A method for preparing precast calcium oxide refractory materials by high-temperature casting

Abstract

This invention discloses a method for preparing high-temperature castable calcium oxide refractory precast components, belonging to the field of refractory material technology. The invention uses high-purity fused calcium oxide aggregate and ultrafine calcium oxide powder as main materials, with waterless medium-temperature asphalt as a binder, combined with anti-hydration additives and waterless plasticizers. The entire process is carried out in a closed, waterless environment. The raw materials are pre-dried and dehydrated before being mixed at a constant temperature. The preheated mold is then vibrated for casting. The temperature is gradually increased to 600℃ and held to allow for deep carbonization of the asphalt, forming a continuous carbonaceous protective film on the particle surface. Finally, the mold is removed and sealed for protection. This invention completely avoids the calcium oxide hydration cracking problem caused by water-based processes. It can be cast into various irregularly shaped precast components. The products have high density, excellent room-temperature mechanical strength, long-term hydration resistance, and outstanding resistance to high-temperature alkaline slag erosion. It is suitable for the industrial production of calcium oxide refractory precast components for steelmaking refining furnaces and ladle linings.

Description

Technical Field

[0001] This invention belongs to the field of inorganic refractory material preparation technology, specifically relating to a method for preparing calcium oxide refractory preforms by high-temperature casting. The method uses anhydrous asphalt as a binder and a completely anhydrous system, and employs a process of casting calcium oxide refractory preforms at 300℃. This method is applicable to calcium oxide refractory preforms used in metallurgical high-temperature kilns, steel ladles, refining furnace linings, and high-temperature alloy smelting. Background Technology

[0002] Calcium oxide (CaO) refractory materials possess excellent resistance to melt erosion, desulfurization and dephosphorization, and good high-temperature stability, making them highly beneficial for the purification and smelting of high-temperature molten metals. They have irreplaceable advantages in special steelmaking refining and high-temperature alloy smelting processes. However, calcium oxide is extremely prone to hydration reaction with moisture in the air, generating calcium hydroxide which expands in volume, causing precast components to crack and pulverize. This is the core pain point restricting the large-scale application of calcium oxide refractory precast components.

[0003] Currently, conventional calcium oxide refractory precast parts are divided into two types of molding processes: (1) Water-based castable process: calcium aluminate cement is combined with water for casting and molding, and then cured and dried at room temperature. The free water in the system cannot be completely eliminated, and the calcium oxide hydration cracking problem is serious. The product storage period is extremely short. (2) Dry pressing process: asphalt is combined with dry pressing. The density of pressure molding is uneven, the molding of irregular precast parts is difficult, the finished product qualification rate is low, the low temperature heat treatment system is simple, the carbonization degree of the asphalt binder phase is insufficient, and it is easy to soften and fall off when used at high temperature.

[0004] Most existing asphalt-bonded calcium oxide products are prepared by low-temperature calcination, which cannot prevent moisture intrusion at the source. At the same time, the carbonization and shaping of the asphalt bonding network are insufficient, resulting in low strength of precast components at room temperature, poor resistance to hydration, easy loss of the binder phase at high temperatures, and short service life. Therefore, there is an urgent need to develop a new process for preparing calcium oxide refractory precast components that are completely waterless, can be cast into irregular shapes, can be shaped by heat treatment at 600℃, and have long-term resistance to hydration. Summary of the Invention

[0005] To address the problems of easy hydration and cracking of calcium oxide, defects in water-based processes, insufficient strength of asphalt-bonded precast parts, and difficulty in forming irregularly shaped parts in existing technologies, this invention provides a method for preparing calcium oxide refractory precast parts by high-temperature casting at 300℃.

