Precision casting back layer and / or surface layer universal modified silica sol and preparation method and application thereof

Abstract

The invention belongs to the technical field of silica sol, and particularly relates to universal modified silica sol for a precision casting back layer and / or surface layer as well as a preparation method and application of the universal modified silica sol. The invention provides universal modified silica sol for a back layer and / or a surface layer of precision casting, which comprises the following components in percentage by mass: 86-95% of silica sol, 1-3% of a coalescing agent, 1-3% of a polymeric dispersant, 1-3% of a silane coupling agent and 1-3% of a water-based polymer emulsion. According to the universal modified silica sol for the back layer and / or the surface layer of precision casting, through the synergistic effect of all the components of the specific dosage, the drying time is remarkably shortened, the strength and stability of a prepared shell are enhanced, the working procedures are reduced, the cost is reduced, the production efficiency is improved, and the high requirements of precision casting on the back layer and the surface layer are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of silica sol, and particularly relates to a general modified silica sol for precision casting back layer and / or surface layer, a preparation method thereof, and an application thereof. Background Art

[0002] Precision casting is a highly accurate manufacturing process aimed at obtaining castings with more accurate dimensions and smoother surfaces. Compared with the traditional sand casting process, precision casting technology can produce more precise, complex and near-final shape parts, reducing or even avoiding subsequent machining processes, belonging to the advanced process category of near-net-shape manufacturing. In the whole process of precision casting, first, a suitable material is selected to make a wax pattern, then a multi-layer refractory slurry and sand are coated on the surface of the wax pattern, and dried and hardened to form a mold shell. Then, by dissolving the wax pattern, the required cavity is formed, and the mold shell is sintered to enhance the strength. Finally, the molten metal is poured into the mold shell. Subsequently, after the metal solidifies and cools, subsequent processing steps such as shell removal and cleaning are carried out, and finally high-precision finished castings are obtained. It should be noted that the quality of precision castings is affected by many factors, including the geometric structure of the casting, material, investment material, shell-making process, pouring temperature, etc. Any improper setting or operation of a process link may cause a change in the quality of the finished product of that process link, thus affecting the final product quality. Therefore, in the process of precision casting, it is crucial to carefully design and strictly control each process link to ensure that the final product meets the specification requirements.

[0003] In precision casting, the performance of the surface layer slurry and the back layer slurry has an important impact on the quality of the final casting. The surface layer slurry is in direct contact with the wax block, determining the surface finish and dimensional accuracy of the casting. The back layer slurry mainly provides the strength and stability of the mold shell. At present, the existing casting surface layer slurries on the market are mainly optimized for surface layer applications, and they have obvious limitations in back layer applications. Specifically, it is manifested in the following aspects:

[0004] (1) Long drying time: The existing casting surface layer slurries have a slow drying speed in back layer applications and cannot meet the requirements of rapid production. This is mainly because the surface layer slurries are usually designed to dry slowly at a lower temperature to ensure the surface quality, but in back layer applications, this characteristic leads to an extended overall production cycle.

[0005] (2) Poor applicability: The formulation and performance parameters of the surface layer slurry are mainly optimized for the special requirements of the surface layer, such as surface finish and dimensional accuracy, and are not suitable for the strength and stability requirements of the back layer. Therefore, directly using the surface layer slurry as the back layer will result in insufficient strength of the mold shell, affecting the quality and production efficiency of the casting.

[0006] (3) Complex processes: The processes of precision casting are complex and numerous, including steps such as investment pattern making, shell mold preparation, pouring, and shell removal. Existing surface slurries cannot shorten the drying time while ensuring surface quality, resulting in low efficiency in the entire production process and failing to meet the requirements of modern industry for high-efficiency and rapid production.

[0007] The prior art provides a back layer slurry to improve the wet strength of the shell mold and reduce the residual strength; however, the preparation method is complex, the production efficiency is low, and it can only prepare the back layer; the prior art also provides a surface layer slurry to improve the wet strength and anti-cracking performance of the casting slurry, but it cannot prepare the back layer, and the drying conditions are harsh and the preparation process is complex. Summary of the Invention

[0008] Therefore, the technical problem to be solved by the present invention is to overcome the defects in the prior art that the surface layer and back layer need to be prepared separately, the steps are cumbersome, and the provided slurries have long drying time, poor wet strength, high residual strength, etc., so as to provide a general-purpose modified silica sol for precision casting back layer and / or surface layer, its preparation method and application.

