Basic Study of Grease Rheology and Correlation with Grease Properties

Abstract

Comprehensive interpretations of grease properties are presented. Dropping point, penetration and rheological properties are examined for a wide variety of greases involving both lithium soap greases and diurea greases. Types and viscosity of the base oils, types and content of the thickeners and manufacturing conditions are extensively varied in the greases examined. Grease exhibits the rubbery region over a wide range of frequency, indicating the network structure formed by thickener fibers. The magnitude of storage modulus, G', in the region is related to the network density of the thickener fiber in analogous to polymer rheology. Two regions are found in the dropping point of grease. In the Region A, dropping point decreases as the network density decreases. In the Region B, the dropping point is almost independent of the network density, but dominated by network collapse. Moreover, the loss modulus, G'', at non-linear regime, representing viscous dissipation of energy, is found to be a controlling factor for the penetration, and it allows for excellent correlation with the extensive body of penetration data.