On Apr 29, 2:38*am, wrote:
"lagagnon" wrote in message news:817062c5-

...





I am about to refurbish an old Hy-Gain TH3-Mk3 Thunderbird tri-band
yagi. This yagi has been used in a coastal environment and thus
the aluminum is slightly pitted and most of the connecting
hardware needs replacing.

I figure steel wool would work fine for the aluminum tubing, I
know how to test the traps, but I am wondering whether to use
stainless steel or galvanized hardware? Which would react least
over time with the aluminum? Also, I remember many years ago there
is an electrical joint compound stuff for using between the tubing
sleeves - can anyone please give me some brand names of this
stuff?

Any other ideas appreciated....

Larry VE7EA

Boy, the partial truths have been flying hot and heavy here. *Allow
me to try to explain what is right and what is wrong...

You do _NOT_ want to use steel wool. *Aluminum is anodic with
respect to steel. *When you use steel wool, you imbed steel fibers
in the aluminum as many have noted. *But what happens next is where
most posters are wrong. *The aluminum around the steel fiber
corrodes protecting the steel from rusting. *Thus your problem
becomes worse. *Eventually the aluminum corrodes enough that it no
longer makes good electrical contact to the steel and the steel will
rust — or else fall out of the pit in the aluminum. *You are left with
highly pitted aluminum.

I would suggest emery cloth, sandpaper, or a Scotchbright pad to
polish the aluminum. *I would avoid stainless steel brushes too as
most grades of stainless are even more cathodic than steel with
respect the aluminum. *Likewise avoid brass or copper brushes too.
For large areas, sand blasting works well if you use a fine sand and
not too much pressure.

As to hardware, I suggest hot-dipped galvanized bolts and nuts.
Zinc is slightly more anodic than aluminum, so neither material will
corrode much when in contact with each other. *Hardware with a heavy
cadmium plating is also suitable, but due to the toxicity of cadmium
it is a little harder to find. *Zinc-plated hardware offers minimal
protection because the zinc coating is so thin. *If the hardware is
used in an application where minimal strength is needed, consider
aluminum hardware itself.

There are many joint compounds on the market for joining aluminum to
aluminum. *Noalox and Penetrox are two common brands. *These
compounds are typically a petroleum grease containing zinc particles.
These particles are usually produced by spraying molten zinc and air
through a nozzle. *This produces small, irregular particles whose sharp
edges pierce the aluminum oxide surface film when the aluminum
pieces are tightly clamped together. *This produces a good
electrical contact, and the zinc is very compatible with the
aluminum from a corrosion standpoint.

Whatever you do, avoid any contact of copper with the aluminum.
Where the transmission line connects, be sure and heavily coat any
copper solder lugs with solder. *Try to keep a hot-dipped galvanized
washer between the lug and the aluminum.

Send me an email and I can send you some good articles on corrosion
that you might find interesting and informative. *My experience
comes from many years working in the chemical industry. *Even so, I
found the plant metallurgist to be a vital resource in material
selection for the instrumentation I designed.

--
73, Dr. Barry L. Ornitz *WA4VZQ
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Ive used anti-sieze compounds, they also are basicaly zinc and grease
and often more economical than the Noalox and Penatrox brands.
I have two of the mentioned antennas,one was given to me and the other
I bought at a hamfest. Apparently the weak link in these is the traps,
now I have two antennas that I cant get to work. The next time I move
which will probably be soon I may have a place where I can at least
use them for parts.


Jimmie