Note: Descriptions are shown in the official language in which they were submitted.
3 5
The present invention relates to a method and an apparatus
for cleaning of spent anodes and more particularly, the
cleaning of prebaked anode butts (residues) from an electro-
lytic smelting process for aluminium production.
A prebaked anode consists of an already calcined carbon
block provided with holes in the top where an
aluminium/steel current-providing rod is fastened to the
anode by means of cast iron or so-called rodding-mix. The
anode rod normally consists of from 2 to 6 vertical cylind-
rical steel nipples connected together by a top steel cross-
bar which in turn is connected to a vertical aluminium rod.
The carbon blocks are consumed during the electrolysis pro-
cess, and consequently each of the 20-30 anodes in the elec-
trolysis cell has to be replaced when the anode thickness is
reduced to approximately 20~ of its original height. The top
of the anode block is then covered by a thick layer of
solidified bath which sticks to the above mentioned nipples
and between the carbon block and the steel cross-bar. This
bath layer (crust), consisting of a solidified mixture hav-
ing variable content of cryolite, aluminium fluoride and
alumina, can be extremely hard. Both bath material and
carbon residues have- to be separately recovered for re-
cycling in the electrolysis process.
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The conventional method used for breaking down this crust
layer is to apply pneumatic chisel machlnes, quite often
manually operated. This is hard work where the chisel is
partly used as a crowbar and furthermore, the method in-
volves considerable environmental problems in the form of
dust and noise. Consequently, several types of both station-
ary and mobile cleaning installations and devices have
recently been developed in order to mechanize the cleaning
of anode butts. These installations/e~uipment are based on
different principles with régard to disintegration and re-
moval of the solidified bath. All the hitherto known
mechanized systems are, however, characterized by one or
several serious drawbacks. E.g. the use of hydraulic
pressure results in a complicated apparatus design where the
steel nipples themselves are applied as a dolly during the
cleaning operation. Because of the relatively large loads
being applied there is a danger for deformation of the anode
rod assembly, damaged welded joints between the Al-rod and
the cross-bar etc. Milling cutters and chisel machines give
a high noise level and dust formation. The light weight
mobile cleaning machines, can only remove a warm bath layer
from the anode butts immediately after their removal from
the electrolysis cells, or possibly a porous bath layer. A
common drawback for all known machines is low reliability of
service, complicated designs and no possibility for an auto-
matic cleaning operation.
It is therefore an object of the present invention to pro-
vide an apparatus and a method for cleaning of anode butts
which overcome the above drawbacks, the apparatus having a
simple and sturdy construction, high efficiency and where
the cleaning operation can be conducted automatically.
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3 26625-88
Another object of the invention is to provide an apparatus and a
method satisfying the strict environmental requirements with
regard to the dust and noise level in workshops.
These objects are achieved according to the invention by providing
a stationary apparatus completely encapsulated and based on
application of an impact tool which under pendulous movement
disintegrates and removes the solidified bath layer on the anode
butts.
According to a first broad aspect of the present invention, there
is provided a method for cleaning of anode butts from an
electrolysis process for an attached solidified bath material,
characterized in that the anode butt is locked in a closed chamber
by means of a vertically movable board and an aligning arm which
clamps the anode cross-bar in the horizontal direction against a
dolly, and where the anode is subsequently exposed to several
reiterated impacts from one or more oscillating impact devices
aimed at the solidified bath material on the anode.
According to a second broad aspect of the present invention, there
is provided an apparatus for cleaning of anode butts for an
electrolysis process for an attached solidified bath material
comprising a closed noise-insulated and dust-insulated chamber, a
clamping device for transport and positioning of the anode in the
chamber, restraining means and a device for disintegration of the
bath material, characterized in that the restraining means
comprise a vertically movable board, a horizontally aligning arm
and a dolly, and where the disintegration device is an oscillating
impact device.
These and other characteristic features of the invention will be
more apparent from the following description, patent claims and
accompanying drawings, Figures 1-3, where
Figure 1 shows schematically and in a cross-section, a preferred
embodiment of an apparatus for cleaning of anode butts,
B
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3a 26625-88
Figure 2 shows the apparatus in a cross-sectional longitudinal
view taken along line I-I in Figure 1, and
Figure 3 illustrates schematically a rotating device applied to
provide a profiled notch in the bath material adjacent
to the anode cross-bar.
The disclosed cleaning machine is situated in a closed chamber 10
built of sound-insulating material and provided with a powerful
vent-hood (not shown on the Figures), so that the machine is
noise- and dust-insulated from the surroundings. A spent anode 2
having a solidified bath layer 21 on the top, as shown in
Figure 1, is fastened and ready for the cleaning operation.
