AU702610B2 - Device for mounting a self-baking composite electrode for an electric arc furnace - Google Patents

Description

S F Ref: 322800

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFCATION FOR A STANDARD PATENT

ORIGIMAL

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=;nr~ir~31 Name and Address of Applicant: Pechiney Electrometallurgie Tour Manhattan-La Defense 2 6 Place de 1'Iris 92400 Courbevoie

FRANCE

Maurice Sales Actual Inventor(s): Address for Service: Invention Title: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Device for Mounting a Self-Baking Composite Electrode for an Electric Arc Furnace The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845 DEVICE FOR MOUNTING A SELF-BAKING COMPOSITE ELECTRODE FOR AN ELECTRIC ARC FURNACE Field oi the Invention The invention relates to the field of electrodes for electric arc furnaces and, more specifically, self-bdking electrodes, known as Sbderberg electrodes, for carbothermic reduction furnaces, such as furnaces for the production of metallurgical silicon.

Prior Art The principle of self-baking electrodes, which consists of inserting a crude carbonaceous paste into the furnace inside a :.o0 cylindrical ferrule and baking this paste continuously during its utilization in the furnace, is known from the patent filed in 1917 by C.W. SSderberg, G. Sem, and J. Westly on behalf of the company Det Norske Aktielselkap for Elektrokemisk Industri (which corresponds to French Patent 488778).

This technique, which is widely used today, leads to the .constitution of continuous electrodes which, if nothing is done to prevent it, contain about 2.5% iron, which originates in the steel ferrule.

In order to constitute continuous electrodes with a lower o0 iron content, several solutions have been proposed, all of which consist of mechanically separating the electrode from its ferrule, so that it is possible to slide the electrode without also stretching the ferrule. In this case, instead of the ferrule equipped with internal ribs for supporting the electrode which was provided in the initial device, a smooth ferrule without ribs is used. This disposition, moreover, has been tested by Elektrokemisk since 1917 (cf. S6derberg Electrode

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Year Anniversary Seminar, Kristiansand, June 6-8, 1994, G. Sem, "The conception and birth of the S6derberg Electrode.") Since the elimination of the ribs no longer allows the weight of the electrode to be supported by means of its ferrule, it is therefore necessary to resort to a mounting arrangement which is different from the standard S6derberg arrangement and which consists of supporting the weight of the electrode by means of a piece enclosed by the baked paste, a piece which is consumed at the same time as the electrode itself.

'C In Italian patent 606568, filed in 1959 by the Edison company, this piece is a strip of perforated steel.

In US patent 4,575,856 to J.A. Persson, granted March 11, 1986, this support piece is a column which forms a pre-baked carbon or graphite electrode, constituted by elements fitted together by means of nipples, that is, fittings with double tapered screw threads, made of the same material, and screwed into the elements to be fitted together. French patent 2683421, filed by the Spanish company Carburos Metallicos, claims various adaptations of this technique.

The arrangement proposed in these last two patents has a certain number of drawbacks.

On one hand, the mechanical load which is necessary to compensate for the weight of the electrode is transmitted to the column by a system of chucks. This load can reach substantial 25 values, on the order of 50,000 to 75,000 N. It is necessary, therefore, to exert considerable clamping pressure on the chuck, since the coefficient of friction between carbon and steel is low. in operation, this type of mounting arrangement causes wear on the surface of the graphite column, which increases the risk of rupture due to the tensile stress to which it is subjected.

This rupture can have serious consequences for the electrode itself as well as for the furnace in which it is mounted.

On the other hand, the positioning of the chucks which clamp onto the column does not allow displacements of large amplitude.

It is therefore necessary to reposition the chucks on the column frequently as the electrode is consumed, which contributes to a worsening of the damage caused to the column by the chucks.

Object of the Invention The object of the invention is a device for mounting a selfiO baking electrode, equipped with a cylindrical metallic ferrule and a central column of graphite or pre-baked carbon constituted by elements fitted together by nipples, that does not have the drawbacks mentioned above.

