JP5180504B2 - Method for manufacturing precast block for metal melting furnace ceiling and precast block for metal melting furnace ceiling - Google Patents

Description

  The present invention relates to a method for producing a precast block for a metal melting furnace ceiling and a precast block for a metal melting furnace ceiling, and more particularly, a method for producing a ceiling precast block for an arc type metal melting furnace, and an arc type metal melting. The present invention relates to a precast block for a furnace ceiling.

  In an arc-type metal melting furnace (electric furnace) used in the steelmaking process, iron scrap is housed in the furnace by passing a current through an electrode inserted into the furnace through a large ceiling (furnace lid). The steel scrap is melted and refined by generating an arc between the two and simultaneously blowing oxygen gas. Traditionally, the ceilings of metal melting furnaces were manufactured by complex assembly of many small refractory bricks. Therefore, the construction period and skilled techniques were necessary. In addition, there is a problem that bricks fall off due to damage to joints.

  Therefore, in recent years, a precast block has been used on the ceiling of a metal melting furnace (for example, Patent Document 1). Here, the precast block is obtained by casting an amorphous refractory material in advance and then drying, and has an advantage that it can be formed into an arbitrary shape and a large product can be manufactured. In addition, there is no joint on the ceiling with the precast block that is integrally molded, and there are few joints on the ceiling that is composed of several large precast blocks. This has the advantage that the ceiling can be easily constructed.

JP-A-11-166792

  However, the conventional precast block for a ceiling of a metal melting furnace is desired to be further improved in terms of spalling resistance. Here, the refractory used for the ceiling of the metal melting furnace is different from the refractory used as a lining material in a container such as a ladle, and therefore the required characteristics are also different. For example, unlike the lining material, the ceiling is not immersed in the molten steel, so “melting loss”, which is a serious problem for the lining material, that is, elution due to a chemical reaction with the molten steel, or the physical effects caused by the flow of the molten steel There is little problem of erosion.

  Instead, the molten steel scattered by the generation of arc and oxygen blowing adheres to the ceiling and is heated by the adhered molten steel, and the surface layer of the refractory changes in quality. The problem of structural spalling that causes delamination is significant. Furthermore, due to thermal shock when extremely hot molten steel splashes and adheres to the ceiling, a sudden temperature drop when iron scrap is thrown in, and a large temperature gradient at the periphery of the hole where the electrode is inserted in the ceiling The problem of thermal spalling that causes cracks and peeling is also significant.

  In addition, the ceiling by the precast block has the above-mentioned advantages because there are few joints, but there are few joints that act as expansion allowances, so the interior caused by the pressure or thermal expansion of water vapor generated inside the block The problem of mechanical spalling that causes cracks and delamination due to stress is also significant.

  Therefore, in view of the above circumstances, an object of the present invention is to provide a method for manufacturing a precast block for a metal melting furnace with excellent spalling resistance, and a precast block for a metal melting furnace with excellent spalling resistance. Is.

In order to solve the above-mentioned problems, the method for producing a precast block for ceiling according to the present invention is described as follows: “The slurry of the irregular refractory material is 0.9 vol% or more and 1.35 % relative to the total volume of the irregular refractory material. The step of mixing a combustible material of less than volume% and the mud mixed with the combustible material are poured into a mold having a shape of the whole or a part of the metal melting furnace ceiling, molded, and dried. A step of obtaining a molded body having an amorphous refractory layer, and a step of heating the molded body and burning the combustible material to generate pores having an average diameter of 3 mm or more and 10 mm or less. Yes.

  “Metal melting furnace ceiling” refers to a furnace lid of an arc type metal melting furnace in which an arc is generated between an electrode and iron scrap and the iron scrap is melted by the heat in the steel making process.

  The kind of “indefinite refractory material” is not particularly limited, and for example, an amorphous refractory material such as alumina, alumina-magnesia, alumina-chromium, alumina-silica, or the like can be used. Moreover, you may use a different kind of refractory material according to the part of a ceiling, such as comprising the peripheral part of the hole part in which an electrode is penetrated in a ceiling with a refractory material with heat resistance higher than another part.

  The “mud” can be prepared by mixing a powder of an irregular refractory material with water and adjusting agents such as a binder, a curing agent, and a dispersing agent. In addition, since the mold for pouring mud is “the shape of the whole or a part of the metal melting furnace ceiling”, the precast block to be manufactured consists of a single block or a plurality of blocks. A block constitutes one ceiling.

  The “flammable material” is not particularly limited as long as it is a material that burns and burns out by heating, and examples thereof include paper materials such as wood, resin, cardboard, and twisted brazing materials. Even if the combustible material is burned when the molded body is dried at the factory of the ceiling precast block, the operation of the metal melting furnace after the ceiling precast block is attached to the metal melting furnace It may be performed by heating accompanying the above.

