WO2002047846A2

WO2002047846A2 - Casting nozzle with gas injection means

Info

Publication number: WO2002047846A2
Application number: PCT/US2001/048216
Authority: WO
Inventors: Patrick Corlas; Bruce Winter; Daniel Leech; Alan Engel; Dominique Janssen
Original assignee: Vesuvius Crucible Co
Current assignee: Vesuvius Crucible Co
Priority date: 2000-12-11
Filing date: 2001-12-06
Publication date: 2002-06-20
Anticipated expiration: 2003-06-11
Also published as: WO2002047846A3; AU2002235199A1

Abstract

A refractory article is described that directs inert gas around a casting channel of a refractory article while reducing leakage. The article is easy to manufacture by conventional techniques. The article comprises a refractory shape within a metal housing. The inner surface of the metal housing includes at least one barrier integrally bonded to the housing. Conveniently, the barrier is a metal washer welded to the inner surface of the housing. The barrier prevents inert gas from leaking along the interface of the refractory shape and the housing. The barrier does not substantially hinder manufacture of the article and can assist production by delimiting the boundaries of refractory compositions.

Description

MECHANICALLY ZONED NOZZLE

Field of the Invention

The present invention relates to a refractory article and method for making the article, where the article is adapted to transport molten steel while enshrouding the molten steel with inert gas. Description of the Prior Art

Oxygen can deleteriously affect steel casting by reacting with the molten steel or a refractory article used to contain or transfer the steel. Problems include, for example, alumina clogging and oxidation of the steel. Manufacturers often take steps to limit contact with oxygen, including encasing refractory articles in a metal housing or shrouding the steel and/or refractory article with inert gas.

These precautions have proven inadequate, awkward or expensive. For example, a metal housing alone does not prevent oxygen from entering at joints between refractory articles. The velocity of the molten steel flowing through the articles exacerbates oxygen penetration by creating a negative pressure, which draws oxygen through the joints. A box containing an overpressure of inert gas, such as described by U.S. Pat. No. 5,368,208, may be built around refractory valves to reduce the ingress of oxygen. While protective, the box limits access to the valve and will often demand large amounts of relatively expensive inert gas as gas leaks from the box or into the molten metal.

An alternative to a box includes a refractory article into which inert gas is directly injected. The inert gas will, in theory, perfuse through the inherently porous refractory article, thereby enshrouding the molten steel with inert gas. Unfortunately, the inert gas will not normally distribute itself uniformly through the article and gas can escape through the outer surface of the article. Inert gas will penetrate more permeable zones of the article in preference to less permeable zones. A metal housing often surrounds the outer surface of the refractory article, thereby preventing inert gas from escaping from the outer surface. Gas is still capable of escaping along the interface between the metal housing and the article.

Prior art has attempted to focus or direct inert gas in the refractory article where needed. Proposed solutions include micro-holes, porous refractory compositions, passages, and distributors or inserts for channeling inert gas to critical areas. U.S. Pat. No. 4,632,283 describes a refractory plate having a series of micro- holes for delivery of inert gas to precise points in the refractory article. The holes are too narrow to permit ingress of steel, but do allow injection of inert gas. U.S. Pat. No. 4,836,508 teaches a porous gas insert near the top of a shroud. The insert is intended to direct inert gas to the junction of the shroud and a nozzle, thereby inhibiting air infiltration to the molten steel through the junction. U.S. Pat. No. 5,723,055 includes both a porous refractory and a distributor for directing inert gas to the stopper seat at the top of a well block nozzle. Bubbles of inert gas rising up from the seat are described as reducing alumina clogging. Unfortunately, high ferrostatic head restricts the amount of gas that actually reaches the seat. U.S. Pat. No. 4,949,885 teaches a channel for inert gas at the junction of a well block nozzle and a shroud. The inert gas is usually expected to diffuse towards the casting channel of the refractory article. Other patents show channels between the refractory article and a metal housing. In both configurations, the gas tends to remain within the channels providing protection over only a fraction of the article. In an attempt to overcome this limitation, U.S. Pat. No. 5,100,035 teaches a nozzle having a plurality of such channels. Leakage still remains a problem as inert gas escapes along and through openings, such as mortar joints.

