Gary,
Thanks for sharing the info on coatings !
I have been trying to find something suitable.
Bob
K6UJ
On 3/21/16 10:22 AM, Gary Johnson wrote:
An effective clear anti-corrosion coating for aluminum is class 3 chemfilm, a.k.a. Alodine
1500, which are all names for a particular chromate conversion coating. You more often see
class 1, which is the familiar gold color. The main difference is that class 3 is guaranteed
to be conductive whereas class 1 is nominally non-conducctive, though you can scratch your
way through it fairly easily. Both offer excellent anti-corrosion performance, though class 1
is somewhat better. We always specify the clear, conductive class 3 for enclosures featuring
EMI/RFI gaskets, where 100% shield continuity is required. Bigger plating shops could
probably handle long tubes of a Yagi and the process normally isn’t too expensive. You
can do it yourself on a small scale, too. So with class 3 chemfilm, you keep your shiny
aluminum while maintaining electrical connections even if you don’t attempt to abrade
it away.
While a clear *anodize* would be the ultimate in protection, the last thing I’d want
to be stuck doing is grinding away at it with silicon carbide paper for many square feet of
tubing in order to guarantee large-area connectivity. Sorry, it’s NOT that easy by
manual processes. You could have the parts masked during plating, however.
As for low observability, that’s my goal here in my CC&R area, so I paint my verticals. I use NATO non-spectral grey… Well, not
the official paint, but grey primer makes a darned good match to the fuselage of any military aircraft that I’ve worked around.
Non-spectral = flat = no glints in the sun. If I miss a small spot, it shows up like a beacon in the sun! Light grey has generally proven best
against the “average” sky, thus its wide military use. I prep the aluminum as follows: 1) buff with fine steel wool, especially if
it’s got any signs of dirt or corrosion 2) degrease with chlorinated solvent 3) wipe down with Aluminum Prep 79 (available from Aircraft
Spruce; it’s basically a phosphoric acid solution with surfactants; it activates the surface) 3) rinse with water (you should see few
water breaks) and let dry 5) paint with Rust-Oleum pro primer #7582838. Some of it has been up about 5 years and it’s good as new upon
close inspection. Haven’t been caught by the neighborhood Nazis. Yet.
Gary, NA6O
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