[0009] The present invention provides a general-purpose modified silica sol for precision casting back layer and / or surface layer that can be used as both surface layer slurry and back layer slurry; it can further improve the wet strength required for the surface layer slurry and optimize the surface quality of the casting; it can also reduce the residual strength of the shell mold made of the back layer slurry, shorten the drying time, and improve the production efficiency on the premise of ensuring the quality and performance of the material itself;

[0010] For this reason, the present invention provides the following technical solutions.

[0011] The present invention provides a general-purpose modified silica sol for precision casting back layer and / or surface layer, including: by mass percentage, 86-95% silica sol, 1-3% film-forming aid, 1-3% polymer dispersant, 1-3% silane coupling agent, 1-3% aqueous polymer emulsion.

[0012] In an optional embodiment, the pH value of the general-purpose modified silica sol for precision casting back layer and / or surface layer is 1-11;

[0013] In an optional embodiment, the solid content of the general-purpose modified silica sol for precision casting back layer and / or surface layer is 20-25%.

[0014] The solid content of the silica sol prepared from the raw materials of each component of the present invention can meet 20-25%;

[0015] In an alternative embodiment, the film-forming aid includes at least one of dodecyl alcohol ester, aqueous polycarbonate, tripropylene glycol n-butyl ether, polyurethane, aqueous polycarbonate diol, ethyl 3-ethoxypropionate, ethylene glycol monobutyl ether acetate, mixed dibasic acid diisobutyl ester, diisobutyl adipate, ethylene glycol monobutyl ether, sodium polystyrene sulfonate, and polystyrene-butadiene copolymer; the film-forming aid reduces the minimum film-forming temperature of the silica sol, enabling the silica sol to form a continuous film at a lower temperature, thereby improving the film-forming efficiency; specific functional groups in the film-forming aid can interact with the hydroxyl groups on the surface of the silica sol particles, promoting the fusion and crosslinking between the particles and accelerating the film-forming process. At the same time, the film-forming aid acts as a temporary plasticizer during the film-forming process, enabling the silica sol particles to be more easily deformed, approach each other, and fuse after the water has evaporated, thus accelerating the drying rate.

[0016] Aqueous polycarbonate refers to the aqueous dispersion form of polycarbonate;

[0017] Aqueous polycarbonate diol refers to the aqueous dispersion form of polycarbonate diol;

[0018] Mixed dibasic acid diisobutyl ester (abbreviated as DIBA) is a mixture composed of isobutyl esters of succinic acid, glutaric acid, and adipic acid;

[0019] In an alternative embodiment, the polymeric dispersant includes at least one of polycaprolactone-polyethyleneimine block copolymer type, polyether-modified polysiloxane, propylene glycol monomethyl ether acidic solution, sodium polyacrylate, and polyvinyl alcohol. The polymeric dispersant keeps the silica sol particles highly dispersed and of uniform particle size in the aqueous phase through electrostatic repulsion and steric hindrance effects. This uniformly dispersed state helps the particles form a closer arrangement during the film-forming process, reduces voids, accelerates the evaporation of water and the bonding between the silica sol particles, and thus improves the drying efficiency;

[0020] The polycaprolactone-polyethyleneimine block copolymer type is a general term for a class of dispersants, and representative ones include: aqueous hyperdispersant 9760 hydrophilic polymer block copolymer (Delk DVK Chemical), Dispex Ultra PX4275 (BASF), etc.;

[0021] In an alternative embodiment, the silane coupling agent includes at least one of amino silane coupling agent and epoxy silane coupling agent; the silane coupling agent reacts chemically with the hydroxyl groups on the surface of the silica sol particles to form chemically bonded organic groups, and these organic groups can further interact with the active groups in the film-forming aid or the aqueous polymer emulsion, accelerating the crosslinking and fusion between the silica sol particles. At the same time, the silane coupling agent also enhances the bonding force between the modified silica sol and the surface of the precision casting, thereby improving the overall stability and drying efficiency of the back layer and the surface layer;

[0022] Preferably, the amino-silane coupling agent includes at least one of N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane;

[0023] Preferably, the epoxy-silane coupling agent includes at least one of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and (3-glycidoxypropyl)trimethoxysilane.

