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

The choice to use a mixture of oxygen and ethyne (also known as acetylene) for welding instead of ethyne and air is primarily due to safety and performance considerations. Let me explain the reasons for this choice:

Flame Temperature:

Oxygen supports combustion and enhances the flame temperature. When ethyne is burned with pure oxygen, it produces a very high-temperature flame (approximately 3,480°C or 6,276°F). This high temperature is essential for effective welding as it can melt and fuse metals together.
Control:

Welders need precise control over the flame temperature to ensure that the base metals are properly fused without overheating or damaging them. Using a mixture of oxygen and ethyne allows for better control over the flame temperature, which is not easily achievable with air as the oxidizing agent.
Safety:

Ethyne can burn in air, but the flame temperature produced by an ethyne-air mixture is significantly lower than that of an ethyne-oxygen mixture. Lower flame temperatures can make welding more challenging and less efficient.
Using an ethyne-air mixture can also lead to incomplete combustion, which may result in the formation of soot and carbon monoxide, both of which can be hazardous to health and safety.
Versatility:

An oxygen-acetylene flame can be adjusted to different flame types, including neutral, oxidizing, and reducing flames, depending on the welding requirements. This versatility is essential for welding various metals and achieving different welding results.
Cleanliness:

Welding with an oxygen-acetylene flame typically produces a cleaner and more controlled weld with minimal contamination from impurities or soot compared to using an ethyne-air flame.
In summary, while ethyne can burn in air, using a mixture of oxygen and ethyne provides several advantages in terms of flame temperature control, safety, versatility, and the quality of the weld produced. These factors make it the preferred choice for many welding applications.