Stricter Rotor Balancing Standards Are Needed

Stricter rotor balancing standards are one of the biggest issues that we have been addressing for clients for the last couple of decades has been improperly balanced rotors. We have armed them with the proper balancing standards that they demand every one of their rotating assemblies (fans, pumps, motors, compressors, couplings, sheaves …) are balanced to with certifications from the manufacturers and contractors to prove this final balance condition of each rotor.

The reason we have provide this guidance was too many clients were having perpetual machinery failures which we found tied to poor initial rotor balance conditions. In an effort to cut costs, many balancing standards that were used successfully for nearly a century have all been loosened resulting in unbalanced rotors, premature machinery wear and frequent repairs.

The most grossly negligent issue we have been resolving for over a decade is improperly balanced rotors (motors, fans, pumps, couplings, and sheaves). In an effort to cut costs many balancing standards that were used successfully for nearly a century have all been loosened resulting in unbalanced machinery leading to premature wear. It only takes a few minutes for an experienced balancing technician to meet the tighter standards from today’s loose ones.

In the industrial age through the Cold War the Navy balancing standard was the gold standard for rotor balancing in the United States. During this time, machinery lasted 20, 30 or more years with simple preventive maintenance measures. Partly because we had the mind set when building machinery if in doubt build it stout. So we built and over engineered machines with more strength and metal than was needed but we wanted to make sure they worked and lasted.

Today we are in a totally different era as we fight for our spot in a global marketplace where costs are all that count. You are not awarded the contract if your machine lasts for twenty years but you are if you can make it cheaper even if it only lasts just past the year warranty.

Obviously we can no longer make the machinery with the over engineered specifications as we did in the past because the time and materials are too costly. So we must make sleeker machinery which in variably runs at faster speeds, making them even more susceptible to the slightest imbalance. So it does not make any sense to us that the rotor balancing standards have been loosened in order to save pennies. It only takes an experienced and knowledgeable balancing technician a few extra minutes to balance a rotor to a tight reliable standard that has stood the test of time.

The difference in machine performance, reliability and infrequency of repairs from a tighter balance is night and day. We learned countless lessons through the Industrial revolution which improved our machinery and maintenance practices. Let us embrace these lessons or we are doomed to relive all the hardships that came with these lessons. Proper rotor balancing is one of the most critical factors in the manufacturing process that does not significantly add to production cost but totally dictates a machines performance, reliability and life span. So demand all your manufacturers and contractors balance every one of your rotors to a tight tolerance or send it to us and we will make sure it is right.

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Thorough Machine Inspections is Critical Before Start Up

Initial Machinery Inspection prior to any start up it is important to validate/identify simple items such as loose bolting, cracked welds, improperly greased bearings, clearances issues between rotors and housings, pipe strain, the rotor statics indicating an unbalance condition, sheave and coupling alignment issues and other simple checks. We are only human so it is only normal that mistakes happen but an initial inspection can find the simplest problems that can quickly turn catastrophic and costly upon start up.

Every time we are called out to conduct a vibration analysis, field rotor balancing or one of our other services, we always conduct a full machine inspection using all of our senses. There are too many opportunities for mistakes to occur in any maintenance procedure such as machinery repairs, installations, preventive maintenance tasks and just normal operations. These inspections are intended to get another set of eyes, hands, ears and nose combing the machine and even the plant to identify anything out of place. Invariably our inspections find an issue the client never noticed even though they already conducted the same check. We have learned that we must not take anyone else’s word and we must inspect every item with our own eyes. Although we are predictive maintenance experts, our personnel can often predict what their vibration spectra will look like even before they take it solely based on their inspection.

We find reassembled fans where the fan rubs the housing or even worst can not even spin which no one would notice unless they put their hands on it. Unfortunately most maintenance staffs have been cut so deeply that personnel need to run from job to job and are not afforded the time to check their or others work. Many downsized staffs use outside contractors to supplement their staff but these problems persist even with them.

Once the unit is started, the problems become obvious but often the staff has moved to the next job so we are called to resolve the vibration issue. Half the time these calls are easily fixed but the other half result in rework for the staff or us when the staff is occupied.

Although no one has any time any more, it is our experience that you can save yourself a tremendous amount of time and money by taking the time to thoroughly inspect your machinery on a regular basis and especially before any repair or new installation start up.

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Bearing Temperature Can Indicate Bearing Problems

Monitoring bearing temperatures is a simple technique for indicating bearing issues. We always use our predictive technologies such as our SV3X vibration analyzer for vibration and envelop analysis as well as ultrasonic detection. In virtually every case, we use infrared thermography scans or temperature readings to verify they are in the acceptable range.

