| The thesis studied on design of cross covering extrusion die. The covering melts flows through its entrance and exit in different directions, which lead to uneven flowing. So studies on the issue was commenced, in which covering material IIR and bird—carreau equation model were used to analyze and software POLYMAT used to fit the material parameters.The melt flowing process in die channel was analyzed by software POLYFLOW. Its relations to die geometry parameters, shape parameters at given process condition were attained. Some parameters such as entrance radius, compress ratio, compress angle, length of sizing section and drawing speed of core wire which have effect on flow equilibrium were analyzed and optimized to attain optimal flow control parameters.According to a great deal of calculation and analysis, the mandrel axial deflexion angle was proved to be more effective to make melt flow evenly and the optimal one was given when the length of sizing section and different drawing speed of the core wire. It is shows in the study, at the situation of the optimal mandrel axial angle; the flow equilibrium for whole melt is notable. In addition, the drag flow resulted from core dragging and swells phenomena after the melt off the die are calculated and analyzed. These conclusions will provide valuable reference for the design and the improvement of die channel in covering extrusion. |
