Anti-erosion magnesium aluminate spinel prefabricated brick for rotary hearth furnace and preparation method of anti-erosion magnesium aluminate spinel prefabricated brick

Abstract

The invention discloses an anti-erosion magnesium aluminate spinel prefabricated brick for a rotary hearth furnace and a preparation method thereof, and relates to the technical field of refractory materials, the anti-erosion magnesium aluminate spinel prefabricated brick comprises the following raw materials by mass fraction: 23-27% of fused magnesite particles with a particle size of 3-5mm, 10-20% of fused magnesite particles with a particle size of 1-3mm, 13-15% of fused magnesite fine powder with a particle size of less than or equal to 0.088 mm, 10-20% of magnesium oxide fine powder with a particle size of less than or equal to 0.088 mm, and the balance of water. The raw materials comprise 10-18% of sintered tabular corundum particles with a particle size of 1-3 mm, 8-15% of sintered tabular corundum fine powder with a particle size of less than or equal to 0.044 mm, 5-12% of pre-synthesized magnesium aluminate spinel fine powder with a particle size of less than or equal to 0.044 mm, and 2-5% of active alumina micro powder with a particle size distribution D50 of less than or equal to 5 [mu] m; the anti-explosion concrete further comprises 1%-3% of zircon sand powder, 1%-3% of SiAlON fine powder, 1%-3% of a sintering agent, 3%-5% of a composite binding agent, 0.1%-0.3% of a water reducing agent and 0.05%-0.1% of anti-explosion fibers. Wherein the composite binding agent is a mixture of thermosetting phenolic resin and rho-Al2O3 in a weight ratio of (2-4): 1. The prefabricated brick prepared by the invention can realize the optimal balance of slag corrosion resistance and thermal shock resistance, has the characteristics of high strength and low porosity, can be directly used as a prefabricated part for installation and use, and greatly shortens the maintenance period.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to an anti-erosion magnesium aluminate spinel precast brick for rotary hearth furnaces and its preparation method. Background Technology

[0002] Rotary hearth furnaces are key equipment for processing metallurgical dust, iron-containing waste, and producing direct reduced iron, playing a vital role in the green recycling of the steel industry. However, the operating environment of rotary hearth furnaces is extremely harsh, with the furnace lining materials simultaneously subjected to multiple stresses: First, chemical erosion: intense chemical erosion and penetration from the FeO-rich alkaline slag formed after the metallurgical dust melts; Second, thermal shock damage: the intermittent or semi-continuous operation of rotary hearth furnaces causes the furnace lining material to undergo frequent rapid heating and cooling, easily leading to spalling and structural damage; Third, mechanical wear: the movement of the furnace charge and mechanical operations cause physical wear on the hearth and furnace lining materials.

[0003] Currently, commonly used refractory materials for rotary hearth furnaces, such as high-alumina bricks and magnesia bricks, have significant shortcomings: high-alumina bricks have poor resistance to alkaline slag erosion and are prone to forming low-melting-point compounds, leading to structural damage; while magnesia bricks have strong resistance to alkaline slag, their thermal shock stability is extremely poor, and they are very prone to cracking and spalling under temperature fluctuations. Magnesia-alumina spinel (MgAl2O4) is considered an ideal alternative due to its excellent slag erosion resistance and thermal shock stability.

[0004] However, traditional magnesia-alumina spinel bricks or castable refractory materials have the following problems: the thermal shock stability of sintered products still has room for improvement, and they are difficult to manufacture into large, irregularly shaped components; the construction cycle for in-situ casting is long, the quality is greatly affected by the construction environment, and the curing process is complex and prone to cracking. Therefore, developing a refractory material that combines excellent slag erosion resistance and superior thermal shock stability, and can be provided in prefabricated form for rapid installation and no-bake operation, is of great significance for improving the operating rate of rotary hearth furnaces, extending furnace life, and reducing maintenance costs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an anti-erosion magnesium aluminum spinel precast brick for rotary hearth furnace and its preparation method. The precast brick can achieve the best balance between slag erosion resistance and thermal shock stability, and has the characteristics of high strength and low porosity. It can be directly used as a precast component and significantly shorten the maintenance cycle.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: On one hand, this invention provides an erosion-resistant magnesia-alumina spinel precast brick for rotary hearth furnaces. The raw material composition and mass fraction content are as follows: 23-27% fused magnesia particles with a particle size of 3-5mm, 10-20% fused magnesia particles with a particle size of 1-3mm, 13-15% fused magnesia fine powder with a particle size ≤0.088mm, 10-18% sintered tabular corundum particles with a particle size of 1-3mm, 8-15% sintered tabular corundum fine powder with a particle size ≤0.044mm, and 5-12% pre-synthesized magnesia-alumina spinel fine powder with a particle size ≤0.044mm. The particle size distribution is D. 50 2-5% of active alumina micro powder ≤5μm; It also includes 1-3% zircon sand powder, 1-3% SiAlON fine powder, 1-3% sintering agent, 3-5% composite binder, 0.1-0.3% water-reducing agent, and 0.05-0.1% explosion-proof fiber; wherein the composite binder is a mixture of thermosetting phenolic resin and p-Al2O3 in a weight ratio of 2-4:1.

