A hot-state repair material for aluminum industrial furnaces and its preparation method

Abstract

This invention relates to the field of industrial furnace repair technology, specifically disclosing a hot-state repair material for aluminum industrial furnaces and its preparation method. This invention introduces sodium metasilicate pentahydrate and borax as composite additives, combined with the self-lubricating effect of flake graphite, enabling the repair material to spread rapidly in the repair area. It introduces short polypropylene fibers to form a network structure, effectively filling cracks while preventing dry powder from leaking into the furnace and contaminating the molten aluminum. It introduces pretreated secondary aluminum ash fine powder and silicon micropowder, filling pores while generating a stable mullite phase at high temperatures, improving the strength of the repair material after sintering. This invention also introduces silicon oxynitride, which has good thermal conductivity and a low coefficient of thermal expansion, improving the thermal stability and oxidation resistance of the repair material after sintering.

Description

Technical Field

[0001] This invention relates to the field of industrial furnace repair technology, specifically to a hot-state repair material for aluminum industrial furnaces and its preparation method. Background Technology

[0002] Reverberating furnaces are critical thermal equipment in the aluminum melting and casting process. The refractory lining of these furnaces typically has a long service life. The furnace top lining is generally a flat-top structure, assembled using a compartmentalized casting method. During long-term operation in high-temperature environments, due to mechanical collisions during charging and slag removal, as well as thermal shock from alternating hot and cold temperatures, the furnace top lining often experiences spalling and chipping at the joints, allowing flames to penetrate the furnace lining and shell steel structure. Traditional maintenance methods involve shutting down the furnace, removing the old lining, recasting, repairing, and then baking the furnace before resuming production. This process is time-consuming and costly.

[0003] The existing patent "CN115286403" (A Heated Self-Flowing Rapid Repair Dry Powder and Its Preparation Method) uses high-alumina bauxite clinker, alumina micro powder, potassium silicate powder, potassium aluminum sulfate dodecahydrate, silica micro powder, zirconium corundum powder, and a composite phosphate binder to prepare a heated self-flowing repair dry powder that can achieve hot repair without shutting down the furnace. However, on the one hand, the repair material requires an operating temperature of over 400℃, while furnace top repair requires the removal of the insulation layer material first, resulting in high operational risks at higher temperatures. On the other hand, the additives used in the formula, such as nitronaphthalene and potassium aluminum sulfate dodecahydrate, decompose upon heating, producing harmful gases, which does not conform to green production. Summary of the Invention

[0004] The purpose of this invention is to provide a hot repair material for aluminum industrial furnaces and its preparation method, thereby solving the problem of difficult maintenance caused by local damage to the furnace lining of aluminum melting and casting reverberatory furnaces under high-temperature conditions.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A hot-state repair material for aluminum industrial furnaces, by mass fraction, comprises 30-60 wt% mullite aggregate, 10-20 wt% pretreated secondary aluminum ash, 5-15 wt% composite additives, 3-8 wt% aluminum dihydrogen phosphate powder, 2-6 wt% silica powder, 0.2-2 wt% flake graphite, and 0.5-2 wt% polypropylene short fibers.

[0007] The mullite aggregate has a particle size of 0.075–5 mm, an alumina content of >60%, and a mullite phase ratio of >95%; the aluminum dihydrogen phosphate powder has a purity of >98% and a particle size of 200 mesh; the silica powder has a particle size D50 of 0.5–1 μm and a silica content of >95%; the lamellar graphite has a lamellar thickness of <20 μm, a particle size distribution D50 of 5–20 μm, and a carbon content of >99.8%; and the polypropylene short fiber has a fiber length of 3–5 μm and a softening point of <120℃.

[0008] As a limitation of the present invention, the chemical composition of the pretreated secondary aluminum ash is: 60-80 wt% aluminum oxide, 5-15 wt% silicon dioxide, 0.5-3 wt% ferric oxide, 0.5-3 wt% calcium oxide, 1-5 wt% potassium oxide, and 0.5-3 wt% sodium oxide.

[0009] As a limitation of the present invention, the method for preparing the pretreated secondary aluminum ash is as follows:

[0010] Secondary aluminum ash is added to hydrochloric acid and soaked at 50-60℃ for 2-3 hours. After soaking, it is washed with deionized water until neutral, then dried at 100-110℃, and then sieved to remove impurities to obtain pretreated secondary aluminum ash.

