V-method precision resin sand mold casting process suitable for gray iron or ductile iron

Abstract

The present invention relates to the technical field of mold cooling capacity control and material-process coordinated optimization, specifically a V-method precision resin sand mold casting process method suitable for gray iron or ductile iron; a V-method precision resin sand mold casting process suitable for gray iron or ductile iron, first preparing gradient functional modified resin sand, mixing spherical regenerated sand with various materials such as phenolic epoxy resin, and undergoing multi-step stirring and surface modification treatment; then preparing an intelligent temperature-controlled sand box, and then undergoing molding negative pressure curing, composite inoculation treatment, vacuum differential pressure pouring, and intelligent cooling control steps; during the process, special materials and structures such as core-shell curing agents, double-layer films, and cored wire are used to achieve precise process control. This process improves the strength and stability of sand molds and reduces casting defects through material innovation and process optimization; precise temperature control and pouring methods improve casting quality, and composite inoculation enhances mechanical properties; it is both environmentally friendly and economical, reduces costs, and improves yield rate, with broad application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of mold cooling capacity regulation and material-process coordinated optimization, and in particular to a V-method precision resin sand mold casting process method suitable for gray iron or ductile iron. Background Art

[0002] Gray iron and ductile iron are widely used in numerous fields, including automotive, machinery manufacturing, and aerospace, due to their excellent casting properties, mechanical properties, and cost advantages. V-method casting, an advanced sand casting process, compacts the sand mold using negative pressure, resulting in smooth casting surfaces, high dimensional accuracy, and reusable sand molds. This effectively reduces production costs and improves production efficiency. However, the traditional V-method precision resin sand mold casting process still faces numerous technical bottlenecks in practical applications, making it difficult to meet the stringent requirements of modern manufacturing for high-quality castings.

[0003] Traditional resin sands mostly utilize ordinary quartz sand and a single resin system. The sand particles are irregularly shaped and have a rough surface, resulting in uneven mold compaction and prone to defects such as pinholes and pores in castings. Furthermore, ordinary resins have poor thermal stability at high temperatures and are prone to thermal decomposition and volatilization, which not only pollutes the environment but also forms carbon deposits on the casting surface, affecting casting quality. Furthermore, existing curing agent systems have low curing efficiency and a difficult-to-control curing process, resulting in insufficient sand mold strength and prone to collapse during the pouring process, affecting the precision of the casting.

[0004] The traditional V-method casting uses a single sand box temperature control method, which cannot accurately control the temperature according to the solidification requirements of different parts of the casting. This leads to inconsistent cooling rates in different parts of the casting, resulting in large thermal stresses, which can easily cause defects such as deformation and cracks in the casting. Moreover, the traditional inoculation treatment method only uses a single inoculant, which makes it difficult to simultaneously meet the requirements of gray iron and ductile iron for graphite morphology, grain refinement, and other aspects, resulting in limited improvement in the mechanical properties of the casting. During the pouring process, the traditional atmospheric pressure pouring method easily causes the molten iron to be entrained with gas and inclusions, reducing the internal quality of the casting. In addition, the cooling process of the casting lacks effective control means, making it impossible to achieve precise regulation of the casting structure and properties.

[0005] As modern manufacturing evolves toward lightweighting, precision, and high performance, higher demands are being placed on the quality and performance of gray and ductile iron castings. For example, in the casting of automotive engine blocks, castings must exhibit superior strength, wear resistance, and dimensional accuracy. In the aerospace sector, even more stringent requirements exist for lightweighting and high-temperature resistance. Therefore, there is an urgent need to develop a new V-method precision resin sand casting process suitable for gray and ductile iron castings. Through innovative material formulations and process designs, this process could address the technical challenges inherent in traditional processes, improve the quality and performance of castings, and meet the development needs of modern manufacturing. Summary of the Invention

[0006] (1) Technical problems solved

[0007] In view of the deficiencies in the prior art, the present invention provides a V-method precision resin sand mold casting process method applicable to gray iron or ductile iron.

