1. Selection of welding materials. Welding wire for welding carbon steel and low-alloy steel has established a new national standard, namely GB/T8110-1995 "Carbon steel and low-alloy steel welding wire for gas shielded arc welding", the standard content is equivalent to the United States AWS gas shielded welding wire.
In order to prevent porosity, reduce spatter and ensure that the weld has high mechanical properties, welding wire containing Si, Mn and other deoxidizing elements must be used. The purity volume fraction of CO2 gas used should not be less than 99.5%, and the mass fraction of water should not exceed 0.005%. In order to reduce the water content of CO2 gas, the following measures should be taken at the welding site: put the newly filled gas bottle upside down and stand for 1~2h, then open the valve to drain the free water deposited in the lower part. Depending on the water content, water can be discharged 2 to 3 times, once every 30 minutes. Then put the cylinder upright. Before use, it needs to be vented for 2~3min, in order to release the gas with more air and moisture in the upper part. A high-pressure dryer and a low-pressure dryer are set in the gas system to further reduce the moisture in the gas. The desiccant is generally silica gel or dehydrated copper sulfate.
2. Preparation before welding. Before welding, the oil stain, rust, moisture and paint within the range of 10~20mm from the weldment groove and both sides must be cleaned.
3. The choice of welding parameters. CO2 gas shielded welding usually uses two types of droplet transfer: one is short-circuit transfer, which is characterized by low arc voltage and small welding current, so it is suitable for welding thin plates and all-position welding, and the diameter of the welding wire is small. , Generally 0.6~1.4mm; the other is the transition of fine particles, which is characterized by large welding current, strong arc penetration, and large penetration of the base metal, so it is suitable for welding medium and thick plates. The current diameter of the welding wire is 1.6 mm and 2.0mm are the most used.
(1) Selection of short-circuit transfer welding parameters. Low voltage should be selected during short-circuit transfer; the welding current should match the diameter of the welding wire and the arc voltage; the welding speed should not be too high or too small, generally around 30m/h; the gas flow is small The welding parameter of small wire is 5~15L/min, and the parameter of medium welding is about 20L/min; the polarity of the power supply generally adopts DC reverse connection; the extension length of the welding wire is within 10~20mm, rarely exceeding 20mm; in order to reduce spatter, The welding circuit requires series adjustable inductance.
(2) Selection of welding parameters for fine particle transition In CO2 gas shielded welding, only when the current is increased to a certain value and matched with a suitable arc voltage can the fine particle transition be formed. The transition of fine particles still uses DC reverse connection. The loop inductance has no effect on the suppression of splash, so no reactor can be added.
Post time: Feb-01-2021