JP7070304B2 - Alumina-Magnesian castable refractory evaluation method for peeling resistance - Google Patents

Description

The present invention relates to a method for evaluating a castable refractory using a method for testing the peel resistance of an alumina-magnesia castable refractory used for a lining furnace material of a molten metal processing container.

Raw material powders for alumina-magnesia castable refractories containing components such as alumina, magnesia and organic substances are commercially available. Water is added to this raw material powder and kneaded, and the kneaded product is poured into a mold to form a predetermined block shape and then dried. If there are no defects such as cracks or cracks by visually observing the dried molded body, the dried molded body can be used as a refractory material for bricks or the like for lining the molten steel ladle. It is lined in a molten metal processing container (hereinafter, simply referred to as "molten steel ladle").

The alumina-magnesian castable refractory placed in the molten steel ladle has a problem of causing peeling wear due to cracks generated during use. The main cause of the cracks in the alumina-magnesian castable refractory during use was thought to be buckling caused by the volume expansion associated with the spinel-forming reaction between alumina, which is the constituent raw material of the refractory, and magnesia.

The following two methods have been studied to prevent buckling during use of alumina-magnesian castable refractories. The first is a method of imparting load softening to an alumina-magnesia castable refractory in order to alleviate the stress generated by the volume expansion associated with the spinel-forming reaction between alumina and magnesia, which causes buckling. .. The second point is a method of controlling the volume expansion accompanying the spinel formation reaction between alumina and magnesia and reducing the stress generated by the volume expansion.

In Patent Document 1 and Patent Document 2, appropriate load softening property is imparted at a high temperature of 1400 ° C. or higher where the volume expansion due to the spinel-forming reaction between alumina and magnesia, which are constituent raw materials of an alumina-magnesia castable refractory, is large. Alumina-magnesia castable refractories that have been made are disclosed.
In Patent Document 3, as a test method of volume expansion during use of an alumina-magnesia castable refractory, the residual linear change rate of the alumina-magnesia castable refractory after firing at 1500 ° C. in the air for 3 hours is adopted. Disclosed are alumina-magnesia castable refractories in which the volume expansion associated with the spinel-forming reaction between alumina and magnesia in use is controlled.

Japanese Unexamined Patent Publication No. 5-185202 Japanese Unexamined Patent Publication No. 2001-253781 Japanese Unexamined Patent Publication No. 9-30859

However, the dried molded body containing a refractory as a main component (hereinafter, "a dried molded body containing a refractory as a main component" is simply referred to as a "refractory material") is lined in a molten steel ladle. Then, they are fixed to each other. Therefore, even if the alumina-magnesian castable refractory described in Patent Documents 1, 2 and 3 is used, there is a problem that the peeling wear caused by the crack generated in the castable refractory during use cannot be eliminated.

However, in the prior art, the refractory is said to be due to cracks caused by the softening shrinkage caused by the liquid phase in a usage environment lined in a molten steel ladle so that the alumina-magnesian castable refractories are fixed to each other. There was no way to evaluate the peeling resistance of an object for peeling wear.

The present invention determines whether or not peeling wear occurs due to cracks caused by softening shrinkage caused by the liquid phase generated during use when an alumina-magnesia castable refractory is fixedly placed in a molten steel ladle. It is an object of the present invention to provide a method for evaluating peel resistance in advance.

The present inventor investigated the wear mechanism of an alumina-magnesia castable refractory used in a molten steel ladle. As a result, the cracks that occur in the refractory during use, which causes peeling wear, are not caused by buckling caused by volume expansion due to the spinel formation reaction between alumina and magnesia, which are the constituent raw materials of the refractory. It was found that it is caused by the softening shrinkage caused by the liquid phase formed in the refractory during use.

Further, in the region where the temperature is 1400 ° C. or higher in the temperature distribution inside the refractory, the refractory raw material reacts with a part of alumina cement and alumina in addition to the spinel generated from the reaction of magnesia and a part of alumina. A liquid phase is formed from the reaction of CaO · 6Al _{2O 3} produced from the reaction of No. 1 and silica with other oxides.

The formation of spinel and CaO · 6Al _{2O 3} is accompanied by volume expansion of about 8% and about 3%, respectively. When the refractory becomes a liquid phase, the volume of the liquid phase becomes larger than that of the solid phase. However, due to the capillary phenomenon, the liquid phase is absorbed and densified in the pores of the fireproof material, and the thermal stress due to the solid portion is relaxed by the liquid phase.

Thus, the amount of shrinkage of the refractory is governed by two factors: the amount of liquid phase formed inside the refractory and the porosity of the refractory.

The liquid phase formed inside the refractory mainly depends on the physical properties of the inorganic compounds constituting the refractory. However, the porosity is determined by the amount of water used for kneading when the refractory material obtained by kneading the raw material and water on site is manufactured or constructed, and the components such as organic substances contained in the raw material. It mainly depends on the environment such as the temperature at the time of manufacturing or construction.

In order to produce the desired refractory, the optimum amount of water is set to make the refractory smelting fluid more fluid within a certain range and easier to construct. However, the smaller the amount of water, the smaller the porosity and the better the durability. Recently, a refractory material for molten steel ladle that is manufactured or constructed using a raw material in which the amount of water added is 4.0 to 6.0% and has an apparent porosity of 13.0 to 16.0. Raw materials are commercially available.

However, even though the refractory raw material is kneaded with the optimum amount of water, the peel resistance may be too low for actual use in a molten steel ladle.

This is due to the fact that some refractories manufactured or constructed within the optimum manufacturing conditions or construction conditions have high porosity and some have low porosity. Porosity is affected by the water content added to the material, but even if the amount of water added is the same, porosity depends on the organic components contained in the thickener and the characteristics of the material. Rates may vary.

When the apparent porosity is about 13.0 to 16.0%, the liquid phase is absorbed into the pores, so that the liquid phase tends to shrink depending on the amount of the liquid phase produced. Peeling occurs when the amount of the liquid phase is more than an appropriate amount, but it can be said that the one having an appropriate amount of the liquid phase to be generated has good peeling resistance. This is because even if an inorganic compound that expands due to heating is generated, the influence of such expansion is alleviated or absorbed by the liquid phase, so that the peel resistance is improved.

