Dear All,

We gave recently performed activity of motor overhauling of a used motor which will be used to drive ID Fan. Following bearings have been installed in motor,

DE: Ball Bearing 6234 MC3 + Cylindrical Roller Bearing NU 234 MC3

NDE: Cylindrical Roller Bearing NU 234 MC3

During motor testing in decouple mode abnormal whistling sound was observed from the motor. After some greasing of bearing the sound vanishes and again after 30 to 45 minutes same sound starts again.

*Vibration values are 0.8~1.2 mm/sec even when abnormal sound is observed so vibration is remains same.

* gE value tends to go on a higher side as soon as the sound starts.

Pictures of electrical motor, abnormal sound video and thermography report has been attached for better understanding and to trace out the possible reason for this abnormal sound.

Attachments

Images (2)
Videos (1)
video_20200623_143705
Files (1)
Thermography of motor bearings
Original Post

I guess first one needs to establish that there is an issue or not.

Based on the vibration readings and typical overall limits, the vibration is acceptable. If your concern is the sound, this is a tricky evaluation. If you don't use an instrument for that and follow an acceptance limit, your concern is subjective and others may argue and diagree.

Are there any other abnormalities like a fast temperature increase, unstable current, unstable axial position etc?

 

Regards- Ali M. Al-Shurafa

There are no abnormalities like fast temperature increase, unstable current, unstable axial position.

First motor was decoupled off load testing so we thought it might be due to skidding so some more greasing work was done. But now it is in operation with load having variation in gE values from 5 to 8 on both DE and NDE bearings. However sound has been reduced as compared to before.

I wonder more greasing should be done or not.Or should we go for gE and temp values if values remain the same then no need to grease to avoid over greasing..Is it so??

When bearings were "greased", was the drain plug removed and grease applied slowly until clean grease exited the drain? The motor looks to be in a dusty environment, so lubricant contamination is possible via the added grease (gun nozzle or grease fitting) or entering the shaft seal.

Check cooling fan and air passages including any air filters for blockage.

Walt

I have been in this situation many times before and the solution was:

1- check if the grease pass through bearing housing from greasing nibble to drain plug is clear as some motors have specific pass for the lubrication inside bearing housing which is adjusted by plate or cover behind bearing housing. if this pass is in wrong orientation then the grease will not go inside the bearing and it will bleed out from your bearing housing and /or go to your motor winding.

2- some motors suffers from abnormal sound during start up and after while the sound will disappear as the shaft reach it's thermal stability.

@Walt Strong posted:

When bearings were "greased", was the drain plug removed and grease applied slowly until clean grease exited the drain? The motor looks to be in a dusty environment, so lubricant contamination is possible via the added grease (gun nozzle or grease fitting) or entering the shaft seal.

Check cooling fan and air passages including any air filters for blockage.

Walt

Thanks dear i will cover all the check points highlighted by you.

Raheel

@Ayman Gamal posted:

I have been in this situation many times before and the solution was:

1- check if the grease pass through bearing housing from greasing nibble to drain plug is clear as some motors have specific pass for the lubrication inside bearing housing which is adjusted by plate or cover behind bearing housing. if this pass is in wrong orientation then the grease will not go inside the bearing and it will bleed out from your bearing housing and /or go to your motor winding.

2- some motors suffers from abnormal sound during start up and after while the sound will disappear as the shaft reach it's thermal stability.

1- Don't know exactly about the bearing fitting and greasing as it was done by electrical department. However i will try to check what you have explained.

 

2-Well understood. Lets wait and hope for the best then.

Thanks,

Raheel

Ralph,

I guess it is just a typo on the header of the chart. It should be 600,000 cpm to me.

Based on the format, the data are most likely collected by Scout/Commtest. The title on the top of the chart is just a text/label and it may have nothing to do with the content. The device has a standard data collection package of 6 sets (6 Pack). If I remember correctly they are something like low-frequency velocity, high-frequency velocity, low-frequency acceleration, high-frequency acceleration and ....

Regards- Ali M. Al-Shurafa

Generally when bearing noise or vibration drops (lowers) after greasing but comes up (increases) again, it is caused by a bearing fault. The bearing fault could be an actual surface fault/flaw on races or rolling element (ball or roller), or there may be solid particle contamination (rust or dust) in bearing/grease. If the motor is still in the shop with this condition issue, then it should not be installed onto fan without resolving the bearing problem. I suggest calculating the bearing fault frequencies and especially look for matches at high harmonics of each fault frequency. Also look for matches with modulation sidebands (appear in your spectra). A less likely scenario is that bearing installation was incorrect, and this can only be resolved by disassembly. Either bearing fault scenario would require replacement before motor leaves the shop. If motor is already installed at plant, then a future maintenance action can be scheduled.

Walt

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