[0007] Furthermore, the mass fraction of MgO in the fused magnesia particles and fused magnesia fine powder is ≥97%, the mass fraction of Al2O3 in the sintered tabular corundum particles and sintered tabular corundum fine powder is ≥99%, and the mass fraction of Al2O3 in the pre-synthesized magnesium aluminum spinel fine powder is 70-80%.

[0008] On the other hand, the present invention also provides a method for preparing erosion-resistant magnesium-aluminum spinel precast bricks for rotary hearth furnaces. The method involves weighing each raw material according to a formula ratio; firstly, fused magnesia particles and tabular corundum particles are mixed, and then further mixed with fine fused magnesia powder, fine tabular corundum powder, fine magnesium-aluminum spinel powder, activated alumina micro powder, zircon sand powder, and a sintering agent to obtain a dry mixture; subsequently, fine SiAlON powder is added to a composite binder and mixed and dispersed to obtain a slurry; then, the slurry, water-reducing agent, and explosion-proof fiber are added to the dry mixture and kneaded to obtain a plastic material; then, the plastic material is pressed into shape to obtain a brick blank; finally, the brick blank is subjected to curing and heat treatment sequentially to obtain the erosion-resistant magnesium-aluminum spinel precast bricks for rotary hearth furnaces.

[0009] Furthermore, the specific steps include: S1. Ingredients and Mixing: After weighing according to the formula, first dry mix the fused magnesia particles and tabular corundum particles for 1-2 minutes, then add the fused magnesia fine powder, tabular corundum fine powder, magnesium aluminum spinel fine powder, activated alumina micro powder, zircon sand powder and sintering agent, and continue to dry mix for 2-3 minutes to obtain a dry mix; add SiAlON fine powder to the composite binder, and disperse by microwave for 10 minutes to obtain a slurry; then add the obtained slurry, water-reducing agent and explosion-proof fiber to the dry mix and wet mix for 8-15 minutes until a uniform plastic state is achieved to obtain a plastic material; S2. Molding: The plastic material obtained in step S1 is transferred into a mold and pressed to form a brick blank. S3. Curing and heat treatment: The brick blank obtained in step S2 is cured for 12-24 hours. After demolding, it is heated to 200-250℃ at a heating rate of ≤20℃ / h and held for 8-12 hours to obtain the corrosion-resistant magnesium aluminum spinel precast brick for rotary hearth furnace.

[0010] Furthermore, in step S1, a dry mixing operation is performed using a mixing mill.

[0011] Furthermore, in step S2, the pressure for pressing and molding is 80-150 MPa.

[0012] Furthermore, in step S2, a friction brick press or a hydraulic press is used for pressing and molding.

[0013] Furthermore, in step S3, the curing is carried out in a curing chamber at 40-60°C.

[0014] According to the above technical solution, the beneficial effects of the present invention are: 1. Synergistically Enhanced Matrix System: With tabular corundum and pre-synthesized magnesium aluminum spinel as the matrix core, a stable framework is provided, which can effectively resist the penetration and erosion of molten slag. Activated alumina micropowder fills the micropores and reacts in situ with MgO to generate secondary spinel, producing a micro-expansion effect, further densifying the structure and compensating for thermal stress.

[0015] 2. Optimized Composite Bonding System: First, the thermosetting phenolic resin provides excellent room-temperature molding strength and demolding strength, enabling precast bricks to possess the strength required for handling and installation even before heat treatment. Second, ρ-Al₂O₃ (hydrated alumina) hydrates during heating to form boehmite gel, and transforms into highly reactive γ-Al₂O₃ at higher temperatures, subsequently reacting with MgO to form a ceramic bond, endowing the product with excellent medium- and high-temperature strength. This bonding system avoids the problems of low melting phase and lengthy baking required by traditional cement bonding, achieving the goal of "no baking required" or "rapid baking" for immediate use.

