Purging Gas
Back purge gas is an inert or reducing gas mixture that protects the back side of a weld from oxygen and prevents oxidation. It ensures a clean weld and improves the mechanical properties.
Physical-Chemical Mechanism of Action
Backing gas forms a protective layer on the back side of the weld, which displaces oxygen from the environment. This prevents oxidation and discoloration. Reducing gases like carbon monoxide can also keep the metal in a reduced state, leading to a finer grain structure.
Metallurgical Relevance & Risks During Welding
Without backing gas, the back side of the weld can oxidize and cause discoloration. This impairs mechanical properties and can lead to cracking. Incorrect selection or application of the gas can result in insufficient shielding, which in turn allows oxidation.
Workshop Practice & Instructions
Use backing gas at the correct concentration and pressure. Make sure the gas is directed directly at the back side of the weld. For highly oxidizing metals or at high temperatures, increase gas pressure and concentration accordingly. Continuously monitor the application and adjust as needed.