A method for rapidly preparing a silica sol shell mold

Abstract

The present invention relates to the technical field of silica sol shell preparation, and particularly relates to a method for rapidly preparing a silica sol shell. The method comprises the following steps: reacting tetraethyl orthosilicate with a silane coupling agent solution to prepare a modified silica sol grafted and modified with a silane coupling agent; then stirring and mixing a refractory powder, the modified silica sol and a strengthening agent to obtain a slurry; the strengthening agent is a mixture of nano-silica and nano-boron oxide in a mass ratio of 1:1; successively coating and sanding the slurry on the surface of a lost foam pattern to form multiple shell layers, thereby obtaining a silica sol shell blank; and through demoulding and sintering, a silica sol shell is obtained. The method of the present invention can not only improve the surface quality of the shell, but also meet the requirements of industrial production, improve the efficiency of shell preparation and reduce the cost on the basis of reducing the shell layer thickness.

Description

Technical Field

[0001] The invention relates to the technical field of silica sol shell preparation, and in particular to a method for rapidly preparing a silica sol shell. Background Art

[0002] At present, the preparation processes of ceramic shells mainly include water glass process and silica sol process. The water glass process has the advantage of a short shell making cycle, but the need to add chloride salts during the shell making process can easily lead to environmental problems, and the product quality is also quite low. Compared with the water glass process, the silica sol process has relatively good surface quality, but the shell making cycle is long and the cost is relatively high. Therefore, how to shorten the shell making cycle of the silica sol process and reduce costs has become a key issue that needs to be solved in current research.

[0003] Silica sol shell mainly uses silica sol as a binder, and has relatively high high temperature strength (>6MPa) and creep resistance. However, it usually takes about 12 hours to dry a layer of shell, resulting in a long shell making cycle and high power consumption, which restricts the development of silica sol shell.

[0004] At present, people mainly improve the drying process and slurry formulation. For example, Yuan Xinqiang (Yuan Xinqiang, Research on the Preparation Process of Silicon-based Ceramic Mold Using Silica Sol as Binder) mainly uses ammonium chloride as a catalyst, and through the combination of vacuum drying, obtains silica sol ceramic shell with good surface quality, and the gelation and hardening time is shortened to within 1 hour. However, since ammonium chloride is easily weakly acidic, the pH of silica sol with a small amount of ammonium chloride will be reduced (from pH = 8.5-10.5 to 8.0-8.5), which will lead to poor stability of silica sol and gelation.

[0005] Based on this, it is necessary to propose a method for quickly preparing silica sol-type shells, which can improve the stability of modified silica sol, shorten the shell making efficiency and reduce the cost. Summary of the invention

[0006] In order to solve the problem of poor stability of silica sol in the existing silica sol shell preparation process, the purpose of the present invention is to provide a method for quickly preparing silica sol shells, which can improve the stability of modified silica sol while shortening the shell making efficiency and reducing costs.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows.

[0008] The present invention provides a method for rapidly preparing a silica sol shell, comprising the following steps:

[0009] Tetraethyl orthosilicate is reacted with a silane coupling agent solution to prepare a modified silica sol grafted and modified with a silane coupling agent; then a refractory powder, the modified silica sol and a strengthening agent are stirred and mixed to obtain a slurry; the strengthening agent is a mixture of nano-silica and nano-boron oxide in a mass ratio of 1:1.

[0010] The slurry is coated and sand is sprinkled on the surface of the lost foam in sequence to form multiple shell layers, and a silica sol shell mold blank is obtained; after demolding and sintering, a silica sol shell mold is obtained.

[0011] The present invention mainly uses a silane coupling agent as a catalyst and a grafting modifier, which can not only improve the stability of the modified silica sol, but also improve its leveling property and coating property; moreover, the ethanol formed during the reaction can also play an infiltration role and contribute to shortening the drying time in the later stage.

