Profile Extrusion Dies

Profile extrusion refers to the extrusion of polymer melts through dies of cross sections that are neither round, annular, or rectangular with an aspect ratio, W/H, greater than 10.0. At present three types of profile dies are used: orifice dies, multistage dies, and tapered profile dies. Basically the orifice die consists of a die base and a die plate in which the profile is formed. These dies are used for the extrusion of inexpensive profiles where dimensional accuracy is not necessary. Because of the abrupt change in cross-sectional area, there is usually a buildup of stagnant material behind the die plate and high extrusion rates are not possible. These dies are not commonly used for most thermoplastics but are restricted primarily to PVC and rubber. Multistage dies exhibit step changes in the cross-sectional area of the flow channel. They consist of a series of die plates of similar geometry but of a decreasing cross-sectional area. Certainly these represent an improvement over the orifice dies, but they still suffer from some of the same deficiencies as the orifice die. Whenever profiles of high-dimensional accuracy are to be produced at high extrusion rates, profile dies with a gradual change of cross-sectional area are required.