A mold release agent based on geopolymer gel-waste heat synergistic curing and its preparation and use method

Abstract

The application belongs to the field of steel die casting auxiliary materials and process technology, and discloses a die casting release agent based on geopolymer gel-heat residual synergistic curing and a preparation and use method thereof. The release agent takes metakaolin as a base body, is matched with sodium silicate activator, nano silicon oxide-boron nitride micro powder composite reinforcing agent, compounded polycarboxylic acid water reducing agent and defoaming agent, and is prepared by adding deionized water according to a water-cement ratio of 0.3-0.5:1; the preparation adopts high-speed stirring at 1500-2000 r / min for 15-20 minutes, and the release agent is coated on an ingot mold by using a gradient coating process during use, is cured by relying on residual heat of a casting of ≥800 DEG C, and a closed-loop recycling system of a die release layer crushing-grinding-circulating proportioning is constructed. The application completely solves the technical problems of carbide residue, dust flying and non-recyclability of the traditional release agent, reduces the casting skin defect rate to ≤1%, controls the oxide skin thickness to 0.05-0.1 mm, and realizes ≥60% of the release agent recycling rate, more than 60% of ton steel cost reduction, and the combination of environmental protection, practicality and economy.

Description

Technical Field

[0001] This invention belongs to the field of auxiliary materials and processes for steel casting, specifically relating to a casting release agent based on the synergistic curing of geopolymer gel and residual heat, and its preparation and application methods. This invention is particularly suitable for the casting production of ultra-thick carbon steel, alloy steel, stainless steel, and heat-resistant steel castings with a thickness ≥450mm. Background Technology

[0002] Release agents, as key auxiliary materials in mold casting production, directly affect the surface quality of castings, subsequent processing efficiency, and environmental protection levels. Traditional mold casting release agents are mainly divided into liquid and powder types, but both have insurmountable technical pain points, which seriously restrict the high-quality development of the industry.

[0003] Liquid release agents, such as engine oil and diesel oil, are convenient to apply, but they are easily combusted and carbonized in the high-temperature environment of molten steel above 1500℃. The residual carbides (such as Fe3C) can penetrate into the surface of the casting, causing "peeling" defects during subsequent rolling processes. The defect rate is as high as 20%, requiring additional grinding and pickling processes to remove the surface carbides, increasing production costs and processing time. At the same time, the volatiles of liquid release agents can pollute the workshop environment, while powdered release agents (such as graphite powder and talc powder) pose a problem of airborne pollution. Long-term inhalation of dust can easily cause respiratory diseases for operators, and fine powder can easily penetrate into the interior of the casting to form inclusions, resulting in a decrease in the mechanical properties of the casting and an increase in scrap rate of 3%-5%. In addition, the coating uniformity of powdered release agents is poor, and local accumulation or missed coating is easy to occur, resulting in uneven demolding and causing scratches on the surface of the casting.

[0004] More importantly, traditional release agents have a single function, only achieving the basic role of "isolation and demolding," and cannot simultaneously address the needs for oxidation prevention and stress relief during the casting solidification process. Ultra-thick castings have long solidification cycles (8-24 hours), and at high temperatures, they easily come into contact with air to form a 0.2-0.5mm thick oxide scale, which is difficult to clean subsequently. Simultaneously, the large temperature gradient between the inside and outside of the casting leads to concentrated thermal stress, easily causing cracks. Traditional release agents lack the function of buffering thermal stress, further exacerbating the defect risk; the overall crack rate in ultra-thick casting production reaches 8%–15%.

[0005] Current improvements to release agents largely focus on optimizing single properties, such as developing synthetic liquid release agents with stronger high-temperature stability or adding binders to reduce powder dispersion. However, these approaches do not fundamentally address the core issues of carbide residue, inclusions, and limited functionality. Some researchers have attempted to use ceramic-based release agents, but these suffer from difficulties in room-temperature application, the need for additional heating for curing, and high costs, hindering industrial-scale adoption. As high-end manufacturing demands increasingly higher surface quality for castings (e.g., cold-rolled steel sheets require a carbide content ≤0.01% and an oxide scale thickness ≤0.1mm), the industry urgently needs to develop a novel release agent technology that is low-pollution, residue-free, multifunctional, and recyclable to fill existing technological gaps. Summary of the Invention

