"What is the typical base oil viscosity of grease used in high-speed bearings?"
The base oil composition of the grease can provide a substantial separation between the two surfaces that may be in contact. Therefore, it is very important to choose the correct viscosity. A common method of determining the appropriate viscosity is to first determine the speed factor, which is calculated based on the bearing speed (revolutions per minute) multiplied by the pitch circle diameter (if using the NDm method). When the bearing speed increases, the speed factor also increases. If the bearing speed and speed coefficient increase, the corresponding viscosity of the application will need to be reduced.
As shown in the figure below, when the speed coefficient is close to 600,000, base oil viscosity below 70 centimetres (40 degrees Celsius) is ideal. Since high-speed applications tend to have higher temperatures and therefore shorter grease life, the overall grease characteristics should be designed to withstand these conditions.