High performance precision cast silica sol shell with smooth inner wall and method for making the same

Abstract

The present application belongs to the technical field of silica sol shell casting, and particularly relates to a high-performance precision casting silica sol shell with smooth inner wall and a preparation method thereof. The method specifically comprises the following steps: firstly, preparing a surface layer slurry by using graded particles; then, preparing a back layer slurry by using organic-inorganic fibers; and finally, immersing a wax mold into the surface layer slurry, and obtaining the high-performance precision casting silica sol shell with smooth inner wall after subsequent treatment. The silica sol shell prepared by the present application has high performance, and the zirconium powder, white corundum powder and silica particles are matched to fill and flatten the small concave-convex of the surface layer coating, thereby increasing the smoothness of the surface layer of the shell. The polyethylene fibers and boron nitride fibers are used in combination to improve the porous structure and heat conduction performance of the shell, and reduce the cracking and deformation of the shell during drying and curing. Meanwhile, the boron nitride fibers form a continuous fiber network structure, which can improve the room temperature strength of the shell without affecting the air permeability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of silica sol type shell casting, and particularly relates to a high-performance precision casting silica sol shell with smooth inner wall and a preparation method thereof. BACKGROUND

[0002] Investment precision casting, also known as investment casting, is a near-net-shape forming technology, which is widely used in the fields of aviation, aerospace, mechanical manufacturing, sports, chemical industry, nuclear energy, etc. It can not only be used to prepare thin-walled devices with complex structure, but also can be used to cast combined integral castings. The preparation of the shell is one of the key processes of investment casting, and is the key to whether the quality of the castings meets the requirements. At present, the dominant shell-making binder in the world is silica sol binder, which has good stability and fluidity, convenient hardening process, and the shell after baking has good high-temperature strength and surface quality, which is suitable for the production of castings with high surface quality requirements. However, the silica sol shell usually has obvious shortcomings, such as low room temperature strength, high residual strength and poor air permeability. The low room temperature strength is very unfavorable for the dewaxing and handling of the shell, and the high residual strength of the shell makes it difficult for the castings to be separated from the shell after pouring, and more importantly, the poor air permeability makes it difficult to discharge the high-temperature gas during pouring in a short time, which seriously hinders the filling of the metal liquid in the shell, and finally leads to the formation of pores in the castings or incomplete pouring. Therefore, improving the comprehensive performance of the shell and developing high-performance precision casting ceramic shell are of great significance for obtaining high-precision castings in industrial production.

[0003] The Chinese patent "Precision Casting Silica Sol Shell Manufacturing Process" (Application No. CN202011400771.1, Authorization No. CN112589052A, Publication Date: April 2, 2021) discloses a precision casting silica sol shell manufacturing process, which includes a three-layer half preparation process of a surface layer, a transition layer, a back layer and a sealing slurry layer, can reduce the number of coating and hanging layers, significantly shorten the shell-making period, and at the same time, the surface layer slurry uses silica sol and zirconium powder and scatters 80-120 mesh mullite sand, and the transition layer slurry is configured by silica sol and mullite powder in a mass ratio of 1:3.4-3.6, and the shell prepared by combining the mesh number of mullite sand, the viscosity of the slurry and the temperature and humidity control can be used for various product shell-making, and the cost is low, but its room temperature strength and air permeability still have a large space for improvement.

[0004] Chinese patent "A shell making method of composite precision casting silica sol shell" (application number: CN201911005992.6, authorization number: CN110814287A, publication date: 2020.02.21) discloses a shell making method of composite precision casting silica sol shell. By adding calcium carbonate coated carbon fiber and calcium carbonate whisker in the reinforcing layer and the sealing layer coating, micro-pores are formed in the shell during baking, improving the permeability of the shell. The improvement of the strength of the shell by calcium carbonate also has a certain influence, but there is still a large space for the improvement of the room temperature strength.

[0005] Chinese patent "High shell making process of silica sol shell" (application number: CN201711333840.X, authorization number: CN108031789A, publication date: 2018.05.15) discloses a high shell making process of silica sol shell. The fully calcined aluminum-silicon refractory sand powder, free iron and hard kaolin with low content of diaspore are used as the main material of silica sol shell, which is combined with quartz sand. The combination can ensure the room temperature strength of the shell and greatly reduce the residual strength of the shell after pouring, but the permeability is insufficient.

