| 摘要 |
Method and apparatus for injection moulding of thermoplastic materials in which a screw in a plasticizer acts as an injection ram to inject plasticized material through a heated runner system into a mould. Part of the injected shot of plasticized material is passed into a reservoir communicating with the runner system. Upon completion of the injection of the shot, the passage from the plasticizer is closed by a valve and the screw is returned to plasticizing position while a pressure is applied to the plasticized material in the reservoir to force it into the runner system to apply a positive pressure so that an article is formed in the mold free of sink marks or weak spots. The reservoir may be provided in series with the shot injecting passage from the screw plasticizer by a nozzle on the plasticizer acting as a piston movable in a cylinder communicating with the runner system of the mould, the valve acting to close the plasticizer from the end of the mould. In an improved arrangement, the mould and cylinder may also constitute a reservoir receiving additional plasticized material from the mould before a succeeding shot of plasticized material is injected by ram action of the screw. In that case, the total amount of plasticized material for the succeeding operation is increased by the amount in the reservoir.
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