Manufacturing method of magnesia-spinel bricks

Abstract

To provide a method for manufacturing a magnesia-spinel brick excellent in both coating adhesion and stability while maintaining compressive strength and slag erosion resistance.SOLUTION: A method for producing a magnesia-spinel brick includes: a first step of mixing a compound to obtain kneaded clay; a second step of forming the kneaded clay to obtain a formed body; and a third step of firing the formed body to obtain a magnesia-spinel brick, wherein: the compound includes a refractory raw material and a binder; the refractory raw material contains 5 to 50 mass% of particles having a particle size of 0.3 mm or less; the refractory raw material includes a magnesia raw material and a spinel raw material; and the refractory raw material contains 5 mass% or more of the magnesia raw material having an apparent porosity of 3 vol.% or more and a pore diameter of 10 μm or less of 20 vol.% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing magnesia-spinel bricks for use in cement rotary kilns and the like. [Background technology]

[0002] The bricks used in the burning zone of a cement rotary kiln are subject to reduced corrosion and improved durability due to the formation of a protective layer called a "coating" during the burning of cement clinker. The coating is formed when the low-to-medium melting point phase (liquid phase) of the cement clinker near the working surface of the brick infiltrates the pores inside the brick, cools, and solidifies.

[0003] For example, Patent Document 1 discloses a basic refractory containing 80 to 99 mass% magnesia clinker, 0.5 to 10 mass% spinel clinker, and 0.5 to 10 mass% zirconia raw material. This basic refractory uses magnesia as the main raw material and contains appropriate amounts of spinel clinker and zirconia raw material, thereby improving spalling resistance, corrosion resistance, and coating adhesion. That is, the difference in thermal expansion coefficient from magnesia generates microcracks inside the brick, thereby improving spalling resistance. Furthermore, the zirconia raw material increases the viscosity of the liquid phase generated when it reacts with the cement raw material, thereby improving corrosion resistance and coating adhesion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-250313 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the basic refractory of Patent Document 1 is operated at a higher firing temperature, cracks increase, reducing compressive strength and slag erosion resistance. Furthermore, the applied coating becomes more likely to peel off due to the cracks, reducing the stability of the coating.

[0006] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a method for producing magnesia-spinel bricks that maintain compressive strength and slag erosion resistance while also achieving excellent coating adhesion and stability. [Means for solving the problem]

[0007] (1) One aspect of the present disclosure is A first step of mixing the composition to obtain a mortar; A second step of molding the mortar to obtain a molded body; and a third step of firing the green body to obtain a magnesia-spinel brick, The formulation includes a refractory raw material and a binder; The refractory raw material contains 5 to 50 mass% of particles having a particle size of 0.3 mm or less, the refractory raw material includes a magnesia raw material and a spinel raw material, The present invention relates to a method for producing magnesia-spinel bricks, characterized in that the refractory raw material contains 5 mass % or more of the magnesia raw material having an apparent porosity of 3 volume % or more and a pore diameter of 10 μm or less of 20 volume % or more.

[0008] In one embodiment of the method for producing magnesia-spinel bricks according to the present disclosure, the refractory raw material contains 5 to 50% by mass of particles with a particle size of 0.3 mm or less, and further contains 5% by mass or more of the magnesia raw material having an apparent porosity of 3% by volume or more and 20% by volume or more of pores with a diameter of 10 μm or less. This allows the production of magnesia-spinel bricks that maintain compressive strength and slag erosion resistance while also achieving excellent coating adhesion and stability. This is believed to be because the medium-low melting point phase of cement clinker preferentially infiltrates the fine pores of the magnesia-spinel bricks, improving coating adhesion. Furthermore, the magnesia raw material acts as an anchor for the coating, improving coating adhesion and stability.

[0009] In one embodiment of the present disclosure, the molded body is preferably fired at 1400 to 2000° C. in the third step, which improves the spalling resistance of the magnesia-spinel brick. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present disclosure will be described in detail below. Note that the embodiments described below do not unduly limit the content of the present disclosure described in the claims, and not all of the configurations described in the embodiments are necessarily essential as means for solving the problems of the present disclosure.