[0006] Chinese patent "A shell making method of water glass-silica sol composite shell" (application number: CN201710777474.0, authorization number: CN107755634A, publication date: 2018.03.06) discloses a shell making method of water glass-silica sol composite shell, mainly including preparation of coating and surface layer, transition layer and water glass coating. The water glass-silica sol shell process proposed by the invention is simple, practical and low in cost, and can achieve casting comparable to silica sol shell, but the strength and permeability still need to be improved.

[0007] Chinese patent "Silica sol shell making process" (application number: CN201711111209.5, authorization number: CN108044034A, publication date: 2018.05.18) discloses a silica sol shell making process. Quartz powder, quartz sand and silica sol are mixed to form mixture I; mullite powder, mullite sand and silica sol are mixed to form mixture II; and mixture I and mixture II are mixed to form the main material powder for making silica sol shell. The silica sol shell preparation process is simple, operable, short in production cycle and low in cost, but the performance is poor. SUMMARY

[0008] To solve the problem of low smoothness of the inner wall surface of the silica sol shell, the room temperature strength and the permeability are difficult to be compatible, the present application provides a high-performance precision casting silica sol shell with smooth inner wall.

[0009] The technical solution adopted by the present application to solve the technical problems is:

[0010] A method for preparing high-performance precision casting silica sol shell, comprising the following steps:

[0011] Step 1, preparing surface layer slurry by graded particles:

[0012] Mixing zirconium powder, white corundum powder, silica particles with silica sol, hydroxypropyl methyl cellulose uniformly, then adding wetting agent and defoaming agent, stirring uniformly to obtain surface layer slurry;

[0013] In the surface layer slurry, the addition amount of white corundum powder is 1% to 5% of the mass of zirconium powder, the addition amount of silica is 0.1% to 0.5% of the mass of zirconium powder, the addition amount of silica sol is 8% to 12% of the mass of zirconium powder, the addition amount of hydroxypropyl methyl cellulose is 0.2% to 0.3% of the mass of zirconium powder, and the addition amount of wetting agent and defoaming agent is 0.015-0.02% of the mass of zirconium powder;

[0014] The particle size of zirconium powder and white corundum powder is 280-320 mesh, and the particle size of silica particles is 200-300 nm; Step 2, preparing back layer slurry by organic-inorganic fibers:

[0015] Mixing polyethylene fibers and boron nitride fibers with silica sol, polyvinylamide, white corundum powder and defoaming agent, stirring uniformly to obtain back layer slurry;

[0016] In the back layer slurry, the addition amount of boron nitride fibers is 4% to 8% of the mass of silica sol, the addition amount of polyethylene fibers is 5% to 10% of the mass of silica sol, the addition amount of polyvinylamide is 0.2% to 0.3% of the mass of silica sol, the addition amount of defoaming agent is 0.015-0.02% of the mass of silica sol, and the mass ratio of silica sol to white corundum powder is 1:1.3-1.6; Step 3, preparing high-strength silica sol shell with smooth inner wall:

[0017] Dipping the wax mold into the surface layer slurry obtained in step 1, then taking it out and sprinkling sand and drying, then dipping it into the back layer slurry obtained in step 2, taking it out and sprinkling sand and drying, repeating multiple times, then sealing the slurry, defatting, and calcining to obtain the silica sol shell.

[0018] Preferably, the SiO2 content in the silica sol in steps 1 and 2 is 29%-30%, the kinematic viscosity is <8×10 -6 m 2 / s, the pH is 9-10, and the specific gravity is 1.20-1.22 g·ml -1 .

[0019] Preferably, in step 2, the length of boron nitride fibers is 2-8 mm and the diameter is 10-50 μm; the length of polyethylene fibers is 4-10 mm and the diameter is 80-150 μm. Controlling the length and diameter of polyethylene fibers and boron nitride fibers can improve the air permeability and strength of the shell.

[0020] As preferred, in step 2, the particle size of the white corundum powder is 280-320 mesh.

[0021] As preferred, in step 3, the face layer slurry is used to prepare the first layer of the silica sol type shell, the back layer slurry is used to prepare the structural layer of the silica sol type shell except the first layer and the sealing layer, and the coating and sanding of the back layer slurry are repeated for 5-6 times.

