Insulated castable refractory

Abstract

To provide a heat-insulating castable refractory that is less susceptible to cracking due to warpage cracking.SOLUTION: An heat-insulating castable refractory comprises, as refractory raw materials: CA6 aggregate having a grain size of 1 mm or more and consisting mainly of CaO_6Al2O3; silica fine powder having a grain size of less than 75 μm; and chamotte. In 100 mass% of the refractory raw materials, a content of the CA6 aggregate is 10 mass% or more and 60 mass% or less, a content of the silica fine powder is 5 mass% or more and 15 mass% or less, and a content of the chamotte is 10 mass% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a heat-insulating castable refractory.

Background Art

[0002] For example, a heat-insulating castable refractory is used in a part that requires not only fire resistance but also heat insulation, such as a skid pipe of a heating furnace or a soaking pit. As such a heat-insulating castable refractory, as disclosed in Patent Document 1, a heat-insulating castable refractory containing CA6 aggregate having a particle size of 1 mm or more and having CaO·6Al2O3 as a main component is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the present inventors constructed the heat-insulating castable refractory disclosed in Patent Document 1 around the skid pipe of a heating furnace and conducted a full-scale furnace test, it was found that cracks due to spalling or the like were likely to occur in the heat-insulating castable refractory.

[0005] Therefore, the problem to be solved by the present invention is to provide a heat-insulating castable refractory in which cracks due to spalling or the like are unlikely to occur.

Means for Solving the Problems

[0006] The inventors investigated and analyzed the causes of cracks such as segregation that occurred in the above-mentioned actual furnace tests and found that a major factor was the high expansion of the CA6 aggregate at high temperatures of 1000°C or higher, which is the temperature at which the insulated castable refractory material is used. Therefore, the inventors considered that in order to suppress the occurrence of cracks such as segregation, it would be effective to construct the refractory material in a way that can absorb or counteract the expansion of the CA6 aggregate at high temperatures of 1000°C or higher, and conducted further tests and research. As a result, they found that it is effective to use an appropriate amount of silica fine powder together with the CA6 aggregate as a refractory material, and to use a predetermined amount or more of chamotte in the remainder, and thus completed the present invention.

[0007] In other words, according to one aspect of the present invention, the following heat-insulating castable refractory material is provided. A heat-insulating castable refractory material containing, as a refractory raw material, CA6 aggregate with a particle size of 1 mm or more, mainly composed of CaO·6Al2O3, silica fine powder with a particle size of less than 75 μm, and chamotte, A heat-insulating castable refractory material in which, as a percentage of 100% by mass of the refractory raw material, the CA6 aggregate content is 10% by mass or more and 60% by mass or less, the silica fine powder content is 5% by mass or more and 15% by mass or less, and the chamotte content is 10% by mass or more. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a heat-insulating castable refractory material that is less prone to cracking due to segregation or other reasons. [Modes for carrying out the invention]

[0009] The heat-insulating castable refractory material of the present invention contains CA6 aggregate, silica fine powder, and chamotte as refractory raw materials. Here, CA6 aggregate refers to a porous, heat-insulating aggregate whose main component is CaO·6Al2O3, with a particle size of 1 mm or larger. While there is no particular upper limit to the particle size of CA6 aggregate, it is generally less than 8 mm, according to common technical knowledge in the field of heat-insulating castable refractories. Furthermore, silica fine powder refers to particles with a particle size of less than 75 μm. Furthermore, chamotte is a refractory material made by firing clay or pyrophyllite at 1300-1400°C, and mainly contains Al2O3 and SiO2 components, with a particular emphasis on materials where the Al2O3 component is less than 50% by mass and more than 10% by mass. In this invention, a particle size of d or more means that the particle remains on a standard sieve with a mesh opening of d as defined in JIS-Z8801, and a particle size of less than d means that the particle passes through the sieve.

