Yarn internal and external transfer and radial distribution
1. Internal and external transfer: When the sliver is spit out from the front roller holding position of the spinning frame, it is subject to the spinning tension and twisting, causing the fibers originally parallel to the sliver to tilt, and the yarn sliver changes from thick to thin. The transition area from the roller discharge point to the yarn is called the twisting triangle area, as shown in Figure 2-15. In the figure, Ty is the spinning tension, β is the angle between the fiber and the yarn axis, Tf is the force on the fiber due to the spinning tension, and Tt is the component force of Tf along the direction of the yarn core, which is called the centripetal force. It can be concluded from Figure 2-15: From the above analysis, as the radius of the fiber in the yarn increases, the centripetal force Tt also increases, that is, the tension and centripetal force of the fiber in the outer layer are larger, and the centripetal force Tt is simply larger. The yarn core squeezes in (transfers inward), while the fibers in the inner layer have smaller tension and centripetal force, and are easily squeezed to the outside (transfer outwards) by the fibers in the outer layer, forming a new relationship between the inner and outer layers. This phenomenon is called Internal and external transfer. A fiber can undergo multiple internal and external transfers in the twisting triangle area, thus forming a complex conical spiral structure, as shown in Figure 2-16. For the internal and external transfer of fibers to occur, the resistance between fibers must be overcome. The size of this resistance is related to factors such as fiber thickness, rigidity, elasticity, surface properties, and the tightness of the whiskers in the twisting triangle area. Therefore, the opportunities for internal and external migration of each fiber are not equal, and not all fibers will undergo internal and external migration. About 60% of the fibers undergo internal and external transfer to form conical spirals. Other fibers do not undergo internal and external transfer in the yarn but form cylindrical spirals, hooks, folds and fiber bundles. For new types of spinning such as rotor spinning, friction spinning, air-jet spinning, vortex spinning, and compact spinning, the geometric characteristics of the fibers are different. Although compact spinning is realized on a ring spinning machine, the internal and external transfer of the fiber is very weak, and the geometric characteristics of the fiber are basically cylindrical spirals. Rotor spinning, vortex spinning and friction spinning are free-end spinning. During the twisting process, the fibers in the twisting area lack active holding and are in a loose state. The tension on the fibers is very small, the straightness is poor, and the degree of internal and external transfer of the fibers is low. The structure of yarn is usually divided into two parts: yarn core and outer fiber. The outer fiber structure is loose and randomly wrapped around the yarn core. Therefore, compared with ring-spun yarn, open-end spun yarn has less hairiness, looser structure, fuller appearance and lower strength. There is peeling phenomenon, the evenness is good, and the wear resistance is good. Air jet spinning is a new spinning method that uses high-speed rotating airflow to gun yarn into yarn. The internal and external transfer of fibers in the spinning yarn is not as obvious as that of ring yarn, and it has a wrapped structure. To observe the geometric shape of fibers arranged in yarn, the immersion projection method is a relatively simple method. The principle is to immerse the yarn in a solution with the same refractive index as the fiber, so that when the completed thread passes through the yarn sliver, no refraction will occur and it will appear transparent. If a small amount of colored tracer fibers are mixed into the yarn during spinning, the geometric shape of the colored fibers arranged in the yarn can be clearly seen in the transparent yarn strips. It is usually viewed magnified under a microscope or projector. 2. Radial distribution Due to the internal and external transfer of fibers, a blended chemical fiber fabric yarn spun from two fibers with different properties will have different distributions on its cross section – radial distribution. There are two limiting cases: uniform distribution and skin-core distribution. Radial distribution is a very complex problem. Even between different sections on the same spinning yarn, the distribution situation is different, so statistical methods must be used to find its changing rules. The quantitative expression of radial distribution uses the Hamilton transfer index M. When M=0, it means that the fibers of the two blended chemical fiber fabrics are evenly distributed in the cross-section of the spinning yarn; when M>0, it means that the calculated fibers tend to transfer and distribute to the outer layer; conversely, when M<0 , indicating that the calculated fibers tend to transfer and distribute toward the inner layer; when |M|=100%, it indicates that one of the two blended chemical fiber fabric fibers is completely transferred inward in the cross-section of the spinning yarn, while the other is completely Transferred outward, showing a skin-core distribution.
AAASDGGERY6UFGH
Extendedreading:https://www.yingjietex.com/product/2-LAYER-BOND-Fabric.html
