US2158625A

US2158625A - Copper refining apparatus

Info

Publication number: US2158625A
Application number: US150427A
Authority: US
Inventors: Heuer Russell Pearce
Original assignee: American Metal Co Ltd
Current assignee: American Metal Co Ltd
Priority date: 1937-06-26
Filing date: 1937-06-26
Publication date: 1939-05-16
Anticipated expiration: 1956-05-16

Description

May 16, 1939. RF. HEUE R v COPPER REFINING APPARATUS 3 Sheets-Sheet 2 Filed June 26, 1937 H n-l Mia ZIGI DEL lllll May 16, 1939. R. P. HEUER 2,158,625

COPPER REFINING APPARATUS Filed June 26, 1937 3 Sheets- Sheet 3 ikm tion Serial No. 109,781, filed November '1, 1936, for one product, more of that product and less for Copper refining process and apparatus, and of the other product can be made, and in case said application is a continuation-in part of my one of the casting plants must be shut down. United States Patents No. 2,060,073,, granted the melting furnace may continue to operate.

November 10, 1936, for Copper refining methods, A further purpose is to preheat and desirably 10 Batented M... 16,1939 r 2,158,625

j UNITED STATES PATENT OFFICE COPPER DEFINING APPARATUS Russell Pearce Heuer, Bryn Mawr, Pa., assignor to The American Metal Company, Limited, New York, N. Y., a corporation of New York Application June 26, 1937, Serial No. 150,427

6 Claims. (01. 2247) The present invention relates to apparatus for protecting atmosphere consisting primarily as an producing coppershapes of the desired quality active ingredient of carbon monoxide. from refined copper such as electrolytically re- A further purpose is to make tough-pitc fined cathodes. This application is a continuacopper and oxygen-free copper using the same tion in part of my United States patent applicamelting furnace, so that, with increased demand and No. 2,060,074, granted November 10, 1936 for concurrently oxidize solid copper masses by fuel Copper refining apparatus. combustion and subsequently to melt the copper A purpose of the invention is to obtain dense masses, desirably submerged in molten copper. oxygen-free copper castings notwithstanding by fuel combustion, the fuel combustion used in contact of the copper with air during casting. preheating being at least in part separate and 5 A further purpose is to expose molten oxygenseparately controlled from the fuel combustionfree copper during casting to a volume of air used in melting.

not more than a few times the volume displaced Further purposes appear in the specification by the casting, preferably rendering the air less and in the claims.

oxidizing by a reducing vapor from a mold dress- The invention relates to novel copper refining 20 ing or the like. apparatus.

A further purpose is to increase the conveni.- The drawings show the apparatus diagram ence of casting oxygen-free copper by dispensing matically. No eifort has been made to show the with the use of carbon monoxide at the point of structural details which'are within the routine casting. skill of those working in the art nor to illustrate A further purpose is to lower the total oxygen the various changes which may be made in the content of molten copper substantially free from structures without departing from the invention. metallic impurities by treatment with solid car- The illustrations have been chosen primarily with bon, to a value sufficiently below that at which a view to convenient explanation of the prina distinct phase .of cuprous oxide appears in the ciples involved.

castings and also sufficiently below that at which Figure 1 is a top plan of the preheating and excessive gas cavities appear in the castings, s0 oxidizing furnace, the melting furnace, the deas to allow fora limited pick-up of oxygen duroxidizing vessels and the casting P ing casting without causing excessive gas cavi- Figure 2 is a broken vertical section along the 5 ties or the, appearance of a distinct phase of line 2-2 of Figure 1.

cuprous oxide in the castings; and then to cast Figure 0 8 a a me t ry V ew corresponding the copper with not more than that exposure to to a port o o F u e 2 a d s wi a variationn of the preheatair which will cause the limited pick-up of Figure 3 isatransverse sectio oxygen. ing and oxidizing furnace on the line 8-3 of 4 :A further purpose. is to obtain the very low Figures 1 and 40 Figure 4 is a fragmentary section on the line total oxygen content of the molten copper necessary to permit casting dense oxygen-free castings of Figure showing 1 top f in air, by deoxidizing the molten copper with g gi gm z in e we ea'ng an solid carbon in a closed vessel at a pressure sub- Figure 5 is a partly broken side elevation of one Stantlauy below atmospheric, pressure of the deoxidizing vessels during decxidation.

A further purpose is to facilitate and accelerate Figure 6 is a sectional elevation corresponding the deoxidation of molten copper by solid carbonto Figure 5 but Showing the oxidizing vessel through the use of reduced pressure, thus assistduring ing the reaction between carbon dioxide and In the drawings k numerals refer v like 6 carbon in molten copper, so as to obtain dense arts.

oxy r e pp m ly. In common practice, refined copper masses A further purpose is to deoxidize molten copper such as cathodes produced by electrolytic copper by solid carbon in a closed vessel under reduced refining are changed into the copper castings pressure and to cast the deoxidized copper in a used in fabrication, such as ingots, wire bars, 55

cakes, billets, etc., by melting in large reverberatory furnaces, some of which hold as much as 300 tons (270 metric tons) and then castin in air. The conventional mode of operation in such reverberatory furnaces is as follows: (1) charging, (2) melting, (3) blowing, (4) skim-. ming, (5) poling, (6) coking, (7) casting. Ordinarily each such reverberatory furnace treats one charge every twenty-four hours.

