The twin-screw extruder has evolved from the single-screw extruder, thanks to its excellent feeding, mixing and plasticizing, venting, and extrusion stability characteristics. It is now widely used in the molding and processing of extruded products.

From a mechanical principle perspective, the co-rotating and counter-rotating as well as non-intermeshing types within a twin-screw extruder are distinct.

Co-rotating Twin-Screw Extruder

These extruders come in two types: low-speed and high-speed. The former is mainly used for profile extrusion, while the latter is for special polymer processing operations.

(1) Tandem Extruder. The low-speed extruder features a tight-meshing screw geometry, where the helical flanks of one screw perfectly match those of the other, forming a conjugate screw profile.

(2) Self-cleaning extruders feature high-speed, co-rotating screws with closely matched screw flanks. This design allows for a significantly small screw gap, enabling an enclosed self-cleaning function. Such twin-screw extruders are known as tight self-cleaning co-rotating twin-screw extruders.

2. Asymmetric Twin-Screw Extruder

The gap between the screw grooves of the tightly meshed, bidirectional rotation twin-screw extruder is very small (much smaller than that of the co-rotating meshing type twin-screw extruder), thereby achieving positive conveying characteristics.

3. Non-intermeshing twin-screw extruder

The center distance between the two screws of a non-intermeshing twin-screw extruder is greater than the sum of the radii of the two screws.