Centrifugal fan thrust load
Centrifugal fan thrust load
(OP)
Hi.
I have a over-hung centrifugal fan with :
Volumetric flow rate = 4400 Nm^3/hr
Dp = 0.07 Bar
Speed = 3273 rpm
Power = 25 KW
This fan is supported with 2 double-row roller bearings.
How can I calculate the reactions on those 2 bearings and make sure the bearings are selected properly ?
Regards,
I have a over-hung centrifugal fan with :
Volumetric flow rate = 4400 Nm^3/hr
Dp = 0.07 Bar
Speed = 3273 rpm
Power = 25 KW
This fan is supported with 2 double-row roller bearings.
How can I calculate the reactions on those 2 bearings and make sure the bearings are selected properly ?
Regards,





RE: Centrifugal fan thrust load
RE: Centrifugal fan thrust load
RE: Centrifugal fan thrust load
Are they spherical roller bearings?
Either the inboard or outboard bearing should be "fixed" to serve as the thrust bearing. But not both.
What was the bearing "failure?"
RE: Centrifugal fan thrust load
The failure was in the bearing in the drive side of the shaft.
What happened is that the bearing balls fall down and stuck up together producing so much heat that actually made the bearing casing become black.
After replacing the bearing and sent the fan to the end user, it ran for 3 days and some problem occurred again!!
Any help will be appreciated.
Regards,
RE: Centrifugal fan thrust load
RE: Centrifugal fan thrust load
RE: Centrifugal fan thrust load
RE: Centrifugal fan thrust load
I don't know the material of the cage, but it was 1 piece as i remember.
Now, i know this kind of bearing can take some of the thrust load. But what i want to know is how to make sure that the thrust load limit of the bearing is more than or equal the actual thrust load of the fan ?
RE: Centrifugal fan thrust load
SKF must have tons of application engineers to solve your
questions.
RE: Centrifugal fan thrust load
So, i'll be so grateful if any one can explain to me how to calculate those loads.
Regards,
RE: Centrifugal fan thrust load
Rolling Bearing Analysis. From the references in his
book, you can go on to other pioneers in this field.
Combined bearing loading section is a must.
You should find this exciting and a new adventure.
The different application catalogues from the manufacturers
will be some help as well but limited in scope.
RE: Centrifugal fan thrust load
http:
If this is a tapered bore bearing, installation includes reducing internal clearance a prescribed amount. If the clearance is reduce too much, heat generation will be excessive, initiating thermal runaway, lubricant failure (generally indicated by cage failure) and could well result in the failure and short life you encountered.
RE: Centrifugal fan thrust load
The problem is that i don't know how to calculate the actual thrust and radial forces in the fan.
I know the suction & the discharge pressure and i have all the dimensions, but don't know how to calculate!
Any help?
RE: Centrifugal fan thrust load
I work for a fan manufacturer, and I work almost exclusively in Imperial units of measure.
I want to convert your fan performance data into Imperial units, but have no idea what the "N" prefix represents in your volumetric flow rate (4400 Nm^3/hr).
I disregarded the "N", and converted 4400 m^3/hr into 2590 ft^3/min. This seems to be a very small value; not correct.
I converted 0.07 bar into 2.07 inches of water (in wg).
I converted 25 kW into 33.52 HP.
If these values are correct, it appears to me that the bearings are very lightly loaded. It is likely that there isn't enough load to properly engage the rollers. The rollers then skid between the inner and outer races instead of rolling, leading to pre-mature failure. (It's more common than one might guess).
Calculating the loads:
Axial thrust = (Total fan static pressure) x (cross sectional area of fan inlet) This is only applicable if the fan wheel has a backplate. If no backplate, the thrust load is negligible, and can be disregarded.
Radial load: The radial load on each bearing is determined using a simple beam diagram. There are two supports and two un-equal loads, one beyond each bearing. One load is the weight of the wheel and the other load is the belt-pull and weight of the sheave. If you have an Arrangement 8 fan (direct drive) there will be virtually no load on the fan outboard bearing.
The simple beam diagram to use is the "Beam Overhanging One Support - Concentrated Load At End of Overhang". It will show a downward force due to the load adjacent to a bearing, and an upward force on the other bearing due to the pivot across the first bearing. The calc's will need to be run twice; once for each load at opposite ends of the fan shaft, and the results added together. Keeping track of positive and negative values is critical!
Best wishes!
RE: Centrifugal fan thrust load
RE: Centrifugal fan thrust load
Best of luck!
RE: Centrifugal fan thrust load
Kind of get my drift. You cant blame the fan for a poor fit or a bad install. If you follow the proper proceedures to install a new bearing I don't think you should have any further issues with it.
Robert
RE: Centrifugal fan thrust load
Russell Giuliano
RE: Centrifugal fan thrust load
A fundamental relation I would start with is: Power=force*velocity
which then can turn into:
P=deltaP*A*V
V*A=Q (flow rate which you have)
So, Power=deltaP*Q
Figure out your deltaP and this can be an approximate pressure on the bearings. This is just a CV analysis.
(note that this is assuming the maximum power out of the motor and no losses)
Hope this helps,
Fe