A resin sand casting method for axle housing castings

Abstract

The application provides a resin sand casting method of a bridge housing casting, belongs to the casting technical field, and the casting method comprises casting and process design, mold and sand core manufacturing, closing and pouring preparation, smelting and pouring, cooling, sand falling and cleaning, heat treatment and finishing, and old sand regeneration. The casting resin sand comprises water-washed quartz sand, biomass modified furan resin, HTAM high-temperature-resistant and migration-resistant modifier, p-toluenesulfonic acid, aluminum dihydrogen phosphate, lactic acid, ammonium bicarbonate, polystyrene, expandable graphite, silane coupling agent, mica powder, calcined kaolin and spodumene powder. The biomass modified furan resin is prepared by the reaction of furfuryl alcohol, bio-based polyol, urea, phenol and p-toluenesulfonic acid and the addition of KH-550. The HTAM high-temperature-resistant and migration-resistant modifier is prepared by the reaction of KH-570 modified activated ceramic microbeads, pyromellitic dianhydride and 4,4'-diamino diphenyl ether and heat treatment.

Description

Technical Field

[0001] This invention pertains to the field of casting technology, specifically relating to a resin sand casting method for bridge shell castings. Background Technology

[0002] As a core load-bearing component of the automotive chassis, the axle housing must withstand alternating loads, impact vibrations, and complex stresses during vehicle operation. The quality of its castings directly determines the overall vehicle's driving safety and chassis durability. Traditional axle housing casting often employs clay sand molding, a process with low raw material costs and wide applicability. However, this process suffers from poor sand collapsibility, high surface roughness, and low dimensional accuracy. Castings are prone to defects such as sand inclusions, porosity, and shrinkage cavities, requiring extensive subsequent machining processes. Material utilization is only 60%–70%, making it difficult to meet the lightweight and high-precision manufacturing requirements of high-end commercial vehicle axle housings.

[0003] With the automotive industry's increasing demands for casting quality, resin sand casting technology has gradually replaced clay sand casting, becoming the mainstream molding method for bridge housing castings. Resin sand uses furan resin, phenolic resin, and other binders, and a curing agent initiates a cross-linking reaction to harden the molding sand. It offers advantages such as high molding sand strength, good collapsibility, high casting dimensional accuracy, and good surface finish, significantly reducing machining allowances and increasing material utilization to over 85%. Furthermore, resin sand molding enables mechanized and automated production, meeting the demand for high-volume, multi-variety bridge housing castings.

[0004] However, existing resin sand casting methods still face the following technical bottlenecks in bridge shell casting production: On the one hand, traditional furan resin sand releases harmful gases such as formaldehyde and phenols during the curing process, creating a harsh working environment; on the other hand, resin sand lacks sufficient high-temperature deformation resistance, making thicker parts of bridge shell castings, such as flanges and shaft ends, prone to mold wall migration during pouring, leading to shrinkage cavities and porosity defects. This necessitates the use of risers for feeding, increasing process complexity and production costs. Furthermore, the collapsibility of conventional resin sand significantly decreases at high temperatures, making casting cleaning difficult, and the recycling rate of waste sand is only 50%–60%, resulting in significant resource waste.

[0005] Currently, the trend towards lightweighting in automobiles is driving axle housing castings towards thinner walls and greater complexity, placing higher demands on the high-temperature performance, environmental friendliness, and recyclability of resin sand. Therefore, it is necessary to develop casting processes and matching resin sands suitable for axle housing castings to meet the high-quality, low-cost manufacturing requirements of these components. Summary of the Invention

[0006] To address the existing problems in resin sand casting of bridge housings, such as mold wall migration in thick sections during pouring, leading to shrinkage cavities and porosity defects, significant attenuation of collapsibility at high temperatures, and difficulty in cleaning, this invention provides a resin sand casting method for bridge housings. The resin sand, designed with optimized bonding systems, functional additives, and processes, systematically solves the bottlenecks of traditional resin sand, including poor high-temperature deformation resistance, decreased collapsibility, and low regeneration rate. This method achieves synergistic effects between room temperature and high-temperature strength, a balance between migration resistance and collapsibility, environmentally friendly regeneration, and good casting quality assurance. The specific technical solution is as follows:

[0007] A resin sand casting method for a bridge shell casting includes the following steps:

[0008] Design the pouring position and parting surface of the casting; select bottom pouring and set risers; prepare several sand cores with a room temperature tensile strength >2.8MPa, a tensile strength >1.2MPa after 10 minutes at 800℃, and a collapsibility index >95%; bond and assemble the sand cores, coat them with refractory coating, and dry them; assemble the lower mold, sand cores, and upper mold, and tighten the mold clamps; place the pouring cup and riser ring; pour the molten casting, cool it to below 500℃ in the mold, vibrate to remove sand, and remove adhering sand, flash, and burrs from the surface of the casting to obtain the casting billet;

[0009] The sand core is prepared using casting resin sand, which contains washed quartz sand, biomass-modified furan resin, HTAM high-temperature resistant and anti-migration modifier, composite curing agent, gradient disintegration agent, silane coupling agent, crack-resistant agent, and high-temperature resistant reinforcing phase. The composite curing agent includes p-toluenesulfonic acid, aluminum dihydrogen phosphate, and lactic acid. The gradient disintegration agent includes ammonium bicarbonate, polystyrene, and expandable graphite. The crack-resistant agent is mica powder. The high-temperature resistant reinforcing phase includes calcined kaolin and spodumene powder.

[0010] The biomass-modified furan resin is prepared by stirring furfuryl alcohol, bio-based polyol, urea, and deionized water, then adding phenol and p-toluenesulfonic acid for a condensation reaction, adjusting the pH to 4.0-4.5, diluting with deionized water, adding KH-550 and stirring, and adjusting the solid content to 75wt%-80wt%. The bio-based polyol is polytrimethylene ether glycol with a number average molecular weight of 500 g / mol.

[0011] The HTAM high-temperature resistant and anti-migration modifier is KH-570 modified activated ceramic microspheres dispersed in N-methylpyrrolidone, with the addition of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether and stirring reaction. After pressure filtration, the filter cake is heat-treated successively at 100℃~110℃, 150℃~160℃, and 200℃~220℃, and after cooling to room temperature, it is dispersed and sieved to obtain the final product.

[0012] In the above casting method, the casting resin sand generated by vibration and sand falling is collected, crushed, air-separated, and magnetically separated, and then calcined at 550℃~650℃ for 1.5h~2h to adjust the particle size to obtain recycled sand with a recycling rate of over 80wt%.

[0013] A casting resin sand is used in the resin sand casting method for a bridge shell casting described above. The casting resin sand comprises the following raw materials in parts by weight: 100 parts washed quartz sand, 1.5 to 2 parts biomass-modified furan resin, 1.2 to 1.8 parts HTAM high-temperature resistant and anti-migration modifier, 0.4 to 0.6 parts composite curing agent, 0.5 to 1.0 parts gradient disintegrating agent, 0.1 to 0.2 parts silane coupling agent, 0.2 to 0.3 parts crack-resistant agent, and 1.5 to 2.5 parts high-temperature resistant reinforcing phase. The composite curing agent includes p-toluenesulfonic acid, aluminum dihydrogen phosphate, and lactic acid. The gradient disintegrating agent includes ammonium bicarbonate, polystyrene, and expandable graphite. The crack-resistant agent is mica powder. The high-temperature resistant reinforcing phase includes calcined kaolin and spodumene powder.

[0014] In the above-mentioned casting resin sand, the particle size of the washed quartz sand is between 40 mesh and 70 mesh.

[0015] In the above-mentioned casting resin sand, the composite curing agent comprises 60wt% to 65wt% p-toluenesulfonic acid aqueous solution, 45wt% to 50wt% aluminum dihydrogen phosphate aqueous solution, and 85wt% to 90wt% lactic acid aqueous solution in a mass ratio of (70 to 75): (25 to 30): (3 to 5).

