Note: Descriptions are shown in the official language in which they were submitted.
~ ~Lt~ 3
-- 1 --
BACKGROUND OF THE INVENT10
1. Field of the Invention
The present invention relates generally to the treatment
o~ molten copper metal, and specifically to apparatus for and
a method of continuously filtering and optionally degassing
molten copper and otherwise extracting impurities therefrom.
2. Description of the Prior ~rt
U.S. Patents 2,429,584, 3,537,987, 3,610,600, 3,820,767,
3,904,180, 3,972,709, 3,067,731, and references therein are
among numerous patents illustrating that filtering and degas-
sing of molten metal are generally well known in the prior
art. Applicants believe that until the present invention,
there has been no effective system for continuously removing
solid and gaseous impurities and contaminants frorn molten
copper.
The majority of molten metal filtering and degassing
technology has ocused on aluminum in part because purity is
particularly critical in aluminum and because the relatively
low melting temperature of aluminum makes it much easler to
treat than most metals. Molten aluminum treatment has prog-
ressed from batch-type slag filtering and fluxing, through in-
line granular and woven refractory filtering and fluxing, to
the in-line use of disposable porous ceramic foam filters such
as those disclosed in U.S. Patents 4,007,923, 9,917,242,
3,893,917, 3,962,081 and 4,092,153. Other metals, including
cast iron and steel, are often degassed by a vacuum using
reactive ingredient methods.
On the other hand, molten copper treatment technology
has been limited to few improvements~ one being the use of
catalytic action to deoxidize a melt. Because of the rela-
tively high temperature and extremely corrosive effects of
molten copper, it has been virtually impossible heretofore to
construct a mechanical filter for extracting contaminants from
molten copper that would have any significant useful life
expectancy.
Three major grades of copper recognized in the molten
copper treatment industry are tough pitch copper, fire-refined
.~7~ ,3
-- 2 --
copper and electrol~tic copper. As used herein these terms
are given what is believed to be their usual and common
meanings in the industry as defined in Volume 1 of Metals
Handbook, Eighth Edition published in 1961 by the ~merican
Society for Metals. Tough pitch copper is: I'Copper containing
Erom 0.02 to 0.5% oxygen, obtained by refining copper in a
reverberatory furnace." Electrolytic copper is: "Copper
which has been refined by electrolytic deposition, including
cathodes which are the direct product of the refining opera-
tion, refinery shapes cast from melted cathodes, and by exten-
sion, fabricators' products made therefrom. Usually when this
term is used alone, it refers to electrolytic tough pitch cop-
per without elements other than oxygen being present in signi-
ficant amounts." Fire-refined copper is: "Copper which has
been refined by the use of a furnace process only, inc]uding
refinery shapes and, by extensionr fabricators' products made
therefrom. Usually, when this term is used alone it refers to
fire-refined tough pitch copper without elements other than
oxygen being present in significant amounts."
Applicants believe that there is no known prior art
method for continuously filtering Ol- cleaning mol-ten copper
and for this reason, most manufacturers of cast copper pro-
ducts rely solely on the inherent purity of electrolytically
refined copper for production of high quality castings. For
molten copper known to be contaminated by refractories or the
like, the only present alternative to accepting a poor quality
product is scrapping the products for remelting. One example
of contamination is where steel strapping normally used to
bundle cathodes for shipment is inadvertently charged into a
meltinq furnace along with the cathodes despite the normal
precautions. Since our invention filters and extracts conta-
minants and impurities from copper, particularly, iron and
calcium, by adsorption, use of the present invention immediat-
ley prior to casting negates duplication of refining effort,
thereby a higher percentage of superior quality cast products
can be produced from a typical melt at less overall cost. One
of the main manufacturing processes which traditionally relies
'7~3
-- 3
on the inherent purity of electrolytically-refined copper is
that of continuous casting and rolling of copper into rod
wherein molten copper is cast into a continuously advancing
mold cavity formed by at least one endless moving mold surface
in conjunc~ion with other mold sur~aces so as to form a closed
mold cavity. The molten copper is solidified in the shape of
said mold cavity to form a cast bar which is then extracted
for further processing such as rolling into copper rod suit-
able for drawing into wire.
