ELECTROMAGNETIC STIRRING AND INDUCTION HEATING … · electromagnetic stirring on a commercial...

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ELECTROMAGNETIC STIRRING AND INDUCTION HEATING SYSTEMS ROTELEC

Transcript of ELECTROMAGNETIC STIRRING AND INDUCTION HEATING … · electromagnetic stirring on a commercial...

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ELECTROMAGNETICSTIRRINGAND INDUCTIONHEATING SYSTEMS

ROTELEC

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Danieli Rotelec

Electromagnetic Stirring

and Induction Heating Systems

France

2 Company profile

20 Electromagnetic stirring for billet/bloom and slab casters

22 EMS for billet/bloom casters

30 EMS for thick slab casters

40 IEH - Induction edge heaters for hot strip mills

Since 1977

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Introduction4

Technological milestones

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Danieli Group history

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Scorecard10

Strength and capabilities

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Production program

Danieli Rotelec is the pioneerand world leader in thedesign and manufacturing of electromagnetic stirrers for continuous castingmachines as well as of induction bar edgeheaters for hot strip mills.

Danieli Rotelec

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Danieli Rotelec's leading position goes back to theearly 1970's when Irsid and CEM developedelectromagnetic stirring (EMS) for continuouscasting machines. Irsid was the world-renownedresearch center serving the French steelmakingindustry. CEM was the Compagnie Electro-Mécanique, one of the two big electrical suppliers inFrance that later merged with its competitorAlsthom. Their world's first industrial application ofelectromagnetic stirring on a commercial continuouscasting machine was a rotative strand stirrer in 1973on the 240-mm square bloom caster of SAFE (nowAscométal) at Hagondange in France. During the following years, the same partnersdeveloped mold and strand stirring of slabs andmold stirring of billets/blooms. The latter appearedthe most promising in the immediate future and ledto the creation of Rotelec.In 1977, Rotelec was incorporated as a joint ventureof Irsid, CEM, Arbed and Usinor to promote thenewly developed mold stirring of billlets/blooms as anewly-patented technology under the name ofMagnetogyr© Process. Arbed and Usinor (now bothpart of Arcelor) were two leading steelmanufacturing companies in Luxemburg andFrance, respectively. By its founders, Danieli Rotelec has the uniqueopportunity of combining in one same companymetallurgical process know how (Irsid), feed-back ofindustrial results (Arbed, Usinor) and expertise inthe designing and manufacturing of specialinductors and electrical power supplies (CEM,Alsthom).The name Rotelec stems from Rotation Electrique(Rotation Electrical) and reminds of the world's firstindustrial application of electromagnetic stirring inthe mold on Arbed’s billet/bloom/round caster atEschweiler (Germany) in 1977.

COMPANY PROFILE

Danieli Rotelec is a highly specializedsupplier of electromagnetictechnologies for the steel industry.

1 Danieli RotelecHeadquarters at LesTours Mercuriales in Bagnolet/Paris.

2 Strand stirring on a bloom caster.

3 Induction Edge Heatingfor hot strip mills.

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In 1987, the company made the decision to apply its electrical/electromagnetic know-how to anothersection of the steel industry, namely the reheating (by induction) of the steel transfer bars as they enterthe finishing stands of the Hot Strip Mills.In cooperation with Irsid and Sollac-Fos (now alsopart of the Arcelor group), a C-type inductor withautomatic gap adjustment was developed andpatented. A breakthrough in the business,the design rapidly superseded and replaced thetraditional U-type concept.Since 1991, Rotelec is part of the Danieli team and,with its technology and equipment, strengthens thebillet/bloom and slab casting activities carried out by Danieli Centro Met, Danieli Davy Distington andDanieli Wean United, respectively. It also cooperateswith the other machine builders on customerdemand.Danieli Rotelec's philosophy is that of tailor-madeprocess and equipment technology with priority tobest metallurgical results and highest equipmentefficiency and life time.It commercializes three product lines:

Electromagnetic stirrers for billet and bloomcasters.

Electromagnetic stirrers for slab casters.Induction bar edge heaters for hot strip mills.

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Danieli Rotelec technological milestones

1968 First trials of electromagneticstirring (EMS) for billets andblooms below the mold by Irsidand CEM. 1

1973 World's first industrial applicationof electromagnetic stirring on acommercial continuous castingmachine; rotative strand stirringon the 4-strand 240-mm squarebloom caster of SAFE (nowAscométal) at Hagondange,France.

1974 First trials of EMS for billets andblooms in the mold by Irsid,Usinor, Arbed and CEM. 3

1977 World's first industrial applicationof mold electromagnetic stirringon a commercial continuouscasting machine; rotative moldstirring on the 4-strandbillet/bloom square/round casterof Arbed at Eschweiler inGermany. 4, 5

1977 Creation of Rotelec andcommercialization of in-moldEMS under the nameMagnetogyr© Process. 2

1978 Developments of In-Roll and in-mold EMS for slab casters by Irsid and CEM. 6, 7

1979 World's first successful industrialapplication of In-Roll EMS on a commercial continuouscasting machine; travelingmagnetic fields in the rolls on the Usinor-Dunkerque slabcaster in France. 8

1980 Collaboration agreementbetween Rotelec in France andKobe Steel in Japan; joint

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licensing and marketing of thebillet/bloom M + F (mold + final)combined stirring configurationunder the name of Kosmostir-Magnetogyr Process. 10

1981 Granting license to JME ofCanada (now part of ABB) forjoint marketing of billet/bloomEMS in North America.

1985 Merger of CEM and Alsthom.

1986 Rotelec becomes a subsidiary of Alsthom and covers the entirefield of EMS activities i.e., in themold and below the mold, forbillets, blooms and slabs. Arbed, Irsid and Usinor/Sacilorremains as minorityshareholders.

1987 Rotelec takes over the Alsthomactivity that deals with inductionheating; this includes steel

bar edge heating in hot stripmills and steel/aluminum stripheating in coating and annealinglines. 9

1991 Rotelec becomes a fully-ownedsubsidiary of Danieli.

2000 Collaboration agreementbetween Rotelec and NipponKokan Kabushiski Kaisha (NKK,now part of JFE); joint licensingand commercialization of theEMLS/EMLA mold stirringtechnology for slabs that allowsslowing down or acceleration ofthe liquid steel stream at theexits of the submerged entrynozzle. 11

2002 Development of Multi Mode EMS(MM EMS) process to addresssteel quality and machineperformance issues on all-speed,all-width thick slab casters.

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EMS and induction heating systems | Company profile

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Danieli Group history

1914 Danieli’s origin dates back to1914 when two brothers, Marioand Timo Danieli, founded theAngelini Steelworks in Brescia,Italy. This was one of the firstItalian companies to use ElectricArc Furnaces in steelmaking. 1

1929 Part of the Angelini Steelworkswas transferred to Buttrio, Italy. In those days the Companymanufactured tools for forgingplants and auxiliary machines for rolling mills.

1955 Luigi Danieli took over the familybusiness which, at that time,employed 50 people and starteddesigning and manufacturingequipment for the steel industry.Mr. Danieli’s idea was tomanufacture more competitiveequipment, simplify layouts andmaximize the use of automation.One of the concepts developed,namely the "EAF - conticaster -rolling mill" production route, has characterized andcontributed to the successfuldevelopment of the minimillprocess which is widely adoptedtoday.

1964The first minimill was installed inGermany and the first continuouscasting plant was installed in Italy with the Riva Group 2.The success of the minimillconcept spread to Spain, the USA and the Far East.

1977 The first large turnkey order wasplaced with Danieli for a completesteel mill in the former GDR 3. Company turnover was 25 millionEuro with 1,700 peopleemployed.

1980Mrs. Cecilia Danieli, who hadmanaged the financial and administrative departmentsof the Group since 1977, was appointed Managing Director and Mr. Gianpietro Benedetti,who had been Group SalesDirector since 1977, was alsonominated Director ofEngineering.

1981_1985Numerous plants were suppliedon a turnkey basis by Danieli inthe USA, the Far East, the formerSoviet Union and North Africaconsiderably increasing theGroup's turnover 4. The large-scale investments made inresearch enabled the company to achieve a leading positionworldwide in plants forcommercial long products.

1986_1990The first direct casting-rollingplant for long products was builtin Italy 5. In the USA Danieliconquered 80% of the longproduct plant market.Morgårdshammar in Sweden

was acquired. The company, founded in 1856, was worldleader in the supply of rollingmills for long products in specialsteels. Centro Met in Sweden was founded as a specializedteam in steel melting and refining processes for quality steel production. The orders from major steel producers like Krupp, Cogne, Ovako, Teledyne,Uddeholm made Danieli aninternational leader in specialtysteels. Futhermore an industrial-scale prototype of the Thin Slab Caster was created forresearch purposes. Group turnover, which in 1980was 67 M Euro, increased to 396 M Euro; employees reached1,870 people.

1991_1995Mrs. Cecilia Danieli wasappointed Chairman of the Boardand Mr. Gianpietro Benedetti wasappointed President and CEO. A strategic decision was made to expand into the flat productsector which, at that time, was

dominated by German, Englishand Japanese plantmanufacturers. Danieli acquiredWean Industries and UnitedEngineering in the USA, foundedin 1929 and 1901 respectivelywhich, between 1950 and 1980,designed and manufactured 60%of the plants for the production of flat products worldwide 6. The value and importance ofDanieli’s technology in the flatproduct sector has beenrecognised since the beginningand this brought to a long seriesof significant orders like: the Thin Slab Caster revamp atNucor Hickman; the Hot StripMill at North Star-BHP Steel;

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special steels was consolidatedwith an international marketshare of 65%. It was furthermoredecided that it would bestrategically sound to continuemanufacturing noble equipmentin-house and, consequently, 130 M Euro were invested in asignificant modernization of themechanical workshops in Buttrio. In 1997 a major research projectfor the first endless casting androlling for long products wasgiven the go-ahead, the results of which could be seen in theyear 2000. In 1999 Danieli entered into ajoint venture with Corus TechnicalServices to integrate its productlines with Blast Furnaces,converter meltshops andassociated services. In the sameyear Danieli also acquired thepatents of the "Arex" directreduction process, an innovativetechnology that improves theefficiency of iron ore reductionprocess granting lower productionand depreciation costs. JosefFröhling, a German companyspecialized in narrow cold striprolling mills and finishing plantsfor stainless steels and non-ferrous metals was acquiered. On June 17, 1999, at the age of56, Mrs. Cecilia Danieli passedaway; her contribution to thedevelopment of the company was invaluable. Danieli acquiredDavy Distington, UK, a companyspecialized in engineering anddesign of slab and bloom casters.In 2000 Danieli had a salesrevenue of over 930 M Euro,

with some 3,200 employees in Italy, Sweden, Germany, USA,UK and France.The most revolutionary endlesscasting-rolling minimill forspecialty steel long products wasstarted up at ABS, Italy 8,10.Thick slab caster orders wereplaced by Thyssen Krupp, andSidmar (for the mosttechnologically-advanced thickslab caster in Europe) 9. An order for Blast Furnacerevamping was awarded toDanieli Corus by Açominas,Brazil, following the ones fromRiva Acciai and Corus UK.During this period Danielicompleted its product rangecovering the whole steelproduction spectrum from ironore to finished products.