[0008] (2) Technical solution

[0009] A V-method precision resin sand mold casting process suitable for gray iron or ductile iron comprises the following steps:

[0010] S1: Prepare gradient functional modified resin sand, by mixing 85-95 parts of spherical regenerated sand, 5-8 parts of phenolic epoxy resin, 2-4 parts of nano zirconium dioxide, 3-6 parts of core-shell structure composite curing agent, 1-2 parts of graphene nanosheets, and 0.5-1 parts of carbon nanotubes by weight; the core-shell structure composite curing agent has hexamethylenetetramine as the core, and is coated with organic sulfonic acid, with a mass ratio of p-toluenesulfonic acid to benzenesulfonic acid of 2:1, to form a 20-50 μm microcapsule structure through interfacial polymerization; when mixing the sand, first heat the spherical regenerated sand and Heat the mixture to 90-110°C, add nano-zirconium dioxide and graphene nanosheets, and stir at a high speed of 500-700 r / min for 15-20 minutes to form a mechanical alloying layer; then add silane coupling agent KH-560, accounting for 0.8-1.2% of the weight of the sand, and continue stirring for 8-12 minutes to allow the silane coupling agent to be grafted onto the surface of the sand particles; finally, add phenolic epoxy resin, carbon nanotubes and core-shell structure composite curing agent, and stir at 300-450 r / min for 25-35 minutes to obtain gradient functional modified resin sand;

[0011] S2: Prepare an intelligent temperature-controlled sand box and lay a 3-5mm thick layer of phase change energy storage material on the inner wall of the sand box. The material is composed of paraffin wax and expanded graphite with a mass ratio of 3:2 and a phase change temperature of 55-65°C. An electromagnetic induction heating coil is installed on the outside of the sand box with a coil spacing of 5-8mm and a power density of 1.5-2.5kW / m².

[0012] S3: Molding and negative pressure curing: fill the gradient functional modified resin sand into the intelligent temperature-controlled sand box and vibrate and compact it at a vibration frequency of 40-60Hz, an amplitude of 0.4-0.6mm, and a compaction time of 4-6 minutes; cover it with a double-layer composite film, with the inner layer being a polyvinyl chloride film with a thickness of 0.1-0.15mm and the outer layer being an aluminum foil composite film with a thickness of 0.05-0.1mm; start the exhaust system to make the negative pressure in the sand box reach 0.05-0.07MPa, and at the same time start the electromagnetic induction heating to raise the temperature of the inner wall of the sand box to 120-140℃ and maintain it for 15-25 minutes to allow the resin to undergo a cross-linking and curing reaction;

[0013] S4: Composite inoculation treatment: Gray iron or ductile iron molten iron is heated to 1450-1550℃, and composite inoculant cored wire is added to the molten iron by wire feeding method. The outer layer of the cored wire is a low-carbon steel strip with an inner diameter of 8-12mm. The core is composed of the following components: 70-80% ferrosilicon alloy, 5-10% nano-calcium carbonate, 3-5% rare earth magnesium alloy, 2-4% boron nitride nanotubes, and the balance is silicon carbide whiskers. The addition amount is 0.3-0.6% of the weight of the molten iron. The wire feeding speed is 1.5-2.5m / s.

[0014] S5: Vacuum differential pressure pouring: Pour the treated molten iron into a holding furnace at a holding temperature of 1380-1430°C; place the sand box in a vacuum chamber and reduce the pressure in the chamber to 0.02-0.03 MPa; use a bottom pouring system, and use a differential pressure device to fill the mold with molten iron under a pressure difference of 0.04-0.06 MPa, at a filling speed of 6-10 kg / s;

[0015] S6: Intelligent cooling control. After pouring is completed, the temperature of the casting is monitored in real time through the temperature sensor installed in the sand box. When the temperature drops to 700-800℃, the air cooling system in the sand box is started with a wind speed of 3-5m / s, so that the casting is cooled to 350-450℃ at a cooling rate of 15-25℃ / min; then the air cooling system is turned off and the casting is allowed to cool naturally to room temperature.

[0016] Preferably, the spherical regenerated sand has a particle size of 0.2-0.5 mm, a roundness coefficient ≥ 0.9, and a loss on ignition ≤ 0.3%, and is obtained by a combined treatment of high-temperature roasting (850-950° C.) and mechanical regeneration.

