Gas Welding Process

Gas welding is a method of joining two metal pieces (similar or dissimilar) together by melting and fusing their edges at the joint. It involves applying intense concentrated flame on the metal pieces (at the joint) until an area (of both pieces) under the flame becomes molten and forms a liquid puddle such that the molten puddle of one metal piece mixes up and runs together with the molten puddle of another metal piece.

The welding rod (or filler rod) may or may not be added to the molten metal puddle. The molten puddle on cooling and solidification results into a strong joint. The flame for melting the metal pieces is produced by burning various fuel gases.

Fuel gases used in gas welding include: acetylene, hydrogen, city gas, natural gas or liquefied petroleum gas (LPG). The gases (oxygen and fuel gas) are mixed in proper proportion in a welding torch which carries two regulators-one for controlling the quantity of oxygen and the other for controlling the quantity of fuel gas. The mixture of oxygen and acetylene is most popularly used for gas welding and produces temperature within a range of 3200-3300°C, which makes it possible to melt and weld all common metals. A filler rod (that also melts during welding) makes the joint stronger on solidification.

Types of Gas Welding Process

Gas welding includes all those welding processes in which gas flame is used as a heat source for melting metals.

It is further divided into three main types:

(a) Air-acetylene welding,

(b) Oxy-acetylene welding and

(a) Air-acetylene welding:

It involves the use of mixture of acetylene gas and oxygen from atmospheric air. A lower temperature flame is obtained. The process is used for welding lead or for brazing and soldering operations.

(b) Oxy-acetylene welding:

It is the most popular process because of higher flame temperatures (about 3200°C), A mixture of acetylene and oxygen is burnt for making flame. Both the gases are readily available in cylinders of different capacity. The combination is used for both welding and cutting of metals.

(c) Oxy-hydrogen welding:

It involves burning of the mixture of hydrogen gas and oxygen for producing flame. The hydrogen flame, however, does not attain that high temperature as obtained by burning oxygen and acetylene. It is with this reason that oxy-hydrogen welding is used for welding metals with low melting point such as aluminium, magnesium or for brazing purposes. Since hydrogen itself is a reducing agent (anti oxidation), its flame minimizes oxidation of metal during welding.

Hydrogen has no odour and is available in cylinders. Hydrogen connections need to be checked regularly as hydrogen makes a powerful explosion with air or oxygen. It is used for underwater gas cutting and welding at depth greater than 5 metres to 50 metres as hydrogen can sustain high pressures than acetylene.

Since the oxy-acetylene welding (and cutting) is the most popular method used in industry, this will be dealt with in detail in the following.

See More: Electroslag Welding(ESW)

See More: Thermit Welding Process

See More: Solid State Welding