EP0576212A2 - Purifying molten metal - Google Patents

Purifying molten metal Download PDF

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Publication number
EP0576212A2
EP0576212A2 EP93304736A EP93304736A EP0576212A2 EP 0576212 A2 EP0576212 A2 EP 0576212A2 EP 93304736 A EP93304736 A EP 93304736A EP 93304736 A EP93304736 A EP 93304736A EP 0576212 A2 EP0576212 A2 EP 0576212A2
Authority
EP
European Patent Office
Prior art keywords
gas
nozzle
nozzle block
refractory
receiving channel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP93304736A
Other languages
German (de)
French (fr)
Other versions
EP0576212A3 (en
EP0576212B1 (en
Inventor
Liam Cullen
Michael Robert Clark
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Foseco International Ltd
Original Assignee
Foseco International Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Foseco International Ltd filed Critical Foseco International Ltd
Publication of EP0576212A2 publication Critical patent/EP0576212A2/en
Publication of EP0576212A3 publication Critical patent/EP0576212A3/en
Application granted granted Critical
Publication of EP0576212B1 publication Critical patent/EP0576212B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D1/00—Treatment of fused masses in the ladle or the supply runners before casting
    • B22D1/002—Treatment with gases
    • B22D1/005—Injection assemblies therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D41/00—Casting melt-holding vessels, e.g. ladles, tundishes, cups or the like
    • B22D41/50—Pouring-nozzles
    • B22D41/58—Pouring-nozzles with gas injecting means

