Patent GB-871019-A (GB)
Title: Overload relief device for power presses
IPC: B30B15/28
Filed: 1957-06-28
Abstract: 871,019. Mechanical presses. DANLY MACHINE SPECIALTIES Inc. June 28, 1957 [Oct. 31, 1956], No. 20431/57. Class 87(2). [Also in Group XXII] A power press having an overload relief system comprising piston and cylinder units transmitting stress between stressed members and a member to which each stressed member is connected, has a system, common to the cylinders, supplying fluid thereto under the control of a corresponding valve assembly, each said valve assembly being responsive to a predetermined pressure difference between the cylinder and the common system. As shown diagrammatically in Fig. 2, four press tie rods 12, 14, 16, 18 are each fitted with a piston 24 which is contained in a fixed cylinder 30. Oil under pressure is supplied to the cylinders 30 from a main supply pipe 94 through valve assemblies 32, 34, 36, 38, the operation of which is similar. The oil is forced by a pump 96 through suitable valves and is kept under the requisite pressure by a pressure accumulator 114. If the strain in one of the tie rods becomes excessive its piston moves and forces oil out of its cylinder into one of the valve assemblies, which operates to open a relief port. The consequent drop in pressure through the rest of the system causes the other valve assemblies to operate and thus to result in corresponding overload relief in the other tie rods. Each of the valve assemblies 32-38 comprises a body 40, Fig. 3, in which is a bore 42 open at one end (the left-hand end as shown) to the appropriate cylinder 24 and closed at the other end except for the oil pressure inlet 68. A hollow piston 48 fits in the bore and is urged to the left by a spring 54, where its head presses on a seat 53. The bore 42 has annular enlargements 60, 74. In normal operation the piston blocks communication between the annuli 60, 74 and oil under pressure passes through openings 72 in the wall of the piston and through a passage 76, past a check valve 78, into the cylinder 24. When excessive pressure in the cylinder 24 forces back the piston 48 against the spring 54 a passage is formed connecting the annuli 60, 74 and the oil passes into the annulus 60 and thence to a relief pipe 64. The passage starts to open before the head of the piston is clear to permit earlier relief of the system pressure. The rightward movement of the piston 48 also operates a switch-actuating pin 180, by cam action, and stops the press. The accumulator 114 comprises a piston 120, of large area, in a cylinder 116 and a piston 122, of small area, which moves with the piston 120 and in a cylinder 118. A pump 127 supplies compressed air, through suitable valves, below the piston 120 as seen in Fig. 3, and the difference in piston areas magnifies the pressure imposed on the oil in the pipe 94. The air pressure is regulated by limit switches 152, 154. A rod 140 projects upwards from the piston 120 and if the air pressure drops a finger 144 closes the switch 152. The circuit of the motor 132 which drives the pump 127 is thus closed, and also that of a holding relay 168; thus as the piston 120 ascends again with increasing air pressure the pump 127 continues to operate until the finger 146 opens the limit switch 154 and breaks the motor circuit. In Fig. 4 the overload pistons and cylinders, instead of being in the tie rods, are between the operating links 186, 188 and the press slide 184, the pistons being indicated by 214, 216 and the cylinders, carried by the slide 184, by 210, 212. The relief valve assemblies are shown at 232, 234. Pressure oil is drawn from a reservoir 236 formed in, or carried by, the slide 184. The hydraulic circuit is similar to that shown in Fig. 2, the same reference numerals being used. Fig. 4 also shows means for adjusting the position of the slide 184 which comprise nuts 206, 208, screw-threaded on pins 202, 204 which project from link connecting heads 198, 200, the nuts being enclosed in housings 228, 230 bolted to the pistons 214, 216. Worms, not shown, rotate the nuts 206, 208 to adjust the position of the slide 184 on the press frame.