Abstract: The present invention provides a mold with gas ejection of pieces formed in the mold. The mold includes a female body part and a male body part. The male body part includes a male molding surface with a surrounding plastic injection shut off face and a reciprocable gas controlling blow off pin slideably trapped within a pin recess at the shut off face. The pin has an enlarged bottom portion and a narrowed upper portion with a gas passage starting upwardly through the lower bottom portion into the upper portion and opening sideways through the pin which has a solid top surface above the sideways opening. The pin receiving recess has an undercut configuration including a small diameter upper region and a larger diameter base region with clearance for sliding of the pin in the recess. The clearance is at a minimum near the solid top surface of the pin and increases downwardly from the upper to the lower portion of the pin.

Abstract: The present invention provides in a stack mold with back to back centrally located mold cavities a multiple sprue bar arrangement including a pair of sprue bars balanced on opposite sides of the mold and connecting bridge across the sprue bars for interfacing to a plastic injector. At least one of the sprue bars provides a plastic flow path from the connecting bridge to the mold cavities.

Abstract: The present invention provides an injection mold apparatus for plastic piece molding. The apparatus includes male and female body parts and a gas blow-off ejection system for ejecting pieces formed on the male body part. The blow-off system includes side and top opening vents in the male body part for initial release and slight lifting of the piece and a further bottom positioned final blow-off vent, which is covered by slideable means during introduction of the plastic to the mold to prevent the plastic from flowing into the final blow-off vent and which is only exposed when required for completing blowing of the piece from the male body part. The slideable means has a slide tolerance to substantially eliminate flowing of the mold material therearound while being readily slideable when required for exposure of the blow-off vent to the male body part.