Spinning quality has a direct impact on post-processing, weaving and fabric quality, while spinning quality is not only related to the process technology, machinery, operation and other technical management work, but also affected by cleaning, carding, drawing, rough processes of the quality of half products. Therefore, the spinning quality control, in addition to the workshop process conditions, mechanical state, temperature and humidity state, technical operation, but also must consider the quality of half products. So how to control the spinning quality to reduce the spinning unevenness?

(1) categories of uneven spinning

Under certain raw material condition, the quality of textile depends on the uniformity of yarn to a great extent. Various technical measures and management systems are adopted in production, such as reasonable operating procedures, mixing, merging, section collocation, quantitative control and equipment maintenance, etc. to ensure that the product unevenness is reduced and eliminated as far as possible and the final product quality is guaranteed.

1. Uneven weight

It is expressed by the coefficient of weight variation between 100m spinning yarns. In order to make sure that the spinning weight (line density) of half products and spinning yarns meet the requirements, the weight deviation (the weight deviation refers to the difference between the actual yarn density and the designed yarn density and the percentage of the designed yarn density) is also used to control the line density of half products and spinning yarns while controlling the variation coefficient of spinning weight in 100 meters.

2, thousands of uneven

The evenness of the filament represents the difference of the length of the filament. According to the regulations, the yarn is wound on the blackboard, and the results obtained from ten blackboards are compared with the standard sample, which represents the dry mass of the short yarn fragments. Or use the evenness tester to measure the evenness of the strip, referred to as the strip CV value.

3. Uneven structure

The difference in yarn structure is called structural unevenness. Such as yarn cross section or longitudinal in a certain area of fiber blending, between the batch and batch of original yarn tone and due to the twist unevenness caused by unevenness, all belong to the spinning structure unevenness.

The uneven weight or evenness of the yarn, when tested by the instrument, often shows a wave pattern, with a certain wavelength and amplitude. When the unevenness waveform of a product is close to periodic fluctuation, it is usually called periodic unevenness. As a result of the roller or roller eccentricity, gear meshing is not uniform, its waveform performance is periodic wave, and has close wavelength and amplitude. Periodic unevenness In yarn-forming 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 segments, this unevenness 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. The unevenness of products in general production mostly belongs to this nature. In individual cases, due to poor operation, too thick joint, flying clip, sometimes form local unevenness.

(2) the formation of uneven spinning yarn

The unevenness of the feeding products such as drawing and roving and the out-of-control pressure in the back area of spinning will form the unevenness of the long segment of spinning. The unreasonable technological parameters in the front area of spinning or other reasons will easily form the unevenness of the short segment. Thus, the unevenness of the spinning is caused by the superposition of the unevenness of the feeding roving and the unevenness of the spinning process, which in most cases has no obvious regularity. In order to facilitate the analysis of the factors causing unevenness, there are four types of unevenness: random unevenness, drawing unevenness, mechanical unevenness and unevenness caused by other factors.

1. Random unevenness

Yarn cross section is composed of a certain number of fibers, according to the practical test and mathematical statistics prove that a certain linear density of yarn cross section of the fiber quantity, become a kind of distribution, even if the yarn in the production of raw materials is very uniform, do not produce any additional uneven, which the weight unevenness of yarn still exists, the uneven as random irregularity. With the decrease of the linear density or the increase of the draft ratio, that is, the average number of fibers on the yarn section decreases, the value of the random unevenness increases. The smaller the yarn density, the greater the unevenness. The random irregularity of the yarn is the low irregularity, so it is sometimes called the ideal irregularity of the yarn.

2. Uneven drafting

Due to the differences in fiber properties and elongation arrangement, especially the existence of short fibers, even if the mechanical condition is relatively normal, the fiber force on the yarn is still changing constantly in the drawing process, resulting in the displacement deviation of the fiber and forming the unevenness. This unevenness is the drawing unevenness or drawing wave. Drafting wave is the unevenness of short segment, which is the main factor affecting the yarn evenness. The formation of unevenness of draft is mainly related to the following factors.

(1) Irreasonable selection of process parameters: when the draft type and the product are fixed, if the selected process parameters, including the draft multiple and distribution, roller spacing, roller pressure, roving twist coefficient, etc. are unreasonable, the uniformity of the product will inevitably deteriorate. In general, when the yarn density is unchanged, for a certain drafting type, the larger the drafting multiple, the greater the unevenness of the short segment of the yarn, and the worse the sliver level. When the draft type and the product are fixed, the relationship between the spacing and the yarn unevenness will be better when the spacing is reasonable, too large and small the yarn unevenness will become larger. For a certain product and a certain type of draft, there is a certain reasonable range of spacing, too large or too small will affect the normal movement of the fiber, increase the unevenness of the yarn. The amount of pressure can affect the drafting efficiency or the normal movement of the fibers. Insufficient pressure will affect the drafting efficiency and the yarn forming quantity. In serious cases, the draft of the roving will not open, resulting in coarse and fine yarn. The roving twist factor also affects the drafting efficiency. If the twist is too large, the yarn can not be drawn, and the yarn joints are coarse and fine, which will destroy the yarn evenness or affect the yarn weight irregularity.

(2) the arrangement of friction boundary is unreasonable or unstable: if the arrangement of friction boundary does not meet the characteristics of the fiber and the requirements of the fiber movement, it will increase the displacement deviation of the fiber and increase the unevenness of the yarn.