Copper masses such as copper cathodes commonly carry sulphur as an impurity picked up during the electrolytic refining and not susceptible of complete removal by ordinary washing. This sulphur, as well as sulphur from the gases of combustion, forms an impurity in the molten copper bath in the reverbatory furnace. The blowing operation is therefore used to remove the sulphur by forming cuprous oxide in the bath ,to react with the sulphur and form volatile sulincreases the oxygen content of the bath to ap-.

proximately 0.9% (in some cases the oxygen content is not carried so high). oxygen is ordinarily removed by poling, through the reducing action of carbon, hydrocarbons and hydrogen present in green poles, which reduce the oxygen tovolatile compounds such as carbon monoxide, carbon dioxide and water vapor. Coking protects the surface of the bath somewhat during casting. O

It has long been a phenomenon of copper metallurgy that the poling operation cannot be carried to the extent of complete removal of oxygen without causing the copper castings to be filled with blow-holes or gas cavities. It is commonly considered bad practice to reduce the oxygen content by poling -much below the point (about 0.033% oxygen) which corresponds to a cuprous oxide content of 0.3%.

As explained in my United States Patent No.

2,060,073, above referred to, the reduction of cuprous oxide under the conditions of poling involves the following reactions:

From Reaction (1) we may derive the expression:

(A.Cu)(A.CO) (A.Cu-2O)(A.C)

AFo=standard free energy change R=gas constant T=absolute temperature ln=logarithm to the base e (A.Cu)=activity of copper (A.C0)=activity of carbon monoxide (A.CuzO)=activity of cuprous oxide (A.C) =activity of carbon AF RT In After blowing, the

tions. At constant temperature this expression becomes:

(A.CllzO) (A.CO) =K1 K1=proper constant It will of course be evident from Equation (7) that decrease in cuprous oxide activity'wiil result in increase in carbon monoxide activity.

- Using the same symbols, the expression for Beaction 3 is:

(A.Cu) (A.H O) AF RT (A.Cu O)(A.I-I

(A.Hz0) =activity of water (Am) =activity of hydrogen If we assume the activities of copper and of water to be constant, this equation becomes at con-,- stant temperature:

(A.CuzO) (A.Hz) =K2 Kz =proper constant From Equation. (9) it will be evident that decrease in the activity of cuprous oxide will result in increase in the activity of hydrogen.

Since the activity of any component is a function of the concentration, it will be evident that the concentrations of carbon monoxide and hydrogen will be low'when the concentration of cuprous oxide is high (say above 0.3%), but that the concentrations of carbon monoxide and hydrogen will increase. rapidly with lowering of the cuprous oxide concentration below about 0.3%.

Large quantities of carbon monoxide and hydrogen present during solidification may cause gas cavities by virtue of their reactions with cuprous oxide whose concentration increases in the supernatant liquid during solidification due to preferential crystallization of pure copper. Reaction 1 can ordinarily not take place during solidification due to the absence of carbon, but Reactions 2 and 3 can occur where both carbon monoxide and hydrogen are present. The condition of excessive gas cavities in the copper castings known as over-poling is thus due just as 'much to the presence of cuprous oxide as to the presence of carbon monoxide and/or hydrogen, as the cuprous oxide on the one hand and the carbon monoxide and/or hydrogen on the other hand contribute to the liberation of carbon dioxide and/or water vapor during solidification of the copper castings.

In my United States Patent Nos. 2,060,073 and 2,060,074, above referred to, the production of cast copper having an oxygen content far below that of tough-pitch copper and nevertheless of high density is described. This product 'is obtained from copper melted under fuel-fired conditions by special deoxidation procedure and avoidance of or minimal exposure to air during casting. Where reference is made herein to casting it is intended to include the conventional process of teeming into molds, as well as special forms of castings, for example continuous solidifying, whether or not accompanied by mechanical working such as extrusion.

As the deoxidation of copper melted in contact with gases of combustion continues below the oxygen content of tough-pitch copper, a point is eventually reached at which the distinct phase of cuprous oxide, previously visible under the microscope in the solidified castings, is no longer visible. Such solid copper which contains no distinct phase of cuprous oxide visible under the microscope may be said to be oxygen-free, notwithstanding that it may contain a relatively some other oxide in solid solution. Molten copper of the proper oxygen content to produce such solid copper may likewise be said to be oxygenfree. The maximum oxygen content which such oxygen-free copper may contain has not been accurately determined, but it would appear to be about 0.007% according to the determination of Rhines a'nd Mathewson, Solubility of oxygen in solid copperfAmerican Institute of Mining and Metallurgical Engineers, Technical Publication No. 534-131 162, paper delivered February, 1934.

Such oxygen-free copper may or may not be free from excessive gas cavities. In order to obtain oxygen-free copper'which is free from ex-. cessive gas cavities, having a bulk specific gravity in excess of 8.8, deoxidation should be continued below the point at which a distinct phase of cuprous oxide ceases to be visible in the castings, thereby changing over carbon dioxide present in the copper to carbon monoxide according to the reaction:

CO2+C=2 CO (10) The oxygen content of oxygen-free copper which is free from excessive gas cavities is difficult to determine.

Analyses have been made under the direction of Dr. Hiram S. Lukens by igniting copper in a silica tube at 14fi2 F. (800 C.) whilst simultaneously passing a stream of purified, water free hydrogen over-the copper; The hydrogen reacted with the oxygen present in the copper in the form of cuprous oxide as well as other oxides including carbon dioxide, to form water vapor. The exit gases were passed through an absorption tube containing Anhydrone (anhydrous magnesium perchlorate). The gain in weight after subtraction for a blank to compensate for possible impurities in the hydrogen was considered to be the oxygen content of the copper. Every precaution was taken in preparing the copper sample to avoid surface contamination with oxygen, and prior to the ignition in hydrogen at 1472" F. (800 C.) the sample was heated in hydrogen to 572 F. (300 C.) to remove surface contamination. Wherever oxygen content is referred to herein it is intended to indicate the oxygen content as determined in the foregoing manner. Such analyses indicate that a total oxygen content of 0.002% is permissible in dense oxygen-free copper.