[0011] As a limitation of this invention, the preparation method of the composite additive is as follows:

[0012] Sodium metasilicate pentahydrate and borax are mixed at a mass ratio of (2-5):1 and mechanically stirred for 5-15 minutes to ensure uniform mixing, thus obtaining a composite additive.

[0013] A method for preparing a hot-state repair material for aluminum industrial furnaces, specifically comprising:

[0014] Flake graphite, polypropylene short fibers, one-third by weight of silica powder and polycarboxylate dispersant are mixed and mechanically stirred for 20-30 minutes at a stirring speed of 400-500 rpm. After stirring is completed, mixed dry material A is obtained.

[0015] Mullite aggregate, pretreated secondary aluminum ash, aluminum dihydrogen phosphate powder, two-thirds by weight of silica powder and composite additives are mixed and mechanically stirred for 3-5 minutes at a stirring speed of 80-100 rpm. After stirring, mixed dry material A is added and stirring is continued for 8-10 minutes at a stirring speed of 40-50 rpm to obtain hot repair material for aluminum industrial furnaces.

[0016] The electrostatic repulsion and steric hindrance effects of polycarboxylic acid dispersants enable the silica powder in the dry material to be uniformly dispersed on the surface of the sheet graphite and polypropylene fibers.

[0017] As a limitation of this invention, the hot repair material for aluminum industrial furnaces contains silicon oxynitride, and its preparation method is as follows:

[0018] Elemental silicon and silicon dioxide were mixed and ball-milled for 3–5 hours to obtain a mixed powder with a particle size D50 of 5–10 μm. Under nitrogen protection, the mixed powder was placed in a graphite crucible lined with graphite paper and sintered at 1400–1450 °C for 12–15 hours. After sintering, the mixture was naturally cooled to room temperature. The sintered product was then pulverized and sieved to obtain silicon oxynitride.

[0019] As a limitation of the present invention, the mass fraction of silicon oxynitride in the hot repair material for aluminum industrial furnaces is 1-3%.

[0020] As a limitation of the present invention, the mass ratio of elemental silicon to silicon dioxide is (6-10):(5-8).

[0021] As a limitation of this invention, the pretreated secondary aluminum ash impregnation modification slurry is used to obtain modified secondary aluminum ash. The preparation method of the modified slurry is as follows:

[0022] Add basic zirconium chloride octahydrate to ethanol and stir continuously to dissolve it, obtaining a zirconium chloride alcohol solution. Add bentonite suspending agent to the zirconium chloride alcohol solution and stir at 800-1000 rpm for 5-10 min to disperse it in the zirconium chloride alcohol solution. Then add fused magnesia powder and corundum powder and continue stirring at 800-1000 rpm for 15-20 min to obtain the modified slurry.

[0023] As a limitation of the present invention, the mass ratio of basic zirconium chloride octahydrate, fused magnesia powder, and corundum powder is (15-18):(12-15):(5-7).

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention introduces sodium metasilicate pentahydrate and borax as composite additives. Utilizing the residual heat of the furnace lining, sodium metasilicate pentahydrate undergoes a dehydration reaction at 100-150°C. The "self-boiling" effect of this dehydration reaction promotes the flow and spread of the dry powder on the furnace lining surface. By leveraging the self-lubricating effect of graphite's lamellar structure, particle friction is further reduced, facilitating rapid spread of the dry material in repair areas. As the furnace lining temperature rises, sodium metasilicate pentahydrate is completely dehydrated to form sodium silicate. By introducing an appropriate amount of borax, its sintering accelerator effect is utilized to form a boron oxide-sodium silicate composite system. This allows sodium silicate to form a eutectic at a relatively low temperature of 700-800°C, achieving low-viscosity flow to fill pores and improve the density of the sintered material. Simultaneously, the introduction of borax as a sintering agent addresses the issue of low sintering strength in the aluminum dihydrogen phosphate bonded system at around 1000°C.

[0026] This invention introduces polypropylene short fibers, utilizing the physical entanglement of these fibers to bond dry powder into a network structure. Through a rational particle size distribution design, when the dry powder is applied to the furnace lining via methods such as scattering, the overall effect effectively fills cracks, preventing leakage into the furnace and contamination of the molten aluminum. This allows for hot repair of cracks up to 10mm wide. The polypropylene short fibers soften upon heating and completely decompose with increasing temperature, leaving no residue. Adding an appropriate amount of polypropylene short fibers does not affect the heat flowability of the dry powder.

