GB2098839A - Electrode for arc furnace and method of producing steel - Google Patents

Electrode for arc furnace and method of producing steel Download PDF

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Publication number
GB2098839A
GB2098839A GB8209202A GB8209202A GB2098839A GB 2098839 A GB2098839 A GB 2098839A GB 8209202 A GB8209202 A GB 8209202A GB 8209202 A GB8209202 A GB 8209202A GB 2098839 A GB2098839 A GB 2098839A
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United Kingdom
Prior art keywords
electrode
set forth
bottom portion
carbon material
graphite
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Application number
GB8209202A
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Arc Technologies Systems Ltd
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Arc Technologies Systems Ltd
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Publication date
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Publication of GB2098839A publication Critical patent/GB2098839A/en
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Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B7/00Heating by electric discharge
    • H05B7/02Details
    • H05B7/06Electrodes
    • H05B7/08Electrodes non-consumable
    • H05B7/085Electrodes non-consumable mainly consisting of carbon
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B7/00Heating by electric discharge
    • H05B7/02Details
    • H05B7/10Mountings, supports, terminals or arrangements for feeding or guiding electrodes
    • H05B7/101Mountings, supports or terminals at head of electrode, i.e. at the end remote from the arc

Description

SPECIFICATION Electrode for arc furnaces and method for producing steel The present invention relates to an electrode for arc furnaces comprising a top portion of metal and a consumable bottom portion of carbon and having a substantially cylindrical shape. The top and bottom portion are joined to each other by, for example, a screw nipple or the like, and the top portion is provided with a liquid cooling device with a feed duct and a return duct. The lower region of the top portion is advantageously protected by a high-temperature resistant coating. The invention also relates to a method for the use of such electrodes. Arc furnaces for producting electrode steel, copper, corumdum, cobalt, silicon etc. have hither to been operated with graphite electrodes as the current carrying elements. An electrode strand usually comprises a plurality of graphite units which are joined to each other by screw connections or the like. Frequently, three electrode strands are used as current carrying elements for each furnace in such electrothermal high-temperature melting processes. The prior art also discloses combination electrodes for arc furnace operation, comprising a metal shank to which a carbon material tip is joined by a screw connection such as for example, a nipple. For example, German Offenlegungsschrift 1 565 751 discloses electric arc furnace electrodes comprising a top metallic headpiece, a bottom metallic headpiece, electrical conductors for joining the two, a ceramic compound enclosing the said conductors and the bottom headpiece and an electrode tip which is interchangeably attached to the bottom headpiece. A liquid cooled electrode is also disclosed by German Offenlegungsschrift 28 45 367 which is provided with a cylindrical clamping part attached to the electrode support arm, a metallic cooling system, attached to the former and adapted to carry the electrode current and supporting at the free end a screwthread portion for screwmounting the electrode tip and the tubular heat shield which contains the cooling system in the region exposed to the furnace atmosphere at a distance and in a fixed spatial co-ordination thereto. The European Published Application 12 573 A1 discloses a combination electrode in which the metallic contact of the metal shank disclosed laterally on the outside is supported in insulated manner with respect to the internally disposed metallic cooling system. A ceramic covering, secured by means of hooks, is provided in the bottom part of the metallic cooling shank and extends approximately to the height of the screw nipple connection by means of which a carbon part is attached. The principle of such combination electrodes has been known for a long time, for example, from the German Patent Specification 268 660 issued in 1912. In arc furnace operation such combination electrodes are exposed to severe stresses. This is explained by the high operating temperatures, for example in electrosteel production, where such electrodes are most frequently used. The high temperatures result in losses due to side oxidation of the carbon material. There is also the risk of migration or lateral striking of the arc which can occur above the carbon part in the event of defects and lead to short circuits. Furthermore, the electrodes are subjected to different temperatures in the feed and return of the coolant as well as in the region of the carbon part in relation to the current carrying and cooling unit. The region of the screw nipple is a particularly endangered zone. The electrodes must however also be able to withstand many mechanical stresses which are caused by the tilting of the furnace, by vibrations-assisted by excessive clearance of the support arms-by scrap movement during melting and when the strand is placed on insulating constituents of the scrap, among others. Furthermore, in order to reduce the melting times, electrodes have been exposed to increasing electrical (and therefore also thermal) stresses in the course of the last 10 to 15 years. Extreme requirements regarding the quality of the carbon strands, irrespective of whether these'are made exclusively of carbon material or those connected by means of a nipple to a cooled metal shank, resulted from the constantly increasing stresses imposed on the electrodes. The demands made on the graphite parts with respect to their