GB2307876A

GB2307876A - Metering nozzle for a tundish

Info

Publication number: GB2307876A
Application number: GB9525247A
Authority: GB
Inventors: Michael Anthony Roberts
Original assignee: Flogates Ltd
Current assignee: Flogates Ltd
Priority date: 1995-12-09
Filing date: 1995-12-09
Publication date: 1997-06-11
Also published as: WO1997021511A1; ZA9610365B; GB9525247D0; AU1069297A

Abstract

A composite refractory insert for a melt containment vessel metering nozzle comprises a refractory inner component defining a flow passage for the melt and a refractory outer component defining an outer dimension of the insert. The insert can be positioned within a hollow recess in a pre-formed refractory metering nozzle body. The insert is produced by forming the inner component of zirconia by a pressing technique and the outer component by casting an alumina composition around the inner component. The nozzle may be formed by moulding a refractory alumina composition using a shaped mandrel to form the hollow recess.

Description

METERING NOZZLE This invention relates to metering nozzles, and is more particularly concerned in one aspect with a metering nozzle for a tundish.

A conventional tundish, for example, of the type used in continuous metal casting, will have a refractory lining and a metering nozzle located within a well nozzle or a seating block in or adjacent the lining of the tundish bottom.

In use, the metering nozzle is subjected to very severe thermal and mechanical stresses during teeming, and erosion of the bore or flow passage of the nozzle is very rapid, leading to frequent replacement of the nozzle.

In order to facilitate the replacement of the metering nozzle, it has been proposed to locate the metering nozzle in a nozzle change device which comprises a slide gate mechanism situated adjacent to the base of the tundish. The nozzle change device is a simple form of slide gate valve which provides the facility to eject the metering nozzle (also called a collector nozzle) and replace it with a new metering nozzle. Thus, if there are any problems during operation, typically either nozzle bore erosion leading to excessive metal flow into the continuous casting machine, or nozzle restriction leading to reduced or blocked metal flow into the continuous casting machine, the metering nozzle can be replaced and casting continued.

The metering nozzle may be attached to, or integrally cast or moulded with, a fixed plate or a sliding plate of the nozzle change device, to permit controlled pouring of molten metal in a compact stream.

In order to increase the life of the metering nozzle, the metering nozzle is provided with an insert of a refractory material, which, though more expensive than the alumina used for the tundish lining, is more resistant to the thermal and mechanical stresses involved in teeming. These inserts can be formed, for example, from zirconia, magnesite, or an alumina-earth composition. In manufacturing the metering nozzle, the insert is separately produced, and the body of the nozzle moulded or cast therearound, and directly against the outer wall of the insert, such that the body of the nozzle surrounds the insert. On drying and curing, the moulded or cast nozzle body shrinks very slightly so that the interface joint with the insert is tight and the body develops a degree of compressive force onto the insert, which gives added strength.

A disadvantage of the present metering nozzles is the expense of the insert, since, in current designs, the insert is not replaceable. It would therefore be a great improvement if a metering nozzle could be produced wherein the worn insert could be replaced without the need to discard the entire nozzle.

In the conventional tundish design this is not possible because the metering nozzle in its well nozzle (or seating block) is destroyed on wrecking the tundish lining. The use of a nozzle change device enables the used composite nozzle to be recovered and offers the opportunity to replace the expensive insert and reuse the composite nozzle.

However, difficulties have been experienced in that it is not possible to remove the insert from a conventional metering nozzle without shattering or damaging the nozzle body.

Attempts by the present applicants to pre-cast the body of the metering nozzle with a hollow recess, and then fix a replaceable insert into place in the recess with a suitable cement have not met with success for the following reasons: (i) The compressive force exerted by the cast body in the direct joint technique previously used and described above was lost. The highly refractive and erosion resistant materials used for the inserts, for example, zirconia, have relatively poor thermal shock resistance and it has been found that cracks and crazes can develop in the insert during metal teeming.Since the compressive force from shrinkage of the body is not available, the thermal shock experienced can result in metal penetration behind the zirconia insert, leading to potential catastrophic failure of the zirconia insert with pieces of the insert breaking off and being carried by the metal stream into the continuous casting mould.

