A method for reinforcing the outer surface of castings during precision valve body casting.

Abstract

This invention discloses a method for reinforcing the outer surface of castings during precision valve body casting, belonging to the field of valve body casting technology. The method involves preparing a wax mold assembly using a wax injection machine; the wax mold assembly is then sequentially coated with a surface layer, a second layer, a first to fourth reinforcement layer, and a sealing layer, and air-dried to form a silica sol mold shell. The first to fourth reinforcement layers are coated with a composite adhesive B, which is a ternary composite precursor powder prepared by ball milling hexagonal boron nitride nanosheets pretreated with γ-aminopropyltriethoxysilane, aluminum phosphate powder, and iron titanate powder, and then compounded with aluminum dihydrogen phosphate solution, polyethylene glycol, and PAN-based chopped carbon fibers. The process includes dewaxing, calcination, casting, shell removal, and post-treatment to obtain the valve body casting. This invention improves the high-temperature strength and density of the shell by optimizing the adhesive formulation and shell-making process, reducing defects such as casting sediment and sand holes, and enhancing the mechanical properties and yield of the valve body casting.

Description

Technical Field

[0001] This invention relates to the field of valve body casting technology, and in particular to a method for reinforcing the outer surface of castings during precision valve body casting. Background Technology

[0002] The valve body is the core pressure-bearing component of a valve, with a complex structure. During use, it must withstand medium pressure and alternating loads, and safety standards are stringent. Therefore, valve body castings require extremely high casting quality, making overall casting production quite challenging. Currently, valve body castings are generally manufactured using investment casting, relying on wax pattern forming and mold shell preparation to complete production. During production, adhesives are often applied to the mold shell surface to improve the regularity of the shell's shape, increase the overall hardness of the shell, and ensure the orderly progress of processes such as dewaxing, baking, and molten metal pouring.

[0003] In the shell preparation process, a multi-layer structure is typically formed by layer-by-layer coating, including a surface layer, a second layer, and a reinforcing layer. The reinforcing layer bears the main structural strength of the shell, and the performance of its adhesive directly determines the overall strength and high-temperature stability of the shell. Currently, silica sol is the most commonly used adhesive for reinforcing layers in investment casting. However, existing traditional silica adhesives, represented by silica sol, have significant shortcomings: in high-temperature alloy investment casting, silica adhesives undergo chemical decomposition at high temperatures, leading to strength loss and limiting their application in high-quality casting production. Higher silica content in the adhesive results in higher shell strength, and higher corundum phase content in the refractory material also increases shell strength; however, chemical drying and hardening of the shell leads to a decrease in strength.

[0004] Furthermore, the existing bonding process for the reinforcing layer of the mold shell in investment casting has significant shortcomings. The adhesive adhesion is uneven, and the strength and density of the traditional mold shell after curing are insufficient to meet production and use requirements, resulting in inadequate structural stability. During high-temperature baking and casting operations, the mold shell is prone to deformation and surface peeling, making the formed valve body castings highly susceptible to casting defects such as slag, sand holes, and bubbles. This not only reduces the product qualification rate but also affects the pressure-bearing performance and reliability of the valve body, making it difficult to meet the needs of large-scale production of high-quality valve body castings. Therefore, the existing process needs to be optimized and improved. Summary of the Invention

[0005] In order to solve the problems mentioned in the background art, the present invention provides a method for reinforcing the outer surface of castings in the process of precision valve body casting.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for reinforcing the outer surface of castings during precision valve body casting includes the following steps: S1. The wax material is pressed into the mold cavity by a wax injection machine, cooled and removed to form a wax mold. After repairing and cleaning the defects on the surface of the wax mold, it is welded onto the sprue bar to form a wax mold assembly. S2. After cleaning the wax mold assembly, apply adhesive to the surface layer, then sprinkle surface powder and sand and air dry. Repeat this process for the second layer. Then apply adhesive B, sprinkle reinforcing powder and sand, and air dry. Repeat this process for the second, third, and fourth reinforcing layers and the sealing layer. Air dry to form a silica sol mold shell. S3. After dewaxing the silica sol module shell in an electric wax melting furnace for 5-7 minutes, bake it and remove the silica sol module shell. S4. Pour the molten metal into the silica sol module shell. After the molten metal solidifies, remove the silica sol module shell outside the module. Then separate the valve body casting on the module from the pouring rod to obtain the blank valve body casting.

[0007] Furthermore, in step S2, the adhesive used for the top layer and the second layer is silica sol, the powder used for the top layer is 320-mesh refined quartz powder, and the sand is 100-mesh refined quartz sand; the powder used for the second layer is 320-mesh refined quartz powder, and the sand is 60-mesh refined quartz sand; the air drying temperature is 22℃-26℃, and the air drying time is 3-5 hours.

