JPH10182259A - Porous plug refractory and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous plug refractory capable of eliminating damage due to crack caused by a sudden temp. change. SOLUTION: This porous plug refractory is composed of a mineral phase, which has a chemical composition of 70-92wt.% Al2 O3 and 8-30wt.% SiO2 and consists essentially of corundum in a coarse granule part, and a glass phase having a joining part consisting essentially of SiO2 . The porous plug refractory is produced by blending 40-90wt.% alumina raw material having 2-0.3mm particle diameter, 5-25wt.% siliceous raw material having <=1mm particle diameter and 5-30wt.% alumina-silica raw material having <=1mm particle diameter, kneading, forming and firing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous plug refractory for gas bubbling used in a molten metal container such as a ladle, a tundish, a lance pipe or a refining furnace for the purpose of stirring molten metal and floating inclusions. It relates to the manufacturing method.

[0002]

2. Description of the Related Art In order to refine a high-purity metal, stirring of the molten metal by gas bubbling using an Ar gas or the like is performed in a process of processing the molten metal. BACKGROUND ART As a refractory for gas bubbling, a porous plug which is made to have air permeability by controlling the distribution, size and shape of pores in a refractory structure is widely used. The porous plug needs to have not only corrosion resistance to molten metal and slag, but also thermal shock resistance to withstand a severe temperature change caused by a cooling effect during gas blowing.

[0003] Various studies have been made on porous plug refractories, and there are many references. Mullite porous plugs have been used since ancient times, and corundum and magnesia porous plugs have also been developed to improve corrosion resistance. For example, refractory [22 (7) 2
06-209, 1970] describes a porous plug using high alumina aggregate and having mullite bonding between particles to improve spalling resistance and corrosion resistance.

Further, refractories [33 (7) 382-38]
8, 1981], comparing three materials of magnesia, corundum and mullite, and reporting that mullite is the most excellent in spalling resistance. Furthermore, in the refractory [37 (1) 50-56, 1985], evaluation results of the filling property and air permeability of a porous plug using spherical particles are discussed.

Japanese Patent Application Laid-Open No. Sho 59-169978 discloses a porous plug which is excellent in corrosion resistance while maintaining air permeability. In addition, there are many inventions on gas bubbling refractories, but most are not inventions of materials and manufacturing methods of porous plug refractories, and plugs with through holes and slits in ordinary dense refractories, plugs and plugs There are many things about the structure.

[0006]

With regard to the thermal shock resistance of porous plug refractories, that is, the spalling resistance, there is no practical material which is superior to mullite or mullite-bonded materials. At least, in the production of high-grade, high-purity metals in recent years, there has been a problem that there is no porous plug refractory exposed to a sudden temperature change that is sufficiently satisfactory in terms of thermal shock resistance.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a porous plug refractory and a method of manufacturing the same, which can eliminate damage caused by cracks caused by a rapid temperature change, which is a problem of conventional porous plug refractories. is there.

[0008]

Porous plug refractory of the present invention According to an aspect of the, Al ₂ O ₃ 70~92% by weight and SiO _2. 8 to
It is characterized by having a chemical composition of 30%, a coarse-grained portion consisting of a mineral phase mainly composed of corundum, and a bonding part consisting of a glass phase mainly composed of SiO ₂ component.

The method for producing a porous plug refractory according to the present invention is characterized in that the alumina raw material 40 to 90 mm 2 to 0.3 mm is used.
%, 1 to 5% by weight of a siliceous raw material of 1 mm or less, and 5 to 30% by weight of an alumina-siliceous material of 1 mm or less are blended, kneaded, molded, and fired.

Further, in the method for manufacturing a porous plug of the present invention, an alumina raw material having a diameter of less than 0.3 mm can be blended in an amount of 20% by weight or less.

In the method for producing a porous plug according to the present invention, the alumina raw material having a diameter of 2 to 0.3 mm is an unmilled raw material, and at least a part of the silica raw material is amorphous silica. At least a part of the raw material is a mullite raw material.

Further, the porous plug manufacturing method of the present invention is characterized in that the maximum firing temperature of the molded body is 1590 to 1780 ° C.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The porous plug refractory of the present invention is characterized in that the coarse-grained portion is mainly composed of corundum, which is a crystal of Al ₂ O ₃ , and the bonding portion is composed of a glass phase mainly composed of SiO ₂ component. There is. In the process of firing the porous plug refractory, Al ₂ O ₃ reacts with SiO ₂ to generate mullite. In the porous plug refractory of the present invention, mullite is formed from a glass phase mainly composed of SiO ₂ components. In a state of being taken in as a coarse or fine particle in the bonding part or present in a part of the periphery of the corundum coarse particle, and the bonding part is substantially formed by the glass phase mainly composed of the SiO ₂ component as described above. ing.

