US3019275A

US3019275A - Apparatus for heating molten metals in a vacuum chamber

Info

Publication number: US3019275A
Application number: US775791A
Authority: US
Inventors: Lorenz Albert
Original assignee: WC Heraus GmbH and Co KG
Current assignee: WC Heraus GmbH and Co KG
Priority date: 1957-11-26
Filing date: 1958-11-24
Publication date: 1962-01-30
Anticipated expiration: 1979-01-30

Description

Jan. 30, 1962 A. LORENZ APPARATUS FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Filed Nov. 24, 1958 2 Sheets-Sheet 1 ELECTRICAL POWER SOURCE l6 X X DIFFERENTIAL &

ACTUATOR MOTORS MECHANICAL PUMP AMPLIFIER A. LORENZ 3,019,275

APPARATUS FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Jan. 30, 1962 2 Sheets-Sheet 2 Filed Nov. 24, 1958 s sssss Q as sssas FIG 2 United States Patent '0 3,019,275 APPARATUS FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Albert Lorenz, Hanan (lVIain), Germany, assignor to W. C. Heraeus G.m.b.H., Hanan (Main), Germany, a corporation of Germany Filed Nov. 24, 1958, Ser. No. 775,791 Claims priority, application Germany Nov. 26, 1957 Claims. (Cl. 13-31) The present invention relates to a method and apparatus for heating metals, and especially steel, for the purpose of extracting the gases therefrom.

Prior to this invention the gases occluded in molten metals, especially steel, were extracted therefrom by passing the 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 eificiency 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. f

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 containerholding the metal. along one path, then passed through an evacuated extraction chamber, and finally returned to the container along a second path which is spaced from the first path. Ac-v 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 pro vision 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 soonas 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 itthereby 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 utilized for effecting and controlling the gas-extraction process.

These and further objects, features, and advantages of the present invention will become more apparant 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 8 into inlet pipe 6, a continuous flow of metal will be started and maintained, rising from the bath in ladle 1 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 fiow of metal passing through the chamber. Hopper 9 is likewise adapted to be sealed 7 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 1. Thus, the pipe portions extending 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 practically closed iron transformer core 12 which also carries a primary coil 13 which is supplied with an alternating current of a standard line frequency. By means of this transformer core 12 a very strong alternating current will be induced in the molten metal flowing 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 chamber 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 265--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 different 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 evacuating pump and control valve 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.

From the 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 claims.

Having thus fully disclosed my invention, What I claim 1. An apparatus for heating up molten metals comprising a container for holding a molten metal, a vacuum chamber having an inlet conduit and an outlet conduit thereon and extending downwardly therefrom, means for suspending said vacuum chamber above said container and for raising and lowering the same relative to said container and for immersing: the free ends of said conduits into said molten metal, means for evacuating said chamber and the unimmersed parts of said conduits above the surface of said molten metal Within said container, means for conveying the molten metal through said inlet conduit into said vacuum chamber, and means for inducing a strong electric current in the entire volume of molten metal circulating through said conduits and said vacuum chamber for increasing the temperature thereof.

2. An apparatus as defined in claim 1, further comprising means for adding other materials under a vacuum to the molten metal within said vacuum chamber for alloying said molten metal with said added materials by the heat of said metal.

3. An apparatus as defined in claim 1, wherein said evacuating means are constructed and arranged to operate continuously to withdraw the gases liberated from said molten metal within said vacuum chamber.

4. An apparatus as defined in claim 1, wherein said conveying means comprise means for injecting a gas into said inlet conduit adapted to take along the molten metal through said inlet conduit into said vacuum chamber.

5. An apparatus as defined in claim 1, wherein said induction means comprise a transformer having a substantially closed iron core and a primary induction coil mounted on said iron core and adapted to be connected to a source of alternating current, said molten metal circulating in a continuous flow from said container through said inlet conduit, said vacuum chamber and said outlet conduit back to said container serving as a secondary circuit of said transformer.

6. An apparatus as defined in claim 5, wherein said substantially closed iron core of said transformer extends between said two conduits, and means for indicating the reaction upon the induction current within said primary coil for determining the beginning of a continuous process of extracting gases from said molten metal within said vacuum chamber.

7. An apparatus as defined in claim 6, further comprising means whereby said reaction upon the primary induction current is utilized for controlling the operation of the gas extraction process.

8. An apparatus as defined in claim 6, wherein said control means comprise means for adjusting the elevation of said vacuum chamber relative to the surface of the molten metal within said container.

9. An apparatus as defined in claim 6, wherein said control means comprise means for adjusting the operation and output of said evacuating means.

10. An apparatus as defined in claim 6, wherein said conveying means comprise means for injecting a gas into said inlet conduit constructed and arranged to take along the molten metal through said inlet conduit into said vacuum chamber, said control means comprising means for controlling the amount of gas injected into said inlet conduit by said injecting means.

References Cited in the file of this patent UNITED STATES PATENTS 761,920 Schneider June 7, 1904 2,587,793 Waldron Mar. 4, 1952 2,848,317 Coupette et al. Aug. 19, 1958 2,859,262 Harders et al. Nov. 4, 1958