JP7705368B2 - Refractory brick and its manufacturing method - Google Patents

Description

The present invention relates to refractory bricks that use used refractories (scrap refractories) as part of the raw materials, and a method for producing the same.

In steelworks, refractories are used in various equipment that processes molten materials (hot metal, molten steel, molten slag) in the pig iron and steel making processes, as well as in the containers that transport the molten materials. These refractories are required to be stable even when in contact with high-temperature molten materials and to experience minimal temperature drop during transportation, but they inevitably deteriorate over time as they are used. These refractories gradually become damaged through long-term use at high temperatures, and when it is determined that stable operation is no longer possible, they are dismantled and turned into refractory scrap. This refractory scrap has limited uses, and much of it is disposed of as industrial waste, but in recent years there has been a demand to reduce the amount of refractory scrap generated, and it is desirable to reuse refractory scrap as a refractory raw material.

Regarding bricks in which used refractories are reused as part of the raw materials, for example, Patent Document 1 describes that recycled bricks in which used refractories made of alumina, silica (rose stone), silicon carbide, and carbonaceous material are crushed to a particle size of 3 mm or less and the crushed material is used as part of the raw materials in an amount of 10 to 60 mass % have spall resistance equal to or greater than that of bricks made using only virgin raw materials, which are unused refractory raw materials, but that the spall resistance decreases when the crushed used refractories are mixed in an amount exceeding 60 mass %.
Furthermore, Patent Document 2 describes that a refractory brick using refractory waste obtained by crushing used refractory materials made of alumina, silica, silicon carbide, and carbon as part of the raw materials has durability equivalent to that of a refractory brick using only virgin raw materials by optimizing the particle size distribution of the refractory waste, the particle size distribution of the virgin raw materials, and the component amounts of the refractory waste and the virgin raw materials.

JP 2010-155764 A JP 2018-62459 A

However, according to the findings of Patent Document 1, when the amount of refractory waste exceeds 60 mass %, spalling resistance and resistance to melting damage decrease, and therefore the amount of refractory waste cannot be increased to more than 60 mass %.
Furthermore, the refractory bricks of Patent Document 2 require the incorporation of a large amount of refractory chips having a particle size of more than 2.8 mm, and it is not possible to incorporate a large amount of refractory chips having a particle size of 2.8 mm or less, which is common among the refractory chips. Furthermore, if the particle size distribution and component amounts of all the refractory raw materials, including the refractory chips and virgin raw materials, are not optimized, the refractory bricks cannot be densified unless a sufficient molding pressure is applied.

The object of the present invention is therefore to solve the problems of the prior art as described above, and to provide a dense refractory brick made of alumina, silica, silicon carbide, or carbonaceous material, which contains a large amount of refractory waste, and which has excellent durability, i.e., spall resistance (crack resistance) and corrosion resistance (resistance to melting and disintegration), comparable to refractory bricks made using only virgin raw materials, even when a large amount of refractory waste with a relatively small particle size (particle size 2.8 mm or less or particle size 2.36 mm or less) is blended. Another object of the present invention is to provide a manufacturing method that can stably manufacture such refractory bricks.

The features of the present invention for solving the above problems are as follows.
[1] In alumina, silica, silicon carbide, and carbonaceous refractory bricks,
The refractory waste (x), which is a crushed product of used refractory material made of alumina, silica, silicon carbide, or carbon, and has a particle size of 8 mm or less, is contained in an amount of 17% by mass or more and 90% by mass or less of all refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials),
The refractory scrap (x) contains 3% by mass or more of refractory scrap having a particle size of more than 2.36 mm in the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials),
A refractory brick characterized in that the content ratio (mass ratio) of refractory shavings (x) having a particle size of more than 2.36 mm and refractory shavings having a particle size of 2.36 mm or less and more than 1 mm is 1:1 to 1:20.
[2] The refractory brick according to the above [1], characterized in that the refractory scrap (x) contains refractory scrap having a particle size of 2.36 mm or less in an amount of 42 mass% or more in the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials).

[3] In alumina, silica, silicon carbide, and carbonaceous refractory bricks,
The refractory waste (x), which is a crushed product of used refractory material made of alumina, silica, silicon carbide, or carbon, and has a particle size of 8 mm or less, is contained in an amount of 17% by mass or more and 90% by mass or less of all refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials),
The refractory scrap (x) contains refractory scrap having a particle size of more than 2.8 mm in an amount of 1 mass% or more in the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials),
A refractory brick characterized in that the content ratio (mass ratio) of refractory shavings (x) having a particle size of more than 2.8 mm and refractory shavings having a particle size of 2.8 mm or less and more than 1 mm is 1:6 to 1:69.

[4] The refractory brick according to the above [3], characterized in that the refractory shavings (x) have a particle size of 2.8 mm or less and account for 42 mass% or more of the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials).
[5] The refractory brick according to any one of the above [1] to [4], characterized in that the refractory scrap (x) is contained in an amount of more than 60 mass% and not more than 90 mass% of all refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials).
[6] The refractory brick according to any one of the above [1] to [5], characterized in that the proportion of refractory raw materials having a particle size of 1 mm or less in the unused refractory raw materials (excluding cases where the unused refractory raw materials contain metal Si) is 10% by mass or more and 40% by mass or less.

[7] The refractory brick according to any one of the above [1] to [6], characterized in that the alumina content in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 50% by mass or more and 70% by mass or less, and the silica content is 10% by mass or more and 30% by mass or less.
[8] The refractory brick according to any one of the above [1] to [7], characterized in that the alumina content in the refractory raw material having a particle size of 1 mm or less (excluding cases where unused refractory raw material contains metallic Si) is 10 mass% or more and 30 mass% or less.
[9] The refractory brick according to any one of the above [1] to [8], characterized in that the free carbon content in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 12 mass% or less.

[10] The refractory brick according to any one of the above [1] to [9], characterized in that the refractory brick contains 2% by mass or more and 30% by mass or less of unused silica raw material in the total refractory raw materials (excluding cases where the unused refractory raw material contains metallic Si).
[11] The refractory brick according to any one of the above [1] to [10], characterized in that the silica raw material is made of rosewood or mullite, and the content ratio (mass ratio) of the silica raw material having a particle size of 2.8 mm or less and exceeding 1 mm to the silica raw material having a particle size of 1 mm or less is 2:1 to 2:4.
[12] The refractory brick according to any one of the above [1] to [11], characterized in that the refractory brick contains unused alumina raw material in an amount of 6 mass% to 45 mass% of the total refractory raw materials (excluding cases where the unused refractory raw material contains metallic Si).
[13] The refractory brick according to any one of the above [1] to [12], characterized in that the refractory brick contains unused silicon carbide raw material in an amount of 2 mass% to 8 mass% in total refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si).

[14] A method for producing an alumina-silica-silicon carbide-carbonaceous refractory brick, comprising the steps of:
A method for producing a refractory brick, comprising: mixing refractory scrap (x) having a particle size of 8 mm or less obtained by pulverizing used refractory material made of alumina, silica, silicon carbide, or carbon, the refractory scrap (x) having a content ratio (mass ratio) of refractory scrap exceeding 2.36 mm in particle size to refractory scrap exceeding 1 mm in particle size of 2.36 mm or less and refractory scrap exceeding 1 mm in particle size of 1:1 to 1:20 with unused refractory raw materials such that the proportion of the refractory scrap (x) in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 17% by mass or more and 90% by mass or less, and the proportion of the refractory scrap (x) having a particle size of more than 2.36 mm in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 3% by mass or more.
[15] The method for producing a refractory brick according to the above [14], characterized in that the refractory scrap (x) is mixed with unused refractory raw materials so that the proportion of the refractory scrap (x) having a particle size of 2.36 mm or less in the total refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 42 mass% or more.

