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What's the Best Test for Used Lubricants?
You've pulled the oil samples, labeled the bottles, boxed them up and sent them off for testing. Play along with me now - suppose your lab could only conduct one test. What would it be?
Tough call? Consider your options. If you've implemented a rigorous proactive maintenance program, and keep your lubes extremely clean and dry, you'd probably opt for a particle count. Why should you choose the particle count?
The particle count is one of those catch-all tests. Almost anything that goes wrong in the machine will result, sooner or later, in increased particle counts. If misalignment, overloading, water contamination, viscosity breakdown, or bearing failure occurs, the particle count should rise.
If you've been trending particle counts on a clean system, you have low background noise. This simply means that there isn't a lot of contamination in the oil, so even a minor change in particle contamination levels will be evident in the particle count results.
Of course, I'd pick different tests for different environments and applications. Some situations may call for wear debris, water or other tests. Do you have a favorite test for your applications? Send me an e-mail and let me know what test and why. I'd like to hear your opinion.
From "Fluid Contamination Control" by Dr. E.C. Fitch
Water in tribological fluids (other than water-based fluids) leads to a multitude of problems in terms of system damage and failure. Perhaps the worst threat of water contamination in storage is its reaction with additives and the damaging reaction products.
Moisture causes a filter-clogging slime to form in fluids containing tricresyl phosphate (TCP), an antiwear additive used in tribological fluids where an alkali is present. If ZDDP (zinc dialkyl dithiophosphate) is used as the antiwear additive instead of TCP, many deteriorating mechanisms could exist; suffice to state here that ZDDP can decompose to form hydrogen sulfide and, in the presence of moisture, transform into a highly corrosive acid (sulfuric acid). Even in fluids of the corrosion-prevention type, moisture causes an egg-white type slime. According to T.N. Dean, when moisture is present, corrosion-preventive additives can exhaust themselves by "wrapping up" the moisture in additive and water dispersion.
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To ensure that the correct lubricant is being used, try using colored plastic grease caps. These fit right on the grease fitting and also help keep dirt and/or water off the grease fitting and hence out of the bearing. The color-coding can be used for the type of grease or the frequency. They cost only a few cents each. (Tip submitted by Ken Brown, Utility Service Associates. Thanks Ken!)
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"What will cause zinc levels in my oil to fluctuate?" -- Todd Machin, Power Resource Tech, Southern Minnesota Power
There are several reasons why zinc may be present in your oil samples. These include wear of zinc containing alloys such as brass, zinc plating and galvanized surfaces; also zinc- containing additives, most notability zinc dialkyl dithiophosphate (ZDDP), a common antiwear and antioxidant additive.
The most common reason for fluctuating data is improper sampling. Sampling accuracy dependents on sampling from the correct location, using the same methods and procedures each and every time. If you do not have a good handle on the correct procedure, this would be the first place to start looking.
Other things that may impact zinc concentrations include the addition of make-up oil (possibly the wrong oil), the method used by the lab to analyze the sample (this is particularly true if the data is being compared between different labs, that may use different instruments) and changes in particle size, if the source of the zinc is from active machine wear.
Mark Barnes, Noria Senior Consultant
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