Further, when the liquid phase generated at a high temperature is cooled, a solid phase accompanied by volume expansion is precipitated at the time of cooling. That is, the amount of volume expansion during cooling is proportional to the amount of liquid phase produced. Therefore, the difference in the coefficient of thermal expansion between the cooling process and the temperature raising process at 1200 ° C. at 1200 ° C. at which the precipitation of the solid phase from the liquid phase is completed is correlated with the amount of the liquid phase generated at high temperature. Further, in general, the smaller the difference in dimensional fluctuation when repeated expansion and contraction, the more difficult it is to peel off.

Therefore, the present inventors have focused on the difference in dimensional fluctuations when expansion and contraction are repeated, and investigated the relationship between the difference in the coefficient of thermal expansion and the peeling resistance in the cooling process and the temperature raising process at 1200 ° C. As a result, when the difference in the coefficient of thermal expansion (%) was 0.1% or less, it was considered to be a criterion for judging the superiority or inferiority of the peel resistance. The "coefficient of linear thermal expansion" is also called the "coefficient of linear expansion".

As a result of further diligent studies by the present inventors using an actual machine, the peeling resistance of the alumina-magnesia castable refractory during actual use is estimated from the difference in the coefficient of thermal expansion between the cooling process and the heating process at 1200 ° C. It has been found that it may differ from the peel resistance to be applied. That is, the present inventors have stated that in the alumina-magnesian castable refractory in use, the temperature distribution is in a steady state from the surface of the refractory in contact with the molten steel at 1600 ° C. to the back surface thereof, and the temperature at which the liquid phase is generated. It was found that the change in the coefficient of linear expansion of the refractory at a temperature of over 1400 ° C. correlates with the peel resistance, and the peel resistance can be grasped from the change in the coefficient of linear thermal expansion.

The present invention is based on the above findings, and the gist of the present invention is as follows.
(1) A method for evaluating the peeling resistance of an alumina-magnesia castable refractory having a residual line change rate of 0% or more after firing at a temperature of 1400 ° C. or higher for 3 hours or longer.
A step of measuring the linear thermal expansion coefficient (%) at 1400 ± 10 ° C. for the castable refractory after firing at 1400 ± 10 ° C. for 3 hours or more.
A step of measuring the linear thermal expansion coefficient (%) at 1500 ± 10 ° C. for the castable refractory after firing at 1500 ± 10 ° C. for 3 hours or more.
A step of measuring the linear thermal expansion coefficient (%) at 1600 ± 10 ° C. for the castable refractory after firing at 1600 ± 10 ° C. for 3 hours or more.
A step of determining whether or not the coefficient of linear thermal expansion (%) at 1500 ± 10 ° C. is equal to or higher than the coefficient of linear thermal expansion (%) at 1400 ± 10 ° C.
Peeling resistance of the alumina-magnesian castable refractory to be evaluated based on the value obtained by subtracting the coefficient of linear thermal expansion (%) at 1600 ± 10 ° C. from the coefficient of linear thermal expansion (%) at 1400 ± 10 ° C. A method for evaluating the peeling resistance of an alumina-magnesia castable refractory, which comprises a step of determining.
(2) Evaluation target when the coefficient of linear thermal expansion at 1500 ± 10 ° C. is equal to or greater than the coefficient of linear thermal expansion (%) at 1400 ± 10 ° C. and the subtracted value is 0.2% or less. The method for evaluating the peeling resistance of an alumina-magnesia castable refractory according to (1), which is characterized by determining that the peeling resistance of the alumina-magnesia castable refractory is high.

It cannot be used in a molten steel ladle without confirming the manufactured refractory. This is because the refractory may have poor peel resistance. In the determination method of the present invention, it is possible to determine the peeling resistance of the manufactured refractory using a part of the manufactured refractory before placing it in the molten steel ladle. INDUSTRIAL APPLICABILITY According to the present invention, the peeling resistance of an alumina-magnesia castable refractory can be evaluated, and an alumina-magnesia castable refractory having extremely excellent durability when actually used can be obtained.

It is a graph which shows the linear thermal expansion coefficient at 1400 ℃, 1500 ℃ and 1600 ℃ of the alumina-magnesian castable refractory 1. It is a graph which shows the linear thermal expansion coefficient at 1400 ℃, 1500 ℃ and 1600 ℃ of the alumina-magnesian castable refractory 2. It is a graph which shows the linear thermal expansion coefficient at 1400 ℃, 1500 ℃ and 1600 ℃ of the alumina-magnesian castable refractory 3. It is a graph which shows the linear thermal expansion coefficient at 1400 ℃, 1500 ℃ and 1600 ℃ of the alumina-magnesian castable refractory 4. It is a graph which shows the linear thermal expansion coefficient at 1400 ℃, 1500 ℃ and 1600 ℃ of the alumina-magnesian castable refractory 5. It is a graph which shows the linear thermal expansion coefficient at 1400 ℃, 1500 ℃ and 1600 ℃ of the alumina-magnesian castable refractory 6.

Since the alumina-magnesia castable refractory to be evaluated in the present invention is mainly used for a molten steel ladle, the case where it is used for a molten steel ladle will be described below as an example. The same applies when used in other containers.

[Chemical reaction of alumina-magnesia castable refractory fixed in a molten steel ladle]
The molten steel ladle is a molten metal processing container that transports molten steel discharged from a converter to a continuous casting machine. Therefore, the alumina-magnesian castable refractory used in the molten steel ladle is heated during the period when the molten steel stays, and the molten steel from the completion of casting to just before the start of steel receiving in the converter exists in the molten steel ladle. It will be cooled during the non-period. That is, the alumina-magnesia castable refractory is used in an environment where heating and cooling are repeated.

