Tap Bai Giang Ve Can
Transcript of Tap Bai Giang Ve Can
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1ME 4563 Fall 05 Dr. S. Haran
(10.06.2005)(10.06.2005)(10.06.2005)
Fall 2005
College of Engineering
Arkansas State University
Fall 2005Fall 2005
College of EngineeringCollege of Engineering
Arkansas State UniversityArkansas State University
Introduction to ManufacturingProcesses
Introduction to ManufacturingIntroduction to Manufacturing
ProcessesProcesses
ME 4563ME 4563ME 4563
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Bulk DeformationBulk Deformation
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RollingRolling
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What is Rolling ?What is Rolling ?
A process of reducing the thicknessA process of reducing the thickness
(or changing the cross(or changing the cross--section of longsection of long
workwork--piecepiece
By applying compressive forcesBy applying compressive forces
through a set of rollsthrough a set of rolls
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Some Rolling FactsSome Rolling Facts
Process developed in late 1500Process developed in late 1500ss
Accounts for over 90% of all metals produced byAccounts for over 90% of all metals produced bymetalworking process by volumemetalworking process by volume
Various crossVarious cross--sectional shapes are achievedsectional shapes are achieved
Major metal that is rolled is Steel, followed byMajor metal that is rolled is Steel, followed byAluminumAluminum
Can be carried out Hot or ColdCan be carried out Hot or Cold
Machinery for Rolling (calledMachinery for Rolling (called MillsMills) have a variety) have a variety
of configurationsof configurations
Several parameters to be considered in practice, inSeveral parameters to be considered in practice, inthe design and selection of machinesthe design and selection of machines
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Schematic outline ofSchematic outline ofvarious flatvarious flat-- andandshapeshape--rollingrollingprocesses.processes. SourceSource::American Iron andAmerican Iron andSteel Institute.Steel Institute.
RollingRolling
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PlatesPlates
SheetsSheets
RodsRods
FoilFoil
Pipes and tubesPipes and tubes
Shape rolled products such as channel, I, L, T,Shape rolled products such as channel, I, L, T,
etc.etc.
Other structural shapes also madeOther structural shapes also made
RollingRolling Products includeProducts include
8ME 4563 Fall 05 Dr. S. Haran
Major Metals that are Rolled include:Major Metals that are Rolled include:
SteelSteel
AluminumAluminum
Others like Copper, Brass, Lead, etc.Others like Copper, Brass, Lead, etc.
Special applicationsSpecial applications Titanium andTitanium andotherother exotic metalsexotic metals
RollingRolling
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Direct ApplicationsDirect Applications --where rolledwhere rolled
plates/sheets are usedplates/sheets are used
Aircraft bodiesAircraft bodies
Ship hullsShip hulls
Reactor vesselReactor vesselwallswalls
BoilersBoilers
BridgesBridges Tanks, etc.Tanks, etc.
RollingRolling
Indirect ApplicationsIndirect Applications --where rolled plates/sheetswhere rolled plates/sheets
are used after furtherare used after furtherprocessingprocessing LocomotivesLocomotives
AutomobilesAutomobiles
AppliancesAppliances Food/BeverageFood/Beverage
containerscontainers
Office equipment,Office equipment, Construction, etc. etc.Construction, etc. etc.
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Classifications of Rolling MaterialClassifications of Rolling MaterialRolling material is separated into classifications basedRolling material is separated into classifications based
on the material's crosson the material's cross--sectional dimensionssectional dimensions
CrossCross--SectionSection ThicknessThickness WidthWidth
BloomBloom SquareSquare >6 in.>6 in.
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What kind of Thickness are we talking about ?What kind of Thickness are we talking about ?
When Manufactured:When Manufactured:
Rolled Plates: normally > 6mmRolled Plates: normally > 6mm
Rolled Sheets: normally < 6mmRolled Sheets: normally < 6mm
Aircraft Body: 1Aircraft Body: 1 2mm thick2mm thick Aluminum beverage cans: 0.1Aluminum beverage cans: 0.1 0.28mm thick0.28mm thick
Aluminum Foil: 0.008mm thick (wrapping)Aluminum Foil: 0.008mm thick (wrapping)
And the range of applicationsAnd the range of applications
RollingRolling
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Two Major types of rolling processesTwo Major types of rolling processes --
Flat rollingFlat rolling to produce Platesto produce Plates
andand Sheets of metalSheets of metal
Profile (or Shape) rollingProfile (or Shape) rolling toto
produce all other possibleproduce all other possible
shapesshapes
RollingRolling
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Flat RollingFlat Rolling
Hot RollingHot Rolling
Cold RollingCold Rolling
Pack RollingPack Rolling
Flat Rolling Process can beFlat Rolling Process can bedivided into THREE majordivided into THREE major
types:types:
RollingRolling
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Flat Rolling ProcessFlat Rolling Process
Hot RollingHot Rolling
Cold RollingCold Rolling
Pack RollingPack Rolling
Converts a cast structure into aConverts a cast structure into awrought structure; rolled above thewrought structure; rolled above therere--crystallization temperaturecrystallization temperature(process in which new(process in which new equiaxedequiaxed / strain free/ strain freegrains are formed, replacing old grains)grains are formed, replacing old grains)
Carried out a room temperature;Carried out a room temperature;better finish, mechanical propertiesbetter finish, mechanical properties
Two or more layers of metals areTwo or more layers of metals arerolled together; improvesrolled together; improvesproductivity (Al foil)productivity (Al foil)
RollingRolling
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Other Flat Rolling ProcessOther Flat Rolling Process
