GB1566369A - Carbon and graphite electrodes for use in steel making - Google Patents

Carbon and graphite electrodes for use in steel making Download PDF

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Publication number
GB1566369A
GB1566369A GB2027778A GB2027778A GB1566369A GB 1566369 A GB1566369 A GB 1566369A GB 2027778 A GB2027778 A GB 2027778A GB 2027778 A GB2027778 A GB 2027778A GB 1566369 A GB1566369 A GB 1566369A
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United Kingdom
Prior art keywords
electrode
layer
fibrous material
protective coating
fibres
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Expired
Application number
GB2027778A
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Sigri GmbH
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Sigri GmbH
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Publication of GB1566369A publication Critical patent/GB1566369A/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/50—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials
    • C04B41/51—Metallising, e.g. infiltration of sintered ceramic preforms with molten metal
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/81—Coating or impregnation
    • C04B41/85—Coating or impregnation with inorganic materials
    • C04B41/88—Metals
    • 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

Description

(54) IMPROVEMENTS IN OR RELATING TO CARBON AND GRAPHITE ELECTRODES FOR USE IN STEEL MAKING (71) We, SIGRI ELEKTROGRAPHIT GESELLSCHAFT MIT BESCHRÄNK- TER HAFTUNG, a German Company, of D-8901 Meitingen bei Augsburg, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to carbon and graphite electrodes for use in steel making and whose surface has a metallic coating for protecting the electrodes against oxidation and which conducts the electric current.
Carbon and graphite electrodes used in arc furnaces tend to undergo gradual mass loss in use as a result of surface oxidation.
This oxidation can generally be reduced by coating the wall surface of the electrode with a temperature-resistant and substantially gas-impervious protective layer. Electrically conducting protective layers are disclosed in British patent specification No.
1,026,055 containing for this purpose mainly aluminium, silicon carbide and other refractory materials. According to British patent specification No. 1,166,429, such coatings contain a base layer consisting of silicon as main constituent and a surface layer containing aluminium as main constituent. The resistivity and the tightness of bonding of such protective layers to the electrode may generally be improved by subjecting the coatings to treatment by an arc at an appropriate elevated temperature or by effecting a sealing of the coating surface which borates, phospates or silicates. In spite of these additional measures, the bonding strength of the protective layers is not satisfactory in all cases.Flaking off of coatings and the formation of fissures therein tends to occur particularly strongly below the contact jaws in the region of the passage through the furnace roof, the frequency with which these defects occur increasing with the number of changes in temperature to which the electrodes are exposed by repeated starting and stopping of use thereof. Damage to the protective layer can also be produced if the contact jaws are pressed with too high a pressure on the surface of the electrode.
According to one aspect of this invention, there is provided a carbon or graphite electrode for use in steel making. the electrode having on a wall surface thereof a single or multi-layer protective coating of which at least one layer is formed of a metallic material and/or silicon, said at least one layer or at least one other said layer comprising a fibrous material.
According to a second aspect of the invention, there is provided a method of providing a protective coating on a carbon or graphite electrode for use in steelmaking, which comprises applying to a wall surface of the electrode a single or multi-layer covering of which at least one layer is formed of metal and/or silicon, said at least one layer or at least one other said layer comprising a fibrous material.
The matrix material of at least one layer of the covering which material is hereinafter referred to generally as "metallic", is silicon or a metal, particularly one of the metals aluminium, titanium and iron. or an alloy of two or more of these elements. The fibrous material may consist of carbon fibres, glass fibres or ceramic fibres. Metallic fibre inlays may also be used especially when the intended residence time of the electrode in the temperature range critical for the stability of the protective coating is very short.
Above this temperature range, the protective coating will no longer be damaged by formation of fissures or flaking off because of the increasing plasticity of the metallic matrix. Hence, a partial or even complete destruction of the fibrous inlay material in this temperature region will not adversely affect the stability of the protective coating.
It has been found to be particularly desirable for the fibrous material to be given an adhesion-promoting surface layer prior to use in the metallic matrix material. This adhesion-promoting layer may be produced mechanically or chemically by etching or surface oxidation. The fibres may also be suitably surface coated for improving adhesion by coating with tantalum, silicides, carbides and other temperature resistant material.
The fibrous material may be employed in a wide variety of forms. For example, discrete cut fibres or whiskers may be employed or alternatively, the fibres may be employed in the form of filaments, fibre bundles or staple fibres. The fibrous material may also be employed in the form of strips and woven and non-woven fabric. A particularly preferred form of fibrous material is an open weave woven fabric.
The amount of fibrous material which is to be added to the protective coating is specifically determined by the nature of the material being used, more especially the mechanical and physical properties thereof and by the fibre geometry thereof. The protective coating preferably contains from 0.1 to 10% by volume of fibrous material, the amount employed depending on the nature of the fibrous material. In general, smaller percentages may be employed when using filaments and fibre bundles and larger proportions when employing staple fibres.
Proportions by volume of about 5% are desirable for strips and non-woven fabrics.
Amounts of fibrous material below 0.1% by volume are generally not very effective for blocking the propagation of fissures and preventing flaking off in the protective coating and larger amounts of fibrous material generally require special means for producing a uniform fibre distribution.
As will be apparent from the foregoing, the fibrous material consists of one or more substnces which are stable in the temperature range critical for the adhesion of the protective coatings to electrodes. The fibrous material will generally be substantially inert with respect to the aforesaid matrix material of the protective coating. The fibrous material is preferably incorporated into the protective coating in such a manner that a major proportion of the fibres thereof extend tangentially with respect to the wall surface of the electrode.
