EXTRUSION OF THERMOPLASTIC TUBE AND APPARATUS FOR PRODUCING THE TUBE

摘要

PURPOSE: To reduce the change in pressure stress caused by the change of a molding material by molding the ribs of a tube in groove parts and changing the effective vol. of an accumulator chamber in order to compensate a change in the demand amt. of a thermoplastic material used in the molding of the groups of the tube at projected parts. CONSTITUTION: During a period when ribs are formed on a tube, the pressure of thermoplastic material 53 is released and a chip 56 is positioned at the front position of a stretched spring 58. As a mold block 16 advances in a B-direction, the pressure of the thermoplastic material 53 increases to press the chip 56 to compress the spring 58. The effective ratio of the advance of the mold block 16 becomes larger than the advance ratio in the region of a projected part. The dimension of a section 50 is changed by the motion of the chip 56 and, when a groove part 36" meets with the thermoplastic material 53, the pressure on the chip 56 is relaxed and the spring 58 extends and the effective ratio of the advance of the mold block 16 is reduced so as to provide the time filling the groove part 36" with the material.