In the alumina-magnesian castable refractory used in such an environment, the peeling damage caused by the crack is the temperature distribution inside the refractory from the surface of the refractory in contact with the molten steel at 1600 ° C to the back surface. It occurs after the steady state is reached. At that time, the position where the crack was generated was found to be the position where the temperature reached about 1400 ° C. according to the steady heat transfer calculation inside the refractory in use.

By the way, the alumina-magnesia castable refractory is composed of alumina, magnesia, silica _, and a refractory raw material such as alumina cement having CaO / _Al2O3 as a main crystal phase. In the region where the temperature inside the refractory is 1400 ° C. or higher, it is considered that these refractory raw materials cause the following chemical reaction (1).
Alumina + magnesia + silica + CaO ・ Al ₂ O ₃
→ Alumina + Spinel + CaO ・ 6Al ₂ O ₃ + Liquid phase ・ ・ ・ (Chemical reaction 1)

That is, at a temperature of 1400 ° C. or higher, the refractory raw material reacts during use, and CaO produced from the reaction between alumina cement and a part of alumina, in addition to the spinel produced from the reaction between magnesia and a part of alumina. A liquid phase is formed from the reaction of 6Al ₂ O ₃ and silica with other oxides. Chemical reaction The amount of each of the spinel, CaO · 6Al ₂ O ₃ and the liquid phase produced in the chemical reaction of the formula (1) depends on the content of the refractory raw material contained in the alumina-magnesia castable refractory. do.

Based on the chemical reaction equation (1), we infer the change in the structure of the alumina-magnesia castable refractory of the molten steel ladle in use. When a certain amount or more of a liquid phase is generated in an alumina-magnesian castable refractory at a temperature of 1400 ° C. or higher, the refractory structure exhibits softening shrinkage due to the capillary force of the liquid phase. That is, since the amount of the liquid phase formed increases from the region inside the refractory whose temperature becomes 1400 ° C. or higher during use to the surface of the refractory in contact with the molten steel, the refractory structure is determined according to the amount of the liquid phase generated. As a result of shrinkage, the amount of shrinkage of the refractory structure on the surface of the refractory is maximized.

Next, during the period in which the molten steel does not exist in the ladle after the casting is completed, that is, in the period in which the refractory is cooled, the reaction of the following chemical reaction (2) proceeds.
Alumina + spinel + CaO · 6Al ₂ O ₃ + liquid phase → Alumina + spinel + CaO · 6Al ₂ O ₃ + CaO-MgO-SiO ₂ -Al ₂ O ₃ system compound ... (Chemical reaction 2)

In the cooling process, solid phases such as CaO · 6Al ₂ O ₃ and CaO-MgO-SiO ₂ -Al ₂ O ₃ system compounds are deposited from the liquid phase. Generally, a heated refractory exhibits volume shrinkage during the cooling process, but in an alumina-magnesia castable refractory, the liquid phase produced during the cooling process by the reaction of the chemical reaction (2). Since the CaO · _6Al2O3 component accompanied by volume expansion is deposited from the above _, volume expansion is caused. Then _, the volume expansion of the refractory becomes maximum at around 1200 ° C. when the precipitation of the CaO ・_6Al2O3 component from the liquid phase is completed.

Based on the chemical reaction equation (2), we infer the change in the structure of the refractory surface during the period when the molten steel is not present in the ladle, that is, during the period when the alumina-magnesia castable refractory is cooled. During cooling, the temperature of the refractory surface drops to about 1200 ° C. In the cooling process, the CaO ・ 6Al ₂ O ₃ component with volume expansion is deposited from the liquid phase generated in the refractory, and the precipitation of the CaO ・ 6Al ₂ O ₃ component from the liquid phase is due to the temperature of the surface of the refractory. The surface structure of the refractory expands in volume because it occurs until it is cooled to around 1200 ° C.

From the above, the surface structure of the alumina-magnesian castable refractory repeats volume shrinkage during use when molten steel stays in the molten steel ladle and volume expansion during cooling when molten steel does not exist in the molten steel ladle. It will be. Repeated volume contraction and volume expansion of the refractory structure on the surface of the refractory accumulates strain inside the refractory, resulting in cracks that cause peeling wear.

As a result, the strain accumulated inside the refractory is reduced by reducing the difference between the volume shrinkage of the alumina-magnesian castable refractory in the heating process up to 1600 ° C and the volume expansion in the cooling process up to 1200 ° C. It can be minimized, and it is considered that the occurrence of cracks that cause peeling wear can be predicted in advance.

However, when the coefficient of linear thermal expansion of the alumina-magnesia castable refractory increases with increasing temperature when heated to 1400 ° C. or higher, the volume expansion in the heating process and the volume shrinkage in the cooling process of the alumina-magnesia castable refractory In the above method for evaluating the peeling resistance from the difference between the above, it may not be possible to determine the peeling resistance of the alumina-magnesia castable refractory actually used in the actual machine.

The present inventor describes the change in the coefficient of linear thermal expansion of the alumina-magnesian refractory refractory in use when the starting temperature of liquid phase formation is 1400 ° C or higher in the steady temperature distribution inside the refractory. As a result of investigating the correlation between the presence and absence of peeling wear in detail, it was found that there is a phenomenon that peeling wear occurs even when the coefficient of linear thermal expansion of the refractory at 1400 ° C. or higher does not decrease with increasing temperature.

[Mechanism of action of the present invention]
In the alumina-magnesian castable refractory, the coefficient of linear thermal expansion at a temperature of 1400 ° C. or higher does not decrease with increasing temperature, because the amount of the liquid phase generated in the above chemical reaction (1) increases with increasing temperature. Because it doesn't.

That is, at a temperature of 1400 ° C. or higher, when the amount of liquid phase formed in the above chemical reaction (1) is larger than the amount of _spinel or CaO · _6Al2O3 with volume expansion, the linear heat of the fireproof material. The coefficient of expansion varies as shown in FIG. On the contrary, at a temperature of 1400 ° C. or higher, if the amount of _spinel or CaO ・_6Al2O3 produced by volume expansion in the above chemical reaction (1) is larger than the amount of liquid phase produced, it is refractory. The coefficient of linear thermal expansion of an object changes as shown in FIG. Further, when the amount of liquid phase formed is larger than the amount of spinel or CaO · 6Al ₂ O ₃ formed at a temperature exceeding 1500 ° C., the coefficient of linear thermal expansion of the refractory changes as shown in FIGS. 3 to 5. However, only at 1500 ° C., when the amount of liquid phase formed is larger than the amount of _spinel or CaO · _6Al2O3 formed, the amount changes as shown in FIG.

