A surface layer slurry, a silica sol shell mold and a preparation method thereof

Abstract

The present invention relates to the field of silica sol shells. In order to solve the problem that the raw material cost required for the existing surface slurry to achieve a high powder-to-material ratio is high, a surface slurry for preparing a silica sol shell is provided, which comprises, by weight, 8-12 parts of silica sol, 20-25 parts of angular quartz powder, and 5-8 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 23wt%-27wt%, the particle size of the angular quartz powder is 180-200 mesh, and the particle size of the spherical zircon powder is 270-350 mesh. The present invention reduces the amount of zircon powder while ensuring the coating performance and surface quality of the surface slurry, improving the maximum thickness that can be achieved in the surface layer, and significantly reducing the cost by reducing the concentration of silica sol, compounding and grading of quartz powder and zircon powder, and selecting the morphology.

Description

Technical Field

[0001] The present invention relates to the field of silica sol shell molds, and more particularly, to a surface layer slurry, a silica sol shell mold and a preparation method thereof. Background Art

[0002] Silica sol shell molds are high-performance shell mold materials widely used in the field of precision casting. It is composed of refractory materials (such as quartz powder, alumina powder, etc.) and silica sol (a silicate solution), and is prepared by a multi-layer coating and roasting process. Silica sol shell molds have high strength, high density and good surface finish, and can meet the requirements of high-precision castings. At present, zircon powder is often used as the refractory material for silica sol shell molds with high performance requirements, but the cost of zircon powder is relatively high, and it is difficult for quartz powder to reach a high powder ratio. Therefore, there is an urgent need for a surface layer slurry that uses quartz powder as the main refractory material and can ensure a high powder ratio of the slurry. Summary of the Invention

[0003] The purpose of the present invention is to provide a surface layer slurry for preparing a silica sol shell mold, so as to solve the problem of high raw material cost required for the existing surface layer slurry to reach a high powder ratio.

[0004] The purpose of the present invention is also to provide a preparation method of a silica sol shell mold, which can improve the air permeability of the surface layer shell mold and the bonding degree between the surface layer and the back layer.

[0005] The purpose of the present invention is also to provide a silica sol shell mold with high strength and high refractoriness using quartz powder as the main refractory material.

[0006] The embodiments of the present invention are achieved by the following technical solutions:

[0007] A surface layer slurry for preparing a silica sol shell mold, in parts by weight, includes: 8-12 parts of silica sol, 20-25 parts of angular quartz powder, and 5-8 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 23wt%-27wt%, the particle size of the angular quartz powder is 180-200 mesh, and the particle size of the spherical zircon powder is 270-350 mesh.

[0008] At present, in the investment casting industry, due to environmental protection issues, the water glass process is facing the situation of being phased out, and is replaced by the silica sol - quartz sand, mullite sand composite shell-making process. The surface layer of this process usually uses silica sol - quartz powder slurry and mullite sand for sanding.

[0009] The silica sol quartz sand shell-making process is mainly used to manufacture metal parts. This process mixes quartz sand with silica sol to form a refractory material coating, and then makes the outer shell (shell mold) of the casting model through a series of steps. Finally, the molten metal is poured into the shell mold and cooled and solidified to obtain the required casting. The main steps of the current silica sol quartz sand shell-making process are as follows:

[0010] Pattern preparation: First, prepare the pattern according to the design of the required casting. The pattern is usually made of materials such as wood, plastic, metal, or wax.

[0011] Coating application: Apply a layer of high-temperature-resistant coating evenly on the surface of the pattern. This step is to improve the surface quality and refractory performance of the shell mold.

[0012] Impregnation with silica sol - quartz sand mortar: Immerse the pattern with the applied coating into the slurry, allowing it to fully adsorb the slurry to form a binder layer.

[0013] Sand sprinkling: After taking out the pattern from the slurry solution, immediately sprinkle a layer of mullite sand on its surface. Mullite sand, as a refractory material, can withstand high temperatures without undergoing chemical changes.

[0014] Drying: The pattern after sand sprinkling needs to be placed in a well-ventilated environment for natural drying, or put into an oven for heating and drying to ensure that the silica sol is completely cured and the refractory aggregate adheres firmly to the surface of the pattern.

[0015] Repeated impregnation and sand sprinkling: To increase the thickness and strength of the shell mold, the above steps of impregnating the slurry and sand sprinkling may need to be repeated multiple times, and drying treatment should be carried out after each sand sprinkling.

[0016] Demolding: When the shell mold reaches sufficient thickness and strength, the internal pattern can be removed, leaving a hollow shell mold.

[0017] Baking: The shell mold needs to be baked at high temperature to further improve its strength and refractory property, and at the same time, any residual moisture or organic substances in the shell mold can be removed.

[0018] Pouring: Finally, pour molten metal into the shell mold. After it cools and solidifies, break the shell mold to obtain the required metal casting.

[0019] For the silica sol shell-making process, to ensure good surface quality of the casting, the surface layer slurry must be able to evenly cover the surface of the wax pattern, and at the same time, it needs to have sufficient coating thickness so that the sand grains cannot penetrate the coating. Therefore, two important parameters of the surface layer slurry need to be controlled: slurry viscosity (η) and powder-liquid ratio (n).

[0020] Slurry viscosity is the thickness of the slurry. If it is too thick, it will affect the coating of the mold assembly; if it is too thin, the required coating thickness cannot be achieved. In principle, without affecting the coating, the maximum thickness should be maintained as much as possible. When the slurry is measured with a standard flow cup and η is more than 40 seconds, the coating effect will be affected. The powder-liquid ratio refers to the ratio of the powder to the liquid in the slurry. The larger the powder-liquid ratio, the greater the coating thickness, the smaller the possibility of the sand sprinkling penetrating the coating, and the better or more stable the surface quality of the casting.

