In most cases, when equipment is in failure mode, it begins to make sounds that are not commonly heard during normal operation conditions. Once this sound is heard a defect (at least one) is already present in the equipment.
Using our vibration tools can assist in detecting the defect before that sound is heard with the naked ear.
Think of a vibration sensor as a stethoscope that allows a vibration instrument to listen to the heartbeat of the equipment. The heartbeat is then recorded and data can be viewed historically for that equipment. The data can then be compared to other readings collected on the equipment to quickly see if any changes have occurred.
by Yolanda Lopez
There are 3 techniques that can facilitate your work in the field: the shielding technique, the covering technique and reflection management.
1. Shielding technique
This technique greatly reduces the influence of interfering leaks. It consists in using a piece of cardboard or foam(*)… to create a barrier between the “parasitic” leak noise and the location where you want to detect/locate a leak.
(*) Any material will work. It will reflect approximately 90% of the energy coming from the interfering leak.
Practical advice: the precision indicator tip placed on the internal or flexible sensor acts as a shield. This technique is very useful when leaks are very close to one another.
2. Covering technique
This technique also greatly reduces the influence of interfering leaks. It consists in:
Either covering an interfering leak with a rag or glove while you inspect an area.
Or covering the sensor with a rag or glove in the zone you want to inspect.
A leaking valve body can be conveniently covered with a cardboard carton too.
3. Reflection management
When searching for leaks, we sometimes get the impression that a leak is coming from a place where there is clearly no compressed air, such as a wall or a partition. This is due to the phenomenon of reflection. Ultrasounds from the leak are bouncing off the reflective surface. You will find the leak by following the angle of reflection. The angle of reflection is equal to the leak’s angle of origin relative to the reflection surface.
Download SDT Leak Surveyors Handbook to learn more!
by Yolanda Lopez
As Published by Solutions Magazine March/April 2018 issue
by Ana Maria Delgado, CRL and Shon Isenhour, CMRP CAMA CCMP, Founding Partner at Eruditio LLC
During the many root cause analysis (RCA) investigations we facilitate and coach, we notice some themes that continue to manifest themselves in the findings. Often, they are grouped under the heading of precision maintenance or lack thereof. Let’s take a look at some of them and determine if they are also killing your reliability.
The six killers are grouped into three areas: Lubrication, Misalignment and Undiagnosed Wear.
Click here to read the full article.
by Ana Maria Delgado, CRL
Guest post by John Lambert at Benchmark PDM
Recently I have been seeing the P to F interval curve popping up a lot on my LinkedIn feed and in articles that I have read. It was a concept that I was first introduced to when I was implementing Reliability Centered Maintenance into the Engineering and Maintenance department at the plant where I worked at the time. It was a great idea, that if done correctly is maintenance benefit. Why, because its cost savings and cost avoidance. Let me explain this.
The P to F curve was used as a learning tool for Condition Based Maintenance. The curve is the life expectancy of a machine, an asset. The P is the point when a change in the condition of the machine is detected. The F is when it reaches functional failure. This means that it is not doing the job it was designed to do. For example, if it were a seal that is designed to keep fluids in and contamination out and is now leaking, its in a state of functional failure. Will this put the machine down? Probably not, but it depends on the importance of the seal and the application. This is an important point because the P (potential failure) is a fixed point when you detect the change in condition but the F (failure) is a moving point. Not all warnings of failure put the machine down very often you have options and time. Consider this: If I have a bucket that has a hole in it, it is in a functional failure state. But can I still use it to bail out my sinking boat? You bet I can!
Failure comes at us in many ways and obviously we have many ways to combat it. If you detect the potential failure early enough (and it can be months and months before actual failure) it means that you can avoid the breakdown. You can schedule an outage to do a repair. It’s not a breakdown, the machine hasn’t stopped, it’s not downtime. This is cost avoidance and the plant can save on the interrupted loss of production because of downtime costs.
There are a lot of examples of cost avoidance and also of cost savings. For instance, at the plant I worked at we used ultrasound to monitor bearings. We detected a very early warning in the sound level and were able to grease the bearing and the sound level dropped. We saved the bearing of any damage, we saved a potential breakdown so this is cost savings. Even if there is some bearing damage, the fact that we are aware and monitoring the situation lets us avoid any secondary damage.
