JP7135691B2 - Evaluation Method of Delamination Resistance of Alumina-Magnesia Castable Refractories - Google Patents

Description

The present invention relates to a test method for spallation resistance of alumina-magnesia castable refractories used for the lining of molten metal processing vessels.

Raw material powders for alumina-magnesia castable refractories containing components such as alumina, magnesia, etc. and organic substances are commercially available. Water was added to this raw material powder and kneaded, and the kneaded product was poured into a mold installed in a molten metal processing vessel such as a molten steel ladle (hereinafter simply referred to as "molten steel ladle") to form a lining wall. It is then dried and used.

Alumina-magnesia castable refractories placed in a molten steel ladle have the problem of spalling wear due to cracks that occur during use. The main cause of cracks in alumina-magnesia castable refractories during use has been thought to be buckling caused by volume expansion associated with the spinel formation reaction between alumina and magnesia, which are the constituent raw materials of the refractories.

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

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

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

However, the above-mentioned dried compact containing refractory as the main component (hereinafter, “dried compact containing refractory as the main component” is simply referred to as “refractory material”) is lined in a molten steel ladle. Then, they are fixed to each other. Therefore, even if the alumina-magnesia castable refractory described in Patent Documents 1, 2, and 3 is used, there is a problem that peeling wear originating from cracks that occur in the castable refractory during use cannot be resolved.

The present inventor investigated the wear mechanism of alumina-magnesia castable refractories used for the lining of molten steel ladles. As a result, the cracks that occur in the castable refractory constructed in the molten steel ladle during use of the molten steel ladle are caused by the volume expansion accompanying the spinel formation reaction between alumina and magnesia, which are the raw materials of the refractory. It has been found that this is not caused by bending, but by shrinkage caused by the liquid phase that forms in the refractory during use of the molten steel ladle.

However, in the prior art, under the service environment where alumina-magnesia castable refractories are lined in a molten steel ladle so as to be fixed to each other, the refractories are damaged by cracks caused by softening shrinkage induced by the liquid phase. There has been no method for evaluating peel resistance to determine whether peel wear occurs on an object.

The present invention investigates 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. An object of the present invention is to provide a method for evaluating peeling resistance in advance.

As a result of examination by the present inventor, during use of a molten steel ladle lined with a construction body made of alumina-magnesia castable refractory (hereinafter simply referred to as "refractory" unless otherwise specified), The temperature distribution is in a steady state from the surface of the refractory that contacts the molten steel at 1600 ° C. to the back of the refractory, and the matrix portion of the refractory that is in chemical equilibrium at a temperature of 1400 ° C. or higher at which the liquid phase is generated. The behavior of the coefficient of linear thermal expansion correlates with resistance to peeling, and the inventors have found that the resistance to peeling can be grasped from the behavior of the coefficient of linear thermal expansion. The "linear thermal expansion coefficient" is also called "linear expansion coefficient".

The present invention is based on the above findings, and the gist of the present invention is as follows.
(1) Delamination resistance of an alumina-magnesia castable refractory having a residual line change rate of 0% or more after firing at temperatures of 1400±10° C., 1500±10° C., and 1600±10° C. for 24 hours or more. An evaluation method for
Among the kneaded materials of the refractory and water, for a thermal expansion measurement test piece produced using a kneaded material that passes through a sieve with an opening of 2.8 mm,
A step of measuring the linear thermal expansion coefficient (%) at 1400 ± 10° C. of the test piece after firing at 1400± 10° C. for 24 hours or more;
A step of measuring the linear thermal expansion coefficient (%) at 1500 ± 10° C. of the test piece after firing at 1500± 10° C. for 24 hours or more;
A step of measuring the linear thermal expansion coefficient (%) at 1600 ± 10° C. of the test piece after firing at 1600± 10° C. for 24 hours or more;
a step of comparing the value of the coefficient of linear thermal expansion (%) at 1500±10° C. with the value of the coefficient of linear thermal expansion (%) at 1400±10° C.;
Alumina-magnesia castable, characterized by comprising a step of comparing the value of the coefficient of linear thermal expansion (%) at 1600 ± 10 ° C. and the value of the coefficient of linear thermal expansion (%) at 1500 ± 10 ° C. Evaluation method for peeling resistance of refractories.
( 2 ) the value of the coefficient of linear thermal expansion (%) at 1500±10°C is equal to or higher than the value of the coefficient of linear thermal expansion (%) at 1400±10°C;
The castable refractory having a linear thermal expansion coefficient (%) value at 1600 ± 10 ° C. that is equal to or higher than the linear thermal expansion coefficient (%) value at 1500 ± 10 ° C. is judged to have high peeling resistance. The method for evaluating the spalling resistance of the alumina-magnesia castable refractory according to (1 ) , characterized in that:

