What are the defects of common screw?

(1) Because the melting mainly occurs at the solid bed interface contacting with the upper melting film, its width, that is to say, the heat transfer area between the melt and the solid decreases gradually with the melting process, and the thermal conductivity of the polymer is small, so the melting performance is low. With the increase of production, the flow rate of polymer along the direction of the spiral groove also increases, so that the length of the spiral groove needed for the complete melting of polymer also increases. For the given length of the transition section, it may not be able to make the complete melting of polymer.

(2) Generally, the shear stress between the upper melting film and the wall of the barrel is several times larger than that between the molten pool and the wall of the barrel, that is to say, the mechanical power consumed per unit area of the upper melting film is several times higher than that in the molten pool, which makes when the screw speed is higher, excessive shear heat will be generated, and the barrel will be cooled to form the waste of energy. As a result, the mechanical power consumed by the melting of ordinary screw is higher and the energy efficiency is lower. (screw)

(3) When the early melted polymer reaches the end of the melting section, it has experienced a certain mixing process, but the polymer melted at the end of the melting section has not been mixed. It can be seen that the mixing process of the melt is uneven to the end of the melting section.

(4) Because of the thin upper melt film, it is sheared by high viscosity, which produces a lot of viscosity heat. After that, the high temperature upper molten film is scraped into the molten pool by the screw edge from time to time, and the melt in the molten pool further accumulates heat due to the viscous activity. Because of the small contact area between the melt and the solid bed, the heat transferred from the melt to the solid bed is also small, that is to say, the temperature of the melt is largely kept in its interior. The solid bed is a perfect medium, which only moves along the direction of the screw groove, so its core temperature rises slowly. Therefore, the temperature distribution of the polymer in the screw groove of the melting section is uneven and the uniform temperature is high, so it is difficult for ordinary screw to improve the output and energy efficiency.