US 3154404 A
Description (OCR text may contain errors)
Oct. 27, 1964 A. LORENZ 3,154,404
METHOD FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Original Filed Nov. 24, 1958 2 Sheets-Sheet 1 ELECTRICAL POWER SOURCE DIFFERENTIAL AND ACTUATOR A MOTORS MECHANICAL FIG. I
Oct. 27, 1964 A. LORENZ 3,154,404
METHOD FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Original Filed Nov. 24, 1958 2 Sheets-Sheet 2 FIG. 2
United States Patent f 3,154,494- METHUD FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Albert Lorenz, Hanan am Main, Germany, assignor to W. (3. Heraeus G.m.b.H., Hanan am Main, Germany Original application Nov. 24, 1958, er. No. 775,791, new Patent No. 3,61%,275, dated .Fan. 30, 1962. Divided and this application Jan. it), i961, Ser. No. 81338 Claims priority, appiication Germany Nov. 26, 1957 ll Claim. (Cl. 75-16) The present invention relates to a method and apparatus for heating metals, and especially steel, for the purpose of extracting the gases therefrom. This application is a division of application Serial No. 775,791, filed November 24, 1958, now United States Letters Patent No. 3,019,275.
Prior to this invention the gases occluded in molten metals, especially steel, were extracted therefrom by passthe metals in a continuous flow through an evacuated chamber. Numerous efforts were then made to improve such gas extraction by further heating the metals while the extraction process was being carried out. This was done by providing arc-heating or resistance heating means within the closed evacuated chamber or by making a part of such chamber in the form of a crucible and surrounding such part with an induction coil. However, these prior methods either do not operate safely and reliably or only very inefficiently since they do not heat up the entire mass of the metal flowing through the evacuated chamber, but only a small part thereof, that is, either only the surface of the metal or only a negligible amount in comparison to the volume of the flow.
It is an object of the present invention to provide a new and surprisingly simple method of heating up the flow of molten metal within the evacuated chamber for the purpose of increasing the efficiency of the gas extraction considerably over the methods hitherto employed.
A further object of the invention consists in the provision of a new apparatus for heating up the flow of molten metal while passing through the evacuated extraction chamber by inducing electric currents within such flow of molten metal in a new and highly improved manner.
Instead of merely heating up a small portion of the flow of molten metal within the evacuated extraction chamber, the present invention provides for a thorough heating of the entire volume of the flow of metal. For this purpose, the present invention utilizes a gas extracting apparatus of the type in which the molten metal is withdrawn from a container holding the metal along one path, then passed through an evacuated extraction chamber, and finally returned to the container along a I second path which is spaced from the first path. Ac-
cording to the invention, electric heating currents are then produced by induction within the entire amount of molten metal of such circulation. This is attained by the provision of a transformer, the secondary circuit of which is formed by the flow of molten metal and the closed core of which passes between the two mentioned paths of the flow of metal and carries a primary induction coil which is energized by an alternating current of a standard frequency. As soon as the molten metal flows over from the first or intake path into the second or return path, the secondary circuit of the transformer will be closed and it thereby reacts upon the current flowing through the primary coil. The beginning of this reaction may be utilized for indicating the beginning of the continuous gas-extraction process, and the strength of this reaction upon the primary current produced by a stronger or weaker flow of molten metal may also be 3,154,404 Patented Oct. 27, 1964 utilized for effecting and controlling the gas-extraction process.
These and further objects, features, and advantages of the present invention will become more apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawings, in which FIGURE 1 shows diagrammatically and partly in section one preferred embodiment of the present invention; while FIGURE 2 shows a cross section taken along line A-A of FIGURE 1.
Referring to the drawings, the container or ladle 1 holds the molten metal 2 from which the gases occluded therein are to be expelled by means of the gas-extraction apparatus 3 which is partly immersed from above into the metal bath. This apparatus consists of an extraction chamber 5 which is continuously evacuated through a pipe 4 leading to a pump and control valve unit 4'. Chamber 5 has a pair of pipes 6 and '7 extending vertically downward therefrom and into the bath of molten metal 2 at a considerable distance from each other. By injecting a gas through a pipe 3 into inlet pipe 6, a continuous flow of metal will be started and maintained, rising from the bath in ladle it through pipe 6 into chamber 5, and then flowing through this chamber toward the return pipe 7 and through the latter back into the bath in ladle 1. The gas bubbles then rising in pipe 6 will take along the metal and convey it upwardly into the actual extraction chamber 5. The gas supply may be regulated by a suitable valve mechanism 8'. A suitable hopper 9 or the like containing alloying constituents is also connected to chamber 5 for supplying these materials to the flow of metal passing through the chamber. Hopper 9 is likewise adapted to be sealed hermetically toward the outside, and it is provided with suitable means, as diagrammatically indicated at 10 in FIGURE 1, for controlling the supply of these alloying constituents into chamber 5.