In my United States Patent No. r 2,060,073, above referred to, reference is. made to casting the deoxidized molten copper in a protecting atmosphere such as carbon monoxide so as to procure dense oxygen-free copper castings. While the use of protecting atmosphere containing carbon monoxide at the point of casting is highly desirable from the standpoint of obtaining a high grade product, uniformity of casting conditions, and minimal deoxldizing efllciency for satisfactory results, there are certain concomitant disadvantages. Y

The structural enclosure often found desirable to economize 0n the atmosphere at the point of casting may be expensive, require maintenance and cause delay in manipulation of the casting.

' gredient, for example a In anycase, however, there should not be suflicient air exposure to cause a distinct phase of cuprous oxide to appear in the castings or to pro-. duce excessivegas cavities in the castings. From the determination of Rhines and Mathewson above referred to, it can be stated that an oxygen pck-up of about 0.007% is too much even assuming that the oxygen content of the molten copper before casting is practically zero. If the total oxygen content of the molten copper before casting reaches practically zero, the Lukens analyses above referred to indicate that an oxygen pick-up of 0.002% -during casting is not objectionable.

Assuming that the air in the mold is at 20 C. and under a pressure of 760 millimeters of mercury, that the copper is exposed only to the volume of air in the mold actually displaced by the copper casting and that the copper absorbs all of the oxygen present in that volume of air, theoxygen pick-up of the copper casting would be about 0.003%. Other conditions remaining the same, if the air in the mold wereheated to C., the oxygen pick-upxof the casting would be about 0.002%. Even though the volume of air in contact with the copper is several times the volume of air displaced by the casting, dense oxygen-free copper may nevertheless be cast if the pouring and solidifying rates, and the surface exposed to the air during pouring, are such that the casting does not absorb all of the oxygen present in the air to which it is exposed. Likewiseif the air in the mold and around the pouring stream is diluted by a harmless or preferably reducing invapor given off from a mold dressing, it may still be possible to cast dense oxygen-free copper in contact with a volume of diluted air several times the volume of the casting.

To render such casting in air feasible as a commercial matter, it is preferable to strictly limit the volume of air which can come in contact with the casting stream by structurally enclosing the stream and the top of the mold. The casting shield used need not, however, be nearly so elaborate as that iptended for casting in gas at superatmospheric pressure or for casting in vacuum. The joints need not be absolutely tight nor need the shield be entirely closed, since there is preferably no appreciable pressure diflerential between the interior of the shield and the outer atmosphere.

The inventor has succeeded in casting dense oxygen-free copper in air by treating the molten copper with solid carbon until the oxygen content of the copper is well below that necessary and commonly used when dense oxygen-free copper casting are to be cast in a protecting atmosphere consisting for example of carbon monoxide. It is possible to obtain the very low oxygen content required where copper is to be cast in air into dense oxygen-free castings, by sumciently long exposure at atmospheric pressure to solid carbon in contact with the molten copper and preferably submerged beneath its surface, in the absence of objectionable contamination with hydrogen-containing gases or oxidizing gases of combustion. The exposure to carbon should be effective to lowerthe oxygen content: (1) below that at which a distinct phase of cuprous oxide by step (2).

would appear in castings which solidify without oxygen pick-up (below' about 0.007% oxygen), (2) far enough below the oxygen content required by step (1) to change carbon dioxide to carbon monoxide until insufllcient carbon dioxide remains to cause objectionable gas cavities in castings which solidify without oxygen pick-up; and (3) far enough 'below the oxygen content required by step (2) so that the oxygen pick-up during casting in air will not cause the oxygen content of the castings to exceed the value required This necessitates an extremely low oxygen content in the molten copper before casting in air, so low in fact that the total oxygen,

percentage will be small or negligible in the third decimal place.

The present invention is applicable to copper substantially free from metallic impurities, such as iron, silicon and arsenic, and having a purity above about 99.95% or better. The presence of any substantial quantity of metallic impurities, especially iron, changes the problem as far as casting in air is concerned, because such metallic impurities, present in any substantial quantity in high quality commercial copper, are themselves oxidizable by air.

The inventor has furthermore discovered that the reduction of carbon dioxide to carbon monox- :de'in molten copper by contact with carbon, as well as the reduction of cuprous oxide, are greatly facilitated by maintaining reduced pressure on the system.

Scott United States Patent No. 1,948,316, grantcd February 20, 1934, for Process of refining copper, proposes to deoxidize copper by carbon under reduced pressure but does not propose to deoxidize carbon dioxide in copper by this means, or to exclude contamination with oxidizing gases of combustion and hydrogen-containing substances. Deoxidation of carbon dioxide can readily be done by confining the molten copper and the carbon in a closed vessel connected with'a vacuum pump. The use of a pressure substantially below atmospheric pressure not only renders the reduction of carbon dioxide much more rapid, but decreases the extent of exposure to carbon necessary and makes it possible to obtain a much lower total oxygen content including a lower content of carbon dioxide. Experiments indicate that halving the pressure substantially more than doubles the reaction velocity; in other words, the reaction velocity increases at a rate substantially greater than inverse proportion to the pressure.

While any reduction in pressure below atmospheric pressure is desirable, and it is preferred to use a pressure of about 35 millimeters of mercury, or below, excellent results are obtained with ptessures below about 300 millimeters of mercury.

An important feature of the deoxidation with carbon at reduced pressure is that the reaction is so accelerated that low total oxygen contents are obtained in the molten copper. in a fraction of the time necessary when reducing under atmospheric pressure. A charge of substantial size may be deoxidized in 10 or 15 minutes. It is therefore possible to apply deoxidation of copper by carbon under reduced pressure advantageously to installations in which dense oxygen-free copper is cast in a protecting atmosphere. A serious limitation upon the production capacity of a plant producing dense oxygen-free copper castings is the time and extent of exposure to carbon necessary for sufficiently complete deoxidation of the molten copper. When, however, the exposure to carbon takes placeunder reduced pressure, the

time of exposure is cut down or the completeness of the deoxidation in a given time is much increased so that higher production by the deoxidizing vessel is possible.