It’s one price to replace a seal and its more if you have to replace a bearing in a gearbox. However, it can be very expensive to have to replace a shaft because the bearing has sized onto it ruined it. Secondary, ancillary damage can mount up very quickly if you don’t heed the warning you are given with the P of potential failure. This warning of potential failure gives you time before any breakdown. The earlier the detection, the more time. Time to plan, view your options. And what people tend not to do is failure analysis while the machine is still in service. A failure analysis gives you a great start on seeking out the root cause but start right away, not when the machine is down.
Condition monitoring or as its often called Condition based maintenance (CBM) does work. However, for me there is a down side to this and I will explain why shortly. CBM is based on measurement, which is good because we all know to control a process we must measure.
Consultants (and I’m guilty) like to put labels on things and you may see:
1. Design, Capability, Precision Maintenance
2. CBM, Predictive Maintenance
3. Preventive Maintenance
4. Run to Failure, Breakdown Maintenance
For me the P to F interval curve starts when the machine starts. That means Design and Precision Maintenance is not in the curve and this happens before startup. A small point but it takes away from the interval meaning.
We use predictive maintenance technologies in CBM. Vibration, Ultrasonic, Infrared, Oil Analysis, NDT (i.e. pipe wall thickness) and Operational Performance. They are all very good technologies, yet it is a combination of cross-technologies that works best. As an example, vibration may give you the most information yet ultrasound may give you the earliest warning on a high-speed bearing. And then there is oil analysis which may be best for a low-speed gearbox. It all depends on the application you have which dictates what’s best for you. A lot of time and effort was placed on having the best CBM program and to buy the right technology.
This, I believe, lead to the maintenance departments putting the focus on Condition based maintenance! This I think is wrong because we still have failure. This means that CBM is no better than Predictive Maintenance. This doesn’t mean that I don’t recommend CBM, I do. To me it’s a must have but it does not improve the maintenance process because you still have machine failure. Machine failures fall into three categories Premature failure, Random failure and Age-related failure. We want the latter of these. We know from studies that say that 11% of machine assets fail because of age-related issues. They grow old and wear out. This means that 89% fail because of some other fault. This is a good thing because it gives us an opportunity to do something about them.
These numbers come from a very famous study by Nowlan and Heap (Google it!) that was commissioned by the US Defense Department. It doesn’t mean these numbers are an exact refection for every industry but the study but it has stood the test of time and I believe it has lead to the development of Reliability Centered Maintenance. But let’s say its wrong and let us double the amount they say is age related (full machine life expectancy). That would make it 22% and 78% would be the amount of random failures. Even if we quadruple it its only 44% meaning random is at 56% and we are still on the wrong side of the equation. The maintenance goal has to be to get the full life expectancy for all their machine assets.
In order to get the full life expectancy for a machine unit I think you have to be assured of two things. One is the design of the unit which includes all related parts (not just the pump but the piping as well). The other is the installation.
If you’re like me, and you believe that Condition Based Maintenance starts when the machine starts then you understand that there is a section of the machines life that happens before. You could make an argument that it starts when you buy it because, as we all know, how we store it can have an effect. However, what is important at this stage is the design and installation of the machine. In most cases, we do not design the pump, gearbox or compressor but we do size them so that they meet the required output (hopefully). We do quite often design the piping configuration or the bases for example. All of which is very important but the reality is that maintenance departments maintain already-in-place machine assets. So, although a new installation, requiring design work is not often done, installation is. Remove and Refit is done constantly. And the installation is something that you can control. In fact, it’s the installation that has the largest influence on the machines life. The goal is to create a stress-free environment for the machine to run in. No pipe strain, no distorted bases, no thermal expansion, no misalignment, etc.
Precision Maintenance was a term I first heard thirty years ago. Its part of our M.A.A.D. training program (Measure, Analyse, Action and Documentation). It’s simple, it means working to a standard. Maintenance departments can set their own standards. However, all must agree on it and adhere to it. This is the only way to control the installation process. This is the way to stop random failure and get the full life expectancy for your machine assets. The issue is that we do not have a general machinery installation standard to work to. Yes, we can and use information from other specific industry sources such as the American Petroleum Institute (API) or the information from the OEM (both of these are guidelines) however nothing for the general industry as a whole. Well this is about to change. The American National Standard Institute (ANSI) has just approved a new standard which is about to be published. I know this because I worked on it and will be writing about it shortly.
