Hot-dip galvanizing
Galvanizing is the process of coating steel and iron products with zinc in order to increase their resistance to corrosion.
The protection method is based on the fact that the zinc in the coating reacts to corrosion first, keeping the base metal “intact”.
The thickness of the zinc layer depends on the temperature and duration of the galvanizing process and ranges from 6 μm (for electroplating) to 1.5 mm.
There are various methods of applying a zinc coating, namely: hot-dip galvanizing (immersion of products in molten zinc at 450–480°C), electrolytic (electroplating) galvanizing, thermal-diffusion galvanizing or sherardizing (saturation of steel products heated to 400–420°C in a zinc powder environment), and cold galvanizing — applying a special zinc-powder composition to a prepared surface.
Metalogalva Prime Moldova's production is focused specifically on hot-dip galvanizing of metal products as the most reliable and economically justified method of protecting steel and iron.
Benefits of zinc coating
Protecting the surface of steel and iron products with a zinc coating offers several advantages:
- high corrosion resistance (close to that of stainless steel),
- the coating's ability to self-heal on micro-damages (zinc spreads at about 2 mm per year at ambient temperatures up to 70°C),
- high throughput of the production lines,
- high thermal and electrical conductivity of the coating.
Technological process
To allow handling of products during hot-dip galvanizing, they are secured on special traverses.
Before galvanizing, the products undergo chemical surface preparation.
The process includes the following stages:
Degreasing
removal of oil and lubricant contamination from product surfaces using acidic solutions.
Pickling
removal of iron oxides from the surface using acids with corrosion inhibitors.
Rinsing
removal of residual acid solution in water.
Fluxing
treatment in a zinc/ammonium chloride solution to prepare the surface for reaction with molten zinc and to prevent oxidation.
Drying
heating products to about 100°C to remove moisture and reduce thermal shock.
Galvanizing
immersing products in molten zinc with at least 98.5% pure zinc at about 450°C; aluminium and other elements may be added as required.
Cooling
carried out by immersion in water.
Passivation
protection against the formation of “white rust”, which appears when zinc oxidizes in humid environments.
Thus, all Metalogalva Prime Moldova products go through a full cycle of preparation, treatment and hot-dip galvanizing on modern equipment, in accordance with current requirements and European standards.