US2054921A - Production of oxygen-free, gas-free metals - Google Patents

Description

Sept. 22, 1936. J. o. BETTE-RTON PRODUCTION OF OXYGEN-FREE, GAS-FREE METALS Filed June 10, 1933 2 Sheets-Sheet 1 INVENTOR 755's? a Bei'ierlam av/Wm W ATTORNEYS Sept. 22, 1936.

J. O. BETTERTO-N PRODUCTION OF OXYGENFREE, GAS-FREE METALS Filed June 10,

1955 2 Sheets-Sheet 2 BY v 7,49- ATTORNEY-S A74 Patented Sept. 22, 1936 UNITED STATES PATENT OFFICE PRODUCTION OF OXYGEN-FREE, GAS-FREE METALS Jesse 0. Betterton, Metuchen,.N. J., assignor to American smelting and Refining Company, New York, N; Y., a corporation of New Jersey Application June 10, 1933, Serial No. 675,149

Claims.

laboratory of the furnace.

Although these precautions are taken to prevent the absorption of any gas into the molten copper,

according to the invention, copper is subjected to a vacuum treatment which removes any small traces of harmful gases which may be left in the copper. The vacuum treated copper is then cast into the desired finished shapes in a chemically inert, non-absorbable atmosphere to prevent absorption of harmful gases during the casting and solidifying process.

According to a preferred form, the vacuum treater comprises a cylinder disposed within the furnace where it is kept at the proper temperature. This cylinder may have a comparatively small vacuum chamber at the top wheresmall amounts of copper are exposed to the vacuum at a. time. The flow of metal through the vacuum chamber may be substantially continuous however.

Although the invention has been described more particularly in connection with copper, it will be understood that it may be applied to other metals, such as aluminum, lead, tin, antimony, bismuth, etc. By the process of the invention, these metals or any alloys thereof may be freed of the gases usually contained in them so that the final castings may be free from porosity caused by occluded gases being released during the solidifying process.

This application is an improvement over my copending application Serial No. 655,208, filed February 4, 1933, Process and apparatus for melting and casting high purity copper.

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 novel features which are believed to be characteristic 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 following description taken in connection with the accompanying drawings forming a part thereof, in which (o1. zoo-s4) Fig. 1 represents diagrammatically a vertical section taken through a furnace of the vacuum treater and pouring apparatus according to the invention;

Fig. 2 is a partial plan view of Fig. 1; and Fig. 3 is a section on the line 3-3 of Fig. 1.

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, forming part of this specification, certain specific disclosure of the invention is made for purposes of explanation, but it will be understoodthat the details may be modified in various respects without departure from the broad aspect of the invention.

Referring now to the drawings, the apparatus shown to illustrate the invention will first be described. It will be understood that this apparatus is merely for purpose of illustration and that different types may be used without departing from the spirit of the invention.

The apparatus, as shown, comprises essentially a furnace l0 preferably of the surface combustion type, vacuum cylinder 40, casting box 80, a casting enclosure 86 and a mould 85. It will be understood that a plurality of vacuum cylinders may be used, if desired. In the drawings, a second vacuum cylinder 4| is shown which may have its own casting box and associated apparatus, as will appear more clearly hereinafter.

The furnace l0 comprises, in general, side walls 53, roof l5, end walls 18 and 20. It will be understood that this furnace is illustrated diagrammatically for simplicity, but, in practice, it will be constructed according to well known engineering principles relating -to metallurgical furnaces. This statement also applies to the other associated apparatus which is shown more or less diagrammatically for purposes of illustration.

, Extending across the furnace are a series of fire flue tubes 52 which are supported by the side walls 53. Each of these fiues 52 is provided with a burner 55. These burners may be of any common construction for burning oil, natural gas or manufactured gas.

The other ends of the fiues 52 communicate with the header 54 leading to a waste heat boiler (not shown) or other desired point. It will be understood that all of the heat producing combustion takes placewithin the fiues 52 and none This permits easy charging of the furnace and the curtain wall 25 provides a hydraulic seal to permit charging of the furnace without affecting atmospheric conditions within the laboratory of 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 I29. The purposes of these layers are explained in detail in my above mentioned copending application.

