GB2216444A - Metallurgical slag flow inhibitor - Google Patents

Abstract

For inhibiting the flow of the slag (3) of a molten metal bath through a tap hole (9) of a metallurgical vessel (11). A hollow body (13) has an outer shell (15) which defines an inner chamber (17). The shell has a plurality of passageways (19) spaced substantially evenly about the shell, extending through the shell from the surface of the shell to the chamber. The shell is formed of a heat stable refractory material having a specific gravity which is greater than that of the slag and less than that of the molten metal (7) in the molten metal bath so that the slag flow inhibitor floats at the interface between the molten metal and the slag. The slag flow inhibitor substantially blocks the tap hole of the metallurgical vessel as the molten metal is being poured therefrom so that when the slag flow inhibitor is in position at the tap hole, the molten metal can flow through the passage- ways and chamber to be discharged from the metallurgical vessel through the tap hole prior to any significant amount of slag being able to flow through the tap hole. <IMAGE>

Description

A METALLURGICAL SLAG FLOW INHIBITOR The invention relates to a slag flow inhibitor, and more particularly, to a slag flow inhibitor for inhibiting the flow of the slag which is usually present on top of a molten metal bath when the molten metal is drained through a tap hole of a metallurgical vessel.

Many processes which involve the formation of molten metal, such as steel, result in a layer of slag, which floats on top of the molten metal.

It is important to prevent the slag from contaminating the molten metal as the molten metal is discharged from the metallurgical vessel.

One method of discharging the contents of such a metallurgical vessel is to cause the contents to flow from the metallurgical vessel through a tap hole in the metallurgical vessel. In order to prevent the slag from contaminating the molten metal, the flow of the molten metal from the metallurgical vessel must be stopped before the slag flows through the tap hole. Generally, the slag begins to flow through the tap hole before all of the molten metal has been discharged from the metallurgical vessel due to the formation of a vortex in the region of the tap hole, which causes the slag to mix with the molten metal. Because mixing of the molten metal and slag begins prior to all of the molten metal being discharged from the metallurgical vessel, the flow of molten metal through the tap hole must be terminated prior to the recovery of all of the molten metal in the metallurgical vessel.

Because it is often difficult for an operator to determine just when the flow of any slag from the metallurgical vessel is about to begin several types of slag flow inhibitors have been developed which partially block the flow of molten metal from the metallurgical vessel near the end of the tap and, as they do, they change the type of flow from the metallurgical vessel, either by simply slowing the flow, as in U.S. Patent No. 4,601,415, or by causing the flow to flare, as in U.S. Patents Nos.

4,462,574, 4,494,734 and 4,709,903. When the change in the flow of molten metal occurs, the operator can stop the discharge of molten metal from the metallurgical vessel. Spherical slag flow inhibitors are also available which completely block the tap hole. While use of such slag flow inhibitors helps to prevent the discharged molten metal from being contaminated by the slag, some molten metal is left in the metallurgical vessel along with the slag.

Such slag flow inhibitors have been developed in various shapes. Spherical slag flow inhibitors are known, as well as slag flow inhibitors in the shape of a polyhedron (U.S. Patent No. 4,462,574), a tapered polygon having a weighted apex (U.S. Patent No. 4,601,415), and a modified cone (U.S. Patents Nos. 4,494,734 and 4,709,903).

U.S. Patent No. 4,526,349 describes an annular disc, preferably used in conjunction with a separate spherical stopper, that settles around the tap hole as the molten metal flows from the metallurgical vessel. The disc has a diameter greater than both the tap hole and the expected vortex at the tap hole. The force of the vortex draws the stopper through the disc to the tap hole, but the presence of the disc at the tap hole resists the force of the vortex and delays that process. Thus, more of the molten metal can be recovered from the metallurgical vessel before being contaminated by the slag and before the tap hole is substantially plugged by the stopper than would otherwise be recovered.

It is an object of the present invention to provide a slag flow inhibitor that enables improved drainage of the molten metal through the tap hole of the metallurgical vessel after the slag flow inhibitor is in position at the tap hole but before the discharged molten metal is contaminated by the slag.

