A precision casting back layer and / or face layer universal modified silica sol, and a preparation method and application thereof

Abstract

This invention belongs to the field of silica sol technology, specifically relating to a universal modified silica sol for precision casting back layers and / or surface layers, its preparation method, and its application. This invention provides a universal modified silica sol for precision casting back layers and / or surface layers, comprising: by mass percentage, 86-95% silica sol, 1-3% film-forming aid, 1-3% polymeric dispersant, 1-3% silane coupling agent, and 1-3% aqueous polymeric emulsion. The universal modified silica sol for precision casting back layers and / or surface layers provided by this invention, through the synergistic effect between the components in the aforementioned specific amounts, significantly shortens the drying time, enhances the strength and stability of the resulting shell, reduces processes, lowers costs, improves production efficiency, and meets the high requirements of precision casting for back layers and surface layers.

Description

Technical Field

[0001] This invention belongs to the field of silica sol technology, specifically relating to a general-purpose modified silica sol for precision casting back layers and / or surface layers, its preparation method, and its application. Background Technology

[0002] Precision casting is a highly precise manufacturing process designed to produce castings with more accurate dimensions and smoother surfaces. Compared to traditional sand casting, precision casting can produce more precise, complex parts that closely resemble their final shape, reducing or even eliminating subsequent machining processes, thus falling under the category of advanced near-net-shape manufacturing. In the precision casting process, a suitable material is first used to create a wax film. Then, multiple layers of refractory slurry and sand are coated onto the wax film surface and allowed to dry and harden to form a shell. Next, the wax film is dissolved to form the required cavity, and the shell is sintered to enhance strength. Finally, molten metal is poured into the shell. After the metal solidifies and cools, subsequent processing steps such as shell removal and cleaning are performed to obtain a high-precision finished casting. It is important to note that the quality of precision castings is affected by many factors, including casting geometry, material, investment casting material, shell-making process, and pouring temperature. Improper setup or operation of any process step can lead to changes in the quality of the finished product, thus affecting the final product quality. Therefore, careful design and strict control of each process step are crucial in precision casting to ensure that the final product meets specifications.

[0003] In precision casting, the properties of the surface layer slurry and the back layer slurry have a significant impact on the quality of the final casting. The surface layer slurry, in direct contact with the wax block, determines the surface finish and dimensional accuracy of the casting. The back layer slurry, on the other hand, primarily provides the strength and stability of the mold shell. Currently, existing casting surface layer slurries on the market are mainly optimized for surface layer applications, exhibiting significant limitations in back layer applications. These limitations are specifically manifested in the following aspects:

[0004] (1) Long drying time: Existing casting surface slurries dry slowly in back layer applications, which cannot meet the needs of rapid production. This is mainly because surface slurries are usually designed to dry slowly at lower temperatures to ensure surface quality, but in back layer applications, this characteristic leads to a longer 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, but 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 of the casting and production efficiency.

[0006] (3) Complex process: Precision casting involves many complex processes, including investment pattern making, shell preparation, pouring, and shell removal. Existing surface slurry cannot shorten the drying time while ensuring surface quality, resulting in low efficiency of the entire production process and failing to meet the demands of modern industry for efficient and rapid production.

[0007] Existing technologies provide a backing slurry to improve the wet strength of the shell and reduce the residual strength; however, the preparation method is complex, the production efficiency is low, and it can only prepare the backing layer. Existing technologies also provide a surface slurry to improve the wet strength and crack resistance of the casting slurry, but it cannot prepare the backing 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 of the prior art, which requires the preparation of slurry for the preparation of the surface layer and the back layer, which is complicated and the slurry has a long drying time, poor wet strength and high residual strength. Thus, the present invention provides a general modified silica sol for precision casting back layer and / or surface layer, its preparation method and application.

[0009] This invention provides a universal modified silica sol for precision casting back layer and / or surface layer that can be used simultaneously as a surface layer slurry and a back layer slurry. It can further improve the wet strength required by the surface layer slurry and optimize the surface quality of the casting. It can also reduce the residual strength of the shell made by the back layer slurry. While ensuring the quality and performance of the material itself, it shortens the drying time and improves the production efficiency.

[0010] To this end, the present invention provides the following technical solution.

[0011] This invention provides a general-purpose modified silica sol for precision casting backing and / or top layer, comprising: 86-95% silica sol, 1-3% film-forming aid, 1-3% polymeric dispersant, 1-3% silane coupling agent, and 1-3% aqueous polymeric emulsion by mass percentage.

