NZ227574A

NZ227574A - Anode connection shield cover for aluminium electrolysis cell made of cardboard

Info

Publication number: NZ227574A
Application number: NZ22757489A
Authority: NZ
Inventors: Leif Meisingseth
Original assignee: Norsk Hydro As
Priority date: 1988-01-12
Filing date: 1989-01-10
Publication date: 1990-09-26
Also published as: NO880099L; AU2843789A; RU1838453C; EP0324632A1; IS3427A7; CA1330320C; ES2031685T3; BR8900109A; NO163141C; EP0324632B1; NO163141B; DE68901461D1; AU609567B2; NO880099D0

Description

V 7 5 74 Priority Date(s): .. Q;. .UB&\....

Complete Specification Fiied: trJjjV?.. Class: .C2^07^.> Pubiiceticri Date: .SEP. .1930. P.O. Journal, No: .. BS.fa Patents Form No;5 PATENTS ACT 1953 COMPLETE SPECIFICATION "COLLARS FOR THE PROTECTION OF ANODE HANGERS IN ALUMINIUM ELECTROLYSIS CELLS" WE, NORSK HYDRO a.s., a Norwegian company of Bygdoy Alle 2, O0p Oslo 2, Norway, hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: 1 (followed by la) ,rJ C « ►"H , - C / 1/ .< 1 227 S7* la The present invention relates to a protecting collar being used in connection with the application of a protecting cover in the form of a carbonaceous paste on the cast connection between a carbon anode and the nipples of an anode hanger and around the lower part of the nipples, as described in the precharacterizing part of the attached claim 1.

Aluminium is mostly produced by electrolysis of aluminium oxide dissolved in a cryolite bath. The electrolysis cells enabling this, consist of a carbon cathode disposed in a steel shell which on the inside is thermally isolated with refractory materials. A carbon anode, or several carbon anode bodies, is provided above the carbon cathode and is partly submerged in the cryolite bath. Thus the oxygen descending from the decomposition of the aluminium oxide will gradually oxidize the carbon anode bodies.

Electric current is led from the top to the bottom of the cells, and the cryolite is kept in its melted condition by means of the Joule-effect at a temperature close to the solidification temperature. The most common temperatures for these cells are between 930 and 980° C. The aluminium produced is therefore in a liquid state and is deposited on the carbon cathode due to gravity. The aluminium produced, or part of the aluminium produced, is regularly removed from the cell by means of a suction pump and transferred to a casting ladle, and is in turn,eH5c2mted^to_ a melting pot. 2 22 7 5 74' The carbon anode bodies are fixedly connected to so-called anode hangers, and to obtain good electrical and mechanical connection the anode hangers are releasebly fixed to the anode bar by means of a clamping device. As the carbon bodies are gradually consumed and as aluminium metal is removed from the cells (the metal actually represents the cathode), the anode bar, with the carbon anodes attached thereto, is lowered to keep a constant distance between the bottom side of the anodes and the cathode.

In an electrolysis cell of common size there is about 20-30 carbon anodes, and since these anodes are consumed gradually, they have to be changed after 20-30 days, depending on the size of the anodes. Thus, in each cell there is one anode exchanged every day.

As mentioned above, the carbon bodies are fixedly connected to anode hangers. The anode hangers serve two different purposes, namely to keep the carbon bodies at a predetermined distance from the cathode, and to conduct the electric current from the anode bar down through the carbon bodies.

The amperage for the electrolysis cell lies between 100 000 and 300 000 amps.

Electric current connections and bus bars are therefore made of industrial metals with good electric conductivity i.e. usually pure copper or aluminium.

Since the lower part of the anode hangers are situated close to the cryolite bath which has high temperature, this part of the anode hanger is, however, made of material which is resistant with regard to the high temperature, i.e. usually steel.

The anode hangers are connected to carbon bodies through a casting connection using cast iron.

Around the lower part of the nipples and over the cast connection is provided a protecting ring of carbonaceous paste. This is done by firstly placing a protecting collar around the nipples and then afterwards filling up the spacing between the collar and the nipples with the carbonaceous paste. The protecting ring of carbonaceous paste is finally hardened approximately 24 hours after the carbon anode has been inserted into the cell and prevents the elecrolytic bath from coming into contact with the steel and the cast iron. Such contact is liable to cause dissolution of the iron and steel which in turn may result in that the nipples and cast iron become corroded such that the carbon falls off the nipples.

