GB794421A - Improvements in or relating to electrolytic cells - Google Patents

Abstract

794,421. Electric furnaces. PECHINEY COMPAGNIE DE PRODUITS CHIMIQUES ET ELECTROMETALLURGIQUES. April 6, 1954 [April 7, 1953; Feb. 19, 1954], No. 10076/54. Class 39(3) [Also in Group XXXVI] A method of reducing or preventing electromagnetically produced variations in the level 1, 2 of the surface of a layer of molten metal, e.g. aluminium, in an electrolytic cell 3 and reducing or preventing similarly produced flows of the metal in the layer, comprises reducing horizontal current components in the metal by making the areas of the anode surface and cathode surface in the metal substantially equal and by containing the molten material in the cell by walls of non-conducting material, and reducing the intensity of the magnetic field due to current flow to and from the cell by dividing at least one of the two paths by which current enters and leaves the cell into a number of parallel conductors A, B. The walls containing the metal are of solidified electrolyte, e.g. a fluoride where the metal is aluminium, and the electrode areas may be made equal by banking the fluoride at the sides of the cell. Vertical and homogeneous current flow in the metal is ensured by arranging for the cathode to have a horizontal equipotential surface by making the current paths from the cathode to the outer circuit of equal resistance, e.g. by employing vertical steel bars 12 as cathode leads. In one embodiment, Fig. 1, a number of cells 3 are connected in series by parallel bars A, B disposed in the same plane, current being taken at each side of the cell from bars B by vertical leads 11 to an anode 4 of the Soderberg type, and leaving the cathode by bars 12 and bars A connected to the succeeding cell. The bars 12 may be horizontal and a prebaked anode may be employed. In another embodiment, Fig. 5, horizontal bars 5 are disposed above the cell and connected at each end to a supply bar B, and the bars 5 may be mounted at such a height above the level 1, 2 that the field there is negligible. Vertical current, components are suppressed by arranging the cells of a row side by side, current being taken either by a vertical conductor between two adjacent cells from the cathode of one cell to the anode of the next. or by vertical conductors at each side of each cell connected to the outlet leads from -the cathode of the preceding cell. Return conductors may be divided and positioned beneath the row of cells or in the centre beneath and between two adjacent rows, the return conductors alternating with the bars A, B. In another embodiment, Fig. 14, current is fed at both ends to a pair of bars 5 by vertical leads from bars 8B which are positioned about exit bars 8A, the bars 12 being horizontal. In a modification of this embodiment, the bars 8A, 8B at each side of the cell lie side by side in the plane of the level 1. 2. and the bars 12 may be vertical. In all the embodiments described above, the conductors may be magnetically screened, e.g. by employing screens a, b, c, d, Fig. 13, where a Soderberg anode is used. Demagnetizing coils may be employed, e.g. around the iron sheath of a Soderberg anode or around the cell, i.e. having a vertical axis, or at the ends of horizontal cathode bars 12 and having a horizontal axis. Specification 657,507 is referred to.