Definitions

  • This invention relates to a means for the purification of molten metal, i.e. the removal of unwanted solid non-metallic inclusions contained in the molten metal.
  • EP-A-404641 discloses the use in a tundish of a gas duct set into the permanent refractory lining and leading to a gas distribution chamber in the bottom of, and extending across, the tundish, the chamber being covered with a gas-permeable plate.
  • GB-A-2164281 discloses the use of a porous refractory tile extending across the width of, and sitting on the floor of, a tundish, the tile containing a gas conduit with a plurality of exits to deliver gas into the tile.
  • EP-A-0239257 discloses passing steel in a tundish through an apertured upright board, while introducing an inert gas at the foot of the board at its upstream side to cause a stream of bubbles to flow over its upstream side.
  • EP-A-0059805 discloses the use of a porous nozzle in the bottom of a molten metal vessel, the nozzle having a flanged upper portion and cylindrical lower portion, its body being enclosed in a gas tight steel shell, with means to provide gas into the porous nozzle to escape into the molten metal in the vessel.
  • the present invention aims to provide an improved means of bubbling gas into molten metal in the region of a nozzle in the bottom of a molten metal vessel.
  • a molten metal vessel such as a tundish used in the continuous casting of steel
  • the vessel will normally be of metal, usually steel, lined with refractory material, e.g. brick or a cast refractory concrete.
  • Each outlet is provided by a nozzle positioned in a correspondingly-shaped hole though the floor of the lined vessel. It is conventional practice not to set the nozzle directly into the vessel lining but to set it into a so-called nozzle block, which latter is set into the vessel lining.
  • the invention provides a means of supplying gas into a refractory-lined vessel containing molten metal in which an outlet through the floor of the vessel comprises a nozzle with a centrally-disposed through bore, the nozzle being sealingly set in a nozzle block which is itself sealingly set in the lining of the floor of the vessel, the nozzle block being gas-permeable and having a gas-receiving channel extending around the nozzle, and means to connect the gas-receiving channel to a source of gas.
  • the gas-receiving channel extends completely around the nozzle.
  • Gas, e.g. argon, supplied to the channel escapes upwardly through the porous nozzle block and emerges into the molten metal in the vessel in streams of bubbles rising from the vessel floor around the nozzle.
  • the gas-receiving channel preferably contains a pipe connected to the source of gas, the pipe having perforations or slots, preferably in its upper surface, to allow escape of the gas into the porous nozzle block.
  • the nozzle block may be a shaped refractory brick containing a centrally-disposed hole shaped to receive the nozzle but preferably it is made of a cast refractory cement into which the nozzle is set.
  • the refractory cement may be of any suitable composition, well known per se in the art, but formulated to have the desired degree of porosity.
  • the nozzle block may be designed to have greater porosity above the gas-receiving channel and lesser, e.g. approaching zero, porosity below the gas-receiving channel so as to help to direct the emerging gas upwardly into the molten metal.
  • the porous refractory composition may be, for example, of a high alumina content formulation containing alumina and cement.
  • the alumina content should be at least 65% by weight of the composition, preferably at least 75% and especially in the range 90 to 97% by weight.
  • an area of different composition or porosity e.g. corresponding to the above-described area of lesser porosity, this may also be a cheaper formulation and hence, contain less of the better refractory component, i.e. alumina.
  • part of the alumina may be replaced by an ore such as andalusite and/or bauxite.
  • the construction of the present invention is particularly useful in that it can provide inert gas scouring in the immediate vicinity of the nozzle which, in a tundish, can prevent unwanted build up of deposits such as alumina on the nozzle itself while, moreover, it provides streams of inert gas in a wider region surrounding the nozzle to give, thereby, very effective inclusion-removal in the vessel itself.
  • the metal tundish 10 has a base 11 and sidewalls 12, one only of the latter being shown. It is lined with a permanent refractory lining 13 which is itself covered with an inner, i.e. molten metal-contacting, expendable lining 14. An outlet 15 is provided in the base 11. This can be opened and closed by any conventional means (not shown), for example, by a stopper rod or a slide-gate valve beneath the base.
  • a nozzle block 16 of cast refractory cement is positioned in a suitably-shaped recess in the tundish lining so as to rest on the base 11 surrounding the outlet 15.
  • a nozzle 17 sits in the nozzle block so that its lower portion 17A protrudes below the base 11 of the tundish.
  • Nozzle block 16 is of gas-permeable formulation and contains a feed pipe 18 to receive gas from a source (not shown). Feed pipe 18 runs completely around the interior of the nozzle block so as to surround the nozzle 17. The pipe 18 is conveniently set into the nozzle block as it is cast. The pipe is perforated in the manner indicated above so as to allow gas to escape into the nozzle block 16 and thereby into the interior of the tundish.
  • Escaping gas is indicated by arrows A and B.
  • the upper surface of nozzle block 16 has a horizontal portion 19, which is set above the level of the upper surface 21 of the nozzle 17, and an angled surface 20 which slopes down to the level of the nozzle surface 21.
  • Gas stream A escapes from horizontal surface 19 and rises vertically to capture inclusions in the molten metal contained in the tundish.
  • Gas stream B escapes upwardly and inwardly over the upper surface 21 of nozzle 17 and thereby helps to scour the nozzle of alumina or other deposits that would otherwise form on the nozzle.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Continuous Casting (AREA)
  • Manufacture And Refinement Of Metals (AREA)

Abstract

Unwanted solid, non-metallic inclusions are removed from molten metal in a refractory-lined vessel by bubbling inert gas upwardly through the metal.
The invention provides a gas permeable nozzle block (16) shaped to contain a nozzle (17) with a centrally-disposed through bore and to be sealingly set in the refractory lining (13) of a vessel (10) to contain molten metal, the nozzle block (16) having a gas-receiving channel (18) to extend around the nozzle (17) and means to connect the gas-receiving channel (18) to a source of gas.

