JP2020059610A - Method for evaluating peeling resistance of alumina-magnesia quality castable refractory - Google Patents

Abstract

To provide a method for evaluating peeling resistance whether or not an alumina-magnesia quality castable refractory is peeled and worn.SOLUTION: A method for evaluating peeling resistance of an alumina-magnesia quality castable refractory in which the refractory has a residual linear change ratio after having been fired at 1,400°C or higher and 1,600°C or lower for 3 or more hours of 0% or more, includes: a step of heat-treating the castable refractory at a temperature T1 equal to or higher than a temperature at which a liquid phase of the refractory is generated for 3 or more hours; a step of measuring a coefficient of linear thermal expansion of the refractory while raising the refractory after heat treatment to a temperature T2 higher than the temperature T1 from a room temperature; a step of measuring a coefficient of linear thermal expansion of the refractory while cooling the refractory to the room temperature from the temperature T2; a step of calculating a differential value between the coefficient of linear thermal expansion in the temperature-raising step and the coefficient of linear thermal expansion in the cooling step at a temperature T3 equal to or lower than the T1; and a step of determining peeling resistance from the differential value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exfoliation resistance evaluation method for an alumina-magnesia castable refractory used as a lining furnace material for a molten metal processing container.

  Alumina-magnesia castable refractories used for molten steel ladle and the like have a problem that peeling wear occurs due to cracks generated during use. It is believed that the main cause of cracking of the alumina-magnesia castable refractory that occurs during use is the buckling caused by the volume expansion accompanying the spinel formation reaction between alumina and magnesia, which are the constituent materials of the refractory.

  In order to prevent buckling of the alumina-magnesia castable refractory during use, the following two methods have been studied. The first point is a method of imparting load softening property to the alumina-magnesia castable refractory in order to relax the stress generated by the volume expansion accompanying the spinel formation 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, a suitable load softening property is imparted at a high temperature of 1400 ° C. or higher at which the volume expansion due to the spinel formation reaction between alumina and magnesia, which are constituent raw materials of the alumina-magnesia castable refractory, becomes large Disclosed are alumina-magnesia castable refractories.
In Patent Document 3, by adopting the residual line change rate of the alumina-magnesia castable refractory after firing at 1500 ° C. for 3 hours in the atmosphere as a test method of volume expansion during use of the alumina-magnesia castable refractory, Alumina-magnesia castable refractories having a controlled volume expansion associated with the spinel formation reaction between alumina and magnesia in use are disclosed.

JP-A-5-185202 JP 2001-253781 A JP, 9-30859, A

  However, even if the alumina-magnesia castable refractories described in Patent Documents 1 to 3 are used, there has been a problem that peeling wear originating from a crack generated in the castable refractory during use is not resolved.

  The present inventor has examined the wear mechanism of alumina-magnesia castable refractory used in a ladle ladle, and found that cracks that occur in the refractory during use, which causes peeling wear, are alumina that is a constituent material of the refractory. It does not occur due to the buckling caused by the volume expansion associated with the spinel formation reaction between strontium and magnesia, and the liquid phase generated by melting the constituent material of the refractory during use, and the formation of solid from the liquid phase. It was found that (precipitation) was involved. However, in the prior art, there has been no method for evaluating the peel resistance of alumina-magnesia castable refractories, whether or not peel wear occurs due to cracks caused by the liquid phase generated during use.

  It is an object of the present invention to provide a method for evaluating the peel resistance of an alumina-magnesia castable refractory, whether or not peel wear occurs due to cracks caused by the liquid phase generated during use.

