Oxyacetylene Welding
Processes
Oxyacetylene Welding (OAW)
When gas welding derives the heat from the combustion of a fuel gas such as acetylene
in combination with oxygen , then the process is called as oxy-acetylene gas welding
The fuel gas generally used is acetylene because of the highest temp generated in the
flame( up to 3500 0C )
The other useful fuel gases used for gas welding are
Propylene ( C3H6 )
Propane ( C3H8 )
Hydrogen ( H2)
Natural Gas ( CH4 + H2 )
Production of Acetylene
(C2H2)
•Virtually all the acetylene distributed
for welding and cutting use is created
by allowing calcium carbide (a man
made product) to react with water.
CaC2 +2H2O  C2H2 + Ca( OH )2
Oxyacetylene Welding
Figure : A typical oxyacetylene welding
operation (OAW).
Two stage chemical reaction of acetylene and oxygen:
First stage reaction (inner cone of flame): Oxygen & acetylene in nearly
equal proportion by volume burn in the inner white cone & forms carbon
monoxide , while the hydrogen is liberated
2C2H2 + 2O2  4CO + 2H2 + heat
Second stage reaction (outer envelope): The CO & H2 produced
in the first stage further combine with atmospheric oxygen & give rise to
outer bluish flame & results in CO2 and water vapours
4CO + 2H2 + 3O2  4CO2 + 2H2O + heat
This CO2 acts as shielding gas to protect the weld from the
surrounding atmosphere
Combining above two equations :
2C2H2 + 5O2  4 CO2 + H2O
From above equations it can be seen that 2 / 5 th of the oxygen
necessary for complete combustion of acetylene is received from
the oxygen cylinder and rest from the surrounding atmospheric air
The oxyacetylene welding process uses a combination
of oxygen and acetylene gas to provide a high
temperature flame.
OAW is a manual process in which the welder must
personally control the the torch movement and filler rod
application
The term oxyfuel gas welding outfit refers to all the
equipment needed to weld.
Cylinders contain oxygen and acetylene gas at
extremely high pressure.
Typical Oxyacetylene Welding (OAW) Station
Regulator Hoses
• Hoses are are fabricated from
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rubber
Oxygen hoses are green in
color and have right hand
thread.
Acetylene hoses are red in
color with left hand thread.
Left hand threads can be
identified by a grove in the
body of the nut and it may
have “ACET” stamped on it
Flame Settings
• There are three distinct types of oxy-acetylene flames,
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usually termed:
– Neutral
– Carburizing (or “excess acetylene”)
– Oxidizing (or “excess oxygen” )
The type of flame produced depends upon the ratio of
oxygen to acetylene in the gas mixture which leaves the
torch tip.
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Neutral and Oxidizing Flame Profiles
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Oxyacetylene Flames Used in Welding
Figure : Three basic types of oxyacetylene flames used in
oxyfuel-gas welding and cutting operations: (a) neutral
flame; (b) oxidizing flame; (c) carburizing, or reducing,
flame. The gas mixture in (a) is basically equal volumes of
oxygen and acetylene.
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Flame definition
• The neutral flame (Fig. 4-1) is produced when the ratio of
oxygen to acetylene, in the mixture leaving the torch, is
almost exactly one-to-one. It’s termed ”neutral” because it
will usually have no chemical effect on the metal being
welded. It will not oxidize the weld metal; it will not cause
an increase in the carbon content of the weld metal.
• The excess acetylene flame (Fig. 4-2), as its name
implies, is created when the proportion of acetylene in the
mixture is higher than that required to produce the neutral
flame. Used on steel, it will cause an increase in the
carbon content of the weld metal.
• The oxidizing flame (Fig. 4-3) results from burning a
mixture which contains more oxygen than required for a
neutral flame. It will oxidize or ”burn” some of the metal
being welded.
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Torch Used in Oxyacetylene Welding
Figure : (a) General view of
and (b) cross-section of a
torch used in oxyacetylene
welding. The acetylene valve
is opened first; the gas is lit
with a spark lighter or a pilot
light; then the oxygen valve is
opened and the flame
adjusted. (c) Basic equipment
used in oxyfuel-gas welding.
To ensure correct
connections, all threads on
acetylene fittings are lefthanded, whereas those for
oxygen are right-handed.
Oxygen regulators are usually
painted green, acetylene
regulators red.
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GAS CUTTING…
Manual Gas Cutting
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GAS CUTTING
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Ferrous metal is heated in to red hot condition and a jet of pure
oxygen is projected onto the surface, which rapidly oxidizes
Oxides having lower melting point than the metal, melt and are blown
away by the force of the jet, to make a cut
Fast and efficient method of cutting steel to a high degree of accuracy
Torch is different from welding
Cutting torch has preheat orifice and one central orifice for oxygen jet
PIERCING and GOUGING are two important operations
Piercing, used to cut a hole at the centre of the plate or away from the
edge of the plate
Gouging, to cut a groove into the steel surface
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