Bi-directional check ring for a two-stage injection unit
AssigneeMilacron LLC
InventorM. Barr Klaus
Life of this patent
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Abstract
The invention is directed to a bi-directional check ring for a two-stage injection unit. More specifically, a close fitting ring is inserted behind the plunger head of the melt accumulator so that normal running clearances between the plunger and barrel bore can be used. The outer diameter of this check ring has a very close fit with the inner diameter the injection barrel, but is not rigidly connected to the plunger. Accordingly, the plunger is free to “floats” while injection and plastication/filling take place. The open volume between the ring and plunger is small, but sufficient to permit the ring to “float” very close to the barrel inner diameter, without being influenced by the alignment of the plunger and injection drive motor.
Claims4
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;
- and
- a 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.
Dependencies are inferred from the claim text.