Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a protecting collar
being used in connection wi~h the application of a protectin~
cover in the form of a carbonaceous paste on the cast connection
- between a carbon anode and ~he nipples or studs of an anode hanger
-,
and around the lower part of the nipples, as described below.
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 insulated with
refractory materials. A carbon anode, or several carbon anode i~
~ bodies are provided above the carbon cathode and are partly
-~` submerged in the cryolite bath. Thus tha oxygen stemming from the ~-~
~ 1,
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 ls kept in its melted condition by
i 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
' decanted to a melting pot.
I The carbon anode bodies are fixedly connected to
;j
s~ so-called anode hangers, and to obtain good electrical and
`i mechanical connectlon the anode hangers are releasably fixed to
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the anode bar by means of a clamping device. As ~he carbon bodies
- l
~ are gradually consumed and as aluminium metal is removed from the
,j
cells (the metal actually represents the cathode) r 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
-~i cathode.
In an electrolysis cell of common size there are 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 i~ 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
i 20 made of industrial metals wlth good electric conductlvity 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 s~eel.
In terms of construction, the steel part of the anode
hanger consists of a cross member or bar with two or more ;;;
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downwardly protruding cylindrical nipples, while the upper part of
the anode han~er has a rectangular or quadratic cross section and
is welded or in some o~her way connected to the st~el part.
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 -
connectlon is provided a protecting ring of carbonaceous pas~e.
, This is done by firstly placing a pro~ecting collar around the
3 nipples and then afterwards filling up the spacing between the
lQ collar and the nipples with the carbonaceous paste. The
protecting ring of carbonaceous paste is finally hardened
approximately 24 hours af~er the carbon anode has been inserted
into the cell and prevents the electrolytic bath from coming into
contact with the steel and the cast iron. Such contact is liable
to cause dissolution of the iron and steel whlch in turn may
` result in the nipple and cast iron becoming corroded such that the
`` carbon falls off the nipples.
The protecting collars which up until today have been
employed having, due to the high temperature, been made of
alumlnium material. These aluminium collars have however been
expensive to manufacture and to use. This is at least in part due
to the fact that it is expensive to remove the aluminium material
before the anode butts are crushed (the carbon is reused).
Surprisingly, in spite of the high temperature of the
cast iron during the casting operation and the high temperature of
the electrolytic bath i~ has according to the invention been found
that the collars can be manufac~ured from paste-board or brown
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cardboard. 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 cardboard collars burn away during the electrolysis process
due to the high temperature, but after the carbonaceous paste has
hardened. ~ `
According to a broad aspec~ of the presen~ invention,
there is provided a protective collar for use with an anode hanger ! "
for supporting an anode in an electrolytic cell for the production
of aluminium by electrolysis, the anode hanger comprising a bar
from which stubs protrude, the stubs being connected to the anode
by means of cast iron connections, a protecting ring of
carbonaceous paste being formed by pouring the paste within
collars to form a cover over the cast iron and around the lower
part of the stub, characterised in that each collar is made of
cardboard.
The invention will now be further descrlbed by way o~
examples and with reference to the drawings in which,
Figure 1 shows an anode hanger onto which is mounted a
carbon anode,
Figure 2 shows an enlarged section of the connection
between a nipple and the carbon anode shown in Figure 1, ~`
Figure 3 shows an example of a cardboard collar -
according to the invention, and
Figure 4 shows another example o~ a cardboard collar
according to the invention.
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~ 33~3~0
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Figure 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. The steel part
further consists of a cross member or bar 15 which is provided
with three downwardly protruding nipples or studs 4.
The carbon anode 2 is fixedly connected to the nipples 4
~ by means of a cast connection 7 (cast iron) as shown in Figure 2.
- 10 Over the cast connection 7 and around the lower part of the
nipp]es is provided a protecting ring 6 made of carbonaceous
- paste. This is, as previously mentioned, made by at first placing
a protecting collar 5 around the nipples 4 and thereafter filling
up the empty space between the collar and the nipple.
, In Figure ~ is shown an example of a pro~ecting collar 8
; of cardboard according to the invention. The collar is made of a
piece of cardboard 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 slot 12.
s 20 The collar is shaped, as will be apparent ~rom Figuxe 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 barbs
which prevent the tongue from being pulled out of the slit.
, :.
.
Figure ~ shows another locking arrangement. Here the
cardboard strip 9 is at its ends provided with transverse
cuts 13,14 stretching from the side edge to the centre line in
opposition directions. The collar is shaped by endlng the
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~ 3~20
26625-84
cardboard 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 cardboard strips where
the ends are overlapping one another and are fixed by means of
gluing, a locking pln or the like.
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