Preparation method of surface layer slurry for large complex titanium alloy investment casting

Abstract

The invention relates to the technical field of investment casting, in particular to a preparation method of surface layer slurry for large complex titanium alloy investment casting. The preparation method of the surface layer slurry for large complex titanium alloy investment casting comprises the following steps: S100, developing a surface layer material; s200, modifying the surface layer slurry, wherein modifiers comprise a wetting agent, a defoaming agent and an A-type modifier; s300, preparing surface layer slurry; and S400, inspecting the performance of the surface layer slurry. The preparation method of the surface layer slurry for large-scale complex titanium alloy investment casting has the advantages that the strength of the slurry surface layer is improved, and the defect that a surface layer shell falls off to form slag inclusion due to the fact that titanium liquid washes the shell during pouring is avoided.

Description

Technical Field

[0001] This invention relates to the field of investment casting technology, and in particular to a method for preparing a surface slurry for investment casting of large and complex titanium alloys. Background Technology

[0002] Titanium alloys possess advantages such as low density, high plasticity, and corrosion resistance, leading to their widespread application in petrochemical, shipbuilding, and aerospace industries. Currently, most domestic titanium enterprises still employ investment casting and graphite mold casting methods. Graphite mold casting, however, suffers from limitations due to the inability to reuse molds, high costs, and relatively poor surface roughness and precision of the castings, thus restricting its application. In contrast, investment casting, with its superior forming accuracy and surface quality, has become the mainstream process. In the investment casting industry, the surface slurry preparation process is one of the core technologies, directly impacting the quality of the castings. Investment casting slurries primarily rely on the surface tension of the binder to adsorb refractory powder particles, forming a network structure that generates a certain bonding strength.

[0003] Current methods for preparing surface coating slurries are mature. For example, Chinese invention patent CN101811174A discloses a method for preparing a surface coating shell. This invention solves the problems of high cost and environmental pollution during dewaxing of shells prepared by existing methods. The method involves: 1. Preparing a mixed adhesive; 2. Preparing a surface coating slurry; 3. Coating, sprinkling with sand, and drying to obtain the surface coating shell. The method for preparing the surface coating slurry includes: adding 0.5-1 ml of wetting agent and 0.8-1.2 ml of defoamer to each kilogram of the mixed adhesive prepared in step 1, and then adding 2-4 kg of 320-mesh refractory powder and stirring for 10-24 hours to obtain the surface coating slurry. Regardless of the method used, the viscosity, density, flow rate, and leveling properties of the slurry will affect the surface strength of the surface coating shell. For example, the slurry prepared by the method in this patent has low surface strength, and the titanium liquid washing away from the surface coating shell during casting can cause the shell to detach, forming inclusion defects. The service life of the slurry determines the quality of the surface shell. Because the surface powder of titanium alloy contains yttrium oxide powder, its anti-gelling ability is poor, resulting in a short service life of the surface layer. Summary of the Invention

[0004] In view of this, the present invention aims to provide a method for preparing a surface slurry for large and complex titanium alloy investment casting. This method employs a silica sol surface binder and yttrium oxide refractory powder. Zirconia and calcium oxide are added to the yttrium oxide refractory powder to modify the surface slurry. The silica sol surface binder is added to a mixing tank all at once while stirring at low speed. Then, yttrium oxide refractory powder is added to the mixing tank in three separate additions while stirring thoroughly. Next, a wetting agent, defoamer, and type A modifier are added. After a certain period of high-speed stirring, the stirring speed is switched back to low speed to form the surface slurry for large and complex titanium alloy investment casting. This method solves the problems of poor anti-gelling ability, shortened service life, low slurry surface strength, and slag inclusion defects caused by the titanium liquid washing away the surface shell during casting. The service life of the slurry determines the quality of the surface shell. Because the titanium alloy surface powder contains yttrium oxide powder, its anti-gelling ability is poor, leading to a short service life of the surface layer.

