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ROLLING
BY. S. LUCAS
ROLLING
Deformation process in which work thickness is reduced by
compressive forces exerted by two opposing rolls
The rolling process (specifically, flat rolling)
ROLLING
 This is the process of reducing the thickness or
changing the cross-section of a work-piece by
compressive forces exerted by a pair of rotating
rolls. or
 The process of plastically deforming
metal by passing it between rolls.
 The products are flat products, like: plates &
sheets.
 Plates are used for structural applications like
bridges, ships & nuclear vessels.
 Sheets (generally 6mm or less in thickness) are
used for automotive, beverage cans, office &
kitchen equipment.
CONT……..
• Rolling is the most widely used
forming process, which provides high
production and close control of final
product.
• The metal is subjected to high
compressive stresses as a result of
the friction between the rolls and the metal
surface
THE ROLLS
The rotating rolls perform two main functions:
• Pull the work into the gap between them by
friction between work-part and rolls
• Simultaneously squeeze the work to reduce
cross section
WHERE
IT
IS
DONE
Rolling mill is a machine or a factoryfor
shaping metal by passing it through
rollers
A rolling mill basically consists of
• rolls
• bearings
• a housing for containing these parts
• a drive (motor) for applying power
to the rolls and controlling the
speed
TERMINOLOGY
Bloom is the product of first breakdown
of ingot
(cross sectional area > 230 cm2).
Billet is the product obtained from a
further reduction by hot rolling
(cross sectional area > 40x40 mm2).
Slab is the hot rolledingot
(cross sectional area > 100 cm2 and with
a width ≥ 2 x thickness).
Continued...
FURTHUR
ROLLING
PROCESSE
S
MILL
PRODUCTS
Plate is the product with a thickness > 6
mm.
Sheet is the product with a thickness<
6 mm and width > 600 mm.
Strip is the product with a thickness < 6
mm and width < 600 mm.
TYPES OF ROLLING
• Based on work piece geometry :
– Flat rolling - used to reduce thickness of a rectangular
cross section
– Shape rolling - square cross section is formed into a
shape such as an I-beam
• Based on work temperature :
– Hot Rolling – most common due to the large amount
of deformation required
– Cold rolling – produces finished sheet and plate stock
Some of the steel products made in a rolling mill
FLAT ROLLING AND ITS
ANALYSIS
R = roller radius
p = roll pressure
L = contact length
θ = contact angle
vr = rollspeed
to = initial plate
thickness
tf = final plate thickness
vo = plate entry speed
vf = plate exitspeed
Side view of flat rolling, indicating before and after thicknesses,
work velocities, angle of contact with rolls, and other features.
FLAT ROLLING AND ITS
ANALYSIS
• The work enters the gap between the rolls at a velocity vo and
exits at a velocity vf. Because the volume flow rate is constant
and the thickness is decreasing, vf should be larger than vo.
• The roll surface velocity vr is larger than vo and smaller than vf.
This means that slipping occurs between the work and the rolls.
• Only at one point along the contact length, there is no slipping
(relative motion) between the work and the roll. This point is
called the “Neutral Point” or the “No Slip Point”.
FLAT ROLLING AND ITS
ANALYSIS
• In flat rolling, the work is squeezed between two rolls
so that its thickness is reduced by an amount called
the draft:
where
d: draft
to: starting thickness
tf : final thickness
d to t f
FLAT ROLLING AND ITS ANALYSIS
• Rolling may not be possible (the sheet will not be pulled) if the
draft is large. The maximum draft for successful rolling per pass
is:
Where:
dmax : maximum draft successful rolling perpass
μ : coefficient of friction
R : roll radius
d 2
R
max
to t f
2
R
of passes
Number
Example:- A series of cold rolling operations is to be used to reduce
the thickness of a plate from 50 mm down to 25 mm in a reversing two
high mill. Roll diameter =700 mm and coefficient of friction between
rolls and work = 0.15. The specification is that the draft is to be equal
on each pass.
