During the installation and laying of the structural platform of galvanized steel grating, it is often encountered that pipelines or equipment need to pass through the steel grating platform vertically. In order to enable the pipeline equipment to pass through the platform smoothly, it is usually necessary to determine the location and size of the openings during the design process, and the steel grating manufacturer will carry out customized production. The process of customized production first requires a lot of communication and information exchange between the steel grating design department and the steel structure design department, equipment provider and surveying and mapping department. Due to the many related factors involved, there is a certain uncertainty in the size and position of the current equipment. During installation, it is often the case that the customized reserved holes cannot meet the needs of the site. In view of this situation, in order to ensure the yield rate of steel gratings and improve the design and production efficiency of steel gratings, in the current design and production process, generally speaking, some holes with smaller diameters that are difficult to determine are not customized and processed, but are replaced by secondary processing procedures such as on-site opening, cutting, welding, and grinding according to the current situation during the installation and construction of the steel grating.
As a new material, galvanized steel grating is increasingly widely used. Galvanizing has become an important anti-corrosion method for steel gratings, not only because zinc can form a dense protective layer on the surface of steel, but also because zinc has a cathodic protection effect. When the galvanized steel grating is transported to the site, secondary processing and welding are sometimes required for installation. The presence of the zinc layer brings certain difficulties to the welding of the galvanized steel grating.
Analysis of the weldability of galvanized steel gratings
Galvanized steel gratings are coated with a layer of metal zinc on the surface of the steel grating to prevent corrosion on the surface of the steel grating and extend its service life. The surface of the galvanized steel grating will be flower-shaped. According to the production and processing methods, it can be divided into the following categories: ① hot-dip galvanized sheet; ② electrogalvanized steel sheet. The melting point of zinc is 419℃ and the boiling point is 907℃, which are far lower than the melting point of iron, 1500℃. Therefore, during the welding process, the galvanized layer first melts the parent material. After the above analysis, the mechanical and physical properties of galvanized sheet are the same as those of ordinary carbon steel sheet. The only difference is that there is a zinc coating on the surface of galvanized steel grating. The welding process of galvanized steel grating
(1) Manual arc welding
In order to reduce welding smoke and prevent the generation of welding cracks and pores, the zinc layer near the groove should be removed before welding. The removal method can be flame baking or sandblasting. The principle of selecting welding rods is that the mechanical properties of the weld metal should be as close as possible to the parent material, and the silicon content in the daily welding rod molten metal should be controlled below 0.2%. For low-carbon steel mirror zinc steel grating, J421/422 or J423 welding rods should be used first. When welding, try to use a short arc and do not swing the arc to prevent the expansion of the molten area of the galvanized layer, ensure the corrosion resistance of the workpiece and reduce the amount of smoke
(2) Metal arc welding
Use CO2 gas shielded welding or mixed gas shielded welding such as Ar+CO2, Ar+02 for welding. The shielding gas has a significant effect on the Zn content in the weld. When pure CO2 or CO2+02 is used, the Zn content in the weld is higher, while when Ar+CO2 or Ar+02 is used, the Zn content in the weld is lower. The current has little effect on the Zn content in the weld. As the welding current increases, the Zn content in the weld decreases slightly. When using gas shielded welding to weld galvanized steel grating, the welding fume is much larger than that of manual arc welding, so special attention should be paid to exhaust. The factors that affect the amount and composition of the fume are mainly the current and the shielding gas. The larger the current, or the greater the CO2 or O2 content in the shielding gas, the larger the welding fume, and the ZnO content in the fume also increases. The maximum ZnO content can reach about 70%. Under the same welding specifications, the penetration depth of galvanized steel grating is greater than that of non-galvanized steel grating.
Post time: Aug-16-2024