Method for evaluating quality of block-shaped refractory

Abstract

To provide a quality evaluation method for a block-shaped refractory that enables selection of a long-life block-shaped refractory capable of effectively suppressing occurrence of cracks and peeling.SOLUTION: A method for evaluating quality of a molded block-shaped refractory 11 used for an inner lining of a molten iron storage container, wherein the block-shaped refractory 11 includes, when applied to the molten iron storage container, an operation surface 13 that comes into contact with molten iron and a side surface 14 that faces another adjacent block-shaped refractory 11. The block-shaped refractory 11 is cut and divided into a plurality of refractory pieces including the operation surface 13, and an end refractory piece 15 including the operation surface 13 and the side surface 14, and a core refractory piece 16 including the operation surface 13 and not including the side surface 14 are sampled. For the end refractory piece 15 and the core refractory piece 16, at least one physical property selected from an apparent porosity, a water absorption rate, an apparent specific gravity, a bulk specific gravity, a true specific gravity, and a compressive strength is measured, and the measured physical property values of the end refractory piece 15 and the core refractory piece 16 are compared.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating the quality of refractory blocks applied to molten iron storage vessels, and more particularly to a method for evaluating the quality of refractory blocks with respect to spalling resistance. [Background technology]

[0002] In the steel industry, shaped refractories (including burned bricks and unburned bricks) are widely used as lining materials for molten iron storage vessels. In addition, a block-shaped unshaped refractory structure may be used for the bottom of a molten steel ladle, which is an example of a molten iron storage vessel. These refractories (i.e., block refractories) are prone to cracking and peeling due to temperature changes from room temperature to the high temperatures experienced during operation, temperature changes caused by cooling from high temperatures, and deterioration of the internal structure due to erosion and penetration by slag. If cracks appear in the refractory or peeling occurs due to the cracks propagating, resulting in a thinning of the remaining thickness of the refractory, it is necessary to stop use of the molten iron storage vessel in order to repair the refractory, which causes a problem of shortening the furnace lifespan. Therefore, techniques for evaluating the spalling resistance of refractories have been proposed.

[0003] For example, Patent Document 1 proposes a testing technique for evaluating spalling resistance (thermal shock resistance) on the premise that when the temperature of a refractory material rises, a temperature gradient occurs from the heating surface side to the back side, and thermal stress occurs according to the temperature gradient, and when this thermal stress becomes greater than the strength (mainly tensile strength) of the brick, cracks will occur. In Patent Document 2, similar to Patent Document 1, temperature gradients are considered to be a problem, and a technology for hot testing of refractory bricks is proposed, based on the premise that the cause of serious damage to refractories is structural spalling due to differences in physical properties between the slag-penetrated layer caused by slag penetration into the brick and the original brick layer, particularly differences in expansion and contraction. Patent Document 3 proposes a slag penetration spalling test technique in which a thermal history is given to a molded and dried refractory test piece, based on the premise that in structural spalling due to slag penetration of monolithic refractories, there is a close relationship between the amount of slag penetrated and the occurrence of cracks, and furthermore, that the progress of sintering and changes in physical properties due to slag penetration, particularly an increase in elastic modulus, are the main cause of stress cracking. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Utility Model Application Publication No. 54-156590 [Patent Document 2] Japanese Patent Application Publication No. 60-82948 [Patent Document 3] Japanese Patent Application Publication No. 8-189886 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned Patent Document 1 describes that thermal spalling of shaped refractories occurs when uneven thermal stress occurs depending on the deviation in the temperature distribution from the heating surface side to the back surface side of the shaped refractory, resulting in cracks. However, cracks and peeling can occur even if the temperature distribution is uniform, and even if this technology evaluates a refractory as having good spalling resistance, in actual use the refractory may have poor spalling resistance and may not be able to achieve the effect of extending its life. Furthermore, Patent Document 2 describes that structural spalling occurs due to the difference in expansion and contraction between the slag-penetrated layer and the original brick layer. However, even when this technology is evaluated as having good spalling resistance, regardless of whether slag is penetrated or not, in actual use, the spalling resistance is poor, and the life extension effect may not be achieved. Patent Document 3 describes that the main cause of structural spalling is an increase in the elastic modulus due to the progress of sintering and slag penetration. However, even when this technology is used to evaluate a material as having good spalling resistance, in actual use the material may have poor spalling resistance and may not be able to achieve the life extension effect.

