1. Definition CO2 gas shielded welding is a gas shielded metal arc welding method using CO2 gas with purity above 99.8% (volume method) as shielding gas. Short circuit transition, spray transition and pulse spray transition can be used for welding. It can be used for spot welding, vertical welding, horizontal welding, overhead welding and all position welding. It is especially suitable for welding black metal materials such as carbon steel, alloy steel and stainless steel.

2. Developing dynamic carbon dioxide gas shielded welding is a new welding technology developed in the 1950s. In the past half century, it has developed into an important fusion welding method. It is widely used in automobile industry, construction machinery manufacturing, shipbuilding, locomotive manufacturing, elevator manufacturing, boiler and pressure vessel manufacturing, and the production of various metal structures and metal processing machinery. Carbon dioxide gas shielded welding has the advantages of good welding quality, low cost and simple operation. It is a foregone conclusion to replace most manual arc welding and submerged arc welding. And carbon dioxide gas shielded welding is easy to realize NC welding on manipulator or robot, which will become the main welding method in the early 21st century. At present, the shielding gas used in carbon dioxide gas shielded welding is divided into CO2 and CO2 + ar. The welding wires used are mainly manganese silicon alloy welding wire, ultra-low carbon alloy welding wire and flux cored welding wire. The main specifications of welding wire are: 0.5 ﹐ 0.8 ﹐ 0.9 ﹐ 1.0 ﹐ 1.2 ﹐ 1.6 ﹐ 2.0 ﹐ 2.5 ﹐ 3.0 ﹐ 4.0, etc.

3. Features 3.1 low welding cost. CO2 gas is a by-product of breweries and chemical plants, with wide sources and low price. Its cost is only 40 ~ 50% of that of submerged arc welding and manual arc welding. 3.2 high productivity, strong penetration of CO2 arc, large melting depth, high melting rate of welding wire and fast deposition speed. Its productivity is 1 ~ 4 times that of manual arc welding. 3.3 wide application range. Thin plate, medium plate and even thick plate can be welded. The deformation of thin plate during welding is small, and all position welding can be carried out. 3.4 strong rust resistance, low hydrogen content in weld and good crack resistance. 3.5 slag removal is not required after welding. 3.6 due to the open arc, it is easy to monitor and control during welding.

4. CO2 welding materials 4.1. CO2 gas 4.1.1co2 gas properties pure CO2 gas is colorless and slightly sour. The density is 1.97kg/m3, which is heavier than air. When CO2 gas is pressurized to 5 ~ 7MPa at room temperature, it becomes liquid. Liquid CO2 is relatively light at room temperature. At 0 ℃, 0.1MPa, 1kg of liquid CO2 can produce 509l of CO2 gas.

4.1.2 the bottled CO2 gas adopts 40L standard steel cylinder, which can be filled with 25kg liquid CO2, accounting for about 80% of the steel cylinder, and the remaining 20% space is filled with CO2 gas. At 0 ℃, the saturated pressure is 3.63mpa; At 20 ℃, the saturation pressure is 5.72mpa; At 30 ℃, the saturated pressure is 7.48 MPa. Therefore, the CO2 cylinder shall be protected from the sun or close to the heat source to avoid explosion.

4.1.3 influence of CO2 gas purity on welding quality