JP2018052776A - Method for production of checker brick for air heating furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for production of checker brick for an air heating furnace, free from cracking in molding and having sufficient strength of a product.SOLUTION: The method for production of a checker brick includes steps of kneading, molding, drying, and then firing of a refractory raw material compound comprising 10-50 mass% of a mullite raw material, 20-60 mass% of a corundum-containing raw material, 10-30 mass% of one or more of a sillimanite mineral selected from andalusite, kyanite, and sillimanite, and 3-20 mass% of a clay. Among the mullite raw material, the corundum-containing raw material, andalusite, kyanite, and/or sillimanite, a raw material having a grain size of 0.2 mm or under is 5-20 mass%. By using the above-mentioned refractory raw material compound, the method for production of a checker brick of a known shape for an air heating furnace, as well as a thin wall checker brick having improved heat exchange efficiency, such as a checker brick having wall thickness T of 10 to less than 15 mm and the number of pores of approximately 7-37, is provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a hot stove checker brick (hereinafter also simply referred to as “checker brick”) incorporated in a heat storage chamber of a hot stove.

  A hot blast furnace is used to supply hot blast to a blast furnace for iron making. In the heat storage chamber of the hot stove, a large number of checker bricks (also referred to as “gitter bricks”) whose outer shape is a hexagonal column shape are arranged as a heat storage material, and are built in layers. The checker brick has a hexagonal column-shaped main body formed of a refractory brick material. The upper surface and the lower surface of the main body are parallel. A plurality of gas passages having a round or hexagonal cross-sectional shape are formed in the main body so as to penetrate in the vertical direction, and each is opened on the upper and lower surfaces of the main body.

  In such a checker brick, heat can be stored in a portion (wall) clogged with a refractory brick material other than the gas flow channel of the main body by passing a high-temperature combustion gas through the gas flow channel. On the other hand, hot air can be generated and supplied to the blast furnace by allowing cold air to pass through the gas flow path and exchanging heat while the heat is stored. At this time, the size and shape of the checker brick greatly affects the heat exchange efficiency between the gas and the refractory brick. For this reason, in recent years, optimization related to the shape of the gas flow path, the thickness of the wall, and the like has been performed, and those having a larger number of holes and a smaller wall thickness have been developed.

  For example, Patent Document 1 discloses a checker brick having 19 gas flow paths and a wall thickness of 15 mm. However, when the wall thickness is reduced, the conventional manufacturing method has a problem that the molded body is likely to crack during molding and a problem that the strength of the product is insufficient.

Patent Document 2 discloses a heat storage brick for a coke oven, which is of a slit type and has a wall thickness of 11 mm. As a method for producing this heat storage brick, in paragraph 0043, “a high alumina-based heat storage brick having an Al ₂ O ₃ content of 75 wt% was manufactured using mullite and corundum crushed by a ball mill as main materials. 5 to 0.8 mm), medium grains (0.8 to 0.08 mm), and fine grains (<0.08 mm) in a ratio of 1: 2: 2, separately containing 3 wt% flint clay and 4 wt% moisture. It was added and molded with a 350-ton friction press ”.

  However, when trying to manufacture the checker brick of Patent Document 1 with the raw material composition of Patent Document 2, there are problems that the molded body is cracked during molding and the strength after firing is insufficient. That is, in the checker brick manufacturing method, a hexagonal column or a cylindrical core rod is used to form a hole during molding, but when the core rod is removed from the molded body after molding because the wall is thin. There is a problem that the wall collapses or cracks occur. Further, the heat storage brick of Patent Document 2 has a rectangular frame with a thickness of 14.5 to 18 mm, and the strength can be maintained by this frame, but in the case of the checker brick of Patent Document 1, the thickness of all the walls is Is as thin as 15 mm, it is easy to cause breakage such as chipping during handling, and it is necessary to increase the strength of the product itself.

JP 2014-118614 A JP 7-172940 A

  The problem to be solved by the present invention is to provide a method for producing a checker brick for a hot stove without causing cracks during molding and having a sufficient strength of the product.

