Why do bearings turn blue or black? Can they still be used?
During the operation of industrial equipment, bearing discoloration is an important visual signal that should not be ignored. It is often an external manifestation of internal issues within the equipment. When bearings turn blue, black, or other colors, it usually indicates that the equipment is already in a high-risk state. So why do bearings discolor? Can they still be used after discoloration? This article will provide an in-depth analysis of the causes of bearing discoloration and corresponding countermeasures.
I. The Temperature Code of Bearing Discoloration: Warnings from Light Yellow to Black
The change in the bearing’s color is essentially a direct reflection of temperature variation:
| Light Yellow (about 150℃): | This is the initial stage of high-temperature oxidation. Although it has little impact on performance in the short term, it signals potential issues in lubrication or heat dissipation. Inspection is recommended. |
|---|---|
| Iridescent Colors (above 200℃): | Caused by the light interference effect of the oxide film, this is a clear sign of overheating. The load and lubrication conditions must be checked immediately. |
| Blue/Purple (above 250℃): | At this temperature, tempering occurs. The material hardness decreases significantly and the load-bearing capacity drops sharply. The machine must be stopped and the bearing replaced. |
| Black (above 400℃): | The surface is covered with iron oxide. The material becomes fully annealed, and the structure is severely damaged and irreversible. Continued use will directly lead to equipment failure. |
II. Root Cause Analysis of Bearing Discoloration
Bearing discoloration is not an accidental phenomenon and is usually triggered by the following factors:
| Lubrication System Issues | Insufficient lubrication oil or improper oil selection; incorrect lubrication method or clogged lubrication points. |
|---|---|
| Excessive Load or Misalignment | Equipment running under overload; shaft misalignment or large installation deviations. |
| Installation and Fit Problems | Improper fit tolerances; unreasonable clearance settings. |
III. Recommendations for Handling Bearing Discoloration
Once bearing discoloration is discovered, the following actions should be taken immediately:
Shut down the equipment to prevent the issue from worsening; conduct a thorough system check of lubrication, load, and installation conditions; replace with high-temperature bearings if the equipment operates in high-temperature environments for extended periods.
IV. Conclusion
Bearing discoloration is a “distress signal” from the equipment. From light yellow to black, every color change reminds us that maintenance cannot be delayed and safety must come first. Only by identifying and addressing these signals in time can equipment life be extended and operational safety ensured. If you encounter issues such as bearing discoloration or overheating, feel free to contact us for professional technical support.
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