equivalent load of a deep groove ballbearing

[Lotusbert]

Goodmorning !

I need to find a formula to calculate the equivalent load of a deep groove ball bearing wich is loaded with an axial load, a normal load and a torque load.This torque pushes the outer ring on one side to the right, 180 degrees further to the left.
How do you calculate this ??

Thanks for the answers

 

[electricpete]

The X and Y parameters allow comparison of axial load and radial load on an equivalent basis.

I'm having a hard time understanding what you meant by torque load... a moment on the shaft?

 

[EnglishMuffin]

The terms nurmally used are "axial load", "radial load" and "moment load". The X and Y parameter method for finding radial equivalent load , found in bearing catalogs,is only approximate. It works in many cases for a system of bearings, provided that you consider the radial load as acting at the point of intersection of the bearing contact angle and the shaft axis. About this point, the bearing has very little tilt stiffness and moment effects can be ignored. In your case, however, whether or not you can use the approximate method depends on whether the bearing is part of a system or not. If a second bearing is involved, and you can consider that your deep groove bearing has a zero contact angle, you can probably ignore the moment loading for the purposes of calculating the equivalent load. If the deep groove bearing is being called upon to carry the full moment load on it's own, however, you may need to use a bearing computer program, such as ABODE, which will calculate all the individual ball contact angles and do a ball by ball analysis. Or maybe you will need to have the bearing manufacturer do an analysis for you.

 

[EnglishMuffin]

I suppose I should add that if your application does indeed involve just a single deep groove ball bearing with a major moment load, this is not a good application for such a bearing. A better choice would be some sort of 4-point contact bearing, if you can find one of a suitable size. With a standard deep groove bearing in this application, the contact angle conditions are not good, and accurate calculations involving this would require among other things that you know the internal clearance very precisely, which is very dependent on fits etc. A ball by ball analysis, only practical with a computer program, would also require that you know the ball diameter and race curvatures, and the latter are often hard to obtain from bearing manufacturers.

 

[Lotusbert]

Thanks for the repies !

In fact my application is the head of a swivel castor. The bearing(s) in the head are most of the time under a static load. I want to design a optimised swivelhead with standard bearings. So to know how to calculate the bearing(s) would be very helpful.
There are designs on the market where they use only one deep groove ball bearing,,even for castors up to 1000 kg ! Most designs use one axial trust ball bearing and one deep groove ballbearing or one spherical bearing. As the assembly is hyperstatic it is very diffucult to make some calculations. Relying on try and error is expensive and time consuming....

Does there exist an eqation or tables where you can find the allowable moment on a bearing ?
All ideas are appreciated !

 

[israelkk]

Lotusbert:

I think you can be on the safe side if you will assume that the tilting torque is carried by two sectors of 90 degrees resisting the tilting torque. Therefore, if the ball bearing can carry an axial force of let say 1000lb then the torque it can carry will be 250 lb multiply by the bearing diameter (the diameter where the balls are located).

By the way, I recall seeing (many years ago) a patent for missile fin supported by only one large diameter bearing as you are trying to do.

 

[EnglishMuffin]

At one time, I had access to a program that would do this (ABODE). But I repeat :
1. It is not a simple calculation
2. To calculate the pure moment load capability of a deep groove ball bearing from first principles requires knowledge of internal bearing geometry which I doubt you possess, although if you are friendly with bearing reps you can sometimes get it
3. It is not a good application for deep groove ball bearings - the loads on the balls become excessivly high. They are intended for radial load and a limited axial load. The designs incorporating a thrust bearing sound better. It is no accident that you cannot find the procedure for doing this calculation in bearing catalogs!
4. Although I am not one of those people who always rely totally on manufacturers recommendations in the case of bearings, in this case you may have to. But lets see what others have to say.