Thermal Cutting:
The great heat release of the second reaction predominates over that of the first reaction that is supplementary in most cutting applications. The third reaction takes place to some extent in heavier cutting applications. Stoichiometrically, 0.29 m3 of oxygen shall oxidise 1 kg of iron to Fe3O4.
In real operations, the consumption of cutting oxygen per unit mass of iron varies with the thickness of the metal. Consumption of Oxygen per unit mass is higher than the ideal stoichiometric reaction for thicknesses less than about 40 mm, and this is lower for greater thicknesses. For thicker sections, the consumption of oxygen is lower than the ideal stoichiometric reaction because only part of the iron is fully oxidised to Fe3O4. Some unoxidised or partly oxidised iron is eliminated by the kinetic energy of the quickly moving oxygen stream.
Chemical analysis has illustrated that, in some instances, over 30 % of the slag is unoxidised metal. The heat produced by the speedy oxidation of iron melts some of the iron adjacent to the reaction surface. This molten iron is swept away along the iron oxide by the motion of the oxygen stream. The concurrent oxidising reaction heats up the layer of iron at the active cutting front.
The heat produced by the iron-oxygen reaction at the focal point of the cutting reaction (the hot spot) should be sufficient to continuously preheat the material to the ignition temperature. By allowing for the loss of heat by conduction and radiation, there is ample heat to sustain the reaction. In real practice, mill scale or rust frequently covers the top surface of the material. That layer ought to be melted away by the preheating flames to expose a clean metal surface to the oxygen stream. Preheating flames help to uphold the cutting reaction by providing heat to the surface. Also they shield the oxygen stream turbulent interaction with air.
Normally the alloying elements found in carbon steels are oxidised or dissolved in the slag without markedly interfering with the cutting procedure. When alloying elements exist in steel in appreciable amounts, their influence on the cutting process might be considered. Steels havening minor additions of oxidation resistant elements, such like nickel and chromium, can still be oxygen cut. However, while oxygen resistant elements are present in large quantities, alteration to the cutting technique is needed to sustain the cutting action. It is true for stainless steels. In the oxyfuel gas cutting, quality of the oxygen plays vital role. So it is essential to study the effect of oxygen quality on the cutting action.