In the prior art, deoxidized copper has been 'degasified under reduced pressure in a carbon vessel, but advantage has not been taken of reduced pressure to deoxidize copper containing substantial quantities of oxygen, say 0.03%, or even as little as is necessary to produce a distinct phase of cuprous oxide in the copper castings, to an extent sufllcient to change over carbon dioxide to carbon monoxide as well as eliminate any .distinct phase of cuprous oxide, in the absence of contamination with oxidizing gases of combustion and hydrogen-containing substances.

As the production requirements for oxygenfree copper and tough-pitch copper vary from time to time, it is quite desirable to obtain both tough-pitch copper and oxygen-free copper from a given installation which is flexible enough to produce at any time entirely .tough-pitch copper, entirely oxygen-free copper or quantities of each as required.

The copper masses such as cathodes are preferably first preheated and oxidized to remove sulphur. This is best conducted by passing the cathodes through a preheating and oxidizing furnace in which they are exposed to gases of combustion which roast the copper masses to remove sulphur and at the same time preheat the copper masses. For certain aspects of the invention, the preheating furnace may be that shown in Lukens and Heuer United States Patent No. 1,733,419, granted October 29, 1929, for Continuous copper melting furnace, or Heuer United States Patent No. 1,914,716, granted June 20, 1933,

for Copper melting furnace.

The preheater illustrated in the drawings of the present application offers the distinct advantage over the above preheaters for the present purpose because it is heated by gases of combustion which are at least in part separate and separately controlled from those employed in the melting furnace. This makes it possible to oxidize the solid copper masses to approximately the proper extent required to give to the molten copper in the melting furnace the oxygen content required for tough-pitch copper (say 0.03% to 0.05% oxygen). This is a real economy as it not only avoids blowing but it also avoids or greatly shortens the necessary poling for toughpitch copper. The correct oxidation in the preheater could not be reliably obtained if the gases of combustion from the melting furnace were relied upon to do the entire preheating, because the oxidizing character of the gases of combustion in the preheater would not be subject to independent control.

The partial and preferably complete independence of the fuel heating means in the preheater from that in the melting furnace not only simpli-- fies the production of tough-pitch copper, but also makes possible the production of oxygenfree copper using tough-pitch copper as an in termediate product. Considerable economy is possible because the fuel used in preheating need not be so closely controlled as to sulphur con tent as the fuel used in the melting furnace.

The preheated copper masses are conducted to a -fuel-fired melting furnace, which preferably melts the copper masses while submerged in a bath of molten copper. In making oxygen-free copper, themolten copper from. the melting fur nace is withdrawn to a separate deoxidizing vessel where it is exposed to contact with carbon, preferably at reduced pressure, until the copper is sumciently deoxidized. The deoxidized molten copper may either be cast in air or in a protecting atmosphere consisting predominantly as an active ingredient of carbon monoxide at sub-atmospheric or superatomspheric pressure. A deoxidizing and casting installation is provided which may be a duplicate of the other installation and which may also be used to produce oxygen-free copper from the same melting furnace. On the other hand, where tough-pitch copper is desired, the second installation may with slight change be used to produce tough-pitc copper or both installations may with slight change be used for making tough-pitch copper.

The apparatus employed in carryin out the processes of the invention may desirably consist of a preheater operatively connected to a melting furnace 2 I. When the entire production is oxygen-free copper, molten copper will be withdrawn from the melting furnace 2| to deoxidizing vessels 22 and 23 which supply casting plants 24 and 25. In case tough-pits copper is being produced,- one or both of the deoxidizlng vessels 22 or 23 will be used as a pouring ladle. In order to simplify the explanation it will be assumed that deoxidi zing vessel 22 and casting-plant '24 are producing oxygen-free copper while pouring ladle 23 and casting. plant 25 are producing tough-pitch copper.

The preheater 20 desirably comprises a substantially horizontal flue 26 containing a suitable movable hearth 21 and supplied with heat by fuel burners 28 in doghouses 29 connected to flue 26 by inlet ports 30. The amount of fuel supplied to the burners 28, as well as the mixture of air and fuel burned which determines the oxidizing character of the gases of combustion, are subject to the control of the operator in any well-known manner, the detail of which is not shown.. The gases of combustion from the inlet ports 30 pass through the flue beneath the roof 3 I, between the side walls 32 and above the floor 33, for substantially the full length of the preheater, to a preheater stack 34. An economizer 35 in the preheater stack 34 may if desired be employed in heating the inlet air to the preheater.

The length of the preheater will, of course, depend upon the desired rate of preheating and the melting capacity of the furnace, but it will ordinarily be substantially longer in proportion to the melting furnace than the flue illustrated in the drawings, in order that the bulk of the sensible heat in the preheater gases may be absorbed by the copper masses. This fact is shown by breaking the preheater at 36. A length as great as 100 feet (30 meters) may in some cases be desirable. The preheater need'not of course be straight. Where a straight preheater is'used, it

is preferred to employ a roller hearth consisting of interlocking rollers 31 on shafts 38 supported in bearings 39. The shafts 38 carry gears 40 which are interconnected by gears 4| on stubshafts 42 in bearings 43. One of the gears 4| may be suitably driven as at 4i.

