Difference between twin screw extruder and single screw extruder

The difference between twin screw extruder and single screw extruder is mainly reflected in the following two aspects.

Material transport mode

In the single screw extruder, friction drag is used in the solid transport section, and viscous drag is used in the melt transport section. The conveying behavior is determined by the friction properties of solid materials and the viscosity of molten materials. If some materials have poor friction performance, if the feeding problem is not solved, it is more difficult to feed the material to the single screw extruder. In the twin screw extruder, especially the meshing type of twin screw extruder, the material transmission in some extent is the forward displacement transmission, the degree of forward displacement depends on the screw edge of one screw and the relative screw groove of another screw close degree. The screw geometry of the closely meshing heterotropic rotary extruder can obtain high forward displacement transport characteristics.

Material velocity distribution

At present, the flow velocity distribution of material in single screw extruder has been described quite clearly, but the flow velocity distribution of material in double screw extruder is rather complicated and difficult to describe. Many researchers just do not consider the material flow in the meshing area to analyze the flow velocity field, but these analysis results are very different from the actual situation. Because the mixing characteristics and overall behavior of twin-screw extruder mainly depend on the leakage flow occurring in the meshing area, however, the flow situation in the meshing area is quite complex. The complex flow spectrum of the material in the twin screw extruder shows the advantages that the single screw extruder is not comparable to on the macro level, such as sufficient mixing, good heat transfer, large melting capacity, strong exhaust capacity and good temperature control of the material.

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