Manufactured or installed refractories cannot be used in molten steel ladles without any confirmation. This is because the refractories may have poor spallation resistance. The determination method of the present invention can determine the spalling resistance of the manufactured or constructed refractory using a portion of the refractory before placing the refractory in the molten steel ladle. According to the present invention, it is possible to evaluate the spalling resistance of alumina-magnesia castable refractories and select alumina-magnesia castable refractories with excellent durability.

4 is a graph showing the temperature dependence of the coefficient of linear thermal expansion of the alumina-magnesia castable refractory of Example A. FIG. 4 is a graph showing the temperature dependence of the coefficient of linear thermal expansion of the alumina-magnesia castable refractory of Comparative Example B. FIG. 4 is a graph showing the temperature dependence of the coefficient of linear thermal expansion of the alumina-magnesia castable refractory of Example C. FIG. 4 is a graph showing the temperature dependence of the coefficient of linear thermal expansion of the alumina-magnesia castable refractory of Example D. FIG. 4 is a graph showing the temperature dependence of the coefficient of linear thermal expansion of the alumina-magnesia castable refractory of Example E. FIG.

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

[Chemical reaction of alumina-magnesia castable refractory fixed in molten steel ladle]
A molten steel ladle is a molten metal processing vessel that conveys molten steel tapped from a converter to a continuous casting machine. Therefore, the alumina-magnesia castable refractory used in the molten steel ladle is heated during the period when the molten steel is staying, and the molten steel is in the molten steel ladle until just before receiving the molten steel from the converter after casting is completed. Non-existent periods will be cooled. That is, alumina-magnesia castable refractories are used in an environment where heating and cooling are repeated.

Alumina-magnesia castable refractories used in such an environment accumulate heat inside during the course of use. According to the unsteady heat transfer calculation of the refractory in use of the molten steel ladle, molten steel is received from the converter, the molten steel is poured into the continuous casting machine, and after casting is completed, the molten steel is received again from the converter. By repeating the series of steps continuously about 12 times (ch), the heat storage inside the refractory is completed, and the temperature distribution inside the refractory from the surface of the refractory in contact with molten steel at 1600 ° C. to the back of the refractory is in a steady state. It turned out to be

The steady state here means the state in which the temperature change that occurs between the period when the molten steel stays in the molten steel ladle and the period when the molten steel does not exist in the ladle becomes the same temperature distribution change repeatedly. To tell.

Also, in alumina-magnesia castable refractories, spalling damage caused by cracks occurs after the temperature distribution inside the refractory reaches a steady state. At that time, it was found that the position where the crack occurred was the position where the temperature reached about 1400°C, according to steady heat transfer calculation inside the refractory when the molten steel ladle was used.

By the way, alumina-magnesia castable refractories are composed of raw materials such as alumina cement having alumina, magnesia, silica, and CaO.Al ₂ O ₃ as main crystal phases. In a region where the temperature inside the refractory is 1400° C. or higher, these raw materials are considered to cause the following chemical reaction (1).
Alumina + Magnesia + Silica _{+ CaO.Al2O3}
→ Alumina + spinel + CaO.6Al ₂ O ₃ + liquid phase (chemical reaction 1)

It is considered that the chemical reaction of the formula (1) progresses particularly in raw materials with a large specific surface area and a particle size of 2.8 mm or less.

