阅读说明：本技术 高温熔融物的精炼容器 (Vessel for refining high temperature melt ) 是由 细原圣司 鸟越淳志 藤吉亮磨 于 2020-03-24 设计创作，主要内容包括：本发明提供气体吹入喷嘴具有高耐用性的高温熔融物的精炼容器。在高温熔融物的精炼容器中,气体吹入喷嘴用耐火物具有埋设有金属细管的中心部耐火物、和包围该中心部耐火物外周的外周部耐火物,在气体吹入喷嘴用耐火物的俯视面中,将包含被埋设的全部金属细管的最小半径的假想圆的半径设为R(mm)时,中心部耐火物的外形为包含于与假想圆同心且半径为R+10mm的圆、和与假想圆同心且半径为R+150mm的圆之间的形状,中心部耐火物由碳含量为30～80质量％的MgO-C质耐火物构成,外周部耐火物由碳含量为10～25质量％的MgO-C质耐火物构成。(The invention provides a refining vessel for high-temperature melt with a gas blowing nozzle having high durability. In a vessel for refining a high-temperature melt, a refractory for a gas injection nozzle has a central portion refractory in which metal tubules are embedded and an outer peripheral portion refractory surrounding the outer periphery of the central portion refractory, and when a radius of a virtual circle including a minimum radius of all the embedded metal tubules is defined as R (mm) in a plan view of the refractory for the gas injection nozzle, an outer shape of the central portion refractory is a shape included between a circle concentric with the virtual circle and having a radius of R +10mm and a circle concentric with the virtual circle and having a radius of R +150mm, the central portion refractory is composed of an MgO-C refractory having a carbon content of 30 to 80 mass%, and the outer peripheral portion refractory is composed of an MgO-C refractory having a carbon content of 10 to 25 mass%.)

1. A vessel for refining a high-temperature melt, comprising a gas injection nozzle made of a refractory for gas injection nozzle in which at least one metal fine tube for injecting a gas is embedded in a refractory containing carbon,

the refractory for a gas injection nozzle comprises: a refractory at the center part in which the metal narrow tube is embedded, and a refractory at the outer peripheral part surrounding the outer periphery of the refractory at the center part,

wherein when a radius of an imaginary circle including a minimum radius of all the metal tubules to be embedded is R (mm) in a plan view of the refractory for a gas injection nozzle, an outer shape of the refractory for a center portion is a shape included between a circle concentric with the imaginary circle and having a radius of R +10mm and a circle concentric with the imaginary circle and having a radius of R +150mm,

the central part refractory is composed of an MgO-C refractory having a carbon content of 30 to 80 mass%, and the outer peripheral part refractory is composed of an MgO-C refractory having a carbon content of 10 to 25 mass%.

2. A high temperature melt refining vessel according to claim 1,

the outer shape of the refractory at the center is a shape included between a circle having a radius of R +40mm and being concentric with the imaginary circle and a circle having a radius of R +70mm and being concentric with the imaginary circle.

3. A vessel for refining a high-temperature melt according to claim 1 or 2,

the outer shape of the refractory at the center portion is a circle concentric with the imaginary circle.

4. A vessel for refining a high-temperature melt according to any one of claims 1 to 3,

the central portion refractory is composed of an MgO-C refractory having a carbon content of 50 to 70 mass%, and the outer peripheral portion refractory is composed of an MgO-C refractory having a carbon content of 15 to 25 mass%.

5. A vessel for refining a high-temperature melt according to any one of claims 1 to 4,

the central refractory contains metal Al, metal Si, Al-Mg, SiC and B₄The content of at least one of C is less than 3.0 mass%.

6. A vessel for refining a high-temperature melt according to any one of claims 1 to 5,

the outer shape of the outer periphery refractory is a shape included between a circle concentric with the virtual circle and having a radius R × 2 and a circle concentric with the virtual circle and having a radius R × 8.

7. A vessel for refining a high-temperature melt according to any one of claims 1 to 6, wherein a gas blowing nozzle is provided at a bottom of the furnace.

Technical Field

The present invention relates to a vessel for refining a high-temperature melt such as a converter or an electric furnace, which is provided with a gas injection nozzle at the bottom of the vessel.

