Let's Talk Bearing Spring Rings

[minger]

OK, in bearings (particularly roller) often times there will be a "spring ring" around it. The ring acts to soften the support structure for the bearing. Ring is typically a thin ring with "pads" on both the inside and outside. They are staggered such to put the thin ring into bending when load is applied at a pad.

OK. So, when analyzing rotordynamics, the stiffness of this ring is crucial. We have been depending on a 50 year old study that we did, which gave us a correlation based on ring thickness, diameter and axial length. It is analagous to an equation which is printed in Roark, which looks something like:
[tex]
k = CEh\left(\frac{t}{D}\right)^3
[/tex]
Where C is a constant, E is the modulus of elasticity, h is the axial length, t is the thickness and d is the nominal diameter.

The Roark solution is for a pure radial load on the pads, whereas in a bearing situation, the load is applied in a global direction (i.e. x or y) rather than simultaneously radial. Our study basically modified that constant.

I was hoping someone else (I imagine you, Fred) have some experience with these things. We have some new experimental data that completely disagrees with our old experimental curve fit. Furthermore, I simply cannot get a numerical run to converge using standard contact (only bonded which severely over-predicts stiffness).

I cannot find a journal article, a design memo, anything else besides this old study that we have. I really really hope someone can shed some light on these things.

p.s. Attached is a numerical representation of the ring if you're having trouble imagining it.

 

[FredGarvin]

Hey Minger. We haven't used those in quite a while. We have been pretty good in having to need to use them. Of course, other issues had to be dealt with. I tried to talk with our rotordynamics guys to see if they had anything handy, but they weren't available (I don't think they ever work). I know I don't have anything readily available. I'll keep hunting and see what I can come up with.

Honestly, when I see experimental data that doesn't follow past trends like that, I take the time to look at the set up and the instrumentation first.

 

[minger]

Right, the problem is that our company has down-sized SOOooo much, that much of the resources that we had say 20 years ago are gone.

After a(nother) day of pulling my hair out, I was able to get some decent numerical results. The study that I referenced had the ultimate goal of designing a spring ring with a spring rate of 15,000 lbf/in. I was able to get a numeric result of 20k lbf/in. I then iterated until I got a spring rate needed for the new application.

Still looming is the inability to solve for the "new" rings that are being tested right now. They are significantly softer and perhaps numerically there are just issues with that converging. Unfortunately I still really need to be able to quantify these new rings. One task done, one remaining.

I appreciate the help Fred, but one question (if I may ask): What do you guys use now? Squeeze film dampers or something along those lines?