Detecting Bearing Faults

By Jason Tranter

This article is the first in a series of four.  In this article we will provide an overview of how vibration analysis can be used to detect bearing faults. We will only consider the typical failure mode where a spall develops in the bearing and the fault slowly worsens until the bearing ultimately fails. In the next article we will explore how techniques such as enveloping, PeakVue, Shock Pulse, time waveform, and spectrum analysis can be used to detect bearing wear. In future articles we will explore additional fault conditions (cocked bearing, EDM,  skidding and other conditions), and in the final article we will examine what the vibration analyst can do to extend the life of the bearing through acceptance testing, correction of unbalance and other conditions, and root cause failure analysis.

Your job relies on accurate fault detection

There is no doubt that the primary focus for most vibration analysts is the detection of rolling element bearing fault conditions. When a bearing fails unexpectedly it costs a great deal of money (downtime, secondary damage, etc.) and it is a black mark on your name and your department. For all the successes you may have achieved, missing just one bearing failure can set your reputation back months.

Dryer Fan

Then again, the opposite is also true. If you report that a bearing has a defect and must be replaced, yet it is found to be in good condition, you also don’t look good. People lose confidence in your skills and in the technology.

So what is the solution? I guess that’s obvious; don’t make mistakes! If only it were that easy . . .

It’s actually not that hard to detect faults . . .

Detecting rolling element bearing defects is not as difficult as it may seem-I bet you did not expect me to say that! With a good screw driver and frequent trips around the machines, most people would be able to detect that a bearing needs to be replaced. There are, of course, a few issues with this approach. First, it is hardly a safe practice. Second, the greatest benefits are achieved when the maintenance and production group have more than a few days warning that a machine needs to be stopped to replace a bearing.

The earlier the better

The challenge is to correctly assess the nature and severity of the defect and the life of the bearing. If you could confidently detect a bearing fault weeks or months before the bearing needs to be replaced, then the work can be planned to minimize the impact of the bearing change. You may even be able to extend the life of the bearing by correcting the root cause of the fault condition (unbalance, misalignment, poor lubrication, etc.).

There is some good news

The good news is that the design of rolling element bearings makes it much easier to detect fault conditions at an early stage. Thanks to the geometry of the bearing (and their unique “defect frequencies”) it is easy to distinguish bearing vibration from other vibration generated by the machine. And thanks to the high frequencies generated in the early stage of wear, again it is easy to distinguish from other fault conditions. Armed with this information we just need to measure the vibration correctly and analyze the data correctly, and we can be very successful.OK, I may have made it sound too easy.  In truth there are a number of challenges to overcome. But understanding the challenges and their solutions is the key to success.

Key #1: Measure the vibration correctly

Assuming the goal is to detect the bearing fault as early as possible, the first thing you have to do is recognize that the way you measure the vibration is absolutely key to success. In the earliest stage of bearing wear, the frequency of the vibration is very high and the amplitude is very low. I don’t care who you are; you just can’t hear it. And if you use “conventional” sensor mounting techniques, you cannot capture these high frequencies.

Techniques such as ultrasound, Shock Pulse, enveloping (demodulation), Spike Energy and PeakVue are designed to detect high frequency, low amplitude vibration. Without getting into the details, these techniques work by first removing the high amplitude, low frequency vibration, then listening carefully to the high frequency vibration for the telltale signs of bearing wear, then transforming that vibration into a form that is easy to analyze.  We’ll examine these techniques more closely in the next article.

A little bit of background . . .

When a defect is first initiated, the surface of the bearing may not actually be damaged; the damage may be subsurface.  Even when the damage does extend to the surface, the vibration generated is still weak. As the balls or rollers move around the bearing and there is contact at the point where the damage exists, two things will happen: there will be a shock wave (also called a stress wave); and the bearing may vibrate (or resonate). The shock wave ripples out from the point of contact very quickly. The vibration that results will be very weak, and thus difficult to detect.

