US3820587A

US3820587A - Apparatus for making metal ingots

Info

Publication number: US3820587A
Application number: US00847891A
Authority: US
Inventors: E Plockinger; G Kuhnelt
Original assignee: Gebrueder Boehler and Co AG
Current assignee: Gebrueder Boehler and Co AG
Priority date: 1969-01-20
Filing date: 1969-08-06
Publication date: 1974-06-28
Anticipated expiration: 1991-06-28
Also published as: US3916978A; DE2001256B2; FR2028729A1; DE2001256A1; CH524413A; BE744684A; FR2028729B1; JPS5013217B1; LU60198A1; SE421877B

Abstract

A body of molten metal is provided in a lower portion of an ingot mold. A body of liquid slag is provided in said mold on top of said body of molten metal within a slag-confining wall. Heat energy is supplied to said body of liquid slag at a rate corresponding to at least 120 kilowatt-hours per metric ton of metal in said mold. The slag-confining wall is supplied on the outside thereof with a cooling fluid to cool said slag-confining wall sufficiently to maintain a layer of solid slag between said wall and said body of liquid slag. The molten metal in said mold is caused to solidify while those parts of said mold which are contacted by said metal are kept out of contact with cooling liquid.

Description

United States Patent 1191 11] 3,820,587 Plockinger et al. 1 June 28, 1974 15 APPARATUS FOR MAKING METAL 2,397,789 4/1946 Hopkins 164/337 x INGOTS 2,858,586 11/1958 Brennan 164/51 2,871,533 2/1959 Swainson 164/252 X 1 Inventors: Erwm. Plockmger; Gert Kuhnelt, 2,935,395 5/1960 Smith, Jr.... 164/51 x both of Kapfenberg, Austria 3,448,790 6/1969 Maskall 164/348 i 3,608,618 /1971 Maskall 1 164/252 1 Ahhlgnw 661111301116" Kdpfenberg, 3,610,318 10/1971 Simmons 164/252 Austrla [22] Fil d; A 6, 1969 Primary Examin'erJ. Spencer Overholser A E pp Nol: 847,891 sszstant xammer V K Rlsmg [57] ABSTRACT Foreign Application Priority Data A body of molten metal is provided in a lower portion Aug. 7, 1969 Austria 530/69 of an ingot mold. A body of liquid slag is provided in said mold on top of said body of molten metal within [52] 11.8. C1 164/252, 164/126, 164/348, a slag-confining wall. Heat energy is supplied to said 249/197 body of liquid'slag at a rate corresponding to at least [51] Int. Cl 822d 27/02 120 kilowatt-hours per metric ton of metal in said [58] Field of Search 1'64/250, 251, 252, 50, mold. The slag-confining wall is supplied on the out- 164/51, 52, 48, 122, 123, 359, 348, 337; side thereof with a cooling fluid to cool said slag- 249/78, 105, 202, 174, 197, 106, 198, 199, confining wall sufficiently to maintain a layer of solid 249/200, 201, 108 slag between said wall and said body of liquid slag. The molten metal in said mold is caused to solidify [56] References Cited while those parts of said mold which are contacted by UNITED STATES PATENTS said'metal are kept out of contact with cooling liquid. 2,369,233 2/ 1.945 Hopkins 164/52 14 Claims, 2 Drawing Figures 50 a -"23 5i 7 25 7' 20 1;;1, I 24 25 1 APPARATUS FOR MAKING METAL INGOTS This invention relates to an apparatus for making ingots from metals, preferably from plain carbon steels or alloy steels, which ingots have a good primary crystallization, a low macrosegregation and a low content of non-metallic inclusions.

