Method for forming duct made of elastomer

A method for forming a duct made of an elastomer having a plurality of corrugated sections in a longitudinal direction thereof as apart of the duct by injection-molding, which comprises

• injecting an elastomer material into a cavity formed with a cavity die for forming an external surface of a duct, and a core die for forming an internal surface of the duct, wherein the core die is a splittable core die which is axially splittable into two parts, one is a core die (i) for forming a duct area containing a first corrugated section, and the other is a core die (ii) for forming the remainder area containing the second corrugated section,
• a first die-removing step for removing the duct area containing the first corrugated section by pulling out the splittable core die (i) with expanding the first corrugated section in the radius direction after opening the cavity die, and
• a second die-removing step for removing the remainder area containing the second corrugated section by pulling out the remainder area from the splittable core die (ii) with expanding the remainder area in the radius direction.

A die unit for forming a duct made of an elastomer having a corrugated section in a longitudinal direction thereof as a part of the duct by injection-molding, which comprises

• a cavity die for forming an external surface of the duct, and a core die for forming an internal surface of the duct, wherein the core die is a splittable core die which is axially splittable into two parts, one is a core die A for forming a duct area at least containing the corrugated section, and the other is a core die B for forming a duct area free from the corrugated section,
• which further comprises an ejection zig or attachment, wherein the ejection zig or attachment is inserted into the inside of one end of the duct, for removing the duct area containing the corrugated section from the core die A with expanding at least the corrugated section in the radius direction by air injection.