High-temperature-resistant precoated sand and preparation method thereof
By adding a composite strengthening system consisting of calcined kaolin, modified silica powder, boric acid, and iron oxide powder to the coated sand, the problem of sand sticking at high temperatures is solved, achieving higher heat resistance and strength, making it suitable for high-temperature metal casting.
Patent Information
- Application Number
- CN202511582601.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-31
- Publication Date
- 2026-01-16
AI Technical Summary
Existing coated sand is prone to sand adhesion during high-temperature molten metal casting, and its heat resistance is poor, especially at temperatures above 1000℃, the bonding strength of the molding sand decreases significantly.
A composite strengthening system is adopted, including calcined kaolin, modified silica powder, boric acid, iron oxide powder and lubricant. By forming a mullite strengthening phase and a glassy phase, the heat-resistant skeleton strength of the coated sand is improved, and the high thermal conductivity and low expansion of iron oxide powder are used to enhance the resistance to the impact of molten metal casting, while improving fluidity and strength.
It significantly reduces the sand adhesion rate, improves the heat resistance and strength of coated sand, effectively resists the intrusion of molten metal in high-temperature environments, reduces agglomeration, and enhances the overall performance of coated sand.
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Abstract
Description
Technical Field
[0001] This application relates to the technical field of coated sand manufacturing, and in particular to a high-temperature resistant coated sand and its preparation method. Background Technology
[0002] Coated sand is molding sand or core sand whose surface is covered with a layer of solid resin film before molding. It comes in a variety of types, including coated sand for centrifugal casting, chilled coated sand, wet coated sand, anti-sticking sand, anti-veining sand, and anti-orange peel coated sand. It is mostly used for cast steel and cast iron parts, and is also one of the best molding materials for automobiles, tractors, hydraulic parts, etc.
[0003] Currently, mainstream coated sand uses thermoplastic phenolic resin as a binder. Its molecular structure features alternating benzene rings and methylene groups forming a rigid network. While it has a high softening point (90-105℃), it is prone to pyrolysis at high temperatures. Experimental data shows that ordinary phenolic resin has a char residue of less than 40% at 500℃, leading to a significant decrease in the bonding strength of the molding sand.
[0004] When resin-infiltrated coated sand is used for pouring molten metal at a high temperature of 1000℃, the molten metal will burn through the resin-infiltrated coated sand, resulting in sand sticking and poor heat resistance. Summary of the Invention
[0005] In order to reduce the problem of sand sticking during the casting of coated sand in high-temperature molten metal, this application provides a high-temperature resistant coated sand and its preparation method.
[0006] In the first aspect, this application provides a high-temperature resistant coated sand, which adopts the following technical solution:
[0007] A high-temperature resistant coated sand is prepared from the following raw materials in parts by weight:
[0008] The ingredients are: 950-1050 parts raw sand, 18-22 parts phenolic resin, 15-30 parts calcined kaolin, 8-15 parts modified silica powder, 3-6 parts boric acid, 8-12 parts iron oxide powder, 7-9 parts curing agent, and 1-2 parts lubricant.
[0009] By adopting the above technical solution, a composite reinforcement system is formed by adding calcined kaolin and modified silica powder. When the molten metal comes into contact with the coated sand, the alumina in the calcined kaolin provides the mullite reinforcing phase, which forms a heat-resistant skeleton under high temperature. The silica powder provides the glass phase and fills the interior of the heat-resistant skeleton to block the pores of the coated sand and prevent the molten metal from penetrating, thereby greatly reducing the sand adhesion rate.
[0010] The addition of boric acid helps to lower the formation temperature of the mullite phase from over 1300℃ to 1150-1250℃. During casting, the mullite phase can be generated earlier to resist the intrusion of the molten metal and reduce the sand adhesion rate.
