Plastic extruders are divided into twin-screw extruders and single screw extruders in accordance with the number of screws. The distinction between them is that one is a screw and one is two screws. They’re all driven by an electric motor, and the power varies from screw to rod. Under normal circumstances, the output of single screw is only half of that of dual-screw. Single screw extruder is straightforward to design and manufacture, and the host price is comparatively low-cost, so it has been widely utilized and suitable for extrusion processing of common materials. However single screw extruders have limitations in their applications.
Mainly in the following facets:
1. the material transportation of the only screw extruder mainly will depend on the friction, so that the feeding efficiency is limited, and the powder, paste, glass fiber and inorganic powder are tough to join.
2., when the head pressure is high, the countercurrent will increase, and the productivity decreases.
3., the only screw extruder has little impact on the surface of the exhaust space, and the exhaust impact is poor.
4. single screw extruder is not suitable for some modification processes, comparable to polymer coloring and thermosetting powder processing. With a purpose to clear up the above problems, a twin screw extruder has been developed.
Its extrusion system consists of two screw and material barrel, which is meshing or non meshing, turning in the identical direction or rotating with completely different direction. Because of the less heat produced by the friction, the more uniform shearing of the material and the higher transmission capacity of the screw, the material is under the identical extrusion quantity. Within the screw, the residence time is brief, so it is suitable for coloring and mixing materials that may solidify or coagulate for a protracted time.