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Premature bearing failure

Premature bearing failure

(OP)
Hi to everyone

In one of our project we have installed a gas rotor blower belt driven, suction pressure 0.4 bar g, discharge pressure 0.8 bar g, capacity maximum 350 cubic meter/h. After about 2000 hours it was noted an unusual noise, even vibration level was in the same range since start-up. It was decided to shut-down and to inspect the bearing. Double Deep Groove Ball bearing failure looks like flaking on inner and outer ring. Also some ball shown same flaking. Lubrication oil is Pneulube 100 ISO 100 recommended by blower vendor. Blower is protected by temperature switch and discharge pressure switch to prevent any overloading. My question is if this failure is a blower design issue or can be attributed to the User care? How this failure could be prevented?

Many thanks in advance for all comments
Aurel Mares

RE: Premature bearing failure

More info is needed.

Describe the vibration measurements. Overall, or detailed frequency information?
Velocity, displacement or acceleration?
Where is the vibration measured? On the bearing housings?

Was the oil level proper in the bearing?
What is the running temperature of the bearings?
By double deep groove do you mean one deep groove bearing at each end of the shaft?
Did both bearings start to spall?
Or, was it just the bearing near the belt drive? (likely if the belts were over-tensioned, or sheaves were on the small side)

RE: Premature bearing failure

First thing I'd check is if the blower assembly is even rated for belt drive, and then I'd back-engineer the drive to check if the belt pull is excessive, etc.

Mike Halloran
Pembroke Pines, FL, USA

RE: Premature bearing failure

(OP)
Hi Tmoose and thank you for your great feedback

We measured velocity over all vibration on the failed bearing house located next to the driven belt. Of course we measured and the opposite bearing vibration and noticed the noise, but was not detected any problem with the second bearing. Oil level was in range and when I said double about bearing I was refereed to the a bearing with two rows of balls. The second bearing didn't have any problem. No overload of motor was detected, no overpressure of discharge was recorded, no over temperature was detected too.

So, in other words, we have installed and we have operated the equipment according blower data sheet but unfortunately we experienced that premature failure. I am wondering what we could do to prevent that failure considering all protections (current trip, discharge temperature switch, discharge pressure switch) mentioned above?

Many thanks and best regards
Aurel Mares





RE: Premature bearing failure

(OP)
Hi Mike

I come back to my dilemma? What we could do to prevent that premature failure? Could we complain to the equipment design?

Many thanks for your comments, I noted all

Best regards
Aurel Mares

RE: Premature bearing failure

Well, if you complained to the equipment supplier or manufacturer, at least they'd be able to dig up the specifications and limitations of the equipment. Since you haven't provided any model/mfgr/serial# info to us, we can't do that for you.

Since you haven't provided a photo or drawing of the installation, we still can't eliminate the most likely possibility, excessive belt tension.

You've provided all sorts of defenses against overload on the gas side, but you've (apparently) provided no defense against an improperly tightened belt or a frozen tensioner.

Have you independently calculated the expected B10 life of the failed bearing, or gotten written calculations from the equipment manufacturer?

Adding hardware to control belt tension, and using appropriate series of belts is an economic/business decision in a sense. Just make sure that your accountants get the cost of bearing replacement into the proper account, for when the peanut butter hits the fan.


Mike Halloran
Pembroke Pines, FL, USA

RE: Premature bearing failure

" What we could do to prevent that premature failure? "

First, I would need to understand pretty well how and why the bearing failed.

The info provided so far is much too high level.
There are MANY questions that NEED to be answered before a reasonable diagnosis can be provided, and a good diagnosis is required before a useful solution can be suggested.

========================
"Could we complain to the equipment design(er)"

Yes, What does the blower manufacturer have to say?
Is the blower fan in warrantee?

============

- What were the "as-new" vibration levels, and how and where did you measure them?
- Were both bearings' "vibration" the same?
- How many of these fans do you have?
- What is your belt tensioning procedure?
- Have you analyzed the oil that came out of the failed, and not-failed bearings?
- Is this equipment subjected to wash-down?
- Does the blower sit idle, when other parts of the plant are in operation? Can you feel vibration on the bearing housings when the blowers are off?

Can you post a picture of the actual installation? If not, post a picture of a similar installation.
- What is the bearing part number? Is it Pillow block or flange mount? Or something else altogether?
- Is the bearing bore cylindrical, or tapered?
- What features are provided to accommodate thermal growth?

Self aligning Double row ball bearings are good for handling misalignment, but sometimes suffer from reduced load capacity due to the point contact.
http://nskprecision.thomasnet.com/Asset/a1027.jpg

Non-self aligning ball bearings need the capability to handle static misalignment. Some have curved outer race outside diameters to accomplish that.
http://www.globalspec.com/ImageRepository/LearnMor...

Like Mike H said, If the belt drive was over-tensioned, and continues to be over-tensioned, the bearing will continue to die young. It may not run hot, but just start to crumble in its tracks.

The report the overall vibration has not changed since new suggests the possibility the bearings were damaged before the equipment was put in service. If the equipment was subjected to impacts or very much background vibration during transportation or storage the bearings could have been brinneled or false brinelled. That surface damage can really shorten bearing life and cause spalling early.

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