[TowerTalk] Info/Advice re: Exothermic Welds

Wed Aug 22 03:42:43 EDT 2012

There are indeed LOTS of different configurations of exothermic molds, 
and the PDF file referenced below covers just about all types ... wire 
to wire, wire to vertical rod or rebar, wire to horizontal rod or rebar, 
wire to flat plate, etc.  Many of them show up on eBay, most in used 
condition but occasionally you can find new ones at reasonable prices.  
I've bought several types myself and all have been usable.  Wear is 
usually not too big a problem since you can shim out oversized holes 
with metal foil or wire, but of course stay away from cracked or broken 
molds.  It is not really necessary to buy the specialized clamps for 
holding the two halves of the mold together.  You can simply drill a 
couple of 1/4 inch diameter holes through the mold and secure them with 
long bolts/nuts.  It's a bit slower than the clamp, but way cheaper and 
easier to use it tight quarters.

The weld powder itself is also available on eBay, with the best deals 
usually being in the larger shot sizes like 150 grams or 200 grams.  A 
typical wire-to-ground-rod connection takes about 70 grams of powder, 
but if you're careful to save the starting material you can divide up a 
200 gram shot into three usable 65 gram shots.  I just took a quick look 
and it seems like the going rate would translate to about $2 per 65 gram 
shot.  You'll need some small foil circles to hold the powder in the 
ignition chamber before you light it off, but almost anything thin 
enough to melt quickly will work.  I think a few layers of aluminum 
kitchen foil would even work fine.

If you're ambitious or have a unique need you can even build your own 
mold from 2 inch thick graphite plate, rather more infrequently 
available on eBay.  Graphite is easy to machine using common woodworking 
tools, but be sure to protect your lungs from the resulting graphite 
dust.  You can see the steps I used to build a mold at 
http://www.ab7e.com/exothermic/AB7E_Homebrew_Exothermic_Mold.html.

A flint lighter probably works best to fire off the powder, but a 
propane torch almost never will.  The weld powder is composed of copper 
oxide and aluminum powder mixed in the right proportions, and the 
chemical reaction to get pure copper is an oxidation process.  The 
atmosphere immediately surrounding the flame from a propane torch is 
actually rich in hot hydrogen ... which makes it a reduction environment.

Lastly, I think it would be possible to make your own weld material but 
I found getting access to the right particle size to be very difficult.  
The oxidation formula is pretty simple ...

3CuO + 2Al  =  Al2O3 + 3Cu + HEAT (lots of it) + LIGHT (lots of it)

i.e.,  4.5  parts  CuO  to  1 part  Al  by  weight

I bought some lab grade copper oxide and aluminum powder on eBay (where 
else), but the grain sizes were so small that my homebrew weld material  
flashed almost like the stuff that photographers used to use back in the 
1800's and the copper literally ended up as a vapor.  My fervent advice 
would be to stick to the commercial stuff ... the coarser particle sizes 
are clearly meant to provide a more controlled reaction.

For what it may be worth ...

