Before the Ji'nan galvanized pipe is welded, the galvanized layer of the welding place must be worn away, otherwise the bubble, the trachoma, the false welding and so on will be produced. It will also make the weld brittle and the rigidity decrease. The galvanized steel tube is generally plated with a layer of zinc outside the low carbon steel, and the galvanized layer is generally 20um thick. The melting point of zinc is 419 C, and the boiling point is about 908 C. In welding, zinc melts into a liquid floating on the surface of the pool or at the root of the weld.
At the same time, zinc and iron can form brittle intermetallic compounds. These brittle phases reduce the plastic properties of the weld metal and produce cracks under the action of tensile stress. If the welded corner welds, especially the T - shaped joint, are most likely to produce a penetrating crack. When galvanized steel pipe is welded, the zinc layer on the surface and edge of the groove will be oxidized, melted, evaporated, and even white smoke and steam will be produced by the galvanized pipe of Ji'nan under the arc heat. It will easily cause the weld porosity.
The ZnO formed by oxidation is relatively high melting point, which is about 1800 degree C. If the parameter is too small in the welding process, it will cause ZnO slag inclusion. Because Zn becomes a deoxidant, it produces FeO-MnO or FeO-MnO-SiO2 low melting point oxide slag. Secondly, because of the evaporation of zinc, a lot of white soot is emitted, which is irritating and harmful to the human body. Therefore, we must polish the galvanized layer of the welding place.
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