In an alumina-magnesian castable refractory, at a temperature of 1400 ° C. or lower, a liquid phase is not formed in the reaction of the chemical reaction (1). That is, the alumina-magnesia castable refractory exhibits thermal expansion at a temperature of 1400 ° C. or lower due to the thermal expansion of the refractory raw material itself and the volume expansion accompanying the formation of spinel and CaO · 6Al ₂ O ₃ .

If the coefficient of linear thermal expansion of the refractory at a temperature of 1400 ° C or higher takes the same value or increases as the temperature rises, it comes into contact with the molten steel from the region inside the refractory that reaches 1400 ° C or higher during use. The refractory structure on the surface of the refractory does not change or expands. That is, since the refractory structure in the region of 1400 ° C or higher inside the refractory does not shrink during use, distortion does not occur, so that cracks that cause peeling do not occur, and the refractory resistance It is judged to be excellent.

In the case of FIGS. 3 and 4, in the alumina-magnesian castable refractory, the value of the coefficient of linear thermal expansion at 1500 ° C is equal to or higher than the value of the coefficient of linear thermal expansion at 1400 ° C. In addition, when the coefficient of linear thermal expansion at 1600 ° C is smaller than the coefficient of linear thermal expansion at 1400 ° C, the refractory is in contact with the molten steel at 1600 ° C from the region inside the refractory that is 1400 ° C or higher during use. Looking at the refractory structure over the surface of the object, distortions that result in the formation of cracks can occur.

However, the smaller the difference value (%) obtained by subtracting the value of the coefficient of linear thermal expansion at 1600 ° C from the value of the coefficient of linear thermal expansion at 1400 ° C, the more the region becomes 1400 ° C or higher inside the refractory during use. Distortion is unlikely to occur in the refractory structure. In particular, when the difference value (%) is 0.2% or less as shown in FIG. 5, the refractory structure in the region where the temperature is 1400 ° C. or higher inside the refractory is not distorted during use. Cracks that cause peeling will not occur, and it is judged that the peeling resistance is excellent.

In the case as shown in FIG. 6, in the alumina-magnesian castable refractory, the value of the coefficient of linear thermal expansion at 1500 ° C. is smaller than the value of the coefficient of linear thermal expansion at 1400 ° C. When the coefficient of expansion is larger than the coefficient of linear thermal expansion at 1500 ° C, the entire refractory structure from the region inside the refractory that becomes 1400 ° C or higher during use to the surface of the refractory in contact with the molten steel at 1600 ° C. It is judged that the peel resistance is inferior because the strain that causes the generation of cracks occurs.

As described above, in the alumina-magnesian castable refractory to be evaluated, the value of the coefficient of linear thermal expansion at 1500 ° C. after firing at 1500 ° C. is equivalent to the value of the coefficient of linear thermal expansion at 1400 ° C. after firing at 1400 ° C. The evaluation target is based on the determination of whether or not the value is higher than that and the difference between the coefficient of linear thermal expansion (%) at 1400 ° C. and the coefficient of linear thermal expansion (%) at 1600 ° C. It is possible to evaluate the peeling resistance when a refractory material is applied to an actual machine.

Further, when the difference value (%) obtained by subtracting the value of the coefficient of linear thermal expansion at 1600 ° C from the value of the coefficient of linear thermal expansion at 1400 ° C is a predetermined value or less, especially at 1400 ° C after firing at 1400 ° C. When the value obtained by subtracting the value of the coefficient of linear thermal expansion at 1600 ° C after firing at 1600 ° C from the value of the coefficient of linear thermal expansion is 0.2% or less, it is judged that the castable refractory has excellent peeling resistance. It is preferable to do so.

Generally, alumina-magnesia castable refractories preferably have a moderate residual expansion after undergoing thermal history. A refractory that shrinks residually, that is, a refractory material having a residual line change rate of less than 0%, has a smaller dimension after being heated and cooled than the original dimension before heating. Such a refractory material having a residual line change rate of less than 0% is clearly cracked during use and is often inferior in peeling resistance in the first place, and therefore cannot be used in the manufacture of an actual machine.

On the other hand, the alumina-magnesia castable refractory may form a liquid phase in the reaction of the chemical reaction (1) at a temperature of 1400 ° C. or higher. The generated liquid phase may shrink the refractory due to volume shrinkage during solidification during cooling. Further, the alumina-magnesia castable refractory can be heated up to 1600 ° C. on the surface of the refractory by coming into contact with molten steel during use. Further, if the firing time at a temperature of 1400 ° C. or higher is 3 hours or longer, it is a sufficient time for the reaction of the chemical reaction (1) to reach a chemical equilibrium state.

Therefore, the present invention is applied to an alumina-magnesia castable refractory having a residual line change rate of 0% or more after firing at a temperature of 1400 ° C. or higher for 3 hours or longer.

As a test method for the residual line change rate, it is preferable to use JIS-R2554 “Line change rate test method for castable refractories”.

Further, in the present invention, as a method for testing the coefficient of linear thermal expansion, it is preferable to use a test piece and test conditions based on JIS-R2207 “Test method for thermal expansion of refractory material”. More preferably, JIS-R2207-1 "non-contact method", which has little effect on the expansion and contraction of the liquid phase, is used.

