Screw Function

The screw functions in the following way:

1) The feed zone conveys the plastics to the transition zone where most of the shearing action takes place.
· Sometimes the transition zone is called the compression zone. In this zone, the flights of the screw are not deep so that the material can be compressed between the screw and barrel.

2) The metering zone will melt any plastics that was not fully melted in the transition zone.
· The material in the metering zone is of even consistency and in a molten state as it builds up in front of the screw.

3) This build-up of material creates pressure at the front of the screw which forces the screw back toward the rear of the injection unit until it reaches a pre-determined distance called the shot size.



4) The screw now moves forward like a piston, and the resulting ram action forces the hot melted material into the closed cool mould.