Description

  • This invention relates to a means for the purification of molten metal, i.e. the removal of unwanted solid non-metallic inclusions contained in the molten metal.
  • The need to provide 'clean' metals, e.g. steel, is well known and many methods have been proposed to that end. One well known general technique is to bubble an inert gas through the molten metal, the gas removing inclusions with which it comes into contact by floating them up to the surface of the molten metal.
  • Various means have been proposed in order to provide the desired stream of inert gas bubbles through the molten metal.
  • For example, EP-A-404641 discloses the use in a tundish of a gas duct set into the permanent refractory lining and leading to a gas distribution chamber in the bottom of, and extending across, the tundish, the chamber being covered with a gas-permeable plate.
  • GB-A-2164281 discloses the use of a porous refractory tile extending across the width of, and sitting on the floor of, a tundish, the tile containing a gas conduit with a plurality of exits to deliver gas into the tile.
  • EP-A-0239257 discloses passing steel in a tundish through an apertured upright board, while introducing an inert gas at the foot of the board at its upstream side to cause a stream of bubbles to flow over its upstream side.
  • EP-A-0059805 discloses the use of a porous nozzle in the bottom of a molten metal vessel, the nozzle having a flanged upper portion and cylindrical lower portion, its body being enclosed in a gas tight steel shell, with means to provide gas into the porous nozzle to escape into the molten metal in the vessel.
  • The present invention aims to provide an improved means of bubbling gas into molten metal in the region of a nozzle in the bottom of a molten metal vessel.
  • In a molten metal vessel, such as a tundish used in the continuous casting of steel, it is usual practice to have one or more outlets in the bottom of the vessel, which can be opened to allow the metal to empty out. The vessel will normally be of metal, usually steel, lined with refractory material, e.g. brick or a cast refractory concrete. Each outlet is provided by a nozzle positioned in a correspondingly-shaped hole though the floor of the lined vessel. It is conventional practice not to set the nozzle directly into the vessel lining but to set it into a so-called nozzle block, which latter is set into the vessel lining.
  • We have now found that an improved means of removing inclusions can be provided by utilising the nozzle block surrounding the nozzle as the conduit for inert gas into the vessel.
  • Accordingly, the invention provides a means of supplying gas into a refractory-lined vessel containing molten metal in which an outlet through the floor of the vessel comprises a nozzle with a centrally-disposed through bore, the nozzle being sealingly set in a nozzle block which is itself sealingly set in the lining of the floor of the vessel, the nozzle block being gas-permeable and having a gas-receiving channel extending around the nozzle, and means to connect the gas-receiving channel to a source of gas.
  • Preferably, the gas-receiving channel extends completely around the nozzle.
  • Gas, e.g. argon, supplied to the channel escapes upwardly through the porous nozzle block and emerges into the molten metal in the vessel in streams of bubbles rising from the vessel floor around the nozzle.
  • The gas-receiving channel preferably contains a pipe connected to the source of gas, the pipe having perforations or slots, preferably in its upper surface, to allow escape of the gas into the porous nozzle block.
  • The nozzle block may be a shaped refractory brick containing a centrally-disposed hole shaped to receive the nozzle but preferably it is made of a cast refractory cement into which the nozzle is set. The refractory cement may be of any suitable composition, well known per se in the art, but formulated to have the desired degree of porosity.
  • If desired the nozzle block may be designed to have greater porosity above the gas-receiving channel and lesser, e.g. approaching zero, porosity below the gas-receiving channel so as to help to direct the emerging gas upwardly into the molten metal.
  • The porous refractory composition may be, for example, of a high alumina content formulation containing alumina and cement. The alumina content should be at least 65% by weight of the composition, preferably at least 75% and especially in the range 90 to 97% by weight. Where an area of different composition or porosity is used, e.g. corresponding to the above-described area of lesser porosity, this may also be a cheaper formulation and hence, contain less of the better refractory component, i.e. alumina. Thus, part of the alumina may be replaced by an ore such as andalusite and/or bauxite.
  • The construction of the present invention is particularly useful in that it can provide inert gas scouring in the immediate vicinity of the nozzle which, in a tundish, can prevent unwanted build up of deposits such as alumina on the nozzle itself while, moreover, it provides streams of inert gas in a wider region surrounding the nozzle to give, thereby, very effective inclusion-removal in the vessel itself.
  • One embodiment of the invention is illustrated in the accompanying drawing, which is a cross-section through a portion of a tundish in the region of an outlet.
  • The metal tundish 10 has a base 11 and sidewalls 12, one only of the latter being shown. It is lined with a permanent refractory lining 13 which is itself covered with an inner, i.e. molten metal-contacting, expendable lining 14. An outlet 15 is provided in the base 11. This can be opened and closed by any conventional means (not shown), for example, by a stopper rod or a slide-gate valve beneath the base.
  • A nozzle block 16 of cast refractory cement is positioned in a suitably-shaped recess in the tundish lining so as to rest on the base 11 surrounding the outlet 15. A nozzle 17 sits in the nozzle block so that its lower portion 17A protrudes below the base 11 of the tundish.
  • Nozzle block 16 is of gas-permeable formulation and contains a feed pipe 18 to receive gas from a source (not shown). Feed pipe 18 runs completely around the interior of the nozzle block so as to surround the nozzle 17. The pipe 18 is conveniently set into the nozzle block as it is cast. The pipe is perforated in the manner indicated above so as to allow gas to escape into the nozzle block 16 and thereby into the interior of the tundish.
  • Escaping gas is indicated by arrows A and B. As shown, the upper surface of nozzle block 16 has a horizontal portion 19, which is set above the level of the upper surface 21 of the nozzle 17, and an angled surface 20 which slopes down to the level of the nozzle surface 21. Gas stream A escapes from horizontal surface 19 and rises vertically to capture inclusions in the molten metal contained in the tundish. Gas stream B escapes upwardly and inwardly over the upper surface 21 of nozzle 17 and thereby helps to scour the nozzle of alumina or other deposits that would otherwise form on the nozzle.