[0022] As preferred, in step 3, the temperature curve of the calcination is as follows: after preheating at 350℃±50℃ for 0.5-0.8h, slowly heating to 700℃±50℃ for 0.5-0.8h, and finally heating to 950-1100℃ for 2-2.5h.

[0023] A high-performance precision casting silica sol type shell prepared by the preparation method.

[0024] The present application has the following advantages:

[0025] 1. By adding zirconium powder and white corundum powder with the same particle size (280-320 mesh) into the face layer slurry, and combining with nano-sized silicon dioxide particles (200-300 nm), the micro concave-convex of the face layer coating can be filled and leveled, and the smoothness of the face layer of the shell is increased.

[0026] 2. The polyethylene fibers form a network structure in the back layer slurry, which can leave micro voids during drying and calcination, so that the gas can be discharged from the inside of the shell through the fiber network, and the air permeability is improved.

[0027] 3. By adding hydroxypropyl methyl cellulose and polyvinylamide into the face layer and back layer slurry, the dispersibility of the particles and fibers in the slurry is improved, so that the mixing uniformity and processing performance of the slurry are effectively improved.

[0028] 4. By adding boron nitride fibers into the back layer slurry, the thermal conductivity of the shell is improved, the concentration degree of thermal stress is effectively reduced, the crack propagation is prevented, and the cracking and deformation of the shell during drying and solidification is reduced. At the same time, the boron nitride fibers can interact with the silica sol, strengthen the consolidation and connection of the medium, and form a continuous fiber network structure in the slurry, so that the room temperature strength of the shell is improved without affecting the air permeability. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic diagram of the cross-sectional morphology of the smooth inner wall of the high-performance precision casting silica sol type shell obtained by the present application;

[0030] In the figure, 1 is zirconium powder, 2 is silicon dioxide particles, 3 is white corundum powder, 4 is polyethylene fiber hole, 5 is boron nitride fiber, and 6 is silica sol.

[0031] Figure 2 Schematic diagram of three-point bending strength test of shell of type DETAILED DESCRIPTION

[0032] The technical solutions of the present application are further described below by specific examples. It should be understood that the implementation of the present application is not limited to the following examples, and any form of variation and / or change made to the present application will fall within the scope of protection of the present application.

[0033] In the present application, all parts and percentages are weight units, and the equipment and raw materials used are commercially available or commonly used in the art, unless otherwise specified. The methods in the following examples are conventional methods in the art, unless otherwise specified.

[0034] The reagents used in the following examples can be purchased from conventional biochemical reagent stores, unless otherwise specified.

[0035] In the following examples, the particle size of zirconium powder and white corundum powder is 320 mesh, the length of boron nitride fiber is 2-8 mm and the diameter is 10-50 μm, the length of polyethylene fiber is 4-10 mm and the diameter is 80-150 μm. The zirconium powder is purchased from Zhongshi New Materials Company, the white corundum powder is purchased from Gongyi Baolai New Materials Factory, the boron nitride fiber is purchased from Shandong Industrial Ceramics Research and Design Institute, and the polyethylene fiber is purchased from Shandong Hao Da Engineering Materials Co., Ltd.

[0036] The SiO2 content of the silica sol is 29-30%, the kinematic viscosity is <8*10 -6 m 2 / s, the pH is 9-10, and the specific gravity is 1.20-1.22 g·ml -1 , purchased from Henan Changyu Chemical Product Co., Ltd.

[0037] Wetting agent, model: JFC wetting agent, purchased from Henan Qida Chemical Raw Materials Co., Ltd.

[0038] Defoaming agent, model: silicone defoaming agent MY-122, purchased from Shandong Meiyu Chemical Co., Ltd.

