High rpm quiet bearings needed

[Sunfire]

Hello,

we have been using high precision angular contact ball bearings to support a shaft with diameter of 1". At some 25,000 rpm, the noise reaches 120 dB. What other mechanical bearings would be a better choice. The current ones are quite loud.

Thanks.

 

[Chronos]

A hybrid bearing with ceramic balls is probably worth a look.

 

[koolraj09]

I am not sure about the cost or availability...but foil bearings? They run at higher rpms...
http://en.wikipedia.org/wiki/Foil_bearing

 

[Chronos]

I question the load capacity of a foil bearing.

 

[Q_Goest]

Hi Sunfire. I'll assume for now you have proper oil lubrication and proper filtration. Do you also have bearing temperature? If so what is it?

Is this a new design? Or has this been running for a long time at these speeds and the noise has increased over time? If the latter, you obviously need to replace the bearings.

If the former, verify the bearings are rated for the rotational speed and loads you're operating at first. Your actual load should be no more than about 1/5 of the dynamic load rating, preferably less.

Next, check the ovality of the location where your bearing is pressed into the housing and on the shaft. Variations of more than about 0.0001" to 0.0002" could be the problem (your bearing manufacturer can give you a specific number). This could happen if stresses in the material build up during machining.

It could also be vibration induced by the rotating shaft. See if you can find someone familiar with rotordynamics and perform an analysis on the system.

Also, and especially if this is a new design, talk to the bearing manufacturer and review the design and problem you're seeing. Without looking at the entire set up, it's impossible to pinpoint the exact problem. There are a lot of diffferent things it could be including some not associated with the bearing.

 

[AlephZero]

That seems an implausibly high noise level to be coming "from the bearing," unless it's going to fail within the next few seconds of running time!

I would look at the frequency content of the noise to see if it is synchronous with the RPM, or has some other strong frequency components (which could be caused by rotordynamics issues, oil whip in the bearings, etc).

I would expect the cure is to identify what is the excitation force and get rid of it, not to guess that changing the bearing will fix the problem.

 

[Sunfire]

Thank you for the comments. I agree that it is more than likely that the noise level may in part be due to some of the attached parts to the system, or shaft vibrations, which for sure are to be analyzed later... Yet it is more than certain the bearings themselves are a major contributor. Just turning the shaft by hand results in audible sound from the bearings (they are brand new). My question is more of the nature of... can we reduce bearings noise at this stage. This may not necessarily render the system noiseless, but for now that's an acceptable goal

Right now we are using brand new high precision angular contact ball bearings. I have been wondering what would be other choices of bearings that would output lower noise levels.

If anyone has experience with airfoil / airdynamic or magnetic bearings, please share esp. availability/prices etc.

Thanks!

 

[AlephZero]

Just turning the shaft by hand results in audible sound from the bearings (they are brand new).

Did they make an audible sound when you turned them by hand, when you first installed them? If so, IMO either you installed them incorrectly, or they were defective when you bought them.

If you have run the system up to 25,000 RPM under load, they are not "brand new" any more, and they might have failed because the design was wrong (i.e. they couldn't handle the loads).

For a high speed rotor, the obvious question is whether you balanced it correctly. At that speed, you may have to take the flexibility of the rotor into account and balance it at something close to its actual running speed, not on a "standard" low speed balancing machine.

I'm more familiar with bigger diameter rotors with a mass of the order of 100 kg running at 10,000 RPM, but those bearings make no noise at all at low speed, and you can turn the rotors easily with one finger.

 

[Chronos]

It's up to you, but, I believe you should take a look at hybrid ceramic bearings.

 

[Sunfire]

At that speed, you may have to take the flexibility of the rotor into account and balance it at something close to its actual running speed, not on a "standard" low speed balancing machine.

I will inquire more on how the balancing was done. Good point!

The rotors you refer to - are their bearings greased or are they lubricated with oil.

 

[AlephZero]

The rotors you refer to - are their bearings greased or are they lubricated with oil.

Oil.

It might help if you post a drawing or photo to give us an idea of what the complete machine is like. "A 1in diameter rotor running at 25,000 RPM" isn't much information to work with.