HUE035556T2 - Device and method for electro-slag remelting - Google Patents

Description

Device a»d method fer ekeíro-síag remeiting ffess ripii'o«

The invention relates to a device for producing metal Ingots using the elcetroslag remeiting •method, Itaving a metal lurgicaliy active slag bath and a preheating .furnace for preheating at least one tip of ;t consumable electrode that is to be supplied io the slag hath. The invention further relates to a eorrespo ná ing t»e shod. in elec ire-slag remeiting (fcSR), fusible consmnahde electrodes are immersed in a resistance-heated, tnetaliurgieaily active slag hath, which is located inside a .convcnuonall.y water-cooled mould. The slag superheats ( 1 ?00°C to 2öU0°O and metal droplets tach off front the cottsumable electrode. The droplets sink through: the slag, in which nonntetailic contaminants ate removed front then! by chemical extraction, and are ultimately caught in the still liquid steel hath, which has already been refined, fitere, the molten metal is densely anti direct irmai I v solidified frottt the bottom upwards, The quality of the finished ESR ingot depends not only on the quality of the consumable electrode and the accuracy of plant control but also, above alb on the quality of ihe slag used. Pre-melted slags in this respect: offer a reliable starting point. They ensure a reliable composition with good homogeneity for a uniform and reproducible remeiting procedure To prevent the ambient air from negatively influencing the slag and the metal melt, ihe fcSR method today conventionally proceeds under protective gas, as described for example in DB löl 28 I fel Cl or BP 0 72? SÖ0 BI.

To produce relatively large metal ingots, a plurality of constnnahle electrodes are melted in succession, wherein in each ease an electrode consumed down to a residue during the ESR process is removed from the slag bath and replaced by a new consumable electrode. To keep the resultant interruption to the melting process as short us possible, the replacement electrodes are preheated before being supplied, tes the slag bath, while the previous electrode is still in the process of being consumed, wherein tit least the region, (hereinafter "tip") of the consumable electrode which is subsequently immersed in the slag bath is preheated. A procedure of this type is described lor example in flu .2 124 960 A2. Preheating of the consumable electrode lor remeiting in an ESR plant today conventjonatiy proceeds using electrically heated preheating furnaces, which are arranged at a distance front the remelting furnace. DE 2 755 4*8 ΛI for example discloses an ESR apparatus in which the tip of a replacement electrode is preheated using an induction coil and then supplied to the melting stage. The electrical preheating furnaces used today provide heating to .between 30<PC and 9O0®£.

Known ESR plants with electrical preheating are associated with a series of disadvantages. On the one hand, the efficiency of such furnaces is very low, which is reflected in the achievable preheating temperatures, which are far below the respective melting temperatures, high power consumption and relatively low product quality, the low product quality also being down not least to the long period of time needed during electrode replacement between removal of the old electrode and heatmg of the tiew one up io melting point. In addition, preheating furnaces heated by electrical resistance are highly maintenance-irtiertsive, which manifests itself in high utainienance costs and frequent stoppages.

An ESR device is known from US 3 546 549 At in which the tip of the consumable electrode is preheated by means of gas burners, which are directed directly onto the electrode tip. Although this plant avoids the disadvantages of electrieaily «pet med ESK plants, it leads to uneven healing of the electrode.

The problem nnderlying the invention is; accordingly that of improving the economic viability of an l.iSR. plant operating with replacement electrodes and of reducing maintenance effort.

This probiere Is solved according to the invent«·)« by a device- having the .features of Patent Claim I and by a method having the features of Patent Claim 8. Advantageous configurations of the invention are claimed in the subeiaims.