(3) the feeding of roving structure is not uniform: the fibers in the feeding of roving are poor in straightness, knot impurities or short lint, which will destroy the normal movement of fibers and cause unevenness. Especially, the content of short fiber in roving is too much or does not adapt to the arrangement of spinning friction boundary, so the fiber can not be effectively controlled, so the drafting wave is produced in the process of drafting.

3. Mechanical unevenness

Mechanical unevenness or mechanical wave is the periodic or non-periodic unevenness formed due to abnormal drafting parts or mechanical factors. For example, the moving of the roller clamp mouth, the unstable control of the roller clamp mouth on the fiber movement, the inflexion or insufficient pressure of the roller, the slippery roller, and the bad work of the leather ring will affect the uniformity of the yarn

(1) Roller jaw movement: if the position of the roller jaw is unstable, the roller spacing will change with time, resulting in uneven yarn yarn. The following roller is round, while the roller is eccentric, bent and the coating of the roller is uneven, and the rotation center of the roller is not its center. When the roller rotates, the center of the roller moves around the center of rotation in a circle, and the roller clamp mouth reciprocates back and forth, so that the spinning yarn is thick and fine. The larger the upper roller eccentricity is, the greater the moving distance of the nipper is, and the thicker and finer the yarn is. In addition, if the lower roller is eccentric or bent, and the roller torsion vibration, etc., the surface speed of the lower roller is not even, and the draft ratio between the rollers often changes, which seriously affects the unevenness of the spinning yarn.

(2) The clamping mouth is not stable in controlling the movement of the fiber: in the drafting process, the roller clamping mouth should be able to control the fiber stably and effectively, so that the fiber can be regularly output from the roller clamping mouth. However, due to the lack of roller pressure or the roller rotation is not flexible, the friction resistance is large, resulting in the roller clamp on the fiber movement control is not stable, so that the spinning yarn is not uniform. This irregularity is rarely regular, and each slippage occurs in a short time, resulting in irregular irregularity of the strip.

Bad: (1) (3) the apron aprons work stability: aprons in the actual operation process, because there are differences between the bending stiffness, friction resistance between apron and pin have change, make the aprons work is not stable, thus affecting the stability of the control action aprons, especially in the apron nip will cause jaw pressure fluctuation, the influence on yarn evenness. The stability of ring speed is usually expressed by the unevenness of ring speed. The so-called ring speed unevenness refers to the change of the speed at any point on the ring working face with respect to time. The ring speed unevenness can be calculated by the formula of average difference unevenness. The main reasons that affect the uneven speed and slipperiness of the apron are the pressure of the middle roller and the mechanical properties of the apron. ② hanging leather ring: hanging leather ring is a performance of the work of the long leather ring is unstable. In operation, if a moment of force imbalance, will make the leather ring tension bar is lifted, the leather ring working face appears concave, even resulting in the leather ring squeezing the end of the pin and the middle roller in the gap, this phenomenon is called hanging leather ring. If the hanging ring is serious, the ring will be crushed or broken due to the friction of the middle roller on the ring. Lightly hanging leather ring, the tension bar is lifted and the leather ring instantaneous working face is concave, affecting the strength of friction. Although the tension rod is restored to its original position because of the increase of the deformation of the spring, there is also the phenomenon of instability in the rotation of the leather ring. To solve the problem of lifting the leather ring, we can increase the tension of the tension rod, adopt the measures of chrome plating and acid treatment of the leather ring, reduce the friction resistance between the leather ring and the pin, and strengthen the maintenance and cleaning work.

4. Other reasons

Such as the yarn passage is not smooth, unexpected draft too large, the operation joint is not good, the assembly position is not right, and the draft speed is too large or the fuselage shakes, all make the yarn evenness increase.

(3) Ways to improve the unevenness of spinning yarn

The unevenness of the spinning yarn is formed by many factors. Therefore, improving the design of the drafting device can effectively control the motion of the fiber and reduce the drafting wave. Improve the mechanical repair quality, so that the machinery in a good state of operation, reduce the mechanical wave; Strengthen raw material mixing, remove impurity, carding, reasonably master the combination of half products; Reasonably controlling the quantity of products in each process is the fundamental way to improve yarn uniformity.

1. Reasonable selection of process parameters

According to the characteristics of the product, fiber properties, roving structure and the draft type of the roving machine used, and through the necessary test and comparison method, the technological parameters are reasonably selected. When the yarn quality requirements are high but the necessary effective measures are lacking, the total draft and local draft distribution should not be close to the upper limit allowed by the machine, and should be controlled by a small amount, which is beneficial to yarn forming. Roller spacing and feeding quantity, draft type should be adapted to the local draft ratio. Roller pressure should be stable and uniform to ensure stable drafting efficiency.

2. Reasonable arrangement of friction force

Under the condition of a certain type of drafting, the distribution of friction force is basically fixed, but the distribution of friction force can be changed and the control state of fiber can be improved by adjusting the drawing roller spacing appropriately and moving the roller forward or backward appropriately.

3. Strictly control the quantity and improve the quality of semi-products

Strengthen the mixing of raw materials, strictly control the quantity of pre-spinning semi-products, reduce the weight unevenness; Reasonably master the combination number of half products, improve fiber straightness; Appropriate type of aggregator is used to strengthen the control of the edge fibers, so that the fibers have a good degree of extension and parallelism during drawing, so as to minimize the drawing wave and improve the evenness of yarn forming.

4, strengthen the mechanical maintenance work

The working condition of the drafting parts is the main factor that affects the yarn dryness. It is necessary to strengthen the maintenance of the drafting parts and check regularly to ensure the accurate position of the spacing and related parts. The vulnerable parts should be replaced regularly to ensure that the machinery is in good running condition.