[0006] The present invention achieves the above objectives by adopting the following technical solution: A method for preparing high-temperature castable calcium oxide refractory preforms employs a completely closed, anhydrous production environment with relative humidity controlled to ≤0.5%. The raw material composition and mass fractions are as follows: 60-70 parts high-purity fused calcium oxide aggregate; 20-25 parts ultrafine calcium oxide powder; 5-8 parts anhydrous medium-temperature asphalt; 3-5 parts anti-hydration composite additive; and 1-2 parts anhydrous plasticizer / flow agent. The specific preparation steps are as follows: S1. Anhydrous pretreatment of raw materials: calcium oxide aggregate and calcium oxide ultrafine powder are placed together in a drying kiln and dried at a constant temperature of 180℃ for 24 hours, with the air and moisture completely isolated throughout the process; anhydrous asphalt is melted and kept at 300℃ and filtered to remove impurities and trace amounts of free water, and then stored at a constant temperature for later use; anti-hydration additives and anhydrous plasticizers are sealed and stored in a moisture-proof environment. S2. High-temperature mixing uses a heated closed mixer. First, the dried calcium oxide aggregate, calcium oxide ultrafine powder, and anti-hydration additive are dry-mixed for 5 minutes, and the temperature of the mixer cavity is maintained at 300-350℃. Then, molten anhydrous asphalt and anhydrous plasticizer are added at a uniform speed, and the mixture is continued to be mixed at a constant temperature for 15-20 minutes to obtain a uniform, flowable hot castable without dry powder agglomeration. S3. Mold Preheating and Hot Vibration Casting: Heat-resistant steel molds are used, and the inner walls of the molds are coated with anhydrous silicone oil-based release agent. The entire mold is preheated to 180°C. The hot castable is quickly injected into the preheated mold and placed on a high-frequency vibration table at a vibration frequency of 50Hz for 3-5 minutes to fully remove internal air bubbles and improve the density of the billet. After casting, the top of the mold is covered with a waterproof sealing film to prevent the adsorption of environmental moisture. S4. Stepped heating to 600℃ for curing and carbonization heat treatment (core process): The sealed mold is sent into a hot air drying kiln, using a segmented slow heating system with complete humidity control throughout. Heating curve: ① Heating from room temperature to 120℃ at a rate of 2℃ / h, and holding at 120℃ for 8 hours to remove the light volatile components inside the asphalt; ② Heating from 120℃ to 200℃ at a rate of 1.5℃ / h, and holding at 200℃ for 12 hours to allow the asphalt to initially condense and solidify, forming a bonding skeleton; ③ Heating from 200℃ to 600℃ at a rate of 1℃ / h, and holding at 600℃ for 24 hours to allow the asphalt to undergo deep pyrolysis and carbonization, forming a continuous carbon film bonding network at the calcium oxide particle interface; ④ Natural and slow cooling at a rate ≤50℃ / h until the overall temperature of the mold is below 60℃. S5. Demolding and Finished Product Protection: Demold at low temperatures, handle with care to avoid damage to the blank; apply a thin layer of molten anhydrous asphalt sealant to the outer surface of the precast part, seal it in a moisture-proof packaging bag, and store it in a dry warehouse.

[0007] The high-purity fused calcium oxide aggregate has a CaO mass content of ≥98% and a particle size classification of 5-10mm; the calcium oxide ultrafine powder has a particle size of ≤0.074mm and an active calcium oxide content of ≥95%; the anhydrous medium-temperature asphalt has a softening point of 80-120℃ and melts, dehydrates, and removes slag at 180℃; the anti-hydration additive is a compound powder of titanium carbonitride and BN micro powder; and the anhydrous modified plasticizer is refined furfural.

[0008] The present invention proposes a method for preparing precast calcium oxide refractory materials by high-temperature casting. Using the above-mentioned technical solution, it has the following beneficial effects: 1. This invention uses an anhydrous system for production throughout the entire process, without adding any external water, thus eliminating the problem of calcium oxide hydrating, expanding, and cracking when it comes into contact with water from the source of the process. Combined with an asphalt carbonization protective film, the product can be placed in an atmospheric environment for 7 days without cracking or powdering, and its hydration resistance is greatly improved. 2. The hot asphalt casting molding process can be used to prepare complex irregular refractory precast parts. Compared with the traditional dry pressing molding, it has a wider range of adaptability. The bulk density of the blank is ≥2.6g / cm³, and the structure is uniform and dense. 3. Through precise stepped heating to 300℃ and long-term heat preservation and carbonization, the asphalt binder phase forms a continuous hard carbon network. The compressive strength at room temperature is ≥40MPa. It is not easy to soften and flow under high temperature conditions. It has excellent alkaline resistance to steel slag corrosion and can be used at temperatures up to 1400~1600℃. 4. The entire production process is controllable, the heat treatment system is stable, the finished product has high consistency, and the shelf life of the sealed asphalt layer is significantly extended, making it suitable for continuous industrial-scale production.