[0016] In the above-mentioned casting resin sand, the gradient disintegrating agent includes ammonium bicarbonate, polystyrene microspheres, and expandable graphite in a mass ratio of (1-1.2):(0.5-0.7):(0.8-1).

[0017] In the above-mentioned casting resin sand, the silane coupling agent is KH-550 or KH-560.

[0018] In the above-mentioned casting resin sand, the high-temperature resistant reinforcing phase includes calcined kaolin and spodumene powder in a mass ratio of (2-2.5):(1-1.2).

[0019] Further, in the above-mentioned casting resin sand, the preparation method of the biomass-modified furan resin includes the following steps: 60-70 parts furfuryl alcohol, 15-25 parts bio-based polyol, 5-10 parts urea and 3-5 parts deionized water are stirred and dissolved; 2-5 parts phenol and 0.5-1.5 parts p-toluenesulfonic acid are added, and the mixture is stirred to induce a condensation reaction. The pH is adjusted to 4.0-4.5, 2-4 parts deionized water is added for dilution, and 0.3-0.8 parts KH-550 are added and stirred. The solid content is adjusted to 75wt%-80wt% with deionized water at room temperature, and the mixture is filtered to obtain the biomass-modified furan resin.

[0020] In the above-mentioned method for preparing biomass-modified furan resin, the bio-based polyol is polytrimethylene ether glycol with a number average molecular weight of 500 g / mol; the stirring and dissolving temperature is 60℃~65℃; the stirring and polycondensation reaction is carried out at 80℃~85℃ for 90 min~120 min; the pH is adjusted with a 5wt%~8wt% sodium carbonate aqueous solution; after pH adjustment, the temperature is lowered to 40℃~50℃; and the filtration is performed through a 100-150 mesh sieve.

[0021] Further, in the above-mentioned casting resin sand, the preparation method of the HTAM high-temperature resistant and anti-migration modifier includes the following steps: under nitrogen protection, activated ceramic microspheres modified by KH-570 are dispersed in 70 to 80 parts of N-methylpyrrolidone, stirred at below 15°C, 20 to 22 parts of NMP solution of pyromellitic dianhydride are added dropwise, 20 to 23 parts of 4,4'-diaminodiphenyl ether are added, the mixture is stirred and reacted, filtered under pressure, and the filter cake is heat-treated successively at 100°C to 110°C, 150°C to 160°C, and 200°C to 220°C, cooled to room temperature, dispersed, and sieved to obtain the HTAM high-temperature resistant and anti-migration modifier.

[0022] In the preparation method of the above-mentioned HTAM high-temperature resistant and anti-migration modifier, the preparation method of the activated ceramic microspheres includes the following steps: adding 30 to 35 parts of hollow closed-cell ceramic microspheres to 60 to 70 parts of ethanol aqueous solution, stirring and dispersing, adding 3 to 4 parts of KH-570, adjusting the pH to 3.5 to 4.5, stirring and reacting at 50 to 55℃ for 3 to 4 hours, filtering, washing the filter cake with ethanol, and vacuum drying to obtain activated ceramic microspheres.

[0023] In the above-mentioned preparation method of HTAM high-temperature resistant and anti-migration modifier, the NMP solution concentration of pyromellitic dianhydride is 40wt% to 45wt%; the stirring reaction is carried out at 15℃ to 20℃ for 5h to 6h; the heat treatment is carried out by heating to 100℃ to 110℃ and holding for 1h to 1.5h, heating to 150℃ to 160℃ and holding for 1h to 1.5h, and heating to 200℃ to 220℃ and holding for 1.5h to 2h; the sieve mesh size is 100 mesh to 150 mesh.

[0024] The resin sand casting method for bridge shell casting provided by this invention has the following beneficial effects:

[0025] I. The resin sand designed by the casting technology of this invention systematically solves the bottlenecks of traditional resin sand, such as poor high-temperature deformation resistance, reduced collapsibility, and low regeneration rate, through the synergistic optimization of the bonding system, functional additives and processes. It achieves synergistic strength at room temperature and high temperature, balance between migration resistance and collapsibility, environmentally friendly regeneration and good quality assurance of castings, and is suitable for the manufacturing needs of thin-walled and complex bridge housing castings.

[0026] 2. Bio-based polyol flexible segments are introduced into the biomass-modified furan resin to form an interpenetrating network with furan rings and benzene rings, which absorbs stress, inhibits the propagation of microcracks, and balances the strength and toughness of the sand core; KH-550 or KH-560 silane coupling agent connects the quartz sand and resin through Si-O-Si chemical bonds, improves the interfacial bonding force, reduces resin film peeling at high temperatures, and ensures synergistic strength at room temperature and high temperature.

[0027] III. In the preparation of HTAM high-temperature resistant and anti-migration modifier, after the hollow closed-cell ceramic microspheres are activated by KH-570, the surface active groups and polyimide form a strong coating layer, constructing a rigid ceramic microsphere and high-temperature resistant polymer composite reinforcement network. The ceramic microspheres provide physical support to resist thermal deformation, and the polyimide network bridges the matrix to inhibit high-temperature plastic deformation. In addition, the high-temperature crystal transformation of calcined kaolin and spodumene powder supplements the strength and reduces mold wall migration.

[0028] IV. In the composite curing agent, p-toluenesulfonic acid dominates the curing process, aluminum dihydrogen phosphate enhances high-temperature stability, and lactic acid regulates the curing rate. Precise proportions ensure complete resin curing, balancing strength and crack resistance, and avoiding casting defects caused by uneven curing.

[0029] V. Gradient Dispersing Agent: Ammonium bicarbonate generates gas at low temperature to create pores, polystyrene melts and weakens at medium temperature, and expandable graphite expands and peels off at high temperature, gradually destroying the bonding structure; combined with the characteristics of biomass modified resin that is easy to decompose at high temperature and has no carbonization residue, it improves the dispersibility and sand removal efficiency.

[0030] VI. The resin sand preparation process follows the logic of interface optimization, enhanced network construction, and step-by-step functional empowerment. First, quartz sand is mixed with a silane coupling agent to build a stable interface in advance. Then, HTAM modifier, crack-resistant agent, and high-temperature resistant reinforcing phase are added to form a composite reinforcement system. Finally, biomass-modified furan resin, gradient disintegrating agent, and composite curing agent are added sequentially to ensure the orderly integration of bonding and disintegration functions. The old sand is crushed, air-separated, magnetically separated, and calcined at 550℃-650℃ to efficiently remove residual resin film, and the material has no recalcitrant components, achieving high recovery rate and high strength retention rate of the recycled sand.

[0031] VII. In the casting process, bottom pouring, precise cooling temperature, and vibration sand removal parameters are matched with material properties to reduce molten metal erosion, casting stress, and sand adhesion, thus ensuring the dimensional accuracy and surface quality of the castings.

[0032] In summary, the bonding system of biomass-modified furan resin and silane coupling agent synergistically combines with the reinforcement system of HTAM high-temperature resistant and migration-resistant modifier and high-temperature resistant reinforcing phase to achieve the dual requirements of room-temperature strength for molding and high-temperature strength to resist heat deformation. The HTAM high-temperature resistant and migration-resistant modifier, in conjunction with the composite curing agent, reduces mold wall migration and shrinkage defects, lowers riser dependence, and reduces riser area by 15%–25% compared to conventional risers. The gradient disintegrating agent, in conjunction with easily degradable resin and high-temperature calcination regeneration technology, improves sand removal efficiency while ensuring efficient recycling of used sand. The reasonable dosage of all components and the absence of antagonistic effects in the formulation create a positive cycle of strength, stability, disintegration, and recyclability, ultimately achieving high-quality, low-cost scientific manufacturing of bridge housing castings. Detailed Implementation

[0033] The present invention will be further described below with reference to specific implementation examples, but the present invention is not limited to these embodiments.

