Hi guys,

I have 4 or 5 motors showing both the cage and BPFO frequencies and the peaks are almost the same levels.So is it indicates that my Motors have both the faults?Or is it common to see outer race bearing fault frequencies accompanied with cage faults or vice versa? Can anybody give some insight on this?

Have a nice day!!

Which_is_contributing_the_fault.pps (167 Kb, 115 downloads)

Yes, you have both cage and outer race faults. Time waveform in acceleration would also aide in severity judgement. First set of readings or has this fault been trending upward?

Cages certainly do fail on occasion and the failure usually proceeds rapidly.

We had a cage failure last week (first that I know of at our plant in 5 years) and the bearing housing paint started smoking due to the heat. I looked at the removed bearing and it was blue/rainbow from the heat (I got some pictures). We hadn't seen anything abnormal on the vibration (although I haven't gone back and looked with my hindsight glasses to see if we overlooked something).

I have a hard time visualizing the mechanism for impacting at FTF. Portion of the cage is contacting stationary object at a rate of ftf? What stationary object? I would think early stages of cage failure would look more like a rub with raised noise floor and chaotic impacting, rather than harmonics and periodic impacting.

Suspicious that you should have 4 or 5 motors behaving like this. Are they invertor driven?

Best Regards,
Tom Murphy

Dave,
It is trending up.. Time waveform in acceleration is showing 7-8gs. I'm wondering how to give a danger sign for 5 motors at the same time..

Tom,
Itz not invertor driven.. .By the way what if it is invertor driven? Will it cause these types of signatures?

I do not recall the size of these motors, typically the larger the motor the farther you are from the bearing. IF you are taking readings from motor endbells you could be as far as 12-16" from the bearings. When a bearing reaches 20 g's (pk-pk acceleration) you will be able to see spalls in bearing components. When the bearing reaches 40 g's you are living on borrowed time. No one knows how long it will take to reach these values but these are a good rule of thumb. Remeber peakvue, shock pulse, spike energy, are all EARLY indicators of bearing faults. Time waveform acceleration amplitudes will tell you how bad the fault is. You may even find that by greasing the motor bearing the peakvue data will decrease and the faults may disappear. NU is typically a roller bearing and they take more grease more often than a ball bearing.

I suspect the fault you are seeing is BPFO that is being amplitude modulated by cage frequency, I see this a lot in PeakVue data. The motor with the waveform amplitude over 30 g's is very high. I would expect to see the BPFO defect in the regular velocity data at this amplitude and would be suprised if cage shows up in velocity. If the waveform is autocorrelated there is probably heavy periodic energy spaced at BPFO with the highest amplitude spaced at each revolution of the cage. I see cage frequency often with lubrication problems but usually you will have high amplitude in the waveform and either no periodic activity or only cage period in the autocorrelated waveform. Cage seems to show up often in PeakVue data and I think it may be due to a slight irregularity in one of the cage pockets or rollers that modulates the defect amplitude.

Does the BPFO show in a normal velocity spectrum?

Does the cage modulate in the normal acceleration waveform as well as in the velocity and acceleration spectrum?

Is the cage seen in the normal velocity spectrum at its fundamental frequency?

More data is really needed to decide whether or not the cage is "bad" or if its "signal" is a result of the outer race?

Hi guys,
I select two motors from the 5 bad ones and i'm attaching some of their signatures...

Ralph,

BPFO is showing even in normal velocity spectrum and there are sidebands of FTF at running speed harmonics. Cage fundamental frequency can also be seen.

Jim,

I think you are right about the BPFO. If it is BPFO, i may get some more time for a replacement,right? We did lubrication on these bearings.But the vibration levels came back after a period of time.

Dave,

They are 1750KW ABB Motor(QLY 630 ga 4)..Big ones,right? About the sensor position, we are taking the readings from the bearing housing. Note that the bearings are at the drive end.Thanks for your alarm levels. But will these levels change between BPFO and FTF? The funny thing is that all the defective bearings are NU234E..

Pete,
What i understood is, FTF can be generated when:
1.Defective balls strikes on the cage.
2.One or more rollers missing from a bearing.
3.In sealed/shielded bearings,when the cage touches the seal due to some deflection in the seal.
4.Excessive clearance in antifriction bearings.

I think i read somewhere that typical failure sequence is: defects form on the races, the balls and then finally the cage!! SO is it mean that my race, balls and the cage have some fault? Ha ha ha...

Have a nice day!!!

Which_is_contributing_the_fault.pps (208 Kb, 41 downloads)

quote:

BPFO is showing even in normal velocity spectrum and there are sidebands of FTF at running speed harmonics. Cage fundamental frequency can also be seen.

Cage fundamental in the normal velocity doesn't sound good.
What do you mean when you say that "there are sidebands of FTF at running speed harmonics."?
Are you saying there are FTF sidebands around 1X harmonics?

What version of RBMware do you use? I have 4.81, if you run less than 4.9x, if you want, you can send me a copy of the machine to view on my computer and we might can tell more about what is what.

Any time I see the fundamental cage frequency in velocity I get real worried (not cage sidebande around a roller defect). When I was talking about seeing cage in peakvue that is completely different. I have only seen cage fundamental in velocity a few times in my career and failure usually is not far behind. I have seen low frequency peaks close to cage frequency due to flow problems in pumps and fans before too.

Ralph,

Actually, I'm seeing harmonics of FTF but not a distinct Cage Fundamental(Sorry for earlier comment )!Also there is FTF sidebands around 1X.Maybe i have problem with both BPFO and cage,ryt?I never did an export from RBMware!!Can u tell me how i have to do it?Using Zip utility?

Have a nice day!!

Jenish,

quote:

I never did an export from RBMware!!Can u tell me how i have to do it?Using Zip utility?

Sure. Glad to. it's rather a long winder explanation. be better to email it to you.

My address is rottenrockyatcomcastdotnet. Email me and I will send it to you.

quote:

No one knows how long it will take to reach these values but these are a good rule of thumb.

Dave,
I agree with your approach to using the waveform as the severity indicator. As you mentioned no one knows exactly when the bearing will make its last rotation and come to a screeching halt It seems reasonable to assess severity and predict a failure within a certain period of time. If the bearing bracket paint is peeling like pork cracklins from extreme heat and the machine's shaking like a dog passing peach seeds then I might be inclined to say "She's guna blow"

About a year ago someone on this site claimed they could predict a failure up to the day or hour, I can't remember exactly which one it was but it sparked one heck of a discussion within the members. Sorry to digress but your comment gave me a flash back.

Regards.

Hi guys,
My Motors are still running and making enough sounds!!
Anyway we concluded with Outer race problem..Thanks for Ralph and others who help..

By the way, if it is an outer race problem, we have to look for causes outside the rotating parts, ryt?This Motors were overhauled only 2 years back..So we have to think about problems like improper installation, improper lubrication procedures, Over loading and what else?? ..

Have a nice time!!