That is, when the temperature of the refractory reaches 1400° C. or higher, among the raw materials of the refractory, the raw materials having a particle size of 2.8 mm or less are particularly reacted. CaO.6Al ₂ O ₃ is produced from the reaction of alumina cement with a portion of the alumina, and a liquid phase is produced from the reaction of silica with other oxides. The amount of each of spinel, CaO.6Al ₂ O ₃ and liquid phase produced in the chemical reaction (1) depends on the content of raw materials contained in the alumina-magnesia castable refractory. In particular, the amount of liquid phase produced increases with increasing temperature.

Based on the chemical reaction formula (1), the behavior of the structure of the alumina-magnesia castable refractory in the molten steel ladle is inferred. At a temperature of 1400° C. or higher in an alumina-magnesia castable refractory, when a certain amount or more of a liquid phase is generated in the matrix, the capillary force of the liquid phase causes the structure of the refractory to shrink. That is, since the amount of liquid phase generated increases from the region inside the refractory that reaches 1400 ° C or higher during use to the surface of the refractory that is in contact with molten steel, the structure of the refractory depends on the amount of liquid phase generated. As a result of the shrinkage, the amount of shrinkage of the refractory structure is maximized on the surface of the refractory.

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

Since the reaction of chemical reaction formula (2) involves the product of chemical reaction formula (1), it is believed that it particularly proceeds in the matrix.

That is, in the process of cooling the refractory, solid phases such as CaO.6Al ₂ O ₃ and CaO-MgO-SiO ₂ -Al ₂ O ₃ based compounds are precipitated from the liquid phase. In general, the heated refractory exhibits volumetric shrinkage during the cooling process, but in the alumina-magnesia castable refractory, the liquid generated during the cooling process is caused by the reaction of chemical reaction (2). Since the CaO.6Al ₂ O ₃ component with volume expansion precipitates from the phase, volume expansion is caused. The volumetric expansion of the refractory becomes maximum at around 1200° C. at which precipitation of the _three components CaO.6Al ₂ O from the liquid phase is completed.

Based on the chemical reaction formula (2), the behavior of the structure of the refractory surface during the period when molten steel is not present in the ladle, that is, during the period when the alumina-magnesia castable refractory is cooled, is speculated as follows. be done.

During cooling, the temperature of the refractory surface drops to about 900°C. _In the cooling process _, the CaO 6Al ₂ O ₃ component with volume expansion precipitates from the liquid phase generated in the refractory. Since it occurs until it is cooled to around 1200°C, the surface texture of the refractory expands up to 1200°C and shrinks in volume from 1200°C to 900°C.

From the above, the following phenomena (3) and (4) are repeated in the surface structure of the alumina-magnesia castable refractory, particularly in the range of 1400° C. or higher during molten steel retention.

Phenomenon (3): The surface temperature of the alumina-magnesia castable refractory is heated from 900°C to 1600°C during the period in which the molten steel stays. During this time, the surface texture of the alumina-magnesia castable refractory material expands in volume from 900°C to 1400°C, but shrinks in volume from 1400°C to 1600°C.

Phenomenon (4): The surface temperature of the alumina-magnesia castable refractory is cooled from 1600°C to 900°C during the period when there is no molten steel in the ladle. During this time, the surface texture of the alumina-magnesia castable refractory expands in volume from 1600°C to 1200°C, but shrinks in volume from 1200°C to 900°C.

In other words, the surface structure of the alumina-magnesia castable refractory undergoes volumetric expansion and volumetric contraction twice in the molten steel conveying process in which the heating process and the cooling process are alternately repeated once. Such repeated volume contraction and volume expansion of the refractory structure on the surface of the refractory causes strain to accumulate inside the refractory, resulting in cracks that cause peeling wear.

By the way, in a regular refractory such as a brick, the surface structure of the refractory monotonously expands in volume during the heating period when molten steel is retained, and monotonously shrinks in volume during the cooling period when molten steel does not exist in the ladle. That is, in a standard refractory such as a brick, the surface structure of the refractory undergoes volumetric expansion and volumetric contraction only once during one repetition of heating and cooling.