[0006] The core objective of this invention is to provide a casting release agent based on the synergistic curing of geopolymer gel and residual heat, along with its preparation and application methods, thoroughly addressing the pain points of traditional release agents such as carbide residue, inclusion contamination, limited functionality, and failure to meet environmental standards. This invention develops a geopolymer gel-based release agent that utilizes residual heat from the casting to achieve synergistic curing, forming a high-temperature resistant ceramic release layer. This controls the carbide content on the casting surface to ≤0.01%, reducing the "peeling" defect rate from 20% to ≤1%, achieving surface quality requirements comparable to cold-rolled products. It integrates release, oxidation prevention, and stress buffering functions, reducing the oxide scale thickness of the casting from 0.2-0.5mm to 0.05-0.1mm, while simultaneously buffering thermal stress, further reducing the casting crack rate by 5%-10%. The invention also optimizes the release agent recycling process, achieving a recycling rate of ≥60% and reducing the cost of the release agent.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A mold release agent based on geopolymer gel-residual heat synergistic curing is disclosed. This agent focuses on the room-temperature gelling properties and high-temperature ceramization characteristics of geopolymers, optimizing the formulation components and proportions to ensure the release agent possesses excellent coating fluidity, room-temperature curing properties, high-temperature stability, and easy peeling. Using metakaolin as the geopolymer matrix, by mass ratio, 20%–30% water glass as an activator, 2%–5% nano-silica and 1%–3% boron nitride micropowder as composite reinforcing agents, 0.5%–1.2% polycarboxylate-based water-reducing agent as an additive, and 0.3%–0.8% defoamer are added to the metakaolin. Deionized water is added to the above mixture at a water-cement ratio of (0.3–0.5):1, and the mixture is stirred evenly to obtain the release agent.

[0008] The geopolymer gel release agent formulation is designed as follows: metakaolin is selected as the geopolymer matrix; water glass (Na2O•nSiO2) is used as an activator, with an addition amount of 20% to 30% of the metakaolin mass; nano-silica and boron nitride (BN) micro powder are used as reinforcing agents, with the following addition amounts: nano-silica at 2% to 5% of the metakaolin mass and boron nitride (BN) micro powder at 1% to 3% of the metakaolin mass; polycarboxylate superplasticizer is used as an additive, with an addition amount of 0.5% to 1.2% of the metakaolin mass; 0.3% to 0.8% of defoamer at the metakaolin mass is added; and deionized water is added at a water-cement ratio of (0.3 to 0.5):1.

[0009] The metakaolin has the following chemical composition: SiO2 content 55%–65%, Al2O3 content 25%–35%, Fe2O3 content ≤2%, CaO content ≤1%, and the metakaolin particle size range is 10–50 μm, with a specific surface area of ​​300–400 m². 2 / kg, to ensure sufficient gelation reaction and subsequent ceramization effect.

[0010] The water glass has a modulus of 3.0 to 3.5 and a solid content of 40% to 50%, which can rapidly stimulate the hydration reaction of metakaolin to form a three-dimensional network gel structure.

[0011] The nano-silica particles have a diameter of 20–50 nm, and their high specific surface area can fill the internal pores of the gel, improving the density and wear resistance of the ceramic film after curing. The boron nitride micropowder has a diameter of 1–5 μm, and the addition of boron nitride further reduces the bonding force between the release layer and the casting, improving the peeling performance.

[0012] Additives include polycarboxylate superplasticizer (40% solid content), which improves gel flowability and reduces the water-cement ratio; and defoamer (organosilicon), which eliminates air bubbles generated during stirring and prevents pores from appearing in the ceramic film after curing.

[0013] The release agent has a viscosity of 500-1000 mPa•s at 25℃. After coating, it is initially cured at room temperature for 30-60 minutes and fully cured at high temperature (≥800℃) by the residual heat of the casting, forming a ceramic film with mullite phase (3Al2O3•2SiO2) as the main component. It is resistant to high temperature (≥1500℃) and has a peel strength (≤0.5MPa).

[0014] A method for preparing a molding release agent based on the synergistic curing of geopolymer gel and residual heat involves adding a geopolymer matrix, an activator, a reinforcing agent, an auxiliary agent, and an antifoaming agent to deionized water, and stirring at a high speed of 1500-2000 r / min for 15-20 minutes to form a uniform and stable geopolymer gel molding release agent.

[0015] A method for using a mold release agent based on the synergistic curing of geopolymer gel and residual heat is disclosed. This method optimizes coating parameters and curing sequence, taking into account the solidification characteristics of ultra-thick castings, to achieve precise synergy between the release agent and the residual heat of the casting. The method includes the following steps: 1) Coating preparation: 1-2 hours before casting, pre-treat the inner wall of the mold to remove residual steel slag and oxide scale, and ensure that the flatness error of the inner wall is ≤0.2mm / m; heat the geopolymer gel release agent to 30-40℃ (to improve fluidity) and apply it evenly through high-pressure spraying equipment.