  In order to improve the strength at the time of molding, the use of clay in the refractory raw material composition is effective, but on the other hand, there is a problem that the firing shrinkage becomes large and cracks are formed. The present inventors have found that cracks during firing can be prevented by using a sillimanite group mineral in combination. As a result, the inventors have devised a method for producing a checker brick that does not generate cracks during molding even when the wall is thin, and has sufficient product strength.

  That is, the method for producing a checker brick for a hot stove according to the present invention includes 10 to 50% by mass of a mullite raw material, 20 to 60% by mass of a corundum-containing raw material, and one or two kinds of andalusite, kyanite, and sillimanite as sillimanite group minerals. It is composed of 10 to 30% by mass and 3 to 20% by mass of clay, and among mullite raw material, corundum-containing raw material, andalusite, kyanite, and / or sillimanite, the raw material having a particle size of 0.2 mm or less is 5 to 20% by mass. A certain refractory raw material composition is kneaded, molded, dried and fired, and is particularly characterized by the constitution of the refractory raw material composition. Hereinafter, the structure of the refractory raw material composition according to the present invention will be described in detail.

  The corundum-containing raw material is used in an amount of 20 to 60% by mass for improving creep resistance and developing strength. When the corundum-containing raw material is less than 20% by mass, creep resistance and strength are insufficient, and when it exceeds 60% by mass, the spalling resistance is lowered.

  The mullite raw material is used in an amount of 10 to 50% by mass for improving creep resistance and spalling resistance. When the mullite raw material is less than 10% by mass, the creep resistance and spalling resistance are insufficient, and when it exceeds 50% by mass, the effect of improving the spalling resistance is not changed and the cost of the raw material is increased.

  Of mullite raw material, corundum-containing raw material, andalusite, kyanite, and / or sillimanite, the raw material with a particle size of 0.2 mm or less increases the filling property at the time of molding to make the structure denser and prevent the brick from being broken and chipped after firing. In order to do so, 5-20 mass% is used. If the raw material having a particle size of 0.2 mm or less is less than 5% by mass, the edge of the wall part will be battered or chipped after firing, and if it exceeds 20% by mass, the structure becomes too dense and the spalling resistance decreases. To do.

  As a silimanite group mineral, andalusite, kayanite, or silimanite itself expands during firing, and therefore, by suppressing the shrinkage of brick during firing due to the use of clay, it has the effect of suppressing cracking due to firing shrinkage. is there. As the sillimanite group mineral, one or more of andalusite, kyanite, and sillimanite are used at 10 to 30% by mass. If these sillimanite group minerals are less than 10% by mass, the effect of suppressing the firing cracks is insufficient, and if it exceeds 30% by mass, the coefficient of thermal expansion becomes too high and the spalling resistance becomes insufficient.

  Clay is used in an amount of 3 to 20% by mass to increase the strength of the molded body at the time of molding to prevent cracking and to develop the strength after firing. If the clay is less than 3% by mass, the molded body has insufficient strength, so that cracks occur in the molded body. If the clay exceeds 20% by mass, firing shrinkage increases and cracks occur during firing. When it is desired to further increase the strength after firing, the clay is preferably used in an amount of 10% by mass or more, that is, 10 to 20% by mass.

Furthermore, in the present invention, in order to prevent oversintering due to the use of a large amount of clay, Fe ₂ O ₃ in the refractory raw material composition is 1.5 mass% or less, and Na ₂ O is 1.0 mass% or less. It is preferable to do.

  According to the present invention, it is possible to manufacture a checker brick for a hot stove without causing cracks during molding and having sufficient product strength.

It is a perspective view which shows an example of the checker brick manufactured by this invention. It is a figure which shows the shape of the sample cut out from the checker brick of FIG.

  In the present invention, as the corundum-containing raw material used for the refractory raw material composition, one or more of the raw materials containing 50% by mass or more of corundum can be used. For example, at least one of electrofused alumina, sintered alumina, bauxite, baked banquet, calcined alumina, and brick scraps can be used.

