PPRuNe Forums - View Single Post - EC225 crash near Bergen, Norway April 2016
Old 20th Jun 2016, 02:34
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Arnie Madsen
 
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Originally Posted by turboshafts

Radial roller bearings outer races are heated up and pressed oval in a die when mounting the balls.
They would not crack with a hammer hit. The standard bearing material is 100Cr6 and has a surface hardness of around 60 HRC.

here are two interesting reports that gives a bit more insight in the materials used

https://www.google.de/url?sa=t&rct=j...,d.ZGg&cad=rja

https://www.google.de/url?sa=t&rct=j...,d.ZGg&cad=rja

And here it refers the material of the 332L2 planet gear outer race material:
Fractured Gear | Flight Safety Foundation
Subsequent testing determined that the particle was not silver or cadmium but 16NCD13 steel, planet gear outer race/gear material.
That is the type of info we need, thanks

I am a layman and speak as a layman but when a chip is produced in a MRGB it is not because a gear is too soft but because it is too hard (brittle)

Obviously soft steel gears would not be used because they would wear out quickly so they harden them to a point where they have a long life at the risk of being brittle and designers walk a fine line trying to find the best balance.

In an earlier post I gave some (poor) examples of witnessing bearing races shatter from impact and I did not make my point properly so I will try a different slant ...

If planetary gears were made of mild steel we could place them on an anvil and hammer them flat and they would never crack or break .... but if they were made of hardened steel they would never bend or distort , they would shatter into several pieces

The failed gears in these MRGB's are never deformed , they break into several pieces as the photos show.
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