Claims (22)

  1. A refractory-lined vessel to contain molten metal having an outlet through its floor and comprising a nozzle with a centrally-disposed through bore, the nozzle being sealingly set in a nozzle block which is itself sealingly set in the lining of the floor of the vessel whereby the outlet is defined, the nozzle block being gas-permeable and having a gas-receiving channel extending around the nozzle, and means to connect the gas-receiving channel to a source of gas.
  2. A refractory-lined vessel according to Claim 1, in which the gas-receiving channel extends completely around the nozzle.
  3. A refractory-lined vessel according to Claim 1 or 2, in which the gas-receiving channel contains a pipe having perforations in its upper surface.
  4. A refractory-lined vessel according to Claim 1, 2, or 3, in which the nozzle block is a shaped refractory brick having a centrally-disposed bore to receive the nozzle.
  5. A refractory-lined vessel according to Claim 1, 2 or 3, in which the nozzle block is of cast refractory cement into which the nozzle is set.
  6. A refractory-lined vessel according to any preceding claim, in which the nozzle block has greater porosity above the gas-receiving channel than below it.
  7. A refractory-lined vessel according to Claim 6, in which the nozzle block is substantially non-porous below the gas-receiving channel.
  8. A refractory-lined vessel according to any preceding claim, in which the composition of the nozzle block comprises at least 75% by weight of alumina.
  9. A refractory-lined vessel according to Claim 8, in which the composition of the nozzle block comprises from 90 to 97% by weight of alumina.
  10. A refractory-lined vessel according to Claim 6, 7, 8 or 9, in which the nozzle block comprises a composition of at least 75% by weight of alumina above the gas-receiving channel and a composition containing less alumina below the gas-receiving channel.
  11. A gas permeable nozzle block shaped to contain a nozzle with a centrally-disposed through bore and to be sealingly set in the refractory lining of a vessel to contain molten metal, the nozzle block having a gas-receiving channel to extend around the nozzle and means to connect the gas-receiving channel to a source of gas.
  12. A nozzle block according to Claim 11, in which the gas-receiving channel extends completely around the nozzle.
  13. A nozzle block according to Claim 11 or 12, in which the gas-receiving channel contains a pipe having perforations in its upper surface.
  14. A nozzle block according to Claim 11, 12 or 13, in which the nozzle block is a shaped refractory brick having a centrally-disposed bore to receive the nozzle.
  15. A nozzle block according to Claim 11, 12 or 13, in which the nozzle block is of cast refractory cement into which the nozzle is set.
  16. A nozzle block according to any one of claims 11 to 15, in which the nozzle block has greater porosity above the gas-receiving channel than below it.
  17. A nozzle block according to Claim 16, in which the nozzle block is substantially non-porous below the gas-receiving channel.
  18. A nozzle block according to any one of Claims 11 to 17, in which the composition of the nozzle block comprises at least 75% by weight of alumina.
  19. A nozzle block according to Claim 18, in which the composition of the nozzle block comprises from 90 to 97% by weight of alumina.
  20. A nozzle block according to Claim 16, 17, 18 or 19, in which the nozzle block comprises a composition of at least 75% by weight of alumina above the gas-receiving channel and a composition containing less alumina below the gas-receiving channel.
  21. A refractory-lined vessel to contain molten metal substantially as hereinbefore described with reference to and as shown in the accompanying drawing.
  22. A gas-permeable nozzle block substantially as hereinbefore described with reference to and as shown in the accompanying drawing.
EP19930304736 1992-06-18 1993-06-17 Purifying molten metal Expired - Lifetime EP0576212B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9212953 1992-06-18
GB929212953A GB9212953D0 (en) 1992-06-18 1992-06-18 Purifying molten metal

