Molding tool for molding with cylindrical core

A molding tool for a molding with a cylindrical core, comprising:

• an upper mold and a lower mold adapted to be clamped directly or through an intermediate mold and including insert dies confronting each other vertically for forming the axial side faces of a molding with a cylindrical core, the inert dies of said upper and lower molds being individually provided with fitting hole portions for supporting the end portions of the cylindrical core set therein, said lower die being provided at its fitting hole portion with a support pin fitted in said cylindrical core from the lower end opening for retaining the lower end of said cylindrical core, said upper die being provided at its fitting hole portion with a core holder confronting said support pin concentrically and fitted on the upper end of said cylindrical core, said upper and lower molds being clamped to form a cavity around the outer circumference of said cylindrical core supported by said support pin and said core holder, and a molding material such as rubber being charged into said cavity so that it may be molded integrally with said cylindrical core,
• wherein the improvement comprises:
• a seal ring mounted in the fitting hole portion of the insert die on the side of said upper mold for fitting the outer circumference of the upper end portion of said cylindrical core while holding a slight air ventilation;
• a molding material injection hole leading from the upper face of said upper mold to said cavity;
• and an air and molding material relief hole leading from said cavity to the upper face of said upper mold.