US2265284A

US2265284A - Melting copper

Info

Publication number: US2265284A
Application number: US362956A
Authority: US
Inventors: Philip M Hulme; Robert A Ghelardi
Original assignee: International Smelting and Refining Co
Current assignee: International Smelting and Refining Co
Priority date: 1940-10-26
Filing date: 1940-10-26
Publication date: 1941-12-09
Anticipated expiration: 1958-12-09

Description

9, 1941. P. M. HULME E-rAL 2,265,284

V MELTING COPPER Filed Oct. 26, 1940 3 Sheets-$11961'l 1 ATTORN EYS EN. fm

i. M. HULME lrrm.v

MELTING COPPER Filed 0G11. 26, 1940 3 Sheets-Sheet 2 am. www D Tad. l m NH, R E O WX n 9, 1941. P. M. HULME ETAL MELTING COPPER 3 sheets-sheet :s

Fileaoct, 26, 1940 4 5 a 5 .Q um bo Rf, MY wuwk why M ,o WM. n A @Mm n, gm. @d Il Pom.

` and remains in the molten copper.

Patented Dec. 9, 1941 MELTING COPPER Philip M. Hnlme and Robert A. Ghelardi, Metuchen, N. li., assignors to International Smelting & Refining Company, a corporation vof Montana Application October 26, 1940, Serial No. 362,956

6 Claims.-

This invention relates to the melting of cathode copper, and has for its object the provision of an improved method of melting such copper to produce substantially. oxygen-free 'molten copper. The substantially oxygen-free molten copper resulting from the practice of the invention may be used tov produce any desired shapes (i. e. bars, billets, cakes etc.) of cast ycopper for subsequent fabrication, and the cast copper may be substantially oxygen-free, flatset or tough-pitch, 'phosphor copper orU other copper alloy, as desired.

Most of the copper commercially produced at the present time is electrolytically refined. While commercial electrolytically refined copper (cathode copper) is usually very pureand substantially free of oxygen, no commercially practical method has heretofore been available for melting such copper in a fuel-fired furnace without contaminating the melted copper with oxygen or other impurity or both. The present in-v vention provides a method of melting cathode copper without contamination in a fuel-fired furnace, and permits the production of either oxygen-free or nat-set copper castings (the latter by controlled incorporation of oxygen in the molten copper), as well as the production of copper alloy castings such as phosphor copper casting them into blocks. Whether or not the poling operation has proceeded to a suflicient extent is determined by observing the nature of the set or. pitch, that is the condition' or the exposed surface of these cast samples upon cooling. When the samples show a proper set, poling is stopped and the molten copper `is cast into suitable shapes.

and the like, without resort to the refiningy procedures heretofore found necessary.

The heretofore customary practice for melting and casting cathode copper follows generally the old Welsh process for fire-refining. It involves first melting the copper in a fuel-fired furnace, skimming any slag formed, oxidizing the molten charge, skimming the oxidized iml purities, and then poling the charge to reduce cuprous oxide. -During the melting operation the copper is in contact with the gaseous combustion products of the fuel, and some of these gases are absorbed in the and contaminate the copper. To remove these contaminants and other impurities, the molten copper is blown with air and then skimmed. In this manner impurities in the copper are largely removed, but some copper oxide is unavoidably formed The molten copper, therefore, is next covered with coke'and subjected to a poling operation' by plunging wooden poles below the surface of the molten metal. As a result 'of this operation, the cuprous oxide in the molten metal is reduced and the metal is conditioned yfor casting.