density, specific electrical resistance, thermal expansion, thermal conductivity, mechanical strength and elasticity as well as thermal shock resistance, constantly increased. This has not only lead to more intensive graphiting processes which were performed for prolonged periods at elevated temperatures but also called for additional post-compaction processes and the like. The very high degree of graphite conversion required to satisfy such demands meant that only petro-chemical needle coke of high quality could be used as starting material for such processes. The use of such expensive prime coke derived for petrochemical raw materials and having a high degree of structural preorientation also involves other difficulties.These are due to the fact, inter alia, that the production quantity of such initial cokes is limited because of the limited amount of low sulphur oil deposits. Moreover, a considerable amount of electrical energy must be employed in I the graphiting stage of the production process for the electrode components in order to achieve the extensive degree of graphiting. Finally, different thermal expansions and electrical overloads of the nipple regions occur in the transition region between the cooled metal shank and the adjoining graphite part due to a temperature difference of the order of 500 K or more. It is the object of the invention to provide electrodes for arc furnace operation capable of meeting the substantial mechanical, thermal and electrical stresses of such operation in a particularly suitable manner. By adapting the cooled metal shank and the carbon part to each other an electrode is made available which is particularly suitable for practical operation and whose production or operation can be performed in a more economical manner then hitherto.According to the present invention there is provided an electrode for arc furnaces, comprising a top portion of metal, a consumable bottom portion of carbon having a substantially cylindrical shape, means for joining said top portion to said bottom portion, a cooling device for said top portion defining a feed duct and a return duct, and carbon of said bottom portion being one of a carbon material formed only partially of graphite structure elements and a carbon material which is free of such elements. The invention is based on the surprising fact that good practical performance of combination electrodes is obtained when using carbon materials of lower quality than that hitherto considered essential for arc furnace operation. More particularly, it has been found that the dangerous crack information or detahments do not occur when using carbon material which is only partially formed of graphite structure elements or is completely or nearly free thereof. The carbon material in the electrode according to the invention is preferably attached to the metal shank by means of a known screw nipple which can also consist of graphite or of metal and can also be cooled. The metal shank, which can also be regarded as the current supply means to the carbon member, usually consists of a high conductivity metal, for example copper. The metal shank is provided with a liquid cooling system with a feed and return duct which is also able, where appropriate, to cool the exterior or the interior of at least part of the screw nipple. Such constructions of the metal shank, the exterior of which is at least partially protected by a high temperature resistant covering, are known. One preferred embodiment of the invention is arranged so that the length and the diameter of the bottom portion are selected so that at least the same electrical loading is obtained by comparison with electrode strands of the same or corresponding overall dimensions but consisting exclusively of graphite carbon material. In an embodiment of the electrode according to the invention, the dimensions of the top portion of metal and the dimensions of the bottom portion of carbon material are adapted to each other so that at least part of the metal shank is regularly introduced into the arc furnace itself. Tests have shown that advantageously the carbon part has an initial length of approximately 2 to 3 mm, given an overall initial electrode length of approximately 51/2 to 8 or more particularly 6 to 7 m. The proportion of graphite structure elements within the bottom portion of carbon material can be of the order of 0 to 9% by weight. It has been found particularly advantageous if the proportion of graphite structural elements amounts to between 50 to 85% by weight and more particularly to 60 to 80% by weight referred to the weight of the carbon material. Within the scope of the present invention the expression "Graphite structure elements" refers substantially to natural graphite or electrographite or a mixture thereof. Waste graphite, for example, obtained from synthetic graphite production, can be used as electrographite. The "non-graphite" structure components of the carbon material comprise anthracite, foundry coke and/or normal petrol coke and within the scope of the present invention the bottom portion can also consist entirely of these materials or mixtures thereof. As already explained above, it has been found advantageous if the carbon material of the bottom portion is formed from electrographite or natural graphite or a mixture thereof at the rate of 0 to 90%, advantageously 50 to 85%, but more particularly 60 to 80% by weight and the remainder is formed of anthracite, foundry coke and/or normal petrol coke. Some typical data of the grades of initial materials of which the bottom portion can consist either partially or completely are given below: Data of electrode grades
