In the air-jet spinning process, the following tasks are mainly completed: opening and drafting the cotton sliver into a single fiber state; removing impurities from the feed raw materials; uniformly mixing the fibers; forming whiskers; condensing the fibers; Combined to improve uniformity; twisting; winding forming.
Theoretically, during air-jet spinning, a single fiber condenses into a fiber ring in the condensation groove of the rotor, and then the fiber ring is pulled up in the opposite direction, but In fact, due to other reasons, fiber hooks, fiber loops, fiber sheets and other deformations will occur during this process, which greatly affects the quality of air-jet spinning. The quality of the finished yarn is affected by the quality of the fed sliver, which is mainly affected by the length, length uniformity, fiber fineness and impurity content of the sliver fiber. On the other hand, the better the separation state of the fibers during the conveying and cohesion processes, the better the yarn quality. The quality of sliver is controlled by the pre-spinning process. Carding is a key process of open-end spinning. It mainly removes impurities, carding and evenly mixes the feed raw materials. Therefore, adjusting the carding process parameters has a great impact on the quality of sliver, and then Affect yarn quality.
The following is an analysis of the five main factors affecting the quality of air-jet spinning:
01 Carding
Cylinder, cover plate and doffer play an important role during carding. When the cylinder arrives at the doffer with a layer of fiber, the end of the fiber touches the surface of the doffer and is grabbed by the doffer card clothing while the other end is still held by the cylinder card clothing. When the cylinder passes through the transfer area, due to its very high surface speed High, the fibers are pulled by the doffer wire and generate tension. This cohesion makes the fiber amount per unit area of the doffer 2 to 3 times that of the cylinder unit area. If the doffer speed increases, more needle teeth can participate in carding. The aggregation effect increases due to the increase in the doffer speed. Even if the linear speed ratio of the cylinder and the doffer surface decreases, the fiber transfer effect will also increase. However, if the doffer speed If it is increased too much, the cohesion effect will be reduced, and the transfer effect is closely related to the formation of fiber hooks. When other parameters remain unchanged, increasing the output by increasing the doffer speed will increase the needle surface load of the cylinder, which will increase the neps and reduce the evenness of the card sliver. Therefore, the yarn quality will deteriorate, that is, the U% value will become larger. , the strength and appearance grade of the yarn will decrease significantly.
By adjusting the flat speed or flat flower content, better quality slivers can be produced by mixing cotton rolls of average quality. When all other parameters remain unchanged, if only the flat speed is increased, the flat pattern will increase. At the same time, due to the enhanced carding effect, the impurities in the card sliver will be reduced, and the short pile will also be reduced. The strength of the yarn can be improved, but the strength CV The % value will be reduced while the measured number of yarn defects and the U% value remain unchanged, so the quality of the yarn and the appearance of the fabric are improved.
02 Fiber length
The length of fiber plays the same role as Its role in ring spinning is different. The fiber length has the following relationship with the diameter of the rotor cup: diameter of the rotor = hand-pulled length of the fiber * 1.2. The twist is transmitted downward to a special point in the rotor condensation tank, called the peeling point. There is a point in the rotor condensation tank. Bundling area, where the fibers are twisted. The length and stability of the bunching area are two parameters that determine whether the spinning process is stable, thus affecting the spinning end breakage rate.
During the spinning process, the length of the bundled area fluctuates around an average value. Once the length of the bundled area is lower than the critical value and impurities hinder the transfer of twist, end breakage will occur. It will happen that the longer the fiber length and the higher the length uniformity, the more stable the spinning process will be.
03 Fiber fineness
Fiber fineness determines yarn breakage and spinning count. One of the main factors of number, the optimal number of fibers (nf) in the yarn cross section can be calculated by the following formula: nf=15030/(Yarn count *mic) This relationship shows that when the fiber becomes thicker, the yarn Strength will decrease. Coarse fiber spinning will also cause the yarn dryness CV% to deteriorate, and a higher twist coefficient must be used during spinning to ensure the strength of the yarn.
04 Fiber strength
The strength and fiber strength of open-end spinning There is a linear relationship. Most of the fibers in air-jet spinning are in a hook state, and the degree of fiber shortening increases with the increase in fiber length. The following relationship can be used to estimate the yarn strength CSP: CSP = K (ls/f) 0.35 where: K – constant; l – takes 50% of the fiber length range (mm); s – takes the fiber strength 1/8 (g/tex); f——fiber fineness (mic).
05 Impurities
The classification of impurities before spinning is as follows: large impurities, Fiber fragments and dust. Large impurities can usually be effectively removed by the impurity removal system of the air-jet spinning machine. However, the kinetic energy exerted by the acceleration force prevents the dust from being deposited between the needle teeth of the opening roller. The ejection path of the dust to be removed will be affected by the The buoyancy of the air becomes flat, and some slightly larger dust will enter the rotor and mix in the fiber ring, resulting in an uneven increase in the short segments of the yarn, resulting in a reduction in yarn strength and breaking elongation.
Fiber fragments include broken seeds, infertile seeds, fibrous seed scraps, soft seed skins, etc., which are difficult to remove during the entire processing process. They affect the transfer of twist in the rotor. , which has a great impact on the appearance of the yarn. Even if they can be removed by the carding roller, they may still accumulate in the condensation tank and cause fly flakes.
The degree of dust deposition increases as the impurity content in the fed sliver increases.��The higher the speed of the rotating cup, the smaller the diameter and the higher the degree of deposition. Due to the uneven twist caused by dust deposition, the fabric will produce “rungs” and “cloud spots”. The deposition of dust will also damage the evenness of the yarn and increase the hairiness of the yarn. Moreover, the deposition of dust will cause an increase in the number of yarn breaks during the spinning process. The causes and proportions of broken ends are as follows:
Generation of cotton bundles: 31.5%;
Dust and flying flowers are deposited in the waste outlet and Taken away by the rotor cup: 28.5%;
Impurities in the cooked strips that were not removed in the blowing and carding processes: 24%;
Dust accumulation on the rotor cup: 16%.
Therefore, choosing good feeding materials can reduce impurity levels and reduce dust accumulation in the rotor cup.
06 Summary
Based on the above analysis, appropriate selection of spinning yarn Raw materials and reasonable configuration of spinning process parameters, strengthening raw material management and process management, especially rationally adjusting the settings of the carding machine process, and taking control measures, so that the quality of the yarn can be guaranteed. </p
