With the continuous development of the modern textile industry, the increase in the international trade volume of textiles, the diversification of textile product varieties, and the continuous improvement of quality levels, the international market has an increasing demand for high-quality cotton yarn, and the quality of domestic cotton yarn has been put forward. higher requirement. More neps in the yarn not only seriously affect the quality and appearance of the yarn and cloth, but also affect the continuity of the dyeing, finishing, spinning and weaving processes. Therefore, the “93 standard” increases the assessment of the number of neps compared to the “78 standard”. Yarn neps have become one of the main indicators to measure yarn quality. How to strictly control the yarn neps during the production process? In order to ensure the quality of the final product, it has become one of the current problems that need to be solved urgently.
1. Definition and inspection method of neps
A large number of experimental studies have shown that 60-70% of neps are caused by poor performance of raw cotton, but some are also caused by poor spinning technology. According to the gb/t398-93 standard, neps are composed of fibers, immature cotton or stiff cotton, which are accumulated due to poor ginning quality or poor handling during the spinning process. The inspection method is: under the illumination of not less than 400lx, light is incident from the rear left side, the installation angle of the inspection surface is 45°±5° with the horizontal plane, the inspector’s line of sight is vertical to the yarn strip, the inspection distance The principle is that the inspection personnel’s eyesight will have no difficulty in identifying defects.
2. The relationship between raw cotton properties and yarn neps
Regarding the relationship between various physical properties of raw cotton and yarn neps, in recent years, a large number of studies at home and abroad have shown that cotton fibers with good maturity have small moisture absorption capacity, high single fiber strength, more natural curls, and fiber It has good elasticity and rigidity. Therefore, it has strong tensile, compressive and bending resistance, and is not easily damaged during processing. The fiber has less chance of being rubbed, kneaded and entangled to form neps due to surface friction. At the same time, the fiber It is less damaged and broken due to mechanical force during the opening, blowing, carding and drafting processes, and the short fiber rate is less increased. Therefore, there are less opportunities for neps to form.
3. The relationship between carding technology and yarn neps
A large number of studies have shown that the number of neps on the cotton web basically determines the number of neps in the yarn. Therefore, how to reduce the number of neps in the cotton web and improve the carding effect of the carding machine is very critical to controlling neps in the yarn. Through the production practice of our school’s internship factory, we mainly did the following aspects of work.
3.1 Reasonably distribute the blowing and carding waste to improve the structural quality of the cotton laps
Large impurities that are generally large and easy to separate and remove are removed by the blowroom process; small impurities with fibers that have strong adhesion are removed by the carding process. As for the carding process itself, the sterile seeds, stiff cotton, and dead fibers in the cotton rolls are removed at the licker-in part, while the fiber seeds, fiber fines, neps, short lint, etc. are removed on the cylinder cover. Partially eliminate, at the same time, focus on improving the structure of the cotton lap, and pay attention to reducing the number of hook-shaped cotton bundles and loose cotton bundles in the cotton lap that are easy to form cotton net neps. Under normal circumstances, the impurity removal efficiency of the licker-in part is controlled between 50-60%, while the impurity removal efficiency of the cylinder cover part is controlled at 3-10%, and the impurity content rate of the card sliver is controlled below 0.15%. Therefore, the licker-in part is the focus of impurity removal in the carding process. By adjusting the licker-in dust removal process, the carding and dust removal elements, the length and the main spacing of the dust removal area can be changed to strengthen the detection of nep impurities. exclude.
3.2 Improve the carding efficiency of the carding machine
The strong carding of the carding machine can increase the degree of fiber single fiberization, which is not only beneficial to the separation of fibers and impurities, reducing the entanglement of fibers, but also loosening some neps in the cotton rolls. Therefore, we have selected new card clothings with good carding effect for the cylinder, flat plate, doffer and licker-in card clothings. Use smaller spacing. It not only enhances the ability of the licker-in part to hold combing, but also improves the efficiency of free combing and repeated combing of the cylinder and cover plate parts.
Through experiments, we can see that the number of neps in the low-speed close-gauge card sliver is greater than the number of neps in the high-speed close-gauge card sliver; as the flat spacing increases, the number of card sliver neps increases significantly; as the cylinder speed increases, the carding degree increases , the fiber is fully carded and neps are easily eliminated. At the same time, the average carding force on the unit needle surface and fiber is reduced, and the fiber is less likely to be stressed and stretched too much, which can reduce the formation of neps and fiber breakage due to fiber rebound. of neps. The tight spacing makes the needle teeth have more contact with the fibers, and the fibers are easily held by the needle teeth. The needle teeth penetrate deeply into the fibers, which enhances the carding effect and makes neps easy to remove.
3.3 Improve fiber transfer and reduce the formation of new neps
The fundamental reason for the formation of new neps on the carding machine is the twisting and rubbing of fibers. Abnormal phenomena such as return, twisting and hanging can often cause severe friction, resulting in fiber twisting and rubbing. Neps. The main causes of return, twisting and hang-up are improper speed ratio or spacing configuration, or insufficient sharpness and smoothness of the opening and carding elements. Therefore, in response to the above reasons, we have mainly taken the following corresponding measures to eliminate fiber twisting and severe friction. The first is to correctly configure the speed ratio of the cylinder licker-in to ensure that the fiber can be transferred normally and reduce the return of flowers; the second is to pay attention to the status of the carding components, “four fronts and one accuracy”In order to comb the card, the licker-in, cylinder, cover plate and doffer needle teeth should be kept sharp and have good puncture performance to ensure accurate spacing of each part. The third is to ensure that the channel through which the fiber passes is smooth and smooth to reduce the friction of the fiber during movement. Flower hanging phenomenon.
3.4 Strengthen temperature and humidity management to control the moisture regain of fibers on the machine
Cotton fiber has great plasticity and poor bending resistance under high temperature and high humidity. It is easy to adhere to each other and form neps. Especially raw cotton with poor maturity is more likely to absorb water and form neps under high temperature and high humidity. Fibers under high temperature and high humidity have poor elasticity and tend to twist into neps in the cover work area because they are not combed out. Therefore, the carding process is maintained at a low relative humidity, generally 55-60%, so that the fibers are in a state of continuous moisture release to control the moisture regain of semi-finished products, reduce the cohesion between fibers, and maintain good elasticity and elasticity. Rigidity is conducive to opening, impurity removal, carding and transfer, and reduces the friction between fibers and needle teeth and the filling of needle gaps.
4 Conclusion
Through the above analysis, we can conclude:
(1) Fibers with poor maturity have a higher probability of forming neps during processing than normal cotton fibers.
(2) The process configuration of the carding process is the key to affecting the number of neps. To enhance the effect of removing neps and impurities in the nip roller part, the process principle of “tight gauge, strong carding” must be implemented, and the cylinder speed should be appropriately increased. And pay attention to the “four fronts and one accuracy” to improve the transfer of fibers and help reduce the formation of new neps.
(3) The temperature and humidity control should be strengthened during the carding process to reduce the formation of neps.
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