The working principle of twin-screw extruder

Although the structure of twin-screw extruder and single-screw extruder is very similar, but the working principle is very different. In the twin-screw extruder, the material from the feeding device (usually quantitative feed) added by the role of the screw reached the nose die. In this process, the movement of material due to the screw meshing, rotation direction is different.
1, non-mesh type twin-screw extrusion system
Materials in the non-intermeshing twin-screw extrusion system, in addition to the direction of the head of the form of movement, there are a variety of flow, see Figure 7. As the two screws do not mesh, the radial clearance between them is large, there is a large leakage. The main flow: 1, due to the relative position of the two screw rib is staggered, that is, a screw thrust surface of the material pressure is greater than the other screw drag surface material pressure, resulting in a flow.
2, the material from the higher pressure of the screw thrust to the surface of the other screw drag surface, along with the rotation of the screw, the material in the gap between the two screws
Continued to be agitated and continuously taken away, updated (regardless of the two screw rotation), especially in the opposite rotation, the material is obstructed at A, resulting in a flow. 3, a variety of material flow patterns
(Including due to the various flows created by the interaction of the two screws) adds to the mixing and shearing of the material. However, this double screw does not self-cleaning effect, generally only for mixing, not suitable for the production of PVC profiles.
2, intermeshing co-rotating twin-screw extrusion system
Material in the co-rotating twin-screw extrusion system full thread section flow situation, due to co-rotating twin screw in the meshing position of the speed of the opposite direction, a screw to pull the material into the meshing gap, while the other screw to The material from the gap in the push, the result of the material from one screw to another screw, was ∞-shaped forward, the change in speed and meshing area of the relative speed of the larger, very conducive to material mixing and homogenization, due to the engagement Area gap is small, meshing Department of thread and screw the opposite speed, high shear rate, has a good self-cleaning effect, that can scrape off any adhering material in the screw, so that the material residence time is very short. This extruder is mainly used for mixing materials and granulation. However, due to the shearing force of the material in the intermeshing range, it is not suitable for the production of PVC profiles.