Patent GB-643847-A (GB)
Title: Plastics molding machine
IPC: B29C45/56
Filed: 1946-10-07
Abstract: 643,847. Moulding thermoplastic materials. TRIGGS, W. W. (Improved Paper Machinery Corporation). Oct. 7, 1946, No. 29831. [A Specification was laid open to inspection under Sect. 91 of the Acts, Nov. 22, 1947.] [Class 87 (ii)] [Also in Group XXIX] A moulding machine comprises a horizontal injection unit A and a vertical die-holder and compression unit B and can be used (a) for injection moulding with or without sprue shearing; (b) compression moulding, hot material being fed to the die cavity and subsequently compression moulded; (c) combined injection and compression moulding with or without sprue shearing. Injection unit.-Material is fed to the injection cylinder 10 from a hopper 54, Fig. 2, by a piston 50 with a cut-away portion 52 reciprocated by an arm 64 attached to the injection. ram 12. The ram 12 is reciprocated by a hydraulic piston 38 working in a cylinder 34. A small auxiliary piston-cylinder arrangement 90, 94 enables rapid initial movement of the ram to be made by injecting fluid at low pressure through conduit 96, fluid being drawn into the main cylinder from a reservoir 98 through a spring-loaded valve 100. The final stage of injection moulding is effected by high-pressure fluid acting on the large face of the piston 38 through the small orifice 91 in the fixed piston 94. Retraction is effected by fluid pressure acting on the small opposite face of the piston 38 through conduit 104, a line 108 feeding pressure fluid to the valve 100 to unload it and allow the reservoir 98 to refill. The whole injection unit can be reciprocated on its bed on guides 66 by a hydraulic piston and cylinder 80, 78 to move the injection nozzle 20 up to and away from the dies. The cylinder 10 and torpedo section 14 are heated by thermostatically controlled electric heaters. Vertical die-holder and compression unit (Fig. 4).-Fixed lower and movable upper platens 150, 152 are mounted on strain rods 154, the upper platen being movable by a double toggle arrangement 156 operated by a hydraulic piston and cylinder 180, 178 in a head 158. The position of the head is adjustable by nuts 160, 190. The lower platen is pierced to provide a cylinder 230 in which works a ram 232 reciprocated by a hydraulic piston and cylinder 214, 212. The cylinder has a base 206 and carries lugs 204 on which the strain rods 154 and entire platen structure are adjustably supported. Rapid adjustments of the platen structure may be made by removing the ram 232, interposing a spacer between the piston-rod 218 and lower platen, slackening the nuts 208 and 210, suitably operating the hydraulic cylinder 212 and finally resetting and tightening the nuts 208, 210. A similar adjustment may be made to the upper platen 152 and head 158 only by using a spacer between the ram 232 and upper platen and slackening the nuts 160, 190. The upper and lower platens carry means for securing upper and lower dies 172, 174 thereto. A fixed head carrying ejector pins is also provided. Compression moulding (Fig. 6).-The injection unit is brought up to the vertical unit, the nozzle 20 coming up against a mating surface at one end of a feed opening 256 formed between the lower die and an intermediate die member 254. Material is then fed by the injection unit into the die cavity 260 and the ram 232, which carries a ram 264 supporting the male portion 266 of the mould is then moved up to mould the material against the female die 258. Vents 270 are provided for gases to escape. In so doing the ram cuts off the feed opening 256. The lug remaining in the feed opening is removed when the injection unit is retracted. In a modification the end of the injection nozzle comes up flush with the wall of the cavity 260 so that no lug is produced. To remove the moulded article the upper platen and die are raised and the ram 264 simultaneously or subsequently lowered. Injection moulding with sprue shearing (Fig. 12).-The ram 232 carries a chuck 316 which holds shearing elements 320-one for each mould cavity. These elements pass up through the dies and intersect the sprue channels leading to the die cavities. Near their tops the elements have apertures which form continuations of the channels when the elements are in their lowest position to allow the die cavities to be filled. After injection but before substantial hardening can occur the ram is raised to shear the sprues, the faces of the shearing elements adjacent the die cavities eventually forming a part of the surfaces of the cavities so that subsequent finishing operations are unnecessary. On reaching the top of the stroke of the shearing elements their apertures communicate with channels 328 and the trapped part of the sprues are ejected by compressed air. It is stated that the shearing action has a slight compression effect on the material in the die cavities. Combined injection and compression (Fig. 18A).