US3565411A

US3565411A - Vacuum vessel for degassing molten metals

Info

Publication number: US3565411A
Application number: US724013A
Authority: US
Inventors: Gerhard Grossmann; Gernot Zahs
Original assignee: Hoesch AG
Current assignee: Fried Krupp AG Hoesch Krupp
Priority date: 1967-04-28
Filing date: 1968-04-25
Publication date: 1971-02-23
Anticipated expiration: 1988-02-23
Also published as: GB1184537A; ES353200A1

Abstract

A vacuum vessel for degassing molten metals of the conventional kind comprising a steel jacket lined with refractory material with an intake pipe at its lower end for dipping into the melt to be degassed and a connection for connecting the vessel to a source of vacuum, is improved by providing a passage in the top of the vessel through which the vacuum connection communicates with the vessel, the passage being shaped so that it changes the direction of flow of gas from the vessel to the vacuum connection through at least 180*. Preferably the refractory lining merges at the top of the vessel into a neck which is surrounded by an annular chamber closed at the top by a cupola. The neck and the annular chamber form the passage and the vacuum connection communicates with one side of the annular chamber.

Description

United States Patent Inventors Appl. No.

Filed Patented Assignee Priority VACUUM VESSEL FOR DEGASSING MOLTEN METALS 8 Claims, 9 Drawing Figs.

US. Cl 266/34, 75/49 Int. Cl C21c 7/10 Field of Search 266/34 (V),

[ References Cited UNITED STATES PATENTS 3,027,150 3/1962 Harders 266/34 3,152,206 10/1964 Philbrick 266/39 Primary ExaminerCharles W. Lanham Assistant Examiner-John S. Brown Attorneys-Curt M. Avery, Arthur E. Wilfond, Herbert L.

Lerner and Daniel J. Tick ABSTRACT: A vacuum vessel for degassing molten metals of the conventional kind comprising a steel jacket lined with refractory material with an intake pipe at its lower end for dipping into the melt to be degassed and a connection for connecting the vessel to a source of vacuum, is improved by providing a passage in the top of the vessel through which the vacuum connection communicates with the vessel, the passage being shaped so that it changes the direction of flow of gas from the vessel to the vacuum connection through at least 180. Preferably the refractory lining merges at the top of the vessel into a neck which is surrounded by an annular chamber closed at the top by a cupola. The neck and the annular chamber form the passage and the vacuum connection communicates with one side of the annular chamber.

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Outstandingly successful in practice has been a method known as the vacuum lift method. The molten metal contained in a ladle is sucked up in successive portions by vacuum into the vacuum vessel through the intake pipe which extends downwards from the bottom of the vacuum vessel. Each portion is degassed in the vacuumvessel and, then discharged again into the ladle. During the degassing process the vacuum vessel itself is repeatedly lifted and; lowered. Another already known process is termed the vacuum circulation degassing process. For this process the bottom of the vacuum vessel is equipped with two pipes which dip into. the molten metal in a ladle. One of these two pipes is the intake pipeor riser, and theother is an outlet pipe or downcomer through which the degassed metal is discharged back again into the pan. The molten metal circulates constantly from the pan up through the riser into the vacuum vessel and then back again through the downcomer into the ladle, the melt being lifted up through the riser by the action of a conveying 'gas. This method has also been termed the gas lift process. 1

However, the already known vacuum vessels as described above have two main disadvantages. In the firstplace there is a risk of spattered particles of molten metal reaching the vacuum connection, that is to say the.,connection leading, to the source of vacuum, and then passing intothe vacuum pipe and even reaching the vacuum pump, a' highly undesirable effect. A further disadvantage is the high rate of heat loss from the vacuum vessel. This occurs largely by radiation, mainly in the region of the vacuum connection. Attempts have been made to interpose a baffle plate inside the vacuum vessel to 7 hold back the spattered metal. However it has been found that the baffle plate retains only the largest particles of spattered metal, the smaller particles still reaching the vacuum connection. Furthermore heat losses by radiation are in practice only slightly reduced by the effect of the baffle plate.

The object of the present invention is to remove these disadvantages, that is to say to provide a vacuum vessel the vacuum connection of which is well screened from destructive influences emanating from the melt, the vacuum vessel at the same time providing a high degree of thermal economy.

To this end, according to this invention, in such a. vacuum vessel, the vacuum connection communicates with the vessel through a passage formed in thetop of the vessel which changes the direction of flow of 'gasfrom the vessel to the vacuum connection through at least 180.