Therefore, by suppressing the amount of volumetric shrinkage in the heating process of alumina-magnesia castable refractories up to 1600 ° C., volumetric expansion and volume expansion can be achieved in the same heating and cooling cycles as with regular refractories such as bricks. If it is possible to create a state in which volumetric shrinkage occurs only once, it is possible to minimize the strain accumulated inside the refractory, and it is thought that the occurrence of cracks that cause peeling and wear can be prevented. .

The present inventors have found that the alumina-magnesia castable refractory when used in a molten steel ladle has a temperature distribution in a steady state inside the refractory, in which the temperature at which the liquid phase starts to form is 1400 ° C. or higher. The correlation between the behavior of the coefficient of linear thermal expansion and the presence or absence of peeling wear was investigated in detail. As a result, the alumina-magnesia castable refractory, which has the characteristic that the coefficient of linear thermal expansion monotonically increases with temperature rise, can Since it is possible to simulate a state in which volumetric expansion and volumetric contraction occur only once, it has been found to be extremely excellent in peeling resistance when used in an actual machine.

[Mechanism of action of the present invention]
In the alumina-magnesia monolithic refractory having a residual linear change rate of 0% or more after heat treatment such as firing at a temperature of 1400 ° C. or more and 1600 ° C. or less for 24 hours or more, from the kneaded alumina-magnesia castable refractory , For a test piece made using a material that has passed through a 2.8 mm sieve, after firing at 1600 ° C. ± 10 ° C. for 24 hours or more, the linear thermal expansion coefficient (%) at 1500 ± 10 ° C. and 1400 ± Compare the linear thermal expansion coefficient (%) value at 10 ° C., and the linear thermal expansion coefficient (%) value at 1600 ± 10 ° C. and the linear thermal expansion coefficient (%) value at 1500 ° C. ± 10 ° C. The reason why the peelability of the castable refractory can be evaluated by comparison is as follows.

First, the alumina-magnesia castable refractory preferably has moderate residual expansion after being subjected to heat history. A refractory with residual shrinkage, ie, a residual linear change rate of less than 0%, has dimensions after being heated and cooled that are smaller than the original dimensions before heating. Such a refractory having a residual line change rate of less than 0% obviously cracks during use, and is often inferior in peeling resistance to begin with, so that it cannot be used in an actual machine.

As described above, the alumina-magnesia castable refractory produces a liquid phase in the matrix in the chemical reaction (1) at a temperature of 1400° C. or higher. The resulting liquid phase can shrink the refractory due to volumetric shrinkage as it solidifies on cooling. Therefore, the present invention is applied to an alumina-magnesia castable refractory having a residual linear change rate of 0% or more after heat treatment such as firing at a temperature of 1400° C. or more and 1600° C. or less for 24 hours or more.

Since the surface of the alumina-magnesia castable refractory can be heated up to 1600°C by coming into contact with molten steel during use, the maximum firing temperature was set at 1600±10°C.

Further, in the evaluation method of the present invention, the firing time of the castable refractory is set to 24 hours or more because the heat storage inside the refractory is completed, and the reaction of the above formula (1) reaches a chemical equilibrium state. because it is a good time.

At least three temperatures T1, T2 and T3 (1400° C.≦T1< T2<T3≦1600° C.), it is preferable to determine whether or not the residual line change rate after heat treatment for 24 hours or more is 0% or more. In addition, the temperature measurement point for determining whether the residual line change rate after heat treatment for 24 hours or more is 0% or more is a temperature of 1400 ° C. or higher and 1600 ° C. or lower, ± (within the allowable range Temperature range) °C is not particularly limited as long as it does not overlap with each other. However, from the viewpoint of efficiency of evaluation, the residual linear change rate after heat treatment at each temperature of 1400 ± 10 ° C., 1500 ± 10 ° C., and 1600 ± 10 ° C. for 24 hours or more is 0. % or more is more preferably determined.