[0008] Furthermore, in step S2, the powder used for the first reinforcement layer is high-alumina synthetic powder, and the sand used is 60-mesh mullite sand; the powder used for the second to fourth reinforcement layers is kaolin clinker powder, and the sand used is 20-mesh kaolin clinker sand; the air-drying temperature for the first to fourth reinforcement layers is 35℃-45℃, the air-drying time is 10-20 minutes, and the hardening time is 10-15 minutes; the sealing layer is coated with water glass-based sealing material, wherein the mass ratio of water glass, high-alumina powder, and quartz powder is 1:(0.4-0.6):(0.4-0.6). The air-drying temperature is 35℃-45℃, and the air-drying time is 20-40 minutes.

[0009] Furthermore, the roasting described in step S3 is performed by roasting at 1000℃-1200℃ for 60-90 minutes.

[0010] Further, the molten metal in step S4 comprises the following components by weight: 35-45 parts of molybdenum-containing austenitic stainless steel base material, 48-58 parts of molybdenum-free austenitic stainless steel base material, 0.8-1.5 parts of pure nickel, 1.8-2.8 parts of ferromolybdenum, 2.0-3.0 parts of low-carbon ferrochrome, 0.15-0.35 parts of low-carbon ferromanganese, and 0.4-0.8 parts of ferrosilicon.

[0011] Furthermore, the preparation steps of adhesive B in step S2 are as follows: A1. Mix hexagonal boron nitride nanosheets pretreated with γ-aminopropyltriethoxysilane, aluminum phosphate powder, and iron titanate powder, add molybdenum trioxide and nano-yttrium oxide, ball mill and mix with anhydrous ethanol as medium for 5-7 hours, vacuum dry at 75-85℃, and pass through a 280-320 mesh sieve to obtain ternary composite precursor powder. A2. Mix the ternary composite precursor powder with aluminum dihydrogen phosphate solution to obtain a mixture, then add polyethylene glycol and PAN-based short-cut carbon fibers, stir for 0.8-1.2 hours and then perform ultrasonic degassing treatment to adjust the viscosity, thus obtaining adhesive B.

[0012] Further, in step A1, the mass ratio of hexagonal boron nitride nanosheets, aluminum phosphate powder, and iron titanate powder is 1:(2.8-3.2):(1.3-1.7); the amount of polyethylene glycol added is 0.3-1.0% of the total solid mass in the mixture; and the amount of PAN-based chopped carbon fiber added is 0.1-0.5% of the total solid mass in the mixture.

[0013] Further, in step A1, the aluminum phosphate powder is prepared by heating aluminum dihydrogen phosphate to 480-520℃ at a heating rate of 5-10℃ / min and pre-dehydrating for 1.5-2.5 hours; the iron titanate powder is prepared by solid-phase synthesis of ferric oxide and titanium dioxide in a mass ratio of (1.9-2.1):1 at 1150-1250℃.

[0014] Further, in step A2, the liquid-to-solid ratio of the ternary composite precursor powder to the aluminum dihydrogen phosphate solution is (0.35-0.45):1, and the amount of polyethylene glycol added is 0.3-0.8% of the total solid mass in the mixture; the PAN-based short-cut carbon fibers have a length of 50-100 μm and are added at 0.2-0.5% of the total solid mass in the mixture; the viscosity is adjusted to 22-25 seconds as measured using a No. 4 flow cup.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention modifies hexagonal boron nitride through molecular bridging using a silane coupling agent. The silanol groups generated by its hydrolysis undergo dehydration condensation with the boron hydroxyl groups at the defects on the boron nitride surface to form a stable Si-OB covalent bond. Simultaneously, the amino group at the other end of the silane is protonated in an acidic system and forms an ionic bond with the phosphate group of aluminum dihydrogen phosphate. This allows the inorganic filler and binder to achieve a stable connection through chemical bonds instead of relying on physical adsorption, significantly improving the thixotropy and suspension stability of the slurry and ensuring uniform spreading without sagging during coating. Polyethylene glycol, with its long-chain ether bonds, adsorbs onto the surface of various powder particles through hydrogen bonds to form a steric hindrance layer, effectively preventing the agglomeration of ultrafine powders and constructing a three-dimensional physical cross-linked network in the slurry, uniformly anchoring the reinforcing layer powder to the network nodes.

