JP7341771B2 - castable refractories - Google Patents

Description

The present invention relates to castable refractories, particularly heat-insulating castable refractories used in soaking furnaces, heat treatment furnaces, skid posts, skid beams, etc. of billet heating furnaces.

Castable refractories containing fine alumina powder and alumina cement undergo volumetric expansion when CaO・6Al ₂ O ₃ (hereinafter abbreviated as CA6) is generated in the matrix in a high-temperature atmosphere of 1400°C or higher. It is known that problems such as cracking, peeling, and protrusion occur.

On the other hand, even in an atmosphere of 1200°C, CaO.2Al ₂ O ₃ (hereinafter abbreviated as CA2) is generated in the matrix, and volumetric expansion also occurs at this time. However, compared to the production and expansion of CA6, less attention has been paid to the production and expansion of CA2.

The expansion of CA2 is a problem among castable refractories, especially in heat-insulating castable refractories. In recent years, lightweight, high-porosity CA6 aggregate and hollow alumina aggregate have often been used as heat-insulating aggregates for heat-insulating castable refractories, and the matrix portion has been designed to improve fire resistance, heat insulation, scale resistance, etc. It is often composed of CA6 fine powder, alumina fine powder, and alumina cement. In other words, insulating castable refractories that are mainly composed of two components, CaO and Al ₂ O ₃ , have become mainstream in recent years. Therefore, it has become difficult to ignore the influence of expansion caused by the formation of CA2 and CA6 on heat-insulating castable refractories.

Therefore, the present inventors believed that if the production of CA2 could be suppressed, the production expansion could be reduced, and conducted extensive research.

Alumina cement in castable hardens by forming hydrates in the matrix. Cement hydrate undergoes a process of crystal conversion and dehydration due to temperature rise due to heating, resulting in 12CaO・7Al ₂ O ₃ (hereinafter abbreviated as C12A7), CaO・Al ₂ O ₃ (hereinafter abbreviated as CA), Generate CA2, CA6, etc. Naturally, minerals such as CA2 and CA6 will not be produced unless there is a sufficient amount of Al ₂ O ₃ relative to CaO, but since insulating castable refractories have alumina sources such as alumina fine powder, CA2 and CA6 will be produced. It's easy to do.

Ordinary castable refractories are multi-component systems, and even if we consider expansion in an atmosphere of 1100 to 1200°C to be a problem, there are so many reactions that they are unlikely to be affected by the expansion caused by the formation of CA2. It wasn't. In addition, when testing castable refractories, it is common to measure the linear change rate of a test piece that has been heated and then cooled.Moreover, the linear change rate and the hot expansion coefficient do not necessarily correspond, so the expansion rate during heating cannot be measured. It wasn't much discussed. In addition, the heat retention time during heating is often 0 to 3 hours, and in the case of insulating castable refractories, heat may be difficult to transfer to the inside, so evaluations have not been conducted that allow sufficient time for the reaction to proceed. Ta. Therefore, there have been few prior art techniques in which expansion during generation of CA2 has been considered as a problem and methods for solving the problem have been studied.

On the other hand, technical ideas have existed since the past to control the type of CA minerals that form in the matrix of castable refractories. In particular, expansion due to the formation of CA6 was considered to be an issue. Most of the countermeasures are to adjust the composition of castable refractories, such as reducing the amount of cement added as a source of CaO to reduce the amount of CA6 generated, or reducing the amount of fine alumina powder, etc. added as a source of Al ₂ O ₃ . This prevents CA6 from being generated.

Patent Document 1 (Japanese Unexamined Patent Publication No. 2016-145117) discloses a heat-insulating castable refractory in which the amount of CaO added is reduced by replacing a part of alumina cement with strontium cement. Patent Document 1 aims to increase curing strength while suppressing expansion at high temperatures, but rather than suppressing the generation of CA2, by reducing the amount of alumina cement added and suppressing the amount of CaO, the amount of CA2 generated can be increased. (Changes in the amount of CA2 produced and changes in the coefficient of expansion when hot at 1000-1200℃ are unknown).

