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Particle contamination is known to cause countless machine failures. One of the best tools to measure and understand this root cause is particle counting. Few facilities utilize the power of this test to its full potential and instead just look at the counts as a way to gauge oil cleanliness. By understanding what the particle counter is telling you and employing proper sampling locations, you can make better use of the information in your oil samples.
One of the most basic forms of proactive maintenance in a lubrication program involves setting target cleanliness levels for different machine types. More often than not, the ISO 4406:99 particle count levels are used for this objective. While this may offer a quick classification of the oil’s cleanliness, you should delve deeper into the numbers to see what truly is occurring.
The ISO standard looks at three different particle size ranges: 4, 6 and 14 microns. However, most particle counters can provide information for several more sizes, sometimes up to 100 microns. These counts are then compared to the Renard series table to establish standard particle count values such as 18/16/12.
Although it is a good practice to set goals and targets based upon these numbers, if your focus is only on the ISO code, you may fail to consider the results from the particle counter. Generally, for every increase in the ISO code, the amount of particles in the oil sample doubles. However, since the chart is arranged as a series, there may be as few as one more particle that raises the ISO code or as many as four times the number of particles. Therefore, it isn’t always sufficient to use this number to drive your actions.
Knowing the individual particle counts and from where the oil sample was extracted will be essential for your oil analysis program. When a report comes back from the lab, it is easy to look at the ISO code and determine a course of action. However, if you examine the individual counts, you can begin to gauge whether the actions you are taking to achieve your cleanliness targets are effective.
For example, say you have a system that is decontaminated with a portable filter cart. The goal is to clean the system to an ISO code of 18/16/13. Your reports continue to show a higher ISO code of 19/17/14. Normally, you might think the oil is still dirty and that you should continue filtering, but upon checking the individual particle counts, you see that you are only a single particle away from achieving the goal. With another quick round of filtering, you can reach your target.
Monitoring individual particle sizes can provide other important information. For instance, take the case of filter performance. A number of filters on the market are touted as 3-micron filters, but not all of them have the same efficiency for capturing particles at that 3-micron size. This is commonly referred to as the filter’s beta rating or beta ratio. By using a particle counter and taking samples before and after the filter, you can look at the individual particle counts to help determine the filter’s true efficiency and micron values.
This practice can also help you select filters for specific machines and understand a filter’s life expectancy. If you analyze particle counts before and after the filter, you can evaluate whether the filter is deteriorating in service. The farther apart the particle counts, the better the filter is performing. The closer the numbers are, the worse the filter is functioning.
For systems without permanently mounted filters or even those that are periodically decontaminated with a filter cart, the particle count can help monitor the size of the contaminants found in the machine. This test can ensure that the seals and breathers are doing their jobs. If the particle counts are increasing and the metal amounts are relatively unchanged, you can be fairly confident that dirt is the contaminant causing the increase.
|52%||of lubrication professionals say their plant utilizes a particle counter, based on a recent survey at MachineryLubrication.com|
One of the most common mistakes when using a particle counter is failing to properly agitate the sample prior to introducing it to the machine. Remember, particles settle to the bottom of the sample bottle and must be agitated to resuspend them. Otherwise, you cannot ensure that you are getting representative information. The ASTM D7647 standard outlines some of the criteria for agitation with the use of optical particle counters.
Depending on the sample volume and the viscosity of the fluid, the agitation time may range from only a couple of minutes to as much as 10 minutes. This is why it is important to leave headspace or ullage in the sample bottle.
While it is possible to agitate or shake a sample by hand, if you have a number of samples to run through the machine, this could take a long time. A paint shaker can make the process easier. Simply mount a sample bottle to the paint shaker, throw the switch and walk away for a couple of minutes. The shaker will resuspend the particles so you can be sure that you are getting accurate results from which to draw conclusions.
It no longer is uncommon to see a particle counter in a lube room. Decades ago, this technology was reserved only for laboratories. Of course, using a lab to run a particle count test is perfectly acceptable, but you can improve your turnaround time by performing this test onsite.
The benefits of particle counters are truly limitless as long as you are conscious of what you are doing and understand the results. These devices have come a long way over the past decade in both their accuracy and affordability. There are now many makes and models available that can work well, provided they are handled with care.
A particle counter can be a great tool in any lube technician’s arsenal. If you haven’t explored the possibility of purchasing one, you should.