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What are the defects of ordinary screws?
(1) Since the melting mainly occurs on the interface of the solid bed in contact with the upper melt film, its 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 relatively high. Small, so the melting performance is low. As the output increases, the flow rate of the polymer along the groove direction also increases, so that the groove length required for the polymer to be melted intact also increases. For a given transition section length, the polymer may not be able to melt intact.
(2) The shear stress between the upper melt film and the wall of the barrel is generally several times larger than the shear stress between the molten pool and the wall of the barrel, that is, the mechanical power consumed per unit area in the upper melt is greater than that of the molten pool. It is several times of medium high, which makes when the screw speed is high, excessive shear heat will be generated, and the barrel needs to be cooled, which constitutes a waste of energy. Therefore, ordinary screw melting consumes higher mechanical power and lower energy efficiency.
(3) The polymer that melted earlier has gone through a certain mixing process when it reaches the end of the melting section, and the polymer that melts at the end of the melting section is hardly subjected to mixing. It can be seen that to the end of the melting section, the mixing process of the melt is uneven.
(4) Because the upper melt film is thin, it is subjected to high-viscosity shearing, which generates a lot of viscous heat. After that, the upper melt film with high temperature is scraped into the molten pool by the spiral edges from time to time, and the melt in the molten pool further accumulates heat due to viscous activity. Because 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 mostly stored inside it. The solid bed is a good medium, which only moves in the direction of the screw groove, so its core temperature rises slowly. Therefore, the temperature of the polymer in the screw groove of the melting section is unevenly distributed and the uniform temperature is high. It is difficult for ordinary screws to increase the output. And energy efficiency.
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