Technical Information Page 1
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| The OCLS Laser Particle Counter |
Particle
counting is probably one of the best tests there is for maintaining system cleanliness. The point of contention lies
with whether or not particle count is an appropriate test for all fluid types and systems. Whilst it is an
excellent method for determining the number and size of particles being generated, particle count won't tell you what the particles are. They could be metallic – both ferrous and non-ferrous – silica (dirt,
dust), silt, filter fibres, bacteria colonies, varnish agglomerations, water, etc. Therefore, the decision to do particle
count testing should be based on the type of information you want to collect.
The
unit types that benefit most from particle count testing are hydraulics, compressors, refrigeration compressors, turbines,
automatic transmissions, natural gas engines, robotics, injection moulding machines and "filtered" bearing or gear systems.
Particle count is also a good test for diesel fuel, solvents, water-based hydraulic fluids and lubricants.
It's
also useful on new oils for the above units as it tells you how clean the oil is when introduced to the system. Many
users aren't aware of the fact that new oil may actually have higher particle counts than the used oil from the machine.
Oil can pick up dirt during the manufacturing process itself, where filtration is expensive and therefore an indication of
the quality control applied during the process. Unwanted particles are also picked up during transport and distribution
as new oils are transferred from container to container.
If a gear system is
filtered, particle count data may be useful. But if the gearbox is not filtered, particle count data doesn't provide
as much information as would other tests such as PQ/FW (Particle Quantifier / Ferrous Wear) or DR (Direct Read) Ferrography.
Diesel engine oil is black and requires different techniques to the tried and trusted lasercounting methods. FW/PQ,
DR Ferrography and Wear Debris Analysis are probably wiser choices. (WDA is a vital tool in failure and warranty issues).
„ Oil Cleanliness:
Let's make it crystal clear...
Cleanliness
is a term used to describe the relative quantity of contaminant particles in any given system. One can gauge a fluid's
cleanliness by referring to a number of internationally-agreed standards. Every machine has an optimum cleanliness level.
This level will be a balance between the maintenance of the machine's efficiency and the cost to maintain cleanliness.
Cleanliness doesn't just refer to the particles that you can see - there are some that are invisible to the naked
eye.
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| Relative Size Comparisons (Click for a better view) |
How is cleanliness measured?
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| Click for a better view |
The
most common standard used to rate cleanliness is ISO 4406. This table shows the ISO Codes that are
used to represent the number of contaminant particles present in 1ml of oil.
The
three-number code relates to the number of particles that are >4µm, >6µm and >14µm in size.
(1.0µm*
= 1.0 x 10-6m = 0.001mm)
*
The unit 'µm' (micrometer) is commonly pronounced as
simply "micron".
So, an oil that gave readings
of...
72,064 particles >4µm;
16,519 particles >6µm;
541 particles >14µm;
...would,
after refering to the table, result in an ISO Code of 23/21/16.
The Effects of Poor Oil Cleanliness
Poor oil cleanliness can:
- Damage interacting components via abrasion;
- Reduce component life via erosion;
- Obstruct critical flow paths;
- Damage servo or proportional valves;
- Increase quality problems;
- Increase customer dissatisfaction;
- Reduce market perception;
- Damage business opportunities;
- Raise costs.
What Failures Are Likely Due
To Poor Oil Cleanliness?
- Sudden or catastrophic - this is caused
when a small number of particles invade a critical space and create a torque reaction large enough to cause a seizure
or fracture which is irreversible.
- Intermittent - similar to that above but usually caused
by smaller size structures. Intermittent events will eventually lead to sudden or catastrophic failures.
Typical examples are temporarily blocked or unseated spool/poppet valves.
- Degradation - Typically characterised by flow erosion,
abrasion, polishing and general wear.
For more information, click on the link below to download a presentation
(in powerpoint format) on oil contamination and particle counting.
Click here to download the presentation
„ FTIR:
What's it all about?
FTIR stands
for Fourier Transform Infrared Spectroscopy. It is often simply referred to as an 'Infrared test'. Infrared
testing allows us to get a picture of an oil's health and also whether any contaminants are present such as fuel or coolant.
