- Buyer's Guide
For years Noria has been saying, “The cost of excluding a gram of dirt is probably only about 10 percent of what it will cost you once it gets into your oil.” Recently, a Noria training client asked us to document proof of this statement.
It reminds me of a widely used quote from Benjamin Franklin: “If you think education is expensive, try ignorance.” Or another familiar one: “Pay me now or a whole lot more later.” Proactively investing in reliability and machine wellness is very often challenged by the need to justify. Management is always asking for financial analysis and to “make the business case.”
Conversely, a financial study rarely is produced to obtain funds to repair a failed machine, especially when plant production has stalled. Sadly, I’ve heard maintenance folks say that they’ve quit trying to propose proactive measures to management. They claim it’s easier to just let the machines fail.
This is like saying it’s easier to just wait until you have a heart attack than to proactively make the lifestyle changes needed to avoid heart disease (diet, fitness, quit smoking, etc.). These differences are often deeply ingrained in management and business culture. Does your organization have the “here and now” folks or those who “plan and prepare?”
On the bright side, an increasing number of companies are led by managers who do “get it.” Much of this has been driven by the growing base of documented success stories from organizations and program leaders who have championed change and happily reported their results. They didn’t need to be beaten over the head but rather took the initiative and captured the benefit.
For those wondering what is meant by excluding a gram of dirt, it’s a rather simple concept. First, figure out what the contaminant is (dirt, coal dust, fly ash, etc.) and then determine the point(s) of entry (tank vent, worn seals, hatch, etc.). Some do this by examining particles found in used filters and sump sediment aided by common laboratory tools (XRF, SEM, optical microscopy, etc.).
For many machines, the inhaling of airborne contaminants into reservoir and tank headspace is the primary source of contamination. Forced convection of air by thermal syphoning, machine-driven air currents (e.g., movement of gears, plunging oil return-line flow) and cyclical changes in the tank oil level (hydraulic cylinder movement) can escalate the ingress. Air typically enters through vents and breathers, past shaft seals, unsealed hatches and cleanout covers, and other unprotected machine openings.
New oil is also a source of contamination, as are invasive inspection and repair activities. Hydraulic systems using linear actuators receive a high percentage of their particles from ingression past worn wiper seals and rod seals. Of course, mechanical wear, corrosion, oil degradation and surface exfoliation are also common sources of solid particles.
The cost of contaminant exclusion relates to both retrofitted hardware and routine maintenance tactics for blocking contaminant entry. These costs include such things as transfer cart filtration, proper breathers on machines and lubricant storage vessels, improved seals (labyrinth, for instance), tighter system closures, greater awareness and care during internal inspections and part replacement (education and better procedures/tools), routine cleaning of machine exteriors and many other similar methods. Depending on the type of machine, this could generate initial costs ranging from $100 to $1,000 per machine. There is also an annual ongoing cost of routine maintenance relating to contaminant exclusion (e.g., replacement breathers).
We are all aware that particles make particles. The number of new particles generated from a single ingressed particle depends on many factors, including the type of machine, filtration, settling, number of frictional zones, working clearances and operating speeds. Basically, it relates to how many surface scratches and indentations a particle is allowed to make before it is pulverized, settles to the tank floor or removed by an oil change or filter. If ingressed particles reach the filters fast, there is less damage and few new wear particles are produced. Conversely, if no filtration or poor filtration is the case, this leads to longer particle residence time in the fluid and thus more damage and more production of wear debris.
An average ingressed dirt particle (left unremoved in the oil) will generate somewhere between five and 20 new particles (secondary particles). Some of these particles will make more particles (tertiary particles). The situation is self-propagating. Additionally, you can imagine that a single scratch mark from a grain of dirt can produce a corkscrew wear particle long enough to crush into five or more particle segments.