Temper RollingTemper Rolling
LevelingLeveling
Sheets subject to a final passSheets subject to a final pass strainstrainin the sheets are removed (sheetsin the sheets are removed (sheetsundergo yield point elongationundergo yield point elongationduring rolling); also calledduring rolling); also called skin pass;skin pass;0.5 to 1.5% reduction in thickness0.5 to 1.5% reduction in thickness
To improve flatness. Sheets mayTo improve flatness. Sheets maynot be sufficiently flat due tonot be sufficiently flat due to
various reasons such as roll gapvarious reasons such as roll gapand process parametersand process parameters
RollingRolling
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Flat Rolling ProcessFlat Rolling Process
ContinuousContinuousCasting or IngotsCasting or Ingots
BloomsBlooms
SlabsSlabs
BilletsBillets
Preliminary RollingPreliminary Rolling :::: Initial breakdown of Ingot or castInitial breakdown of Ingot or castslabslab
HotHot
RollingRolling
RollingRolling
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BloomsBlooms
SlabsSlabs
BilletsBillets
Preliminary Rolling ::Preliminary Rolling ::
About 6About 6 square in crosssquare in crosssection; various lengthssection; various lengths
Thinner rectangular crossThinner rectangular crosssection; various lengths (thinnersection; various lengths (thinnerversion of a bloom)version of a bloom)
Smaller square cross sections;Smaller square cross sections;various lengthsvarious lengths
RollingRolling
Flat Rolling ProcessFlat Rolling Process
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ContinuousContinuous
Casting or IngotsCasting or Ingots
BloomsBlooms
SlabsSlabs
BilletsBillets
Preliminary RollingPreliminary Rolling ::::
HotHot
RollingRolling
Continuous Flat RollingContinuous Flat RollingProcessProcess A SchematicA Schematic
Casting
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SlabsSlabs
Hot StripHot StripMillMill
Directly toDirectly toRollingRolling
Pre RollingPre Rolling
PlatesPlates
TubesTubes
PicklingPickling ColdColdRollingRolling
(acid bath)(acid bath)
Flat Rolling ProcessFlat Rolling Process -- ProductsProducts
RollingRolling
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BilletsBillets
Hot RolledHot RolledBarsBars
RodsRods
TubeTubeRoundsRounds
Wire & wireWire & wire
productsproducts
SeamlessSeamlessTubesTubes
ColdCold--drawndrawnBarsBars
Flat Rolling ProcessFlat Rolling Process -- ProductsProducts
RollingRolling
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BloomsBlooms
StructuralStructuralShapesShapes
RailsRails
Flat Rolling ProcessFlat Rolling Process -- ProductsProducts
RollingRolling
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Consists of these major categories:Consists of these major categories:
Shape RollingShape Rolling
Ring RollingRing Rolling
Thread RollingThread Rolling
Rotary Tube PiercingRotary Tube Piercing
Tube RollingTube Rolling
Other Rolling OperationsOther Rolling Operations
RollingRolling
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Raw materials is usually the BloomRaw materials is usually the Bloom
Straight structural shapes such as bars of variousStraight structural shapes such as bars of variouscross sections, channel sections, Icross sections, channel sections, I--beams, and railsbeams, and rails
Rolled by passing the stock through a number ofRolled by passing the stock through a number ofsets of rolls specially designed for thesesets of rolls specially designed for these
applicationsapplications
Designing the roll systems for this applicationDesigning the roll systems for this application
takes experience and care, as material failure istakes experience and care, as material failure isfairly frequent in case of poor designsfairly frequent in case of poor designs
A.A. Shape RollingShape Rolling
Other Rolling OperationsOther Rolling Operations
RollingRolling
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Stages in the shapeStages in the shaperolling of an Hrolling of an H--sectionsectionpart.part.
Various otherVarious otherstructural sections,structural sections,such as channels andsuch as channels andII--beams, are alsobeams, are alsorolled by this kind ofrolled by this kind ofprocess.process.
Shape RollingShape Rolling
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A.A. Shape RollingShape Rolling
Shape RollingShape Rolling
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Rolling out anRolling out anangular sectionangular section
Shape RollingShape Rolling
A. Shape RollingA. Shape Rolling
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Rolling out aRolling out aVV--SectionSection
Shape RollingShape Rolling
A. Shape RollingA. Shape Rolling
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Smaller diameter thickSmaller diameter thickring is expanded into aring is expanded into alarger diameter thinnerlarger diameter thinnerringring
System consists of twoSystem consists of tworollsrolls one which performsone which performsthe rolling and the otherthe rolling and the other
to support and guideto support and guide
With each rotation, theWith each rotation, thethickness is reduced asthickness is reduced asthe rings come closerthe rings come closertogethertogether
B.B. Ring RollingRing Rolling
RollingRolling
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(a)(a) Schematic illustration of a ringSchematic illustration of a ring--rolling operation. Thicknessrolling operation. Thicknessreduction results in anreduction results in anincrease in the part diameter.increase in the part diameter.
(b)(b) Examples of crossExamples of cross--sectionssectionsthat can be formed by ringthat can be formed by ringrolling.rolling.
Ring RollingRing Rolling
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Variety of cross sections can be ringVariety of cross sections can be ring--rolledrolled with shaped rollswith shaped rolls
Short production runs, materialShort production runs, materialsavings,savings, closer tolerances, favorablecloser tolerances, favorable
grain flowgrain flow
Rockets, turbines, gearwheel rims,Rockets, turbines, gearwheel rims,bearingbearing races, etc.races, etc.