[0021] For zircon powder coatings, on the premise of ensuring that the slurry viscosity does not affect the coating application, the powder-liquid ratio can easily reach above 3.0, and the coating thickness can also reach above 0.08 mm. Therefore, both the powder-liquid ratio and the coating thickness are relatively ideal. However, for quartz powder coatings, it is very difficult for the powder-liquid ratio to exceed 1.8. If it is higher, the slurry will become viscous, seriously affecting the coating application, and the coating thickness is also difficult to reach 0.06 mm. There may be a phenomenon of sand scattering and piercing through the coating during the production process. Therefore, it is difficult to achieve an ideal surface quality of the casting.

[0022] Although the performance of zircon powder coatings is more excellent, the cost of zircon powder is much higher than that of quartz powder. The price of better-quality quartz powder is about 1000 - 2000 yuan per ton, while the price of zircon powder per ton is generally above 10,000 yuan. Therefore, the applicant hopes to make the performance of quartz powder coatings reach or approach that of zircon powder coatings through process improvement, thereby significantly reducing the production cost. The applicant considered whether the dosage of zircon powder could be significantly reduced through the compounding of the two, reducing the economic cost and making the coating performance applicable to most castings. Since spherical quartz powder has a higher bulk density, better dispersibility and fluidity, it can reduce the system viscosity and reduce powder agglomeration. Therefore, the applicant initially compounded spherical quartz powder and zircon powder. However, it was found that when the proportion of zircon powder in the powder was less than 50%, the powder-liquid ratio exceeding 2.0 would affect the coating application. Thus, one of the core concepts of the present invention is how to further reduce the proportion of zircon powder without affecting the coating application.

[0023] Based on the commonly used 830 silica sol in the existing process, the applicant added distilled water to reduce its overall viscosity, so that the dosage of powder can be increased under the condition of a certain final viscosity. However, the reduction of the bonding performance will affect the strength of the mold shell. Therefore, in this case, the silica content in the silica sol is not limited to be too low.

[0024] In order to further increase the bonding performance, angular quartz powder and spherical zircon powder are compounded. The angular quartz powder has an irregular shape and a larger contact area with the binder, which can increase the bonding area between the angular quartz powder and the binder. However, the fluidity of the angular quartz powder is lower than that of the spherical quartz powder, and the fluidity will affect the powder-liquid ratio that this case wants to increase. Therefore, this case increases the particle size of the angular quartz powder and increases the gaps between the connected angular quartz powders, thereby reducing the mutual friction and obstruction between the quartz powders and reducing the fluidity. At the same time, using finer spherical zircon powder to fill the gaps can not only increase the density of the coating, thereby increasing its strength, but also further reduce the mutual obstruction and aggregation between the quartz powders, and increase fluidity and dispersibility. In addition, the irregular quartz powder is more in contact with the spherical zircon powder, and the contact between it and the spherical zircon powder is mainly point contact, so the use of spherical zircon powder will further increase the fluidity of the slurry. When the casting has high requirements for surface quality, the particle size of the powder in the surface slurry should not be too large, so the use of finer zircon powder can also improve the surface quality of the casting.

[0025] In theory, the above purpose can also be achieved by using angular zircon powder and spherical quartz powder, but the applicant found in the test process that when using angular zircon powder and spherical quartz powder, the powder-liquid ratio of the slurry is lower than the above solution at the same viscosity. The applicant guesses that one of the reasons is that this case hopes to increase the fluidity of the system by reducing the viscosity of the silica sol, but in order to compensate for the reduction in bonding performance, angular powder is used, and angular powder will essentially increase the viscosity of the system. Therefore, it is necessary to ensure that the fluidity of the slurry with the same powder-liquid ratio is increased after the effects of the two are offset. The change curve of the influence of the two on fluidity is irregular, so it is necessary to find a suitable balance point to increase the final fluidity. At this time, the ratio of angular powder to spherical powder and particle size grading are particularly important, otherwise the fluidity of the slurry may be reduced. When angular zircon powder and spherical quartz powder are used, the increase in fluidity after the effects of the above two powders offset each other is lower than that when angular stone powder and spherical zircon powder are used. Therefore, the applicant found during the test that it is difficult to meet the needs of fluidity and adhesion at the same time. When the fluidity meets the needs, the bonding degree between the powders is low due to the small amount of angular powder.

[0026] A method for preparing a silica sol shell, comprising:

[0027] S100, immersing the pattern into the surface layer slurry for hanging the pattern, and then sanding and drying to obtain the surface layer pattern; the surface layer slurry adopts the surface layer slurry;

[0028] S200, hanging the surface layer pattern in the back layer slurry, and then sanding and drying, after repeating for multiple times, to obtain a back layer shell mold;

[0029] S300. Hang the back shell mold in the sealant slurry, demold after drying to obtain a preliminary shell mold;

[0030] S400. Bake the preliminary shell mold to obtain a silica sol shell mold;

[0031] Use mullite sand with a mesh size of 80 - 100 for the surface layer sanding.

[0032] The pattern can be a wax pattern. Although a large amount of quartz powder is used in the surface layer slurry of the present invention, the thickness of the surface layer can still reach more than 0.075 mm. Therefore, during sanding, the phenomenon of coating penetration is not likely to occur. Furthermore, the particle size of the mullite sand can be appropriately increased, the gap between the mullite sands can be increased, facilitating the penetration of the back layer slurry into the surface layer coating, increasing the bonding degree between the two, reducing the possibility of cracking during baking, and improving the mechanical properties and refractory properties of the shell mold.

[0033] Preferably, the S200 includes:

[0034] D100. Hang the surface layer pattern in the first back layer slurry, then perform sanding and drying to obtain a first back layer pattern; the first back layer slurry includes: 10 - 15 parts of 830 silica sol and 18 - 24 parts of spherical quartz powder; the particle size of the spherical quartz powder is 200 - 230 mesh, and 120 - 140 mesh mullite sand is used for sanding;

[0035] D200. Hang the first back layer pattern in the second back layer slurry, then perform sanding and drying to obtain a back shell mold; the second back layer slurry includes: 10 - 15 parts of 1430 silica sol and 13 - 17 parts of spherical quartz powder; the particle size of the spherical quartz powder is 150 - 180 mesh, and 40 - 60 mesh mullite sand is used for sanding.

