A group of welding processes that produces coalescence of workpieces by heating them with an oxyfuel gas flame. The processes are used with or without the application of pressure and with or without filler metal.

Oxyfuel gas welding is an inclusive term used to describe any welding process that uses a fuel gas combined with oxygen to produce a flame having sufficient energy to melt the base metal. The fuel gas and oxygen are mixed in the proper proportions in a chamber which is generally a part of the welding torch assembly. The torch is designed to give the welder complete control of the welding flame to melt the base metal and the filler metal in the joint.

Oxyfuel gas welding is normally done with acetylene as the fuel gas. Other fuel gases, such as methylacetylene propadiene and hydrogen, are sometimes used for oxyfuel gas welding of low-melting metals. The welding flame must provide high localized energy to produce and sustain a molten weld pool. With proper adjustment, the flames can also supply a protective reducing atmosphere over the molten weld pool. Hydrocarbon fuel gases such as propane, butane, natural gas, and various mixtures of these gases are not suitable for welding ferrous materials because the heat output of the flame is too low or the flame atmosphere is oxidizing.

In combination with pressure, oxyfuel gas flames can be used to make upset welds in butt joints without filler metals. This process is called pressure gas welding (PGW). In PGW, abutting surfaces are heated with oxyfuel gas flames and forced together to obtain the forging action needed to produce a sound weld. The process is ideally adapted to a mechanized operation, and practically all commercial applications are either partly or fully mechanized.

Since the OFW processes are primarily manual, it is essential that the welder be adequately trained and highly skilled for specific critical welding jobs such as pipe welding. The skill required by the welding operator for a fully mechanized PGW machine would be lower that than required by the manual welder, since the machine control, when set, performs the complete operation.

Oxyfuel gas welding can be used for joining thick plate, but welding is slow and high heat input is required. Welding speed is adequate to produce economical welds in sheet metal and thin-wall and small diameter piping. Thus, OFW is best applied on material up to about 6 mm (1/4 in.). Pressure gas welding is used to join sections up to 25 mm (1 in.) thick.

Oxyfuel gas welding equipment is versatile and can be used with most construction materials. The equipment involved is easily portable. For these reasons, the cost effectiveness is good. However, when parts are to be made in quantity, other welding processes are usually more suitable. See OXYACETYLENE WELDING.

 

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