Guys I'm about beside myself on this particular motor. Those involved with the issue I'm referring to that 350hp blower motor I took out of service due to a bearing failure.

Well, the motor comes back from the shop but still had a problem. Cocked and or defective bearings was what I found. Motor shop changed the bearings again. Okay...

I reinstalled the motor again and did the alignment Monday, took out all the soft foot, etc...I ran the blower and all vibration readings looking real good, and all in the green zone, okay...When I left work yesterday I walked by it again and put my finger on it. Looked good, felt good no vibration. By this time the blower had been running almost 4 hours.

Now the fun part...

This morning I do a follow-up reading. I'll be whooped if I ain't getting the very same readings I had after the original overhaul job. 1 & 2 HVELL IN the yellow alarm, and and 2AVEL in the red, running .59 ips. Soooooo I uncoupled the motor again and ran it... Still have the axial vibration, and the 2HVEL in the alarm. Axial in the red alarm...2AVEL

Me and the other vib tech worked it together this time so he could see what I saw.

We did a coast down twice with ultrasonic equipment and I noticed real bad popping and static in the #2 axial direction in the 3 and 9 position. Not so bad at 12 & 6...Cocked perhaps? hmmmm, but why, and why twice?? Same on the #1 bearing, sounded really bad, axial direction...!

I also felt with my hands at the center of the motor housing and it appeared to be doing some scraping or grinding from within the motor...Strange, I think so...

We will decide what to do with this in the morning. My recommendation to the boss was to get the motor shop out here, and or take the motor to the shop, us with it, and we'll all watch while they run it and tear it down.

Still have not received the report on the last repair which was warranty, other than they changed the bearing again. I want to know what excactly they found, but cannot seem to get an answer to my emails about it. Boss is calling them in the morning!

My gut tells the internal motor parts, electric, and or mechanical are defective, causing the bearings to go bad...I thought I proved this already, but in fact it is my belief the motor shop has not addressed the ROOT cause...

What say ya'll? <SCREAM>!

Is it specified in the contract for the motor shop to find root cause?

I thought the owner's rep should be implementing the QA/QC plan for the motor overhaul including witness or hold point at soem critical stages.

Rod,
Provided motor has ball bearings:
To me it smells like a bearing arrangement insufficiently able to slide in the bore in axial direction when trying to compensate for thermal expansion.
Ask the repair shop to thoroughly check endshield bore and shaft collar dimensionals, and re-machine if necessary!
Arie Mol, NL

We talked to the motor shop this morning. They confirmed my report was accurate. Bearings in their own words were, "trash"...They only had 2 days running time on them.

We pulled the motor for the third time. This time we will go to the motor shop for their test run and tear down while they are doing it.
They said they will do a more extensive investigation on it to determine failures...

Problem is I needed that motor back and running right the first time because I have another one getting ready to crash and burn. I think we can maintain our production with two blowers out since the temps are cooling down now.

I have three out of our nine blowers with motor failure pending... DB's on the second one are running at 39-45 db....

I'll be sure to fill ya'll in on the details after I find out whats up with it...Lot of lost time here over that one motor...!

Here is the promised update on the 350hp blower motor problem. The report from the motor shop this morning was that the bearings had lubrication failure both times. Lack of lubrication that is...

I'm still perplexed as to what they reasoned that on, but the best I can figure, as told us by our maint superindendent, is that the bearing, SKF 6219 are shielded bearings, prelubricated, and should not need lubrication throughout the life of the motor.

I had aproblem with that right off the bat. Why are we greasing these motors every three months if these are shielded bearings?? Anyway, the motor shop on the second set of new bearings removed the shield and hand packed the bearings. They also noticed when the motor went back the first time about 3 weeks ago that the grease was being slung out of the bearing, and this was why it failed...Confused yet? I was/am when I heard this. Why did they not see the lack of lube the first time??

We also deviated from using the OEM grease 5 years ago, instead opting for the red synthetic type grease, thereby voiding our warranties on all the new motors we've replaced over the past 5 years since changing greases. This was not our call, but was from a former superintendent. Motor shop recommended going back to the OEM grease which the manufactures use, so we will...

Okay, now this morning the motor shop tells us they will have this motor ready by 2:00pm today. So myself and two other guys are waiting around past 3:00pm today, still no motor. We get a call from the motor shop telling us that they found some other problems with the motor, internal electrical in nature!!! If they finish it tonight we will install it in the morning...

This confirms what I was telling my supervisor, after the first time I installed this motor after the initial repair, I still noticed a 2X Line Frequency peak(s) in the spectrum, duhhh...Whats wrong with this picture? The axial vibration never did subside through out all the repairs.

