Injection molding apparatus for making a hollow object

Details Injection molding apparatus for making a hollow object Injection molding apparatus for making a hollow object

1988-11-02

1991-05-14

Heitbrink, Timothy

Plastic article or earthenware shaping or treating: apparatus

Control means responsive to or actuated by means sensing or...

Molding pressure control means responsive to pressure at...

264 403, 26432813, 264572, 425535, 425573, 425584, 425812, B29C 4978

Patent

active

050151665

ABSTRACT:
An apparatus for making a plastic injection molded part with a smooth surface or skin and a hollow core wherein thermoplastic material is injected as a molten stream into the mold cavity through a sprue bushing fixed in the mold. Simultaneously, an unmeasured quantity of inert gas is introduced through an adapter into the molten stream at the sprue bushing substantially coaxially with the melt stream and at a pressure sufficient to penetrate the thermoplastic material to form a gas cavity in the molten material in the mold. For retrofitting an existing mold, an adapter can be added to the existing sprue bushing. During plastic injection and cooling in the mold the gas is maintained at a high pressure, preset, constant and adequate to maintain the plastic against the mold surface until it is self-supporting. The gas is exhausted from the mold, back through the sprue bushing and adapter, before the mold is opened. Adequate preset high pressure is maintained at the gas supply by a large cylinder having a positive displacement member therein that is controlled by a pressure sensor in the gas pressure line to the mold to maintain preset adequate gas pressure within the cavity.

REFERENCES:
patent: 4101617 (1978-07-01), Friederich
patent: 4136220 (1979-01-01), Olabisi
patent: 4474717 (1984-10-01), Hendry
patent: 4498860 (1985-02-01), Gahan
patent: 4740150 (1988-04-01), Sayer
patent: 4781554 (1988-11-01), Hendry

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