Patent GB-557033-A (GB)
Title: Improvements in and relating to hydraulic presses
IPC: B30B15/24
Filed: 1942-12-31
Abstract: 557,033. Hydraulic presses. FLOWERS, P. E. Dec. 31, 1942, No. 18597. [Class 69 (ii)] In a hydraulic press in which a pressure platen 8 is operable by plungers 6, 7, means are provided for changing the supply of liquid to the cylinders 4, 5 should tilting of the platen occur due to unequal stresses. The means for changing the liquid supply may be valve means controlling the supply of pressure fluid from a single source of supply, or as shown the cylinders 4, 5 are supplied by separate adjustable and reversible pumps 21, 21a controlled by servomotor mechanism 26 of the kind described in Specification 535,625, in which movement of valve rods 27, 27a shifts the flow control rings of the pumps so as to change the quantity and direction of the pump output. The actual control is governed by the relative movement between the platen 8 and a reference bar 95 which moves with the platen to which it is connected by a universal joint but which maintains its horizontal movement throughout. A plunger 96 is attached to the bar 95 and is arranged to slide in a gland 94 attached to a control cylinder 91 formed in the platen 8. The cylinder 91 can be supplied with fluid through a shut-off valve 114 and its volume is controllable by a screw 115. Should the platen tilt so that its left end is lower than the right the pressure in the cylinder 91 will be lowered, and consequently a spring-pressed plunger 98 which projects through, a gland 100 into a bore 97 connected to the cylinder will be depressed so as to cause a cam 101 on it to actuate one or other of three switch arms 102, 103, 105 in circuits which control the supply of liquid to the press. The circuits are governed by a starting switch 71 which energizes an electromagnet 69 to close a main switch with blades 64. 65, 66. The blade 64 closes a holding circuit for the electromagnet 69. The blade 65 causes energization of electromagnets 81, 81a which actuate three-armed levers 83, 83a connected by lever-and-link mechanism to the rods 27, 27a of the servomotor controls which are started by outward movements of the rods to set the pumps in motion. The lever-andlink mechanism comprises a link 31 formed of an outer cylinder 31 movable relatively to an inner member 36 with a piston 35 over which the end of the cylinder 31 can slide. An electromagnet 55 attached to the cylinder 31 is energized when the cam 101 actuates the first switch arm 102, and this causes outward movement of the cylinder 31 and consequent clockwise movement of a lever 30 with movement to. the left of the rod 27 and consequent diminution of liquid supply to the cylinder 4 thereby tending to bring the platen back to a level position. The cylinder 31 carries a switch formed of a contact 50 on a snap-lever 45 and a contact 51. At a predetermined position a fixed latch 42 acts upon a projection 43 of the snap-lever to break the circuit to the magnet 55 and permit a spring 40 to return the link 31 to collapsed condition. The movements of the cylinder 31 are controlled in the outward direction by a check valve 33, and in the reverse direction by a choke valve 34. Should the actuation of the switch arm 102 not check the tilting, the plunger 98 may be depressed further to actuate a switch arm 104 and this causes energization of the magnet 55 and extension of the link 31 but the means for de-energizing the magnet is not operative. Should this not be effective to restore the platen a further switch arm 105 is operated and this opens normally closed switches 74, 74a and breaks the holding circuits of the electromagnets 81, 81a so that the levers 83, 83a are returned by spring action to a position in which the pumps are reversed so that the plungers 6, 7 are retracted. The plungers are normally retracted at the end of the pressing stroke in known manner by mechanism operated in response to increase of pressure in the cylinders 4, 5, and rods 89, 89a may restore the pumps to neutral position. The retraction is assisted by a valve 19 of the kind described in Specification 540,166. In a modification the plunger 92 instead of working in a recess 91 formed in the platen works in a cylinder screwed on to the platen. The platen may be operated by more than two plungers, and the correction of levelling may be operated in response to a decrease in the distance between an end of the platen and the reference bar 95 instead of an increase as described above.