[0036] 830 silica sol means that the particle size of the colloidal particles in the silica sol is 8 nm and the mass concentration is 30%. Since the coating formed by the first back layer slurry is used to connect the surface layer coating and the coating formed by the second back layer slurry, its powder ratio is lower than that of the surface layer slurry, which is convenient for the first back layer slurry to migrate to the surface layer coating. One of the purposes of selecting spherical quartz powder instead of zircon powder for the first back layer slurry is to reduce the thickness of the coating formed by the first back layer slurry. When sandblasting, part of the mullite sand with relatively smaller particle size penetrates through the first back layer, and the end extends into the sandblasted layer of the surface layer, thereby improving the bonding degree of the two coatings. Normally, in order to ensure the air permeability of the mold shell, the particle size of the back layer sandblasting is higher than that of the surface layer. The reason why the particle size of the sandblasting in the first back layer can be smaller than that of the surface layer in this case is that the particle size of the mullite sand used for the surface layer sandblasting is higher than that of the surface layer of the conventional quartz powder slurry. Therefore, when sandblasting the first back layer, although the particle size seems smaller, the difference in air permeability compared with the conventional back layer is not significant. In addition, since the particle size of the mullite sand used for the surface layer sandblasting is relatively large, the density is reduced. When sandblasting the first back layer, the interlocking of the two sandblasted layers can improve the density and increase the strength of the mold shell.

[0037] The coating formed by the second back layer slurry is used to connect the first back layer and the sealant layer. Its powder ratio is lower than that of the first back layer slurry. At the same time, in order to ensure air permeability, reduce the drying time, facilitate subsequent demolding, and improve the subsequent casting effect, both the powder particle size and the sandblasting particle size are increased. In order to improve the strength of the mold shell, the second back layer slurry can be applied multiple times by hanging.

[0038] Preferably, the spherical quartz powder used in the first back layer slurry is modified quartz powder. The preparation steps of the modified quartz powder include: adding spherical quartz powder into a polysaccharide solution and obtaining the modified quartz powder by spray drying.

[0039] Coating polysaccharide on the surface of quartz powder can improve its dispersibility, so that the coating of the first back layer slurry can better combine with the surface layer and improve the structural strength of the mold shell. In addition, the decomposition of the coating layer during the roasting process can also increase the air permeability of the coating formed by the first back layer slurry and reduce the influence of the small particle size of the first back layer sandblasting on the air permeability. One of the purposes of choosing physical coating instead of chemical coating is to reduce the decomposition problem of the coating layer.

[0040] Preferably, the mass concentration of the polysaccharide solution is 15%-20%, the polysaccharide includes one or more of chitosan, sodium alginate, cellulose, and cyclodextrin, and the mass ratio of spherical quartz powder to the polysaccharide solution is 1:2-2:3.

[0041] On the premise that the quartz powder can be stably coated, it is also necessary for the quartz powder to be highly dispersed and stably suspended in the polysaccharide solution. Therefore, the mass concentration of the polysaccharide solution is limited in this case.

[0042] Preferably, the baking process in S400 includes: first heating up to 700 - 800 °C at a rate of 10 - 20 °C / min and holding for 15 - 25 min, then heating up to 950 - 1050 °C at a rate of 25 - 30 °C / min and holding for 20 - 30 min.

[0043] The main purpose of the baking process is to remove moisture, residual pattern materials and volatiles, improve the high-temperature mechanical properties of the shell mold, and enhance the air permeability and filling ability of the shell mold. During the baking process, attention should be paid to the cracking caused by the shrinkage rate differences of each layer of the shell mold, especially the relatively thinner surface layer. Therefore, it is necessary to control the initial heating rate. In this case, the powder materials of the back layer slurry are different from those of the surface layer, and the surface layer is heated first compared with the back layer, so the temperature control requirements are higher. Under normal circumstances, after the shell mold is fully heated, due to the gradual increase in the particle size of the sanding layer and the powder materials of each layer, the moisture migration direction of the surface layer tends to the sealant layer, which will increase the drying degree difference between the surface layer and the other layers, and the shrinkage difference between the layers is relatively large. However, in this case, the particle size of the powder materials of the first back layer and the particle size of the sanding layer between it and the second back layer are relatively small, which relatively increases the proportion of the surface layer moisture directly overflowing from the surface layer, increases the drying degree of the other layers, and then reduces the shrinkage difference between the surface layer and the other layers, making the surface layer not easily cracked. After holding for a period of time during the first heat preservation, the silica sol sinters to form a porous structure. At this time, the bound water in the surface layer is more likely to directly overflow from the surface layer. Therefore, it can be sintered continuously after heating up, and the strength and refractory performance of the shell mold can be increased through high-temperature sintering.

[0044] Preferably, the drying conditions in S100 are: drying temperature is 20 - 25 °C, relative humidity is 50% - 60%, and drying time is 10 - 15 h; the drying conditions in S200 are: drying temperature is 30 - 35 °C, relative humidity is 30% - 40%, and drying time is 6 - 8 h.

[0045] The density of the surface layer is relatively high, and the requirement for smoothness is also relatively high. Therefore, the drying temperature is relatively low and the relative humidity is relatively high to ensure that the drying speed of each part of the surface layer is consistent as much as possible and avoid cracking of the surface layer shell mold. Since the back layer is located in the middle of the shell mold, the requirement for smoothness is lower than that of the surface layer, so the drying temperature is relatively high and the relative humidity is relatively low. During the preparation process of the shell mold, most of the time is used for the drying of each layer of slurry. Therefore, shortening the drying time can greatly improve the process efficiency. And the drying time is closely related to the air permeability. Good air permeability is conducive to the migration of water vapor. The back layer mold shell of the present invention has good air permeability, so the drying time is relatively short, improving the process efficiency.

