What is Cold Rolling ?

Cold rolling is a process by which the sheet metal or strip stock is introduced between rollers and then compressed and squeezed. The amount of strain introduced determines the hardness and other material properties of the finished product.

Why is Cold Rolling done ?
ANS – For Good Formability ,Superior Surface Finish and Reasonable Strength

Cold Rolling Process:

flowchart

Pickling

Why is Pickling done ?
To remove scales and oxide layers present on the surface of hot rolled steel Make the steel surface suitable for cold rolling Scales and oxide layers are harder than steel and hence hinder the process of cold rolling of low carbon
steel

How’s scale and oxide removal are achieved?
Hot rolled strip is passed through tanks containing hydrochloric acid wherein the acid dissolves the oxide layer The strip is then rinsed with water to remove any excess acid. dried and the strip is ready for cold rolling.

Pickling Process Variables.
Temperature : Strip temperature of 50 to 55degrees centigrade is maintained. This ensures
faster rate of reaction with the acid.
Acid Concentration: Acid concentration in tanks influence the dissolution of scales and oxides. Higher concentration is maintained in the first tank and decreases in the
subsequent tanks

Cold Rolling.

cold rolling mill

The advantages of cold rolling are good dimensional accuracy and surface finish. rolled Pickled Coils are reduced to the desired thickness.

Cold rolled sheet can be produced in various conditions such as skin-rolled, quarter hard, half hard, full hard depending on how much cold work has been performed. This cold working (hardness) is often called temper, although this has nothing to do with heat treatment temper.

In skin rolling, the metal is reduced by 0.5 to 1% and results in a surface that is smooth and the yield point phenomenon–excessive stretching and wrinkling in subsequent operations, is eliminated. This makes the metal more ductile for further forming and stretching operations.

Quarter Hard, Half Hard, Full Hard stock have higher amounts of reduction, up to 50%. This increases the yield point; grain orientation and material properties assume different properties along the grain orientation. However, while the yield point increases, ductility decreases.

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