[0006] An object of the present invention is to provide a method for evaluating the quality of massive refractories, which enables the selection of massive refractories that can effectively suppress the occurrence of cracks and spalling and have a long life. [Means for solving the problem]

[0007] First, the previously recognized mechanism of spalling occurring in actual use of a molten steel ladle or the like lined with lumpy refractories will be explained. Spalling is considered to be divided into thermal spalling and structural spalling. Thermal spalling occurs when cracks occur due to thermal stress caused by heating and cooling of the refractory mass, which causes a deviation in the temperature distribution of the refractory mass from the working surface that comes into contact with molten iron to the back surface. On the other hand, structural spalling occurs when cracks occur due to stress generated by changes in physical properties caused by heating from the working surface or by slag penetration, and thermal stress generated by uneven temperature distribution is exacerbated by changes in physical properties. As described above, it has been conventionally recognized that cracks occur due to the temperature difference between the working surface and the back surface of the refractory block.

[0008] The present inventors have changed the way of thinking of the above-mentioned conventional recognition and have conducted various studies on the above-mentioned problems, and as a result have newly discovered the following findings. Even if the temperature distribution of the granular refractory from the working surface to the back surface is uniform, cracks and peeling may occur.The cause of this is thought to be that the physical properties of the granular refractory vary depending on the part of the granular refractory that is molded, i.e., there is a large variation in the physical properties. Particular attention was paid to the variation in physical properties at the working surface side. That is, the difference in physical properties between the end portion, which includes the side surface facing the adjacent refractory block, and the core portion, which does not include the side surface, on the working surface side has a greater effect on spalling than the difference in physical properties between the working surface side and the back surface side of the working surface. Furthermore, the difference in physical properties between the end portion and the core portion on the working surface side has a greater effect on spalling than the temperature difference between the working surface side and the back surface side of the massive refractory material.

[0009] If there is a large variation in the physical properties between the ends and core of the refractory block, it is thought that distortion will occur on the working surface, which is most affected by heat, due to the difference in thermal expansion between the ends and core of the refractory block, resulting in cracks and peeling. The inventors prepared refractory pieces by dividing the lumpy refractory into two halves, vertically or horizontally, across the center, rather than into the end and core portions, and compared the physical properties of both. However, even when no significant difference in physical properties was observed, spalling sometimes occurred when lumpy refractories manufactured in the same lot (a unit of production of the same type of material from the same raw materials in a specified production volume; the same applies hereinafter) as this lumpy refractory were used in an actual machine. On the other hand, when refractory pieces were prepared by dividing the lumpy refractory from the same lot into the end and core portions and the physical properties were compared, significant differences were observed. As described above, the present inventors have found that variations in the physical properties of the massive refractory material on the working surface side have a significant effect on the occurrence of spalling.

[0010] The present invention conceived by the present inventors is as follows. A method for evaluating the quality of a formed block refractory material used for lining a molten iron storage vessel, comprising: The refractory mass has a working surface that contacts molten iron when applied to the molten iron storage vessel and a side surface that faces other adjacent refractory masses, cutting the refractory block into a plurality of refractory pieces including the working surface, and extracting end refractory pieces including the working surface and the side surface, and core refractory pieces including the working surface but not the side surface; measuring any one of the physical property values ​​of apparent porosity, water absorption, apparent specific gravity, bulk specific gravity, true specific gravity, and compressive strength for the end refractory pieces and the core refractory pieces; A method for evaluating the quality of lumpy refractory material, characterized in that physical property values ​​of the end refractory pieces and the core refractory pieces are compared. [Effects of the Invention]