  As the mullite raw material, those commercially available as ordinary refractory raw materials can be used. For example, synthetic mullite, electrofused mullite, or sintered mullite can be used. Mullite may contain corundum or cristobalite as impurities, and those having a mullite purity of 85% or more are preferably used.

The clay can be used those commercially available as a raw material for regular refractory, for example, SiO ₂ content of 40 to 70 wt%, _Al 2 _{O 3} content, such as those of 20 to 30 wt% Can be used.

As the sillimanite group mineral, one or more of sillimanite, andalusite, and kyanite are used. Since the thermal expansion coefficient of these sillimanite group minerals is higher than that of mullite, chamotte, and alumina, cracking due to firing shrinkage is suppressed by suppressing the shrinkage of bricks during firing due to the use of clay. There is an effect to. These raw materials are minerals mined from nature and can be used by refining them. When it is desired to further ensure the creep resistance, iron oxide (Fe ₂ O ₃ ) as an impurity can be about 2 mass% or less, preferably 1 mass% or less.

  In addition, it can be used for a refractory raw material composition within a range that does not adversely affect other raw materials. For example, wax stone, silica stone, fused silica, chamotte, etc. can be used at 10% by mass or less, preferably 5% by mass or less. It is.

  In the checker brick manufacturing method of the present invention, the refractory raw material composition having the above-described configuration is used, and a general checker brick manufacturing method can be employed thereafter. That is, it can be fired at 1300 to 1600 ° C. after kneading, forming and drying by adding a binder to the refractory raw material composition.

  According to the present invention, in addition to a checker brick having a known shape used in a hot stove, a thin wall checker brick having a more excellent heat exchange efficiency, for example, a wall thickness of 10 mm or more and less than 15 mm and a number of holes of 7 About 37 checker bricks can be produced without problems.

  A water-based binder was added to the refractory raw material blends shown in Tables 1 and 2 and kneaded. The checker brick shown in FIG. The checker brick of FIG. 1 has a wall thickness T of 11 mm, a brick height H of 130 mm, a length L of one side of the brick (one side of the hexagonal shape) of 130 mm, and 19 holes. .

The baked banquet used as the corundum-containing material was a corundum containing 80% by mass. Similarly, the brick scrap used as the corundum-containing raw material was 50% by mass of corundum and 40% by mass of mullite as a mineral phase. The synthetic mullite used as the mullite raw material was 92% by mass of mullite as a mineral. Andalusite as a sillimanite group mineral has an Al ₂ O ₃ content of 60% by mass and SiO ₂ content of 37% by mass, and kyanite has an Al ₂ O ₃ content of 58% by mass and an SiO ₂ content of 39%. The sillimanite having an Al ₂ O ₃ content of 75% by mass and an SiO ₂ content of 20% by mass was used. A clay having an Al ₂ O ₃ content of 25% by mass and an SiO ₂ content of 55% by mass was used.

As described above, a water-based binder is added to the refractory raw material composition shown in Table 1 and Table 2 and kneaded. The checker brick shown in FIG. 1 is formed by a press machine, dried, and fired at 1400 ° C. The cracks during molding and the appearance after firing were evaluated.
As for the cracks at the time of molding, the state of the surface after molding 10 pieces was visually observed.
As for the appearance after firing, the state of the surface after firing the 10 bricks is visually observed, and if even one piece has cracks or wall roughness, it is X, and there is no crack or wall roughness. Was marked as ○.

Moreover, the sample of FIG. 2 was cut out from the checker brick of FIG. 1 after firing, the compressive strength was measured, and a creep test and a spalling test were performed. The dimensions of the sample in FIG. 2 are 74 mm for A, B, and C, and 60 mm in height.
The compressive strength was measured according to JIS-R2206.
The creep test was conducted in accordance with JIS-R2658 at 1300 ° C. for 5 hours under the condition of 0.2 MPa. A creep value of 1% or less was evaluated as ◯, and a value exceeding 1% was evaluated as ×.
The spalling test was carried out 20 times by a water cooling method after heating at 800 ° C. in accordance with JIS-R2657.
In the comparative example having cracks after firing, only the compressive strength of bricks without cracks was measured, and the spalling test and creep test were not performed.

