In order to make the yarn have certain physical and mechanical properties such as strength, elasticity, elongation, luster, hand feeling, etc., the properties of the yarn must be changed by twisting. Short fibers need to be twisted in order to be spun into yarns, and filaments need to be twisted in order to facilitate processing or improve tightness. The twist has a direct impact on the structure of the yarn, the physical properties, the style of the fabric, and the wearability of the finished garment. Yarn breaking strength refers to the maximum force exerted by the sample being stretched to break in the yarn tensile test
. The ratio of the breaking strength to its linear density is called the breaking strength of the yarn . Twist and strength are the most basic test items in textile production, an important index to characterize material performance and quality, and an important basis for textile mills to evaluate yarn quality. In this paper, 26S/2 ring-spun cashmere yarn and running-spun cashmere yarn are selected to test their twist and strength respectively, so as to compare the relationship between the twist and strength of the two cashmere yarns. twist test: twist test principle twist is usually not evenly distributed on the whole yarn. When testing the twist, take a sample with 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 constituent 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. Twist test method Yarn twist test methods include: direct counting method and untwisting method. Among them, the untwisting and twisting method is divided into: untwisting and twisting A method, untwisting and twisting B method and three untwisting and twisting method; the direct counting method is suitable for short fiber single yarn, twisted multifilament, strand, cable Thread; untwisting method is suitable for single yarn of cotton, wool, silk, linen and their blended fibers. In this test, the YG155A electronic yarn twist meter is used to test the twist of 26S/2 cashmere strands by the direct counting method. The samples select 4 kinds of ring-spun cashmere yarns and 4 kinds of running cashmere yarns for testing, and each sample is tested 5 Second, compare the twists of ring-spun cashmere yarn and running-spun cashmere yarn. Test results calculate the average twist value Xe of each yarn, the average twist value X L below the average value, the mean square deviation S, the number of times below the average value NL, the coefficient of variation CV, the average difference unevenness rate H, the twist coefficient a, etc. strength test: strength test principle yarn breaking strength measurement is to use special equipment to stretch the sample until it breaks, and record the breaking strength and breaking elongation at the same time . The yarn strength of this test is tested by YG023C full-automatic single-yarn strength machine. The working principle is to use a force sensor to convert the force of the tested sample into an electrical signal. After amplification, a signal proportional to the force is obtained. Display load value and breaking strength. A digital pulse proportional to the deformation of the sample is generated through a certain mechanism, the deformation of the sample is displayed through a counting circuit, and the instrument automatically records and prints the test data. Strength test method This test uses a clamping length of 500 mm, a tensile speed of 500 mm/min, the pre-tension of the humidity control sample is (0.5+0.1) cN/tex, and the standard atmospheric temperature for humidity control and test is (20 ±2)℃, relative humidity is (65±3)%. The hank sample should be placed for more than 8 hours under standard atmospheric conditions, and the tightly packaged sample should be placed for more than 48 hours. According to the test regulations, prepare 4 samples of 2626S/2 pure cashmere ring-spun yarn and running-spun yarn, which are consistent with the above-mentioned twist test samples. Perform pre-conditioning and humidity conditioning treatments as required by regulations, and test in standard atmosphere. Test results Calculate the breaking strength, breaking strength, breaking length, average value, coefficient of variation, etc., and the statistical results are shown in Table 2 and Table 3. From the above ring-spun cashmere yarn strength test data and running-spinning cashmere yarn strength test data, it can be concluded that the average breaking strength and breaking strength of ring-spun cashmere yarns are greater than those of the same number of running-spinning cashmere yarns. . The relationship between yarn twist and strength: summarize the data obtained from the above yarn twist test and yarn strength test, and obtain the cashmere yarn twist and strength test data summary table (Table 4), as the basis for analysis. In the test to test the strength of the yarn, when the yarn was stretched to break, it was found that not all the fibers on the fractured section were broken, but some of the fibers were broken, and the other part of the fibers slipped, and the broken part of the fibers did not break at the same time. It can be seen that this breaking performance is closely related to the strength of the yarn and its twist. After the yarn is twisted, it not only affects the appearance of the yarn's diameter and gloss, but also affects the inherent quality and feel of the yarn's strength, elasticity, and elongation. For cashmere yarn, the most direct effect of twisting is to gain strength. However, it can be seen from Table 4 that it is not that the greater the degree of twisting, the greater the strength of the yarn. The reason is that there are factors that are beneficial to the increase of yarn strength and that are not conducive to the strength of the yarn. (1) Favorable factors: the twist coefficient increases, the centripetal pressure of the fiber on the yarn axis increases, the friction resistance between the fibers increases, and the possibility of yarn breaking due to slippage between the fibers decreases. Twisting reduces the strength unevenness of the yarn in the length direction. Under the action of external stretching force, yarn breakage always occurs at the point where the yarn strength is the smallest, and the yarn strength is the external force that the weak loop can withstand.
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