Shell for investment casting, preparation method of shell and preparation method of casting

Abstract

The invention relates to a shell for investment casting, a preparation method of the shell and a preparation method of a casting, and the preparation method of the shell for investment casting comprises the following steps that pre-wetting slurry is adopted to conduct pre-wetting treatment on a wax pattern module, and the wax pattern module with a pre-wetting layer on the surface is obtained; wherein the viscosity of the pre-wetted slurry is 8 to 11 seconds; preparing a surface layer and a back layer on the wax mold module with the pre-wetting layer to obtain a mold shell containing a wax mold; wherein the viscosity of surface layer slurry used for preparing the surface layer is greater than that of the pre-wetting slurry; the viscosity of back layer slurry used for preparing the back layer is greater than that of the pre-wetting slurry; carrying out dewaxing treatment on the shell containing the wax mold to obtain a dewaxed shell; and the shell subjected to dewaxing treatment is roasted, and the shell for investment casting is obtained. In the preparation process of the shell, bubbles at the corners of the wax mold are effectively reduced, so that the dead angle part of the shell is prevented from being entrained with the bubbles, and the surface quality and the yield of castings are ensured.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy investment casting technology, and in particular to a mold shell for investment casting and its preparation method, as well as a method for preparing castings. Background Technology

[0002] In the investment casting process, a fusible wax model is generally made from wax material. Then, several layers of special refractory coating are applied to the wax model. After drying and hardening, a whole shell is formed. Then, the wax material is dissolved from the shell by steam pressure. Finally, the shell is placed in a baking furnace and baked at high temperature to obtain a high-strength shell.

[0003] In precision casting, mold preparation is one of the most critical factors affecting the quality of castings. It not only determines the dimensional accuracy and surface roughness of castings, but also directly affects the manufacturing cost and production efficiency of castings.

[0004] Among them, the surface quality of the shell directly affects the surface quality of the casting. Due to the high viscosity and relatively poor fluidity of the surface slurry, during the slurry pouring process, for some castings with complex shapes and dimensions, very small air bubbles are easily trapped in the dead corners of the casting and are not easy to detect, resulting in low strength in these areas. During the subsequent pouring of high-temperature alloy liquid, the impact of the alloy liquid will cause casting defects to form in these areas, which greatly increases the difficulty of subsequent polishing and repair, thereby reducing the yield of the casting. Summary of the Invention

[0005] In view of this, the present invention provides a mold shell for investment casting and a method for preparing the same, as well as a method for preparing castings. The main purpose is to effectively reduce the generation of air bubbles at the corners of the wax pattern during the preparation of the mold shell, so as to avoid the dead corners of the mold shell from trapping air bubbles, thereby ensuring the surface quality and yield of the castings.

[0006] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0007] On one hand, embodiments of the present invention provide a method for preparing a mold shell for investment casting, which includes the following steps:

[0008] Pre-wetting treatment: The wax model assembly is pre-wetted with a pre-wetting slurry to obtain a wax model assembly with a pre-wetted layer on the surface; wherein, the viscosity of the pre-wetting slurry is 8-11s;

[0009] Shell making process: On the wax mold assembly with the pre-wetted layer, a surface layer and a back layer are prepared to obtain a shell containing the wax mold; wherein, the viscosity of the surface layer slurry used to prepare the surface layer is greater than the viscosity of the pre-wetted slurry; the viscosity of the back layer slurry used to prepare the back layer is greater than the viscosity of the pre-wetted slurry;

[0010] Dewaxing and firing treatment: The shell containing the wax pattern is dewaxed to obtain a dewaxed shell; the dewaxed shell is then fired to obtain a shell for investment casting.

[0011] Preferably, the pre-wetted slurry comprises ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer; wherein the mass ratio of the ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(1.6-1.8):(0.001-0.003):(0.001-0.003).

