1. The dimensional error of the wall thickness of the circumferential section of the pipe and the poor concentricity accuracy between the mold and the mandrel in the assembled forming mold make the melt flow gap between the two parts uneven. The concentricity accuracy of the two parts should be adjusted. After pipe extrusion production for a period of time, the dimension error of circumferential section wall thickness appears out of tolerance.
2. If there is too much moisture or volatile matter in the raw material, it is necessary to dry the raw material, and if the compression ratio of the molding die is too small, it is necessary to appropriately increase the compression ratio of the die to melt molding.