[0027] This invention introduces ultrafine pretreated secondary aluminum ash powder and silica powder to fill the pores. Utilizing the high activity of the ultrafine powder, a sintering reaction occurs, generating a lamellar mullite phase with excellent high-temperature resistance and thermal shock resistance. The mullite phase is interspersed in the matrix, significantly improving high-temperature performance. At the same time, the active alumina in the secondary aluminum ash reacts with the binder aluminum dihydrogen phosphate upon heating to generate aluminum phosphate, improving the strength of the material and enabling the recyclable use of industrial hazardous waste secondary aluminum ash.

[0028] Through the synergistic effect of composite additives, high-temperature binders, and lamellar graphite, the dry material can begin to flow at around 200°C using the residual heat of the furnace lining and exhibits excellent fluidity at around 300°C. At around 400°C, it achieves initial strength through sintering of aluminum dihydrogen phosphate and curing of sodium metasilicate pentahydrate. In the working environment of aluminum reverberatory furnaces above 800°C, the anti-oxidation effect of graphite and the strengthening effect of mullitization meet the high-temperature working conditions of the furnace lining. It is environmentally friendly, low-cost, and high-performance, and is suitable for rapid hot repair of aluminum reverberatory furnaces.

[0029] Introducing silicon oxynitride into hot-dip mortar generates aluminum nitride and aluminum carbide-aluminum nitride-silicon carbide compounds during the repair process. These compounds have good thermal conductivity and a low coefficient of thermal expansion, which helps improve the thermal stability and oxidation resistance of the sintered mortar. Furthermore, silicon oxynitride exhibits good slag resistance and resistance to slag erosion. The silicon oxide produced by its thermal decomposition at high temperatures can block pores that cannot be repaired, slowing down the penetration and erosion of slag molten metal into the mortar, thereby improving the mechanical properties of the sintered mortar.

[0030] Before use, the secondary aluminum ash is impregnated with a slurry containing fused magnesia powder, corundum powder, and basic zirconium chloride for modification. At 600℃, the basic zirconium chloride decomposes to form zirconium oxide. During slag erosion, it reacts with the slag slurry and expands in volume, blocking pores and preventing slag erosion while also generating microcracks. This can refine the cracks caused by phase transformation of aggregates and other materials during sintering, and improve the thermal shock resistance of dry-mixed materials after sintering. Fused magnesia powder and corundum powder form magnesium aluminum spinel phase during sintering, further improving the strength and thermal stability of dry-mixed materials after sintering. Attached Figure Description

[0031] Figure 1The figure shows the test results of the bonding performance between the dry material and the original lining material, where the dry material is the hot repair material for aluminum industrial furnaces prepared in Example 1;

[0032] Figure 2 The figure shows the test results of the bonding performance between the dry material and the original lining material, where the dry material is the hot repair material for aluminum industrial furnaces prepared in Example 2. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Mullite aggregate (alumina content > 60%, particle size: 0.075-5mm) was provided by Zhengzhou Daorui Refractories; aluminum dihydrogen phosphate powder (particle size: 200 mesh) was provided by Henan Bangnai; silica powder (particle size D50: 0.5-1μm) was provided by Lianyungang Huwei; lamellar graphite (particle size D50: 5-20μm) was provided by Henan Huiju; polypropylene short fiber (length: 3-5μm) was provided by Henan Tiansheng; secondary aluminum ash (particle size: <270μm) was provided by Henan Mingtai; polycarboxylate dispersant (brand: PAA, free monomer AA≤0.5) was provided by Zaozhuang Jialu; fused magnesia powder (particle size: 200 mesh) was provided by Qingdao Xibu Meiye; corundum powder (particle size: 200 mesh) and bentonite suspending agent (particle size: 325 mesh, expansion degree: >12.5) were from Lingshou County Aokai Mineral Products Processing Plant.

[0035] Example 1: A method for preparing a hot repair material for aluminum industrial furnaces, specifically as follows:

[0036] Step 1: Mix the sheet graphite, polypropylene short fibers, a portion of silica powder (1 / 3 of the total mass of silica powder) and polycarboxylate dispersant, and mechanically stir for 30 minutes at a stirring speed of 500 rpm. After stirring is complete, the mixed dry material A is obtained.

[0037] Step 2: Mix sodium metasilicate pentahydrate and borax at a mass ratio of 4:1, and mechanically stir for 10 minutes to ensure uniform mixing, thus obtaining a composite additive;

[0038] Step 3: Add the secondary aluminum ash to 5% hydrochloric acid and soak it at 60°C for 2 hours. After soaking, wash it with deionized water until neutral, then dry it at 110°C, and then pass it through a 325-mesh sieve to remove impurities to obtain pretreated secondary aluminum ash.

