The grounding of a tower often involves the use of several welds using
Cadweld or similar copper/aluminum thermite. One of the associated
problems is that the Cadweld powder can be tricky to ignite since the
reaction of the aluminum powder and the copper oxide is a reduction
process, and most means of getting something really hot (propane torch,
match, etc) are basically oxidation reactions. That's why flint-based
igniters or the electronic one used in some of Cadweld's One-Shot
systems are employed instead.
The latest ARRL Contest Update shows a couple of hams using magnesium
flakes and a campfire starter to fire off some One-Shots
(https://www.youtube.com/watch?v=l2REAd6YD6w) for which they elected to
not buy the ridiculously expensive Cadweld electronic igniter, but there
is a far simpler way to do it. A 4th of July sparkler works really
well. You can start the sparkler with a match or cigarette lighter, and
the sparkler will easily (and more safely) fire off the Cadweld powder.
A secondary advantage of using a sparkler is that it will fire off
Cadweld powder even if you don't have the finer starter material that
Cadweld supplies with each shot. The molds I typically use (#4 wire to
a 1/2 inch ground rod) require 65 grams of powder, and by keeping an eye
on eBay I can usually find 200 gram canisters selling for very little
money. Splitting them into thirds gives me what I need ... often for
less than $1.00 per shot ... but I lose the finer starting powder when I
do that and the sparkler will still fire it off.
By the way, it is also possible to make your own Cadweld graphite mold.
See http://www.ab7e.com/exothermic/AB7E_Homebrew_Exothermic_Mold.html
73,
Dave AB7E
p.s. I also once tried making my own Cadweld powder. The formulation
is simple ... just aluminum powder and copper oxide. I figured up the
right ratio by weight, bought some material off eBay, and mixed it up in
a rock tumbler. The problem was that the material I used was lab grade
and VERY fine particles, and when I fired it off it flashed like the
stuff photographers used in the 1800's ... lots of light and the copper
seemed to just evaporate. I assume that such fine material is what
Cadweld uses for starter powder, and that the bulk of the material is
much more coarse to slow down the reaction.
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