As a result of diligent studies by the present inventors, in the alumina-magnesia castable refractory in use, a liquid formed in the refractory structure in a high temperature state when in contact with molten steel and a relatively low temperature state after discharging the molten steel. It was found that the change in the amount of the phase / solid phase correlates with the peeling resistance, and the peeling resistance can be grasped from the change in the linear thermal expansion coefficient (also referred to as “linear expansion coefficient”), and the present invention has been completed. It was
That is, the gist of the present invention is as follows.
(1) A method for evaluating peeling resistance of an alumina-magnesia castable refractory, wherein the castable refractory has a residual line change rate of 0% or more after firing at 1400 ° C or more and 1600 ° C or less for 3 hours or more. A step of heat treating the castable refractory for 3 hours or more at a temperature T1 higher than a temperature at which the liquid phase of the castable refractory is generated, and a temperature T2 higher than the temperature T1 from room temperature to the castable refractory after the heat treatment. Measuring the coefficient of linear thermal expansion of the castable refractory while raising the temperature, measuring the coefficient of linear thermal expansion of the castable refractory while cooling from the temperature T2 to room temperature, and the temperature of T1 or lower. A step of calculating a difference value between the linear thermal expansion coefficient in the temperature raising process and a linear thermal expansion coefficient in the cooling process at T3; and a step of judging peeling resistance from the difference value. Evaluation method of peeling resistance of the castable refractory, characterized in that it comprises a.
(2) The method for evaluating the peeling resistance of castable refractories according to (1), wherein the predetermined temperature T1 is a constant temperature selected from 1400 to 1500 ° C.
(3) The predetermined temperature T1 is 1400 ° C., the method for evaluating the peeling resistance of castable refractories according to (1).
(4) The peeling resistance evaluation method of the castable refractory according to any one of (1) to (3), wherein the predetermined temperature T2 is a constant temperature selected from more than 1400 ° C and 1600 ° C or less.
(5) The method for evaluating the peeling resistance of castable refractories according to any one of (1) to (3), wherein the predetermined temperature T2 is 1500 ° C.
(6) In the step of judging the exfoliation resistance, the maximum value of the difference value is determined between the temperature T1 at which the deposition of the liquid phase of the castable refractory after the heat treatment is completed and the temperature T1. The peel resistance is determined by comparing the maximum value with a predetermined target value and determining whether the maximum value is less than or equal to the target value (1) to (5). The evaluation method of the peeling resistance of the castable refractory according to any one of (1) to (4).
(7) The method for evaluating the peeling resistance of castable refractories according to any one of (1) to (5), wherein the predetermined temperature T3 is a constant temperature selected from 1200 to 1400 ° C.
(8) The method for evaluating peeling resistance of castable refractories according to any one of (1) to (5), wherein the predetermined temperature T3 is 1200 ° C.
(9) The target value is set to 0.1% in advance, and it is determined that the castable refractory having the difference value of 0.1% or less has high peel resistance. Evaluation method for peeling resistance of castable refractories.

  According to the present invention, it is possible to accurately evaluate the peeling resistance of an alumina-magnesia castable refractory, whether or not peeling wear occurs due to cracks caused by a liquid phase generated during use.

It is a conceptual diagram of a linear thermal expansion coefficient curve of the temperature rising process from room temperature to 1600 ° C and the cooling process from 1600 ° C to room temperature of the alumina-magnesia castable refractory after firing at 1400 ° C. It is a figure which shows the result of having measured the linear thermal expansion coefficient of the temperature rising process from room temperature to 1500 degreeC of test example 1, and the cooling process from 1500 degreeC to room temperature.

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

  The molten steel ladle is a molten metal processing container that conveys the molten steel discharged from the converter to a continuous casting machine. Therefore, the alumina-magnesia castable refractory used in the ladle ladle is heated during the period during which the molten steel stays, and there is no molten steel in the ladle after the completion of casting until immediately before the start of receiving steel in the converter. The period will be cooled. That is, the alumina-magnesia castable refractory is used in an environment where heating and cooling are repeated.

  In the alumina-magnesia castable refractory used under such an environment, peeling damage caused by cracks occurs after the temperature distribution inside the refractory reaches a steady state. According to the steady-state heat transfer calculation inside the refractory during use, it was found that the position where the crack had occurred was the position where it reached about 1400 ° C.

By the way, the alumina-magnesia castable refractory is composed of a refractory raw material such as alumina, magnesia, silica, and alumina cement having CaO.Al ₂ O ₃ as a main crystal phase. Then, in the region where the temperature inside the refractory is 1400 ° C. or higher, it is considered that these refractory raw materials cause the reaction of the following formula (1).

That is, the refractory raw material reacts during use, and at 1400 ° C. or higher, in addition to spinel produced from the reaction of magnesia and part of alumina, CaO · 6Al produced from the reaction of alumina cement and part of alumina. _A liquid phase forms from ₂ O ₃ and the reaction of silica with other oxides. The amounts of spinel, CaO.6Al ₂ O ₃ , and liquid phase produced in the reaction of the formula (1) depend on the content of the refractory raw material contained in the alumina-magnesia castable refractory. Then, as the temperature rises, the amount of liquid phase produced increases.

