EP0453188A2 - Réchauffage du plasma utilisé dans un tundish - Google Patents

Réchauffage du plasma utilisé dans un tundish Download PDF

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Publication number
EP0453188A2
EP0453188A2 EP91303238A EP91303238A EP0453188A2 EP 0453188 A2 EP0453188 A2 EP 0453188A2 EP 91303238 A EP91303238 A EP 91303238A EP 91303238 A EP91303238 A EP 91303238A EP 0453188 A2 EP0453188 A2 EP 0453188A2
Authority
EP
European Patent Office
Prior art keywords
plasma
tundish
torch
argon
helium
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.)
Withdrawn
Application number
EP91303238A
Other languages
German (de)
English (en)
Other versions
EP0453188A3 (en
Inventor
Colin Moore
Charles Peter Heanley
Peter Malcolm Cowx
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.)
BOC Group Ltd
Original Assignee
BOC Group 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 BOC Group Ltd filed Critical BOC Group Ltd
Publication of EP0453188A2 publication Critical patent/EP0453188A2/fr
Publication of EP0453188A3 publication Critical patent/EP0453188A3/en
Withdrawn legal-status Critical Current

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal

Definitions

  • This invention relates to a method and apparatus for heating.
  • it relates to the heating of molten metal in a tundish by means of a thermal plasma.
  • a thermal plasma is a gas of sufficient energy content that a significant fraction of the species present are ionised permitting the conduction of electrical energy.
  • Thermal plasmas are used in for example smelting ores. Energy from a transferred arc torch is typically transferred directly to the ore being smelted, although if desired, a non-transferred arc torch can be used to heat a large volume of gas which in turn is used to heat a feedstock.
  • the electrode of the plasma torch is typically mounted within a framework on the top of the furnace and passes through a sleeve arrangement in the lid, allowing the length of the electrode on the underside to be varied according to the operating level within the furnace.
  • a gas used to form the plasma is argon.
  • Tundishes are widely used in the continuous casting of steel to transfer the molten steel from a vessel, for example a ladle, to the casting machines.
  • the temperature of the molten metal can fall by up to 25°C in the tundish. The effect of this temperature fall can be to produce a variable micro structure in the resulting steel.
  • the grain size may be particularly affected. Where a fine grain size is needed it may not be possible to maintain the metallurgically desirable low level of super heat in the ladle for fine grain structure without employing a means of heating the molten metal in the tundish.
  • Heating the molten metal in the tundish by means of a thermal plasma offers two main advantages. First, the ladle tapping temperature can be reduced saving costs on power and electrodes and reducing the interval of time between consecutive batches. Second, it permits the required tundish temperatures to be held throughout casting to improve the quality and the fineness and consistency of grain size.
  • a method of heating molten material in a tundish by means of a thermal plasma wherein the plasma is of a gas comprising a mixture of argon and one or more of nitrogen, hydrogen, neon and helium.
  • a proportion of nitrogen, neon, helium or hydrogen in the gas from which the plasma is formed increases the voltage for a given arc length and given amperage and hence increases power. Accordingly, a shorter arc length preferably in the range 20 to 45 cm can be employed without loss of power and without increasing the amperage.
  • the order of effectiveness is nitrogen > hydrogen > neon > helium.
  • Nitrogen is however suitable only for use with some steels, hydrogen is generally undesirable for most metallurgical applications, while neon is particularly expensive. Accordingly, helium is usually the additional gas of choice for steel and some non-ferrous metals (e.g. aluminium), and nitrogen for other non-ferrous metals.
  • a gas mixture comprising 50 to 95% by volume of argon and 5 to 50% by volume of helium or nitrogen is employed to form the plasma. More preferably, the mixture comprises 80 to 90% by volume of argon and 10 to 20% by volume of helium or nitrogen.
  • the plasma torch preferably comprises a generally, vertical electrode, typically hollow, detachably engaging a generally horizontal support arm which is employed to carry the electrode services, typically comprising the plasma gas, electrical power cable and cooling water for the electrodes.
  • the support arm is preferably pivotally mounted on an extensible support, e.g. a pillar.
  • the invention also provides apparatus for heating molten metal in a tundish including a plasma torch comprising a generally vertical electrode detachably engaging a generally horizontal support arm carrying necessary services to the electrode, the support arm being pivotally mounted on an extensible support.
  • more than one plasma torch may be employed to heat the molten metal therein.
  • a ladle 2 mounted on a turret has a tapping outlet 4 which terminates beneath the level of molten metal in a tundish 6.
  • the tundish is provided with a plasma radiation shroud 8 through which extends the end of a transferred arc plasma torch 10.
  • Means may be provided for adjusting the height of the tip of the torch 10 above the level of molten metal 12 in the tundish 6.
  • the torch 10 typically comprises a hollow cathodic electrode made of copper.
  • the electrode is preferably formed with passages (not shown) in its wall for the circulation of a liquid coolant typically water. It is also provided with an electrical power supply by means not shown in Figure 1.
  • the gas from which the plasma is formed is supplied to the hollow interior of the torch 10.
  • the plasma gas comprises a mixture of argon and one or more of nitrogen, helium, hydrogen and neon.
  • the gas mixture preferably comprises argon and helium.
  • the tundish is provided with an anode return which may be a plate of steel built into an appropriate dummy wall in the tundish.
  • anode return which may be a plate of steel built into an appropriate dummy wall in the tundish.
  • a dip graphite electrode may be used for this purpose.
  • the tundish 6 is filled from the ladle 2 via the submerged outlet 4.
  • Stopper or starter cones can be used to prevent mould feeding from the tundish until the operating level of steel in the tundish has been reached. This is usually at a depth of 400 to 800 mm in a 1000 mm deep tundish.