[0024] In an alternative embodiment, the aqueous polymer emulsion includes an acrylic emulsion; during the drying process, the aqueous polymer emulsion can form a continuous polymer film that interweaves with the silica sol film to form a composite film with a three-dimensional network structure; enabling the back layer and the surface layer of the precision casting to have good air permeability, flexibility, and tensile strength, and not being easily broken during the drying process, thereby accelerating the overall drying speed.

[0025] Preferably, the acrylic emulsion includes at least one of an epoxy-modified aqueous acrylic emulsion, an organosilicon-modified aqueous acrylic emulsion, and an organofluorine-modified aqueous acrylic emulsion.

[0026] The present invention also provides a method for preparing a general-purpose modified silica sol for the back layer and / or the surface layer of precision casting, comprising the following steps:

[0027] Mix silica sol, water, and a polymer dispersant, disperse, then add a silane coupling agent, stir for the first time, add a film-forming aid and an aqueous polymer emulsion, and stir for the second time to obtain a general-purpose modified silica sol for the back layer and / or the surface layer of precision casting.

[0028] In an alternative embodiment, the dispersion is selected from ultrasonic dispersion;

[0029] In an alternative embodiment, the time of the dispersion is 20 - 40 min.

[0030] In an alternative embodiment, the preparation method is carried out at 20 - 25 °C;

[0031] In an alternative embodiment, the rotation speed of the first stirring is 500 - 1000 rpm;

[0032] In an alternative embodiment, the time of the first stirring is 1 - 2 h.

[0033] In an alternative embodiment, the rotation speed of the second stirring is 500 - 1000 rpm;

[0034] In an alternative embodiment, the time of the second stirring is 10 - 30 min.

[0035] The present invention also provides an application of the above-mentioned general modified silica sol for the investment casting back layer and / or surface layer or the modified silica sol prepared by the above-mentioned preparation method in the surface layer and / or back layer of the mold shell.

[0036] Here, a general slurry is listed, which includes refractory materials and the above-mentioned general modified silica sol for the investment casting back layer and / or surface layer or the general modified silica sol for the investment casting back layer and / or surface layer prepared by the above-mentioned preparation method; the refractory materials include at least one of mullite powder and zircon powder; the mass ratio of the general modified silica sol for the investment casting back layer and / or surface layer to the refractory materials is 1:2;

[0037] Here, a preparation method of a shell film substrate is listed, which includes the following steps:

[0038] Place the investment casting wax block substrate in the above-mentioned general slurry for slurry coating, and dry it without wind at room temperature to obtain the shell film substrate.

[0039] The technical solution of the present invention has the following advantages:

[0040] 1. The general modified silica sol for the investment casting back layer and / or surface layer provided by the present invention includes: 86-95% silica sol, 1-3% film-forming aid, 1-3% polymer dispersant, 1-3% silane coupling agent, 1-3% water-based polymer emulsion by mass percentage. The general modified silica sol for the investment casting back layer and / or surface layer provided by the present invention, through the synergistic effect among the components with the above specific dosages, significantly shortens the drying time, enhances the strength and stability of the obtained mold shell, reduces the processes, lowers the cost, improves the production efficiency, and meets the high requirements of investment casting for the back layer and surface layer; the pH value is 1-11, and it has a wide application range.

[0041] The present invention adds silica sol, film-forming aid, polymer dispersant, silane coupling agent, and water-based polymer emulsion and limits the mass ratio, which has a good synergistic effect, can effectively improve the quality and performance of the mold shell prepared from the general modified silica sol for the investment casting back layer and / or surface layer, not only improves the wet strength of the shell film surface layer, but also reduces the residual strength of the shell film back layer. At the same time, the drying time is shortened to ≤1h, and the drying time of the traditional surface layer slurry in the prior art is shortened by 40%, significantly reducing the production cycle and the occupation of factory building space; using the general modified silica sol for the investment casting back layer and / or surface layer provided by the present invention, the back layer and surface layer of the mold shell can be prepared simultaneously, greatly shortening the production cycle and improving the production efficiency.