[0011] A detailed investigation of bricks used in the burning zone of a cement rotary kiln revealed the following findings regarding the adhesion mechanism of the coating. 1. The low-to-medium melting point phase (liquid phase) of cement clinker near the working surface of the brick infiltrates through the pores inside the brick. 2. The low and medium melting point phases in the cement clinker near the working surface of the brick decrease, and sintering progresses. 3. The temperature inside the brick decreases from the working surface to the back (from the inside to the outside of the cement rotary kiln), so the low- and medium-melting-point phase becomes a solid phase at a certain position inside the brick. 4. The temperature inside the brick decreases due to the insulating effect of the cement clinker that has been sintered near the working surface of the brick, and the position where the medium-low melting point phase becomes solid approaches the working surface of the brick. 5. The solid phase inside the brick acts as an anchor for the coating near the working surface, like the roots of a plant, improving the adhesion and stability of the coating.

[0012] The pores inside the bricks range in diameter from approximately 10 μm to over 100 μm. It was found that the medium-low melting point phase penetrates into the bricks mainly through fine pores with a diameter of approximately 10 μm. This is thought to be due to capillary action. Therefore, we came up with the idea that to penetrate the medium-low melting point phase into the bricks and improve the adhesion and stability of the coating, we should create an appropriate proportion of fine pores with a diameter of approximately 10 μm. As a result of our investigations using various magnesia raw materials, we arrived at a manufacturing method for magnesia-spinel bricks that maintains compressive strength and slag erosion resistance while also achieving excellent coating adhesion and stability.

[0013] The method for producing magnesia-spinel bricks of this embodiment includes a first step of mixing a compound to obtain a mortar, a second step of molding the mortar to obtain a green body, and a third step of firing the green body to obtain a magnesia-spinel brick, wherein the compound includes a refractory raw material and a binder, and the refractory raw material contains 5 to 50 mass% of particles with a particle size of 0.3 mm or less, a magnesia raw material and a spinel raw material, and the refractory raw material contains 5 mass% or more of magnesia raw material with an apparent porosity of 3 vol% or more and 20 vol% or more of pores with a diameter of 10 μm or less.

[0014] In the method for producing magnesia-spinel bricks of this embodiment, the refractory raw material contains 5 to 50 mass% of particles with a particle size of 0.3 mm or less, and further contains 5 mass% or more of the magnesia raw material with an apparent porosity of 3 volume% or more and 20 volume% or more of pores with a diameter of 10 μm or less. This allows the production of magnesia-spinel bricks that maintain compressive strength and slag erosion resistance while also achieving excellent coating adhesion and stability. This is thought to be because the medium-low melting point phase of cement clinker preferentially infiltrates the fine pores of the magnesia-spinel bricks, improving coating adhesion. Furthermore, the magnesia raw material acts as an anchor for the coating, improving coating adhesion and stability.

[0015] The compound of this embodiment contains refractory raw materials and a binder, and may contain additives as necessary. In this specification, the refractory raw materials refer to raw materials that constitute the magnesia-spinel brick obtained by firing, excluding components that will be lost during firing in the third step. However, in the case of inorganic binders, as described below, even if they do not lose their constituents during firing and form magnesia-spinel bricks, they are not included in the refractory raw materials.

[0016] The refractory raw material of this embodiment contains particles having a particle size of 0.3 mm or less in an amount of 5 to 50 mass %, preferably 10 to 45 mass %, and more preferably 15 to 40 mass %, which is thought to increase the penetration of the medium-to-low melting point phase into the magnesia-spinel brick, stabilize the anchor of the coating, and improve the adhesion and stability of the coating.

[0017] The refractory raw material of this embodiment includes a magnesia raw material and a spinel raw material, and may include an alumina raw material or other refractory raw materials as needed.

[0018] <Magnesia raw material> The refractory raw material of this embodiment contains 5% by mass or more, preferably 10 to 93% by mass, and more preferably 20 to 85% by mass of magnesia raw material having an apparent porosity of 3% by volume or more and a pore size of 10 μm or less of 20% by volume or more. The magnesia raw material is not particularly limited as long as it is one generally used in refractories, and examples include burned magnesia such as heavy-burned magnesia and dead-burned magnesia. When the magnesia raw material having an apparent porosity of 3% by volume or more and a pore size of 10 μm or less of 20% by volume or more is 5% by mass or more, it is thought that infiltration of the medium-low melting point phase into the magnesia particles is increased, the anchoring of the coating is stabilized, and the adhesion and stability of the coating are improved.

