RE: [TowerTalk] Site Grounding

[Jim Lux <jimlux@earthlink.net>]

At 02:33 PM 10/21/2003 +0000, kb9cry@comcast.net wrote:
> I believe a brazed joint will pop open if hit with a lightning induced 
> surge.  Phil  KB9CRY
> > If you have but one chance to bury in the ditches and you're pressed for
> > time, go get some copper plumbing pipe.  Brazing the joints would be best.
> >
> > 73,
> > Tony
> >

Hard to imagine a scenario where that would happen. It would require that 
the IR losses in the joint be high enough to melt the braze material.

By the way, I'm not sure what you really want here is a brazed 
copper/copper joint.  Brazing is usually used to refer to a joint using 
brass or copper to join, e.g. steel, making use of the fact that the 
melting point of the brazing metal is lower than that of the materials 
being joined (otherwise it would be called "welding", no?)
Using brass or copper to join copper would require getting the bond metal 
almost as hot as the MP of the metal being joined.  Why not just use 
thermite (exothermic welding) and make it a real copper/copper/copper bond, 
in that case?

If you want a good structural join of copper (as opposed to good 
electrical, but poor structural) you probably want hard solder (e.g. silver 
solder) as opposed to soft solder (e.g. tin/lead eutectic).  Even a high 
tin solder (e.g. 50/50 as (formerly) used in plumbing) will be stronger 
than the higher lead content eutectic 63/37 which melts at a lower temperature.

Silver soldering will provide a good structural bond, and have good 
electrical properties as well.  Yes, you'll need a HOT torch to do it. I 
haven't tried it with straight MAPP, but oxy-acetylene and oxy-MAPP both 
work quite well.  For precision work, oxy-hydrogen is popular, because 
there's no soot. There are also a wide variety of hard solders available, 
so a bit of time with the catalog/data sheets might be worth while.

Jim, W6RMK 

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