  In Examples 1 to 3, the amount of andalusite used was different, but all were good. On the other hand, in Comparative Example 1, the amount of andalusite used was 5 mass%, which was lower than the lower limit of the present invention, and cracks occurred in 5 out of 10 bricks after firing. In Comparative Example 2, the amount of andalusite used was 35% by mass, exceeding the upper limit of the present invention. In the spalling test, it peeled off 17 times, and there was a problem in spalling resistance.

  In Examples 4 to 7, the amount of clay used was different, but all were good. In Example 4, cracks did not occur at the time of molding and after firing, but care was required in handling during molding so as not to cause cracks during molding. Further, the strength after firing in Example 4 was slightly low although it was at a level where there was no practical problem. On the other hand, in Comparative Example 3, the amount of clay used was 1% by mass and lower than the lower limit of the present invention, and cracks occurred in 4 out of 10 bricks after molding due to insufficient strength during molding, After firing, cracks occurred in 6 out of 10 bricks. Moreover, when the compressive strength of the brick without a crack was measured, it was a low level of 30 MPa and a practically problematic level. On the other hand, in Comparative Example 4, the amount of clay used was 25% by mass, exceeding the upper limit of the present invention, and cracking occurred in 3 out of 10 bricks after firing because the firing shrinkage was too large.

  Examples 8 to 10 are cases where the amount of mullite raw material having a particle size of 0.2 mm or less is different, but all have good results. On the other hand, Comparative Example 5 is a case where a mullite raw material having a particle size of 0.2 mm or less is not used, and the compressive strength after firing is sufficient, but the wall portion of 5 out of 10 bricks after firing Boring and chipping occurred at the edge. In Comparative Example 6, the amount of the mullite raw material having a particle size of 0.2 mm or less exceeds 25% by mass, exceeding the upper limit of the present invention. There was a problem with sex.

  Example 11 is a case in which kayanite is used as the silimanite group mineral, and Example 12 is a case in which silimanite is used as the silimanite group mineral, and good results were obtained as in the case of using andalusite.

  In Example 13 and Example 14, when a baked banquet was used as a corundum-containing raw material having a particle size of 0.2 mm or less, Example 15 used a baked banquet and synthetic mullite as a raw material having a particle size of 0.2 mm or less. Is a case where baked banquet, synthetic mullite, and andalusite are used in combination as raw materials having a particle size of 0.2 mm or less, and in any case, similarly to the case where a mullite raw material having a particle size of 0.2 mm or less is used alone, As a result, the slab became dense and was free from crushed and chipped bricks after firing.

  Next, when the same refractory raw material composition as in Example 4 and Example 7 was used to produce checker bricks having wall thicknesses of 15 mm and 10 mm in FIG. 1, there was no crack after molding and after firing. Met.

Claims (3)

  From 10 to 50% by weight of mullite raw material, 20 to 60% by weight of corundum-containing raw material, and from 10 and 30% by weight of one or more of andalusite, kyanite, and sillimanite as a sillimanite group mineral, and 3 to 20% by weight of clay Mullite raw material, corundum-containing raw material, andalusite, kyanite, and / or sillimanite, kneading a refractory raw material composition having a particle size of 0.2 mm or less is 5 to 20% by mass, molding, drying, firing To manufacture checker bricks for hot stove.   The method for producing a hot stove checker brick according to claim 1, wherein the clay is 10 to 20% by mass. The method for producing a checkered brick for a hot stove according to claim 1 or 2, wherein Fe ₂ O ₃ in the refractory raw material composition is 1.5% by mass or less and Na ₂ O is 1.0% by mass or less. .

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