In the process of rotor spinning, the main tasks are as follows: loosen the sliver and draft it to a single fiber state; Remove impurities from feed materials; Mix the fibers evenly; Forming a whisker; Condensed fiber; Improve uniformity by merging; Twisting; Winding forming.
Theoretically, during rotor spinning, a single fiber condenses into a fiber ring in the cotton coagulation tank of the rotor, and then the fiber ring is pulled up reversely, but in fact, due to other reasons, fiber hooks, fiber rings, fiber sheets and other deformation will occur in this process, which will greatly affect the quality of rotor spinning. The quality of yarn is affected by the quality of sliver fed, mainly the length, length uniformity, fiber fineness and impurity content of sliver fiber. On the other hand, in the process of transportation and agglomeration, the better the separation state of fiber, the better the yarn quality. The sliver quality is controlled by the front spinning process. Carding is the key process of rotor spinning. It mainly carries out impurity removal, carding and uniform mixing of feed raw materials. Therefore, adjusting carding process parameters has a great impact on the sliver quality, and then on the yarn quality. The following five main factors affecting the quality of rotor spinning are analyzed:
Cylinder, cover plate and doffer play an important role in carding. When the cylinder reaches the doffer with a layer of fiber, the end of the fiber touches the doffer’s surface and is grabbed by the doffer’s needle cloth, while the other end is still held by the cylinder’s needle cloth. When the cylinder passes through the transfer area, due to its high surface speed, the fiber is pulled by the doffer’s needle cloth and generates tension. This condensation makes the amount of fiber per unit area of doffer 2 ~ 3 times that of cylinder. If the doffer speed increases, more needle teeth can participate in carding. The coagulation effect increases due to the increase of doffer speed. Even if the ratio of linear speed on the surface of cylinder and doffer decreases, the fiber transfer effect willincrease. However, if the doffer speed increases too much, the coagulation effect will decrease. 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 load of the cylinder, and then increase the NEP and reduce the evenness of the sliver. Therefore, the yarn quality deteriorates, that is, the U% value increases, and the strength and appearance grade of the yarn will decrease significantly.
By adjusting the speed of the cover plate or the flower content of the cover plate, the sliver with good quality can be produced by mixing the cotton rolls with general quality. When all other parameters remain unchanged, only increasing the cover speed will increase the cover flower. At the same time, due to the enhanced carding effect, the impurities in the green sliver will be reduced, the short pile will also be reduced, and the yarn strength can be improved, but the strength CV% value will be reduced, while the measured yarn defect number and U% value will not change, so the yarn quality and fabric appearance will be improved.
The effect of fiber length is different from that in ring spinning. The fiber length has the following relationship with the diameter of the rotating cup:
The twist is transferred downward to a special point in the rotating cup coagulation tank, which is called the stripping point. There is a cluster area in the rotating cup coagulation tank where the fibers are twisted. The length and stability of the cluster area are two parameters that determine the stability of the spinning process, thus affecting the spinning end breakage rate.
During the spinning process, the length of the cluster area fluctuates up and down around an average value. Once the length of the cluster area is lower than the critical value and impurities hinder the transmission of twist, head breakage will occur. The longer the fiber length and the higher the length uniformity, the more stable the spinning process will be.
Fiber fineness is one of the main factors determining yarn breakage and yarn count. The optimal number of fibers (NF) in the yarn section can be calculated by the following formula:
This relationship shows that when the fiber becomes thicker, the yarn strength decreases. Coarse fiber spinning will also lead to the deterioration of yarn evenness CV%, and a higher twist coefficient should be used to ensure the strength of the yarn.
The strength of rotor spinning has a linear relationship with the fiber strength. Most fibers in rotor spinning are in the state of hook, and the degree of fiber shortening increases with the increase of fiber length. The strength CSP of yarn can be estimated by the following relationship:
K——constant；l——Take the fiber length range 50%（mm）；s——Take fiber strength 1/8（g/tex）；f——Fiber fineness（mic）。
The pre spinning impurities are classified as follows: large impurities, fiber fragments and dust impurities. Large impurities can usually be effectively removed by the trash removal system of the rotor spinning machine. However, due to the kinetic energy exerted by the acceleration force, the dust impurities will not be deposited between the needle teeth of the combing roller. The ejection track of these dust impurities to be removed will become flat due to air buoyancy, and some slightly large dust impurities will enter the rotor and mix in the fiber ring, resulting in the increase of yarn short segment unevenness, Resulting in reduced yarn strength and elongation at break.
Fiber fragments include broken seeds, sterile seeds, seed chips with fiber and soft seed epidermis, which are not easy to remove in the whole processing process. They affect the transmission of twist in the rotating cup and have a great impact on the appearance of yarn. Even if they can be removed by the carding roller, they may still deposit in the coagulation tank and cause flying flowers.
The degree of dust deposition increases with the increase of impurity content in the feeding sliver. The higher the rotating cup speed is, the smaller the diameter is, the higher the degree of deposition is. Because of the uneven twist caused by dust deposition, the fabric has “rungs” and “cloud spots”. The deposition of dust will also damage the evenness of yarn and increase the hairiness of yarn. Moreover, the deposition of dust in the spinning process will increase the number of yarn breaks。
Therefore, choosing a good feed material can reduce the impurity level and reduce the dust accumulation in the rotating cup.
Based on the above analysis, properly select spinning raw materials and reasonably configure spinning process parameters, strengthen raw material management and process management, especially reasonably adjust the setting of carding machine process and take measures to control, so that the yarn quality can be guaranteed.