As a test method for the residual linear change rate, it is preferable to use JIS-R2554 "Test method for linear change rate of castable refractories".

Next, in addition to the above requirements regarding the residual linear change rate, the present invention determines whether the linear thermal expansion coefficient of the refractory at a temperature of 1400 ° C. or higher takes the same value as the temperature rises or increases monotonically. It is characterized by determining whether or not This is for the following reasons.

As described above, the chemical reactions (1) and (2) that cause the expansion and contraction of the alumina-magnesia castable refractory are composed of raw materials with a large specific surface area and a particle size of 2.8 mm or less. It is thought that it progresses particularly in a matrix with Therefore, in the present invention, in order to clarify the expansion and contraction behavior of the alumina-magnesia castable refractory, a coarse grain having a function of slowing the expansion and contraction behavior is added from the kneaded alumina-magnesia castable refractory. Thermal expansion measurements are performed using specimens made from material that has been deaggregated and passed through a 2.8 mm sieve.

At a temperature of 1400 ° C. or higher, when the amount of spinel and CaO.6Al ₂ O ₃ that are accompanied by volume expansion in the chemical reaction (1) is greater than the amount of liquid phase, linear thermal expansion of the test piece The rate varies as shown in FIG. At a temperature of 1400° C. or higher, in the chemical reaction (1), when the liquid phase is generated more than the amount of spinel and CaO.6Al ₂ O ₃ generated, the coefficient of linear thermal expansion of the test piece is as shown in FIG. _, changes as shown in _FIG . 3 changes as shown. Only at 1500° C., when the amount of liquid phase produced becomes smaller than the amount of spinel and CaO.6Al ₂ O ₃ produced, changes as shown in FIG.

On the other hand, at a temperature of 1400° C. or less, no liquid phase is generated in the chemical reaction (1). That is, at a temperature of 1400° C. or less, thermal expansion is exhibited due to thermal expansion of the refractory raw material itself and volume expansion associated with the formation of spinel and CaO.6Al ₂ O ₃ .

When the coefficient of linear thermal expansion of the refractory at a temperature of 1400° C. or higher takes the same value as the temperature rises or monotonically increases, molten steel is Looking at the behavior of the matrix portion of the refractory structure over the refractory surface in contact with the refractory structure, the refractory structure either remains unchanged or expands. That is, since the matrix portion of the refractory structure in the region of 1400 ° C. or higher inside the refractory does not shrink during use, no strain occurs, so cracks that cause peeling do not occur. It is judged to be excellent in peeling resistance.

In the alumina-magnesia castable refractory, if the linear thermal expansion coefficient of the refractory at a temperature of 1400 ° C. or higher does not monotonically increase with the temperature rise, cracks will occur in the matrix part inside the refractory near the working surface. It is judged that the peeling resistance is inferior because of the strain that causes the generation.

Thus, the value of the coefficient of linear thermal expansion at 1500°C after firing at 1500°C is equal to or higher than the value of the coefficient of linear thermal expansion at 1400°C after firing at 1400°C for 24 hours. And, the value of the coefficient of linear thermal expansion at 1600°C after firing at 1600°C for 24 hours is equal to or higher than the value of the coefficient of linear thermal expansion at 1500°C after firing at 1500°C for 24 hours. When the value is shown, the monolithic refractory can be judged to be excellent in peeling resistance.

[Peeling resistance of alumina-magnesia castable refractory fixed to molten steel ladle]
FIG. 1 shows the coefficient of linear thermal expansion at temperatures of 1400° C., 1500° C. and 1600° C. of the alumina-magnesia castable refractory shown in Example A to be described later.