[0017] Preferably, the epoxy value of the novolac epoxy resin is 0.4-0.5eq / 100g, the softening point is 80-90°C, and the novolac epoxy resin is prepared by reacting bisphenol A epoxy resin with linear phenolic resin in the presence of a catalyst.

[0018] Preferably, the nano zirconium dioxide has a particle size of 30-80 nm, a crystal form of a mixture of tetragonal phase and monoclinic phase, a mass ratio of 7:3, and a specific surface area of 60-100 m² / g.

[0019] Preferably, the graphene nanosheets have a sheet thickness of 3-8 nm, a sheet diameter of 5-15 μm, a carbon content of ≥98%, are prepared by an oxidation-reduction method and are surface hydroxylated, with a hydroxyl content of 2-5%.

[0020] Preferably, in step S3, a breathable insulation layer with a thickness of 0.5-1 mm is laid between the double-layer composite film and the sand mold, which is a composite of ceramic fiber and aerogel, has a porosity of 70-80%, and a thermal conductivity coefficient of ≤0.03W / (m·K).

[0021] Preferably, the preparation method of the composite inoculant cored wire in step S4 is: after mixing the components in proportion, pressing them into a core rod by powder metallurgy, and then wrapping them with low-carbon steel strips and seam welding them.

[0022] Preferably, in the step S5, the gates of the bottom pouring system are arranged in a stepped manner, the distance between each layer of gates is 50-80 mm, and the cross-sectional area of the gates decreases by 10-15% layer by layer from bottom to top.

[0023] Preferably, in step S6, the air ducts of the air cooling system are evenly distributed around the flask, the distance between the air duct outlet and the casting surface is 80-120 mm, and a temperature-adjustable electric heating wire is installed in the air duct to adjust the cooling speed.

[0024] Preferably, after the casting is cooled to room temperature, laser surface alloying treatment is performed, using a carbon dioxide laser with a laser power of 1.5-3kW and a scanning speed of 5-10mm / s to clad a layer of alloy with a thickness of 0.3-0.8mm on the surface of the casting, wherein the composition of the alloy layer is as follows by weight: Cr 15-20%, Ni 8-12%, Mo 3-5%, V 1-3%, and the balance is Fe.

[0025] (3) Beneficial technical effects

[0026] Compared with the existing technology, the beneficial effects of the present invention are:

[0027] 1. Utilizing gradient-functional modified resin sand and spherical regenerated sand combined with additives such as nano-zirconium dioxide and graphene nanosheets, mechanical alloying and surface modification significantly enhance the sand's surface properties and mold compactness, significantly increasing mold strength and effectively reducing casting defects such as sand holes and pores. The use of a core-shell composite curing agent enables controlled curing of the resin, shortening curing time and significantly improving the thermal stability of the cured sand mold, reducing thermal decomposition and carbon deposition at high temperatures.

[0028] 2. The application of intelligent temperature-controlled sand boxes, through the combination of phase change energy storage materials and electromagnetic induction heating, achieves precise control of the sand box temperature, ensuring uniform cooling rates across all parts of the casting, significantly reducing thermal stress and effectively avoiding deformation and cracking of the casting. The composite inoculation treatment uses cored wire composed of a variety of high-performance additives to simultaneously meet the graphite morphology and grain refinement requirements of both gray iron and ductile iron, thereby increasing the tensile strength and hardness of the casting. The application of vacuum differential pressure casting technology reduces the amount of gas and inclusions entrained in the molten iron during the pouring process, significantly improving the internal quality of the casting and significantly reducing defects such as pores and inclusions. Intelligent cooling control enables precise regulation of the cooling rate of the casting, enabling ideal microstructure and performance to be achieved based on the different requirements of the casting.

[0029] 3. The process of the present invention is also environmentally friendly and economical. The use of spherical reclaimed sand improves sand resource utilization and reduces new sand mining; the application of a novel resin and curing agent system reduces pollutant emissions. Furthermore, this process improves the yield and quality of castings, reduces subsequent processing steps, and lowers production costs, offering broad application prospects and significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of the V-method precision resin sand mold casting process suitable for gray iron or ductile iron;

[0031] Figure 2 This is a bar chart comparing the normal temperature compressive strength of the sand molds and the high temperature compressive strength of the sand molds of the embodiment and the comparative example;

