Principle of twist test
: Twist is usually not evenly distributed on the whole yarn. When testing the twist, take a sample at a distance of 1 m. Under the specified tension, clamp the two ends of a certain length of the sample, rotate one end of the sample, and remove the twist of the yarn sample until the component units of the tested yarn are parallel. The twist of the yarn is obtained according to the number of revolutions required to remove the twist of the yarn. When the yarn was stretched to break, it was found that not all fibers on the fractured section were broken, but one part of the fiber was broken, and the other part of the fiber slipped, and the broken part of the fiber did not break at the same time. Performance and single yarn strength are closely related to the twist of the yarn. As the twist increases, the yarn strength continues to increase, but after a certain twist, the twist continues, and the strength decreases. The advantage is that the twist increases and the friction resistance between fibers The increase increases the strong component during the breaking process.The disadvantage is that the twist increases, the inclination angle of the fiber and the yarn axis increases, and the component force that the fiber strength can withstand in the yarn axis decreases, and the twist is too large to increase the inner and outer fibers of the yarn. Uneven stress distribution will aggravate the different timing 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. As the twist increases, the twist angle increases, and the light reflects to the side, poor gloss and poor hand feel. On the contrary, the hand feels soft, but if the twist is too small, hairiness and loose hand feel will occur, and the gloss may not be good. The twist coefficient and twist direction are mainly determined by the quality requirements of the final product. The twist coefficient is different for different purposes. The twist direction depends on the needs of the finished product and post-processing. In order to reduce the inconvenience of modification and operation on the yarn machine, the Z twist direction is generally . For example, cotton with long fiber length, fineness, and high grade, the twist coefficient can be less, and the twist coefficient of fine yarn is larger than that of thick yarn. The elongation is cotton yarn under a certain tensile load, and the cotton yarn is stretched and stretched. , Its length is called total elongation. When the load is removed, the stretched cotton yarn quickly retracts, but cannot return to the original length, which is a shrinkable length, which is elastic elongation, that is, the elastic elongation and the total elongation In percentage, the elasticity of the yarn increases with the increase of the twist, but starts to decrease after a certain twist. Generally, the twist range is close to the maximum elasticity. Commonly used twist coefficient, carded warp yarn is higher, while knitting is generally lower, about 3.5-3.6. Because of the different uses of yarns, there are different twist coefficient yarn products. According to the calculation data of Japan Textile, they are divided into: ordinary twistu003d4.0 (twist coefficient), loose twistu003d3.4 (twist coefficient), special loose twistu003d1.32- 2.8 (twist factor), strong twist u003d 5.0-5.4 (twist factor), especially strong twist u003d 5.0-6.5 (twist factor). High-twist yarns generally need to go through the steaming process before weaving, and sometimes it is necessary to install a de-twisting device to weave. Twist or twist coefficient is a comprehensive parameter that affects a variety of yarn properties. It is not only closely related to single yarn breaking strength and single yarn breaking elongation, but also affects yarn linear density, evenness CV%, and thickness. Knots, details, neps, hairiness and many other factors; these factors change in different trends due to different degrees of yarn twisting. Therefore, in the normal yarn twist process adjustment, not only the changes in twist, single yarn breaking strength, and single yarn breaking elongation, but also the corresponding changes in the overall quality of the yarn due to different trends. It is an important condition to strengthen overall quality management to meet customer needs.
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