1、Mechanics of ShapeIntroductionObjective of the Session-What do you want?What is Shape/Flatness?What are the different types of off-Flatness?Why do we require Flatness?How is Flatness measured/quantified?What are the various factors that effect Flatness?How is Flatness Controlled at the Mills?Off-lin
2、e Flatness/Shape errorsWhat is Shape/Flatness?Shape or Flatness is defines as the strain profile or strain differential across the width of the strip.In simple languages,it is the ability of all portions of the strip,sheet or foil to touch the base when rested on a flat base.In the process of Rollin
3、g,the large forces imposed on the rolls causes them to bend or flatten.Also a lot of heat is generated in the Rolling Process.This and other factors can create a non-parallel roll gap This causes uneven reduction across the width of the strip.What is Shape/Flatness?(cont.)This leads to non-uniform e
4、longation such that the emerging strip is longer in certain portions.For example,the emerging strip may be longer at the middle than at the edges.The middle portion will therefore become wavy to accommodate the extra length and the strip will not lie flat when relaxedStrip Lengths across the widthLa
5、HOW DO THE DEFECTS LOOK LIKE?Full Center BuckleEdge PocketsEdge PocketsEdge Wave/RippleEdge RippleEdgeRipple(plant light)EdgeRipple(office light)WAVY EDGESCENTRE BUCKLESQUARTER POCKETSBBAABBAABBAALateral CurvatureCoil-setCross-bowDefinitions:Lateral Curvature,Cross-bow and Coil-setDefinition:Anticla
6、stic CurvatureAnticlastic CurvatureAnticlastic curvature is a curvature which is induced when a sheet that is curved in one plane is elastically flattenedTensileCompressiveForces at the Upper and Lower Surfaces of a Strip being bent around a Radius of CurvatureSources of Flatness Variation:Bending o
7、f sheetr=the radius at which the outer portion of the sheet will deform under applied stress aProductivity Acceleration&deceleration Higher top speedsRecovery Threading Strip breaks Weaving Coil Build-UpQuality Customer and Process demandsWhy do we need good shape/flat strip?Litho ClosureFoilstockAn
8、odising Quality SheetPre-painted StockSheets for Panellingetc.Which Products need good shape?Measurement of ShapeThe I Unit is the standard Engineering unit for the measurement of Shape throughout the Rolling Industry.The I Unit is defined as the Shape error resulting from a strain differential betw
9、een adjacent elements of a strip of 0.001%or one part in 100,000.That is,if a 1000 mm long strip is rolled with an edge that is 1000.01 mm long when relaxed,then the shape error between the centre and the edge would be 1 I Unit.LaDefinitions:Flatness IndexIU=105*L/LaldLDefinitions for a Sinusoidal B
10、uckleOn-line measurement of ShapeWhen the strip is under high tensions and the waviness is less apparent,the elongation differences are converted into strain variations,which in turn give rise to a uneven stress profile across the width of the strip.These stress variations represent the latent shape
11、 of the relaxed material and can be measured by means of a tension monitoring device such as the Vidimon Shapemeter RollWhat are the factors that affect the Shape of the Outgoing Strip?Factors that affect the on-line ShapeFactors that affect the off-line ShapeLonger middleIncoming SheetUniform Thick
12、nessRoll gapNarrower at centreSources of Flatness Variation:Roll Gap GeometryFull CentreEdge WaveQuarter BuckleTensionDistributionOn MillRollBiteStripAppearanceOn-line Shape is affected by the roll gap geometryFactors that Effect Shape/FlatnessProcess(Method)Pass ScheduleMill SchedulingOptimum Groun
13、d Camber on the RollsCoil TemperatureWarm-Up PracticeMill Zeroing PracticesVidimon Zeroing PracticeCoiling TensionsRolling oil temperaturesFactors that Effect Shape/Flatness(cont.)MachineResponse of the Shape Control Systems viz.Bending,Steer/tilt,Spray nozzles etc.by a leak proof systemsTouch Roll
14、alignmentsRegular Calibration of the ShapemeterFactors that Effect Shape/Flatness(cont.)ManStrip Centering while feedingProper Tail-out in Previous PassesRolling on FoldsRegular Roll CoolingMinimize Turn Around TimeFactors that Effect Shape/Flatness(cont.)MaterialGood ShapeGood ProfileQuality of Spo
15、olOptimization of Strip width-so that the rotor coverage area is more than 50%Difference in Online and Offline ShapeCan be caused by inaccuracy in the measurement,or ifsomething happens to the strip between the time it is measured on the mill and when it is processed downstream Bad Input Coil Profil
16、e Improper Coil Centering at the Mill Incorrect Coil Widths High Rewind Stress Higher Entry Temperature of the Coils Wide Differential temperature across the width of the coil Higher Absolute Coil temperature Higher Roll Coolant temperature Reduction Schedule Usage of Bad SpoolsFactors that cause di
17、fference in On-line and Off-line ShapeProfile-Flatness RelationshipWith No Lateral Flow-Off-Flat-Length change in fibre lengths across strip-Edges longer than middleOver-roll EdgesWith Lateral Flow-Profile is changed-Flatness is not changed“Hot mill”“Cold mill”Relationship between profile and flatne
