Rheology and Local Flow Behaviour of Ceramic Slurries in the Tape Casting Head

摘要

The rheological behaviour of ceramic slurries is the dominant factor in the tape casting process using the Doctor Blade method. It determines the fluid mechanical behaviour in the casting unit, the spreading behaviour of the cast film on the tape carrier, its drying behaviour, and therefore the quality of the final green tape. The rheology of the slurries is determined by their composition, by the temperature, and by the occurring shear stresses and other fluid mechanical parameters in the casting unit. These interrelations between rheology and fluid mechanics during the tape casting process are described in this paper. The composition of non aqueous zirconia suspensions and polymer solutions was varied. The modification of the rheology was examined by viscosity and oscillation measurements. The measured stress, the time and temperature dependence of the viscosity and their interrelation with the slurry composition are discussed. Beneath the rheological behaviour of ceramic slurries a detailed knowledge of the local flow behaviour is important for the optimization of processing parameters during tape casting. To get information on the local flow behaviour in the flow channel of the casting unit, laser-Doppler-velocimetry (LDV) was applied. By means of the LDV equipment the local flow behaviour was directly investigated in the casting head during casting. The accuracy and the high spatial and temporal resolution of the used LDV-system opens a way to get a detailed insight into the complicated flow phenomena and to check the validity of model calculations. The results of these investigations are discussed and compared with theoretical model calculations of the velocity profiles.