Got a question on Fan Bearings

[ShelleyGA]

We have had numerous bearing failures because we have had the fixed type bearing closes to the fan housing and the "floating" bearing on the outboard. Our seasoned maintenanc guys say the fixed should be on the outboard and floater inboard. Engineering says the opposite. Our drawings aren't detailed enough to determine which goes where....so what do you all say? I'm trying to find documentation but can't. OEM hasn't gotten back to me yet.

ShelleyGA

 

[JJPellin]

All fans are not the same in this regard. The last overhung fan I worked on showed the fixed bearing toward the coupling and the floating bearing toward the wheel. But this is a low temperature fan drawing in ambient air. this fan is a single inlet wheel with an inlet cone that could accomodate perhaps 1/2" of axial movement with no problem. The configuration of the fan wheel, the axial internal clearances, the type of coupling, the temperature of the service could all affect the decision.

 

[diskullman]

Assuming the fan is belt driven, the fixed bearing is usually closest to the fan housing, so the belts aren't shifted out of alignment from expansion. Fan applications can be murder on bearings as they are hard to keep balanced. The first bug to hit a perfectly balanced fan throws off the balance.

Russell Giuliano

 

[dimjim]

Haven't you answered your own question?

Try the opposite and see what happens.
I find it hard to believe that you do
not have a manual for replacement parts
that would define which bearing is which.
I would expect that the radial bearing be
near the blade and the thrust bearing at
the other end. Too bad the OEM did not
make the bearings different enough so that
they could not be interchanged.

 

[ShelleyGA]

Thanks for the responses. These are motor driven direct coupled. Apparently the company wanted to save some $ during installation so they didn't get the more detailed drawings. Also OEM manuals are not available because our corporate group doesn't always get us the info we need to maintain. I have my bearing rep looking for the info on these fans right now and we did call the OEM but their expert is out of the country.

 

[dimjim]

You could ask the OEM for a drawing
of the motor or service manual.
So sad that they are not more helpful.

 

[Skogsgurra]

Are these fans constant speed (DOL) or do you have a varable frequency drive on them?

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ShelleyGA]

They are variable. Heard from the OEM on this and fixed is outboard which is logical.

 

[blanco1666]

It pains me to say it, as they are a competitor of mine, but SKF have had good success with their CARB bearings on fans. They have a few application examples on their website, for example:

http://www.skf.com/files/003920.pdf

Its difficult to compete with CARB in fans, but easy in other applications. They tend to complicate most apps, its easier to stick to sphericals...

 

[blanco1666]

Note that on the SKF design, the floating CARB bearing is next to the fan, the fixed spherical next to the coupling and drive

 

[Skogsgurra]

What size are the fans? CARB? I thought they were more for long cylinders, radial loads and bending moment. Not fans so much.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Tmoose]

What are these bearing "failures"?

If a warm shaft expands axially against 2 identical bearings they both die.

The "correct" location for the fixed bearings will abso,utely vary with application. What is important is Axial shaft growth should never result in bearings fighting each other on one shaft OR between the driving and driven machines

The axially fixed bearing should go at the end that can least afford axial growth, and the floating bearing must be set so that it will not be axially restrained while in operation.

If the coupling has limited axial expansion capabilities (unfortunate coupling choice) then the fixed bearing should go near the coupling, being sure the coupling gap starts centered or biased to prevent the driver/driven shaft ends ever bump or the coupling axial compliance is exceeded.

If there is close fitting shrouding and the fan is in a hot process then keeping the fan wheel axially positioned at operating temperatures may be most important, and the axially fixed bearing belongs near the fan wheel, with the wheel centered, and still with the couping gap set to accomadate all intended axial shaft expansion.

 

[rmw]

Is this a high temp fan? And if so, is there a heat slinger between the fan and the bearing?

rmw