The common welding methods in steel structure engineering are arc welding and resistance welding.

Arc welding: the quality of arc welding is good and reliable.It is the most commonly used welding method in steel structure engineering.Arc welding can also be divided into manual arc welding, automatic or semi-automatic arc welding, CO2 gas shielded welding, etc.

Manual arc welding is to form an arc between the flux coated electrode and the weldment.The arc provides a heat source to melt the electrode and drop it into a small tank blown by the arc.It forms welding with the melted part of the welding part.Manual arc welding electrodes shall be suitable for all kinds of welding metals.E43 series electrodes are used for Q235 steel welding, E50 series electrodes are used for 16Mn steel welding and E55 series electrodes are used for 15MnV steel welding.

In automatic or semi-automatic arc welding, the electrodes are embedded under the flux layer.After being electrified, the electrode and flux melt due to the action of arc.The molten flux floats on the surface of the molten metal to protect the molten metal from outside air.Sometimes the flux can also provide necessary alloy elements to improve the welding quality and indirectly improve the quality of Guiyang steel structure engineering.The automatic welding seam has uniform quality, good plasticity and high impact toughness.In addition to manual operation, semi-automatic welding process is the same as automatic welding process, and the welding quality is between automatic welding and manual welding.The welding wire and flux used in automatic and semi-automatic welding shall ensure that the tensile strength of the deposited metal is not lower than that of the corresponding manual welding rod.

CO2 gas shielded welding uses CO2 as the shielding gas, the molten metal does not contact with air, the arc heating is centralized, the welding speed is fast, the melting depth is large, the welding strength is high, and the plasticity is good.CO2 gas shielded welding adopts high manganese and high silicon welding wire, which has strong rust resistance and is not easy to produce pores.Suitable for welding low carbon steel, low alloy high strength steel and other alloy steel. 

Resistance welding: resistance welding is to use the current to melt the metal through the hot scene generated by welding contact surface resistance, and then to weld it through pressure.This kind of contact spot welding is often used in the welding of cold-formed section steel.Resistance welding is only applicable to welding with thickness not exceeding 12mm.In steel structure engineering, steel members are first cleaned and dried with wire brush, cleaning brush, degreaser, compressed air or cotton yarn after oil-water separation.

Before opening the barrel, dust and dirt shall be removed to prevent the barrel from falling when it is opened.After opening the cylinder, the paint shall be evenly mixed with an electric mixer and the surface paint shall be removed.When the coating is agglomerated, gel and precipitated uniformly, it indicates that the paint has become mass and can not be used.

The viscosity of the coating is set at the lower side of the standard condition (temperature 25C).When the temperature changes, with the increase and decrease of temperature, the temperature will become thinner and thicker.At the same time, the viscosity required by different construction methods is also different, so it should be adjusted to the appropriate viscosity before construction.When adjusting viscosity, special diluent shall be used, which shall be determined by experiment when it needs to be replaced.