WALL FRICTION IN THE COMPACTION OF AGGLOMERATED CERAMIC POWDERS

The paper describes an experimental study of the single-sided uniaxial cylindrical compaction of zirconia and alumina powders which were agglomerated with two water-soluble organic polymers; poly(vinyl alcohol) and poly(ethylene glycol). In some cases, the die walls were lubricated with calcium stearate powder, an established wall lubricant. The transmitted stress ratio, that is, the ratio of the transmitted stress to the applied stress, has been continuously measured as a function of the aspect ratio of the compact during its compaction. The wall friction has been deduced and the values obtained have been compared with data obtained in a variety of subsidiary experiments. The comparison has been made by assuming that an extension of an established model of friction is applicable to compaction and the subsidiary experiments. The model assumes that the frictional work is dissipated at the walls in the organic component or wall lubricant and that the friction arises from interface shear at real areas of contact. The various data, when compared within the framework of this model, are generally self-consistent. The quality of the comparison is interpreted as evidence to support this model as a viable means of interpreting and predicting wall friction in compaction. For the systems studied, it is shown that the wall friction coefficient is given, to a fair approximation in compaction, by the pressure coefficient of the interface shear stress of the organic species present at the walls.