Rheological Studies on Aqueous Alumina Extrusion Mixes

Abstract

The study describes the flow behaviour of alumina powder based extrusion dough used for fabricating simple and complex shapes. Based on the assessment of the critical binder volume concentration, alumina dough was prepared and flow data was obtained using a capillary extrusion setup mounted on an INSTRON universal-testing machine. The data was analyzed using the Benbow model as well as the viscosity model both commonly used with polymeric and ceramic injection moulding mixes. While the Benbow model was found to be sufficient for predicting the pressure drop that occurs in the die entry and die land regions during extrusion, it is not adequate for generating the viscosity data as a function of the shear rate and solids loading, that is essential for modeling the extrusion process. An attempt has also been made to correct the viscosity data using the Bagley correction technique which has demonstrated the necessity as well as the effectiveness of the technique. Viscosity model indicates a strong non-Newtonian behaviour at all shear rates as indicated by the shear rate exponent of 0.55. The viscosity data generated on such extrusion dough can be directly used in numerical simulation and modeling of the extrusion process.