Twin-screw extruders are developed on the basis of single-screw extruders. They have been widely used in extrusion products due to their excellent properties such as good feeding properties, mixing and plasticizing properties, exhaustability, and extrusion stability. Molding processing. 
　　From the point of view of motion, the twin-screw extruder has different concentric and opposite meshing and non-meshing types. 
　　1. Co-rotating intermeshing twin-screw extruder 
　　This type of extruder has two kinds of low speed and high speed. The former is mainly used for profile extrusion, while the latter is used for special polymer processing operations. 
　　(1) Closely intermeshing extruder. The low speed extruder has a tightly meshing screw geometry in which the screw profile of one screw fits closely to the profile of the screw of the other screw, ie, the conjugated screw profile. 
　　(2) Self-cleaning extruder. The high-speed co-directional extruder has a closely matched screw profile. The screw can be designed to have a relatively small screw gap, so that the screw has a self-cleaning effect. This twin-screw extruder is called a compact self-cleaning co-rotating twin-screw extruder. 
　　2. Meshing type twin-screw extruder 
　　closely meshing The space between the two screw grooves of the counter-rotating twin-screw extruder is very small (much smaller than the gap in the co-rotating twin-screw extruder) Therefore, positive delivery characteristics can be achieved.