Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/490438
IDENTIFYINg ABRASIVE CONTAMINATION: PARTICLE COUNTINg 13 19/16/11 4416 339 39 12 4 2 1 0 14 20/18/15 5546 1300 493 303 139 24 2 1 15 19/17/14 4346 676 251 156 72 10 1 0 16 23/21/14 44549 10995 456 111 28 3 1 0 This sample also had mildly elevated silicon levels. much cleaner than the lubricant in the sump and can in effect dilute the problem contami- nant, reducing the abrasive wear. Some type of exception testing may also be recommended. This will depend on whether there is obvious wear in the system. Analytical ferrography or filter patch analysis can help determine the extent of the damage and if you need to take immediate action. Water Water is the second most common contam- inant that can cause equipment problems. There are three forms of water: dissolved, emulsified and free. Dissolved water is usually benign except in extreme cases that require exceptionally low moisture levels. This form of water generally enters the lubricant via humidity or a similar process. The lubricant simply absorbs the water up to the saturation point and does not exhibit any signs of water contamination such as clouding. Emulsified water is the most damaging form of water contamination. It occurs when the amount of water is beyond the saturation point and has likely entered the lubricating stream. A mixing action in the equipment may have emulsified the water, or it may be a func- tion of a lubricant additive. Regardless, the initial identifier of this type of water contami- nation is that the lubricant is usually cloudy. This cloudiness comes from the water becoming small droplets within the oil. Emulsi- fied water is the most damaging because it is free flowing with all of the lubricant and will be in the load zone. Free water is somewhat less damaging than emulsified water but is still problematic. Some lubricants will not hold water in suspension past the saturation point, so it falls to the bottom of the sump. Among the problems resulting from this type of contamination include allowing water to become part of the lubricating stream, impacting the lubricant's ability to shed water (demulsibility) and letting it emulsify, initiating biological contamination that will further degrade the oil, and plugging the filter. There is also the possibility of a safety hazard if free water is allowed to continue to enter the sump and overflow it. With water contamination, there is just as much if not more damage to the lubricant as there is to the equipment. The main source of equipment degradation will be rust. Any time you have a degraded lubricant with water contamination, there is the possibility of rust on nearly any iron/steel surface. Rust is ver y hard (harder than steel) and creates abrasive particles in addition to the existing water problem. Another problem with water contamina- tion involves hydrogen embrittlement. In this phenomenon, water is cracked into oxygen and hydrogen, and the hydrogen is absorbed into metal surfaces. This creates a harder but more brittle surface that is unable to flex as needed for rolling elements to work properly. This results in cracking of the rolling surfaces and spalling. In regards to lubricant degradation, the primary issue is having water in the equip- ment's load zone. Water in a load zone is incapable of supporting a load, so the load continuously collapses onto a much thinner lubricant film. This allows significant surface- to-surface contact, which leads to wear. Water contamination will also cause premature aging of the lubricant. It is esti- mated that water in a lubricant can reduce the lubricant's lifespan by one-tenth. In addition, water in a lubricant sump can produce sludge. This is primarily a factor of simple premature aging of the lubricant but should be consid- ered because it can give rise to a number of other issues such as thickening of the lubri- cant's viscosity, preventing splash lubrication or plugging a filter. Water usually does not enter a lubricating system by itself. External machine surfaces tend to be dirty, and the water will suspend this dirt and then enter the system with it. This not www.machinerylubrication.com | March - April 2015 | 21