[16] A method for producing an alumina-silica-silicon carbide-carbonaceous refractory brick, comprising the steps of:
A method for producing a refractory brick, comprising: mixing refractory scrap (x) having a particle size of 8 mm or less obtained by pulverizing used refractory material made of alumina, silica, silicon carbide, or carbon, with unused refractory raw materials, the refractory scrap (x) having a content ratio (mass ratio) of refractory scrap exceeding 2.8 mm in particle size to refractory scrap exceeding 1 mm in particle size of 2.8 mm or less and refractory scrap exceeding 1 mm in particle size of 1:6 to 1:69, the refractory scrap (x) being 17% by mass or more and 90% by mass or less in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si), and mixing the refractory scrap (x) having a particle size of more than 2.8 mm in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si), so that the proportion of the refractory scrap (x) in all refractory raw materials is 17% by mass or more and 90% by mass or less, and the proportion of the refractory scrap (x) having a particle size of more than 2.8 mm in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si), is 1% by mass or more.

[17] The method for producing a refractory brick according to the above [16], characterized in that the refractory scrap (x) is mixed with unused refractory raw materials so that the proportion of the refractory scrap (x) having a particle size of 2.8 mm or less in the total refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 42 mass% or more.
[18] A method for producing a refractory brick according to any one of the above-mentioned [14] to [17], characterized in that the refractory scrap (x) is mixed with unused refractory raw materials so that the proportion of the refractory scrap (x) in the total refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is more than 60 mass% and not more than 90 mass%.
[19] The method for producing a refractory brick according to any one of the above [14] to [18], characterized in that the proportion of refractory raw materials having a particle size of 1 mm or less in the unused refractory raw materials (excluding cases where the unused refractory raw materials contain metal Si) is 10 mass % or more and 40 mass % or less.

[20] In any one of the manufacturing methods according to [14] to [19] above, the method for manufacturing a refractory brick comprises blending refractory waste (x) with unused refractory raw materials so that the alumina content in the total refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 50% by mass or more and 70% by mass or less, and the silica content is 10% by mass or more and 30% by mass or less.
[21] A method for producing a refractory brick according to any one of the above [14] to [20], characterized in that refractory waste (x) is mixed with unused refractory raw materials so that the alumina content in the refractory raw materials having a particle size of 1 mm or less (excluding cases where the unused refractory raw materials contain metal Si) is 10 mass% or more and 30 mass% or less.
[22] A method for producing a refractory brick according to any one of the above-mentioned [14] to [21], characterized in that refractory waste (x) is mixed with unused refractory raw materials so that the free carbon content in all refractory raw materials (excluding cases where unused refractory raw materials contain metal Si) is 12 mass% or less.

[23] A method for producing a refractory brick according to any one of the above-mentioned [14] to [22], characterized in that the unused silica raw material is blended in such a manner that the ratio of the unused silica raw material in the total refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 2% by mass or more and 30% by mass or less.
[24] The method for producing a refractory brick according to any one of the above [14] to [23], wherein the silica raw material is made of rosewood or mullite, and the content ratio (mass ratio) of the silica raw material having a particle size of 2.8 mm or less and exceeding 1 mm to the silica raw material having a particle size of 1 mm or less is 2:1 to 2:4.
[25] A method for producing a refractory brick according to any one of the above-mentioned [14] to [24], characterized in that the unused alumina raw material is blended in such a manner that the ratio of the unused alumina raw material in the total refractory raw materials (excluding cases in which the unused refractory raw materials contain metallic Si) is 6 mass% or more and 45 mass% or less.
[26] A method for producing a refractory brick according to any one of the above [14] to [25], characterized in that unused silicon carbide raw materials are blended in such a manner that the ratio of the unused silicon carbide raw materials in the total refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 2% by mass or more and 8% by mass or less.

The refractory brick of the present invention contains a considerable amount of used refractory material made of alumina, silica, silicon carbide, and carbon, and the used refractory material has a relatively small particle size. Nevertheless, the refractory brick of the present invention has excellent durability, i.e., spalling resistance (crack resistance) and corrosion resistance (resistance to melting and corrosion), which is not inferior to refractory bricks made using only virgin raw materials.
The blast furnace ladle used for molten iron pretreatment has an open structure with no lid on the roof, and since the molten iron is repeatedly received and discharged, the temperature changes during operation are large, so alumina, silica, silicon carbide, and carbonaceous refractory bricks are used because they are less likely to become embrittled due to repeated heating and cooling over a long period of time. In steelworks, a large amount of used refractory is generated from such blast furnace ladle, but according to the present invention, it is possible to produce refractory bricks with a high ratio of used refractory, which is highly effective in reducing the raw material costs for refractories.

FIG. 1 is an explanatory diagram showing a manufacturing process of a refractory brick in an embodiment.

As described below, the present inventors have developed a refractory brick and a method for manufacturing the same, which contains a relatively large amount of used refractory material made of alumina, silica, silicon carbide, and carbon, and which has a relatively large amount of used refractory material with a relatively small particle size, and which has excellent durability (crack resistance and resistance to melting damage) that is not inferior to refractory bricks made using only unused refractory raw materials.
The refractory brick of the present invention is a brick made of an alumina-silica-silicon carbide-carbonaceous refractory, i.e., a refractory mainly composed of alumina, silica, silicon carbide and carbon, and contains a predetermined ratio of pulverized used alumina-silica-silicon carbide-carbonaceous refractories (hereinafter sometimes referred to as "recycled raw materials") as refractory raw materials in order to recycle used refractories.

The remainder of the refractory raw material is new, unused refractory raw material (hereinafter referred to as "virgin raw material"). The virgin raw material usually contains oxide-based raw materials (alumina raw material, silica raw material, etc.), carbon raw material, silicon carbide, metal Si, etc. Here, examples of oxide-based raw materials include alumina shale, brown alumina, white alumina, wax stone, mullite, etc., and one or more of these may be blended. Examples of carbon raw materials include scaly graphite, etc., and one or more of these may be blended. In this application, alumina raw materials are those with an alumina content of more than 50 mass% and a silica content of 15 mass% or less, such as alumina shale, brown alumina, and white alumina, and those with a silica content of more than 15 mass%, such as wax stone and mullite, are referred to as silica raw materials.

In the present invention, the recycled raw material is refractory waste with a particle size of 8 mm or less (hereinafter referred to as refractory waste (x)) which is crushed used refractory material made of alumina, silica, silicon carbide, or carbon. By using refractory waste (x) with such a particle size, the pores in the brick structure can be reduced during molding, and the required packing density can be obtained. If refractory waste (x) with a particle size exceeding 8 mm is included, the packing density of the molded body cannot be increased, and the proportion of pores in the brick structure increases, which may make molding difficult. In addition, like refractory waste, it is preferable that virgin raw materials also have a particle size of 8 mm or less.

Here, materials with a particle size of 8 mm or less (such as refractory waste) refer to materials that are under the sieve when sieved with a sieve with mesh size of 8 mm (nominal size), and materials with a particle size of more than 8 mm (such as refractory waste) refer to materials that are on the sieve. In the following description, materials with a particle size of 2.8 mm or less (such as refractory waste) refer to materials that are under the sieve when sieved with a sieve with mesh size of 2.8 mm (nominal size), and materials with a particle size of more than 2.8 mm (such as refractory waste) refer to materials that are on the sieve. In addition, materials with a particle size of 2.36 mm or less (such as refractory waste) refer to materials that are under the sieve when sieved with a sieve with mesh size of 2.36 mm (nominal size), and materials with a particle size of more than 2.36 mm (such as refractory waste) refer to materials that are on the sieve. In addition, materials with a particle size of 1 mm or less (such as refractory waste) refer to materials that fall under a sieve with 1 mm (nominal size) mesh, and materials with a particle size of more than 1 mm (such as refractory waste) refer to materials that fall over the sieve. In addition, materials with a particle size of 4.7 mm or less refer to materials that fall under a sieve with 4.7 mm (nominal size) mesh, and materials with a particle size of 5.15 mm or less (such as refractory waste) refer to materials that fall under a sieve with 5.15 mm (nominal size).

