Which of the following bearing assemblies must be greased?

• A. Ball bearings
• B. Bronze bearings
• C. Sleeve bearings
• D. Brass bearings

Answer: (A)

Lubrication is essential to keep bearings from rubbing metal-to-metal and overheating. In rolling-element bearings, a thin film of lubricant between the balls and the raceways is what actually carries the load and prevents wear. Grease provides that film, helps seal out dirt, and aids in removing heat during operation. Because maintaining that lubricant film is so critical for reliable performance, ball bearings are typically greased to operate properly. Other bearing types can be designed to use self-lubricating materials or different lubrication schemes, so they aren’t universally dependent on grease in the same way.