systems or the combined system machines – in one step only where the wrap (hollow spindle) system is used, or in two stages on the modified ring spindles. Whereas most often we would expect fancy yarns to have an irregular outline, chainette, chenille, cover and laminated yarns are usually of regular outline, the effect being achieved by the surface of the yarn. In the case of chainette, chenille and cover yarns the profile of the yarn is circular, like a plain yarn, whereas the laminate metallic film yarns have a flat profile, and provide the greatest sparkle and reflectance when they lie flat across the fabric surface. The chenille, by contrast, offers a ‘velvety’ look resulting from the cut threads in the pile. Another yarn that involves cut threads, the eyelash or feather yarn is asymmetric in appearance, consisting of a spine with a fringe on one side of it. So far this is the only truly asymmetric yarn.
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Diagrams of these structures are provided in order to provide some framework of understanding for an overview of the developments in fancy spinning. The yarn structures have necessarily been simplified in the diagrams that follow, in order to show the important elements of each structure. Marl yarn The simplest of the fancy effects, a marl yarn is one in which two yarns of the same count and twist, but of different colours or textures, are folded together to form a balanced yarn. The yarn diagram in Fig. 4.1 shows clearly both the alternation of the colours that is the primary effect of a marl yarn, and the plain structure, which is that of an ordinary folded yarn.
4.1 Marl yarn.
Spiral or corkscrew yarn A spiral or corkscrew yarn is a plied yarn that displays a characteristic smooth spiralling of one component around the other. Figure 4.2 shows the basic structure, which can be produced relatively simply on a doubling frame or under the ring spinning system.
4.2 Spiral or corkscrew yarn.
Gimp yarn A gimp yarn consists of a twisted core with an effect yarn wrapped around it so as to produce wavy projections on its surface. This structure is shown in Fig. 4.3.
4.3 Gimp yarn.
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Since a binder is needed to ensure the stability of the structure, the yarn is produced in two stages. First, two yarns of widely differing count are plied together, thick around thin. In the second stage they are then reverse bound. The process of reverse binding removes most of the twist inserted during the first process. It is this removal of twist that creates the wavy profiles, by making the effect yarns longer than the actual length of the completed yarn. Eccentric yarn An eccentric yarn is an undulating gimp yarn, often produced by binding an irregular yarn, for example a stripe, slub or knop yarn, in the direction opposite to the initial stage, creating graduated half-circular loops along the compound yarn. It produces an uneven but relatively controllable texture. Because it can be produced using one of several different irregular yarns to create the effect, and because the basic morphology is very similar to that of a gimp yarn, no diagram of the structure has been included, since at its most straightforward it would be a repeat of Fig. 4.3. Mock-chenille yarn A mock chenille does not at all resemble a true chenille yarn in its appearance as a yarn, but when it is woven into a fabric it will give a very similar effect. It is in fact a doubled corkscrew or gimp yarn, and it is made by doubling together two or more unbalanced corkscrew or gimp yarns in the reverse direction with sufficient twist to form a balanced structure. Diamond yarn A diamond yarn is made by folding a thick single yarn or roving with a fine yarn or filament of contrasting colour using an S-twist, and cabling it with a similar fine yarn using a Z-twist. A true diamond yarn will show some compression effect upon the thick yarn from the thin ones, an effect which in the interests of clarity has been omitted from Fig. 4.4.
4.4 Diamond yarn.
Bouclé yarn Figure 4.5 shows the basic structure of a bouclé yarn. This is a compound yarn comprising a twisted core with an effect yarn (or roving) combined with it so as
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4.5 Bouclé yarn.
to produce wavy projections on its surface. The core has been shown as a single bar, rather than as two yarns twisted together and around the effect yarn, as would be the case in reality. It is this dedicated core that differentiates the bouclé from the gimp yarn, since their superficial appearances are similar. Loop yarn This compound yarn consists of a core with an effect yarn wrapped around it and overfed so as to produce almost circular projections on its surface. Figure 4.6 shows the structure of a loop yarn, simplified by showing the core as two straight bars. In reality, the core – which for a loop yarn always consists of two yarns – is twisted, and partially entraps the effect. As a general rule, four yarns are involved, of which two form the core or ‘ground’ yarns. The effect yarn or yarns are overfed by 200% or more, and it is important that these are of the correct type and quality: an elastic and pliable yarn is required with an even, low twist. The effect yarn or fibre is not completely entrapped by the ground threads, so a binder is needed. The size of the loops may be influenced by the amount of overfeed, the groove space on the drafting rollers, the spinning tension, or the twist level of the effect yarn. Loop yarns may also be made using fibre instead of yarn feeds to create the effect.
4.6 Loop yarn.
Snarl yarn Like the loop yarn, the snarl yarn is based around a twisted core, although the core has been shown in Fig. 4.7 as two parallel bars. A snarl yarn is one that displays ‘snarls’ or ‘twists’ projecting from the core. It is made by a similar method to the loop yarn, but uses as the effect a lively, high-twist yarn, and a much greater degree of overfeed.
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4.7 Snarl yarn.
Knop yarn A knop yarn is one that contains prominent bunches of one or more of its component threads, arranged at regular or irregular intervals along its length, as shown in very simplified form in Fig. 4.8.
4.8 Knop yarn.
Stripe yarn A stripe yarn contains alternating elongated knops, revealing a separate core. The sections of yarn between the knops take on the appearance of a multi-threaded marl yarn. Cloud or grandrelle yarn A cloud or grandrelle yarn is made using the apparatus used to create knop yarns. The two threads of different colours used to create the yarn are manipulated in such a manner that each thread alternately forms the base and cover to ‘cloud’ the opposing thread. It is made by alternate fast and slow deliveries from two pairs of rollers. Because the yarns alternate in forming the base yarn, no dedicated core yarn is required. The structure is shown in Fig. 4.9.
4.9 Cloud or grandrelle yarn.
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4.10 Slub yarn.
Slub yarn A slub yarn is one in which slubs (thick places in the yarn) have been deliberately created to produce the desired effect, which may be slow and subtle or strong and sudden (see Fig. 4.10). Nepp and fleck yarns Structurally, these yarns are plain in appearance – in this case it is the colour effect that makes them ‘fancy’. The basic method for nepp and fleck yarns is the same: the differences lie in the degree to which the additional material is affected by the carding process and in the choice of fibre used for the additional material. Balls of effect fibres are added to the feed or at a later stage during carding; at the last worker–cylinder contact point for example. The settings of the card following the introduction of the nepps will have to be wider than normal to ensure that the nepps are not carded out, and they will then appear randomly along the yarn. A fleck yarn is shown in Fig. 4.11.
4.11 Fleck yarn.
Nepp yarns These are made on the woollen system. They show strongly contrasting spots on the surface of the yarn, which are made by dropping in small balls of wool at the latter part of the carding process. The nepps may also be incorporated in the blend, with the carding machine set to ensure that these small lumps are not carded out. Fleck yarns This yarn presents a mixed appearance, combining spotted and short streaky effects, due to the introduction of a minority of fibres of different colour and/or lustre; it looks similar to the nepp yarn, but some of the nubs will have been slightly opened out during carding, creating the streaky effect.
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Button yarn The ‘button’ is an intermittent effect, created by a sudden pause in the progress of the core yarns, which allows a build-up of the effect material, usually in this case a sliver or roving (Fig. 4.12). While in yarn form it can offer a truly dramatic effect, it is less than straightforward to process into fabric, and in practice it is usually found in its more discreet manifestations. The exception to this is of course in hand knitting yarns, since it can be expected that a hand knitter will be able to devote the time and care required to achieve a successful result.
4.12 Button yarn.
Fasciated yarn This is a staple fibre yarn which, by virtue of the method used in its manufacture, consists of a core of parallel fibres bound together by wrapper fibres (Fig. 4.13). The yarns produced under the hollow spindle method are also frequently described as fasciated, since the binder is applied to an essentially twistless core of parallel fibres.
4.13 Fasciated yarn.
Tape yarn Tape yarns may be made by a variety of methods, and take the form of flat ribbons or tapes. In recent years, these materials have become better known, especially in fashion knitwear. They may take the form of genuine ribbons or tapes, woven on narrow-fabric looms, or they may have a knitted or braided structure. Chainette yarn Chainette yarns are made by a miniaturised circular weft knitting process (Fig. 4.14). The feed may be a filament or fine spun yarn, or may even include a metallic laminate film, depending upon the characteristics desired. These yarns
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4.14 Chainette yarn.
appear most often in fashion knitwear, although chainette yarns have been used in weaving and passementerie, and they have become extremely popular with textile artists and embroiderers as well. Eyelash or feather yarn The eyelash or feather yarn has an asymmetric structure consisting of a looped spine or core, with a fringe of effect yarn to one side of it. It is created using enhancements to the chainette process and is popular in fashion knitwear, where it creates a shaggy pile effect. In Fig. 4.15 the eyelash yarn has been shown with both cut and uncut fringe loops.
4.15 Eyelash or feather yarn.
Chenille yarn Figure 4.16 shows the basic structure of a chenille yarn. It consists of a cut pile, which may be made of a variety of fibres helically disposed around the two axial threads that secure it. Chenille yarns are traditionally used in the manufacture of
4.16 Chenille yarn.
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furnishing fabrics and trimmings, fashion knitwear, and as decorative threads in embellishment. Pompom yarn The most recent addition to the armoury of the chenille spinner is the development of an intermittent chenille yarn, often referred to as a ‘pompom’ or ‘marshmallow’ yarn. This yarn alternates sections of chenille yarn with a simple cabled yarn, and is targeted at the hand knitting market. It results from refinements in the technology and process control, and has created considerable interest in its target market. Cover yarn A cover yarn (Fig. 4.17) is one in which a yarn at the core is completely covered by fibre or yarn wrapped around it. It is familiar to embroiderers, because many metallic embroidery threads take the form of a core thread with a metallic thread, film or flat ribbon wrapped around it, but the method is most commonly used to cover elastomeric yarns, which would otherwise be extremely uncomfortable to wear. The extremely eccentric ‘bubblegum yarn’, which consists of a core of filaments surrounded by a bubbled froth of soft resin, could also be described as a cover yarn.
4.17 Cover yarn.
Metallic yarn True metal threads, of the type used since antiquity for embellishment, are made by extruding metal to create a fine thread, called ‘wyre’, and then wrapping it around a former to create the characteristic coiled shape (Fig. 4.18 shows a slightly stretched ‘pearl purl’, one of the most identifiable of the true metal threads used in embellishment). The metal used is a specially composed alloy, with several standard compositions laid down for the differing qualities of material. In Britain these were laid down by the Worshipful Company of Gold and Silver Wyre
4.18 Pearl purl.
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Drawers in the seventeenth century (Glover, 1978). Particular qualities of strength and ductility are required, both in the core of the metal and in the coating which must not crack or split as the metal is drawn to create ever finer wyre. In ancient times, another metallic thread was made by burnishing gold leaf onto parchment, vellum, or animal gut, cutting it into strips and then wrapping it around a core thread of linen or silk, creating a ‘cover yarn’ structure identical to that shown in Fig. 4.17 (von Folsach and Bernsted, 1993). This technique is still used today to make small quantities for restoration work. Modern metallic laminate yarns are made of films, usually of polyester, or sometimes of nylon, which have been cut to the chosen width. They are not confined to the colours of metal, and are used not for embellishment, but as components in yarns for processing into fabric. If the resultant yarns are to be used in knitting, the strands of film are further supported by twisting filaments around them using the standard hollow spindle process. Figure 4.19 shows a laminated film supported in this way.
4.19 Supported slit film yarn.
4.4
Production methods for fancy yarns
4.4.1 Feed systems for producing fancy yarns Fancy yarns that involve yarn effects contain one or more ground yarns, one or more effect yarns and in most cases a binder yarn. These fancy yarns are produced in two or more separate stages, not counting the production of the individual yarns that are combined to make up the final fancy yarn. Figure 4.20 shows a typical feeding arrangement when the fancy yarn to be produced is a loop yarn, which always requires two ground yarns. These two ground yarns are fed by the back feed rollers while the effect yarn is fed by the front feed rollers. As the ground yarns and the effect yarn are fed at different speeds, the ground yarns are made to pass through the grooves cut in the top front roller, instead of being nipped, as they would be if the grooves were not in place. This allows the ground yarns and the effect yarn to converge in the twisting zone after they have emerged from the front rollers. The two ground yarns, kept separate by the two grooves, form a triangle between the front rollers and the twisting point, at which they come together. This triangle provides the essential space in which the overfed effect can form the loops. In order to maintain good control of the yarn, the effect yarn (which is overfed, and therefore not under tension between the feed roller and the twisting zone)
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4.20 Creating a loop yarn.
is fed by the front rollers. It is also important that the effect yarn should be fed in such a way that the ground yarns are placed one on each side of it. The feed system for snarl yarn production is the same as it is for producing loop yarns. The main difference between the loop yarn and the snarl yarn lies in the properties of the effect yarn. To create a snarl yarn, the effect yarn should have a relatively high level of twist, which will facilitate the formation of the snarl effect. The overfeed ratio is also higher. The feed system described for the loop yarn may also be used for yarn effects where only one ground yarn is needed. The effect yarn is fed by the front rollers, while the ground yarn is fed by the back rollers and passes through a groove in the top front roller. If the effect yarn is considerably thicker than the ground, a smooth top roller may be used instead of the grooved roller. In this case, the top roller is lifted by the thicker effect yarn and cannot exert any nip pressure on the ground yarns.
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For the production of knop yarns (shown in Fig. 4.21), the ground yarn is fed intermittently. The effect yarn and the ground yarns converge below the control bar. The knop effect is formed when the ground yarns stop while the effect yarn continues to be fed, forming a prominent ‘bunch’ on the yarn surface. To achieve a neat knop, the control bar remains stationary so that the effect yarn is given as little play as possible. During the formation of the knop, the control bar can be moved up and down to spread the knop over a desired length of the yarn. In producing some effects, such as the gimp yarn, the initial twisting process only lays the foundation for the desired effect, and a reverse twisting process is required to make the effect visible. For most other effects (loops, snarls or bouclés), the effect yarn or yarns may appear to be twisted in by the ground yarns,
4.21 Creating a knop yarn.
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but in fact the strands are merely twisted around each other. To prevent the effect sliding along the yarn length during subsequent processing, the effects must be bound to the ground yarn by twisting-in one or more binder yarns using an additional twisting process.
4.4.2 Producing fancy yarns on the ring system The ring-spinning system is still the most flexible yarn production system in terms of both raw material handling and the range of yarn counts produced. Its main drawback lies in the lengthy and costly processes involved in production by this route. When produced using the ring-spinning technique, most fancy yarns require several twisting processes. Each component yarn has to be spun separately. The ground yarns and the effect yarn are then twisted together, followed by the final twisting process required for binding. Thus, even if we do not include the production of the component yarns, two separate stages are involved. In recent years, several alternative techniques for making fancy yarns in a single-stage process have emerged and become more popular.
4.4.3 Producing fancy yarns on the hollow spindle system The hollow spindle principle of spinning replaces twist in a yarn by wrapping a filament binder around the materials being used (Fig. 4.22 shows a basic hollow spindle system). This results in a fasciated yarn structure, in which most of the elements lie parallel to one another, while the binder imparts the necessary cohesion. The primary advantage of this system for the manufacture of fancy yarns is that most such yarns can be made using a single passage of the machine. It is important to be aware that although the yarns are superficially similar, fancy yarns produced on the hollow spindle system are quite different in structure from those made using the conventional ring-spinning system, and will differ in appearance and behaviour during processing. In the production of fancy yarns, the hollow spindle technique is used to add the binder immediately the effect is produced, rather than in a second, separate operation. There is no twist holding the elements together, so the yarn has no cohesion beyond that imparted by the binder. If the binder breaks, the yarn falls into its separate components. A very wide range of fancy effects can be produced using the hollow spindle system. These effects can be controlled by altering the speed of each of the different feeding devices (core and effect). Although the technique was primarily devised for creating yarns from a sliver feed, it is also possible to use the hollow spindle system to create fancy yarns that include spun threads in their effect.
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4.22 Hollow spindle system.
4.4.4 Combined systems The combined systems were first developed in order to unite the benefits of the ring and hollow spindle systems in a single machine, since a yarn with twist has a more stable and reliable structure than a fasciated yarn.
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Then it was realised that two hollow spindles could also be mounted in series, offering a different variety of resultant yarns, and a different range of benefits. This technique is used to produce special effect yarns that have a more stable structure, resulting from the fact that the effect fibres are trapped by two binders, instead of one. Figure 4.23 shows the original combined system in which the hollow spindle and ring spindle were combined in a single machine. In this case, the wrapped yarn is being given some true twist by the ring spindle located immediately beneath the hollow spindle. Thus the speed of assembly offered by the hollow spindle, enhanced
4.23 Original combined system.
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by the true twist inserted by the ring spindle, creates yarns less expensive than true ring-spun yarns, while still retaining some of their desirable characteristics. In its earliest form the combined system involved at most two spinning points, in a choice of only two configurations (hollow spindle followed by hollow spindle or hollow spindle followed by ring spindle). However, much has changed in recent years. The changes have resulted in part from advances in electronic process control, processor power, and (crucially) in the usability of the machine control interface, and in part from truly inspired engineering. In the past process control was limited to basic parameters for the yarn, with a little variability to reduce the possibility of striping effects; now the control is such that several different structures may be created within a single process. Figure 4.24 indicates the various points at which changes in the machine set up have occurred. Whereas before the feed into the hollow spindle involved only one set of four drafting rollers, now there are two separate fibre feeds, each consisting of four drafting rollers. Each roller is individually controllable, and the third of each set of four has an apron to improve fibre control. As a result of this development it is now possible, for example, to create a yarn with an ‘ombré dyed’ fibre effect purely by a series of programmed changes to the proportions of delivery from each feed. Indeed, such is the detailed level of control available through the
4.24 Changes in the combined system.
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programming interface that the system may even be used to create Fair Isle-effect yarns, which when knitted produce an impression of the familiar Fair Isle patterns seen in knitwear. On some equipment the hollow spindle may be removed or bypassed, while maintaining the feed variability. This allows the production of ring spun slub yarns, or of the ombré effects on ring spun yarns. Alternatively, on certain equipment, the hollow spindle may be replaced by a chainette knitting head, to create an entirely different range of effects. A further detail in the hollow spindle element of these machines is the introduction of a double belt system, allowing differing speeds, or even contrary motion, between the spindle itself and the false twist insertion, still further increasing the range of resulting yarns. Again, it is the excellent work that has been done on the details of the programming interface that makes these developments useable within the production environment. In certain equipment set-ups, the core yarns are guided from the creel through tubes to ensure that the necessary separation is maintained – this is, again, a refinement of the equipment rather than a radical change, but it reduces the risk of yarns catching and tangling with one another, especially when the machine is stopped suddenly. Such additional refinements improve machine efficiency, improve yarn quality, and thus contribute to improved margins for the spinner. Some machines offer a choice of package draw off, including precision winding to create dye-vessel-ready packages. This in turn reduces the number of processes involved in preparing the yarn for further processing. Since it is now also possible to produce loop yarns on this system straight from sliver without an intervening roving process, the new equipment will change the economics of fancy yarn production in a variety of ways that might not have been foreseen prior to its introduction.
4.4.5 The doubling system In this relatively simple system, the general arrangement is to provide two or more yarns that can be fed independently at controlled speeds, which may include uniform, fluctuating or intermittent feeds. This equipment permits the production of spiral or marl type yarns very simply. The doubling frame allows the production of some of the simpler fancy yarn structures by ordinary spinners who do not specialise in fancy yarn production, or even by some knitters and weavers. The combination of fancy yarns as feedstock in the creation of other fancy yarns has become particularly marked, especially in the area of yarns for hand knitting.
4.4.6 Condenser yarns Although it is used primarily for short staple wool and recovered fibres for woollen fabrics, and not for the production of very high quality yarns, this spinning
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method may still be used to produce nepped and flecked fancy yarns of a particular type. The effect components are introduced into the blend either prior to or during the carding operation. For example, a controlled flow of coloured nepps may be fed to the card just before the condenser; or the nepps may be incorporated into the blend. The yarns thus produced will have small colour flecks, spread out to a lesser or greater extent, depending upon the closeness of the settings.
4.4.7 Rotor-spun yarns Rotor spinning was developed to spin plain yarns from short staple fibres at high speed. However, some of the more recent developments in electronic control have allowed the development of rotor-spinning machinery that is capable of producing slub yarns. The mechanisms involved range from additional feed paths to changes in feed or delivery speed, and all have their own advantages and disadvantages. Additional complexity in the equipment required is a disadvantage that may be accepted in the interests of producing a new type of yarn, but the creation of weak points in the yarn is viewed as a backward step when so much effort has been put into the creation of slub yarns without that disadvantage. Other developments have made it possible to produce multi-component rotorspun yarns, combining a continuous component with one spun on the rotor. The continuous component is fed directly into the rotor, rather than being combined with the spun component afterwards. It is even possible to change the tension in the continuous component during the spinning process, again resulting in changes in the finished yarn structure and appearance. Note that these yarns do not have a regular cross-section, but that the continuous component and the spun component may change their positions within the cross-section of the yarn, partly contributing to the fancy effect. As is the case with many of the other developments reported here, much of the thrust of the research and development has been to provide new ways to manufacture particular yarns or yarn structures. This may seem a duplication of effort, but the details of a different manufacturing technique may well result in a new characteristics in the yarn itself – always an intriguing possibility. The new characteristics may include improved behaviour in further processing – especially important since fancy yarns laboured for many years under the disadvantage of a reputation for requiring slow and delicate processing.
4.4.8 Friction-spun yarns The main application of friction spinning is for the production of industrial yarns and using recycled fibres. The process can also be used to produce yarns using aramid and glass fibres and with various core components including wires.
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Slub yarns, which are potentially important for decorative effects, can be produced on the friction system by changing the feed speed of one or more of the slivers, or by injecting fibres directly into the friction zone. However, the yarn tends to offer low performance in processing and use as a result of the poor binding of the fibres.
4.4.9 Chenille Weaving The original tufted weft yarn was made by weaving a fabric in which the warp threads are arranged in small groups of between two and six ends, which interlace in a gauze or cross-weaving manner, the groups being a set distance apart to suit the intended length of pile, as shown in Fig. 4.25. This is a time-consuming method of production, now superseded by newer methods, except in cases of yarns produced for the restoration of textiles of the earlier period, or in experiments in textile archaeology.
4.25 The woven process for chenille.
The chenille spinning machine A method of producing a chenille yarn has been developed that produces two ends, each with a core of two ground yarns, at each spinning point. This is illustrated in Fig. 4.26 and 4.27.
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4.26 Chenille spinning – close-up of the former.
The effect yarns are wrapped around a gauge or former which is triangularly shaped at the top, narrowing towards the base to allow the effect yarn coils to slide downwards onto the cutting knife. The width at the bottom of the gauge determines the effect length, by maintaining the depth of the pile or ‘beard’ in the final yarn. The two ground yarns are twisted together, usually by a ring spindle at the lower part of the machine, to produce the final yarn. Developments in the chenille process have related to the introduction of carefully calculated repeated intermittent effects. Often marketed as ‘marshmallow’ or ‘pompom’ yarns, these are used at present exclusively by hand-knitters and are intended for use in accessories, such as scarves. Contrary to the usual practice in producing intermittent effects in textiles, the effect is produced at carefully calculated regular intervals, intended to bring the pompom to the same point in every knitted stitch. It produces a fabric consisting of rows of fluffy pompoms
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4.27 Chenille spinning – view of the machine from the front.
without the density associated with knitting up a continuous chenille of the same dimensions. The hand knit market has seen an explosion of scarf and bag patterns that are easily and quickly knitted using a single ball of a dramatic yarn such as this intermittent chenille, on a particular needle size, using the most basic of stitches.
4.4.10 The flocking process for chenille-type yarns Chenille effects can also be produced by a flocking process in which a ground yarn coated with adhesive is flocked electrostatically with loose fibres. This is a very economical production method, but the yarn has poor abrasion resistance because the anchor of the loose fibres onto the ground yarn is small.
4.4.11 The chainette knitting process The basic chainette process Chainette yarns are made by a miniature circular weft knitting process, using a ring of between six and 40 needles. Fig. 4.28 shows a knitting head without
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4.28 Knitting head assembly for chainette knitting.
needles, but also clearly showing the cam race which guides the needles up and down as it turns. The machines may have between six and 24 knitting heads, which need not all be mounted with the same size of knitting cylinder or even fed with the same yarns. Certain equipment makes use of positive feed systems, such as those commonly used in the larger-scale weft-knitting processes. This reduces stresses both on the thread and on the equipment itself, especially the needles, thus improving the quality of the finished product and reducing maintenance costs. Changes in the cam system may be used to create horizontal stripes, although given the process of circular weft knitting, these appear to be diagonal rather than exactly horizontal. A further variation is permitted by the addition of a second cam race while building the knitting head assembly, making it possible to create vertical stripes in the final chainette structure. Refinements for the eyelash or feather yarn The eyelash or feather yarn is made on the same machine as the chainette, by dint of some variations incorporated while building the knitting head. Two groups of needles are used, each consisting of between one and five needles. One group consists of ordinary latched needles knitting the spine, while the other consists of
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latchless cutting needles creating the fringe by cutting the thread as it draws down to cast off. The cutting needles are bought in as blank latchless needles and the blade is ground in-house to the desired length, and in the desired position, which depends on the details of the manufacturing most common to a given plant. The needle-bed cylinder has a small section cut out of it, which marks the area in which the bladed cutting needle may be placed, and reduces the risk of the cut ends catching on the needle-bed (Fig. 4.29). The distance between the needles determines the length of the fringe. That distance is a chord across the circle of the needle-bed, up to a maximum of the diameter of the needle-bed cylinder (Fig. 4.30).
4.29 Bladed needle placement.
4.30 Yarn path for effect (or hair) yarn in knitting a feather yarn.
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The spine and the effect, or ‘hair’, yarns are loop-stitched together in the spine, but whereas the spine yarn is only ever cast around the latched needle, which knits the spine, the effect yarn is cast over the bladed needle by the effect of the eccentric guide head. Fig. 4.31 shows the guide head assembly as it is attached to the knitting head. The effect is trapped in the spine by each successive stitch, ensuring that the fringe is not lost from the yarn during manufacture, subsequent processing, or wear. The exact position of the guide itself within the head assembly is adjustable by means of screws (Fig. 4.32), and this will also affect the precise structure of the yarn. The effect may consist of several yarn feeds. It is also possible, using a slightly different set-up, to make the yarn without cutting the fringe, or to make the yarn with two spines, creating a tape with a ladder-like structure.
4.31 Addition of eccentric yarn guide system for feather yarn production.
4.32 Overhead view of the eccentric yarn guide, showing screws for positional adjustment.
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4.4.12 Metallic laminate manufacture Modern metallic laminate yarns begin as broad width films, usually of polyester, or sometimes of nylon. The colour is printed on using gravure rollers or screens, then cut into manageable breadths before going through the microslitter, which creates the final width. This may be one millimetre or even less, with sizes of onetwo-hundredth of an inch being destined for hosiery, for example. The resultant fine strands of film are then wound onto packages. If the finished yarns are to be used in knitting, the strands of film are further supported by twisting filaments around them using the standard hollow spindle process. Two spindles mounted in sequence may be used to twist support yarns in both S and Z directions in the course of a single passage of the machine, and Fig. 4.33 shows an example of the sequential hollow spindle arrangement that may be used.
4.4.13 Making metal threads The precise details of the equipment used to create the purls, pearl purls, plates, and other metal threads used primarily in embellishment, together with the metallurgical knowledge necessary to make them successfully, may have changed and developed over the years, but the structures described were used for that purpose by the Arabs of the ancient world, together with methods that must in outline have remained unaltered by the centuries. The process for making purls, pearl purls and plates begins with a suitably prepared ingot of metal alloy, which has the required colour, ductility and cohesion. That ingot is then beaten into a cylindrical form and then gradually and repeatedly ‘drawn’ – stretched – until it reaches the required size. At this point the various processes diverge. The ‘wyre’, as it is now called, may be flattened to form ‘plate’ (effectively a flat metal ribbon), or wound on a former to create purls and pearl purls, or instead, the flattened wyre may be spun around a core of cotton, linen or silk to create a thread. The method used to achieve this last is shown in Fig. 4.34, which shows the silk core thread being brought through the spinning head. Behind the spinning head is placed a spool of the drawn and flattened metal thread, which is carried over wings placed on the spinning head, which in turn then wrap the metal thread around the core as it emerges through the spinning head, creating the cover yarn structure we have already described. The making of metal threads may also begin with the production of metal leaf, which is then applied to a substrate, such as the suitably prepared animal skin or gut which the ancients used, and which when cut into strips may be wound around a core of silk, linen or cotton. Research has suggested that moisture in the freshly prepared strips would react with the animal gut, creating a glue that helped the strips to adhere to the core. However, there is also evidence for some very durable threads of this type being made using paper as the substrate (von Folsach and Bernsted, 1993).
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4.33 Use of combined hollow spindle system to apply supporting threads to metal laminate films.
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4.34 Detail of method used to spin metal thread around a core.
4.4.14 Dyeing Fancy coloured yarns may be produced by such techniques as space dyeing. Cross-dyeing effects and dye-injected rovings or slivers all contribute to a range of fancy effects. Fair Isle effects in the final knitted fabric may now be created by carefully planned printing upon the yarns, reducing the complexity of the knitting involved. Other relevant changes in this area have related primarily to a greatly increased concern among consumers about the environmental effects of textile dyeing and finishing, which do not fall within the scope of this chapter. Natural or plant-based dyes have become increasingly important across the textile industry, although they remain very much a niche market. It will be most interesting to observe the changes in this section of the market over the next few years.
4.5
Applications for fancy yarns
4.5.1 Homewares Upholstery and home furnishings have offered a relatively new field to spinners of fancy yarns over the past 20 years. The now surprisingly long-lived trend for ‘shabby chic’ furnishing fabrics favours the use of fabrics involving fancy yarns, because the inherently uneven surface of a fancy yarn is enhanced when it is woven or knitted into a fabric, giving that fabric itself a broken surface. In addition to drapes and upholstery – which are expected to have a certain durability – fancy yarns have been used lavishly in accessories such as cushions and throws. Furthermore, as textural details have become an important part of interior design, an additional application for all fancy yarns has been found in making tassels and braids for furnishings and drapes.
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4.5.2 Fashion Fancy yarns have wide-ranging application in apparel at all levels of the market. Where once the extreme complexity and difficulty of making and using fancy yarns inhibited their production in sufficient quantity or at a low enough price for the mass market, improved process control has now greatly extended their market penetration. In particular, fancy yarns have become an increasingly prominent part of the revived hand knitting market, although this can best be seen as further evidence for the overall change in attitude within the market, which is discussed in the next section.
4.5.3 Overview Some of the most interesting developments in the market for fancy yarns relate to a change in outlook within the industry and the market, rather than to any specific changes in technology, fascinating though such technological developments may be. For example, controlled printing onto roving, sliver, or even yarns has been available for some time, and has been further extended, enhanced and varied by the use of dye resist techniques, but it was for a considerable period used to produce fairly large-scale, relatively unsubtle effects. With the advent of advanced electronic process control and machinery, the technique has been refined so that it is now possible to buy hand-knitting yarns which are designed to produce a Fair Isle patterned effect when knitted up using ordinary stocking stitch. This brings complex-seeming patterns within the range of the relatively unskilled knitter, which in turn helps to maintain interest in the activity and which can therefore help to build the market for hand-knitting yarns. This in turn suggests that there has been a further development in attitude, in that manufacturers are becoming more heavily involved in assisting patterndesigners and retailers in both developing and supporting the ultimate market. Certainly it seems to be the case that – even in the uncertain economic climate at the time of writing – the more knowledgeable customers can still be persuaded to buy more expensive materials for special occasions, for a treat, or (perhaps most important of all) because the material has some particular and desirable quality of comfort or warmth. The recent resurgence of the noble fibres is evidence enough of that. This in turn suggests that education of the ultimate customer – the general public – is one of the key elements in maintaining the health of the textile industry. Furthermore, even in the past decade, the fashion market has been changing and diverging. Where once the fashionable customer bought new outfits every season (perhaps twice or at most four times each year), now certain sections of the market are continually buying new clothes. These are then worn a few times
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before being thrown away, passed on, or simply languishing at the back of the wardrobe. Naturally this both reduces any concern with durability and at the same time increases the amount of fabric – and thus yarn – required for this market sector. In addition, it makes continuous demands concerning novelty of design, perhaps as simple as a new colour, but perhaps a new fabric or a different trim. Each of these elements involves the production of more yarns, more fabrics, more patterns, and even more trims and fringes. At the opposite extreme, other sections of the market are returning to more sparing buying habits as a result of a concern for the environment, an increasing dislike of poor-quality ‘disposable’ garments, and unease about conditions in the factories where such items are made. This market sector will pay a premium for higher-quality, more durable items. Environmental concerns are also driving a search for fibres, yarns and fabrics that produce warmer garments, allowing reduced power consumption, or for more economical or environmentally friendly ways to produce and process our textiles.
4.6
Future trends in fancy yarns
Whereas once it was lamented that fancy yarns only ever experience very short periods of popularity because of their expense and the difficulty of meeting demand, over the past ten years fancy yarns of one sort or another have remained available in the high street more or less continually. We can expect that this trend will continue. Although lot sizes are smaller than they were, there is the opportunity for great variety in the effects chosen and employed each season. In some market sectors, new effects may be introduced six times or even more often every year. Developments over the past decade have been largely in the realms of process management and control rather than in the creation of entirely new production methods. This period can therefore be seen as a period of consolidation and development, rather than one marking a caesura in technology. This must not be taken as a criticism of the work that has been done: the advances in the technology have been considerable; it is simply that they have not been radical changes introducing entirely new structures as did the hollow spindle machine or the chenille machine. Even feather yarns are the result of extending an existing manufacturing technique. In this respect we can see that as the developments of the past 50 years have been subject to more detailed process control, and as the structures themselves become better understood, this period of consolidation is preparing the way for new research which may mark a new departure in yarn manufacture, or may alternatively continue the work of consolidation and development that has been begun. The most marked changes have lain in a new understanding of, and attitude towards, the final customer. The development of hand-knitting yarns that can
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create dramatic, interesting and fashionable effects without demanding great skill from the knitter is one example of this. Whereas once hand-knitters knitted garments because it was cheaper than buying them, now they knit garments that will be unique – they want something fashionable and fun, not merely something utilitarian. Another such example lies in the increased acceptance within the industry of relatively short runs and low volumes of any particular yarn. It is this change that is driving alterations in the market and changes in the focus of manufacturing, concentrating on responsiveness to changes in demand, and on an understanding of, and contribution to, the development of products from fibre right through to fabric, instead of considering that the spinner’s task relates purely to changing fibre into thread. Spinners are taking an interest in initiatives relating to customer education and support, rather than confining themselves to the single process that is their main responsibility. There is also the possibility that further changes will spring not from machine development, but from research into the fabrics of the past. Textile archaeology is a growing field, and the vast collections of historical garments in museums across the world could yet prove a fruitful area for inspiration. We may find historical yarns being re-developed and re-issued, first of all in the process of verifying hypotheses concerning the early manufacturing processes, but then extending into the current market ranges. In the future, we can expect further consolidation, and perhaps still greater agility in the markets. It seems reasonable to assume that the last word on yarn structures has not yet been spoken.
4.7
Sources of further information and advice
British Wool Marketing Board, Wool House, Roydsdale Way, Euroway Trading Estate, Bradford, West Yorkshire, BD4 6SE – initiatives concerning the use and marketing of wool fibres. Golden Threads, Brimstone Cottage, Pounsley, Blackboys, East Sussex, TN22 5HS – manufacturers of metal threads for embellishment. Laxons Limited, Netherfield Road, Guiseley, West Yorkshire, LS20 9PD – spinners of fancy yarns. Lorella Marketing Ltd, Armston Farm, Broughton Road, Leicester, LE9 1RD – manufacturers of chainettes, feather and chenille yarns. Spectrum Yarns Ltd, Spa Mill, New Street, Huddersfield, West Yorkshire, HD7 5BB – makers and importers of fancy yarns. Textile Institute International Headquarters, 1st Floor, St. James’s Buildings, Oxford Street, Manchester, M1 6FQ. The archive of the Thistle Threads blog (http://www.thistle-threads.com/embroidery/ ebsblog/index.html) describing the Plimoth Jacket Project, contains information on historical research in textiles and the development of reproductions of early structures. There is much that could still be done, but this blog offers information on the process and research involved.
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4.8
Bibliography
Allen, L. A. Method of producing knop yarn, USP3945189, March 1976. Ball, A. Quick response in short staple spinning, Textile Horizons 8 (12), December 1988. Barham, E. The sarcophagus from Roman London: New discoveries, Minerva 11 (1), January/February 2000. Biermann, I., Birlem, O., Grecksh, H., Haase, C., Rienas, G. Method and device for the production of a fancy yarn, USP0137165A1, June 2007. Boldrini, L. Machines for the production of chenille yarns and spooling thereof, USP3969881, July 1976. Brown, M. W., Powell, L. K., Slagle Jr, J. C., Croker, B. M., Hance, M. H. Making slub yarn on open end machine, and composite fabric, USP5419952, May 1995. Chatin, R. Process for producing fancy effect yarns, USP3717959, February 1973. Dawson, B. Metal Thread Embroidery, Batsford, London, 1976. de Saint-Aubin, C. G. Art of the Embroiderer, facsimile of eighteenth-century book (trans. Nikki Scheuer), Los Angeles, 1983. Eschenbach, P. W. and Goineau, A. M. Method of forming air textured bouclé yarn, USP4610131, September 1986. Folsach, K. von, and Bernsted, A-M. K. Woven treasures – Textiles from the world of Islam, David Collection, 1993. Gemmill and Dunsmore Ltd. The GDM production system, Textile Month, April 1978. Glover, E. The Gold and Silver Wyre Drawers, Phillimore & Co Ltd, London and Chichester, 1978. Gong, R. H. and Wright, R. M. Fancy Yarns: Their Manufacture and Application, Woodhead Publishing, Sawston, Cambridge, 2002. Grecksh, H., Rienas, G., Haase, C., Birlem, O., Biermann, I. Method for the production of a fancy yarn, USP0243288A1, October 2008. Higgins, J. P. P. Cloth of Gold – A History of Metallized Textiles, Lurex Company, London, 1993. Ingham Jr, R. M. Open end spun slub yarn, USP4144703, March 1979. Kim, S. B. Nep yarn production with the cotton spinning machine, KRP9507793, July 1995. Lemon, J. Metal Thread Embroidery – Tools, Materials and Techniques, London, Batsford, 1987. Oxtoby, E. Spun Yarn Technology, Butterworths, London, 1987. Rheinburg, L. The romance of silk, Textile Progress, 21 (4), 1991. Sloupensky, J., Ludovicek, J., Kubovy, M., Hehl, R. and Halfar, M. Multi-component fancy yarn and method and device for its production, EP1338687A1, August 2003. Textile Institute. Tomorrow’s Yarns, Textile Institute, Manchester, 1984. Textile Institute. Textile Terms and Definitions, Ninth Edition, Textile Institute, Manchester, 1991. Wayland Barber, E. The Mummies of Urumchi, Macmillan, 1999. Wilson, I. Before the Flood, Orion, 2001. Wilson-Nguyen, P. The Embroiderer’s Story blog, available at http://www.thistle-threads. com/embroidery/ebsblog/index.html.
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5 Developments in 3D knitted structures Z. GUO, Zhongyuan University of Technology, China
Abstract: This chapter reviews the developments of 3D knitted fabrics. It provides a description of the three types of 3D knitted fabrics currently available, which are broadly categorized as multiaxial warp-knitted fabrics, space fabrics (or sandwich fabrics), and fully-fashioned 3D knitted fabrics (or near-net-shape knitted fabrics). The structures, properties, production, and applications of these different 3D knitted fabrics are described separately. Key words: 3D knitted fabrics, multiaxial warp-knitted fabrics, space fabrics, fully-fashioned 3D knitted fabrics, technical textiles.
5.1
Introduction to 3D knitted structures
Three-dimensional knitted fabrics have been widely used in many fields, especially in technical textiles. The development of 3D knitted fabrics is based on 2D knitted fabrics. However, while a considerable amount of research has been performed on 2D knitted fabrics, by comparison little is known about the mechanical properties and applications of 3D knitted fabrics. This chapter provides a description of the three types of 3D knitted fabrics currently available, which are broadly categorized as multiaxial warp-knitted fabrics, space fabrics (or sandwich fabrics), and 3D knitted fabrics (or near-net-shaped knitted fabrics). The structures, properties, production, and applications of these different 3D knitted fabrics are described separately.
5.2
Multiaxial warp-knitted fabrics
5.2.1 Structure This type of fabric is defined as a base fabric combined by a knitting system. Multiaxial warp-knitted fabrics possess inlay yarns at directions of 0°, 90° and ±θ. Yarn layers are tied together by tricot stitch or pillar stitch. Therefore, multiaxial warp-knitted fabrics are mutilayered fabrics. Fibers are laid along different directions in one plane and along the thickness direction to form 3D net structures. The fabric consists of one or many parallel yarn layers, each of which can be arranged at a different orientation. Each layer can possess different densities and can be combined with fiber net, film and other materials. The orientation of each layer depends on the production orientation. The production direction is defined as 0°. The direction of each layer is expressed by the angle between the layer and 0°. As shown in Fig. 5.1, the multiaxial warp-knitted fabric includes four yarn-inlay systems (warp inlay yarn, weft inlay yarn and two series of slant inlay yarn), and a 109 © Woodhead Publishing Limited, 2011
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5.1 Multiaxial warp-knitted fabric.
binding system. Four series of inlay yarns form four yarn layers combined by knitted stitches. The direction of inlay yarns is 0°, 90°, +45° and −45° respectively.
5.2.2 Properties Tensile properties Multiaxial warp-knitted fabrics possess good tensile properties. Compared with traditional laminated plates, warp stitches significantly improve the interlaminar properties of laminates. The tensile property along any direction in the fabric plane depends on tensile strength and the direction of inlay yarns. Multiaxial warp-knitted fabrics can be designed as the isotropy or anisotropy materials. If Θ = ±45°, the fabric can be considered as the isotropy material. Shear properties Multiaxial warp-knitted fabrics possess slant inlay yarns, which restrain the deformation due to shear force. Therefore, multiaxial warp-knitted fabrics possess good shear properties.
5.2.3 Production methods Equipment Multiaxial warp-knitted fabrics are manufactured using the MULtiaxial machine (KARL MAYER company). It is a high-tech warp-knitting machine that includes several yarn-inlay systems.
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Materials High-performance fibers are used as the inlay yarns, for example: PET, PA, PP, HD-PE, PA, GF, CF, and Kevlar. The inlay yarn can be the staple fiber yarn or the filament yarn, but the filament yarn is usually used as the reinforced yarn. The linear density of the inlay yarn is large, and the maximum linear density is about 2,500 tex. The ground yarn is made from common fibers, and the linear density is about 160 dtex. High-performance fibers, e.g. high-strength PET, can be used in the knitting system if performance along the thickness orientation is required. The linear density and orientation of each yarn can be changed with the change of load type. Fabric texture The orientation of inlay yarns is usually −45°, 90°, +45°, 0°, and the orientation can be changed with the fabric purpose, which makes the materials anisotropic. The materials are reinforced along the forced direction. Tricot stitch or pillar stitch is used in knitting system, which improves the interlaminar properties and the dimensional stability of laminates.
5.2.4 Applications Multiaxial warp-knitted fabrics have been widely used in technical fields due to their low cost, high production efficiency, structural integrity, design flexibility and good shear property. In particular, multiaxial warp-knitted fabrics are usually used as the reinforcement of composites. Aeronautical and astronautics fields Multiaxial warp-knitted fabrics have been widely used in the aeronautical and astronautics field for reinforcing composites. Fiber-reinforced composites are suitable for use in the aeronautical and astronautics fields due to the high ratio between their strength and their mass. The use of composites reduces weight, increases service life, and prevents fire from spreading in the aircraft. Above all, the strength of aircraft components can be designed precisely. Train and ship manufacture Multiaxial warp-knitted fabrics have been widely used in train and ship manufacture. These fabrics are made from glass fiber, aramid fiber, carbon fiber and high-strength polyester fiber, and nonwoven fabrics can be fed in during fabric production. Ships are used in extremely hostile environments, facing temperature changes and water erosion. Therefore, resistance of the composite to
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stripping is critically important. Multiaxial warp-knitted fabrics used for reinforcement purposes are more resistant to stripping of the composite than woven fabrics. Multiaxial warp-knitted fabrics are also used in train manufacture. Wind power generation Multiaxial warp-knitted fabrics have been widely used in wind power generation. Composites using multiaxial warp-knitted fabrics as reinforcement are suitable for use in wind power generator blades. These blades are made from glass fiberreinforced composites. At present, multiaxial warp-knitted fabrics are usually used to reinforce the composites. Construction Multiaxial warp-knitted fabrics can be used for reinforcing concrete for rebuilding or repairs in the construction industry. Reinforced concrete uprights on islands used for electricity transmission are situated in extremely hostile conditions. They can be seriously damaged after about 15 years. The damage can be repaired using multiaxial warp-knitted fabrics. Such repair work not only recovers stability but using multiaxial warp-knitted fabrics to wrap the uprights also improves resistance to torsion stress and bending stress. Other fields Multiaxial warp-knitted fabrics can be used to reinforce composites that can be fabricated into flak suits and helmets. The fabrics are manufactured using the Multiaxial machine. The yarns are inlaid at only ±45°, which gives the fabric good forming property. Multiaxial warp-knitted fabrics can be coated to form cylinder containers that can be used as an air film. Multiaxial warp-knitted fabrics are also used for producing snowboard, board and canvas.
5.3
Space fabrics (or sandwich fabrics)
5.3.1 Structure Two plane fabrics are connected by fibers or yarns to form a fabric. The space exists between two surfaces, so it is called ‘space fabric’. The thickness of space fabric is about 3 to 10 mm, and depends on the type of space fabric being produced. The structure of space fabric is like a sandwich, so it is also called ‘sandwich fabric’. Space fabric comprises two surface layers and one space layer. The yarns in the space layer are at right angles to the two surface layers and connect
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5.2 Warp-knitted space fabric.
them together. There are two types of space fabric: warp-knitted space fabric, and weft-knitted space fabric. The structure of warp-knitted space fabric is shown in Fig. 5.2.
5.3.2 Properties Compression elasticity Space fabrics are anisotropic materials. Their mechanical properties along the thickness direction differ from their mechanical properties along the other two directions. Space filaments carry the loads along the thickness direction. The compression elasticity of space fabrics depends on type, fineness and the density of space filaments. The spacing distance and the angle between the space filament and the fabric surface also affect the compression elasticity of space fabrics. Air permeability Space fabrics have been used as bandages, linings, cups, sports shoes and seat fabrics. Therefore, space fabrics are required to possess good air permeability for use in the above fields. The air permeability of space fabrics relies on the thickness, density and structure of fabrics. Light, thin or net-structured fabrics possess good air permeability.
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Moisture absorption and conductivity The moisture absorption properties of the two surfaces of space fabrics are identical if they possess the same material and structure. Good moisture conductivity is achieved if one surface is composed of natural fibers and the other is composed of chemical fibers. In this case, the surface composed of natural fibers absorbs moisture from air, and then transmits moisture to the surface composed of chemical fibers by the capillary effect of space filaments. Space filaments must possess good moisture conductivity if good moisture conductivity of space fabrics is required. Sound absorption and insulation Space fabrics can be designed as sound absorption and insulation materials. One side is compact, and the other is loose. Sound wave transmission is from the compact surface to the loose surface. Sound intensity decreases due to the existence of a space filament layer.
5.3.3 Production methods Equipment Warp-knitted space fabrics are manufactured using the double needle bed raschel machine. The machine possesses at least four guide bars, but between five and seven guide bars are used most of the time. The distance between two needle beds can be adjusted to produce different thicknesses according to requirements. Weft-knitted space fabrics are manufactured using a circular or a flat knitting machine. Two surface layers are manufactured on two needle beds respectively, and they are connected by tuck stitch. The distance between two needle beds can be adjusted to produce different thicknesses according to the requirement. At present, weft-knitted space fabrics are usually manufactured using an automatic flat knitting machine. Materials Many types of fine yarns can be used in space fabrics, and the yarn can be selected from a wide range. Usually, polyester, nylon or polypropylene fiber can be selected as the material according to the application requirement. The surface yarns and space yarns can be the same or different according to the fabric’s application. Usually, multifilament is selected as the surface yarn, but polyester monofilament is selected as the space yarn, because the space yarn carries the stress loads. The space layer connects one surface with the other, and keeps a distance between them. Therefore, space yarn must possess good stiffness, and its fineness depends on the space distance.
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Fabric texture Two surface layers are manufactured using one or two guide bars on two needle beds. The texture depends on their structure. If the structure is compact, two bar tricot stitch or lock-knit stitch can be used. If the surface is net-structured, some guide needles can be empty. If the surface possesses a figured effect, one guide bar produces ground texture, while the other one produces the pattern. The space yarn forms the loops at the front and the back beds in turn to connect the two surface layers together. The distance between the two surface layers depends on the distance between the front and the back beds.
5.3.4 Applications Garments Space fabrics contain an air layer between two surfaces so that they possess good air permeability and moisture conductivity. Therefore they can be applied in a cup lining instead of in a sponge. Space fabrics can be applied in firemen’s uniforms. Firemen work in extremely high temperatures, so the space layer must be able to provide heat protection. Therefore, the surface structure of the fabric must be compact and the twisted aramid filament, like the space yarn, maintains the thickness of the space layer. In addition, the space fabric can be applied in policemen’s safety vests.
Home textiles Space fabrics have been used in home textiles, such as bedding, carpets, non-slip mats and towels.
Sports equipment Sports shoes are the main market for applying space fabric in sports equipment. The fabric thickness is about 1.5 to 1.8 cm. The fabric can possess two compact surfaces, or one compact surface and one loose surface according to requirements. Space fabrics are mainly used in the upper, tongue and ankle of the shoe. The fabric is made from polyester and nylon. Elastomeric yarn can be knitted into two surfaces to obtain good elasticity. Space fabrics are also used for producing children’s sandals. Space fabric is easily dried, and possesses a soft handle and good resistance to erosion, so it can be applied in the lining of swim-suits. The space layer contains a lot of air, which makes the wearer warm and comfortable, so it can be also applied in diving suits. In addition, space fabrics can be applied in protective sports and golf garments.
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Automobile textiles Space fabrics can be applied in automobile textiles, such as seat covers, instrument packs and sun-visors. Medicine As medical textiles, space fabrics possess good durability and stability, so they can be applied in operating table mats and bandages. Composites Space fabrics composed of high-performance fibers can combine with resin to form high-performance composites. The composites can be applied in construction and hydraulic engineering.
5.4
Fully-fashioned 3D knitted fabrics (or near-net-shaped knitted fabrics)
Fully-fashioned 3D knitted fabrics can be produced by a two-bed weft knitting machine, however additional needle beds are required for producing 3D (multilayer) fully-fashioned fabrics. Additional needles and yarn guides are needed both to create the different layers of knits and to facilitate the transfer of yarns between the layers. The final near-net-shaped fabric is predominantly a result of careful stitch control during the knitting process, including the use of different fabric textures and different loop lengths and changing the number of working needles in one course. Fully-fashioned 3D knitted fabrics have been applied in many fields, including jet engine vanes, T-shape connectors, I-beams, rudder tip fairings for a mid-size jet engine aircraft, and even medical prosthesis. Despite these successful trials, the development of 3D knitted near-net-shaped composites is still at an early stage, and the high cost of machine and software development stands in the way of more rapid progress.
5.5 1
2
Bibliography
Verpoest, I., Ivens, I., van Vuure, A. W., Gommers, B., Vendeurzen, P., Efstratiou, V. et al. New developments in advanced textiles for composites, Proceedings of the Fourth Japan International SAMPESymposium, 25–28, 1995, 644. Phillips, D., Verpoest, I., van Raemdonck J. 3D-knitted fabrics for sandwich panels, Proceedings of Texcomp-3, 1996, paper 18.
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Bibo, G. A., Hogg, P. J., Kemp, M. Mechanical characterization of glass and carbonfibre-reinforced composites made with non-crimp fabrics. Composites Science and Technology 1997; 57:1221. Bibo, G. A., Hogg, P. J., Backhouse, R., Mills, A. Carbon-fibre non-crimp fabric laminates for cost-effective damage-tolerant structures. Composites Science and Technology 1998; 58:129. Clayton, G., Falzon, P., Georgiadis, S., Liu, X. J. Towards a composite civil aircraft wing, Proceedings of the Eleventh International Conference on Composite Materials, ICCM-11, 14–18 July 1997, pp. I310–I319. Hamilton, S., Schinske, N. Multiaxial stitched preform reinforcement, Proceedings of the Sixth Annual ASM/ESD Advanced Composites Conference, 8–11 October 1990, pp. 433–434. Wang, Y., Li, J., Do, P. B. Properties of composite laminates reinforced with E-glass multiaxial non-crimp fabrics. Journal of Composite Materials 1995;29: 2317–2333. Sheffer, E., Dias, T. Knitting novel 3-D solid structures with multiple needle bars, Proceedings of the UMIST Textile Conferences – Textile Engineered for Performance, Manchester, UK, April 1998, pp. 20–22.
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6 Developments in leno-weave fabrics Y. CHEN, Soochow University, China
Abstract: This chapter discusses leno-weave and leno-weave fabrics. The characteristics of leno-weave and leno-weave fabrics are introduced, followed by a discussion of the structure and working principles of special leno heald systems used for leno fabric production, in order to show the process of fabric formation. The application of leno fabric in various areas and new technologies in leno fabric production are also reviewed. Key words: fabric structure, leno-weave, textile.