Since the porous plug refractory is exposed to a high-temperature molten metal or slag, it must have corrosion resistance against the molten metal or slag. Even in the porous plug refractory of the present invention, the coarse-grained portion is mainly composed of Al ₂ having excellent corrosion resistance. It is composed of corundum which is a crystal of O ₃ .

In order to obtain excellent thermal shock resistance which is a feature of the porous plug refractory of the present invention, it is necessary that the portion connecting the coarse particles is made of a glass phase mainly composed of SiO ₂ component. The glass phase mainly composed of the SiO ₂ component has a low coefficient of thermal expansion and can absorb the expansion and contraction of corundum. It should be noted that mullite has a considerably lower expansion than corundum, and a porous plug refractory that combines corundum with mullite has been used conventionally. Both corundum and mullite are high melting point crystals, and corundum crystals ( Solid) and mullite crystal (solid) are directly bonded,
Easy to crack.

On the other hand, the joint portion of the porous plug refractory of the present invention is a glass phase and has a structure similar to that of a glass body, so that it has high flexibility. In addition, since the glass phase is softened to some extent at a high temperature in contact with the molten metal during use, the porous plug refractory of the present invention can reduce the strain generated in the porous plug refractory due to a rapid temperature change. Therefore, there is a characteristic that cracks are hardly generated.

Further, in the porous plug refractory of the present invention, fine cracks are often observed in a joint portion composed of a glass phase around a coarse grain portion mainly composed of corundum. this is,
In the process of refractory cooling to room temperature, it seems to be caused by the difference in the expansion behavior between corundum and glass phase. Although not fully confirmed experimentally, in a lower temperature range where the glass phase constituting the bonding portion softens, it is presumed that the fine crack has an effect of absorbing strain and suppressing cracking. Although the strength of the porous plug refractory of the present invention at room temperature is not high due to the micro-cracks, a structure in which the micro-cracks are welded is formed in a higher temperature range where the glass phase starts to soften. It also has the feature of greatly improving the strength of the steel sheet, and it is considered that, as the overall strength is improved, the resistance to cracking is also a factor in improving the thermal shock resistance.

The coupling portion of the porous plug refractory of the present invention must be an glass phase SiO ₂ component mainly the Al ₂ O ₃ principal components constituting a coarse portion, the main component of the coupling portion It is common that SiO ₂ generates mullite in the process of firing at a high temperature. However, as a result of various experiments by the present inventors, when the SiO ₂ content in the porous plug refractory is 8% by weight or more, all of the generated mullite is taken into the glass phase mainly composed of SiO _2. In this state, the bonding is formed by a glass phase mainly composed of SiO ₂ components. Therefore, if the amount of SiO ₂ is less than 8% by weight, the glass phase becomes insufficient and the bonding portion may become mullite, which is not preferable. Note that SiO ₂
In order to ensure the bonding by the glass phase mainly composed of the components, the SiO ₂ content is more preferably set to 10% by weight or more.

Mullite, which is taken into the glass phase or present around the corundum grains, has a relatively low expansion itself, as has been noticed in the past, and is a feature of the porous plug refractory of the present invention. It does not impair certain excellent thermal shock resistance. The size of the mullite generated in the firing process varies depending on firing conditions and cooling conditions, but from the size corresponding to coarse particles of about 1 mm,
There are even fine particles of 0.3 mm or less.

The SiO in the porous plug refractory of the present invention
_{When the} content of ₂ exceeds 30% by weight, there is no problem in terms of thermal shock resistance, but A in the porous plug refractory.
Since the content of l ₂ O ₃ is relatively reduced, the corrosion resistance to a high-temperature molten metal or slag is undesirably reduced. A more preferred SiO ₂ content is 25% by weight or less.

Al ₂ in the porous plug refractory of the present invention
The O ₃ content is 70 to 9 which is substantially the balance of the SiO ₂ content.
It is in the range of 2% by weight.

As described above, the coarse-grained portion is composed of a mineral phase mainly composed of corundum, the binding portion is composed of a glass phase mainly composed of SiO ₂ components, and mullite is mainly taken into the binding portion as coarse or fine particles. It can be confirmed by a micrograph that the particles are present in an inclined state. To determine the composition of the mineral phase and glass phase in the porous plug refractory,
An X-ray microanalyzer or the like can be used.