[0010] The heat-insulating castable refractory material of the present invention contains 10% to 60% by mass of CA6 aggregate in proportion to 100% by mass of the refractory raw material. If the CA6 aggregate content is less than 10% by mass, heat insulation cannot be guaranteed. On the other hand, if the CA6 aggregate content exceeds 60% by mass, as described above, the CA6 aggregate exhibits high expansion at high temperatures of 1000°C or higher, which is the temperature at which the heat-insulating castable refractory material is used. As a result, cracks due to cracking caused by the expansion of the CA6 aggregate are likely to occur during use of the heat-insulating castable refractory material.

[0011] The heat-insulating castable refractory of the present invention contains 5% to 15% by mass of silica fine powder in proportion to 100% by mass of the refractory raw material. Since the silica fine powder melts and forms a liquid phase at temperatures above 1000°C, it exhibits the effect of absorbing the expansion of the CA6 aggregate and the effect of shrinking the heat-insulating castable refractory itself. That is, the silica fine powder absorbs or counteracts the expansion of the CA6 aggregate at high temperatures above 1000°C. If the silica fine powder content is less than 5% by mass, the above effect is not sufficiently obtained, and as a result, cracks due to cracking caused by the expansion of the CA6 aggregate are more likely to occur during use of the heat-insulating castable refractory. On the other hand, if the silica fine powder content exceeds 15% by mass, the formation of the liquid phase becomes excessive, and as a result, the shrinkage of the heat-insulating castable refractory becomes too large, making it prone to cracking. Furthermore, as mentioned above, silica fine powder melts and forms a liquid phase at temperatures above 1000°C, thus promoting the sintering of adiabatic castable refractories and increasing their strength. This increased strength of adiabatic castable refractories contributes to suppressing crack formation due to segregation. In addition, silica fine powder also contributes to improving the fluidity of adiabatic castable refractories. In this invention, taking all of the above into consideration, the particle size of the silica fine powder is set to less than 75 μm, and its content is set to 5% by mass or more and 15% by mass or less.

[0012] The heat-insulating castable refractory material of the present invention contains 10% by mass or more of chamotte in proportion to 100% by mass of the refractory raw material. Chamotte is a refractory raw material that contributes to improving the volume stability of the heat-insulating castable refractory material because it does not easily form a liquid phase in the temperature range of 1000°C or higher and has a low coefficient of thermal expansion in the same temperature range. For this reason, in the present invention, 10% by mass or more of chamotte is used as the remaining refractory raw material other than the CA6 aggregate and silica fine powder mentioned above. If the chamotte content in proportion to 100% by mass of the refractory raw material is less than 10% by mass, cracks such as burr cracks are likely to occur during use of the heat-insulating castable refractory material. There is no particular upper limit to the chamotte content, but a content of 85% by mass when all of the remaining refractory raw material other than the CA6 aggregate and silica fine powder is chamotte is the de facto upper limit. However, as will be described later, other refractory materials besides chamotte can be used as appropriate for the remaining refractory materials other than CA6 aggregate and silica powder. Therefore, the present invention does not specify an upper limit for the chamotte content. In short, in the present invention, it is sufficient for the remaining refractory materials other than CA6 aggregate and silica powder to contain at least 10% by mass of chamotte. Furthermore, the particle size of the chamotte is not particularly limited; it can be 1 mm or larger, or less than 1 mm, similar to the CA6 aggregate, or a combination of 1 mm or larger and less than 1 mm. There is also no particular upper limit to the particle size of the chamotte, but similar to the CA6 aggregate mentioned above, it is generally less than 8 mm, based on common technical knowledge in the field of thermal insulation castable refractories.

[0013] The heat-insulating castable refractory material of the present invention may contain, in addition to chamotte, alumina-silica raw materials such as clay and pyrophyllite, and alumina raw materials such as bauxite and calcined alumina, as the remaining refractory raw materials other than the CA6 aggregate and silica powder described above. It may also contain CA6 powder with a particle size of less than 1 mm, mainly composed of CaO·6Al2O3. In the following description, the refractory raw materials other than the CA6 aggregate, silica powder, and chamotte described above will be collectively referred to as "other refractory raw materials." The particle size of these other refractory raw materials is not particularly limited and can generally be in the range of less than 8 mm. Examples of other refractory raw materials include bauxite, calcined alumina, electrofused alumina, sintered aluminumlite, and van shale.

