The general hot-dip galvanizing process consists of applying zinc surface coatings to iron and steel parts and elements, by dipping them in molten zinc baths at a temperature of 450ºC. The purpose of this process is to achieve the protection of metal elements and parts against corrosion caused by moisture and air pollution.
The main phases of the process are as follows:
- The process starts when the parts are received and loaded. The material is then weighed, coded and placed in various tools and equipment ready to be galvanized.
- Remains of grease and oil are removed from the parts by acidic degreasing.
- Slag, scaling and rust are removed from the metal parts by stripping with hydrochloric acid diluted in water.
- After the stripping process, the parts are rinsed or washed with water.
- The flux-dip process consists of submerging parts in a solution of zinc chloride and ammonium chloride salts, thereby achieving activation of the metal surface. It is actually an etching process.
- The parts are then placed into a drying kiln for approximately 45 minutes at 90ºC. The salts become crystallized and moisture is eliminated, thereby avoiding splashing and the production of slag in the later stage.
- The hot-dip galvanizing stage consists of submerging metal parts in a bath with molten zinc at 450ºC. Here an Fe-Zn reaction occurs resulting in the formation of alloy layers and a pure zinc coating.
- Parts can be cooled by submerging them in water or simply leaving them to cool, which is what we do at GALVASA, unless the customer requests otherwise.
- GALVASA offers its customers the option of organic passivation to avoid white spots and to guarantee shine and an aesthetic appearance of the newly galvanized material.
- Lastly, the materials are inspected and packed to be collected by the customer.
Formation of Alloy Layers
During the hot-dip galvanization process, three alloy layers are formed in the Fe-Zn inter-metallic phase, apart from a pure zinc outer layer that provides the material with very high corrosion resistance properties.
With this coating, the so-called "galvanic cell" is formed, which protects galvanized parts from any local scratches or damages in areas in which the base steel is exposed. This is a form of local cathodic protection in which zinc acts as a sacrificial anode.