Analysis of spinning process on rotor spinning machine

       Rotor spinning, commonly known as air flow spinning, belongs to free end spinning. At present, rotor spinning machines have been widely used in cotton spinning systems, and have developed towards combed yarn, low tex yarn, and knitted yarn, with a focus on spinning medium to coarse tex yarns. The raw materials are also becoming more diverse. The rotor spinning system includes two departments: front spinning (sliver making) and rear spinning (yarn forming), which are used for cotton spinning

       As an example, it is explained as follows.

       （1） Pre spinning process of rotor spinning

       The spinning process before rotor spinning is not significantly different from ring spinning, but the roving process is omitted.

       1. Opening and cleaning cotton

       The rotor spinning opening and cleaning process follows the process guidelines of multiple bag grabbing, exquisite cotton grabbing, average mixing, gradual opening and loosening, combing instead of beating, early falling with less crushing, and less fiber damage. 2. Carding

       The single carding machine is widely used in the rotor spinning pre spinning process, and the double carding machine can be used to produce high-quality yarns. The dual carding machine is composed of two carding machines connected in series (Figure 3-8-3). After feeding the cotton coil through the first carding ring 3-8-3 dual carding mechanism, it enters the first cylinder and first cover plate working area for carding. The side conveyor mechanism composed of cotton stripping rollers, rollers, and two transfer rollers transfers the fiber layer condensed by the first doffer to the second carding roller in the form of a cotton web, and then enters the second cylinder and second cover plate working area for carding, The fiber layer condensed by the second doffer is peeled off by the three roller cotton stripping device to form a cotton web, gathered into strips, and placed in the strip drum through a pre stretching device and a coil device.

       3. Drawing

       The spinning and drawing process before rotor spinning focuses on controlling the quality unevenness and evenness value of the cooked sliver, improving the fiber draft value and parallel level, and making the fibers fully separate.

       （2） The spinning process of rotor spinning machine

       The rotor spinning machine feeds people with slivers, which are loosened, condensed, twisted, and wound into yarn.

       1. Feed

       The rotor spinning machine adopts the direct feeding method of fiber strips. The fiber strip drawn from the tube is fed into the bell mouth (Figure 3-8-4), and the fiber strip is held and actively conveyed forward by the feeding roller and feeding plate. The function of the feeding horn is to make the sliver undergo necessary cleaning and tightening before entering the feeding roller and cotton feeding board, compressing the width of the sliver within a certain range and transforming the cross-sectional state of the sliver, so that it enters the gripping area with a flat cross-section and makes the density on the sliver cross-section consistent, and the lateral pressure distribution relatively uniform. When the strip is conveyed forward through the gripping mechanism, it is subjected to a certain amount of tension, causing the fibers to straighten out.

       2. Loosening

       The rotor spinning machine uses carding rollers to adequately sort the fiber strips. After the fiber strip is combed by fire, the carding roller loosens the fiber strip into a single fiber state and enters the cotton conveying pipeline under the centrifugal force and harmonious flow of the carding roller. The carding roller is nominally wrapped with a metal saw blade or planted with a comb needle, and the fibers are sorted at a speed of 5000-9000f/rain. There is a fixed or adjustable impurity removal installation around the combing roller (Figure 3-8-5 and Figure 3-8-6), which may eliminate small impurities and local short fibers.

       3. Coagulation

       The spinning cup is an important component of rotor spinning (see Figure 3-8-7), which is formed by connecting two hollow truncated cones, forming a groove for condensing fibers at the junction (maximum diameter) of the two cones, which is called condensation. When the fiber flow is sucked into the spinning cup, the emergence of the wrapping machine not only changed the textile production of primitive society, but also had a profound impact on the development of future spinning tools, as the outlet of the cotton conveying pipe faces the inner surface of the spinning cup population. Moreover, as a simple spinning tool, it has been used for thousands of years, even in the 20th century, some nomadic Tibetans in Tibet still used it for spinning., So, the fibers first fall on the inner surface at the entrance of the spinning cup. Due to the small diameter of the spinning cup and the large diameter of the condensation groove, when the spinning cup rotates at high speed, the fibers are subjected to centrifugal force. Airflow spinning is a new spinning technology that uses airflow to condense, twist, and output fibers into yarn in the high-speed rotating spinning cup. He does not use spindles, but mainly relies on multiple components such as carding rollers, spinning cups, and false twisting devices. The carding roller is used to grasp and comb the cotton sliver fibers fed, and the centrifugal force generated by its high-speed rotation can swing the captured fibers out and slide them into the condensation groove from the inlet of the spinning cup. The fibers form a complete fiber ring in the coagulation tank.