Bottom line is this motor has been removed for repair, and reinstalled going on three times now, Since August...This last set of bearings only lasted 5-10 hours. I felt from the beginning I had a two fold problem, bearing failure due to carbon black contamination, as well as internal electrical problems. Why they did not find the internal elec problem during the first repair, I'll never know...So when this is all over I will demand a repair report on the third failure...

Sorry to be so long winded. I'll sign off now for your comments...I'm still confused on the lubrication issues...

Thank You,

quote:

Originally posted by arie mol:
Rod,
Provided motor has ball bearings:
To me it smells like a bearing arrangement insufficiently able to slide in the bore in axial direction when trying to compensate for thermal expansion.
Ask the repair shop to thoroughly check endshield bore and shaft collar dimensionals, and re-machine if necessary!
Arie Mol, NL

Please tell me what the speed of your motor is. And if you say 3600 rpm, please be prepared for my rant about why grease lubrication is not suitable for that application (6219 at 3600rpm). Double shielded would be even worse in that application.

Out of curiosity, is the red synth grease Mobilith SHC100? Is the OEM grease Polyrex EM?

Rod

I recommend that your repair shop gets with their bearing supplier and has some training on bearing operation and installation.

Motor bearings are not lubricated by the grease, they are lubricated by the oil in the grease. The fact that they 'hand-packed' the bearings is a testimony to their lack of understanding of the lubrication of a motor bearing. Of course the bearings are 'throwing out' the grease, they need to as there is less than 3-mil's clearance in the bearing itself and the soap used tends to be thicker.

Shielded bearings ARE greaseable bearings, sealed and non-contact sealed bearings are not. Shielded bearings have a small opening on the inner race of the shield that allows a small amount of oil and soap into the moving parts of the bearings.

A common problem that occurs following motor repair (and having done this myself when I was a novice in the motor repair business in the mid-1980's) is when the bearing caps are not installed properly. Another issue that can occur is if there is work done on the motor shaft, such as returning the surface back to the original size or making a new shaft, if the bearing shoulders are too far apart, or too close (basically not machined right). I did have one issue that drove me crazy in 1991 and that was a motor that had a spacer on the shaft between the bearing shoulder and the inner race of the bearing. Another mechanic had taken the motor apart and did not note or mark the part. When I put it together, everything seemed to work just fine until the bearings warmed up.

Finally, you have to consider whether or not the OEM and motor repair shop grease is compatable and if your company greased the bearing when the motor was installed (or after you left that evening). Always a poor practice.

I am including the presentation on bearing lubrication I was asked to give at pdm-2007. Perhaps it can also provide some guidance.

Howard

Bearing_Greasing.pdf (667 Kb, 28 downloads)

No problem...I appreciate the rant believe me! I was right about the internal motor problems with that other motor too. Makes me affirm that I'm on the right track. I've been trying to get things straightened out here so input is good...

I'll get back to you on that red synthetic. It was recommended by the motor shop to go back to the OEM. I'll have to find the number spec on that. Not sure what it is off hand...



Please tell me what the speed of your motor is. And if you say 3600 rpm, please be prepared for my rant about why grease lubrication is not suitable for that application (6219 at 3600rpm). Double shielded would be even worse in that application.

Out of curiosity, is the red synth grease Mobilith SHC100? Is the OEM grease Polyrex EM?

Forgot to mention. The machine speeds on our blowers are all 3600 -slip freq. hehe

Yes, confirmed that the red grease in indeed SHC-100...We will be using Polyrex EM as recommended by the motor shop from here on in...

Feedback on this please.

Thanks,

Yesterday morning after installing the motor and doing the soft foot and alignment, I started it and warmed up the blower for over an hour. Noticed the bearing temps were running 125-135 degrees. All the other comparable motors, same design brand, etc are all running 95-100 degrees. I'm assuming this difference is due to the different greases now, am I correct?

I also brought up the issue of mixing grease. Probably not a good idea since we've been pumping in SHC100 for the past 5 years...

quote:

Originally posted by MotorDoc:
Rod

I recommend that your repair shop gets with their bearing supplier and has some training on bearing operation and installation.

Motor bearings are not lubricated by the grease, they are lubricated by the oil in the grease. The fact that they 'hand-packed' the bearings is a testimony to their lack of understanding of the lubrication of a motor bearing. Of course the bearings are 'throwing out' the grease, they need to as there is less than 3-mil's clearance in the bearing itself and the soap used tends to be thicker.

