manufacturing week 2a- rolling of metals
TRANSCRIPT
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MCB3073 Manufacturing Technology 2
Week 2
Metal Forming-Rolling of Metals
Lecturer:
Dr. Turnad Lenggo Ginta
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Course Outcome
Students should be able to:
Understand the process of rolling of metals.
Calculate the rolling force during manufacturing
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Rolling
Process of reducing the thickness of long workpiece by
compressive forces applied through a set of rolls.
Carried out at elevated temperatures where cast metal is
broken down with finer grain size and improvedproperties.
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The Flat-Rolling Process
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The Flat-Rolling Process
The maximum possible draft is defined as the difference
between the initial and final strip thicknesses. It can be shown
that this is a function of the coefficient of friction, between the
strip and the roll and the roll radius, R, by the following
relationship:
Thus, as expected, the higher the friction and the larger the roll
radius, the greater the maximum possible draft becomes.
1.132Rhhfo
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13.2.1 Roll force, torque and power requirement
The rolls apply pressure on the flat strip in order to reduce its
thickness, resulting in a roll force, F.
The roll force in flat rolling can be estimated from the formula
where L is the roll-strip contact length, w is the width of the
strip, and Yavgis the average true stress
2.13avg
LwYF
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13.2.1 Roll force, torque and power requirement
The total power (for two rolls) in S.I. units is
where F is in newtons, L is in meters, and N is the
revolutions per minute of the roll.
In traditional English units, the total power can be
expressed as
3.13kW000,60
2 FLNPower
4.13hp000,33
2 FLNPower
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Example 13.1 Calculation of roll and torque in flat rolling
An annealed copper strip, 250 mm wide and 25 mmthick, is rolled to a thicknes of 20 mm in one pass. The
roll radius is 300 mm, and the rolls rotate at 100 rpm.
Calculate the roll force and the power required in this
operation.
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Example 13.1 Calculation of roll and torque in flat rolling
Solution The roll force is determined from Eq. (13.2) in
which L is the roll-strip contact length. It can be shown
from simple geometry that this length is given
approximately by
The average true stress for annealed copper is
determined as follows. First note that the absolute value
of the true strain that the strip undergoes in thisoperation is
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Referring to Fig. 2.6, note that annealed copper has a
true stress of about 80 MPa in the unstrained condition,
and at a true strain of 0.223, the true stress is 280 MPa.
Thus, the average true stress is (80+280)/2=180 MPa.
We can now define the roll force as
The total power is calculated from Eq. (13.3), noting that
N = 100 rpm. Thus,
Example 13.1 Calculation of roll and torque in flat rolling
MN74.1MPa1801000
250
1000
7.38
avgLwYF
kW705
000,60
100
1000
7.381074.12
000,60
2Power 6
FLN
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Fig. 2.6
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Defects in rolled products
Successful rolling practice requires material properties,
process variables and lubrication.
Surface defects result from inclusions and impurities in
the material. Structural defects affect the integrity of the rolled
product.
Wavy edges are caused by bending of the rolls.
Wavy edges Zipper cracks Edge cracks Alligatoring
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Defects in rolled products
Residual stresses
Develop due to inhomogeneous plastic deformation in
the roll gap.
Generates compressive residual stresses on the surfacesand tensile stresses in the bulk.
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13.5 Various rolling processes and mills
Shape rolling
Straight and long structural shapes (such as channels, I-
beams, railroad rails, and solid bars) are formed at
elevated temperatures by shape rolling (profile rolling), in
which the stock goes through a set of specially designed
rolls.
Cold shape rolling also can be done with the starting
materials in the shape of wire with various cross-sections.
Fig 13.12 shows the Steps in the shape rolling of an I-beampart. Various other structural sections, such as channels
and rails, also are rolled by this kind of process.
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13.5 Various rolling processes and mills
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13.5 Various rolling processes and mills
Roll Forging
In this operation (also called cross rolling), the cross-
section of a round bar is shaped by passing it through
a pair of rolls with profiled grooves.
Fig 13.13 shows two examples of the roll-forgingoperation, also known as cross-rolling. Tapered leaf
springs and knives can be made by this process.
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13.5 Various rolling processes and mills
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13.5 Various rolling processes and mills
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13.5 Various rolling processes and mills
Ring Rolling
In ring rolling, a thick ring is expanded into a large-diameter
thinner one.
The ring is placed between sets of two rolls, one of which is
driven while the other is idle.
Fig 13.15 (a) shows schematic illustration of a ring-rolling
operation. Thickness reduction results in an increase in the part
diameter. (b) through (d) Examples of cross-sections that can
be formed by ring rolling.
Typical applications of ring rolling are large rings for rockets
and turbines, jet engine cases, gearwheel rims, ball-bearing and
roller-bearing races, flanges, and reinforcing rings for pipes.
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13.5 Various rolling processes and mills
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13.5 Various rolling processes and mills
Thread Rolling
Thread rolling is a cold-forming process by which
straight or tapered threads are formed on round rods
or wire by passing them between dies.
Threads are formed on the rod or wire with eachstroke of a pair of flat reciprocating dies.
Fig 13.16 shows Thread rolling processes: (a) and (b)
reciprocating flat dies; (c) two-roller dies; (d) A
collection of thread-rolled parts made economically at
high production rates.
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13.5 Various rolling processes and mills
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13.5 Various rolling processes and mills
Thread Rolling
Thread rolling is superior to the other methods of
manufacturing threads, because machining the threads
cuts through the grain-flow lines of the material, whereas
rolling the threads results in a grain-flow pattern thatimproves the strength of the thread.
Fig 13.17 (a) shows features of a machined or rolled
thread. Grain flow in (b) machined and (c) rolled threads.
Unlike machining, which cuts through the grains of themetal, the rolling of threads imparts improved strength
because of cold working and favorable grain flow.
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13.5 Various rolling processes and mills
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13.5 Various rolling processes and mills
Thread Rolling
Lubrication is important in thread-rolling operations in
order to obtain a good surface finish and surface
integrity and to minimize defects.
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13.5 Various rolling processes and mills
Tube Rolling
The diameter and thickness of pipes and tubing can be
reduced by tube rolling, which utilizes shaped rolls.
Fig 13.19 shows the schematic illustration of various
tube-rolling processes: (a) with a fixed mandrel; (b)with a floating mandrel; (c) without a mandrel; and (d)
pilger rolling over a mandrel and a pair of shaped rolls.
Tube diameters and thicknesses also can be changed
by other processes, such as drawing, extrusion, and
spinning.
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13.5 Various rolling processes and mills
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13.5.1 Various mills
Integrated mills
These mills are large facilities that involve complete
integration of the activitiesfrom the production of
hot metal in a blast furnace to the casting and rolling
of finished products ready to be shipped to thecustomer.
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End of class