Since the production of heat is very necessary for welding metals, a mixture of oxygen and ethyne is burned instead of ethyne and air. When oxygen and ethyne are burned together, they fully burn and create a higher temperature than when air and ethyne are burned separately. The combination of oxygen and ethyne produces a very hot blue flame, while the mixture of air and ethyne produces a sooty flame, indicating that there are unburned particles and therefore less heat.
Why a mixture of ethyne and air is not used for welding?
- When ethyne is burnt in the air incomplete burning takes place and produce sooty flame due to the limited supply of oxygen present in the air.
- If ethyne is burnt in oxygen, it gives a clean flame with high temperature (3000 °C ) due to the complete combustion of ethyne.
- Hence, this oxyacetylene flame is used for welding, and it is not possible to attain such a high temperature with air. That is why a mixture of ethyne and air is not used for welding.