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Bearing design assitance for a fan

Bearing design assitance for a fan

(OP)
Hi all.

I need to do an industrial fan (horizontal or vertical position).
The fan is on overhang (end of the shaft). Distance between the first bearing is "L1".
The length of the assemblies (fan + 2 bearing + coupling + electric motor) needed to be minimum.
Bearings can be oversized.
Weight of the fan is 88 lbs - 2000 rpm with a Ø 18 in

What is the minimal distance between 2 bearings ?

Many thancks in advance.

Julian

RE: Bearing design assitance for a fan

The answer to your question is 0.0, bearing face to bearing face.

But you have to provide enough radial capacity in the bearing pair to resist the moment developed by the overhung fan. ... and you need moment capacity in the shaft, which will give you a minimum for the bearing bore. But first...

An 18 inch fan that weighs 88 lb? The blades are made of what; Tungsten?

Mike Halloran
Pembroke Pines, FL, USA

RE: Bearing design assitance for a fan

(OP)
Hi Mike.
Thank you very much.
the correct diameter is 22.8 inch. I'm sorry.
Mike, you can see in this PDF file a FAG housing unit:
http://www.schaeffler.com/remotemedien/media/_shar...
I'll go to see the minimum distance between the 2 bearings pillow Block Bearings NP.

Have a nice day.
Julian

RE: Bearing design assitance for a fan

Note that the VRE plummer block unit includes two bearings at a predetermined spacing, and a shaft, so I don't understand what you are trying to compute.

Mike Halloran
Pembroke Pines, FL, USA

RE: Bearing design assitance for a fan

(OP)
Hi Mike
I need to make a plummer block with a spacing smaller.
Regards.
Julian

RE: Bearing design assitance for a fan

Belt drive, or direct coupled?

"The loads acting on a bearing can be calculated according to the laws of mechanics if the external forces (e.g. forces from power transmission, work forces or inertia forces) are known or can be calculated. When calculating the load components for a single bearing, the shaft is considered as a beam resting on rigid, moment-free supports for the sake of simplification."
http://www.skf.com/group/products/bearings-units-h...

http://www.ntn.co.jp/english/products/pdf/ball/pdf...

RE: Bearing design assitance for a fan

(OP)
Hi
Thank very much.
Belt driving create too much loads and probably causes vibrations and bad lubrification on the free bearing.
I prefer a direct coupled.
2 documents are very interesting. I see is not very good to have a smaller spacing with a belt driving. We have to multiplied by a factor 4.5 .
With a coupling.......no problems.....or less
Have a nice day
Julian

RE: Bearing design assitance for a fan

Sounds like your fan arrangement is still in the early design stage.

Plenty of successful designs use belt drive. The ability to vary fan rpm while using a simple induction motor comes in very handy sometimes.
A small but useful amount of relief starting a heavy fan via brief belt slip is possible too.

Ball and roller bearings have minimum load requirements for proper tracking and to avoid potentially damaging roller/ball skidding, and the drive-end bearing of A direct coupled over hung/cantilevered fan will often be lightly loaded, and be susceptible to creeping unless bearing OD fit is carefully controlled. A belt drive can actually have more balanced radial bearing loads.

Yes, belt drives are likely to have some amount of "vibration" due to varying belt tension forces from belt thickness variations and pulley/sheave runout. There are ways to minimize but not eliminate those effects. It can be a tricky compromise between higher "vibration" from base flexibility (to reduce bearing loads from tension variations) and lower vibration with a stout structure but somewhat increased bearing loads.
Designing a base that keeps a direct drive motor and fan in good 3D alignment is not a trivial task either. Some Name brand fan manufacturers muck it up from time to time.

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