US2256481A - Producing flat-set copper shapes - Google Patents

Description

Sept. 23, 1941. P. M. HULME ETAL PRODUCING FLAT-SET COPPER SHAPES Filed 001'.. 3C`), 1940.`

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Ro 63mg Sept. 23, 1941. P. M. HULME ET AL.

PRODUCING FLAT-SET COPPER SHAPES Filed Oct. 50, 1940 2 Sheets-Sheet 2 INVENTORS PHILIP M. HULME ROBERT A.

GHELARDI ATTO R N EY5 Patented Sept. 23, 1941 Pnonucmo FLAT-sor corro-n. sucres Philip M. Holme and Robert A. Ghelardi, Meituchen, N. J., assignors to International Smelting & Refining Company, a corporation of Montana Application (ictoher 30, 1940, Serial No. 363,5?18

`(Cl'. 'i5-76) 9' Claims.

This invention relates to the production of substantially flat-set cast copper shapes, and has for its object the provision of an improved meth-v od for producing such shapes. Y

Most of the copperbeing produced commercially at the present time is electrolytically refined. Such copper is very pure, lbut physically it is unsuited for rolling, drawing, or other fabricating operations for producing commercial articles. Accordingly, it is necessary to melt the cathode copper produced by electrolytic refining methods and cast it into wire bars, billets, cakes, or other shapes from which commercial articles may be made.

The common practice for melting and casting electrolytic cathode copper heretofore has followed the old Welsh process for fire-reining, and is in fact known as a reningf process. It involves first melting the copper in a fuel-fired furnace, skimming any slag formed, oxidizing the molten charge, skimming the oxidized impurities, 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 and contamina-tothe 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 and remains in the molten copper. The molten copper, therefore, is next covered with coke and subjected to a poling operation by plunging wooden poles below the surfacev of the molten metal. As a result of this operation, the cuprous oxide in the molten metal isV reduced and the metal is conditioned for cast- The progress of the pcling operation is carefully watched by taking frequent samples and casting them into blocks. Whether or not the poling operation has proceeded to a sufcient extent is determined by observing the nature of the set or pitch, that is, the condition of the exposed surface of these cast samples upon cooling. When the test samples show a proper set, poling is stopped and the molten copper is cast into suitable shapes.

The cast product solidifying in the mold with a substantially flat or slightly crowned surface, or set, is known as tough-pitch or flat-set copper. This copper invariably contains a small amount of oxygen (0.01 to 0.05%), as-the presence, of av small amount of oxygen is necessary to insure the flat-set desired for rolling and Cilv drawing operations.I The precisel mannerL in which the oxygen functionsto producefa' flat-set is not fullyv understood, but it is generally bee lieved that the' oxygen reacts with very' small amounts of impurities (partioularly sulphur) present even in cathode copper,` andl formsa gas which comes out of solution as-V the copper cools. |This gas expandsy and counteracts.f the tendency of metallic copper to shrink upon'freezing b-y forming minute-cavities in the castingin sufcient amount to preventt'he formation of` a shrinkage cavity or pipe If insufficientgasis evolved, the surface willbe depressed; or' ifthere istoo muc-h, the surfacewllfraise andrnay even be broken by a spew of metal forced throughthe frozen surface scum. The former is known as low-set copper'and the latter as crown-set copper, or over-poled copper wheremetal has been forced or spewed through the frozen5scum. Only the flat-set or slightly-crowned copper is properly called-tough-pitch copper, since by'long usage the term tough-pitch has come to` des-` ignate copper which uponl casting solidifiesy with this desirablel set.- Althoughy true4 toughepitch copper invariablyy containsabout 0.01 %Y to- 0.05% oxygen, the term tough-pitch may' not properly be applied to any copper containingthis amount of oxygen, for in some cases` (depending upon the amounts-of impuritiessuch as sulphur, in the copper) the presence otoxygen within these limits will not produce the fiat-set or slightly crowned setrequired for commercial purposes. Y

Because ofthe commercial importance of'producing true toughfpitch copper castings,vv the pol'a ing operation of the refining-,process must be very closely watched., andthe melting andcasting of copper by this process is truly an art requiring longy experience to master, vrather than a process subject to scientific control. Attempts have heretofore been made to simplify the process, but exceptfor improvements ofa mechanical nature for lightening the hand work involved, these attempts have been unsuccessfulandthe metallurgy of the process has remainedhk unchanged. 1 In addition to being difcult to` controlm properly, the refining process is subject to other disadvantages which heretofore have not been overcome. One of these disadvantages is thatv the process is inherently a batch operation. ach furnace charge must be heatedl andmelted,.oxi dized and poled before casting canA commence, and so the casting operation, during whi'chtime the furnace is actually producing a n'iarllzetable product, is limited to a small fraction of the time required for each cycle f operation. In the case of the usual twenty-four hour cycle, for example, casting proceeds for only about ve hours. Attempts heretofore made to make the melting and casting operation continuous have been unsuccessful.

