If the silicon content of the steel grating is high, zinc-nickel alloy can be added to reduce the amount of zinc. Plating flux additives can also be added to make the galvanized layer beautiful. During the hot-dip galvanizing process of steel gratings, it is necessary to make the surface of steel gratings bright and the coating thin. This has a lot to do with each process. The pickling is not in place, the formula of the plating solution is wrong, the zinc temperature is uneven, and manual operations are required. The lifting speed of the vehicle is closely related. Let me briefly analyze it below.
The formation process of the hot-dip galvanized layer of the grating is the process of forming an iron-zinc alloy between the flat iron matrix and the outermost pure zinc layer. The surface of the steel grating workpiece forms an iron-zinc alloy layer during hot-dip plating, which makes the iron It has an excellent relationship with the pure zinc layer, and the process can be briefly described as:
When the steel grating workpiece is immersed in the molten zinc liquid, a zinc-iron (body core) solid solution is first formed on the interface. This is a crystal formed by the steel grating base metal iron dissolved in zinc atoms in a solid state. The two metal atoms are fused, and the gravitational force between the atoms is relatively small. Therefore, when zinc reaches saturation in the solid solution, the atoms of zinc and iron are dispersed with each other. The zinc atoms dispersed into (or called into) the iron matrix migrate in the matrix lattice and gradually form an alloy with iron, and the zinc atoms dispersed into The iron in the molten zinc liquid forms an intermetallic compound FeZn13 with zinc, which sinks to the bottom of the hot-dip galvanizing pot and becomes zinc slag. When the steel grating workpiece is removed from the zinc immersion solution, the pure zinc layer on the surface is formed into a hexagonal crystal. Its iron content is no more than 0.003%.
Increase the hot-dip galvanizing temperature of the grating, but you must consider the condition of the zinc pot. The iron pot should not exceed 480 degrees, while the ceramic pot can reach 530 degrees. Reduce the zinc immersion time and take it out slowly. Increasing the zinc-aluminum alloy can reduce the coating thickness. Slow down the workpiece of the grating plate to increase the speed; try to control the galvanizing time of the grating plate; appropriately increase the thinning of the alloy.
Hot dip galvanizing of grating is a metallurgical reaction process. From a microscopic perspective, the hot-dip galvanizing process is a dynamic balance of two:
Thermal balance and zinc-iron exchange balance. When the grating workpiece is immersed in the molten zinc liquid at about 450°C, the steel grating workpiece at room temperature absorbs the heat of the zinc liquid. When it reaches above 200°C, the interaction between zinc and iron gradually becomes apparent, and zinc enters the surface of the iron workpiece. As the steel grating The temperature of the plate workpiece gradually approaches the temperature of the zinc liquid, and the surface of the workpiece forms an alloy layer containing different proportions of zinc and iron, forming a layered structure of the zinc coating. As time goes by, different alloy layers in the steel grating coating show different growth rates. From a microscopic perspective, the above process is manifested as the steel grating workpiece being immersed in the zinc liquid, and the zinc liquid level becomes ebullient. When the zinc-iron reaction gradually becomes balanced, the zinc liquid level gradually calms down. The steel grating workpiece is lifted out of the zinc liquid surface, and the temperature of the workpiece gradually decreases. When it reaches below 200, the zinc-iron reaction stops, the hot-dip galvanized coating of the steel grating is formed, and the thickness is determined.?
1. What are the thickness requirements for hot-dip galvanizing?
The current international and Chinese hot-dip galvanizing standards for steel grating hot-dip galvanizing technology are divided into sections according to the thickness of the plate. The average thickness and partial thickness of the zinc coating should reach the corresponding thickness to determine the anti-corrosion performance of the zinc coating. Steel grating workpieces with different thicknesses require different times to achieve thermal equilibrium and zinc-iron exchange balance, and the resulting coating thicknesses are also different. The uniform thickness of the coating in the standard is based on the industrial production experience value of the above-mentioned galvanizing mechanism. The partial thickness is the empirical value required to take into account the uneven distribution of zinc coating thickness and the requirements for the corrosion resistance of the coating. Therefore, ISO standards, American ASTM standards, Japanese JIS standards and Chinese standards have slightly different requirements for zinc coating thickness. According to the rules in the hot-dip galvanizing specification of the People's Republic of China GB/B 13912-2002. The zinc amount specifications for hot-dip galvanized steel grating products are as follows: if the thickness of hot-dip galvanized steel grating is greater than or equal to 6mm, the average thickness of the zinc amount on the hot-dip galvanized steel grating should be greater than 85 microns, and the partial thickness should be greater than 70 microns. If the thickness of the hot-dip galvanized steel grating is less than 6mm and greater than 3mm, the uniform thickness of the zinc content on the hot-dip galvanized steel grating should be greater than 70 microns, and the partial thickness should be greater than 55 microns. If the thickness of the hot-dip galvanized steel grating is less than 3mm and greater than 1.5mm, the uniform thickness of the zinc content on the hot-dip galvanized steel grating should be greater than 55 microns, and some parts should be greater than 45 microns.
2. What are the effects and influences of hot-dip galvanizing coating thickness?
The thickness of the hot-dip galvanized coating of the steel grating determines the anti-corrosion performance of the steel grating. Users can choose a zinc coating thickness that is higher or lower than the standard. For thin steel gratings with smooth surfaces below 3mm, it is difficult to obtain thicker coatings in industrial production. In addition, zinc coatings that are not commensurate with the thickness of steel gratings Thickness affects the bonding strength between the coating and the substrate as well as the appearance quality of the coating. Excessively thick coating will cause the coating to be rough in appearance and easy to peel off. The plated steel grating cannot withstand the bumps during transportation and installation. If there are more active elements silicon and phosphorus in the raw materials of steel grating, it will be very difficult to obtain a thin coating in industrial production. This is because the silicon content in the steel affects the growth method of the alloy layer between zinc and iron, which will cause the phase to form. The zinc-iron alloy layer grows rapidly and will move toward the surface of the coating, causing the surface of the coating to be rough and dull, forming a dull coating with poor adhesion.
Therefore, as shown in the above comments, there is uncertainty in the growth of the galvanized layer of steel gratings. It is often difficult to obtain a certain range of coating thickness in actual production. The thickness specified in the hot-dip galvanizing specifications for steel gratings is determined after many tests. The experience value generated takes into account various factors and requirements and is relatively reasonable.
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