US2876269A - Electrode casing for self-baking electrodes - Google Patents

Description

March 3, 1959 E. TOMMELSTYAD 2,

ELECTRODE CASING FOR SELF-BAKING ELECTRODES Filed Nov. 4, 1957 INVENTOR.

EINAR TOM M ELSTAD ATTORNEYS ELECTRODE CASING FOR SELF-BAKING ELECTRODES Einar Tommelstad, Oslo, Norway, assignor to Elektrokemisk A/ S, Oslo, Norway, a corporation of Norway Application November 4, 1957, Serial No. 694,401

Claims priority, application Norway November 8, 1956 Claims. (Cl. 13-18) This invention relates to casings for electrodes of the type used in smelting furnaces and the. like and in which the actual electrode is put into the casing in the form of so-called paste which is progressively heated and baked as the electrode moves down in the furnace. Herctofore, such electrode casings have consisted of metallic (steelsheet) tubes made with a substantially smooth exterior and have been provided with an internal rib system. Casings of this type are shown, for example, in United States Patent No. 2,666,087,, issued January 12, 1954, to Johansson et al.

Such an electrode casing in operation is, held by an electrode holder which grips the casing so that it supports the electrode and transmits electric current to it. The holders are so arranged that the electrode casing may, when desired, be moved down. through the holder as the electrode is consumed. ()rdinarily the electrode holder is positioned a very short distance above the roof of the furnace in which the electrode operates.

So-called paste is filled into the top of the electrode holder. This paste is made of carbonaceous particles and a binder. While it may be solid at ordinary temperatures, the binder has a melting point such that the paste will soften in the electrode casing from the heat of the furnace. When soft, the paste fills out the casing and gradually, as it moves downwardly, it becomes hotter until it reaches a temperature of about 400 to 450 C. In this temperature range the volatiles of the binder are driven off and the electrode paste is baked into a solid carbonaceous mass. The baked electrode has good electrical conductivity but prior to baking its conductivity is negligible.

The electrode holders used with such casings ordinarily are water-cooled. A number of different forms of such holders have been employed and two of them are illustrated, for example, in United States Patents Nos. 2,671,816 and 2,673,227.

Experience has shown that with the usual type of casing the baking zone will be located immediately below the bottom of the electrode holder. This means that just at the bottom of the electrode holder the electrode will still be mechanically weak and the electrical conductivity of the carbonaceous mass will be low or negligible, with the result that in some cases there will be too high a current density in the casing around the unbaked part of the electrode and the casing may melt.

According to the present invention, I overcome these difiiculties by replacing the usual smooth electrode casing with a corrugated casing or a casing with projections shaped so that the contact surface between the casing and electrode holder is reduced. This reduces the heat loss from the electrode passed through the casing to the cooling water of the electrode holder and raises the level of the baking zone. This effect is increased when the corrugations are so shaped that they permit hot furnace gases to go up around the casing through the electrode holder. Interrupted corrugations may be employed but even when they are used, it is preferable to atent 0 ICC have continuous channels between the corrugations to permit the gases to escape.

This reduction in the area of contact between the electrode casing and electrode holder should be substantial, usually reducing the area of contact by at least 30% and preferably by at least 60%. Such a reduction in area would appear to reduce the area for electrical contact, but it has been found that the overall electric conductivity is actually improved because the raising of the baking zone more than compensates for the reduction of the. contact area.

It has further been found that by using a. corrugated.

casing the use of the internal rib system is no longer necessary and this may substantially reduce. the cost. of the casings. It is also the fact that by eliminating or simplifying the rib system within the casing, the. elec trode will show a more favorable surface at its working lower end and thereby the electrode consumption may be reduced. per unit of production.

This invention may be readily understood by reference to the accompanying drawings which show several different forms of corrugations illustrative of my invention.

In the. drawings--- Fig. 1 is a side view of a casing embodying. my invention with the electrode holder and furnace roof indicated in section in conventional form;

Fig. 2 is a horizontal section through Fig. 1;

Fig. 3 is a short section of an electrode casing illustrating the use of spirally arranged corrugations;

Fig. 4 shows. an example in which the. corrugations are non-continuous;

Fig. 5 shows. a casing in which continuous. corrugations are combined with non-continuous indentations of greater depth, and

Fig. 6 is a detailed section through a portion of the casing of Fig. 5.

In Fig. 1 the casing proper is designated by the numeral 10. This casing is made of iron and is suspended by the electrode holder conventionally indicated at 12. This holder 12 is provided with a water cooling chamber 14. It is understood that the casing 10 is filled with electrode paste 16 and the approximate baking zone is indicated at 18 in Fig. 1, though it is of course to be understood that the baking takes place gradually and is not properly rep resented by a sharp line. The line 18 is intended to indicate that at this point the paste has acquired appreciable strength and electric conductivity. The furnace roof is indicated at 17, and 19 is a usual packing ring to reduce (though it will not entirely prevent) the escape of hot gases from the furnace.