The progress of the poling operation is care-A fully Watched by taking frequent samples and `The cast copper solidifying in the mold with a substantially at or slightly crowned surface is known as tough-pitch or flat-set copper. This copper invariably contains a small amount of oxygen (0.01 to 0.05%), since the presence of a small amount of oxygen is necessary to `nsure the flat-set desired for rolling and drawing operations. The precise manner in which the oxygen functions to produce a flat-set is not I'uiiy understood, but it is generally believed that the oxygen reacts with very small amounts of impurities (particularly sulphur) present even in cathode copper, and forms a gas, which comes out of solution as the copper cools. This gas expands and counteracts the tendency of the copper to shrink upon freezing by forming minute cavities in the casting in suiiicient amount to prevent the formation of a shrinkage cavity or pipe If insufficient gas is evolved. the surface will be depressed, or if too much gas is evolved, they surface will rise and may even be broken by y'a spew of metal forced through the frozen surface scum. The former is known as low-set copper and the latter as applied to any copper containing this amount of oxygen, for in some cases (depending upon the amounts of impurities, such as sulphur, in the copper) the presence of oxygen within these limits will not produce the flat-set or slightly crownedset required for commercial purposes.

' The melting and casting of cathode copper in fuel-fired furnacesrequires the close attention and careful control of experienced and skilled operators, particularlyduring the poling operation. Furthermore, the practice hasv the further disadvantage of being a batch operation. Each furnace charge must be melted, oxidized and poled before casting vcan commence, so that the actual casting period, during which the furnace is producing a marketable product, is a small fraction of the time required for each cycle of theJ operation. In the case of the customary twenty-four hour cycle, for example, casting proceeds for only about five hours.- A- stillprovements of a mechanical nature for lightening the manual work involved, these attempts lhave been commercially unsuccessful and the general technique of the mained unchanged.

-Molten copper containing oxygen may be deoxidized by suitable metallic deoxidizing agents, such as phosphorus, silicon, calcium, lithium etc. The use of such deoxidizing agents is usually objectionable because the amount required for deoxidation of the copper is such that some of the deoxidizer remains in the copper and lowers practice has long reits electrical conductivity. Thus, for example,4

phosphorus deoxidized copper usually contains from 0.015 to 0.025% phosphorus. However, for certain uses this small amount of phosphorus is considered advantageous, in addition to evidencing complete deoxidation of the copper.

Oxygen-free copper of high electrical conductivity possesses certain desirable properties for a number of uses, but its production by processes now availableis expensive, and consequently the commercial demand for such oxygen-free copper is limited. Suclr oxygen-free copper has heretofore been produced in electric melting furnaces, and by subjecting molten copper, meltedv and refined as hereinbefore described, to a special deoxidizing treatment by bringing it into intimate contact with charcoal.

The present invention contemplates an improved method of melting cathode copper for producing substantially oxygen-free molten copper, which may be cast as such, or may be used to produce flat-set cast copper shapes, phosphor copper and other copper alloys. In accordance with the invention, the cathode copper. is melted lin the melting chamber of a fuel-fired muilie furnace under conditions inhibiting the presence of slag on the surface of the resulting molten copper, while maintaining in-the melting chamber above the molten copper therein a gaseous reducing atmosphere free of any constituent l, capable under the operating conditions prevailing within the melting cham-ber of deleteriously affecting the molten copper. A bath of substantiallyy oxygen-free molten copper is maintained in the melting chamber under conditions permitting unhindered transfer of radiant heat to the surface thereof. In other words, no medium of relatively poor heat conductivity, sucliv as slag, charcoal and the like," covers the surface of the molten metal andimpedes the transfer of radiant heat.- thereto. Preferably, Athe gaseous 'atmosphere within the melting chamber consists principally of carbon monoxide and nitrogen, and may advantageously be derived by appropriate treatment of exhaust combustion )its incorporation in the bath of molten copper.

IThe melting operation is carried out continuously by maintaining a substantially uniform volume of molten copper in the melting chamber and suitably correlating the amount of cathode copper introduced into the chamber for melting with the amount of molten copper withdrawn from the chamber. Substantially oxygen-free molten copper is withdrawn from the melting chamber, and may be cast into shapes of substantially oxygen-free copper by withdrawing the molten metal and casting under conditions inhibiting the inclusion of oxygen in the resulting cast shapes. By the controlled incorporation of oxygen in the substantially oxygen-free molten copper withdrawn from the furnace, flatset copper castings may be produced. Phosphorus or other alloying metal may be incorcopper withdrawn from the furnace to produce phosphor copper and the like.

