Coated Steel – Galvanized steel:

Coated Steel – Galvanized steel:

Steel sheet coated through a heat process or through electrolysis with a layer of substance to protect the base metal (substrate) against corrosion. The most commonly used material is zinc which can be applied either using the heat process (hot-dip galvanizing) or using electrolysis (electro-galvanizing).

A. Galvanized steel products - Zinc coated galvanized GP and GC steel products are sturdy, light weight, bright and corrosion resistant. The functions of the zinc layer are mainly three folds:

(a) To retain the steel intact with its full initial strength

(b) To provide the surface a more pleasing appearance

(c) To increase the life of any suitable organic finishing system applied over it

In fact, zinc coatings provide the most effective and economic way of protecting steel against corrosion. Zinc coated steel is very environment friendly. Zinc is an integral part of our environment and occurs naturally in rocks, soil, air and water. Zinc is also an essential element for all life, from humans and animals to plants and micro – organisms. All types of zinc coated steel products are recyclable. In the last few decades, both the recycling technology and its capacity has been developed considerably in response to increasing environmental awareness and the cost-effective alternative supplies of raw materials for the steel and zinc industries. Presently, about 80 percent of the zinc is available from zinc coated steel that is recycled in India.

B. Galvanizing process: There are two main processes used in the production galvanized product namely: (i) Hot – dipped galvanizing and (ii) Electrolytic Galvanizing

(i) Hot – dipped Galvanizing – It is one of the basic and efficient corrosion resistant technique for producing galvanized steel. During the galvanizing process, steel coils are previously cleaned and pickled and then dipped into a bath of molten zinc to form a series of zinc / iron alloys integrated with the steel surface. As steel is removed from the bath, a layer of relatively pure zinc is deposited on the top of alloy layers. On solid deification, the zinc assumes a crystalline metallic luster, often known as “spangling”. The spangles can be enhanced and reduced depending on the end use. The life of galvanized coating in steel structures permanently immersed in liquids depends on the corrosion properties of the liquid and the thickness of the galvanized coating in the structure. Hot-dipped galvanizing technology has been greatly improved over the years and by the introduction of the sendzimir process or one of its variants, HDG products are introducing on the market share of electrolytic galvanized products in the western world because it is more cost effective.

(ii) Electrolytic Galvanized Steel - In the electrolytic galvanizing process, zinc ions from the electrolytic is deposited on the strip surface (cathode) under the influence of electric current using either soluble or insoluble anodes. The electrolyte is usually zinc sulfate or zinc chloride or mixed. The electro–galvanized strips are post treated with passivation solutions such as phosphate or chromate. The plating process controls the coating thickness resulting in much thinner coatings as well as double-side coatings. The automobile industries in Japan and the U.S. are using between 35 to 45 percent of the total steel consumed in the form of electro-galvanized steel sheets. These sheets have excellent surface finish and press formability for protection from corrosion of auto body, fuel tanks, exhaust pipes etc.