If you look at the life cycle of a machine, we need to know and manage the failure as best we can. If we only focus or mainly focus on the failure, we will not improve the reliability of the machine. We cannot control the failure. What we can control is the installation and done correctly this will improve the process giving the optimum life for the machine.
I sell laser alignment systems as well a vibration instruments. If a customer were to buy a vibration monitoring tool before they bought a laser system. I would think their focus is on the effect of the issue not the cause. What do you think?
by Ana Maria Delgado, CRL
1. A Change in the Quantity of Grease Consumed
Maintenance departments track their grease consumption to monitor and control costs. A change in consumption is a sure sign that your lubrication program is on the right track. Most organizations are guilty of over-lubricating. Expect lower grease consumption as your program matures. Bad procedures lead to bearings routinely receiving more grease than they’re designed to handle. The excess ends up being pushed into the motor casing or purged onto the floor.
Over lubrication happens when re-greasing intervals are scheduled based on time instead of condition. Control lubrication tasks with ultrasound to monitor the condition and maintain optimal friction. The time between greasing intervals increases, resulting in less grease used per bearing.
2. Fewer Lube-Related Failures
Do you track failures and perform root cause analysis?
Organizations with optimized greasing programs experience fewer lube-related failures. Less fixing and fire-fighting translates to more creative time for maintenance. Use that time to bring more machines into the greasing program.
Additionally, with ultrasound, you find many non-trendable defects. For example, broken or blocked grease pipes and incorrectly fitted grease paths prevent grease from reaching the bearing.
3. Optimized MRO Spares Management
Your new and improved lubrication program is delivering wins; better control of grease consumption, fewer failures, and more productivity for maintenance. Use this time to study trends and better manage your storeroom.
A decrease in bearing related failures improves spares optimization. Share your ultrasonic lubrication data with your MRO Stores manager to create a plan to reduce the number of emergency parts on hand.
Since you’re taking stock, why not shift some burden to your suppliers? Ask them to confirm your emergency parts against their own stock. If it can be supplied on the same day then it doesn’t need to be on the balance sheet.
4. Increased Number of Machines Monitored
One benefit of an effective lubrication program is time.
• Time allotted to monitoring machines instead of fixing them.
• Time allotted to correctly assessing the real needs for lubrication.
• Time to look at the big picture.
Take, for instance, criticality assessment. Many lubrication programs begin with small steps. All the “A” critical machines receive priority, rightly so. But what about the rest? With more time to plan, organize, and schedule, the number of machines acoustically monitored for optimal lubrication increases.
5. Save Time. Combine Acoustic Lubrication and Condition Monitoring
You worked hard for these results. It’s time to use your data for more than just lubrication.
Acoustic lubrication is the proven method to ensure precise bearing lubrication. New technology from SDT, LUBExpert, combines the power of onboard lubrication guidance with Four Condition Indicators for bearing condition assessment.
The time savings from assessing bearing condition during the lubrication process is beyond valuable and another sign your acoustic lubrication program is on the right track.
6. Inspector Confidence at an All-Time High
Reliable machines are the product of an effective lubrication program. You have:
• Managed grease consumption
• Fewer grease related to bearing failures
• Optimized MRO spares
• More machines under watch
• Increased data collection intervals
The power of adding ultrasound to your greasing program delivers win after win for reliability. Reliability breeds confidence. More confident inspectors making the right calls and infecting a positive culture throughout the organization.
by Allan Rienstra - SDT Ultrasound Solutions
In the 35+ years of experience that LUDECA has in shaft alignment, we have been asked this question many times. How long does it take to do an alignment? People in charge of scheduling have a tough task when allotting time for technicians to do an alignment with precision. In many cases they may just take a guess, based on the average time it has taken in the past. The answer is not so simple. During a one-day seminar, I had to perform an alignment on a motor to a pump to show the proper steps when aligning a machine. When the time came to start the alignment, all the safety procedures had been taken care of, and the machine had been rough aligned. The soft foot values were within tolerances. So I was able to align the machine in under 45 minutes, within the tolerances specified for 1200 RPM.
