Injection molding machine screw configurations

The screw configuration is as follows thread depth ratio, approximately 1 2, and L/D ratio, 17/1 to 23/1 (standard three-zone screws feed, transition or middle, and metering or feed zones). Screws are equipped with a nonreturn valve to prevent backflow. Decompression-controlled injection-molding machines have an open nozzle. A short nozzle with a wide bore (3-mm minimum) is recommended in order to minimize pressure loss and heat due to friction. Residence time should be as short as possible, and this is accomplished with barrel temperatures at the lower limits of recommended settings. ... 

Some machines have a two-stage injection unit. A rotating-screw preplasticizer feeds molten polymer into an injection cylinder, from which it is injected into the mold by a hydraulically driven plunger. This configuration is claimed to provide better control of... 

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