Patent Document 2 (Japanese Unexamined Patent Publication No. 2009-203090) discloses a heat-insulating castable refractory in which the C/A in the fine grain region with a grain size of less than 75 μm in CA6 castable is 0.03 to 0.13, and CA6 is generated in the matrix. There is. Patent Document 2 discloses that by crystallizing the same CA6 around the CA6 aggregate in the coarse grain region, the integrity or continuity of the structure between the CA6 aggregate and the matrix is improved, the bonding strength between the two is increased, and the heat insulation is improved. This aims to improve the strength of castable refractories. Patent Document 2 discloses that when the CaO/ _{Al 2} O ₃ mass ratio exceeds 0.08, CA2 is also _generated along with CA6, causing shrinkage or cracking of the construction body. It states that it is preferable to suppress CA2 production as much as possible.

Here, as mentioned above, the cement hydrate in the castable undergoes the processes of crystal conversion and dehydration due to the temperature increase due to heating, and the following reactions occur in each temperature range.
Reaction (1) C12A7 + 5A → 12CA (1000-1100℃)
Reaction (2) CA + A → CA2 (1000-1200℃)
Reaction (3) CA2 + 4A → CA6 (1400-1600℃)
[In the equations of reactions (1), (2) and (3), C is CaO, A is Al ₂ O ₃ , C12A7 is 12CaO・7Al ₂ O ₃ , CA is CaO・Al ₂ O ₃ , and CA2 is CaO.2Al ₂ O ₃ and CA6 represent CaO.6Al ₂ O ₃ . ]

Therefore, in order to generate CA6 in the matrix portion, an atmosphere of 1400° C. or higher is usually required, and under such an atmosphere, CA6 is generated after the generation of CA and CA2. At this time, when the amount of A is small (when C/A is large), CA2 is produced by reactions (1) and (2), but there is not enough A required for reaction (3), and reaction (3) It does not progress sufficiently and the production of CA6 decreases. On the other hand, when the amount of A is large (when C/A is small), there is enough A required for reaction (3), so reaction (3) reduces CA2 and generates CA6. The invention described in Patent Document 2 makes the CaO/Al ₂ O ₃ mass ratio (C/A) 0.08 or less, that is, by increasing the amount of A, the reaction (3) proceeds quickly and generates CA2. It is thought that this was an attempt to reduce the amount of CA6 produced and increase the amount of CA6 produced.

However, although the heat-insulating castable refractory described in Patent Document 2 apparently suppresses the amount of CA2 produced by setting the CaO/Al ₂ O ₃ mass ratio (C/A) to 0.08 or less, in reality, the amount of CA2 produced is suppressed. Since CA6 is produced through a production reaction, the production of CA2 in reaction (2) is not suppressed, and the expansion caused by CA2 production remains unresolved.

Patent Document 3 (Japanese Unexamined Patent Publication No. 2014-037327) discloses a heat-insulating castable refractory in which the C/A in the fine grain region with a grain size of less than 1 mm in CA6 castable is 0.24 to 0.32, and CA2 is generated in the matrix. ing. Patent Document 3 attempts to suppress the generation and expansion of CA6 in Patent Document 2, but in any case, generation and expansion of CA2 occurs, and no attention is paid to the problem of generation and expansion of CA2.

In the heat insulating castable refractories described in Patent Documents 1 to 3, CA2 can be prevented from being generated by reducing Al ₂ O ₃ to make C/A 0.55 or more. However, in recent years, many alumina cements used in castable refractories contain 70% by mass or more of Al ₂ O ₃ due to their fire resistance, corrosion resistance, scale resistance, etc. C/A is less than 0.43. Adding alumina fine powder or CA6 aggregate further reduces C/A, so it has been virtually difficult to suppress CA2 formation in castable refractories using alumina cement. For example, in Comparative Example 5 of Patent Document 3, the matrix portion is composed only of alumina cement and the C/A is 0.38, but a large amount of CA2 is generated.

On the other hand, as a technique for suppressing the generation of CA6, for example, Patent Document 4 (Japanese Unexamined Patent Publication No. 9-142943) discloses that α-alumina is added at 1000 to 1200°C before CA6 is generated at 1350 to 1450°C. Discloses a monolithic refractory that is made to react with magnesia to form magnesia spinel and suppresses the formation of CA6. However, magnesia spinel undergoes a large volumetric expansion during production, and in addition, the spinelization reaction does not proceed sufficiently at 1100°C, so it cannot be used as a means to solve the expansion caused by the production of CA2.