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

[0013] In one alternative embodiment, the solid content of the precision-cast backing and / or surface layer universal modified silica sol is 20-25%.

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

[0015] In one optional embodiment, the film-forming aid includes at least one of the following: dodecyl alcohol ester, aqueous polycarbonate, tripropylene glycol n-butyl ether, polyurethane, aqueous polycarbonate diol, ethyl 3-ethoxypropionate, ethylene glycol butyl ether acetate, mixed diacid diisobutyl ester, diisobutyl adipate, ethylene glycol monobutyl ether, sodium polystyrene sulfonate, and polystyrene-butadiene copolymer. The film-forming aid lowers the minimum film-forming temperature of the silica sol, enabling continuous film formation at lower temperatures and improving 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 particle fusion and cross-linking, and accelerating the film-forming process. Simultaneously, the film-forming aid acts as a temporary plasticizer during film formation, making the silica sol particles more easily deformable, closer together, and fused after moisture evaporation, thereby accelerating the drying speed.

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

[0017] Waterborne polycarbonate diols refer to the aqueous dispersion form of polycarbonate diols;

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

[0019] In one optional embodiment, the polymeric dispersant comprises at least one of the following: polycaprolactone polyol-polyethyleneimine block copolymer, polyether-modified polysiloxane, propylene glycol monomethyl ether acidic solution, sodium polyacrylate, and polyvinyl alcohol. The polymeric dispersant, through electrostatic repulsion and steric hindrance, enables silica sol particles to maintain high dispersion and uniform particle size in the aqueous phase. This uniform dispersion facilitates a closer arrangement of particles during film formation, reducing voids, accelerating water evaporation and the bonding between silica sol particles, thereby improving drying efficiency.

[0020] Polycaprolactone polyol-polyethyleneimine block copolymer is a general term for a class of dispersants, including representative ones such as: waterborne superdispersant 9760 hydrophilic polymer block copolymer (DVK Chemicals), Dispex UltraPX4275 (BASF), etc.

[0021] In one optional embodiment, the silane coupling agent includes at least one of aminosilane coupling agents and epoxysilane coupling agents; the silane coupling agent reacts chemically with the hydroxyl groups on the surface of silica sol particles to form chemically bonded organic groups, which can further interact with the active groups in the film-forming aid or aqueous polymer emulsion, accelerating the cross-linking and fusion between 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 aminosilane coupling agent comprises at least one selected from 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-epoxypropoxypropyl)trimethoxysilane.

[0024] In one optional embodiment, the aqueous polymeric emulsion includes an acrylic emulsion; the aqueous polymeric emulsion can form a continuous polymer film during the drying process, which interweaves with the silica sol film to form a composite film with a three-dimensional network structure; this gives the back and surface layers of the precision casting good air permeability, flexibility and tensile strength, making it less prone to cracking during the drying process, thereby accelerating the overall drying speed.

[0025] Preferably, the acrylic emulsion includes at least one of epoxy-modified waterborne acrylic emulsion, silicone-modified waterborne acrylic emulsion, and organofluorine-modified waterborne acrylic emulsion.

[0026] This invention also provides a method for preparing a universal modified silica sol for precision casting back layer and / or surface layer, comprising the following steps:

[0027] Silica sol, water, and a polymeric dispersant are mixed and dispersed. Then, a silane coupling agent is added, followed by a first stirring. Film-forming aids and an aqueous polymeric emulsion are added, followed by a second stirring to obtain a general-purpose modified silica sol for precision casting back layers and / or surface layers.

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

[0029] In one alternative implementation, the dispersion time is 20-40 minutes.

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

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

[0032] In one alternative implementation, the first stirring time is 1-2 hours.

[0033] In one optional embodiment, the second stirring speed is 500-1000 rpm;

[0034] In one optional embodiment, the second stirring time is 10-30 minutes.

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

[0036] This document describes a general-purpose slurry comprising a refractory material and the aforementioned general-purpose modified silica sol for precision casting backing and / or surface layers, or a general-purpose modified silica sol for precision casting backing and / or surface layers prepared by the aforementioned method; the refractory material comprises at least one of mullite powder and zircon powder; the mass ratio of the general-purpose modified silica sol for precision casting backing and / or surface layers to the refractory material is 1:2.