The spattered metal particles cannot follow the change in direction and therefore do not reach the vacuum connection. Furthermore radiated heat is intercepted before reaching the vacuum connection, which therefore remains comparatively cool and the gas is aspirated at a high mass rate or flow.

In a preferred example of the invention the top of the vacuum vessel is' provided with a passage as follows. The upper part of the refractory lining merges into a neck, which is surrounded by an annular chamber closed at the top by a eupola. The vacuum connection is in the side of the annular chamber and there is a through passage between the neck and With regard to the detailed construction of the neck,,two-

advantageous alternatives are possible. In one example the neck is open at the top and: its top edge is situated above the LII top of the vacuum connection but spaced below the undersurface of the cupola. The other possibility is to make the neck closed or substantially closed at the top but with a side opening into the annular chamber at its side remote from the vacuum connection.

Vacuum vessels constructed in this wayshow a considerable improvement in thermal efficiency. However a great deal of heat is still lost during the pauses between two successive degassing. operations, the heat flowing through the neck of the vessel and over its top edgeto the vacuum connection. This disadvantage is remedied in thepreferred example of the invention by providing a movable closure between the neck and the surrounding annular chamber. By closing this passage during the pauses between successive degassing operations the entire loss of heat from they interior of vessel to the vacuum connection is practically prevented. The heat is retained'in the vacuum vessel and the vacuum connection is kept cool.

The closure between the neck. and the surrounding annularv chamber can takevarious forms. If the neck is open at the top there can be a cover mounted in the cupola in such a way that it can be lowered on to the top of the neck.

In order to ensure that the vacuum vessel iseasily accessible from outside, for cleaning or repairs, it is, preferable to connect a part of the cupola to the vacuum vessel in sucha way that the part can be opened up or moved out of the way. The part can be pivoted about a horizontal axis on the steel jacket of the vessel. Y

Furthermore 'the vacuum vessel may be provided with a heating device situated below the neck, for example in the form. of an electric heating rod, inorder to keep the temperature of the melt up to the desired value during the degassing process. However it is-a particular advantage of the invention. that the flow of extra heat which has to be supplied in this way is comparatively small owing to the construction of the vacuum ve'sselwith the; passage on its top.

Some examples of vacuum vessels constructed in accordance with the invention are illustrated in the accompanyingdrawings in which: i

FIG. 1 is a vertical section through one example;

FIG. 2 is a cross section along the line 2-2 in FIG. 1;.

FIG. 3 is a vertical section, similar to FIG. 1 but of a second example; a

FIG. 4 is a partly sectional side view of the example shown in FIG. 1;

FIG. 5 is a verticalsection through example;

FIG. 6 is a verticalsection similar to FIG. 5, but of a fourth example;

FIG. 7 is a cross section along theline 7-7 in FIG. 6;

FIG. 8 is a vertical section similar to FIGS. 5 and 6, but of a fifth example; and 7 FIG. 9 is a cross section along the line 9-9'in FIG. 8.

In the examplesillustrated the vacuum vessels are operated: by the vacuum lift method. In each FIG. the vessel as a whole has the index numerall. At the bottom of the vessel there is a single-intake pipe 2, which is made of refractory material and is capable of beingimmersed in the molten metal contained in a ladle 3. Either the vessel 1 or the-ladle 3 is vertically movable. The means for providing the vertical movement are not a the upper part of a third part of the present invention. They are already known and are therefore not shown in the drawing.

The vacuum vessel 1- has a steel jacket4 with a lining 5' ofrefractory material, for example magnesite or alumina. The vacuum chamber 6, inside the lining 5, is equipped with a horizontal heating rod 7 of carbon or silica, situated a little; above the middle of the vacuum chamber 6. When the vessel is in operation an electric current flbws through the heating. rod 7. The vacuum chamber 6 also has at one side an inclined branchpipe 8,.projecting upwards. The branch pipe 8-.can-be used as an inspection opening, or for. feeding additives to the vacuum vessel;

The upper partiof the refractory lining S-merges into a-cylindrical neck 9, which is surrounded by an-annular chamber 10*.

A vacuum connection 11 leading to a vacuum pump which is not shown in the drawing, is connected to one side to the annular chamber 10.