       4. Twisting

       There is a trumpet shaped false twisting disc in the center of the spinning cup. When the seed yarn end of the joint protrudes from the central hole of the false twisting disc, it begins to rotate under the action of the rotating flow field in the spinning cup, but this rotation does not cause the yarn to achieve twist. This is because the head end of the seed yarn has not yet been held, and the yarn only revolves around the core of the false twisting disc, without rotating around the axis of the yarn itself. When the joint seed yarn is continuously fed to the person, the yarn head of the seed yarn contacts the fiber ring that has already been fed into the spinning cup condensation groove. Under centrifugal force, the seed yarn tightly adheres to the fiber ring of the spinning cup condensation groove. Therefore, the seed yarn head and spinning cup rotate simultaneously, and for each turn of the seed yarn around the false twisting disc, a twist is added to the yarn. Because the spinning cup does high-speed return

       3. Coagulation

       The spinning cup is the main component of rotor spinning (see Figure 3-8-7), which is formed by connecting two hollow truncated cones. The texturing machine is a textile machine that can process untwisted fibers such as polyester (POY) and polypropylene into elastic fibers with medium and low elasticity properties through false twisting deformation. At the intersection of the two cones (at the maximum diameter), a groove for condensed fibers is formed, which is called the condensation groove. When the fiber flow is sucked into the spinning cup, as the outlet of the cotton conveying tube faces the inner surface of the inlet of the spinning cup, a considerable amount of twisting is applied to the segment of yarn (i.e. the arm segment) between the false twisting disc and the condensation groove in the spinning cup in a very short period of time. The seed yarn is twisted together with the fiber ring in the condensation groove of the spinning cup, forming a joint.

       5. Winding

       After achieving the joint, the fibers are continuously fed in and the yarn is continuously drawn out, forming a continuous spinning process. The extracted yarn is wound on the bobbin, directly causing the bobbin yarn.

       Rotor spinning belongs to free end spinning: one end of the yarn is held (pulled by the yarn roller), and the other end is twisted as the twister rotates around the grip point in the same direction and speed. Figure 3-1 shows a schematic diagram of the process of rotor spinning, with the central components including the rotor, feeding roller, carding mechanism, false twister, and yarn guiding mechanism. They are assembled in a box called a spinner. The cotton sliver is fed from the inside of the barrel through the bell mouth between the feeding plate and the feeding roller, held under its pressure, and then sorted through the carding roller. The inlet and outlet cross-sections of the bell mouth are gradually reduced, and the cotton sliver undergoes necessary pre consolidation and pre compression, with consistent density and uniform pressure distribution. Finally, it enters the gripping area with a flat cross-section. The size of the bell mouth should be designed based on the quantity of feeding strips. The surface of the feeding plate is lubricated, and there are thin and shallow grooves on the surface of the feeding roller and pressure is applied to maintain a certain grip force on the fibers.

       The carding roller divides the cotton sliver into a single fiber state through a feeding plate. The carding length of the feeding plate and the spacing between the carding roller and the feeding plate directly affect the carding results and carding quality, so it needs to be set based on the length of the spun fibers. The surface of the carding roller has serrations or planting needles, and their specifications should also change depending on the fiber being processed. The carding roller fully combs the fiber strips at a speed of 5000-9000r/min individually; Under the feeding plate, the combing roller is equipped with a impurity removal device at the fiber conveying channel to effectively remove impurities and fine dust in the fiber flow. The fibers that are sorted into a single fiber state rely on the centrifugal force of the sorting roller and the negative pressure airflow suction in the rotor to completely detach from the surface of the sorting roller and enter the conveying pipeline. The gradually shrinking conveying pipeline accelerates the movement of fibers in the pipeline with the airflow, thereby improving the fiber straightness. Through the outlet of the conveying pipeline, the fibers are sent to the inclined surface of the inner wall of the spinning rotor. The rotary cup is composed of two hollow truncated cones (see Figure 3-4), and the intersection of the two cones is the maximum diameter inside the cup, forming a groove for condensing fibers, known as the "coagulation groove". Under the centrifugal force of high-speed rotation of the rotor, fibers slide from the inclined surface of the cup wall (referred to as the slip surface) to the condensation groove at the maximum diameter of the inner wall, and stack here to form a circular condensation strand called the "yarn tail fiber ring". Due to the cyclic arrangement of fibers along their circumference in the coagulation tank, a grand coalescence effect is generated.