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 it is turned off when producing high purity copper, as explaned hereinafter;

For supplying a proper, chemically inert, nonabsorbable atmosphere within the laboratory of the furnace, pipe Ill is provided, preferably near the bath level. Pipe I10 is provided, preferably at the top of the furnace, for a gas outlet. During the time the auxiliary burner 30 is used, the gas outlet I10 provides an outlet for the gases of combustion.

For keeping the metal fiuid in the alcove I25 auxiliary heating may be provided. This may be in the form of a fire tube 3| having a fuel burner at one end and communicating with the header, if desired.

Instead of leading the molten metal directly from the bath to the pouring and casting apparatus, as in my above mentioned application, the molten copper may be led through a vacuum treating device. One or more vacuum treating devices 40, 4I may be used. These may take the form of upright cylinders. These cylinders are placed within the furnace, preferably along the end wall 20, where they can receive heat from the furnace. I

Since each cylinder 40 or 4|, and the subsequent casting apparatus used therewith, is identical in construction, it is only necessary to describe one set of apparatus in detail. Each cylinder is preferably made of graphite for copper and higher melting metals and alloys, and is made of iron or other suitable material for other metals and alloys.

The cylinder 40 is provided with a comparatively small treating chamber 42 in its upper end above the roof of the furnace. Connecting with this chamber is a restricted inlet passage 43 extending to the bottom of the bath 26 and a restricted outlet passage 44 extending to a point below the level of the bath 26 outside the furnace. If desired, the special tube 63 may connect with the cylinder 40 providing an extension of the passage 44 to lead the metal to the casting box 80.

The chamber 42 is connected by pipe 41 to a source of vacuum, for example, the commonly used steam jet type exhauster. As an example of the amount of vacuum, a vacuum equivalent to 24 inches of mercury may be used. In this case,

the cylinder will be made sufliciently long so that this vacuum will just raise the molten copper from the bath up into the vacuum chamber 42 allowing this to fill somewhat, say to line I42, and overflow downwardly through the outlet passage 44. The result is that the apparatus forms a siphon and copper will flow from the furnace to the casting box in proportion to the cross section of the passage and the difference in level between the surface of the bath and the discharge valve 60 at the exit of passage 44, provided the level in box 80 remains below valve 60.

For copper and copper alloys, the graphite cylinder may be from, say, 12 to 14 inches in diameter. In the case of molten copper, the length of passage 44 may be, for example, a little over 4 feet. The graphite cylinder can be most emciently made from furnace electrodes which have been glazed on the outer surface to decrease their porosity and the tendency to burn away. Accordingly, when a vacuum is placed in the metal reservoir, at the top of the cylinder there will be no influx of furnace gases or other gases through the walls of the graphite cylinder to destroy the vacuum in the chamber 42.

If desired, a suitable heating element, which may be electric, may surround the vacuum chamber 42 to keep this part at the proper temperature. The electric heater element is denoted by 46 and may be surrounded by a jacket 45 of heat insulating material. It is necessary to take care that this portion of the cylinder is not chilled sufiiciently to cause the copper to freeze.

Each cylinder 40 or 4| is provided with a casting box which receives the vacuum treated metal from the vacuum chamber 42. The casting box 80 is provided with a conical control valve which seats on the discharge end of the passage 44. This control valve 60 is operated by a handle 6I to control the flow of metal into the casting box 80. This conical valve may be made of graphite or other material which will stand up under the temperatures used. The casting box 80 is also provided with a silica glass window 62 for inspection purposes. Pipe I62 supplies box 80 with chemically inert, non-absorbable gas to protect the metal here.

For pouring the copper, an opening 8I is provided in the bottom of the casting box 8|]. This opening leads to an enclosure or hood 86 which is supported above the moulds which pass underneath on cars 84. The flow of copper through the opening BI is controlled by a conical valve plug 82 which is operated by a handle 83.

