Composite sand core casting process and application thereof

Abstract

The invention relates to a composite sand core casting process and application thereof.The composite sand core casting process comprises the following steps that S1, according to a casting structure, a whole sand core is decomposed into a bearing main core and at least one functional sub-core, sand in the bearing main core is mixed sand of chromite sand, silica sand and graphene, the adding amount of the graphene is 0.3%-0.6% of the weight of the chromite sand, and the adding amount of the functional sub-core is 0.3%-0.6% of the weight of the silica sand; sand in the functional sub-core is mixed sand of forsterite and chromite sand; by optimizing the material composition and proportion of the bearing main core and the functional sub-core, the material compatibility and interface matching performance of the bearing main core and the functional sub-core reach the optimal state, the optimization can effectively relieve the problem of interface stress concentration caused by performance difference between different materials, and then the comprehensive performance of the casting is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of casting technology, in particular to a composite sand core casting process and application thereof. Background Art

[0002] Casting is a forming method in which liquid metal is poured into a casting cavity that is adapted to the shape of the part, and after it cools and solidifies, a metal part blank with a certain shape, size and performance is obtained.

[0003] In order to solve the performance shortcomings of single sand cores, composite structures are gradually adopted. However, the interfaces of existing composite sand cores are prone to stress concentration due to material differences, resulting in interface cracking, metal liquid leakage and other problems during casting, which affects the quality of castings. Summary of the Invention

[0004] The present invention aims to solve the problems existing in the prior art and provides the following technical solutions:

[0005] In a first aspect, the present invention provides a composite sand core casting process comprising the following steps:

[0006] S1: According to the casting structure, the whole sand core is decomposed into a load-bearing main core and at least one functional sub-core. The medium-molded sand of the load-bearing main core is a mixture of chromite sand, silica sand and graphene, and the graphene addition amount is 0.3%-0.6% of the weight of the chromite sand. The medium-molded sand of the functional sub-core is a mixture of forsterite and chromite sand.

[0007] S2: The load-bearing main core is placed and fixed in the core box of the large sand core. The functional sub-core filled after sand shooting is in contact with and combined with the load-bearing main core, and the whole is solidified and formed to form an integrated composite sand core.

[0008] As an improvement of the above technical solution, step S2 further includes applying an interface agent on the load-bearing main core, wherein the interface agent is polyborosiloxane and nano-zirconium oxide.

[0009] As an improvement to the above technical solution, the method for making the load-bearing main core is to put the molding sand into a sand mixer, then add a binder, a curing agent and a lubricant to mix the sand; put the mixed molding sand into the sand shooting barrel of the core shooting machine, heat the core box to the target temperature and then shoot the core to make a sand sample, demold it after hardening, and take out the functional sub-core.

[0010] As an improvement of the above technical solution, the adhesive is a composite system of phenolic resin and melamine, and the added amount of melamine is 7%-9% of the mass of the phenolic resin.

[0011] As an improvement of the above technical solution, the curing agent is p-toluenesulfonic acid.

[0012] In a second aspect, the present invention provides an application of the above-mentioned composite sand core casting process, wherein the composite sand core casting process is applied to coated sand casting.

[0013] Beneficial effects of the present invention:

[0014] The introduction of graphene in the load-bearing core enhances the interface bonding strength through the construction of a three-dimensional heat conduction network, stress dispersion, and crack deflection. It also inhibits the phase change expansion of silica sand, compensates for the high expansion of chromite sand, and further improves the interface stability.

[0015] The functional sub-core is compounded with chromite sand and forsterite. Through particle size complementation and thermal expansion behavior regulation, the interfacial thermal mismatch stress with the load-bearing main core is reduced, thus avoiding problems such as interface debonding and microcracks.