The upper part of the annular chamber is covered by a cupola 12, which is closed by a plate 13 capable of pivoting about a pivot 15 by means of an arm 14, to which the plate is attached. The arrangement allows the plate 13 to be pivoted upwards and out of the way, as shown in FIG. 4, giving access to the vacuum chamber for cleaning and repairs. Through the plate 13, which is customarily clamped down on the top of the cupola 12, a rod 17 slides in a bush l6.

Attached to the lower end of the rod 17 is a closure plate 18, lined with a refractory material 19. As shown in FIG. 3 the closure plate 18 can be lowered so that its lining 19 rests on the lip of the neck 9, by means of the sliding rod 17, so as to close the upper opening of the vacuum chamber 6.

FIG. 1 shows the vacuum vessel in its operating position. The molten metal is not shown. The chamber 6 is under vacuum and the molten metal it contains is being degassed. The gas released from the melt passes upwards through the neck 9 and so into the annular chamber 10, and from here is sucked away through the vacuum connection 11. The flowing gas has its direction changed several times on its path, so that most of the spattered metal impinges on the lining l9, and the remainder impinges on the walls of the cupola 12. In this way it is ensured that the spattered metal does not reach the vacuum connection 11.

As soon as a vacuum operation has been completed, the melt is drained out of the vacuum chamber 6, and the closure l8, 19 is closed so as to retain the heat stored in the vessel and prevent it from passing out through the vacuum connection 11 via the annular chamber 10. Under certain circumstances it can be advisable to apply extra cooling to the annular chamber 10 and the vacuum connection 11. For this purpose the example shown in FIG. 3 has cooling coils 21 and 22.

The example shown in FIG. 3 also has a further modification, in that the cupola has an internal lining 23 around the annular chamber 10.

The example shown in FIG. 5 also has a refractory lining 23 for the annular chamber 10. However in this case there is no movable closure for closing the mouth of the neck 9.

In FIGS. 1 to 3 the neck 9 is surrounded by a steel jacket 24. The example of FIG. 5 also has this steel jacket, but between the neck 9 and the steel jacket 24 there is a layer 25 of heat-insulating material, which can for example be fireclay of Superex. The insulating layer 25 reduces the flow of heat from the wall of the neck 5 outwards through the annular chamber 10 to the vacuum connection 11.

In the example shown in FIGS. 6 and 7 the neck 9 extends upwards almost as far as the lower surface of the cupola 12, allowing very little space for the flow of gas over the upper lip of the neck 9 into the annular chamber 10. However the neck 9 has a side opening 26 on its side facing away from the suction connection 11. In this way an even better protection is provided for the suction connection 11 against spattered metal. The gases sucked off pass along two different paths from the neck 9 to the suction connection 11, most of the gas passing through the side opening 26 and only a little over the upper lip of the neck 9.

In the example shown in FIGS. 8 and 9 the neck 9 extends all the way up as far as the lower surface of the cupola 12, allowing no flow of gas over the upper lip of the neck 9. All the aspirated gas leaves the neck 9 through its side opening 26 which, as in the example of FIGS. 6 and 7, is situated in the side of the neck 9 furthest away from the vacuum connection 11. In the example of FIGS. 8 and 9 there is a closure 27 capable of closing the side opening 26. The closure 27 is mounted on a sliding rod 28. The method of functioning is similar to that of the closures of the examples shown in FIGS. 1, 3 and 4. In the example of FIGS. 8 and 9 however the closure 27 moves in a radial direction with respect to the axis of the vacuum vessel. The closure 27 of FIGS. 8 and 9 and the closure l8, 19 of FIG. 1 both have the same purpose.

We claim: 1. In a vacuum vessel for degassing molten metals, said vessel including a steel jacket, a lining of refractory material in said jacket, intake tube means at the bottom of said jacket for dipping into said.molten metal, and means defining a connection for connecting said vessel to a source of vacuum, the improvement comprising means in the top of said vessel defining a passage communicating said connection with said vessel, said passage being shaped to deflect the direction of flow of gas through at least between said vessel and said connection, said passage defining means comprising a neck formed at the top of said refractory lining, means defining an annular chamber surrounding said neck, and a cupolaextending over said neck and said chamber, said vessel communicating with said neck and said connection communicating with one side of said annular chamber, and further comprising means closing the top of said neck and means defining an opening in one side of said neck, said one side being angularly spaced around said annular chamber from said connection.

