METHOD FOR HEATING AND COOLING MOLD FOR MOLDING PLASTIC AND PLASTIC MOLDING APPARATUS

PROBLEM TO BE SOLVED: To prevent the damage of piping or a valve, the generation of the back flow of cooling water or steam or the stopping of the flow thereof caused by such a phenomenon that cooling water is boiled by the contact with steam to be expanded in its volume in a case such that heating and cooling are alternately repeated with respect to molds 1 and 2 for molding a plastic and performed by steam and cooling water passing through a common fluid passage arranged to the mold for molding the plastic. SOLUTION: The fluid passages of the molds 1 and 2 are allowed to communicate with a pressure air source 53 during the period from the completion of heating to the start of cooling and during the completion of cooling to the start of heating to purge the fluid passages with air. COPYRIGHT: (C)2003,JPO