2001_2004Danieli increased its market share in China also with regard to flat products (e.g. Tangshan,Handan, Benxi, Tonghua,Anyang, Shaoguan) and startedup several thin slab castingplants, setting the worldwideproduction record of 3 Mtpy with a 2-strand TSC at TISCO.Also the important thin slabcasting and rolling plants of Ezz Flat Steel 7, 11 and Niscowere started up. Thanks to thesesuccessful start-ups Danielidefinitively ranks among thefront-runners in the supply of hot and cold rolling plants and processing lines for flatproducts. A second Casttgrind®

plant for grinding of hot stainless

steel slabs was supplied to Outokumpu Stainless.The most advancedconticasters for stainless steelswere supplied andcommissioned at AcciaierieValbruna and NAS (Acerinox)with excellent performances in terms of surface and internal quality.Significant orders for varioustechnologically-advanced plantsfeaturing Spooled bars-in-coil,endless rolling by billet welding,wire rod finishing at speed of 115 mps, the modernizationand complete revamping of the VAS Donawitz rail mill in Austria and the startup of a complete minimill for specialsteels at Baosteel Shanghai No. 5, were acquired.At Deacero, Mexico, a DanieliEAF with the performance of 42heats per day set a new record.Important orders for thick slabcasters from Baosteel andArcelor confirmed Danielitechnology leadership.Pelletizing and beneficiationplants supplied in Middle Eastopened new opportunities forthe Company also in this field.Danieli entered the market ofplants for seamless pipes andthe newly formed Danieli CentroTube was blessed by theacquisition of the order for thefirst hot and cold seamless pipecomplex.

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the Thin Slab Caster and HSM at Algoma Steel, the first in theworld to produce a wide range ofquality steels, including peritectic; World leading companies Sund Birsta - finishing and tying services for long products,Sweden -and Rotelec -electromagnetic stirrers forcasters, France - were acquired.The second unique "directcasing-rolling" plant in the worldfor quality steels at RepublicEngineered Steels in the USA was commissioned 15.Kia Steel, Korea, ordered anautomatic conditioning plant for specialty engineering steels.

1996_2000Cold Strip Mills were alsosupplied to Nucor Hickman,Usinor, Sidmar and StripProcessing Lines to WorthingtonSteel, US Steel, Galvak,Hoogovens, Sidmar, StahlwerkeBremen 12, 13, 14. Thin SlabCasters and Plate Mills weresupplied to Nucor and to IPSCO,in the USA obtaining in 1999 the 30% market share. Danieli’sworld leadership for longproducts in commercial and

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101 Complete turnkey plants | 96 Blast furnace projects | 129 AC and DC Electric ArcFurnaces | 198 Secondary metallurgy stations | 1,414 Billet and bloom casting strands1,541 Electromagnetic Stirrers for billets and blooms | 95 Thick and thin slab castingstrands | 196 Electromagnetic Stirrers for slabs | 236 Hot and Cold strip mills

Danieli started its activity in 1914 and since then has manufactured:

Scorecard

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1 Aerial view of an80,000-tpy steelcomplex for producingbillets, blooms, forgingsand heavy-drill rods.

2 400,000-tpy minimillfor bars and sections.

3 700,000-tpy specialtysteels producing complex.

4 1.2-Mtpy turnkey Thin Slab Casting andRolling plant for theproduction of Ultra-Thinstrip gauges.

Danieli Rotelec

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23 Induction Edge Heaters for hot strip mills | 752 Strip processing lines282 Specialty rolling and cluster mills | 342 Rolling mills for long products64 Plant automation and process control systems | 1,050 Grinding machines 450 Drawing lines | 274 Extrusion and forging presses

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5 185-t AC Danarc EAFequipped with Moduletechnology.

6 Plate mill complexproducing plates directlyfrom medium/thin slabs provided by a 1-Mtpy Caster.

7 Danieli high-speed barmill in a 500,000-tpyminimill complex.

8 6-stand finishing mill of the 1.35-Mtpy fTSR-flexible Thin Slab Rollingplant.

EMS and induction heating systems | Company profile

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Danieli Rotelec offers electromagnetic technology to fulfil the most demanding applications in terms of both quality and productivity.

Strength and capabilities

Danieli RotelecDanieli Rotelec

Danieli Rotelec is the idealsupplier that brings unmatchedcapability to design and build acomplete range ofelectromagnetic stirrers forcontinuous casting machines, for commercial and specialtysteels, for long and flat products. It also brings 15+ years ofexpertise in the design andconstruction of induction edgeheaters for hot strip mills.

Headquartered in Bagnolet/Paris,base of commercial/ developmentengineering, it has its ownmechanical and electricalconstruction departments as wellas manufacturing, assembling,testing and training facilities at Saint-Quentin-Fallavier/Lyon.

Danieli Rotelec is metallurgicalknow-how. Danieli Rotelec is metallurgicalknow-how since its inception. The company finds its origin in1968 after an idea from Irsid, theworld-renowned research institutethat served the French steelindustry (now part of Arcelor, a 40-million ton-per-year group). It was the beginning of a long

technical relationship that is stillstanding. In 30 years, its engineers commissioned closeto 2,000 electromagnetic stirrersand induction edge heaters in 40countries.

Danieli Rotelec is uniquecombination of concept anddesign. All Rotelec stirrers and heatersare tailor-made. Each unit isconceived and designed at thecompany's technical departmentafter discussions with thecustomers and the understandingof their metallurgical/productivityneeds and goals. All stirrers and heaters are builtand tested at the Rotelec's ownworkshop. It is also wherecustomers "get their feet wet" andreceive hands-on training beforetheir own equipment is packedand shipped to their steel plants.Each equipment is fully testedbefore shipping, includingperformance tests at maximumpower.

1-2 Assembly and functionaltest of single-head edgeinductor for slab/transferbar edge heating.

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Danieli Rotelec is wide scope of services. The company does not sellequipment and licenses only. It also provides extensiveelectrical, mechanical, processand maintenance training thatusually takes place during thefinal tests at Rotelec's facilities on the running equipment, beforedelivery. It offers metallurgicalguarantees, performanceguarantees, on-site training and continued assistance afterstartup.

Research and Development.Danieli Rotelec is a technicalpartner whose publications andpresentations are internationallyregarded for their right-to-the-point and stimulating topics. The company's R&D efforts cover such domains asmathematical modeling of liquidsteel with or without theimposition of electromagneticforces, pilot plant experiments

on low-temperature meltingalloys, and determination of liquidsteel flow pattern in industrialcaster molds.

Danieli Rotelec is versatility. Its autonomous subsidiary statuswithin the Danieli group entitles it to supply equipment regardlessof machine builder.

3 External view of theDanieli Rotelec workshopat Saint-Quentin-Fallavier/Lyon.

4-5-6 Mold stirrers for slaband billet casters, and single-head IEH pre-assembled and ready to be shipped.

7 3D rendering of a slabmold stirrer on a CADstation at thedevelopment engineeringdepartment.

8 Mathematical simulationof electromagnetic stirringin a billet/bloom castermold.

9-10 Danieli Rotelectraining activity.

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Billet and bloom casters userotative electromagnetic stirrersthat generate the force requiredto move the liquid steel. Indeed,rotative stirrers can easily fitaround billet/bloom product. A rotative stirrer acts like thestator of an AC motor fed by a 3-phase electrical current. The stirrer surrounds thebillet/bloom. The liquid steelbecomes the rotor of the motorand is put in rotation around its axis in a plane perpendicularto the casting direction. The movement propagates in 2 directions: above the stirrer by viscosity, below the stirrer by inertia. Billet/bloom rotativestirrers may be installed in themold, along the strand, in thefinal stage of solidification, andany combination of it. Current frequency is between 2 and 50 Hz depending on theapplication.

Linear, also called traveling,electromagnetic stirrers are usedon slab casters as their large sizewould prevent the installation ofrotative stirrers surrounding thecast product. Linear stirrers arefed with 2-phase AC current.They have to be understood asthe stator of a motor that hasbeen cut open and uncoiledalong the width of the slab. The result is a one-direction forcein the slab that moves from onenarrow face of the slab to theother. If the stirrer is installed inthe strand, the inducedmovement generates circulatingloops in the liquid steel, up anddown, that are known as"butterfly" patterns. If the stirrer is installed in the mold, the forcemay be used to slow down oraccelerate the liquid steel streamas it exits the submerged entrynozzle; it may also be used to putin rotation the liquid steel at themeniscus. Current frequency isbetween 0.5 and 6 Hz dependingon the application.

Induction edge heaters act aselectrical current transformersthat generate fixed, transversemagnetic fields. In practice, theprimary coils are disposed on amagnetic core that forms a C,with the hot band traveling in thegap. The primary coils arepowered with single-phase ACcurrent at medium frequency(300 Hz). The traveling steel barsact as the secondary coils; theeddy currents that are createdheat up the steel. The originalityof the Danieli-Rotelec-patenteddesign lies in an articulation inthe magnetic core that allowsadjusting the gap, withoutmagnetic losses, by independentmovement of the upper and lowerarms. As a result, high heatingefficiency is maintained, even atlarge gaps, allowing to correctlyreheat the bar heads and tailsthat are frequently deformed.

