Rheological properties of lubricating greases

The flow characteristics of lubricating soap-base greases were investigated using a capillary rheometer. At low shear rates the shear stress increases because of mechanical degradation of the grease structure which results in softening of the grease and a decrease in the apparent viscosity. At high shear rates the grease flows as a newtonian liquid but with a higher viscosity than that of its base oil. Sodium-base grease showed better temperature and shear stability than aluminium-base grease.