[TowerTalk] Penetrox; Scotchbrite & steel wool

Bill Coleman AA4LR aa4lr@radio.org
Fri, 17 Mar 2000 10:26:45 -0500

On 3/16/00 10:13 PM, Brad Anbro at n9en@hotmail.com wrote:

>In regards to cleaning antenna elements to insure a good electrical
>connection, and to give the material a "new-looking" appearance, I
>use the following method.
>First, I get some VERY FINE steel wool, wet the element piece down
>with water (to keep the friction to a minumum - the idea is to clean
>and polish the material, not to scour it!) and add a small amount of
>liquid dishwashing detergent to the steel wool. I then scrub the el-
>ement, moving the steel wool in the same line as the element (not
>twirling the element in the steel wool) and the steel wool removes
>the dirt & oxidation while leaving the material with a bright, pol-
>ished-looking appearance.

I wonder if this is advisble. The problem with using steel wool is that 
microscopic bits of steel will imbed themselves in the aluminum. The two 
dissimilar metals will already be in contact with (dirty) water, because 
that's what you used as a lubricant. This will actually ACCELERATE 
corrosion of the aluminum, due to the redox reaction with the steel.

In aircraft, if you want to remove corrosion, the most abrasive thing to 
use is a plastic scouring pad - Scotchbrite. Do NOT use steel wool, no 
matter how fine, or any other metals.

You can get aluminum just as shiny with Scotchbrite as you can with steel 
wool. It may just take a bit more elbow grease. Using power tools in some 
cases can cause problems, as with some aluminum alloys (particularly the 
6061-T6 often used in antennas). If used too long in one spot, such tools 
can cause localized heating which anneals and softens the metal.

>For the INSIDE of the element ends, where the next piece fits inside
>of it, I use various sizes of stainless steel bristle brushes, with
>detergent applied to the bristle brush, as in the steel wool.

Again, don't use steel, use a plastic brush, or scotchbrite. 

In any case, you can't remove all of the aluminum oxide off the aluminum 
anyway. Aluminum reacts very powerfully with oxygen to produce a thin 
layer about 50 molecules thick. Fortunately, Aluminum oxide is fairly 
conductive. This thin layer actually protects the aluminum from further 
oxidation. We just need to take steps to ensure that we don't encourage 
further  oxidation of the aluminum.

A friend of mine has stripped a 1947 Ercoupe down to bare metal. He found 
some corrosion in the structural sandwich of the wing walk -- evidentally 
where water seeped in and stayed. Oddly, though, in the tail cone, he can 
find little or no corrosion -- even after being periodically exposed to 
the elements for over 50 years. Aluminum is pretty strong stuff. We're 
amused that the builders of the Ercoupe didn't use Zinc Chromate (a 
common anti-corrosion primer) anywhere in the airframe. They probably did 
not expect the plane to be around 50 years later! Zinc Chromate would 
probably have prevented the corrosion in the wing walk.

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@radio.org
Quote: "Boot, you transistorized tormentor! Boot!"
            -- Archibald Asparagus, VeggieTales

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