DEVICE FOR THE PROTECTION OF ANODE HANGER NIPPLES

DISPOSITIF DE PROTECTION DE SUPPORT D'ANODE

English Abstract

A B S T R A C T
The present invention concerns a device for protecting
anode hanger nipples when manufacturing aluminium in a
Hall-Heroult electrolysis process, made of a composite
material consisting of carbon residues, hardening
material, water and a catalyst. The device is
characterised by two or more prefabricated,
dimensionally stable parts which are designed to be
joined in an arrangement in situ.

Claims

5
C L A I M S
1. Device (5) for protecting anode hanger nipples (6) when
manufacturing aluminium in a Hall-Heroult electrolysis process,
made, for example, of a composite material consisting of carbon
residues, hardening material, water and catalyst,
c h a r a c t e r i s e d b y two or more prefabricated,
dimensionally stable parts which are designed to be joined in an
arrangement (5) around each of the nipples.
2. Device in accordance with claim 1,
c h a r a c t e r i s e d i n t h a t the parts of the
device can be locked together at the ends, which are designed in
the form of a male/female connection (11).
3. Device in accordance with claims 1 and 2,
c h a r a c t e r i s e d i n t h a t the device (5) is
designed in such a way that an annulus (9) is formed between the
nipple (6) and the device (5), which can be filled with, for
example, crushed bath and aluminium oxide so that the expansion
of the nipples (6) in connection with a rise in temperature does
not affect the device (5).
4. Device in accordance with claim 3,
c h a r a c t e r i s e d i n t h a t the upper part of the
device is provided with a diagonal part (10) to make it easier to
pour crushed bath and aluminium oxide into the annulus (9).

5. Device in accordance with claims 3 and 4,
c h a r a c t e r i s e d i n t h a t the size of the
annulus (9) is sufficiently large for the crushed bath and
aluminium oxide material to cover the whole of the surface of the
nipple which is enclosed by the device (5).
6. Device in accordance with claims 1-5,
c h a r a c t e r i s e d i n t h a t the parts are jointed
together by means of a binder.
7. Device in accordance with claims 1-6,
c h a r a e t e r i s e d i n t h a t the parts are fastened
to the nipples and/or the anode by means of a binder.

Description

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The present lnvention concerns a device for the protection of the
lower part of an anode hanger (hereinafter called a nipple~
during the production of aluminium in a Hall-Heroult electrolysis
process, made of a composite material consisting of carbon
residues, hardening material, water and a catalyst.
The anode hanger functions like an electric current conductor and
fastening device for the anode in an electrolysis cell. The lower
part of the anode hanger consists of two or more steel bolts
which are fixed in the anode by casting.
Aluminium is generally manufactured from aluminium oxide
dissolved in a bath consisting mainly of melted cryolite. The
bath is typically kept at a temperature of 940 - 980C. The
cathode represents the bottom of an electrolysis cell formed like
a vessel containing the bath, while the anodes are submerged into
the bath from above. The current is passed through an
electrolysis cell from the anode hanger and through the anode and
the bath/metal layer to the cathode. The anode is oxidised from
its base surface upwards by the oxygen which is formed in the
decomposition phase of the aluminium oxide. In order to be able
to utilise the anode to the maximum, the nipples to which the
anode is fastened must be protected against the liquid bath which
is forced in towards the nipples when the anode approaches
critical consumption level.
Without a protective device the bath would attack the nipples
with erosion of the iron as a result, which is very damaging for
the quality of the metal.
The normal method of protecting the nipples today is to make a
formwork of aluminium tape or cardboard around the nipple so that
an annulus is formed between the formwork and the nipple which is
filled with a granulate consisting of carbon, preferably coke,
and a binding material consisting of pitch.
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This composite is heated up by the temperature transition from
the anode and ls melted and calcinàted to form a solid,
dimensionally stable protective device. The disadvantage of this
procedure is that during this process the composite gives off PAH
(polycyclic aromatic hydrocarbons) gases which are registered
today as possible carcinogens. Furthermore, it is an expensive
procedure as high quality raw materials are used.
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The aim of the present invention was to improve commonly known
solutions for protecting nipples beyond the known technology. A
further aim was to produce a device which is reasonable to
produce in terms of cost, is simple to join around the nipples
after the anode is in place and which provides effective nipple
protection.
In accordance with the present invention, this was achieved by
means of a device mentioned in the introduction and which is ;;
characterised in that it consists of two or more prefabricated
parts which are designed to be joined in an arrangement around
each of the nipples.
The present invention will be described in the following with one
example and with reference to the enclosed drawings.
Fig.1 shows a section through a Hall-Heroult electrolysis
cell in which a new, almost consumed anode is located.
Fig. 2 shows an anode hanger with a mounted anode and a
protective device.
Fig. 3 shows a protective device in perspective. ` `
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Fig. 1 shows the principle of a conventional Hall-Heroult
electrolysis cell in which the cathode 1, together with the
liquid aluminium metal 2, forms the base of an electrolysis
- vessel. The anode 4 is moved down into the liquid cryolite bath
towards the base of the electrolysis vessel as the anode becomes
worn and in order to preserve a roughly constant distance between
the wear surface of the anode and the base of the electrolysis
vessel. The device 5 prevents the aggressive bath attacking and
eroding the steel nipples 6 to which the anode 4 is fastened and
which conduct electric current to the anode. The bath is covered
with an insulating layer 7 of crushed bath materials and
aluminium oxide.
Fig. 2 shows an anode hanger with a mounted anode 4 and nipples
6 with an example of a device 5 in accordance with the present
invention for protection against the cryolite bath. Section A-A
shows an annulus 9 between nipple 6 and the device 5 which can be
,
filled with crushed bath and aluminium oxide to avoid cracks in
the device 5 on account of the effects of the dilation forces.
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Fig. 3 shows an advantageous design of the present invention in
which the upper part is provided with a diagonal part 10 to ease
filling the annulus 9 with crushed bath and aluminium oxide, as
well as a male/female connection 11. The design of the
male/female connection is shown in section B-B which shows that,
using diagonal surfaces between the male and female parts, it is
possible to fasten the two parts together with a simple grip. The
simple design of the male and female parts makes the device 5
easy to mass-produce and means that it can be joined in a very
short time and effectively protect the nipple, which results in -~-~
large savings in production. ~-~
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In the examples mentioned in the above and shown in Figs. 2 and
3, the protective device 5 is designed so that an annulus is
formed between it and the nipples. The present invention, as it
is defined in the claims, is not, however, restricted to this
design but can be produced from a material which eliminates the ~ `~
dilation forces and allows them to reach right in to the nipples.
Furthermore, the parts which make up the device 5 can be fastened -
to each other by means of a binder, and/or the parts can be
fastened to the anode and/or the nipples by means of such a ~ -
binder.
Furthermore, the protective device 5 can have a shape different
to the ring shape shown in the diagrams, for example a square.
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Representative Drawing