What does discoloration on bearing surfaces most commonly indicate?

What does discoloration on bearing surfaces most commonly indicate?

• A. Improper lubrication only
• B. Excessive load cycling
• C. Overheating
• D. Surface corrosion

Answer: (C)

Discoloration on bearing surfaces signals overheating. When bearing metal gets too hot, oxide films form and temper colors appear in the surface—often progressing from straw to brown to blue as temperatures rise. This color change is a direct record of heat exposure, usually from friction that wasn’t adequately controlled by lubrication, cooling, or proper load distribution. While improper lubrication can lead to the heat that causes discoloration, the key takeaway is that the color change itself is a thermal indicator. Surface corrosion can also alter color, but it typically shows corrosion patterns and signs of chemical attack rather than the heat-related temper colors seen with overheating. Excessive load cycling tends to produce wear and pitting rather than the characteristic overheating discoloration. So, the most reliable interpretation of such discoloration is that the bearing has experienced overheating.

Discoloration on bearing surfaces signals overheating. When bearing metal gets too hot, oxide films form and temper colors appear in the surface—often progressing from straw to brown to blue as temperatures rise. This color change is a direct record of heat exposure, usually from friction that wasn’t adequately controlled by lubrication, cooling, or proper load distribution. While improper lubrication can lead to the heat that causes discoloration, the key takeaway is that the color change itself is a thermal indicator. Surface corrosion can also alter color, but it typically shows corrosion patterns and signs of chemical attack rather than the heat-related temper colors seen with overheating. Excessive load cycling tends to produce wear and pitting rather than the characteristic overheating discoloration. So, the most reliable interpretation of such discoloration is that the bearing has experienced overheating.