Expansion injection molding process on machine with all electric drive system involves piston compression of melt, oil and accumulator gas and injection of compressed melt by opening valve at set pressure

摘要

The injection unit has a closed hydraulic system and pressure accumulator(7). A piston(6) of a hydraulic operating cylinder(5) connected to the melt injection unit(3,4) is actuated by a threaded spindle(12) and electric servomotor(13). During an injection cycle the piston compresses the melt(V1), oil(V2) in the injection cylinder and operating cylinder and gas(V3) in the accumulator. When melt pressure at the front of the screw tip reaches a set level a valve(15) is opened and compressed melt is injected into a tool cavity(21). Control of pressure during the holding and metering phase is effected by movement of the piston(6) in the operating cylinder(5). A slide valve(22) in a connecting line between the accumulator(7) and operating cylinder(5) closes the connection after the tool has filled and before application of holding pressure to prevent further pressure drop in the accumulator. The slide valve reconnects the operating cylinder and accumulator again when pressure in the operating cylinder and accumulator during the compression phase are equal. Slide operation and pressure balance are governed by sensors(26,27). Constant oil temperature is maintained by cooling jackets(19) around the injection cylinder(3) and operating cylinder. Piston diameter in the operating cylinder is greater than the screw(2) diameter, but smaller than the injection cylinder piston diameter. Both injection and operating cylinders may be combined in a single cast block.