US2837790A - Process for degassing ferrous metals - Google Patents

Description

June 10, 1958 w. ROZIAN 2,337,790 PROCESS FOR DEGASSING FERROUS METALS 7 Filed Dec. 28, less :wyawmw III A TTORNEYS United States Patent 2,837,790 PROCESS FOR DEGASSING FERROUS METALS Irving W. Rozian, Detroit, Mich., assignor to Ford Motor Company, Dearborn, Mich, a corporation of Delaware Application December 28, 1953, Serial No. 460,681

6 Claims. (Cl. 22--57.2)

This invention deals with ferrous metallurgy and more particularly with an improvement upon the well known process of continuously casting ferrous metals. There has been much work done in the-past decade upon processes for continuously casting molten steel into bar form which may be rolled directly into finished shapes without the necessity of going through the usual procedure of casting an ingot, reheating the ingot and rolling the heated ingot into bars.

Steel produced by this process has shown excellent physical properties and is adaptable for most uses. How ever, continuously cast steel bars cannot be used for'purposes requiring a fine surface finish due to the presence of seed shaped cavities just under the cast surface. The origin of these cavities is obscure but it is believed that they are caused by the release of gas from the metal during solidification. The instant invention has been evolved to avoid this difliculty and also to produce a thoroughly deoxidized and desulphurized product having superior properties due to the almost quantitative absence of oxygen and sulphur as well as the more inert constituents such as nitrogen and hydrogen in the finished,

product.

This invention is probably understood best by reference to the drawings in which:

Figure 1 is a vertical section through one form of the apparatus of this invention,

Figure 2 is a portion of another form of this invention, and

Figure 3 is still another section of another phase of this invention.

Turning to Figure 1, a stream of molten metal 10 is seen flowing from container 11 into the degassing apparatus which is generally indicated 12. This degassing apparatus is lined throughout with a refractory 13 and is heated as required by conductors 14 which heat the metal passing through the degassing apparatus either by an induction effect or by ordinary resistance heating, de-

pending upon the requirements of the specific instance. It is, of course, to be understood that if the metal is to be heated inductively, conductors 14 will take the form of tubing through which cooling water may be circulated as is conventional in high frequency induction heating. Metal 10 falling from container 11 is caught in tapered receptacle 15 which terminates at its lower end in nozzle 16 which is provided with a restricted throat 17. Throat 17, opens into vacuum degassing chamber 18 which, in common with the rest of the apparatus, is provided with a refractory lining 13. The vacuum de gassing chamber 18 is evacuated through conduit 19 connected to any vacuum producing apparatus, not shown. The lower portion of vacuum degassing chamber 18 connects with conduit 20, the purpose of which will be 'described.

The metal 10 which falls from container 11 collects in tapered receptacle 15 and from there flows through nozzle 16 into vacuum degassing chamber 18. The metal passing through nozzle throat 17 is shattered and broken into a very large number of droplets which fall freely under the influence of gravity to the bottom of vacuum degassing chamber 18. During their free fall through vacuum chamber 18, which is maintained under a pressure from a few microns up to twenty millimeters of mercury, the metal is practically free of pressure except that exerted by surface tension. During this period the metal is effectively degassed of such materials as nitrogen and hydrogen and the reaction between the iron oxide and carbon to produce carbon monoxide and iron is caused to occur with the simultaneous elimination of carbon and oxygen. The chemical analysis of the final product may advantageously be altered by the addition to the metal prior to its entrance into degassing chamber 18 of material which is capable of reacting with the charge to produce volatile reaction products, or reaction products which can be tolerated in the final product or reaction products capable of gravity separation in chamber 18. For example carbon may be added to the metal in tapered receptacle 15 so that the elimination of carbon by reaction with the iron oxide content of the melt in chamber 18 will leave the desired carbon residue. Conversely metallic compounds such as oxides may be added to alloy the product or add to the yield. Typical oxides are iron oxide and nickel oxide.

For further rectification of the metal, gaseous purifying substances may be introduced through conduit 20 and exhausted through conduit 19 with the products of reaction. These rectifying metals may well be any of the volatile highly reactive metals such as magnesium, barium, strontium, calcium, lithium, sodium or potassium. These metals, due to the high heat of formation of their sulfides and oxides even at steel pouring temperatures, result in a product extremely low in sulphur and oxygen. By virtue of their low specific gravity, the reaction products produced within chamber 18 will float on the reguline metal and a separation thereby effected.

