Main factors affecting yarn tensile breaking strength
1. Fiber properties: (1) Fiber length: Fibers whose length is shorter than 2Lc (Lc is the slip length) will cause the yarn strength to decrease as its content increases. For example, the short lint rate of cotton fiber increases by 1% on average, and the tensile breaking strength of spinning yarn decreases by 1%-1.2%. (2) Fiber strength: The higher the relative strength of the fiber, the higher the strength of the spinning yarn. At the same time, various factors that affect fiber strength will also appear on the spinning yarn, but because they are related to the structure of the spinning yarn, the effects are not exactly the same. The strength of several different spinning yarns is affected by temperature and moisture regain, as shown in Figure 2-20 and Figure 2-21. (3) Fiber fineness: The fibers are thinner and softer. When they hug each other in the yarn, they are closer to each other. The slip length may be shortened. The number of fibers in the yarn cross section may be greater, which increases the chance of fiber transfer between the inner and outer layers of the yarn. , each fiber receives external force relatively uniformly, so the yarn strength is improved. (4) Others: The surface properties, crimp, uniformity, toughness modulus, etc. of the fiber will all affect the tensile breaking strength of the spinning yarn. 2. The structure of spinning yarn The structure of traditional spinning yarn also has a great influence on the tensile properties and other properties. In addition to the parallelism, straightness, and number of inner and outer layer transfers of the fibers in the spinning yarn, the important influencing factor is the twist of the spinning yarn. In traditional spinning yarns, as the twist increases, the strength begins to increase, and then decreases when the twist reaches a certain level. The maximum value is the critical twist (twist coefficient). The effect of traditional spinning yarn twist on the elongation at break is shown in Figure 2-22. When the twist direction of the strands is the same as that of the single yarn, the strength of the strands gradually increases and then decreases as the twist increases. The pattern is similar to that of single yarn twisting. When the twisting direction of the strands is opposite to the twisting direction of the single yarn, the reverse twisting of the plies will cause the single yarn to untwist and the structure will become loose, and the strength will decrease. However, when twisting continues, the structure of the spun yarn will become tight again, and due to the fibers in the strands, the twisting direction will be opposite. The angle between the direction in the thread and the direction of the strands becomes smaller, which increases the effective component of fiber tension in the stretching direction. After the strands are reversely twisted, the difference in tension between the inner and outer layers of the single yarn is reduced, and the prestress of the outer layer of fibers is reduced. decreases, increasing the number of fibers that bear external forces. At the same time, the fibers in the single yarn, even the fibers in the outer layer, are clamped between the single yarns in the strands, so that the outer fibers of the spinning yarn are not easy to slip and disintegrate. Therefore, the strength of the strands increases and is greater than the sum of the strengths of the plying single yarns. When it reaches the critical value, it is even about 1.4 times the sum of the strengths of the single yarns, as shown in Figure 2-23. 3. The external factors that affect the tensile new crack strength of spinning yarn are mainly temperature, humidity, sample length, testing speed and type of testing instrument. These factors have the same effect on the tensile breaking strength of spun yarns as on fibers. When spinning yarn needs to be tested quickly under extraordinary circumstances (the sample is tested directly without humidity control), the measured strength value must be corrected, and the calculation formula is: Where: P——Corrected spinning yarn Strength; P5—the strength of the spinning yarn measured under actual atmospheric conditions; K—the correction coefficient, obtained by looking up the table based on the moisture regain of the spinning yarn and the test temperature.
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