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Bearing noise due to overgreasing ?

Bearing noise due to overgreasing ?

Bearing noise due to overgreasing ?

(OP)
Two 3000 KW, 6 Pole, 994 RPM sq. cage motors driving reciprocating gas compressors have NU 244M + 6244C3 bearings on DE and NU 244M bearing on ODE. Motor OEM (Hyundai) specified to charge grease (Alvania 2) every six months of continuous running with 2100 gms in DE and 1000 gms in ODE, which is the original total grease quantity for a new motor.

After regreasing as per above OEM schedule and quantity, we hear a high frequency squeal from both the motors. This noise is cyclic with a 3-4 second duration between peaks like a beat. No such noise before regreasing. We do not have any SPM or other noise measuring devices at present. No abnormal vibrations and the bearing temps not more than 60 deg C.

1. Did regreasing introduce this noise and if so, how ?
2. Normally, for such slow speed machines, regreasing amount is small and interval is large. Why in this case, the OEM has recommended a full grease replenishment within six months of continuous running?
3. After regreasing the above entire quantity, not a bit of old grease came out of grease outlet. What happened to all the old grease (3 kilos) ?
4. Do we need to open up this motor immediately and check the bearings, grease etc?
5. Finally, is it not abnormal to use rolling element bearings for such a large capacity of 3 MW ?

RE: Bearing noise due to overgreasing ?

1 - I am pretty sure the regreasing did cause the squeal although I can't say how (did you follow proper greasing procedures.. clean drain port, run with drain open or relief after greasing, etc).

I have seen bearing do very similar thing after accidental overgreasing.  (we got a new motor from the factory, someone wasn't sure if it had grease in the bearings, instead of disassembling to check they attempted to add grease until it came out... stopped attempting after injecting about 16 ounces on 6313 bearing cavity... it did come out when they ran the motor).

I am not sure of the reason.  It has continued to intermittently make that noise ever since. But not hot. We'll get a look at the bearing soon.  Suspect possibly  extra grease causes skidding??? (I'm not sure if that makes sense... I do know skidding is somewhat lub dependent, but we do have normal weight of the motor load on the bearing)

2 - good question.
3 - It is very normal NOT see grease appear at any time during regreasing or run after regreasing. The bearing cavity is usually intially 1/2 full. Subsequent charges start to fill the remaining half.  I feel better if I don't see any grease... if I do then I know there is too much in there.

4 - Our motor has run for 3 or 4 months.  After initial regreasing first 14 minutes the noise was almost constant on 5 seconds off 5 seconds back on etc.  Then it got less frequent. Still it remains and you usually hear it if you wait a few minutes.  No guarantees on your situation, but we have gotten some life out of ours. My gut feel is that you are safe to run for a few months if necessary perhaps with extra monitoring but you will eventually need to take a look and may have to replace those bearings.

5 - Ball bearings with grease lubrication are supposed to be limited in the neighborhood of D*N ~ 300,000 where D is shaft diameter in mm and N is speed in RPM... above that they supposedly may overheat.  For oil lubrication the same bearing can run a little faster.  For horizontal motors, I never see ball bearings on machines above a few hundred horsepower (few hundred kw).  For vertical motors I often see greased ball bearings on the lower guide bearing even for large... have a 4000hp 1200rpm vertical with  ball bearings on the bottom (232R).  I never understood why the 300,000 DN limit doesn't apply here for vertical motor lower guide bearings... perhaps because those bearings don't see much load?






RE: Bearing noise due to overgreasing ?

(OP)
epete,

As usual, your comments are precise and helpful. I am also not worried unduly about taking out the motors out of service right now since a planned shut down is around the corner.

I still can't digest the fact about regreasing quanity and interval given by the OEM.

RE: Bearing noise due to overgreasing ?

(OP)
The guide bearings in vertical motors do not see much of radial loads.