[0046] Preferably, the sealant slurry in S300 includes: 10 - 15 parts of 830 silica sol and 18 - 20 parts of spherical quartz powder; the particle size of the spherical quartz powder is 150 - 180 mesh.

[0047] Due to the relatively high particle size of the sand sprinkled on the second back layer, the sealant layer needs to have a certain thickness to cover the sand layer to ensure the surface strength of the shell mold.

[0048] Preferably, the drying conditions in S300 are: the drying temperature is 25 - 30 °C, the relative humidity is 40% - 45%, and the drying time is 5 - 8 h.

[0049] A silica sol shell mold prepared by the described preparation method.

[0050] The present invention has at least the following beneficial effects:

[0051] By reducing the concentration of silica sol, compounding and grading quartz powder and zircon powder, and selecting the morphology, etc., the present invention ensures the coating performance and surface quality of the surface layer slurry while reducing the amount of zircon powder used, increases the maximum thickness that can be achieved for the surface layer. Tests show that the average coating thickness can reach 0.082, and the cost is significantly reduced.

[0052] Due to the improvement of the surface layer slurry in the present invention, the sand sprinkling particle size of the surface layer can be increased, the bonding degree between the surface layer and the back layer can be increased, the possibility of cracking during roasting can be reduced, and the mechanical properties and refractory properties of the shell mold can be improved, and the air permeability of the surface layer is also better. Specific Embodiments

[0053] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0054] Embodiment 1: A surface layer slurry for preparing a silica sol shell mold, in parts by weight, includes: 10 parts of silica sol, 20 parts of angular quartz powder, and 5 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 26 wt%, the particle size of the angular quartz powder is 180 mesh, and the particle size of the spherical zircon powder is 300 mesh.

[0055] Embodiment 2: A surface layer slurry for preparing a silica sol shell mold, in parts by weight, includes: 10 parts of silica sol, 25 parts of angular quartz powder, and 8 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 26 wt%, the particle size of the angular quartz powder is 180 mesh, and the particle size of the spherical zircon powder is 300 mesh.

[0056] Embodiment 3: A surface layer slurry for preparing a silica sol shell mold, in parts by weight, includes: 10 parts of silica sol, 23 parts of angular quartz powder, and 7 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 26 wt%, the particle size of the angular quartz powder is 180 mesh, and the particle size of the spherical zircon powder is 300 mesh.

[0057] Example 4: A surface layer slurry for preparing a silica sol shell mold, calculated by weight, includes: 10 parts of silica sol, 23 parts of angular quartz powder, and 7 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 26 wt%, the particle size of the angular quartz powder is 200 mesh, and the particle size of the spherical zircon powder is 300 mesh.

[0058] Example 5: A surface layer slurry for preparing a silica sol shell mold, calculated by weight, includes: 10 parts of silica sol, 23 parts of angular quartz powder, and 7 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 26 wt%, the particle size of the angular quartz powder is 200 mesh, and the particle size of the spherical zircon powder is 350 mesh.

[0059] Example 6: A surface layer slurry for preparing a silica sol shell mold, calculated by weight, includes: 10 parts of silica sol, 23 parts of angular quartz powder, and 7 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 26 wt%, the particle size of the angular quartz powder is 200 mesh, and the particle size of the spherical zircon powder is 270 mesh.

[0060] Comparative Example 1: A surface layer slurry for preparing a silica sol shell mold, calculated by weight, includes: 10 parts of silica sol, 23 parts of angular quartz powder, and 7 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 30 wt%, the particle size of the angular quartz powder is 200 mesh, and the particle size of the spherical zircon powder is 300 mesh.

[0061] Comparative Example 2: A surface layer slurry for preparing a silica sol shell mold, calculated by weight, includes: 10 parts of silica sol, 23 parts of spherical quartz powder, and 7 parts of angular zircon powder; the content of silicon dioxide in the silica sol is 26 wt%, the particle size of the angular zircon powder is 200 mesh, and the particle size of the spherical quartz powder is 300 mesh.

[0062] Comparative Example 3: A surface layer slurry for preparing a silica sol shell mold, calculated by weight, includes: 10 parts of silica sol and 30 parts of spherical quartz powder; the content of silicon dioxide in the silica sol is 26 wt%, and the particle size of the spherical quartz powder is 300 mesh.

[0063] Comparative Example 4: A surface layer slurry for preparing a silica sol shell mold, calculated by weight, includes: 10 parts of silica sol and 30 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 26 wt%, and the particle size of the spherical zircon powder is 300 mesh.

[0064] Experiment 1: Prepare the surface layer slurries according to the formulations of Examples 1 - 6 and Comparative Examples 1 - 4, measure the viscosities of each surface layer slurry by a standard flow cup, use the time for the liquid to flow out of the flow cup to characterize the slurry viscosity, the longer the time, the higher the viscosity. Take the average value after measuring five times for each group of experiments. The specific test results are shown in Table 1.

[0065] Table 1

[0066]

[0067] From the test results of Examples 1 - 6, it can be seen that without affecting the viscosity of the surface layer slurry, the powder ratio of the surface layer slurry of the present invention can reach 3.3, which is much higher than that of pure quartz powder silica sol, and can greatly reduce the process cost.

[0068] From the comparison between Comparative Example 1 and Example 4, it can be seen that when using 830 silica sol without dilution with distilled water to reduce the concentration, the viscosity of the system will increase significantly.

[0069] From the comparison between Comparative Example 2 and Example 4, it can be seen that when using a compound of angular zircon powder and spherical quartz powder, with the powder ratio unchanged, the viscosity of the system increases significantly.

