What is galvanizing?
During galvanizing, a layer of zinc is applied to a metal element that is prone to corrosion. The purpose of the process is to protect metals from rusting, thereby extending their lifespan.
Before a metal element is treated with zinc, it is thoroughly cleaned — for example, by abrasive blasting or vibratory finishing. As a result, we get a surface free from gaseous corrosion traces, rust, old coatings, or sand.
The next step is degreasing the material and etching it – to remove non-metallic particles such as scale. For this purpose, steel is immersed in hydrochloric or hydrofluoric acid, then it is subjected to fluxing — another bath, but this time in an aqueous solution of zinc chloride and ammonium chloride. What does fluxing do? After this bath, the steel is completely free of oxides. Finally, the metal element is dried at a temperature of up to 150 °C. With that, the steel is ready for galvanizing.
What are the types of galvanization?
There are several methods of galvanizing, which differ in how the protective zinc layer is applied:
Hot-dip galvanizing – also called immersion galvanizing. This method involves immersing steel in liquid zinc heated to 450–500 °C. This produces a durable and thick zinc coating that can last up to 100 years. This method is more expensive than electro-galvanizing.
Electro-galvanizing – this technique involves immersing steel in a special electrolytic bath containing zinc compounds. Zinc particles — under the influence of electric current — deposit on the metal item, which is then passivated and finally rinsed. This method yields an evenly distributed zinc layer, but unfortunately quite thin – 3 to 6 μm -which makes it less resistant to mechanical damage.
Spray – used mostly for large items or those sensitive to high temperatures. Here, zinc wire is melted and then sprayed onto the element using compressed air.
Powder galvanizing – a rather labor-intensive method, and thus increasingly rare. It involves placing a cleaned metal element in powdered zinc containing about 6% zinc oxide. This bath lasts several hours.
Applications of galvanizing
Galvanized elements are more durable, which is why they are widely used both in households and industry. Galvanized steel can be found in private homes — e.g., in electrical and heating installations. Important components of cars, motorcycles, and even bicycles are also made from such elements. Thus, galvanized steel is appreciated in the automotive, electrical, and also construction industries.