Plain bearing failure index

9.0 Incompatible Journal or Thrust Collar Material

9.1 Failure of Bearings with Nitrided Steel Shaft
9.2 Wire-Wool Failure of Journal and Thrust Bearing
9.3 Unsuitable Journal or Thrust Collar Materials - Summary


The design philosophy with plain bearings is that, should failure occur, the shaft or thrust collar should be unharmed with any damage limited to the bearing. This imposes little restriction on the choice of the shaft or thrust collar, which is normally of steel, apart from the general rule that they should have a hardness at least three times that of the bearing material. This means that mild steel is perfectly satisfactory with white metal bearings, though hardened steels are required for harder bearing alloys, such as the lead-bronzes. Again, this poses no particular problems, though nitrided steels must be cleaned by lapping before use, otherwise they are liable to cause bearing damage.

The one exception is that steels containing more than 1.5% chromium should not be used where peripheral speeds exceed 25 m/sec to avoid the risk of a destructive failure mechanism known as wire-wool failure (black-scab failure). The failures occur most frequently with steels having chromium contents in the range 3-18% in bearings operating with surface speeds greater than 80 ft/sec (25 m/sec).  

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