The invention will be better understood from the following description, taken in conjunction with the accompanying drawings, in which Fig. 1 is a longitudinal sectional elevation of a fuel-nred muiile furnace adapted for the practice of the invention,

Fig. 2 is a sectional detail of the mechanical seal for the entering copper cathodes,

Fig. 3 is asectional elevation, taken on the section line 3 3- of Fig. 1, showing the molten copper discharge launder and pouring ladle,

l ',Fig. 4.is a sectional plan of the launder and ladle shown in Fig. 3,

. Fig. 5 is a sectional detail taken on the section line 5-5 of Fig. 4, and y Fig. 6 is a ydiagrammatic flow sheet of the equipment for providing the reducing gas required in the practice of the invention.

The furnace shown in the drawings has side walls III and II, end walls I2 and I3, a oor or hearth I4 and an arched roof I5, all of refractory brick. The interior of the furnace is divided into a 'melting chamber I 6 and a combustion chamber I'I by ankarch I8 sprung between the side walls of the furnace. The arch I8 is relatively thin and of high refractory material possessingv good heat-conducting properties, such for example as silicon carbide. The arch should be as thin as it is practical to make it in order to permit maximum heat transfer therethrough. Silicon carbide (particularly that commercially known as carbofrax) is mechanically strong, highly refractory and possesses relatively good heat'conducting properties.

Oil' burners I9 extend through each of the end walls I 2 and I3 into the combustionchamber II. The side wall I0 has near its center a flue 20 for the withdrawal of combustion gases from the combustion chamber. Each end wall I2 and I3- has a charge opening 2| for introducing the copper cathodes to be melted into the melting 22 is provided for advancing the lowermost copper cathode of the pile or stack of cathodes 23 along a downwardly inclined floor 24 towards the charge opening 2|. lie end to end on the floor 24 and are advanced or fed at predetermined time intervals towards and into the melting chamber I6 by the advance or feeding of the lowermost cathode in the stack 23.

The melting chamber I6 has a tap hole 29, for the withdrawal of molten metal, approximately in the center of the side wall Il. A curtain wall 30, at ythe inner end of the tap hole,

directs the molten metal into a discharge well 3l, and provides a positive molten metal seal for the melting chamber. The tap hole 29 communicates with and discharges into a covered launder 32 for conveying the molten metal to a tilting casting ladle 33.

The launder 32 is built of suitable refractory material, such as clay, and is effectively insulated to prevent freezing of the molten copper flowing therethrough. A heating chamber 34 overlays the top of the launder and is separated fromthe launder by a thin layer of silicon carbide rtile 35 (Figs. 4 and 5). The heatingchamber has at one end a fuel burner opening 36 and at the other end a ue 31 communicating with a stack 38 for the exhaust combustion gases.

A mechanical seal is provided to prevent air entering the melting chamber I6 through the charge openings 2|. This seal comprises a pipe 25 appropriately secured to the outside of the furnace structure adjacent the charge opening 2I (Fig. 2). A longitudinal segment is' cut from the lower part of the pipe 25 to provide a slot 26 therein extending across the Width of the charge opening. A plurality of contacting thin metal washers 21, of larger diameter than the width of the slot 26, are positioned for the most part within the pipe 25 and are operatively held in position by the longitudinal edges of the slot 26. A fixed pipe 28 extends through the washers 21 and prevents any accidental dropping of the washers. The washers are free to move vertically a certain distance and thus conform across, the entire width of the charge opening 2l with any surface irregularities on the face of the copper cathodes.

