Wear on the oter race and bearing housing cap

[BrianGomez]

Over the last few months I have witnessed a large number of bearing being changed during routine maintenance, for wear appearing on the outside, of the outer race and bearing housing caps. Upon inspecting the bearing and cap, it would appear that the bearing has been rotating in the housing and wearing a groove into the bearing cap. I understand that there is a lot of factors to consider why this could be happening, such as clearances, torque setting, shaft run out and so on and so.

I'm asking if anyone has experiencing this problem, and is the a way to detect it?

 

[JJPellin]

We could provide better responses if you provide more information. What type of bearing (ball, cylindrical roller, spherical roller)? What type of housing (split pillow block, other)? What type of machine (pump, turbine, gearbox, fan, mixer)? What method of lubrication (pure mist, purge mist, oil, grease)? What type of drive (flexible coupling, belt)? How big is the bearing and how fast is the shaft spinning?

In the machines I deal with, we very rarely see evidence of an outer race spinning in the housing. This usually happens as a result of a bearing failure. It is more likely a consequence than a cause.


Johnny Pellin

 

[BrianGomez]

Split pillow block housing (SKF SNL 516-613)
Spherical Roller Bearings
Belt Driven Fan running 2735rpm
Routinely greased

 

[JJPellin]

I assume these fans have horizontal shafts. Vibration is the key tool to detect problems. This could be detected as looseness in the vibration spectra. The damage could be from relative movement rather than a spinning race. High vibration from imbalance or run-out could contribute. Belt drive problems such as an eccentric pulley could also contribute. If you are sure that the damage is from the race spinning in the housing, then there are fewer causes to explore. As I noted above, this usually occurs after the bearing has failed. This could be old damage from previous failures. I would expect a failure of a bearing like this to result from over-greasing or the mixing of incompatible grease. We have seen failures of these bearings from over-tightening or under-tightening of the tapered-sleeve mounting nut.

The keys to avoiding these failures are to mount the bearing correctly on a shaft with low run-out and a rotor with a good balance. Apply the correct grease in the correct amount at the correct frequency.


Johnny Pellin

 

[Tmoose]

Are the blower wheels over hung relative to the bearings ?

http://www.rpsindustries.in/wp-content/uploads/2016/01/pic3.jpg

Or, mounted between the bearings ?

http://www.fanair.in/images/products/blower-and-fans/id-fd-fans-250x250.jpg

Got pictures of the worn bearings and housings?

I'm guessing the blower is heavy, and overhung and mounted outboard of the bearings on the horizontal shaft.
I also guess the housing that wears is the bearing close to the belt drive, and the belt pull is close to horizontal

The usual reason for worn housings is improper fit for the application, which lets the bearing creep in response to loading that changes direction.

 

[BrianGomez]

I am trying to retrieve the bearings but seem to have been discard of as soon as they were changed, I have uploaded a photo of the most recent fan tat has had this issue.

I hope to have some more information on this issues later today.

 

[Tmoose]

Well, from your picture the only detail missing from my dream/nightmare configuration is confirming it is the drive end bearing that is wearing out its housing.

Preventing bearing creep with that configuration is not usually a catalog solution.

 

[BrianGomez]

It is the DE bearing that is wearing on the housing. The bearings and housings are now long gone as I suspected, so I can not provide any pictures unless it happens again.

 

[MikeHalloran]

For detection, if space permits, matching paint dots on the outer race and housing, and occasional visual inspection, might be sufficient.

For prevention, I'd be inclined to install the outer race with some slow-curing Loctite applied to its OD, and a few rotations of the fan while the bearing cap is being torqued down, to allow any necessary self-alignment to take place. Nowadays, I tend to use Loctite PST for everything, because it's not too weak, not too strong, visually apparent, and I just carry the one tube.





Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

I'd be a little cautious using Loctite. One of the two bearings' outer race should be axially "fixed" (Often with a spacer on each side of the outer race, not with a tight OD fit).
The other should be allowed to "float" to accommodate axial thermal expansion.
Gluing the fixed bearing outer race in the housing might cause an axial load problem.