  Next, the behavior of the structure of the alumina-magnesia castable refractory in the molten steel ladle in use will be inferred. During the period when the molten steel stays after the first steel is received, the liquid phase is generated based on the reaction of the equation (1) in the region of 1400 ° C or higher inside the refractory, and the refractory contacting with the molten steel at about 1600 ° C In terms of product operation, the amount of liquid phase produced is maximum. When the liquid phase is generated, the refractory material shrinks due to the capillary force of the liquid phase. That is, during use, the refractory structure shrinks from the region of 1400 ° C. inside the refractory to the refractory working surface in contact with the molten steel due to the liquid phase generated. Then, the greater the amount of liquid phase generated inside the refractory during use, the greater the amount of shrinkage of the refractory structure.

Next, in the period in which molten steel is not present in the ladle after the casting is completed, that is, in the period in which the refractory is being cooled, the reaction of the following formula (2) proceeds.

That is, in the process of cooling, solid phases such as CaO.6Al ₂ O ₃ and CaO-MgO-SiO ₂ -Al ₂ O ₃ compounds are precipitated from the liquid phase.
The reaction of the formula (1) occurs irreversibly when the temperature reaches 1400 ° C or higher. On the other hand, the reaction of the formula (2) reversibly occurs in a tissue that has once been subjected to a heat history of 1400 ° C. or higher in response to a temperature change. That is, an irreversible reaction of the equation (1) and a reversible reaction of the equation (2) occur in a region where peeling wear occurs during use of the molten steel ladle.

  As a result of detailed investigation of the precipitation phenomenon of the solid phase from the liquid phase during the cooling process using the phase diagram, the present inventor estimated that different components are precipitated stepwise as follows.

First, the CaO · 6Al ₂ O ₃ component from the liquid phase is deposited on the surface of the CaO · 6Al ₂ O ₃ particles that are still unmelted, and the particle size of the CaO · 6Al ₂ O ₃ particles increases, Causes volume expansion (first precipitation process). _{Subsequently, CaO-MgO-SiO 2 -Al} 2 O 3 based compound from the liquid phase remaining, by precipitation between the particles present as already solid phase, the precipitation of the solid phase from the liquid phase is completed (the Second precipitation process). When CaO—MgO—SiO ₂ —Al ₂ O ₃ based compound is precipitated from the liquid phase, the volume difference is reduced due to the difference in density between the two. In the first precipitation process, the refractory material expands, and the expansion coefficient is highest at around 1200 ° C. where all CaO · 6Al ₂ O ₃ components are precipitated.

  Next, the thermal expansion and contraction behavior of the refractory which is heated up to about 1600 ° C. and repeatedly heated and cooled during use is estimated.

  Fig. 1 shows a continuous line heat of the temperature rising process from room temperature to 1600 ° C and the cooling process from 1600 ° C to room temperature of the alumina-magnesia castable refractory which was heat-treated at 1400 ° C in the atmosphere for 3 hours. The conceptual diagram of an expansion coefficient curve is shown.

The alumina-magnesia castable refractory that has been heat-treated at 1400 ° C. for 3 hours undergoes the reactions of the above formulas (1) and (2), so that at room temperature, alumina, spinel, CaO.6Al ₂ O ₃ and a solid phase of CaO—MgO—SiO ₂ —Al ₂ O ₃ based compound exists.

In the temperature rising process from room temperature to 1600 ° C., expansion of these solids occurs only up to about 1200 ° C. (process O → A). Further, in the process of raising the temperature from 1200 ° C. to 1600 ° C. (process A → B), CaO · 6Al ₂ O ₃ and CaO—MgO—SiO ₂ —Al ₂ O ₃ based compound are melted and a liquid phase starts to be generated. Then, as the temperature rises, the production amount of the liquid phase increases, and the refractory material contracts due to the production of the liquid phase as described above. As in the case of receiving molten steel, the working surface of the refractory, which has a temperature of 1600 ° C., contracts most due to the decrease of the solid phase and the generation of the liquid phase.

Subsequently, when the refractory is cooled to about 1200 ° C. (process B → C → D), as when molten steel is discharged from the ladle, CaO.6Al ₂ O ₃ is precipitated from the liquid phase. comprising the steps of precipitation, by a second deposition process to deposit the _{CaO-MgO-SiO 2 -Al 2} O 3 compound, refractory tissue operating near the surface to volume expansion. If the ladle receives molten steel again during the process B → C → D, the precipitated solid phase returns to the liquid phase and contracts (process D → C → B).

  The above is the behavior of the alumina-magnesia castable refractory that has been heat-treated at 1400 ° C. for 3 hours, and the thermal expansion / shrinkage behavior of the working surface that has been subjected to a thermal history of 1400 ° C. or higher during use.