The refractory brick of the present invention has a content of refractory scrap (x) of 17% by mass or more and 90% by mass or less, preferably more than 60% by mass and 90% by mass or less, in the total refractory raw material (excluding cases where metal Si is contained as virgin raw material), and the remainder is virgin raw material. By blending the refractory scrap (x) in such a ratio, high spall resistance (crack resistance) and corrosion resistance (melting resistance) can be achieved at the same time, and low thermal conductivity can also be achieved (especially when the content of refractory scrap (x) is more than 60% by mass). The reason for this is that although recycled raw materials have a lower purity than virgin raw materials, by using recycled raw materials and virgin raw materials in combination, a significant decrease in the corrosion resistance of the alumina component in the recycled raw materials can be suppressed. Furthermore, by using recycled raw materials in combination with virgin raw materials, the bulk density and thermal conductivity are reduced compared to bricks made entirely from virgin raw materials (hereinafter referred to as "virgin bricks").

In the present invention, the particle size distribution of the refractory scrap (x) (proportion of refractory scrap of a specified particle size, blending ratio of refractory scrap divided by particle size), the proportion of virgin raw material of a specified particle size, the alumina and silica contents of the refractory raw material, etc. are optimized under the conditions described below, thereby making it possible to produce a refractory brick with excellent durability and low thermal conductivity. Note that the values of the content and content ratio (mass ratio) of the refractory scrap, the content of virgin raw material, and the component contents of the refractory raw material (free carbon amount, alumina and silica content) specified in the present invention are numbers rounded off to the nearest whole number.

In addition, the refractory brick of the first invention of the present application contains refractory scrap (x) having a particle size of more than 2.36 mm (coarse refractory scrap) in the total refractory raw material (excluding cases where metal Si is contained as virgin raw material) at 3 mass% or more, preferably 5 mass% or more. By setting the ratio of refractory scrap having a particle size of more than 2.36 mm in the total refractory raw material at 3 mass% or more, preferably 5 mass% or more, it is possible to suppress a decrease in crack resistance and melting damage resistance. Note that even if the ratio of refractory scrap having a particle size of more than 2.36 mm is somewhat high, it is sufficient as long as it is within a range in which other conditions are satisfied and molding is possible, so there is no particular upper limit for the ratio of refractory scrap having a particle size of more than 2.36 mm.
Furthermore, the content ratio (mass ratio) of refractory scrap with a particle size of more than 2.36 mm (coarse refractory scrap) and refractory scrap with a particle size of 2.36 mm or less and more than 1 mm (medium refractory scrap) in the refractory scrap (x) is set to 1:1 to 1:20. By setting the content ratio of the coarse refractory scrap to the medium refractory scrap within the above range, the densification of the bricks does not progress too much, so that the dynamic elastic modulus does not increase significantly, and the penetration of slag into the pores in the brick structure is suppressed, thereby improving the cracking resistance and the resistance to melting damage.

In addition, it is preferable that the proportion of refractory scrap (x) with a particle size of 2.36 mm or less (medium and fine refractory scrap) in the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials) is 42 mass% or more. This is because by making the proportion of medium and fine refractory scrap in the total refractory raw materials 42 mass% or more, high cracking resistance and resistance to melting damage are ensured while improving moldability, making it easier to densify the bricks and enabling mass production. Note that even if the proportion of refractory scrap with a particle size of 2.36 mm or less is somewhat high, it is sufficient as long as it is within a range that satisfies other conditions and can be molded, so there is no particular upper limit on the proportion of refractory scrap with a particle size of 2.36 mm or less.

First, the refractory brick of the second invention of the present application contains refractory scrap (x) having a particle size of more than 2.8 mm (coarse refractory scrap) in the total refractory raw material (excluding cases where metal Si is contained as virgin raw material) at 1 mass % or more, preferably 5 mass % or more. By setting the ratio of refractory scrap having a particle size of more than 2.8 mm in the total refractory raw material to 1 mass % or more, preferably 5 mass % or more, it is possible to suppress the deterioration of cracking resistance and melting damage resistance. Note that even if the ratio of refractory scrap having a particle size of more than 2.8 mm is somewhat high, it is sufficient as long as it is within a range in which other conditions are satisfied and molding is possible, so there is no particular upper limit for the ratio of refractory scrap having a particle size of more than 2.8 mm.
Furthermore, the content ratio (mass ratio) of refractory scrap with a particle size of more than 2.8 mm (coarse refractory scrap) and refractory scrap with a particle size of 2.8 mm or less and more than 1 mm (medium refractory scrap) in the refractory scrap (x) is set to 1:6 to 1:69. By setting the content ratio of the coarse refractory scrap to the medium refractory scrap within the above range, the densification of the bricks does not progress too much, so that the dynamic elastic modulus does not increase significantly, and the penetration of slag into the pores in the brick structure is suppressed, thereby improving the cracking resistance and the resistance to melting damage.

In addition, it is preferable that the proportion of refractory scrap (x) with a particle size of 2.8 mm or less (medium and fine refractory scrap) in the total refractory raw materials (excluding cases where metal Si is contained as virgin raw materials) is 42 mass% or more. This is because by making the proportion of medium and fine refractory scrap in the total refractory raw materials 42 mass% or more, high cracking resistance and resistance to melting damage are ensured while improving moldability, making it easier to densify the bricks and enabling mass production. Note that even if the proportion of refractory scrap with a particle size of 2.8 mm or less is somewhat high, it is sufficient as long as it is within a range that satisfies other conditions and can be molded, so there is no particular upper limit on the proportion of refractory scrap with a particle size of 2.8 mm or less.

The optimum conditions common to the first and second aspects of the present invention will now be described.
The refractory brick of the present invention contains virgin raw materials (excluding cases where the virgin raw materials contain metal Si) in an amount of 10% by mass to 83% by mass, preferably 10% by mass to less than 40% by mass, of the total refractory raw materials (excluding cases where the virgin raw materials contain metal Si). It is preferable that the proportion of virgin raw materials having a particle size of 1 mm or less among the virgin raw materials is 10% by mass to 40% by mass. This further improves the corrosion resistance and maintains a high residual expansion coefficient. The reason for this is that if the proportion of virgin raw materials having a particle size of 1 mm or less is within the above range, virgin raw materials having a particle size of 1 mm or less are added to the matrix in the brick structure, so that the penetration of slag into the matrix can be further suppressed, and the densification of the brick does not progress too much, so that a high residual expansion coefficient can be maintained.

It is preferable that the alumina content in all refractory raw materials (excluding cases where metal Si is contained as virgin raw materials) is 50% by mass or more and 70% by mass or less, and the silica content is 10% by mass or more and 30% by mass or less, thereby maintaining high crack resistance and corrosion resistance. The reason is as follows. Alumina is a high melting point material of 2000°C or more, and has a corrosion resistance effect for slags of a relatively wide composition range, and when the alumina content is 50% by mass or more, the corrosion resistance effect appears significantly. However, when the alumina content exceeds 70% by mass, the silica content becomes less than 30% by mass, and the crack resistance decreases. In addition, when silica undergoes a phase transition reaction at high temperatures, it expands to generate fine cracks, and these fine cracks reduce the elastic modulus, thereby increasing the thermal shock fracture resistance proportional to the strength/elastic modulus ratio. If the silica content is 10% by mass or more, the thermal shock fracture resistance increases, but if it is less than 10% by mass, the amount of expansion is small and fine cracks do not form, so the thermal shock fracture resistance does not increase and the crack resistance decreases. However, if the silica content exceeds 30% by mass, low-melting point substances are easily generated at high temperatures and the amount of liquid phase generated also increases, so the resistance to melting damage decreases.