[0005] To address the above problems, this invention provides a method for preparing a surface slurry for large and complex titanium alloy investment casting, comprising:

[0006] S100, development of surface layer materials;

[0007] S200, surface slurry modification, the modifier types are wetting agent, defoamer and type A modifier;

[0008] Wetting agents include: organic alcohols, phosphate esters, and nonionic surfactants;

[0009] Type A modifiers include: Kathon, hydrogen peroxide, and polyvinylpyrrolidone;

[0010] S300, preparation of surface slurry;

[0011] Slurry is prepared in a continuously rotating slurry mixing tank;

[0012] S400, Inspect the performance of the surface layer slurry;

[0013] The inspection items include: appearance, viscosity, density, suspension properties, service life, bending strength, and flexural strength.

[0014] Furthermore, in step S100, the method for developing the surface layer material includes:

[0015] S110. Select a silica sol surface adhesive. The characteristics of the silica sol surface adhesive are: SiO2 content of 10%~15%, Na2O content ≤0.5%, SiO2 particle size of 5nm~12nm, density of 1.05~1.20g / cm3, and pH value of 9~11.

[0016] S120. Select surface layer powder, select yttrium oxide refractory powder. The characteristics of yttrium oxide refractory powder are: zirconium oxide and calcium oxide content is 5%~15%, the overall particle size of the powder is 200~320 mesh, of which 1000 mesh fine powder content is 50%~70%, and the particle size distribution of the powder is bimodal.

[0017] Furthermore, in step S300, the method for preparing the surface layer slurry includes:

[0018] S310. Weigh m1 of silica sol surface adhesive using an electronic balance and add it to the mixing tank at once. Turn on the mixing tank and start the low-speed stirring mode, with a speed of 200~500 r / min.

[0019] S320. Weigh out m2 units of yttrium oxide refractory powder and add it to the mixing tank in two to three portions. Stir for at least 3 minutes after each addition to ensure there are no dispersed lumps of powder in the slurry tank. The ratio of m2 to m1 is (4~5.5):1.

[0020] S330. Weigh out m3 of wetting agent, m4 of defoamer, and m5 of type A modifier, and add them to the slurry tank, where m3:m1 = (0.3%~0.6%):1, m4:m1 = (0.1%~0.3%):1, and m5:m1 = (0.05%~0.3%):1.

[0021] S340. Turn on the high-speed stirring mode to eliminate the clustered agglomerates in the slurry and form dispersed elongated aggregates. The stirring time is 10~30min, and the speed of the high-speed stirring mode is 1000~1800r / min.

[0022] S350, turn on the low-speed stirring mode, stir for ≥1 hour to obtain a surface slurry with the preset viscosity.

[0023] Furthermore, in step S400, the method for checking the appearance includes: taking a small amount of slurry sample, distributing it evenly on a glass slide or casting plate, and visually inspecting whether the selected sample is uniform and whether there are any inclusions.

[0024] Furthermore, in step S400, the method for checking the viscosity includes:

[0025] The flow cup is lifted and immersed in the slurry twice to fully wet it;

[0026] Immerse the flow cup into the slurry from the middle of the slurry tank to a depth of about 150mm, then lift it vertically. Start timing the moment the bottom of the cup leaves the liquid surface and stop timing when the liquid flow changes from a streamline to a droplet.

[0027] Repeat the above steps at least twice. If the difference between the consecutive test results does not exceed 2 seconds, take the average value. The internal control viscosity is considered qualified if it is between 20 seconds and 26 seconds.

[0028] Furthermore, in step S400, the method for detecting the density of the slurry includes: detecting the density using a 100mL graduated cylinder. First, weigh the mass m6 of the graduated cylinder, then add slurry into the graduated cylinder until it reaches the 100mL mark, and then weigh the mass m7. The slurry density ρ = (m7 - m6) / 100, and the internal control density value is ≥2.9 g / cm3.

[0029] Furthermore, in step S400, the method for detecting the suspension of the slurry includes: pouring the prepared surface slurry into a graduated cylinder to reach a height of 100 mL, leaving it in a static state for 24 hours, measuring the volume V (in mL) of the clarified layer at the top of the slurry column in the graduated cylinder, and the suspension rate of the slurry C = (100-V) / 100, with an internal control suspension rate ≥90%.

