METHOD FOR REPAIRING ELECTROLYSIS CATHODES

PROCEDE DE REPARATION DE CATHODES D'ELECTROLYSE

English Abstract

The invention relates to a method for repairing electrolysis cathodes that,
together with anodes in a galvanic bath provided for carrying out a galvanic
electrolysis, are connected to a power source. The electrolysis cathodes are
comprised of a crossbeam, which is arranged above the galvanic bath for being
electrically connected to at least one supply bar, and of a metal cathode that
projects into the galvanic bath. At least one portion of the cathode sheet
metal is detached from the crossbeam by subjecting it to thermal action in an
essentially uniform manner in the area of a first cutting edge. In order to
provide a second cutting edge, a replacement sheet metal is cut to size at
least in the area of an extension, which can be turned towards the crossbeam,
by subjecting it to thermal action in an essentially uniform manner. The
replacement sheet metal is welded to the first cutting edge in the area of the
second cutting edge by subjecting the sheet metal to thermal action in an
essentially uniform manner.

French Abstract

La présente invention concerne un procédé permettant la réparation de cathodes d'électrolyse qui, avec des anodes, sont connectées à une source de courant dans un bain galvanique pour permettre la mise en oeuvre d'une électrolyse galvanique. Les cathodes d'électrolyse sont constituées d'un support transversal disposé au-dessus du bain galvanique pour permettre le contact électrique avec au moins une barre de connexion, et d'une cathode métallique dépassant dans le bain galvanique. Au moins une partie de la plaque cathodique est séparée du support transversal grâce à l'application d'une contrainte thermique sensiblement uniforme au niveau d'une première arête. Pour permettre la formation d'une seconde arête, une lame de remplacement est découpée au moins au niveau d'un élargissement qui peut être dirigé vers le support transversal, grâce à l'application d'une contrainte thermique sensiblement uniforme. La plaque de remplacement est soudée à la première arête grâce à l'application d'une contrainte thermique sensiblement uniforme au niveau de la seconde arête.

Claims

Claims
1. Method for repairing electrolysis cathodes, which are connected to a power
source together with anodes provided in a galvanic bath for carrying out a
galvanic electrolysis, said electrolysis cathodes comprising a cross beam that
is
arranged above the galvanic bath for being electrically connected to a least
one
supply bar, and cathode plate that extends into the galvanic bath,
characterized in
that least a portion of the cathode sheet metal is cut off from the cross beam
in the
area of a first cut edge of the cross beam (2) by subjecting it to thermal
action in
an essentially uniform manner; in that replacement sheet metal is cut to size
at
least along its dimension that can be turned towards the cross beam (2), by
subjecting it to thermal action in an essentially uniform manner so as to
provide a
second cut edge; and in that the replacement sheet metal is welded to the
first cut
edge in the area of the second cut edge by subjecting it to thermal action in
an
essentially uniform manner.
2. Method as defined in Claim 1, characterized in that the used cathode sheet
metal
(3) is separated from the cross beam (2) in the area of the first cut in edge
by
using a laser.
3 Method as defined in Claim 1 or Claimed 2, characterized in that the
replacement
sheet metal is cut to size with a laser, at least along its dimension that can
be
turned towards the cross beam, so as to prepare the second cut edge.
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4. Method as defined in one of the Claims 1 to 3, characterized in that the
second
cut edge is welded to the first cut edge by using a laser.
5. Method as defined in one of the Claims 1 to 4, characterized in that the
structural
elements that are to be joined to one another are clamped prior to the welding
process.
6. Method as defined in one of the Claims 1 to 5, characterized in that prior
to the
welding process the structural elements that are to be joined to one another
are
oriented so as to be parallel to one another.
7. Method as defined in one of the Claims 1 to 6, characterized in that the
first cut
edge is clamped relative to the second cut edge during the welding process.
8. Method as defined in one of the Claims 1 to 7, characterized in that in the
area of
the welded seam, a cover is produced between the welded seam and the weld root
9. Method as defined in one of the Claims 1 to 8, characterized in that the
recesses
in the cathode sheet metal (3) for attaching the insulating rails (6, 7) are
produced
with the help of a laser.
10. Method as defined in one of the Claims 1 to 9, characterized in that
plates of
stainless steel are used as the cathode sheet metal (3).
11. Method as defined in one of the Claims 1 to 10, characterized in that
copper
plates are used as the anodes.
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12. Method as defined in one of the Claims 1 to 11, characterized in that a
source of
DC power is used as the power source.
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Description