Shielded bearings ARE greaseable bearings, sealed and non-contact sealed bearings are not. Shielded bearings have a small opening on the inner race of the shield that allows a small amount of oil and soap into the moving parts of the bearings.

A common problem that occurs following motor repair (and having done this myself when I was a novice in the motor repair business in the mid-1980's) is when the bearing caps are not installed properly. Another issue that can occur is if there is work done on the motor shaft, such as returning the surface back to the original size or making a new shaft, if the bearing shoulders are too far apart, or too close (basically not machined right). I did have one issue that drove me crazy in 1991 and that was a motor that had a spacer on the shaft between the bearing shoulder and the inner race of the bearing. Another mechanic had taken the motor apart and did not note or mark the part. When I put it together, everything seemed to work just fine until the bearings warmed up.

Finally, you have to consider whether or not the OEM and motor repair shop grease is compatable and if your company greased the bearing when the motor was installed (or after you left that evening). Always a poor practice.

I am including the presentation on bearing lubrication I was asked to give at pdm-2007. Perhaps it can also provide some guidance.

Howard

3600 rpm 6219 grease lubricated bearing?! Arrggghhhh! Without getting on my soapbox, I will simply say that is far beyond the bounds of grease lubrication (based on the D*N number) and you will need to devote extra effort to doing everything right in terms of greasing techniques and having lucky phases of the moon in order to have a prayer at making it even half as long as most of your other bearings. I will post more to backup these statements later tonight.

130F on the housing does not concern me at all. It is not uncommon for greased bearings to run hotter shortly after bearings have been replaced (or motor regreased for that matter). It takes awhile for the grease to redistribute.

We use Mobilith SHC100. Our luck hasn't been great with that grease in these high D*N applications, but I'm not sure if it's the grease or the application or both. Could be since most people use Polyrex EM and perhaps most people don't have the same problems as us on high D*N (I haven't seen many others sharing my pain on this subject in the forums), the grease might be the difference. One thing I don't like is that the viscosity (VG100) is much higher than it needs to be for this high D*N. Polyrex EM has the same viscosity, a few different properties including better high temperature shear stability. We don't have experience with Polyrex EM. I am keenly interested in any comments anyone has on the best grease for high D*N applications (I posted a thread on this in the lube forum but didn't get a lot of response.

Bring me up to speed on this D*N application...What does that refer too? I think I can get the moon to cooperate since I am an amateur astronomer, hehe...

I will monitor this thread closely, or perhaps I should post my lube problem to the Lubrication section.

I need to get up to speed on lubrication of motors.

We use Mobil Synthetic 629 on all our driven fan bearings in the plant. Has been working real well for us...

I guess one question I would have would be, will changing grease and mixing with the SHC-100 cause my motor bearings to fail or will the transition be unnoticeable?

Thanks,

Good information Howard. Thanks

We have been lubing our motors every three months. Never after a repair since we know the motor shop did that.

quote:

Originally posted by Rockin' Rod:
Yesterday morning after installing the motor and doing the soft foot and alignment, I started it and warmed up the blower for over an hour. Noticed the bearing temps were running 125-135 degrees. All the other comparable motors, same design brand, etc are all running 95-100 degrees. I'm assuming this difference is due to the different greases now, am I correct?

I also brought up the issue of mixing grease. Probably not a good idea since we've been pumping in SHC100 for the past 5 years...

quote:

Originally posted by MotorDoc:
Rod

I recommend that your repair shop gets with their bearing supplier and has some training on bearing operation and installation.

Motor bearings are not lubricated by the grease, they are lubricated by the oil in the grease. The fact that they 'hand-packed' the bearings is a testimony to their lack of understanding of the lubrication of a motor bearing. Of course the bearings are 'throwing out' the grease, they need to as there is less than 3-mil's clearance in the bearing itself and the soap used tends to be thicker.

Shielded bearings ARE greaseable bearings, sealed and non-contact sealed bearings are not. Shielded bearings have a small opening on the inner race of the shield that allows a small amount of oil and soap into the moving parts of the bearings.

A common problem that occurs following motor repair (and having done this myself when I was a novice in the motor repair business in the mid-1980's) is when the bearing caps are not installed properly. Another issue that can occur is if there is work done on the motor shaft, such as returning the surface back to the original size or making a new shaft, if the bearing shoulders are too far apart, or too close (basically not machined right). I did have one issue that drove me crazy in 1991 and that was a motor that had a spacer on the shaft between the bearing shoulder and the inner race of the bearing. Another mechanic had taken the motor apart and did not note or mark the part. When I put it together, everything seemed to work just fine until the bearings warmed up.

