Fired bricks for medium frequency furnaces and their preparation method and application

Abstract

The present invention provides a fired brick for a medium frequency furnace and its preparation method and application, which relate to the technical field of refractory materials. The fired brick for a medium frequency furnace is mainly made of mixed granular material, fired powder, activated alumina and aluminum fluoride solution, wherein the mixed granular material includes magnesium aluminum spinel particles and sintered corundum particles, and the fired powder is mainly obtained by firing matrix fine powders such as sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder; through the combination of the above raw materials, the prepared fired brick for a medium frequency furnace has high strength, high density, strong corrosion resistance, low thermal expansion coefficient and high thermal shock stability, and can replace amorphous dry materials for alloy smelting in a medium frequency furnace; in addition, the raw materials used in the present invention are common, easy to obtain, and low in price, which can effectively reduce the production cost of fired bricks for a medium frequency furnace. The present invention also provides a preparation method for the above-mentioned fired brick for a medium frequency furnace, the preparation process is simple, and the performance of the fired brick for a medium frequency furnace obtained is stable.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractory materials, and in particular relates to a fired brick for a medium frequency furnace and a preparation method and application thereof. Background Art

[0002] Medium frequency induction furnace (hereinafter referred to as medium frequency furnace) is widely used in the smelting of metals or alloys due to its advantages such as high melting efficiency, fast heating speed and simple furnace structure (Hu Deng, Zhang Han, Huang Xuezhong, et al., Effect of CaO addition on the performance of aluminum-magnesium dry ramming material for medium frequency furnace [J]. Refractories, 2023, 57(4): 347-350). Unlike other high-temperature kilns, the lining of medium frequency furnace is mostly made of amorphous dry material for ramming (without water combination) to form. The rapid heating characteristic of medium frequency furnace induction is used to achieve the purpose of rapid sintering of refractory lining, and the volume expansion of the lining material during the sintering process is combined to achieve the densification of the lining of the medium frequency furnace. In addition, the construction and removal of amorphous dry material are also relatively convenient.

[0003] At present, the lining refractory materials for alloy smelting medium frequency furnaces include three types of dry materials: alkaline, neutral and acidic, and there are also many related patent documents. Among them, the alkaline dry material is represented by magnesium, such as the Chinese patent application with application number 201811645498.1 and invention name "Configuration and sintering process of aluminum-magnesium dry ramming material for medium frequency furnace lining"; the neutral material dry material is represented by corundum, corundum spinel, aluminum-magnesium and other materials, such as the document "Research on the sintering properties of corundum dry ramming material for medium frequency induction furnace" (Xiao Guoqing, Liu Minsheng, Duan Feng, et al., Refractories, 2003, 37(1): 2 8-29+33), and the literature "The influence of the introduction of pre-synthesized spinel on the performance of aluminum-magnesium dry material" (Rao Kang, Wang Xitang, Wang Zhoufu, et al., Refractories, 2020, 54(3): 205-209) have studied this; and the acidic material is represented by SiO2 dry material, for example, the literature "Application of acidic dry furnace charge in medium frequency induction furnace" (Gao Liguang. Modern Cast Iron, 2009, 29(6): 54-56) reported on this. However, with the development of medium frequency furnace smelting technology, the service requirements for refractory linings have become more stringent. Traditional amorphous dry materials have the following major problems during construction and service:

[0004] (1) The sintering of amorphous dry materials for medium frequency furnace lining only occurs on the high-temperature working surface, that is, the sintering is dense near the high-temperature metal melt side, but there is still an unburned layer inside the dry material, which has a loose structure and low strength, resulting in poor sintering performance and low bonding strength of the dry material, affecting the integrity of the dry material for the medium frequency furnace lining.

[0005] (2) As the high-temperature metal is smelted, the eddy current of the melt continuously erodes the lining of the medium-frequency furnace during its rotation. Due to the low strength of the dry material, the amorphous dry material continuously peels off, is eroded and damaged, which reduces the service life of the dry material lining.

[0006] (3) The dry material in the lining of the medium frequency furnace is mainly metal oxides. During the migration to the metal melt, the inclusions in the alloy melt increase and the grade decreases.

