Blow molding process and apparatus for use therein

摘要

The invention relates to blow molding of an article having an inwardly projecting hollow boss with a closed end. A portion of a molten parison conforms to the shape of a fixed pin projecting from the face of a mold part to thereby form the hollow boss. An apparatus disclosed herein includes a reciprocable sleeve slidably received within the mold part over the pin. It has been found that by blow molding the parison with the sleeve initially extended with its end substantially flush with the end of the pin, followed by retracting the sleeve to a retracted position after a predetermined delay time, a boss with a thicker end results. Consequently, the boss end has greater structural integrity, and thus minimizes or eliminates the possibility of penetration and/or cracking of the boss end when a screw is threadedly received in the hollow boss.