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The galvanized layer of the workpiece is dark and not bright after passivation. Is it due to improper use of alkaline galvanizing additives?

2022-03-23

    We all know that alkaline galvanized workpieces need to have good decorative properties, so they need to have good brightness and uniform passivated appearance.Sometimes, the coating of the galvanized workpiece on the customer's site turns black, and the film is not bright after the workpiece is passivated. They will think that this is caused by the improper use of alkaline galvanizing additives. Is this really the case?

    This is the case in Mr. Huang's galvanizing plant in Shenzhen.The composition of the plating solution is normal, the operating parameters are also normal, the coating of the produced workpiece is dark, and the passivation film after passivation is not bright, and the product cannot be shipped.Mr. Huang was very anxious, so he asked Bigolly's engineers to help solve the problem.

    First of all, whether the darkening of the coating is because the content of alkaline galvanizing additives in the plating solution is too small, the engineer needs to use the Hull cell experiment to determine.As a result, there was no obvious difference in the brightness purity of the plating solution before and after adding the additive, which ruled out the reason that the content of the brightener was too small.

    Next, the engineer took the plating solution from the site for zinc powder treatment. After treatment, it was found that the brightness of the plating layer has improved significantly, which indicates that Mr. Huang's plating solution has the influence of foreign metal impurities.Therefore, the engineer carried out electrolysis and zinc powder treatment on Mr. Huang's alkaline zinc plating solution.A day later, Mr. Huang's production line resumed normal production.


    In fact, there is no other strong complexing agent in the alkaline zinc plating solution, and the plating solution is very sensitive to impurities, and many faults in production are also caused by impurities.When the metal impurity concentration in the plating solution exceeds the allowable value, such as lead 15mg/L, copper 20mg/L, iron 50mg/L, the zinc coating will be black and dark, and the workpiece will not be bright after passivation.Therefore, in the production process, 1~3g/L zinc powder should be regularly used to treat metal impurities in the plating solution to reduce the occurrence of failures.

    Later, Mr. Huang exclaimed: "It turns out that the darkening of the workpiece coating is not necessarily due to improper use of alkaline galvanizing additives, and impurities will also affect the brightness of the coating.With the considerate service of Bigolly engineers, I have a new understanding of the galvanizing process, Bigolly is trustworthy. "

    Therefore, there are many faults in the alkaline galvanizing process, and many times we will look at the problems one-sidedly.For example, if the brightness of the galvanized layer is poor, it will be considered that the content of alkaline galvanizing additives is insufficient, but it is not necessarily true.For example, if the brightness of the galvanized layer is poor, it will be considered that the content of alkaline galvanizing additives is insufficient, but it is not necessarily true.