[0019] The refractory raw material of this embodiment may be used in combination with a magnesia raw material generally used for magnesia-spinel bricks, and examples of the magnesia raw material to be used in combination include natural magnesia, electrofused magnesia, etc. The total content of the magnesia raw materials is preferably 60% by mass or more and less than 90% by mass of the refractory raw material.

[0020] <Spinel raw material> The chemical composition of the spinel raw material is preferably 90% by mass or more, more preferably 98% by mass or more, in total of MgO and Al2O3, and preferably 40 to 75% by mass of Al2O3. When Al2O3 is 40% by mass or more, the amount of Al2O3-MgO spinel crystal increases, and when it is 75% by mass or less, the thermal expansion coefficient decreases. As the spinel raw material, one or both of a sintered product and an electrofused product can be used. The content of the spinel raw material is preferably 3 to 45% by mass of the refractory raw material. When it is 3% by mass or more, spalling resistance is improved, and when it is 40% by mass or less, slag erosion resistance is improved.

[0021] <Alumina raw material> The refractory raw material of this embodiment may contain an alumina raw material to improve spalling resistance. The alumina raw material is not particularly limited as long as it is an alumina raw material generally used for refractories, and examples thereof include white fused alumina, brown fused alumina, sintered alumina, and calcined alumina, each containing 95 mass % or more of AlO.

[0022] <Other refractory materials> The other refractory raw materials are not particularly limited as long as they are generally used for refractories. For example, a zirconia raw material may be used to improve wettability with semi-molten cement and improve coating adhesion.

[0023] <Binder> The binder used in this embodiment may be an organic binder or an inorganic binder. Examples of the organic binder include pitch, phenolic resin, molasses, pulp waste liquor, dextrin, methylcelluloses, and polyvinyl alcohol.

[0024] <First step> The compound is mixed using a general mixer, either a fixed-container or a driven-container type. A predetermined amount of water may be added as needed. The mixing time is adjusted depending on the type and content of the refractory raw material, the type and content of the binder, the air temperature, the temperature of the compound, the type and size of the mixer, etc., but is usually several minutes to several hours. The mixer may be equipped with a pressure or pressure reduction device, a temperature control device, etc.

[0025] <Second process> The obtained kneaded clay is molded in a molding machine such as a friction press. The molding machine may be equipped with a pressure or pressure reducing device, a temperature control device, etc. The molding pressure and number of clamping times are adjusted depending on the size of the molded body, the type and content of the refractory raw material, the type and content of the binder, the air temperature, the temperature of the compound, etc., the type and size of the molding machine, etc.

[0026] <Third process> The firing temperature is preferably 1400 to 2000°C, more preferably 1500 to 1850°C. At 1400°C or higher, sufficient strength is obtained and spalling resistance is improved. At 2000°C or lower, sintering proceeds moderately, spalling resistance is improved, and the brick shape can be maintained. [Example]

[0027] Hereinafter, examples of the present disclosure will be described in detail.

[0028] First, the following measurements were carried out on the two types of magnesia raw materials A and B used.

[0029] <Chemical analysis> The chemical composition was measured in accordance with JIS R 2216 (fluorescent X-ray analysis method for refractory products).

[0030] <Apparent porosity> The magnesia raw materials A and B were sieved to have particle sizes of 3 to 2 mm, and the apparent porosity was measured in accordance with JIS R 2205 (method for measuring apparent porosity, water absorption, and specific gravity).

[0031] <Pore size distribution> The magnesia raw materials A and B were sieved to have particle sizes of 3 to 2 mm, and the pore size distribution was measured in accordance with JIS R 1655 (molded body pore size distribution test by mercury intrusion method).