Background

In a converter, an electric furnace, or the like, so-called bottom blowing is performed by blowing a stirring gas (usually an inert gas such as nitrogen or Ar) or a refining gas into molten metal from a furnace bottom in order to improve refining efficiency and alloy yield. As the bottom blowing method, the following methods (1) to (3) and the like are available.

(1) A double tube system in which oxygen for decarburization is blown from an inner tube and a hydrocarbon gas (propane or the like) for cooling the molten steel contact portion is blown from an outer tube.

(2) A method in which a slit-like opening is provided in a gap between a metal pipe and a brick, and an inert gas is blown through the opening (slit method)

(3) A method in which a plurality of (several to several hundred) metal narrow tubes are buried in a carbon-containing brick, an inert gas is supplied to the metal narrow tubes from the bottom of the brick through a gas introduction tube and a gas storage device, and the inert gas is blown into the metal narrow tubes.

Among them, in the modes (1), (2), the tuyere block is generally manufactured in advance by a conventional method, and a space where a double-walled tube, a metal tube where a slit is formed, or a tuyere block is divided into 2 or 4 parts is processed, thereby forming a metal tube to be installed, a metal tube to be blown with gas is set in advance at the time of construction, and a nozzle block is installed around it.

On the other hand, the gas blowing plug (nozzle) used in the method (3) is called a porous plug (hereinafter referred to as MHP). For example, patent document 1 discloses that the MHP can be 0.01 to 0.20Nm³Controlling the gas flow in the range of/min.t. Therefore, compared with the double-tube system and the slit system, MHP is easier to use.

MHP is a structure in which a plurality of metal fine tubes connected to a gas storage device are embedded in a carbon-containing refractory such as magnesia carbon brick. Therefore, unlike the double-tube type and slit type nozzles, MHP is produced by the following method.

That is, a raw material obtained by adding a carbon source such as flake graphite and a binder such as pitch, metals and phenol resin to an aggregate such as a raw material of magnesium oxide is kneaded using a kneading apparatus such as a high-speed mixer having high dispersibility to obtain a kneaded product of a carbon-containing refractory material to be embedded in a metal tubule.

MHPs can be manufactured by the following method: a method in which a metal narrow tube is laid on the kneaded material, the metal narrow tube is embedded in a layered state, and then the resultant is molded under a predetermined pressure by a press machine, and then a predetermined heat treatment such as drying and firing is performed (the metal narrow tube is subsequently joined to a gas storage member by welding); or, a method of joining a metal tubule to a gas storage member by welding in advance, filling the kneaded material around the metal tubule, molding the resultant product under a predetermined pressure by a press, and then drying the molded product; and the like.

Since the amount of damage (loss) of the bottom-blowing nozzle is larger than that of a refractory such as a furnace wall and is an important member for determining the furnace life, various proposals have been made to suppress the damage. For MHP, for example, the following improvements are also proposed.

Patent document 2 discloses that early melting loss and abrasion from a joint portion can be reduced by integrating a gas injection nozzle portion of MHP with a peripheral tuyere. However, this technique is not effective and cannot be an effective countermeasure.

As a measure against the melting point lowering (early damage to the metal tubule) caused by carburization of the metal tubule embedded in the refractory, the following is proposed.

Patent document 3 discloses that an oxide layer is formed on the surface of a stainless steel thin metal tube by spray plating in order to suppress carburization of the thin metal tube embedded in a carbon-containing refractory material such as a magnesia carbon brick. However, this technique has a problem that the thickness of the oxide layer is insufficient and the carburization suppression effect is poor in a refining furnace used for a long period of time (for example, a use period of 2 months to half a year) such as a converter.

Patent document 4 discloses that a refractory sintered body is disposed between a metal narrow tube and a carbon-containing refractory material in order to suppress carburization of the metal narrow tube. However, although this technique has confirmed the effect of suppressing carburization, it is difficult to arrange a refractory sintered body in a nozzle in which a plurality of metal narrow tubes are embedded because the spacing between the metal narrow tubes is narrow, and it is difficult to put the sintered body into practical use.

On the other hand, as a technique of employing a method of impregnating an organic material after temporarily reducing and firing a carbon-containing refractory, the following has been proposed.

