The Difference Between Single Screw Extruder and Twin Screw Extruder

It is widely known that extruder is one of the types of plastic machinery and is a common machine in the modified plastics industry, widely used in the polymer processing industry and other production and processing fields. Extruders can be divided into single screw extruders and twin screw extruders, both of which have different working principles and application areas, and each has its own advantages and disadvantages.

First of all, single screw extruders and twin screw extruders have many differences in terms of plasticizing capacity, material delivery methods, velocity fields and cleaning, as follows.

1. The plasticizing ability of single screw extruder and twin screw extruder is different

Single screw is suitable for plasticizing polymer extrusion, suitable for extrusion processing of granular materials; the shear degradation of polymer is small, but the material stays in the extruder for a long time. Twin screw has good mixing and plasticizing ability, short residence time of materials in the extruder, suitable for powder processing.

2. The material transport theory of single screw extruder and twin screw extruder is different

The material transport method of single screw extruder is drag flow, friction drag in the solid transport process, and viscous drag in the melt transport process. The size of the friction factor between the solid material and the metal surface and the viscosity of the melt material, to a large extent, determine the transport capacity of the single screw extruder. As for the twin screw extruder, the material is transported in positive displacement, and as the screw rotates, the material is forced forward by the intermeshing threads, and its ability to transport in positive displacement depends on the proximity of the screw ribs of one screw to the screw grooves of the other screw. Greater positive displacement transport can be achieved with a tightly meshed, anisotropic twin screw extruder.

3. The velocity field of single screw extruder and twin screw extruder is different

The velocity distribution in single screw extruders is relatively clear and easy to describe, while the situation in twin screw extruders is quite complex and difficult to describe. This is mainly due to the meshing zone in twin screw extruders. The complex flow in the meshing zone makes twin screw extruders have many advantages such as adequate mixing, uniform heat transfer, high melt capacity, and good exhaust performance, but it is difficult to accurately analyze the flow state in the meshing zone.

4. The self-cleaning capacity of single screw extruder and twin screw extruder is different

Due to the opposite direction of the speed of the screw and the screw groove in the meshing zone, the relative speed of the twin screw extruder is large, so it has a very high shear speed, can scrape off any accumulated material adhering to the screw, and has a very good self-cleaning effect, so that the material residence time is very short, and it is not easy to produce local degradation metamorphism. The single screw extruder does not have this function.

In addition to the different working principles, they also have different application areas. Twin screw extruders are widely used for physicochemical modification of matrix resins, such as filling, reinforcement, toughening, reactive extrusion, etc.; single screw extruders are mainly used in the fields of pipes, plates, sheets and profiles.

As one of top extrusion machine suppliers in China, jwell extruder provides both types of extruders.