In addition, the alumina content in the refractory raw material having a particle size of 1 mm or less (excluding cases where metallic Si is contained as a virgin raw material) is preferably 10% by mass or more and 30% by mass or less, which makes it possible to maintain high corrosion resistance and crack resistance. The reason for this is that it is possible to suppress the penetration of slag into the matrix, which greatly affects the corrosion resistance of the brick.
In addition, the free carbon content in all refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials) is preferably 12 mass% or less. That is, by adding virgin carbon raw materials so that the free carbon content in all refractory raw materials is 12 mass% or less, the thermal conductivity of the brick can be made almost constant at about 10 to 12 W/mK, and low thermal conductivity can be realized.

To investigate the relationship between the amount of free carbon and thermal conductivity of alumina-silica-silicon carbide-carbonaceous refractory bricks, bricks made from refractory raw materials (virgin raw materials) as shown in Table 1, with five levels of scaly graphite content (1 mass%, 6 mass%, 9 mass%, 12 mass%, and 15 mass%) were manufactured using the process shown in Figure 1, and the thermal conductivity of these refractory bricks was measured using the laser flash method. As shown in Table 1, the thermal conductivity decreased with decreasing free carbon content, but was almost constant at about 10 to 12 W/mK when the free carbon content was 12 mass% or less. This result shows that alumina-silica-silicon carbide-carbonaceous refractory bricks can have low thermal conductivity if the free carbon content is 12 mass% or less.

As at least a part of the virgin raw material, the silica raw material is preferably contained in an amount of 2% by mass to 30% by mass in the total refractory raw material (excluding the case where metal Si is contained as an unused refractory raw material). By making the content of the virgin silica raw material in the total refractory raw material 2% by mass to 30% by mass, both high crack resistance and high erosion resistance can be achieved. If the content of the virgin silica raw material in the total refractory raw material is less than 2% by mass, the expansion amount of quartz (SiO ₂ ) contained in the raw material is small when it undergoes phase transition at high temperatures, and fine cracks are not generated, so that the elastic modulus is not reduced, and the thermal shock fracture resistance is not increased, and the crack resistance is likely to be reduced. In addition, if the content of the virgin silica raw material in the total refractory raw material exceeds 30% by mass, the high-temperature molten material containing a large amount of slag components is easily penetrated, and the erosion resistance is likely to be reduced.

As virgin silica raw material, waxstone or mullite is preferred, and in this case, the silica raw material (waxstone or mullite) preferably has a content ratio (mass ratio) of silica raw material with a particle size of 2.8 mm or less but over 1 mm to silica raw material with a particle size of 1 mm or less of 2:1 to 2:4. This can improve crack resistance and resistance to melting damage in particular. The reason for this is that within the above particle size range, the grain boundary area through which the slag penetrates can be reduced, and since aggregate with a particle size of 1 mm or less is present in the matrix within the brick structure, slag penetration into the matrix can be suppressed. In addition, since the bricks do not become too dense and creep deformation is imparted, in addition to suppressing the opening of joints between bricks, a significant increase in the dynamic modulus can be suppressed, and the crack resistance is improved, thereby suppressing the occurrence of cracks and peeling.

As at least a part of the virgin raw material, it is preferable that the alumina raw material is contained in an amount of 6% by mass to 45% by mass in the total refractory raw material (excluding cases where metal Si is contained as unused refractory raw material). By making the content of the virgin alumina raw material in the total refractory raw material 6% by mass to 45% by mass, erosion of the slag can be suppressed and high erosion resistance can be maintained. If the content of the virgin alumina raw material in the total refractory raw material is less than 6% by mass, erosion of the slag cannot be suppressed and erosion resistance is likely to decrease. The reason is that alumina is a high melting point substance and shows excellent erosion resistance effect against slag in a relatively wide composition range at 2000 ° C or more, but if the content of the alumina raw material is less than 6% by mass, the amount of alumina in the raw material decreases, and the erosion resistance effect decreases. On the other hand, if the content of virgin alumina raw material in the total refractory raw material exceeds 45 mass%, the impurity components in the alumina raw material increase, making it easier for the molten material to penetrate, and the corrosion resistance tends to decrease.

As at least a part of the virgin raw material, the silicon carbide raw material is preferably contained in an amount of 2% by mass to 8% by mass in the total refractory raw material (excluding the case where metal Si is contained as an unused refractory raw material). By making the content of the virgin silicon carbide raw material in the total refractory raw material 2% by mass to 8% by mass, the oxidation prevention effect of carbon and high corrosion resistance can be maintained. If the content of the virgin silicon carbide raw material in the total refractory raw material is less than 2% by mass, the oxidation prevention effect of carbon is small and oxidation of carbon progresses, so that crack resistance is likely to decrease. On the other hand, if the content of the virgin silicon carbide raw material in the total refractory raw material exceeds 8% by mass, the oxidation reaction of SiC progresses and changes to SiO ₂ , so that corrosion resistance is likely to decrease.

In the present invention, the used refractory material to be recycled may contain impurities such as slag. If the amount of impurities mixed in increases, the quality of the refractory brick may be reduced. Therefore, it is preferable that the amount of impurities such as slag contained in the used refractory material is 3.5 mass% or less.
In the refractory brick of the present invention, particularly when the content of the refractory scrap (x) is more than 60 mass % and not more than 90 mass % of the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials), it is preferable to mix the refractory raw materials so as to satisfy all of the above-mentioned conditions, and this makes it possible to obtain a recycled refractory scrap brick that has particularly excellent cracking resistance and melting wear resistance, is dense, and has low thermal conductivity.

Next, a method for producing the refractory brick of the present invention will be described.
In producing the refractory brick of the present invention, first, recovered used alumina-silica-silicon carbide-carbon refractories are pulverized and then classified to prepare refractory shavings (x) having a particle size of 8 mm or less as a recycled raw material, the refractory shavings (x) having a content ratio (mass ratio) of refractory shavings having a particle size of more than 2.36 mm to refractory shavings having a particle size of 2.36 mm or less and over 1 mm of 1:1 to 1:20, or the refractory shavings (x) having a content ratio (mass ratio) of refractory shavings having a particle size of more than 2.8 mm to refractory shavings having a particle size of 2.8 mm or less and over 1 mm of 1:6 to 1:69. In a specific preparation method, the recovered used refractory material made of alumina, silica, silicon carbide, or carbon is crushed by a crusher to a particle size of, for example, 8 mm or less, and then sieved to separate the refractory waste into three particle size classes: refractory waste with a particle size of more than 2.36 mm (8 mm or less), refractory waste with a particle size of 2.36 mm or less and over 1 mm, and refractory waste with a particle size of 1 mm or less, or refractory waste with a particle size of more than 2.8 mm (8 mm or less), refractory waste with a particle size of 2.8 mm or less and over 1 mm, and refractory waste with a particle size of 1 mm or less. Then, the refractory waste of these three particle size classes is blended (mixed) in a predetermined ratio to prepare the refractory waste (x) satisfying the above conditions.

