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Cause analysis and control measures of small yarn defects

2020-04-01

With the wide application of new cellulose fibers such as Modal and Tencel in high-end apparel fabrics, customers have high requirements for the quality indicators of yarns produced by such fibers, and even some small yarn defects are often intolerable, so spinning Enterprises should carefully analyze the causes of small yarn defects, strengthen technical and management measures, and effectively reduce small yarn defects.

Basic definition and classification of yarn defects

1.1 Frequent yarn defects

Frequently occurring yarn defects refer to the details, lumps and neps tested with the Uster strip tester. The reference length of the neps is 1 mm, the longest is no more than 4 mm, and the sensitivity is generally set to + 140%, + 200%, + 280%; the detection length of the thick knot is about the average fiber length, and the sensitivity is generally set to + 35% , + 50%; the length of the details is about the average fiber length, and the sensitivity is generally set to -30%, -40%, -50%.

1.2 Sporadic yarn defects

Occasional yarn defects are detected by a yarn defect classifier. Occasional yarn defects are mainly divided into four types: neps (N), short thick knuckles (S), long thick knuckles (L), and details (T), and support deviation C, CC), etc., usually expressed by the number of occurrences on every 100,000 meters of yarn, neps (N) refers to short thick knuckles under 1 cm; short thick knuckles (S) refers to 1-8 cm thick knuckles ; Long thick section (L) refers to thick section above 8 cm; T refers to detail. Frequent and imperfect yarn defects have different probability and number of occurrences, different impacts on the trail, and the causes are very different.

The distribution area of the normal and occasional yarn defects on the yarn defect classification chart is shown in Figure 1 and Figure 2.


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图1 乌斯特电清纱疵分级图


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图2 常发性纱疵和偶发性纱疵对比图


It can be clearly seen from Figures 1 and 2 that the occurrence frequency of frequent yarn defects is relatively high, and the length and cross-sectional area of the yarn defects are relatively small. When the number of frequent yarn defects is too large, it will also have a serious impact on the fabric style of the fabric. Although the occurrence of sporadic yarn defects is relatively small, it is more harmful to the fabric. Such yarn defects are usually caused by poor production management, poor operation and unreasonable process design.

1.3 Small yarn defect

The author refers to the common yarn defects and the occasional yarn defects such as A1, A2, B1, and B2 as small yarn defects. The characteristics of small yarn defects are relatively small length and cross-sectional area, but the probability of occurrence is relatively high. High, difficult to control, but it has a very serious impact on the quality of high-grade fabrics.


Experiment on the effect of carding quality on small yarn defects

We selected the No. 12 and No. 15 carding machines with significant differences in the quality of the cotton web. The viscose film produced with the same plate of clear flowers was spun on the No. 12 and No. 15 carding machines, respectively. The R14.8KSJ varieties are produced on the coarse, fine and fine machine tables, and a total of 150,000 meters of bobbins are spun respectively. The quality indicators of birth bars, bobbins and bobbins are tested, as shown in Table 1.


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It can be seen from Table 1 that the clarity of the cotton web of No. 15 card is better than that of No. 12 card; the quality index of the bobbins spun from the sliver of No. 15 card is obviously better than that of No. 12 card Especially thick knuckles and neps; the difference in fine yarn defects of cones is also obvious.


Analysis of the causes of small yarn defects

The small yarn defect essentially reflects the distribution of the number of fibers in the yarn cross section and the uniformity of its structure. There are differences in the characteristics, number and straightness of the fibers on different segments of the yarn, which makes the yarn appear uneven in thickness along the axial direction, and small yarn defects appear. In this sense, The existence of small yarn defects is inevitable, and can be reduced through technical measures, but it cannot be completely avoided and eliminated. There are many factors affecting small yarn defects, which involve various aspects of spinning engineering, mainly including raw materials, process parameters, mechanical status, operation management, temperature and humidity. To control the small yarn defects of the yarn, it is necessary to design the opening, carding, impurity removal, and knot-reducing processes reasonably to ensure that the fibers have a high degree of separation, straightness, and parallelism, and reduce the number of neps in the sliver .