[0034] Example 1

[0035] A resin sand casting method for a bridge shell casting includes the following steps:

[0036] S1, Casting and Process Design:

[0037] Based on the three-dimensional model of the bridge housing, a casting process simulation analysis was conducted to determine the pouring position and parting surface of the casting. A bottom-pouring gating system was adopted to ensure stable filling of the mold with molten casting, reduce scouring and splashing, and the ingate was distributed to avoid local overheating. Based on the simulation thermal analysis results, risers were set above the thick parts of the bridge housing flange, bearing housing, and shaft head.

[0038] S2, Mold and Sand Core Manufacturing:

[0039] Casting resin sand is filled into a mold coated with a release agent, and a self-hardening process is used. The compaction pressure is 0.5 MPa. After compaction, the mold is removed to obtain several sand cores that meet the following specifications: tensile strength at room temperature above 2.8 MPa, tensile strength at 800℃ for 10 minutes above 1.2 MPa, and collapse index above 95%. The sand cores are then bonded and assembled. A refractory coating is applied to the surface of the sand cores, and they are dried at 130℃ for 2.5 hours.

[0040] S3, Preparation for Casing Assembly and Pouring:

[0041] Place the lower box stably, insert the assembled sand core, and ensure accurate positioning; close the upper box, tighten the box clamps to prevent the box from lifting during pouring; place the pouring cup and riser ring, and prepare for pouring;

[0042] S4, Melting and Casting:

[0043] The molten casting is poured smoothly, continuously, and rapidly at a speed of 1 kg / s, and the pouring cup is kept full during pouring.

[0044] S5, Cooling, Sand Removal and Cleaning:

[0045] After pouring, allow the casting to cool to 420°C in the mold to prevent deformation or stress. Vibrate the sand at a frequency of 35Hz and an amplitude of 1mm to allow the molding sand to disintegrate on its own. Remove the adhering sand, burrs, and flash from the surface of the casting to obtain the casting blank.

[0046] S6, Heat Treatment and Finishing:

[0047] The casting blank is heat-treated to obtain the required metallographic structure and mechanical properties; shot peening is performed with a shot particle size range of 0.8 mm to 1.5 mm and a shot peening pressure of 0.5 MPa to further clean the surface and improve the surface compressive stress; the casting is then subjected to dimensional inspection, non-destructive testing, and sampling inspection of mechanical properties.

[0048] S7, Reclaimed Sand:

[0049] The casting resin sand after the sand is removed is collected, crushed, air-separated, and magnetically separated. It is then calcined at 600℃ for 1.5 hours to remove the residual resin film on the surface of the sand particles, resulting in recycled sand with a recycling rate of over 80wt%. The recycled sand is then cooled and its particle size is adjusted before being reused for molding and core making.

[0050] A casting resin sand is used in a resin sand casting method for a bridge shell casting. The casting resin sand comprises the following raw materials in parts by weight: 100 parts washed quartz sand, 1.8 parts biomass modified furan resin, 1.5 parts HTAM high-temperature resistant and anti-migration modifier, 0.5 parts composite curing agent, 0.8 parts gradient disintegrating agent, 0.15 parts silane coupling agent, 0.25 parts crack-resistant agent, and 2 parts high-temperature resistant reinforcing phase.

[0051] The washed quartz sand has a particle size between 40 and 70 mesh, a SiO2 content of 98.5 wt%, and a moisture content of 0.16 wt%. The composite curing agent consists of a 63 wt% p-toluenesulfonic acid aqueous solution, a 48 wt% aluminum dihydrogen phosphate aqueous solution, and an 88 wt% lactic acid aqueous solution in a mass ratio of 73:28:4. The gradient disintegrating agent consists of ammonium bicarbonate, polystyrene microspheres, and expandable graphite in a mass ratio of 1.1:0.6:0.9. The silane coupling agent is KH-550. The crack-resistant additive is mica powder. The high-temperature reinforcing phase consists of calcined kaolin and spodumene powder in a mass ratio of 2.3:1.1; the spodumene powder is calcined at 820℃ for 2 hours.

[0052] The preparation method of biomass-modified furan resin includes the following steps: 65 parts furfuryl alcohol, 20 parts bio-based polyol, 8 parts urea and 4 parts deionized water are stirred at 250 rpm for 40 min in a temperature range of 60℃~65℃ until dissolved. 3.5 parts phenol and 1 part p-toluenesulfonic acid are added, the temperature is raised to 80℃~85℃, and the polycondensation reaction is carried out at 250 rpm for 100 min. The pH is adjusted to 4.2 with 6.5wt% sodium carbonate aqueous solution, the temperature is lowered to 45℃, 3 parts deionized water are added for dilution, 0.6 parts KH-550 are added, the mixture is stirred at 250 rpm for 30 min, the temperature is lowered to room temperature, the solid content is adjusted to 78wt% with deionized water, and impurities are removed by filtration through a 100-mesh sieve to obtain biomass-modified furan resin.

[0053] The preparation method of HTAM high-temperature resistant and anti-migration modifier includes the following steps: 33 parts of hollow closed-cell ceramic microspheres are added to 65 parts of 75 vol% ethanol aqueous solution, stirred and dispersed at 280 rpm, 3.5 parts of KH-570 are added, the pH is adjusted to 4.0 with acetic acid, the temperature is raised to 50℃~55℃, and the reaction is stirred for 3.5 h. The mixture is then filtered, the filter cake is washed twice with ethanol, and vacuum dried at 78℃ for 2.5 h to obtain activated ceramic microspheres. Under nitrogen protection, all activated ceramic microspheres are dispersed in 75 parts of N-methylpyrrolidone (NMP), and 21 parts of 42 wt% pyromellitic dianhydride (PMDA) NMP solution are added dropwise at 280 rpm below 15℃. Solution P was prepared, and the system temperature was controlled to not exceed 20℃. 22 parts of 4,4'-diaminodiphenyl ether (ODA) were added, and the mixture was stirred and reacted in the temperature range of 15℃ to 20℃ for 5.5 hours to obtain a slurry of polyamic acid (PAA)-coated ceramic microspheres (PMDA and ODA undergo condensation polymerization on the surface of the microspheres and in the liquid phase at low temperature to generate polyamic acid and form a coating). The mixture was then filtered by pressure, and the filter cake was washed with NMP and filtered once. Afterward, the temperature was increased to 105℃ at 2℃ / min and held for 1 hour, increased to 155℃ at 2℃ / min and held for 1 hour, and increased to 210℃ at 3℃ / min and held for 2 hours to ensure that PAA was completely converted into polyimide. The mixture was then cooled to room temperature, dispersed, and passed through a 100-mesh sieve to obtain HTAM high-temperature resistant and anti-migration modifier.

[0054] The above-mentioned method for preparing casting resin sand includes the following steps:

[0055] According to the formula, mix the washed quartz sand and silane coupling agent evenly; add HTAM high-temperature resistant migration-resistant modifier, crack-resistant agent and high-temperature resistant reinforcing phase, and mix evenly; add biomass-modified furan resin and gradient disintegrating agent in sequence, and mix evenly; add composite curing agent, mix evenly, and immediately discharge sand. If a self-hardening process is used, it should be used within 15 minutes.

[0056] Example 2

[0057] A resin sand casting method for a bridge shell casting includes the following steps:

[0058] S1, Casting and Process Design:

[0059] Based on the three-dimensional model of the bridge housing, a casting process simulation analysis was conducted to determine the pouring position and parting surface of the casting. A bottom-pouring gating system was adopted to ensure stable filling of the mold with molten casting, reduce scouring and splashing, and the ingate was distributed to avoid local overheating. Based on the simulation thermal analysis results, risers were set above the thick parts of the bridge housing flange, bearing housing, and shaft head.

[0060] S2, Mold and Sand Core Manufacturing:

[0061] Casting resin sand is filled into a mold coated with a release agent, and a blowing hardening process is used. The compaction pressure is 0.4 MPa. After compaction, the mold is removed to obtain several sand cores that meet the following specifications: tensile strength at room temperature above 2.8 MPa, tensile strength at 800℃ for 10 minutes above 1.2 MPa, and collapse index above 95%. The sand cores are then bonded and assembled. A refractory coating is applied to the surface of the sand cores, and they are dried at 120℃ for 3 hours.