The prepared refractory scrap (x) is mixed with virgin raw materials so that the proportion of the refractory scrap (x) in the total refractory raw materials (excluding cases where metal Si is contained as a virgin raw material) is 17% by mass or more and 90% by mass or less, and the proportion of the refractory scrap with a particle size of more than 2.36 mm in the total refractory raw materials (excluding cases where metal Si is contained as a virgin raw material) is 3% by mass or more, or the proportion of the refractory scrap with a particle size of more than 2.8 mm in the total refractory raw materials (excluding cases where metal Si is contained as a virgin raw material) is 1% by mass or more, to form a refractory raw material for molding into bricks.

Preferably, the raw materials are blended under one or more of the following conditions (i) to (x):
(i) The refractory scrap (x) is blended with virgin raw materials so that the proportion of the refractory scrap (x) having a particle size of 2.36 mm or less or the refractory scrap having a particle size of 2.8 mm or less in the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials) is 42 mass% or more.
(ii) The refractory scrap (x) is blended with virgin raw materials so that the proportion of the refractory scrap (x) in the total refractory raw materials (excluding cases where the virgin raw materials contain metallic Si) is more than 60 mass% and not more than 90 mass%.
(iii) The proportion of virgin raw material having a particle size of 1 mm or less among the virgin raw material (excluding cases where metallic Si is contained) is set to 10 mass % or more and 40 mass % or less.

(iv) Refractory shavings (x) are blended with virgin raw materials so that the alumina content in the total refractory raw materials (excluding cases where the virgin raw materials contain metallic Si) is 50% by mass or more and 70% by mass or less, and the silica content is 10% by mass or more and 30% by mass or less.
(v) Refractory scrap (x) is mixed with virgin raw materials having a particle size of 1 mm or less (excluding cases where the virgin raw materials contain metallic Si) so that the alumina content in the virgin raw materials is 10 mass % or more and 30 mass % or less.
(vi) Refractory scrap (x) is mixed with virgin raw materials so that the free carbon content in all refractory raw materials (excluding cases where the virgin raw materials contain metallic Si) is 12 mass% or less.

(vii) The unused silica raw material is blended so that its proportion in the total refractory raw materials (excluding cases in which metallic Si is contained as unused refractory raw materials) is 2% by mass or more and 30% by mass or less.
(viii) The silica raw material is made of rosewood or mullite, and the content ratio (mass ratio) of the silica raw material having a particle size of 2.8 mm or less but exceeding 1 mm to the silica raw material having a particle size of 1 mm or less is 2:1 to 2:4.
(ix) The unused alumina raw material is blended so that its proportion in the total refractory raw materials (excluding cases in which the unused refractory raw materials contain metallic Si) is 6 mass % or more and 45 mass % or less.
(x) The unused silicon carbide raw material is blended so that its proportion in the total refractory raw materials (excluding cases in which the unused refractory raw materials contain metallic Si) is 2 mass % or more and 8 mass % or less.
The reasons for limiting the particle size, blending amount, blending ratio (mass ratio), free carbon content, particle size of the virgin raw material, alumina and silica contents, etc. of the refractory waste are as described above.

The refractory raw material prepared as above is mixed with a binder, then molded (press molded) into a brick shape, and then typically cured (dried) to produce a finished brick (unfired brick). Alternatively, after curing (drying), the brick may be further subjected to reduction firing (caulking treatment) to produce a finished brick (fired brick). Examples of binders that can be used include phenolic resin (base material) + hexamine (hardener), carbon bond, and ceramic bond. For example, in the case of phenolic resin (base material) + hexamine (hardener), the amount of binder added is usually about 3 mass % of phenolic resin and 0.3 mass % of hexamine, based on the outer percentage of the refractory raw material.
The molding pressure when molding (press molding) the refractory raw material is preferably 150 MPa or more in order to obtain a dense brick.

Usually, curing (drying) is carried out at 200 to 230° C. for about 18 to 48 hours, and when reduction firing (caulking treatment) is carried out, it is carried out at 1400 to 1500° C. for about 3 to 5 hours.
The refractory brick of the present invention can be used as a refractory material for various facilities and containers. In particular, the refractory brick is suitable as a refractory material lining the refining facilities of steelworks and transport containers for molten materials (molten pig iron, slag), and is particularly suitable as a refractory material for blast furnace ladles used in the preliminary treatment of molten pig iron.

In the following explanation, among the refractory scraps used as recycled raw materials, refractory scraps with a particle size of more than 2.8 mm (5.15 mm or less) are referred to as "+2.8 mm refractory scraps", refractory scraps with a particle size of 2.8 mm or less but more than 1 mm are referred to as "2.8-1 mm refractory scraps", refractory scraps with a particle size of more than 2.36 mm (5.15 mm or less) are referred to as "+2.36 mm refractory scraps", refractory scraps with a particle size of 2.36 mm or less but more than 1 mm are referred to as "2.36-1 mm refractory scraps", and refractory scraps with a particle size of 1 mm or less are referred to as "-1 mm refractory scraps". In addition, virgin raw materials with a particle size of 1 mm or less are referred to as "-1 mm virgin raw materials", and refractory raw materials with a particle size of 1 mm or less are referred to as "-1 mm refractory raw materials".

The collected used refractory materials (bricks) made of alumina, silica, silicon carbide, and carbon were crushed in a crusher to a particle size of 5.15 mm or less, then sieved and separated into three particle size categories: coarse (+2.8 mm or +2.36 mm) refractory scrap, medium (2.8-1 mm or 2.36-1 mm) refractory scrap, and fine (-1 mm) refractory scrap. The virgin raw materials used were oxide-based refractory raw materials such as aluminium shale of -1 mm, and 2.8-1 mm or 2.36-1 mm rosewood, SiC (fine powder), scaly graphite (fine powder), and metallic silicon (fine powder). The above refractory scrap and virgin raw materials were mixed in the ratios shown in Tables 2 to 9 and Tables 11 to 14 to produce refractory bricks using the manufacturing process shown in Figure 1. When kneading and molding the refractory raw materials, 3% by mass of phenolic resin and 0.3% by mass of hexamine were mixed as binders on an outer basis relative to the refractory raw materials.

Here, the examples in Table 2 examine the content (mixture amount) of +2.36 mm refractory scrap and the content ratio (mixture ratio) of +2.36 mm refractory scrap and 2.36-1 mm refractory scrap, the examples in Table 3 examine the content (mixture amount) of +2.8 mm refractory scrap and the content ratio (mixture ratio) of +2.8 mm refractory scrap and 2.8-1 mm refractory scrap, and the examples in Table 4 examine the content (mixture amount) of -2.36 mm refractory scrap. The examples in Table 5 are those that investigated the content (mixture amount) of refractory scrap, the examples in Table 6 are those that investigated the content (mixture amount) of -1 mm virgin raw material, the examples in Table 7 are those that investigated the alumina content and silica content in the refractory raw material, the examples in Table 8 are those that investigated the alumina content in the -1 mm refractory raw material, and the examples in Table 9 are those that investigated the molding pressure when molding (press molding) the refractory raw material. The examples in Table 11 are those that investigated the content of virgin silica raw material (rose stone) in the refractory raw material, the examples in Table 12 are those that investigated the effect of the particle size range of the virgin silica raw material (rose stone), the examples in Table 13 are those that investigated the content of virgin alumina raw material in the refractory raw material, and the examples in Table 14 are those that investigated the content of virgin silicon carbide raw material in the refractory raw material. For convenience of explanation, invention examples 2-3 listed in Table 3 are also listed in Tables 5, 7, and 9.