Despite various attempts to deliver inert gas precisely to critical areas, prior art continues to suffer because of leakage of inert gas. Thermal and mechanical stresses distort refractory articles, open cracks in the article, and cause leaks. Leaks reduce the amount of gas available to protect the steel, so large volumes and an overpressure of inert gas are typically used to ensure a sufficient quantity of inert gas. Overpressure can force inert gas into the steel, thereby reducing the quality of the finished steel.

A need persists for a refractory article that retains inert gas around the molten steel while avoiding excessive leakage of the gas. The article should direct the inert gas to the necessary areas, and preferably will be easy to manufacture. Summary of the Invention The article and method of the present invention involve substantially confining and directing inert gas within a refractory article. The article is tolerant of thermo- mechanical stresses, which can open cracks that permit gas to leak from the article. The article permits positive control of inert gas over a large portion of the article. Advantageously, the manufacture and installation of the article are uncomplicated and can be adapted to standard nozzle designs.

In a broad aspect, the article includes a refractory piece surrounded by a metal housing. At least one gas-impermeable barrier is joined to the interior of the housing and defines a first zone within the housing. The barrier reduces the likelihood that an inert gas injected into the first zone can leak out of the first zone through, for example, mortar joints between the housing and piece. A plurality of barriers may define several zones, which enable an operator to precisely control the amount of inert gas in each.

In a further aspect, the gas-impermeable barrier is a metal shape and is welded to the inside of the housing. The metal shape and housing define a gas-impermeable perimeter around the first zone. The perimeter contains the inert gas despite cracking in the mortar joint or in the refractory piece caused by thermo-mechanical stresses.

Another aspect of the article describes the metal shape as a washer. The washer can separate two different refractory compositions. The compositions may differ in, for example, gas permeability or erosion-resistance. Compositions include, for example, castable refractory materials and particulate refractories. The latter may be resin-bonded or carbon-bonded.

The method of the invention involves constructing an article comprising at least one zone adapted to contain inert gas. Conveniently, at least one gas- impermeable barrier is fixed to the inside surface of a metal housing. The barrier and housing substantially define a perimeter around the zone. The housing is filled with refractory material in a manner known to one of reasonable skill in the art.

In one embodiment, a pressed, particulate refractory material is secured in the housing using mechanical fasteners or mortar. Alternatively, a castable material may be used in combination with or in place of the particulate material. The barrier provides a convenient boundary between different refractory materials comprising the refractory piece. Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments, which refers to the accompanying drawings. Brief Description of the Drawings Figure 1 is a vertical cross-section of a well nozzle of the present invention.

Figure 2 is a vertical cross-section of a well nozzle showing a containment zone for inert gas.

Figure 3 is a vertical cross-section of a well nozzle of the prior art.

Figure 4 is a vertical cross-section of a well nozzle of the present invention showing a refractory piece comprising a castable part and a porous part. Detailed Description of the Preferred Embodiment

Figure 1 shows an article 1 of the present invention, specifically a tundish well nozzle. The article comprises a metal housing 2 substantially surrounding a refractory piece 3. The article 1 is adapted to transfer molten steel from one vessel to another vessel or mold (not shown), and includes a bore 4 adapted to carry the molten steel. The article 1 may be, for example, a nozzle, shroud or slide gate plate. The housing 2 will typically not cover the entire top 5 or bottom 6 of the piece 3 because, in use, these will connect with another article or open into a metallurgical vessel or mold.

