Forming slots in soderberg anodes

Abstract

Claims

3. METHOD OF OPERATING AN ALUMINA REDUCTION CELL HAVING A CONTINUOUS SELF-BAKING ANODE COMPRISING THE STEPS OF FEEDING CARBON ANODE PASTE TO FORM SELF-BAKED CARBON ANODE SECTIONS, WHILE SIMULTANEOUSLY FEEDING WITH THE PASTE AT LEAST ONE ALUMINUM SHEET TO BECOME INTERLEAVED WITH SAID ANODE SECTIONS, SAID PASTE BEING IN DIRECT CONTACT WITH BOTH SIDES OF EACH SHEET, PASSING BOTH THE PASTE AND THE SHEET THROUGH A BAKING ZONE TO CAUSE HARDENING OF THE PASTE, AND TO PRODUCE A TRANSVERSE SLOT AT THE LOWER FACE OF THE ANODE, SAID SLOT BEING LOCATED BELOW AND PARALLEL TO SAID SHEET AND TAPERING INWARDLY TOWARD THE LOWER END OF SAID SHEET.
April 5, 1969 H. c. MARSHALL, JR 3,438,876 FORMING SLOTS IN SODERBERG ANODES Filed Sept. 25, 1966 FIG. I INVENTOR HERBERT CHARLES MARSHALL, JR. ATTORNEYS. Q United States Patent ()1 ice 3,438,876 Patented Apr. 15, 1969 3,438,876 FORMING SLOTS IN SODERBERG ANODES Herbert Charles Marshall, Jr., Florence, Ala., assignor to Reynolds Metals Company, Richmond, Va., a corporation of Delaware Filed Sept. 23, 1966, Ser. No. 581,520 Int. Cl. C22d 1/08; 801k 3/04 US. Cl. 204--67 3 Claims This invention relates to novel self-baking anodes for alumina reduction cells and the method of their use in such cells. More particularly, the invention concerns the provision of such anodes having slots or channels extending along the working face of the anode. There are two types of carbon anodes in general use in alumina reduction cells: (1) prebaked carbon blocks which extend downwardly into the molten electrolyte, and (2) self-baking continuous or Soderberg types of anodes in which carbonaceous anode paste is moved downwardly into the electrolyte and is baked to hardness as it approaches the electrolyte zone of the cell. In the operation of reduction cells employing either of these types of anode, there is a problem of effectively collecting waste cell gases and of maintaining low electrical resistance in the anode. In US. Patent No. 2,958,641 of J. Louis Reynolds, there is disclosed a prebaked type anode for alumina re duction cells comprising a pack or bundle of prebaked carbon slabs arranged with the lower ends of the slabs extending downwardly into the molten electrolyte, the opposed surfaces of the slabs being spaced apart slightly over at least a substantial area of their lower portions to provide deep preformed channels or slots. These slots extend upwardly from the bottom of the anode, and also extend from side to side and are closed at the top. The carbon slabs are interleaved with electrical contact plates made of steel, which extend from side to side of the anode and are located just a little above the bath surface so that their lower edges form the top of the slots. The contact plates are vertically adjustable relative to the slabs so that the anode can be lowered as it burns away while maintaining the depth of the preformed slots within predetermined limits and while keeping the electrical contacts to the slabs close to the molten electrolyte. This arrangement facilitates gas release and collection, but owing to the inherent nature of prebaked anodes, requires an elaborate suspension system. In U.S. Patent No. 2,822,328, there is described a selfbaking anode for alumina reduction cells, which is bifurcated by means of a centrally disposed gas and tar collecting chamber. This chamber, around which the anode paste passes during formation of the baked portion, provides a wide aperture at the lower end of the anode which serves as a feed opening for the collecting chamber, the upper end of the collecting chamber terminating in a dividing vane. The chamber and the vane are of hollow construction and are fixed in position. In accordance with the present invention, there is provided a novel self-baking anode construction whereby the advantages of the pack type of prebaked anode are adapted and extended, for the first time, to self-baking anode production, but with certain additional advantages. The method of the invention comprises the steps of feed ing a self-baking anode paste from a conventional feeding system while simultaneously feeding with the paste at least one, and preferably a multiplicity, of aluminum sheets, passing both the paste and the aluminum sheet through a baking zone to cause hardening of the paste, and, by the progressive melting of such sheet, to produce a slot across the lower face of the anode. This type of anode construction has several advantages, among which are that it provides for quiet and uniform gas