For this purpose, apparatus are known which consist essentially of an ingot mold, which is closed at the bottom, and one or more fusible or non-fusible electrodes, which are adapted to be lowered from above intosaid mold and may be connected to a source of electric current. When it is desired to make an ingot of steel, the mold, may consist, e.g., of cast iron and maybe cooled without need for a separate liquid or gaseous cooling medium. In this case, the mold may be filled with molten steel, the free surface of which is covered by a liquid slag layer, and the top portion of the molten steel may be heated as in crop end heating by a supply of electric current to the electrodes which are immersed in the liquid slag layer. As a result, the uppermost part of the molten steel immediately below said slag will be heated and maintained in a liquid state until a major part of the steel has progressively solidified from the bottom to form a solid ingot. Compared to the ingots cast in conventional molds, the crop ends which cannot be used because they are non-homogeneous are smaller in-these ingots, which have also smaller contraction cavities'in their top portion.

In these known apparatus, a refractory lining is provided in the upper part of the mold, which upper part serves to accommodate the liquid slag layer floating on the molten steel. This lining is subjected to the attack by the slag and the molten steel and requires a frequent renewal so that the maintenance costs are high. Be-

sides, constituents of the refractory lining enter into solution and change the chemical composition of the liquid slag which is in contactwith the lining; these concontrol of the structure of the ingot.

It is an object of the invention to avoid said disadvantages by providing an improved apparatus, in which much higher currents at a rate of at least 120 kilowatthours per metric ton of the weight of the solidifying molten steel can be suppliedand the liquid slag cover and/or the molten steel or other metal under said slag cover are subjected by said supply or electric current or other energy to a high temperature rise in a large cross-sectional area whereas the erosion at the inside surfaces of the mold, particularly those which are contacted by the liquid slag layer, is only small.

In an apparatus of the kind described hereinbefore, this object is accomplished according to the invention in that the mold is not cooled with liquid and is pro-' top part is filled with thefliquid slag, that portion of the mostly metallic inside wall surface of thetop partwhich confines the liquid slag is covered by a solidified slag In another embodiment of the apparatus according to the invention, the toppart which serves to accommodate the liquid slag consists of a double-walled hollow body, which may be made, e.g., of metal, and, if desired, may be provided with internal guiding surfaces, and the space between the outside and inside walls is provided with inlet and outlet pipes for supplying and withdrawing the cooling liquid.

An embodiment of the invention will now be explained more fully and by way of example with reference to the drawing wherein FIG. 1 is a longitudinal sectional view of the apparatus of the invention; and,

FIG. 2 is a view similar to FIG. 1 wherein a conventional plasma torch for use with the apparatus of the invention is illustrated.

The body 10 of the mold consists, e.g., of cast-iron and is exposed only to the ambient atmosphere rather than cooled by a special medium, such as a liquid. A top part 20 is secured to the mold body and consists of sheet metal elements, e.g., of steel or another material, which are joined by welding. An annular distributing chamber 22 is attached to the top edge of the top part 20 and contains a cooling liquid, such as water. The distributing chamber 22 is connected to the liquid supply conduit 21 and along its underside is provided with outlet openings 23 or spray nozzles for discharging the cooling liquid against the outside of the wall 26 of the top part 20. On the underside of the top part 20, a trough 24 is provided for collecting the downflowing cooling liquid. This trough communicates with the drain conduit 25.

The mold body 10 rests on a bottom plate 40 and is sealed against the same so that the mold body can be filled to its top rim, e.g., with steel, when an ingot is to be cast, without a leakage of steel at the bottom joint. The top part 20 is in sealed engagement with the top edge of the mold body so that premelted slag can be poured in over the level of the molten steel. The walls of the top part are covered on the, inside with a layer 51 of solidified slag. Owing to the cooling on the outside of the top part, this solidified slag cannot be melted even when the liquid slag layer is heated to a high temperature by a supply of electric current or other energy.

The solidified slag forms a solid separating=layer be tween the liquid slag layer and the wall.