But usage of rolling element bearings in such large capacity (though at a medium speed) is the first time I am seeing in my 18 years experience. May be the motor designers who participate in this forum (teco comes to mind) can shed more light on this.

RE: Bearing noise due to overgreasing ?

Sounds like it could be a skidding roller in one of the bearings. Its quite a common occurance on overhauled machines and we see/hear it all the time. It will probably disapear when the grease flows fully round the bearing and when the motor is mechanicaly loaded.

RE: Bearing noise due to overgreasing ?

Suggestion: The grease should have been approved equivalent by the Hyundai since there may be differences in grease composition, viscosity, heat conductivity, etc.

RE: Bearing noise due to overgreasing ?

(OP)
stardelta,
The bearings were regreased about a month back but beat like noise has not gone. Both the motors are running on load, one at 100% and the other at 50%.

jbartos,
The grease used for regrease was from OEM.

Another interesting thing I noted was that the stator ammeter fitted near the motor shows a swing of about 10 to 20 amps in tune with the bearing noise. When the noise is hitting the maximum, the current also hits the maximum. Any ideas on this phenomenon ?

RE: Bearing noise due to overgreasing ?

Going back to the original problem… I can throw out one more possible scenario. Excessive grease increases friction torque.   This can lead to intermittent/excessive spinning of the outer race within the housing. Less likely would be spinning of the inner race on the shaft.  Spinning of races is one thing that is well known to come and go intermittently and make a chattering noise.

Another scenario... contamination introduced during greasing? Hard to imagine that would give these symtpoms.

Oscillation of motor amps in similar time to bearing noise… that is very strange.   I have never seen or heard anything like it.  I have no idea but I can throw a few wild ideas:

Intermittent high friction in the bearing is actually adding load to the motor.  It's hard to believe there could be any sustained difference in real power loading and still not produce a very hot bearing housing.  But perhaps it is very momentary binding which causes the current to swing high.  (is the curent high for only a short time?).  If this scenario were true obviously a big cause for concern.

One other possible explanation – maybe there is an actual mechanical load (pump?) increase going on.  More torque on coupling causes it to stiffen up and can add load to bearings.  So load affects both current and bearings. Kind of a stretch.

Hard to imagine any way a bearing could affect the air gap (magnetizing current).    

Just wild guesses.  I'm sure you have a few gueses of your own.

Good luck. We will be going into our motor within a week or two and I'll let you know what we find.  

RE: Bearing noise due to overgreasing ?

(OP)
pete,

Spinning of outer race simultaneously at two motors. Unlikely.

The connected load is a gas boosting reciprocating compressor, whose performance has not changed a bit.

I am also first time seeing current oscillation with bearing noise (it entirely coincides with the noise level, max 10 A / 20 A swing with maximum noise amplitude.

Somehow this bearing noise and the stator current swing are related. but how ?

RE: Bearing noise due to overgreasing ?

Hello edison123.

I have a tough time to believe that your problem is related to overgreasing.
When we overgrease a bearing, its operating temperature
will increase and if there is no room for that grease to expend to,bearing may fail in short order.
The problem related to overgreasing would be noticed right after you run your motor under load and short after your regreasing.
Your noise is most likely coming from the Roller Bearing NU244.Roller bearings have a peculiar behavior when running at no load.They have a tendency to "squeel" due to skiding of the rollers when motor is operated at no load.
Note;The Rotor wieght does not load up the bearing sufficiently to eliminate this condition.For this reason  one should not let motors with roller bearings run for extended periods without load.Ball bearings are not as prone to the "skiding" condition.If bearings skid for a long time they will score the races and in fact destroy the bearing.
As for the grease quantities recommended by Hyundai for regreasing of their motors,I have reason to believe that they are excessive.I had the same concern with Hyundai motors and contacted the Manufacturer about their recommended amounts for regreasing of most of their motors.We have 600/800/1500/2500 and 5000 Hp motors.The 5000 hps are sleeve bearings all others are Anti-friction
Balls and Rollers.After I contacted the Factory we reduced the recommended amounts by large amounts.I remember one particular motor that called for something like 800 Gr and we brougt this down to 200 Gr for a 6 month regreasing schedule.
As for the fact that you don't see any old grease being expelled from the bearing,it may be because the grease in the drain pipe may have hardened suficiently to the point of not letting grease out.I would remove the drain pipe and you should see grease coming out of the cavity when you grease the bearing.If it does not come out of the drain pipe it is possible that it is going into to the windings.
Edison, contact your Vendor and make sure that they reevaluate their recommended amounts for bearing relubrication.As I mention before,you have to be carefull when running Roller Bearings without load.They will be damaged if "skiding" happens and motor continuous to run.The Overgreasing may destroy the bearings  but not to cause the noises you reported.The overgreasing fauilure is fairly rapid ,either in bearings or seals.