The article 1 is adapted to receive a gas connection 7. The gas connection is capable of injecting inert gas through the housing 2. A plurality of channels 8 is often present in the article 1. Conveniently, channels 8 are between the housing 2 and the piece 3; although, channels 8 may be formed using forms, inserts, distributors, and transient materials such as waxes, etc., which are known to one skilled in the art. The article 1 includes at least one substantially gas-impermeable barrier 9 secured to the housing 2 and extending into the refractory piece 3. The barrier 9 extends towards the bore 4, but should terminate short of the bore 4. The exact position of the barrier 9 will depend on casting conditions and the required geometry of the article 1. The junction 10 between the barrier 9 and the housing 2 should be substantially gas-tight. Conveniently, the barrier 9 is metal and the junction 10 is a weld between the barrier 9 and the inner surface of the housing 2. Alternatively, a barrier may be created by connecting two housings, where at least one of the housings includes a joining surface comprising a substantially gas-impermeable material. The joining surface will be open around the bore, and will form the barrier when the housings are connected.

In a cylindrical article, such as a nozzle or shroud, the barrier 9 will often have the shape of a washer. An article may even comprise a plurality of barriers when an operator wishes to control inert gas over a number of sections of the article. Each section may or may not have independent gas sources. The amount of gas present in each section varies according to such factors as refractory composition, porosity, channels and other known variations. Multiple barriers permit multiple zones, into which different gases, backpressures, and gas volumes may be used.

The housing 2, barrier 9 and bore 4 substantially define a perimeter 11 as shown in Figure 2, that defines a gas containment zone 12. Inert gas within the containment zone 12 will be constrained by the housing 2 and the barrier 9. The gas can only "leak" into the bore 4, and is substantially prevented from otherwise leaking out of the containment zone 12. In contrast, a tundish well nozzle of the prior art, as shown in Figure 3, has no barrier preventing gas from flowing along the interface 13 between the housing 2 and the piece 3. Gas traveling along this interface 13 eventually leaks from the top 5 or bottom 6 of the piece, and does not effectively protect molten steel within the bore 4. Leakage requires larger volumes of gas and greater overpressures to attempt protection of molten steel. Such measures increase costs and can affect the quality of finished steel by, for example, increasing defects created by gas bubbles in the steel.

One embodiment of the present invention, as shown in Figure 4, comprises a gas-impermeable barrier 9 and junction 10 that inhibit the flow of gas along the interface 13 of the housing 2 and the piece 3, thereby containing the gas and reducing leakage. The junction 10 and the barrier 9 are adapted to deflect any gas migrating along the interface 13 toward the bore 4. The barrier may extend to the bore but more frequently a gap 14 exists between the barrier and the bore 4. The gap will typically be between 5-15 mm. Gas attempting to escape around the gap 14 between the barrier 9 and the bore 4 may be drawn into the bore 4. Less leakage permits greater control of gas backpressure, reduces the amount of gas needed, and more precisely targets inert gas in the article.

The piece 3 may comprise a single refractory composition, but will often include at least two different refractory compositions. A gas containment zone 12, which is adapted to receive inert gas, will often include a porous refractory composition. A second zone 15 can include a second refractory. The second refractory could have, for example, superior erosion- or chemical-resistance. The presence of the barrier 9 provides a convenient mechanical boundary between the gas- containment zone 12 and the second zone 15 and can facilitate assembly as described below. The method of the present invention includes producing an article having a substantially gas-impermeable barrier within a housing. In one embodiment, the barrier is fixed within a metal housing. Typically, the barrier is metal and is welded to the inside surface of the housing. Alternatively, the barrier may be created by joining two housings, at least one of which includes an end that incorporates a barrier.

A refractory piece is secured within the housing, and.may comprise one or more refractory compositions. Suitable compositions include pressed refractories, castable refractories and combinations thereof. Pressed refractories include particulate refractory compositions suitable for steel casting, and may include fired and unfired refractories. Examples include, but are not limited to, carbon-bonded, resin-bonded, sintered and fused compositions comprising alumina, zirconia, magnesia, calcia, silica and chemical and mechanical combinations thereof.

In one embodiment, a pressed part is inserted into a volume defined by the housing and a castable fills the remainder of the volume. Figure 4 shows what could be a pressed part below the barrier and a castable above the barrier. Other examples include the use of the pressed part as a liner immediately surrounding the bore. The pressed part may be a porous body.