:i According to the invention, the central column is suspended from a support which is movable in the vertical direction with respect to the ferrule along a length which is greater than the S length of the elements. The displacement of the support can be obtained by means of screw jacks. The column can be fastened to S the movable support by means of a threaded piece which is integral wihi the support whose threading is identical to that of the nipples for fitting the elements of the column together.

eoee0: 0O Description of the Invention One particular mode of embodiment of the invention will be described with the aid of the sole drawing figure, which a represents an axial cutaway view of the composite electrode and its mounting device. The composite electrode is constituted by a cylindrical metallic ferrule which serves to contain the carbonaceous paste inserted at its top end, which will bake progressively as it descends into the furnace. A cylindrical

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central column with the same axis as the ferrule, is constituted by identical elements of pre-baked carbon or graphite, equipped at their two ends with tapered threaded holes and fitted to one another by means of nipples The column is held at its top end by a metallic piece which has at its end the same threading as the nipples The piece is directly screwed into the topmost element of the column This piece is supported by a frame whose relative position with respect to the ferrule and to the base with to which it is integral, is driven by two screw jacks whose travel is greater than the length of the elements which form the column This mounting arrangement makes it possible to slide the electrode along a length which is greater than or equal to the length of one element of the column without having to re- S attach the fastening between the column and the piece The travel of the screw jacks is sufficient to allow the length of the column to be extended by one element by performing only one take-up operation on the column Thus, the surface of the carbon or graphite elements is not damaged by any clamping system and the tensile strength of the column is S retained in full.

Example In a 20 MW furnace for the production of metallurgical silicon, originally equipped with pre-baked electrodes of 1250 mm in diameter, a mounting device according to the invention was mounted, on a trial basis, on one of the electrodes, The column is constituted by elements with a unit length of 1700 mm and a diameter of 450 mm fitted together by nipples o The topmost element of the column is fastened to a steel piece which ends in a shape identical to that of a nipple

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A movable apparatus constituted by a chassis which supports the piece and screw jacks which make it possible to support and position the electrode along a length of 1850 mm solely by acting upon the volume of oil injected into the screw jacks.

This mounting arrangement made it possible to verify that the surface of the elements constituting the column remained intact and that the operation was carried out without difficulty, despite the exertion of a tensile stress of 75,000 N on the I0 column a stress measured by means of the oil pressure on the screw jacks Siiii ogo e•.

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Claims (3)

1. A device for mounting a self-baking composite electrode for an electric furnace, which includes a metallic ferrule a central column of graphite or pre-baked carbon constituted by elements fitted together by means of nipples (4) and a carbonaceous paste between the ferrule and the column characterized in that the column is suspended from a support which is movable in the vertical direction with respect to the ferrule along a length which is greater than the length of each of the elements.

2. The device according to claim 1, characterized in that the relative movement of the support with respect to the column is obtained by means of screw jacks S

3. The device according to either of claims 1 or 2, characterized in that the column is fastened to the support by means of a'threaded piece whose threading is identical to that of the nipples DATED this TWENTY-FIRST day of DECEMBER 1995 Pechiney Electrometallurgie Patent Attorneys for the Applicant SPRUSON FERGUSON Device for Mounting a Self-Baking Composite Electrode for an Electric Arc Furnace ABSTRACT The invention relates to a device for mounting a self-baking composite electrode for an electric furnace, which includes a metallic ferrule a central column of graphite or pre- baked carbon constituted by elements fitted together by means of nipples and a carbonaceous paste between the ferrule and the column This device is characterized in that the column is suspended from a support which is movable in the vertical direction with respect to the ferrule along a length which is greater than each of the elements. 0 0*0900 9 The invention particularly applies to furnaces for the production of silicon by carbothermic means. 0060 00 0 1 C 00 0 0 0 *r