Apparatus for injection molding fiber-reinforced thermoset plastic articles

摘要

A technique including an apparatus for injection molding fiber- reinforced thermoset plastic articles is disclosed. The technique includes forming a mixture of short lengths of reinforcing fibers with a thermosetting resin in a predetermined fiber-to-resin ratio and introducing the mixture to an injection molding cylinder. The volume of mixture introduced is at least a multiple of two of the volume of the mold chamber so that the injection plunger traverses the intersection between the molding cylinder and a stuffer cylinder a single time for a multiplicity of molding shots to minimize fiber breakage and balling. The injection plunger is adapted to precompact the mixture by being forced forward until a predetermined high pressure is sensed, indicating a hydraulically locked condition of the plunger wherein substantially all entrapped gases have been expressed from the mixture and there exists no substantial forward movement of the plunger. The position of the plunger in its precompacted position is noted and recorded so that further multiple injection shots may be made in predetermined volumetric amounts.