[0011] The addition of iron oxide powder can increase the curing thickness of the heated surface of the coated sand. During casting, the heated surface of the coated sand needs to be in direct contact with the high temperature of the molten metal. Utilizing the high thermal conductivity and low expansion of iron oxide powder, the high temperature during casting can be quickly transferred, thereby enhancing the ability to resist the impact of the molten metal and making it less prone to collapse.
[0012] The addition of lubricant can improve the fluidity of coated sand, reduce clumping, enhance the strength of coated sand, and reduce the sand adhesion rate.
[0013] Optionally, the preparation method of the modified silica powder includes the following steps:
[0014] After drying 95-105 parts of silicon micro powder at 100-110℃ for 2.5-3.5h, 0.5-1.5 parts of silane coupling agent are added for silane modification. The mixture is then mixed at a heating temperature of 75-85℃ for 1-1.5h to remove moisture and obtain modified silicon micro powder.
[0015] Optionally, the silane coupling agent is γ-aminopropyltriethoxysilane.
[0016] By adopting the above technical solution and modifying the silica powder with silane, on the one hand, its dispersibility is improved, preventing the problems of reduced strength and poor heat resistance caused by agglomeration. On the other hand, since the surface of unmodified silica powder has a large number of hydrophilic groups, the binding effect with the lipophilic groups on the surface of phenolic resin is not good. After the silica powder is modified with silane coupling agent, the bonding ability between silica powder and phenolic resin can also be improved, preventing the inorganic silica powder from hindering the formation of resin connecting bridges, thereby ensuring the strength improvement of the coated sand.
[0017] Optionally, the phenolic resin is a thermoplastic phenolic resin.
[0018] Optionally, the raw sand is calcined sand with an average fineness of 55-60. The average fineness of the raw sand can be 55, 56, 57, 58, 59, 60, etc.
[0019] Optionally, the particle size of the iron oxide powder is 10-15 μm. Specifically, the particle size of the iron oxide powder can be 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, etc.
[0020] Optionally, the curing agent is hexamethylenetetramine.
[0021] Optionally, the lubricant is calcium stearate.
[0022] Secondly, this application provides a method for preparing high-temperature resistant coated sand, using the following technical solution:
[0023] A method for preparing high-temperature resistant coated sand includes the following steps:
[0024] (1) Take the raw sand, heat it to 140-160℃, and then add phenolic resin to mix the sand;
[0025] (2) Then add calcined kaolin, modified silica powder, boric acid and iron oxide powder to mix sand;
[0026] (3) Finally, add curing agent and lubricant and mix evenly to obtain coated sand.
[0027] Optionally, the sand mixing time in steps (1) and (2) is 25-35 seconds.
[0028] In summary, this application has the following beneficial effects:
[0029] 1. By adding calcined kaolin and modified silica powder to form a composite reinforcement system, when the molten metal comes into contact with the coated sand, the alumina in the calcined kaolin provides the mullite reinforcing phase, which forms a heat-resistant skeleton under high temperature. The silica powder provides the glass phase and fills the interior of the heat-resistant skeleton to block the pores of the coated sand, preventing the molten metal from penetrating, thereby greatly reducing the sand adhesion rate.
[0030] The addition of boric acid helps to lower the formation temperature of the mullite phase, allowing the mullite phase to form earlier during casting to resist the intrusion of the molten metal and reduce the sand adhesion rate.
[0031] The addition of iron oxide powder can increase the curing thickness of the heated surface of the coated sand. During casting, the heated surface of the coated sand needs to be in direct contact with the high temperature of the molten metal. By utilizing the high thermal conductivity and low expansion of iron oxide powder, the high temperature during casting can be quickly transferred to achieve rapid curing, thereby enhancing the ability to resist the impact of the molten metal and making it less prone to collapse.
[0032] The addition of lubricant can improve the fluidity of coated sand, reduce clumping, enhance the strength of coated sand, and reduce the sand adhesion rate.