[0030] Furthermore, in step S400, the method for detecting the service life of the slurry includes: characterizing the service life of the slurry by the viscosity method; after the slurry is prepared, the viscosity of the slurry is detected and recorded every 5 minutes until the difference between the detected viscosity value and the initial viscosity value is >2s. The time taken is the service life of the slurry, and the internal control service life is ≥40min.

[0031] Furthermore, in step S400, the method for detecting bending strength includes: detecting bending strength by firing the shell after baking, measuring the width a and thickness h of the sample, placing the sample on the support, and then gently pressing the indenter on the sample surface, with it in the middle position of the sample, recording the span L = 30 mm between the two support points, starting the testing machine and loading at a speed of 5 mm / min until the sample breaks, recording the load P when the sample breaks, then the bending strength σ = 3PL / 2ah2, with no less than 3 valid measurements, taking their arithmetic mean, and the internal control bending strength ≥ 5.0 MPa.

[0032] Furthermore, in step S400, the method for detecting flexural strength includes: scraping the surface of the molded shell test block with a scraper, the molded shell test block being fixed on a worktable, the scraper being connected to a drive device, and the drive device driving the scraper to perform linear motion scraping on the surface of the molded shell test block; the scraper has a force of 5.4N, a blade diameter of Φ4mm, a speed of 12mm / s, and a total stroke of 600mm; after each scraping, the scrap is collected; the molded shell test block for each type of slurry is repeated 10 times; the scrap is collected and weighed using an electronic balance; the less scrap from the detached molded shell test block, the greater the flexural strength of the molded shell surface, that is, the stronger the molded shell's resistance to molten metal erosion and scraping; the internal control of the molded shell scrap is ≤1g.

[0033] Compared with existing technologies, the method for preparing a surface slurry for large and complex titanium alloy investment casting described in this invention has the following advantages:

[0034] The advantages of this technical solution lie in the use of silica sol surface binder and yttrium oxide refractory powder. Zirconia and calcium oxide are added to the yttrium oxide refractory powder to modify the surface slurry. After the silica sol surface binder is added to the mixing tank all at once and stirred at low speed, the yttrium oxide refractory powder is added to the mixing tank in three batches and stirred thoroughly. Then, wetting agent, defoamer and type A modifier are added. After stirring at high speed for a certain period of time, the stirring speed is switched to low speed to form the surface slurry for large and complex titanium alloy investment casting. This enhances the anti-gelling ability, extends the service life, improves the surface strength of the slurry, and avoids the shell falling off and forming inclusion defects caused by the titanium liquid washing away the surface shell during casting. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0036] In this invention, the terms "first," "second," "upper," and "lower," etc., are used for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," "upper," or "lower" may explicitly or implicitly include at least one of those features. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. Where the technical solutions of the embodiments can be combined, they are all within the scope of protection claimed by this invention.

[0037] The present invention will now be described in detail with reference to embodiments.

[0038] A method for preparing a surface slurry for large and complex titanium alloy investment casting, comprising:

[0039] S100, development of surface layer materials;

[0040] S110. Select a silica sol surface adhesive. The characteristics of the silica sol surface adhesive are: SiO2 content of 10%~15%, Na2O content ≤0.5%, SiO2 particle size of 5nm~12nm, density of 1.05~1.20g / cm3, and pH value of 9~11.

[0041] S120. Select surface layer powder, select yttrium oxide refractory powder. The characteristics of yttrium oxide refractory powder are: zirconium oxide and calcium oxide content is 5%~15%, the overall particle size of the powder is 200~320 mesh, of which 1000 mesh fine powder content is 50%~70%, and the particle size distribution of the powder is bimodal.

[0042] S200, surface slurry modification, the modifier types are wetting agent, defoamer and type A modifier;

[0043] Wetting agents are used to improve the wettability and coatability of slurries. The main types include: organic alcohols, phosphate esters, and nonionic surfactants.

[0044] Type A modifiers mainly extend the service life of slurries and include: Kathon, hydrogen peroxide, and polyvinylpyrrolidone.

[0045] S300, preparation of surface slurry;

[0046] Methods for preparing surface slurry by mixing slurry in a continuously rotating slurry mixing tank include:

[0047] S310. Use an electronic balance to weigh m1 of silica sol surface adhesive and add it to the mixing tank at once. Turn on the mixing tank and start the low-speed mixing mode with a rotation speed of 200~500r / min.

