Coating processes – Measuring – testing – or indicating
Reexamination Certificate
2000-09-16
2002-09-24
Barr, Michael (Department: 1762)
Coating processes
Measuring, testing, or indicating
C427S058000, C427S113000, C427S294000, C427S282000, C427S314000, C427S430100, C118S050000, C118S064000, C118S668000, C118S679000, C118S689000, C118S406000
Reexamination Certificate
active
06455097
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to a method of applying a treating liquid to a porous body, in particular a prebaked carbon component of an aluminium production cell, such as an anode block or a cathode block, by placing the body in a treating chamber and impregnating at least a part thereof with the treating liquid, this impregnation being assisted by the application of a pressure differential.
The invention also relates to an apparatus for carrying out this method and use of the apparatus for applying a treating liquid to a prebaked carbon component of an aluminium production cell.
BACKGROUND OF THE INVENTION
The treatment of prebaked carbon components of aluminium production cells, such as anode blocks, cathode blocks or cell sidewalls to improve their resistance to the conditions prevailing in the cell has already been proposed.
WO 94/29200 (Manga niello et al.) discloses treating a prebaked carbon-based anode of an electrolytic cell for the production of aluminium, in particular by the electrolysis of alumina in a molten fluoride electrolyte, over its sides and top to improve the resistance thereof to erosion during operation of the cell by air and oxidising gases released at the anode, by immersing the anode in a boron-containing solution containing 5-60 weight % of H
3
BO
3
or B
2
O
3
in methanol, ethylene glycol, glycerin or water.
It was found advantageous to carry out this treatment with a heated solution, but this involved heating of the anode, which consumed large quantities of energy. Attempts were therefore made to carry out the process at ambient temperature because no special heating equipment would be required. Low temperature application however required the careful choice of solvents and surfactant agents in order to reduce the treatment time as far as possible.
For prebaked anodes, only the top and top side surfaces need to be protected, so it was suggested to dip the anode upside down into the solution. But this is impractical when the anodes are fitted with rods for connection to a suspension device which also serves as a current lead-in. Furthermore, it is inconvenient to treat the anodes first and then fix the suspension rods.
To overcome this difficulty it would be possible to dip the anode in the treating solution with the rodded top side up, and protect the bottom part of the anode by blocking its pores with a fugitive agent that prevents impregnation with the boron-containing compound, and can be removed afterwards. This however entails additional operations and careful selection of the fugitive agent.
To speed up the process, it was suggested to assist the impregnation by the application of a pressure differential, by pressure or vacuum. However, no practical way of doing this was disclosed.
It is known from WO 93/25731 (Sekhar/de Nora) to treat carbon-containing components of an aluminium production cell to protect them from attack by liquid elements, ions or compounds by applying a coating of a refractory boride from a slurry composed of particulate refractory boride in a colloidal carrier. Sometimes it is desirable to apply such coatings selectively to the parts of the components which will be exposed, but methods and apparatus for doing this remain to be developed.
WO 94/24069 (Sekhar) describes treating components of aluminium production cells by impregnating them with various colloidal agents. U.S. Pat. No. 5,534,130 (Sekhar) describes the protection of the cell sidewalls of aluminium production cells by impregnating them with agents based on aluminium phosphate. Again, it would be desirable to perfect ways of applying these methods to selected parts of the components in an efficient manner.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate the above-described problems and shortcomings of the available methods and apparatus.
It is another object of the invention to provide a method and apparatus of the above type in which anode blocks or other bodies can be treated without necessarily pre-heating the bodies, while assuring an effective impregnation of the treating liquid into the pores of the treated part, and enabling the treatment of large numbers of the bodies in an efficient manner.
A particular object of the invention is to provide a method and apparatus which can use a hot treating solution in a very efficient manner to treat selected parts of the body, without necessarily heating the treated body substantially above ambient temperatures (although it is contemplated that treatments with cold solutions and hot anodes are also possible).
The method and apparatus of the invention were developed specifically with a view to overcoming the above-mentioned difficulties encountered when treating rodded prebaked anodes, but the method and apparatus can be used to treat other components of aluminium production cells and generally any porous bodies that need to be treated over part of their surface.
A method according to the invention comprises the following steps.
First, the body to be treated, in particular an anode block, a cathode block or a sidewall for an aluminium electrowinning cell is inserted, with its part to be treated facing up, in the treating chamber.
At least one sealing member is then applied to the inserted body in such a manner as to isolate the chamber into two parts: an upper part of the treating chamber around the part of the body to be treated, isolated from a lower part of the treating chamber around a bottom part of the body which is not to be treated.
Next, the upper part of the treating chamber is filled with a treating liquid to cover the part of the body to be treated, and a pressure differential is applied to intake an amount of the treating liquid into pores in the part of the body to be treated so that the pores of the body become impregnated with the treating liquid. The pressure differential may be applied simply by evacuating the lower part of the treating chamber. Application of the pressure differential is usually continued until all of the pores of the part of the body to be treated are filled. The exact degree of penetration can however be chosen for any particular application, e.g,. stopping the application of the pressure differential before all the pores are filled, or continuing the pressure differential for some time after the pores have been filled.
After completion of the impregnation, treating liquid which has not been absorbed by the body but remains in the upper part of the treating chamber is removed from the treating chamber, before or after the sealing member or members is/are released to free the body, and the treated body is removed from the treating chamber.
The sealing member may be arranged to surround the body and fit around its sides. In this case, the sealing member(s) is/are preferably arranged to allow a loose fit around a body, permitting insertion and removal thereof into or from the treating chamber, or to provide a sealing fit around a body in the treating chamber. Adjustment of the sealing member(s) can for example be controlled hydraulically, pneumatically, mechanically or electro-mechanically.
Bringing the sealing member to the sealing position can for example be controlled by detecting when the body reaches a given position, and actuating the sealing member(s) to sealably engage with the body when the body has reached said given position.
The or each sealing member preferably comprises an elastomeric body which is elastically deformed to provide sealing contact when applied against a body to be treated.
Alternatively, the sealing member can be arranged to apply or be applied against the bottom face of the body to be treated, thus allowing treatment of the entire sides and top of the body, or at least the lower parts of the sides.
The treating liquid in the upper part of the treating chamber is usually maintained at a temperature well above that of the body to be treated, for example a temperature in the range 60° to 120° C. To maintain the treating liquid at a more-or-less constant temperature, it is necessary to heat it to co
Berclaz Georges
de Nora Vittorio
Johnston Gaynor
Barr Michael
Deshmukh Jayadeep R.
Moltech Invent S.A.
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