US2528905A - Construction of the lower portion of igneous electrolytic cells - Google Patents

Description

Nov. 7, 1950 P. J. M. c. OLLIVIER ETAL 2,528,905

CONSTRUCTION OF THE LOWER PORTION OF IGNEOUS ELECTROLYTIC CELLS Filed April 1, 1948 2 Sheets-Sheet 1 Final Fie.4-

I 3nue ntors Pierre, Jean-Marie I.O1'luner nd. Rene A.P.G.Per1eres (Ittomeg 2 Sheets-Sheet 2 III/ Fie

C. OLLIVIER ET AL IGNEOUS ELECTROLYTIC CELLS P. J. CONSTRUCTION OF THE LOWER PORTION OF Nov. 7, 1950 Filed April 1, 194a v Q Zfipveqfors Pierre Jean-Mane C..O111u1er nd Rene A. P. G.Peri.eres

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/ attorney Patented Nov. 7, 1950 CONSEREJCTION OF THE LOWER PORTION OF IGNEGUS ELECTROLYTIC CELLS Pierre Jean Marie Oasimir Ollivier, Savoie, and Rene Amans Pierre Gabriel Perieres, Paris, France, assignors to Compagnie cle Frcduits Chirniques et Electrometallurgiques Alais,

Froges et Oamargue, Paris, France, a corporation of France Application April '1, 1948, Serial No. 18,388 in France September '8, 1947 2 Claims.

The present invention relates to the construction of the lower portion of igneous electrolytic cells, for instance of the bottom which constitutes the cathode portion of the cell in the case of electrolysis of alumina dissolved in molten cryolite for the obtainment of aluminium, or of thebottom portion constituting the anode portionin the super purity aluminium cells.

At the present time, igneous electrolytic cells, for the manufacture or refining of aluminium, have their current lead bars disposed parallel to the bottom of the pot, that is to say in horizontal position.

This arrangement involves some drawbacks. The cross section of the metallic bars is calculated as a function of the current density where said bars roject from the carbon blocks, that is to say where the current is maximum, Whereas, under the central portion of the pot the current density is much lower. As the bar is of the same cross section over its whole length, the amount of metal that is used is too great.

When, for the same current value, the interval between anodes and sides of the cell is increased, as it is the present tendency, or when the electrolytic cell is fitted, on its lateral faces, with a heat insulating layer, the length of the current lead bars is increased in accordance with the thickness of this layer, which further increases the amount of metal to be used. Finally, in the case of electrolytic cells to be operated with high current values, for instance 100,000 amperes, the weight of the current lead bars, which is to be increased in accordance with the value of the cell width or with the thickness of this layer, is so high that it becomes very difficult to make the bottom portion of the electrolytic cell.

The object of the present invention is to eliminate'these drawbacks.

' A feature of our invention consists in disposing the current lead bars no longer parallel to the bottom of the electrolytic cell, but perpendicular to this bottom, so that the ends of these bars, after passing freely through the bricks that form a heat insulating layer under the carbon lining of the cell and the vault that supports said cell (the expression passing freely meaning that said bars are not fixed to said bricks nor to said vault),-with the interposition of a packing device, open into a'free space provided under the electrolytic cell.

Other features of our invention consist in'particular constructions of the bottom portion of the" electrolytic cells for the manufacture or refining of aluminium, with vertical current leads.

Preferred embodiments of our invention will. be hereinafter described with reference to the ac-. companying drawings, given merely by way of example, and in which:

Fig. l is a vertical sectional View of the pot of an electrolytic cell for the manufacture or refining of aluminium, the bottom of the pot being made of a paste consisting of carbon and pitch in which the intermediate portions of the current leading conductors are embedded, the ends of said conductors projecting from the bottom of the pot at rightangles thereto;

Fig. 2 shows the pot of a similar cell, the bottom of which is constituted by carbon blocks, previously baked, in which the current leading. conductors, which project vertically therefrom, are fixed by means of a molten metal;

Figs. 3 and 4 are detail views in section, at right angles to each other, illustrating. the sealing of a metal bar in a block of the cell bottom, in the case of a bar of usual section; i

Figs. 5 to 9 inclusive show a preferred form of current leading conductor, of cross-shaped transverse section;

Fig. 5 is a perspective view of such a conductor;

Fig. 6 shows in plan view the shape of the notch to be provided in the under face of the carbon block for sealing the conductor therein;

Figs. 7 and 8 show the conductor after sealingthereof in the carbon block, Fig. 7 being a sectional view on the line 'l-l of Fig. 6 and Fig. 8 a sectional View on the line 8-8 of Fig. 6;

Fig. 9 is a view similar to Fig. '7, but with a slight deflection of the top part of the conductor, in order to improve the fixation;

Fig. 10 shows a portion of the bottom of the electrolytic cell, with its heat insulating lining, this construction including an advantageous device for obtaining airtightness in the passage of the cross-shaped current lead through the heat insulating lining and the concrete vault that supports the electrolytic cell, while enabling this conductor, to follow the upward movement of the carbon block in which it is sealed.