  On the other hand, at the site where the temperature does not reach 1400 ° C or higher during use, the reaction of the above formula (1) does not occur, and even when the temperature reaches 1200 ° C in FIG. The expansion of the raw material continues (process A → B ′). That is, the part where the temperature does not reach 1400 ° C. or higher shows the linear thermal expansion coefficient in the process A → B ′, whereas the part where the temperature reaches 1400 ° C. or higher shows the linear thermal expansion coefficient in the process B → C → D. . Further, since there is a considerable amount of stress relaxation due to the liquid phase at the site where the temperature is 1400 ° C. or higher during use, peeling wear occurs at the site at 1200 ° C. to 1400 ° C. as shown in FIG.

  In this way, the alumina-magnesia castable refractory has a refractory structure in which the refractory near the working surface undergoes a process of composition change and volume decrease due to melting during use, and a volume increase due to precipitation from the liquid phase to the solid phase. The thermal expansion with the inside becomes discontinuous, and strain is accumulated in the vicinity of the position where the temperature reaches about 1400 ° C., which is the boundary, and cracks that cause peeling wear occur.

(Peeling resistance evaluation target)
The alumina-magnesia castable refractory to which the evaluation method according to the present invention is applied has a residual linear change rate of 0% or more after firing at 1400 ° C to 1600 ° C for 3 hours or more. As a test method for the residual line change rate, it is preferable to use JIS-R2554 "Castable refractory line change rate test method". Although the firing temperature and the firing time are not specified in the method, in the present invention, 1600 ° C. and 3 hours or more are recommended.

  Generally, it is preferred that the alumina-magnesia castable refractories have a suitable residual expansion after undergoing thermal history. A refractory that contracts residually, that is, a refractory having a residual linear change rate of less than 0% has a smaller dimension after being heated and cooled than the original dimension before heating. Refractories with a residual line change rate of less than 0% near 1400 ° C. are clearly cracked during use, and often have poor peel resistance in the first place, so they cannot be used in the production of actual machines. . Therefore, the present invention is applied to an alumina-magnesia castable refractory having a positive residual expansion, in other words, a residual contraction.

  Since the alumina-magnesia castable refractory can be heated to a maximum of 1600 ° C on the operating surface by contacting with molten steel during use, it is fired at a temperature of up to 1600 ° C. Further, it is sufficient to calcine for 3 hours or more in consideration of the time of receiving molten steel at about 1600 ° C. Therefore, the present invention is applied to an alumina-magnesia castable refractory having a residual linear change rate of 0% or more when heated at a temperature of 1400 ° C. or more and 1600 ° C. or less for 3 hours or more, that is, no residual shrinkage.

(Castable refractory heat treatment process)
In the present invention, first, with respect to the alumina-magnesia castable refractory to be evaluated, at a temperature equal to or higher than a temperature at which a liquid phase of the castable refractory is generated (this temperature is defined as "predetermined temperature T1"). Heat treatment for 3 hours or more.

  The heat treatment for 3 hours or more at the predetermined temperature T1 is performed in advance in order to cause the reaction of the formula (1). The reaction of formula (1) above occurs irreversibly above about 1400 ° C. Even if the evaluation method according to the present invention is applied to a refractory that is not subjected to the heat treatment, an appropriate evaluation of peel resistance cannot be performed. This is because the refractory part heated to 1400 ° C. or higher in the actual use environment repeats expansion and contraction due to the reaction of the formula (2) after the reaction of the formula (1) occurs initially. This is because the thermal expansion behavior of the refractory material in which the reaction of the formula (1) is completed affects the peel resistance.

  The predetermined temperature T1 may be a temperature at which the reaction of the formula (1) proceeds, but a constant temperature selected from 1400 to 1500 ° C. is preferable. More preferably, the temperature is as close as possible to 1400 ° C. Further, the heat treatment time is set to 3 hours or more in order to reach the equilibrium in the reaction of the formula (1). The thermal expansion behavior of the refractory in use can be reproduced by using a test piece that has been heat-treated at 1400 ° C. for 3 hours or more.