According to this invention there is provided a slag flow inhibitor for inhibiting the flow of the slag of a molten metal bath through a tap hole of a metallurgical vessel comprising: a hollow body having an outer shell defining an inner chamber, said shell having a plurality of passageways spaced substantially evenly about said shell extending through said shell from the surface of said shell to said chamber, said shell being formed of a heat stable refractory material having a density which is greater than that of the slag and less than that of the molten metal in said molten metal bath so that said slag flow inhibitor floats at the interface between the molten metal and the slag;; said slag flow inhibitor being adapted to substantially block a said tap hole of a said metallurgical vessel as the said molten metal is being tapped therefrom so that when said slag flow inhibitor is in position at a said tap hole, the said molten metal can flow through said passageways and chamber of said flag flow inhibitor to be discharged from the said metallurgical vessel through the said tap hole prior to any significant amount of said slag being able to flow through said tap holes.

A slag flow inhibitor of the invention inhibits the flow of the slag of a molten metal bath through a tap hole of a metallurgical vessel and includes a hollow body having an outer shell which defines an inner chamber. The shell has a plurality of passageways which are spaced substantially evenly about the shell, and which extend through the shell from the surface of the shell to the chamber.

The shell is formed of a heat stable refractory material having a specific gravity which is greater than that of the slag and less than that of the molten metal in the molten metal bath so that the slag flow inhibitor floats at the interface between the molten metal and the slag.

In use, the slag flow inhibitor substantially blocks the tap hole of the metallurgical vessel as the molten metal is being poured therefrom so that when the slag flow inhibitor is in position at the tap hole, the molten metal can flow through the passageways and chamber of the slag flow inhibitor to be discharged from the metallurgical vessel through the tap hole prior to any significant amount of slag being able to flow through the tap hole.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a plan view of a slag flow inhibitor in accordance with the invention; Figure 2 is a cross-sectional view through the centre of the slag flow inhibitor of Figure 1, taken along the line II-II of Figure 1; Figure 3 is a cross-sectional view of a metallurgical vessel showing the slag flow inhibitor of Figure 1 floating at the interface of the molten metal and slag of a molten metal bath; Figure 4 is an enlarged cross-sectional view of the tap hole region of a metallurgical vessel showing the slag flow inhibitor of Figure 1 in position at a tap hole; Figure 5 is a perspective view of a second embodiment of the slag flow inhibitor of the invention;; Figure 6 is a perspective view of a third embodiment of the slag flow inhibitor of the invention; and Figure 7 is a perspective view of a fourth embodiment of the slag flow inhibitor of the invention.

Referring initially to Figures 1 to 4 of the drawings a slag flow inhibitor 1 in accordance with the present invention inhibits the flow of the slag 3 from a molten metal bath 5 containing slag 3 and molten metal 7, such as steel, through a tap hole 9 of a metallurgical vessel 11 (Figures 3 and 4). As illustrated, the metallurgical vessel 11 is a ladle, however it will be readily understood that the invention can be used in connection with many other types of vessels, such as a BOF furnace.

The slag flow inhibitor 1 is a hollow spherical body 13 (Figures 1 and 2) having an outer shell 15 which defines an inner chamber 17. The outer periphery of the shell 15 is larger than the diameter of the tap hole 9 so that the slag flow inhibitor 1 substantially blocks the tap hole 9 when the slag flow inhibitor 1 is seated at the tap hole 9. Preferably, the width of the slag flow inhibitor 1, is about double that of the diameter of the tap hole 9.

Generally, a tap hole 9 has a diameter of between about 12.5 cms and 23 cms (5 and 9 inches). Thus, preferably, the slag flow inhibitor 1 has a width of between about 25 cms and 46 cms (10 and 18 inches).

The thickness of the shell 15 of the hollow body 13 is preferably between about 5 and 7.5 cms (2 and 3 inches).

The shell 15 has a plurality of passageways 19 which are spaced substantially evenly about the shell 15 and which extend through the shell 15 from the outer surface 21 of the shall 15 to the chamber 17. The appropriate size and number of the passageways 19 vary according to the size of the chamber and the diameter of the tap hole 9. The passageways 19 should be as large as possible without becoming so close together when they reach the inner surface 29 of the shell 15 such that the strength of the shell 15 is compromised. Preferably, the passageways 19 are at least about 1 cm (one-half inch) apart on the inner surface 29 of the shell 15.Further, the passageways 19 are preferably spaced substantially evenly about the shell 15 and are close enough together on the outer surface 21 of the shell 1 so that when the slag flow inhibitor 1 is seated at a tap hole 9 (Figure 4) at least one passageway 19 is exposed to the tap hole 9. The size of the cross-sections of the passageways 19 should be substantially the same, although the size of the cross-sections will vary between specific examples of the invention in order to achieve the even spacing of the passageways 19. Ideally, the equivalent of at least two passageways 19 are exposed to the tap hole 9. Thus, it is readily understood that the preferred size and number of passageways 19 through the hollow body 13 for a particular shell 15 is easily determined. The passageways 19 can have a variety of shapes. Preferably, the passageways 19 are cylindrical.

