Shear Rate Coat-Hanger Die Using Casson Viscosity Model

Abstract

Coat-hanger die design aims for optimization of the die geometry of the body and the flow distribution manifold, such that through the exit at the die lip homogeneous distribution of the polymer melt is achieved. This paper proposes a novel methodology for deriving the design equations of the coat-hanger die geometry for some specific extrusion materials and provides fluid–solid interaction simulations for validations. The basis for the calculations is the Casson rheological model, analytic velocity profiles for the pseudoplastic flow through circular pipe and slit, and the constant shear rate coat-hanger die design methodology developed by Winter and Fritz. The geometry obtained was then evaluated using the fluid-structure interaction numerical simulation approach. The sensitivity of the outlet velocity uniformity and die body deformation due to the material and mass flow rate change were investigated using the finite element software, Ansys. It was found that the homogeneity of the outlet velocity is very sensitive to the extrusion materials. The structural analysis of the solid die body also resulted in higher deformations when using some other extrusion materials different from the initial design. Mass flow rate increase only resulted in large zones of stagnation, which occurred around the melt as it passes from the manifold to the slit region. Therefore, it is recommended to define the required range of mass flow rate to prevent the formation of stagnation zones.