In the welding process, a mixed gas is used as a shielding gas instead of a single gas, which can effectively refine droplets, reduce spatter, improve forming, control penetration, prevent defects, and reduce porosity productivity, thereby significantly improving welding quality .
The commonly used welding shielding gas mixture includes binary gas mixture, ternary gas mixture and quaternary gas mixture.
Binary gas mixture has Ar-He, Ar-N2, Ar-H2, Ar-O2, Ar-CO2, CO2-O2, N2-H2, etc.; _p
p0ternary gas mixture has Ar-He-CO2, Ar-He-N2, Ar-HeO2, Ar-O2-CO2, etc.;
quaternary gas mixture for comparison It is mainly made of Ar, He, N2, O2, H2, CO2, etc.
The proportion of each component in various mixed gases can be changed within a large range, which is mainly determined by many factors such as welding process, welding material, welding wire type and so on. Generally speaking, the higher the requirements for the quality of the weld, the higher the purity requirements for the single gas used to prepare the mixed gas.
01
binary mixed gas
(1) an argon - oxygen
Add a small amount of oxygen to argon for MIG welding,It can improve the stability of the arc, improve the droplet refinement rate, reduce the spray transition current, improve the wettability and weld bead formation, such as Ar+(1%-2%)O2 is commonly used in carbon steel, low alloy steel, and stainless steel Jet arc welding.
Properly increase the oxidation of the arc atmosphere to increase the temperature of the molten metal in the molten pool and improve the fluidity. The molten metal can fully flow to the weld toe, reducing the tendency of undercut and making the weld bead Flat, such as Ar+(5%-10%)O2 for carbon steel welding, can increase the welding speed. Sometimes a small amount of oxygen is added for welding non-ferrous metals. For example, when welding a very clean aluminum plate, adding 1% oxygen by volume can make the arc stabilization effect good.
(2) Argon-carbon dioxide
1span1 for limited welding applications of carbon steel and low- steel alloys Ar-CO2 has less spatter than pure CO2, and reduces the burning loss of alloy elements, which helps to improve the strength and impact toughness of the weld. Adding a small amount of CO2 to Ar produces a spray arc like adding a small amount of O2. The biggest difference is that the critical current of the Ar-CO2 mixture is higher than that of the Ar-O2 mixture.
Ar-CO2 is the most widely used welding binary gas mixture in my country. In order to meet the needs of the market and regulate the quality requirements, the chemical industry standard HG/T3728-2004 Gas argon-carbon dioxide", which stipulates the purity of the raw material gas used in the preparation of the Ar-CO2 mixed gas, the technical requirements of the mixed gas product, test methods, inspection rules, etc.The ratio of
Ar-CO2 mixed gas can be almost any ratio. For example, it is common to add 5% CO2 gas mixture for all-position pulse MAG welding of low alloy steel thick plates. It is usually less oxidized than when 2% O2 is added, and improves penetration and has fewer pores;
Ar+ (10%-20%) CO2 is used for narrow gap welding of carbon steel, low alloy steel, all-position welding of thin plates and high-speed MAG welding; Ar+ (21%-25%) CO2 is often used for short-circuit transfer of low carbon steel Welding; Ar+50%CO2 is used for high heat input deep penetration welding; Ar+70%CO2 is used for welding thick-walled pipes.
(3) Argon-helium
Ar-He mixture is used for welding non-ferrous metals, nickel alloys, span3span3, such as aluminum and copper, regardless of its proportion With active metals, these gases use different combinations to increase the arc voltage and heat of TIG welding and MIG welding, while maintaining the beneficial characteristics of argon, which is especially suitable for occasions that require high weld quality. The amount of helium added should be at least 20% to produce and maintain the effect of a stable spray arc.
(4) Argon-nitrogen
When welding duplex stainless steel ,2%-3% N2 can be added to the mixed gas to improve the pitting and stress corrosion resistance of the joint.
(5) Argon-helium
H2 is a mixture of diatomic gas , which can improve the thermal conductivity of Ar-span-H2. Temperature, increase penetration capacity, increase welding speed, and prevent undercut. In addition, hydrogen has a reducing effect and can prevent the formation of CO pores. Ar-H2 mixed gas is mainly used for welding nickel-based alloys, nickel-copper alloys, stainless steel, etc. Generally, the hydrogen content should be controlled below 6%.
02
ternary mixed gas
(1) Ar - CO - oxo
contains a mixture of these three components. Generally, CO2 is below 20% and O2 is below 5%. The main advantage is that it can weld various thicknesses of carbon steel, low alloy steel, and stainless steel, regardless of the transition form. It is adaptable in many ways.
(2) argon-carbon dioxide-hydrogen
2M welding is 1% H2M volume fraction of stainless steel.The wetting of the weld is improved, and the arc is stable. Therefore, CO2 should also be less (volume fraction of 1%-3%), so that the amount of carburization is small, and good arc stability is maintained. This gas is not recommended for low-alloy steel, because it causes excessive hydrogen content in the weld metal, poor mechanical properties, and cracks.
(3) Argon-Helium-Carbon dioxide
2 Ar, which can increase the welding stability of the arc welding and increase the welding stability of the welding seam. And shape better. When welding carbon steel and low-alloy steel , adding He is used to increase heat input and improve the fluidity of the molten pool. He is also inert and has no effect on the burning loss of the weld metal oxide alloy.
For example, Ar+(10%-30%)He+(5%-15%)CO2 is used for pulse jet arc welding of carbon steel and low alloy steel; (60%-70%)He+( 20%-35%)Ar+5%CO2 is used for high-strength steel, especially all-position short-circuit transfer welding; 90%He+7.5%Ar+2.5%CO2 is widely used for all-position short-circuit arc welding of stainless steel.
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