US2065207A - Process for melting and casting high purity metal - Google Patents

Description

Dec. 22, 1936. J. o. BETTERTON I 2,065,207 I PROCESS FOR MELTING AND CASTING HIGH PURITY METAL Filed Feb. 4, 1933 4 Sheets-Sheet 1 INVENTOR Jsse 0 .Bei'ienora.

ATTORNEYS I D 1936- J. o. BETTERTON 2,065,207

PROCESS FOR MELTING AND CASTING HIGH PURITY METAL Filed Feb. 4, 1933 4 Sheets-Sheet 2 INVENTOR Jssa 0. Be iieriolz ATTO R N EY-S Dec. 22, 1936. TERTO 2,065,207

PROCESS FOR-MELTING AND CASTING HIGH PURITY METAL Filed Feb. 4, 1933 4 Sheets-Sheet 3 Y, sq,

ATTORNEYS Dec; 22, 1936. J O -mu 2,065,207

PROCESS FOR MELTING AND CASTING HIGH PURITY METAL Filed Feb. 4, 1935 4 Sheets-Sheet 4 'INVENTOR Jsse 0. Zea Z0804. BY

ATTORNEYS Patented Dec. 22, 1936 PATENT OFFICE PROCESS FOR MELTING AND CASTING HIGH PURITY METAL Jesse Oatman Betterton, Metuchen, N. J., as-

signor to American Smelting and Refining Company, New York, N. Y., a corporation of New Jersey Application February 4, 1933, Serial No. 655,208

' 5 Claims.

The invention relates to the melting and casting of metals, and more particularly to the melting of pure copper cathodes and casting the molten metal into refined copper shapes.

According to one embodiment of the invention, cathodes of high purity copper may be melted in a surface combustion type furnace in which a chemically inert, non-absorbable atmosphere is maintained within the laboratory of the furnace. The molten copper may then be poured and cast into the refined copper shapes while maintained under a chemically inert, non-absorbable atmosphere.

The copper cathodes or other metal may be fed frequently to the furnace as by sliding down an inclined chute. The furnace may be provided with a charging alcove and a hydraulic seal to permit charging of the furnace without affecting the chemically inert, non-absorbable atmosphere in the furnace.

The furnace may be tapped and the molten metal poured into a ladle, which in turn may feed moulds for refined copper shapes which may be arranged on a casting wheel. A plurality of hoods may be provided over the spout, ladle and moulds while the latter are in casting position to insure a chemically inert, non-absorbable atmosphere over the molten metal until the same has solidified.

The furnace is preferably of the muffle type where the heat producing gases are not permitted to come in contact with the molten metal. The combustion may take place in special fiues of refractory material passing through the laboratory of the furnace or may take place in a separate combustion chamber arranged above the laboratory of the furnace.

The invention further consists in new and novel features of construction and operation hereinafter described and more particularly set forth in the claims.

Although the 'LOVEI features which are believed to be characteristics of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the folowing description taken in connection with the accompanying drawings forming a part thereof, in which Fig. 1 represents diagrammatically an apparatus for carrying out the invention;

Fig. 2 is a cross section through the furnace;

Fig. 3 is a. diagrammatic side elevation illustrating the pouring hoods;

and end walls I8 and 20.

Fig. .4 diagrammatically illustrates the relation of furnace and casting wheel;

Fig. 5 illustrates diagrammatically a modified form of furnace;

Fig. 6 is a section through the furnace of Fig. 5;

Fig. 7' illustrates another modified form of furnace, and a modified pouring arrangement; and

Fig. 8 is a section taken through Fig. 7.

In the following description and in the claims, various details will be identified by specific names for convenience, but they are intended to be as generic in their application as the art will permit.

Like reference characters denote like parts in the several figures of the drawings.

In the drawings accompanying and formin part of this specification, certain specific disclosure of the invention is made for purposes of explanation, but it will be understood that the details may be modified in various respects without departure from the broad aspect of the invention.

