There are three major links in electroplating zinc: pre-plating treatment, electroplating process control, and post-plating treatment.
Pre-plating treatment
Pre-plating treatment is the basis for electroplating and the key to ensuring product quality. If the substrate to be plated is not treated to the specified requirements before electroplating, even if there is a good electroplating solution, appropriate electroplating parameters and good control of the electroplating parameters equipment and highly skilled personnel, it is impossible to obtain an electroplating layer that meets quality requirements. Before electroplating, not only the grease present on the base metal and foreign matter that affects the adhesion of the coating and other quality requirements must be removed, but also its surface oxide must be removed. The surface must have a specified cleanliness and a certain activity to ensure that the coating is firmly bonded to the substrate. Sometimes, some other special pre-plating treatments are also required based on the required appearance of the electroplated layer.
Electroplating process control
The use conditions and service life of electroplated zinc metal or components are closely related to the thickness of the electroplated layer. The stricter the use conditions and the longer the service life, the thicker the required electroplated zinc layer should be. Different products should be based on the specific environment of use (Temperature, humidity, rainfall, atmospheric composition, etc.) to determine the thickness of the electroplating layer for the expected service life. Blind thickening will cause various wastes. But if the thickness is insufficient, the expected service life requirements will not be met.
Different manufacturers, based on their own equipment conditions, must first compile a relatively complete and reasonable process flow when determining the plating type, clarify the plating parameters, control the concentration of the plating solution, and carry out standardized operations.
Post-plating treatment
Electroplating post-processing (passivation, hot melting, sealing and hydrogen removal, etc.) for the purpose of enhancing the protective performance, decorativeness and other special purposes of plated parts.
After galvanizing, chromate passivation or other conversion treatments are generally performed to form a corresponding type of conversion film. This is one of the key processes to ensure the quality of post-plating. After passivation, it is best to undergo aging treatment (70% in the oven). ~80oC). Passivation can be divided into the following forms:
a. Color blunt: HNO3, H2SO4, CrO3 (three acids are indispensable)
b. Blue and white blunt: F+Cr
c. Silver blunt: Ba+Cr
d. Black blunt: Cr+Ag or Cr+Cu
e. Golden yellow blunt: Cr+reducing agent.
Color passivation: Suitable for zincate galvanizing. After passivation, the surface of the parts will be red, green, and slightly yellow (Cr+6 red, Cr+3 green), and purple cannot appear (the appearance indicates that the passivation film layer is loose). The simplest method is to rub your fingers back and forth on the surface of the part several times without any discoloration (fading).
Blue-white passivation: Since the fluoride in the passivation solution gradually decreases with time, the blue color on the surface of the parts will gradually become lighter, and the color of workpieces produced in the same shift cannot be maintained well. Therefore, the passivation process must be strictly controlled , and pay attention to the thickness.
Silvery white blunt: Does not change with time, and the color maintains good consistency.