In the injection screw, the function of the screw head is: when pre-plasticizing, the plasticized melt can be discharged into the storage chamber, and at the time of high-pressure injection, the melt at the front of the screw head can be effectively closed to prevent Backflow.

The screw heads are divided into two categories, with anti-reverse rings and without anti-reverse rings. For pre-reverse rings, the melt of the screw homogenization section pushes the anti-reverse ring away, through the screw head. The formed gap flows into the storage chamber. When injected, the melt pressure of the screw head forms a thrust, and the anti-reverse loop is retracted from the return passage to prevent backflow.

For some high-viscosity materials such as PMMA, PC, AC or PVC with poor thermal stability, in order to reduce the shearing effect and the residence time of the material, it is not necessary to use the reverse ring, but such injection will generate reflux and prolong the holding pressure. time.

Requirements for the screw head:

1 screw head should be flexible and smooth;

2 The anti-reverse ring and the barrel should be suitable for the clearance, that is, to prevent the melt from flowing back, and to be flexible;

3 There is sufficient flow cross section, and it is necessary to ensure that the end face of the anti-reverse ring has a return force, so that it can be quickly closed at the time of injection;

4 The structure should be easy to disassemble and assemble, easy to clean;

5 The thread of the screw head is opposite to the thread direction of the screw to prevent the screw head from loosening during pre-plasticization.