In addition, after several heats, metal penetration of the mortar joint can prohibit "push-out" of the worn zirconia insert and replacement with a new insert.

(ii) The aspect ratio of the zirconia insert required for the metering nozzle, coupled with the high density required to give long life without bore erosion, favours isostatic pressing and this is the optimum processing route for manufacturing the zirconia insert.

The isostatic pressing technique permits very accurate bore diameters to be manufactured, but provides unsatisfactory control of the outer dimensions of the insert. A further machining operation is therefore required to achieve the necessary tight tolerances on the outer dimensions to fit the recess in the pre-formed body. The cost of this extra machining step is generally prohibitive.

As a result of the poor tolerances of the outer dimensions of the insert, it has been found in practice that the insert cannot be accurately fitted into the hollow recess of the preformed metering nozzle body.

Some inserts are too loose, increasing the possibility that metal can penetrate the mortar joint, and others are oversize, such that they cannot be fitted into the recess provided at all.

According to the present invention, an insert for a metering nozzle is provided with an outer refractory sheath component which permits more accurate control of the outer dimensions of the insert.

In one aspect, the invention provides a composite refractory insert for a melt containment vessel metering nozzle, which comprises a refractory inner component defining a flow passage for the melt, and a refractory outer component defining the outer diameter of the insert.

In another aspect, the invention provides a metering nozzle for a melt containment vessel, which comprises a refractory body provided with a hollow recess and a composite refractory insert positioned therein, the insert comprising a refractory inner component defining a flow passage for the melt, and a refractory outer component defining an outer dimension of the insert.

In a further aspect, the invention provides a method for the manufacture of a metering nozzle for a melt containment vessel, which comprises forming a refractory nozzle body provided with a hollow recess, forming a composite refractory insert for the metering nozzle by providing an inner refractory component defining a flow passage for the melt and forming a refractory outer component therearound to define an outer dimension of the insert, such that the insert is a tight fit into the hollow recess, and cementing the insert into the hollow recess.

In a still further aspect, the invention provides a nozzle change device provided with a metering nozzle according to the invention.

Preferably the refractory outer component of the insert is cast around the inner refractory component in the form of a sheath, such that, on drying and curing, it exerts a shrinkage force on the inner refractory component.

The refractory inner component of the insert is selected from a first refractory material that has a high resistance to thermal and mechanical stresses.

Zirconia is preferred, although other refractory materials, such as, magnesite and various refractory alumina-earth compositions are not excluded from the invention. Preferably the inner component has a relatively constant wall thickness, and preferably a bell-shaped mouth and a corresponding bell-shaped outer periphery.

The refractory outer component can be formed from any suitable second refractory material, but usually comprises a refractory material different from that of the inner component. The outer component is preferably formed from an alumina casting composition, or similar inexpensive casting or moulding material and is preferably cast or moulded as a sheath around the inner component. The outer wall of the outer component of the insert is preferably tapered, at least for part of its length, and is preferably provided with a step or shoulder positioned at a point or region along the length thereof.

In a preferred embodiment of a refractory insert according to the invention, the refractory inner component comprises zirconia, which has been formed by a pressing technique, for example, isostatic pressing, and the outer sheath component comprises a cast alumina composition. In this way, very tight tolerances for the bore of the nozzle and for the outer dimensions of the insert can be achieved.

The metering nozzle body is preferably cast from a refractory alumina, or similar casting or moulding composition, using an appropriately shaped mandrel to form the hollow recess. The casting technique enables a very good control of the dimensional tolerances of the hollow recess in the pre-formed body to be maintained.

In a preferred embodiment of a metering nozzle according to the invention, the hollow recess of the nozzle body and the outer wall of the insert outer component are provided with cooperating shoulders which, when the insert is positioned in the recess, are spaced apart by a distance of from, for example, 2mm to 6mm, in order to provide a reservoir for the cement or mortar joining the nozzle body and the insert.

In assembling the metering nozzle, cement or mortar can be placed around the shoulder region and the components pressed together, forcing the cement from the shoulder region along the interface between the body and the composite insert.