[0032] Figure 3 1. is a line graph comparing the porosity of castings and the area ratio of shrinkage defects of castings of Example and Comparative Example;

[0033] Figure 4 It is a bar graph comparing the tensile strength and elongation of castings of the embodiment and the comparative example. DETAILED DESCRIPTION

[0034] Example 1

[0035] Preparation of gradient functional modified resin sand

[0036] First, spherical regenerated sand, which had undergone a combined high-temperature calcination (880°C) and mechanical regeneration process, was selected. Its particle size was 0.3 mm, roundness coefficient was 0.93, loss on ignition was 0.25%, and silica content was 96%. 90 parts of this spherical regenerated sand were added to a heated sand mixer and heated to 100°C. Next, 3 parts of nano-zirconium dioxide (50 nm particle size, tetragonal to monoclinic phase mass ratio of 7:3, specific surface area of 80 m² / g) and 1.5 parts of graphene nanosheets (5 nm thickness, 10 μm diameter) that had been surface-hydroxylated (hydroxyl content 3%) were added. The mixture was stirred at 600 rpm for 18 minutes, forming a mechanical alloying layer on the sand surface through a tribochemical reaction. Subsequently, 1% of the sand weight was added as a silane coupling agent, KH-560, and stirring was continued for 10 minutes to graft the silane coupling agent onto the sand surface. Then add 6 parts of phenolic epoxy resin (epoxy value 0.45eq / 100g, softening point 85℃, prepared by bisphenol A epoxy resin and linear phenolic resin under the action of catalyst), 1.2 parts of carbon nanotubes, and 5 parts of core-shell structure composite curing agent (with hexamethylenetetramine as the core, the outer layer is coated with organic sulfonic acid with a mass ratio of p-toluenesulfonic acid to benzenesulfonic acid of 2:1, and a microcapsule structure with an average particle size of 30μm is formed by interfacial polymerization), stir at a speed of 400r / min for 30 minutes, mix thoroughly, and obtain gradient functional modified resin sand.

[0037] Preparation of intelligent temperature-controlled sand box

[0038] A 4mm thick layer of paraffin wax / expanded graphite composite phase change material (mass ratio 3:2, phase change temperature 60°C) is evenly applied to the inner wall of the sand box. This material absorbs and releases heat during the casting solidification process, acting as a temperature buffer. Electromagnetic induction heating coils with a 6mm pitch and a power density of 2kW / m² are wound around the outside of the sand box to provide precise temperature control during the sand curing stage.

[0039] Molding and negative pressure curing

[0040] The modified resin sand is filled into an intelligent temperature-controlled sand box. The vibration compaction equipment is turned on, with the vibration frequency set to 50 Hz, the amplitude to 0.5 mm, and the compaction time to 5 minutes, so that the sand mold is evenly compacted. After compaction, it is covered with a polyvinyl chloride film with an inner layer thickness of 0.12 mm and an aluminum foil composite film with an outer layer thickness of 0.08 mm to form a sealed structure. The exhaust system is started to increase the negative pressure in the sand box to 0.06 MPa. At the same time, electromagnetic induction heating is turned on to raise the temperature of the inner wall of the sand box to 130°C and maintain it for 20 minutes. This allows the phenolic epoxy resin and the composite curing agent to undergo a cross-linking and curing reaction, forming a sand mold with high strength and thermal stability.

[0041] Composite inoculation treatment

[0042] Molten ductile iron is heated to 1500°C in a medium-frequency induction furnace. A composite inoculant cored wire (the outer layer of the cored wire is a low-carbon steel strip with an inner diameter of 10mm, and the core is composed of 75% ferrosilicon alloy (containing 75% Si), 8% nano-calcium carbonate, 4% rare earth magnesium alloy, 3% boron nitride nanotubes, 5% silicon carbide whiskers, and the balance iron) is fed into the molten iron via a wire feeder at a speed of 2m / s. The inoculant is added in an amount of 0.5% by weight of the molten iron to ensure that the molten iron is fully inoculated before pouring, improving the graphite morphology and grain structure.

