Method of improving shot repeatability in multilayer reciprocating screw injection molding machines

Patent metadata

Field	Value
Publication number	US-12304126-B2
Application number	US-202118004914-A
Country	US
Kind code	B2
Filing date	Jul 13, 2021
Priority date	Jul 29, 2020
Publication date	May 20, 2025
Grant date	May 20, 2025

Abstract

In one aspect there is disclosed a method of improving shot repeatability in a multilayer reciprocating screw injection molding apparatus by preventing pressure communication or “cross-talk” between melt channels. In the first aspect an outlet nozzle valve is closed prior to closing a check valve within an injection unit of the multilayer reciprocating screw injection molding apparatus. In another aspect there is disclosed a method of improving shot repeatability in a reciprocating screw injection molding apparatus by recording a first position of a screw within the barrel of an injection unit of a reciprocating screw injection molding apparatus, the first position corresponding to a volume of melt within the barrel of the material injection unit. A second position of the screw is then calculated based on the first position, the second position corresponding to a transition position of the screw within the barrel of the injection unit of the reciprocating screw injection molding apparatus.

First claim

What is claimed is:

1. A method of improving shot repeatability in a reciprocating screw injection molding machine, the reciprocating screw injection molding machine comprising a mold gate, a mold cavity, a first injection unit, and a second injection unit including a longitudinal barrel having a downstream end proximate to an outlet nozzle valve and an upstream end proximate to a resin source, and a screw positioned coaxially within the longitudinal barrel including a check ring, the method comprising the steps of:
plasticizing and metering a first injection unit resin in the first injection unit to form a first melt;
closing the outlet nozzle valve of the second injection unit;
transferring a resin from the resin source to the screw within the longitudinal barrel of the second injection unit;
plasticizing the resin and metering the plasticized resin in the downstream end of the longitudinal barrel of the second injection unit via rotational actuation of the screw to produce a second melt;
ceasing application of rotational actuation of the screw;
applying an axial force upon the screw in the downstream direction to increase a pressure gradient across the check ring sufficient to close the check ring;
ceasing application of the axial force upon the screw in the downstream direction after the check ring is closed;
beginning injection of the first melt from the first injection unit;
thereafter opening the outlet nozzle valve of the second injection unit; and
applying the axial force upon the screw in the downstream direction to begin injection of the second melt from the second injection unit through the mold gate and into the mold cavity to begin coinjection of the second melt from the second injection unit into the mold cavity via the mold gate.

2. The method of claim 1 , the first injection unit further comprising a second longitudinal barrel having a downstream end proximate to a second outlet nozzle valve and an upstream end proximate to a second resin source, and a second screw positioned coaxially within the second longitudinal barrel comprising a second check ring.

3. The method of claim 1 comprising, after the step of ceasing application of the axial force upon the screw in the downstream direction, the further steps of:
recording a first position of the screw;
calculating a transition position (T) of the screw based at least on the first position of the screw;
applying the axial force upon the screw in the downstream direction to inject the first second melt through the mold gate and into the mold cavity according to a velocity profile (VP); and
applying the axial force upon the screw according to a pressure profile (PP) when the screw reaches the transition position (T).

4. The method of claim 1 comprising, after the step of beginning coinjection of the second melt from the second injection unit into the mold cavity via the mold gate, the further step of:
ceasing coinjection of the second melt from the second injection unit into the mold cavity via the mold gate.

5. The method of claim 4 comprising, after the step of ceasing coinjection of the second melt from the second injection unit into the mold cavity via the mold gate, the further step of:
ceasing injection of the first melt through the mold gate and into the mold cavity.

6. A method of improving shot repeatability in a reciprocating screw injection molding machine, the reciprocating screw injection molding machine comprising a mold gate, a mold cavity, a first injection unit, and a second injection unit including a longitudinal barrel having a downstream end proximate to an outlet nozzle valve and an upstream end proximate to a resin source, and a screw positioned coaxially within the longitudinal barrel comprising a check ring, the method comprising the steps of:
plasticizing and metering a first injection unit resin in the first injection unit to form a first melt;
closing the outlet nozzle valve of the second injection unit;
transferring a resin from the resin source to the screw within the longitudinal barrel of the second injection unit;
plasticizing the resin and metering the plasticized resin in the downstream end of the longitudinal barrel of the second injection unit via rotational actuation of the screw to produce a second melt;
ceasing application of rotational actuation of the screw;
applying an axial force upon the screw in the downstream direction to increase a pressure gradient across the check ring sufficient to close the check ring;
ceasing application of the axial force upon the screw in the downstream direction after the check ring is closed;
recording a first position of the screw;
calculating a transition position (T) of the screw based at least on the first position of the screw;
beginning injection of the first melt from the first injection unit;
thereafter opening the outlet nozzle valve of the second injection unit;
applying the axial force upon the screw in the downstream direction to inject the second melt from the second injection unit through the mold gate and into the mold cavity according to a velocity profile (VP); and
applying the axial force upon the screw according to a pressure profile (PP) when the screw reaches the transition position (T).

7. The method of claim 6 , the first injection unit further comprising a second longitudinal barrel having a downstream end proximate to a second outlet nozzle valve and an upstream end proximate to a second resin source, and a second screw positioned coaxially within the second longitudinal barrel comprising a second check valve.

8. The method of claim 6 comprising, after the step of beginning injection of a second melt from the second injection unit into the mold cavity via the mold gate and prior to the step of applying an axial force upon the screw according to a pressure profile (PP) when the screw reaches the transition position (T), the further step of:
ceasing injection of the second melt from the second injection unit into the mold cavity via the mold gate.

9. The method of claim 8 comprising, after the step of ceasing coinjection of the second melt from the second injection unit into the mold cavity via the mold gate, the further step of:
ceasing injection of the first melt through the mold gate and into the mold cavity.

Assignees

• Husky Injection Molding Systems Ltd

Inventors

• Weatherall Douglas James

Classifications

• B29C45/1646

  Injecting parison-like articles (B29C45/1643 takes precedence) · CPC title

• B29C45/1642 Primary

  having a "sandwich" structure (B29C45/1603 takes precedence) · CPC title

• B29C45/1607

  having at least three different ways · CPC title

• B29C2945/76876

  Switch-over · CPC title

• B29K2105/258

  Tubular · CPC title