Patent ID: 6884061

Claim:
A hot runner injection molding apparatus comprising: a manifold having a manifold channel for receiving a melt stream of moldable material under pressure, said manifold channel having an outlet for delivering the melt stream to a nozzle channel of a hot runner nozzle, said nozzle being positioned within a nozzle bore of a mold cavity plate and being spaced from said mold cavity plate by an insulative air space; a mold cavity for receiving said melt stream from said nozzle, said nozzle channel directly communicating with said mold cavity through a mold gate; a gating mechanism driven by an actuation means for selectively opening and closing said mold gate; an injection piston extending through said nozzle channel of said nozzle and being slidable therethrough, an outer wall of said injection piston abutting an inner wall of said nozzle channel, said injection piston being movable from a retracted position to an extended position to force melt into said mold cavity; a valve located at a forward end of said injection piston, said valve being selectively movable to block communication between a recess, which is provided in said outer wall of said injection piston upstream of said valve, and a melt chamber of said nozzle channel that is proximate to said mold gate, said valve being open to allow melt to flow from said manifold channel into said recess and into said melt chamber of said nozzle channel when said injection piston is in said retracted position; wherein movement of said injection piston towards said extended position forces melt located in said melt chamber of said nozzle channel to flow through said mold gate into said mold cavity when said gating mechanism is in an open position.