On another occasion, I was hired to help align a generator to a turbine. Quite a few things went right as well. The safety procedures had been taken care of by the time I got there. The coupling guard and coupling element had been removed. The machine had also been rough aligned. The special-order shims for the generator feet were available on-site. Even with all these things going my way, this alignment took a day and a half to finish. There are things that come up during an alignment that cannot be planned for. One of them is a soft foot condition. Not checking for soft foot can greatly increase the time it takes to align a machine, mainly because the response to corrections stipulated by your alignment tool will not be accurate. Therefore, knowing the soft foot condition and minimizing it, is key. However, that in itself can take up a long time, depending on the condition of the baseplate, the condition of the anchor bolts, washer, pipe stress, etc.
In both cases, they were a single coupling alignment. Aligning a large generator is obviously more difficult than a 200HP motor. In the first case, I was able to turn the motor with a strap wrench by myself. In the case of the generator, it needed to be uncoupled because the two machines could not be turned together. In most cases, a larger machine takes longer to align because breaking the bolts loose, alone, could take 20 to 30 minutes. Furthermore, there can be a large difference in the amount of time it takes to finish an alignment, between two identical machines sets. The information obtained here can help reduce the alignment time.
I recommend to download our 5-Step Shaft Alignment Procedure and/or request our Shaft Alignment Fundamentals Wallchart for your alignment team. The point is that there is no fixed amount of time required for an alignment of a machine. If a scheduler should err, it should always be on the conservative side.
by Adam Stredel CRL
Just what does it take to be successful at balancing? Let’s start with some basics. First you need to have an understanding of the balancing process, next nomenclature: is it unbalance, imbalance, out of balance, or what? Use a consistent description and stick with it. Next, think about what the source of unbalance could be: is it uneven wear on parts? Voids within castings? Damage from impacting? Material buildup? Even though buildup is not usually a problem, when it begins to come off it rarely does so evenly thus creating an unbalance. In other words, unbalance is simply the uneven distribution of mass.
Simply review or collect data to ensure that the undesirable vibration is from unbalance and not some other issue such as a belt problem, misalignment, electrical issue, etc. Once you’ve determined that the vibration is indeed unbalance you need to inspect the object to be balanced. If it is not clean, clean it. Look for damaged or broken parts. On belt driven equipment inspect the belts as their frequency can be very close to running speed and can hinder the balance job. Make sure you have the proper tools for doing the balancing job, such as a balancing instrument capable of reading the vibration that is produced at running speed or what is commonly referred to as 1×or 1 times and capable of indicating the phase angle at 1×. This could involve utilizing an optical tachometer, laser tachometer, magnetic pickup or even a stroboscope. Some tachometers will require a piece of reflective tape on the shaft for the tachometer to read from and this might require stopping the machine if still in service.
Tip: I try to place the tape horizontally, or along the axis of the shaft, with the leading edge of the tape on the trailing edge of the key way. This can be helpful if you ever have to return for another balancing job on the same machine. You need to determine if you will be adding or removing material in order to balance the rotating component. If removing material, how will you determine how much you’ve removed;if adding weight, you need to make sure the weight you are adding is of a material that is compatible with the service the machine is exposed to. If adding material “weights”, how will they be attached? With set screws? Bolts? Clamps? Welded on? All this should be considered. One last tip: if after two runs you’re not there or almost there yet, you might need to stop and examine your process to ensure no mistakes have been made.
Download LUDECA’s 5-Step Balancing Procedure.
by Gary James CRL
1. Collect the best data you can, using a high quality ultrasonic data collector.
2. Consistent sensor placement must fundamentally be observed.
3. Identifying boundaries that impact data transmission is imperative.
Ultrasound is Shy… It Keeps Boundaries
Think of ultrasound as the quiet introvert. It prefers to stay in, and rarely mixes well with ultrasounds from other places. We call this “boundary behavior” and it’s another characteristic that makes ultrasound such an attractive condition monitoring technology. Ultrasound signals remain isolated to their source, making it easy to pinpoint defects without interference from other elements of the machine.
Inspectors tempted to place their ultrasound sensor directly on the gearbox cover, should reconsider. This common mistake affects data integrity. A gasket seals the cover plate to the gearbox housing. The specific acoustic impedance of the gasket material differs greatly from the cast metal of the gearbox. The change in materials a boundary barrier through which bashful ultrasound is reluctant to is pass. A better option is to place the sensor on a bolt head, which is directly connected to the gearbox housing. The result is crystal clear ultrasound signals for listening, trending, and condition assessment. HearMore: Click here to listen to Damaged Gearbox.
