Screw-preplasticising

In order to overcome such disadvantages the injection-compression process has been developed. A conventional compression press is coupled to a screw preplasticising unit which can deliver preheated and softened material direct to a compression mould cavity. 

Ln-line screw system. The in-line screw system, or screw ram system as it is sometimes called, is the most important development in injection moulding. In this system the plastics is softened by passing it through a heated cylinder by the use of an extruder type screw, the softened plastics building-up in front of the screw. The build up of plastics in front of the screw causes the screw to move axially backwards. The shot size can therefore be easily controlled by stopping the screw rotation at a predetermined position. When the preplasticising operation is complete, the screw is moved forward under pressure pushing the plastics into the mould (Fig. 2). 

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