[BC] brazing

[Lamar Owen]

On Friday 20 May 2005 21:51, Milton R. Holladay Jr. wrote:
> The toughest thing that I've attached to is galvanized steel. Usually, it
> works to use a BIG torch and flow some brass rod onto/into the surface and
> silver solder the copper to that..........

Watch the zinc fumes brazing to galvanized steel.  Best to brush or grind the 
zinc off, and flow enough braze to cover the ground surface.  Then paint it 
afterwards to prevent rust.  Same thing is true brazing to brass (rather than 
bronze).  The zinc can boil out of the alloy, and create all manner of 
problems  (for your health!).

For a joint that is a single-step, use borax flux and 45% silver-copper braze 
that contains no phosphorus.  Yes, the $35 per ounce stuff.  This way, you 
can use minimum heat (to prevent boiling off all the zinc) and still get a 
good braze.  Or you could braze a strap to a piece of square steel stock, 
then weld to stock to the galvanized steel portion.

Either way, you don't do this to a tower leg; the heat of the operation is 
just simply too high for safety; one of the lessons of the WTC disaster is 
how weak steel really can get at temperatures well below melting.  Welding or 
brazing to a tower leg is something only a certified professional weldor 
should or could do, and only under the supervision of a properly licensed 
professional engineer who is willing to seal the work (putting his liability 
on the line).  And even then I'd be really really leery of having it done.  
Better to bolt and clamp or use other mechanical means of attachment.

In the case of WGCR's sea containers, we brazed 0.062 strap to the galvanized 
frame to ground the outer shell of our two refrigerated sea containers (see 
the BE Radio archives for the sidebar I did on those containers a few years 
back).  We used $75 worth of Silvaloy 45 to do the job, and it has lasted 
very well.  I have some pics somewhere of the joints underneath, as well as 
the joints I did to the generator frame and mount in one of the containers.
-- 
Lamar Owen
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
(828)862-5554
www.pari.edu