Skip to main content

Read our primer articles on Vibration Analysis and Laser Alignment Tools.

On August 10, 2005 we had a screw conveyor go down due to lack of lubrication in a SKF6012 2Z bearing. This is a motor mounting bracket bearing that is separated from the oil sump of the gearbox by a lip seal. I use vibration analysis to prevent these unscheduled breakdowns but I missed this one.
On July 12 my normal route vibration data did not trigger any alarms. On this equipment I monitor 9 parameters from Overall to PK-PK waveform.
On July 9 I was asked to collect vibration reading on this screw because it had tripped out on the evening shift the day before. The results of these readings were in the normal range except for the vHFD was over 7 G’s. The waveform amplitude was 6.18 g’s PK-PK. This was about a 10% increase but nothing to start running around about. The spectrum did not show any high vibration peaks. The highest peak in velocity was .04 at one order. The highest peak in the higher frequencies was .2 g’s at 2264 hertz. I decided I needed more data so I doubled my F-max to 5000hertz and collected another spectrum.
Now this spectrum showed me why I had a vHFD alarm. Now my PK-PK was 62.67 g’s PK-PK. My spectrum in acceleration was .86g’s at 3198.3 hertz. But nothing matches any bearing frequencies. And the bearing locked up the next day before I could collect any more readings and make the call to change out this bearing.

My questions are:
Is this the bearing’s natural frequency?
Should any bearing frequencies be present?
There is a lot of non-synchronous data but non matches this bearing.
Original Post

Replies sorted oldest to newest

With that amount of PK-PK vibration the bearing is wearing itself down, if it wasn't destroyed already. One thing to remember iswhen the bearings starts to get severe wear the faults frequencies will not line up with the calculated values. Was the bearing running hot when you checked it the last time? They tend to generate alot of heat when they are that close to self destruction.
This bearing was very dry and it locked up due to cage failure. This was a steel cage and most likely failed due to heat from lack of lubrication. The balls, inner, and outer race show no obvisious defects. The speed on this bearing was around 1785 rpm.
My question is at what frequency range show i expect to see the natural frequency of this bearing? It showed up around 3200 hertz but I was expecting it to be in a range of about half of that.
I think there are a number of factors which will affect the frequency region where your series of fault frequency harmonics are highest. One is the resonancne of the bearing and also the mounting. Also the characteristic of the impact can make a difference.

Anyway I was going to look through my files fo find some similar bearings and see what region the peak of the haystack was at.

Are you sure about 6012-2Z?

Maybe 6212-2Z? or 6312-2Z?
I have included as a vibration paramenter a band of 4 to 8 Khz accelration.

We have noticed that when a bearing is a bit dry, (in the early stages) this acceleration level will trend up. If you catch it in reasonable time an appropiate dose of grease will bring the level back down staight away. However if the bearing is damaged then this vibration measurement will not stay down. In 10-15 minutes it will be up again.

I agree with the previous postings it sounds like your bearings were already 'gone' and to damaged for nice discrete frequencies.
attend Reliable Plant 2024
Link copied to your clipboard.