[0012] Preferably, the preparation steps of the ethyl silicate hydrolysate include:

[0013] Distilled water and alcohol are added to a hydrolysis stirring device and stirring is started. Then, ethyl silicate is added, and finally hydrochloric acid is added. The hydrolysis reaction is carried out for 50-70 minutes to obtain ethyl silicate hydrolysate. Preferably, the mass ratio of ethyl silicate, hydrochloric acid, distilled water, and alcohol is (4.8-5.2):(39-41):(0.9-1.1):(2.9-3.1), more preferably 5:40:1:3. Preferably, the concentration of hydrochloric acid is 14-16%, more preferably 15%, and the concentration of alcohol is 94-96%, more preferably 95%.

[0014] Preferably, in the pre-wetting treatment step: the wax mold assembly is immersed in the pre-wetting slurry for 4 to 5 seconds; after immersion, the wax mold assembly is removed from the pre-wetting slurry and dried at room temperature for 8 to 12 minutes to obtain a wax mold assembly with a pre-wetting layer on the surface.

[0015] Preferably, the preparation step of the pre-wetted slurry includes:

[0016] First, stir the ethyl silicate hydrolysate, then add a wetting agent and stir to obtain a first mixture; add corundum powder to the first mixture and stir until there are no lumps or powder particles on the surface of the slurry to obtain a second mixture; add a defoamer to the second mixture and stir to obtain a pre-wetted slurry;

[0017] Preferably, during the process of adding the corundum powder to the first mixture, continuous stirring is required to prevent the powder from clumping or agglomerating.

[0018] Preferably, in the pre-wetting treatment step: before pre-wetting the wax mold assembly with the pre-wetting slurry, the wax mold assembly needs to be cleaned and dried to remove oil stains from the wax mold assembly.

[0019] Preferably, prior to the pre-wetting treatment step, the procedure further includes:

[0020] Preparation of wax mold assembly: Place the gating system containing embedded rods and metal tooling into the mold, close the mold, inject liquid wax into the mold and hold it under pressure. After the wax solidifies and forms, a wax mold assembly including the wax mold and the gating system is obtained.

[0021] Preferably, in the shell-making process: the surface layer slurry used to prepare the surface layer includes: ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer; wherein the mass ratio of ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(2.2-2.5):(0.001-0.003):(0.001-0.003); and / or the viscosity of the surface layer slurry used to prepare the surface layer is 45-49 s; and / or the back layer slurry used to prepare the back layer includes: ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer; wherein the mass ratio of ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(2.0-2.2):(0.001-0.003):(0.001-0.003); and / or the viscosity of the back layer slurry used to prepare the back layer is 12-17 s.

[0022] Preferably, in the shell-making process: after sequentially coating the wax mold assembly with the pre-wetted layer with a top layer and a back layer, a sealant is applied, and after drying, a shell containing the wax mold is formed; preferably, in the top layer preparation step: after each top layer is applied, drying is performed under the following conditions: temperature 22±5℃, humidity 75±10%RH, drying time ≥210min; and / or preferably, in the back layer preparation step: after each back layer is applied, drying is performed under the following conditions: temperature 22±5℃, humidity 75±10%RH, drying time ≥120min; and / or preferably, after sealing, drying is performed for a drying time ≥48h; preferably, the total number of top and back layers is 7-8.

[0023] Preferably, in the dewaxing and firing process: the dewaxing process is a steam-pressurized dewaxing process; and / or in the firing process: the dewaxed shell is rapidly heated to 900℃±20℃ at a heating rate of 8-10℃ / min, and fired for 2h±0.5h. After firing, when the shell cools down to below 400℃ in the furnace, the furnace door is opened for 40-60min to accelerate cooling. After the furnace temperature naturally cools to room temperature, the shell is removed.

[0024] Preferably, the corundum powder is 320# corundum powder; and / or the wetting agent is Nalco 7667; and / or the defoamer is Nalco 2305.

[0025] On the other hand, embodiments of the present invention provide a mold shell for investment casting, wherein the mold shell for investment casting is prepared by the preparation method for the mold shell for investment casting described in any one of the above claims.

