The single-screw pre-plasticization type is a twin-screw working in the barrel, which can rotate to evenly plasticize the material. It can also move back and forth to push the plasticized material into the mold cavity. This type of plastic injection structure is currently the most widely used structure in extruders, as shown in Figure 2-3. Its working method is: the pellets enter the barrel, and under the action of the process conditions of the rotating screw, the extrusion and the external heating of the barrel, it starts to move forward and gradually plasticizes into a molten state, and the material moves forward to resist.
Under the action of the material advancing and adhering force, the screw moves backward while rotating, and then a certain volume of injection is formed in front of the screw to retain the molten material. When the injection process starts, the screw is pushed forward by the piston in the injection cylinder, and the screw pre-plastic structure is composed as shown in Figure 2-4.