[0070] From the comparison between Comparative Example 3 and Example 4, it can be seen that when only using spherical quartz powder as the refractory material, even when the content ratio of silicon dioxide in the silica sol is reduced and the powder ratio reaches 3.0, the viscosity of the slurry will seriously affect the coating.

[0071] From the comparison between Comparative Example 4 and Example 4, it can be seen that although the present invention uses quartz powder as the main refractory material, its performance has approached that of pure zircon powder slurry. The cost is equivalent to a 60 - 70% reduction in pure zircon powder slurry.

[0072] Example 7: A preparation method of a silica sol shell mold, comprising:

[0073] S100. Immerse the pattern in the surface layer slurry described in Example 4 for mold hanging, then perform sand scattering and drying to obtain a surface layer pattern; Drying conditions: drying temperature is 20°C, relative humidity is 60%, and drying time is 15 h; 100 - mesh mullite sand is used for sand scattering on the surface layer.

[0074] S200. Immerse the surface layer pattern in the back layer slurry for mold hanging, then perform sand scattering and drying. After repeating multiple times, obtain a back layer shell mold; Drying conditions: drying temperature is 32°C, relative humidity is 35%, and drying time is 7 h;

[0075] The S200 includes:

[0076] D100. Immerse the surface layer pattern in the first back layer slurry for mold hanging, then perform sand scattering and drying to obtain a first back layer pattern; The first back layer slurry includes: 15 parts of 830 silica sol and 24 parts of spherical quartz powder; The particle size of the spherical quartz powder is 220 mesh, and 120 - mesh mullite sand is used for sand scattering;

[0077] D200. Hang the first back layer pattern in the second back layer slurry, then perform sand sprinkling and drying to obtain a back layer shell mold; the second back layer slurry includes: 12 parts of 1430 silica sol and 17 parts of spherical quartz powder; the particle size of the spherical quartz powder is 160 mesh, and 40-mesh mullite sand is used for sand sprinkling.

[0078] S300. Hang the back layer shell mold in the sealant slurry, and demold after drying to obtain a preliminary shell mold; the sealant slurry includes: 15 parts of 830 silica sol and 18 parts of spherical quartz powder; the particle size of the spherical quartz powder is 160 mesh. Drying conditions: drying temperature is 30 °C, relative humidity is 45%, and drying time is 6 h.

[0079] S400. The preliminary shell mold is obtained by a baking process to obtain a silica sol shell mold; the baking process includes: first heating at a rate of 15 °C / min to 800 °C and holding for 20 min, then heating at a rate of 28 °C / min to 1050 °C and holding for 30 min.

[0080] Example 8: A method for preparing a silica sol shell mold, including:

[0081] S100. Immerse the pattern in the surface layer slurry described in Example 4 for mold hanging, then perform sand sprinkling and drying to obtain a surface layer pattern; drying conditions: drying temperature is 20 °C, relative humidity is 60%, and drying time is 15 h; 100-mesh mullite sand is used for sand sprinkling on the surface layer.

[0082] S200. Hang the surface layer pattern in the back layer slurry, then perform sand sprinkling and drying, and repeat multiple times to obtain a back layer shell mold; drying conditions: drying temperature is 32 °C, relative humidity is 35%, and drying time is 7 h;

[0083] S200 includes:

[0084] D100. Hang the surface layer pattern in the first back layer slurry, then perform sand sprinkling and drying to obtain a first back layer pattern; the first back layer slurry includes: 15 parts of 830 silica sol and 24 parts of spherical quartz powder; the particle size of the spherical quartz powder is 220 mesh, and 140-mesh mullite sand is used for sand sprinkling;

[0085] D200. Hang the first back layer pattern in the second back layer slurry, then perform sand sprinkling and drying to obtain a back layer shell mold; the second back layer slurry includes: 12 parts of 1430 silica sol and 17 parts of spherical quartz powder; the particle size of the spherical quartz powder is 160 mesh, and 40-mesh mullite sand is used for sand sprinkling.

[0086] S300. Hang the back-layer shell mold in the sealant slurry, demold after drying to obtain a preliminary shell mold. The sealant slurry includes: 15 parts of 830 silica sol and 18 parts of spherical quartz powder. The particle size of the spherical quartz powder is 160 mesh. Drying conditions: drying temperature is 30°C, relative humidity is 45%, and drying time is 6h.

[0087] S400. The preliminary shell mold is obtained by a baking process to obtain a silica sol shell mold. The baking process includes: first heating at a rate of 15°C / min to 800°C and holding for 20 min, then heating at a rate of 28°C / min to 1050°C and holding for 30 min.

[0088] Example 9: A method for preparing a silica sol shell mold, including:

[0089] S100. Immerse the pattern in the surface layer slurry described in Example 4 for mold hanging, then perform sand spreading and drying to obtain a surface layer pattern. Drying conditions: drying temperature is 20°C, relative humidity is 60%, and drying time is 15h. The surface layer is sand-spread with 100-mesh mullite sand.

[0090] S200. Hang the surface layer pattern in the back layer slurry, then perform sand spreading and drying. After repeating multiple times, a back layer shell mold is obtained. Drying conditions: drying temperature is 32°C, relative humidity is 35%, and drying time is 7h.

[0091] S200 includes:

[0092] D100. Hang the surface layer pattern in the first back layer slurry, then perform sand spreading and drying to obtain a first back layer pattern. The first back layer slurry includes: 15 parts of 830 silica sol and 24 parts of spherical quartz powder. The particle size of the spherical quartz powder is 220 mesh, and the sand spreading uses 130-mesh mullite sand.

[0093] D200. Hang the first back layer pattern in the second back layer slurry, then perform sand spreading and drying to obtain a back layer shell mold. The second back layer slurry includes: 12 parts of 1430 silica sol and 17 parts of spherical quartz powder. The particle size of the spherical quartz powder is 160 mesh, and the sand spreading uses 40-mesh mullite sand.

