What is a Shield/Shielding Gas in Welding?

Shielding gas is a gas that forms a shield around the arc and weld pool in welding. It protects the weld from atmospheric contaminants, such as oxygen and nitrogen. shielding gases can be either inert or active. Inert gases, such as argon and helium, do not chemically react with the weld or base metal. Active shielding gases, such as carbon dioxide and oxygen, do react with the weld to form a protective slag on the surface of the weld.

What is shield gas used for?

Shielding gases are used in all types of welding, including gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), flux-cored arc welding (FCAW), and submerged arc welding. The type of gas used depends on the welding process, the materials being welded, and the desired properties of the weld.

What are the most common shielding gases?

The most common shielding gases are:

Argon (100%): Used for GTAW of non-ferrous metals, such as aluminum, magnesium, and stainless steel. Argon is also used for GMAW of aluminum and stainless steel.
Helium (25-75%): Used for GTAW of non-ferrous metals, such as aluminum and magnesium. Helium is also used for GMAW of aluminum.
Carbon dioxide (20-80%): Used for GMAW of all metals. Carbon dioxide is the most commonly used gas for welding mild steel. It can be used alone or in combination with other gases, such as oxygen or Argon.
Oxygen (5-25%): Used for GMAW of all metals. Oxygen can be used alone or in combination with other gases, such as carbon dioxide or argon.
Nitrogen (0-5%): Used for GTAW of non-ferrous metals, such as aluminum and magnesium. Nitrogen is also used for GMAW of aluminum and stainless steel.

Shielding gas mixtures are typically stored in pressurized cylinders and delivered to the welding machine through a hose and regulator. The gas flow rate is controlled by a flowmeter on the welding machine. The most common flow rates are 15-20 cubic feet per hour (cfh) for argon and 5-10 cfh for helium.

The composition of the shielding gas can have a significant effect on the quality of the weld. The gas must be properly selected to match the welding process, the materials being welded and the desired properties of the weld. Improper selection of the shielding gas can result in poor weld quality, excessive spatter, and porosity.

Shielding gases are typically used in conjunction with a filler metal to create a strong joint between two pieces of metal. The type of filler metal used depends on the materials being welded and the desired properties of the weld. For example, aluminum is often joined with aluminum oxide to create a strong bond that is resistant to heat and corrosion.