There are several important silent assumptions of bearing reliability. However, before I address these assumptions, some even more basic assumptions and statements of fact must be established. While it might be a bit of a leap, I’m going to assume that the bearing is well-designed, well-manufactured, properly handled and stored, and finally, correctly selected for the intended application. With that said, we’re now ready to talk about those silent assumptions that are in the maintenance function’s domain.
These assumptions relate to the internal environment and duty cycle to which a bearing is exposed. Bearing manufacturers will frequently report that only a small percentage of bearings reach their fatigue limit (catalog life). According to one major supplier, typically only 10 percent of rolling element bearings reach their L10 life (it should instead be 90 percent by definition). The old saying that bearings don’t just die, they’re murdered, is rooted in fact. For a bearing to have a normal life expectancy, it is assumed that the following, often unspoken, root causes of failure (our silent assumptions) will not occur at any time after commissioning.
Mechanical Causes
Exceeding a bearing’s dynamic load rating translates to a disproportionate reduction of fatigue life. For most bearings, doubling bearing load can reduce bearing life to roughly one-eighth of its normal life. Mechanical assaults on bearings by misalignment (Figure 1) and unbalance can produce similar consequences.
There are many vital lubricant properties that when altered or impaired can sharply diminish bearing life and reliability. These include such things as additives (AW, EP, etc.), acid number, lubricity, viscosity, pressure-viscosity coefficient and viscosity index. Using the wrong lubricants, degraded lubricants, mixed lubricants (including incompatibility) and/or contaminated lubricants can cause a loss of fluid properties.
Fluid Contamination
The “most wanted” fluid contamination assassins include dirt, water (Figures 2 and 3), fuel, glycol and soot. However, there are many others – too long to list here.
Heat too is a contaminant. Its aggressive tendencies can be dependably viewed as both a cause and effect of most types of fluid and mechanical problems – including many of those found elsewhere on this list. Overlubrication (too much grease) is a common cause of heat in grease-lubricated bearings.
Starvation
A surprising number of bearings are simply starved to death. Over time, they run dry of lubricating oil or grease unless properly and frequently relubricated. The wrong relubrication intervals are often the culprit, but such things as cold starts, dry starts and grease bleed problems can also contribute to starvation. …
… Other contributors of starvation relate to the failure of lubricating mechanisms such as flingers, slingers, rings, single-point devices, oil mist, oil pumps, centralized systems, etc.
While it is true that a bearing damaged from fatigue or wear won’t heal over by itself, it also won’t tell you where it hurts unless you ask. To be attentive to bearing reliability you must tune into these silent assumptions and their symptoms. This is where oil analysis can play an important life-extending role.
If you review each item in my list of silent assumptions, you will discover that, surprisingly, oil or grease analysis can in almost every instance call attention to these concerns, either directly or indirectly. When things go wrong, both the causes and symptoms of a problem are often revealed by the oil’s properties and contaminants. In fact, the alarms are silent only when you choose not to listen. To listen, you must:
sample correctly,
sample at the right frequency,
run the proper slate of tests,
set alarms and limits correctly,
possess suitable knowledge of data interpretation, and
timely and appropriately respond to nonconforming conditions.
Too often, oil is changed without real cause. Imbedded in the oil is a message about its health, the bearing’s health, contamination and other vital properties. We lose this message when the oil is changed without sampling. After all, problems such as misalignment or coolant leaks are never solved simply by an oil change alone. In such cases, changing the oil results not only in ultimately murdering the bearing but shooting the messenger as well.
When you ask front line supervisors or team leaders if all people in their teams are performing to the same standards or if some are doing more work and achieving more results than others, you will often get the same answer. All over the world, the most common answer, after some analysis, verifies that about 30% of the people do 70% of the work.
When you ask front line supervisors or team leaders if all people in their teams are performing to the same standards or if some are doing more work and achieving more results than others, you will often get the same answer. All over the world, the most common answer, after some analysis, verifies that about 30% of the people do 70% of the work.