[0039] Step 4: Mix the mullite aggregate, pretreated secondary aluminum ash, aluminum dihydrogen phosphate powder, remaining silicon micropowder (2 / 3 of the total mass of silicon micropowder) and composite additives, and mechanically stir for 5 minutes at a stirring speed of 100 rpm. After stirring, add mixed dry material A and continue stirring for 10 minutes at a stirring speed of 50 rpm to obtain hot repair material for aluminum industrial furnaces.

[0040] In the hot repair material for aluminum industrial furnaces, the mass fraction of mullite aggregate is 55%, the mass fraction of pretreated secondary aluminum ash is 20%, the mass fraction of composite additives is 10%, the mass fraction of aluminum dihydrogen phosphate powder is 8%, the mass fraction of silica powder is 4.5%, the mass fraction of flake graphite is 1%, the mass fraction of polypropylene short fiber is 1%, and the mass fraction of polycarboxylic acid dispersant is 0.5%.

[0041] Example 2: A method for preparing a hot repair material for aluminum industrial furnaces, specifically as follows:

[0042] Step 1: Mix the sheet graphite, polypropylene short fibers, a portion of silica powder (1 / 3 of the total mass of silica powder) and polycarboxylate dispersant, and mechanically stir for 30 minutes at a stirring speed of 500 rpm. After stirring is complete, the mixed dry material A is obtained.

[0043] Step 2: Mix sodium metasilicate pentahydrate and borax at a mass ratio of 3:1, and mechanically stir for 10 minutes to ensure uniform mixing, thus obtaining a composite additive;

[0044] Step 3: Add the secondary aluminum ash to 5% hydrochloric acid and soak it at 60°C for 2 hours. After soaking, wash it with deionized water until neutral, then dry it at 110°C, and then pass it through a 325-mesh sieve to remove impurities to obtain pretreated secondary aluminum ash.

[0045] Step 4: Mix the mullite aggregate, pretreated secondary aluminum ash, aluminum dihydrogen phosphate powder, remaining silicon micropowder (2 / 3 of the total mass of silicon micropowder) and composite additives, and mechanically stir for 5 minutes at a stirring speed of 100 rpm. After stirring, add mixed dry material A and continue stirring for 10 minutes at a stirring speed of 50 rpm to obtain hot repair material for aluminum industrial furnaces.

[0046] In the hot repair material for aluminum industrial furnaces, the mass fraction of mullite aggregate is 60%, the mass fraction of pretreated secondary aluminum ash is 20%, the mass fraction of composite additives is 5%, the mass fraction of aluminum dihydrogen phosphate powder is 7%, the mass fraction of silica powder is 5%, the mass fraction of flake graphite is 1.5%, the mass fraction of polypropylene short fiber is 1%, and the mass fraction of polycarboxylic acid dispersant is 0.5%.

[0047] Example 3: A method for preparing a hot repair material for aluminum industrial furnaces, specifically as follows:

[0048] Step 1: Mix the sheet graphite, polypropylene short fibers, a portion of silica powder (1 / 3 of the total mass of silica powder) and polycarboxylate dispersant, and mechanically stir for 30 minutes at a stirring speed of 500 rpm. After stirring is complete, the mixed dry material A is obtained.

[0049] Step 2: Mix sodium metasilicate pentahydrate and borax at a mass ratio of 4:1, and mechanically stir for 10 minutes to ensure uniform mixing, thus obtaining a composite additive;

[0050] Step 3: Add the secondary aluminum ash to 5% hydrochloric acid and soak it at 60°C for 2 hours. After soaking, wash it with deionized water until neutral, then dry it at 110°C, and then pass it through a 325-mesh sieve to remove impurities to obtain pretreated secondary aluminum ash.

[0051] Step 4: Mix the mullite aggregate, pretreated secondary aluminum ash, aluminum dihydrogen phosphate powder, remaining silicon micropowder (2 / 3 of the total mass of silicon micropowder) and composite additives, and mechanically stir for 5 minutes at a stirring speed of 100 rpm. After stirring, add mixed dry material A and continue stirring for 10 minutes at a stirring speed of 50 rpm to obtain hot repair material for aluminum industrial furnaces.

