Stubborn silk refers to tightly twisted strands of continuous, non fluffy yarn that appear on DTY.

Tight points refer to less severe stiff threads, where the continuous length of the stiff thread is very short and almost in the form of dots.

Stiffness and tightness can be identified through visual inspection, appearance, and other methods. Stiff silk can also be distinguished on dyed socks, as it is darker in color than normal silk and appears in a strip shape. Tight spots refer to dark spots on the sock, which are generally difficult to distinguish.

The main reasons for causing stiff threads and tight spots are: ① high unevenness of POY yarn and elongation; ② poor wettability of POY spinning oil; ③ uneven distribution of yarn surface; ④ POY spinning speed does not match DTY processing speed; ⑤ Fluctuations in the speed of the incoming and outgoing filaments in the stretching deformation zone; ⑥ There is bonding phenomenon between individual fibers in the twisting area; ⑦ False twisters are not suitable; ⑧ Improper selection of D/Y ratio and stretching ratio; ⑨ Insufficient tension of the filament in the second hot box, etc.