[0042] The silane coupling agent reacts chemically with the hydroxyl groups on the surface of silica sol particles to form chemically bonded organic groups. These organic groups can further interact with the active groups in the film-forming aid or the aqueous polymerization emulsion, accelerating the cross-linking and fusion between silica sol particles. The addition amount of the aqueous polymerization emulsion causes the polymer film and the silica sol film to interweave with each other, and the formed three-dimensional network structure composite film improves the air permeability and flexibility of the back layer and the surface layer, making the modified silica sol have good film-forming properties, long service life, and short drying time. Furthermore, it improves the strength and stability of the prepared shell back layer or surface layer, and increases the yield and quality of the castings. The compressive strength of the shell back layer prepared by the present invention is increased by 30% compared with the traditional back layer slurry.

[0043] In addition, the addition amount of the film-forming aid defined in the present invention does not destroy the stability of the silica sol, and at the same time has good film-forming properties, which is convenient for subsequent preparation of the slurry. The addition amount of the polymer dispersant makes the modified silica sol have good dispersibility. The fast volatilization of water makes the drying speed fast while the modified silica sol has good stability, enabling the slurry to be continuously used and reducing costs. The addition amount of the silane coupling agent makes the modified silica sol have better compatibility and the wet strength of the prepared shell film surface layer or back layer is high.

[0044] If the dosage of the film-forming aid is less than 1%, the wax block cannot form a film, which affects the subsequent pulping of the general modified silica sol for the back layer and / or surface layer of precision casting. If it is higher than 3%, it will destroy the stability of the modified silica sol, resulting in the inability to form a film. If the dosage of the polymer dispersant is less than 1%, the silica sol cannot be dispersed, resulting in the aggregation of the general modified silica sol for the back layer and / or surface layer of precision casting itself and making it unusable. If it is higher than 3%, it will reduce the stability of the subsequent slurry of the general modified silica sol for the back layer and / or surface layer of precision casting, resulting in the slurry being unable to be continuously used and increasing costs. If the dosage of the silane coupling agent is less than 1%, the silica sol itself cannot be modified, affecting subsequent preparation and reducing the compatibility of the silica sol. If it is higher than 3%, the silane coupling agent itself hydrolyzes too much, which will affect the shell film strength of the subsequent slurry formed by the general modified silica sol for the back layer and / or surface layer of precision casting. If the dosage of the aqueous polymerization emulsion is less than 1%, it cannot interweave with the silica sol film, which will reduce the air permeability and flexibility of the back layer and the surface layer and increase the drying time. If it is higher than 3%, it will affect the film-forming properties of the general modified silica sol for the back layer and / or surface layer of precision casting and the service life of the slurry prepared from the silica sol.

[0045] 2. The general modified silica sol for the back layer and / or surface layer of precision casting provided by the present invention has good industry universality, enabling the back layer or surface layer to dry without any complex auxiliary processes, equipment or environments, simplifying the process, reducing costs such as labor and equipment, having good environmental adaptability and process compatibility, being able to stably produce under different temperature and humidity environments, being able to seamlessly connect with the existing casting process, facilitating the rapid application of enterprises, and realizing the upgrade of precision casting technology without significantly transforming the existing production line, improving production efficiency and the quality of castings, and enhancing market competitiveness.

[0046] 3. The application of the precision casting back layer and / or surface layer general modified silica sol provided by the present invention in the shell surface layer and the shell back layer of the mold shell constructs a back layer and / or surface layer slurry system with high wet strength, low residual strength, rapid drying, reduced processes, and rapid shell film disintegration ability in the precision casting mold shell. This general modified silica sol for the back layer and surface layer not only improves the efficiency of the casting process and the quality of the castings, but also has good environmental adaptability and process compatibility, providing new possibilities for the development of precision casting technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0048] Figure 1 is the SEM electron micrograph of the precision casting back layer and / or surface layer general modified silica sol in Example 1 of the present invention;

[0049] Figure 2 is the slurry surface layer hanging slurry diagram prepared from the precision casting back layer and / or surface layer general modified silica sol in Example 1 of the present invention;

[0050] Figure 3 is the slurry back layer hanging slurry diagram prepared from the precision casting back layer and / or surface layer general modified silica sol in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] The following embodiments are provided to better further understand the present invention. They are not limited to the best embodiment, and do not limit the content and protection scope of the present invention. Any product that is the same as or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0052] For those not specifying the specific experimental steps or conditions in the embodiments, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For the reagents or instruments not specifying the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0053] The silica sol used in the following embodiments is the high-purity SKP series silica sol of Guangdong Huierte Nano Technology Co., Ltd.;

