Effective Viscosity Determination for Lubrication Systems Using the Lincoln Ventmeter

The selection criteria for lubricating grease in rolling bearings are different from those for a lubrication system that provides the bearings with grease. For optimum performance in bearings, the main properties are related to lubrication, whereas for optimum performance in a lubrication system, the grease should fulfill flow criteria. The main flow properties of a grease are its viscosity at low shear rates (including shear thinning) and its yield stress. In this article, a simple and robust method is described to measure both parameters simultaneously. The method is based on measuring flow through a pipe, simulating the so-called venting process, which makes the method directly applicable to lubrication systems. The Ventmeter measurements are compared to those obtained with plate-plate and capillary flow rheometers. It will be shown that the measured effective viscosity can readily be used to predict the pressure drop in lubrication systems, which makes it possible to design the system for optimum performance.