[0052] In the hot repair material for aluminum industrial furnaces, the mass fraction of mullite aggregate is 50%, the mass fraction of pretreated secondary aluminum ash is 20%, the mass fraction of composite additives is 12%, the mass fraction of aluminum dihydrogen phosphate powder is 10%, the mass fraction of silica powder is 5.5%, the mass fraction of flake graphite is 1.5%, the mass fraction of polypropylene short fiber is 1.5%, and the mass fraction of polycarboxylic acid dispersant is 0.5%.

[0053] Example 4: A method for preparing a hot repair material for aluminum industrial furnaces, specifically as follows:

[0054] Step 1: Mix the sheet graphite, polypropylene short fibers, a portion of silica powder (1 / 3 of the total mass of silica powder) and polycarboxylate dispersant, and mechanically stir for 30 minutes at a stirring speed of 500 rpm. After stirring is complete, the mixed dry material A is obtained.

[0055] Step 2: Mix sodium metasilicate pentahydrate and borax at a mass ratio of 4:1, and mechanically stir for 10 minutes to ensure uniform mixing, thus obtaining a composite additive;

[0056] Step 3: Add the secondary aluminum ash to 5% hydrochloric acid and soak it at 60°C for 2 hours. After soaking, wash it with deionized water until neutral, then dry it at 110°C, and then pass it through a 325-mesh sieve to remove impurities to obtain pretreated secondary aluminum ash.

[0057] Step 4: Add 16g of basic zirconium chloride octahydrate to 100mL of ethanol and stir continuously to dissolve it, obtaining a zirconium chloride alcohol solution. Add 0.52g of bentonite suspending agent to the zirconium chloride alcohol solution and stir at 1000rpm for 10min to disperse it in the zirconium chloride alcohol solution. Then add 14g of fused magnesia powder and 6g of corundum powder and continue stirring at 1000rpm for 15min to form a modified slurry. Then, immerse the pretreated secondary aluminum ash in the modified slurry for 30min. After 30min, filter and dry at 110℃ for 1h to obtain modified secondary aluminum ash.

[0058] Step 5: Mix elemental silicon and silicon dioxide at a mass ratio of 7:5.8 until homogeneous, transfer to a vibratory ball mill and ball mill for 5 hours to obtain a mixed powder with a particle size D50 of 5 μm. Under nitrogen protection, place the mixed powder into a graphite crucible lined with graphite paper and sinter at 1430℃ for 14 hours. After sintering, allow it to cool naturally to room temperature. Then, pulverize the sintered product and pass it through a 325-mesh sieve to obtain silicon oxynitride.

[0059] Step 6: Mix mullite aggregate, modified secondary aluminum ash, aluminum dihydrogen phosphate powder, silicon oxynitride, remaining silicon micro powder (2 / 3 of the total mass of silicon micro powder) and composite additives, and mechanically stir for 5 minutes at a stirring speed of 100 rpm. After stirring, add mixed dry material A and continue stirring for 10 minutes at a stirring speed of 50 rpm to obtain hot repair material for aluminum industrial furnaces.

[0060] In the hot-state repair material for aluminum industrial furnaces, the mass fraction of mullite aggregate is 53%, the mass fraction of modified secondary aluminum ash is 20%, the mass fraction of silicon oxynitride is 2%, the mass fraction of composite additives is 10%, the mass fraction of aluminum dihydrogen phosphate powder is 8%, the mass fraction of silica fume is 4.5%, the mass fraction of flake graphite is 1%, the mass fraction of polypropylene short fibers is 1%, and the mass fraction of polycarboxylic acid dispersant is 0.5%.

[0061] Based on Example 1, the following comparative experiments were conducted, specifically Comparative Example 1, Comparative Example 2, and Comparative Example 3, as described below:

[0062] Comparative Example 1: This comparative example relates to a method for preparing a hot-state repair material for aluminum industrial furnaces. The difference from Example 1 is that no composite additives are added. Specifically:

[0063] Step 1: Mix the sheet graphite, polypropylene short fibers, a portion of silica powder (1 / 3 of the total mass of silica powder) and polycarboxylate dispersant, and mechanically stir for 30 minutes at a stirring speed of 500 rpm. After stirring is complete, the mixed dry material A is obtained.

[0064] Step 2: Add the secondary aluminum ash to 5% hydrochloric acid and soak it at 60°C for 2 hours. After soaking, wash it with deionized water until neutral, then dry it at 110°C, and then pass it through a 325-mesh sieve to remove impurities to obtain pretreated secondary aluminum ash.