The method according to the invention is distinguished in that the preheating of the tip of the eonsmnabte electrode in the preheafing furnace proceeds by combustion of a fuel with an oxidant. The preheating furnace Is operated in Ibis respect in the manner of a cyclone furnace, i.e. fuel and/or oxidant are introduced with <r tangential dtreettosa component - when viewed its n plane petzend ten Ur to the Socgirutlinal axis of the preheating furnace — into the combustion region of the furnace, '1 bis loads to .swirl flow. Is which fnei. and oxidant ate guided past the tip of the consmoabie electrode to be preneated. .After Ignition of tits fuoAoxldats mixture, a. flame cyclone is thus foumsd, which envelops and -hereby uniformly beats the tip of the consumable electrode. The lip of the consumable electrode may thus: be heated up io a temperature which lies is the vicinity of the melting point of the respective material to be remel-ed; in this way. ut particular, the duration of interruption of the remehisg process during electrode replacement, i.e. the tinte between stoppage of the process of melting tire old electrode and start of tire process of melting the new one, is shortened considerably.

Sut table fuels are both gaseous fuels, such as for example natural gas. and liquid fuels atomized to form an aerosol or fluidized solid particles (dusts), Fuels may in particular be used which contain carbon, hydrogen, sulfur or a mixture of two or three of these substances or st compound comprising one or more of these substances. The oxidant used may be air or as oxygen-enriched gas {with an oxygen content of over 21 voffo); pure oxygen wish ah oxygen cosedhtfatfon of over hO vbl,%. is preferred; an oxygen couehtstratioh of over ffo vol.% being partichlarly preferred, 1rs the axial direction; the introduetron devices are arranged either perpendicular to the lotrgifodirtai axis of the preheating furnace of indeed at mr angle, with their dischutge opening pointing upuatds, t V towatd.·» (he .’.»osumabie el-woide to be piehc.ned, m oidei to pituuote the formation of n helical flow. la tiro process, however, direct exposure of the consumable electrode So a burner flame should be avoided, since tins -nay lead to local overbeating ot the consumable electrode

The introduction devices may for example lake I he form of an arrangement of lances, by means of which fuel and oxidant are introduced at respectively separate locations into the combustion region and then mixed and ignited. Preferably, however, one or more burners are used, which each comprise at least one supply for a fuel and at least one supply for an oxidant, and in which mixing and ignition of the fool-οχ dmt mixture takes place as early as upstream of the discharge opening of the respective hunter.

Preferably, a plurality oi lances or burners providing tangential introduction are arranged at least in the end section of the preheating furtswe, preferably at regular angular intervals, In order to U ív iu uni ο n 1 emiun ot 1 >' e e< rode ,)»| > ,<

Another ad\ antageous .onucut,Ui«n ot She mvenímn i\ caaructetizcd tn thai She rntrvdnctivu device ur she introduction devices is/are. ananged in the wall of the. preheating furnace so as io be adjustable in terms of lestgllt and/or angular position. The position of the introduction device may in this way be adapted so the geometry of sise electrode respectively so be preheated. Is. is moreover likewise conceivable, for she purposes of she invention, io modify the position of the 'introduction device relative to She electrode during the course of She heating process, ;tt order So achieve optimum exposure to heat with minimum energy input, tor example the electrode may be mounted so as to be rotatable relative to the preheating furnace or the latter may he mounted so as to be rotatable relative to the electrode about the longitudinal axis thereof, in order to allow uniform exposure of the electrode tip to heat even in the •ease of tt small -numbêt of infrodnesbon devices in the preheating furnace.

In another advantageous further development of the invention, the end section of the preheating· •f&amp;mace Is equipped with a cover in order to prevent ingress of ambient atmosphere, la the ease of long consumable electrodes, it is recommended, in tin« respect, that the cover be equipped with an opening for ihe electrode, such that in operation the consumable electrode projects merely with its tip into the combustion region enclosed by the cover. In this configuration of the invention, therefore, only the régióst of the electrode tip is exposed istteisstvely to ltot burner gases, wherein the: cover at least largely provenu gases front the ambient atmosphere, m particular oxygen, front penetrating into the heated region of the preheating furnace rand resulting itt undesired reactions at Ihe surface of the electrode. Alternatively, a cowl completely -enveloping the electrode may moreover also he used, for example a cowl design of the type described in 8Ï* 0 /27 döfi 131.

