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Relationship between yarn twist and strength
Principle of twist test: The twist is usually not evenly distributed over the entire yarn. When testing the twist, take a sample from 1 m away. Under the specified tension, clamp both ends of the sample of a certain length, rotate one end of the sample, and withdraw the twist of the yarn sample until the constituent units of the yarn to be tested are parallel. The twist of the yarn is obtained from the number of turns required to remove the twist of the yarn. When the yarn is stretched to break, it is found that not all fibers are broken on the broken cross-section, but some fibers are broken, and the other is slipped, and the broken fibers are not broken at the same time. The performance and single yarn strength are closely related to the twist of the yarn. With the increase of twist, the yarn strength continues to increase, but after a certain twist, the strength decreases when the twist is continued. Increase, the component of strength increases during the breaking process. The disadvantage is that the twist increases, the inclination of the fiber and the sliver axis increases, and the component force that the fiber strength can withstand in the sliver axis decreases, and the twist is too large to increase the inner and outer fibers of the sliver. The uneven distribution of stress aggravates the non-synchronization of fiber breakage, so that the strength increases with the increase of twist. When the two are equal, the strength is the largest. At this time, the twist is the critical twist, and the twist coefficient corresponding to the critical twist is called the critical coefficient. When the twist increases, the twist angle increases, the light is reflected to the side, the gloss is poor, and the hand feel is poor. On the contrary, the hand feels soft, but if the twist is too small, hairiness occurs, the hand feels loose, and the luster is not necessarily good. The twist coefficient and twist direction mainly depend on the quality requirements of the final product. The twist coefficient is different for different purposes, and the twist direction depends on the needs of the finished product and post-processing. In order to reduce the inconvenience of overhauling and operation on the yarn machine, it is generally the Z twist direction. . For example, cotton with long fiber length, fineness and high grade can have less twist coefficient, and the twist coefficient of fine yarn is larger than that of thick yarn. , its length is called the total elongation. When the load is removed, the stretched cotton yarn quickly retracts, but cannot return to the original length. This retractable length is elastic elongation, that is, the elastic elongation and the total elongation. Percentage, the elasticity of the yarn increases with the increase of the twist, but starts to decrease after a certain twist, and the twist is generally close to the range of the maximum elasticity. The twist coefficient is commonly used, the warp yarn of carding is higher, and the knitting is generally lower, about 3.5-3.6. Due to the different uses of the yarn, there are yarn products with different twist coefficients. According to the calculation data of Japan Textile, they are divided into: ordinary twist = 4.0 (twist coefficient), loose twist = 3.4 (twist coefficient), special loose twist = 1.32- 2.8 (twist coefficient), strong twist = 5.0-5.4 (twist coefficient), especially strong twist = 5.0-6.5 (twist coefficient). High-twist yarn generally needs to go through the steaming process before it can be woven, and sometimes it needs to be equipped with a twister before it can be woven. The twist or twist coefficient is a comprehensive parameter that affects various properties of the yarn. It is not only closely related to the single yarn breaking strength and single yarn breaking elongation, but also affects the yarn linear density, evenness CV%, thickness of the yarn. knots, details, neps, hairiness and many other factors; these factors change in different trends due to different degrees of yarn twist. Therefore, in the normal yarn twist process adjustment, not only should pay attention to the change of twist, single yarn breaking strength, single yarn breaking elongation, but also pay attention to the corresponding changes in the overall quality of the yarn. It is an important condition to strengthen total quality management to meet customer needs.
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