[0016] By optimizing the material composition and ratio of the load-bearing main core and the functional sub-core, the material compatibility and interface matching between the two are optimized. This optimization can effectively alleviate the problem of interface stress concentration caused by performance differences between different materials, thereby significantly improving the overall performance of the casting. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] The composite sand core casting process described in this application is described as follows:

[0019] Make the load-bearing main core; A. Sand pretreatment: Add chromite sand and silica sand to the sand mixer and dry mix for 2-3 minutes; add graphene / ethanol dispersion and wet mix for 5-7 minutes until the ethanol is completely evaporated; then add binder, curing agent, and lubricant and mix for 3-6 minutes;

[0020] C. Core shooting and curing: inject the mixed sand into the core box at 210±5℃, with an injection pressure of 0.65-0.75MPa for 5-10s; step hardening: 100℃×30s→210℃×120s, demoulding to obtain the load-bearing main core;

[0021] Functional sub-core composite: A. Sandblasting treatment of the main bearing core joint surface, roughness Ra ≥ 12.5μm; spraying interface agent on the joint surface, coating thickness 50±5μm, 80℃×3mi pre-curing, and fixing the main bearing core to the core box through alumina ceramic positioning pins.

[0022] B. Inject the functional core sand, add forsterite and chromite sand into the sand mixer and dry mix for 2-3 minutes, add binder, curing agent and lubricant, mix the sand for 3-6 minutes, and mix the sand for 3 minutes;

[0023] Injection pressure 0.65-0.75MPa;

[0024] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0025] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0026] Preparation Example A1

[0027] In the main bearing core, the phenolic resin is 6.5%, calcium stearate is 0.35%, the addition amount of p-toluenesulfonic acid is 7.5% of the adhesive, the content of chromite sand is 62%, the graphene is 0.186%, and the balance is silica sand;

[0028] Preparation Example A2

[0029] In the main bearing core, phenolic resin is 7%, calcium stearate is 0.3%, the addition amount of p-toluenesulfonic acid is 7% of the adhesive, the content of chromite sand is 70%, graphene is 0.21%, and the balance is silica sand;

[0030] Preparation Example A3

[0031] In the main bearing core, the phenolic resin is 7.5%, calcium stearate is 0.25%, the addition amount of p-toluenesulfonic acid is 6% of the adhesive, the content of chromite sand is 78%, graphene is 0.234%, and the balance is silica sand;

[0032] Preparation Example A4

[0033] In the main bearing core, phenolic resin is 7%, calcium stearate is 0.3%, the addition amount of p-toluenesulfonic acid is 7% of the adhesive, the content of chromite sand is 70%, and the balance is silica sand;

[0034] The adhesive is a composite system of phenolic resin and melamine.

[0035] Preparation Example B1

[0036] In the functional sub-core, phenolic resin is 6.5%, calcium stearate is 0.35%, the addition amount of p-toluenesulfonic acid is 7.5% of the adhesive, chromite sand is 70%, and the balance is forsterite;

[0037] Preparation Example B2

[0038] In the functional sub-core, phenolic resin is 7%, calcium stearate is 0.3%, the addition amount of p-toluenesulfonic acid is 6.5% of the adhesive, chromite sand is 75%, and the balance is forsterite;

[0039] Preparation Example B3

[0040] In the functional sub-core, phenolic resin is 7.5%, calcium stearate is 0.25%, the addition amount of p-toluenesulfonic acid is 7.5% of the adhesive, chromite sand is 80%, and the balance is forsterite;

[0041] Preparation Example B4

[0042] In the functional sub-core, phenolic resin is 7%, calcium stearate is 0.3%, the addition amount of p-toluenesulfonic acid is 6.5% of the adhesive, and the balance is chromite sand;

[0043] Unless otherwise specified in this application, "%" refers to mass percentage, i.e. wt%.

[0044] Example 1

[0045] Chromite sand and silica sand in the proportions described in Preparation Example A1 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.65 MPa for 10 seconds. Step curing was performed: 100°C for 30 seconds → 210°C for 120 seconds. The load-bearing main core was then demolded.

[0046] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm, and the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm. It is pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box through alumina ceramic positioning pins.

[0047] The forsterite and chromite sand in the proportions described in Preparation Example B1 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.65 MPa.

[0048] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0049] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0050] Example 2

[0051] Chromite sand and silica sand in the proportions described in Preparation Example A1 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.65 MPa for 5 seconds. Step hardening was performed: 100°C for 30 seconds → 210°C for 120 seconds. Demolding was performed to obtain the load-bearing main core.

[0052] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0053] The forsterite and chromite sand in the proportion described in Preparation Example B2 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.65 MPa.