The preheating furnace is conveniently equipped with an exhaust gas system for regulating the furnace presume. The exhaust gas system for example comprises means for regulating the pressure or composition of the atmosphere in the furnace chamber, such as tor example an extraction system or means for recirculating fine gases.

The method according to the mrenoon for producing metal ingots using eleclros.lng remehing of metals. In which a consumable electrode ss preheated and is then lowered at. least with its dp into a meinlhu'gsealiy active slag hath, is shuraererwed is that preheating of the consumable electrode, prior to supplying the latter to the slag hath, is effected by acting on at lettsí the tip of ihe consumable electrode using a mixture of fuel and oxidant that react with one another.

According to the invention, the tip of She consumable electrode is preheated by forming a flame cyclone that surrounds the tip. A flame cyclone arises on tangential introduction of fuel and/or oxidant by moans of lances or burners, fite eo-reaetlng substances are passed around the tip of the consumable electrode In a swtrl flow, heating tt uniformly and largely eliminating the risk of local overheating.

It has been found that the duration of electrode replacement has a significant influence on the crystallization process and thus the quality of the metal ingot produced by KSR. The longer the time between removal of the old electrode residue and the start of melting of the replacement electrode, the greater the risk of defective crystallization arming in the boundary region between the matériái sections of the re-melted metal ingot associated with successive consumable electrodes. To keep the remeibog process interruption period during électrode replacement as short as possible, at least the tip of the consumable electrode is therefore heated:, during preheafisg, to a temperature of between IfXAC and the molting pomt of the material of the ccnsumabio electrode respectively to be preheated, preferably between 900°C and tddtf'C. By heating the consumable electrode to such high temperatures which approach flu; inching point of the respective metal to be remélted, it is ensured that the consumable electrode does not have to be heated or lias to be heated only briefly during subsequent supply to the slag bath before the renteloug process starts agam;

In one advantageous further development of the invention, a controller is provided, by means of which the ratio of burner fuel turd oxidant may he modified during the preheating process. In this way. firing in the preheating furnace may be optimized and in particular the iempstatutc of the hunier flame precisely adjusted, it is likewise also possible to modify ot regulate the oxygen content in the oxidant used during operation, of the preheating furnace using the controller Λ further preferred vonfigurattoa ot the itucminn i.·, characterized m that menviucs arc Sähet: to allow the recirculation of fuel: gases into the region upstream of the: burner outlet or outieis. so resulting in flanteless, and thus particularly low-pollutant and energy-efficient, combustion:. i\u exemplary embodiment of the Invention is explained below with reference to the drawings. Tits' single drawing- (big. 1} is a: schematic representation· of the stmetnre of a preheating formice according to tbc invention for an t:SR plant, in longitudinal section.

The preheating furnace 1 shown m fig. 1 comprises a furnace shell 2 constructed from refractory material, the downwardly pointing end section 3 of which tapers conically. Λ covet plate 4, which is equipped with a central opening 5, closes the furnace shell 2 at the top ami thus, together with the walls of the farnace shell 2, defines a combustion region 6. In the region of the end section 3, passages 7, 8 are provided in the wall of the furnace shell 2» in which passages a plurality of burners, two 9, 10 in the exemplary embodiment, are arranged at regular angular intervals, in the exemplary embodiment shown, the bntnet,- ’b 1-p comprise burnera b> means ot wbtett a gaseous tact, fot example urtuiri mis. ..us! otsnen are mtredmeu itao Ίη contb»»non region b and combusted Pro fot the purposes of tin invention, however other burners may also be used, such as for example burners which operate with a solid or liquid fael and/or burners which use as oxidant air, oxygen-enriched air or a gas with an oxygen content: that may be varied during operation. The burners 9:. 10 here project: iangcntiaily into the preheating furnace 1 and., as seers in the. axial direction, are arranged angled relative to a plane perpendicular to the ioisgitwdtnal axis o f the preheating fo.rnnoe Î, with their dischttrge openings in each ease pointing upwards. In the upper region of the furnace shell 2. close under the cover plate 4, a futtitet passage 11 is arranged, in which an exhaust gas litte 12 is installed for removing the flue gas.

