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The development of the double screw plastic extruder, first developed in Italy in the 1930 s, early seventy s to 60 s developing rapidly. Mesh differential twin screw is along with the development of RPVC products, meshing direction is developed with the polymer modification, twin screw extruder research will not be able to adapt to the development of application of the theory of formed a consensus around the world, and become the research hot spot.

First of all, the twin screw extruder has the extruder principle of single screw extruder: solid conveyance, melting, pressurization and pumping, mixing, stripping and devolatilization, but it is not simple. The research on twin screw extrusion theory started late, and its type is many, the screw geometry is complex, and the extrusion process is complex, which brings many difficulties to the research.

On the whole, the study of twin screw extrusion theory is still in the initial stage, which is called "craftsmanship more than science ".

The physical model is established to guide the design of double screw plastic extruder and the optimization of extrusion process.

2. It is necessary to make clear the actual situation of the change of state of two or more polymers and materials in the extrusion process, the process of mixing morphology, structure change, and the relationship between final mixture and performance.

Iii. As a double-screw plastic extruder, the internal relationship between the reaction process, performance, speed, screw configuration and operating conditions during extrusion reaction is established to guide the extrusion reaction.