[0007] (4) The amorphous dry materials used for the lining of the medium frequency furnace are mainly compacted by ramming during the construction process, resulting in a large amount of dust in the working environment and harsh working conditions.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of the present invention is to provide a fired brick for a medium frequency furnace and a preparation method and application thereof. The fired brick for a medium frequency furnace has the characteristics of high strength, high density, strong corrosion resistance, small thermal expansion coefficient and high thermal shock stability.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] The present invention provides a fired brick for a medium frequency furnace, which is mainly made of mixed granular material, fired powder, activated alumina and aluminum fluoride solution;

[0012] Wherein, the mixed particle material comprises the following raw materials: magnesium aluminum spinel particles and sintered corundum particles;

[0013] The calcined powder is mainly formed by calcining the following raw materials: sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder.

[0014] Furthermore, based on the above technical solution of the present invention, the particle size of the magnesia-alumina spinel particles is 0.1 to 5 mm;

[0015] And / or, the main chemical components and mass contents of the magnesia-alumina spinel particles are: MgO ≥ 25 wt %, Al 2 O 3 ≥ 72 wt %;

[0016] and / or, the particle size of the sintered corundum particles is 0.1 to 3 mm;

[0017] And / or, the main chemical composition and mass content of the sintered corundum particles are: Al2O3≥99wt%.

[0018] Furthermore, based on the above technical solution of the present invention, in the mixed particle material, the mass ratio of the magnesia-alumina spinel particles to the sintered corundum particles is (15-25):100.

[0019] Furthermore, based on the above technical solution of the present invention, the particle sizes of the sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder are independently ≤60 μm;

[0020] And / or, the mass ratio of the sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder is 100:(3-7):(4-8):(12-15).

[0021] Furthermore, based on the above technical solution of the present invention, the method for preparing the fired powder includes: mixing the sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder in proportion and firing them once, and crushing the obtained fired material to obtain fired powder.

[0022] Furthermore, based on the above technical solution of the present invention, the primary firing temperature is 1380-1420° C., and the primary firing temperature is kept at this temperature for 6-8 hours;

[0023] and / or, crushing the obtained calcined material to a particle size of 50 to 80 μm.

[0024] Furthermore, based on the above technical solution of the present invention, the mass ratio of the mixed granular material, the calcined powder and the activated alumina is 100: (40-60): (4-8);

[0025] and / or, the mass of the aluminum fluoride solution accounts for 5.5-6.5 wt% of the total mass of the mixed granular material, the calcined powder and the activated alumina;

[0026] And / or, the concentration of the aluminum fluoride solution is 0.8 to 1.5 mol / L.

[0027] The present invention also provides a method for preparing the fired bricks for the above-mentioned medium frequency furnace, comprising the following steps:

[0028] (a) mixing the mixed granular material, the calcined powder and the activated alumina to obtain a mixed material;

[0029] (b) The mixed material is mixed with aluminum fluoride solution and then pressed into shape. The obtained molding material is first heat-treated and then fired twice to obtain fired bricks for medium frequency furnaces.

[0030] Furthermore, based on the above technical solution of the present invention, in step (a), the mixing time is 25 to 30 minutes;

[0031] and / or, in step (b), the pressure of the compression molding is 100 to 120 MPa;

[0032] And / or, in step (b), the heat treatment temperature is 100-110° C., and the heat treatment time is 12-15 h;

[0033] And / or, in step (b), the secondary sintering temperature is 1400-1450° C., and the holding time at the secondary sintering temperature is 4-5 hours.

[0034] The present invention also provides the use of the fired bricks for the medium frequency furnace or the fired bricks for the medium frequency furnace prepared by the above-mentioned preparation method in a medium frequency furnace.

[0035] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0036] (1) The present invention provides a fired brick for a medium frequency furnace, which is mainly made of mixed granular material, fired powder, activated alumina and aluminum fluoride solution, wherein the mixed granular material includes magnesium aluminum spinel particles and sintered corundum particles, and the fired powder is mainly obtained by firing matrix fine powders such as sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder; through the combination of the above raw materials, the prepared fired brick for a medium frequency furnace has high strength, high density, strong corrosion resistance, low thermal expansion coefficient and high thermal shock stability, and can replace amorphous dry materials for alloy smelting in a medium frequency furnace. In addition, the raw materials used in the present invention are common and easy to obtain, and the price is low, which can effectively reduce the production cost of fired bricks for a medium frequency furnace.

[0037] (2) The present invention provides a method for preparing the fired bricks for the above-mentioned medium frequency furnace, which has a simple preparation process and the performance of the fired bricks for the medium frequency furnace obtained is stable.

