[R-390] Alodine and hexavalent chromium

[John KA1XC]

After Alodine is applied and dried I believe it's totally safe (as long as
you don't eat it). It is commonly used as a surface finish on all kinds of
aluminum parts or as a surface prep for painted aluminum to increase paint
adhesion, like on the R-39x dial bezel. It is a very, very thin coating,
usually 0.5 to 3 thousands of an inch, and is easily removed by sanding or
by phosphoric acid metal prep solution or a lye bath as Hank suggested.

If you are sending your pieces to an Alodiner are you sure you need to
remove what's already there?; they will probably throw the parts in an acid
bath first thing.

It IS something you can do at home, but aside from the cost of buying a
gallon and having it shipped, you need to practice a bit to get the coating
to be uniform and the correct thickness to match the other parts. (longer
soak or brushing = heavier coat = darker color). If you screw up the part
you can always throw it back in the lye bath and start over :^)  I've done
the R-390 IF coil cans, dial bezels, and a back panel with good results, but
it's not something I'd want to do frequently.

For *small* quantities of the stuff that are used for home projects I
wouldn't worry about disposal issues, but please don't throw the used stuff
on the ground. You definitely want to wear gloves to protect your skin (and
to keep hand oils off the prepped part), and it can permanently stain
anything it touches.

John

----- Original Message ----- 
From: <N4BUQ at aol.com>
To: <R-390 at mailman.qth.net>
Sent: Thursday, January 13, 2005 11:48 AM
Subject: [R-390] Alodine and hexavalent chromium


> I've been doing a bit more looking into getting the panels for my R390A's
re-alodined.  Turns out this stuff is hazardous as it contains hexavalent
chromium (chrome?).  Around here, you have to dispose of this stuff properly
so I might not be trying this at home after all.  Fortunately I've found a
place that will do the lot of parts for a reasonable price.
>
> This got me to wondering how hazardous it is to remove this coating.  Is
it safe to wet-sand the parts to remove the old coating?  Is the amount of
coating removed so small that it is insignificant?
>
> Just wondering...
>
> Barry - N4BUQ
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