[0048] S320. Weigh out m2 of yttrium oxide refractory powder and add it to the mixing tank in two to three portions. After each addition, the mixing time should be no less than 3 minutes to ensure that there are no dispersed powder lumps in the slurry tank. The ratio of m2 to m1 is (4~5.5):1.

[0049] S330, weigh out m3 of wetting agent, m4 of defoamer, and m5 of type A modifier, and add them to the slurry tank, wherein m3:m1 = (0.3%~0.6%):1, m4:m1 = (0.1%~0.3%):1, and m5:m1 = (0.05%~0.3%):1;

[0050] S340. Turn on the high-speed stirring mode to eliminate the agglomerates in the slurry and form dispersed elongated aggregates. The stirring time is 10~30min and the speed of the high-speed stirring mode is 1000~1800r / min.

[0051] S350, turn on the low-speed stirring mode, stir for ≥1 hour to obtain a surface slurry with the preset viscosity;

[0052] S400, Inspect the performance of the surface layer slurry;

[0053] The inspection items include: appearance, viscosity, density, suspension properties, service life, bending strength, and flexural strength.

[0054] Methods for checking the appearance include: taking a small amount of slurry sample, distributing it evenly on a glass slide or casting plate, and visually inspecting whether the selected sample is uniform and whether there are any inclusions.

[0055] Methods for checking viscosity include:

[0056] The flow cup is lifted and immersed in the slurry twice to fully wet it;

[0057] Immerse the flow cup into the slurry from the middle of the slurry tank to a depth of about 150mm, then lift it vertically. Start timing the moment the bottom of the cup leaves the liquid surface and stop timing when the liquid flow changes from a streamline to a droplet.

[0058] Repeat the above steps at least twice. If the difference between the consecutive test results does not exceed 2 seconds, take the average value. The internal control viscosity is considered qualified if it is between 20 seconds and 26 seconds.

[0059] The method for testing the density of the slurry includes: measuring the density using a 100mL graduated cylinder. First, weigh the graduated cylinder (m6, accurate to 0.01g). Then, add slurry to the graduated cylinder until it reaches the 100mL mark. Next, weigh the cylinder again (m7, in g) with the same accuracy. The slurry density ρ = (m7 - m6) / 100, with an internal control density value ≥ 2.9 g / cm³. 3 .

[0060] The method for testing the suspension of slurry includes: pouring the prepared surface slurry into a graduated cylinder to a height of 100 mL, leaving it in a static state for 24 hours, and measuring the volume V (in mL) of the clarified layer at the top of the slurry column in the graduated cylinder. The suspension rate of the slurry is C = (100 - V) / 100, and the internal control suspension rate is ≥90%.

[0061] The method for testing the service life of slurry includes: characterizing the service life of slurry by viscosity method. After the slurry is prepared, the viscosity of the slurry is tested and recorded every 5 minutes until the difference between the tested viscosity value and the initial viscosity value is >2 seconds. The time taken is the service life of the slurry, and the internal control service life is ≥40 minutes.

[0062] The method for testing bending strength includes: testing the bending strength of the shell after firing, measuring the width a and thickness h of the specimen, placing the specimen on the support, and then gently pressing the indenter on the surface of the specimen, with the indenter in the middle position of the specimen, recording the span L = 30 mm between the two support points, starting the testing machine and loading at a speed of 5 mm / min until the specimen breaks, recording the load P when the specimen breaks, then the bending strength σ = 3PL / 2ah2, with no less than 3 valid measurements, taking their arithmetic mean, and the internal control bending strength ≥ 5.0 MPa.

[0063] The method for testing flexural strength includes: scraping the surface of the molded shell test block with a scraper. The shell test block is fixed on the worktable, and the scraper is connected to a drive device. The drive device drives the scraper to perform linear scraping on the surface of the shell test block. The scraper has a force of 5.4N, a blade diameter of Φ4mm, a speed of 12mm / s, and a total stroke of 600mm. After each scraping, the scrap is collected. The shell test is repeated 10 times for each type of slurry. The scrap is collected and weighed using an electronic balance. The less scrap the shell test block detaches, the greater the flexural strength of the shell surface, that is, the stronger the shell's resistance to molten metal erosion and scratching. The internal control of shell scrap is ≤1g.