The cylindrical tilting ladle 33 has at one end a feed tube 39 in communication with the discharge end of the launder. 32 throughout the operative tilting movement of th'e ladle. The communicating openings of the launder 32 andthe feed tube 39 are enclosed by a sealing hood 40 havingan observation window 4I. A normally covered funnel 42 projects through the top of the hood 4I) directly above the feed tube 39. The feed tube 39 extends below the surface of the molten copper in the ladle 33. The ladle is tilted through a small angle for pouring and molten copper ows over a discharge lip 43. In Figs. 3 and 4 of the drawings, the ladle 33 is shown casting molten copper into a vertical mold 44, the pouring and casting being carried out under a protecting hood'45.

Reducing gas is introduced into the melting chamber I6, above the molten copper therein, through two pipes 46 on opposite sides of the tap hole 29 (Fig. 4). The pipes 46 are connected by a pipe 41 to the reducing gas supply main 48. Pipesr 49 and 50, connected to the main 48, supply reducing gas to the interior of the hoods 40 and45', respectively (Fig. 3). Reducing gas Several cathodes 23 face of the molten copper in ture is derived by treatment of the exhaust com.-

bustion gas from the furnace. A certain amount of the combustion gas is withdrawn from the fiue 20 through a pipe 5I and a water chamber 52 by a pump 53 (Fig. 6). The cooled gas is forced through a water spray tower 54 for the removal of sulphur dioxide and vthen through an iron oxide tower 55 for the removal of hydrogen sulphide. The thus-purified gas next passes through a moisture trap 56 into an electrodryer 51. Such an electrodryer may be of the type known by the trade-name Lectrodryer and manufactured by the Pittsburgh Lectrodryer Corp., Pittsburgh, JPennsylvania.. The electrodryer is filled with activated alumina, and two are provided so that one may be regenerated while the other is in use. The purified and dried gas, consisting now principally of carbon dioxide and nitrogen, next passes through an. electrically heated charcoal reducer 58 where the carbon dioxide is reduced to carbon monoxide. Two reducers 58 are provided so that one may be refilled with charcoal while the other is in use. After passing through a filter 59 the reducing gas mixture flows into the supply main 48. The supply main may of course include a gasometer for storage of the reducing gas mixture, 4Where irregularities in the production of or demandfor the reducing 'gas make its direct supply to the melting chamber and the protecting hoods impracticable.

In practicing the invention in the apparatus shown in the drawings, the furnace is fired by the oil burners I9 to heat the melting or muifie chamber I6 above the melting point of copper. The melting chamber is heated largely by radiant heat from the silicon carbide arch I8, and to a lesser extent by heat conducted through the side and end walls of the furnace. Pure copper melts at a temperature of about 1980 F., but for practical purposes the molten copper should be heated to a temperature of about 2050 F. for satisfactory casting. vIn order to vmaintainan adequate melting rate in the'furnace for economic commercial operation, a temperature approximating 2500 F. should .preferably be maintained directly beneath the arch I8.

Since the copper in the melting chamber I6 is heated largely by heat radiated to it from the under surface of the arch, it is important to establish and maintain conditions favoring the transfer of radiant heat to the copper.

To this end, the surface of the molten copper shouldl possess high emissivity. In a sense this emissivity is a measure of the capacity of the molten copper to absorb the heat radiated to it. The emissivity of molten copper is adequately high to insure melting of the copper cathodes at .the desired rate when the temperature at the under surface of the arch I8 approximates 2500" F.

Fused slags generally possess higher emmissivity than molten copper, but they are poor conductors of heat. If present on the surface of the molten copper, they impede `rather than aidin the transfer of radiant'.A heat to the copper. Accordingly, "in practicing the invention, the surthemelting chamb` er is maintained free of` slag, and to this end the copper cathodes are melted under conditions inhibiting the formation of slag and hence inhibiting the presence of slag on the surface of the molten copper.