In Fig. 1 of the drawings, reference numeral 1! designates thepotlining, made of a paste ofcarbon and, pitch, in which the current leads 15 are embedded. There are many of these current leads, made of small cross section, soas to increase the surface cf contact between the bars and the carbon paste. The barsmay, asshoyvn by the drawing, be of T-shaped transverse section, so as to reduce their length toa minimum. They extend through the lay-er of .brieks L2 which constitutes the heat. insulating supportiof the cell, and also through the concrete vault H which supports the whole of the cell and thus constituting a carrier structure for the latter, passages I 8 being provided for said bars when heat insulating layer [2 and vault I! are built.

In the embodiment illustrated by Fig. 2, the current leading bars have 'a T-shaped forged end which is sealed in the carbon paste or in metal poured in grooves provided in the lower portion of the carbon blocks. Said bars l5 extend vertically through passages l8 as above referred to.

As shown by Figs. 3 and 4, bar [5 is sealed in block M by means of a carbon paste or a molten metal layer 13.

The cross-shaped sealing arrangement illustrated by Figs. 5 to 9 permits of combining a satisfactory strength with an advantageous electric contact between the bar and the carbon block.

In order to obtain this result, according to our invention, we provide in the under face of carbon block M (Fig. 6) two notches forming a cross 19, these notches running along the diagonals of the rectangle formed by the under face of said carbon block and stopping at a distance from the edges of this rectangle. Said notches are made of suitable length and depth to ensure a good sealing connection both from the mechanical and from the electrical point of view.

The cathode or'anode connection is obtained through two metal sheets of a thickness calculated according to the current density to be obtained where the molten metal is in contact with the carbon block.

The shape given to this connection device (Fig. 5) ensures a good rigidity thereof, which may be a supplementary advantage. 'The device in question is constituted by two metal sheets 20, folded and welded together at some points 2|, or assembled in any suitable manner. If it is desired to increase the contact area between the connecting metal plates and the molten metal cast at [3, the portion of said plates located in grooves I9 is made of larger width at 22 (Fig. 5).

This arrangement ensures an important advantage, to wit that of not weakening the block by grooves of large dimensions opening to the outside and of requiring a relatively small amount of cast metal, so that it produces neither an excessive thermal shock nor an undue expense of metal when the sealing operation is performed.

Various shapes of grooves may be imagined. Two of them are given by way of example. 7

Fig. 7 illustrates the sealing of a cross-shaped current lead 23 which does not include an enlarged portion as shown at 22 in Fig. 5. This Fig. '7 corresponds to a section on the line 1-l of Fig. 6. Fig. 8 is a section on the line 8-8 of Fig. 6. In both of these views, reference numeral l4 designates the carbon block and I3 the metal used for sealing purposes. Fig. 9 shows, another type of sealing, according to which the top portion 25 of the current leading conductor 23 is slightly bent, that is to say laterally deflected, so as to improve the strength with which the'current leading bar is sealed in the metal portion I3. In this case, of course, the groove 26 provided in carbon block 14 must also be slightlyoblique.

, In view of the narrowness of the groove formed in the block. the space to be filled with sealing metal is much smaller in the case of cross-shaped sealing than in that of ordinary sealing, an advantage which exists, although to a lower degree, in the case of vertical sealing.

When the current leading bars are disposed perpendicular to the bottom of the electrolytic cell crucible, it is necessary toplace the cells on 'a raised floor or above a hollow space so as to permit of easily reaching the lower ends of the metallic bars, to which are to be fixed the conductors that connect the outgoing terminal of a cell to the incoming terminal of the next one,

or vice-versa.

The vertical current leading bars therefore extend through the whole of the heat insulating layer l2, provided under carbon blocks 14 (or under the crucible bottom constituted by a single paste layer) and also through the vault ll of the concrete floor that supports the cell, in a hollow l8 provided in the masonry when the floor and the cell are built. The interval between the metallic bar and the wall that limits this hollow space l8 must be filled in such manner as to remain practically airtight. For, if air could penetrate to the carbon element heated to a temperature of 900 C., it would burn it and the life of the lower portion of the retort would be greatly reduced. It has been found that this airtightness could be obtained solely by means of pulverulent refractory matters. As a matter of fact, after a certain time of operation, it happens that the bottom of the retort moves upwardly. This displacement may be as high as fifteen centimeters. If the current leading bar were fixed rigidly in the hollow space I8, the sealing l3 would be torn off from the carbon block l4, and current could no longer fiow to said carbon block.

It is therefore necessary, according to a very important feature of the present invention, to have the current leadin bar free to move in the hollow space I8 through which it passes. Various arrangements may be imagined for this purpose. One of them is shown by Way of example on Fig. 10. It relates to the case of the metallic bar being of cross-shaped section.

