Process conditions and bath maintenance of zincate zinc plating

This plating solution is stable, and only an appropriate amount of additives need to be added in daily life. Pay attention to adding less and more frequently each time; Regularly test the sampling solution and adjust it in a timely manner to ensure that Zn: NaOH is between 1:12. Pay attention to adjusting the anode so that the area ratio of soluble anode (Zn electrode) to insoluble anode is 1:3, and the area ratio of cathode to anode is between 1:2. The relative position of the anode and cathode and the arrangement of the electrodes are related to the uniformity of the coating. The electrode distance should not be too close, otherwise the convex part is prone to combustion and the concave part becomes dark. Increasing the distance between the cathode and anode is beneficial for uniform coating. The plating of composite parts should be kept at 200-250mm, with 100-150mm gaps left at both ends of the groove. The total length of the anode should be 100-150mm shorter than that of the hanging tool.
Pay attention to the relationship between the control tank liquid and the current density. Zinc salt zinc plating has a wide working temperature range, generally between 10 and 45 ℃, and qualified coatings can be obtained. As the temperature increases, the cathode current efficiency increases, the applied current density range shifts up, the deposition speed increases, and the production efficiency improves. However, the decomposition ability of the electrolyte decreases, and the self dissolution rate of the zinc anode accelerates, making the tank liquid unstable. Therefore, it cannot work at excessively high temperatures. From this, it can be seen that controlling temperature is quite important to keep it within the process range. Zinc salt zinc plating has a wide current density range, generally between 1-5A/dm2. When its composition and temperature are constant, it is advisable to maintain a high current density. It can improve the dispersion ability of the electrolyte to a certain extent, increase cathodic polarization, and is conducive to obtaining excellent coatings. However, if the current density is too high, the coatings will crystallize coarsely, have no luster, and even have burnt edges.
Temperature and current density are closely related. When the temperature is low, the conductivity of the electrolyte is poor, the adsorption of additives is strong, and desorption is difficult. At this time, high current should not be used, otherwise it will cause burning at the edges, inclusion of additives, brittleness of the coating, and blistering. When the temperature is high, the adsorption of additives is weak, leading to a decrease in polarization. At this time, a higher current density is needed to improve cathodic polarization, refine crystallization, and prevent negative and positive surfaces. Therefore, the appropriate current density should be selected based on temperature.
When copper impurities are present in the zincate zinc plating solution, the coating will become rough and matte. Low current electrolysis or zinc powder (0.5-1g/L) stirring and standing, filtration treatment can be used. Lead can cause the coating to turn black and not shiny. 0.1-0.2g/L sodium sulfide can be added to generate lead sulfide precipitation treatment, especially for impure anodes (lead>15mg/L, copper>20mg/L, iron>50mg/L), which can cause the above-mentioned problems of dark and black spots and stripes. Therefore, in addition to chemical methods such as adding sodium sulfide, in recent years, CK-778 has been widely used in China for impurity purification treatment. Add about 0.5-1g/L, stir for 30 minutes, stop for 10-20 minutes, and then stir for 30 minutes to continuously remove the liquid surface dirt, Stop filtering for 8 hours to purify. In normal production, it is not advisable to use low current electrolysis method for treatment. The main reason is to maintain it well in daily life, pay attention to the quality of chemical materials and anodes, and use zinc plates instead of using zinc ingots as anodes. Zinc ingots need to be cast into zinc plates to prevent the generation of impurities.