[0038] (3) The present invention also provides the application of the fired bricks for medium frequency furnaces or the fired bricks for medium frequency furnaces obtained by the above-mentioned preparation method. In view of the advantages of the fired bricks for medium frequency furnaces, they have good application prospects in medium frequency furnaces. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0040] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0041] According to a first aspect of the present invention, there is provided a fired brick for a medium frequency furnace, which is mainly made of mixed granular material, fired powder, activated alumina and aluminum fluoride solution;

[0042] The mixed granular material includes the following raw materials: magnesium aluminum spinel particles and sintered corundum particles;

[0043] The sintered powder is mainly made by sintering the following raw materials: sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder.

[0044] In the present invention, the calcined powder is mainly formed by sintering sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder, wherein the sillimanite fine powder can form mullite microcrystals at high temperature, and form single-phase cordierite in situ with the magnesium-silicon components in the talc fine powder and forsterite fine powder, wherein the mother salt illusion produced by the high-temperature thermal dehydration of the talc fine powder plays an inductive role, and the clay fine powder can provide a liquid medium environment, and its high-temperature shrinkage can offset the volume expansion caused by reactions such as mullitization.

[0045] Activated alumina is mainly used to promote sintering and reduce the sintering temperature, and aluminum fluoride solution is mainly used to enhance bonding and volatilize at high temperature to promote the formation of whiskers.

[0046] The fired bricks for medium frequency furnaces provided by the present invention are mainly made of mixed granular materials, fired powder, activated alumina and aluminum fluoride solution, wherein the mixed granular materials include magnesia-alumina spinel particles and sintered corundum particles, and the fired powder is mainly obtained by firing matrix fine powders such as sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder; by utilizing the component design and in-situ reaction of the matrix fine powder (i.e., fired powder), a low expansion phase (such as cordierite, mullite, etc.) is generated, and then compounded with phase components such as spinel (magnesia-alumina spinel is also formed by the reaction of sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder), which significantly improves the performance of the intermediate frequency furnace. The thermal expansion coefficient of the material is reduced and the thermal shock resistance of the material is improved; by in-situ forming mullite whiskers and combining with two-step calcination to reduce the aspect ratio of the mullite whiskers, the development of the whiskers is promoted, the bonding strength between the spinel particle aggregate and the matrix (i.e., the fired powder) is improved, and the mechanical properties of the spinel fired brick are effectively improved; at the same time, the present invention combines the liquid medium environment in the MgO-Al2O3-SiO2 system to adjust the interface wettability between the spinel fired brick and the high-temperature melt, thereby improving its anti-stripping and erosion resistance, and combined with the high density of the fired brick, further enhances the material's ability to resist erosion by the high-temperature melt.

[0047] By combining various raw materials, the present invention produces fired bricks for medium-frequency furnaces that exhibit high strength, high density, strong corrosion resistance, low thermal expansion, and high thermal shock stability. These bricks can replace amorphous dry materials for alloy smelting in medium-frequency furnaces. Furthermore, the raw materials used in the present invention are readily available and inexpensive, effectively reducing the production cost of fired bricks for medium-frequency furnaces.

[0048] As an optional embodiment of the present invention, the particle size of the magnesium aluminum spinel particles is 0.1 to 5 mm; typical but non-limiting particle sizes are 0.1 mm, 0.5 mm, 1 mm, 2 mm, 4 mm or 5 mm.

[0049] As an optional embodiment of the present invention, the main chemical components and mass contents of the magnesia-alumina spinel particles are: MgO ≥ 25 wt %, Al 2 O 3 ≥ 72 wt %.

[0050] As an optional embodiment of the present invention, the particle size of the sintered corundum particles is 0.1 to 3 mm; typical but non-limiting particle sizes are 0.1 mm, 0.5 mm, 1 mm, 1.5 mm, 2 mm, 2.5 mm or 3 mm, etc.

[0051] As an optional embodiment of the present invention, the main chemical composition and mass content of the sintered corundum particles are: Al2O3≥99wt%.

[0052] As an optional embodiment of the present invention, in the mixed granular material, the mass ratio of magnesia-alumina spinel particles to sintered corundum particles is (15-25):100; typical but non-limiting mass ratios are 15:100, 18:100, 20:100, 22:100, 24:100 or 25:100, etc.

[0053] As an optional embodiment of the present invention, the particle sizes of the sillimanite fine powder, the talc fine powder, the forsterite fine powder and the clay fine powder are independently ≤60 μm.