B.B. Ring RollingRing Rolling
Ring RollingRing Rolling
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B.B. Ring RollingRing Rolling
Ring Rolling MachineRing Rolling Machine
RollingRolling
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B.B. Ring RollingRing Rolling
RollingRolling
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B.B. Ring RollingRing Rolling -- ExamplesExamples
RollingRolling
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C.C. Thread RollingThread Rolling
Threads or gear teeth formed on round rods by rollingThreads or gear teeth formed on round rods by rolling
Flat reciprocating dies and round rotating dies are usedFlat reciprocating dies and round rotating dies are used
Good for external threadsGood for external threads -- High production rate forHigh production rate forscrews, boltsscrews, bolts
No loss of materialNo loss of material smaller diameter rods to start withsmaller diameter rods to start with
Greater strength due to cold working, as compared to aGreater strength due to cold working, as compared to a
regular thread cutting processregular thread cutting process
Ductility of material is crucial as well as goodDuctility of material is crucial as well as goodlubrication in thelubrication in the processprocess
Typically fasterTypically faster -- at three times the cutting processat three times the cutting process
Thread RollingThread Rolling
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ThreadThread--rolling processes:rolling processes:(a)(a) and (c) reciprocatingand (c) reciprocating
flat dies;flat dies;(b)(b) twotwo--roller dies.roller dies.
Threaded fasteners,Threaded fasteners,such as bolts, aresuch as bolts, aremade economicallymade economicallyby these processes, atby these processes, athigh rates ofhigh rates ofproduction.production.
Thread RollingThread Rolling
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(a)(a) Features of aFeatures of amachined or rolledmachined or rolledthread.thread.
(b)(b) Grain flow inGrain flow inmachined and rolledmachined and rolledthreads. Unlikethreads. Unlikemachining, whichmachining, whichcuts through thecuts through thegrains of the metal,grains of the metal,the rolling of threadsthe rolling of threads
causes improvedcauses improvedstrength, because ofstrength, because ofcold working andcold working andfavorablefavorable grain flow.grain flow.
Thread RollingThread Rolling
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C.C. Thread RollingThread Rolling Material is not wastedMaterial is not wasted
Cut ThreadCut Thread Rolled ThreadRolled Thread
Thread RollingThread Rolling
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C.C. Thread RollingThread Rolling
Thread RollingThread Rolling
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C.C. Thread RollingThread Rolling
Thread RollingThread Rolling
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ExamplesExamples
Thread RollingThread Rolling
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A hotA hot--working processworking process used to make long thickused to make long thickwall seamless tubingwall seamless tubing
When a round bar is subject to radial compressionWhen a round bar is subject to radial compressiontensile stress develops in the center of the rodtensile stress develops in the center of the rod
D.D. Rotary Tube PiercingRotary Tube Piercing
Can be demonstratedCan be demonstratedusing a round eraser andusing a round eraser androlling it on the table !rolling it on the table !
RollingRolling
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When subject to cyclic compressive stresses aWhen subject to cyclic compressive stresses acavity begins to form in the centercavity begins to form in the center
By means of piercing this hole with a mandrel ofBy means of piercing this hole with a mandrel ofrequired diameter, the hole size is expandedrequired diameter, the hole size is expanded
Special roll arrangement withSpecial roll arrangement withthe mandrel are usedthe mandrel are used
High quality defect free barsHigh quality defect free barsmust be used for thismust be used for thisprocessprocess
D.D. Rotary Tube PiercingRotary Tube Piercing
RollingRolling
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Rolls
Rotary Tube PiercingRotary Tube Piercing A SchematicA Schematic
Rolls are normally arranged in aRolls are normally arranged in askewed manner (axes at an angle)skewed manner (axes at an angle)
Rotary Tube piercing isRotary Tube piercing isalso called thealso called theMannesmann processMannesmann process
RollingRolling
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Rotary Tube PiercingRotary Tube Piercing
RollingRolling
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SchematicSchematicillustration ofillustration ofvarious tubevarious tube--rollingrollingprocesses:processes:
(a)(a) with fixedwith fixedmandrel;mandrel;
(b)(b) with movingwith movingmandrel;mandrel;
(c)(c) withoutwithoutmandrel; andmandrel; and
(d)(d) pilgerpilger rollingrollingover aover a
mandrel andmandrel anda pair ofa pair ofshaped rolls.shaped rolls.
E. Tube RollingE. Tube Rolling
RollingRolling
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Spray casting (OspreySpray casting (Ospreyprocess), in whichprocess), in whichmolten metal ismolten metal issprayed over a rotatingsprayed over a rotatingmandrel to producemandrel to produceseamless tubing andseamless tubing andpipe.pipe. SourceSource: J .: J .SzekelySzekely,, ScientificScientific
AmericanAmerican, J uly 1987., J uly 1987.
RollingRolling Spray CastingSpray Casting
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Rolling MillsRolling Mills
Several types of Rolling mills & equipment are built,Several types of Rolling mills & equipment are built,using diverse rolls arrangementusing diverse rolls arrangement
Equipment for Hot and Cold rolling is essentially theEquipment for Hot and Cold rolling is essentially thesame, except the process parameters, roll materials,same, except the process parameters, roll materials,lubricants and cooling systemlubricants and cooling system
Very capital intensiveVery capital intensive
Highly automatedHighly automated
Rolling MillsRolling Mills
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Rolling MillRolling Mill
Rolling MillsRolling Mills
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Rolls in a SemiRolls in a Semi--continuous hot strip millcontinuous hot strip mill
Rolling MillsRolling Mills
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TwoTwo--HighHighMillMill
ThreeThree--HighHighMillMill
RollRollArrangementsArrangements TwoTwo-- and Threeand Three--highhigh
MillsMills
Used in hotUsed in hot--rollingrollingfor initial breakdownfor initial breakdownpasses on cast ingotspasses on cast ingotsor in continuousor in continuouscasting processcasting process
ThreeThree--high reversinghigh reversingmill used as a twomill used as a twostage rolling processstage rolling process
Rolling MillsRolling Mills
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FourFour--HighHighMillMill
FourFour--high Millshigh Mills
Based on principle that smallerBased on principle that smallerrolls lower roll forces and power,rolls lower roll forces and power,as well as spreading of sheets;as well as spreading of sheets;easily replaced when broken oreasily replaced when broken orwornworn
DrawbacksDrawbacks small rolls deflectsmall rolls deflectmore; have to be supported bymore; have to be supported byother rolls as in the fourother rolls as in the four--high andhigh andcluster arrangementscluster arrangements
Cluster rolls (Cluster rolls (SendzimirSendzimir) most) mostsuited for cold rollingsuited for cold rolling
Roll ArrangementsRoll Arrangements
Rolling MillsRolling Mills
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Schematic illustrationSchematic illustrationof a fourof a four--high rollinghigh rolling--mill stand, showing itsmill stand, showing itsvarious features.various features.
