How can the proper bearing lubricant be selected?
Lubricant selection depends on many factors. For instance, grease lubrication may be used with rolling element bearings because it allows for the thorough dissemination of lubricant over the contact surfaces and provides simplified maintenance. Contact pressures cause the grease to release oils and facilitate lubrication of the rolling elements. The proper grease should be chosen based on factors such as moisture, bearing load, speed, temperature and shaft orientation.
Oil lubrication is another common bearing lubricant. There are various forms of oil lubrication. Oil rings or slingers are used either to augment flood oil circulation or as a separate lubrication design.
Oil rings are usually used when allowing the bearing passing through an oil bath produces too much heat due to churning. Oil mist lubrication is a centralized system providing a continuous pressurized feed of atomized oil throughout the bearing housing.
Temperature is an important factor when determining the type of, or application of, lubricants. Bearing lubricant temperatures, typically above 176 F (80 C), may cause the lubricants to oxidize and lose their lubricating ability, which will then reduce bearing life or even cause bearing failure.
It is possible with special bearings and synthetic lubricants to operate at temperatures approaching 500 F (260 C). Additionally, different bearing types such as ball bearings versus roller bearings may have different recommended oils and viscosities.
The bearing manufacturer will have recommendations on the proper bearing lubricant to be used.
For more information on bearing lubrication, refer to ANSI/HI 14.3 Rotodynamic pumps for design and application and HI’s new free white paper “Proper Lubrication Methods for Bearings” at www.pumps.org.