[0012] In the present invention, nano-silica and nano-boron oxide are added to the slurry as strengthening agents. Nano-silica mainly plays a role in promoting coagulation; nano-boron oxide mainly plays a role in repairing silicon-oxygen bonds to form a dense network structure; through the mutual cooperation of nano-silica, nano-boron oxide and other components, the strength of the prepared shell mold is improved on the basis of not reducing the viscosity of the slurry. Thus, on the basis of reducing the shell mold layer thickness, the requirements of industrial production are met, the efficiency of preparing the shell mold is improved, and the cost is reduced.

[0013] Preferably, the slurry is prepared from the following raw materials by weight percentage:

[0014] Modified silica sol 20% - 45%, refractory powder 50% - 78%, strengthening agent 2% - 5%, total 100%.

[0015] Further preferably, the specific process for preparing the silica sol shell mold blank is as follows:

[0016] The lost foam is immersed in the surface layer slurry, and after being evenly coated, surface layer sand is sprinkled and dried to obtain a surface layer shell layer;

[0017] Then it is immersed in the transition layer slurry, and after being evenly coated, transition layer sand is sprinkled and dried to obtain a transition layer shell layer;

[0018] Then it is immersed in the back layer slurry, and after being evenly coated, back layer sand is sprinkled and dried to obtain a back layer shell layer;

[0019] After that, it is immersed in the sealant layer slurry, and after being evenly coated, it is dried to obtain a silica sol shell mold blank.

[0020] Further preferably, the refractory powder of the surface layer slurry is zirconia powder; the refractory powder of the transition layer slurry is alumina powder; the refractory powder of the back layer slurry is at least one of kaolinite powder, mullite powder, and zircon powder; the refractory powder of the sealant layer slurry is the same as that of the back layer slurry. In the back layer slurry of the present invention, both kaolinite powder and mullite powder contain an appropriate amount of alumina. The introduction of alumina can increase the viscosity of the back layer slurry at high temperatures and cooperate with the strengthening agent to reinforce the back layer. Since zircon powder (ZrSiO4) has a small linear expansion coefficient, introducing zircon powder into the back layer can reduce the shrinkage rate of the back layer and improve the back layer strength.

[0021] Further preferably, the material of the sand of each layer of the shell is the same as that of the refractory powder of its corresponding shell layer.

[0022] Further preferably, the particle size of the refractory powder is 200 - 1000 mesh, and along the shell layer from the inside to the outside, the particle size of the refractory powder decreases in turn; the particle size of the surface layer sand, transition layer sand, and back layer sand is 50 - 150 mesh.

[0023] Preferably, the silane coupling agent is 3-aminopropyltriethoxysilane. In the present invention, the amino group in the silane coupling agent forms an intermolecular hydrogen bond with the silanol group on the surface of the silica sol, making the modified silica sol not easily aggregated and improving the stability of the modified silica sol. In addition, grafting with the silane coupling agent also helps to improve the coating property and leveling property of the silica sol and improve the surface quality of the mold shell.

[0024] Further preferably, the mass ratio of tetraethyl orthosilicate to the silane coupling agent is 2 - 3:1;

[0025] The silane coupling agent solution is obtained by mixing the silane coupling agent with water; the addition amount of the silane coupling agent is 14wt% - 20wt%. For example, 14wt%, 16wt%, 18wt%, 20wt%, etc. Part of the silane coupling agent is grafted on the surface of the silica sol, playing a role in improving the dispersibility of the modified silica sol. However, adding an excessive amount of the silane coupling agent easily causes the generated nano-silica particles to agglomerate, making the particle size of the modified silica sol larger and affecting the surface quality of the mold shell.

[0026] Preferably, the reaction temperature for preparing the silane coupling agent grafted modified silica sol is 30 - 50°C. For example, 30°C, 35°C, 40°C, 45°C, 50°C, etc.

[0027] Preferably, the average particle size of nano-silica and nano-boron oxide is 50nm, and the purity ≥ 99.9%.

[0028] Preferably, the lost foam pattern is a wax film; the demolding temperature is 500 - 600°C; the sintering temperature is 1050 - 1150°C.