Publications (3)

Publication Number Publication Date
EP0576212A2 true EP0576212A2 (en) 1993-12-29
EP0576212A3 EP0576212A3 (en) 1994-11-23
EP0576212B1 EP0576212B1 (en) 1999-04-14

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EP19930304736 Expired - Lifetime EP0576212B1 (en) 1992-06-18 1993-06-17 Purifying molten metal

Country Status (4)

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EP (1) EP0576212B1 (en)
DE (1) DE69324408T2 (en)
ES (1) ES2132188T3 (en)
GB (2) GB9212953D0 (en)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5723055A (en) * 1995-10-10 1998-03-03 Vesuvius Crucible Company Nozzle assembly having inert gas distributor
WO2000050190A1 (en) * 1999-02-22 2000-08-31 Foseco International Limited Tundish impact pad
WO2004035249A1 (en) * 2002-10-16 2004-04-29 Vesuvius Crucible Company Permeable refractory material for a gas purged nozzle
EP2025431A1 (en) * 2007-08-17 2009-02-18 LLC "TMT" Peresechenie Logoiskiy tr&MKAD Device for metal refining in the pony ladle
DE102008015323A1 (en) * 2008-03-20 2009-10-01 Raadts, Monika Distributor device for continuous casting
KR100986053B1 (en) 2008-09-23 2010-10-08 조선내화 주식회사 Well block for molten metal molding
JP2023515903A (en) * 2020-07-25 2023-04-14 莱蕪鋼鉄集団銀山型鋼有限公司 Breathable Nozzle Receiving Brick with Microporous Ceramic Rod for LF Refining Ladle, and Argon Gas Blowing Control Method Therefor

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19520897C1 (en) * 1995-06-01 1996-10-31 Mannesmann Ag Continuous casting distribution channel
EP1243361A1 (en) * 2001-03-19 2002-09-25 Vesuvius Crucible Company Apparatus for injecting gas into molten metal
CL2010000833A1 (en) * 2010-08-05 2010-12-03 Bezanilla Y Cia Ltda Automated mechanism of melting of molten metal from melting and conversion furnaces, with a refractory block interspersed in a wall with a conical orifice, a guillotine valve and a refractory cone assembly that has an internal perforation, and a pipe and injection system Of gas; associated process.
JP2021049564A (en) * 2019-09-26 2021-04-01 黒崎播磨株式会社 Tundish upper nozzle structure and method of continuous casting

