The quality of spun yarn directly affects the post-processing and weaving work as well as the quality of fabrics. The quality of spun yarn is not only related to the technical management of this process, machinery, operations, etc., but also affected by the semi-finished products of the cleaning, carding, combining, and roughing processes. quality impact. Therefore, in addition to the process conditions, mechanical status, temperature and humidity status, and technical operations of the workshop, the quality of spinning yarn must also consider the quality of semi-finished products. So how to control the quality of spinning yarn and reduce the unevenness of spinning yarn?
(1) Types of uneven spun yarns
Under certain raw material conditions, the quality of textiles To a large extent, it depends on the uniformity of the yarn. Various technical measures and management systems are adopted in production, such as reasonable operating procedures, mixing, combining, segmented matching, quantitative control and equipment maintenance, etc., all to ensure that product unevenness is minimized and eliminated and the quality of the final product is ensured.
1. Uneven weight
Based on the weight of 100m of fine yarn expressed as the coefficient of variation. In order to control the weight (linear density) of semi-finished products and spun yarns that meet the specified requirements during production, while controlling the weight variation coefficient of 100 meters of spun yarns, the weight deviation is also used (the weight deviation refers to the difference between the actual linear density of the spun yarns and the designed linear density). Design percentage of linear density) to control semi-finished products and fine yarn density.
2. The strips are uneven
The spun yarn is uneven. Uniform represents the degree of difference in thickness of short segments of spun yarn. The spun yarn is wound on the blackboard according to the regulations and compared with the standard sample. The results obtained by observing ten blackboards represent the evenness quality of short segments of the spun yarn; or the evenness unevenness can be measured with an evenness evenness tester, which is referred to as evenness CV. value.
3. Uneven structure
The difference in the structure of the spun yarn is called Because of uneven structure. For example, the uneven mixing of fibers in the cross-section or longitudinal area of the spun yarn, the different tones of raw yarns between batches, and the uneven twist caused by uneven evenness, etc., all belong to the uneven structure of the spun yarns.
The uneven weight or unevenness of spun yarn often shows a wave form when tested with instruments, with a certain wavelength and amplitude. When the uneven waveform of a product approaches periodic fluctuations, it is usually called periodic unevenness. For example, unevenness caused by eccentricity of rollers or top rollers and poor gear meshing will cause the waveform to appear as periodic fluctuations with similar wavelengths and amplitudes. Periodic unevenness in yarn products. If the waveform is short, the unevenness within tens of millimeters often affects the evenness of the product; if the waveform is long, such as tens of meters or longer, this unevenness will Affects the weight unevenness of the product.
Uneven waveforms formed by random or accidental factors often have no obvious rules. This kind of unevenness is non-periodic unevenness. Most of the uneven products in general production are of this nature. In some cases, local unevenness may sometimes occur due to poor operation, too thick joints, inclusion of flying flowers, etc.
(2) The formation of uneven spinning yarn
Drawing, Uneven feed products such as roving and out-of-control pressure in the rear area of the spinning yarn will cause uneven long segments of the spinning yarn. Unreasonable process parameters in the front area of the spinning yarn or other reasons may easily lead to uneven short segments. Therefore, uneven spinning is caused by the superposition of uneven feeding of roving and unevenness caused by the spinning process. In most cases, this unevenness has no obvious regularity. In order to facilitate the analysis of factors causing unevenness, there are four types: random unevenness, drafting unevenness, mechanical unevenness and unevenness caused by other factors.
1. Random unevenness
The yarn cross-section is determined by a certain number According to actual tests and mathematical statistics, the number of fibers in a yarn cross-section with a certain linear density becomes a distribution. Even if the yarn raw material is very uniform and no additional unevenness occurs during production, the yarn There is still uneven thickness, which is random unevenness. Random unevenness increases as the linear density of the yarn becomes smaller or the draft ratio increases, that is, the average number of fibers in the yarn cross-section decreases, and the unevenness value becomes higher. In the finished spun yarn, the smaller the density of the spun yarn, the greater the unevenness of the yarn. The random unevenness of yarn is the lowest unevenness, so it is sometimes called the ideal unevenness of yarn.
2. Uneven drafting
Due to fiber properties and elongation Due to the difference in the alignment state, especially the presence of short fibers, even if the mechanical state is relatively normal, the stress on the fibers (drafting force) on the yarn sliver will continue to change during the drafting process, causing the fiber displacement deviation and unevenness. This unevenness is drafting unevenness or drafting wave. Drafting waves are all manifested as unevenness in shorter segments, which is the main factor affecting the evenness of spun yarns. The formation of uneven drafting is mainly related to the following factors.
(1) Unreasonable selection of process parameters: When the drafting type and product are certain, if the selected process parameters include drafting multiple and drafting distribution, roller spacing, If the roller pressure and roving twist coefficient are unreasonable, the uniformity of the product will inevitably deteriorate. Under normal circumstances, when the density of the spun yarn remains unchanged, for a certain drafting type, the greater the drafting multiple, the greater the unevenness of the short segments of the spun yarn, and the worse the evenness level. When the drafting type and product are certain, the relationship between the gauge and yarn unevenness is best when the gauge is reasonable. If the gauge is too large or small, the yarn unevenness will become larger. For certain products and certain drafting types,The drafting mode should be compatible with the local drafting multiple. The roller pressure should be stable and uniform to ensure stable drafting efficiency.
2. Reasonably arrange the friction boundary
In the drafting mode Under certain conditions, the distribution characteristics of the friction force boundary are basically fixed, but proper adjustment of the distance between the draft rollers and the appropriate movement of the top roller forward or backward can change the distribution of the friction force boundary and improve the control state of the fiber.
3. Strictly control the quantity and improve the quality of semi-finished products
Strengthen When mixing raw materials, strictly control the quantity of semi-finished products before spinning to reduce weight unevenness; reasonably control the number of combined semi-finished products and improve fiber straightness; use appropriate types of collectors to strengthen the control of edge fibers so that the fibers can be stretched during drafting. There is good straightening parallelism at all times to minimize draft waves and improve yarn uniformity.
4. Strengthen mechanical maintenance and repair work
Drawing components The working state is the main factor affecting the evenness of the yarn. It is necessary to strengthen the maintenance of the drafting components and conduct regular inspections to ensure the accurate position of the gauge and related components. Wearable parts need to be replaced regularly to ensure that the machine is in good operating condition. </p
