In many cases, in order to improve the surface gloss of hardware fasteners, surface treatment - electroplating of nickel is usually used. During this process, there will be copper ions, which are one of the more common impurities in bright nickel plating. If the plating solution is contaminated by Cu2+, the brightness of the plated parts in the low current density area will be poor. Excessive Cu2+ will also cause the brittleness of the coating and poor bonding.
So how to remove impurities from the plating solution of hardware fasteners? China Standard Parts Network summarizes it as follows:
Electrolysis method: a method that uses low current density to deposit Cu2+ in the plating solution on the cathode plate. There are three types of cathode plates used for processing: corrugated plates, sawtooth plates and flat plates. When a certain current is applied to the corrugated plate for electrolysis, the Jκ range on the cathode plate is wider, with a larger Jκ at the peak and a smaller Jκ at the trough, so Cu2+ and other metal impurities can be deposited at the same time to achieve the purpose of removing multiple impurities. The zigzag cathode plate is affected by the * effect. Ni2+ and Cu2+ are deposited at the same time during the electrolysis process, resulting in increased loss of nickel salt in the plating solution. Using a flat cathode can use different Jκ to achieve the purpose of selectively removing metal impurities. According to experience, when Jκ is 0.5A/dm2, it is beneficial for Cu2+ to precipitate at the cathode.
No matter which type of cathode is used for electrolysis treatment, several issues should be paid attention to: a. During long-term electrolysis treatment, the electrolytic plate should be cleaned regularly to prevent the loose coating on the electrolytic plate from falling off and re-contaminating the plating solution; b. Using cathode movement or air Stirring can improve the treatment effect; c. The anode plate used in electrolysis treatment must be a high-quality nickel anode plate, otherwise the treatment effect will be affected and unnecessary waste will be caused.
Chemical precipitant method: The common one is QT copper removal agent. The main component of this precipitant is ferrocyanide. It combines with Cu2+ in the plating solution to form copper ferrocyanide precipitate, and then filters out the precipitate to achieve the purpose of removing copper impurities. The disadvantage of this method is that it requires precision filtration, which is time-consuming.
Chelating agent method: Chelating agents are generally organic substances with aromatic rings or heterocyclic structures, which form chelates with Cu2+ in the plating solution. Since the chelates and Ni2+ are co-deposited during electrolysis, ρ(Cu2+) in the plating solution can be It won't rise too high. This method is simple and easy to implement, and is currently a better and more effective method for treating impurities in nickel plating solutions. High-quality chelating agents must be selected during application, especially to ensure that they do not have any adverse effects on the coating.