The manufactured refractory bricks were measured for bulk density, apparent porosity, thermal conductivity, bending strength, dynamic elastic modulus, residual expansion coefficient, and free carbon content, and were also evaluated for crack resistance and corrosion resistance. The measurement and evaluation methods are as follows:
The bulk density and apparent porosity were measured by the method specified in JIS R2205, the thermal conductivity was measured by the laser flash method, the bending strength was measured by the method specified in JIS R2213, and the dynamic elastic modulus was measured in accordance with the sound velocity measurement method. In addition, the amount of free carbon was measured by the chemical analysis method specified in JIS R2011.
Regarding the residual expansion coefficient, a thermal expansion test was carried out using a cylindrical sample according to the method specified in JIS R2207, and the difference ΔL = L ₁ - L ₀ between the dimension L ₀ before the test and the dimension L ₁ after the test was completed was calculated, and the residual expansion coefficient E _i was calculated using the following formula.
Residual expansion coefficient E _i (%) = ΔL/L ₀ ×100
The alumina content and silica content of the refractory raw material were determined by component analysis in accordance with "Chemical analysis method for refractories containing carbon and silicon carbide" described in JIS R2011.

For crack resistance, the dynamic modulus of elasticity _E0 in the longitudinal direction of a 30 x 30 x 100 mm sample was measured in accordance with the ultrasonic pulse method specified in JIS R1605, and then spalling was repeated three times, with one cycle consisting of heating at 1500°C for 10 minutes, water cooling for 5 minutes, and air cooling for 10 minutes. After spalling was completed, the dynamic modulus of elasticity _E3 was measured again, and the rate of change in the dynamic modulus of elasticity before and after the test, _E3 / _E0, was used as an index for evaluation.
The corrosion resistance was evaluated by a lining method using a high-frequency induction furnace. The test temperature was 1500°C, and the synthetic slag shown in Table 10 was added four times every hour. After the test, the amount of corrosion was measured, and a corrosion index was calculated by setting the amount of corrosion of Reference Example A in Table 1 as 100.
The above measured values of bulk density, apparent porosity, thermal conductivity, bending strength, dynamic elastic modulus, residual expansion coefficient and free carbon content, as well as the evaluation results of cracking resistance and corrosion resistance are shown in Tables 2 to 9 and Tables 11 to 14 together with the raw material blend ratios and brick configurations.

As shown in Table 2, the content of +2.36 mm refractory scrap and the content ratio of +2.36 mm refractory scrap to 2.36-1 mm refractory scrap were examined, and as shown in Examples 1-1 to 1-7, refractory bricks containing 3 mass% or more of +2.36 mm refractory scrap and having a content ratio of +2.36 mm refractory scrap to 2.36-1 mm refractory scrap in the range of 1:1 to 1:20 had bulk density, apparent porosity, residual expansion coefficient, cracking resistance, and corrosion resistance comparable to those of virgin bricks. In contrast, as shown in Comparative Examples 1-1 to 1-3, when the content of +2.36 mm refractory scrap was less than 3 mass% or the content ratio of +2.36 mm refractory scrap to 2.36-1 mm refractory scrap was outside the range of 1:1 to 1:20, the cracking resistance or corrosion resistance was significantly reduced.
From these results, it was found that the content of +2.36 mm refractory chipping should be 3 mass% or more, and the content ratio of +2.36 refractory chipping to 2.36-1 mm refractory chipping should be within the range of 1:1 to 1:20.

As shown in Table 3, the content of +2.8 mm refractory chipping and the content ratio of +2.8 mm refractory chipping to 2.8-1 mm refractory chipping were examined, and as shown in Examples 2-1 to 2-5, refractory bricks containing 1 mass% or more of +2.8 mm refractory chipping and having a content ratio of +2.8 mm refractory chipping to 2.8-1 mm refractory chipping in the range of 1:6 to 1:69 had bulk density, apparent porosity, residual expansion coefficient, cracking resistance, and corrosion resistance comparable to those of virgin bricks. In contrast, as shown in Comparative Examples 2-1 to 2-3, when the content of +2.8 mm refractory chipping was less than 1 mass% or the content ratio of +2.8 mm refractory chipping to 2.8-1 mm refractory chipping was outside the range of 1:6 to 1:69, the cracking resistance or corrosion resistance was significantly reduced.
From these results, it was found that the content of +2.8 mm refractory chips should be 1 mass% or more, and the content ratio of +2.8 mm refractory chips to 2.8-1 mm refractory chips should be within the range of 1:6 to 1:69.

As shown in Table 4-1, when the content of refractory chips having a particle size of 2.36 mm or less was examined, as shown in Example 3-1, when the content of refractory chips having a particle size of 2.36 mm or less was less than 42 mass%, the cracking resistance was about the same as when the content of refractory chips having a particle size of 2.36 mm or less was 42 mass% or more, but the resistance to melting damage was slightly inferior. However, the amount of deterioration was not so great as to have a significant effect on use in an actual machine.
Furthermore, as shown in Table 4-2, when the content of refractory chips having a particle size of 2.8 mm or less was examined, as shown in Example 3-5, when the content of refractory chips having a particle size of 2.8 mm or less was less than 42 mass%, the cracking resistance was about the same as when the content of refractory chips having a particle size of 2.8 mm or less was 42 mass% or more, but the melting damage resistance was slightly inferior. However, the amount of deterioration was not so great as to have a significant effect on the use in an actual machine.
As shown in Table 5, when the content of refractory scrap was examined, as shown in Examples 2-3 and 4-2 to 4-4, when the content of refractory scrap was more than 60 mass% and not more than 90 mass%, the same level of corrosion resistance as that of virgin bricks was obtained. On the other hand, as shown in Example 4-1, when the content of refractory scrap was less than 60 mass%, the bulk density was high and the thermal conductivity was quite high. Moreover, as shown in Comparative Example 4-1, when the content of refractory scrap was more than 90 mass%, the corrosion resistance was significantly reduced.

As shown in Table 6, when the content of -1 mm virgin raw material (excluding metallic Si; the same applies below) was examined, as shown in Examples 5-2 to 5-5, when the content of -1 mm virgin raw material was 10% by mass or more and 40% by mass or less, the bulk density, apparent porosity, residual expansion rate, crack resistance, and corrosion resistance were comparable to those of virgin bricks. On the other hand, as shown in Example 5-1, when the content of -1 mm virgin raw material was less than 10% by mass, compared to when the content of -1 mm virgin raw material was 10% by mass or more and 40% by mass or less, the crack resistance was comparable, but the corrosion resistance was slightly inferior. However, the amount of deterioration was such that it did not have a significant impact on use in actual equipment. Also, as shown in Example 5-6, when the content of -1 mm virgin raw material is more than 40 mass%, the resistance to corrosion is about the same as when the content of -1 mm virgin raw material is 10 mass% or more and 40 mass% or less, but the crack resistance is slightly inferior. However, the amount of deterioration is not so great that it has a significant effect on use in actual equipment.

As shown in Table 7, when the alumina and silica contents of all refractory raw materials, including recycled raw materials (scrap refractory materials) and virgin raw materials, were examined, as shown in Examples 2-3 and 6-2 and 6-3, when the alumina content was 50% by mass or more and 70% by mass or less and the silica content was 10% by mass or more and 30% by mass or less, cracking resistance and corrosion resistance equivalent to those of virgin bricks were obtained. On the other hand, as shown in Example 6-1, when the alumina content was less than 50% by mass and the silica content was more than 30% by mass, corrosion resistance was slightly inferior compared to when the alumina content was 50% by mass or less and 70% by mass or less and the silica content was 10% by mass or more and 30% by mass or less. However, the amount of deterioration was such that it did not have a significant effect on use in actual equipment. Also, as shown in Example 6-4, when the alumina content was over 70% by mass and the silica content was less than 10% by mass, the crack resistance was slightly inferior compared to when the alumina content was 50% to 70% by mass or less and the silica content was 10% to 30% by mass or less. However, the amount of deterioration was not significant enough to affect use in an actual machine.