[0029] Advantages of the present invention:

[0030] 1. The present invention mainly grafts and modifies silica sol, which can not only improve the stability of the modified silica sol, but also improve its leveling property and drapability, and can shorten the drying and curing time. The present invention also adds nano-silica and nano-boron oxide as strengthening agents. Through the mutual cooperation of the strengthening agents and other components, on the basis of not reducing the viscosity of the slurry, the strength of the prepared mold shell is improved. Thus, on the basis of reducing the thickness of the mold shell layer, the requirements of industrial production are met, the efficiency of preparing the mold shell is improved, and the cost is reduced.

[0031] 2. The present invention introduces kaolinite powder or mullite powder into the back layer slurry. The appropriate amount of alumina in it increases the viscosity of the back layer slurry at high temperature and cooperates with the strengthening agent to play a role in strengthening the back layer.

[0032] 3. The present invention uses silane coupling agent for grafting, which also helps to improve the drapability and leveling property of silica sol and improve the surface quality of the mold shell. Brief Description of the Drawings

[0033] Figure 1 It is a bar chart showing the influence of different strengthening agents on the strength of the silica sol mold shell.

[0034] Figure 2 It is a bar chart showing the influence of different refractory powders in the back layer mold shell on the strength of the silica sol mold shell. Detailed Embodiments

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0037] The following further illustrates the technical solutions of the present invention through specific embodiments. Unless otherwise specified, the methods described in the following embodiments are all conventional methods; the reagents and materials, unless otherwise specified, can all be purchased in the market.

[0038] In the following embodiments, the crystal chemical formula of kaolinite is 2SiO2·Al2O3·2H2O, and its chemical composition is mainly SiO2 46.54%, Al2O3 39.5%, H2O 13.96%. The chemical formula of mullite is 3AlO3·2SiO2, and its chemical composition is mainly Al2O3 71.8%, SiO2 28.2%.

[0039] In the following examples, the average particle size of nano-silica (SiO2) and nano-boron oxide (B2O3) is 50 nm, and the purity is ≥ 99.9%.

[0040] Example 1

[0041] A method for rapidly preparing a silica sol shell mold includes the following steps:

[0042] (1) Prepare modified silica sol:

[0043] Mix 3-aminopropyltriethoxysilane with water at 30 - 35 °C with stirring for 30 min to obtain a mixed solution; then dropwise add tetraethyl orthosilicate under stirring, and control the reaction temperature at 45 - 50 °C for 1 h; cool to room temperature to obtain modified silica sol.

[0044] Among them, the mass ratio of 3-aminopropyltriethoxysilane to tetraethyl orthosilicate is 2.3:1. In the mixed solution, the addition amount of 3-aminopropyltriethoxysilane is 14 wt%.

[0045] (2) Prepare a silica sol shell mold blank:

[0046] Surface shell making: Immerse the cleaned wax film in the prepared surface layer slurry, lift it above the liquid surface for about 20 s, and rotate for 1 min to evenly coat the surface layer slurry; then sprinkle zirconia sand with a mesh size of 100 - 150, shake and rotate to remove the excess zirconia sand; perform vacuum drying at 0.06 - 0.07 MPa, with a drying temperature of 80 - 90 °C and a drying time of 4 h; form a surface shell layer on the wax film. By mass percentage, the surface layer slurry is prepared by mixing 45% of modified silica sol, 53% of zirconia powder with a mesh size of 500, 1% of nano-silica, and 1% of nano-boron oxide.

[0047] Intermediate layer shell making: Immerse the wax film with the formed surface shell layer in the prepared intermediate layer slurry, lift it above the liquid surface for about 20 s, and rotate for 1 min to evenly coat the intermediate layer slurry; then sprinkle alumina sand with a mesh size of 100 - 150, shake and rotate to remove the excess alumina sand; perform vacuum drying at 0.06 - 0.07 MPa, with a drying temperature of 80 - 90 °C and a drying time of 2.5 h; form an intermediate layer shell layer on the wax film. By mass percentage, the intermediate layer slurry is prepared by mixing 37% of modified silica sol, 60% of alumina powder with a mesh size of 500, 1.5% of nano-silica, and 1.5% of nano-boron oxide.