Good Luck.

GusD

RE: Bearing noise due to overgreasing ?

(OP)
Thanks GusD for your suggestions. I too think the regreasing amount (too high) and interval (too low) are abnormal.

Both the motors are running, one at 50% (150 Amps) and other at 100% (300 amps) loads.

You said you contacted hyundai about their grease schedule and amount. Did they give any explanation for their original recommendation for such grease schedule and amount ? How did you finally arrive at the regrease quantity on your own or on hyundai's advice?

RE: Bearing noise due to overgreasing ?

Was the drain port cleaned prior to greasing the bearing(s). What you may be experiencing is an overgreasing of the bearing (lack of old greases ability to exhaust). The result is a displaced seal/shield or worse, the overheating of lubricant which can lead to immediate bearing compromise. The frequency is very likely early signs of bearing failure. Don't leave it too long as your bearing seats will erode.

RE: Bearing noise due to overgreasing ?

Out of curiosity - Is there a belt load or flywheel on this machine?  Those would be determining factors for load on the bearing (along with rotor weight). The only

Is there an rtd monitoring the bearing outer ring temperature?  Given this size of machine I would think there would be.  If not then judging bearing temperature from housing have to consider where the bearing is in relation to the accessible surface measurement.

It is right to question the notion of overgreasing based upon temperature.  The example I provided otherwise does suggest overgreasing resulting in noise and no high temperature, although I have no real explanation.  To add a little to that example: ite was clearly overgreased (16oz added in 6313, then motor ejected most of the grease when started ), started making the noise, and never overheated as indicated by bearing housing surface temperature.  It was a new motor never run at our facility so there is small possibility that it was simply a problem unrelated to our overgreasing... BUT we installed 5 other new motors, didn't overgrease any of the others, didn't see noise on any of the others.  Draw what conclusions you will.  I'll know more shortly.

RE: Bearing noise due to overgreasing ?

I see now the roller is in the ode.  So belt or flywheel even if present on shaft end would not explain the roller.  Why is there roller in ode?  Perhaps that is just an easy way to allow motor rotor expansion... control position on de and use roller on ode end.  I have never seen it done that way on smaller antifriction bearing motors.

Is the following sequence correct?
- New motors.
- Operated ok for awhile.
- First regreasing was performed
- immediately started making noise

I know you have followed the manufacturer's recommendation for grease type... I would ask them if they could provide evidence of the type of grease which was in the motor when new so you can check compatibility for yourself.

RE: Bearing noise due to overgreasing ?

My first impression about 'where did all the old grease go' would be what GusD touched on...that the grease was under pressure when being pumped in and it ended up going past the seal and into the windings. This may account for the cyclic noise and current draw.

RE: Bearing noise due to overgreasing ?

I didn't pick up on the fact that it is an enormous quantity of grease.

Using SKF guidelines
Gp = 0,005 D B
where   
Gp = grease quantity to be added when replenishing, g
D = bearing outside diameter, mm
B = total bearing width (for thrust bearings use total height H), mm
For 6244 we have D=400, B=65 => Gp=130.
1000 grams is way too much.