It is a generally accepted principle of the casting arts
that the quality of a cast product is more related to the par~-
ticule size of inclusions in the matrix than to the number of
inclusions and this is particularly true when the casting is
intended for reduction into wire rod ~hich will ultimately be
drawn into wire for use in electrical conductor, magnet wire
or telephone wire. When copper rod containing an inclusion is
drawn to a point fine enough that the inclusion's diameter
becomes significant with resp~ct to the diameter of the wire a
reduction in effect cross-sectional area is produced. Those
in the art assume that a wire break will occur when the inclu-
sion diameter "d" becomes an appreciable fraction of the
"downstream" wire diameter. It is also generally assumed in
the wire making industry that there exists A critical inclu-
sion size ''dc'' Eor a given "downs~ream" wire diameter and that
the condition for a break is: d~dC. Thus it is apparent that
there is a need for apparatus for a method of controlling the
diameter of inclusions cas-t into the matrix o copper castings
intended for use in the copper wire industry. A detailed
analysis of this problem of the wire industry is found in
"Wire Breaks in Copper: A Classification and Analysis"; Chia
et al; Wire Journal, February 1976.
Fire refined copper often contains many metallic and
nonmetallic impurities which are detrimental to finished
products such as wire made directly from fire refined copper.
When fire refined copper is cast into anodes for electrolytic
refining, these impurities result in heavy accumulations of
waste sludge in the electrolytic reservoirs or cells. Use of
~7
-- 4
the present invention as a filter for molten fire refined
copper impoves its quality, thereby making it acceptable for
some applications without additional refininy, and reduces
impurities in cast anodes destined for electrolytic refining.
Another problem often occurring in the prior art is
clogging of the tundish spout. The ceramic spout disclosed in
U.S. Patent Number 3,752,372 is representative of -the type of
spouts used to cast molten copper. Molten copper will not wet
or stick to a spout of this type; however, certain impurities
and contaminants such as iron will deposit on the surface of
the spout, which in turn results in casting difficulties which
take the form of a clogged spout which often interrupts the
molten metal flow. By lowering the amount of these impurities
and contaminants from the melt through the application of our
invention, this problem is substantially reduced.
SUMMARY OF THE INVENTION
The present invention solves many problems caused by
contamination during processin~ o~, e.g. molten electrolyti-
cally refined copper, by serving as a final precautionary fil-
ter which removes solid contaminants introduced into themolten metal by the process itself as well as dissolved metal-
lic and nonmetallic impurities such as iron and calcium. In
addition it improves the quality of fire refined copper when
used as a primar~ filter.
The present invention is an apparatus for and a metho~
of continuously Eiltering and degassing molten copper compri~
sing, in its basic sense, a disposable porous ceramic foam
filtering means cooperating with optional degassing means dis-
posed within a chamber through which flows a stream of molten
copper. The filtering means is an open pore structure prefer-
ably having about 25 to 35 pores per linear inch and a volume
fraction of voids of about 75 to 93 percent, preferably 85 to
95 percent, and is composed mainly of metallic oxides and met-
allic phosphates such as aluminum oxide, chromic oxide, alumi-
num phosphate and the like.
Additionally, we believe the ceramic foam filtering
means is conditioned by exposure to heat and/or the copper
3~2~3
-- 5
oxides and dissolved oxygen contained in the molten copper to
enable it to extract dissolved iron .~rom solution in the mol-
ten copper. This is believed to be accomplished by first for-
ming a discrete layer of precipitated copper oxide upon the
filtering means which layer of copper oxide causes dissolved
metallic and nonmetallic impurities and contaminants such as
iron and calcium to be adsorbed upon the surface of the condi-
tioned filtering means to such an extent that reductions in
concentration of dissolved metallic and nonmetallic impurities
and contaminants such as iron and calcium can be effected.
Consequently, there is presented in accordance with this
invention a method of continuously casting copper, comprising
casting molten copper into a continuousl~ advancing mold
cavity formed by at least one endless moving mold surface in
conjunction with other mold surfaces so as to form a closed
mold cavity, solidifying the molten copper substantially in
the shape of said mold cavity to form a cast bar, and then
extracting the cast bar from the mold cavity for further pro-
cessing; characterized by passing said molten copper through
at least one open pore ceramic foam filter disposed i.n a plane
across the path of said molten copper substantially immedia-
tely before said mol-ten copper is cast to extract impurities
therefrom.