[0039] The core of the present application is to provide a preparation method of high-performance precision casting silica sol shell, which comprises the following steps:

[0040] Step 1, preparation of surface layer slurry by grading particles:

[0041] The zirconium powder, white corundum powder, and silica particles are uniformly mixed with the silica sol and hydroxypropyl methylcellulose, and then the wetting agent and the defoaming agent are added and uniformly stirred to obtain the surface layer slurry;

[0042] The amount of white corundum powder added in the surface layer slurry is 1% to 5% of the mass of the zirconium powder, the amount of silicon dioxide added is 0.1% to 0.5% of the mass of the zirconium powder, the amount of silicon sol added is 8% to 12% of the mass of the zirconium powder, the amount of hydroxypropyl methyl cellulose added is 0.2% to 0.3% of the mass of the zirconium powder, and the amounts of wetting agent and defoaming agent added are both 0.015-0.02% of the mass of the zirconium powder;

[0043] The particle size of the zirconium powder and the white corundum powder is 280-320 mesh, and the particle size of the silicon dioxide particles is 200-300 nm;

[0044] Step 2: Preparation of the organic-inorganic fiber mixed back layer slurry

[0045] The polyethylene fibers and boron nitride fibers are mixed with the silicon sol, polyvinyl amide, white corundum powder, and defoaming agent, and stirred uniformly to obtain the back layer slurry;

[0046] In the back layer slurry, the amount of boron nitride fibers added is 4% to 8% of the mass of the silicon sol, the amount of polyethylene fibers added is 5% to 10% of the mass of the silicon sol, the amount of polyvinyl amide added is 0.2% to 0.3% of the mass of the silicon sol, the amount of defoaming agent added is 0.015-0.02% of the mass of the silicon sol, and the mass ratio of the silicon sol to the white corundum powder is 1:1.3-1.6;

[0047] Step 3: Preparation of a high-strength silicon sol type shell with smooth inner walls

[0048] The wax mold is immersed in the surface layer slurry obtained in step 1, and after being taken out, sand is sprinkled and dried, then the back layer slurry obtained in step 2 is immersed, and after being taken out, sand is sprinkled and dried, and the process is repeated multiple times, and then the slurry is sealed, dewaxed, and calcined to obtain a silicon sol type shell.

[0049] Example 1

[0050] A method for preparing a high-performance precision casting silicon sol type shell with smooth inner walls, the specific steps are as follows:

[0051] First, 4 kg of silicon sol is weighed and stirred, then 50 kg of zirconium powder and 0.5 kg of white corundum powder are slowly added, stirred for a few moments, 0.05 kg of silicon dioxide particles with a particle size of 200 nm and 0.1 kg of hydroxypropyl methyl cellulose are added and stirred for half an hour, and finally 3.75 g of wetting agent and 3.75 g of defoaming agent are added, and stirred for 12 h to obtain a surface layer slurry;

[0052] Secondly, 40 kg of silica sol is weighed and stirred, 1.6 kg of boron nitride fiber (diameter in the range of 10-50 μm, length 2 mm) and 2 kg of polyethylene fiber (diameter in the range of 80-150 μm, length 4 mm) are added into the continuously stirred silica sol, 0.08 kg of polyvinyl amide is added and stirred uniformly, then ultrasonic treatment is performed for 30 min, finally 64 kg of white corundum powder and 6 g of defoaming agent are added and stirred for 12 h to obtain the back layer slurry;

[0053] After the wax mold is immersed in the surface layer slurry and evenly coated, it is taken out for sanding, drying, and placing for a period of time to allow the coating sol to gel, the back layer slurry is coated and sanded, and dried. After the back layer slurry is coated for 5 times, the shell sample is placed in a boiling container until the wax mold on the surface of the shell is completely melted, and the dewaxing treatment is performed; finally, calcination is performed in a vacuum high-pressure gas quenching furnace, and the temperature curve is as follows: after preheating at 350°C for half an hour, slowly heating to 700°C for half an hour, and finally heating to 950°C for 2 h, cooling to room temperature, a high-strength silica sol shell with smooth inner wall is obtained.

[0054] Example 2

[0055] A method for preparing a high-performance precision casting silica sol shell with smooth inner wall, the specific steps are:

[0056] First, 6 kg of silica sol is weighed and stirred, then 50 kg of zirconium powder and 2.5 kg of white corundum powder are slowly added, stirred for a few minutes, 0.25 kg of silica particles with a particle size of 300 nm and 0.15 kg of hydroxypropyl methyl cellulose are added and stirred for half an hour, finally 5 g of wetting agent and 5 g of defoaming agent are added, and stirred for 12 h to obtain the surface layer slurry;

