 |
|
 |
|
|
Spectrochemical
Analysis
The identification of the trace metals contained in an oil sample
is of prime importance in Condition Monitoring. Typically, an Atomic
Emission Spectrometer is used to identify common wear metals, contaminates,
and inorganic additives found in lubricants. This analysis is typically
rapid and inexpensive. Spectrochemical data is reported in parts per
million.
Common Sources of Metals
Wear Metals
Wear metals are the result of components in the system making contact
and creating a wear regime that is not desirable. Common sources of
wear metals are:
| • |
Iron - Cylinders, liners,
pistons, rings, valves, valve guides, anti-friction bearings,
gear train, accessory gear drives, shafts, clutch plates, rust.
|
| • |
Aluminum - Pistons, bearing,
blower/turbos, pump vanes, thrust washers. |
| • |
Chromium - Compression rings,
chromate from cooling system, anti-friction bearings, shafts.
|
| • |
Copper - Bearings, bushings,
thrust washers, valve guides, injector shields, oil cooler core
tubes, some clutches. Additive in some oils, anti-seize and
gasket compound. |
| • |
Lead - Bearings, plating's,
leaded gear lubes, leaded gasoline.
Tin - Bearins, plating's. |
| • |
Nickel - Shafts, valves,
anti-friction bearings. |
| • |
Silver - Silver solder,
wrist pin bushings (EMD). |
| • |
Vanadium - By-products of
heavy fuel oil and occasionally a wear metal. |
Contaminants
Contaminants are usually the result of outside ingression of undesirable
elements in the oil.
| • |
Silicon - Sand, dirt, dust,
also contained as Silicone in new oil as anti-foam agent,low
concentrations. Also anti-freeze and gasket sealing compounds.
|
| • |
Sodium - Contained in some
new oils. Also contamination from anti-freeze, salt water. |
| • |
Boron - A contamination
from anti-freeze. Is also used as an additive is some gear oil
formulations. |
Additive Metals
We also measure certain metallic elements that are found as additives
in a variety of lubricating oils. The primary purpose of analyzing
for the additives is to ensure that the appropriate additives are
present and that there are no other inorganic additives that indicate
that cross-contamination has occurred. Performing an analysis on the
fresh un-used lubricant will show which additives are there and which
are not. Subsequent oil samples can be compared to this baseline.
| • |
Zinc - Is a component
of the lubricant additive ZDDP (zinc-dithio-dialkyl-phosphate),
which is an anti-wear (AW)additive for hydraulic oils, engine
oils, transmission fluids, and some circulating oils. |
| • |
Phosphorus - Is the other
component of the lubricant additive ZDDP (zinc-dithio-dialkyl-phosphate),
which is an anti-wear (AW) additive for hydraulic oils, engine
oils, transmission fluids, and some circulating oils. Phosphorus
can also be present in some turbine type oils and gear oils
as an anti-scuff additive. |
| • |
Calcium - Engine oils , hydraulic oils, transmission
fluids, and some circulating oils contain calcium in the form
of calcium sulfonate or calcium phenate. It is formulated to
act as a detergent /dispersant. |
| • |
Barium & Magnesium -
These inorganic additives are sometimes used in the place of
or combination with calcium for the same purpose. |
| • |
Molybdenum - Most often
molybdenum is in the form of molybdenum disulfide, which is
intended to act as a mechanical friction modifier. |
| • |
Cadmium - Contained in some
new oils as an additive. |
| • |
Manganese - Contained
in some new oils as an additive. |
| • |
Titanium - Contained in
some alloys. |
How It Works
The oil sample is ionized in a control chamber; the light from this
burning process is separated by a diffraction grating (much like a
prism). Each element emits its own characteristic wavelength of light
(energy). Photomultiplier tubes are positioned to collect this light
from the specific metals. With the aid of a computer, the intensity
of light is compared to a standard and converted to parts per million.
The value of emission spectroscopy is well known. The laboratory can
evaluate trends in wear rates, cross contamination with different
lubricants (additives), contamination from silicon (dirt) and coolant
additives. However, the user should be aware of certain drawbacks.
The particle size of the elements in question has a great impact on
the ability of the spectrometer to completely and consistently excite
them to the state required for accurate analysis (for a solution to
this problem, see Ferrography). This problem is so extreme in certain
applications that a digesting process is required prior to the analysis
in order to get all of the particles in the sample to a soluble state
for accurate and consistent results.
For more information call 1-888-HERGUTH (437-4884) |
|
|
