Galvanizing refers to a surface treatment technique that involves coating a layer of zinc on the surface of a metal, alloy, or other material for aesthetic and rust prevention purposes. The main method used is hot-dip galvanizing.

Zinc is easily soluble in acids and can also dissolve in bases, hence it is called a zwitterionic metal. Zinc hardly changes in dry air. In humid air, a dense alkaline zinc carbonate film is formed on the surface of zinc. In environments containing sulfur dioxide, hydrogen sulfide, and marine environments, zinc has poor corrosion resistance, especially in high temperature and humidity environments containing organic acids, where zinc coatings are highly susceptible to corrosion. Zinc is mainly used to prevent corrosion of steel, and its protective performance is closely related to the thickness of the coating. After passivation treatment, dyeing, or coating with protective agents, the protective and decorative properties of zinc coatings can be significantly improved.

The difference between colored zinc and white zinc plating on metal surfaces

After passivation of zinc coatings, different colored passivation films or white passivation films are usually obtained depending on the passivation solution used. The corrosion resistance of rainbow colored passivation film is more than 5 times higher than that of white passivation film, and rainbow colored passivation film is thicker than white passivation film; On the other hand, when the surface of the rainbow colored passivation film is scratched, in humid air, the hexavalent chromium in the passivation film near the scratched area has a "re passivation" effect on the scratched area, repairing the damage and restoring the passivation film to its integrity. Therefore, rainbow colored passivation is often used for galvanizing.

The colorless passivation film has a clean white appearance and is often used in daily hardware, construction hardware, and other products that require a white uniform surface. In addition, there are black passivation and military green passivation, which are also applied in industry.

Color zinc plating is a passivation treatment on the basis of galvanizing, also known as "sealing" in actual industrial production. After the electroplating process, it is placed in a specialized solution, and after a certain period of time, a layer of film is attached to it. The product color remains unchanged, but the corrosion resistance of the electroplated surface is greatly improved. The galvanized film after passivation has stronger corrosion resistance than the galvanized film alone. Plating white zinc and plating color zinc are mainly due to the different formulation of the plating solution. There is now another type of plating blue white zinc, which is very beautiful.

The main purpose of galvanizing is rust prevention, followed by appearance. Therefore, the inspection of galvanized products is mainly based on salt spray testing, with time as the standard, mainly depending on design and usage requirements. Generally, there are 12 hours and 24 hours. If there is no corrosion or rust phenomenon within the specified time, it is qualified. There is a specialized salt spray testing machine, and appearance inspection is not enough. The salt spray test for color zinc plating can definitely pass, while white zinc plating is relatively difficult and difficult to pass.

With the development of technology and the adoption of high-performance galvanizing brighteners, galvanizing has moved from a simple protective purpose to a protective decorative application

There are two types of zinc plating solutions: cyanide plating solution and cyanide free plating solution. Cyanide plating solution has good plating ability, and the obtained coating is smooth and fine. It has been widely used in production for a long time. In recent years, due to the high toxicity of cyanide and serious environmental pollution, low cyanide, micro cyanide, and cyanide free plating solutions have been tended to be used.

Types of galvanizing

01 Cold galvanizing

Cold galvanizing, also known as electrogalvanizing, is the process of using electrolytic equipment to process and then galvanize pipes. After treatment, the pipe fittings are placed in the solution and connected to the negative electrode of the electrolysis equipment. A zinc plate is placed opposite the pipe fittings and connected to the positive electrode of the electrolysis equipment