EP0145219B1 - Improved electrode assembly for electric arc furnaces - Google Patents
Improved electrode assembly for electric arc furnaces Download PDFInfo
- Publication number
- EP0145219B1 EP0145219B1 EP84307459A EP84307459A EP0145219B1 EP 0145219 B1 EP0145219 B1 EP 0145219B1 EP 84307459 A EP84307459 A EP 84307459A EP 84307459 A EP84307459 A EP 84307459A EP 0145219 B1 EP0145219 B1 EP 0145219B1
- Authority
- EP
- European Patent Office
- Prior art keywords
- sleeve
- furnace
- electrode
- seal
- passageway
- 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.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B7/00—Heating by electric discharge
- H05B7/02—Details
- H05B7/12—Arrangements for cooling, sealing or protecting electrodes
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B7/00—Heating by electric discharge
- H05B7/02—Details
- H05B7/10—Mountings, supports, terminals or arrangements for feeding or guiding electrodes
Definitions
- a useful degree of shielding and cooling of a vulnerable portion of the electrode is achieved, without in any way obstructing normal advance of the electrode through the clamp, and without obstructing vertical movement of the electrode. It is unnecessary to insulate the sleeve electrically from the electrode clamp, and unnecessary and undesirable to provide guides for the electrode within the sleeve.
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Vertical, Hearth, Or Arc Furnaces (AREA)
- Discharge Heating (AREA)
- Furnace Details (AREA)
Abstract
Description
- This invention relates to improvements in electrode assemblies for electric arc furnaces, particularly but not exclusively arc furnaces used for steel making.
- In a widely used form of electric arc furnace, several, usually three, consumable graphite electrodes extend substantially vertically downwardly from electrode clamps, through apertures in the roof of the furnace (if a roof is provided) and into the furnace charge. In order to strike and maintain a proper arc during operation of the furnace, it is necessary to allow for significant vertical movement of the individual electrodes, whilst in the case of steel making furnaces, it must be possible to withdraw the electrodes sufficiently upward relative to the furnace roof to allow the latter to be swung clear of the remainder of the furnace structure. It must also be possible to feed the electrode downwardly relative to the clamp to compensate for erosion of the electrode tip during use.
- Various problems are associated with the facts that a substantial distance separates the effective lower tip of each electrode and its supporting clamp, and that substantial vertical relative movement is necessary between the electrodes and the furnace roof. Gases may escape from the furnace between the electrode and the furnace roof, or if the furnace is operated at subatmospheric pressure, cold air may be drawn in through the same gap. The outer surface of the electrode is subject to erosion through oxidation caused by the hot gases within the furnace, and this problem is aggravated by heating of the electrode caused both by heat from the furnace interior and by electrical heating caused by the electrical resistance of the electrode to the current passing therethrough.
- Two main approaches have been adopted in response to these problems. Firstly, various forms of telescoping seal have been proposed for use between individual electrodes and the furnace roof. For example, in FR-A-1,418,153 (IRSID), a sleeve extending downwardly from the electrode clamp moves vertically in a water filled annular chamber extending upwardly from the furnace roof. In US-A-4,306,726 (Lefebvre) a series of concentric sleeves with sliding seals provides a telescoping gas seal between the electrodes and the furnace roof. Both of these arrangements have the disadvantage that it is not practicable to accommodate the large range of vertical electrode movement required in a steel making furnace, whilst a major part of the weight of the seal structure must be supported by the furnace roof in an area where it is normally sought to avoid unnecessary loadings.
- The second approach has been to seek reduction of heating of the electrode. Numerous proposals have been made for fluid (usually water) cooled electrode structures, which reduce the length of graphite electrodes required. Examples may be found in US-A-4,121,042 and 4,168,392 (Prenn), 4,287,381 (Montgomery), FR-A-1,418,153 referred to above and FR-A-Nos. 2,176,546 and 2,222,821 (IRSID), DE-A-2430817 (Sigri), GB-A-1,223,162 (Ost- berg) and BE-A-867,876 (Korf-Stahl AG). All of these proposals have in common that the cooling arrangement is more or less complex and expensive, and that it is not possible continuously to add additional electrode sections to the top of the electrode to replace erosion from the bottom of the electrode. Rather, the entire electrode assembly must sooner or later be removed in order to replace the tip portion if this is consumable.