A further disadvantage of the refining process is that it imposes severe treatment on the furnace employed. The alternate heating and cooling of the furnace refractories due to the repeated emptying of molten metal, charging with cold metal, and again melting, results in extensive heat losses and causes the furnace refractories to crack and spall. The average life of a furnace used in the refining process is only about ve to six months.

In recent years, certain processes for the production of oxygen-free copper of high electrical conductivity have been developed. Such oxygenfree copper possesses certain desirable properties for a number of uses, and in view of the success that has been attained in its production, it might appear that the production of tough-pitch copper is ldoomed to obsolescence. Actually, however, this is not the case, for tough-pitch copper possesses some advantages over even oxygen-free copper. Moreover, the production of oxygen-free copper by the processes now available is expensive, and the demand for the consequently relatively expensive oxygen-free product is limited.

By far the greater amount of copper now being sold is the less expensive tough-pitch copper, and it is likely that it will continue to be the most common form of copper sold for many years to come. f

The present invention provides an improved method for producing tough-pitch or flat-set cast copper shapes in a manner that overcomes the disadvantages of the heretofore customary refining process. In accordance with the invention, substantially oxygen-free copper (e. g. cathode copper) to be melted is introduced into the melting chamber of a fuel-fired mule furnace and therein is heated and melted largely by radiant heat. In this manner the copper during melting is kept out of contact with combustion gases, and so is not contaminated thereby during melting. A gaseous non-oxidizing (and preferably reducductivity. A bath of substantially oxygen-free molten copper is established and 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,` such as slag, charcoal and the like covers the surface of the molten metal. The copper to be melted is introduced into the melting chamber under conditions substantially inhibiting the introduction of air into the chamber, and fuel is introduced and burned `in the combustion chamber above the arch in a ing) atmosphere is maintained in the melting manner to heat the arch and establish and maintain at its under surface a temperature at least equal to the melting point of copper, and preferably several hundred degrees thereabove. The copper in the melting chamber is melted largely by heat radiated thereto from the arch, while maintaining the aforesaid slag-free bath of substantially oxygen-free molten copper.

It has been found that the surface of the copper in the melting chamber should be maintained substantially free of reactive fused slag. The presence of such slag interferes with the transfer of radiant heat to the metal charge, and may attack the refractory lining of the melting chamber unless expensive refractories resistant to such attack are employed. It may be advantageous, however, to maintain on the surface of the copper in the melting chamber a layer of finely divided refractory material having a relatively high emissivity and of good heat conductivity, such as finely divided or granular silicon carbide. Such a layer may improve the transfer of radiant heat to the furnace charge.

The copper to be melted advantageously is charged continuously into the furnace and molten copper is withdrawn continuously therefrom for casting. The copper may be withdrawn through an open launder, with a layer of charcoal being maintained over, but not completely covering, the surface of the copper flowing through the launder. The amount of charcoal so employed is controlled so as to control the area of copper exposed to the air in a manner to permit incorporation in the copper of a proper amount of oxygen to produce a fiat-set upon casting and cooling.

The oxygen-bearing product flowing from the launder is cast in any desired manner into suitable shapes.

The invention will be better understood from the following description, considered in connection with the accompanying drawings, in which Fig. 1 is a longitudinal cross section through a furnace suitable for use in carrying out the invention; and

Fig. 2 is a horizontal cross section taken substantially along the line 2 2, of Fig. 1.

The furnace shown in the drawings comprises side walls I0 and II and en-d walls I 2 and I3 of refractory brickwork. The furnace is provided with a refractory iioor I4 adapted to support a body of molten copper, and an arched masonry roof I5 of refractory brick. The furnace is braced by vertical buckstays I6 and I'I connected by horizontal tie-rods I8 and I9 above and below the furnace. To conserve heat and enable development of adequately high temperatures (which the brickwork must be sufficiently refractory to withstand), the roof of the furnace is covered with a layer of insulation material 20 and the walls are insulated by layers of insulating brick 2l and 22.