In FIG. 1, the linear thermal expansion coefficient at 1400 ° C. is about the refractory fired at 1400 ± 10 ° C. for 24 hours (hereinafter simply referred to as "the refractory fired at 1400 ° C." unless otherwise specified). It is a linear thermal expansion coefficient measured in the process of increasing temperature from room temperature to 1400 ± 10 ° C. (Hereinafter, unless otherwise specified, such a linear thermal expansion coefficient is simply referred to as "linear thermal expansion coefficient at 1400 ° C." ). Similarly, the coefficient of linear thermal expansion at 1500 ° C. is the same as that of the refractory fired at 1500 ± 10 ° C. for 24 hours (hereinafter simply referred to as "the refractory fired at 1500 ° C." unless otherwise specified). to 1500 ± 10 ° C. (Hereinafter, unless otherwise specified, such a linear thermal expansion coefficient is simply referred to as "linear thermal expansion coefficient at 1500 ° C.") . Similarly, the coefficient of linear thermal expansion at 1600 ° C. is the refractory fired at 1600 ± 10 ° C. for 24 hours (hereinafter, unless otherwise specified, such a linear thermal expansion coefficient is simply “the refractory fired at 1600 ° C. It is the linear thermal expansion coefficient measured in the process of increasing the temperature from room temperature to 1600 ± 10 ° C. (hereinafter simply referred to as "linear thermal expansion coefficient at 1600 ° C." unless otherwise specified) .

As a method for testing the coefficient of linear thermal expansion, it is preferable to use a test piece and test conditions conforming to JIS-R2207 "Method for testing thermal expansion of refractories". More preferably, JIS-R2207-1 "non-contact method" is used, which has little effect on the expansion and contraction of the liquid phase.

Further, in the present invention, as described above, in order to clarify the behavior of expansion and contraction of the alumina-magnesia castable refractory, coarse aggregate that acts to slow down the behavior of expansion and contraction is removed, and alumina-magnesia castable refractory A test piece prepared from a kneaded magnesia castable refractory material passed through a 2.8 mm sieve is used.

In FIG. 1, the alumina-magnesia castable refractory shown in Example A to be described later has a linear thermal expansion coefficient that increases with temperature rise at temperatures of 1400 ° C. or higher, so it is not actually used in a molten steel ladle. However, it was free from peeling wear due to cracks caused by shrinkage, and had excellent peeling resistance.

FIG. 2 is a graph of the coefficient of linear thermal expansion at temperatures of 1400° C., 1500° C., and 1600° C. for the alumina-magnesia castable refractory shown in Comparative Example B, which will be described later. Depending on the alumina-magnesia castable refractory, the coefficient of linear thermal expansion may change as shown in FIG. The present invention can evaluate the spalling resistance of alumina-magnesia castable refractories whose coefficient of linear thermal expansion changes as shown in FIG. However, as shown in Table 1, the castable refractory of Comparative Example B has a residual linear change rate of 1400 ° C. value is less than 0%. As described above, castable refractories with a residual linear change rate of less than 0% at 1400 ° C. and 1600 ° C. are often inferior in peeling resistance in the first place, so they cannot be used in actual equipment. Even if changes as shown in FIGS. 1 to 5, they are excluded from the evaluation of the present invention.

FIG. 3 shows the coefficient of linear thermal expansion at temperatures of 1400° C., 1500° C. and 1600° C. of the alumina-magnesia castable refractory shown in Example C described later. Looking at the coefficient of linear thermal expansion at temperatures above 1400°C in Fig. 3, since the coefficient of linear thermal expansion does not increase with temperature rise, even if it is actually used in a molten steel ladle, cracks caused by shrinkage will not occur. Peeling wear occurred and the peeling resistance was poor.

FIG. 4 shows the coefficient of linear thermal expansion at temperatures of 1400° C., 1500° C. and 1600° C. of the alumina-magnesia castable refractory shown in Example D, which will be described later. Looking at the coefficient of linear thermal expansion at temperatures above 1400°C in Fig. 4, the coefficient of linear thermal expansion decreases as the temperature rises. Peeling wear occurred and the peeling resistance was poor.

FIG. 5 shows the coefficient of linear thermal expansion at temperatures of 1400° C., 1500° C. and 1600° C. of the alumina-magnesia castable refractory shown in Example E described later. Looking at the coefficient of linear thermal expansion at temperatures above 1400°C in Fig. 5, the coefficient of linear thermal expansion decreases as the temperature rises. Peeling wear occurred and the peeling resistance was poor.