[0094] S300. Hang the back layer shell mold in the sealant slurry, demold after drying to obtain a preliminary shell mold. The sealant slurry includes: 15 parts of 830 silica sol and 18 parts of spherical quartz powder. The particle size of the spherical quartz powder is 160 mesh. Drying conditions: drying temperature is 30°C, relative humidity is 45%, and drying time is 6h.

[0095] S400. The as-prepared shell mold is calcined to obtain a silica sol shell mold. The calcination process includes: first heating to 800 °C at a rate of 15 °C / min and holding for 20 min, then heating to 1050 °C at a rate of 28 °C / min and holding for 30 min.

[0096] Example 10: A method for preparing a silica sol shell mold, comprising:

[0097] S100. Immerse the pattern in the surface layer slurry described in Example 4 for shell building, then perform sand spreading and drying to obtain a surface layer pattern. Drying conditions: drying temperature is 20 °C, relative humidity is 60%, and drying time is 15 h. The surface layer is sand spread with 100-mesh mullite sand.

[0098] S200. Immerse the surface layer pattern in the back layer slurry for shell building, then perform sand spreading and drying. After repeating multiple times, a back layer shell mold is obtained. Drying conditions: drying temperature is 32 °C, relative humidity is 35%, and drying time is 7 h.

[0099] S200 includes:

[0100] D100. Immerse the surface layer pattern in the first back layer slurry for shell building, then perform sand spreading and drying to obtain a first back layer pattern. The first back layer slurry includes: 15 parts of 830 silica sol and 24 parts of spherical quartz powder. The particle size of the spherical quartz powder is 220 mesh, and the sand spreading uses 130-mesh mullite sand.

[0101] D200. Immerse the first back layer pattern in the second back layer slurry for shell building, then perform sand spreading and drying to obtain a back layer shell mold. The second back layer slurry includes: 12 parts of 1430 silica sol and 17 parts of spherical quartz powder. The particle size of the spherical quartz powder is 160 mesh, and the sand spreading uses 40-mesh mullite sand.

[0102] S300. Immerse the back layer shell mold in the sealant slurry for shell building, and after drying, demold to obtain an as-prepared shell mold. The sealant slurry includes: 15 parts of 830 silica sol and 18 parts of spherical quartz powder. The particle size of the spherical quartz powder is 160 mesh. Drying conditions: drying temperature is 30 °C, relative humidity is 45%, and drying time is 6 h.

[0103] S400. The as-prepared shell mold is calcined to obtain a silica sol shell mold. The calcination process includes: first heating to 800 °C at a rate of 20 °C / min and holding for 20 min, then heating to 1050 °C at a rate of 28 °C / min and holding for 30 min.

[0104] Example 11: A method for preparing a silica sol shell mold, comprising:

[0105] S100. Immerse the pattern into the surface layer slurry described in Example 4 for pattern hanging, then perform sand spreading and drying to obtain the surface layer pattern; Drying conditions: drying temperature is 20 °C, relative humidity is 60%, and drying time is 15 h; For the surface layer, use 100-mesh mullite sand for sand spreading.

[0106] S200. Immerse the surface layer pattern into the backing layer slurry for pattern hanging, then perform sand spreading and drying. After repeating multiple times, obtain the backing layer shell mold; Drying conditions: drying temperature is 32 °C, relative humidity is 35%, and drying time is 7 h;

[0107] S200 includes:

[0108] D100. Immerse the surface layer pattern into the first backing layer slurry for pattern hanging, then perform sand spreading and drying to obtain the first backing layer pattern; The first backing layer slurry includes: 15 parts of 830 silica sol and 24 parts of spherical quartz powder; The particle size of the spherical quartz powder is 220 mesh, and 130-mesh mullite sand is used for sand spreading;

[0109] D200. Immerse the first backing layer pattern into the second backing layer slurry for pattern hanging, then perform sand spreading and drying to obtain the backing layer shell mold; The second backing layer slurry includes: 12 parts of 1430 silica sol and 17 parts of spherical quartz powder; The particle size of the spherical quartz powder is 160 mesh, and 40-mesh mullite sand is used for sand spreading.

[0110] S300. Immerse the backing layer shell mold into the sealant slurry for pattern hanging, and after drying, demold to obtain the preliminary shell mold; The sealant slurry includes: 15 parts of 830 silica sol and 18 parts of spherical quartz powder; The particle size of the spherical quartz powder is 160 mesh. Drying conditions: drying temperature is 30 °C, relative humidity is 45%, and drying time is 6 h.

[0111] S400. The preliminary shell mold is made into a silica sol shell mold through a baking process; The baking process includes: first heating to 800 °C at a rate of 10 °C / min and holding for 20 min, then heating to 1050 °C at a rate of 28 °C / min and holding for 30 min.

[0112] Example 12: A method for preparing a silica sol shell mold, including:

[0113] S100. Immerse the pattern into the surface layer slurry described in Example 4 for pattern hanging, then perform sand spreading and drying to obtain the surface layer pattern; Drying conditions: drying temperature is 20 °C, relative humidity is 60%, and drying time is 15 h; For the surface layer, use 100-mesh mullite sand for sand spreading.

[0114] S200. Immerse the surface layer pattern into the backing layer slurry for pattern hanging, then perform sand spreading and drying. After repeating multiple times, obtain the backing layer shell mold; Drying conditions: drying temperature is 32 °C, relative humidity is 35%, and drying time is 7 h;

[0115] The S200 includes:

[0116] D100: Hanging the surface layer pattern in the first back layer slurry, then performing sand scattering and drying to obtain the first back layer pattern; the first back layer slurry includes: 15 parts of 830 silica sol and 24 parts of spherical quartz powder; the particle size of the spherical quartz powder is 220 mesh, and 130-mesh mullite sand is used for sand scattering.

