Why the mixture of ethyne and air is not used for welding though air is easily available. Instead, a mixture of ethyne and oxygen is used for welding.
In the process of welding, ethyne undergoes combustion and the heat produced in the process is used to melt the metals and join them together . In order to ensure that sufficient heat is produced, it is necessary that complete combustion takes place.
Since air is a mixture of gases in which nitrogen is the predominant gas , ethylene with air is not used for welding because enough oxygen will not be available to carry out combustion.
So, a mixture of oxygen and ethylene is used.