  With the above configuration, pores are formed later in the matrix of the amorphous refractory layer densely filled by casting by burning of the combustible material. Thereby, the magnitude | size and porosity of a pore are controllable by addition of a combustible material. Further, the pores can be dispersed in the matrix by casting after mixing the combustible material with the slurry of the irregular refractory material. Therefore, according to the present invention, pores positively formed in the irregular refractory layer become an absorption allowance (expansion allowance), and the volume change of the surface layer altered by the molten steel scattered and adhered to the ceiling, the metal dissolution Internal stress generated due to thermal expansion of particles in the irregular refractory layer due to heating during operation of the furnace, pressure due to water vapor generated in the irregular refractory layer, etc. is absorbed and relaxed, and cracks are generated And peeling is suppressed.

  In addition, the irregular refractory layer is caused by thermal shock when the molten steel adheres to the ceiling, rapid temperature drop when iron scrap is thrown in, and a large temperature gradient at the periphery of the hole through which the electrode is inserted. Even if a crack occurs in the inside, the progress of the crack is suppressed by the pores dispersed in the matrix of the amorphous refractory layer.

  Here, when the ratio of the flammable material to the total volume of the irregular refractory material is smaller than 0.5% by volume, the generated pores are few, and the action of absorbing and relaxing internal stress and the action of suppressing the progress of cracks. Not enough. Moreover, when it exceeds 25 volume%, while the number of produced | generated pores will increase, a several pore will connect and it will be easy to become a large diameter, it will become a defect, and the cause of reducing the intensity | strength of the precast block for metal melting furnace ceilings It is easy to become.

  In addition, in addition to said structure, this invention can be comprised by adding the process of curing the molded object cast-molded.

Next, the precast block for a metal melting furnace ceiling according to the present invention is “ combustible of 0.9 vol% or more and 1.35 vol% or less with respect to the total volume of the irregular refractory material. The amorphous refractory layer containing the material is formed in the whole or part of the shape of the metal melting furnace ceiling, and the average refractory layer has an average diameter of 3 mm or more due to combustion of the combustible material. It is a layer in which pores of 10 mm or less are generated .

  The precast block for a metal melting furnace ceiling having such a configuration can be manufactured by the above manufacturing method. The size of the pores to be generated can be controlled by the size of the combustible material to be added. Here, when the average pore diameter (diameter) is smaller than 3 mm, the effect of absorbing and relaxing internal stress cannot be sufficiently obtained. When the average pore diameter is larger than 10 mm, it acts as a defect and is precast for a metal melting furnace ceiling. It is likely to cause a decrease in the strength of the block.

  The “average diameter” of the pores can be obtained by converting the pores into circles from the total pore area and the number of pores by image analysis of the cross section or surface of the precast block for the metal melting furnace ceiling.

  The “apparent porosity” can be measured by a method defined in JIS R2205. Here, when the apparent porosity is smaller than 15%, the effect of absorbing and relaxing internal stress by the pores and the effect of suppressing the progress of cracks cannot be obtained sufficiently. On the other hand, if it exceeds 20%, the amount of the introduced pores is too large, resulting in a defect, which tends to cause a decrease in the strength of the precast block for the metal melting furnace.

  With the above configuration, the precast block for a metal melting furnace having the above-described effects and excellent in spalling resistance is obtained.

  As described above, as an effect of the present invention, it is possible to provide a method for producing a precast block for a metal melting furnace with excellent spalling resistance, and a precast block for a metal melting furnace with excellent spalling resistance.

  Hereinafter, the manufacturing method of the precast block for metal melting furnace ceilings and the precast block for metal melting furnace ceilings which are the best embodiment of this invention are demonstrated based on FIG.1 and FIG.2. Here, FIG. 1 is a process diagram of a method for manufacturing a precast block for a metal melting furnace according to the present embodiment, and FIG. 2 is a plan view illustrating the configuration of the precast block for the metal melting furnace ceiling according to the present embodiment. In addition, FIG. 2 is a schematic diagram and does not accurately represent the shape and dimensional ratio of the precast block for the metal melting furnace ceiling.

  As shown in FIG. 1, the manufacturing method of the precast block for metal melting furnace ceiling of the present embodiment (hereinafter simply referred to as “manufacturing method”) includes the entire volume of the amorphous refractory material in the slurry of the amorphous refractory material. The slurry preparation step S1 in which 0.5% by volume or more and 25% by volume or less of combustible material is mixed, and the slurry in which the combustible material is mixed, the shape of the whole or part of the metal melting furnace ceiling A molding step S2 for casting and molding an irregular refractory layer, a curing step S3 for curing the cast molded body, a demolding step S4 for demolding the molded body after curing, And heating step S5 for heating the demolded molded body to burn the combustible material to generate pores having an average diameter of 3 mm or more and 10 mm or less.