[0016] 2) Coating parameters: The coating thickness is distributed in a gradient along the height of the mold. The coating thickness in the bottom area (15%–25% of the mold height) is 1.2–1.5 mm (this area has high temperature and a high risk of adhesion), the coating thickness in the middle area (55%–65% of the mold height) is 0.8–1.2 mm, and the coating thickness in the top area (15%–25% of the mold height) is 0.5–0.8 mm (to accommodate shrinkage and demolding). During spraying, the distance between the nozzle and the inner wall of the mold should be maintained at 300–500 mm, the moving speed should be 50–80 mm / s, and the working pressure should be 0.4–0.6 MPa. Ensure that the coating is uniform, without any missed areas or accumulation.

[0017] 3) Curing sequence: After coating, allow to stand naturally for 30–60 minutes. The release agent will initially cure at room temperature, forming a dense gel film that seals the pores in the mold wall. After casting, utilize the residual heat from the casting (temperature ≥800℃) to gradually and completely cure the gel film over 8–16 hours. This transforms into a dense ceramic release layer, preventing direct contact between the molten steel and the mold wall. During solidification, the ceramic release layer continuously provides anti-oxidation protection, while its elastic modulus (80–120 GPa) buffers thermal stress and inhibits crack formation.

[0018] Design a closed-loop recycling system to achieve the recycling of release agent and reduce raw material consumption: 4) Demolding and peeling: After the casting solidifies (the surface temperature drops to 800-900℃), the ceramic release layer has weak adhesion to the casting surface and can fall off naturally with the casting. Some residual release agent fragments can be removed by light tapping (impact force ≤5kN). After peeling, there are no residues or scratches on the casting surface.

[0019] 5) Recycling: Collect the released agent fragments, crush them to a particle size ≤ 5mm using a jaw crusher, remove large particles such as steel slag and iron oxide scale by a vibrating screen, then grind them to a particle size ≤ 0.1mm using a ball mill, remove ultrafine dust and residual trace metal impurities by an air classifier, and finally obtain recycled powder with a purity ≥ 95%.

[0020] 6) Recycling ratio: Add the recycled powder to the newly prepared geopolymer gel release agent at a ratio of 30% to 50%, add an appropriate amount of water glass (the amount of addition is 10% to 15% of the mass of the recycled powder) and deionized water, and adjust the viscosity to 500 to 1000 mPa•s (at 25℃), and it can be used for coating again.

[0021] The core of the technical solution of this invention lies in the formulation design of the geopolymer gel release agent, the optimization of the coating-curing process and the construction of the recycling system. Through the synergistic effect of the initial curing of the geopolymer at room temperature and the complete curing by the residual heat of the casting, a multifunctional integrated release agent is achieved.

[0022] The core technology of this invention lies in overcoming the single function and pollution problems of traditional release agents, and constructing an integrated technology system of "material formulation - process synergy - recycling", which is mainly reflected in the following three aspects: 1. For the first time, the technology of geopolymers in the construction field is introduced into the field of mold release agents. Using metakaolin as the matrix, combined with water glass activator, nano-silica reinforcing agent and boron nitride micro powder, a gel system with both room temperature fluidity and high temperature ceramicization properties is formed, completely eliminating the oil-based components of traditional liquid mold release agents and the powder matrix of powder mold release agents.

[0023] After curing, a mullite phase ceramic film is formed, which is resistant to high temperature ≥1500℃ and has no carbide residue. It solves the casting defects caused by combustion carbonization and powder inclusions of traditional release agents. The carbide content on the casting surface can be controlled to ≤0.01%.

[0024] 2. Utilizing the synergistic process of "preliminary curing at room temperature + complete curing with residual heat of casting", no additional heating equipment is required. By utilizing the residual heat of ≥800℃ released during the solidification process of ultra-thick castings, the release agent can complete the ceramic transformation within 8-16 hours, simultaneously achieving the three major functions of demolding, anti-oxidation, and stress buffering.

[0025] The gradient coating process was designed to optimize the coating thickness based on the temperature differences in different areas of the ingot mold: 1.2-1.5mm at the bottom, 0.8-1.2mm in the middle, and 0.5-0.8mm at the top. This solved the technical pain points of poor coating uniformity, local adhesion, or missed coating in traditional coating methods.