- In GB-A-664,298, an arrangement is proposed in which the electrode is supported within a water cooled sleeve, the lower end of which is in electrical contact with the electrode, and the upper end of which is held by the electrode clamp instead of the electrode itself. In this arrangement, the portion of the electrode within the sleeve does not have to transmit electric current, and the outer surface of this same portion is shielded from the electrode gases. In practice, it is extremely difficult to maintain adequate electrical contact between the bottom of the sleeve and the electrode. The arrangement described relies upon external screw threading of the electrode, both for transmitting current and for advancing the electrode through the sleeve, which means that electrodes of conventional design cannot be employed. Moreover, in order to achieve the object of the invention, the sleeve must extend close to the tip of the electrode. This is not practicable in many applications because of the risk that the sleeve will be damaged or destroyed by arcing from the furnace charge. An alternative approach is found described in GB-A-2,000,947A (Korf-Stahl AG) in which a water cooled jacket is provided around the electrode so as to shroud and support the entire electrode apart from the tip. In order to protect the jacket from arcing, it is insulated from the electrode, and provided with a refractory cladding. Additionally, an arc control magnet must be provided so as further to reduce the risk of arcing. The sleeve is supported from an electrode support arm which supports the electrode through a drive mechanism which also must maintain insulation between the electrode and the arm, a separate electrical connection being made to the electrode. It is suggested that the sleeve might be supported from a conductive electrode clamp but in this case some arrangement would be necessary to isolate the sleeve electrically from the clamp. In order to maintain insulation between the sleeve and the electrode it is necessary to provide guides for the electrode within the lower part of the sleeve in a vulnerable position near the tip of the electrode.
- We have found a means of significantly reducing undesirable erosion of consumable electrodes in electric arc furnaces, and where applicable reducing or substantially preventing gas leakage between the electrodes and a furnace roof, whilst permitting a large range of vertical reciprocal movement of the electrode relative thereto, without either unduly stressing the furnace roof or obstructing replacement of consumable electrodes by the coupling of additional electrode elements to the top end of the electrode.
- What constitutes the invention is defined in the following
claim 1. - By using a sleeve depending from an electrode clamp, a useful degree of shielding and cooling of a vulnerable portion of the electrode is achieved, without in any way obstructing normal advance of the electrode through the clamp, and without obstructing vertical movement of the electrode. It is unnecessary to insulate the sleeve electrically from the electrode clamp, and unnecessary and undesirable to provide guides for the electrode within the sleeve.
- Preferably, a furnace according to the invention further includes means for defining a passageway for the electrode through a roof of the furnace, the vertical extent of the sleeve being such that it will extend into the passageway throughout its normal range of movement. This provides some degree of restriction of the gap through which gases may pass around the electrode, and provides some shielding of the roof structure. Apart from the passageway-defining means, no additional load is applied to the furnace roof, and the arrangement is well adapted to the provision of a more effective electrode seal.
- Preferably also an annular seal is provided sliding on the sleeve and providing a seal between the sleeve and the passageway-defining means when the sleeve extends into the latter. In one arrangement means can be provided retaining the seal on the external surface of the sleeve. In an alternative arrangement, the seal is captive at the top of the passageway-defining means and defines a tapered top entry thereto for the bottom end of the sleeve.
- The invention will be further described in the accompanying drawingsin which:-
- Figure 1 is a vertical section through an electric arc furnace incorporating electrode assemblies in accordance with a first embodiment of the invention;
- Figure 2 is a fragmentary view on a larger scale showing additional detail of those portions of the electrode assemblies which differ from conventional practice;
- Figure 3 is a fragmentary view on a still larger scale showing portions of the electrode assembly when the electrode is raised above its normal operating range of movements so as to permit swinging of the upper portion of the furnace to one side;
- Figure 4 is a view of part of an electrode assembly in accordance with a second embodiment of the invention;
- Figure 5 is a view corresponding to Figure 3 and showing the second embodiment;
- Figure 6 is a view corresponding to Figure 4 and showing an electrode assembly in accordance with a third embodiment;
- Figure 7 is a view corresponding to Figure 4 and showing a fourth embodiment;
- Figure 8 is a view corresponding to Figure 3 and showing the fourth embodiment; and
- Figure 9 is a fragmentary vertical section showing parts of a fifth embodiment.