The interior of the furnace is divided into a mufle or melting chamber 23 and a combustion chamber 24 by means of a melting chamber arch 25 sprung between the side walls of the furnace. The arch 25 is relatively thin and of highly refractory material possessing good heat-conducting properties. The most satisfactory refractory material for the arch is silicon carbide (e. g, that known commercially as Carborundum), which is mechanically strong, highly refractory, and

g possessed of fairly good properties as a heat conductor. The arch should be as thin as it is practical to make it in order that there will be a gesamt maximum heat transfer therethrough. Silicon' carbide is sufficiently strong mechanically toenable construction of a thin arch, of the order of a few inches in thickness, about six feet or sov wide.

The arch is sprung between refractory blocks 25 extending the length of the furnace; Advantageously these refractory blocksv also are of silicon carbide. K

Gil burners 2l extend into the interior of the combustion chamber Z'through one end'wall i2 of the furnace. A iiue 2S' at thel opposite end of the furnace is provided for the Withdrawalof combustion gasesI from the combustion chamber.

One or more charge openings 2i) are provided in the side Walls of the furnace for introducing copper to bem-eltedinto the meltingfchamber-2-3; The charge opening 29 slopes downwardly toward the melting chamber. Copper cathodes are passed to the charge opening througha` charging lock iclosed by two doors Sil hinged attheir upper ends. The oor of the charging lock 3S slopesin conformity with the charge opening so that' cathodes may be slid easily into the melting chamber. hibits the introduction of air into the melting chamber and thus aids in maintaining the con templated non-oxidizing atmosphere in the melting chamber. A vent stack 32 may be provided at the outer end of the` charging lock for the Withdrawal of gases leaking from the furnace through the lock.

Gas inlet conduits 33 extending through thev side walls of the furnace are provided for introducing gas into the melting chamber 23 for the purpose of maintaining therein an atmosphere of the desired composition.

A tap hole 3'!! is provided in the end wall l2 of the furnace for withdrawing molten copper therefrom. The tap hole may be partially or wholly plugged with clay, and the clay may be gradually broken down for intermittent tapping, or the tap hole may be left open for the continuous run-out of metal in continuous operations. The tap hole opens into a launder 35 for conducting molten copper to a tilting pouring ladle or furnace or other suitable casting equipment not shown).

A curtain wall 3S may be provided in the furnace adjacent the tap hole 313. A single opening El through the curtain wall is disposed adjacent the bottom thereof below the normal level of molten copper in the furnace. A normal depth of molten copper in the furnace forms a liquid seal of the opening through the curtain wall, without preventing out-now of the copper. In combination with the curtain wall, this liquid sealeectively excludes air entering through the tap hole from passing into the melting chamber behind the curtain wall. per in the furnace between the tap hole and the curtain wall may be covered with charcoal, if necessary, to protect it from the air.

In practicing the invention, copper to be melted is introduced through the charging lock 3S and the charge opening 29 into the melting chamber underneath the inciting chamber arch 25. Fuel oil is admitted through the burner 21 and burned inthe combustion chamber 24 above the arch 25 in a manner to heat the arch and establish and maintain at its under surface a temperature at least equal to the melting point of copper. The melting chamber is heated largely by radiant heat from the arch 25, and to a lesser extent by heat conducted through the side and end walls:

Qf-'thefurnace' Pure copper melts at a temper- The charging lock 3B substantially in- The small body of copetere of: about' 19eo and accordingly therein;

perature `maintained"at the under-surfacefof the archl must at leastl equal-thisv value in'y order' to meltcop'per largely by radiationfof heat to it from the'. arch. For practic-alfpurposes, however, itis desirable to heat the molten? copper to' a temperatureV of' about 2050 Ff in'l order to secure satisfactory casting results, andJ inorder to achieve an adequate melting ratezinlthe furnace for economic. commercialop'erations; itis desirable to maintain! ar` t'enfipenfature-v considerably higher even than' this figure 'at the under surface of the arch.. Accordingly'atemperature of-about 25G0 F. preferably ismaintained at. the under surface of the arch.4

Since the-copper int` the melting chamber 23ris melted largely by heatra'diated to itfrom thev un der surface-'of the archyit is important` to establish and vmaintain?conditions favoring `the translferoffradiantheat' to the-copper.- Oneisuch conidition is the emissivity ofv the material at ,the surfaceofthecharge. In a sense'thisemissivity is a measurei of=thefability ofl the charge to absorb the heatv radiated: to it. The emissivity: of molten copper isadequately highto lenable meltingto proceed at a reasonable ratewhen thetemperature `at the under surface of the arch is maintai-ned-sufciently high (at'about 2506" FJ.