[0026] 3. Construct a closed-loop recycling system of "demolding and peeling - crushing and grinding - recycling ratio". The detached ceramic demolding layer can be crushed and ground, and then mixed with new agent at a ratio of 30%-50% for recycling 3-5 times. The recycling rate is ≥60%, and the cost per ton of steel is reduced from the traditional 30 yuan to less than 12 yuan.

[0027] The entire process produces no volatile pollutants or dust, meeting both environmental protection requirements for ultra-low emissions and compatibility with existing mold casting production lines. The cost of modifying a single production line is ≤500,000 yuan, solving the industry problem of traditional mold release agents failing to meet environmental standards and being non-recyclable.

[0028] Compared with the prior art, the beneficial effects of the present invention are: This invention achieves multi-dimensional breakthroughs compared to traditional release agents through innovative geopolymer gel formulations, optimized waste heat synergistic curing processes, and the construction of a recycling system. Specific beneficial effects are as follows: 1) The surface quality of castings is significantly improved and the defect rate is greatly reduced: the ceramic release layer has no carbide residue, the carbide content on the surface of the casting is reduced to ≤0.01%, the "peeling" defect rate is reduced from 20% to ≤1%, and the surface roughness Ra≤1.6μm, which meets the requirements of cold-rolled surface. No further grinding is required, saving more than 25% of processing costs.

[0029] 2) Achieving multi-functional integration with outstanding anti-oxidation and stress buffering effects: The ceramic film can effectively isolate air, reducing the oxide scale thickness of castings from 0.2-0.5mm to 0.05-0.1mm, and reducing subsequent cleaning workload by 80%; at the same time, the elastic modulus and thermal conductivity (1.5-2.0W / (m•K)) of the release layer can buffer thermal stress, reducing the actual crack rate of castings to 2%~5%, which is 5%-10% lower than traditional processes, and improving mechanical property stability by 20%.

[0030] 3) High recycling rate and significant cost and environmental advantages: The recycling rate of release agent is ≥60%, and the cost of release agent per ton of steel is reduced from RMB30 to less than RMB12, a reduction of more than 60%; there are no volatile pollutants and dust flying, and the air quality in the workshop meets the requirements of GBZ2.1-2019 "Occupational Exposure Limits for Hazardous Factors in the Workplace", achieving green production.

[0031] 4) Strong process adaptability and high promotion value: The release agent coating is compatible with existing high-pressure spraying equipment, without the need for new special equipment, and the transformation cost of a single production line is ≤500,000 yuan; it can be adapted to the production of ultra-thick castings of different materials and thicknesses, and the recycling process is simple and easy to implement, with broad industrial application prospects.

[0032] 5) Eliminates release agent volatile pollution and dust, meets environmental protection ultra-low emission requirements, and has strong process adaptability, compatible with existing mold casting production lines, without the need for additional heating equipment. Detailed Implementation

[0033] To further describe the present invention, specific embodiments are provided below, which will more clearly demonstrate the advantages and various effects of the present invention. Those skilled in the art should understand that these specific embodiments are illustrative of the invention and not intended to limit it.

[0034] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] This invention is applicable to the mold casting production of various castings, including ultra-thick carbon steel, alloy steel, stainless steel, and heat-resistant steel, with a thickness ≥450mm. It is particularly suitable for castings used in high-end equipment with stringent surface quality and environmental protection requirements (such as cold-rolled substrate steel, nuclear power steel, and precision mechanical parts). It completely solves the problems of traditional release agents, such as contamination, inclusions, and limited functionality, achieving integrated functions of demolding, oxidation prevention, and stress buffering. The following six specific embodiments illustrate the invention in detail. These embodiments are for illustrative purposes only and do not constitute a limitation on the scope of protection.

[0037] Example 1: Q235 carbon steel ultra-thick casting (for cold-rolled substrate, thickness 450mm); The casting dimensions are 450mm × 1200mm × 3000mm, using an H13 ingot mold; the geopolymer gel release agent formula is: metakaolin (SiO2 content 60%, Al2O3 content 30%, Fe2O3 content 2%, CaO content 1%, particle size 20-40μm, specific surface area 350m²). 2 100 kg of water glass (modulus 3.2, solid content 45%), 25 kg of nano-silica (particle size 30 nm), 3 kg of boron nitride micro powder (particle size 2-4 μm), 1.5 kg of polycarboxylate superplasticizer (solid content 40%), 0.8 kg of organosilicon defoamer, and 0.5 kg of deionized water; stir at 1800 r / min for 18 minutes. The viscosity after stirring is 650 mPa•s (25℃).