Determine (a) minimum number of passes required, and
(b) draft for each pass.
Solution
4 passes
3.17
0.15 350
50 - 25
of passes
number 2
2
R
to t f
4
50 - 25
of passes
number
per pass
Draft 6.25 mm
to t f
HOT ROLLING
Hot rolling is
a metalworking process that occurs above
the recrystallization temperature of the
material.
Hot rolled metals generally have little directionality
in their mechanical properties and deformation
induced residual stresses.
However, in certain instances non- metallic
inclusions will impart some directionality
Also includes
cooling ....
Hot rolling is used mainly to produce sheet metal
or simple cross sections, such as rail tracks.
Non-uniformed cooling will
induce a lot of residual
stresses, which usually occurs
in shapes that have a non-
uniform cross-section, such
as I-beams and H-beams.
APPLICATION
Advantages Of Hot Rolling Process
 Hot rolling can greatly reduce energy consumption and costs.
 The metal plastic deformation is high during hot rolling, and the
deformation resistance is low,
which reduces the energy consumption of metal deformation.
 Hot rolling can improve the processing performance of metals and
alloys. That is to say, the coarse grains during foundry are broken, the
cracks are healed, the casting
defects are reduced or eliminated, and the as-cast microstructure is
transformed into a
deformed structure to improve the processing properties of the alloy.
 Hot rolling usually uses large ingots and large reduction rolling, which
not only improves
production efficiency, but also creates conditions for increasing rolling
speed and achieving
continuous and automated rolling process.
Disadvantages Of Hot Rolling Process
After hot rolling, non-metallic inclusions (mainly
sulfides and oxides, as well as silicates) inside the
steel are pressed into thin
sheets, causing delamination (sandwich).
The delamination greatly deteriorates the tensile
properties of the steel in the thickness direction,
and it is possible that interlinear tearing occurs
when the weld is shrunk.
The local strain induced by weld shrinkage often
reaches several times the yield point strain and is
much larger than the strain caused by the load.
Residual stress caused by uneven cooling.
The residual stress is the internal
self-phase equilibrium stress without
external force.
The hot-rolled steel of various
sections has such residual stress.
 The larger the section size of the
general section steel, the larger the
residual stress.
 Although the residual stress is self-
phase-balanced, it still has some
influence on the performance of
steel members under external force.
 Such as deformation, stability, fatigue and other aspects may
have adverse effects.
 Hot rolling does not control the mechanical properties required
for the product accurately, and the microstructure and
properties of the hot rolled product are not uniform.
 The strength index is lower than that of the cold work
hardened product, and higher than the fully annealed product,
the
plasticity index is higher than that of the cold work hardened
product, and lower than the fully annealed product.
 The thickness of the hot rolled product is difficult to control
and the control precision is relatively poor; the rough Ra value
of
the surface of the hot rolled product is generally 0.5 to 1.5 μm.
 Therefore, hot rolled products are generally used as blanks for
cold rolling.
COLD ROLLING
Cold rolling occurs with the
metal below its
recrystallization temperature
(usually at room temperature).
It also improves the surface finish and
holds tighter tolerances.
Due to smaller size of the workpieces
and their greater strength than hot
rolled stock, four-high or cluster mills
are used.
Commonly cold-rolled products include
sheets, strips and rods; products being
smaller than the same products that are
hot rolled.
Cold Rolling Process
Advantages Of Cold Rolling Process
No heating required
Better surface finish obtained
Superior dimension control
 Better reproducibility and
interchangeability of parts
Improved strength properties
Directional properties can be
minimized
Disadvantages Of Cold Rolling Process
Higher forces required for deformation
Heavier and more powerful equipment
required
Less ductility available
Metal surfaces must be clean and scale-free
Strain hardening occurs (may require
intermediate anneals)
Imparted directional properties may be
detrimental
May produce undesirable residual stresses
Application Of Cold Rolling Process
▪
Foil- The Thickness is less than 0.2 mm, used
mainly in the packaging industry Foil is also used
for building insulation, electrical applications and
in the printing industry.
