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PLASMA CUTTING AND GOUGING
Introduction
In flame cutting, the cutting torch with its high flame temperature of 3100 °C (5612°F) is used to heat the steel to its kindling temperature (ignition temperature) and then by introducing a stream of pure oxygen, to create a rapid oxidation of the steel (the steel
catches fire and burns to become a slag). The stream of oxygen, at high pressure, also assists in removing the material from the cut. Steel melts at 1535°C (2795°F) but can be ignited at 884°C (1623°F). This process is referred to as a chemical process
Cutting direction Heating to k indling tempe rature. Jet of pure oxygen leads to rapid oxidation and removal of slag.
Cutting nozzle Pre-heating flame Stream of pure O2
Base material
So why cannot aluminum, copper, stainless steel and those other metals be cut by this process? In order for a metal to be flame cut the following conditions must apply: 1) The melting point of the metal must be above kindling point (ignition point).
2) The oxides (rust) of the metal should melt at a lower temperature than the metal itself.
3) The heat produced by the combustion of the metal with oxygen must be sufficient to maintain the flame cutting operation.
4) The thermal conductivity must be low enough so that the material can be brought to its kindling temperature.
5) The oxides formed in cutting should be fluid when molten so as not to interrupt the cutting operation. Some metals have refractory oxides (sluggish heavy kind of oxides with high melting point).
Iron and low carbon steels fit all the above requirements and are readily flame cut.
Cast iron is not readily flame cut because the kindling temperature is above the melting point. It melts before it can be ignited. It also has a refractory silicate oxide, which produces a slag coating.
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Aluminum and its alloys are not possible to flame cut because its oxides have a higher melting point than the metal itself. Pure aluminum melts at 658°C (1216°F) but the aluminum oxides melts at 1926°C (3500°F) 443