The diameter and number of carded cotton knots will directly affect the number of yarn knots and yarn defects, especially the number of A1 and A2 yarn defects, while the raw yarn short pile rate will directly affect the yarn strength, minimum strength, hairiness index H and weaving warping breakage. Carding should not only control AFIS knot and short pile rate in the traditional sense, but also consider fiber carding state, knot diameter and fiber uniformity.
Common problems of cotton cleaning
Catching parameters are adjusted frequently and the running efficiency is low. The operation efficiency of reciprocating grabber is controlled above 90%. The grasping depth and speed can be determined according to the running efficiency of the cotton grabber, and the falling depth can be adjusted reasonably to realize the holding and opening of the raw cotton by beaters and ribs, and further improve the opening effect of the cotton grabber. To strictly implement the process to determine the grasping speed and depth, to prevent arbitrary adjustment of cotton parameters. Continuous feeding is the key factor to ensure the uneven weight of sliver and the mixing effect of raw materials, as well as the stability of cotton flow, the opening effect and the removal efficiency of cotton impurities and foreign fibers. According to the cotton composition and seasonal changes, adjust the speed and spacing of each single machine to control the growth rate of cotton knot and short nap at a low level, ensure the effective removal of cotton knot, impurities, short nap and foreign fiber, and ensure the raw cotton opening effect and mixing effect.
Common problems with carding
At present, the spinning mills often focus on the removal efficiency of nep and short pile, but do not pay much attention to the carding degree of fiber. Although carding cotton and short nap is better, but may cause fiber damage due to excessive carding, yarn quality is not satisfactory. Carding is done by combing components, combing components state is not good, can not achieve the ideal combing effect. The chain of movable cover plate is elongated, the chain is not flexible, the heel and toe wear of movable cover plate and the fluctuation of cover plate are common management problems in enterprises. The heel and toe wear of the cover plate and the fluctuation of the cover plate often lead to inaccurate separation, which can occur in sliding friction and bearing type rolling friction. In the maintenance of cover chain and movable cover framework, the following points should be noted:
1) the length of the cover plate chain must be ensured within 76 mm of the whole elongation and 3 mm of the double root difference. Secondly, the star guide plate must not be worn, twisted or damaged.
2) clean the chain regularly and add oil. Measure the cycle length. Install the short root chain on the side of the main drive to eliminate the difference in length and prevent the cover plate from running in parallel.
3) correctly adjust the chain tension, with the middle foot as the main part and the rear foot as the auxiliary part. Pay attention to the horizontal condition of the top surface of the adjustable cover plate to ensure the same tension on both sides and prevent uneven and excessive or small tension on both sides of the cover plate.
4) pay attention to the lubrication of the lead powder block of the movable cover plate to ensure good lubrication and prevent excessive resistance of the cover plate and elongation of the chain caused by poor lubrication.
To strengthen the management of cotton card clothing. Carding parts of the needle cloth is not only periodic parts, but also vulnerable parts. In the needle cloth management, the general enterprise has the following problems.
1) the replacement cycle of the needle cloth is not clear, and the use of the needle cloth beyond the specified period is serious, even more than 6 years, without paying attention to the carding quality. It is suggested to set the service cycle of the needle cloth according to the actual output and the quality of the needle cloth, and observe the state of the needle cloth and carding quality at any time to ensure the service time of the needle cloth and the quality of the finished product. For example, if 100% cotton long-staple cotton combing 7.4 Tex and combing table produces 24 kg/h, the service cycle of imported top brand cylinder knitting cloth is 3 years, that of imported general brand is 2 years, and that of domestic top brand knitting cloth is 1.5 years, which can meet the quality requirements of USTER 2013.
2) needle cloth belt injury and illness are in operation. When the needle cloth is replaced due to unexpected reasons, strict review must be carried out. For the needle cloth with accidental damage, the reason must be found to prevent the secondary damage on the machine.
3) there is no perfect management regulation and use ledger for the needle cloth. The needle cloth is slack and can be replaced at will. It is suggested to set up a needle cloth replacement ledger, constantly optimize the selection test of the needle cloth model, and select the brand and model suitable for the enterprise with high cost performance. If the variety changes frequently and the raw material changes greatly, it is suggested to choose the universal needle cloth to take into account the yarn quality level between different raw materials.
