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What are the shortcomings of ordinary screw

Update:28 Mar 2019
Summary:

(1) Since the melting mainly occurs at the interface of […]

(1) Since the melting mainly occurs at the interface of the solid bed in contact with the upper melt film, the width, that is, the heat transfer area between the melt and the solid, gradually decreases with the melting process, and the thermal conductivity of the polymer is increased. Small, so the melting performance is low. As the yield progresses, the flow rate of the polymer in the direction of the groove also increases, so that the length of the groove required for the polymer to melt well is also increased, and for a given transition length, the polymer may not be melted intact.

(2) The shear stress between the upper melt film and the wall surface of the barrel is generally several times larger than the shear stress between the molten pool and the wall surface of the barrel, that is, the mechanical power per unit area of ​​the upper melting film is higher than that of the molten pool. The height is several times higher, which causes excessive shear heat when the screw speed is high, and the barrel is cooled to constitute an energy waste. Therefore, ordinary screw melting consumes higher mechanical power and lower energy efficiency. (screw)

(3) The polymer which melted earlier had experienced a certain mixing process when it reached the end of the melting section, and the polymer which melted at the end of the melting section was not subjected to the kneading effect. It can be seen that the mixing process of the melt is not uniform to the end of the melting section.

(4) Due to the thin film on the upper film, it is subjected to high-viscosity shearing, resulting in a large amount of viscous heat. Thereafter, the upper melt film having a high temperature is scraped into the molten pool from time to time, and the melt in the molten pool further accumulates heat due to viscous activity. Since the contact area between the melt and the solid bed is small, the heat transferred from the melt to the solid bed is also small, that is, the temperature of the melt is largely stored inside. The solid bed is a good medium and only moves in the direction of the groove, so the temperature rise of the core is slow. Therefore, the temperature of the polymer in the groove of the melting section is unevenly distributed and the uniform temperature is high, and the ordinary screw is difficult to improve the output. And energy efficiency.