Electrogalvanizing is an efficient metal surface treatment technology. It deposits a fine and strong zinc coating evenly on the surface of metal substrates such as steel and copper through electrolysis. This can not only significantly improve the corrosion resistance of the substrate, effectively resist oxidation and rust, but also enhance the aesthetics, improve the overall quality and service life of the product. The whole process is precisely controllable, the coating thickness is uniform, and it is environmentally friendly and pollution-free. It is one of the metal protection and decoration methods widely used in modern industry.
- 1. Process flow
Take galvanized iron alloy as an example, the process flow is as follows:
Chemical degreasing → hot water washing → water washing → electrolytic degreasing → hot water washing → water washing → strong corrosion → water washing → electrogalvanized iron alloy → water washing → water was
2. Preparation of electroplating solution for zinc plating (taking lL as an example):
(1) Add 1/3 volume of pure water into the plating tank first;
(2) Dissolve sodium hydroxide in 1/3 pure water (it will generate heat when dissolved, so be careful);
(3) Mix zinc oxide into a paste with a small amount of water, then add more pure water and stir thoroughly. Slowly add the stirred zinc oxide to the dissolved sodium hydroxide solution, stirring while adding to fully complex it, and then add it to the plating tank;
(4) After the temperature of the plating solution drops below 30 ℃, add 85g of Baser and stir thoroughly;
(5) Dissolve 15mL of BaseF in 15g of BaseR, and then add the mixture to the plating bath;
(6) Add 4mL of H-0624 and stir thoroughly; Add water to the specified volume;
(7) Add brighteners ZF-105A and ZF-105B; stir thoroughly. Black passivation process flow: water washing → light emission → water washing → black passivation → water washing → post-treatment → drying.
3. Factors affecting electroplating zinc
(1) The influence of zinc content: If the zinc content is too high and the brightness range is narrow, it is easy to obtain thick coatings, and the iron content in the coating decreases; The zinc content is too low, the brightness range is wide, and it takes a long time to reach the required thickness. The iron content in the coating is high.
(2) The influence of sodium hydroxide: When the sodium hydroxide content is too high, high-temperature operation is prone to burning; When the content of sodium hydroxide is too low, the dispersibility is poor
(3) Iron content significantly affects the coating’s properties. When iron content is too high, the coating’s iron concentration increases, resulting in a dull passivation film. Conversely, if the iron content is too low, the coating’s iron concentration decreases, leading to reduced corrosion resistance and an olive hue.
(4) The influence of brightener ZF-100A is too high, and the coating is brittle; Too low, no coating in low current areas, uneven passivation color; ZF-100B is too high, and the coating is brittle; Too low, the entire coating is not shiny.
(5) Temperature plays a crucial role in coating quality. When the temperature is too high, dispersion ability decreases, leading to higher iron content in the coating, reduced corrosion resistance, uneven passivation film color, and discoloration. On the other hand, if the temperature is too low, the high current density area burns, the coating becomes brittle, and the deposition rate slows down.
(6) The impact of cathode movement must be addressed through cathode movement. Moving too fast, the coating in the high current density area is rough; Too slow, may generate airflow, locally uncoated.
Common faults in galvanizing
1. Unclean oil removal
(1) The temperature of the pre-treatment solution is too low, heat it up to the required process range.
(2) Adjust the ultrasonic power or electrolysis current within the process range if either is too low.
(3) Regularly add and replace the pre-treatment solution as it ages.
(4) For parts with heavy oil stains that cannot be fully removed through standard processes, reduce oil consumption or use qualified rust-proof oil. Before hanging, manually wipe to remove the majority of oil stains.
(5) Clean the surface of the pre-treatment solution to remove excess floating oil stains, preventing them from adhering to the workpiece.
(6) Clean the rust removal tank and subsequent water washing tank if they become contaminated with oil.
(7) Clean the post-galvanization cleaning tank or the washing tank after brightening if they are contaminated with oil.
(8) Check the conductivity of the hanging fixtures, copper bars, flying target triangles, circular seats, and rectifiers in the oil removal tank. Clean or maintain them as necessary to ensure good conductivity.
2. The coating is not shiny
(1) Low current, check if the current is within the process range and make adjustments.
(2) If the anode area is too small or uneven, resulting in partial or partial unlightiness of the component, the condition and distribution of the anode should be checked and necessary adjustments should be made.
(3) The content of brightener is low, and brightener should be added at most 20% of the cylinder opening amount at a time. If it still does not light up, other reasons should be investigated.
(4) The content of zinc oxide is high, and the cyanide zinc ratio is too low. The concentration of zinc oxide should be reduced or sodium cyanide should be added to make the cyanide zinc ratio 1.5-2.0
(5) If there is dirt or low roughness on the surface of the substrate of the workpiece, or if the substrate is corroded, the workpiece should be polished or ground.
(6) In case of poor conductivity, it is necessary to check whether the hanging fixtures, copper bars, flying target triangles, round seats, and rectifiers have good conductivity, and clean or repair them if necessary.
(7) Intermittent current causes extinction corrosion of the coating, check the working condition of the rectifier.
3. Burnt parts
(1) The galvanizing current is too high and should be adjusted to the normal range.
(2) The area of the component is too small, and the component matching should be adjusted to facilitate current adjustment.
(3) The concentration of zinc oxide is too low to meet the normal current density requirements. Zinc oxide should be added or the zinc anode should be increased, or the concentration of sodium hydroxide should be increased to improve the anodic zinc dissolution rate.
(4) The workpiece should be subjected to corrosion during anodic electrolysis, and the anodic electrolysis should be adjusted or replaced.
(5) Cathodic electrolysis aging, excessive adsorption of impurities on the workpiece, and the formation of burnt like coatings in poor rust removal solution should be replaced with cathodic electrolysis and hydrochloric acid rust removal.
(6) The repaired parts have incomplete plating, forming a burnt coating. The unqualified coating should be cleaned before electroplating.
(7) There are too many impurities in hydrochloric acid rust removal, which forms a displacement layer on the surface of the workpiece. After galvanizing, a coating similar to burnt coating is formed, and hydrochloric acid rust removal should be replaced.