Sheet-Thickness ranges from 0.2 mm and 6mm,
used for a wide variety of industry including
construction where it is used in aluminum siding
and roofing. Sheet is also used in transport sectors
for making automobile body panels, airframes etc.
Plate-It is the rolled product, which is over 6mm
in thickness. It also has a number of applications
including airframes, defence vehicles and
structural components in building
VARIOUS CONFIGURATIONS OF
ROLLING MILLS
(a) 2-high rolling mill
(b) 3-high rolling mill
VARIOUS CONFIGURATIONS OF
ROLLING MILLS
(c) four high rolling mill (d) cluster mill
Various configurations of rolling mills
(e) tandem rolling mill
TYPES OF ROLLING
PROCESSES
CONTINOUS
TRANSVERSE
SECTION OR SHAPE
RING
CONTINOUS CASTING AND HOT ROLLING
THREAD
CONTINOUS
The objective is to decrease the
thickness of the metal with an
increase in length and with little
increase in width.
TRANSVERSE
•Using circular wedge rolls.
•Heated bar is cropped to
length and
fed in transversely between
rolls.
•Rolls are revolved in one
direction.
SECTION OR SHAPE
 Flat slap is progressively bent into complex shapes
 Suitable for producing moulded sections such as irregular
shaped channels and trim.
SHAPE-ROLLING OPERATIONS
• Various shapes can be produced by shape rolling
– Bars
– Channels
– I-beams
– Railroad rails
• Roll-pass design requires considerable experience in
order to avoid external and internal defects
RING
A specialized type of hot rolling that increases the
diameter of a ring
The resulting grain structure is circumferential, which
gives better mechanical properties
RING ROLLING
Deformation process in which a thick-walled ring of smaller diameter
is rolled into a thin walled ring of larger diameter
• As thick-walled ring is compressed, deformed metal elongates,
causing diameter of ring to be enlarged
• Hot working process for large rings and cold working process for
smaller rings
• Applications: ball and roller bearing races, steel tires for railroad
wheels, and rings for pipes, pressure vessels, and rotating
machinery
• Advantages: material savings, ideal grain orientation,
strengthening through cold working
RING ROLLING
Ring rolling used to reduce the wall thickness and increase
the diameter of a ring:
(1) start, and (2) completion of process
CONTINOUS CASTING
AND HOT ROLLING
• Metal is melted, cast and hot rolled continuously
through a series of rolling mills within the same
process.
THREAD
• Rolled threads are produced in a single pass at speeds
far in excess of those used to cut threads.
• Dies are pressed against the surface of cylindrical
blank. As the blank rolls against the in-feeding die
faces, the material is displaced to form the roots of
the thread, and the displaced material flows radially
outward to form the thread's crest.
THREAD ROLLING
Bulk deformation process used to form threads on cylindrical parts
by rolling them between two dies
• Most important commercial process for mass producing bolts and
screws
• Performed by cold working in thread rolling machines
• Advantages over thread cutting (machining):
– Higher production rates
– Better material utilization
– Stronger threads due to work hardening
– Better fatigue resistance due to compressive stresses
introduced by rolling
THREAD ROLLING
Thread rolling with flat dies:
(1) start of cycle, and (2) end of cycle
WorKrast
Moving
lindric
Blank
Stationary die
ThreadoÖ part
Stationary
Iindr›caI
die
Defects in Rolled Products:
Some of the common defects in rolled products are given
below:
(i) Edge Cracking:
Edge cracking generally occurs in rolled ingots, slabs, or
plates. This is due to, either limited ductility of the work metal
or uneven deformation, especially at the edges.
(ii) Folds:
Folds are a defect generally occurs in plate rolling. This is
caused if the reduction per pass is too small.