[0048] Reinforced backing layer I shell making: Immerse the wax film forming the transition layer shell into the prepared reinforced backing layer I slurry, lift it above the liquid surface for about 20 s, and rotate for 1 min to evenly coat the reinforced backing layer I slurry; then sprinkle 50-100 mesh kaolin sand, shake and rotate to remove the excess kaolin sand; conduct vacuum drying at 0.06-0.07 MPa, with a drying temperature of 80-90 °C and a drying time of 2 h; form a reinforced backing layer I shell on the surface of the wax film. By mass percentage, the reinforced backing layer I slurry is prepared by mixing 31% of modified silica sol, 65% of 400-mesh kaolin powder, 2% of nano-silica, and 2% of nano-boron oxide.

[0049] Reinforced backing layer II shell making: Immerse the wax film forming the reinforced backing layer I shell into the prepared reinforced backing layer II slurry, lift it above the liquid surface for about 20 s, and rotate for 1 min to evenly coat the reinforced backing layer II slurry; then sprinkle 50-100 mesh zircon sand, shake and rotate to remove the excess zircon sand; conduct vacuum drying at 0.06-0.07 MPa, with a drying temperature of 80-90 °C and a drying time of 2 h; form a reinforced backing layer II shell on the surface of the wax film. By mass percentage, the reinforced backing layer II slurry is prepared by mixing 25% of modified silica sol, 70% of 280-mesh zircon powder, 2.5% of nano-silica, and 2.5% of nano-boron oxide.

[0050] Sealing slurry layer shell making: Immerse the wax film forming the reinforced backing layer II shell into the prepared sealing slurry layer slurry, lift it above the liquid surface for about 20 s, and rotate for 1 min to evenly coat the sealing slurry layer slurry; conduct vacuum drying at 0.06-0.07 MPa, with a drying temperature of 80-90 °C and a drying time of 0.5 h; form a sealing slurry layer shell on the surface of the wax film. That is, a silica sol shell blank. By mass percentage, the sealing slurry layer slurry is prepared by mixing 25% of modified silica sol, 70% of 280-mesh zircon powder, 2.5% of nano-silica, and 2.5% of nano-boron oxide.

[0051] (3) Preparation of silica sol shell:

[0052] Transfer the silica sol shell blank to a heat treatment furnace, first heat up to 580-600 °C, hold for 2 h to remove the wax film, then heat up to 1050 °C, hold for 1 h, and take it out after cooling to room temperature with the furnace to obtain a silica sol shell.

[0053] Example 2

[0054] A method for rapidly preparing a silica sol shell, comprising the following steps:

[0055] (1) Preparation of modified silica sol:

[0056] Mix 3-aminopropyltriethoxysilane and water at 30 - 35 °C with stirring for 30 min to obtain a mixed solution; then, while stirring, dropwise add tetraethyl orthosilicate, and control the reaction temperature at 45 - 50 °C for 1 h; cool to room temperature to obtain the modified silica sol.

[0057] Among them, the mass ratio of 3-aminopropyltriethoxysilane to tetraethyl orthosilicate is 3:1. In the mixed solution, the addition amount of 3-aminopropyltriethoxysilane is 20 wt%.

[0058] (2) Prepare the silica sol shell blank:

[0059] Surface shell making: Immerse the cleaned wax pattern into the prepared surface layer slurry, lift it above the liquid surface for about 20 s, and rotate for 1 min to make the surface layer slurry evenly coated; then sprinkle zirconia sand with a mesh size of 100 - 150, shake and rotate to remove the excess zirconia sand; carry out vacuum drying at 0.06 - 0.07 MPa, the drying temperature is 80 - 90 °C, and the drying time is 4 h; form a surface layer shell on the wax pattern surface. By mass percentage, the surface layer slurry is prepared by mixing 45% of the modified silica sol, 53% of zirconia powder with a mesh size of 500, 1% of nano-silica, and 1% of nano-boron oxide.