[0016] 2. The phosphate component in adhesive B of this invention undergoes a vigorous intermolecular dehydration and condensation reaction at 1000-1200℃, gradually polymerizing into polyaluminum polymethphosphate with a three-dimensional infinite network structure. The bonding mode is transformed into an Al-OP ordered covalent bond skeleton, which is not easy to break at high temperatures. This allows the silica sol module shell to maintain excellent creep resistance and rigidity during calcination and casting. At the same time, the high-alumina synthetic powder used in the reinforcing layer and the mullite sand undergo a solid-phase diffusion reaction at high temperatures, where the free alumina in the adhesive and the silica in the sand react to generate needle-like or columnar secondary mullite whiskers in situ. These whiskers grow interlaced, firmly welding the reinforcing layer with the surface layer and the back layer to form a gradient transition chemical bonding layer. This not only eliminates interlayer interface stress but also gives the silica sol module shell excellent thermal shock resistance, effectively preventing surface peeling during rapid heating and casting.

[0017] 3. The molybdenum trioxide added to the precursor powder of this invention first forms a viscous liquid phase during the calcination and heating process. Based on the capillary force-driven rearrangement and densification mechanism, it rapidly wets and fills the pores between particles. The nano-yttrium oxide acts as a surfactant, segregating at the grain boundaries to inhibit bubble aggregation and growth, so that the reinforcement layer reaches a closed-pore state before casting, physically blocking the capillary channels for molten steel penetration and reducing mechanical sand adhesion and subcutaneous sand pores. The silane-modified hexagonal boron nitride, with its two-dimensional layered structure, forms a dense physical barrier layer through directional arrangement during the coating process. At the same time, the boron oxide micro-atmosphere generated by its high-temperature decomposition can passivate the inner surface of the shell, effectively inhibiting the violent redox reaction between oxygen and nitrogen in the stainless steel molten metal and silicon dioxide in the silica sol module shell, and inhibiting the growth of interfacial reaction bubbles. Attached Figure Description

[0018] The invention will now be further described with reference to the accompanying drawings.

[0019] Figure 1 This is a product image of the blank valve body casting prepared in Comparative Example 1; Figure 2 This is a product image of the blank valve body casting prepared in Comparative Example 2; Figure 3 This is a product image of the blank valve body casting prepared in Example 3. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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.

[0021] Preparation Example 1 Preparation of adhesive B: A1. Weigh 1000g of aluminum dihydrogen phosphate and place it in a muffle furnace. At a heating rate of 5℃ / min, pre-dehydrate it at 480℃ for 2.5 hours. After cooling, grind it to obtain about 680g of aluminum phosphate powder. Weigh 655g of ferric oxide and 345g of titanium dioxide, mix them evenly, and then perform solid-state synthesis at 1150℃ for 4 hours. After the reaction is completed, cool it to room temperature with the furnace. After cooling, ball mill it to 320 mesh to obtain iron titanate powder. Weigh 200g of hexagonal boron nitride nanosheets pretreated with γ-aminopropyltriethoxysilane, 560g of the above-mentioned aluminum phosphate powder, and 260g of iron titanate powder. After mixing, add 15.3g of molybdenum trioxide and 8.2g of nano-yttrium oxide with an average particle size of 20nm. Add 1500ml of anhydrous ethanol as a medium and ball mill the mixture in a ball mill for 5 hours. After removing the mixture, dry it in a vacuum drying oven at 75℃ for 12 hours and pass it through a 280-mesh sieve to obtain ternary composite precursor powder.

[0022] A2. Weigh 1000g of ternary composite precursor powder and slowly add 2860g of aluminum dihydrogen phosphate solution. Mix the mixture while mechanically stirring. Then weigh 3.0g of polyethylene glycol and 2.0g of PAN-based short-cut carbon fibers with a length of 50μm. Continue stirring for 0.8 hours. Use an ultrasonic power of 200W, a frequency of 40kHz, a treatment temperature of 25℃, and a treatment time of 15 minutes. Measure and adjust the viscosity to 22 seconds using a No. 4 flow cup to obtain adhesive B.

[0023] The steps for pretreating hexagonal boron nitride nanosheets with γ-aminopropyltriethoxysilane are as follows: 200g of hexagonal boron nitride nanosheets are weighed and added to 2000mL of a mixed solvent of ethanol / water (volume ratio of ethanol to water: 95:5). The mixture is ultrasonically dispersed for 30 minutes. 20g of γ-aminopropyltriethoxysilane is added, and the pH of the system is adjusted to 4.5 with glacial acetic acid. The mixture is stirred in a 60℃ water bath for 4 hours. After the reaction, the mixture is filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80℃ for 12 hours. The nanosheets are then ground through a 300-mesh sieve to obtain hexagonal boron nitride nanosheets pretreated with γ-aminopropyltriethoxysilane. Examples 2 and 3 were prepared using the same method as in Example 1, yielding hexagonal boron nitride nanosheets pretreated with γ-aminopropyltriethoxysilane.

