Design and analysis of crosshead annular die for braided medical tubing extrusion

A theoretical method is proposed for optimum design of a crosshead annular die used for medical tubing. According to this method, the geometric variab les are determined to minimize the change in gapwisely-averaged flow veloci ties due to the variation in flow patterns inside the transitional region o f the flow channel of the die, namely the gum space. To achieve this, a num erical approach to flow analysis is put forward based upon the simplified m otion and energy equations as well as the approximation of the flow channel using a series of varying annular slits, each having constant geometric pa rameters. Accordingly, the numerical schemes for flow analysis and design o ptimization are established, and the computer program is developed using Mi crosoft Visual C++ 6.0. For an optimum die design, the heat adhesion betwee n the cold-fed inner tube and the hot melt during the over-extrusion is eva luated based upon the temperature rise and pressure profile of the melt in the die land. Based upon the optimum die design obtained from the method, t he flow is well balanced with enhancement of extrusion quality. Also, it is found that the optimum die designs are less sensitive to extrusion conditi ons within a certain range.