Which of the following is a common bearing failure mode?

• A. Wear
• B. Magnetic pull
• C. Surface rust on housing
• D. Electrical arcing

Answer: (A)

Wear is the most common bearing failure mode because the bearing surfaces are constantly sliding under load and must be kept separate by a lubricant film. When lubrication breaks down, gets contaminated, or the operating conditions exceed design, metal-to-metal contact occurs. This wears away material, roughens raceways and rollers, and changes clearances, which raises heat and vibration and eventually leads to failure. Various wear mechanisms contribute to this progression: adhesive wear from material transfer between surfaces, abrasive wear from hard particles or rough surfaces cutting into metal, and fatigue wear from repeated loading that causes cracks and spalling. The result is a gradual decline in performance, often seen as increased noise, warmth, and vibration, eventually culminating in failure if not corrected.

Other options aren’t the typical path to bearing failure. Magnetic pull isn’t a common mechanism inside bearings, as it doesn’t describe wear or surface degradation. Surface rust on the housing doesn’t directly describe the bearing surfaces’ wear, though it can indicate moisture issues that may affect mounting or lubrication. Electrical arcing through a bearing can cause pitting and damage, especially in electric motors, but this is a more specific and less frequent failure mode compared to ordinary wear under normal operating conditions.