3.1 Effect of opening and carding process effects on small yarn defects

During the drafting process, the fibers are fully separated, kept straight and parallel, which is an important condition to ensure their normal operation and speed change. To ensure that the yarn produces fewer small yarn defects, the opening before the draw, The carding process should ensure that the fibers have a high degree of separation, straightness and parallelism.

3.2Effect of fiber separation on small yarn defects

Poor fiber separation, with more fiber bundles, is equivalent to increased fiber thickness uniformity and length dispersion, because unseparated fibers will generally change speed as a whole during the drawing process, destroying on the one hand The normal movement law of fibers in the drafting zone , on the other hand, also destroys the uniformity of the number of fibers in the cross section of the yarn and the uniformity of the fiber structure in the short section of the yarn. As a result, fine yarn defects will increase.

3.3 Effects of fiber straightness and parallelism on small yarn defects

The difference in fiber straightening and parallelism shortens the projected length of the fiber in the axial direction of the sliver, which is equivalent to shortening the fiber length. At the same time, due to the fiber straightening and parallelism, the fiber will not only have the axial direction of the sliver during the drawing process The movement will also produce irregular movement in the warp direction of the sliver, which not only destroys the normal movement law of the fibers in the draft zone, but also easily entangles with other fibers to form neps, which further destroys the number of fibers in the cross section of the yarn. The uniformity of the fiber structure and the uniformity of the fiber structure distribution in the short section of the yarn will cause the increase of fine yarn defects. In the process of fiber opening and carding, it is required to increase the degree of fiber separation and straightness as much as possible.

3.4Influence of raw material mixing effect on small yarn defects

Even if it is pure chemical fiber spinning, each fiber in the raw material will not be exactly the same in length, fineness, surface performance and other indicators, and the natural fiber will have a greater difference. Moreover, we generally do not use single label production. Multi-category mixed spinning will inevitably lead to large differences in fiber properties. This difference will be reflected in different characteristics during the carding and drawing of fibers. If the fibers of different properties are mixed unevenly, the drawing force will fluctuate in the subsequent drawing process, the operation of the fiber is unstable, the distribution of fibers in the sliver is uneven, the structure is inconsistent, and it will show in the instrument detection The increase of fine yarn defects will also lead to problems of inconsistent color in weaving and dyeing. This situation is more prominent in the blending of different varieties of raw materials.

The essence of spinning is to ensure the orderly arrangement of fibers in the axial direction. To accomplish this task, sorting out is the foundation. The main task of opening and cleaning cotton is to turn cotton lumps into cotton bundles and remove large impurities; the main task of carding is to card the cotton bundle into single fibers and complete the fiber orientation initially, while excluding neps impurities and parts Short pile. In the third degree of carding, separation is the premise, and both straightness and parallelism must be taken into account; carding quality and yarn quality are positively correlated, and indicators such as neps, hairiness, strength, sliver, yarn defects, and broken ends are all related to carding The quality is closely related. The "third degree" of the fiber in the sliver and the content of the short pile directly affect the quality of the yarn.

The test data in Table 1 shows that the difference in the state of the carding machine will have a great influence on the difference in the quality of the carding machine. Degree is a very critical factor affecting the quality of the finished yarn.

The basic ideas and specific measures to reduce small yarn defects

4.1 The basic idea

(1) Strictly manage the five basic tasks of human, machine, material, law, and environment, implement the quality responsibilities of each manager and employee, improve the skill level of equipment and operating personnel, carry forward the spirit of craftsman, and be meticulous and keep improving ; Managers should improve their technical and management qualities, learn systematic analysis methods, improve their ability to solve quality problems, and develop good work habits.

