Difference Between Hot Rolling and Cold Rolling
Comparison Between Hot Rolling and Cold Rolling
The Major Difference Between Hot Rolling and Cold Rolling is that Hot rolling the metal above recrystallization temperatures. Whereas Cold rolling is processed in cold reduction mills followed by annealing and tempering.
|Metal is fed into the rolls after being heated above the recrystallization temperature.
|Metal is fed into the rolls when its temperature is below the recrystallization temperature.
|Hot rolled metal does not show a work hardening effect.
|Cold rolled metal hardening effect.
|Coefficient of friction between the rolls and stock is higher.
|Coefficient of friction between rolls and stock is relatively lower.
|The heavy reduction in cross-sectional area is possible.
|A heavy reduction in area is not possible.
|Close dimensional tolerances cannot be obtained.
|Section dimensions can be finished to close tolerances
|Very thin obtained.
|Aluminum foils up to 0.02 mm can be made.
|Poor surface finish with a scale on it.
|The smooth and oxide-free surface can be obtained
|Roll radius is larger.
|Roll radius is smaller.
- The process of rolling consists of passing the hot ingot through the two rolls, rotating in opposite directions, at a uniform peripheral speed.
- To confirm the desired thickness of the rolled section, the space between the rolls is adjusted and is always less than the thickness of the ingot being fed.
- When the metal passes through the rolls, there is a change in its grain structure.
- Due to squeezing, the grains are elongated in the direction of rolling and the velocity of material at the exit is higher than that at the entry.
- After crossing the stress zone, the grains start refining.
- Cold rolling is used for producing bars of all shapes, rods, sheets, and strips.
- Cold rolling is generally employed for providing a smooth and bright surface finish to the previously hot rolled steel.
- It is used to finish the hot rolled components, to close tolerances and improve their hardness and toughness.
- Before cold rolling, the hot rolled articles are cleaned through pickling and other operations.
- The same types of rolling mills, as in hot rolling, are used for cold rolling.
- The part being rolled is generally annealed and pickled before the final pass is made, so as to bring it to accurate size and obtain a perfectly clean surface.