GB2265805A

GB2265805A - A combined electro-slag remelting/cold induction crucible system

Info

Publication number: GB2265805A
Application number: GB9304934A
Authority: GB
Inventors: Alok Choudhury; Matthias Blum; Norbert Ludwig; Harald Scholz; Michael Hohmann; Franz Hugo
Original assignee: Leybold Durferrit GmbH
Current assignee: Leybold Durferrit GmbH
Priority date: 1992-03-11
Filing date: 1993-03-10
Publication date: 1993-10-06
Also published as: GB9304934D0; JPH06200334A; FR2688516A1; DE4207694A1

Description

2265805 1 ARRANGEMENT FOR THE PRODUCTION OF HIGH-PURITY METALS AND METAL

ALLOYS

The invention relates to an arrangement according to the preamble of Patent Claim 1.

Highly stressed parts, for example turbine blades must be produced of a material having high purity. If in the material are enclosed foreign substances, these inclusions under high stress become starting points of hairline fractures and the like which finally lead to the destruction of the entire part.

A conventional process for producing highly pure metal or metals alloys comprises that a starting material is remelted through vacuum induction melting (VIM) into an ingot. The purity of the ingot obtained in this way, however, is still not sufficient for many cases. Moreover, it has as a rule an inhomogeneous structure which inter alia can be traced back to the fact that the solidification of the metal in a form which determines the outer contours of the ingot takes place from the outside toward the inside. In order to achieve a still higher degree of purity, the ingot is subjected to a vacuum arc remelting (VAR) process. The ingot has herein the form of a cylindrical electrode connected to one pole of an electrical voltage source while the container into which falls the material dropping from the electrode is connected to the other pole of this voltage source. In that case between the electrode and the ingot to be produced in the chill mould an arc is f ormed which leads to the melting of f of the one end of the ingot electrode.

In another known process, the electro-slag remelting (=ESR cf.DEZ:Korousic,B.et al.:ESR Technology of High Purity Copper Alloys, Metall, February 1987,pages 153 to 155) process, no open arc is formed between an electrode and melt material in a chill mould even though an electrical voltage in similar form is applied as in the VAR process (German allowed patent application No. 2349721). Hereby through the current flow via an electrode immersed in the slag, the slag is heated by resistance heating whereby the electrode material melts off. The melted-off material penetrates the slag. Between the melt 2 n,at----ial and ithe- slag sll--faC,-- rat,--,Ul=gical reac-z--1w.S take Dlace so that below the slag a nalt ret,a--ial of high purity is dispsed. -An advantage of the ESSIR process c=prises that = can be carried cat at no=al atmos-pheric, pressure.

nia work pieces thwnselves, for' ei--=!e tu--rbin-- parts, can be prmdljced f= the purified by forginci. But it is also possible Jr-o at= e the- Purified and liwified ratp-rial to fo= place it into a mould vessel, and densify it subsequert,--'-y tb--ougi., pressure.

In the VAR process as well as in the E5Rprocess the heat enegy ecniirecl for is intzi:m"ced thrOufn the cul-=e'-nt flow across a In so-called hsatiz-g the neltlng energy. ntrast, is in co, introduced il-ú'-'0 the Ire-1 t raterial through eddy cm=ezil,--s -,fuch, 2-n t=, are generated by a nagna-tic ac field in a coil. Here-in!:-!lis coil is dismosed about a crucible in -YIiich. -t-- disposea the Mterial(Cexma'3Pate-ntNO. 3026722).

in or-der for the ragnertic fiellds to.be able the melt th-e crucible =ist c=. letelly or at least parl,--lly I>-- to th-ese f ields. if me crucible c=r rises ce,-ai cs, t le f -, ei ds De,--. .

=to the naterial wi-thcrit in th-e c--sa of ce-Enic =. ucibles 2-n is b--'---)g re-1 0 t--- e---szs znat m le they have- a high !, thl- 3- i M-Rl-ting tem:>---at=e arri allow =a-jn--7L.2.c ac f ilelds 'm thley reaat in sc71r,-- ca-ses with the malt or na.--,-s of thle bridt-le crucible cer=c bec= d&Lach--d and are- b---jagtit =CO -cne as LnClusions.

