MACHINERY LUBRICATION- INDIA NOVEMBER-DECEMBER 2019

MLI find out which ISO calibration standard was employed. Again, the most current calibration standard is ISO 11171. SAE AS4059F While ISO 4406:87 and 4406:99 have been widely accepted, there is still a significant portion of industries and countries that use SAE AS4059. Several revisions have been made to this standard over time. The most current revision of this standard occurred in September 2013, which is SAE AS4059F. The reporting of this standard utilizes the same table as the NAS 1638 standard shown. The most current revision has added optional reporting methods to include the ability to report on the specified cumulative particle size count instead of a single code that represents the cleanliness of the oil. You will be able to identify if the code is specific to a cumulative particle size count by a suffix letter after the class. The letter will be between A-E and will tell you what cumulative particle size count category the code represents. For example, a Class 6B would indicate how many particles are greater than 5 microns (optical microscope) or 6 microns (most APCs). Be careful, though, as the revision of AS4059 may result in different cleanliness classes from those obtained with previous versions whenever the class was specified without any letter size suffix and in some cases when the class was specified with a suffix. Cleanliness classes with no suffix from previous versions of AS4059 are based on particles greater than 6 microns, whereas classes from this revision are based on the number of particles in each of the size ranges except the smallest, 4 microns. AS4059 now permits contamination limits to be identified in a variety of ways: • Identical to NAS 1638 — For example, AS4059 Class 8 is the same as NAS 1638 Class 8. The size of particles counted varies depending upon whether an optical microscope or light blockage APC is used. • Cumulative count above a specified size — Examples: AS4059 Class 8A, AS4059 Class 8B • Differential counts for various sizes — Examples: AS4059 Class 8B-D or Class 8A-D • Different classes for cumulative counts of particles greater than a particular size range — An example would be 7B/6C/5D or 7B/4C. There isn’t a right or wrong cleanliness standard to use when setting up a lubrication program. The important thing is that you follow a standard and use it correctly. Setting Cleanliness Targets Unlike most of the information in an oil analysis report, particle counts should not use the same trending methods of iron, silica, copper, etc. You will want to watch which direction your particle counts are moving, but this alone should not be used as a failure indicator. There are just too many variables in play. The difference between codes can be one particle or several hundred or thousand particles. For this reason, it is recommended to set cleanliness targets and track particle counts or ISO codes relative to those targets. Both cautionary and critical alarm limits should be established. Ideally, the cautionary limit will be your target or one code above. The alarm limit might be two or three codes above your target. These limits will help make your decision- making process easier if you should consider cleaning your oil with a filter cart or performing a full drain, flush and fill. Setting cleanliness targets for each lubricant offers many benefits. The main advantage is the extension of overall machine life, which can lower maintenance costs and increase production cycles. Case studies have shown particle contamination to be the leading cause of machine failures. Therefore, it only makes sense to monitor the concentration of these particles. Other benefits of setting cleanliness targets include increasing the awareness and visibility of the efforts being made through various lubrication activities. Establishing a moderately aggressive target for your lubricants will require everyone to follow lubrication best practices. It can also create a common goal among maintenance and operations personnel for plants in which the lubrication duties are spread across multiple departments or divisions. Since not all machines are treated equally, it will be important that cleanliness targets be set appropriately for each machine. For example, hydraulic and turbine systems are far more sensitive to solid contaminants than a gearbox or process pump. The oil’s viscosity will also play a significant role. The higher the viscosity, the more difficult it will be to remove particles. The machine’s environment can impact your cleanliness targets as well. A hydraulic system in a controlled environment, such as a pharmaceutical production area, may have a different target than the same hydraulic system inside a cement plant. More potential contaminants in the air can increase the need to maintain cleaner oils, which will require a more aggressive standard. A high-contaminant area may also demand a larger investment to help maintain the appropriate oil cleanliness levels. Most original equipment manufacturers (OEMs) provide general lubricant cleanliness levels for their machines to meet the warranty expectations. While these OEM targets make for a great starting point, they often do not take into consideration your specific environment or plant reliability goals. www.machinerylubricationindia.com | November - December 2019 | 29

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