(iii) Alligatoring:
Alligatoring is the defect, usually occurs in the rolling of slabs
(particularly aluminum and alloys). In this defect, the work
piece splits along a horizontal plane on exit, with the top and
bottom. This defect always occurs when the ratio of slab
thickness to the length of contact fall within the range of 1.4
to 1.65. Fig. 2.15. Shows the defect of Alligatoring.
Rolling Process Explained

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Rolling Process Explained

  • 2. ROLLING Deformation process in which work thickness is reduced by compressive forces exerted by two opposing rolls The rolling process (specifically, flat rolling)
  • 3. ROLLING  This is the process of reducing the thickness or changing the cross-section of a work-piece by compressive forces exerted by a pair of rotating rolls. or  The process of plastically deforming metal by passing it between rolls.  The products are flat products, like: plates & sheets.  Plates are used for structural applications like bridges, ships & nuclear vessels.  Sheets (generally 6mm or less in thickness) are used for automotive, beverage cans, office & kitchen equipment.
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  • 6. CONT…….. • Rolling is the most widely used forming process, which provides high production and close control of final product. • The metal is subjected to high compressive stresses as a result of the friction between the rolls and the metal surface
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  • 8. THE ROLLS The rotating rolls perform two main functions: • Pull the work into the gap between them by friction between work-part and rolls • Simultaneously squeeze the work to reduce cross section
  • 9. WHERE IT IS DONE Rolling mill is a machine or a factoryfor shaping metal by passing it through rollers A rolling mill basically consists of • rolls • bearings • a housing for containing these parts • a drive (motor) for applying power to the rolls and controlling the speed
  • 10. TERMINOLOGY Bloom is the product of first breakdown of ingot (cross sectional area > 230 cm2). Billet is the product obtained from a further reduction by hot rolling (cross sectional area > 40x40 mm2). Slab is the hot rolledingot (cross sectional area > 100 cm2 and with a width ≥ 2 x thickness).
  • 11. Continued... FURTHUR ROLLING PROCESSE S MILL PRODUCTS Plate is the product with a thickness > 6 mm. Sheet is the product with a thickness< 6 mm and width > 600 mm. Strip is the product with a thickness < 6 mm and width < 600 mm.
  • 12. TYPES OF ROLLING • Based on work piece geometry : – Flat rolling - used to reduce thickness of a rectangular cross section – Shape rolling - square cross section is formed into a shape such as an I-beam • Based on work temperature : – Hot Rolling – most common due to the large amount of deformation required – Cold rolling – produces finished sheet and plate stock
  • 13. Some of the steel products made in a rolling mill
  • 14. FLAT ROLLING AND ITS ANALYSIS R = roller radius p = roll pressure L = contact length θ = contact angle vr = rollspeed to = initial plate thickness tf = final plate thickness vo = plate entry speed vf = plate exitspeed Side view of flat rolling, indicating before and after thicknesses, work velocities, angle of contact with rolls, and other features.
  • 15. FLAT ROLLING AND ITS ANALYSIS • The work enters the gap between the rolls at a velocity vo and exits at a velocity vf. Because the volume flow rate is constant and the thickness is decreasing, vf should be larger than vo. • The roll surface velocity vr is larger than vo and smaller than vf. This means that slipping occurs between the work and the rolls. • Only at one point along the contact length, there is no slipping (relative motion) between the work and the roll. This point is called the “Neutral Point” or the “No Slip Point”.
