Page 69 - CITS - Welder - Trade Theory

WELDER - CITS

Chemistry of oxy - acetylene flame and types of

oxy acetylene flame and application

Objectives : At the end of this lesson you shall be able to
• identify the features and illustrate the different zones of an oxy-acetylene flame with their corresponding
temperatures
• explain the chemical reaction between oxygen and acetylene during primary and secondary combustion in the
flame.

Chemistry of oxy-acetylene flame:
Introduction: Oxy-acetylene flame is produced by the combustion of a mixture of oxygen and acetylene in
various proportions. The temperature and characteristics of the flame depend on the ratio of the two gases in the
mixture.
To know the characteristics and effects of oxy-acetylene flame a welder must know the chemistry of the flame.
Features of neutral flame: Oxy-acetylene flame consists of the following features by appearance.
Inner cone
Inner reducing zone
Outer zone or envelope
Different zone sand temperature: To know and make the best use of oxy-acetylene flame, the temperature in
different zones is shown in.

The greatest amount of heat is produced at just ahead of the inner cone called the hottest point or region of
maximum temperature.

Combustion ratio of oxygen and acetylene inflame
For complete combustion /burning one volume of acetylene requires two and a half volumes of oxygen.
Acetylene : Oxygen+O
1litre : 2.5litres

Equal volumes of acetylene and oxygen are supplied from the blow pipe to produce a neutral flame.
Acetylene : Oxygen
1litre : 1 liter (primary combustion)
So another 1.5 liters of oxygen is required for complete burning of acetylene.
The flame takes an additional 1.5 liters of oxygen from the surrounding atmosphere. (Secondary combustion)
Chemical reaction: 1 volume of acetylene combines with 2 1/2 volumes of oxygen and burns to form 2 volumes
of carbon dioxide and 1 volume of water vapors plus heat.
Primary combustion: It takes place in the inner cone right in the tip of the nozzle. (Fig 1)
In the bright nucleus:
C2 H2 ↑ 2C + H2 + Heat
In the inner cone - first burning stage:

2C + H2 O2 ↑ 2CO + H2 + Heat

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CITS : C G & M - Welder - Lesson 14-26 CITS : C G & M - Welder - Lesson 14-26