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Upgrading and Diversification of Rotor Spinning

N.Balasubramanian 9869716298

Retired Jt. Director(BTRA) & Consultant

Abstract Rotor spinning is one of the well established technologies for coarse and medium counts. However, lower strength is one of its limitations. Some methods for overcoming this to some extent are discussed in this article. Further diversifations of this technology to increase product range are also detailed.
Addition of small % of viscose
Rakshit and Balasubramanian1 showed that strength of rotor yarn can be improved significantly by adding 16 % viscose to cotton. The improvement is more marked at low twist multiplier as shown in fig 1 .Presence of long staple viscose helps to reduce yarn breakage due to fibre slippage at lower TM. Addition of viscose will therefore help to lower twist multiplier and improve production. Evenness and thick and thin places show a marginal reduction with addition of viscose but neps tend to increase because of higher incidence of wrapper fibres. When the yarns were woven into fabric and bleached, the improvement in strength by addition of viscose gets reduced. Similar trends were observed when a long staple cotton is added in small amounts in place of viscose.
Fig 1 : Influence of TM on 100 % cotton and 84% cotton/16% viscose on yarn strength
Combed rotor yarns
Combing is normally not done for rotor spinning as fibre parallelization achieved in combing is destroyed during deposition of fibres on rotor and it adds to the cost. However, some studies have shown significant improvements in yarn quality and productivity with combing which may offset the increased costs especially in fine counts. Removal of seed coats and trash in combing helps to reduce trash in sliver thereby contributing to better performance in rotor spinning. According to Landwehrkamp2 trash content in sliver is reduced by 50 80 % with less trash deposition in rotor groove with combing. Yarn strength is improved by 10 % and neps reduced by 30 50 %. Bursting strength of knitted fabric and grab strength of woven fabric increased by 5 10 %. Combing reduces end breakage rate by a factor of 3.5 and improves spinnability of fine yarns3.
Hybrid Spinning
Hybrid spinning combines rotor spinning with ring spinning to get benefits of both as illustrated in Fig 2. Rotor speed is kept constant and yarn delivery rate is increased to the point of minimum twist.Twisting is then completed in ring spinning. Alternately rotor speed is increased keeping delivery rate constant to the point of minimum twist. Remaining twist is given in ring spinning. Hybrid spinning Fig 2 Hybrid Spinning
Cover spun yarn
Fig 3 shows cover spinning rotor machine. The rotor shaft is made hollow to allow insertion of filament. Filament fed by feed rollers is tensioned by a tensioning device and fed to hollow rotor shaft. Feed rate of filament is kept higher than yarn delivery rate and filament tension kept lower than staple fibre tension to ensure wrapping of filament on staple yarn. The filament is thrown on rotor surface and yarn formation takes place close to the rotor collecting surface with filament wrapped around staple fibre. Adjustment of filament tension also ensures proper wrapping. Matsumoto3 et al found the twist angle of staple fibre in wrap yarn to be lower than normal rotor yarn of the same twist. The filament has also a lower twist than staple fibre in wrap yarn because of untwisting of false twist.
Fig 3 Cover spun yarn Rotor machine
Cheng and Murray4 reported that cover spun rotor yarn made from cotton core and texturised filament cover are more uniform and have better properties than normal cotton rotor yarns. Guide position and feeding tension have to be optimized to get best yarn quality and performance.
Core spun Yarn
Core spun yarn can also made in this system by having a higher delivery roller speed in relation feed roller speed of filament. The filament tension under such conditions is higher than staple fibre to ensure that filament occupies the core. The core spun yarn has a better strength and appearance than wrap spun yarn. Nield and Ali5 employed a similar method for making core spun yarns. They used a rotating doffing tube which is rotated opposite to rotor. This produces false twist which flows up to peeling point and rotation of rotor wraps the spun yarn around the filament.Zhang6 et al found cotton/spandex core spun rotor yarn to have higher breaking strength, elongation, elastic recovery, better evenness and lower hairiness than normal cotton rotor yarn. Increasing draft ratio between delivery roller and spandex feeding roller up to 3.5 increased breaking strength and elastic recovery. Coarser denier spandex core spun rotor yarn has higher breaking elongation, lower irregularity and imperfections than finer denier core spun yarn.