[0024] Preparation Example 2 Preparation of adhesive B: A1. Weigh 1000g of aluminum dihydrogen phosphate and pre-dehydrate it at 500℃ for 2 hours at a heating rate of 10℃ / min to obtain approximately 660g of aluminum phosphate powder. Weigh 667g of ferric oxide and 333g of titanium dioxide and synthesize them in a solid-state environment at 1200℃ for 3.5 hours. After the reaction, cool the mixture to room temperature in the furnace and ball-mill to obtain iron titanate powder. Weigh 200g of silane-pretreated hexagonal boron nitride nanosheets, 600g of the above aluminum phosphate powder, and 300g of iron titanate powder. Add 22.0g of molybdenum trioxide and 13.2g of yttrium oxide nanoparticles with an average particle size of 35nm. Add 1600ml of anhydrous ethanol and ball-mill for 6 hours. Vacuum dry at 80℃ for 12 hours and pass through a 300-mesh sieve to obtain ternary composite precursor powder.

[0025] A2. Weigh 1000g of ternary composite precursor powder and slowly add 2500g of aluminum dihydrogen phosphate solution. Mix the mixture while mechanically stirring. Then weigh 5.0g of polyethylene glycol and 3.5g of PAN-based short-cut carbon fibers with a length of 80μm. Continue stirring for 1.0 hour. Use an ultrasonic power of 400W, a frequency of 40kHz, a treatment temperature of 30℃, and a treatment time of 20 minutes. Adjust the viscosity to 24 seconds using a No. 4 flow cup to obtain adhesive B.

[0026] Preparation Example 3 Preparation of adhesive B: A1. Weigh 1000g of aluminum dihydrogen phosphate and pre-dehydrate it at 520℃ for 1.5 hours at a heating rate of 7℃ / min to obtain approximately 650g of aluminum phosphate powder. Weigh 677g of ferric oxide and 323g of titanium dioxide and synthesize them in a solid-state environment at 1250℃ for 3 hours. After the reaction, cool the mixture to room temperature in the furnace and ball-mill to obtain iron titanate powder. Weigh 200g of silane-pretreated hexagonal boron nitride nanosheets, 640g of the above-mentioned aluminum phosphate powder, and 340g of iron titanate powder. Add 29.5g of molybdenum trioxide and 17.7g of yttrium oxide nanoparticles with an average particle size of 50nm. Add 1800ml of anhydrous ethanol and ball-mill the mixture for 7 hours. Vacuum dry at 85℃ for 12 hours and pass through a 320-mesh sieve to obtain ternary composite precursor powder.

[0027] A2. Weigh 1000g of ternary composite precursor powder and slowly add 2220g of aluminum dihydrogen phosphate solution. Mix the mixture while mechanically stirring. Then weigh 8.0g of polyethylene glycol and 5.0g of PAN-based short-cut carbon fibers with a length of 100μm. Continue stirring for 1.2 hours. Use an ultrasonic power of 300W, a frequency of 40kHz, a treatment temperature of 27℃, and a treatment time of 10 minutes. Adjust the viscosity to 25 seconds using a No. 4 flow cup to obtain adhesive B.

[0028] Example 1

[0029] S1. The wax material is pressed into the mold cavity by a wax injection machine, cooled and removed to form a wax mold. After repairing and cleaning the defects on the surface of the wax mold, it is welded onto the sprue bar to form a wax mold assembly.

[0030] S2. After cleaning the wax mold assembly, the surface layer is immersed in silica sol slurry, wherein the mass ratio of silica sol to 320-mesh refined quartz powder is 1:3.2. The assembly is rotated while dipping, then removed and sprinkled with 100-mesh refined quartz sand. It is then air-dried in a 22°C constant temperature oven for 3 hours. Next, the second layer is immersed again in silica sol slurry of the same formula, removed, and sprinkled with 60-mesh refined quartz sand. It is then air-dried at 22°C for 3 hours. In this invention, the second layer is the intermediate layer located between the surface layer and the reinforcing layer. The assembly is then immersed in adhesive B slurry from Preparation Example 1, removed, and sprinkled with a mixture of high-alumina synthetic powder and 60-mesh mullite sand. It is then air-dried at 35°C for 10 minutes and hardened for 10 minutes to form a reinforcing layer. Reinforcing layers two through four are then continued to be coated with adhesive B from Preparation Example 1, sprinkled with kaolin clinker powder and 20-mesh kaolin clinker sand, and each layer is air-dried at 35°C for 10 minutes and hardened for 10 minutes. Finally, a water glass-based sealant is applied, which contains water glass, high alumina powder, and quartz powder in a ratio of 1:0.5:0.5. No sand is sprinkled on it. It is then air-dried at 35°C for 40 minutes to form a silica sol module shell.