Patent document 5 discloses a treatment in which a magnesia carbon brick to which metallic Al powder is added is fired at 500 to 1000 ℃ and then impregnated with an organic material having a carbonization yield of 25% or more into pores of the brick. According to patent document 5, the thermal strength and corrosion resistance of the magnesia carbon brick can be improved. Patent document 6 discloses that the thermal spalling resistance can be improved by reducing and firing a magnesia carbon brick containing 0.5 to 10 wt% of calcined anthracite coal at 600 to 1500 ℃. In addition, tar can be impregnated after firing, and impregnation with tar realizes sealing of pores, improvement of strength, and improvement of water resistance. However, these techniques are not effective and cannot be effective countermeasures.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 59-31810

Patent document 2 Japanese patent laid-open No. Sho 63-24008

Patent document 3 Japanese laid-open patent publication No. 2000-212634

Patent document 4, Japanese patent laid-open No. 20030-31912

Patent document 5 Japanese patent laid-open publication No. 58-15072

Patent document 6 Japanese patent No. 3201678

Disclosure of Invention

Problems to be solved by the invention

As described above, various studies have been made on the material and structure of a carbon-containing refractory in order to improve durability in a gas blowing nozzle (MHP or the like) in which a metal narrow tube is embedded in the refractory, but a sufficient improvement effect has not been obtained at present. Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a refining vessel including a high-temperature molten material, which is formed by embedding one or more metal fine tubes for blowing gas in a carbon-containing refractory material, and has high durability in the gas blowing nozzle.

Means for solving the problems

It is considered that the cause of damage to MHPs used in converters and electric furnaces has been mainly caused by melting and abrasion due to molten steel flow in the vicinity of the nozzle face, which is caused by vigorous gas blowing from a metal narrow tube. The countermeasure of patent document 2 is proposed from such a viewpoint. It is also considered that the damage is increased by the fact that the thin metal tube is consumed first by carburization or the like, and carburization into the thin metal tube can be prevented by the methods as described in patent documents 3 and 4. On the other hand, there are various viewpoints that the refractory is cooled by blowing inert gas vigorously during blowing and that the refractory is peeled and damaged due to the temperature difference between the blowing and non-blowing, and that the carbon-containing refractory has the lowest strength at around 600 ℃, and that the working surface of the part is cracked and damaged, and no conclusion is made. As a result, effective measures cannot be taken, and satisfactory durability is not always obtained as described above.

Therefore, the present inventors recovered a used product (MHP) used in an actual furnace in order to search for a true cause of damage to the MHP, and conducted detailed investigation on a refractory structure in the vicinity of the nozzle face. As a result, it was found that a very large temperature change of 500 to 600 ℃ occurred in the refractory having a depth of about 10 to 20mm from the working surface, and further that cracks parallel to the working surface were observed in the portions. From the results of such detailed investigations repeated in the vicinity of the working surface of the product after use of the actual furnace, the following conclusions were drawn: the damage form of MHP is not damage caused by melting loss and abrasion, but damage caused mainly by thermal shock caused by a severe temperature gradient generated in the vicinity of the working surface.

Then, the present inventors have conducted extensive studies on the improvement of the material properties for reducing the thermal stress generated in the tuyere refractory, and as a result, it has been found that a refractory having a high thermal conductivity (high thermal conductivity reduces the temperature gradient) and a low thermal expansion coefficient, in which the C content is increased, is effective. However, when the C content is increased, the wear resistance and the erosion resistance are remarkably reduced, and the life is remarkably reduced by abrasion and erosion by molten metal. As a result of further studies, it has been found that the problem can be solved by a configuration in which an MgO — C material having a large C content is disposed in the peripheral portion (the center portion of a predetermined range) of the metal tubule that is most cooled, and an MgO — C material having a normal C content is disposed around the peripheral portion (the outer peripheral portion).

That is, the outer peripheral portion is made of a refractory (MgO — C material) having a normal C content, thereby suppressing the deterioration of wear resistance and erosion resistance. On the other hand, in the peripheral portion of the metal narrow tube, the generation of cracks due to thermal shock is suppressed by using a refractory (MgO — C material) having high thermal conductivity and low thermal expansion coefficient in which the C content is increased. Further, it has been found that since the refractory has a high thermal conductivity, a solidified film of slag or metal (so-called mushroom head) is formed on the working surface side by cooling the gas flowing through the thin metal tube, and the surface of the refractory is separated (protected) from the molten steel by the solidified film, thereby obtaining an effect of suppressing wear and loss due to melting loss.

