In the production process of using alkaline cyanide free zinc plating brightener, sometimes the coating in the low current density area of the workpiece will turn black. What should we do?
Based on on-site experience and product characteristics, Bigely Technology has conducted the following analysis:
1.Lead ion pollution. When the lead ion impurities in the alkaline zinc plating solution exceed 15mg/L, the dispersion ability of the plating solution will significantly decrease, and the galvanized layer will appear black or gray stripes after being exposed to dilute nitric acid. Lead ions are mainly brought in by inferior zinc anode plates. To prevent lead pollution, zinc anodes require 0 # zinc or 1 # zinc.
2. Iron ion pollution. When the iron ion content in alkaline zinc plating solution reaches 50mg/L, if the iron ion content is further increased, colloidal flocs will appear in the alkaline zinc plating solution, and the galvanized layer will appear purple blue after passivation, and it is easy to produce bubbles. Iron ions are mainly introduced by inferior sodium hydroxide or workpieces. Therefore, white flake alkali should be used, and sodium hydroxide with red color should not be used. The workpiece entering the galvanizing tank should be thoroughly cleaned. Adjust the ratio of anode and cathode area, and try to use nickel plate or nickel plated iron plate as the anode.
3. Copper ion pollution. When the copper ion content in the alkaline galvanizing solution reaches 20mg/L, the obtained galvanized layer is rough, the brightness decreases, and the range of bright current density gradually decreases with the increase of copper ion content. Copper ions are mainly brought in by hooking and washing copper rods.
Therefore, in the production process of using alkaline cyanide free zinc plating brightener, the blackening of the coating in the low current density area of the workpiece is generally caused by the contamination of metal ion impurities. During the production process, it is advisable to avoid introducing these impurities into the galvanizing tank and regularly maintain the plating solution. If you want to learn more about alkaline cyanide free zinc plating brightener, please feel free to call us for consultation. Bigely Technology is always at your service.
