Unevenness of yarn evenness is one of the main indexes to measure yarn quality, which is closely related to the efficiency of subsequent process and the appearance quality of fabric. In recent years, with the development of textile technology and the increase of capital investment of spinning factories, the equipment level has been improved. New type cots, non mechanical rollers and other key spinning equipment have been widely used. The evenness caused by mechanical defects such as roller, eccentric cots and gear defects is very few, and the sudden evenness is particularly prominent. It not only increases the defective products, but also reduces the qualified rate of the joint. It also affects the efficiency of the subsequent process and is the main defect of yarn forming, especially the spinning process, which is characterized by short duration, strong contingency and high fabric appearance rate. Therefore, it is necessary to find out the causes of the sudden unevenness and take effective preventive measures.
1. The wavelength range and characteristics of yarn sudden unevenness
According to the spectrum theory of evenness, the wavelength range of evenness in spinning process is π D ～ π D ′ e, where D and D ′ are the front and back roller diameters respectively, and E is the total multiple of drafting. When D and d 'are 25 mm and E is 35 times (generally 20-45), the wavelength range of yarn evenness is about 7.8 cm-274.7 cm.
In the initial occurrence of sudden strip drying defects, due to uncertain reasons, the yarn is often disassembled and winded and tested on the strip drying instrument; then the production process and general reasons are inferred according to the test spectrum results, and then targeted inspection and repair. After several years of accumulation, it is concluded that the sudden evenness of cloth surface is mostly produced in spinning process (83% in general spinning process, 11% in pre spinning process and 6% in other processes), which is characterized by strong suddenness and obvious cloth surface; because of its strong contingency, the duration is different, sometimes even if the cause is not found, it will disappear after a period of time.
In the process of long-term tracing of sudden yarn unevenness (cloth removal test and corresponding inspection test), the typical spectrum and unevenness curve of two cases of yarn sudden yarn unevenness are shown in Fig. 1 and Fig. 2. Among them, figure 1 is mechanical wave, which is characterized by "chimney" like wave peak in 195px-9.0cm area, most of which have obvious harmonic near 2.5cm (λ / 3) and 4cm (λ / 2); Figure 2 is draft wave, whose peak in the spectrum is obviously higher than the normal peak curve.
Compared with the normal yarn, the CV value of the sudden evenness yarn is significantly worse, and the frequent yarn defects are also increased (see Table 1).
2. Causes
2.1 causes of mechanical waves
2.1.1 mechanical defects of front roller and front cot, including roller or cot eccentricity, bearing oil shortage, wear, cot knife damage, etc. With the strengthening of management, equipment maintenance and improvement of roller, cot and other spinning equipment quality in textile enterprises, there are few such problems.
2.1.2 the front roller or rubber roller is inlaid with sundries such as flower clothes, neps, etc. Due to the sugar in raw cotton and impurities not cleaned up, they are fully exposed after drafting in spinning process. With the effect of temperature and humidity (especially in summer) and other factors, they are easy to stick into roller groove (occasionally rubber roller adhesion), so that roller or rubber roller form a similar eccentricity or ellipse, resulting in unevenness of strip and obvious harmonic in the spectrum. Some of the sticky and inlaid sundries will fall off and be eliminated after running for a period of time, which is the reason why sometimes the sudden strip dry defects disappear after a period of time. In addition, the dust and oil floccules in the old air-conditioning duct blown by the air-conditioning wind are also one of the reasons for the inclusion of debris in the roller. See Figure 3 for the comparison between the unevenness spectrum caused by such defects and the unevenness spectrum caused by the eccentricity of the front roller (rubber roller).
2.1.3 one end of the front cot is wrapped with flowers and the other end is spinning. Due to the influence of the front cot twining, the axial pressure of the front cot spinning at the other end is uneven, resulting in mechanical evenness.
2.2 cause of draft wave
Theoretically, there is the possibility of unevenness of draft wavy yarn in the front and back area of spinning draft. In practice, the unevenness of draft wavy yarn produced by the back area is rarely seen. Therefore, this paper mainly discusses the causes of unevenness of draft wavy yarn in the front area.
2.2.1 draft gear defect. Unevenness of strip caused by defects such as poor maintenance, wear of light and heavy teeth, and poor engagement during operation.
2.2.2 upper and lower pins fail. It includes broken and deformed spring of upper pin, unfilled lower pin, lack of spacing block and paper clip of spacing block for upper pin, insertion of (roving) i-no. paper and dead flower in the middle of upper and lower apron, defect of lower apron, failure of holding upper and lower apron, twisting of roving in rear area, etc.
3 preventive measures
3.1 strengthen equipment maintenance and basic management
In the above analysis, due to the small proportion of mechanical reasons such as rubber roller, roller eccentricity, oil shortage, gear wear, etc., it is based on the premise of high equipment maintenance quality level; therefore, it is very important to improve the equipment (roller, gear) maintenance quality and rubber roller production quality, and do a good job in quality inspection and control of each link of equipment maintenance. According to the actual situation of the enterprise, high-quality roller, rubber roller and bearing shall be used to master the wear rule of key special parts and equipment, and solve the problem before the sudden unevenness of strip occurs. If the roller is wiped once with alcohol along with the maintenance and wiping cycle, the unevenness of strip caused by the adhesion of debris by roller can be effectively reduced, and the cycle shall be shortened in summer; various equipment maintenance and quality inspection shall be carried out. Only when it is included in the normal working system and a good equipment foundation is ensured, can the sudden strip unevenness caused by mechanical defects such as roller and cot be kept less.
3.2 assign special personnel for special inspection and maintenance
Special personnel shall be assigned to carry out special inspection and maintenance for roller or rubber roller sticking debris, upper and lower pin failure, roller or rubber roller damage that may occur at any time (handle roller, rubber roller, abnormal front and rear area of the eye, yarn jamming found and repair), and at the same time, take into account the feedback and defect tracking work of the sudden uneven strip fabric, find out the cause of the problem, and try to control the problem in the initial stage, so as to It can effectively control the unevenness of the strip.
3.3 establish the awareness of group prevention
Strengthen the quality awareness training for the shift workers, doffing workers, operation maintenance workers and other personnel, establish the inspection awareness of the whole staff, and solve the problems that may occur at any time, such as the paper jam (dead flower) of the upper and lower aprons, the gap block defect, the failure of the upper and lower pins, only when they are found at any time and solved at any time, can the sudden strip unevenness defects caused by them be minimized.
3.4 short period net pulling inspection
Under certain conditions, the short cycle (no more than 3 days) pull type full detection method can be used to detect and repair the backward spindles in time, so as to reduce and eliminate the occurrence of sudden unevenness. After several years' efforts, we have found out the effective measures to control the sudden unevenness of the strip, and put them into the daily work, forming a system to fix it, so that the rate of the sudden unevenness of the strip can be reduced from 2.5% to 0.13% - 0.4% in recent years, and can be maintained stably.
4 Conclusion
4.1 with the improvement of equipment quality and maintenance quality, the causes of sudden evenness in spinning process have changed a lot, and the random problems in normal production and operation become the main reason; therefore, finding out the rules and taking effective preventive measures are the key to reduce the sudden evenness.
4.2 effective measures to control sudden irregularity shall be included in daily work, and a system shall be formed to prevent accidents in advance.
