ROLLS LIFELINE OF ROLLING MILLS. Gireesh Madan Manager (Monitoring & Evaluation) Project Management Cell New Delhi

Transcription

1 ROLLS LIFELINE OF ROLLING MILLS Gireesh Madan Manager (Monitoring & Evaluation) Project Management Cell New Delhi

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3 a h W s i t o m m o c e r u t c i p e h t l l a n i n? s

4 m o r f d e c u d o r p e s r l l a i e M s e g h n i T l l Ro

5 What is Rolling?

6 Rolling - a process Where in metal is formed to the desired shape gradually through a pair of revolving rolls ( plain or grooved) barrels. Rolling is a major and a most widely used mechanical working technique.

7 Classification of Rolling Mills Product Layouts Temperature Roughing or cogging mills Section mills Merchant Mills Plate, sheet and strip mills Tube mills Special mills Repeater Mills Semi-continuous Mills Continous Single Strand Multi strand Hot Rolling:---- above the recrystalization temperature Cold Rolling:---- below the recrystalization temperature

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9 ROLLS FUNCTIONS EXECUTE SPECIFIC AND DEMANDING FUNCTIONS UNDER SEVERE CONDITIONS OF HEAT AND PRESSURE

10 Product quality Production Rolls being the costliest consumable in the mill EXPENSIVE TOOL 60% CONVERSION COST 8% to 12 % TIME LOSS

11 FAILURE ROLL FAILURE ECONOMIC DISATSTER PRODUCTION LOSSES GENERAL REASONS DEFECTIVE MATERIAL FIRE CRA CKING SPALLING COLD MATERIAL

12 ROLL REQUIREMENT BLEND OF HARDNESS & STRENGTH RESISTANCE TO THERMAL CRACKING SHOCK LOADING WEAR

13 ROLL CLASSIFICATION BASED ON APPLICATION LONGITUDINAL ROLLING CROSS SPIRAL ROLLING TUBES PERIODIC PROFILES MACHINE PARTS SMOOTH ROLLS GROOVED ROLLS PLATES SHEETS SKELPS (Patra( Patra) SECTIONS MERCHANT PRODUCTS WIRE RODS/ROUNDS

14 ROLL CLASSIFICATION BASED ON PROPERTIES SOFT BHN SH SEMI-HARD HARD HARD BHN SH HARD BHN SH VERY HARD BHN SH BASED ON GRADE IRON ROLLS STEEL BASED ROLLS BASED ON MANUFACTURING PROCESS FORGED CAST

15 ROLL DEFECTS HIGH AND NONUNIFORM WEAR (poor surface finish & shape) FIRE CRACK (mark on the product as well as poor surface finish) PITTING localized indentation ON SURFACE (mark on the product as well as poor surface finish)

16 SPALLING/CHIPING ROLL DEFECTS SPALLING/CHIPING (mark on the product as well as poor surface finish) (tearing of rolled product during rolling) BANDING/PEELING BANDING/PEELING (harmful for strip rolling, lead to rolled in scale along with roll).

17 ROLL DEFECTS HARD AND SOFT SPOT (Harmful particularly during structural/sectional rolling. These defects will lead to poor dimensional accuracy as well as mark on the product) Casting defect like blow holes/pinholes/inclusions will lead to mark on the rolled product.) ROLL CASTING DEFECT (Casting

18 DEFECT MITIGATION Defects can be minimized by Proper selection of roll Proper cooling water arrangement Proper roll maintenance

19 FROM SELECTION CRITEREA CONCEPT CONCEPT OF SPECIFIC CONSUMPTION SURFACE QUALITY OF THE PRODUCT

20 SELECTION CRITEREA PRODUCT SHAPED FLATS ROUNDS STRUCTURALS PLATES SHEETS PASS DESIGN OPEN CLOSED MILL CONFIGURATION MANUAL SEMICONTINUOUS CONTINUOUS

21 SELECTION CRITEREA TYPE OF STANDS 2 Hi, 3 Hi, ALTERNATE 2 Hi, HOUSINGLESS ROLLING TEMPERATURE COLD ROLLING OR HOT ROLLING ROLL COOLING WITH COOLING TOWER / WITHOUT COOLING TOWER PRODUCITON RATE

22 ROLL MANAGEMENT FACTORS TO BE CONSIDERED ORDERING SPECIFICATIONS (Hardness/tensile strength/composition/structure/chill depth) TEST CERTIFICATES (Demand certificates/documentary evidence wherever possible) MAINTENANCE OF ROLL HISTORY SHEETS (Evaluate the performance in each campaign) MONITORING OF ROLL COOLING WATER (Quantity/pressure and temperature) OPERATIONAL SETTINGS AND DISCIPLINE (minimizing vibrations/proper alignments/metal control etc.)

23 ORDERING SPECIFICATIONS

24 MAINTENANCE OF ROLL HISTORY SHEETS

25 MONITORING OF ROLL Good roll cooling means Roll at ambient temperature COOLING WATER Uniform 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 a common header and nozzles

26 ROLL COOLING 2Hi Water Inlet Top Roll Header made of Steel Sheet Entry Side Exit Side Hot Bar Entering the roll pass Hot Bar after Rolling Bottom Roll Water Header Design

27 ROLL COOLING 3Hi

28 LATEST DEVELOPMENTS IN ROLLS DISPERSED CARBIDE INDEFINITE CHILLED ROLL Increased life of about 30% to 40% over normal indefinite chilled led roll Application Hot 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 crack Application HIGH SPEED ST EEL ROLL Bar & rod mill. & Structural mill This is the latest developed roll material.rolling mill all over r the world have started using this grade getting wide benefits. Application Bar & rod mill (both intermediate & finishing stand), Small section like channel & angle mill. & Hot strip mill.

29 LATEST DEVELOPMENTS IN ROLLS SOFT ANNEALED NODULAR IRON ROLLS : High fire crack resistance Lower amount of dressing Application Roughing stand for bar & rod mill & Structural mill BAINITIC S.G. IRON ROLLS COMPOSITE ROLLS Higher tensile impact strength due to Bainitic structure Due to very good wear resistance &,higher pass life Application Intermediate stand rolls of Bar & Rod Mills & Pre & Finishing Stands of Structural Mills for channel rolling Tungusten/HSS rings on Nitrided shaft with adequate clamping system

30 Roll management is the key requisite for the survival of the rerolling industry in this globally competitive market scenario

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