M--ta-1 Crucibles, in cw"--st, have. a high degre-e of toughness and do not c'L react wit"h the melt. r-i'i= dlisad-var-5tage lies In the fact, thar- eddy cu-rr--Tr--s develcm in them arid the racne-tic ac fields are prevented pa=r=-::"C:Ing ir _o the melt nie-y have-,:Ln addition, a rela:-,-'.ve- lly low lrelting teuperatu--y----.

It is already known to use metal crucibles in spite of the stated negative properties for inductive melting of metals and metal alloys (DEP 518 499l EP 0 276 544, DE-A-39 40 029, EP-A-0 480 845). Herein, on the one hand, the crucible wall is divided into several segments in order to decrease the formation of shielding eddy currents and to permit in this way an inductive heating of the melt material, and. on the other hand, the crucible segments are for example cooled by water so that they are not melted by a potentially higher 3 of the re:.t IrateX- al. 3y:L-=lmren-,ixg tba cr,,.,cible seg--,,,-:tnts in a sp-=cie-l,-ay the, iri---cduct-,'on of a ml mat-e-- Can b4e v Lnto th t t riall 1-, is mrec;ve-r for w--Arwle rcss=le the racliation of the -0Lip-lds f--m the coil to kee-p the Uvelt f--,= the 4 Lner wall of the c--ucb-, Ph l_n the coollsd =,cible- a nelt is Cle-jen-ted Tohici-. sLe-,itly is raOV-2d f= t'.,.,e crucible by tilting it. it is hwever aiso 3nc7,m to p--ovJide at the bcttcm of such a crucible a-n cper-iln - ar-c= 't so that a pmd at--)ct to - 'zi-. the rd-,!t stream cut of -- er or a&,?l c>cida pm.e-r ils (DE-A-40 1-1 392). For shaping the pa=:Lrg Cxeam therain a conicall or rotationally hielic:5=;nel is py--,vided c=rising fl-uid---x)led segny----s and su-,i. Sed by an --,-,aar-tion coL'-. gi=cpi the shape- of the funnel, through the -self----ti4cn of the ac c=ent f-- ecaerr-y W11"11 -Oihicl th-2. indur-tion. coil I -- cp.---zited, a:xl the- selection of the current distribution of the rg:ac-ien coil the p=irg st----,an can b_. shaped a:U spread.

rne irv--it:ton is based' on the task.of a pouring sl"-e-am.

a raterial cti to- the. zate.--ia.ILs prcduced with thd st--ted P---'Cl--sses has a--I

Claims

TtLl,s task is solved to the fearLi-res of Patt-ent Claim i.

Mie acz,-ar,,-.-ages achieved with the rvention c=.,wrise mi-ri-f of the -IES-R ellectrode- inC,-erial by:.iyaants of slag react.,or-.:;, the =lrif ication of t.'.ic irp-l-t rateriall heat-',.-ig in tb.e cve.-,i as we:1.1 as pote,.itial-ly in the cono-crit-tation of tt-he:',-n cap m the cold c-,icWie s=face. 7-u--tharm--.e, thr-cugh the ltrGcp-cje- of two t.-bzblcg--es Jin w:a and in lone- rel, to separate energy ssw,7Lrigs, snoC"---1r-g of the duration of thes, pr--c--s --r-A, potent-Lany, a hictier- purity =,i be- ach i Paved. aLdvar3,----ges EL-e addit-norally by a spec-"-= 2.n the ere- prcducts. T-h-e Process, noreaver, c--n be ca=iecl otr', tzdp-- any g^-tven type of atr,,cire,:Eor e=ple _in wn a=, in -:L-ie-,rt gas w-d urder Tn the =ie-al-laticn is prefewably integrated an -Yffi-icli the of 'Unia cord.,tio-.z wr4-ch are the rcst fravon-c-ble for particullar erd produzl,-.