[0062] S3, Preparation for Casing Assembly and Pouring:

[0063] Place the lower box stably, insert the assembled sand core, and ensure accurate positioning; close the upper box, tighten the box clamps to prevent the box from lifting during pouring; place the pouring cup and riser ring, and prepare for pouring;

[0064] S4, Melting and Casting:

[0065] The molten casting is poured smoothly, continuously, and rapidly at a speed of 0.8 kg / s, and the pouring cup is kept full during pouring.

[0066] S5, Cooling, Sand Removal and Cleaning:

[0067] After pouring, allow the casting to cool to 450°C in the mold to prevent deformation or stress. Vibrate the sand at a frequency of 30Hz and an amplitude of 1.2mm to allow the molding sand to disintegrate on its own. Remove the adhering sand, burrs, and flash from the surface of the casting to obtain the casting blank.

[0068] S6, Heat Treatment and Finishing:

[0069] The casting blank is heat-treated to obtain the required metallographic structure and mechanical properties; shot peening is performed with a shot particle size range of 0.8 mm to 1.5 mm and a shot peening pressure of 0.4 MPa to further clean the surface and improve the surface compressive stress; the casting is then subjected to dimensional inspection, non-destructive testing, and sampling inspection of mechanical properties.

[0070] S7, Reclaimed Sand:

[0071] The casting resin sand after the sand is removed is collected, crushed, air-separated, and magnetically separated. It is then calcined at 650℃ for 1.5 hours to remove the residual resin film on the surface of the sand particles, resulting in recycled sand with a recycling rate of over 80wt%. The recycled sand is then cooled and its particle size is adjusted before being reused for molding and core making.

[0072] A casting resin sand is used in a resin sand casting method for a bridge shell casting. The casting resin sand comprises the following raw materials in parts by weight: 100 parts washed quartz sand, 1.5 parts biomass modified furan resin, 1.8 parts HTAM high-temperature resistant and anti-migration modifier, 0.4 parts composite curing agent, 1.0 part gradient disintegrating agent, 0.1 parts silane coupling agent, 0.3 parts crack-resistant agent, and 1.5 parts high-temperature resistant reinforcing phase.

[0073] The washed quartz sand has a particle size between 40 and 70 mesh, a SiO2 content of 98.2 wt%, and a moisture content of 0.2 wt%. The composite curing agent consists of a 60 wt% p-toluenesulfonic acid aqueous solution, a 45 wt% aluminum dihydrogen phosphate aqueous solution, and an 85 wt% lactic acid aqueous solution, all in a mass ratio of 70:25:3. The gradient disintegrating agent consists of ammonium bicarbonate, polystyrene microspheres, and expandable graphite in a mass ratio of 1:0.7:0.8. The silane coupling agent is KH-560. The crack-resistant agent is mica powder. The high-temperature reinforcing phase consists of calcined kaolin and spodumene powder in a mass ratio of 2:1.2; the spodumene powder is calcined at 800℃ for 2.5 hours.

[0074] The preparation method of biomass-modified furan resin includes the following steps: 70 parts furfuryl alcohol, 15 parts bio-based polyol, 10 parts urea and 3 parts deionized water are dissolved by stirring at 300 rpm for 30 min in a temperature range of 60℃~65℃. 5 parts phenol and 0.5 parts p-toluenesulfonic acid are added, the temperature is raised to 80℃~85℃, and the polycondensation reaction is carried out by stirring at 300 rpm for 90 min. The pH is adjusted to 4.0 with 8wt% sodium carbonate aqueous solution, the temperature is lowered to 50℃, 2 parts deionized water are added for dilution, 0.8 parts KH-550 are added, the mixture is stirred at 200 rpm for 40 min, the temperature is lowered to room temperature, the solid content is adjusted to 75wt% with deionized water, and impurities are removed by filtration through a 150-mesh sieve to obtain biomass-modified furan resin.

[0075] The preparation method of HTAM high-temperature resistant and anti-migration modifier includes the following steps: 30 parts of hollow closed-cell ceramic microspheres are added to 70 parts of 70 vol% ethanol aqueous solution, stirred and dispersed at 300 rpm, 3 parts of KH-570 are added, the pH is adjusted to 4.5 with acetic acid, the temperature is raised to 50℃~55℃, and the reaction is stirred for 3 h. The mixture is then filtered, the filter cake is washed three times with ethanol, and vacuum dried at 75℃ for 3 h to obtain activated ceramic microspheres. Under nitrogen protection, all activated ceramic microspheres are dispersed in 70 parts of N-methylpyrrolidone (NMP), and 20 parts of NMP solution with 45 wt% pyromellitic dianhydride (PMDA) are added dropwise at 300 rpm below 15℃. The system temperature was controlled to not exceed 20℃. 20 parts of 4,4'-diaminodiphenyl ether (ODA) were added, and the mixture was stirred and reacted for 6 hours in the temperature range of 15℃ to 20℃ to obtain a slurry of polyamic acid (PAA)-coated ceramic microspheres (PMDA and ODA undergo condensation polymerization on the surface of the microspheres and in the liquid phase at low temperature to generate polyamic acid and form a coating). The mixture was then filtered by pressure, and the filter cake was washed with NMP and filtered once. After that, the temperature was increased to 100℃ at 3℃ / min and held for 1.5 hours, increased to 160℃ at 1℃ / min and held for 1 hour, and increased to 200℃ at 3℃ / min and held for 2 hours to ensure that PAA was completely converted into polyimide. The mixture was then cooled to room temperature, dispersed, and passed through a 100-mesh sieve to obtain HTAM high-temperature resistant and anti-migration modifier.

[0076] The above-mentioned method for preparing casting resin sand includes the following steps:

[0077] According to the formula, mix the washed quartz sand and silane coupling agent evenly; add HTAM high-temperature resistant migration-resistant modifier, crack-resistant agent and high-temperature resistant reinforcing phase, and mix evenly; add biomass-modified furan resin and gradient disintegrating agent in sequence, and mix evenly; add composite curing agent, mix evenly, and immediately discharge sand. If a self-hardening process is used, it should be used within 15 minutes.

[0078] Example 3

[0079] A resin sand casting method for a bridge shell casting includes the following steps:

[0080] S1, Casting and Process Design:

[0081] Based on the three-dimensional model of the bridge housing, a casting process simulation analysis was conducted to determine the pouring position and parting surface of the casting. A bottom-pouring gating system was adopted to ensure stable filling of the mold with molten casting, reduce scouring and splashing, and the ingate was distributed to avoid local overheating. Based on the simulation thermal analysis results, risers were set above the thick parts of the bridge housing flange, bearing housing, and shaft head.

[0082] S2, Mold and Sand Core Manufacturing:

[0083] Casting resin sand is filled into a mold coated with a release agent. A hot core box process is used, with a compaction pressure of 0.6 MPa. After compaction, the mold is removed to obtain several sand cores that meet the following specifications: tensile strength at room temperature above 2.8 MPa, tensile strength at 800℃ for 10 minutes above 1.2 MPa, and a collapse index above 95%. The sand cores are then bonded and assembled. A refractory coating is applied to the surface of the sand cores, and they are dried at 150℃ for 2 hours.

[0084] S3, Preparation for Casing Assembly and Pouring:

[0085] Place the lower box stably, insert the assembled sand core, and ensure accurate positioning; close the upper box, tighten the box clamps to prevent the box from lifting during pouring; place the pouring cup and riser ring, and prepare for pouring;

[0086] S4, Melting and Casting:

[0087] The molten casting is poured smoothly, continuously, and rapidly at a speed of 1.2 kg / s, and the pouring cup is kept full during pouring.

[0088] S5, Cooling, Sand Removal and Cleaning:

[0089] After pouring, allow the casting to cool to 400℃ in the mold to prevent deformation or stress. Vibrate the sand at a frequency of 40Hz and an amplitude of 0.8mm to allow the molding sand to disintegrate on its own. Remove the adhering sand, burrs, and flash from the surface of the casting to obtain the casting blank.