Danieli Rotelec designs andbuilds electromagnetic stirrersfor billet, bloom and thick slabcasters; it also designs andbuilds induction edge heatersfor steel bars as they travelthrough hot strip mills.Both technologies applyelectromagnetic power that iseither transformed into a forcethat moves liquid steel or intothermal energy that heats upsolid steel. Danieli Rotelecengineers use Maxwell andLaplace fundamental equationsto size the equipment that isrequired to generate the aimfunction.

Production program

Danieli RotelecDanieli Rotelec

Electromagneticstirring forbillet/bloom casters

Electromagneticstirring for slabcasters

Induction edgeheaters for hot stripmills

1 High-speed bloomcaster for special steelsat ABS Luna, Italy.

2 High-productivity two-strand slab caster forULC, LC, MC and HC steels, includingperitectic andmicroalloyed grades.

3 6-stand finishing mill ina 2.2-Mtpy slab castingand rolling plant.

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EMS and induction heating systems | Company profile

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Danieli Rotelec

4-strand bloom conticasterfor special and stainlesssteels and high andmedium alloys, equippedwith mould (internal) andfinal EMS.

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EMS and induction heating systems | Company profile

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Danieli Rotelec

Exit end of a two-strandslab caster equipped withINMO mould and Multi-Mode EMS.

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EMS and induction heating systems | Company profile

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Danieli Rotelec

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EMS and induction heating systems | Company profile

Six-stand finishing mill in a 800,000-tpy hot stripmill for structural steels.

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EMS for billet/bloomcasters

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EMS for thick slabcasters

Danieli Rotelec

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ELECTROMAGNETIC STIRRINGFOR BILLET/BLOOMAND SLAB CASTERS

Danieli Rotelec designs and builds electromagnetic stirrers for billet, bloom and thick slab casters. These technologies apply electromagnetic principles to generateforces that move the liquid steel. Control of the liquid steelmovement improves product quality and caster productivity. Principle Liquid steel cannot be movedmagnetically, since it is alwaysabove the Curie temperature andthus nonmagnetic. EMS does not mean magnetic butelectromagnetic stirring. In otherwords, EMS uses electromagneticforces like in an electricalasynchronous AC motor. One hasto distinguish between rotationaland linear stirrers (inductors,motors), the former applied tobillet and bloom sections, thelatter applied to slabs.

Faraday and Lorentz The stirrer performance for bothrotational and linear systems is given by the stirring force F,more precisely by theelectromagnetic force density F (N/m3), which depends on the relative velocity betweenliquid steel and magnetic field

and on the magnetic induction B (Tesla or Gauss). Faraday's law says that themagnetic field moving at speed V (m/sec) induces eddy currentsJ (A/m2) that are perpendicular to V and B. Lorentz's law saysthat the eddy currents Jcombined with the magneticinduction B produce a volumeforce F that is perpendicular to J and B ('three-finger' rule) and thus parallel to V:The velocity V of the magneticfield is given by the frequency f of the electrical power supplyand Faraday and Lorentz lawsbecome respectively

Jz = σ Vx By and

Fx = σ Vx By2 ∝ f By

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i.e., the volume force generatedby a given stirrer in a given point

of the steel is proportional to thepower supply frequency and tothe square of the magneticinduction in the same point insidethe steel. To compute the totaltorque (in case of rotationalstirring) or total thrust (in case oflinear stirring) one obviously hasto take the integral of F over thefull volume of the liquid steel inthe vicinity of the stirrer. That means, the performance ofa stirrer can not be characterizedby the magnetic induction in only one point, although manypeople believe so.

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EMS for billet/bloom casters

Strand EMS or MoldEMS?In 1973, at Hagondange, thepurpose of strand stirring was toimprove internal quality of as-castbillets and blooms by eliminatingmini-ingots, reducing centerporosity and generating equiaxestructure. Less than 4 years later,driven by new metallurgical goals(surface quality improvement)and made possible by theavailability of low-frequencycurrent converters, the world'sfirst industrial moldelectromagnetic stirringapplication went on stream atARBED-Eschweiler in Germanyon a 4-strand square/roundbillet/bloom caster designed andbuilt by Irsid/CEM.

In the decade that followed, bothS-EMS (S for Strand) and M-EMS(M for Mold) co-existed, withM-EMS (Figure 2) progressivelytaking the lead as it was observedthat M-EMS could improve notonly surface quality (by washingthe solidification front) but also

internal quality. As a matter offact, M-EMS could improveinternal quality better than strandstirring! The reason for thissecond, unexpected result waspuzzling, as in the early daysmany people believed that theenhancement of equiaxed zoneobserved with S-EMS was due toa mechanical effect of the stirrerthat would break the tip of thedendrites. That opinion waswrong.The explanation, that is nowstate-of-the-art, calls for a thermaleffect, not a mechanical effect:

equiaxed structure can onlydevelop if liquid steel is belowliquidus temperature i.e., ifsuperheat has been removed;

heat extraction from the liquidsteel to the exterior is better in themold than in the strand;

heat extraction is better whenthe liquid steel is in movement.Stirring in the mold combinesboth mechanisms and is,therefore, a very strong steelsuperheat remover and equiaxedzone maker!

Billet and bloom casters use rotative electromagneticstirrers that generate the forcerequired to move the liquidsteel. Indeed, rotative stirrerscan easily fit aroundbillet/bloom product. A rotative stirrer acts like thestator of an AC motor fed by a 3-phase electrical current.The stirrer surrounds thebillet/bloom. The liquid steelbecomes the rotor of the motorand is put in rotation aroundits axis in a planeperpendicular to the castingdirection (Figure 1). The movement propagates in 2 directions: above thestirrer by viscosity, below thestirrer by inertia. Billet/bloomrotative stirrers may beinstalled in the mold, along the strand, in the final stage of solidification, and anycombination of it. Currentfrequency is 50/60 Hz forstrand and final stirrers ofbillets and < 10 Hz for allmold stirrers.

X

Z

Y

N

V

Y

SB

-Fx

+Fx

S EMSM EMS

M + F EMS M + S + F EMS

1 Schematic of EMS forbillet/bloom casters.

2 Stirrers may be installedin the mold, along thestrand or in the finalsolidification zone.

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Type of stirrer M-EMS S-EMS

Surface / subsurface

Pinholes decrease ≈ 70% no effects

Blow holes decrease ≈ 70% no effects

Slag entrapments decrease ≈ 70% no effects

Subsurface inclusions decrease ≈ 70% no effects

Surface cracks eliminated under certain conditions eliminated under certain conditions

Internal

Equiaxe zone 40% 30%

White bands no yes

Internal cracks eliminated under certain conditions eliminated under certain conditions

Bridging eliminated eliminated

Porosity index reduced by 2 index reduced by 1

Macro segregation reduced by 40% reduced by 20%

S-EMSM-EMS

100 20 30 30

Superheat (°C)

0

10

20

30

(Cm

ax -

Cm

in)

/ Cav

erag

e

0100 20 30

Superheat (°C)

50

100

Equi

axed

zon

e (%

)

M EMSS EMSnon stirred

g

M-EMS and S-EMScomparison: metallurgicalresults on blooms andbillets.

3-4Mold EMS is better thanstrand EMS for equiaxedzone formation (240-mmsize bloom AISI1548), bothfor centerline segregation(0.45% C rail grade,240-mm square blooms).

3 4

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24

stirring (a stirring mode thatconsists of reversing stirringdirection periodically). Figure 8.

Significant reduction ofcenterline porosity.

Reduced centerlinesegregation.

If used in conjunction with F-EMS (an additional stirrerappropriately positioned in theFinal mushy zone), the M+F EMSconfiguration will further minimizeinternal segregation andcenterline porosity in specifichigh-carbon and high-alloy steelapplications (Figure 10, 11).

Nowadays, S-EMS is little used,except for some special casesand in multi-stage stirringcombinations. M-EMS hasreplaced S-EMS for all billet andbloom sections and this up to the400 mm x 600 mm section ofBHP Newcastle.

Mold EMS for surfaceand internal quality

Currently, M-EMS, in spite of itshigher cost, has replaced S-EMSbecause of the following specificadvantages:

Improved surface andsubsurface quality, an objectivethat is not achievable with strandstirring that comes after the fact(Figure 6, 7).

More uniform shell thickness,which may result in significantgains in casting speed andbreakout frequency (Figure 5).

More equiaxed zone thanwith S-EMS due to the earlierelimination/dissipation of the steelsuperheat. As a result, centersegregation and porosity are alsobetter than with S-EMS (Figure 9).

Large elimination of negativesegregation, the white-banddefect typical of S-EMS, althoughin the latter case, white band canbe improved with alternate

100 mm square billet

127 mm square billet

non stirred stirred non stirred stirred

0

20

40

60

80

100

freq

uenc

y (%

)

4

3

2

1

01 1.5 2 2.5 7 10

poor

good

3Depth from billet surface (mm)

15

StreakFlawIndex

Non stirred

Stirred M-EMS

B BA A

View A-A View B-B B-B

B BA A

View A A-AA View B-B

STR

ON

G <

Whi

te b

and

> W

EAK

Power setting of stirrers50% 100%0

0.80

S-EMS

M-EMS

Neg

ativ

e se

greg

atio

n (C

/Co)

0.85

0.90

0.95

1.00

Danieli Rotelec 5 Mold EMS makes shellthickness more uniformallowing higher castingspeeds without breakouts.

6 Mold EMS improvesbillet/bloom surfacequality significantly(DIN 2275 grades):

0-2 defects / m2,no conditioning;

2-20 defects / m2,

local manual conditioning;over 20 defects / m2,

grinding of the entiresurface.

7 Subsurface cleanliness for a 300x400 mm highcarbon steel bloom.

8 Mold EMS is better than Strand EMS for whitebands (negativesegregation).

6

7

8

5

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25

PL1

40

X = 1.02

X = 0.91

Freq

uenc

y (%

)Fr

eque

ncy

(%)

Freq

uenc

y (%

)

20

40

30

10

0

X = 0.94

20

40

30

10

0

0.9 1.0 1.1

Carbon (%)

1.2 1.3 1.40.8

20

30

10

0

M EMS + F EMSC/Co = 1.08

M EMSC/Co = 1.12

No stirrerC/Co = 1.21

9 10

11

10 Final EMS incombination with MoldEMS further reducescenter segregationon high-carbon grades(from 1.12 to 1.08).

9 Mold EMS increasesequiaxed zonesignificantly (up); 160-mm square blooms,AISI 409Nb grade.

11 F-EMS needs:A) Efficient mould stirrerB) Sufficient power andlength of final stirrerC) Fixed conditions of casting speed and cooling pattern: position P of final stirrer fixed –> L1 metallurgicallength and casting speedfixed.