  And, by the heating in the heating step S5, the combustible material is burned and burned, so that pores are dispersed in the matrix of the amorphous refractory layer (hereinafter simply referred to as “ceiling precast block”). Is formed). Here, the size of the pores can be controlled in consideration of the size of the flammable material and the volume change of the amorphous refractory layer from the combustion temperature of the flammable material to the use temperature of the ceiling precast block, The average pore diameter (diameter) can be 3 mm to 10 mm.

  The shape of the ceiling precast block can be set by the shape of the molding die into which the slurry is cast in the molding step S2. For example, as shown in FIG. (See FIG. 2 (a)), a small ceiling having a hole 9 through which an electrode is inserted is constituted by a single ceiling precast block 2a, and the surrounding large ceiling is precast for a plurality of ceilings. Examples include shapes formed by the blocks 3b (see FIG. 2B), shapes formed by a plurality of precast blocks 2b and 3b for the ceiling (see FIG. 2C), and the like. it can.

  With the above configuration, according to the ceiling precast block manufactured by the manufacturing method of the present embodiment, the pores dispersed in the matrix of the irregular refractory layer serve as an absorption allowance, and the molten steel adhered to the ceiling is scattered and heated. The internal stress due to the volume change of the surface layer due to heat, the thermal expansion of particles in the amorphous refractory layer due to heating accompanying the operation of the metal melting furnace, the pressure due to water vapor generated inside the amorphous refractory layer is alleviated , Cracking and peeling are suppressed.

  In addition, the irregular refractory layer is caused by thermal shock when the molten steel adheres to the ceiling, rapid temperature drop when iron scrap is thrown in, and a large temperature gradient at the periphery of the hole through which the electrode is inserted. Even if a crack occurs in the inside, the progress of the crack is suppressed by the pores dispersed in the matrix.

  Hereinafter, Sample 1 to Sample 3 of one example of the present embodiment will be described in comparison with the control sample. In this example, an alumina refractory material was used as the amorphous refractory material, and wood having a size of 4 mm × 5 mm × 20 mm was used as the flammable material. Moreover, the ratio of the combustible material with respect to the amorphous refractory material was set to 0.90% by volume, 1.35% by volume, and 1.80% by volume for Sample 1 to Sample 3, respectively. In the control sample, no flammable material was added.

  For each sample and control sample, in order to evaluate the spalling resistance of the ceiling precast block obtained through the above-described mud preparation step S1 to heating step S5, the precast ceiling for the parallel size specified in JIS R2101 Only one side of the block was heated in an electric furnace at 1400 ° C. for 15 minutes and then rapidly cooled using a blower for 5 cycles. And (1) structure | tissue observation of the cut surface of the heating side after completion | finish of 5 cycles, and (2) the volume elastic modulus after each cycle were measured. FIG. 3 shows the elastic modulus change rate (when the volume elastic modulus at 0 cycle is 100, it becomes an index of how much “ease of deformation with respect to pressure” has decreased after each cycle).

  Moreover, the apparent porosity, bulk specific gravity, bending strength, and compressive strength were measured for the precast blocks for ceiling of each sample and the control sample. Here, the apparent porosity and bulk specific gravity were measured by the method defined in JIS R2205, and the bending strength and compressive strength were measured by the method defined in JIS R2553. Each measurement was performed under conditions of heating at 110 ° C. for 24 hours (condition A), heating at 1000 ° C. for 3 hours (condition B), and heating at 1500 ° C. for 3 hours (condition C). As a result, in any of the A condition, the B condition, and the C condition, the physical property values changed with the same tendency as the amount of the flammable material added increased. As an example, the apparent porosity and bulk specific gravity in C condition are shown in FIG. 4, and the bending strength and compressive strength are shown in FIG.

  Although the linear change rate was also measured by the method specified in JIS R2554, it is almost zero, and in the case of the refractory material used in this embodiment, it is considered that there is almost no residual expansion due to phase change or the like. It was.

  As a result of each of the above measurements, the apparent porosity (1500 ° C., 3 hours) of the ceiling precast block as the amount of wood added increased from 0 to 1.80% by volume, as shown in FIG. Increased from about 15% to about 17%. In addition, according to the observation of the structure of the cut surface, Samples 1 to 3 to which wood was added had more pores having a diameter of about 3 mm to 8 mm than the control sample to which wood was not added, and the number of cracks. It was confirmed that the degree of crack propagation was small as well as the amount of cracking. In particular, when the amount of wood added was 0.9% by volume (Sample 1), it was observed that there were few cracks that were greatly developed.

