The acid washing and rinsing process before the production of hot-dip galvanized sheet is very strict, only in this way can high-quality and qualified production be produced.
1. Before preparing the acid washing solution, the acid tank must be washed clean, and no rust, sediment, or other attachments are allowed to remain in the tank.
2. The pickling solution is diluted hydrochloric acid, with a working concentration of 40-200 grams per liter and a working temperature of room temperature.
3. Preparation of acid pickling solution: Industrial hydrochloric acid with a concentration of 28% or higher is used to prepare an acid pickling solution with a concentration of 200 grams per liter by adding water in a ratio of 2:1. During use, no acid is generally added until the concentration drops below 40 grams per liter. When the ferrous chloride content of the solution rises to 200 grams per liter, the waste acid is treated in a neutralization tank and discharged after meeting the standards (emission requirements are specified by the environmental protection department). If the content of ferrous chloride is less than 200 grams per liter and the concentration of hydrochloric acid is below 40 grams per liter, concentrated hydrochloric acid can be added appropriately to continue use.
4. The pickling solution is tested twice a week, and the measurement results are reported to the shift supervisor of the hot-dip galvanized sheet workshop to guide the pickling operators.
5. The pickling time should be related to the surface oxidation layer and pickling concentration of hot-dip galvanized sheet, generally 30-40 minutes. During the pickling process, the workpiece should be moved up and down two to three times, and the liquid level should be checked for pickling quality. For surfaces that are partially under pickled, tools such as grinding wheels and wire brushes can be used to remove them before pickling them clean, so as to achieve no residual oxidation layer and other pollutants adhering to the steel surface, and the surface should have a gray white luster.
6. The hot-dip galvanized sheet that has passed the acid washing process must be rinsed with running water to remove any residual acid solution on the surface. After being lifted out of the rinsing tank, the plated part should be left on the tank for no less than 15 seconds. After the surface water is dripped off, it should immediately enter the plating aid tank for solvent treatment.
7. The rinse water should be clear, keep flowing, clean, and have a pH value greater than 6.