An embodiment of a metering nozzle according to the invention will now be described, by way of example only, with reference to the accompanying Drawings in which: Figures l(a) and (b) show a prior art metering nozzle provided with a zirconia insert, respectively in sectional side elevation and end elevation.

Figures 2(a) and (b) show an insert for a metering nozzle according to the invention respectively in sectional side elevation and end elevation; Figures 3(a) and (b) show a body for a metering nozzle according to the invention respectively in sectional side elevation and plan view; and Figures 4(a) and (b) show an assembled metering nozzle according to the invention respectively in sectional side elevation and plan view.

Referring firstly to Figure 1, there is shown a prior art metering nozzle illustrated generally at 1, having a tubular zirconia insert 2, with a melt flow passage or bore 3, and a nozzle body 4 formed from a castable alumina composition. Integrally formed with the nozzle body 4 is a base or plate 5, which is surrounded by a metal bush or bottom can 6.

In practice, the zirconia insert is first produced by isostatic pressing, and the alumina body 4 is then directly moulded or cast around the insert 2. The shrinkage forces developed during drying and curing of the nozzle body 4 enable the body to grip the insert 2 very tightly, but have the disadvantage that the insert cannot be removed without destroying the body.

Figure 2 shows a composite insert according to the invention, illustrated generally at 10. The insert comprises an inner zirconia component 11, having a bore 12 and an outer alumina sheath 13. The inner component 11 is again formed by isostatic pressing of zirconia, and has a rather more bell-shaped mouth region, internally and externally, than the conventional zirconia insert.

The outer sheath component 13 is formed from a castable alumina composition and is cast directly onto the inner zirconia component of the insert 11. By casting in this way, it is possible to obtain very accurate outer dimensions for the outer sheath component 13, and, because the outer sheath component is cast directly onto the inner zirconia component, on drying and curing it exerts a shrinkage force upon the inner zirconia component giving a tight joint and an improved thermal shock resistance.

The outer wall 17 of the sheath 13 is tapered from the mouth to the outlet, which enables the entire composite insert 10 to be knocked or pushed out of the nozzle body as will be described hereinafter. A suitable taper is from 89" to 80 , for example about 85".

The outer wall 17 of the sheath 13 is also provided with a shoulder or step 16, having an angle of from about 110 to 140 , for example 1200, the function of which will also be described hereinafter.

Turning now to Figure 3, the body 20 of the metering nozzle comprises a generally tubular portion 21 integrally formed with a rectangular plate 22, the latter being surrounded by a metal bottom can 23. A tubular recess 24 in the nozzle body 20 is shaped to receive the composite insert 10 of Figure 2, having a tapering region 25 and a shoulder 26.

The body 20 can readily be formed by casting an alumina castable composition using a mandrel of outer configuration of, for example, approximately 2mm greater than the configuration of the composite insert 10.

The assembled metering nozzle is shown in Figure 4 and illustrated generally at 30.

In assembling the metering nozzle 30, the composite insert 10 is positioned within the recess 24 of the nozzle body 20, and, due to the tapering of the inner wall 25 of the body recess 24 and the outer wall 17 of the sheath 13, the insert 10 is a tight fit in the body 20.

Shoulders 16 and 26, respectively on the composite insert 10 and the body 20 are arranged such that, when the insert and body are assembled together, a small annular gap 31 remains between them. Prior to assembly, mortar or cement is placed around either or both of shoulders 16 and 26 such that, on assembly of the composite insert and body, the mortar or cement is compressed in the annular gap 31 and spreads along the interface between the insert 10 and the body 20, forming a good bond and seal to prevent metal ingress.

The assembled metering nozzle can be placed in a nozzle change device as described hereinbefore. Whilst this is the preferred method of implementing the invention, it will be recognised that, in suitable circumstances, it would be possible to form a metering nozzle which could be located, for example, within the lining of a tundish bottom.

When the zirconia inner component 11 finally becomes too worn for further pouring, it is a simple matter to tap out the composite insert 10 from the body 20, leaving the body intact such that a replacement composite insert can be positioned in the recess 24 and cemented in place.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A composite refractory insert for a melt containment vessel metering nozzle, which comprises a refractory inner component defining a flow passage for the melt, and a refractory outer component defining the outer diameter of the insert.

