| Summary: | 碩士 === 中原大學 === 機械工程研究所 === 98 === This study focus on melt flow toward to the viscosity under ultra high speed injection molding. This experiment use the Polystyrene resin in 2 mm thickness with narrow rectangular section and keep mold and melt at the same temperature equal to 200, 215 and 230 oC with the maximum injection pressure condition. The experiment method will change the injection speed from 100 to 1500 mm/s and obtained the pressure drop and flow rate through sensors. The experimental results will be calculated with slit flow model and corrected for the effect of the viscous dissipation and wall slip by comparing with the ideal viscosity curve. Finally, the reason of the second Newton area will be conjectured by the free volume theory.
The experimental results show that the effect ratio of viscous dissipation and the wall slip increases with the increase of injection speed and decreases with the increase of mold and melt temperature. When the injection speed is over 1000 mm/s, the shear strain rate is between 150000 and 200000 s-1. The material viscosity curve become constant and reached the second Newton area. By the free volume theory conjecture which under the ultra high speed injection molding, the high injection pressure with the shear stress and high injection speed with the shear strain rate reach into balanced state and result in the second Newton area. For different molecular weight, molecular structure, density and other polymer molecular characteristics of materials will affect the pressure sensitivity and the range of the second Newton area.
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