[0043] Vacuum differential pressure casting

[0044] The treated molten iron is poured into a holding furnace, maintained at 1400°C. The flask is placed in a vacuum chamber, and the vacuum pump is activated to reduce the pressure inside the chamber to 0.025 MPa. A bottom-pouring stepped gating system (with a lower gating cross-sectional area of 15 cm² and an upper gating cross-sectional area decreasing by 12%) is used. A differential pressure device ensures that the molten iron is steadily filled at a rate of 8 kg / s under a pressure differential of 0.05 MPa, minimizing the entrapment of gas and inclusions during the filling process.

[0045] Intelligent cooling control

[0046] After pouring, the casting temperature is monitored in real time using temperature sensors installed at various locations within the sand box. When the casting temperature drops to 750°C, the air cooling system is activated, with a wind speed set at 4m / s, allowing the casting to cool to 400°C at a rate of 20°C / min. The air cooling system is then shut off, and the casting is allowed to cool naturally to room temperature within the sand mold. By precisely controlling the cooling rate, ideal casting structure and properties are achieved.

[0047] Example 2

[0048] Preparation of gradient functional modified resin sand

[0049] 92 parts of spherical regenerated sand processed in the same batch as Example 1 were selected, and their various indicators were consistent. 2.5 parts of nano zirconium dioxide and 1.2 parts of graphene nanosheets were added, and in the same sand mixer, the mixture was first stirred at 620 r / min for 17 minutes, and then 0.9% of silane coupling agent KH-560 was added and stirred for 9 minutes. Then 5.5 parts of phenolic epoxy resin, 1 part of carbon nanotubes, and 4.5 parts of core-shell structure composite curing agent were added, and the mixture was stirred at 380 r / min for 32 minutes to obtain modified resin sand.

[0050] Preparation of intelligent temperature-controlled sand box

[0051] The thickness of the phase change material layer on the inner wall of the sand box is adjusted to 3.8 mm, the spacing between the electromagnetic induction heating coils is set to 6.5 mm, the power density is adjusted to 1.8 kW / m², and the other structures are the same as those in Example 1.

[0052] Molding and negative pressure curing

[0053] Modified resin sand was placed in a sandbox and vibrated for 48 Hz, 0.48 mm, and 4.5 minutes. The sandbox was then covered with a double layer of film: an inner PVC film 0.11 mm thick and an outer aluminum foil composite film 0.07 mm thick. The sandbox was evacuated to a negative pressure of 0.058 MPa. Electromagnetic induction heating was used to raise the inner wall temperature to 125°C, where it was maintained for 22 minutes to complete curing.

[0054] Composite inoculation treatment

[0055] Gray iron molten iron is heated to 1480℃, and composite inoculant cored wire (the core composition ratio is fine-tuned to 72% ferrosilicon alloy, 9% nano-calcium carbonate, 3.5% rare earth magnesium alloy, 3.5% boron nitride nanotubes, 6% silicon carbide whiskers, and the balance is iron) is fed into the molten iron at a speed of 1.8m / s. The added amount is 0.45% of the weight of the molten iron.

[0056] Vacuum differential pressure casting

[0057] The molten iron is kept at a temperature of 1380°C, the pressure in the vacuum chamber is reduced to 0.022 MPa, and a bottom-pouring stepped ingode is used (the cross-sectional area of the lower ingode is 14 cm², and the upper ingode decreases by 13%). The casting is carried out at a speed of 7.5 kg / s under a pressure difference of 0.045 MPa.

[0058] Intelligent cooling control

[0059] When the casting temperature drops to 760℃, air cooling is started with a wind speed of 3.8m / s. After cooling to 420℃, it is cooled naturally. The cooling rate of the entire cooling process is controlled at about 18℃ / min.

[0060] Example 3

[0061] Preparation of gradient functional modified resin sand

[0062] Take 88 parts of spherical regenerated sand, add 3.5 parts of nano-zirconium dioxide and 1.8 parts of graphene nanosheets, and stir in a sand mixer at 580 rpm for 19 minutes. Then add 1.1% of silane coupling agent KH-560 and stir for 11 minutes. Then add 6.5 parts of phenolic epoxy resin, 1.5 parts of carbon nanotubes, and 5.5 parts of core-shell composite curing agent, and stir at 420 rpm for 28 minutes to produce modified resin sand.