Furthermore, Patent Document 5 (Japanese Unexamined Patent Publication No. 06-263527) discloses an alumina refractory in which zinc oxide is added to alumina fine powder and alumina cement, and a refractory with improved corrosion resistance and spalling resistance can be obtained. It is stated that it is possible. However, the alumina refractory described in Patent Document 5 has a low strength as a construction body because it contains a small amount of alumina cement, and for example, castable refractories for heating furnace skid posts and skid beams require strength. It cannot be used as a castable refractory. Furthermore, since the amount of alumina cement blended is small, almost no CA2 is generated, and expansion due to CA2 does not become a problem.

Japanese Patent Application Publication No. 2016-145117 Japanese Patent Application Publication No. 2009-203090 Japanese Patent Application Publication No. 2014-037327 Japanese Patent Application Publication No. 9-142943 Japanese Patent Application Publication No. 06-263527

Therefore, an object of the present invention is to provide a castable refractory using alumina fine powder and alumina cement, without limiting the amount of alumina cement used to an excessively small amount, and to reduce the amount of matrix that is caused by the formation of CA2 at 1100 to 1200°C. An object of the present invention is to provide a castable refractory whose expansion is suppressed.

In view of the above objective, the present inventors did not reduce the blending amount of raw materials serving as CaO and Al ₂ O ₃ sources during blending, but rather increased free Al ₂ O ₃ in the matrix by 1100°C, when CA2 generation begins. We conducted intensive research on castable refractories that can suppress the generation of CA2 and reduce the expansion of CA2 by reducing the amount of . The present inventors conducted various studies on minerals that bond with alumina in a temperature range lower than 1100°C and do not undergo large expansion during compound formation, and as a result, they came up with the solution of adding zinc oxide fine powder.

Zinc oxide is a mineral that is easily reduced and gasified at high temperatures. In particular, when it comes into contact with iron in a reducing atmosphere, reactions such as ZnO(s) + nFe(s) = Zn(g) + FenO(s) occur (the melting point of zinc is 419.5°C). Therefore, it is a mineral that has not been used much in castable refractories, and there is little prior art that has studied its behavior in castable refractories.

Although it is known that zinc oxide and alumina form spinel compounds, no research has been conducted on the temperature range in which they form spinel in castable refractories or the expansion behavior they exhibit at high temperatures. .

For example, Patent Document 5 only states that zinc oxide does not form a specific low-melting compound with alumina and that zinc oxide itself has a low coefficient of thermal expansion, but does not describe spinelization. . Further, in the alumina refractory described in Patent Document 5, the amount of alumina cement blended is as small as 5% by mass (Comparative Example 5), so it is thought that almost no CA2 is generated. Therefore, there is no problem of suppressing the production of CA2 and reducing the expansion of CA2 production, and therefore, there is no technical idea of suppressing the production of CA2 by adding zinc oxide (for example, Example 4).

Therefore, the present inventors developed a conventional fire-resistant composition containing CA6 aggregate as a refractory aggregate of 1 mm or more, and CA6 fine powder, alumina fine powder, and alumina cement as a refractory fine powder of less than 1 mm, by adding water. The heat-insulating castable refractories produced by replacing part of the alumina fine powder with zinc oxide powder were kept at various temperature atmospheres, and the reaction products were measured by X-ray diffraction. As a result, zinc spinel was detected at an insulating temperature of 800°C or higher, and it was found that CA2 production was suppressed at an insulating temperature of 1000°C or higher.

Although the production of zinc spinel is also a reaction that involves expansion, the expansion rate is lower than that of CA2, and the effect on the overall expansion of the castable in an atmosphere of 1100 to 1200°C is small. That is, even though an expandable raw material is added to a castable refractory that expands at 1100°C, expansion can be reduced. Furthermore, even when zinc oxide is turned into spinel, it tends to evaporate when it comes into contact with scale or hot metal at high temperatures, but since only a portion of the surface side evaporates, it does not impair the various properties of the castable.

