Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1475671
32 | July - August 2022 | www . machinerylubrication.com high speeds and loads and has tight dynamic tolerances. Typically, hydraulics will require the cleanest oil of any system in our facili- ties, followed closely by turbine systems and bearing lubricants. While other equipment benefits from cleaner oil, the primary focus on cleanliness should be here. Gearboxes, engines and compressors can have slightly higher contaminated fluid and still function well. Once we start focusing on the machine type, we are forced to dive into the lubricant type. For the sake of this discussion, we will focus solely on oils, as greases are not commonly filtered, and there are more factors to be concerned with in their formulation. Lubricating oils that are used in heavily loaded systems, such as gears, are increasingly likely to be formulated with any number of solid additives. Defoamants Defoamants can be affected by very stringent filtration conditions. While the additives' phys- ical size makes a difference in this process, the issue comes when the concentration of these additives is too high, typically after someone adds a retrofit kit to try and remedy a high foam condition. Once the concentration is too high, the additives are not able to exist in the semi-dissolved state that allows them to slip through the pores of most filters. Once these additives are removed, the oil is more prone to foaming tendency and stability. Anti-scuff Additives Another common additive type found in highly loaded systems is solid extreme pressure or anti-scuff additives. ese come in many forms with different chemical and atomic structures but are not dissolved; rather, they are suspended in the oil. Tight filtration removes these additives, and the machine suffers more catastrophic wear in high-contact zones — especially those with sliding motion. Additionally, each additive type will have a common size that must be considered when selecting a filter to use. For instance, if we are using a gear oil with a Molybdenum Disulfide additive at a size of ten microns, we would try to avoid filtering down to that level (and lower) to preserve the additive. Other fluids may not have a solid additive in them but may instead have many dissolved additives: these too can be filtered out, but the process is different than the physical trapping previously mentioned. Many additives func- tion based on polarity (the natural attraction to other polar items) inside the fluid. Some of these additives are very common, such as anti-wear, corrosion inhibitors and dispersants. If a filter media is selected that is an adsor- bent type, it attracts these additives due to the polarity, and they are removed from the fluid. Naturally, if these additives are already clinging to a particle or contaminant in the bulk of the oil, and the particle gets trapped in the filter, the additive level also drops. Filter Media Types While the filter media makes a difference, there are a couple things to look at to determine if it will strip additives. For systems seeking low ISO codes, such as an ISO 16/14/12 or lower, the need to employ a fine filter, such as a three-micron beta 200, becomes more apparent. For higher particle counts, the filter can be larger or the capture efficiency lower. While some additives like the solids mentioned above might be screened out due to size exclu- sion, others are prone to different mechanisms leading to their removal from the fluid. Active filter media, such as clay, diatoma- ceous earth, Fuller's earth and the like, are very polar. While these may work fine in such applications as Electrohydraulic Control (EHC) systems using Phosphate Esters, we would not want to employ them for work in systems containing high amounts of polar additives, such as gears, compressors or engine oils. ese filters have an enormous surface area, and the additives are preferentially sticking to them rather than the machine parts (which can lead to a huge drop in addi - tive levels and performance). Other filter media types, such as cellulose, are less prone to stripping additives, but the filtration system can impact this as well. Using full-flow and bypass filtration might not affect additive levels much, but if we employ settling tanks, the story is different. In settling tanks, the additives may fall out of the dissolved state due to a lack of movement or by sticking to other particles that are settling out as well. While settling tanks are a less common mechanism for cleaning oil for industrial equipment, it is common to find the settling out of additives in lubricant storage tanks or even in drums that have been sitting static for an extended time. Understanding Additive Levels A drop in additive levels is normal, and once they drop by approximately twenty-five percent of their original values, we start to wonder if they are still valid or not. e oil analysis reports are simply stating the number of the concentrations of the signatures found in the oil, not really telling us if they are still active. In order to know for sure, we would have to do some performance testing of the oil to determine if the chemical and physical properties have changed to an unsafe level. It is typically only economically feasible to do this when a large volume of oil is at risk. Filtration is a great place to start any proac- tive maintenance program, and by taking sound choices to selection and understanding the risks of over filtration, you can ensure that you are getting the most benefit from your efforts without damaging the oil. ML About the Author Wes Cash is the Vice President of Services for Noria Corpo- ration. He serves as a senior technical consultant for Lubrication Program Development projects and as a senior instructor for Noria's Oil Analysis I and Machinery Lubrication I and II training courses. He holds a Machinery Lubrication Engineer (MLE) Machine Lubrication Technician (MLT) Level II certification and a Machine Lubricant Analyst (MLA) Level III certification through the Inter- national Council for Machinery Lubrication (ICML). Contact Wes at wcash@noria.com. CONTAMINATION CONTROL & LUBRICANT RECONDITIONING