6.1
Introduction to leno-weave fabrics
Leno-weave fabric has a long history of use in apparel for the nobility owing to its graceful appearance and durable performance. With advances in fiber and fabric production technology, leno fabric is now more widely used in many areas besides clothing. Leno fabric is made from two warp yarns and one weft yarn. Leno-weave is also known as gauze or doup weave, and differs from normal fabric weaves in its level of complexity both in terms of fabric formation and structure. In normal fabrics, warp ends lay parallel to and interlace with the weft threads. During leno fabric weaving, on the other hand, the warp ends are themselves crossed in addition to being interlaced with the weft threads. Warp yarns in leno fabrics comprise of stationary ends (also called standard ends or straight ends) and crossing ends (or looping ends). Two groups of warp threads are arranged in leno pairs. The weft yarns are arranged in parallel fashion while the paired warp threads are twisted together. The crossing warp yarns are twisted with the stationary warp yarn in alternate wefts, or after two or more weft yarns that are inserted during the weaving process. In a leno pair the crossing warp threads are located on alternate ends of the ground warp threads. Leno-weave fabric was initially used principally to prevent the shifting of fibers in open-weave fabrics. It gradually came to be used in clothing and home textiles because of its special fancy appearance and excellent structural stability. Lenoweave is also used in cloth edge weaving on shuttle-less looms, in order to lock the selvedge areas of the fabric. Once high performance fibers are applied, leno fabrics can be used in industry, agriculture, the medical sector, construction, and many other areas. 118 © Woodhead Publishing Limited, 2011
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The structure of leno-weave fabrics
6.2.1 Leno-weave structure The structure of leno-weave fabric differs substantially from that of other weaves. The adjacent warps in leno-weave fabrics are twisted together to form a special open structure. Warp yarns are divided into stationary ends and crossing ends. The stationary ends stay parallel with the fabric lengthways during weaving, while crossing ends appear on both the right side and left side of the ground ends alternately. The crossing ends are twisted with the stationary ends, as the former change position on the stationary end side. Once removed from the loom the stationary ends are bent under the stress of the crossing ends. Figure 6.1 shows the structure of leno-weave.
6.2.2 Structures of leno-weave fabrics Several different structures of leno-weave fabrics exist. As shown in Fig. 6.2, two ends of warp yarn are grouped in a leno pair comprising of one crossing end and one stationary end. The crossing end is interlaced with the weft in the same position during weaving in all leno pairs. In Fig. 6.3, the crossing ends in adjacent
6.1 Structure of leno-weave. Notes: 1 – stationary end; 2 – crossing end; 3 – weft.
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6.2 All-over gauze. Notes: 1 – stationary end; 2 – crossing end; 3 – weft.
6.3 Symmetrical gauze. Notes: 1 – stationary end; 2 – crossing end; 3 – weft.
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leno pairs are interlaced with the weft in the opposite positions. The fabric weave for Fig. 6.2 is known as all-over gauze, while the weave for Fig. 6.3 is known as symmetrical gauze. In the weaves displayed in both Fig. 6.2 and Fig. 6.3, the crossing warp thread is interlaced with the ground warp thread at every weft insertion and is defined as single weft gauze. The number of warp threads in one leno pair and the number of weft yarns inserted between the crossing warp of every twist are variable. In Fig. 6.4, the warp pair is composed of one crossing yarn and two stationary yarns: this is known as ‘one-twist-two gauze’. The crossing end is twisted with the stationary ends every two wefts in the same cloth fell, which is known as ‘two-weft gauze’. In Fig. 6.5, the warp pair is composed of two crossing yarns and two ground yarns. The crossing ends are twisted with the ground end every two wefts in the same fell, creating ‘two twist two double-weft gauze’. In Fig. 6.6, the crossing end and ground end are interlaced in plain weave at the twist interval, which is typical three-weft leno. Figure 6.7 provides an example of fancy leno-weaves. There is a great deal of variation in the structure of leno-weave. The following factors can be individually modified or used together to create fabrics with a variety of appearances:
• •
The twist direction of the crossing ends in adjacent warp thread pairs; The total number of warp yarns in leno pairs;
6.4 One-twist-two gauze. Notes: 1 – stationary end; 2 – crossing end; 3 – weft.
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6.5 Two-twist double-weft gauze. Notes: 1 – stationary end; 2 – crossing end; 3 – weft.
6.6 Three-weft leno. Notes: 1 – stationary end; 2 – crossing end; 3 – weft.
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6.7 Fancy leno. Notes: 1 – stationary end; 2 – crossing end; 3 – weft.
• •
The number of crossing warp threads and ground warp threads in leno pairs; The number of wefts inserted and the weave between warp twists.
6.3
Fabrics with leno-weave
6.3.1 Gauze Gauze is an all-over leno-weave fabric characterized by a thin and translucent appearance and a loose open structure. The weave shown in Fig. 6.2 is a typical gauze fabric. Leno-weave is applied to the whole of the fabric to form tiny meshes. Gauze was originally made of silk and was used for clothing. Other fibers are now widely used for gauze production, with modern gauze usually made of synthetic fibers, especially when used in clothing. Gauze is often used for a decorative fashionable effect in scrim fabrics. The application of this fabric has now been extended into other areas, most notably for
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medical purposes. Gauze made of cotton is especially useful for dressing wounds, as it prevents the dressing materials from sticking to the burn or laceration. Gauze can also be made of metal, in applications such as safety lamps or spark arrestors (wire gauze), or as a material for fences.
6.3.2 Grenadine Grenadine is a fine leno-weave mesh. It is usually categorized as an all-over lenoweave, but various different patterns can also be formed. Stripes, checks and figures can be produced through the combination of leno-weave with other weaves. In this case, grenadine is known as fancy organza. Grenadine is usually made of hard twist yarns. The fabric can be made of silk, a silk/cotton blend or cotton yarns, with wool and man-made fibers also occasionally used. Grenadine can be used as a dress fabric and also as a curtain fabric. The mesh for curtain fabrics is larger than that for dress fabrics. Grenadine used for curtain fabrics usually appears as a fine but looser weave with figures or dots.
6.3.3 Merquisette Merquisette is a sheer, light and open meshed fabric used for clothing, curtains, and mosquito nets. The mesh size of this fabric is larger than grenadine and is similar to netting. Cotton, wool, silk, rayon and synthetic fibers are most commonly used for this type of leno-weave fabric, and the warp threads can be composed of single or multi-ply yarns. Stiff cotton yarns are used for Merquisette in order to imitate the appearance of scrim fabric. Merquisette is widely used as a curtain fabric and is also popular in apparel uses such as veils, overskirts for dresses or formal wear.
6.3.4 Tulle and net Tulle is a fine mesh fabric or very fine netting. It is totally transparent and lightweight, and can be made of various fibers, including silk, nylon, rayon and other synthetic fibers. The fabric can be produced in a wide array of colors and is used for veils, gowns and ballet tutus. Tulle and net are used in clothing such as bridal dresses, ball gowns, evening wear, scarves, shawls, ribbons and veils, as well as in home textiles. Tulle is also widely used for crafts, hats, hair accessories and gift-wrap.
6.3.5 Leno Leno fabric is made of silk and is characterized by its striped pattern, with lenoweave and plain weave applied on alternate stripes. There are two kinds of leno fabric: vertical leno fabric and horizontal leno fabric.
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In vertical leno fabric, plain weave ends and leno-weave ends are arranged according to the desired stripe size. In horizontal leno fabric, all warp ends are grouped in pairs. The crossing ends in all the warp pairs interlace the stationary warp ends at the same weft insertion. After that, the odd number wefts are woven in plain weave. Horizontal leno is more widely used for clothing.
6.4
The production of leno-weave fabric
6.4.1 The leno heald system Producing leno-weave fabric is significantly more complicated than producing normal weave fabrics. The weaving of leno fabrics is mostly carried out on rapier, projectile or shuttle looms. Special doup mounting devices, which are called leno heald frames, should be used during leno fabric production, in addition to the normal heald devices. The leno heald frame is used in combination with the standard healds to control the crossing ends. The crossing warp yarns are controlled by the gauze attachment of the leno heald and by the side-to-side movement of the ground warp yarns. Two warp yarns in the same leno pair cross over each other and interlace with one or more weft threads. There are two kinds of leno heald system: the twine leno heald and the metallic leno heald, as presented in Fig. 6.8 and Fig. 6.9 respectively. The twine heald
6.8 Twine leno heald system (a). Notes: 1 – stationary end; 2 – crossing end; 3 – half heald; 4 – standard harness; 5 – normal harness.
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6.9 Metallic leno heald system (a). Notes: 1 – stationary end; 2 – crossing end; 3 – back standard harness; 4 – front standard harness; 5 – half heald; 6 – normal harness.
system is mainly used with jacquard, while the metallic leno heald system is used with dobby. The twine leno heald is composed of a standard harness and a half heald. The crossing warp end should be drafted through both the half heald and the normal heald. The metallic leno heald is composed of two standard harnesses and a half heald, which are all made from metal. The standard harnesses are controlled by two heald frames: the front standard harness frame and the back standard harness frame. The stationary warp ends are drafted through the same healds as those used for normal fabric, and are then passed through the middle of the leno heald system of the crossing warp end within the same leno pair. There are two different forms of half heald. The bottom doups and top doups of the twine heald are shown in Fig. 6.10 and Fig. 6.11 respectively. Bottom doups and top doups of leno heald systems are used when crossing ends change their positions, in the back and in the top of the stationary ends, respectively. The bottom doup system is more widely used in industry. The crossing warp ends are drafted through both the half heald and normal heald. The original positions of the crossing end can be either to the left or to the right of the stationary end. The crossing end in the twine leno heald as in Fig 6.8 is located to the left of the ground end, while the crossing end as in Fig 6.12 is located to the right of the ground end. Figure 6.9 and Fig. 6.13 present the two original locations of the respective crossing ends in the metallic leno heald system. © Woodhead Publishing Limited, 2011
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6.10 Bottom doups of twine leno heald system. Notes: 1 – stationary end; 2 – crossing end; 3 – half heald; 4 – standard harness.
6.11 Top doups of twine leno heald system. Notes: 1 – stationary end; 2 – crossing end; 3 – half heald; 4 – standard harness.
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6.12 Twine leno heald system (b). Notes: 1 – stationary end; 2 – crossing end; 3 – half heald; 4 – standard harness; 5 – normal harness.
6.13 Metallic leno heald system (b). Notes: 1 – stationary end; 2 – crossing end; 3 – back standard harness; 4 – front standard harness; 5 – half heald; 6 – normal harness.
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6.4.2 Sheds of leno-weave fabric Three different sheds should be applied in leno fabric weaving: the crossing shed, the opening shed and the standard shed. The crossing shed is used to interlace the warp threads during weft insertion. The ground ends stay in their original position to form the bottom of the shed. The crossing ends move from their original position to around the ground ends and are lifted to form the top of the shed, as shown in Fig. 6.14 and Fig. 6.15.
6.14 Crossing shed of twine leno heald system. Notes: 1 – stationary end; 2 – crossing end; 3 – half heald; 4 – standard harness; 5 – normal harness.
6.15 Crossing shed of metallic leno heald system. Notes: 1 – stationary end; 2 – crossing end; 3 – back standard harness; 4 – front standard harness; 5 – half heald; 6 – normal harness.
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In the opening shed, the ground ends stay in their original position to form the bottom of the shed. The crossing ends are lifted from their original position to form the top of the shed, as shown in Fig. 6.16 and Fig. 6.17. The standard shed of leno fabric is similar to that of normal weave fabrics. The ground ends are lifted to form the top of the shed, while the crossing ends keep their original position to form the bottom of the shed, as shown in Fig. 6.18 and Fig. 6.19. The relative right and left position of the ends in the leno warp group is the same as that of previous weft insertion.
6.16 Opening shed of twine leno heald system. Notes: 1 – stationary end; 2 – crossing end; 3 – half heald; 4 – standard harness; 5 – normal harness.
6.17 Opening shed of metallic leno heald system. Notes: 1 – stationary end; 2 – crossing end; 3 – back standard harness; 4 – front standard harness; 5 – half heald; 6 – normal harness.
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6.18 Standard shed of twine leno heald system. Notes: 1 – stationary end; 2 – crossing end; 3 – half heald; 4 – standard harness; 5 – normal harness.
6.19 Standard shed of metallic leno heald system. Notes: 1 – stationary end; 2 – crossing end; 3 – back standard harness; 4 – front standard harness; 5 – half heald; 6 – normal harness.
By combining these three sheds in different ways, many leno fabrics with various structures can be obtained. Figure 6.20 shows a novel application of leno heald systems developed on the same basis as the normal metallic leno heald system. The crossing end is drawn into the doup heald of the first leno heald frame, while the standard end is drawn into the inverted doup heald of the second leno heald frame. The crossing end is under the standard end in the center shed position. The crossing end is raised either by the left heald frame or the right heald frame and the standard end is © Woodhead Publishing Limited, 2011
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6.20 Innovated metallic leno heald. Notes: 1 – stationary end; 2 – crossing end; 3 – front left harness; 4 – front right harness; 5 – front doup heald; 6 – back left harness; 7 – back right harness; 8 – back doup heald.
6.21 Crossing shed of innovated metallic leno heald. Notes: 1 – stationary end; 2 – crossing end; 3 – front left harness; 4 – front right harness; 5 – front doup heald; 6 – back left harness; 7 – back right harness; 8 – back doup heald.
lowered to form the crossing shed or opening shed depending on the original position of the leno warp ends. Figure 6.21 and 6.22 show the crossing shed and opening shed when the crossing warp ends are originally to the right of the ground warp ends. During plain weave, i.e. with standard shed, the crossing end is in the lower shed, while the standard end in the upper shed is as shown in Fig. 6.23. © Woodhead Publishing Limited, 2011
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6.22 Opening shed of innovated metallic leno heald. Notes: 1 – stationary end; 2 – crossing end; 3 – front left harness; 4 – front right harness; 5 – front doup heald; 6 – back left harness; 7 – back right harness; 8 – back doup heald.
6.23 Standard shed of innovated metallic leno heald. Notes: 1 – stationary end; 2 – crossing end; 3 – front left harness; 4 – front right harness; 5 – front doup heald; 6 – back left harness; 7 – back right harness; 8 – back doup heald.
6.5
Properties of leno-weave fabrics
In leno-weave fabrics, the warp ends cross one another. This interlacing occupies more space in the warp direction in order to limit the maximum possible weft density. On the other hand, the warp ends in the leno pairs are grouped together to © Woodhead Publishing Limited, 2011
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leave more spaces between leno pairs. These factors give rise to the typical lenoweave mesh structure and transparency. The open structure of leno fabric can be enhanced through the application of low count yarns and filament yarns. Lenoweave fabric constructions are usually only considered for light mesh and transparent structures in fashion and home textile applications. Because the warp threads in leno-weave fabric interlace with one another in addition to the normal interlacing with weft threads, there is more friction between threads, and leno-weave fabric is more slip-resistant than plain, twill and satin weaves. In geo-textiles, medical textiles and many other applications, the stable mesh size and fabric structure offered by leno-weave fabrics are extremely desirable. Leno-weave fabric is durable and dimensionally stable because no yarn slippage occurs during its end uses. It is stronger and firmer than other weave fabrics, and its open structure permits the passage of both light and air through the fabric. It is used for warm weather clothing as it allows the wearer to keep cool and refreshed.
6.6
Applications of leno-weave fabrics
In addition to its traditional applications in fashion and home textiles, the uses of leno-weave fabric now extend into industry, civil engineering, the medical sector, agriculture, and other areas where light, loosely-woven fabrics with high slip resistance are in high demand. In fashion and home textile applications, the main advantage of leno-weave fabrics is their fancy and transparent appearance, while in other areas leno-weave fabrics are used as reinforcement materials to improve the flexibility, durability and structural strength and stability of the relevant materials.
6.6.1 Fashion and home textiles Leno-weave fabrics are often used for decorative and fashionable effect in scrim fabrics and dress fabrics. Veils and overskirts made from leno-weave fabrics are light, sheer and graceful. Leno-weave fabrics are also popular in hats, hair accessories, scarves, shawls and other decorative fashion elements. Leno-weave fabrics with large meshes and patterns are widely used as curtain fabrics and mosquito nets. In these applications, leno-weave fabrics allow air and light to freely pass through the material. When used as a mosquito net, the fabric can protect people from insects. Leno-weave fabrics have also been used as backing material for blankets.
6.6.2 Grinding wheel reinforcement All-over leno-weave fabric can be coated with phenolic resin or epoxy resin. The coated fabric is then baked to create a netlike composite material. This reinforced material is cut for use on a grinding wheel. The leno-weave fabric is used as the © Woodhead Publishing Limited, 2011
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base material for the grinding wheel, which uses resin as the adhesive agent. Grinding wheels made of this composite material have excellent heat resistant properties, strong structural strength, and can be used for high-speed cutting with great durability.
6.6.3 Lightweight membranes Leno-weave fabric can also used as the base material in lightweight membranes. When these membranes are used for architectural purposes, the flexibility of the material offers great advantages in the realization of various designs. The membrane can be transparent thanks to the open structure of the leno-weave base fabric, and is widely used to create soft and ambient exterior luminescence both in daylight and under artificial lighting. Improvements in modern construction techniques have led to leno fabric-based lightweight membranes being used as building materials. Large fabricated membrane panels can be installed and removed quickly and easily: and these panels therefore represent a more costeffective solution than traditional building materials. The membrane can provide heat insulation and can be self-cleaning if photo-catalytic treatment is carried out. These properties are very important in reducing costs related to both energy consumption and maintenance.
6.6.4 Laminating fabrics Leno-weave fabric can be laminated and used as a base fabric. The protective film coating can be applied to one or both sides of the leno-weave fabric. Leno fabrics are selected for this type of application because of their structural stability and high strength, which improves durability and maintains product quality. Water cannot pass through laminated leno fabrics, allowing their range of application to be significantly expanded. Laminated leno fabrics are widely used in packaging for various kinds of products such as food and sugar as well as many others. This fabric can also be used as a waterproof lining in geo textiles to avoid seepage of liquid or water. In these cases, leno fabric offers substantial advantages: it is lightweight, retains its shape, and involves lower costs
6.6.5 Biomedical plaster casts Leno-weave fabric is also used as the base for medical materials and is widely used for wound dressings and bandages. Monofilament, multifilament and staple fibers from synthetic polymers, natural polymers and genetically engineered polymers can be used for this purpose. Leno-weave fabrics have great advantages in this area of application. The loose structure and meshes provide excellent water/blood and air permeability, which
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are important aspects for wound recovery, while the high flexibility and stretch rate also offer improved levels of comfort. Leno-weave fabric is stronger than the nonwovens and knitted fabrics that are currently used for the same purposes. Finally, the porosity level of the fabric can be adjusted by modifying the fabric density, the arrangement of the crossing ends and the crossing format of the ends in leno warp pairs. As new and innovative fibers, structures and therapies are developed, it can be expected that leno-weave fabric will be used in still more medical applications, including tissue-engineered scaffolds, vascular implants and so on.
6.6.6 Shelter and storage Leno-weave fabric is also used in nets offering shelter in agriculture or plant nurseries. In this case, polyethylene yarns are woven using a high-density leno-weave process. The net is structurally stable and strong enough to prevent damage to a wide variety of crops. The use of a leno-weave net can reduce the UV rays reaching the crop by around 10%, depending on the density of the yarn. These leno-weave nets are flexible, light and strong, and can be easily spread and secured on support structures. They are also easily rolled up and stored for later use. Leno-weave fabrics can also be used for the storage of various goods including fruits, seafood, and vegetables. Leno-weave bags are structurally stable and strong enough to hold the goods, and are important in delivering and protecting a variety of products. They are usually woven using high-density polyethylene or polypropylene. Leno fabric can also be used as a backing material for paper or fabrics used for storage of chemicals, fertilizer, cement, sugar, etc. Fabrics used for this purpose are usually water- and chemical-proof.
6.6.7 Filters Filters are one of the important end uses of leno-weave fabrics. The use of lenoweave offers significant benefits thanks to the stable structure of the fabric. Monofilament nylon, polyester and fiberglass are most widely used for filters, while metal wire can also be used. The mesh size is a very important factor in the use of this fabric, which is designed according to the size of particles to be filtered. Normally, one-twist-one all-over leno-weave is used and the mesh size is controlled by both warp and weft densities, after the thread sizes have been decided.
6.7
Future trends in leno-weave fabrics
Warp interlacing is the most critical element for leno-weave fabric. The twine heald and metallic leno heald systems used restrict the speed of the
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weaving machine and cause excessive wear on the leno heddle system. Further techniques and devices for leno-weave fabric production have recently been developed with the aim of improving productivity, flexibility and durability of leno healds.
6.7.1 Easyleno The Easyleno system was developed by Lindauer Dornier, a leading manufacturer of high-class weaving looms in Germany. The Easyleno system makes it possible to produce leno-weave fabrics on rapier looms or air-jet looms. Leno healds such as those used in the traditional system are not used in the Easyleno system. Two needle bars, one stationary and one movable, are installed behind the reed that is normally used. The ground warp ends and crossing warp ends are drawn into the stationary needle bar and movable needle bar respectively. The stationary needle bar is shifted once each time the weaving machine cycles from left to right or vice versa. To create interlacing, the crossing warp ends must be moved up and down between the upper and lower shed. The Easyleno system overcomes the disadvantages of the previous leno heald system. The speed, productivity, flexibility and working life of the equipment can be greatly improved: the style change time is significantly reduced, and speeds of up to 450 rpm on rapier machines and 720 rpm on airjet machines have been reported. The maintenance of needle bars is much easier than that of additional shedding devices in a normal leno-weaving machine. The warp densities can be greatly increased as the leno heald system is substituted by needle bars, leading to the possibility of developing different density leno fabrics for a variety of technical applications. In the Easyleno system, two different warp tension control devices are introduced in order to regulate the two systems of warp end separately. This device, allows the elongation caused by warp crossing to be greatly reduced, so that wefts and ground warps remain straight or curly in the fabric, as shown in Fig. 6.24 and Fig. 6.25 respectively. The Easyleno system allows the use of other weaves alongside leno, or of two groups of warp yarns with different stretch properties within the same fabric. The interlacing of the warp ends will no longer be diagonal and a new type of lenoweave with a different appearance will be produced.
6.7.2 Powerleno Powerleno is a new technology for leno fabric production invented by Sulser. A guide bar and eyeleted reed are introduced into the weaving system, replacing the traditional leno healds. The crossing warp threads run through the apertures in the guide bar and eyeleted reed, while the ground warp yarns run through the eyelet of the eyeleted reed.
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6.24 Straight ground warp in the fabric by Easyleno. Notes: 1 – stationary end; 2 – crossing end; 3 – weft; 4 – cross-section of fabric.
6.25 Curved ground warp in the fabric by Easyleno. Notes: 1 – stationary end; 2 – crossing end; 3 – weft; 4 – cross-section of fabric.
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In the Powerleno system, shedding is accomplished through the opposing upward and downward movements of the eyeleted reed and the guide bar. An additional lateral movement of the guide bar results in twisting of the warp. Following weft insertion, the guide bar moves upward, and the eyeleted reed moves in the opposite direction until the leno thread is above the stationary end. Then the guide bar is displaced laterally until the leno thread is on the opposite side of the aperture in the eyeleted reed. When the guide bar moves downward and the eyeleted reed moves upward, the leno thread comes to lie over the ground warp thread. The shed is then open for the next weft insertion. This invention has significantly increased the productivity of leno-weave machines. The Powerleno system can be used on high-speed shuttle looms, and the strains on warp and weft yarns can be greatly reduced, improving the uniformity of the fabric surface.
6.7.3 PosiLeno PosiLeno is one of the new simplified and flexible leno systems invented by GROB Textile, Switzerland. The system can be installed on modern weaving machines with very limited investment. PosiLeno consists of two lifting frames: one positively controlled doup frame and another form-optimized leno heald. The positive control of the doup frame takes place via movement of the lifting frames, which are controlled either by a dobby or by a cam-shedding motion. The movement sequence of the lifting frame can be translated into an optimal sequence for the movement of the doup frame and the leno healds. The positively controlled leno system can be successfully used for all leno fabrics. It is reported that the production speeds of PosiLeno increased 100% compared to those of conventional leno systems. This system can be used for weaving various patterns, and offers great flexibility. Another advantage of this system is that it can be used on the same machines as those used for normal fabric weaving.
6.7.4 Other trends in leno-weave fabrics Leno-weave fabrics have a broad range of uses and are also being used increasingly in technical applications. This is resulting in great market potential. It is expected that high-performance fibers will be increasingly used for leno fabrics in order to obtain stable and lightweight base materials with open structures, for use in composites with various applications. A circular leno loom has been developed to produce a seamless leno bag. Four or six shuttles are used in this machine, which produces tubular leno fabric at very high speed. As the use of leno fabric for storage purposes increases, improvements will be made to this machine with the aim of lowering cost, improving efficiency and facilitating maintenance.
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6.8
Sources of further information and advice
1 2 3 4 5 6 7 8 9 10 11
6.9 1 2 3 4 5 6 7 8
B. K. Behera and P. K. Hari (2010), Woven Textile Structure: Theory and Applications, Cambridge: Woodhead Publishing Limited. J. W. Parchure (2009), Fundamentals of Designing for Textiles and Other End Uses, Cambridge: Woodhead Publishing Limited. Y. El Mogahzy. (2008), Engineering textiles: Integrating the design and manufacture of textile products, Cambridge: Woodhead Publishing Limited. D. X. Cai and M. L. Qin (2008), Fabric Structure and Design, Beijing: China Textile & Apparel Press. A. M. Seyam (2008), Structural Design of Woven Fabrics: Theory and Practice, Cambridge: Woodhead Publishing Limited. J. Y. Yan, P. Gu (2008), Fabric Weave and Jaquard, Beijing: China Textile & Apparel Press. A. Ormerod and W. S. Sondhelm (1995), Weaving: Technology and Operations, Cambridge: Woodhead Publishing Limited. P. R. Lord and M. H. Mohamed (1982), Weaving: Conversion of Yarn to Fabric, Cambridge: Woodhead Publishing Limited. Chinese Silk. Available from: http://www.kepu.net.cn/gb/civilization/china-silk/silk_ history.html [accessed 2 July 2010]. PosiLeno® Leno system. Available from: http://www.grob.com/website/ghag/en/ products_productinformation_337_339.html [accessed 12 July 2010]. The System Family with EasyLeno®. Available from: http://www.lindauerdornier. com/weaving-machine/easylenoae [accessed 8 August 2010].
References J. Y. Yan, P. Gu (2008), Fabric Weave and Jaquard, Beijing: China Textile & Apparel Press. D. X. Cai, M. L. Qin (2008), Fabric Structure and Design, Beijing: China Textile & Apparel Press. J. B. Nie (2004), Woven Structure and Design, Beijing: China Textile & Apparel Press. P. Gu (2004), Fabric Structure and Design, Shanghai: Dong Hua University Press A. Wahhoud (2007) Leno Technology For Plane Structure, Melliand – China, 35 (9) 22–26, 30. Chinese Silk. Available from: http://www.kepu.net.cn/gb/civilization/china-silk/silk_ history.html [accessed 2 July. 2010]. PosiLeno® Leno system. Available from: http://www.grob.com/website/ghag/en/ products_productinformation_337_339.html [accessed 12 July 2010]. The system family with EasyLeno®. Available from: http://www.lindauerdornier. com/weaving-machine/easylenoae [accessed 8 August 2010].
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7 Developments in triaxial woven fabrics T. TYLER, Consultant, UK
Abstract: Triaxial weaving is used to manufacture woven fabrics with three sets of parallel fibres. It covers a range of weaving and braiding techniques that produce fabrics with a range of weights and properties. The history and possible future of the weaving technique are discussed, and the associated applications and manufacturing techniques are surveyed. Key words: triaxial, weaving, braiding, textiles, review.
7.1
Introduction
Triaxial weaving uses three sets of parallel fibres, known as the warp, the whug and the weft. These fibres are typically at angles of 60 degrees to each other. The whug is not present in conventional, biaxial weaving. The three sets of parallel fibres can be interwoven in a variety of patterns, producing fabrics with a variety of different weights and properties. Desirable properties exhibited by triaxial fabrics include extremely light weight, good resistance to damage, near-isotropic strain resistance and the ability to withstand shearing forces. The fabrics have a long history in traditional cultures, mainly in basketry. In modern times, some of these fabrics have found uses in a variety of industrial applications, most notably the reinforcement of composite materials.
7.2
Basic patterns
Triaxial weaving comes in a variety of forms with different properties and relative densities. The simplest and most basic patterns are described below. The fabric shown in Fig. 7.1 is sparse. It typically has about half as many structural elements per unit area as a rectangular woven fabric made using the same elements. One of the features of this fabric is that it has holes in it. While this makes it unsuitable for some applications, it does help with applications that require holes or ventilation, such as chair fabric, linen baskets and light shades. Alternatively, it is appropriate where a light material is required but that is still very strong. This fabric is sometimes known as the basic triaxial weave. This sort of weave is one of the lightest simple weaves known. Its relative density (compared with the density of a single flat sheet) is 1.0. The type of triaxial weaving fabric shown in Fig. 7.2 can be thought of as being composed of two mirror-image versions of the sparse fabric, interwoven with each other. Its relative density is 2.0. 141 © Woodhead Publishing Limited, 2011
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7.1 Sparse triaxial weave.
7.2 Medium triaxial weave.
The fabric shown in Fig. 7.3 has three layers of material at any point. It is thus stronger than a rectangular woven piece of fabric made using the same elements. It is very regular and isotropic. Its relative density is 3.0. Unfortunately, this fabric is relatively difficult to manufacture. It can be thought of as consisting of three ‘sparse’ triaxial weaves interwoven with one another.
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7.3 Dense triaxial weave.
7.4 Herringbone triaxial weave.
The type of triaxial weaving shown in Fig. 7.4 is not isotropic – but it is fairly common, partly as a result of being relatively simple to manufacture. This pattern can be thought of as being based on an ordinary biaxial weave. Alternatively, it can be thought of as being based on two interwoven sheets of sparse triaxial weave. Its relative density is 2.0.
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7.3
A history of triaxial woven fabrics
Triaxial weaving is a component of traditional basketry practices in many cultures – and so likely dates back many thousands of years. Early traditional applications included baskets, hats, marine traps and snowshoes. Until 2007, the earliestknown example was dated as belonging to the Nara period in Japan (AD 710 to 794) (McCarty and McQuaid 1998). Samples of these textiles are preserved in the Shosoin repository in Nara. In 2007, archaeological finds in Higashimyo in Japan dated triaxial weaving back to the earliest Jomon period. More than 400 woven baskets were recovered, including some with ‘mutsume ami’ (hexagonal eyes). Carbon dating one of the baskets resulted in a date range of 5891 to 5790 BC (Nishida 2010). Unfortunately, basket-making materials decay constantly, destroying most of the evidence relating to weaving patterns. Hence, use of the pattern may pre-date what are currently the earliest finds. The most common evidence of ancient knowledge of basketry techniques is an imprint of the weave on fragments of baked clay pots that are constructed by using the basket as scaffolding – however, no early triaxial finds have been reported so far. Large-scale weaving patterns can also sometimes be preserved in sculptures or statues. We have triaxial weaving patterns from China, which have been carved in ivory, that date back to the nineteenth century (Snelson, 2009), but so far not from earlier eras. In modern times, Sepak Takraw balls (see Fig. 7.5) are made using
7.5 Sepak Takraw ball (dense weave).
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triaxial weaving patterns. Sepak Takraw is a modern version of a much older game called ‘Chinlone’, which is a non-competitive version that has been played in Myanmar (formerly Burma) for over 1500 years. The word ‘Chinlone’ means ‘cane ball’ in Burmese. Modern versions of these balls are made using triaxial weaving, and it seems quite possible that ancient ones were too. Balls were made with both sparse and dense triaxial weaves. Snowshoes were one of humankind’s earliest inventions, and the North American Indians developed woven snowshoes that used the basic sparse triaxial weaving pattern. The pattern may be thousands of years old, but no one seems to know when it was first invented. The situation is similar with hats. Traditional Chinese hats are often manufactured with two layers of sparse triaxial weaving, with a layer of banana leaves sandwiched between them. The traditional ‘Knup’ rain shields of Khasi farmers are made in a similar manner. These patterns are old, but it is not known how old. The geographical distribution of triaxial weaving in traditional cultures is wide. Traditional use has been observed in Kenya, Madagascar, Brazil, Ecuador, Canada, Alaska, China, Japan, India, Malaysia, Indonesia and the Philippines (Gerdes 1999). Basketry was the most common application (see Fig. 7.6 and Fig. 7.7). Notable early modern developments include: a triaxial tennis racquet that was patented in England by Nightingale (1886); a book on the making of woven mats in the Philippines by Miller and Miller (1913), which illustrated dense triaxial weaving and herringbone triaxial weaving; the patenting of a triaxial weaving structure by Cobb (1916); and the patenting of a triaxial weaving machine in 1921 (Stewart 1921). Stewart’s patent illustrates a rather unusual triaxial
7.6 Woven basket.
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7.7 Woven light shade.
weaving pattern, suggesting that the properties of the various triaxial weaving patterns were poorly understood by Stewart at the time. The sparse triaxial weaving pattern was mentioned in a 1934 patent (Tice 1934), where it was clearly illustrated. In the early 1960s, Norris F. Dow encountered triaxial weaving. After several years of research, Dow concluded there was an opportunity in this area. In 1965 he founded N. F. Doweave, Inc. to develop and market the fabric. Dow was contracted by NASA to research the fabric, and he authored a paper on the topic that illustrated the manufacturing process in some detail (Dow and Tranfield 1969). He patented the concept in the USA (Dow 1969) and 16 other textileproducing countries, assigning the US patent to General Electric Company. Dow was involved in the design and construction of the first known commercial triaxial weaving machine. Prototypes were made by the Barber-Colman Textile Division under licence from Doweave. By 1974, 17 production machines were operating in a pilot mill in King of Prussia, Pennsylvania, each producing approximately 500 yards of triaxial material a week. Unfortunately by 1978 Dow had run out of funds and went out of business. Subsequently triaxial weaving was popularised by Buckminster Fuller. He pictured a woven Sepak Takraw ball in Synergetics II (Fuller 1979) – and what appears to be a triaxial woven fabric appeared on the cover of some reprints of his book Nine Chains To The Moon (Fuller 1938). Fuller’s work went on to inspire artists to experiment with triaxial weaving techniques. Notable among them was David Mooney, who went on to write a series of papers on the topic (Mooney 1984, 1984a, 1986, 1988). Mooney traced
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the technique back into the eighteenth century, and documented the triaxial weaving patterns and explored simple techniques for manufacturing them. Various geodesic-like dome structures were constructed based on the pattern. The surface of the Yomiuri Inagamachi Golf Club Field House in Japan sported the distinctive Star of David pattern. Tents from Mountain Hardware and Shelter Systems were constructed with frames based on the pattern, and other more recent examples were to follow. Meanwhile, Madeline Hauptman developed an innovative triaxial racquet (see Fig. 7.8), inspired by the weave of a traditional American-Indian snowshoe. She developed the racquet in the hope of reducing the vibration transmitted into players’ arms. These racquets were christened ‘Mad Raq’ (Madeline’s Racquets). The design was patented (Mishel 1980). Dunlop licensed Madeline’s patent and came out with the ‘Dunlop Mcenroe Mad Racquet’. These racquets are on permanent display in both the Wimbledon Lawn Tennis Museum in London, England and the Museum of the International Tennis Hall of Fame in Newport, Rhode Island. Madeline sold ‘Mad Raq’ tennis racquets, and licensed her patent to several companies, selling more than 500 000 racquetball racquets and 10 000 tennis racquets with the ‘Mad
7.8 Triaxial tennis racquet.
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Raq’ stringing pattern. However, commercial production of the pattern was discontinued, probably partly due to the difficulty of stringing the racquet. More recent history will be covered in sections devoted to particular application domains.
7.4
Classification
There are a considerable number of triaxial fabrics, which raises the issue of how to classify, measure and name them. They include:
•
• • •
• •
Symmetries: listing the plane symmetries of the fabric is one obvious classification method. Fabrics with six-fold rotational symmetry can generally be used to make spheres and other curved surfaces in three dimensions. Whether the fabric has the same appearance front and back is another related means of classification. Holes: whether the fabric covers the plane (or has holes in it, if made from ribbon-like material) is another important property. Fabrics with holes in them are unsuitable for some applications. Geometry: triaxial fabrics tend to come in families with related geometrical structures. This property is not easy to define, but it seems to be useful for providing a framework for naming the fabrics. Density: the thickness of the fabric is an important measure, since it affects the cost per unit area of the raw materials used in making the fabric. In this article, sparse triaxial weaving is considered to have a relative density of 1.0: the same as a single sheet of parallel fibres. Herringbone triaxial weaving has a relative density of 2.0: the same as a typical biaxial fabric. Dense triaxial weaving has a relative density of 3.0. Fibre spacing: the distances between the parallel fibre elements suggests another means of classification. Sparse triaxial weaving has spacing of 2.0. Herringbone triaxial weaving has spacing of 0.5. Dense triaxial weaving has spacing of 0.0. Unit cell size: this is another useful measure. It indicates the regularity of the repeating pattern in the fabric.
In addition, standard measures of fabric properties may be employed – strain resistance, tear resistance, bursting resistance, and so on.
7.5
Variations
Triaxial weaving techniques can result in many possible variations of the weaving pattern in the resulting fabrics. Doubling up fibres generates many variations on the basic patterns (see Fig. 7.9). The overall effect is broadly similar to that obtained by using thicker, flatter fibres. Another way of doubling up fibres is illustrated in Fig. 7.10. Removing fibres is another way of generating variations. In Fig. 7.11, the herringbone triaxial weave has half of the fibres that run in one direction removed. Several variations based
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7.9 Double sparse triaxial weave.
7.10 Double sparse triaxial weave II.
on the various rectangular twill patterns exist. The pattern shown in Fig. 7.12 is used commercially, in the form of the QISO™ triaxial braid. Figure 7.13 shows another variation that is based on a rectangular twill pattern. Figure 7.14 shows a variation with pleasing surface aesthetics. Figure 7.15 shows an irregular triaxial weave with a larger unit cell. There are a great many such variations.
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7.11 Sparse herringbone triaxial weave.
7.12 Herringbone triaxial weave (2,2 twill variation).
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7.13 Herringbone triaxial weave (1,2 twill variation).
7.14 Chequerboard triaxial weave.
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7.15 Less regular triaxial weave.
7.6
Properties
Triaxial woven fabrics take many forms. While there are only a few fundamental biaxial fabrics there are quite a large number of different triaxial patterns with a range of different properties. Triaxial fabrics typically have good tear resistance, abrasion resistance and bursting resistance. They also have good isotropic strain resistance, due to fibres running in many directions. Ladders in the fabric tend not to propagate very easily, since two-thirds of the elements in the fabric have to break for a ladder to propagate. Also planar shear resistance is typically good owing to the locked intersections found in most triaxial fabrics. Triaxial fabrics also exhibit much more isotropic strain resistance, relative to biaxial fabrics. The near-isotropic character of triaxial fabric strain resistance is quantified in Bowman et al. (2004). Failure modes of the fabrics are explored in Littell et al. (2008, 2009). The basic sparse triaxial fabric is typically lighter than a biaxial fabric made from similar materials. However, one of its drawbacks is that the fabric has many small holes in it. That makes it unsuitable for some applications: where a continuous barrier is needed, many small holes are undesirable. However, there are other applications where small holes are either irrelevant or positively desirable. Isotropy, shear resistance and low density can be advantages over biaxial fabrics, while the relatively low quantity of material used is the main advantage over quadraxial fabrics. The simplest herringbone triaxial fabric has most of the desirable properties of other triaxial fabrics, while completely filling the plane with no holes. It has
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less-than-perfect isotropic characteristics, but they are good enough for many purposes. There are other triaxial fabrics of the same relative density with six-fold rotational symmetry, but the herringbone triaxial fabric has some desirable properties that make it superior for many applications. In particular, the spacing between the elements of the fabric can be easily varied, making it suitable for braiding around curved surfaces.
7.7
Advantages
In the context of reinforcing applications, triaxial fabrics face competition from stitch-bonded fabrics. Stitching layers of parallel fibres together with flexible yarn has some advantages and disadvantages compared to braiding or weaving. An advantage of stitch bonding is that relatively thick and inflexible fibres can be employed, since the fibres do not need to be woven in and out. The fibres are not bent by the weaving process: a process that can cause damage to some types of fibre. Also production costs can be lower, since no triaxial weaving machine is required. The use of stitch-bonded fabrics still permits use of the name ‘triaxial’, which has become a desirable indicator of quality for many manufacturers. A disadvantage of stitch-bonded fabrics is that they cannot so easily be contoured to fit around curved surfaces or completely wrapped around boards. For manufacturers of flat objects, like skateboards, using stitch-bonded triaxial fabrics can seem like an attractive cost-cutting measure. Using stitch-bonded triaxial fabrics on the top and bottom of a board defends it well against bending stresses, giving the board a rigid feel. It also offers good resistance to most kinds of impact. However, there is still a remaining failure mode if the board is twisted – where the board can fracture without disturbing the integrity of the top or bottom fabric. Wrapping the fabric around the edges of the board would be much more effective at preventing such torsional fractures, but this is not always practical. Also, such a configuration does not offer much protection to the edges of the board. So, unless the edge is protected in some other way, it can be a point of weakness where the fabric can get scuffed and start to peel off or unravel. Triaxial weaving also faces competition from quadraxial fabrics. A common application of multiaxial weaving is the use of fabrics in cane chair seats and backs. Triaxial fabrics are sometimes used in these contexts, but very rarely. Cane chair seats are often hand-woven. They are made with rectangular frames, and with quadraxial weaving; the anchors for the cane webbing can be holes drilled regularly around the edge. The importance of the rectangular frame of the fabric in this context means that triaxial weaving would often be an unnecessary complication. The most basic sparse triaxial fabric is of a very similar weight to the most commonly used quadraxial fabric, so there would not be any significant material saving. Triaxial fabrics face substantial competition from conventional rectangular (biaxial) fabrics. Biaxial fabrics typically fill the plane. They are easy to
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manufacture, cheap and ubiquitous. However, they have some structural problems. Their strain resistance is nowhere near isotropic, and the fabric offers very poor resistance to in-plane shearing forces. In response to non-axial strains, the fabric buckles and distorts. Behaviour in response to penetration by pointed objects differs dramatically between biaxial and triaxial fabrics. In a triaxial fabric the locked intersections effectively prevent the fibres from moving laterally, so an incoming pointed object cannot easily penetrate the fabric, unless it manages to break the fibres or pull them through the surrounding fabric. In a biaxial fabric, because the intersections are not locked, the fibres can often be pushed to one side by an incoming sharp object much more easily, resulting in a puncture wound in the fabric. This can sometimes be an advantage for the biaxial fabric, since the bunched-up displaced fibres can help provide strength to each other, defending the puncture wound from further damage. Another difference is how easily cuts and tears propagate. At least half the fibres have to break for a tear to propagate in a biaxial fabric, while two-thirds of the fibres have to break for a tear to propagate in a triaxial one.
7.8
Applications
Traditional applications of triaxial weaving include baskets (Kudo 1982), hats, marine traps, snowshoes and cane chairs. A little more recently, triaxial weaving has been used in light shades, furniture, racquetball racquets (Hauptman 2000), and architectural woven structures. In modern times, the biggest application of triaxial weaving has probably been reinforcement using fabric–resin composites. Triaxial-braided carbon fibre composites have been used to reinforce skis, jet engine fan cases (Roberts et al. 2009a), baseball bats (Seki 1994), hockey sticks, lacrosse shafts and prosthetics. The fabric has also been used for filtration, solar panels, safety clothing, sailcloth for boats, balloons, aircraft evacuation slides, life rafts, life vests, radio telescopes (Wood 2009), aircraft components and components for satellites (Stover 1989). Probably the most common industrial application of triaxial weaving is the surface reinforcement of materials – often wood. By coating an element with a layer of triaxial woven fabric, the element is protected against forces that would otherwise distort it increasing the risk of a break. Also, its surface is toughened. When fabrics based on triaxial weaving are used in this context they are often referred to as triaxial woven fabrics (TWF). One of the most common materials that are reinforced with a coating of triaxial fabric is wood. Wood is a common construction material for skis, snow-boards, skate boards and surfboards. However, such structures are frequently exposed to considerable stress and strain, resulting in broken boards. A coating of triaxial fabric has the result of putting part of the fabric into tension whenever the board is distorted. Triaxial fabrics typically have good isotropic strain resistance, so
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most types of bending or twisting force in the board rapidly run into tensile resistance from the fabric. Some of the more important triaxial fabrics allow the spacing between fabric elements to be varied to some extent, allowing braided fabrics to be manufactured that conform to the curved surfaces of objects they are wrapped around, without excessive distortion of the weaving pattern. Skis are one of the important applications for triaxial reinforcement of composite materials. Skis must be light, narrow, very strong and invulnerable to breaking. Also their surfaces must strongly resist damage from abrasion. Triaxial braiding was first used in this context in 1988 by the ski manufacturer K2. The process consists of sending the core through a circular triaxial braiding machine, where strands of fibreglass are braided around it. This braiding process is still widely regarded as being the best way to apply fibreglass to the wooden core of skis. In 2001 braiding experts, A&P Technology (Cincinnati, Ohio) partnered with the NASA Glenn Research Center (Cleveland, Ohio) in a project funded by the NASA Aviation Safety and Security Program. Their aim was to develop a braiding technology to improve the safety of jet engine fan cases. They used carbon fibre-reinforced polymer in a herringbone triaxial braiding pattern. Their work is now in commercial production – in the form of General Electric’s GEnx™ engine. Another pioneer in this area is Fiber Innovations who have worked on sports equipment, aeroplane engine components, spacecraft components, missiles and launch tubes. For an overview of their efforts, see Sharpless (2005). Triaxial fabrics have several properties that make them especially suitable for weaving structures in three dimensions:
• • •
They have good shear resistance, so the resulting structures are protected from shearing deformations; They have locked intersections, so the resulting structures have reduced susceptibility to local distortions; A hexagon–pentagon geometry can be employed to create curved surfaces. This is the same geometry that is used to create the surfaces of most geodesic domes.
Figure 7.16 shows a computer-generated woven sphere that illustrates the geometry. The sparse, medium and dense fabrics can all be woven into spheres (see Fig. 7.17). Several of the traditional applications for triaxial weaving exploit these properties, to make three-dimensional baskets and hats out of continuous sheets of woven triaxial fabric. The Star of David pattern associated with the sparse weave has been used on an architectural scale. Examples include the Eden Project domes, the Pompidou Metz centre in France by Shigeru-Ban, and Fuller’s Yomiuri Inagamachi Golf
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7.16 Sparse triaxial woven sphere.
7.17 Medium triaxial woven sphere.
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Club Field House. The Pompidou Metz centre was explicitly modelled on a Chinese triaxial woven hat.
7.9
Aesthetics
Fabrics are frequently selected for aesthetic appeal, as well as for more functional properties. The ways of modulating the appearance of fabrics include the use of dyes, printing, embroidery, the use of different coloured threads and using different weaving patterns in different places. Using different coloured threads that run in different directions is a technique often used in conjunction with highly reflective threads to create fabrics that reflect the light differently when seen from different angles. This emphasises the contours of the fabric, and can provide a pleasing effect when used with figure-hugging garments and pleated fabrics. Triaxial weaving allows three different colours to be employed to produce a multicoloured effect that is visible from a wider range of angles. Different coloured threads are frequently used to create patterns in striped, chequered, herringbone and tartan fabrics. Tartan (plaid) illustrates the potential of this approach to create crisp images that do not fade, run, or otherwise become damaged. Triaxial tartan is dominated by triangular and hexagonal patterns. One such pattern is shown in Fig. 7.18. The book A Ribbon Weaver’s Handbook (Shore 2008) gives an indication of some of the possibilities in this area.
7.18 Star of David pattern.
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Weaving also allows the thread on top of the fabric to be altered in a systematic way in order to create patterns. The most common application for this is to create herringbone patterns on tweed fabrics. This technique uses a twill-weaving pattern to create a stripe, and then changes the twill pattern that is used, so the result is stripes that run in zig-zag patterns. With a biaxial fabric the two different directions allow monochrome patterns to be generated in this way. Triaxial fabrics permit three directions, and so three colours, allowing colour images to be woven directly into the fabric. The process typically involves dense triaxial weaving, a programmable loom, and a computer program designed to find the optimal weaving strategy to produce the desired pattern. Unfortunately, the three axes of triaxial weaving are not really sufficient to reproduce full CMYK (Cyan, Magenta, Yellow, and Key/black) patterns at the fabric’s natural resolution. Quadraxial fabrics potentially allow full CMYK patterns to be generated, but if the individual layers of colour are space-filling, the weave becomes quite a mess. The problem of weaving in full colour is one without a terribly neat solution. Still, even with only three layers (and thus solid colours), some interesting patterns and effects are possible. Though the potential for full-colour images is limited, triaxial weaving shows considerable potential for creating monochrome images and abstract coloured patterns by weaving them directly into the fabric.
7.10
Manufacturing
Traditional triaxial weaving was performed by hand. Automating triaxial weaving is no trivial feat and was not done until the 1970s, long after the automation of the production of biaxial fabrics. Large-scale manufacturing of triaxial fabric is done typically using techniques derived from traditional looms, or via techniques derived from automating braiding. Looms are used to produce flat sheets of fabric, while braiding techniques are used to produce tubes of triaxial fabric, which are then typically used to reinforce the skin of compression members. The first triaxial weaving machines were designed by Norris F. Dow and manufactured by Barber-Colman under licence in the 1970s. Many patents have been published which relate to the manufacture of triaxial weaving machines: for example, see Dow (1974, 1975), Townsend and Trumpio (1976), Kulczycki (1976, 1976a, 1977, 1977a). The manufacture of triaxial fabrics is normally performed via a weaving or braiding process. Braiding techniques make cylindrical tubes of material. Tubes are often desirable in the context of composite reinforcement. However, tubes must be cut if a flat sheet of material is required, and cutting introduces the possibility that the edges of the fabric will fray. Braiding is the easier process to understand. Braiding techniques have traditionally been employed manually on a small scale to make candlewicks, shoelaces and clothing ties. However, with the application of triaxial braiding to
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reinforce the shells of airline and rocket engines, mechanical ‘megabraiders’ have been produced, which implement triaxial braiding on an enormous scale. These machines typically have a large ring, which is perpendicular to the resulting braid. The fabric’s warp yarns are supplied from spindles on the ring which rotate around it as though on a carousel, weaving between each other. Braiding allows triaxial fabrics to deform slightly during the manufacturing process so as to conform to the curved surfaces of objects they are wrapped around more closely than is possible with a pre-woven fabric. This effect is familiar to those who have encountered a Chinese finger trap. A quick way to obtain a basic understanding of how automation of the braiding process works is to look at one of the online videos about braiding machines. One video illustrates the K2 Triaxial braiding machine. There an A&P Technology promotional video online shows a triaxial braiding machine. Fiber Innovations has a couple of videos of their triaxial braiding machines online. There is also a video that shows a Lexus biaxial carbon fibre-braiding machine. For more details about these videos, see Tyler’s web site (2010). Braiding machines with up to 800 carriers have been produced (Braley and Dingeldein 2009). Weaving resembles braiding, but has the added complication of dealing with the edges of the fabric without breaking the threads. The triaxial weaving processes have been described in many patents. Curiskis et al. (1997) review some of the techniques employed. One method, illustrated in (Dow 1975), involves laying down the warp and the whug using a rotating wheel with mounted spindles: see Fig. 7.19.
7.19 Rotating wheel with mounted spindles.
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Heddles are then used to create a shed for weft insertion, which may be performed using a rigid rapier or a shuttle.
7.11
Future trends
Triaxial fabrics have a number of attractive properties, but their market penetration has so far remained very low. The main problem appears to be the difficulty of manufacturing these fabrics. This requires specialised and somewhat more complex machinery than is needed for biaxial fabrics. Also a small market creates higher manufacturing costs, which leads to higher cost to end users, which creates a vicious circle of lack of demand. In traditional applications of weaving, where objects are hand-woven, triaxial patterns are used more frequently. However, even there, they are not used very often, and it seems likely that difficulty of manufacture is also involved here. Triaxial patterns are not the most obvious patterns to use. They are not the first patterns people learn, and many people never learn them. In the case of the triaxial tennis racquets one of the main problems was the difficulty of stringing them. In the future, lack of knowledge seems unlikely to be such an issue. A global marketplace leads to large global suppliers and the associated economies of scale, which should help reduce production costs. The ‘long tail’ of such marketplaces means that even minority interests can be catered to inexpensively. It seems likely that triaxial fabrics will be judged more on the merits of their properties, and less on the difficulty of manufacturing them in the future. Consequently they are more likely be used in those applications where they are appropriate. In the short term, probably the main area of expansion will be surface structural reinforcement. This is an area where the virtues of triaxial fabrics are well proven, but they currently have limited market penetration. Triaxial fabrics can usually be used where biaxial fabrics currently are, and frequently offer structural benefits. In the case of structures encased within braided tubes of material, the triaxial braiding process is not really much more difficult than biaxial braiding is. Carbon fibre composites are used in high-status applications such as cars, surfboards, sports equipment and high-end musical instruments. The carbon fibre is sometimes exposed by using transparent resin, so it is publicly visible and is thus an opportunity for displaying triaxial tartan. Consumers may not know much about triaxial weaving: however, reviewers will probably learn enough to recognise it as a selling point, which means that manufacturers will want it as a feature. Something similar to this has already happened in the worlds of skiing and skateboarding. Another possibility is that some of the weave’s potential for making woven three-dimensional structures will be realised eventually. Currently, while machines can manufacture triaxial fabrics, they are typically unable to insert the pentagons needed to bend the fabric around into convex shapes, and so triaxial basket weaving is still left mostly to human fingers. One day, that situation will change,
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and we will have mechanical weavers that can create arbitrary curved surfaces made of triaxial fabric, complete with the required pentagons. It seems desirable to be able to give a robot some fibres, tell it to weave objects for you from a specified design and allow it to execute the task. Designs could include chairs, stools, lampshades, baskets, boxes, etc. It seems likely that we will have such capabilities at some stage, and then it seems likely that triaxial weaving’s potential for creating sturdy three-dimensional structures will be more fully realised.