Special thanks to our partner Allan Rienstra from SDT Ultrasound Solutions for sharing his great knowledge with us!
by Allan Rienstra - SDT Ultrasound Solutions
With the proliferation of online monitoring systems utilizing permanently mounted sensors, users will need to beware of “direction sensitive” vibration and possible sudden unexpected failure due to insufficient data. The thought of insufficient data may seem incredible when thinking of constantly monitored equipment, but consider the all too common (imho) practice of uni-directional (one direction) monitoring of machine trains.
Many installations, due to initial cost, are mounting a single vibration sensor at each bearing. While this may be sufficient for most equipment trains, most of the time, it will certainly not be sufficient for all equipment trains all of the time. Although I don’t have hard data available, if I were to make a statement based on personal experience, and anecdotal evidence from other practitioners, my statement would be something like this: “80% of horizontal equipment could be pretty well monitored by sensors mounted at the horizontal radial position on each bearing.” I say pretty well monitored because I just can’t bring myself (as an analyst) to be completely satisfied without the vertical and axial data.
This setup would catch virtually all unbalance and roller bearing faults (excluding thrust bearings), some to most misalignment faults and a sprinkling of others. I use the word “catch”, to mean it would give an indication of a developing problem. Accurate diagnosis of unbalance, misalignment, bent shaft, and even looseness in many cases (as well as a host of other possible faults) would require more data.
If the online vibration program manager takes these facts into account and governs the program accordingly, they should be pretty successful. If they add to the online program a “full battery” vibration survey, maybe semi-annually, just to catch the less common, but possibly very destructive defects that could develop undetected by the uni-directional monitoring, they would most likely be very successful.
What could be so destructive and yet be completely undetected by the uni-directional sensors? The Big R for one, Resonance. Resonance is often extremely directional. Consider a case history LUDECA co-published with one of our customers in the December 2012 Wastewater Processing magazine:
In the table below (Figure 1), the 1× amplitudes are displayed. I have hidden all but the vertical data, as though it were monitored only by vertical sensors.
Everything is wonderful right? Look at the motor outboard vertical, only 0.00384 inches per second—very impressive. Of course, at this point you are thinking “he is setting me up for something” and you are correct. Even though most anyone would love to have these amplitudes on virtually any machine, this particular machine was tearing itself apart with vibration!
We will give the reader a little more data, just to help add emphasis to the directional nature of a resonance. We will add the axial data to our table in Figure 2:
Still very, very good… so far. Now look at Figure 3, with the addition of the horizontal data.
The motor outboard horizontal amplitude is 162 times the amplitude of the motor outboard vertical! What if the user had only vertically mounted sensors? What about vertical with the added information of axial? You may be thinking “if I had only horizontal sensors, I would have been ok”, and for sure you would have been better off than having only vertical. You would at least have known you had a problem, but you would not have known what that problem actually was. You would likely have assumed the vertical and axial are probably vibrating badly too. Hopefully you would have verified the vibration in the other directions. As it was, the user had data from all directions and a simple glance told the analyst with a high degree of confidence what the problem was. Resonance is almost alone in creating that kind of directional disparity.
To reiterate, the online vibration program manager should be successful if they take into account the fact of limited data and supplement the online program with a “full battery” vibration survey at a cost effective interval, just to catch the less common, but possibly very destructive defects that could be developing undetected by uni-directional monitoring.
by Mike Fitch CRL
While the person in charge of collecting vibration data is actually collecting the data, they should watch the data “live” for unusually high amplitudes or discontinuities in the data. This will not increase the data collection time, and if any of these issues are detected, the person can evaluate whether or not the data is “good” or not; if not, the data can be recollected, or if it is “good” then additional data may need to be collected to ensure that proper analysis can be performed on the equipment. Field notes can be made about the machine condition and its status. If the machine condition is determined to require attention, the analyst might need to contact someone at the facility. Remember that sudden increases or decreases are usually a sign of machine problems. Looking at or analyzing the data in the field can give the analyst a good idea of what issues need to be analyzed, thereby reducing the time analyzing data in the office. If not analyzing the data on the spot, one can at least make notes to aid in later analysis.
by Gary James CRL
♫ And it’s too late baby now, it’s too late; though we really did try to make it. Something inside has died and I can’t hide and I just can’t fake it…♫
So go some of the lines of the old Carole King hit from 1971. Unfortunately, that pretty well sums up the situation for those sad contemporary souls who have computer crashes, but didn’t have their databases backed up on a regular, frequent basis. The part about “I just can’t fake it” is especially true after “Something inside has died” (that is, inside of the computer). When you lose your database or databases, there’s just no faking it.
