A customer inquired that during the production process of using alkaline zinc plating brightener, the galvanized layer of the workpiece is prone to dark gray and black in the deep recesses. What is the reason for this?
Bigley Technology analyzed the characteristics of the alkaline zinc plating brightener BZ-515 based on on-site experience and the product. This phenomenon is mainly caused by the contamination of copper impurities in the plating solution, which are usually brought in by the copper hook or copper rod of the hanging tool touching the plating solution. When the copper impurity content in the plating solution is high, phenomena such as dark, gray, and difficult passivation treatment will appear in the low current density area, that is, the deep recesses of the workpiece. So, when there are many copper impurities in the alkaline plating solution, we can use the following four methods to treat the plating solution:
1. Sodium sulfide treated plating solution. Take 0.1-0.5g/L chemically pure sodium sulfide and dissolve it in more than 20 times pure water. Under intense stirring, slowly add it to the plating solution. After adding, continue stirring for 20 minutes to fully react with heavy metal ions in the plating solution, generate sulfide precipitates, and then filter to remove them.
2. Zinc powder treated plating solution. Take 1~3g/L zinc powder and slowly add it into the plating solution under intense stirring to make it single displacement reaction with heavy metal ions. After adding, continue to stir for 30min. Filter it after standing for 2h. The standing time should not be too long, or it will lose the significance of treatment.
3. Low current electrolytic treatment of plating solution. Take several nickel plated iron plates as cathodes and conduct electrolytic treatment at a current density of 0.1-0.3A/dm2. The treatment time is generally more than 4 hours, depending on the situation after the trial plating. The black coating on the surface of the used nickel plated iron plate needs to be removed thoroughly in concentrated acid before it can be used as an anode. The advantage of this method is that it is easy to operate and does not consume the plating solution.
4. Use CK-778 to treat the plating solution. Take 2-3 g/L of CK-778 treatment agent and use the same method as zinc powder, but do not need to filter. After adding the treatment agent to the plating bath, floating objects may appear in the plating solution during further stirring and standing. They can be removed with a cloth net while stirring. After the plating solution is treated, it needs to be slightly treated with low current, and one-third of the original formula amount of additives and brighteners should be added.
So, in the production process of using alkaline zinc plating brightener, when there is a dark gray black phenomenon in the deep concave part of the workpiece zinc coating, we can use these four methods to treat the plating solution, solve the problem as soon as possible, and reduce losses. If you are interested in alkaline zinc plating brightener, please contact Bigley customer service for free samples and detailed technical information!
If you want to learn more about galvanizing, you can click to view the "Electroplating Encyclopedia".