The key to ensuring the quality of hot-dip galvanizing lies in controlling a number of critical aspects, including surface pretreatment, zinc coating thickness, zinc solution temperature, strip dwell time, lead-in method, and zinc solution composition.
Author: Anna
The key to ensuring the quality of hot-dip galvanizing lies in controlling a number of critical aspects, including surface pretreatment, zinc coating thickness, zinc solution temperature, strip dwell time, lead-in method, and zinc solution composition.
Surface pretreatment is a critical step in the hot-dip galvanizing process. Steel in the factory, storage, transportation and processing may be stained with paint, mineral grease and other impurities, these impurities, if not completely removed, will lead to leakage of plating (exposed iron) phenomenon. Pickling process if the pickling pieces stacked densely, pickling concentration is too high or water washing is not complete, will also cause under pickling and pinch line, which in turn affects the quality of the plating layer. In addition, factors such as aging of solvents and excessive drying time can also lead to leakage of plating1.
Zinc coating thickness is one of the most important factors affecting the quality of hot-dip galvanizing. The temperature of the zinc solution, the residence time of the strip in the zinc solution and the method of drawing out all affect the thickness of the coating. The temperature of the zinc solution should be controlled between 430°C and 460°C. The residence time of the strip in the zinc solution should be determined according to the thickness of the strip, generally 3 to 8 minutes. The strip should be led vertically out of the zinc bath to avoid thinning of the zinc layer.
The temperature and composition of the zinc bath have a direct influence on the quality of the coating. When the temperature of zinc liquid is lower than 430℃, the diffusion speed of zinc and iron is slow, and it is not easy to generate enough iron and zinc alloy layer, which leads to thin plating layer; if the temperature is too high, the zinc liquid will become thin, and the plating layer will also become thin. In addition, too much other metal components or harmful elements in the zinc solution will affect the quality of the plating layer.
The process flow of hot-dip galvanizing includes the steps of degreasing, descaling, washing, pickling, solvent dipping, hot-dip galvanizing, removing residual zinc, cooling in clear water, and inspection and trimming. Each step needs to be strictly controlled to ensure the quality of the final product.
Through the above measures, the quality of hot-dip galvanizing can be effectively controlled to ensure that the corrosion resistance, adhesion and other properties of the product meet the expected standards.