Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1005929
6 | July - August 2018 | www . machinerylubrication.com AS I SEE IT nism. e more particles, the more the depletion. is results in lost or impaired corrosion protection, oxidation stability, film strength, dispersa nc y (soot control) a nd deposit control. Loss of Demulsibility Many particles are emulsifying agents. In other words, they inhibit the natural settling of free water out of the moving oil and instead bind the water into a tight emulsion within the body of the oil. is allows the water to be carried into frictional zones, leading to acceler- ated wear, and also exposes the polar oil additive to microscopic water globules, contributing to hydrolysis and depletion. Small rust particles are particularly prone to forming oil-water emulsions. Oxidation by Metal Catalysts Metal particles (especially iron and copper) promote or catalyze base oil oxidation. is condition is more pronounced when the parti- cles are in the presence of abnormal levels of heat and water contamina- tion. Wear debris is the principal source of metal particles in the oil. If this debris is not quickly filtered out, these particles can be crushed into smaller particles. e commi- nution of particles exposes a greater nascent metal surface area to the oil and its additives. Eventually, the oxidation inhibitors are spent (fully depleted), and the base oil reaches its breaking point, followed by a runaway state of oxidation. ere is no way to remediate oxidation other than a complete drain, flush and oil change. High Air Hang Time All lubricants have significant levels of dissolved air (invisible to the naked eye). Changes in oil pressure and temperature can cause the air to evolve from a dissolved state to a bubbly, entrained-air state (Henry's law). Small particles aid the transi- tion by providing nucleation sites for emerging air bubbles. Highly pure lubricants have a greater tendency to produce large, buoyant air bubbles (rapid air release). Conversely, highly contaminated oils, including those rich with organic solids, lead to the formation of small air bubbles, which impair buoyancy and result in slower air detrainment (Stoke's law effects). As has been discussed previously in this magazine, there are numerous negative consequences to bubbly, aerated oil. Exposing Ghost Riders Through Oil Analysis Many machines that hold large volumes of circulating oil have no scheduled oil change interval. Instead, oil analysis is used to alert the approaching end of the remaining useful life (RUL). is is referred to as a condition-based oil change. is works very well if the tests conducted by the laboratory fully assess all factors that define the oil's health and condition. For instance, if you only monitor oxidation stability, the premature depletion of corrosion inhibitors might go unnoticed. Condition-based oil changes depend on vigilance and the comprehensive assessment of all important factors and attributes of lubricant health and performance. Some labs do a good job with this. Others cut corners. Ma ny c om mon laborator y methods have substantial blind spots when it comes to quanti- fying the actual concentration of small particles in oil. is is true for particle counting, elemental spect roscopy, ferrou s densit y, analytical ferro graphy and others. Table 1 provides a list of various oil analysis tests and the ability of these methods to quantify or even roughly indicate the presence of ghost-rider size particles in oil. One test stands out due to its capability to report a single numer- ical value for total solids (hard and soft). is test is gravimetric analysis. It can be enhanced using solvents like toluene and hexane to isolate and quantify the soft insoluble particles and hard particles separately. Other tests in this table can also be effec- tive, especially when combined with additional testing methods. For example, data from two or more of the following tests can provide a practical understanding of small particle contamination: ultracen- trifuge, MPC, blotter spot testing, elemental spectroscopy and sub mi- cron patch testing. Removing Ghost Riders from Your Oil and Machine Some types of depth filters have the ability to remove many particles well into the submicron range. is can impart significant control, partic- ularly if the filters are used throughout the life of the oil. Often the effective- ness of these filters will vary depending on the particle size and composition. ere are also charged-particle sepa- rators of various types that can prove effective. When all else fails, the most practical solution may simply be to perform an oil change. is is a more logical choice for small sump machines compared to those holding thousands of gallons of oil. ML About the Author Jim Fitch has a wealth of "in the trenches" experience in lubri- c ation, oil a na lysis, tribolog y and machinery failure investiga- tions. Over the past two decades, he ha s presented hundreds of courses on these subjects. Jim ha s a lso published more t ha n 200 technical articles, papers and publications. He serves as a U.S. delegate to the ISO tribology and oil analysis working group. Since 2002, he has been the director and a board member of the Inter- national Council for Machiner y Lubrication. He is the CEO and a co-founder of Noria Corporation. Contact Jim at jfitch@noria.com.