[0063] Preparation of intelligent temperature-controlled sand box

[0064] The thickness of the phase change material layer on the inner wall of the sand box is 3.5 mm, the power density of the electromagnetic induction heating coil is set to 2.2 kW / m², and the spacing is 5.5 mm.

[0065] Molding and negative pressure curing

[0066] After filling the sandbox with sand, it was vibrated and compacted for 5.5 minutes at a frequency of 45Hz and an amplitude of 0.45mm. The double-layer film (the inner PVC film was 0.13mm thick, and the outer aluminum foil composite film was 0.09mm thick) was then vacuumed to 0.062MPa and heated to 135°C for 18 minutes to cure.

[0067] Composite inoculation treatment

[0068] The ductile iron molten iron was heated to 1520℃ and the composite inoculant cored wire (the rare earth magnesium alloy content in the core was increased to 6% and the proportions of other components were slightly adjusted) was fed into the molten iron at a speed of 2.2m / s. The addition amount was 0.55% of the molten iron weight.

[0069] Vacuum differential pressure casting

[0070] The molten iron was kept at 1420℃, the pressure in the vacuum chamber was reduced to 0.028MPa, and a bottom-pouring stepped ingode (the cross-sectional area of the lower ingode was 16cm², and the upper ingode decreased by 10%) was used. The casting was carried out at a speed of 8.5kg / s under a pressure difference of 0.055MPa.

[0071] Intelligent cooling control

[0072] When the casting temperature drops to 780℃, air cooling is started with a wind speed of 3.5m / s. After cooling to 380℃, it is naturally cooled with a cooling rate controlled at about 22℃ / min.

[0073] Comparative Example

[0074] Using the traditional V-method casting process, ordinary 40-70 mesh quartz sand (0.8% mud content, 92% silica content) is selected. Phenolic resin and a single hexamethylenetetramine curing agent are added in conventional proportions and simply mixed in a sand mixer. After compaction, the sand mold is covered with a single layer of ordinary plastic film, 0.15mm thick. The molten iron is poured at normal pressure without composite inoculation. After pouring, the casting is cooled in the natural environment without any temperature control measures.

[0075] Performance Testing

[0076] A performance comparison of Examples 1 to 3 with the comparative example shows that the new V-method casting process significantly improves the quality of castings. The compressive strength of the sand mold at room temperature reaches 11.8 to 13.2 MPa, and the high-temperature compressive strength is 6.5 to 7.2 MPa, which is much higher than the 7.5 and 3.2 MPa of the comparative example. The surface roughness of the casting is controlled at 6.5 to 7.2 microns, the porosity is only 1.0% to 1.5%, and the shrinkage defect area accounts for 0.6% to 1.2%, which is a significant improvement over the 12.3 microns, 5.8% and 4.5% of the comparative example. In terms of mechanical properties, the tensile strength reaches 405 to 435 MPa, the elongation is 2.5% to 3.0%, and the hardness is 178 to 192 HB, all of which are better than the 320 MPa, 1.2% and 150 HB of the comparative example. These data show that the new process has made breakthrough progress in sand mold strength, casting surface quality and mechanical properties.

[0077] The physical properties of the sand molds and castings of the embodiment and the comparative example are compared in Table 1:

[0078]

[0079] Conclusion: Examples 1-3 have significantly higher compressive strength of sand molds at room temperature and high temperature than the control example, the surface roughness of the castings is lower, and the porosity and shrinkage defects account for a smaller proportion, reflecting the optimization effect of the process of the present invention on the physical properties of sand molds and castings.

[0080] The mechanical properties of the castings of the embodiment and the comparative example are compared in Table 2:

[0081]

[0082] Conclusion: The tensile strength, elongation and hardness of the castings of the three embodiments are better than those of the comparative example. Example 3 performs best in various mechanical properties, indicating that the process of the present invention can effectively improve the mechanical properties of castings.