18、ssThicknessMetal Sensitivity to Gap MismatchFlatnessProfile0.2”2”Flatness ChangesDuring Hot Strip RollingOn latercold Rolling or RecoilingProfile ChangesfromtoororororChanges Between Profile and FlatnessSources of Flatness Variation:Thermal EffectsNon-uniform heating or cooling=relative strain in sh
19、eetThe Coefficient of Linear Thermal Expansion is defined as:where t is temperature.For Aluminium a temperature difference of 4C between one section and another produces about 10 I-units of strain.This will not cause permanent off-flatness unless the total stress takes the material beyond its yield
20、point.Long-middleWavy EdgesSources of Flatness Variation:CoilingB arrelled CoilNon-Uniform StressDistributionCylindrical CoilUniform StressDistributionCoiling EffectsCoiling a sheet under tension can create flatness variations.When coiling,a sheet under tension is wrapped around a spool/core and the
21、 internal stresses generated are redistributed as each new lap affects the ones under it.These stresses are affected by The compliance of the wraps The effect of the mandrel The profile of the strip Subsequent temperature changes of the coil The bending of the sheet to conform to the sheet under itC
22、oiling EffectsThe general effect is to concentrate the forces in the areas where the sheet is thick.On most mills the sheet is thickest in the center.The concentration of forces can lead to a plastic change in the coils length.Thus creating a center pocket or belly.The effect is“additive”in that the
23、 center pocket will slowly disappear as the coil is unwound.The sheet next to the core is likely to have an edge wave.The cooling of a hot/warm coil will greatly increase the effect as will coiling under higher tensions.Flatness Control Flatness control is simple.There is only one rule:“The%reductio
24、n must be the same at every point across the sheets width”Tilt/Steer The Tilt loop of the control system is typically the fastest control loop as it uses the Automatic Gauge Control(AGC)cylinders to tilt the mill.The amount of correction needed is usually determined by a linear regression(best fit)a
25、pproach.However,many different methods have been used.A comparison of the sum of the outer 2 edge zones An independent linear fit A polynomial fit with the linear term used for tilt A linear term plus a 7th order term BendingThe bending loop of the control system is typically the“middle”control loop
26、 and it uses the bending jacks to open or close the ends of the work rollsThe amount of correction needed is usually determined by a using best fit approach to a curve.However,many different methods have been used.A comparison of the outer 2 edges to the center zone.An independent polynomial(X2)fit
27、A polynomial fit with the X2 or X4 term used for tilt A cosine fit.Coolant/SpraysThe coolant loop of the control system is typically the“last”control loop and it uses the coolant sprays to locally cool a section of the workroll.This is a thermal process and the total control cycle is usually measure
28、d in seconds.There are two general approaches to sprays.#1)Variable volume(1,2,4 ratio in volumes giving 8 levels)#2)Duty cycle control(Assumes that 100%volume for 20%of the time is the equivalent of 20%volume for 100%of the time)Coolant/SpraysA change in the given amount of error(if loose)will resu
29、lt in a increase in cooling applied.There may also be a lubricating function built into the spray logic.Please note that very little coolant is actually required for lubrication.Establish the Ground Camber-Done at the Canron and theDavy MillCanron Mill Stabilised at 25Davy Mill Pass Schedules and An
30、nealing point Pass Schedules of the following products Rationalized at theCanron MillLampcap 5.5 3.0 1.8 1.0 IA 0.50 0.30EXPCB 5.5 3.0-1.7 1.1 IA-0.60 0.30 0.18-SRFS 5.0 2.5 1.2 0.60 IA-0.30LP 5.5 3.0 1.5 0.80-IA 0.47 0.28 Coolant Flow Coolant Levels operating at 75%of the maximum levels at theCanro
31、n Mill.Leading to lesser Heat Levels in the Mill Alignment of Mill Widths to cover Vidimon Rotors Actions taken to Improve Shape Existing widths (mm)Widths To match the VidimonROTORS(mm)775 765815 820875 875920 9259651000 9801040 10351090 10901165 11451320 1305 Usage of Good Spools in Finishing Pass
32、es Being Practised at the Davy MillProcess of Identification of Spools tolerable for CanronMill is On.Optimum Coiling Tensions Established at both the MillsExit Tensions at the Finishing Passes are at a rangeof 10 12%of the YS of the strip Low Deflection to be Avoided at the Finishing Passes Strip B
33、reakage Analysis Off-line Shape and Corrective ActionsActions taken to Improve Shape(contd.)Indal Sheet Technology ApplicationFlatnessBliss Mill4 Hi,1300 mmManual control-Coolant.Nobending.Canron Mill4Hi,1500 mm.Manual control-Coolant,Bending Davy Mill4 Hi,1140mm,AFC-Coolant,Bend,Bow,Tilt,Air bearin
34、gVidimon rollBelur 1938Taloja 1971Taloja 1983 60 I units 20 I UnitsFlatness Facility Works 20 I units 12 I unitsSMS Mill4Hi,1270AFC-Coolant,Bend,Tilt,ABBStresometerCanron UpgradeAFC-Coolant,Bend,and Tilt,Air bearingVidimon Roll.Belur 1993Taloja 1999 10 I unitsDavy Upgrade4Hi,1220 mmAFC-Coolant,Bend,Bow,Tilt,Air bearingVidimon rollTaloja 200