[0057] Secondly, 60 kg of silica sol is weighed and stirred, 4.8 kg of boron nitride fiber (diameter in the range of 10-50 μm, length 8 mm) and 6 kg of polyethylene fiber (diameter in the range of 80-150 μm, length 10 mm) are added into the continuously stirred silica sol, 0.18 kg of polyvinyl amide is added and stirred uniformly, then ultrasonic treatment is performed for 30 min, finally 96 kg of white corundum powder and 12 g of defoaming agent are added and stirred for 12 h to obtain the back layer slurry;

[0058] The wax model is immersed into the surface layer slurry and taken out after uniform coating, sanding, drying, and placing for a period of time to make the coating sol gel, then the back layer slurry is coated and sanded, and dried. The back layer slurry coating is repeated 6 times, then the shell sample is placed into a boiling container until the wax model on the shell surface is completely melted, and the dewaxing treatment is performed; finally, calcination is performed in a vacuum high-pressure gas quenching furnace, and the temperature curve is as follows: preheating stage, temperature rising to 350°C, holding for half an hour, then slowly rising to 700°C, holding for half an hour, finally rising to 1100°C, holding for 2 hours, and cooling to room temperature, to obtain a high-strength silica sol shell with smooth inner wall.

[0059] Example 3

[0060] A preparation method of a high-performance precision casting silica sol shell with smooth inner wall, and the specific steps are:

[0061] First, 5 kg of silica sol is weighed and stirred, then 50 kg of zirconium powder and 1 kg of white corundum powder are slowly added, stirred for a moment, 0.15 kg of silica particles with a particle size of 200 nm and 0.12 kg of hydroxypropyl methylcellulose are added and stirred for half an hour, and finally 4 g of wetting agent and 4 g of defoaming agent are added and stirred for 12 hours to obtain a surface layer slurry;

[0062] Secondly, 50 kg of silica sol is weighed and stirred, 3 kg of boron nitride fiber (diameter in the range of 10-50 μm, length 4 mm) and 3 kg of polyethylene fiber (diameter in the range of 80-150 μm, length 6 mm) are added to the continuously stirred silica sol, 0.1 kg of polyvinylamide is added and stirred uniformly, then ultrasonic treatment is performed for 30 minutes, and finally 80 kg of white corundum powder and 8 g of defoaming agent are added and stirred for 12 hours to obtain a back layer slurry;

[0063] The wax model is immersed into the surface layer slurry and taken out after uniform coating, sanding, drying, and placing for a period of time to make the coating sol gel, then the back layer slurry is coated and sanded, and dried. The back layer slurry coating is repeated 6 times, then the shell sample is placed into a boiling container until the wax model on the shell surface is completely melted, and the dewaxing treatment is performed; finally, calcination is performed in a vacuum high-pressure gas quenching furnace, and the temperature curve is as follows: preheating stage, temperature rising to 350°C, holding for half an hour, then slowly rising to 700°C, holding for half an hour, finally rising to 1100°C, holding for 2 hours, and cooling to room temperature, to obtain a high-strength silica sol shell with smooth inner wall.

[0064] Example 4

[0065] A preparation method of a high-performance precision casting silica sol shell with smooth inner wall, and the specific steps are:

[0066] Firstly, 5 kg of silica sol was weighed and stirred, then 50 kg of zirconium powder and 2 kg of white corundum powder were slowly added, stirred for a while, 0.2 kg of silica particles with a particle size of 300 nm and 0.1 kg of hydroxypropyl methyl cellulose were added and stirred for half an hour, finally 4.5 g of wetting agent and 4.5 g of defoaming agent were added and stirred for 12 h to obtain the face layer slurry;

[0067] Secondly, 50 kg of silica sol was weighed and stirred, 4 kg of boron nitride fibers (diameter in the interval of 10-50 μm, length 7 mm) and 4 kg of polyethylene fibers (diameter in the interval of 80-150 μm, length 8 mm) were added to the continuously stirred silica sol, 0.12 kg of polyvinyl amide was added and stirred uniformly, then ultrasonic treatment was performed for 30 min, finally 80 kg of white corundum powder and 10 g of defoaming agent were added and stirred for 12 h to obtain the back layer slurry;

[0068] The wax mold was immersed in the face layer slurry until the coating was uniform, then taken out and sand was sprinkled, dried, and placed for a period of time to make the coating sol gel, then the back layer slurry was coated and sand was sprinkled, dried. After the back layer slurry was coated repeatedly for 6 times, the shell sample was placed in a boiling container until the wax mold on the surface of the shell completely melted, and the dewaxing treatment was performed; finally, calcination was performed in a vacuum high-pressure gas quenching furnace, and the temperature curve was as follows: after preheating at 350℃ for half an hour, the temperature was slowly increased to 700℃ for half an hour, then the temperature was increased to 1050℃ for 2 h, and cooled to room temperature, to obtain a high-strength silica sol shell with smooth inner wall.

