A yarn is formed via the process of spinning, which takes fibers and twists them. This process holds fibers together (whether they are staple fibers or continuous filaments) and adds strength to them so they are not easily pulled apart. There are number of conventional and modern spinning technologies. In this article I will discuss all modern and new spinning technologies with appropriate diagrams.
In the latter part of the last century, most spinning innovations were aimed at improving production rates. The thinking that drove many of these developments was that if the twist insertion method could be separated from the yarn package formation, then larger packages could be achieved and at much higher speeds. The method that made the first and probably the biggest entry into spinning mills was that of rotor spinning also called open-end spinning.
Modern and New Spinning Technologies:
The newer spinning systems developed since then include rotor spinning, air-jet spinning, friction spinning, vortex spinning, electrostatic spinning, core spinning, wrap spinning, twistless spinning and others. The structures of yarn obtained from these systems are also different and vary in many aspects.
Rotor / Open-end spinning:
Rotor Spinning – also known as open-end spinning. It uses a carded sliver that is fed onto a succession of single-spiked rollers that run at high speed. These rollers open the sliver so that the fibers can be fed almost individually via an airstream onto a grooved funnel that spins at a fast rate. The spinning funnel collects a thin layer of fibers that are twisted together as they pass through to form the yarn. This system produces yarn five to ten times quicker than ring-spinning processes, but the structures are harsher, which makes them less popular than ring-spun yarn.
Rotor spinning is used as an alternative to the ring spinning of short-staple yarns. A sliver from a drawing frame is fed into a very fast revolving opening roller, which breaks down the sliver and feeds it into a tube, which delivers the fibers individually into the groove around the inside edge of a high-speed revolving rotor. The revolving of the rotor causes a centrifugal airflow, which allows the fibers to be sucked off the opening roller and fed to the groove. An open end of preformed yarn is then sucked into the groove and the fibers join onto the end of this yarn and twist is inserted by the revolving rotor (Figure-1). The winding force (pull) of the package is sufficient to overcome the suction force of the rotor and so the formed yarn is delivered to the winding system, which produces a large cone package.
The structure of rotor spun yarns is different from that of ring spun. The fibers closest to the core of the yarn have much more twist than those on layers closer to the surface of the yarn. An easy way to identify if a yarn has been rotor spun is to try to carry out a conventional twist test, it simply cannot be done. The strength and elongation properties are adequate for most purposes and the evenness is often better. The handle of fabrics made from rotor spun yarn, however, is significantly harsher than ring spun and the abrasion resistance is poorer. These last two properties/design principles limit the end uses of rotor spun yarns, although the volume of consumer demand has resulted in rotor spun yarns having around 35% of the textile and apparel market, much higher than any other alternative spinning system developed since the late 1960s. In recent years, a number of marketing ploys have been used by fashion retailers by branding products as ring spun, but the significance is rarely understood by consumers, unless of course they are design technologists.
Air Jet / Fasciated yarn spinning system:
Air jet is the next invention of the 1970/1980s that has made a significant impression on the textile market. The generic term is fasciated and air jet is the trade name of the most successful of this type of spinning system. The term fasciated comes from the structure of the yarn (Figure-2), which resembles the fasces held as a badge of office by the praetorian guard in ancient Rome. The fasces was a bundle of axes held together by leather straps.
Air jet spinning system makes use of false twist, which you were first introduced to in the description of a woolen ring frame. You will remember that if we turn a strand of fibers in the middle, we get opposite twist directions on both sides of the strand and if the strand is moving, we get a resultant zero twist. This is what happens with air jet/fasciated yarns, but the action of the fast-revolving air jets causes a few of the fibers on the extreme outside of the strand to escape the twist in one of the directions and therefore they receive real twist as they emerge from the air jet and so they wrap around the core. Nowadays, two air jets in series, revolving in opposite directions, are used to give more strength (Figure-3). Even so, air jet/fasciated yarns have low strength and elongation but sufficient for certain fabrics and end uses and their softness is good. The market for these yarns has been dwindling from around a maximum of 5%.