It should be noted that FIGS. 1 to 6 show only the linear thermal expansion rates at 1400 ° C, 1500 ° C and 1600 ° C. However, if the coefficient of linear thermal expansion is measured in the temperature range of 1400 ± 10 ° C., the difference in the coefficient of linear thermal expansion is less than 0.01% in absolute value. The expansion coefficient may be used as the "linear thermal expansion coefficient of 1400 ° C." in the evaluation method of the present invention. Similarly, in the evaluation method of the present invention, the coefficient of linear thermal expansion (%) measured at 1500 ± 10 ° C. is defined as “the coefficient of linear thermal expansion at 1500 ° C.”, and the coefficient of linear thermal expansion measured at 1600 ± 10 ° C. ( %) May be used as the "linear thermal expansion coefficient of 1600 ° C.".

[Temperature change in coefficient of linear thermal expansion and peel resistance of refractories fixed to molten steel ladle]
What is the actual temperature change of the linear thermal expansion coefficient of the alumina-magnesia castable refractory under the usage environment lined in the molten steel ladle so that the alumina-magnesia castable refractory is fixed to each other? In addition, the peel resistance when applied to the actual machine will be specifically explained.

In order to observe the temperature change of the linear thermal expansion coefficient under the usage environment lined in the molten steel ladle so as to be fixed to each other, the alumina-magnesia having the composition of No. 1 to No. 6 shown in Table 1 is observed. Quality Castable refractory was used.

Further, as a test method for the coefficient of linear thermal expansion, a test piece and test conditions based on JIS-R2207 "Test method for thermal expansion of refractory material" were used.

In order to make a comparison with the evaluation method for determining the peel resistance from the difference between the volume shrinkage amount in the heating process and the volume expansion amount in the cooling process (“evaluation method for comparison” in Table 1), firing at 1400 ° C. for 3 hours. The difference value of the coefficient of linear thermal expansion at 1200 ° C. in the linear thermal expansion curve of the subsequent fireproof material was measured as follows. That is, after firing at 1400 ° C. for 3 hours and cooling to room temperature, the linear thermal expansion coefficient of the temperature raising process from room temperature to 1600 ° C. and the cooling process from 1600 ° C. to room temperature is continuously measured, and the cooling process is performed. The difference (%) in the coefficient of linear thermal expansion at 1200 ° C. in the process of raising the temperature was defined as the difference value (%). The evaluation method of the comparison target is the evaluation method focusing on the difference in the coefficient of thermal expansion between the cooling process and the heating process at 1200 ° C. at 1200 ° C. at which the precipitation of the solid phase from the liquid phase is completed, and the difference value is ± 0. If it is within 1%, it is judged that the peel resistance is good.

FIG. 1 shows the linear thermal expansion rates of the alumina-magnesian castable refractory 1 at 1400 ° C, 1500 ° C, and 1600 ° C. At temperatures above 1400 ° C, the coefficient of linear thermal expansion decreases with increasing temperature. It was judged that the evaluation method of the comparison target was excellent in peeling resistance (Table 1: code “◯”).

In FIGS. 1 to 6, the coefficient of linear thermal expansion at 1400 ° C. is an alumina-magnesia castable refractory fired at 1400 ± 10 ° C. for 3 hours (hereinafter, unless otherwise specified, it is simply fired at 1400 ° C. The coefficient of linear thermal expansion measured in the process of raising the temperature from room temperature to 1400 ° C. (hereinafter referred to as “refractory”) is simply “the coefficient of linear thermal expansion at 1400 ° C.” unless otherwise specified. Linear thermal expansion rate "). Similarly, the coefficient of linear thermal expansion at 1500 ° C. is an alumina-magnesia castable refractory fired at 1500 ± 10 ° C. for 3 hours (hereinafter, simply referred to as “fireproof material fired at 1500 ° C.” unless otherwise specified). The coefficient of linear thermal expansion measured in the process of raising the temperature from room temperature to 1500 ° C. (hereinafter, unless otherwise specified, such a coefficient of linear thermal expansion is simply referred to as "the coefficient of linear thermal expansion at 1500 ° C." ). The coefficient of linear thermal expansion at 1600 ° C is an alumina-magnesian castable refractory fired at 1600 ± 10 ° C for 3 hours (hereinafter, unless otherwise specified, such a coefficient of linear thermal expansion is simply “fire resistance fired at 1600 ° C”. It is the coefficient of linear thermal expansion measured in the process of raising the temperature from room temperature to 1600 ° C. (hereinafter, simply referred to as "the coefficient of linear thermal expansion at 1600 ° C." unless otherwise specified).

The coefficient of linear thermal expansion in the process of raising the temperature from 1200 ° C to 1600 ° C and the coefficient of linear thermal expansion in the process of cooling to room temperature were continuously measured for the fire-resistant material fired at 1400 ° C. The difference value (%) between the coefficient of linear thermal expansion in the cooling process and the coefficient of linear thermal expansion in the process of raising the temperature was 0.05%. Therefore, it was judged that the evaluation method of the comparison target was excellent in peeling resistance, and even when it was actually used in a molten steel ladle, there was no peeling wear due to cracks caused by softening shrinkage, and it was excellent in peeling resistance (Table). 1: Sign "○").

FIG. 2 shows the linear heat of the alumina-magnesian castable refractory 2 judged to be inferior in peel resistance by the evaluation method of the comparison target at 1400 ° C, 1500 ° C, and 1600 ° C. Shows the expansion rate. Looking at the coefficient of linear thermal expansion at a temperature of 1400 ° C. or higher in FIG. 2, the coefficient of linear thermal expansion increases with increasing temperature.

The coefficient of linear thermal expansion in the heating process from 1200 ° C to 1600 ° C and the coefficient of linear thermal expansion in the cooling process to room temperature were continuously measured for the fire-resistant material fired at 1400 ° C. The difference value (%) between the coefficient of linear thermal expansion at 1200 ° C. and the coefficient of linear thermal expansion at 1200 ° C. in the heating process was 0.5%. Therefore, it is judged that the evaluation method of the comparison target is inferior in peel resistance. However, the difference value (%) between the value of the coefficient of linear thermal expansion at 1400 ° C and the value of the coefficient of linear thermal expansion at 1600 ° C is -0.15%, and this difference value is 0.2% or less. According to the method of the present invention, it is determined that the peel resistance is excellent. When it was actually used in a molten steel ladle, there was no peeling wear due to cracks caused by softening and shrinkage, and it was excellent in peeling resistance.

