Thermal stability, oxidation resistance and temperature extremes must be considered when selecting a grease for high temperature applications. In non-relubrication applications, where operating temperatures above 121°C, it is important to choose a refined mineral oil or a stable synthetic oil as the base oil. Table 28. Grease temperature ranges Contaminants Abrasive particles When rolling bearing types are operated in a clean environment, the main source of bearing damage is fatigue of the rolling contact surfaces. However, when particulate contamination enters the bearing system, it can cause damage such as galling, a phenomenon that shortens bearing life. Wear can become a major cause of bearing damage when contaminants in the environment or metal burrs on certain components in the application contaminate the lubricant. If, due to particulate contamination of the lubricant, bearing wear becomes significant, critical bearing dimensions can change, which can affect machine operation.

Bearings operating in contaminated lubricants have higher initial wear rates than non-contaminated lubricants. However, this rate of wear decreases quickly when there is no further intrusion of the lubricant, as the contaminants shrink in size as they pass through the bearing contact surfaces during normal operation. Moisture and humidity are important factors in bearing damage. Grease can provide a safeguard against such damage. Certain greases, such as calcium complex and aluminum complex greases, have very high water resistance. Sodium based greases are water soluble and therefore cannot be used in applications containing water. Whether it is dissolved water or suspended water in lubricating oil, it can have a fatal impact on bearing fatigue life. Water can corrode bearings, and corrosion can reduce bearing fatigue life. The exact mechanism by which water can reduce fatigue life is not fully understood. But it has been suggested that water can enter microcracks in the bearing raceways, which are caused by repeated cyclic stress. This can lead to corrosion and hydrogen embrittlement of microcracks, greatly reducing the time required for these cracks to grow to unacceptable crack sizes. Water-based fluids such as water glycol and converted emulsions have also shown a reduction in bearing fatigue life. Although the water from which it is derived is not the same as contaminated water, the results support previous arguments that water contaminates lubricants. Both ends of the mounting sleeve should be vertical, the inner and outer surfaces should be thoroughly cleaned, and the sleeve should be long enough to ensure that the end of the sleeve is still longer than the shaft end after the bearing is installed. The outside diameter should be slightly smaller than the inside diameter of the housing. Bore diameter not smaller than the diameter of the housing shoulder recommended in the Timken® Spherical Roller Bearing Selection Guide (Order No. 10446C) at timken.com/catalogs The required force is to carefully install the bearing on the shaft and ensure that it is perpendicular to the centerline of the shaft. Apply a steady pressure with the hand lever to hold the bearing firmly against the shaft or housing shoulder.