The upper pin is an important spinning draft special piece [1], and the stability of the jaw pressure composed of it and the lower roller has an important influence on the quality of the yarn. Due to the influence of the market situation, the economic benefits of domestic middle and low-end textile enterprises have generally declined, production costs have risen, market competition is fierce, and enterprises are under greater pressure. In this case, textile enterprises can only improve their market competitiveness by improving product quality. Under the premise of the same cost of raw materials, the spinning special parts are continuously selected, and through a large number of special parts comparison tests, it is found that the new lengthened upper pin can greatly improve the yarn quality index.

1. Design principle of lengthening upper pin

1.1 Q187028 type extended upper pin

Q187028 type extended upper pin is an improved spinning upper pin developed by Jiangxi Rongxing Technology Co., Ltd., which is suitable for pneumatic cradle. Its structural diagram is shown in Figure 1.

As can be seen from Figure 1(a) and Figure 1 (B), the elastic and contraction blocks are divided into left and right, and are symmetrically arranged on the connecting blocks on both sides of the upper pin frame. The upper end of the elastic and contraction block is provided with an upper protrusion. The lower end is provided with a lower protrusion, and the upper protrusion and the lower protrusion have a cylindrical structure, which makes the belt rotate more smoothly, reduces the wear of the belt and improves the service life of the belt. As can be seen from fig. 1(c), the clip includes a plate body, an abutment plate, a clip plate and a through groove. the abutment plate and the clip plate are respectively connected to the upper bending end and the lower bending end of the plate body, and the clip plate is provided with a through groove. during clamping, the clip plate is connected to the upper pin frame. The bend of the clip plate is set in an oblique triangle shape, which can further improve fatigue resistance, thereby prolonging the service life of the spring sheet; the end of the abutment sheet away from the sheet body has an arc-shaped structure.

1.2 T187028 type extended upper pin

The T187028 type lengthened upper pin (developed by Jiangxi Rongxing Technology Co., Ltd.) uses a new type of snap plate, which is suitable for the spring cradle. Its structural diagram is shown in Figure 2.

As can be seen from Figure 2, the upper side of the sheet body is bent and connected with the offset sheet, and the other end on the offset sheet is provided with an upturned end. The lower side of the sheet body is bent and connected with a snap plate, the middle of the snap plate is provided with a through groove, and the bending section at the connection between the sheet body and the snap plate is inclined triangle. This design can further improve the fatigue resistance and prolong the service life of the snap plate. When working, the snap plate is fixed in the slot of the pin on the carbon fiber, and the spring fixing member is fastened on the side of the pin on the carbon fiber through the pin through the slot, both sides of the clip plate are respectively fixedly connected with a left clamping block and a right clamping block, and the left clamping block and the right clamping block are arranged opposite to each other, both of which have a circular arc device structure, which can play a better clamping role. The snap plate is provided with a limit groove matching the through groove, and a limit block is provided under one end of the opening of the limit groove. When the snap plate is fixed on the carbon fiber upper pin, the left clamping block and the right clamping block can better prevent the snap plate from falling off the carbon fiber upper pin. The setting of the limit block and the limit groove can better limit the external retaining piece and prevent the external fixing piece from falling off.

2. The function of lengthening the upper pin

The drawing of the spinning front area is the main drawing area, and the middle friction boundary formed by a pair of middle rollers and upper and lower rubber ring jaws controls the moving fibers in the drawing area, which plays a key role in the drawing performance of the whole system. However, in the floating area from the front edge of the upper and lower pin to the jaw of the front roller, the friction boundary strength is relatively weak, and the control of the floating fiber is poor, which expands the distribution range and instability of the floating fiber variable speed point. Therefore, reducing the length of the front floating zone is the key to improve the quality of the yarn. Shortening the length of the floating fiber means that on the one hand, the number of uncontrolled short fibers in the floating area is reduced, and on the other hand, the friction force of the rubber ring jaw extends forward accordingly, so as to give full play to the advantages of the rubber ring control fiber and the elastic floating jaw, and strengthen the control force of the floating fiber in the floating area [2]. In order to solve the above problems, we have verified through many tests that lengthening the upper pin has greatly improved the above problems. The main feature of the upper pin is that the holding distance is lengthened, which shortens the floating area distance in the drafting area, increases the control range of the fiber, changes the uncontrolled state of the floating area fiber, controls the running speed of the fiber, and effectively prevents the fiber from changing speed in advance, so that the yarn quality has been greatly improved.