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1601944A (en) * 1978-03-14 1981-11-04 Glocast Products Ltd Well blocks for ladles
FR2516415A1 (en) * 1981-11-13 1983-05-20 Daussan & Co DEVICE FOR REMOVING THE INCLUSIONS CONTAINED IN LIQUID METALS
JPS59211522A (en) * 1983-05-13 1984-11-30 Harima Refract Co Ltd Porous plug
GB2149699A (en) * 1983-11-18 1985-06-19 Uss Eng & Consult Method and apparatus for avoiding vortexing in a bottom pour vessel
EP0187924A1 (en) * 1984-11-26 1986-07-23 Cometus AG Process and ladle for gas purging molten metals

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GB1493880A (en) * 1975-03-08 1977-11-30 Flogates Ltd Pouring of metals
GB2164281A (en) * 1984-09-18 1986-03-19 Dresser Ind Tundish with gas injection tile
GB8703717D0 (en) * 1987-02-18 1987-03-25 Injectall Ltd Injecting gas into metal melts
IN168760B (en) * 1987-04-10 1991-06-01 Injectall Ltd
SE8702601L (en) * 1987-06-23 1988-12-24 Hoeganaes Ab METALLURGICAL NOZZLE
DE4012952C2 (en) * 1990-04-24 1995-03-23 Didier Werke Ag Gas purging device on a metallurgical vessel
JPH0510443U (en) * 1991-07-29 1993-02-09 東京窯業株式会社 Gas injection plug

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1601944A (en) * 1978-03-14 1981-11-04 Glocast Products Ltd Well blocks for ladles
FR2516415A1 (en) * 1981-11-13 1983-05-20 Daussan & Co DEVICE FOR REMOVING THE INCLUSIONS CONTAINED IN LIQUID METALS
JPS59211522A (en) * 1983-05-13 1984-11-30 Harima Refract Co Ltd Porous plug
GB2149699A (en) * 1983-11-18 1985-06-19 Uss Eng & Consult Method and apparatus for avoiding vortexing in a bottom pour vessel
EP0187924A1 (en) * 1984-11-26 1986-07-23 Cometus AG Process and ladle for gas purging molten metals

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Derwent Publications Ltd., London, GB; AN 85-015337 & JP-A-59 211 522 (HARIMA TAIKA RENGA) 30 November 1984 *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5723055A (en) * 1995-10-10 1998-03-03 Vesuvius Crucible Company Nozzle assembly having inert gas distributor
WO2000050190A1 (en) * 1999-02-22 2000-08-31 Foseco International Limited Tundish impact pad
WO2004035249A1 (en) * 2002-10-16 2004-04-29 Vesuvius Crucible Company Permeable refractory material for a gas purged nozzle
EP2025431A1 (en) * 2007-08-17 2009-02-18 LLC "TMT" Peresechenie Logoiskiy tr&MKAD Device for metal refining in the pony ladle
DE102008015323A1 (en) * 2008-03-20 2009-10-01 Raadts, Monika Distributor device for continuous casting
KR100986053B1 (en) 2008-09-23 2010-10-08 조선내화 주식회사 Well block for molten metal molding
JP2023515903A (en) * 2020-07-25 2023-04-14 莱蕪鋼鉄集団銀山型鋼有限公司 Breathable Nozzle Receiving Brick with Microporous Ceramic Rod for LF Refining Ladle, and Argon Gas Blowing Control Method Therefor
JP7299430B2 (en) 2020-07-25 2023-06-27 莱蕪鋼鉄集団銀山型鋼有限公司 Breathable Nozzle Receiving Brick with Microporous Ceramic Rod for LF Refining Ladle, and Argon Gas Blowing Control Method Therefor

Also Published As

Publication number Publication date
GB9312074D0 (en) 1993-07-28
ES2132188T3 (en) 1999-08-16
DE69324408D1 (en) 1999-05-20
GB2267855B (en) 1995-09-20
DE69324408T2 (en) 1999-12-16
GB9212953D0 (en) 1992-07-29
EP0576212A3 (en) 1994-11-23
GB2267855A (en) 1993-12-22
EP0576212B1 (en) 1999-04-14

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