- Referring now to the drawings, and more particularly to Figs. 1-4, the apparatus for carrying out the invention comprises essentially a mufiie furnace III, a ladle, ll, casting wheel l2 having a series of multiple moulds l3.

The furnace comprises side walls l4, arch 15 It will be understood that this furnace is illustrated diagrammatically for simplicity, but in practice it will be constructed according to well known principles relating to metallurgical furnaces.

The side .walls are provided with linings [6 over which are fire flues H, which' are of suitable fire resisting material, such as silicon carbide or any other similar or suitable refractory. These flues project through the end walls and are provided at the discharge end of the furnace with burners Is, one for each flue. These burners may be of any common construction for burning oil or city gas.

The other ends of the fiues ll communicate with a flue leading to waste heat boiler 2| for recovering the heat left in the gases of combustion. It will be understood that all the combustion producing the heat takes place within the flues l1 and none of the gases of combustion arein contact with the laboratory 22 of the furnace.

For charging the furnace, an inclined wall 23 is provided having the same lining 24 as the bottom of the furnace. For forming a charging alcove I25 a curtain Wall 25 is provided having an opening below the level of the bath 26. The solid metal to be melted, such as acopper cathode 21,

alcove I25 into the laboratory of the furnace. This permits easy charging of the furnace. The curtain wall 25 provides a hydraulic seal to permit charging of the furnace without affecting atmospheric conditions in the furnace.

Floating on the bath 26 within the laboratory 22 of the furnace is a thin layer of cover slag 28 which may be in molten condition. Floating on the charge in the alcove I25 may be a protecting layer 29. The purposes of these layers will be explained hereinafter more in detail.

If desired, an auxiliary burner 30 may be provided in the laboratory of the'furnace for assisting in initially warming up the furnace. This burner may be fired the same as the burners described above, but it will be understood that this burner is turned off when producing the high purity copper, as explained hereinafter. The auxiliary burner 30 saves time, fuel and stress on the fines or tubes. It reduces the temperature gradient across the silicon carbide tile during the warming up period.

For supplying a proper, chemically inert, non-- absorbable atmosphere within the laboratory of the furnace, pipe 10 is provided, preferably near Pipe no is provided, preferably fire tubes above described and having a fuel burner 33 at one end and communicating with the waste heat boiler 2| at the other end.

For casting the metal in moulds, the furnace T ,is provided with the usual tapping spout 34.

This spout leads the molten metal into ladle Ii of arms 31 between which the open face multiple wire bar moulds l3 are pivoted at 39. It will be understood that the mould space may be of any desired shape for casting any desired billet or refined shape, but for purposes of illustration, mould spaces for wire bars are shown. It will be understood that the separate mould spaces are not connected and they are of the proper size and shape' for casting wire bars.

.In order to maintain the molten metal in a chemically inert non-absorbable atmosphere during the entire casting operation until it becomes solid, a series of hoods are provided. Covering the spout 34 is a ,hood 4|]. Qovering the ladle II is hood 4| and covering the mould l3, when at the pouring position, is hood 42. Additional hoods 43 and 44 are provided to keep the moulds covered as the wheel rotates until the molten metal has solidified. The above hoods form a continuous chain which keeps the metal in a protecting atmosphere while in the molten state.

To hold the hot protecting gases in proper contact with the molten metal, each hood is separate and the hoods 42, 43 and 44 are sub-divided into compartments 45. The several compartis slid down the inclined wall 23 through the merits 65 are fed by manifolds 46 and 41 and these manifolds and the hoods 40 and 4| are fed by piping 49 which may be connected both to pump ldl and pipe 50. Pipe 50 may be connected to a special source of chemically inert, non-absorbable gas. Pump I41 isconnected to the fiue 48 leading from the waste heat boiler 2 i. It will be noted that suitable valves are provided for using the desired gas and for supplying the gas to the desired points.