7.12
Sources of further information and advice
The author’s triaxial weaving web site (Tyler 2010) is a useful resource for those seeking further information. Pictures illustrate some of the many pattern variations possible, videos illustrate the basic patterns and the manufacturing process, and there are links to other resources. The properties of triaxial fabrics have been studied in the scientific literature. Often these studies are sponsored by the fabric manufacturers in the process of exploring their properties: e.g. Bowman (2003). Patents are an important source of information relating to the manufacturing techniques that have previously been explored. There are also a number of weaving patterns in the patent literature. Tyler (2010) has a list of relevant patents. Many of these patents date from the 1970s, when the pattern was first being commercially explored. Books associated with the pattern include basketry books, e.g. Kudo (1982), and technical textiles books, e.g. Horrocks and Anand (2000). There have also been numerous specialist articles relating to the topic, e.g. LaPlantz (1984), Mooney (1984) and Shore (2008).
7.13
References
Bowman C. L., Roberts, G. D., Braley, M. S. Xie, M., and Booker, M. (2003), Mechanical Properties of Triaxial Braided Carbon/Epoxy Composites. Thirty-fifth ISTC, Dayton, OH, September–October. Braley M. and Dingeldein M. (2009), Advancements in braided materials technology. At http://saltshake.com/?get=1.10.107 [accessed 24 April 2011]. Cobb (1916), Fabric for tires, USP 1201257. Curiskis J. I., Durie A., Nicolaidis A., Herszberg I. (1997), Developments in multiaxial weaving for advanced composite materials. Proceedings of International Conference on Composite Materials: ICCM-11, 14=N18 July, Melbourne, Volume 5, pp. 86–89. Dow N. F. (1969), Triaxial fabric, USP 1368215. Dow N. F. (1974), Machine for forming triaxial fabrics, with Murray Halton, USP 03799209. Dow N. F. (1975), Warp beam for triaxial weaving – USP 03884429. Dow N. F. and Tranfield G. (1969), Preliminary investigations of feasibility of weaving triaxial fabrics. Textile Research Journal, November 1970, 40(11) 986–998.
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Fuller R. B. and Applewhite E. J. (1979), Synergetics II: Explorations in the geometry of thinking. Macmillan. Fuller R. B. (1938), Nine Chains To The Moon. Doubleday. Gerdes P. (1999), Geometry from Africa: mathematical and educational explorations. Mathematical Association of America, Washington, D.C. Hauptman, M. M. (2000), Method and apparatus for stringing game racket and the racket so strung, USP 6089997. Horrocks, A. R. and S. C. Anand (2000), Handbook of Technical Textiles. Woodhead Publishing, Sawston, Cambridge, UK. Kudo, K. (1982), Japanese Bamboo Baskets (Form and function series). Kodansha America, Inc., New York, NY. Kulczycki, K. and Burns D. (1976), Heddle for a weaving machine for making triaxial fabrics, USP 03985160. Kulczycki, K. (1976a), Triaxial weaving machine with heddle shifting means and method, USP 03999578. Kulczycki K. (1977), Triaxial weaving machine with heddle shedding means, USP 04046173. Kulczycki K. (1977a), Triaxial weaving machine with heddle transfer and method, USP 04013013. LaPlantz S. (1984), The Mad Weave Book. La Plantz Studio, Santa Fe, NM. Littell J. D., Binienda W. K., Goldberg R. K. and Roberts G. D. (2008), Full-field strain methods for investigating failure mechanisms in triaxial braided composites. Earth & Space 2008: Engineering, Science, Construction, and Operations in Challenging Environments. Littell J. D., Binienda W. K., Goldberg R. K. and Roberts G. D. (2009), Characterization of damage in triaxial braid composites under tensile loading. Journal of Aerospace Engineering, 22, 270. McCarty C. and McQuaid M. (1998), Structure and surface: contemporary Japanese textiles, Museum of Modern Art, New York, NY. Miller H. H. and Miller J. F. (1913), Philippine Mats. Manila Bureau of Printing. Miller B. and Widess J. (1991), The Caner’s Handbook. Lark Books, Asheville, NC. Mishel M. H. (1980), Game racket and method of making same, USP 4184679. Mooney D. R. (1984), Handweaving triaxial weaves with braiding techniques. Ars Textrina 3 (Fall), 99–124. Mooney D. R. (1984a), Triaxial weaves and weaving: An exploration for handweavers. Ars Textrina 2 (Spring), 9–68. Mooney D. R. (1986), Braiding triaxial weaves: Enhancements and design for artworks. Ars Textrina 5 (June), 9–31. Mooney D. R. (1988), David Mooney’s new portraits utilize his pioneering triaxial weave to create effective shading. Fiberarts, March–April, 5:2, 17. Moroyama M., Oguchi M. and Cotsen L. (2007), Japanese Bamboo Baskets: Meiji, Modern and Contemporary. Kodansha International, at http://www.kodanshaintl.com/. Nightingale W. D. (1886), Improvements in the method of stringing lawn tennis racquet, and other bats. British Patent No. 5177. Nishida I. (2010), The Higashimyo Wetland Site. At http://newswarp.info/wp-content/ uploads/2010/03/Higashimyo-News-3-5-102.pdf [accessed 24 April 2011]. Roberts G. D., Pereira J. M., Braley M. S. and Arnold W. A. (2009a), Braided composite fan case materials and components. ISABE–2009–1201.
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Roberts G. D., Goldberg R. K., Binienda W. K., Arnold W. A., Littell J. D., Kohlman L. W. (2009b), Characterization of triaxial braided composite material properties for impact simulation. NASA/TM–2009–215660. Seki T. S. Y. (1994), Baseball bat and production thereof, USP 5301940. Sharpless G. C. (2005), Triaxial braiding: processes for large composite structures. Composites Manufacturing, October. Shore S. (2008), A Ribbon Weaver’s Handbook. Locust Valley, New York. Snelson K. (2009), The Five Basic Weave Cells. http://kennethsnelson.net/new/2009/thefive-basic-weave-cells/ [accessed 24 April 2011]. Stewart F. H. (1921), Woven fabric, USP 1368215. Stover D. (1989), Braiding and RTM succeed in aircraft primary structures. Advanced Composites May–June. Tice J. H. (1934), Ventilated hat, USP 1955986. Townsend F. L. L. and Trumpio F. P. (1976), Heddle transfer apparatus and method for triaxial weaving machine, USP 03985159. Tyler T. (2010), Triaxial weaving. At http://hexdome.com/weaving/triaxial/ [accessed 31 May 2010]. Wood G. (2009), Quasi-isotropic braid reduces cost in large composite tooling. JEC Composites, 53, November–December. 7.20
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8 Interwoven fabrics and their applications X. CHEN, University of Manchester, UK
Abstract: Weaving is one of the major textile technologies for making fabrics from yarns. This chapter describes the construction of 2D and 3D interwoven fabrics and their applications. Single layer fabrics also known as the 2D fabrics are mainly used for clothing and other domestic applications. Weave structures of the 2D fabrics are classified and classified in details, emphasising the elementary and derivative weaves. 3D woven structures, which lead to woven fabrics with noticeable thickness, attract much attention because of their diversity and the potential uses in many different industrial areas. 3D solid woven structures are explained in detail and some information is also provided for 3D cellular fabrics. Key words: woven fabric, weaves, interlacement, warp and weft, 2D and 3D fabrics.
8.1
Introduction
Woven fabrics are made by interlacing warp and weft yarns at right angles according to a pre-designed weave structure. Most woven fabrics are single-layer, constructed from one set of each of warp and weft yarns. These are mainly used for clothing and other domestic applications such as bedding and furnishing. Woven fabrics can also be made from multiple sets of warp and weft yarns, leading to more complicated structures. As examples, terry towel fabrics are made from two sets of warp yarns and one set of weft yarn; weft-backed woollen blankets are made from one set of warp yarn and two sets of featured woollen yarns; and a triple-layered fabric is created from three sets of warp and weft yarns. In general, the conventional weaving principle permits fabrics to be made in many different ways from interlacing warp and weft yarns. On the other hand, woven materials made from various types of fibres have found applications beyond traditional domestic applications in technical and industrial domains. Typical examples include textile preforms for advanced composites and body armour against high-velocity ballistic impact.
8.1.1 Definition and classification of woven fabrics Woven structures were the first to be used for making fabrics from fibrous materials (Adanur, 2001). The woven structure is fundamentally different from the knitted structure in that woven fabrics are formed by interlacing or interweaving warp and weft yarns whereas the knitted fabrics are made by forming loops in the width or 164 © Woodhead Publishing Limited, 2011
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length direction of the fabric (Hatch, 1993). Another type of fabric that can be made with substantial dimension is non-woven fabric, which is made directly from mainly staple but occasionally continuous fibres (Kittelmann et al., 2003). The classification of woven fabrics can be based on different criteria. According to the complexity of the weave structures used, woven fabrics can be classified into fabrics using elementary weaves, derivative weaves, combination weaves, and compound weaves. With reference to the number of yarn sets used to construct the fabrics, there are single-layered fabrics, backed fabrics, and multi-layered fabrics. When considering the surface features of woven fabrics, the woven fabrics can be subdivided into flat surface fabrics, uneven surface fabrics, and pile fabrics. In terms of 3D woven fabrics, they can be classified into solid fabrics, hollow fabrics, shell fabrics, and nodal fabrics (Chen et al., 2011).
8.1.2 Structural features of different woven fabrics Single-layered fabrics In most cases, the appearance requirement for single-layered fabrics is that they give a geometrically stable fabric with flat fabric surfaces. Such fabrics are featured by having different weave patterns shown on the surfaces of the fabric. Figure 8.1 shows computer-simulated appearances of single-layered fabrics with different weaves. Figure 8.1(a) is the appearance of the plain woven fabric. The plain woven fabric has the most intersection points, and therefore it is the tightest fabric using the elementary weaves (plain, twill and satin/sateen weaves), other conditions being the same. Figure 8.1(b) depicts a twill weave fabric. Twill fabrics are featured by diagonal twill lines in either the Z or S directions. They are a group of woven structures that lead to softer and fuller fabrics but yet have good dimensional stability. They are widely used in making suits and dresses in lightweight to medium weight fabrics. Figure 8.1(c) is an illustration of fabric with a diamond weave. It belongs to the twill fabric family, as the weave is one of the derivatives from original twill weaves. Figure 8.1(d) is a simulated fabric constructed using an entwined twill weave. It gives an interesting weave pattern, while the performance is close to the twill fabrics. Figure 8.1(e) is called a hopsack fabric and the hopsack weave is a derivative from the plain weave. Because this type of weave involves only two types of warp end (like the plain weave), the fabric can be made on very simple looms. The hopsack fabrics are one of the popular choices for ladies’ outer garments. 3D solid fabrics This is a group of woven fabrics that is mainly intended for technical applications. Using weaving technology, 3D solid fabrics can be manufactured with different designs providing different fabric features. Figure 8.2 shows three types of 3D
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8.1 Simulated images of single-layered fabrics with different weaves: (a) plain weave; (b) two-twill weave; (c) diamond weave; (d) entwined weave; and (e) hopsack weave.
solid fabrics, which are (a) a multi-layered fabric, (b) an orthogonal fabric, and (c) an angle-interlock fabric. Multi-layered fabrics involve distinctive layers of fabrics, which may or may not be stitched together during the process of weaving. Integrity of the fabric is achieved by introducing stitching yarns between the layers. All the warp and weft yarns are crimped and therefore the initial modulus could be low under tensile loading. It is possible to add wadding yarns in either warp or weft directions between any two layers as an attempt to increase the initial fabric modulus. The depth of the stitches through the fabric layers is controllable. Figure 8.2(a) is the simulated image of a multi-layered fabric with every two adjacent layers stitched together. Figure 8.2(b) is the image of an enhanced orthogonal woven fabric.
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8.2 Some examples of 3D solid fabrics: (a) multi-layered fabric; (b) enhanced orthogonal fabric; (c) angle-interlock fabric with added straight warp yarns.
A distinctive feature of this type of fabric is that there are straight yarn sections in all three principal dictions. This would be of interest to some particular application fields. Angle-interlock is a woven structure that incorporates straight weft yarns and diagonally binding warp yarns. As a derivative, straight warp yarns can be added between the weft yarn layers. The binding warp yarn can bind at different depth (Chen and Potiyaraj, 1999; Chen et al, 1999). Figure 8.2(c) illustrates an angle-interlock fabric with added straight warp yarns.
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8.1.3 Application areas of woven fabrics Woven fabrics are usually used as materials for making clothing and it is still true that woven fabrics are the principal clothing materials used because of their performance in dimensional stability, good drape, and appropriate rigidity/flexibility. Different weave structures are used to form fabrics for different end uses. For example, plain woven fabrics are used for shirt and other light garments. Twill fabrics are popular for suits and dresses. Heavy coats can be made from backed cloths that use more sets of warp or weft yarns to achieve the required warmth and thickness. Many domestic textiles are made from woven fabrics, such as bedding, curtains, bathing towels, upholstery, and kitchen towels (Joseph, 1977). When technical yarns are employed, woven fabrics, most notably the plain woven, are used for many different technical applications. Due to their structural tightness, plain woven fabrics are used to make airbags for cars (Adanur, 1995). Plain woven fabrics are popularly used in modern ballistic body armour for effective strain wave propagation and therefore impact energy absorption (Chen and Sun, 2009). In the textile composite industry, the plain weave is a popularly used structure for textile reinforcements. 3D woven fabrics have nowadays found their applications in different areas. Many 3D preforms for advanced textile composites are made from tapered 3D woven solid fabrics.
8.2
Structure and design
Woven fabrics are formed by interlacing warp and weft yarns at the right angles according to the weave specified. Weave is a plan indicating the interlacement of the warp and weft yarns, and it is usually expressed on the weave design paper, which is checked paper. Figure 8.3 is part of the weave design paper used for recording weaves. A vertical interval between two lines represents a warp end,
8.3 A specimen of weave design paper.
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and a horizontal interval stands for a pick or weft yarn. A crossover of the warp and weft is represented by the grid formed by these two intervals. At a crossover where the warp end and pick meet, there are only two possible situations, i.e. warp over weft or weft over warp. These are denoted by marking the grid and leaving it blank, respectively. Figure 8.4 shows the two types of crossover, and the corresponding notation on the weave design paper.
8.4 Crossover types and notation on weave design paper: (a) warp over weft; (b) weft over warp.
8.2.1 Single-layered fabrics The most popular classification of single-layered fabric weaves defines them as elementary weaves, derivative weaves, combination weaves and compound weaves (Grosicki, 1975; Georner, 1986). Elementary weaves These represent the most basic weave types. Elementary weaves are used widely for making fabrics and are also taken as the original weaves for deriving new ones. Elementary weaves feature two floats along each warp and weft yarn in a weave unit, with one of the floats being a single float. Elementary weaves include the plain weave, original twill weaves, and original satin/sateen weaves. The plain weave Figure 8.5 illustrates the plain weave structure and the weave. A repeat of the plain weave structure is formed from two warp ends following the opposite interlacing route, and two picks following the opposite route, as is shown in Figure 8.5(a). Accordingly, a repeat of the plain weave diagram involves two vertical gaps and two horizontal gaps. The plain weave diagram is exhibited in Figure 8.5(b). The plain weave can also be expressed using the numerical expression 1 , indicating the movement of the first warp end from lower to 1 higher. The notation reads one-up-one-down.
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8.5 The plain weave construction: (a) plain weave structure; (b) plain weave diagram.
Original twill weaves Twill weaves require at least three warp ends and three picks in a repeat. The 1 2 1 5 elementary twills include and so on. An elementary twill weave , , , 2 1 3 1 is defined by specifying the numerical weave expression and the step number which determines the twill line direction. The step number is the specification of the relative movement of the next warp end in relation to the current one. For example, if the step number is 1, the next warp end will start on the weave design paper one position higher than the current; and if step number is −1, then the next warp end will start one position lower than the current one. When the step number is a positive number, the twill line will be in the Z direction. If the step number is a negative number, then the twill line will be in the S direction. In the case where the step number is 0, the next warp end movement will be the same as the current. 2 Figure 8.6 displays (a) the construction and (b) weave diagram of the twill 1 weave with step number being 1. It is evident that a Z twill line is formed by, most notably, the warp up-floats. When a twill weave is specified, the warp repeat (the number of warp ends in the weave unit) and the weft repeat (number of picks in the weave unit) of the weave can be worked out. Let re be the warp repeat, rp the weft repeat, S and the step number (|S| is the absolute value of S). Then: rp = Σ (all numbers in the weave expression)
8.6
2 1
twill construction: (a) twill weave structure; (b) twill weave
diagram.
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For example, for the 3
twill with S = −1, we have rp = 4 and re = 4. The weave 1 diagram for this twill is shown in Figure 8.7. It can be seen that when the step number is a negative number, it produces a twill weave with a twill line in the S direction. It needs be added that for twills the larger the absolute value of the step number, the steeper the twill line becomes.
8.7 The weave for
3 1
twill with S = −1.
Satin/sateen weaves refer to a group of weaves that has a long float of yarns on the face of the fabric. If warp ends form the long floats on the face side of the fabric then the weave is a satin; if weft yarns form the long floats then the weave is a sateen. Figure 8.8 shows examples of satin/sateen weaves.
8.8 Examples of sateen (a) and satin (b) weave.
Original satin/sateen weaves A satin/sateen weave requires at least five warp ends and five picks in a weave unit for most situations, and is usually specified in the following format:
In the above expression, M is the move number, indicating the starting point of the next warp or weft yarn in relation to the current one. It is similar to the step number for twill weaves and it can be applied in the warp direction (warp-wise) or the weft direction (weft-wise). n is the repeat size of the weave (the number of warp and weft yarns in a weave repeat). In order to achieve a valid satin/sateen weave, n and M are confined to the following conditions:
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1. 1 < M < (n − 1); 2. n and M must not have common divisors. A valid specification of a weave of this type is: 7-end satin with M = 4 warpwise. The diagram for this weave is exhibited in Figure 8.9.
8.9 Weave diagram for 7-end satin with M = 4 warp-wise.
Derivative weaves New weaves created from the elementary weaves are known as the derivative weaves. Hence, we have plain derivatives, twill derivatives, and satin/sateen derivatives. Plain derivative weaves Plain derivative weaves can be created by extending the plain weave or by following the plain weave logic. Extending the plain weave in one direction leads to the creation of rib weaves. If the plain weave is extended in both warp and weft directions simultaneously, the hopsack weaves are created. In Figure 8.10, (a) is the plain weave from which the plain derivatives are to be created; (b) is a warp rib weave achieved by extending the first pick into two picks and the second into three; (c) is a weft rib weave obtained by extending the first warp end into two warp ends and the second into three; and (d) is an hopsack weave by extending the plain weave in both the
8.10 Plain derivatives created by extending the plain weave.
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warp and weft directions simultaneously, the first warp and weft yarns in the plain weave extending into two and the second warp and weft in the plain weave extending into three. In fact, more than one repeat of the plain weave can be used for derivation. Figure 8.10(e) is a hopsack weave that is derived from four repeats of the plain weave. Plain weave derivatives by extension leads to a fanciful fabric appearance, yet can be woven easily because there are only two different types of warp ends in terms of interlacement. Plain derivative weaves can also be created by following the plain weave logic. It is clear that the plain weave has four quarters (in this case grids), and any quarter has the opposite weave marks to its adjacent quarters. Following this, a weave may be created to have four quarters, each having numerous grids as a group. Each quarter can have a weave pattern that is opposite to the adjacent quarters. If a weave is created like this, then the weave is referred to as a basket weave. Figure 8.11 illustrates the composition of a basket weave, where (a) is the pattern for the lower left quarter, and (b) is the basket weave created from (a) following the plain weave logic.
8.11 Composition of a basket weave: (a) the first quarter; (b) the full weave.
Twill derivative weaves Twill derivative weaves can be generated to use many different techniques, such as reinforcing, compounding, shading, step number changing, mirroring technique, and inverse mirroring. The reinforcing method is used to increase the thickness of the twill line formed by the single float in a twill weave. Two examples of reinforced twills are shown in Figure 8.12, where (a) is derived from and (b) is derived from
Z twill, leading to a
Z twill, forming a Z twill.
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8.12 Reinforced twills: (a) reinforced
Z twill; (b) reinforced
Z twill.
In this context, compounding refers to increasing the number of twill lines in a twill weave repeat. There is only one twill line in an elementary twill weave, whereas in a compound twill there could be many, enhancing the twill effect. Figure 8.13 displays three compound twill weaves as example, where (a) is the Z twill, (b) is the
Z twill, and (c) is the
S twill.
8.13 Examples of compounded twills.
Usually, the step numbers used for twill weaves are either 1 or −1. In creating derivative twills, the step number may be specified to be ±2, ±3 etc. to make the twill lines steeper. Figure 8.14(a) shows the twill weave
Z twill with step
number 2. It is obvious that the Z twill line is steeper than in the case where the step number assumes the default value of 1. Figure 8.14(b) is a
twill
developed horizontally, with the step number being 2. This makes the twill lines flatter. Figure 8.14(c) is the
Z twill, the same as Figure 8.13(b), but with
the step number 2. Comparison shows that the change in step number not only changes the angle of the twill lines, but also the appearance and the style of the weave become quite different too. Changing twill line directions results in new twill derivatives. The two methods used for changing the twill line directions are the mirroring method and the inverse mirroring method. The former leads to waved weaves (horizontal and
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8.14 Derivative twills achieved by a step number change.
vertical) and diamond weaves, and the latter results in herringbone weaves (horizontal and vertical) and diaper weaves. When the mirroring method is used, the same time the twill line direction is changed, the float type of twill lines is kept the same. To specify a waved weave or a diamond weave, it is necessary to designate the base twill, and the peak position(s). Based on these, the warp repeat, Re, and weft repeat, Rp, of the weave can be calculated as follows. For a horizontal waved weave: Re = 2( pe − 1)
[8.3]
Rp = rp
[8.4]
For a vertical waved weave: Re = re
[8.5]
Rp = 2( pp − 1)
[8.6]
For a diamond weave: Re = 2( pe − 1)
[8.7]
Rp − 2( pp − 1)
[8.8]
In Equations (8.3) to (8.8), re and rp are the warp and weft repeats of the base twill respectively, and pe and pp are the peak positions in the warp and weft directions respectively. The peak position is measured by the number of yarns in the due direction, and it can be smaller than, equal to, or larger than the weave repeat in the due direction. Figure 8.15 shows (a) a horizontal waved weave, (b) a vertical waved weave, and (c) a diamond weave from the base twill
S, with pe = pp = 9.
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8.15 Use of mirroring method based
S twill for (a) horizontal
waved weave, (b) vertical waved weave and (c) diamond weave.
When the inverse mirroring method is to be used, the twill lines will change direction and also the float type of the twill lines will be changed too. Based on the specification of the base twill and the peak position(s), the warp repeat, Re, and weft repeat, Rp, of the new weave can be calculated as follows: for a horizontal herringbone weave: Re = 2pe
[8.9]
Rp = rp
[8.10]
For a vertical herringbone weave: Re = re
[8.11]
Re = 2pe
[8.12]
For a diaper weave: Re = 2pe
[8.13]
Re = 2pe
[8.14]
In Equations (8.9) to (8.14), re and rp are the warp and weft repeats of the base twill respectively, and pe and pp are the peak positions in the warp and weft directions respectively. The peak position, as in the case of weaves created by using the mirroring method, can be smaller than, equal to, or larger than the weave repeat in the due direction. Figure 8.16 shows (a) the horizontal herringbone weave, (b) the vertical herringbone weave and (c) the diaper derived from the Z twill, with with pe = pp = 8.
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8.16 Use of mirroring method based on
177
Z twill for (a) horizontal
herringbone weave, (b) vertical herringbone weave, and (c) a diaper weave.
Entwined twills are another group of twill derivative weaves, where the Z and S twill lines are intermingled together to give an interesting pattern. Figure 8.17 shows an entwined twill created from the lines in each direction.
8.17 The entwined twill from the lines in each direction.
even-sided twill with three twill
even-sided twill with three twill
When even-sided twill is specified, it is known that the warp and weft repeats of the base twill is re = rp = r. In the case that there are n twill lines in each direction, the warp and weft repeats of the entwined twill will be Re = Rp = R = n × r. Each of the twill lines will cover R warp ends. In the case of the entwined 2 twill in Figure 8.17, R = 18, and each twill line covers nine warp ends. © Woodhead Publishing Limited, 2011
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In general, the Z twill lines and the S twill lines can be developed according the procedure below, assume that the float length of twill line is l. For the Z twill lines: 1. Draw the first Z twill line from the lower left-hand corner of the repeat area, covering R warp ends. 2 2. Locate the starting position of the next Z twill line by moving, from the starting position of the previous Z twill line, by l grids to the right and then l grids downwards. 3. Draw this Z twill line, covering R warp ends. 2 4. Repeat steps (2) and (3) until all the Z twill lines are drawn. For the S twill lines: 1. Draw the first S twill line on the rightmost warp end of the repeat area, from R the (l + 1)th pick, developing it to the left, covering warp ends. 2 2. Locate the starting position of the next S twill line by moving, from the starting position of the previous S twill line, by l grids to the right and then l grids upwards. R 3. Draw this S twill line, covering warp ends. 2 Repeat steps (2) and (3) until all the S twill lines are drawn.
8.2.2 Backed cloth Backed cloth is a type of woven fabric that is composed of unequal numbers of sets of warp and weft yarns, resulting in thicker fabrics whose weave patterns on the face and back are independent of each other. This type of weave structure is used to increase the warmth of the fabric and provide featured yarns, usually weft, for patterns. The basic requirement for the backed cloth fabric design is that the interlacing points of the yarn responsible for the back is not seen from the face, and the interlacing points of the yarn responsible for the face is not seen from the back. Backed cloth can be subdivided into warp-backed and weft-backed. In the simplest form, the former is woven using two sets of warp ends with one set of weft yarn, whereas the latter is a fabric created from weaving one set of warp ends with two sets of weft yarns. Warp-backed cloth This type of fabric is made from weaving two sets of warp ends and one set of weft yarn. The top set of warp ends weaves with weft yarn according to the face weave, and the back set of warp ends interlaces with the weft according to the back weave. In order to hide the face and back weaves from each other, the face weave and back weave should be compatible with each other. Basically, the face © Woodhead Publishing Limited, 2011
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weave should be warp-faced, and the back weave should be weft-faced. It is usually necessary to specify the warp–yarn ratio between the top and back sets of warp ends. Theoretically, the warp yarn ratio can be anything, such as 2:1 and 2:3, but in many cases, the warp yarn ratio is usually 1:1 when a similar type of yarn is used for both sets of warp ends. Figure 8.18(a) displays the weave diagram of a warpbacked cloth weave, with the face weave being
S twill and back weave being
S twill. The yarn ratio between the top and back warp ends is 1:1. The black marks represent the face weave and the lighter marks represent the back weave.
8.18 Backed cloth weaves: (a) warp-backed; (b) weft-backed.
Weft-backed cloth A weft-backed cloth is made from one set of warp ends weaving with two sets of weft yarns. Again, the face weave and the back weave must not interfere with each other. Figure 8.18(b) is a weft-backed weave, with a five-end sateen being the face weave and a five-end satin being the back weave. The weft–yarn ration is 1:1. Again, the black marks represent the face weave, and the lighter marks represent the back weave.
8.2.3 3D solid woven fabrics 3D solid fabrics refer to those fabrics with a substantial thickness measured by layers of yarns or fabrics. Such fabrics may assume a cuboid shape leading to a board material; they may also be made tapered for components that have variable cross-sectional shapes. Several constructions can be used for making 3D solid fabrics, including most typically the multi-layered construction, orthogonal construction and angle-interlock construction. Multi-layered fabrics An important feature of a multi-layered fabric is that it has distinctive layers in the fabric. These layers may be separate or stitched, and the may also interchange
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positions if needed. For an n-layered fabric, it involves the used of n sets of warp ends and n sets of picks. The minimum number of layers in a multi-layered fabric is two. Let us use a three-layered fabric as example to explain the creation of a multi-layered fabric. Specification To specify a multi-layered fabric, the number of layers is the first information that need be provided. For a three-layered fabric, three weaves should be provided, one for each layer. In this example, assume that the first layer weave is twill, the second being
Z twill, and the third
Z
Z twill. Assume also the
warp and weft yarn ratios are 1:1:1. Weave repeat size Once a multi-layer has been specified, the repeat size need be calculated from the specification of all the weaves and the yarn ratios. In the case of this three-layered example, the warp and weft repeats should both be 24. Superimposition of weaves At this stage, the weaves used for each layer will be superimposed according to the yarn ratios in the war and weft directions. Figure 8.19(a) illustrates the weave diagram when the three weaves have been put together, where the first layer weaves marks are represented by , the second layer by , and the third layer .
8.19 Development of a three-layered fabric: (a) superimposition of three weaves; (b) weave representing three separate layers.
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It needs be made clear that the weave diagram is achieved only by mixing the three weaves together according to the yarn ratios, and it represents the weave with three separate layers. Instead, the weave diagram now will only lead to a single-layered fabric. Extra work is needed to separate the layers from each other. Layer separation Let us consider a multi-layered fabric that has n layers. When a pick for the ith layer (1 < i < n) is to be inserted into the shed for fabric formation, the shedding mechanism will have to lift all warp ends for the above (i – 1) layers, whereas the warp ends for layers (i + 1) to n will be at the lower level of the shed. To reflect that in the weave design paper, when inserting a pick for the ith layer, warp ends for all the layers above must be made above this pick by adding a mark in the relevant grid in the weave design paper. Such marks are called lifters represented by forward slash in this context. Based on the principle, lifters are added to the weave diagram in Figure 8.19(b), which represent the weave for the three-layered fabric. Introduction of stitches When a multi-layered fabric is used as a 3D solid structure, the layers need be stitched together by weaving. There are two types of stitching methods, i.e. central stitching and self-stitching. The central stitching method will require extra sets of warp and/or weft yarns to carry out stitching, whereas the self-stitching method will stitch up the layers using the existing yarns. Conventionally, the stitching points should be concealed from the top and bottom surfaces of the multi-layered fabric. If self-stitching is used, then the introduction of stitches should not affect the weave of the layer where the stitching is from. Figure 8.20 shows the three-layered fabric with stitches among the three layers, using the self-stitching method. The mark indicates a warp end stitching up (or equivalently a pick stitching down), and suggests a warp end stitching down (or equivalently a pick stitching up). Stuffed multi-layered fabrics It sometimes becomes necessary to add stuffing yarns in either warp or weft direction for reasons such as creating a more solid structure or achieving improved mechanical properties. Stuff yarns can be added to either warp or weft or both directions between any two fabric layers, and they are not normally interwoven with the fabric layers. Orthogonal fabrics An important feature of an orthogonal woven fabric is that there are straight fibres/yarns in all three principal directions of the fabric. The number of layers of
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8.20 Three-layered fabric with self stitching.
straight weft yarn is always one more than that of the straight warp yarn. The binding warp yarn travels vertically through the thickness of the fabric and it may bind using any weave. In an orthogonal structure the straight warp and weft yarn are arranged neatly in stacks, and the numbers of stacks of straight warp and weft yarns depends on the binding weave specified. Each binding warp end is placed between two adjacent stacks of straight warp yarns. The binding weave determines the density of straight-through-the-thickness yarns in the fabric, with plain weaving providing the highest density of vertical yarns. The orthogonal fabrics can be further classified into two types, i.e. the ordinary and the enhanced. An ordinary orthogonal structure is one in which there is only one binding yarn between two adjacent stacks of straight warp yarns, whereas an enhanced structure is one that has two binding warp ends between two adjacent stacks of straight want yarns, these two binding yarns following opposite movements. Figure 8.21(a) is a simulated ordinary orthogonal fabric, with three layers of straight
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8.21 Orthogonal fabrics and weaves: (a) visualization of an ordinary orthogonal fabric; (b) weave of the ordinary orthogonal fabric; (c) visualization of an enhanced orthogonal fabric; (d) weave of the enhanced orthogonal fabric.
warp ends using
Z twill as the binding weave. Figure 8.21(b) is the weave
diagram for it. Figure 8.21(c) shows the visualization of the enhanced orthogonal fabric, and (d) is the corresponding weave diagram. Angle-interlock fabrics Basically, an angle-interlock fabric contains layers of straight weft yarns weaving with a set of warp yarns that travels diagonally in the thickness direction. For an angle-interlock fabric that has n layers of straight weft yarns, there will be (n + 1) picks per layer in the repeat, hence n(n + 1) picks in total in the fabric. The number of warp ends will be (n + 1). Figure 8.22(a) shows the cross-sectional view of the angle interlock fabric with five layers of straight weft yarns. Therefore, there are 30 picks and six warp ends in one repeat of the fabric. As a variation, layers of
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8.22 Cross-sectional view of angle-interlock woven fabrics along the warp direction: (a) without stuffing yarns; (b) with stuffing yarns.
straight warp yarns can be stuffed into the angle-interlock fabric. Figure 8.22(b) shows the same angle-interlock fabric with stuffing warp yarns.
8.2.4 3D cellular woven fabrics In this context, 3D cellular fabrics refer to those that have designed tunnels running between the top and bottom surfaces in warp, weft, or any diagonal direction. The relationship of these tunnels can be one above the other, or can be intersecting with each other (Chen, Zhang, patent). For woven cellular fabrics, two types of cellular fabrics can be defined. The first one has flat top and bottom surfaces, and the other has uneven surfaces. These two types of cellular woven fabrics are illustrated in Figure 8.23.
8.23 The two types of 3D cellular woven fabrics: (a) cellular fabric with flat surfaces; (b) cellular fabric with uneven surfaces.
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It is evident that 3D cellular woven fabrics are created based on multi-layered fabrics. The layers are joined and separated in a pre-designed fashion in order to obtain the required cell shapes and sizes. In cellular fabrics with flat surfaces, the length of the fabric layer will have to be made different, with the middle layer longer than the layers for the surfaces. Using this method, the cell shapes could be rectangular, triangular, and trapezoidal. On the other hand, for the cellular fabric with uneven surfaces, all the constituent fabric layers are of the same length and they are joined and separated at regular intervals to create the cells. The cell shapes created using this method can be hexagonal and rectangular. Software Hollow CAD®, developed at the University of Manchester, is a specialized development tool for 3D cellular woven fabrics (TexEng Software Ltd).
8.3
Properties and applications
Woven fabrics are formed by interlacing warp and weft yarns at right angles. Owing to the interlacement, yarns in woven fabrics are general crimped to some extent. In comparison with knitted fabrics, woven fabrics give much higher tensile modulus and in-plane shear rigidity. Such properties lead to better fabric stability and therefore make woven fabrics suitable for more formal clothing and other domestic applications. Everyday clothing and fashion materials are basically single-layered fabrics made using different fibres, yarn types and weave structures. While the single-layered fabrics are widely used in everyday life, fabrics with other geometric features can offer special functions for some specific application. Upholstery fabrics such as those used for sofas are required to be strong and abrasion resistant. Apart from selecting strong yarns, such fabrics are usually made using a backed cloth structure in order to achieve the required thickness and patterns in the fabrics. The growth in the use of technical textiles has greatly extended the application of different types of woven fabrics. Technical textiles, according to the Textile Institute (Denton and Daniels, 2002), are textile materials and products manufactured primarily for their technical performance and functional properties rather than their aesthetic or decorative characteristics. Technical textiles cover a very wide range of applications, including civil engineering, medical, personal and property protection, sports, automobile, and aerospace. One very important application has been reinforcements and preforms for advanced textile composites. Textile composites started with laminating single-layered fabrics made from high-performance fibres. Nowadays, advanced textile composites demand that textile reinforcements and preforms provide required mechanical, thermal and other properties for the end applications and demand net-shaped preforms for composite components. The construction of various types of 3D fabric plays an important role in satisfying property requirements, because 3D fabric formation technology makes it possible to reinforce fabrics with various geometrical features that can be engineered and manufactured.
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Weaving technology is a unique technology that coverts linear materials into plane or volumetric structures and materials. Together with other forms of textiles technologies such as those for knitting, braiding and non-wovens, weaving technology and hence the woven fabrics will find more application areas.
8.4
Future trends
As one of the primary needs of mankind, the need for clothing will certainly be with us for the foreseeable future and hence textile fabrics will always be required. As ever, there will be new fibres created and these will be used in engineering fabrics with added functions for domestic and technical applications. In the fashion industry, woven fabrics will continue to be one of the most important materials for texture, dimension stability, drape, and aesthetics. The emergence of new fibres will make the fabrics more suitable to meet the demands of comfort and environmental adaptability, as well as aesthetics. Further understanding of the structure and property of woven fabrics through continued modelling and experimental study will enable woven fabrics to be manufactured to provide behaviour that satisfies the end uses more accurately. However, there has been no sign that the woven structures will evolve greatly from where they are, nor will weaving technology itself. More complex woven fabric regimes such as the backed cloth and 3D fabrics will be further explored corresponding to arising demands, but it is likely that the more complex fabrics will be developed for technical applications rather than for the fashion industry. Probably it will witness more development and innovation in the areas of technical textiles, whose end uses may be in the water, on land, or in the air, and may be for agricultural, medical, or industrial uses. Since the areas of application are so many, it is believed novel developments will take place to accommodate demands from these areas. More 3D solutions will be made available and technical fabrics will be engineered to provide more accurate performance for the intended applications.
8.5
Sources of further information and advice
Adanur, S., Handbook of Weaving, Technomic Publishing Company, Lancaster, 2001. Chen, X., Modelling and Predicting Textile Behaviour, Textile Institute/Woodhead Publishing, Sawston, Cambridge, 2009 Georner, D., Woven Structure and Design, Part 1, Single Cloth Construction, Wira, Leeds, 1986. Georner, D., Woven Structure and Design, Part 2, Compound Structures, British Textile Technology Group, Leeds, 1989. Grosicki, Z., Watson’s Textile Design and Colour: Elementary Weaves and Figured Fabrics, Newnes-Butterworths, London, 1975. Grosicki, Z., Watson’s Advanced Textile Design and Colour: Compound Woven Structures, Newnes-Butterworths, London, 1977.
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Hearle, J. W. S., High-Performance Fibres, Textile Institute/Woodhead Publishing, Sawston, Cambridge, 2001. Horrocks. A. R., Anand, S., Handbook of Technical Textiles, Textile Institute/Woodhead Publishing, Sawston, Cambridge, 2000. Marks, R., Robinson, A.T.C., Principles of Weaving, Textile Institute, Manchester, 1976. Robinson, A.T.C., Marks, R., Woven Cloth Construction, Textile Institute/Butterworths, London and Manchester, 1967.
8.6
References
Adanur, S., Wellington Sears Handbook of Technical Textiles, Technomic Publishing Company, Lancaster, 1995. Adanur S., Handbook of Weaving, Technomic Publishing Company, Lancaster, 2001. Chen X. and Potiyaraj, P., CAD/CAM of complex woven fabrics, Part 2: Multi-layer fabrics, J Text Inst, 1999, 90, Part 1 (1), pp. 73–90. Chen, X. and Sun, D., Textile materials and personal protection equipment for police and military personnel, Journal of Xi’an Polytechnic University, 23 (2), 2009, pp. 67–74. Chen, X., Spola, M., Gisbert Paya, J. and Molist Sellabona, P., Experimental studies on structure and mechanical properties of multi-layer and angle-interlock woven structures, J Text Inst, 1999, 90, Part 1 (1), pp. 91–99. Chen, X., Taylor, L.W. and Tsai, L-J., An overview on fabrication of 3D woven textile preforms for composites, Textile Research Journal, 2011, doi: 10.1177/ 0040517510392471. Chen, X. and Zhang, H., Woven textile structure, UK Patent GB2404669, 2006. Denton, M.J. and Daniels, P.N. (editors), Textile terms and definitions (11th edition), Textile Institute, Manchester, 2002. Georner, D., Woven Structure and Design, Part 1, Single Cloth Construction, Wira, Leeds, 1986. Georner, D., Woven Structure and Design, Part 2, Compound Structures, British Textile Technology Group, Leeds, 1989. Grosicki, Z., Watson’s Textile Design and Colour: Elementary Weaves and Figured Fabrics, Newnes-Butterworths, London, 1975. Grosicki, Z., Watson’s Advanced Textile Design and Colour: Compound Woven Structures, Newnes-Butterworths, London, 1977. Hatch, K. L., Textile Science, West Publishing Company, Minneapolis, USA, 1993. Joseph, M. L., Introductory Textile Science, Holt, Rinehart & Winston, London, 1977. Kittelmann W., Albrecht, W. and Fuchs, H., Nonwoven Fabrics, Wiley-VCH, Weinheim, 2003.
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9 Pile carpets G. H. CRAWSHAW, formerly of the IWS Interior Textiles Group, UK
Abstract: Textile pile structures in the areas of apparel, home textiles and carpets comprise too large a group to be considered effectively in a single chapter. Pile carpets have been selected as a particularly interesting case where the composition and range of structures affect the design scope, facets of the performance in use, and positive effects on the environment. Typically, they have three layers, presenting a special challenge for recycling. Tufting remains by far the most important method of carpet manufacture, although recent technical developments have mostly been in the area of weaving. The position of nylon as the leading pile fibre is being challenged by polypropylene, which is based on a cheaper monomer and provides better cover in the carpet because of its low specific gravity. Polyester fibres are becoming more important for two reasons: PET fibre is being manufactured from recycled drinks bottles; and PTT fibre has been shown to provide superior carpet properties compared with PET. Wool remains important in the higher qualities of carpets. Polymer pigmentation has become the most important coloration technique and, associated with the improved flexibility of the technique, BCF yarn production is increasingly being carried out by carpet manufacturing companies. The weak market position of soft floor coverings has prompted extensive R&D efforts to make carpet manufacture more environmentally friendly and to provide information about the positive effects of carpets on the interior environment. Key words: carpet, tufting, Axminster, Wilton, face-to-face weaving, needling, adhesive bonding, nylon, polyester (PET), polyester (PTT), polypropylene, melt bonding fibres, conductive fibres, hygienic fibres, wool, cellulosic fibres, backing materials, polymer pigmentation, textile sports surfaces, environment, environmentally-friendly, VOCs, cleaning, recycling.
9.1
Market background
The carpet industry is a mature one, faced with a level market for floor coverings of all kinds. This situation contrasts with that pertaining in the 1950s, 1960s, 1970s and early 1980s, when there was overall dynamic expansion and a mood for accepting new technology. There was pent-up demand following the restrictions of the Second World War, a move from carpet squares to wall-to-wall installations in residential accommodation, use of carpets in areas of the home other than living rooms (bedrooms, bathrooms, kitchens, decks) and increasing use of carpets in ‘contract’ locations such as offices and transportation. Central to the expansion was the adaptation of tufting technology widely used in Georgia, USA for manufacturing pile bedspreads to the manufacture of carpets. American 188 © Woodhead Publishing Limited, 2011
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consumers were suddenly offered spectacularly cheaper carpets resulting not only from high-output tufting, but cheaper pile fibres (wool was scarce) and cheaper labour as the carpet industry moved south. The early tufted carpets were crude products, limited in patterning scope, and had technical drawbacks. New primary backing fabrics had to be developed, as the cotton fabrics used for bedspreads were inappropriate; lamination of secondary fabrics was required to provide dimensional stability; the synthetic fibre industry solved many problems by developing special yarns for tufting; and the coloration industry provided machinery and techniques for piece dying and printing. Inventive people were attracted to this lively industry. Carpet weaving suffered competition from tufting. China is not yet a major exporter of carpets and the $38 billion global market for carpets is dominated by the industries of the USA and Europe (Hayes, 2007). There are important differences between these two areas in terms of the structure of the industries, fibre usage and carpet styles. Generally, domestic consumers in Anglo-Saxon countries prefer wall-to-wall carpets, whereas carpet squares are more popular in most other countries. Handcrafted squares are highly regarded and there have been geographic and even technical developments relating to them. Over the past 10 years or so the carpet markets in the USA and Europe have contracted (Hart, 2007). Carpets in Europe have lost ground to laminates and now account for less than half of the total market for floor coverings (Vankann, 2005). A sector that has experienced expansion in recent years is weaving, stimulated by new technology. Reactions to this difficult market situation have been similar but not identical in the USA and Europe. In both cases the industries’ organizations are working to correct misperceptions that carpet is unhealthy and unsustainable. In the USA, the Carpet and Rug Institute (Peoples, 2005; Braun, 2007) has concentrated heavily on health and cleanliness and has introduced CRI Green Labels relating to indoor air quality for carpet cushion, adhesive, and vacuum cleaners, each supported by a testing programme. A Seal of Approval for professional cleaners aims at keeping carpets healthy and looking good over an extended life. The associated promotion claims: ‘Carpet cleaning is rocket science’. In Europe, the industry has been advised (Vankann, 2005) to concentrate on the advantages of carpets: greater aesthetic opportunities compared with smooth floor coverings, excellent acoustic properties, good thermal comfort, and low volatile organic compounds (VOCs) compared with other organic floor coverings. Strongly associated with the campaign is involvement in the development of European standards (Simeons, 2005) and industry standards (Ruys et al., 2007). Standards associated with the GuT label for environmentally friendly carpets have been tightened. There have been a few highly innovative approaches. Janetzki (2005) revealed a ‘Thinking Carpet’ that incorporates sensors linked to a computer. Applications range from simple alarms and light switches to guiding
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visitors round museums or navigating robot vacuum cleaners. DuraAir (Farber, 2003) is a carpet containing catalysts based on platinum, rhodium and palladium that convert odours and VOCs from other sources into odour-free substances, mostly carbon dioxide and water vapour and, sometimes, nitrogenous compounds, enhancing the quality of indoor air. The mood over the past decade has resulted in environmental issues becoming the most intensive area of research on carpets.
9.2
Environmental considerations
Although the impact of carpets on the environment is currently the greatest area of concern for the industry, a detailed review of progress is inappropriate in a book on textile structures. However, the construction and composition of carpets is highly relevant to many environmental aspects so a brief review is important. Details are available in the CRI’s International E-Journal of Flooring Sciences, the CRI’s White Papers, and many of the papers presented at the International Man-Made Fibers Congress, Dornbirn, Austria. Crawshaw’s literature survey Section 2 (2003) covers the subject, with greater emphasis on manufacturing aspects than the sources mentioned above.
9.2.1 Positive effects of carpet on the environment
•
•
• •
Walking comfort and walking safety. With the exception of very thick carpets, when the sense of balance may suffer a slight adverse reaction, it is more comfortable to walk and stand on carpets than on hard floors, and there is very little risk of slipping and falling. Falls, if they do happen, are much less likely to result in injury – extremely important for the over-65s. Acoustic comfort. Carpet is one of the best acoustic materials available to architects. In particular, it has high Impact Insulation values (it minimizes noise generation) and high Noise Reduction Coefficients (it absorbs airborne sound). Thick, heavy carpets perform best. Thermal comfort. Depending on the design of the building, insulation by carpets may reduce heating costs. With bare feet, thermal comfort is clearly apparent. Indoor air quality. Wool carpets in particular have been shown to provide lower concentrations of pollutants such as sulphur dioxide and oxides of nitrogen than outdoors. Because of their high capacity to absorb moisture, they are able to buffer changes in room humidity.
9.2.2 Health and cleanliness Because of a widespread misperception that carpets are unhealthy, despite lack of factual evidence, a high level of research effort has been applied in this area.
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Allergies. A health campaign in Sweden resulted in an 80% decline in carpet usage between 1973 and 1990 but there was a threefold increase in the incidence of asthma and allergies over the same period. This is because carpets act as a sink for contaminants, so that airborne levels of dust and biocontaminants are higher over smooth floor coverings. Loadings of contaminants in carpets greater than 2 g/m2 may release matter into the environment, however. The principal contaminants likely to aggravate allergies are moulds, fungi, dust mite and cockroach excrement, and cat allergens. The first three do not feature in dry carpets. Cat allergens are the most serious domestically and may persist in heavily worn carpets, so carpets should be renewed more frequently in cat-friendly households. Volatile organic compounds (VOCs). It has been pointed out that, as well as VOCs, humans may be exposed to tobacco smoke, radon, formaldehyde, polychlorinated biphenyls, household chemicals, asbestos and artificial mineral fibres, building products and reactants from them, chemicals from office machinery and human emissions. Odours from new carpets are short-lived and are less serious than those from alternative floor coverings, wall coverings, adhesives and furniture. They arise from unreacted monomers, 4-phenyl cyclohexene, and vinyl cyclohexene, by-products from the polymerization of latex. Attention to the polymerization process minimizes objectionable compounds, and they may be reduced further by steam distilling the latex. VOCs are a much more serious problem in automobile carpets because cars can become extremely hot when parked in sunshine, so that windscreens may become fogged by volatiles, and problems of odours and even health may be serious. Latex-free automobile carpets are now used to alleviate such problems. Cleaning. It is recognized that carpet cleaning must be carried out in relation to the source of contaminants. Machines for vacuum cleaning, foam cleaning and hot water extraction should be selected according to the state of the carpet. There are accreditation schemes for cleaning machines and cleaning chemicals and literature from central organizations that recommend cleaning procedures.
9.2.3 Manufacturing and the environment Local, national, European and US federal legislation regulates water and air pollution by industries. The carpet industries in Europe and the USA have taken a stance of being ‘greener’ than required by legislation. The Gemeinschaft Umweltfreundlichen Teppichboden (GuT) has a Signet for carpets that requires that the site of manufacture be audited for compliance with its standards, a list of possible contaminants in the product must be absent, and limits are set for VOCs and odours. Members of GuT are encouraged to participate in working groups to advance various environmental issues. Not only are there campaigns to minimize energy usage in manufacture, but a mood to consider the total carbon footprint ‘from cradle to cradle’, i.e. after recycling.
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Recycling Used carpets are typically composed of pile fibre (or mixed pile fibres), backing fabrics, an organic adhesive, an inorganic filler, plus liberal amounts of soil, so that the problem of recycling is not an easy one to solve. Aspects being studied include collection systems for used carpets, identification of fibre (e.g. by NIR analysis), disintegration, textile processing, purification of fibres (from dirt, chalk and latex), remelting of fibres into plastics, depolymerization, and thermal reclamation. Some companies operate integrated waste management policies and market various recovered products. A different approach is to make carpets entirely from olefin fibres and adhesives so that they provide clean-burning fuel. Scrap carpet may be coarsely shredded and hot-pressed into boards to be used as building materials; or converted into geotextiles, including land drainage filtration ducts. Full-life cycle costing takes into consideration transport costs (and the carbon footprint of transport) and cleaning costs throughout the product’s life, as well as the costs of manufacturing and recycling. Aspects of all this have been formulated by voluntary and regulatory bodies.
9.3
Pile fibres
9.3.1 Nylon (PA) Nylon is the leading pile fibre used in the carpet tufting industry, and is also used as a blending fibre in woven carpets (Collins et al., 2005). Nylon 6,6 and nylon 6 are equally satisfactory once in the carpet: the difference in melting points is irrelevant in carpet products. During processing, account must be taken of differences in dyeability and conditions required for heat setting. The volumes of filament nylon used are greater than staple in both the USA and Europe, and are applied principally in loop-pile carpets. Cut-pile carpets, which are often in plain colours, usually use staple fibre, which can be blended to circumvent problems of variable dye uptake. Imperfect cutting of tough filaments can cause serious faults in cut-pile carpets. Nylon’s toughness and excellent elastic recovery translate into durable resilient carpets. However, the basic round fibre is prone to soiling and staining in use and a great deal of research has been devoted to overcoming these problems. Stain- and soil-resistance are usually achieved by chemical finishing processes (see Section 9.13), although a convex triangular fibre cross-section is said to reduce the adhesion of soil. Soil may be hidden by a trick of physics – increasing the light-scattering coefficient of the fibre, achieved by incorporating white pigments (usually anatase titanium dioxide), microvoids and hollow channels. Dupont has promoted its square-section filament with four channels and its convex-triangular filament with six channels.
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9.3.2 Polypropylene (PP) Polypropylene comes a very close second to nylon in volume consumption in Europe. Staple fibre consumption of the two fibres is roughly equal. In the USA, staple PP is less popular than staple PA, but huge volumes of BCF PP are used. In Britain, blends of PP with wool are widely used. The two principal advantages of PP are the low cost of its monomer and its low specific gravity – for a given decitex the fibre diameter is 12% greater than for nylon. Polypropylene carpets are generally cheaper than nylon carpets. Although the elastic recovery of PP is not as good as that of nylon, this can be compensated to some extent by employing a high pile density. In the USA, carpets are generally heavier than in Europe so the performance difference may not be as great there. Technical improvements have also been made. By blending shrinkable olefin fibre with conventional PP staple, spinning on the semi-worsted system, and steaming, a particularly bulky yarn is achieved. Moreover, the interlocking of fibres that takes place when the yarn is bulked contributes significantly to the stabilization of twist. A low-temperature bulking fibre is available for producing a wool/PP-blended yarn. Among the fibre variants are products with built-in antifungal and antimicrobial properties. Versions of PP with exceptionally high resistance to degradation by light have been developed for the pile of textile sports surfaces and other outdoor applications. Fibre cross-sections are most commonly round, although split film and fibrillated film are used to simulate the texture of grass more closely.
9.3.3 Polyester Conventional poly(ethylene terepthalate) (PET) is eminently heat-settable but has inferior resilience to nylon. It found its way into the US carpet industry in particular through providing tufted structures from set staple yarns that resisted the rather severe action of winch (beck) dyeing. PET is now widely used in the USA in needlefelts as well as tufted carpets. Interest in Europe has been more limited. Drinks bottles are made from high-grade PET and recycled polymer from this source is a significant item in the carpet industry. Its properties may be enhanced by a solid-state polymerization that increases the viscosity of the melt and extracts some contaminants (Bhatt, 2009). Poly(trimethylene terepthalate) (PTT) was presented as an exciting new carpet fibre by Shell Chemicals in 1996. Launching an entirely new fibre is a major project and only a few products are yet on the market. The Shell Chemicals web site (2011) updates the commercial programme for Corterra fibre (and plastic) and reviews the technical advantages of the fibre in carpets. The molecular dimensions of PTT provide a unique three-dimensional helical structure in the fibre that makes the elastic recovery virtually identical to that of nylon. Staining of carpets is less of a problem. Dyeing is more
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straightforward than for PET and colour-fastness to light, oxides of nitrogen and ozone are better than for acid-dyed nylon. The energy footprint in fibre manufacture is said to be 60 to 70% lower than for nylon. Although PTT was first synthesized in 1942, it is only recently that the manufacture of the intermediate 1,3 propanediol has become economically viable. DuPont’s Sorona is their competitor to Corterra and the company is stressing that their 1,3 propanediol is renewably sourced from glucose by a biochemical process (Kurian and Fields, 2007).