[0054] As an optional embodiment of the present invention, the mass ratio of sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder is 100:(3-7):(4-8):(12-15); a typical but non-limiting mass ratio is 100:3:4:12, 100:5:4:12, 100:7:4:12, 100:3:5:12, 100:3:8:12, 100:3:4:14, 100:3:4:15, 100:4:5:13, 100:5:5:15 or 100:7:8:15, etc.

[0055] As an optional embodiment of the present invention, a method for preparing a calcined powder includes: mixing sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder in proportion, calcining the mixture once, and crushing the obtained calcined material to obtain a calcined powder.

[0056] The specific firing conditions for the sillimanite, talc, forsterite, and clay powders can be determined based on the physicochemical properties of each substance. As an optional embodiment of the present invention, the primary firing temperature is 1380-1420°C, and the material is held at the primary firing temperature for 6-8 hours. Typical but non-limiting primary firing temperatures are 1380°C, 1385°C, 1380°C, 1390°C, 1395°C, 1400°C, 1405°C, 1410°C, 1415°C, or 1420°C, and typical but non-limiting holding times are 6 hours, 6.5 hours, 7 hours, 7.5 hours, or 8 hours.

[0057] Since the particle size of the fired material obtained after the primary firing is relatively large, it needs to be crushed. The crushing can be carried out by a crushing method commonly used in the art, such as grinding.

[0058] The particle size of the pulverized fired material can be determined according to actual conditions. As an optional embodiment of the present invention, the pulverized fired material is pulverized to a particle size of 50 to 80 μm; typical but non-limiting particle sizes are 50 μm, 52 μm, 55 μm, 58 μm, 60 μm, 62 μm, 65 μm, 68 μm, 70 μm, 72 μm, 75 μm, 78 μm, or 80 μm.

[0059] As an optional embodiment of the present invention, the mass ratio of the mixed granular material, the sintered powder and the activated alumina is 100:(40-60):(4-8); typical but non-limiting mass ratios are 100:40:4, 100:45:4, 100:50:4, 100:55:4, 100:60:4, 100:40:5, 100:40:6, 100:40:8, 100:45:5, 100:50:5, 100:60:6, 100:60:7 or 100:60:8, etc.

[0060] As an optional embodiment of the present invention, the weight of the aluminum fluoride solution accounts for 5.5-6.5 wt% of the total weight of the mixed granular material, the calcined powder, and the activated alumina. Typical but non-limiting weight ratios are 5.5 wt%, 5.6 wt%, 5.8 wt%, 6.0 wt%, 6.2 wt%, 6.4 wt%, or 6.5 wt%.

[0061] As an optional embodiment of the present invention, the concentration of the aluminum fluoride solution (i.e., aluminum fluoride aqueous solution) is 0.8 to 1.5 mol / L, and a typical but non-limiting concentration is 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L or 1.5 mol / L, etc.

[0062] By further limiting the mass or concentration of the mixed granular material, sintered powder, activated alumina and aluminum fluoride solution, the integrity and dispersibility of the mixed material system are improved, which is conducive to the sintering of the material system.

[0063] As an optional embodiment of the present invention, it has been measured that the performance indicators of fired bricks for medium frequency furnaces are as follows: compressive strength is 85-95 MPa; apparent porosity is 13-17%; re-fired volume expansion rate is 0.22-0.35%; 1600℃×3h static crucible method slag resistance test erosion index is 1.7-2.6%; 1100℃ thermal shock resistance test residual strength retention rate (water cooling) is 82-85%.

[0064] Typical but non-limiting compressive strengths are 85 MPa, 86 MPa, 88 MPa, 90 MPa, 92 MPa, 94 MPa, or 95 MPa, etc. Typical but non-limiting apparent porosity is 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 15.8%, 16.0%, 16.5%, 16.8%, or 17%, etc. Typical but non-limiting refired volume expansion is 0.22%, 0.25%, 0.28%, 0.30%, 0.32%, 0.34%, or 0.35%, etc. Typical but non-limiting 1600°C × 3h static crucible slag corrosion resistance index is 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.4%, 2.5%, or 2.6%, etc. Typical but non-limiting 1100°C thermal shock resistance test residual strength retention (water cooling) is 82%, 82.5%, 83%, 83.5%, 84%, 84.5% or 85%.

