The Process of Galvanising
Hot dip galvanisation is the process of coating steel, iron, or ferrous materials with a layer of zinc. This is done by passing the metal piece through a molten mixture of zinc at a specific temperature. The main purpose of this is for rust prevention and protection of ferrous materials from corrosion.
How does the process of galvanisation work?
Preparation of Work
It is critical to ensure that the materials are cleaned before hot dipping. This is to make sure that the molten zinc will form a sound and complete a metallurgical bond with the material. For the items to be thoroughly cleaned, they will be passed through a pickling process before entering the galvanising kettle. Any rust, paint, oil, and other surface contaminants are carefully removed from the steel by preliminary treatment.
Other cleaning methods are done such as subsequent acid cleaning, hydraulic acids, or pickling in sulphuric acid, which is then followed by rinsing. Rolled steel surfaces that are covered by heavy mill scale will require abrasive blast cleaning prior to acid cleaning.
After cleaning the material with acid, it is then immersed in a flux solution. Usually, the solution contains 30% of zinc ammonium with wetting agents that are maintained at 65°C. With this, the oxide film will be removed
The steel surface is now wetted by the molten zinc and will react to form zinc-iron alloy layers. The material remains in the bath until the required temperature is reached to allow the formation of the metallurgic bond. It will then be withdrawn at a controlled rate and carry the outer layer of zinc, which solidifies to form the outer zinc coating.
The period of the immersion in the galvanising bath may differ from several minutes up to half an hour or longer. The result of the galvanised coating is durable and tough, which comprises relatively zinc-iron and pure zinc alloy layers bonded metallurgically to the underlying metal. It will completely cover it inside and out, making it abrasion-resistant. The galvanised material provides internal as well as external protection, giving it superior protection over normal protective paint.
Another good thing about galvanising process is it gives a quality coating and a completely protected metal work. Protection is maintained by the surrounding galvanised coating as it provides abrasion resistance and rust prevention.