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Method for Repairing Electrolysis Cathodes
The present invention relates to a method for repairing electrolysis cathodes,
which are
connected to a power source together with anodes provided in a galvanic bath
for carrying
out galvanic electrolysis,. The electrolysis cathodes comprise a cross beam
that is arranged
above the galvanic bath for being electrically connected to a least one supply
bar, and a
metal cathode plate that extends into the galvanic bath.
Cathodes of this type can be used, for example, when producing electrolytic
copper, when
the anode plates are of impure cast copper plates that are dissolved in the
electrolyte during
electrolysis, the copper from them being then deposited on the stainless steel
plates as pure
copper. The impurities accumulate within the electrolysis bath, mainly in the
form of
bottom sludge. A typical procedure is that approximately once each week the
cathodes are
removed from the galvanic bath, the copper is removed from them, and they are
then
reinstalled. After approximately three weeks, the copper anodes have dissolved
to the
point that they have to be replaced. The cross beam of the cathodes typically
consists of a
copper-plated supporting rod so as to ensure a low transitional resistance
between the cross
beam and the conductor rail.
Because of the weekly, mechanical cleaning of the cathodes and because of the
process
conditions that act on the cathodes, these are subjected to wear. This wear
leads to the fact
that when the copper is being removed from the stainless steel plates, the
cathode will be
deformed. This deformation of the cathodes results in degraded efficiency
during
electrolysis and thus slows down the rate at which the copper is deposited on
the cathodes.
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Once a certain degree of deformation has been reached, it is no longer
possible to use the
cathodes for electrolysis. When galvanic electrolysis is used on an industrial
scale to
deposit copper, many thousands of cathodes are used at the same time. The
useful life of
the cathodes is thus an important cost factor when producing copper.
Since the cross beam for the cathodes exhibits almost no signs of wear,
attempts were made
to cut off the used stainless steel plate and weld new stainless steel plate
onto the cross
beam. When this was done, however, it turned out that using the procedure that
was tried,
considerable stresses were generated in the stainless steel sheet metal and
this led to the
fact that cathodes repaired in this way warped very rapidly in the hot
electrolysis bath. For
this reason, known repair procedures have been unsatisfactory and this has led
to the fact
that once the cathode sheet metal has reached a degree of deformation that is
no longer
acceptable, the complete cathode together with the cross beam must be replaced
by a new
cathode, and the old cathode must be scrapped.
For this reason, it is the objective of the present invention to describe a
method of the type
described in the introduction hereto so that electrolysis cathodes that had
been repaired
have a sufficiently long service life.
According to the present invention, this objective has been achieved in that
at least a
portion of the cathode plate is cut off from the cross beam in the area of a
first cut edge by
subjecting it to thermal action in an is essentially uniform manner; in that
replacement
sheet metal is cut to size at least in the area of its dimension that can be
turned towards the
cross beam, by subjecting it to thermal action in an essentially uniform
manner so as to
provide a second cut edge; and in that the replacement sheet metal is welded
to the first cut
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edge in the area of the second cut edge by subjecting it to thermal action in
an essentially
uniform manner.
By separating the used cathode sheet metal from of the remaining part of the
cathode by an
essentially uniform thermal action, only a very small amount of thermal load
acts on the
remaining part. Furthermore, the first cut edge that has been prepared can be
subjected to a
subsequent welding process without any additional processing. Any extra
thermal and
mechanical stresses that could occur during an additional processing step are
thus avoided.
The same advantages are achieve by cutting with the help of an essentially
uniform thermal
action in the area of the replacement sheet metal.
Finally, carrying out the welding procedure by an essentially uniform thermal
action leads
to very small amount of thermal stress, and the residual thermal stress occurs
with a very
high level of uniformity. Practical test show that electrolysis cathodes
repaired in this way
display almost the same resistance to deformation as new cathodes. Compared to
a total
replacement of the cathode, it is thus possible to a achieve a clear cost
advantage by doing
this.
A very high level of uniformity can be achieved when completing the separation
procedure
in that the used cathode sheet metal is separated from the cross beam in the
area of the first
cut edge by using a laser.
As far as assembly of the replacement sheet metal is concerned, it is
advantageous if the
first replacement sheet metal be cut to size with a laser, at least along its
dimension that can
be turned to face the cross beam, so as to produce the second cut edge.

