GB538247A - Improvements in or relating to fluid-operated slow-down mechanism for presses - Google Patents

Abstract

538,247. Hydraulic presses. LINDNER, P. J. April 17, 1940, No. 6975. Convention date, Jan. 11, 1940. [Class 69 (ii)] A hydraulic press is provided with fluidcontrolled means for gradually varying the speed of the plunger during a desired variable position of the retraction stroke. The press shown in Fig. 2 comprises a platen 10 provided with a plunger 8, and push-back pistons 12 mounted in cylinders 9, 13 which communicate through pipes 24, 15 with a variable-delivery pump 7. A servomotor for adjusting the pump has a control-valve in connection with a spring- urged bell-crank 41 which is connected to the armature 55 of an electromagnet 56 in circuit with contacts 61, 65. The bell-crank abuts on a push-rod 31 having a collar 37 for engaging a collar 38 on the platen. The pump-circuit includes a valve 17 formed with chambers 18, 20, 19 which are connected to the pipes 15, 24 and a tank 21 respectively under control of a floating valve 26. For controlling the return speed of the platen, the push-rod is now associated with a dashpot consisting of a piston 69 mounted in a cylinder 67 which communicates with the pump-circuit through choke-valves 83, 85, a shut-off valve 87, and a check valve 91 which permits flow only in the direction of the arrow. The piston is provided with a head 73, adjustable by a screw 72, for engaging the push-rod. The piston, when at the bottom of its stroke, is spaced from the bottom of a cylinder by a projection. To slow down the press at the beginning of the return strcke, the valves 83, 87 are closed and the valve 85 is opened. When the contacts 61, 65 close, the electromagnet 56 is energized, the pump delivers liquid to the cylinder 9, and the plunger 8 is depressed. Supplementary liquid is delivered from the tank 21 through the pipes 23, 24. The piston 69 remains in depressed position until the platen 10 engages the work, whereupon pressure builds up in the pipes 23, 24, 92, the valve 26 shifts, and the piston and thereby the push-rod are raised. When the stroke of the platen is almost complete, the contacts 61, 65 open, the electromagnet is de-energized, a spring 57 moves the bell-crank into engagement with the push-rod, the pump is adjusted to slightly beyond the neutral position, and the platen begins to return very slowly. The valve 26 again shifts to permit flow of liquid from the cylinder 9 to the tank 21, the spring 57 is effective to depress gradually the push-rod and the piston 69, and the pump is gradually adjusted to full-delivery position. To slow down the press at an intermediate part of return stroke, the valves 83, 87 are opened and the valve 85 is closed. During the down-stroke of the plunger 8, liquid can flow from the cylinder 67 through the valves 87, 91, and the piston 69 and push-rod 31 descend. When the contacts 61, 65 open, the electromagnet is de-energized, the spring 57 rocks the bell-crank 41, the pump is adjusted to full-stroke position and the platen is quickly reversed. Thereupon, liquid flows through the valve 83 into the cylinder 67, the piston 69 and push-rod 31 are slowly raised, and the pump is adjusted to slow down the return-stroke. Adjustment of the valve 83 determines the slow-down rate.