[0065] According to a second aspect of the present invention, there is also provided a method for preparing the fired bricks for the intermediate frequency furnace, comprising the following steps:

[0066] (a) mixing the mixed granular material, the calcined powder and the activated alumina to obtain a mixed material;

[0067] (b) The mixed material is mixed with aluminum fluoride solution and then pressed into shape. The obtained molding material is then heat-treated and then fired twice to obtain fired bricks for medium frequency furnaces.

[0068] In the present invention, after the mixture is mixed with the aluminum fluoride solution and pressed into shape, it needs to be heat treated before being fired. The purpose of the heat treatment is to solidify the shape and remove moisture to prevent the product from cracking due to excessive moisture escape during firing.

[0069] The preparation process of the fired bricks for the medium frequency furnace is simple, and the prepared fired bricks for the medium frequency furnace have stable performance.

[0070] As an optional embodiment of the present invention, in step (a), the mixing time is 25 to 30 minutes; typical but non-limiting mixing time is 25 minutes, 26 minutes, 28 minutes or 30 minutes.

[0071] As an optional embodiment of the present invention, in step (b), the pressing pressure is 100-120 MPa; typical but non-limiting pressing pressures are 100 MPa, 102 MPa, 105 MPa, 108 MPa, 110 MPa, 112 MPa, 115 MPa, 118 MPa or 120 MPa, etc.

[0072] As an optional embodiment of the present invention, in step (b), the heat treatment temperature is 100-110°C, and the heat treatment time is 12-15h; a typical but non-limiting heat treatment temperature is 100°C, 102°C, 104°C, 105°C, 108°C or 110°C, and a typical but non-limiting heat treatment time is 12h, 12.5h, 13h, 13.5h, 14h, 14.5h or 15h, etc.

[0073] As an optional embodiment of the present invention, in step (b), the secondary firing temperature is 1400-1450°C, and the holding time at the secondary firing temperature is 4-5h; typical but non-limiting secondary firing temperatures are 1400°C, 1405°C, 1410°C, 1415°C, 1420°C, 1425°C, 1430°C, 1435°C, 1440°C, 1445°C or 1450°C, etc., and typical but non-limiting holding times are 4h, 4.5h or 5h, etc.

[0074] By further limiting the above process parameters, the secondary firing is complete, which is beneficial to the growth and development of mullite whiskers.

[0075] By selecting the material system and optimizing the preparation process, the fired bricks for the medium frequency furnace produced by the present invention have high strength, high density and excellent corrosion resistance and thermal shock resistance. The shaped fired products can be used instead of the amorphous dry materials for alloy smelting in the medium frequency furnace.

[0076] According to the third aspect of the present invention, there is also provided the use of the fired bricks for medium frequency furnaces or the fired bricks for medium frequency furnaces prepared by the above preparation method in medium frequency furnaces.

[0077] In view of the advantages of the above-mentioned fired bricks for medium frequency furnaces, they have good application prospects in medium frequency furnaces and can be used as lining materials for medium frequency furnaces, thereby effectively improving the service life of medium frequency furnaces.

[0078] The present invention will be described in further detail below with reference to specific examples and comparative examples. The particle sizes and compositions of the raw materials in the examples and comparative examples are described as follows:

[0079] The particle size of the magnesia-alumina spinel particles is 0.1-5 mm; the chemical composition and content of the magnesia-alumina spinel particles are: MgO≥25wt%, Al2O3≥72wt%.

[0080] The particle size of the sintered corundum particles is 0.1-3 mm; the chemical composition and content of the sintered corundum particles are: Al2O3≥99wt%.

[0081] The particle size of the sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder is 40 to 60 μm.

[0082] The particle size of the activated alumina fine powder is 20 to 40 μm; the chemical composition and content of the activated alumina fine powder are: Al2O3≥99.5wt%.

[0083] The concentration of the aluminum fluoride solution (i.e., aluminum fluoride aqueous solution) is 0.8 to 1.5 mol / L.

[0084] Example 1

[0085] This embodiment provides a medium frequency furnace fired brick, which is mainly made of mixed granular material, fired powder, activated alumina and aluminum fluoride solution;

[0086] The mixed granular material includes the following raw materials: magnesium aluminum spinel particles and sintered corundum particles, and the mass ratio of magnesium aluminum spinel particles to sintered corundum particles is 16:100;

[0087] The calcined powder is mainly made by calcining the following raw materials: sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder, and the mass ratio of sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder is 100:4:5:15;

[0088] The mass ratio of the mixed granular material, the calcined powder and the activated alumina is 100:42:5, the mass fraction of the aluminum fluoride solution to the mixture formed by the mixed granular material, the calcined powder and the activated alumina is 5.8wt%, and the concentration of the aluminum fluoride solution is 1.2mol / L.

