In carburising welding flame, there is a supply of _______ in the combustible mixture.

Explanation:

Carburising Welding Flame

• In welding, the carburising flame is one of the three types of oxy-acetylene flames used. The characteristics of these flames are determined by the proportion of acetylene and oxygen in the combustible mixture. Understanding the correct composition and application of these flames is crucial for achieving the desired welding quality and material properties.
• A carburising flame, also known as a reducing flame, has an excess of acetylene in the mixture compared to oxygen. This type of flame is rich in carbon and is identified by its three distinct zones: the inner cone, the intermediate feather, and the outer envelope. The intermediate feather, which is a luminous white zone, is longer than in other flame types, indicating the surplus of acetylene.

In the carburising flame, the combustion process occurs in two stages due to the excess acetylene:

• Primary Combustion: The acetylene reacts with oxygen in the inner cone to produce carbon monoxide (CO) and hydrogen (H₂). This reaction can be represented as:

  2C2H2 + O2 → 4CO + 2H2

• Secondary Combustion: The carbon monoxide and hydrogen produced in the primary combustion react with the oxygen from the surrounding air in the outer envelope, producing carbon dioxide (CO₂) and water (H₂O):

  4CO + 2H2 + 3O2 → 4CO2 + 2H2O

Applications:

The carburising flame is primarily used in the welding of high-carbon steels and other ferrous metals that benefit from a reducing atmosphere. It is also employed in applications where surface carburising is desired to improve wear resistance.