GB800223A - New or improved control for power presses and other machines - Google Patents

Abstract

800,223. Machinery guards. PRESS GUARDS, Ltd. March 16, 1956 [March 16, 1955], No. 7625/55. Class 80 (4). In a mechanical or fluid-pressure press, or other machine, which is caused to make a single operative stroke by the automatic actuation of a clutch, valve or other means when a poweroperated guard completes its closing movement, a control mechanism is provided whereby the guard-closing means is energized automatically at regular and predetermined time intervals. In the control mechanism shown in Fig. 1 the guard (not shown) is closed by an air cylinder (not shown) connected through a pipe line G to an air supply union 26 through a valve 25 which is opened by a cam 34 on a crosshead 17 reciprocable on rods 18. The crosshead 17 is actuated by a piston in a cylinder 10 whose opposite ends are alternately supplied with air by a reversing valve 22. The valve 22 is actuated by air pressure through a reducing connector 27 and pilot valves 20, 21 which are alternately opened by pegs 19 on the crosshead 17. The crosshead 17 is coupled to a piston in an oil cylinder 13 connected to an oil reservoir 16 through one-way restrictor valves 14 adjustment of which varies the speed of the crosshead 17 and so varies the time interval between successive actuations of the guard-opening valve 25. The cam 23 is of wedge shape and is transversely adjustable to vary the period during which the valve 25 is held open. The valves 20, 21 may be replaced by limit switches controlling a solenoid or solenoids actuating the valve 22. Alternatively the valves 20, 21 may be replaced by a single double-acting valve, which may be operated through a throw-over spring toggle device. The guard may be locked in the closed position by a lever coacting with a cam on the press crankshaft, the lock being released as the crankshaft passes bottom dead-centre, or as it reaches top dead-centre. The control mechanism is mounted on a bracket 28 for fitting to an existing press, and may control a number of presses. In modifications, a guard-closing air valve is intermittently opened by a cam driven through hydraulic or other variable speed gear by an electric motor, or by a press flywheel. In the control mechanism shown in Fig. 5, an air supply pipe 40 is connected through a guardclosing valve 42 and emergency stop valve 52 to a guard-closing cylinder (not shown), and is also connected through a reducing valve 44 to a valve 45 actuated by a cam on a press crankshaft, or a cam on the press slide. In the top dead-centre position shown the valve 45 is closed and air is supplied through valve 42 to close the guard and start the press. As the crankshaft rotates the valve 45 is opened to admit air to the upper end of a cylinder 49 whose piston 50 is thus depressed and closes valve 42, oil below the piston 50 being moved freely past a one-way restrictor 51 into a reservoir 41. At the completion of a press stroke the valve 45 is closed and air pressure in the oil reservoir 41 slowly raises the piston 50 to reopen valve 42 and start another cycle after a time interval determined by the adjustable oneway restrictor 51. In a modification a guardclosing valve 61, Fig. 6, supplying air to a guardclosing cylinder through an emergency stop valve 62, is opened by a head 63 on the rod of a piston 64 in a cylinder 65 whose lower end is connected to the air supply and whose upper end is connected to an oil reservoir 67 through a one-way adjustable restrictor 66 restricting oil flow towards the reservoir. The head 63 is engaged by a fork on a bracket 68 adjustably mounted on a press-slide, shown at top deadcentre. When the air supply is turned on, air flows through valve 61 to close the guard, whereupon the press starts and the bracket 68 moves the head 63 to allow the valve 61 to close. When the press slide and the bracket 68 return to their uppermost positions, the head 63 is left behind but is slowly raised by the air pressure acting on piston 64, the rate of return being controlled by the restrictor 66, which thus determines the time interval before the head 63 reopens the valve 61 to start another cycle. Instead of being actuated by the bracket 68, the head 63 may be moved by mechanism actuated by the press crankshaft.