[0038] Application process: Apply the release agent 1.5 hours before casting, with a release agent temperature of 35℃ and a spraying pressure of 0.5MPa. The coating thickness is 1.5mm for the bottom (20% of the mold height), 1.0mm for the middle (60% of the mold height), and 0.6mm for the top (20% of the mold height). Allow the coating to cure naturally for 45 minutes after application. The casting temperature is 1520-1550℃, utilizing the residual heat of the casting for curing. The demolding temperature is 830℃. After demolding, recover the release agent fragments, crush and grind them to a particle size ≤0.1mm, and mix them with new agent at a ratio of 40% for recycling. The water glass replenishment amount is 12% of the mass of the recovered powder. Add deionized water to adjust the viscosity to 650mPa•s (25℃).

[0039] Results: The ceramic film formed after the release agent cures has a high temperature resistance of 1580℃ and a peel strength of 0.3MPa from the casting; the carbide content on the casting surface is 0.008%, the "peeling" defect rate is 0.8%, the oxide scale thickness is 0.06mm, and the surface roughness Ra is 1.2μm; the measured crack rate of the casting is 3.2%, which is 7.8 percentage points lower than that of the traditional process; the release agent recycling rate is 62%, and the cost per ton of steel is 11.5 yuan, which fully meets the requirements for cold-rolled substrate steel.

[0040] Example 2: Ultra-thick casting of 42CrMo alloy steel (for precision machinery, thickness 600mm); The casting dimensions are 600mm × 1500mm × 2800mm, using a 3Cr2W8V ingot mold; the geopolymer gel release agent formula is: metakaolin (SiO2 content 58%, Al2O3 content 32%, Fe2O3 content 1.5%, CaO content 0.8%, particle size 15~45μm, specific surface area 320m²). 2 100 kg of water glass (modulus 3.0, solid content 48%), 28 kg of nano-silica (particle size 25 nm), 4 kg of boron nitride micro powder (particle size 1-3 μm), 1.0 kg of polycarboxylate superplasticizer (solid content 40%), 0.6 kg of organosilicon defoamer, and 45 kg of deionized water; stir at 1700 r / min for 20 minutes, and the viscosity after stirring is 750 mPa•s (25℃).

[0041] Application process: Apply the release agent 2 hours before casting, with a release agent temperature of 32℃ and a spraying pressure of 0.55MPa. The coating thickness is 1.4mm for the bottom (20% of the mold height), 1.2mm for the middle (60% of the mold height), and 0.7mm for the top (20% of the mold height). Allow the coating to cure naturally for 50 minutes after application. The casting temperature is 1540-1570℃, and the casting is cured using the residual heat of the casting. The demolding temperature is 820℃. After demolding, recover the release agent fragments, crush and grind them to a particle size ≤0.1mm, and mix them with new agent at a ratio of 35% for recycling. The water glass replenishment amount is 13% of the mass of the recovered powder. Add deionized water to adjust the viscosity to 750mPa•s (25℃).

[0042] Results: The ceramic film formed after the release agent cures has a high temperature resistance of 1600℃ and a peel strength of 0.25MPa from the casting; the carbide content on the casting surface is 0.009%, the "peeling" defect rate is 0.9%, the oxide scale thickness is 0.07mm, and the surface roughness Ra is 1.4μm; the measured crack rate of the casting is 2.5%, which is 8.5 percentage points lower than that of the traditional process; the measured tensile strength of the casting body is 985MPa, the yield strength is 855MPa, and the mechanical property deviation of the same batch of castings is ±3MPa, which is 22% higher than that of castings produced by the traditional process; the release agent recycling rate is 65%, and the cost per ton of steel is 11.8 yuan, which fully meets the requirements of precision machinery steel.

[0043] Example 3: 304 stainless steel ultra-thick casting (for nuclear power, thickness 750mm); The casting dimensions are 750mm × 1800mm × 2500mm, using H13 material ingot mold; the geopolymer gel release agent formula is: metakaolin (SiO2 content 62%, Al2O3 content 28%, Fe2O3 content 1.8%, CaO content 0.6%, particle size 25~50μm, specific surface area 380m²). 2 100 kg of water glass (modulus 3.5, solid content 42%), 22 kg of nano-silica (particle size 40 nm), 2.5 kg of boron nitride micro powder (particle size 3-5 μm), 1.8 kg of polycarboxylate superplasticizer (solid content 40%), 0.7 kg of organosilicon defoamer, and 0.4 kg of deionized water; the mixture was stirred at 1900 r / min for 16 minutes, and the viscosity after stirring was 580 mPa•s (25℃).