9.3.4 Acrylic (PAC) Acrylic pile fibres are now used principally in Japan and south-east Asia, where a soft handle is valued. PAC fibres can be dyed to very high standards of fastness to light. Using high-shrink/low-shrink blends, bulky yarns can be produced and the associated fibre entanglement enhances tuft definition in cut-pile carpets. Relief textures can be produced by using bulking yarns and relaxed yarns in different areas of a design and heat-treating the carpet after weaving (Celik et al., 2009).
9.3.5 Melt-bonding fibres Melt-bonding fibres were first applied in carpet pile yarns in the mid-1990s to enhance the twist setting of wool-rich carpet yarns. By using a blend, typically 80/10/10 wool/nylon/melt-bonding fibre and heating the yarn to fuse the bonding fires to each other and possibly to the nylon, a network is formed to create a more cohesive structure. Around the same time, the concept was applied to fully synthetic yarns, and a little later to cotton and to filament yarns. The advantages of incorporating melt-bonding fibres include improved tuft definition in cut-pile carpets, reduced fibre shedding in the early stages of wear, and the possibility of substituting singles yarns for plied yarns. Bicomponent bonding fibres commonly have a polyester core and a sheath of low-melting polymer – typically 110°C for wool and 130°C for nylon. Singlecompound bonding fibres, usually olefin copolymers, are suitable for use in nylon or polypropylene yarns.
9.3.6 Conductive fibres Under conditions of low atmospheric humidity, the action of persons walking on insulating carpet may cause charge separation so that they accumulate static charges of several thousand volts. When they touch a conductor and discharge the static electricity, they may experience unpleasant shocks. The usual solution to this problem is to make the carpet (pile and backing) moderately conductive. The pile may be made conductive by incorporating a very small proportion of a conductive fibre. The backing materials must also be conductive.
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Stainless steel fibre, typically 9 dtex, in a proportion as low as 0.2%, is sufficient to make carpet pile conductive. Blending such a small proportion uniformly is not easy so the material is marketed as a pre-blend. Nylon fibres may be made conductive by incorporating a core, sheath, stripe or multiple stripes of carbon. ‘Antistatic’ brands of nylon contain a small proportion of conductive fibres or filaments. In Japan, filament nylon is made conductive by coating with copper sulphide after fibre manufacture. Polyester, polyamide and acrylic fibres containing cuprous salts are marketed as blending fibres from Poland.
9.3.7 Self-disinfecting fibres Fibres are available that inhibit the growth of bacteria and fungi, which may occur if the carpet becomes wet. Odour control is an important objective, although a generally healthy environment is claimed, including inhibiting the growth of dust mites. Three classes of product are available (Bertamini, 2003) based on the following chemicals:
• • •
Organo-metallic compounds Trichlosan Silver.
Conductive fibres based on copper compounds are also said to be anti-bacterial.
9.3.8 Wool Wool is the traditional pile fibre and continues to be associated with high-quality carpets. It accounts for about 12% of carpet pile fibre used in Europe and is the principal fibre in hand-knotted carpets. Wool carpet’s resilience in wear is equal to that of nylon. The fibre shows slow but excellent recovery from stress under the influence of water, so that wet cleaning revives the pile as well as removing the soil. Wool carpets have good resistance to burning, even if ignition takes place, which is important in some contract applications, e.g. aircraft carpets. A negative aspect of wool is its limited resistance to abrasion in carpets of low pile density. This problem can largely be overcome in cut-pile carpets by blending with 20% nylon or 10% nylon and 10% melt-bonding fibre.
9.3.9 Cellulosic fibres Sisal is a hard fibre obtained from the plant Agave sisalana by a combined mechanical and washing procedure. It is extensively used in flat-woven rather than pile carpets, usually in its natural colour.
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Coir, from the shell of the coconut, is used in similar styles to sisal, although the products tend to fall in the lower price brackets. Cut-pile entry mats are commonly made from coir, by weaving or by adhesive bonding. Jute, once the most important backing fibre, has achieved some success as pile material in tiles woven on the face-to-face system. Chemical modifications have been made to improve the performance characteristics in carpets (Rahman et al., 2007). Cotton is widely used in washable bath sets and in a few speciality broadloom products. Improvements in the resilience of cotton pile have been made by incorporating melt-bonding fibres. Tencel, according to Manner et al., 2009, is a wood-based cellulosic fibre with a modulus much higher than that of cotton, giving better resilience in carpet pile than most cellulosics. Tencel absorbs 40% more moisture than cotton, contributing to a comfortable room humidity. No electrostatic problems are associated with Tencel. Renewability is being promoted as a motivation to produce carpets commercially.
9.3.10 Others Poly(lactic acid) fibre is biodegradable and should find its way into carpets for this reason alone.
9.4
Pile yarns
9.4.1 Filament yarns An important trend in the carpet industry is for filament yarns to be produced in-house by large carpet manufacturers. Hart, 2007, reported that 55% of BCF nylon and almost 80% of BCF polypropylene was produced in Europe by integrated companies. In the USA, the situation has moved a little more slowly, but integrated products there include polyester. BCF carpet yarns are produced in linear densities ranging from 650 to 5 400 dtex, with filament dtex in the 11 to 30 region. Texturing is by the hot fluid technique, as part of a single-step process of spinning, drawing and texturing in one machine. Two or more extruders may produce filaments that are then drawn and textured in parallel. The parallel yarns may have the same composition, or may differ in colour, dyeability or decitex. If an intermingled yarn is required, the ends that were generated in parallel are passed through a tangle chamber where they are subjected to jets of cool air. Different types of jet can produce different visual effects; and ends may by-pass the intermingling unit to give greater contrast. Figure 9.1 is a diagram of a modern texturing unit in which the plug of yarn is formed after leaving the exhaust air and is fed directly onto the cooling drum. ,
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9.1 Diagram of a texturing unit in which the plug of yarn is formed between a low friction shoe and the cooling drum (Bauer, 2003).
Formation of the plug is controlled by a combination of texturing jet and cooling drum settings. The most critical application of BCF yarns is for carpets in plain colours, or subsequently dyed to a plain colour. Every aspect of production must be tightly controlled to avoid irregularities in the final carpet. This is one reason why a high proportion of plain carpets are produced from spun yarns where fibre irregularities can be blended uniformly. Texturing can be an important source of irregularities, and one of the objectives of the texturing element shown in Fig. 9.1 is to allow plain carpets to be produced satisfactorily. An alternative machine (Schenken, 2003) also aims to produce stable and reproducible process parameters. It incorporates hardened ceramic nozzles with hydrophobic surfaces, ceramic lamellas and a longer residence time on the cooling drum.
9.4.2 Spun yarns Spun yarns are produced principally on the semi-worsted or woollen systems, although the worsted system is used for some fine yarns destined to be woven on face-to-face machinery. Unconventional systems such as wrap spinning, the PLYfiL process of Suessen, and core spinning for exceptionally heavy linear densities are used to a more limited extent. Wool tufting yarns and Axminster yarns are usually woollen spun. The system’s flexibility in its requirements for raw material allows carpet manufacturers to select wools that provide the pile characteristics required in the carpet; and the
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system can introduce nep, slub and flame effects in the yarn. The somewhat random fibre orientation in woollen yarns facilitates the setting of twist. The drafting processes that are a feature of the semi-worsted system require a high mean fibre length and minimum short fibre content. Relative conversion costs move in favour of the semi-worsted system as yarn linear densities become finer. Tuft definition is a valued characteristic of plain cut-pile carpets. Two-ply yarns are commonly used, although the more expensive three-ply yarns give a rounder tuft. A twist setting process is required for optimum tuft definition and higher levels of folding twist than used in balanced yarns stress fibres and enhance setting. An extreme case is the highly over-twisted yarn used to provide friezé carpets. The friezé wool carpet is a structure that has retained its popularity in the UK over many decades and the style is now widely used in synthetic carpets. Wool pile yarns are normally set by boiling in water, namely by hank (skein) dyeing. Like synthetic yarns they can be set by autoclaving, though the details of steaming conditions are different. Continuous autoclaving of coiled warp has been used extensively for many years and is still being refined, for example for development of kinks in friezé yarns in line with setting. Wool yarns may be continuously scoured and set in coil form on the WRONZ Twistset machine. Thick heavy wool yarns having little twist are not amenable to twist setting, but the integrity of the loops or tufts can be provided by felting the yarns. Felting is achieved when the hot, wet yarns are subjected to mechanical action. The most common causes of stoppages in tufting are poor yarn joints, knots, and yarn faults. Joints that satisfactorily pass through the tufting elements are routinely produced by air splicing or fusion splicing.
9.5
Tufting
Tufted carpet manufacture is basically a matter of stitching a pile yarn into a preformed backing fabric and subsequently fixing the tufts in place with an adhesive, usually latex.
9.5.1 Principles of tufting Loop pile is produced when an eyed needle threaded with yarn penetrates the backing fabric and a looper moves between the needle and the yarn. When the needle withdraws a loop of yarn is held by the looper, which then retracts ready for the next cycle. In cut-pile tufting the looper or hook faces counter to the movement of the backing fabric and loops accumulate on it. The throat of the hook is ground to a shear angle and a knife in the form of a steel blade moves towards the throat so that the oldest loop is cut by a scissor action as shown in Fig. 9.2.
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9.2 The actions in cut-pile tufting, from top to bottom: the needle is inserted through the backing fabric; the hook moves between the needle and the hook; the needle withdraws to leave an additional loop on the hook, while the knife moves upwards to cut a previously formed loop (Cobble Blackburn Ltd).
Multiple needles (typically more than 1 000) span the working width of the tufting machine and all must operate in precisely the same manner if good-quality carpet is to be produced. The first carpet tufting machines were 5/8 gauge (tufting gauge originated in Anglo-Saxon countries and is defined as the distance in inches between needle centres) but engineering improvements have allowed gauges as fine as 1/20 to be produced, and 1/10 gauge carpets are now widely available. The introduction of modular tufting elements (needle blocks, loopers, lines) all precisely located on bars, improving the accuracy of their interaction, allowed tufting machines to
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operate more reliably and at higher speeds to produce better quality carpets. A recent innovation is to form the needle bar from fibre-reinforced resin (Hanuschik, 2005) reducing the mass from 14.8 kg for metal to 4.8 kg for composite. The mass of the whole moving assembly is reduced by 38%, allowing maximum speed to be increased from 1 000 rpm to 1 250 rpm. Power consumption is decreased and lower thermal expansion contributes to more reliable interaction of the tufting elements using a composite looper bar. Cobble’s high speed Panterra machine can operate at 2 000 rpm on plain loop pile. When manufacturing plain carpets it is sometimes considered desirable to break up the regimented structure of the tuft knives. The simplest mechanism for achieving, say, a half-gauge width placement is by means of a crank drive to reciprocate the primary backing fabric. More precise mechanisms are available that involve reciprocating the needlebar at the point of tufting. In coarse gauge loop-piles, displacing the stitches by half a gauge width tends to turn the loops and gives an attractive random structure. In both loop and cut-pile styles, a half-gauge movement can be used to give a denser carpet, i.e. simulating a finer gauge. Using monitoring and control systems, reliable setting of carpet construction can be achieved on machinery having yarn and cloth feed driven by servo motors and with motorized adjustment of the bed plate (controlling pile length), all controlled from a central panel. Additional systems are used for detecting broken ends or tight ends of pile yarn and screening for yarn faults. The quality of the carpet immediately after tufting may also be scanned. Such devices may be integrated with a computerized management system, incorporating data such as shift records and waste statistics.
9.5.2 Patterning systems Patterning systems on tufting machines are mostly in three general categories:
• • •
Yarn tensioning systems, that usually vary pile height Crossover interchange systems that displace pile yarn colours laterally Colour interchange systems that allow one colour of yarn to be selected for insertion at the required position in the design.
The first two technologies can be combined to give quite elaborate patterns. A skilled designer may simulate design styles previously available only from weaving. Yarn tensioning systems Over the years, various mechanical, photoelectrical and digital systems have been used to control yarn tension and therefore loop length in loop-pile tufting. Systems based on servo-motors are now highly popular.
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A typical machine may have 120 servo-motors, each driving yarn feed rollers, so that 120 ends of yarn may participate in a design repeat. To achieve 10 repeats across the width of a carpet, 10 yarn ends are fed over each set of feed rollers and are then conducted to tufting needles at equal intervals across the machine via a tube bank assembly. CMC’s Infinity system has mini-servo-motors controlling each end of yarn. Cobble’s sophisticated Full Repeat Scroll system has up to three pairs of feed rollers operating at three different speeds, respectively, and an electro-pneumatic system nips pile yarn onto rollers at the speed required by a digital design. A design repeat may span the full width of the carpet. In the simplest case, a sculptured loop-pile carpet in a single colour in two or three pile heights is produced. The tips of the high pile may be shorn in carpet finishing to give a ‘tip-sheared’ pattern of cut pile among the loops. With alternate needles threaded with different colours of yarn, very low loops in one colour can be totally hidden by high pile in the other colour. A digital patterning system can pulse the yarn feeds to select high or low loops at will, creating a design in two colours. A special case is cut/loop tufting, by the mechanism shown in Fig. 9.3. The hook has a spring to retain the high loop, which is then cut, while the tensioned loop is pulled past the spring to give a low loop, and a design consisting of areas of cut and loop pile in one colour. Using the buried pile technique a cut-pile design in two colours can be created, simulating a two-frame Wilton carpet (see Section 9.7) but in lower tuft density. Level cut/loop systems do not depend on yarn tension but depend on a gate rather than a spring to determine whether the loop is cut or not. In one such system a loop is formed just on the tip of the hook, whereas an open gate admits it to the throat when it is cut. Crossover structures Zig-zag designs: variously coloured pile yarns, threaded in a sequence selected by the designer, may be changed in position by reciprocating a sliding needlebar over one gauge width at a time so that needles interact with different loopers or hooks. Simple zig-zag or sinusoidal designs are obtained in this way. Such simple effects may be disguised by using space-dyed yarns. Rapid and precise movements of the needlebar are achieved by use of stepping motors (positioning motors). Simple chequered effects may be produced using a single needlebar and staggering the needles into two rows (see Fig. 9.4) and with staggered loopers, short and long. This is because the front row and the back row of needles essentially create different rows of tufts during the same needle stroke. It is therefore possible to interchange the positions of the colours: the zig-zag back stitches overlap. Because of the alternate short and long loopers, the needlebar must move two gauge widths for correct interaction of the tufting elements to take place.
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9.3 The sequence of cut/loop tufting (Cobble Blackburn Ltd).
Elaborate small repeats: with two sliding needlebars moving independently, the staggered needles can be displaced by more than two gauge steps at a time, and bars may move in the opposite directions, together, or singly. ‘High definition’ crossover tufting can be achieved by using only one length of hook and reducing the stagger between the two rows of needles so that either row of needles may interact with any hook. Single gauge-width movements, rather than two, are possible on such machines. When aiming for the more elaborate effects, refinements in machinery are required: yarn feed mechanisms that allow for the variable length of the backstitch, and stopping the cloth momentarily to facilitate insertion and removal of the needles. Crossover structures may be made in loop-pile or cut-pile, using the appropriate machinery.
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9.4 A module of a staggered needlebar (Cobble Blackburn Ltd).
Combinations of patterning attachments The two foregoing principles for producing patterns in colour each have fundamental limitations: the buried pile technique utilizes a small number of colours, while the sliding needlebar technique can have many more colours but all the colours are always visible in the pile. By combining variations on these techniques, the patterning scope of tufting can be extended enormously. Generally, combination systems are based on double-sliding-needlebar machines, with a patterning system controlling pulses of yarn fed to the needles. One needlebar may be tufting plain carpet and the other a pattern; or both needlbars may be tufting a pattern. The patterning systems may be fairly simple: the ultimate is having a Full Repeat Scroll controlling each needlebar. As an alternative to high/low loops for buried pile, the patterning system may be mini-cut/loop. In that case, the same kinds of small repeat designs are obtained as from conventional double-sliding-needlebar machines, but the pile is a combination of cut and loop. With so many variables to control, a digital recall system for the carpet quality and pattern is essential. Designing the carpet is a highly complex matter, too, and a sophisticated CAD system is equally important.
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Colour interchange systems Almost from its inception, the tufting industry has had the ambition to combine the patterning scope of weaving with the production rates of tufting. Cobble’s Individually Controlled Needle for cut-pile tufting (Fig. 9.5) represents considerable progress towards this goal, although it should be noted that all patterning systems are associated with reduced output compared with plain tufting. When the design does not require an ICN for tufting, it is held in its upper position by a spring. When required for tufting, a latch pin connects it to a reciprocating mechanism and it penetrates the backing fabric to interact with a conventional cut-pile hook. There are no yarn feed rollers: instead the pile yarn is clamped to the needle infeed so that yarn is pulled from the creel by the needle on its downstroke. Yarn slips through the clamp on the upstroke. Each needle carries only one colour of yarn. The Colortec machine of Ohno (Japan) and Cobble (USA) combines ICN, sliding needlebar and servo cloth-feed technologies. On the Colortec machine, a
9.5 The Individually Controlled Needle (Cobble Blackburn Ltd).
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single-sliding needlebar is fitted with ICN needles and they are threaded with up to six colours of yarn in the same repeating sequence across the machine. A cycle of the machine is required to tuft each colour in a row and the needlebar moves one gauge width each time a new colour is tufted, the backing fabric remains stationary. For a five-colour design, five cycles are required for each row so that the row of coloured tufts is filled progressively. Carpets similar to an Axminster are produced but at a higher rate (depending on which generation of Axminster machine is selected for comparison) and the creel is much smaller so that re-creeling is accomplished more quickly. CMC’s Colorpoint machine may, in some ways, be regarded as a loop-pile equivalent of the Colortec.
9.6
Backing materials, back-coating and laminating
The structure of a tufted carpet is a laminate. A primary backing is required to receive and hold the tufts; and a secondary backing is required to provide dimensional stability, additional mass and improve the appearance.
9.6.1 Primary backing fabrics Primary backing fabrics for residential carpets are mostly woven from polypropylene tapes, whereas primary backings for many contract applications are nonwovens (needled and then bonded in some way, or spunbonded) composed of polypropylene or polyester fibres. Woven primaries contain about 1% of a lubricant to facilitate the tufting process. They have the advantage of gripping tufts well but their structure can deflect needles, and moiré effects in the pile can result from interference patterns between the tuft lines and the grid of the backing material. A backing construction appropriate for the carpet construction must be selected. The uniformity of primary backings for fine gauges of tufted carpet may be enhanced by using fibrillated tapes, ribbed tapes or by treatments after weaving. Pre-needling or calendering is commonly used. A different approach is to cap the woven fabric by needling a fleece onto the upper surface: using surface fibre in a subdued colour also eliminates the risk of grinning of the backing through low-density pile. Nonwoven primaries composed of polyester are selected for the more critical contract applications. Automobile carpets need to be moulded well to the shape of the floor. This is achieved with the aid of a back coating of hot-melt material. Polyester’s resistance to temperatures up to 180°C is advantageous for this application, and for the manufacture of carpet tiles, where a heavy coating is applied under hot conditions. Polyester primaries have excellent dimensional stability, which is important if the tiles are to lie flat. The non-fraying characteristics of nonwovens are important in tiles too. Heat resistance is of decisive importance
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for contract applications specifying flammability requirements based on radiant panel tests: carpets based on polyester primaries have high critical radiant flux values.
9.6.2 Secondary backing fabrics Secondary backing fabrics are laminated to the soft tufted cloth to transform it into a practical carpet. The adhesive used for laminating also provides tuft and fibre bind. In Europe, foam backings were often used as an alternative to secondary fabrics, representing an integrated underlay (pad) but the current trend is back towards jute secondary fabrics. Plain weave jute fabrics of around 270 g/m2 have a green image and are technically satisfactory. Woven polypropylene secondary backings are also technically satisfactory provided they have an open structure and usefully incorporate hairy or textured yarns to enhance adhesion. They are also designed to simulate roughly the appearance of the back of a woven carpet, with white yarns for cotton and beige yarns for jute. Some manufacturers select their own colours and constructions to provide corporate identity. Nonwoven secondary backing fabrics are rarely used for residential carpets, but may be applied to contract carpets to meet particular technical requirements. Needlefelts are increasingly laminated to tufted cloths. They compete with foam backing as integrated underlays (pads).
9.6.3 Backcoating and laminating The simplest form of secondary backing is the unitary backing – a layer of at least 1kg/m2 rubber latex with calcium carbonate filler. Such unitary backings are used for direct-stick installations where a high level of cushioning is not required. Most commonly, both the primary and secondary materials are coated with latex by lick roller, married together by nip rollers and conveyed by a stenter frame to a drying and curing oven. Using a jute secondary fabric, only the tufted cloth requires latex. Foam backing requires a pre-coat, similar in composition to that used for laminating, to lock the tufts. This is dried and cured and, in the same line, a latex foam is hosed over. A surface skin is formed by infrared heaters, the surface is optionally embossed, and the chemically complex foam is slowly cured in a continuous oven. Hot-melt systems are routinely used for automobile carpets that are later to be moulded. A powder-scattering machine dispenses polyethylene powder over the back of the carpet and infra-red heaters create a sintered coating which is re-softened for a carpet piece to be moulded to the floor well. Alternatives to standard PE are LDPE, LLDE and EVA. Powder scattering has been adapted for laminating to provide a latex-free carpet that has advantages for recycling.
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Carpet tiles require a very heavy coating (3 to 4 kg/m2) of backing material in order to provide self-laying characteristics, rather than using an adhesive for installation. Bitumen and PVC are most commonly used: alternatives are atactic polypropylene, vinyl acetate/ethylene copolymer (EVA) to meet flammability specifications, and polyurethane, and low-density polyethylene (LDPE) for lighter tiles. A glass fibre scrim is usually incorporated to provide the required high level of dimensional stability. Bitumen tiles have a final layer of nonwoven material so that tiles may be boxed for transportation without risk of soiling the pile with bitumen. Adhesives for laminating create complications if the various components of a carpet are to be recycled. Fleissner (2008) has filed a patent for bonding a nonwoven secondary backing to the primary by water needling. Fibres from the secondary backing become integrated with the pile material and the primary fabric. Carpets may be constructed entirely from polyolefin materials to facilitate recycling as fuel. If the primary backing has a fusible fleece of melt-bonding fibre on its underside and the secondary fabric has a similar fleece on its upper side, lamination may be accomplished simply by the use of heat and pressure. Alternatively, the heated primary fabric may be covered with hot-melt powder before applying a standard secondary fabric.
9.7
Wireloom weaving
The first truly mechanical form of carpet manufacture (by treadle, although an engine was later applied) was to loop the pile material, delivered as a warp, over rods (‘wires’) while also weaving it among backing yarns. If a wire incorporates a blade at one end, the pile is cut when the wire is withdrawn and the style is known as Wilton; without a knife, a loop-pile style, Brussels, is formed. To create a patterned carpet, pile warps of different colours (‘frames’) are woven. When a colour is required by the design it is looped over a wire and all the other colours remain incorporated (‘dead’) in the backing. The cost of incorporated pile contributed to the decline of multi-frame Wilton carpets; two-frame Wiltons were used extensively for contract carpets for many years. Face-to-face weaving (Section 9.8) shares the incorporated pile between two carpets, has very high productivity, can weave polypropylene pile yarns that are fused by withdrawal of wires, and has grown in popularity accordingly. Wire looms are advantageous in that they can be used to create a wide variety of textured structures. Tonal chequered effects may be obtained by using groups of rounded wires followed by groups of bladed wires with tonal groups of pile yarns. Loop-pile textures are formed when using wavy wires: withdrawing the wires causes previously formed loops to be robbed to various heights. Carved designs in a single colour are formed when a cut-pile motif is surrounded by
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narrow areas bare of pile. Pile may be floated over a number of wefts to create low, dense, lightweight structures favoured for aircraft carpets. Enormous loops may be formed from yarns of exceptionally high linear density, floated over two or three wires to give the required loop spacing. There are many combinations of floats and pile – see Figure 9.6 for example.
9.6 Two-frame cut/loop structures with loops floated over one wire and one weft (above) and over three wires and two wefts (below) (Michel Van de Wiele NV).
The rate-determining steps in wire loom weaving are inserting and removing the wires, which prompted the development by Van de Wiele of a machine in which the loops are formed over dummy wefts supported by lancets. Lancets are thin metal rods, threaded on a metal bar that holds them in a warpwise orientation, one for each dent, through the point of weaving. The loom does not utilize the traditional Wilton shuttles but is a double-rapier machine. Figure 9.7 clarifies the use of lancets.
9.7 Formation of a three-frame sculptured pile carpet using lancets (Michel Van de Wiele NV).
9.8
Face-to-face weaving
Adapting to carpet manufacture the highly productive face-to-face technique of weaving velvets was slow because the target was to produce patterned carpets, principally squares. The technique is now used extensively for broadloom carpets as well as for squares. Machinery manufacturers have been particularly innovative
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over the past 20 years. Early in the period, developments focused on higher speeds and on electronic jacquards and the associated CAD systems. More recently, improved versatility has been the principal target. The range of possible carpet structures is now so great that dedicated looms are offered for producing particular styles. Weft insertion on a modern loom is by handover rapier and there are double-rapier and triple-rapier looms. The clearest advantage of the third rapier is to increase rates of production: it may participate in weaving either part of the sandwich. Triple-rapier weaving is now used extensively for styling purposes. Figure 9.8 shows a commonly used multi-frame structure before cutting, illustrating the sharing of incorporated pile between the two carpets. There are numerous possible weave structures and several of them are used under different circumstances for weaving carpet squares depending on whether or not the design is woven through to the back, as in hand-knotted carpets, on the pile mass to be woven, the linear density of the pile yarns, the location of the dead pile, and on the number of rapiers available in the loom.
9.8 A six-frame 1/2 V-weave with incorporated pile, produced on double-rapier looms (Michel Van de Wiele NV).
Applying electronic jacquards interfaced with CAD design systems, plus larger creels holding a palette of colours from which the colours required for a particular carpet may be selected, has enabled very short runs of different carpet squares to be woven. Indeed, a production run may include different sizes of product and widely different designs, traditional and modern. If the widths of the squares required summate to less than the loom width, a runner may usefully be woven alongside the squares. Shaggy pile structures have become popular and may be formed in different ways. Van de Wiele’s SRP92 machine utilizes spoon lancets as shown in Figure 9.9. Depending on the dimensions of the lancets, pile heights of 2 × 50 mm or up to 2 × 70 mm may be produced. On the same machine, with other types of lancet, a wide variety of structures may be woven.
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9.9 Diagram of Van de Wiele’s SRP92 face-to-face machine with spoon lancets up to 140 mm (Michel Van de Wiele NV).
The USP92 has double lancets as shown in Fig. 9.10 and can be used to create designs with areas of shaggy pile, loop pile and flat weave.
9.10 Weave diagram for a structure incorporating shaggy pile, looppile and flat weave, produced with the aid of double lancets (Michel Van de Wiele NV).
Another specialized machine is the triple-rapier Handlook Carpet Pioneer HCPX2, producing squares with the design showing on the back, as in handknotted carpets. It is a high-production machine as a result of an advanced four-position robust jacquard and the fact that yarns incorporated in the backing remain stationary during the weaving cycle. Quite thick pile yarns can be woven. The Tapestry Rug Pioneer TRP92 specializes in tapestry carpets combining cut pile and ground effects, both in jacquard.
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Face-to-face machines are now being used regularly for producing loop-pile carpets. Figure 9.11 is a weave diagram for a sisal-look carpet having a structured surface. A third rapier is required to insert a thick weft alternately into the top and bottom carpets. Such styles of carpet are woven in a small number of natural colours.
9.11 Example of a sisal-look weave structure produced on the SLP93 triple-rapier loom (Michel Van de Wiele NV).
In addition to weave structures produced by the Tourney (conventional) technique, Goessl (2005) has listed eight structured patterning possibilities: looppile with the same pile height, patterning on the ground weave (sisal effect), additional patterns on the back (e.g. logos), weft patterning, partially different pile densities in the same carpet, carved effects, double/triple cut-pile, and double/ triple loop-pile. Some of these structures require a programmable dobby, some a third rapier, and some lancets.
9.9
Axminster weaving
The Axminster technique of weaving is theoretically a highly effective one: tufts in a pre-selected colour are cut to length and inserted into the point of weaving, so that there is no incorporated pile. More elaborate designs are possible than by Wilton weaving and the system was favoured for British residential carpets for many years, but tufting became more popular. Figure 9.12 shows some alternative weave structures, two of them with the pile woven through to the back, as in hand knotting, which are used for squares. For many years only incremental improvements to Axminster looms were made but the system is undergoing a revival as a result of important technical developments. The introduction of electronic jacquards interfaced with a CAD studio made short production runs feasible and long design repeats or even non-repeating designs possible. The Axminster industry exploited this situation to secure the hospitality market (hotels, cruise ships, casinos) with prestigious carpets in 80/20
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9.12 Some commonly used Axminster weave structures (Michel Van de Wiele).
wool/synthetic pile. Creels have up to 16 colour frames, and do not necessarily have to be changed for, say, a five-colour design. The rather crude system for inserting a double weft shot by means of a heavy needle has been superseded by modern techniques. First, Griffith developed an Axminster machine on the basis of a Sulzer projectile loom and a little later Crabtree introduced a flexible rapier system. In 2007, Van de Wiele launched a totally redesigned loom, their MAX91. Weft insertion is by means of a free-flying flexible rapier; the 17-position horizontal yarn carriers allow 16 colours to be woven in a design and are driven by stepping motors, the grippers are in one piece and can handle a wide range of linear densities, even in the same carpet; and the knife motion is servo-driven. The machine control panel is touch-screen and covers quality control aspects as well as design and structure. The machine operates at up to 160 rpm. Figure 9.13 shows the principle of the weaving process. An alternative Smart Creel with a measured-length winding system is offered with the MAX91 loom and is particularly useful for short production runs. Pile yarns are taken by a robot from a creel holding a relatively small number of large cones. The robot then fills a larger number of storage cells with the exact amount of yarn required to weave a certain order. The loom then takes these yarns from the storage cells. At the end of the order, the yarns in the cells are all used but, meanwhile, the robot has re-filled the cells with the yarns and colours required for the next order, spliced to the yarns of the previous run. In this way, different orders are produced with minimum yarn waste and downtime.
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9.13 The weaving cycle of the MAX91 Axminster loom: (a) gripping the pile yarn from the carrier; (b) cutting a tuft length from the carrier; (c) inserting the tuft into the weaving position.
The new versatile loom has inspired ideas for special structures. For example, relief effects formed from conventional pile and flat weave are made aesthetically acceptable by using chenille weft. For further information about weaving see Demey’s (2009) review of developments in all techniques of weaving.
9.10
Needling
The principle of consolidating a web of fibres by the action of multiple barbed needles was developed in the nineteenth century for producing carpet underlays. By dense needling followed by impregnation with adhesives, usually carboxylated SBR latex in the form of foam, but sometimes EVA, durable floor coverings are now manufactured. Melt-bonding fibres may be used instead of an adhesive. Basic needlefelts are not pile products, but simulated pile may be created by post-needling. Using forked needles mounted at right angles to the direction of manufacture and using intermittent fabric feed, loops of fibre are pushed among
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lamellae having spacing equal to the spacing of the forked needles. A ribbed structure is produced. With the forked needles mounted parallel to the direction of manufacture, ribbed velour effects are created. A random distribution of surface pile is now favoured. Dilo’s Di-Lour machine utilizes crown needles in a random array and a brush belt rather than a lamellae table to accept the tufts. Surface designs may be obtained by using forked needles arranged in a design. Two-colour products may be produced first by needling the principal base fabric into a velour structure; then a soft needlefelt of a different colour is fed with the first one to a second needling unit. The second colour is pushed to the surface of the basic needlefelt using a special needling arrangement and a mechanism for raising and lowering the brush, to create a pattern in two colours. Fehrer’s Carpet Star (Purn, 2003) is a structuring needlepunch machine with two independent needling zones that can be equipped with needlebeds in partial patterns. Thickened needling zones can be combined to form complementary patterns in long repeats. The main field of application is the production of rib and velour squares with borders on all sides.
9.11
Other methods of manufacture
9.11.1 Adhesive bonding Probably the most widely used system is a face-to-face system of fusion bonding. Two backing fabrics are coated with a paste of PVC powder and plasticizer and are fed towards each other and towards the point of carpet formation. Pre-dyed pile yarn is supplied from beam and folded and pressed into the PVC plastisol by two reciprocating blades. The sandwich is heated in an infrared oven to fuse the plastisol into a stiff gel and, after a short cooling passage, is cut with a reciprocating knife to provide two carpets. Patterned carpet tiles in U-tuft structures are manufactured on a machine that utilizes an electronic jacquard gripper system to prepare rows of pile that are pressed into a pre-coated backing material in the size of tiles. Fixation of the tufts is completed in a conveyor oven. The Westbond system is also dedicated to the manufacture of tiles, but provides an I-tuft structure. A rope of pile yarns in up to 12 colours is cut into lengths of twice the required pile height and conveyed by tapes to be implanted between two fibreglass scrims coated with PVC adhesive. The tiles typically display coloured flecks on a plain or tweedy background.
9.11.2 Knitting Although carpets have been produced by weft knitting, warp knitting is more common and is embraced by a number of specialist carpet manufacturers.
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Essentially, a backing fabric is knitted from flat filament yarn and the pile yarn is laid in. One of the advantages of warp knitting is that the pile yarn does not pass through the eye of a needle so that exceptionally bulky and irregular yarns may be used as pile. Face-to-face knitting machines have also been developed, and utilize conventional yarns. The first textile sports surfaces were produced by knitting.
9.11.3 Electrostatic flocking Low-density pile products with a velvet texture are made from chopped fibre. The flock is aligned electrostatically and is attracted to an earthed fabric coated with adhesive and fixed by fusing. The products are promoted as suitable for wet cleaning by rotary scrubbing machines, which makes them suitable for use in hospitals, among other locations.
9.12
Coloration
All possible coloration routes are used by the carpet industry: polymer pigmentation, stock dyeing, yarn dyeing, yarn printing, piece dyeing by exhaustion, continuous piece dyeing and carpet printing. Polymer pigmentation (solution dyeing) is essential for polypropylene, and flexible extruders were first developed for PP. Typically an extruder is fed with bulk polymer chips, and heavily pigmented chips, usually in three primary colours plus black, in proportions required by colour physics for the desired colour, are fed into the barrel of the extruder. Extremely good standards of colour-fastness are achieved by polymer pigmentation, there is no aqueous effluent, and very little additional energy is needed. For such reasons polymer pigmentation has become the most widely used, for nylon as well as polypropylene. Stock dyeing is widely used for wool and some other fibres. It is essential if multi-coloured yarns such as tweeds, mixtures and flames are to be produced. Large quantities of yarn in a single uniform colour can be produced by blending a number of dye lots, minimizing the risk of streaks and stripes in plain carpet. Yarn dyeing is convenient for producing the lot sizes required for patterned woven carpets. Improvement in dyeing technology, mostly centred around colour physics, have made yarn dyeing more controllable in terms of accuracy of colour matching and level results. Winch (beck) dyeing of carpet piece goods facilitates a rapid response to market needs and rapid tufting of plain carpets. Multi-coloured patterns may be achieved in carpet tufted from standard nylon and variants having different dyeing properties. Continuous dyeing, by impregnating the carpet with dye liquor and steaming while wet, has become very sophisticated. Equipment for injecting liquor into the
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carpet pile minimizes energy usage and allows colours to be changed without stopping the range. Printing of carpets is done by screen or computer-activated jet. Rotary screens have superseded flat screens, except for special markets such as design and display. Displacement and resist techniques have eliminated the problem of white fibre showing at the base of the tufts or between inaccurately registered motifs; for example, the carpet may be impregnated with dye liquor based on sulphonated metal complex dyes and then overprinted with acid dyes plus a resist agent for the metal complex dyes at a lower pH value. The printing pastes displace the ground colour. Jet printing is a non-contact system for printing without the need to prepare screens. The Millitron system is based on continuous coherent jets of dye liquor directed at the carpet that are deflected selectively by air jets and recirculated. The Chromojet system has jets controlled by electromagnectic needle valves. Digital design systems provide the same flexibility and facility for large repeats as in modern weaving.
9.13
Chemical and other treatments
9.13.1 Stain and soil resistance Although fluorocarbon products have been available to the textile industry for over 55 years, intense interest in their application to carpets developed only in the mid-1980s because of adverse consumer reactions in the USA to problems of soiling and staining of nylon carpets. The early treatments were recommended only for domestic situations, being considered insufficiently durable to intense wear. A sophisticated range of products and techniques of application is now available and durable effects are claimed (Baumann, 2003). Two chemicals are applied sequentially to the carpet at the final wet processing stage. A stain-blocker, essentially a dye resist agent, is first applied and prevents food colorants, beverages and so on being chemically bound to the fibre. A fluorocarbon product based on a urethane backbone is then applied to reduce the surface energy of the fibre. The fluorocarbon finish limits the penetration of aqueous and oily spills, and also facilitates soil removal in cleaning. A wide variety of fluorocarbon dispersions is available: anionic, cationic, nonionic and amphoteric, suitable for different fibres and different techniques of application (e.g. winch, continuous). Fluorocarbon carpet protectors are available for application to laid carpets.
9.13.2 Hygienic finishes Supplementing the use of self-disinfecting fibres (Section 9.3.7), organic finishes are available for treating carpets made from more common fibres (Zimmermann,
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2003). Agents are available that provide protection against mites as well as bacteria: some inhibit the growth of bacteria alone.
9.13.3 Insect-resistant treatments Wool fibre and yarns are routinely treated against attack by particular moth larvae and beetles with permethrin at the stage of dyeing. Other techniques of application are available for treating wool that is not to be dyed.
9.13.4 Antistatic treatments Carpets found to be susceptible to electrostatic problems may be treated in situ with recommended anionic agents. Re-treatment may be needed at intervals. Disperstat W, a cationic antistat, is recommended for application to wool from a cold bath post-dyeing. Durability of effect is adequate for residential carpets, although the treatment does not affect the conductivity of the carpet.
9.13.5 Flame-resistant treatments To meet particularly stringent flammability specifications, wool carpets are usually used. For additional safety, the Zirpro treatment with anionic zirconium may be applied to the wool post-dyeing. Benisek (2009) reports that the treatment is also effective against insects and bacteria.
9.13.6 Anti-shading treatment Cut-pile carpets in particular are susceptible to developing a patchy appearance through the pile leaning in different directions according to the pattern of foot traffic, or even crushing of the pile during transport, handling or fitting. This ‘shading’ is an optical effect obtained by viewing the sides or ends of the tufts according to pile lay. Further foot traffic renders the effect permanent. Wood (2009) has described the TRUTRAC machine, developed originally for wool carpets by WRONZ, which uses a combination of heat, water, and pressure to impart a pronounced and consistent direction of pile lean. See Figure 9.14. Foot traffic on a treated carpet tends to reinforce this imposed pile lay, rather than push it in various directions, as can occur with a carpet having a near-vertical pile.
9.14
Textile sports surfaces
Speciality carpet structures are produced for a variety of purposes: electroluminescent carpets for entertainment and display; ‘hot’ carpets used in Japan to provide comfort for bare feet; lightweight flame-resist carpets for aircraft;
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9.14 Principle of the TRUTRAC anti-shading process (AgResearch, Lincoln, New Zealand).
carpets of limited conductivity for computer rooms, and so on. The example chosen is textile sports surfaces. Artificial turf was developed so as to be independent of growing conditions; to be sufficiently durable to allow numerous games per week to be played; in some cases to be removable so that alternative events can be held in a stadium; and to provide specific playing characteristics. Haitchi (2005) has recorded a history of artificial turf. The first commercial product was warp knitted and had a nylon pile. Special polypropylene or other polyolefins containing photodegradation inhibitors are now most commonly used in pile. Schoukens (2009) has drawn attention to the need to control the cold drawing conditions for the filaments so as to achieve low friction against human skin (the effect is surprisingly large); to avoid reduced thermal resistance (flattening of the turf can occur after it has been exposed to elevated temperatures); and to avoid too high an elastic modulus, which can lead to reduced resilience (repeated play can release internal strains in the polymer). Specialized yarns have been developed better to simulate natural grass: for example, shrinkable components may be included to create ‘thatch’ that underlies surface fibre. High-quality woven products are used for cricket pitches and golf teeing areas. Knitted turf may be selected for its no-fraying properties. Apart from the special pile, tufted turf needs dark coloured backing material that is resistant to photodegradation and an adhesive layer that is permeable to rainwater. Secondary fabrics are not usually used, but there are products with closed-cell polyurethane foam that resist uptake of water. One solution to the drainage problem is to avoid the use of adhesives, for example by bonding a needle-felt shock pad incorporating melt-bonding fibres.
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The earlier artificial grasses were regarded as utilitarian products suitable for sports at low levels. Since that time a great deal of effort has been devoted to providing the playing characteristics required for particular games. Tests for ball/ surface interactions as well as tests for player/surface interactions have been developed. Parameters used to control these requirements include pile height, pile density, fibre properties, and the ‘shock pad’ over which the artificial turf may be laid. Textile surfaces may be laid over a thick pad composed of rubber and aggregate on an engineered base, or on a carefully graded base of coarse aggregate/ fine aggregate/sand. Existing soil is sometimes satisfactory as a base. In the search for particular playing characteristics, products were developed having low-density pile filled with sand. Hockey was the first sport to accept textile surfaces at the highest level of the game. In fact, textile surfaces are now the only ones accepted at the highest levels of the game because of the more consistent ball roll and bounce. The two principal problems – too-fast ball roll and friction burns suffered when a player fell – were solved by irrigating the pitch before a game and again at half-time. Other sports bodies have developed recommendations for textile surfaces based on standardized tests. The most difficult sport to satisfy was Association Football. Ball roll speed and bounce with most products was too high and there were problems with ‘foot lock’ and achieving the required player/surface interaction in sliding tackles. The solution was to design a high-pile product, partially filled (Fig. 9.15). The lower layer of filling is sand and the upper layer rubber crumb to provide resistance to compaction. Special machines have been developed to tuft the required long piles.
9.15 Structure of a composite surface suitable for Association Football (G. Schoukens, University of Ghent).
In 2005, UEFA and FIFA issued common standards and have approved such surfaces for championship matches. It is expected that artificial turf will be used increasingly for soccer in regions where the climate makes it difficult to maintain good natural turf all year round.
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9.15
Sources of further information and advice
Research organizations studying of their work are now mostly funders, and so the scientific information on the subject. The E-Journal of Flooring Sciences papers on:
• • • • •
carpets that once might have published most under contract and report privately to their literature provides a rather thin source of Carpet and Rug Institute, USA, operates the which makes freely available peer-reviewed
human response and ergonomics environmental attributes product formulation and chemistry cleaning services product and materials recovery, recycling and reuse.
The journal provides a wealth of positive information on various environmental aspects of carpets. New information in Europe over an extended period was mostly revealed in conference papers. The Textile Institute’s Floor Coverings Group Conference (Tifcon) was last convened in 1999. The Intercarpet conference, once held in Baden, Austria, was merged with the International Man-Made Fibers Congress, Dornbirn, Austria, and papers on carpet subjects were given in even years until 2008. The conference papers are available on disk. Unitex, Belgium, held carpet conferences in odd-numbered years, alternating with the Austrian conference and these now seems to have eclipsed Intercarpet. It is not easy to access the papers. Of course, organizations servicing the carpet industry submit media releases to the trade press and the same information is usually made available on their web sites. Crawshaw’s book Carpet Manufacture (2002) details the technology in use by the carpet industry and associated industries at the beginning of the twenty-first century. A little later (2003) he surveyed the literature on new developments. A more recent book, Goswami’s Advances in Carpet Manufacture (2009) is especially notable for two highly informative chapters on handmade carpets and for the absence of information on tufting.
9.16
References
Bauer, J. (2003). BCF texturing – the key to success. Proceedings of the Forty-second International Man-Made Fibres Congress, Dornbirn, Austria. September. Vienna: Austrian Man-Made Fibers Institute. Baumann, M. (2003). Soil protection for carpets. Proceedings of the Forty-second International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Benisek, L. (2009). Private communication.
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Bertamini, L. (2003). Fibre innovation by Aquafil. Proceedings of the Forty-second International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Bhatt, G. M. (2009). Value adding to recycled PET flakes. Revista de la Industria Textil, 466,45–48. Braun, W. (2007). The state of soft floorcoverings in North America. Proceedings of the Forty-sixth International Man-made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Celik, N., Kaynak, H. K. and Dirgmanci, Z. (2009). Performance properties of Wilton-type carpets with relief texture effects produced using shrinkable, high-bulk and relaxed acrylic pile yarns. AATCC Review, 9(September), 43–47. Collins, G., Morley, B. and Bartsch, P. (2005). Tencel – the new age fibre for carpets. Proceedings of the Forty-fourth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Crawshaw, G. H. (2002). Carpet Manufacture. Christchurch, New Zealand: WRONZ Developments. 1–403. Crawshaw, G. H. (2003). Textile floorcoverings updated. Textile Progress, 34 (3/4), 1–71. Demey, S. (2009). Advances in carpet weaving. In K. K. Goswami, ed. Advances in Carpet Manufacture. Cambridge, UK: Woodhead Publishing, pp. 44–76. Farber, P. (2003). Healthier air through textile floorcoverings. Proceedings of the Forty-second International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Fleissner, G. (2008). Method and device for stabilization of pile goods such as pile carpet with a reinforcing back. US Patent and Trademark Office Application (week 22) 3 January. Goessl, R. (2005). New trends and possibilities of double carpet weaving. Proceedings of the forty-fourth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Goswami, K. K. ed. (2009). Advances in Carpet Manufacture. Cambridge, UK: Woodhead Publishing. Haitchi, M. (2005). Improvements in artificial turf. Proceedings of the Forty-fourth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Hanuschik, G. (2005). Nadel- und Greifferbarre aus Faserverbundwerkstoff (FVW). Proceedings of the Forty-fourth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Hart, D. (2007). European and global carpet markets. Proceedings of the Forty-sixth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Hayes, E. (2007). Global textile fiber market trends. Chemical Fibers International, 57(5) 228. Janetzki, U. (2005). Renaissance of floorcovering. Proceedings of the Forty-Fourth International Man-Made Fibres Congress, Dornbirn, Austria. September. Vienna: Austrian Man-Made Fibers Institute. Kurian, J. V. and Fields, W. L. (2007). DuPont Sorona renewably sourced polymer and high performance fibers. Proceedings of the Forty-sixth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Manner, J., Ivanoff, D., Morley, R. J. and Lenzing, S. J. (2009). Tencel – new cellulosic fibre for carpets. Industrie Textile, 1396, 57–62.
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Peoples, R. (2005). Business model to promote soft floorcoverings. Proceedings of the Forty-fourth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Purn, H. (2003). Fehrer’s Carpet Star – a new process for the production of structured nonwovens. Proceedings of the Forty-second International Man-Made fibers Congress. Dornbirn, Austria, September 2003. Vienna: Austrian Man-Made Fibers Institute. Rahman, S. M. B., Uddin, M. K., Sayeed, M. M. A., Samad, M. A. and Rahman, A. R. (2007). Study on cross-linked dyed jute carpets pile yarns. Indian Journal of Fibre and Textile Research, 32 (4), 477–480. Ruys, L., Vanneste, M., van Olmen, R. and Hoogewys, J. (2007). Carpet innovation and standards. Proceedings of the Forty-sixth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Schenken, M. (2003). Latest developments in BCF technology. Proceedings of the Forty-second International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Schoukens, G. (2009). Developments in textile sports surfaces. In Goswami, K. K., Advances in Carpet Manufacture. Cambridge, UK: Woodhead Publishing. Simeons, D. (2005). New CEN standards for carpets and implications on the carpet business in Europe. Proceedings of the Forty-fourth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Vankann, E. (2005). The European carpet industry and its challenges. Proceedings of the Forty-fourth International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute. Wood, E. J. (2009). Developments in wool carpet manufacture. In Goswami, K. K., ed. Advances in Carpet Manufacture. Cambridge, UK: Woodhead Publishing. Zimmermann, D. (2003). Possibilities and limits of hygiene protection treatments. Proceedings of the Forty-second International Man-Made Fibers Congress. Dornbirn, Austria, September. Vienna: Austrian Man-Made Fibers Institute.
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10 Developments in Jacquard woven fabrics A. M. SEYAM, North Carolina State University, USA
Abstract: Recent developments in Jacquard shedding systems and their flexibility and capabilities in producing intricate striking designs (such as Damask, Brocade, Brocatelle, Matelasee, and Tapestry fabrics) are explained. The capacity of Jacquard shedding systems in the production of smart electronic textiles, industrial textiles, and shaped seamless garments are also described. The production procedures of converting artwork to Jacquard patterns using weave structures combined with coloured warp and filling yarns and computer-aided design (CAD) systems are reviewed. The properties of Jacquard woven fabrics as related to the weave design as well as the constituents of the woven structure are covered. Key words: Jacquard design, Jacquard weaving, tapestry weaves, damask weaves, brocade and brocatelle, recent developments in Jacquard, smart textiles, industrial textiles, seamless shaped garment, shedding systems.
This chapter starts with an introductory section that deals with woven fabric constituents, basic weaves, and the shedding systems (cam, dobby, and Jacquard), and their relationship to the weave design, thus providing the reader with a better understanding of why Jacquard systems were developed for producing intricate large woven designs. The second section provides a description of the mechanical and electronic Jacquard parts and how the shed is formed in relation to the weave design by selecting warp yarns for the upper and lower sheds. It also provides information related to that Jacquard system’s standard capacities, which is related to the weave repeat size and the types of Jacquard ties that are related to the weave design shape. The third section explains how a Jacquard weave design is created starting from the artwork, using CAD systems. The fourth section reviews the new development in Jacquard shedding systems and their advantages over the traditional systems. Section 10.5 defines and explains speciality Jacquard woven patterning (such as Brocade, Brocatelle, Damask, and Tapestry) and its structures and uses. The sixth section highlights the most significant applications of Jacquard weaving including new applications such as technical, three-dimensional, seamless shaped textiles. The seventh section deals with the properties of Jacquard woven fabrics and explains how a property is related to the weave design as well as to the constituents of the woven structure. The eighth section sheds light on the predicted trends of Jacquard applications. Recommendations for further information are given for the reader in Section 10.9. These include related books and articles to further the reader’s knowledge. Trade magazines that may publish articles addressing new trends are also identified. Sources of information and images are shown in the last section. 223 © Woodhead Publishing Limited, 2011
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10.1
Introduction to Jacquard woven fabrics
In their simplest form, woven fabrics are formed by interlacing two sets of yarns. The first set is vertically arranged and known as ‘warp yarns’ or ‘ends’, and the second set is horizontally arranged and termed ‘weft yarns’. There are endless ways to interlace (interweave) warp and weft yarns. The method of interlacing is referred to as weave design. There are essential or basic weaves from which all weave designs are created. These are plain weave and its derivatives (warp rib weaves, weft rib weaves, and basket weaves), twill weaves and their derivatives (such as elongated twill, broken twill, pointed twill, waved twill, etc.), and stain/ sateen weaves and their derivatives (such as extended sateen weaves, designs on sateen base, etc.). While the basic weaves are simple and are repeated on a small number of warp and weft yarns, they are used to create large intricate designs that require large numbers of warp and weft yarns in the weave repeat. Using coloured warp and weft yarns allow the creation of intricate, coloured design whether using small or large weave repeat size. Figure 10.1(a)–(c) depicts plain weave presentations. Figure 10.1(a) is known as ‘flat view (or top view)’, which results from observing the fabric projection in a plane parallel to the fabric. While plain weave is the smallest size, its flat view takes time to draw and larger size weaves would be time-consuming to present in this manner. Figures 10.1(b) and 10.1(c) show plain weave in a form known as ‘weave design’ that is much simpler and faster to construct. The weave design presentation was developed to present weaves visually without the need for writing confusing instructions. The weave design is presented on squared paper
10.1 Plain weave presented in different methods and terminology, and notation associated with woven fabric design.
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known as weave design paper. The design paper has equally spaced vertical and horizontal lines. The space between two adjacent vertical lines represents a warp yarn. The distance between two adjacent horizontal lines represents a weft yarn. A small square represents a crossover point of one warp and one weft. The notation followed for indicating a warp riser (a warp is over a weft) is to fill in the square using a color or shade (or any mark in the square such as x, /, and \). Figure 10.1(b) represents the plain weave of Fig. 10.1(a). Figure 10.1(c) shows one repeat of plain weave. The notation is best understood by comparing Figs. 10.1(a) to 10.1(b), which are two different ways of presenting the same weave. Figure 10.1(c) indicates that plain weave repeats on 2 warp yarns × 2 weft yarns. Warp yarns are drawn in heddle wires that are mounted in harnesses. The number of variations of warp yarns interlacing in a weave design decides the number of harnesses needed. For example, in plain weave (Fig. 10.1), there are two different forms of interlacing. The odd-numbered warp yarns are interlaced differently compared to the even-numbered warp yarns. Thus plain weave (the simplest weave) requires two harnesses. More detail regarding the relationship between weave design and the number of harnesses is published elsewhere (Kipp, 1989; Watson 1946). The harnesses are part of the shedding motion that forms a ‘shed’ by dividing the warp yarns into two sheets (by raising some harnesses and lowering the other harnesses), thus providing a path for the weft yarn to be inserted. The harnesses’ movement is dictated by the weave design and the pattern of assigning warp ends to harnesses known as draw or draft. Figure 10.2 shows how the shed is formed to construct the plain weave of Fig. 10.1. There are several shedding systems, namely cam, dobby and Jacquard.
