What is Lubricant Cleanliness?

When we speak in terms of cleanliness, we often refer to the ISO particle count of the oil. According to the ISO 4406:99 standard, the ISO particle count is a measure of the number of particles greater than 4, 6, and 14 microns in every milliliter of fluid. The number of particles is then converted to what is referred to as the ISO Code or Range Code. The range code represents the number of particles of a given size in one milliliter of sample. Results from an oil cleanliness testing are typically reported in a three number format such as 20/15/11, where 20 represents the range code representing the number of particles that are 4 microns and larger, 15 the range of particles that are 6 microns and larger, and 11 represents particles 14 microns and larger.


While the process of converting the raw particle count data to a range code is simple, there is a key takeaway:

For each one unit increase in the code number, the number of particles in the range on average doubles. As a result, an oil that is one range code different is potentially twice as dirty, two range codes means four times dirtier, three range codes, eight times dirtier and so on. For example, if the number of particles went from 641 to 2,499, the number of particles has almost quadrupled but the ISO Code only changed from 17 to 18. For this reason, it’s important to look at the actual number of particles as well as the ISO range code when interpreting particle count data.

If particle count can increase so dramatically with one unit change in the code number, than it is also true that equipment life can dramatically IMPROVE by lowering a code number. For example, in the table below, a gearbox can add as much as 20% more life just dropping one range code. 


Increasing system cleanliness has multiple benefits to the component and the lubricant, but the number one benefit is increased component life. In terms of damage, hard particle contaminants can be brutal to internal moving components. Under rolling contacts, particles are often the precursor to premature fatigue failure, while in high pressure systems, particles can “sandblast” a component from the inside out. In other systems, particles enter the dynamic clearances between moving surfaces and wear components through a three-body abrasion.

The path to increased cleanliness may not always be clear, and sometimes it may seem that major tasks must be undertaken to increase lubricant cleanliness. Fortunately, that is not necessarily the case. A systematic approach and investment in the right products and tools can show a significant return on investment, more uptime on your factory floor, and less money spent on equipment repairs.

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