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Reasons and Solutions for Uneven Twist of Double Twisting Machine

October 07,2023

Uneven twist in the double Twisting machine can result in different fiber cohesion within each segment of the strand, and inconsistent inclination of surface fibers, affecting the physical and mechanical properties and appearance characteristics of the strand, such as strength, elasticity, elongation, luster, and wear resistance, and affecting the style and quality of the fabric.

The following is an analysis and solution to the problem of uneven twist in the double twisting machine.

Ⅰ Fault Cause Analysis

1. Uneven tension of the dragon belt

Due to the double twisting machine relying on the friction transmission spindle of the dragon belt to twist the strands, the tension of the dragon belt directly affects the spindle speed of the entire vehicle. Due to the elasticity of the dragon belt itself, and its tension is greatly affected by climate. When parking for a long time in autumn and winter, the large contraction of the conveyor belt leads to an increase in tension, resulting in an increase in spindle speed, while in spring and summer, the opposite is true.

2.Tensioning wheel in and out position deviation

The entry and exit position of each tensioning wheel directly affects the spindle speed of adjacent two spindles, and there are strict requirements for the entry and exit position of the tensioning wheel in the equipment technical conditions. Practice has found that the deviation of each adjustment unit will affect the proximity between the conveyor belt and the spindle, resulting in an increase in spindle speed deviation.

3. Insufficient lubrication of spindle

When the spindle rotates at high speed under the friction transmission of the dragon belt, it simultaneously acts on two torques: one is the rotational torque caused by the friction force of the dragon belt, and the other is the resistance torque caused by the friction force between the spindle and the spindle foot bearing. The magnitude of these two torques directly affects the spindle speed. The role of spindle oil is to form an oil film between the spindle tip and the spindle liner to reduce the frictional resistance of the bearings on the spindle. Therefore, the lubrication of the spindle directly affects the spindle speed. The change in spindle speed will inevitably cause uneven twist of the strand, and the twist unevenness increases with the increase of the difference rate of spindle speed change.

4. The bearing of the large and small collets is not flexible

The size chuck of the double twisting machine relies on the rotation of two small bearings to achieve the rotation and winding of the bobbin. If the chuck bearings do not rotate flexibly or the clamping force of the cradle on the bobbin is insufficient, it may affect the normal yarn feeding speed. The speed of yarn drawing will inevitably cause uneven twist of the strands, and the larger the difference in yarn drawing speed, the more severe the uneven twist of the strands.

5. Poor operation of ingot wings

If the production environment of the double twisting machine is not good, such as scattered flower hair or poor cleaning of the machine, it will cause flower hair to be sandwiched between the spindle wing and the spindle tube, causing jerking when the spindle wing rotates, resulting in uneven twist.

6. Improper setting of tension spring parameters

In the early stages of production, the twist unevenness of some brands of double twisting machines has been consistently high, at one point exceeding 3.5%. After research, it was found that the main reason was that the set value of the tension spring in the spindle tensioner was too small, resulting in uneven and high twist.  

Ⅱ Solution to the problem

1. process planning

Adjustment of spinning tension. Different varieties require different spinning tensions. The basis for determining the tension is that it is more appropriate to wind the yarn on the spindle disc by 1.5 to 2.0 turns, with a maximum of 2.5 turns.

Reasonably determine the ingot speed. In general, it should be determined based on the situation of head breakage during 1000 ingots. Control the breakage of fine count yarn and high-end varieties within 5 pieces during 1000 spindles, and control the breakage of medium coarse count yarn within 10 pieces. On the basis of meeting production and quality requirements, maximize the spindle speed. After random sampling inspection, the unevenness of twisting can be controlled within 5%, and the unevenness of the entire vehicle can be controlled within 2.5%.

Choose the overfeeding rate correctly. The change in overfeeding rate affects the winding tension, thereby changing the winding density of the package. Under the condition of meeting the forming requirements, the overfeeding rate is selected based on the fineness of the yarn, which is generally controlled at around 160% to reduce the increase in breakage caused by winding tension and reduce the chance of uneven twisting.

2. Equipment status maintenance

Ensure the tension of the dragon belt. Replace the dragon belt that is not flexible or jumping during operation, adjust its tension to ensure that the tension of the dragon belt meets the specified standards, and ensure that the tension between the machine and the ingot is consistent. When using a dedicated gauge for calibration, ensure that the distance between the dragon belt and the spindle wheel is about 2 millimeters or more, and the distance between the dragon belt and the tension roller is about 2 millimeters or more.

Adjust the pressure exerted by the dragon on the spindle wheel. A high tension of the dragon belt can increase the contact surface with the spindle wheel, reduce twisting unevenness, but at the same time, it will increase the loss of the spindle belt. Therefore, on the premise of meeting the quality requirements, the pressure brought by the dragon to the spindle wheel is relatively small, in order to extend the service life of the dragon belt.

Check the tension device. For the peak twist of a single spindle on the machine, it is necessary to promptly check the wear of the tension head, tension rod, and tension head seat inside the tension device. For tension heads that are not flexible in expansion and contraction, they should be replaced and repaired in a timely manner; Replace damaged tension rods, tension head seats, and other components to ensure that the tension difference between each spindle is minimized. It is also necessary to adjust the position of the spindle in a timely manner to ensure that the contact surface with the conveyor belt is in a reasonable position.

Check the spindle bearings. Inspect and refuel the transmission bearings of the double twisting machine spindle, and replace the spindle bearings that are not functioning properly or damaged when stopped to ensure that the spindle speed difference between spindles is controlled within the internal control indicators, reducing the chance of weak twisting. Strengthen the inspection of spindle operation, eliminate deteriorated spindles, reduce the difference in spindle speed and yarn tension of the entire machine, and ensure the consistency of the entire machine.

3. Operations Management

The yarn blending process reflects the setting of fixed length, and according to user requirements, adopts the mode of overall yarn loading and overall yarn dropping to reduce the number of joints in the double twisting process.

Strictly follow the operating method, and improper control of the brake release time can also cause local unevenness, eliminating the occurrence of untwisted or weakly twisted yarn during the joint process. During the patrol, the car blocker discovered a broken end and stepped on the brake disc joint. After the joint was completed, he twisted the joint with his hand and released the brake disc for 5-10 seconds. After the untwisted yarn section was fully twisted, he released the hand roll and wrapped it onto the drum. The time from releasing the brake disc to winding the knotted yarn onto the bobbin is selected based on the degree of twist, ranging from 7 seconds to 10 seconds for high twist and 5 seconds to 7 seconds for low twist.

The blocking worker should do a good job of cleaning after yarn shedding, and the residual yarn on the spindle wheel should be treated in a timely manner to eliminate the decrease in spindle speed caused by yarn entanglement and reduce the chance of weak twisting.

The power outage, shutdown, and restart of the equipment have a significant impact on the twist. During production, it was found that the twist unevenness of the machine before the power outage was 2.9%, and after the power outage, the restart test was 4.3%. Therefore, it is necessary to minimize the shutdown time and frequency of the double twist machine as much as possible. When parking during holidays, it is necessary to request an empty car to be delivered before driving and retesting.