[0011] According to the method for evaluating the quality of lumpy refractories of the present invention, it is possible to select lumpy refractories that have a long life and can effectively suppress the occurrence of cracks and peeling. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a side cross-sectional view of a molten steel ladle lined with lumpy refractories to which a method for evaluating the quality of lumpy refractories according to one embodiment of the present invention is applied. [Figure 2] FIG. 2 is an explanatory diagram of a quality evaluation method for the refractory block. DETAILED DESCRIPTION OF THE INVENTION

[0013] The method for evaluating the quality of lumpy refractories of the present invention is a method for evaluating the quality of molded lumpy refractories used as a lining for a molten iron storage vessel, The refractory mass has a working surface that contacts the molten iron when applied to a molten iron storage vessel, and a side surface that faces other adjacent refractory masses; cutting the refractory block into a plurality of refractory pieces including the working surface, and extracting end refractory pieces including the working surface and the side surface, and core refractory pieces including the working surface but not the side surface; The end refractory pieces and the core refractory pieces are measured for any one of the physical properties of apparent porosity, water absorption, apparent specific gravity, bulk specific gravity, true specific gravity, and compressive strength; The method is characterized by comparing the physical properties of the end refractory pieces and the core refractory pieces. A detailed explanation is provided below.

[0014] (1) "Quality evaluation method for formed refractory blocks used for lining molten iron storage vessels" This is a prerequisite for the present invention. The refractory lumps to be evaluated in the present invention are specified to be those used for lining molten iron storage vessels where spalling occurs. An example of a molten iron storage vessel is a molten steel ladle 10 for storing molten steel shown in FIG. 1 , but it is not particularly limited as long as it is lined with massive refractories, and examples thereof include a torpedo car and a converter.

[0015] The formed lumpy refractories include shaped refractories and unshaped refractories. Here, shaped refractories generally include fired bricks and unfired bricks. Furthermore, monolithic refractories are those that have been shaped by pouring or the like, and monolithic refractories in powder form or in slurry form are not included in the above-mentioned "molded block refractories." As shown in Figure 1, the massive refractories lining the molten steel ladle 10 are shaped refractories 11 and monolithic refractories 12, but depending on the type of molten iron storage vessel, only shaped refractories or only monolithic refractories may be used.

[0016] (2) Regarding "When applied to a molten iron storage vessel, the refractory block has a working surface that comes into contact with the molten iron and a side surface that faces other adjacent refractory blocks." 1 and 2, the surface that comes into contact with molten steel is the working surface 13, and the surfaces of the "certain shaped refractory 11" that face the "other shaped refractory 11" adjacent to the "certain shaped refractory 11" on the top, bottom, left, and right are the side surfaces 14. Here, "facing" includes not only the case where the above-mentioned "certain shaped refractory 11" and "other shaped refractory 11" are arranged in direct contact with each other, but also the case where they are arranged in a non-contact state via a joint material such as mortar (the same applies to the unshaped refractory 12).

[0017] (3) Regarding "Cutting the refractory block into multiple refractory pieces including the working surface, and extracting end refractory pieces including the working surface and side surface, and core refractory pieces including the working surface but not the side surface" As mentioned above, the difference in physical properties between the core refractory piece and the end refractory piece on the working surface affects spalling, so it is specified that refractory pieces (test pieces) be taken from that portion. In particular, the reason why the refractory piece was divided so that the core refractory piece and the end refractory piece could be taken is that, as mentioned above, it is not possible to evaluate spalling properties by dividing the refractory piece into two.

[0018] Specifically, as shown in FIG. 2, one cubic shaped refractory 11 is cut and divided into three pieces in the front-rear direction (the direction from the working surface side to the back surface side, the same applies below), the left-right direction, and the horizontal direction, to produce a total of 27 refractory pieces. This cutting may be performed so as to obtain at least refractory pieces on the working surface 13 side. For example, the cutting in the front-rear direction may be performed only at one location on the front side. Furthermore, it is preferable that the refractory pieces on the working surface 13 side obtained by cutting are cut as evenly as possible. Note that although FIG. 2 shows the shaped refractory 11 as a cube, since it has a shape to be used to line a molten iron storage vessel, in reality, the working surface side and the back surface side are distinguishable, for example, because the back surface side is longer.

