False twist tension control in DTY process
With the increase of wire speed, the deformation and cooling time are reduced, the thermoplasticity of the yarn is reduced, and the false twist tension is increased.
When stretching and deforming POY, the remaining stretching ratio of the filament should be considered, and the stretching ratio should be reasonably selected. The false twist tension increases with the increase of the draw ratio, but the speed of increase is that the twisting tension is greater than the untwisting tension (T1>T2). According to the principle that T2 must be greater than T1.
The relationship between the D/Y ratio and the false twist tension, as the D/Y ratio increases, the twisting tension T1 increases, while the untwisting tension T2 decreases.
As the temperature increases, the rigidity of the filament decreases, the thermal stress tends to ease, and the false twist tension decreases accordingly. Usually, the method of changing the temperature of the first hot box is not used to adjust the false twist tension.
With the increase of the number of friction discs, the untwisting tension drops sharply, while the twisting tension drops slowly. As the number of friction discs increases, the component force of the friction force in the advancing direction of the filament increases.
If the ratio of the untwisting tension to the twisting tension (T2/T1) is too small, the twisting efficiency will be low and the twisting will be uneven; if the T2/T1 is too large, the frictional resistance will increase, and it is easy to produce wool and incomplete untwisting , forming tight spots or stiff threads. The untwisting tension must be greater than the twisting tension, otherwise the threads between the friction discs are in a loose state, and the friction discs and the threads are easy to slip, resulting in uneven false twist, tight spots in DTY, and striped threads on the dyed socks.
Twisting tension and untwisting tension must also be uniform and stable, otherwise, the obtained low elastic yarn has obvious stiff yarn, poor elasticity and bulkiness. The twisting tension should be kept as low as possible. Because in the first hot box, the lower the tension of the filament, the better the deformation effect, and the lower the internal stress of the textured filament, the twist shrinkage of the obtained low elastic filament is increased, the crimp peak is deepened, and the bundling property is good. In addition, the low tension can reduce the frictional resistance of each part of the machine, and the wear and tear on the machine parts, especially the top rollers and aprons, is small. However, if the tension is too low, the air circle of the filament in the first heating box will be unstable, and the contact between the hot plate and the filament will be poor, causing tension fluctuations, which is not conducive to deformation processing. On the contrary, if the tension is too high, the twist shrinkage of the stretched textured yarn will be reduced, the crimp peak will be shallower, the clustering property will be deteriorated, the internal stress will be increased, etc., and even crimped yarn will be generated; in addition, the damage of parts will be large.
The size and ratio of twisting tension and untwisting tension vary with conditions such as raw silk varieties, process conditions, and machine operating conditions.