AU2001256017A1

AU2001256017A1 - Refractory component and assembly with improved sealing for injection of an inert gas

Info

Publication number: AU2001256017A1
Application number: AU2001256017A
Authority: AU
Inventors: Eric Hanse; Johan Richaud
Original assignee: Vesuvius Crucible Co
Current assignee: Vesuvius Crucible Co
Priority date: 2000-04-28
Filing date: 2001-04-27
Publication date: 2001-11-12
Also published as: BR0110284A; TW494139B; WO2001083138A1; CA2406828A1; RU2002128609A; AR028542A1; PL357772A1; ZA200207839B; MXPA02010599A; US20030090043A1; JP2003531728A; CN1444514A; KR20030004368A; EP1296787A1; SK15162002A3

Description

Refractory component and assembly with improved sealing for injection of an inert gas.

[0001] The present invention relates to a refractory component used in the processing of a metal in the molten state, for example steel, fitted with a gas supply and providing improved sealing. In particular, the invention relates to such a component used in continuous casting of a metal in the molten state. [0002] It is known that casting of a liquid metal is generally carried out by means of an installation comprising various refractory components forming a channel between two successive metallurgical vessels. These refractory components perform various functions, namely conveyance of the liquid metal, protection of the liquid metal against cooling and chemical attack from the surrounding atmosphere and, where appropriate, regulation of the rate of pouring of the liquid metal. These components may be, for example, an inner nozzle supported on a well block integral with the bottom of the upper metallurgical vessel, a submerged entry nozzle or a pouring shroud, a collector nozzle, or the fixed or mobile plates of a slide valve. [0003] The joint surfaces between these various components forming a pouring channel all constitute points of potential ingress for the ambient air. In effect, by virtue of the flow of liquid metal through the pouring channel, substantial negative pressure is generated which is conducive to air ingress through these joint surfaces. The detrimental effects of such air ingress (nitrogen and oxygen) on the quality of the cast metal are known, and efforts have been made over a long period of time to remedy this. [0004] One of the known solutions in the current state of the art involves injecting an inert gas, for example argon, into the joint surface between two adjacent refractory components in the pouring channel. This injection may be effected for example via a groove made for this purpose in the surface of at least one of the components. To be effective, this groove must as far as possible encircle the pouring orifice so that the inert gas which is under positive pressure can prevent any ingress of air into the pouring channel. Recently, an improvement to this system was proposed in international patent application WO 98/ 17421, involving the additional injection of a seaJing agent in suspension in a carrier fluid (which may be an inert gas) so that any sealing defect liable to appear between two adjacent surfaces during casting is immediately eliminated. [0005] Another known solution in the current state of the art entails injecting an inert gas directly into the pouring channel so as to form a protective barrier against pollution by the ambient air along the entire length of the pouring channel. In this case, the injection of inert gas into the liquid metal is generally carried out by diffusion through a porous wall of the component forming part of the pouring channel or, in another known variant, via one or more orifices in form of holes or slots arranged around the pouring channel.

[0006] Furthermore, a method is also known wherein an inert gas is injected directly into the pouring channel in a manner such that the inert gas cooperates mechanically with the liquid metal. The purpose of this type of inert gas injection may be to protect against erosion of certain refractory components located downstream of the injection point and which are particularly susceptible to the erosive action of the stream of liquid metal, such as for example the edges of the pouring orifice of the mobile plate of a slide valve designed to regulate the rate of flow. Another known effect of injecting an inert gas into a pouring channel is that it reduces problems of clogging of the pouring channel. In effect, problems due to the formation of alumina deposits against the walls of the pouring channel have been known for a long time, particularly in the case of casting of alurrtiniuin-killed steels. The inert gas thus injected downstream of a point where this type of clogging can occur mechanically, or even thermally, isolates the liquid metal from the pouring channel and, consequently, prevents or reduces the formation of such deposits.

[0007] Finally, it is also possible to inject a gas for the purpose of cooling the refractory component in question. It will be noted that the invention also relates to components used for the injection of gas into the bottom of a metallurgical vessel containing a bath of metal in the molten state, such as for example porous plugs.

[0008] For the purposes of the present patent application, the expression "injection of gas" will therefore refer both to the direct injection of an inert gas into a pouring channel or into the bottom of a metallurgical vessel and to the injection of an inert gas (or a sealing agent in suspension in a carrier fluid as described in international patent application

WO 98/ 17421) into the joint surface between two adjacent refractory components of a pouring channel via a groove encircling at least partially the pouring orifice of the liquid metal, or to the injection of a cooling gas. [0009] The refractory components designed for the injection of an inert gas generally include means of delivering the gas to the means of injection (via a groove or the pouring channel). However, assemblies of refractory components are known in which the means of delivery and means of injection of the gas are provided by adjacent inter- communicating components (possibly they may even be separated by intermediate refractory components, the essential feature being that the gas can be transferred from the means of delivery to the means of injection) . For the purposes of the present patent application, where reference is made to a component equipped with means of delivery and means of injection of gas, this will refer equally to a component including both means of delivery and means of injection of gas or a component fitted with means of delivering gas and means of transfer and/ or communication to means of injection which may be provided by another refractory component.

