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Twin Screw Extruder Working Principle

The twin screw extruder working principle is mainly reflected in different screw shapes, and different shapes can show different production efficiency. in addition, there are a variety of speed modes that can be adjusted to ensure efficiency in production. and the processing of the product can also be reflected in a more stable support effect, ensuring the shape of the screw and the working ability of another screw. 

In order to ensure stability in the process of use, it is also very important to understand the characteristics of the twin-screw extruder. The twin screw extruder has the characteristics of high efficiency and high output, and the production is also very convenient. All kinds of materials can also be processed and manufactured reasonably to ensure the full utilization of materials, so the twin-screw extruder will be used frequently.

Although the structure of twin-screw extruder is similar to that of single-screw extruder, its working principle is very different. In the twin-screw extruder, the material is added by the feeding device (usually quantitative feeding), and the die is reached by the action of the screw. In this process, the movement of the material varies according to the meshing mode and rotation direction of the screw. 

Twin-screw extruder+PLC

Non-meshing twin-screw extrusion system

Because the two screws are not meshing, the radial clearance between them is very large, and there is a large leakage current. 

The main mode of flow: 

Because the relative position of the screw edges of the two screws is staggered, that is, the material pressure on the thrust surface of one screw is greater than that on the towing surface of the other screw, resulting in flow. 

The material flows from the thrust of the screw with high pressure to the drag surface of another screw, and at the same time, with the rotation of the screw, the material is constantly stirred and taken away and renewed at the gap between the two screws (no matter how the two screws turn). Especially in the process of counter-rotation, the material is hindered at A, resulting in flow. 

Various forms of material flow (including various flows due to the interaction of two screws) increase the mixing and shearing of materials. However, this kind of twin screw has no self-cleaning effect and is generally only used for mixing, which is not suitable for the production of PVC profiles.

Meshing co-rotating twin screw extrusion system

The flow of the material in the full thread section of the co-rotating twin-screw extrusion system is shown.

Because the speed of the co-rotating twin screw is in the opposite direction in the meshing position, one screw pulls the material into the meshing gap, while the other screw pushes the material out of the gap, so that the material is transferred from one screw to another screw and moves forward in the shape of ∞. The change of this speed and the larger relative speed in the meshing area are very beneficial to material mixing and homogenization because the gap in the meshing area is very small. 

The speed of the thread and the screw groove in the meshing place is opposite, the shear speed is high, and it has a good effect of self-cleaning, that is, it can scrape off any accumulated material adhered to the screw so that the residence time of the material is very short. This kind of extruder is mainly used for mixing materials and granulation. However, because the material is subjected to a large shear force in the meshing zone, it is not suitable for the production of PVC profiles.

Meshing counter-rotating twin screw extrusion system

In the intermeshing counter-rotating twin screw extrusion, the two screws are symmetrical. Due to the different rotation directions, the spiral path of the material on one screw is blocked by the screw edge of the other screw, so the “∞” shape motion can not be formed. 

In the solid conveying part, the material is transported forward in the form of an approximate closed “C”-shaped chamber. However, in order to make the material mixing design, there is a certain gap between the outer diameter of one screw and the root diameter of another screw, so that the material can pass through. 

When the material passes through the radial gap between the two screws, it is subjected to strong shearing, stirring and Calendering, so the plasticizing of the material is better and is mostly used for processing products. 

Because the radial clearance between the two screws is relatively small, it has a certain self-cleaning performance, but the self-cleaning performance is worse than that of the twin screws rotating in the same direction.

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