Unfettered expression and spiritual satisfaction? How does this relate to managing a maintenance department, especially one in the U.S. Postal Service? Open your mind. Take a page from the Zen Buddhist monks who preach: When you are quiet and listen, you become aware of sounds not normally heard. USPS maintenance leaders are listening and beginning to understand that maintenance success doesn't come through closed minds and closed doors.
Unfettered expression and spiritual satisfaction? How does this relate to managing a maintenance department, especially one in the U.S. Postal Service? Open your mind. Take a page from the Zen Buddhist monks who preach: When you are quiet and listen, you become aware of sounds not normally heard. USPS maintenance leaders are listening and beginning to understand that maintenance success doesn't come through closed minds and closed doors.
It is not uncommon that many reliability and maintenance improvement initiatives fail to deliver expected results. Why is it so? Some of the most common causes I have observed include:
It is not uncommon that many reliability and maintenance improvement initiatives fail to deliver expected results. Why is it so? Some of the most common causes I have observed include:
Why do improvement efforts fail or perhaps not sustain the gains? There are many reasons, but those most often stated are “lack of commitment” and not “following the process”. But why is there lack of commitment, and why aren’t processes followed? Here are a few of the reasons that I’ve seen:
Why do improvement efforts fail or perhaps not sustain the gains? There are many reasons, but those most often stated are “lack of commitment” and not “following the process”. But why is there lack of commitment, and why aren’t processes followed? Here are a few of the reasons that I’ve seen:
When a piece of production machinery broke down at the Whirlpool plant in Findlay, Ohio, several years back, it was accepted practice for the machine operator to call maintenance and then sit back and wait for the problem to be fixed. Critical information and knowledge was not shared between the operator and maintenance technician. Like many companies, these workers were stuck in traditional roles - operators run the machines, maintenance fixes the machines, and the two do not cross. As a result, productivity opportunities were missed.
When a piece of production machinery broke down at the Whirlpool plant in Findlay, Ohio, several years back, it was accepted practice for the machine operator to call maintenance and then sit back and wait for the problem to be fixed. Critical information and knowledge was not shared between the operator and maintenance technician. Like many companies, these workers were stuck in traditional roles - operators run the machines, maintenance fixes the machines, and the two do not cross. As a result, productivity opportunities were missed.
Many managers are unaware that best-in-class companies routinely design-out maintenance at the inception of a project. That, clearly, is the first key to highest equipment reliability and plant profitability. Whenever maintenance events occur as time goes on, the real industry leaders see every one of these events as an opportunity to upgrade. Indeed, upgrading is the second key, and upgrading is the job of highly trained, well-organized, knowledgeable reliability professionals.
Many managers are unaware that best-in-class companies routinely design-out maintenance at the inception of a project. That, clearly, is the first key to highest equipment reliability and plant profitability. Whenever maintenance events occur as time goes on, the real industry leaders see every one of these events as an opportunity to upgrade. Indeed, upgrading is the second key, and upgrading is the job of highly trained, well-organized, knowledgeable reliability professionals.
The true translation — might it be proper to say a new and improved translation? — is being used today by Cervecería Cuauhtemoc Moctezuma, one of the largest brewers of beer in Latin America. Known throughout this company as Mantenimiento Alto Desempeño (MAD), or translated as High-Performance Maintenance, the concept of TPM is alive and well at the company's six plants in Mexico. Perhaps the best example is at CCM's brewery in Tecate, located a short drive from the U.S.-Mexico border on the Baja California peninsula.
The true translation — might it be proper to say a new and improved translation? — is being used today by Cervecería Cuauhtemoc Moctezuma, one of the largest brewers of beer in Latin America. Known throughout this company as Mantenimiento Alto Desempeño (MAD), or translated as High-Performance Maintenance, the concept of TPM is alive and well at the company's six plants in Mexico. Perhaps the best example is at CCM's brewery in Tecate, located a short drive from the U.S.-Mexico border on the Baja California peninsula.
