Stabilized-core injection molding of hollow thin-walled plastic products

Abstract

An injection molding method for controlling the dimensions of a hollow plastic product by using a mold having a first and second mold parts; wherein one of the mold parts includes a retractable portion adjacent a gate. The retractable portion is movable between a protracted position and a retracted position while the mold is closed; and the mold parts define primary flow channels extending from the gate, which, when the retractable portion of the one mold part is protracted, direct initially injected molten plastic from the gate to create stabilizing regions of stiffened plastic. The method includes the steps of (a) protracting the retractable mold part; (b) injecting molten plastic from the gate and through the primary flow channels to create the stabilizing regions; (c) retracting the retractable mold part; (d) subsequently injecting additional molten plastic from the gate between the stabilizing regions into the side wall defining region of the mold cavity. Step (d) includes the step of (e) directing the subsequently injected molten plastic through secondary flow channels defined by the mold parts, which secondary flow channels are significantly thicker than adjacent portions of the mold cavity; are adjacent to the gate but, when the retractable portion is protracted, are isolated from the gate by the retractable portion; are interposed between the primary flow channel; and, when the retractable portion is retracted, direct the subsequently injected molten plastic between the stabilizing regions of stiffened plastic and into the side-wall-defining region of the mold cavity.