[0016] 3. Excellent thermal shock resistance: By controlling the ratio of magnesia to alumina and utilizing the superior microstructure of tabular corundum, the material exhibits high thermal conductivity and fracture toughness. Simultaneously, the micro-expansion generated by the in-situ formed secondary spinel creates microcracks within the material, effectively absorbing and dispersing thermal stress, thereby significantly enhancing its thermal shock resistance.

[0017] 4. Excellent resistance to slag erosion: High-purity raw materials (high MgO, high Al2O3) fundamentally reduce the content of impurity phases (such as CaO, SiO2), reducing the possibility of reacting with slag to form low-melting-point substances. The dense microstructure and fine pore size greatly hinder the penetration of molten slag.

[0018] 5. Under an oxidizing atmosphere, the surface of SiAlON slowly oxidizes, forming a protective film of silica (SiO2) or mullite (3Al2O3·2SiO2). This film can react with alumina, magnesium oxide, or spinel in the system to generate high-melting-point secondary phases (such as more spinel or mullite), strengthening and repairing the matrix bonding network. Under weak oxidizing or reducing atmospheres, SiAlON itself has extremely high chemical inertness, and its resistance to alkaline slag, molten metal, and reducing gases is far superior to that of oxides. Simultaneously, fine SiAlON powder possesses high hardness, high strength, and excellent thermal shock resistance. When uniformly dispersed in the matrix, it acts like countless tiny "steel bars," effectively hindering crack propagation and improving the material's fracture toughness and resistance to spalling. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments.

[0021] In the following examples, the MgO mass fraction of the fused magnesia particles and fused magnesia fine powder used in the raw materials is ≥97%, the Al2O3 mass fraction of the sintered tabular corundum particles and sintered tabular corundum fine powder is ≥99%, and the Al2O3 mass fraction of the pre-synthesized magnesium aluminum spinel is 70-80%.

[0022] Example 1 In the example, the raw materials added by mass fraction are: 23% fused magnesia particles with a particle size of 3-5 mm, 13% fused magnesia particles with a particle size of 1-3 mm, 13% fused magnesia fine powder with a particle size ≤0.088 mm, 18% sintered tabular corundum particles with a particle size of 1-3 mm, 8% sintered tabular corundum fine powder with a particle size ≤0.044 mm, and 10% pre-synthesized magnesium aluminum spinel fine powder with a particle size ≤0.044 mm. The particle size distribution is D. 50 5% of ≤5μm active alumina micro powder; 1.6% zircon sand powder; 3% SiAlON fine powder; 2% sintering agent; 3% composite binder; 0.3% water-reducing agent; and 0.1% explosion-proof fiber.

[0023] The preparation method of the corrosion-resistant magnesium aluminate spinel precast bricks for rotary hearth furnaces in this embodiment is as follows: S1. Ingredients and Mixing: After weighing according to the formula, first put the fused magnesia granules and tabular corundum granules into the mixer and dry mix for 1-2 minutes. Then add the fused magnesia fine powder, tabular corundum fine powder, magnesium aluminum spinel fine powder, activated alumina micro powder, zircon sand powder and sintering agent, and continue to dry mix for 2-3 minutes until uniformly mixed to obtain a dry mixture. Add SiAlON fine powder to the composite binder, wherein the thermosetting phenolic resin:ρ-Al2O3=2:1 in the composite binder. Disperse by microwave for 10 minutes to obtain a slurry. Then add the obtained slurry, 0.1% water-reducing agent and 0.08% explosion-proof fiber to the dry mixture and wet mix for 8-15 minutes until a uniform plastic state is achieved to obtain a plastic material.

[0024] S2. Molding: The plastic material obtained in step S1 is transferred into a mold and pressed into shape on a friction brick press or hydraulic press with a pressure of 80-150MPa to obtain a brick blank.

[0025] S3. Curing and heat treatment: The brick blanks obtained in step S2 are cured in a curing room at 40-60℃ for 12-24 hours. After demolding, they are heated to 200-250℃ at a heating rate of ≤20℃ / h and held for 8-12 hours to obtain the corrosion-resistant magnesium aluminum spinel precast bricks for rotary hearth furnaces.