Bearing Series

We can calculate, or search bearing databases for the telltale frequencies: the ball-pass inner race frequency, ball-pass outer race frequency, ball (or roller) spin frequency, and cage (or fundamental train) frequency. If you can visualize the shaft turning inside the bearing, and the balls rolling around, there will be a fixed time between each impact. The time will be different depending upon where the bearing is damaged; on the inner race, the outer race, or on the rolling elements themselves.

Good news!

The good news is that this frequency will always be non-synchronous; it will never be exactly 2.0, 3.0, 4.0 (or any other integer) times the turning speed of the shaft. It will be a non-integer number such as 3.09, 6.71, or 11.43 times the speed of the shaft. That’s the good news. It makes it easier to distinguish these sources of vibration from the numerous sources of vibration that occur at exact integer multiples of the running speed-from rotating elements such as pump vanes, fan blades, gear teeth, and so on.

More good news!

Another piece of good news is that when these impacts occur, the vibration that results is not smooth; the vibration will suddenly spike in amplitude before it settles again.  That causes harmonics to appear in the spectrum. And even more good news is that under certain conditions the amplitude of those spikes will rise and fall (as a spall on the inner race of the bearing, or the damaged rolling elements, move in and out of the load zone). That causes sidebands to appear in the spectrum.

All of these telltale signs, which we can look for even if we do not know which bearing is installed in the machine, provide an early warning that the bearing is damaged. We can look for these signs well before we would ever hear a change in vibration, even with the best screwdriver.

Some bad news . . .

The bad news is that in the earliest stage of bearing wear, we will not be able to see peaks at these telltale frequencies in the standard velocity spectrum when it is displayed in the linear format that most people use. (In truth, we might see them in a logarithmic spectrum or in an acceleration spectrum.) So we have to look elsewhere. And that’s where enveloping (and the other techniques listed previously) can be put to good use.

So, what is the solution?

There are a few ways to tackle this challenge.

1. There are simple meters that focus on higher frequencies can be used to get an indication that a fault exists.  However, other fault conditions can be confused with bearing faults.

2. Shock Pulse meters are specifically designed to detect bearing faults. When used properly they provide an affordable way to get started.

3. Ultrasound meters allow you to listen for the presence of high frequencies. It is possible to detect lubrication problems and bearing defects. Again, they offer an affordable way to get started.

4. If you rely on “standard” velocity spectra (in linear format) then you will find it difficult to detect the fault until the fault has become more severe. Switching to log can help, and using units of acceleration and setting a higher Fmax will help.

5. The best solution is to use more sophisticated techniques such as enveloping (also known as demodulation), Shock Pulse (with access to the spectra and time waveforms), Spike Energy, and PeakVue.

Detecting Bearing Faults Part 2

This article is the second in a series of four. The first article provided a summary of how the vibration patterns change as the bearing fails. After very briefly recapping the basics, this article will discuss the detection and analysis tools that can be used to determine the nature and severity of the bearing fault: ultrasound, Shock Pulse, PeakVue, enveloping, and spectrum and time waveform analysis.

 

“Metal-to-metal contact sets off a ripple effect: A stress wave races through the metal components, causing the components to vibrate due to resonance”.

How Much of a Risk Are You Willing to Take?

What are your goals? Do you want to know that a bearing may fail just days before it is likely to fail, with no prior warning? Or would you like to know that a bearing has been poorly lubricated, or has a minor defect that will develop into a major fault? With the techniques described in this article you could learn these things months (certainly weeks) before the bearing is likely to fail. With that extra time you could

change the lubrication, order parts, organize the labor, and look for the best opportunity to perform the bearing replacement. The result is a safer plant with less downtime, less stress, and higher profits.

Brief Recap

In the previous article, a few important points were made that are pertinent to this article:

1. As bearings begin to fail, the vibration is very low in amplitude, and the frequency is very high (beyond your ability to hear, even with the best screw driver).2. Simple spectrum analysis will not reveal the fault until it has developed to stage three, unless you take special precautions (listed later in the article).3. To measure high frequency vibration you must mount the sensor correctly.

