Cathode rod comprising a metal sole, for hall-heroult electrolys

Chemistry: electrical and wave energy – Apparatus – Electrolytic

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Details

204289, 204294, 204290R, C25C 308, C25C 316

Patent

active

046473564

DESCRIPTION:

BRIEF SUMMARY
The invention relates to the construction of electrolysis cells for the production of aluminium by the Hall-Heroult process. It relates, more particularly, to a cathode rod comprising a metal sole intended to increase the cross-section for passage and to make the distribution of the cathode current uniform.


DESCRIPTION OF THE PRIOR ART

The cathode of a Hall-Heroult electrolysis cell is formed by juxtaposing a group of carbonated blocks provided on their bottom face with 1 (or sometimes 2) open grooves in which there are fixed, generally by pouring cast iron, some steel rods of square, rectangular or circular cross-section to which there are connected the conductors joining the successive cells forming a series.
The steel rods used for extracting the cathode current thus offer a limited contact surface with the carbon causing a considerable drop in voltage at the carbon/cast iron interface.
To reduce this voltage drop, it is also known to increase the cross-section of the steel rod, at least in the sealed zone in the carbon, while maintaining a normal or reduced cross-section when passing through the external portion of cell insulation so as to avoid excessive thermal leakages.
However, such action is necessarily limited as the thickness of carbon on the flanks of the groove must be sufficient mechanically to resist the stresses due to thermal expansion of the cathode rod and of its sealing means when the cell is set into operation.


OBJECT OF THE INVENTION

The object of the present invention is substantially to increase (by more than 10%) the cross-section of steel available for removing the cathode current, and the contact surface between the carbon and the cathode conductors. It involves providing each cathode rod with a metal sole in electrical contact with the horizontal base of each carbonated block, the sole being welded to the cathode rod to permit the passage of the electric current. Moreover, a continuous steel screen may he arranged beneath the sole in electrical contact with the sole, thus preventing infiltration of liquid aluminium and molten cryolite and substantially increasing the service life of the electrolysis cell.
FIG. 1 relates to the prior art.
FIGS. 2 to 15 illustrate the implementation of the invention.
All the figures are shown in a vertical section.


DESCRIPTION OF THE FIGURES

FIG. 1 shows the conventional arrangement of a carbonated cathode block 1 in which the rod 2A is sealed by cast iron 3.
In this case, the rod is flush with the base of the carbonated block. In the right-hand portion of FIG. 1, the rod 2B in an alternative embodiment can extend, more or less, beyond the base plane of the carbonated block 3. The successive cathode blocks are usually assembled by a gasket 4 made of carbonated paste.
FIG. 2 shows a first embodiment of the invention. Two thick sheets of mild steel 5 connected to the base of the carbonated block 1 by a layer of electrically conductive elastic material 6 have been welded to the cathode rod.
In a variation (FIG. 2A), the steel sole 5 can be formed by a steel-copper colaminate, the copper face 5A being in contact either directly with the carbonated block 1 or via the elastic conductive layer 6. The thickness of the copper layer 5A should preferably exceed a minimum value which can be estimated as about 5% of the steel layer, corresponding to the solubility of copper in steel at 900.degree.-950.degree. C. so that the entire copper layer does not disappear by diffusion in the solid state into the steel.
The malleability of hot copper facilitates the establishment of good contact with the cathode block and, if necessary, can partially compensate the deformations of the steel sole.
Moreover, since copper is a much better conductor of electricity than steel, a significant reduction in the voltage drop takes place in the cathode collectors.
FIG. 3 shows the four stages, 3a, 3b, 3c, 3d, in the procedure used for constructing the assembly in FIG. 2.
FIG. 3a shows the first stage:
After the carbon block 1 has been turned so that the groove 7 ls upper-m

REFERENCES:
patent: 2528905 (1950-11-01), Ollivier et al.
patent: 2593751 (1952-04-01), Grolee
patent: 2846388 (1958-08-01), Morel
patent: 3551319 (1970-12-01), Elliot
patent: 4488955 (1984-12-01), Bertaud et al.

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