FIG. 3 shows the linear thermal expansion rates of the alumina-magnesia castable refractory 3 judged to be excellent in peeling resistance by the evaluation method of the comparison target at 1400 ° C, 1500 ° C, and 1600 ° C. The coefficient of linear thermal expansion at 1400 ° C., 1500 ° C., and 1600 ° C. in FIG. 3 was measured under the same conditions as the alumina-magnesia castable refractory in FIG. Looking at the coefficient of linear thermal expansion at a temperature of 1400 ° C or higher in FIG. 3, the coefficient of linear thermal expansion at 1500 ° C is higher than that at 1400 ° C, and the coefficient of linear thermal expansion at 1600 ° C is that at 1500 ° C. The coefficient of linear expansion of fire-resistant materials above 1400 ° C does not decrease with increasing temperature.

The coefficient of linear thermal expansion in the heating process from 1200 ° C to 1600 ° C and the coefficient of linear thermal expansion in the cooling process to room temperature were continuously measured for the fire-resistant material fired at 1400 ° C. The difference between the coefficient of linear thermal expansion at 1200 ° C. and the coefficient of linear thermal expansion at 1200 ° C. in the heating process was 0.01%. Therefore, it is judged that the evaluation method of the comparison target is excellent in peeling resistance. However, since the difference value (%) between the linear thermal expansion coefficient at 1400 ° C. and the linear thermal expansion coefficient at 1600 ° C. is more than 0.2%, it is determined that the peel resistance is inferior according to the method of the present invention. Will be done. When actually used in a molten steel ladle, peeling wear due to cracks occurred due to softening shrinkage, and the peeling resistance was inferior.

FIG. 4 shows the linear thermal expansion rates of the alumina-magnesia castable refractory 4 judged to be excellent in peeling resistance by the evaluation method of the comparison target at 1400 ° C, 1500 ° C, and 1600 ° C. The coefficient of linear thermal expansion at 1400 ° C., 1500 ° C., and 1600 ° C. in FIG. 4 was measured under the same conditions as the alumina-magnesia castable refractory in FIG. Looking at the coefficient of linear thermal expansion at a temperature of 1400 ° C or higher in FIG. 4, the coefficient of linear thermal expansion at 1500 ° C is equivalent to that at 1400 ° C, and the coefficient of linear thermal expansion at 1600 ° C is higher than that at 1500 ° C. The coefficient of linear expansion of fire-resistant materials above 1400 ° C does not decrease as the temperature rises.

The coefficient of linear thermal expansion in the heating process from 1200 ° C to 1600 ° C and the coefficient of linear thermal expansion in the cooling process to room temperature were continuously measured for the fire-resistant material fired at 1400 ° C. The difference value (%) between the coefficient of linear thermal expansion at 1200 ° C. and the coefficient of linear thermal expansion at 1200 ° C. in the heating process was 0.03%. Therefore, it is judged that the evaluation method of the comparison target is excellent in peeling resistance. However, since the difference value (%) between the value of the coefficient of linear thermal expansion at 1400 ° C. and the value of the coefficient of linear thermal expansion at 1600 ° C. is 0.21%, the peel resistance is improved according to the method of the present invention. It is judged to be inferior. When actually used in a molten steel ladle, peeling wear due to cracks occurred due to softening shrinkage, and the peeling resistance was inferior.

FIG. 5 shows the linear thermal expansion rates of the alumina-magnesia castable refractory 5 judged to be inferior in peeling resistance by the evaluation method of the comparison target at 1400 ° C, 1500 ° C, and 1600 ° C. The coefficient of linear thermal expansion at 1400 ° C., 1500 ° C., and 1600 ° C. in FIG. 5 was measured under the same conditions as the alumina-magnesia castable refractory in FIG. Looking at the coefficient of linear thermal expansion at a temperature of 1400 ° C or higher in FIG. 5, the coefficient of linear thermal expansion at 1500 ° C is higher than that at 1400 ° C, and the coefficient of linear thermal expansion at 1600 ° C is that at 1500 ° C. The coefficient of linear expansion of fire-resistant materials above 1400 ° C does not decrease with increasing temperature.

The coefficient of linear thermal expansion in the process of raising the temperature from 1200 ° C to 1600 ° C and the coefficient of linear thermal expansion in the process of cooling to room temperature were continuously measured for the fire-resistant material fired at 1400 ° C. The difference value (%) between the linear thermal expansion coefficient of 1200 ° C. and the linear thermal expansion coefficient of 1200 ° C. in the heating process was 0.2%. Therefore, it is judged that the evaluation method of the comparison target is inferior in peel resistance. However, the difference value (%) between the value of the coefficient of linear thermal expansion at 1400 ° C. and the value of the coefficient of linear thermal expansion at 1600 ° C. was 0.2%. This is determined to be excellent in peel resistance according to the method of the present invention. When it was actually used in a molten steel ladle, there was no peeling wear due to cracks caused by softening and shrinkage, and it was excellent in peeling resistance.

FIG. 6 shows the linear thermal expansion rates of the alumina-magnesia castable refractory 6 judged to be excellent in peeling resistance by the evaluation method of the comparison target at 1400 ° C, 1500 ° C, and 1600 ° C. The coefficient of linear thermal expansion at 1400 ° C., 1500 ° C., and 1600 ° C. in FIG. 6 was measured under the same conditions as the alumina-magnesia castable refractory in FIG. Looking at the coefficient of linear thermal expansion at a temperature of 1400 ° C or higher in FIG. 6, the coefficient of linear thermal expansion at 1500 ° C is lower than that at 1400 ° C, and the coefficient of linear thermal expansion at 1600 ° C is that at 1500 ° C. The coefficient of linear expansion of fire-resistant materials above 1400 ° C does not decrease with increasing temperature.