The bottom portion of the electrode according to the invention can be produced in known manner. Production by vibration or extrusion should be specially mentioned in this context. Such methods are known. The carbon material used at the bottom portion in the electrode has a specific electrical resistance, more particularly in the region of 10 to 30 ohms mm /m. A particularly advantageous operational performance of the electrodes was found by tests, where the carbon material of such electrodes had a specific electrical resistance in the region of 10 to 20 ohms mm /m, more particularly 13 to 20 ohms mm /m. The diameter of the bottom portion is usually in the region of 200 to 600 mm. Particularly advantageous results were obtained with diameters of the bottom portion in the region of approximately 300 to 400 mm. The diameter of the top portion of metal can be selected to be greater or smaller than the diameter of the bottom portion. The particularly preferred bulk density of the carbon material of the bottom portion is in the region between 1.50 and 1.65 g/cm . An electrode, which is particularly advantageous embodiment of the present invention and in which the top portion of metal amounts to approximately half the overall length of the electrode or more has a carbon proportion of approximately 50 to 85% consisting of graphite structure elements of natural graphite and/or electrographite and the non-graphite structure elements consist of anthracite, foundry coke and/or normal petrol coke and the specific electric resistance of the bottom portion is in the region of 10 to 20 ohms mm /mm given a bulk density of the order 1.50 and 1.65 g/cm . The electrodes according to the invention are characterized by advantageous performance and trouble-free operation. Compared with conventional solid graphite electrodes, the carbon materials of the bottom portion can be produced by less expensive raw materials and simpler production processes. Cost reduction of electrode operation is therefore made possible, given the same electric loading capacity. Although a carbon material of lesser quality is used by comparison with conventionally employed high grade graphite, no substantial detachments and crack formation have been observed, even in the transition zone between the top and bottom portion. The use of nipples of high grade graphite with a density higher than that of the carbon material of the bottom portion and a lower electrical resistance has been found particularly advantageous. The electrode according to the invention is used preferably for the production of steel in arc furnace operation. It can however also be used for the production of non-ferrous metal such as for example, copper or cobalt but can also be used for the production of for example, corundum, silicon and the like. In the production of electrosteel, the combination electrodes according to the invention and having bottom portions of carbon materials with a diameter of the order of 300 to 400 mm are used advantageously with maximum phase currents in the region of 10 to 30 kA. Embodiments of the present invention will now be described by way of example with reference to the accompanying drawing which shows a longitudinal section through one embodiment of an electrode according to the invention. In the electrode illustrated, a cooling medium, usually water, is introduced through a feed duct 2 and returns through a return duct 3. The cooling medium also enters a chamber with a screw nipple 1, which can be formed of, for example, cast iron. A top portion 5 of the electrode is of metal and in this case, comprises a top region of larger diameter and a lower region of smaller diameter, extending into the screw nipple 1 which represents the connection to a bottom portion 6 of carbon material which is formed only partially of graphite structure elements or is free thereof. The high temperature covering 4 comprises a plurality of individual mouldings which can be supported by a bearing.The high temperature resistant insulation 4 is adjoined by an electrically conductive intermediate stratum 11 which is defined towards the interior by the extended, internally disposed metal shank or its portion of smaller diameter 12. Bores with pins inserted therein, which ensure proper seating via a spring, for the high temperature resistant mouldings, can be provided in addition to cooling bores 15. The electrode of the present invention is however not confined to the construction shown in the illustration. For example, constructions with modifications of the kind of electrode shown in the drawing are particularly advantageous. In such preferred electrodes, the metal shank has a substantially constant diameter. The rings of high temperature material-more particularly those of graphite-can be screwmounted thereon. The cooling system can advantageously be constructed so that the cooling medium flows around the top outer region of the nipple but does not enter the same. An electrically conductive intermediate stratum is not always provided in such constructions.These and other embodiments of the electrode according to the invention are within the scope of the invention to the extent that the carbon material of the consumable bottom portion is formed only partially of graphite structure elements or is free thereof. The use of an embodiment of an electrode according to the invention is described in the following example. Example: A combination electrode comprising a water-cooled copper shank, cooled with water by means of a cooling system comprising a feed duct and a return duct was used. The copper shank was protected by a high temperature resistant covering in the region of the furnace. The copper shank was screwmounted by means of a graphite nipple to the carbon material which consisted substantially of waste graphite obtained from synthetic graphite production. The carbon material had a bulk density of 1.62 g/cm and a specific electrical resistance of 18.5 ohms mm /m. Three such electrodes were used in a furnace with a capacity of 50 tonnes and three phase with a maximum phase current of 50 000 A were used with an operating voltage of 490 V. The specific electrode consumption of the order of 4.8 kg/tonne of steel was obtained with substantially trouble-free operation.