[0044] Application process: Apply the release agent 1.8 hours before casting, with a release agent temperature of 38℃ and a spraying pressure of 0.45MPa. The coating thickness is 1.3mm for the bottom (20% of the mold height), 1.1mm for the middle (60% of the mold height), and 0.8mm for the top (20% of the mold height). Allow the coating to cure naturally for 40 minutes after application. The casting temperature is 1530-1560℃, and the casting is cured using the residual heat of the casting. The demolding temperature is 800℃. After demolding, recover the release agent fragments, crush and grind them to a particle size ≤0.1mm, and mix them with new agent at a ratio of 45% for recycling. The water glass replenishment amount is 11% of the mass of the recovered powder. Add deionized water to adjust the viscosity to 580mPa•s (25℃).

[0045] Implementation Results: The ceramic film formed after the release agent cures has a high temperature resistance of 1550℃ and a peel strength of 0.4MPa from the casting; the carbide content on the casting surface is 0.007%, the "peeling" defect rate is 0.7%, the oxide scale thickness is 0.05mm, and the surface roughness Ra is 1.0μm; the measured crack rate of the casting is 2.2%, which is 9.2 percentage points lower than that of the traditional process; the corrosion resistance of the casting is tested according to GB / T17897-2018 standard, and the average corrosion rate is ≤0.01mm / a, which meets the corrosion resistance requirements of nuclear power steel; the release agent recycling rate is 68%, and the cost per ton of steel is 11.2 yuan, which fully meets the technical requirements of nuclear power steel.

[0046] Example 4: Ultra-thick casting of 12Cr1MoV heat-resistant steel (for thermal power plants, thickness 900mm) The casting dimensions are 900mm × 2000mm × 2200mm, using a 3Cr2W8V ingot mold; the geopolymer gel release agent formula is: metakaolin (SiO2 content 55%, Al2O3 content 35%, Fe2O3 content 2%, CaO content 1%, particle size 10~35μm, specific surface area 400m²). 2 100 kg of water glass (modulus 3.3, solid content 46%), 30 kg of nano-silica (particle size 35 nm), 5 kg of boron nitride micro powder (particle size 2-5 μm), 2.5 kg of polycarboxylate superplasticizer (solid content 40%), 1.2 kg of organosilicon defoamer, 0.7 kg of deionized water; stir at 1500 r / min for 20 minutes. The viscosity after stirring is 900 mPa•s (25℃).

[0047] Application process: Apply the release agent 2 hours before casting, with a release agent temperature of 33℃ and a spraying pressure of 0.6MPa. The coating thickness is 1.5mm for the bottom (20% of the mold height), 1.2mm for the middle (60% of the mold height), and 0.8mm for the top (20% of the mold height). Allow the coating to cure naturally for 60 minutes after application. The casting temperature is 1550-1580℃, utilizing the residual heat of the casting for curing. The demolding temperature is 890℃. After demolding, recover the release agent fragments, crush and grind them to a particle size ≤0.1mm, and mix them with new agent at a ratio of 30% for recycling. The water glass replenishment amount is 15% of the mass of the recovered powder. Add deionized water to adjust the viscosity to 900mPa•s (25℃).

[0048] Implementation Results: The ceramic film formed after the release agent cures has a high temperature resistance of 1620℃ and a peel strength of 0.35MPa from the casting; the carbide content on the casting surface is 0.01%, the "peeling" defect rate is 1.0%, the oxide scale thickness is 0.08mm, and the surface roughness Ra is 1.5μm; the measured crack rate of the casting is 4.5%, which is 10 percentage points lower than that of the traditional process; the casting is tested according to GB / T2039-2012 standard, and the high temperature creep strength at 550℃ for 1000h is 185MPa, which meets the high temperature service performance requirements of steel for thermal power plants; the release agent recycling rate is 61%, and the cost per ton of steel is 12.0 yuan, which fully meets the technical requirements of steel for thermal power plants.

[0049] Example 5: Ultra-thick Q345B low-alloy high-strength steel casting (for engineering machinery, thickness 500mm) The casting dimensions are 500mm × 1400mm × 2900mm, using an H13 ingot mold; the geopolymer gel release agent formula is: metakaolin (SiO2 content 63%, Al2O3 content 27%, Fe2O3 content 1.6%, CaO content 0.5%, particle size 20~45μm, specific surface area 330m²). 2 100 kg of water glass (modulus 3.1, solid content 44%), 24 kg of nano-silica (particle size 20 nm), 3.5 kg of boron nitride micro powder (particle size 1-4 μm), 1.2 kg of polycarboxylate superplasticizer (solid content 40%), 0.6 kg of organosilicon defoamer, and 0.3 kg of deionized water; stir at 2000 r / min for 15 minutes. The viscosity after stirring is 600 mPa•s (25℃).