[0026] In another aspect, embodiments of the present invention provide a method for preparing a casting, which includes the following steps:

[0027] High-temperature alloy liquid is poured into the cavity of the above-mentioned investment casting mold shell. When pouring the high-temperature alloy liquid, the temperature of the investment casting mold shell is a set temperature. After the investment casting mold shell cools down, the shell is removed to obtain the casting. Preferably, the set temperature is 900-1000℃.

[0028] Preferably, the high-temperature alloy liquid comprises the following chemical components by weight percentage: carbon: 0.06-0.10 wt%, chromium: 12-13.0 wt%, cobalt: 8.5-9.5 wt%, tungsten: 3.85-4.5 wt%, molybdenum: 1.65-2.15 wt%, aluminum: 3.15-3.6 wt%, titanium: 3.75-4.20 wt%, zirconium: 0.01-0.05 wt%, boron: 0.01-0.02 wt%, tantalum: 3.85-4.5 wt%, with the balance being nickel.

[0029] Preferably, the pouring temperature of the high-temperature alloy liquid is 1520℃±10℃, and the pouring time is ≤10s; and / or the casting is cut to obtain an equiaxed polycrystalline nickel-based high-temperature alloy casting.

[0030] Compared with the prior art, the present invention provides a mold shell for investment casting, a method for preparing the same, and a method for preparing castings, which have at least the following beneficial effects:

[0031] On one hand, this invention provides a method for preparing a mold shell for investment casting. Before the shell preparation process, a pre-wetting slurry is used to pre-wet the wax mold assembly to obtain a wax mold assembly with a pre-wetted layer on the surface. The viscosity of the pre-wetted slurry is 8-11s. During the shell preparation process, the viscosity of the surface layer slurry used to prepare the surface layer is greater than the viscosity of the pre-wetted slurry. The viscosity of the back layer slurry used to prepare the back layer is greater than the viscosity of the pre-wetted slurry. It should be noted that in the precision casting process, the preparation of the mold shell is one of the most critical factors affecting the quality of the casting. The surface layer quality of the mold shell directly affects the surface quality of the casting. Due to the high viscosity and relatively poor fluidity of the surface layer slurry, during the slurry pouring process, for some castings with complex shapes and dimensions, very small air bubbles are easily trapped in the dead corners of the casting and are not easily detected, resulting in low shell strength in these areas. During the subsequent pouring of high-temperature alloy liquid, the impact of the alloy liquid will cause casting defects to form in these areas, greatly increasing the difficulty of subsequent polishing and reducing the yield of the casting. For the reasons mentioned above, in the shell preparation process of this invention, before applying the top coat, a pre-wetting slurry with a viscosity of 8-11s is used to pre-wet the entire wax mold assembly. Then, during the shell preparation process, a high-viscosity slurry is used to prepare the top and back coats. Here, because the pre-wetted layer has a low viscosity and the slurry has good fluidity and is easy to adhere to the surface of the assembly, the pre-wetting of the wax mold assembly before applying the top coat can effectively reduce the generation of casting defects, thus ensuring the surface quality of the casting and improving the yield of the casting.

[0032] Furthermore, the formulation of the pre-wetting slurry used in this invention is as follows: the mass ratio of ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(1.6-1.8):(0.001-0.003):(0.001-0.003), preferably 1:(1.6-1.8):0.003:0.003. Here, the ethyl silicate hydrolysate in the pre-wetting agent acts as a binder primarily to uniformly mix the corundum powder with the defoamer and wetting agent, and to adhere the slurry to the surface of the wax mold assembly. The defoamer effectively removes air bubbles generated during the mixing process. The wetting agent reduces the surface tension of the coating, decreases the wetting angle, and allows the slurry to spread on the mold surface, achieving good wetting properties and thus improving the adhesion of the coating.