[0117] D200: Hanging the first back layer pattern in the second back layer slurry, then performing sand scattering and drying to obtain the back layer shell mold; the second back layer slurry includes: 12 parts of 1430 silica sol and 17 parts of spherical quartz powder; the particle size of the spherical quartz powder is 160 mesh, and 40-mesh mullite sand is used for sand scattering.

[0118] S300: Hanging the back layer shell mold in the sealant slurry, and demolding after drying to obtain the preliminary shell mold; the sealant slurry includes: 15 parts of 830 silica sol and 18 parts of spherical quartz powder; the particle size of the spherical quartz powder is 160 mesh. Drying conditions: drying temperature is 30 °C, relative humidity is 45%, and drying time is 6 h.

[0119] S400: The preliminary shell mold is made into a silica sol shell mold through a roasting process; the roasting process includes: first heating to 700 °C at a rate of 20 °C / min and holding for 20 min, then heating to 1050 °C at a rate of 28 °C / min and holding for 30 min.

[0120] Example 13: A method for preparing a silica sol shell mold, including:

[0121] S100: Immersing the pattern in the surface layer slurry described in Example 4 for hanging the mold, then performing sand scattering and drying to obtain the surface layer pattern; drying conditions: drying temperature is 20 °C, relative humidity is 60%, and drying time is 15 h; 100-mesh mullite sand is used for sand scattering on the surface layer.

[0122] S200: Hanging the surface layer pattern in the back layer slurry, then performing sand scattering and drying, and repeating multiple times to obtain the back layer shell mold; drying conditions: drying temperature is 32 °C, relative humidity is 35%, and drying time is 7 h;

[0123] The S200 includes:

[0124] D100: Hanging the surface layer pattern in the first back layer slurry, then performing sand scattering and drying to obtain the first back layer pattern; the first back layer slurry includes: 15 parts of 830 silica sol and 24 parts of spherical quartz powder; the particle size of the spherical quartz powder is 220 mesh, and 130-mesh mullite sand is used for sand scattering.

[0125] D200. Hang the first back-layer pattern in the second back-layer slurry, then perform sand sprinkling and drying to obtain a back-layer shell mold; the second back-layer slurry includes: 12 parts of 1430 silica sol and 17 parts of spherical quartz powder; the particle size of the spherical quartz powder is 160 mesh, and 40-mesh mullite sand is used for sand sprinkling.

[0126] S300. Hang the back-layer shell mold in the sealant slurry, and demold after drying to obtain a preliminary shell mold; the sealant slurry includes: 15 parts of 830 silica sol and 18 parts of spherical quartz powder; the particle size of the spherical quartz powder is 160 mesh. Drying conditions: the drying temperature is 30 °C, the relative humidity is 45%, and the drying time is 6 h.

[0127] S400. The preliminary shell mold is obtained by a baking process to obtain a silica sol shell mold; the baking process includes: first heating to 800 °C at a rate of 20 °C / min and holding for 20 min, then heating to 1050 °C at a rate of 30 °C / min and holding for 30 min.

[0128] Example 14: On the basis of Example 12, the spherical quartz powder used in the first back-layer slurry is modified quartz powder, and the preparation steps of the modified quartz powder include: adding spherical quartz powder to a polysaccharide solution, and then obtaining the modified quartz powder by spray drying. The mass concentration of the polysaccharide solution is 20%, the polysaccharide includes chitosan, and the mass ratio of the spherical quartz powder to the polysaccharide solution is 1:2.

[0129] Example 15: On the basis of Example 12, the spherical quartz powder used in the first back-layer slurry is modified quartz powder, and the preparation steps of the modified quartz powder include: adding spherical quartz powder to a polysaccharide solution, and then obtaining the modified quartz powder by spray drying. The mass concentration of the polysaccharide solution is 20%, the polysaccharide includes cyclodextrin, and the mass ratio of the spherical quartz powder to the polysaccharide solution is 1:2.

[0130] Example 16: On the basis of Example 12, the spherical quartz powder used in the first back-layer slurry is modified quartz powder, and the preparation steps of the modified quartz powder include: adding spherical quartz powder to a polysaccharide solution, and then obtaining the modified quartz powder by spray drying. The mass concentration of the polysaccharide solution is 20%, the polysaccharide includes sodium alginate, and the mass ratio of the spherical quartz powder to the polysaccharide solution is 1:2.

[0131] Example 17: On the basis of Example 12, the spherical quartz powder used in the first back-layer slurry is modified quartz powder, and the preparation steps of the modified quartz powder include: adding spherical quartz powder to a polysaccharide solution, and then obtaining the modified quartz powder by spray drying. The mass concentration of the polysaccharide solution is 20%, the polysaccharide includes cellulose, and the mass ratio of the spherical quartz powder to the polysaccharide solution is 1:2.

[0132] Comparative Example 5: Except that the grit size of the sand spraying in D100 is 70 mesh, the remaining process steps are the same as those in Example 15.

[0133] Comparative Example 6: The roasting process in S400 includes: first heating up to 800 °C at a rate of 25 °C / min and holding for 20 min, then heating up to 1050 °C at a rate of 30 °C / min and holding for 30 min. The remaining process steps are the same as those in Example 15.

[0134] Comparative Example 7: The roasting process in S400 includes: first heating up to 800 °C at a rate of 20 °C / min and holding for 20 min, then heating up to 1050 °C at a rate of 35 °C / min and holding for 30 min. The remaining process steps are the same as those in Example 15.

[0135] Comparative Example 8: The roasting process in S400 includes: first heating up to 800 °C at a rate of 20 °C / min and holding for 10 min, then heating up to 1050 °C at a rate of 30 °C / min and holding for 30 min. The remaining process steps are the same as those in Example 15.

