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There are two sides to every story
and that is the case with oil analysis. The figure
below depicts the traditional used oil analysis (UOA)
and the wear particle analysis. Each have a place
in your oil analysis program, the question that needs
to be answered is what information are you looking
for?
Used oil analysis involves sampling
and analyzing oil for various properties and materials
in order to monitor
wear and contamination in an engine, transmission
or hydraulic system. Sampling and analyzing on a
regular basis establishes a baseline of normal wear
and can help indicate when abnormal wear or contamination
is occurring.
Used oil analysis works like this. Oil that has
been inside any moving mechanical apparatus for a
period of time reflects the exact condition of that
assembly. Oil is in contact with mechanical components
as wear metallic trace particles enter the oil. These
particles are so small they remain in suspension.
The oil becomes a working history of the machine.
There are two main characteristics of used oil analysis
that are of particular importance: physical properties
and elemental analysis. Physical properties include:
- Viscosity
- Oxidation
- Water Content
These three properties control many of the aspects
of the lubricant. Changes in any of these, up or
down, indicates an abnormal condition and would need
to be addressed.
Elemental analysis, also known as spectroscopy,
is the analysis of the chemical composition. A sample
of the lubricant is subjected to a high energy source
usually either an electric arc or plasma flame. The
lubricant is vaporized and the light generated is
based through a series of prisms and detectors. The
count, given in parts per million (ppm), is displayed.
The elements are broken down into wear, additive
and contaminant.
Wear
Elements |
Additive
Elements |
Contaminant Elements |
- Iron
- Lead
- Tin
- Aluminum
- Copper
- Silver
- Nickel
|
- Phosphorus
- Zinc
- Barium
- Calcium
- Magnesium
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- Sodium
- Silicon
- Vanadium
- Titanium
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Wear particle analysis is also known as Ferrography.
Ferrography is determined by using precision magnets
to strip iron-laden and other susceptible particles
from a used lube oil for study; results indicate extent
of equipment wear and likelihood of imminent failure.
Direct-Reading Ferrography uses
optical sensors to measure the density of particles
collected and the ratio of large particles to
small (fatigue-related catastrophic failure generally
is
characterized by generation of particles larger
than 10-15 microns or um).
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