Now, I look at some other parts of the SKF guideance:
"For large roller bearings having a bore diameter of 300 mm and above, the high specific loads in the bearing mean that adequate lubrication will be obtained only if the bearing is more frequently relubricated than indicated by the diagram, and the lines are therefore broken. It is recommended in such cases that continuous lubrication is practised for technical and economic reasons. The grease quantity to be supplied can be obtained from the equation below for applications where conditions are otherwise normal, i.e. where external heat is not applied
Gk = (0,3 ... 0,5) D B ´ 10–4
where
Gk = grease quantity to be continuously supplied, g/h
D =  bearing outside diameter, mm
B = total bearing width (for thrust bearings use total height H), mm"

** In summary it looks like they are recommending continuous grease-feed for grease lub of large roller bearings. Is it possible that 1000g/6mo and 2100g/6mo represent quantities to be added by continuous feed (in conjunction with self-releiving path), rather than as a single re-lub?

RE: Bearing noise due to overgreasing ?

Apply the above formula above for continuous relubrication of NU224.  It has same D and B dimensions as 6244.
Gk = (0,3 ... 0,5) D B ´ 10–4
Gk =  0.4 *  400* 65 * 1.00E-04
x24 hrs/day
x30days/mo
x6 mo
=4,500 grams per 6 months.
Now this is only a factor of 2 off from 2,100g, where the calculated batch lub quantity was a factor almost 10 off.  This seems to suggest again that the quantity may have been intended for continuous relub. Manufactuer can surely clarify. Maybe I am completely wrong and they have something special about their motor.

To Dan - how does grease getting into the winding cause current fluctuation?  I am just curious to understand.

RE: Bearing noise due to overgreasing ?

Going back to the question of whether ball bearings and grease lub are appropriate on this large motor:

I may have botched up the DN rule before (I think D is mean diameter, not bore). For 6244 and NU244, SKF lists the max speed for grease lub as 1500rpm.  Derating for higher load than assumed or external heat sources.

SKF's speed rating is based upon thermal considerations at an assumed load. The assumed load is that which gives an L10h life of 150,000 hours.  Now I understand as you said that lack of load explains how vertical motors use these big grease lubed rolling element bearings at higher speeds.

RE: Bearing noise due to overgreasing ?

(OP)

As per SKF General Catalogue, relubrication interval for our bearings (220 mm ID) is about 3000 hours for roller bearings and 6000 hours for ball bearings for a speed of 1000 RPM. This works out to 4 month (roller) and 9 months (ball) of continuous running. (These intervals can be extended by two times if the bearing temperature did not exceed 70 deg C.)

If the relubrication interval is shorter than 6 months, then replenishment grease as per DB rule (0.0005 D B grams) is 130 gms at intervals of half of the relubrication interval (i.e. every 1500 hours for roller bearing and 3000 hours for ball bearings fro our case). SKF recommends a maximum of three grease replenishments after which the entire grease has to be replaced. If the relubrication interval is more than 6 months, then all grease had to be replaced after six months. So, apparently six months is the upper limit for any grease in use and I guess that Hyundai was right after all.

For vertical shafts, the above relubrication intervals have to be halved. Could anyone give valid reason for this restriction for vertical shafts?



RE: Bearing noise due to overgreasing ?

I can guess that on vertical shafts there is more of a concern for grease running out but that is just a guess.  Anyone else?

Regarding SKF recommendation to REPLACE (vs replenish) the grease after 6 months, for smaller motors I know that very few people will actually replace the grease because it generally requires motor disassembly.  

I don't understand how you say the Hyundai is following SKF recommendations.  SKF recommends 130g at a time (for either bearing by my calc since they both have same D and B dimensions) whereas Hyundai is recommending 1000 or 2100g at a time. What am I misunderstanding?  

Also as a side note it appears SKF recommends continuous relub for this roller bearing.  That recommendation is not followed.

