Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/490438
www.machinerylubrication.com | March - April 2015 | 5 ML minutes, approximately 47 percent more particles appeared in the 55-millimeter entry region of ferrogram slides compared to samples agitated vigorously by hand for 30 seconds. Likewise, 59 percent more particles appeared at the 10-millimeter region on ferrogram slides (representing smaller particles). The best way to break up these agglom- erates and dislodge particles from container walls with aged samples is to use an ultrasonic bath followed by vigorous mechanical agitation (e.g., a paint shaker) for three minutes. Some procedures call for use of an ultrasonic bath after mechanical agitation to aid in the coalescence of air bubbles before vacuum degas. Perhaps the best method is to sonicate both before and after mechanical agitation. While it may be wishful thinking on my part to expect samples to be properly collected in the plant and properly agitated in the lab, I am hopeful. I also realize that proper agitation comes at a cost. However, there is also a cost to bad oil analysis data. Remember, the very oil analysis tests that need agitation the most are the ones the labs charge the most for and the ones that provide critical informa- tion on machine health. Editor's Note: References for this article can be found at MachineryLubrication.com. About the Author Jim Fitch has a wealth of "in the trenches" experience in lubrication, oil analysis, tribology and machinery failure investigations. Over the past two decades, he has presented hundreds of courses on these subjects. Jim has published more than 200 technical articles, papers and publications. He ser ves as a U.S. delegate to the ISO tribology and oil analysis working group. Since 2002, he has been director and board member of the International Council for Machinery Lubrication. He is the CEO and a co-founder of Noria Corporation. Contact Jim at jfitch@noria.com. Oil Sample Preparation Pointers Some oil samples and laboratory tests have higher risks than others. These would include low viscosity fluids (e.g., ISO VG 46 and below), large particles (greater than 20 microns), oils with high varnish potential, heavy particles, aged samples, ferrous density tests, particle counting and wear particle anal- ysis. The best ways to mitigate these risks are delineated in the list of laboratory do's and don'ts that follows: LabOr aTOry DOn'TS • Use hand agitation. • Utilize a laboratory rocker, orbital oscillator or roll device (e.g., hot dog roller) for agitation (except to keep a previously mechanically agitated sample fresh). • attempt to mechanically agitate completely full bottles. • Dilute samples with thin solvents. If dilution is required, use ultraclean oil instead. Low viscosity solvents accelerate particle drop-out. • Wait several minutes while the sample sits motionless before analysis. • assume no one cares about agitation. LabOr aTOry DO'S • Place samples in an ultrasonic bath prior to mechanical agitation for at least 30 seconds (especially with aged samples). • agitate samples vigorously in a mechanical shaker for no less than three minutes (bottle ullage no less than 25 percent). • Degas the sample (ultrasonic followed by vacuum works best) immediately after agitation. (Degas procedure required only for particle counting.) • analyze samples immediately after degas.