[OOIO] The means of delivery generally include an inlet aperture opening on the outside wall of the refractory component and connected to a gas delivery line. This delivery line is connected to the fixed gas supply circuit of the casting installation, possibly via flexible pipes protected against thermal radiation. Conventionally, during the fabrication of said refractory component, a metal connector is mounted in the inlet aperture; the connector and the material then form an integral assembly upon sintering of the constituent refractory material of the component. The connector can then be connected to the gas delivery line by screwing (either the connector is fitted with a male threaded part projecting beyond the component onto which the female end of the line is screwed, or the connector has a female thread into which the male-threaded end of the line is screwed), by welding or by various means of mechanical coupling. These means of gas delivery are not entirely satisfactory in that, firstly, it is not obvious that a threaded joint can be made airtight, and particularly a joint that will remain airtight at the very high temperatures to which the installation is subjected during casting operations and, secondly, by virtue of the difference between the coefficients of expansion of the metal of which the connector is made and the refractory material, it is inevitable that the sealing tightness between the connector and the refractory will gradually deteriorate. The negative effects of this loss of sealing tightness are three-fold: firstly, the quantities of gas to be injected are that much greater (the high price of inert gases such as argon is well known), secondly, as indicated above, given that the whole of the pouring channel is under negative pressure relative to the ambient environment, there is a risk that air will be drawn in through these defective joints and, thirdly, in case of loss of sealing tightness, precise control of the quantity of gas actually injected into the system is lost and it becomes impossible to establish a perfectly reproducible system. [0011] Various attempts have been made to improve this situation, such as for example "packing" the refractory component in a metal casing incorporating an aperture at the connector, welding to ensure mechanical retention of the connector and improve the gas tightness. A number of drawbacks associated with this "improvement" have already been reported. For instance, as the connector is integral with the metal casing, it has a tendency to work loose from the refractory material and to move about in its seating, which gives rise to losses of inert gases and, as indicated above, ingress of air into the liquid metal.

[0012] More recently, a very simple device was proposed in European patent application EP 703,028 for the delivery of inert gas to an inner nozzle, wherein the external surface of the refractory component receiving the gas feed simply incorporates a gas inlet aperture against which a connection fitting connected to an inert gas delivery line is held in compression. Where appropriate, it may even be possible to provide a seal between the fitting and the inlet aperture.

[0013] Although this device greatly improves the situation, the applicant observed that it was not yet wholly satisfactory in that sealing tightness between the connection fitting and the gas inlet aperture at the surface of the component was not totally assured, even when a seal is engaged between the fitting and the aperture.

[0014] A refractory component provided with means of injecting or conveying gas and means of delivering said gas from an external wall of the component to said means of injection, the means of delivery of the gas comprising a part of enlarged cross-section extending from an external wall of the component and a part of reduced cross-section comrnunicating, at one end, with the inner end of the part of enlarged cross-section and, at the other end, with the means of injecting or conveying gas, the said component also comprising a seal fitted against the inner end of the part of enlarged cross-section, said seal, comprising an orifice at least partially in register with the commumcating orifice between the parts of enlarged and reduced cross-section is known from FR-A-2,763,012. [0015] By virtue of this particular arrangement of the refractory component, the gas delivery line can be engaged more deeply into said component so that, when an appropriate seal is fitted therein, sealing tightness is assured not only at the cornmunication between the two parts of the means of delivery, but also at the walls of the part of enlarged cross-section. A very substantial improvement in sealing tightness compared with the device disclosed in European patent application 703,028 (reduction of the consumption of inert gas, reduction of air ingress, and precise control of the quantity of gas injected) was observed. However, it is desirable to still improve the sealing tightness. [0016] According to the invention, the seal presents a cross-section substantially similar to the cross- section of the enlarged part. Thus, when the seal is placed in compression in an appropriate manner, it bears not only on the end of the part of enlarged cross-section, but also on the side walls of the latter, thereby providing an even tighter seal. [0017] It is advantageous that the thickness of the seal does not exceed the depth of the part of enlarged cross-section, otherwise, under the effect of compression by the gas delivery line, the plastic seal will bear on the rim of the outer orifice of the means of delivery as it deforms, and sealing tightness will no longer be assured at the inner end of the part of enlarged cross-section.

