Patent GB-637676-A (GB)
Title: Hydraulic press
IPC: B30B15/16
Filed: 1947-08-05
Abstract: 637,676. Hydraulic presses ; working valves. OIL GEAR CO. Aug. 5, 1947, No. 21269. Convention date, Nov. 25, 1940. [Class 69 (ii)] [Also in Group XXVIII] A hydraulic press comprises a main cylinder and a rapid traverse cylinder and rams 8 and 6a respectively associated therewith, a pump 21 connectable to both cylinders, a decompression valve 120 fitted to the main cylinder and means 71, 72 for operating a control valve 56, the means 71, 72 being actuable to direct liquid from the pump 21 to the main cylinder and from the rapid traverse cylinder to the pump 21 to cause the press to perform a working stroke and means, such as switches LS2 or PS2 operable at the end of the stroke to cause the control valve 56 to stop delivery of the liquid to the main cylinder ; in addition, means, such as gear pump 51, are provided for opening the valve 120 to permit liquid to escape from the main cylinder to reduce the pressure therein ; pressure-responsive means, such as switch PS1, are also provided whereby on pressure reduction in the main cylinder a return stroke is initiated by valve 56, at the completion of which delivery of the pump to the rapid traverse cylinder is stopped. The press platen 3 has two rapidtraverse pistons 6 and 6a in addition to the ram 8 attached thereto and when the press is idle, the parts are as shown in Fig. 1, and the weight of the platen and other moving parts causes pistons 6 and 6a to create a pressure beneath them which extends through a channel 85 to the port 84 of a resistance valve 82, thereby tending to move to the right the piston 87 of valve 82. However, the pressure at port 84 traverses the valve portion 86 of piston 87, a pressure-responsive valve 93 and conduit 101 to the right-hand end of piston 87 so that the tapered end of the piston is held against a valve seat 89 and the platen 3 cannot descend. When the reversible variable-delivery pump 21 and the pump 51 are started, pressure from the latter extends to the right end of one of the displacement control-cylinders (see Group XXVIII) of the main pump 21 via conduit 52, valve 56 and conduit 63 to hold the pump at zero stroke since the smaller left-hand cylinder 41 is permanently under pressure from pump 51. Liquid in conduit 52 also passes through a conduit 127 and throttle valve 128 and moves to the left the valve member 121 of valve 120. A starting switch is then closed to energize solenoids 71 and 118 ; solenoid 71 moves the valve member 57 of valve 56 to the left so that pump 21 discharges into a channel 25 and conduit 127 is vented so that valve 120 moves to the right and blocks a conduit 25b. Energization of solenoid 118 causes the valve member 111 of a pilot valve 110 to shift and join its ports 113 and 114 so that the pressure underneath pistons 6 and 6a will move piston 87 to the right and move the tapered part of piston 87 away from seating 89. Liquid from the right of piston 87 is exhausted through a throttle valve 116. If resistance to the downward movement of the platen is sufficient to prevent it from descending by gravity, pump 21 will tend to discharge through a resistance valve 33 into a reservoir 31, the resistance of which valve causes pressure to rise and liquid to flow through a channel 35 and move leftwardly a differential valve 34. The liquid now delivered by pump 21 into channel 25 will no longer flow to the reservoir, but will cause pistons 6 and 6a to move downwards at high speed, whilst the liquid beneath these pistons will be passed through valve 82 to the input of pump 21, which latter draws the additional liquid it requires through channel 26 from reservoir 31. If the platen 3 and other parts are of sufficient weight to descend by gravity the liquid discharged by the pistons 6 and 6a flows into channel 26 where a part will tend to return to the reservoir 31 through valve 33, but is prevented from doing so' since valve 34 is in the position of Fig. 1, so that the pump 21 meters all the discharge to cause the pistons 6 and 6a to descend at high speed, additional liquid being taken by the pump from the reservoir via channel 25. As soon as the platen moves downwardly, an actuator 135 permits closure of a limit switch LS3 and the ram 8 is supplied with liquid from a surge tank 16 through a surge valve 10. If switch LS1 is not operated before the platen engages the work, the pump pressure will rise and open another resistance valve 37 so that liquid enters a surge-valve operating-cylinder 17 and causes valve 10 to move and cut-off communication between the tank 16 and ram 8, in order that liquid from the pump 21 may be directed through channel 25 and a conduit 25a to move the platen 3 at a slow speed, since the liquid is acting upon the combined areas of ram 8 and pistons 6 and 6a. The engagement of the platen with the work or the closure of valve 82 due to the operation of a limit switch LS1 will then as before cause valve 34 to shift leftwardly. The downward movement of pistons 6 and 6a causes pressure to rise in channel 85 and actuates the valve 93 so that piston 87 moves and thus permits the liquid underneath the pistons 6 and 6a to return to channel 26. Since the pressure to shift valve 93 is at least as great as the pressure required to open valve 37 the platen 3 commences the slow-speed part of its stroke before valve 82 opens. Pressure switch PS1 is adjusted to break the circuit to a solenoid 72 when the pressure is sufficient to open valve 37 so that solenoid 72 cannot initiate an upstroke when switches PS2 or LS2 are operated. Platen 3 will continue to move at slow speed until either switch LS2 or PS2 is operated, depending upon the adjustment of the press, so de-energizing solenoid 71, whereupon pressure on the ram 8 drops as a result of the pump displacement being adjusted to zero, thereby enabling switch PS1 to close and energize solenoid 72, so shifting the valve member 57 to the right in order that the pump 21 may discharge into channel 26. If limit switch LS1 has not been operated or is not employed, solenoid 118 is also de-energized. The platen will be raised by pistons 6 and 6a after a rise in pressure has caused actuation of the valve 10 to enable the liquid over the rain 8 to be ejected into tank 16. If switch PS2 is effective it will operate as soon as pressure on the ram 8 is reduced, and bring about deenergization of solenoid 72 so that valve member 57 is returned to the neutral position shown in Fig. 1. The valve 120 is held open by gear-pump pressure until another cycle is initiated or the pump stopped.