Fused slags generally possesshigher emissivitiesithan molten coppen-but they are poor conn ductors of heat. If` present onthe surface ofl the molten copper, they impede rather than. aid in the-transfer of heat to-vthezcopper. Since reactive fused slags yare not required inthe melting chamber to remove iimpuritiesfrom the'copper, theirpresenceis undesirable,.and in the preferred practicebfthe invention care Visiexercised Vto maintain the surface of the` moltenv copper substantially free of such slags.`

Reactive fused slags also have been found' objectionable for the reason thatfthey4 are apt to attack the refractory lining of theside walls of the melting chamber. MoltenA copperA which-is substantially. free of oxygen or oxides4 exerts practically no effect upon commonandinexpensive silica refractories, so that suchrefractories may be employedl in constructing the melting chamber side Walls. Many. fused reactiveslags, however, quickly attack silica refractori'easo that the presence of slag in the meltingchamber, while accomplishing no usefulV purpose, necessitates the use of'expensve refractorie's resistant to such attack, or results in serious damagev to the furnace linings.

It has heretofore been proposed to deoxidize molten copper by maintainingv a layer ofl charcoal on the surface thereof'. Such Va layer of charcoal would perform no' useful purpose in the 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 surfaceof the molten copper is apt to be attended by the further dis- 'advantagev of coating the under-side of the arch 25'with a nlm of finely divided charcoal which may objectionably decrease the heat. conductivity'of the arch.

While the surface of the molten copper in the melting chamber is-'free of slag and of anyy other medium impeding the transfer of radiant heat thereto, floating' patches of'unfused orr partially fused refractory material may gather on the surface of the molten copper. Where the melting chamber is lined` with. silica brick, -theseffloating patchescon's'st mainlyv of'silica and appear to be due to mechanical erosion of the lining by the molten copper.y This 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 off the surface of the molten copper from time to time, in order to insure efficient transfer of radiant heat to the surface of the molten copper as well as effective direct exposure of the surface of the molten copper to the gaseous reducing atmosphere.

The copper in the melting chamber is kept out of contact with the combustion gases of the fuel by means of the melting chamber arch 25, and so is not contaminated from this source. A bath of substantially oxygen-free molten copper is established and maintained in the melting chamber, and a non-oxidizing, and preferably reducing, atmosphere is maintained above the surface of the molten copper. A satisfactory reducing atmosphere is one of charcoal producer gas consisting predominantly of carbon monoxide and nitrogen, say about 25% carbon monoxide and about 75% nitrogen. Under favorable operating conditions, nitrogen alone may be employed, but it is relatively expensive, and the reducing quality of carbon monoxide is usually advantageous, and may be necessary, to establish and maintain the desired bath of substantially oxygen-free molten copper.

The non-oxidizing (or reducing) atmosphere above the molten copper should be free of any constituent capable under the operating conditions prevailing within the `melting chamber of deleteriously affecting the oxygen-free molten copper. The presence of hydrogen 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 amount (of the order of a few per cent) of water vapor in the gases admitted to the melting chamber is objectionable, for at the temperature prevailing in the chamber, water vapor decomposes into hydrogen and oxygen (particularly in the presence of carbon monoxide) and the resulting hydrogen may affect the set of the copper during casting.

The melting chamber atmosphere should be reasonably free of carbon dioxide, since carbon dioxide 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 carbon monoxide may not be detrimental, since in the presence of the carbon monoxide the formation of cuprous oxide is for most practical purposes suiciently retarded.

The presence of decomposable hydrocarbons in the melting chamberatmosphere is undesirable, since such hydrocarbons are cracked at the prevailing temperature and carbon is deposited on the surface of the metal or on the under surface of the arch or on both. Such deposits of carbon, Whether'on the surface of the metal or on the undersurface of the arch, materially lower the melting rate of the furnace. The illuminants present in coal gas or in enriched producer gas orwater gas such as is available in most cities are examples of decomposable hydrocarbons which behave in this fashion.