[0018] According to a particular embodiment of the invention, the inner end of the part of enlarged cross-section forms a surface presenting an orifice, the said parts of enlarged and reduced cross-section communicating via this orifice. In this way, it is possible to use a gas delivery line of essentially tubular form.

[0019] Advantageously, the part of enlarged cross- section consists of a bore of substantially circular cross-section which is easy to make. [0020] Provision can also be made so that the surface forming the inner end of the part of enlarged cross-section is flat and essentially orthogonal to the axis of the bore. Not only is this arrangement easy to achieve, but its sealing tightness will be improved where it is made by the pressing of parallel elements.

[0021] According to a particular aspect of the invention. The thickness of the seal does not exceed the depth of the part of enlarged cross-section. It is to be noted that the seal can be made integral with the component.

[0022] Advantageously, the seal presents a cross-section substantially similar to the cross-section of the enlarged part. Thus, when the seal is placed in compression in an appropriate manner, it bears not only on the end of the part of enlarged cross-section, but also on the side walls of the latter, thereby providing an even tighter seal. It is essential that the thickness of the seal does not exceed the depth of the part of enlarged cross- section, otherwise, under the effect of compression by the gas delivery line, the plastic seal will bear on the rim of the outer orifice of the means of delivery as it deforms, and sealing tightness will no longer be assured at the inner end of the part of enlarged cross- section.

[0023] Preferably, the seal takes the form of a washer. Provision may be made however for a stack of such washers depending on the required thickness of the seal. The person skilled in the art will readily determine the optimal thickness of the seal. [0024] Advantageously, the seal is made of a plastic material so that, at operating temperatures, it is able to deform sufficiently when pressure is exerted on it to form a tight seal with the bottom wall and with the side walls of the end of the part of enlarged cross- section. Clay and graphite are materials potentially suitable for such use, graphite being the preferred choice.

[0025] According to another of its aspects, the invention relates to an assembly including a refractory component as described above and a gas delivery line, wherein one end of the gas delivery line is engaged in the part of enlarged cross-section which holds the seal in compression at the inner end and against the side walls of the part of enlarged cross- section. The advantages of such an assembly have already been described above. [0026] According to a particular embodiment of the invention, the refractory component is fitted with a metal casing (in the case of an inner nozzle for example) or band (in the case of a slide valve plate for example) covering it at least partially in the area of the gas delivery means. It is thus possible to form a solid attachment between the delivery line (by welding or screwing) and the casing or band, thereby avoiding accidental loss of sealing tightness in case of vibration for example.

[0027] Advantageously, the end of the line engaged in the part of enlarged cross-section is configured so as to form a tight joint with the seal. For example, the end may be shaped as a cone or truncated cone so that it "keys" into the joint. As a variant, the end of the line may be threaded to enable the line to "screw" into the joint. Provision may also be made for a self-tapping end so that a perfectly fitting thread is formed in situ in the seal and the line/ seal joint is totally tight. According to this variant, it is advantageously the action of screwing the end of the line into the seal that compresses said seal towards the side walls of the part of enlarged cross-section.

[0028] Finally, according to a most particular embodiment of the invention, the part of enlarged cross-section is sufficiently deep so that, under the effect of thermal expansion of the end of the line engaged in the part of enlarged cross-section, the compression of the seal increases. In effect, once the line is made solid with the casing or band, its only possibility of expansion is towards the end of the part of enlarged cross-section where the seal is located.

[0029] In order to better explain the invention, two embodiments given by way of a non- limitative example are described below with reference to the attached diagrams in which :

- figure 1 is an axial sectional view of an inner nozzle; - figure 2 is an enlarged view of the circle I in figure 1.

- figure 3 is an axial sectional view of a slide valve plate. [0030] Figure 1 shows an inner nozzle 1 comprising a refractory body 2 forming a pouring channel 3 and a plate 4. The inner nozzle 1 also includes means of injecting gas, for example an inert gas such as argon, into the pouring channel 3. These means of injecting gas are formed for example by a sleeve 5 in porous material mounted in a groove 6 formed in the refractory body 2. The groove 6 is connected to means of delivery of gas (7, 8) . As shown in figure 1, these means of delivery may emerge at the upper surface of the plate 4. Also shown is part of the gas delivery line 9, together with a metal casing 10 surrounding the plate 4 of the inner nozzle. [0031] Figure 2 shows the details of the connection between the gas inlet and the means of delivery of the gas at the plate 4 of the inner nozzle. These means of delivery of gas include a part of enlarged cross-section 7 and a part of reduced cross-section 8 cornπiunicating via an orifice 11. The inner end of the part of enlarged cross- section is fitted with a seal 12 for example in graphite. Also shown is one end of the gas delivery line 9 engaged in the part of enlarged cross-section 7. It can be seen that the line 9 is made solid with the casing 10 by means of a circular weld 13.

