GB522631A - Hydraulic presses - Google Patents

Abstract

522,631. Hydraulic presses. BLISS CO. E. W. Dec. 12, 1938, No. 36186. Convention date, Dec. 14, 1937. [Class 69 (ii)] In a hydraulic press in which the exhaust pipe from the ram return chamber contains a yieldable variable pressure control valve by which the exhaust pressure in the pipe and thus the speed of the working stroke of the ram may be varied, hydraulic means, responsive to the pressure of the liquid passing through the valve, is provided for increasing the load on the valve to increase the pressure in the pipe. Fig. 1 shows the device applied to a press having a prefill valve as described in Specification 511,993, in which the ram 34 is moved rapidly by high pressure liquid passing from a pipe 52, and fixed tube 49 into a square advance chamber 51 until the ram meets with sufficient resistance, e.g., by engagement with the work, to allow the prefill valve 21 to close and admit high pressure liquid to the ram work chamber 45. The ram moves against the pressure in the ram return chamber 46 which is connected by pipe 64a, variable pressure valve 65 and pipe 64 to a reversing valve 63 to which the pipe 52 is also connected. The high.pressure liquid is supplied by a pump 60 drawing from a tank 58 and passing to the valve 63 which is held in neutral position by a spring and moved to extreme positions by electro magnets 90. The valve 65 comprises a casing 101, Fig. 2, having ports 102, 106 connected respectively to the pipes 64, 64a, these ports being on opposite sides of two non-return valves 104, 108 urged to closed position respectively bv a light spring 107 and a heavier adjustable spring 110 arranged within a piston 112 between which and the valve 108 is a plunger 113. The spurs 116, 117 above and below the piston communicate with a passage 118 which, by means of a piston valve 122 can be put into communication either with a passage 126 leading to a chamber 109 into which the port 102 opens, or with a passage 128 leading to the port 106. The valve 122 is normally held by a spring so that the passage 118 connects with the chamber 109. The pressureof the spring 110 is thus normally augmented by the pressure of the liquid in chamber 109 acting upon the area of the plunger 113. The valve 122 is moved to its other position by lever mechanism actuated by a solenoid 66 controlled by a switch 67, Fig. 1, actuated by a dog 68 adjustably fixed on a rod 69 carried by the press member 39 carried by the ram. During the rapid downward movement of the ram, the pressure of the liquid in the chamber 46 and pipe 64a is higher than that in chamber 109 which is connected to the tank through the pipe 64 and valve 63. When the dog 68 actuates the switch 67, the valve 122 is moved to connect the passage 118 with the pipe 64a so that increased pressure is applied to the valve 108. The consequent building up of the pressure in the chamber 46 retards the ram sufficiently to allow the prefill valve 16 to close and further movement of the ram takes place at a slower speed. The change from high to low speed of the downward movement of the ram is determined by the position of the dog 68. When the valve 63 is reversed, pipe 52 is connected to thetank and the pressure liquid from the tank passes through pipe 64, valve 104 and pipe 64a to raise the ram 34 and re-open the prefill valve. The Specification, as open to inspection under Sect. 91, comprises also means for controlling- the electromagnets 90 by switches similar to switch 67 and actuated by dogs on a second rod such as 69 carried by the press member 39, one switch acting to de-energize both magnets when the ram reaches the upper end of its stroke so that the press stops, and the other switch serving to de-energize one and energize the other magnet so that the ram movement is reversed. This subject-matter does not appear in the Specification as accepted.