Above: cutting wear debris in a hydraulic fluid.
Below: large ferrous particle.
Info Centre >> Fuel and Lube Oil Technical Manual >> 7. Lube Oil - Test Results >> 7.8 Spectrochemical Oil Analysis
This type of analysis requires equipment only available in a good laboratory. It is used to analyse the constituent elements in particles of typically less than 5 micrometers in size. Selected metallic elements present in the oil are identified and measured in parts per million by weight. The elements are grouped into three main categories of Wear Metals, Contaminants and Additives from the base oil.
Some of the particles removed during normal wear are small enough to remain suspended in the circulating oil. Since these wear products are composed of the same materials as the surfaces from which they originated, the level of each wear metal remaining in the used oil indicates the relative wear condition of the lubricated parts.
Five of the most commonly accepted types of wear are:
Adhesive wear - occurs when the oil film becomes so thin that the roughest points of the opposing surfaces begin to touch each other. It occurs normally during both break-in and route service as the parts wear slightly to maintain alignment. If severe adhesion occurs due to load, speed or temperature conditions, scuffing and scoring will result. In normal service, adhesive wear is controlled with antiwear additives.
Fatigue wear - occurs when cyclic or repeated load stresses cause cracking, spalling, and pitting of the component part surfaces. This type of wear is more commonly associated with rolling element bearings and gears where the part surfaces roll past each other.
Corrosive (chemical) wear - Results when chemical reactions cause corrosion or oxidation of part surfaces and part movement or fluid pressure dislodges material from this surface layer. This type of wear is associated with rust promoting conditions, corrosive contaminants and excessively high levels of chemically active additives.
Cavitation wear - occurs when metal is removed from parts by the impact of collapsing cavitation bubbles on the surfaces. Cavitation itself is associated with partial vacuums formed in a liquid by sudden changes in pressure. It may be caused by vibration and reduced or uneven liquid flow conditions.
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