The droplets of molten metal falling freely through vacuum degassing chamber 18 are again collected as a mass of reguline metal in the tapered bottom portion of this chamber which terminates in barometric leg 21. This barometric leg must, of course, be lined with refractory and in most instances must be provided with heating means to compensate for loss of temperature of the metal, at least upon starting. Barometric leg 21 must be sufficiently long to enable the ferrostatic head developed therein to equal the existing barometric pressure plus the frictional loss through the system. For starting purposes, the apparatus is provided with a bott 22 arranged to close off the bottom of barometric leg 21 and to be moved into position by lever system 23. From the bottom of barometric leg 21 the metal enters the top of continuous casting apparatus generally indicated by 24.

This continuous casting apparatus 24 comprises a mold 25 connected to barometric leg 21 by bellows 26. Bellows 26 are protected from the thermal action of the molten metal by telescoping radiation shields 27. Pipes.

28 and 29 are provided for the entry and exit of a purging gas such as argon or helium which serve to protect the degasified metal from contamination prior to solidification in mold 25. The pressure within bellows 26 will probably be substantially atmospheric although this is not necessary and it may be varied either above or below atmospheric as required. In any event, the length of barometric leg 21 must be adjusted with the pressure in bellows 26 in mind. The diameter of the conduit provided for the flow of metal through barometric leg 21 must be chosen in relationship to the amount of metal per unit time to pass through so that the downward velocity of the metal exceeds the velocity at which a bubble of the gas within bellows 26 could rise through the metal being handled.

Mold may be any. of the molds described in the patent literature as suitable for continuously forming molten iron or steel into a bar. It is not considered necessary to detail mold 25 since the patent and current literature are very rich in such descriptions.

Figure 2 represents a variation of Figure 1 in which the starting bott 22 and the argon purge apparatus is deleted and the metal passes directly from bell mouthed end of barometric leg 21 into continuous casting mold 25. This results in a decided simplification of the apparatus described in Figure 1 and in some cases may result in economies.

Similarly, Figure 3 presents a variation of Figures l and 2. Here again occurs the bell mouthed portion 38 of barometric leg 21 which is similar to that shown in Figure 2 except it is turned through a 90 degree angle. This turn eliminates the necessity for the excessively high structures usually associated with continuous casting apparatus and permits the solidifying metal to be fed directly into the rolling machinery. In each case the solidifying metal within continuous casting apparatus 25 has been depicted in the conical shape usually assumed.

This method and apparatus has been described as primarily intended for use with ordinary carbon steel; however, it is by no means so limited and may be applied to any material which it is desired to degas and purify. Such materials may well be cast iron or alloy steels. In the case of cast -iron, the purifying material may also serve as a nodularizing agent and enable the direct production of nodular iron without further addition agents.

I claim as my invention:

1. A process for degassing ferrous metals comprising establishing a body of molten ferrous metal, flowing the molten metal through a restricted nozzle into an evacuated chamber whereby it is shattered into discrete droplets, permitting these discrete droplets to descend under the influence of gravity through the evacuated chamber, coalescing the discrete droplets into reguline metal in the lower portion of the evacuated chamber, withdrawing molten metal from the evacuated chamber through a barometric leg and discharging the barometric leg into a continuous casting mold, said molten metal being protected from gaseous contamination after it leaves the barometric leg.

2. A process for degassing ferrous metals comprising establishing a body of molten ferrous metal, adding a carbonaceous material to the molten body, flowing the molten metal through a restricted nozzle into an evacuated chamber whereby it is shattered into discrete droplets, permitting these discrete droplets to descend under the influence of gravity through the evacuated chamber, coalescing the discrete droplets into reguline metal in the lower portion of the evacuated chamber, withdrawing molten metal from the evacuated chamber through a barometric leg and discharging the barometric leg into a continuous casting mold, said molten metal being protected from gaseous contamination after it leaves the barometric leg.

