Patent GB-690163-A (GB)
Abstract: 690,163. Machinery guards. BROUGHTON & SON (ENGINEERS),. Ltd:, J., and BROUGHTON, G. J. Feb. 23, 1950 [Feb. 23, 1949], No. 4890/49. Class 80 (iv). A guard for a press or bending brake in which the workpiece lifts during the operation thereon, is adapted to be lifted during each cycle of operations by a fluid control system operatively associated with the ram of the machine. A pneumatic control system for a press is shown diagrammatically the guard being indicated at 10 supported on a pivoted beam 11 having at its other end a pneumatic balancing cylinder 13 and an actuating cylinder 12. A starting valve 26 when actuated by the operator, by for example the usual foot pedal, supplies air pressure from a supply conduit 17 to a transfer valve 35 and then to the cylinder 47 of a relay unit 27 while it also exhausts a conduit 49 to operate a change-over valve 30. A valve 52 of the relay unit 27 is operated through a trip catch 51 which passes air pressure to a control valve 24 which is operated to exhaust the air from the top of cylinder 12 to allow the guard 10 to descend. As soon as the guard has reached its closed or safety position a valve 31 is operated by a cam 32 on the arm 11 to supply air pressure to a cylinder 60 of a guard locking mechanism 33 to hold the guard closed. Simultaneously a lever 38 of a control valve 25 is moved to supply air to an operating cylinder 22 of the machine clutch whereby the crankshaft 21 of the machine is driven and the ram descends upon the workpiece. Before the working stroke is actually completed a cam 63 on the crankshaft 21 actuates a valve 28 which supplies pressure to operate the change-over valve 30 which in turn actuates the control valve 24 which exhausts the air from the guard lock mechanism 33 and the piston 12. of the guard operating mechanism to allow the guard to lift to allow for the upward deflection of the workpiece. The guard continues to lift whilst the ram is on its return stroke. Before the crankshaft reaches its top dead centre position the cam 63 actuates a valve 34 which supplies air pressure to operate valve 25 which releases the pressure in the clutch operating cylinder 22 to disengage the clutch and apply the brake normally provided to arrest the crankshaft in a position ready for another working operation. Running the above cycle of operations the operator must maintain pressure on the starting lever or pedal or the second operation of the change-over valve 30 will be prematurely effected resulting in the lifting of the guard and disengagement of the machine clutch. The starting lever or pedal must be released however in order to exhaust the cylinder 47 of the relay unit 27 before a second cycle of operations can be initiated. For '' inching " operations a manually operable lever is provided for setting the transfer valve 35 in a position in which the guard is not closed during such operations and this lever also switches on a warning light when the transfer valve is in this position. In order to prevent rapid descent of the guard should the air supply fail a safety lock 18 is provided which is normally held inoperative by the pressure in a cylinder 19 but if the supply fails moves to engage the arm 11. The actual point in the movement of the ram at which the guard commences to lift can be varied by adjusting the relative position of the follower 64 of the valve 28 with respect to the high part of the cam 63.