Welding protective gas is to improve the quality of welding. It can be a single gas or a mixed gas. Mixed gas is a mixture of two or more different gases in proportion. Because there are two different kinds of gases mixing at the same time, it can provide additive protection for welding through composite action, and the effect is very good.
For example, the following commonly used mixtures have different effects.
Ar+O2
Adding a small amount of O2 in Ar for gas shielded arc welding can improve arc stability, droplet refining rate and weld bead formation. For example, Ar+ (1%-2%) O2 is often used in arc welding of carbon steel, low alloy steel and non-embroidered steel. The combustion-supporting property of oxygen can increase the temperature and fluidity of molten metal in molten pool. The molten metal can flow to the weld toe sufficiently, reduce the tendency of undercutting, and make the weld bead flat. For example, Ar+ (5%-10%) O2 used in carbon steel welding can improve the welding speed. Sometimes a small amount of oxygen is added to weld non-ferrous metals. For example, when welding clean aluminium sheets, adding 1% oxygen can make the arc stable.
Ar+CO2
This kind of mixed gas is mainly used for carbon steel and low alloy welding, not suitable for stainless steel welding. The mixed gas of Ar+CO2 can not only reduce the metal spatter caused by pure CO2 by using the property of Ar inactive wave, but also reduce the burning loss of alloy elements, improve the strength and impact toughness of welds and improve the corrosion resistance. Experiments show that the spatter rate reaches a low point at 80% Ar+20% CO2.
Ar+He
Ar+He mixed gas is mainly used for welding non-ferrous metals such as aluminium, copper, nickel alloy and active metals. Helium has the function of stabilizing spraying arc. The mixed gas can improve the voltage and heat of welding arc. It has a high degree of completion for the quality of welding seam. In Ar+He mixed gas, the proportion of He should be no less than 20% in order to play its role.
In addition, ternary gas mixtures are also popular in recent years. The welding effect of three different gases is better than that of binary gas mixtures.
For example, Ar+CO2+O2 can simultaneously have the protection advantages of the above two binary mixtures, and can be widely used. Carbon steel, low alloy steel and non-embroidered steel of various thicknesses can be used.
