Bearing Failure

Logic: if a bearing has failed, and there is no sign of a bearing failure, how would anyone know that the bearing has failed?

We have used vibration monitoring for the checking of healthiness of the motor.We could not find any abnormality in vibration levels.But,we observed very very minute (Very low) knocking sound.That is the criteria for our doubt.

That constitutes an indication, which falls outside the postulate in the original posting.

Hi,

The low level sound like knocking sound is sometimes heard if roller bearing is used or large sized ball bearings. Many a times these go away after sometime.

If the knocking sound increases then one need to investigate.

By using instruments like SPM bearing analyser one can have correlation to determine if there is damage to bearing.

You can also pump in grease as specified and see if the knocking sound goes away.

These types are typically due to underloading of the bearing, which in some case lead to bearing damage - bearing damage due to underloaded or oversized bearing- more specifically larger sized ball bearings or roller bearings of even standard size.

The kocking sound is a complex phenomenon.

I like to have a detailed discussion with you.Can I have your phone no.

We have used vibration monitoring for the checking of healthiness of the motor.We could not find any abnormality in vibration levels.But,we observed very very minute (Very low) knocking sound.That is the criteria for our doubt.

That constitutes an indication, which falls outside the postulate in the original posting.

Simple, it fails to show failure? Excuse me, what was it again?

If there are no physical signs of vibration nor any signs of failure, what is the motivation for your question?

Quite. "If it ain't broke, don't fix it." - Anon

We have used vibration monitoring for the checking of healthiness of the motor.We could not find any abnormality in vibration levels.But,we observed very very minute (Very low) knocking sound.That is the criteria for our doubt.

That constitutes an indication, which falls outside the postulate in the original posting.

"But,we observed very very minute (Very low) knocking sound.That is the criteria for our doubt."

You and somebody else marked PWSlack's comments Off-Topic, but they really aren't. Had you said you heard a "minute knocking sound" at the outset it would not have been necessary for you to go to the effort to repeat it here, what, six times now, and you would have gotten your answer much sooner. There's nothing quite like supplying enough information to answer a question. Don't tell us what don't see, tell us what you do see, the real reason you're asking the question. Next time put all the cards on the table so we can properly assist you.

Mark this Off-Topic if you like, but PWSlack has a point. Meanwhile I'm marking his comments On-Topic.

We have used vibration monitoring for the checking of healthiness of the motor.We could not find any abnormality in vibration levels.But,we observed very very minute (Very low) knocking sound.That is the criteria for our doubt.

That constitutes an indication, which falls outside the postulate in the original posting.

Axial or thrust direction? What frequency? Is it in the bandwidth of the bearing assembly?

What monitoring methods do you have (or not) that enable you say there were no prior indications?

We have used vibration monitoring for the checking of healthiness of the motor.We could not find any abnormality in vibration levels.But,we observed very very minute (Very low) knocking sound.That is the criteria for our doubt.

That constitutes an indication, which falls outside the postulate in the original posting.

Even though there is a very small knocking sound,the vibration analysis showed no abnormality and result shown in the report is no problem with bearing.That is why, I am in doubt,whether this will cause any harm to the bearing.

That constitutes an indication, which falls outside the postulate in the original posting.

We have an indication that we believe is our bearing failing, but we have detected no vibration, just a subtle knocking sound....What could the problem be?

I would check the temperature of the bearing under load....

http://www.engr.uconn.edu/~aly/Courses/ME343/Reading_1_Sound%20and%20Vibration%20in%20Rolling%20Bearings.pdf

Yes. If the motor were idle, one couldn't know that the bearing had failed without investigating for signs of failure.

one aspect to check is the lubrication. this can affect the life of the bearing and this may have something to do with the current situation.

Jeez, is there an echo in the room?

Might be there is a gig of bearing parts down there, somewhere.

No, just <...a very small knocking sound...>.

Bad bearings.

This is the best clue I can help you with

maybe the guy should turn into QA/QC confidence level of batches of bearing from the manufacturer. The book says if it has a confidence level of 98% that means 2% from the batch of the bearing the guy used will certainly fail prior to its expected lifecycle. Though there may be other factors to consider, like intermittent or continuous service, heavy or light, and others unaccounted.

My experience would suggest that you also diagnose with ultrasound and trend the bearings. Your first signature of damage leading to failure will always be ultrasound. You can trend the condition daily, weekly or what ever and you may also be able to compare it to others. Ultrasound can also be used for proper lubrication. Check out the companies that provide this equipment, two I am familiar with are UE and SDT. I am not affiliated with either.

A motor bearing is extremely unlikely to fail without showing signs of the failure through vibration...if the testing setup is adequate. Your accelerometers should be mounted in horizontal/vertical/axial positions, as close to the bearing as possible. How your accelerometer is mounted has a significant effect on the frequency range detectable by the sensors. For example, a magnetically mounted probe has the smallest frequency range, and a sensor stud mounted directly to a machined flat on the motor would have the largest.

If the noise is audible, and your setup is adequate, you should see it with vibration. If you are hearing the noise with an ultrasound tool, the vibration may not be detectable yet though. Ultrasound has the capability for earliest detection of a potential failure, with vibration not too far behind. If you can detect the bearing failure with an infrared camera, you likely don't have long until the bearing functionally fails.

If you post a spectral plot of the bearings' vibration, I'm sure we could identify the issue, if one exists. If all you have is overall vibration readings, you'll have to wait until closer to functional failure before it is detectable.

Some questions to help with troubleshooting:

What is the frequency of the audible noise? RPM of the motor?

How many rotor bars on motor? How many balls/rollers in the bearings?

How many cooling fan blades on the motor?

Have you tried realignment of the system? Checked any couplings?

Yes, but only if you give a time frame - 5 seconds before failure, 5 years before failure or some where in between? -- JHF

Hi,

Almost all HT motors are custom built, with known data of load. Hence bearing suitabilty vis-a-vis load is always checked. In addition bearing temeperature sensors are always used which has both alarm and trip settings. Sometimes vibration monitoring sensors are also used. When damage to bearing inner surface, cages or ball/ rollers start then the vibration level always increase, the bearing temerature also increases. The trend would indicate deterioration of the bearing. Hence sudden bearing failure rarely occurs unless these sensors are not provided, or not properly wired to the system.

In some rare condition of multistage pumps, or compressors if the axial thrust is more than what is specified to the manufacturer, the failure is so rapid that increase in temperature, vibration and bearing damage are almost simultaneous.

R. Gopalakrishnan

You need to provide full details as per under:-

1.Make of motor.

2. H.P/KW.

3.RPM.

4. Application.

5.All above details for bearing.

There is some doubt about quality of bearings.

The facility's maintenance records for the equipment in question would provide a level of guidance on the matter.