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United States Patent 4099904
Douris , ê et al. July 11, 1978

Nozzle shut-off valve for injection molding machine

Dawson July 11, 1978

Abstract

A nozzle shut-off valve for placing between the injection apparatus and the mold cavity uses two pins of different lengths for the valve elements and switches air pressure back and forth between pistons on opposite (outer) ends of the pins. The pistons have no fixed connection to the pins. Each pin is actuated either by force from the piston on its outer end or pressure by the plastic melt on its innermost other end. The longer pin has a length sufficient to extend completely across the injection passage and block it to prevent any flow. The shorter pin is deliberately made short enough that it cannot block the passage. The valve is actuated by air pressure on the two pistons in timed relation to injection molding events. Pressure on the piston engaging the longer pin compels blocking of the injection passage during plastication. Switching of pressure to the other pin during injection permits the pressure of molten plastic to spread the pins apart whereupon injection proceeds in the ususal manner.