[0069] Comparative Example 1

[0070] The specific preparation method was the same as that of Example 3, and the only difference was that the boron nitride fibers and the polyethylene fibers were not added in the back layer slurry.

[0071] Comparative Example 2

[0072] The specific preparation method was the same as that of Example 3, and the only difference was that the polyethylene fibers were not added in the back layer slurry.

[0073] Comparative Example 3

[0074] The specific preparation method was the same as that of Example 3, and the only difference was that the boron nitride fibers were not added in the back layer slurry.

[0075] Comparative Example 4

[0076] The specific preparation method was the same as that of Example 3, and the only difference was that the silica particles were not added in the face layer slurry.

[0077] Comparative Example 5

[0078] The specific preparation method was the same as that of Example 3, and the only difference was that the hydroxypropyl methyl cellulose and the polyvinyl amide were not added in the face layer and the back layer slurry.

[0079] Comparative Example 6

[0080] The specific preparation method is the same as that of Example 3, except that the mass of the boron nitride fiber and the polyethylene fiber added in the back layer slurry is 2% of the silica sol.

[0081] Comparative Example 7

[0082] The specific preparation method is the same as that of Example 3, except that the mass of the boron nitride fiber and the polyethylene fiber added in the back layer slurry is 12% of the silica sol.

[0083] Figure 1 is a schematic diagram of the cross-sectional morphology of a high-performance precision casting silica sol shell prepared by the present application, wherein the face layer comprises zirconium powder 1, silica particles 2, and white corundum powder 3, and the back layer comprises polyethylene fiber holes 4, boron nitride fibers 5, and silica sol 6.

[0084] The room temperature strength and air permeability of the high-strength silica sol shell with smooth inner wall in Examples 1 to 4 and the silica sol shell of Comparative Examples 1 to 7 are shown in Table 1.

[0085] The room temperature strength is detected by using a SWY universal digital bending strength tester, and a schematic diagram of the three-point bending strength test of the shell is shown in Figure 2 .

[0086] The air permeability detection method is to first prepare a wafer test sample, and then use a ZTY intelligent sand mold air permeability tester to detect the air permeability of the shell sample.

[0087] Table 1

[0088]

[0089]

[0090] According to the data in Table 1, compared with Example 3, the room temperature strength and air permeability of Example 1, Example 2 and Example 4 are insufficient, and too much or too little boron nitride and polyethylene fiber has limited effect on improving the room temperature strength and air permeability, so the performance of Example 3 is the best. In the back layer sizing material of Comparative Example 1, boron nitride fiber and polyethylene fiber are not added, and there are problems of low room temperature strength and insufficient air permeability; in the back layer sizing material of Comparative Example 2, polyethylene fiber is not added, compared with Comparative Example 1, the addition of boron nitride fiber improves the thermal conductivity of the shell, effectively reduces the concentration degree of thermal stress, prevents crack propagation, strengthens the consolidation and connection of the medium, and improves the room temperature strength, but the air permeability is insufficient; in the back layer sizing material of Comparative Example 3, boron nitride fiber is not added, compared with Comparative Example 1, the addition of polyethylene fiber effectively improves the air permeability of the shell, but the strength is still insufficient. In Comparative Example 4, the addition of silica particles improves the air permeability, but the room temperature strength decreases. In Comparative Example 5, hydroxypropyl methyl cellulose and polyvinylamide are not added, so the particles and fibers are easy to aggregate, and the dispersibility is poor, so the air permeability and room temperature strength decrease. In Comparative Example 6 and Comparative Example 7, too little and too much boron nitride fiber and polyethylene fiber are added, respectively, and compared with the examples, the room temperature strength and air permeability decrease obviously. In Example 3, the optimal proportion of boron nitride fiber and polyethylene fiber is added, which improves the room temperature strength of the shell on the premise of ensuring high air permeability of the shell.

