This section is from the book "Applied Science For Metal Workers", by William H. Dooley. Also available from Amazon: Applied Science For Metal Workers.
Thermit welding depends upon the chemical combination of certain substances which produce a great heat. It is particularly successful in combining broken parts of machines. The work is carried out by building around the two ends, a mold, into which the molten metal or steel generated by this process is poured. New metal is thus added to the ends and the parts are united.
 
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