The hearth is charged with copper masses, suitably cathodes 44, at the charging end 45, which is desirably equipped with a vestibule 46 having doors 4'! and 41' operated through flexible connections 48 and 48' passing around motor driven drums 49 and 50. Copper masses, such as copper cathodes 44, can thus be conveniently placed on the movable hearth at when the door 41 is open and then the door 4'! can be closed until the time for supplying the next charge.

Where refined products such as wire bars.

- tubing, rods, bus bars,copper clippings and other salvaged products, which will preferably be consolidated into blocks or bales before charging.

In operation of the preferred preheater, the copper masses are progressed through the preheater aud are discharged into the melting furnace at 5| when they reach the end ,of the movable hearth. The preheater is preferably heated to a maximum temperature of about 1800 F. (about 980 C.) by means of oil, natural or manufactured gas, powdered coaliless desirable on account of the ash) or other suitable fuel applied at the burners 28. The combustion gases pass through the preheater in a direction countercurrent to the direction of the movement of the copper masses. The time of preheating will vary with the installation, but in a typical case it may be about one hour. The copper are efliciently preheated to a temperature approximating 1600" F. (870 0.). This temperature is close enough to the melting temperature so that the melting furnace need supply little heat except the latent heat of fusion, and is low enough so that there is little danger of melting in the preheater, which would be undesirable not only because it-would prevent the movable hearth from functioning, but also because molten copper readily absorbs sulphur from the combustion gases while solid copper does not. Molten copper dissolves cuprous oxide and cuprous sulphide, reducing the thermodynamic activity and preventing the quantitative ehmination of sulphur.

It is preferable to control the atmosphere of the preheater so that slight oxidation of the copper occurs during preheating. This oxidation serves to remove as sulphur'dioxide gas the sulphur adhering to the surfaces of the copper masses. Other volatile impurities may be removed to some extent. In the case of scrap cupper charges, adhering organic substances are 1 desirable that the oxygen content of the molten copper after melting be between about 0.03% and' 0.10% oxygen, so that only a little poling will be required to reduce the oxygen content to that of tough-pitch copper, if poling be required at all.

' The use of fuel heating means for the preheater which is at leastinpart separate and separately controlled from the fuel heatingmeians for the melting furnace,'makes possible accurate adjustmentof the extent of oxidation in the preheater, as well as of the preheater temperature, and it is with these ends in view that dependence is no longer placed upon preheating with the the melting furnace may be allowed to enter the preheater, as through an opening 51, Figure 2a, but the size of this opening should not be sufficient to permit melting furnace gases to do all-of the preheating, since it is important that the burners in the preheater control both the preheater temperature and the oxidizing character of the preheater gases. Air is of course admitted to the preheater at the preheater burners.

Preheated copper masses are plunged at periodic intervals through the-opening or 5| and into a bath 53 of molten copper covered with a slag'54 and resting on the hearth 55 of the melting furnace 2 I. The masses are melted while submerged in molten copper, thus reducing contamination from exposure to combustion gases during melting and permitting solution melting, that is, dissolving of solid copper in already molten copper.

The melting furnace 2| is provided with burners 56 for oil, natural, or manufactured gas, powdered coal or other suitable fuel combustion means, in a burner box 51. Coal firing may be substituted, in which case the burners 56 and burner box 51 will be replaced by a suitable coalburning grate. The gases of combustion from the melting furnace pass beneath the. furnace roof 58 to a stack 59 (in the form of Figure 2a, some of the melting furnace gases enter the preheater). An economizer 60 in the stack 59 may be used to heat the inlet air to'the burners 56 or a waste heater may be installed to recover the heat carried away from the furnace by the exit gases. The side walls SI of the melting furnace 2| are provided with suitable -doors 62 to permit access to the furnace interior, particularly for the purpose of poling if this be necessary, and a tap hole 63 is provided to remove the slag 54, which is desirably the slag normally forming on molten copper due to oxidation.

The molten copper is maintained at a suitable temperature for the treating and casting operations which follow. To prevent excessive oxidation, it may be covered with a layer of charcoal or coke 64 which of course is not effective to completely deoxidize the copper because of the presence of oxidizing combustion gases.

- The copper bath 53 preferably has an oxygen content suitable for casting "tough-pitch copper. This oxygen content is preferably maintained by regulating the oxidation in the preheater, and with a minimum of blowing or poling. It is possible to avoid excessive blowing, such as to an oxygen content of 0.9%, as in the prior art, because the sulphur content of the copper masses is substantially removed during preheating. On the other hand, it is desirable to avoid excessive oxidation' during preheating, as'

this .would necessitate considerable poling. Where the oxygen content of the bath 53 becomes excessive, green poles may be introduced beneath the copper bath through the doors 62.

Assuming that it is desired to cast toughpitch copper in the casting plant 25, the molten copper from the bath 53 may simply be withdrawn through a tap opening 65 and runner 66 to the pouring ladle 23. The pouring ladle 23 itself (called at other points deoxidizing vessel 23, when it is used to make dense oxygen-free castings) may be identical with the deoxidizing vessel 22, but it should not contain submerged carbon. Floating carbon in the pouring ladle 23 is not objectionable. The pouring ladle 23 may if desired be oil fired, by means not shown (but no oil firing should be used in thedeoxidizing vessel). Should the oxygen content of the tough-pitch copper withdrawn from melting furnace 2| to pouring ladle 23 be improper, it may be adjusted in pouring ladle 23 by blowing or poling. If any substantial deoxidation of the tough-pitch copper is desired, this may be accomplished by poling in the pouring ladle 23 in the usual manner, although the operation will be stopped of course before the oxygen content reaches the low value attained in the deoxidizing furnace 22.