2. A vacuum vessel according to claim 1, further comprising a refractory lining in said annular chamber.

3. A vacuum vessel according to claim 1, further comprising a steel jacket surrounding said neck.

4. In a vacuum vessel for degassing molten metals, said vessel including a steel jacket, a lining of refractory material in said jacket, intake tube means at the bottom of said jacket for dipping into said molten metal, and means defining a connection for connecting said vessel to a source of vacuum, the improvement comprising means in the top of said vessel defining a passage communicating said connection with said vessel, said passage being shaped to deflect the direction of flow of gas through at least 180 between said vessel and said connection, said passage defining means comprising a neck formed at the top of said refractory lining, means defining an annular chamber surrounding said neck, and a cupola extending over said neck and said chamber, said vessel communicating with said neck and said connection communicating with one side of said annular chamber, and further comprising means defining an opening in the top of said neck, said opening being at a level higher than said connection, but spaced below said cupola, and a movable closure between said neck and said annular chamber, and means for moving said closure to block said neck from said chamber. 7

5. A vacuum vessel according to claim 4, further comprising means slidably mounting said closure in said cupola for lowering movement on to the top of said neck.

6. In a vacuum vessel for degassing molten metals, said vessel including a steel jacket, a lining of refractory material in said jacket, intake tube means at the bottom of said jacket for dipping into said molten metal, and means defining a connection for connecting said vessel to a source of vacuum, the improvement comprising means in the top of said vessel defining a passage communicating said connection with said vessel, said passage being shaped to deflect the direction of flow of gas through at least 180 between said vessel and said connection, said passage defining means comprising a neck formed at the top of said refractory lining-means defining an annular chamber surrounding said neck, and a cupola extending over said neck and said chamber, said vessel communicating with said neck and said connection communicating with one side of said annular chamber, and further comprising means detachably mounting a part of said cupola.

7. A vacuum vessel according to claim 6, wherein said part of said cupola is a cover and said mounting means comprises means pivotally mounting said cover on said vessel for swinging movement about a horizontal axis.

8. A vessel according to claim 1, further comprising heating means in said vessel and means mounting said heating means below said neck.

Claims

1. In a vacuum vessel for degassing molten metals, said vessel including a steel jacket, a lining of refractory material in said jacket, intake tube means at the bottom of said jacket for dipping into said molten metal, and means defining a connection for connecting said vessel to a source of vacuum, the improvement comprising means in the top of said vessel defining a passage communicating said connection with said vessel, said passage being shaped to deflect the direction of flow of gas through at least 180* between said vessel and said connection, said passage defining means comprising a neck formed at the top of said refractory lining, means defining an annular chamber surrounding said neck, and a cupola extending over said neck and said chamber, said vessel communicating with said neck and said connection communicating with one side of said annular chamber, and further comprising means closing the top of said neck and means defining an opening in one side of said neck, said one side being angularly spaced around said annular chamber from said connection.

4. In a vacuum vessel for degassing molten metals, said vessel including a steel jacket, a lining of refractory material in said jacket, intake tube means at the bottom of said jacket for dipping into said molten metal, and means defining a connection for connecting said vessel to a source of vacuum, the improvement comprising means in the top of said vessel defining a passage communicating said connection with said vessel, said passage being shaped to deflect the direction of flow of gas through at least 180* between said vessel and said connection, said passage defining means comprising a neck formed at the top of said refractory lining, means defining an annular chamber surrounding said neck, and a cupola extending over said neck and said chamber, said vessel communicating with said neck and said connection communicating with one side of said annular chamber, and further comprising means defining an opening in the top of said neck, said opening being at a level higher than said connection, but spaced below said cupola, and a movable closure between said neck and said annular chamber, and means for moving said closure to block said neck from said chamber.

6. In a vacuum vessel for degassing molten metals, said vessel including a steel jacket, a lining of refractory material in said jacket, intake tube means at the bottom of said jacket for dipping into said molten metal, and means defining a connection for connecting said vessel to a source of vacuum, the improvement comprising means in the top of said vessel defining a passage communicating said connection with said vessel, said passage being shaped to deflect the direction of flow of gas through at least 180* between said vessel and said connection, said passage defining means comprising a neck formed at the top of said refractory lining, means defining an annular chamber surrounding said neck, and a cupola extending over said neck and said chamber, said vessel communicating with said neck and said connection communicating with one side of said annular chamber, and further comprising means detachably mounting a part of said cupola.