[0089] The method for preparing bricks fired in a frequency furnace in this embodiment comprises the following steps:

[0090] (a) mixing magnesia-alumina spinel particles and sintered corundum particles in proportion for 20 minutes to prepare a mixed particle material;

[0091] (b) adding sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder into a blender and mixing for 45 minutes to prepare a mixed fine powder;

[0092] The mixed fine powder is placed in a high-temperature furnace for primary calcination at a temperature of 1390°C, kept at 1390°C for 6 hours, and then ground to 70 μm after cooling in the furnace to obtain calcined powder;

[0093] (c) adding the mixed granular material, the calcined powder, and the activated alumina fine powder into a blender in proportion and mixing for 30 minutes to prepare a mixture;

[0094] (d) Add 5.8 wt% of aluminum fluoride solution to the mixture, mix well and add to a mold, press and form at 120 MPa, and then heat treat the obtained molding material at a temperature of 110°C for 14 hours, and then perform a secondary firing at a temperature of 1450°C. Keep at 1450°C for 4 hours, and cool to room temperature with the furnace to obtain medium frequency furnace fired bricks.

[0095] Example 2

[0096] This embodiment provides a medium frequency furnace fired brick, which is mainly made of mixed granular material, fired powder, activated alumina and aluminum fluoride solution;

[0097] The mixed granular material includes the following raw materials: magnesium aluminum spinel particles and sintered corundum particles, and the mass ratio of magnesium aluminum spinel particles to sintered corundum particles is 22:100;

[0098] The calcined powder is mainly made by calcining the following raw materials: sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder, and the mass ratio of sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder is 100:6:8:13;

[0099] The mass ratio of the mixed granular material, the calcined powder and the activated alumina is 100:55:6, the mass fraction of the aluminum fluoride solution to the mixture formed by the mixed granular material, the calcined powder and the activated alumina is 6.5wt%, and the concentration of the aluminum fluoride solution is 1.0mol / L.

[0100] The method for preparing bricks fired in a frequency furnace in this embodiment comprises the following steps:

[0101] (a) mixing magnesia-alumina spinel particles and sintered corundum particles in proportion for 25 minutes to prepare a mixed particle material;

[0102] (b) adding sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder into a blender and mixing for 40 minutes to prepare a mixed fine powder;

[0103] The mixed fine powder is placed in a high-temperature furnace for primary sintering at a temperature of 1400°C, kept at 1400°C for 7 hours, and then ground to 50 μm after cooling to obtain sintered powder;

[0104] (c) adding the mixed granular material, the calcined powder, and the activated alumina fine powder into a blender in appropriate proportions and mixing for 25 minutes to prepare a mixture;

[0105] (d) Add 6.5 wt% of aluminum fluoride solution to the mixture, mix well and add to the mold, press and form at 100 MPa, and then heat treat the obtained molding material at 100 ° C for 15 hours, and then perform a secondary firing at 1430 ° C. Keep at 1430 ° C for 5 hours, and cool to room temperature with the furnace to obtain medium frequency furnace fired bricks.

[0106] Example 3

[0107] This embodiment provides a medium frequency furnace fired brick, which is mainly made of mixed granular material, fired powder, activated alumina and aluminum fluoride solution;

[0108] The mixed granular material includes the following raw materials: magnesium aluminum spinel particles and sintered corundum particles, and the mass ratio of magnesium aluminum spinel particles to sintered corundum particles is 18:100;

[0109] The calcined powder is mainly made by calcining the following raw materials: sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder, and the mass ratio of sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder is 100:7:6:12;

[0110] The mass ratio of the mixed granular material, the calcined powder and the activated alumina is 100:50:4, the mass fraction of the aluminum fluoride solution to the total mass of the mixed granular material, the calcined powder and the activated alumina is 6.2wt%, and the concentration of the aluminum fluoride solution is 0.8mol / L.