When the preheating furnace 1 is ;.n operation, a consumable electrode 13 to be preheated is guided with its tip 14 through the opening 5 itt the cover plate 4 attd positioned in such, a way tinit the tip 14 is arranged in tbc region os' the end section 3, but. without coming into contact with the wails of the furnace shell 2. Alternatively, the cover plate 4 may also be made in two parts and be placed in stibstamially gas-tight manner from both sides against the eottsumubtc electrode 13 only after positioning of the lauer, in any event, the central opening ? m die cover plate 4 is. adapted: to the external diameter of the consumable electrode 13 and ideally does not allow any, ami as a rale: only allows slight, gas exchange between the combustion region h and the ambient atmosphere.

The consumable electrode 13 is positioned for example ussng a crane arrangement 15. which also allows perpendicular displacement of the consumable electrode 13 into the preheating furnace 1 arid oui therefrom. Fuel or oxygen is «applied to ihe burners 9, 10 via a fuel feed line 16 and at! oxygen feed line 17, and ihe fnel oxrdant nuxtnre is ignited in each ease upstream of the discharges of the burners 0, 10. The fucl-oxidant mixture is introduced in each case tangentially into the combustion zone, wherein ihe inclination, as seen m the axtal direction, of the burners 9, 10 towards the tip 14 of the consumable electrode 13 and the corneal (apering of the end section 5 overall bring about a helical flow profile in the combustion region 6. After ignition of the fuel oxidant, mixture, a flame cyclone is Stormed, whseh envelops the tip 14 of the consumable electrode Í3 and heals it uniformly and brings it So a temperature in the vicinity of the melting point of the txtaterial of the consumable electrode 13, for example So a value between 9S)0':'<? and · 40(543. The temperature may in this ease be adjusted and/or regulated by means of a eonttoiler, not shows here, which controls tnljow of fuel amb'df oxrdant. To allow opitinmn exposure to fuel gases in the event of different electrode lip configurations, the burners 9, ;0 are: accommodated with adjustable angles and/or lengths in the furnace shell 3. The fine gases arising during <.»mbn^lnm ate dtuwn off \ la me evhaus.’ gas bm 1? \n e\ti Mtvn swim. H attar.reo iti the exbnuM gas line 13 at the same time allows regulation or adjustment, of the pressure in the combustion regton 6.

The '-»urners 9, tt) are particular!;, advantageous!} designed such ihat llameless combustion occurs within the combustion region o end Puts regular beating of <ne op 14 of the consumable electrode 13 arises nt the same roue as reduced pollutant emissions

Ones the tip 14 of the consumable electrode 13 has been heated to a specified temperature value, the suppls et'juel and oxygen via the teed Imo, to, !” w blocked, 1 he consumable electrode 13 is icmorcd hot:» the ptohetuotn fuiruee 1' mid supphed to the nmutd of an elentede slag temeltrng furnace, not slt-mu hmc. the pteheanne tatn-ux s w> thou avaiiabk* >o nxeire a futiber consumable electrode.

With the preheating furnace according to the invention and operated by combusting a fuel, the preheating of consumable electrodes may be made farmore economically viable and operated at higher temperatures than is the ease with eonveniionai, electrically operated preheating fnrnaees,

Claims (6)

1. l'»t of reference numerate- 1 Preheating furnace 2 Furaace shell 3 End section 4 Cover plate 5 Opere.ng b Combustion region 7 Passage 8 Passage 9 Burner SO Burner i 1 Passage 12 Exhaust gas Une 13 Consumableelectrode 14 Tip (of cons eatable electrode) 15 Crane arrangement lő Fuel feed line 17 Oxygen feed line ' IS Extract ion system BERENDEZÉS ÉS ELJÁRÁS ELEKTROSALAK-ÚJRAÖLVASZTÁSHÖZ 52« hű Jo i r« i igényp ontok