The stiffness of theThe stiffness of thehousing, the rolls, andhousing, the rolls, andthe roll bearings arethe roll bearings areall important inall important incontrolling andcontrolling andmaintaining themaintaining thethickness of the rolledthickness of the rolledstrip.strip.
Rolling MillsRolling Mills
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Schematic illustration of various roll arrangements: (a) two-high; (b)three- high; (c) four-high; (d) cluster (Sendzimir) mill.
Roll ArrangementsRoll Arrangements
Rolling MillsRolling Mills
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Tandem MillsTandem Mills
Strip is rolled continuously through a number ofStrip is rolled continuously through a number ofstands to smaller gauges with each passstands to smaller gauges with each pass
Each stand has its own set of rolls and controlsEach stand has its own set of rolls and controls
A groups of stands is called aA groups of stands is called a TrainTrain
Roll ArrangementsRoll Arrangements
Rolling MillsRolling Mills
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Tandem MillsTandem Mills
Dimensions at different stagesDimensions at different stages
Roll ArrangementsRoll Arrangements
Rolling MillsRolling Mills
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Strength and Resistance to wearStrength and Resistance to wear
Made of Cast iron, cast steel & forged steel.Made of Cast iron, cast steel & forged steel.Tungsten carbide for smaller diameter rollsTungsten carbide for smaller diameter rolls
Forged steel among the best materialsForged steel among the best materials greatergreaterstrength, stiffness and toughnessstrength, stiffness and toughness
Rolls are ground to fine finish for cold rolling.Rolls are ground to fine finish for cold rolling.
Polished for special applicationsPolished for special applications
Rolls for hot and cold rolling are notRolls for hot and cold rolling are not
interchangeableinterchangeable
Rolling MillsRolling Mills -- RollsRolls
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Because of forces acting on them, rollsBecause of forces acting on them, rolls
undergo geometric changesundergo geometric changes
As a result, there are problems with theAs a result, there are problems with the
resulting rolled productresulting rolled product
Problems with Rolls in PracticeProblems with Rolls in Practice
RollingRolling
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The forces result from theThe forces result from the
resistance of the material toresistance of the material to
deformation, and causedeformation, and cause
Roll bendingRoll bending
Non flat materialNon flat material
Cambered sheetCambered sheet
BucklingBuckling
Roll flatteningRoll flattening Poor tolerancesPoor tolerances
Increased forces (larger contactIncreased forces (larger contact
area)area)
Effect of Roll ForcesEffect of Roll Forces
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Rolling forces set the energy required for the process andRolling forces set the energy required for the process and
the size of the equipment requiredthe size of the equipment required
Roll Forces can be decreased by:Roll Forces can be decreased by:
Reducing frictionReducing friction use of Lubricantsuse of Lubricants
Using smaller diameter rolls (e.g., in theUsing smaller diameter rolls (e.g., in the SendzimirSendzimir mill)mill)
Smaller reductions per pass (lesser Residual stresses)Smaller reductions per pass (lesser Residual stresses)
Increasing the temperature (via Hot rolling)Increasing the temperature (via Hot rolling)
Provide backup rolls (four high)Provide backup rolls (four high)
Camber rolls to compensate roll deflectionCamber rolls to compensate roll deflection
Bend rolls backBend rolls back
Roll Force CompensationRoll Force Compensation
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Lowering the frictionLowering the friction
Friction is lower for cold rolling than for hotFriction is lower for cold rolling than for hot .. With effectiveWith effective
lubricant:lubricant:
Cold RollingCold Rolling -- frict ion = 0.2 to 0.3fricti on = 0.2 to 0.3
Hot RollingHot Rolling -- fricti on = 0.2 to 0.7frict ion = 0.2 to 0.7
Choose the right material for rollsChoose the right material for rolls
Modify the lubrication parametersModify the lubrication parameters ((Type, Amoun t, Method ofType, Amount, Method of
Appl ication)Appl ication)
Reduce the Roll RadiusReduce the Roll Radius
This also lowers the energyThis also lowers the energy
Reducing the roll radius shortens the length of contactReducing the roll radius shortens the length of contact
However, rolls will be more prone to deflection (see defects)However, rolls will be more prone to deflection (see defects)
Reducing the Roll ForceReducing the Roll Force
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Use Lower ReductionsUse Lower ReductionsThis may increase the number of required passes, thusThis may increase the number of required passes, thus
requiring:requiring:
More timeMore time
Possibly more equipment requirementsPossibly more equipment requirements
Possibly more energyPossibly more energy
Increase the Work piece TemperatureIncrease the Work piece Temperature
This lowers the yield pointThis lowers the yield point
This allowThis allow recrystallizationrecrystallization and reduces strain hardeningand reduces strain hardening
App ly TensionApply Tension
Either side will reduce the forceEither side will reduce the force
If applied at the entrance, termed back tensionIf applied at the entrance, termed back tension
If applied at the exit, termed front tensionIf applied at the exit, termed front tension
Reducing the Roll ForceReducing the Roll Force
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LubricantsLubricants
Normally none used for rolling Ferrous alloys; GraphiteNormally none used for rolling Ferrous alloys; Graphitemay be used sometimesmay be used sometimes
WaterWater--based solutions are used to cool the rollsbased solutions are used to cool the rolls
NonNon--ferrous alloys are hotferrous alloys are hot--rolled with variety ofrolled with variety oflubricants such as oils and fatty acidslubricants such as oils and fatty acids
Cold rolling is carried out with lowCold rolling is carried out with low--viscosity lubricantsviscosity lubricantssuchsuch as mineral oils, paraffin, etc.as mineral oils, paraffin, etc.