2. An insert according to Claim 1, in which the refractory outer component is cast around the refractory inner component in the form of a sheath, such that, after casting, the refractory outer component exerts a shrinkage force on the refractory inner component.

3. An insert according to Claim 1 or 2, in which the refractory inner component comprises zirconia.

4. An insert according to any of the preceding claims, in which the inner component has a bell-shaped mouth and a corresponding bell-shaped outer periphery.

5. An insert according to any of the preceding claims, in which the refractory outer component is formed from an alumina casting composition.

6. An insert according to any of the preceding claims, in which the outer wall of the outer component is tapered, for at least a part of its length.

7. An insert according to any of the preceding claims, in which the outer wall of the outer component is provided with a step or shoulder.

8. An insert according to any of the preceding claims, in which the refractory inner component comprises zirconia, which has been formed by a pressing technique, and the outer component comprises alumina and has been formed by casting an alumina casting composition.

9. A composite refractory insert for a melt containment vessel metering nozzle substantially as hereinbefore described with reference to and as illustrated in Figures 2 to 4 of the accompanying Drawings.

10. A composite refractory insert for a melt containment vessel metering nozzle substantially as hereinbefore described.

11. A metering nozzle for a melt containment vessel, which comprises a refractory body provided with a hollow recess and a composite refractory insert positioned therein, the insert comprising a refractory inner component defining a flow passage for the melt, and a refractory outer component defining an outer dimension of the insert.

12. A nozzle according to Claim 11, in which the body comprises a cast or moulded refractory alumina composition.

13. A nozzle according to Claim 11 or 12, in which the body and the composite insert are each pre-formed before assembling them together.

14. A nozzle according to any of Claims 11 to 13, in which the outer wall of the outer component of the insert and the inner wall of the hollow recess are each provided with a complementary taper.

15. A nozzle according to any of Claims 11 to 14, in which the hollow recess of the nozzle body and the outer wall of the insert are provided with cooperating shoulders.

16. A nozzle according to Claim 15, in which, when the body and the insert are assembled together, the cooperating shoulders are spaced apart by a distance of from 2mm to 6mm.

17. A nozzle according to any of Claims 11 to 16, which comprises a composite refractory insert according to any of Claims 1 to 10.

18. A nozzle according to any of Claims 11 to 17 substantially as hereinbefore described with reference to and as illustrated in Figures 2 to 4 of the accompanying Drawings.

19. A metering nozzle for a melt containment vessel comprising a composite refractory insert substantially as hereinbefore described.

20. A method for the manufacture of a metering nozzle for a melt containment vessel, which comprises forming a refractory nozzle body provided with a hollow recess, forming a composite refractory insert for the metering nozzle by providing an inner refractory component defining a flow passage for the melt and forming a refractory outer component therearound to define an outer dimension of the insert, such that the insert is a tight fit into the hollow recess, and cementing the insert into the hollow recess.

21. A method according to Claim 20, in which the outer refractory component of the insert is cast around the inner refractory component in the form of a sheath, such that, after casting, the refractory outer component exerts a shrinkage force on the refractory inner component.

22. A method according to Claim 20 or 21, in which the refractory inner component of the insert is formed from zirconia by a pressing technique, and the outer component of the insert is formed by casting a castable alumina composition around the inner component.

23. A method according to any of Claims 20 to 22, in which the metering nozzle body is formed by casting or moulding a refractory alumina composition using an appropriately shaped mandrel to form the hollow recess.

24. A method according to any of Claims 20 to 23, in which the hollow recess of the nozzle body and the outer wall of the insert are provided with cooperating shoulders, and in which cement or mortar is placed around one or both of the shoulder regions and the insert and the body are pressed together, forcing the cement or mortar from the shoulder region along the interface between the body and the composite insert.

25. A method according to any of Claims 20 to 24 substantially as hereinbefore described.

26. A metering nozzle according to any of Claims 11 to 19, produced by a method according to any of Claims 20 to 25.

27. A nozzle changing device provided with a metering nozzle according to any of Claims 11 to 19 and 26.