When producing a protective coating which comprises short-cut fibres or whiskers as fibrous material, the metallic matrix material may be applied to the electrode simultaneously with the fibrous material by flame spraying. Alternatively, in such a case, the matrix material containing short cut fibres or whiskers therein may be applied by trowelling to the wall surface of the electrode; in general in such a case a binder will be incorporated in such a mixture. In a preferred procedure for providing a surface protected electrode according to this invention, a first layer of a metal and/or silicon is applied to the electrode wall surface and on to this basic layer is wound a filament, a strip or a non-woven fabric formed of the fibrous material. A surface layer of metal and/or silicon is then applied to the wound layer.If desired, in fact, the procedure of applying alternating layers of metallic material and fibrous material may be repeated to provide a protective coating which contains several matrix layers and fibrous layers in alternating manner. Depending upon the number of layers of metal and/or silicon and inlays of fibrous material to be employed in such manner, two or more flame-spraying pistols and one or more winding arrangements may be arranged in alternating manner alongside the electrode which is rotated during the coating procedure and is moved axially in relation to the flame-spraying pistols and winding arrangement or arrangements.
The incorporation of the fibrous material into a protective coating according to this invention increases the stability of the protective coatings with respect to tangential stresses which are caused by rapid changes in temperature or a temperature gradient between the electrode and the protective coating. It is these temperature phenomena which are largely responsible for the detachment of the protective coating from the electrode or the formation of cracks within the protective coating which now tend to be small if they occur at all. In addition, the inclusion of the fibrous material in the protective coating inhibits the propagation of cracks or fissures in this layer as well as the flowing of matallic matrix material above the melting temperature thereof.
The following Examples illustrate this invention: Example electrically 1 An oxidation-inhibiting electrically conductive protective coating which was resistant to sudden change in temperature was applied to a graphite cylinder. For this purpose, there was applied to the cylindrical wall surface of the cylinder a first layer having a thickness of 0.1 mm and containing 98.7% by weight silicon, 0.8% by weight iron and 0.5% by weight aluminium, this layer being applied by use of a first flamespraying pistol. This first layer was followed by a layer of glass silk yarn drawn onto the first layer in synchronisation therewith. A second flame-spraying pistol was then employed to apply over the glass silk yarn a surface layer containing 99.5% by weight aluminium and having a thickness of about 0.15 mm.During the course of this application procedure, the graphite cylinder which had a diameter of 400 mm was moved parallel to the spraying pistols and to the winding arrangement employed for drawing the glass silk yarn onto the first layer. The graphite cylinder was moved at a relative speed of 150 mm per minute in the axial direction with respect to the pistols and winding arrangement and was rotated at 40 r.p.m. about its longitudinal axis. The fibre inlay produced amounted to 0.15% by volume of the total protective coating.
The adhesive strength of the applied protective layer to the graphite layer was checked by heating the electrode by direct resistance heating within about ten minutes from ambient temperature to about 1200"C and then cooling in a stream of air to ambient temperature. Even after five changes in temperature in this manner, the protective coating adhered tightly to the graphite cylinder and did not show any visible defects, such as formation of fissures and flaking.
Example 2 The flame-spraying procedure of Example 1 was employed to provide a graphite cylinder having a diameter of 400 mm with a layer having a thickness of about 0.1 mm and containing 50% by weight of aluminium and 50% by weight of silicon. A viscous aqueous solution of sodium borate and sodium Phosphate containing 20 parts by weight of short cut carbon fibres and 3 parts by weight of methyl cellulose, as adhesive, the amounts being based on 100 parts weight of sodium salts was then brushed onto the first layer in a thickness of about 0.05 mm. This coating solution was then dried by heating to 1100C. In order to improve the bond strength of the carbon fibres to the first layer, the carbon fibres had been briefly heated beforehand in air to 800"C as a result of which shallow pits were etched onto the surface thereof.The total amount of fibres applied in this manner amounted to about 8% by volume of the protective coating which was formed.
The adhesion of the protective layer to the graphite cylinder was checked in the manner indicated in Example 1. The protective coating was free from visible defects even after undergoing five temperature changes.
WHAT WE CLAIM IS: 1. A carbon or graphite electrode for use in steelmaking, the electrode having on a wall surface thereof a single or multi-layer protective coating of which at least one layer ts formed of a metal and/or silicon, said at least one leyer or at least one other said layer comprising a fibrous material.
2. An electrode as claimed in claim 1, wherein the protective coating is formed of silicon, iron, aluminium or titanium or an alloy of two or more such elements, having the inclusion of fibrous material therein.
3. An electrode as claimed in claim 1 or 2, wherein the fibrous material is formed of carbon fibre, glass fibre or ceramic fibre material.
4. An electrode as claimed in claim 1 or 2, wherein the fibrous material is formed of metallic fibres.
5. An electrode as claimed in any one of the preceding claims, wherein the fibrous material has been chemically or mechanically surface pretreated.
6. An electrode as claimed in claim 5, wherein the fibres of the fibrous material have been etched or subjected to surface oxidation.
7. An electrode as claimed in any one of claims 1 to 4, wherein the fibres of the fibrous material have been subjected to coating with a temperature resistant material.
8. An electrode as claimed in claim 7, wherein the temperature resistant material is tantalum, a silicide or a carbide.
9. An electrode as claimed in any one of the preceding claims, wherein the major part of the fibres of the fibrous material extend tangentially to the wall surface of the electrode.
10. An electrode as claimed in any one of the preceding claims, wherein the fibrous material constitutes from 0.1 to 10% by volume of the protective coating.
11. An electrode as claimed in any one of the preceding claims, wherein the fibrous material is in the form of an open weave woven fabric.
12. An electrode as claimed in any one of the preceding claims, wherein the fibrous material is wound in continuous manner around the electrode.
13. A carbon or graphite electrode having a protective coating, substantially as described in either of the foregoing Examples.
14. A method of providing a protective coating on a carbon or graphite electrode for use in steelmaking, which comprises applying to a wall surface of the electrode a single or multi-layer covering of which at least one layer is formed of metal and/or silicon, said at least one layer or at least one other said layer comprising a fibrous material.
15. A method as claimed in claim 14, wherein a first layer of metal and/or silicon is applied to the wall surface of the electrode, a filament or strip of a said fibrous material is wound onto the first layer and a second layer of metal and/or silicon is applied to the layer of fibrous material
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (21)