[0033] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0034] Figure 1 This is a photograph of the casting prepared in Example 1;

[0035] Figure 2 This is a photograph of the casting prepared in Comparative Example 1;

[0036] Figure 3 This is a photograph of the casting prepared in Example 2;

[0037] Figure 4 This is a photograph of the casting prepared in Example 3;

[0038] Figure 5 This is a physical image of the casting prepared in Comparative Example 2. Detailed Implementation

[0039] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0040] On one hand, this invention provides a method for preparing a mold shell for investment casting. The main method involves pre-wetting the entire wax mold assembly with a predetermined low-viscosity pre-wetting slurry before applying the top coat during the shell preparation process. This forms a low-viscosity pre-wetted layer. Then, during the shell preparation process, a high-viscosity slurry is used to prepare the top and back coats. Because the slurry in the pre-wetted layer has good fluidity and easily adheres to the surface of the wax mold assembly, pre-wetting the wax mold assembly before applying the top coat effectively reduces the generation of air bubbles at the corners of the wax mold, ensuring the surface quality of the casting and improving the casting yield. The main components of this invention are as follows:

[0041] This invention provides a method for preparing a mold shell for investment casting, which includes the following steps:

[0042] Preparation of the wax model module: A suitable mold is selected based on the product's shape and size. A gating system containing embedded rods and metal tooling is placed inside and the mold is closed. Liquid wax is then injected into the mold and pressure is maintained. After the wax solidifies, a wax model is obtained. This wax model is then combined with the gating system according to the assembly plan requirements to obtain a wax model module consisting of the wax model and the gating system. Here, the gating system is used for subsequent pouring of molten alloy into the mold shell.

[0043] Pre-wetting treatment: The wax mold assembly is pre-wetted using a pre-wetting slurry to obtain a wax mold assembly with a pre-wetted layer on the surface; wherein the viscosity of the pre-wetting slurry is 8-11s. The components of the pre-wetting slurry include ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer; wherein the mass ratio of ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(1.6-1.8):(0.001-0.003):(0.001-0.003), preferably 1:(1.9-2.1):0.003:0.003.

[0044] It should be noted that the ethyl silicate hydrolysate in the pre-wetted slurry acts as a binder primarily to uniformly mix the corundum powder with the defoamer and wetting agent, and to adhere the surface slurry to the surface of the wax mold assembly. The defoamer effectively removes air bubbles generated during the mixing process. The wetting agent reduces the surface tension of the slurry and decreases the wetting angle, allowing the slurry to spread on the mold surface, achieving good wettability and thus improving the adhesion of the slurry.

[0045] To improve the pre-wetting effect, before pre-wetting, clean the wax mold assembly with a special cleaning solution to remove any oily substances from the surface, ensuring there are no impurities. Then, immerse the assembly in the pre-wetting slurry for 4-5 seconds to ensure the slurry adheres evenly to the surface of the wax mold assembly. After wetting, let the wax mold assembly stand for about 3 minutes, until the pre-wetting slurry is no longer fluid and the surface is slightly dry, achieving a good pre-wetting effect.

[0046] Here, due to the use of the above-mentioned pre-wetted slurry, the viscosity of the pre-wetted layer is low, and the slurry has good fluidity and can easily adhere to the surface of the wax mold assembly. Therefore, when the surface layer is applied after the assembly is pre-wetted, the generation of air bubbles at the corners of the wax mold can be effectively reduced, which not only ensures the surface quality of the casting, but also improves the yield of the casting.

[0047] After coating, allow to dry at room temperature for 8-12 minutes.

[0048] In addition, the preparation steps of the ethyl silicate hydrolysate raw material include: first, weighing distilled water and alcohol and pouring them separately into the hydrolysate stirring device and starting stirring; then, adding ethyl silicate; and finally, adding hydrochloric acid. The hydrolysis process generally requires machine stirring to increase the uniformity of the reaction and also to increase the strength of the hydrolysate coating. The hydrolysis reaction time should be controlled within 50–70 minutes. The hydrolysate is generally stored for 24 hours after hydrolysis before use. Under sealed and constant temperature conditions, the well-stirred hydrolysate can be stably stored for about one week.

[0049] In addition, the pre-wetted slurry is prepared according to the following method:

[0050] 1) Pour all the weighed ethyl silicate hydrolysate into the mixing slurry bucket and stir until it is evenly mixed.