In this example the casing 10 is so corrugated as to form outwardly extending ribs 20 between which are shallow grooves or channels 22. It will be noted that the actual area of contact between the casing 19 and the electrode holder 12 is greatly reduced as the outwardly projecting ribs 20 are here shown as being appreciably narrower than the channels 22. The channels 22 permit the upward flow of furnace gases through the holder 312 and thereby maintain the electrode paste in the casing at the baking temperature up to a higher level than is the case with a smooth cylindrical casing. For example, in Fig. 1 it will be noted that the baking zone 18 is indicated as being slightly above the bottom of the electrode holder 12. Because of this fact there can be a direct flow of electric current from the holder 12 through the casing 10 into the baked electrode and it will not be necessary for the electrode casing to carry the heavy load of current which it would have to conduct downwardly if the paste within the electrode casing had not been baked to the point where it had become conductive. This improved electrical conductivity resulting from raising :the

baking zone is one of the important reasons why it is possible to do away with the internal rib system heretofore employed.

In my construction the ridges extending outwardly from the casing should be made with approximately flat outer faces following the curvature of the casing and not in the form of sine wave corrugations such as are ordinarily used in making corrugated metal. It must be remembered that the electrode holder must grip the casing very tightly to keep it from slipping, and if the sine wave corrugations were used, they would tend to distort, making desired slippage of the casing through the holder very difiicult.

The remaining figures show alternate constructions which operate in the same manner.- In Fig. 3 the raised spiral ribs 24 are shown as only slightly wider than the shallow spiral grooves 26. Nevertheless, the grooves will serve to reduce the direct heat transfer to the electrode holder and to permit the flow of hot furnace gases through the holder.

In Fig. 4 the outwardly extending ribs 28 have continuous channels or depressions between them, as at 30. The cross-section on line 2--2 of Fig. 4 will have the same appearance as the section of Fig. 1 shown in Fig. 2.

In Fig. 5 the grooves 32 between the outwardly extending ridges 34 are provided with indentations 36. Such indentations further serve to prevent slippage of the electrode within the casing. Indentations may project inside the casing or out towards the electrode holder. The outside projections may be cupshaped to provide outside faces following the curvature of the casing. Such indentations alone will give valuable efiect without the use of continuous corrugations, but ordinarily the use of continuous corrugations is found desirable.

It is understood that the examples given are presented only by way of illustration and that the same may be modified in many particulars.

What I claim is:

1. An electrode casing for self-baking electrodes of the type adapted to be gripped by an electrode holder and held in a smelting furnace, consisting of a metallic casing surrounding the electrode having corrugations or projections formed in its outer wall whereby substantially less than all of its surface area within such an electrode holder will be in contact with such holder whereby heat transfer to such holder will be materially reduced.

2. A structure as specified in claim 1 in which not over of the area of the casing within the holder will be in contact with the holder.

3. A structure as specified in claim 1 in which the corrugationsform continuous channels in the surface of the casing through which hot, gasesmay pass up between the casing and the electrode holder.

4. A structure as specified in claim 3 in which the projections extending outwardly between the said channels are discontinuous.

5. In combination with a water-cooled electrode holder adapted to hold an electrode casing above a smelting furnace, a generally circular electrode casing within such holder adapted to receive carbonaceous paste and to carry such paste slowly down toward the furnace whereby the paste will gradually be heated and baked, such electrode holder being characterized by the fact that it has shallow longitudinal channels formed in its outer wall whereby substantially less than all of its surface area within the electrode holder will be in contact with such holder so that heat transfer from the casing to such holder will be materially reduced and whereby furnace gases may pass upwardly between the casing and the holder in sufficient volume so that the baking zone of paste material within the casing will be raised to a level above the bottom of the electrode holder.

No references cited.

Patent No.1 2,876,269 March 3, 959

Einar Tommelstad It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 21, for "casing above a" read casing in a Signed and sealed this 30th day of June 1959.

(SEAL) Attest: v

KARL H.- AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Ofl'icer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,876,269 March 3-, 1959 Einar Tommelstad n the printed specification It is hereby certified that error appears i n and that the said Letters of the above numbered patent requiring correctio Patent should read as corrected below.

Column 4, line 21, for "casing above a" read casing in a Signed and sealed this 30th day of June 1959.

(SEAL) Attest:

KARL H. AXLINE Attesting Officer ROBERT C. WATSON Commissioner of Patents

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