Beyond Your Hearing: Ultrasound

The ultrasound technique is very easy to implement. The measurement tool listens for very high frequency vibration and provides an indication of amplitude. It also amplifies the vibration and shifts (heterodynes) the frequency so that you can hear it through headphones. Therefore, you can listen for the telltale sounds of poor lubrication and bearing distress. When used correctly and appropriately, ultrasound instruments can be very complimentary to the other techniques described in this article.

What Are “Stress Waves,” and Why Should I Care?

Before describing the next two techniques it is important to briefly introduce the concept of the stress wave (also known as shock pulse). Metal-to-metal contact sets off a ripple effect: a stress wave races through the metal components, causing the components to vibrate due to resonance. The stress wave is a very short-duration, low-amplitude, high-frequency wave. Every time the rolling elements roll over the damaged area on the inner and/or outer race (or as the damaged areas on the rolling elements contact the raceways), a stress wave will be generated. We can seek to detect that wave with techniques such as Shock Pulse, PeakVue, and SWAN (Stress Wave ANalysis, not discussed further in this brief article). The vibration that results can also be detected via the envelope method, and as the fault develops further, via the time waveform and spectrum.

There is one very key point you must be aware of: we are talking about very high frequencies, and as such the vibration sensor must be mounted correctly. Unless specifically designed for the purpose (e.g., Shock Pulse), a handheld probe is horribly inadequate. Even a two-pole magnet mounted directly to the machine surface is not adequate! All of the analyzer vendors will tell you, you must properly prepare the surface and use an attachment pad (or stud mount) in order to achieve the best results.

It is also important to note that there are other defects that will generate stress waves and high-frequency vibration, including looseness, gear wear, and cavitation. That can help us to detect those conditions, but it can confuse our attempts to detect bearing and lubrication faults.

Shock Pulse

The vibration sensors provided by SPM and PRÜFTECHNIK are designed to amplify (through resonance) high-frequency vibration (at approximately 35 kHz). As noted earlier, lubrication and physical defects (including wear/spalls) will generate vibration around this frequency. The vibration can be displayed as an amplitude to be trended, or a spectrum can be displayed in order to better understand the specifics of the defect: inner race, outer race, etc.

Spike Energy

The Spike Energy (units of gSE) technique aims to utilize the accelerometer’s mounted resonance to amplify the high frequency vibration. However, in more recent years, the accelerometers provided have not been manufactured to have a repeatable resonance characteristic. What that means is that when you change your accelerometer, the amplitudes will change.

PeakVue

The PeakVue technique, developed by Emerson Process Management (CSi Division), is also designed to detect the stress wave; however, it is performed in a different way. The signal from the accelerometer is digitally sampled (converted from analog voltages to digital numbers) at a very high rate so that the very short duration stress waves can be detected and quantified. The PeakVue waveform and spectrum provide an indication of the bearing defect. As with all of the techniques, the accelerometer must be mounted correctly, and the filter settings (used to “tune in” to the bearing vibration) must be set correctly.

Enveloping

Also known as “demodulation,” the enveloping technique, which is used by a large number of vibration analyzer vendors, has been optimized to measure the low-amplitude, high-frequency bearing vibration. See Figure 1.

The envelope spectrum is then checked for signs of the fault condition. Similar to the spectrum that results in the Shock Pulse, Spike Energy, and PeakVue systems, we are looking for peaks, sidebands, and harmonics that are related to the four characteristic bearing frequencies: Ball Pass Frequency Outer race (BPFO), Ball Pass Frequency Inner race (BPFI), Ball (or roller) Spin Frequency (BSF), and Fundamental Train (or cage) Frequency (FTF). See Figure 2 for a summary of the progression we expect to see.

The Spike Energy (units of gSE) technique aims to utilize the accelerometer’s mounted resonance to amplify the high frequency vibration. However, in more recent years, the accelerometers provided have not been manufactured to have a repeatable resonance characteristic. What that means is that when you change your accelerometer, the amplitudes will change. See Figure 1.