[0009] In summary, the entire process of closed-loop anhydrous mixing, hot vibration casting, and precise stepped heating to 600℃ for curing is a zero-water system. It uses molten asphalt as a high-temperature fluidizing agent, hot vibration casting, and stepped heating to 600℃ for carbonization and shaping. This process forms a continuous carbonaceous protective film on the surface of aggregate particles, which significantly inhibits calcium oxide hydration and improves the room temperature structural strength and high temperature slag resistance of precast components. It is suitable for the mass production of various irregular shaped refractory precast components. Detailed Implementation

[0010] The present invention will be described in detail with reference to specific embodiments: Example 1:

[0011] Raw material weight parts: 65 parts of fused calcium oxide aggregate, 23 parts of calcium oxide ultrafine powder, 7 parts of tar pitch with a softening point of 100℃, 3.5 parts of titanium carbonitride + BN composite additive, and 1.5 parts of anhydrous furfural plasticizer flow agent. step: ① Aggregate powder is dried at 180℃ for 24 hours and then sealed and cooled; asphalt is melted at 300℃, filtered, and kept warm. ② Mix in a closed system at 300℃ for 5 minutes, then add asphalt and plasticizer and mix for 18 minutes. ③ Preheat the steel mold to 180℃, vibrate and pour for 4 minutes, then cover and seal with a film; ④ Stepwise temperature increase: room temperature → 120℃ (2℃ / h, hold for 8h) → 200℃ (1.5℃ / h, hold for 12h) → 600℃ (1℃ / h, hold for 24h), then slowly decrease the temperature; ⑤ Demold below 60℃, seal surface with asphalt film for moisture protection and packaging. Testing indicators: porosity 2%, bulk density 2.66g / cm³, room temperature pressure resistance 45MPa, no visible cracks after 7 days in air. Example 2:

[0012] Raw material weight parts: 65 parts of fused calcium oxide aggregate, 20 parts of calcium oxide ultrafine powder, 10 parts of tar pitch with softening point of 110℃, 2.5 parts of titanium carbonitride + BN composite additive, and 2.5 parts of anhydrous furfural plasticizer flow agent. step: ① Aggregate powder is dried at 180℃ for 24 hours and then sealed and cooled; asphalt is melted at 300℃, filtered, and kept warm. ② Mix in a closed system at 300℃ for 5 minutes, then add asphalt and plasticizer and mix for 18 minutes. ③ Preheat the steel mold to 180℃, vibrate and pour for 4 minutes, then cover and seal with a film; ④ Stepwise temperature increase: room temperature → 120℃ (2℃ / h, hold for 8h) → 200℃ (1.5℃ / h, hold for 12h) → 600℃ (1℃ / h, hold for 24h), then slowly decrease the temperature; ⑤ Demold below 60℃, seal surface with asphalt film for moisture protection and packaging. Testing indicators: porosity 2.5%, bulk density 2.68g / cm³, room temperature pressure resistance 48MPa, no visible cracks after 7 days in air. Example 3:

[0013] Raw material weight parts: 70 parts of fused calcium oxide aggregate, 22 parts of calcium oxide ultrafine powder, 6 parts of high-temperature modified asphalt with a softening point of 120℃, 0.5 parts of titanium carbonitride + BN composite additive, and 1.5 parts of anhydrous furfural plasticizer. step: ① Aggregate powder is dried at 180℃ for 24 hours and then sealed and cooled; asphalt is melted and filtered at 300℃. ② Mix in a closed system at 300℃ for 5 minutes, then add asphalt and plasticizer and mix for 18 minutes. ③ Preheat the steel mold to 180℃, vibrate and pour for 4 minutes, then cover and seal with a film; ④ Stepwise temperature increase: room temperature → 120℃ (2℃ / h, keep warm for 8h) → 200℃ (1.5℃ / h, keep warm for 12h) → 600℃ (1℃ / h, keep warm for 24h), then slowly decrease the temperature; ⑤ Demold below 60℃, seal surface with asphalt film for moisture protection and packaging. Testing indicators: porosity 2.0%, bulk density 2.90 g / cm³, room temperature pressure resistance 40 MPa, no visible cracks after 7 days in air.

