ROLLS LIFELINE OF ROLLING MILLS - IIM
ROLLS LIFELINE OF ROLLING MILLS - IIM
ROLLS LIFELINE OF ROLLING MILLS - IIM
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<strong>ROLLS</strong><strong>LIFELINE</strong> <strong>OF</strong> <strong>ROLLING</strong> <strong>MILLS</strong>Gireesh MadanManager (Monitoring & Evaluation)Project Management CellNew Delhi
What is common in all the pictures ?
These are produced fromRolling Mills
What is Rolling ?
Rolling - a processWhere in metal is formed to the desired shapegradually through a pair of revolving rolls ( plain orgrooved) barrels.Rolling is a major and a most widely usedmechanical working technique.
Classification of Rolling MillsProductLayoutsTemperatureRoughing or cogging millsSection millsMerchant MillsPlate, sheet and strip millsTube millsSpecial millsRepeater MillsSemi-continuous MillsContinousSingle StrandMulti strandHot Rolling:---- above the recrystalizationtemperatureCold Rolling:---- below the recrystalizationtemperature
<strong>ROLLS</strong>•FUNCTIONS•EXECUTE– SPECIFIC AND DEMANDINGFUNCTIONS UNDER SEVERE CONDITIONS <strong>OF</strong>HEAT AND PRESSURE
Product qualityProduction•Rolls being the costliest consumable inthe millEXPENSIVE TOOL60% CONVERSION COST8% to 12 % TIME LOSS
FAILURE•ROLL FAILURE–ECONOMIC DISATSTER–PRODUCTION LOSSES•GENERAL REASONS• DEFECTIVE MATERIAL• FIRE CRA CKING• SPALLING• COLD MATERIAL
ROLL REQUIREMENT• BLEND <strong>OF</strong>HARDNESS&STRENGTH• RESISTANCE TOTHERMAL CRACKINGSHOCK LOADINGWEAR
ROLL CLASSIFICATIONBASED ON APPLICATIONLONGITUDINAL <strong>ROLLING</strong> CROSS SPIRAL <strong>ROLLING</strong>TUBESPERIODIC PR<strong>OF</strong>ILESMACHINE PARTSSMOOTH <strong>ROLLS</strong> GROOVED <strong>ROLLS</strong>PLATESSHEETSSKELPS (Patra(Patra)SECTIONSMERCHANT PRODUCTSWIRE RODS/ROUNDS
ROLL CLASSIFICATIONBASED ON PROPERTIESS<strong>OF</strong>T BHN 150-250 SH 25-35SEMI-HARDHARDHARD BHN 250-400 SH 35-60HARD BHN 400-600 SH 60-85VERY HARD BHN 600-800 SH 85-100BASED ON GRADEIRON <strong>ROLLS</strong>STEEL BASED <strong>ROLLS</strong>BASED ON MANUFACTURING PROCESSFORGEDCAST
ROLL DEFECTS• HIGH AND NONUNIFORM WEAR (poor surfacefinish & shape)• FIRE CRACK (mark on the product as well as poorsurface finish)• PITTING localized indentation ON SURFACE(mark on the product as well as poor surfacefinish)
• SPALLING/CHIPINGROLL DEFECTSSPALLING/CHIPING (mark on the product aswell as poor surface finish) (tearing of rolledproduct during rolling)• BANDING/PEELINGBANDING/PEELING (harmful for strip rolling,lead to rolled in scale along with roll).
ROLL DEFECTS• HARD AND S<strong>OF</strong>T SPOT (Harmfulparticularly during structural/sectionalrolling. These defects will lead to poordimensional accuracy as well as mark onthe product)Castingdefect like blowholes/pinholes/inclusions will lead tomark on the rolled product.)• ROLL CASTING DEFECT (Casting
DEFECT MITIGATIONDefects can be minimized by• Proper selection of roll• Proper cooling water arrangement• Proper roll maintenance
• FROMSELECTION CRITEREACONCEPTCONCEPT <strong>OF</strong> SPECIFICCONSUMPTIONSURFACE QUALITY <strong>OF</strong> THE PRODUCT
SELECTION CRITEREA• PRODUCTSHAPEDFLATSROUNDSSTRUCTURALSPLATESSHEETS• PASS DESIGNOPENCLOSED• MILL CONFIGURATIONMANUALSEMICONTINUOUSCONTINUOUS
SELECTION CRITEREA• TYPE <strong>OF</strong> STANDS2 Hi, 3 Hi, ALTERNATE 2 Hi, HOUSINGLESS• <strong>ROLLING</strong> TEMPERATURECOLD <strong>ROLLING</strong> OR HOT <strong>ROLLING</strong>• ROLL COOLINGWITH COOLING TOWER / WITHOUT COOLING TOWER• PRODUCITON RATE
ROLL MANAGEMENTFACTORS TO BE CONSIDERED• ORDERING – SPECIFICATIONS(Hardness/tensile strength/composition/structure/chill depth)• TEST CERTIFICATES(Demand certificates/documentary evidence wherever possible)• MAINTENANCE <strong>OF</strong> ROLL HISTORY SHEETS(Evaluate the performance in each campaign)• MONITORING <strong>OF</strong> ROLL COOLING WATER(Quantity/pressure and temperature)• OPERATIONAL SETTINGS AND DISCIPLINE(minimizing vibrations/proper alignments/metal control etc.)
ORDERING – SPECIFICATIONS
MAINTENANCE <strong>OF</strong> ROLLHISTORY SHEETS
MONITORING <strong>OF</strong> ROLL• Good roll cooling meansRoll at ambient temperatureCOOLING WATERUniform distribution of temperature throughout the barrel length.• Optimizing water requirement• 1/3 rd of roll surface should be water cooled.• Water is directed to the rolling passes through acommon header and nozzles
ROLL COOLING – 2HiWater InletTop RollHeader made ofSteel SheetEntry SideExit SideHot Bar Entering the roll passHot Bar after RollingBottom RollWater Header Design
ROLL COOLING – 3Hi
LATEST DEVELOPMENTS IN<strong>ROLLS</strong>• DISPERSED CARBIDE INDEFINITE CHILLED ROLLIncreased life of about 30% to 40% over normal indefinite chilled led rollApplicationHot strip mill finishing stand & Bar & rod mill• DISPERSED CARBIDE NODULAR IRON ROLL• Increased life of about 30 to 40% over normal nodular iron.Resistant to fire crackApplication• HIGH SPEED ST EEL ROLLBar & rod mill. & Structural millThis is the latest developed roll material .Rolling mill all over r the worldhave started using this grade getting wide benefits.ApplicationBar & rod mill (both intermediate & finishingstand), Small section like channel & angle mill. & Hot strip mill.
LATEST DEVELOPMENTS IN<strong>ROLLS</strong>• S<strong>OF</strong>T ANNEALED NODULAR IRON <strong>ROLLS</strong> :High fire crack resistance Lower amount of dressingApplicationRoughing stand for bar & rod mill &Structural mill• BAINITIC S.G. IRON <strong>ROLLS</strong>• COMPOSITE <strong>ROLLS</strong>Higher tensile impact strength due to Bainitic structure Due tovery good wear resistance & ,higher pass lifeApplication Intermediate stand rolls of Bar & Rod Mills & Pre& Finishing Stands of Structural Mills forchannel rollingTungusten/HSS rings on Nitrided shaft with adequate clamping system
• Roll management is the key requisite forthe survival of the rerolling industry in thisglobally competitive market scenario
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