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The anode rod assembly 1, comprising an aluminium rod 11,
attached to carriers in an overhead conveyor is fed into the
cleaning chamber. The aluminium rod 11 is connected to a
steel cross-bar 12, provided with welded nipples 13, em-
bedded by solidified bath 21, on the top of the anode butt
2. A clamping device 3, grasps the aluminium rod and pro-
vides transport and alignment of the anode assembly through
the machine in the cleaning chamber.
The cleaning machine itself comprises an impact tool 7, a
dolly 4 provided with an aligning arm 6 and a vertically
movable grate board 5 providing support for the anode during
the cleaning operation. The impact tool 7 is illustrated on
the Figure as a pendulous hammer, e.g. pneumatically powered
hammer.
The lower part of the chamber is intentionally narrowed into
a hopper and terminated by transport means, e.g. a conveyor
9 for removal of bath lumps from the disintegrated bath
layer 21. A specially designed accessory device for removal
of possible broken anode pieces from the grate board 5 con-
sists of a tipping board and a pusher 15. Their function and
mode of operation will be described in more detail in con-
nection with a detailed description of the method for clean-
ing of the anode butts.
Fig. 2 shows the machine in a longitudinal cross-section
taken along the line I-I in Fig. 1 and illustrates in more
details a preferred embodiment of the grate board and the
pendulous hammer 7. The hammers are shown as two separate
oscillating hammers which aim their impact outside of the
three steel nipples 13 connected to the cross-bar 12 being
in iks turn attached to the rod 11, and at the solidified
bath surrounding the nipples between the cross-bar and the
1315~35
anode butt. It should be noted that the impact surfaces 71
of the hammers have a butt configuration without any acute
or oblong parties so that the impact energy of the hammers
is fully utilized.
The vertically movable board 5 is intentionally designed as
a grate or gitter Some of the gitter parts are furthermore
intentionally provided as longitudinally extending ribs 53
protruding in the vertical direction so that during the
downward movement of the board these ribs will co-operate
with a stationary grate and break any possible larger lumps
of the disintegrated bath layer.
The cleaning of the spent anodes from the solidified bath by
means of the above disclosed apparatus is executed in the
following manner: Anode butts 2 are fastened through their
aluminium rods 11 to a transport means, e.g. suspended rails
which convey the anodes into the closed chamber 10. Clamping
device 3 grasps the aluminium rod and pulls the anode pass-
ing a rotating tool, e.g. a milling cutter, which removes
possible bath depositions from the cross-bar 12 on its dolly
side.
Fig. 3 illustrates schematically the rotating device 18
comprising several parallel arranged and vertically adapted
rotating discs to provide a profiled groove along the cross-
bar 12 and the nipples 13 in the bath layer 21 so that the
dolly 4 can be aligned close to the nipples under the dis-
integration step of the operation. At the impact tool 7 a
restraining arm 6 grasps the cross-bar 12 on the hanger 1
and simultaneously the grate board 5 lifts the anode against
the restraining arm which clamps the cross-bar against the
dolly 4. In this manner a proper fixation of the anode butt,
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both vertically and horizontally, is achieved. Simultaneous-
ly, by such releasing of the transport carrier and the
aluminium rod for the load, the conducted cleaning operation
is very lenient with regard to these parts. The dolly is
dimensioned with regard to the applied impact force of the
impact tool (the hammers) and is shielded from vibration by
means of inserted blocks 42. The two shown pneumatic hammers
7 are sequence controlled and each hammer has its individual
steering with regard to the number of strokes against the
solidified bath 21 between the cross-bar 12 and the ancde 2.
Because of the butt shape of the impact surfaces cf the
hammers the impact energy of the oscillating hammers is
exploited maximally. Tests conducted with the hammers having
an acute or an oblong shape failed to achieve an efficient
cleaning of the anodes in spite of the high hammer weight
and a countless number of conducted blows. The bath layer 21
is disintegrated and thrown outside of the anode and the
grate board 5, being collected in the hopper shaped lower
part of the chamber 10 and conveyed out of the chamber, e.g.
by means of a conveyor 9.
After terminated disintegration operation, the restraining
arm 6 is released from the cross-bar, the grate board 5 goes
down and simultaneously larger bath lumps being retained on
the stationary grate 55 are crushed under the movement of
the board. The anode is released from the fastening means 3
and is conveyed further inwardly into the chamber or to a
next chamber for a possible additional post-cleaning step by
means of conventional means like sand blasting, rotating
brushes stc. When the anode is removed from the hammer
station the tilting board 8 is turned to a horizontal posi-
tion. The grate board is elevated to a level corresponding
to the surface of the tilting board and a pusher 15 trans-
fers possible broken carbon pieces from the anode on the
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ti:Lting board. The pusher, the grate board and the tilting
board are retracted to their start positions, the carbon
rests fall down on a conveyor or a hopper (not shown on the
Figures) and the machine is automatically reset to receive
the next anode. The apparatus hereby automatically ensures
an efficient separation of bath residues from the carbon
residues which currently represents a problem for the
hitherto known cleaning installations and machines.
