3. • Rolling is the process in which the metals and alloys
are plastically deformed into semi finished or
finished condition by passing between circular
cylinders.
• Due to the frictional forces the metal is drawn into
the opening.
• Metal Changes its shape due to high compressive
forces.
• Both hot(for drastic shape changing) and cold
rolling(for finishing) process are there.
• From the start ingot- blooms- billet- slaps which are
further rolled into plat, sheet, rod, bar, pipe, rails.YoucaN
6. • The metal contact
each of the roller
along the arc(AB),
which is known as the
“flat strip” arc of
contact.
• This arc corresponds
to the central angle “α”
called angle of contact
or Bite.
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7. 900
900 - α
Resolving horizontal component forces
If α value is higher than the metal
would not enter the space between the
rolls automatically.YoucaN
8. • It depends on lubrication, work material and also
on the temperature.
• In cold rolling the value of coefficient of friction is
around 0.1 and in warm working it is around 0.2.
• In hot rolling it is around 0.4 In hot rolling sticking
friction condition is also seen and then friction
coefficient is observed up to 0.7.
• In sticking the hot wok surface adheres to roll
and thus the central part of the strip undergoes with
a severe deformation.
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9. ingot Slab
Strips
From the start ingot- blooms- billet- slaps
which are further rolled into plat, sheet, rod,
bar, pipe, rails.
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17. Roll force
F= contact Length* width of strip * average ture stress
=L * w * True stress average
Power per roll
P= 2*3.14*Force* Length * speed in rpm / 6000
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18. • Classifications based on number of rolls
• Two high rolling mills
• Three high rolling mills
• Four high rolling mills
• Multi roll rolling mills
• Universal rolling mill
• Planetary rolling mill
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19. • Two high rolling mills(single
direction)
• Constant direction rolling
• Upper rolls is moveable one to set the distance.
• For single step reduction it is better one.
• If successive reduction is need we have
to change the distance for each operations.
• Least expensive
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20. • Two high rolling mills(both
direction)
• For successive reduction this is better than single direction
rolling.
• We can set a different distance for each direction.
• Two high reversing mills are often used for the first rolling of
an ingot into blooms and slabs.
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21. • Three high rolling mills
• Three rolls with constant direction
of rotation are arranged in a single vertical plane.
• Lifting table used to rise or lower
the metal after each pass.
• Both top and bottom rolls
are driver rolls
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22. • Four high rolling mills
• The bending of the roller is less if the diameter of the roller is
high. At the same time the power consumption and force P
value also very high for big diameter rollers.
• To over come this problem small Diameter rollers with
larger diameter back up rollers are used. This can be used
for both directions.
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23. • Multiple roll mills
• By reducing the work roll diameter will produce
bending effect on the back up rolls.
• So in multiple roll mills a cluster of 6, 12, 20 rolls are
used to manufacturing strips. Form 0.001mm thick
and 2000 mm wide. YoucaN
In four high rolling the
diameter of the back up
rolls can not be greater
that 2 to 3 times that of
the work rolls.
32. • Universal rolling mill
• Metal reduction occurs in both
horizontal and vertical rolls.
• Vertical rolls are mounted either one side
or both sides
• Horizontal rolls may be either two, three
or four high arrangement.
• Used for roll wide strips, sheets, plates
and slabs that requires both rolling
edges and also for rolling of H sectioins.
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35. • Classifications based on number of rolls
• Planetary roll mills
• Consist of a pair of heavy backing rolls surrounded by a
large number of planetary rolls.
• Each planetary roll gives an almost constant reduction to the
slab as it sweeps out a circular path between the backing rolls
and the slab.
• As each pair of planetary rolls ceases to have contact with the
work piece, another pair of rolls makes contact and repeat that
reduction.
• The overall reduction is the summation of a series of small
reductions by each pair of rolls. Therefore, the planetary mill
can hot reduces a
slab directly to strip in one pass through the mill.
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37. • Continuous rolling mills(tandom)
• Arrangement is similar to two- high rolling mill.
• Here the metal work piece passes from one roll pass to
another and we get continuous reduction in size.
• Used for mass production
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39. • Various shapes can be produced
• Straight and long structural shapes, solid bars, I-beams,
channels, railroad rails.
• Ring rolling
• Thread rolling
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40. • Thick ring is expanded into a large diameter ring with a
reduced cross section.
• Ring is placed between two rolls and one of the roll is
driven and the ring thickness is reduced by bringing the
rolls closer together as they rotate.
• The reduction in thickness of the ring is compensated by
an increase in the rings diameter.
• Short production time, close tolerances and material
savings.
Video- 4. Forging, Ring Rolling, Open-Die Forging,
Hammer Forging-Kihlsteel.se
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45. • It is a cold forming process by which straight or tapered
threads are formed.
• Threads are formed on the rod or on wire with each stroke of
a pair of flat reciprocating dies.
• In the die we have the required thread impressions.
• One die is stationary and another is moveable one.
• The thread is formed by rotating and squeezing the blank
between hardened steel dies.
• The displaced material forms the roots of the thread and,
at the same time it forced radially outward to form the
crests.
• The die penetrated on the work, so this will create the
impressions on workpiece. YoucaN
46. • Here with out loss of material we can prepare the thread.
• Good surface finish and good fatigue life products
• Machining thread cuts the grain flow lines of the material.
• Rolled threads have a grain flow pattern that improves
the strength of the thread.
• The threads are rolled on metals in the soft conditions
and threaded fastness such as bolts are made by this
process.
• The lubrication is very important in thread rolling process
to minimize the defects.
• Spur and helical gears can be produced by cold rolling
process similar to thread rolling.
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53. When a round bar is subjected to radial compressive forces,
stresses develop at the center of the bar.
When it is subjected continuously to these cyclic
compressive stresses, the bar begins to develop a small
cavity at its center, which then begins to grow.
The axes of the rolls are skewed in order to pull the round bar
through the rolls by the axial component of the rotary motion.
An internal mandrel assists the operation by expanding the
hole and sizing the inside diameter of the tube.
The mandrel may be held in place by a long rod, or it may be
a floating mandrel without a support.
Because of the severe deformation that the bar undergoes,
the material must be high in quality and free from defects
(since internal defects may propagate rapidly and cause
premature failure of the part during forming).
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56. • Surface defects
• Internal structural defects
• Surface Defects:
• Defects such as scale, rust, scratches, cracks etc.
• Due to impurities and inclusions in the original cast
material or various other conditions related to material
preparation and rolling operations.
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57. • Wavy edges can be caused because of the elastic
deflection of the rolls due to the rolling force acting
on them.
• The edges of the rolled part gets thin and will experience
compressive stresses.
• These compressive stresses cause the rolled sheet to
be wavy at the edges.
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59. • These are also caused due to the bending of rolls
under the rolling pressure similar to wavy edges.
• Zipped cracks will be seen at the centre due to the
bending deformation of the rolls.
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60. • Due to the non uniform deformation of metal across the
width.
• The lateral spread is more prominent towards the edges
which will cause the edge cracks.
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61. • The top and bottom surface of the rolled part expands
less compared to the middle portion of the part. So the
middle portion will tear.
• Due to the Defects in the original cast material also
reason for alligatoring
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