[0065] Step 3: Mix mullite aggregate, pretreated secondary aluminum ash, aluminum dihydrogen phosphate powder, remaining silicon micro powder (2 / 3 of the total mass of silicon micro powder) and composite additives, and mechanically stir for 5 minutes at a stirring speed of 100 rpm. After stirring, add mixed dry material A and continue stirring for 10 minutes at a stirring speed of 50 rpm to obtain hot repair material for aluminum industrial furnaces.

[0066] In the hot repair material for aluminum industrial furnaces, the mass fraction of mullite aggregate is 65%, the mass fraction of pretreated secondary aluminum ash is 20%, the mass fraction of aluminum dihydrogen phosphate powder is 8%, the mass fraction of silica powder is 4.5%, the mass fraction of flake graphite is 1%, the mass fraction of polypropylene short fiber is 1%, and the mass fraction of polycarboxylic acid dispersant is 0.5%.

[0067] Comparative Example 2: This comparative example relates to a method for preparing a hot-state repair material for aluminum industrial furnaces. The difference from Example 1 is that polypropylene short fibers are not added. Specifically:

[0068] Step 1: Mix sheet graphite, a portion of silicon micro powder (1 / 3 of the total mass of silicon micro powder) and polycarboxylate dispersant, and mechanically stir for 30 minutes at a stirring speed of 500 rpm. After stirring is complete, the mixed dry material A is obtained.

[0069] Step 2: Mix sodium metasilicate pentahydrate and borax at a mass ratio of 4:1, and mechanically stir for 10 minutes to ensure uniform mixing, thus obtaining a composite additive;

[0070] Step 3: Add the secondary aluminum ash to 5% hydrochloric acid and soak it at 60°C for 2 hours. After soaking, wash it with deionized water until neutral, then dry it at 110°C, and then pass it through a 325-mesh sieve to remove impurities to obtain pretreated secondary aluminum ash.

[0071] Step 4: Mix the mullite aggregate, pretreated secondary aluminum ash, aluminum dihydrogen phosphate powder, remaining silicon micropowder (2 / 3 of the total mass of silicon micropowder) and composite additives, and mechanically stir for 5 minutes at a stirring speed of 100 rpm. After stirring, add mixed dry material A and continue stirring for 10 minutes at a stirring speed of 50 rpm to obtain hot repair material for aluminum industrial furnaces.

[0072] In the hot repair material for aluminum industrial furnaces, the mass fraction of mullite aggregate is 56%, the mass fraction of pretreated secondary aluminum ash is 20%, the mass fraction of composite additives is 10%, the mass fraction of aluminum dihydrogen phosphate powder is 8%, the mass fraction of silica powder is 4.5%, the mass fraction of flake graphite is 1%, and the mass fraction of polycarboxylic acid dispersant is 0.5%.

[0073] Comparative Example 3: This comparative example relates to a method for preparing a hot-state repair material for aluminum industrial furnaces. The difference from Example 1 is that aluminum dihydrogen phosphate powder is not added. Specifically:

[0074] Step 1: Mix the sheet graphite, polypropylene short fibers, a portion of silica powder (1 / 3 of the total mass of silica powder) and polycarboxylate dispersant, and mechanically stir for 30 minutes at a stirring speed of 500 rpm. After stirring is complete, the mixed dry material A is obtained.

[0075] Step 2: Mix sodium metasilicate pentahydrate and borax at a mass ratio of 4:1, and mechanically stir for 10 minutes to ensure uniform mixing, thus obtaining a composite additive;

[0076] Step 3: Add the secondary aluminum ash to 5% hydrochloric acid and soak it at 60°C for 2 hours. After soaking, wash it with deionized water until neutral, then dry it at 110°C, and then pass it through a 325-mesh sieve to remove impurities to obtain pretreated secondary aluminum ash.

[0077] Step 4: Mix the mullite aggregate, pretreated secondary aluminum ash, remaining silica powder (2 / 3 of the total mass of silica powder) and composite additives, and mechanically stir for 5 minutes at a stirring speed of 100 rpm. After stirring, add mixed dry material A and continue stirring for 10 minutes at a stirring speed of 50 rpm to obtain hot repair material for aluminum industrial furnaces.

[0078] In the hot repair material for aluminum industrial furnaces, the mass fraction of mullite aggregate is 63%, the mass fraction of pretreated secondary aluminum ash is 20%, the mass fraction of composite additives is 10%, the mass fraction of silica fume is 4.5%, the mass fraction of flake graphite is 1%, the mass fraction of polypropylene short fiber is 1%, and the mass fraction of polycarboxylic acid dispersant is 0.5%.

