A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

Question

Answer

Oxygen supports combustion and hence it provides the correct atmosphere for welding to be carried out effectively, which requires high temperatures. We can use air for this purpose also, but the oxygen content in air is less (21%) for the combustion to be carried out and to produce high temperatures for welding to be done.

Answer

This is due to incomplete combustion caused by limited supply of air. However, if ethyne is burnt with oxygen, it gives a clean flame with temperature 30000 C because of complete combustion. This oxy-acetylene flame is used for welding...

Answer

Introduction:
In welding, a mixture of oxygen and a fuel gas is used to produce a high-temperature flame for melting and joining metals. Ethyne, also known as acetylene, is commonly used as a fuel gas in welding due to its high flame temperature and good heat transfer capabilities. However, using a mixture of ethyne and air instead of oxygen can have significant drawbacks.

Explanation:

1. Flame Temperature:
- The flame temperature is a crucial factor in welding, as it determines the melting and joining characteristics of the metals.
- The flame temperature of ethyne and air mixture is significantly lower than that of ethyne and oxygen mixture.
- Air contains only about 21% oxygen, while oxygen itself is almost pure oxygen.
- The presence of nitrogen and other gases in air dilutes the oxygen content, resulting in a lower flame temperature.
- Therefore, using a mixture of ethyne and air would result in a lower flame temperature, making it less effective for welding applications.

2. Heat Transfer:
- Another important aspect of welding is the heat transfer capability of the flame.
- Oxygen supports combustion and promotes rapid heat transfer, allowing efficient melting and joining of metals.
- In contrast, air contains nitrogen, which acts as an inert gas and does not support combustion.
- The absence of oxygen in air would result in a slower and less efficient heat transfer, leading to poor welding performance.

3. Safety Concerns:
- Ethyne is a highly flammable gas, and its combustion with oxygen produces a very hot flame.
- However, when ethyne is mixed with air, the lower oxygen content reduces the flame temperature and makes it less stable.
- This can result in an unstable flame, which may cause welding defects, such as incomplete fusion or poor penetration.
- Additionally, an unstable flame increases the risk of flashback, where the flame travels back into the gas supply system, potentially causing an explosion.
- Therefore, to ensure safety during welding, it is essential to use a controlled mixture of ethyne and oxygen rather than ethyne and air.

Conclusion:
In summary, using a mixture of ethyne and air for welding is not preferred due to the lower flame temperature, reduced heat transfer capability, and safety concerns. Ethyne and oxygen mixture provides a higher flame temperature, better heat transfer, and improved safety, making it the ideal choice for welding applications.

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