It is also desirable to avoid the presence of sulphur in the melting chamber atmosphere. Some sulphur (usually in the form of copper sulphate or sulphuric acid occluded in the cathode) is unmeager avoidably introduced into the melting chamber with the charge. The small amount of sulphur so introduced is not objectionable, for it cooperates with the oxygen incorporated in the copper as it is withdrawn from the melting chamber to produce the desired set of tough-pitch copper. The copper charged to the melting chamber usually contains as much sulphur -as it is desirable to have, however, and so it is best to avoid the presence of sulphur or sulphur compounds in the melting chamber atmosphere.

, The gas providing the non-oxidizing or reducing atmosphere in the melting chamber is admitted thereto through the inlet conduits 33, and preferably is maintained in the melting chamber under a slight positive pressure of the order of IAO@ of an inch of water to prevent air or combustion gases from leaking into the melting chamber.

Since the copper melted in the melting chamber is not 'allowed to come in contact with contaminants, it is substantially as pure as the metal charged. The process is particularly adapted for melting electrolytic copper cathodes, and when this material is used as the charge, the molten copper in the melting chamber is substantially oxygen-free. This substantially oxygen-free copper is withdrawn through the furnace tap hole 34 and the launder 35 to the casting equipment.

The copper owing through the launder is covered with a layer of charcoal to prevent it from becoming oxidized to an undesirable 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 to incorporate therein 'a proper amount of oxygen to produce a flat-set upon casting and cooling. A number of variable factors, such as the temperature of the metal flowing through the launder, the rate of flow of metal therethrough, and the presence of air currents in the Vicinity of the launder influence the amount of oxygen 'absorbed by the copper as it flows through the launder. variable factors, such as the amount of sulphur present in the copper, affect 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 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 may be added to the launder, or if the set indicates a deficiency of oxygen, some of the charcoal may be raked from the surface of the copper in the launder. It has been found that in general about 0.01% to 0.05%( oxygen by weight of the copper 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 common refining process, the amount of oxygen incorporated in the molten copper is very much easier to control in the new process than is the poling operation of the rening process.

The copper flowing from the launder 35 may be introduced into any suitable casting equipment for casting into molds. Ordinarily a small reservoir in the nature of a tilting furnace or ladle is interposed between the launder and the mold. Almost any of the pieces of equipment Other Y acca-ce1 commonly in use forfthis purpose maybe employedr For example,l the copper fromV the launder-'mayibe introduced into a tilting electric furnace` from'` which it may be poured into the molds, oritlmayY be introduced into a pouring ladle suitably heated, for example, byA anoil fiame; It has-been found that contact of the copper with combustion gases in an oil' heated ladle is not objectionable, apparently-because `the copper remains in the ladle for so shortr a period of time that it does not become contaminated thereby.

AlthoughV the method of the invention-may be operatedlintermittently as a batch process, it is suited'- to continuous operation and is' most economically practiced when carried out continuously. Thecopper oathodes` to be melted maybe charged continuously into the furnace, andi melted copper may be' continuously Withdrawnth'ereirom at substantially the same rate as the cathodes are charged.

The hooks of the initial starting sheets` of copper cathodes are preferably out oif before charging the oathodes into the melting chamber. Undesirable amounts of oxidizedcopper, copper sulphate, etc., are frequently associated with these --hooks and'it'is'hence betternot to attempt to melt them in--practicing the present invention. Whatever slight amount of oxidized copper that be introduced into the bath of molten copper during charging and melting of' cathodes and the like is readily reduced by the gaseous reducingatmosphere, so that the bath of molten.

copper in the meltingl chamber is for all practical' :ur-poses substantially oxygen-free. In addition to copper cathodes, other forms of equally pure'substantially oxygen-free copper may'constitute allor-part of the copper charged into the melting chamber. Where insufficient sulphur is naturally present inthe copper to be melted, a controlled amount oi sulphur may be incorporated iny the'molten copper in' the melting chamber; asV for example, by the controlled. introduction' of sulphur dioxide' gas or by the addition` of elemental sulphur along with the copper asA charged intoV the melting chamber.