10.2 Plain weave of Fig. 10.1 during insertion of weft yarn B, with even-numbered warp yarns raised by harness 2 and odd-numbered warp yarns lowered by harness 1.
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10.1.1 Cam shedding system In cam shedding, several cams are used (a minimum of two for plain weave production). Each cam controls the movement of one harness. The cams are mounted on a shaft (the cam shaft) that rotates continuously during weaving. The cam is a disc (Fig. 10.3) of small dimensions that fits (with other cams) inside a cam box under or beside the weaving machine. The cam profile (or the shape of the circumference of the cam) is designed according to a cam plan derived from the weave design. Each cam has a follower that follows its profile and hence it is given up-and-down motions. Through links between the cam follower and its harness, the follower motion is transferred to the harness and hence to the warp yarns drawn in the harness. The cam shedding system is limited to simple weave designs due to the limited number of up-and-down motions that can be achieved by a cam profile. Intricate weave designs require extremely large numbers of up-and-down motions of different sizes and sequences. In the cam shedding system, a reasonable number of up-and-down motions is two each (Fig. 10.3). An additional disadvantage of the cam shedding system is that to change the weave design the set of cams must be replaced or adjusted, which is time consuming. This is not acceptable since today’s weaving machines are high-speed. Stopping such machines for a long time (it takes about 20 to 30 minutes to exchange cam sets or adjust cams) is a premium as it would lower productivity. The invention of electronic dobby and electronic Jacquard has allowed the weave pattern change in extremely short time, or on the fly, without the need to stop the weaving process (Seyam 2004, 2008).
10.3 A shedding cam designed to move the associated harness up, down, up, and down during one revolution of the cam shaft.
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10.1.2 Dobby shedding system The dobby shedding system is designed to construct more intricate weave designs compared to the cam shedding system. It is a compact system that uses pattern cards and small size links, hooks, and knives in the case of the mechanical dobby (Fig. 10.4). The selection of harnesses to be raised is made by the aid of pegs mounted on cards. Each card corresponds to one pick (or two picks in the case of a double-indexed dobby). A peg on the location of a given harness on a pattern card means the harness is to be raised when the pattern card is in the active position (the top position in Fig. 10.4). Harnesses that do not have pegs will be lowered. Figure 10.4 shows a simple illustration of a mechanical dobby showing one harness that is selected for raising. Due to the compactness of dobby shedding systems, they can manipulate a much larger number of harnesses compared to the cam shedding system. Dobby shedding systems with 18 to 24 harnesses are common. It is clear that the number of up-and-down motions for a given harness per weave repeat is unlimited, since it is controlled by the presence or absence of pegs in the pattern cards and the number of pattern cards is unlimited. A large weave repeat size (such as geometric shape, crepe weaves, fancy twills, mock leno, rip-stop, etc.) can be constructed using a dobby shedding system. Figure 10.5 shows examples of weaves that require a dobby shedding system. In these weaves, the up-and-down motions exceed two each and/or the number of variations in wrap yarns interlacing is high and requires more harnesses than the cam shedding system can handle. The limitation in the number of harnesses in the case of dobby (up to 24 harnesses) is decided by the added mass, which causes lower weaving speeds, and the manipulation of warp yarns during weaving, specifically when a warp yarn breaks. Finding the broken ends and repairing the break would be obviously more difficult as
10.4 Principle of the mechanical dobby shedding system.
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10.5 (a) 3 × 2 × 1 × 2 × 2 × 1 fancy basket weave; (b) 3 × 2 × 2 × 1 × 1 × 1 multiple twill weave; (c) rip-stop weave; (d) honeycomb weave.
the number of harnesses increases and becomes impossible with more than 24 harnesses. While mechanical dobby systems still exist, their number is declining and they are being replaced by the more modern faster electronic dobby. The harness selection in the electronic dobby is achieved by electronic pattern cards stored in the controller of the shedding system. The weave patterns are created on a CAD system and transferred to the shedding system. Several transfer options are available such as the interface of the CAD and the weaving machine, floppy disc, or recently USB (Universal Serial Bus, known as the memory stick). The harness selection is transferred to an electromagnet dedicated to each harness, which attracts or repels a hook that is connected to it. The principle of the electronic dobby is similar to the electronic Jacquard, which is detailed in the next section.
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10.1.3 Jacquard shedding system The Jacquard shedding system is capable of producing large intricate weave designs. Here, the harnesses are replaced by harness cords, which are connected to hooks from the top and heddle wires from the bottom. Each warp yarn is threaded in the eye of a heddle wire. Figures 10.6 and 10.7 illustrate simple diagrams to show how the selection of hooks/warp yarns (which hook is to be raised and which hooks to be lowered) is achieved in mechanical and electronic Jacquard respectively.
10.6 Mechanical Jacquard.
10.2
Jacquard construction
A Jacquard machine is constructed of three main parts: (a) the engine, (b) the harness tie, and (c) the Jacquard engine drive that is connected to the weaving machine main drive, to provide motion for the different parts of the Jacquard engine.
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10.7 Electronic Jacquard (Staubli Corporation). Notes: a = pulleys b & c = hooks d & e = retaining hooks f & g = knives h = electromagnet i = harness cord
10.2.1 Mechanical Jacquard In mechanical Jacquard, the essential parts of the engine that work in harmony to select hooks are the cylinder, pattern cards, needles, springs, and knives (Fig. 10.6). The cylinder is a perforated square prism with a number of holes on each side equal to the number of needles. The centreline of each hole coincides with the centreline of a needle. Each needle is in contact with a spring. The pattern cards are made of cardboard and formed into an endless chain. One pattern card
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corresponds to the formation of one weft yarn in the Jacquard weave repeat. The needles and hooks are arranged in short and long rows. A pattern card has locations that are also arranged in short and long rows, with each location dedicated to a needle or hook since each hook resides in the bent of a needle. Location in the pattern cards is punched or left unpunched, depending whether the corresponding hook (or warp yarn(s)) is to be raised or lowered respectively according to the weave design. After a weft yarn is woven, the cylinder moves away from the needles (left in Fig. 10.6), turns a quarter revolution (clockwise in Fig. 10.6), then moves toward the needles and press against them. Figure 10.6, for clarity, shows only two needles and their corresponding hooks with a needle facing a punched hole in the active pattern card and the other facing no hole. The first needle stays in place, while the other needle is pushed to the right. The hook of the first needle is now against the knife and the hook of the second needle is pushed away from the knife. The knives are given upward and downward motions per cycle. Thus the hooks with holes in the pattern card will be raised and the other hooks will stay down to form the shed and insert the weft through the shed to form the weave design. The cylinder motions are repeated for each weft yarn. When all cards have gone through the active position (one revolution of the chained pattern cards), one weave repeat is formed. Mechanical Jacquard systems have numerous mechanical parts and motions that hinder the weaving speed, which did not allow them to work with high-speed shuttleless weaving systems. The electronic Jacquard was developed for this reason. In a Jacquard shedding system, each hook is connected to a harness cord (in the case of individual control of warp yarns, i.e. each hook controls one harness cord, which in turn controls one warp yarn) or a neck cord (in this case, each hook controls several harness cords/warp yarns). Each harness cord passes through a hole in the comber board that maintains the harness cords in position. The bottom end of the harness cord is connected to a heddle wire, which in turn is connected from its bottom to a spring or elastomer. Each warp yarn is threaded through an eye of a heddle wire. The function of the spring is to return the hook and its corresponding harness cord and warp yarn to the bottom shed if the warp end is required to be lowered after it was raised up. Earlier Jacquard systems used small weights (or lingoes) attached to the end of the harness cord, rather than a spring, to return raised warp ends/hooks to the bottom shed. The use of lingoes was stopped owing to the time taken to return a warp yarn to the bottom shed since the lingoes are under free fall. High-speed weaving requires much a faster return of raised warp yarns to the bottom shed, which can be realized by the use of spring or elastomer.
10.2.2 Electronic Jacquard In the electronic Jacquard system, the pattern cards are in an electronic file stored digitally in a computer and known as a punch file. Thus physical pattern cards, the
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cylinder and the needles are eliminated. Figure 10.7 shows the main parts of the electronic Jacquard. Only a group of parts that control a harness cord (i) is shown for clarity. These are pulleys (a), hooks (b & c), retaining hooks (d & e), knives (f & g), and an electromagnet (h). The figure shows how the harness cord (i) is selected to be raised or lowered. Figure 10.7, position 1 indicates the electromagnet (h) is activated and the top part of the retaining hook (d) is attracted to the magnet. Since the retaining hook (d) is fixed in its middle and allowed to rotate around its centre, its bottom moves to the right and does not engage to the hook (b). Thus hooks (a & b) will remain in contact with the knives (f & g) and the pulleys (a) and the harness cord (i) remain in their down position as seen from position 2. Positions 3 and 4 indicate how the harness cord is raised by not activating the electromagnet (h). The retaining hook (e) engages with hook (c), knife (f) raises hook (b), which causes the pulleys (a) and the harness cord (i) to rise.
10.2.3 Conversion of mechanical Jacquard to electronic needle/hook selection Even though electronic Jacquard systems are on the rise, there are still many mechanical Jacquard machines in companies around the world. Machine manufacturers saw the opportunity of developing systems that converted mechanical Jacquard to electronic Jacquard systems. Figure 10.8 shows one of such conversion system. The conversion system replaces the cylinder and the pattern cards of Fig. 10.6. It consists of electronically activated small parts (needle selectors). Each needle selector coincides with a needle and has a dent to accommodate the needle end. Like an electronic Jacquard system, the needle selectors are activated by an
10.8 Electronic needle selector for converting a mechanical Jacquard to an electronic Jacquard machine.
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electronic punch file. If a needle selector is activated, it moves toward the needle and pushes it along with the corresponding hook and this will cause the hook to stay down (since it misses the knife) along with the warp yarn(s) connected to it. Needle and hooks that are not selected by the needle selectors are kept stationary and the hooks are raised since they are against the knives.
10.2.4 Jacquard size The Jacquard size, capacity, or power is defined as maximum number of hooks in the Jacquard machine. There are two common standards, known as British, which is coarse gauge, and Continental, which is fine gauge. The British standard Jacquard size range is 100 to 900 (or 104 to 924 kooks) as shown in Table 10.1. In the British system the size is lower than the total number of hooks. For example in machine size 100 there are four extra hooks (or one short row) and in machine size 900 there are 24 extra hooks (or two short rows). The extra rows are provided for selvage motions, harnesses for formation of ground weave, and/or filling selection motions. Table 10.2 shows the standard sizes of continental Jacquard. The size range is 448 to 1792. The size and total number of hooks are identical in the continental standard. These sizes allow the weaving of large weave designs made of fine-warp yarns. Table 10.1 Standard British Jacquard sizes (coarse gauge) Size, capacity, or power
Number of hooks/ long row
Number of hooks/ short row
Total number of hooks
100 200 300 400 500 600 900
26 26 38 51 51 51 77
4 8 8 8 10 12 12
104 208 304 408 510 612 924
Table 10.2 Standard Continental Jacquard sizes (fine gauge) Size, capacity, or power
Number of hooks/ long row
Number of hooks/ short row
Total number of hooks
448 896 1344 1792
16 16 16 16
28 56 84 112
448 896 1344 1792
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Recently, larger sizes of Jacquard machines were developed for the production of extremely large patterns. Numerous machines were developed to produce one large weave design repeat across the entire fabric width. Such Jacquard machines require to be extremely large and to possess individual control of warp yarns (i.e. the total number of warp yarns equals the number of hooks). Examples of Jacquard sizes produced by Staubli for example are 1408, 2688, 3,072, 4096, 5120, 6144, 8192, 10 240, 12 288, 14 336 and 18 432 hooks. If required, two or more Jacquard machines may be placed side by side to obtain the required number of hooks for large weave designs. For example two size 12 288 Jacquard machines can be placed on top of a weaving machine to obtain a combined size of 24 576 hooks. These large Jacquard Machines are referred to as ‘Mega Jacquards’.
10.2.5 Jacquard harness tie and types A harness tie in Jacquard weaving refers to the arrangement of harness cords, which are connected to hooks, in the comber board. It describes how the harness cords are threaded through the holes of the comber board. A harness tie in Jacquard weaving is similar to drawing-in in cam and dobby weaving. Harness ties are classified as ordinary ties and special ties. Ordinary ties are sub-classified as straight ties and center or pointed ties. Special ties are sub-classified as mixed ties and ties for bordered fabrics. A straight harness tie is similar to a straight draw in cam and dobby weaving. It is used for a weave pattern with each warp yarn interlaced differently. Figure 10.9 shows such a weave design. It depicts an example of a straight harness tie on Jacquard with 448 hooks, which is arranged in 16 hooks/short row and 28 hooks/long row (Table 10.2). For clarity only the first and last short rows of hooks, along with their harness cords, appear in Figure 10.9; and only hook numbers 1 and 16 of the first short row and hook numbers 433 and 488 of the last short row are shown. The comber board and the weave pattern are shown at the bottom. The number of weave pattern repeats (which depends on the fabric width and repeat width) decides the number of harness cords per hook. In a straight tie, the number of weave pattern repeats equals the number of harness cords per hook. Figure 10.9 shows only two repeats and a part of the third. The figure shows that hook 1 controls warp end 1 of each weave pattern repeat and hook number 448 controls warp end number 448 of each weave repeat. Assume there are 10 weave patterns across the fabric width. This will require 10 harness cords for each hook and a total number of 4480 harness cords (or warp yarns). This calculation is required to build the Jacquard tie. A simpler method of presenting the harness tie or drawing-in of harness cords in the comber board is shown in Fig. 10.10. This figure shows one repeat of a harness tie along with the number of repeats, as commonly practised.
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10.9 Straight harness tie (Damasks pattern: courtesy of Manual Woodworkers and Weavers, Hendersonville, NC, USA).
10.10 A simple presentation of a straight harness tie.
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A centre or pointed tie is used for symmetrical weave patterns (Fig. 10.11). The advantage of a centre harness tie is the ability to produce larger patterns (double the size) compared to a straight tie. Figure 10.11 depicts a pointed harness tie on Jacquard size 448, which is the same size as the straight tie of Fig. 10.9 for the purpose of comparison. The weave pattern of Fig. 10.11 repeats on 896 ends (2 × 448). Ends number 1 and 896 weave exactly the same, as do ends 2 and 895, and so on. Harness cords 1 and 896 are connected to hook 1 and harness cords 2 and 895 are connected to hook 2, and so on. A correction must be made with pointed ties to avoid weaving two ends with the same interlacing at the centre of the pattern and at the start of new repeat. If left without correction the two yarns that weave the same way would show as a defect.
10.11 Centre or pointed harness tie (pattern courtesy of Manual Woodworkers and Weavers, Hendersonville, NC, USA).
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The top of Fig. 10.11 shows the incorrect tie and the bottom tie is shown with the correction made. The harness cords connected to hooks 1 and 448 are removed. Assume 10 repeats are woven, then the number of harness cords per hook is 20 with the exception of hook 1 and 448 with only 10 harness cords each. The total number of harness cords (or the total number of wrap ends) is 8940 (2 × 448 × 10 − 2 × 10). Mixed harness ties are used for weave design repeats with mixed symmetrical and straight parts in the pattern, such as the pattern in Fig. 10.12. The first part of the design is symmetrical and requires 160 hooks (hooks 1 to 160), the second part is repeated twice within the design and requires 160 hooks (hooks 161 to 320), the third part requires 128 hooks (hook 321 to 448). Table 10.3 shows the calculation associated with the harness tie. These calculations are needed to construct the Jacquard harness tie. Border harness ties are dedicated to woven fabrics with border. An example of a border tie is shown in Fig. 10.13. Here the entire harness tie is shown along with the bordered fabric weave design. Usually the left and right sides of the border are
10.12 Mixed harness tie (pattern courtesy of Tamer Hamouda, PhD, Fiber and Polymer Science, NC State University).
Table 10.3 Harness tie calculations of mixed tie (Fig 10.12) Hook #
Number of hooks
Number of harness cords/hooks/repeats
1–159 160 161–320 321–448
159 2 1 1 160 2 128 1 Total harness cords (warp ends)
Number of repeats
Sub-total number of harness cords
5 5 5 5
1590 5 1600 640 3835
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10.13 Border harness tie (pattern courtesy of Tamer Hamouda, PhD, Fiber and Polymer Science, NC State University).
Table 10.4 Harness tie calculations of border tie (Fig. 10.13) Hook #
Number of hooks
Number of harness cords/hook
1–224 225–448
224 224
2 4
Total harness cords (warp ends)
Sub-total number of harness cords 448 896 1344
a symmetrical pattern or they may be basic twill or satin/sateen. Many of these fabrics combine two borders with a basic weave for the outer border and the inside border is a symmetrical pattern. The Jacquard size used in the example shown in Fig. 10.13 has 448 hooks. Half the hooks (hooks 1 to 224) are dedicated to forming the border and the other half of the hooks form the ground of the fabric (hooks 225 to 448). The associated harness tie calculations are shown in Table 10.4.
10.2.6 Limitations of Jacquard harness ties The examples of harness ties in Figures 10.9 to 10.13 demonstrate the relationship between the harness tie and the weave pattern type. Each of the standard Jacquard sizes in Tables 10.1 and 10.2 provides a limited number of hooks that is usually lower than the number of total warp yarns needed to form the fabric: a matter that dictates the construction of harness tie as shown in Figures 10.9 to 10.13, in order to form fabrics with multiple repeats across the fabric width. A number of disadvantages arise from this:
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1. The harness tie, which is made from expensive high-performance cords, takes a long time to construct and is kept in the original configuration for a long time (over 15 years), and is thus limited to the formation of a fixed pattern size and its smaller multiples. For example, the harness tie of Fig. 10.10 may be used to weave a pattern repeat size of 448 ends, 224 ends, or 112 ends, etc. 2. The distance occupied by the harness tie (that is parallel to the weft direction) is constant and equals to in-loom fabric width if all hooks are active. Reducing the in-loom fabric width is possible by reducing the number of warp ends and drawing-in the ends in the middle of the harness tie, which requires use of the correct harness cords. 3. Each hook controls several harness cords of different inclination. This is the reason why the Jacquard head has to be mounted at least two meters higher than the comber board and accounts for the need of the huge structure known as the ‘gantry’. Lower heights cause drastic variation in the shed height at the centre compared to that at the selvages: a matter that requires a higher shed size to accommodate the filling insertion element at the selvages. This will lead to tension variation (with the highest tension at the centre and the lowest at the selvages) and excessive warp breaks due to this variation in tension. A geometrical analysis of the shed height distribution and the distance of the Jacquard head from the comber board are given elsewhere (Seyam 2000). 4. Another limitation arises from the rigid dimension of the comber board. The harness cord density (and hence warp yarn density) is constant. The limitation addressed in point 1 above is resolved by developing of the larger Jacquard machines, stated in Section 10.2.4. As mentioned above, Jacquard machines using up to 24 576 hooks are available. In these mega Jacquard shedding systems, the warp yarns are individually controlled and the harness tie is straight with one repeat (an example of this is the pattern in Fig. 10.16). This allows the formation of extremely large weave patterns of any type (non-symmetrical, symmetrical, mixed or bordered patterns). One large repeat or several smaller repeats across the fabric width can be formed. Assume that it is required to weave a fabric as illustrated in Fig. 10.12. According to Table 10.3, the total number of ends is 3835. A Jacquard head with straight tie and 4096 hooks can be used to produce the fabric. The extra hooks will be cast out (as idle). Of course the cost of large-capacity Jacquard machines is high but the flexibility in producing unlimited designs offsets the cost. The issue of harness cord inclination is also resolved by arranging each harness cord vertically. Theoretically, such Jacquard machines can be directly mounted on the weaving machine frame and the need for a massive gantry is eliminated. A reduction in fabric width is thereby much easier to handle since the cords are vertical (no crossing) and the harness tie is one repeat with one harness cord (or warp end) per hook.
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The warp density may be reduced by deactivating some hooks and their associated harness cords. At ITMA 1995, TIS showed a flexible comber board with a changeable width. The comber board is made of sections that can be moved to increase or reduce the width. This is achieved by mounting or removing spacers between the sections of the comber board (Fig. 10.14). It seems that this system did not make it commercially, and the industry is still employing the traditional comber board. This may be related to the complexity associated with changing the density and adjusting the height of the harness cords and the shed. Moreover, to
10.14 A variable density Jacquard harness by TIS.
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meet the width standard, the increase in density requires more hooks, and drawing-in instead of tying-in of the warp.
10.3
Converting artwork to woven Jacquard patterns
Numerous colours and colour effects can be generated using weave structures combined with coloured warp and filling yarns. For example, the perceived colour of a plain weave fabric from white warp and black weft yarns of the same yarn size and thread count is grey. If the weave changed to 2 × 1 twill the perceived colour is darker grey and if the weave changed to 7 × 1 twill the perceived colour is black. It is obvious then that these two colours could produce white, black, and many shades of grey colours. With a higher number of colours of warp and weft yarns and weave structures the possibility of generating a number of colours increases dramatically. Finer yarns, a higher thread count and suitable weaves produce a better colour mix and the fabric design that would show continuous well-blended colours even from a short distance. Intricate Jacquard woven fabrics are created by using coloured warp and/or weft yarns. The final visualized colour of each part of the design is the result of assigning weaves to different parts of the design. The creation of a Jacquard woven pattern starts from the development of artwork. The objective is to match the woven pattern to the target artwork. The artwork is then scanned and converted to an image file (a digital file) and stored in a computer with special hardware and software known as a CAD system. The CAD operator interfaces with the system through the monitor and commands in form of icons. The operator selects weaves from a weave database stored in the CAD system based on pre-woven blanket or colour gamut. Examples of a blanket with details of colours, yarns, and weaves used are published elsewhere (Mathur 2006). The CAD creates a punch file that is transferred to an electronic Jacquard machine in order to weave a sample of the fabric. A visual assessment of the woven sample is conducted by comparing the woven sample with the artwork. If the assessment reveals visual differences, the assignment of different weave(s) (which is a colour(s)) is repeated and the second sample is woven and compared to the artwork again. Several trials may be conducted before the woven sample matches the target artwork. The procedure of creating Jacquard woven patterns is depicted in Fig. 10.15, which shows that three trials were conducted to achieve a match between the woven fabric and the artwork. Before the era of CAD and electronic Jacquard shedding systems, the process of creating Jacquard woven fabrics was tedious and very long. Then, the artwork was manually transferred to a large sheet of design paper and the suitable weaves, which are selected from pre-woven blanket, were manually drawn on each part of the repeat. Pattern cards were then punched using a manually operated puncher and installed around the cylinder (Fig. 10.6). The processes of creating weaving samples and visual assessment were done as above. Depending on the size of the
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10.15 Converting artwork to a woven Jacquard pattern.
Jacquard pattern, several weeks to several months may be required to achieve the final fabric, compared to several hours when employing CAD and an electronic Jacquard machine.
10.4
Recent developments in Jacquard systems
At ITMA’s 1999 show, a new era of Jacquard weaving started with the introduction of the UNISHED by Grosse and the UNIVAL 100 by Staubli (Seyam 2000). The two machines were shown in their prototype versions. While the shed formations of these systems are achieved by completely different mechanisms, there are common features: (1) an individual actuator for each harness cord/warp yarn, (2) fewer Jacquard engine parts and (3) elimination of the gantry.
10.4.1 The UNISHED Jacquard shedding system At ITMA in 1999 Grosse showed, for the first time, their earliest version of UNISHED (termed now as UNISHED 1) as a prototype. The machine was shown again at ITMA in 2003 with little improvement (Seyam 2004). At ITMA 2007 an improved version of the machine was introduced, with the name UNISHED 2 (Seyam 2008). The machine was still in its prototype stage. Now the machine is available commercially. Figure 10.16 shows the commercial version of UNISHED 2 mounted directly on the weaving machine frame and Fig. 10.17 depicts the shed formation principle of UNISHED. The shed formation in UNISHED is achieved by buckling leaf springs. In this system, a set of leaf springs is connected to a heddle wire that controls one warp end. The leaf springs, which are controlled by an actuator, control the bottom shed by buckling downward as well as controlling the top shed by buckling upward (positive shed). The difference between
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10.16 Grosse’s UNISHED 2 mounted on the weaving machine frame (http://www.grossechina.com/En_Product/ShowProduct.aspx?ID=14).
10.17 The shed formation principle of UNISHED.
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UNSHED 1 and UNISHED 2 is in the way the leafs springs set is deformed. UNISHED 1 uses the Euler 2 mode of deformation, in which the leaf spring is hinged from both sides, while UNISHED 2 employs Euler 4 mode of deformation, in which the leaf spring is clamped from both sides. The deformation of the leaf springs in the Euler 2 mode of deformation provides a half sine wave while the Euler 4 mode of deformation causes complete sine wave. Euler 2 thus causes the ends of the leaf springs to slide past each other, a matter that causes instability between the heddle wire and the leaf springs. Euler 4 (UNISHED 2) does not cause this problem. Configuring the Jacquard head and the individual control of each heddle wire (or warp end) allow the heddles to be set vertically. The design of UNISHED permits the elimination of harness cords, magnets, hooks, pulleys, springs and the gantry. This results in lower building, air conditioning and heating costs. The Jacquard head can be mounted directly on the frame of the weaving machine, thus making Quick Style Change (QSC) possible in Jacquard weaving, since it is easy to exchange the entire Jacquard head including the heddles. The preparation of the new style can be done in the drawing-in room with the desired number of warp yarns and warp density. However, QSC requires the purchase of additional Jacquard machines, which is an expensive approach. Table 10.5 shows the comparison between UNISHED 1 and UNISHED 2, as shown at ITMA 1999, 2003 and 2007. The table indicates that by 2007 the machine improved in speed (in comparison with ITMA 1999 and 2003) as a result of shifting from Euler 2 mode to Euler 4 mode of deformation. Table 10.5 Comparison between UNISHED at different ITMA shows Item
UNISHED 1 (ITMA 1999 and 2003)
UNISHED 2 (ITMA 2007)
Weaving machine Fabric Warp yarn count Warp density Filling yarn count Pick density Width in reed, cm Speed, picks/min RFI, m/min
Dornier LWV6/J air jet Upholstery 70/2 Nm 40 ends/cm 70/2 and 32/2 Nm Variable 142 800 1136
Dornier LWV6/J air jet Hotel and table cloth 60/2 Nm 30 ends/cm 60/2 Nm 28 picks/cm 147 900–1000 1323–1470
10.4.2 The UNIVAL 100 Jacquard shedding system At ITMA 2003, UNIVAL 100 was introduced in its commercial form (Fig. 10.18). The shed formation in UNIVAL 100 is achieved by controlling each individual warp end by a stepping motor (termed as ‘Jactuator’). Figure 10.19 is an illustration
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10.18 Staubli’s UNIVAL 100 Jacquard machine (Staubli Corporation).
10.19 Shed formation in UNIVAL 100 (Seyam, Staubli Open House, Duncan, SC, USA, September 15, 2006). Left: a JACTUATOR is activated to raise a harness cord. Right: a JACTUATOR is activated to lower a harness cord.
of how the shed is formed. The stepping motor activates a small rod that is connected to a harness cord. For selection of a warp yarn to be raised in the upper shed, the harness cord is wound on the rod. For lowering the harness cord, the stepping motor reverses the direction of rotation of the rod, and the harness cord is unwrapped. The harness cord (or warp end) selection is performed electronically and hence the fabric design is achieved in the same way as any current electronic Jacquard system. The dimensions of the Jacquard head (the width of the Jacquard head and harness cords is the same as the warp width in the reed) and the control of individual warp ends by a stepping motor permits the harness cords to be set vertically. The design of UNIVAL 100 permits the elimination of hooks, knives,
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magnets, and pulleys since each harness cord or heddle is directly attached to a stepping motor. The UNIVAL 100 ran on Picanol OMNIplus-6-J 250 with the following specifications: Style: Warp yarn material: Warp yarn count: Warp density: Filling yarn material: Filling yarn count: Pick density: Width in reed: Speed: RFI: Total number of ends:
Mattress ticking and table cloth (pattern changes on the fly) Polyester/cotton 50/2 Nm 33 ends/cm Polyester/cotton + nylon 50/2 Nm+ 2100 dtex 25–28 picks/cm 2.4 m 1025 picks/min 2460 m/min 7920 (7920 stepping motors).
The specifications above are much different from the specifications of ITMA 1999. The rate of filling insertion in the above specifications is the highest rate of filling insertion in Jacquard weaving history and the highest at ITMA 2003 compared to any other shedding motions demonstrated. With this technology, weavers can manufacture intricate Jacquard designs at the speed of commodity fabrics (Seyam 2004). The UNIVAL design provides the weavers with new opportunities that have never been available before in Jacquard shedding. With such a system, the shed height can be easily set, and several sheds can be formed if so desired that allow the weaving of face-to-face pile fabrics and threedimensional structures. All settings can be conducted electronically through a user interface without the need of mechanical adjustments. Another significant feature of the UNIVAL 100 is its independence from the weaving machine drive, since it has its own drive without mechanical coupling to the weaving machine. The UNIVAL 100 modular construction enables a Jacquard capacity range of 5120 to 20 480 warp threads (stepping motors). At ITMA 2007, Staubli expanded the concept of UNIVAL 100 to UNIVAL 200 and 500 shedding systems for narrow Jacquard and dobby shedding systems respectively (Seyam 2008). The UNIVAL 200 system was shown in label weaving. The same actuator (with different power and size) of UNIVAL 100 is used. The actuation is not limited to the control of the shedding motion but also controls the main motions of the machine. The actuators are used to control: (1) weft tension with individual control for each weft yarn that can be pre-programmed digitally, (2) weft feed rate, (3) warp tension, (4) cloth take-up rate, (5) the latch needle for securing the filling yarn, and (6) filling selection (up to eight colours). The principle of shed formation in UNIVAL 200 is shown in Fig. 10.20. Each warp yarn is controlled by an actuator and a toothed rack (the yarn is threaded
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10.20 The principle of shed formation in the UNIVAL 200 Jacquard shedding system.
through an eye at the top end of the toothed rack). The selection of warp yarns (to be raised or lowered) depends on the rotational direction of the gear connected to the actuator as shown in Fig. 10.20. The gear is turned a certain angle in a counter-clockwise direction to raise its associated warp end. It is turned a certain angle in a clockwise direction to lower the warp end. This is a positive shedding system, since the lower and upper sheds are controlled by the actuation and no returning springs are used. The UNVAL 200 system can be extended to weave wide Jacquard fabric using any insertion system. Obviously, such a system eliminates gantry, comber board, pulleys, magnets, springs, and harness cords.
10.4.3 Jakob Muller MDLA Jacquard shedding system At ITMA 2003, Jakob Muller showed the MDLA that is equipped with a new Jacquard shedding system. The machine was weaving labels using a needle weft insertion system (Seyam 2004). At ITMA 2007, the MDLA was shown weaving fabric for labels using air-jet weft insertion (Seyam 2008). The new Jacquard shedding system allows the elimination of gantry, pulleys, harness cords, and comber board. In this system each warp yarn is individually controlled by a special heddle and retaining hook (Fig. 10.21). The heddle and the hook elements are shown disassembled in Fig. 10.21(a). The heddle element is a hollow structure to accommodate the hook element inside. Figures 10.21(b) and 10.21(c) show how the warp yarn (circle) is positioned
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10.21 Heddle and hook elements: (a) elements disassembled; (b) hook element holds warp yarn in the bottom shed; (c) warp yarn in upper shed.
in the upper or lower shed. The shed formation is achieved by a roller that moves down and up every weaving cycle. The initial warp sheet position is in the upper shed, and the bottom shed is formed when the roller pushes the warp sheet down and a selection is made of warp yarns for the lower shed. The selected warp yarns are retained at the lower shed by the hook elements. Figure 10.21(c) shows the heddle element in its upper position due to magnet activation and as a result the hook is not obstructing the warp end, which moves up with the roller. If the magnet is not activated, the heddle is kept down by a spring and thus the hook retains the corresponding warp at the bottom shed. The machine produced multiple labels with the following specifications: • • • • • • • • •
Machine type: MDLA 1/1150 Fabric: Label Width-in-reed: 1150 mm Total ends: 5836 (Capacity 6144 ends or hooks) Warp: PES 100 dtex, 600 t/m Ground weft: PES textured 110 dtex Pattern weft: PES textured 50 & 110 dtex Speed: 1250 PPM Filling insertion type: air jet
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While the MDLA machine was shown weaving fabric 1.15 meters wide for labels using an air-filling insertion system, this new Jacquard shedding system is capable of weaving any type of Jacquard fabric using any type of filling insertion system.
10.5
Patterns in Jacquard woven fabrics
10.5.1 Damask Damask fabric end-uses include women’s dresses, intimate apparel, table linen, bed linen, curtains and hangings. Damask Jacquard fabrics feature figured designs (flowers, fruit, animals and other figures). The figured design is usually constructed from warp satin (satin) weave (warp dominates the fabric surface) while the ground is usually constructed from weft satin (sateen) weave. The fabric may be printed using heat transfer or digital printing. Printing patterns over the weave pattern provides endless pleasant effects. Other types of weaves may be employed. Figure 10.22 shows a piece of damask design woven on five-harness (or five-thread) satin on five-harness sateen ground. The warp yarns may be flat, continuous, bright or semi-bright polyester or silk to promote brightness as a result of light reflection in one direction. The weft yarn may be spun or highly twisted filament polyester, rayon, or silk yarn to provide a dull background. The
10.22 Piece of reversible damask Jacquard design with satin weave for the figure and sateen weave for the ground.
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reverse side of the fabric could be the desired side with dull a figure and bright background. Done like this, the fabric is known as reversible damask. One-sided or irreversible damask is produced by developing a warp weave figure on sateen ground. The yarns may be left with their natural colour or dyed with a single colour. Two-colour damasks fabrics may be produced, with one colour for the warp yarns and the other colour for the weft yarns. More than two colours in damask designs are now common. Figure 10.23 is an example of damask fabric in polyester/rayon. The warp is dressed in black while the weft is dressed in different colours to provide colour effects in the weft weave areas.
10.23 Damask pattern (pattern courtesy of Valdese Weavers, Valdese, NC, USA).
10.5.2 Brocade and brocatelle Brocade fabrics are woven with elaborate designs and are characterized by their raised figures. The raised figures are produced by using extra weft yarns on ground fabric woven from warp and weft yarns. The extra weft yarns are raised as a result
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10.24 Piece of brocade Jacquard design with extra weft figure on plain weave ground.
of using figures with long floats. These fabrics resemble embroidered fabric without the need for an additional embroidery machine or labour. Figure 10.24 shows a piece of brocade fabric from extra weft figure on a plain weave ground. Satin weaves are commonly used for ground. The ground is tightly woven, while the figure is a loose weave because of the long floats. The extra weft yarns are kept floating in the back of the fabric and may be left or clipped. If the extra weft is cut, interlacing the weft yarns with the warp around the figure is necessary to prevent fraying. If the extra weft yarns left unclipped, it is necessary to lightly interlace them so that they are properly integrated in the structure to prevent their snagging and being pulled out of the structure. Brocade fabrics are woven from cotton, nylon, rayon, silk and their blends. Gold or silver yarns may be also used. Brocade fabrics are used for luxurious dresses, garments, upholstery and drapes. Figure 10.25 shows an example of brocade fabric woven from polyester/rayon. The warp is beige-coloured yarn and the weft dressed in several colours. One colour (grey) is woven with warp to provide the background. The other colours (white, two shades of gold and two shades of brown) are extra wefts to provide a raised intricate design.
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10.25 Brocade Jacquard design (pattern courtesy of Valdese Weavers, Valdese, NC, USA).
Brocatelle fabrics are similar to brocade in materials and end uses. The figure in brocatelle fabrics is, however, formed from extra warp yarns.
10.5.3 Matelasse fabrics This class of fabric gives the appearance of a quilted surface or padded effect. It is used for drapery, dresses, vests, table linens and upholstery. The quilted surface effect is produced by weaving a shape using multi-layer weaves (two to four layers) surrounded by stitches at the interchange from the shape to the ground. The differential shrinkage between the loose weave of the shape compared to the ground causes the shape to pucker or bulge in the fabric thickness direction. Figure 10.26 shows an example of matelasse Jacquard design with solid colour.
10.5.4 Tapestry fabrics Tapestry is a class of patterned woven fabric that is closely woven. Tapestrypattern fabrics can be produced employing numerous methods ranging from one
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10.26 Matelasse design (pattern is courtesy of Valdese Weavers, Valdese, NC, USA).
warp yarn and one weft yarn to several coloured warp and weft yarns (Watson 1947; Mathur 2006). The figure in the pattern can be produced mainly from weft yarn(s) using weft weaves, warp yarn(s) using warp weaves, and/or a combination of both. For example if one warp yarn (say black) and one weft yarn (say white) are used, a white figure can be produced on black ground with weft weave (such as 1 × 7 twill, eight-harness sateen, etc.) for the figure and warp weave (such as 7 × 1 twill, eight-harness satin, etc) for the ground. Intricate patterns with shading effects could be produced if the warp and weft yarns are combined in the shaded areas in different proportions. It is also obvious that a black figure on a white ground could be obtained. Figures with more striking colour effects could be produced with more than one colour in the warp and/or weft. Several coloured weft yarns could contribute to forming the figure on a one-colour warp for ground. Here the figure is formed using weft weaves of several colours with the warp lightly interlacing the weft floats, while the ground is structured from warp weave with weft yarns lightly interlacing the warp float. The warp colour could also be used as an additional colour in the figure, which provides the opportunity for more colours in the figure
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10.27 Tapestry Jacquard design from coloured warp and weft yarns (pattern courtesy of Valdese Weavers, Valdese, NC, USA).
through a solid-colour effect from the warp or colour mixing with the weft colours. Figure 10.27 depicts an example of tapestry fabric from coloured warp and filling yarns. Over 200 distinct colours can be obtained using four colours for warp yarns (one green, one yellow, one red, and one blue) and two colours for weft yarns (one white and one black). Tapestry weaves could be produced from weft colours, warp colours, warp and weft colours (no mixing), and/or mixed warp and weft colours. Examples of these are provided in Mathur (2006). Tapestry weaves with solid colour effects in the figure could be formed by a warp and weft arrangement of the same colours. For example, warp and weft could be dressed in one red followed by one blue. Double cloth weave could create a figure of solid red and solid blue on a mixture of blue/red (purple) ground of a single-layer weave. Other combinations are obvious. This approach could be expanded for three colours and four colours employing three-layer and four-layer weaves respectively.
10.6
Applications of Jacquard woven fabrics
There are broad types of applications of Jacquard woven fabrics. Today, these fabrics are used in intricate striking designs for upholstery, draperies, table covers,
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wall décor, decorative fabrics, terry, and carpets. Additional recent applications include technical textiles (seamless airbags) and seamless shaped products. Traditionally, textile products with a desired shape and dimensions were obtained by cutting pieces of a pattern from flat fabric and sewing them together to obtain the target product. There are a number of adverse consequences from cutting and sewing (Anderson and Seyam, 2004) that include: (1) the process of cutting and sewing is the most labour-intensive step in forming a product, (2) the sewing process can also create needle holes in the fabric as well as damaging the fibre within the yarn (the presence of needle holes and damaged fibres could adversely affect the strength and performance of the fabric), (3) there is a concentration of stress where the seams are located, which jeopardizes the performance properties and ultimately results in premature product failure, (4) seams in a product can create bulkiness, which may cause discomfort to the user and (5) cutting and sewing are done manually, which introduces the potential for human error. Several methods have been proposed to produce seamless shaped fabrics. It has been demonstrated through extensive research that seamless shaped products can be produced using double cloth and strategically placed filling yarns with different shrinkage, different weaves and different pick density to obtain differential shrinkage in different parts of the fabric so as to produce the shape. The double cloth provides the cavity for the body enclosure. Products can be created using a weaving machine with a dobby shedding system (Anderson and Seyam 2004). This technique could be combined with other techniques that require Jacquard weaving to produce specific effects. In October 1995, Technical Textiles International reported on a new weaving process developed by Alexander Busgen (Anonymous 1995). The author describes a weaving process in which three-dimensional (3D) shapes are produced directly from the loom. The process can be used to create and produce any 3D shell (or dome) shape (Fig. 10.28).
10.28 Dome shape.
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A variety of different shell geometries can be produced. The shapes are intended for a number of potential applications, including automotive interiors, sporting goods or medical and filtration products. A computer-controlled Jacquard weaving machine is used. The weaving machine is equipped with shaping devices that are fitted to the loom. The fitting devices control the length of the weft and warp yarn, since shaping requires different lengths of warp and weft yarns. In US patent #5 707 711 (Kitamura et al. 1998), a method for producing a seamless shaped air bag is detailed. A variety of weaves have been used including plain, twill and satin weaves. As usual for this application, polyester or polyamide yarns can be used to construct the bag. The air bag is created using a combination of connected and unconnected double woven constructions. In Fig. 10.29, B2 is two-layer unstitched weave, B1 is one-layer weave, and A is a one-layer weave as a transition from a repeat to the next. This structure can only be woven using a weaving machine equipped with a Jacquard shedding system. In their paper titled ‘Integrated design of seamless fashion in woven textile with multilayer’, Ng et al. (2007) documented how the concept of using multi-layered woven structures can be expanded to produce fashionable apparel articles with striking Jacquard designs such as shown in Table 3 of their paper. The multi-layer weaves provide the functionality such as cavity to fit the body shape, collar, pockets, etc. The different areas of the dress may be used to exhibit Jacquard designs. The obvious challenge of such an approach is to produce zero defect articles since any defect in the dress may require discarding, selling the dress as second-best quality, or involving an expensive manual repair. Other issues include finishing after weaving to improve hand, acceptance of wearers in the way the articles are handled during put-on or take-off, etc. Despite the challenges that face this approach, the potential of its advancement do exist and its success depends to a great extent on further research and development, and intimate collaboration between Jacquard and apparel designers as well as fabric finishers.
10.29 Seamless woven air bag (Kitamura et al. 1998).
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Relationship between structures and properties of Jacquard woven fabrics
While Jacquard fabrics exhibit pleasant attractive aesthetic effects, they must meet performance properties and comfort characteristics that are required based on their end use. The structural parameters that determine the performance properties and comfort of a woven fabric include warp and weft fibre types and fibre blend, warp and weft yarn types determined by spinning method, warp and weft yarn sizes, warp and weft thread densities, weave, and finishing (such as antibacterial, flame retardant, stain resistance, etc.). Perhaps the most common performance properties of Jacquard woven fabrics include abrasion resistance, drape, pilling resistance, tensile and tear strength, flame resistance, colourfastness, UV resistance (for outdoor use), stain resistance, and resistance to bacteria. When several performance properties are required the correct blend of key structural parameters must be revealed to achieve the target levels of the relevant properties. The public domain includes over 100 years of published work that deals with the relationship between the structural parameters of woven fabrics and their physical and mechanical properties. In regards to weaving, most of the research dealt with the influence of basic weaves (plain, twill, basket, and satin weaves) on fabric properties. Jacquard designers are faced with the challenge that Jacquard woven fabrics are structured from several basic weaves, which may be simple (such as reversible damask of Fig. 10.22) or complex (such as Tapestry designs), and must make use of the published research to interpret and predict how such mixed weaves impact the properties of interest. While the effect of other structural parameters on Jacquard fabric properties may not pose the same degree of challenge as weave structure does, the effect of their interaction with the weave must be understood to help with designing fabrics that will meet performance requirements. Below are some examples of weave/property relationships.
10.7.1 Weave/tear resistance relationship It has been established by Taylor (1959) and Scelzo et al. (1994) that tongue tear strength is influenced by the weave. The tear strength increases with the weave float length, which means that plain weave exhibits the lowest tear strength. The reason behind this behaviour is the fact that in the plain weave structure each yarn is woven individually. When the fabric experiences tear force, each yarn breaks individually with minimum or no share from neighbouring yarns. On the contrary, weaves with two or more threads per float (such as 2 × 2 basket, 3 × 3 basket, 2 × 2 twill, etc.) there are two or more yarns that resist the tear load and hence such a structure provides higher tear resistance than a plain weave. If a plain weave is desired in a woven structure and tear strength is a key property, the designer should consider one or more of the following solutions:
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1. Using a rip-stop weave (Fig. 10.5(c)) 2. Inserting a stronger yarn (from fibres such as nylon, polyester, Kevlar, etc.) at intervals 3. Constructing the fabric from blended yarn with one or more strong fibres 4. Finishing the fabric with lubricant to ease the yarn mobility, which will encourage load sharing by neighbouring yarns 5. Using a different yarn type (for example, compact spun yarn is stronger than traditional ring-spun yarn, which is in turn is stronger than open-end yarn). See Mohamed and Lord (1973). 6. Reducing crossed thread density to provide mobility in yarns being torn.
10.7.2 Weave/tensile strength relationship The weave affects the tensile strength in an opposite way to tear resistance. A plain weave shows higher tensile strength than any other weave and as the float length increases the fabric tensile strength gets lower. Taylor (1959) and Mohamed and Lord (1973) related the trend to the so-called fabric assistance (defined as the ratio of the yarn’s strength in the fabric to its strength in the free state). In the free state spun yarns’ breaking strength is the result of fibre breakage and fibre slippage. The yarn in the weave is supported by the weave intersections and a weave with more intersections provides more support to yarns subjected to the tensile force owing to frictional forces at the crossover points. Since plain weave has the highest number of weave intersections, it shows the highest tensile strength. Numerous Jacquard fabrics are constructed with weaves that have a long float. If high tensile strength is required, one or more of the following may be considered: 1. Increasing thread density to increase the number of weave intersections per unit length 2. Constructing the fabric from blended yarns with one or more strong fibre 3. Using a stronger type of yarn. It is obvious from the above that fabrics with good tear resistance and tensile strength could be designed if so desired by selecting structure parameters that support both requirements. This approach could also be applied to achieve other properties.
10.7.3 Weave/abrasion resistance relationship Woven fabric abrasion resistance depends on the true geometrical area of contact between the fabric surface and the abrader. For a given force between the fabric and abrader, less contact area causes a high stress concentration and leads to a reduction in fabric abrasion resistance determined by the number of cycles that will rapture the fabric. Factors that cause an increase in the area of contact lead to high abrasion resistance. Plain weaves with an unbalanced crimp (a higher warp
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than weft crimp) causes the warp yarn crown to protrude out of the fabric surface and thus the abrader only has contact with the warp yarns at the top of the crimp crown. A balanced plain weave with equal crimp and yarn size provides more contact area with the abrader, and exhibits improved abrasion resistance. Plain weave with yarns of round cross-sections (high-twist yarns) provides less contact area compared to yarns of flattened cross-sections. Industry practises calendaring of woven fabric to deliberately increase yarn flattening, surface area, and hence abrasion resistance. Increase in fabric sett (or cover factor) and/or yarn size cause an increase in contact area and fabric thickness leading to improved abrasion resistance, provided that the balance of warp and weft crimp is not compromised. A weave with reasonable float length (other than plain) could improve abrasion resistance (Backer and Tanenhaus 1951; Seyam and El-Sheikh 1995). However, too long a float may cause snagging and in fact lead to reduction in abrasion resistance and negatively impact fabric appearance.
10.8
Future trends in Jacquard woven fabrics
This section covers topics that are believed to be within reach using Jacquard weaving, and sheds light on challenging questions that need to be answered in order to further the technology to new interesting markets.
10.8.1 Electronic smart structures Electrotextiles is a fast growing research and development area due to its potential for producing smart fabrics that can sense, response, and adjust to stimuli. Thermal clothing to protect from cold weather, musical jackets, and flexible foldable computer keyboards are some products that are commercially available (Seyam 2003). Their research and development targets civilian and military applications such as woven antennas, acoustic array that identifies sources of sound such as gun shots, enemy vehicles, etc., the formation of transistors on flexible substrates (thin ribbon yarns), yarn batteries, and flexible and conformable solar cells that can harvest and provide electric power to electrotextiles (Grant et al. 2004; Dhawan et al., 2004; Seyam 2003). Jacquard weaving is the most potential technology for producing electronic textiles. In Jacquard weaving, every warp yarn and weft yarn (and hence every crossover point of warp/weft) location is known during weaving, a matter that provides opportunities for producing woven circuit and electrotextiles at high speed. Traditional rigid printed circuit boards (which are structured with wiring layers separated by insulating layers with vias connecting power, ground lines and wiring of different layers to process/transfer signals) are fabricated by photolithography, which is a slow process that can be potentially replaced with flexible stitched multi-layered woven fabric structures (Fig. 10.30). The stitches in such fabrics constitute the vias.
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10.30 Stitched multi-layered woven structure with stitches as vias.
Forming woven circuits requires interconnecting (welding) and cutting orthogonal yarns at selected crossover points. As stated above, in Jacquard weaving the location of crossover points is known while weaving. Welding devices and cutters guided by small robotic arms would provide an automated solution for forming such woven circuits. The electronic industry is using similar systems to build integrated circuits that could be modified to fit Jacquard weaving. It is realized that the constituents of electrowoven structures are traditional textile yarns, conducting metallic and potentially battery yarns, solar cell yarns, and yarns with built-in electronic devices. These yarns are expected to possess different properties. Moreover, yarns with devices may be in ribbon form and yarn orientation is necessary. In such cases, twisting of ribbon yarns must be avoided during weaving. Recent advances in weaving technology may meet some of these challenges. Variable speed weaving is an essential requirement for handling different filling yarns. Filling selection mechanisms for up to 16 colours are now available, providing the versatility that is required for electrowoven fabrics. Eletroweaving is expected to require modification of existing filling yarn feeders. The same is true for electronic warp yarns; feeding such yarns from a creel or separate warp beam is required. Owing to their versatility, it is expected that Jacquard electrotextile products will find their way to new markets such as healthcare, entertainment, safety, homeland security, computation, communication, protective clothing, energy harvesting from giant areas of fabric such as tensioned structures, wearable electronics, etc.
10.8.2 Automatic selection of weave/colour In Section 10.3, the current practice of converting artwork to woven Jacquard patterns using a CAD system was explained. It is indicated that the process of weave/colour selection for each area of a Jacquard pattern requires the intervention of the CAD system operator/designer, who works from a colour gamut. Several trials may be conducted before the woven sample matches the target artwork.
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Relying on the CAD operator/designer’s subjective assessment, multiple weaving trials may be needed to produce a fabric that matches the target artwork or sample. There is no automated colour methodology yet available to assist designers in developing fabrics without the need of producing samples. Therefore, Jacquard fabric producers need an automated process to assist with colour generation and selection of weaves without the need for human intervention. Mathur (2006) reviewed attempts to predict colour attributes from weave and yarn colours and pointed to their limitations. Recently Seyam and Mathur (2008) and Mathur et al. (2008) developed a general geometric model combined with sound existing colour-mixing equations and verified the model experimentally. The model predicts the contribution of each colour component present on the surface of the fabric structure in terms of warp and pick densities, warp and filling yarn sizes, weave, size of the colour repeat of warp and filling yarns, and number of yarns of different colours. Such geometrical modelling, combined with sound existing colour-mixing equations, paves the road for automating the process of weaves and colour selection and could dramatically reduce the production cycle. With the increase in demand for short-cycle and small orders, combined with the increasing cost of labour, it is expected that such automation will be incorporated in CAD systems in the near future.
10.8.3 Automatic repair of warp breaks Today’s weaving machines are highly automated. They are equipped with devices to stop automatically when the warp yarn or the weft yarn breaks, repair weft yarn automatically, pre-program coloured weft yarns and the insertion speed for each weft yarn, etc. Automatic repairs of warp yarn breaks constitute a challenging problem, involving locating the break, picking the broken ends and joining and threading them through machine parts (the heddle eye and reed dent). Recently, Lee et al. (2007) developed a Micro-Electro-Mechanical or MEMS-based system to detect warp breaks. MEMS accelerometers were mounted on the harness cords of a Jacquard machine. The difference in the signals of an accelerometer in the presence or absence (in case of a break) of the associated warp yarn is significant and thus a warp break could be detected. Since the harness cord address is known, the Jacquard head could be programmed to identify the warp location to the weaver. Identifying the location of broken yarns reduces repair time and hence increases productivity. Lee et al. (2007) indicated that the warp break repair could potentially be automated using the Jacquard head combined with small robotic devices.
10.8.4 Flexible comber board (variable warp density) The limitations of Jacquard shedding systems and solutions to overcome them were discussed in Section 10.2.6. One limitation has not been met so far, which is
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varying warp density. While the TIS system (Fig. 10.14) provided a solution, it did not succeed commercially, and the industry still employs the traditional rigid dimension comber board, perhaps owing to the complexity associated with changing the density, and adjusting the height of the harness cords and shed. Thus, there is a need to develop a commercially acceptable flexible comber board to allow changes in warp density. It is not difficult to develop a flexible comber board. The challenging issue is how to design movable hooks (or an actuator or stepping motor) along with their associated harness cords to match the warp density required.
10.9
Sources of further information and advice
In recent decades, Jacquard machine producers have brought major technological advances that have allowed the weavers to fully control their machines electronically from user-friendly interfaces, to produce broad range of woven fabrics, to manufacture intricate Jacquard designs at the speed of commodity fabrics, to inspect fabrics on-loom, to use optical and laser detection of warp breaks and to reduce down-time due to higher levels of automation and quick style and warp beam changes. It is expected that better understanding of such technology will lead to their effective use in producing innovative products with attractive design, as well as high-performance textile products. Weaving industry technical personnel, researchers, fabric developers, academia, and students interested in new developments should attend machinery shows such as ITMA, ITMA ASIA, CEMATEX, etc., which are expected to bring more advances into the field. It is also recommended to read reviews and critical articles that cover the shows, which are published in trade magazines and scientific journals such as Textile World, Textiles, Textile Forum, Textile Asia, Technical Textiles International, Textile Research Journal, Journal of the Textiles Institute, etc. Patents are also a rich source of new Jacquard shedding systems and Jacquard products.