At the upper part of this hollow space [8,

bar 23 is surrounded with a grout of a pulverulent.

refractory material 21. A sheet of asbestos 28 is interposed between the heat-insulating coating [2 and the vault ll. This sheet is previously slit along two lines forming a cross, the edges of the slits being normally closely 'juxtaposed, so that connection bar 23, when inserted in position, forces these edges away from each other, thus forming a joint which is sufiiciently tight for preventing alumina mixed with fine refractory dust, located at 29 above the refractory sheet, from flowin out. The sheet of asbestos 28 should be given a certain degree of mobility so as to permit of adjusting it in position with respect to the connection bar, whereby the lat ter can be'arranged to pass correctly through the slits provided in advance in said sheet.

This sheet of asbestos 28 is housed in a recess proovided in the upper face of a layer of re-: fractory grout 32, interposed between the heat insulating layer of refractory bricks l2 and the vault l1. 1 y

In the thickness of the concrete of said vault [1, there is provided a heat'insulating portion 30, constituted by slag wool, which forms a sec-- ondfzoneintended to ensure air-tightness. This material will be held in position by means of connection bar 23.

When the bottom of the recess happens to move upwardly, which generally takes place while the electrolytic cell is in operation, these sheets 3|, driven by the metallic bar, gradually come to pack the slag W001 tighter and tighter and thus improve the air-tightness of the device.

The arrangement of the current leading conductors at right angles to the bottom of the pot permits of avoiding the drawbacks above mentioned. For instance, when the bottom of the pot is constituted by carbon blocks of square cross section of 500 x 500 mm. or 600 x 600 mm. size, it is possible to seal a vertical bar to every carbon block, whereas with the horizontal arrangement, every bar had to be sealed simultaneously in several blocks. With the present invention, the transverse section of the vertical conductor bar can therefore be adapted exactly to the area that corresponds thereto. Its length is reduced to a minimum, so that its weight is much lower than in the case of horizontally disposed current leading bars, and it becomes easy to build electrolytic cells for high current intensity, as high as 100,000 amperes. But the vertical arrangement of the connection bars has still other advantages such as, for instance, a reduction of the weight of the materials, a gain on the potential drops and the weights of the connections due to the fact that some of the circuits of the plant are shortened.

Cells constructed according to the present invention are thus placed above a vault, on a culvert, on a raised floor or other carrier structure providing a hollow space thereunder, so as to ensure easy access to the current leading elements. This construction therefore facilitates control of the current distribution in the bottom portion of the pot, and it is even possible to insulate one of the vertical bars having a defective sealing, and which corresponds to only a small portion of the bottom area. Finally when the bottom of the retort is constituted by carbon blocks that have been subjected to a preliminary baking, sealing of the current leading elements can be performed much more easily and requires a smaller amount of precautions than in the case of a horizontal bar arrangement.

This improved method of making the lower portion of pots, above described in a detailed manner for igneous electrolytic cells, and in particular those for use in the manufacture of aluminium, can also be applied to electro-metallurgical furnaces.

While we have, in the above description, disclosed what We deem to be practical and efiicient embodiments of the present invention, it should be well understood that we do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the 6 parts without departing from the principle of our invention, as comprehended within the scope of the appended claims.

What we claim is:

1. A construction of the lower portion of an electrolytic cell, which comprises, in combination, a plurality of prebaked carbon blocks disposed in adjacent relation to one another to form a carbon lining at the bottom of said cell, a heat insulating layer under said carbon lining, a carrier structure under said heat insulating layer providing a hollow space thereunder, a plurality of current leading metallic bars each sealed to one of said carbon blocks and extending at right angles to said carbon lining, said bars passing freely through said heat insulating layer and through said carrier structure and projecting into said hollow space, and packing means interposed between said metallic bars and said heat insulating layer and said carrier structure, said packing means including in combination, a pulverulent refractory material filling the space between each bar and the heat insulating layer, a sheet of asbestos arranged between the heat insulating layer and the carrier structure therefor transversely to said bar and frictionally engaged thereon, a compressible packing material filling the space between said bar and said carrier structure below said sheet, and a metal sheet fixed to said bar below said last mentioned packing material and in contact therewith. Y t

2. A construction according to claim 1, characterized in that the current leading metallic bars have a cross-shaped transverse section.

PIERRE JEAN MARIE CASIMIR CLLIVIER.

RENE AMANS PIERRE GABRIEL PERIERES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 673,453 Roberts May 7, 1901 2,012,365 Werner Aug. 27, 1935 2,034,339 Gadeau Mar. 17, 1936 2,344,859 Fox Mar. 21, 1944 2,451,490 Johnson Oct. 19, 1948 FOREIGN PATENTS Number Country Date 542,886 Great Britain Jan. 30, 1942 367,165 France Oct. 22, 1906 OTHER REFERENCES Electrochemistry, 2d edition, 1944, vol. II, page 244, by Creighton and Koehler, Wiley & Sons, Inc., New York.

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