Proper Method for Balancing a 2 Stage Fan Rotor
Proper Method for Balancing a 2 Stage Fan Rotor
(OP)
Hi
I would like to get some input from some experienced vibration/balancing people. There has been some debate (between me and some others), about the proper way to balance a 2 stage axial fan rotor. I believe that it should be treated like a 2 plane imbalance and can use a vibration analyzer/balancing computer to 2 plane balance the rotor. Other 'old timers' think it should be treated like a single plane most time and just split the weight between the two hubs of the rotor. Some think the weight split ratio should be determined by the ratio of vibration amplitudes. Some think you should just try to balance the end that is highest with a single plane balance. I want to know the best, fool proof way of balancing these rotors if the issue at hand is in fact a mass imbalance in the rotor, somewhere. This is a main shaft assembly supported by two sleeve bearings (sometimes a anti-friction bearing assembly, but most times two large sleeve bearings). Each 'hub' is it's own assembly that is mounted to the main shaft. It is very possible that one 'hub' had a mass imbalance and the other one doesn't. Treating the whole rotor (both hubs and the main shaft) at a single plane and splitting the weights seems ridiculous to me. I could possibly see where it could be addressed as two separate single planes? I suppose the test would be, does putting a weight on one 'hub', change the vibration in the second plane? But, the bearings are so close to each other (between the two stages of the rotor) that of course they are.
I would think you should do an initial run and collect your data from both planes (IB and OB bearings) along with the phase, then place a trail weight on plane (hub) #1 and collect data, then remove the trail weight from plane #1 and place it on plane #2, then calc. the balance for both planes. Is there a reason this wont work or might not be the best approach!?!
I am trying to attach a quick sketch of the basic rotor configuration. Let me know if it's not showing up.
Thank you very much for any input you might have!
aero
I would like to get some input from some experienced vibration/balancing people. There has been some debate (between me and some others), about the proper way to balance a 2 stage axial fan rotor. I believe that it should be treated like a 2 plane imbalance and can use a vibration analyzer/balancing computer to 2 plane balance the rotor. Other 'old timers' think it should be treated like a single plane most time and just split the weight between the two hubs of the rotor. Some think the weight split ratio should be determined by the ratio of vibration amplitudes. Some think you should just try to balance the end that is highest with a single plane balance. I want to know the best, fool proof way of balancing these rotors if the issue at hand is in fact a mass imbalance in the rotor, somewhere. This is a main shaft assembly supported by two sleeve bearings (sometimes a anti-friction bearing assembly, but most times two large sleeve bearings). Each 'hub' is it's own assembly that is mounted to the main shaft. It is very possible that one 'hub' had a mass imbalance and the other one doesn't. Treating the whole rotor (both hubs and the main shaft) at a single plane and splitting the weights seems ridiculous to me. I could possibly see where it could be addressed as two separate single planes? I suppose the test would be, does putting a weight on one 'hub', change the vibration in the second plane? But, the bearings are so close to each other (between the two stages of the rotor) that of course they are.
I would think you should do an initial run and collect your data from both planes (IB and OB bearings) along with the phase, then place a trail weight on plane (hub) #1 and collect data, then remove the trail weight from plane #1 and place it on plane #2, then calc. the balance for both planes. Is there a reason this wont work or might not be the best approach!?!
I am trying to attach a quick sketch of the basic rotor configuration. Let me know if it's not showing up.
Thank you very much for any input you might have!
aero





RE: Proper Method for Balancing a 2 Stage Fan Rotor
Cheers
Greg Locock
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RE: Proper Method for Balancing a 2 Stage Fan Rotor
Johnny Pellin
RE: Proper Method for Balancing a 2 Stage Fan Rotor
At a previous job, we field balanced a number of vertical, 2 stage, vane axial fans. Although symmetrical, the lower fan wheels were more sensitive to balance weights than the upper.
Good luck.
RE: Proper Method for Balancing a 2 Stage Fan Rotor
http://patentimages.storage.googleapis.com/US20120...
If the proportions in your image are nearly right the overhung rotors are going to boss the bearings around pretty bad.
I'd be ready for trouble.
Typical fan support coNstRuCtioN is pretty wimpy sometimes, narrowly missing resonances at best, and frequently quite flexible.
If either rotors is "tipped" at all large amounts of couple imbalance result.
RE: Proper Method for Balancing a 2 Stage Fan Rotor