As shown in Table 8, when the alumina content in the refractory raw material of -1 mm was examined, as shown in Examples 7-2 and 7-3, when the alumina content was 10% by mass or more and 30% by mass or less, the same level of corrosion resistance and cracking resistance as that of virgin bricks was obtained. On the other hand, as shown in Example 7-1, when the alumina content was less than 10% by mass, the corrosion resistance was slightly inferior to that when the alumina content was 10% by mass or more and 30% by mass or less. However, the deterioration amount was not so large that it had a significant effect on the use in the actual machine. Also, as shown in Example 7-3, when the alumina content was more than 30% by mass, the cracking resistance was slightly inferior to that when the alumina content was 10% by mass or more and 30% by mass or less. However, the deterioration amount was not so large that it had a significant effect on the use in the actual machine.
As shown in Table 9, when the raw materials having the composition of Inventive Example 2-3 are molded using devices with different molding pressures, it is found that in order to obtain a particularly dense refractory brick, it is preferable to set the molding pressure to 150 MPa or more.

As shown in Table 11, when the content of virgin silica raw material (rose stone) in all refractory raw materials was examined, as shown in Examples 9-2 to 9-5, when the content of virgin silica raw material (rose stone) in all refractory raw materials was 2% by mass or more and 30% by mass or less, both high crack resistance and high corrosion resistance were achieved. In contrast, as shown in Example 9-1, when the content of silica raw material (rose stone) was less than 2% by mass, corrosion resistance was maintained, but the crack resistance was slightly inferior. Also, as shown in Example 9-6, when the content of silica raw material (rose stone) was more than 30% by mass, crack resistance was maintained, but the corrosion resistance was slightly inferior. However, the amount of deterioration was not significant enough to affect use in actual equipment.

As shown in Table 12, when the effect of the particle size range of virgin silica raw material (rosewood) was examined, high cracking resistance and high erosion resistance were achieved when the content ratio (mass ratio) of the 2.8-1 mm silica raw material (rosewood) to the -1 mm silica raw material (rosewood) was within the range of 2:1 to 2:4, as shown in Examples 10-3 to 10-6. In contrast, when the content ratio (mass ratio) of the 2.8-1 mm silica raw material (rosewood) to the -1 mm silica raw material (rosewood) was outside the range of 2:1 to 2:4, there was a slight deterioration in erosion resistance due to slag penetration into the matrix, or a slight deterioration in cracking resistance due to the bricks becoming too dense. However, the amount of deterioration was not significant enough to affect use in an actual machine.

As shown in Table 13, when the content of virgin alumina raw material in all refractory raw materials was examined, as shown in Examples 11-2 to 11-5, when the content of virgin alumina raw material in all refractory raw materials was 6% by mass or more and 45% by mass or less, high corrosion resistance was maintained. On the other hand, as shown in Example 11-1, when the content of virgin alumina raw material in all refractory raw materials was less than 6% by mass, crack resistance was maintained but corrosion resistance was slightly inferior. On the other hand, as shown in Example 11-6, when the content of virgin alumina raw material in all refractory raw materials was more than 45% by mass, corrosion resistance was maintained but corrosion resistance was slightly inferior. However, the amount of deterioration was not so great as to have a significant effect on use in actual equipment.

As shown in Table 14, when the content of virgin silicon carbide raw material in all refractory raw materials was examined, as shown in Examples 12-2 to 12-5, when the content of virgin silicon carbide raw material in all refractory raw materials was 2% by mass or more and 8% by mass or less, the oxidation prevention effect of carbon was manifested, and both high crack resistance and high corrosion resistance were achieved. In contrast, as shown in Example 12-1, when the content of virgin silicon carbide raw material in all refractory raw materials was less than 2% by mass, the oxidation prevention effect of carbon decreased, and the crack resistance decreased slightly. On the other hand, as shown in Example 12-6, when the content of virgin silicon carbide raw material in all refractory raw materials was more than 8% by mass, the oxidation reaction of the silicon carbide raw material progressed too much, and the corrosion resistance decreased slightly. However, the amount of deterioration was not significant enough to affect the use in an actual machine.

Based on the above results, in order to produce alumina-silica-silicon carbide-carbon refractory bricks that use recycled refractory waste as part of the raw materials and have the same resistance to cracking and resistance to melting as virgin bricks and low thermal conductivity, it is necessary that the refractory waste (x) with a particle size of 8 mm or less, which is crushed used alumina-silica-silicon carbide-carbon refractory, accounts for 17% by mass to 90% by mass of the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials), and that the refractory waste (x) with a particle size of more than 2.36 mm accounts for 17% by mass to 90% by mass of the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials). It is found that it is necessary to contain 3 mass% or more of refractory shavings (x) in the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials) and the content ratio (mass ratio) of refractory shavings with a particle size of more than 2.36 mm to refractory shavings with a particle size of 2.36 mm or less and over 1 mm in the refractory shavings (x) is 1:1 to 1:20, or to contain refractory shavings with a particle size of more than 2.8 mm in the refractory shavings (x) in the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials) and the content ratio (mass ratio) of refractory shavings with a particle size of more than 2.8 mm to refractory shavings with a particle size of 2.8 mm or less and over 1 mm in the refractory shavings (x) is 1:6 to 1:69.

In addition, more preferable conditions for the above refractory bricks are: (i) the refractory scrap (x) having a particle size of 2.8 mm or less is contained in 42 mass% or more of the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials); (ii) the refractory scrap (x) is contained in more than 60 mass% and 90 mass% or less of the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials); (iii) the virgin raw materials (excluding cases where metallic Si is contained as virgin raw materials) are contained in 10 mass% or more of the total refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials). (iv) the alumina content in all refractory raw materials (excluding cases where metallic Si is contained as a virgin raw material) is 50% by mass to 70% by mass and the silica content is 10% by mass to 30% by mass; (v) the alumina content in all refractory raw materials (excluding cases where metallic Si is contained as a virgin raw material) is 10% by mass to 30% by mass. (vi) the free carbon content in all refractory raw materials (excluding cases where metallic Si is contained as virgin raw materials) is 12 mass% or less; (vii) the unused silica raw material is contained in the all refractory raw materials (excluding cases where metallic Si is contained as unused refractory raw materials), from 2 mass% to 30 mass%; (viii) the silica raw material is made of rosewood or mullite, and the silica raw material having a particle size of 2.8 mm or less and exceeding 1 mm, and the silica raw material having a particle size of 1 mm or less are mixed. The content ratio (mass ratio) of is 2:1 to 2:4, (ix) unused alumina raw material is contained in the total refractory raw material (however, this does not include cases where unused refractory raw material contains metallic Si), and (x) unused silicon carbide raw material is contained in the total refractory raw material (however, this does not include cases where unused refractory raw material contains metallic Si), and it is found that by satisfying these conditions, particularly excellent performance can be obtained.

