GB671483A - Improvements in or relating to control means for hydraulic presses for producing plastic mouldings - Google Patents

Abstract

671,483. Hydraulic presses. COLLIER, R. Feb. 14, 1950 [Aug. 25, 1949], No. 22126/49. Class 69 (ii). Control means for a hydraulic press for producing plastic mouldings comprises a rotary element intermittently driven by an electric motor and carrying a first series of cams or the equivalent adapted to actuate in a predetermined sequence inlet and exhaust valves through which the liquid pressure medium passes to and from the press and a second .series of cams or the equivalent which are correlated with the valve actuating cams and movable simultaneously therewith, which coact with a number' of switches including some for opening the motor circuit to bring the rotary element to rest at predetermined positions in its cycle of movement in combination with one or more switches operated independently of the cams for closing the motor circuit to restart the rotary element in accordance with a cycle of press operations. Fig. 2 shows an electric motor 3 which drives a cam disc 2 carrying a first series of cams comprising cams 5-7 on one side of the disc and cams 8 and 9 on the-other side of the disc and a second series of cams on trip rollers 22-26. The cams 5-7 are arranged to operate through a lever 11 an inlet valve 13 which as best shown in Fig. 5 controls the supply of liquid under pressure from a pressure supply line 14 to an operating cylinder of a press P while the cams 8 and 9 operate an exhaust valve 17 through a lever 16b to control the exhaust of liquid from the press cylinder. The cams 22-26, as best shown in Fig. 4, co-operate with three switches 29, 30, 31. These switches are in the circuit of the electric motor which also includes a relay operated switch controlled by a push button switch, a switch operated by the insertion of a safety guard, a further switch operated either by pressure on the press cylinder or by complete closure of the press during a moulding operation and finally a time switch which is maintained open for a predetermined time. By means of these switches and the cams it is possible to control the press so that it performs the following sequence of operations : (a) slight raising of a movable die 15 so that the die clears ejector pins, (b) stopping of the die so that it can be changed and the guard be moved into position, (c) closing of the press, (d) a moulding breathing operation by opening the exhaust valve momentarily, (e) closing the mould for a curing operation for a predetermined time, (f) return of the die to its lowest position. The control arrangement is preferably enclosed in a casing placed alongside of the moulding press. Modifications are referred to in which the cams 5-9 can operate means other than levers 11, 16b. The cams may be provided on separate discs. The relay switch may be dispensed with and a switch which will remain closed for a predetermined time may be used. The cams maybe adjustable to enable different moulding materials to be used. They can be replaced by equivalent members. The invention has been described with reference to the adaptation of an existing press.