According to the changes of Screw Barrel lift and screw groove depth, the screws of conventional full-thread three-stage extruders can be divided into three types:

Ⅰ. Isometric variable depth extruder screw

From the perspective of the depth change speed of the screw groove, the screw of the equidistant variable-depth extruder can be divided into two ways:

1. Equidistant progressive extruder screw: a screw whose groove depth gradually becomes shallower from the beginning of the feed section to the last of the homogenization section. On the longer melting section, the depth of the groove gradually becomes shallower.

2. Equal-distance mutation extruder screw: the screw groove depth of the feed section and the homogenization section does not change, and the screw groove depth of the melting section suddenly becomes shallow.

Ⅱ. Constant-depth variable-pitch extruder screw

The screw of the fixed-depth variable-pitch extruder means that the depth of the screw groove is constant, and the screw pitch suddenly narrows from the opening of the first screw groove of the feed section to the end of the homogenization section.

The characteristic of the screw of the constant-depth variable-pitch extruder is that the screw groove is equal in depth, the cross-sectional area of ​​the screw feed port direction is large, and it has sufficient strength, which is beneficial to increase the speed and greatly improve the productivity. However, the extruder screw is difficult to process, the melt flow rate is high, and the homogenization effect is poor, so it is rarely used.

3. Variable-depth variable-pitch extruder screw

The variable-depth variable-pitch extruder screw refers to the gradual change of the screw groove depth and screw rising angle from the beginning of the feed section to the end of homogenization. This kind of screw has the characteristics of the first two kinds of screws, but it is difficult to process and less used.

The above are the three basic structural forms of general extruder screws. 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.