Take a look at the data below from 17 hydraulic systems (ref. Pall Corporation). The highly filtered five cleanest systems only had 7 percent wear particles (metallic). The destructive dirt was removed quickly, preventing the generation of secondary and tertiary particles. On the other hand, the five dirtiest systems generated 117,768 new particles, representing 42 percent of all the particles in the fluid. If a better filter was then applied, the filter would plug quickly from the high concentration of particles, of which nearly half were formally a part of the machine.
In well-filtered, high-ingression systems such as off-road hydraulics, more than 90 percent of the particles found in oil filters are likely to be terrain dust (ingested from the air). For indoor equipment running in a relatively clean environment, the filter might be loaded with 50 to 90 percent metallic particles. By comparison, particles in unfiltered systems such as splash-fed gearboxes might be more than 95 percent metallic due to self-propagating particle generation.
Filters cost less to maintain (last longer) when:
If you can’t keep ingression in check, you are left with using filtration to stabilize high oil cleanliness targets. This is best done by removing particles quickly. Remember, the longer particles are allowed to stay in the oil, the more secondary and tertiary particles are generated. Then, they too have to be filtered out (increasing the cost of filtration). One or more of the following methods are the best ways to remove particles quickly:
Of course, all of this costs money, plus the hassle to maintain. In contrast, a filter used as an air breather will hold more particle mass (perhaps two to five times more) than the same filter used to clean oil (same size and micron performance).
As a final note on filtration, while many contaminant-exclusion tactics can prevent the entry of particles of all sizes, oil filtration, on the other hand, is selective. It generally only removes particles above the micron rating (say, 10 microns), leaving the smaller particles undeterred and available to do damage to the base oil, additives and the machine.
Most people don’t associate particle contamination with lubricant service life, oil change frequency or the overall cost of lubricant consumption. We’ve reported many times in Machinery Lubrication on how oils age. For instance, one of the well-known drivers of oil oxidation is the presence of catalytic wear metals in the oil. Wear particles don’t get into the oil by themselves. One very common source of wear particles is particle-induced wear (secondary and tertiary, as previously discussed). Suspended dirt particles also provide a site for oil additives to hitch a ride. This ties up these additives, which suppresses their ability to perform their intended function.
So less dirt ingression means less wear debris production, which means less antioxidant additive depletion, which means less oil consumption (from additive depletion and base oil oxidation) and less downtime from oil changes and flushing. We’ve also reported in the past the many hidden costs of an oil change. One consultant (Ken Brown) has estimated that an oil change can cost more than 40 times the cost of the oil and labor.
An oil change is disruptive to the machine. It not only can cause downtime but also an internal disturbance that can lead to collateral damage. One common and serious disturbance is called the “fish bowl effect,” which relates to the redistribution of sediment as a result of an oil change.
Of course, dirty oil is also a primary cause of oil leakage. Particle contamination abrades seals over time. Some companies have reported more than an 80-percent reduction in leakage as a result of maintaining higher oil cleanliness.
Wear not only leads to machine operational failure but also impedes performance in the intervening period leading up to repair or overhaul. During this period there is usually impaired productivity due to sluggish or erratic machine function. There is also increased energy consumption. For instance, when hydraulic pumps and actuators wear, they lose volumetric efficiency. This slows work (pumps and actuators move slower) and increases the consumption of energy (and heat distress to the lubricant). Gears and bearings also consume more energy as a result of wear.
Even diesel engines suffer from decreasing combustion efficiency due to wear in the valve train, bottom-end bearings and combustion chambers (rings, piston, cylinder wall, etc.). A corresponding increase in fuel consumption results. Wear in these zones is often associated with particles in the lubricating oil. One simple way to exclude particles from entering the crankcase is to enhance the quality of the induction air filter.
As you can see, many variables and factors influence the cost of excluding a gram of dirt. However, there are many more costly consequences associated with failing to exclude. The quote at the beginning of this article claimed a 10-to-1 difference. On closer inspection, the actual difference is arguably more than 100-to-1 when taken across the life of the machine.