Rolling Bearing Failure Modes - Rolling Bearing Failure Mode Classification - Corrosion (Moisture Corrosion)
Poor sealing performance of bearings during storage or use may result in the entry of moisture, water, and corrosive liquid pollutants into the bearings. Once the intrusion of liquid pollutants exceeds the bearing capacity of the lubricant, the surface of the steel will rust.
Bearing oxidation
The surface of steel exposed to air will form a thin protective oxide film. However, this oxide film is not impermeable. If moisture or corrosive liquids come into contact with the surface of the steel, oxidation will occur. Shortened the service life of stainless steel bearings.
Bearing corrosion
For process equipment in the paper machine and food and beverage industries, corrosion of customized bearings may be the most common cause of early bearing failure. When the bearings in these devices are running, they are easily invaded by water or other liquids used as processing flow. In addition, when the mechanical equipment is shut down for flushing, water may enter the bearings, causing gray black spots to form at equal intervals on the rolling elements (see figure below).
Corrosion diagram of bearing rolling elements and bearing outer rings
Bearing etching
In the shutdown state, free water in the lubricant will accumulate at the bottom of the bearing. Among them, the degree of water accumulation at a specific distance from the rolling contact surface will be the most severe (see the figure below). The reason for this phenomenon is that water has a higher specific gravity than oil, so it will sink until the gap between the rolling elements and the raceway reaches an appropriate size
Water accumulates at the bottom of the bearing in the lubricant
This phenomenon may also lead to deep corrosion, which we call etching (see figure below). Etching damage usually occurs in applications with corrosive chemicals and high temperatures, such as the dry parts of paper machines.
Initial etched spots on the rolling element pitch circle on the inner raceway of the bearing
Etching often leads to premature and expansive peeling of bearings, as the material undergoes structural changes and the surface of components in the load zone deteriorates until overload occurs. The best way to prevent this corrosion is to perform reliable sealing to ensure that the lubricant does not contain moisture or any corrosive liquids. In addition, using lubricants with good rust prevention properties can also help alleviate corrosion.
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