[0079] Testing experiments: Test samples of hot repair materials for aluminum industrial furnaces were prepared according to the preparation methods in each embodiment and comparative example. The samples were tested for dry material flowability, flexural strength at 400℃, strength retention after water cooling thermal shock at 800℃, cold linear change after calcination at 1000℃ for 3 hours, and bonding performance between dry material and original lining material.

[0080] Dry material flowability test: Place a mold with inner dimensions of φ50mm and φ100mm respectively and a height of 50mm on a high-temperature resistant ceramic plate. Take the repair material sample, mix it well, pile it into the mold and smooth it. Then transfer the mold and the sample into the test furnace and heat it at 300℃ for 10 minutes. After heating, take it out, cool it to room temperature and remove the mold. Measure the diagonal diameter of the dry material and take the average value as the method to evaluate the heat flowability of the repair material.

[0081] 400℃ flexural strength test: The repair material sample is filled into a metal mold, and then the metal mold filled with repair material is transferred into a test furnace and sintered at 400℃. After cooling to room temperature, the formed standard sample block with a size of 160mm×40mm×40mm is taken out from the mold. The standard sample block is then fixed on the fixture of the high-temperature flexural strength tester, and the hot flexural strength of each standard sample block formed at 400℃ is tested using the high-temperature flexural strength tester.

[0082] 800℃ Water-Cooled Thermal Shock Strength Retention Test: The repair material sample is filled into a metal mold, and then the metal mold filled with repair material is transferred to a test furnace and sintered at 400℃. After cooling to room temperature, the formed standard sample block with dimensions of 230mm×115mm×64mm is removed from the mold. After testing the initial compressive strength of each standard sample block at room temperature, the standard sample block is fixed on a water-cooled thermal shock testing machine and subjected to 10 water-cooled thermal shock cycles at 800℃. After that, the standard sample block is removed, and the compressive strength of the sample block after the 800℃ water-cooled thermal shock test is measured and compared with the initial compressive strength of the sample block. This is the strength retention rate after the 800℃ water-cooled thermal shock.

[0083] Cold-state linear change test after calcination at 1000℃ for 3 hours: The repair material sample was filled into a metal mold, and then the metal mold filled with repair material was transferred into a test furnace and sintered at 400℃. After cooling to room temperature, the formed standard sample block with dimensions of 160mm×40mm×40mm was taken out from the mold. The initial length of the sample block was measured, and then the sample block was sent into the test furnace and heat-treated at 1000℃ for 3 hours. After the heat treatment was completed, it was cooled to room temperature, and the length of the sample block after heat treatment was measured. The rate of change between the length after heat treatment and the initial length is the cold-state linear change after calcination at 1000℃ for 3 hours.

[0084] Test on the bonding performance between dry refractory and original lining material: The original lining material was cast into a standard sample block of 160mm×40mm×40mm using a standard triple mold. After firing at 1000℃ for 3 hours, the standard sample block was broken in the middle according to the "Test Method for Flexural Strength of Refractory Materials at Room Temperature" (GB / T 3001-2007). The two broken halves of the standard sample block were then placed in the standard triple mold, with the end face of the sample block flush with the mold and the broken surface exposed. The standard triple mold was then transferred to a high-temperature furnace and filled with dry refractory containing half of the standard sample block. The temperature was raised to 1000℃ and held for 3 hours. After holding for 3 hours, the temperature was naturally cooled to room temperature to obtain the bonding specimen for testing. The four-point flexural strength of the bonding specimen was tested according to the "Test Method for Flexural Strength of Fine Ceramics" (GB / T6569-2006).

[0085]

[0086] in conclusion: Figure 1 , Figure 2 To combine the performance test results of the dry-mix material and the original lining material, the following diagram is provided: Figure 1 The sample block used was the hot repair material for aluminum industrial furnaces prepared in Example 1. Figure 2 The sample block used was the hot-state repair material for aluminum industrial furnaces prepared in Example 2. Figure 1 In the case where the fracture is not at the joint, it indicates that the strength of the hot-pressed repair material after sintering is higher than its own strength, and that the hot-pressed repair material has good bonding performance with the original lining material. Figure 2 The fracture point is at the joint, indicating that the hot-state repair material prepared in Example 2 has poor bonding ability with the original lining material compared to Example 1.