[0033] 2. By modifying silica powder with silane, on the one hand, its dispersibility is improved, preventing the problems of reduced strength and poor heat resistance caused by agglomeration. On the other hand, since the surface of unmodified silica powder has a large number of hydrophilic groups, the binding effect with the lipophilic groups on the surface of phenolic resin is not good. After the silica powder is modified with silane coupling agent, the binding ability between silica powder and phenolic resin can also be improved, preventing the inorganic silica powder from hindering the formation of resin connecting bridges, thereby ensuring the strength improvement of the coated sand. Detailed Implementation
[0034] Experimental methods in the following embodiments of this application that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. All commonly used chemical reagents used in the embodiments are commercially available products. The disclosure of the sources of the raw materials below is for clarification only and should not be construed as limiting the scope of protection.
[0035] Raw material source:
[0036] Thermoplastic phenolic resin was purchased from Jinan Shengquan Group Co., Ltd.
[0037] Calcined sand: SiO2 content > 93%. The average fineness of the calcined sand is obtained by referring to the "Calculation method of average fineness of foundry sand" in GB / T2684-2009 Test Methods for Foundry Sand and Mixtures.
[0038] Calcined kaolin: particle size 325 mesh, composition includes 40wt%-50wt% aluminum oxide and 50wt%-60wt% silicon dioxide;
[0039] Silica powder, SiO2 > 96%;
[0040] Iron oxide powder, Fe2O3 > 95%;
[0041] Urotropin, C6H 12 N4≥99%;
[0042] Calcium stearate powder: particle size 400 mesh.
[0043] Example
[0044] Example 1
[0045] A high-temperature resistant coated sand is prepared from the following raw materials by weight:
[0046] The ingredients are: 950 kg raw sand, 18 kg phenolic resin, 15 kg calcined kaolin, 8 kg modified silica powder, 3 kg boric acid, 8 kg iron oxide powder, 7 kg curing agent, and 1 kg lubricant.
[0047] Among them, the phenolic resin is thermoplastic phenolic resin, the raw sand is calcined sand with an average fineness of 55, the iron oxide powder has a particle size of 12μm, the curing agent is hexamethylenetetramine, and the lubricant is calcium stearate.
[0048] A method for preparing high-temperature resistant coated sand includes the following steps:
[0049] (1) Take the raw sand, heat it to 150°C, and then add phenolic resin to mix the sand for 30 seconds;
[0050] (2) Then add calcined kaolin, modified silica powder, boric acid and iron oxide powder and mix for 30 seconds;
[0051] (3) Finally, add curing agent and lubricant and mix evenly to obtain coated sand.
[0052] The modified silica powder is prepared by the following steps:
[0053] 100 kg of silicon micro powder (D50≤5μm) was dried at 105℃ for 3 h, and then 1 kg of γ-aminopropyltriethoxysilane was added as a silane coupling agent for silane modification. The mixture was stirred and mixed at 80℃ for 1 h to remove moisture and obtain modified silicon micro powder.
[0054] Example 2
[0055] A high-temperature resistant coated sand, which differs from Example 1 in that it is prepared from the following raw materials by weight:
[0056] The ingredients are: 1000 kg raw sand, 20 kg phenolic resin, 22 kg calcined kaolin, 11 kg modified silica powder, 4.5 kg boric acid, 10 kg iron oxide powder, 8 kg curing agent, and 1.5 kg lubricant.
[0057] Among them, the phenolic resin is thermoplastic phenolic resin, the raw sand is calcined sand with an average fineness of 58, the iron oxide powder has a particle size of 10μm, the curing agent is hexamethylenetetramine, and the lubricant is calcium stearate.
[0058] The remaining steps are the same.
[0059] Example 3
[0060] A high-temperature resistant coated sand, which differs from Example 1 in that it is prepared from the following raw materials by weight:
[0061] The ingredients are: 1050 kg raw sand, 22 kg phenolic resin, 30 kg calcined kaolin, 15 kg modified silica powder, 6 kg boric acid, 12 kg iron oxide powder, 9 kg curing agent, and 2 kg lubricant.