It will be noted that the piping illustrated is so arranged that the laboratory of the furnace and the protecting hoods may be supplied with either flue gas from pump I41 orgas from pipe 50. These gases will be discussed more fully below.

For controlling the flow through tap spout 34, arrangement is made for inserting a suitable tool through hoods Q0 and 4|. Hood 4| is provided with a swinging plate 5|, closing an opening to permit the insertion of this tool. It will be understood that hood 40 is cut away at its lower edge topermit the passage of this tool. It will be further understood that the flow of molten copper through spout34 may be controlled at will, but that frequent control during the pouring operation is not necessary. The ladle |l operates as an auxiliary reservoir for receiving the molten metal during the intervals when the flow to'the moulds is interrupted when passing from one mould to the other.

Referring now to Figs. 5 and 6, in this modified form, the furnace is provided with a series of fire tubes 52 of suitable refractory material extending between the side walls 53. These tubes are provided with burners 55, one for each tube, for burning a fiuid fuel, such as oil or gas. These burners may be of any desired construction.

The other ends of the fire tubes 52 communicate with a fiue 54 which extends to the waste heat boiler 2| in a manner similar to the construction in Figs. 1-4. The pouring arrangement to be used with this form'may also be similar to that described in connection with Figs.

A laboratory atmosphere supply pipe 10, an auxiliary burner 30, a gas outlet pipe I10, fire tube 3| for heating charging alcove I25, may be provided in this form, similar in construction and in purpose to the corresponding elements in Figs. 1-4.

Referring now to Figs. 7 and 8, in this modified form, a secondary arch 56 is provided having radiating flanges 63 and dividing the laboratory 51 of the furnace from the combustion chamber 58. The discharge wall of the furnace is providedwith a burner 59 for supplying the necessary heat and fiue 6|! connects the discharge end of the combustion chamber with the waste heat boiler 2|.

An auxiliary burner (not shown) may, if desired, be provided in the laboratory 51 for assisting in bringing the furnace to operating temperature similar to the auxiliary burners 30 in igs. 1-6. I

In this form, a charging alcove 6| is provided having an inclined bottom wall down which the It is obvious that the furnace in this form may a v by the 34 and pouring and be provided with a spout casting arrangements similar-to those described above.

If desired, however, the pouring and casting arrangement shown in Figs. 7 and 8 may be provided for casting vertical billets, wire bars or cakes. It will be understood that this pouring and casting arrangement may also be used with the furnaces in Figs. 1-6 instead of the pouring and casting arrangements shown in these figures.

In the form shown in Fig. '7, the furnace laboratory is provided with an extension 80, the lower wall of which is provided with a pouring opening 8|. A plunger 82 operated by handle 83, opens and closes the pouring opening 8|.

Under the furnace extension 80 is shown a trackway for cars 84 carrying the moulds 85. These moulds are vertical moulds for any desired finished shapes such as wire bars. A hood or closure 86 is positioned under the extension 80 and supplied with protecting atmosphere by pipe 49 for maintaining the metal in a chemically inert, non-absorbable atmosphere during the pouring and casting operations. I

The operation of the apparatus and the method according to the invention will be explained with particular reference to Figs. 1-4. It is thought that the use of the forms shown in Figs. 5-8 will be obvious from this description.

In use, the copper cathodes or other pieces of metal to be melted will be slid down the inclined surface 23 through the hydraulic seal into the laboratory of the furnace. After the copper has been melted and raised to the proper temperature, the furnace may be tapped and the molten copper poured into the ladle H. The casting wheel i2 will be started and, as each mould I3 is brought to. casting position, the ladle II will be tipped about its trunnions 35 to fill the individual mould spaces with copper from the separate spouts 36. After each mould is filled, the ladle II will be tipped back to its non-pouring position and the wheel l2 moved to bring the next mould into pouring position when the ladle ll will be tipped again to fill this mould.