Rolling MillsRolling Mills -- LubricantsLubricants
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Significant effect on product Quality and ProductivitySignificant effect on product Quality and Productivity
Chatter (self excited vibration) can occur in rolling as wellChatter (self excited vibration) can occur in rolling as well asasother processes (extrusion, drawing, machining, etc.)other processes (extrusion, drawing, machining, etc.)
Related to the dynamics of the rolling actionRelated to the dynamics of the rolling action
In RollingIn Rolling predominantly occurs in Tandem millspredominantly occurs in Tandem mills
variation in thickness, poor surface finish, high levels ofvariation in thickness, poor surface finish, high levels ofscrapscrap
frequencies related to the resonance as well as other naturalfrequencies related to the resonance as well as other naturalfrequencies of the systemfrequencies of the system
Controlled by process parameters: distance between roll sets,Controlled by process parameters: distance between roll sets,width of job, speed of rolling, increasing damping, etc.width of job, speed of rolling, increasing damping, etc.
RollingRolling Vibration and ChatterVibration and Chatter
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The forces of rolling will flatten the rollers elasticallyThe forces of rolling will flatten the rollers elasticallysimilar to tires on the road surfacesimilar to tires on the road surface (Roll radius,(Roll radius,Modulus of elasticity, roll forces)Modulus of elasticity, roll forces)
This flattening causes an increase in the contactThis flattening causes an increase in the contactareaarea
The increased contact area causes the forces toThe increased contact area causes the forces toincreaseincrease
Roll Flattening can be reduced by:Roll Flattening can be reduced by:
Using a roller material with a higher modulus ofUsing a roller material with a higher modulus ofelasticityelasticity
Reducing the roll forceReducing the roll force
RollingRolling Problems with RollsProblems with Rolls
Roll FlatteningRoll Flattening
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Roll DeflectionRoll Deflection
Roll forces tend to bend the rolls: leading to a stripthat is thicker at the center than at the edges
Solution: Grind the rolls such that the diameter atthe center is slightly larger than at the edges
This is known as giving them CAMBER Inpractice, this would generally be around 0.25 mmor less on the radius. Camber is only correct for a
given load on the roll
thickness of the strip
Hence normally done for a large batch, due toeconomic reasons
RollingRolling Problems with RollsProblems with Rolls
66ME 4563 Fall 05 Dr. S. Haran
(a)(a) Bending of straightBending of straightcylindrical rolls,cylindrical rolls,caused by the rollcaused by the rollforce.force.
(b)(b) Bending of rollsBending of rollsground with camber,ground with camber,producing a stripproducing a stripwith uniformwith uniform
thickness.thickness.
RollRollDeflectionDeflection
RollingRolling Problems with RollsProblems with Rolls
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67ME 4563 Fall 05 Dr. S. Haran
SpreadingSpreading
Rolling plates sometimes causes theRolling plates sometimes causes thewidth to increase considerablywidth to increase considerably
This increase is calledThis increase is called SPREADINGSPREADING
Controlled with:Controlled with:
high widthhigh width--toto--thickness ratiothickness ratio
roll radius to strip thicknessroll radius to strip thicknessratioratio
decreasing friction between rollsdecreasing friction between rolls
and materialand materialSpreading can be observed whenSpreading can be observed whendough is rolled with a rolling pin.dough is rolled with a rolling pin.
RollingRolling Problems with RollsProblems with Rolls
68ME 4563 Fall 05 Dr. S. Haran
Successful Rolling depends upon various factorsSuccessful Rolling depends upon various factorsincluding material properties, process variables, andincluding material properties, process variables, andlubricationlubrication Defects:Defects:
on theon the surfacesurface of the rolled materialof the rolled material
structural defectsstructural defects within the rolled materialwithin the rolled material
Surface Defects:Surface Defects:
inclusions and impurities in the materialinclusions and impurities in the material scale, rust, dirt, roll marks, etc., caused due toscale, rust, dirt, roll marks, etc., caused due to
prior treatment and working of the materialprior treatment and working of the material
Remedy:Remedy: precondition the material by cleaningprecondition the material by cleaningit byit by various meansvarious means
Defects due to RollingDefects due to Rolling
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69ME 4563 Fall 05 Dr. S. Haran
Structural Defects:Structural Defects: distort or affect the integrity ofdistort or affect the integrity ofthe rolled productthe rolled product
Wavy EdgesWavy Edges Edges are thinner than the centerEdges are thinner than the centercaused by bending of the rollscaused by bending of the rolls
the edges elongate more then the center andthe edges elongate more then the center andare restrained from expanding freely, theyare restrained from expanding freely, theybucklebuckle
CracksCracks in the Rolled Productin the Rolled Product usually caused byusually caused by
low ductility and barreling (in the edges & middle)low ductility and barreling (in the edges & middle)
AlligatoringAlligatoring resulting from inhomogeneousresulting from inhomogeneous
material deformation during rolling and defects inmaterial deformation during rolling and defects inthe original cast ingot itselfthe original cast ingot itself
Defects due to RollingDefects due to Rolling
70ME 4563 Fall 05 Dr. S. Haran
SchematicSchematicillustration ofillustration oftypical defects intypical defects inflat rolling:flat rolling:
(a)(a) wavy edges;wavy edges;(b)(b) zipper cracks inzipper cracks in
thethe centercenter of theof thestrip;strip;
(c)(c) edge cracks;edge cracks;andand(d)(d) alligatoringalligatoring..