The shell 15 of the hollow body 13 is formed of a heat stable refractory material, preferably, a castable refractory material. Suitable refractory materials which can be used to form the slag flow inhibitor 1 of the invention include mixtures of refractory cement, iron ore, steel shot and water.

The refractory material has a density which is greater than that of the slag 3 of the molten metal bath 5 and less than that of the molten metal 7. Generally, the molten metal 7 has a density of about 8.03 g per cc (0.29 pound per cubic inch) and the slag 3 has a density of between about 2.49 and 2.76 g per cc (0.09 and 0.1 pound per cubic inch). Thus, the refractory material preferably has a density of greater than about 2.49 g per cc (0.09 pound per cubic inch) and less than about 8.03 g per cc (0.29 pound per cubic inch). One way to achieve the desired specific gravity of the refractory material is to adjust the concentration of steel shot in the refractory material.As a result, the slag flow inhibitor 1 floats at the interface 23 between the molten metal 7 and the slag 3 and does not interfere with the discharge of the molten metal 7 in the molten metal bath 5 until near the end of the tapping process when discharge of the slag 3 along with the molten metal 7 is imminent.

Preferably, the density of the slag flow inhibitor 1 is such that the inhibitor floats with about 40 per cent of the slag flow inhibitor 1 in the slag 3 and the remaining about 60 per cent of the slag flow inhibitor 1 in the molten metal 7.

The slag flow inhibitor 1 may be of a variety of shapes and sizes. Particularly suitable shapes for the slag flow inhibitor, labelled 1, 1a, 1b and 1c, respectively, include a sphere 25 (Figures 1 to 4), tapered polygon 25a having a weighted apex 27 to ensure the proper orientation at the tap hole 9 (Figure 5), polyhedron 25b (Figure 6), and modified cone 25c being properly weighted, again to ensure the proper orientation at the tap hole 9 (Figure 7). Preferably, the hollow body 13 of the slag flow inhibitor 1 is a hollow sphere 25.

The preferred hollow sphere 25 has an outer diameter of between about 25 cms and 46 cms (about 10 and 18 inches) more preferably, about 30.5 cms (12 inches) and an inner diameter of between about 15 cms and 41 cms (6 and 16 inches) more preferably about 20 cms (8 inches). The preferred hollow sphere 25 preferably has about twelve substantially evenly spaced cylindrical passageways 19 each having a cross-sectional diameter of about 7.5 cms (3 inches).

The slag flow inhibitor 1 of the present invention is preferably placed into the metallurgical vessel 11 being tapped as the vortex begins to form at the tap hole 9, generally after about two-thirds of the time period of the tapping process or about four minutes into the tapping process, to reduce wear and tear on the slag flow inhibitor 1. The vortex draws the slag flow inhibitor 1 towards the tap hole 9 and tends to cause the slag 3 to mix with the molten metal 7. The presence of the slag flow inhibitor 1 in the vortex blocks the slag 3 from being drawn down into the vortex to the tap hole 9 and prevents the slag 3 from prematurely mixing with and contaminating the molten metal 7.

Eventually, the vortex draws the slag flow inhibitor 1 towards the tap hole so that it is seated at the tap hole 9 and substantially blocks the tap hole 9 (Figure 4) of the metallurgical vessel 11 as the molten metal 7 is being poured therefrom.

The passageways 19 and chamber 17 of the slag flow inhibitor 1 initially fill with slag because the slag flow inhibitor is placed into the molten metal bath 5 through the slag 3. While not intended to be bound hereby, it is believed that as the slag flow inhibitor 1 is drawn into the vortex, the slag flow inhibitor 1 spins, and the resulting centrifugal force causes the slag 3 to discharge from the chamber 17 through the side passageways 19 of the slag flow inhibitor 1. As the rate of spin of the slag flow inhibitor 1 slows, the emptied chamber 17 and passageways 19 fill with the molten metal 7 and the slag 3 to the levels that are represented by the relative portions of the slag flow inhibitor 1 that are within the molten metal 7 and slag 3, respectively, of the molten metal bath 5.Thus, when the slag ball 1 is in place at the tap hole 9, the portion of the slag flow inhibitor 1 within the slag 3 portion of the bath 5 fills with slag 3. Similarly, molten metal 7 flows into the passageways 19 and chamber 17 within the molten metal 7 portion of the bath 5, and from the lower passageways 19 through the tap hole 9, as indicated by the arrows in Figures 2 and 4. As the level of molten metal 7 decreases within the vessel 11, the slag 3 replaces the molten metal 7 in the uppermost portions of the passageways 19 and chamber 17 of the slag flow inhibitor 1.