-The male parts 364 of the moulds are carried in a block 360 and are a sliding fit in the female parts which are split, the separate portions being carried in the split dies 366, 368. Shearing elements 376 are carried on a rectangular plate 356 on the end of the ram 354 operated by the piston 214 (Fig. 4). After injection and shearing the sprues the plate 356 abuts against the block 360 forcing the male parts of the mould into the female parts, a slight clearance 382 being provided for this purpose, thus effecting compression of the moulded article. After hardening, the dies are opened and the ram retracted as before. Operation and control.-The hydraulic system for the operation of the machine comprises a pair of dual purpose (high and low pressure) pumps driven by a single motor, one supplying high and low pressure liquid for the injection and compression rams and high pressure liquid to assist in the action of the die-clamping cylinder 178 and the other supplying low pressure liquid for the operation of the pilotoperated control valves and high pressure liquid for the die-clamping cylinder. The control valves are solenoid-controlled or solenoidoperated and the electric circuit for the control of the solenoids may be set for automatic or hand working. In the former four timers are provided and a switch to throw the cylinder operating the compression ram into and out of use. With compression, one timer controls the injection period, one the compression period and one byepasses the high pressure side of the pump supplying the injection ram, when injection is completed. Without compression the compression timer is not used and the fourth timer controls the opening of the dies which are otherwise opened at the end of the compression period. In hand operation an electrical-interlock is provided to prevent bringing the injection unit up to the dies before the dies are closed. A mechanical interlock is also provided to prevent the valves controlling both up and down movement of the upper die from being open at the same time. In both automatic and hand operation two master switches are provided to prevent any operation unless the safety guard of the die clamping unit is down. Heat control of the dies (Fig. 9).-The dies are provided with channels for the circulation of heating and cooling fluid, the same channels being used for both, the fluids being circulated by pumps 280, 290 and passing through a cooler 281 and heater 291 respectively. Two interlocked valves 285, 295 are provided to connect the dies either with the heating circuit or the cooling circuit and to byepass the other at appropriate times in the moulding cycle. The Specification as open to inspection under Sect. 91 describes a turret arrangement, Figs. 21 and 24 (Cancelled), in which an injection unit A<SP>1</SP> is mounted at the centre of a circular track on which revolves a number (three as shown) of die-holder and compression units C, D, E rigidly connected by girders 400 and driven by a stationary hydraulic motor with a pinion engaging a rack connected to the units C, D, E. On one of the girders are mounted an electric motor and pump 410 for supplying pressure liquid to the various die-clamping and compression ram cylinders. As each platen unit C, D or E comes opposite the injection unit a T-headed projection 436 on the unit engages a corresponding socket 426 on the injection unit to hold the two securely together during injection. At the same time a spring-returned hydraulic valve 438 on the end of the injection unit is closed by a cam 440 on the platen unit to stop the hydraulic motor rotating the three units C, D, E, and a cam 467 on the platen unit operates a switch 466 on the injection unit to start the unit forward and initiate the injection cycle. This switch is connected across the safety-guard switches of the other arrangement. A solenoid 448 is mounted on the end of the injection unit to operate a valve 444 on the platen unit controlling the upward movement of the compression ram. The solenoid may be manually operated or incorporated in the automatic electric circuit for operation after injection is complete. After injection (and compression, if used) the rotary unit is started moving again by byepassing valve 438 by a manually-controlled valve until valve 438 reopens, due to the rotation of the units C, D, E, allowing the next platen unit to come opposite the injection unit. The opening and closing of the dies of each platen unit is controlled by fixed cams 450, 456 positioned just before and just after the unloading station, operating a valve 442 on each unit. It is also stated that thermocouples may be mounted within the dies to prevent actuation of the injection means unless the dies are at the proper temperature. This subject-matter does not appear in the Specification as accepted.