7. Reverse-flow screw

This system can only be used on single-screw extruders.

The material in its plastic state exits the extrusion screw in a spiral pattern which varies according to the characteristics of the screw. In addition, the part of the material resting on the cylinder which is fixed, has physical characteristics which differ from those of the material resting on the screw, which is rotating. As a result, the spiral of material contained by the screw and exiting the extruder is neither homogeneous nor uniform.

A suitably shaped part of the extruder rotates and reverses the plastic flow in order to activate a mixing function that makes it physically homogeneous.

Flow reversal can only be activated on single-screw extruders of any size. The part of the screw where flow reversal is carried out is sized according to the type of material to be extruded and the diameter of the screw.

Within certain limits, an existing traditional screw can be modified.