Patent GB-530252-A (GB)
Title: Improvements in or relating to fluid pressure power transmission mechanisms
IPC: B29C45/82
Filed: 1939-06-01
Abstract: 530,252. Hydraulically-operated injection moulding machines. VICKERS, Inc. June 1, 1939, No. 16103. Convention date, June 3, 1938. [Class 87 (ii)] [Also in Group XXIX] A fluid power-transmission system particularly for operating a pressure-casting machine has a pump supplying a pair of fluid motors in a predetermined cycle, the fluid delivery to the motors being automatically controlled and the pump output being independently reducible by means which are rendered ineffective during a predetermined part of the cycle, such as the injection of metal into the mould. In one form a double pump consisting of a low pressure-low volume section 11 driven from a motor 12, delivers to a valve assembly comprising a bye pass section 22 for diverting the delivery of pump 10 back to the tank through line 29, a check valve 24, and a relief valve 26. Delivery from this assembly passes through check valve 39 to a solenoid-operated four-way valve 42 having two connections to an exhaust line 60 and two 50, 54 leading to opposite ends of a cylinder 52 whose piston 98 operates the movable mould section 100. A branch delivery connection 62 leads to an adjustable spring- loaded pressure-reducing valve 64 connected by a line 66 to a four-way solenoid operated valve 68 having two connections to exhaust line 60 and two, 76, 80 leading to opposite ends of a cylinder 108 operating the charging piston 110. Material is fed from a hopper 114 to a chamber 115 where it is heated to casting temperature by a heating element 116. A branch 82 from the line 76 leads to a solenoidoperated two-way valve 84 leading either to exhaust line 60 or through a line 86 to the chamber 88 of valve 22. Any pressure in chamber 88 holds down valve 22 and prevents by pass of the output of pump 10 to line 29. The supply line 54 of cylinder 52 also has a branch 94 leading to a spring closed valve 92 which may be opened to exhaust by a cam 106 on the movable mould part 100. The electrical circuits are energized by lines LI, L2. A pushbutton 118 controls one solenoid 122 of the valve 42. Limit switches 128, 130 are actuated by a rod 124 secured to piston 98 and similarly a rod on piston 108 actuates switch 136 and snap switch 138 connected to a delay relay 142 connecting the circuit of solenoid 146 of valve 84. Switch 136 controls a relay 148 whose centre circuit includes line 152 collector 153 and magnetic clutch element 154 the clutch connecting a constant speed shaft to delay mechanism 156. A spring urges the disc 157 against a pin 158 but the spring pressure is overcome when the clutch is energized and cam pieces 161, 162, are caused to actuate switches 163, 164. In operation, in the starting position shown, the combined pump output flows to port 46 and thence through lead 54 to the right of cylinder 52 but no movement is caused as piston 98 is in its left hand position. The valve 92 being open the pump delivery passes to exhaust line 60. Pressure fluid is also directed through line 62 valves 64, 68 to the left of cylinder 78. The machine is started by depressing switch 118 to actuate solenoid 122 and shift valve 42 to the right. This opens line 50 to pressure and line 54 to exhaust and closes the mould, also closing valve 92. When piston 98 stops the pressure rise may momentarily open valve 22 and bye pass the pump 10 to the tank. The cam 126 actuates switch 130 which through relay 148 and switch 163 energizes solenoid 170 thereby admitting fluid to the right of cylinder 78. As soon as pressure reaches line 76 the valve 84 is lowered and pressure admitted to line 86. This closes valve 22 and ensures that the full combined pump delivery is available for the charging stroke. During this stroke the relay 142 is actuated and just after completion of the stroke the solenoid 146 is actuated to raise valve 84 and cut off line 86 so that valve 22 may open and byepass the pump 10 while flow from pump 11 maintains pressure in cylinder 78 and passes to exhaust through valve 26. Just before completion of the charging stroke the cam 134 actuates switch 136. This de-energizes solenoid 170 and also engages magnetic clutch so that cam disc 157 rotates and after a predetermined time energizes solenoid 171 and shifts valve 68 to the right for the return stroke. During this return switch 138 is broken, and solenoid 146, de-energized. After a further predetermined time switch 164 is actuated to energize solenoid 174, operate valve 42 and retract the mould part 100 after the required cooling interval. Finally cam 126 breaks the circuit of the delay mechanism clutch 154, the disc 157 is returned by its spring and the solenoids 170, 174 de-energized. The machine then stops in readiness for another cycle. In a modification, Fig. 2, a variable delivery pump 177 delivers through line 188 connected to suitable reversing valves such as 42, 68. The line 190 corresponding to the line 76, Fig. 1, is connected to valve 84 and thence by a line 192 to a pump control cylinder 184. In operation when substantial resistance to any piston movement is encountered pressure builds up in line 188 and actuates piston 180 to decrease the pump delivery. While the injection piston is operating both ends of cylinder 182 are open to pressure but the spring overcomes the effect of such differential pressure and maintains full pump delivery until on completion of the stroke the valve 84 is raised to cut off line 192 and cause a reduced pump delivery. On the return stroke of the injection piston, pressure in line 196 falls and the spring causes the pump to be moved to maximum delivery position.