[Evaluation object of the evaluation method according to the present invention]
The evaluation object of the evaluation method according to the present invention can be produced, for example, by using materials having the following compositions as raw materials. 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 at a temperature of 1400 ° C. or more and 1600 ° C. or less for 24 hours or more is 0% or more , the composition of which is not limited to the following examples.

Alumina raw materials used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention include sintered alumina, electrofused alumina, heavily burned alumina, calcined alumina, bauxite, electrofused bauxite, Sand shale and the like can be used. As for 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 desirably in the range of 78% to 93.5% by mass in the total amount of the alumina-magnesia castable refractory.

Sintered magnesia or electrofused 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 blending ratio of magnesia is desirably in the range of 3% to 10% by mass in the total amount of the alumina-magnesia castable refractory.

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

Alumina cement containing CaO.Al ₂ O ₃ can be used 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 alumina or spinel other than CaO.Al ₂ O ₃ may be used. The blending ratio of the alumina cement is desirably in the range of 3% to 10% by mass in the total amount of the alumina-magnesia castable refractory.

Generally used dispersants may be used for the alumina-magnesia castable refractories to be evaluated by the evaluation method according to the present invention. For example, sodium tripolyphosphate, sodium hexametaphosphate, acidic sodium hexametaphosphate, sodium polyacrylate, sodium polycarboxylate, sodium sulfonate, sodium naphthalenesulfonate, sodium lignosulfonate, sodium ultrapolyphosphate, sodium carbonate, sodium borate, Sodium citrate or the like can be used. The blending ratio of the dispersant may also be a general prescription. 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 prevention agent used for the alumina-magnesia castable refractory to be evaluated by the evaluation method according to the present invention, a commonly used one may be used. For example, vinylon fiber, aluminum lactate, metal aluminum as a foaming agent, and azodicarbonamide can be used. The blending ratio of the explosion-proof agent may also be a general formulation. For example, it is desirable to add the explosion inhibitor in the range of 0.01 to 0.03% with respect to 100% by mass of the alumina-magnesia castable refractory.

Alumina-magnesia castable refractory test pieces provided for carrying out the evaluation method according to the present invention are made from a kneaded alumina-magnesia castable refractory using a material passed through a 2.8 mm sieve. . It is preferable that the construction conditions are the same as those of the actual machine.

For example, 4 to 6% by mass of water is added to 100% by mass of the refractory raw material satisfying the above composition, and after kneading with a mixer, the material is passed through a 2.8 mm sieve and poured into a mold. can be In order to improve filling properties during production, vibration may be imparted to the mold into which the kneaded material is poured.

Examples of the present invention and reference examples thereof are shown below.

Table 1 shows the composition of raw materials for the alumina-magnesia castable refractories and the evaluation results. Sodium polyacrylate or sodium polycarboxylate was added as a dispersing agent to the castable refractory produced with the formulation shown in Table 1 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 explosion prevention agent based on the mass of the refractory. Furthermore, tap water is added in the range of 4 to 6% by mass with respect to the amount of refractory material, kneaded for 4 minutes using a twin-screw mixer, and the kneaded product is sieved with a 2.8 mm sieve. The kneaded material that passed through the sieve was poured into a metal frame of a predetermined size while being vibrated. Then, after the kneaded product was allowed to stand in the atmosphere at room temperature for 24 hours while being poured into the mold, the kneaded product was removed from the mold and dried at 110 ° C. for 24 hours. was made.

The residual linear change rate of refractories fired at temperatures of 1400° C., 1500° C. and 1600° C. for 24 hours was measured using the test method for linear change rate of castable refractories of JIS-R2554. The coefficient of linear thermal expansion of the refractories after firing at temperatures of 1400° C., 1500° C. and 1600° C. for 24 hours was measured using the test method for thermal expansion of refractories of JIS-R2207.