  • Heating can be effected by striking an arc between the tip of the torch 10 and the molten metal in the tundish 6.
  • the power to the individual torch may be varied by control of arc current using a thyristor rectifier unit (not shown) with a smoothing reactance. Then, the arc length is set and the out voltage finds its own value from the particular system.
  • the given arc length for a given voltage and amperage will vary according to the particular characteristics of the apparatus used, but for any given apparatus in a particular environment, the arc length for a given voltage and amperage may be reduced by including a greater proportion of the additional gas (one or more of helium, nitrogen, neon and hydrogen) in the gas mixture with argon. If the apparatus gives an arc length of some 300 mm for a given voltage and amperage when argon is the sole plasma gas, then by using a gas mixture in accordance with the invention containing up to 50% by volume of helium, the arc length may be reduced by up to 40% for a given voltage (or the voltage similarly increased for a given arc length). For example, with an arc length of 300mm it is possible to increase the voltage from 120V to 150 to 180V by using as the plasma an argon-helium gas mixture containing from 10 to 20% by volume of helium.
  • the additional gas one or more of helium, nitrogen, neon and hydrogen
  • the method according to the invention it is generally not necessary to use the method according to the invention to heat the molten metal in the tundish continuously.
  • the steel will tend to be cool and the method according to the invention may be used at this stage because of the low steel temperature and high filling rate. Full depth in the tundish is typically reached generally in 5 to 10 minutes.
  • the method according to the invention need not be used to apply extra heating. As it cools at the end of the ladle, the method according to the invention is applied to prevent such cooling resulting in a lowering of the temperature.
  • the temperature can typically be controlled within + or - 5°C.
  • the plasma torch 10 typically has a power up to 1.25 MW and operate with a current in the range of 1000 to 8000 amps DC and a voltage of 100 to 200 volts DC. It may typically be supplied with the plasma gas at pressure (say 3 atmospheres) at a rate of 25 to 50 l per minute per 1000 A.
  • the length of the cathodic electrode may typically be in the range 1000 to 2000 mm, and it may typically have a diameter in the order 50 to 100 mm.
  • a deionised water coolant may be employed typically at elevated pressure (for example in the range 10 to 15 bar) with a coolant flow rate of 50 to 200 l per minute.
  • the torch includes a hollow tubular vertically disposed electrode body 20 engaged in a plasma head 22.
  • the body 20 may engage the head 22 by means of a push fit, the body 20 being retained in the head 20 by means of a jubilee or other clip 24.
  • a jubilee or other clip 24 By this means, quick electrode changes are possible, with all the electrode services connections being broken and re-made merely by loosening the retaining clip 24, removing the old electrode 20, inserting the replacement and tightening the clip.
  • the electrode head 24 forms part of a pivotally mounted rigid hollow arm 26 which carries the services to the torch. (These services are not shown in Figure 2A and 2B.)
  • the services comprise plasma gas, cooling water flowing to and from the electrode 20, and electricity.
  • the services are connected to the electrode head 22 typically by means of flexible tubing and conductors. Such flexible tubing and conductors exit the opposite end of the arm 26 and may be connected to the necessary sources of supply (not shown in Figures 2A and 2B) with sufficient slack to enable the electrode to be lowered and raised, and the arm rotated to and from the working site.
  • the services may be taken through the arm 26 using metal or other relatively inflexible pipework and suitably insulated electrical bus bars for connecting manifold at the pivoted end of the arm remote from the electrode head.
  • the arm 26 is pivoted to an extensible support pillar 28.
  • the arrangement is such that the electrode body 20 may be swung into and out of position over a tundish (not shown in Figures 2A and 2B), while the height of the support pillar 28 may be adjusted in accordance with the desired arc length between the tip of the electrode 20 and the tundish.
  • the tip of the electrode 20 may be fabricated from thoriated tungsten.
  • the tip may be attached to the body 20 (which is typically made of copper) by means of soldering using a silver solder.
  • FIG. 3 of the drawings illustrates the services supplied to an apparatus for use in performing the method according to the invention where two separate plasma torches are used to heat the metal in the tundish.
  • tundish 40 provided with torches 42 and 44 at either end.
  • the torches respectively have service manifolds 46 and 48.
  • the manifolds 46 and 48 receive a DC electricity supply via means comprising high voltage switch gear 50, a transformer 52, and a thyristor rectifier 54 having a smoothing reactance.
  • the electrical power is supplied from the rectifier 54 to the torches 42 and 44 via the manifolds 46 and 48 with current return being provided by anodes 56 and 58 associated with the tundish 40.
  • the rectifier 54 will also typically be associated with a control box 60 (which if desired may be located in a control room (not shown)) which may be used to adjust the rectifier appropriately.
  • the manifolds 46 and 48 are also associated with respective high frequency start units 62 and 64 which are operable to enable an arc to be struck between the respective torch and the molten metal in the tundish 40.
  • Each torch manifold 46 and 48 also receives a flow of cold water via conduit 70 and 72 respectively and returns the cooling water via conduit 74 and 76.
  • the manifolds 46 and 48 each receive a supply of plasma gas via conduit.
  • the torch is cathodic. It is however possible to use alternatively an anodic torch (particularly for example in the melting of titanium). It is also possible to use more than one torch to heat the molten material.
EP19910303238 1990-04-19 1991-04-11 Plasma tundish heating Withdrawn EP0453188A3 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9008833 1990-04-19
GB909008833A GB9008833D0 (en) 1990-04-19 1990-04-19 Heating