The present invention has been completed based on such findings, and the gist thereof is as follows.

[1] A vessel for refining a high-temperature melt, comprising a gas injection nozzle made of a refractory for gas injection nozzle in which at least one metal fine tube for injecting a gas is embedded in a refractory containing carbon,

the refractory for a gas injection nozzle comprises: a refractory at the center part in which the metal narrow tube is embedded, and a refractory at the outer peripheral part surrounding the outer periphery of the refractory at the center part,

wherein when a radius of an imaginary circle including a minimum radius of all the metal tubules to be embedded is R (mm) in a plan view of the refractory for a gas injection nozzle, an outer shape of the refractory for a center portion is a shape included between a circle concentric with the imaginary circle and having a radius of R +10mm and a circle concentric with the imaginary circle and having a radius of R +150mm,

the central part refractory is composed of an MgO-C refractory having a carbon content of 30 to 80 mass%, and the outer peripheral part refractory is composed of an MgO-C refractory having a carbon content of 10 to 25 mass%.

[2] A vessel for refining a high-temperature melt according to [1], wherein,

the outer shape of the refractory at the center is a shape included between a circle having a radius of R +40mm and being concentric with the imaginary circle and a circle having a radius of R +70mm and being concentric with the imaginary circle.

[3] The vessel for refining a high-temperature melt according to [1] or [2], wherein,

the outer shape of the refractory at the center portion is a circle concentric with the imaginary circle.

[4] The vessel for refining a high-temperature melt according to any one of [1] to [3], wherein,

the central portion refractory is composed of an MgO-C refractory having a carbon content of 50 to 70 mass%, and the outer peripheral portion refractory is composed of an MgO-C refractory having a carbon content of 15 to 25 mass%.

[5] The vessel for refining a high-temperature melt according to any one of [1] to [4], wherein,

the central refractory contains metal Al, metal Si, Al-Mg, SiC and B₄The content of at least one of C is less than 3.0 mass%.

[6] The vessel for refining a high-temperature melt according to any one of [1] to [5], wherein,

the outer shape of the outer periphery refractory is a shape included between a circle concentric with the virtual circle and having a radius R × 2 and a circle concentric with the virtual circle and having a radius R × 8.

[7] The vessel for refining a high-temperature melt according to any one of [1] to [6], which comprises a gas blowing nozzle at a bottom of the furnace.

ADVANTAGEOUS EFFECTS OF INVENTION

The gas blowing nozzle of the vessel for refining a high-temperature melt according to the present invention can suppress the occurrence of cracks due to thermal shock and has high durability. Therefore, a long-life refining vessel can be produced.

Drawings

Fig. 1 is a plan view showing one embodiment of a gas injection nozzle refractory 10 constituting a gas injection nozzle provided in a refining vessel of the present invention.

Description of the symbols

10 refractory for gas blowing nozzle

12 center refractory

14 peripheral part refractory

16 imaginary circle

18 round

20 metal thin tube

Detailed Description

The refining vessel of the present invention is provided with a gas blowing nozzle comprising a refractory 10 for gas blowing nozzle in which one or more metal narrow tubes 20 for blowing gas are embedded in a carbon-containing refractory. The refractory 10 for a gas injection nozzle includes: a central refractory 12 in which a narrow metal tube 20 is embedded, and an outer peripheral refractory 14 surrounding the outer periphery of the central refractory 12.

As mentioned above, the main cause of loss of MHP tuyere is thermal shock. In particular, the peripheral portion of the metal tubule 20 of the MHP tuyere is cooled by the gas flowing through the metal tubule 20, and thus the thermal stress becomes large. In order to suppress thermal shock and thermal stress, it is effective to increase the C content of the MgO — C refractory. On the other hand, when the C content of the MgO — C refractory is increased, the refractory is easily dissolved in molten steel, and the wear resistance and the melting loss resistance are reduced. In this regard, the present inventors have found that the peripheral portion of the narrow metal tube 20 having an increased C content is cooled by the gas flowing through the narrow metal tube 20 due to its high thermal conductivity, and as a result, a solidified film of slag or metal (so-called mushroom head) is formed on the working surface side, and the solidified film protects the surface of the refractory from molten steel, thereby providing an effect of suppressing wear and loss due to melting.

