Interconversion of grease flow curves between rheometers

Abstract

In order to reduce testing time and to cover a wide range of shear rates, it is desirable to be able to predict pipe flow curves for grease from measurements on modern rotary viscometers. Previous papers have shown that reliable measurements of grease flow curves can be made in grease rheometers and also how pipe flow curves may be calculated from flow curves obtained in cone and plate or concentric cylinder viscometers. In this paper results are presented of a correlation study between two rotary viscometers and two pipe rheometers used for grease. It is shown that grease pipe flow curves can be predicted from measurements in rotary viscometers. Flow curves obtained in this way correspond to the undisturbed grease under start-up conditions. The influence of long shearing times on the grease during flow in long pipes is shown to explain apparently anomalous results obtained with one rheometer.