Defects due to RollingDefects due to Rolling
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71ME 4563 Fall 05 Dr. S. Haran
Defects due to RollingDefects due to Rolling
72ME 4563 Fall 05 Dr. S. Haran
Defects due to RollingDefects due to Rolling
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73ME 4563 Fall 05 Dr. S. Haran
Taking care of wavy edgesTaking care of wavy edges
Defects due to RollingDefects due to Rolling
74ME 4563 Fall 05 Dr. S. Haran
Defects due to RollingDefects due to Rolling
Taking care of wavyTaking care of wavyedgesedges
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75ME 4563 Fall 05 Dr. S. Haran
Hot RollingHot Rolling
76ME 4563 Fall 05 Dr. S. Haran
Hot Rolling is done between 100 and 200 degrees FHot Rolling is done between 100 and 200 degrees F
above the reabove the re--crystallization temperature forcrystallization temperature for
most metalsmost metals
Hot rolling gives a final product with a fine grainHot rolling gives a final product with a fine grain
size and little strain hardeningsize and little strain hardening
This provides increased material yield strengthThis provides increased material yield strength
This also provides increased ductility, by breakingThis also provides increased ductility, by breakinggraingrain boundaries, closing internal defects andboundaries, closing internal defects and
breaking inclusionsbreaking inclusions
Hot RollingHot Rolling
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77ME 4563 Fall 05 Dr. S. Haran
Stresses lowerStresses lower
Forces smallerForces smaller
Power requirements lessPower requirements less
No work hardeningNo work hardening
Large deformations possibleLarge deformations possible
Breaks up the cast structure into preferable formsBreaks up the cast structure into preferable forms
Closes porosityCloses porosity
Sometimes the only way to create sheetSometimes the only way to create sheet
Hot RollingHot Rolling
AdvantagesAdvantages
78ME 4563 Fall 05 Dr. S. Haran
Higher frictionHigher friction
Rolls need to be cooledRolls need to be cooled
Material handling difficultMaterial handling difficult
Personnel must be protected from heatPersonnel must be protected from heat
Hot RollingHot Rolling
DisadvantagesDisadvantages
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79ME 4563 Fall 05 Dr. S. Haran
Causes changes in the grain structure of cast or ofCauses changes in the grain structure of cast or oflargelarge--grain wrought metalsgrain wrought metals Hot rolling is an effective way to reduce grain size inHot rolling is an effective way to reduce grain size in
metals, for improved strength and ductilitymetals, for improved strength and ductility
Hot RollingHot Rolling
80ME 4563 Fall 05 Dr. S. Haran
Hot RollingHot Rolling some pointssome points
The final product has little directionality, however:The final product has little directionality, however:
If there are nonIf there are non--metallic inclusions, they will notmetallic inclusions, they will not recrystallizerecrystallize andandmay impart directionalitymay impart directionality
Alloying elements that have a highAlloying elements that have a high recrystalliztionrecrystalliztion temperaturetemperaturemay cause the same effectmay cause the same effect
Thinner sheets will have more directional characteristicsThinner sheets will have more directional characteristics
The final product has few residual stresses, however:The final product has few residual stresses, however:
NonNon--uniform cooling can induce substantial residual stressesuniform cooling can induce substantial residual stresses
The edges may warp due to rapid cooling, especially in moreThe edges may warp due to rapid cooling, especially in morecomplicated shapes (Icomplicated shapes (I--beam, Flanges do this)beam, Flanges do this)
The final surface is rougher, surface will contain difficult toThe final surface is rougher, surface will contain difficult to removeremovehighhigh--temperature oxides (termed mill scale), tolerances cantemperature oxides (termed mill scale), tolerances can
usually be held to 2usually be held to 2 -- 5% of the specified dimension5% of the specified dimension
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81ME 4563 Fall 05 Dr. S. Haran
Casting & Hot RollingCasting & Hot Rolling a schematica schematic
82ME 4563 Fall 05 Dr. S. Haran
Slab
Hot mill
Roller table
Warm millTake-up roll
Hot Rolling Mill DesignHot Rolling Mill Design
Basically the same as cold mills, but designed forBasically the same as cold mills, but designed for
higher temperatures and are reversiblehigher temperatures and are reversible
Typically have edging rolls to control thicknessTypically have edging rolls to control thickness
Often have a warm mill at the endOften have a warm mill at the end
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83ME 4563 Fall 05 Dr. S. Haran
Hot Rolling Mill DesignHot Rolling Mill Design
Basically the same as cold mills, but designed forBasically the same as cold mills, but designed forhigher temperatures and are reversiblehigher temperatures and are reversible
Typically have edging rolls to control thicknessTypically have edging rolls to control thickness
Often have a warm mill at the endOften have a warm mill at the end
Slab
Hot mill
Roller table
Warm millTake-up roll
84ME 4563 Fall 05 Dr. S. Haran
Hot Rolling ProcessHot Rolling Process -- ExampleExample
Start with 12in. thick slab, 20 feet longStart with 12in. thick slab, 20 feet long
Hot mill converts to 2 in thick slab, 120 feet long withHot mill converts to 2 in thick slab, 120 feet long with
11 passes (six forward and 5 reverse)11 passes (six forward and 5 reverse)
Front end sheared off to eliminate alligatoringFront end sheared off to eliminate alligatoring
Warm mill converts this toWarm mill converts this to rollroll of sheet 0.25 in thick,of sheet 0.25 in thick,
960 feet long960 feet long
Rolls more easily handled by overhead cranes toRolls more easily handled by overhead cranes to
