Abstract: 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.

Abstract: In an automatic gas pressure welding system wherein a couple of steel members are butted, the butted section is subjected to heating in a pressed state, to thus cause the steel members to be subjected to pressure welding. The pressing and heating periods are controlled in conformity with the amount of contraction of the heated section of the steel members.

Abstract: In an automatic gas pressure welding system wherein a couple of steel members are butted, the butted section is subjected to heating in a pressed state, to thus cause the steel members to be subjected to pressure welding. The pressing and heating periods are connected in conformity with the amount of contraction of the heated section of the steel members.