JPGandyman
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Thermite welding vs. exothermic welding edit
Seeing how you seem to be an expert on the subject of thermite welding, perhaps you can answer a long standing question: is thermite welding the same as exothermic welding? Thanks. Wizard191 (talk) 22:32, 17 May 2011 (UTC)
Just as it is the case that all shoes are footwear, yet not all footwear is shoes; so also, all thermite welding is exothermic yet it is not necessary that all exothermic welding is thermite. It may be the case that other exothemic reactions can generate enough heat for the purpose of welding. My welding specialty is track welding, including the use of a thermite compound for joining steel rails. Railway signal maintainers used an aluminothermic compound with copper for the purpose of bonding signal wires to steel rails by brazing.
I have used thermite for welding rails for 25 years. During that time I estimate that I have made between 1,000 and 2,000 such welds. None of my welds has failed under traffic. I have had fewer than 10 welding process failures, nearly always due to inadequate sealing or luting of the mold to the rail. For what it is worth, I have been acquainted with contract welders who have regularly made 500 thermite rail welds per year for several years. Of course, that is all they have done. In my case I was doing a wide variety of track welding projects during my tenure.
Part of your question may be addressed by recognizing a standard definition if there is one, for "thermite". Another issue is "exothermic".
In my own very narrow experience, thermite has been either of two products. The older formulation is a blend of aluminum powder and iron oxide, plus suitable alloying filler material to produce a steel alloy rather than simple straight iron. The other product, used in signal work is a mix of aluminum powder and some formulation of powdered copper "stuff" for the purpose of producing a quantity of molten copper or copper alloy which will braze to a steel surface.
Both of these products engage in a chemical reaction which releases a lot of heat, plus a mass of molten metal, plus some slag.
Any reaction which releases heat is an exothermic reaction, and so any process which can produce a weld as a consequence of an exothermic reaction could be exothermic welding. One example that I can think of is explosion welding. Another possibility might be oxyacetylene welding - another of my specialties. An OA flame produces great heat at a very high temperature as a result of a chemical reaction. When that heat is applied to a piece of metal and filler rod, a weld can be made. Depending on how strictly the term "exothermic welding" is applied, then OA welding qualifies. So might forge welding, when an exothermic reaction - the burning of coal, coke or charcoal is used to heat pieces of metal to a white heat. The pieces of metal are then placed together and struck with a hammer to finish the weld. In TIG welding or carbon-arc "torch" welding, heat is produced by means of an electric arc for the purpose of raising the target metal to a welding heat. An electric arc or plasma is not a heat-releasing chemical reaction, and would not be exothermic. Friction welding and resistance welding are common processes but neither uses externally applied heat and would not be exothermic. Some might argue that the term "thermite" is or was a trade name for the iron/aluminum product, and so the more general term "aluminothermic" would be better. JPGandyman (talk) 02:39, 18 May 2011 (UTC)