It should be noted that because the slag flow inhibitor 1 is larger than the tap hole 9, more passageways 19 are exposed to the molten metal bath 5 than are exposed to the tap hole 9 when the slag flow inhibitor is seated at the tap hole 9.

Thus, the molten metal 7 builds up within the chamber 17 and passageways 19 of the slag flow inhibitor 1. Because of the build-up of molten metal 7 within the chamber 17 and passageways 19 of the slag flow inhibitor 1, and because the density of the slag 3 is less than that of the molten metal, the pressure of the slag 3 within the chamber 19 and upper passageways 19 is not sufficient to force any of the slag 3 through the molten metal 7 and lower passageways 19 to the tap hole 9. Thus, the molten metal 7 can flow through the passageways 19 and chamber 17 of the slag flow inhibitor 1 to be discharged from the metallurgical vessel 11 through the tap hole 9 prior to any significant amount of slag 3 being able to flow through the tap hole 9.

Use of the present slag flow inhibitor 1 allows for improved recovery of the molten metal 7 from the metallurgical vessel 11 over currently available slag flow inhibitors. A significant portion of molten metal 7, which would be trapped within the metallurgical vessel 11 using currently available slag flow inhibitors, can flow through the passageways 19, chamber 17 and the tap hole 9 of the present slag flow inhibitor 1 to be discharged from the metallurgical vessel 11.

Claims (14)

1. A slag flow inhibitor for inhibiting the flow of the slag of a molten metal bath through a tap hole of a metallurgical vessel comprising: a hollow body having an outer shell defining an inner chamber, said shell having a plurality of passageways spaced substantially evenly about said shell extending through said shell from the surface of said shell to said chamber, said shell being formed of a heat stable refractory material having a density which is greater than that of the slag and less than that of the molten metal in said molten metal bath so that said slag flow inhibitor floats at the interface between that molten metal and the slag;; said slag flow inhibitor being adapted to substantially block a said tap hole of a said metallurgical vessel as the said molten metal is being tapped therefrom so that when said slag flow inhibitor is in position at a said tap hole, the said molten metal can flow through said passageways and chamber of said slag flow inhibitor to be discharged from the said metallurgical vessel through the said tap hole prior to any significant amount of said slag being able to flow through said tap hole.

2. The slag flow inhibitor of claim 1 in which said hollow body is a hollow sphere.

3. The slag flow inhibitor of claim 2 in which said hollow sphere has an outer diameter of between about 25 cms and 46 cms (10 and 18 inches).

4. The slag flow inhibitor of claim 2 or 3 in which said hollow sphere has an inner diameter of between about 15 and 41 cms (6 and 16 inches).

5. The slag flow inhibitor of any one of the preceding claims in which said passageways are cylindrical.

6. The slag flow inhibitor of claim 5 in which said shell has twelve said passageways, each said passageway having a cross-sectional diameter of about 7.5 cms (3 inches).

7. The slag flow inhibitor of claim 1 in which said hollow body is a hollow tapered polygon having a weighted apex.

8. The slag flow inhibitor of claim 1 in which said hollow body is a hollow polyhedron.

9. The slag flow inhibitor of claim 1 in which said hollow body is a hollow modified cone.

10. A metallurgical slag flow inhibitor substantially as herein described with reference to and as shown in Figures 1 to 4 of the accompanying drawings.

11. A metallurgical slag flow inhibitor substantially as herein described with reference to and as shown in Figure 5 of the accompanying drawings.

12. A metallurgical slag flow inhibitor substantially as herein described with reference to and as shown in Figure 6 of the accompanying drawings.

13. A metallurgical slag flow inhibitor substantially as herein described with reference to and as shown in Figure 7 of the accompanying drawings.

14. Any novel feature or combination of features disclosed herein.