Galvanizing refers to a surface treatment technology that coats on the surface of the metal, steel or alloy with a protective layer of zinc to prevent rust problems and maintain aesthetics.
Zinc is an amphoteric metal that can be soluble in acids and alkalis. In addition, the corrosion of zinc is very slow. In a humid environment, a zinc carbonate film will be formed on the surface of zinc. When zinc is galvanized on steel, it becomes alloyed and protected by the yin and yang. The working principle of galvanizing is using a plating tank equipped with a galvanizing solution, and there are specially treated parts to be plated (cathode) and plated metal (anode). The two poles are connected with the DC power supply's positive pole and negative pole. After being energized, the metal ions in the zinc plating bath will move to the cathode due to the effect of the potential difference, and at the same time, form a layer of plating. At this time, the metal ions of the anode will enter the galvanizing bath in order to maintain the concentration of the metal ions being plated. During the process of galvanizing, we need to control the temperature, the power-on time, the composition of the galvanizing bath, and the quality of the anode material, because these factors will influence the quality of the galvanizing process.
The protective performance after galvanizing is related to the thickness of the coating. With the development of galvanizing technology and the use of brighteners, galvanizing can greatly improve protection performance and aesthetics. Compared with general paint coatings, galvanizing is more durable. When a part of the steel is corroded, the paint coating will peel off easily. Therefore, the best way to protect steel is to use galvanizing. The most commonly used galvanizing method is to use hot-dip galvanizing. We will explain its characteristics and methods in detail below.
Steel material is often used to build structures. After a long time of external environmental factors, steel is easily oxidized, resulting in rust and corrosion. Therefore, we can choose to use hot-dip galvanizing to extend the service life of steel and reduce maintenance costs. We do not need to apply a layer of protective paint on the galvanized steel. The cost for galvanizing steel is relatively lower than stainless steel.
Types of galvanizing
Hot-dip Galvanizing
Most of the surface galvanizing methods of steel plates are using hot-dip galvanizing. The method of hot-dip galvanizing is to immerse the metal in liquid molten zinc for galvanizing. First of all, the metal that needs to be galvanized will be cleaned manually or chemically to ensure the metal has a co-solvent that can eliminate the residual oxide after the cleaning process. Subsequently, the metal is completely immersed in the molten zinc to form a uniform coating of zinc and zinc-iron alloy on the surface. The zinc ions in the alloy layer will further diffuse to the substrate, thereby forming a mutual soluble layer of zinc and iron. Then, the surface of the alloy layer will be wrapped with a zinc layer. Hot-dip galvanizing is suitable for use in strong corrosive environments such as high-strength acid and alkali medium.
The feature of hot-dip galvanizing is the steel surface is covered with a layer of pure zinc, which can prevent the surface of steel from contacting with other corrosive solvents and play a protective role. Besides, zinc has good ductility, so various forming tasks such as cold punching, bending, and wire drawing can be performed without damaging the coating during the process of hot-dip galvanizing. After the hot-dip galvanizing process, the steel surface is bright and beautiful.
Electro-galvanizing
Electro-galvanizing is a method that does not require the use of molten zinc to galvanize， but uses the current in the electrolyte solution to transfer the zinc ions to the metal. Zinc will produce a protective zinc carbonate film in a humid environment, which can protect the internal metal from corrosion by external factors. This is a very economical and versatile method to form protective coatings. The zinc layer produced by electro-galvanizing is relatively pure, so it has high corrosion resistance and can protect metal objects more effectively. The electro-galvanizing method is suitable for the galvanizing process of small fasteners, such as fine-threaded fasteners. Besides, the method of electro-galvanization is widely used, whether it is in the aerospace field, chemical engineering, electronics industry or instrument, etc.
Mechanical plating
Mechanical plating is an "electroless plating" method of electroplating. Its main feature is to put zinc powder, water, accelerator, glass balls, metal plating parts, etc. into a rotating drum. As the roller drum rolls, the glass balls will rub and impact on the metal-plated parts, and under the action of the chemical accelerator, the zinc powder will be evenly plated on the surface of the metal-plated parts. The zinc outer layer of mechanical plating is thicker than normal electro-galvanizing. The method of mechanical plating is mainly suitable for threaded parts made of steel.
Sherardizing
The sherardizing process uses zinc powder to diffuse to the surface of the metal under the action of high temperature (usually above 300°C) to form a protective layer. This process needs to be completed in a closed drum, and sand needs to be added as a filler during the process. Now, a few people will use this type of galvanizing method to galvanize the metal, because this galvanizing method is very time-consuming and expensive.
Above we have roughly described several common galvanizing methods, the more extensive one is still hot-dip galvanizing. Through the above articles, we hope all of you can better understand the advantages and types of galvanizing. If you are looking for any galvanized products or services, please contact MecHero at 011-7000 7687 or send your inquiry to my.mechero@gmail.com. We look forward to assisting with your construction projects.
Photo credit: Premier Galvanizing, GB Galvanizing, Pexels