What Is Galvanizing?
Galvanizing is a surface treatment metal plating process in which iron or steel components are coated with a thin layer of zinc. Zinc acts as a protective layer, protecting the underlying layer from corrosion and extending its service life. The process may sometimes be driven by electricity until a sufficiently thick layer of zinc is formed. This layer is not discrete, that is, the zinc is integrated with the steel on the surface to strengthen the surface.
Surface galvanizing is required where metal needs to work in harsh environments, or in structural applications where metal needs to maintain its strength for decades. The galvanized coating ensures that the raw material can withstand challenging conditions without compromising its key properties such as tensile strength, elasticity and durability. Extensive use of galvanized steel can be observed in the construction of bridges, guardrails and steel equipment in chemical plants.
Why Choose Galvanized Steel?
The main reason to galvanize steel is to extend its lifespan. Ordinary steel components, if not galvanized, may be subject to corrosion and rapid deterioration. Even when embedded in concrete, steel products can corrode due to acidification from carbon dioxide, moisture and high chloride content. The galvanized layer improves the anti-corrosion properties of the raw material, thereby enhancing its durability.
The galvanizing process also provides the toughest coating to resist mechanical damage during transportation, storage and installation. Installation costs are also low as the galvanized components are ready to use on arrival. Galvanized steel does not require any surface preparation, painting or inspection before installation. Even with a zinc coating, it still won't cause corrosion because zinc has a higher negative reduction potential. This causes the zinc to oxidize instead of the iron, ensuring product safety.
Galvanized steel is generally one of the most cost-effective alternatives to galvanizing, except for some large-scale applications. In the construction world, galvanized steel can become so expensive that builders may abandon the idea of using it entirely if they are on a budget. The second disadvantage is that while the zinc layer is resistant to red rust, it can still develop white rust when exposed to continued moisture.
Galvanizing Method
There are several galvanizing processes available, each with its own advantages and limitations. Let's take a look at some of the most common galvanizing methods used today.
Hot Dip Galvanized
Hot dip galvanizing is one of the most direct and economical galvanizing methods. It can cover a variety of complex shapes with relative ease. The surface of the material is cleaned of contaminants and any oxides before being immersed in the molten zinc bath. The molten zinc coats the steel parts with a zinc coating. The quality of metallurgical bonding depends on the efficiency of prior cleaning of the surface.
Electrolytic Zinc Plating
Electrolytic zinc plating, also known as electrogalvanizing, is the second most popular galvanizing method. It uses electrolysis to coat the metal with a layer of zinc, making it a form of electroplating. In this process, a steel workpiece is placed into a zinc solution with a second electrode, and direct current is passed through it. The electrical current ionizes the zinc solution, depositing a pure zinc coating on the metal.
Sherardising
It uses heat diffusion to create a zinc coating on ferrous metals. During this process, the metal to be coated is placed in a container filled with zinc metal dust. In the presence of this dust, the temperature of the workpiece increases to 400-450°C. The high temperatures cause the dust to diffuse into the metal, forming a zinc-iron alloy.
Pre-galvanized
Pre-galvanizing can be understood as a hot-dip process specifically suitable for long steel plates. During this process, the sheets are passed through a cleaning agent to prepare the material for galvanizing. After the metal sheets are cleaned, they are quickly passed through a bath of molten zinc. The rapid movement creates a thin, protective zinc coating that is more uniform than traditional hot-dip galvanizing methods. This method provides the fastest turnaround time for sheet metal.
