Apparatus for making a twin-wall, internally corrugated plastic

Abstract

A method and apparatus for making a twin-wall internally corrugated plastic structural part provided with a smooth, dense, solid, thin walled, non-cellular skin comprising injecting a thermoplastic or resin material into a pair of closed mold members which define a sealed cavity. A small amount of plastic material is initially injected into the cavity with the material impinging upon and being dispersed over the mold members thereby forming a generally continuous thin skin substantially the mold surfaces. Thereafter, successively and intermittently injecting an inert gas under pressure through one mold member during continued injection of the plastic material into the cavity thereby pressurizing the skin against the walls of the mold cavity and progressively commingling the inert gas under pressure and the inwardly flowing plastic material as both enter the cavity until the cavity is filled with an internal corrugated body integral with and bonded to the skin. Further steps include cooling the twin-wall internally corrugated structural part to permit the same to solidify as an integral unit and venting the mold cavity to atmosphere to relieve pressure from the corrugated plastic structural part. The intermittent injection of the inert gas introduces minute amounts of pressurized gas into the continuously injected plastic material.