Patent GB-549950-A (GB)
Title: Improvements in or relating to hydraulic systems
IPC: B30B15/20
Filed: 1942-04-15
Abstract: 549,950. Hydraulic presses. ERNST, W., and LINDNER, P. April 15, 1942, No. 4946. [Class 69 (ii)] A hydraulic press having a cylinder 2, press ram 3 with an operating platen 4 is so constructed that after an initial rapid descent of the ram 3 the supply of operative liquid is restricted at a position reached prior to that at which the normal pressing stroke is supposed to begin and me pressure is again increased only when a predetermined resistance is encountered by the ram before the latter reaches the end of the advancing stroke. The stroke is finally reversed at a predetermined high pressure and if reversal does not occur before the ram reaches the end of the normal pressing stroke the ram is slowed down. The press may be stopped in case of emergency, and on reversal the ram moves during one portion of its stroke at low speed and during another portion at high speed. As applied to a press in which a reversible variable displacement pump 6 is employed for delivering the pressure fluid through a pipe 5 and retraction fluid through a pipe 7, the direction of rotation and :speed of the pump is controlled by a rod 81 with a plunger acted upon by a spring 82 in a casing 80, and a lever 77 pivoted to the rod 81 and to a link 78 pivoted to an arm 79 fixed to the casing. The lever 77 is pivoted to a rod 75 the position of which controls the rotation and speed of the pump, and the rod 75 is itself controlled by a piston 74 to which it is connected, and the piston 74 is moved to various positions by means of fluid pressure derived from a source 24 and distributed under control of valves 18, 32, 27, 37 to the cylinder 53 in which the piston 74 moves, and to attached cylinders 50, 55 in which move other pistons 67, 70 and 83 which control the position of the piston 74 and rod 75. The valves 18, 32, 27, 37 are normally closed by springs arranged in cylinders with bleed ports, and are opened by electromagnets 17, 35, 30, 40 which are energized in desired sequence under control of switches 16, 93, 94, 96, 98 operated by projections 92, 95, 97 on the platen, and by switches 8a, 15a operated by low and high pressure hydraulic valves 8, 15 connected to surge tank 9, in which is arranged a surge valve 10, and to the inlet conduit 5. The valve 8 is of the kind described in Specification 519,824, [Group XXXVII], and a pump byepass valve 14 is of the kind described in Specification 540,166. The electromagnets 17, 35, 30, 40 are operated under control of a starting switch 103, an emergency switch 131 and other switches operated by electromagnetic relays with solenoids 104, 115, 125, 134. Starting at the normal inactive or neutral position -of the pump 6 and with the ram an raised position and with the various switches in the position shown in Fig. 2 and with the valves 18, 32, 27, 37 all closed, the switch 103 is closed and the solenoid 104 energized to close switches 109, 111 which respectively close circuits to maintain the solenoid 104 energized and to energize the solenoid 30. The valve 27 is thereby opened and pressure fluid from source 24 passes via pipe 63 to the left of piston 74 which is moved to the right to operate the pump 6 so as to deliver liquid to the press at full delivery and the ram descends until switch 16 is closed by projection 97-causing energization of solenoid 17 and opening of valve 18 which delivers pressure fluid via 'pipe 66 to the right 'of piston 67. As this piston is of larger area than piston 74 the movement of piston 67 to the left causes its rod 68 to engage and overcome piston 74 moving it to the left and so moving the lever 77 to cause the pump to act with a restricted output and the movement of the ram is slowed down. When the pressure builds up owing to engagement of the ram with the work, the switch 8a is opened and solenoid 17 de-energized thus permitting the piston 74 to return to a position which causes the pump to operate with full output. This continues until a predetermined high pressure is built up in the upper portion of 'the cylinder bore 2 whereupon the high pressure control valve 15 actuates switch blade 15a to break the holding circuit for the solenoid 104 thus de-energizing solenoid 30 and cutting off pressure from the piston 74 and permitting the spring 82 to reverse the pump 6 which starts a quick return movement of the piston. Should the switch 45a fail to be operated before the platen moves to such a position 'that an arm 95 on the platen engages a switch 96, then the opening of the switch 96 operates in the same way as the switch 15a to cause the reversal 'of the piston. When the platen has been raised until its arm 92 closes a switch 94 the solenoid 40 is energized to open valve 37 and permit pressure fluid to pass to the left of a piston 83 which shifts the piston 74 and its rod 75 to a position in which the pump operates at slow speed to raise the piston. Finally the pump is returned to neutral position by the raising of a spring-depressed push-rod 87 by means of the platen arm 92, the rod 87 having a collar 86 which acts upon the rounded end 85 of lever 77. An emergency stop switch 131 is provided which causes actuation of the valve 32 which acts to stop the press, and by actuation of the switches described the press can be set to move forwards or to retract. By means of valves 21a, 26a the means for operating the emergency valve and the slow down retraction valve may be cut out. In a modification the pistons 70, 83 are dispensed with and the means for slowing down the retraction stroke of the press ram is omitted. In place of the piston 83 a latch is provided and is projected into the bore of the cylinder to stop the piston 74 in the position corresponding to the neutral position of the pump when the emergency control valve is operated to cut off the fluid pressure from the cylinder of the piston 74. In a further modification a one-way variable delivery pump is used and the supply of liquid to the press is controlled by a four-way valve operated by a solenoid to control the direction of movement of the ram or to cause the ram to be stationary. The rate of delivery of the liquid and the rate of movement of the ram is controlled by a restrictor valve operated electromagnetically. The energization of the control electromagnets is controlled in a manner similar to the control of the valves 18, 32, 27, 37 of the first modification.