[0051] 2) Measure out the required wetting agent, then pour it into the mixture in step 1) and stir well.

[0052] 3) Slowly add the corundum powder to the mixed solution in step 2), and continuously stir the powder with a wooden stick to prevent clumping. Continue stirring with the wooden stick after adding all the powder until there are no "lumps" or "clumps" on the surface of the slurry.

[0053] 4) Measure out the required amount of defoamer, then pour it into the solution from step 3) and stir until homogeneous. After all the materials have been added, continue stirring for 24 hours to obtain the pre-wetted slurry.

[0054] Shell preparation: On the wax mold assembly with the pre-wetted layer, a surface layer and a back layer are prepared to obtain a shell containing the wax mold.

[0055] In this step, the surface layer and back layer are prepared, and the sealing process is repeated multiple times to complete the sealing process and then undergo final drying treatment.

[0056] In this step: the surface slurry includes ethyl silicate hydrolysate, corundum powder, wetting agent and defoamer, wherein the ratio of ethyl silicate hydrolysate: corundum powder: wetting agent: defoamer is 1:(2.2~2.5):(0.001~0.003):(0.001~0.003), and the viscosity reaches 45~49s.

[0057] In this step: the backing slurry includes ethyl silicate hydrolysate, corundum powder, wetting agent and defoamer, wherein the ratio of ethyl silicate hydrolysate: corundum powder: wetting agent: defoamer is 1:(2.0~2.2):(0.001~0.003):(0.001~0.003), and its viscosity is 12~17s.

[0058] In the preparation of the top layer: after each layer is coated, it is dried. The drying environment is as follows: temperature 22±5℃, humidity 75±10%RH, drying time ≥210min.

[0059] In the backing layer preparation step: after each backing layer is coated, it will be dried. The drying environment is as follows: temperature 22±5℃, humidity 75±10%RH, drying time ≥120min.

[0060] Preferably, after sealing, the mixture is dried for 48 hours.

[0061] Preferably, the total number of coating layers, including the top and back layers, is 7.5.

[0062] Dewaxing and firing treatment: The shell containing the wax pattern is dewaxed sequentially to obtain a dewaxed shell; the dewaxed shell is then fired to obtain a shell for investment casting.

[0063] In this step, the dewaxing process is a steam-pressurized dewaxing process.

[0064] In the baking process: the dewaxed shell is rapidly heated to 900℃±20℃ and baked for 2h±0.5h. After baking, when the shell cools down to below 400℃ in the furnace, the furnace door is opened for 40-60min to accelerate cooling. After the furnace temperature cools down to room temperature, the shell is removed.

[0065] In another aspect, embodiments of the present invention provide a method for preparing a casting, which includes the following steps:

[0066] High-temperature alloy liquid is poured into the cavity of the above-mentioned investment casting mold shell. When pouring the high-temperature alloy liquid, the temperature of the investment casting mold shell is a set temperature. After the investment casting mold shell cools down, the shell is removed to obtain the casting. Preferably, the set temperature is 900-1000℃.

[0067] Preferably, the high-temperature alloy liquid comprises the following chemical components by weight percentage: carbon: 0.06-0.10 wt%, chromium: 12-13.0 wt%, cobalt: 8.5-9.5 wt%, tungsten: 3.85-4.5 wt%, molybdenum: 1.65-2.15 wt%, aluminum: 3.15-3.6 wt%, titanium: 3.75-4.20 wt%, zirconium: 0.01-0.05 wt%, boron: 0.01-0.02 wt%, tantalum: 3.85-4.5 wt%, with the balance being nickel.

[0068] Preferably, the specific casting process parameters for the casting are as follows:

[0069] Refining temperature: 1550℃±10℃ Refining time: 1min-2min

[0070] Pouring temperature: 1520℃±10℃; Pouring time: ≤10s

[0071] Vacuum degree after alloy melting: ≤5Pa; Standing time: ≥2min

[0072] Furthermore, the casting obtained after pouring is cut to obtain an equiaxed nickel-based superalloy casting.

