GB839572A - Improvements in and relating to presses - Google Patents

Abstract

839,572. Screw presses. SCHWARZ, E. Nov. 13, 1956, No. 34738/56. Class 87(2). A screw press of the type in which friction discs selectively engage a disc on the screw spindle to raise or lower the ram is controlled by an electro-fluid-pressure system incorporating starting switches and a time-delay relay with an adjustable duration of operation. The ram 3 of the press is carried on a spindle 4 which is screw-threaded through a yoke 2 and also carries a spindle disc 5. Friction discs 8, 9 are mounted on a shaft 7, driven from a motor 10, which can be moved from side-to-side to cause one or other of the discs 8, 9 to drive the disc 5. Both of two push-button switches 30 are closed, requiring the use of both the operator's hands. The switches 30 are in series with one another and with a solenoid 27 and the low-tension winding 26 of a mains transformer. The solenoid 27 closes contacts 29, 28, completing respectively a circuit from the mains through a time relay 31 which closes a mercury switch 32, and a circuit through the contacts of a solenoid 21, the mercury switch, and the low tension winding 26. The solenoid 21 opens a valve 23 and compressed air from a container 19, passing through a pressurereducing valve 20, passes through an air line 18 to a cylinder 17 and moves a piston 16 to rock an arm 12 so moving the shaft 7 in a direction which engages the friction disc 8 with a spindle disc 5. At this, the ram 3 moves down on its working stroke. The time relay 31, having run down in the time to which it was adjusted, opens the switch 32 and de-energizes the solenoid 21, thus allowing the spring 24 to close the valve 23. With air pressure removed from under the piston 16, a spring 13 rocks back the arm 12, changing the drive to the disc 5 from the friction disc 8 to the friction disc 9 and causing the ram 3 to rise. Near the top of its stroke the ram 3, through a lug 35, raises a finger 34 and with it a rod 33 which results in the pull of the spring 13 being just sufficient to hold the disc 9 against the disc 5 with a pressure such that the ram 3 remains stationary. The rod 33 extends downwards for adjustment purposes during erection. Retardation is applied to the ram near the top of its stroke by the closing of a limit switch 36 by a cam 38 on the ram, whereby a relay 40 is caused to close contacts 41, 42 through the second of which the solenoid 21 is re-energized, so operating the valve 23 and moving the discs 8 and 9 again so that the disc 8 engages the disc 5 with an opposing motion. A time relay 44, set in motion by the closing of the contact 41, runs down and opens its switch 43, whereupon the solenoid 21 is deenergized and valve 23 changes over. A separately constructed brake may be used, Fig..4, .wherein brake levers 48 are rocked about pivots 47 to press against the disc 5 from opposite sides. When the ram nears the top of its stroke it causes a limit switch to operate a solenoid 52 which controls a compressed air cylinder 49, the piston of which moves the levers 48. If the pneumatic system fails a spring 53 operates to apply the brake.