What are the two basic methods of arc shielding?
The correct answer and explanation is:
The two basic methods of arc shielding in welding are shielding gas protection and slag shielding.
1. Shielding Gas Protection:
This method involves the use of inert or active gases (or their mixtures) to protect the welding arc and molten metal from atmospheric contamination. Common gases used include argon, helium, carbon dioxide, and oxygen. The gas is directed over the welding area through a nozzle or torch, creating a shield around the arc. This prevents reactive gases like oxygen, nitrogen, and hydrogen from entering the weld pool, which could cause defects such as porosity, cracks, or weak welds.
- Inert gases (Argon, Helium): Typically used for non-reactive shielding, especially in processes like Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) for materials like aluminum and stainless steel.
- Active gases (Carbon dioxide, Oxygen): These may be used in small amounts with inert gases to stabilize the arc and improve weld penetration.
2. Slag Shielding:
This method relies on a layer of molten or solidified slag formed over the weld pool to protect it from atmospheric exposure. It is commonly used in processes such as Shielded Metal Arc Welding (SMAW) and Submerged Arc Welding (SAW). The slag forms from flux coatings or granular flux materials that melt during welding.
- Flux-coated electrodes (SMAW): The flux burns and creates gases that shield the arc while also producing a layer of slag that covers the molten metal.
- Granular flux (SAW): A layer of flux covers the welding area, melts into slag, and provides protection.
Explanation:
Arc shielding is critical to achieving high-quality welds because the molten metal is highly reactive at high temperatures. Atmospheric gases like oxygen and nitrogen can cause porosity, inclusions, and other defects. By isolating the weld pool, shielding methods ensure better mechanical properties, appearance, and durability of the weld. Each method is chosen based on the welding process, material, and desired results.