Next, a method for manufacturing the porous plug refractory of the present invention will be described. In manufacturing the porous plug refractory of the present invention, (1) air permeability, (2) corrosion resistance,
(3) Thermal shock resistance and (4) strength must be ensured. The air permeability (1) is related to the particle size and content of the coarse-grained portion, and the corrosion resistance (2) is related to the Al ₂ O ₃ content.

The thermal shock resistance of (3) is a feature of the present invention as described above, and depends on the glass phase mainly composed of SiO ₂ component. Is important, and depends on the structure and bonding state of the entire porous plug refractory. Therefore, the overall composition including the raw materials and the particle size is important and closely related to the firing conditions. Therefore,
In order to satisfy all the characteristics required for each application in a well-balanced manner, specific raw material blending and firing conditions are required.

For a detailed explanation, the Al ₂ O ₃ − in FIG.
A phase equilibrium diagram of a binary system of SiO ₂ is used. The left end is Al ₂ O
₃ 100%, corundum crystal has a high melting point of 2000 ° C. or higher and has high corrosion resistance. In order to provide the porous plug refractory of the present invention with corrosion resistance, an alumina-based material mainly composed of corundum is used for the coarse-grained portion.

On the other hand, in order to make the bonding portion a glass phase mainly composed of SiO ₂ components, it is necessary to use a siliceous raw material and generate a liquid phase by heating and firing. Since the liquid phase does not crystallize and is solidified as it is the glass phase, bonding by the glass phase cannot be obtained unless the liquid phase is generated by firing and heating. That is, in FIG. 1, a liquid phase is generated at 1590 ° C. or higher between 100% of the rightmost SiO _{2 and} a mullite composition represented by 3Al ₂ O ₃ .2SiO ₂ ,
_At 100%, the melting point is 1,723 ° C, and unless it is higher than this, it does not become a liquid phase. When the alumina material and the siliceous material in the coarse portion are heated to 1590 ° C. or higher, a reaction occurs at the contact surface between the alumina material and the siliceous material, and a liquid phase is generated. It takes a very long time because the diffusion rate is determined by the diffusion rate. Therefore, when an alumina-silica-based two-component raw material is added, a liquid phase is generated if the raw material itself is heated to 1590 ° C. or higher. It becomes possible.

Even if the alumina raw material is added as fine powder in addition to the alumina raw material in the coarse-grained portion, the reaction with the silica raw material is relatively quick if the fine powder is used. The effect can be obtained. Further, FIG.
As can be seen, if the SiO ₂ content is too high at about 94% or more, cristobalite will be present together with the liquid phase. However, in the porous plug refractory of the present invention, although mullite is present as described above, there is no problem in thermal shock resistance, but cristobalite is not preferable because it shows abnormal expansion accompanying crystal transformation.

Therefore, it is also possible to add an alumina-based material as fine powder so as not to generate cristobalite, and to adjust so as to be in a region where a liquid phase and mullite exist.

Here, the particle size of each raw material is also important.
If the alumina-based raw material in the coarse-grained portion is not present as corundum coarse particles even after firing and heating, it is impossible to stably secure air permeability and the corrosion resistance is reduced.
These grain sizes should be used. However, if a large amount of particles exceeding 2 mm is contained, the particles may fall off due to a difference in expansion behavior with the surrounding bonding portion glass phase. In addition, it is more preferably 1 to 0.3 mm.

On the other hand, since the siliceous raw material is used to form the bonding portion, if it is liquefied by baking and heating, the particle size of the starting raw material does not matter, but 1 mm is used so that it can be more easily liquefied. The following particles are preferably used: More preferably, it is 0.5 mm or less.

Similarly, the particle size of the alumina-siliceous raw material does not essentially matter, but since it is used to promote the liquid phase, particles of 1 mm or less are used to facilitate the liquid phase. Is preferred. More preferably, it is 0.5 mm or less.

Since the fine alumina powder other than the coarse alumina powder is used for liquid phase generation or composition adjustment as described above, a fine powder of less than 0.3 mm is preferable.

Alumina raw materials of 2 to 0.3 mm should be used in an amount of 40% by weight or more in order to maintain stable air permeability and good corrosion resistance. On the other hand, if it exceeds 90% by weight, it is necessary to form a glass phase mainly composed of SiO ₂ within the remaining range of less than 10% by weight. In order to form a glass phase, the alumina raw material should be 90% by weight or less. In addition, it is more preferably in the range of 50 to 85% by weight.

The siliceous raw material of 1 mm or less is required to be 5% by weight or more to form a glass phase bond. If it is used in excess of 25% by weight, the absolute amount of the glass phase becomes too large, which may cause problems such as a decrease in hot strength, which is not preferable. More preferably, it is in the range of 8 to 20% by weight.

