GB855360A - Improvements in hydraulic presses with valves operated by servo-motors - Google Patents

Abstract

855,360. Hydraulic presses. SCHLOEMANN A.G. March 21, 1958 [April 20, 1957], No. 9179/58. Class 69 (2). In a fine control for an hydraulic press, the pressure and exhaust pipes 18 and 19 are connected to the withdrawal cylinder 10 by pairs of valves RES, REL, RAS, RAL in parallel, the valves RES, RAS permitting a quick flow of liquid relative to valves REL, RAL. When the press ram 1 nears one of its required final positions, the corresponding quick flow valve is closed, enabling the ram to be positioned accurately with the use of the low flow valve. Valves PE, PA control the pressure and exhaust pipes to the working cylinder 4. The hydraulic circuit which controls the various valves is shown in Fig. 3. Each valve is connected to a servomotor 30 PE, for example, to which corresponds a slide valve 32 PE, which can be shifted in an upward direction by an electromagnet 34 PE. In order to start the pressing operation, magnets 34 PE, 34 RAL, 34 RAS are energized by manually closing switches and valves 32 PE, 32 RAL, 32 RAS are therefore lifted. Pressure liquid flows from line 75 to servomotors 30 REL, 30 RES. It then passes via valves 32 RAS, 32 RAL to the underneath of servomotors 30 RAS, 30 RAL which rise to open valves RAS, RAL. Since the pressure liquid can only pass servomotors 30 REL, 30 RES when they are in their lowest position, valves RAS, RAL cannot be opened unless valves RES, REL are both closed. The pressure liquid then flows via the open valve RAS and valve 32 PE to the underneath of the servomotor 30 PE to open valve PE. Pressing then commences under the control of throttle valve DR. After the pressing operation is complete, the magnets 34 PE, 34 RAS, 34 RAL are manually de-energized, and the underneaths of servomotors 30 PE, 30 RAS, 30 RAL are connected to exhaust via lines 61, 57, 64, closing valves PE, RAS, RAL. If fine control is required, the switches S/RAS, S/RAL are used (see below). In order to withdraw the press, magnets 34 PA, 34 REL, 34 RES are manually energized. Pressure liquid flows via servomotor 30 PE and valve 32 PA to raise servomotor 30 PA. Since the liquid can only pass servomotor 30 PE when it is in its lowest position, valve PA can only be opened when valve PE is closed. Liquid then flows via the raised servomotor 30 PA and valves 32 REL, 32 RES to the underneath of servomotors 30 REL, 30 RES to open valves REL, RES. At the end of the withdrawal stroke, abutment 11 actuates switch S/RES and magnet 34 RES is de-energized, closing valve RES. Withdrawal then continues at a reduced speed, pressure liquid flowing to withdrawal cylinder 10 via low flow valve REL, until abutment 11 actuates switch S/REL, closing valve REL. The stopping of the pressing stroke may also be effected in two stages in this way by automatic actuation of the switches S/RAS, S/RAL. Specification 838,740 is referred to.