The protecting collars which up until today have been employed, have due to the high temperature been made of aluminium material. These aluminium collars have however been expensive to manufacture and to use. The last not least due to the fact that it is expensive to remove the aluminium material before the anode buts are crunched (the carbon is reused).

Surprisingly, in spite of the high temperature of the cast iron during the casting operation andftwthe high temperature of the electrolytic bath it has accord: >n 227574 22lSltf 4 been found that the collars can be manufactured from pasteboard or brown card board. Hereby large savings have been achieved with regard to reduced manufacturing costs. Further, it has been possible to avoid the problems related to the cleaning of the anode hangers as the card board collars burns away during the electrolysis process due to the high temperature, but after the carbonaceous paste has hardened.

The invention is characterized by the features of the attached claim 1 and the independent claims 2-6.

The invention will now be further described by way of examples and with reference to the drawings in which: Fig. 1 shows an anode hanger onto which is mounted a carbon anode, Fig. 2 shows an enlarged section of the connection between a nipple and the carbon anode shown in Fig. 1, Fig. 3 shows an example of a card board collar according to the invention, and Fig. 4 shows another example of a card board collar according to the invention.

Fig. 1 shows as mentioned above an anode hanger 1 which has mounted thereto a so-called prebaked carbon anode 2 which is used in cells producing aluminium by electrolysis.

The anode hanger 1 consists of an upper part, anode rod 3, of aluminium, and a lower part of steel. Tlre~stegl part further consists of a cross member 15 which downwardly protruding nipples 4.

Z.11SlUc The carbon anode 2 is fixedly connected to the nipples 4 by means of a cast connection 7 (cast iron) as shown in Fig. 2. Over the cast connection 4 and around the lower part of the niples is provided a protecting ring made of carbonac eous paste. This is, as previously mentioned, made by at first placing a protecting collar around the nipples and thereafter filling up the empty space between the collar and the nipple- In Fig. 3 is shown an example of a protecting collar 8 of card board according to the invention. The collar is made of a piece of card board strip which is provided with a locking arrangement at its ends. The locking arrangement as here shown consists of locking tongue 10 and a slit or cut 12.

The collar is shaped, as will be appearant from Fig. 3, by bending the collar so that the tongue may be lead through the slit 12. Cuts 11 at the inner end of the tongue provides barbes which prevents the tongue from being pulled out of the slit.

Fig. 4 shows another locking arrangement. Here the card board strip 9 is at its ends provided with transverse cuts 13,14 streching from the side edge to the centre line in opposite directions. The collar is shaped by bending the card board strip and letting the two slots (cuts) 13,14 grip into one another.

The invention is not in any way limited to the above examples. Thus the collars may be made of card board strips where the ends are overlapping one another and are fixed by means of gluing, locing pin or the like.

Z 2."1 sntf

Claims

WHAT WE CLAIM IS:

1. A protecting collar being used with a protecting cover of carbonaceous paste over a casting connection between a carbon anode and a nipple of an anode hanger, and around the lower part of the nipple, where the collar is placed around the nipple and the carbonaceous paste thereafter is provided in the spacing between the collar and the nipple, characterized in that the collar is made of card board.

2. A protecting collar according to Claim 1 characterized in that the card board is brown paste board.

3. A protecting collar according to either Claim 1 or Claim 2 characterized in that the collar is made of a strip of card board and that ends of the card board strip are attached to each other by means of a connecting arrangement.

4. A protecting collar according to Claim 3, characterized in that the connecting arrangement comprises a locking tongue and a slot.

5. A protecting collar according to Claim 3, characterized in that the connecting arrangement comprises two cuts one at each end of the strip.

6. A protecting collar according to Claim~57~c -7- 0 74 2^75?V in that the ends of the strip overlap and are glued to each other.

7. A protecting collar according to Claim 3, characterized in that the ends of the strip are overlapping and attached to each other by means of a locking pin or the like.

8. A protecting collar substantially as hereinbefore described with reference to and as shown in figure 3 or figure 4 of the accompanying drawings. NORSK HYDRO a.s.. by their authorised agents P.L. BERRY & ASSOCIATES per: ^