[0037] This section describes a method for preparing a membrane substrate, including the following steps:

[0038] The precision-cast wax block substrate is placed in the general slurry and coated, and then dried at room temperature without wind to obtain the shell film substrate.

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

[0040] 1. The universal modified silica sol for precision casting back layers and / or surface layers provided by this invention comprises: 86-95% silica sol, 1-3% film-forming aid, 1-3% polymeric dispersant, 1-3% silane coupling agent, and 1-3% aqueous polymeric emulsion by mass percentage. Through the synergistic effect of the components in the above-mentioned specific amounts, the universal modified silica sol for precision casting back layers and / or surface layers provided by this invention significantly shortens drying time, enhances the strength and stability of the resulting mold shell, reduces processes, lowers costs, and improves production efficiency, meeting the high requirements of precision casting for back layers and surface layers; its pH value is 1-11, and it has a wide range of applications.

[0041] This invention incorporates silica sol, film-forming aids, polymeric dispersants, silane coupling agents, and aqueous polymeric emulsions in a defined mass ratio, exhibiting a synergistic effect. This effectively improves the quality and performance of shells prepared from universally modified silica sols for precision casting back layers and / or surface layers. It enhances the wet strength of the shell film surface layer while reducing the residual strength of the shell film back layer. Simultaneously, the drying time is shortened to ≤1 hour, which is 40% shorter than the drying time of traditional surface layer slurries in existing technologies. This significantly reduces the production cycle and factory space requirements. Using the universally modified silica sols for precision casting back layers and / or surface layers provided by this invention, both the back layer and surface layer of the shell can be prepared simultaneously, greatly shortening the production cycle and improving production efficiency.

[0042] Silane coupling agents react 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 film-forming aids or aqueous polymeric emulsions, accelerating the cross-linking and fusion between silica sol particles. The addition of aqueous polymeric emulsions causes the polymer film and silica sol film to intertwine, forming a three-dimensional network structure composite film that improves the air permeability and flexibility of the back and surface layers. This results in good film-forming properties, long service life, and short drying time for the modified silica sol, thereby improving the strength and stability of the obtained shell back or surface layer and increasing the yield and quality of castings. The compressive strength of the shell back layer obtained by this invention is 30% higher than that of traditional back layer slurries.

[0043] Furthermore, the amount of film-forming aids specified in this invention does not compromise the stability of the silica sol, while exhibiting good film-forming properties, facilitating subsequent slurry preparation; the amount of polymeric dispersant added improves the dispersibility of the modified silica sol, and the rapid evaporation of water ensures fast drying while maintaining good stability, allowing the slurry to be used continuously and reducing costs; the amount of silane coupling agent added enhances the compatibility of the modified silica sol and results in high wet strength of the prepared shell or back layer.

[0044] If the amount of film-forming aid is less than 1%, the wax block cannot form a film, affecting the subsequent slurry preparation of the general-purpose modified silica sol for precision casting back layers and / or top layers. A concentration above 3% will damage the stability of the modified silica sol, leading to failure to form a film. If the amount of polymeric dispersant is less than 1%, the silica sol cannot be dispersed, causing the prepared general-purpose modified silica sol for precision casting back layers and / or top layers to aggregate and become unusable. A concentration above 3% will reduce the stability of the subsequent slurry for the general-purpose modified silica sol for precision casting back layers and / or top layers, resulting in unusable slurry and increased costs. If the amount of silane coupling agent is less than 1%, the silica sol itself cannot be modified, affecting subsequent preparation and reducing silica sol compatibility. A concentration above 3% will result in excessive hydrolysis of the silane coupling agent, affecting the shell strength of the subsequent slurry formed by the general-purpose modified silica sol for precision casting back layers and / or top layers. If the amount of aqueous polymeric emulsion is less than 1%, it cannot interweave with the silica sol film, reducing the air permeability and flexibility of the back and top layers and increasing drying time. A concentration higher than 3% can affect the film-forming properties of general-purpose modified silica sols for precision casting back layers and / or surface layers, as well as the service life of silica sol slurries.

[0045] 2. The universal modified silica sol for precision casting backing and / or surface layers provided by this invention has good industry applicability, eliminating the need for any complex auxiliary processes, equipment, or environments during backing or surface layer drying, simplifying procedures, reducing labor and equipment costs, and exhibiting good environmental adaptability and process compatibility. It can be stably produced under different temperature and humidity conditions and can be seamlessly integrated with existing casting processes, facilitating rapid application by enterprises. It enables precision casting technology upgrades without significant modifications to existing production lines, improving production efficiency and casting quality, and enhancing market competitiveness.

