What Causes this Damage on Generator Shaft?

Have you measure the shaft for wear with a good quality micrometer? What does the bearing manufacture recommend for min max on shaft dia.? Especially if you are saying already there was vibration.

Is this the shaft where a ball bearing race was running, and should have been a tight press fit. The photo is of a shaft, and in my ignorance, I can't tell what I'm looking at.

You would help the forum if you show (a photo of) the bearing that was running on the shaft. If the inner race was running on this shaft, what is the clearance.

The periodic horizontal marks look like vibration hammer marks from the failing of the bearings, to me. The pitting marks looks to me like inconsistency in the steel matrix. I think I also see a little surface rust.

Now some motors or generators require at least one of their bearings to be non-conductive to break a closed loop from drawing excessive power. A failing bearing and this power robbing closed loop current path might induce similar marks as the circuit gets randomly interrupted.

Now, specifically which mark has you worried?

My old mentor called this Fretting corrosion. So now I'm confused if this is Brinelling.

In his context he was talking about Jeeps and other machinery hauled on railroad flat cars during WWII. And roller bearing failure from the vibrations caused rail gaps.

I don't (for once) claim to know about bearing wear and the finer points of metal wear.

But, it looks like a periodic pattern and MAY or MAY NOT be due to brinelling.

Just threw it into the mix.

Lyn:

I'm not challenging you on this, heck from reading wiki for either one, they may be indistinguishable, as results look the same. My career experience with vibration was material fatigue during shake-bake qualification. The only thing that had bearings were the cooling fans. Those failed as they were hall effect electrical commutated motors, and the parts would fall off the internal circuit boards. EG&G Rotron made killer product, and we could never find any other vendor that would pass the vibration test. We tried more then 5 years to value engineer their $350 price to a $20 version. 5 minutes of a 1 hour sine sweep (4- 15 minute sweeps from .01hz to 500hz) was the best we could do.

My skid-steer with hydrostatic drives is the only place I've seen this sort of shaft damage, (needle roller bearing on hardened shaft) and it makes the classic whining sound, so this was a no brainer as to cause.

Sorry for the off topic!

From the OP, are we looking at a shaft that had the inner race running on this, or is this some sort of needle roller bearing running on a hardened shaft (heat treat problem maybe).

Shaft speed?

Bearing diameter?

Bearing material?

Number of rollers?

Depending on the your maintenance periods, it is possible to have this wear induced through the electrical characteristics of the generator.

Motor slot rate induces mechanical vibration which will naturally appear as physical wear on the rotational surfaces.

It appears, to me, to be more due to the electrical nature of the generator set than brinneling, which is more mechanical in nature. They do, however, ultimately have the same results: corrective maintenance required.

i think you may want to look at a few things

why did the bearing come apart (it could be a power over bearing issue ) saw this in early test we did here with generation equipment we found power likes a easy path to ground same marks on a shaft here

now there is more then likely a shaft issue as it has damage now needs to be fixed looking at it i would think the bearring has spun a few times and the crush on the bearing will be not enough to hold it in place and it will spin as well if not fixed

If the image is of the shaft surface that contacts the inner race, then it is very unlikely to be brinelling - the compression forces have to be quite low.

I am not familiar with images of electrical erosion but I could not conceive it would produce such a regular pattern.

A general impression is that there is wear/movement over the entire mating surface and that suggests to me that the race may have been sliding/creeping over the shaft, specially if it was subject to vibration, and out of all this some form of fretting corrosion seems likely.

The post did not indicate the time to failure of the bearing - if this was substantial, then the obvious hypothesis is that the bearing was due to fail and the shaft surface matter is of no matter.

My experience does not allow me to pass final judgement, but my guess is that this is not a major issue, and perhaps a little more interference would be a good thing.

This looks like a hardened & ground bearing journal. In my opinion the cause of the high spots on the surface are caused by an out of balanced grinding wheel when originally ground.

1. no one has said there are high spots.

2. no one would ever put this shaft in service looking like this right off the grinder.

3. Out of balance grinding wheel? Really? I don't think so.

Nobody has indicated which of the variety of marks on the machined or painted surfaces appear to be troubling. We don't even know if the machined surface is the support for a roller bearing, the contact area for a raced bearing, or the coupling to the engine of this generator. For all we know this could even be vestigial evidence that this shaft once had splines that were machined off.

We have another "hit and run" OP that provides us no feedback. I still like your idea that this is a brinelling failure. You gave the proper name for what I tried to describe.

Agreed.

My response to protoman still stands.

NO ONE would ever submit a shaft that looked like this as a freshly GROUND shaft surface.

The response, #13, is misleading and incorrect.

When I see the pits near the radius to the bearing mounting diameter on the shaft, it makes me suspect the shaft has been weld built-up, machined, to a bearing diameter (ID). The chatter appearance may be due to weld hardness difference and may be the problem depending upon the type of bearing you want to seat on the shaft.

What was different about this installation from other installations? Do you think there is a correlation between those marks and a perceived vibration? How do you know?

Is this even a bearing race?

Electrical arcing on bearings looks like that, but then, so does brinelling, and a dozen other possiblilties.

Is this shaft always kept turning? I've seen large motors that were kept turning at all times to prevent brinnelling caused by the weight of the rotor pressing in one spot. It might develop a pattern similar to this if started and stopped on a continual basis.

Just my tuppence for consideration.

i am in the process of checking diameters at the moment. Will post more info soon. Bearing is a deep groove ball bearing BTW. This is a generator so is onjly stopped for service/ overhaul etc.

You might want to check for a loose poll on the generator rotor. Or the vibration dampener on the engine could be low on fluid. The marks look like a result and not a cause. The marks look like they were formed from a torsional vibration.

What is the make of the gen set?

I'm thinking somewhat the same thing. Seeing the pattern and knowing it's from a generator makes me think the poles are somehow causing that.

Poor Earth Ground.

The gentleman said that there was vibration so it is highly likely the type of marks are indicative of Brinelling. But we cannot eliminate Electrical arcs. I would try to eliminate both in the absence of more detailed information. I would take depth measurements to ensure that they are not deep and I suspect that they are not. Then a light polish and re-install new bearings.

Balance the shaft and service the grounding brush on this and other generators. These are almost always ignored until someone points out damages caused by improperly connected grounding brushes. Balance the other generator(s) also. When a rotating equipment stands for long periods while receiving vibration pulses for other vibrating equipment nearby, Brinelling will occur with rolling element bearings.

Yes, sorry i missed the Vibration comment, Brinelling makes better sense.

you can over analyze anything. get out the Emory cloth and dress the shaft...get it back online!