73,
Dave   AB7E

On 8/21/2012 2:21 PM, Dick Green WC1M wrote:
> The Erico website and their Cadweld catalog contain a wealth of information
> on their products:
>
> http://www.erico.com
>
> http://www.erico.com/public/library/fep/LT0355.pdf
>
> They even have a jig to prevent wires from moving.
>
> Until I looked through the catalog, I wasn't aware that they had molds for
> rebar. Had I known, I might have gone that route instead of using mechanical
> clamps on the rebar in my Ufer ground.
>
> I used many one-shot molds for grounding towers and my single-point ground
> with good success. Never had problems with molten metal leaking out of the
> molds, probably because I used very large gauge wire: stranded 1/0. Speaking
> of stranded wire, I think it's interesting that the conventional wisdom on
> this site is to use #2 solid conductor, while virtually all of the
> illustrations in the Erico catalog show stranded wire.
>
> Out of dozens of connections, I had ignition failures on maybe two or three
> charges. They pack the igniter dust into the bottom of the charge capsule
> and you have to be careful when dumping the charge into the mold not to mix
> the charge and the igniter. You should slowly pour the charge into the mold,
> then lightly tap the capsule to deposit the igniter on top of the charge. A
> good bit of igniter has to be directly under the hole in the mold cap to
> capture a spark from the flint gun.
>
> I also bought a 4-wire reusable mold for several spots where I had more than
> two wires converging. The mold takes a larger, more expensive charge, so it
> was still cost effective to use the one-shots for all the 2-wire
> connections, and a lot more convenient.
>
> When I did my second tower in 2007, Erico was selling a new kind of one-shot
> mold made of Styrofoam. It was very similar to a Styrofoam cup with a
> special lid with a hole in the middle to ignite the charge. I had all kinds
> of trouble with those molds, keeping them level, keeping dirt out of them,
> having them break, lighting the charge, etc. I had some ceramic molds left
> over from my first tower project in 1997, and had much better results with
> those. Looking through the Cadweld catalog, it appears that Erico has
> discontinued the Styrofoam one-shots. Good!
>
> That said, when I first saw the One-Shot Plus molds, I thought they were
> made of Styrofoam -- they look exactly like the Styrofoam one-shots. But it
> appears that they're made of ceramic, and are designed to be used with their
> electronic igniter and new ignition system. That system would be great to
> have, but I'll bet it's much more expensive than the old flint gun --
> probably only a good idea if you have ton of connections to make.
>
> 73, Dick WC1M
>
>
>   
>
>> -----Original Message-----
>> From: ve4xt at mymts.net [mailto:ve4xt at mymts.net]
>> Sent: Monday, August 20, 2012 7:55 PM
>> To: ersmar at verizon.net; knowkode at verizon.net; towertalk at contesting.com
>> Subject: Re: [TowerTalk] Info/Advice re: Exothermic Welds
>>
>>
>> I would also recommend ensuring the wire is secured from movement before
>> letting off the charge.I had one wire get blown out of the mould by the
>> charge. The putty Gene and Jim mentions might hold it in, but a brick
>> over the wire to keep it from moving wouldn't hurt.
>> 73, kellyve4xt
>>
>>> From: ersmar at verizon.net
>>> To: knowkode at verizon.net; towertalk at contesting.com
>>> Date: Mon, 20 Aug 2012 19:14:58 -0400
>>> Subject: Re: [TowerTalk] Info/Advice re: Exothermic Welds
>>>
>>> TT:
>>>
>>>       I second Jim's recommendaton about using electrician's putty to
>>> seal the holes in the Cadweld Oneshot molds.  I didn't do that for the
>>> first shot I fired and lost most of the liquid charge into the dirt.
>>> The second and all subsequent charges went well for me after I used
>>> the putty, especially underneath the mold where the ground rod
>> penetrates.
>>>       As an aside, I had expected a lot of fireworks when the shot went
>> off.
>>> I was disappointed - it was mainly smoke and very little flame.  Stay
>>> upwind!
>>>
>>>
>>> 73 de
>>> Gene Smar  AD3F
>>>
>>>
>>> ----- Original Message -----
>>> From: "Jim Hoge" <knowkode at verizon.net>
>>> To: "towertalk" <towertalk at contesting.com>
>>> Sent: Monday, August 20, 2012 5:00 PM
>>> Subject: Re: [TowerTalk] Info/Advice re: Exothermic Welds
>>>
>>>
>>>
>>>
>>> Art,
>>>
>>> Cadweld is one product, made by Erico. Thermoweld is another. Erico
>>> calls their single use products Oneshot and yes, the ceramic mold can
>>> remain after the fact. One shots are cheaper up front because you are
>>> not buying the molds and the handles. A different mold is required for
>>> each different application, ie: one wire #4 to ground rod, 2 wire to
>>> rod, a #2 wire to ground, etc. I know Thermoweld makes products for
>>> flat strap to rod or plate. One note on the Cadweld Oneshots- the wire
>>> openings on the molds are a bit oversized and weld material can run
>>> out. If you wrap the mold with electrician's putty, it will remain in
>>> place long enough to prevent the runout. The thermite weld mix lights
>>> very easily with a flint igniter. I was surprised the first time I
>> used it.
>>>
>>> 73,
>>> Jim W5QM
>>>
>>>
>>>
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