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Online Catalogue last updated 17th of September 2023

Thermit Welding by Ethan Vial

cover photo

Back in the 1890's Dr. Hans Schmidt in Germany patented what he called "Thermit" which was a mixture of powdered aluminum and ferric oxide (not much more than rust). Once ignited the mixture burns ferociously. And hot? Incredibly hot! About TWICE the temperature needed to melt steel.

It burns in a special crucible/furnace, flows out the bottom, produces a lot of slag naturally, but also very useful steel. Back a hundred years ago it was routinely used for welding railroad track, broken crankshafts on huge steam engines, and many other things. These days you don't see it much, but there are firms still offering thermit. It might be a useful way to produce small steel castings needed for model making.

This is a collection of articles that ran in American Machinist magazine in 1919 covering all forms of welding which was a new field at the time. Their plan was to gather up these articles and publish a book. Here you get just those articles on the thermit process.

You get six detailed chapters covering the history, the fusion welding of heavy sections, welding crankshafts etc, welding new necks on large steel pinions, rail welding for electric railways, welding compromise rail joints, and welding of cast iron and other parts.

You learn in detail what kind of thermit to use, how to create a mold around the part you're welding or repairing, how to repair and set up the crucible needed, how ignite the thermit and make the "pour". The real trick in welding broken parts was in preparing them by aligning, cutting away some broken edges, and separating by a critical amount to compensate for inevitable shrinkage due to cooling.

One amazing example showed how a broken pinion gear so large it had to be brought in on a railroad flat car was repaired. The broken pieces were aligned, and a mold around the break fabricated. As much as a thousand pounds of thermit was ignited and allowed to flow into the mold. But! The only job of the thermit was to heat the broken ends. At 6000 degrees F the thermit softened the hard steel in seconds. Immediately a ladle of high-quality open-hearth steel was poured in, displacing the thermit, and then being allowed to cool for several days. The gear was a good as new. As much trouble as it was, the whole process was far faster and cheaper than manufacturing a new gear.

Most of this is bigger than anything you and I want to do: welding an ship's rudder or anchor. But you quickly see how powerful this technique was. And it's something we may be able to use to produce steel without an arc furnace.

Code No. 014494, 96 pages, $17.00

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