[0054] Example 1

[0055] This embodiment provides a modified silica sol, comprising: 90% silica sol, 2% film-forming aid, 2% polyvinyl alcohol (Aladdin reagent, P434370), 2% silane coupling agent, 2% epoxy-modified waterborne acrylic emulsion (Jining Tangyi Chemical Co., Ltd., WR-888W), and 2% deionized water by mass percentage; the film-forming aid is a mixture of waterborne polycarbonate diol (Asahi Kasei, Japan, PCDL T5652), polyurethane (Guangzhou Changhao Trading Co., Ltd., SGR-2106W), and sodium polystyrene sulfonate (Wuhan Lanabai Medical and Chemical Co., Ltd., 9080-79-9) in a mass ratio of 1:1:1; the silane coupling agent is a mixture of N-2-aminoethyl-3-aminopropylmethyldimethoxysilane (Sigma-Aldrich, 679356) and 3-aminopropyltriethoxysilane (Thermo Scientific, B20997) in a mass ratio of 1:1. The SEM electron micrograph of the modified silica sol is shown in Figure 1 , Figure 1 The scale bar is 500 nm.

[0056] This embodiment also provides a preparation method of the modified silica sol, comprising the following steps:

[0057] (1) Mix the silica sol and water, add polyvinyl alcohol, and ultrasonically disperse for 20 - 40 min to obtain a uniformly dispersed suspension;

[0058] (2) Add the silane coupling agent to the suspension and stir at room temperature for 1 - 2 h;

[0059] (3) Then add the film-forming aid and the epoxy-modified waterborne acrylic emulsion, and stir at room temperature until completely uniform to obtain the modified silica sol; the production temperature in steps (1)-(3) is controlled at 20 - 25 °C.

[0060] Example 2

[0061] This embodiment provides a modified silica sol, comprising: 95% silica sol, 1% film-forming aid, 1% polyvinyl alcohol, 1% N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, 1% waterborne polymer emulsion, and 1% deionized water by mass percentage; the film-forming aid is a mixture of diisobutyl adipate (Zhejiang Boju New Materials Co., Ltd.) and diisobutyl adipate (Shandong Kaiyue Chemical Co., Ltd.) in a mass ratio of 1:1; the waterborne polymer emulsion is a mixture of epoxy-modified waterborne acrylic emulsion and organosilicon-modified waterborne acrylic emulsion (Jining Tangyi Chemical Co., Ltd.) in a mass ratio of 1:1.

[0062] The modified silica sol provided in this embodiment is prepared according to the preparation method provided in Example 1.

[0063] Example 3

[0064] This embodiment provides a modified silica sol, comprising: 86% silica sol, 3% aqueous polycarbonate, 3% sodium polyacrylate, 3% (3-glycidoxypropyl) trimethoxysilane, 3% epoxy-modified aqueous acrylic emulsion, and 1% deionized water, by mass percentage.

[0065] The modified silica sol provided in this embodiment is prepared according to the preparation method provided in Example 1.

[0066] Example 4

[0067] This embodiment provides a modified silica sol, comprising: 89% silica sol, 3% aqueous polycarbonate, 2% polycaprolactone-polyethyleneimine block copolymer, 3% N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, 2% epoxy-modified aqueous acrylic emulsion, and 1% deionized water, by mass percentage. The film-forming aid is a mixture of sodium polystyrene sulfonate and styrene-butadiene copolymer in a mass ratio of 1:1; the aqueous polymer emulsion is a mixture of epoxy-modified aqueous acrylic emulsion and organosilicon-modified aqueous acrylic emulsion in a mass ratio of 1:1.

[0068] The modified silica sol provided in this embodiment is prepared according to the preparation method provided in Example 1.

[0069] Comparative Example 1

[0070] This comparative example provides a modified silica sol, comprising: 92% silica sol, 2% polyvinyl alcohol, 2% silane coupling agent, 2% epoxy-modified aqueous acrylic emulsion, and 2% deionized water, by mass percentage. The silane coupling agent is a mixture of N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane and 3-aminopropyltriethoxysilane in a mass ratio of 1:1.