It will be understood that the moulds 85 pass in. close contact under the hood 86 which is supplied with chemically inert, non-absorbable gas by pipe 49. Pipes I0, I62, and 49 may, of course, be supplied by the same source of chemically inert, non-absorbable gas, passing through pipe I49; suitable"valves being provided for controlling each branch pipe separately.

The gas supplied by pipe 49 is used for blowing out the passage within the hood 86 and the mould space within the mould 85 so that the copper flowing from the casting box passes into this inert, non-absorbable atmosphere. In this way, any absorption of oxygen from the air is entirely prevented. The hinged door 81 is for the purpose of permitting the air which is displaced by the inert atmosphere from pipe 49 to escape.

It will be understood that the copper may be cast in finished shapes other than the billets indicated, as for instance, vertical cast wirebars.

If desired, the several different forms of pouring apparatus disclosed in my above mentioned application may also be used in place of the pouring apparatus disclosed here.

In order to facilitate the ready working of the furnace, it may be desirable at times to completely tap out the molten bath directly and, for this purpose, a suitable tap, indicated by 63, is provided.

In use, the copper cathodes or other pieces of metal will be slid down the inclined surface 23 through the hydraulic seal into the laboratory of I the furnace. After the copper has been melted and raised to the proper temperature and properly treated, the vacuum may be applied to the chamber 42 to start the vacuum treatment of the copper and subsequent casting thereof. The chemically inert,non-absorbable gases within the laboratory 22 of the furnace serves to displace all oxygen and. absorbable gases so that the molten copper will be as free as possible of occluded gases and other impurities. Carbon dioxide, carbon monoxide or nitrogen, or mixtures of these gases, for example, may be supplied bypipe 10 to provide the proper atmosphere within the laboratory of the furnace Hydrogen and hydrocarbons, as well as water Napor, are readily absorbed by the molten copper and these impurities are excluded by the blanket of inert, non-absorbable gas within the furnace.

When starting the operation of the vacuum treating cylinders, the valve 60 is first closed to permit the vacuum pump to create the required vacuum in the vacuum chamber 42. The amount of vacuum is so related to the weight of the metal and height of the vacuum chamber 42 above the surface of the bath to cause the metal to partially fill the vacuum chamber 42, this metal then overflowing into the outlet passage 44, whence it is controlled by valve 60.

Thus, itwill be seen that the vacuum treating cylinder is caused to operate in a manner similar to a siphon, and copper will flow from the furnace into the casting box, since the level of the discharge passage 44 at valve 60 is below the level of the metal in the furnace at all times. The flow of copper to the moulds is controlled by valve 82 and the flow of copper into the casting box 80 is controlled by valve 60 so as to get the proper amount of copper in the casting box.

There will be no considerable depth of metal in the casting box 80-only suflicient to properly take care of casting the final shape. In brief, the level of the metal in the casting box 80 will range all the way from a height equal to valve 60 down to a complete emptying of casting box 80 in order to properly cast the final shape. Therefore the important level in connection with the working of the siphon tap is the level of valve 60 and not the surface of the metal in casting box 80.

In normal Ioperation of the process it is not intended to lower the level of the metal in the laboratory of the furnace below the bottom of the curtain wall 25. If this were done, air from the outside would of ,course enter the laboratory of the furnace and result in oxidation of the metal. Therefore, in normal working the level of the metal in the laboratory of the furnace would range from the bottom of the curtain wall 25 to that shown in the drawings. It will be noted that the height of vacuum chamber 42 is greater than the distance from the bottom of the curtain wall to the level of the metal in the laboratory of the furnace. There has been cited for example a 3 vacuum of 24". Suppose a 24" vacuum was just sufficient to comfortably lead the copper from the furnace containing copper as shown in the drawings, up to vacuum chamber 42. It would, of course, then flow across vacuum chamber 42 and down channel 44. It is important that no great depth of copper be present in vacuum chamber 42 as otherwise the evacuation of the metal would not be thorough. In brief, the shallower the depth of metal in chamber 42, the greater the effective evacuation. Now, considering further, if in the normal operation of the furnace the level of the metal in the laboratory is lowered nearly to the bottom of the curtain wall 25, it would be necessary to correspondingly increase the 24" vacuum so as to just bring the metal over the bottom bridge in vacuum chamber 42 and in a thin layer so as to completely evacuate it. It will thus be seen that it is not expected to work on constant vacuum but to vary the vacuum in accordance with the level of the metal in the labora-- I tory of the furnace.

