GB1007513A - Improvements in die casting machines - Google Patents

Abstract

1,007,513. Die casting machines. MATHER & PLATT (SCOTLAND) Ltd. April 21, 1964 [May 3, 1963], No. 17519/63. Heading B3F. In a pressure die casting machine a device is provided to effect two-stage pneumatic control of the injection plunger movement during injection of metal into the die. The device comprises a slide valve 25 which alternately permits the supply of compressed air above and below the piston 16 to effect upward and downward movement thereof, and a pneumatically operated check valve 38 which in association with needle valves 34a and 35a controls the flow of compressed air to the cylinder 17. Solenoid valves 37 and 39 effect actuation of the slide and check valves respectively. Means for controlling the length of stroke of the piston 16 is provided in the form of a rod 42 which is biased pneumatically in contact with the piston. The rod actuates a limit switch 46 by means of an adjustable trip 44 which energizes the solenoid of valve 39. When solenoid valve 37 is actuated the slide valve 25 operates to permit compressed air to pass via chamber 27 and 21 and valve 34a into the top of the cyclotron cylinder 17 causing downward movement of the piston 16 and plunger 14. Since the air admission to the cylinder is via needle valve 34a, this initial movement of the piston and plunger is slow, but as the piston descends the limit switch 46 is actuated by the trip 44 on the rod 42 which operates valve 39 to open the check valve 33a which permits a sudden increase in pressure on the piston and plunger which forces molten metal into the die cavity. Timing means (not shown) is incorporated so that the downward injection stroke of the piston and plunger is terminated after a predetermined time by the actuation of the solenoid valve 37 which actuates the slide valve 25 so as to supply compressed air to the underside of the piston which is retracted to its uppermost starting position. The return movement is controlled by adjustable valve 35a. Means are provided by a pressure sensitive switch 48 to prevent the dies of the machine opening if there is any pressure above the piston 16.