Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1171112
e RCL is derived from a calculation involving several factors, including the machine's components, operating conditions and environmental infl uences, among others. Figure 1 shows the resulting plot between the calculated sum of contributing factors and the RCL represented using the ISO 4406 cleanliness code. For those unfamiliar with the cleanliness code, the three range numbers, such as 15/13/10, correspond to the number of contaminants greater than 4, 6 and 14 microns, respectively. e calculated sum of contributing factors is known as the total weight. ese factors, six in total, each have their own weighting table and are summarized below. Working Pressure and Duty Cycle – is scale, from 1 to 8, is not only defi ned by the range of working pressure but also by the level of inconsistency the system pressure experiences during operation. The more consistent and lower the pressure, the lower the number. e greater the variations and pressure, the larger the number. Component Contaminant Sensitivity – is scale, from 1 to 8, looks at the types of components to which the hydraulic fl uid is exposed. e most sensitive components, such as valves and pumps, should be the primar y consideration. For example, a high-performance servo-valve will warrant a higher weight factor because of the potential for contaminants to jam the spool against the valve block due to the clearance and pressure diff erentials. System Life Expectancy – is scale, from 1 to 5, requires an expected life-cycle time (in hours) of the hydraulic system. e longer the system is expected to remain in service, the greater the control of contamina- tion should be. If signifi cant contamination is perpetually permitted to remain in the system over an extended period of time, the degree of damage it may cause is greater. Total Cost of Component Replacement – is scale, from 1 to 4, takes into consider- ation the types of components in the system, primarily by the amount of labor and cost it would take to replace them. Larger compo- nents and more complex systems usually warrant a higher weight factor. Cost of Downtime – is scale, from 1 to 4, depends on the equipment's overall impact on production. It might be the most intuitive consideration. If production is not impacted by the component, then the weight factor remains low. e more disruption to produc- tion and overall downtime costs caused by a system failure, the higher the weight factor. Risk – is scale, from 1 to 6, is similar in consideration to the cost of downtime, but instead of a production risk, it is a safety risk. is is associated to potential hazards that might be created for individuals in the surrounding area as a result of a system failure. (Although the ISO 12669 standard does not explicitly list environmental impact as a factor, I would suggest this risk factor to consider the environment as well.) After the weights for the six categories have been determined, all the contributing factors can be totaled to a single number. is number can then be correlated to an ISO contamination code as a target for the hydraulic system's RCL. In general, this approach should be appropriate for most applications. However, it is still a guideline, not a hard and fast rule, especially when the RCL is at the ends of the scale where ISO contamination codes are high (above 20) or low (below 10). If the calculated RCL suggests 20/18/15 as the target for the system, the incoming oil might be cleaner than this level, in which case doing nothing to clean the oil may be accept- able. If the oil is considerably cleaner than the target, it might be worthwhile to keep the oil at this level rather than permitting it to become more contaminated. After all, the cost to keep contaminants out of the oil may only be about 10 percent in comparison to what it takes to fi lter them out. On the other hand, if the calculated RCL is extremely low, such as 10/8/5 or less, it will require more than just fi ltration to accomplish the goal. is may not be realistic given your machine's environment. As stated earlier, the net eff ect across both the investment in cleaner oil and the return in benefi ts must be minimized. Understanding ISO 12669 ISO 12669 is designed for hydraulic systems, although the essential strategy can be adapted for application in other lubri- cated systems. is standard reviews the need for setting targets on solid particulate contamination levels only. erefore, it does not include a cleanliness target level consid- eration for soft insolubles, water or any other contaminants. e standard is also intended to provide considerations of fl uid cleanliness for the initial fl ushing requirements, manu- facturing process, assembly, commissioning and operating fi ltration requirements. W he n c omp one nt c on s id e r a t ion s are relevant in calculating the RCL, the 38 | September - October 2019 | www . machinerylubrication.com LESSONS IN LUBRICATION Figure 1. Resulting plot between the calculated sum of contributing factors and the RCL represented using the ISO 4406 cleanliness code