[0060] Intermediate layer shell making: Immerse the wax pattern with the surface layer shell into the prepared intermediate layer slurry, lift it above the liquid surface for about 20 s, and rotate for 1 min to make the intermediate layer slurry evenly coated; then sprinkle alumina sand with a mesh size of 100 - 150, shake and rotate to remove the excess alumina sand; carry out vacuum drying at 0.06 - 0.07 MPa, the drying temperature is 80 - 90 °C, and the drying time is 3 h; form an intermediate layer shell on the wax pattern surface. By mass percentage, the intermediate layer slurry is prepared by mixing 40% of the modified silica sol, 57% of alumina powder with a mesh size of 500, 1.5% of nano-silica, and 1.5% of nano-boron oxide.

[0061] Reinforcing back layer I shell making: Immerse the wax pattern with the intermediate layer shell into the prepared reinforcing back layer I slurry, lift it above the liquid surface for about 20 s, and rotate for 1 min to make the reinforcing back layer I slurry evenly coated; then sprinkle mullite sand with a mesh size of 50 - 100, shake and rotate to remove the excess mullite sand; carry out vacuum drying at 0.06 - 0.07 MPa, the drying temperature is 80 - 90 °C, and the drying time is 2 h; form a reinforcing back layer I shell on the wax pattern surface. By mass percentage, the reinforcing back layer I slurry is prepared by mixing 33% of the modified silica sol, 63% of mullite powder with a mesh size of 400, 2% of nano-silica, and 2% of nano-boron oxide.

[0062] Reinforced backing layer II shell making: Immerse the wax film forming the reinforced backing layer I shell into the prepared reinforced backing layer II slurry, lift it above the liquid surface for about 20 s, rotate for 1 min to evenly coat the reinforced backing layer II slurry; then sprinkle zircon sand with a mesh size of 50 - 100, shake and rotate to remove the excess zircon sand; conduct vacuum drying at 0.06 - 0.07 MPa, with a drying temperature of 80 - 90 °C and a drying time of 2 h; form a reinforced backing layer II shell on the surface of the wax film. By mass percentage, the reinforced backing layer II slurry is prepared by mixing 25% of modified silica sol, 70% of zircon powder with a mesh size of 280, 2.5% of nano-silica, and 2.5% of nano-boron oxide.

[0063] Sealing slurry layer shell making: Immerse the wax film forming the reinforced backing layer II shell into the prepared sealing slurry layer slurry, lift it above the liquid surface for about 20 s, rotate for 1 min to evenly coat the sealing slurry layer slurry; conduct vacuum drying at 0.06 - 0.07 MPa, with a drying temperature of 80 - 90 °C and a drying time of 0.5 h; form a sealing slurry layer shell on the surface of the wax film. That is, a silica sol shell blank. By mass percentage, the sealing slurry layer slurry is prepared by mixing 25% of modified silica sol, 70% of zircon powder with a mesh size of 280, 2.5% of nano-silica, and 2.5% of nano-boron oxide.

[0064] (3) Preparation of silica sol shell:

[0065] Transfer the silica sol shell blank to a heat treatment furnace, first heat it up to 580 - 600 °C, hold for 2 h to remove the wax film, then heat it up to 1100 °C, hold for 1 h, and take it out after cooling to room temperature with the furnace to obtain a silica sol shell.

[0066] Comparative Example 1

[0067] A method for preparing a silica sol shell, the difference from the method of Example 1 lies in:

[0068] The surface layer slurry is prepared by mixing 45% of modified silica sol, 53% of zirconia powder with a mesh size of 500, and 2% of nano-silica. The transition layer slurry is prepared by mixing 37% of modified silica sol, 60% of alumina powder with a mesh size of 500, and 3% of nano-silica. The reinforced backing layer I slurry is prepared by mixing 31% of modified silica sol, 65% of kaolinite powder with a mesh size of 400, and 4% of nano-silica. The reinforced backing layer II slurry is prepared by mixing 25% of modified silica sol, 70% of zircon powder with a mesh size of 280, and 5% of nano-silica. The sealing slurry layer slurry is prepared by mixing 25% of modified silica sol, 70% of zircon powder with a mesh size of 280, and 5% of nano-silica.