Friction spinning system:
The best known of the friction spinning system was and is Dref, an acronym formed from the name of its inventor Dr. Ernst Fehrer. The system employs a rotating carding drum for opening slivers into single fibers (Figure-4). The fibers are then stripped off the carding drum by centrifugal force and carried into the nip of two perforated spinning drums rotating in the same direction. The fibers are then twisted by mechanical friction on the surface of the drums and join an open end of yarn introduced to collect the fibers in the same way as in rotor spinning. The yarn is then wound onto a cone.
The main problem for friction spinning has been the low breaking strength and some similar systems, for example, the Platt friction spinner, failed commercially. To overcome this problem, a core continuous filament is introduced around which the staple fibers gather. This limits the end uses for which this type of yarn is used, but it can be successful for elasticated hosiery yarns and other speciality products; however, market share is and will remain very low.
Vortex spinning process:
Vortex spinning technology was introduced by Murata Machinery Ltd in Japan in 1997. This technology is best explained as a development of air jet spinning, making use of air jets for yarn twisting. The main feature of Murata vortex spinning (MVS) is its ability to produce yarn at 400 m/min, which is almost 20 times greater than ring spinning frame production. Other advantages include low maintenance costs, a fully automated piecing system and elimination of roving frame. The yarn and the fabric properties of MVS yarn are claimed by the manufacturer to be comparable to those of ring spun yarn.
The basic principle of operation is shown in Figure-5 and Figure-6. The sliver is fed to a 4-over-4 (or a four-pair) drafting unit. As the fibers come out of the front rollers, they are sucked into the spiral-shaped opening of the air jet nozzle. The nozzle provides a swirling air current which twists the fibers. A guide needle within the nozzle controls the movement of the fibers towards a hollow spindle. After the fibers have passed through the nozzle, they twine over the hollow spindle. The leading ends of the fiber bundle are drawn into the hollow spindle by the fibers of the preceding portion of the fiber bundle being twisted into a spun yarn. The finished yarn is then wound onto a package.
Compact spinning system:
This is not a nonconventional spinning system, rather an effective development and refinement of normal ring spinning that produces a quality of yarn that is a real improvement on conventional ring-spun short-staple/cotton yarns (Figure-7a). Basically, the bottom front drafting roller has a perforated center of around 1 cm through which air is drawn, which causes the drafted fiber strand to be drawn/compacted to form a narrow fiber stream (Figure-7b) as it emerges from the nip of the front roller to be met by twist. This means that there are very few fibers on the outside edges of the fiber stream and therefore an excellent reduction in the level of hairiness. This system has made great inroads into the fine cotton yarn system (i.e., 4-10 TEX). For coarser counts like the ubiquitous 2/30 Ne or R40 TEX × 2 (each single yarn being 20 Tex), it is probably an unnecessary expensive complication. The demand for yarn of this quality, however, may continue to grow.
This was developed in the 1970s and was aimed at Worsted spinning of wool. The idea was that, rather than spinning two single yarns and plying them into a two-fold yarn, two rovings could be fed side-by-side into the drafting zone of a worsted ring frame. The fiber strands are kept separated until they emerge from the nip of the front rollers and the strands are twisted together (Figure-7c). If the resultant yarn is untwisted, the two strands will be easily observed and therefore identification of this type of yarn is quite simple. The advantage of Siro-spinning is that hairiness is reduced, as the surface fibers are better trapped in the yarn structure and a process stage (twisting/plying) is removed. Disadvantages are that the yarn is not as well balanced, which may show in the fabric, and the load/elongation values are not as good as conventional plied yarns. Siro-spun yarns are not popular now among worsted spinners, but the technology has been, to a limited extent, adopted by the spinners of very fine cotton yarns in their efforts to reduce hairiness and the technology can also be combined with compact spinning technology.
Finally, it has to be noted that other nonconventional yarn spinning techniques have been developed, particularly in the second half of the twentieth century. Most of these enjoyed limited success and many have simply disappeared. It is unlikely that the design technologist will be called upon to use the yarns produced by those technologies, but he or she can use the understanding provided by this chapter to help them to observe, investigate, and understand new entrants to the market place, although, so far in this century, new spinning technology entrants are not much in evidence.
- Textile and Clothing Design Technology by Tom Cassidy & Parikshit Goswami
- Advances in Yarn Spinning Technology by C. A. Lawrence
- Fibres to Fabrics by Bev Ashford
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- Murata Vortex Spinning (MVS) Process | Principle of Vortex Spinning Technology
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.