That is, the castable refractory of the present invention is a castable refractory comprising water and a refractory composition consisting of a refractory aggregate with a particle size of 1 mm or more and a refractory fine powder with a particle size of less than 1 mm,
The refractory fine powder with a particle size of less than 1 mm includes alumina cement, alumina fine powder, and zinc oxide fine powder,
The amount of Al ₂ O ₃ component in the alumina cement is 70% by mass or more,
In 100% by mass of the fireproof composition, 8% by mass or more and less than 50% by mass of the alumina cement and 0.5% by mass or more and less than 25% by mass of the zinc oxide fine powder are blended.

The amount of CaO component derived from the alumina cement is preferably 2% by mass or more and less than 15% by mass based on 100% by mass of the refractory composition.

The castable refractory of the present invention is preferably an insulating castable refractory that includes lightweight refractory aggregate in the refractory aggregate having a particle size of 1 mm or more.

The castable refractory of the present invention is preferably an insulating castable refractory that includes a lightweight refractory aggregate having a composition of CaO.6Al ₂ O ₃ in the refractory aggregate having a particle size of 1 mm or more.

In the present invention, by adding fine zinc oxide powder to a castable refractory containing fine alumina powder and alumina cement, it is possible to suppress the generation and expansion of CA2 and reduce problems such as cracking, peeling, and protrusion. In addition, a particularly large suppressing effect can be obtained by adding zinc oxide fine powder to a heat-insulating castable refractory whose composition mainly includes CaO and Al ₂ O ₃ .

2 is a graph showing the change in thermal expansion coefficient over time when test pieces of the castable refractory of Comparative Example 1 were kept at 1000°C, 1100°C, 1200°C, and 1300°C for 6 hours, respectively. 2 is a graph showing the change in thermal expansion coefficient over time when test pieces of castable refractories of Comparative Example 1 and Examples 2 to 5 were kept at 1000° C. for 6 hours. 2 is a graph showing the change in thermal expansion coefficient over time when test pieces of castable refractories of Comparative Example 1 and Examples 2 to 5 were kept at 1100° C. for 6 hours. 2 is a graph showing the change in thermal expansion coefficient over time when test pieces of castable refractories of Comparative Example 1 and Examples 2 to 5 were kept at 1200° C. for 6 hours. 2 is a graph showing the change in thermal expansion coefficient over time when test pieces of castable refractories of Comparative Example 1 and Example 5 were kept at 1000°C, 1100°C, and 1200°C for 6 hours.

An embodiment of the present invention will be described below. In addition, in this specification, the particle size of a particle of d or more means that the particle remains on a standard sieve with aperture d specified in JIS-Z8801, and the particle size of a particle of less than d means that the particle remains on a standard sieve with aperture d defined in JIS-Z8801 This means that the particles pass through the same sieve.

[1] Castable refractories
(A) Chemical component composition The castable refractory of the present invention comprises a refractory composition consisting of a refractory aggregate with a particle size of 1 mm or more and a refractory fine powder with a particle size of less than 1 mm, and construction water. The refractory fine powder with a diameter of less than 1 mm includes alumina cement, alumina fine powder, and zinc oxide fine powder, and the amount of Al ₂ O ₃ component in the alumina cement is 70% by mass or more, and in 100% by mass of the refractory composition. , the alumina cement is blended in an amount of 8% by mass or more and less than 50% by mass, and the zinc oxide fine powder is blended in an amount of 0.5% by mass or more but less than 25% by mass.

The castable refractory of the present invention is characterized by containing zinc oxide. Zinc oxide reacts with free alumina to form zinc spinel (ZnAl ₂ O ₄ ). This reaction consumes free alumina, and as a result, the generation of CA2 can be suppressed.

(1) Alumina Cement As mentioned above, the alumina cement used in the present invention preferably has an Al ₂ O ₃ content of 70% by mass or more from the viewpoint of fire resistance, corrosion resistance, scale resistance, etc. If the amount of alumina cement blended is small, the problem of generation expansion due to CA2 will not occur, but the strength of the construction body will be insufficient, so it is preferable that the amount of alumina cement blended is 8% by mass or more. When strength is required, such as in castable refractories for skid posts and skid beams in heating furnaces, a more preferred amount of alumina cement is 20% by mass or more. On the other hand, if the blending amount of alumina cement is 50% by mass or more, fluidity and heat insulation properties will deteriorate, so the blending amount is preferably less than 50% by mass. Further, the amount of CaO component derived from alumina cement is preferably 2% by mass or more and less than 15% by mass based on 100% by mass of the refractory composition.

