The attached picture is of a bearing journal of a pump shaft that had used a 6319 ball bearing. This plant has experienced a lot of bearing damage from their VFDs (electrical fluting), so with fluting on their mind they immediately attributed the appearance of the bearing fit to shaft currents.

I have not seen this shaft (only pictures) as it came from another plant, but the question posed to me was... "Is the pattern seen on the bearing fit fluting?".

From what I see, it just appears that the bearing was removed without heating or it had a very tight fit (perhaps too tight) thereby leaving the pattern seen in the photo. I can't imagine that fluting would reveal itself in such a manner.

Could I be missing something?

Chilled_Water_Pump_Shaft_Bearing_Fit.jpg (256 KB, 126 downloads)

You mentioned "journal", but there is no sleeve bearing involved here, just a rolling bearing, correct?

If yes, I agree with you. It would be solid electrical contact between the bearing inner ring and the shaft - no reason to get fluting at that location.

I would suspect that this finish was due to poor machining. Under the right (wrong) conditions the workpiece or cutting tool can vibrate and result in a finish like this. It's called chatter and there's information on it at this site. http://highspeedmachining.mae....ite/faq.html#chatter. When I worked as a machinist, this was never an acceptable finish. Since the inner race of the bearing is shrunk to the shaft, My concern would be that the raceway would mirror the shaft shape, and not be round.

Michel,

This does look an awful lot like electrical fluting. The only problem is that fluting occurs between the roller elements and the race. This pattern is on the shaft where the inner race is positioned. There is no movement between the shaft and inner race so I would expect if you are having current passage between these two it would appear as pits, not fluting.

Now... if we discount fluting, what could cause such a failure? It's hard to diagnose from a picture but some things to check might be the fit of the inner race onto the shaft, the run-out of the shaft (as someone else has already mentioned), run-out of the outer fit bore, or possibly machine marks but I doubt it since the rest of the shaft seems to be smooth. I would look at a possible loose inner race fit, it sort of looks like the race was moving on the shaft.

Good luck,
Charles

My comment is similar to those above. It looks like the journal was loose and was knurled to provide a tighter fit for the bearing. This is rarely (but sometimes) done at low volume manufacturers, but will often be done at some pump and motor repair shops.

Definitely not electrical fluting.

Sincerely,
Howard

Thanks for all the replies... All the input was greatly appreciated!

I agree with above posters that this is not fluting from electrical damage. Fluting occurs on active raceways only. I understand this is the ID mounting surface of a ball bearing.

Knurling is frowned upon by bearing manufacturers. Rule of thumb is to maintain at least 80% intimate contact on mount surface. Any less contact can result in movement (fretting) at the mount surfaces. If knurled, this surface shows only about 50% contact.