[0031] S3. Place the silica sol module shell into an electric wax melting furnace and dewax it for 5 minutes under 160°C steam. After taking it out, place it in a high-temperature baking furnace and heat it to 1000°C at a rate of 5°C / min. Hold it at that temperature for 60 minutes and then let it cool naturally to 300°C with the furnace at a cooling rate of 1°C / min. After that, take out the silica sol module shell.

[0032] S4. Weigh the following metal furnace charge according to the proportions: 35 kg of molybdenum-containing austenitic stainless steel base material, 48 kg of molybdenum-free austenitic stainless steel base material, 0.8 kg of pure nickel, 1.8 kg of ferromolybdenum, 2.0 kg of low-carbon ferrochrome, 0.15 kg of low-carbon ferromanganese, and 0.4 kg of ferrosilicon. Melt the metal in a medium-frequency induction furnace to 1620℃. After deoxidation and slag removal, pour the molten metal into a silica sol mold shell preheated to 800℃. After complete solidification and cooling, mechanically vibrate to remove the silica sol mold shell from the outside of the mold. Then, use a cutting machine to separate the valve body casting from the pouring rod to obtain the blank valve body casting.

[0033] Example 2

[0034] S1. The wax material is pressed into the mold cavity by a wax injection machine, cooled and removed to form a wax mold. After repairing and cleaning the defects on the surface of the wax mold, it is welded onto the sprue bar to form a wax mold assembly.

[0035] S2. After cleaning the wax mold assembly, immerse the surface layer in silica sol slurry, wherein the mass ratio of silica sol to 320-mesh refined quartz powder is 1:3.2. Rotate to dip in the slurry, remove and sprinkle with 100-mesh refined quartz sand, and air dry at 24°C for 4 hours. Then, immerse the second layer again in silica sol slurry with the same formula, remove and sprinkle with 60-mesh refined quartz sand, and air dry at 24°C for 4 hours as well. Reinforce with a layer of adhesive B from Preparation Example 2, sprinkle with a mixture of high-alumina synthetic powder and 60-mesh mullite sand, air dry at 40°C for 15 minutes and harden for 12 minutes; reinforce with layers two to four by continuing to immerse with adhesive B from Preparation Example 2, sprinkle with kaolin clinker powder and 20-mesh kaolin clinker sand, and air dry each layer at 40°C for 15 minutes and harden for 12 minutes. The sealing layer is coated with a water glass-based sealing material, which contains water glass, high alumina powder, and quartz powder in a ratio of 1:0.4:0.4. It is then air-dried at 40°C for 30 minutes to form a silica sol module shell.

[0036] S3. Send the silica sol module shell into the electric wax melting furnace and dewax it at 160°C for 6 minutes. After taking it out, put it into the high-temperature baking furnace. The baking furnace is heated to 1100°C at 5°C / min and held for 75 minutes. Then, it is cooled naturally to 300°C with the furnace at a cooling rate of 2°C / min. Take out the silica sol module shell.

[0037] S4. Weigh the following metal furnace charge according to the proportions: 40 kg of molybdenum-containing austenitic stainless steel base material, 53 kg of molybdenum-free austenitic stainless steel base material, 1.2 kg of pure nickel, 2.3 kg of ferromolybdenum, 2.5 kg of low-carbon ferrochrome, 0.25 kg of low-carbon ferromanganese, and 0.6 kg of ferrosilicon. Melt the charge in an induction furnace to 1630℃, deoxidize and remove slag, pour the charge into a preheated silica sol mold shell at 800℃ for solidification, and then cut the shell to obtain the blank casting.

[0038] Example 3

[0039] S1. The wax material is pressed into the mold cavity by a wax injection machine, cooled and removed to form a wax mold. After repairing and cleaning the defects on the surface of the wax mold, it is welded onto the sprue bar to form a wax mold assembly.

[0040] S2. After cleaning the wax mold assembly, the surface layer is immersed in silica sol slurry, wherein the mass ratio of silica sol to 320-mesh refined quartz powder is 1:3.2, and 100-mesh refined quartz sand is sprinkled on top. It is then air-dried at 26°C for 5 hours. The second layer is immersed in silica sol slurry with the same formula, sprinkled with 60-mesh refined quartz sand, and air-dried at 26°C for 5 hours. A reinforcing layer is then applied using adhesive B from Preparation Example 3, sprinkled with a mixture of high-alumina synthetic powder and 60-mesh mullite sand, and air-dried at 45°C for 20 minutes and then hardened for 15 minutes. The second to fourth reinforcing layers are then applied using adhesive B from Preparation Example 3, sprinkled with kaolin clinker powder and 20-mesh kaolin clinker sand, and each layer is air-dried at 45°C for 20 minutes and then hardened for 15 minutes. The sealing layer is coated with a water glass-based sealing material, containing water glass:high-alumina powder:quartz powder = 1:0.6:0.6, and air-dried at 45°C for 20 minutes to obtain the silica sol module shell.

