Inner raceway radius

[BevanSmith]

I read in an earlier thread that the inner race radius of a deep groove ball bearing is approximately 52% of the ball diameter. Where does this info come from?

Where can I find info on diameters of inner races? I need to reference equations that give this information.

Thanks for any help.

 

[MikeHalloran]

If the groove radius were 50 pct of the ball diameter, the ball would scuff the groove as it rolled. So the groove radius is made just a little larger than the ball radius, enough to guarantee no scuffing with reasonable tolerances.

If the groove radius were a lot larger than the ball radius, then the Hertzian stresses might be too high. Perhaps the equations for Hertzian stress are what you seek.

You're asking for information that no one outside of the bearing industry would ordinarily be interested it. Perhaps if we knew what you're actually trying to do, we could be more helpful.





Mike Halloran
Pembroke Pines, FL, USA

 

[BevanSmith]

Thanks for the reply.

I am trying to calculate the contact stress between the ball and the inner race in a deep groove ball bearing. I have all the equations but I had to estimate the inner race radius because I could find no info on it.

I estimated it as 105% of the ball radius.

Any further help?

 

[MikeHalloran]

It may well be that.
It may well be something else.
You might be able to infer it from some axial play measurements of an assembled bearing.
I'd expect it to vary among manufacturers, and even depending on the application for which the bearing was designed and sold. E.g. they might (conjecturally) increase the groove radius of the bearing is expected to tolerate a little misalignment.

I.e., if you want exact numbers, you have to ask a bearing manufacturer, and you may have to specify exactly which sub-design you to consider.
There is also the possibility that they won't tell you anyway, or that they will intentionally give you a false number or accidentally give you an erroneous one.




Mike Halloran
Pembroke Pines, FL, USA

 

[dinjin]

Mike is on the money. Most manufacturer's will tell you the conformity if you ask. Some use the same conformity for the inner an outer races, some use two different radii for the inner and outer. Like Mike says, it does matter on the application. The tighter the conformity, the higher the turning torque, and greater care is needed in the grinding operation. You did post this in two different areas which is kind of a no no. Are you a student?
Osculation and conformity radius are two terms describing these ratios in much of the literature.

 

[caoimhin1]

This is the black art of deep groove ball bearing design. You can call and ask, you might get lucky, but very unlikely a bearing manufacturer will give away the raceway radius values unless theres a good business reason behind it.

 

[dinjin]

When we submitted drawings to customers, we put that information on the drawing in the upper left hand corner of our drawings as well as the RC hardness, type of separator,
and also the material designation of the rings, as well as the contact angle.

If a customer is paying for a bearing we always felt they should have knowledge of what they are buying. This also alerted the application folks what the customer had bought.
Some privy information not included was the internal clearance. We normally shipped the inspection record with the bearing which listed the internal clearance information.
The depth of hardness was not stated anywhere but listed in our design specs for that bearing.

 

[Tmoose]

Hidden beside the danger of " scuffing" with closely fitted curvatures is an improvement in "speedablity" from reduced heat generation with a more open curvature.

http://www.bardenbearings.com/scan pdf/catalog4.pdf

I heard from a fellow who was there that when FAG bought Barden there were positive comments, maybe even a certain amount of appreciation between engineers about Barden's choice of raceway curvature open-ness.

 

[caoimhin1]

SKF use larger raceway radii on their "energy efficient" bearing range.

http://www.skf.com/files/774060.pdf

They don't mention this change in radius in any of their literature. Maybe not surprisingly, they don't mention the accompanying reduction in dynamic load rating either.

 

[dinjin]

SKF catalogue further states:
In working to meet the targets of the SKF E2 performance class, the development team was limited by the lubricants currently available on the market today. The solution was the development of new grease formulas that adequately lubricate SKF E2 bearings and extend lubrication intervals. Results have shown that the new low friction SKF E2 grease, when applied to a shielded deep groove ball bearing, will last at least two times longer than conventional greases
used in similar standard bearings.

If that grease really does what they claim, then they could achieve the same life by using their grease and a greater radius. That is impressive if true.

 

[caoimhin1]

Depends on your definition of "conventional" grease I suppose. Doubling grease life is a big claim. (you can probably tell I'm not an SKF fan)

 

[dinjin]

It would and will be interesting to see if Timken tests SKF's new grease in some of their bearings. If it is true, it will be a great boon to the environment and save energy.
I hope it is not all sales hype.

 

[Hup]

For estimation of the ring radii I use manufacturer's information on the preload/stiffness relation. They usually state values of both for 3 preload classes in catalogues.

I have a mathematical model built according to Harris' book which calculates the axial force/deflection/stiffness curves for specified bearing materials and geometry.

Then I juggle with the ball/ring radii ratio (osculations)and try to fit stiffness values from the catalogue.

I assume:
- both inner and outer osculations the same,
- the radial position of rings is constant.
- that bearing makers use similar model for calculating the stiffness values in their catalogues.

It gives some idea how the radii look like, however I can not estimate if inner radius differ from the outer one

Cheers, H-up