One or more fusible electrodes are disposed over the mold body 10 and adapted to be lowered into and lifted from the slag layer disposed over the level of the molten steel. Two terminals of a source of alternating current are respectively connected to the electrode 60 and via the bottom plate 40 to the ingot 30 so that the circuit is closed by the slag layer 50 when the electrode is or the electrodes are immersed in said slag layer. By resistance heating, the slag layer is maintained at a high temperature and heat is supplied to the ingot as it solidifies. The power source and all conductors of this circuit are dimensioned for a supply of energy of .at least kilowatt-hours per metric ton of the weight of the ingot at a voltage of 30-100 volts. This supply of energy is required to ensure a high purity of the ingot and a dense, segregation-free structure in all portions of the ingot.

In another embodiment of the invention, which is not shown in the drawing, one or more non-fusible electrodes are disposed over the mold body and mold top part and adapted to be lifted and lowered. When the electrodes are lowered into contact with the liquid slag, the circuit will be closed so that the slag will be heated by resistance heating. Plasma torches or other energy sources may be used rather than current-supplying electrodes to heat the slag cover. Such a conventional plasma torch 80 is illustrated in FIG. 2 and comprises a rod-shaped electrode 81 and tubular counterelectrode 82 which surrounds the electrode 81 and is open at its lower end. The tubular counter-electrode 82 has an inlet pipe 83 through which an ionizable gas, such as argon, can be introduced. An A.C. current source 84 is connected between

electrodes

81, 82. (The current source can also be a DC. current source.)

Steel ingots made with the aid of the apparatus according to the invention have after solidification a good primary crystallization, a perfectly dense structure and a low content of non-metallic inclusions everywhere. If the solidification rate is properly controlled, for instance, the apparatus may be used to make ingots which are free of the known V-segregation near the axis of the ingot.

If the mold is to be arranged in a pit or in an evacuated container, it is advantageous to provide the mold with a metallic top part consisting of a double-walled hollow body, which may be provided in its interior with surfaces for guiding the liquid flowing through. In this case too, the top part may consist of welded sheet steel elements and the guiding surfaces are preferably helical so that the cooling water flows around the inside wall of the top part from bottom to top substantially along a helix at an adequate velocity. The use of a doublewalled top part affords the advantage that the draining of the cooling water does not depend on a natural gradient but the conduits may be laid out as desired, e.g., through the wall of the evacuated vessel.

Although the invention is illustrated and described with reference to a plurality of preferred embodiments thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a plurality of preferred embodiments, but is capable of numerous modifications within the scope of the appended claims.

What is claimed is:

1. Apparatus for making metal ingots, which comprises an ingot mold body having an open bottom and top and being free of means for a liquid cooling of said mold body,

a bottom plate closing said end, V said mold body and bottom plate being adapted to hold molten metal as it solidifies to form an ingot,

mold body at its lower an annular mold top part coaxially carried by said mold body over its upper end and extending above the upper end of the mold body,

said mold top part comprising a slag-confining wall having an outside surface and an inside surface adapted to confine a body of liquid slag which is heated by the supply of energy, said liquid slag floating on top of said molten metal in said mold body,

energy-supplying means operable to supply heating energy to said body of liquid slag at an energy supply rate corresponding to at least kilowatthours per metric ton of metal in said mold body when the latter is filled with metal to capacity, and

cooling means operable to supply a cooling fluid to said outside surface in order to cool said slagconfining wall sufficiently to maintain a layer of solid slag between said inside surface and said liquid slag when said mold is filled with metal to capacity and is being operated with said energysupplying meansto supply heating energy to said liquid slag at said energy supply rate;

an annular distributing chamber surrounding said slag-confining wall at the top thereof and formed with peripherally spaced outlets directed against said outside surface, and

an annular trough disposed under said slag-confining wall and arranged to collect said cooling liquid flowing down on said outside surface;

at least said outside surface is inclined outwardly relative to the vertical axis of said mold body.

2. Apparatus as set forth in claim 1, in which said energy-supplying means comprise electrode means which are disposed over said mold top part and adapted to be lowered into and lifted from said body of liquid slag, and

a source of electric current electrically connected to said electrode means and to said bottom closure.

3. Apparatus as set forth in claim 2, in which said energy-supplying means are dimensioned for a supply of heating energy at said energy supply rate at a voltage of 30-100 volts.

