I have several large SAG mills that are experiencing repeated failures on the pinion bearings(6 of 16 bearings!). The pinions are driven at 180 RPM by 3500 HP Reducers. The coupling(DE) bearings are fracturing in the inner race, and the outboard(ODE) bearings are seeing fractured rollers. I have documented recent failures as initial "microdot" defects leading to fracture. Lubrication on these bearings is next to perfect, and I'm having a hard time believing it is a lube/contaminant issue as suggested by the manufacturer (Lube analysis performed monthly).
My question is, has anyone else experienced repeated failures like this on their bearings.
These are 24" I.D.bearings and VERY expensive.

Thank you for any suggestions.

Most of the cracked races I have ever seen have been related to overload or shafts and housings being out of round
Graham

Thanks Graham,
I have noticed also that there are striations on the outer races of the coupling bearings, as though there were no retaining pins.
If I look at it in the limiting sense, say a bearing WAY too small for the application, then of course the first things to go would be the rollers. Perhaps the bearings might be too small for this application. I am told there was never any problem until just recently however.
I will check the runout of the shafts and see if there is some problem here. As I have detected another fault, I will also be able to mic the housing and check for any defects there.
Thanks again, I will keep an update.