By Jane Alexander, Managing Editor
Whether you call it world-class, best-practice or use the currently popular term—precision—the procedure is the same when it comes to lubrication: using the right lubricant for your equipment, in the right amount and at the right frequency. And it requires that lubricant condition be managed.
Jarrod Potteiger of Des-Case explains that the precision approach also excludes two common lubrication practices: the default use of high-quality lubricants and routine over-lubrication. Many steps are required to get a significant benefit from high-performance lubricants in most machines, and performing lubrication tasks at intervals shorter than those required is a waste of time and resources at best, and can lead to component failure at worst. Precision lubrication requires that lubrication PMs be rationalized and optimized to ensure that lubricant conditions and amounts will provide the most effective lubrication. Potteiger offers the following advice on developing and maintaining successful precision-lubrication programs.
Program success starts with having the right lubricant—oil and/or grease—in every component. This is probably the simplest precision-lubrication aspect to achieve, yet is rarely done right. Lubricants are often specified incorrectly due to initial misinterpretation of OEM specs or, over time, due to a misdiagnosed problem or misplaced perception of benefit. Whatever the reason, Potteiger says, it’s usually prudent to go through each lube point in a facility and verify or correct the lube specs if it has not been done recently. When specifying lubricants, however, he adds that it is important to not just create a proper spec, but to define the methods by which decisions are made. Doing so eliminates future questions about the accuracy of the selection.
With regard to accuracy, Potteiger notes that while it’s not uncommon for machines to have the wrong oil in them, grease is a different story. As he describes the situation, “Most maintenance professionals don’t really understand grease.” Rather, they tend to characterize different greases by the type of thickener they use or by vague terms such as “hi-temp.”
Grease, though, is actually just thickened lubricating oil. The purpose of the thickener is to hold the lubricating oil in place (like a sponge)—not to provide lubrication. For the most part, grease specification should use the same processes as oil, but with additional considerations.
According to Potteiger, the misunderstanding of grease runs so deep that many OEMs don’t provide adequate descriptions for grease specification. In a precision-lubrication program, each lubricated component should have a generic lube spec that identifies viscosity grade, base oil type and the proper additive system. Grease-lubricated components should have the same, and should include thickener type and NLGI grade.
Application amount and frequency
With the proper lubricant installed in every application, the rest of a precision-lubrication program is designed to ensure the proper condition of those lubricants. Lubricant condition has two components: 1) that the lubricant be suitably free of contaminants; and 2) that the lubricant be in acceptable condition from a chemical and performance standpoint. For oil, this means maintaining the proper oil level and replacing it at the right frequency. For grease, it means installing the correct amount initially, then replenishing with the correct amount at the right frequency going forward.
Oil-fill levels and replacement frequencies are typically pretty straightforward, Potteiger says. “OEM instructions usually cover this adequately.” Correct oil levels, however, can vary for similar components, based on factors such as their orientation or operating speed. OEM oil-level instructions should be reviewed carefully to determine that there is either a single, correct level or that the correct option has been chosen if there is more than one.
Oil-replacement frequencies can also vary. Typical recommendations are conservative because, to be on the safe side, the OEM must recommend for harsh operating conditions. Actual, useful oil service life, however, can vary dramatically. Factors such as high operating temperatures, wear debris, moisture and sludge can shorten oil life. In a given application, the severity of these items, or lack thereof, can alter useful service life by an order of magnitude. Nonetheless, most oil-change frequencies for similar equipment can fit into neat periods, such as three, six or 12 months, and should only be scrutinized when severe conditions exist. Use of oil analysis allows for oil to be replaced based on actual conditions, which, in turn, removes guesswork.
As with grease selection, grease application amounts and frequencies are often wrong. For grease-lubricated bearings, Potteiger says, the most common mistake is “too much grease too often.” This is especially true for electric motors. “The real problem,” he explains, “is that most people don’t realize they have a problem.” When the problem is recognized, correcting it is a simple, though time-consuming process that can depend on tapping several resources for information, including bearing manufacturers, electric-motor manufacturers and lubrication textbooks, among others.
To determine the proper initial fill amounts and replenishment rates for grease-lubricated bearings, one needs to know the bearing sizes, speeds and types. Secondary considerations such as temperature, vibration, contamination and bearing orientation are also important to know for fine-tuning default values. Whichever combination of factors is chosen, it is essential to use a consistent source for both amount and frequency determination.
While it’s a given that use of the correct lubricants—and ensuring that they are in suitable chemical condition—is a pre-requisite for success, Potteiger notes that big (i.e., positive) changes in the service-life of components can be achieved through the aggressive management of contamination. In most cases, he notes, the amount of particle contamination in oil is the single biggest factor that determines how long a lubricated component will last. “Many maintenance professionals,” he says, “don’t realize they have a problem with lubrication-related failures because they don’t properly characterize the failure or root cause. Most equipment failures are, in fact, lubrication-related.”
The normal way in which most machines fail is to “wear out,” but wear rates can be controlled, and the primary purpose of lubrication is to do just that. Studies show that approximately half of lost machine life is due to mechanical wear—and, as shown in Fig. 1, approximately 80% of mechanical wear is caused by particle contamination in the oil. It therefore stands to reason that when particle contamination is reduced, wears rates go down and component service life goes up.