Molten copper substantially free of oxygen or oxides exerts practically no effect upon common and inexpensive silica refractories, so that such refractories may be employed for the linings of the melting chamber. Many fused reactive slags vigorously attack silica refractories, so that the presence of such slags on the surface of the molten copper, while accomplishing no useful purpose in the practice of the invention, would necessitate the use of expensive refractories to avoid serious damage to the lining of the melting chamber.

It has heretofore been proposed to deoxidize molten copper bymaintaining a layer of charcoal on the surface thereof. Such a layer of charcoal would perform no useful purpose inthe practice of the present invention, and would moreover be objectionable since its relatively poor heat conductivity would impede the transfer of radiant heat to -the molten copper. The presence of charcoal on the surface of the molten copper is apt to be attended by the further disadvantage of coating the under-side of the arch I8 with a lm of finely divided charcoal which may objectionably decrease the heat conductivity of the arch. h

While the surface of the molten copper in the melting chamber is free of slag and of any other medium impeding the transfer of radiant, heat thereto, oating patches' of unfused or partially fused refractory material may gather on the surface of the moltencopper. Where the melting chamber is lined with silica brick, these floating patches consist mainly of silica and appear to be due to mechanical erosion of the lining by the molten copper. 'I'his has been observed to occur to a small extent in a newly-lined furnace when .it is rst put in operation. So long as these floating patches cover in the aggregate only a small part of the surface of the molten copper,

they are of no practical significance. However, they should be raked or pulled olf the surface of the molten copper from time to time, in order to insure elcient transfer of radiant heat to the surface of the molten copper aswell as eective direct exposure of the surface of the molten copper to the gaseous reducing atmosphere.

A bath of substantially oxygen-free molten copper is maintained in the melting chamber I6. The level of this bath of molten copper is determined by the height of the overowof the discharge well 3| into the launder 32. A gaseous reducing atmosphere is maintained above the surface of the molten copper in the melting chamber I6. In the apparatus of the drawings,

this gas is supplied to the melting chambervv through the pipes 46 and consists principally of carbon monoxide and nitrogen and is derived by treatment of exhaust combustion gas from the furnace as hereinbefore described. The pressure of the reducing gas atmosphere within the melting chamber I6 is slightly higher than the atmospheric pressure (e. g. around IAO@ of an inch of water) thus insuring against the entrance of air and combustion gases into the chamber. 'I'he reducing gas escapes from the melting chamber through cracks in the furnace structure and through the charge openings 2 I.

While it is our preferred practice to obtain the reducing gas mixture by treatment of exhaust combustion gas.'other sources may be availed 'of ducer gas consisting predominantly of carbon monoxide and nitrogen is suitable. The reducing gas mixture should be free of any constituent 'capable under the operating conditions prevailing within the melting chamber of deleteriously affecting the oxygen-free molten copper. presence of hydrogen in the reducing gas mixture should be avoided, since hydrogen is readily absorbed by molten copper and adversely affects the set of copper upon casting. Even the presence of a small amountv of water vapor is ob# jectionable, since at the temperature prevailing in the melting chamber water vapor decomposes into hydrogen and oxygen (particularly in the presence of carbon monoxide) and the resulting hydrogen may adversely affect the set of the copper during casting.

The reducing gas mixture should be reasonably free of carbon dioxide, since carbon dioxide l reacts with molten copper to yield carbon monoxide and cuprous oxide. A small amount of carbon dioxide in the presence of a large amount of v mation of cuprous oxide is for most practical v purposes sufficiently retarded.

'I'he presence of decomposable hydrocarbons in the reducing gas, atmosphere in the melting chamber is undesirable, since such hydrocarbons are cracked at the prevailing temperature-and carbon is deposited on the surfaceof the metal or on the under-surface of the arch or on both. Such deposits of carbon,`whether on thesu'rface of the metal or on the under-surface of the arch, materially lower the melting rate of the-furnace by impeding the transfer of radiant heat to the molten copper. The illuminants present in coal gas or any enriched-producer gas or"water gas such as is available in most cities are examples of decomposable hydrocarbons which behave in this manner.

