The most commonly used inert gas is argon. It is a colorless, odorless gas having an air content of 0.935% by volume and argon having a boiling point of -186 ℃ between the oxygen and the boiling point of hydrazine. Argon is a by-product of the oxygen plant's fractionation of liquid air to produce oxygen.
In China, bottled argon is used for welding. At room temperature, the filling pressure is 15 MPa. The cylinder is painted in grey and marked with the word "argon".
The chemical composition requirements of pure argon are:
total carbon amount≤0.001%;
Argon gas is an ideal protective gas, which is 25% larger than air density. It is beneficial to protect the welding arc during flat welding and reduce the consumption of shielding gas. Argon is a chemically inactive gas that does not chemically react with metals even at high temperatures, thus eliminating the oxidative burning of alloying elements and the resulting problems. Argon is also insoluble in liquid metal and thus does not cause pores.
Argon is a monoatomic gas that exists in an atomic state and has no molecular decomposition or atomic absorption at high temperatures. The specific heat capacity and heat conduction capacity of argon gas are small, that is, the absorption amount is small, the heat transfer is small, the heat in the arc is not easily lost, the welding arc is stable in combustion, and the heat is concentrated, which is favorable for welding.
The disadvantage of argon is that the ionization potential is higher. When the arc space is filled with argon, the ignition of the arc is more difficult, but the arc is very stable once it is ignited.