[0073] The present invention will be further illustrated below through specific experimental examples:

[0074] Example 1

[0075] This embodiment prepares a mold shell for investment casting, and uses the mold shell to pour high-temperature alloy liquid to prepare small-sized high-pressure turbine blades.

[0076] The method for preparing the mold shell for investment casting in this embodiment mainly includes the following steps:

[0077] Preparation of wax mold assembly: Select a suitable mold according to the shape and size of the product, place the gating system containing the embedded rod and metal tooling into it and close the mold, then inject liquid wax into the mold and hold it under pressure. After the mold material solidifies and forms, the wax mold is obtained. Combine it with the gating system according to the assembly scheme requirements to obtain the wax mold assembly.

[0078] Pre-wetting treatment: After cleaning the wax model assembly in a cleaning solution to remove surface oil, allow it to air dry. Then, directly pre-wet the surface of the assembly. Specifically, immerse the assembly in the pre-wetting slurry for 4-5 seconds to ensure the slurry adheres evenly to the surface of the wax model assembly. After immersion, let the wax model assembly stand for about 3 minutes until the pre-wetting slurry is no longer fluid and the surface is slightly dry, achieving a good pre-wetting effect. The viscosity of the pre-wetting slurry is 8-11s. After application, allow it to dry at room temperature for 10 minutes.

[0079] The pre-wetting slurry includes ethyl silicate hydrolysate, 320# corundum powder, wetting agent (Nalco 7667), and defoamer (Nalco 2305). The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:1.6:0.003:0.003.

[0080] The pre-wetted slurry is prepared by the following method: Step (a) Pour all the weighed ethyl silicate hydrolysate into the mixing tank and stir until homogeneous. Step (b) Measure the required wetting agent and add it to the mixture in step (a), stirring until homogeneous. Step (c) Slowly add 320# corundum powder to the mixture in step (b), stirring continuously with a wooden stick to prevent clumping. Continue stirring with the wooden stick until no lumps or clumps remain on the slurry surface. Step (d) Measure the required defoamer and add it to the solution in step (c), stirring until homogeneous. After all the additions are complete, continue stirring for 24 hours to obtain the pre-wetted slurry layer.

[0081] The preparation steps of the ethyl silicate hydrolysate are as follows: First, weigh distilled water and alcohol and pour them separately into the hydrolysate stirring device and start stirring. Then, add ethyl silicate, and finally add hydrochloric acid. The hydrolysis process generally requires machine stirring to increase the uniformity of the reaction and also to increase the strength of the hydrolysate coating. The hydrolysis reaction time should be controlled at around 60 minutes. The hydrolysate is generally stored for 24 hours after hydrolysis before use. Under sealed and constant temperature conditions, the well-stirred hydrolysate can be stably stored for about one week. The mass ratio of ethyl silicate, hydrochloric acid, distilled water, and alcohol is 5:40:1:3; the concentration of hydrochloric acid is 15%, and the concentration of alcohol is 95%.

[0082] Shell preparation: After pre-wetting treatment, the surface layer and back layer are prepared. This process is repeated multiple times to complete the sealing process and then the final drying treatment is carried out.

[0083] The surface slurry comprises ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2.2:0.003:0.003, and the viscosity reaches 45s.

[0084] The backing slurry includes ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2:0.003:0.003, and its viscosity is 12s.

[0085] The shell drying environment is as follows:

[0086] Surface drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 210min

[0087] Backing drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 120min

[0088] Before applying each layer of coating, inspect the mold in the drying room to ensure that there are no defects such as cracks, expansion, or peeling on the surface. During the slurry application, pay special attention to whether air bubbles are generated in the corners of the casting. If air bubbles are found, use an adjustable compressed air gun to blow them off to prevent casting defects.

[0089] After sealing, the mold shell dries for 48 hours, and the number of layers of the mold shell coating is 7.5.