If you are like most, you get a sick feeling inside just thinking about it, and you resolve to get started soon at making a habit of backing it all up. Procrastinate no longer, friend. Get help from your I.T. department, or if you don’t have one, there are numerous players now, that for a small fee, will back up and protect your important data, either locally or in the cloud.
Don’t wait until you are singing the old Carole King song, “It’s Too Late”. Go ahead and protect yourself.
by Trent Phillips CRL CMRP - Novelis
How many facilities only collect vibration data when it doesn’t interfere with other activities? So often collecting and analyzing data is only one part of a given person’s responsibilities and workloads dictate that the collection and/or analysis take a back seat. When this happens, machine problems are not detected and therefore not reported for corrective action to be taken. If a machine then fails management has all the right to ask why the problem was not found and reported, even if management itself is the reason the data was not collected or analyzed! Vibration data collected should also be analyzed in a timely manner (within two business days of collection) to allow for proper scheduling of any needed repairs; of course, if problems are detected while collecting data that are believed to be severe enough to merit immediate attention, then they should be reported immediately to the facility. Many analysts do not know how long it will take to approve, plan, order parts, kit out, and schedule the resources to execute the repair work. Therefore, one must collect, analyze, and report the data as soon as possible. Generally, you may find several problems in most facilities; however, if you hand in 20 or 30 reports to the Reliability contact, they can quickly be overloaded. I would collate and deliver all the necessary reports but would focus on the top 5 priority problems first, based on safety, criticality, severity, and production demand.
by Trent Phillips CRL CMRP - Novelis
Condition Monitoring Expert Tip #9 by Mobius Institute
No, sadly, that may not be correct. If the spectrum (and phase readings) indicate misalignment, then the machine will be misaligned. But if there is no indication of misalignment, the machine may still be misaligned. I know that may not make sense, but unfortunately it is true.
A number of experiments have been performed where real machines were misaligned and the vibration pattern did not change. The vibration pattern depended upon the type of coupling and other conditions, but the bottom line is that the only way you can be sure that the machine is precision aligned is to precision align the machine with a laser alignment tool.
We appreciate Mobius Institute for allowing us to share this tip with you!
by Ana Maria Delgado, CRL
Using ultrasound to locate compressed gas leaks is relatively easy, but it occasionally it can present some challenges. The reason ultrasound is so successful is that it is a high frequency, short wavelength signal that does not like to penetrate 2nd mediums. While performing compressed gas leak inspections, keep in mind that strong ultrasonic signals can bounce off most materials leading to false indications.
To overcome this challenge, turn your ultrasonic detector 180° and see if the signal is stronger coming from that direction.
Download Find-and-Fix Leaks Procedure
by Paul Klimuc CRL - SDT Ultrasound Solutions
Condition Monitoring Expert Tip #7 by Mobius Institute
Spectrum analysis provides a great deal of information about the health of rotating machinery. But you should consider the spectrum as a summary of the vibration within the machine.
The Fast Fourier Transform takes the time waveform and computes how much of each frequency is present and displays that as a line in the spectrum (grossly summarized, but that is basically the case). Therefore, if the vibration from the machine is generated by smooth periodic motion, then the spectrum provides a very good representation of what is happening inside the machine. But as damaged gears mesh together, and rolling elements pass over damaged areas on the raceway of the bearing, and as the pump vanes push through the fluid causing turbulence or cavitation, the vibration generated is not smooth and periodic. And there are a lot of other fault conditions that likewise do not generate smooth and periodic vibration. Thus, the only way to really understand what is happening inside the machine is to study the time waveform.
The time waveform is a record of exactly what happened from moment to moment as the shaft turns, the gears mesh, the vanes pass through fluid, and the rolling elements roll around the bearing. Each minute change that results from impacts, rubs, scrapes, rattles, surges, and so much more is recorded in the time waveform and then summarized in the spectrum. Therefore, it is critical to record the time waveform correctly and analyze it when you have any suspicion that a fault condition exists.
Special thanks to Mobius Institute for letting us share this condition monitoring expert tip with you!
by Ana Maria Delgado, CRL
But, once the pulley alignment is done, equally important is set the belts to the proper tension. Typically, the correct tension is one that allows the belt to be deflected on its tight side by a specified amount of force to an amount of 1/64th inch per inch of span length. The span length is the distance between the nearest points of contact of the belts on their sheaves. If this distance is not known, you can use the center distance between the pulleys; that’ll be close enough.
