Plain Bearing Damage

[bcruxen]

We've stopped our eletrical generator for maintainence. It was made a repair using welding. The grabs were put on the main structure of the generator. The repair was made. Then we started up the machine, and there was a failure in the bearing. It looks like the babbit is completely gone because of melting. What could have caused this problem? Is it possible that because of the weld electrical current the babbit material maymelted and then during start up of the machine it could have collapsed?

I would appreciate any help,
thank you
bcruxen

 

[TheBlacksmith]

It would depend on where the welding site was relative to your "grabs" (ground lead). If the lowest resistance path was through the bearings, you may have damaged them. We require the bearings to be protected from any current during repairs or hi-pot tests, etc.

Blacksmith

 

[GregLocock]

I've often heard of this problem, down on the farm we routinely took care to avoid this. I would have though a trained welder would know to do this.
Cheers

Greg Locock

 

[bcruxen]

I'd like to ask if someone has references about plain bearing damage due to eletrical current coming from a welding process that was made at the generator's structure.

thanks in advance!
bcruxen

 

[MikeMilburn]

Sorry, I don't have any references just have seen it happen more than once, electricity will take the path of least resistence be it thru the frame or thru a bearing.
The last time I've seen this was a bearing on a loader arm, lasted about a week before the bearing went bad, you could still see the arc burns on the surface. I get a kick out of people that stick the ground on one end of the machine and start welding at the other, a costly mistake.Mike

 

[moseley]

Rule of thumb never ever ground through a bearing! Or any other rotating equipment.

 

[bobc]

i have seen this same thing happen many times in the last 40 years.
this is more likely to happen when the framework of a building is used as a ground source, millwrights or weldors often overlook a connection between the building and the object they are working on, such as a lift chain or cable connected to a crane used to position the object. a poorly placed ground will fail and the current travels back to the welder via the crane and building structure damaging rolling components.
i have seen machine beds also damaged in the same manner. we always emphasize independent fixed grounds be placed as close to the weld area as physically possible and remove any connection to cranes or machine tools if possible, or the use of nylon lift slings.
once this is explained to the workers, they seem to check themselves and others automatically.
good luck with the training,
bob creely

 

[fubar]

VERY POSSIBLE AND NOT UNCOMMON. WE SEE THIS ALOT IN THE DIESEL DRIVEN GENERATOR AREA. THE SOURCE OF CURRENT CAN BE CARELESS WELDING, GENERATOR BEARING INSULATION FAILURE, STRAY (EDDY) CURRENT FROM GENERATOR, SHORTED TEMP PROB, ETC.. MOST DIESEL MANUFACTURERS SHOW FAILURES OF THIS TYPE IN THIER FAILURE ANALYSIS COARSE LITERATURE. CATEPILLAR, STEWART&STEVENSON, AND DETROIT DIESEL TO NAME A FEW. IT MAY SEEM STRANGE BUT WE HAVE FOUND THAT THE CURRENT BRIDGES THE GAP ACCROSS THE TIGHTEST BEARING AREA FIRST. ONCE THIS METAL IS DISPLACED IT MOVES TO THE NEXT SHORTEST GAP WHICH COULD BE ANY OTHER BEARING IN THE UNIT (DRIVE OR DRIVEN COMPONENT). I'VE SEEN SIGN'S IN THE GEAR TRAINS ON THE FORWARD END OF A DIESEL DRIVEN GEN SET.
I SUGGEST YOU TAKE A LOOK AT THE REST OF THE BEARINGS IN YOUR GEN SET PRIOR TO NEXT START. YOU MAY FIND MORE TO TALK ABOUT! GOOD LUCK.