Publications (2)

Publication Number Publication Date
EP0453188A2 true EP0453188A2 (fr) 1991-10-23
EP0453188A3 EP0453188A3 (en) 1993-04-28

Family

ID=10674679

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19910303238 Withdrawn EP0453188A3 (en) 1990-04-19 1991-04-11 Plasma tundish heating

Country Status (7)

Country Link
EP (1) EP0453188A3 (fr)
JP (1) JPH05305422A (fr)
KR (1) KR910019483A (fr)
CN (1) CN1057416A (fr)
AU (1) AU7500291A (fr)
GB (1) GB9008833D0 (fr)
ZA (1) ZA912855B (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2666819A1 (fr) * 1990-09-19 1992-03-20 Inst Aluminievoi Magnievoi Procede et dispositif pour fabriquer un materiau composite a partir d'un metal de base.
EP0627275A2 (fr) * 1993-05-27 1994-12-07 Ishikawajima-Harima Heavy Industries Co., Ltd. Coulée de bandes métalliques
GB2306361A (en) * 1995-10-16 1997-05-07 Ishikawajima Harima Heavy Ind Heating molten metal using plasma torch an adjustable electrode
FR2762535A1 (fr) * 1997-04-23 1998-10-30 Lorraine Laminage Repartiteur de coulee continue des metaux, du type comportant au moins une torche a plasma pour le rechauffage du metal
FR2767081A1 (fr) * 1997-08-11 1999-02-12 Lorraine Laminage Procede de rechauffage d'un metal liquide dans un repartiteur de coulee continue au moyen d'une torche a plasma, et repartiteur pour sa mise en oeuvre

