Technology | Advantages of twisted yarn and process quality control

What is twisted yarn?

In order to make the yarn have certain physical and mechanical properties such as strength, elasticity, and elongation, the cotton yarn must be changed by twisting. The twisting of yarn by fiber structure is actually to use the relative angular displacement between the cross-sections of the cotton yarn to change the yarn structure by tilting the originally straight and parallel fibers and the yarn axis. The width of the thick strip gradually shrinks during the twisting process and rolls into the center of the yarn strip, forming a twisting triangle, which changes the width and cross-section of the cotton strip, and gradually changes from a flat ribbon to a cylindrical yarn.

Twisted yarn fully meets the requirements of modern people in terms of comprehensive performance, and it has a large cotton content and uses plant fibers, so it has no harm to the human body. It has strong plasticity, and the clothes made are diverse. It is very comfortable to wear, soft to the touch, and has a very strong drape. There is no smell after burning. It is a healthy and green textile.

Twisted yarn is mainly used for woven weft yarn, which can make the cloth surface wrinkle in a unique style. As a special yarn, strong twisted yarn has always occupied a place in the yarn market. Strong twist yarn can be produced without improving equipment and adding accessories, and the product has high technical content and added value. However, the production of strong twist yarn is difficult, and the product quality is difficult to control. The production enterprise must have certain technical capabilities and management experience.

Pre-spinning

The pre-spinning production process and quality control of twisted yarn are basically the same as those of conventional yarn, except that the twist coefficient of fine yarn exceeds the critical twist coefficient of yarn, and the yarn strength is lower than that of conventional weaving yarn. The larger the twist coefficient, the lower the yarn strength, and the higher the weight CV value and strength CV value; at the same time, in order to obtain relatively high production efficiency, the spindle speed of fine yarn is generally not lower than that of weaving yarn of the same number. The above factors increase the breakage of fine yarn and increase the difficulty of production. Therefore, the cotton grade of twisted yarn should be higher than that of weaving yarn of the same number. Twisted yarn generally has a short delivery period and a small batch, and it is sometimes difficult to make a separate cotton. At this time, the combing noil should be increased, and the drawing machine and roving machine with good mechanical condition should be selected to organize production. The quality of roving is the guarantee of the quality of strong twist yarn.

Fine yarn

Fine yarn twist. In order to achieve the special effect of wrinkling the cloth surface, the twist of the strong twist yarn is more than 1.5 times that of the same number of weaving yarn. The specific twist value is generally specified by the manufacturer according to the fabric requirements. Due to factors such as the slip rate of the spindle belt, in order to ensure that the twist requirements of the customer are met, the calculated twist of the spun yarn should generally be larger. The twist coefficient of the strong twist yarn is large, that is, the twist angle is large, and the stress of the inner and outer fibers of the yarn is seriously unevenly distributed. When the twist is tested by untwisting and twisting, some fibers are displaced and cannot be restored to their original state. Sometimes a falsely high twist value appears, which needs to be removed at any time during the test.In daily production, the process management must ensure the accurate loading of the spun yarn process parameters, and the equipment management must eliminate the crooked spindles, resolutely overcome the "fierce" spindles, maintain uniform spindle belt tension, and good spindle belt joints, so that the twist average value is basically stable and the twist CV value is kept at a good level. The twist CV value of the spun yarn directly affects the single strength CV value and the weight CV value.

Spun yarn quality (weight) control. The drafting efficiency of the spinning machine is affected by many factors such as raw materials, mechanical state, process, temperature and humidity. Among them, due to twist shrinkage, the drafting efficiency of yarns with different twist coefficients varies greatly. Strong twist yarn has greater twist shrinkage, and the drafting efficiency is generally between 85% and 92%. Only by mastering the drafting efficiency of the production variety can the weight deviation be effectively controlled and yarn that meets the specified weight requirements be produced. In the process design, the drafting efficiency is considered based on experience, and the drafting change gear is initially determined. When the machine is put into production, samples are taken in time for weight testing and the process gear is adjusted.

Cop winding density. The winding of the cop yarn needs to be tightly wound, with clear layers and no entanglement. It should not be unwound during the subsequent process, and the package size should be appropriate. If the package size is too large, the yarn is easy to wear the steel collar and form bad yarn; if the package size is too small, the number of yarn dropping increases, the number of winding and tube changing increases, the labor intensity increases, and the production efficiency decreases. Strong twisted yarn has high twist, high tightness, good elasticity and small cross-sectional diameter. The bobbin is obviously smaller. When the bobbin is full, the automatic doffing car cannot pull out the bobbin normally, resulting in increased doffing workload and affecting production efficiency. The winding density of the bobbin must be appropriately increased.

Control of yarn breakage. The average strength of strong twisted yarn is low, and the strength CV value is larger than that of the same number of weaving yarn. The yarn breakage rate is high and the joint is difficult. More broken ends affect the yarn production and quality, increase the labor intensity of the stopper, and must be highly valued from many aspects of operation and management.

Practice has proved that the use of variable frequency speed regulation technology of spinning machine, lowering the spindle speed when large and small yarns; selecting machines with steel collars in the mature stage, and appropriately shortening the replacement cycle of steel rings; strengthening maintenance inspections, and timely correcting crooked spindles, concave rubber rollers, rubber ring deviation, loose yarn guide hooks, and rough yarn guide hooks are effective in reducing yarn breakage. The output is not high when the yarn is twisted, and the operator is not under much pressure to change the coarse yarn. He should concentrate on cleaning the machine, strengthen the patrol, and connect the broken ends in time.

Winding

The winding machine should be adjusted and inspected spindle by spindle to ensure that the twisting parts and components are coordinated and in place, and the equipment is in good condition. The twisting joint of the strong twist yarn winding is prone to insufficient untwisting and untwisting of the yarn head, and the phenomenon of climbing at the yarn joint. The untwisting and twisting air pressure must be guaranteed, and the untwisting and twisting scales are adjusted from the maximum to adjust the overlap length to the best. Strong twist yarn has high elasticity, the yarn bobbin is tightly wound, and the winding pressure should be below 50 MPa. Strong twist yarn has low strength, many yarn defects, frequent electronic yarn cleaning, and the winding speed is lower than that of conventional yarn. The cotton knots and impurities of the combed strong twist yarn are more, which is lower than the production efficiency of the same number of combed strong twist yarn.

In short, high-twist yarn products have high technical content and are difficult to produce and process. It is necessary to do a good job in technical basic management such as the operation of process equipment, strengthen the maintenance of spinning equipment, reduce the difference between spindles, ensure the untwisting and twisting air pressure of the winding, and adjust the overlap length and other process parameters to improve the joint quality and reduce the phenomenon of yarn head climbing at the twisting point.