US 4,099,904 AGranted

Nozzle shut-off valve for injection molding machine

AssigneeCincinnati Milacron Inc.

InventorJames Earl Dawson

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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.

Claims2

Dependent claims

In an injection molding apparatus comprising a chamber having a nozzle attached near one end thereof, means for forcing molten material from said chamber through a passageway formed in said nozzle, a mold having a sprue formed therein, which sprue is in communication with the passageway formed in said nozzle, and a nozzle shut-off device interposed between said nozzle and said chamber the improvement comprising:

(a) a body for said device having a first passageway in communication with both said chamber and the passageway formed in said nozzle and a second passageway intersecting said first passageway, and a third passageway substantially coaxial with said second passageway and having common intersection with said first and second passageway;
(b) a long pin reciprocal in said second passageway and having a length sufficient to extend at least along said second passageway, completely across said first passageway and to enter said third passageway;
(c) a short pin reciprocal in said third passageway but having a length less than said long pin length yet sufficient to extend completely along said third passageway and to protrude not more than partly across said first passageway and being substantially coaxial with said long pin;
(d) first and second pistons respectively engaging that end of said long pin and said short pin most remote from said first passageway;
(e) first and second cylinders encompassing said first and second pistons, respectively, each being mounted on said body and having means for connecting same to a fluid pressure source;
and
(f) means in each of said cylinders to establish communication from one side of its said piston to a source of fluid pressure.

4 more elements

Dependencies are inferred from the claim text.