CA1173623A

CA1173623A - Continuous filtering and degassing of molten copper

Info

Publication number: CA1173623A
Application number: CA000358420A
Authority: CA
Inventors: Enrique H. Chia; John G. Weber
Original assignee: Southwire Co LLC
Current assignee: Southwire Co LLC
Priority date: 1979-08-16
Filing date: 1980-08-15
Publication date: 1984-09-04
Also published as: DE3030738C2; FR2468655A1; ZA804994B; AU534172B2; ES494278A0; ES8106248A1; IT1188948B; DE3030738A1; IT8049494A1; SE8005775L; IT8049494A0; GB2057904B; FR2468655B1; AU6148480A; GB2057904A

Abstract

ABSTRACT OF THE DISCLOSURE
Disclosed is apparatus for and a method of continuously filtering and optionally degassing molten copper and otherwise extracting impurities therefrom comprising disposable porous ceramic foam filtering means and means for supplying a deoxidiz-ing or cleaning gas advantageously disposed within a chamber containing a flowing stream of molten copper.

Description

~ ~Lt~ 3 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 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 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 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 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 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 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 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 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.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of continuously casting copper, comprising casting molten copper into a continuously 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 processing; characterized by passing said molten copper through at least one open pore ceramic foam filter disposed in a place across the path of said molten copper substantially immediately before said molten copper is cast to extract impurities therefrom.

2. A method according to claim 1, further characterized by extracting from the molten copper metals from Group 8 of the periodic chart of the elements.

3. A method according to claim 1, further characterized by extracting from the molten copper nonmetals from Group 2a of the periodic chart of the elements.

4. A method according to claim 2, characterized in that the Group 8 metal extracted is iron.

5. A method according to claim 3, characterized in that the Group 2a nonmetal extracted is calcium.

6. A method according to claim 1, further characterized by introducing a reactive gas into said molten copper in the proximity of said filter and adjusting the oxygen content of said molten copper as said molten copper passes through said filter.

7. A method according to claim 1, further characterized by simultaneously introducing a reactive gas and an inert gas into said molten copper through said filter, adjusting the oxygen content of said molten copper and purging said molten copper of excess reactive gas and other dissolved gases substantially immediately before said molten copper is cast into said continuously advancing closed mold.

8. Apparatus, particularly suitable for use in continuously casting copper into a continuously advancing mold cavity and for continuously filtering solid contaminants and extracting dissolved metals and non-metals from solution in molten copper, comprising a tundish having an inlet for continuously receiving molten copper from a furnace and an outlet for delivering molten copper through a spout to a continuous casting mold; characterized by filtering and extracting means interposed between said inlet and said outlet across the path of flow of the molten copper, and wherein said filtering and extracting means is constructed of open pore ceramic foam material.

9. Apparatus according to claim 8, further characterized in that said open pore ceramic foam material is selected from the group consisting of metallic oxides and metallic phosphates.

10. Apparatus according to claim 9, further characterized in that said open pore ceramic foam material is predominately aluminum oxide and aluminum phosphate.

11. Apparatus according to claim 8, 9 or 10, further characterized in that said open pore ceramic foam material has volume fraction voids of from 75 percent to 95 percent.

12. Apparatus according to claim 8, further characterized in that said filtering and extracting means is disposed in a plane between 30 and 150 degrees relative to the primary direction of flow of the molten copper through said tundish.

13. Apparatus according to claim 8, further characterized by vacuum means for degassing the molten copper either while or after it flows through said filtering and extracting means.

14. Apparatus according to claim 8, further characterized by means for bringing inert gas into contact with the molten copper including means for percolating gas up through said ceramic foam material to remove copper oxide particles therefrom.