The wear rate during actual use was measured under the following conditions. First, to the alumina-magnesia castable refractories having the compounding ratio of each example shown in Table 1, the same amounts of the dispersant and the explosion inhibitor were added under the same conditions as the test pieces were prepared. Furthermore, the same amount of water was added, kneaded for 7 minutes using a twin-screw mixer, and the kneaded product was applied to the side wall of a molten steel ladle with a capacity of 400 tons. After visually confirming the drying of the kneaded material, measure the thickness of the refractory after using the molten steel ladle 150 times (ch), and divide the value obtained by subtracting the original thickness by the number of times of use. was calculated as an average wear rate (mm/ch). At the same time, the state of peeling wear due to cracks during use of the molten steel ladle was visually observed. The results are shown in Table 1.

The castable refractory of Example A had a residual linear change rate of 0% or more after being fired at temperatures of 1400°C, 1500°C, and 1600°C for 24 hours. The coefficient of linear thermal expansion of the refractory after firing at each temperature of ° C. for 24 hours shows a behavior in which the coefficient of linear thermal expansion monotonically increases with the temperature rise, and it is judged that the peeling resistance is excellent. Since no peeling wear occurred when the refractory was used in an actual machine, the present invention was able to accurately evaluate the peeling resistance of the refractory.

In the castable refractory of Comparative Example B, the values at 1400 ° C. and 1600 ° C. are less than 0% among the residual linear change rates of the refractories fired at each temperature of 1400 ° C., 1500 ° C., and 1600 ° C. for 24 hours. , were excluded from the evaluation of the present invention.

The castable refractories of Examples C to E had a residual linear change rate of 0% or more after firing at temperatures of 1400°C, 1500°C, and 1600°C for 24 hours. The coefficient of linear thermal expansion of the refractory after firing for 24 hours at each temperature of 1600 ° C. does not monotonically increase with increasing temperature, so it is judged that the peeling resistance is inferior. . Since peeling wear occurs when the refractory is used in an actual machine, the present invention can accurately evaluate the peeling resistance of the refractory.

According to the present invention, the spalling resistance of the alumina-magnesia castable refractory to be used can be accurately evaluated before construction of an actual machine. Therefore, by using the evaluation method according to the present invention, it is possible to compare and study the peeling resistance of various castable refractories, and to manufacture actual equipment using alumina-magnesia castable refractories with extremely excellent durability. can do.

Claims (2)

Method for evaluating peel resistance of alumina-magnesia castable refractories having a residual line change rate of 0% or more after firing at temperatures of 1400±10° C., 1500±10° C., and 1600±10° C. for 24 hours or longer and
Among the kneaded materials of the refractory and water, for a thermal expansion measurement test piece produced using a kneaded material that passes through a sieve with an opening of 2.8 mm,
A step of measuring the linear thermal expansion coefficient (%) at 1400 ± 10° C. of the test piece after firing at 1400± 10° C. for 24 hours or more;
A step of measuring the linear thermal expansion coefficient (%) at 1500 ± 10° C. of the test piece after firing at 1500± 10° C. for 24 hours or more;
A step of measuring the linear thermal expansion coefficient (%) at 1600 ± 10° C. of the test piece after firing at 1600± 10° C. for 24 hours or more;
a step of comparing the value of the coefficient of linear thermal expansion (%) at 1500±10° C. with the value of the coefficient of linear thermal expansion (%) at 1400±10° C.;
Alumina-magnesia castable refractory, characterized by including a step of comparing the linear thermal expansion coefficient (%) value at 1600 ± 10 ° C. and the linear thermal expansion coefficient (%) at 1500 ± 10 ° C. A method for evaluating the peeling resistance of objects. 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., and
The castable refractory having a linear thermal expansion coefficient (%) value at 1600 ± 10 ° C. that is equal to or higher than the linear thermal expansion coefficient (%) value at 1500 ± 10 ° C. is judged to have high peeling resistance. A method for evaluating spalling resistance of an alumina-magnesia castable refractory according to claim 1 , characterized in that:

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