板形培訓(xùn)資料ppt課件

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?O

2、ff-line Flatness / Shape errors.What 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 proc

3、ess of Rolling, 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 l

4、eads to non-uniform elongation 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 relaxed.Strip L

5、engths across the widthLa.HOW DO THE DEFECTS LOOK LIKE?.Full Center Buckle.Edge PocketsEdge Pockets.Edge Wave / RippleEdge RippleEdgeRipple(plant light)EdgeRipple(office light).WAVY EDGESCENTRE BUCKLESQUARTER POCKETS.BBAABBAABBAALateral CurvatureCoil-setCross-bowDefinitions: Lateral Curvature, Cross

6、-bow and Coil-set.Definition: Anticlastic CurvatureAnticlastic CurvatureAnticlastic curvature is a curvature which is induced when a sheet that is curved in one plane is elastically flattened.TensileCompressiveForces at the Upper and Lower Surfaces of a Strip being bent around a Radius of CurvatureS

7、ources of Flatness Variation: Bending of sheetr = the radius at which the outer portion of the sheet will deform under applied stress a.Productivity Acceleration & deceleration Higher top speedsRecovery Threading Strip breaks Weaving Coil Build-UpQuality Customer and Process demandsWhy do we need go

8、od shape / flat strip?.Litho ClosureFoilstockAnodising 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

9、 error resulting from a strain differential between 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: Flatn

10、ess IndexIU = 105* L/La.ldLDefinitions for a Sinusoidal Buckle.On-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

11、the strip.These stress variations represent the latent shape of the relaxed material and can be measured by means of a tension monitoring device such as the Vidimon Shapemeter Roll.What are the factors that affect the Shape of the Outgoing Strip?Factors that affect the on-line ShapeFactors that affe

12、ct the off-line Shape.Longer middleIncoming SheetUniform ThicknessRoll gapNarrower at centreSources of Flatness Variation: Roll Gap Geometry.Full CentreEdge WaveQuarter BuckleTensionDistributionOn MillRollBiteStripAppearanceOn-line Shape is affected by the roll gap geometry.Factors that Effect Shape

13、 / FlatnessProcess (Method)Pass ScheduleMill SchedulingOptimum Ground Camber on the RollsCoil TemperatureWarm-Up PracticeMill Zeroing PracticesVidimon Zeroing PracticeCoiling TensionsRolling oil temperatures.Factors that Effect Shape / Flatness (cont.)MachineResponse of the Shape Control Systems viz

14、. Bending, Steer / tilt, Spray nozzles etc. by a leak proof systemsTouch Roll alignmentsRegular Calibration of the Shapemeter.Factors that Effect Shape / Flatness (cont.)ManStrip Centering while feedingProper Tail-out in Previous PassesRolling on FoldsRegular Roll CoolingMinimize Turn Around Time.Fa

15、ctors that Effect Shape / Flatness (cont.)MaterialGood ShapeGood ProfileQuality of SpoolOptimization 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

16、 time it is measured on the mill and when it is processed downstream.Bad Input Coil ProfileImproper Coil Centering at the MillIncorrect Coil WidthsHigh Rewind StressHigher Entry Temperature of the CoilsWide Differential temperature across the width of the coilHigher Absolute Coil temperatureHigher R

17、oll Coolant temperatureReduction ScheduleUsage of Bad SpoolsFactors that cause difference in On-line and Off-line Shape.Profile - Flatness RelationshipWith No Lateral Flow - Off-Flat- Length change in fibre lengths across strip- Edges longer than middleOver-roll EdgesWith Lateral Flow- Profile is ch

18、anged- Flatness is not changed“Hot mill “Cold mill .Relationship between profile and flatness.Flatness ChangesDuring Hot Strip RollingOn latercold Rolling or RecoilingProfile ChangesfromtoororororChanges Between Profile and Flatness.Sources of Flatness Variation: Thermal EffectsNon-uniform heating o

19、r cooling = relative strain in sheetThe 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

20、takes the material beyond its yield point. .Long-middleWavy EdgesSources of Flatness Variation: Coiling.Coiling EffectsCoiling a sheet under tension can create flatness variations.When coiling, a sheet under tension is wrapped around a spool/core and the internal stresses generated are redistributed

21、 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 it.Coiling EffectsThe general effect is to concen

22、trate 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 center pocket will slowly disappear as

23、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 % reduction must be the same at every point ac

24、ross 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) approach. However, many differe

25、nt 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 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 A poly