Injection molding apparatus

A sprue bushing for use with a mold in plastics injection molding operations wherein a sprue is integrally formed at each injection with the part being molded, said sprue bushing comprising:

• a generally cylindrical body member having an inner end, an outer injection end, and a longitudinal frusto-conical bore extending therethrough between said ends, said bore being concentric with the central longitudinal axis of the body member and tapering outwardly toward said inner end, and
• a plurality of straight elongate grooves formed in the wall of said bore extending longitudinally over at least 50% of the length thereof and converging toward said injection end, adjacent sides of adjacent grooves converging to apices at a first radial distance from the central longitudinal axis of the bore, and sides of each groove converging to points at a radial distance from the central longitudinal axis substantially greater than said first radial distance,
• said grooves thereby increasing the surface area of the bore to enhance heat transfer and producing a sprue which is readily released from the bushing with simple longitudinal and non-rotational relative movement therebetween.