A Comprehensive Comparison of Single and Twin Screw Extruders

Currently, the extruders in the plastic industry in China can be roughly divided into two types: single-screw extruders and twin screw extruders. Both types of equipment have their own characteristics and are widely used in the plastic industry. So what are the advantages of these two types of extruders and what are the differences between them? After reading this article, you won't be confused anymore.

Introduction and applications of single and twin screw extruders

Single screw extruder

As the name suggests, a single-screw extruder has only one screw in the barrel.

Main Applications

Mainly used for extruding pipes, sheets, plates, profiles, and partially modified materials for granulation.

Twin screw extruder

Similarly, a twin screw extruder has two screws in the barrel.

Classification: Compared with the single-screw extruder, the classification of twin screw extruders is relatively complex, and there are many classification methods:

According to the position of the two screws, it can be divided into parallel and conical;
According to the degree of screw intermeshing, it can be divided into intermeshing and non-intermeshing;
According to the rotation direction of the two screws, it can be divided into the same and opposite directions, and the opposite direction can be further divided into inward and outward;
According to the screw rotation speed, it can be divided into high-speed and low-speed;
According to the structure of the screw and barrel, it can be divided into integral and combination.

Main Applications:

Mainly used for granulating of modified plastics such as fiber reinforced, flame retardant, and increased filling, blending extrusion of thermosetting plastics, extrusion granulation of hot melt adhesives and PU reactions.

Differences between single and twin screw extruders

After briefly introducing single and twin screw extruders, let's take a closer look at the differences between these two extruders in terms of price, operability, and screws.

Single screw extruders are cheaper

Single-screw extruders, which contain fewer extruder elements, are relatively simpler and less expensive than twin screw extruders. twin screw extruders have a complex structure and are more expensive. The price of a twin screw extruder is generally about twice as high as that of a single-screw extruder, but it may vary depending on the manufacturer and model.

Single screw extruders are easier to operate

To be honest, in terms of operation, there isn't much difference between the two. However, the process and formula of a single-screw extruder are simpler than those of a twin screw extruder.

Twin screw extruders can freely combine screws

The threads of a twin screw extruder can be freely combined according to the material conditions and the operator's mood.

A single-screw extruder is relatively inflexible and cannot combine screws.

twin screw extruders are more efficient

Twin screw extruders have a higher output and extrusion speed, and lower energy consumption per unit of output compared to single-screw extruders. The efficiency of a twin screw extruder is generally about twice that of a single-screw extruder, but it varies depending on the twin screw extruder manufacturer and model.

Twin screw extruders have stronger mixing and plasticizing ability

Simply put, single-screw extruders are suitable for plasticizing extrusion of polymers and processing extrusion of pellet materials, such as molding, blow molding, and injection molding, with a wide range of materials.

Twin screw extruders have good mixing and plasticizing ability and are more suitable for modifying plastics. Twin screw extruders can also produce two colors.

Single screw extruders are easier to maintain

In terms of maintenance, a single-screw extruder is simpler than a twin screw extruder, as its structure is simpler and easier to repair.

Conveying mechanism

The conveying mechanism of a single-screw extruder mainly relies on the friction between the material and the barrel, while a counter-rotating twin screw extruder has a positive conveying effect and can also apply shear to the material at the intermeshing point of the two screws.

Velocity field

The velocity distribution in a single-screw extruder is relatively clear and easy to describe, while the situation in a counter-rotating twin screw extruder is very complicated and difficult to describe. This is mainly due to the intermeshing zone of the screw, where the complex flow makes it 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 intermeshing zone.