The envelope spectrum is then checked for signs of the fault condition. Similar to the spectrum that results in the Shock Pulse, Spike Energy, and PeakVue systems, we are looking for peaks, sidebands, and harmonics that are related to the four characteristic bearing frequencies: Ball Pass Frequency Outer race (BPFO), Ball Pass Frequency Inner race (BPFI), Ball (or roller) Spin Frequency (BSF), and Fundamental Train (or cage) Frequency (FTF). See Figure 2 for a summary of the progression we expect to see.

Figure 2

Spectrum Analysis

If we do not use one of these techniques and simply view a spectrum, then we may have limited success unless we take precautions:

1. Acceleration is most sensitive to high-frequency vibration, so if we view the spectrum in units of acceleration (Gs or mm/s2) and have a high Fmax (70X or higher) and, better yet, we view the spectrum in logarithmic format, then we will achieve the best results (with a spectrum alone).

2. If we view the spectrum in units of velocity (in/sec or mm/s), then we may need to wait until the bearing is at stage three until we see positive signs of the fault. Increasing the Fmax and viewing the spectrum in logarithmic format will help significantly.

When viewing the velocity or acceleration spectrum (or any spectrum from PeakVue, enveloping, etc.) there are a few techniques that help to achieve the best results:

1. Look for peaks at frequencies that are non-integer multiples of the shaft speed (e.g., 3.09X, 4.65X, 7.89X, etc.).

2. There should be harmonics of those frequencies (e.g., peaks at 3.09X, 6.18X, 9.27X, etc.).3. Check for sidebands of the turning speed of the shaft. If they exist, then suspect a fault on the

inner race. If there are no sidebands, suspect an outer race fault.4. Check for sidebands of the fundamental train frequency (slightly less than half the turning

speed of the shaft). If they exist, then suspect a fault on the rollers/balls.

Time waveform analysis

It is typically possible to view the time waveform from the Shock Pulse, PeakVue, and envelope process, but I’ll focus on the raw waveform from the accelerometer. In the early stages of the fault condition it will be very difficult to detect the fault with a time waveform. However, as the fault develops, an acceleration waveform can reveal the fault, especially when taken from low-speed machinery. As the fault develops, the waveform will have characteristic “pulses” and patterns that indicate the condition of the bearing fault. In the later stages of the fault, a waveform in velocity units can display the defect quite clearly.

Characteristic “modulated” pattern in the acceleration waveform (often called the “angel fish” pattern).

“Spikes” in the velocity waveform indicate the presence of a severe fault.

Conclusion

I hope this article has helped to provide a basic understanding of these techniques. They have all been used for many years to successfully detect bearing faults at a very early stage. The key is to mount the sensor correctly, choose the correct settings, and analyze the data correctly.

In the two previous articles (Dec/Jan 2011, Apr/May 2011), the focus has been on how the vibration changes when a “typical” bearing fault develops. We have explored spectrum analysis, time waveform analysis, and a raft of high frequency detection techniques. But there are a number of fault conditions related to rolling element bearings that will not necessarily change the vibration patterns in the ways described thus far. Thus, in this article we will explore fault conditions that relate to poor installation (cocked on the shaft or on in the housing), current flow through the bearing (EDM damage), skidding, and slipping.

Poor installation: cocked bearing

Bearing installation is very important. If a hammer is used to pound a bearing into place, the rolling elements and raceways can be, and almost surely will be, damaged. Poor installation can also damage the shaft or the raceways via surface gouging or scratching. Those damaged areas will cause the vibration to change in ways described in the previous two articles; periodic stress waves and vibration will be detected at the key forcing frequencies (depending on the damage inflicted on the bearing).

However, if the outer race of the bearing is cocked in the housing, or the inner race is cocked on the shaft (i.e. there is an angle between the outer race and the housing or between the inner race and the shaft), then with time the additional load on the rolling elements and raceways will cause excessive wear and premature failure of the bearing. But we can detect this situation so that it can be corrected before damage is done!