[0019] From the cut and divided refractory pieces, nine refractory pieces on the working surface 13 side are sampled, including an end refractory piece 15 located at a corner and including the working surface 13 and two side surfaces 14, and a core refractory piece 16 including the working surface 13 but not the side surfaces 14. Note that reference numeral 17 denotes an end refractory piece (hereinafter also referred to as other end refractory) having one side surface 14 located between the end refractory pieces 15 located at the corner.

[0020] In the above-described cutting, the shaped refractory is divided into three parts in each of the front-rear direction, the left-right direction, and the horizontal direction, but it can also be divided into four or more parts depending on, for example, the shape, size, and quality evaluation level of the shaped refractory. For example, it can be divided into three parts in the front-rear direction and four or more parts in each of the left-right direction and the horizontal direction, or it can be divided into four or more parts in each of the front-rear direction, the left-right direction, and the horizontal direction. This cutting only requires that refractory pieces at least on the working surface side be obtained from the shaped refractory, so the working surface side portion of the shaped refractory may be cut in advance, and then the end refractory pieces and core refractory pieces may be cut and collected from this working surface side portion.

[0021] (4) Regarding "Measure any of the physical properties of the end refractory pieces and core refractory pieces, namely apparent porosity, water absorption, apparent specific gravity, bulk specific gravity, true specific gravity, and compressive strength" Measurement of physical properties is performed on the core refractory piece and one or more edge refractory pieces located on the outer periphery on the working surface side. Measurement of physical properties may be performed on all (eight pieces in FIG. 2) of the edge refractory pieces, for example. However, it is more preferable to perform measurements on at least one or more of some of the edge refractory pieces that are thought to have significantly different physical properties from those of the core refractory piece, specifically, one or more of the edge refractory pieces located at the corners (four pieces in FIG. 2). When measuring two or more edge refractory pieces, for example, an average value can be used as a measured value for comparison.

[0022] Here, when manufacturing shaped refractories, which are massive refractories, various pulverized raw materials are blended and kneaded, and then the powder raw materials are filled into a mold and compacted using a friction press or hydraulic press. Variations in physical properties are thought to be caused by the raw material particle size, the filling conditions of the raw materials into the mold (e.g., segregation of coarse particles), and the compacting pressure distribution. Meanwhile, when manufacturing monolithic refractories, which are massive refractories, various pulverized raw materials are blended and mixed, and then water is added and the mixture is fluidized in a mixer. The mixture is then poured into a mold. Variations in physical properties are thought to be caused by the raw material particle size, the mixing conditions in the mixer, and the conditions of pouring into the mold. Since significant differences in physical properties are expected between the core refractory pieces and the edge refractory pieces located at the corners, it is preferable to measure these values ​​and compare them in the next process.

[0023] The physical property values ​​may be measured by any one of the above-mentioned apparent porosity, water absorption, apparent specific gravity, bulk specific gravity, true specific gravity, and compressive strength, or may be measured by two or more of them. Spalling occurs when stress generated by thermal expansion exceeds the strength of the refractory block. On the other hand, in the same material, the apparent porosity, water absorption, apparent specific gravity, bulk specific gravity, true specific gravity, and compressive strength are generally correlated with the amount of thermal expansion, and therefore can be used to evaluate spalling resistance based on variations in physical property values ​​in the present invention.

[0024] The above physical property values ​​can be determined by general measuring methods for refractory blocks. Specifically, the apparent porosity, water absorption rate, apparent specific gravity, and bulk specific gravity can be measured using the vacuum method (using kerosene as the liquid medium) described in JIS R2205:1992, but other methods (vacuum method using water as the liquid medium, boiling method) may also be used. The true specific gravity is determined according to the method described in JIS R2205:1992. For the compressive strength of monolithic refractories, a method using packing as described in JIS R2206-2: 2007 is recommended, but a method not using packing as described in JIS R2206-1: 2007 is also acceptable. For the compressive strength of monolithic refractories, a machine-mixing method as described in JIS R2553: 2005 is recommended, but a hand-mixing method may also be used.

