Grandual change type screw

The so-called conventional full-threaded three-section screw is the earliest to appear and most widely used. The entire screw is composed of three sections, and its extrusion process is completely accomplished by the full-threaded form. 
(1) Regarding the determination of screw type, according to the traditional classification, the conventional full-threaded three-section screw is divided into the gradual change type screw and the abrupt change type screw. The so-called gradual change type screw refers to the transition from the deeper screw channel in the feeding section to the shallower one in the homogenization section, which is accomplished over a relatively long axial distance of the screw. In contrast, the so-called abrupt change type screw completes the above-mentioned transition over a relatively short axial distance of the screw, as shown in Figure 2-15. 
Figure 2-15 Gradual-change Screw and Abrupt-change Screw 
Gradient screws are mostly used in the processing of amorphous plastics. They can provide better heat conduction for most materials, have a relatively small shearing effect on the materials and this effect can be controlled. Their mixing characteristics are not very high. They are suitable for heat-sensitive plastics and can also be used for crystalline plastics.