Plain Bearing Failure - Wiping damage caused by excessive load at start-up

PLAIN BEARING FAILURE

Plain bearing failure index

1.0 Lubrication breakdown

Lubrication breakdown index

1.2 Wiping damage caused by excessive load at start-up

Click on photograph to enlarge
	Wiping of white metal thrust pad caused by successive starts under excessive load.
Main Characteristics	Obvious melting of bearing metal that has been carried over the trailing edge of the pad and solidified in layers once subjected to the cool oil flowing between the pads.
Cause	Excessive thrust load at starting has meant that the bearing metal has been subjected to rubbing and frictional overheating before the development of hydrodynamic lubricating film. The molten white metal has resolidified on coming into contact with the cool oil flowing between the pads. The photograph shows successive layers of resolidified white metal following a number of starts. For more information on causes of lubrication breakdown and possible actions to take, see Lubrication breakdown - Summary
Note	With thrust pads, successive wear at start-up can change the profile of fixed inclined pads leading to a reduction in load capacity. With tilting pads thrust bearings the effect is not so severe since the pads can compensate for wear and therefore maintain a thrust capacity. With profiled journal bearings (e.g. multi-lobe, offset half bearings), small amounts of wear can lead to changes in the rotor stability and hence machine vibration which in turn can result in further bearing wear.
Possible Confusion with Other Types of Damage	It is not always straightforward to distinguish between wear at start-up and wear during normal operation. With journal bearings, if the angular position of the region of wear is in-line with the direction of load then this supports the case for wear at start-up
Comment	If the load at start up cannot be reduced, the only cure is to use a larger bearing. Changing lubricant viscosity and/or lubricant additives is unlikely to help.