It is also desirable to avoid the presence of sulphur in the gaseous reducing atmosphere in the melting chamber. Some sulphur (usually in the form of copper sulphate or sulphuric acid occludedin the cathode) is unavoidably introduced yinto the melting chamber with the charge. The

molten copper. to produce the desired set of tough-pitch copper, as hereinbefore explained.

.The copper charged into the melting chamber usually contains as much sulphur as is desirable, and therefore the presence of sulphur or sulphur compounds in the gaseous reducing atmosphere of the melting chamber should usually be avoided.

The hooks of the initial starting sheets of the copper cathodes are preferably cut off before charging the cathodes into the melting chamber. Undesirable amounts of oxidized copper, copper sulphate etc. are frequently associated with these hooks and it is hence better not to attempt to melt them in practicing the present invention. The cathodes are stacked (23) and automatically fed into the melting chamber alternately by the two sheet-feeding devices (22) at the opposite ends of the furnace. The plus pressure of the gaseous reducing atmosphere within-the melting chamber and the mechanical seal alongside the charge opening 2| effectively prevents the introsheet-feeding device operates at 8 minute intervals. The preheating of the cathode for this interval of 8 minutes in contact with the gaseousY reducing atmosphere effectively reduces any copper oxide on its surface, and substantially insures the absence of oxygen on or within the cathode when it is ultimately pushed off the feeding floor into the bath of `molten copper. Whatever slight amount of ozidized copper that may be introduced into the bath of molten copper during charging and melting of the cathodes is readily reduced by the gaseous reducing atmosphere, so that the" bath 'of molten copper maintained continuously in the melting chamber I6 is for all practical purposes substantially oxygen-free.

The apparatus illustrated in the drawings is adapted for the production of castings of substantially oxygen-free copper of high electrical conductivity. The reducing gas mixture is supplied to the hoods 40 and 45 so that the substantially oxygen-free molten copper withdrawn from the melting chamber is not allowed to come in contact with air or other oxidizing influence while flowing down the launder 32 or while in the ladle 33 or during casting.

In practicing the invention for the production of tough pitch copper, the removable covers E@ of the heating chamber 34 and the covering tiles 35 for the launder 32 are removed, or the launder structure is replaced by a substantially open launder. The moltenlcopper flowing through the open launder is covered with a layer of charcoal -toprevent it from becoming oxidized to anundesirable extent, but the coverage of the copper by the charcoal is incomplete, so as to` permit the copper to be exposed to the air sufficiently presence of air currents in the vicinity of the.

launder, influence the amount of oxygen absorbed by the molten copper as it flows through the launder. Other variable factors, such as the amount of sulphur present in the copper, alect easier of control in the practice of the invention than it is in the poling operation of the prior art refining practice.

The molten copper, with its oxygen content controlled as just described, flows into-the tilting ladle 33, which need not for this operation be provided with the hood 45. If necessary or desirable, the ladle may be heated by an oil flame through the end opening Bl. It has been found that contact of the molten copper with combination gases in a oil heated ladle is not objectionable, apparently because the molten 4copper re'mains in the ladle for too short a period of time to become contaminated by the gases.

Copper alloys, such as phosphor copper or silicon copper, may Lbe produced by adding controlled amounts of the alloying metal to the substantially oxygen-free molten copper Withdrawn from the melting chamber. Such alloying metals are preferably added to the molten copper in'the ladle just before casting, as for example through the normally covered funnel 42. Alloying metals may be similarly added to the molten copper in the ladle after the controlled incorporation of oxygen therein, as hereinbefore described. l

While the copper cathodes are charged periodically, at predetermined short time intervals, the melting and casting operation is for all practical purposes continuous; substantially oxygenfree molten copper being withdrawn from the melting chamber at substantially the same rate as the cathodes are charged. The substantially oxygen-free molten copper does not affect the refractory lining of the melting chamber, and no s lagis present to attack the lining. The furnace is not repeatedly heated and cooled, as heretofore customary in melting copper cathodes, and the fumace refractories are hence not subject to thermal shock.