According to AFIS test verification, card suction pipe blockage, the nep will appear more than twice the growth. To ensure the ventilation system of the card is also conducive to ensure the quality of carding sliver. The key to ensure that the air suction system of the card is unobstructed is a suitable amount of dust air, the second is the operation of personnel timely check and eliminate.
The control of | card – card zone on cotton – nep
Roller carding is the first carding of fibers into the card, and the cotton into the card is a large piece of cotton or cotton bundle, fiber entanglement and disorder, the fiber by the axial and radial stress is large, the probability of being cut off is also large, is the production of the most short pile process point.
Effect of the speed of roller on nep and short pile
The spinning speed of the barbed roller is fast, and the carding effect is good. There are many cotton knots and impurities thrown off. The impact force on the cotton lump is large, and the fiber damage rate is high. On the contrary, poor carding, low fiber damage rate; Therefore, according to the performance of raw materials should be appropriate carding degree (the speed of the roller). The test showed that the per unit yield of the card was not more than 35 kg/h, the impurity rate was not more than 1.7%, the nep content of the feeding layer was not more than 400 /g, the quality of the rolling mill was higher than P2 grade cotton, and the speed of the needling roller was not more than 800 r/min, which was favorable for the control of nep and short pile. The influence of different needling roller speed on the quality of sliver was shown in table 1.
Table 1 the effect of the speed of piercing roller on the quality of sliver
The effect of metal needle cloth state on nep and short pile
The piercing roller metal needle cloth has high sharpness, fast piercing to the fiber, little impact force and less short nap. On the contrary, the short pile produced more, so, to use a higher sharpness of the metal needle cloth with a lower speed to carding roller. FIG. 1 shows the carding effect of a 630 kg/day card on a barbed metal card.
FIG. 1 comparison of carding effect of metal needlepoint cloth with different machine duration
Effect of carding point spacing on nep and short pile
The carding process length is determined by the spacing between the feeding plate and the piercing roller. If the spacing is small, the carding process length is short. The metal needle cloth is easy to Pierce through the cotton layer and tear fully, and the carding effect is good. However, the distance between the holding point of the cotton board and the holding point of the metal needle cloth is small and the penetration is deep, resulting in a high probability of fiber fracture. Large spacing is just the opposite, of course, too much spacing will make the cotton layer have space expansion, roller metal needle cloth is not easy to penetrate the cotton layer, when the fiber at the bottom of the cotton layer out of the cotton board to hold, not be effectively held by the metal needle cloth resulting in white problem. Therefore, the spacing between feeding plate and thorn roller should be determined according to the fiber nature and length, cotton layer density and structure (degree of entanglement and size of cotton patch). It is recommended that the main body length should not be less than 28 mm and the spacing of cotton patch should not be more than 30 mg. The feeding interval of yan cotton was 0.43 mm~0.55 mm.
Effect of the separation distance between the licker and comber plate on nep and short pile
The two are free combing. When the fibers held by the barbed roller pass through the combing area, the combing board will only tear and pull the fibers once, so that the fiber bundles are initially dispersed to reduce the load of cylinder. Generally, the separation distance between the thorn roller and the combing board is 1.5mm, and only the larger cotton bundle held by the thorn roller is carded once for the first time. If it can be carded, it will be carded, and if it cannot be carded, it will be released. The small fiber bundle close to the surface of the needle tip is not carded deliberately, so as not to cause fiber fracture.
Effect of transfer rate on nep and lint
Under the conditions of existing technologies and equipment technologies, it is impossible to complete a good carding of fibers in one carding area, so the fibers have to be transferred in different carding areas. In fact, this transfer is a destruction of carding results (including cylinder – rotary cover between the transfer comb). There are three transfers in the carding process, namely cylinder – roller, cylinder – rotary cover, cylinder – doffer. It is transfer likewise, the requirement of 3 place is different. The transfer between roller and cylinder should be complete, and it is better to achieve a transfer rate of 100%. The smaller the distance between the two, the easier it is for cylinder metal needle cloth to grasp the fiber on the surface of roller. The greater the surface line speed ratio, the greater the chance that the cylinder wire will grab the fiber. When the surface linear speed ratio of the two was 2.5:1, the indexes of cotton netting and short staple were significantly improved (see table 2). When the ratio is greater than 2.5, the fiber will have very large draft and the short pile will increase.
