Too loose would seem more likely to give rise to stress conditions necessary to bring about inner race cracking.

the idea of a too tight fit is the best scenario. but take a look at a few other things as well

the id of the race is it the same as the od oof the shaft?

was the shaft smoothed down with a whets stone before the bearing was set in place /

was the shaft or the bearing innner ring prelubed before the bearing was mounted?

what angle was the shaft end beveled at before the bearing was remounted?

after your cleaned up the shaft and before you returned it to the work site was it tested for bend using a dial indicator?

did you check shaft alignments?

a few years ago the problem of the rollers cages kept coming up like that so we looked at how the bearings were being mounted on the shafts of the crushers, turns out the quick way was being used.

whats the quick way? take a piece of schedule 60 pipe with a id. somewhere near outside race of the bearing, put the bearing at the end of the shaft then hammer the bearing on using the pipe as a driving flange. guaranteed race fractures.

'da ber

Applying pressure to the outer race while installing on a shaft?

Ouch!

My first thought is that the shaft is heating up in operation. The expansion of which does not match that of the inner race. AS mentioned elsewhere the fit of shaft to bearing (race) is very important. If the shaft gets hot it will always expand more than the bearing as the gap/oxice layer between the two prevents total heat transfer between the two.

Some people interference fit the two, that is they have .003 inch or less gap between shaft and bearing to lock the bearing in place. This is bad practice; if you can't use a collar (which can be shrunk fit over the shaft), use bearings with key locks or grub screws. You might consider whether it actually needs locking in place on the shaft at all.

Finally make sure there is no end loading on the bearing, that is the inner and outer races are out of alignment as this will crack one or other of teh races and wear the ball/rollers.

Hi,

if the ring is cracked axially then the above explanations are very likely, if the bearing is thermally expanded it is easy to over-stress the ring.

But there may have been an unintended notch on the ring that was causing the start of the crack: notch sensitivity in hardened chromium-steel is significant. If you want to be sure then post a good foto of the cracked surface.

And may be the hardening and tempering was not done properly or there was a hard (carbide) inclusion.

Highest quality ballbearings are made from twice CEVM steel (consumable electrode vacuum melted) that removes the soft inclusions as sulfides. Then filtered (liquid steel through ceramic sieves of 1mm pore size) to remove the bigger sized carbide inclusions. Aircraft, spacecraft, machine-tools get these bearings that are much too expensive for ordinary use.)

And there is the possibility that the crack was circumferential , I saw this in a situation of excessive overload in a planetary gear where the designers had forgotten about misalignment and about recirculating power in the planetary gear being higher than input power.

RHABE

On GM and Ford cars (at least the once I've worked on) the shaft and the race are tapered. When you install the bearing and then the brake rotor, then the outer bearings a washer and nut goes on last. You tighten them and spin the wheel then tighten and spin until you feel resistance and then back the nut off a little and install the cotter pin. However, with the straight bores you just tighten everything up and you are done.

Having said all that. I someone was use to installing the straight bore bearings and just tightened everything up and did not seat the bearings on a tapered shaft it would be easy for them to bind and break.

Some of the major reasons can be -

- shaft dia. is much larger than the tolerance for press fit i.e., n6 or p6 or s6.

- shaft alignment is not correct. If it is ball bearing, it can take misalignment upto about 2.5 degrees.

- shaft is getting heated.

- finally, does it crack with another new bearing also? If no then the earlier bearing may be spurious / duplicate.

The one thing that nobody appears to have addressed are environmental factors. Chlorides, hydrogen sulfide, hydrogen ions generated by corrosion, or pitting combined with fatigue all could have played a role. No mention of the environment this bearing operated in or any environmental upsets it may have experienced were noted. I assure you, toss a bearing into a concentrated hydrochloric acid bath and watch how long before it shatters from it's own internal stresses and you'll be convinced.

Evironment is one of the factors. But,if bearing is used in such corrosive environment then the shaft, key, rotor etc. will also get corroded, probably slightly before bearing race.

Not necessarily, heat treating is a huge factor in the speed of attack. The shaft/key/rotor are probably not hardened to around 60-70 HRc the way the bearing race likely was. Additionally, the bearing race likely has a much lower ductility which means that if there was a corrosion pit/flaw that formed, it would succumb to fatigue far faster than the rest of the assembly. Bearings are always going to be the weak corrosion link for that reason.

Question with proofs: What are some of the determining factors >faults< that will >could< cause the inner race of a ball bearing >assembly< to crack on a rotor >during service<?

Preliminary response:

Question is incomplete:

• Crack the first time?
• Crack repeatedly with (each) replacement bearing assembly?
• Nature of crack is unstated?
• Radial crack? Complete or incomplete?
• Transverse crack? Complete or incomplete?
• Single crack? Multiple cracks?
• ID or OD?
• Penetrating or superficial?
• Accompanied with tempering/burnishing/burning?

Thank you.

Determining "factor" is most likely accelerated fatigue due to heat. Could be due to "rotor" axle out of true...imparting continuous twisting moments on race due to precession-like oscillations in rotor axle.

(Note: by "determining" factor is meant [must be meant] the very last stress immediately preceding the crack event...the penultimate failure event backwards from which can be determined a failure mode sequence leading to the crack. Everything prior to that last instantaneous fault before crack failure would be deemed as predeterminant . . . as being likely in some degree to cause the crack eventually, but not determinantly so.)