Views:1 Author:Site Editor Publish Time: 2021-11-26 Origin:Site
Yarn evenness refers to the uniformity of thickness or weight in shorter segments of the yarn, sliver or roving in the axial direction, and can also be expressed as yarn unevenness. The quality of textiles depends largely on the yarn evenness.
Yarn unevenness is divided into short segment unevenness, middle segment unevenness and long segment unevenness. The interval length of unevenness is 1-10 times the fiber length, and the interval length is about 1 m or less, which is called short fragment unevenness; the interval length of unevenness is 10-100 times the fiber length, and the interval length is about A few meters is called the uneven segment; the length of the uneven interval is 100 to 3,000 times the fiber length, and the length of the interval is about tens of meters, which is called the long segment uneven.
When weaving yarns with high unevenness in short segments, there is a greater probability that several thick knots or details will be juxtaposed on the fabric surface, and fabric defects are prone to appear, which will have a greater impact on the quality of the fabric. The cloth surface woven with long and uneven yarns will have obvious horizontal stripes, which will also have a greater impact on the cloth surface. Relatively speaking, when weaving yarns with uneven segments, the chance of defects on the fabric surface is slightly lower, and it is related to the width of the fabric. When there is a certain multiple relationship, obvious defects such as streaks or cloud spots will appear. The uneven yarn evenness during the weaving process will also increase the end breakage rate and decrease the production efficiency. Therefore, the evenness of yarn is an important index for evaluating yarn quality.
1) The effect of cotton fiber length on cotton yarn evenness. In the spinning process, because the fibers of different lengths cannot be given the same effective control, the short fibers are out of control and floating, which makes the spinning even worse, especially when the fiber length unevenness is large. Is serious. Therefore, it is not only necessary to pay attention to the length of cotton fiber when assembling cotton, but also to control the degree of difference in length.
2) The influence of cotton fiber linear density on cotton yarn evenness. When spinning a yarn with a certain linear density, the thinner the fiber, the more the average number of fibers in the cross section of the yarn, and the better the evenness of the yarn. Therefore, in order to obtain a yarn with excellent evenness, it is necessary to control the linear density of the cotton fiber. In addition, the degree of linear density difference must be controlled.
3) The influence of short linters and harmful defects on the evenness of cotton yarn. Linter refers to cotton fibers less than 16 mm in length. In the drafting process, the short pile length is not easy to be controlled, and the floating time is long, which deteriorates the yarn sliver. Similarly, during the drafting process, harmful defects in the cotton fiber can cause irregular movement of the fiber, disrupt the normal drafting, and deteriorate the yarn evenness. Therefore, when selecting raw cotton, the content of short linters and harmful defects should be strictly controlled.
1) The effect of cotton fiber straightness on cotton yarn evenness. Firstly, when the cotton fiber is not fully straightened and there are hooks, it shortens the effective length of the fiber in the drafting zone and increases the floating stroke of the cotton fiber; secondly, the cotton fiber is not straightened during the drafting process. Cause entanglement, resulting in fiber bundle movement; and when the unstraightened cotton fiber itself is stretched, the process of stretching and breaking the law of its movement will deteriorate the evenness.
2) The effect of cotton fiber separation on cotton yarn evenness. When the cotton fiber separation is poor, there are small cotton tufts, neps, impurities, etc. in the feeding yarn, which will inevitably cause the difference in the tightness of each part of the yarn. Even under the condition that the applied pressure of the yarn is stable, the cohesive force between the cotton fibers is still different, especially when there are small cotton bundles, this part of the cotton fibers will move due to the large internal friction, thereby worsening the drag. During the stretching process, serious drafting waves are caused, and the unevenness of the sliver increases sharply.
1) Differences in the properties of fiber raw materials
Various natural fibers have unevenness in length, linear density or other properties. This unevenness is not only manifested between roots, but also in different parts of the same fiber; this unevenness of chemical fibers It has better properties than natural fibers, but there are still some differences in properties. The non-uniformity of the properties or the difference in performance of the fiber, processed by the same machinery and technology, will cause the unevenness of the yarn evenness, which is manifested by the increase of the evenness CV value and the increase of the spectrogram.
2) The random arrangement of fibers means that the yarn is uneven due to the random arrangement of fibers. According to the principle of short-fiber spinning, an ideal yarn can be assumed to be composed of fibers randomly arranged. This randomly arranged yarn has a certain unevenness, which is called random unevenness. The value is equal to the average number of fibers in the cross-section of the yarn. The square root of is inversely proportional, and random unevenness will increase when the number of fibers is small. This unevenness is the lowest extreme unevenness, also known as extreme unevenness.
3) Poor selection of spinning process parameters means that the yarn is uneven due to poor selection of spinning process parameters. For example, improper selection of process parameters such as the gauge and pressure of the drafting mechanism will result in poor control of the fiber movement, which will cause the problem of the thickness of the knots and the uneven thickness.
4) Spinning mechanical defects are uneven yarns caused by spinning mechanical defects. For example, eccentric rollers or rubber rollers, gear defects, etc., will cause the yarn to produce obvious periodic unevenness, often showing undulating wave changes. Shorter wavelengths are called uneven short segments, and long ones are uneven. Generally, the short-segment unevenness produced by the front spinning machine, due to the longer drafting, presents long-segment unevenness in the yarn; the unevenness produced on the spinning frame is the short-segment unevenness.
Commonly used methods for measuring unevenness in spinning production mainly include three-section weighing method, visual inspection method for black evenness and instrument detection method.
The segment weighing method can be used for various semi-products and spun yarns;
The visual inspection method of the black stripe is mainly used for spun yarn;
The instrument detection method can be divided into capacitive detection and mechanical detection.
Capacitive detection is suitable for sliver, roving and spun yarn, and mechanical detection is only suitable for sliver and roving.