Table 2 fiber quality comparison of surface linear speed ratio of different cylinder – roller
Hobbing rack selection
The deep tooth and large working Angle of the barbed roller metal needle cloth are beneficial to puncture but not beneficial to fiber release. However, large longitudinal tooth densities are detrimental to fiber transfer. When the back of tooth is arcuate, it is very advantageous to strip the fiber on the surface of cylinder metal needle cloth and improve the fiber transfer rate.
Elimination and flow control
Excluding the influence of technology, when the speed of the thorn roller is lower than 1000 r/min, the total amount or unit content of nep and short pile in the exclusion is higher than that in the cover exclusion. With the increase of the speed of the thorn roller, the content of 16 mm short pile in the drop of the rear carriage belly decreased from about 50% to about 40%, while the content of 16 mm short pile in the cover flower increased from about 40% to about 50%.
In fact, the total length of the three exclusion zones is the same whether it is the bottom leakage type or the fixed cover type under the barbed roller, but the main exclusion zones are different. The essence of designing the barbed roller exclusion process is to carry out the length ratio of the three exclusion zones and adjust the air distribution, as shown in figure 2. There are four kinds of airflow: complementary airflow (solid line), cutting airflow (dotted line), running airflow (double-dotted line) and eddy current (double-dotted line). The air flow on the surface of the roller should be supplemented and continuously organized. The airflow boundary layer is continuously cut by the surrounding parts during the operation to remove relatively heavy neps, impurities and some short fibers not held by the needle cloth of the roller. The uncut airflow continues to run with the roller and the air pressure changes with the change of resistance in different areas. The length of the air flow arrow in figure 2 can roughly reflect the air pressure of different parts on the surface of the two cylinders.
FIG. 2 schematic diagram of air flow behind the card
The high and low position of the dust remover determines the length of the first exclusion zone. If it is too high, the length of the first exclusion zone will be too short. The impact of the supplemental air will cause the dust remover to cut the air rotation and make it difficult to discharge sundries. If the spacing between the dust remover and the puncture roller cannot be adjusted to about 0.38mm due to mechanical conditions and other reasons, the cutting airflow will be less and the falling objects excluded in the first exclusion zone will not be too much.
The airflow in the second exclusion zone is relatively complex. If the cutting airflow in the first zone is too much, the zone will form a negative pressure state, and the airflow needs to be reorganized and supplemented. At this time, the flow guide plate under the first dust remover plays the role of blocking and recovering the falling objects in the first exclusion zone with the supplemented airflow. However, if the first dust remover is too low, the length of the second exclusion zone will become shorter, and the complementary airflow and the cutting airflow of the second dust remover will impact each other to form eddy current, which will reduce the recovery and elimination of falling objects in the zone. At present, most of the high-speed card have realized the semi-closed or closed absorption of nodules in the post-tribal area, which can reduce the clogging of nodules and the recycling of nodules caused by it. However, the closed structure removes the falling objects and part of the air, so that the air flow on the surface of the roller can not be supplemented, which affects the airflow organization of the boundary layer, and then affects the removal of falling objects and the holding of the fiber on the surface of the cloth.
The airflow adjustment in the spinning-cylinder triangle area affects the exclusion of the spinning-roller area and the airflow inside the large leakage bottom, which further affects the control of nep and short pile. If the puncture roller — cylinder spacing is 0.20mm ~ 0.25mm, only a small part of airflow from the direction of small leakage bottom and large leakage bottom passes through, and most of it is discharged into the lower part of the equipment. If the big leakage bottom air flow and the small leakage bottom air flow do not match, it will cause the small leakage bottom air pressure increase, make the mesh small leakage bottom paste flowers or spray flowers at the entrance of small leakage bottom, or the big leakage bottom air pressure is too high to form the big leakage bottom vortex, so that the fiber on the surface of cylinder is disarranged or twisted into cotton; When the gap between the licker roller and cylinder is too large, it will cause insufficient transfer, and more airflow will pass through the triangle area, causing the air pressure inside the licker roller low-pressure cover to rise, and the spray will be formed at the licker roller low-pressure cover.