Depending on the material of the alumina-magnesia castable refractory material, as the heat treatment temperature exceeds 1400 ° C., the amount of liquid phase produced in the reaction of the above equation (1) becomes excessive, and the inter-material particles produced by liquid phase sintering are Refractory structure densification may occur with the formation of strong bonds. In such a refractory in which a strong bond has been generated between the raw material particles, when measuring the linear thermal expansion coefficient, even if the liquid phase is generated in the temperature rising process, the maximum temperature reached from the maximum temperature rise to room temperature The volume expansion that occurs during precipitation of CaO · 6Al ₂ O ₃ from the liquid phase in the cooling process up to is suppressed. As a result, in the cooling process, the value of the coefficient of linear thermal expansion measured in the temperature region equal to or lower than the predetermined temperature T1 may not properly reflect the state change of the refractory structure in the actual use environment. Therefore, in the present invention, although the predetermined temperature T1 can be selected depending on the refractory, 1400 ° C. is most preferable, and 1400 ° C. is sufficiently applicable.

(Step of measuring linear thermal expansion coefficient in temperature rising process and cooling process between room temperature and predetermined temperature T2)
The linear thermal expansion coefficient of the alumina-magnesia castable refractory that has undergone the heat treatment step is measured while increasing the temperature from room temperature to a predetermined temperature T2 (T2> T1). The predetermined temperature T2 is set higher than the temperature T1 in order to allow the reverse reaction of the equation (2) to proceed. After the temperature is raised, the coefficient of linear thermal expansion is measured while cooling from the predetermined temperature T2 to room temperature.

  The predetermined temperature T2 is the highest reaching temperature of the linear thermal expansion coefficient measurement temperature, is a temperature at which the equilibrium state reached in the heat treatment step can be achieved, and may be within the range of the molten steel temperature at the maximum. The predetermined temperature T2 is preferably a constant temperature selected from more than 1400 ° C and 1600 ° C or less. More preferably, it is 1500 ° C.

  When the predetermined temperature T2 is set to 1500 ° C., it is possible to use a test device that can perform a thermal expansion test of refractories according to JIS-R2207-1 that is generally popular. Further, when the temperature is raised to 1500 ° C., it is also a region where a liquid phase is generated and stress relaxation occurs. Therefore, the peeling resistance can be sufficiently evaluated without raising the temperature to the molten steel temperature of about 1600 ° C.

  The test method of the linear thermal expansion coefficient used in the present invention is not particularly limited as long as the linear thermal expansion coefficient from room temperature to the predetermined temperature T2 can be measured. As will be described later, when obtaining the maximum value of the difference between the linear thermal expansion coefficient during the temperature rising process and the linear thermal expansion coefficient during the cooling process, the linear thermal expansion coefficient from room temperature to the predetermined temperature T1 It is preferable that the measurement be possible. It is preferable to use a test piece and test conditions based on JIS-R2207 "Test method for thermal expansion of refractory material" because it is easy to compare with conventional evaluation results and physical property values. More preferably, JIS-R2207-1 "non-contact method", which has little influence on the expansion and contraction of the liquid phase, is used.

(Calculation of difference value between linear thermal expansion coefficient during heating process and linear thermal expansion coefficient during cooling process)
In the present invention, the difference between the linear thermal expansion coefficient during the temperature increasing process and the linear thermal expansion coefficient during the cooling process at a temperature equal to or lower than the predetermined temperature T1 (this temperature is defined as “predetermined temperature T3”). The step of calculating a value is included. As mentioned above, the peeling is caused by the strain caused by the discontinuity of the coefficient of linear thermal expansion between the refractory operating surface side and the inside, so that the region where the difference in the coefficient of linear thermal expansion between the heating process and the cooling process occurs. The temperature may be evaluated at a temperature at which the first precipitation process is completed, for example, 1200 ° C. or higher.

  When the refractory to be evaluated by the evaluation method according to the present invention has a temperature of 1200 ° C. or higher during the temperature rising process of the linear thermal expansion coefficient measurement step, a liquid phase starts to be generated, and the linear thermal expansion coefficient decreases, Although it becomes the minimum at the temperature T2, the difference in thermal expansion during the formation of the liquid phase causes less strain due to stress relaxation. In the subsequent cooling process, expansion occurs due to crystal precipitation, and the maximum linear thermal expansion coefficient is reached at 1200 ° C.

  On the other hand, as described above, the temperature is lower than 1200 ° C in the temperature range below the temperature at which the irreversible reaction of the formula (1) occurs, for example, in the region where the refractory material in actual use receives a thermal history of less than 1400 ° C. Also, a liquid phase is not generated while it is not heated to 1400 ° C. or higher, and its thermal expansion behavior shows expansion as a solid phase up to 1400 ° C. Therefore, the strain occurs due to the difference in the coefficient of linear thermal expansion up to about 1400 ° C. Therefore, the predetermined temperature T3 may be set to a temperature range including a temperature at which the first precipitation process is completed to a temperature at which the irreversible reaction of the formula (1) occurs. Specifically, the predetermined temperature T3 is a temperature range from the temperature at which the deposition of the liquid phase of the castable refractory material after the heat treatment at the predetermined temperature T1 is completed to the predetermined temperature T1, or It is preferably a constant temperature selected from 1200 to 1400 ° C.