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26

SEN erosion and moldpowder entrainmentdependent on SEN depth

Danieli Rotelec

Until the late 1990s, viewsagainst M-EMS were expressed inthe literature emphasizingpowder/slag entrapment and SENrefractory wear as dangerousdrawbacks. The point was that alarger equiaxed zone requires ahigher stirring intensity and that,beyond a threshold intensity,excessive steel/slag movementsentrain mold powder, generateinclusions (figure 13) andincrease SEN wear. Note that theSEN wear (figure 14) was not atthe slag line but inside the boreand at the tip of the SEN.

As an immediate result of theseobservations, several alternateEMS configurations wereproposed in the market place asapparent "fancy"countermeasures (the Sub-mould, Combi and Dual designs).

A scientific, rational explanationof these observations anddevelopments took much effortand long time (intensiveexperiments with Wood metal,comparative trials on an industrialbillet caster, extensive steelcleanliness evaluations, sulfurprints, blue brittle tests) and ledto thorough understanding of themechanisms of M-EMS that was

presented for the first time at the Madrid Conference in 1998.

Not only was it confirmed thatimprovement of internal qualityon long products is best withM-EMS stirrer close to themeniscus, also it wasdemonstrated that powder/slagentrapment and SEN wear do notrequire "fancy" Mold-EMScountermeasures. They simplyrequire stable mold levelconditions i.e., a sufficient SENimmersion depth (and the use ofmold level sensors that are notaffected/fooled by mold powderslag thickness)!

1

0

2

3

4

5

6

Stirring intensity (A)

Incl

usio

n in

dex

Noz

zle

wea

rN

o no

zzle

wea

r

0 50 100 150 200 250 300

Stirring intensity (A)

0 50 100 150 200 250 300

No EMSSEN = 80 mm SEN = 80 mm + brakeSEN > 100 mm

13

14

12 SEN-Submerged EntryNozzle wear that wasbelieved to be due to M-EMS was in fact dueto insufficient SENimmersion depth.

13-14 High stirringintensities above acertain threshold cangenerate powderinclusions, slagentrapment, andincreased SEN refractorywear. That, however,depends on SENimmersion depth andcan be prevented if theimmersion of the SEN isdeep enough: 130 mmvs. 80 mm in thisexample of a 150 mmsquare billet machine.

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27

What for What?

Table 15 lists internal and surfacedefects frequently observed onbillets and blooms, for carbonand alloy steels. Typical EMScountermeasures are also listed.The comparison should helpsteelmakers determine whatconfiguration is most appropriateto maximize the quality of theirproduct.

The two predominant,successful EMS applications forbillet and bloom casting are (1)M-EMS for low and mediumcarbon grades, and (2) M+F EMSfor high carbon and high alloygrades.

S-EMS is only applied insome special conditions (largesections, in combination withMold EMS).

Benefits and incentivesToday, there is practically no quality-oriented billet/bloom caster in theworld that does not haveelectromagnetic stirring. Simplysaid, it is a must.

Besides the very specificmetallurgical benefits that werelisted above (improvedsurface/subsurface quality, moreuniform shell thickness, moreequiaxed zone, less centersegregation/porosity, less whiteband), other incentives include:

Extension of the product mix tohigh-quality specialty steel grades,

Maximization of casterproductivity

And increase of primebillet/bloom application ratio up to 100%.

15

EMS Configuration Steel Grades Domain of Improvement Primary Mechanismand Sections

Mold EMS - All sections 1) Surface/subsurface cleanliness Mechanically move inclusions, blowholes (at meniscus level) - All grades 2) Surface/subsurface integrity and pinholes away from surface thru:

- Cleaning waves at the meniscus- Washing of the solidification front- Centrifugation of steel vs. inclusions

3) Segregation - Mix hot and cold steel4) Porosity - Promote early superheat removal5) Intercolumnar cracking - Promote wide/fine equiaxed zone6) Grain/structure refinement - Reduce mini-heterogeneities

- Chip/break large porosities- Eliminate long dendrite structure- Increase number of crystal nuclei and germs

7) Shell thickness uniformity - Reduce thermal unevenness betweenBreakouts frequency mid faces and corners

- Move large inclusions away from first solidification shell

Strand EMS - No surface quality improvement - Not recommended unless used for large section(below the mold; (items 1, 2, 7) in conjunction with a Mold EMS unitbefore the mushy zone) - Limited internal quality

improvement (items 3 thru 6)

Mold EMS + Strand EMS - Large sections - Consolidate/reinforce all above - Additional mixing of hot and cold steel(between the mold e.g. 300x300 mm improvements (items 1 thru 7) - Prevent dendrites to form again in the longand the mushy zone) - All grades - Specific focus on centerline liquid pool

porosity and segregation

Mold EMS + Final EMS - High carbon - Consolidate/reinforce all above - Additional mixing of high- and low-segregated(in the mushy zone) - High alloy with wide improvements (items 1 thru 7) domains within the mushy zone

liquidus/solidus interval - Specific focus on center - Prevent segregation to propagate in mushy zone; - All sections segregation destroy V-segregation channels

15 Carbon and AlloySteels - Internal/Surface Defects onBillets and Blooms andEMS Countermeasures.

EMS for billet/bloom casters

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28

Interface with Plant

Mold/EMS mechanical interfaceAmong the various technologicaloptions offered by DanieliRotelec, are the internal/externalinstallations to the mold, theimmersed or hollow copperconductor constructions, and theseparate or shared coolingsystem with the mold. Regardingthis last item, it is important tomention that only the DanieliRotelec coil technology ofimmersed windings is able tooperate with normal, industrialmold water quality. Internal vs.external installation of the stirrersaffects investment, operatingcosts and equipment reliability.Internal stirrers (one per mold)are closer to the strand; henceelectrical consumption is less fora same stirring force (typically20% less). External stirrers (oneper strand) are further away fromthe strand but do not requireelectrical/water connections/disconnections at each moldchange; hence, less risk ofpolluting the water cooling systemor damaging the electricalconnectors. Internal stirrers arewell suited for machines that castwide ranges of sections or stirringperformance would be veryerratic. External stirrers may notbe suited for installation onexisting machines where onlylimited space may be availablebetween strands. Otherconsiderations are of importance.To name a few, external stirrersrequire the entire body of themold assembly to be made ofnon-magnetic stainless steelwhile internal stirrers only requirechanges of the cooling chamberplates; also, depending on thetype of construction that isadopted, the stirrer weight mustbe compatible with the moldoscillation system. Water flow rates that arenecessary to cool the stirrersdepend on the electrical power

1

10

100130 ohms

52 ohms

1,000

10,000

100,000

1994 1995 1996 1997 1998Year

ohm

s

1999 2000 2001 2002 2003

1

2

Power rating

3

Met

allu

rgic

al r

esul

ts

16 Molds stirrers are installed in the mold cooling chamber (left) or around the mold (right);500/1,200-mm diameter,200/1,500 kg, 80/500kVA,200/1,000 A, < 10Hz.

17 Internal mold stirrers are cooled by mold water;electrical insulation is maintained for severalyears.

18 Justification of apparent,confusing, over-rating ofelectromagnetic stirrers:different steel gradesrespond differently to EMSsettings (red and greencurves) and need differentpower settings to reach aimresults.

19 Equiaxed zone increasedepends on power settingbut is not linear.

16

17

18

19

I = 150 A ZE ≈ 35%

I = 200 A ZE ≈ 55%

I = 300 A ZE ≈ 60%

20 21

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29

that is installed. Water quality istypically mold water quality, freeof any solid particles, in particularlyof ferro-magnetic particles thatcould damage the coils. Waterflow meters and water temperaturemeasurements are part of eachstirrer protection system:electrical supply is automaticallyswitched off when water failure isdetected.

Power supply and utilitiesIt is the philosophy of DanieliRotelec to maintainindependence between eachstrand of the machine; hence,each strand stirrer is powered by its own electrical supply withits own transformer and PLC.Power supply is 3-phase, low- frequency and uses VVVF(variable voltage, variablefrequency) transistor inverterswith digital bus interface forcurrent and frequency control.

Final stirrersFinal stirrers are always large andlong as they need high stirringforce to stir the mushy zone withsmall diameter and high viscosity.Their position(s) along themachine is (are) determined afterthorough analysis of the castingconditions and metallurgical goals(casting speed, cooling rate,section size, grades) that need tobe standardized to minimize thenumber of positions to becontemplated along the machine.Guiding rolls need to be placedbefore and after the stirrer toprevent damage to the coils.Water cooling and water flush arenecessary.

Installation, commissioningand acceptanceInspection and testing of theentire EMS equipment (electrical/mechanical materials,components and sub-units)

are integrated in the DanieliRotelec manufacturing process.More specifically, completefunctional and performancetesting of the entire equipment is done at Danieli Rotelecworkshop before shipment. This includes verification andcalibration of electronics, controlsand securities, completeelectrical and thermalmeasurement, and establishmentof stirrer’s performance curves(magnetic torque vs. current andfrequency. After assembling andtesting, stirrers and powercabinets/ supplies are operated at full power for a minimum of 4 hours.As a result, after installation onthe caster, cold commissioning in presence of Danieli Rotelecsupervisors, with control andadjustment of the operatingparameters is very simple.Torque measurements are

repeated (without steelin the mold) and coil currentintensity/frequency settingrecommendations are made infunction of steel grades, sectionsand casting conditions; thesesettings are given as tables thatcan easily be integrated in thecaster control computers.Experience shows that theserecommendations are rapidlyadopted by the customers afterstart-up, without modifications,allowing quick hot commissioningand acceptance.