Finally, you have to consider whether or not the OEM and motor repair shop grease is compatable and if your company greased the bearing when the motor was installed (or after you left that evening). Always a poor practice.

I am including the presentation on bearing lubrication I was asked to give at pdm-2007. Perhaps it can also provide some guidance.

Howard

Don't keep me in suspense. Tell me why the SKF 6219's are not good in blower motors running at 3600 rpm....We have 6 more just like that one...!Our larger 600hp motors are using journal sleeve bearings.

quote:

Originally posted by electricpete:
Please tell me what the speed of your motor is. And if you say 3600 rpm, please be prepared for my rant about why grease lubrication is not suitable for that application (6219 at 3600rpm). Double shielded would be even worse in that application.

Out of curiosity, is the red synth grease Mobilith SHC100? Is the OEM grease Polyrex EM?

quote:

Don't keep me in suspense. Tell me why the SKF 6219's are not good in blower motors running at 3600 rpm....We have 6 more just like that one...!Our larger 600hp motors are using journal sleeve bearings.

OK, you asked for it. Why do I consider grease lubrication of 6219 to be a problem....

First I need to talk about D*N. D is the diameter in mm and N is the speed in rpm. The surface speed is proportional to the D*N value of a bearing and many lubrication parameters are dependent on D*N.

In the literature, people use two varieties of D*N:
Di*N means we use the inner diameter for D
Dm*N means we use the mean diameter (ID+OD)/2 for D

Let's look at your bearing. See attached slide page one for dimensions
d = Di = 19*5 = 95mm
D = OD = 170mm
Dm = 132.5 mm

Even though you have been diligent enough to mention slip, I'm going to completely ignore it and assume the machine runs at 3600 rpm (what's a percent or two among friends!)
Di * N = 95*3600 = 342,000
Dm * N = 132.5*3600 = 477,000

Now that we know your bearing, let's see what some authors have to say about grease lubrication in this range of D*N:

quote:

Tribology in Machine Design, Stolarski, ISBN 0 7506 3623 8
The speed limitations for greased bearings are due mainly to a limited capacity to dissipate heat, but are also affected by bearing type and cage type. Standard quality ball and cylindrical roller-bearings with stamped steel cages are generally limited to 0.2 to 0.3 x 106 DN, where DN is a speed parameter which is the bore in millimetres multiplied by the speed in r.p.m. Precision bearings with machined metallic or phenolic cages may be operated at speeds as high as 0.4 to 0.6 x 106 DN. Grease lubricated tapered roller-bearings and spherical roller-bearings are generally limited to less than 0.2 x 106 DN and 0.1 x 106 DN respectively. These limits are basically those stated in bearing manufacturers' catalogues. The selection of a type or a classification of grease (by both consistency and type of thickener) is based on the temperatures, speeds and pressures

Note the above author is using Di*N and he says the upper limit for grease is 200,000 – 300,000 (you have 342,000). He says that bearing precision and cage type make a difference.

quote:

Bearing Design in Machinery by Avraham Harnoy ISBN: 0-8247-0703-6
"Empirical criterion that is widely used by engineers for the selection of oil
versus grease is the DN value, which is the product of rolling bearing bore (equal to shaft diameter) in mm and shaft speed in RPM. Rolling bearings operating at DN value above 0.2 million usually require liquid oil, although there are special high-temperature greases that can operate above this limit. Below this limit, both greases and oils can be used. This is an approximate criterion, which considers only the bearing speed for medium loads. In fact, the load, friction coefficient, and heat sources outside the bearing also affect the bearing temperature."

The above author also uses Di*N and his upper limit for grease is 200,000. Yours is 342,000. He mentions that special greases can extend the range.

quote:

ASM Handbook Volume 18, "Friction, Lubrication and Wear Technology" page 981:
Grease Lubrication. Most rolling-element applications are lubricated with grease because such lubrication is the most economical and simplest mechanical means to accomplish the task. Greases are combinations of fluid lubricants (oils) with metallic soap thickeners; the oil contained in the grease provides most of its lubricating ability. For grease lubrication to be effective, however, bearing operating speeds must be relatively slow (<3 × 105 n · dm). This is due to the inability of the grease to dissipate friction heat generation caused by high speed and also its inability to replenish rollingcontact surface fluid lubricant due to insufficient bleeding (flow) rate (lubricant starvation). Heat dissipation from the bearing is achieved mainly by conduction through metal structures.

The above author uses an upper limit of Dm*N=300,000. You have Dm*N = 477,000

When I contacted Mobil about Mobilith SHC100 on the phone they told me once that the Di*N limit for that grease is 250,000. I have never gotten that in writing.