Aside from the usually minute amount of oxidized copper present on the .surface of copper 1 cathodes, the method of the invention removes no impurities. from the copper. But the method of the invention does effectively reduced whatever amount 'of oxidized copper is ordinarily associated with the copper cathode. The surface of the molten copper is exposed tothe direct influence of the gaseous reducing atmosphere the amount of oxygen required to produce a fiat-set' upon casting and cooling. Accordingly, it is not possible to formulate precisely what proportion of the surface of the molten copper flowing through the launder should be exposed to the air. This can be determined, however, by the usual procedure of casting small test blocks and observing the set thereof upon solidifying. If the set indicates that too much oxygen is present in the copper, additional charcoal is added to the launder, or if the set indicates a deficiency of oxygen, some 4of the charcoal is raked from the surface of the molten copper in the launder. About 0.01 to 0.05% oxygen by Weight should be .incorporated in the copper to obtain the desired flat-set. Although the test here employed is the same as that used in the heretofore customary rei'lning practice, the amount of oxygen ultimately incorporated in the molten copper is very much and any cuprous oxide in the molten copper is thereby reduced. Such cuprous oxide tends naturally to migrate to the surface of the molten copper, and this tendency is promoted by the agitation of the molten copper as the cathodes drop into the molten copper alternately from the two ends of the melting chamber. In addition to copper cathodes, other forms of equally pure substantially oxygen-free copper may constitute all or part of the copper charged into the melting chamber. Where, in the production of tough-pitch cast copper, insufficient sulphur is present in the cathodes to be melted, a controlled amount of sulphur may be incorporated in the molten copper in the melting chamber, as for example by the controlled introduction of sulphur dioxide gas or by the addition of elemental 'sulphur along with the cathodes as charged into the melting chamber.

We-claim: f'

1. The method of melting cathode copper which comprises heating the melting chamber of a fuel-fired muflie furnace to a temperature above the melting point of copper, maintaining a bath of substantially oxygen-free molten copper in said melting chamber, the surface ofsaid bath of molten copper being free of slag and of any other medium impeding the transfer of radiant heat thereto, maintaining in the melting chamberV above the molten copper therein a gaseous reducing atmosphere free of any constituent capable under the operating conditions prevailing within the chamber of deleteriously affecting the oxygen-free molten copper, introducing the cathvfired muilie furnace to a temperature above the melting point of copper, maintaining a bath of substantially oxygen-free molten copper in said melting chamber, the surface of said bath of` molten copper being free of slag and charcoal, maintaining in the melting chamber above the molten copper therein a gaseous reducing atmosphere free of any constituent capable under th'e operating conditions prevailing within the chamber of deleteriously affecting the oxygen-free molten copper, introducing the cathode copper to be melted into the melting chamber under conditions substantially inhibiting the introduction of air into the chamber and melting the copper so -introduced while maintaining the aforesaid slagand charcoal-free bath of substantially oxygen-free molten copper, and withdrawing substantially oxygen-free molten copper from the melting chamber.

' 3. The method of melting cathode copper which comprises heating the melting chamber of a fuelred muiile furnace to a temperature 'above the melting chamber, the surface of said bath of substantially oxygen-free molten copper in said meltingY chamber, the surface of said bath of molten copper being free of slag and charcoal, maintaining in the melting chamber above the molten copper therein a gaseous reducing atmosphere consisting principally of carbon monoxide and nitrogen, introducing the cathode' copper to be melted into the melting chamber under conditions substantially inhibiting the introduction` of air into the chamber and melting the copper so introduced while maintaining the aforesaid slagand charcoal-free bath of substantially` oxygen-free molten copper, and withdrawing substantially oxygen-free molten copper from the melting chamber.