The drawings show passage 44 much longer than the difference in level between the metal in the laboratory of the furnace and vacuum chamber 42. This has been done purposely so that the furnace could be completely tapped out down to a level corresponding to the entrance to channel 43. This would be necessary or desirable if it is wished to put the furnace out of commission for any reason. Accordingly it is important that channel 44 must be sufficiently long to discharge molten copper to the atmosphere and offset a complete vacuum. In practice, the channel 43 is made of sufficient length so that it would req ire nearly a complete vacuum to remove the copper from the furnace down to a level corresponding to the entrance to channel 43. Inasmuch as the discharge from channel 44 is lower in any event than the level of the copper in the furnace, it will be evident that the siphon will flow and the copper will be discharged from the furnace. However, it will also be evident that, as the copper is emptied from the furnace, the amount of vacuum must be correspondingly increased up to a full vacuum in order to accomplish a complete emptying of the furnace.

The small portions of copper exposed to vacuum at any time causes a thorough removal of the absorbed gases, these absorbed gases being discharged to waste through the vacuum pump. The copper leaving the vacuum chamber 42 is a substantially gas-free metal. Furthermore, the use of a small vacuum chamber is advantageous in that it is comparatively easy to maintain the desired vacuum in a small space.

The vacuum treatment removes undesirable gases, such as hydrogen, oxygen, hydrocarbons, sulphur gases, etc., so that the resultant cast copper is of very high purity and is not porous.

It will thus be seen that the placing of the vacuum cylinders against the end wall of the furnace makes them an integral part of the furnace lining and they are anchored and held firmly in place at all times. Furthermore, during the operation of the furnace they are kept at the proper temperature to enable the process to be moved. With the present type of furnace, as disclosed in the above application, there would be very little gas to be removed because of the precautions taken to prevent the absorption of gas during the melting operation. Thus by taking utmost precautions to prevent the dissolving or absorption of gases into the molten copper during the melting process, and by removing whatever traces of gases have been dissolved or absorbed, and then taking care to prevent contamination during the pouring and casting operation, oxygen-free and gas-free cast copper of very great purity is obtained.

It will be understood that the invention may be applied to the melting and casting of other metals, such as aluminum, tin, lead, bismuth, antimony, etc. In the case of these metals, the length of the vacuum cylinders may have to be modified, depending upon the weight of the metal, but the manner of treatment and the advantages obtained are the same as with copper.

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: I

1. In apparatus for de-gasifying metal, a furnace for melting the metal, a vacuum apparatus extending a substantial distance into the furnace and directly heated by said furnace, and means for leading the molten metal through said vacuum apparatus.

2. In apparatus for de-gasifying metal, a furnace for melting the metal, a vacuum treating apparatus comprising an upright body in the discharge end of said furnace, said body projecting up through the roof of the furnace, said body having a vacuum chamber above said roof, a heating device for said vacuum chamber, said body having an inlet passage extending the length thereof from the bottom of said furnace to said vacuum chamber, said body having an outlet passage connecting said vacuum chamber to a point outside said furnace and below the bottom of the bath.

3. In apparatus for de-gasifying metal, a furnace for melting the metal, a vacuum treating apparatus comprising a graphite cylinder standing upright in the discharge end of said furnace, said cylinder being glazed on its exterior and projecting up through the roof of the furnace, said cylinder having a vacuum chamber above said roof, an electric heating element around said vacuum chamber, insulation around said electric heating element, said cylinder having a long restricted inlet passage extending the length thereof from the bottom of said furnace to said vacuum chamber, said cylinder having a long restricted outlet passage connecting said vacuum chamber to a point outside said furnace and below the. bottom of the bath,'and a valve for controlling the flow of metal in said outlet passage.

