MRO Magazine

Count to zero: Avoid breakdowns with proper lubrication


Industry

March 8, 2010
By PEM Magazine

In the textbook Zero Breakdown Strategies, lubrication is identified as one of the maintenance basics that can eliminate a significant number of rotating equipment failures in a plant or facility. One can only imagine the cost of lubrication-related repairs, both labour and materials, and the resulting lubrication-related equipment downtime costs.

CONTENTS: Browse this page

Types of fluid film barriers
Why lubrication is delegated to the "new person"
Preventive maintenance
Dealing with water and lubrication

One of the basic concepts of lubrication is the type of fluid film barrier that’s designed for a bearing. The three most common conditions are:
• full-film,
• partial-film, and
• boundary lubrication.

Full-film lubrication occurs when the lubricant viscosity, bearing speed, bearing load, etc., allow a full film of lubricant to microscopically separate the moving components in the bearing. This condition allows for the maximum life from the bearing.

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Partial-film lubrication will allow for some microscopic asperity contact between the rotating bearing elements. This contact, even though microscopic, accelerates the wear (through welding and tearing of the asperity contacts), reducing the life of the bearing. As the welding and tearing occurs, the lubricant can no longer fill the voids in the contact points and even greater amounts of welding and tearing occur, which increases the damage to the bearing. Since metal-to-metal contact is occurring under load, the internal bearing temperatures rise, thinning the lubricant even further. This continues until the bearing is destroyed.

Boundary conditions begin with very little separation of the rolling elements. With almost no lubrication separation, when the bearing is subjected to normal speed and loads, rapid deterioration and failure occurs. In some cases, if rotating equipment is brought from rest to full speed and load (i.e. during a start-up) boundary lubrication conditions occur, with partial or full-film conditions developing as the equipment transitions into its normal run state. The rolling elements and raceways are damaged each time this occurs, however, resulting in more rapid wear and premature failure of the bearing.

Since lubrication has such a pervasive influence on how rotating equipment operates, there are volumes of reference material on lubrication-related issues. In fact, lubrication, tribology and equipment operating dynamics can be presented in very technical, often scientific, terminology. With lubrication being a more complex and technical discipline, one would expect that the more senior, technical competent tradespersons would be assigned the responsibility for lubrication in an organization.

With rare exceptions, however, this isn’t the case. In most maintenance organizations, the responsibility for lubrication activities is delegated to the "new person." Since these people are anxious to do a good job and be accepted in the organization, they will make sure that all of the points on the lube route are lubricated. In addition, they’re likely using a power grease gun by this time.

So, when a grease fitting is identified, the new person attaches the grease gun to the fitting and pulls the trigger. How does he/she know when the fitting has enough lubricant? Typically, the new person wants to ensure that there’s plenty of lubricant in the bearing. As a result, they stop when the lubricant begins to run out of the seals.

Is this a best practice for lubricating a bearing? In the case of a pillow block bearing, it should only be one-third full of oil or grease to allow space for the dissipation of the heat that’s generated, while the bearing is in operation and churning the lubricant. With the bearing packed full, however, there’s no air space; the heat builds up, reducing the viscosity of the lubricant.

This creates a condition where the bearing lubricant condition changes from full film to partial film and eventually boundary, where metal-to-metal contact is occurring. At this point, extremely rapid wear occurs and the bearing fails prematurely. When a root-cause analysis is performed, the bearing has usually been destroyed, preventing the detection of the true root cause of the failure.

If this example were typical in your plant or facility, would it not be worth investigating in a lubrication-training program for your employees? With training, proper lubrication techniques can be utilized by all workers. This helps to increase the life of rotating equipment and minimize lubrication-related downtime.

Preventive maintenance
When developing a lubrication program as part of an overall preventive maintenance (PM) program, there are four factors that need to be considered, including:
1. The right lubricant;
2. The right quantity;
3. The right frequency; and
4. The right application method.

The right lubricant means that the correct lubricant is specified for the application. In some cases, improperly trained employees (both operations and maintenance) feel that "oil is oil and grease is grease." In many cases, no consideration is given to the viscosity, the chemical additives or the specific usage, etc. There are many examples of mixing oil and grease that were incompatible, resulting in coagulation, thinning viscosity and thickening viscosity. They all result in equipment failure.

The right quantity can be related to the previous example of over filling a pillow block bearing. Over heating and lubricant failure will be the result. The right frequency means applying the lubricant at specific intervals. The "hit it a couple shots every time you walk by" approach will only lead to premature failure of the bearing.

The right application method means understanding the quantity of the lubricant that’s being applied to the bearing. There are different sized chambers on various manufacturers’ grease guns. As a result, pumping twice with one grease gun isn’t necessarily the same as two pumps with another grease gun. In addition, you have the example of the power grease gun (mentioned previously), which adds another level of complexity as to the quantity of grease being applied to a bearing.

As a part of an overall PM program, the real key to setting up a lubrication program is to understand the four above points. While this may seem like a tremendous amount of work initially, it will repay the investment many times over during the design life of the equipment.

Water and lubrication
It’s acknowledged that lubricants containing water will dramatically reduce the life expectancy of rotating equipment. Few people in the industry, however, comprehend the enormity of the reduction. Studies have shown (depending on the application) the following:
• Water content of .03 percent to .2 percent will result in a 50 to 83 percent reduction in the life expectancy of the bearings;
• Water content of one percent will result in a 94 percent reduction in the life expectancy of the bearings; and
• Water content of two percent will result in a 96 percent reduction in the life expectancy of the bearing.

While companies may strive to keep water out of their lubricants, it’s the small basic items that must be given consideration (i.e. in plants, whether indoors or outdoor) where equipment is subjected to extremes in temperature and humidity. A gear case will typically have a breather. This is to allow for the air inside the gear case to expand, as it warms during operation and contact during a shutdown period when it cools.

If the air is humid, the temperature differential may drop below the dew point, allowing condensation and the development of water droplets to occur. Over time, this condensation will begin to accumulate in the lubricant. How many heating and cooling cycles will it take to produce enough water to reduce the bearing life by 50, 75 or 90 percent?

Companies may take adequate precautions to prevent water from directly entering their lubricants. Do they spend enough time and resources, however, monitoring the indirect routes? No matter how water is introduced into lubricants, it’s still water and has a dramatic impact on the maintenance and operation costs for rotating equipment. 

Organizations have spent extensive resources on trying to eliminate equipment failures. They’ve developed predictive techniques and tools; implemented reliability programs, including reliability centred maintenance (RCM); and put in place operator-based maintenance programs, etc. If they’re not going to train their employees on the basic concepts of equipment maintenance, however, all of these advanced efforts will meet with sub-optimal results.


Terry Wireman, CPMM, is vice-president with Stamford, CT-based Vesta Partners LLC. You can reach him by email: twireman@vestapartners.com.