yellow grease

[JeanMicheling]

Hello folks,

I just breakdown a spindle. On one side the grease (NBU 15) was white, which is the initial color, but on the other side, the grease turned yellow. Does someone know why? Overheating?

Thanks,

 

[unclesyd]

Generally the change in color of grease is due to oxidation. This process usually involves a temperature above the normal operating range.
You may have caught this at a good time.

After say that I've have seen greases with color indicators that tell one when to change the lubricant.

I would also check the manual to see if the proper grease was used and if they may have used two different lubricants.

 

[Tmoose]

I often call Kluber tech USA directly in New Hampshire. 1.603.434.7704. NBU 15 is excellent high speed spindle grease. They have a newer product that offers quicker run in, which is very helpful important for spindles running over 500,000 dN.

Was the discoloration towards the seal side? Did the bearing fail in some way, necessitating the rebuild?

 

[JeanMicheling]

There was a unique oval spal on the bearing closer to the tool. I'm still invertigating to find out what it is. Don't you think that if the grease would have turned yellow because it's overheated, the bearing raceways should be discolored? The raceways looked pretty clean, just a clowdy white path which is normal. You talked about oxydation, could water cause that?

 

[Tmoose]

I think Kluber tech support will offer some suggestions as to the normal level of discoloration.
Just thinking out loud, if the discolored grease is toward the seal, and not really extending close to the bearing, I'd wonder what snuck in the spindle nose.

I' be looking carefully for a local high spot under the spall. Only has to be 0.001 inch high.

Other threads point to some good bearing failure analysis info

 

[Tmoose]

"Only has to be 0.001 inch high."

Meant to say only has to be 0.0001 inch high