Added to tbi s is the fact that the- ar--angentenl,-- ac=.

ding to Lnver&,ion can be- cpe,,-a--ecl in as well as also in air or L-1 ar. inext gas 4 chamber or under excess pressure.

An mTLbodimmt example of the invention is depicted in the drawing and will be described in greater detail in the follading.

In the Figure is depicted an arrangement 1 in which elements of the electro-slag remelting process are linked with elements of the induction crucible tedbnology. ahe melting of an electrode 2 therein tzkes place by means of an electrical energy source 3 whose first tarminal 4 is connected with the electrode 2 while its second terminal 5 is connected to a crucible 6. A starter plate, not shown in the Figure, can also be provided. The energy source 3 can moreaver be a dc or ac current source. This crucible 6 is a slotted crucible coaprising several vertically di-sposed fins of which only some fins 7 to 13 are visible in the Figure. The end of electrode 2 is immersed in a liquid slag layer 14 and is there melted off due to the high heat develcpment in the slag layer 14. The melted and purified melt material collects underneath the slag layer 14. Up to this point it is the conventional electrc:r-slag remelting process. In this knmm process underneath the slag layer 14 dmm to a particular depth a sLmp develops ccmprising liquified electxode material 15. Underneath this sump the material is again solidified. The slowness-of the ESR process in general does not permit keeping liquid the entire contents of the crucible 6 underneath the slag layer 4 and possibly to pour it off through an opening in the crucible 6 and to atomize it. A continuous progression of the melting process is achieved according to the invention therehy that the crucible 6 is a cold induction cru cible. This crucible has around its circumference a water-cooled induction coil 16 which is connected via two tez:minals 17, 18 to an ac current source 19. With the aid of this induction coi I the melt material 15 can be kept in the liquid state. At the lower end of the crucible 6 is disposed an opening 20 which during the normal melting operation is closed by a stopper 21 ccaprising the same material as the electrode 2. This stcpper 21 is formed due to the cooling through the wall of the crucible 6 or is set in place beforehand. If the melting energy coupled in via the coil 16 is not sufficient, the solidified stopper continues in a solidified layer 22 in the upward direction. The remaining melt 15 is kept in the liquid state through the induction of coil 16 and caused to form currents. nese currents are illustrated by curved arrows 23 to 26 wherein the arrows indicate only symbolically the very complicated current motions and do not make any reference to the actual currents. In any case, however, the slag currents bring about that inclusions and impurities still pre-sent in the slag arrive at the outside, are picked up by the slag layer and can in this way be removed from, the melt. Herel7y the remelted material is once again purified.

The electxode 2 can be rotated with the aid of a motor 36. It is also possible to lower or raise vertically the electrode 2 by means of a lifting mechanism 27 movable on a vertical rail 28 and fastened on an arrangement 29.

If the melt 15 is sufficiently purified, it can be removed from the crucible 6 for further processing. For this purpote a further induction coil 31 is provided at the lower end 30 of the crucible 6 which is fed from an ac current source 37. If tl=aagh this coil 31 a current flows, the induction heat energy is concentrated on the stzpper 21 and melts it. After this stopper has been melted, the liquid material 15 can stream from the crucible 6 through the opening 20 downwardly and can be processed further to form metal and alloy powder. It is also possible to produce semifinished products via continuous casting or bottom. retraction. This process can also be carried out continuously by means of melting off the electrode and pouring off the material.

This further processing is known per se (cf. for example USP 4 762 553, USP 4 869 469) and for that reason does not need to be described further. it is understood that the known cold-finger technology can be used for pouring off the s't-ream. or that an ingot retractor device is used. The ac current of source 3, which is used for the FSR process proper, can have variable frequencies. Instzad of one electrode 2, two or more electxodes, can also be melted simm1taneously. In the case of three electrodes the current source 3 can be a three-phase current source.