Vibration amplitude will be higher than normal in the axial direction; however, instead of generating vibration at the bearing defect frequencies (BPFI, BPFO, BSF, and FT), the vibration will be generated at the speed of rotation, i.e. 1X. The vibration at twice running speed (2X) and at harmonics can also increase in amplitude. The only problem is that vibration at these frequencies can be elevated for other reasons, including unbalance, misalignment, and a bent shaft. (Figures 1 and 2)

Phase analysis can aid in this diagnostic process. In the case of the bearing cocked on the shaft, with each rotation you have a “wobble” motion. Phase analysis would reveal that as you move an accelerometer around the face of the bearing at different clock positions, the phase reading would change accordingly. For example, if the phase reading (compared to a tachometer reference or a second accelerometer) was 0 degrees at the 12 o’clock position, the reading would be approximately 90° (or 270°) at 3:00, 180° at 6:00, and 270° (or 90°) at the 9:00 position. (Figure 3)

If the outer race is cocked in the housing, the phase readings will depend on how it is cocked (i.e. which point on the bearing is furthest from the machine face, and which is closest). By moving the accelerometer around (safely), the analyst would find a 180° phase difference between those two points. (Figure 4)

Fluting or EDM

If current flows between the inner race and outer race, through the rollers or balls, a fluting pattern will be etched onto the bearing surfaces. The pattern is quite unusual, although very recognizable, as shown in the photograph. (Figure 5)

Current flow can occur for a variety of reasons (including poor grounding when welding is performed, insulation breakdown, brush problems on DC drives, and other reasons). The fault condition is common in DC motors, and it is now increasingly common to see this problem on variable frequency drives.

Because of the “washboard” pattern on the bearing surfaces, a series of peaks is often seen clustered together up in a high-frequency band, typically between 100,000 CPM and 180,000 CPM. It is believed that the peaks appear in this range because they are exciting a bearing resonance; therefore, where they actually appear will depend upon the bearing. The peaks may be separated by BPFO, BPFI, or sometimes BSF; however, they are often not observed in the lower frequencies (i.e. at BPFO, BPFI, etc.). (Figure 6)

Skidding

If a bearing is correctly selected for its application, the lubricant is functioning correctly, and there is adequate load on the rolling elements, then the rolling elements should continuously roll around the raceways. However, it is not uncommon for the rolling elements to slide or skid from time to time when these conditions are not met. This is more common on non-drive-end bearings, especially on vertical machines, and far more commonly with cylindrical roller bearings (as against deep groove ball bearings). In many cases, when skidding is observed, a shot of grease may stop the bearing from skidding, but minutes or hours later the skidding will resume. In some cases the skidding will occur when the machine is started, or on cold days because the lubricant is more viscous.

There are actually a number of situations in which skidding, sliding, or smearing can occur, but for now the focus is where the rolling elements skid through the unloaded portion of the bearing (i.e. opposite the load zone). I think it goes without saying that skidding is very harmful to the bearing. The metal-to-metal contact causes excessive wear, and heat is also generated. In more than one case fire and/or explosions have resulted.

The vibration pattern will change when a bearing is skidding. The recording must be taken, however, when the skidding is occurring (which can be intermittent). It is common to be able to hear a high-pitched sound from the bearing when skidding occurs. That should be enough to get your attention; however, an acceleration time waveform also will show high G levels; often above 10 Gs. High-frequency “noise” is generated, which will excite the bearing resonance (as described when fluting occurs); however, in this case we may expect to see a “hump” in the spectrum, like a mountain. It is not uncommon for peaks to emerge out of the hump that are separated by BPFO.

If the surface is damaged, peaks may be observed at the defect frequencies. You may notice that the peaks become “smeared” (broader and shorter), because the frequency of vibration is not consistent.