(2) Fine alumina powder In order to ensure fluidity, corrosion resistance, fire resistance, etc. of the castable, fine alumina powder is preferably blended in such a way that free zinc oxide is not generated in an atmosphere of at least 1200°C or higher. The blending amount that does not produce free zinc oxide is such that the molar ratio of Al ₂ O ₃ (molar mass: 102.0) to ZnO (molar mass: 81.4) in zinc spinel (ZnAl ₂ O ₄ ) is 1 or more. The amount is such that the mass ratio of Al ₂ O ₃ /ZnO in the refractory fine powder with a particle size of less than 1 mm is 1.25 or more. Note that the amount of Al ₂ O ₃ in the refractory fine powder with a particle size of less than 1 mm is the total of that derived from alumina cement and that derived from alumina fine powder.

(3) Zinc oxide fine powder The blending amount of zinc oxide fine powder is 0.5% by mass or more and less than 25% by mass in 100% by mass of the fireproof composition. The effect of suppressing CA2 generation can be seen in proportion to the amount of zinc oxide fine powder mixed, but the extent to which expansion at 1100 to 1200°C is suppressed cannot be calculated accurately because it depends on the amount of alumina cement mixed. Therefore, when 50% by mass of alumina cement is mixed with 100% by mass of the refractory composition (the amount of CaO contained in the refractory fine powder with a particle size of less than 1 mm is 12.7% by mass in 100% by mass of the refractory composition), the refractory composition A test was conducted when 8% by mass of alumina cement was mixed with 100% by mass of the composition (the amount of CaO contained in the refractory fine powder with a particle size of less than 1 mm was 2% by mass in 100% by mass of the refractory composition). In all cases, the expansion suppression effect was confirmed by adding 0.5% by mass or more of zinc oxide fine powder, but the amount of expansion suppression was insufficient when it was less than 0.5% by mass. Therefore, it is preferable that the zinc oxide fine powder be blended in an amount of at least 0.5% by mass or more based on 100% by mass of the refractory composition. In addition, if the blending amount exceeds 25% by mass, the difference in specific gravity with the aggregate will increase, causing separation between the aggregate and the matrix, and the uniformity of the construction body will be likely to be lost. It is preferable to have one. A more preferable amount of zinc oxide fine powder is 3% by mass or more and less than 15% by mass.

In order to improve the reactivity of zinc oxide fine powder with alumina, the smaller the particle size, the better. The preferred average particle size is less than 30 μm.

Metallic zinc has a melting point of 419.5°C and oxidizes while the temperature of the refractory increases, so that the same effect as adding zinc oxide can be obtained, so metal zinc powder may be used. However, from the viewpoint of cost, it is preferable to add zinc oxide fine powder. Also, zinc hydroxide may be used instead of zinc oxide.

(4) Lightweight refractory aggregate When the present invention is applied to heat-insulating castable refractories, it is preferable that the refractory aggregate with a particle size of 1 mm or more contains a lightweight refractory aggregate. As the lightweight fire-resistant aggregate, for example, CA6 aggregate or a hollow material having an Al ₂ O ₃ composition can be used, but it is preferable to use CA6 aggregate, which has excellent heat insulation and fire resistance. It is preferable to use CA6 aggregate that contains 90% by mass or more of the Al ₂ O ₃ component and has a bulk specific gravity of less than 1.0. A specific example is "SLA-92" manufactured by Alcoa. Further, in order to ensure sufficient fire resistance, light weight, heat insulation, and scale resistance of the entire refractory, it is preferably contained in an amount of 30% by mass or more based on 100% by mass of the refractory composition.

