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What are the structural characteristics of the twin-screw extruder

Update:27 Feb 2019
Summary:

Non-intermeshing counter-rotating twin-screw extruder: […]

Non-intermeshing counter-rotating twin-screw extruder: the application is less than the meshing type, and its working mechanism is different from that of the meshing type, but similar to the single-screw extruder, that is, the material is conveyed by friction and viscous drag. In addition to the movement of the material in the direction of the machine head, there are various flow forms. See Figure: Since the two screws are not meshed, the radial gap is large, and there is a large leakage flow 1; The position is staggered, that is, the material pressure of the thrust surface of one screw is greater than the material pressure of the towing surface of the other screw, thereby generating the flow 2, that is, the flow of the material from the higher pressure screw thrust surface to the other screw towing surface; At the same time, the material rotated with the screw is obstructed at A, resulting in flow 3 and various other flow forms, so it has certain applications in mixing, exhausting, devolatilization and the like.

Compared with the parallel meshing counter-rotating twin-screw extruder, the volume of a series of C-shaped chambers formed by the two screws and the barrel is gradually reduced from the feeding section to the discharging section. In the feeding section, a larger volume of powdery material can be added, and as the screw becomes smaller, the material is compressed and melted. In the discharge section, because the screw diameter is small and the peripheral speed of the screw is small, the material is subjected to a low shear rate here, and the frictional heat generated is also small.