  • 16. FLAT ROLLING AND ITS ANALYSIS • In flat rolling, the work is squeezed between two rolls so that its thickness is reduced by an amount called the draft: where d: draft to: starting thickness tf : final thickness d to t f
  • 17. FLAT ROLLING AND ITS ANALYSIS • Rolling may not be possible (the sheet will not be pulled) if the draft is large. The maximum draft for successful rolling per pass is: Where: dmax : maximum draft successful rolling perpass μ : coefficient of friction R : roll radius d 2 R max to t f 2 R of passes Number
  • 18. Example:- A series of cold rolling operations is to be used to reduce the thickness of a plate from 50 mm down to 25 mm in a reversing two high mill. Roll diameter =700 mm and coefficient of friction between rolls and work = 0.15. The specification is that the draft is to be equal on each pass. Determine (a) minimum number of passes required, and (b) draft for each pass. Solution 4 passes 3.17 0.15 350 50 - 25 of passes number 2 2 R to t f 4 50 - 25 of passes number per pass Draft 6.25 mm to t f
  • 19. HOT ROLLING Hot rolling is a metalworking process that occurs above the recrystallization temperature of the material. Hot rolled metals generally have little directionality in their mechanical properties and deformation induced residual stresses. However, in certain instances non- metallic inclusions will impart some directionality
  • 20. Also includes cooling .... Hot rolling is used mainly to produce sheet metal or simple cross sections, such as rail tracks. Non-uniformed cooling will induce a lot of residual stresses, which usually occurs in shapes that have a non- uniform cross-section, such as I-beams and H-beams. APPLICATION
  • 21. Advantages Of Hot Rolling Process  Hot rolling can greatly reduce energy consumption and costs.  The metal plastic deformation is high during hot rolling, and the deformation resistance is low, which reduces the energy consumption of metal deformation.  Hot rolling can improve the processing performance of metals and alloys. That is to say, the coarse grains during foundry are broken, the cracks are healed, the casting defects are reduced or eliminated, and the as-cast microstructure is transformed into a deformed structure to improve the processing properties of the alloy.  Hot rolling usually uses large ingots and large reduction rolling, which not only improves production efficiency, but also creates conditions for increasing rolling speed and achieving continuous and automated rolling process.
  • 22. Disadvantages Of Hot Rolling Process After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, causing delamination (sandwich). The delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible that interlinear tearing occurs when the weld is shrunk. The local strain induced by weld shrinkage often reaches several times the yield point strain and is much larger than the strain caused by the load. Residual stress caused by uneven cooling.
  • 23. The residual stress is the internal self-phase equilibrium stress without external force. The hot-rolled steel of various sections has such residual stress.  The larger the section size of the general section steel, the larger the residual stress.  Although the residual stress is self- phase-balanced, it still has some influence on the performance of steel members under external force.
  • 24.  Such as deformation, stability, fatigue and other aspects may have adverse effects.  Hot rolling does not control the mechanical properties required for the product accurately, and the microstructure and properties of the hot rolled product are not uniform.  The strength index is lower than that of the cold work hardened product, and higher than the fully annealed product, the plasticity index is higher than that of the cold work hardened product, and lower than the fully annealed product.  The thickness of the hot rolled product is difficult to control and the control precision is relatively poor; the rough Ra value of the surface of the hot rolled product is generally 0.5 to 1.5 μm.  Therefore, hot rolled products are generally used as blanks for cold rolling.
  • 25. COLD ROLLING Cold rolling occurs with the metal below its recrystallization temperature (usually at room temperature). It also improves the surface finish and holds tighter tolerances. Due to smaller size of the workpieces and their greater strength than hot rolled stock, four-high or cluster mills are used. Commonly cold-rolled products include sheets, strips and rods; products being smaller than the same products that are hot rolled.
