Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Case: K-0399-KCC
~049743
The lnvention relates to the production of copper
anodes for use in the electrolytic refining of impure copper
by castin~ molten im~ure copper into molds made of copper.
Copper anodes used in electrolytic copper refining
are cast in solid copper molds weighing up to 6,000 or more
pounds. It is common practice totreat the interior surfaces
of such a mold be~ore each pour with a slurry ~ade up of a
finely divided inorganic release material, such as silica,
suspended in a liquid medium, such as water. The liquid
medlum is vaporized by the heat of the mold, resulting in the
deposition of a coating of the release material on the interior
surfaces of the mold. The temperature of the mold during the
treatment with the slurry is normally between about 200F.
and 1000F. Molten copper, at a temperature of ~OOO~F.
or more is introduced into the treated mold and the mold is
then cooled until the molten metal has solidified. The
cast copper anode is removed, and the mold is a~ain treated
with the slurry for the subsequent pour. Cracking of the
molds is a serious problem that has long plagued the casting
~0 operation. Small cracks develop in a mold after about a week
of use, and the small cracks rapidly enlarge to an extent
that makes it necessary to take the mold out of service and
replace it with a new mold. The cracking problem has long
been considered to be a difficulty that simply had to be
tolerated, and molds have customarily been replaced after
only short intervals of use.
It has now been found that the cracking problem
can be reduced or eliminated by the process of this invention.
In accordance with the present invention, the slurry that is
~0 normally applied at room temperature or below to the interior
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surfaces of a copper anode mold is heated, before application,
to a temperature of from about 150 to about 200F and is
applied to the mold within that temperature range.
Thus, according to one aspect of the invention there
is provided in the casting of copper anodes wherein copper
molds are successively filled with molten copper and the
solidified anodes are successively removed therefrom on a
cyclic basis, and coatings of an inorganic release
material are applied as a slurry thereof in a liquid
medium capable of being volatilized within the range of
200F to about 1000F to the internal surfaces of the
respective molds prior to the introduction of the molten
copper thereinto, the improvement wherein the slurry is
heated and applied to the interior surfaces of said
molds at a temperature of from about 150F. to about
200F.
The release agent may be selected from the group
consisting of silica, bone ash, alumina, clay, ganister, lime, and
graphite, and is slurried with a liquid medium capable of being
volatilized at the temperature of the mold, i.e. from about 200 to
1000F. In accordance with conventional practice, the release agent
is finely divided sllica and the liquid medium is water. The heated
slurry is applied to the interior surfaces of the mold by convent-
ional means, usually by spraying, but other methods of applying it
may be used, e.g. painting, splashing, or otherwise allowing the
slurry to flow over the surfaces of the mold to form a coating
thereon. The residual heat remaining in the mold from pour to pour
vaporizes the liquid medium from the slurry coating, leaving a
residual coating of the release agent on the interior surfaces of
the mold.
In accordance with the invention, undesirable cracking
of a mold is greatly reduced. Operating life of the mold
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is significan-tly longer -than has been the case in the past.
Conventional casting procedures are preferably
followed in carrying out the invention. Thus, the usual
casting l.~hich is normally employed, with the molten copper
being poured sequentially from the usual ladle into a series
of solid copper molds carried circumferentially of the wheel.
The only difference over conventional practice is the heating
of the usual slurry prior to its application to the interior
surfaces of the molds.
1~ Heating of the slurry may be accomplished in any
suitable manner, bu-t is conveniently carried out by injecting
steam into the reservoir of slurry maintained at the usual
mold-coating station.
The sequence of steps involved in conventional casting
operations comprises pouring mol~en copper into the mold,
cooling the mold, removing the solidified copper casing
from the mold, and applying a coating of the slurry to the
interior surfaces of the empty molds. The empty molds are
then returne,1 to the pour step and the sequence is repeated.
The slurry comprises a finely divided release material suspended
in a liquid medium. The residual heat remaining in the mold
from pour to pour vaporizes the liquid rnedium from the slurry
coating, leaving a coating of -the release material on the
interior surfaces of the mold. The molds can be cycled
through tha sequence of steps as a group, or, preferably,
they are cycled therethrough sequentially in a continuous
series.
