When Steel or Iron is coated with zinc in order to be able to provide stronger protection against corrosion of the base, the process is called Galvanizing. Developed simultaneously in France as well as English in 1837, the process of galvanizing sheet iron employed a hot dipping method to coat the metal with zinc. Early galvanized metals were hand dipped, very similar to tinplate. These days, with the advent of modern technological innovations, almost all galvanized iron and steel is electroplated.
There are
various methods using which steel sheets can be galvanized –
a. Hot Dip Galvanizing: This is a simple process in which steel or iron
is immersed in molten zinc, after the base metal’s surface has been properly
cleaned. When the molten zinc freezes, it provides a relatively thick coating
that forms a crystalline surface pattern known as spangles. During this
process, a multiple layered structure of steel-zinc alloy is formed between the
base metal and the inner surface of the applied coating. These layers thus when
formed are hard, fragile and may peel if the steel element is bent.
b. Electro galvanizing: This method involves the immersion of the metal
in an electrolyte, which is basically a solution of zinc sulphate or cyanide.
Electrolytic action deposits a direct coating of pure zinc on the surface of
the metal and hence the thickness of the coating can be accurately controlled
using the process. But the thick coatings that are sought by the hot-dip
galvanizing process are usually not possible with this process.
c. Sherardizing: A very interesting process in which a thoroughly
cleaned metal sheet is placed in an air-free enclosure where it is surrounded
by metallic zinc dust. The architectural element is then heated to produce a
thin zinc alloy coating that fits exactly to the configurations of the sheet
metal. The only limitation of this process is that it can be applied only to
relatively smaller steel sheets.
d. Metallic Spraying: A spray of molten zinc is applied to a clean
metal sheet and the coating is then heated to fuse with the surface to produce
an alloy. The coating acquired by this process would be less brittle and won’t
peel on bending. But the coating is also more porous and becomes impermeable
with time as corrosion fills the process.
Galvanizing has
a lot of advantages thus galvanizedsteel sheet has a lot of applications. The
construction industry is one of the greatest consumers of galvanized steel
products, with steel sheets being used for support beams, piping, heating and metal
roofing, which is popular in some regions because of its
durability, rust-resistance, and ability to withstand extreme weather
conditions. Steel buildings are relatively low-cost construction options
because they are strong, yet much lighter in weight than traditional building
materials and have a lower foundation load.
The automobile and aircraft
manufacturing industries are also large consumers of galvanized metals. Sheets coated
by hot dip galvanizing are used for the roof, seats, parking brakes, oil pans,
and spring housings. Galvanized steel is used to make outdoor grates, which are
available in a variety of sizes and can have either smooth or serrated,
slip-resistant surfaces. These are frequently used for industrial walkways and
road grate covers. Galvanized sheets are also used in electronic appliances,
computers, and precision instruments.
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