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Injection Molding Operations ©

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Patentpedia Index 

3/31/2016 through 3/30/2016

1 Patent Abstracts

2 Patent Titles

1 Topics

1 Subtopics

1 Notes

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1 Topics

C. Injection Molding (1 Topics) (4 Subtopics) (3 Notes ) (17 Patent Titles ) (0 Patent Abstracts) (3/30/2016)

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1 Subtopics

E. Injection Molding Overmolding (1 Topics) (0 Subtopics) (1 Notes) (8 Patent Titles)   (2 Patent Abstracts) (3/31/2016)

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0 Notes

1. Injection Molding Operations

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1. Injection Molding Operations

With injection molding, granular plastic is fed by a forced ram from a hopper into a heated barrel. As the granules are slowly moved forward by a screw-type plunger, the plastic is forced into a heated chamber, where it is melted. As the plunger advances, the melted plastic is forced through a nozzle that rests against the mold, allowing it to enter the mold cavity through a gate and runner system. The mold remains cold so the plastic solidifies almost as soon as the mold is filled.

Injection molding cycle

The sequence of events during the injection mold of a plastic part is called the injection molding cycle. The cycle begins when the mold closes, followed by the injection of the polymer into the mold cavity. Once the cavity is filled, a holding pressure is maintained to compensate for material shrinkage. In the next step, the screw turns, feeding the next shot to the front screw. This causes the screw to retract as the next shot is prepared. Once the part is sufficiently cool, the mold opens and the part is ejected.

Scientific versus traditional molding

“Traditionally, the injection portion of the molding process was done at one constant pressure to fill and pack the cavity.  This method, however, allowed for a large variation in dimensions from cycle-to-cycle.  More commonly used now is scientific or decoupled moulding, a method pioneered by RJG Inc.  n this the injection of the plastic is "decoupled" into stages to allow better control of part dimensions and more cycle-to-cycle (commonly called shot-to-shot in the industry) consistency.  First the cavity is filled to approximately 98% full using velocity (speed) control. Although the pressure should be sufficient to allow for the desired speed, pressure limitations during this stage are undesirable.  Once the cavity is 98% full, the machine switches from velocity control to pressure control, where the cavity is "packed out" at a constant pressure, where sufficient velocity to reach desired pressures is required.  This allows part dimensions to be controlled to within thousandths of an inch or better.”

Different types of injection molding processes

“Although most injection moulding processes are covered by the conventional process description above, there are several important moulding variations including, but not limited to:
Die casting
Metal injection moulding
Thin-wall injection moulding
Injection moulding of liquid silicone rubber

Injection Molding Operations, Wikipedia, 3/30/2016

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Copyright 2016 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen

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Roger D. Corneliussen, Editor
Professor Emeritus
Materials Engineering
Drexel University, Philadelphia, PA
Editor
Maro Publications
327 Huffman Drive
Exton, PA 19341
Telephone: 610 363 1533
Email:
cornelrd@bee.net
Website: 
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