(2) Improve the understanding of the importance of opening, blending, and carding, and improve the separation, straightness, and parallelism of the fibers in the sliver, laying a good foundation for the subsequent process. Improve the mechanical status of the equipment, strictly implement the three-level inspection management system for equipment maintenance, improve the pass rate of the process on the machine, and maintain the finish of the spinning channel; strictly implement the equipment replacement and maintenance cycle to maintain the consistency of the equipment on the train. Carding equipment status is the basis for stable quality, process optimization is a means to improve quality, and equipment configuration is a way to improve quality. Now we do the stand-alone bobbin test spinning test on the 2nd, 7th and 20th days after the maintenance of Class A of all carding machines, and the implementation effect is good. According to the test results, the test time and frequency are being continuously optimized.

(3) Establish a combing cotton web quality inspection mechanism that combines teams, workshops and the company's biotechnology department, unify the visual inspection standards, and rectify problems in a timely manner.

4.2 Control measures

Carding should follow the process principles of "moderate carding and transfer, mixed short velvet; good mechanical foundation, card clothing wrapping specifications; suitable configuration of card clothing and card clothing three degrees; air flow parameter guarantee, smooth fiber flow"

(1) Optimize the speed and spacing configuration. The tin-prick ratio is selected through experiment optimization according to different fiber properties to ensure that it is between 2.4-2.6; the carding distance should not be too large or too small.

(2) Choose clothing reasonably, and choose new clothing styles of "short, shallow, small, pointed, thin, dense". The tooth height is short, which is good for resisting rolling damage; the depth of the tooth is shallow, and the fiber support is not easy to settle to the bottom of the tooth, which is good for transfer and carding; the front angle is small, the gripping and combing ability is strong; It is beneficial to puncture and sharpness is improved; the thickness of the base of the needle teeth is thin, which can increase the lateral density and improve the combability; the large density of the needle teeth is beneficial to improve the combability.

(3) Maintain a good card clothing state. The sharpness of the card clothing can ensure the carding effect; the flatness of the card clothing can ensure the accurate and consistent spacing and normal airflow; the smooth and clean card clothing can ensure that the fibers are not hung or entangled, and the carding is smooth. To prevent damage to the clothing during use.

(4) A new type of adjustable fixed cover is used to ensure the accuracy of the distance between the fixed cover and the cylinder.

(5) Maintain the good mechanical condition and the accuracy of the technology on board. Bare grinding of cylinder rollers: radial runout ≤0.02 mm, straightness ≤0.02 mm. The surface is smooth and even, and there is no room for low concavities. Perform oblique grinding as required. Cylinder dynamic balance: amplitude ≤0.05 mm.

If the iron of the cover plate is worn, it must be replaced or repaired. The height difference of the single root of the cover plate is ≤0.04 mm, and the maximum difference between the roots is ≤0.06 mm.

The quality of the wrapping should meet the requirements, and the high needles should be processed after the clothing is wrapped to ensure that the flatness meets the requirements.

Get on the train according to the process spacing, and all process spacing must reach the tolerance range. To ensure the consistency, accuracy and rationality of the technology on the train.

Do the maintenance work of the equipment regularly to keep the airflow running smoothly.


(6) Maintain the stability of the temperature and humidity of the workshop, and adjust it in a targeted manner for special fiber varieties.

(7) Improve the operation skills of employees, especially the operation skills of equipment maintenance personnel.

(8) Standardize the cleanliness of each process, and implement the "five set" of cleanliness.

(9) Strengthen and improve the identification and control of various types of defects by frontline operators, at the same time master and identify equipment defects or faults, and timely feedback if problems are found.


Conclusion

When the raw material performance is determined, the spinning process should be optimized according to the performance characteristics of the fiber, the temperature and humidity control requirements should be determined, the detailed management during the production process should be strengthened, and the control of the processes of clearing, carding and combing should be strengthened. Thereby reducing fine yarn defects in the yarn.


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