gear surface damage due to electrical discharge?

[rob768]

I am looking at a gear with a damage that resembles that of electicral pitting due to arc discharging. Is there anyone who has seen this before? I have seen it, but in bearing. The appearance is very similar, which makes me thinks this is electrical to.

 

[rob768]

Sorry, upload of the image didn't work. This link shows the photo/

 

[dinjin]

What type of application is this and what is the
rpm? Number of teeth in gear vs pinion?
What type of lubrication is used?

 

[rob768]

This is a marine gear box, reduction 4.5 something : 1. I have no idea about the grease, but the standard type (for this application) was used. It is the second damage in the application, and this one is some 4 months old.
Pinion shows some wear, but far less than the main wheel. No info on hardness, but should be approximately similar.

 

[rob768]

Sorry, I said grease, but that should off course be oil.

 

[dinjin]

Electrical pitting is possible in a gear set. Somehow you are going to have to find the source of the electric current passing thru your system and ground it. It is recommended that gear and pinions be of different hardness to also help or prevent small welding to take place between the two materials.

 

[unclesyd]

Is this reduction box lubricated off the engine lube or does it have s separate system with cooler?

This doesn't look like like electrical as it is to uniform and with a pattern.

Can we have one more photo to show better where the damage is located on the gear.

 

[rob768]

I added a second photo. The pattern is present over the full width of eacht tooth, evenly distributed and on the pressure side only. May also be scuffing, but i have never seen this in the pitch area only.

 

[rob768]

and here's the link...

http://files.engineering.com/getfil...0c68-42ba-9191-5ed203519bd5&file=IMG_0223.jpg

 

[unclesyd]

Your original analysis may have hit the proverbial nail. After seeing the second picture I may have to eat my words.
Here are some examples of "Frosting" caused by electrical discharge.

http://www.sohreturbo.com/damage-examples/gear-tooth.php

 

[rob768]

Thanks for the big help. Much appreciated.