release and ease of collection, and it avoids contamination of the electrolyte and of the aluminum produced by the introduction of iron or iron oxides, such as might arise from the presence of steel plates or dividers. The aluminum sheets may serve as electrical contact plates, thus increasing the contact area with the carbon. The arrangement of carbon anode material, aluminum sheets, and slots is shown schematically in the accompanying drawing, in which: FIG. 1 is a side elevation of a feeding anode with the aluminum sheet separators in place; and FIG. 2 is a vertical sectional view of the anode, showing the contour of the transverse slot. In the drawing, FIG. 1 illustrates schematically an alumina reduction cell having anodes of the self-baking or Soderberg type. The anode paste is supplied to a feeding mechanism shown schematically at 1, from which it is fed downwardly to form carbon anode slabs 2, which extend into molten electrolyte 3 in the reduction cell, at the bottom of which there accumulates a pool 4 of molten aluminum. Interleaved between the anode slabs are aluminum sheets 5 which are fed downwardly with the anode paste, as explained previously. In connection with the feeding of the anode paste and the aluminum sheets, slots 6 are formed in the baked carbon at the working end of the anode. These slots extend traversely across the anode face, and are tapered toward the edge of the aluminum sheets, as shown in FIG. 2, where is shown a pair of adjacent carbon sections 2-2, with an aluminum sheet 5 interposed between them. The upper portion 7 of the slot corresponds in size to the width of the aluminum sheet. Toward the lower end of the slot, out-ward tapering occurs, producing an increased width of the slot as shown at 8. The bottom edge of the aluminum sheet forms the upper margin 9 of the slot. Each slot formed by the provision of an aluminum sheet may extend all the way to opposite sides of the anode, or may terminate inwardly of the anode adjacent the sides thereof, whichever is desired. The practice of the invention is illustrated by the following example, which is not, however, to be regarded as limiting: EXAMPLE In a 10,000 ampere alumina reduction cell, having a Soderberg type anode, a A" thickness of aluminum sheet was fed vertically in the top of the anode with the carbon paste. At the working end of the anode, a slot was formed in the baked carbon. This slot was approximately 1 /2" across on the face of the anode, tapering fairly uniformly upward directly under the aluminum sheet to a 'width of about /2". The slot depth was of the order of 8". The cell was found to operate normally in other respects, and the slot was readily maintained during such operation. What is claimed is: 1. An alumina reduction cell having an anode comprising self-baking carbon sections and an aluminum sheet disposed between and in direct contact with adjacent sections, said anode having a transverse slot at the lower face thereof, said slot being located below and parallel to said aluminum sheet and tapering inwardly toward the lower end of said aluminum sheet. 2. An alumina reduction cell in accordance with claim 1, wherein said anode comprises self-baking carbon sections interleaved with a plurality of aluminum sheets, said anode having a series of transverse slots at the lower face thereof, each of said slots being located below and parallel to a corresponding aluminum sheet and tapering inwardly toward the lower end of said aluminum sheet. 3. Method of operating an alumina reduction cell having a continuous self-baking anode comprising the steps of feeding carbon anode paste to form self-baked carbon anode sections, while simultaneously feeding with the paste at least one aluminum sheet to become interleaved with said anode sections, said paste being in direct contact with both sides of each sheet, passing both the paste and the sheet through a baking zone to cause hardening of the paste, and to produce a transverse slot at the lower face of the anode, said slot being located below and parallel to said sheet and tapering inwardly toward the lower end of said sheet. References Cited UNITED STATES PATENTS 473,118 4/ 1892 Heroult 204-29O 2,758,964 8/1956 Liles 204290 XR 2,917,441 12/1959 Donald 204-247 XR 4 5/1967 Sem 204--67 FOREIGN PATENTS 762,812 4/1934 France. OTHER REFERENCES A.P.C. Publication, j. No. 444,238, Hagerup-Larssen, Cl. 13, Subcl. 18, June 1943. 10 JOHN H. MACK, Primary Examiner. D. R. VALENTINE, Assistant Examiner. US. Cl. X.R.

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