How should the structural form of the screw tip be selected?

During the extrusion production process, the structural form of the screw head should be selected according to the properties of the processed materials. Generally, for processing plastics with good thermal stability (such as polyolefins), a blunt-type screw head should be chosen, as shown in the figure. 

screw


There is a large space between the screw head and the die head, and a plate and a filter screen can be installed in front of it. However, it is easy for the materials to get stuck in front of the screw head and undergo thermal decomposition, so it is not suitable for processing materials with poor thermal stability. For processing plastics with poor thermal stability (such as PVC), a conical screw head is generally used, as shown in the figure.


screw


When processing PVC wires and cables, a screw head with a threaded conical part is usually used. The materials move with the help of the threaded part of the conical part, which can better prevent the material from stagnant flow and decomposition. When extruding plastics with high viscosity, poor thermal conductivity, or obvious melting points, such as cellulose, polystyrene, polyamide, and plexiglass, a torpedo-shaped screw head with grooves or a specific geometric shape on the surface can be selected. It has a good mixing and shear effect and can increase the pressure of the fluid and eliminate fluctuation phenomena.
Top
Inquiry
Inquiry