[0090] S6, Heat Treatment and Finishing:

[0091] The casting blank is heat-treated to obtain the required metallographic structure and mechanical properties; shot peening is performed with a shot particle size range of 0.8 mm to 1.5 mm and a shot peening pressure of 0.6 MPa to further clean the surface and improve the surface compressive stress; the casting is then subjected to dimensional inspection, non-destructive testing, and sampling inspection of mechanical properties.

[0092] S7, Reclaimed Sand:

[0093] The casting resin sand after the sand is removed is collected, crushed, air-separated, and magnetically separated. It is then calcined at 550℃ for 2 hours to remove the residual resin film on the surface of the sand particles, resulting in recycled sand with a recycling rate of over 80wt%. The recycled sand is then cooled and its particle size is adjusted before being reused for molding and core making.

[0094] A casting resin sand is used in a resin sand casting method for a bridge shell casting. The casting resin sand comprises the following raw materials in parts by weight: 100 parts washed quartz sand, 2 parts biomass modified furan resin, 1.2 parts HTAM high-temperature resistant and anti-migration modifier, 0.6 parts composite curing agent, 0.5 parts gradient disintegrating agent, 0.2 parts silane coupling agent, 0.2 parts crack-resistant agent, and 2.5 parts high-temperature resistant reinforcing phase.

[0095] The washed quartz sand has a particle size between 40 and 70 mesh, a SiO2 content of 98.8 wt%, and a moisture content of 0.12 wt%. The composite curing agent consists of a 65 wt% p-toluenesulfonic acid aqueous solution, a 50 wt% aluminum dihydrogen phosphate aqueous solution, and a 90 wt% lactic acid aqueous solution, all in a mass ratio of 75:30:5. The gradient disintegrating agent consists of ammonium bicarbonate, polystyrene microspheres, and expandable graphite in a mass ratio of 1.2:0.5:1. The silane coupling agent is KH-550. The crack-resistant agent is mica powder. The high-temperature reinforcing phase consists of calcined kaolin and spodumene powder in a mass ratio of 2.5:1; the spodumene powder is calcined at 850℃ for 2 hours.

[0096] The preparation method of biomass-modified furan resin includes the following steps: 60 parts furfuryl alcohol, 25 parts bio-based polyol, 5 parts urea and 5 parts deionized water are stirred at 200 rpm for 50 min at a temperature range of 60℃~65℃ until dissolved. 2 parts phenol and 1.5 parts p-toluenesulfonic acid are added, the temperature is raised to 80℃~85℃, and the polycondensation reaction is carried out at 200 rpm for 120 min. The pH is adjusted to 4.5 with 5wt% sodium carbonate aqueous solution, the temperature is lowered to 40℃, 4 parts deionized water are added for dilution, 0.3 parts KH-550 are added, the mixture is stirred at 300 rpm for 20 min, the temperature is lowered to room temperature, the solid content is adjusted to 80wt% with deionized water, and impurities are removed by filtration through a 100-mesh sieve to obtain biomass-modified furan resin.

[0097] The preparation method of HTAM high-temperature resistant and anti-migration modifier includes the following steps: 35 parts of hollow closed-cell ceramic microspheres are added to 60 parts of 80 vol% ethanol aqueous solution, stirred and dispersed at 250 rpm, 4 parts of KH-570 are added, the pH is adjusted to 3.5 with acetic acid, the temperature is raised to 50℃~55℃, and the reaction is stirred for 4 h. After filtration, the filter cake is washed twice with ethanol and dried under vacuum at 80℃ for 2 h to obtain activated ceramic microspheres; under nitrogen protection, all activated ceramic microspheres are dispersed in 80 parts of N-methylpyrrolidone (NMP), and 22 parts of NMP solution with 40 wt% pyromellitic dianhydride (PMDA) are added dropwise at 250 rpm below 15℃. The system temperature was controlled to not exceed 20℃. 23 parts of 4,4'-diaminodiphenyl ether (ODA) were added, and the mixture was stirred and reacted for 5 hours in the temperature range of 15℃ to 20℃ to obtain a slurry of polyamic acid (PAA)-coated ceramic microspheres (PMDA and ODA undergo condensation polymerization on the surface of the microspheres and in the liquid phase at low temperature to generate polyamic acid and form a coating). The mixture was then filtered by pressure, and the filter cake was washed with NMP and filtered twice. After that, the temperature was increased to 110℃ at 2℃ / min and held for 1 hour, increased to 150℃ at 2℃ / min and held for 1.5 hours, and increased to 220℃ at 2℃ / min and held for 1.5 hours to ensure that PAA was completely converted into polyimide. The mixture was then cooled to room temperature, dispersed, and passed through a 150-mesh sieve to obtain HTAM high-temperature resistant and anti-migration modifier.

[0098] The above-mentioned method for preparing casting resin sand includes the following steps:

[0099] According to the formula, mix the washed quartz sand and silane coupling agent evenly; add HTAM high-temperature resistant migration-resistant modifier, crack-resistant agent and high-temperature resistant reinforcing phase, and mix evenly; add biomass-modified furan resin and gradient disintegrating agent in sequence, and mix evenly; add composite curing agent, mix evenly, and immediately discharge sand. If a self-hardening process is used, it should be used within 15 minutes.

[0100] The raw material specifications and sources involved in the above embodiments are as follows: The release agent is Jiadan JD-3028 boron nitride release agent. The refractory coating is a foundry coating sourced from Xinmi Zhengyang Foundry Materials Factory. The washed quartz sand has a particle size of 40-70 mesh, SiO2 > 98%, and a moisture content ≤ 0.2%. The purity of p-toluenesulfonic acid is 99%. The purity of aluminum dihydrogen phosphate is above 98%. The purity of lactic acid is 99%. The purity of ammonium bicarbonate is above 98%. The particle size of polystyrene microspheres is 30μm-50μm, sourced from Wenzhou Pinzhuo Biotechnology Co., Ltd. The expandable graphite has a particle size of 100-150 mesh, sourced from Qingdao Risheng Graphite Co., Ltd. KH-550 is sourced from Shandong Huanzheng Chemical Co., Ltd. KH-560 is sourced from Shandong Huanzheng Chemical Co., Ltd. The mica powder has a particle size of 800-2000 mesh, sourced from Lingshou Shuntian Mineral Products Processing Plant. Calcined kaolin, passing through a 4000-mesh sieve, is sourced from Shuntian Mineral Products Processing Plant in Lingshou County. Spodumene powder, passing through a 325-mesh sieve, is sourced from Qianhao Mineral Products Processing Plant in Lingshou County. Furfuryl alcohol has a purity of 99%. Bio-based polyol, PO3G H500 polytrimethylene ether glycol, is sourced from Guangzhou Haoyi New Material Technology Co., Ltd. Urea has a purity of over 98%. Phenol has a purity of over 99%. p-Toluenesulfonic acid has a purity of 99%. Sodium carbonate has a purity of 99%. Hollow closed-cell ceramic microspheres, between 100-200 mesh, are sourced from Gongyi Jinliang Refractory Materials Co., Ltd. KH-570 is sourced from Shandong Huanzheng Chemical Co., Ltd. Acetic acid has a purity of over 99%. N-methylpyrrolidone (NMP) has a purity of over 99%. Pyromellitic dianhydride (PMDA) has a purity of over 99%. The purity of 4,4'-diaminodiphenyl ether (ODA) is above 99%.

[0101] Comparative Example 1

[0102] The difference from Example 1 is that the amount of biomass modified furan resin added is changed to 6 parts.

[0103] Comparative Example 2

[0104] The difference from Example 1 is that no bio-based polyols are added in the preparation of the biomass-modified furan resin.

[0105] Comparative Example 3

[0106] The difference from Example 1 is that KH-550 is not added in the preparation of biomass modified furan resin.