[0054] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0055] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0056] Example 3

[0057] Chromite sand and silica sand in the proportions described in Preparation Example A1 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.75 MPa for 5 seconds. Step hardening was performed: 100°C for 30 seconds → 210°C for 120 seconds. Demolding was performed to obtain the load-bearing main core.

[0058] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0059] The forsterite and chromite sand in the proportions described in Preparation Example B3 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.75 MPa.

[0060] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0061] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0062] Example 4

[0063] Chromite sand and silica sand in the proportions described in Preparation Example A2 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.75 MPa for 10 seconds. Step hardening was performed: 100°C for 30 seconds → 210°C for 120 seconds. The load-bearing main core was then demolded.

[0064] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0065] The forsterite and chromite sand in the proportions described in Preparation Example B1 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.65 MPa.

[0066] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0067] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0068] Example 5

[0069] Chromite sand and silica sand in the proportions described in Preparation Example A2 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.7 MPa for 5 seconds. Step curing was performed: 100°C for 30 seconds → 210°C for 120 seconds. The load-bearing main core was then demolded.

[0070] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0071] The forsterite and chromite sand in the proportion described in Preparation Example B2 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.7 MPa.

[0072] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0073] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0074] Example 6

[0075] Chromite sand and silica sand in the proportions described in Preparation Example A2 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 5 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.65 MPa for 10 seconds. Step hardening was performed: 100°C for 30 seconds → 210°C for 120 seconds. The load-bearing main core was then demolded.

[0076] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0077] The forsterite and chromite sand in the proportion described in Preparation Example B3 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.65 MPa.

[0078] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0079] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0080] Example 7

[0081] Chromite sand and silica sand in the proportions described in Preparation Example A3 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.7 MPa for 5 seconds. Step curing was performed: 100°C for 30 seconds → 210°C for 120 seconds. Demolding was performed to obtain the load-bearing main core.

[0082] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0083] The forsterite and chromite sand in the proportions described in Preparation Example B1 were added to a sand mixer and dry-mixed for 3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.65 MPa.

[0084] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0085] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0086] Example 8

[0087] Chromite sand and silica sand in the proportions described in Preparation Example A3 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 5 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.75 MPa for 10 seconds. Step curing was performed: 100°C for 30 seconds → 210°C for 120 seconds. The load-bearing main core was then demolded.

[0088] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0089] The forsterite and chromite sand in the proportions described in Preparation Example B2 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 5 minutes at a shot pressure of 0.75 MPa.

[0090] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0091] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0092] Example 9

[0093] Chromite sand and silica sand in the proportions described in Preparation Example A3 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.65 MPa for 5 seconds. Step hardening was performed: 100°C for 30 seconds → 210°C for 120 seconds. The load-bearing main core was then demolded.

[0094] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0095] The forsterite and chromite sand in the proportions described in Preparation Example B3 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes at a shot pressure of 0.65 MPa.

[0096] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0097] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0098] Comparative Example 1

[0099] Chromite sand and silica sand in the proportions described in Preparation Example A4 were added to a sand mixer and dry-mixed for 2 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was injected into a core box at 210±5°C at a pressure of 0.75 MPa for 10 seconds. Step hardening was performed: 100°C for 30 seconds → 210°C for 120 seconds. The load-bearing main core was then demolded.

[0100] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0101] The forsterite and chromite sand in the proportions described in Preparation Example B1 were added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.65 MPa.

[0102] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0103] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0104] Comparative Example 2

[0105] Chromite sand and silica sand in the proportions described in Preparation Example A2 were added to a sand mixer and dry-mixed for 2 minutes. Graphene / ethanol dispersion was then added and wet-mixed until the ethanol was completely evaporated. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were then added and mixed for 3 minutes. The mixed sand was then injected into a core box at 210±5°C at a pressure of 0.75 MPa for 10 seconds. Step hardening was performed: 100°C for 30 seconds → 210°C for 120 seconds. The load-bearing main core was then demolded.

[0106] The main bearing core joint surface is sandblasted, with a roughness of Ra ≥ 12.5 μm; the joint surface is sprayed with an interface agent with a coating thickness of 50 ± 5 μm, pre-cured at 80 ° C × 3 min, and the main bearing core is fixed to the core box by an alumina ceramic positioning pin.

