A twin screw extruder not only shares the common operation principles with a single screw extruder: solid conveying, melting, admixture of pressurizing and pumping up, etc., but also owns its distinct characteristics. There are several factors that tackle the study of basic principles of co-rotating twin screw extruder, such as the late research of extrusion theory, various types, complex screw geometry, and complicated extruding process.

Basically speaking, the study of twin screw extruding theory is still at the initial stage, which indicates that the study is still more art than science. There are three links of its operation principles according to the extruding process:

1.The design of twin screw extruder and optimization of extruding process could be improved by material change laws, conveying theory ,including convey of solid and melt, also gas filling and ejecting characteristics, which can form a mathematics and physical model in the extruding process.

2.Make sure to have a clear command of the change regulation of two or more polymers and materials in the extruding process, their mixing state, the process of their structural change, and the relationship between final mixtures and their functions.

3.A model that is helpful for the molding-filling process can be formed by   the internal relationship among the reaction process, speed, function of extruding process and screw’s structure, as well as operation condition.

The development of twin screw extruders: it was first invented in 1930s in Italy, while in the late 1960s and early 1970s, it experienced a rapid development. With the development of RPVC products, counter-rotating twin screw extruder came into being; while co-rotating twin screw extruder appeared, companying with the polymer modification. It is useful to study the twin screw extruding theory, because it can not only be applied effectively, but also has become a consensus and a hot research in the world.