Twin screw extruder have three kinds of head thread:
Used for co-rotating twin-screws. It is mainly used for processing hard PVC. Because the screw groove is deep, it is not suitable for other resins.
If used on counter-rotating twin-screws, they do not have a self-cleaning effect,so they are more like single-screw extruders and are suitable for mixing.
With deeper groove, it has a larger free volume per unit length. Under the same number of screw rotations, the average shearing heat of the material is relatively low, and the mixing effect is gentle.
When it is working with the same shear stress and torque as the three-headed thread, it can be opened to a higher number of revolutions;
Suitable for compounding, especially for processing of powders, low bulk materials, difficult to add materials, high shear or shear sensitive, temperature sensitive materials.
The screw groove is shallow. At the same screw speed, the material is more highly sheared than the double-head thread. Mainly used for the processing of high shear materials.