  Furthermore, the difference in the coefficient of linear thermal expansion between the part that has received a thermal history of 1400 ° C or higher near the operating surface and the part that has received only a thermal history of 1400 ° C or lower in the refractory is between 1200 and 1400 ° C. It is considered that the maximum is at 1200 ° C. Since it is considered that the larger the difference value is, the larger the strain is and the influence on the peeling is. Therefore, in the present invention, it is recommended to judge the peeling resistance by the difference value of the linear thermal expansion coefficient at the predetermined temperature T3 of 1200 ° C. As the difference value, a value that depends on the material of the refractory material, the firing temperature in advance, and the use environment and has the highest correlation with the peelability may be used.

(Peeling resistance judgment process)
The present invention includes a step of judging peel resistance from the difference value. This step determines the maximum absolute value of the difference value, compares the maximum value with a target value, and determines peel resistance by determining whether the maximum value is less than or equal to a target value. Is done by doing. The target value can be appropriately set in advance. For example, when the predetermined temperature T3 is 1200 ° C. and the difference value is 0.1% or less, it may be determined that the peeling resistance is high. .

  As a result of intensive investigations by the inventors, at 1200 ° C., almost no liquid phase was formed during the temperature rising process and the cooling process, and the difference in the linear thermal expansion coefficient was the maximum within the operating temperature range (up to 1600 ° C.). Therefore, a good correlation is obtained with the presence or absence of peeling wear of the alumina-magnesia castable refractory, and especially when used in a ladle, the peeling resistance is remarkable when the difference value is 0.1% or less. It was found that it would be extremely high.

(Composition of alumina-magnesia castable refractory raw material)
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 object of the evaluation method according to the present invention is an alumina-magnesia castable refractory, and if the residual linear change rate after firing for 3 hours or more at a temperature of 1400 ° C. or more and 1600 ° C. or less is 0% or more. , Its composition is not limited to the following examples.

  Alumina used in the evaluation target of the evaluation method according to the present invention-alumina used in the magnesia castable refractory, sintered alumina, fused alumina, heavy burned alumina, calcined alumina, bauxite, fused bauxite, clay Shale etc. can be used. As the particle size of alumina, a general particle 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% in mass% in the total amount of the alumina-magnesia castable refractory.

  Sintered magnesia or electro-melting magnesia can be used as the magnesia used in 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 refractories.

  As the silica used in the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention, silica such as silica flour or silica fume produced as a by-product during the production of silicon and a silicon alloy, or a vapor phase method It is possible to use the aerosol-shaped silica produced in the above and the dried amorphous amorphous hydrous silica synthesized by the wet method. 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% in mass% in the total amount of alumina-magnesia castable refractory.

As the alumina cement used for the alumina-magnesia castable refractory targeted for evaluation by the evaluation method according to the present invention, an alumina cement containing CaO.Al ₂ O ₃ can be used. Alumina cement containing alumina or spinel may be used in addition to CaO.Al ₂ O ₃ . The mixing ratio of the 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, which is the object of evaluation by the evaluation method according to the present invention, those generally used may be used. For example, sodium tripolyphosphate, sodium hexametaphosphate, acidic sodium hexametaphosphate, sodium polyacrylate, sodium sulfonate, sodium naphthalenesulfonate, sodium lignin sulfonate, sodium ultrapolyphosphate, sodium carbonate, sodium borate, sodium citrate, etc. Can be used. The compounding ratio of the dispersant may be a general formulation. For example, the range of 0.03% to 0.1% is preferably applied to 100% by mass of the alumina-magnesia castable refractory.

  The explosion-proof agent used in the alumina-magnesia castable refractory, which is the object of evaluation by the evaluation method according to the present invention, may be one generally used. Examples thereof include vinylon fiber, aluminum lactate, aluminum metal as a foaming agent, and azodicarbonamide. The compounding ratio of the explosion proof agent may be a general formulation. For example, the range of 0.01 to 0.03% by external coating is preferable with respect to 100% by mass of the alumina-magnesia castable refractory.

