Blow molding a closed plastic drum including two speed compression

Abstract

A closed one-piece plastic drum having an integral handling ring at a head end is formed in a blow mold having mold halves and an articulating mold section. While the mold is open and the articulating section is spaced from the mold halves, a heated plastic parison is placed in the open mold and blown at a first blowing pressure (30-60 psi) to completely expand the parison into the shape of the inside surface of the mold and fill the open articulating section. This blow molding step forms an open handling ring as well as the drum body. A second blowing operation at a second lower pressure (15-40 psi) is then performed to stabilize the expanded parison inside the mold. The mold articulating section is closed during the second blowing operation in first and second sequences. In each sequence, the articulating section is moved over a different distance and at a different speed while compressing the blow-molded open handling ring into a solid handling ring. After the articulating section is completely closed, a third blowing operation at a third pressure (90-110 psi) is performed. The third pressure is higher than both the first and second pressures and is held for a sufficient time to allow cooling of the molded plastic drum.