[0069] Comparative Example 2

[0070] A method for preparing a silica sol shell, the difference from the method of Example 1 lies in:

[0071] The surface layer slurry is prepared by mixing 45% of modified silica sol, 53% of zirconia powder with a mesh size of 500, and 2% of nano boron oxide. The transition layer slurry is prepared by mixing 37% of modified silica sol, 60% of alumina powder with a mesh size of 500, and 3% of nano boron oxide. The reinforcing back layer I slurry is prepared by mixing 31% of modified silica sol, 65% of kaolinite powder with a mesh size of 400, and 4% of nano boron oxide. The reinforcing back layer II slurry is prepared by mixing 25% of modified silica sol, 70% of zircon powder with a mesh size of 280, and 5% of nano boron oxide. The sealing slurry layer is prepared by mixing 25% of modified silica sol, 70% of zircon powder with a mesh size of 280, and 5% of nano boron oxide.

[0072] Comparative Example 3

[0073] A method for preparing a silica sol shell mold, which is different from the method of Example 1 in that:

[0074] The surface layer slurry is prepared by mixing 45% of modified silica sol and 55% of zirconia powder with a mesh size of 500. The transition layer slurry is prepared by mixing 37% of modified silica sol and 63% of alumina powder with a mesh size of 500. The reinforcing back layer I slurry is prepared by mixing 31% of modified silica sol and 69% of kaolinite powder with a mesh size of 400. The reinforcing back layer II slurry is prepared by mixing 25% of modified silica sol and 75% of zircon powder with a mesh size of 280. The sealing slurry layer is prepared by mixing 25% of modified silica sol and 75% of zircon powder with a mesh size of 280.

[0075] Comparative Example 4

[0076] A method for preparing a silica sol shell mold, which is different from the method of Example 1 in that:

[0077] The reinforcing back layer I slurry is prepared by mixing 31% of modified silica sol, 65% of alumina powder with a mesh size of 400, 2% of nano silicon oxide, and 2% of nano boron oxide. The reinforcing back layer II slurry is prepared by mixing 25% of modified silica sol, 70% of alumina powder with a mesh size of 280, 2.5% of nano silicon oxide, and 2.5% of nano boron oxide. The sealing slurry layer is prepared by mixing 25% of modified silica sol, 70% of alumina powder with a mesh size of 280, 2.5% of nano silicon oxide, and 2.5% of nano boron oxide.

[0078] Comparative Example 5

[0079] A method for preparing a silica sol shell mold, which is different from the method of Example 1 in that:

[0080] (1) Prepare modified silica sol:

[0081] 3-aminopropyltriethoxysilane and water were stirred and mixed at 30 - 35 °C for 30 min to obtain a mixed solution; then tetraethyl orthosilicate was added dropwise with stirring, and the reaction temperature was controlled at 45 - 50 °C for 1 h; after cooling to room temperature, a modified silica sol was obtained.

[0082] Among them, the mass ratio of 3-aminopropyltriethoxysilane to tetraethyl orthosilicate was 5:1. In the mixed solution, the addition amount of 3-aminopropyltriethoxysilane was 14 wt%.

[0083] Comparative Example 6

[0084] A method for preparing a silica sol shell mold, which is different from the method of Example 1 in that:

[0085] (1) Preparation of modified silica sol:

[0086] 3-aminopropyltriethoxysilane and water were stirred and mixed at 30 - 35 °C for 30 min to obtain a mixed solution; then tetraethyl orthosilicate was added dropwise with stirring, and the reaction temperature was controlled at 45 - 50 °C for 1 h; after cooling to room temperature, a modified silica sol was obtained.