**WARNING** start of CLMS field may overlap end of DESC **. aluminium and having a thickness of about 0.15 mm. During the course of this application procedure, the graphite cylinder which had a diameter of 400 mm was moved parallel to the spraying pistols and to the winding arrangement employed for drawing the glass silk yarn onto the first layer. The graphite cylinder was moved at a relative speed of 150 mm per minute in the axial direction with respect to the pistols and winding arrangement and was rotated at 40 r.p.m. about its longitudinal axis. The fibre inlay produced amounted to 0.15% by volume of the total protective coating. The adhesive strength of the applied protective layer to the graphite layer was checked by heating the electrode by direct resistance heating within about ten minutes from ambient temperature to about 1200"C and then cooling in a stream of air to ambient temperature. Even after five changes in temperature in this manner, the protective coating adhered tightly to the graphite cylinder and did not show any visible defects, such as formation of fissures and flaking. Example 2 The flame-spraying procedure of Example 1 was employed to provide a graphite cylinder having a diameter of 400 mm with a layer having a thickness of about 0.1 mm and containing 50% by weight of aluminium and 50% by weight of silicon. A viscous aqueous solution of sodium borate and sodium Phosphate containing 20 parts by weight of short cut carbon fibres and 3 parts by weight of methyl cellulose, as adhesive, the amounts being based on 100 parts weight of sodium salts was then brushed onto the first layer in a thickness of about 0.05 mm. This coating solution was then dried by heating to 1100C. In order to improve the bond strength of the carbon fibres to the first layer, the carbon fibres had been briefly heated beforehand in air to 800"C as a result of which shallow pits were etched onto the surface thereof.The total amount of fibres applied in this manner amounted to about 8% by volume of the protective coating which was formed. The adhesion of the protective layer to the graphite cylinder was checked in the manner indicated in Example 1. The protective coating was free from visible defects even after undergoing five temperature changes. WHAT WE CLAIM IS:
1. A carbon or graphite electrode for use in steelmaking, the electrode having on a wall surface thereof a single or multi-layer protective coating of which at least one layer ts formed of a metal and/or silicon, said at least one leyer or at least one other said layer comprising a fibrous material.
2. An electrode as claimed in claim 1, wherein the protective coating is formed of silicon, iron, aluminium or titanium or an alloy of two or more such elements, having the inclusion of fibrous material therein.
3. An electrode as claimed in claim 1 or 2, wherein the fibrous material is formed of carbon fibre, glass fibre or ceramic fibre material.
4. An electrode as claimed in claim 1 or 2, wherein the fibrous material is formed of metallic fibres.
5. An electrode as claimed in any one of the preceding claims, wherein the fibrous material has been chemically or mechanically surface pretreated.
6. An electrode as claimed in claim 5, wherein the fibres of the fibrous material have been etched or subjected to surface oxidation.
7. An electrode as claimed in any one of claims 1 to 4, wherein the fibres of the fibrous material have been subjected to coating with a temperature resistant material.
8. An electrode as claimed in claim 7, wherein the temperature resistant material is tantalum, a silicide or a carbide.
9. An electrode as claimed in any one of the preceding claims, wherein the major part of the fibres of the fibrous material extend tangentially to the wall surface of the electrode.
10. An electrode as claimed in any one of the preceding claims, wherein the fibrous material constitutes from 0.1 to 10% by volume of the protective coating.
11. An electrode as claimed in any one of the preceding claims, wherein the fibrous material is in the form of an open weave woven fabric.
12. An electrode as claimed in any one of the preceding claims, wherein the fibrous material is wound in continuous manner around the electrode.
13. A carbon or graphite electrode having a protective coating, substantially as described in either of the foregoing Examples.
14. A method of providing a protective coating on a carbon or graphite electrode for use in steelmaking, which comprises applying to a wall surface of the electrode a single or multi-layer covering of which at least one layer is formed of metal and/or silicon, said at least one layer or at least one other said layer comprising a fibrous material.
15. A method as claimed in claim 14, wherein a first layer of metal and/or silicon is applied to the wall surface of the electrode, a filament or strip of a said fibrous material is wound onto the first layer and a second layer of metal and/or silicon is applied to the layer of fibrous material
wound on to the electrode.
16. A method as claimed in claim 15, wherein said strip has a net-like structure.
17. A method as claimed in any one of claims 14 to 16, wherein said fibrous material is employed in an amount such that said covering contains from 0.1 to 10% by volume of fibrous material.
18. A method as claimed in claim 14 or 17, wherein a mixture of said metal and/or silicon and short cut fibres or whiskers is applied to the electrode.
19. A method as claimed in any one of claims 14 to 18, wherein said metal and/or silicon is applied to the electrode by flamespraying.
20. A method of providing a protective coating on a carbon or graphite electrode for use in steelmaking, substantially as described in either of the foregoing Examples.
21. A carbon or graphite electrode for use in steelmaking having a protective coating thereon provided by the method claimed in any one of claims 14 to 20.
GB2027778A 1977-05-18 1978-05-17 Carbon and graphite electrodes for use in steel making Expired GB1566369A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19772722438 DE2722438C2 (en) 1977-05-18 1977-05-18 Protective layer for carbon and graphite arc electrodes and processes for their manufacture