[0111] The method for preparing bricks fired in a frequency furnace in this embodiment comprises the following steps:

[0112] (a) mixing magnesia-alumina spinel particles and sintered corundum particles in proportion for 23 minutes to prepare a mixed granular material;

[0113] (b) adding sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder into a blender and mixing for 50 minutes to prepare a mixed fine powder;

[0114] The mixed fine powder is placed in a high-temperature furnace for primary calcination at a temperature of 1385°C, kept at 1385°C for 7 hours, and then ground to 65 μm after cooling in the furnace to obtain calcined powder;

[0115] (c) adding the mixed granular material, the calcined powder, and the activated alumina fine powder into a blender in appropriate proportions and mixing for 28 minutes to prepare a mixture;

[0116] (d) Aluminum fluoride solution accounting for 6.2 wt% of the mixture is added to the mixture, mixed evenly and added to a mold, and pressed into shape at 110 MPa. The obtained molding material is then heat-treated at a temperature of 105°C for 12 hours, and then fired for the second time at a temperature of 1420°C. The mixture is kept at 1420°C for 4 hours, and then cooled to room temperature with the furnace to obtain medium frequency furnace fired bricks.

[0117] Example 4

[0118] This embodiment provides a medium frequency furnace fired brick and a preparation method thereof. Except that the mass ratio of mixed granular material, fired powder and activated alumina is replaced from 100:42:5 to 100:60:5, the remaining raw materials, types and preparation methods are the same as those in Example 1.

[0119] Example 5

[0120] This embodiment provides a medium frequency furnace fired brick and a preparation method thereof. Except that the mass of the aluminum fluoride solution is adjusted from 6.5wt% to 5.5wt% of the total mass of the mixed granular material, fired powder and activated alumina, the remaining raw materials, types and preparation methods are the same as those in Example 2.

[0121] Comparative Example 1

[0122] This comparative example provides a medium frequency furnace fired brick and its preparation method. Except that the fired powder is replaced by a mixed fine powder of sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder (i.e., without a single firing treatment), the other raw materials and types are the same as those in Example 2.

[0123] The method for preparing the bricks fired in the medium frequency furnace of this comparative example comprises the following steps:

[0124] (a) The same as step (a) of Example 2;

[0125] (b) adding sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder into a blender and mixing for 40 minutes to prepare a mixed fine powder;

[0126] (c) adding the mixed granular material, the mixed fine powder material, and the activated alumina fine powder into a blender in proportion and mixing for 25 minutes to prepare a mixture;

[0127] (d) The same as step (d) in Example 2.

[0128] Comparative Example 2

[0129] This comparative example provides a medium frequency furnace fired brick and its preparation method. Except that no talc powder is added to the raw materials of the fired powder and no talc powder is added in the corresponding step (b) of the preparation method, the remaining raw materials, types and preparation methods are the same as those in Example 2.

[0130] Comparative Example 3

[0131] This comparative example provides a medium frequency furnace fired brick and its preparation method. Except that no clay fine powder is added to the raw materials of the fired powder and no clay fine powder is added in the corresponding step (b) of the preparation method, the remaining raw materials, types and preparation methods are the same as those in Example 2.

[0132] Comparative Example 4

[0133] This comparative example provides a medium frequency furnace fired brick and its preparation method. Except that no aluminum fluoride solution is added to the raw materials and no aluminum fluoride solution is added in the corresponding step (d) of the preparation method, the remaining raw materials, types and preparation methods are the same as those in Example 2.

[0134] Comparative Example 5

[0135] This comparative example provides a medium frequency furnace fired brick and its preparation method. Except that in step (d) of the preparation method, the obtained molding material is not heat-treated but directly subjected to secondary firing, the remaining raw materials, types and preparation methods are the same as those in Example 2.

[0136] In order to further verify the technical effects of the above embodiments and comparative examples, the following experimental examples are specially set up.

[0137] Experimental Example 1

[0138] The properties of the medium-frequency furnace-fired bricks provided in each embodiment and comparative example were tested. Compressive strength was tested in accordance with GB / T 5072-2008, apparent porosity was tested in accordance with GB / T 2997-2015, refired volume expansion was tested in accordance with GB / T 5998-2022, erosion index was tested in a 1600°C × 3h static crucible method slag resistance test in accordance with GB / T 8931-2007, and residual strength retention (water-cooled) in a 1100°C thermal shock resistance test in accordance with GB / T 30873-2014. The specific test results are shown in Table 1.

[0139] Table 1

[0140]

[0141] As shown in Table 1 and the experimental data above, the embodiments of the present invention are superior to the comparative examples in terms of performance in all aspects.