transport it to cold mills than 1000 ft long slabstransport it to cold mills than 1000 ft long slabs
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85ME 4563 Fall 05 Dr. S. Haran
Overall Process for Sheet and PlateOverall Process for Sheet and Plate
Cast ingotCast ingot Scalp (not always)Scalp (not always)
Reheat and homogenize (uniform)Reheat and homogenize (uniform)
Hot roll in reversing mill to ~1Hot roll in reversing mill to ~1--2 in thick2 in thick
Cut off ends (alligators)Cut off ends (alligators)
Warm roll to 0.1Warm roll to 0.1--2 in thick2 in thick
Heat treat to recrystallize (sometimes)Heat treat to recrystallize (sometimes)
CoolCool
Cold roll to finish thicknessCold roll to finish thickness
Heat treat (where appropriate)Heat treat (where appropriate)
Results in material which must be further workedResults in material which must be further worked
86ME 4563 Fall 05 Dr. S. Haran
Hot RollingHot Rolling
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87ME 4563 Fall 05 Dr. S. Haran
Hot RollingHot Rolling
88ME 4563 Fall 05 Dr. S. Haran
RollingRollingMillMill
Hot RollingHot Rolling
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89ME 4563 Fall 05 Dr. S. Haran
Hot RollingHot Rolling
Closer LookCloser Look
Hot RollingHot Rolling
90ME 4563 Fall 05 Dr. S. Haran
ContinuousContinuousSteelSteel
Casting LineCasting Linerolling outrolling out
billetsbillets
Hot RollingHot Rolling
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91ME 4563 Fall 05 Dr. S. Haran
ContinuousContinuousRolling ofRolling of
BilletsBillets
Hot RollingHot Rolling
92ME 4563 Fall 05 Dr. S. Haran
Steel BilletsSteel BilletsSteel Slabs (from slab caster)Steel Slabs (from slab caster)
BilletsBilletsCastingCasting
Hot RollingHot Rolling
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93ME 4563 Fall 05 Dr. S. Haran
Hot rolled stripsHot rolled stripsbeing coiledbeing coiled
Hot RollingHot Rolling
94ME 4563 Fall 05 Dr. S. Haran
Rolling ofRolling of
RailsRails
Hot RollingHot Rolling
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95ME 4563 Fall 05 Dr. S. Haran
Hot CuttingHot Cutting
the rolledthe rolled
RailsRails
Hot RollingHot Rolling
96ME 4563 Fall 05 Dr. S. Haran
Section of theSection of theMill whereMill where
rolling isrolling istaking placetaking place
Hot RollingHot Rolling
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97ME 4563 Fall 05 Dr. S. Haran
Profiled colorProfiled color--coated steelcoated steelsheetssheets
UU--section long barssection long bars
RollingRolling Further ProcessingFurther Processing
98ME 4563 Fall 05 Dr. S. Haran
Wire rods inWire rods ina coila coil
UU--section long barssection long bars
RollingRolling Further ProcessingFurther Processing
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99ME 4563 Fall 05 Dr. S. Haran
Cold RollingCold Rolling
100ME 4563 Fall 05 Dr. S. Haran
Hot rolled coil is commonly cold rolled (also known as coldHot rolled coil is commonly cold rolled (also known as coldreduced).reduced).
The strip is first deThe strip is first de--coiled (uncoiled) and then passes through acoiled (uncoiled) and then passes through aseries of rolling mill stands which apply pressure to the stripseries of rolling mill stands which apply pressure to the strip andandprogressively reduce its thicknessprogressively reduce its thickness -- down to as low as 0.15 mm.down to as low as 0.15 mm.
The strip is then recoiled.The strip is then recoiled.
Cold rolling processes are also used to improve the surfaceCold rolling processes are also used to improve the surfacequality of the steel.quality of the steel.
Cold rolling also has the effect of hardening steel, so coldCold rolling also has the effect of hardening steel, so coldreduced strip is subsequently annealed: a process of veryreduced strip is subsequently annealed: a process of verycarefully controlled heating and cooling to soften itcarefully controlled heating and cooling to soften it
Cold RollingCold Rolling
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101ME 4563 Fall 05 Dr. S. Haran
AdvantagesAdvantages Deformations of ~ 50 to 80%Deformations of ~ 50 to 80%
Work hardening increases strengthWork hardening increases strength
Excellent surface finishExcellent surface finish
Excellent tolerance on thickness and shapeExcellent tolerance on thickness and shape
DisadvantagesDisadvantages High forcesHigh forces
Small reductions give rise to surface stresses andSmall reductions give rise to surface stresses andnonnon--uniform stress distributionsuniform stress distributions
??
Cold RollingCold Rolling
102ME 4563 Fall 05 Dr. S. Haran
Input and output coils with tensioning controlInput and output coils with tensioning control
Shape meters consisting of segmented coilsShape meters consisting of segmented coils
measuring forcemeasuring force
Tandem mills allow multiple reductions in oneTandem mills allow multiple reductions in one
operationoperation
Laser inspection systems for surface finish inspectionLaser inspection systems for surface finish inspection
becoming popular (especially for canstock)becoming popular (especially for canstock)
Surface condition of rolls critical to maintain surfaceSurface condition of rolls critical to maintain surfacefinishfinish
Roll bending almost essential to provide crownRoll bending almost essential to provide crown
controlcontrol
Cold Rolling Mill DesignCold Rolling Mill Design
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103ME 4563 Fall 05 Dr. S. Haran
Cold RollingCold Rolling
--
SchematicSchematic
Cold RollingCold Rolling
104ME 4563 Fall 05 Dr. S. Haran
Cold rolled sheet can be produced in various conditionsCold rolled sheet can be produced in various conditionssuch assuch as skinskin--rolledrolled, quarter hard, half hard, full hard, quarter hard, half hard, full harddepending on how much cold work has been performed.depending on how much cold work has been performed.