[0136] Experiment 2: The air permeability test and high-temperature strength test were carried out on the silica sol shell molds prepared by the preparation methods of Examples 7 - 17 and Comparative Examples 5 - 8. Each group of tests was carried out five times and the average value was taken. The air permeability test was carried out according to the standard method of JB / T 4153 - 1999 "Test Method for High-temperature Air Permeability of Shell Molds". The test temperature was 950 °C, and the unit of air permeability was m 4 / (N·min). The high-temperature strength was measured according to HB5352.1 - 2004 "Test Method for the Properties of Investment Casting Shell Molds - Part 1: Determination of Bending Strength". The test temperature was 1300 °C, and the unit of high-temperature strength was MPa. The test results are shown in Table 2.

[0137] Table 2

[0138]

[0139]

[0140] From the test results of Examples 7 - 17, it can be seen that the silica sol shell molds prepared by the preparation method of the present invention have good air permeability and high-temperature strength.

[0141] From the test results of Examples 7 - 9, it can be seen that when the grit size of the sand spraying in D100 is 130 mesh, the air permeability is the best.

[0142] From the test results of Examples 9 - 11, it can be seen that during roasting, when the initial heating rate reaches 20 °C / min, the shell mold still has good high-temperature strength, and the drying time can be reduced; when the heating rate is 20 °C / min, the air permeability of the shell mold is the best. When the heating rates are 15 °C / min and 20 °C / min, the high-temperature strengths of the shell molds are comparable.

[0143] From the comparison between Example 10 and Example 12, it can be seen that when the primary heat preservation temperature is 800 °C, the air permeability of the shell mold is the best.

[0144] From the comparison between Example 10 and Example 13, it can be seen that when the secondary heating rate reaches 30 °C / min, the high-temperature strength of the shell mold will not decrease, and the drying time can be shortened.

[0145] From the comparison between Example 12 and Examples 14 - 17, it can be seen that after using modified quartz powder, the high-temperature strength of the shell mold will not be significantly reduced. At the same time, the air permeability of the shell mold can be improved, and it is best to use cyclodextrin polysaccharide solution.

[0146] From the comparison between Comparative Example 5 and Example 14, it can be seen that when the particle size of the sand sprinkled in D100 is larger than that of the surface layer according to the conventional process, under the same sintering conditions, the high-temperature strength will be significantly reduced.

[0147] From the comparison between Comparative Examples 6 - 7 and Example 14, it can be seen that during roasting, when the heating rate in the first stage and the heating rate in the second stage are too high, it will seriously affect the high-temperature strength of the shell mold.

[0148] From the comparison between Comparative Example 8 and Example 14, it can be seen that when the heat preservation time in the first stage is insufficient, both the air permeability and the high-temperature strength of the shell mold are affected.

[0149] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. 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 preparing a silica sol shell, characterized in that: include: S100, immersing the pattern into the surface layer slurry for hanging the pattern, and then sanding and drying to obtain the surface layer pattern; The surface layer is sanded with 80-100 mesh Mullite sand; The surface slurry comprises, by weight, 8-12 parts of silica sol, 20-25 parts of angular quartz powder, and 5-8 parts of spherical zircon powder; the content of silicon dioxide in the silica sol is 23wt%-27wt%, the particle size of the angular quartz powder is 180-200 mesh, and the particle size of the spherical zircon powder is 270-350 mesh; S200, the surface layer pattern is molded in the back layer slurry, and then sanded and dried, and the process is repeated for multiple times to obtain a back layer shell mold; the back layer slurry includes a first back layer slurry and a second back layer slurry, and the first back layer slurry is sanded with 120-140 mesh mullite sand; the second back layer slurry is sanded with 40-60 mesh mullite sand; S300, hanging the back layer shell mold in the sealing slurry, and demoulding after drying to obtain a primary shell mold; S400, the primary shell mold is subjected to a calcination process to obtain a silica sol shell.

2. The preparation method according to claim 1, characterized in that: The S200 includes: D100, the surface layer pattern is molded in the first back layer slurry, and then sanded and dried to obtain the first back layer pattern; the first back layer slurry comprises: 10-15 parts of 830 silica sol and 18-24 parts of spherical quartz powder; the particle size of the spherical quartz powder is 200-230 mesh; D200, the first back layer pattern is hung in the second back layer slurry, and then sanded and dried to obtain a back layer shell mold; the second back layer slurry includes: 10-15 parts of 1430 silica sol and 13-17 parts of spherical quartz powder; the particle size of the spherical quartz powder is 150-180 mesh.

3. The preparation method according to claim 2, characterized in that: The spherical quartz powder used in the first backing layer slurry is modified quartz powder. The preparation steps of the modified quartz powder include: adding the spherical quartz powder to a polysaccharide solution, and obtaining the modified quartz powder by a spray drying method.

4. The preparation method according to claim 3, characterized in that: The mass concentration of the polysaccharide solution is 15%-20%, the polysaccharide includes one or more of chitosan, sodium alginate, cellulose, and cyclodextrin, and the mass ratio of spherical quartz powder to the polysaccharide solution is 1:2-2:

3.

5. The preparation method according to claim 4, characterized in that: The calcination process in S400 includes: firstly heating to 700-800°C at a rate of 10-20°C / min and keeping the temperature for 15-25min, and then heating to 950-1050°C at a rate of 25-30°C / min and keeping the temperature for 20-30min.

6. The preparation method according to any one of claims 1 to 5, characterized in that: Drying conditions in S100: drying temperature is 20-25℃, relative humidity is 50%-60%, and drying time is 10-15h; drying conditions in S200: drying temperature is 30-35℃, relative humidity is 30%-40%, and drying time is 6-8h.

7. The preparation method according to claim 6, characterized in that: The sealing slurry in S300 includes: 10-15 parts of 830 silica sol and 18-20 parts of spherical quartz powder; the particle size of the spherical quartz powder is 150-180 meshes.

8. The preparation method according to claim 7, characterized in that: Drying conditions in S300: drying temperature is 25-30℃, relative humidity is 40%-45%, and drying time is 5-8h.

9. A silica sol shell obtained by the preparation method according to any one of claims 1 to 8.

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