[0142] Specifically, Comparative Example 1 is a comparative experiment of Example 2. By comparing the two, it can be seen that the sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder are first calcined to form a calcined powder, in which low-expansion cordierite and mullite can be formed, and the material system is stabilized; if the fine powders are directly mixed without calcination, no low-expansion phase will be produced, and the material will have poor high-temperature volume stability and will be prone to cracking, or a liquid phase will be formed, which will impair the high-temperature performance of the material.

[0143] Comparative Examples 2-5 are also comparative experiments of Example 2. It can be seen from the above data that the decomposition and dehydration of talc fine powder can play a significant inductive role, promote the formation of cordierite, and thus reduce the expansion of the material. At the same time, the compressive strength, erosion resistance and thermal shock resistance of the material are also improved to a certain extent; the liquid medium condition and shrinkage effect of the clay fine powder are conducive to the mullitization reaction, significantly improving the mechanical strength of the material, while also helping to improve the erosion resistance and thermal shock resistance of the material, reducing the expansion of the material; and the introduction of aluminum fluoride solution provides a gas phase condition at high temperature, accelerating the growth of mullite whiskers, not only improving the thermal shock resistance of the material, but also improving the compressive strength and erosion resistance of the material, and the re-fired volume expansion rate of the material is also significantly reduced; under the condition of no heat treatment, the bonding performance of the material is significantly reduced, the volume stability is weakened, resulting in a significant increase in the re-fired volume expansion rate.

[0144] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A fired brick for a medium frequency furnace, characterized in that: It is mainly made of mixed granular materials, calcined powder, activated alumina and aluminum fluoride solution; Wherein, the mixed particle material comprises the following raw materials: magnesium aluminum spinel particles and sintered corundum particles; The calcined powder is mainly formed by calcining the following raw materials: sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder; The mass ratio of the magnesia-alumina spinel particles to the sintered corundum particles is (15-25):100; The mass ratio of the sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder is 100: (3-7): (4-8): (12-15); The mass ratio of the mixed granular material, the calcined powder and the activated alumina is 100: (40-60): (4-8); The mass of the aluminum fluoride solution accounts for 5.5-6.5wt% of the total mass of the mixed granular material, calcined powder and activated alumina; The concentration of the aluminum fluoride solution is 0.8 to 1.5 mol / L; The method for preparing fired bricks for medium frequency furnaces comprises the following steps: (a) mixing the mixed granular material, the calcined powder and the activated alumina to obtain a mixed material; (b) mixing the mixed material with the aluminum fluoride solution and then pressing and molding the obtained molding material, first heat-treating the obtained molding material, and then performing secondary firing to obtain fired bricks for the medium frequency furnace; In the step (b), the heat treatment temperature is 100-110° C., and the heat treatment time is 12-15 hours.

2. The fired brick for medium frequency furnace according to claim 1, characterized in that: The particle size of the magnesia-alumina spinel particles is 0.1 to 5 mm; And / or, the main chemical components and mass contents of the magnesia-alumina spinel particles are: MgO ≥ 25 wt %, Al 2 O 3 ≥ 72 wt %; and / or, the particle size of the sintered corundum particles is 0.1 to 3 mm; And / or, the main chemical composition and mass content of the sintered corundum particles are: Al2O3≥99wt%.

3. The fired brick for medium frequency furnace according to claim 1, characterized in that: The particle sizes of the sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder are independently ≤60 μm.

4. The fired brick for medium frequency furnace according to claim 1, characterized in that: The method for preparing the fired powder comprises: mixing the sillimanite fine powder, talc fine powder, forsterite fine powder and clay fine powder in proportion, firing the mixture once, and crushing the obtained fired material to obtain the fired powder.

5. The fired brick for medium frequency furnace according to claim 4, characterized in that: The primary firing temperature is 1380-1420°C, and the primary firing temperature is kept at this temperature for 6-8 hours; and / or, crushing the obtained calcined material to a particle size of 50 to 80 μm.

6. The fired brick for medium frequency furnace according to claim 1, characterized in that: In step (a), the mixing time is 25 to 30 minutes; and / or, in step (b), the pressure of the compression molding is 100 to 120 MPa; And / or, in step (b), the secondary sintering temperature is 1400-1450° C., and the holding time at the secondary sintering temperature is 4-5 hours.

7. Use of the fired bricks for medium frequency furnaces according to any one of claims 1 to 6 in medium frequency furnaces.

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