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Plain Bearing Failure
2.0 Wear
2.6 Summary
Characteristics
Wear by hard particles larger than the minimum oil film thickness in the bearing give characteristic continuous scores extending to a discontinuity in the bearing surface (oil groove, trailing edge of thrust pad) or ending in an embedded foreign particle.
Erosive wear is a fatigue process causing small scale removal of material that results in a characteristic roughening of the surface. Superficially this can resemble cavitation erosion and electric erosion/spark erosion, but the former occurs in the centre of bearing lands away from oil feed holes and the latter results in small rounded shiny melt pits that are quite different in appearance.
Possible Causes
Two causes of wear damage are discussed in this section: abrasive wear caused by the cutting action of hard particles that bridge the
hydrodynamic oil film; erosive wear, the small scale removal of material by fatigue resulting from the mechanical action of small particles repeatedly striking the surface.
Actions
Where damage is caused by solid particles in the lubricant, the only remedy is improved filtration of the oil. This should be no problem where there are duplicate filters, but single filters with over-pressure relief can release particles into the lubricant when the filter becomes blocked and there is a risk of particle release when filter changes are made.
Magnetic plugs should be fitted to reduce damage by ferrous wear particles.
Analytical Methods
Analysis of filter debris may be useful in identifying the source of solid contaminants, with iron printing using absorbent paper soaked in potassium ferrocyanide a useful technique for the identification of ferrous particles embedded in soft bearing materials.