A comparison of paste rheology and extrudate strength with respect to binder formulation and forming technique

Abstract

Two series of ceramic injection moulding (CIM) pastes were prepared using three different mixing methods. Two Newtonian binder systems, were employed composed of EVA-paraffin wax and EVA-vegetable fat mixed in varying proportions to give a wide range of binder viscosities. The powder loading of each paste system was adjusted using the Chong equation to compensate for the variation in binder viscosity. The mixing methodologies employed were convectional Z blade mixing, twin roll milling (TRM), and Extrumixing (a combination of Z blade mixing and single-screw extrusion). The rheology of the pastes was characterised by extrusion, with the data being rheologically analysed by the Benbow/Bridgwater and Herschel/Bulkley models. The most rheologically favourable systems produced relatively low yield values and were not highly velocity dependent. Extrudates from these two paste systems were mechanically tested after undergoing identical debinding and sintering regimes, and found to possess strengths of 360 and 580 MPa, respectively. The most promising mixing methodology employed was Extrumixing due to the high shear mixing action in combination with the extrusion action used in removing the paste from the mixer.