[0087] Among them, the mass ratio of 3-aminopropyltriethoxysilane to tetraethyl orthosilicate was 1:1. In the mixed solution, the addition amount of 3-aminopropyltriethoxysilane was 14 wt%.

[0088] Test 1:

[0089] In order to explore the influence of the strengthening agent on the performance of the silica sol shell mold, Example 1 and Comparative Examples 1 - 3 were compared. The solidification time of each shell layer under different methods was explored. The results are shown in Table 1.

[0090] Table 1 Influence of the strengthening agent on the solidification time

[0091] Surface layer Transition layer Reinforced backing layer I Reinforced backing layer II Grouting layer Example 1 4h 2.5h 2h 2h 0.5h Comparative example 1 4h 3h 2h 2h 0.5h Comparative example 2 6h 5h 3h 3h 2h Comparative example 3 6h 6h 4h 3h 2h

[0092] Through the comparison of the results in Table 1, it was found that in Comparative Examples 2 and 3, due to the absence of nano-silica, the solidification time of each shell layer increased significantly. This is mainly because the average particle size of nano-silica is 50 nm, and the particle size is very small. By adding an appropriate amount of nano-silica, the viscosity of the silica sol can be increased, which plays an auxiliary role in promoting the coagulation of the silica sol.

[0093] Explore the influence of the strengthening agent on the strength of the silica sol shell mold. Specimens were prepared according to the high-temperature bending strength test method for investment casting shell molds of JBT2980.2 - 1999, and the bending strength at 980 °C was tested. The results are shown in Figure 1 . Figure 1 It is a bar chart of the influence of different strengthening agents on the strength of the silica sol shell mold.

[0094] From Figure 1 By comparing the results, it is found that Comparative Example 1 and Comparative Example 3 showed relatively weak high-temperature strength due to the absence of nano-boron oxide. The high-temperature strength of the silica sol shell prepared in Example 1 reached 6.75 MPa. This further verified that nano-boron oxide can assist in improving the strength of the shell.

[0095] Test 2:

[0096] In order to explore the influence of the refractory powder of the back layer shell on the strength of the silica sol shell. Specimens were prepared according to the test method for high-temperature bending strength of investment casting shells in JBT 2980.2-1999, and the bending strength at 980 °C was tested. The results are shown in Figure 2 . Figure 2 It is a column chart showing the influence of different refractory powders in the back layer shell on the strength of the silica sol shell.

[0097] From Figure 2 By comparing the results, it is found that compared with Comparative Example 4, the silica sol shell strengths of Example 1 and Example 2 are relatively large. This is mainly because kaolin powder / zircon sand or mullite powder / zircon sand is used in the back layer shell layer. By adding an appropriate amount of alumina therein, the viscosity of the back layer slurry at high temperature can be increased, and it can cooperate with the strengthening agent to play a role in strengthening the back layer. In Comparative Example 4, since alumina powder is directly used as the refractory powder in the back layer shell layer, the introduction of too much alumina is prone to high-temperature fracture, increasing the high-temperature deformation amount and reducing the high-temperature strength.

[0098] Test 3:

[0099] In order to explore the influence of the amount of silane coupling agent on the drying time. Example 1 was compared with Comparative Examples 5 to 6. The results are shown in Table 2.

[0100] Table 2 Influence of the amount of silane coupling agent on the curing time

[0101] Surface layer Transition layer Reinforced backing layer I Reinforced backing layer II Grouting layer Example 1 4h 2.5h 2h 2h 0.5h Comparative example 5 4h 4h 3h 2.5h 0.8h Comparative example 6 4h 3h 2h 3h 0.5h

[0102] By observing the curing process and combining the results in Table 2, it can be seen that in Comparative Example 5, the excessive silane coupling agent easily promotes the agglomeration of the generated nano-silica particles, affecting the surface quality of the shell. Moreover, the excessive silane coupling agent will also cause the coating to be too thick or uneven, affecting the drying time and resulting in an extended drying time. In Comparative Example 6, when the amount of silane coupling agent is too small, the catalytic and graft modification effects cannot be fully exerted, resulting in a decrease in the stability of the modified silica sol, thus affecting the leveling and coating properties of the modified silica sol, leading to uneven coating phenomena, and further resulting in incomplete drying or uneven drying speed of the shell layer, ultimately affecting the surface quality of the silica sol shell. This shows that an appropriate amount of silane coupling agent helps to shorten the drying and curing time and improve the surface quality of the shell.

