I am new to fluid testing have a question about optical particle counters that I hope you can help with.
I am planning on using a LPC LCM20 to test automatic transmission fluid in fleets of vehicles with various models of transmissions which may have new oil of different types/brands as well as used oil. The purpose of the testing is to identify excessive amounts of harmful wear particles and/or verify cleanliness levels. One of our customers has questioned the validity of testing automotive transmission fluid with optical particle counters because of comments in a report from one of the major oil companies that is also their oil supplier. In addition to particle counting, the oil supplier used UC (ultra centrifuge) equipment to test fluid samples from the customer. The comments follow. . .
"It should be noted that optical particle count instruments are based on the disruption of a light beam. Any material that disrupts the light beam will be counted as a particle and not all of these will be abrasive particles. Certain lubricant additives, particularly antifoam, viscosity index improver and detergent additives can be read as particles by the counter under certain conditions. For this reason, lubricants with higher levels of these additives, such as most automotive lubricants, will exhibit higher particle counts than lubricants with lower levels or different types of additives altogether, such as industrial lubricants."
My main question is how much variability in results can be related to differences in the oil additives in automotive transmission fluids (i.e. different brands or synthetic vs. non) ?
And, is laser particle equipment (Parker LCM20) a valid method for identification of excessive amounts of harmful wear particles in the fleets described above.

Thanks,
Gregg (newbie)

I tend to think that the change in colur of the transmission fluid would have a larger impact in this type of equipment on the optical particle count than the change in additives, although the comment the oil company made is true. Particle count is a good indication of contamination but should not be used as the only means of determining wear in a transmission. There are too many variables that can affect the result i.e. colour of oil, water contamination. Also a high particle count does not guarentee a wear situation and there is no way of telling with a particle count only what it is attributed to. It is a good idea to filter the oil through a 5 micron filter pad and examine it under a microscope if a high particle count is obtained. By doing this one can see what caused the high count i.e. wear particles (magnetic, metallic or other), dirt, colour etc. Rather use the optical particle count as a screening test.

Dear Axelhouse,
Particle counting for in-service fluids is extremely valuable. ASTM is currently concluding the publication of a new standard for this parctace. Typical impediments to accurate counting of in-service oils will be Soot (very Dark) Air bubbles, water drops, or high silt loads. Also remember that the repeatability of the method is +/- 50% so small changes should not be a source of concern, but trends are the important factor.
See http://www.bentlytribology.com/publications/appnotes/app6b.php for more details.
Further, particle counting alone is not enough. You also need to know what is there. Spectrographic analysis is very informative for the price. and will identify the metals in the fluid so that all but organic contamination can usually be identified.
See http://www.bentlytribology.com/publications/appnotes.php for more information.
If you rely wish to learn about this oil analysis business I suggest you read the newly revised book: Machinery Oil Analysis: Methods, Automation & Benefits: A Guide for Maintenance Managers, Supervisors & Technicians, Third Edition

Availale at https://www.stle.org/secure/publications/index.cfm

Michelle,
Thank you for your response. It has been suggested to supplement my testing with the filter pads. I will look into this further.
I think your reference to ‘screening’ appropriately describes what I am doing. To clarify, this is not a maintenance type inspection regime, rather I am doing follow up on vehicles (transmissions) that are being returned to service after prior failure and subsequent overhaul. While all have automotive ATF fluid, brand and specific fluid are not consistent or controllable. Additionally I am documenting contaminate levels in new OEM transmissions or transmissions/vehicles prior to any failure to use as a benchmark.
Initial efforts have provided apparently reliable results with good used units (prior to failure) and units with supplemental filtration having categorically lower contaminate levels and units after overhaul having far greater contamination (5 to 50 times greater).
I am confident with the results but as noted, the validity of my testing has been questioned and I am trying to formulate a response to support my efforts.
My main concern is to fully understand how much variability in particle counts I can expect in this family of fluids (automotive ATF) and whether any variability will invalidate my test results.
Thanks again.
Gregg

Dear Axelhouse

Let me know your e mail and I will send you information about pore blockage cleanliness test

AXLEHOUSE@earthlink.net

Thank you for the offer,
Gregg

I agree with Michelle that backing up particle counts with a membrane patch examination is useful, with either optical or pore-blockage type particle counters.

Very intersting project.
New oil is not clean anyway, would expect some variation in Particle count due to lack of care with oil change /top ups, more so than formulation variations. Don't think that particle count will pick up VI improvers as I understand these (and additives)are soluble in the base fluid( unlike silicon)
Had some experience in the past with PSV/coach transmissions in the UK where clutch debris was a major concern(metalic and non metalic debris)
Also laser particle counting has a major drawback with large debris blocking the sensors.