Metal Rolling
Metal Rolling
Prof. K.N.WakchaureDept. of Mechanical EngineeringSRES COLLEGE
OF ENGINEERING, KOPARGAONProf K N Wakchaure
METAL FORMINGMetal forming can be defined as a process in which
the desired size and shape are obtained through the deformation of
metals plastically under the action of externally applied
forces.Metal forming processes like rolling, forging, drawing etc.
are gaining ground lately. It is due to the fact that metal forming
is the wasteless process which is highly economical. They give high
dimensional accuracy, easy formability for complex shapes and good
surface finish with desired metallurgical properties.Prof K N
Wakchaure
HOT WORKING AND COLD WORKINGHot Working(a) Properties1. Hot
working is done at a temperature above recrystallization but below
its melting point. 2. Hardening due to plastic deformation is
completely eliminated by recovery and recrystallization.3.
Improvement of mechanical properties such as elongation, reduction
of area and impact values.4. No effect on ultimate tensile
strength, yield point, fatigue strength and hardness.5. Poor
surface finish due to oxidation and scaling.6. Refinement of
crystals occurs.
Prof K N Wakchaure
HOT WORKING AND COLD WORKINGHot Working6. Refinement of crystals
occurs.7. Due to hot working cracks and blowholes are welded up.8.
No internal or residual stress developed.9. Force required for
deformation is less.10. Light equipment is used in hot working.11.
Difficult to handle a hot worked metal.12. Hot working processes
arehot forging, hot rolling, hot spinning, hot extrusion, hot
drawing, and hot piercing, pipe welding.
Prof K N Wakchaure
HOT WORKING AND COLD WORKINGAdvantages:Porosity in the metal is
largely eliminated. Impurities in the form of inclusions are broken
up and distributed throughout the metal.3. Coarse or columnar
grains are refined. 4. Physical properties are generally improved
owing principally to grain refinement. Ductility and resistance to
impact are improved, strength is increased, and greater homogeneity
is developedin the metal. 5. The amount of energy necessary to
change the shape of steel in the plastic state is far less than
that required when the steel is cold.Prof K N Wakchaure
HOT WORKING AND COLD WORKINGDisadvantages/Limitations of Hot
Working1. rapid oxidation or scaling of thesurface with
accompanying poor surface finish.2. Difficult to achieve close
tolerances due to scaling.3. Hot working equipment and maintenance
costs are high.Prof K N Wakchaure
HOT WORKING AND COLD WORKINGCold WorkingProperties
l. Cold working is done at temperature below recrystallization
temperature. 2. Hardening is not eliminated since working is done
below recrystallization temperature.3. Decreases elongation,
reduction of area etc.4. Increase in ultimate tensile strength,
yield point and hardness.5. Good surface finish is obtained.6.
Crystallization does not occur. Grains are only elongated.7.
Possibility of crack formation and propagation is great.8. Internal
and residual stresses are developed in the metal.9. Force required
for deformation is high.10. Heavy and powerful equipment is used
for cold working.11. Easier to handle cold parts.12. Cold working
processes arecold rolling, cold extrusion, press work (drawing,
squeezing, bending, and shearing).Prof K N Wakchaure
HOT WORKING AND COLD WORKINGAdvantages of Cold Working
1. Cold working increases the strength and hardness of the
material due to the strain hardening which would be beneficial in
some situations.2. Since the working is done in cold state, hence
no oxide formation on the surface and consequently,good surface
finish is obtained.3. Greater dimensional accuracy is achieved.4.
Easier to handle cold parts and also economical for small sizes.5.