[0026] Example 2 In the example, the raw materials added by mass fraction are: 25% fused magnesia particles with a particle size of 3-5 mm, 15% fused magnesia particles with a particle size of 1-3 mm, 15% fused magnesia fine powder with a particle size ≤0.088 mm, 10% sintered tabular corundum particles with a particle size of 1-3 mm, 15% sintered tabular corundum fine powder with a particle size ≤0.044 mm, and 5% pre-synthesized magnesium aluminum spinel fine powder with a particle size ≤0.044 mm. The particle size distribution is D. 50 3% of ≤5μm active alumina micro powder; 2.7% zircon sand powder; 1% SiAlON fine powder; 3% sintering agent; 5% composite binder; 0.25% water-reducing agent; and 0.05% explosion-proof fiber.

[0027] The preparation method of the corrosion-resistant magnesium aluminate spinel precast bricks for rotary hearth furnaces in this embodiment is as follows: S1. Ingredients and Mixing: After weighing according to the formula, first put the fused magnesia granules and tabular corundum granules into the mixer and dry mix for 1-2 minutes. Then add the fused magnesia fine powder, tabular corundum fine powder, magnesium aluminum spinel fine powder, activated alumina micro powder, zircon sand powder and sintering agent, and continue to dry mix for 2-3 minutes until uniformly mixed to obtain a dry mixture. Add SiAlON fine powder to the composite binder, wherein the thermosetting phenolic resin:ρ-Al2O3=4:1 in the composite binder. Disperse by microwave for 10 minutes to obtain a slurry. Then add the obtained slurry, 0.3% water-reducing agent and 0.08% explosion-proof fiber to the dry mixture and wet mix for 8-15 minutes until a uniform plastic state is achieved to obtain a plastic material.

[0028] S2. Molding: The plastic material obtained in step S1 is transferred into a mold and pressed into shape on a friction brick press or hydraulic press with a pressure of 80-150MPa to obtain a brick blank.

[0029] S3. Curing and heat treatment: The brick blanks obtained in step S2 are cured in a curing room at 40-60℃ for 12-24 hours. After demolding, they are heated to 200-250℃ at a heating rate of ≤20℃ / h and held for 8-12 hours to obtain the corrosion-resistant magnesium aluminum spinel precast bricks for rotary hearth furnaces.

[0030] Comparative Example In the comparative example, the raw materials added by mass fraction were: 23% fused magnesia particles with a particle size of 3-5 mm, 18% fused magnesia particles with a particle size of 1-3 mm, 13% fused magnesia fine powder with a particle size ≤0.088 mm, 15% sintered tabular corundum particles with a particle size of 1-3 mm, 11% sintered tabular corundum fine powder with a particle size ≤0.044 mm, and 10% pre-synthesized magnesium aluminum spinel fine powder with a particle size ≤0.044 mm. The particle size distribution D 50 4% activated alumina micropowder with a particle size of ≤5μm, 5.7% cement, 0.22% water-reducing agent, and 0.08% explosion-proof fiber.

[0031] The preparation method of the corrosion-resistant magnesium aluminate spinel precast bricks for rotary hearth furnaces in this comparative example is as follows: S1. Ingredients and Mixing: After weighing according to the formula, first put the fused magnesia particles and tabular corundum particles into the mixer and dry mix for 1-2 minutes. Then add the fused magnesia fine powder, tabular corundum fine powder, magnesium aluminum spinel fine powder, activated alumina micro powder and cement, and continue to dry mix for 2-3 minutes until uniformly mixed to obtain a dry mix. After microwave dispersion for 10 minutes, a slurry is obtained. Then add the obtained slurry, water-reducing agent and explosion-proof fiber to the dry mix and wet mix for 8-15 minutes until a uniform plastic state is achieved to obtain a plastic material.

[0032] S2. Molding: The plastic material obtained in step S1 is transferred into a mold and pressed into shape on a friction brick press or hydraulic press with a pressure of 80-150MPa to obtain a brick blank.

[0033] S3. Curing and heat treatment: The brick blanks obtained in step S2 are cured in a curing room at 40-60℃ for 12-24 hours. After demolding, they are heated to 200-250℃ at a heating rate of ≤20℃ / h and held for 8-12 hours to obtain the corrosion-resistant magnesium aluminum spinel precast bricks for rotary hearth furnaces.

[0034] The performance indicators of the precast bricks prepared in Examples 1-2 and the comparative examples are shown in Table 1. The standards used for testing are as follows: bulk density (GB / T 2998), room temperature compressive strength (GB / T 5072), permanent linear change upon heating (GB / T 5988), and thermal shock resistance (GB / T 30873).

[0035] Table 1 Performance indicators of precast bricks prepared in Examples 1-2 and comparative examples As shown in Table 1, compared with the comparative example, the precast bricks prepared in Examples 1-2 are significantly superior to the traditional cement-bonded castable in terms of bulk density, room temperature strength, especially resistance to thermal shock and slag erosion. Their micro-expansion linear change rate helps maintain the integrity of the masonry and prevents gaps. This enhances their erosion resistance, greatly extends the service life of the rotary hearth furnace, and creates economic value.