The gas extracting apparatus as such is enclosed by a metallic covering 11 which is adapted to take up the outside pressure acting upon the apparatus, and it is provided at the inside with a lining of refractory material. Covering 11 also extends around the intake and return pipes 6 and 7 to a point closely above the surface of the bath of molten metal 2 in ladle ll. Thus, the pipe portions extend ing into the bath of metal only consist of refractory material and are carried by the metal covering 11.
interposed between the inlet and return pipes 6 and 7 is a practicaliy ciosed iron transformer core 12 which also carries a primary coil 13 which is supplied with an alternating current of a standard line frequency. B means of this transformer core 12 a very strong alternating current will be induced in the molten metal fiowing from the bath 2 in ladle 1 through inlet pipe 6, chamber 5, and return pipe 7 back into bath 2. The path of the current in the metal bath 2 is indicated in FIGURE 1 by the dotted line 14. Since the cross-sectional area of the bath itself is very large, the resistance incurred by the current passing therethrough is very small. As the metal covering 11 of the apparatus does not extend entirely to the surface of the metal bath 2, there is no danger of a short circuit of the induced current due to such covering. Within the extraction cham ber 5, however, the molten metal flows from inlet pipe 6 to return pipe 7, and during such passage it strongly sprays and spatters. The cross-sectional area of the molten metal which is present at this passage at all times is therefore relatively small, with the result that the electric resistance and the heating effect produced within the metal in the chamber itself is very high.
The heat is therefore generated primarily within the upper part of the heated path 2-65-72 of the molten metal. This, however, is the place where only a small amount of the molten metal is separated from the great mass of the bath 2 and where it is therefore to be expected more than at any other place that the molten metal will cool off or may even solidify. On the other hand, this is also the point where relatively cold alloying constituents may be added from the hopper 9 by its feed control device 10. It is therefore necessary that the heat required for melting or dissolving these additions will also be supplied at this point.
The most important requirement for carrying out the method according to the invention is the fact that the molten metal passing through the apparatus always has to form a closed electric circuit. Obviously the circulation of the molten metal by means of an added gas as previously described may also be attained by difierent means, for example, by centrifugal conveying means of the type described in the inventors previous United States Letters Patent No. 2,893,860, or the like.
The method according to the present invention has, however, certain other very important advantages. As already stated, the uninterrupted circulation of the molten metal forms the secondary circuit of a transformer. This secondary circuit is closed after the apparatus has been evacuated and the conveying gas has been introduced through pipe 8 and at the very moment when the molten metal flows over from pipe 6 to pipe 7. After the electric current has been switched on to operate the transformer 12, 13, this moment may be easily determined by an ammeter 15. This serves as a clear indication of the fact that the continuous gas extraction process has been started. The ammeter will also indicate any interferences in the normal operation of the apparatus, for example, an interruption in the continuous flow of metal, and the like.
The strength of the alternating line current which may be about 100 kw. or more may, however, to a certain extent also furnish an indication of the volume of the flow of metal through vacuum chamber 5. The amperage indicated by ammeter may therefore indicate the volume and velocity of the flow and it may also be used for controlling the flow, for example, by an adjustment of the position and elevation of the gas extracting apparatus relative to the bath of molten metal 2 vertical positioning device indicated generally at 16, by an adjustment of the amount of conveying gas supplied through pipe 8, or by an adjustment of the output of the evacul ating pump and control unit 4' which is connected to pipe 4, or by similar means. Such adjustments may also be produced automatically by suitable means known in the art which operate in response to the indication of ammeter 15 and the changes in the strength of the primary current.
Fromthe above description, it will be clearly apparent that the new method of expelling the gases occluded in a molten metal, and particularly in steel, is very simple and highly efficient, and requires only a very simple and relatively inexpensive apparatus.
Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no Way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claim.
Having thus fully disclosed my invention, what I claim In the method of treating molten metal by circulating the molten metal from a container zone having a large cross-sectional area in an amount of lesser cross-sectional area via a first path to a molten metal treating zone, said molten metal entering said treating zone and passing therethrough while strongly spraying and spattering, thence through said treating zone and thereafter via a second path spaced from said first path back to said container zone, the improvement which comprises passing primary electric current through a primary transformer circuit situated adjacent the circulating molten metal to induce secondary electric current to flow through said circulating molten metal along the entire circulating course of such molten metal which acts as secondary transformer circuit, whereby to cause the heating of said circulating molten metal by the electrical resistance heat generated during the passage of induced electric current therethrough.
References Cited in the file of this patent UNITED STATES PATENTS 428,552 Colby May 20, 1890 1,277,523 Yensen Sept. 3, 1918 1,921,060 Williams Aug. 8, 1933 2,587,793 Waldron Mar. 4, 1952 2,788,270 Nisbet et al Apr. 9, 1957 2,893,715 Harders July 7, 1959 2,893,860 Lorenz July 7, 1959