[0046] 3. The application of the universal modified silica sol for precision casting back layers and / or surface layers provided by this invention in the shell surface layer and shell back layer jointly 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 collapse capability in precision casting shells. This universal modified silica sol for both back layers and surface layers not only improves the efficiency of the casting process and the quality of castings, but also has good environmental adaptability and process compatibility, providing new possibilities for the development of precision casting technology. Attached Figure Description

[0047] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0048] Figure 1 This is an SEM image of the universal modified silica sol for precision casting back layer and / or surface layer in Embodiment 1 of the present invention;

[0049] Figure 2 This is a slurry coating diagram of the surface layer prepared by the general modified silica sol for precision casting back layer and / or surface layer in Embodiment 1 of the present invention.

[0050] Figure 3 This is a diagram of the slurry backing layer prepared from a general modified silica sol for precision casting in Embodiment 1 of the present invention. Detailed Implementation

[0051] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0052] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0053] The silica sol used in the following examples is the high-purity SKP series silica sol from Guangdong Huierte Nanotechnology Co., Ltd.

[0054] Example 1

[0055] This embodiment provides a modified silica sol, comprising: by mass percentage, 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; the film-forming aid is a mixture of waterborne polycarbonate diol (Asahi Kasei Corporation, Japan, PCDL T5652), polyurethane (Guangzhou Changhao Trading Co., Ltd., SGR-2106W), and sodium polystyrene sulfonate (Wuhan Lanabai Pharmaceutical 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. SEM images of the modified silica sol are shown below. Figure 1 , Figure 1 The metric bar is 500 nm.

[0056] This embodiment also provides a method for preparing modified silica sol, including the following steps:

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

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

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

[0060] Example 2

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

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

[0063] Example 3

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

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

[0066] Example 4

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

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

[0069] Comparative Example 1

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

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

[0075] Comparative Example 3

[0076] This comparative example provides a modified silica sol comprising: 92% silica sol, 2% film-forming aid, 2% polyvinyl alcohol, 2% epoxy-modified waterborne acrylic emulsion, and 2% deionized water by mass percentage. 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 was prepared according to the preparation method provided in Example 1.

[0078] Comparative Example 4

[0079] This comparative example provides a modified silica sol comprising: 92% silica sol, 2% film-forming aid, 2% polyvinyl alcohol, 2% silane coupling agent, 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.

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

[0081] Test case

[0082] The modified silica sols obtained in Examples 1-4 and Comparative Examples 1-4 were mixed with refractory materials (mullite powder and zirconia powder, manufacturer: Guanxing Guwang Technology Co., Ltd.) at a mass ratio of 1:2.5 to prepare a slurry, and its performance was tested. The slurry surface coating diagram of the slurry obtained in Example 1 is shown in the figure. Figure 2 The back layer coating diagram of the slurry prepared in Example 1 is shown below. Figure 3 The details are as follows:

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

[0084] (2) Interlayer drying time of the shell: The prepared slurry was coated onto the mold, and the drying time was recorded after drying. The coating was repeated until the shell was prepared. The drying time of each coating layer was counted and the average value was taken to obtain the interlayer drying time of the shell. Drying was completed by measuring the moisture content, which means that the moisture content of the coating layer surface is between 5% and 10%, or the shell no longer continues to lose water (crystallization water). The results are shown in Table 1.

[0085] (3) Wet strength of the shell: The test was conducted using the method of JB / T 13038-2017. The results are shown in Table 1.

[0086] (4) Residual strength of the shell: The test was conducted using the method of JB / T 13038-2017; the results are shown in Table 1.

[0087] (5) Mortar Residual Rate: After the vibratory shell is poured, the sand is cleaned, and the mass of residual sand particles in the workpiece is measured to be 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 rework rate: After the final shell casting, the workpiece is visually evaluated for burrs, punctures, dents, etc. Workpieces that do not meet the standards are returned for rework; the results are shown in Table 1. The calculation formula is as follows:

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

[0091] Table 1

[0092]

[0093] As shown in Table 1, the modified silica sol prepared by this invention has a short drying time, high wet strength, low residual strength, low slurry residue rate, and low workpiece rework rate, indicating that the resulting castings are of good quality and meet the high requirements of precision casting for the back layer and surface layer; the pH value is 1-11, which has a wide range of applications.