I can cite many more references with similar information. And yet still there have for many years been motors built far beyond these limits. As far as I can tell talking to the motor OEM's, our plant is the only plant in the entire universe they have ever heard of having this type problem (surprise, surprise). The bearing OEM's and lub OEM's seem a little more receptive to my theory of cause/effect high D*N greased motor => low reliability, and have made a few suggestions somewhat similar to those described above (change in bearing precision, cage and lub may help those high D*N applications) but I'm not sure they fully embrace the idea that high D*N kills bearings either.

As you may have gathered, we have had terrible experience with those motors at my plant. Sometimes within one or two years after bearing replacement, we are already seeing warning signs on vibration (either random elevated noise floor with randome spiking in TWF or 2*BSF with cage sidebands). The housings on most of them don't run too hot. But many of those will cool housings when opened up for inspection have localized discolored grease and sometimes stained races suggesting overheating. How can you have evidence of overheating when the housing is cool? Now starts the world according to electricpete: My theory is that the grease lubrication is a very transient phenomenon (actually I read that somewhere ...didn't make it up). When lub conditions start to get bad, everything heats up, the grease releases a little oil and possible redistributes and everything gets better for awhile. But sooner or later after too much abuse, your grease will age. That's the big problem with high D*N bearings, they age the grease rapidly. And one moral of the story is not to take a lot of comfort from that relatively cool 130F housing reading. Another moral of the story is that if these high D*N application bearings are to survive you need to take very good care of them with frequent replenishments of small amounts of grease. And when the housing gets full, these bearings most definitely will overheat and require bearing replacment (unlike smaller slower beairngs which will tolerate being full). I have a few documents prepared that summarize bearing failures on some of these families of our motors at our plant. I'll take a look and see what I might be able to share.

Regarding seals and shields, one generally accepted philophsy is that the small and slow speed machines (perhaps below 100,000 Di*N) don't need re-lubrication (oxidation is very slow at low D*N), so they can get away with sealed maintenance free bearings (the grease will last almost as long as the bearing). That much is not disputed. For higher D*N (especially continuously operated) grease aging becomes an issue and you cannot use sealed bearings and need to build in a way to replenish the grease. It is somewhat controversial how effective is greasing on double-shielded bearings. I can cite you articles that say it works and articles that say it doesn't. Some say it depends on the shield clearance. Not a lot of consensus... I definitely recommend unshielded for these very high D*N bearings that already have enough lubrication challenges without adding the shields. You will note that on the attachment they list 6219 (unshielded) and 62192Z (double-shielded). The "limiting speed" for the unshielded earing is 5000rpm and for the shielded bearing is 4000rpm (not a helluva lot higher than 3600rpm). The definition of limiting speed is on slide 2. I am not sure the exact reason for this difference in speed rating, but I have the general feeling it is the same kinds of issues that cause these high D*N lubrication failures and I would recommend the unshielded to give yourself more margin.

As you might have guessed, it's a hot topic for me. I definitely don't have all the answers on this topic because we haven't resolved it at our plant.

This message has been edited. Last edited by: electricpete,

6219.ppt (338 Kb, 28 downloads)

Another reference on the limit (suggests Dm*N<340,000... yours is 477,000)

quote:

HANDBOOK of LUBRICATION and TRIBOLOGY, Volume 1, - Application and Maintenance
Ch 13 (multiple authors of the book.. Drew Troyer of Noria is the author of Chapter 13)
A motor equipped with radial ball bearings may be lubricated with conventional grease if the speed factor [Dm*N] is less than 340,000. If the motor is equipped with spherical rolling element bearings, conventional grease is suitable if the speed factor less than 145,000. If the speed factors exceed the limit for the application, the bearing will run hot and/or the grease will be damaged. If the bearing cannot be lubricated with conventional grease due to speed factor limitations, a specialty high DmN grease may be an option. Otherwise, it must be lubricated with bath oil, force circulation oil, mist, drip oil, or spray, all of which provide higher speed factor limitations.

I'm on my way to work early. Looks like a good post electipete. I'll pick through it good when I get there...

BTW, the motor shop is sending us a chart with a lubrication formula on it bearing size, vs speed, intervals etc...

Thanks

Howard & All,

Can you tell me approximately what the temperature difference would be using the SHC100 vs the Polyrex EM? I noticed all my blower motors with SHC100 are running 95-100 and the new rebuilt 350 hp is running 145-150 degrees. I assume this is normal, is it not? The rebuilt has Polyrex EM...

Thanks