Thread: Hot Spindle Bearings

Originally Posted by Stustoys

Do you do your own wheel bearing work on your bike?

Stuart

Yep, do everything on my bikes, from the initial build onwards. All of the different types of wheel bearings use pre-load.

Pete

Pete
I have some maths on the preload of cup and cone bearings, but I cant remember where. I'll see if I can dig it up.
Stuart

Originally Posted by Pete F

G'day, from what you've said, and I highlighted above, it would mean that the races and/or the rollers would actually distort under the pre-load. I'm afraid I'm a little sceptical that occurs in hardened races at the sort of pre-load levels being discussed here, so would be very interested if you could provide more information if you know that to indeed be the case. One of my precision spindles is pre-loaded with a simple spring, and again I'd be very interested to find that spring had enough power to distort 4 precision bearings and achieve negative clearance.

I'm keen to be corrected if wrong, but my understanding is that the pre-load removes unnecessary clearance, to effectively "zero", along the axis that they are pre-loaded. However I believe there is still an extremely small amount of clearance still there due to the physical imperfections of the bearing and the requirement to function without overheating.

Again, I'd be keen to hear more if you believe that I'm mistaken.

Pete

Yes Pete your are correct when you say that preload (negative clearence) distorts the bearings, and maybe some of the other components also, depending on the setup used.

Have a good look around this SKF site, it has plenty if info on this topic-
Application of bearings - SKF.com / Products / Interactive Engineering Catalogue/Rolling bearings

Hi Metmachmad,

Thanks for posting that link, that all makes perfect sense now. The bearings compress elastically by an amount given by the bearing stiffness ( measured in kN/um) and the more compression (more preload force applied) means the heat generated by the compression increases. (same as the truck tyre example I gave earlier in this thread)

Here is an example of pre-load calculation, refer to the graphs for bearing stiffness ( elasticity)
http://www.dynaroll.com/preload-calculation.asp

Stuart,
The word I was looking for was not dimpling, but brinelling, which happens when
the preload gets too high and the bearings are deformed beyond the elastic limit.
And yes they do make little dents in the races, after which you chuck em out.

http://www.dynaroll.com/excessive-force.asp

There is another similar effect which can be caused by vibration, rather than excessive preload.

Regards
Ray

Originally Posted by RayG

There is another similar effect which can be caused by vibration, rather than excessive preload.

Regards
Ray

I think that it is called False Brinelling

you mainly get it in bearings that are, say in a electric motor, in transit via a steel boat.

they used to rotate the shafts of motors to prevent it happening while in transit

Apparently it doesnt happen on a truck due to the tyres (rubber)
They say it can also happen on a train

Thanks guys, yes I think Ray's analogy of a truck tyre is the most accurate from what I've now read, it's the contact points on the bearing that are distorted much like the bottom of a truck tyre as Ray said. I couldn't believe the whole bearing was "flattened", and indeed that's not the case. Also because there are different levels of pre-load, there will be greater or lesser yielding at the contact points, with virtually nothing on the spring preloaded surface grinder I mentioned (and I'd expect behaving much more like I mentioned by simply "flattening the peaks"), but considerably more on something like a lathe spindle. All very interesting, though I don't know if it was any assistance to the OP

Pete

Ray I think its a little rough to call the load of incorrect press fitting of the bearing "preload", but I see your point. Would be interesting to know that the max preload would be on a bearing used in a lathe headstock.

eskimo As I understand it False Brinelling first became a problem on the wheel bearings of new cars moved by rail(bikes had been putting up with it for years by then). Improved surface finish on the bear shells fixed the problem. (So the story goes)

Stuart

p.s. lol wiki backs me up. (I really added this for the second paragraph about "back up" motors/pumps, I thought might be interesting to anyone that has a system like that).

"The discovery of false brinelling is unclear but one story describes how, in the 1930s, new automobiles were loaded on to trains for delivery; when they were unloaded, some would show severe wheel bearing damage. On further inspection, it turned out that many wheel bearings were slightly damaged. The damage was eventually traced to rocking of the autos and the regular impact every time a railroad car wheel passed a track joint. These conditions led to false brinelling.
Although the auto-delivery problem has been solved, there are many modern examples. For example, generators or pumps may fail or need service, so it is common to have a nearby spare unit which is left off most of the time but brought in to service when needed. Surprisingly, however, vibration from the operating unit can cause bearing failure in the unit which is switched off. When that unit is turned on, the bearings may be noisy due to damage, and may fail completely within a few days or weeks even though the unit and its bearings are otherwise new. Common solutions include: keeping the spare unit at a distance from the one which is on and vibrating; manually rotating shafts of the spare units on a regular (for example, weekly) basis; or regularly switching between the units so that both are in regular (for example, weekly) operation."

I imagine that the discussion generated by my original post has been beneficial to more than just me, that in it's self makes it worthwhile.

Bob T

Hi All,

Interesting discussion, I'm not sure it has solved Bob's problem, but it seems to me that measuring the temperature is a simple way of checking if you've got the pre-load correct.

Stuart,
Further down that page, is the bit about pre-loaded bearings. Sorry, I should have highlighted it a bit better...

"Bearings are susceptible to shock or impact loads, especially when the axial play has been removed through preload. Dropping a preloaded assembly, or even placing it on a hard surface, can cause brinelling. It is recommended that assembly work surfaces are covered with a layer of shock-absorbing material."

Delicate little buggers....

Regards
Ray

It has been interesting to me Bob(sorry if we haven't fixed your problem yet)
I find bearings interesting because the worse ones you can buy(from good suppliers) are out of round by 0.0002".
One thing I just thought of which maybe confusing people. "preload" isn't metal to metal -.XXXmm there is still a film of oil between the metal parts you are squeezing it thinner. (or maybe I am the one that is confused)

Ray they are still talking about extra loads doing the damage not the preload. Also it would be nice if they mentioned what they consider a "small bearing". They also seem to be talking about balls, I assume rollers would have the same problem but the loads would need to be much higher. The loads a "normal" sized bearing can take must be pretty high. Think about the load that can be placed on the bottom head stem bearing or the tiny little suckers in clipless pedal spindles. As someone once said "if you think impact load is the cause of brinelling on a head stem put one together and start hitting it with a hammer"

Stuart

Originally Posted by Stustoys

One thing I just thought of which maybe confusing people. "preload" isn't metal to metal -.XXXmm there is still a film of oil between the metal parts you are squeezing it thinner. (or maybe I am the one that is confused)

I can only speak for myself, but personally I found the term "negative clearance" somewhat confusing as it implied (to me at least) the entire bearing was deformed in the process of pre-loading. I couldn't believe there was enough force being generated to do that, and indeed there isn't. Instead it is the very small contact point that is being deformed within the elastic limits of the material concerned. The analogy of the flat part of a tyre is an extremely good one, as the tyre as a whole remains essentially "round" however it is deformed where it contacts the road surface.

Pete