[0094] The comparison of the examples and comparative examples shows that the silica sol, film-forming aid, polymeric dispersant, silane coupling agent, and aqueous polymeric emulsion in the modified silica sol have a good synergistic effect. The interlayer fast drying time of Comparative Example 1 without film-forming aid is significantly increased; the interlayer fast drying time of Comparative Example 2 without polymeric dispersant is significantly increased while the wet strength decreases and the residual strength increases; the interlayer fast drying time of Comparative Example 3 without silane coupling agent is increased while the wet strength decreases and the residual strength increases; the fast drying time and strength of Comparative Example 4 without aqueous polymeric emulsion are also significantly worse; the mortar residue rate and workpiece rework rate of the comparative examples also increase significantly, indicating that the quality of the castings is poor.

[0095] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A universal modified silica sol for precision casting backing and / or surface layers, characterized in that, include: By mass percentage, it consists of 86-95% silica sol, 1-3% film-forming aid, 1-3% polymeric dispersant, 1-3% silane coupling agent, and 1-3% aqueous polymeric emulsion. The film-forming aid includes at least one of the following: dodecyl alcohol ester, aqueous polycarbonate, tripropylene glycol n-butyl ether, polyurethane, aqueous polycarbonate diol, ethyl 3-ethoxypropionate, ethylene glycol butyl ether acetate, mixed dicarboxylic acid diisobutyl ester, diisobutyl adipate, ethylene glycol monobutyl ether, sodium polystyrene sulfonate, and polystyrene butadiene copolymer. The polymeric dispersant includes at least one of the following: polycaprolactone polyol-polyethyleneimine block copolymer, polyether-modified polysiloxane, propylene glycol monomethyl ether acidic solution, sodium polyacrylate, and polyvinyl alcohol.

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

3. The universal modified silica sol for precision casting back layer and / or surface layer according to claim 1, characterized in that, The silane coupling agent includes at least one of aminosilane coupling agents and epoxysilane coupling agents.

4. The universal modified silica sol for precision casting back layer and / or surface layer according to claim 3, characterized in that, The aminosilane coupling agent includes at least one of N-2-aminoethyl-3-aminopropylmethyldimethoxysilane, N-2-aminoethyl-3-aminopropyltrimethoxysilane, and 3-aminopropyltriethoxysilane.

5. The universal modified silica sol for precision casting back layer and / or surface layer according to claim 3, characterized in that, The epoxy silane coupling agent includes at least one of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and (3-epoxypropoxypropyl)trimethoxysilane.

6. The universal modified silica sol for precision casting backing and / or surface layers according to any one of claims 1-5, characterized in that, The aqueous polymeric emulsion includes an acrylic emulsion.

7. The universal modified silica sol for precision casting back layer and / or surface layer according to claim 6, characterized in that, The acrylic emulsion includes at least one of epoxy-modified waterborne acrylic emulsion, silicone-modified waterborne acrylic emulsion, and organofluorine-modified waterborne acrylic emulsion.

8. A method for preparing a universal modified silica sol for precision casting back layer and / or surface layer as described in any one of claims 1-7, characterized in that, Includes the following steps: Silica sol, water, and a polymeric dispersant are mixed and dispersed. Then, a silane coupling agent is added, followed by a first stirring. Next, a film-forming aid and an aqueous polymeric emulsion are added, followed by a second stirring, to obtain a general-purpose modified silica sol for precision casting back layers and / or surface layers.

9. The method for preparing the universal modified silica sol for precision casting back layer and / or surface layer according to claim 8, characterized in that, The dispersion is selected from ultrasonic dispersion; and / or, The dispersion time is 20-40 minutes.

10. The method for preparing the universal modified silica sol for precision casting back layer and / or surface layer according to claim 8 or 9, characterized in that, The preparation method is carried out at 20-25°C; and / or, The first stirring speed is 500-1000 rpm; and / or, The first stirring time is 1-2 hours.

11. The method for preparing the universal modified silica sol for precision casting back layer and / or surface layer according to claim 8 or 9, characterized in that, The second stirring speed is 500-1000 rpm; and / or, The second stirring time is 10-30 minutes.

12. The application of the general modified silica sol for precision casting back layer and / or face layer prepared by any of the methods of the general modified silica sol for precision casting back layer and / or face layer according to any one of claims 1-7 in the shell face layer and / or shell back layer.

Images