[0064] Example 1

[0065] Preparation of large-scale complex thin-walled titanium alloy surface slurry

[0066] S100, surface material development:

[0067] S110, selection of surface adhesive;

[0068] The selected surface adhesive is a silica sol with a SiO2 content of 12%, a Na2O content of ≤0.3%, a SiO2 particle size of 7nm, a density of 1.1g / cm3, and a pH value of 10.

[0069] S120, Selection of surface powder;

[0070] Yttrium oxide refractory powder was selected, with zirconium oxide and calcium oxide content of 10%, and the overall particle size of the powder was 320 mesh, of which 1000 mesh fine powder content was 60%, which is a bimodal gradation powder.

[0071] S200, Modification of Surface Slurry

[0072] The wetting agent is fatty alcohol polyoxyethyl ether, and the addition amount is 0.6% of the mass of the surface layer adhesive; the defoamer is n-octanol, and the addition amount is 0.2% of the mass of the surface layer adhesive; the type A modifier is Kathon, and the addition amount is 0.1% of the total mass of the slurry.

[0073] S300, preparation of surface slurry

[0074] The slurry preparation is completed in a continuously rotating slurry mixing tank. The order of adding materials and the mixing requirements are as follows:

[0075] S310. Weigh mg of surface adhesive using an electronic balance and add it to the mixing tank at once. Turn on the mixing tank and start low-speed stirring. The low-speed mode speed is 300r / min.

[0076] S320. Weigh 5mg of yttrium oxide powder and add it to the mixing tank in two to three portions. Stir for 5 minutes after each addition to ensure that there are no dispersed lumps of powder in the slurry tank.

[0077] S330, weigh out 0.6% mg of wetting agent, 0.2% mg of defoamer and 0.1% mg of Kathon, and add them to the slurry tank.

[0078] S340. Turn on the high-speed stirring mode to break up the clustered agglomerates in the slurry and form dispersed elongated aggregates. Stirring time: 20 minutes. High-speed stirring mode speed: 1200 r / min.

[0079] S350, turn on the low-speed stirring mode, stir for 1 hour, and obtain a surface slurry with qualified viscosity.

[0080] S400, Inspect the performance of the surface layer slurry;

[0081] After testing, the appearance, viscosity, density, and suspension rate of the surface slurry met the standards; the service life of the slurry was 50 minutes, which is 20 minutes longer than that of ordinary slurry; the bending strength of the surface shell was 6.49 MPa, which is 70% higher than that of ordinary slurry; and the flexural strength of the surface shell was 0.3 g, which meets the requirements for the production of large thin-walled titanium alloy castings.

[0082] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a surface slurry for investment casting of large and complex titanium alloys, characterized in that, include: S100, development of surface layer materials; S200, surface slurry modification, the modifier types are wetting agent, defoamer and type A modifier; Wetting agents include: organic alcohols, phosphate esters, and nonionic surfactants; Type A modifiers include: Kathon, hydrogen peroxide, and polyvinylpyrrolidone; S300, preparation of surface slurry; Slurry is prepared in a continuously rotating slurry mixing tank; S400, Inspect the performance of the surface layer slurry; The inspection items include: appearance, viscosity, density, suspension properties, service life, bending strength, and flexural strength.

2. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S100, the method for developing the surface layer material includes: S110. Select a silica sol surface adhesive. The characteristics of the silica sol surface adhesive are: SiO2 content of 10%~15%, Na2O content ≤0.5%, SiO2 particle size of 5nm~12nm, density of 1.05~1.20g / cm3, and pH value of 9~11. S120. Select surface layer powder. Select yttrium oxide refractory powder. The characteristics of yttrium oxide refractory powder are: zirconium oxide and calcium oxide content is 5%~15%, the overall particle size of the powder is 200~320 mesh, of which 1000 mesh fine powder content is 50%~70%, and the particle size distribution of the powder is bimodal.

3. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S300, the method for preparing the surface layer slurry includes: S310. Weigh m1 of silica sol surface adhesive using an electronic balance and add it to the mixing tank all at once. Turn on the mixing tank and start the low-speed mixing mode with a rotation speed of 200~500 r / min. S320. Weigh out m2 units of yttrium oxide refractory powder and add it to the mixing tank in two to three portions. Stir for at least 3 minutes after each addition to ensure there are no dispersed lumps of powder in the slurry tank. The ratio of m2 to m1 is (4~5.5):

1. S330. Weigh out m3 of wetting agent, m4 of defoamer, and m5 of type A modifier, and add them to the slurry tank, where m3:m1 = (0.3%~0.6%):1, m4:m1 = (0.1%~0.3%):1, and m5:m1 = (0.05%~0.3%):

1. S340. Turn on the high-speed stirring mode to eliminate the clustered agglomerates in the slurry and form dispersed elongated aggregates. The stirring time is 10~30min, and the speed of the high-speed stirring mode is 1000~1800r / min. S350, turn on the low-speed stirring mode, stir for ≥1 hour to obtain a surface slurry with the preset viscosity.

4. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S400, the method for checking the appearance includes: taking a small amount of slurry sample, distributing it evenly on a glass slide or casting plate, and visually inspecting whether the selected sample is uniform and whether there are any inclusions.

5. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S400, the method for checking viscosity includes: The flow cup is lifted and immersed in the slurry twice to fully wet it; Immerse the flow cup into the slurry from the middle of the slurry tank to a depth of about 150mm, then lift it vertically. Start timing the moment the bottom of the cup leaves the liquid surface and stop timing when the liquid flow changes from a streamline to a droplet. Repeat the above steps at least twice. If the difference between the consecutive test results does not exceed 2 seconds, take the average value. The internal control viscosity is considered qualified if it is between 20 seconds and 26 seconds.

6. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S400, the method for detecting the slurry density includes: detecting the density using a 100mL graduated cylinder. First, weigh the graduated cylinder (m6). Then, add slurry to the graduated cylinder until it reaches the 100mL mark, and weigh it again (m7). The slurry density ρ = (m7 - m6) / 100, and the internal control density value is ≥2.9 g / cm³. 3 .

7. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S400, the method for detecting the suspension of the slurry includes: pouring the prepared surface slurry into a graduated cylinder to reach the 100 mL mark, leaving it in a static state for 24 hours, measuring the volume V (in mL) of the clarified layer at the top of the slurry column in the graduated cylinder, and the suspension rate of the slurry C = (100-V) / 100, with an internal control suspension rate ≥90%.

8. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S400, the method for detecting the service life of the slurry includes: characterizing the service life of the slurry by the viscosity method; after the slurry is prepared, the viscosity of the slurry is detected and recorded every 5 minutes until the difference between the detected viscosity value and the initial viscosity value is >2s. The time taken is the service life of the slurry, and the internal control service life is ≥40min.

9. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S400, the method for detecting bending strength includes: detecting bending strength by firing the shell after baking, measuring the width a and thickness h of the sample, placing the sample on the support, and then gently pressing the indenter on the sample surface, with the indenter in the middle position of the sample, recording the span L = 30 mm between the two support points, starting the testing machine and loading at a speed of 5 mm / min until the sample breaks, recording the load P when the sample breaks, then the bending strength σ = 3PL / 2ah2, with no less than 3 valid measurements, taking their arithmetic mean, and the internal control bending strength ≥ 5.0 MPa.

10. The method for preparing the surface slurry for large and complex titanium alloy investment casting according to claim 1, characterized in that, In step S400, the method for detecting flexural strength includes: scraping the surface of the molded shell test block with a scraper. The molded shell test block is fixed on the worktable, and the scraper is connected to a drive device. The drive device drives the scraper to perform linear motion on the surface of the molded shell test block for scraping. The scraper has a force of 5.4N, a blade diameter of Φ4mm, a speed of 12mm / s, and a total stroke of 600mm. After each scraping, the scrap is collected. The molded shell test block is repeated 10 times for each type of slurry. The scrap is collected and weighed using an electronic balance. The less scrap from the molded shell test block, the greater the flexural strength of the molded shell surface, that is, the stronger the molded shell's resistance to molten metal erosion and scraping. The internal control of the molded shell scrap is ≤1g.