Hi all,

Just looked at a 150 h.p. vertical motor driving a pump via a 25' splinend line shaft with 2 universal joints. The motor is making a sporadic grinding sound coming from the ODE bearing. The sound is so sporadic i really can't capture it with my analyzer. I am working on identifying what the bearings are in the motor, but I suspect an angular thrust roller bearing on the ODE.

I believe the bearing is skidding, but a coworker seems to have a different idea as to what skidding is and sounds like. Any input on causes, symptoms, and fixes for bearing skidding would be greatly appreciated.

Thanks, brian

Increased temp?
Olov

Anyone have any actual spectrums of "skidding" bearing?

Have you tried using the "Peak-Hold" funtion when trying to capture your "sporadic" noise?

Here is a discussion of skidding from another forum I found by searching "skidding bearing".
http://forums.noria.com/eve/fo...0104902/m/7611001322

Do you have the capability to capture a long time waveform? If you can capture 4 or 5 of the bursts in the WF, you may be able to diagnose it better. Periodic skidding will probably just excite natural frequencies in the bearing from 1kHz-2.5kHz sidebanded potentially by the skidding repition rate. May see some BPFO or BSF harmonics.

Contributors to bearing skidding:
1 - Loading does not meet minimum load to prevent skidding.
2 - Poor lubrication contributes to bearing skidding (because skidding is when cage/ball friction overcomes traction between ball/race). I have a suspicion that the screach you hear on a greased bearing motor when starting is sometimes skidding because the grease is cold right at start. Of course all motors make various noises at start and not all of them are skidding.
3- High speed, large bearing diameter, and large rolling element size all contribute to skidding especially on an angle contact. The gyroscopic action also fights against the traction just like the friction does. When traction loses the battle there is skidding. Bearing manufacturer can provide minimum load to prevent skidding for a given beairng as function of speed and lubrication.

I have a suspicion there are at least 3 things that might cause intermittent noise in bearings:
1 - skidding
2 - outer ring moving in housing
3 - ball defect, may wobble so it sometimes hits and sometimes doesn't.
4 - others? (interested in other things that cause noise that comes and goes)

We have chased a lot of intermittent noises on bearings. Never have a lot of luck diagnosing them. If you're lucky, there might be something in the spectrum like a defect that justifies pulling the bearing at some point. Otherwise it's a tough call for us.

Good luck.

What lube are you using? Was there a change made without cleaning the bearing?

Could it be described as more of a squeal, screech, or buzz? "Cage noise" is discussed in hushed tones at various bearing manufacturers. the few times I saw (heard) it was brand new precision spindles with very nice machining and preloaded bearings ( no skidding ) and was related to subtle differences internal differences. Some perfectly good spindle greases in some perfectly fine bearings would suffer intermittent "cage noise". Sometimes after run-in it was gone. Sometimes change to Kluber NBU-15 or 52, and the noise was gone.

In your app I sort of tend to suspect some cage wear or something related is setting it off