Asideirom the usually minute amount of oxidized'copper present on the surface of copper cathodes; the method of" the invention removes noimpurities.fromv the copper. But the method or the` invention. does effectively reduce Whatever kamount of oxidized copper is ordinarily associatedwith the copper cathode. The surface of the' molten copper is exposed to the direct in.- iiuenceofthe gaseous reducing atmosphere and anyouprous oxide in the moltencopper is thereby reduced; Such cuprousoxide tends naturally to migrate to the surface of the molten copper, and this tendency is promoted by the agitation of the molten copper asthe cathodes drop into it. When conducted as a continuous operation, the method of the invention permits of marked fuel economy, higher output cf cast copper shapes and greatly increased furnace life than in the heretofore customary melting and refining proc- The invention eliminates the former operns of oxidizing and poling the molten copper their attendant diiculties, particularly in `,ontrolling the quality oi the copper produced. The only variable control that need be exercised in practicing the invention is the incorporation of oxygen in the molten copper withdrawn from the melting chamber, and this control is not diiiicult to maintain.

The method of the invention imposes no severe to nd treatmenton the furnace refractories. The sub'- stantiall-y oxygen-free molten copper does lnot aifect they refractory lining of the meltingchamber, and no slagispresent to-attack'the-linirlg.V

Thefurnace is not repeatedly heated and cooled; as heretofore customaryfin meltingl copper cathodes, and-the furnace refractories areV hence not subject to thermal shock, and the extensive heat losses inherent in the prior'art intermittentv operationare eliminated. The lireof furnaces used in carrying out the invention is thereforemeas.- ured'inyears insteadof'months; as inthe case offurnacesused in the heretofore customary ree' ning process. Y Y

This application is a continuation-in-part of our. pending and allowed application Serial-No. 30`467 filed November 16, 1939.-

`We claim:

l. The method of producing substantiallyatset cast copper lshapes `which comprises introduce ing substantially oxygen-freel copper,y into the.

melting chamber of a fuel-fired mufllefurnace,r

heating and melting the copper therein largely., by means of radiant heat while maintainingl a.

non-oxidizing atmosphere vwithin thexmelting. chamber; withdrawing substantially oxygen-free moltenl copper from the meltingV chamber. and.

exposing itto an oxidizing atmosphere su.-

ciently to incorporate therein a proper amountY of oxygen` to produce a flat-set upon castingand.' cooling, and castingtlie resulting oxygen-bear ingmolten copper.` into a'suitable shape..

2. The method ofproducing substantially` flat set cast copper shapes whichcomprises heating the melting chamber. of 'a fuel-redmuiefur.- nace to a temperature above the melting pointofcopper, maintaining a bath ofsubstantially oxygen-freel molten copper in said melting cham-- ber, the surface ofv said bath of molten copperbeing free of slag, maintaining. intheA melting chamber above. the molten copper. therein. a gaseous-'reducing atmosphere, introducing the sub--v stantially oxygen-free copper to be melted intoY the melting chamber under` conditions substan-A tially inhibiting the introduction of air intothe. chamber `and melting the copper so introduced-l while maintaining theY aforesaid slag-free bathofsubstaritially oxygen-free molten copper, with drawing substantially oxygen-free molten copper from the melting chamber. and exposing it to an oxidizing atmosphere suficiently to incorporate thereina proper amount of oxygen to produce a at-'setupon castingand cooling, andcasting the resulting oxygen-bearing molten copper vrinto a.

suitable shape..

3.'. The method of producing substantiallyhat?.r set cast copper shapes which comprises intro-V ducing copper cathodes into the melting chamber of a fuel-ii'red` muffle furnace, heating-rand melting the copper therein largely by means ofheat radiated tothe exposed' surface of the copper, maintaining the surface of the copper in the melting chamber substantially free of reactive fused slag, maintaining a non-oxidizing atmosphere within the melting chamber, withdrawing y substantially oxygen-free molten copper from the melting chamber and exposing it to an oxidizing atmosphere sufficiently to incorporate therein a proper amount of oxygen to produce a flat-set upon casting and cooling, and casting the resulting oxygen-bearing molten copper into a suitable shape,

4. The method of producing substantially flatset cast copper shapes which comprises introducing substantially oxygen-free copper into the melting chamber of a fuel-fired muiile furnace, heating and melting the copper therein largely by means of heat radiated` to the exposed surface of the copper, maintaining a layer of finely divided refractory material having a relatively high emissivity and good heat conductivity over the surface of the molten copper in the melting chamber while at the same time maintaining the surface of the molten copper free of any medium impeding the transfer of radiant heat thereto, maintaining a non-oxidizing atmosphere within the melting chamber, withdrawing substantially oxygen-free molten copper from the melting chamber and exposing it to an oxidizing atmosphere sufficiently to incorporate therein a proper amount of oxygen to produce a fiat-set upon casting and cooling, and casting the resulting oxygen-bearing molten copper into a suitable shape.

