Influence of screw back position on PP plasticization and injection

On different screw back positions, the 3-D non-isothermal flow field of Polypropylene melt in non-return injection screw is simulated by FEM. Simulation results indicate that the velocity of screw back and injection increase with the increment of the screw back position. The velocity, the shear stress, the viscosity heating and the temperature increase, but the viscosity decreases in plasticization and injection processes. The pressure increases with the increment of the screw back position in injection process. The pressure does not monotonically increase with the increment of the screw back position in plasticization process, but decreases for larger screw back position. Therefore, it is necessary to consider the quality and cost of the products, when the screw back position is selected.