Patent ID: 6200127
Filing Date: 2001-03-13
Classification: B29C

Abstract:
A two-stage injection unit including an extruder for generating a flow of plastic melt, and a melt accumulator for receiving the melt from the extruder and subsequently injecting the melt into a mold cavity, wherein the melt accumulator comprises:a generally cylindrical barrel having longitudinal bore;a plunger received within the bore of the barrel, the plunger having a head attached to an elongated shaft, the plunger being movable relative to the barrel so that it retracts when melt is transferred into the accumulator and advances to inject melt into the mold cavity; anda bi-directional check ring fitted between bearing surfaces associated with the plunger head and plunger shaft, the ring having an outer diameter sized to match closely the diameter of the barrel bore, such that the check ring substantially prevents (i) the melt from leaking past the head of the plunger and remaining in the barrel after injection and (ii) plastic residue behind the plunger head from mixing into the flow of melt from the extruder.