10.10 References Anderson, K. and Seyam, A. M., 2004. Developing seamless shaped woven medical products. Journal of Medical Engineering & Technology 28, May/June, pp. 110–116. Anonymous, 1995. Woven 3-D shapes directly out of the loom. Technical Textiles International, October, pp. 18–19. Backer, S. and Tanenhaus, S. J., 1951. The relationship between the structural geometry of a textile fabric and its physical properties, Part III: Textile geometry and abrasionresistance. Textile Research Journal, 21(9), pp. 635–654. Dhawan, A., Seyam, A. M., Ghosh, T. K. and Muth, J. F., 2004. Woven fabric-based electrical circuits, Part I: Evaluating interconnect methods. Textile Research Journal 74(10), pp. 913–919. Grant, E., Luthy, K. A., Muth, J. F., Mattos, L. S., Braly, J. C., Seyam, A., Ghosh T., Dhawan, A. and Natarajan, K., 2004. Developing portable acoustic arrays on a
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large-scale e-textile substrate. International Journal of Clothing Science & Technology 16(1/2), pp. 73–83. Kipp, H. W., 1989. Narrow Fabric Weaving. Switzerland: Sauerlander. Kitamura, A., 1998. Impact absorbing air bag and method for manufacturing same, US Patent #5 707 711, January 13. Lee, J. H., Seyam, A. M., Hodge, G., Oxenham, W. and Grant, E., 2007. Warp breaks detection in Jacquard weaving using MEMS: System development. Journal of the Textile Institute, 98(3), pp.275–280. Mathur, K., 2006. Color Prediction Model For Jacquard Tapestry Woven Fabrics, Ph.D. Thesis, North Carolina State University, Raleigh, NC, USA. Mathur, K., Seyam, A. M., Hinks, D. and Donaldson, A., 2008. Prediction of color attributes through geometrical modeling. Research Journal of Textile and Apparel 12(1), pp. 19–31. Mohamed, M. H. and Lord, P. R., 1973. Comparison of physical properties of fabrics woven from open-end and ring spun yarns. Textile Research Journal 43(3), pp. 154–166. Ng, F. M. C., Hu, J., Szeto, Y.-c. and Wang, X., 2007. Integrated design of seamless fashion in woven textile with multilayer. Research Journal of Textile and Apparel 11(2), pp.67–74. Scelzo, W. A., Backer, S. and Boyce, M., 1994. Mechanistic role of yarn and fabric structure in determining tear resistance of woven cloth, Part I: Understanding tongue tear. Textile Research Journal 64(5), pp. 291–304. Seyam, A. M., 2008. Weaving and weaving preparation at ITMA 2007. Textile World January/February, pp. 42–47. Seyam, A. M., 2004. ITMA 2003: Weaving technology. Textile World February, pp. 34–39. Seyam, A. M., 2003. Electrifying opportunities: The continued development of woven fabric technology paves the way for electrotextile growth, Textile World February, pp. 30–33. Seyam, A. M., 2000. Advances in weaving and weaving preparation at ITMA 1999. Textile Progress Journal 30 (1/2), pp. 22–40. Seyam, A. M. and El-Sheikh, A., 1995. Mechanics of woven fabric, Part V: Impact of weavability limit parameters on properties of fabrics from yarns with thickness variation. Textile Research Journal, 65(1), pp. 14–25. Seyam, A. M. and Mathur, K., 2008. A general geometrical model for predicting color mixing of woven fabrics from colored warp and filling yarns, Second International Scientific Conference, Textiles of the Future. Kortrijk, Belgium, 13–15 November 2008. Taylor, H. M., 1959. Tensile strength and tear strength of cotton cloth. Journal of the Textile Institute. 50, T161–188. Watson, W., 1946. Textile Design and Colour. London: Longmans Green. Watson, W., 1947. Advanced Textile Design. London: Longmans Green.
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11 Developments in 3D nonwovens R. H. GONG, University of Manchester, UK
Abstract: This chapter provides a critical review of the developments of three-dimensional nonwovens. Two types of nonwovens are commonly referred to as three-dimensional: one with significant thickness or high bulk; and the other, shell structures with a three-dimensional contour. High-bulk nonwovens are more developed and are commercially produced for applications such as insulation products. Three-dimensional shell structures, especially those with textile characteristics, are still in the development stage. Because of difficulties in achieving a combination of good strength and softness, nonwovens have not had much success in the general apparel field. Three-dimensional shell structures are likely to be used mainly for disposable applications, lining and interlining products. Key words: three-dimensional, 3D, nonwovens, high-bulk, shaped nonwovens.
11.1
Introduction
Nonwoven fabrics are made by forming fibrous webs directly from fibres or polymer granules and then consolidating the webs. Official definitions from professional organisations such as EDANA (European Disposables and Nonwovens Association) and INDA (International Nonwovens and Disposables Association) differ from each other in some aspects, reflecting the diversity of nonwoven fabrics. According to ISO 9092:1988, a nonwoven fabric is ‘a manufactured sheet, web or batt of directionally or randomly orientated fibres, bonded by friction, and/ or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch-bonded incorporating binding yarns or filaments, or felted by wet-milling, whether or not additionally needled. The fibres may be of natural or man-made origin.’ Regardless of the precise wordings of the definition, the usual requirement of a nonwoven fabric is that it is directly made from fibres or filaments without the need of converting the fibres or filaments into yarns. The production process is distinctive from traditional weaving, knitting or braiding. The production of nonwoven fabrics typically involves two major processes: web formation and web consolidation. The main web formation methods are carding, air laying, wet laying, spun-bonding, melt-blowing and more recently electro-spinning. The main web consolidating methods are needle punching, spunlacing, chemical bonding, and thermal bonding. Although these two processes are usually sequential, they are sometimes combined into a single step. Compared with traditional fabric forming processes, mainly weaving and knitting, the production processes of nonwoven fabrics are much shorter, faster, 264 © Woodhead Publishing Limited, 2011
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and more economical. Economic advantage has been the primary driver behind the rapid development of nonwovens since the 1930s. However, modern nonwovens have become much more technically driven due to the flexibility of the processes and products. There is a large body of literature available for more in-depth discussions of the general nonwoven processes and products. These can be found readily from academic journals such as the Textile Research Journal and the Journal or the Textile Institute, as well as numerous text-books (Albrecht et al. 2003; Jirsa’k and Wadsworth 1999; Krcma 1971; Russell 2007; Turbak and Vigo 1989; Turbak 1993; Ward 1976). Nonwoven fabrics are mainly manufactured in a flat form (two dimensional or 2D). However, these flat fabrics are referred to as three-dimensional (3D) when their thickness becomes significant. This is illustrated in Fig. 11.1. In the figure, x and y indicate the flat plane while z indicates the thickness. It is difficult to define exactly how thick a fabric has to be for it to be classified as 3D. One way is to measure the thickness of the fabric relative to the fibre diameter. The thickness of a 3D nonwoven is usually several hundred times the fibre diameter. Another way of defining 3D nonwovens of this type is to consider the importance of the function of the thickness or bulk. For 3D nonwovens, the thickness is a major functional parameter. This is typified by applications such as insulation and absorption. In a more strict sense, however, 3D nonwovens are shaped shell structures, such as the one illustrated in Fig. 11.2. Nonwoven fabrics having surface features such as apertures or projections, or both, are also called shaped nonwovens. Thus, there are two distinctive types of 3D nonwovens: flat structures with high bulk and shell structures with threedimensional contours.
11.1 Three-dimensional structure of large thickness.
11.2 Three-dimensional shaped structure.
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11.2
High-bulk flat nonwovens
High-bulk three-dimensional nonwovens can achieve their three-dimensional form, i.e. large thickness, during the initial web formation or through layering multiple webs after the initial web formation. Air laying is the most widely used process for producing single-layer high-bulk nonwovens. The basic principle of the process is illustrated in Fig. 11.3. In order to form a web with homogeneous fibre composition, the fibres usually need to be fully opened and mixed prior to the air-laying process. The opening by the cylinder and any workers around the cylinder is limited and usually only serves the purpose of dispersing the fibres in the air stream. The fibres on the cylinder are taken off by the air stream, which is generated by blowing from the top and/or suction from underneath the moving condensing screen. The fibres are separated from the air by the screen to form the web. Because of air turbulence in the air stream, the fibres in the web are much more randomly orientated than in carded webs. Also, since the web density is not dependent on the amount of fibres that the cylinder can handle, as is the case for carded webs, it can be much heavier than carded webs. By the combined action of the screen movement and air turbulence, some fibres can also have some degree of orientation in the thickness direction, thus increasing the web volume and resistance to pressure. There is a limit to how thick the web can be, owing to the gradual loss of air flow with increasing web thickness. The exact limit depends on fibre length, fibre linear density, and the parameters of blowing and suction. Another method of making high-bulk webs is layering. In this case, the bulk is achieved by layering individual webs on top of each other, or folding the individual web in the thickness direction. There are three principal methods of web layering. The simplest method is parallel layering, shown in Fig. 11.4. In this case, the final web width is the same as the original web and the fibre orientation in the final web is also the same as that in the original web. In the
11.3 Air laying.
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11.4 Parallel layering.
figure, MD indicates Machine Direction, CD indicates the Cross-machine Direction. For carded webs, the fibre orientation is predominantly along the MD. Webs made in this way are much stronger in the MD than in the CD. This may or may not be a disadvantage depending on the end use. One disadvantage of this layering method is that the number of layers is limited by the number of feed webs, which usually depends on the number of web formers. However, using parallel layering it is straightforward to form multi-layered products, in which different layers have distinctive properties for fulfilling different functions in the end use. A more widely used web layering method is cross layering or cross folding. This is illustrated in Fig. 11.5. In this case, the final web is built up from a single feed web. The final web width and thickness can be easily changed by altering the cross-layering angle α. As the fibres in the feed web are mostly oriented along MD, the fibres in the final web are predominantly oriented in two directions as indicated in Fig. 11.5. The crossing of fibres from alternating layers makes the final product more stable than parallel-layered products. However, the layering angle is usually small, and the fibres are oriented more in CD than MD in the final web. The fibres can be re-orientated to some degree by stretching after layering. Both parallel layering and cross layering produce webs in which the fibres lie in the plane of the web. There is very little fibre orientation in the thickness direction, although some thickness orientation can be introduced by needle punching or stitching the web during the bonding process. In order to produce products with better bulk and compression resilience, the individual web can be folded vertically in the perpendicular direction of the web plane, as illustrated in Fig. 11.6. In this way, the significant fibre orientation will be in the thickness direction of the final web. This increases bulk and resilience against compression. The first perpendicular- or vertical-layering technology is the STRUTO Vertical Lapper developed in the Czech Republic (Jaroslav and Dalibor 1985; Krcma and Silhavy 1989; Krcma and Jaroslav 1992). There are two implementations of the
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11.5 Cross layering.
11.6 Perpendicular layering.
technology: rotating vertical lapper and reciprocating vertical lapper. These are shown in Fig. 11.7 and Fig. 11.8. In the rotating vertical lapper, the vertical fold, or pleat, is formed between the rotating folding element and the feed drum. In the reciprocating vertical lapper, the vertical fold is created by the strokes of the forming comb. The reciprocating presser bar moves the folded web along the wire guide and the conveyor belt. In order to maximise the bulk, the bonding of the web is usually carried out by through-air thermal bonding. This also means that the web must contain thermal plastic fibres or other thermal bonding agents. The feed web is commonly prepared by carding, although other types such as melt-blown webs can be used for making speciality products. The STRUTO nonwoven structure provides excellent resilience to compression deformation because of the large degree of fibre orientation in the vertical
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11.7 Rotating vertical lapper.
11.8 Reciprocating vertical lapper.
direction. The end product provides high absorption and insulation performance while remaining lightweight. The products are used in a variety of industries including transport, filtration, home furnishing, insulation and building. There are some more recent developments in the vertical lapping technology. Cooper and Roberts (2008) replaced the guide wire of the STRUDO reciprocating © Woodhead Publishing Limited, 2011
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11.9 Vertical lapper with shark plate (adapted from Cooper and Roberts 2008).
vertical lapper with a movable shark plate, shown in Fig. 11.9. This helps to keep the pleat in the vertical plane to improve the vertical orientation of the fibres. Dumas and Schaffhauser (2010) proposed another process, shown in Fig. 11.10 and Fig. 11.11, in which two-toothed rotating folding elements are used instead of the one in the STRUDO process. The angle of the two folding elements can be adjusted to make pleats at any angle and, if desired, to ensure the pleats are in a perfectly vertical direction. Composite nonwoven structures composed of two parallel layers kept at a distance can be made by the 3D Web Linker from Laroche, France. This is based on the Napco technology shown in Fig. 11.12. The two feed webs are linked by vertical fibres generated through needling. The final product is essentially a spacer fabric with a largely hollow centre between the two face webs. This can be further processed to make a variety of composites (Le Roy 1995; Poillet and Le Roy 2003). The hollow space may also be filled with other filling materials. In addition to flat high-bulk nonwovens, products with surface features such as projections and recesses are sometimes also referred to as 3D nonwovens or 2.5D © Woodhead Publishing Limited, 2011
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11.10 Rotating vertical lapper with two circular folding elements (adapted from Dumas and Schaffhauser 2010).
11.11 Rotating vertical lapper with two belt folding elements (adapted from Dumas and Schaffhauser 2010).
nonwovens. For example, Enloe (1988) described a method for forming an airlaid absorbent batt that has tailored absorbency zones, which have a higher basis weight, and are made to provide a higher absorbency than other zones. This is shown in Fig. 11.13. The areas of recess in the forming drum surface allow more fibres to be deposited during the web forming process. These recessed areas in the forming drum correspond to the high-thickness areas of the web. A very similar process was developed by Griesbach (1996) for continuous spunbond filaments. The discrete surface features on the fabric in the form of
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11.12 Nepco 3D web linking process (adapted from Le Roy 1995).
11.13 Airlaid webs with local surface projections (Enloe 1988).
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apertures or projections are designed to provide particular fluid handling, strength and abrasive and aesthetic properties in applications such as personal care, medical and cleaning products.
11.3
Shaped 3D nonwovens
Nonwovens are currently manufactured commercially as sheet materials. However, for many applications three-dimensionally shaped products, such as the simple example shown in Fig. 11.2, have to be constructed from flat material. The process typically involves the flat material being packaged and despatched by the fabric producer to a converter, who then has to unpack the fabric, lay it out, cut the appropriate panels from it, and produce the final product by sewing and/or fusing the panels together. The packaging, freight, and labour costs, and the cost of wastage inevitably generated during panel cutting, make significant contributions to production costs. The flat fabric may be moulded into a 3D shaped product. This is a well-known process and will be described only briefly here. For moulding, the fabric needs to contain thermoplastic or thermoset polymeric materials. The flat fabric is heated to a certain temperature and subjected to the pressure of two matching male and female moulds. This produces a 3D shaped product without the joints, but during the moulding process, the flat fabric undergoes variable deformation and the fibres in the fabric are subjected to uneven stretching. These can lead to variations of thickness and performance in the final product. Also, 3D products with low area density or high depth-to-width ratios are very difficult to manufacture by moulding. Shallow 3D patterns may also be produced on 2D nonwoven fabrics by embossing. This is typically for decorative purposes, not individual shaped 3D products. In order to enhance the efficiency of the process and the functionality of the products, it is desirable to produce the shaped 3D products directly from the fibres. The earliest 3D nonwoven product is arguably the felted hat, shown in Fig. 11.14. Although felts are excluded from the ISO nonwovens definition, they are nonwovens in almost every aspect. The process of making felt hats is well known. Two main steps are involved in a similar way to most nonwovens processes, i.e. web forming and web consolidation. The first step involves forming a 3D shaped web around a perforated mould. This is very similar to the air-laying process as it involves the drawing of air through the perforated mould and depositing the fibres on the mould to form the web. Once the required amount of web thickness is achieved, the 3D web is consolidated through felting in the second step. The felting results in considerable shrinking of the web, thus the initial web has to have a much larger dimension than the eventual product. In 1952, Shearer (1952) described a process similar to the felted hat process but for making bra cups from thermoplastic fibres. This is shown in Fig. 11.15. Fibres are drawn by suction onto a 3D mould to form the initial web. The web is wetted
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11.14 Felt hat.
and then bonded by heat. This process is similar in principle to modern air-laying although there are no details as to the means of fibre opening and fibre control during web formation. The heating for thermal bonding is provided by heating the mould internally but it is possible to carry out the bonding in a separate stage. Smith (1975) described a method to produce gloves directly from fibres. This is illustrated in Fig. 11.16. A foam dispersion of fibre and binder is supplied to the inside of the mould, which is porous and flexible. The fluid is drained through the mould by suction and the fibres and binder are deposited on the inside of the mould to form the glove. It is possible to use fusible bonding agents for thermal bonding after the web-forming stage. In order to prevent fibre flocculation, only relatively short fibres can be used, although the fibres may be longer than papermaking due to the foaming method. Clearly, because of the lack of fibre control, the web formed will be thinner at the top and thicker towards the bottom. In contrast to the above process by Smith, Adilieta (1987) patented a process for forming a fibre coating on the outside of a fabric glove. As shown in Fig. 11.17, the fibres are suspended in a liquid in the same way as in paper-making and, in order to prevent fibre flocculation, the suspension is agitated by a mechanical device. The suction from inside the mould causes the fibres to be deposited onto the mould surface. The process was aimed at producing a breathable
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11.15 Nonwoven bra cup production (Shearer 1952).
fibre coating to provide better protection against contamination. As the process is similar to paper-making, only very short fibres can be used. Thomas (1975) patented a machine for producing preforms for fibre-reinforced plastic articles. The objective is to form a product without the uneven joints that
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11.16 Process for making nonwoven glove (Smith 1975).
otherwise result from joining panels together. As shown in Fig. 11.18, the final product is formed on the inside of a perforated mould, which is rotated by the mould holder. Chopped fibres are blown onto the inside surface of the mould through a nozzle which moves over the inside surface of the mould. The fibres are held in position by air pressure created by a suction fan from the outside of the mould. Once the mould is covered by the desired amount of fibres, resin is sprayed onto the fibre web. This is done gradually over the whole mould surface. After the complete product is formed, the resin is cured by heated air drawn through the web. A rigid 3D shell structure suitable for moulding plastic articles is thus created without uneven seams. This process is for producing large rigid shell objects with a simple geometry. Similar processes were also described by Wiltshire (1971, 1972).
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11.17 Fibre coating of gloves (Adiletta 1987).
11.18 Fibre reinforced shaped perform (Thomas 1975).
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Miura and Hosokawa (1979) reported an experiment in making 3D nonwoven structures using an eletrochemical process. In this process, a shaped anode and a cathode are immersed in a diluted chemical binder solution containing short nylon fibres (0.8 mm in length). The fibres are deposited on the surface of the anode and then cured by heat to produce nonwoven structures in the shape of the anode. The nonwoven structures so produced are very resin-rich with a resin-to-fibre ratio of 3~4 to 1. The fibres used are only 0.8 mm in length. The short fibre length limits the application of the process as textile fibres are much longer. The fibres also tend to stand on the anode surface, similar to what happens in the flocking process described in Chapter 12, and the integrity of any nonwoven web made in this way would be very poor. Brucciani (1988) patented a process of moulding thermally bonded fibrous articles. This is shown in Fig. 11.19.
11.19 Thermally bonded shaped nonwovens (Brucciani 1988).
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An air flow containing fibres is drawn through a perforated mould so that a fibrous web is formed on the surface of the mould. The web is then consolidated in situ by drawing hot air through the mould to thermally bond the fibres in the web. In many ways this process is similar to that of Thomas, but more adapted to producing flexible textile shell structures. The lack of fibre flow control, however, makes it difficult to produce a structure with the desired fibre distribution. The alternating supply of cold and hot air through the same forming chamber also makes this process very inefficient both in terms of productivity and energy usage. A novel method of making nonwoven clothing directly from short fibres was patented by Johnson (1993). In this process, shown in Fig. 11.20, a mould in the shape of desired clothing is moved into a chamber containing a mixture of fibre and fluid. The mould has porous parts corresponding to the desired clothing shape and suction is applied though the mould. Fibres are deposited onto the porous parts of
11.20 Nonwoven clothing production (Johnson 1993).
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the mould. The mould is then moved into another chamber for bonding. This is a highly idealised process in that it is almost impossible in practice to maintain the required homogeneous mixture of fibre and fluid in a large chamber. Even for paper-making with a very short fibre length and a large water-to-fibre volume ratio, constant agitation is required to prevent fibre flocculation. For longer textile fibres, the problem becomes much more severe. In any case, nonwovens have not been widely used as the main material for apparel due primarily to the poor combination of drape, softness and strength. Since the late 1990s, a major effort has been made in the University of Manchester to develop a single-step process for manufacturing 3D shaped nonwoven products (Gong et al. 2000; Gong and Porat 2001a; Gong et al. 2003). This process, schematically shown in Fig. 11.21, is based on the air-laying principle. Staple fibres are opened by an opening unit. The opened fibres are stripped off the cylinder by high velocity airflow and are carried to perforated 3D moulds, which are located in the mould chamber. The moulds are placed on a guide track and are moved out of the mould chamber across the machine width into a bonding section for consolidation. In the web-forming section, the air-transporting system design is critical to the formation of 3D webs with the required fibre distribution. Common to all airlaying systems, the inlet of the duct, which is adjacent to the surface of the cylinder, should be narrow to provide a sufficiently high air velocity for stripping the fibres from the cylinder. The outlet of the duct is connected to the mould chamber that must be able to accommodate the moulds whose size is determined by the final product. The duct is thus divergent in the vertical direction. The geometry of the duct, especially the divergent angle, and the airflow control requirements need to be optimised in order to minimise air turbulence and fibre entanglement. Theoretical analysis using CFD modelling was reported to be a
11.21 Air-laying 3D shaped nonwoven process (Gong et al. 2003).
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valuable tool for this purpose (Gong et al. 2000; Gong and Porat 2001a; Gong et al. 2001b; Gong et al. 2003). For forming 2D webs, the angle between the fibre flow and the condensing screen is a constant. Therefore, theoretically, as long as the fibre flow in the duct and the fibre distribution in the flow are uniform, the resulting fibre web will be uniform. For 3D webs, this angle varies significantly over the 3D surface and this variation depends on the shape of the 3D web. To successfully produce a 3D textile shell structure with the correct fibre distribution, it is essential the fibre distribution be controlled positively. This can be achieved through a variety of means, such as by using air guides in the duct (Gong and Porat 2001a) and by varying the porosity of the 3D mould (Ravirala and Gong 2003). The 3D moulds may also be rotated in order to improve the evenness of the web. After forming the 3D web, an appropriate consolidation technique is required to give the structure the correct textile properties. In principle, the widely used nonwoven bonding methods such as chemical bonding, mechanical bonding and thermal bonding can all be used. The system in the University of Manchester uses thermal through-air bonding. This requires the web to contain thermoplastic bonding agents, most commonly as part of the constituent fibres of the web. After hot air is drawn through the web, the fibres in the web are bonded by the melting or partial melting of these bonding agents. Similar to the web forming section, the air flow in the bonding section needs to be controlled to achieve an even bonding. The air flow in the bonding section is more complex due to the involvement of temperature distribution and heat exchange. Although through-air thermal bonding does not achieve the high strength levels of thermal calendering owing to the low pressure on the web, limited to a maximum of one atmospheric pressure, it provides the final product with a softer finish. The final product may also be pressed by a pair of matching male–female moulds to impart further characteristics such as surface pattern. Figure 11.22 shows some example products made from the process. It is possible to produce products with complicated surface contours and with a large depth, which is difficult to achieve by moulding 2D webs. Similar to the usual air-laying process, this process is applicable to a wide range of fibres and fibre specifications. More detailed evaluation of the products from this process is reported in a series of reports (Wang and Gong 2006a; Wang and Gong 2006b; Wang et al. 2006c, Wang et al. 2007). Another interesting method for forming 3D shaped nonwovens, the Robotic Fibre Assembly and Control System (RFACS), was developed in the North Carolina State University, USA (Velu 2003; Velu et al. 2003; Velu et al. 2004). This method, shown in Figure 11.23, is based on the melt-blowing process. Melt-blowing is a well established nonwoven process. Molten polymer is extruded through the orifices of a die. High-velocity hot air blows the molten polymer out and draws the polymer flow into short fibres. Owing to the uncontrolled nature of the drawing action, the fibres tend to vary in length and thickness, but are usually in the order of a few microns. The fibres are collected on a moving screen
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11.22 Air-laid 3D shaped nonwoven products.
to form a nonwoven web. In the 3D process shown in Fig. 11.23, the melt-blowing die is mounted on a movable robotic arm. The melt-blown fibres are sprayed on a 3D mould to form a 3D shaped nonwoven product. The mould itself can also be moved to enable the production of complex-shaped products. Clearly, controlling the movements of the die and the mould is critical in achieving the desired fibre distribution in the final product. This is in some ways similar to paint spraying, but it is more difficult because the unevenness of fibre distribution is more visible than that of paint. The melt-blowing process is complex, involving numerous interacting variables and large numbers of fibres. The varying curvature of the 3D shape further adds to the complexity. The final product property will be affected by a
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11.23 Meltblown 3D nonwovens process (adapted from Velu 2003).
range of parameters including the choice of polymer, the various flow conditions, the fibre density distribution and the fibre orientation distribution (Farer et al., 2002; Farer et al., 2003; Velu et al., 2004). This technique combines fibre production and 3D product manufacture into a single process and the fibre product is composed of very fine fibres. However, the material is limited to synthetic thermoplastic fibres, the production speed is likely to be limited and the cost high because each product requires a robotically controlled melt-blowing die. More recently, Torres and Luckham (2009) developed a technique to produce nonwoven fabrics by spraying a mixture of fibres, binder and diluent from an aerosol can. This can be done under room temperature. By spraying onto a 3D shaped mould or even directly onto the human body, a 3D shaped clothing product can be made. In order to avoid blockage during spraying, the fibres are milled into very short length, less than a few hundred microns, and with an aspect ratio of less than 10. During spraying, these short fibres are bonded together to form longer fibres, which subsequently form the nonwoven fabric. In order to provide sufficient fibre bonding, the eventual fabric contains a substantial amount of binder. The binder-to-fibre ratio can be as high as 2:1. A variety of fibres or fibre blends may be used. There is currently little information available about the properties of the nonwoven fabrics formed by this spraying technique. However, it is unlikely that the fabric will have the combination of strength and softness required for normal apparel applications, given the difficulty that has hindered the development of such fabrics without the restrictions of having to spray from a can. The technique may find applications in areas such as coating a textile layer onto another surface to provide protection or texture and wound dressing.
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11.4
Future trends
Being able to produce clothing directly from fibres without the lengthy and costly spinning, fabric-making (weaving and knitting) and making-up processes is perhaps one of the main motivations in the initial development of nonwovens. Although progress in this area has been very limited, nonwovens have found widespread applications in other non-traditional clothing fields. High-bulk 3D nonwovens, both solid and spacer structures, have been successfully used commercially. In comparison, producing shaped 3D nonwoven products directly from fibres has had very little commercial success although attempts have been made since as early as the 1950s. The main difficulty is to control the fibre distribution and the end product properties reliably. Commercial viability will also need to be tested. However, the introduction of new fibre technology, the increasing demand for 3D products that do not have the unevenness of seams and joints, and the drive for greater manufacturing efficiency will motivate further research and development in producing 3D shaped nonwovens directly from fibres. It may finally lead to realising the dream to produce clothing directly from fibres quickly.
11.5
References
Adiletta, J. G. 1987, Protective handcovering, GB2186183. Albrecht, W., Fuchs, H. and Kittelmann, W. (eds) 2003, Nonwoven Fabrics, Weinheim, Cambridge: Wiley-VCH. Brucciani, R. L. 1988, Moulding thermally bonded fibrous articles, UK Patent 2204525. Cooper, J. I. and Roberts, E. 2008, Textile lapping machine, US2008155787. Dumas, J. L. and Schaffhauser, J. B. 2010, Process for the manufacture of a threedimensional nonwoven, manufacturing line for implementing this process and resulting three-dimensional, nonwoven product, US2010/0064491. Enloe, K. M. 1988, Controlled formation of light and heavy fluff zones, US4761258. European Disposables and Nonwovens Association, available at http://www.edana.org/. Farer, R., Seyam, A. M., Ghosh, T. K., Batra, S. K., Grant, E. and Lee, G. 2003, Forming shaped/molded structures by integrating of meltblowing and robotic technologies. Textile Research Journal, 73, 15–21. Farer, R., Seyam, A. M., Ghosh, T. K., Grant, E. and Batra, S. K. 2002, Meltblown structures formed by a robotic and meltblowing integrated system: Impact of process parameters on fiber orientation and diameter distribution. Textile Research Journal, 72, 1,033–1,040. Gong, R. H., Fang, C. Y. and Porat, I. 2000, Single process production of 3d nonwoven shell structures: Part 1 CFD modelling of the web forming system. International Nonwovens Journal, 9 (4), 20–24. Gong, R. H. and Porat, I. 2001a, Moulded fibre product, GB2361891. Gong, R. H., Dong, Z. and Porat, I. 2001b, Single process production of 3D nonwoven shell structures: Part 2 CFD Modelling of thermal bonding process. International Nonwovens Journal, 10 (1), 24–28. Gong, R. H., Dong, Z. and Porat, I. 2003, Novel technology for 3D nonwovens. Textile Research Journal, 73 (2), 120–123.
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Griesbach, H. L., Pike, R. D.; Gwaltney, S. W.; Levy, R. L.; Sawyer, L. H.; Shane, R. M. et al. 1996, Method for making shaped nonwoven fabric, US5575874. International Nonwovens and Disposables Association (INDA), available at http://www. inda.org/. Jaroslav, H. and Dalibor, R. 1985, Fibre layer, method of its production and equipment for application of fibre layer production method, CS235494. Jirsák, O. and Wadsworth, L. C. 1999, Nonwoven textiles, Durham, NC: Carolina Academic Press. Johnson, K. D. B. 1993, Rapid clothing manufacture, GB2265077. Krcma, R. 1971, Manual of Nonwovens, Manchester: Textile Trade Press. Krcma, R. and Jaroslav, R. 1992, Device for producing nonwovens with vertical pile arrangement, EP0516964. Krcma, R. and Silhavy, O. 1989, Method for voluminous bonded textiles production, CS263075. Le Roy, G. 1995, Method and device for producing composite laps and composites thereby obtained, US5475904. Miura, Y. and Hosokawa, J. 1979, The electrochemical process in the molding of nonwoven structures, Textile Research Journal, 49, 685–690. Poillet, P. and Le Roy, G. 2003, Needle-punched 3D nonwoven structures with technical functions, Asian Textile Journal, 6, 46–47. Ravirala, N. and Gong, R. H. 2003, Effects of mould porosity on fibre distribution in a 3D nonwoven process. Textile Research Journal, 73, No. 7, 588–592. Russell, S. J. 2007 Handbook of Nonwovens, Cambridge: Woodhead Publishing. Shearer, H. E. 1952, Bust receiving and supporting member, US2609539. Smith, M. K. 1975, Method of manufacturing non-planar non-woven fibrous articles, GB1411438. Struto International, Inc., available at http://www.struto.com/. Thomas, C. H. 1975, Apparatus for making fiber preforms, GB1380027. Torres, M. and Luckham, P. 2009, Non-woven fabric. US2009/0036014. Turbak, A. F. 1993, Nonwovens: Theory, Process, Performance, and Testing, Atlanta, GA: TAPPI Press. Turbak, A. F. and Vigo, T. L. 1989, Nonwovens: An Advanced Tutorial, Atlanta, GA: TAPPI Press. Velu, Y. 2003, 3D Structures formed by a robotic and meltblowing integrated system, PhD Thesis, North Carolina State University, Raleigh, USA. Velu, Y. K., Ghosh, T. K. and Seyam, A. M. 2003, Meltblown structures formed by a robotic and meltblowing integrated system: Impact of process parameters on the pore size. Textile Research Journal, 73, 971–979. Velu, Y. K., Seyam, A. M. and Ghosh, T. K. 2004, Meltblown structures formed by robotic and meltblowing integrated system: The influence of the curvature of collector on the structural properties of meltblown fiberwebs. International Nonwovens Journal, 13 (3), 35–42. Wang, X. Y. and Gong, R. H. 2006a, Thermally bonded nonwoven filters composed of bi-component PP/PET Fibre: I. Statistical approach for minimizing the pore size. Journal of Applied Polymer Science, 101 (4), 2,689–2,699. Wang, X. Y. and Gong, R. H. 2006b, Thermally bonded nonwoven filters prepared using bi-component PP/PET Fibre: II. Relationships between fabric area density, air permeability and pore size distribution. Journal of Applied Polymer Science, 102 (3), 2,264–2,274.
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Wang, X. Y., Gong, R. H., Dong, Z. and Porat, I. 2006c, Frictional properties of thermally bonded 3D nonwoven fabrics prepared from polypropylene/polyester bi-component staple fiber. Polymer Engineering and Science, 46 (7), 853–863. Wang, X. Y., Gong, R. H., Dong, Z. and Porat, I. 2007, abrasion resistance of thermally bonded 3D nonwoven fabrics. Wear, 262, 424–431. Ward, D. T. (ed.) 1976, Modern Nonwovens Technology, University of Manchester Institute of Science and Technology, Manchester, UK. Wiltshire, A. J., Ranallo, H.U. and Czumber, F E. 1971, Tubular fiber preforms and methods and machines for making same, US1312019. Wiltshire, A. J. 1972, Apparatus for forming fiber preforms, US3687587.
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12 Flocked fabrics and structures Y. K. KIM, University of Massachusetts Dartmouth, USA
Abstract: Flocked articles are manufactured by various flocking techniques. Fiber coating (flocking) involves applying flock fibers on uncured adhesivecoated substrate surfaces by applying an electrostatic driving force on charged flock fibers. Flock fibers are finely cut natural or manufactured synthetic fibers with electrically conductive surface finishes. Flocked materials and products are applied in numerous fields such as upholstery, toys and crafts, jewelry display backings, the clothing industry, the automotive industry, carpets and technical textiles, because of their visual, technical and economical advantages. This chapter discusses electrostatic flocking theory, flock fiber preparation, flocking adhesives, flocking processes, flocked products and market trends. Key words: electrostatic flocking, flock fiber, flocking adhesives, flocking processes, object flocking.
12.1
Introduction
Flocking techniques were first used in China around 1000 BC for decorating objects. Here, flock particles in the form of short segments of wool or silk fiber were scattered onto a resin-coated surface of these objects (Der Manouelian 2010). These fibers were randomly oriented on the resin-coated substrate surface. In fifteenth-century Germany fine natural fiber particles were sprayed onto adhesive-coated areas of a substrate for wall coverings. This technique re-emerged in the middle of the nineteenth century when the French began to produce wall coverings (Mueller 1986). Simpson et al. (1864) obtained a US patent for manufacturing flocked fabrics, which is the earliest-recorded flocking technology on fabric substrate in the US. All these early flocking techniques are simple strewing or sifting of fiber dust over the natural adhesive-coated substrates. A considerable improvement in the flocked fabric quality was achieved by introducing a mechanical flocking process that sifted the fibers onto the adhesivecoated substrate and vibrated the substrate by the action of beater bars to cause the fibers to be vertically oriented and imbedded into the adhesive layer securely. Modern electrostatic flocking processes started when King (1945) applied for a US patent for making pile fabrics. King’s patent explained that an electrostatic field force is used to propel and align the fibers along the electric field line within the flocking zone. The electrostatic field can be formed by parallel plate electrodes connected to a 40kV 25 Hz alternating current (AC) power source or direct current (DC) and pulsating DC high potential. The US Patent and Trademark Office’s (USPTO) patent database listed 238 utility patents issued or applied for with the 287 © Woodhead Publishing Limited, 2011
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key word ‘electrostatic flocking’ between 1 January 1930 and 31 May 2010. From this, it can be concluded that the flocking technology is fully developed and the flock industry has reached a mature stage. The electrostatic flocking combined with beater bar vibration enabled the production of quality flocked fabrics with a high flock density. By the end of the 1970s, applications of flocked surfaces expanded dramatically to cover upholstery, the automotive industry, apparel fabrics, floor coverings, packaging, and decorations such as greeting cards.
12.1.1 Flock, flocking and applications Flocking involves the covering of fine particles onto a wet (uncured) adhesivecoated substrate surface. Recently, flocking has been renamed as ‘fiber coating’ by the American Flock Association. Fiber coating involves applying flock fibers to uncured adhesive-coated surfaces by applying an electrostatic driving force on charged flock fibers. Flock fibers are finely cut natural (cotton, wool, etc.) or manufactured synthetic (nylon, polyester, rayon, acrylics, etc.) fibers with electrically conductive surface finishes. Three main types of applications with flock technology are: flat surfaces (rollto-roll) flocking, three-dimensional objects flocking and yarn flocking (Mueller 1997). Figure 12.1 shows the first two processes. Yarn flocking requires dual electrodes (positive and negative high-tension electrodes) to generate flock clouds, through which adhesive-coated filament yarns of suitable linear density pass to form flocked yarn structures. Flocked yarn has very similar geometry to that of a chenille yarn. All these three groups involve similar steps for manufacturing products: pretreating the substrate, adhesive coating of the substrate, the flocking procedure, drying, curing and final cleaning by vacuuming off any unattached flock particles. There are several types of flocking methods: mechanical (beater bar), electrostatic (DC or AC), electrostatic accompanied by a pneumatic process, or a
12.1 Principles of flocking processes: (a) roll-to-roll flocking and (b) 3D object flocking.
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combination of mechanical and electrostatic techniques (Kleber and Marton 1994). Presently, electrostatic flocking is the most commonly applied process in the flocking industry. In this process, for example, electrically charged flock fibers are transferred by electrostatic forces to the substrate surface and impinged into an uncured (viscous fluid) adhesive layer. In this way the electrical field forces are able to align flock fibers more or less perpendicularly to the substrate surface, thus bringing about the desired surface effects. There are three raw material components in any flocked product: the flock fibers, the flocking adhesive, and the substrate. All these components must be carefully selected to match each other so that a high-quality flocked product can be developed. Moreover, the methods of applying the adhesive and the subsequent application of the flock fibers onto the surfaces greatly influence the appearance of the finished articles. Increasingly sophisticated and unique products are being produced by incorporating newly developed flocking techniques together with modern technologies involving synthetic fibers, high-voltage electrostatic generators, and polymeric adhesives (Woodruff 1993). Flocked materials and products are applied in numerous fields such as upholstery, toys and crafts, jewelry display backing, the clothing industry, the automotive industry, carpets and technical textiles because of their visual, technical and economical advantages. A wide area of application fields results in the need for much higher requirements in flock quality. The quality of a flocked product is judged by its flock density (the number of fibers per unit area) and abrasion resistance properties. The flock industry meets the challenges by improving quality and processes in flock cutting and finishing, adhesive formulation and curing kinetics, flock dosing, application and cleaning after flocking.
12.1.2 Market trends It is very difficult to estimate the market size of flocked materials and products. This is because usage of flock fibers is strongly influenced by application sectors of the flock industry. Moreover, supply chain structures are drastically different from region to region around the world. Mueller (1994) estimated flock consumption based on personal interviews and data obtained from lectures at the International Flock Symposium in 1976 and 1978. It can be observed that there was a strong demand established in clothing, shoe material and home textiles by 1972. After peaking in 1972, there was a sharp decline in flock consumption due to the poor public reputation that flocking processes had attained because of the distribution of inferior products by a number of manufacturers. As shown in Figure 12.2, public acceptance of flocked products dipped in the 1973 to 1977 period. By 1978, these quality problems had been overcome by improvements in raw materials (fiber cutting, finish, and adhesives), manufacturing technologies and an expansion of the product spectrum to technical applications. While Western
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12.2 Flock consumption in Japan, America (USA, Canada, and Latin America) and Western Europe (Mueller 1994).
Europe and Japan were improving their flock output throughout the 1980s, America encountered a sharp decline in the mid-1980s. This time, the flocked upholstery textiles sector could not maintain the price due to overcapacity and the poor quality of products as seen earlier in the mid-1970s in a different product sector. In 1992, a global recession caused weak demand in upholsteries, automotive fabrics and profiles, blankets and other technical application areas. In 1994, worldwide flock production was estimated at approximately 50 000 metric tons, which is roughly twice that of 1978 as shown in Fig. 12.2. However, overall flocked surface areas produced are even higher, since the flock fiber weight applied per square meter is less and fiber linear density used is increasingly in the finer titers (Mueller 1994). Flock fiber consumption data in the US after 1994 is available from Fiber Organon. However the Fiber Organon listed flock fiber consumption in the ‘Fiberfill, Stuffing and Flock’ category. Thus, any reliable estimate of flock fiber production alone beyond 1994 cannot be found from this data set.
12.2
The theory of fiber coating
12.2.1 Flock motions in the flocking zone An idealized flocking process, using a DC electric field, is depicted in Fig. 12.3. Flock fibers are treated with a conductive surface finish and well sifted and supplied to the flock-dosing device, which is equipped with a set of roll brushes. The bristles of the rotating brush are in contact with a stainless-steel screen
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12.3 A DC flocking process. The dosing unit has three feeding rotating stiff-bristle brushes, which push the flock fibers through the charging stainless steel screen.
electrode and push the flock fibers in the dosing unit through the meshes of the electrode screen. The electrode screen is connected to negative DC high voltage from the power supply. The flock fibers, with semi-conductive surfaces, will acquire the negative charges according to the contact time through the charging screen on the bottom of the dosing unit. Bershev (1993) gave a mathematical model of the direct charging of fibers in contact with a charged metal electrode surface. This can be used to understand the amount of charge that q accepted by the individual fiber in t seconds’ contact with electrode. [12.1] where q0 = the theoretical maximum charge in Coulombs, τ = the time constant of the charging or relaxation time of the fiber = ε0εr/β, εr = the dielectric constant of the fiber, ε0 = the permittivity of free space = 8.85 × 10−12 F/m, and β = the fiber conductivity in S/m. The theoretical maximum charge, q0 is given as: [12.2]
where E = the electrostatic field strength in V/m, l = length of the fiber in m, d = diameter of the fiber. For example, cotton fiber (l = 2.5 × 10−2 m, d = 20 × 10−6 m, εr = 1.3, β = 10−7 S/m) in contact with an electrode field strength of E = 4 × 105 V/m have q0 = 0.56 × 10−11 C and τ = 1.15 × 10−4 s.
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For a nylon flock (l = 0.5 × 10−2 m, d = 5.05 × 10−5 m, εr = 3.5, β = 10−7 S/m) contact with E = 4 × 105 V/m, q0 = 0.28 × 10−11 C and τ = 30.98 × 10−3 s. The time constant of charging is inversely proportional to the resulting conductivity from the surface finish application and directly proportional to the dielectric constant. For poorly treated polyester flock (l = 1.27 × 10−2 m, d = 2.14 × 10−5 m, εr = 3.2, β = 10−10 S/m), q0 = 0.3025 × 10−11 C and τ = 28.32 s for E = 4 × 105 V/m. However, τ = 28.32 × 10−3 s for fiber with a conductivity of 10−7 S/m after a surface conductive finish treatment. This is why flock fiber requires a certain level of surface conductivity. This demonstrates that flock fibers should all have uniform good quality conductive finishes on their surfaces to acquire a proper charge in a shorter contact time period. For three-time constant duration, the fiber will acquire 95% of the theoretical maximum charge attainable. The maximum theoretical charge on the fiber strongly depends on the fiber’s geometry. Once the charged fibers leave the charging screen electrode, they will be oriented along the electric field line by the induced dipole moment and accelerated along the field line by the Coulombic driving force (qE). Then the fiber will experience the air drag and reach terminal velocity. It finally impinges into the adhesive layer to form a pile. However, the electric field lines are not uniformly parallel and normal to the substrate surfaces. Higher flock cloud density will distort the field line by the space charge effect and the anchored pile will elevate the ground potential line and later arrivals will form a ‘tuft’ rather than the desirable vertical piles in some cases. Thus, it is advisable to use three consecutive flocking zones with low to high electric field strength for more or less vertical pile formation by minimizing the tuft formation. Kleber and Marton (1994) developed a simple model for flock motion in the flocking zone: ma = q E − Kv + mg,
[12.3]
where a, E, v, and g are acceleration, electric field, air flow field and gravitational vector, respectively. Air drag coefficient, K = C0 πρL (γL dF)1/2 lF /2, where ρL, γL are the specific density and kinematic viscosity of air; dF , lF are diameter and length of fiber; C0 = 0.6 for nylon. Assuming E varies only with respect to z direction, Equation (12.3) can be integrated as: [12.4]
v = dz/dt = A [1 − exp (− Kt/m)], where A = (qEz + mg)/K.
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In the flocking zone qE >> mg, terminal velocity is vt = qE/m. Hou (2000) reported the velocity profile of nylon flock motion in the flocking zone as shown in Fig. 12.4 and Fig. 12.5. It can be observed that the velocity profile does not follow the model (equation 12.4 and 12.5) proposed by Kleber and Marton (1994). This discrepancy can be explained by the fact that the acquired surface charge on the flock fiber surface
12.4 Velocity profile of 1.5 d nylon flock in 2.0 kV/cm 40% RH.
12.5 Velocity profile of 3.0 d nylon flock in 3.5 kV/cm 60% RH.
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is not uniform, owing to the uneven application of conductive finish and flock fiber length distribution in commercially prepared flock fibers. Hou (2000) measured the flock motion in the flocking zone with the set-up shown in Fig. 12.6. Data obtained from this experiment were used to obtain the results shown in Fig. 12.4 and Fig. 12.5. The velocity distribution of flock fibers moving under all the processing conditions employed in the study shows that the flock fibers can attain a maximum speed of 5 to 7 m/sec under most the favorable circumstances. The majority of flocks in the flocking zone move at a speed of 1 to 2 m/sec, as shown in Fig. 12.7. The measured speed distribution and its order are comparable to the earlier study of flight motion of flock in an electrostatic field using the flock activity tester (Gabler 1980). This also agrees well with the theoretical upper limit of flock fiber velocity (<10 m/s) based on particle mobility in an electric field strength of about 30 kV/cm or below, which is near to the electrical break down field strength of air (Kleber and Marton 1994). The direct (contact) charging described for DC flocking is not the only way to impart a surface charge on flock fibers. Other methods of flock charging are used in various flocking techniques. Selecting the proper charging technique depends on the surface resistivity of the flock fiber to be used. Direct charging is suitable for the conductor/semiconductor level of surface resistivity (10−4 – 108 Ω), while corona charging is useful for the conductor to dielectric material (10−4 to 1016 Ω). A third method is called tribo-charging, which is suitable for flocking electrical insulators (108 to 1018 Ω) (Kleber and Marton 1994).
12.6 High-speed digital CCD camera used for flock motion analysis.
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12.7 Velocity distribution of flock fibers under various processing variables.
A hand-held DC flocking unit, which has a built-in wire mesh electrode in the flock-dispensing hopper, is based on corona charging of the flock fibers. The ion bombardment generated by a corona discharge from the flock hopper electrode is an effective means of imparting an electric charge to both insulating and conductive particles. The maximum charge of a spherical particle in a monoionized electric field (corona charging) was first calculated by Pauthenier and Moreau-Hanot (Younes 2009): qc = 4πε0r2[3εr /(2 + εr)]E.
[12.6]
The maximum corona charge, qc, depends on the particle radius (r) and electric field (E) only. However, the particle charging is not instantaneous and is limited by a supply of space charges (Singh 1981): q = qc /(1 + τc /t),
[12.7]
where t = time, the charging time constant, τc = 4ε0 / ρb, ρ = space charge density and b = the mobility of ions. Thus charging dynamics depends on the space charge density and the mobility of ionic species in ambient gas (typically air). Charging the dynamics of direct charging (eqn 12.1 and 12.2) can be substituted (by eqn 12.6 and 12.7) for a flocking device based on corona charging. Then the corona charged flock motion can be described by the eqn 12.3, 12.4 and 12.5. Corona charging is assumed to occur in AC flocking too. Kleber and Marton (1994) argued that the corona particles of negative and positive polarity are
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generated during the positive and negative quarter-cycles of AC high tension applied on the upper electrode, respectively. AC flocking can be treated with the help of eqn 12.6 and 12.7 by considering the polarity change, charged flock mobility and polarity with respect to electric field direction. Triboelectric charging occurs when highly dielectric flock fibers (109 to 1016 Ω) are in frictional contact with and/or separated from other dielectric surfaces. At least one of the contacting materials is dielectric to generate tribocharges. The amount of charge generated and the polarity of the charge are highly influenced by local surface conditions. Thus, it is necessary to control the environment and material chemistry for the required specific quality of the tribocharge. One of advantage of this charging mode is that it needs no power supply and the desired charging effects are obtained by proper environmental controls. However, the most significant disadvantage is that the amount of charge generated is relatively low and it often occurs in unwanted situations causing electrostatic hazards. In summary, fiber coating (flocking) begins with charging the flock fibers with a selected mode of charging. Then charged fibers are dispensed from flock dosing units into the flocking zone (electric field). The charged flock fibers are oriented and accelerated along the electric field lines by Coulombic and gravitational forces. When the initially accelerated fibers reach a threshold speed, air drag decelerates and the fibers will acquire a terminal velocity of 1 to 5 m/s. From this kinetic energy, impingement fibers will be anchored vertically into the uncured adhesive layer coated on a substrate, which is defined as pile generation and discussed in the next section.
12.2.2 Pile generation and flocking process control Flock fibers anchored in the adhesive layer on substrate form piles. The number of piles per unit area is called flock density. The typical flock density of commercially produced flock materials is in the range of 10 to 500 fibers/mm2. The quality of flocked products depends on flock density. Thus flocked product quality is interchangeably used for flock density. Bershev and Lovova (1997) modeled pile generation in terms of flocking plant process variables. They derived a differential equation, assuming that the rate of increase in flock density (dn/dt) is proportional to the number of piles to be covered (nmax − n): dn/dt = K (nmax − n).
[12.8]
By integrating eqn 12.8, n = nmax [1 − exp(−zt/ABnmax)],
[12.9]
where n = flock density at time t, nmax = maximum attainable flock density, z = number of flock fibers dosed in the flocking zone per second, A = flock dosing screen dimension along the machine direction, B = width of dosing screen or
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substrate, v = substrate moving speed = A/t, and t is flocking time. When flocking time is extremely long or the substrate is not moving n reaches the nmax. Production speed is obtained by inverting eqn 12.9: v = −z/[Bnmax ln(1 − n/nmax)].
[12.10]
Bershev and Lovova (1997) demonstrated the applicability of the derived equations with a practical example for manufacturing a nylon flock (2 mm long, 2.2 tex) floor covering (material width = 2 m, v = 5 m/min). The floor covering has a flock mass per square meter of 150 g/m2 and single flock fiber mass = 4.48 × 10−6 g. Typically 90% of the maximum flock pile density is attained. Under this condition, nmax = 37.2/mm2, dosing rate = 63.96 g/sec. By predicting flock density, we can control the production rate and production capacity of a fiber-coating plant, and the flocked product quality. Flocked articles with higher flock density will have better abrasion resistance and aesthetic quality. Once pile is generated, excess flock fibers that are not anchored in the wet adhesive layer are removed by a vacuum device. The vacuumed fiber-coated layer is then fed into a curing oven. Flocking adhesives are cured and hardened in the oven to impart the desired mechanical performance properties. Depending on their application, the flocked fabrics are dyed, printed and finished to meet requirements.
