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

Two series of ceramic injection moulding (CIM) pastes were prepared using t hree different mixing methods. Two Newtonian binder systems, were employed composed of EVA-paraffin wax and EVA-vegetable fat mixed in varying proport ions 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 v ariation in binder viscosity. The mixing methodologies employed were convec tional Z blade mixing, twin roll milling (TRM), and Extrumixing (a combinat ion of Z blade mixing and single-screw extrusion). The rheology of the past es was characterised by extrusion, with the data being theologically analys ed by the Benbow/Bridgwater and Herschel/Bulkley models. The most theologic ally favourable systems produced relatively low yield values and were not h ighly velocity dependent. Extrudates from these two paste systems were mech anically 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 th e paste from the mixer. (C) 1999 Elsevier Science S.A. All rights reserved.