Effectively controlling contamination requires, among other things, a good strategy. Potteiger says that while implementing a contamination-control policy may take time and effort, developing the strategy is rather simple:
Step 1: Identify goals in the form of target-lubricant cleanliness and moisture limits for different types of machinery.
Step 2: Identify all potential measures to improve cleanliness.
Step 3: Verify the effectiveness of implemented measures with oil analysis.
The two basic approaches to controlling lubricant contamination are exclusion and remediation. Of these, contamination exclusion is typically the least costly and should always be the first—and sometimes only—measure taken. Improvements to contamination removal capabilities should be considered when exclusion measures prove inadequate.
Preventing contamination in lubricated equipment starts with new oil. For several reasons, new oil from drums or bulk deliveries usually contains anywhere from 2 to 20 times the amount of particles that is acceptable for most lubricated equipment. This is not an indictment of lubricant suppliers, but a fact that must be addressed before cleanliness targets in machinery can be met.
In general, Potteiger says, it’s good practice to maintain the cleanliness of new oil at least two ISO codes cleaner than the targets for in-service oil. This will allow modest amounts of contamination to be introduced during transfer and application while still meeting the targets. Unfortunately, typical handling methods will add a lot more than a modest amount of contamination. Thus, for the average plant, lubricant-handling methods and equipment will need to be revised and upgraded to ensure oil cleanliness.
For small sumps that are filled from oil-cans, transfer containers should be made of plastic, sealed, marked for product type and maintained in a clean state. The use of funnels should be avoided when possible and separate handling equipment should be maintained for different lubricants. The simplest and most effective way to ensure that new oil additions are clean is to simply filter it as it is applied using portable filtration equipment. To do this, the reservoirs must be fitted with the proper fittings to effectively attach the transfer equipment.
Another effective and essential technique for preventing contamination is to stop airborne contaminants from entering machine reservoirs during service. Most reservoirs exchange air with the ambient environment regularly, and if that air is not filtered it can be a major source of contamination for both particles and moisture. “The good news,” Potteiger says, “is that this is one of the easiest problems to address through good headspace management.”
Headspace management is the process of managing the condition of the air that enters a sump when oil level is lowered or air pressure drops when the temperature goes down. Replacing typical OEM breathers with high-quality desiccant breathers will strip particles and moisture from the air as it enters the sump to a point where contamination is negligible. Other methods include purging reservoirs with clean, dry air or nitrogen to maintain positive pressure in the headspace, or using expansion chambers that effectively capture and re-circulate the air in the headspace.
For many common applications, such as small gearboxes and process pumps, contamination exclusion is the only practical approach. This makes good application practices and headspace management all the more crucial.
Sometimes contamination exclusion is not enough. High ingression rates and/or sensitivity to contamination in some machines like hydraulics and those with circulating lube systems require improvements in contamination-removal capabilities as well. “When this is necessary,” Potteiger says, “the first step is to review existing filtration to see if the filters can be upgraded in terms of pore size, capture-efficiency or other factor.” If this is not the case, or if filter upgrades don’t achieve the desired results, offline filtration may be the best option.
Offline filtration systems, commonly referred to as kidney loops, offer several advantages over active filters in the oil-circulation system. Offline filtration is cost-effective because the kidney loop functions independently and is not bound by the flow rate and pressure requirements of the active circulating system. These systems also allow the use of alternative filter media and types such as depth media, electro-static, water-stripping and others that can remove more than just hard particles.
For critical applications where moisture contamination cannot be prevented, water-removal options include vacuum dehydrators, centrifuges, coalescing filters and water-absorbing filters. Vacuum dehydrators in particular are extremely effective at removing water from lube systems to the point that its presence is insignificant. Additionally, most vac systems include high-efficiency mechanical filters to remove particles, which makes them an excellent choice for contamination removal in any application where the cost can be justified.
Although most plants use oil analysis in some fashion, Potteiger believes few reap its full benefit. He views effective oil analysis as “the perfect condition-monitoring technology for proactive maintenance” because it can positively identify and quantify the top three root causes of machine failure: particle contamination, moisture contamination and use of the wrong (or degraded) lubricant.
Oil analysis is not difficult, Potteiger says. “Even a novice can easily learn to use viscosity and elemental analysis to verify oil for use in a machine.” Tests such as acid number, FTIR and QSA can be used to determine if the oil is suitable for use or has degraded, while particle counts and moisture concentrations require no deciphering at all. “Good oil analysis,” he continues, “depends on good oil-sampling practices, data analysis and data management, and with the proper education all of these things can be easily achieved.”
Potteiger sums up precision lubrication as a fundamental component of any good reliability program. Although it can take time to transform an average program into a great one, he reminds end-users that the fundamentals are simple: “Use the right lubricant, in the right amount, at the right frequency, maintain the lubricant’s condition with aggressive contamination control and verify condition with effective oil analysis.”
Jarrod Potteiger, Sr., is Technical Consultant/Manager–Training Services for Des-Case Corp. (descase.com).