Surface treatment
Corrosion
Corrosion is a complicated chemical process. In extremely simple terms, it could be described as a reaction between a
substance and its surroundings. In the case of the sheet metal used in cars, it is iron which reacts with water and oxygen to
form ferric hydroxide or what we usually call rust.
One of the first steps in manufacturing iron is to remove the oxygen from the iron ore. This is necessary to make the iron
sufficiently strong for further processing. Pure iron is, however, chemically unstable. The iron always strives to take back
the oxygen and form ferric hydroxide (rust), which is stable.
If iron is to be able to form ferric hydroxide to any greater extent, then water is needed as well as oxygen. The water acts as
an electrolyte and starts the electromagnetic process that helps the unstable iron to absorb oxygen from the atmosphere.
Ferric hydroxide has a larger volume than iron, which makes the sheet metal crack when it corrodes. More oxygen and
water forces its way in and the corrosion worsens.
The corrosive process will be accelerated if the electrolyte (water) contains salt. Other factors that help cause corrosion are
heat and impurities in the surface of the iron.
The sheet metal is protected against corrosion by eliminating the factors that lead to its onset. The most common method is
to prevent water and oxygen from coming into contact with the sheet metal. On the Samand this is accomplished by
applying several coats of paint. In addition, large parts of the body are coated with zinc, which makes the metal less prone
to corrosion.
The surface treatment process
Samand
32
Technical description
To Next Page
Loading...
Need help?
General