12.3
Flock fibers and preparation
Flock fibers can be prepared from virtually any fiber. Fibers are originated from nature or manufactured from natural or synthetic polymers. Natural fibers are classified into three groups according to their origins: vegetable fibers (cotton, jute, flax, ramie, sisal); animal fibers (wool, silk, cashmere); and mineral fibers (asbestos, quartz). Manufactured fibers are produced from polymers recovered form natural sources. For example rayon, acetate, and triacetate fibers are derived from cellulose fibers made from wood pulp. Protein fibers are manufactured from casein, soy protein, etc. Synthetic polymer-based fibers are polyamides (nylons, aramids), polyesters, polyolefins, polyvinyl derivatives (acrylics, modacrylics, PVC, PVDC, PTFE), polyurethanes, glass and carbon/graphite fibers. The most commonly used flock fibers are polyamides (nylon 6-6, nylon 6, nylon 3, nylon 6-10), rayons (viscose, Lyocell®, Tencel® etc.), acrylics, modacrylics, and polyesters (PET, PTT, PBT, etc.) For some specialty applications, ground cotton, aramid (Kevlar®, Nomex®), glass, ceramic, metal and carbon/ graphite fibers are used. Flock fibers are manufactured by milling or cutting processes. Milled flock fibers are available in two grades: fine: 0.2 to 0.5 mm, and coarse: 0.4 to 1.1 mm. The fiber length of cut flocks is typically 0.2 to 6 mm. However, larger diameter
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fibers can be cut up to 12 mm. Fineness index (FI = dtex/length in mm) is a significant parameter to be controlled for achieving the maximum flock density of flocked fabric. In flock industry practices, a FI of 2.2 to 3 for 3.3 dtex (3Denier) flock gives maximum flock density. A lower limit of fineness for reasonable flock density is 1.0. Thus, flock fibers cut longer than 3.3 mm of 3Denier flocks will not yield a flocked surface of acceptable flock density. Recently flock fibers cut from microfibers were introduced. The fibers are 0.4 to 1.0 denier per filament (dpf), but the flock fibers are difficult to process owing to their high surface area and low stiffness. Moreover, to have acceptable FI, the flock length is far below the cutting limit of a precision cutter. Flock fiber ends should not have melt or irregular edges introduced by the improper setting of the cutter. These defects will increase aerodynamic resistance and impair the anchoring of flock fibers into the adhesive layer. These defects have the potential to generate polymeric microdust (‘snow’). Flock fibers are available in various cross-sections (depending on spinneret geometry and spinning methods). These are round, dog-bone, trilobal or multilobal and serrated. The most common is the round cross-section. For the same linear density trilobal fibers have a higher bending rigidity, which gives better flockability. After milling or cutting the fibers, flock fibers are treated with a formulation containing humectants, salts, and surface active agents to impart proper surface conductivity to the flock fibers. With typical formulations for DC flocks, surface resistivity can be adjusted to between 1 and 100 mega ohm (Ω); and for AC flocks, treated flock surface resistivity reaches 100 to 10 000 mega ohm. The relationship between volume specific resistivity (Ω cm) and surface resistivity (Ω) has been established as 109Ω, which is approximately equivalent to 1010Ω cm based on the published safety manual (Kleber and Marton 1994). The surface conductivity treatments are formulated to promote adhesion between the treated flock and the flock adhesive to be used, to provide stability at specified temperatures and the RH% range used in the flocking room, and to minimize agglomeration of flocks. Nylon fibers (nylon 66 and nylon 6), which have an official regain of around 4%, are the most widely used flock fibers. These fiber titers range from 1.7 to 22 dtex (1.5 to 20 denier) in bright, semi-dull, dull grades. Flock fiber producers supply ground and cut nylon flocks of 0.3 to 12 mm in length. There is no significant market for nylon flocks longer than 3 mm. The advantages of nylons are their outstanding elastic recovery and excellent abrasion resistance. The fiber cross-sections available are round and trilobal/multilobal. The trilobal nylon flock has good stiffness for high flock density and luster in the flocked surface. Nylons are used to produce flocked articles such as upholstery, blankets, apparels and carpets. The second most used flocks are rayon. Rayon flocks were the first cut flocks manufactured from regenerated cellulose fibers. Currently produced rayons are
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viscose, Lyocell® and Tencel® (Lenzing AG, Lenzing Austria). Flock manufacturers supply 0.9 to 18 dtex rayon ground or cut flocks of 0.3 to 0.4 mm length. Rayons have a moisture regain of 11 to 15%, and poor mechanical properties (low wet and dry tenacity), and abrasion resistance and elastic recovery are also poor. However, rayon fibers have the advantages of high cutting efficiency and are more easily dyed with brighter colors. Applications are mainly in decorative fields such as book-binding, toys, wall coverings, etc. Acrylic fibers (PAN) are made up of at least 85% by weight of acrylonitrile units (CH2CH(C ≡ N)). Modacrylic (MAC) fibers make up less than 85% of PAN with high flame retardancy. Cross-sectional shapes are round, bean, dogbone shaped or multilobal, which provide good stiffness and softness. Flock application titers range from 0.6 to 3.3 dtex, and the most popular ones are flocks of between 0.6 dtex and 0.6 mm in length, although titers available for PAN are 0.6 to 25 dtex, and those for MAC are 1.5 to 26 dtex. Acrylic flocks show excellent light-fastness, UV resistance, softness and dimensional stability. Applications include the automotive industry, apparel, upholstery, decorative and packaging products. Polyester fibers are the most actively produced synthetic fibers in tonnage. PET (polyethylene terephthalate) was the first commercially produced and is the most successful fiber. Other polyesters later developed are PBT (polybutylene terephthalate), PEN (polyethylene naphthalate) and PTT (polytrimethylene trephthalate). Recently PLA (polylactic acid) is commercially produced for fibers, plastics and films. PLA is biodegradable aliphatic polyester derived from renewable resources, such as corn starch or sugarcane. For flock production, glossy and opaque solution-dyed black PET fibers are used, which show maximum light-fastness and low moisture regain (0.4%). Typical PET flock fibers have a round cross-section and titers range from 1.7 to 6.7 dtex. Applications of PET flocks include window channels and automobile window accessories, which require low moisture absorption, high abrasion resistance and lower friction. For specialized applications, flock fibers are derived from ground cotton, aramids (Nomex, Kevlar), PBI (polybenzimidazole), glass fibers, carbon/graphite fibers, ceramic fibers and metallic fibers (copper, stainless steel, etc.) Flock fibers are selected based on application requirements. The most significant factor among the requirements is cost. Depending on a desired application, the following factors should be considered: abrasion resistance, hand/softness, resistance to marking (‘writing’), crushing capacity, dyeing cost and dyeability, light-fastness, crock-fastness, cutting efficiency, UV resistance, and launderability. For example, if abrasion resistance and elastic recovery properties are the most important requirements for a given product, then nylon flock, the most expensive in terms of cost, should be used. For maximum UV resistance, polyester or PAN flock fibers are used. For maximum flame retardancy, modacrylic flocks are employed. Cotton or PAN flocks are used for applications requiring softness.
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The coloration of the flock fibers can be done by fiber producers, which results in a limited number of shades available owing to the limited range of pigment shades that are added to the spinning solution (i.e. for spin dyeing). Spun-dyed flock fibers have excellent UV resistance, light- and wet-fastness. However, some applications require more diverse shades of color. To match the customer’s color preference, a traditional textile dyeing process is employed. Cut flock fibers are scoured and dyed with stock dyeing machines and washed. Then surface conductive finishes are applied. The dyed and finished flocks are dried, separated with a cyclone drier and packaged in units of the desired weight.
12.4
Flocking substrates
Flock substrates are materials onto which adhesive layers are applied so as to bond flock fibers. Thus, substrates can be classified by their forms and compositions: textiles (yarns, fabrics, and nonwovens), papers, molded plastic parts, rubber and plastic profiles, and thermoplastic films.
12.4.1 Textile substrates Flocked yarns for upholstery and car seat fabrics are produced by running adhesive-coated filament yarns through the flock cloud chamber and a curing oven. Flocked yarn has advantages over chenille yarn such as not shedding, and creating a dense coverage of pile fibers. Flocked yarns are also used in a filter construction for air or liquid. Flock products for apparel and home furnishing are produced on woven or knitted textile fabric substrates. A real density of these fabrics ranges from 65 to 200 g/m2. Typical weave structures are plain, twill, sateen and drills made of rayon or a polyester/cotton blend. For example, flocked furniture upholstery fabrics are produced on 65/35 polyester/cotton Osnaburg substrate. One can obtain optimum cost/performance ratio from this fiber blend ratio and fabric structure. In general, the tear strength of coated fabrics such as flocked fabrics is poor. When tear resistance is a required property, fabric structures such as knits, drills and sateen are used. For some applications textile substrates require pretreatments (singeing, desizing, scouring, heat setting, calendaring) and pre-dyeing and finishing before flocking. Nonwoven substrates are used for various industrial and decorative end uses. For example, optical polishing pads are fabricated on a nonwoven substrate.
12.4.2 Non-textile substrates Non-textile substrates are increasingly used for special applications. Paper substrates are commonly used to produce packaging and decorative end uses. Molded parts made of plastics are being flocked for applications ranging from
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toys to automotives to high-technology applications. Styrene rolls are flocked for packaging applications and flocked PVC is used in the belt trade. Various foams are flocked for packaging material, while wide rolls of polyurethane foam sheets are flocked for manufacturing blankets. Automotive window channels are fabricated from flocked rubber profiles. Rolled goods of vinyl substrate are used for the manufacture of medical products. Thermoplastic films of PET, PBT and PP and surfaces of other engineering polymers (polycarbonates, polymethylmethacrylates, ABS, etc.) are routinely flocked for packaging and other specialty applications. Non-textile substrates are not only plastics. They include metal (steel, aluminum, alloys, etc.), wood, composite wood and any other structured material surfaces. For example, the inner walls of steel computer cases are flocked to reduce the vibration and noise generated by the enclosed fans and electronic components.
12.5
Adhesives for flocking
The quality and performance properties of finished flock products are determined primarily by the proper selection of flock adhesive. The flock adhesive is selected by considering substrate, flock fiber, and end-use environmental and product specifications. In general, flock adhesives require adequate wetting and spreading over adherends (fiber and substrate), solidification, and sufficient elasticity during bond formation. Schultz and Nardin (1999) listed many theories of adhesion: 1) mechanical interlocking theory; 2) electrical double layer; 3) theory of boundary layers and inter-phases (or weak boundary layer theory); 4) adsorption theory (or wettability and acid base theory); 5) diffusion theory; and 6) chemical bonding theory. Actual adhesion between two solids cannot be explained by a single model, but some combination of the above theories. The mechanical interlocking theory can explain adhesion of flock fibers on textile substrates, which are porous. However, there may be adhesion based on secondary or electrostatic bonds between fiber and substrates with the help of flock adhesive used in roll-to-roll flocking. There are four types of flock adhesives one can select to meet the specific application requirements. These are discussed in the following sections.
12.5.1 Water-based adhesives Water-based flock adhesives are in colloidal dispersion form, which is called latex emulsion. The polymer used is prepared by emulsion polymerization. The latex materials available for water-based flock adhesives are styrene butadiene rubber (SBR), nitrile, chloroprene, vinylacetate, ethylene vinylacetate (EVA), acrylics, vinylchloride, vinylidenechloride and styrenes. Latex-based adhesives based on acrylics are the ‘workhorse’ in the industry. Most acrylic latex-based adhesives are supplied at about 50% solids content by weight with a suitable emulsifier for stability.
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The advantages of water-based adhesives are lower cost, non-flammability, high solid contents, adjustable viscosity, controlled penetration and wetting, wide range of engineered physical and chemical properties; they are environmentally friendly and easy to apply and clean up.
12.5.2 Solvent-based adhesives For many low surface energy substrates such as rubber and engineered plastic profiles, adhesive polymer solutions in organic solvents are used. The solvent lowers the viscosity of formulation significantly to allow wetting and spreading the adhesive on substrate and fiber. The adhesive is solidified by removing the organic solvent. Solvent-based adhesive formulations include natural and synthetic rubbers and resins, which are referred to as cements, lacquers or resin solutions. In addition many cellulose derivatives such as nitrocellulose, ethyl cellulose and cellulose acetate are used to prepare solvent-based adhesives. Elastomeric materials such as chlorinated rubber, butyl rubber and polyisobutylene are also used to prepare solvent-based flock adhesives. Epoxy and polyurethane resins are diluted in appropriate solvents for use in fiber-coating adhesives. Advantages of solvent-based adhesives are good wetting of hydrophobic surfaces (rubber, plastics and polymers), adjustable pot-life and drying time, high wet adhesion strength, higher water resistance and no curl or shrink of paper and fabric substrates. Solvent-based adhesives have good wet tack and do not increase corrosion on steel and other metal substrates.
12.5.3 Thermosetting adhesives Flock adhesives of this type include polyurethanes, unsaturated polyesters and epoxies. This type of flock adhesives is derived from 100% liquid resin materials (no solvents) in one-part or two-part systems. In addition it may need hardeners and/or accelerators. A latent hardener (or blocked curative) is used in one-part systems, which is activated by proper time and temperature curing conditions. For two-part systems resin (Part A) and hardener (Part B) are mixed before application and exposed to a suitable curing temperatures in a predetermined schedule for completing solidification of the adhesion bonding.
12.5.4 Plastisols Plastisols are pastes composed of fine polyvinylchloride (PVC) particles suspended in liquid plasticizer. Plastisols sometimes include small amounts of extenders, stabilizers, pigments and fillers. Typical PVC to plasticizer ratio is
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50/50 by weight. However, this ratio may be adjusted to achieve proper viscosity and wetting rheology for a plastisol adhesive. Organosols are plastisols containing a large amount of volatile solvents such as gasoline or glycols to reduce viscosity making them suitable for coatable lacquers. For paper or textile substrates, plastisols are applied by rotary screen-printing techniques to produce flocked products such as tarps, artificial leather, and floor and wall coverings (Osswald et al. (2006). The four groups of flock adhesives have their own advantages and disadvantages. A proper flock adhesive for a given application is selected to satisfy requirements such as better abrasion resistance of a flocked surface, ease of processing, safety and environmental impact.
12.6
Flocking processes
Flocking methods practiced in industry are 1) mechanical, 2) AC/mechanical, 3) DC/mechanical, 4) pneumatic/DC, and 5) bipolar DC. For roll-to-roll manufacturing, methods 2 and 3 are commonly used. For 3D objects a pneumatic/ electrostatic-DC flocking device is employed, as shown in Fig. 12.8. Flocked yarn is produced by passing adhesive-coated filament yarns through flock clouds created by a bipolar DC electrostatic field (method 5).
12.8 Handheld electrostatic/pneumatic 3D flocking device.
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12.6.1 Mechanical flocking Prepared flock fiber particles are fed by gravity from the dosing unit onto an adhesive-coated substrate, which is on a beater blanket vibrated by beater bars (Fig. 12.9). The vibration promotes better anchorage of the flock and upright alignment of fibers. The beater bar arrangement enables higher flock densities than achievable by simple hand casting. Flocking plants based on this technique are still in operation.
12.9 A schematic of mechanical flocking (courtesy of American Flock Association).
12.6.2 Alternating current (AC) flocking Electrostatic force from AC electric fields has been employed in the USA since around the mid-1930s. This technique was utilized in manufacturing abrasive paper (Mueller 1986). A high-voltage grid electrode is placed between the dosing unit and substrate. Both the dosing screen and substrates are at ground potential. The flock fibers acquire charges from the AC electrode, but the electrokinetic energy imparted by the AC in the direction of the adhesive-coated substrate is very small. Thus, embedding of flock fibers into the adhesive layer is accomplished by the energy supplied by beater bars. The US flocking industry adopted the AC process for roll-to-roll manufacturing over DC processes owing to the belief that DC flocking cannot match the production speed of the AC process. However a DC production line with multiple dosing units and a proper dosing rate can match or exceed AC line speed with a comparable flock density, as pointed out by Bershev and Lovova (1997). The advantage of AC processing is that AC corona charging requires flock fiber conductivity several orders of magnitude lower than the DC direct charging technique. This means that conductive surface finishing for the fiber during the AC flocking process is not critical. Therefore, the AC flocking line can process longer flock fibers.
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The AC flocking system cannot process very fine denier flock fibers for very high flock density, which is achievable by parallel fiber alignment using the DC field. In general, the AC process is not suitable for unstable substrates such as foams or knitted fabrics, which cannot be vibrated vigorously by beater bars. The AC flocking techniques are also not used for graphic fiber flocking, open-mesh flocking, T-shirts and sportswear or 3D object flocking.
12.6.3 Direct current (DC) flocking In the early 1980s, non-traditional flock products for technical and industrial applications were developed with super fine denier flocks. These nonconventional products required precision flocking, which cannot be achieved with AC processes. There are two types of DC flocking systems: the direct charging system and separate electrode system. The latter is very similar in arrangement to an AC flocking system. Here the separated electrodes are not covered by the insulation found in AC systems. Flock fibers are dropped from a mechanical doser onto the grid electrode by gravitation. These fibers are charged by corona ions generated by grid electrodes made of bare metal screens. However the amount of charge on individual fibers is not uniform because of the non-uniformity of the conductive surface finish applied to the fibers. Thus, this system requires an intensive beater bar track system under the substrate-carrying belt for good quality finished flock products (Mueller 1986). Direct-charging flocking systems emerged around the late 1940s in Germany. These systems have been refined and adopted by European flocking machinery manufacturers (see Fig. 12.10). In this system the dosing unit and electrode are consolidated. Typical dosing units are equipped with two rotating roller brushes, which push flock fibers through metal-mesh sieve electrodes installed on the base plate of the doser. The
12.10 A schematic of direct charging DC flocking system (courtesy of American Flock Association).
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mesh count of the metal sieve electrode can be adjusted for different flock characteristics and the electrodes are connected to a high-tension DC power supply. Thus the fibers pushed through the mesh-electrode are directly charged, as explained in Section 12.2.1. The uniform electric field formed between the doser plate electrode and the ground electrode underneath the substrate carrier belt transports the charged flock fibers with proper impinging force onto the wet adhesive layer on the substrate as described in the flock motion experimental section above. If the flock is prepared properly, beater bar action is not required to secure pile generation. However, a typical direct charging system can be equipped with a beater bar train if necessary. Mueller (1986) pointed out the advantages of the direct charging DC system:
• • • • •
Less well-prepared flocks can be processed A very low current (0.2 to 0.7 mA) is carried by the charged flocks during the flocking Precise control of the flock dosing rate (i.e. the number of flock fibers per flocking zone per second) is maintained Low excess flock dosing (1 to 5%) Minimum damage to the flock by gentle handling.
A properly designed dosing system can handle ‘balling’ and agglomeration of flock fibers. Thus the system can process slender flock or even poor quality flocks.
12.6.4 3D object flocking DC flocking systems described in the previous section are suitable for roll-to-roll flocking of textile webs, plastic films and other webs. The DC system can be used to flock 3D objects with proper modifications to accommodate their shape and size. 3D objects to be flocked have various shapes: axial symmetry (spheres, cones, cylinders), irregular shapes (toy animals, automotive trims, items for window displays, etc.), and hollow objects (automotive glove compartments, coin trays, etc.) Sizes vary from small cosmetic tubes (3 mm diameter × 15 mm long) to large window displays (600 × 2 000 mm) and art objects (500 × 3 000 mm). Depending on the surface geometry and size, simple DC flocking methods can be combined with pneumatic conveyance of flock fibers, imparting vibration, rotational or swinging motion to the objects. An example of the electrostatic– pneumatic flocking principle is shown in Fig. 12.11 and a commercially available system is shown in Fig. 12.8 (the electrostatic–pneumatic flocking (EPF) unit from Maag Flockmachinen GmbH, Gomaringen, Germany). In this type of 3D object flocking device, flock fibers or particles are introduced at a uniform rate into an air stream by a helical feeder. The flock fibers are then conveyed by the air flow along a flexible hose to an applicator nozzle, which has a charging electrode, depicted as a suspended metal sphere in Fig. 12.11. The charged flock fibers are then released to the air stream. The suspended and charged
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12.11 A schematic of electrostatic–pneumatic 3D object flocking principle (courtesy of American Flock Association).
12.12 Automatic flocking line (courtesy of American Flock Association).
flocks in the air stream are driven to the electrically grounded complex geometry work piece by electrostatic and pneumatic forces. All types of flocking units are available for flocking different articles as semi-automatic plants or fully automatic lines as shown in Fig. 12.12.
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12.7
Testing and quality assurance
Most textile fiber, yarn and fabric quality testing methods are well defined in ASTM books 7.01 and 7.02. However, flock quality testing was not standardized until the early 1970s when the European Flock Industry working group prepared a list of unified testing procedures. Based on these procedures, standard test instruments were developed and made commercially available (Mueller 1986). They developed a special ‘test sheet’, which listed and described the tests and had spaces on the sheet where the test results could be recorded. An outline of this ‘test sheet’ follows:
• • • • • •
Flock fiber, type, color, luster, dtex, length and other ordering information. Moisture percentage and surface resistance of the flock fibers, determined by a Textometer (Fig. 12.13). Electrostatic behavior such as rise time, residual amount, determined by a Flock Activity Meter (Fig. 12.14). Sievability, how well flock fiber/particles are separated in the dosing unit, determined by the Siftability Tester (Fig. 12.15). Flock geometry, nominal fiber length, bend radius, kinkiness, fused heads, foreign matter, excess length, determined by the Flock-In-Spec Tester (Fig. 12.16) Hydrophobicity of flock fibers, wetting characteristics of flock adhesives, which indicate the need of modification of the adhesive formulation.
12.13 Textometer with ring electrode.
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12.14 Flock Activity Meter.
12.15 Siftability Tester.
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12.16 Flock-In-Spec tester for optical characterization of flock fibers (24 × and 72 × magnification).
12.17 Chisel Abrasion Tester for flocked surface.
Basically this assessment of flock characteristics will enable the reproducible flocking results and assure a high-quality product. The abrasion resistance of the flock fabrics is tested by chisel testing under defined loads, typically 500 g or 1 kg (Fig. 12.17).
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Flocked yarns and fabrics are tested in accordance with the ASTM standard textile yarn and fabrics test methods (ASTM 2009).
12.8
New developments in the application of flocked fabrics and structures
Flocked fabrics are dyed in solid colors or printed patterns either by thermal transfer printing or screen printing as shown in Fig. 12.18. They are typically used in traditional applications such as apparel production or decorative and visually appealing purposes. Since the end of the 1970s, the flock industry saw improving qualities in raw materials: new/improved fibers, fiber-cutting processes, new effective finishes, adhesives and advancements in manufacturing technologies. These developments in associated industries (fiber manufacturing, adhesive and finishing chemicals, coating technology, process control and computer monitoring) enabled the expansion of the flock product spectrum into novel technical applications beyond the traditional apparel, floor covering and upholstery industry sectors. Some recent developments in flock technology applications are summarized below:
• •
Decorative and visual appeal – apparel, wall coverings, greeting cards, jewelry display backings, toys and crafts, and numerous other applications Friction/drag modification – flocked finishes designed either to increase or decrease the frictional characteristics of the substrates. For example, a super
12.18 Transfer-printed flocked fabric (courtesy of Barry Ripley, American Flock Association).
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oil tanker with a flocked bottom can save fuel because of drag reduction and less-biofouling Sound dampening and insulation – flocked wall coverings for music studios, flocked coatings for car ventilation units, flocked automotive trays (Fig. 12.19), flocked computer and printer housings Heat insulation, dissipation and thermal stability – flocked blankets, comforters and flocked upholstery products. For effective heat dissipation, carbon fiberflocked fins were proposed (Uchida et al. 2008) Increasing surface area for evaporation and filtration – small, but effective humidifiers, filtration media, flocked panels and machinery parts with reduced condensation Transition-less power transmission – flocked clutch surfaces for electronic equipment Liquid retention or dispersal – paint /cosmetic applicators, biofluid collections for medical laboratory Buffing and polishing – flocked buffing and polishing wheels for the optical industry Cushioning and protection – flocked packaging materials for sensitive instruments and jewelry products, scratch-proofing of surfaces. Fiber graphics for apparel, sportswear, and surface relief effects (Fig. 12.20) Screen printing of flocked fibers (Fig. 12.21) Technical textile structures derived from fiber coating – automotive head liner, trunk lining, door panels and interior trims, insulation material for aerospace application (Fig. 12.22) Biomedical scaffolds for implants.
12.19 Flocked thermoplastic tray (courtesy of Barry Ripley, American Flock Association).
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12.20 Fiber graphics transfer (courtesy of Barry Ripley, American Flock Association).
12.21 Flat screen carousel for multi-color flock printing of T-shirt (courtesy of Maag Flockmaschinen GmbH, Gomaringen Germany).
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12.22 Insulation material for aerospace application (courtesy of Barry Ripley, American Flock Association).
12.9
Conclusions and future trends
Modern fiber coating (flocking) technology has advanced significantly during the past 50 years. The enabling factors for this advancement were improvements in: fiber materials, flock-cutting procedures and chemical finishing technologies, flock-processing techniques and operational control, adhesives and microelectronics-based DC charging systems. Major developments occurred in the use of flocked fabrics in apparel, shoe components and furniture upholstery between the 1960s and the 1980s. Automotive interiors (headliners and glove-box coatings, etc.) and dashboard profiles were added in the 1970s to 1990s. However, there were setbacks during this period owing to serious product quality issues coupled with economic recessions. These problems and setbacks were overcome by the flocked products manufacturers emphasizing and assuring product quality and performance. Also, the applications for flock technology and materials were expanded into new technical textile areas such as super-insulation (Freudenberg 2001), noise barriers (Mrozik 2003), filtration, high-impact composites(Kim et al. 2007), biofiltration media (Kim et al. 2005), fuel cell electrodes (Partrissi et al. 2008) and biomedical structures (Offerman et al. 2004). Furthermore, surface interests can be imparted by fiber graphics, direct/transfer printing, laser embossing and 3D flocking technologies, which provide flexibility in the techniques of surface coloration and effect. While the development and use of the new water-based
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flock adhesives require high-energy consumption for curing (for water evaporation during cure), the safety (non-flammability), environmentally more friendly and easy ‘clean-up’ of these water-based adhesive systems more than makes up for this. In some very recent developments, some flock adhesive manufacturers are developing UV/blue light curable adhesives that save energy and shorten processing time and processing line geometry (Kisters 2001).
12.10 Sources of further information and advice For basic information on flock technology and US fiber coating industry, contact the American Flock Association (http://www.flocking.org/). In this website, you can find information regarding flocking methods, manufacturers of flock fibers, flocked fabrics, flocked profiles and so on. The author has carried out many research projects related to fiber coating theory and practices: the results have been reported in various journals and the National Textile Center annual reports (http://www.ntcresearch.org/PDFindex.html). The International Trade Journal for the Flock Industry was published between 1960 and 2004 in Buedingen, Germany. This trade journal has abundant technical information together with industry news in Europe and US. This journal has not been published since the publisher, Joachim Mueller, retired in 2004. However, FLOCK-News has been published by the Association of the Flock Industry Europe (TM) (http://www.flock.de), since the first quarter of 2006. The free newsletter of the Association of Flock Industry Europe is available by contacting the association (
[email protected]). This newsletter has up-to-date product development news, new applications and news on member companies. The American Flock Association runs the triennial Flock School at the University of Massachusetts, Dartmouth, which has a Flock Materials and Technology Laboratory. This seminar discusses fundamental of flock technology and applications. Speakers at the seminar are include the flock industry, academia, and material suppliers. The Seventh Triennial Flock School was held on 4–6 August 2010. The Association of the Flock Industry Europe (TM) sponsors biennial International Flock Symposium in Germany. Topics presented at this technology conference are diverse, from fiber science, adhesion science, flocking theory, automated flocking line systems, and environmental issues and industrial safety. The proceedings of the International Seminar are available from the association (
[email protected]). The Twenty-First International Flock Symposium was held in Muenchen Germany 28–29 March 2011.
12.11 Acknowledgements Flock science and technology research has been established at the University of Massachusetts, Dartmouth (UMD) since 1994 when a Flock Science and
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Technology research program was established with the encouragement of the American Flock Association. Since this time the program has grown and discoveries have been made. In appreciation of this, the author wishes to thank the following institutions and agencies for their initial and continued financial support: the National Textile Center (US Department of Commerce), the State of Massachusetts, the STEP program and the American Flock Association. In addition, the author wishes to thank a number of individuals without whose support and encouragement this UMD research program could not have succeeded and flourished. These people are Peter Hadley, Claremont Flock; Robert Borowski, Creative Coatings; Joachim Mueller, flock publisher and Flock Industry Consultant. Special thanks is given to Dr Armand F. Lewis (Adjunct Professor) who has worked on flock science and technology projects with the author since the establishment of the present UMD Flock Research Center program. Finally, research projects cannot function without capable graduate students. Therefore the author wishes to thank personally the members of his past and present graduate student research team for their diligent and creative work over the years and at present: these students are: Yuejun Hou (2000), Sunil Hoskote (2001), Francis Pottokaran (2002), Liang Feng (2006), Pankaj-Kumar Sarda (2007), Sandip Pawar (2008), Jia Ren (2009), Mayur Kumbhani (2010) and Yu Sun (expected to graduate 2011).
12.12 References ASTM Book 7.01 and 7.02, ASTM International, West Conshohocken, PA, 19428-2959 USA (2009). Bershev E. N., Physical modeling of the electrostatic flocking by direct current, International Trade Journal for the Flock Industry, 19(69), pp. 22–28 (1993). Bershv E. N., and L. V. Lovova, Influence of the flock quality upon the quality of the flocked articles and the productivity, Proceedings of the Fourteenth International Flock Seminar, Darmstadt, Germany (1997). Der Manouelian, T. http://www.flocking.org/ask.php, accessed 16 February 2010. Freudenberg C., A Doerfel, G. Hoffmann, and P. Offermann et al., Electrostatic flocking for technical textiles, Proceedings of Sixteenth International Flock Symposium, lecture 13, Dresden, Germany, 19–20 March (2001). Gabler, K., Investiation of flight characteristics of flock by means of high-speed photographic camera, Proceedings of Sixth International Flock Symposium Paper No. 8, 10 September (1980). Hou, Y. J., Unpublished MS thesis from Textile Sciences Department, University of Massachusetts Dartmouth (2000). Kim, Y. K., L. A. Feng, J. M. Rice, Fracture toughness of the through-thickness flock fiber reinforced laminar composites, Proceedings of AUTEX2007 Conference, Tampere, Finland, 26–28 June (2007). Kim, Y. K., A. F. Lewis, R. Laoulache and F. Scarano, Compact fiber-based bioconversion and biofiltration for National Textile Center (NTC: F04-MD11), Annual Report, 31 August (2005).
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King, W. H., Method of and apparatus for making pile fabrics, US Patent 2 376 922, 29 May 1945. Kisters, K and T. Wendel, New findings by the pure-UV-technology with the adhesive curing, Proceedings of Sixteenth International Flock Symposium, lecture 7, Dresden, Germany, 19–20 March (2001). Kleber, W. and Marton, K. Comparison of flocking methods with various current types, Proceedings of Thirteenth International Flock Symposium, lecture 1, Darmstadt, Germany (1994). Mrozik, B., Combination materials from flocked surfaces for secondary sound insulation in vehicle interiors, Proceedings of the Seventeenth International Flock Symposium, lecture 13, Dresden, Germany, 31 March–1 April (2003). Mueller J., Flocking, in Satas D. (ed.) Plastics Finishing and Decoration, Van Nostrand Reinhold, New York (1986). Mueller, J., How big is our market? An analysis attempt, Proceedings of the Thirteenth International Flock Symposium, lecture 14, Seeheim, near Darmstadt, 4–5 October 1994. Mueller, J., Physics of flocking, Proceedings of Flock Fundamentals Seminar, American Flock Association and U. Mass Dartmouth, N. Dartmouth, MA, 6–8 August (1997). Offermann, P., H. Worch et al., Support material for tissue engineering, for producing implants or implant materials, and an implant produced with the support material, US 2004266000(A1), 30 December (2004). Osswald, T. A., E. Bauer, S. Brinkman, K. Oberbach and E. Schmachtenberg, International Plastics Handbook, Hanser, Munich (2006). Patrissi, C. J., R. R. Bessette, Y. K. Kim, and C. R. Schumacher, Fabrication and rate performance of a microfiber cathode in a Mg–H2O2 flowing electrolyte semi-fuel cell, J Electrochem Soc, 155 (6), pp. B558–B562 (2008). Schultz, J. and M. Nardin, Theories and mechanisms of adhesion in adhesion promotion techniques, in K. L. Mittal and A. Pizzi (ed.) Adhesion Promotion Techniques, Marcel Dekker, NewYork (1999). Singh, S., Charging characteristics of some powders used in electrostatic coating. IEEE Transactions On Industry Applications, Vol. Ia-17(1), January/February (1981). Simpson, E. L., J. W. Post and C. C. Post, Improvement in manufacture of the flocked fabrics, US Patent 1, 688, 31 May (1864). Uchida Hiromoto, E. Tokuhira Eiji et al., Heat dissipation fin, Japanese patent application: JP2008103773 (A), 1 May (2008). Woodruff, F. A. Development in coating and electrostatic flocking, Journal of Coated Fabrics, 22, 290–297 (April, 1993). Younes, M., A. Tilmatine et al., Numerical modeling of insulating particles trajectories in roll-type Corona electrostatic separators, IEEE Transactions on Dielectrics and Electrical Insulation, 16 (3), June (2009).
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13 Knotted fabrics L. PHILPOTT, International Guild of Knot Tyers Pacific Americas branch, USA
Abstract: Knotted fabrics are formed using a variety of techniques, in order to manufacture by hand or by machine a translucent or open fabric suitable for a variety of home ware, clothing, adornment, furnishings, jewelry, fishing tools and suspension systems. Industrial production continues to use technology that has not changed very much over the last two hundred years. This chapter examines the principal fabrics, their methods of production and the likely future directions for knotted fabrics. Key words: bobbinet, carpets, chemical lace, crochet, fibre, filet, granary knot, Ghiordes knot, Heathcot, Josephine knot, knot, lace, lacis, lark’s head, Leavers, macramé, needle point, net, oya, Raschel, Schiffli, Senneh knot, sheet bend, square knot, strand, tatting, tulle, warp, weft, yarn.
13.1
Introduction
Knotting is an ancient craft and a necessary precursor to weaving and sewing, both of which techniques rely on the use of knots to secure the forming thread, warp and weft. Knots are ill defined in technical terms. One of the most famous reference works for knot-tyers is The Ashley Book of Knots, written by Clifford Warren Ashley in 1944. Ashley studied and drew artistic and mostly accurate representations of knots for about eleven years in compiling the nearly 3,900 entries in his enormous work. In that book he describes a knot as ‘Broadly, any complication in rope except (a) accidental ones, as snarls and kinks, and (b) arrangements for storage, coils, balls, skeins, hanks, etc. . . . further excluding sinnets, splices, hitches and bends.’ The Cordage Institute of Wayne, Pennsylvania, appears not to have a definition for ‘knot’ or ‘knotting’. The work of Himmelfarb, 1957, also fails to define a knot and the Handbook of Fibre Rope Technology (McKenna et al. 2004) published by The Textile Institute under Woodhead Publishing’s banner states simply that ‘the terminology is variable, but “knot” is commonly used to cover all interlacings of ropes and cords’. In this chapter, the notion or definition of a knot is referred to simply as the interlacing of one or more cords or twines. The term ‘knotted fabric’ in this chapter does not, however, refer to the interlacing of a finished fabric length with itself or other finished pieces to form, say, a bow. Natural fibres are not a continuous length, being limited by the plant source, and normally extend only to about as long as 15 feet (nearly three metres) in the case of hemp (Cannabis sativa) or to as short as one or two inches (a few 318 © Woodhead Publishing Limited, 2011
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centimetres) in the case of cotton fibres (Gossypium hirsutum). Although fibres of the plant may be twisted together to allow for the development of longer yarns and strands, the breakage of a yarn or a strand will give rise to the need for a joining with a new yarn or strand. This action may alternatively be performed by splicing, weaving or by knotting. The expediency of forming a knot gives rise to the deliberate introduction of the knot as a form of textile structure. Weaving and splicing were necessarily time-consuming and did not result in an undisturbed fabric, particularly with the machine manufacture of fabrics. Knotting was an essential element of the making of carpets and rugs in civilizations dating to 6000 BCE (Helloproskill (Wikipedia), 2010). Warp threads were normally strung first, followed by several weft threads to form a starting end. The warp ends may have been left out to form a fringe on completion of the carpet. The carpet was then begun using short staples of the carpet fibre, usually wool yarn, that were knotted into the pattern to be formed. Two principal forms of knot were used, the Ghiordes knot (Fig. 13.1) and the Senneh knot (Fig. 13.2).
13.1 The Ghiordes form of knotting, producing a symmetrical pattern of yarns, where each fibre end pair exits between two warp threads and is secured firmly with locking half-hitches.
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13.2 The Senneh form of knotting, producing an asymmetrical pattern of yarns, so-called because the action of securing each end of each fibre differs, where each fibre end exits between two warp threads first as a half-hitch and then a simple wrap around the next warp thread.
Having cast the first one or two rows of knots with coloured threads to suit the pattern, a further pair of weft threads was inserted, alternating the warp between each. There then followed the next one or two rows of knotted fibres, continuing until the entire pattern had been completed. The knots are made as tightly together as 30 to 50 knots per square centimetre, the lower quality being those with 30 knots per square centimetre. A knotter could produce 10 000 knots per day, whether using the Ghiordes knot (symmetrical) or the Senneh knot (asymmetrical). Progressing from carpet making to knotted fabrics was not a huge leap of intellect. Indeed, the fringes of the carpets were frequently finished with macramé (mukrameh in Arabic, meaning fringe) tassels or patterns. Knotted fabrics continued with the use of split-ply braiding in Siberian and other Asian continental areas for girth straps and load-holding straps. Other knotted fabrics are noted in loop braiding (Benns and Barrett, 2006), which represents one of the remaining older techniques for knotted fabrics of the fifteenth century. The full development of knotted fabrics as lace did not begin until well into the sixteenth century, when
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lace was developed in Italy and elsewhere in Europe, as far as is known. One of the earliest design books for lacework is titled La Verra Perfettione del Disegno written by Di Giovanni Ostaus in 1561. Barbara Uttmann, in 1561, introduced lace manufacture into the Erzgebirge, the natural mountain border between Saxony and Bohemia. She introduced pillow lace into Germany, having learned lace making from a native of Brabant in the Netherlands and Belgium. Smaller darned fabric squares known as opus filatorium were present probably as early as the thirteenth century, but these were forerunners to lace and not lace itself as produced by hand on pillows using bobbins. By the middle of the sixteenth century lace-work was beginning to become more refined, with a variety of patterns developing. Various movements away from pure lace were experimented with and used in the making of cut-work and other non-knotted fabrics.
13.2
Types of knotted fabrics
13.2.1 Nets (tulle, etc.): structure and properties Nets are generally a series of holes encompassed by thread or twine (see Fig 13.3). Nets, as knotted fabrics, were originally formed by tying knots at the corners of an enclosed space, such as a diamond, rectangle (usually a square), hexagon or triangle, using the cords that form the edges of the shape to make the knots. Net, when made by hand, is built up using a single length of cord wound onto a bobbin known as a netting needle. The needle with cord, together known as a hank of cord, are passed through spaces created with a gage to form a consistent size of mesh, measured from corner to corner. Net fabrics stretch from corner to corner of the diamond shape, losing the width of the piece as the top and bottom of the diamond are extended. Hexagonal mesh nets are more stable in this regard, being limited by the side length of each of the three principal directions in which the net is stretched, and can be formed by twisting threads together, which is the basis for modern machinemade nets such as bobbinet or tulle. Machine-made nets are made using a hexagonal instead of a square shape and may be of a fine mesh gauge up to a relatively coarse mesh gauge. Machine-made tulle nets do not incorporate actual knots such as sheet bends or square knots in their manufacture, the threads being too fine for the finest of net needles. Machine-made nets today use twisted threads to form the edges of the hexagonal or square shape that is later stitched over to form the lacework (see Fig 13.4). The structure is unusually stable and resists slipping that some other twisted net forms suffer. However, when a square shape is formed using the sides of each square as the vertical and horizontal (warp and weft), greater stability is achieved than in using the diamond alignment, because it is the warp and weft upon which the strain is taken. Nets allow a wide flexibility but, with finer threads, are susceptible to breakage and ‘runs’ if not heat-sealed after manufacture.
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13.3 Fruit captured in a knotted net to allow full air circulation, with the ends of the net fabric gathered and wrapped, using a mariners’ technique known as serving, to allow the creation of handles at each end of the fabric.
13.2.2 Macramé: structure and properties Macramé is a heavily knotted fabric, having three to four times the thickness of the original tying thread. Macramé is formed as a series of knots in vertically, horizontally and diagonally aligned individual lengths of (usually) cord, hung from a stretcher or top cord (see Fig 13.5). The cords are normally cotton or jute, although polypropylene cord is enjoying use with the current resurgence in macramé. Each of the cords is usually centred and knotted on a top cord, and hung evenly on one or both sides of that top cord with a ring hitch, also known as a ‘lark’s head’ in some
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13.4 The form of bobbinet tulle shows clearly the tri-directional weave obtained by twisting the threads around each other, the warp running from top to bottom and each diagonal wrapped once around warp threads consecutively, first from the right as here and then the left.
macramé texts. Knotting proceeds under consistent tension in each of the knots used. Normally only the square knot, half hitch, ring hitch, sheet bend and Carrick bend (or Josephine knot) are used alone or in combination. Because the knotted pairs of each side of the same cord are used repeatedly, the formed fabric is stiff in relation to the original cord, depending on the type and tightness of the knots used. Macramé may be made using bobbins for each cord, to ensure that the lengths of cord do not tangle each other during the making of each knot. Originally used to finish the tassels or fringe of carpets, macramé was used extensively during the 1960s to make craft items, such as wall hangings, toys, clothing and plant hangers. The structure of macramé allows great flexibility when planning a piece for decorative fabric. The greatest uncertainty for making macramé is in determining the length of the individual cords needed for the finished article. That length is sometimes given in the list of materials for patterns developed from prior efforts at making such an object, or it may require the maker to add further lengths to the piece during the manufacturing process. The added length is usually knotted in with the other cords, thus making joints harder to see.
13.2.3 Lace (needlepoint lace/bobbinet lace/tatting): structure and properties Lace is a fabric that is formed as a light netting or other network of threads, with patterns made in the body of the network fabric by use of embroidery or other
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13.5 A section of macramé used in a wall hanging, here displayed in front of a clock; note the addition of beads to enhance the final appearance and the four principal hanging warp pairs, formed with square knots, separated with double rows of half hitches, with panels changing between using repeated half-hitches, crossed square knots, granary knots and three-strand braiding.
stitching. Needlepoint lace is made by being worked (stitched) over a paper pattern with buttonhole stitch (Preston, 1938). A pattern is first traced on to paper. The pattern is then traced around with the coarser trace thread (the cordonnet), and the cordonnet is stitched to the pattern with a sewing thread at intervals. Buttonhole stitch is then used over the cordonnet without stitching through the pattern paper.
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Buttonhole stitch itself is formed as a series of interconnected half hitches, sewn around the cordonnet base over the paper pattern. The lace is then separated from the paper with a knife or fine scissors, leaving the buttonhole stitches interconnected over the cordonnet. Needlepoint lace is stable and can be made into an almost infinite series of patterns. Needlepoint lace depends upon the base fabric for its resilience. Bobbinet lace is one form of tulle fabric, made by wrapping the silk, rayon or nylon thread weft yarns around the vertical warp yarn along the diagonal from each side of the piece. It is sometimes also described as bobbin net, in that the formed net uses bobbins to interlace the threads to form the hexagonal shape of the net openings. The fabric thus formed therefore results in opposing hitches of weft around the warp threads to make a hexagonal ‘net’, which is extraordinarily stable. The formed tulle fabric is then used as the base for lace addition, being so light and having such great intrinsic strength. The fabric formed is uniform and flexible, with a durable quality that allows for its high strength:weight ratio. Tatting is a needle or bobbin (shuttle) fabric, formed by interlocking loops, whorls and picots to form shaped pieces of fabric. Tatting is formed either with a shuttle, with a blunt needle or with a crochet hook and blunt needle (cro-tatting). Shuttle tatting is made by passing a loaded shuttle of cotton thread by hand over and around the thread as a half hitch, to form loops and rings into chains that are intertwined to form the pattern. A loop that is left through the normal double stitch (the double stitch is a ring hitch or cow hitch) is used to form a tricot structure that is later used to connect rings and loops. Needle tatting is made by casting a series of ring hitch loops over a smooth untapered needle, through the eye of which is cast either a single or double thread. When the loops have all been cast onto the needle, the needle and thread(s) are pulled through to support the formed loops. Needle tatting is looser than shuttle tatting and depends on the thickness of the needle for the final fabric. Crochet tatting (cro-tatting) uses a tatting needle with a crochet hook at the end. The stitches are cast into rings with the tatting needle and then arches, whorls and other shapes are crocheted with the hook.
13.2.4 Turkish fabric: structure and properties Turkish fabric is made using bright floral motifs formed with silk, wool or precious metal threads, principally as an edging technique known as ‘oya’ or as a technique to make stand-alone doilies (Dickson, 2006). Some also refer to the fabric as knotted lace, Armenian lace, billila, Nazareth lace, Smyrna stitch, and Phoenician lace. The fabric is made by a variety of techniques, such as using a shuttle, bobbin, crochet hook or needle, but the simplest forms use only a darning needle and cotton thread. The wearing of oya flowers such as roses, jasmine and violets was usually limited to young women and girls; it is said older women adorned themselves with a bent tulip. Emotions, relationships and other heart-felt expressions of the soul were made evident through the assembly of different flowers, shapes and motifs, created using knotted fabrics.
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Lace in the form of intricate flowers wrapped around the head is only one of many applications of Turkish fabric. Edging adorns garments, scarves, wraps and undergarments. Today, Turkish lace – often still handmade in small villages and craft shops – is found bordering towels, pillows, curtains, drapes and other housewares. This extends to window blinds, which may have a lace finish with tassels, and to throw rugs and pillows. These are often made of patchwork, embroidered with sequins and gold thread.
13.2.5 Crochet: structure and properties Crochet is a single-needle fabric, made by hand using a single cord. The cord is formed into interconnected loops from a starting slipped knot, through which subsequent loops are pulled using the crochet needle to hook the fine cotton cord. Other cords used include wool and linen. Wool is normally used for clothing, while cotton and linen are used for lace-making. Crochet loops are joined together in loops, chains and bars in patterns in which the stitches are designated according to printed instructions. Crochet is a stable and readily shaped fabric, depending on the tension (or gauge) applied by the person, which enables the making of highly convoluted and intricately curved structures such as may be seen in coral reefs. Crochet work is more stable than knitting because, if a stitch in knitting is dropped, the whole fabric may be lost; a dropped or broken stitch in crochet will result in a hole but will not result in continuing ‘runs’, having locked loops to each side of the broken location for every stitch.
13.3
Production methods for knotted fabrics
13.3.1 Filet/lacis work ‘Filet’ is the French word for net or mesh, while ‘lacis’ is the word for lattice, tracery or network by filling and making shapes on netting. Because the base fabric is a net, the stretch in the direction of the warp and weft (not strictly warp and weft but described here as such) is minimal, while the stretch diagonally can be extensive. Filet or lacis work is performed by use of a special needle that has a fork at each end of a slender steel shaft. The thread is wound over the forks, much after the fashion of the netting needle used when repairing or making a fishing net, and is then passed through the mesh from top surface to underneath to delineate certain sections of the mesh, making them stand out as a pattern of the maker’s choosing (see Fig 13.6). The production of the lace requires that each needle be set up with an appropriate quantity of thread to suit the task and that the base net be stretched over a rigid form, to prevent the sides of each mesh from buckling or distorting. Filet lace is made with cotton thread or silk. The base net may be either cotton or flax. The rigid form of the stretched base net need not restrict the artist to rectangular forms,
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13.6 A sample of filet lace, showing the square net base, with stitched form applied over the base to create the desired figures of leaves, flowers, animals, etc.
13.7 Filet lace, showing the development of quite complex patterns on a square mesh base fabric, here showing the familiar fox and crow tale from Aesop; note the typical ‘stair-step’ edges to the shapes.
because with this type of net one is able to produce curves in the final form (see Fig 13.7).
13.3.2 Bobbinet lace machines The bobbinet lace machine, originally made by John Heathcot in the UK, is fitted with warp threads that unwind downwards as the making of the lace progresses (Earnshaw, 1986). Each bobbin is moved alternately to each side of the warp threads, so as to wind around them. In this manner, each bobbin is moved laterally, the left one moving to the right and the right one moving to the left. As the
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wrapping is completed for each hexagonal mesh formed, a comb pushes up the wraps to ensure the tension of the finished product. This basic principle did not change much until the advent of the Leavers machines (see below). The effect of this type of knotted fabric production was to create remarkably firm fabrics. However, the machines themselves required a very solid structure in which they could be housed, weighing in excess of 17 tonnes.
13.3.3 Macramé bobbins Bobbins for macramé work are usually made of turned wood, having a mushroom or expanded top and bottom, so that they may be used vertically in either direction. The cord to be used is spooled on to each of the bobbins, which are then hung below the work in progress. The cord itself is allowed to extend only as far as necessary to be able to continue to work the cords without interference from each other. The cord is held in place on the spool by using a half hitch around the top end of the spool. The use of the spools is an extension of using hanks or knittles of cord and was promoted as being more organized. Certainly, the weight of the individual spools helped in keeping even tension, which the use of hanks was unable to provide.
13.3.4 Leavers machines Leavers machines are among the older technologies used for making lace (Earnshaw, 1986). Beam threads (the warp) are wrapped with bobbin threads (the weft), which twisted wraps are then combed with finely separated steel plates to tighten the structure. The Leavers machine represented a slight departure from the earlier Heathcot machine because of its lighter construction. The twist imparted to the finished fabric resulted in a heavier ridge to the fabric, providing greater definition. Leavers machines with their smaller footprint are much sought after in the production of lace, because of their ease of maintenance and the consistency of their fabric, with less breakage of threads.
13.3.5 Raschel machines The Raschel machine is a machine that relies on warp knits. As such, the warps are laid diagonally to form the fabric. Each warp is then twisted, locked with a loop from the adjacent warp and then shifted back, by one warp, to the prior column of knitting. The needles in the machine move in a ground steel plate. This plate is known as a trick plate. It limits the top level of the loops, known as the verge. The loops are limited by the pull of the yarn and sinkers that are located between the needles. The machine has locking belts that are fixed in location relative to a plane that is perpendicular to the shaking motion, the motion usually referred to in the industry as shogging. In addition, the yarn laying-in comb, and at least one guide bar for the stitch yarns, is movable not only in a plane perpendicular to the shaking direction but
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also in a plane parallel to it. The motion of the laying-in comb allows large under laps without the associated risk of faulty lapping of the yarns. Coarser yarns are generally used for Raschel knitting, and there has recently been interest in knitting staple yarns on these machines. In a knitting cycle, the needles start at the lowest point, when the preceding loop has just been cast off, and the new loop joins the needle hook to the fabric. The needles rise, while the new loop opens the latches and ends up on the shank below the latch. The guide bars then swing through the needles and the front bar moves one needle space sideways. When the guide bar swings back to the front of the machine, the front bar has laid the thread on the hooks. The needles fall, the earlier loops close the latch to trap the new loops, and the old loops are cast off. Raschel knits, made in a variety of forms, are usually more open in construction and coarser in texture than are other warp knits. The structure of the finished fabric is subject to some minimal failure if a thread breaks after manufacture, because of the continuous locking of adjacent stitches. However, as with any increase in complexity, there is an increased maintenance cost to ensure that all parts remain fully functional.
13.3.6 Schiffli machines Schiffli lace or chemical lace is made by embroidering the pattern onto a base fabric that is then chemically removed using solvents that dissolve the base fabric without harming or affecting the embroidery (Earnshaw, 1986). Because of environmental limitations concerning the disposal of the effluent from this process, the original process is now limited to third-world countries or to home and small business applications only. Larger Western manufacturers use watersoluble fabrics or heat-soluble base fabrics that are removed from the finished article with water or heat respectively. The embroidery is performed using a multi-head or multi-needle machine to apply the threads distally and proximally through the base fabric, allowing the use of multiple colours also on each needle. As each needle passes through the base fabric, a bobbin behind that stitch moves up into the formed loop, allowing the insertion of the locking thread. The needles and the bobbins are normally controlled by a Jacquard process to ensure consistency of the finished product. Because the embroidered stitches rely on their own adjacent stitches for support, there being no remaining base fabric, the final fabric tends to react poorly to excessive tension in any one direction. In addition, the thickness of the finished fabric may vary considerably.
13.4
Applications for knotted fabrics
13.4.1 Nets Netting is used in many different ways today, and was widely used in the past. Bridal veil applications come most readily and quickly to mind, together with that
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other more morbid sector of life when coffins are lined with a light, gauzy form of netting. As a base for the application of embroidery, netting is invaluable. It was, however, in the application of veils and headdress trains that netting came into its own, forming the light and airy covering to the face that allowed vision and yet kept secret the identity of the wearer. Of a rather more practical and everyday use, rather than special occasion use, netting was used extensively in fishing, as it has been for many thousands of years. Fishing nets were first developed as circular cast nets for use from the shore, then as elongated nets placed across a river’s mouth, or in fish traps where tides allowed, catching the incoming spawning fish. Later they were developed as purse or seine nets, to draw through the water from the stern of a fishing boat, either catching shoals of herring or trawling oysters from the sea-bottom. In the rather more specialized arena of the world of fashion, whether everyday fashion or high fashion, nets have come to be used to hide and to accentuate figures, forms and flaws. Nets have been used almost continuously for adding to millinery to accentuate its features, have been added as shawls to enhance the perhaps more drab fustian clothing beneath, to provide pockets of peek-a-boo interest and titillation to dresses, and to act as accents in the form of delicate lacy handkerchiefs. Nets have also found great use in the home and when abroad. At home, hammock nets are used to hold fruits and vegetables in the dry air to encourage the circulation of air and maintain ripeness, whilst relaxing seat and full-length hammocks are being used to suspend people in a relaxed manner. When abroad, mosquito nets were frequently an essential item to be packed to ensure a trouble-free sleeping area away from annoying biting insects. Nets were also used to separate rooms from one another and to act as discreet shelters from prying eyes.
13.4.2 Macramé Macramé was used in high fashion and as a fad decorative fabric. From its early days in the edging of Eastern rugs and carpets, macramé was developed in fashionable houses throughout Europe, but more particularly in Spain where it was imported by the Moors, as a screen, wall-hanging, clothing accent or other necessary addition to improving one’s social status. In home ware, macramé has found extensive use in place mats, coasters and other tabletop coverings. Macramé has also been used extensively in making jewellery, whether formed from hemp twine in the making of friendship bracelets for school-age wearers, or in the form of cavandoli and micro-macramé for more adult wear. Macramé has found great popularity for use as a wall hanging. Pieces of macramé in addition to collage, upholstery and other fabrics, have been used by famous artists, like Joan Miró (1893–1983), to adorn large open walls or may be used as an accent to frame photographs or other pictures. Macramé has also been used as the central art in wall hangings of a more limited size.
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13.4.3 Lace Lace is most famously used in lingerie, whether as pieces of the whole costume or as the fabric of the costume itself. Delicately shaped flowers, symbolic hearts and animals, leaves, whorls, circles and other shapes have all been used to wonderful effect in the manufacture of lace for lingerie. Strategic placement of the essential decorations ensures that the rather flimsy base net does not permit too much visible flesh. Coloured lace is especially useful for making lingerie. When lace is used for the entire piece, it drapes very well and may even be formed into a robe or cape. The use of lace for lingerie pieces is limited only by the imagination. Lace used for headscarves is now somewhat less used in the Western world than in Spain and Spanish-speaking countries where it is used as a mantilla. Lace is still used for making scarves for special occasions rather than for everyday use. Lace as a fashion accessory may be used in women’s fans, accents to millinery, trim to dresses and gowns, edgings to wraps, skirts and dozens of other locations that require an accent. Home ware that incorporates lace is also found in the form of tablecloths, runners and doilies. Formerly, when men used to apply macassar oil to their hair, lacy antimacassars would be made for chairs and sofas, using cotton treated to resist the rather smelly oil. Delicate cutwork is also decorated with lace edgings and borders to enhance the appearance of an embroidered or sewn piece.