A quick comment on minimum load to prevent skidding. SKF recommends minimum load to prevent skidding is  > 3% of dynamic load rating for roller bearings and 2% for ball bearings.  Since roller bearing has higher load rating to begin with the minimum load is much higher for roller.

Can you identify which end the noise is coming?  If the outboard end (with the roller) that is consistent with skidding.

Dynamic load rating per SKF of the NU224 is 172,000 pounds.
To prevent skidding half rotor weight W/2 > 0.03*172,000
W > 10,000 pounds.  Is your rotor weight at least this much?  Note that skidding is lub-sensitive.  

Sorry to do a lot of talking on this thread. I take it as an opportunity to review this stuff. Hope others will continue to contribute as well.

RE: Bearing noise due to overgreasing ?

(OP)
Hyundai says "charge 2100 gms in DE and 1000 gms in NDE every six months of continuous running". These are total amounts of grease used in the first fill by Hyundai. So, that agrees with SKF recommendation to replace the entire grease after six months.

As far 2100 gms in DE, remember there are two bearings NU244 + 6244. The noise is definitely coming from DE.

The total motor weight is about 14 tons. So, I guess rotor weight will at least be 6 tons. Remember, this noise is coming even when the motor is fully loaded or 50% loaded. So, obviously it is not related to load.

SKF recommends continous relube only with roller bearings of ID over 300 mm.

I still cant understand the stator current hunt in both motors after relubrication.

RE: Bearing noise due to overgreasing ?

You are right and I was wrong about continuous relub. Bore is 200mm<300mm as you say.

Using SKF guideline based on 0.005*D*B (same DB both bearings) I come up with same quantity for either bearing, although the replenishment interval is different.

The SKF recommendation to replace the entire grease every 6 months involves removing all of the old grease from bearing and cavity and adding new grease.  You probably have to disassemble the motor to do it, unless you have some way to clean out all the existing grease in-place.  SKF does not recommend adding that grease all at one time to a bearing without removing existing grease.

RE: Bearing noise due to overgreasing ?

(correction 220mm).

On the subject of loading to prevent skidding, it is the radial load on the bearing that is of interest, not the torque loading applied by the pump/compressor or whatever.  In your case with no belt or flywheel it is very much dependent upon the weight of the rotor.

RE: Bearing noise due to overgreasing ?

"...this agrees with SKF recommendation to replace the entire grease after six months."

I think you are interpretting the SKF guidance wrong. "Replenish" means to add more to the existing. "Replace" means to remove all existing and repack again.   Not many people choose to replace (and I don't think that's what you did) even though SKF recommends it.

RE: Bearing noise due to overgreasing ?

I wasn't paying close attention to your configuration. Two bearings on DE... roller and ball. One bearing on ODE... roller.

That would change the way to compute minimum loading.  Presumably each end carries half of the rotor load, but how to divide among the two bearings on the DE???  IF we assumed that DE load divided equally among those two (a big assumption), then we would double the minimum rotor weight required to 20,000 pounds.  But it seems like it is very tough to assure minimum radial load on two adjacent bearings.  Small change in tolerances, internal clearances, temperature etc might cause one to hold more than the other.  Might certainly be a good question to ask the manufacturer how they maintain that minimum load.  

The fact that the noise coming from the roller with less load (DE) is consistent with skidding.

RE: Bearing noise due to overgreasing ?

Out of curiosity, how is it connected to the compressor?  Belt or coupling? What type coupling?

RE: Bearing noise due to overgreasing ?

(OP)
I quote SKF verbatim

"When the end of the lubrication interval has been reached, the used grease in the bearing arrangement should be completely removed and replaced by fresh grease"

"In order to be able to renew the grease fill it is essential that the bearing housing is easily accessible and easily opened..... After removing the used grease, fresh grease should first be packed between the rolling elements... When the housings are less accessible but are provided with grease nipples and exit holes or grease valves it is possible to completely renew the grease fill by relubricating several times in close succession until it can be assumed that all old grease has been pressed out of the housing. This procedure requires much more grease than is needed for manual renewal of the grease fill"

"The six month limit represents a very rough guideline recommendation and may be adapted to fall in line with lubrication and maintenance recommendations applying to the particular machine or plant".

