[TowerTalk] Al-to-Al

[Patrick Greenlee]

On 2/13/2018 8:47 PM, Kirk Kleinschmidt via TowerTalk wrote:
> "Not intended for use with aluminum where galvanic corrosion
> could be a significant issue".
>
If I saw comments from the MFG telling me to not use the product where 
galvanic corrosion could be significant I'd listen up.

Galvanic corrosion is another way of saying dissimilar metals corrosion. 
   If   A L L   metals in contact with each other are the same then no 
galvanic corrosion. I'd be leery of a powdered copper in a paste agent 
on an aluminum to aluminum or aluminum to xxxx joint.

Back when the big rocks were still hot I took a sabbatical and did some 
marine field service engineering.  (Commercial radiotelephone lisc with 
ship's radar endorsement) I saw lots of antenna installations where coax 
shields were connected to aluminum antenna mounts welded to the vessel's 
aluminum superstructure. Typically a stainless steel bolt would hold a 
tin coated copper terminal (ring or spade) to the aluminum antenna 
mount, sometimes with silicone caulk over the connection.  Galvanic 
corrosion ate big pits or made holes in the aluminum.  Improperly 
protected shield would be mush or gone and sometimes the terminals were 
eaten or nearly so themselves.

The longest lasting connections seemed to be with stainless bolts with 
stainless flat washers on both sides of the aluminum.  The ring or spade 
terminal would then only contact the stainless. Generous cover of 
silicone caulk over all exposed coax shield, crimp terminals, and all of 
the stainless mounting hardware.  YMMV  but this is what I saw.   Oh, 
some techs painted all exposed non aluminum components in the mix with 
liquid tape before covering with silicone caulk.  They used the GE 50  
year caulk, not the cheaper varieties.

Patrick        NJ5G