Spinning Quality And Cots

Cots and aprons are important equipment for drafting mechanism of spinning frame. They, together with cradle, upper and lower pins, rollers, spindles, rings and their technological parameters, affect the spinning performance of the drafting mechanism. It is reported that in general, the cost of cots and aprons accounts for about 0.4% of the spinning cost in China, while the influence of cots and aprons on yarn quality reaches 60%. Therefore, the quality level of cots and aprons determines the spinning quality level in a certain sense.

　　01

The role of cots in spinning

The function of Cots

The top roller is the main drafting part, and the spinning frame must have two points to hold the sliver actively, and keep a certain distance between the two holding points and make relative movement. The linear velocity of the output end is greater than that of the feeding end, and there must be a certain holding force on the holding point. In order to realize the drafting, the minimum holding force must be greater than the maximum pulling force, and the relationship between the two forces should be well handled. The cot is a direct pressure body on the fiber and roller. It forms a gripping jaw with the roller to directly hold and draft the whisker. The main effect on the grip force of the rubber roll is the production practice.

The role of aprons

The main function of spinning apron is to carry out the transition between micro draft and holding in the back zone. The draft multiple is determined by the factors such as fiber length, roving weight, drafting form and quality requirements. Its working state must be accurate and continuous, so as to ensure the realization of drafting motion and spinning strength, weight unevenness, coarse pitch, details and other technical quality indicators, increase the fiber straightness and orderly parallel arrangement, and effectively and stably control the parallel movement of fibers under a certain pressure. In the two sliver drafting areas on the spinning frame, the aprons are in the middle position, which not only plays the role of drafting, but also plays the role of holding and conveying.

　　02

Influence of cots and aprons on yarn quality

Design of cots and aprons

The design, design, design and high elasticity of the rubber ring. The design level of cots and aprons affects the yarn quality from the source.

Wear of cots and aprons

Modern spinning technology will develop to heavy weight, high speed and large package in the front process, while spinning will develop to high speed and small package. As increasing speed, increasing production, improving efficiency and reducing cost have gradually become the consensus of people. Therefore, higher requirements will be put forward for the high wear resistance and heavy press resistance of cots. Therefore, the wear rate of rubber cots should not exceed the designed wear rate.

Resilient Cots

Resilience is the most important physical property of cots and aprons. Good resilience can eliminate the "viscoelastic" problem of cots and aprons in fast spinning, and effectively improve the spinning quality. At present, after several spinning tests under conventional conditions, the spinning quality of domestic untreated cots is equivalent to that of imported cots, and there is only a gap in resilience, especially in the case of low temperature in the workshop, it is easy to cause hardening. Therefore, in order to narrow the internal quality gap with imported cots, it is necessary to further improve the resilience of cots and aprons.

Winding resistance of cots and aprons

It has been proved that the main factors affecting the winding of rubber cots and aprons are: 1) mutual attraction of free energy of electrostatic interface; 2) adhesion of surface surface of different substances used in rubber composition; 3) adhesion of fibers to aprons caused by different areas and temperature and humidity. In recent years, the surface treatment methods appeared in the application of cots in order to improve the surface anti winding performance. In the case of unstable cotton distribution, temperature and humidity, this method can achieve certain improvement, but also lead to a certain decline in yarn quality. Therefore, on the premise of ensuring yarn quality, reasonable selection or development of cots and aprons materials and their surface treatment methods are effective measures to improve the anti winding property of cots and aprons.

Dynamic design of cots and aprons

The spinning speed of spinning frame has been increased from 10 Kr / min ~ 12 Kr / min to 20 Kr / min, even up to 25 Kr / min, which puts forward higher requirements for the overall design of spinning frame; meanwhile, it puts forward higher requirements for the design of cots and aprons. Dynamic design should be included in the design of modern cots and aprons. In short, the motion equation of COTS or aprons is established by finite element method. The damping has little effect on the motion of cots and aprons. By adjusting the mass and stiffness of COTS or aprons, the motion stability of COTS or aprons can be ensured and the yarn quality can be improved.