Claims

1. A V-method precision resin sand mold casting process suitable for gray iron or ductile iron, characterized in that: The following steps are involved: S1: preparing gradient functional modified resin sand, mixing spherical regenerated sand, phenolic epoxy resin, nano zirconium dioxide, core-shell structure composite curing agent, graphene nanosheets, and carbon nanotubes; the core-shell structure composite curing agent has hexamethylenetetramine as the core and an outer layer coated with organic sulfonic acid; when mixing the sand, first heat the spherical regenerated sand to 90-110° C., add nano zirconium dioxide and graphene nanosheets and stir; then add silane coupling agent KH-560 and continue stirring; finally, add phenolic epoxy resin, carbon nanotubes and core-shell structure composite curing agent and stir to prepare gradient functional modified resin sand; S2: Prepare an intelligent temperature-controlled sand box, lay a phase change energy storage material layer composed of paraffin wax / expanded graphite on the inner wall of the sand box; install an electromagnetic induction heating coil on the outside of the sand box; S3: Molding and negative pressure curing: Fill the gradient functional modified resin sand into the intelligent temperature-controlled sand box and vibrate to compact it; cover it with a double-layer composite film; start the exhaust system and electromagnetic induction heating at the same time to cause the resin to undergo a cross-linking and curing reaction; S4: Composite inoculation treatment: Gray iron or ductile iron molten iron is heated to 1450-1550℃, and composite inoculant cored wire is added to the molten iron using the wire feeding method. The outer layer of the cored wire is a low-carbon steel strip, and the core is composed of ferrosilicon alloy, nano-calcium carbonate, rare earth magnesium alloy, boron nitride nanotubes, and silicon carbide whiskers; S5: Vacuum differential pressure pouring: Pour the treated molten iron into the holding furnace; place the sand box in the vacuum chamber; use a bottom pouring system, and use a differential pressure device to fill the mold with molten iron under the action of pressure difference; S6: Intelligent cooling control. After pouring is completed, the temperature of the casting is monitored in real time through the temperature sensor installed in the sand box. When the temperature drops to 700-800℃, the air cooling system in the sand box is started to cool the casting to 350-450℃; then the air cooling system is turned off to allow the casting to cool naturally to room temperature.

2. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: The spherical regenerated sand has a particle size of 0.2-0.5 mm, a roundness coefficient of ≥0.9, and a loss on ignition of ≤0.3%, and is obtained by a combined treatment of high-temperature roasting and mechanical regeneration.

3. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: The phenolic epoxy resin has an epoxy value of 0.4-0.5eq / 100g and a softening point of 80-90°C, and is prepared by reacting bisphenol A epoxy resin with linear phenolic resin under the action of a catalyst.

4. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: The nano zirconium dioxide also has a particle size of 30-80 nm, a crystal form that is a mixture of tetragonal phase and monoclinic phase, a mass ratio of 7:3, and a specific surface area of 60-100 m² / g.

5. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: The graphene nanosheets also have a sheet thickness of 3-8 nm, a sheet diameter of 5-15 μm, a carbon content of ≥98%, are prepared by an oxidation-reduction method and are surface hydroxylated, with a hydroxyl content of 2-5%.

6. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: The method further includes laying a breathable insulation layer with a thickness of 0.5-1 mm between the double-layer composite film and the sand mold in step S3. The breathable insulation layer is composed of a composite of ceramic fiber and aerogel, has a porosity of 70-80%, and a thermal conductivity coefficient of ≤0.03 W / (m·K).

7. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: The preparation method of the composite inoculant cored wire in step S4 is as follows: after mixing the components in proportion, pressing them into a core rod by powder metallurgy, and then wrapping them with low-carbon steel strips and seam welding them.

8. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: In the step S5, the ingates of the bottom pouring system are arranged in a stepped manner, the spacing between the ingates of each layer is 50-80 mm, and the cross-sectional area of the ingates decreases by 10-15% layer by layer from bottom to top.

9. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: In step S6, the air ducts of the air cooling system are evenly distributed around the sand box, the distance between the air duct outlet and the casting surface is 80-120 mm, and a temperature-adjustable electric heating wire is installed in the air duct to adjust the cooling speed.

10. The V-method precision resin sand mold casting process for gray iron or ductile iron according to claim 1, characterized in that: The method also includes performing laser surface alloying treatment on the casting after the casting is cooled to room temperature, using a carbon dioxide laser with a laser power of 1.5-3kW and a scanning speed of 5-10mm / s to clad a 0.3-0.8mm thick alloy layer on the surface of the casting. The composition of the alloy layer is as follows by weight: Cr 15-20%, Ni 8-12%, Mo 3-5%, V 1-3%, and the balance is Fe.

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