20 Small internal stirrerlocated inside moldassembly.

21 Big external stirrersurrounding the moldassembly.

22 Size comparison ofstrand (right) and final(left) stirrer designed forthe same section size.

22 EMS for billet/bloom casters

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30

Strand EMS or MoldEMS?Backed by the experience gainedwith electromagnetic stirring forbillet and bloom casters, DanieliRotelec started as early as 1973to develop strand- andsubsequently mold- stirrers forthick slab continuous castingmachines.

Strand stirrers Strand stirrers address superheatremoval, hence internalsolidification structure, e.g.,equiaxed zone, segregation andcenterline porosity. Historically, the first application of strand stirring on thick slab casters was for plate andtube grades with the goal ofimproving center segregation and porosity. This function has now beenreplaced by soft reduction.Nowadays, strand stirring ismostly used for ferritic stainlesssteels and high-silicon steelswhere the increase in equiaxedzone is known to reduce ridgingand roping (a defect caused by solidification dendrites that"print out" on the coil surfaceafter cold rolling) and sheetflatness (for example for electricaltransformers).

Mold stirrers Mold stirrers address surface and subsurface slab/coil quality,e.g., slivers, longitudinal cracks,and inclusion content. Their primary application is for low, extra-low and ultra-lowcarbon steels. Examples of goalsare to maximize surface quality

EMS for thick slab casters

Linear -also called travelingfield- electromagnetic stirrersare used on slab casters as theslab width would prevent theinstallation of rotative stirrerssurrounding the cast product.Linear stirrers are fed with2-phase AC current. They have to be understood as the statorof a motor that has been cutopen and uncoiled along thewidth of the slab. The result is a one-directionforce in the slab that movesfrom one narrow face of theslab to the other. If the stirreris installed in the strand, theinduced movement generatescirculating loops in the liquidsteel, up and down, that areknown as "butterfly" patterns.If the stirrer is installed in themold, the force may be used to slow down or accelerate theliquid steel stream as it exitsthe submerged entry nozzle; it may also be used to put in rotation the liquid steel up to the meniscus. Current frequency is between0.5 and 6 Hz depending onthe application.

JZ -JZ

By -By

Fx Fx

zy

x

N S

Vx

1 Principle of linear stirrerwith magnetic field By (Gauss) traveling at velocity v (m/sec) in x-direction inducingeddy currents J (A/m2)in z-direction andgenerating volumeforces F (N/m3) in x-direction inside theliquid steel thatdecrease with increasingdistance from thestirrer.

1

of coils for automotiveapplications, enhance internalcleanliness of D&I product forbeverage cans, and eliminatelongitudinal cracks on peritecticgrades. In some instances, moldstirring also significantly improvescasting operations, i.e.,productivity (higher castingspeed, less breakout alarms),yield (more direct prime slabs,higher slab application ratio) andenergy consumption (higherdirect hot rolling fraction).

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31

Y

Z

Z

X

1st 2nd 3th 4th four independentstirrers

EMLS

EMLA

EMRS

3 Four independentstirrers positioned atmid-height in a slabcaster mold can slow-down, accelerate or putliquid steel in rotation(mold top view,MM-EMS process):EMLS, slowing-downfunction, magneticfield traveling inward;EMLA, acceleratingfunction, magneticfield traveling outward.EMRS, rotative stirring,magnetic field travelingopposite.

2a 2b 2c 2 Different configuration of slab stirring:a) M-EMSb) Single stage S-EMSc) Double stage S-EMS Butterfly and triple-zeroloops are generated bysingle-stage or double-stage stirring, respectively.

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32

Danieli Rotelec

Strand EMS forInternal Quality

As a rule of thumb, the higher thestirrer in the machine, the betterthe heat removal and the largerthe equiaxed zone, provided thatthe upper loop does not disturbthe mold flow pattern that, as willbe shown later, is key for steelsurface quality.

Danieli Rotelec designs andbuilds two types of strand stirrers:

The box-type strand stirrerthat is a good solution in the topof the caster where roll diametersare small, and the distancebetween stirrer and slab can beshort (beyond 250 mm, veryhigh electrical power is neededmaking this configurationexpensive and space-demanding).

The In-Roll stirrers that areinstalled inside slab supportingrolls. They typically have a > 240-mm diameter. Machine buildersnow can design segments thataccommodate such rolls even ifthe neighbor rolls do not have thesame diameter. In-Roll stirrers arealways used in pair to maximizestirring forces. If installed side-by-side, their function is equivalentto that of the box-type with theadvantage that they can also beused in the lower part of thecaster where roll diameter islarger. Front-to-front (one on each side of the strand) is thesecond possible configuration.

Strand stirrers can be installed in single or double-stageconfiguration. In-Roll stirrers areparticularly suitable for double-stage stirring because of theireasy positioning at differentlocations along the strand.

The macrograph on Figure 5refers to stainless steel with 35 °C superheat and single-stage strand stirring. The typicalasymmetrical equiaxed structure

due to sedimentation of thesolidification crystals to the outerradius of the strand is veryapparent.

The Figure 6 shows that double-stage stirring can eliminate thatasymmetrical distribution of theequiaxed zone. The Figure showsthat double-stage stirring alsomakes equiaxed zone larger andmore consistent than just single-stage stirring.

Wid

th o

f equ

iaxe

d zo

ne (

mm

)

Out

side

rad

ius

Insi

de r

adiu

s

Superheat(˚C)

ageDouble-staggstirring

No stirring

80

60

40

20

80

60

40

20

010 40

Outer radius

Inner radius

4 a) Box-type EMS forslab caster strands; b) In-Roll stirrers canbe installed side-by-side or front-to-frontc) In-Roll stirrers aresuitable for single-stage or double-stagestirring.

5 Macrograph of a stainlesssteel slab with 35 °Csuperheat and single-stage strand stirring.

6 Equiaxed zone versussuperheat with In-RollEMS (in beige) andwithout (in blue).

Double-stage stirringeliminates theasymmetrical distributionof the equiaxed zone. Slab size: 1500-1800 mmx 250 mm; C content: 0.1-0.2 %; casting speed:0.6-0.7 mpm.

4a 4b 4c

65

4c4b

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33

It changes all the time duringcasting because of the changingcasting parameters (e.g., slabwidth because of product mix,casting speed because ofsequence casting, SENimmersion depth because ofrefractory erosion, argon flow ratebecause there are not necessarilystandard operating practices onthis item). However, both single-roll and unstable flows are causesof defect, and there is onepreferred flow pattern: a not-too-

weak, not-too-strong double-roll.Hence the dilemma: steel flowpattern controls slab/coil quality,but caster operators cannotcontrol the flow. It becameobvious, therefore, that the steelindustry needed a technology thatcan steer the steel in the moldand drive it to follow the preferredflow pattern.

Mold EMS for SurfaceQuality

In 2000, Danieli Rotelec and NKK(now JFE) entered into anagreement to exchange their slabcontinuous casting know-howand jointly market the NKKEMLS/EMLA technology that canSlow down or Accelerate the steelas it exits the submerged entryports.

The technology uses four DanieliRotelec stirrers that are installedat mid-height in the mold (behindthe back-up plates, two by two,on each side of the submergedentry nozzle) and extend over theentire width of the mold. The technology is very versatileas, with proper electrical control,the direction of the four travelingfields can be selected so thatforces can be generated inwardsto slow down (EMLS), outwards to accelerate (EMLA) the liquidsteel and also to put the steel inrotation in a horizontal plane atthe meniscus (EMRS). (Figure 3).Note that the left/rightconfiguration of the four stirrerson each side of the SEN allows, ifappropriate sensors are available,asymmetrical adjustment of theelectromagnetic forces tocompensate for biased/cloggedSEN flow.

Mold EMS - Liquid steel flowpattern conceptThe question of selecting themost appropriate electromagneticstirrer to install on a moldremained puzzling until 2000when the results of actual steelmeniscus velocity measurementson two industrial casters weresuccessively presented at theNashville (1995) and Pittsburgh(2000) conferences.

It became clear that steel flowpattern in the mold is not justof any kind. It can be naturallysingle-roll, double-roll or unstable.The kind of flow that establishesitself depends on slab width,casting speed, argon flow rateand SEN depth/design (Figure 7).

Double rollSingle roll Unstable, un-symmetrical

Single roll is favoured by - high argon- large slab- slow speed- shallow SEN- flat-up port angle.

Unstable flow can be anywhere (depending on the four parameters) and can be "permanently"unstable.

Double roll is favoured by: - low argon- narrow slab- high speed- deep SEN- steep port angle.

7 The flow pattern in themould of a slab casterdepends on 4parameters: argon flow,slab width, castingspeed, SEN geometryand position.

7

EMS for thick slab casters

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34

EMS for thick slab casters 8 Surface defects on coldrolled coils as functionof meniscus velocity.

9 Blowholes count onbroad and narrow slabfaces with or withoutthe use of EMRS.

Mold EMS - EMLS/EMLA mode for high-speed castersEMLS/EMLA is a technologyspecifically designed for high-speed (> 1.8 m/min) slab casterstypically operating in the double-roll flow domain. Initially installedin the late ‘80s on the NKKFukuyama No.5 slab caster, thetechnology was subsequentlyimplemented in 1993 on theFukuyama No.6 caster also. The early 2000s witnessed aboom in the development of thetechnology, with 4 units installedat POSCO: machines 3-3 and 2-1 at POSCO Pohang(commissioned in March 2002and June 2005, respectively),machines 1-3 and 2-4 at POSCOGwangyang (in June 2003 andAugust 2005, respectively). The purpose is to controlmeniscus steel velocity within anoptimized operational window,independently of throughput andslab size. Indeed, operation/quality data shows that surfacedefects on cold rolled coils areminimum at this optimizedmeniscus flow velocity, alternatelyfor that not-too-strong, not-too-weak double-roll flow pattern thatwas mentioned above:

At slow meniscus steel-flowvelocity (i.e., low casting speed1.0 m/min), alumina-basedinclusions are formed becauseof weak heat transfer to themeniscus and long solidificationhooks. Acceleration of the steelflow (EMLA) will bring more heatto the meniscus and save thesituation.

At medium meniscus flowvelocity (casting speed1.5 m/min), the optimum of theoperational window is attained,and inclusion content isminimum.