[0025] The measurement of the above-mentioned physical properties includes measurements after exposing the collected end refractory pieces and core refractory to actual use temperatures. The lumpy refractories used to line molten iron storage vessels are subject to high actual use temperatures of 1300°C to 1500°C, and even as high as 1800°C. Unfired lumpy refractory bricks are often heat-treated at approximately 300°C, which is lower than the actual use temperature. Even fired bricks are often heat-treated at approximately 1300°C, which is lower than the actual use temperature. Therefore, exposing the end refractory pieces and core refractory pieces used for physical property measurement to actual use temperatures makes it possible to evaluate the occurrence of spalling under conditions closer to those observed during actual use, thereby enabling the selection of an ideal lumpy refractory with a long life. While a reducing atmosphere is recommended for firing unfired bricks, which inhibits oxidation of the bricks, an oxidizing atmosphere is also acceptable.

[0026] (5) Regarding "Comparison of physical properties of end refractory pieces and core refractory pieces" Variations in the physical properties of each part of the molded lumpy refractory affect its spalling resistance. In particular, when there is a large variation in the physical properties between the edge and core of the lumpy refractory, the refractory on the working surface side, which is most affected by heat, will be distorted due to the difference in thermal expansion between the edge located on the outer periphery of the working surface and the core, resulting in cracks and peeling. Therefore, the physical properties of the end refractory pieces and the core refractory pieces are compared, and for example, pieces having similar physical properties are evaluated as non-defective.

[0027] The comparison is made between a core refractory piece and an edge refractory piece. For example, the edge refractory piece having the largest difference in physical properties between the core refractory piece and the edge refractory piece. This edge refractory piece is preferably an edge refractory piece 15 located at a corner in FIG. 2, but may also be another edge refractory piece 17 located between adjacent edge refractory pieces 15. Furthermore, depending on how the block refractory is cut, for example, when the block refractory is divided into four or more pieces in the front-rear direction, the left-right direction, and the horizontal direction as described above, a plurality of core refractory pieces will be generated. In this case, of the plurality of core refractory pieces, the core refractory piece that has the largest difference from the end refractory piece can be used as the object of comparison, but the average values ​​of the physical properties of the plurality of core refractory pieces can also be used as the object of comparison.

[0028] This comparison can be carried out by a known method that uses the difference, ratio, deviation, etc. of the physical property values ​​of the end refractory pieces and the core refractory pieces. When using lumpy refractories, the required quality varies depending on the material, shape (dimensions, etc.), conditions of use, etc. On the other hand, a person skilled in the art can determine the required quality conditions depending on the conditions of use of the lumpy refractories. That is, a person skilled in the art can easily select a lumpy refractory having a quality that satisfies the requirements by comparing the physical properties of the end refractory pieces and the core refractory pieces. [Example]

[0029] Next, examples carried out to confirm the effects of the present invention will be described. 1. Experimental Conditions The experiment was conducted on lumpy refractories for use in molten iron storage vessels. The molten steel ladle (see Figure 1) was used as the molten iron storage vessel, and magnesia-carbon bricks, a shaped refractory material, were used as the lump refractory material. These magnesia-carbon bricks are unfired and have an approximately rectangular parallelepiped shape (after being formed into the specified approximately rectangular parallelepiped shape, only a drying process is performed).

[0030] The refractory blocks used in the experiment were spare bricks purchased from the same production lot during refractory repair work, in which a brick on the working surface of a molten iron storage vessel, among multiple blocks arranged in the thickness direction as the lining of the vessel, was replaced with a new one. Two representative spare bricks were divided into the refractory pieces shown in Figure 2: core refractory block 16 with only a working surface, edge refractory block 15 with a working surface and two side surfaces, and other edge refractory block 17 with a working surface and one side surface. The divided refractory blocks were rectangular parallelepipeds with sides of 20 to 50 mm.