For heating the melt 15 two separate ac current sources 19, 37 are depicted in the Figure. Instead of two ac current sources, it is however also sufficient to have one if it can be switched to one or the other winding.

The invention can also advantageously be combined with the cold-finger tadhnolcgy for pouring off stzvans (A. Gubchenko, Y. Norikov, A. Choudhury, F. Hugo: Vacuum Induction and Induction Plasma Furnaces with Cold Crucible, 6 Paper presented at the Vacumu Metallurgy Conference, 1991, Pittsburgh/LTSA) or with an ingot retractor device (A. Chcmdhuty: Vacuum Metallu-L-gy, AsM International, 1990, pp. 136, 137).

A pouring stream coming f=m the crucible 6 can be txansferred into a chi11 mould where it solidifies to form an ingot. It is also possible to use a pouring stream from the crucible 6 for filling lost-4ax moulds. The pouring stream can moreover be atomized by mans of inert gas so that fine matal powder is produced. Furthenwre, from the tapered region of the crucible' 6 a continuous rcpe can be drawn whose diameter is variable. 11he induction coil 16 can be divided into two or more parts which are connected to the same or to different voltages.

7 Patent Claims 1. Arrangement for the production of high-purity metals and metal alloys with a cooled crucible rising one or several metallic segments, which is surrounded by an induction coil, characterized in that in the crucible (6) a liquid slag layer (14) is provided in which is i=sed at least one electrode (2) ccuprising a metal or a metal alloy, and that this electrode (2) is connected to a voltage source (3).
2. Arrangement as stated in Claim 1, characterized in that a metal plate is provided as an opposing electrode.
3. Arrangement as stated in Claim 1, characterized in that into the slag layer (14) are immrsed two or nore electrodes rising a metal or a metal alloy, and that these electrodes are connected to a voltage source (3) wherein one or several electrodes serve as opposing electrodes.
4. Arrangement as stated in Claim 1, characterized in that the crucible (6) has in its bottom an opening (20).
5. Arrangement as stated in Claim 1, characterized in that the crucible (6) tapers in the direction toward its bottom and the tapered region of the crucible is surrounded by an induction coil (31) which is connected to an ac voltage source (37).
6. Arrangement as stated in claim 1, characterized in that the electrode (2) is rotatable about its longitudinal axis by means of a drive (36).
7. Arrangement, as stated in claim 1, characterized in that the electrode (2) can be lowered by means of a drive (27).

8. Arrangement as stated in Claim 4, characterized in that the opening (20) is closed by a stopper (21) c=prising the same material as the electrode (2).
8
9. Ar-nangement as stated in claim 5 and Clain 8, characterized in tliat the inductive heating power of the- induction coil (31) is so high that the stp-.-r (21) can be melted.
10. Arrangenen:t as stated in Cla-in 1, characterized in that instead of a crucible bottom an ingot retractor device is disposed.
U. Arrangement as stated in Cla:lm 1, characterized in that a pouring stream is transferred frcm the crucible (6) into a chill mould where it solidifies to form an ingot.
12. Arrangeaent as- stated in claim 1, characterized in that a pouring fr the crucible (6) is used for filling lost-w-ax moulds.
13. Ar--angenent as stated in Claim 1, characterized in that pmder is forne-d tbrough a pouring stre-an f= thle, crucible (6) by means of inert gas atomization.
14. as stated in Claim 5, characterized in that f= the region Of t_he crucible (6) a r'cp-- is drawn wherein the rope diameter is variable.
15. Arwangement as stated in Claim 1, characterized in that the process is carried out in vacuo, air, excess pressure or inert gas.
16. A=angement as stated in Cla:bn 1, characterized in that the induction coil (16) is seted.
17. Arrangement for the production of high purity metals and metal alloys substantially as hereinbef ore described with reference to and as illustrated in the accompanying drawing.
18. A method for the production of high purity metals and metal alloys substantially as hereinbef ore described with reference to and as illustrated in the accompanying drawing.