Galvanized steel pipes, which have the dual advantages of corrosion resistance and long service life, and the price is relatively low, so now its usage rate is getting higher and higher, but sometimes it is not paid attention to when welded with a zinc galvanized pipe, which leads to some some of them, which leads to some some, which leads to some some, which leads to some some. Unnecessary trouble, so what problems should be paid attention to when welding?
1. The premise is to polish
Galvanize the welding at the welding at the welding, otherwise it will produce bubbles, trachoma, fake welding, etc. It will also make the welds crispy and rigid.
2. Welding characteristics of galvanized steel
Galvanized steel is generally placed with zinc at 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. During the welding, zinc melted into liquid floating on the surface of the molten tank or on the root of the weld. Zinc has a large solid solution in the iron. Zinc liquids will deeply etch the welded metal along the crystal boundary, and low melting point zinc forms a "liquid metal crisp".
At the same time, zinc and iron can form a metal crispy compound. These crispy phases reduce the plasticity of the weld metal and cracks under the action of tensile stress. If the welding angle weld, especially the corner welding of the T -shaped joint, it is prone to penetrate cracks. During the welding of galvanized steel, the zinc layer on the surface and edges of the ramp is under the action of arc thermal fever, which produces oxidation, melting, evaporation and even volatilization of white smoke and steam, which can easily cause welded air holes.
The ZNO formed by oxidation has a high melting point, about 1800 ° C. If the parameters are small during the welding process, the ZnO residue will be caused, and at the same time. Since Zn becomes a deoxyer. Generate Feo-Mno or Feo-Mno-SIO2 low melting point oxide slag. Secondly, due to the evaporation of zinc, a large amount of white smoke and dust are evaporated, which has a stimulating and damage effect on the human body. Therefore, the galvanized layer of the welding place is polished.
3. Welding process control
The pre -welding preparation of galvanized steel is the same as the general low -carbon steel. It should be noted that the size of the slope and the nearby galvanized layer should be carefully handled. In order to weld, the size of the slopes should be appropriate, generally 60 ~ 65 °, and there must be a certain gap, generally 1.5 ~ 2.5mm; in order to reduce the penetration of zinc to welded seams, before welding Welding after the layer is cleared.
Welding method: When welding the first layer of welded welding, the zinc layer is melted and vaporized, evaporated and the welds can be greatly reduced, which can greatly reduce liquid zinc in the weld. When welding welds welded, try to melt the zinc layer and vaporize, evaporate and reconcile the welded seams on the first layer. After melting, return to the original position and continue to welded forward. When welding and standing welded, if the short slag welding, such as J427, the bite tendency will be small; if you use the front and rear rounds of bars, you can also obtain the flawless welding quality.
