Abstract
The evenness of yarn refers to the uniformity of thickness or weight within a short segment of yarn, sliver or roving along the axial direction. It can also be expressed as the evenness of yarn. Unevenness. The quality of textiles depends largely on yarn evenness.
Classification of uneven yarn evenness
Uneven yarn evenness is divided into short segment unevenness, medium segment unevenness and long segment unevenness. Uneven. The length of the uneven intervals is 1 to 10 times the fiber length, and the interval length is about 1 m or less, which is called short segment unevenness; the uneven interval length is 10 to 100 times the fiber length, and the interval length is about A few meters is called medium segment unevenness; the interval length where unevenness occurs is 100 to 3,000 times the fiber length, and the interval length is about tens of meters, is called long segment unevenness.
The influence of uneven yarn stems
When weaving with short segments of yarn with high unevenness, several thick spots or details will appear in the cloth. The probability of the surfaces being juxtaposed is high, and cloth surface defects are prone to occur, which has a greater impact on the quality of the cloth surface. Cloth woven with long and uneven yarns will have obvious horizontal stripes, which will also have a greater impact on the cloth. Relatively speaking, the chance of defects on the cloth surface when weaving yarn with uneven medium segments is slightly lower, and it depends on the width of the cloth. When there is a certain multiple relationship, obvious defects such as stripes or cloud spots will appear. Uneven yarn evenness will also lead to an increase in the end-break rate and a decrease in production efficiency during the weaving process. Therefore, yarn evenness is an important indicator for evaluating yarn quality.
The effect of cotton fiber properties on yarn evenness
1) The effect of cotton fiber length on cotton yarn evenness. During the spinning process, the same effective control cannot be given to fibers of different lengths, resulting in the out-of-control and floating phenomena of short fibers, which worsens the evenness of the spinning yarn, especially when the fiber length unevenness is large. For serious. Therefore, when matching cotton, we must not only pay attention to the length of cotton fibers, but more importantly, 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 finer the fiber, the greater the average number of fibers in the yarn cross section, and the better the evenness of the yarn. Therefore, in order to obtain a yarn with excellent evenness, the linear density of cotton fiber must be controlled. In addition, the degree of difference in linear density must be controlled.
3) The impact of short lint and harmful defects on the evenness of cotton yarn. Short velvet refers to cotton fibers with a length less than 16 mm. During the drafting process, due to the short length of the lint, it is difficult to control and the floating time is long, which deteriorates the yarn sliver. Similarly, during the drafting process, harmful defects in cotton fibers will cause irregular movement of the fibers, disrupt normal drafting, and worsen the yarn evenness. Therefore, when selecting raw cotton, the short lint content and harmful defect content should be strictly controlled.
The influence of semi-finished product structure on yarn evenness
1) The influence of cotton fiber straightness on cotton yarn evenness. First, when the cotton fiber is not completely straightened, that is, when there is a hook, the effective length of the fiber in the drafting zone is shortened, which increases the floating range of the cotton fiber. Secondly, the cotton fiber is not straightened during the drafting process. Cause mutual entanglement, resulting in fiber bundle movement; and when the unstretched cotton fiber itself is drafted, it is subject to the process of straightening and destroys the regularity of its movement, which will worsen the evenness.
2) The effect of cotton fiber separation on the evenness of cotton yarn. When the cotton fiber separation is poor, there are small cotton bundles, neps, impurities, etc. in the feeding yarn, which will inevitably cause differences in the tightness of each part of the yarn. Even under the condition that the external pressure of the yarn is stable, the cohesion force between cotton fibers is still different everywhere. Especially when there are small cotton bundles, these cotton fibers will move in bundles due to extremely large internal friction, thus worsening the pulling force. During the stretching process, severe drafting waves are caused, which causes the unevenness of the evenness to increase sharply.
Causes for uneven yarn dryness
1) Differences in fiber raw material properties
Various natural fibers are uneven in length, linear density or other properties. This unevenness is not only reflected between roots, but also between roots. It manifests itself in different parts of the same fiber; this unevenness of chemical fibers is better than that of natural fibers, but there are still some differences in properties. This kind of non-uniformity or difference in performance of the fiber will cause uneven yarn dryness after being processed by the same machine and process, which will be manifested as an increase in the CV value of the yarn and an increase in the spectrum.
2) Random arrangement of fibers
That is, uneven yarn sliver caused by random arrangement of fibers. According to the principle of short fiber spinning, the ideal sliver can be assumed to be composed of randomly arranged fibers. This randomly arranged sliver has a certain unevenness, which is called random unevenness. The value is the same as the average number of fibers in the sliver cross section. is inversely proportional to the square root of , and random unevenness will increase when the number of fiber roots is small. This kind of unevenness is the lowest limit unevenness, also called limit unevenness.
3) Poor selection of spinning process parameters
That is, uneven yarn slivers occur due to poor selection of spinning process parameters. For example, improper selection of process parameters such as drafting mechanism spacing and pressure will lead to poor fiber movement control, which will cause problems with pitch thickness and detail, resulting in uneven thickness.
4) Spinning mechanical defects
That is, uneven yarn sliver caused by defects in spinning machinery. Such as roller or rubber roller eccentricity.��Gear defects, etc. will cause obvious periodic unevenness in the yarn, often showing undulating wavy changes in thickness. Shorter wavelengths are called unevenness in short segments, and long segments are called unevenness. Generally, the short segment unevenness produced by the pre-spinning machine is due to the longer draft, and long segment unevenness appears in the yarn; the unevenness produced by the spinning machine is the short segment unevenness.
Method for determination of yarn evenness unevenness
Methods for determination of evenness unevenness commonly used in spinning production , there are three main methods: cutting and weighing method, blackboard dry visual inspection method and instrument detection method. The cutting and weighing method can be used for each semi-finished product and spun yarn; the blackboard dry visual inspection method is mainly used for spun yarn; the instrumental detection method can be divided into capacitive detection and mechanical detection. Capacitive detection is suitable for slivers, rovings and spun yarns, while mechanical detection is only suitable for slivers and rovings.
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