[0087] The test data shows that the hot repair material for aluminum industrial furnaces prepared by this invention has good fluidity at 300℃, which makes it easy to spread the repair material on the surface of the original lining material and quickly repair the damaged area of ​​the original lining. After sintering, the repair material not only has high flexural strength, but also maintains a high strength after water cooling and thermal shock. It also has good bonding performance with the original lining material, which can meet the high-temperature working conditions of the furnace lining and is suitable for rapid repair of aluminum reactors.

[0088] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A hot-state repair material for aluminum industrial furnaces, characterized in that: By mass fraction, it contains 30–60 wt% mullite aggregate, 10–20 wt% pretreated secondary aluminum ash, 5–15 wt% composite additives, 3–8 wt% aluminum dihydrogen phosphate powder, 2–6 wt% silica powder, 0.2–2 wt% flake graphite and 0.5–2 wt% polypropylene short fibers. The preparation method of the composite additive is as follows: Sodium metasilicate pentahydrate and borax are mixed at a mass ratio of (2-5):1 and mechanically stirred for 5-15 minutes to ensure uniform mixing, thus obtaining a composite additive.

2. The hot repair material for aluminum industrial furnaces according to claim 1, characterized in that: The chemical composition of the pretreated secondary aluminum ash is as follows: 60-80 wt% aluminum oxide, 5-15 wt% silicon dioxide, 0.5-3 wt% ferric oxide, 0.5-3 wt% calcium oxide, 1-5 wt% potassium oxide, and 0.5-3 wt% sodium oxide.

3. The hot repair material for aluminum industrial furnaces according to claim 2, characterized in that: The preparation method of pretreated secondary aluminum ash is as follows: add secondary aluminum ash to hydrochloric acid and soak and react at 50-60℃ for 2-3 hours. After soaking, wash with deionized water until neutral, then dry at 100-110℃, and then sieve to remove impurities to obtain pretreated secondary aluminum ash.

4. The method for preparing a hot-state repair material for aluminum industrial furnaces according to claim 1, characterized in that: Specifically: Flake graphite, polypropylene short fibers, one-third by weight of silica powder and polycarboxylate dispersant are mixed and mechanically stirred for 20-30 minutes at a stirring speed of 400-500 rpm. After stirring is completed, mixed dry material A is obtained. Mullite aggregate, pretreated secondary aluminum ash, aluminum dihydrogen phosphate powder, silicon oxynitride, two-thirds by weight of silicon micro powder and composite additives are mixed and mechanically stirred for 3-5 minutes at a stirring speed of 80-100 rpm. After stirring, mixed dry material A is added and stirring is continued for 8-10 minutes at a stirring speed of 40-50 rpm to obtain hot repair material for aluminum industrial furnaces. The mass fraction of silicon oxynitride in the hot repair material for aluminum industrial furnaces is 1-3%.

5. The method for preparing a hot-state repair material for aluminum industrial furnaces according to claim 4, characterized in that: Hot-state repair material for aluminum industrial furnaces contains silicon oxynitride, and its preparation method is as follows: Elemental silicon and silicon dioxide were mixed and ball-milled for 3–5 hours to obtain a mixed powder with a particle size D50 of 5–10 μm. Under nitrogen protection, the mixed powder was placed in a graphite crucible lined with graphite paper and sintered at 1400–1450 °C for 12–15 hours. After sintering, the mixture was naturally cooled to room temperature. The sintered product was then pulverized and sieved to obtain silicon oxynitride.

6. The method for preparing a hot-state repair material for aluminum industrial furnaces according to claim 5, characterized in that: The mass ratio of elemental silicon to silicon dioxide is (6-10):(5-8).

7. The method for preparing a hot-state repair material for aluminum industrial furnaces according to claim 4, characterized in that: The pretreated secondary aluminum ash is added to the impregnation modification slurry. The modification slurry is specifically as follows: Add basic zirconium chloride octahydrate to ethanol and stir continuously to dissolve it, obtaining a zirconium chloride alcohol solution. Add bentonite suspending agent to the zirconium chloride alcohol solution and stir at 800-1000 rpm for 5-10 min to disperse it in the zirconium chloride alcohol solution. Then add fused magnesia powder and corundum powder and continue stirring at 800-1000 rpm for 15-20 min to obtain the modified slurry.

8. The method for preparing a hot-state repair material for aluminum industrial furnaces according to claim 7, characterized in that: The mass ratio of basic zirconium chloride octahydrate, fused magnesia powder, and corundum powder is (15-18):(12-15):(5-7).

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