hardened gear failure

[rob768]

Hi all,

i am facing a failure of a gear box in which one of the gear wheels, which was originally nitrided, has been replaced by a carburized wheel. All wheels suffered serious damage and the gearbox is a wreck. I personally didn't think the combination carburizing and nitriding was a problem, but am i wrong there?
Any literature refences on this subject?

thanks
rob

 

[Metalguy]

Well-nitrided Nitraloy steel wears a lot less than carb. steel-that's why it's used for very highly gears such as in helicopters.

Sounds like the designer knew what was required---.

 

[rob768]

Metalguy,

The question is not which heat treatment is best suited for the application (in this case the gearbox is used in moderately loaded hydraulic system), but whether the combination nitrided wheel running against a carburized (instead of 2 nitrided wheels, as was the original condition) can be a problem. Is that combination a potential problem, or not?

I agree with you on the superb properties of nitreded steel with regards to wear and seizure problems (but not with regards to pitting resistance of root fatigue fractures).

 

[Carburize]

There should be no problem running a carburized gear in place of a nitrided gear in terms of pitting or bending strength.
I disagree with Metalguy regarding helicopter gears - all the ones I know are carburized when ever possible and it is only when carburizing is ruled out because of issues such as unacceptable levels of distortion on very thin section components that nitriding is substituted as a second choice alternate. There is clear evidence that nitrided gears are far less tolerant of occasional high random loads than carburized gears and for this reason there range of application tends to be more restricted.

 

[TVP]

The Mechanical Components Branch of NASA's Glenn Research Center has some good information on durability of gears, including those for helicopter gearboxes. Use the following link for more information:

http://www.grc.nasa.gov/

http://WWW/5900/5950/Publicat.htm

 

[rob768]

thanks all, you confirmed what I thought but wasn't sure about