Extrusion Die Swell Simulation of Tire tread Compound using Phan Thien & Tanner (PTT) Model

摘要

Tire manufacturing involves mixing of raw materials such as rubber, carbon black, and chemicals followed by shaping of different specific components that are assembled and cured. Some of the important components like tire tread and sidewalls are exclusively produced by extrusion process in which the molten polymer is conveyed by a ram or a screw and the melt is then forced through a shaping die in a continuous process. The flow properties of the extrudate, including its morphology, depend on the deformation characteristics defined by induced stresses and strains. Rubber, being a very high molecular weight material, shows a strong shear-dependence and finite normal stresses in the direction of rectilinear flow. The final shape of the extrudate is determined by both die geometry and flow characteristics of the rubber compounds. Typically, a successful die design for viscoelastic material is achieved through much 'trial and error' method which consumes lot of time and money. However, with the use of a fully three dimensional finite element program, the conventional 'trial and error' method can be greatly reduced. Commercial FEM software has been utilized in the present study to predict the die swell phenomenon of tread compound. The numerical scheme of the tyre tread compound obeying a differential constitutive model is established. The rheological properties of tyre tread compound are obtained by rubber process analyzer, Capillary Rheometer and Elongational viscometer. The data obtained is used to fit the material function in PTT model. The observed flow patterns (velocity profile, pressure contour and shear rate contour) of tyre tread compound are discussed in detail to realize the complexity associated with the die swell phenomenon. Inverse extrusion technique will provide the geometry of the die for required profile.