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6760036B2 (ja) * 2016-12-16 2020-09-23 日本製鉄株式会社 プラズマ加熱装置における黒鉛電極の異常放電抑制方法
CN111136253B (zh) * 2020-01-13 2021-01-08 北京科技大学 一种中间包钢液的等离子加热方法和等离子加热系统
CN113714495B (zh) * 2020-05-25 2022-11-11 上海梅山钢铁股份有限公司 连铸中间包直流等离子电弧加热控制方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6024333A (ja) * 1983-07-21 1985-02-07 Daido Steel Co Ltd 金属等の溶融方法
EP0216398A1 (fr) * 1985-09-23 1987-04-01 METALLURGIE HOBOKEN-OVERPELT Société anonyme dite: Procédé pour préparer du tantale ou du niobium affiné
EP0232961A1 (fr) * 1986-01-10 1987-08-19 Plasma Energy Corporation Procédé et appareil pour chauffer des bains d'acier en utilisant une torche à plasma

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6024333A (ja) * 1983-07-21 1985-02-07 Daido Steel Co Ltd 金属等の溶融方法
EP0216398A1 (fr) * 1985-09-23 1987-04-01 METALLURGIE HOBOKEN-OVERPELT Société anonyme dite: Procédé pour préparer du tantale ou du niobium affiné
EP0232961A1 (fr) * 1986-01-10 1987-08-19 Plasma Energy Corporation Procédé et appareil pour chauffer des bains d'acier en utilisant une torche à plasma

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Section Ch, Week 7820, Derwent Publications Ltd., London, GB; Class M22, AN 78-35386A *
PATENT ABSTRACTS OF JAPAN vol. 16, no. 34 (M-1204)28 January 1992 & JP-A-32 43 254 ( NKK CORP ) 30 October 1991 *
PATENT ABSTRACTS OF JAPAN vol. 9, no. 138 (C-286)13 June 1985 & JP-A-60 024 333 ( DAIDO TOKUSHUKO KK ) 7 February 1985 *
STEEL TIMES INTERNATIONAL - INCORPORATING IRON & STEEL INTERNATIONAL vol. 13, no. 2, May 1989, ENGLAND GB pages 44 - 46 , XP46437 C.MOORE 'plasma tundish heating as an integral part of continuous casting' *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2666819A1 (fr) * 1990-09-19 1992-03-20 Inst Aluminievoi Magnievoi Procede et dispositif pour fabriquer un materiau composite a partir d'un metal de base.
EP0627275A2 (fr) * 1993-05-27 1994-12-07 Ishikawajima-Harima Heavy Industries Co., Ltd. Coulée de bandes métalliques
EP0627275A3 (fr) * 1993-05-27 1996-02-28 Ishikawajima Harima Heavy Ind Coulée de bandes métalliques.
GB2306361A (en) * 1995-10-16 1997-05-07 Ishikawajima Harima Heavy Ind Heating molten metal using plasma torch an adjustable electrode
GB2306361B (en) * 1995-10-16 1999-06-30 Ishikawajima Harima Heavy Ind Heating molten metal
FR2762535A1 (fr) * 1997-04-23 1998-10-30 Lorraine Laminage Repartiteur de coulee continue des metaux, du type comportant au moins une torche a plasma pour le rechauffage du metal
EP0875319A1 (fr) * 1997-04-23 1998-11-04 Sollac Répartiteur de coulée continue des métaux, du type comportant au moins une torche à plasma pour le réchauffage du métal
US6110416A (en) * 1997-04-23 2000-08-29 Sollac Tundish for continuous casting of metals having at least one plasma torch for reheating the metal
FR2767081A1 (fr) * 1997-08-11 1999-02-12 Lorraine Laminage Procede de rechauffage d'un metal liquide dans un repartiteur de coulee continue au moyen d'une torche a plasma, et repartiteur pour sa mise en oeuvre
EP0897770A1 (fr) * 1997-08-11 1999-02-24 Sollac Procédé de réchauffage d'un métal liquide dans un répartiteur de coulée continue au moyen d'une torche à plasma, et répartiteur pour sa mise en oeuvre
US5963579A (en) * 1997-08-11 1999-10-05 Sollac Method of heating a molten metal in a continuous casting tundish using a plasma torch, and tundish for its implementation

Also Published As

Publication number Publication date
CN1057416A (zh) 1992-01-01
KR910019483A (ko) 1991-11-30
GB9008833D0 (en) 1990-06-13
ZA912855B (en) 1992-04-29
AU7500291A (en) 1991-10-24
JPH05305422A (ja) 1993-11-19
EP0453188A3 (en) 1993-04-28

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