Difference between single screw extruder and twin screw extruder

Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with nearly 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.

Extruder is one of the types of plastic machinery. It is the most common machinery in the modified plastic industry. It is widely used in polymer processing industry and other production and processing fields. Extruder can be divided into single screw extruder and twin screw extruder. Their working principles and application fields are different, and they have their own advantages and disadvantages.

First of all, there are many differences between single screw extruder and twin screw extruder in terms of plasticizing capacity, material conveying mode, speed and cleaning, as follows:

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

The material conveying mechanism is different: the material conveying in the single screw extruder is drag flow, the solid conveying process is friction drag, and the melt conveying process is viscous drag. The size of the friction coefficient between the solid material and the metal surface and the viscosity of the melt material determine the conveying capacity of the single screw extruder to a great extent. The conveying of materials in twin-screw extruder is positive displacement conveying. With the rotation of the screw, the materials are forcibly pushed forward by the meshing threads. The ability of positive displacement conveying depends on the proximity between the screw edge of one screw and the screw groove of the other screw. The maximum positive displacement conveying can be obtained by close meshing counter rotating twin-screw extruder.

Different velocity fields: the velocity distribution in single screw extruder is relatively clear and easy to describe, while the situation in twin screw extruder is quite complex and difficult to describe. This is mainly due to the meshing area in the twin-screw extruder. The complex flow in the meshing area makes the twin-screw extruder have many advantages, such as full mixing, uniform heat transfer, strong melting capacity, good exhaust performance and so on, but it is difficult to accurately analyze the flow state in the meshing area.

Self cleaning: due to the opposite speed direction and large relative speed of the screw edge and screw groove in the meshing area, the twin-screw extruder has a very high shear speed, which can scrape off any accumulated material adhered to the screw and has a very good self-cleaning effect, so that the residence time of the material is very short and is not easy to produce local degradation and deterioration. The single screw extruder does not have this function.

If you need more information, Ningbo Fangli Technology Co., Ltd. welcomes you to contact for a detailed inquiry, we will provide you with professional technical guidance or equipment procurement suggestions.