[0107] The chromite ore in the proportion described in Preparation Example B4 was added to a sand mixer and dry-mixed for 2-3 minutes. Phenolic resin, p-toluenesulfonic acid, and calcium stearate were added and mixed for 3 minutes. The injection pressure was 0.65 MPa.

[0108] Overall step curing: 180℃×90s→240℃×180s, demoulding to obtain an integrated composite sand core.

[0109] In the above process, the interface agent is a compound of polyborosiloxane and nano-zirconia.

[0110] Performance testing:

[0111] Hardness test: Based on GB / T231.1-2018 "Brinell hardness test for metallic materials - Part 1: Test method", etc., a Brinell hardness tester is used to test the hardness of the specified parts of the casting (the middle, both ends, and the flange of the hollow cylinder). Each part is tested at three points and the average value is taken.

[0112] Appearance inspection: Based on GB / T6414-2017 "Dimensional Tolerances and Machining Allowances for Castings", observe the casting surface with the naked eye and a low-power magnifying glass to check for defects such as pores, sand sticking, and cracks.

[0113] Internal defect detection: Based on GB / T5616-2014 "Guidelines for the Application of Nondestructive Testing", ultrasonic flaw detectors are used to perform internal flaw detection on castings to detect defects such as internal pores and shrinkage.

[0114] The sand cores prepared in Examples 1-9 and Comparative Examples 1-2 were used to cast castings and performance tests were performed. The results are shown in Table 1:

[0115]

[0116]

[0117] Table 1

[0118] As can be seen from Table 1, the castings of Examples 1-8 have very good performance. As can be seen from the data in Table 1, for Examples 4-6, when the chromite sand in the load-bearing main core is 70% and the chromite sand in the functional sub-core is 70%-80%, the material compatibility and interface matching of the two sand cores reach the optimal state, which can effectively alleviate the stress concentration problem caused by material differences, thereby making the castings present more excellent comprehensive performance in appearance, hardness and internal quality. Among them, chromite sand serves as the dominant heat carrier, and graphene is directionally spread on the surface of silica sand particles, bridging isolated chromite sand to form a three-dimensional heat conduction network; graphene improves the overall thermal conductivity, making the temperature distribution of the sand core more uniform, reducing local incomplete solidification areas, promoting uniform solidification of the casting, eliminating shrinkage pores, and suppressing the phase change expansion of silica sand through graphene to compensate for the high expansion of chromite sand. The chromite sand and forsterite composite materials are compounded to improve the performance of the sand core and avoid the generation of micro cracks. Graphene fills the gaps between the sand particles and enhances the toughness of the resin matrix through crack deflection and interface stress transfer. The functional sub-core is made of chromite sand and forsterite. The particle size and pore size of the two sand particles complement each other, which optimizes the overall air permeability of the sand core and ensures the smooth discharge of gas. The introduction of forsterite makes the thermal expansion behavior of the functional sub-core closer to the load-bearing main core, significantly reduces the interface thermal mismatch stress, avoids interface debonding, micro cracks or local peeling caused by asynchronous thermal expansion and contraction, thereby ensuring the integrity of the connection, making the sand core more uniform during the compaction process, avoiding problems such as sand sticking and shrinkage caused by local looseness, and making the sand mold have sufficient strength and stability to withstand the erosion and pressure of the molten metal, and prevent the sand mold from collapsing or disintegrating during the pouring process; it helps to ensure the dimensional accuracy and surface quality of the casting.

[0119] Example 10

[0120] The difference from Example 4 is that: the amount of graphene added is 0.4% of the weight of the chromite ore;

[0121] Example 11

[0122] The difference from Example 4 is that: the amount of graphene added is 0.5% of the weight of the chromite ore;

[0123] Example 12

[0124] The difference from Example 4 is that: the amount of graphene added is 0.6% of the weight of the chromite ore;

[0125] The sand cores prepared in Examples 10-12 and Example 4 were used to cast castings and performance tests were performed. The results are shown in Table 2:

[0126]

[0127] Table 2

[0128] As can be seen from Table 2, with the increase of graphene addition, the hardness shows an upward trend and then a downward trend. Graphene forms a uniform "reinforcement network" at the interface, which not only ensures the rigid support of the load-bearing main core, but also buffers the local deformation of the functional sub-core through the flexible transition layer. When the addition exceeds 0.4%, graphene is prone to agglomeration, resulting in local stress concentration, which in turn weakens the synergistic effect of the interface and reduces the bonding strength.