Claims (21)

1. An electrode for arc furnaces, comprising a top portion of metal, a consumable bottom portion of carbon having a substantially cylindrical shape, means for joining said top portion to said bottom portion, a cooling device for said top portion defining a feed duct and a return duct, the carbon of said bottom portion being one of a carbon material formed only partially of graphite structure elements and a carbon material which is free of such elements.
2. An electrode as set forth in claim 1, wherein said joining means is a screw nipple and said top portion has a lower region protected by a high-temperature resistant coating.
3. An electrode as set forth in claim 1 or 2, wherein the length and the diameter of said bottom portion are selected so that at least the same electrical loading is provided by comparison to electrode strands of the corresponding overall dimensions but consisting exclusively of graphite carbon material.
4. An electrode as set forth in any preceding claims, wherein the proportion of said graphite structural elements in said carbon material amounts to between 0 and 90% by weight.
5. An electrode as set forth in claim 4, wherein the proportion of said graphite structural elements in said carbon material amounts to between 50 and 85% by weight.
6. An electrode as set forth in any preceding claims, wherein said graphite structural elements comprise material selected from the group consisting of natural graphite, electrographite, and combinations thereof.
7. An electrode as set forth in any preceding claims, wherein the non-graphite structural components of said carbon material are formed from material selected from the group consisting of anthracite, foundry coke, normal petrol coke, and combinations thereof.
8. An electrode as set forth in any of claims 1 to 6, wherein said bottom portion is formed entirely of material selected from the group consisting of anthracite, foundry coke, normal petrol coke, and combinations thereof.
9. An electrode as set forth in any preceding claim, wherein said bottom portion is produced by vibration.
10. An electrode as set forth in any one of claims 1 to 8, wherein said bottom portion is produced by extrusion.
11. An electrode as set forth in any preceding claim, wherein the specific electrical resistance of said bottom portion is in the region of 10 to 20 ohms/mm .
12. An electrode as set forth in claim 11, wherein the specific electrical resistance of said bottom portion is in the region of 10 to 20 ohms/mm .
13. An electrode as set forth in any preceding claim, wherein the diameter of said bottom portion is in the region of approximately 200 to 800 mm.
14. An electrode as set forth in claim 13, wherein the diameter of said bottom portion is in the region of approximately 300 to 400 mm.
15. An electrode as set forth in any preceding claim, wherein the diameter of said bottom portion is less than that of said top portion of metal.
16. An electrode as set forth in any preceding claim, wherein the bulk density of said carbon material is in the region between 1.50 to 1.65 g/cm .
17. An electrode for arc furnace substantially as herein described with reference to the Example.
18. An electrode for arc furnaces substantially as herein described with reference to the accompanying drawing.
19. A method of producing steel in an arc furnace, comprising passing an electric current through an arc furnace electrode, which comprises a top portion of metal, a consumable bottom portion of carbon which has a substantially cylindrical shape, means for joining said top portion to said bottom portion, a cooling device for said top portion defining a feed duct and a return duct, the carbon of said bottom portion being one of a carbon material formed only partially of graphite structure elements and a carbon material which is free of such elements.
20. A method as set forth in claim 19, using phase electrodes whose diameters are approximately 300 to 400 mm with maximum phase currents are from 10 to 30 kA.
20. A method as set forth in claim 19, using phase electrodes whose maximum phase currents are from 10 to 30 kA and whose diameters are approximately 300 to 400 mm.
21. A method of producing steel substantially as herein described with reference to the Example. CLAIMS (8 Jul 1982)
11. An electrode as set forth in any preceding claim, wherein the specific electrical resistance of said bottom portion is in the region of 10 to 30 ohms/mm .
GB8209202A 1981-04-23 1982-03-29 Electrode for arc furnace and method of producing steel Withdrawn GB2098839A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE3116258A DE3116258A1 (en) 1981-04-23 1981-04-23 ELECTRODE FOR ARC OVENS AND METHOD FOR USE THEREOF