RE: Bearing noise due to overgreasing ?

(OP)
The motor is directly coupled to the compressor line shaft.

RE: Bearing noise due to overgreasing ?

I'm sorry. You are right about what SKF says. I see it on their CD-Rom. Still it sounds like horrible practice to me which invites overlubrication and I have not heard of anyone using it.

There is some other hardcopy SKF guidance that leads me to believe this method is less effective for large bearings, and also requires the machine running and look for grease expelled during the process.

RE: Bearing noise due to overgreasing ?

(OP)
pete,

In the two bearing arrangement in DE, the ball bearing does not carry any radial load. It is only used as an axial locating bearing to prevent axial movement of the rotor. As a matter of fact, the ball bearing, while tight in the shaft, has a clearance fit with the housing (the outer race is loose in the housing). So, in this case, the rotor weight is carried by the two roller bearings only and not by the ball bearing.

RE: Bearing noise due to overgreasing ?

Hello edison123

The Bearing arrangement is pretty common on motors with Roller bearings.The Ball bearing Outer race is not captive and is kept snug by the springs compressing the outer race.
On motors with mid size bearings, the housing on the ball bearing side is usually machined .5 mm oversize.
As you say ,the ball bearing does not carry any radial load and is simply in place to locate the rotor in its Mag center.
As per my previous post regarding greasing concerns with Hyundai motors,if you like you could contact me at this E-mail--gdalmeida@shaw.ca.
I'll send you  the info on what we had to do to deal with the problem.

Take care

GusD

RE: Bearing noise due to overgreasing ?

(OP)
GusD,

I do not know whether you recd my last e-mail to you. If not, could you pls mail your Hyundai details to eewemf@myrealbox.com ?

RE: Bearing noise due to overgreasing ?

(OP)
To all,

Today we had an opportunity to shut down one of the motors. When we removed the DE bearing front cover, lot of grease was seen to have collected in the cover (The cavity seems too big, may be the OEM designed it such a manner to collect the excess grease there ?). Also, grease had turned from original light yellow color to dark brown indicating high temp (though our probe fixed on bearing casing showed only 60 deg C).

Removed some excess grease from both bearing front covers. Motor restarted but the cyclic noise persists. So, asked for machine shut down to pull the rotor out and check the bearings. Probably this may happen by month end.  Hope nothing goes awry with the bearings before then.

RE: Bearing noise due to overgreasing ?

Discoloration of the grease within a short time but no sign of high temperature is as you say strange. Some obvious guesses:
1 - Temperature detector is not positioned properly or some other instrument problem. Although depending on the setup maybe you have also been able to confirm using your hand that there was not excessive temperature?
2 - There was actually a different type (color) of grease installed by OEM.  When mixed it caused a change in characteristics.
3 - Some type of fine wear products
4 - Contamination.
Although we haven't used it, I understand that rotating equipment grease analysis is offered by many labs like Herguth. I would suspect they can tell you if the grease was intermingled or exposed to high temp or contamination.

RE: Bearing noise due to overgreasing ?

Suggestion/question: Please, how is the motor started and controlled? Sometimes, various electrical currents flowing through the bearings damage them. The time may somewhat coincide with regreasing.

RE: Bearing noise due to overgreasing ?

(OP)
pete,

The temperature detector is fitted to the front face of the front bearing cover. As I said, the front bearing cover has copious space to accumulate the excess grease, which I suspect, acts as a heat shield. This would account for not so high temp readings both by probe or by hand. So, we plan to shift the temp probe to read the bearing outer race during tear down in two weeks.

The greases (original and replenishment) are supplied by OEM. Contamination - Nah, since this is a gas turbine station with clean environment. Wear products - what would that be ?

