METHOD OF MOLDING INNER THREAD ON NECK PORTION OF PREFORM

摘要

A method for forming an inner thread of a preform is provided, in which an injection core can be removed after molding the inner thread on an inner surface of a neck portion with the base portion of the injection core by enlarging the diameter of the neck portion by blowing air. An inner wall 42b with a transferred inner thread is molded by using a barrel spacer 16 inserted removably into a neck mold 6 from an injection mold 1 side and a base portion 10a of the injection core 10 that has a thread pattern 12 on the outer surface and is inserted into the injection mold 1 through the neck mold 6. While the temperature of the inner wall 42b is high enough for deforming, the spacer 16 is removed to form an expansion space in the neck mold. An air is blown between the injection core 10 and the inner wall 42b to enlarge the inner wall 42b fully in the expansion space, thereby a gap 19 for removing the core between the inner surface of the inner wall 42b and the outer surface of the base portion of the injection core 10.