Shielding Gas Post-Flow Time
Shielding gas post-flow time is the time during which shielding gas continues to flow after the arc is extinguished, to protect the cooling electrode and weld bead from oxidation. This prevents porosity and increases weld strength.
Physical-Chemical Mechanism of Action
After the arc goes out, the metal starts to cool down. Without shielding gas it would oxidize quickly and cause porosity. The post-flow time ensures that the shielding gas continues to cover the surface and prevents oxidation.
Metallurgical Relevance & Risks in Welding
A too short post-flow time (e.g., less than 10 seconds) can cause porosity in the weld and reduce strength. A too long post-flow time (e.g., more than 30 seconds) can cause unwanted changes in the structure and increased resistance.
Workshop Practice & Action Instructions
For most welding processes, a post-flow time of 15 to 20 seconds should be chosen. This is a good average that prevents porosity and minimizes unwanted structural changes. For special materials or processes, the post-flow time can be adjusted slightly, but always stay within the specified range.