Publications (1)

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GB2098839A true GB2098839A (en) 1982-11-24

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GB8209202A Withdrawn GB2098839A (en) 1981-04-23 1982-03-29 Electrode for arc furnace and method of producing steel

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EP (1) EP0063710A1 (en)
JP (1) JPS5894793A (en)
AU (1) AU8185782A (en)
BR (1) BR8202308A (en)
DD (1) DD202363A5 (en)
DE (1) DE3116258A1 (en)
DK (1) DK181882A (en)
ES (1) ES511724A0 (en)
FI (1) FI820868L (en)
GB (1) GB2098839A (en)
HU (1) HU186609B (en)
NO (1) NO820800L (en)
PL (1) PL236042A1 (en)
PT (1) PT74763B (en)
TR (1) TR21298A (en)
ZA (1) ZA822012B (en)

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JPS59108294A (en) * 1982-11-19 1984-06-22 ユニオン,カ−バイド,コ−ポレ−シヨン Carbon boride for electrode

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Publication number Priority date Publication date Assignee Title
DE268660C (en) *
SE337435B (en) * 1965-07-13 1971-08-09 J Oestberg
FR2176546A1 (en) * 1972-03-23 1973-11-02 Siderurgie Fse Inst Rech Composite furnace electrode - esp for steel prodn
CA1074381A (en) * 1978-05-09 1980-03-25 Otto E. Prenn Composite electrode with non-consumable upper section
DE2725537A1 (en) * 1977-06-06 1978-12-14 Korf Stahl ELECTRODE FOR ARC FURNACE
US4287381A (en) * 1978-12-19 1981-09-01 British Steel Corporation Electric arc furnace electrodes

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PL236042A1 (en) 1983-02-28
DK181882A (en) 1982-10-24
BR8202308A (en) 1983-04-05
PT74763A (en) 1982-05-01
JPS5894793A (en) 1983-06-06
AU8185782A (en) 1982-10-28
ES8400645A1 (en) 1983-11-01
TR21298A (en) 1984-03-22
FI820868L (en) 1982-10-24
ES511724A0 (en) 1983-11-01
HU186609B (en) 1985-08-28
DD202363A5 (en) 1983-09-07
ZA822012B (en) 1983-02-23
EP0063710A1 (en) 1982-11-03
DE3116258A1 (en) 1982-11-11
NO820800L (en) 1982-10-25
PT74763B (en) 1983-10-28

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