Galvanizing is mainly used to prevent corrosion of steel, and the quality of its protective performance is closely related to the thickness of the coating.
As a cheap metal electroplating layer, zinc plating has good corrosion resistance, and the electroplating process is relatively mature, and it is easier to obtain better positioning and leveling performance. At present, the environmental pollution in my country is relatively serious, and zinc plating can completely abandon the drama. Toxic cyanide. If the zinc electroplated layer can be used as a primer, the brightness and fill-in properties of the zinc electroplated layer can be fully utilized, and the zinc coating requires relatively simple pretreatment of various materials, and then the nickel layer can be electroplated on the zinc, so that it can be greatly improved. Reduce costs and ensure product quality. In the current electroplating industry, nickel plating on zinc has always been a problem that electroplaters dream of solving!
The nickel plating solution has always been very sensitive to zinc pollution. A little bit of zinc ions will easily cause the nickel plating to turn black. If the zinc content is above 0.02g/L, the coating stress will increase, brittle, and black streaks will appear. Even the coating will turn black.
Jinhua Dongwei Surface Treatment Technology Co., Ltd. has been focusing on zinc alloy electroplating. After years of thorough analysis and beneficial exploration of the characteristics of zinc in nickel solution, it screened the top ten complexing agents for zinc and finally found A complex system that can be automatically balanced has successfully inhibited the effect of zinc on the nickel plating bath. Based on this, a complete process plan for nickel plating on zinc was explored.
The characteristics of the process;
1. Hanging or barrel plating is possible, the plating layer is white and bright, suitable for PH6.5-7.0 plating solution. The amount of additives is small.
2. The coating looks very full. The low potential is as good as the high potential. It is easy to control, the plating solution has good impurity resistance, and the plating solution is clear, unlike the previous neutral nickel solution which is easy to be turbid. It is stable and has a long processing cycle. Even in the field, the zinc dross at the bottom of the plating tank does not affect the normal electroplating even after the plating solution has worked for a period of time. The plating layer is not easy to spot. The coating is white and bright.
3. The coating has good compactness and good corrosion resistance. The iron electroplated products were electroplated with zinc for one hour and then nickel-plated for 20 minutes. The salt spray test showed white rust for more than 64 hours. If rack plating, the performance of subsequent sets of chromium is better.
4. It can be electroplated with nickel directly after bright galvanizing, the coating is white, bright, and the low-zone performance is particularly good.
5. If it is to use cyanide plating alkaline copper and then nickel plating process; zinc alloy electroplating does not have too strict requirements on the thickness and compactness of the alkaline copper coating. It can shorten the alkaline copper electroplating time. Therefore, it is particularly suitable for zinc alloy and aluminum alloy workpieces.
6. Electroplating at room temperature, no cyanide, simple sewage treatment, obvious cost saving.
Reference formula of plating solution;
Nickel sulfate; 90-150g/L.
Sodium chloride 45-65. g/L.
Sodium citrate 80-130. g/L.
PH6.5-7.2.
Temperature 15-25℃ is room temperature
Neutral nickel brightener 0.5ml/l
Adjuvant 0.5-1ml/l
Neutral nickel cylinder opening agent 35ml/l
Recommendations for bath control during production:
1. Pay attention to the addition of nickel sulfate to sodium citrate when preparing the tank. And add the cylinder opening agent appropriately. Suggestions for plating solution control; if too much sodium citrate, the plating layer will be foggy and not bright. If there is too much complexing agent or the pH is too high, the coating will be black.
2. The Baume degree should not be adjusted too high 13-15. Too high costs increase, and stability and positioning are not good.
3. When the temperature is 15-25℃, the temperature is too high, it is easy to have black spots. The temperature is too low to crystallize and make the composition imbalance. In order to prevent zinc contamination, it is recommended that the temperature of the nickel plating solution be controlled at about 20°C. A refrigerator should be equipped for barrel plating production.
4. As long as the opening agent is added when opening the tank and replenishing nickel sulfate, or when there are black spots or the plating solution is turbid during electroplating, it is not necessary to add it at ordinary times. Usually add brightener to maintain the brightness of the coating. The coating has a certain brightness. Auxiliary agent is conducive to positioning and impurity removal.
5. It is recommended that the content of nickel sulfate is slightly higher than that of sodium citrate. When matching the tank, pay attention to the nickel sulfate and sodium citrate to be complexed and added! , Usually add 1 packet of nickel sulfate with 1 packet of sodium citrate. And add the cylinder opening agent appropriately. When the temperature is low, it should be kept at about 20°C to prevent the composition of the plating solution from crystallizing and making the composition of the plating solution unbalanced.
6. Neutral nickel brightener consumption; 150-250ml/kAh. Neutral nickel starter consumption 50-100ml/kAh auxiliary agent 50-100ml/kAh.
Conclusion:
This process has been used in the production lines of several large factories for several months. Practice has proved that the process is stable, and the color of the coating is not much different from that of direct nickel electroplating. The corrosion resistance of the coating far exceeds that of direct nickel plating. Containing lead, amine, cyanide and other harmful substances, the process is simple, and the labor cost is reduced. Electroplating at room temperature saves energy. There are no strict requirements on the materials of the products to be electroplated. Copper, iron, zinc alloys, etc. can all be electroplated directly. Aluminum alloy parts can be electroplated only after the second zinc dip. Plastic parts should be electroless copper or nickel, and then galvanized. All pre-treatments are in accordance with the conventional electroplating treatment of galvanizing, which is easy to control. Social benefits, environmental benefits, and economic benefits are quite obvious.
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Link to this article：New Process of Nickel Electroplating on Zinc
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