Mitsubishi Gas Chemical Company, Inc.

Nireco Corporation

Hiroshi Harada

Akimasa Kaneishi

Hiromi Hayashi

Yasuaki Ichinose

A gas injection technique of injecting an inert gas (e.g., nitrogen gas) into a molten resin in a cavity, involves utilizing the strokes of reciprocation of a piston in the compression cylinder are used in a series mode, to perform a two-stage compression within the same cylinder, thereby providing a high-pressure gas. The method can also include establishing a relationship or pattern of the amount of movement of the piston with the speed of movement of the piston established to provide optimum control of the relationship between the pressure generated and piston stroke, and quantity of gas injected. The injecting gas pressure can be detected, to control a hold pressure, or the relationship between a piston stroke and generated pressure, so as to obtain optimal injecting pressure during the injection molding operation. A gas injection apparatus comprises a compression cylinder with a piston wherein the volumes of the two chambers on both sides of the piston are of such a compression ratio to provide the first compression. The apparatus also includes pipe lines communicating the two chambers with each other through a check valve, a gas supplying conduit pipe connected upstream of the check valve, and a conduit pipe connecting the chamber located downstream of the check valve to the cavity, wherein the piston is reciprocated to perform two-stage compression to provide a high pressure gas as required.

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Kanagawa,, Japan

Hiroshi Harada