Screw is an important part of a plastic injection machine, its function is to transport, melt plastic, compaction, mixing with pressure. All of these are through the rotation of the screw within the barrel, therefore, the role of screw in plastic machinery is very important.

During the screw rotates, the plastic barrel inside, screw screw groove bottom, and push the surface as well as between plastic and plastic screw arris in produces friction and mutual movement. Plastic forward is the outcome of this motion combination, and the heat generated by the friction also absorbed to promote plastic temperature and the melting plastic. The structure of the screw will directly affect the degree of these effects.

At the same time, the rotation of the screw between the solid bed with barrel inner surface of the molten film produce shearing action, so that the melt film with solid fusion between the solid bed interface. With the spiral history of the solid bed, the volume of a solid bed gradually narrowed, and the volume of molten pool increase gradually.

If the speed of the solid bed thickness decreases below the speed of the screw groove depth becomes shallow, the solid bed may be partially or completely block the screw groove, the plasticizing fluctuations, or because of partial pressure because of all kinds of plastic material melting speed, melt viscosity, melting temperature range, the sensitive degree of viscosity to temperature and shear rate, pyrolysis gas corrosion, friction coefficient difference between plastic particles is very large, usually in the sense of ordinary general screw in some melt processing features compared with outstanding plastic for a period of high shear heat occurs phenomenon, this phenomenon is general by reducing the screw rotation speed to eliminate, but this is bound to affect the production efficiency.