The alumina-siliceous raw material of 1 mm or less is
In combination with a siliceous raw material, 5% by weight or more is required to easily form a glass phase. However, if it exceeds 30% by weight, silica may be insufficient, which is not preferable. More preferably, it is in the range of 8 to 25% by weight.

It is not always necessary to use an alumina raw material having a size of less than 0.3 mm, but the use of a small amount can increase the degree of freedom in selecting the entire raw material. The reason for using it is as described above. If the content exceeds 20% by weight, the content of Al ₂ O ₃ in the glass phase component increases, and the low expansion property characteristic of the glass mainly composed of the SiO ₂ component is gradually lost. It is more preferably at most 15% by weight.

The composition having the raw material composition described in detail above may contain a binder, such as pulp waste liquor and molasses, as well as various sugars, starches and modified products thereof, and resins such as celluloses and phenolic resins. Mixed and kneaded. The amount of the binder to be added is about 1 to 12% by weight based on the solution in terms of the solution, preferably about 1.5 to 4% by weight in press molding and vibration molding, and 4 to 4% in cast molding.
About 12% by weight. After kneading, the obtained kneaded soil is
It can be formed by a usual method of forming a brick, for example, press forming, vibration forming, casting, and the like.

In the manufacturing process of the porous plug refractory of the present invention, the most important point together with the raw material composition is the firing conditions. In order to make the bonding part, which is a feature of the present invention, a glass phase mainly composed of a SiO ₂ component, a liquid phase must be generated during firing. For this purpose, as can be seen from FIG. 1, the raw material mixture as described above is used, and the maximum firing temperature is 1590.
Must be at least ° C. When the temperature is lower than 1590 ° C., a liquid phase is not generated or even if it is generated very little, it is impossible to form a bonding portion mainly composed of a glass phase of the present invention. On the other hand, if the maximum firing temperature exceeds 1780 ° C., the content of Al ₂ O ₃ in the liquid phase increases, and the low expansion property may be impaired, which is not preferable. Most preferably 16
20-1750 ° C.

Furthermore, in order to maintain the liquid phase generated during firing at room temperature after cooling, it is preferable that the rate of temperature decrease after passing through the maximum temperature is somewhat faster. It is preferable that the temperature drop rate from the maximum temperature to 800 ° C. is 30 ° C./hour or more. If the cooling rate is less than 30 ° C./hour, crystal precipitation from the liquid phase increases, or microcracks around the coarse-grained portion may undesirably increase. Although it is not a big problem that the cooling rate is somewhat fast, it is about 100 ° C /
If the time is less than the time, a stable tissue can be obtained.

Although the method for producing the porous plug refractory of the present invention has been described in detail, it goes without saying that the ventilation characteristics are important for the porous plug refractory. In the porous plug refractory of the present invention as well, in order to ensure sufficient air permeability, it is preferable to use an unmilled raw material for the alumina raw material of 2 to 0.3 mm. In the case of a pulverized raw material, since the shape of the particles includes non-uniform and flat particles, the air permeability changes depending on the arrangement of the particles. The unmilled raw material has a rounded particle surface, and has little effect on air permeability even if there is some change in the arrangement. More preferably, when a raw material which is an unground material and has a particle shape close to a sphere is used, a change in air permeability can be minimized. On the other hand, 0.3m
Since the alumina raw material having a molecular weight of m or less reacts with the silica raw material, it may be a pulverized raw material. Alumina raw material is Al
Sintered or electrofused alumina having a high ₂ O ₃ content is preferably used.

Since the siliceous raw material is used to form a liquid phase by firing and heating, and finally to form a bonding part by a glass phase, the type of the crystalline phase of the starting material or whether it is amorphous or not is determined. Does not matter, so anything is fine. If the SiO ₂ purity is high,
Siliceous, cristobalite, amorphous silica flour, fused quartz, or the like can be used. However,
When the siliceous raw material itself is amorphous from the beginning, that is, it is better to use a raw material such as a glassy fused silica raw material or silica flour instead of a crystal. Even if it occurs, the danger of remaining crystals can be avoided by using a glassy raw material.

