Geometric improvement of the sheet/film extrusion die using Rabinowitsch-Mooney analysis

The well-known Winter-Fritz horseshoe die introduced in the 1980s has been used in polymer sheet/film extrusion die and coating die industries with success. The geometric design of the die manifold enables the flows to keep a constant wall shear rate along the manifold wall and in the walls of the preland slit. It produces uniform outlet velocity and a uniform average residence time of material in the die. These properties reduce degradation and provide high-precision extrusion and coating. The Winter-Fritz die is very useful for blow film, wire, profile, and coating applications. However, the depth of the die is proportional to the width, which limits its applicability for wide sheets/films productions. The rectangular manifold Winter-Fritz die known as “large aspect ratio extrusion die” is independent of the power-law parameters with the shape factor approaching unity. This shape factor of 1.0 is the case for cross-sections with a large aspect ratio, W/H>10. We propose to use some more general geometric factors, known as the Rabinowitsch-Mooney geometric factors, for the design of the manifold. As a result, a narrower and wider Winter-Fritz type of die with a rectangular manifold is designed. By implementing this innovative method, a lower ratio of die depth to outlet length is achieved, resulting in significant benefits such as decreased die body weight and increased cost-efficiency while keeping most of the good qualities of the original Winter-Fritz die. Additionally, it enables the extrusion of wider sheets/films, which was not possible with the original Winter-Fritz design.