GENERALIZED FLUID-FLOW MODEL FOR CERAMIC TAPE CASTING

The fluid mechanics associated with the flow of a ceramic slurry durin g the tape casting process is analyzed in this paper. The rheology of the slurry is described in generalized terms using the Ostwald-de Wael e power-law equation, tau = m\gamma\(n), where the yield constant, m, and the shear rate exponent, n, are empirical functions of the particl e loading in the slurry, the particle shape and size distributions in the slurry, and the slurry temperature. The effects of an imposed pres sure gradient due to the height of the slurry in the casting head, as well as those of the drag due to the moving substrate on the slurry fl ow, are accounted for by modeling the slurry discharge as a generalize d planar Couette flow. The model yields an analytical expression for t he tape thickness as a function of various slurry and process paramete rs. The influence of the physical parameters of the slurry and the geo metrical dimensions of the casting head on the tape thickness are exam ined in the context of a commonly used BaTiO3 system. It is shown that the various parametric effects may be represented concisely in the fo rm of a nondimensional design plot employing (a) a flow parameter, alp ha, (b) a shrinkage parameter, beta, and (c) the theology exponent, n.