The alumina-siliceous raw material is used to promote the formation of a liquid phase, and is not particularly limited as long as it is a raw material containing alumina-silica as a main component. Alternatively, a raw material or the like obtained by making them spherical or hollow can be used. Preferably, a raw material containing Al ₂ O _{3 in an amount} of 5% by weight or more is preferable since cristobalite is not easily produced when a liquid phase is formed. When the Al ₂ O ₃ content exceeds 72% by weight, the raw material itself does not start to form a liquid phase at 1590 ° C., but the alumina-siliceous raw material is a silica-based raw material used in an equivalent particle size range. When,
Liquid phase generation is possible by very slight contact,
A liquid phase can be formed much more easily than the reaction between an alumina material and a silica material of 2 to 0.3 mm.
Therefore, even if the Al ₂ O ₃ content exceeds 72% by weight, there is no particular problem. The most preferred alumina-siliceous feedstock is a mullite feedstock. Use of a mullite raw material such as synthetic mullite as an alumina-siliceous raw material is advantageous because even if all of the raw material does not become a liquid phase and remains, it hardly affects the thermal shock resistance of the entire porous plug refractory. is there.

In addition, a small amount of chromium oxide, zirconia, zircon, etc., for example, 0.3 to 5% by weight is used to adjust and improve the corrosion resistance and slag infiltration of the porous plug refractory.
A small amount of a boron compound or a lithium compound, for example, about 0.1 to 3% by weight, may be added for adjusting glass formation.

[0044]

【Example】

Example 3% by weight of pulp waste liquid was externally added as a binder to a raw material compound having a compounding ratio shown in the following table, kneaded, formed into a predetermined shape, and then fired at the maximum firing temperature described in the table. As a result, porous plug refractories of the present invention and comparative products were produced. The resulting porous plug refractory was subjected to a thermal shock resistance, a hot strength, and a slag erosion test, and the obtained results are shown in the following table. The thermal shock resistance was measured by placing the sample in an electric furnace heated to 1200 ° C., holding it for 15 minutes, taking it out, and immediately putting it in water.
This operation was repeated, and the number of repetitions until the sample was broken was counted. Therefore, the larger the numerical value is, the more the number of times until the crack is broken, indicating that it is difficult to break. As for the hot strength, a hot bending strength at 1400 ° C. was measured. Furthermore, the slag erosion test was performed using a rotating crucible method, and the erosion amount and the infiltration amount were compared. The value of each sample at the left end in the table is represented by an index with 100 being the value. The smaller the numerical value of both erosion and infiltration, the better.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

It is clear from the results in the above table that all of the porous plug refractories of the present invention have excellent thermal shock resistance and high hot strength. The erosion amount is related to the Al ₂ O ₃ content (chemical component value) in the porous plug refractory, but it can be seen that the slag infiltration amount of the present invention is smaller. This is presumably due to the effect of glass phase bonding mainly composed of the SiO ₂ component.

FIG. 2 shows a micrograph showing the particle structure in the structure of the porous plug refractory of the product 9 of the present invention. In FIG. 2, C is corundum, M is mullite, G is a glass phase,
P indicates pores, respectively. From FIG. 2, the porous plug refractory of the present invention has a coarse-grained portion composed of a mineral phase mainly composed of corundum, a binding portion composed of a glass phase mainly composed of SiO ₂ component, and mullite having a coarse or fine particle in the binding portion. It turns out that it exists in the state taken in.

[0050]

The porous plug refractory of the present invention has the effects of excellent thermal shock resistance, high hot strength, and low slag infiltration.

[Brief description of the drawings]

FIG. 1 is an alumina-silica-based phase diagram.

FIG. 2 is a micrograph showing the particle structure in the structure of the porous plug refractory of the product 9 of the present invention.

Claims (5)

[Claims] 1. 70 to 92% by weight of Al ₂ O ₃ and SiO ₂
A porous plug refractory having a chemical composition of 8 to 30% by weight, wherein a coarse-grained portion is composed of a mineral phase mainly composed of corundum, and a bonding portion is composed of a glass phase mainly composed of SiO ₂ component. 2. The method for producing a porous plug refractory according to claim 1, wherein the alumina raw material 4 has a thickness of 2 to 0.3 mm.
0 to 90% by weight, 5 to 25% by weight of 1 mm or less siliceous raw material and 5 to 30% of 1 mm or less alumina-siliceous raw material
A method for producing a porous plug refractory, comprising blending, kneading, molding and baking by weight. 3. An alumina-based raw material having a size of less than 0.3 mm is used for 20 times.
The method for producing a porous plug refractory according to claim 2, wherein the refractory is blended in an amount of not more than% by weight. 4. An alumina raw material having a diameter of 2 to 0.3 mm is an unground material, at least a part of a siliceous raw material is amorphous silica, and at least a part of an alumina-siliceous raw material is a mullite raw material. The method for producing a porous plug refractory according to claim 2 or 3. 5. The maximum firing temperature of the molded product is 1590-17.
The method for producing a porous plug refractory according to any one of claims 2 to 4, wherein the temperature is 80 ° C.