The coefficient of linear thermal expansion in the process of raising the temperature from 1200 ° C to 1600 ° C and the coefficient of linear thermal expansion in the process of cooling to room temperature were continuously measured for the fire-resistant material fired at 1400 ° C. The difference value (%) between the linear thermal expansion coefficient in the cooling process and the linear thermal expansion coefficient in the heating process was 0.03%. Therefore, it is judged that the evaluation method of the comparison target is excellent in peeling resistance.

As shown in FIG. 6, in the alumina-magnesian castable refractory 6 to be measured, the difference value (%) between the value of the coefficient of linear thermal expansion at 1400 ° C and the value of the coefficient of linear thermal expansion at 1600 ° C is-. It is 0.55% and 0.2% or less. However, this is out of the scope of the present invention because the coefficient of linear thermal expansion at 1500 ° C. is lower than the coefficient of linear thermal expansion at 1400 ° C. When it was actually used in a molten steel ladle, peeling wear due to cracks occurred due to softening shrinkage, and the peeling resistance was inferior.

From the above, if the coefficient of linear thermal expansion at a temperature of 1400 ° C. or higher does not decrease with increasing temperature in the alumina-magnesian castable refractory, the evaluation method of the comparative object determines the peeling resistance of the refractory. It became clear that there were cases where it could not be determined.
[Evaluation target of the evaluation method according to the present invention]
The evaluation target of the evaluation method according to the present invention can be produced, for example, by using a material having the following composition as a raw material. However, the evaluation target of the evaluation method according to the present invention is an alumina-magnesia castable refractory, and if the residual line change rate after firing at a temperature of 1400 ° C. or higher for 3 hours or longer is 0% or higher, the composition thereof. Is not limited to the following examples.

Alumina raw materials used in the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention include sintered alumina, fused alumina, heavy-fired alumina, calcined alumina, bauxite, and fused bauxite. Bauxite rocks can be used. As the particle size of alumina, a general one having a maximum particle size of less than 10 mm can be used. The blending ratio of alumina is preferably in the range of 78% to 93.5% by mass in the total amount of the alumina-magnesia castable refractory.

Sintered magnesia or fused magnesia can be used as the magnesia raw material used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention. As the particle size of magnesia, a general one having a maximum particle size of less than 1 mm can be used. The mixing ratio of magnesia is preferably in the range of 3% to 10% by mass in the total amount of alumina-magnesia castable refractory.

As the siliceous raw material used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention, silica such as silica flower or silica fume produced as a by-product during the production of silicon or a silicon alloy, or ki Aerosol-like silica produced by the phase method, amorphous hydrous silica synthesized by the wet method, and dried thereof can be used. The particle size of silica is preferably 1 μm or less. The blending ratio of silica is preferably in the range of 0.5% to 2% by mass in the total amount of the alumina-magnesia castable refractory.

As the alumina cement used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention _, alumina cement containing CaO / _Al2O3 can be used. Alumina cement containing alumina or spinel may be used in addition to CaO / Al ₂ O ₃ . The blending ratio of alumina cement is preferably in the range of 3% to 10% by mass in the total amount of the alumina-magnesia castable refractory.

As the dispersant used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention, it may be generally used. For example, tripolyphosphate sodium, hexametaphosphate sodium, acid hexamethaphosphate sodium, polyacrylic acid sodium, polycarboxylic acid sodium, sulfonic acid sodium, naphthalene sulfonic acid sodium, lignin sulfonic acid sodium, ultrapolyphosphate sodium, carbonated soda, borate soda, Sodium citrate can be used. The compounding ratio of the dispersant may be a general formulation. For example, it is desirable to add the dispersant in the range of 0.03% to 0.1% with respect to 100% by mass of the alumina-magnesia castable refractory.

As the explosion inhibitor used in the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention, it may be generally used. For example, vinylon fiber, aluminum lactate, metallic aluminum as a foaming agent, azodicarbonamide and the like can be mentioned. The compounding ratio of the anti-explosion agent may be a general prescription. For example, it is desirable to add the anti-explosion agent in the range of 0.01 to 0.03% with respect to 100% by mass of the alumina-magnesia castable refractory.

It is preferable that the test piece of the alumina-magnesia castable refractory used for carrying out the evaluation method according to the present invention is made as equivalent as possible to the conditions to be applied in the actual machine. However, as long as the produced test piece has a residual line change rate of 0% or more after firing at a temperature of 1400 ° C. or higher for 3 hours or longer, the method for producing the test piece is not particularly limited.

For example, it may be produced by adding 4 to 6% by mass of water to 100% by mass of a refractory raw material satisfying the above composition, kneading it with a mixer, and pouring it into a mold. In order to improve the filling property at the time of production, vibration may be applied to the mold into which the kneaded material is poured.

Therefore, it is preferable to prepare the test piece of the alumina-magnesia castable refractory used for carrying out the present invention as much as possible under the conditions to be applied in the actual machine. However, it is sufficient to apply the conventionally used method.

Examples of the present invention are shown below.

Table 2 shows the raw material composition and evaluation results of the alumina-magnesia castable refractory. Add sodium polyacrylic acid or sodium polycarboxylic acid as a dispersant to the castable refractory prepared according to the formulation shown in Table 2 in the range of 0.03% by mass to 0.1% by mass with respect to the mass of the refractory. , 0.01% by mass of vinylon fiber was added as an anti-explosion agent to the mass of the refractory. Further, tap water was added in the range of 4 to 6% by mass with respect to the mass of the refractory, kneaded for 3 minutes using a twin-screw mixer, and the kneaded material was poured into a metal frame having a predetermined size while applying vibration. .. Then, after allowing the kneaded product to stand for 24 hours while being poured into the mold at room temperature in the air, the kneaded product is taken out from the mold and dried at 110 ° C. for 24 hours to prepare an evaluation sample. bottom.

The linear change rate test method for the castable refractory of JIS-R2554 was used to measure the residual line change rate of the refractory fired at each temperature of 1400 ° C., 1500 ° C. and 1600 ° C. for 3 hours. The coefficient of linear thermal expansion of the refractory fired at each temperature of 1400 ° C., 1500 ° C. and 1600 ° C. for 3 hours was measured by using the test method of thermal expansion of the refractory material of JIS-R2207.