- Referring first to Figure 1, an illustrative
electric arc furnace 2 is shown. Since however the features of the furnace other than the electrode assemblies form no part of the invention, they will not be described in detail. Thefurnace 2 has a roof 4, and arefractory lining 6 for containing a charge which may have amaximum melt level 8. Means (not shown) are provided for swinging the roof 4 and electrode assemblies relative to the furnace, for example so that a fresh charge may be introduced. To permit this, it will be apparent thatelectrode assemblies 10 must be raised to a level such that thelower tips 12 ofelectrodes 14 will clear the remainder of the furnace structure. The electrodes shown are convention consumable electrodes, formed by connectingstandard electrode elements 16 end to end in vertical alignment. The electrodes pass throughconventional electrode clamps 18 which releasably support the electrodes so that the string of electrode elements can be moved through the clamp to compensate for the erosion which occurs attip 12 as the electrode is consumed. Each clamp also served to conduct current to the respective electrode. Particularly during the early stages of a melt, a substantial degree of up and down movement of electrodes may be necessary as an arc is struck and a desired current level maintained, and a further range of movement is necessary to accommodate erosion of the electrode between successive adjustments of theclamps 18. The clamps are supported, by means not shown, so as to provide this normal operating range of movement, together with the additional range of upward movement required when the roof of the furnace is to be swung as described above. To accommodate this movement the electrodes pass throughapertures 20 in a central electricallyinsulative portion 22 of the furnace roof. Although only two electrodes are actually shown in Figure 1, there will normally be a group of three symmetrically placed electrodes, one for each phase of a three phase current supply. - Thus far, the elements described have been entirely conventional, and indeed it is a feature of the invention that it can readily be incorporated into existing furnace installations without major modification of the original structure of the latter. As compared with a conventional furnace structure, each electrode clamp supports a depending water cooled
sleeve 24 which surrounds the portion of theelectrode 14 beneath theclamp 18. The sleeve is supported from the electrode clamps bybolts 26, and aseal 28 is provided to prevent a through flow of gas between the sleeve and the electrode. The sleeve has water inlet and outlet connections 30 (only one is shown), andinternal ribs 32 to strengthen the sleeve and guide the flow of water or alternative cooling fluid within the sleeve to provide effective cooling of the latter. The sleeve is preferably fabricated from non-magnetic stainless 'steel in order to resist corrosion and magnetically induced eddy currents. The vertical extent of the sleeve is such that during normal operation of the furnace, i.e. except during charging and initial start-up, it will at all times extend into theopening 20, as extended in this instance by a water cooledannulus 34 which is supplied with cooling water through connections 36 (again only one is shown). The annulus may also be fabricated from non-magnetic stainless steel. - In order to render unlikely the striking of an arc to the
sleeve 24 and thus damaging it, and to minimize the adherence to the sleeve of material spattered within the furnace, the lower end of the sleeve ends well short of the lower end of the electrode. In practice, the extent of the sleeve should be such that it will never extend down to arcing proximity of a level at which conductive material is found in the furnace. This level will be above themaximum melt level 8 in the furnace by an amount depending on how "quietly" the furnace operates and the nature of the furnace charge. For example, in a furnace used for melting steel scrap, unmolten metallic material could contact the electrode substantially above the melt level, and the same could occur in other operations in which there is violent activity within the furnace. - Even this limited degree of shrouding provides very important advantages. Although the sleeve is dimensioned so that it is loose on the electrode and preferably spaced from it so that it will not obstruct longitudinal movement of the
electrode 14 through theclamp 18, it will shroud the electrode sufficiently to eliminate any substantial sidewall oxidation of the electrode within the sleeve, and will provide significant cooling of this portion of the electrode. Even without the sealing arrangement to be described below, the sleeve will also act to restrict the flow of gases through theopening 20, and will-shield the electrode from this flow. - The provision of the sleeve moreover makes it particularly easy to provide sealing of the
opening 20 in a manner which will not obstruct upward movement of the electrode beyond its normal range of movement when it is desired to swing the furnace roof 4. As best seen in Figure 2, ametallic sealing ring 40 rests on a seating formed by theannulus 34 and supports a hightemperature seal element 42, for example of silica fibre, in sliding contact with the outer surface of thesleeve 24, so as to maintain a substantially gas-tight seal throughout the normal range of movement of the electrodes, this range being illustrated by the electrode assemblies shown in the right and left hand sides respectively of Figures 1 and 2. Since the seal elements slide on the water cooled surface of thesleeve 24, problems that would otherwise occur in maintaining a seal with the hot, rough and irregular surface of the electrode itself are eliminated. Theannulus 34 not only provides a seating for thering 40, but also defines theopening 20 and protects the fabric of the furnace roof. - In order to provide for additional upward movement of the electrode, the sleeve is provided with a
lip 44 at its lower end, which engages the sealingring 40 and lifts it clear of theannulus 34 as shown in Figure 3. The loss of sealing at this stage is not important, since it will usually occur only during short parts of the furnace operating cycle. The ability of the sealingring 40 to lift from theannulus 34 will also prevent theseal 42 from being damaged should foreign matter adhere to the exterior of thesleeve 24. - In some instances it may be desirable to extend the
annulus 34 vertically to provide arrangements such as those shown in Figures 4, 5 and 6. In Figure 4, theannulus 34 is replaced by a water cooled sleeve inportions portion 46 extends through theopening 20, and defines a passageway sufficiently long to shroud thesleeve 24 even when the latter is in its lowermost position. The external surface of theportion 46 of the sleeve extending into the furnace has arefractory coating 50. Such an arrangement may be necessary in some cases to shield thesleeve 24 from exceptionally severe spattering within the furnace. Theportion 48 provides an upward extension of theopening 20 which reduces the extent to which thesleeve 24 needs to project within the furnace. The arrangement of Figures 4 and 5 has the disadvantage that it applies additional loading to the furnace roof, and the simplified arrangement using anannulus 34, or ashorter sleeve 52 as shown in Figure 6, will often be adequate. - It should also be understood that not all electric arc furnaces even have a roof, and in the absence of such a roof, the annulus or sleeve is of course not required.