[0032] Figure 3 shows a refractory plate 14 of a slide valve presenting an orifice 15 for the pouring of metal. The plate is provided with a circular groove 16 circumscribing the pouring orifice 15 and forming with the surface of the refractory part (not shown) adjacent to the plate 14 a channel for the injection of a gas between these adjacent parts. The groove 16 is connected to gas delivery means including a portion of enlarged cross- section 17 and a portion of reduced cross- section 18 corriinunicating via an orifice 21. Also shown is the gas delivery line 19 engaged in the part of enlarged cross-section and made solid with the metal band 20 of the plate 14 by a spot weld 23. When the plate is in service, under the effect of the temperature to which the assembly is raised, the part of the line 19 between the spot weld 23 and its inner end expands towards the inner end of the enlarged part 17 and compresses the seal 22.

References:

1. Inner nozzle

2. Refractory body

3. Pouring channel 4. Plate

5. Porous sleeve

6. Groove

7. Part of enlarged cross- section

8. Part of reduced cross-section 9. Gas delivery line

10. Metal casing

11. Communication orifice

12. Seal

13. Weld 14. Plate

15. Pouring orifice of the plate

16. Gas circulation groove

17. Part of enlarged cross-section

18. Part of reduced cross- section 19. Gas delivery line

20. Metal band

21. Communication orifice

22. Seal

23. Weld

Claims

Claims.

1. Refractory component (1, 14) provided with means of injecting or conveying (5, 16) gas and means of delivering said gas from an external wall of the component to said means of injection (5, 16), the means of delivery of the gas comprising a part of enlarged cross-section (7, 17) extending from an external wall of the component and a part of reduced cross-section (8, 18) communicating, at one end, with the inner end of the part of enlarged cross- section (7, 17) and, at the other end, with the means of injecting or conveying gas (5, 16), the said component also comprising a seal (12, 22) fitted against the inner end of the part of enlarged cross-section, said seal (12, 22), comprising an orifice at least partially in register with the communicating orifice (11, 21) between the parts of enlarged and reduced cross-section, characterised in that the seal (12, 22) presents a cross-section substantially similar to the cross- section of the enlarged part (7, 17).

2. Refractory component according to claim 1, characterised in that the inner end of the part of enlarged cross- section (7, 17) forms a surface presenting an orifice (11, 21), the said parts of enlarged (7, 17) and reduced (8, 18) cross- section communicating via this orifice (11, 21).

3. Refractory component according to claim 1 or 2, characterised in that the part of enlarged cross-section (7, 17) consists of a bore of substantially circular cross- section.

4. Refractory component according to claim 3, characterised in that the surface forming the inner end of the part of enlarged cross-section (7, 17) is flat and essentially orthogonal to the axis of the bore.

5. Refractory component according to any of claims 1 to 4, characterised in that the thickness of the seal (12, 22) does not exceed the depth of the part of enlarged cross-section (7, 17).

6. Refractory component according to claim 5, characterised in that the seal (12, 22) is constituted of one or more washer(s) in a plastic material.

7. Assembly including a refractory component (1, 14) according to any of claims 5 to 6 and a gas delivery line (9, 19), wherein one end of the gas delivery line holds the seal (12, 22) in compression against the side walls of the part of enlarged cross-section (7, 17).

8. Assembly according to claim 7, characterised in that the refractory component is provided with a metal casing (10) or band (20), in that the gas delivery line

(9, 19) passes through or is contiguous with said casing or band, and in that a solid connection is made between the line and the casing or band.

9. Assembly according to one of claims 7 or 8, characterised in that the end of the gas delivery line (9, 19) engaged in the refractory component is configured so as to form a tight joint with the seal (12, 22).

10. Assembly according to claim 9, characterised in that the end of the gas delivery line (9, 19) engaged in the refractory component comprises a thread which engages in the seal.

11. Assembly according to claim 9, characterised in that the end of the gas delivery line (9, 19) engaged in the refractory component is shaped as a cone or truncated cone which engages in the seal (12, 22).

12. Assembly according to any of claims 7 to 11, characterised in that the part of enlarged cross-section (7, 17) is sufficiently deep so that, under the effect of expansion of the part of the gas delivery line (9, 19) engaged in said part of enlarged cross-section, the seal (12, 22) is compressed against the inner end and against the side walls of the part of enlarged cross-section (7, 17).