[0071] The modified silica sol provided in this comparative example is prepared according to the preparation method provided in Example 1.

[0072] Comparative Example 2

[0073] This comparative example provides a modified silica sol, comprising: 92% silica sol, 2% film-forming aid, 2% silane coupling agent, 2% epoxy-modified aqueous acrylic emulsion, and 2% deionized water, by mass percentage. The film-forming aid is a mixture of aqueous polycarbonate, polyurethane, and sodium polystyrene sulfonate in a mass ratio of 1:1:1; the silane coupling agent is a mixture of N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane and 3-aminopropyltriethoxysilane in a mass ratio of 1:1.

[0074] The modified silica sol provided in this comparative example is prepared according to the preparation method provided in Example 1.

[0075] Comparative Example 3

[0076] This comparative example provides a modified silica sol, including: by mass percentage, 92% silica sol, 2% film-forming aid, 2% polyvinyl alcohol, 2% epoxy-modified waterborne acrylic emulsion, and 2% deionized water. The film-forming aid is a mixture of waterborne polycarbonate, polyurethane, and sodium polystyrene sulfonate in a mass ratio of 1:1:1.

[0077] The modified silica sol provided in this comparative example is prepared according to the preparation method provided in Example 1.

[0078] Comparative Example 4

[0079] This comparative example provides a modified silica sol, including: by mass percentage, 92% silica sol, 2% film-forming aid, 2% polyvinyl alcohol, 2% silane coupling agent, and 2% deionized water. The film-forming aid is a mixture of waterborne polycarbonate, polyurethane, and sodium polystyrene sulfonate in a mass ratio of 1:1:1; the silane coupling agent is a mixture of N-2-aminoethyl-3-aminopropylmethyldimethoxysilane and 3-aminopropyltriethoxysilane in a mass ratio of 1:1.

[0080] The modified silica sol provided in this comparative example is prepared according to the preparation method provided in Example 1.

[0081] Test Example

[0082] The modified silica sols prepared in Examples 1-4 and Comparative Examples 1-4 and refractory materials (mullite powder and zircon powder, manufacturer: Guwang Technology Co., Ltd., Guanxing City) are mixed in a mass ratio of 1:2.5 to prepare a slurry for performance testing; the slurry surface layer hanging slurry diagram prepared in Example 1 is shown in Figure 2 ; the slurry back layer hanging slurry diagram prepared in Example 1 is shown in Figure 3 . Specifically as follows:

[0083] (1) pH value of the modified silica sol: Measured by a pH meter. The results are shown in Table 1.

[0084] (2) Interlayer fast-drying time of the shell mold: The prepared slurry is coated on the mold, and the time is recorded after drying is completed. The coating is repeated until the shell mold is prepared, and the drying time of each coating layer is statistically averaged to obtain the interlayer fast-drying time of the shell mold; the completion of drying is measured by the moisture content, which means the surface moisture content of the coating layer is 5% - 10%, or the shell mold no longer continuously loses water (crystalline water). The results are shown in Table 1.

[0085] (3) Wet strength of the shell mold: Tested by the method of JB / T 13038-2017. The results are shown in Table 1.

[0086] (4) Residual strength of the shell mold: Tested by the method of JB / T 13038-2017; the results are shown in Table 1.

[0087] (5) Mortar residue rate: After casting and vibrating the shell, clean the sand. Measure the mass of the residual sand grains on the workpiece as m 残留砂粒 ; The total mass of the workpiece is m; The results are shown in Table 1. The calculation formula is as follows:

[0088] Mortar residue rate = (m 残留砂粒 / m) × 100%

[0089] (6) Workpiece repair rate: After casting the final shell film, visually comprehensively evaluate the surface burrs, punctures, depressions, etc. of the workpiece. If it does not meet the standard, it will be returned for repair; The results are shown in Table 1. The calculation formula is as follows:

[0090] Workpiece repair rate = Number of returned workpieces / Total number of workpieces

[0091] Table 1

[0092]

[0093] As can be seen from Table 1, the modified silica sol prepared by the present invention has a short drying time, high wet strength, low residual strength, low mortar residue rate, and low workpiece repair rate, indicating that the castings obtained have good quality and meet the high requirements of precision casting for the back layer and the surface layer; The pH value is 1 - 11, and it has a wide application range.