[0041] S3. Send the silica sol module shell into the electric wax melting furnace, dewax it at 160°C for 7 minutes, take it out and put it into the high temperature baking furnace, bake it at 1200°C at 5°C / min for 90 minutes, and then let it cool naturally to 300°C with the furnace at a cooling rate of 3°C / min before taking out the silica sol module shell.

[0042] S4. Weigh the following metal furnace charge according to the proportions: 45 kg of molybdenum-containing austenitic stainless steel base material, 58 kg of molybdenum-free austenitic stainless steel base material, 1.5 kg of pure nickel, 2.8 kg of ferromolybdenum, 3.0 kg of low-carbon ferrochrome, 0.35 kg of low-carbon ferromanganese, and 0.8 kg of ferrosilicon. Melt the charge in an induction furnace to 1640℃, deoxidize and remove slag, then pour it into a preheated silica sol mold shell at 850℃. After solidification, separate the shell using a vibrating motion to obtain the blank valve body casting. The finished product is shown below. Figure 1-3 As shown.

[0043] Comparative Example 1 The reinforcement layer in this comparative example uses a silica sol adhesive, which is the same as the surface layer, and the remaining steps are the same as in Example 1.

[0044] Comparative Example 2 In this comparative example, adhesive B was replaced with unmodified aluminum dihydrogen phosphate solution. 2000g of commercially available 50% aluminum dihydrogen phosphate solution was directly taken, 6.0g of polyethylene glycol was added, and the mixture was stirred for 0.5 hours. The mixture was then ultrasonically degassed, and the viscosity was measured and adjusted to 22 seconds using a No. 4 flow cup to prepare the unmodified aluminum dihydrogen phosphate solution. The remaining steps were the same as in Example 1.

[0045] I. Tensile Test 1. Experimental Materials Referring to GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Test at room temperature", the test specimen used is a circular cross-section proportional specimen cut and machined from the valve body casting. The diameter of the parallel section of the specimen is 10 mm, the gauge length is 50 mm, and the total length is approximately 120 mm.

[0046] 2. Experimental Procedure Inspect the sample's appearance to confirm there are no visible cracks or obvious defects. Use a micrometer to measure the diameter at three locations: both ends and the middle of the parallel section (measure in two perpendicular directions at each location and take the average). Use the average of the three measurements as the original diameter d0, accurate to 0.01 mm. Calculate the original cross-sectional area S0 = πd0. 2 / 4. Mark the original gauge length L0 = 50 mm on the parallel section. Center the specimen and install it into the upper and lower clamps, ensuring axial loading. After clamping, set the force value to zero and install the extensometer on the parallel section. Using the stress rate control method, set the stress rate in the elastic and yield stages to 2-20 MPa / s, and the strain rate after yielding should not exceed 0.008 / s. Start the testing machine and continuously load until the specimen fractures. Read the force value corresponding to 0.2% plastic elongation from the force-elongation curve to calculate the yield strength Rp0.2, and calculate the tensile strength Rm = Fm / S0 using the maximum force Fm. After fracture, tightly butt the specimens, measure the gauge length Lu after fracture, and calculate the elongation after fracture A = (Lu − L0) / L0 × 100%.

[0047] II. Brinell Hardness Test 1. Experimental Materials Referring to GB / T231.1-2018 "Metallic materials - Brinell hardness test - Part 1: Test method", the test specimen used is a hardness test specimen block cut from the valve body casting body, with a size of not less than 30mm × 30mm × 15mm. The test surface is ground flat, with a surface roughness Ra of not more than 1.6μm, and is free of oxide scale and oil stains.

[0048] 2. Experimental Procedure The diameter of the cemented carbide ball indenter is D=10mm, the test force is F=3000kgf (29.42kN), and the holding time is 10-15s. The specimen is placed firmly on the test platform, and the hardness tester is started so that the indenter is vertically pressed into the specimen surface within 2-8s. After reaching the test force, the load is held for 10-15s, and the test force is smoothly released. The diameters of the indentation in two mutually perpendicular directions are measured using a reading microscope, and the average value is taken as the average diameter d of the indentation, accurate to 0.01mm. The effective indentation diameter should be within the range of 2.4-6.0mm, calculated using the formula HBW=0.102×2F / [πD(D−√(D)]]. 2 -d 2 ))]calculate.

[0049] III. Charpy pendulum impact test 1. Experimental Materials Referring to GB / T229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials", the test specimen is a Charpy V-notch impact specimen with dimensions of 55mm × 10mm × 10mm, a V-notch root radius of 0.25mm ± 0.05mm, a notch depth of 2mm, and a notch angle of 45°. The specimen notch should be smooth, burr-free, and free of obvious scratches, pits, or other defects.

