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An oxygen lance is a device used to melt or cut steel too thick to be cut with a conventional oxy-acetylene torch using a long alloy steel tube or pipe to feed oxygen under pressure to a preheated area. The oxygen lance achieves this cutting action by causing an oxidation and melting reaction of a preheated area of the material to be cut by directing the jet of oxygen onto it. The stream of oxygen then blows this area of melted steel away to form a cut. Steel and cast iron up to eight feet (about 240 cm) thick can be melted using an oxygen lance which is not possible using conventional cutting apparatus.
The typical oxygen lance is a very simple device which consists of a alloy steel tube with an inside diameter of 0.15 to 0.25 inches (about 3-6 mm), a specially designed long reach oxy-acetylene torch, an oxygen source capable of supplying a constant 40-50 PSI (2.7-3.5 bar) flow to the lance, and suitable fire proof safety equipment. The lance tube itself should be as long as is practical since it is steadily consumed during the cutting process and should keep the operator at a safe distance from the cutting area.
The cutting procedure is also fairly simple considering the thickness of material that it melts. The edge of the section of steel is heated to a bright cherry red with the oxy-acetylene torch and the tip of the oxygen lance is then applied to this area. The pressurized flow of oxygen causes a vigorous oxidation reaction on the surface of the steel which, in turn, causes a peak in localized temperature sufficient to melt the material. The jet of oxygen also serves to blast away this melted material creating a channel or cut in the steel. This process creates an impressive shower of sparks over a considerable distance so care should be taken to ensure that workers and equipment are kept away from the cutting area.
If the material being cut is of nominal thickness then the oxy-acetylene torch can be removed after the cutting process begins. In the case of thicker materials, the torch should be used to constantly keep an area of preheated material preceding the oxygen lance. During the operation, the lance tube will be consumed by the intense heat at the cut point and should be discarded once it becomes too short to be safely used.
These characteristics of the oxygen lance make it a particularly efficient and cost-effective method of cutting steel and cast iron materials too thick to be cut with a normal oxy-acetylene torch. The oxygen lance should, however, not be confused with a thermal or thermic lance. That device operates on a similar principle but uses a bundle of iron and magnesium rods inside the lance tube to create a self-sustaining and extremely hot cutting flame.