Wear metal measurement
The elements quantified are usually referred to as "wear metals" but this
is something of a misnomer since they are not all metal; for example,
silicon is included, which is not a metal. Also not all the elements are wear
derived; some are contaminants originating outside the machinery and
others are additives.
Wear metals may be quantified by Atomic Absorption/Atomic Emission
e.g. spectroscopy. Both are well established procedures but the latter -
using the Inductively Coupled Plasma (ICP) spectrometer - is increasing
in popularity due to its very high speed of operation.
ICP spectrometers installed at the Castrol Laboratories quantify the
following 22 elements. Other machines may have the facility to identify
and measure the amounts of different elements if required:
- Aluminium
- Barium
- Boron
- Cadmium
- Calcium
- Chromium
- Copper
- Iron
- Lead
- Magnesium
- Manganese
- Molybdenum
- Nickel
- Phosphurus
- Silicon
- Silver
- Sodium
- Sulphur
- Tin
- Titanium
- Vanadium
- Zinc
With all wear metals and contaminants, the important factor is the
change in the quantities of material identified i.e. the trend not the actual
measurement. The number of parts per million recorded has significance
only when it is compared with previous samples.
Also, it must be remembered that the trend in wear metal elements
primarily indicates the condition of the machine rather than the condition
of the oil. However, the deterioration of the condition of the oil will also be
highlighted by this trend as the amount of contamination may build up to
a point where the oil may have to be changed, or a regime of intensive
purification, or filtration, of the oil introduced. Wear debris which is by
nature abrasive may generate secondary wear material. Also as larger
particles become worn down, small pieces of debris will be formed which
increase the total "wear metal" count.
Only very small (up to approx. 8 micron) particles are collected and
quantified in a spectrometer; larger pieces of debris in the oil are
screened out. Consequently catastrophic engine failures are unlikely to be
predicted from ICP element counts since such failures usually involve the
generation of relatively large metallic particles. However, ICP ANALYSIS
can provide reliable indicators of long term wear patterns since these are
associated with the production of small particles.
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