[0050] Application process: Apply the release agent 1.2 hours before casting, with a release agent temperature of 36℃ and a spraying pressure of 0.4MPa. The coating thickness is 1.2mm for the bottom (20% of the mold height), 0.9mm for the middle (60% of the mold height), and 0.5mm for the top (20% of the mold height). Allow the coating to cure naturally for 35 minutes after application. The casting temperature is 1510-1540℃, utilizing the residual heat of the casting for curing. The demolding temperature is 880℃. After demolding, recover the release agent fragments, crush and grind them to a particle size ≤0.1mm, and mix them with new agent at a ratio of 42% for recycling. The water glass replenishment amount is 10% of the mass of the recovered powder. Add deionized water to adjust the viscosity to 600mPa•s (25℃).

[0051] Implementation Results: The ceramic film formed after the release agent cures has a high temperature resistance of 1560℃ and a peel strength of 0.45MPa from the casting; the carbide content on the casting surface is 0.008%, the "peeling" defect rate is 0.6%, the oxide scale thickness is 0.06mm, and the surface roughness Ra is 1.3μm; the measured crack rate of the casting is 3.0%, which is 7.5 percentage points lower than that of the traditional process; the casting is tested according to GB / T229-2020 standard, and the V-notch impact energy at -20℃ is 68J, which meets the requirements of heavy-duty low-temperature service for engineering machinery; the release agent recycling rate is 66%, and the cost per ton of steel is 11.0 yuan, which fully meets the technical requirements for steel used in engineering machinery.

[0052] Example 6: Ultra-thick casting of 20CrMnTi gear steel (for automotive gearboxes, thickness 550mm) The casting dimensions are 550mm × 1600mm × 2700mm, using a 3Cr2W8V ingot mold; the geopolymer gel release agent formula is: metakaolin (SiO2 content 59%, Al2O3 content 31%, Fe2O3 content 2%, CaO content 1%, particle size 15~40μm, specific surface area 360m²). 2 100 kg of water glass (modulus 3.4, solid content 43%), 26 kg of nano-silica (particle size 45 nm), 2.8 kg of boron nitride micro powder (particle size 2-4 μm), 1.6 kg of polycarboxylate superplasticizer (solid content 40%), 0.9 kg of organosilicon defoamer, and 0.5 kg of deionized water; the mixture was stirred at 1600 r / min for 19 minutes, and the viscosity after stirring was 700 mPa•s (25℃).

[0053] Application process: Apply the coating 1.6 hours before casting, with a release agent temperature of 31℃ and a spraying pressure of 0.5MPa. The coating thickness is 1.3mm for the bottom (20% of the mold height), 1.0mm for the middle (60% of the mold height), and 0.6mm for the top (20% of the mold height). Allow the coating to cure naturally for 42 minutes after application. The casting temperature is 1530-1560℃, utilizing the residual heat of the casting for curing. The demolding temperature is 860℃. After demolding, recover the release agent fragments, crush and grind them to a particle size ≤0.1mm, and mix them with new agent at a ratio of 38% for recycling. The water glass replenishment amount is 12% of the mass of the recovered powder. Add deionized water to adjust the viscosity to 700mPa•s (25℃).

[0054] Implementation Results: The ceramic film formed after the release agent cures has a high temperature resistance of 1570℃ and a peel strength of 0.32MPa from the casting; the carbide content on the casting surface is 0.009%, the "peeling" defect rate is 0.8%, the oxide scale thickness is 0.07mm, and the surface roughness Ra is 1.3μm; the measured crack rate of the casting is 2.8%, which is 8.2 percentage points lower than that of the traditional process; after carburizing and quenching, the tooth surface hardness of the casting is HRC59-61, which meets the wear resistance and fatigue strength requirements of automotive gearbox gears; the release agent recycling rate is 64%, and the cost per ton of steel is 11.6 yuan, which fully meets the technical requirements for automotive steel.

[0055] The above embodiments demonstrate that the geopolymer gel-residual heat synergistic curing release agent and its application process of the present invention can play a stable role in the production of ultra-thick castings of different thicknesses and materials. Through formula innovation and process synergy, it achieves integrated functions of demolding, anti-oxidation, and stress buffering, and has advantages in quality, cost, and environmental protection, and has significant industrial application value and promotion prospects.