Structure design of cots and aprons

The friction factor and the surface roughness of aprons are closely related to the service life of aprons. Therefore, in addition to controlling the grinding of products, the manufacturers also carry out chlorination treatment to change the surface structure of aprons. However, the surface friction coefficient of the product changes with the extension of service time, which seriously affects the spinning stability. In addition, rubber cots and aprons are generally made of elastic materials, and the advantage of elastic materials is that they have good anti vibration performance, but they will inevitably produce elastic deformation after being stressed. Therefore, when the aprons work under the friction principle, it is bound to produce elastic sliding, resulting in poor synchronous operation of aprons and rollers, resulting in poor yarn evenness, and also causing apron wear; at high speed, heating makes the aprons temperature rise, affecting the yarn quality and reducing the life of aprons. At present, the countermeasures are to use low hardness or inner pattern aprons, and to use aprons without surface treatment can also achieve certain results. Although the surface morphology of domestic aprons has been explored, there is no substantial breakthrough in technology. If the apron structure is designed as a toothed belt structure, the slip ratio will be eliminated and the yarn quality will be improved.

The practice shows that the top roller without surface treatment of aluminum liner is the development direction of cot structure design, and the material selection of cot tends to be high resilience and low hardness, because it can improve the gripping performance of the drawing roller jaw, and correctly solve the problems of the adaptability between the drawing force and the holding force, the guiding force and the control force in the drawing process.

Manufacture of cots and aprons

When making COTS, the iron core should be cleaned to ensure that the inner layer of cots can be partially embedded in the groove on the surface of the core shell after rounding and shaping, so as to increase the cohesion of the two. At the same time, the iron core should not be deformed and the bearing should not be worn or loose; otherwise, the cots made by the sleeve will seriously affect the spinning quality. When making COTS, the stress on the circumferential end face of COTS should be vertical and uniform to minimize the stress difference caused by extrusion of the two ends after the rubber tube is jacketed; when the top roller is pressed and reshaped, the top and bottom rollers of the calender must be in close contact, and the force shall be uniform. In the production of cots, the grinding quality of COTS is the key to ensure the inner quality, spinnability and stability of cots. At the same time, the diameter of the same batch of COTS should be consistent.

Its upper and lower rubber ring must have good wear resistance after manufacturing to avoid serious wear-resistant factors. Before leaving the factory, rubber ring should be cleaned carefully to avoid corrosion of iron roller by residual acid.

Use of cots and aprons

The use of aprons should consider the selection of high-quality products that meet the requirements of spinning quality, improve and stabilize the consistency of aprons in the use process, reduce the impact on yarn quality unevenness, and ensure the consistency of relevant drafting components to reduce the impact on the normal operation of aprons. In the process of use, it must be done that the aprons of different models, structures, specifications, surface treatments, hardness and new and old degree must not be mixed. When the cots are used, it is necessary to consider the matching of the spinning variety and the selected cot hardness, so as to ensure the improvement of the comprehensive level of yarn quality. In addition, in order to improve the quality of maintenance, it should be used.

Management of cots and aprons

Strengthening the management of cots and aprons is one of the links to improve yarn quality. The cot room specially set up by textile enterprises is specifically responsible for the daily management of cots and aprons, and the division of work among cots is led by the equipment department in charge or the workshop. The division of work between cots is mainly about cot production management and apron finishing. The process includes inspection, return and cover rubber roller production, rounding shaping, grinding, surface treatment, oil filling, marking and suit, daily equipment maintenance and repair. Implement the inspection and acceptance work and the economic responsibility system assessment work, to serve the normal production of the workshop and improve the overall level of yarn quality. The cost of equipment should be reasonably managed. Through scientific management, reduce the occurrence rate and amount of difference, so as to give full play to the best performance of cots and aprons.

Standardized Cots

Standardization is an important guarantee for organizing modern production and intensive production. At present, there are many types of cots and aprons manufacturers, which are suitable for different spinning varieties and sizes. They are sensitive to temperature, humidity and climate change. In the case of frequent variety change in textile enterprises, it brings many difficulties to the production. Therefore, the standards of cots and aprons should be improved in time, so as to improve their consistency and stability and create conditions for reducing the quality difference of cotton yarn.

With the development of science and technology, cots and aprons should develop in the direction of high winding resistance, high wear resistance, high resilience, low slip ratio, heavy pressure resistance and high spinnability; the promotion and application of new products should be combined with strict management, maintenance and new process matching, and the self-developed products should be transformed into standards in time to meet the increasingly high requirements of the market for yarn quality.