Because the shrinkage rate of PP is large, it often occurs when the pipe is deformed and not round in extrusion.
Kalshine after a long time to understand the communication, enumerated a number of reasons to facilitate the reference:
(1) the roundness of the sizing sleeve is not enough, and the cross section may be inconsistent with the thickness.
(2) the cooling is not uniform at all places in the cooling setting, which leads to the uncircle of the cooling stage.
(3) when the vacuum diameter is fixed, the vacuum degree is not reasonable, which causes the deformation of the tube blank to not be attached to the inner wall of the diameter sleeve.
(4) the instability of the traction pressure is not uniform, resulting in the deformation of the pipe.