As the wheel I2 rotates, the moulds are kept 'under the hoods 63 and 44 while'the metal is cooling and the events are so designed that time themoulds move out from under the last hood M, the metal has sufiiciently solidifled to prevent any appreciable oxidation. After the wire bars are cooled sufflciently, the moulds are tipped about their pivots 39 to discharge the castings therefrom and then they are turned back to be in condition for receiving further charges of molten metal.

It will be understood that the inclined slide 23 will be of sufficient slope to project the metal through the alcove into the laboratory of the furnace with considerable force. The protecting layer 29 on the surface cove prevents contamination by exposure inthe atmosphere.

The complete separation of the combustion space and the laboratory of the furnace prevents any contamination of the metal from the fuel used. Experiments have shown that heat may be transferred very satisfactorily to the underlying surface or bath in radiant form from the tubes or.

secondary arch.

It will be understood that the waste heat apparatus may comprise not only a waste heat boiler as shown, but, if desired, recuperators, regenerators, driers, etc. By the proper selection of fuel, for example, by selecting a low sulphur entire heat transfer is of the metal in the alfuel, as is customary in casting refined copper shapes, and operating the combustion slightly reducing and, if desired, by sufficiently cooling the combustion gases to eflect condensation and separation of water vapor, combustion gases supplied by the blower M'I may be used as a source of protecting gas both for the furnace laboratory and for the casting hoods.

In case it is not desirable to use the combustion gases, special chemically inert, non-absorbable gases may be supplied to the pipe 50. For example, waste power plant gases, if slightly reducing and sufficiently free of reacting or absorbable sulphur compounds may be used. Also carbon dioxide gas manufactured by the combustion with air of carbonaceous materials, such as specially selected coke, as is done in the Carter white lead process, may be used.

The cover slag on the metal in the laboratory of the furnace may be very thin because of the quiet atmosphere prevailing in the furnace. The by radiation and there is no blast of hot combustion gases in contact I with the bath. It is not necessary to use a thick cover slag as used in some practices in the prior art since it is neither needed nor desired.

The thin cover slag assists materially in transmission of heat directly to the bath. Surface films, interfacial contacts,'etc., exert practically no resistance to heat transfer by radiation.

The function of the cover slag over the bath in the laboratory of the furnace is to complete ly seal the molten copper and to prevent chemical reaction with the gaseous atmosphere, such as oxidation by free oxygen or water vapor or contamination by sulphur and also absorption of reducing gases, such as hydrogen and sulphur compounds. For this purpose, a thin layer of fluid slag gives desired results. Calcium fluoride, sodium fluoride, sodium aluminum fluorate, borax, complex silicates of sodium. and copper, the silicate glasses with and without copper in composition, any of these or their mixtures give a wide choice for selection as the material for the slag.

The second function of the slag cover is to remove impurities from the copper, particularly sulphur and arsenic. Commercial sodium carbonate or sodium hydroxide may be used either alone or added in proper amounts to the protecting slag above mentioned. The latter practice will result in a slag performing a double function and with a minimum amount of reagent for producing the necessary amount of slag.

For the protecting coating in the alcove, charcoal or other carbonaceous material may be used. Preferably, however, a thin layer of fluid slag of the same or similar composition to that used in the laboratory of the furnace may be used.

In passing combustion gases directly over a bath of molten copper, it is well known that the copper becomes contaminated with sulphur from the fuel. This is due probably to the absorption of sulphur dioxide, hydrogen sulphide or other sulphur compounds contained in the combustion gases with or without chemical reaciii:

will be readily absorbed by the molten copper. Carbon monoxide, if present, may also be absorbed in considerable quantities. Nitrogen and carbon dioxide are absorbed in very small quantities, if at all.

The purpose of keeping the atmosphere in the furnace laboratory entirely separate from the combustion .of the fuel is to prevent contamination of the molten copper by the above gases. Even water vapor is detrimental in the atmosphere of the furnace laboratory. It is, therefore, first necessary to exclude all gases from the laboratory oi the furnace during the melting of the copper by using the controlled gaseous atmosphere supplied by pipe 10 to sweep the laboratory clean of these gases which are preferably forced out of the laboratory through gas outlet lid.