In its broadest apparatus aspect, this invention is dir-
ected to apparatus Eor continuously filtering solid contami-
nants and extracting dissolved metals and non-metals from sol-
ution in molten copper, comprising a tundish having an inlet
for continuously receiving molten copper rom a furnace and an
outlet for delivering molten copper through a spout to a con-
tinuous casting mold; characterized by filtering and extrac-
ting means interposed between said inlet and said outlet
across the path o ~low of the molten copper, and wherein said
filtering and extracting means is constructed of open pore
ceramic foam material.
BRIEF DESCRIPTION OF THE DRAWING
. . . _ . . . _ .
While the specification concludes with claims particu-
larly pointing out and distinctly claiming the subject matter
, ~.
~'7~3
-- 6 --
which is regarded as the inven-tion, it is believed that the
invention, objects, features and advantages thereof will be
better understood from the following description taken in con-
nection with the accompanying drawing in which:
Fig. 1 is a schematic sectional view of the present in-
vention adapted to a tundish for handling the continuous flow
of molten copper.
Fig. 2 is a photomicrograph, at a magnification of 400X,
of a copper specimen which was cast without benefit of the
present invention.
Fig. 3 is a photomicrograph, also at a magnification of
400X, of a similar copper specimen which was cast using the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now in detail to the drawing, there is illus-
trated in Fig~ 1 a tundish 11 of the type commonly used inter-
mediate a melting or refining furnace (not shown) and a cont-
inuous or semi-continuous casting machine ~not shown) and a
continuous or semi-continuous casting machine (not shown~.
Molten copper, usually above 2000F, is poured into one end
(left end of Fig.l) of the tundish through the open top and
flows toward a pouring spout 13, such as the one disclosed in
U.S. Patent Number 3,752,372, located in the opposite end.
Angularly disposed in the flow path of the molten copper is at
least one filter element 15 which is positioned so as to be
easily removable from the top of the tundish yet tightly
fitted when seated to the bottom of the tundish. The filter
element 15 may be a type o~ ceramic foam known in the art by
the tradename "Selee~" foam, marketed by the Consolidated
Aluminum Corporation of St. Louis, Missouri and in the prefer-
red embodiment of the present invention such filter elements
15 are disposed in a plane between 30 and 150 degrees relative
to the primary direction of travel of molten copper from its
entry into the tundish 11 to its exit therefrom through pour
spout 130 In Figure 1 filter elements 15 are disposed in a 90
degree plane. Each filter element 15 is an open pore struc-
ture preferably having about 25 to 35 pores per linear inch
~7~ 2~3
-- 7
and a volume fraction of voids of about 75 to 95 percent, pre-
ferably 85 to 95 percent. Each filter elemen-t is composed
mainly of aluminum oxide and other metallic oxides and
phosphates.
We believe the metallic oxide and/or phosphates from
which the porous ceramic foam ~ilter element 15 is made is
conditioned by exposure to heat and/or the copper oxides and
dissolved oxygen contained in the molten copper to withdraw
dissolved iron from solution in the molten copper. We believe
this first forms a discre-te layer of copper oxide upon the
filter element 15 to such an extent that reductions in concen-
tration of dissolved iron and calcium of up to fi~ty percent
can be affected. Similar ceramic foam materials are known in
the art and are described, for example, in U.S. Patents
3,090,094 and 3,097,930, although we do not believe our parti-
cular application of these ceramic foam materials has been
previously known.
In our preferred embodiment filter element 15 is gene-
rally in the shape of a trapezoid being so shaped to promote
easy mounting in mounting grooves 17 which are inscribed in
the downwardly sloping and converging sidewalls 20 of tundish
ll. Each mounting groove 17 (two, for example, forming three
subchambers A, ~, C are shown in Fig. 1) inscribed in bevelled
sidewalls 20 corresponds to and is interconnected with b~ttom
mounting grooves 17' (two shown in Fig. l) formed in the floor
21 of tundish ll, the interconnection of 17-17'-17 ~orming a
wide-topped "u" shaped groove open at the top of tundish 11.