[0036] It should be noted that the above embodiments are only used to illustrate the present invention, but the present invention is not limited to the above embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A type of corrosion-resistant magnesium-aluminate spinel precast brick for rotary hearth furnaces, characterized in that, The raw material composition and mass fraction content are as follows: 23-27% fused magnesia particles with a particle size of 3-5mm, 10-20% fused magnesia particles with a particle size of 1-3mm, 13-15% fused magnesia fine powder with a particle size ≤0.088mm, 10-18% sintered tabular corundum particles with a particle size of 1-3mm, 8-15% sintered tabular corundum fine powder with a particle size ≤0.044mm, and 5-12% pre-synthesized magnesium aluminum spinel fine powder with a particle size ≤0.044mm. The particle size distribution is D... 50 2-5% of active alumina micro powder ≤5μm; It also includes 1-3% zircon sand powder, 1-3% SiAlON fine powder, 1-3% sintering agent, 3-5% composite binder, 0.1-0.3% water-reducing agent, and 0.05-0.1% explosion-proof fiber; wherein the composite binder is a mixture of thermosetting phenolic resin and p-Al2O3 in a weight ratio of 2-4:

1.

2. The corrosion-resistant magnesium-aluminate spinel precast brick for a rotary hearth furnace according to claim 1, characterized in that: The fused magnesia particles and fused magnesia fine powder contain MgO with a mass fraction of ≥97%, the sintered tabular corundum particles and sintered tabular corundum fine powder contain Al2O3 with a mass fraction of ≥99%, and the pre-synthesized magnesium aluminum spinel fine powder contains Al2O3 with a mass fraction of 70-80%.

3. A method for preparing erosion-resistant magnesium-aluminate spinel precast bricks for rotary hearth furnaces, used to prepare the erosion-resistant magnesium-aluminate spinel precast bricks for rotary hearth furnaces as described in any one of claims 1-2, characterized in that: Weigh each raw material according to the formula ratio; first, mix fused magnesia particles and tabular corundum particles, then mix with fused magnesia fine powder, tabular corundum fine powder, magnesium aluminum spinel fine powder, activated alumina micro powder, zircon sand powder and sintering agent to obtain a dry mixture; then add SiAlON fine powder to the composite binder and mix and disperse to obtain a slurry; then add the slurry, water-reducing agent and explosion-proof fiber to the dry mixture and knead to obtain a plastic material; then press the plastic material into shape to obtain a brick blank; finally, the brick blank is cured and heat-treated in sequence to obtain the corrosion-resistant magnesium aluminum spinel precast brick for rotary hearth furnace.

4. The method for preparing an erosion-resistant magnesium aluminate spinel precast brick for a rotary hearth furnace according to claim 3, characterized in that, Specifically, the following steps are included: S1. Ingredients and Mixing: After weighing according to the formula, first dry mix the fused magnesia particles and tabular corundum particles for 1-2 minutes, then add the fused magnesia fine powder, tabular corundum fine powder, magnesium aluminum spinel fine powder, activated alumina micro powder, zircon sand powder and sintering agent, and continue to dry mix for 2-3 minutes to obtain a dry mix; add SiAlON fine powder to the composite binder, and disperse by microwave for 10 minutes to obtain a slurry; then add the obtained slurry, water-reducing agent and explosion-proof fiber to the dry mix and wet mix for 8-15 minutes until a uniform plastic state is achieved to obtain a plastic material; S2. Molding: The plastic material obtained in step S1 is transferred into a mold and pressed to form a brick blank. S3. Curing and heat treatment: The brick blank obtained in step S2 is cured for 12-24 hours. After demolding, it is heated to 200-250℃ at a heating rate of ≤20℃ / h and held for 8-12 hours to obtain the corrosion-resistant magnesium aluminum spinel precast brick for rotary hearth furnace.

5. The preparation method according to claim 4, characterized in that: In step S1, a dry mixing operation is performed using a mixing mill.

6. The preparation method according to claim 4, characterized in that: In step S2, the pressure for pressing and molding is 80-150 MPa.

7. The preparation method according to claim 4, characterized in that: In step S2, a friction brick press or a hydraulic press is used for pressing and molding.

8. The preparation method according to claim 4, characterized in that: In step S3, the curing is carried out in a curing chamber at 40-60℃.

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