[0056] Those skilled in the art should recognize that the above embodiments are merely illustrative of the invention and not intended to limit it, but are similarly limited to the scope of the invention. Variations and modifications to the above embodiments will fall within the protection scope of the claims. It should be understood that the endpoints and values ​​of the ranges 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 endpoint values ​​of various ranges, the endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0057] It should be noted that in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the term "and / or" as used herein is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone.

[0058] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A molding release agent based on geopolymer gel-residual heat synergistic curing, characterized in that, Using metakaolin as the geopolymer matrix, by mass ratio, 20%–30% water glass as an activator, 2%–5% nano-silica and 1%–3% boron nitride micro powder as composite reinforcing agents, 0.5%–1.2% polycarboxylate superplasticizer as an additive, and 0.3%–0.8% defoamer are added to the metakaolin; deionized water is added to the above mixture at a water-cement ratio of (0.3–0.5):1, and the mixture is mixed evenly to obtain the release agent.

2. The molding release agent based on geopolymer gel-residual heat synergistic curing according to claim 1, characterized in that, The chemical composition of the metakaolin meets the following requirements: SiO2 content 55%–65%, Al2O3 content 25%–35%, Fe2O3 content ≤2%, CaO content ≤1%; the particle size of the metakaolin is 10–50 μm, and the specific surface area is 300–400 m². 2 / kg.

3. The molding release agent based on geopolymer gel-residual heat synergistic curing according to claim 1, characterized in that, The water glass has a modulus of 3.0 to 3.5 and a solid content of 40% to 50%.

4. The molding release agent based on geopolymer gel-residual heat synergistic curing according to claim 1, characterized in that, The nano-silica has a particle size of 20-50 nm, the boron nitride micro powder has a particle size of 1-5 μm, the defoamer is an organosilicon defoamer, and the polycarboxylate superplasticizer has a solid content of 40%.

5. The molding release agent based on geopolymer gel-residual heat synergistic curing according to claim 1, characterized in that, The release agent has a viscosity of 500-1000 mPa•s at 25°C. After coating, it undergoes initial curing at room temperature for 30-60 minutes and completes curing under the residual heat of the casting at ≥800°C, forming a ceramic film with mullite phase as its main component. The ceramic film has a high temperature resistance of ≥1500°C and a peel strength from the casting of ≤0.5 MPa.

6. A method for preparing a molding release agent based on geopolymer gel-residual heat synergistic curing as described in any one of claims 1-5, characterized in that, The process includes the following steps: adding metakaolin, water glass, nano-silica, boron nitride micro powder, polycarboxylate superplasticizer, and defoamer sequentially to deionized water, and stirring at a high speed of 1500-2000 r / min for 15-20 minutes to obtain a uniform and stable geopolymer gel release agent.

7. A method of using a molding release agent based on geopolymer gel-residual heat synergistic curing as described in any one of claims 1-5, characterized in that, Includes the following steps: 1) Coating preparation: 1-2 hours before pouring, apply the release agent heated to 30-40℃ using a high-pressure spraying device; 2) Gradient coating: The coating thickness is distributed in a gradient along the height of the mold, with a coating thickness of 1.2-1.5 mm at the bottom, 0.8-1.2 mm in the middle, and 0.5-0.8 mm at the top; the spraying pressure is 0.4-0.6 MPa. 3) Step-by-step curing: After coating, let it stand naturally for 30-60 minutes to allow the release agent to complete the initial curing at room temperature; after pouring, use the residual heat of ≥800℃ emitted by the casting to completely cure the gel film of the release agent to form a ceramic release layer. 4) Demolding and peeling: When the casting solidifies and the surface temperature drops to 800-900℃, the ceramic release layer naturally falls off with the casting and the remaining release agent fragments are removed by a slight tap with an impact force ≤5kN. 5) Recycling: Collect the detached mold release agent fragments, grind them to a particle size ≤0.1mm, and obtain recycled powder; 6) Recycling and reuse: The recycled powder is added to the newly prepared geopolymer gel release agent at a ratio of 30wt% to 50wt%, water glass and deionized water are added, and the viscosity of the release agent at 25°C is adjusted to 500 to 1000 mPa•s, and then used for ingot coating again.

8. The method of using the molding release agent based on geopolymer gel-residual heat synergistic curing according to claim 7, characterized in that, In step 6), the amount of water glass added is 10% to 15% of the mass of the recovered powder.

9. The method of using the molding release agent based on geopolymer gel-residual heat synergistic curing according to claim 7, characterized in that, The bottom region of the ingot mold occupies 15% to 25% of the ingot mold height, the middle region occupies 55% to 65% of the ingot mold height, and the top region occupies 15% to 25% of the ingot mold height.