[0050] 2. Experimental Procedure The specimen was placed on two supports in a simply supported beam configuration, with the notch facing away from the pendulum's edge. The specimen was positioned in the center of the two supports, with a support span of 40 mm ± 0.2 mm. The room temperature was controlled at 23℃ ± 5℃. The pendulum was raised to the specified height and locked. After the specimen was in place, the safety pin was removed, and the pendulum was released to fall freely and impact the specimen. The pendulum automatically retracted after breaking the specimen. The impact absorbed energy KV2 (J) was recorded, and the fracture morphology was observed. The characteristics of plastic deformation or brittle fracture were recorded. The final results are shown in Table 1.

[0051] From Table 1 and Figure 1-3 It can be seen that the tensile strength of Examples 1-3 all reached above 612 MPa, the yield strength was not less than 386 MPa, the elongation after fracture was all above 38.5%, the Brinell hardness was not less than 229 HBW, and the impact absorption energy was all above 87 J. This indicates that the present invention modifies hexagonal boron nitride through molecular bridging using a silane coupling agent, thereby forming a stable chemical bond between the inorganic filler and the phosphate binder. Combined with the three-dimensional physical cross-linking network constructed by polyethylene glycol, uniform coating of the reinforcing layer slurry and stable dispersion of the powder are achieved.

[0052] In Comparative Example 1, the reinforcement layer was replaced with ordinary silica sol adhesive instead of composite adhesive B. Its tensile strength decreased to 538 MPa, yield strength to 312 MPa, elongation after fracture to 30.5%, Brinell hardness to 201 HBW, and impact energy to 61 J. Ordinary silica sol relies solely on glass phase bonding at high temperatures, lacking the chemical transformation of phosphate components into the Al-OP covalent framework and the pinning reinforcement effect of in-situ mullite whiskers. The silica sol module shell lacks sufficient creep resistance and rigidity during high-temperature calcination and casting, with interlayer interfaces primarily based on physical bonding, making it prone to microcracks under thermal stress. Furthermore, the lack of densification from molybdenum trioxide and hexagonal boron nitride results in high porosity in the silica sol module shell. After molten metal seeps in, mechanical sand adhesion and micro-shrinkage porosity form on the casting surface, leading to a comprehensive deterioration of all mechanical properties.

[0053] Comparative Example 2 used unmodified aluminum dihydrogen phosphate solution to replace composite binder B. The tensile strength of the product further decreased to 505 MPa, the yield strength to 286 MPa, the elongation after fracture to 26.0%, the Brinell hardness to 188 HBW, and the impact energy to 48 J. Although the aluminum dihydrogen phosphate binder alone can undergo a polycondensation reaction at high temperatures, the lack of two-dimensional layered interface strengthening by hexagonal boron nitride and the matching and regulating effect of the thermal expansion coefficient of iron titanate resulted in severe interlayer thermal stress mismatch in the silica sol module shell under rapid heating conditions, leading to microcracks. The lack of multiple synergistic mechanisms caused deformation, microcrack propagation, and molten metal penetration of the silica sol module shell during the molten metal pouring process. A large amount of stress concentration inside the casting originated from micro-casting defects. Therefore, all mechanical properties were lower than those of the example, and the Brinell hardness no longer met the usual requirements for valve castings.

[0054] In summary, this invention improves the high-temperature strength, density, and interlayer bonding of the silica sol module shell through multiple chemical synergistic mechanisms, including silane coupling agent molecular bridging modification, high-temperature covalent bond network construction of phosphate, liquid-phase sintering aid of molybdenum trioxide, and hexagonal boron nitride barrier.

[0055] In the description of this specification, the terms "preparation example," "example," "various examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that example or preparation example, which are included in at least one example or preparation example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparation examples.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for reinforcing the outer surface of castings during precision valve body casting, characterized in that, Includes the following steps: S1. The wax material is pressed into the mold cavity by a wax injection machine, cooled and removed to form a wax mold. After repairing and cleaning the defects on the surface of the wax mold, it is welded onto the sprue bar to form a wax mold assembly. S2. After cleaning the wax mold assembly, apply adhesive to the surface layer, then sprinkle surface powder and sand and air dry. Repeat this process for the second layer. Then apply adhesive B, sprinkle reinforcing powder and sand, and air dry. Repeat this process for the second, third, and fourth reinforcing layers and the sealing layer. Air dry to form a silica sol mold shell. Among them, adhesive B is prepared by molecular bridging modification of hexagonal boron nitride through silane coupling agent. The silanol generated by its hydrolysis undergoes dehydration condensation with the boronol at the defects on the surface of boron nitride to form a stable Si-OB covalent bond. At the same time, the amino group at the other end of the silane is protonated in an acidic system and then forms an ionic bond with the phosphate group of aluminum dihydrogen phosphate. S3. After dewaxing the silica sol module shell in an electric wax melting furnace for 5-7 minutes, bake it and remove the silica sol module shell. S4. Pour the molten metal into the silica sol module shell. After the molten metal solidifies, remove the silica sol module shell outside the module. Then separate the valve body casting on the module from the pouring rod to obtain the blank valve body casting.

