Steel and iron are galvanized by applying a layer of zinc over. Since zinc acts as a sacrificial coating, it can protect the steel or iron underneath, so it can extend the life of metal parts. But galvanizing is a complicated process, and there are several ways to achieve it. There are different forms of galvanizing, including hot-dip galvanizing and thermal diffusion galvanizing. These changes have their own unique advantages and disadvantages.
Therefore, it is helpful to understand the different forms of galvanizing before incorporating them into a prototype or manufacturing project. Galvanized metal is more common than you think. Structures such as building frames, metal benches, balconies, ladders and fire escapes can all be made of galvanized metal to ensure a longer service life and adequate protection from corrosion and damage.
Other examples can be found in auto parts and electrical appliances. In addition, galvanized steel and galvanized iron can be used in different manufacturing processes, from sheet metal manufacturing to CNC machining, making them the main manufacturing process.
This article reviews the basic knowledge of galvanizing and answers questions such as what is galvanizing, which metals can be galvanized, what is the purpose of galvanizing, what is the type of galvanizing, and how galvanizing can improve metal parts.
1. What is Galvanizing?
Galvanizing (or galvanizing) is the process of adding a layer of zinc to the outer surface of a metal, that is, steel or iron. The purpose of this is to add a protective coating to the underlying metal to reduce the possibility of corrosion or rust. The galvanizing process differs depending on the specific technology.
However, the most important part of this process is that it usually involves surrounding steel or iron in zinc, which may be in a liquid or dusty state. When zinc is introduced, the iron in the surrounding metal reacts with zinc to form a tightly bonded alloy coating. The end-to-end galvanizing process can be divided into three stages:
- Prepare the surface of steel or iron
- Actual galvanizing
- Post-galvanization surface treatment
Galvanizing is a relatively simple coating process that produces a fairly thin surface coating, usually about 80 µm, which is about three times the thickness of the electroplated coating.
2. Galvanized Material
The base materials that can be galvanized are mainly steel and iron. There is, however, the possibility of galvanizing other ferrous metals. The coating material for galvanizing is usually zinc.
However, the process similar to zinc plating is tin plating, that is, zinc is used instead of tin. In simple applications such as food storage, tin plating is possible, but its reliability is not as good as galvanizing: if the coating is damaged, tin will corrode the iron below.
3. Type of galvanized
The two most common forms of galvanizing are hot-dip galvanizing and electro-galvanizing. These two methods and other methods will be discussed below. To know which type of galvanizing to choose may require expert help.
1) Hot-dip Galvanizing
In the hot-dip galvanizing process, the metal is immersed in a hot-dip galvanizing bath at about 450°C. Zinc oxide forms on the surface of the coating when it is removed when oxygen and carbon dioxide react to form zinc carbonate.
Before galvanizing, the metal must be cleaned with a corrosive solution, and then pickled in an acid solution; Zinc ammonium chloride can also be used to prevent premature oxidation of the metal before galvanizing.
2) Electro-Galvanizing
Electro-galvanization is a combination of galvanizing and galvanizing: the current passes through a zinc bath with a zinc anode and a steel conductor. The coating produced by this process is thinner than hot-dip galvanizing and also creates a brighter surface finish suitable for cosmetic applications.
3) Sherardizing
This form of galvanizing has several names: zinc infiltration, thermal diffusion galvanizing, vapour galvanizing and dry galvanizing. It involves heating steel parts to 500°C and containing zinc powder in a closed rotating drum. The evaporated zinc diffuses to the surface of the steel part to form a strong bonding layer. It is ideal for small parts and internal parts of parts that need to be coated.
4) Galvannealing
Galvanizing is a combination of hot-dip galvanizing and annealing. The hot-dip galvanizing process is normal before the coated metal is passed through an air knife to remove excess zinc. Then, the metal is briefly heated at 500-565°C in the annealing furnace, so that the iron and zinc layers are mutually diffused to form a zinc-iron alloy layer.
4. Advantages of Galvanizing
The purpose of galvanizing is to form a protective coating of zinc on top of steel or iron parts. But why is this useful and what are the main advantages of galvanizing?
In order to prevent corrosive materials from reaching the weaker metal substrate beneath the zinc layer, the surface of galvanized steel is coated with zinc. This can extend the life of the substrate, especially in demanding applications.
- Prevent rust: galvanizing can significantly delay the time of rust.
- Create a sacrificial anode: The zinc coating is consumed by corrosive substances, so it provides protection to the underlying metal until it is completely exhausted. Even if scratches penetrate the coating, zinc will be used up before iron.
- Long duration: The zinc coating produced by galvanizing is tough and durable, and usually provides protection for the underlying metal for decades.
- Affordable price: Galvanizing is a fairly simple and affordable procedure that provides significant benefits with minimal expenditure.
- Creating a thick coating: The coating produced by galvanizing is thicker than the coating produced by galvanizing, though it may not be suitable for all applications.
5. Application of Galvanizing
The ability to prevent steel corrosion makes galvanizing widely used in many industries. The most common application is galvanized steel for construction: hundreds of thousands of tons of galvanized construction steel are produced every year for the manufacture of structures such as building frames, street furniture, fire escapes, ladders, and balconies.
Galvanized steel is also very common in the automotive industry. It can be made into anti-rust parts, including most of the car’s “white body”: its skeleton basis. Bumpers, beams, frames and chassis can also be made of galvanized steel.
In the telecommunications industry, rust prevention is a desirable feature, because telephone lines and electrical boxes are affected by various factors every day. Galvanizing can extend the life of these items.
6. Galvanized Metal Manufacturing
Galvanized materials are widely used, such as galvanized sheet metal, suitable for sheet metal processing, such as bending, stamping, or galvanized metal rods, tubes, rods, and suitable for CNC machining and other processes.
Galvanized materials are easy to process because the galvanized layer is softer than the underlying steel. Galvanized metal can also be welded, but zinc emits dangerous fumes, so proper ventilation is necessary. Unless the material is galvanized, painting on zinc-coated steel or iron is not particularly effective.
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