CO2 gas shielded welding is a kind of welding method, which is widely used in the welding of low carbon steel and low alloy steel. Low alloy steel gas shielded welding wire has developed a new national standard, that is, GB/T8110-1995 "Carbon steel, low alloy steel welding wire for gas shielded arc welding", the standard content is equivalent to using AWS gas shielded welding wire. In order to prevent the production of pores, reduce spatter and ensure that the weld has higher mechanical properties, it is necessary to use the welding wire containing Si, Mn and other deoxidation elements.
The purity volume fraction of CO2 gas used should not be less than 99.5%, and the mass fraction quantity of water should not exceed 0.005%. In order to reduce the water content of CO2 gas, the new filling cylinder can be stood upside down for 1~2 hours at the welding site, and then the valve can be opened to discharge the free water deposited in the lower part. According to the different water content, water can be drained 2~3 times, every 30 minutes or so.
Then put the cylinder right. Before use, it is necessary to vent 2~ 3min, in order to release the upper part of the gas mixed with more air and water. High pressure dryer and low pressure dryer are set up in the gas path system to further reduce the moisture in the gas. The desiccant is generally made of silica gel or dehydrated copper sulfate. Before welding, clean the oil, rust, moisture, and paint on the groove of the welded parts and its sides within 10 to 20mm.
Two droplet transition forms are usually adopted in CO2 gas shielded welding: one is short circuit transition, which is characterized by low arc current and small welding current, so it is suitable for welding thin sheet and all-position welding, and the diameter of welding wire is small, generally 0.6~1.4mm. The other is the fine particle transition, which is characterized by large welding current, strong arc penetration and large base metal penetration, so it is suitable for medium and thick plate welding. At present, the diameter of the welding wire is used more with 1.6mm and 2.0mm.
Short-circuit transition to choose low voltage; The welding current should match the diameter of welding wire and arc voltage. Welding speed can not be too big, can not be too small, generally around 30m/h; The gas flow rate is 5~15L/min for small welding parameters and about 20L/min for medium welding parameters. The polarity of the power supply generally adopts DC reverse connection; The length of the welding wire is within 10~20mm, rarely more than 20mm; To reduce spatter, the welding loop requires a series adjustable inductor.
In the process of CO2 gas shielded welding, the transition of fine particles can be formed only when the current increases to a certain value and the arc voltage is suitable. Dc reverse connection is still used for fine particle transition. Loop inductance has no effect on splash suppression, so a reactor can be omitted.
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