The inorganic release ma-ter 1 contained in the slurry
includes such materials as silica, bone ash, alumina, clay,
ganister, lime and graphite, preferably silica. The liquid
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medium is preferably water. The slurry itself may vary in
the concentration of solids present depending upon the method
of applying the slurry to the surfaces of the molds. For
spraying operations, the solids concentration may be as low
as 2~o to 5~ by weight, but generally will be between about
10% and 25~ by weight. In splashing and other methods of
applying the slurry to the mold surfaces, the solids concen-
tration may be as high as ~0% by weight. The particle si~e
of the solids in the slurry can also vary over a wide range
1~ depending upon the method of applying the slurry to the
surfaces of the molds. For spraying operations, the particle
size is preferably such that the dry solids are capable of
passing through a 200 mesh screen. For other methods of
applying the slurry to the mold surfaces, the particle size
of the solids is not criticall the only requirements being
that a homogeneous slurry be maintained, and that the coating
of solids applied to the mold surfaces is uniform. Generally,
the solids will have a particle size capable of passing through
a 200 mesh screen.
The temperature of the mold during the application of
the slurry thereto is generally between about 200Fo and 1000F.
The residual heat remaining in the molds from pour to pour,
as mentioned hereinbefore, vaporizes the liquid medium from
the slurry coating, leaving a residual coating of the release
rnaterial on the interior surfaces of the mold.
Cooling of the mold following a pour can be accomp-
lished by circulating water through internal passageways if
the molds are constructed with such passageways. Generally,
however, the molds are not provided with internal passageways,
~0 and are simply allowed to cool in the ambient air and/or
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spra~red with water.
The invention is furthe,r described by reference to
the following example which is given for purposes of illus~
tration only and wi-~hout any in-tention that the invention
be limited thereto.
EXAMPLE
A comparison test was run using the apparatus of a
conventional, operating facility for producing cast copper
anodes. The apparatus comprised a castin~ wheel which
supported a series of copper molds, each mold ~eighing
approximately 6,000 pounds. F,ach mold was capable of
casting, a 700 pound copper anode. As the casting wheel
rotated, each of the molds supported thereon progressively
advanced from a filling station wherein molten copper was
charged to the molds, to an anode discharge station where
the anodes, which had cooled and solidified during their
travel between the filling station and the discharge station,
were removed from the molds. The empty molds then rnoved past
a mold wash station wherein a slurry of silica in water
2~ was applied as a coating to the interior surfaces of the mold.
The temperature of the molds during the application of the
silica generally was between about 300F. and 1000F., and
the heat content of the molds rapidly vaporized the water
content of the slurry coating, leaving only a coating of
silica on the sur~aces of the moldO The molds were then
returned to the filling station.
This casting c~cle had been operated commercially for
several years using a slurry comprising approximately 500
pounds of silica to S gallons of water. The silica used
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had a particle size capable o~` passing through a ~00 mesh
screen. The temperature of the silica solution as it
was applied to the molds was appro~imately that of the a~bient
atmosphere, i.e., between about 50F. and about lOO~F.
Experience with this process indicated that small cracks
developed in the molds after about one week of use, and the
small cracks would rapidly increase in size to where the mold
had to be discarded.
In the comparison test, all of the molds on the
1o casting wheel, with the exception of one, were replaced with
new molds. One old mold, which had developed one small crack,
was left in place on the casting wheel. The procedure used
in casting anodes with the new molds was exactly as given
hereinabove with the single exception that the silica siurry
was heated to a temperature between about 150F. and 200F.
prior to its being applied to the surface of the empty molds.
Following a two months' period in which these molds were
continuously used in casting copper anodes, not a single
crack develo,ped in any of the new molds which had been
~ installed on the casting wheel. The one old mold, which had
a small crack therein at the start of the two months' test,
still had only one crack therein, and that one crack was
o~ the same size that it had been at the beginning of the
two months' test.
Whereas, there is here described a certain preferred
procedure which is presently regarded as the best mode of
carrying out the invention, it should be understood that
various changes may be made and other procedures adopted
without departing from the disclosed inventive concepts
~0 particularly pointed out and claimed hereinafter.
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