(B) Production amount of CA2
The amount of CA2 produced is affected by the contents of Al ₂ O ₃ , CaO and ZnO in the fine grain region of less than 1 mm. As mentioned above, the generation of CA2 can be suppressed by having a refractory fine powder with a particle size of less than 1 mm having a chemical composition with a CaO/Al ₂ O ₃ mass ratio (C/A) of 0.55 or more. Here, if we consider that the effective concentration of Al ₂ O ₃ (the amount of free alumina) is decreasing due to the reaction between Al ₂ O ₃ and zinc oxide, the refractory fine powder with a particle size of less than 1 mm will The following formula:
(CaO mass) / (Al ₂ O ₃ mass - 1.25 x ZnO mass)
(Hereinafter abbreviated as C/(A-1.25Z).) It is thought that the production of CA2 can be suppressed by having a chemical composition such that the value expressed by C/(A-1.25Z) is 0.55 or more.

However, the actual effect of zinc oxide on suppressing the production of CA2 is greater than the expected effect due to the consumption of free alumina due to the formation of zinc spinel due to the added zinc oxide. In other words, even if the value of C/(A-1.25Z) of castable with zinc oxide fine powder added is the same as the C/A value of castable without zinc oxide fine powder, castable with zinc oxide fine powder added In some cases, the generation of CA2 in an atmosphere of 1100°C or higher is more suppressed. Therefore, it is presumed that zinc oxide reduces free alumina by some factor beyond the amount consumed by zinc spinel formation.

For example, when a test piece of castable (C/A=0.19 and C/(A-1.25Z)=0.22) to which zinc oxide was added was kept warm in an atmosphere of 1000℃ and 1200℃ for 6 hours and the mineral composition was investigated. No new CA2 was generated under both 1000°C and 1200°C conditions. On the other hand, when the same experiment was carried out using castable with C/A=0.17 without adding zinc oxide, CA2 generation was observed under both conditions of 1000°C and 1200°C, and the amount produced was particularly large at 1200°C. Therefore, in the case of castable with zinc oxide added, the generation of CA2 was almost suppressed even though the value of C/(A-1.25Z) was much lower than 0.55.

In addition, even if the amount of zinc oxide fine powder added is small and the generation of CA2 cannot be completely suppressed, the amount of CA2 generated will decrease depending on the amount of zinc oxide added, so the amount of hot expansion after 1100℃ decreases. As explained later, there is a proportional relationship between the amount of zinc oxide added and the amount of suppression of hot expansion after 1100℃, so how much expansion of refractories should be suppressed at 1100 to 1200℃? , can be controlled by appropriately adjusting the blending amounts of alumina cement and zinc oxide.

The present invention will be explained in more detail with reference to the following examples, but the present invention is not limited to these examples.

Table 1 shows the chemical compositions of the refractory aggregate and refractory fine powder used in the Examples and Comparative Examples of the present application.

注(1)：SiO₂、Na₂O、Fe₂O₃等の不純物が含まれる。

Note (1): Contains impurities such as SiO ₂ , Na ₂ O, and Fe ₂ O ₃ .

Comparative example 1
In order to investigate the hot volume expansion of conventional heat-insulating castable refractories, water was added to the refractory composition with the composition shown in Table 2, and after kneading, it was poured into a prescribed formwork, cured, hardened, and desorbed. The frame was dried at 110°C for 24 hours to obtain a test piece of heat-insulating castable refractory. Using this test piece, the hot expansion coefficient, etc., were measured as follows. The coefficient of thermal expansion was measured using an optical scanning method on a test piece placed in an electric furnace. The maximum temperature inside the furnace (heat retention temperature) is set in 100℃ increments, the temperature increase rate is 5℃/min, and the heat retention time after the furnace reaches the maximum temperature is 6 hours, taking into account the reaction time. Naturally cooled until Figure 1 shows the measurement results of the coefficient of thermal expansion at maximum temperatures of 1000°C, 1100°C, 1200°C, and 1300°C.

注1：耐火組成物100質量%に対する質量%を示す

Note 1: Shows mass % based on 100 mass % of fireproof composition

As shown in Figure 1, a heat-insulating castable refractory exhibits no volume change during heat retention in an atmosphere of 1000°C, but volumetric expansion progresses during heat retention in an atmosphere of 1100°C. In an atmosphere of 1200°C or higher, expansion converges during or immediately after temperature rise, while there is little change in volume during incubation at 1200°C, and in an atmosphere of 1300°C, expansion decreases during incubation, probably due to the effect of sintering.