   1,. Berendezés ícmbygák clcktres«ls.k-öjiuoivssxtásös eljárással történő gyártásához, a berendezés ί tartalmaz ínetallurglailag aktiv xídakfürdók valantint s sulskrürdőbe táplálni szándékozott fogyoeiektrod (15} legalább egy csóoss {14} elöhevitésére szolgáló elöhevttö kemencéi (1), azzal jellemezve, hogy az elöltevitő kemence (1) egy az előbevltö kemence <l) Üzemi állapotában a fogyóé lektröd (13) csúcsát (14} fogadd egéstartományban (ó) tüzelőanyag és oxidáldszer szántára legalább egy bevezetdeszk.ezzel Λ srn eltarta mely o>’w' a iuzeteansugot e-vagy <υ oxukdöszett az civhevu· kemence 0> ? égéstaricunányáha (6) tangeneiáilsau bevezetői} van elrendezve. \z 1 ·ζθ'^ρ<.πί ->/e))i)O besende/Cs. azzal jcíiemezse, a»gv a be\e/et>us/ko/ok i,9, lm ·· axialts irányban tekirirte szögben állón, kiömőnyílásukkal ;·. fogsoelekíród (13) csúcsa O4) tele dőlten vaniîak e I rendezve,
2. 3, Az s. vagy a 2. igénypont szerinti berendezés, azzal jellemezve, hogy a hevezeíöeszközöket égőfejek • i'> 14» kopr/ík, meh>.k miíKtegxjke legalább t r\ tüzelőanyag beve’vu’ssO iendelkez'.k, továbbá legalább egy oxidálószer bevezetéssel rendelkezik
3. 4. Az előző igénypontok bármelyike szerinti berendezés, azzal jellemezve, hogy az elohevito kemence 11} tegtartományaban <31, előnyösen azonv» szögűn otsagbau. több egofej (4. |o) van elrendezve
4. 5. Az előző igénypontok bármelyike szórtat i berendezés, azzal jellemezve, hogy az égőfej, illetve égőfejek íSy 10) hosszuk és/vagy szögbeiyzetük tekintetében az eióbevítő kemence (1) falában állíthatón van/vannak elrendezve,
5. 6. Az előző igénypontok bármelyike szerinti betendezés, azzal jellemezve, hogy az előhevítö kemence f.|.) végtattománya (J> a külső légkör behatolásának -elkerülése érdekében fedéllel 14} van ellátva, ?. Az előző igénypontok bármelyike szerinti berendezés, azzal jellemezve, hogy kemencenyomás szabályozására szolgáló íüstgáz-elvezető összeállítása^ ( 12, 18} van.
6. 8. Eljárás fémbugáknak fémek elektroaalak-újraolvasztássa! történő gyártására, ahol fogyöelektródot f 13) élöhévítünk és ezt kővetően esnCéSítl (14) snetaHürgiállag aktív ssdákfürdöbé süllyesztnák, ahöl. 8 fogyóöléktfóő (13) ölőhevítését - &amp; iógyöelektród sákrkfürdöbé Váló betáplálását íftegélőzősm -egymássá) teákelőbá. lépő tÜZelónayagZoxidálószer keverékké! legalább a Íbgyőelefcíród (13) csnósásA hatva végezzük, azzal jellemezve, hogy a fogyóelektród t ! J) csíksának (14) előheviíését egy a csúcsot ! 14} körülvevő langotklonnal végezzük V. A 8. igénypont szerinti eljárás, azzal jellemezve, hogy az elóhevltés során a Ibgyoelektród tilt csúcsát (Í4) KKf'C és a iögyóéléfcífőd áíiyágának: óly&amp;dáspoiítjá közötti hőmé rsék létre, előnyősén 9()ö!'C ás 1400'kf közötti hőmérsékletre hevítjük. iff A &amp; vágy á 4. igénypont szerinti eljárás, azzal jellemezve, hogy az elóhevltés során a tüzelőanyag és az oxtdáloszer arányát, év'vagy az oxidáló szer oxigéntartalmai változtatjuk vagy szabályozzuk. II. A 8- 10, igénypontok bármelyike szerinti eljárás, azzal jellemezve, hogy a tüzelőanyag égetését king mentesen végezzük.