I still go with overgreasing (because of grease discoloration) but I can't account for the cylic noise with attendant current swing.


jb,

The motor is DOL start since no ghosts of bearing currents there due to soft starters or VFD's.

RE: Bearing noise due to overgreasing ?

Hello edison123

I just revisited your original post to see what I had missed regarding some of the questions.
As you hinted about too large a motor for the bearing arrangement.I totally agree that this drive is probably a toss up in between Anti-friction bearings and sleeve bearings.All our 5000 Hp Hyunday motors (11 metric tons) are of the sleeve bearing type.True they also have a higher speed (1800).All of the 2500 Hp,1800 rpm are fitted with anti-friction bearings.So I would say your motors probaby fell on the grey area of bearing application.
Regardless the bearing type,it should not experience  abnormal noise.
I find it interesting about your correlation of noise with surging amps and the fact it is driving a compressor.
The compressor cycling load is most likely the cause of hunting.As for the "Hi-frequency" noise,it still there even after removing some excess grease.You say that vibration analyses have not indicated any problem.The noise may appear to be coming from bearing housing but it may not necessarily be from the bearing.You have grease slingers,spacers and possibly a snap ring to keep the assembly in place.Any one of this can cause some noise.
I don't know if the motors were overhauled or new,but there is a possibility that the Outer race of the Ball bearing is not being made captive by the tension springs and it slides against them under shaft torsional forces?
As for the installation of the RTD ,it should be mounted as close to the outer race as possible.Normally a hole is drilled on the bearing housing just short of going through it.If the bearing temps don't go higher than 70C under full load conditions,I don't think your motor is at risk.
You have to make sure that temperature measurement is reasonably accurate.If noise remains as is and temp. rise stays put,I would keep monitoring motors until one of them changes.

Good luck Edison  
on   inside    the cause of huntingis probably    edge   syour specific questions.

GusD

RE: Bearing noise due to overgreasing ?

Suggestion: The bearing might be inspected since large motors may experience another type of currents, (no the VFD ghost current) that can potentially be detrimental to the bearings. There are currents flowing through the bearings due to motor magnetic circuit asymmetries. Visit
http://www.reliance.com/pdf/white_papers/Inverter_Driven_Indct_Mtrs_Shft_Brngs.pdf
for a homopolar flux condition creating bearing currents.

RE: Bearing noise due to overgreasing ?

I've seen motor bearings that suffer from "caved-in" metal shields due to the hydrualic pressure of over greasing a bearing cavity.  I supose there is a chance that the shields could begin rubbing on the bearing's ball carriage.

 However, most large bearings don't have shields and the over-greasing problem in their case would have to be explained by some other phenomena. Perhaps, over-greasing interferes with the seperation of oil from the wax or carrier in some heavy greases, thus increasing noise and reducing bearing life...

  Richard Anderson
  GP Mill, Camas, WA.

RE: Bearing noise due to overgreasing ?

On 7/12/03 I described a bearing which I thought we had overgreased and was making noise.  Today bearings were replaced and inspected.  There is some mixture of old and new grease but much less than expected.  Electricians think the cause of the noise was in fact lack of grease.  I'm not sure what I learned but now I am sure that there was not excessive grease present in this motor that was making the noise.  Also none of the races were spinning. I am having the shop cut the bearing open for inspeciton.
Sorry for the detour.

RE: Bearing noise due to overgreasing ?

Although it sounds like this is not the problem it might come in handy in the future.

I was taaught many years ago that overgreasing a ball, and presumably a roller, bearing retards the movement of the ball/roller in the race. This causes the balls or rollers to "collide" with each other as the bearing rotates. This is evidenced by gauling on the ball/roller. It is noisey and the increased friction of the balls rubbing together would add to the load current of the motor in time with the noise caused.

Hope this helps.

RE: Bearing noise due to overgreasing ?

steamboat - What if the bearing has a cage?

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