[0091] In summary, the high-performance silica sol shell prepared by the present application fills and fills the small concave-convex of the surface layer coating by combining zirconium powder, white corundum powder and silica particles, increases the smoothness of the shell surface layer; the combination of polyethylene fiber and boron nitride fiber improves the porous structure and thermal conductivity of the shell, reduces the cracking and deformation of the shell during drying and curing. At the same time, the continuous fiber network structure formed by the boron nitride fiber can improve the room temperature strength of the shell without affecting the air permeability.

[0092] The embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts of each embodiment can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the related parts can be referred to the method part.

[0093] The high-performance precision casting silica sol shell with smooth inner wall and the preparation method thereof are described in detail. The principles and implementation manners of the present application are described by using specific examples. The above examples are only used to help understand the method of the present application and its core idea. It should be pointed out that those skilled in the art can make some improvements and modifications to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for preparing a high-performance precision-cast silica sol shell, characterized in that... The method includes the following steps: Step 1: Prepare the surface slurry by classifying particles: Zirconium powder, white corundum powder, silica particles, silica sol, and hydroxypropyl methylcellulose are mixed evenly, and then a wetting agent and defoamer are added and stirred evenly to obtain the surface slurry. In the surface slurry, the amount of white fused alumina powder added is 1%~5% of the mass of zirconium powder, the amount of silica added is 0.1%~0.5% of the mass of zirconium powder, the amount of silica sol added is 8%~12% of the mass of zirconium powder, the amount of hydroxypropyl methylcellulose added is 0.2%~0.3% of the mass of zirconium powder, and the amounts of wetting agent and defoamer added are both 0.015-0.02% of the mass of zirconium powder. The particle size of zirconium powder and white corundum powder is 280-320 mesh, and the particle size of silica particles is 200-300 nm. Step 2, Organic-Inorganic Fiber Blending of Backing Layer Slurry: Polyethylene fiber and boron nitride fiber are mixed with silica sol, polyvinylamide, white corundum powder and defoamer, and stirred evenly to obtain back layer slurry; In the backing slurry, the amount of boron nitride fiber added is 4%~8% of the silica sol mass, the amount of polyethylene fiber added is 5%~10% of the silica sol mass, the amount of polyvinylamide added is 0.2%~0.3% of the silica sol mass, the amount of defoamer added is 0.015-0.02% of the silica sol mass, and the mass ratio of silica sol to white fused alumina powder is 1:1.3~1.6; Step 3: Prepare a high-strength silica sol shell with a smooth inner wall. The wax model is immersed in the surface slurry obtained in step 1, removed, sprinkled with sand, and dried. Then it is immersed in the back slurry obtained in step 2, removed, sprinkled with sand, and dried. After repeating this process several times, the model is sealed, dewaxed, and calcined to obtain a silica sol shell. The silica sol in steps 1 and 2 contains 29%–30% SiO2 and has a kinematic viscosity of <8 × 10⁻⁶. -6 m 2 / s, pH 9~10, specific gravity 1.20~1.22g·ml -1 ; In step 2, the boron nitride fiber has a length of 2-8 mm and a diameter of 10-50 μm; the polyethylene fiber has a length of 4-10 mm and a diameter of 80-150 μm.

2. The method for preparing a high-performance precision-cast silica sol shell according to claim 1, characterized in that: In step 2, the particle size of the white fused alumina powder is 280 mesh to 320 mesh.

3. The method for preparing a high-performance precision-cast silica sol shell according to claim 1, characterized in that: In step 3, the surface slurry is used to prepare the first layer of the silica sol shell, and the back slurry is used to prepare the structural layers of the silica sol shell other than the first layer and the sealing layer. The coating and sanding of the back slurry are repeated 5 to 6 times.

4. The method for preparing the high-performance precision-cast silica sol shell according to claim 1, characterized in that: In step 3, the calcination temperature curve is as follows: in the preheating stage, the temperature is raised to 350℃±50℃ and held for 0.5~0.8 h, then slowly raised to 700℃±50℃ and held for 0.5~0.8 h, and finally the temperature is raised to 950~1100℃ and held for 2h~2.5h.

5. A high-performance precision-cast silica sol shell prepared by the preparation method of claim 1.

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