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Weaving & Spinning

Single-Step Spinning

Uniplex spun yarn technology is a single-step process for converting filament yarns into spun yarns, offering flexibility and high speeds.

A prototype of the Uniplex machine as it will be shown at ITMA 2003 in the SSM AG booth. Licenses are available from DuPont for the Uniplex spun yarn process technology.Developments in staple fiber spinning are characterized by the idea that natural fibers such as cotton and wool, as well as man-made fibers, can be processed using the same technology. This forms the basis for the production of blends, in addition to 100-percent man-made or natural fiber spun yarns.Such production requires processes that adapt man-made fibers in terms of fiber length distribution, force/elongation ratio (modulus), fineness and crimp as closely as possible to the natural fiber characteristics endowed by nature. These factors further define major processing parameters and yarn properties. Yarn irregularity, the number of fibers in the yarn cross-section and the yarn count are further defined by these parameters. In this case, man-made fibers are merely components for blends with natural fibers. Up until now, cotton has been by far the most processed fiber in the world. Staple fiber yarns provide hitherto unique end-product aesthetics. A specifically desirable degree of functionality for example, ease of care is achieved by engineering specific blends.The goal of shortening man-made fiber processing has been apparent for some time. In order to avoid the roundabout route via carding for fiber orientation and parallelization, filaments are sometimes processed into suitable fiber lengths by cutting or tearing, and formed into a sliver immediately afterwards. Then comes spinning by the conventional process of drawing, roving production and consolidation by means of true twist. Actual yarn production and consolidation by true twist are the most cost-intensive portions of the entire process. They have led to the well-known development of unconventional spinning processes such as rotor, friction and air-jet spinning. These highly productive processes have shortened processing times, where a directly further processable bobbin is produced from sliver in which yarn quality is 100-percent checked. Ring spinning also has improved its economics by way of advances in automation and the linking process. Filament technology consistently follows the idea of continuously producing as far as possible a directly processable continuous yarn. Advances in texturing have led to a broad market for these yarns. Filaments dominate today, especially in the industrial filament sector. Here, filament costs are determined largely by fineness, as production per spinneret decreases with fineness. If one considers the blended yarn production route in man-made fiber processing, and concentrates on the production of 100-percent man-made fibers of specific functionality, new, unconventional direct staple fiber yarn production processes are possible. The obligation to adapt staple lengths to those of natural fibers is eliminated. This means that refinement does not have to be achieved using conventional drawframes, and staple lengths, which are considerably longer than those used today, can be processed.Uniplex Direct Spun Staple Fiber Yarn ProductionDeveloped by Wilmington, Del.-based DuPont, Uniplex spun yarn technology is a new, single-step process that converts filament yarns into spun yarns. The starting point of the process is a filament supply that is four to 10 times coarser than that used in classic filament yarn production. This is a significantly more economical aspect of the direct staple fiber yarn process. The raw material basis for low orientation, partially oriented and fully oriented yarn production is correspondingly more cost-effective because of the higher productivity of the primary spinning process. Supply bobbins are doubled four to 10 times, producing a similar effect with regard to thorough blending to that achieved in the classic drafting process (See Figure 1).
The ProcessThe filaments are continuously drawn in a drafting zone by means of heated godet wheels, followed by a relatively long break zone. Technological problems consist of continuously tearing the individual capillaries without breaking the sliver as a whole. Clamping in the break zone must be reliable. The speed ratio of the clamping rollers at the entry and exit of the break zone must be adjusted to the fiber modulus, and must significantly exceed fiber elongation at break. The fibers then are further shortened definitively in a rebreaking zone with simultaneous refinement to produce the required final yarn count. The length of the break zone and the downstream rebreaking and refining zones largely determine the fiber length and fiber length distribution of Uniplex-spun yarns. It is clear that both mean and