[TowerTalk] Igniting Cadweld Powder

[David Gilbert]

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.