1. Rolling of Metals
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2. Flat-Rolling and Shape-Rolling Processes
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3. The rolling process (specifically, flat rolling).
Deformation process in which work thickness is reduced by compressive forces exerted by two opposing rolls
The rolling process (specifically, flat rolling).
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4. Types of Rolling Based on workpiece 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
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5. Rolled Products Made of Steel
Some of the steel products made in a rolling mill.
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6. Hot Rolling for I‑beam Product
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7. Steps in the shape rolling of an
I–section part.
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8. Blooms, Billets, Slaps
After casting, ingots are rolled into one of three intermediate shapes called blooms, billets, and slaps:
Blooms have square cross section 6” x 6” or larger. They are rolled into structural shapes.
Billets have square cross section 1.5” x 1.5” or larger. they are rolled into bars and rods.
Slabs have rectangular cross section 10” x 1.5” or larger. They are rolled into plates, sheets and strips.
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9. Production Line
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10. Flat rolling and its analysis
R = roller radius
p = roll pressure
L = contact length
θ = contact angle
vr = roll speed
to = initial plate thickness
tf = final plate thickness
vo = plate entry speed
vf = plate exit speed
Side view of flat rolling, indicating before and after thicknesses, work velocities, angle of contact with rolls, and other features.
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11. Roll bite condition
For the work piece to enter the throat of the roll, the component of the friction force must be equal to or greater than the horizontal
component of the normal force.
But we know
Therefore
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12. 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”.
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13. Flat rolling and its analysis
1. Constant material volume
where
Lo = initial plate length
Lf = final plate length
2. Continuity of volume flow rate
3. Forward slip
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14. After three passes, tf = (0.75)(0.75)(0.75)(2.0) = 0.844 in.
Example:- A 2.0-in-thick slab is 10.0 in. wide and 12.0 ft long. Thickness is to be reduced in three steps in a hot rolling operations. Each step will reduce the slap to 75% of its pervious thickness. It is expected that for this metal and reduction the slap will widen by 3% in each step. If the entry speed of the slap in the first step is 40 ft/min. and roll speed is the same for the three steps, determine (a) length and (b) exit velocity of the slap after the final reduction.
Solution
After three passes, tf = (0.75)(0.75)(0.75)(2.0) = in.
wf = (1.03)(1.03)(1.03)(10.0) = in.
(2.0)(10.0)(12) = (0.844)(10.927)Lf
Lf = (2.0)(10.0)(12)/(0.844)(10.927) = ft
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15. (b) Given that roll speed is the same at all three stands and that
(2.0)(10.0)(40) = (0.844)(10.927)Vf
Vf = (2.0)(10.0)(40)/(0.844)(10.927) = ft/min.
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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
As a reduction of the starting thickness (r):
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17. From triangle ABC, we have
The maximum draft
From triangle ABC, we have
As a is much smaller than R, we
can then ignore a2.
Where Δh = ho – hf = 2a
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18. 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 per pass
μ : coefficient of friction
R : roll radius
As can be seen from the equation, if μ is zero, then dmax is also zero (rolling is not possible)
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19. 2. If reduction = constant
Number of passes
1. If draft = constant
2. If reduction = constant
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20. 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 two­high mill. Roll diameter =700 mm and coefficient of friction between rolls and work = 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
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21. Flat rolling and its analysis
Rolling force, F Where the deformation strain the average flow stress and Contact length
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22. Flat rolling and its analysis
The torque in rolling can be estimated by:
T = 0.5 F L
Where:
T: Torque (lb.in or N.m)
F: Roll Force
L: Contact length
The Power required to drive the two rolls is calculated as follows:
P = 2πNFL
P: Power (in J/s =Watt or in-lb/min)
N: Rolls rotational speed (RPM)
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23. Flat rolling and its analysis
From the previous equations we can conclude the following:
The contact length decreases by decreasing the roll radius.
The roll force depends on the contact length, and therefore, reducing the roll radius will reduce the roll force.
The torque and power depend on the roll force and contact length, and therefore, reducing the roll radius will reduce both the torque and power.
The power also depends on the rotational speed of the rolls, and therefore, reducing the rolls RPM will reduce the power.
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24. Example:- A 10 in wide, 1.0 in thick plate is to be reduced in a single pass in a two-high rolling mill to a thickness of 0.8 in . The roll has a radius = 20 in., and its speed = 50 ft/min. The work material has a strength coefficient = 35,00 Ib/in2 and a strain hardening exponent = 0.2. Determine (a) roll force, (b) roll torque, and (c) power required to accomplish this operation.
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25. Rolling Mills Equipment is massive and expensive
Rolling mill configurations:
Two-high – two opposing rolls
Three-high – work passes through rolls in both directions
Four-high – backing rolls support smaller work rolls
Cluster mill – multiple backing rolls on smaller rolls
Tandem rolling mill – sequence of two-high mills
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26. Two-High Rolling Mill
Various configurations of rolling mills: (a) 2‑high rolling mill.
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27. Three-High Rolling Mill
Various configurations of rolling mills: (b) 3‑high rolling mill.
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28. Four-High Rolling Mill
Various configurations of rolling mills: (c) four‑high rolling mill.
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29. Various configurations of rolling mills: (d) cluster mill
Multiple backing rolls allow even smaller roll diameters
Various configurations of rolling mills: (d) cluster mill
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30. A series of rolling stands in sequence
Tandem Rolling Mill
A series of rolling stands in sequence
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31. Ring Rolling
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32. Actual ring rolling mill
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33. Steps in the ring rolling
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34. 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
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35. Thread Rolling (1) start of cycle (2) end of cycle
Thread rolling with flat dies:
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36. Thread Rolling
Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies
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 and better fatigue resistance due to work hardening
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37. Effect of hot rolling on the grain structure
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38. Bending of Rolls
Bending of straight cylindrical rolls caused by roll forces.
(b) Bending of rolls ground with camber, producing a strip with uniform thickness through the strip width.

39. Defects in Rolled Plates & Sheets
• a) Wavy edges • c) Edge cracks
• b) Cracks • d) Alligatoring
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