Sliding and loose fit

Another fault condition you may encounter is where the inner race slides on the shaft, or the outer race slides in the housing, due to a loose fit. It is not uncommon to see a 3X peak (and harmonics) rise in amplitude when the bearing is slipping on the shaft, and you may also witness an increase in the 4X peak when the bearing is loose in the housing.

Observe the bearing

It is highly recommended that you look closely at the surface of a bearing when it is removed from the machine. It will tell you a great deal about the failure mode. All of the major bearing suppliers offer application notes with images that allow you to recognize the markings on the bearing surfaces, helping you to determine the root cause. If a bearing is slipping on a shaft or is loose in the housing, or if the rollers are skidding, the surfaces of the bearing will provide tell-tale signs. (Figure 7)

Using a stroboscope

If the cover of the bearing can be safely removed so that the rolling elements can be observed, a stroboscope can help to diagnose the slipping and skidding faults conditions discussed in this article. If you synchronize the strobe to the shaft speed, you should not see relative movement between the inner race and the shaft. If the strobe is synchronized to the cage frequency, the cage should appear to be stationary, unless skidding occurs. The relative position of the outer race to the housing should not change.

Conclusion

There are a number of fault conditions related to rolling element bearings that can be detected with vibration analysis. As always, serious thought must be given to the root cause of these fault conditions. You need a good vibration monitoring program, but you also need to adopt precision maintenance practices. In the fourth and final article (Coming out Oct/Nov 11) we will explore how vibration analysts can contribute to reliability improvement.

This is the final part of the series on dealing with rolling element bearing defects. In previous articles, we looked at how vibration analysis can be used to detect a range of faults conditions, including lubrication problems; wear, spalls, cracks and other defects; and problems that relate to poor installation practices.  In this article, we will discuss how the vibration analyst (and others within the maintenance and operations group) can minimize the number and severity of bearing faults. This is arguably the most important of the four articles.

If you asked most people whether vibration analysis improved reliability, they would answer, “Yes.” But I would disagree.

What is your definition of reliability?

If your definition of “reliability” is whether or not bearings are failing catastrophically and unexpectedly, then it would be true to say that vibration analysis does improve reliability. But let’s draw a parallel with your car for a moment.

How would you feel if your car failed as often as most rotating machines?

If you found that every three months your car engine failed and thus you often found yourself stranded on the side of the road, then you would correctly say that your car is unreliable. But if the mechanics added a red light to your car’s dashboard that warned of imminent failure so you could avoid being stranded on the side of the road, you would feel like that was a step in the right direction. But if the red light comes on every three months, you would still feel as if your car is unreliable. You would be within your rights to ask the mechanics to make a change so that your car would run six years - or much longer - without the red light coming on.

We need red lights on our motors and pumps

The same is true with your rotating machinery. In most plants, the vibration analysts are the “red light” on the dashboard. They take readings, see that there is a problem, then wave their hands to say, “you need to take action because the bearing is about to fail.” If the vibration analyst does a good job, then there will

be more time between the red light coming on and the machine failing. As a result, the maintenance department will have more time to deal with the repair: order the parts, find the most convenient time to shut the machine down, operate the machine through a critical period, operate the machine more safely, etc.

But there is much more that the vibration analyst and the maintenance and operations departments can do. The goal has to be to increase the life of the bearing - that’s what makes a machine more reliable.

How can you improve reliability?

There are four key components to improving the reliability of rotating machinery.

Purchase and design

Rotating machinery and its support structures should be designed and purchased with reliability in mind. The lifetime costs should be prioritized over the up-front purchase price. Vibration analysts can contribute to the design and selection process by referencing the experience gained from similar machines - that is, if a certain design has proven to have problems, do not use it again. Vibration analysts can also contribute by performing “acceptance testing” (incoming inspections) of new and overhauled machines to ensure that they are fit for your company’s use.

Operation

If a machine is operated correctly, there are less stresses on the components (bearings, shaft, seals, etc.). It is primarily up to the operators to ensure a machine is operating correctly, but the vibration analyst and other condition monitoring technicians can perform tests to verify that it is operating properly.