Therefore, in the present invention, the refractory for gas injection nozzle 10 is composed of the central portion refractory 12 in which the narrow metal tube 20 is embedded and the outer peripheral portion refractory 14 surrounding the outer periphery of the central portion refractory 12, the refractory for gas injection nozzle 10 constitutes the gas injection nozzle of the refining vessel, and the central portion refractory 12 is composed of the MgO — C refractory having a large C content. The refractory constituting the central portion refractory 12 and the outer peripheral portion refractory 14 is, for example, a brick.

In order to obtain the above-described effects, the central refractory 12 made of the MgO — C refractory having a high C content needs to have a given size (outer shape) as shown below.

Fig. 1 is a plan view showing one embodiment of a gas injection nozzle refractory 10 constituting a gas injection nozzle provided in a refining vessel of the present invention. As shown in fig. 1, when the radius of a virtual circle including all the embedded metal tubules 20 is R (mm) in a plan view (i.e., in a plan view) of the refractory 10 for a gas injection nozzle, the outer shape of the refractory 12 in the center portion is a shape included between a circle concentric with the virtual circle 16 and having a radius of R +10mm and a circle concentric with the virtual circle and having a radius of R +150 mm. That is, in fig. 1, the outer shape of the central refractory 12 is an arbitrary shape included in the range of the radius R + R and R of 10mm to 150 mm. If the radius of the outer shape of the refractory 12 at the center portion is smaller than R +10mm, the metal narrow tube 20 is too close to the boundary between the refractory 14 at the outer peripheral portion and the refractory 12 at the center portion, and there is a possibility that the metal narrow tube is deformed during the refractory molding. Therefore, the outer shape of the refractory 12 at the center portion needs to have a radius of R +10mm or more. The outer shape of the refractory 12 at the center is preferably a circle concentric with the virtual circle 16 and having a radius of R +40mm or more.

On the other hand, if the outer shape of the center refractory 12 is larger than a circle concentric with the virtual circle 16 and having a radius of R +150mm, a portion not covered with the so-called mushroom head is generated on the working surface of the center refractory 12, and damage due to contact with molten steel occurs. Therefore, the outer shape of the refractory 12 at the center portion needs to be a circle concentric with the virtual circle 16 and having a radius of R +150mm or less. The outer shape of the refractory 12 at the center is preferably a circle concentric with the virtual circle 16 and having a radius of R +70mm or less. In fig. 1, the outer shape of the central refractory 12 is preferably an arbitrary shape included in a range of a radius R + R and R of 40mm to 70 mm. The outer shape of the center portion refractory 12 is preferably a circle concentric with the imaginary circle 16. Here, the plan view of the gas injection nozzle refractory 10 is a plane perpendicular to the axis of the thin metal tube 20 on the surface of the gas injection nozzle refractory 10.

The carbon content of the MgO — C refractory constituting the central refractory 12 is 30 mass% or more and 80 mass% or less. If the carbon content of the MgO — C refractory constituting the central refractory 12 is less than 30 mass%, the thermal shock resistance is insufficient, and if the carbon content is more than 80 mass%, the corrosion resistance to molten steel is deteriorated, and the reliability is insufficient. Therefore, the carbon content of the MgO — C refractory constituting the center portion refractory 12 needs to be 30 mass% or more and 80 mass% or less, and preferably 50 mass% or more and 70 mass% or less.

The carbon content of the MgO — C refractory constituting the outer peripheral portion refractory 14 is 10 mass% or more and 25 mass% or less. When the carbon content of the MgO — C refractory constituting the outer peripheral refractory portion 14 is less than 10 mass%, damage due to thermal shock becomes large, and when the carbon content is more than 25 mass%, abrasion resistance and melting loss resistance are deteriorated, so satisfactory durability cannot be obtained. Therefore, the carbon content of the MgO — C refractory constituting the outer peripheral refractory portion 14 needs to be 10 mass% or more and 25 mass% or less, and preferably 15 mass% or more and 25 mass% or less.