(Preparation of test pieces to be evaluated)
It is preferable that the test pieces of the alumina-magnesia castable refractory used for carrying out the evaluation method according to the present invention are manufactured under the same conditions as the actual conditions. However, if the produced test piece has a residual linear change rate of 0% or more after firing at 1400 ° C. or more and 1600 ° C. or less for 3 hours or more, the method for producing the test piece is not particularly limited.

  For example, 4 to 8% by mass of water may be added to 100% by mass of a refractory raw material satisfying the above composition, and the mixture may be kneaded with a mixer and poured into a mold. At the time of production, in order to improve the filling property, vibration may be applied to the mold in which the kneaded product is poured.

  The test examples of the present invention and their reference examples are shown below.

  Table 1 shows the raw material composition and evaluation results of the alumina-magnesia castable refractory material. To the castable refractory made with the composition of Table 1, sodium polyacrylate as a dispersant was added to the amount of the refractory substance in the range of 0.06% by mass to 0.1% by mass, and water was further added to the amount of the refractory substance. It was added in the range of 5 to 6.5% by mass on the outside and kneaded for 3 minutes using a biaxial mixer, and the kneaded product was poured into a metal frame having a predetermined size while vibrating. Then, after being cured at room temperature for 24 hours, it was dried at 110 ° C. for 24 hours to prepare an evaluation sample.

  As a reference example of conventional peeling resistance evaluation, the residual line change rate after firing at 1500 ° C. for 3 hours (h) was measured. The residual line change rate was measured by the JIS-R2554 castable refractory line change rate test method.

  The linear thermal expansion coefficient curve of the alumina-magnesia castable refractory in the present invention was measured according to the thermal expansion test method of the refractory of JIS-R2207-1. The test piece was previously heat-treated at a predetermined temperature T1 of 1400 ° C. for 3 hours. The linear thermal expansion coefficient of the test piece during the temperature rising process from room temperature to a predetermined temperature T2 up to 1500 ° C. and the cooling process from 1500 ° C. to room temperature is continuously measured to determine the predetermined temperature T3 during the cooling process and the temperature rising process. Read the coefficient of linear thermal expansion at 1200 ° C.

  On the other hand, the wear rate at the time of using the actual equipment is 0.06 mass% to 0% by weight of alumina-magnesia castable refractory having the compounding ratio of each example in Table 1 with sodium polyacrylate as a dispersant to the amount of refractory material. 0.1% by mass, water is added to the amount of the refractory substance in an amount of 5 to 6.5% by mass, and the mixture is kneaded for 3 minutes by using a biaxial mixer to prepare a kneaded product having a volume of 300 t. The average wear rate is calculated by dividing the value obtained by subtracting the original thickness from the thickness of the refractory after applying it to the side wall of the molten steel ladle and using the molten steel ladle 70 times (ch) It was calculated as (mm / ch). At the same time, the state of peeling wear due to cracks during use was visually observed.

  FIG. 2 shows the results obtained by continuously measuring the linear thermal expansion coefficient in the temperature rising process from room temperature to a predetermined temperature T1500 ° C. and the cooling process from 1500 ° C. to room temperature in Test Example 1. It can be seen that the difference in the coefficient of linear thermal expansion when the predetermined temperature T3 is 1200 ° C. in the cooling process and the temperature raising process is 0.1% or less.

  Since the castable refractories of Test Examples 1 to 3 have a relatively small rate of change in residual line after firing at 1500 ° C. for 3 hours, it was expected from conventional experience that there is not much concern about peeling. Since the residual linear change rate after firing at 1600 ° C for 3 hours became a positive value, the test piece that had been heat-treated at 1400 ° C in the atmosphere for 3 hours had a cooling process from 1500 ° C to room temperature, and from room temperature to 1500 ° C. The coefficient of linear thermal expansion in the temperature rising process was measured. The difference in linear thermal expansion coefficient at 1200 ° C. in both processes was 0.1% or less, and it was judged that the peeling resistance was high. As a result of using the actual machine, peeling wear did not occur when the actual machine was used, and the rate of wear was relatively small. Therefore, the peeling resistance of the refractory can be accurately evaluated.

  In Test Example 4, the residual line change rate after firing at 1500 ° C. for 3 hours was relatively larger than that in Test Examples 1 to 3, and there was a concern of peeling wear from conventional experience. However, the residual line change rate after firing at 1600 ° C. for 3 hours was a positive value. When the linear thermal expansion coefficient of the present invention was subsequently measured, the difference in linear thermal expansion coefficient at 1200 ° C. was 0.1% or less, and it was judged that the peel resistance was high. When used in an actual machine, peeling wear was not observed, and the wear rate was almost the same as in Test Examples 1 to 3, so the peeling resistance of the refractory could be accurately evaluated.