Maintenance

Similarly, if a machine runs more smoothly, there will be less stress on the components and it will be more reliable. The maintenance department has an important role to play. The bearings and gears should be lubricated correctly. In addition, the shafts should be precision aligned; there should be no soft foot; the rotating elements should be correctly balanced; there should be minimal resonance; the bearings should be installed correctly; and so on. If the maintenance department gets all of the fundamental maintenance issues right, then the machine will be far more reliable. As a result, the vibration analyst should see very few fault conditions develop.

So what is the role of the vibration analyst? The vibration analyst may be involved in precision alignment and should be involved with field balancing. The vibration analyst can certainly take the required readings to check for misalignment, soft foot, lubrication problems, bearing installation problems, unbalance, looseness, resonance, flow problems, and so on. If these tests are performed correctly and the conditions are corrected quickly, the machine will provide many years of reliable operation.

Yes, it will take cooperation between maintenance and the condition monitoring group, and it will require the vibration analyst to master all the necessary skills, but it is definitely worth it.

Continuous improvement

Even with the best intentions, there will still be failures. The important factor is to learn from failure. Root cause failure analysis can be used to determine why a machine failed - but it is important to go back and make changes so that the failure does not occur again. A vibration analyst can play a very important role. The vibration data can hold the clue as to why a machine failed. It may be that a bearing failed, for example, but careful examination of the data may identify a condition (unbalance, misalignment, resonance, etc.) that led to the failure. When the bearing is removed from the machine, it should be examined to determine why the failure occurred. In the example in Figure 1, the pump was in standby mode for long periods and experiencing vibration from a second unit, thus “false brinelling” occurred.

Figure 1 - This bearing has failed due to false brinelling. Image adapted from FAG Publ. No. WL 82 102/2 ED

How do you make all this happen?

The answer is training and communication. Unless you have buy-in at all levels in the organization, reliability will always be a seemingly impossible dream. Everyone must believe that reliability is a very high priority (safety may be a higher priority, but reliable plants are safer plants). Reliability adds to the bottom line of the balance sheet. While there will be an initial investment (training, instrumentation, design modifications, etc.), the improvements in production, quality and energy efficiency, and the reduction in maintenance costs (parts and labor) and safety incidences will result in a very fast return on investment.

What type of training is required?

In this author’s opinion, you need three types of training: awareness, management and practitioner.

Awareness: Operators, millwrights and everyone up through to management need to have basic training on the concept of reliability, condition- based maintenance and the condition monitoring technologies. People should not feel threatened by the technology; and everyone should be pulling in the same direction. And they should all believe in the philosophy so that when recommendations for repairs and changes to procedure are made, they are followed without question.

Management: Managers, engineers and purchasing personnel need a deeper understanding of the same three areas (reliability, condition-based maintenance and the condition monitoring technologies) so the program can be run correctly and all design and repair decisions are made with reliability in mind.

Practitioner: It may seem obvious that the vibration analysts, aligners, balancers, lubricators, bearing installers and other people need training to do their job properly, but you would be surprised at how few actually have adequate training. Assumptions are made about a person’s knowledge; sadly each person learns the same mistakes from their fellow workers. Companies may buy modern vibration analyzers, state-of-the-art laser alignment systems and other high-tech equipment, but without adequate training, the money is wasted (and the opportunity is lost). See Figure 2.

Figure 2 - Laser alignment systems are great, but without adequate training, they will be misused

Conclusion

A good vibration analyst will detect a bearing defect before it fails. A better analyst will detect the defect earlier and communicate the status so action can be taken to minimize the cost of repair. But the best vibration analysts do everything possible to reduce the likelihood that the bearing will ever develop a defect in the first place.

Jason Tranter is the founder of Mobius Institute and author of iLearnVibration and other training materials and products. Jason has been involved in vibration analysis in the USA and his native Australia since 1984. Before starting Mobius Institute, Jason was involved in vibration consulting and the development of vibration monitoring systems. www.mobiusinstitute.com

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