The main function of pouring ladle 23 when operating on tough-pitch copper is that of pouring into molds 61. Although the casting shield 68 is unnecessary in casting tough-pitch copper, it will preferably be retained, as it is desired to make the same casting plant with slight change serve whether "tough-pitch or oxygen-free copper castings are being made. The casting plant 25 is similar to the casting plant 24 which will be described more in detail below, except that preferably no carbon is present in the strainer (as lining or otherwise) or in the molds when tough-pitch copper is being cast, and a non-volatile mold dressing such as bone ash is employed, without a protecting atmosphere at the point of casting. The molds for "tough-pitch copper are preferably made of copper.

In certain cases it may be desirable to use the pouring ladle 23 for the complete adjustment of the oxygen content ofthe tough-pitch'copper. In this case the preheater and melting furnace may be operated without regard to the oxygen content of the copper bath 53 and the molten copper in the pouring ladle 23 may have its oxygen content adjusted by blowing, or poling with green poles, charcoal, coke, etc.

The production of oxygen-free copper has been described in my United States Patent Nos. 2,060,- 073 and 2,060,074, aforesaid.

It has been discovered that molten copper which contains oxygen and other gases inthe amounts present in tough-pitch copper can be used in accordance with the present invention as a source of copper for the production of oxygen-free copper. Molten copper from the copper bath 53 is withdrawn through the tap hole 69 and runner 10 into the charging opening II of the deoxidizing vessel 22. The deoxidizing vessel 22 comprises a completely closed vacuumtight outside casing "lined with heat insulation I3 and then a refractory lining 14. The vessel is tiltably supported on structure preferably having the axis of tilting at 16 near the end of the pouring spout 11, so that accurate control may be had of the pouring from the vessel. The tilting mechanism may also be used to a limited extent to agitate the contents of 'the deoxidizing vessel.

The deoxidizing vessel contains molten copper I8 and solid carbon 19 in contact with the molten copper and desirably submerged beneath its surface. The carbon bed should preferably extend 12 inches (30 centimeters) or more below the surface of the molten copper. The carbon may be charcoal or coke, substantially free from hydrogen, hydrocarbons and water. The carbon will preferably be introduced before a charge of molten copper is placed in the deoxidizing vessel, and will be replenished from time to time as it becomes exhausted. A suitable strainer 11' in the pouring spout, having a plurality of openings of about 0.25 inch (6 millimeters) diameter, prevents carbon from being poured out .of the deoxidizing vessel with the molten copper. a

It is preferred to have no heating means associated with the deoxidizing vessel. The metal charged into the deoxidizing vessel should have suiiicient superheat to remain molten for the,

time of treatment. The heat insulation I3 will assist in preventing heat losses. In case heating means are to be used, to control the pouring temperature, prevent freezing of metal in the deoxidizing vessel, etc., the heating means rior of the deoxidizing vessel 22. The vacuum connection 84 is suitably connected with a vacuum pump 86. The opening of the pouring spout 11 may be made vacuum tight by a cap 91 which is bolted at "to a flange 99 on the casing 12, the joint being rendered vacuum tight by a gasket 90. When it is desired to pour oxygenfree copper from the deoxidizing vessel 22, the cap 81 is removed. As an alternative, a barometric molten copper .seal protected at the .exposed end from oxygen and hydrogen contamination might be used.

It is possible to pour dense oxygen-free copper castings without use of a shield by pouring into a vertical mold from a position as close to'the mold as possible. It is much preferable however to pour through a casting shield which will cut down the introduction of air from theoutside atmosphere into the vicinity of the pouring stream. The casting shield 9| is detachably mounted on the support 92 adjacent the pouring spout 11 after the cap 91 is removed from the pouring-spout. The casting shield 9| includes a strainer 93 having openings 94 communicating with a plurality (usually four) vertical molds 61 which are simultaneously positioned below the strainer on the casting wheel 24. The strainer casing 95 contains refractory lining 99 and an inner carbon lining 91 (in the case of "toughpitch" copper, the carbon lining should be omitted as already explained). A silica ,window 98 enables the operator to observe the stream.

The pouring spout I1 is articulated at 99 to the casting shield 9] by an arcuate member I99 removably secured to the pouring spout and continuously engaging the casting shield as the deoxidizing vessel swings about its axis 16.

The molds 61 are desirably of the vertical type disclosed in Eppensteiner United States Patent No. 1,779,534, although they may permissibly be of some other type. Steel molds will desirably be used in casting oxygen-free copper, since they have produced sound castings in some instances in which castings obtained from molds made of another materi were unsound (for "toughpitch copper, the molds are desirably of copper). The molds are suitably water cooled as at llll and their bottoms are closed by a door I02 hinged at I93 and latched at I04. When the castings have solidified they, are allowed to drop out of the molds by releasing the latch 104. It will of course be evident that the molds could be arranged for casting one at a time or several-at a time as desired.

In the preferred deoxidation procedure, the copper in the deoxidizing vessel is subjected to intimate contact with carbon under a reduced pressure of say 35 millimeters of mercury. This greatly accelerates the deoxidation, so that copper having the oxygen content of tough-pitch copper can in a short time be deoxidized so completely that it not only will not produce castings containing a distinct phase of cuprous oxide visible under the microscope, nor containing excessive gas cavities when cast under a protecting atmosphere, but it will even yield dense oxygen-free castings when cast with limited exposure to air within the molds and the shield.

Under best conditions the bulk specific gravity of the castings should reach 8.87 and in general bulk specific gravities in excess of 8.8 should be obtained. To reach such high specific gravities, particularly when casting in air, the deoxidation must be managed carefully.

The reactions taking place in the deoxidizing vessel appear to be:

Carbon monoxide from Reaction 1: between this difiiculty. Therefore, by prolonged deoxidation with carbon, the content. of carbon dioxide is lowered to such a value by Reaction 10 that it does not cause objectionable gas cavities when the copper solidifies.