[0031] As physical property values ​​of the core refractory piece, end refractory piece, and other end refractory piece, bulk specific gravity was measured according to the vacuum method (liquid medium: kerosene) described in JIS R2205: 1992. The measured bulk specific gravity was in the range of 3.00 to 3.30.

[0032] The difference in physical properties between the core refractory piece and the end refractory piece was determined by the following method. For each of two spare bricks from the same lot, the physical properties of the core refractory piece 16 (1) and the end refractory piece 15 (2) shown in Fig. 2 were determined, and the difference in physical properties was evaluated as "large" if the maximum difference (there were two difference values) between the physical properties of the core refractory piece and the end refractory piece was 0.03 or more, and as "small" if the maximum difference was less than 0.03. Furthermore, in evaluating the difference in physical properties of the two spare bricks, if one or two of the two spare bricks had a "large" difference in physical properties, the difference in physical properties of that lot was evaluated as "large." Only when both of the differences in physical properties of the two spare bricks were "small," was the difference in physical properties of that lot evaluated as "small," and these results were recorded in the "Core" - "End" columns of "Difference in Physical Properties" in Table 1, which will be described later. Here, two end refractory pieces 15 are used for one spare brick, but since there are a total of four end refractory pieces 15 as shown in Fig. 2, the physical property values ​​of three or four (all) end refractory pieces 15 can also be obtained to calculate the difference. In this case, there are three or four difference values.

[0033] The difference in physical properties between the end refractory piece and the other end refractory piece was determined by the following method. For each of the two spare bricks of the same lot, the physical properties of the two end refractory pieces 15 and two other end refractory pieces 17 shown in Fig. 2 were determined, and the difference between the physical properties of the end refractory piece and the other end refractory piece was determined to be "large" if the maximum difference (there were four difference values) between the end refractory piece and the other end refractory piece was 0.03 or more, and the difference between the physical properties was determined to be "small" if the maximum difference was less than 0.03. Furthermore, in evaluating the difference in the physical properties of the two spare bricks, if one or two of the two spare bricks had a "large" difference in physical properties, the difference in the physical properties of that lot was determined to be "large." Only when both of the differences in the physical properties of the two spare bricks were "small," was the difference in the physical properties of that lot evaluated as "small," and these results were recorded in the "End" - "Other End" column of "Difference in Physical Properties" in Table 1 described below. Here, two other end refractory pieces 17 were used for one spare brick, but as shown in Fig. 2, there are a total of four other end refractory pieces 17, so the above difference can also be calculated by finding the physical property values ​​of three or four (all) other end refractory pieces 17. In this case, there are six or eight difference values.

[0034] The spalling resistance of the lumpy refractories applied to the molten steel ladle was evaluated by visually checking for the occurrence of peeling (cracks) of the magnesia-carbon bricks in the immersed side wall under two conditions: treatment where the molten steel temperature was high in the immersed side wall of the molten steel ladle (treatment of special steel, an example where the temperature difference between the working surface and the back side is large), and treatment where the molten steel temperature was low (treatment of ordinary steel, an example where the temperature difference between the working surface and the back side is small).The number of times the molten steel ladle was used (number of CHs) at which peeling became visible was recorded. The confirmation and recording were carried out for multiple lots of refractories with the same physical property difference conditions. The range of the number of uses of the molten steel ladle under the same conditions of difference in physical properties (for each experimental example in Table 1) was determined, and the number of uses was divided by the number of uses within the lifespan of a conventional molten steel ladle (CH number; specifically, the number of uses of the molten steel ladle until the refractory peeling spreads over the entire surface and the remaining thickness of the refractory is subsequently reduced to the repair control value), and the ratioed number of uses (CH number) is shown in Table 1.

