Application of Flow Behavior to Design of Rubber Extrusion Dies

Abstract

Abstract It is common in the tire industry to extrude profiles like treads using a hot-feed dual extrusion line. There is a need to extrude the profiles with zero drawdown in the extrusion line after exiting from the die. Also, the extrudate from the two extruders in a dual extrusion must knit together to form a well-defined and reproducible junction line. A contoured flow channel called a preform is customarily used to achieve a desired junction line and to roughly preshape the stream before passing it through the final die. In practice, several trials are usually required to arrive at an optimum die combination to obtain desired size and shape of extrudate after due allowance for extrudate swell, as well as uniform velocity across the width of the extrudate profile. It is helpful to eliminate some of these trials by developing calculation methods for estimating pressure profile, velocity and swell distribution. There are a number of articles on calculating pressure drop from flow rate for non-Newtonian fluids in odd shaped ducts and tapered channels. Also, many simple techniques are available for analyzing non-Newtonian flow of polymer melts in simple extrusion dies. Most of these calculations assume a one-dimensional flow. More recently, there has been much work on developing finite element and other numerical methods for computing complex die flows. This paper describes and tests the utility of a quick and easy method of estimating extrusion pressures and velocities in and at the exit of extrusion dies using material properties and geometry. This method allows for abrupt changes in geometry such as sudden contractions in the flow channel.