WORLD OF STEEL Presented By:- Subhajit Karmakar.
What is HR Coils?Hot rolling is a hot working metalworkingprocess where large pieces of metal, such asslabs or billets, are heated above their re-crystallization temperature and thendeformed between rollers to form thinnercross sections.
Manufacturing Process:-1. The Hot Rolling Process:-The starting material is usually large pieces of metal,like semi-finished casting products, such as slabs, blooms, andbillets.In continuous casting, rolling mill is mostly integrated to saveenergy.for larger work pieces gas- or oil-fired soaking pitfor smaller work pieces induction heating. a finishing temperature is defined (50 to 100 C above therecrystallization temperature) If the temperature does dropbelow this temperature the material must be re-heated beforemore hot rolling.
2. ReheatingCritical to the Hot Strip Mill is its walking-beam reheat furnace,state-of-the art equipment that replaced and now outperforms threeolder- (pusher-) style furnaces.3. DescalingAfter exiting the reheat furnace, the slab passes through a descalingunit, an enclosure employing two pairs ofspray headers that blast the intensely hot slab with 1,500 psipressurized water to remove the 1/8-inch thick layerof oxidized iron that forms at the surface of the slab in the oxygen-rich atmosphere of the reheat furnace.4. RoughingThe roughing mill is made up of six independent rolling mill stands,the last four of which incorporate smallvertical rolling mills called edgers. Slabs heated in the furnace untilthey glow bright orange-yellow are rolledthrough one stand at a time to produce so-called transfer barssuitable for finish rolling.
Contd…Approximately 96% of steel is continuously cast (theremaining - ingots ).After hot rolling the cooling should be done uniformly elseresidual stress is generated due to shrinkage that affectsthe mechanical properties.Mill scale is the oxide layer formed on the surface due toreaction with atmosphere at high temperatures.Pickling is done with HCl to remove this scale.
5. EdgingAt the very high temperatures at which the steel is rolled in theroughing mill, it is very plastic and ‘flows’ easily like cookie doughbeneath a rolling pin. Consequently, as the slab is reduced fromeight to nine inches thick to the final bar thickness of one to one andone-half inches, bars tend to spread width-wise by a few inches attheir extremities, and by as much as an inch through the body.6. DescalingIt is Descaled by the low pressure headers. After descaling by thelow-pressure headers, the bar is pinched by a pair of pneumatically-actuated rolls to mechanically loosen any remaining scale, which, asthe processing temperatures cool off, becomes increasingly stickyeven as it returns ever more slowly to the surfaces of the still red-hot steel.7. CroppingThe head- and tail-ends of nearly every transfer bar are cropped bya pair of large steel drums each with a shear blade extending alongits length.
8. FinishingPrior to the finish rolling operation, the head- and tail-ends ofthe transfer bar will be sheared to square them up, helping toensure proper threading and tail-out. A final two-stagedescaling operation is performed to clean off the scale that hasgrown on the bar during roughing.Controlling Factors:-I. Temperature ControlII. Gauge ControlIII.Flatness & CrownIV.Laminar CoolingV. CoilingVI.Coil Handling
Other Applications:-General structures:-Simple cross sections, such as rail tracks, storage tanks,storage bins, tubes & pipes, cold-rolled steel,Automotive parts:-High-pressure gas cylinders, oil well pipes, pipelines ,bearing plates for buildings and other structuralapplications.
Application of HR coils in Various productmanufacturing:-Tube makingManufacture of Hamilton and other poles, flanging applicationsManufacture of pipes mostly for oil and gas sectorCold reduction and for manufacture of galvanized sheetsGeneral structural applicationsStrapping, cycle chainManufacture of electrical equipmentStructural fabricationVarious applications in auto sectorManufacture of corrosion resistant structural materialsFor high tensile structural applicationsManufacture of propeller shaftManufacture of fork for two wheelersManufacture of wheel disc
Major players :-Dominated by 6-7 players:-• Main : SAIL, TISCO, Jindal Steel• Secondary : Essar Steel, Jindal Vijayanagar Steel Ltd (JVSL), Jindal Iron and Steel Company (JISCO), Uttam Steel• The global market price of HR Coils is regarded as an indicator of the market trend of all its downstream products in the flat product segment.• Its downstream products like CR Sheets / Coils, GP/GC Sheets, Electrical Steel, Sheets, Tinplate, Pipes etc. play a vital role in the industrial development of a country.
User segments•Pipes & tubes and CR coils major users of HR coils•CR coils used mainly for automobiles, consumer durables,general engineering, construction as galvanized products Some More User:- •Railways •Power •Irrigation •Coal •Oil •Product & Technology •Furniture makers •Consumer durables •Agricultural Implements