Development and validation of a modified annular shear cell (MASC) to study frictional properties of lubricants

Abstract

Mostly, lubricants in the past have been evaluated on a tablet press. Some of the techniques used have been the force difference between the upper and lower punches (FD), the punch force ratio (R-value), the remaining force on the lower punch (REF) and the ejection force (EJF) (Holzer and Sjogren, 1981). These techniques generate parameters which effectively integrate over the whole compact-die interfacial area but preclude a point-to-point examination of the frictional conditions. The above parameters are also dependent on the stress transmission characteristics of the host material, which are not generally known. Since these parameters are usually measured on single punch presses using a filler binder excipient as the host material, it becomes almost impossible to comment decisively on the frictional properties of the lubricant under study. Thus it was proposed to develop a basic analytical tool which would provide reproducible measurement of friction data between pure lubricants and metal wall material under a controlled set of conditions. The modified annular shear cell (MASC) (Fig. l), similar to the annular shear cell designed to measure failure properties of powders (Carr and Walker, 1967/68; Kocova and Pilpel, 1971/72) but with a smooth polished surface on the underside of the lid instead of the recessed vanes, was designed and constructed to quantitate the amount of friction between a thin powder bed of the test lubricant and the polished steel underside of the lid. The MASC had an inner diameter of 15.24 cm and an outer wall diameter of 25.40 cm; these dimensions being chosen to give a reasonable size cell without too large a ratio