Description of the Process

Oxygen cutting is more partial disintegration than cutting. It relies on the fact that when steel is heated in the presence of oxygen it will combine with the oxygen to form a magnetic oxide (slag).

The velocity of the oxygen has a scouring effect on the sides of the cut which removes particles of oxidised metal adjacent to the oxygen stream. To start cutting the steel requires to be at a temperature of approximately 900°C which is known as the ignition temperature. This is below the melting point of steel. A slight hardening at the surface of the cut edge is unavoidable, however this can easily be removed by a non-thermal process.(e.g. grinding).

Note : Iron and steel can be cut by the Oxy-hydrogen, Oxy-propane, Oxy-natural gas, and Oxy-acetylene

Equipment

Regulators

Regulators for cutting must allow a higher outlet pressure than the equivalent welding regulator:-

Oxygen regulators, for cutting, should read up to 14 bar.

Acetylene regulators, for cutting, should read up to 2 bar

(14.505 psi = 1 bar)

Cutting Torches

Torches for use with propane or acetylene gas may either be of the injector type or nozzle mix pattern, therefore torches are either:-

High pressure, where the gases are generally mixed in the cutting nozzle.

Low pressure, where an injector system is used.

Cutting Nozzles

High pressure nozzles usually have three seats, where as low pressure have two seats. Certain types of nozzles are made in two pieces, i.e. propane. The correct size nozzle for the plate being cut with the correct pressures is essential for good quality cutting.

Application

Oxy-fuel cutting can be performed on all plain carbon steels, but not on aluminium, stainless steels or cast iron. It is an extremely fast and versatile process and because of the ease of use accidents do happen.

Gases Used in Welding and Cutting Processes

Selection of the appropriate gas depends on :-

The compatibility of the gas with the material being welded

Joint type and thickness of material

Physical properties of the material

The welding process and mode of operation

If the material has a high thermal conductivity a shielding gas which increases the heat transferred to the workpiece should be used. For copper and aluminium, helium/argon mixtures are particularly useful as they reduce preheat requirements and improve penetration particularly on thicker sections. A table of the most common gases used is given below.

Name	Contents	Colour	Application
Oxygen	Oxygen O2	Black	Cutting/Heating
Acetylene	Acetylene	Maroon	Cutting/Heating
Propane	Propane	Red	Cutting/Heating
Argon	Argon Ar	Blue	Welding
Argoshield	Ar and CO2	Blue/Green	Welding
CO2 (Carbon Dioxide)	CO2	Black	Welding