In the air spinning process, the following tasks are mainly completed: opening and drafting the cotton sliver to the single fiber state; removing impurities from the feed raw materials; uniformly mixing the fibers; forming whiskers; condensing fibers; and improving uniformity through merging. degree; twisting; winding and 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. However, in fact, fiber bending will occur during this process due to other reasons. Hooks, fiber loops, fiber sheets and other deformations greatly affect 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:
1. Carding
The 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 flattening speed or flattening 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.
2. Fiber length
Fiber length plays a different role than it does in ring spinning. The fiber length has the following relationship with the diameter of the rotor:
Rotary cup diameter = fiber hand pulled length * 1.2
The twist is passed down to a special point in the rotor condensation tank, called the peeling point. There is a clustering area in the rotor condensation tank 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 a critical value and impurities hinder the transmission of twist, end breakage will occur. The longer the fiber length, the higher the length uniformity. , the spinning process will be more stable.
3. Fiber fineness
Fiber fineness is one of the main factors that determines yarn breakage and spinning count. 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 as fibers become thicker, yarn strength decreases. 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.
4. Fiber strength
The strength of air-end spinning has a linear relationship with the fiber strength. Most of the fibers in air-end spinning are in a hook state, and the degree of fiber shortening increases with the increase of fiber length. The following relationship can estimate the strength CSP of yarn:
CSP=K（ls/f）0.35
Among them: K – constant; l – take 50% of the fiber length range (mm); s – take 1/8 of the fiber strength (g/tex); f – fiber fineness (mic).
5. Impurities
Pre-spun impurities are classified 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 rotating cup.�, mixed 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 and have 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 rotor speed and the smaller the diameter, the higher the degree of dust deposition. Due to uneven twist due to 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 head breakage are as follows:
Produces cotton tufts: 31.5%;
Dust and flying particles are deposited in the waste outlet and taken away by the rotating cup: 28.5%;
Impurities in cooked strips that were not removed during blow cleaning 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.
6. Summary
Based on the above analysis, appropriate selection of spinning raw materials and reasonable configuration of spinning process parameters, strengthening raw material management and process management, especially rational adjustment of carding machine process settings, and taking control measures, can ensure yarn quality.
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