This cold working (hardness) is often calledThis cold working (hardness) is often called tempertemper
InIn Skin RollingSkin Rolling, the metal is reduced by 0.5 to 1% and, the metal is reduced by 0.5 to 1% andresults in a surface that is smooth and the yield pointresults in a surface that is smooth and the yield point
phenomenonphenomenon----excessive stretching and wrinkling inexcessive stretching and wrinkling insubsequent operations, is eliminated.subsequent operations, is eliminated.
This makes the metal more ductile for further formingThis makes the metal more ductile for further formingand stretching operationsand stretching operations
Cold RollingCold Rolling
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105ME 4563 Fall 05 Dr. S. Haran
Quarter Hard, Half Hard, Full HardQuarter Hard, Half Hard, Full Hard stock have higherstock have higheramounts of reduction,amounts of reduction, uptoupto 50%.50%.
This increases the yield point; grain orientation andThis increases the yield point; grain orientation andmaterial properties assume different properties along thematerial properties assume different properties along thegrain orientation.grain orientation.
However, while the yield point increases, ductilityHowever, while the yield point increases, ductilitydecreasesdecreases Quarter HardQuarter Hard material can be bent (perpendicular to thematerial can be bent (perpendicular to thedirection of rolling) on itself without fracturing.direction of rolling) on itself without fracturing. Half hardHalf hardmaterial can be bent 90material can be bent 90;; Full hardFull hard can be bent 45can be bent 45..
Thus, these materials can be used for in applicationsThus, these materials can be used for in applicationsinvolving great amounts of bending and deformation,involving great amounts of bending and deformation,
without fracturingwithout fracturing
Cold RollingCold Rolling
106ME 4563 Fall 05 Dr. S. Haran
Another form of cold processing is cold drawingAnother form of cold processing is cold drawing
Steel rod is dragged at pressure (drawn) through a seriesSteel rod is dragged at pressure (drawn) through a seriesof dies which progressively reduce the rod's circumference toof dies which progressively reduce the rod's circumference toproduce wireproduce wire
The drawing process substantially increases the steel'sThe drawing process substantially increases the steel's
tensile strengthtensile strength
Steel wires can be spun into huge ropes strong enough toSteel wires can be spun into huge ropes strong enough tosupport the world's largest suspension bridgessupport the world's largest suspension bridges
Cold DrawingCold Drawing
Cold RollingCold Rolling
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107ME 4563 Fall 05 Dr. S. Haran
Cold rolling MillCold rolling Mill
Cold RollingCold Rolling
108ME 4563 Fall 05 Dr. S. Haran
Cold rolling MillCold rolling Mill
Cold RollingCold Rolling
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109ME 4563 Fall 05 Dr. S. Haran
Cold RollingCold Rolling
Cold RollingCold Rolling
110ME 4563 Fall 05 Dr. S. Haran
Cold rolled coil beingCold rolled coil beingsplit into narrow stripssplit into narrow strips
Cold rolled coilsCold rolled coils
Cold RollingCold Rolling
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111ME 4563 Fall 05 Dr. S. Haran
Al Sheet being rolledout
Rolling AluminumRolling Aluminum
112ME 4563 Fall 05 Dr. S. Haran
Al Foil RollAl Foil Roll
Rolling AluminumRolling Aluminum
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113ME 4563 Fall 05 Dr. S. Haran
Independent Variables for RollingIndependent Variables for Rolling
For a given rolling setFor a given rolling set--up:up:
Roll speedRoll speed
Draft (amount of thickness reduction) or roll gapDraft (amount of thickness reduction) or roll gap
Billet thicknessBillet thickness
Billet widthBillet width
Billet material (not always allowed to select)Billet material (not always allowed to select)
Billet temperatureBillet temperature
LubricantLubricant
114ME 4563 Fall 05 Dr. S. Haran
For a given rolling setFor a given rolling set--up:up:
Roll forceRoll force
PowerPower
Speed of exiting stripSpeed of exiting strip
Final strip temperatureFinal strip temperature
Maximum draftMaximum draft
Roll strip contact lengthRoll strip contact length
Sheet or plate shapeSheet or plate shape
Dependent Variables for RollingDependent Variables for Rolling
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115ME 4563 Fall 05 Dr. S. Haran
Control of Overall PropertiesControl of Overall Properties
ThicknessThickness Roll gap which impacts roll force and hence the dimensionsRoll gap which impacts roll force and hence the dimensions
of the mill frameof the mill frame
WidthWidth (due to spreading of slab)(due to spreading of slab)
Edge rollers (push material back)Edge rollers (push material back)
Edge shears (cut material off)Edge shears (cut material off)
LengthLength
End shearsEnd shears
Mechanical PropertiesMechanical Properties
Controlled by the microstructures which is controlled by theControlled by the microstructures which is controlled by the
rolling parameters (reduction, temperature, etc)rolling parameters (reduction, temperature, etc)
ToleranceTolerance ThicknessThickness
Operator skill/automationOperator skill/automation
Gauges measure thicknessGauges measure thicknessof input and outputof input and output
Computers control roll gapComputers control roll gap
CamberCamber Roll bending/automationRoll bending/automation
Special segmented tensionSpecial segmented tensionmeters measure "shape"meters measure "shape"
Computers bend the rollsComputers bend the rolls
Surface finishSurface finish
Bearing reaction forces
Control of Overall PropertiesControl of Overall Properties