Better mechanical properties are achieved.Prof K N Wakchaure
HOT WORKING AND COLD WORKINGDisadvantages/Limitations of Cold
Working1. Only small sized components can be easily worked as
greater forces are required for large sections2. The grain
structure is not refined and residual stresses have harmful effects
on certain properties of metals.3. Many of the metals have less
ductility e.g., carbon steel and certain alloy steels, cannot be
cold worked at room temperature. It is therefore, limited to
ductile metals and the range of shapes produced is not as wide as
can be obtained by machining.4. Tooling costs are high and as such
it is used when large quantities of similar components are
required.Prof K N Wakchaure
Sr. No.ParametersHot Working Cold Working 1.Recrystalization
temp.AboveBelow2.Residual stressesNot inducedInduced3.Pressure
requiredLowerHigher4.Grain
refinementYesNO5.HardeningNoYes6.Oxidation & Scaling
YesNO7.Closed dimensional tolerancesCan not be maintained Can be
maintained
Prof K N Wakchaure
Metal rollingProf K N Wakchaure
Prof K N Wakchaure
Prof K N Wakchaure
Prof K N Wakchaure
Prof K N Wakchaure
Metal rolling is one of the most important manufacturing
processes in the modern world. The large majority of all metal
products produced today are subject to metal rolling at one point
in their manufacture. Metal rolling is often the first step in
creating raw metal forms. Theingotis hot rolled into a bloom or a
slab, these are the basic structures for the creation of a wide
range of manufactured forms. Blooms typically have a square cross
section of greater than 6x6 inches. Slabs are rectangular and are
usually greater than 10 inches in width and more than 1.5 inches in
thickness. Rolling is most often, Prof K N Wakchaure
Prof K N Wakchaure
Principles Of Metal RollingMost metal rolling operations are
similar in that the work material is plastically deformed by
compressive forces between two constantly spinning rolls. These
forces act to reduce the thickness of the metal and effect its
grain structure. The reduction in thickness can be measured by the
difference in thickness before and after the reduction, this value
is called thedraft. In addition to reducing the thickness of the
work, the rolls also act to feed the material as they spin in
opposite directions to each other. Friction is therefore a
necessary part of the rolling operation, but too much friction can
be detrimental for a variety of reasons. It is essential that in a
metal rolling process the level of friction between the rolls and
work material is controlled, lubricants can help with this. Prof K
N Wakchaure
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Prof K N Wakchaure
Prof K N Wakchaure
Prof K N Wakchaure
This technique will assist the forces necessary to form the
work, and is usually used on hard to roll materials.
Prof K N Wakchaure
Spreading In Roll FormingIn metal rolling operations the plastic
deformation causing a reduction in thickness will also cause an
increase in the width of the part, this is calledspreading.
Prof K N Wakchaure
Vertical rolls can be employed to edge the work and maintain a
constant width.
Prof K N Wakchaure
Grain Structure In Metal Rolling
Prof K N Wakchaure
Prof K N Wakchaure
Rolls For FormingMetal rolling operations can produce a wide
range of different formed products. The width of rolled work can be
as much as several meters, or narrower than a thousandth of an
inch. Metal forming manufacture also creates rolled work over a
wide range of thicknesses. Metal plates for some boilers may be
rolled to a thickness of 12 inches, while foil for wrapping
cigarettes and candy can be .0003 inches thick. Rolls used in metal
forming are of various sizes and geometries. In flat rolling
industrial manufacture, the rolls may typically be 24 to 54 inches
in diameter. In some rolling operations, in the forming of very
thin work, the rolls can be as small as 1/4 inch.
Prof K N Wakchaure
Rolls are subject to extreme operating conditions including,
tremendous forces, bending moments, thermal stresses, and wear.
Roll materials are selected for strength, rigidity, and wear
resistance. Roll materials vary dependent upon the specific forming
process. Common roll materials are cast iron, cast steel, and
forged steel. Forged rolls are stronger and more rigid than cast
rolls but are more difficult to manufacture. In some industrial
forming processes rolls are made from nickel steel or molybdenum
steel alloys. With metal rolling operations of certain materials,
rolls made of tungsten carbide can provide extreme resistance to
deflection.
