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Used oil analysis is
comparable to a medical analysis with a blood test. Like blood, lubricating oil
contains a good deal of information about the envelope in which it circulates.
Wear of metallic parts, for example, produces a lot of minute particles, which
are carried by the lubricant. These small metal particles can give information
about the machine elements that are wearing, and can be detected by various
methods, for example, Atomic Emission Spectrometry. Determination of larger
particles can be done using optical or electronic microscopy, or ferrography
The acidity of an oil shows whether the oil is oxidised as a result of
operation at high temperature, if there is a high percentage of moisture, or
whether the oil has been in service for too long. The viscosity of the oil is a
very important parameter and must be in conformity with the requirements of the
machine builder. The alkalinity or the loss of alkalinity of the oil, proves
that the oil is in contact with inorganic acids such as sulphuric acid or
nitric acid.
The causes of oil contamination are many, and can be classified according to
source. Thus there is contamination coming from outside the system - dust
(silica); liquids (mixture with other oils, water, other contaminated oil). The
second is in open systems - chains, cables, gears in contact with dust, water,
and so on. The third is in closed systems
Oils undergo destructive changes in property when subjected to oxygen,
combustion gasses and high temperatures. Viscosity change, as well as additive
depletion and oxidation occur to degrade the oil.
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