, Lowering the pressure in the deoxidlzing vessel below atmospheric pressure reduces the carbon monoxide activity in Equation (4) for Reaction 1, and so lowers the activity of cuprous oxide, the activities of copper and carbon remaining unchanged. In Reaction 2 the lowering of the pressure in the deoxidizing vessel below atmospheric pressure to reduce the carbon monoxide activity and the simultaneous lowering of the activity of cuprous oxide yield a lower activity of carbon dioxide. According to Reaction l0 equilibrium requires at constant temperature that:

Since the activity of the carbon is constant, the lowering of the pressure in the deoxidizing vessel lowers the carbon monoxide activity and the carbon dioxide activity in such a way that the reduced activity of the carbon dioxide remains proportional to the square pf the reduced activity of the carbon monoxide. Thus the activity of carbon dioxide is reduced rapidly by reducing the pressure.

The quantity of carbon dioxide which will remain dissolved in the copper under reduced pressure is substantially lower than that which will remain dissolved under atmospheric pressure, so that the copper deoxidizied under reduced pressure is likely to be lower in carbon dioxide than copper deoxidized under atmospheric pressure, thus allowing for a certain oxygen pick-up without producing excessive carbon dioxide during pouring.

During the deoxidation there is always a relation between carbon dioxide and carbon monoxide present in the molten copper, depending upon th oxygen content, temperature, pressure and ap roach to equilibrium conditions. The eifect of the reduced pressure is therefore to establish a lower ratio between the carbon dioxide and carbon monoxide present in the molten copper. After the deoxidation is finished in the deoxidizing vessel and atmospheric pressure is restored, the molten copper will be unsaturated with carbon dioxide not only because of the effect of Reaction 101but also because of the much greater solubility of carbon dioxide at atmospheric pressure than at the reduced pressure.

It would appear to be impossible to determine the small oxygen content of the molten copper remaining after-deoxidation in the deoxidizing vessel 22. The oxygen content in the molten copper should be small or negligible in the third decimal place, and preferably below about 0.002%. To the operator skilled in the art, the attainment of the desired oxygen content is not difficult, as castings are poured and the deoxidation time varied until the absence of a distinct phase of cuprous oxide in the castings as viewed under the microscope shows that they are oxygen-free and the bulk specific gravity in excess of 8.8 (preferably in excess of 8.87) shows that they contain insufllcient gas forming substances present in the molten copper to produce gas cavities which would interfere with the mechanical working of the copper.

The deoxidation under reduced pressure appears to be advantageous from the standpoint of removal of other contaminating gases which may be present in tough-pitch copper. Water vapor and the like are successfully removed under the reduced pressure. It will, of course, be evident that the deoxidizing vessel should be kept from contact with hydrogen-containing substances to prevent objectionable hydrogen contamination of the molten'copper. Contamination with oxidizing gases of combustion is of course not possible during the deoxidation.

The deoxidizing vessel is completely sealed when the reduced pressure is maintained in it. In restoring the atmospheric pressure prior to casting, it is preferable to introduce into the deoxidizing vessel through a valved connection I05, a noncontafninating reducing gas such as carbon monoxide or the gas recommended below as a protected casting atmosphere, at a pressure at least as high as atmospheric pressure.

The functions of the single deoxidizing vessel may, of course, be divided among several vessels which can be unheated or heated as desired.

As already explained, the molds and the casting shield 81 may permissibly contain air when oxygen-free copper is cast. The volume of air in the molds and casting shield should preferably 'be not more than about four times the volume diluted by a nod-oxidizing or, better, reducing gas or vapor. In casting oxygen-free copper,

the interiors of the molds are preferably coated with a mold dressing, consisting for-example of a film-forming substance such as lard oil or a petroleum distillate or hydrocarbon mixed with carbon in the form of powdered graphite or lamp black. The molds before use are preferably warmed to about 187 F. (86 C.) and they become filled with vapor from the oil which lowers the oxygen content of the air and exerts some reducing action. The presence of hydrogen .in the vapor of the oil does not appear to be objectionable because of the short time of exposure, and the slight contact, which is not suf- The vapor from,

flcient to cause gas cavities. the mold dressing is more convenient than the use of a protecting gas because the vapor is heavier than air and stays in the molds, it is not necessary to sweep air out of the molds, and the molds and shield need not be constructed and maintained absolutely gas tight.

As already noted, for tough-pitch copper, a non-volatile mold dressing such as bone ash should be used.

In making oxygen-free copper, the use of vertical molds'reducesthe area of the "set surface of the casting. By pouring from a point as near as possible to the top of the molds, .the length of the pouring stream is cut down, so that the exposure to air in contact with the pouring stream is at a minimum. By making the shield as small as possible, the volume of air additional to that in the mold which can come in contact with the copper is kept at a minimum and the air is rendered less oxidizing by the vapor from the mold dressing. If the deoxidation has carried the oxygen content of the copper far below the point at which excessive gas cavities or a distinct phase of cuprous oxide form in the solidifying copper, the limited pick-up of oxygen during casting is not effective to prevent the casting from being dense and oxygen-free.

The deoxidation of copper containing a substantial amount (say 0.04% or even 0.01%) of oxygen by carbon under reduced pressure as already explained is advantageous notwithstanding that casting is to take place in a protecting gaseous atmosphere at reduced pressure, atmospheric pressure or superatmospheric pressure, because the reduced pressure accelerates and facilitates the deoxidation and makes it possible to maintain the total oxygen content, and particularly the content of dissolved carbon dioxide, at a lower value.