maximum fiber lengths are far longer than the fiber lengths usually processed today using drawframes. Perhaps only in jute, flax and hemp spinning are longer fiber lengths used. These yarns are coarse, with fiber fineness correspondingly coarse as well. Individual fiber fineness is usually 1 decitex (dtex) or finer for the new, unconventional direct staple fiber yarn production process, resulting in a coefficient of fiber fineness approximately 10 to 20 times higher than is the case with natural fibers. The coefficient of fineness is a function of the fiber length/fiber thickness ratio. A specific coefficient of fineness must be maintained in the case of conventional fibers because of carding capability. The coefficient of fineness figures obtained with the new process would not permit fiber carding. For this reason, only an on-line direct process would be worth considering. The absolutely parallel fibers must be consolidated into yarn after passing through the breaking zones. True twist processes via mechanical twist-imparting elements like rings and travelers must be excluded on the grounds of their lower achievable take-off speed. Consolidation using two-spinneret air-jet false-twist technology is achieved on the basis of existing know-how and experience of diverse air-jet spinning processes at the Institute of Textile Technology and Process Engineering (ITV), Germany. Experience has shown that good strength values can be obtained with man-made fibers. In the case of new direct staple-fiber yarn production processes, consideration must be given to the fact that fewer free fiber ends are available for pneumatic wrapping. On the other hand, due to the high interlacing figure in the woven fabric, the long staple length ensures woven fabric strengths that inevitably are determined by polymer substance strength. Therefore, yarn strength is not, as with all air-jet false-twist yarns, directly decisive to woven fabric strength. The yarn strength and elongation behavior of a 230-dtex polyester yarn demonstrates that the coefficient of strength variation for air-jet false-twist yarns is higher than for comparable ring-spun yarns. With a clamping length of 0.8 meter, a mean fiber strength of 19.4 centinewtons per tex is achieved with a small number of wrapping fibers. This is significantly higher than the strength of comparable 100-percent polyester (PET) rotor or air-jet false-twist yarns. The minimum values from 10,000 break trials on a Tensojet also reveal that the process leads to a yarn with uniform wrapping over considerable lengths. Structural photographs clearly show the wrapping fibers and the parallel-lying fiber core (See Figure 2).The delivery speed of the process as a whole is determined by the efficiency of the air-jet wrapping process, with the geometric arrangement and the pressure conditions in the injector and twist nozzle playing a decisive role. Depending on yarn count, delivery speeds of 500 to 600 meters per minute are realistic. Yarn strength must largely guarantee perfect further yarn processing behavior in weaving. Special requirements in the end-product in terms of pilling and abrasion resistance can be met by additional twist. Trials reveal that low real twist (100-200 turns per meter) can greatly change end-product characteristics.When the yarn is inserted in the warp, additional twist is essential because of the skim-back resistance required. In the end-product, the yarns produce a markedly different fabric appearance compared with products produced from filaments. Greater roughness is always attributed to air-jet false-twist yarns. This provides noticeably greater woven fabric slippage resistance compared with filament.
Figure 2: Structural photograph of a 230-dtex polyester Uniplex yarn clearly shows wrapping fibers and the parallel-lying fiber core.Functionality Of Uniplex Spun YarnsA wide variety of polymers can be processed into fine yarns using Uniplex spun yarn technology, including:extremely high-strength fibers; highly elastic fibers;flame-resistant fibers;low-friction fibers; andmicrofibers.End-product functionality is determined by the polymer employed. It is possible to mix or combine functionalities using Uniplex technology. Maximum-strength yarns with a high degree of elasticity are possible by combining para-aramid with elastic fibers in the process.The Uniplex spun yarn process has strong potential. Both speed and application of the targeted use of these yarns open up a wide field for optimization. The technology is extremely flexible in terms of yarn count. Success will be determined by the additional functionality of the yarn in the end-product.Editors Note: Peter Artzt, Ph.D., is head of Staple Fiber Technology, and Anette Arnold is a scientific associate at the Germany-based Institute of Textile Technology and Process Engineering (ITV). Glen E. Simmonds is a senior research associate with Wilmington, Del.-based DuPont.

August 2003