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Minimal thermal warping can also be ensured if the second cut edge is welded
to the first
cut edge by using a laser.
In order to produce a very uniform weld, it has been found to be advantageous
if the
structural elements that are to be joined are clamped prior to the welding
process.
Similarly, a uniform weld and uniform heat dispersion can be facilitated if
the structural
elements that are to be joined to each other are oriented so as to be parallel
relative to each
other, before the welding process is carried out.
In order to ensure low additional electrical resistance in the area of the
weld, it is suggested
that the first cut edge the braced relative to the second cut edge during the
welding process.
Similarly, a reduction of cross section in the area of the weld, and the
resulting increase of
electrical resistance, can be avoided in that a covering between the weld seam
and the weld
root be produced in the area of the weld seam.
In order to ensure a long service life for the electrolysis cathodes, it is
also useful if
recesses for securing insulating rails are made in the cathode sheet metal
with the help of a
laser.
Embodiments of the present invention are shown in the drawings appended
hereto. These
drawings show the following:
Figure 1: a side view of an electrolysis cathode;
Figure 2: a side view as seen in the direction II indicated in Figure l;
Figure 3: an enlarged view of the detail III indicated in Figure 2;
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Figure 4: an enlarged view of one end area of a cross beam of the electrolysis
cathode;
Figure 5: a perspective view of the electrolysis cathode shown in Figure 1;
Figure 6: a cross section through an electrolysis cathode that is clamped in
the area of a
welding device and which is to be provided with new cathode sheet metal;
Figure 7: an enlarged cross sectional view in the area of the weld seam.
Figure 1 shows an electrolysis cathode (1) that has a cross beam (2) and
cathode plate (3).
The cathode plate (3) is of stainless steel and is welded to the cross beam
(2). It is
preferred that the cross beam (2) be a copper-coated supporting rod.
The cathode plate (3) is provided with insulating rails (6, 7) along its side
edges (4, 5).
These insulating rails (6, 7) can be in the form of plastic rails. In order to
secure the
insulating rails (6, 7), the cathode plate (3) incorporates recesses through
which attachment
elements extend. End segments (8, 9) of the cross beam (2) extend beyond the
insulating
rails (6, 7), so that the electrolysis cathode (1) can be suspended in an
electrolysis bath (not
shown herein).
Figure 1 shows an electrolysis cathode (1) from which original cathode sheet
metal (3) has
been separated and replaced by new sheet metal, so that a welded seam (10)
extends from
one side edge (4) to the other side edge (5). In order to simplify
transportation, the
electrolysis cathode (1) incorporates two recesses (11, 12) beneath the cross
beam (2),
through which the holding devices of a transportation apparatus can be passed.
Positioning the welded seam ( 10) slightly below the recesses ( 11, 12)
entails the advantage
that the welding process can be completed in one operation, without having to
reposition
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the welding electrodes. However, in order to provide for the greatest possible
space
between the welded seam (10) and the surface of the electrolysis bath, thought
was also
given to having the weld seam extend at the level of lower limits of the
recesses (11, 12).
Admittedly, if this is done, the welding electrodes must be repositioned three
times during
the welding process, but if this is done the distance between the welded seam
and the
surface of the electrolyte when it has been immersed in the electrolysis bath
can be
increased. Furthermore, the actual length of the welded seam is reduced by the
extent of
the recesses ( 11, 12).
The side view in Figure 2 shows that the cross beam (2) can be configured as
an I-beam. It
can also be seen that the insulating rails (6, 7) essentially cover the whole
area of the side
edges (4, 5).
From the enlarged view shown at Figure 3, it can be seen that the cathode
plate (3) is
connected to the cross beam (2) through welded seams (13).
Figure 4 is a cross section through one of the end segments (8, 9). It can be
seen that a
lower area of the end segments (8, 9) is configured as a taper (14). This
configuration
ensures that when the end segments (8, 9) rests on a conductor rail (15),
there is greater
contact pressure per unit area and thus less transitional resistance to
electric current.
Figure 5 is a perspective view that illustrates the structure of the
electrolysis cathode (1).
The rugged configuration of the cross beam (2) as well as the lateral
extension of the end
segments (8, 9) of the cross beam (2) can be seen in particular.
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Figure 6 shows the arrangement of the electrolysis cathode (1) in the area of
a welder (25)
that is used to produce the welded seam (10). Both the new cathode sheet metal
(3) and the
cross beam (2) with the residual portion (16) of the original cathode sheet
metal (3) are
held in place by clamping devices (17, 18) and acted upon by clamping forces
(19, 20, 21,
22). A transverse force (24) is generated by means of a feed device (23) that
guides the
new cathode sheet metal (3) and the segment (16) of the old sheet metal
together with a
specific amount of contact pressure on their surfaces. In this state the
welder (25) is moved
along the welded seam (10) that is to be produced.
The structure of the welded seam (10) is shown in detail in Figure 7. The
welded seam
(10) has a seam root (26) and a seam cover (27) that extend along opposite
sides of the
electrolysis cathode (1). The seam root (26) and the seam cover (27) are
joined to one
another by a weld (28) that runs between a first cut edge (29) of the segment
(16) of
residual sheet metal and the second cut edge (30) of the new cathode sheet
metal (3).
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Representative Drawing