[Milsurplus] [Vintage-Military-RADAR] Re: Mil Circular Material Questions

[Mike Hanz]

On Mar 28, 2014, at 10:13 AM, "J. Forster" <jfor at quikus.com> wrote:
 I think the alloy has more Mg in it
> than current alloys, hence the corrosion issues.

I don't think so, John.  Mg darkens quickly in alloys with Al, and I haven't noticed that characteristic with the Cannon connectors in question unless they have had a very hard environmental life...then even Al darkens.

>> The castings
>> respond well with glass bead blasting...perhaps a gem tumbler would
>> provide the same effect but I would suggest doing only one at a time.
> 
> Well, I'd really rather not have to remove the connectors from the
> chassis. That's the nexus of thye matter. I'd like to find a way of
> cleaning off the corrosion in situ.

Sorry, I thought you were asking about loose connectors.  I'm afraid you're outta luck for anything easy, though the wired inserts can be removed from the shell fairly easily with a dental tool.

>> The bead blasting is the original finish, and it does present a more
>> reactive surface to moist air, but aluminum has a self-anodizing
>> characteristic over time.
> 
> Yes, it self-passivates. Anodizing also creates an Al2O3 film, but thicker
> and faster.

Having worked in a plating business in college, I do seem to vaguely recall such....:-)

>> The nut rings appear to be extrusions that are then fully machined, based
>> on their bright original condition.  I use a very fine wire brush on them,
>> followed by immersion in aluminum etching solution available from a
>> professional paint supplier.
> 
> The etchant is either NaOH or KOH most like;ly...  both strong alkalis.

Some are, but I prefer the phosphoric acid based specialty brands.  FWIW, mIne is Sherwin Williams Dual-Etch Metal Cleaner and Conditioner - W4K263.  A gallon lasts a long time since it is concentrated.  You do have to handle the parts with gloves...not so much for safety as to keep skin oils off the cleaned part until the self-passivation is substantially complete.