If a protecting atmosphere is to be used, it may be introduced into the shield 9| through the connection I06 and allowed to sweep out the molds before the door I02 at the bottom is closed. If superatmospheric pressure is employed, the noncontaminating reducing gas will escape through any leaks in the shield or at the point of connection between the molds and the shield. Carbon monoxide is a desirable protecting gas as the copper contains substantial quantities of carbon monoxide when it comes from a deoxidizing vessel in any case, and the carbon monoxide does not therefore additionally contaminate the copper. Carbon monoxide dissolved in the copper in fact exerts a slight protecting action by reacting with oxidizing gases. Carbon monoxide also has the desirable property of burning when it comes in contact with the atmosphere.

A gas containing carbon monoxide as an active ingredient, for example producer gas made from charcoal or coke, may be used. Typical analyses of such a gas are:

Gas No. 2 is of course preferable to gas No. 1. In somecases it is desirable to have the protect.-

ing atmosphere low in hydrogen to prevent ex-, cessive gas cavities caused by hydrogen, where- 15 upon the air and charcoal used in making the coal producer gasshould be first freed from we r vapor.

If the casting wheel is to be removed to the next position before the tops of the castings 20 have solidified, itis desirable to protect the tops of the castings by' placing powdered carbon such as charcoal on them as the wheel is moved. The carbon should be so finely divided that it will behave as a fluid.

Although it is preferred to carry out the deoxidation under reduced pressure, the deoxidation may nevertheless be conducted at atmospheric pressure and the castings'can still be cast in air providing the deoxidation is sufficiently prolonged. If the deoxidation is to be carried on under atmospheric pressure, the connection to the vacuum pump 86 can simply be removed and the small opening used as a vent for gases.

By the process explained herein, it is possible 35' toobtain dense oxygen-free copper castings by casting in air. It is also possible to facilitate andaccelerate the deoxidation of copper whether 2;! is to be cast in a protecting-atmosphere or in It will be evident that a distinct advantage of the present invention is the use of the same equipment to produce "tough-pitch copper and oxygen-free copper, so that within a considerable range of flexibility, increased demand for 45 one product may be met by increased supply of that product and correspondingly decreased supply of the other product.

It will further be evident that the deoxidation under reduced pressure in the deoxidizing vessel,'while explained herein as an intermittent process, can if desired be made continuous by equipping the inletand outlet of the deoxidizing vessel with barometric molten copper column seals, provided of course that the oxygen removed (whether as oxygemor oxygen'compounds) in a given time equals or exceeds that introduced by diffusion through the seals plus Ext born by the copper charged during the given In view of my invention and disclosin'e'varia tions and modifications to'meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtiin'ali orpart of the benefits ofmy invention withoi'it' the shown.-and'.I.'therefore.-.Qh1m all fin so far as they fail-within reasonable 8 sands onef mr nr n iqn thus. my invention, claim as new and desire Patentis: 1. In apparatus for produci coppercastings,

a melting furnace'containingimolten copper of approximately "tough-pitch" grada'a deoxidiz ing vessel receiving? coppe'r'directly from the meltinrfurnace, an oxygen-free copper casting an exit connection forthe products of combusplant for the deoxidizing vessel including molds and a casting shield surrounding the pouring stream from the deoxidizing vessel to a mold which is in pouring position, a pouring ladle receiving molten copper from the melting furnace independently of the deoxidizing' vessel and a tough-pitch copper casting plant for the pouring ladle.

2. In apparatus for preparing copper to make, castings from copper masses, a preheater for the copper masses, fuel-fired means for heating the preheater and oxidizing the copper masses in it, a. continuous melting furnace connected to the discharge end of the preheater, means for submerging copper masses in solid condition from the preheater beneath the molten copper in the melting furnace and means for heating the melting furnace, the fuel-fired means for heating the preheater being at least in part separate from the means for heating the melting furnace.

3. In apparatus for preparing copper to make castings from copper masses, a preheater for the copper masses, fuel-fired means for heating the preheater and oxidizing the copper masses in it,

a continuous melting furnace connected to the discharge end of the preheater, fuel-fired means for heating the melting furnace, the fuel-fired means for heating the preheater being at least in part separate from the fuel-fired means for heating the melting furnace, and a combustion gas exit connection to the melting furnace carrying off at least part of the combustion gases from the melting furnace independent of the preheater.

4. In copper melting and casting apparatus, a substantially horizontal preheater having a hearth which supports copper masses while they are. carried from the inlet to the discharge end of the preheater, means for progressing the copper masses through the preheater, fuel-fired means for heating the preheater and oxidizing the copper masses'in it, a. continuous melting furnace connected to the discharge end of the preheater, fuel-fired means for heating the melting furnace, the fuel-fired means for heating the preheater being at least in part separate from dizing vessel and a casting shield around the pouring stream at the point of casting.

5. In a copper melting and casting apparatus,

a preheater having a hearth which supports the copper masses while they are carried from the inlet to the discharge end of the preheater, means for progressing the copper masses through the preheater, fuel-fired means for heating the preheater and oxidizing the copper masses in it, a continuous melting furnace connected to the discharge end of the preheater and containing molten copper of approximately tough-pitch" grade, fuel-fired means for heating the melting I furnace, the fuel-fired means for heating the. preheater being at least in part separate from the fuel-fired meansior heating the melting furnace,

tion from the melting furnace at; least in part independent of the preheater. deoxidizing vmeizreceiving molten copper'frf melting furnace, closed-to the atmosphe' and containconnected to the deoxidizlng vessel and having a casting shield around the pouring stream at the point 'of casting and-a tough-pitch" copper casting plant receiving molten copper from the melting furnace.

6. In apparatus to produce tom-Ditch copper, a preheating and oxidizing furnace, fuel means for heating the preheating and oxidizing furnace, a melting furnace connected to the preheating and oxidizing furnace, fuel means for heating the melting furnace,. the fuel means for heating the preheating and oxidizing furnace being at least in part separate and separately controlled from the fuel means for heating the melt-