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Re: New CadWeld system [Re: homer] #194324 05/23/10 05:23 PM
Joined: Jun 2005
Posts: 124
poorboy Offline
Yes, and if you are working with old molds or do not take care to get all gaps closed in new ones, the whole thing becomes an exothermic cutting torch instead. It is not my favorite task, but it's always in the specs and crimps or mechanical means are not permitted.

Darn specs!!

Tesla, I sure would like to see that compression type catch on a bit more.

Last edited by poorboy; 05/23/10 05:28 PM.
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Re: New CadWeld system [Re: poorboy] #194326 05/23/10 07:03 PM
Joined: Mar 2005
Posts: 1,803
Alan Belson Offline
Can't see how electrical grade copper cable will be embrittled by a very fast casting of a copper alloy slug to weld two sections together. If anything, I'd expect the copper to soften by being annealed. From a Cadweld spec sheet I see that the thermit reaction is copper oxide [oxidant] and aluminum powder [fuel], with fluorspar flux, tin, vanadium and copper powder. In buried environments, a molecular bond has to be better than a mechanical crimp, which is subject to electrolyte corrosion at the connexion.

Wood work but can't!
Re: New CadWeld system [Re: Alan Belson] #194327 05/23/10 10:39 PM
Joined: Jul 2004
Posts: 9,439
gfretwell Offline OP
I agree with Alan, the only way this would harden the wire is if you got in a hurry and quenched it with water or something. If you did that I wouldn't even be surprised if it cracked.
If you just let it cool in the air it should be annealed.

Greg Fretwell
Re: New CadWeld system [Re: gfretwell] #194388 05/28/10 08:01 PM
Joined: Mar 2005
Posts: 1,803
Alan Belson Offline
Just to note: Pure copper, [as pure as that used for conductors at any rate] is not hardenable at all by the application of heat, nor by the rate of cooling, however fast or slow - even by quenching in water. It will start to anneal if heated to somewhere between one third and one half of its melting point in degrees kelvin [k], [ = 300DEG F - 760DEG F] depending on how much work hardening it has been subjected to. Work hardening is an effect caused by the distortion of the metal 'grains' by drawing, bending or hammering and is not to be confused with the hardening of steel, which is caused by specific alloys of carbon and iron retained in the steel alloy by supercooling. When copper is heated, distorted grains are simply 'healed' back to a more normal shape, [in layman's terms], so hardening is just not possible by heating.

It is possible to embrittle copper if it is heated for long enough and hot enough in the presence of oxygen, because copper oxide in the metal reduces its ductility or 'pitch'. This effect is sometimes seen when insulation is burned off to obtain scrap in large batches. Interestingly, annealed copper has a better conductivity than work hardened metal, [ the usual condition in drawn wire], so that the conductivity of the cable in the vicinity of a Cadweld would be marginally improved. An alloy of the Cadweld and the copper wire will very likely form, in a very thin layer a few atoms thick, at the boundary between the weld and the wire surface. This is what makes the good electrical connexion, and gives the improved resistance to corrosion when buried.

Wood work but can't!
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