ASTM D1092 Measuring Apparent Viscosity of Lubricating Greases
Stationary grease requires pressure to start flowing. Once movement begins, a different amount of pressure, usually (but not always) less, is required to keep it flowing. Viscosity is defined as the resistance to flow of a substance. Since a moving grease usually shows less resistance to flow than a stationary one, its viscosity appears to change as the shear rate changes, thus grease is a non-Newtonian fluid. The viscosity of grease observed when the grease is flowing, the apparent viscosity is determined in this method.
In this test, grease is packed into a large cylinder, which is fitted at one end with a nozzle and the other with a hydraulic piston. Pressure is applied to the hydraulic piston, which causes the grease to exit through the nozzle. When the grease is flowing steadily, the pressure is recorded, and the apparent viscosity and shear rate are calculated. Eight different nozzle diameters are tested. The report includes a graph of apparent viscosity in poise versus shear rate in seconds-1, and the data used to generate the graph. When requesting this test, please specify the test temperature.