[0032] The results of the above measurements, that is, the chemical compositions of magnesia raw materials A and B, the apparent porosity, and the proportion of pores with a diameter of 10 μm or less, are shown in Table 1. [Table 1]

[0033] Magnesia raw material A had an apparent porosity of 3% by volume or more and a proportion of pores with a pore diameter of 10 μm or less of 20% by volume or more, whereas magnesia raw material B had a low apparent porosity of 0.9% and a proportion of pores with a pore diameter of 10 μm or less of less than 20% by volume. In particular, magnesia raw material A had a proportion of pores with a pore diameter of 5 μm or less of 36% by volume.

[0034] Next, a mixture containing refractory raw materials and a binder was mixed to obtain a mixture. The mixture was then molded into a green body, which was then fired to obtain a magnesia-spinel brick. The binder used was a novolac-type phenolic resin solution (resin content: 60% by mass) with a 3% outer weight ratio relative to the refractory raw materials. The molding conditions were 118 MPa and eight strokes using a hydraulic press to obtain a green body measuring 115 mm x 65 mm x 80 mm. The green body was dried at 200°C for 24 hours and then fired in an electrically heated box-type electric furnace. The firing conditions were to hold the temperature at 1700°C for 10 hours, then cool to 500°C at a rate of 5°C / min, and then allow it to cool naturally in the electric furnace.

[0035] The composition of the refractory raw materials is shown in Table 2. Examples 1 to 11 contain 5 mass% or more of magnesia raw material A having an apparent porosity of 3 volume% or more and a pore size of 10 μm or less of 20 volume% or more, while Comparative Example 1 does not contain magnesia raw material A. Furthermore, Examples 1 to 11 contain 5 to 50 mass% of particles having a particle size of 0.3 mm or less, while Comparative Example 2 contains more than 50 mass% of particles having a particle size of 0.3 mm or less. Example 1 has a low content of magnesia raw material A (6 mass%). Example 4 has a high content of refractory raw materials having a particle size of 0.3 mm or less (42 mass%). Example 9 has a low content of refractory raw materials having a particle size of 0.3 mm or less (12 mass%). Example 10 has a high content of Al2O3 in the chemical composition (24.1 mass%).

[0036] The following measurements were carried out on the obtained magnesia-spinel bricks.

[0037] <Chemical analysis> The chemical composition was measured in accordance with JIS R 2216 (fluorescent X-ray analysis method for refractory products).

[0038] <Compression strength> The compressive strength of magnesia-spinel bricks cut into cubes with sides of 60 mm was measured at room temperature in accordance with JIS R 2206 (testing method for compressive strength of refractory bricks).

[0039] <Slag erosion resistance> Slag corrosion resistance was measured using a rotating drum corrosion test. Heating was performed using oxygen and propane, and commercially available Portland cement was used as the corrosion agent. The test was carried out at 1750°C for 5 hours, with the corrosion agent being replaced every hour. After the test, the magnesia-spinel bricks were cut lengthwise, the amount of corrosion measured, and the corrosion index calculated using the formula below to index the slag corrosion resistance. The smaller the corrosion index, the smaller the amount of wear and the higher the slag corrosion resistance. Erosion index = amount of erosion in each rotating drum erosion test ÷ amount of erosion in Example 6 × 100

[0040] <Coating adhesion> Coating adhesion was measured using the button method. The coating material was molded into pellets 30 mm in diameter and 30 mm in height and placed on a 50 mm cube of magnesia-spinel brick. The temperature was raised to 1500°C at a rate of 5°C / min in a box-type electric furnace, held at 1500°C for 1 hour, allowed to cool naturally in the furnace, and the specimen was removed. Each coating material was tested three times to determine whether the pellets adhered to the specimen. Coating adhesion was evaluated as excellent (◎) if three adhesions occurred, good (〇) if two adhesions occurred, fair (△) if one adhesion occurred, and poor (×) if no adhesions occurred. The coating material used was a mixture of Portland cement and 4CaO·Al2O3·SiO2 compound in a mass ratio of 8:2.

[0041] <Coating stability> Magnesia-spinel bricks were cut into cubes with sides of 50 mm and heated for 15 minutes in a box-type electric furnace preheated to 1400°C, then removed from the furnace and allowed to cool naturally for 15 minutes. This process was repeated three times to give the specimens thermal shock, and the same button test was performed on the specimens to evaluate coating adhesion. Coating stability was evaluated as excellent (◎) when adhesion occurred three times, good (〇) when adhesion occurred two times, fair (△) when adhesion occurred one time, and poor (×) when adhesion occurred zero times.

