Originally Posted by
Arnie Madsen
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.
From the REDL report the epicyclic planets are made of the following steels: Gear/outer raceway 16NCD13, rollers M50, inner race M50.
The REDL gives the reasons for the different materials and details manufacture.
From experience a normal spalling failure would start on the inner race if all of the materials were the same due to the increased loading of the inner race. The gear/outer race on the 225 planet is a "softer" material due to the load cycle of the gear teeth, therefore there is a tendency of the 225/332 planets to start with outer race spalling