4. The method of melting cathode copper which comprises heating a silica-lined melting chamber of a fuel-firedmule furnace to a temperature above the melting point of copper, maintaining a bath of substantially oxygen-free molten copper in said melting chamber, the surface of said bath of molten copper being freel of slag and charcoal, maintaining in the melting chamber above the moltencopper therein a gaseous reducing atmosphere consisting principally of carbon monoxide and nitrogen and free of any constituent capable under the operating conditions `prevailing within the chamber of deleteriously affecting the oxygen-free molten copper, introducing the cathode copper to be melted into the melting chamber under conditions substantially inhibiting the introduction of air into the chamber and melting the copper so introduced while maintaining thel aforesaid slagand charcoal-free molten bath of substantially oxygen-free copper, and withdrawing substantially oxygen-free molten copper from the melting chamber. Y

5. The method of melting cathode copper in a continuously operated fuel-nred munie furnace which comprises heating the melting chamber of the furnace to a'temperature above the melting point of copper, maintaining a bath of substantially oxygen-free molten Icopper in said melting chamber, the surface of said bath of molten copper being free of slag and charcoal, maintaining in the melting chamber above the molten copper therein a gaseous reducing atmosphere free of any constituent capable under the operating conditionsl prevailing within the chamber of deleteriously affecting the oxygen-free molten copper, introducing the cathode copper to be melted into the melting chamber under conditions substantially inhibiting the introduction of air into the chamber and melting the copper so introduced while maintaining the aforesaid slagand charcoal-free bath of substantially oxygen-free molten copper, withdrawing substantially oxygen-free molten copperfrom the melting chamber, and maintaining a substantially uniform volume of molten copper in the melting chamber by correlating the amount of cathode copper introduced into the chamber for melting with the amount of 'molten copper withdrawn from the chamber.

6. The method of melting cathode copper to produce cast `shapes of substantially oxygen-free copper which comprises heating the melting chamber of a fuel-fired mufe furnace to a temperature above the melting point of copper,

maintaining a bath of substantially oxygen-free molten copper in said melting chamber, the surface of said bath of molten copper being freel of slag and charcoal, maintaining in the melting chamber above the molten copper therein a gaseous reducing atmosphere free of any constituent capable under the operating conditions prevailing within the chamber of deleteriously affecting the oxygen-free molten copper, introducing the cathode copper to be melted into the melting chamber under conditions substantially inhibiting the introduction of air into the chamber and melting the copper so introduced while maintaining the aforesaid slag- 'and charcoalfree bath of substantially .oxygen-free molten copper, and withdrawing from the melting chamber and casting` substantially oxygen-free molten copper under conditions inhibiting the inclusion of oxygen in the resulting cast shapes.

PHILIP M. HULME. ROBERT A. GHELARDI.

CERTIFICATE oE CORRECTION. Patent Np. 2,265,28h. December 9, 191m.-

PHILIP M. EUIME. ET AL.

I Itis hereby certified that error appears in the printed specification` of the above numbered patent requiring correction as followsz' Page l, first column, line lll, strike out "the" first occurrence; pagej, second column line 68- 69, v for "emmissiv-ity"read--emissivity-e; page '5, first column, line 18, for "ozidized" read "oxidized-; l-ine )4.7, for "incomporate". read '--incorporat e; and second column, line'll, for "combination gases in a oil read --combustion gases in an oil; line )4.5, for reduced read --reduce--gv page 6, first column, lineA )4.1, claim 5, for the words "melting chamber, the surface of'said bath of" read --nelting point of copper, maintaining a bath of; and second column, line l5, claim 5, for "muffie" read muffle; and that thesaid Letters Patent should be read with this correction therein that `the same may conform tothe record of the case in the Patent Office.

Signed and sealed this 20th day of January, A. D. 19142.

. Y Henry Van Arsdale, (Seal) Acting Commissionerl of Patents.