Selection of twist coefficient
1. Twist coefficient of roving The twist coefficient of roving is related to factors such as fiber type, length and roving yarn density. When the fiber is long, the linear density is small, and the uniformity is good, the twist coefficient should be small because of the strong cohesion between fibers, and vice versa. For example, the roving twist coefficient of medium-long fibers can be smaller than that of cotton fibers; the roving twist coefficient of combed cotton yarn can be smaller than that of carded cotton yarn. When the density of woolen yarn is high, the number of fibers in the cross section is large, and the twist coefficient should be small, and vice versa. Rovings are used for knitted fabrics. Due to the higher evenness requirements of fine yarns, the twist coefficient of the rovings used should be higher than that of woven yarns with the same linear density. When finishing medium-length cotton fibers, the selection of roving twist coefficient can be referred to Table 3-13. When finishing various chemical fibers (pure spinning and blended chemical fiber fabrics), the range of roving twist coefficient can be referred to Table 3-14. 2. Spinning yarn twist coefficient (1) Ring spinning twist coefficient: Spinning yarn twist coefficient is closely related to the output of the spinning machine. In addition, the twist coefficient is also positively related to the type of spinning yarn and the yarn breakage rate on the spinning machine. Under normal circumstances, in order to increase the output of the spinning machine and reduce the “weft shrinkage” defects during weaving, the spinning twist coefficient always takes a smaller value within the agreed range. However, according to the principle that all products serve users, the twist coefficient of the spun yarn needs to be determined according to the purpose of the spun yarn. Generally, the twist coefficient of weft yarn is smaller than that of warp yarn; the twist coefficient of knitted fabric yarn is close to the same linear density as weft yarn; the twist coefficient of cotton sweater yarn is lower. Sweatshirts require a cool feeling, and the twist coefficient is slightly larger; it is used for pile fabrics and twisted threads. The twist coefficient of the yarn is small. The twist coefficient ranges of commonly used spun yarns and common fabric yarns are shown in Table 3-15.
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