At high meniscus flow velocity(casting speed 2.0 m/min), large

mold powder-based inclusionsup to 300 microns are formedbecause of excessive meniscusflow velocity, mold levelfluctuations and mold powdershearing. If at high casting speed,the EMLS slow down function isactuated, the powder-basedinclusions disappear (Figure 8).

Mold EMS - EMRS for specificapplicationsThe specific objective of therotative function is to enhancecirculation of the liquid steel atthe solidification front with thegoal of reducing/eliminating argonpinholes and CO-based blowholesas in pseudo-rimming steels forexample (Figure 9).Backed by more than 30 years ofexperience in the conception andmanufacturing of electromagneticstirrers, the Danieli Rotelecstirrers are strong and do notneed to be installed close to themeniscus to generate therequired rotative movement of thesteel. The Danieli Rotelec solutionmaintains mold construction thatis balanced, stiff and self-standing: no designcomplications such as thinnermold copper, reducedconductivity, shortened bolt pitchor asymmetrical structure.

MM EMS - A new Multi-ModeEMS concept for all-speeds,all-widths castersMulti-mode EMS is a thirdgeneration of process control thatwas presented for the first time atthe Birmingham conference inOctober 2002. Multi-Mode EMScombines, on one same caster,three electromagnetic stirringfunctions, namely slowing down,accelerating and rotating, and itscontrol applies the most recentdevelopments and knowledge onsteel defect analysis/causes, fluid

Surf

ace

defe

cts

on C

R c

oils

(in

dex)

Meniscus steel flow velocity(index)

Low Optimum High

20

0

40

60

80

100

1 2 3 4 5 6

4

6

10

Blo

who

les

coun

t

without EMRS

with EMRS

0

2

20 4 6 8 10 12 14 16 18Depth from surface (mm)

8

flow mechanics and MHDcalculations. Its three functionsare used in three operatingmodes:

The EMLS/EMLA operatingmode that is used for high-speedcasting.

The rotative EMRS operatingmode that is used on specificgrades.

The permanent operatingEMLA accelerating mode that isused to transform defect-proneunstable and single-roll steel flowpatterns into the preferred stableand optimized double-roll flowpattern. This is every casteroperator's dream comes true:being able to create identical

meniscus steel velocities andsteel flow patterns regardless ofchanges in casting speed, slabwidth, argon flow rate, SENimmersion depth or design(Figure 10).

MM EMS - Process Control The rotative EMRS mode is anon/off function. For specificapplications (for exampleelimination of blowholes onpseudo-rimming steels), EMRS isswitched on at full currentintensity without any adjustmentmade in function of the castingconditions. With EMLS/EMLAwe enter into a second generationof sophisticated flow control that

8

9

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35

a feed-back regulation mechanismis not possible yet. Hence,models have been developed thatcan (1) predict the "natural" steelflow pattern that results from theactual casting conditions: this is afluid mechanics problem, and (2)predict the "electromagnetically-forced" steel flow pattern thatresults from the application ofEMS forces: this is a MHDproblem. Those models havebeen presented for the first timeat the EPM conference in Lyon inOctober 2003. They were verifiedwith data from four casters:LTV Indiana Harbor No. 2, JFEFukuyama No. 5, POSCO PohangNo. 3-3 and POSCO GwangyangNo. 1-3 (nail board and refractorypaddle measurements).

Figure 11 shows that the fluidflow model reacts well tochanging argon flow rates withfive simulations presented at0.0, 3.5, 4.1, 4.5 and 10.0 l/minargon. Slab width is 2,000 mm,cast at 1.0 m/min, 20° downwardrectangular-port SEN and180-mm immersion depth.For each simulation, steel flowtrajectory is displayed on the left-hand side of the figure (half ofmold width). Correspondingmeniscus horizontal flowvelocities are on the right-handside. Double-roll flow (DR)that is characterized by negativemeniscus flow velocities (from thenarrow slab face to the SEN) isobtained without argon. Single-roll flow (SR) that is characterizedby positive meniscus flowvelocities (from the SEN to thenarrow faces) is obtained at10 Nl/min argon. Unstable flow(U) appears around 4 Nl/minargon: the progressive breaking/fracture of the upper loop of theflow and the simultaneoustransition from double to single-roll flow are well apparent.

can no more be operatedmanually. The decision to slowdown or accelerate, and at whatintensity, is made in real timeby a predictive computer modelin function of slab size, castingspeed, SEN geometry/depth andargon flow rate. It is the so-calledF-value process control operationintroduced by NKK (now JFE) inthe early '90s. The industrial applicationof MM-EMS requires automaticprocess control similar to thatof the EMLS/EMLA operation.As there are, currently, no on-linesteel velocity sensors thatare compatible with EMS underindustrial caster operation,

10 EMLA progressivelytransforms single-rollflow patterns intounstable and eventuallydouble-roll flow patterns(mathematical simulationon one half mold).

11 2D simulation showinghow increasing argon flowrate can transform adouble-roll flow patterninto an unstable andeventually a single-rollflow pattern.

0

-0.2

-0.4

-0.6

-0.8

Mou

ld h

eigh

t (m

)

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ld h

eigh

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)

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Mou

ld h

eigh

t (m

)

0Distance from SEN to narrow face (m)

0.2

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Mou

ld h

eigh

t (m

)

Men

iscu

s flo

w v

eloc

ity (

m/s

ec)

Mould width (m)

0 Nl/min Ar

3.5 Nl/min Ar

4.1 Nl/min Ar

4.5 Nl/min Ar

10 Nl/min Ar

10 11

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1 - Internal defects on slabs/coils and strand EMS countermeasure (Carbon and stainless steels).

Strand EMS Steel Grades Typical Associated Defects Superheat Primary mechanismCountermeasures

Single-Stage EMS Stainless Steels Ferritic - Dendritic solidification structure < 25° C - Mix hot and cold steelBox-type (behind - Segregation - Promote early superheat removalthe rolls) or In-Roll - Ridging/roping - Promote wide/fine equiaxed zonetype one pair Stainless Steels Austenitic - Intergranular precipitation - Reduce mini-heterogeneities

of non-dissolved components - Chip/break large porositiesthat create large undeformable - Eliminate long dendrite structureinclusions - Increase number of crystal nuclei

Silicon steels - Dendritic solidification and germs

structure

Medium to high carbon steels - Centerline segregationfor plates and tubes - Centerline porosity

- Crack susceptibility

Double-Stage EMS Same as above Same as above > 35° C Same as aboveIn-Roll type two pairs

2 - Surface/subsurface defects on slabs and coils, and Mold EMS countermeasures (Carbon steels).

Flow Pattern Associated Negatives Examples of Induced SolutionSteel Defects

Too fast - Excessive narrow-face wave height - Mold powder-based defects EMLSDouble-Roll - Excessive meniscus velocities (slivers, pipe) (slowing down mode)

- Excessive mold level fluctuations - Loss of lubrication- Slag thinning near the narrow faces - Breakout events- Mold powder shearing - Breakout alarms

Optimum - Minimum defectsDouble-Roll

Weak - Reduced heat transfer to meniscus - Alumina-based defects EMLADouble-Roll - Reduced mold powder melting rate - Cold/frozen meniscus (accelerating mode)

- Slow meniscus velocities - Slag spots- Sticking alarms

Permanent - Steel flow reversion - Slab casting abnormalities EMLAUnstable and - Abrupt/local meniscus velocity increase - Downgraded slabs (accelerating mode)Transitioning - Flux entrainment - Various unexplained defectsDouble/Single - Flux vortexing

Single-Roll - Slag thinning near the SEN - Mid broad-face longitudinal cracks EMLA- Un-opposed, full-momentum flow - Alumina-based inclusions (accelerating mode)of steel to the narrow faces - Argon bubbles and inclusions - Un-opposed drive of argon bubbles accumulation in a 30-cm band and inclusions to the slab edges along the slab edges

Biased Right/Left - Asymmetrical/unbalanced flow - One-side accumulation Asymmetrical ForcesFlow - Mold level fluctuations of bubbles/inclusions (individual right/left control)

- Non-uniform molten slag layer

Sluggish Flow - Non-uniform steel velocities and - Subsurface alumina and calcium EMRSat the meniscus temperature gradients along mold aluminate inclusions (rotative mode)

perimeter - Argon-based pinholes in fully-killed steels- Non-uniform solidification shell thickness - CO-based blowholes in pseudo-rimming- Weak heat convection to the mold faces steels

- Longitudinal cracks on peritectic grades

36

Mold or Strand EMS,What for What? Tables 1 and 2 are decision-

making trees that should helpsteelmakers determine what typeof stirrers they may need.

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37

3 - Benefit areas of Multi Mode EMS.

Molten slag layer thickness (constant over entire mold width)

Mold flow pattern (same, regardless of casting conditions)

Slivers (mold powder and alumina-based)

Subsurface cleanliness

Inclusion index

Blowholes and pinholes

First, last and transitioning slabs

Breakout alarms

Mold level control performance

Frozen meniscus

Maximum casting speed

Average casting speed

Caster productivity

Steelmaking rejection on cold-rolled product

Customer satisfaction (claims)

Slab application ratio

Benefits and IncentivesTable 3 lists typical benefit areasof the Multi-Mode EMS system.Customer satisfaction (less claimsand better coil quality ratings),better yield (less slabdowngrading abnormalities, moreprime slabs, less alumina/powder

defects, less conditioning) andcasting operation improvement(higher productivity, castingspeed increase without defectincrease, better copper/strandlubrication) are some of theincentives that are claimed forthis technology.

EMS for thick slab casters

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38

Design and installation

S-EMS Interface with caster -Mechanical interfaceDanieli Rotelec has extensivecollaborative experience with theworld's main machine buildersregarding implementation ofS-EMS for new or revamped slabcasters.Basically, the installation of In-Roll stirrers on an existing casterrequires much less mechanicalmodifications of the involvedsegment(s) than a box-typestirrer, especially if the normalrolls have a diameter close to theIn-Roll stirrers.The implementation of stirringrolls in a segment (typically insegment No. 1 (Figure 12),sometimes in segment No. 0)is just like for normal rolls.The solution is very flexible,as roll positions may be diversealong the machine; the positionsmay be relatively easily modifiedafter startup provided optionshave been provisioned for at theengineering stage.