The difference in slope of the graph between the 1100°C atmosphere and the 1200°C atmosphere is the difference in reaction rate. The reaction progresses more easily in a high-temperature atmosphere, so the reaction is slower in a 1100°C atmosphere than in a 1200°C atmosphere. Therefore, immediately after the temperature is raised, there is a large expansion difference between the 1100°C atmosphere and the 1200°C atmosphere, but when compared after 6 hours of heat retention, the expansion difference between the 1000°C atmosphere and the 1100°C atmosphere becomes large.

When the mineral composition of the specimens kept warm at each temperature was investigated by X-ray, an increase in CA2 was confirmed in the specimens kept warm in an atmosphere of 1100°C or higher, indicating that the reaction that causes this expansion is the cause of CA2 This is thought to be a reaction that produces (see Table 5-2).

Examples 1 to 5 and comparative example 2
A test piece of a heat-insulating castable refractory was prepared in the same manner as in Comparative Example 1, except that the refractory composition having the formulation shown in Table 3 was used, and the hot expansion coefficient was measured in the same manner as in Comparative Example 1. The measurement results of the coefficient of thermal expansion at maximum temperatures of 1000°C, 1100°C, and 1200°C are shown in Table 4 and Figures 2 to 5.

In addition, all of the test pieces that were kept warm in an atmosphere of 1300°C or higher experienced sintering and decreased expansion during the heat keeping, as in Comparative Example 1 (see Figure 1). Since no difference was observed in the amount, it is omitted. In addition, the test pieces kept at temperatures below 900°C had almost the same expansion curves, so they are omitted.

注(1)：耐火組成物100質量%に対する質量%を示す

Note (1): Shows mass % based on 100 mass % of fireproof composition

注(1)：耐火組成物100質量%に対する質量%を示す。

Note (1): Shows mass % based on 100 mass % of fireproof composition.

(1) About the coefficient of hot expansion From Table 4 and Figures 2 to 4, it can be seen that when the test piece is kept warm in an atmosphere of 1000℃ (Figure 2), compared to Comparative Example 1, Examples 3 to 5 are On the other hand, when the test pieces were kept at 1100°C and 1200°C (Figures 3 and 4), the thermal expansion coefficient decreased as the amount of zinc oxide fine powder added increased. It was found that expansion was suppressed depending on the amount of zinc oxide fine powder added in an atmosphere of 1100°C and 1200°C.

When the test piece was kept in an atmosphere of 1000°C, the thermal expansion coefficient increased as the amount of zinc oxide fine powder added increased, which is thought to be due to expansion due to the formation of zinc spinel. However, because of this expansion at 1000°C, we were able to further reduce the difference in expansion with temperatures above 1100°C.

In other words, as shown in Table 4 and Figure 5, when comparing Comparative Example 1, in which no zinc oxide fine powder was added, and Example 5, in which 7% by mass of zinc oxide fine powder was added, in Comparative Example 1, after heating in an atmosphere of 1000°C, The difference in expansion rate after incubation in an atmosphere of 1100° C. was 1.01%, whereas in Example 5, it decreased to 0.26%, indicating a reduction in the expansion gap. Furthermore, even if the reaction was not completed after 6 hours of incubation in a 1100°C atmosphere, the expansion rate curve during incubation in a 1200°C atmosphere became flat during incubation, indicating that the reaction had finished to some extent. Therefore, when comparing the difference in expansion after incubation between a 1000° C. atmosphere and a 1200° C. atmosphere, it is 1.13% in Comparative Example 1, while it is 0.45% in Example 5, which again shows an expansion reduction effect.

On the other hand, in Comparative Example 2 in which the amount of zinc oxide fine powder added was 0.3% by mass, there was almost no difference in the thermal expansion coefficient from Comparative Example 1 in which no zinc oxide fine powder was added, and no effect of suppressing the generation of CA2 was observed.