The outer shape of the outer peripheral refractory portion 14 is preferably any shape included between a circle concentric with the virtual circle 16 and having a radius R × 2 and a circle concentric with the virtual circle 16 and having a radius R × 8. By making the outer shape of the outer peripheral refractory portion 14 a circle concentric with the imaginary circle 16 and having a radius R × 2 or more, it is possible to suppress a decrease in the wear resistance and melting loss resistance of the gas injection nozzle refractory 10. By making the outer shape of the outer peripheral refractory portion 14 a circle concentric with the imaginary circle 16 and having a radius R × 8 or less, it is possible to suppress a decrease in thermal shock resistance of the gas injection nozzle refractory 10. Since the outer peripheral refractory portion 14 is provided so as to surround the outer periphery of the central refractory 12, the narrow metal tube 20 is provided so that the radius of the imaginary circle 16 is larger than 10mm in the central refractory 12.

The material of the thin metal tube 20 is not particularly limited, and a metal material having a melting point of 1300 ℃ or higher is preferably used. Examples of the metal material include a metal material (metal or alloy) containing at least one of iron, chromium, cobalt, and nickel. The metal material generally used for the thin metal tube 20 is stainless steel (ferrite, martensite, austenite), ordinary steel, heat-resistant steel, or the like. The inner diameter of the thin metal tube 20 is preferably 1mm to 4 mm. If the inner diameter of the narrow metal tube 20 is less than 1mm, it may be difficult to sufficiently supply a gas for stirring the molten metal in the furnace. On the other hand, if the inner diameter of the narrow metal tube 20 is larger than 4mm, the molten metal may flow into the narrow metal tube 20 and be clogged. The thickness of the metal thin tube 20 is about 1 to 2 mm.

The number of the metal tubules 20 embedded in the carbon-containing refractory is not particularly limited, and may be appropriately selected according to the required gas blowing flow rate and the area of the working portion. For those requiring a high flow rate such as a converter, about 60 to 250 thin metal tubes 20 are usually buried, and for those having a small gas injection flow rate such as an electric furnace or a ladle, about 1 to 10 thin metal tubes 20 are usually buried.

Next, a method for producing a refractory for a gas injection nozzle constituting a gas injection nozzle provided in a refining vessel of the present invention will be described.

The main raw materials of the carbon-containing refractory (the central refractory 12 and the outer peripheral refractory 14) are aggregate and a carbon source, and may contain other additives, a binder, and the like.

Magnesia, alumina, dolomite, zirconia, chromia, spinel (alumina-magnesia, chromia-magnesia) and the like can be used as the aggregate of the carbon-containing refractory, and in the present invention, magnesia is used as the main aggregate from the viewpoint of corrosion resistance to the molten metal or molten slag.

The carbon source of the carbonaceous refractory is not particularly limited, and flake graphite, expanded graphite, soil graphite, calcined anthracite, petroleum pitch, carbon black, and the like can be used. The amount of carbon source added is determined according to the carbon content of each of the central portion refractory 12 and the outer peripheral portion refractory 14.

Examples of the additive other than the aggregate and the carbon source include metals such as metallic Al, metallic Si, and Al-Mg alloys, SiC, and B₄C, and the like, and these may contain one or more kinds. The amount of these additives is usually 3.0 mass% or less. For example, although these additives are blended in order to suppress the oxidation of carbon, they are inferior in the melting loss resistance to MgO and carbon, and therefore, metal Al, metal Si, Al-Mg, SiC and B₄The amount of one or more of C is preferably less than 3.0% by mass, and the lower limit of the amount of these additives is 0% by mass.

The feedstock for the carbon-containing refractory generally comprises a binder. As the binder, a binder that can be generally used as a binder for molding a refractory, such as a phenol resin or liquid asphalt, can be used. The amount of the binder is usually about 1 to 5 mass% (additional mass%).

The refractory 10 for a gas injection nozzle can be produced by a known production method, and an example thereof will be described below. First, the refractory raw materials for the central portion refractory 12 and the outer peripheral portion refractory 14 are mixed and kneaded by a mixer to prepare a kneaded material. The narrow metal tube 20 is disposed at a predetermined position in the kneaded material for the refractory 12 at the center, and then molded by uniaxial pressing, thereby producing the refractory 12 at the center in which the narrow metal tube 20 is embedded. Further, the periphery of the central refractory 12 is filled with a kneaded material for the outer peripheral refractory 14, and then integrated by isostatic pressing (cold isostatic pressing, hereinafter referred to as "CIP molding"), and molded into a base material of the refractory 10 for a gas injection nozzle. Then, the base material is subjected to a predetermined heat treatment such as drying by a conventional method. If necessary, machining for adjusting the outer shape may be performed.

