Rolling

Rolling
Process)

(Deformation

Rolling:
Rolling is plastic deformation of the metal by passing
between rolls to give it the desired shape.
 Metal is passed between two rolls that rotate in opposite
directions.
 Gap between the rolls being somewhat less than the
thickness of the entering metal.

Process:
• In the process of rolling the workpiece is fed from one side
into the rolls
• Reduces in thickness according to the section and gap
between the rolls.
• The reduction ratios have maximum allowable values for
different metals beyond which reduction is not practicable
in a single process.

Classification:
Rolling is classified according to the temperature of the metal
rolled:
 Cold Rolling
 Hot Rolling

Hot Rolling:
If the temperature of the metal is above its recrystallization
temperature, then the process is termed as hot rolling.

In hot rolling;
• Hot rolling permits large deformations of the metal to be
achieved with low number of rolling cycles.
• As the hot rolling process breaks up the grains, they
recrystallize and preventing the metal from hardening.
• Hot rolled material typically does not require annealing.
• Hot rolling is primarily concerned with manipulating
material shape and geometry rather than mechanical
properties.

Cold Rolling:
If the temperature of the metal is below its recrystallization
temperature, the process is termed as cold rolling.
In cold rolling;
• Cold rolling increases the yield strength and hardness of a
metal by introducing defects into the metal’s crystal
structure (dislocation density).
• These defects prevent further slip and can reduce the
grain size of the metal, resulting in hardening.
• Cold rolling is most often used to decrease the thickness
of plate and sheet metal.
• In cold rolling, high densities of imperfections
introduced throughout the deformed area.

are

• These defects can be either point defects (a vacancy on
the crystal lattice) or a line defect

Rolling Mills:
A rolling mill is a machine or factory for shaping metal by
passing it between a pair of work rolls.

Classification:
There are fundamentally two types of rolls:

 Supporting rolls
 Driving rolls
Rolling mills can be conventionally classified with respect to the
number and arrangement of the rolls:
 Two-high mills
 Two-high reversing mills
 Three-high mills
 Four-high mills
 Cluster mills
 Continuous mills
 Planetary mills

Rolled Products:
 Bloom (First breakdown product of ingots)
 Billet (Reduction of bloom by rolling)
 Slab (Hot rolled ingot)
 Plate (thickness greater than ¼ in.)
 Sheet & strip (thickness less than ¼ in.)
 Foil (very Small thickness just 0.002 in.)
Advantages:
 For large reduction in cross sectional area. (Hot rolling
carried out)
 Hot rolling doesn’t require annealing.
 For high strength. (Cold rolling carried out.)
 It reduces ductility of metals.
 In cold rolling, there is no need to control temperature.
 Good surface finish.

Applications
 Bars, Rods, Rails.
 To produce sheets & strips.
 Piping
 Parts for airplane