So, say the span length of a given belt drive is 36 inches. You should deflect the belt (in a group of belts, usually the center one, but measure the two outside ones as well) by 36/64″, (or 9/16″) which is 1/64″ of deflection for every inch of span length, and measure how many pounds or newtons of force it takes to do that. This force should not be less (too loose) or more (too tight) than what the manufacturer of the belts recommends for that drive or for that set of belts. Also, you perform this test by pressing down with your gauge upon the belts in the middle of their span length on the “tight side” of the belts. The tight side of the belts is the side that is stretched as the drive turns andthe driver pulley applies rotational force to the driven pulley. The return side is slack side of the belts.
The recommended belt tension deflection forces are usually supplied in a table that takes into account the size, length and type of belts, the number of belts in the drive, the anticipated application loads and drive ratios of the sheaves. Move the driver until the recommended force specification is met for the desired deflection, being careful not to mess up the sheave alignment while doing so!
by Alan Luedeking CRL CMRP
Condition Monitoring Expert Tip #10 by Mobius Institute
No, sadly, that is not right. Unless the person has been properly trained, and unless the company has specified precision alignment tolerances, and unless the training is followed and the tolerances are achieved, then you are not performing precision alignment.
We see this as a very common problem. Laser alignment systems can achieve terrific results. And a precision aligned machine is far more reliable than a machine that has been “roughly” aligned with an alignment system, and far superior to a machine aligned with a straight edge. But if your maintenance technicians do not appreciate why that last shim should be installed, and why the motor must be moved such a small amount to the left or right, then those corrections will not be made – and yes, it does matter.
Research by Tedric A. Harris, in the book “Rolling Element Bearing Analysis” (John Wiley & Sons) showed that just 5 minutes (5/60 of a degree) of angular misalignment can reduce the life of a bearing by half. Yes, precision matters!
by Yolanda Lopez
- Make sure the surfaces of the vertical posts are clean.
- Improve the contact between the vertical post and the crossbar by applying a light coat of Vaseline or grease to the contact surface of the vertical post.
- The temperature probe should always be placed on or as close as possible to the inner race or ID of the workpiece being heated.
- When possible make sure a second probe is placed on the outer race or OD of the workpiece being heated to also track the temperature of the OD, in line with the ID probe.
- For the most efficient heating, always use the largest possible crossbar that will fit through the ID of the workpiece being heated. Stacking of multiple crossbars is permissible.
- It is not a requirement that the workpiece must touch the crossbar(s). Just so long as the bar goes through the bore (ID) someplace.
- Most important of all is that the workpiece being heated always be automatically demagnetized. Any induction heater that does not do this automatically COSTS you money instead of saving it.
by Bernd Seidenthal CRL
Condition Monitoring Expert Tip #5 by Mobius Institute
Now this is a tricky question to answer… We have a few contenders: high frequency vibration analysis, regular vibration analysis, ultrasound, oil analysis, wear particle analysis, and infrared analysis. Let’s start by ruling a few of them out.
Infrared analysis is used to detect heat in a bearing, which is a late stage fault condition, so that’s not your best option. Regular oil analysis can detect the presence of the wear metals within the bearing, but wear particle analysis is a better tool for that. Regular vibration analysis (i.e. velocity spectra) provide very clear indications of bearing faults, however the high-frequency detection techniques provide an earlier warning. That leaves high-frequency vibration analysis, ultrasound, and wear particle analysis.
Ultrasound is easiest to use. Push the probe against the bearing and listen carefully and you will hear if the bearing is in distress. (You can also record and analyze a waveform, but now you may as well be performing vibration analysis). Many would argue that high-frequency vibration analysis (such as enveloping, PeakVue, shock pulse, and others) provide a clearer indication of the nature and the severity of the fault. But it does require more training and potentially a more expensive system to perform the collection and analysis.
And that leaves wear particle analysis. Let’s just say that if you own critical gearboxes, you absolutely must perform wear particle analysis. Performed correctly, you will detect the first signs of wear, and complex gearboxes provide a greater challenge for the vibration analyst and the ultrasound tools.
Although I haven’t really answered the question, I am hoping to have put you in a position to make the right decision for your situation.
