The metal is rapidly oxidized, and slag is formed. This slag is washed out by the jet of oxygen.
The processes of cutting steel consist of the following reaction:
3Fe + 2O2 → Fe3 O4 + heat (27,000 cal.)
The successfulness of gas cutting process depends upon two factors:
(i) It employed only when the ignition (oxidation) temperature of the metal being cut is lower than its melting point.
(ii) The process involves ensuring that the melting points of the formed oxides are lower than that of the base metal itself.
Although acetylene is commonly used as a fuel in this process, other gases can also be used including butane, methane, propane, natural gas. Hydrogen is sometimes used as a fuel gas, especially under water to provide a powerful pre-heating flame.
Efficiency of Gas-Cutting:
Generally, there is a relationship between the speed of travel of the cutting torch and the smoothness of the cut edge. The higher the speed of travel, the coarser the cut edge.
A uniform wide slot, called kerf, is cut by the high pressure stream of oxygen. The marking on the sides of the keft are called drag as shown in Fig. 7.42. If the speed of travel of torch is high, the bottom cut lags behind the top cut and the drag lines are curved.