[0107] Comparative Example 4

[0108] The difference from Example 1 is that the HTAM high-temperature resistant and anti-migration modifier is changed to 5 parts.

[0109] Comparative Example 5

[0110] The difference from Example 1 is that the HTAM high-temperature resistant and migration-resistant modifier is directly replaced by hollow closed-cell ceramic microspheres.

[0111] Comparative Example 6

[0112] The difference from Example 1 is that in the preparation of the HTAM high-temperature resistant and anti-migration modifier, KH-570 activation is not performed, that is, "the activation of ceramic microspheres is directly replaced by hollow closed-cell ceramic microspheres, which are dispersed in N-methylpyrrolidone".

[0113] Comparative Example 7

[0114] The difference from Example 1 is that the preparation of the HTAM high-temperature resistant and anti-migration modifier omits the phrase "heating to 210°C at 3°C / min and holding for 2 hours".

[0115] Comparative Example 8

[0116] The difference from Example 1 is that the mass ratio of 63wt% p-toluenesulfonic acid aqueous solution, 48wt% aluminum dihydrogen phosphate aqueous solution, and 88wt% lactic acid aqueous solution in the composite curing agent is 28:73:1.

[0117] Comparative Example 9

[0118] The difference from Example 1 is that the mass ratio of ammonium bicarbonate, polystyrene microspheres, and expandable graphite in the gradient disintegrating agent is 0.6:1.1:0.4.

[0119] The following tests involve ZG35 cast steel automotive axle housings. The main chemical components of the casting, by mass percentage, are: carbon 0.35%, silicon 0.30%, manganese 0.60%, sulfur ≤0.04%, phosphorus ≤0.04%, with the balance being iron and trace impurities. The casting temperature is 1560±10℃. The casting is a hollow beam structure with flanges at both ends for mounting wheel hubs, and the main body in the middle for connecting other vehicle components. The design sample is simplified to a hollow cylinder 1000mm long, 200mm outer diameter, and 180mm inner diameter, with flanges at both ends of 300mm diameter and 30mm thickness, and eight evenly distributed 20mm diameter bolt mounting holes.

[0120] To ensure comparability of the test samples, all resin sand specimens were prepared using a self-hardening process. The specimens in Examples 2 and 3 were also prepared using a self-hardening process.

[0121] I. Mechanical property testing of resin sand at room temperature and high temperature:

[0122] 1. Tensile and Bending Strength at Room Temperature: Tested according to GB / T 2684 "Test Methods for Foundry Sand and Mixtures". Figure-eight shaped tensile specimens and 22.36mm × 22.36mm × 172mm bending specimens were prepared according to the standard. After sand mixing, specimen preparation was completed within 15 minutes at 20±2℃ and 50±2% humidity. Six specimens were prepared per group. After 24 hours of self-hardening, the specimens were tested using a strength testing machine. The tensile strength loading rate was 0.1MPa / s, and the bending strength loading rate was constant at 0.1MPa / s. The fracture load was recorded, and the strength was calculated. The average tensile strength and the average bending strength were taken.

[0123] 2. Tensile strength at 800℃: According to GB / T 2684 "Test Methods for Foundry Sand and Mixtures". Using specimens of the same specifications as those used for room temperature tensile strength testing, after self-hardening for 24 hours, they were dried at 105℃ for 2 hours for later use. Six specimens were used in each group. The specimens were installed in a high-temperature fixture, heated to 800℃ at a rate of 10℃ / min under nitrogen protection, held at this temperature for 10 minutes, and then subjected to tensile testing at a beam displacement rate of 1 mm / min until fracture. The average high-temperature tensile strength was recorded.

[0124] II. High-Temperature Dimensional Stability Testing of Resin Sand:

[0125] Prepare cylindrical specimens with a diameter of 30 mm × 50 mm, with an Al₂O₃ ceramic probe pre-embedded at one end. Five specimens are prepared per group. Under nitrogen protection, the temperature is increased from room temperature to 1350 °C at a rate of 10 °C / min, and held for 30 min. Calculate the percentage change in length (%) of the specimen at the end of the 1350 °C holding period relative to its initial length at room temperature.

[0126] III. Resin Sand Collapsibility Test:

[0127] Prepare figure-eight shaped tensile test specimens and weigh them (m0) after 24 hours of self-hardening. Each group contains 6 specimens. Place the specimens in a muffle furnace preheated to 800℃ and hold for 10 minutes. After removal, place them on a 1mm sieve of a vibrating sieve machine (amplitude 1.0mm, frequency 35Hz) and vibrate for 60 seconds. Collect the sand particles passing through the sieve and weigh them (m1). The collapsibility index K = (m1 / m0) × 100%.

[0128] IV. Testing of Recycling Performance of Used Sand:

[0129] According to GB / T 26659 "Recycled Silica Sand for Foundry". Collect 10.0 kg of used sand after sand removal, and remove obvious metallic impurities. Test 3 parallel samples.

[0130] Regeneration rate: Regenerated sand is obtained after processing old sand, and its mass (mregenerated) is measured. Regeneration rate R = (mregenerated / 10.0) × 100%.

[0131] Recycled sand reuse strength: Use 100% recycled sand, remix the sand according to the original formula and process, prepare the sample according to the "room temperature tensile strength" in Experiment 1 above, and test the room temperature tensile strength of the recycled sand. Compare it with the "room temperature tensile strength" result in Experiment 1, and calculate the room temperature tensile strength retention rate (%).

[0132] V. Mold stability and casting cleaning verification:

[0133] 1. Mold Wall Migration: A flat mold is manufactured using resin sand. A high-temperature displacement sensor probe is pre-embedded in the sidewall of the mold cavity. Molten steel (ZG35) at 1560±10℃ is poured in. From the start of pouring until the casting is completely solidified, the maximum migration of the mold wall into the mold cavity is recorded. The average value of 3 parallel samples is calculated.

[0134] 2. Casting Shaking Efficiency: After casting the bridge shell, the casting is cooled to 420℃ and then placed on a vibratory sand-removing machine (frequency 35Hz, amplitude 1.0mm). The time (T, s) required for 90% of the molding sand to automatically fall off the surface and inner cavity of the casting is recorded. The weight of the casting billet is weighed (W, kg), and the sand-removal time per unit weight of casting, T / W (s / kg), is calculated. The average value of three parallel samples is recorded.

[0135] VI. Quality Inspection of Finished Bridge Shell Castings:

[0136] 1. Dimensional Accuracy: Five bridge housing castings were randomly selected. A coordinate measuring machine was used to inspect the dimensions at 10 key locations. Each dimension was measured three times on the same casting, and the average value was taken. The tolerance rating was based on GB / T 6414 "Dimensional Tolerances, Geometric Tolerances and Machining Allowances for Castings".

[0137] 2. Surface roughness: According to GB / T 15056 "Method for evaluating the surface roughness of castings", five locations were selected on the outer surface of the bridge housing casting blank, with three measurements taken at each location, and the average value was recorded. The average value of all five samples was taken.

[0138] 3. Take 5 casting blanks for surface defect inspection:

[0139] Surface porosity size and quantity factors are classified into grades: Grade 1: The casting surface has basically no obvious porosity, with pores within 100cm². 2 In terms of area, no more than 3 pores with a diameter less than 0.5 mm are allowed. Secondary: A small number of smaller pores are permitted within 100 cm². 2 In terms of area, there are no more than 5 pores with a diameter of 0.5-1mm, and no pores larger than 1mm. Level 3: The number and size of pores increase, within 100cm².2 In terms of area, no more than 8 pores with a diameter of 1-2 mm are allowed, while a small number of pores with a diameter of less than 0.5 mm are permitted.

[0140] Surface sand adhesion classification: Level 1: The casting surface is smooth with virtually no sand adhesion; the thickness of locally adhered sand does not exceed 0.5 mm. Level 2: The casting surface has slight sand adhesion, with a thickness between 0.5-1 mm, and the area of ​​adhered sand does not exceed 10% of the casting surface area. Level 3: The casting surface has relatively obvious sand adhesion, with a thickness of 1-2 mm, and the area of ​​adhered sand does not exceed 20% of the casting surface area.