3. A process for degassing ferrous metals comprising establishing a body of molten ferrous metal, adding a material to the molten body capable of reacting therewith to produce a volatile product, flowing the molten 4 metal through a restricted nozzle into an evacuated chamber whereby it is shattered into discrete droplets, permitting these'discrete droplets to descend under the influence of gravity through the evacuated chamber, coalescing the discrete droplets into reguline metal in the lower portion of the evacuated chamber, withdrawing molten metal from the evacuated chamber through a barometric leg and discharging the barometric leg into a continuous casting mold, said molten metal being prot d from gaseous contamination after it leaves the barometric leg.

4. A process for degassing ferrous metals comprising establishing a body of molten ferrous metal, flowing the molten metal through a restricted nozzle into an evacuated chamber whereby it is shattered into discrete drop lets, permitting these discrete droplets to descend under the influence of gravity through the evacuated chamber, flowing vapors of a volatile reactive metal past said droplets, coalescing the discrete droplets into reguline metal in the lower portion of the evacuated chamber, withdrawing molten metal from the evacuated chamber through a barometric leg and discharging the barometric leg into a continuous casting mold, said molten metal being protected from gaseous contamination after it leaves the barometric leg.

5. A continuous casting machine comprising a receptacle for molten metal, an enlarged chamber connected to said receptacle via a restricted nozzle, a barometric leg communicating with the enlarged chamber and a continuous casting mold below and communicating with the end of the barometric leg remote from the enlarged chamber.

6. A process for degassing ferrous metals comprising establishing a body of molten ferrous metal, flowing the molten metal through a'restricted nozzle into an evacuated chamber whereby it is shattered into discrete droplets, permitting these discrete droplets to descend under the influence of gravity through the evacuated cham ber, flowing a gaseous purifying substance past said droplets, coalescing the discrete droplets into reguline metal 'in the lower portion of the evacuated chamber, withdrawing molten metal from the evacuated chamber through a barometric leg and discharging the barometric leg into a continuous casting mold, said molten metal being protected from gaseous contamination after it leaves the barometric leg.

References Cited in the file of this patent UNITED STATES PATENTS 211,953 Barnum Feb. 4, 1879 448,945 Durfee et a1 Mar. 24, 1891 1,568,854 Larner Jan. 5, 1926 1,590,730 Evans June 29, 1926 1,633,992 Madden June 28, 1927 2,253,421 De Mare Aug. 19, 1941 2,303,139 Roemer Nov. 24, 1942 2,587,793 Waldron Mar. 4, 1952 2,590,311 Hatter et al. Mar. 25, 1952 2,625,472 Scheuer Jan. 13, 1953 2,709,842 Findley June 7, 1955 2,734,240 0 Southern Feb. 14, 1956 FOREIGN PATENTS 891,444 Germany Sept. 28, 1953

Claims (2)

1. A PROCESS FOR DEGASSING FERROUS METALS COMPRISING ESTABLISHING A BODY OF MOLTEN FERROUS METAL, FLOWING MOLTEN METAL THROUGH A RESTRICTED NOZZLE INTO AN EVACUATED CHAMBER WHEREBY IT IS SHATTERED INTO DISCRETE DROPLETS, PERMITTING THESE DISCRETE DROPLETS TO DESCEND UNDER THE INFLUENCE OF GRAVITY THROUGH THE EVACUTTED CHAMBER, COALESCING THE DISCRETE DROPLETS INTO REGULINE METAL IN THE LOWER PORTION OF THE EVACUTATED CHAMBER, WITHDRAWING MOLTEN METAL FROM THE EVACUATED CHAMBER THROUGH A BAROMETRIC LEG AND DISCHARGING THE BAROMETRIC LEG INTO A CONTINUOUS CASTING MOLD, SAID MOLTEN METAL BEING PROTECTED FROM GASEOUS CONTAMINATION AFTER IT LEAVES THE BAROMETRIC LEG.

5. A CONTINUOUS CASTING MACHINE COMPRISING A RECEPTACLE FOR MOLTEN METAL, AN ENLARGED CHAMBER CONNECTED TO SAID RECEPTACLE VIA A RESTRICTED NOZZLE, A BAROMETRIC LEG COMMUNICATING WITH THE ENLARGED CHAMBER AND A CONTINUOUS CASTING MOLD BELOW AND COMMUNICATING WITH THE END OF THE BAROMETRIC LEG REMOTE FROM THE ENLARGED CHAMBER.

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