According to the change of the screw lift and the depth of the screw groove, the screw of the conventional full-thread three-stage extruder can be divided into three types:
From the depth change speed of the screw groove, the isometric variable depth extruder screw can be divided into two ways:
1. Isometric gradual extruder screw: the screw whose depth from the beginning of the feeding section to the last groove of the homogenizing section is gradually shallow. On the longer melting section, the depth of the groove gradually becomes shallower.
2. Isometric mutation extruder screw: the screw groove depth of the feeding section and the homogenization section do not change, and the screw groove depth at the melting section suddenly becomes shallow.
The screw of constant-depth variable pitch extruder means that the depth of the screw groove is constant, and the screw pitch is suddenly narrowed from the opening of the first screw groove of the feeding section to the end of the homogenizing section.
The characteristic of the constant-depth variable pitch extruder screw is that the screw groove is of equal depth, and the cross-sectional area of the screw in the feeding port direction is larger, and it has sufficient strength, which is beneficial to increase the speed and greatly improve the productivity. However, it is difficult to process the extruder screw, the melt flow rate is large, and the homogenization effect is poor, so it is less used.
The variable-depth and variable pitch extruder screw refers to the screw groove depth and the screw rise angle, which are gradually changed from the beginning of the feeding section to the end of the homogenization. This screw has the characteristics of the first two screws, but it is difficult to machine and is less used.
The above are the three basic structural forms of the general extruder screw. In addition, the screw is a key component of the extruder. The material of the screw must have the characteristics of high temperature resistance, wear resistance, corrosion resistance, and high strength. At the same time, it should also have the characteristics of good cutting performance, small residual stress after heat treatment, and small thermal deformation.