Claims (26)

Alumina, silica, silicon carbide, and carbonaceous refractory bricks used as refractory linings for refining equipment or molten material transport vessels in steelworks .
The refractory waste (x), which is a crushed product of used refractory material made of alumina, silica, silicon carbide, or carbon, and has a particle size of 8 mm or less, is contained in an amount of 17% by mass or more and 90% by mass or less of all refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials),
The refractory scrap (x) contains 3% by mass or more of refractory scrap having a particle size of more than 2.36 mm in the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials),
A refractory brick characterized in that the content ratio (mass ratio) of refractory shavings (x) having a particle size of more than 2.36 mm and refractory shavings having a particle size of 2.36 mm or less and more than 1 mm is 1:1 to 1:20. Refractory brick according to claim 1, characterized in that the refractory scrap (x) contains refractory scrap with a particle size of 2.36 mm or less in an amount of 42 mass% or more of the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials). Alumina, silica, silicon carbide, and carbonaceous refractory bricks used as refractory linings for refining equipment or molten material transport vessels in steelworks .
The refractory waste (x), which is a crushed product of used refractory material made of alumina, silica, silicon carbide, or carbon, and has a particle size of 8 mm or less, is contained in an amount of 17% by mass or more and 90% by mass or less of all refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials),
The refractory scrap (x) contains refractory scrap having a particle size of more than 2.8 mm in an amount of 1 mass% or more in the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials),
A refractory brick characterized in that the content ratio (mass ratio) of refractory shavings (x) having a particle size of more than 2.8 mm and refractory shavings having a particle size of 2.8 mm or less and more than 1 mm is 1:6 to 1:69. Refractory brick according to claim 3, characterized in that the refractory scrap (x) contains refractory scrap with a particle size of 2.8 mm or less in an amount of 42 mass% or more of the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials). Refractory brick according to any one of claims 1 to 4, characterized in that the refractory waste (x) is contained in an amount of more than 60 mass% and not more than 90 mass% of the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials). Refractory brick according to any one of claims 1 to 4, characterized in that the proportion of refractory raw materials with a particle size of 1 mm or less among the unused refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 10% by mass or more and 40% by mass or less. The refractory brick according to any one of claims 1 to 4, characterized in that the alumina content in the total refractory raw materials (excluding cases where metal Si is contained as unused refractory raw materials) is 50% by mass or more and 70% by mass or less, and the silica content is 10% by mass or more and 30% by mass or less. Refractory brick according to any one of claims 1 to 4, characterized in that the alumina content in the refractory raw material having a particle size of 1 mm or less (excluding cases where unused refractory raw material contains metallic Si) is 10% by mass or more and 30% by mass or less. The refractory brick according to any one of claims 1 to 4, characterized in that the free carbon content in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 12 mass% or less. The refractory brick according to any one of claims 1 to 4, characterized in that the unused silica raw material is contained in an amount of 2% by mass to 30% by mass of the total refractory raw material (excluding cases where the unused refractory raw material contains metallic Si). The refractory brick according to any one of claims 1 to 4, characterized in that the silica raw material is made of rosewood or mullite, and the content ratio (mass ratio) of the silica raw material with a particle size of 2.8 mm or less and over 1 mm to the silica raw material with a particle size of 1 mm or less is 2:1 to 2:4. Refractory brick according to any one of claims 1 to 4, characterized in that the unused alumina raw material is contained in an amount of 6% by mass to 45% by mass of the total refractory raw material (excluding cases where the unused refractory raw material contains metallic Si). The refractory brick according to any one of claims 1 to 4, characterized in that the unused silicon carbide raw material is contained in an amount of 2% by mass to 8% by mass of the total refractory raw material (excluding cases where the unused refractory raw material contains metallic Si). A method for producing alumina-silica-silicon carbide-carbonaceous refractory bricks used as lining refractory materials for refining equipment or molten material transport vessels in steelworks , comprising the steps of:
A method for producing a refractory brick, comprising: mixing refractory scrap (x) having a particle size of 8 mm or less obtained by pulverizing used refractory material made of alumina, silica, silicon carbide, or carbon, the refractory scrap (x) having a content ratio (mass ratio) of refractory scrap exceeding 2.36 mm in particle size to refractory scrap exceeding 1 mm in particle size of 2.36 mm or less and refractory scrap exceeding 1 mm in particle size of 1:1 to 1:20 with unused refractory raw materials such that the proportion of the refractory scrap (x) in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 17% by mass or more and 90% by mass or less, and the proportion of the refractory scrap (x) having a particle size of more than 2.36 mm in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 3% by mass or more. The method for producing refractory bricks according to claim 14, characterized in that the refractory scrap (x) is mixed with the unused refractory raw material so that the proportion of the refractory scrap (x) with a particle size of 2.36 mm or less in the total refractory raw material (excluding cases where the unused refractory raw material contains metallic Si) is 42 mass% or more. A method for producing alumina-silica-silicon carbide-carbonaceous refractory bricks used as lining refractory materials for refining equipment or molten material transport vessels in steelworks , comprising the steps of:
A method for producing a refractory brick, comprising: mixing refractory scrap (x) having a particle size of 8 mm or less obtained by pulverizing used refractory material made of alumina, silica, silicon carbide, or carbon, with unused refractory raw materials, the refractory scrap (x) having a content ratio (mass ratio) of refractory scrap exceeding 2.8 mm in particle size to refractory scrap exceeding 1 mm in particle size of 2.8 mm or less and refractory scrap exceeding 1 mm in particle size of 1:6 to 1:69, the refractory scrap (x) being 17% by mass or more and 90% by mass or less in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si), and mixing the refractory scrap (x) having a particle size of more than 2.8 mm in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si), so that the proportion of the refractory scrap (x) in all refractory raw materials is 17% by mass or more and 90% by mass or less, and the proportion of the refractory scrap (x) having a particle size of more than 2.8 mm in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si), is 1% by mass or more. The method for producing refractory bricks according to claim 16, characterized in that the refractory scrap (x) is mixed with the unused refractory raw material so that the proportion of the refractory scrap (x) with a particle size of 2.8 mm or less in the total refractory raw material (excluding cases where the unused refractory raw material contains metallic Si) is 42 mass% or more. The method for producing refractory bricks according to any one of claims 14 to 17, characterized in that the refractory waste (x) is mixed with unused refractory raw materials so that the proportion of the refractory waste (x) in the total refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is more than 60 mass% and not more than 90 mass%. The method for manufacturing refractory bricks according to any one of claims 14 to 17, characterized in that the proportion of refractory raw materials with a particle size of 1 mm or less among the unused refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 10% by mass or more and 40% by mass or less. The method for producing refractory bricks according to any one of claims 14 to 17, characterized in that refractory waste (x) is mixed with unused refractory raw materials so that the alumina content in the total refractory raw materials (excluding cases where metallic Si is contained as unused refractory raw materials) is 50% by mass or more and 70% by mass or less, and the silica content is 10% by mass or more and 30% by mass or less. The method for manufacturing refractory bricks according to any one of claims 14 to 17, characterized in that refractory waste (x) is mixed with unused refractory raw materials so that the alumina content in the refractory raw materials having a particle size of 1 mm or less (excluding cases where the unused refractory raw materials contain metallic Si) is 10% by mass or more and 30% by mass or less. The method for producing refractory bricks according to any one of claims 14 to 17, characterized in that refractory waste (x) is mixed with unused refractory raw materials so that the free carbon content in all refractory raw materials (excluding cases where unused refractory raw materials contain metallic Si) is 12 mass% or less. The method for manufacturing refractory bricks according to any one of claims 14 to 17, characterized in that the unused silica raw material is mixed so that its proportion in the total refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 2% by mass or more and 30% by mass or less. The method for manufacturing refractory bricks according to any one of claims 14 to 17, characterized in that the silica raw material is made of rosewood or mullite, and the content ratio (mass ratio) of the silica raw material with a particle size of 2.8 mm or less but more than 1 mm and the silica raw material with a particle size of 1 mm or less is 2:1 to 2:4. A method for manufacturing refractory bricks according to any one of claims 14 to 17, characterized in that the unused alumina raw material is mixed so that its proportion in the total refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 6% by mass or more and 45% by mass or less. The method for manufacturing refractory bricks according to any one of claims 14 to 17, characterized in that the unused silicon carbide raw material is mixed so that its proportion in the total refractory raw materials (excluding cases where the unused refractory raw materials contain metallic Si) is 2% by mass or more and 8% by mass or less.

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