Shielding gases

Shielding gases

Shielding gases are covered under welding consumables. These gases are used to protect the weld pool from harmful atmospheric gases, their main use is to keep moisture away from the weld and to protect the weld pool from other chemical actions such as oxidation, etc. The atmosphere contains oxygen, nitrogen, and hydrogen which causes the most difficulty in welding iron content. When the metal is heated at the time of welding, the possibility of atmospheric gases entering the weld pool is increased and resistance is required at the time of welding as a barrier to protect the weld pool from such. unwanted objects 

Fluxes or gases are used to protect them, which can vary according to different materials.

Structure of Shielding Gases

Gases mainly used as shielding gases are inert in a structure that does not react chemically by exposure to other gases and creates a vacuum around the weld pool.Depending on the availability of gas, the shielding gases can be described as follows:

Shielding Gases

Argon(Ar)

In all inert gases, argon has been used extensively in fusion welding because it is more available. It is about 0.94% available in the air by volume, and even though this seems like a small amount, one needs only to remember that outside of 21% oxygen and 78% nitrogen, all other gases make up just 0.04%of  the atmosphere. Argon was first isolated in 1894 by Lord Rayleigh and Sir William Ramsay at University College London by removing oxygen, carbon dioxide, water, and nitrogen from a sample of clean air. In addition to its availability, argon has proved to be an excellent shielding gas because of its low ionization capacity. Argon releases electrons independently, which produces a more stable and quieter arc during welding. By 1957, Argon's symbol was "A", but now it is "Ar".

Helium(He)

Helium is the next most abundant inert gas, available for shielding gas for welding purposes. Helium is named for the Greek Titan of the Sun, Helios. It was first found in sunlight as an unknown, yellow spectral line signature, during the 1868 solar eclipse Janssen recorded the helium spectral line, a formalization of this element in 1895 by two Swedish chemists, Perodode Cleeve. The discovery was made by Nils Abraham Langlet. , Which found uranium ore, and helium emanating from helium. In 1903, large reserves of helium were found in natural gas fields in parts of the United States, which is today the largest supplier of gas.

It has a higher ionization potential than argon. it has a high electrical resistance, which means the voltage required to produce an arc in helium, is much higher than in other gases.

Carbon dioxide(CO2)

CO2 is a chemical compound composed of one carbon and two oxygen atoms. It is present in the Earth's atmosphere in low concentrations and acts as a greenhouse gas. It is a major component of the carbon cycle.

Atmospheric carbon dioxide is derived from many natural sources, including volcanic outbreaks, combustion of organic materials, and respiratory processes of living aerobic organisms; Man-made sources of carbon dioxide come mainly from the burning of various fossil fuels for power generation and transportation use. Carbon dioxide, as well as inert gases containing a small amount of oxygen, can be used successfully as a shielding gas as long as oxidizers are part of the GMAW filler wire.

When using CO2 as a shielding gas, the filler wire must contain deoxidizers such as silicon and manganese that readily react with the oxygen and prevent it from reacting with the weld metal.

Nitrogen (N2)

N2 covers 78% of the Earth's atmosphere. It is colorless, odorless, tasteless, and nontoxic, nitrogen is present as a non-useful gas at atmospheric temperature and pressure.

Nitrogen is used as a purge gas with stainless steel tube welding. Nitrogen can enhance plasma cutting, food processing, and heat treatment. Small additions of argon-based shielding gases can be used for stainless steel welding by the gas metal arc welding (GMAW or MIG) process.

Apart from this, other mixer gases are also used such as:

Hydrogen (H2) :

It is the lightest. Colorless, odorless, tasteless, and non-toxic, hydrogen is present as a gas at atmospheric temperature and pressure. 

Welding is usually mixed with argon for stainless.

Propane (C3H8):

Is a colorless, flammable, liquefied gas with a natural color odor. Oxy-propane flame temperatures are lower than those of acetylene and propylene.

other mixture gases are as follows:

• TRI-MIX – 66.1% Argon – 33% Helium – 0.9% Co2
• TRI-MIX – 66% Argon – 26.5% Helium – 7.5% Co2
• TRI-MIX - 90% Helium - 7.5% Argon - 2.5% Co2 
• ARGON 95% - 5% OXYGEN
• ARGON 98% - 2% OXYGEN 
• ARGON 99% - 1% OXYGEN
• ARGON 75% - 25% Co2 
• ARGON 80% - 20% Co2
• ARGON 85% - 15% Co2
• ARGON 90% - 10% Co2 
• ARGON 95% - 5% Co2