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United States Patent 5470514
Douris , ê et al. November 28, 1995

Injection molding method for a shot of determined mass

Dray November 28, 1995

Abstract

A non-return valve primarily for use with an injection molding machine utilizes a frame which surrounds a first bore and a second bore. The second bore is accessed by inlets. Outlet passages are located downstream of said inlet and connect second bore with an accumulation area. A piston is dimensioned to slidably fit within the first bore and extend into the second bore. In a downstream position, the piston allows positive flow of material from the inlet to the outlet. In an upstream position, the piston positively blocks flow of material from the inlet to the outlet. The piston can be forced to its upstream position at the beginning of the injection step or can be preclosed by eliminating rearward movement prior to injection. A method of injection molding involves precisely determining the mass of the shot and by limiting the rearward translation of the screw during recovery and then building the pressure of the accumulated material to a predetermined pressure