(2) Regarding reaction products The mineral compositions of the test pieces of Example 5 and Comparative Example 1 that were kept at each temperature for 6 hours were analyzed by X-ray diffraction, and the results are shown in Tables 5-1 and 5-2, respectively. The amount of CA2 in the test piece of Example 5 after being kept warm in an atmosphere of 1100°C and 1200°C was almost unchanged compared to the test piece kept being kept warm in an atmosphere of 1000°C. In other words, it is thought that the generation of CA2 at a heat retention temperature of 1000°C or higher is suppressed.

（X線回析によって求めた各種成分の相対強度比を＋で表現した。）
注(1) Z：酸化亜鉛
注(2) ZA：亜鉛スピネル

(The relative intensity ratio of various components determined by X-ray diffraction is expressed as +.)
Note (1) Z: Zinc oxide Note (2) ZA: Zinc spinel

On the other hand, the amount of CA2 in the test piece of Comparative Example 1 increased as the insulating temperature was increased from 700°C to 1100°C, 1100°C, and 1200°C.

（X線回析によって求めた各種成分の相対強度比を＋で表現した。）

(The relative intensity ratio of various components determined by X-ray diffraction is expressed as +.)

Further, according to the X-ray diffraction measurement of Example 5, zinc spinel was detected in the test piece whose heat retention temperature was 800°C or higher. As the insulation temperature increased, the amount of zinc spinel increased, and the amounts of zinc oxide and alumina decreased. Zinc oxide and alumina are almost completely gone in the test piece after being kept warm in an atmosphere of 1200°C, indicating that the zinc spinel reaction has been completed. This indicates that zinc spinel is formed in castable refractories under an atmosphere of 800 to 1200°C.

On the other hand, in Example 5 in which zinc oxide was added compared to Comparative Example 1 in which zinc oxide was not added, it was confirmed that CA increased in the test piece after being kept warm in an atmosphere of 1000°C. On the other hand, no change was observed in the amount of CA2. From this, zinc oxide reduces free alumina in the matrix of castable refractories by turning it into spinel in an atmosphere of 800 to 1200℃, and as a result, the formation of CA2 in the matrix is suppressed, and instead CA It is thought that a large amount of is generated.

From the above, it was found that although the formation of zinc spinel is also a reaction that involves expansion, the expansion rate is lower than that of CA2 formation, and the effect on the expansion of the entire castable in an atmosphere of 1100 to 1200°C is small. That is, even though an expandable raw material is added to a castable refractory that expands in an atmosphere of 1100°C, expansion can be reduced. Furthermore, even when zinc oxide is turned into spinel, it tends to evaporate when it comes into contact with scale or hot metal at high temperatures, but since only a portion of the surface side evaporates, it does not impair the various properties of the castable.

The present invention can be preferably used in heat-insulating castable refractories used in soaking furnaces, heat treatment furnaces, skid posts of billet heating furnaces, skid beams, etc., but alumina fine powder and alumina cement can also be used in other applications. Castable refractories can be used to suppress expansion. Moreover, the castable refractory of the present invention can be constructed not only by pouring construction, but also by methods such as troweling construction and wet spraying construction by adding a shape retaining agent, quick setting agent, etc.

Claims (4)

A castable refractory comprising a refractory composition consisting of a refractory aggregate with a particle size of 1 mm or more and a refractory fine powder with a particle size of less than 1 mm, and water,
The refractory fine powder with a particle size of less than 1 mm includes alumina cement, alumina fine powder, and zinc oxide fine powder,
The amount of Al ₂ O ₃ component in the alumina cement is 70% by mass or more,
A castable refractory, wherein 8% by mass or more and less than 50% by mass of the alumina cement and 0.5% by mass or more and less than 25% by mass of the zinc oxide fine powder are blended in 100% by mass of the refractory composition. The castable refractory according to claim 1,
A castable refractory in which the amount of CaO component derived from the alumina cement is 2% by mass or more and less than 15% by mass based on 100% by mass of the refractory composition. The castable refractory according to claim 1 or 2,
A heat-insulating castable refractory that includes lightweight fire-resistant aggregate in the fire-resistant aggregate with a particle size of 1 mm or more. The castable refractory according to any one of claims 1 to 3,
A heat-insulating castable refractory comprising a lightweight refractory aggregate having a composition of CaO.6Al ₂ O ₃ in the refractory aggregate having a particle size of 1 mm or more.

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