4. In apparatus for producing substantially gas-free, oxygen-free copper, a melting furnace comprising a laboratory, a separate combustion chamber, a hydraulically sealed feed opening,

means to supply a protecting atmosphere to the bath in said laboratory, a vacuum device comprising a member standing upright in the discharge end of said laboratory, said member having a vacuum chamber in its upper end, a reduced inlet passage extending from the bottom of said 5. In apparatus for producing substantially gas-free cast metal, a melting furnace comprising a laboratory, a separate combustion chamber, a hydraulically sealed feed opening, means to supply a protecting atmosphere to the bath in said laboratory, a vacuum device comprising a member standing upright in the discharge end of said laboratory, said member having a vacuum chamber in its upper end, an inlet passage extending from the bottom of said bath to said vacuum chamber, an outlet passage connecting said vacuum chamber and extending downwardly, a casting box connected to said outlet passage, a pouring enclosure connected to said pouring box, a conveyor movable under said enclosure, a. mould on said conveyor, means to supply nonabsorbable gas to said enclosure, and a source of vacuum connected to said vacuum chamber.

6. Metallurgical apparatus comprising a melting furnace of the mufiie type, a casting box, means for applying and maintaining a non-absorbable atmosphere 'in the laboratory of said furnace and in said casting box and a vacuum chamber communicating with said furnace and said box respectively via passageways in an upright member positioned within said furnace at its discharge end.

7. Metallurgical combination with a melting furnace for containing a bath of metal of predetermined depth, of a housing extending into the furnace to below the level of the metal bath therein, the said housing defining a chamber wherein metal from the furnace may be subjected to a vacuum for removal of gases, the chamber communicating through the housing with the metal bathof the furnace, a portion of the housing being heated directly by the furnace, supplemental heating means for the chamber, and means enabling the said chamber to be evacuated.

8. Metallurgical apparatus comprising the combination with a melting furnace for containing a bath of metal of predetermined depth, of a housing extending into the furnace to below the level of the metal bath therein and extending through the roof of the furnace to a point thereabove, the said housing defining a chamber above the roof of the furnace wherein metal from the furnace may be subjected to a vacuum for removal of gases, the chamber communicating through the housing with the metal bath of the furnace, the portion of the housing extending into the furnace being heated directly by the furnace, supplemental heating means for the chamber to maintain the temperature thereof above the melting point of the metal being treated, and means enabling the said chamber to be evacuated.

9. Metallurgical apparatus comprising the combination with a melting furnace, of a housing extending into the furnace defining a vacuum chamber wherein metal from the furnace may be subjected to a vacuum for removal of gases, casting mechanism for receiving metal apparatus ,comprising the from the furnace and comprising a closed casting box, a closed mold, and a closed passage connecting the casting box and mold, passages through the said housing connecting the chamber with the metal in the furnace and with the casting box, the passage to the furnace having its inlet at substantially the bottom of the metal in the furnace, and the passage to the casting box having its outlet below the level of the passage to the furnace, means enabling the said vacuum chamber to be evacuated whereby metal may be siphoned from the furnace through the chamber where the metal is substantially completely freed from gases and means for injecting into the casting mechanism and into the furnace,

gases non-absorbable by the metal being treated. 10. Metallurgical apparatus comprising the combination with a melting furnace for containing a bath of metal of predetermined depth, of a housing extending into the furnace to below the level of the metal bath therein, the said housing defining a chamber wherein metal from the furnace may be subjected to a vacuum for removal of gases, the chamber communicating through the housing with the metal bath orthe furnace, a portion of the housing being heated directly by the furnace, supplemental heating means for the chamber, and means enabling the said chamber to be evacuated.

. JESSE O. BE'I'IERTON.

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