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PLAIN BEARING FAILURE
6.0 Chemical effects
- Chemical effects Index
6.1 Lubricant Oxidation Deposits
| Click on photograph to enlarge | |
 | Lubricant oxidation deposits on the trailing edge of a thrust pad. |
 | Lubricant oxidation deposits on trailing edges of thrust pads. |
| Main Characteristics | Deposit forms in the loaded (high temperature) part of the bearing: the load line in a journal bearing, or the trailing edge of the pad in a thrust bearing (Photographs above). The deposit ranges in colour from reddish-brown to almost black depending on the degree of oxidation (a function of the temperature) and is characteristically patchy rather than continuous. |
| Cause | Excessive temperature. The rate of chemical reaction is a function of temperature. Although the time of exposure to the high temperature in the bearing is very short (milliseconds), oxidation of mineral hydrocarbon lubricating oils, even those containing anti-oxidants, can occur if the temperature exceeds about 150°C. |
| Note | Lubricant oxidation deposits are a clear sign of excessive temperature and are frequently associated with other effects such as wiping and plastic deformation. In the case of thrust bearings the deposits may be restricted to only a few of the pads, showing differences in the pad heights with the affected pads carrying most of the load. |
| Possible Confusion with Other Types of Damage | Other deposits described in this Section tend to look superficially similar. The final diagnosis requires chemical analysis. |
| Comment | Oil degradation deposits are usually soluble or partly soluble in aromatic solvents and can be removed by wiping with a swab soaked in the solvent, but see Summary Sheet at end of this Section for possible analytical techniques. |