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  • 30. Advantages Of Cold Rolling Process No heating required Better surface finish obtained Superior dimension control  Better reproducibility and interchangeability of parts Improved strength properties Directional properties can be minimized
  • 31. Disadvantages Of Cold Rolling Process Higher forces required for deformation Heavier and more powerful equipment required Less ductility available Metal surfaces must be clean and scale-free Strain hardening occurs (may require intermediate anneals) Imparted directional properties may be detrimental May produce undesirable residual stresses
  • 32. Application Of Cold Rolling Process ▪ Foil- The Thickness is less than 0.2 mm, used mainly in the packaging industry Foil is also used for building insulation, electrical applications and in the printing industry. Sheet-Thickness ranges from 0.2 mm and 6mm, used for a wide variety of industry including construction where it is used in aluminum siding and roofing. Sheet is also used in transport sectors for making automobile body panels, airframes etc. Plate-It is the rolled product, which is over 6mm in thickness. It also has a number of applications including airframes, defence vehicles and structural components in building
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  • 34. VARIOUS CONFIGURATIONS OF ROLLING MILLS (a) 2-high rolling mill (b) 3-high rolling mill
  • 35. VARIOUS CONFIGURATIONS OF ROLLING MILLS (c) four high rolling mill (d) cluster mill
  • 36. Various configurations of rolling mills (e) tandem rolling mill
  • 37. TYPES OF ROLLING PROCESSES CONTINOUS TRANSVERSE SECTION OR SHAPE RING CONTINOUS CASTING AND HOT ROLLING THREAD
  • 38. CONTINOUS The objective is to decrease the thickness of the metal with an increase in length and with little increase in width.
  • 39. TRANSVERSE •Using circular wedge rolls. •Heated bar is cropped to length and fed in transversely between rolls. •Rolls are revolved in one direction.
  • 40. SECTION OR SHAPE  Flat slap is progressively bent into complex shapes  Suitable for producing moulded sections such as irregular shaped channels and trim.
  • 41. SHAPE-ROLLING OPERATIONS • Various shapes can be produced by shape rolling – Bars – Channels – I-beams – Railroad rails • Roll-pass design requires considerable experience in order to avoid external and internal defects
  • 42. RING A specialized type of hot rolling that increases the diameter of a ring The resulting grain structure is circumferential, which gives better mechanical properties
  • 43. RING ROLLING Deformation process in which a thick-walled ring of smaller diameter is rolled into a thin walled ring of larger diameter • As thick-walled ring is compressed, deformed metal elongates, causing diameter of ring to be enlarged • Hot working process for large rings and cold working process for smaller rings • Applications: ball and roller bearing races, steel tires for railroad wheels, and rings for pipes, pressure vessels, and rotating machinery • Advantages: material savings, ideal grain orientation, strengthening through cold working
  • 44. RING ROLLING Ring rolling used to reduce the wall thickness and increase the diameter of a ring: (1) start, and (2) completion of process
  • 45. CONTINOUS CASTING AND HOT ROLLING • Metal is melted, cast and hot rolled continuously through a series of rolling mills within the same process.
  • 46. THREAD • Rolled threads are produced in a single pass at speeds far in excess of those used to cut threads. • Dies are pressed against the surface of cylindrical blank. As the blank rolls against the in-feeding die faces, the material is displaced to form the roots of the thread, and the displaced material flows radially outward to form the thread's crest.
  • 47. THREAD ROLLING Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies • Most important commercial process for mass producing bolts and screws • Performed by cold working in thread rolling machines • Advantages over thread cutting (machining): – Higher production rates – Better material utilization – Stronger threads due to work hardening – Better fatigue resistance due to compressive stresses introduced by rolling
  • 48. THREAD ROLLING Thread rolling with flat dies: (1) start of cycle, and (2) end of cycle
  • 50. Defects in Rolled Products: Some of the common defects in rolled products are given below: (i) Edge Cracking: Edge cracking generally occurs in rolled ingots, slabs, or plates. This is due to, either limited ductility of the work metal or uneven deformation, especially at the edges. (ii) Folds: Folds are a defect generally occurs in plate rolling. This is caused if the reduction per pass is too small. (iii) Alligatoring: Alligatoring is the defect, usually occurs in the rolling of slabs (particularly aluminum and alloys). In this defect, the work piece splits along a horizontal plane on exit, with the top and bottom. This defect always occurs when the ratio of slab thickness to the length of contact fall within the range of 1.4 to 1.65. Fig. 2.15. Shows the defect of Alligatoring.