In contrast, box-type stirrersrequire heavier mechanicaladaptations/alterations to thedesign of the machineenvironment:

Special segment designfor insertion of the stirrer closeto slab surface, while minimizingroll and segment bending.

Part of the segment madeof non-magnetic stainless steel.

Rolls in front of the stirrermade of heat-resisting, non-magnetic stainless steel (samematerial as the sleeves of the In-Roll stirrers).

Insulated bearings for therolls located in the magnetic field.

Optional stirrer-withdrawaldevice for quick segment change.

S-EMS - Single-line diagramElectrical power supply of thestirrers consists of the followingdevices (Figure 13):

One medium-voltage panel(usually supplied by the End User).

One power transformerfor voltage adaptation.

One power-supply cubicle,including a diode rectifier and an IGBT inverter controlled by Pulse Width Modulation.

Two connecting boxes. to switch from normal powercables to heat resisting ones.

Because of the longer stirrer-to-slab distance, box-type stirrersdemand, of course, moreelectrical power than In-Rollstirrers.

S-EMS Interface with Plant -UtilitiesStrand EMS equipment needsthe following utilities:

Electrical power supplyfrom the medium voltage mains.

Electrical auxiliary powersupply.

Mold-water quality coolingwater for In-Roll stirrers,de-ionized cooling water forbox-type stirrer. Danieli Rotelecmay alternately supply a watercooling and de-ionizing unit,for which primary industrialwater will be required.

Industrial cooling water forhigh-power inverter of box-typestirrer.

Dry air or nitrogen topressurize box-type stirrer.

MM EMS Interface with Caster - Mold mechanical interfaceDanieli Rotelec has extensivecollaborative experience with theworld's main machine buildersregarding implementation ofMM-EMS equipment in slabcaster molds. A typical moldmechanical interface is shownin Figure 14.

MM-EMS does not require anyspecial mold design. Copper typeand thickness are standard, andthe stirrers only need a cavityto be inserted in, behind thebackup plates, between the twowater boxes. In contrast to otherelectromagnetic mouldequipment, MM-EMS moldsremain balanced, stiff and self-standing.

Backup plate thickness alsoremains standard.Typical dimensions are:

40-mm thick copper plateand 50-mm thick back-up plate(or 30/80 mm, respectively).

In conjunction with 81-%

Line CircuitBreaker

Step DownTransformer

FrequencyConverter

Box TypeEMS

RC 800 / 1800

Power CenterSwitchboard

L.V.

PLC

Bus-Interface

Back-upspacemin 620

Mold opening485 ± 1

Mold opening480 ± 5

Bolts 750Stirrer 800

Clearance 10 mm (*)Back-up plate max 50 mm (*)Cu plate max 40 mm (*)

12

13

14

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39

IACS mold copper and 15-mmstirrer to back-up plate air gap.

Neighboring steel parts exposedto the magnetic field must bemade of non-magnetic material,typically austenitic stainless steel,to minimize magnetic losses:

The back-up plates.The mold cover (totally or

partly according to its design).And some mechanical

components in the mold widthchange system.

MM EMS Interface with Caster -Electrical couplingElectrical coupling betweenpower supply and stirrerscan be accomplished two ways:

1. With the Danieli Rotelec-patented QCS (for Quick CouplingSystem) that also allows quickmold change. It consists of(i) an upper part (including maleconnectors) that is assembledonto the mold and oscillates withit, (ii) and a lower part (includingfemale connectors) that is movedup and down, by (iii) ahydraulically-actuated carriagefixed on the machine structure.QCS requires a simplemechanical interface to beagreed on with the machinebuilder.2. With connection boardsmounted on the mold frameor the machine structure nearby,for manual connecting anddisconnecting.

MM EMS Interface with caster -Influence of magnetic fields onneighboring sensors

The anti-breakoutthermocouples are affectedby the low-frequency AC field,and a noise filtering systemis included in the supply thateliminates interferences.

The NKK/JFE-NIRECO moldlevel sensor is not affected by themagnetic field.

Other mould width andmould level sensors may or maynot be affected by the magneticfield. Countermeasures arespecific to casters and must beaddressed by each End User,individually.

MM EMS Single-line diagramThe electrical power supplyof the stirrers consists of thefollowing devices:

One or two medium-voltagepanels (usually supplied by theEnd User).

One or two powertransformers for voltageadaptation.

Two power-supply cubicles(left and right sides), eachincluding a diode rectifier and anIGBT inverter controlled by PulseWidth Modulation.

Two inversor-switch cubiclesto switch between EMLS/EMLAand EMRS.

Two connecting boxes toswitch from normal power cablesto heat resisting ones.

Two coupling devices.Two double stirrers (inner

and outer sides).

MM EMS Interface with Plant -UtilitiesMM EMS equipment needs thefollowing utilities (Figure 15):

Electrical power supply fromthe medium voltage mains.

Electrical auxiliary powersupply.

De-ionized cooling water forstirrers. Rotelec may alternatelysupply a water cooling and de-ionizing unit, for which primaryindustrial water will be required.

Industrial cooling water forinverters.

Dry air or nitrogen topressurize stirrers.

For optional Quick CouplingSystem: (i) hydraulic oil andpressurized air for actuators, (ii)clean air for anti-steam and anti-dust pressurizing.

M-EMS Data interface - SystemconfigurationAutomatic process control isperformed by a ProcessComputer interfaced with boththe End User's caster PLC andHMI, and a dedicated EMS-PLC.

The End User's level II or thecaster PLC sends the followingdata to the Process Computer:

Heat No.Steel grade.Operating mode.

Nozzle geometry.Nozzle immersion depth.Slab thickness.Slab width.Casting speed.Argon flow rate.

Based on those actual data, theProcess Computer determineswhat stirring function (EMLS,EMLA or EMRS) must be appliedto optimize the in-mold moltensteel flow and the related stirrersettings (such as travelingmagnetic field direction, coilcurrent and frequency), andsends them to the EMS-PLC.The settings are recalculatedevery 5 seconds, allowing anautomatic adaptation of theMM-EMS to changing castingconditions. In turn, all thenecessary feed-backs (measuredvalues, equipment status, alarmsand faults) are transmitted to theEnd User's control system.

FrequencyConverter

Cooling WaterCoil

CoilCoil

Coil

Mould

Dry Air

Operation RoomGraphic Operation Terminal

I/O

MM-EMSComputer

Transformer

Quick Coupling System

Power CenterSwitchboard

PLC

12 In-Roll EMSarrangement in a slabcaster.

13 Schematic of aelectrical power supplyfor a box-type stirrer.

14 Section view of atypical moldmechanical interface:

Back-up plates and mold assembly in non magneticstainless steel;Note: otherarrangement possibledepending on spaceand goals.

15 Block diagram ofMM-EMS equipment.

15

EMS for thick slab casters

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42

Introduction44

The C-Type DanieliRotelec system

Danieli Rotelec

40

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INDUCTION EDGE HEATERSFOR HOT STRIP MILLS

Danieli Rotelec designs and builds induction edge heaters for steel bars as they travel through hot strip mills. This technology applies electromagnetic principles to generate eddy currents on the bar edges that compensatethe heat losses. Reheating of the bar edges before the finishingmill reduces coil edge trimming and improves strip thicknesscontrol. Work roll wear may also be significantly diminished.

41

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42

C-Type inductor systems withadjustable arm gap enhanceheating efficiency, improvemetallurgical results and reducetrimming on full bar length foradded-value coils.

Principle and historicaldevelopmentThe principle of induction heatingis shown on Figure 1. Coils on amagnetic core and powered withAC current generate a magneticflux that crosses a traveling steelbar. The magnetic flux induceseddy currents that circulate inhorizontal loops in thevolume/thickness of the bar. By positioning the poles of themagnetic core toward the edgesof the bar, the section of metalthrough which the eddy currentscirculate is reduced, andconsequently current density andheating effect (Joule's Law) at theedges of the bar are increased.Such heating is applied totransfer bars before they enterthe finishing stands of the hotstrip mills. Initially developed in Japan usingU-type inductors, edge heatingnow exclusively uses C-typeinductors (Figures 1 and 2): inthe C-type configuration, heatingefficiency is considerablyincreased as magnetic fluxcrosses the bar only once vs.twice in the U-type.In 1989, in cooperation withIRSID, Danieli Rotelec developedand patented a C-type inductorwith adjustable gap. It wassimultaneously installed at Sollac-Fos (today Arcelor), France andNKK/Keihin (today JFE) andrapidly became a success.

Why heating?During hot rolling, thetemperature of the transfer bargradually decreases; the edges

Induction Edge Heaters for hot strip mills (IEH)

Induction edge heaters act as electrical currenttransformers that generateeddy current in the bars.In practice, the primary coilsare disposed on a magneticcore that forms a C, with thehot band traveling in the gap. The primary coils are poweredwith single-phase AC current at medium frequency(300 Hz). The traveling steelbars act as the secondary coils;the eddy currents that arecreated heat up the steel. The originality of the Danieli-Rotelec-patented design lies in an articulation in themagnetic core that allowsadjusting the gap, withoutmagnetic losses, byindependent movementof the upper and lower arms. As a result, high heatingefficiency is maintained, evenat large gaps, allowing tocorrectly reheat the bar headsand tails that are frequentlydeformed.

U-type inductorC-type inductor

gap

Half thickness

Bar edge temperature distribution

1010 1020

10301040

0 50 100 150

1025

1000

975

950

Distance from edge (mm)

Ave

rage

tem

pera

ture

in

thic

knes

s di

rect

ion

(°C

)

Distance from hot band edge (mm)

900

800

700

600

500Strip

edg

e su

rfac

e te

mpe

ratu

re (

° C)

0 50 100 150

Strip microstructure at 25 mm from edge

without edge heater

with edge heater

Ar3

1

3

4

2

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43

cool down faster than the middleof the bar due to the largersurface that is exposed to radiantcooling (Figure 3). On low carbon steels, cold edgesreduce the mechanical propertiesof the steel because of austenitetransformation, rapid re-crystallization and formation ofbrittle/coarse ferrite grains.On stainless steels, temperaturedrop at the bar edges (hencelower ductility of the steel)combines with the necessaryhigher rolling pressure andcauses rolled-in scale, surfacedefects and cracks.