Claims

1. A method for preparing a precast calcium oxide refractory material component by high-temperature casting, characterized in that: The entire process is carried out in a completely closed, waterless production environment with relative humidity controlled to ≤0.5%. The raw material composition and weight percentages are as follows: 60-70 parts high-purity fused calcium oxide aggregate; 20-25 parts ultrafine calcium oxide powder; 5-8 parts waterless medium-temperature asphalt; 3-5 parts anti-hydration composite additive; 1-2 parts waterless plasticizer / flow agent. The specific preparation steps are as follows: S1. Anhydrous pretreatment of raw materials: Calcium oxide aggregate and ultrafine powder are dried at 180℃ for 24 hours, then sealed and cooled to prevent moisture. Anhydrous asphalt is melted at 300℃, filtered to remove impurities, and kept warm for later use. S2. Constant temperature closed mixing: First, dry mix aggregates, powders and additives at 60-80℃, then add molten asphalt and plasticizer and mix at constant temperature to obtain hot flowable castable; S2. High-temperature mixing uses a heated closed mixer. First, the dried calcium oxide aggregate, calcium oxide ultrafine powder, and anti-hydration additive are dry-mixed for 5 minutes, and the temperature of the mixer cavity is maintained at 300-350℃. Then, molten anhydrous asphalt and anhydrous plasticizer are added at a uniform speed, and the mixture is continued to be mixed at a constant temperature for 15-20 minutes to obtain a uniform, flowable hot castable without dry powder agglomeration. S3. Preheating the mold and hot vibration casting: Preheat the mold to 180℃ and apply anhydrous release agent. After the hot casting material is injected into the mold, vibrate at 50Hz for 3-5 minutes to vent and compact the material. Seal the top of the mold with a film to prevent moisture. S4. Stepwise heating to 600℃ for carbonization and curing heat treatment: slow heating in stages, from room temperature to 120℃ at 2℃ / h and hold for 8 hours, then to 200℃ at 1.5℃ / h and hold for 12 hours, then to 600℃ at 1℃ / h and hold for 24 hours, then slowly cool down to below 60℃ at ≤50℃ / h. S5. After demolding, apply anhydrous asphalt sealant to the surface of the precast component and seal it for moisture protection during storage.

2. The method for preparing a high-temperature castable calcium oxide refractory preform as described in claim 1, characterized in that: The high-purity fused calcium oxide aggregate has a CaO mass fraction ≥98% and a particle size of 5-10 mm; the calcium oxide ultrafine powder has a particle size ≤0.074 mm and an active CaO ≥95%.

3. The method for preparing a high-temperature castable calcium oxide refractory preform as described in claim 1, characterized in that: The softening point of the anhydrous medium-temperature asphalt is 80-120℃; the anti-hydration composite additive is a compound powder of titanium carbonitride micro powder and BN micro powder; the anhydrous modified plasticizer is refined anhydrous furfural.

4. The method for preparing a high-temperature castable calcium oxide refractory preform as described in claim 1, characterized in that: In step S2, the raw materials are dry-mixed for 5 minutes, and after adding the binder, the mixing time is 15-20 minutes.

5. The method for preparing a high-temperature castable calcium oxide refractory preform as described in claim 1, characterized in that: The release agent used in step S3 is an anhydrous release agent based on methyl silicone oil.

6. The method for preparing a high-temperature castable calcium oxide refractory preform as described in claim 1, characterized in that: The prepared calcium oxide refractory preforms have a porosity of ≤3.0%, a bulk density of ≥2.6g / cm³, and a room temperature compressive strength of ≥40MPa.