  In Test Examples 5 and 6, since the value of the residual line change rate after firing at 1500 ° C. for 3 hours was relatively low, it was expected from conventional experience that there was not much concern about peeling. Then, the value of the residual line change rate after firing at 1600 ° C. for 3 hours also showed a positive value although it was small. However, in the linear thermal expansion coefficient curve of the test piece heat-treated at 1400 ° C. in the atmosphere for 3 hours, the linear thermal expansion coefficient at 1200 ° C. in the cooling process from 1500 ° C. to room temperature and the temperature increase from room temperature to 1500 ° C. The difference in the coefficient of linear thermal expansion at 1200 ° C in the process was more than 0.1%, and it was judged that the peel resistance was poor. In the actual machine test, peeling wear occurred and the wear rate increased. Therefore, it was possible to accurately evaluate the peeling resistance of the refractory material.

  Reference Example 1 is a refractory material having a low residual expansion rate after firing at 1500 ° C. for 3 hours and a low rate of change in residual line, and although there is little fear of peeling from conventional experience. Therefore, when the residual linear change rate after firing at 1600 ° C. for 3 hours was measured, a negative value was obtained, and it was expected that the residual expandability was inferior. Generally, such refractories are not used in actual equipment. For reference, in a test piece corresponding to the present invention, which was heat-treated at 1400 ° C. in the atmosphere for 3 hours, the coefficient of linear thermal expansion at 1200 ° C. in the cooling process from 1500 ° C. to room temperature and the increase from room temperature to 1500 ° C. When the coefficient of linear thermal expansion at 1200 ° C. in the warming process was measured, the difference was 0.1% or less. However, when an actual machine test was performed, peeling wear was observed and the wear rate was high. As described above, the castable refractory having a negative linear change rate after firing at 1600 ° C. for 3 hours, that is, the castable refractory having residual shrinkage, melts even when the difference in linear thermal expansion coefficient is small. There is a possibility that it cannot be suitably used as a furnace material for a lining of a metal processing container.

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

Claims (9)

Alumina-A method of evaluating the flammability of magnesia castable refractory,
The castable refractory has a residual linear change rate of 0% or more after firing at 1400 ° C. or more and 1600 ° C. or less for 3 hours or more,
Heat treating the castable refractory for 3 hours or more at a temperature T1 which is equal to or higher than a temperature at which a liquid phase of the castable refractory is generated;
Measuring the linear thermal expansion coefficient of the castable refractory while increasing the temperature of the castable refractory after the heat treatment from room temperature to a temperature T2 higher than the temperature T1, and cooling the temperature from the temperature T2 to the room temperature. A step of measuring the linear thermal expansion coefficient of the castable refractory,
Calculating a difference value between the linear thermal expansion coefficient in the temperature increasing process and the linear thermal expansion coefficient in the cooling process at a temperature T3 equal to or lower than T1;
A step of judging peel resistance from the difference value,
A method for evaluating the peeling resistance of a castable refractory material, which comprises:
The peeling resistance evaluation method according to claim 1, wherein the temperature T1 is a constant temperature selected from 1400 to 1500 ° C.
The method for evaluating peeling resistance of a castable refractory according to claim 1, wherein the temperature T1 is 1400 ° C.
The method for evaluating the peeling resistance of castable refractories according to any one of claims 1 to 3, wherein the temperature T2 is a constant temperature selected from more than 1,400 ° C and 1,600 ° C or less.
The method for evaluating the peeling resistance of castable refractories according to claim 1, wherein the temperature T2 is 1500 ° C.
The step of determining the peeling resistance determines the maximum value of the difference value between the temperature T1 and the temperature at which the deposition of the liquid phase of the castable refractory after the heat treatment is completed, and determines the maximum value. The peeling resistance is determined by comparing a value with a predetermined target value and determining whether or not the maximum value is equal to or less than the target value. The method for evaluating the peeling resistance of castable refractories according to the item.
The peeling resistance evaluation method according to any one of claims 1 to 5, wherein the temperature T3 is a constant temperature selected from 1200 to 1400 ° C.
The method for evaluating peeling resistance of castable refractories according to any one of claims 1 to 5, wherein the temperature T3 is 1200 ° C.
  The castable refractory according to claim 8, wherein the target value is set to 0.1% in advance, and the castable refractory having the difference value of 0.1% or less is determined to have high peeling resistance. Evaluation method of peel resistance.

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