13.5
Future trends for knotted fabrics
Knotted fabrics will continue to find a place in many fabric applications, even extending to the use of matrix forms used for manufacturing carbon-fibre elements of structural elements of space vehicles for lightness, ships that travel in highstress ocean waves and fabrics for protection from the elements. However, it is important to recognize that plastics and other combinations of materials are derived from non-renewable oil and that plant-fibre origin fabrics will soon supplant other non-renewable sources. Knotted fabrics, in addition, can be produced by a manufacturing method that does not rely on machinery, which requires tremendous energy to both create and maintain. Knotted fabrics also are very useful for creating clothing that traps air next to the body, allowing body heat to control thermal regulation.
13.6
Sources of further information and advice
Textile Institute (Manchester, England). M. C. Tubbs and P. N. Daniels (eds), Textile Terms and Definitions, Manchester, UK: Textile Institute, 9th edn, revised and enlarged (1991). Judith Jerde, Encyclopedia of Textiles, Australia: Warner Books (1992). William R. Cline, The Future of World Trade in Textiles and Apparel, Washington, D.C., Peter G. Peterson Institute for International Economics, revised edn (1990). F. Happey (ed.), Contemporary Textile Engineering, MO: Academic Press (1982).
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D. G. B. Thomas, An Introduction to Warp Knitting, Watford, UK: Merrow Publishing Company Ltd (1976). John E. Nettles, Handbook of Chemical Specialties: Textile Fiber Processing, Preparation, and Bleaching, NJ: John Wiley & Sons (1983). Journal of the Textile Institute (bi-monthly), Taylor & Francis, UK. Textile Progress (quarterly), Taylor & Francis, UK. Textile World (irregular), GA, USA.
13.7
References
Ashley, C. W., 1944. The Ashley Book of Knots. Garden City, New York: Doubleday & Company, Inc. Benns, E. and Barrett, G., 2006. Tak V Bowes Departed: A 15th Century Braiding Manual Examined. Cheapside, London: Soper Lane. Dickson, E., 2006. Mediterranean Knotted Lace. Bowral, NSW: Sally Milner Publishing. Earnshaw, P., 1986. Lace Machines and Machine Laces. London: B.T. Batsford Ltd. Helloproskill, 2010. At http://en.wikipedia.org/wiki/Carpet, last updated 15 January 2011 (accessed 18 January 2011). Himmelfarb, D., 1957. The Technology of Cordage Fibres and Rope. London: Leonard Hill (Books) Ltd. McKenna, H. A., Hearle, J. W. S. and O’Hear, N., 2004. Handbook of Fibre Rope Technology. Cambridge, UK: Woodhead Publishing Limited. Preston, D. C., 1938. Needle-Made Laces and Net Embroideries: Reticella Work, Carrickmacross Lace, Princess Lace and Other Traditional Techniques. London: Woman’s Magazine Office.
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14 Developments in braided fabrics P. POTLURI and S. NAWAZ, University of Manchester, UK
Abstract: Braiding is a bias interlacement technique for creating rope-like structures. This chapter covers the basic concept of maypole braiding, in which yarn carriers rotate around a circular track similar to a maypole dance. Braid classification is presented in terms of 2D and 3D braids; biaxial and triaxial braids; circular and flat braids; diamond, regular and Hercules braids. Mandrel over-braiding is a convenient method for manufacturing flexible hoses as well as fibre-reinforced composites. Geometry of the braided structure in terms of braid angle and cover factor, as well as geometrical relations in a jammed state, has been presented. Applications for braiding in fibre-reinforced composites, flexible hoses, sporting goods, wiring harness and medical devices have been presented. The final part of this chapter discusses newer applications, such as air beams for inflated shelters and a large diameter airlock developed by NASA. Key words: maypole braiding, braid angle, cover factor, yarn carrier, mandrel over-braiding.
14.1
Introduction
Considering the large number of application areas, braiding is a relatively less explored subject area within the textiles curriculum. Brunnschweiler was the first author, certainly in the English language, to publish a systematic study of braids as a technical subject in 1953. He presented a systematic analysis of braided structures and the concept of braiding machines prevailing at that time.1 In a follow-on paper, Brunnschweiler, based on his master’s degree research at Manchester University, described the structure and tensile properties of braids.2 This is a classical paper on the mechanics of braided structures. Shortage of up-todate information on braiding technology prompted Douglass3 to publish a book entitled Braiding and Braiding Machinery in 1964. To this date, this is the only book dedicated to braiding technology. This chapter aims to cover the gap in textile literature on braiding from the product rather than machinery point of view. The basic concept of maypole braiding is explained with reference to the maypole dance. Braid classification is presented in terms of interlacement patterns, materials types and the number of yarns systems. The geometry of the braided structure and its influence on physical and mechanical properties of the final products are also described. The loadextension behaviour of braided structures has been examined briefly for structures with and without a core. This chapter also presents a detailed list of application areas with product examples. 333 © Woodhead Publishing Limited, 2011
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14.2
Braiding
Braiding is the formation of comparatively narrow fabrics or rope-like structures by diagonally interlacing three or more strands of material. In conventional braiders, yarn carriers rotate along a circular track with half the carriers in a clockwise direction while the remaining carriers travel in a counter clockwise direction, similar to a maypole arrangement. As a result, the two sets of yarns interlace with each other at a biased angle to the machine axis. By contrast with lace-making, braiding may also be defined as the production of ribbon-like or rope-like textures by interlacing of one set of threads in such a manner that no two adjacent threads make complete turns about each other.1 Braiding has traditionally been used for producing textile structures such as shoelaces and ropes. However, in recent years, technical application areas such as fibre-reinforced composites and medical implants have become popular. By using three-dimensional mandrels, one can produce 3D textile preforms for applications such as aircraft rotor blades. Braided structures are similar to woven structures in terms of the topology of yarn interlacement. For example, Diamond, Regular and Hercules braids are similar to Plain, 2/2 Twill and 3/3 Twill weaves respectively. Braids are commonly produced in a tubular form, only a few inches in diameter owing to the limited number of yarns used, whereas woven fabrics are often produced as a broad cloth, several metres wide.
14.2.1 The maypole dance Braiding resembles a traditional maypole dance, in which people dance around a pole holding ribbons tied to the pole at the centre (Fig. 14.1). Dancers are divided
14.1 Maypole dancing.
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into two groups (typically men in one group and women in the second group) with half travelling around the pole in a clockwise direction while the other half travel in an anti-clockwise direction. Dancers move from the inner circle to outer circle or from the outer circle to the inner circle, after passing each dancer moving in the opposite direction. As a result, each dancer is constantly moving between inner and outer circles causing the ribbons to interlace with each other. The resulting ribbon structure is identical to a braid. A similar concept has been replicated in maypole braiding machines.
14.2.2 Maypole braiding The traditional maypole braider (Fig. 14.2) is a relatively simple mechanism to control. It has two sets of yarn carriers rotating on a circular track, one set rotating
14.2 A maypole braiding machine.4
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in the clockwise direction and the other set rotating in the anti-clockwise direction; during this process, they interlace with each other to form a tubular braided structure. The braided structure is either created as a continuous sleeve or is deposited on a solid mandrel. The resulting braid is continuously moved forward using a take-up mechanism. The maypole braiding machine consists of a track plate with two sinusoidal tracks criss-crossing each other (Fig. 14.3). Each yarn carrier is located in a slot of a horndog and hence propelled either in a clockwise or an anti-clockwise direction. The horndogs are driven by horngears (Fig. 14.4). Adjacent horngears mesh with each other, therefore, they rotate in opposite directions and drive adjacent horndogs in opposite directions. Yarn carriers are transferred from one horndog to the next when the slots are aligned. For example, yarn carriers, shaded black in Fig. 14.3, continue to travel in the anti-clockwise direction and yarn carriers, shaded white in Fig. 14.3, continue to travel in the clockwise direction. Since the yarn carriers move continuously from the inner circle to the outer circle, the change in yarn length (difference in length between L1, L2 or R1, R2) must be compensated for (Fig. 14.5). As shown in Fig. 14.4, yarn passes around a roller mounted on a dancing arm. The dancing arm, tensioned by a spring, can retract the yarn when the yarn carrier is closer to the centre and release extra length when the yarn carrier is farther from the centre. Yarn tension can be adjusted by the dancing arm tension.
14.3 Arrangement of circular maypole braiding.
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14.4 Arrangement of a yarn carrier.
14.5 Change in yarn length in relation to position on the track.
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14.6 Biaxial (a) and triaxial (b) braid construction.
14.3
Classifying braids
The braid structures can be classified into two main groups:
• •
Two-dimensional (2D) braids Three-dimensional (3D) braids.
Two-dimensional braids refer to single layer structures whereas 3D braids refer to multi-layered inter-connected structures.
14.3.1 2D braid structures Two-dimensional braided structures are either biaxial or triaxial in configuration (see Fig. 14.6). The biaxial construction is the most commonly used and has two sets of yarns travelling in opposite directions, where yarns in one direction are passing under and over the other yarns. This is a popular structure because the construction is predictable, it has consistency in lay-up and the braid can match any shape. Biaxial braided sleeves can be draped over a mandrel with varying cross-sections without creating wrinkles. The triaxial braid consists of a third set of longitudinal yarns in addition to the biaxial interlacing yarns. They are supplied from a stationary creel and fed through the centre of horngears/horndogs. These longitudinal yarns are often referred to as axial/warp yarns. These warp yarns are not necessary for the braid formation, but provide the braid with its essential characteristics, such as tensile and compression strength in addition to an improved modulus in applications such as fibre-reinforced © Woodhead Publishing Limited, 2011
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composites. However, the use of these warp yarns can lock the diameter of the braid and prevents its natural tendency to expand and contract; but if elastomeric yarns are used then this limitation can be overcome. Smart fibres can also be incorporated into the triaxial braid as the warp threads, for example, to give a smart braid that can be used as an actuator/sensor.
14.3.2 Mandrel over-braiding For structural composite applications, it may be necessary to braid directly over a mandrel (see Fig. 14.7) for the following reasons:
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Triaxial sleeves cannot be draped over rigid mandrels and hence triaxial braided structures have to be formed directly over a mandrel;
14.7 Mandrel over-braiding.
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Biaxial sleeves can be draped over complex mandrels; however, the braid angle is a function of mandrel diameter and hence cannot be controlled. In mandrel over-braiding, the braid angle can be controlled (by varying the take-up speed) independent of the mandrel diameter; Mandrel over-braiding is convenient for creating shapes with multiple braid layers by passing the mandrel back and forth through the braiding machine.
The over-braiding process is also used for producing hoses, electrical cables and cords with a solid core.
14.3.3 Braided structures with different interlacement patterns The braid interlacement patterns are very similar to woven structures. Diamond braids are similar to a plain weave with 1/1 configuration. Regular braids have a 2/2 twill weave repeat, whereas Hercules braids have 3/3 twill weave repeat (Fig. 14.8).
14.8 Braided structures: (a) diamond braid; (b) regular braid; (c) Hercules braid.
14.3.4 Flat braids Conventional braiding machines produce tubular fabrics. However these machines can be modified to produce flat fabrics. The simplest braid structure is the soutache braid; this uses the minimum of three yarn carriers and two horndogs with an odd number of slots (Fig. 14.9). The yarn carriers move in figure-of-eight
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14.9 Soutache braider.3
motions. This type of braid is usually used for candle-wicks, embroidery and trimmings. Flat braids can be produced by extending the concept of soutache braiding, by placing several horndogs in line (Fig. 14.10(a). Two horndogs at each end of the track need to have an extra slot. By placing the horndogs along a circular arc (Fig. 14.10(b), variation in the yarn length between the carrier and the braid fell position can be minimized. Both biaxial and triaxial flat braids can be produced using this arrangement.
14.3.5 3D solid braided structures Three-dimensional solid braids consist of several inter-connected layers. Horngears can be positioned in different arrangements in order to produce 3D fabrics. Depending on the placement of the horngears, tubular and rectangular shaped structures can be formed. In 3D tubular braids the yarns also pass under and over each other in the wall thickness direction as well as moving in a helical clockwise and anti-clockwise direction. Fig. 14.11(a) shows a square braid produced using four horngears showing interlacement around four warp yarns. This concept can be extended to a larger matrix by placing several horngears in a
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14.10 Flat braiding.
14.11 (a) square braid; (b) horngear arrangement for a 3D solid braid; (c) 3D braid formation.
two-dimensional grid. Another example is the 3D rectangular braided fabric (Fig. 14.11(b) and (c)), which is produced on a rectangular loom; however several different braid structure and complex shapes such as an I or T shape can be formed by modifying the appropriate yarn carrier settings.
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14.3.6 Hybrid braids A hybrid braid is produced by using two or more different types of yarn. It is advantageous for applications where the fabric requires the properties of various materials. It is also possible to produce braids with an assortment of aesthetic properties.
14.3.7 Other examples of braids
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Rick-rack braid: The rick-rack braid has a distinctive wave-like structure and is mainly used as a trimming. It is produced on a flat braider and the zig-zag structure is achieved by adjusting the yarn carrier tensions. Multiple-layer braid: If there is a need for a thick braid, then multiple layers/ plies of braid can be braided on top of each other in order to create the required thickness. Square braid: The square braid, as the name suggests, has a square shape and consist of a hole through the centre. This is because the square-braiding machine differs from the circular machine in the sense that it consists of four
14.12 A lay.3
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or more horngears, which support the movement of the yarn carriers in a square pattern. The number of yarn carriers can range between four and twenty-four, and the machine requires less space than the maypole-braiding machine which is another advantage of square braiding.
14.4
The geometry of the braided structure
The braid output is usually measured in stitches/picks per centimetre for both flat braid and tubular braids. The output can also be measured by the lay distance: this is the length the braid has travelled during a complete cycle of any one yarn carrier. The way to measure this is at the beginning of the braid, to soil one of the yarns to act as a marker (this fault on the yarn will not matter if it is at the beginning of the braid because it can be discarded). Then run the machine for a few centimetres, the marked yarn will be visible, and the lay distance can be measured, as shown in Fig. 14.12. The braid angle (θ) is the angle of interlacing yarns with respect to the braid axis (Fig. 14.13). The braid angle depends on the lay (L) and the radius (r) of the braid: [14.1] If the braid is being used to cover a core yarn or a product, such as metal wire for electrical purposes, then the area of the core which the braid covers is referred to as the braid cover factor. This is determined by the diameter of the core/mandrel (which is being covered), the braid angle, the number of yarn carriers and the width of the yarn. The width of the yarn depends both on the linear density and the twist of the yarn.
14.13 (a) The braid angle; (b) unit cell for the cover factor calculation.5
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The braided structure forms a number of parallelograms in the circumferential direction equal to Nc /2 where Nc is number of yarn carriers. ABCD represents the unit cell for analysing the braid geometry. The cover factor may be calculated using the following formula.5 [14.2] where: W = yarn width (or diameter if it is a round yarn) Nc = number of yarn carriers R = effective mandrel/braid radius θ = braid angle. While the cover factor is important for applications such as cables and cords, fibre volume fraction is important for applications in fibre-reinforced composites. Fibre volume fraction may be calculated as5 [14.3]
where: C = yarn crimp measure similar to a weave T = yarn linear density in Tex (g/km) ρ = material density (g/cc) tc = composite laminate thickness. Biaxial braided fabrics behave like a trellis during tensile or compressive deformation and offer very little resistance until a state of jamming is reached. Since the yarns are at an angle to the braid axis, effective yarn width is . Geometrically, a braided structure is considered to be jammed if half the yarns are in contact with each other: [14.4] In fact, half the yarns form a circle in a tensile jammed state while all the yarns form a circle in a compression jammed state. In order to consider both the states, a yarn compaction factor has been introduced into equation (14.4)6: [14.5]
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where: Rj = jammed braid radius ∇= yarn compaction factor ranging from 1 (in case of compression) to 2 (in case of tension); (see Fig. 14.14). When a braid is stretched (Fig. 14.15), the braid angle decreases from θ1 to θ2 while the unit cell height increases from l1 to l2. Initially, the force required to extend the braid is relatively small in order to overcome frictional resistance at the interlacement points. Once the braid is jammed, load-extension behaviour is dominated by de-crimping and yarn
(a)
(b) 14.14 Jammed state in (a) tension and (b) compression.
14.15 Braid geometry in an extended state.
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transverse compaction. Tensile strain in a braid may be calculated using the following formula: [14.6] Tensile force versus the strain relationship of biaxial braids has been studied by several authors. Phoenix7 and subsequently Hopper et al.8 studied the mechanics of biaxial braids with an elastic core. Hopper et al. identified four modes of deformation depending on the relative diameters of the core and the braided sleeve. Subsequently, Hristov et al.9 modelled a biaxial sleeve without a core. Potluri et al.10 modelled stress–strain behaviour of a braided cored for a knee ligament prosthesis. These mechanical models are useful in predicting the braid behaviour in a number of products including ropes, cords and medical prostheses.
14.5
Applications of braided fabrics
Braided fabrics were traditionally used as shoe laces, candle wicks, parachute cords, sash cords, fishing lines and dress trimmings. Industrial products such as hydraulic hoses, electrical cables, wiring harness have been developed through the twentieth century. However, since the 1970s, the main focus has been on fibrereinforced composites owing to a phenomenal growth in space technologies.
14.5.1 Fibre-reinforced composites Braided structures used as composite preforms have a number of advantages over other competing processes such as filament winding and weaving:
•
•
•
• •
Braided composites have superior toughness and fatigue strength in comparison to filament wound composites. In filament wound composites, cracks propagate readily along the fibres, while points of interlacement in braided composites act as crack arresters; Woven fabrics have orthogonal interlacement while the braids can be constructed over a wide range of angles, from 10° to 85°. An additional set of axial yarns can be introduced to the braiding process to produce triaxial braids; triaxial braids are more stable and exhibit nearly isotropic properties; Braids can be produced either as seamless tubes or as flat ribbon with a continuous selvedge. Composites produced with the braided preforms exhibit superior strength and crack resistance in comparison to broadcloth composites, owing to fibre continuity; Composites with braided holes exhibit about 1.8 times the strength in comparison to cut drilled holes, again due to fibre continuity. (Figure 14.16); Branching and rejoining of various sections is very conveniently done with braiding;
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14.16 A braided hole versus a cut hole.
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Braids are relatively narrow structures. However, companies such as A&P Technologies11 produce over braided fabrics that are 0.5m wide using large braiders; The braiding process can be integrated with pultrusion to produce a variety of pultruded structural parts (pultrusion is a composites manufacturing process in which a textile preform such as a braided tube is pulled through a die in order to impregnate it with a resin).
Braided composites have been used in a variety of applications in aerospace, recreational, medical prosthetic, automotive and industrial applications. Aerospace applications include composite ducting, rocket nozzles, missile casings and helicopter drive shafts. Recently, GE developed a braided composite fan casing for its next generation of aero engines (GEnx)12 using the braided fabrics developed by A&P Technology. These braided composite casings offer 30% better containment in comparison to metallic casings, and do not suffer from fatigue. A&P Technology11 developed a range of braided fabrics in a number of configurations using carbon, glass, Aramid and hybrid fibre systems. Braided architectures include standard biaxial and triaxial sleeves, flat fabrics, unidirectional reinforcements with elastic bias yarns for conformability, quasi-isotropic fabrics with 0/±60° and shaped fabrics for draping over corrugated shapes (example, fan containment casings). A&P demonstrated braided fabrics over pressure cylinders. Recreational composites include sports bicycle frames, hockey sticks, baseball bats, tennis racquets and fishing rods. Braided socks have been used in the manufacture of medical prosthetic devices such as artificial limbs, especially in the socket area due to the highly conformable nature of braids.11
14.5.2 Braided hoses Hydraulic and fuel hoses in cars, trucks, earth-moving equipment, marine engines and aeroplanes are a common feature. Braids provide the hoses with excellent burst strength and flex-fatigue to the hoses and hence are used universally in hose
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14.17 Hose braiding.4
manufacture. Synthetic rubber is most commonly used as matrix material although PTFE is used for higher temperature application. Hose braids are made with a range of fibres including polyester, Kevlar, glass as well as metal wires (stainless steel in a number of applications). A mandrel is typically covered with a rubber layer before over-braiding (Fig. 14.17); this is followed by application of a final layer of rubber.
14.5.3 Sports applications •
• • •
Sail masts: The braided cord/rope is tightly braided so it has tight braid angles, which enable the rope to maintain its hardness and retain its constant diameter. These can be made from several different materials such as polyester, aramid and vectran. Archery string: Braided cord is used in archery to reinforce the bow string at the nock (where the arrow fits) so that it lasts longer. This is usually made from high-modulus polyethylene or polyester, or a hybrid of both. Bungee cords: Cord used for a bungee jump is a braided shock cord. This is a hybrid cord that incorporates a latex strand within the tough outer layer. Fishing lines: Braided finishing lines are becoming more popular as opposed to monofilament nylon or polyester fishing lines. This is because the braided structure gives strength toughness and abrasion resistance, so a fish is very unlikely to break it. However, braids are visible in water, so are not suitable in clear water where they might drive away the fish.
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14.5.4 Electrical
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Multi-media cords: Multi-media cords use a braid structure because it is flexible but tough enough to withstand repeated movement. Also, for example, earphones have nylon-braided cords to minimize entanglements. Wiring harness: Automotive and aircraft wiring harnesses (Fig. 14.18) can be overbraided due to the unique ability of braiding to create branches.
14.5.5 Medical applications
•
•
Dental posts: A braided dental post is used in tooth restoration as opposed to one made from stainless steel because it is more fracture-resistant and longer lasting. The stiffness can be altered along the length of the post by altering the braided structure, eliminating stress concentration at the root region, which is another problem faced when using a stainless steel post. Maxbraid ™ PE sutures: Maxbraid™ suture comprises of 100% polyethylene, to help eliminate suture fray and breakage. The braid allows outstanding
14.18 Wiring harness.
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flexibility, pliability, and surgical ease-of-use. It has a high tensile strength and a silky smooth feel, but also great knot-tying characteristics.15 Ligament scaffolds: Braided fibrous scaffolds are used in tissue engineering for structural tissue repairs (such as nerve, blood vessel, tendon, ligament, cartilage). The braided scaffold provides a base around which the tissue can regenerate.
14.5.6 Wire braided cords
•
•
Coaxial cables: Coaxial cables use two sets of wires: one is covered with a layer of insulation and is placed through the centre of a braided sheath, which is then covered with another insulation layer. The inner wire is the primary conductor and the braided sheath acts as a shield against external interference. These cables are widely used for TVs, telephones, computers, and data transferring. Braided wire cords: Braiding wires into cords is appealing mainly owing to their flexibility, and is used in a range of applications such as flexible connectors and battery cables; it is also used as a flexible earthing solution.
14.6
Future trends in braided fabrics
New markets are opening for braided products especially in aerospace and the automotive composites, especially with the development of large braiders with as many as 800 bobbins or more. GEnx fan casing is one example.12 Recently, largedrive shafts for helicopters are being developed using braiding technology.13 Fabric preforming technology developed by A&P is also very interesting from the point of view of manufacturing composites with complex shapes. Lexus has recently announced the development of a radial braider for manufacturing automotive parts.14 Large braiding machines have opened up interesting applications in inflatable structures for use in military, space as well as civil defence. Figure 14.19 shows a shelter made using braided air beams.11 A&P developed a Vectron sock 2 metres in diameter and 3 metres in length using an 800 carrier braiding machine. Figure 14.20 shows a prototype airlock developed for NASA using the braided sock developed by A&P. The carbon fibre composites market will grow from the current 40 000 tonnes to 1 million tonnes in the next decade or so. This growth is propelled by civil aircraft (Boeing 787, Airbus A350XWB) as well as the automotive and wind turbine industries. A substantial proportion of this work will utilize dry-fibre preforming technologies such as 3D weaving and braiding. Braiding has an advantage over 3D weaving in its ability to place bias yarns. In addition, 3D
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14.19 Inflatable shelter with curved braided airbeams.11
14.20 Braided airlock developed for NASA.
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braiding technologies developed during the 1970s for the US space programme are likely to see a re-emergence due to the buoyant growth in applications for carbon composites.
14.7
References
1. Brunnschweiler, D. Braids and braiding. Journal of the Textile Institute Proceedings, 1953, 44(9): 666–686. 2. Brunnschweiler, D. The structure and tensile properties of braids. Journal of the Textile Institute Transactions, 1954, 45(1): 55–77. 3. Douglass, W. A. Braiding and Braiding Machinery, Centrex Publishing Company, Eindhoven, Netherlands, 1964. 4. Cobra Braiding Machinery, Congleton, Cheshire, UK, www.cobrabraids.co.uk. 5. Potluri P., Rawal A., Rivaldi M. and Porat I., Geometrical modeling and control of a triaxial braiding machine for producing 3D preforms, Composites Part A, 2003, 34:481–492. 6. Lyons J., Pastore C. M., Effect of braid structure on yarn cross-sectional shape, Fibres and Polymers, 2004, 5(3): 182–186. 7. Phoenix S. L., Mechanical response of a tubular braided cable with an elastic core, Textile Research Journal, 1978, 48: 81–91. 8. Hopper R. H., Grant J. W. and Popper P., Mechanics of a hybrid circular braid with an elastic core, Textile Research Journal, 1995, 65: 709–722. 9. Hristov K. E., Armstrong-Carroll E., Dunn M., Pastore C. and Gowayed Y., Mechanical behaviour of circular hybrid braids under tensile loads, Textile Research Journal, 2004, 74(20): 20–26. 10. Potluri P., Cooke W. D., Lora Lamia A. and Corral Ortega E., Designing the carbon– polyester braids for ligaments, Journal of Textile and Apparel, Technology and Management, 2003, 33(2): 1–12. 11. A&P Technology, Cincinnati, Ohio, USA: www.braider.com. 12. Griffiths B., Composite fan blade containment case, High Performance Composites, May 2005. 13. Garhart J, Development and qualification of composite tail rotor drive shaft for the UH-60M, Nineteenth AeroMat Conference & Exposition, Austin, TX, 23–26 June 2008. 14. Giant 3D loom weaves parts for supercar, 10 February 2011, at http://www.newscientist. com/blogs/nstv/2011/02/giant-3d-loom-weaves-parts-for-supercar.html?DCMP=OTCrss&nsref=online-news. 15. www. biomet.com/sportsmedicine.
© Woodhead Publishing Limited, 2011
Index
A & P Technology, 155 acoustic comfort, 190 acrylic, 194 acrylic fibres, 299 adhesive bonding, 214 adhesives flocking, 301–3 plastisols, 302–3 solvent-based adhesives, 302 thermosetting adhesives, 302 water-based adhesives, 301–2 air-jet spinning, 16–18 air-jet compound yarns structure, 17 technological process, 16 air-jet texturing, 39–41 principle, 39 air layering, 266 allergies, 191 angle-interlock fabrics, 183–4 anti-shading treatments, 217 TRUTRAC anti-shading principle, 218 apparel, 49–50 hybrid yarns in apparel application, 50 Axminster weaving, 211–13 commonly used weave structure, 212 weaving cycle of the MAX91 Axminster loom, 213 backcoating, 206–7 backed cloth, 178–9 illustration of warp- and weft-backed cloth, 179 warp-backed cloth, 178–9 weft-backed cloth, 179 backing materials, 205–7 primary backing fabrics, 205–6 secondary backing fabrics, 206 bare core type yarn, 8 basic triaxial weave, 141 BD 340 filea, 32 bobbinet lace machine, 327–8 bouclé yarn, 80–1 braid angle braid axis and cover factor calculation, 344
braid interlacement patterns, 340 braided structures, 340 braided fabrics, 333–53 applications of braided structure, 347–51 braided hoses, 348–9 electrical applications, 350 fibre-reinforced composites, 347–8 medical applications, 350–1 sports applications, 349 wire-braided cords, 351 wiring harness, 350 braiding, 334–7 Maypole braiding, 335–7 maypole dance, 334–5 classification, 338–44 biaxial and triaxial braid construction, 338 braid interlacement patterns, 340 2D braid structures, 338–9 3D solid braided structure, 341–2 flat braids, 340–1 hybrid braids, 343 mandrel over-braiding, 339–40 other examples, 343–4 future trends, 351–3 geometry of braided structure, 344–7 A lay, 343 braid angle, 344 extended state, 346 jammed state, 346 braided hoses, 348–9 hose braiding, 349 braided ropes, 60–2 braided rope with jacket, 62 double-braid or braid-on-braid ropes, 62 eight-strand plaited ropes, 60–1, 61 overview, 60 single hollow braid ropes, 61–2 twelve-strand rope, 61 braiding, 334–7 Maypole dancing, 334 braiding technique, 158 break-out device (BOD), 10
355 © Woodhead Publishing Limited, 2011
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356 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 20 1 2 3 4 5 6 7 8 9 30 1 2 3 4 5 6 7 8 9 40 1 2 43X
Index
brocade, 250–2 brocade Jacquard design, 252 brocade Jacquard design with extra weft figure on plain weave ground, 251 brocatelle fabrics, 252 button yarn, 84 CAD, 241 cam shedding system, 226 illustration, 226 carbon fibre composites, 160 carpet cleaning, 191 Carpet Star, 214 cellulosic fibres, 195–6 chainette knitting process, 98–101 basic process, 98–9 knitting head assembly, 99 eyelash or feather yarn refinements, 99–101 addition of eccentric yarn guide system, 101 bladed needle placement, 100 overhead view of eccentric yarn guide, 101 yarn path for effect (or hair) yarn in feather yarn knitting, 100 chainette yarn, 84–5, 85 chenille, 96–8 spinning machine, 96–8 chenille spinning, 97 front view of machine, 98 weaving, 96 woven process, 96 chenille yarn, 85–6 Chinlone, 145 circular knitting machine, 114 circular leno loom, 139 cloud or grandelle yarn, 82 co-polyester resin (PET) matrix, 42 coloration, 215–16 Colorpoint machine, 205 Colortec machine, 204–5 combined system, 91–4 changes, 93 original combined system, 92 commingling, 42–4 commingled yarn cross-section, 46 commingling machine for hybrid yarn, 45 commingling process principle, 44 Twintex commingled yarn cross-section, 42 Twintex process, 43 Commonwealth Scientific and Industrial Research Organisation (CSIRO), 9 compound yarns, 1–19 applications, 13–14 future trends, 14–19 air-jet spinning, 16–18 friction spinning, 18–19 product developments, 19 raw materials development, 14 rotor spinning, 14–16
production methods, 5–13 conventional ring spinning system, 6–9 siro spinning system, 9–13 types, 1–5 compound yarns with elastomer core, 2–3 compound yarns with polyester core, 3–4 compound yarns with worsted core, 4–5 cross-section, worsted core-spun yarn, 5 cross-section diagram, polyester core-spun yarn, 4 longitudinal morphology of polyurethane core-spun yarn, 2 condenser yarns, 94–5 conductive fibres, 194–5 conductive hybrid yarns, 49–50 continuous filament yarns, 57–8 conventional ring spinning system, 6–9 compound yarns forming conditions, 8 technological process of compound yarns, 6–7 wrapping effects factors, 8–9 core filament percentage, 9 core filament tension, 8 twist, 9 core-spun yarns, 1–2 CRI Green Labels, 189 crochet, 326 cross layering, 267 illustration, 268 Cyan, Magenta, Yellow and Key/black (CMYK) patterns, 158 3D cellular woven fabrics, 184–5 fabric with flat and uneven surfaces, 184 3D knitted structures developments, 109–16 fully-fashioned 3D knitted fabrics (near-net-shaped knitted fabrics), 116 multiaxial warp-knitted fabrics, 109–12 space fabrics (sandwich fabrics), 112–16 3D nonwovens, 264–84 future trends, 284 high-bulk flat nonwovens, 266–73 shaped 3D nonwovens, 273–83 three-dimensional shaped structure, 265 three-dimensional structure of large thickness, 265 3D solid braids, 341–2 braid formation, 342 3D solid woven fabrics, 179–84 angle-interlock fabrics, 183–4 cross-sectional view, 184 multi-layer fabrics, 179–80 specification, 180 orthogonal fabrics, 181–3 fabric visualisation, 183 weave repeat size, 180–1 introduction of stitches, 181 layer separation, 181 stuffed multi-layered fabrics, 181
© Woodhead Publishing Limited, 2011
Index superimposition of weaves, 180–1 three-layered fabric development, 180 three-layered fabric with self stitching, 182 3D Web Linker, 270 damask, 249–50 damask pattern, 250 reversible damask Jacquard design, 249 Di-Lour machine, 214 diamond yarn, 80 direct charging, 294 direct twist covering, 38 Disperstat W, 217 dobby shedding system, 227–8 examples of weaves, 228 principle of the mechanical system, 227 double needle bed raschel machine, 114 doubling system, 94 DREFF spinning, 33–5 core (glass) spun (polypropylene) DREFF yarn cross-section, 34 DREFF friction spinning system, 33–4 new DREFF friction spinning system, 35 Dunlop Mcenroe Mad Racquet, 147–8 DuraAir, 190 dyeing, 104 Easyleno system, 137 curved ground warp in fabric, 138 straight ground warp in fabric, 138 eccentric yarn, 80 elastane fibre, 2 electro spinning technique, 52–3 electronic smart structures, 259–60 stitched multi-layered woven structure with stitches as vias, 260 electrostatic flocking, 215 excentral type yarn, 8 eyelash yarn, 85 face-to-face weaving, 208–11 diagram of Van de Wiele’s SRP92 face-toface machine, 210 multi-frame structure, 209 sisal-look weave structure produced on SLP93 triple-rapier loom, 211 weave diagram for shaggy pile, loop-pile and flat weave, 210 Fair Isle-effect, 94 fancy yarns, 75–107 applications, 104–6 fashion, 105 housewares, 104 overview, 105–6 future trends, 106–7 history, 76–8 production methods, 87–104 chainette knitting process, 98–101 chenille, 96–8 combined systems, 91–4 condenser yarns, 94–5
357
doubling systems, 94 dyeing, 104 feed systems, 87–90 flocking process for chenille-type yarns, 98 friction-spun yarns, 95–6 hollow spindle system, 90–1 making metal threads, 102–4 metallic laminate manufacture, 102 ring system, 90 rotor-spun yarns, 95 types, 78–87 structure and formation, 78–87 yarn properties, 76 yarn structures, 75–6 fasciated yarn, 84 feather yarn, 85 feeding systems, 87–90 creating knop yarn, 89 creating loop yarn, 88 fibre coating, 290–7 flock motions in flocking zone, 290–6 DC flocking process, 291 high-speed digital CCD camera used for flock motion analysis, 294 velocity distribution of flock fibres, 295 velocity profile of 1.5 d nylon flock, 293 velocity profile of 3.0 d nylon flock, 293 pile generation and flocking process control, 296–7 fibre-reinforced composites, 347–8 braided vs cut hole, 348 filament yarns, 196–7 filament–filament wrapping, 36 filet/lacis work, 326–7 complex patterns on filet lace, 327 sample of filet lace, 327 fine gold thread, 77 fineness index, 298 flat braids, 340–1 braiding sample, 342 Soutache braider, 341 flat knitting machine, 114 fleck yarn, 83 Flock Activity Meter, 308 flock fibres preparation, 297–300 Flock-In-Spec Tester, 308 flock substrates, 300–1 non-textile substrates, 300–1 textile substrates, 300 flocking processes, 303–7 alternating current flocking, 304–5 3D object flocking, 306–7 automatic flocking line, 307 schematic of electrostatic–pneumatic 3D object flocking principle, 307 direct current flocking, 305–6 schematic illustration, 305 handheld electrostatic/pneumatic 3D flocking device, 303
© Woodhead Publishing Limited, 2011
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358 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 20 1 2 3 4 5 6 7 8 9 30 1 2 3 4 5 6 7 8 9 40 1 2 43X
Index
mechanical flocking, 304 schematic of mechanical flocking, 304 flocking techniques, 287–316 adhesives for flocking, 301–3 flock, flocking and applications, 288–9 principle of flocking process, 288 flock fibres and preparation, 297–300 flocking processes, 303–7 flocking substrates, 300–1 future trends, 314–15 market trends, 289–90 flock consumption, 290 new developments, 311–14 fibre graphics transfer, 313 flat screen carousel for multicolour flock printing of T-shirt, 313 flocked thermoplastic tray, 312 insulation material for aerospace application, 314 transfer-printed flocked fabric, 311 testing and quality assurance, 308–11 Chisel Abrasion Tester, 310 Flock Activity Meter, 309 Flock-In-Spec tester, 310 Siftability Tester, 309 textometer with ring electrode, 308 theory of fibre coating, 290–7 floss silk, 78 friction spinning, 18–19 technological process, 18 friction-spun yarns, 95–6 Full Repeat Scroll system, 201 gauze, 123–4 Gemeinschaft Umweltfreundlichen Teppichboden, 191 GEnx engine, 155 Ghiordes knot, 319 gimp yarn, 79–80 gimp yarn effect, 89–90 grenadine, 124 HandLook Carpet Pioneer HCP X2, 210 high-bulk flat nonwovens, 266–73 air laying, 266 airlaid webs with local surface projections, 272 cross layering, 268 Nepco 3D web linking process, 272 parallel layering, 267 perpendicular layering, 268 reciprocating vertical lapper, 269 rotating vertical lapper, 269 vertical lapper with shark plate belt folding elements, 271 circular folding elements, 271 high-performance fibres, 58 Hollow CAD, 185 hollow spindle system, 36, 90–1 hybrid braids, 343
hybrid yarns applications, 49–52 apparel, 49–50 industrial applications, 51–2 non-apparel, 50–1 developments, 21–54 different types of hybrid yarns, 23 future trends, 52–3 production methods, 26–49 types, 22–3 yarn developments, 23 structures and properties, 24–6 basic structure, 24 structures based on production method, 25–6 Individually Controlled Needle, 204 indoor air quality, 190 International Wool Secretariat (IWS), 9 interwoven fabrics applications, 164–86 areas, 168 definition and classification, 164–5 future trends, 186 properties and applications, 185–6 structural features, 165–7 3D solid fabrics, 165–7 samples of 3D solid fabrics, 167 simulated images, 166 single-layered fabrics, 165 structure and design, 168–85 backed cloth, 178–9 crossover types and notation on weave design paper, 169 3D cellular woven fabrics, 184–5 3D solid woven fabrics, 179–84 single-layered fabrics, 169–78 weave design paper, 168 Jacquard harness tie, 234–8 border harness tie, 238 centre or pointed harness ties, 236 harness tie calculations in mixed tie, 237 harness tie calculations of border tie, 238 limitations, 238–41 variable density Jacquard harness, 240 mixed harness ties, 237 simple presentation of straight harness ties, 235 straight harness ties, 235 Jacquard shedding system, 229 construction, 229–41 electronic Jacquard, 230, 231–2 electronic needle selector, 232 Jacquard harness tie and types, 234–8 Jacquard size, 233–4 limitations of Jacquard harness tie, 238–41 mechanical Jacquard, 229, 230–1 mechanical Jacquard conversion to electronic needle/hook selection, 232–3
© Woodhead Publishing Limited, 2011
Index Jacquard size, 233–4 standard British Jacquard sizes, 233 standard Continental Jacquard sizes, 233 Jacquard woven fabrics, 223–62 applications, 254–6 dome shape, 255 seamless woven air bag, 256 artworks conversion to woven patterns, 241–2 illustration, 242 cam shedding system, 226 dobby shedding system, 227–8 formation of shed during plain weave construction, 225 future trends, 259–62 automatic repair of warp breaks, 261 automatic weave/colour selection, 260–1 electronic smart structures, 259–60 flexible comber board, 261–2 Jacquard machine construction, 229–41 Jacquard shedding system, 229 plain weave, 224 recent development, 242–9 Jakob Muller MDLA Jacquard shedding system, 247–9 UNISHED Jacquard shedding system, 242–4 UNIVAL 100 Jacquard shedding system, 244–7 structures and properties, 257–9 weave/abrasion resistance, 258–9 weave/tear resistance, 257–8 weave/tensile strength, 258 woven fabric patterns, 249–54 ‘Jactuator,’ 244–5 Jakob Muller MDLA Jacquard shedding system, 247–9 heddle and hook elements, 248 Kemafil Machine Model 3602, 48 KEMAFIL technology, 47–8 Kevlar, 297, 299, 349 Kevlar rope, 73 knitting, 214–15 knop effect, 89 knop yarn, 82 knotted fabrics, 318–31 applications, 329–31 lace, 331 Macramé, 330 nets, 329–30 future trends, 331 Ghiordes form of knotting, 319 production methods, 326–9 bobbinet lace machine, 327–8 filet/lacis work, 326–7 leavers machines, 328 Macramé bobbins, 328 Raschel machine, 328–9 Schiffli machine, 329 Senneh form of knotting, 320
359
types, 321–6 crochet, 326 lace, 323–5 Macramé, 322–3 nets, 321–2 Turkish fabric, 325–6 knotting, 318 La Verra Perfettione del Disegno, 321 lace, 323–5, 331 laid ropes, 59–60 other laid ropes, 59 three-strand ropes, 59, 60 structure levels, 59 laminating, 206–7 latex emulsion, 301 layering, 266 parallel layering, 267 leavers machines, 328 leno, 124–5 leno heald system, 125–8 bottom doups of twine leno heald system, 127 metallic leno heald system, 126, 128 top doups of twine leno heald system, 127 twine leno heald system, 125, 128 leno-weave fabric sheds, 129–33 crossing shed of innovated metallic leno heald, 132 crossing shed of metallic leno heald system, 129 crossing shed of twine leno heald system, 129 innovated metallic leno heald, 132 opening shed of innovated metallic leno heald, 133 opening shed of metallic leno heald system, 130 opening shed of twine leno heald system, 130 standard shed of innovated metallic leno heald, 133 standard shed of metallic leno heald system, 131 standard shed of twine leno heald system, 131 leno-weave fabrics, 118–39 applications, 134–6 biomedical plaster casts, 135–6 fashion and home textiles, 134 filters, 136 grinding wheel reinforcement, 134–5 laminating fabrics, 135 lightweight membranes, 135 shelter and storage, 136 fabrics with leno-weave, 123–5 future trends, 136–9 Easyleno, 137 other trends, 139 PosiLeno, 139 Powerleno, 137–9 production, 125–33 leno heald system, 125–8 sheds, 129–33
© Woodhead Publishing Limited, 2011
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360 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 20 1 2 3 4 5 6 7 8 9 30 1 2 3 4 5 6 7 8 9 40 1 2 43X
Index
properties, 133–4 structure, 119–23 all over gauze, 120 fancy leno, 123 leno-weave, 119 one-twist-two gauze, 121 stationary end, crossing end, weft, 119 symmetrical gauze, 120 three-weft leno, 122 two-twist double-weft gauze, 122 weave structure, 119 looms, 158 loop yarn, 81 low-twist ropes, 63–5 advantages and disadvantages, 63 kernmantle rope, 64–5 parafil rope, 63–4 parallel-strand rope, 64 wire-rope constructions, 65 Lycra, 2 Lycra 3D, 14 Lyocell, 297, 299 Macramé, 322–3, 330 section used in wall hanging, 324 Macramé bobbins, 328 Mad Raq, 147–8 Madeline’s Racquet see Mad Raq Mandrel over-braiding, 339–40 illustration, 339 marl yarn, 79 marshmallow yarn see pompom yarn matelasse fabrics, 252 fabric design, 253 MAX91, 212 Maxbraid PE sutures, 350–1 Maypole braiding, 335–7 a maypole braiding machine, 335 arrangement of circular braiding, 336 yarn carrier arrangement, 337 yarn length changes, 337 melt-blowing, 281–2 melt-bonding fibres, 194 MEMS accelerometers, 261 merquisette, 124 metallic laminate manufacture, 102 combined hollow spindle system, 103 metallic thread, 77, 102 method used to spin metal thread around a core, 104 metallic yarn, 86–7 pearl purl, 86 supported slit film yarn, 87 mirroring method, 175 mock-chenille yarn, 80 MULtiaxial machine, 110 multiaxial warp-knitted fabrics, 109–12 applications, 111–12 aeronautical and astronautics fields, 111 construction, 112
other fields, 112 train and ship manufacture, 111–12 wind power generation, 112 illustration, 110 production methods, 110–11 equipment, 110 fabric texture, 111 materials, 111 properties, 110 shear properties, 110 tensile properties, 110 structure, 109–10 Multiple-layer braid, 343 nanofibre technology, 52 NASA Aviation Safety and Security Program, 155 NASA Glenn Research Centre, 155 needling, 213–14 negative feeding device, 7 nepp yarn, 83 nets, 321–2, 329–30 bobbinet tulle, 323 fruit captured in knotted net to allow full circulation, 322 Nomex, 297, 299 non-apparel, 50–1 hybrid yarns in non-apparel applications, 50 nonwoven fabric, 264 nylon, 58, 192 nylon fibres, 298 olefins, 58 OMNIplus-6-J 250, 246 open end spinning, 22 orthogonal fabrics, 181–3 parallel winding, 44–5 flow chart, 47 patterning systems, 200–5 colour interchange systems, 204–5 Individually Controlled Needle, 204 combinations of patterning attachments, 203 crossover structures, 200–5 module of a staggered needlebar, 203 perpendicular layering, 267–8 illustration, 268 pile carpets, 188–219 Axminster weaving, 211–13 backing materials, back-coating and laminating, 205–7 chemical and other treatments, 216–17 anti-shading treatments, 217 antistatic treatments, 217 flame-resistant treatments, 217 hygienic finishes, 216–17 insect-resistance treatments, 217 stain and soil resistance, 216 coloration, 215–16 environmental considerations, 190–2 health and cleanliness, 190–1
© Woodhead Publishing Limited, 2011
Index manufacturing, 191–2 positive effects, 190 face-to-face weaving, 208–11 market background, 188–90 needling, 213–14 other manufacturing methods, 214–15 pile fibres, 192–6 pile yarns, 196–8 textile sports surfaces, 217–19 composite surface structure, 219 tufting, 198–205 wireloom weaving, 207–8 pile fibres, 192–6 acrylic, 194 cellulosic fibres, 195–6 conductive fibres, 194–5 melt-bonding fibres, 194 nylon, 192 others, 196 polyester, 193–4 polypropylene, 193 self-disinfecting fibres, 195 wool, 195 pile yarns, 196–8 filament yarns, 196–7 diagram of texturing unit, 197 spun yarns, 197–8 pillar stitch, 109 plain derivative weave, 172–3 basket weave, 173 plain weave extension, 172 plain weave, 169 structure and diagram, 170 plastisols, 302–3 polyester, 58, 193–4 polyester fibres, 299 poly(ethylene terepthalate), 193–4 poly(lactic acid) fibre, 196 polypropylene, 42, 193 poly(trimethylene terepthalate), 193–4 pompom yarn, 86 PosiLeno, 139 positive feeding device, 7 Powerleno system, 137–9 QISO triaxial braid, 149 Quadraxial fabrics, 158 Raschel machine, 328–9 rayon flocks, 298–9 recycling, 192 Rick-rack braid, 343 ring spinning, 27–31, 90 ARC spinning system, 29 conventional ring spinning core-spun system, 27 elasto yarn by combined core-spun and siro-spun process, 30 retro feed, 29 SRRC core wrap spinning system, 28
361
Robotic Fibre Assembly and Control System, 281 ropes developments and technology, 56–74 braided ropes, 60–2 laid ropes, 59–60 low-twist ropes, 63–5 ropes usage, 71–4 history, 56–7 rope construction on ropewalk, 57 manufacturing technology, 65–9 braid paths, 69 braided ropes, 68 integral rope-making machine, 68 new machinery and new routes, 65–7 parafil ropes, 68 planetary strander, 67 post-production treatments, 69 strand production, 67 three-(and four-) strand ropes, 67–8 three-strand rope production sequence, 66 tubular strander, 67 new fibres, 57–8 continuous filament yarns, 57–8 high-performance fibres, 58 nylon, 58 olefins, 58 polyester, 58 post-1950 developments, 57 terminations, 69–71 barrel-and spike termination, 70 external grips, 71 knots, 69 mechanical terminations, 70 socketed terminations, 70 splice in double braid rope, 70 splices, 69–70 usage, 71–4 deepwater mooring, 71–2 diversity and specialisation, 71 load-elongation curves for yachting ropes, 73 sailing, 72–3 two unusual uses, 73–4 rotor core spun, 32 rotor folded spun, 32 rotor spinning, 14–16, 31–2 core-spun yarn, 31 core-spun yarn by modified rotor spinning process, 32 rotor spinning principle for compound yarns, 15 rotor-spun yarns, 95 rotor wrapped spun, 32 Rotorcraft’s Rotorcraft Compact Spinning system, 28–30 satin/sateen weaves, 171–2 diagram for 7-end satin with M = 4 warp-wise, 172
© Woodhead Publishing Limited, 2011
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362 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 20 1 2 3 4 5 6 7 8 9 30 1 2 3 4 5 6 7 8 9 40 1 2 43X
Index
schappe technology, 49 Schiffli machine, 329 self-disinfecting fibres, 195 Senneh knot, 319–20 illustration, 320 shaped 3D nonwovens, 273–83 air-laid 3D shaped nonwoven products, 282 air-laying 3D shaped nonwoven process, 280 felt hat, 274 fibre coating of gloves, 277 fibre reinforced shaped perform, 277 meltblown 3D nonwovens process, 283 nonwoven bra cup production, 275 nonwoven clothing production, 279 process for making nonwoven glove, 276 thermally bonded shaped nonwovens, 278 Siftability Tester, 308 silver thread, 77 single-layered fabrics, 169–78 derivative weaves, 172–8 plain derivative weave, 172–3 twill derivative weaves, 173–8 elementary weaves, 169–72 original satin/sateen weaves, 171–2 original twill weave, 170–1 plain weave, 169 single-wall carbon nanotubes, 53 siro spinning system, 9–13 spinning parameters effects on yarn properties, 10–13 convergence guide, 12 drafting ratio and roving linear density, 13 front zone condenser, 12 strand spacing, 11–12 traveller number, 12 twist multiplier, 13 technological process, 9–10, 10 siro spinning principle, 11 Sirospun yarn, 9 slub yarn, 83 snarl yarn, 81–2, 82 solvent-based adhesives, 302 Southern Regional Research Centre, 28 space fabrics, 112–16 applications, 115–16 automobile textiles, 116 composites, 116 garments, 115 home textiles, 115 medicine, 116 sports equipment, 115 production methods, 114–15 equipment, 114 fabric texture, 115 materials, 114 properties, 113–14 air permeability, 113 compression elasticity, 113 moisture absorption and conductivity, 114 sound absorption and conductivity, 114
structure, 112–13 warp-knitted space fabrics, 113 spandex, 2 spangles, 77 spiral corkscrew yarn, 79 splicing method, 69 spun yarns, 197–8 Square braid, 343–4 SRP92, 209 Star of David pattern, 155 stretch breaking, 45–7 process, 47 stripe yarn, 82 STRUTO Vertical Lapper, 267–8 Tactel, 14 tape yarn, 84 tapestry, 252–4 tapestry Jacquard design, 254 Tapestry Rug Pioneer TRP92, 210 tartan, 157 Tencel, 297, 299 Textometer, 308 thermal comfort, 190 thermosetting adhesives, 302 ‘Thinking Carpet,’ 189–90 triaxial braiding, 155 triaxial weaving, 146–7 triaxial woven fabrics, 141–61, 154 aesthetics, 157–8 Star of David pattern, 157 applications, 154–7 medium triaxial woven sphere, 156 sparse triaxial woven sphere, 156 basic patterns, 141–43 dense triaxial weave, 143 herringbone triaxial weave, 143 medium triaxial weave, 142 sparse triaxial weave, 142 classification, 148 density, 148 fibre spacing, 148 geometry, 148 holes, 148 symmetries, 148 unit cell size, 148 developments, 141–61 advantages, 153–4 future trends, 160–1 properties, 152–3 history, 144–8 sepak takraw balls (dense weave), 144 triaxial tennis racquet, 147 woven basket, 145 woven light shade, 146 manufacturing, 158–60 rotating wheel with mounted spindles, 159 variations, 148–52 checquerboard triaxial weave, 151 double sparse triaxial weave, 149
© Woodhead Publishing Limited, 2011
Index double sparse triaxial weave II, 149 herringbone triaxial weave (1,2 twill variation), 151 herringbone triaxial weave (2,2 twill variation), 150 less regular triaxial weave, 152 sparse herringbone triaxial weave, 150 tribo-charging, 294 tricot stitch, 109 TRUTRAC machine, 217 tufting, 198–205 patterning systems, 200–5 colour interchange systems, 204–5 combinations of patterning attachments, 203 crossover structures, 200–5 yarn tensioning systems, 200–1 principles, 198–200 actions in cut-pile tufting, 199 tulle and net, 124 Turkish fabric, 325–6 twill derivative weaves, 173–8 entwined twill, 177 example of compounded twills, 174 mirroring method, 176 mirroring method for herringbone weave, 177 mirroring method for horizontal and vertical waved weave, 176 reinforce twills, 174 step number change, 175 twill weaves, 170–1 2/1 twill construction, 170 examples of sateen and satin weave, 171 weave for 3/1 twill, 171 Twintex, 42 two-weft gauze, 121
363
UNISHED Jacquard shedding system, 242–4 Grosse’s UNISHED 2 mounted on the weaving machine frame, 243 shed formation principle, 243 UNISHED 1 vs UNISHED 2, 244 UNIVAL 100 Jacquard shedding system, 244–7 principle of shed formation in the UNIVAL 200, 247 shed formation, 245 shed formation in UNIVAL 200, 247 Staubli’s UNIVAL 100 Jacquard machine, 245 US patent #5 707 711, 256 volatile organic compounds, 191 walking comfort, 190 water-based adhesives, 301–2 wire-rope constructions, 65 other wire rope, 66 six-strand wire rope, 66 wireloom weaving, 207–8 three-frame sculptured pile carpet, 208 two-frame cut/loop structures with loops, 208 wool, 195 wrap spinning, 35–9, 36 core (glass filament)/wrap (polypropylene filament) hollow spindle yarn crosssection, 39 hollow spindle unit attachment, 38 wrap yarn by hollow spindle process, 37 wrapping fibres, 1–2 yarn tensioning systems, 200–1 cut/loop tufting, 202
© Woodhead Publishing Limited, 2011
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