In another embodiment, the piece comprises particulate refractory compositions. The barrier provides a convenient demarcation between different refractory compositions. The inclusion of a barrier permits a manufacturer to place precisely the separation of the first and second zones. The barrier also may increase ease of fabrication by allowing manufacturers to omit careful measurement of the location and amount of material placed in the housing. The barrier automatically identifies the quantity and volume of refractory needed in each zone. Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art.

Claims

What is claimed:

1. A gas-injection nozzle for use in the casting of molten metal comprising: a) a substantially gas-impeπneable housing having a first inner surface; b) a refractory piece disposed at least partially within the housing, the refractory piece having a second inner surface defining a bore and an outer peripheral surface adjacent to the housing; and c) at least one gas channel within the nozzle adapted to be in fluid connection with a gas connection; the nozzle characterized by the first inner surface and a substantially gas- impermeable barrier defining a gas-containment zone substantially surrounding the gas channel and at least a portion of the bore.

2. The gas-injection nozzle of claim 1 , further characterized in that the housing and the barrier consist essentially of metal.

3. The gas-injection nozzle of claim 2, further characterized in that the housing and barrier are welded together to create a substantially gas-tight joint.

4. The gas-injection nozzle of any one of claims 1-3, further characterized in that the nozzle comprises a cylindrical shape and the barrier comprises a washer.

5. The gas-injection nozzle of any one of claims 1 -4, further characterized in that a gap exists between the barrier and the bore.

6. The gas-injection nozzle of claim 5, further characterized in that the gap is at least 5 mm and up to 15 mm.

7. The gas-injection nozzle of any one of claims 1-6, further characterized in that the gas channel comprises a void between the first inner surface of the housing and the outer peripheral surface of the refractory piece.

8. The gas-injection nozzle of any one of claims 1 -7, further characterized in that the barrier divides the refractory piece into a downstream section and an upstream section, and the sections comprise different refractory compositions.

9. The gas-injection nozzle of claim 8, further characterized in that the sections comprise refractory compositions selected from the group consisting of pressed and cast refractories.

10. The gas-injection nozzle of any one of claims 8 or 9, further characterized in that the gas-containment zone includes the downstream zone and the downstream zone comprises a porous refractory composition.

11. The gas-injection nozzle of claim 1 , further characterized in that the nozzle comprises a plurality of gas-impermeable barriers, whereby the nozzle is divided into a plurality of gas-containment zones.

12. The gas-injection nozzle of claim 11, further characterized in that each gas- containment zone includes at least one gas channel adapted to be in fluid connection with a gas supply.

13. A method of forming the gas-injection nozzle of claim 1 , the method characterized by: a) providing a substantially gas-impermeable housing adapted to receive a gas connection and having a first inner surface defining a space; b) fixedly securing within the space at least a portion of refractory piece comprising a second inner surface defining a bore, thereby forming a nozzle assembly; c) dividing the nozzle assembly with a gas-impermeable barrier into at least two zones, including a gas containment zone in fluid connection with the gas connection.

14. The method of claim 13, further characterized in that the housing and refractory piece cooperate to form a gas channel.

15. The method of claim 13 , further characterized in that the nozzle assembly includes a first zone comprising a first refractory composition and a second zone comprising a different refractory composition.

16. The method of claim 13, further characterized in that the gas-containment zone comprises a porous refractory composition.

17. A method of forming the gas-injection nozzle of claim 1, the method characterized by: a) providing a substantially gas-impermeable housing adapted to receive a gas connection; a) placing into the gas-impermeable housing a first refractory piece having a first inner surface defining a first bore, thereby forming a first nozzle assembly; b) providing a second housing; c) placing into the second housing a second refractory piece having a second inner surface defining a second bore, thereby forming a second nozzle assembly; d) securing a substantially gas-impermeable barrier to the first assembly, so that the barrier surrounds the first bore and forms a joining surface; and e) joining the first nozzle assembly to the second nozzle assembly at the joining surface so that the first and second bores align at the joining surface.