- Referring now to Figures 7 and 8, an alternative form of
seal 54 is illustrated, which remains captive on theupper portion 56 of two water cooledsleeve portions passage 20 through the furnace roof. The seal comprises anannular seal member 60 defining a frusto-conical passage, the narrow end of which will just pass thesleeve 24. The seal member rest on anannular bearing pad 62 within aholder 64 within which the seal member is urged towards a centred position by locatingpins 66 andspring 68. Thesleeve 24, which in this case lacks alip 44, can withdraw from themember 60 when it is desired to lift the electrode beyond their normal range of movement. The tapered opening at the top of theelement 60, and the centering action of thesprings 68, assist the sleeve to re-enter theseal 60 when the electrode is lowered. Since the interengaging parts are water cooled and shielded from the heat of the furnace, a fairly small clearance is permissible between theseal 60 and thesleeve 24. - Particularly where accumulation of foreign matter on the
sleeve 24 is a problem, the arrangement shown in Figure 9 may be preferred. Here a seal assembly is mounted on the annulus 34 (see Figures 1 and 2), and comprises a plurality of hinged segments 70 (only one is shown), connected byhinges 72 to a mountingring 74 supported on theannulus 34. Each segment carries at its inner end agraphite sealing element 76 which is urged inwardly and upwardly towards thesleeve 24 by acounterweight 80 at the outer end of the segment. The sealing element can, because of its hinged mounting, ride over obstructions on the surface of thesleeve 24 as the electrode moves up and down. The geometry of the arrangement precludes a perfect seal as the segments hinge independently, but a large measure of control can nevertheless be exercised over gas flow into or out of the furnace.
Claims (11)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT84307459T ATE41582T1 (en) | 1983-10-31 | 1984-10-30 | ELECTRODE DEVICE FOR ELECTRIC ARC FURNACES. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US54747483A | 1983-10-31 | 1983-10-31 | |
US547474 | 2000-04-12 |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0145219A1 EP0145219A1 (en) | 1985-06-19 |
EP0145219B1 true EP0145219B1 (en) | 1989-03-15 |
Family
ID=24184776
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP84307459A Expired EP0145219B1 (en) | 1983-10-31 | 1984-10-30 | Improved electrode assembly for electric arc furnaces |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP0145219B1 (en) |
AT (1) | ATE41582T1 (en) |
CA (1) | CA1268200A (en) |
DE (1) | DE3477336D1 (en) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6377605B1 (en) * | 2001-03-02 | 2002-04-23 | Hatch Associates Ltd. | Electrode seal for arc furnace |
KR100648614B1 (en) | 2005-12-09 | 2006-11-23 | 주식회사 포스코 | Electrode rod clamping apparatus with electrode rod cut prevention function |
CN115506033A (en) * | 2022-09-28 | 2022-12-23 | 乌海市京运通新材料科技有限公司 | Thermal field centering structure and centering method of single crystal furnace |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1690795A (en) * | 1923-05-28 | 1928-11-06 | Sagramoso Guido | Electric furnace |
US2551420A (en) * | 1948-04-14 | 1951-05-01 | Siemens Spa Italiana | Gastight electrode seal |
GB809986A (en) * | 1956-04-13 | 1959-03-04 | Sunrod Mfg Corp | Electrode clamp |
DE1030481B (en) * | 1956-09-01 | 1958-05-22 | Demag Elektrometallurgie Gmbh | Deep electrode holder with cylinder holder designed as protective jacket |
US2979550A (en) * | 1959-03-13 | 1961-04-11 | Tennessee Products And Chemica | Electrode seal |
US3835233A (en) * | 1973-12-07 | 1974-09-10 | Canada Steel Co | Electrode seals for electric-arc furnaces |
-
1984
- 1984-10-15 CA CA000465467A patent/CA1268200A/en not_active Expired - Fee Related
- 1984-10-30 DE DE8484307459T patent/DE3477336D1/en not_active Expired
- 1984-10-30 AT AT84307459T patent/ATE41582T1/en active
- 1984-10-30 EP EP84307459A patent/EP0145219B1/en not_active Expired
Also Published As
Publication number | Publication date |
---|---|
ATE41582T1 (en) | 1989-04-15 |
DE3477336D1 (en) | 1989-04-20 |
CA1268200A (en) | 1990-04-24 |
EP0145219A1 (en) | 1985-06-19 |
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