4. Apparatus as set forth in claim 2, in which said electrode means comprise fusible electrode means.

5. Apparatus as set forth in claim 2, in which said electrode means comprise non-fusible electrode means.

6. Apparatus as set forth in claim 1, in which said energy-supplying means comprise a plasma torch.

7. Apparatus as set forth in claim 1, in which said cooling means are operable to supply a cooling liquid to said outside surface to cool said slag-confining wall.

8. Apparatus as set forth in claim 1, in which said outlets comprise spray nozzles.

9. Apparatus as set forth in claim 1, in which said mold top part comprises an annular outer wall spaced around said slag confining wall and defining an annular cooling chamber therewith,

an inlet connected to said cooling chamber to supply said cooling fluid thereto, and

an outlet connected to said cooling chamber to withdraw said cooling fluid therefrom.

10. Apparatus as set forth in claim 9, in which said outside surface of said slag-confining wall and the inside surface of said outer wall are provided with means arranged to guide said cooling fluid along a predetermined path from said inlet to said outlet.

11. Apparatus as set forth in claim 1, wherein said mold body is made of metal.

6 12. Apparatus as set forth in claim 11, wherein said body. mold body is made of cast iron. 14. Apparatus as set forth in claim 13, wherein said 13. Apparatus as set forth in claim 1, wherein said mold top part is made of metal. mold top part is removably mounted on said mold UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,820,587 June 28, 1974 Patent No. Dated Erwin Ploeckinger et al. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet item [30] "August 7, 1969" should read January 20, 1969 5igned and %eaicd this eleventh Day of May 1976 [SEAL] Artesr:

RUTH C. MASON C. MARSHALL DANN Aucsmzg Officer (unmzissioncr nj'lun'nls and Trademarks

Claims

1. Apparatus for making metal ingots, which comprises an ingot mold body having an open bottom and top and being free of means for a liquid cooling of said mold body, a bottom plate closing said mold body at its lower end, said mold body and bottom plate being adapted to hold molten metal as it solidifies to form an ingot, an annular mold top part coaxially carried by said mold body over its upper end and extending above the upper end of the mold body, said mold top part comprising a slag-confining wall having an outside surface and an inside surface adapted to confine a body of liquid slag which is heated by the supply of energy, said liquid slag floating on top of said molten metal in said mold body, energy-supplying means operable to supply heating energy to said body of liquid slag at an energy supply rate corresponding to at least 120 kilowatt-hours per metric ton of metal iN said mold body when the latter is filled with metal to capacity, and cooling means operable to supply a cooling fluid to said outside surface in order to cool said slag-confining wall sufficiently to maintain a layer of solid slag between said inside surface and said liquid slag when said mold is filled with metal to capacity and is being operated with said energy-supplying means to supply heating energy to said liquid slag at said energy supply rate; an annular distributing chamber surrounding said slag-confining wall at the top thereof and formed with peripherally spaced outlets directed against said outside surface, and an annular trough disposed under said slag-confining wall and arranged to collect said cooling liquid flowing down on said outside surface; at least said outside surface is inclined outwardly relative to the vertical axis of said mold body.

2. Apparatus as set forth in claim 1, in which said energy-supplying means comprise electrode means which are disposed over said mold top part and adapted to be lowered into and lifted from said body of liquid slag, and a source of electric current electrically connected to said electrode means and to said bottom closure.

9. Apparatus as set forth in claim 1, in which said mold top part comprises an annular outer wall spaced around said slag-confining wall and defining an annular cooling chamber therewith, an inlet connected to said cooling chamber to supply said cooling fluid thereto, and an outlet connected to said cooling chamber to withdraw said cooling fluid therefrom.

11. Apparatus as set forth in claim 1, wherein said mold body is made of metal.

12. Apparatus as set forth in claim 11, wherein said mold body is made of cast iron.

13. Apparatus as set forth in claim 1, wherein said mold top part is removably mounted on said mold body.

14. Apparatus as set forth in claim 13, wherein said mold top part is made of metal.