[0035] The experimental conditions and results are shown in Table 1. [Table 1]

[0036] Experimental Examples 1 and 2 shown in Table 1 are experimental examples to verify the conventional mechanism of spalling occurrence. The experiment with the larger temperature difference between the working surface and the back surface of the massive refractory, i.e., Experimental Example 1, showed lower spalling resistance than Experimental Example 2. Experimental Examples 1 and 3 are experimental examples in which the temperature difference between the working surface side and the back surface side of the lumpy refractory material was large. However, the one with the larger difference in physical property values ​​between the core refractory pieces and the end refractory pieces on the working surface side, i.e., Experimental Example 3, showed significantly lower spalling resistance than Experimental Example 1. Experimental Examples 2 and 4 are experimental examples in which the temperature difference between the working surface side and the back surface side of the lumpy refractory material was small. However, the experiment in which the difference in physical property values ​​between the core refractory piece and the end refractory piece on the working surface side was larger, i.e., Experimental Example 4, showed significantly lower spalling resistance than Experimental Example 2.

[0037] In the above-mentioned Experimental Examples 1 and 3 and Experimental Examples 2 and 4, when there was a large difference in the physical properties between the core refractory pieces on the working surface side of the massive refractory and the end refractory pieces, the spalling resistance decreased. In other words, even though no difference in the physical properties was observed when comparing the physical properties of the end refractory pieces (end and other end), the spalling resistance changed, which showed that the difference in the physical properties between the end refractory pieces does not affect the spalling resistance. Furthermore, when comparing Experimental Example 4 and Experimental Example 5, when differences in physical properties are observed only between the end refractory pieces (one end and another end), no change in spalling resistance is observed, which shows that differences in physical properties between the end refractory pieces do not affect spalling resistance. Finally, from Experimental Examples 1 and 4, it was found that the number of CHs required for visual confirmation of peeling was lower in Experimental Example 4 than in Experimental Example 1, and therefore it was found that the difference in physical property values ​​between the core refractory pieces and the end refractory pieces of the lumpy refractory has a greater effect on spalling resistance than the temperature difference between the working surface and the back surface of the lumpy refractory.

[0038] In the above examples, the case where bulk specific gravity was used as the physical property value to be compared was described. However, as described above, for the same material, the other physical properties such as apparent porosity, water absorption, apparent specific gravity, true specific gravity, and compressive strength also generally have a correlation with the amount of thermal expansion, similar to bulk specific gravity, and therefore similar trends can be obtained. Furthermore, when evaluating the quality of a refractory block, any two or more of apparent porosity, water absorption, apparent specific gravity, bulk specific gravity, true specific gravity, and compressive strength may be used in combination.

[0039] As described above, by using the method for evaluating the quality of lumpy refractories of the present invention, it is possible to select lumpy refractories that have a long life and can effectively suppress the occurrence of cracks and peeling.

[0040] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the configurations described in the above embodiments and includes other embodiments and modifications that are conceivable within the scope of the claims. For example, a method for evaluating the quality of refractory aggregates of the present invention that combines some or all of the above embodiments and modifications is also within the scope of the present invention. [Industrial Applicability]

[0041] INDUSTRIAL APPLICABILITY The present invention is industrially useful because it provides a method for evaluating the quality of massive refractories that can select massive refractories that can effectively suppress the occurrence of cracks and peeling and have a long life. [Explanation of symbols]

[0042] 10: molten steel ladle, 11: shaped refractory (lump refractory), 12: monolithic refractory (lump refractory), 13: working surface, 14: side, 15: end refractory piece, 16: core refractory piece, 17: other end refractory piece

Claims

[Claim 1] A method for evaluating the quality of a formed block refractory material used for lining a molten iron storage vessel, comprising: The refractory mass has a working surface that contacts molten iron when applied to the molten iron storage vessel and a side surface that faces other adjacent refractory masses, cutting the refractory block into a plurality of refractory pieces including the working surface, and extracting end refractory pieces including the working surface and the side surface, and core refractory pieces including the working surface but not the side surface; measuring any one of the physical property values ​​of apparent porosity, water absorption, apparent specific gravity, bulk specific gravity, true specific gravity, and compressive strength for the end refractory pieces and the core refractory pieces; A method for evaluating the quality of lumpy refractory material, characterized in that physical property values ​​of the end refractory pieces and the core refractory pieces are compared.

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