  The decrease in the elastic modulus change rate due to repeated heating and quenching was suppressed by the addition of wood, as shown in FIG. 3, and it was considered that the internal stress was absorbed and relaxed by the pores. Further, when the amount of wood added was 0.9% by volume (Sample 1), the effect of suppressing the decrease in the elastic modulus change rate was the largest.

  Regarding the strength, as shown in FIG. 5, the compressive strength decreases with the addition of wood, and the bending strength hardly changes until 1.35% by volume (Sample 2), but 1.80% by volume. Decreased by addition (sample 3). When the measurement results regarding these strengths are combined with the results of the structure observation and the elastic modulus change rate described above, the amount of wood added is 0.9 vol% to suppress the decrease in strength and increase the spalling resistance. 1.35% by volume is suitable, and in the case of a refractory material having a low linear change rate, it was considered that the spalling resistance can be improved by introducing a small amount of pores.

  Next, the precast blocks for the ceilings of Sample 5 to Sample 13 in which the size and the addition amount of the combustible material were changed were actually used as the ceiling of the metal melting furnace, and the state after use a predetermined number of times was examined. Here, wood was used as the flammable material, and an alumina refractory material was used as the amorphous refractory material. In addition, all of the precast blocks for the ceilings of Sample 5 to Sample 13 were manufactured for a ceiling of a 90-ton metal melting furnace having a thickness of 500 mm.

  For each sample, the size of the combustible material (diameter φmm × length mm), the amount of combustible material added (volume% with respect to the amorphous refractory material), the apparent porosity after heating at 1500 ° C. for 3 hours (condition C) ( %), The remaining size after use 300 charges (mm), and the evaluation as a practical product are summarized in Table 1. In addition, the evaluation is a comprehensive judgment of the remaining size and the degree of cracking / peeling. “◎” indicates that it is suitable for practical use, “×” indicates that it is unsuitable, and “△” indicates that it is slightly unsuitable. Is shown.

  As a result of the observation of the structure of the cut surface, in Samples 5 to 12, the average diameter of the formed pores was almost within the range of 3 mm to 10 mm.

  According to this example, when the amount of flammable material added was small (Sample 6), the evaluation as a practical product was low, and it was considered that pores sufficient to improve the spalling resistance were not introduced. . On the other hand, when the amount of flammable material added is large (sample 11) or when the apparent porosity is high (samples 11 and 13), the evaluation as a practical product is low, and many introduced pores become defects and cracks occur. It was thought that the generation and exfoliation were promoted. And when the addition amount of the combustible material was 0.5 volume% to 25 volume% and the apparent porosity was 15% to 20%, it was considered suitable as a practical product.

  The present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to the above-described embodiments, and various improvements can be made without departing from the scope of the present invention as described below. And design changes are possible.

  For example, in the above embodiment, the case where an alumina refractory material is used as the amorphous refractory material is exemplified, but the present invention is not limited to this, and it is possible to use a refractory material such as alumina-magnesia or alumina-chromium. it can. Moreover, although the case where wood was used as a combustible material was illustrated, it is not limited to this, Paper materials, such as resin and corrugated cardboard, the twisted brazing material, etc. can be used.

It is process drawing of the manufacturing method of the precast block for metal melting furnace ceilings of this embodiment. It is a top view which illustrates the composition of the precast block for metal melting furnace ceilings of this embodiment. It is a graph which shows the relationship between the cycle number of a heating rapid cooling process, and an elastic modulus change rate about sample 1 thru | or sample 3, and a control sample. It is a graph which shows the relationship between the addition amount of a combustible material, apparent porosity, and bulk specific gravity about the sample 1 thru | or sample 3, and a control sample. It is a graph which shows the relationship between the addition amount of a combustible material, bending strength, and compressive strength about the sample 1 thru | or sample 3, and a control sample.

Explanation of symbols

1, 2a, 2b, 3b Ceiling precast block S1 Mud preparation process S2 Molding process

Claims (2)

Mixing the combustible material of 0.9 vol% or more and 1.35 vol% or less with respect to the total volume of the irregular refractory material into the slurry of the irregular refractory material;
Pouring the mud mixed with the combustible material into a molding die having a shape of the whole or a part of the metal melting furnace ceiling, and drying to obtain a molded body having an amorphous refractory layer ; ,
A precast block for a metal melting furnace ceiling, comprising a step of heating the compact and burning the combustible material to generate pores having an average diameter of 3 mm to 10 mm. Manufacturing method. An amorphous refractory layer formed of an amorphous refractory material and containing a combustible material of 0.9 volume% or more and 1.35 volume% or less with respect to the total volume of the amorphous refractory material is formed on the entire metal melting furnace ceiling. Or formed in some shape ,
The precast block for a metal melting furnace ceiling , wherein the amorphous refractory layer is a layer in which pores having an average diameter of 3 mm to 10 mm are generated by combustion of the combustible material .

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