Gas Post-Flow Time
The post-flow time is the time shielding gas continues to flow after the arc is extinguished. It protects the solidifying weld pool and the hot electrode from oxidation in the air.
Physico-chemical mechanism of action
After the arc is extinguished, the weld pool and the electrode are still warm. Without shielding gas, oxygen from the air would condense on these surfaces and oxidations would occur, leading to porosity and loss of strength.
Metallurgical relevance & risks in welding
A too short post-flow time (e.g., less than 10 seconds) can cause oxidation on the electrode and in the weld pool. This can lead to porosity in the weld and reduced strength. A too long post-flow time (e.g., more than 30 seconds) can lead to unwanted gases in the metal that can affect the microstructure.
Workshop practice & instructions
The optimal post-flow time is generally between 15 and 20 seconds. Make sure the shielding gas post-flow is set correctly to ensure a clean weld. Check the gas supply regularly and adjust as needed.