[0042] <Evaluation results> The results of the above measurements are shown in Table 2. [Table 2]

[0043] Examples 1 to 11, which contained 5% by mass or more of magnesia raw material A with an apparent porosity of 3% by volume or more and 20% by volume or more of pores 10 μm or less, and the refractory raw material contained 5 to 50% by mass of particles with a particle size of 0.3 mm or less, all achieved excellent results in both coating adhesion and stability while maintaining compressive strength and slag erosion resistance. On the other hand, Comparative Example 1, which did not contain magnesia raw material A, showed poor coating adhesion and stability, and Comparative Example 2, which contained a refractory raw material with more than 50% by mass of particles with a particle size of 0.3 mm or less, showed a significant loss of thermal shock resistance and poor coating stability.

[0044] In Example 1, the coating adhesion was good, but the coating stability was slightly reduced. This is thought to be because the amount of magnesia raw material A was only 6% by mass, which resulted in little penetration of the medium-low melting point phase into the interior of the brick. Therefore, the content of magnesia raw material A with an apparent porosity of 3% by volume or more and pore diameters of 10 μm or less of 20% by volume or more is 5% by mass or more, preferably 10 to 93% by mass, and more preferably 20 to 85% by mass.

[0045] Example 4 had excellent compressive strength and coating adhesion, but slightly reduced coating stability. This is thought to be because the refractory raw material contained a large amount of refractory raw material with a particle size of 0.3 mm or less, which led to the progression of sintering and reduced thermal shock resistance. Example 9 had good coating adhesion, despite the low content of refractory raw material with a particle size of 0.3 mm or less. This is thought to be because, although there were few pores with a diameter of about 10 μm inside the brick, the content of magnesia raw material A was sufficient, which promoted the infiltration of the medium-low melting point phase into the brick interior. Therefore, the content of refractory raw material with a particle size of 0.3 mm or less is 5 to 50 mass%, preferably 10 to 45 mass%, and more preferably 15 to 40 mass%.

[0046] Although the slag corrosion resistance (corrosion index) of Example 10 was slightly reduced, the adhesion and stability of the coating were excellent. This is thought to be due to the promotion of infiltration of the low-to-medium melting point phase by Al2O3.

[0047] Although the present embodiment has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and advantages of the present disclosure. Therefore, all such modifications are included within the scope of the present disclosure. For example, a term described at least once in the specification together with a different term having a broader or equivalent meaning may be replaced with that different term anywhere in the specification. Furthermore, the configuration and operation of the manufacturing apparatus and the like of the present embodiment are not limited to those described in the present embodiment, and various modifications are possible.

Claims

1. A first step of mixing the composition to obtain a mortar; A second step of molding the mortar to obtain a molded body; a third step of firing the compact to obtain a magnesia-spinel brick, The formulation includes a refractory raw material and a binder; The refractory raw material contains 5 to 50 mass% of particles having a particle size of 0.3 mm or less, the refractory raw material includes a magnesia raw material and a spinel raw material, The content of the magnesia raw material is 54% by mass or more and less than 90% by mass of the refractory raw material, the content of the spinel raw material is 3 to 45 mass% based on the refractory raw material, a total content of the magnesia raw material and the spinel raw material is 95% by mass or more relative to the refractory raw material; 1. A method for producing a magnesia-spinel brick, wherein the refractory raw material contains 5% by mass or more of the magnesia raw material having an apparent porosity of 3% by volume or more and 20% by volume or more of pores with diameters of 10 μm or less.

2. 2. The method for producing magnesia-spinel bricks according to claim 1, A method for producing magnesia-spinel bricks, characterized in that in the third step, the green body is fired at 1400 to 2000°C.

3. A method for producing magnesia-spinel bricks according to claim 1 or 2, 1. A method for producing magnesia-spinel bricks, wherein the refractory raw material contains an alumina raw material and / or a zirconia raw material as other refractory raw materials.

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