[0062] Among them, the phenolic resin is thermoplastic phenolic resin, the raw sand is calcined sand with an average fineness of 60, the iron oxide powder has a particle size of 15μm, the curing agent is hexamethylenetetramine, and the lubricant is calcium stearate.
[0063] The remaining steps are the same.
[0064] Comparative Example 1
[0065] A high-temperature resistant coated sand differs from Example 2 in that the amount of calcined kaolin used is 0 kg, while the other steps are the same.
[0066] Comparative Example 2
[0067] A high-temperature resistant coated sand differs from Example 2 in that the amount of calcined kaolin used is 40 kg, while the other steps are the same.
[0068] Comparative Example 3
[0069] A high-temperature resistant coated sand differs from Example 2 in that the amount of modified silica powder used is 0 kg, while the other steps are the same.
[0070] Comparative Example 4
[0071] A high-temperature resistant coated sand differs from Example 2 in that the amount of modified silica powder used is 20 kg, while the other steps are the same.
[0072] Comparative Example 5
[0073] A high-temperature resistant coated sand differs from Example 2 in that an equal amount of unmodified silica powder is used to replace the modified silica powder, while the other steps are the same.
[0074] Comparative Example 6
[0075] A high-temperature resistant coated sand differs from Example 2 in that the amount of boric acid used is 0 kg, while the other steps are the same.
[0076] Comparative Example 7
[0077] A high-temperature resistant coated sand differs from Example 2 in that the amount of boric acid used is 9 kg, while the other steps are the same.
[0078] Comparative Example 8
[0079] A high-temperature resistant coated sand differs from Example 2 in that it uses an equal amount of hydrochloric acid instead of boric acid, while the other steps are the same.
[0080] Comparative Example 9
[0081] A high-temperature resistant coated sand differs from Example 2 in that boric acid is replaced with an equal amount of oxalic acid, while the other steps are the same.
[0082] Comparative Example 10
[0083] A high-temperature resistant coated sand differs from Example 2 in that an equal amount of calcium oxide powder is used to replace iron oxide powder, while the other steps are the same.
[0084] Comparative Example 11
[0085] A high-temperature resistant coated sand differs from Example 2 in that the amount of iron oxide powder used is 0 kg, while the other steps are the same.
[0086] Comparative Example 12
[0087] A high-temperature resistant coated sand differs from Example 2 in that the amount of iron oxide powder used is 15 kg, while the other steps are the same.
[0088] Performance testing experiment
[0089] 1. Strength test
[0090] The bending strength, tensile strength and hot tensile strength were tested according to the methods specified in GB / T 2684 2009 "Test Methods for Foundry Sand and Mixtures".
[0091] 2. High temperature resistance test
[0092] The coated sand was made into cylindrical samples and subjected to a 2 kg load at a high temperature of 1000℃. The collapse time of the cylindrical samples, i.e., the heat resistance time, was tested. The longer the heat resistance time, the less likely the high-temperature molten metal is to penetrate the coated sand and cause sand adhesion, and the lower the sand adhesion rate.
[0093] The coated sands prepared in Examples 1-3 and Comparative Examples 1-12 were subjected to strength tests and high temperature resistance tests, respectively. The test results are shown in the table below.
[0094] Table 1. Strength and high-temperature resistance test results of the coated sand prepared in Examples 1-3 and Comparative Examples 1-12.
[0095]
[0096] Based on the test results of Examples 1-3 and Comparative Examples 1-2, and in conjunction with the results in Table 1, it can be seen that the strength and high-temperature resistance of the coated sand in Examples 1-3 are superior to those in Comparative Examples 1-2, and Example 2 is the preferred embodiment. The reason for this is that this application forms a composite reinforcement system by adding calcined kaolin and modified silica powder. When the molten metal comes into contact with the coated sand, the alumina in the calcined kaolin provides a mullite reinforcing phase, which forms a heat-resistant skeleton under high-temperature conditions. The silica powder provides a glassy phase and fills the interior of the heat-resistant skeleton to block the pores of the coated sand, preventing the high-temperature molten metal from penetrating, thereby greatly reducing the sand adhesion rate and giving it higher heat resistance.