[0141] Surface crack classification: Level 1: No cracks are allowed on the surface of the casting. Level 2: A very small number of micro-cracks are allowed on the surface of the casting, with a crack length not exceeding 1 mm and a depth not exceeding 10% of the casting wall thickness. Level 3: A small number of shorter cracks are allowed on the surface of the casting, with a crack length not exceeding 3 mm and a depth not exceeding 20% ​​of the casting wall thickness.

[0142] Table 1. Test Results (Average Values)

[0143]

[0144] Table 1. Continuing test results (average)

[0145]

[0146] Examples 1 to 3 systematically address the bottlenecks of traditional resin sand casting through synergistic innovation across the entire chain of bonding systems, functional additives, and process parameters. Their performance advantages stem from multi-dimensional synergistic effects. Biomass-modified furan resin introduces flexible segments of bio-based polyols, forming an interpenetrating network with furan and benzene rings. This effectively absorbs stress, inhibits microcrack propagation, and balances the strength and toughness of the sand core. KH-550 or KH-560 silane coupling agents form stable Si-O-Si chemical bonds with the quartz sand surface through silanol groups, while simultaneously covalently bonding with the resin network, enhancing interfacial adhesion, reducing the risk of resin film peeling at high temperatures, and ensuring synergistic improvement in strength at both room and high temperatures. After activation with KH-570, the HTAM high-temperature resistant and anti-migration modifier introduces active groups on its surface, forming a strong coating layer with polyimide. This constructs a composite reinforcing network of rigid ceramic microspheres and high-temperature resistant polymers. The ceramic microspheres provide physical support to resist thermal deformation, while the polyimide coating layer forms a continuous network bridging the microspheres and the sand core matrix, effectively suppressing plastic deformation at temperatures above 800℃. Combined with the high-temperature crystal transformation of calcined kaolin and spodumene powder to supplement strength, it significantly reduces mold wall migration and minimizes shrinkage defects in thick areas. The gradient disintegrating agent achieves stepwise degradation through low-temperature gas generation and pore formation, medium-temperature melting and weakening, and high-temperature expansion and peeling, thus orderly destroying the bonding structure of the sand core. Compared with traditional furan resin, the biomass-modified resin is more easily decomposed at high temperatures and leaves no carbonization residue. Combined with the vibration sand removal process, it significantly improves the disintegration and sand removal efficiency. During the regeneration process, calcination at around 600℃ efficiently removes the residual resin film on the surface of the sand particles. Furthermore, the HTAM modifier and the gradient disintegrating agent have no difficult-to-degrade components, which significantly improves the old sand regeneration rate and the strength retention rate of the regenerated sand, realizing resource recycling.

[0147] Reasons for the performance changes in the comparative model:

[0148] When excessive amounts of biomass-modified furan resin are added (Comparative Example 1), an excessively thick adhesive film is formed. This film is prone to carbonization at high temperatures, hindering the sand core's disintegration, prolonging the sand removal time, reducing the sand core's permeability, increasing the risk of porosity in the casting, and making it difficult to completely remove the thick resin film. This leads to a decrease in the old sand regeneration rate and the strength retention rate of the regenerated sand. Biomass-modified furan resin itself contains a small amount of volatile components. Excessive addition increases the total amount of volatile substances in the sand core. Under curing and high-temperature conditions, these volatile substances escape rapidly, forming internal pores and causing uneven volume shrinkage, resulting in an increased dimensional change rate. Excessive resin forms an excessively thick adhesive film on the sand grain surface. This adhesive film is prone to generating internal stress during cooling, and the uneven distribution of internal stress further exacerbates the deformation trend of the sand core, ultimately increasing the dimensional change rate. When resin is excessive, the thickness of the adhesive film on the sand grain surface exceeds a reasonable range, making it difficult to completely remove residual adhesive during regeneration. The residual adhesive ages and becomes brittle, leading to a decrease in the bonding strength of the regenerated sand after molding. Meanwhile, the bonding layer formed after excessive resin curing is highly tough, requiring greater mechanical force to break the sand blocks during regeneration. This easily leads to wear on the edges of sand particles and structural damage, further reducing the strength retention capacity of the regenerated sand. Excessive addition of biomass-modified furan resin causes the binder inside the sand core to be in a supersaturated state. During high-temperature casting, the excess resin has a lower melt viscosity and increased fluidity, further accelerating the migration and diffusion of binder components. Excess resin also reduces the dispersion uniformity of the HTAM high-temperature anti-migration modifier, weakening its inhibitory effect on binder migration and indirectly exacerbating the migration phenomenon. Uneven release of volatile substances and imbalanced internal stress distribution caused by excessive resin can lead to microscopic deformation of the sand core after curing, resulting in a fundamental decrease in molding accuracy. During high-temperature casting, an excessively thick resin bonding film will produce a significant difference in thermal expansion due to the large difference in thermal expansion coefficient between the resin and the quartz sand aggregate, causing localized expansion and contraction deformation of the sand core and resulting in dimensional deviations in corresponding parts of the casting.

[0149] Defects in biomass-modified furan resin formulations: When bio-based polyols are missing, the resin network exhibits a rigid, dominant structure with insufficient toughness, resulting in ineffective stress dissipation. This leads to decreased strength of the molding core at both room and high temperatures, poor crack resistance, and deteriorated high-temperature stability, causing an increase in the dimensional change rate of the molding sand. When KH-550 is missing, the resin and sand particles rely solely on physical adsorption, resulting in weak interfacial bonding. Under external forces or high temperatures, the resin film is easily peeled off, significantly reducing the overall strength and dimensional stability of the molding core, and decreasing the surface activity of the recycled sand.

[0150] Defects of HTAM high-temperature resistant and anti-migration modifier: When added in excess, rigid particles tend to agglomerate, forming stress concentration points, which disrupts the uniformity of the internal structure of the sand core. The improvement in room temperature strength is not significant, and the agglomerates hinder the degradation of the gradient disintegrating agent, leading to a decrease in collapsibility. When unactivated, uncoated, or not fully imidized at high temperatures, the interfacial bonding between the modifier and the resin / sand particles is poor, failing to form an effective reinforcing network. This results in a significant reduction in high-temperature strength and anti-migration ability, making the sand core prone to casting defects due to thermal deformation.

[0151] Imbalance in the ratio of the composite curing agent (Comparative Example 8): In the composite curing agent, p-toluenesulfonic acid is the main curing agent, aluminum dihydrogen phosphate improves high-temperature stability, and lactic acid regulates the curing rate. The ratio of the composite curing agent is unbalanced, deviating from the reasonable ratio range defined in this invention. As the core functional component of biomass-modified furan resin cores, the ratio of each component in the composite curing agent directly determines the integrity of the resin cross-linking and curing reaction, the efficiency of bond strength formation, and the overall performance of the core. An imbalance in the ratio will disrupt the synergistic balance of curing rate, bond strength, and collapse performance, leading to abnormalities in various data. p-Toluenesulfonic acid, as an acidic curing agent, is the core initiator of the furan resin cross-linking reaction. If its ratio is too high or too low, it will directly affect the curing reaction rate. When the ratio is too low, the curing reaction is incomplete, the resin cannot form a sufficient cross-linking network, and the adhesive film strength is insufficient. An imbalance in the ratio of aluminum dihydrogen phosphate (ADPH) to lactic acid disrupts the curing synergy. ADPH enhances the high-temperature resistance of the adhesive film, while lactic acid moderates the curing reaction. An imbalance leads to softening and degradation of the adhesive film at high temperatures, resulting in the breakage of the cross-linked structure after high-temperature treatment and a more significant decrease in high-temperature tensile strength, ultimately manifesting as low tensile strength at both room and high temperatures. Excessive ADPH further enhances the high-temperature stability of the adhesive film due to its superior high-temperature resistance; even after casting and cooling, the adhesive film maintains a certain structural strength and cannot quickly disintegrate from the casting. Simultaneously, insufficient lactic acid leads to an overly vigorous curing reaction, resulting in low porosity within the adhesive film, further reducing its collapse performance and ultimately causing a low collapse index. Improper formulation of the composite curing agent prevents some furan resin from completing the cross-linking reaction, leaving a large amount of free resin components. During high-temperature casting, these free components exhibit increased fluidity and migrate along the sand core pores to the surface and casting interface. An imbalance in the composite curing agent ratio and poor curing rate cause uneven volume shrinkage, leading to internal stress. Internal stress is gradually released during cooling and high-temperature pouring, causing deformation of the sand core and consequently reducing dimensional accuracy. It also affects surface defects. Uneven solidification can lead to uneven distribution of sand core porosity, increasing surface defects in the casting.