2. The method for reinforcing the outer surface of castings during precision valve body casting according to claim 1, characterized in that, In step S2, the adhesive used for the top layer and the second layer is silica sol. The powder used for the top layer is 320-mesh refined quartz powder, and the sand is 100-mesh refined quartz sand. The powder used for the second layer is 320-mesh refined quartz powder, and the sand is 60-mesh refined quartz sand. The air drying temperature is 22℃-26℃, and the air drying time is 3-5 hours.

3. The method for reinforcing the outer surface of castings during precision valve body casting according to claim 1, characterized in that, In step S2, the powder used for reinforcing the first layer is high-alumina synthetic powder, and the sand used is 60-mesh mullite sand; the powder used for reinforcing the second to fourth layers is kaolin clinker powder, and the sand used is 20-mesh kaolin clinker sand; the air-drying temperature for reinforcing the first to fourth layers is 35℃-45℃, the air-drying time is 10-20 minutes, and the hardening time is 10-15 minutes; the sealing layer is coated with water glass-based sealing material, wherein the mass ratio of water glass, high-alumina powder and quartz powder is 1:(0.4-0.6):(0.4-0.6), the air-drying temperature is 35℃-45℃, and the air-drying time is 20-40 minutes.

4. The method for reinforcing the outer surface of a casting during precision valve body casting according to claim 1, characterized in that, The roasting described in step S3 involves roasting at 1000℃-1200℃ for 60-90 minutes.

5. A method for reinforcing the outer surface of a casting during precision valve body casting according to claim 1, characterized in that, The molten metal in step S4 comprises the following components by weight: 35-45 parts of molybdenum-containing austenitic stainless steel base material, 48-58 parts of molybdenum-free austenitic stainless steel base material, 0.8-1.5 parts of pure nickel, 1.8-2.8 parts of ferromolybdenum, 2.0-3.0 parts of low-carbon ferrochrome, 0.15-0.35 parts of low-carbon ferromanganese, and 0.4-0.8 parts of ferrosilicon.

6. A method for reinforcing the outer surface of a casting during precision valve body casting according to claim 1, characterized in that, The preparation steps of adhesive B in step S2 are as follows: A1. Mix hexagonal boron nitride nanosheets pretreated with γ-aminopropyltriethoxysilane, aluminum phosphate powder, and iron titanate powder, add molybdenum trioxide and nano-yttrium oxide, ball mill and mix with anhydrous ethanol as medium for 5-7 hours, vacuum dry at 75-85℃, and pass through a 280-320 mesh sieve to obtain ternary composite precursor powder. A2. Mix the ternary composite precursor powder with aluminum dihydrogen phosphate solution to obtain a mixture, then add polyethylene glycol and PAN-based short-cut carbon fibers, stir for 0.8-1.2 hours and then perform ultrasonic degassing treatment to adjust the viscosity, thus obtaining adhesive B.

7. A method for reinforcing the outer surface of a casting during precision valve body casting according to claim 6, characterized in that, In step A1, the mass ratio of hexagonal boron nitride nanosheets, aluminum phosphate powder, and iron titanate powder is 1:(2.8-3.2):(1.3-1.7); the amount of polyethylene glycol added is 0.3-1.0% of the total solid mass in the mixture; and the amount of PAN-based chopped carbon fiber added is 0.1-0.5% of the total solid mass in the mixture.

8. A method for reinforcing the outer surface of a casting during precision valve body casting according to claim 6, characterized in that, In step A1, aluminum phosphate powder is prepared by heating aluminum dihydrogen phosphate to 480-520℃ at a heating rate of 5-10℃ / min and pre-dehydrating for 1.5-2.5 hours; the iron titanate powder is prepared by solid-phase synthesis of ferric oxide and titanium dioxide in a mass ratio of (1.9-2.1):1 at 1150-1250℃.

9. A method for reinforcing the outer surface of a casting during precision valve body casting according to claim 6, characterized in that, In step A2, the liquid-to-solid ratio of the ternary composite precursor powder to the aluminum dihydrogen phosphate solution is (0.35-0.45):1, and the amount of polyethylene glycol added is 0.3-0.8% of the total solid mass in the mixture; the PAN-based short-cut carbon fibers have a length of 50-100μm and are added at 0.2-0.5% of the total solid mass in the mixture; the viscosity is adjusted to 22-25 seconds as measured using a No. 4 flow cup.

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