Benefits from heated edgesThe purpose of edge heating is to compensate the temperaturedrop in the edges of the transferbar (Figure 3) typically resultingin the following benefits:

Improve elongation on lowcarbon steels (Figure 5);

Reduce rolled-in scale onferritic stainless steels (Figure 6);

Significantly reduce coil edgetrimming (Figure 4).

Enhanced results with theDanieli Rotelec systemIn addition to the intrinsic benefitsof edge heating listed above, the

Danieli Rotelec C-type technologybrings additional specificadvantages regarding bar heatingand bar quality:

Full-bar length heatingincluding head and tail.

Consistent temperatureprofile control.

Power regulation.Warp detection above and

below mill pass line andoptimized gap adjustment.

Process automation.Prevent bar hits and damage

to equipment.

1.1

1

0.9

0.8

0.715 50 85 1550851/2 1/41/4 edgeedge

Distance across hot band width (mm)

Deg

ree

of e

long

atio

n

With edge heaterWithout edge heater

Number of hot rolling sequence

Without Edge HeaterWith Edge Heater

% o

f def

ectiv

e co

ils

-2

0

2

4

6

8

10

12

14

73 74 75 76 77 78 79 80 81 82 83 1 2 3 47170 726968

5 6

Almost constant quality/properties are obtained over theentire width of the reheated bars, whereas considerabledeterioration is observed on the non-heated hot bands in a 50-mm band along the edges.

The x-axis represents the number of hot rolling sequences; the y-axis represents the percentage of defective coils in eachsequence. Edge heating reduces defect ratio by a factor of three.

1-2 Bar Edge Heating withtransverse flux: U-typeand C-type inductors.

3 Computer-simulatedtemperature distributionthrough bar thickness.Temperature drop at baredges must becompensated by edgeheating. Calculationsdetermine amount andprofile of the drops as a function of the barrolling history, typically100°C on 50mm.

4 Effect of edge heating on hot band temperatureand grain structure. Hot band thickness2 mm, rollingtemperature AR3 + 20°C,samples taken 25 mmfrom edge. Edge heatingreduces the 30-mmcoarse grain bandto 14 mm thus saving16 mm trimming.

5 Bar Edge Heating:improvement ofelongation on low carbonsteels.

6 Bar Edge Heating:reduction of rolled-inscale on ferritic stainlesssteel.

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44

The C-Type Danieli Rotelec system

Each C-type inductor consists ofa battery of capacitors, two coils,two magnetic poles and onearticulated magnetic core withupper and lower arms. The coils are powered withmedium-frequency current. The upper- and lower- armpositions are independentlyadjusted in function of barthickness and actual shape of the bar as detected by infra red cameras.One or two inductors may benecessary on each side of thebar. They are installed on carsthat can move in- and outwardsaccording to bar width. The number of inductorsdepends not only on the powerrequired but also on the spaceavailable for installation in anexisting mill.

Temperature controlThe temperature rise (∆T) thathas to be generated in the edgesis controlled by the electricalpower that is supplied to theinductor. Constant electricalpower, constant speed of the barand constant pole gap meanconstant temperature rise alongthe bar length. In the bar thickness, thetemperature rise is almostconstant because of thetransverse flux configuration andthe fact that the thermal energygenerated by the induction isalmost constant through the barthickness.Across bar width, however,heating must be the inverse ofthe temperature drop profile inthe bar (Figure 3).The heating profile can be madesteeper or flatter by moving theinductor poles outward or inwardwith respect to the bar edges(Figure 7).

Power requirement and powerratingThe thermal power to be injectedin the bar depends on thespecific heat of the steel andthree process variables namelythe temperature drop that has tobe compensated (or thetemperature rise that has to begenerated), the bar thickness and the bar traveling speed.Coil design determines themaximum electrical current thatcan be supplied to an inductor. In turn, the maximum heat thatcan be generated in a bar willdepend on the efficiency of thesystem and the gap between thetwo poles of the inductor: the larger the gap, the smaller the maximum thermal power PTH that can be generated by theinductors (Figure 8).Typical data are:

Temperature rise aim: 100 °C.Bar thickness: 32.5 mm. Bar speed: 1.5 m/sec. Thermal power to be

generated in the bar:700 kW/edge.

150-mm electrical gapbetween inductor poles.

Inductor efficiency: 70%Electrical power to be

supplied to the inductor: 1,000 kW/edge.

Medium-frequency powersupply: 2,300 kW for the 2 edges.

Adjustable vs. Fixed Arm GapHeaterThe gap adjustment, madepossible with the Danieli Rotelecupper/lower arms independentpositioning system, results in veryimportant advantages:

Increase of the maximumavailable heating power PTH

Reduction of the number of inductors necessary, i.e., veryoften there is the possibility of

0

20

40

60

80

100

120

140

standard slope 30steep slope 23flat slope 40

distance from edge (mm)

0 50 100 150

Tem

pera

ture

ris

e de

lta T

(∞

C)

Computation data:Specific heat 0.157 kcal/kg°CSpecific weight 7:55 kg/cm3

Required thermal power PTH = 538 kW at DeltaT=100 °C, speed 1.25 m/s, thickness 30 mm

0

200

400

600

800

1000

1200

50 100 150 200

Electrical gap (mm)

Constant coil current

Ther

mal

pow

er P

th (

kW)

250 300 350

Danieli Rotelec

7

8

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45

Induction Edge Heaters for hot strip mills

7 Example of heatingtemperature profile. ∆T decreasesexponentially withincreasing distance frombar edge. The slope of thedecrease can be madesteeper or flatter bymoving the inductor polesoutward or inward withrespect to the edge.

In this example,∆T=100°C is obtained in a 30-mm thick barrunning at 1.25 m/sthrough the inductor, for a thermal power PTH = 538 kW generatedby the inductor.

8 Maximum availableheating power versus pole gap. The x-axis is called“electrical” gap, as thevalues refer to the realdistance betweenthe magnetic core of thepoles, not to the apparentdistance between thermalscreens.

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46

Danieli Rotelec

9-10 Overall systemcontrol and powersupply control HMIdisplay for InductionEdgen Heater.

11 Bar Induction EdgeHeater installedbetween descaler and F1 stand.

11

9 10

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47

operator for process control, to the HSM computer for qualitycontrol, and may be archived in the edge heater PC history logsfor subsequent checking.

ConclusionC-type edge heaters weredeveloped in the late 1980s byDanieli Rotelec and Irsid and arenow very sophisticated machinesthanks to several exclusive,proprietary features such as(table Figure 13):

Compact design, hencecompact integration into existinghot strip mills.

Quick gap openingmechanism for safe operation inemergency situations.

Independent positioning ofthe upper and lower inductorarms for high electrical efficiency.

Optical warp detector for highpower availability for head and tailheating.

Real time generation of actualedge temperature rise foreffective hot band quality controlalong bar length.

13

Exclusive features Benefits

- C-type adjustable gap (patent) High efficiency- Multi-conductor Roebel-type Long lifecoil (patent)- Ceramic thermal screen (patent)

- Quick gap opening Safety in emergency situation

- Independent positioning High power availability for of upper/lower arms head and tail heating- Optical warp detector

- Real time generation of actual Hot band quality control edge T° rise versus bar length

∆T heating, variation of ∆T alonglength, power correction) andother mill data (date, time, steelgrade) are given by the millcomputer.

Bar speed and position aregiven by the mill PLC.The operator can switch fromautomatic to semi-automaticoperation and choose the heatingvalue ∆T manually also.

Quality controlComparison between aim andactual bar-edge ∆Ts is mostimportant information for qualitycontrol of the hot coils. As surface temperaturemeasurements are not veryreliable and do not permitaccuracy better than ± 15%,Danieli Rotelec developed asophisticated system thatcombines performance testmeasurements under steady-state conditions with real-timemeasurements under operatingconditions, and real-timecomputation that determines theactual temperature rise ∆T, with a high reproducibility. Suchinformation is made available via HMI screen to the HSM

using one single-inductor peredge vs. one double-inductor.

Higher heating capacityavailable for bar heads and tails

Better heating efficiencyalong the entire bar length, henceelectrical power savingsThis is explained in Figure 12.The example refers to a 30-mmthick bar traveling at 1.25 m/swith upward/downward warps of100 mm and 50 mm,respectively. Aim temperature riseis 100 °C at the edges; requiredthermal power is 538 kW in eachbar edge.With a fixed arm gap machine(Figure 12 left), the gap must beset at an excessive 230 mm toaccept the +100/-50 mm barwarps (150 mm total warp plustwo 20 mm clearances plus two20 mm heat shield = 230 mm). It can be calculated that in theseconditions, the power generatedin the bar with one inductor willbe 390 kW only.In contrast, with independent/adjustable upper and lower arms(Figure 12 center and right), gapsettings of 170 mm and 150 mmrespectively, are sufficient toaccept the same +100/-50 mm

bar warps as above. As thesmaller the gap, the larger thethermal power in the bar, theavailable power is 565 kW and640 kW, respectively; this is morethan the 538 kW required.

Interface with Hot Strip Mill -Installation on the roller tableFrom a practical point of view, thebest location for the inductionedge heater is on the roller table,before the crop shear. However when the installation ison an existing mill, other positionsmay have to be considered suchas between descaler and F1(Figure 11) or between cropshear and descaler.

Interface with Mill Computerand Logic Controllers - ProcessautomationThe edge heater PLC/PC systemoperates and controls the entireinstallation fully automatically.The system also generatesdetailed bar heating reports forautomatic display and archiving.

Heating temperature settingdata, bar data (number/width/thickness/length), heatingmode data (cold run, constant

201030

50

2020

2020

100

2010

2020

100

50

2020

Fixed gap

Gap setting 230 mmfor up/down warp +100/-50 mmHeating power < 390 kW

Adjustable gapBar head

Gap setting 170 mmfor up warp +100 mmHeating power < 565 kW

Adjustable gapBar tail

Gap setting 150 mmfor down warp -50 mmHeating power < 640 kW

12 Benefits of gapadjustment: threeexamples of maximumavailable heatingpower versus pole gap.

12

Induction Edge Heaters for hot strip mills

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Electromagnetic Stirring and Induction Heating SystemsSince 1977

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