GB1454513A - Production of bodies from synthetic plastics material - Google Patents

Abstract

1454513 Injection moulding GKN GROUP SERVICES Ltd 6 June 1974 [14 April 1973] 18116/73 Heading B5A A series of articles, e.g. polypropylene preforms are injection moulded in mould means comprising a series of interconnected mould cavities 24 having an input end and an output end by accumulating a charge of material in a chamber 72, injecting the accumulated material through a nozzle 70 into the mould cavity 24a at the input end of the series, separating the nozzle 70 from the moulds, removing mould means 22, 23 from the output end and after they have been emptied inserting them at the input end of the series, engaging the empty mould cavity so formed with the nozzle, and repeating the injection cycle, there being a compensating chamber 73 connected to the accumulation chamber 72 by a cut-off valve 57 and having means to apply pressure to material therein in order to supply further material to the moulds to compensate for shrinkage on cooling, independently of the accumulation of material in the chamber 72. The mould cavities are formed by rings 23 and apertured discs 22 within a tube 19 mounted on a movable table 14 of an hydraulic mould damping unit. A ram 27 ejects the lowest ring and disc when the material therein has solidified. The top mould disc 22 is engaged by a valved nozzle 70 which is spring biased downwardly. With the slide valve 57 open a screw 36 is forced forward by a ram 47 into the chamber 72 to inject the accumulated charge through the nozzle 70 via the compensating chamber 73. The material flows through bores 54, 51 and 63. A piston 53 passes through a sleeve 52 in bore 51 and terminates in bore 63 in a head portion 65 having inclined vanes. The compensating chamber 73 is formed by the portion of bore 63 below the piston head 65 which is raised by the pressure of the material being injected against the pressure of a ram 69. After injection valve 57 is closed and the pressure of ram 69 on the material in chamber 63 supplies material to the moulds to compensate for shrinkage while the screw 36 is rotated by a drive 38 and moves backwards to accumulate a further charge in chamber 72. To prevent degradation of material on the walls of the bore 63, the valve 57 is opened while the moulds are disconnected from the nozzle 70, part of the charge is displaced from chamber 72 by the screw 36 into chamber 73 thereby raising piston 53 to its top position, and the material is forced back into chamber 73 by lowering ram 69 thereby wiping material from the walls of the bore 63. The material may alternatively be injected directly from the accumulation chamber into the moulds through a passage from which the compensating chamber branches off so that material is fed to the compensating chamber and the mould simultaneously.