Plain bearing failure index

8.0 Electrical damage

Electrical Damage Index


8.4 Electrostatic Erosion Damage on Journal Bearing

Click on photograph to enlarge
	Electrostatic erosion damage to bottom half bearing from centrifugal compressor
	Journal corresponding to the bearing shown in Photograph 'a'
Main Characteristics	Typical 'frosting' appearance of electrostatic arcing damage. This tends to be on a finer scale than electromagnetic current erosion, but at low magnification (5-10X), the characteristic shiny pits can be seen
Cause	Electrostatic built up on rotor of centrifugal compressor caused by droplet impingement on the wheels
Note	Note that the damage to the bearing is limited to the region of low oil film thickness, the loaded region, of the bottom half bearing, but is continuous on the journal.
Possible Confusion with Other Types of Damage	Dirt erosion (see Section 2: Erosion of White Metal Journal Bearing) and cavitation erosion (see Section 4) give a superficially similar matt finish on the bearing surface, but both of these have an arrow shape pointing against the direction of motion. Moreover, there is no corresponding damage on the journal
Comment	Electrostatic build up can result from either solid particle or liquid droplet impingement on the rotor. A build up about 20V at least is necessary for damage to be caused.

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