Our experienced has shown that when bearings begin to have trouble particularly with over and under lubrication issues, temperature is a great indicator. We recommend, after our clients install or conduct a preventive maintenance bearing repack, that they monitor the bearing temperatures at least once a shift for a few days.

In most cases, the temperatures will always rise fairly rapidly after start up and continue an ascent for few hours. After three or four hours the temperatures normally stabilize or even reduce some as the bearing dissipates the heat. It may remain at these levels for around 24 hours as the bearing and grease break in. After a day though you would expect to see the levels come down and fall to within the manufacturer’s acceptable temperature range.

Whenever a bearing lubrication issue occurs you can typically see the temperatures continue on an upward climb. If the bearing can not cool itself due to too much grease or increased friction from too little grease, the temperature gives it away. If the temperatures do not stabilize after 4-6 hours or if the temperatures exceed the manufacturers recommended range, it is always smart to bring the machine down and inspect the bearings. There are actually other bearing faults that can also create friction and reveal themselves through elevated temperatures so a simple inspection is always well advised.

If you find that the amount of grease looks to be correct and you can not see any mechanical faults always make sure you are using the correct grease. Selecting the correct lubricant for the bearing is critical and applying the wrong one can be catastrophic. Remember to do your homework when selecting a lubricant so you can be assured it can handle the duty requirements.

Besides making sure you have the correct lubricant, it can never hurt to ensure you have the correct bearing. Even if the bearing box and nameplates say it is the correct bearing, simply inspect the new bearings against each other as well as the old bearings to make sure they all look the same. If you find any aspect of a bearing that is different from the others you should consider checking with the supplier. Some suppliers modify their bearings for a customer’s special need or they can just make a mistake. In either case, the different bearing may not meet the original specifications you need, resulting in a premature failure.

We provide our SV3X and Protect Wireless systems for online monitoring of a newly repaired or installed bearing during its break in period and we always recommend including temperature monitoring. If you can not have an online system monitor your bearings during the break in period make sure you at least follow the temperatures so you are notified of a potential problem before it goes catastrophic.

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Using Rotor Balancing as a Diagnostic Tool

Recently we were asked to balance a large ID Fan in the field. Our engineer took his vibration analysis readings on all the bearings and found what looked to be a large static unbalance in the rotor. He went through his normal balancing procedure and put on his weight where everything told him it should be. Unfortunately the vibration levels actually increased. Wondering if he put the weight in the wrong position, he went through his calculations and found everything was correct. Next he did a sanity check and started the fan without any changes to the fan to make sure the amplitude and phase repeated. The amplitudes were similar and the phase changed about 5%.

Since the numbers were close, although not exact, he was hesitant about what was going on. The customer insisted on trying to balance it again but we had the same exact problem. This time our engineer was sure he made all the correct moves and that something was not acting linear like a normal balance issue. So we recommended bringing the unit to our dynamic rotor balancing center so we could verify the balance condition. The customer was already two days late in starting up the plant and did not want any additional delays but saw no other options as the vibration was too high to continue to operate the machine.

We quickly saw the issue with the fan after a couple of runs on the balancing machine. The readings were always changing and we could hear material inside the fan. Our curiosity quickly had us to drill a hole in the area of the noise and suddenly all kinds of fine dirt and rust started to flow out from the opening. When it was done, we measured six pounds of material was taken from the center of the fan.

Now with all that weight removed, the fan balancing made sense once again. We made a precision balance on the unit to 2W/N and put it back into service. Before the unit started up some personnel took cover but it came up below 0.1 ips and running smoother than ever.

Our engineer learned to trust his instincts. When a rotor does not look like it is repeating, take another run or so to verify it and if the rotor does not show normal linear results then there is soemthing else going on.

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Predictive Maintenance Can Change Your Future

Each day our economy struggles, it makes it much less likely that corporations will rehire the people they let go during the crisis.  In many or most cases the first personnel released by corporations are the maintenance workers.  So fewer workers are charged with maintaining the same amount of equipment.  Unfortunately in most circumstances the maintenance departments operate in a run to failure mode frantically jumping from one failure to the next.   Handcuffed with limited time, help and budgets these maintenance personnel do what ever it takes to get each machine back up and running.  Whether its chewing gum or bailing wire whatever keeps production moving is all that matters. 

So many repairs are band-aids that unfortunately will be revisited in the not too distant future creating the never ending spiral.  These Herculian efforts go unappreciated as eventually the problems overwhelm the department and more heads roll.  Most often the best personnel are let go or the department is outsourced so all the competency and knowledge is lost.    