[0014] The heat-insulating castable refractory material of the present invention contains a binder in addition to the above-mentioned refractory raw materials. Typically, alumina cement can be used as the binder. The amount of alumina cement used can be 5% to 20% by mass on the outside, relative to 100% by mass of the refractory raw materials, and from the viewpoint of ensuring heat insulation, it is preferable to use 10% to 15% by mass.

[0015] Furthermore, the heat-insulating castable refractory material of the present invention may contain additives in addition to the refractory raw materials described above. Examples of additives include dispersants, thickeners, surfactants, curing time adjusters, and spalling inhibitors.

[0016] The insulated castable refractory material described above is poured in after adding an appropriate amount of water. When pouring, the material can also be transported to the construction site by methods such as pumping. [Examples]

[0017] For each example shown in Table 1, 10% by mass of alumina cement was added as a binder to 100% by mass of the refractory raw material to create an insulating castable refractory material. An appropriate amount of water was added and mixed, then poured into a designated mold, cured and dried to obtain test specimens. The insulating properties and thermal expansion properties were then evaluated using these test specimens.

[0018]

Table 1

[0019] The evaluation of heat insulation property was carried out by measuring the thermal conductivity. The measurement of the thermal conductivity was carried out in accordance with JIS R 2616 "Test Method for Thermal Conductivity of Refractory Insulating Bricks". The dimensions of the test piece were 230×114×65 mm, and the measurement temperature was 800 °C. The evaluation criteria were that when the thermal conductivity was 1.0 W / (m·K) or less, it was rated as ○ (good), and when it exceeded 1.0 W / (m·K), it was rated as × (bad).

[0020] The evaluation of thermal expansibility was carried out by measuring the thermal expansion rate. The measurement of the thermal expansion rate was carried out in accordance with JIS R 2207-1 "Test Method for Thermal Expansion of Refractory Materials - Part 1: Non-contact Method". The dimensions of the test piece were 20×20×80 mm or 20×20×120 mm, and the heating rate was 4 °C / min. The evaluation criteria were that when the maximum value of the thermal expansion rate in the temperature range of 1000 °C or higher and 1400 °C or lower was 0% or more and 0.8% or less, it was rated as ○ (good), and when it exceeded 0.8% or was less than 0%, it was rated as × (bad).

[0021] In Table 1, Examples 1 to 7 are all insulating castable refractories within the scope of the present invention, and good evaluation results were obtained for both heat insulation property and thermal expansibility. In contrast, Comparative Example 1 is an example where the content rate of CA6 aggregate is lower than the lower limit value of the present invention, and the evaluation result of heat insulation property was poor. On the other hand, Comparative Example 2 is an example where the content rate of CA6 aggregate exceeds the upper limit value of the present invention, resulting in high expansion. Also, Comparative Example 3 is an example where the content rate of silica fine powder is lower than the lower limit value of the present invention, resulting in high expansion. On the other hand, Comparative Example 4 is an example where the content rate of silica fine powder exceeds the upper limit value of the present invention, resulting in excessive generation of liquid phase and shrinkage. Also, Comparative Example 5 is an example where the content rate of chamotte is lower than the lower limit value of the present invention, resulting in high expansion.

Claims

[Claim 1] As a refractory material, CaO·6Al ２ O ３ A heat-insulating castable refractory comprising CA6 aggregate with a particle size of 1 mm or more, silica fine powder with a particle size of less than 75 μm, and chamotte, A heat-insulating castable refractory material in which, as a percentage of 100% by mass of the refractory raw material, the CA6 aggregate content is 10% by mass or more and 60% by mass or less, the silica fine powder content is 5% by mass or more and 15% by mass or less, and the chamotte content is 10% by mass or more.

Images