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GB1566369A true GB1566369A (en) 1980-04-30

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4594722A (en) * 1984-05-22 1986-06-10 Sigri Gmbh Graphite electrode for arc furnaces and method for manufacturing same
GB2177120A (en) * 1985-06-26 1987-01-14 John Michael Slater Improvements in and relating to metal coated carbon gouging rods
US4772514A (en) * 1985-12-24 1988-09-20 Ceskoslovenska Akademie Ved Protective layer for carbonaceous materials and method of applying the same
GB2202552A (en) * 1987-03-06 1988-09-28 Coated Electrodes Internationa Coating elongated carbon articles by spraying
EP0963449A1 (en) * 1996-12-27 1999-12-15 Alabama Power Company Electric furnace with insulated electrodes and process for producing molten metals

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2313995C3 (en) * 1972-03-22 1979-01-25 Foseco International Ltd., Nechells, Birmingham (Grossbritannien) Method for protecting a carbon electrode

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4594722A (en) * 1984-05-22 1986-06-10 Sigri Gmbh Graphite electrode for arc furnaces and method for manufacturing same
GB2177120A (en) * 1985-06-26 1987-01-14 John Michael Slater Improvements in and relating to metal coated carbon gouging rods
US4772514A (en) * 1985-12-24 1988-09-20 Ceskoslovenska Akademie Ved Protective layer for carbonaceous materials and method of applying the same
GB2202552A (en) * 1987-03-06 1988-09-28 Coated Electrodes Internationa Coating elongated carbon articles by spraying
EP0963449A1 (en) * 1996-12-27 1999-12-15 Alabama Power Company Electric furnace with insulated electrodes and process for producing molten metals
EP0963449A4 (en) * 1996-12-27 2000-03-22 Alabama Power Co Electric furnace with insulated electrodes and process for producing molten metals

Also Published As

Publication number Publication date
DE2722438A1 (en) 1978-11-30
DE2722438C2 (en) 1985-03-21

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