Thank you Mobius Institute for this valuable tip!
by Yolanda Lopez
Belts are a critical part of the design and function of belt-driven equipment. The majority of belts never reach their intended design life due to improper selection, storage and installation. Unfortunately, this results in compromised equipment operation, lost capacity and increased costs. Do not condemn your equipment to death through improper belt installation practices. Below are some guidelines to help your facility ensure belt-driven equipment reliability:
- Follow all site specific safety procedures.
- The same basic installation steps are required for both synchronous and V-belts.
- Loosen motor mounting bolts or adjustment screws.
- Move the motor until the belt to be replaced is slack and can be removed easily without prying or any other means of force. Prying off a belt or chain can damage a sheave or sprocket and increase the risk of injury. Never use a screw driver to remove belts, because this may damage belt cords, sheaves and sprockets.
- After removal, inspect old belt for unusual wear that may indicate problems with design or maintenance issues.
- Visually inspect and replace sheaves or sprockets that have excessive wear, nicks, rust, pits or are bent. Grooves that appear “shiny” or polished could indicate heavy wear and should not be ignored. Never sand or scrape groves. Doing so will insert points of wear leading to premature belt or sheave failure.
- Sheave gauges should be used to measure for excessive wear and determine if sheave replacement is necessary. Total wear should not exceed 1/32 in or 0.8 mm.
- Sheaves and sprockets should be checked for proper alignment. A laser alignment tool is the recommended means. Most major belt manufacturers recommend a nominal tolerance of 0.5 degrees. However, better alignment tolerances should be achieved if possible. The table below can be used to determine proper alignment.For maximum resolution, always mount the laser alignment tool on the smaller sheave and the targets on the larger sheave. Ensure that the alignment tool being used can indicate misalignment in all three degrees of freedom (axial offset, horizontal angularity and twist angle).
Note 1: Check and correct any run out conditions prior to belt installation. Tighten bolts in the proper sequence to prevent axial run out.
Replace all belts on multiple belt drives with new belts from the same manufacturer. Never replace a single belt or a portion of a multiple belt drive. Mixing old and new belts will create unevenly shared loading and lead to premature belt failure and/or sheave wear.
- When installing the new belt, ensure that enough clearance is available to slip the new belt(s) over the sheave or sprocket. Never pry or use force to install the belt(s). Never use a screw driver to roll belts into position, because this may damage belt cords, sheaves and sprockets.
- Adjust the motor base until the belts are tight. Motor should be checked for soft foot conditions using a feeler guage or other suitable means and corrections made if required. No reading of soft foot should be greater than 0.002 inches or 0.05 mm.
- Use a tension gauge or sonic tension meter until the correct tension is measured according to specifications.
- Rotate the belt drive by hand a few revolutions and re-check and adjust belt tension as necessary.
- Re-check the sheave or sprocket alignment and re-adjust if necessary.
- Secure motor mounting bolts to the correct torque specifications.
- Replace equipment guards and follow any other site specific safety requirements to return the equipment to operation.
- Upon equipment startup listen and visually inspect for any unusual vibration, noise or heat. Other corrective actions may be required (lubrication, tension adjustment, etc.) to ensure equipment is ready for proper operation.
Note 2: Contact the belt manufacturer and provide the drive information to receive the most accurate tension information for the required operating loads. Belt tension charts may specify more tension than is required by the application. The proper tension for the belt is the minimum tension required to prevent the belt from slipping at maximum load. A good guideline in the absence of any other information is to use a spring scale, and press down on the belt in the approximate center of its span (on the tight side), to deflect the belt 1/64″ per inch of span length and observe the force required to do so. If you are not sure of the belt span length you may also use the center-to-center distance of the pulleys, which will be similar. Tension the belts until the force required for this deflection equals the belt manufacturer’s maximum recommended force values for the specific belts you are using.
Note 3: Belts should not squeal on startup when adjusted to proper tension. This can be an indication that the drive is not proper for the application.
Note 4: A run-in procedure may be required for V-belt drives or other installations to ensure optimal belt life and equipment reliability. It is recommended to check and adjust belt tension under full load after 20 minutes, 24 hours and 48 hours of operation to properly seat the belts in the sheave grooves. Consult belt manufacturer and engineering specifications to determine if a run-in period is required and length of time.
by Trent Phillips CRL CMRP - Novelis