The controlled gaseous atmosphere may be supplied by either fan Ml from the waste heat gases or by pipe 56 depending on conditions. The gaseous atmosphere should consist essentially of carbon dioxide and nitrogen and free, ,or nearly free, of water. vapor, sulphur gases, reducing gases, particularly hydrogen, and large amounts of carbon monoxide. Secondly, it is necessary to keep the surface of the molten bath sealed with a thin layer of fiuid slag against the absorption or chemical reaction with any gases which may be present in the controlled atmosphere.

It will be understood that sumcient pressure on all displacing gases will be provided to prevent ingress of atmospheric air, either into the furnace or into the hoods. In this manner there will be a slight loss of the displacing gas outwardly and because of such loss the gas must be continually replenished.

When melting cathodes of copper, it may be advisable to wash the slabs thoroughly to prevent any adherent electrolyte or contaminating salts or substances. These cathodes may be washed in .a bath of sodium hydroxide or sodium carbonate for the purpose of combining an alkaline base with the sulphate radical present either as copper sulphate or sulphuric acid.

Thus a very high purity copper or other metal may be provided. Furthermore, the process maybe continuous in that the cathodes may be eontinually and uniformly fed to the furnace and .simultaneously'molten, refined copper cast either into wire bars or other desired shapes. The metal level in the furnace would thus be maintained at a given height at all times, insuring a proper hydraulic seal.

While certain novel features of the invention have been disclosed and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes may be made by those skilled in the art without departing from the spirit of the invention.

What is claimed is:

1. The method of melting copper cathodes and casting them into refined copper shapes which comprises charging the cathodes into a melting furnace through an alcove having a hydraulic 5 seal, maintaining a layer of carbonaceous-maing a substantially non-absorbable gas to the laboratory of the furnace, tapping said furnace into a ladle, pouring molten copper'from said ladle into moulds for the refined copper shape and maintaining a non-absorbable atmosphere over said ladle and over said moulds while the metal in said moulds is molten.

2. The method of meltingmetal and casting it to moulds which comprises charging the metal into a melting furnace through a hydraulic seal, melting the metal byradiant heat in a quiescent atmosphere, keeping the surface of the bath covered with a layer of protecting material, applying a protecting gas to the laboratory of the furnace, tapping said furnace into a ladle, pouring molten metal from said ladle into moulds and maintaining a protecting atmosphere which comprises charging the cathodes into a melting furnace through an alcove, providing a hydraulic seal.,m aintaining a protecting layer on the surface of the metal in the alcove, melting the metal by radiant heat in a quiescent atmosphere. keeping the surface of the bath covered with a layer of slag to remove arsenic and sulphur, applying a substantially non-absorbable gas to the laboratory of the furnace, tapping said furnace into a ladle, pouring molten copper from said ladle into moulds for refined copper shapes and maintaining a non-absorbable atmosphere over said ladle and over said moulds while the metal in said moulds is molten.

4. The method of melting and casting copper which comprises displacing the air from a melting furnace by a gaseous atmosphere which is substantially non-absorbable by molten copper, charging copper into the melting furnace while preventing admission of air thereto, melting the copper by radiant heat in the presence of a quiet atmosphere, maintaining the surface of the bath covered with a layer of protecting slag, pouring the. molten copper into moulds for refined copper while maintaining the said moulds in an atmosphere which is substantially non-absorbable by the copper, and maintaining the said substantially non-absorbable atmosphere over thenon-absorbable by molten copper, charging cop-v per into the melting furnace while preventing admission of air thereto, melting the copper by radiant heat in the presence of a quiet atmosphere while maintaining the surface of thebath covered with a layer of protecting slag, and excluding air from the furnace while a bath of molten copper. is being maintained therein.

JESSE OATMAN BETI'ERTON.

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