Processing properties of ceramic paste in radial flow

In order to produce better ceramics, it is important lo study processing behaviour, especially during forming. In the present paper, radial flow between two flat and parallel discs is studied, flow being provided from a central hole in one of tile discs. A theoretical model for such radial flow is presented by the analysis of the force balance on the paste in the gap. It demonstrates that both the friction force (shear stress at wall) and the shape change in the hoop direction control the filling pressure. The relative magnitude of each component is dependent on the gap size for all pastes used. The effects of absolute pressure on the shear stress and the yield stress in radial flow are experimentally evaluated. Two kinds of monolithic paste, mainly based on alumina but with different binders, in addition to their composites with various glass fibre contents, are used to verify this model. It is shown that the experimental data can be well described by the theoretical model. Additionally, the flow behaviour constants obtained during die extrusion may be used in predicting radial flow. The theoretical model presented provides a useful platform for further study of radial flow of ceramic pastes. BCT/302 The authors are in the IRC in Materials and School of Chemical Engineering, The University of Birmingham, Birmingham B15 2TT, UK. Manuscript received 21 November 1997; in final form 16 March 1998.