[0152] Imbalance in the ratio of gradient dispersant: The stepwise degradation effect of gradient dispersant depends on the precise ratio of each component and its compatibility with the curing agent. When the proportion of ammonium bicarbonate and expandable graphite is insufficient, the driving force for low-temperature gas generation and high-temperature expansion is insufficient. Excessive polystyrene microspheres are prone to residue, resulting in insufficient sand core dispersal, prolonged sand removal and cleaning time, and sand residue on the surface of the casting, leading to a decrease in the dispersibility index.

Claims

1. A resin sand casting method for a bridge shell casting, characterized in that, Includes the following steps: Design the pouring position and parting surface of the casting; select bottom pouring and set risers; prepare several sand cores with a room temperature tensile strength >2.8MPa, a tensile strength >1.2MPa after 10 minutes at 800℃, and a collapsibility index >95%; bond and assemble the sand cores, coat them with refractory coating, and dry them; assemble the lower mold, sand cores, and upper mold, and tighten the mold clamps; place the pouring cup and riser ring; pour the molten casting, cool it to below 500℃ in the mold, vibrate to remove sand, and remove adhering sand, flash, and burrs from the surface of the casting to obtain the casting billet; The sand core is prepared using casting resin sand, which comprises the following raw materials in parts by weight: 100 parts washed quartz sand, 1.5 to 2 parts biomass-modified furan resin, 1.2 to 1.8 parts HTAM high-temperature resistant and anti-migration modifier, 0.4 to 0.6 parts composite curing agent, 0.5 to 1.0 parts gradient disintegrating agent, 0.1 to 0.2 parts silane coupling agent, 0.2 to 0.3 parts crack-resistant agent, and 1.5 to 2.5 parts high-temperature resistant reinforcing phase; the composite curing agent includes p-toluenesulfonic acid, aluminum dihydrogen phosphate, and lactic acid; the gradient disintegrating agent includes ammonium bicarbonate, polystyrene, and expandable graphite; the crack-resistant agent is mica powder; and the high-temperature resistant reinforcing phase includes calcined kaolin and spodumene powder. The biomass-modified furan resin is prepared by stirring furfuryl alcohol, bio-based polyol, urea and deionized water, adding phenol and p-toluenesulfonic acid to carry out a condensation reaction, adjusting the pH to 4.0-4.5, diluting with deionized water, adding KH-550 and stirring, and adjusting the solid content to 75wt%-80wt%. The HTAM high-temperature resistant and anti-migration modifier is KH-570 modified activated ceramic microspheres dispersed in N-methylpyrrolidone, with the addition of pyromellitic dianhydride and 4,4'-diaminodiphenyl ether and stirring reaction. After pressure filtration, the filter cake is heat-treated successively at 100℃~110℃, 150℃~160℃, and 200℃~220℃, and after cooling to room temperature, it is dispersed and sieved to obtain the final product.

2. The resin sand casting method for a bridge shell casting according to claim 1, characterized in that, The foundry resin sand generated by vibration and sand falling is collected, crushed, air-separated, and magnetically separated. It is then calcined at 550℃~650℃ for 1.5h~2h to adjust the particle size, resulting in recycled sand with a recycling rate of over 80wt%.

3. The resin sand casting method for a bridge shell casting according to claim 1, characterized in that, The particle size of the washed quartz sand is between 40 mesh and 70 mesh; the composite curing agent comprises 60wt% to 65wt% p-toluenesulfonic acid aqueous solution, 45wt% to 50wt% aluminum dihydrogen phosphate aqueous solution, and 85wt% to 90wt% lactic acid aqueous solution in a mass ratio of (70 to 75): (25 to 30): (3 to 5).

4. The resin sand casting method for a bridge shell casting according to claim 1, characterized in that, The gradient disintegrating agent comprises ammonium bicarbonate, polystyrene microspheres, and expandable graphite in a mass ratio of (1-1.2):(0.5-0.7):(0.8-1); the silane coupling agent is KH-550 or KH-560; the high-temperature resistant reinforcing phase comprises calcined kaolin and spodumene powder in a mass ratio of (2-2.5):(1-1.2).

5. The resin sand casting method for a bridge shell casting according to claim 1, characterized in that, The preparation method of the biomass-modified furan resin includes the following steps: 60-70 parts furfuryl alcohol, 15-25 parts bio-based polyol, 5-10 parts urea and 3-5 parts deionized water are stirred and dissolved; 2-5 parts phenol and 0.5-1.5 parts p-toluenesulfonic acid are added, and the mixture is stirred to induce a condensation reaction. The pH is adjusted to 4.0-4.5, and 2-4 parts deionized water is added for dilution. 0.3-0.8 parts KH-550 are added and stirred. The solid content is adjusted to 75wt%-80wt% with deionized water at room temperature. The mixture is then filtered to obtain the biomass-modified furan resin.

6. The resin sand casting method for a bridge shell casting according to claim 5, characterized in that, The bio-based polyol is polytrimethylene ether glycol with a number average molecular weight of 500 g / mol; the stirring and dissolving temperature is 60℃~65℃; the stirring and polycondensation reaction is carried out at 80℃~85℃ for 90min~120min; the pH is adjusted with a 5wt%~8wt% sodium carbonate aqueous solution; after pH adjustment, the temperature is lowered to 40℃~50℃; the filtration is performed through a 100-150 mesh sieve.

7. The resin sand casting method for a bridge shell casting according to claim 1, characterized in that, The preparation method of the HTAM high-temperature resistant and anti-migration modifier includes the following steps: Under nitrogen protection, activated ceramic microspheres modified by KH-570 are dispersed in 70 to 80 parts of N-methylpyrrolidone, stirred at below 15°C, 20 to 22 parts of NMP solution of pyromellitic dianhydride are added dropwise, 20 to 23 parts of 4,4'-diaminodiphenyl ether are added, the mixture is stirred and reacted, filtered under pressure, and the filter cake is heat-treated successively at 100°C to 110°C, 150°C to 160°C, and 200°C to 220°C, cooled to room temperature, dispersed, and sieved to obtain the HTAM high-temperature resistant and anti-migration modifier.

8. The resin sand casting method for a bridge shell casting according to claim 7, characterized in that, The preparation method of the activated ceramic microspheres includes the following steps: 30 to 35 parts of hollow closed-cell ceramic microspheres are added to 60 to 70 parts of ethanol aqueous solution, stirred and dispersed, 3 to 4 parts of KH-570 are added, the pH is adjusted to 3.5 to 4.5, the mixture is stirred and reacted at 50 to 55℃ for 3 to 4 hours, filtered, the filter cake is washed with ethanol, and dried under vacuum to obtain activated ceramic microspheres.

9. The resin sand casting method for a bridge shell casting according to claim 7, characterized in that, The NMP solution concentration of the pyromellitic dianhydride is 40wt%–45wt%; the stirring reaction is carried out at 15℃–20℃ for 5h–6h; the heat treatment is carried out by heating to 100℃–110℃ and holding for 1h–1.5h, heating to 150℃–160℃ and holding for 1h–1.5h, and heating to 200℃–220℃ and holding for 1.5h–2h; the sieve mesh size is 100 mesh–150 mesh.

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