Differences between the Single Screw Extruder and Double Screw Extruder

Extruder is a kind of plastic machinery, which is commonly used in the modified plastic industry. It is widely used in the polymer processing industry and other production and processing fields. The extruder can be divided into the single screw extruder and double screw extruder. They work differently:

double screw extruder

First of all, there are many differences between single screw extruders and double screw extruders in plasticizing capacity, material conveying mode, speed, cleaning and other aspects:

1. Different plasticizing ability: Single screw is suitable for the plasticizing extrusion of polymer and the extrusion processing of granular material. The shear degradation of the polymer is small, but the material stays in the extruder for a long time. Twin screw boasts a good mixing plasticizing ability, and the dwelling time of material in the extruder is short, which is suitable for the powder processing.

2. The mechanism of material conveying is different: For the single screw extruder, material conveying is conducted by the flow drag, solid conveying process by the friction drag, and melt conveying process by the viscous drag. The friction coefficient of solid material and metal surface and the viscosity of melt material to a large extent determine the conveying capacity of the single screw extruder. Material conveyed in the double screw extruder is conducted by positive displacement conveying. As the screw rotates, the material is forced forward by inter-meshing screw threads. The ability of positive displacement conveying depends on the proximity between the screw edge of one screw and the screw grain of another screw. Large positive displacement can be obtained by using tightly meshing contra-rotating double screw extruders.

3. Cleaning in different speed and occasions: The speed distribution in the single screw extruder is relatively clear and easy to describe, while the condition in the double screw extruder is more complex and difficult to describe. This is mainly due to the meshing area of the double screw extruder. The complex flow in the meshing zone makes the double screw extruders have many advantages such as full mixing, uniform heat transfer, strong melting ability and good exhaust performance, but it is difficult to accurately analyze the flow state in the meshing zone.

4. Different self-cleaning ability: The shear speed of the double screw extruder is fast, because the speed of the spiral reinforcement and the spiral groove in the meshing area are opposite, SO the relative speed is fast, and it can scrape off any accumulated materials attached to the screw. It has a good self-cleaning effect, and the material has a short dwelling time, which is not vulnerable to local degradation. Single screw extruders do not have this function.