As the press molding method of the refractory 12 at the center portion, a multi-step press molding method of filling a small amount of kneaded material into a molding die and pressing, then arranging the narrow metal tube 20 at a predetermined position, then filling a predetermined amount of kneaded material and pressing, and repeating the above steps, or a single press molding method of molding the narrow metal tube 20 by pressing at one time together with the entire amount of kneaded material while holding both ends of the narrow metal tube 20 so that the narrow metal tube 20 is moved together with the movement of the kneaded material at the time of pressing, may be used.

The thin metal tubes 20 and the gas reservoir may be joined by welding them at any stage after the central refractory 12 is molded, after the base material is molded, or after the base material is heat-treated, or by arranging the thin metal tubes 20, to which the upper plate of the gas reservoir is welded in advance, in the mixture for the central refractory 12 when the central refractory 12 is molded.

The method for kneading the raw materials of the carbon-containing refractory is not particularly limited, and a kneading system using a high-speed mixer, a type mixer (Koner mixer), an erich mixer or the like as a kneading device for the molded refractory can be used.

The kneaded material can be molded by a uniaxial molding machine such as a hydraulic press or a friction press, or a press machine generally used for molding refractories such as a CIP molding machine. The molded carbon-containing refractory can be dried at a drying temperature of 180 ℃ for about 5 to 30 hours.

The refractory 10 for gas injection nozzles manufactured as described above is attached to a refining vessel for high-temperature molten materials such as a converter and an electric furnace, and constitutes a gas injection nozzle. The position of the gas blowing nozzle is generally at the bottom of the furnace, but is not limited thereto. In the case of the bottom of the furnace, the gas injection nozzle refractories 10 are attached as bottom bricks around the bottom-blowing tuyere to constitute the gas injection nozzle.

Examples

Refractories for gas injection nozzles, in which 81 metal thin tubes were concentrically arranged as shown in fig. 1, were produced under the conditions shown in tables 1 to 4.

In a plan view of the refractory 10 for a gas injection nozzle, a radius R of an imaginary circle including the minimum radius of all the embedded metal tubules 20 is 50mm, and a radius R + R of the refractory in the center portion is changed within a range of R8 to 200 mm.

As the metal narrow tube 20 embedded in the carbon-containing refractory, a metal narrow tube made of ordinary steel or stainless steel (SUS304) having an outer diameter of 3.5mm and an inner diameter of 2.0mm was used.

The respective refractory raw materials were mixed in the proportions shown in tables 1 to 4, and kneaded by a mixer. The metal narrow tube 20 is disposed in the kneaded material for the central refractory 12, and is molded into the central refractory 12 by uniaxial pressing. Further, the periphery of the central refractory 12 is filled with a kneaded material for the outer peripheral refractory 14, and then the base material is molded by CIP molding. Then, the base material is dried by a conventional method to produce a product.

The gas injection nozzle was constructed by using the produced refractory 10 for a gas injection nozzle as a bottom brick around a bottom tuyere of a 250-ton converter, and refining vessels of the inventive example and the comparative example were manufactured. After 2500 charges (charges, ch) were used, the wear rate (mm/ch) was determined from the remaining thickness of the refractory, and the wear rate ratio (index) was determined with the wear rate of comparative example 1 being "1", and the results are shown in tables 1 to 4.

As shown in tables 1 to 4, the refractory for a gas injection nozzle of the present invention was confirmed to have a lower wear rate and superior durability as compared with the refractory for a gas injection nozzle of the comparative example. In the present example, the gas injection nozzle having the MgO-C refractory having the central part refractory 12 with a carbon content of 50 to 70 mass% and the MgO-C refractory having the outer part refractory with a carbon content of 15 to 25 mass% has particularly excellent durability. It was confirmed that, in the present example, the gas injection nozzle refractory having the center portion refractory 12 with a radius of R +40mm or more and R +70mm or less had particularly excellent durability.