| 摘要 |
A method of molding an inner thread on a preform, wherein the extraction of an injection core after a thread has been formed on an inner circumferential surface of a neck portion of a preform by a base portion of the injection core is rendered possible by expanding the neck portion by an air blowing operation. An inner wall (42b) onto an inner surface of which a thread is transferred is formed by a short cylinder type spacer (16), which is withdrawably inserted from the side of an injection mold (1) into a neck mold (6), and by a base portion (10a), which is provided on its outer circumferential surface with a threading mold (12), of an injection core (10) inserted into the injection mold (1) through the neck mold (6). Within a period of time in which the temperature remains at such a level that permits the inner wall (42b) to be deformed, an expansion space left by the extracted spacer (16) is formed in the neck mold. The expansion space is fully expanded by blowing air between the injection core (10) and inner wall (42b) to form a core extraction clearance (19) between the inner circumferential surface of the inner wall (42b) and the outer circumferential surface of the base portion of the injection core (10). |