[0094] From the comparison between the examples and the comparative examples, it can be seen that the silica sol, film-forming aid, polymer dispersant, silane coupling agent, and water-based polymer emulsion in the modified silica sol have good synergistic effects. The interlayer quick-drying time of Comparative Example 1 without the film-forming aid increases significantly; The interlayer quick-drying time of Comparative Example 2 without the polymer dispersant increases greatly, while the wet strength decreases and the residual strength becomes higher; The interlayer quick-drying time of Comparative Example 3 without the silane coupling agent decreases while the wet strength decreases and the residual strength becomes higher; The quick-drying time and strength of Comparative Example 4 without the water-based polymer emulsion also deteriorate significantly; The mortar residue rate and workpiece repair rate of the comparative examples also increase significantly, indicating that the castings obtained have poor quality.

[0095] Obviously, the above examples are only for clear illustration and are not limitations on the implementation methods. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A general modified silica sol for investment casting back layer and / or surface layer, characterized in that, Comprising: 86 - 95% silica sol, 1 - 3% film-forming aid, 1 - 3% polymer dispersant, 1 - 3% silane coupling agent, 1 - 3% aqueous polymer emulsion, by mass percentage.

2. The precision casting back layer and / or surface layer general modified silica sol according to claim 1, characterized in that, The pH value of the general modified silica sol for the precision casting back layer and / or surface layer is 1 - 11; and / or, The solid content of the general modified silica sol for the precision casting back layer and / or surface layer is 20 - 25%.

3. The precision casting back layer and / or surface layer general modified silica sol according to claim 1 or 2, characterized in that The film-forming aid includes at least one of dodecyl alcohol ester, aqueous polycarbonate, tripropylene glycol n-butyl ether, polyurethane, aqueous polycarbonate diol, ethyl 3-ethoxypropionate, ethylene glycol monobutyl ether acetate, mixed dibasic acid diisobutyl ester, diisobutyl adipate, ethylene glycol monobutyl ether, sodium polystyrene sulfonate, styrene-butadiene copolymer; and / or, The polymer dispersant includes at least one of polycaprolactone-polyethyleneimine block copolymer type, polyether-modified polysiloxane, propylene glycol monomethyl ether acidic solution, sodium polyacrylate, polyvinyl alcohol.

4. The precision casting back layer and / or surface layer general modified silica sol according to any one of claims 1-3, characterized in that The silane coupling agent includes at least one of amino silane coupling agent and epoxy silane coupling agent; Preferably, the amino silane coupling agent includes at least one of N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane; Preferably, the epoxy silane coupling agent includes at least one of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and (3-glycidoxypropyl)trimethoxysilane.

5. The precision casting back layer and / or surface layer general modified silica sol according to any one of claims 1-4, characterized in that The aqueous polymer emulsion includes acrylic emulsion; Preferably, the acrylic emulsion includes at least one of epoxy-modified aqueous acrylic emulsion, organosilicon-modified aqueous acrylic emulsion, and organofluorine-modified aqueous acrylic emulsion.

6. A preparation method of a general modified silica sol for precision casting back layer and / or surface layer, characterized in that, Including the following steps: Mix silica sol, water and polymer dispersant, disperse, then add silane coupling agent, first stir, add film-forming aid and aqueous polymer emulsion, second stir, to obtain the general modified silica sol for the precision casting back layer and / or surface layer.

7. The preparation method according to claim 6, characterized in that, The dispersion is selected from ultrasonic dispersion; and / or, The dispersion time is 20 - 40 min.

8. The preparation method according to claim 6 or 7, characterized in that, The preparation method is carried out at 20 - 25 °C; and / or, The rotation speed of the first stir is 500 - 1000 rpm; and / or, The time of the first stir is 1 - 2 h.

9. The preparation method according to any one of claims 6-8, characterized in that, The rotation speed of the second stir is 500 - 1000 rpm; and / or, The time of the second stir is 10 - 30 min.

10. Application of the general modified silica sol for the precision casting back layer and / or surface layer according to any one of claims 1 - 5 or the modified silica sol prepared by the preparation method according to any one of claims 6 - 9 in the shell surface layer and / or shell back layer.

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