The difference value (%) of the coefficient of linear thermal expansion at 1200 ° C. in the linear thermal expansion curve of the refractory after firing at 1400 ° C. for 3 hours is from room temperature to 1600 ° C. after firing at 1400 ° C. for 3 hours and then cooling to room temperature. The coefficient of linear thermal expansion in the heating process and the cooling process from 1600 ° C. to room temperature was continuously measured, and calculated from the coefficient of linear thermal expansion at 1200 ° C. in the cooling process and the heating process. According to the evaluation method for determining the peeling resistance from the difference between the volume shrinkage amount in the heating process and the volume expansion amount in the cooling process (hereinafter, simply referred to as "evaluation method for comparison"), the cooling process and the rise. If the difference value of the coefficient of linear thermal expansion at 1200 ° C. in the warming process is within ± 0.1%, it is judged that the peeling resistance is good.

On the other hand, the wear rate when using the actual machine is as follows: Alumina-magnesia castable refractory consisting of the compounding ratios of each example in Table 2, polyacrylic acid sodium or polycarboxylic acid sodium as a dispersant with respect to the mass of the refractory. It was added in the range of 0.06% by mass to 0.1% by mass, and 0.01% by mass of vinylon fiber was added as an explosion inhibitor. Further, water was added in the range of 4 to 6% by mass with respect to the mass of the refractory, kneaded for 3 minutes using a twin-screw mixer, and the kneaded material was applied to the side wall of the molten steel ladle having a capacity of 300 tons. After using the molten steel ladle 70 times (ch), the thickness of the refractory was measured, and the value subtracted from the original thickness was divided by the number of times of use to calculate the average wear rate (mm / ch). At the same time, the state of peeling wear due to cracks during use was visually observed. The results are shown in Table 2.

In the castable refractories of Test Examples 1 to 4, the difference value of the coefficient of linear thermal expansion at 1200 ° C. in the linear thermal expansion curve of the refractory after firing at 1400 ° C. for 3 hours is more than 0.1%, which is the subject of the comparison. It is judged that the evaluation method is inferior in peel resistance. However, the value of the coefficient of linear thermal expansion at 1500 ° C. is equal to or higher than the value of the coefficient of linear thermal expansion at 1400 ° C., and the value of the coefficient of linear thermal expansion at 1400 ° C. is 1600 ° C. Since the value obtained by subtracting the value of the coefficient of linear thermal expansion in 1 is within ± 0.2%, it is determined by the evaluation method according to the present invention that the castable refractories of Test Examples 1 to 4 have excellent peeling resistance. bottom.

Even when the castable refractories of Test Examples 1 to 4 were used in an actual machine, peeling wear did not occur and the wear rate was relatively low. Therefore, the present invention has a linear thermal expansion coefficient of the refractory at 1400 ° C. or higher. However, it is possible to accurately evaluate the peeling resistance of refractories that do not decrease with increasing temperature.

The castable refractories of Test Examples 5 and 6 have a difference value of the coefficient of linear thermal expansion at 1200 ° C. in the linear thermal expansion curve of the refractory after firing at 1400 ° C. for 3 hours, which is 0.1% or less. It is judged that the evaluation method of is excellent in peeling resistance.

The castable refractories of Test Examples 5 and 6 show a value of the coefficient of linear thermal expansion at 1500 ° C. equal to or higher than the value of the coefficient of linear thermal expansion at 1400 ° C. However, since the difference between the value of the coefficient of linear thermal expansion at 1400 ° C. and the value of the coefficient of linear thermal expansion at 1600 ° C. is more than 0.2%, the evaluation method according to the present invention is different from Test Example 5. The castable refractory of 6 is determined to be inferior in peel resistance. In fact, since peeling wear occurs when used in an actual machine, the present invention can accurately evaluate the peeling resistance of a refractory whose linear thermal expansion coefficient at 1400 ° C or higher does not decrease with increasing temperature. I understand.

According to the present invention, it is possible to accurately evaluate the peeling resistance of the alumina-magnesia castable refractory using the alumina-magnesia castable refractory to be used before constructing the actual machine. Therefore, by using the evaluation method according to the present invention, it is possible to compare and examine the peeling resistance of various castable refractories, and the alumina-magnesia castable refractory and the castable refractory having extremely excellent durability can be obtained. The actual machine used can be manufactured.

Claims (2)

A method for evaluating the peeling resistance of an alumina-magnesia castable refractory having a residual line change rate of 0% or more after firing at a temperature of 1400 ° C. or higher for 3 hours or longer.
A step of measuring the linear thermal expansion coefficient (%) at 1400 ± 10 ° C. for the castable refractory after firing at 1400 ± 10 ° C. for 3 hours or more.
A step of measuring the linear thermal expansion coefficient (%) at 1500 ± 10 ° C. for the castable refractory after firing at 1500 ± 10 ° C. for 3 hours or more.
A step of measuring the linear thermal expansion coefficient (%) at 1600 ± 10 ° C. for the castable refractory after firing at 1600 ± 10 ° C. for 3 hours or more.
A step of determining whether or not the coefficient of linear thermal expansion (%) at 1500 ± 10 ° C. is equal to or higher than the coefficient of linear thermal expansion (%) at 1400 ± 10 ° C.
Peeling resistance of the alumina-magnesian castable refractory to be evaluated based on the value obtained by subtracting the coefficient of linear thermal expansion (%) at 1600 ± 10 ° C. from the coefficient of linear thermal expansion (%) at 1400 ± 10 ° C. A method for evaluating the peeling resistance of an alumina-magnesia castable refractory, which comprises a step of determining. Alumina to be evaluated when the coefficient of linear thermal expansion at 1500 ± 10 ° C. is equal to or greater than the coefficient of linear thermal expansion (%) at 1400 ± 10 ° C. and the subtracted value is 0.2% or less. The method for evaluating the peeling resistance of an alumina-magnesia castable refractory according to claim 1, wherein it is determined that the peeling resistance of the magnesia castable refractory is high.

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