Loop yarns
Fig 4 : Loop yarns in rotor spinning
Loop yarns are made by feeding two filaments, one at lower tension and other higher tension to rotor machine as illustrated in Fig 4. The filament at lower tension forms loops while the filament at higher tension forms the core. The loop filament combines with staple fibre at collecting surface to form loops over staple fibre. The wrap yarn with loops combines with core filament at a point close to navel7. Loop diameter increases and loop pitch decreases with increase in overfeed of filament or increase in core filament tension. When base core yarn is made under stable conditions loop yarn is also stable. Matsumoto8 et al examined rotor spun loop yarns (RSL) by combining rotor spun filament core yarns (RSC) and filament wrapped rotor yarn in one process. The stable conditions for RSL are within the range effect filament over feed (EFOF) ≥4 m/min and -6≤core filament overfeed(CFOF)≤-4 m/min. Loop shape is dependent upon elastic recovery of filament and overfeed length of effect filament.
Effect Yarn/Slub yarn
Fig 5 : Rotor machine for Rotor yarn
A common method of making fancy/effect yarns in rotor machine is by feeding excess material to the rotor in the same feeding unit by varying the speed of feed roller by means of an electronically controlled device. Feed roller is driven by servo motor,controlled by micro processor.The slub thus produced will have a length longer than circumference of rotor because of back doubling. Wang and Huang9 showed that slub length will increase with increase in ratio of slub linear density to amplitude of feed roller variation, termed as slub multiple.Higher amplitude of feed roller speed variation for a given slub linear density will reduce slub length, which means that a servo motor with better control over variation in feed roller speed can produce shorter slubs. A second feeding unit can also be used as shown in Fig 5 to produce effect yarns.The rotor machine is fed by base material as well as effect material by separate feeding units.Effect material passes though a drafting unit or a feeding unit which works intermittently to feed a tuft, controlled by a computer, to the opening roller. Random effects as well as effects of a known pattern can be produced. Another method of producing fancy yarn is by varying the rate of flow of fibres in transport tube by injecting pressurised air in a programmed manner. Kwasniak10 used this method to produce slubs on laboratory model running at 44000 rpm. Length and size of slub produced will depend upon duration of injected air. Air injection method has the merit that it can produce slubs/effects shorter than circumference of rotor. However, it cannot produce slubs/effects longer than rotor circumference. Moreover, variations in fibre flow caused by air injection result in limited range of slubs.Kwasniak and Peterson11examined theoretically rotor yarn produced by injection method and analysed production limitations. By combining excess material feeding method with pressurised air injection in transport tube, new type of fancy yarns can be produced12. Kwasniak13 extended this study to commercial machines Ingolstadt RU11 and Autocoro operating at 70000 rpm. The quality of slub effects depends on rotor speed, diameter and air pressure. Fancy effects can also be produced in rotor yarns by using negative rake opening roller with cotton material whereby fibres accumulate and form slubs. By repeated carding with flats set wider, neps can be produced which can then be added in some proportion to the material to produce neppy yarn By altering twist randomly, rotor yarns with multi twist effects can be produced.
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4. K.B. Cheng and R. Murray, Effects of spinning conditions on structure and properties of open end cover spun yarns, Textile Research J, 2000, 70, p 690
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11. A. Kwasniak and E. Peterson, The formation and structure of fancy yarns produced by a pressurised air method, J. Textile Institute, 1997, 88, 3, p 174
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13. J. Kwasniak, Application of pressurised air method of fancy yarn formation to industrial rotor spinning machines, J. Textile Institute, 1997, 88, p 185.