Prof K N Wakchaure
Roll Deflections
Prof K N Wakchaure
Prof K N Wakchaure
Defects In Metal RollingSurface defects commonly occur due to
impurities in the material, scale, rust, or dirt. Adequate surface
preparation prior to the metal rolling operation can help avoid
these. Most serious internal defects are caused by improper
material distribution in the final product. Defects such as edge
cracks, center cracks, and wavy edges, are all common when metal
forming by this method.Another interesting defect that can occur in
flat rolling is alligatoring, where the work being rolled actually
splits in two during the process. The two parts of the work
material travel in opposite directions relative to their respective
rolls.
Prof K N Wakchaure
Prof K N Wakchaure
Different Types Of Metal Rolling MillsIn metal forming industry,
rolls themselves do not function in isolation. In a metal rolling
process, rolls stands, bearings, housing, motors, and other
mechanical equipment are all a necessary part of the manufacturing
operation. The place where all the equipment for metal rolling
manufacture is set up is called a rolling mill. Rolling mills often
vary in the type, number, and position of rolls. Rolling mill
arrangements commonly used in manufacturing industry today include
the two high mill, the three high mill, the four high mill, the
cluster mill, and the tandem rolling mill.
Prof K N Wakchaure
Prof K N Wakchaure
In the two high reversing mill the direction of spin of the
rolls can be reversed. This enables the work to travel through in
one direction, then back through in the other direction. A series
of reductions can be made using the same set of rolls, by passing
the work back and forth. Disadvantages of the two high reversing
mill include the mechanical requirements and power to constantly
overcome and reverse the angular momentum of the rolls.
Prof K N Wakchaure
Prof K N Wakchaure
Prof K N Wakchaure
The three high rolling mill utilizes the principle of passing
the work back and forth to achieve a series of reductions. Unlike
the two high reversing mill, the three high mill has three rolls
that always spin in the same direction. An elevator mechanism lifts
and lowers the work so that it can be passed back and forth through
the rolls.
Prof K N Wakchaure
It is known that the amount of roll force is reduced with a
smaller radius of the rolls. Smaller radius rolls however deflect
easier and must be supported by other rolls. The four high mill
uses this principle with two smaller work rolls each supported by a
larger backing roll.
Prof K N Wakchaure
The cluster mill or Sendzimir mill, uses a small work roll
backed up by many other rolls. This extremely rigid setup is often
used for cold rolling high strength material to a very thin
width.
Prof K N Wakchaure
Prof K N Wakchaure
Shape RollingShape rolling is a broad term for a range of metal
rolling operations, that involve forming the work with rolls of a
certain geometry. The rolls form the part to a specific shape. Most
shape rolling involves passing the material through several steps.
Two very common examples of continuous shape rolled product are the
I beam for structural purposes and the rail for railroad track.
Prof K N Wakchaure
Prof K N Wakchaure
Prof K N Wakchaure
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Prof K N Wakchaure
Prof K N Wakchaure
Ring RollingRing rolling is a particular category of metal
rolling in which a ring of smaller diameter is rolled into a
precise ring of larger diameter and a reduced cross section. This
is accomplished by the use of two rollers one driven and one idle
acting on either side of the ring's cross section.
Prof K N Wakchaure
Prof K N Wakchaure
Prof K N Wakchaure
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Prof K N Wakchaure
Prof K N Wakchaure
Thread RollingThread rolling is a metal rolling process used
extensively in manufacturing industry to produce screws, bolts and
other fasteners. A common thread rolling process used in industry
to manufacture threaded parts involves forming the threads into the
metal of a blank by a pressing and rolling action between two die.
The die surfaces hold the shape and the force of the action forms
the threads into the material. A similar metal forming process has
been developed for the production of gears.Producing threads by
this method has several other benefits over machining. Forming will
harden the metal through cold working, does not waste material by
cutting, and produces a favorable grain structure to strengthen the
part with respect to its function.
Prof K N Wakchaure
Prof K N Wakchaure
Prof K N Wakchaure
Rotary Tube PiercingRotary tube piercing, also called roll
piercing, or the mannesmann process, is a hot forming process that
can manufacture long lengths of seamless tube and pipe. Compressive
forces applied to a cylinder will create internal stresses at the
center. These stresses result in crack propagation.
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Prof K N Wakchaure
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Prof K N Wakchaure
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