Bearing Limiting speed 3

[Mr_Curious]

Hello Dear Engineers.

I am designing a traction motor and have selected SKF NJ 2228 bearings for them. I am wondering what is the Bearing Limiting Speed and how to calculate it?
SKF catalog says that limiting speed of the bearing is 4800 rpm. I think it is for oil lubrication.
I'm wondering if these bearings can run at 3600 rpm with grease lubrication.

Tell me please how to calculate the bearing limiting speed for a roller bearing? Can't find.

 

[dvd]

Call SKF and talk to an applications engineer.

 

[TugboatEng]

One factor people fail to recognize between grease and oil lubrication is that both are dependent on the viscosity of the oil. Most greases have an oil viscosity of ISO 220. This limits the speed of the bearing because of the high viscosity. Use a grease. For higher speeds specify a grease with a lower viscosity oil. The NGLI thickness is not related to this.

You also mention limiting speed which is a mechanical limit where dynamic forces begin to shorten the life of the bearing. There is also a reference speed where heat shortens the life of the bearing. If your application is to spend extended periods of time at speeds you should consider the reference speed as the limit or use circulated oil with a cooler.

With a reference speed of 2800 rpm, I would say no, these bearings can't operate at 3600 rpm with grease lubrication.

The bearing cage is a major factor in speed limits. If you must run this size bearing consider looking at different cage materials.

 

[electricpete]

what is the limiting speed

In the context of the SKF webpage that you linked, you should look for the term in SKF literature. Here is what SKF says about limiting speed (which is what they describe under mechanical speed limit)

how to calculate it?

You don't calculate it. SKF told you the limiting speed for the beairng on that website.

I'm wondering if these bearings can run at 3600 rpm with grease lubrication.

NJ 2228
D = 250 mm, d=140, Dm = (250+140)/2 = 195mm
Dm*N = 195mm*3600rpm = 700,000 mm*rpm.

That's a big number. I'm used to limits like max 350k or 450k for greased deep groove bearings. And the limits for greased crb's are even lower.

If this thing has to run continously for any length of time (let's say an hour or more... long enough to reach thermal equilibrium), then I'm in agreement with TugBoat: Grease is not an option for that bearing at that speed.



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(2B)+(2B)' ?

 

[Mr_Curious]

Thank you guys.
Helped me a lot!

 

[romke]

Some grease manufacturers are able to supply greases that are capable of lubricating bearings with higher n*Dm values up to 750.000 for certain bearing types. Given the n*Dm value in this specific application those might be of interest. The fact that those greases might be able to lubricate the bearing quite well however does not necessarily indicate that the bearing temperature stays within the range that the bearing can accept. If heat build up is a problem, a grease cannot be used since it will not be able to transport excess heat away to somewhere where it can be dissipated into the environment.