[0097] Combining the test results of Example 2 and Comparative Examples 3-5 with those in Table 1, it can be seen that the strength and heat resistance of the coated sand in Example 2 are better than those in Comparative Examples 3-5. The reason for this is that by modifying the silica powder with silane, on the one hand, its dispersibility is improved, preventing the problem of reduced strength and poor heat resistance caused by agglomeration. On the other hand, since the surface of unmodified silica powder has a large number of hydrophilic groups, the binding effect with the lipophilic groups on the surface of phenolic resin is not good. After the silica powder is modified with silane coupling agent, the binding ability between silica powder and phenolic resin can be improved, preventing the inorganic silica powder from hindering the formation of resin connecting bridges, thereby ensuring the improvement of the strength of the coated sand.
[0098] Based on the test results of Example 2 and Comparative Examples 6-9, and combined with the results in Table 1, it can be seen that the strength and heat resistance of the coated sand in Example 2 are better than those of Comparative Examples 6-9. The reason for this is that the addition of boric acid helps to lower the formation temperature of the mullite phase from above 1300℃ to 1150-1250℃. During casting, the mullite phase can be generated earlier to resist the intrusion of the molten metal and reduce the sand adhesion rate.
[0099] Based on the test results in Table 1, and in conjunction with Examples 2 and Comparative Examples 10-12, it can be seen that Example 2 is superior to Comparative Examples 10-12. The reason for this is that the addition of iron oxide powder can increase the curing thickness of the heated surface of the coated sand. During casting, the heated surface of the coated sand needs to be in direct contact with the high-temperature molten metal. By utilizing the high thermal conductivity and low expansion of iron oxide powder, the high temperature during casting can be quickly transferred, thereby enhancing the ability to resist the impact of molten metal and making it less prone to collapse.
[0100] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.
Claims
1. A high-temperature resistant coated sand, characterized in that: It is prepared from the following raw materials in parts by weight: The ingredients are: 950-1050 parts raw sand, 18-22 parts phenolic resin, 15-30 parts calcined kaolin, 8-15 parts modified silica powder, 3-6 parts boric acid, 8-12 parts iron oxide powder, 7-9 parts curing agent, and 1-2 parts lubricant.
2. The high-temperature resistant coated sand according to claim 1, characterized in that: The method for preparing the modified silicon micropowder includes the following steps: After drying 95-105 parts of silicon micro powder at 100-110℃ for 2.5-3.5h, 0.5-1.5 parts of silane coupling agent are added for silane modification. The mixture is then mixed at a heating temperature of 75-85℃ for 1-1.5h to remove moisture and obtain modified silicon micro powder.
3. The high-temperature resistant coated sand according to claim 2, characterized in that: The silane coupling agent is γ-aminopropyltriethoxysilane.
4. The high-temperature resistant coated sand according to claim 1, characterized in that: The phenolic resin is a thermoplastic phenolic resin.
5. The high-temperature resistant coated sand according to claim 1, characterized in that: The raw sand is roasted sand with an average fineness of 55-60.
6. The high-temperature resistant coated sand according to claim 1, characterized in that: The iron oxide powder has a particle size of 10-15 μm.
7. The high-temperature resistant coated sand according to claim 1, characterized in that: The curing agent is hexamethylenetetramine.
8. The high-temperature resistant coated sand according to claim 1, characterized in that: The lubricant is calcium stearate.
9. A method for preparing high-temperature resistant coated sand according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Take the raw sand, heat it to 140-160℃, and then add phenolic resin to mix the sand; (2) Then add calcined kaolin, modified silica powder, boric acid and iron oxide powder to mix sand; (3) Finally, add curing agent and lubricant and mix evenly to obtain coated sand.
10. The method for preparing a high-temperature resistant coated sand according to claim 9, characterized in that, The sand mixing time in steps (1) and (2) is 25-35 seconds.