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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
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