Chroming and hydrogen embrittlement

[jezzie]

Hello Everyone and Merry Christmas,

I did some research on rechroming and I noticed a term used called Hydrogen embrittlement if the items are not heat treated properly after rechroming  Is this something to be concerned about? I'm relating specifically to an entry in the work sheet on my J model where it says that the control rods were rechromed and reinstalled. Is this generally a problem with Mooney control tubes? How is it normally dealt with? Anyone had any experience or thoughts. I am waiting for an answer from my AME.

Thanks for you help

Eldon

 

[N601RX]

I looked into this a while back and basically any stressed part made from 4130 is affected.  It has to be immediatley baked for several hours after being chromed to prevent embrittlement.  Basically parts that are subject to shock and high stress should not be plated unless they have a known process in place to properly bake afterwards.  I think I remember seeing a FAA repair station around Tulsa that had an approved chroming process. 

You might check with United Plating in Tulsa, I had them replate all my engine hardware with a gold color CAD platting.  I don't think they offer chroming, but could probably give you the name of the shop that does.

 

[Bolter]

There are different kinds of chrome out there.  Depending on what you need, I can recommend 3 shops I spec for aerospace level parts used in my employer's gas turbines (NADCAP approved facilities).   The chrome we use is NOT the same as used for the applications you refer to, but these shops should cover what you need as well.  This reference comes without warranty.  Ask questions, do your own research, your mileage may vary...

Electrolyzing of Los Angeles, http://www.electrolizingofla.com/

Multi Chrome (also LA area), http://www.multiplate.com/

Armoloy of Connecticut, http://www.armoloyct.com

-dan

[eldeano]

Chroming any steel part is generaly not an accepted method on any structural parts.  The process for normalizing a chromed part is usually only used on the inside of cylinder walls, or on certain bearing surfaces that require extra hardness.  You can refer to the AC 43.13-2b Aircraft Inspection, Repair and Alterations Acceptable methods tecniques , and practices for further reference. It is available on the FAA website.  

However, when you debur the tubing for the rod ends you  zinc chromate the tube before reinstalling the end tubes, which is I'm sure what they meant, which is the accepted method.

http://www.experimentalaircraft.info/articles/aircraft-building-7.php