As many companies learn, in these circumstances during the lean times, predictive maintenance, condition monitoring and NDT technologies can turn this whole situation around.  Instead of running from failure to failure, these technologies identify problems sooner so they are much smaller and much less costly to resolve.  They can identify the specific faults in the equipment so you do not just apply a band-aid to only part of the problem but you fix all the issues.  However if you are not committed to making all the necessary repairs identified by the technologies, then nothing really changes except that now you know that the crack in the bearing cage will probably give out in the next 3-6 months. 

If your management does not believe in you, having this knowledge is an extremely powerful way to turn them to your side.  If they are unwilling to provide you the funds and time to make the total repair, you can become a prophet by explaining the problem and how it will ultimately fail creating additional work in a few months.  Some managers will ignore your wisdom but as your predictions come true you will quickly gain their attention and trust.   

Just remember that knowledge is power and the predictive technologies give you all the knowledge you could ever want.  It is never nice to watch the train wreck as it approaches but sometimes that is the way management wants it until they get the bill.   Now capture the momentum to articulate your argument that the predictive technologies see the future and help you avoid the train wrecks.

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Integrate PdM Technologies for the Whole Picture

All of the predictive maintenance technologies produce wonderful results on their own but when you pool them all together it opens an entirely new world.  One of the most important aspects of predictive maintenance is to make your machinery more reliable.  So wouldn’t it be appropriate if your diagnosis was more reliable as well. 

A vibration spectrum can show you that you have a bearing problem or a misaligned coupling but wouldn’t you like to verify your analysis with a different technology to confirm those findings. How difficult is it to take an infared scan to see what the coupling looks like and if it confirms your diagnosis.  Or how about pulling out your ultrasound to make sure the bearing sounds rough. 

You will find taking the time to confirm your results will ensure you make the right call.  More importantly you will most likely find additional faults that the initial technology did not even identify.  As a result, you will resolve more equipment problems meanwhile raising the reliability of your plant.

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The Maintenance World Stays The Same

Vibration Specialty (VSC) was founded in 1918 by a Russian immigrant who came to the United States with an idea that was important to the Industrial Revolution.  At the time, manufacturers were making all types of new industrial equipment like motors, pumps, fans, generators, turbines, rolls and even cars.  Initially, these manufacturers were just happy to get the equipment to work correctly and were not worried about how long the machinery lasted.  Back then vibration was just accepted as normal as they did not know any better.  Just like with any evolution the products were refined and improved. 

One critical refinement came when Nicholas Akimoff, Vibration Specialty’s founder, developed a balancing machine.  Instantly he became a part of high society in the United States as his new machine allowed Henry Ford to balance his crank shafts and Thomas Edison to balance his motors, generators and turbines.  Suddenly machinery vibration was no longer tolerable and every product required balancing if it were to be accepted by industry.  In fact, during World War II all VSC employees were exempt from the draft because our balancing machines and services were vital to the defense of the country as we balanced all the Navy’s propellers. 

Knowing this history of the evolution of machinery vibration and balancing makes it easy for us to see how the world seems to be forgetting many of the lessons our forefathers spent learning and refining.  Every day we see new and repaired parts such as sheaves, couplings, pumps and fans that are not even balanced or have extremely loose balance tolerances to make them seem as if they were not balanced at all. 

Unlike today, in three quarters of the last century, machinery was built on stout bases with ample concrete and solid I beams.  These extremely solid foundations provided a huge margin of error that even if a machine was improperly balanced it still ran decently. Now everything revolves around the mighty dollar.  Every part must be manufactured with the least amount of material so we can remain competitive by keeping the price down.  As a result, machinery is made of rinky dink sheet metal with L brackets as the foundation.  Then in order to save energy we run this machine on a Variable Frequency Drive motor and wonder why the machine either lasts only a year or is shaking itself to death. 

There is nothing wrong with making machinery with less materials but we must remember nothing is for free.   If you want to save money using less material then you must spend more time designing the system to tolerate all the forces it will encounter.  As we use less and less materials our tolerance for error becomes extremely fine.  We need to become more precise with our balance tolerances, clearances, materials and parts if we expect the machinery to operate well and last for years.  

From where we sit right now, there is no end to this less is more mentality. As a result, this makes VSC’s technologies and services in vibration analysis, infrared thermography, ultrasound, dynamic balancing, and laser alignment even more critical to making your machinery operate well with a long life expectancy.      

One thing we know is if we do not learn from history, we are doomed to repeat it and at this moment it looks like we are heading toward inferior maintenance practice that at some point will bite us.  Predictive and Precision Maintenance are the only solutions that will allow todays equipment to operate as smoothly and as long as it did in years past.

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