I came up with this project in an effort to replicate industrially made thermic lances in a small, mobile form factor. In this way I can throw them easily in the toolbox of my truck for use on road trips or on the trail in case of emergency. Their use commercially is usually for demolition purposes as they have the ability to cut through incredible thicknesses of steel. Both because of the extreme heat they produce as well as their ability to oxidize and burn whatever material they are cutting, in addition to the simple melting action that would be provided by a torch.
The video I have embedded above will provide the clearest demonstration of the lance kit I have created, but I will also include some written descriptions in the following pages.
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Step 1: Principles of Combustion
The function by which a thermic lance works is the rapid oxidation of iron into Fe2O3, iron oxide (rust). The same reaction occurs when steel wool is ignited and spun on a wire, creating a large amount of sparks as molten iron is thrown into the air. In that case the steel is able to oxidize quickly enough to sustain a combustion reaction because it has been very finely divided into strands, creating a large amount of surface area to react with atmospheric air. A thermic lance has far less surface area so it requires a much higher concentration of oxygen to sustain combustion.
Step 2: Materials
Industrial thermic lances would usually use the oxygen supply from large cylinders made for oxy-acetylene torches, but the purpose of my kit is to be portable. For that reason I have chosen to use disposable oxygen bottles. These bottles are equipped with a reverse thread, made so to prevent someone from threading them into a torch or fitting not made for use with oxygen. To attach to these cylinders I purchased a fitting made to adapt them to a 1/4" hose output. These usually are used for certain aspects of homebrewing, so they may be available locally at a well equipped brewing supply store. I purchased mine on ebay.
A length of 1/4" vinyl tube is also necessary, and can be connected directly to the hose barb on the tank fitting.
The lances themselves are simply a 5/16" diameter automotive brake line, approximately 2-3 feet in length. I purchase them in longer lengths then necessary, then cut them in half to get two lances for a better value.
Step 3: Construction
Whether or not the brake line used for this project is purchased as a double length and cut in half, at least one end will need to be cut off to remove the flare. This will allow the line to fit snugly inside the 1/4" vinyl tube on the oxygen fitting.
Igniting a steel brake line is a difficult task, even with the assistance of pure oxygen. A commercially made thermic lance would typically require a secondary oxy-acetylene torch in order to produce a flame hot enough to get the reaction started. For my lances I realized that fine 0000 grade steel wool with the assistance of a pure oxygen supply would burn more than hot enough to get the job done. A small portion of wool is inserted into the open end of the lance to prepare it for use.
Step 4: Ignition and Use
The steel wool that has been inserted into the end of the line can be easily ignited with the standard flame from a lighter. If the oxygen supply is slowly turned on while the wool burns it quickly increases in temperature, enough so that the end of the brake line is able to catch fire itself. At this point so long as the oxygen is flowing the lance will burn from the end, allowing it to cut through whatever material it is directed against.
I have found this design to work very well. The primary concern is for safety, as using a vinyl tube to carry oxygen poses a very real risk of the tube catching fire, whether by a leak or a wayward droplet of molten iron. For that reason it is important to wear full safety gear, including welding gloves and mask. An oxygen rich flame has the ability to burn through any organic material quite quickly, even leather, so that can pose other risks. No one should attempt working with thermic lances of any kind without previous experience and training using oxygen supplied cutting methods.
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