[0103] In addition, preparing a silica sol shell mold by traditional processes often requires preparing 7 shell layers to meet the process requirements. The curing times required for preparing 7 shell layers are usually as follows: the first layer (surface layer) takes 5 - 6 h, the second layer (surface layer) takes 18 h, the third layer (reinforcing layer) takes 2 h, and the fourth to seventh layers (reinforcing layers) take 2 - 3 h (Shaw, Research on Silica Sol Shell Mold Process). This further verifies that in the embodiments of the present invention, by modifying the silica sol and adding a strengthening agent and coordinating with other components, while reducing the thickness of the shell mold layer, the requirements for industrial production are met, the efficiency of preparing the shell mold is improved, and the cost is reduced.

[0104] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for rapidly preparing a silica sol shell mold, characterized in that, It includes the following steps: React tetraethyl orthosilicate and a silane coupling agent solution to prepare a modified silica sol grafted with a silane coupling agent; then stir and mix refractory powder, the modified silica sol and a strengthening agent to obtain a slurry; the strengthening agent is a mixture of nano-silica and nano-boron oxide with a mass ratio of 1:1; the silane coupling agent is 3-aminopropyltriethoxysilane; the mass ratio of tetraethyl orthosilicate to the silane coupling agent is 2-3:1; Apply the slurry and sprinkle sand on the surface of the expendable pattern in sequence to form multiple shell layers and obtain a silica sol shell blank; after demolding and sintering, obtain a silica sol shell; The slurry is prepared from the following raw materials by weight percentage: 20%-45% of the modified silica sol, 50%-78% of the refractory powder, 2%-5% of the strengthening agent, with a total of 100%.

2. The method for rapidly preparing a silica sol shell according to claim 1, wherein The specific process for preparing the silica sol shell blank is as follows: Immerse the expendable pattern in the surface layer slurry, sprinkle the surface layer sand after evenly applying it, and dry to obtain the surface layer shell; Then immerse it in the transition layer slurry, sprinkle the transition layer sand after evenly applying it, and dry to obtain the transition layer shell; Then immerse it in the backing layer slurry, sprinkle the backing layer sand after evenly applying it, and dry to obtain the backing layer shell; After that, immerse it in the sealant layer slurry, sprinkle the sealant layer sand after evenly applying it, and dry to obtain the silica sol shell blank.

3. The method for rapidly preparing a silica sol shell according to claim 2, characterized in that, The refractory powder of the surface layer slurry is zirconia powder; the refractory powder of the transition layer slurry is alumina powder; the refractory powder of the backing layer slurry is at least one of kaolinite powder, mullite powder, and zircon powder; the refractory powder of the sealant layer slurry is the same as that of the backing layer slurry.

4. The method for rapidly preparing a silica sol shell according to claim 2, wherein The material of the sand for each layer of the shell is the same as that of the refractory powder of its corresponding shell layer.

5. The method for rapidly preparing a silica sol shell mold according to claim 1, characterized in that, The silane coupling agent solution is obtained by mixing a silane coupling agent and water; the addition amount of the silane coupling agent is 14wt%-20wt%.

6. The method for rapidly preparing a silica sol shell according to claim 1, wherein The reaction temperature for preparing the modified silica sol grafted with a silane coupling agent is 30-50°C.

7. The method for rapidly preparing a silica sol shell according to claim 1, wherein, The average particle size of nano-silica and nano-boron oxide is 50nm, and the purity is 99.9%.

8. The method for rapidly preparing a silica sol shell according to claim 1, characterized in that, The expendable pattern is a wax film; the demolding temperature is 500-600°C; the sintering temperature is 1050-1150°C.

Images