[0129] Example 13

[0130] The difference from Example 4 is that the amount of melamine added is 7% of the mass of the phenolic resin.

[0131] Example 14

[0132] The difference from Example 4 is that the amount of melamine added is 7.5% of the mass of the phenolic resin.

[0133] Example 15

[0134] The difference from Example 4 is that the amount of melamine added is 8% of the mass of the phenolic resin.

[0135] Example 16

[0136] The difference from Example 4 is that the amount of melamine added is 8.5% of the mass of the phenolic resin.

[0137] Example 17

[0138] The difference from Example 4 is that the amount of melamine added is 9% of the mass of the phenolic resin.

[0139] The sand cores prepared in Examples 13-17 and Example 4 were used to cast castings and performance tests were performed. The results are shown in Table 3:

[0140]

[0141]

[0142] Table 3

[0143] Since phenolic resin and melamine form a copolymer cross-linked structure, the triazine ring in the melamine molecule can undergo a condensation reaction with the hydroxymethyl group of the phenolic resin, introducing a rigid group and increasing the cross-linking point density. Therefore, as shown in Table 3, when the melamine addition amount is ≤8%, the cross-linking density gradually increases with the increase in the amount, the room temperature and high temperature strength of the sand core is enhanced, and the hardness of the casting increases due to the improved support force of the sand core.

[0144] When the addition amount is greater than 8%, the excess melamine will cause free melamine molecules to aggregate into clusters, destroying the uniformity of the copolymer network and generating microcracks between the self-aggregates and the phenolic matrix, which become stress concentration points, resulting in a decrease in the local strength of the sand core, weakening the bearing capacity of the casting, and reducing the hardness.

[0145] The cross-linked network supports the sand core structure and resists erosion by molten metal; the thermal conductivity of graphene accelerates heat diffusion, avoiding excessive decomposition of the adhesive caused by local high temperature; the low expansion of chromite sand matches the elastic modulus of the composite adhesive, reducing defects caused by thermal stress.

[0146] The above are all preferred embodiments of the present application, and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. Composite sand core casting process, characterized in that, The following steps are involved: S1: According to the casting structure, the whole sand core is decomposed into a load-bearing main core and at least one functional sub-core. The medium-molded sand of the load-bearing main core is a mixture of chromite sand, silica sand and graphene, and the graphene addition amount is 0.3%-0.6% of the weight of the chromite sand. The medium-molded sand of the functional sub-core is a mixture of forsterite and chromite sand. S2: The load-bearing main core is placed and fixed in the core box of the large sand core. The functional sub-core filled after sand shooting is in contact with and combined with the load-bearing main core, and the whole is solidified and formed to form an integrated composite sand core.

2. The composite sand core casting process according to claim 1, characterized in that: Step S2 also includes applying an interface agent on the load-bearing main core, wherein the interface agent is polyborosiloxane and nano-zirconium oxide.

3. The composite sand core casting process according to claim 1, characterized in that: The method for manufacturing the load-bearing main core comprises the following steps: placing molding sand into a sand mixer, adding a binder, a curing agent, and a lubricant to mix the sand; placing the mixed molding sand into a sand shooting barrel of a core shooting machine, heating the core box to a target temperature, and then shooting the core to form a sand sample; demolding the sand after hardening, and taking out the functional sub-core.

4. The composite sand core casting process according to claim 1, characterized in that: The adhesive is a composite system of phenolic resin and melamine, and the added amount of melamine is 7%-9% of the mass of the phenolic resin.

5. The composite sand core casting process according to claim 4, characterized in that: The curing agent is p-toluenesulfonic acid.

6. The composite sand core casting process according to claim 1, characterized in that: The composite sand core casting process is applied to coated sand casting.

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