3. The use effect of lengthening the upper pin

After half a year of lengthening and selling on the testing machine, when the high temperature and humidity season came in June, there was an abnormal production phenomenon. In production, there is a phenomenon of "hard head, more broken head"; The machine with lengthened upper pin is 30% more instantaneous broken head than the machine with ordinary upper pin. And there is the phenomenon of clamping down apron. According to the analysis of the above problems, first, after using the lengthened upper pin, the iron roller in the upper pin moves backward relative to the middle roller, resulting in insufficient pressurization and poor synchronization of the upper and lower rubber rings during operation. Second, after using the lengthened upper pin, the circumference of the rubber ring increases, resulting in an increase in the contact area of the upper and lower rubber rings, thus increasing the running resistance of the upper and lower rubber rings, especially affected by environmental changes in high temperature and humidity seasons; when the temperature and humidity are low, the rubber ring is hard and its operation is blocked. When the temperature and humidity are high, the rubber ring is astringent and elongated, resulting in increased running resistance and poor synchronization of the upper and lower rubber rings, resulting in the phenomenon of "uneven drafting and hard head" [3].

To this end, we take the following measures: fine adjustment of the position between the three rollers and the lower pin; Appropriately reduce the upper pin pressure; Reduce the roving twist coefficient to ensure the flexibility of the spinning spindle; Reduce the main drafting multiple of spun yarn; Increase the jaw spacing; Adjust the position of the upper pin, stagger the gap between the three rollers and the lower pin at the back of the iron rod in the upper pin to ensure that the floating area is 0. 5 mm ~ 1.

Our company conducts spinning contrast tests on the new lengthened upper pin and the pressure bar upper pin under different cotton blending conditions.

Test 1: Use of T187028-type lengthening upper pins. The raw material is 100 Xinjiang machine-picked cotton. AFIS data: average length 29. 0mm, fineness 163 mtex, micronaire value 4. 3,16. 5 mm short pile rate 14. 3%, impurity content 2. 7%, nep 293 grains/g. TH578J type spinning frame (leaf spring cradle) is adopted, the roller spacing is 16. 7 mm × 45mm, and the front rubber roller is punched forward +3mm. C 14. 6 tex and JC 14. 6 tex agglomerated knitting yarns were spun respectively. The test results are compared in Table 1. In the table, the upper pin 1 is the T187028 type lengthened upper pin +3.25mm gauge block, the upper pin 2 is the pressure bar upper pin +3.25mm gauge block, the upper pin 3 is the T187028 type lengthened upper pin +2.75mm gauge block, and the upper pin 4 is the pressure bar upper pin +2.75mm gauge block.

Test 2: Use of Q187028-type extension upper pins. The raw materials are 20% Brazilian cotton and 80% Xinjiang cotton. AFIS data: average length 29. 33mm, fineness 158 mtex, micronaire value 4. 13, short staple rate below 16.5mm 15. 1%, impurity rate 3. 0%, neps 293 grains/g. The SXF1568B spinning frame (pneumatic cradle) is adopted, the roller spacing is 16. 7 mm × 45mm, and the front rubber roller is punched +3mm. C 9. 7 tex and JC 9. 7 tex agglomerated knitting yarns were spun respectively. The test results are compared in Table 1. In the table, the upper pin 5 is a Q187028 type lengthened upper pin +2.5mm gauge block, and the upper pin 6 is a pressure rod upper pin +2.5mm gauge block.

From the above test results, it can be seen that under the test conditions of the same spindle and roving, the strip dry CV of the extended pin is reduced by 1 percentage point, the details, coarse knots and neps are reduced by more than 20%, and the quality indexes such as breaking strength, strong CV and 100,000-meter yarn defects are improved to varying degrees. Although the improvement of quality indexes of combed varieties is not obvious, but after a period of tracking, the yarn quality is stable.

4. Concluding remarks

The focus of our company's use of lengthening and selling is to solve the problem of high neps in C 14. 6 tex agglomerate knitting yarn to meet user requirements. On the premise that other process equipment does not need to invest a large amount of machine materials, we use T187028 type lengthened upper pin to match appropriate spinning special parts in spinning process, and reasonably optimize the process parameters, so that the finished yarn neps, details, coarse knots, strength, etc. have been improved to varying degrees, effectively improving the product quality, meeting the needs of downstream users, and the use effect is better. After nearly 9 months of follow-up tests, it has been widely used in our company.

References:
[1] Luo Bin. Design and development of a new type of pin [J]. Textile Equipment, 2019,46(1):23-24,50.
[2] Liu Xianyu, Dong Shijia, Yan Feng. Spinning Practice of Applying New Type Spinning [J]. Cotton Textile Technology, 2008,36(12):38-40.