Bearing Vibration Prevention

[iucu]

My Rotor spin to 18,000 RPM max and Shaft is on 2 deep groove ball bearings, about this size, 30-35 x 62-72 x 12-17
The issue I have at high RPM is Vibration.
What is the best practice to prevent this ?

 

[BrianE22]

Find the source of the vibration and minimize it. Maybe shaft balance?

 

[Tmoose]

Do you know the frequency(S) of vibration?

Did you talk to the bearing manufacturer about
the bearing arrangement design?

Are the bearings preloaded axially with wavy springs or something similar?

Is th4e shaft vertical or horizontal?

Is there side load on the rotor, perhaps a belt or gear drive?

Howzabout some pictures and drawings?

7 down, 13 to go.

 

[spciesla]

Lubrication type?
8 down, 12 to go.

 

[tbuelna]

iucu-

It would help if you would provide more details. Based on your limited description, it sounds like you have either a dynamic imbalance issue or a rotor/shaft dynamics issue.

To keep things simple I'll assume your shaft is operating at a safe margin (maybe 25%) below its critical speed. However, one thing that can affect critical speed is stiffness of the shaft bearing system, and bearing preload will usually increase shaft critical speed. Your deep groove ball bearings probably operate with some internal radial clearance and are not preloaded. So Tmoose's suggestion to use a pair of angular contact ball bearings axially preloaded with a wave spring is definitely worth considering if critical speed is a concern

Dynamic imbalance is fairly easy to resolve. You simply need to dynamically balance your rotating assembly. Take a look at ISO 1940/1 for details of the procedure. Your application sounds like it would require balancing in two planes to quality grade G6.3 or G2.5.

If the vibration is due to excitation of some structural mode (torsion, bending, whirling, etc) in the rotating assembly, resolving the problem may require much more effort. As BrianE22 suggests, before making any changes the first thing you need to do is diagnose the existing situation. Measure the vibration characteristics of your operating system. Calculate the operating frequency range of all potential sources of excitation in the system, such as gear/belt/chain meshing frequencies, bearing element passing frequencies, input/output forces acting on the rotor, etc. And if you have the capability, perform an analysis to determine if your rotating assembly has any structural modes that might couple with the excitation frequencies. Resolving this type of issue can usually be achieved by modifying the rotating component size/shape/section to shift the particular structural mode outside of the operating range, by using larger/stiffer shaft bearings with increased preload, or by modifying associated drivetrain component characteristics (such as meshing or passing frequencies) to eliminate the source of excitation.

 

[iucu]

Yes.
Application is this : Electric Motor (Stator, Rotor)
Rotor RPM go to 18,000 .
Rotor RPM come from a Dyne.
I am using 2 bearings on rotor shaft like SKF 35 x 62 x 14, C3 internal clearance.
Problem is that at high RPM, over 14,000, application/fixture start to vibrate and vibration come from bearings because if I Shim them, it is better.

 

[Tmoose]

where are you applying the "shim" to reduce "vibration ?"

Light axial preloading of deep groove ball bearings( not angular contact) is a legitimate method to improve running accuracy and improve running stability and reduce noise.

Lots of basic electric motors do that by means of a wavy spring in the end bell with the "floating" bearing.

http://www.skf.com/binary/30-124512/1109%200075%20-%2010000_tcm_12-124512.png

http://www.skf.com/us/products/bear...procedures/preloading-with-springs/index.html

Are you going to post some drawings or pictures?

10 down, 10 to go.