Filter element 15 when removably placed in mountiny grooves
17-17'-17 fills the u-shaped groove and is oriented across the
direction of molten copper flow. Handling means 18 are
attached to the long top edge of trapezoidal filter element 15
from tundish ll even when twndish ll is filled with continu
ously flowing molten copper.
In addition to filtering the molten copper, which elemi-
nates or breaks up any large slag inclusions or impurities,
the present invention contemplates the addition of a gas
stream through ~ilter elemen-t 15 to either control the oxygen
-- 8
content of the copper, degas the copper, or both, and to sim-
ultaneously purge filter element 15 of oxides and other ref-
ractory inclusions trapped therein by the filtering action.
For example, each bottom mounting groove 17' has mounted
therein a gas delivery tube 14' which is an extension of gas
delivery manifold 14. A channel 19 may be formed in the
bottom of each filter element 15 to receive and encase gas
delivery tube 14'. Gas delivery tube 14' is perforated along
its entire length so that reducing gases such as ammonia or
carbon monoxide or oxidizing gases such as oxygen or air may
be introduced into molten copper contained in tundish ll and
percolated up along and through porous filter element 15 to
the surface of the molten metal pool contained in tundish ll
where unreacted gases are vented to the atmosphere through the
open tundish entrance or through vent means 16 which project
through removable cover 12 from the area above the surface of
the molten metal in tundish ll. In one embodiment of the
present invention an inert carrier gas such as nitrogen or
argon is mixed with the reducing or oxidizing gases to perform
the additional function of purging the filter element 15 of
oxides and other refractories trapped therein or thereon as
the molten copper is being either oxidized or reduced. In
another embodiment of the present invention means for creating
a vacuum may be attached to vent means 16 to create a vacuum
in the space between the surface of the molten copper and
cover 12 to induce any gases dissolved in the molten copper to
be expelled from the copper thereby reducing the gas-induced
porosity of a cast product produced from the molten copper so
treated. Where it is not desirable to reduce copper oxides
which are in solution in the molten metal an inert gas may be
used alone to transport undissolved copper oxides trapped by
filter element 15 to the top of the molten metal pool. A
major benefit of using a gas stream directly beneath filter
element 15 is the increased cleansing action of the gas
bubbles as they flow through the filter because the porosity
of filter element 15 effectively increases the surface areas
of both the gas and the molten metal thereby increasing the
~r
~7~
. y
contact efficiency of the purifying gas exponentially and also
causing partLcles trapped in filter element 15 to be carried
towards the top of the tundish 11 where they may, if neces-
sary, be periodically removed by skimming. While the filter
element 15 may be mounted at any suitable location in the mol-
ten copper flow, for example in a launder (not shown) between
the melting furnace (not shown) and the tundish 11, we believe
there are advantages to locating it as close as practical to
the pouring spout 13.
In the simplest embodiment of the inven-tion the filter
element 15 is 90 to the flow path but, preferably, the filter
element 15 should be disposed in the flow path at an angle be-
tween about 30 and 150. This provides for a larger effec-
tive filter area for any given size of flow channel. For
example a commonly used launder has a cross-sectional area of
about one square foot through which flows molten copper at a
rate of about two cubic feet per minute. So that this, de-
sired, flow rate is not significantly impeded, the filer 15
should be kept relatively thin, about two inches thick, or the
~0 effective surface area could be increased by disposing the
filter element 15 at an angle to the normal direction of
flow. An angle of 30 or 150 more than doubles the effective
area of the filter element 15. This problem is not as great
when the filter element 15 is located in a tundish, as they
usually have larger cross-sectional areas and lower flow
rates, but in that case an angularly disposed filter element
lS will have a longer service time before becoming glogged
with adsorbed metals.
While the invention has been illustrated and described
as embodied in an arrangment for use in a tundish it is not
intended to be limited to the details shown, since various
modifications, application and structural changes may be made
without departing from the spirit and scope of the present
invention.
Without further analysis, we believe the foregoing will
fully reveal the gist of the present invention so that others
can, by applying current knowledge or reasonable experimenta-
~ ~ 7
-- 10 --
tion, readily adapt it for various applications wi-thout omit-
ting features that, from the standpoint of prior art, airly
constitute essential characteristics of the generic or speci-
fic aspects of this invention and, therefore, such adaptations
should and are intended to be comprehended within the meaning
and scope of equivalence of the following claims.