5. The method of continuously producing substantially nat-set cast copper shapes which comprises continuously introducing substantially oxygen-free copper into the melting chamber of a fuel-red muiile furnace, heating and melting the copper therein largely by means of radiant heat while maintaining a non-oxidizing atmosphere within the melting chamber, continuously withdrawing substantially oxygen-free molten copper from the melting chamber and exposing it to an oxidizing atmosphere suiciently to incorporate therein a proper amount of oxygen to produce a flat-set upon casting and cooling, and continuously casting the resulting oxygen-bearing molten copper into a suitable shape.

6. The method of producing substantially atset cast copper shapes which comprises introducng substantially oxygen-free copper into the melting chamber of a fuel-lired muie furnace, heating Iand melting the copper therein largely by means of radiant heat while maintaining a non-oxidizing atmosphere within the melting chamber, withdrawing substantially oxygen-free molten copper from the melting chamber through an open launder, maintaining the surface of the copper in the launder partially but incompletely covered with charcoal, controlling the area of copper in the launder exposed to the air in a manner to permit incorporation in the copper of Va proper amount of oxygen to produce a fiat-set upon casting and cooling, and casting the resulting oxygen-bearing molten copper into a suitable shape.

7. The method of producing substantially flatset cast copper shapes which comprises introducing substantially oxygen-free copper into a melting chamber of a furnace below a melting chamber arch, introducing and burning fuel in a combustion chamber above said arch in a manner to heat the arch and establish and maintain at its under surface a temperature of about 2500 F., whereby copper in the melting chamber is melted largely by heat radiated thereto from the arch, withdrawing substantially oxygen-free molten copper from the melting chamber and exposing it to an oxidizing atmosphere sufficiently to incorporate therein a proper amount of oxygen to produce a flat-set upon casting and cooling, and casting the resulting oxygen-bearing molten copper into a suitable shape.

8. The method of producing substantially flatset cast copper shapes which comprises introducing substantially oxygen-free copper into the melting chamber of a furnace below a melting chamber arch, maintaining a non-oxidizing atmosphere substantially free of hydrogen and decomposable hydrocarbons in the melting chamber, introducing and burning fuel in a combustion chamber above the arch in a manner to heat the arch and establish and maintain at its under surface a temperature at least equal to the melting point of copper whereby copper in the melting chamber is melted largely by heat radiated thereto from the arch, withdrawing substantially oxygen-free molten copper from the melting chamber and exposing it to an oxidizing atmosphere sufficiently to incorporate therein a proper amount of oxygen to produce a Hat-set upon casting and cooling, and casting the resulting oxygen-bearing molten copper into a suitable shape.

9. The method of continuously producing sub. stantially flat-set cast copper shapes which comprises continuously introducing substantially oxygen-free copper into a melting chamber of a furnace below a melting chamber arch, continuously introducing and burning fuel in a combustion chamber above said arch in a manner to heat the -arch and to establish and maintain at its under surface a temperature substantially `above the melting point of copper, whereby copper in the melting chamber is heated and melted largely by heat radiated thereto from the arch, maintaining a non-oxidizing atmosphere substantially free of hydrogen and decomposable hydrocarbons and consisting predominantly of carbon monoxide and nitrogen in the melting chamber, maintaining the surface of the copper in the melting chamber substantially free of reactive fused slag, continuously withdrawing substantially oxygen-free molten copper from the furnace through an open launder, maintaining the surface of the copper in the launder partially `but incompletely covered with charcoal, controlling the area of copper in the launder exposed to the air in a manner to lpermit incorporation in the copper of an amount of oxygen from 0.01% to 0.05% sufficient to produce a flatset upon casting and cooling, and casting the resulting oxygeinbearing molten copper into a suitable shape.

PHILIP M. HULME. ROBERT A. GHELARDI.

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