An infrared spectrometer works by passing an infrared beam
through a fixed thickness of oil, usually 100µm (0.1mm).
Firstly, a sample of new oil is tested to establish a baseline
reading.
Then, a sample of the used oil is tested. Oil contaminants and additive
molecules will absorb some of the infrared radiation, but only at certain frequencies. Soot and other particles will
absorb the radiation at all frequencies.
After testing, the frequency spectrum of the used oil is compared to that of
the new 'reference' oil tested beforehand.
We can then see how the oil condition has changed from its virgin state to
is used state and make recommendations as necessary.
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| A typical infrared spectrum |
It is very important that we receive a sample of virgin oil
to get the most out of this test - the accuracy improves considerably if the correct reference oil is used.
Accurate measurements of fuel dilution and glycol content are highly dependent
on the correct reference oil.
With this test, we gain an appreciation for the oil condition by determining
values for:
- Oxidation;
- Sulphation;
- Nitration;
- Soot.
Oxidation is the reaction of
Oxygen from the air with oil. This reaction usually occurs as a result of high running temperatures or the
presence of water, acids or other contaminants. An increase in oxidation usually causes an increase in the viscosity
which can lead to further problems (see viscosity section).
Sulphation is usually a result
of abnormal blow-by in diesel crankcase engines. It can also occur due to the use of high-sulphur fuels. A high
sulphation value indicates the presence of sulphur oxides and sulphuric acids. Engine over-cooling and also short journeys
can result in an increase in sulphation. Sulphation correlates inversely with the TBN (see TAN & TBN section).
Nitration is
similar to oxidation but concerns the reaction of Nitrogen from the air with oil rather than Oxygen. The nitration process
is linked to high running temperatures and can form such organic compounds as nitrate esters. High nitration can lead
to the formation of grease-like sludge deposits and varnishing.
Soot is produced as a result
of the incomplete combustion of fuel. It is made up of black, impure particles of carbon. High soot can occur
due to an incorrect fuel-air ratio in the combustion chamber of an engine. Faulty injectors can also lead to high soot.
High soot can cause sticking rings, piston damage and bore polishing.
„
ICP-AES:
It's elementary!
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| The plasma flame |
ICP-AES stands for Inductively Coupled
Plasma Atomic Emission Spectroscopy. This technique uses the inductively coupled plasma (left) to produce excited
atoms and ions that give off electromagnetic radiation of varying wavelengths. Each element of the periodic table has
a corresponding wavelength. The detector within the ICP detects this wavelength and also its intensity and can
therefore calculate the amount of each element present within a sample.
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| OCLS ICP |
The flame seen in the picture above is generated by ionizing argon gas
and running it through an intense magnetic field. The temperature of the flame
is about 7000K (6727°C). In comparison, our Sun's surface temperature
is about 5778K
(5505°C). The flame appears green
but this is because it is being seen through a green filter which protects the eyes of the operator from harmful ultraviolet
radiation. The true colour of the flame is white.
The ICP reports the amount of each element in ppm (parts per million).
The data gathered from the ICP constitutes a large chunk of the overall OCLS report.
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| The optics of our ICP |
An ICP works by using a complex system of prisms, mirrors
and detectors. The following is a brief outline of it is able to work out element concentrations (even down to 1 ppm!) in
a sample of your oil.
An overview of the entire process can be seen in the picture to the right.
- The plasma emissions from the torch are focussed through a
series of mirrors.
- The positioning mirrors self-adjust to maximise the light sensitivity.
- A collimating mirror directs the light beam onto an Echelle grating.
- This grating diffracts the monochromatic light into its constituent wavelengths.
- From here, it travels through a prism which cross-disperses the light beam into
its constituent wavelength orders.
- The resultant beam from the prism forms a 2D image called an Echellogram which
shows a cascade of wavelengths varying from 167 - 785 nm. (1 nm [nanometer] = 1 x 10-9
m......one millionth of a millimeter!)
- Then, a camera mirror then focuses this image onto an extremely sensitive
detector chip which is cooled to -35°C to improve accuracy.
- Finally, the computer calculates the amounts of each element present in the
sample based on the wavelength patterns on the detector chip.