[0090] Dewaxing and firing treatment: The dried shell is placed in a dewaxing axe for steam pressure dewaxing. The dewaxed shell is then fired. The specific firing steps are as follows:

[0091] After steam dewaxing, the mold shell is rapidly heated to 900℃ and baked for 2±0.5h. After baking, wait for the furnace to cool down. When the mold shell drops below 400℃, open the furnace door for 40-60min to accelerate cooling. After the furnace temperature naturally cools to room temperature, remove the trolley and take out the mold shell to obtain the mold shell for investment casting.

[0092] The high-temperature alloy liquid is poured into the above-mentioned investment casting shell, wherein the shell temperature is 900℃. After the shell cools, it is demolded to finally obtain the finished casting.

[0093] The composition of the high-temperature alloy liquid, by weight percentage, is as follows:

[0094] Carbon: 0.07 wt%, Chromium: 12.55 wt%, Cobalt: 8.5 wt%, Tungsten: 3.85 wt%, Molybdenum: 1.70 wt%, Aluminum: 3.25 wt%, Titanium: 3.95 wt%, Zirconium: 0.01 wt%, Boron: 0.01 wt%, Tantalum: 4.00 wt%, with the balance being nickel.

[0095] The specific casting process parameters are as follows:

[0096] Refining temperature: 1550℃±10℃ Refining time: 1min-2min

[0097] Pouring temperature: 1520℃±10℃; Pouring time: ≤10s

[0098] Vacuum degree after alloy melting: ≤5Pa; Standing time: ≥2min

[0099] The castings were de-shelled and cut after pouring to obtain equiaxed nickel-based superalloy castings.

[0100] For a physical image of the casting (small-sized low-pressure turbine equiaxed blade) obtained in this embodiment, please refer to [link / reference]. Figure 1 As shown, it can be seen that the surface quality of the small-sized low-pressure turbine equiaxial blades is good, and the casting defects at the corners and dead corners of the casting surface are relatively minor, with only a small number of spherical granular casting defects present. However, these defects can be removed by polishing the casting, and the initial inspection pass rate can reach over 95%.

[0101] Comparative Example 1

[0102] Comparative Example 1 prepared a mold shell for investment casting, and used the mold shell to pour high-temperature alloy liquid to prepare small-sized high-pressure turbine blades.

[0103] Preparation of wax mold assembly: Select a suitable mold according to the shape and size of the product, then inject liquid wax into the mold and hold it under pressure. After the mold material solidifies and forms, a wax mold is obtained. Combine it with the gating system according to the assembly scheme requirements to obtain the wax mold assembly.

[0104] Shell preparation: After cleaning the wax mold assembly in the cleaning solution to remove surface oil, it is dried. Then, the surface layer and back layer are prepared directly. After repeating this process multiple times, the sealing process is completed and the final drying process is carried out.

[0105] The surface slurry comprises ethyl silicate hydrolysate, 320# corundum powder, wetting agent (Nalco 7667), and defoamer (Nalco 2305). The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2.2:0.003:0.003, and the viscosity reaches 45s.

[0106] The backing slurry comprises ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2:0.003:0.003, and its viscosity is 13s.

[0107] The shell drying environment is as follows:

[0108] Surface drying environment: temperature 22±5℃, humidity 75±10%RH, drying time ≥210min

[0109] Backing drying environment: temperature 22±5℃, humidity 75±10%RH, drying time ≥120min. After sealing, the shell is dried for 48h. The number of shell coating layers is 7.5.

[0110] Dewaxing and firing treatment: The dried shell is placed in a dewaxing axe for steam pressure dewaxing. The dewaxed shell is then fired. The specific firing steps are as follows:

[0111] After steam dewaxing, the mold shell is rapidly heated to 900℃ and baked for 2±0.5h. After baking, wait for the furnace to cool down. When the mold shell drops below 400℃, open the furnace door for 40-60min to accelerate cooling. After the furnace temperature naturally cools to room temperature, remove the trolley and take out the mold shell to obtain the mold shell for investment casting.

[0112] The high-temperature alloy liquid is poured into the above-mentioned investment casting shell, wherein the shell temperature is 900℃. After the shell cools, it is demolded to finally obtain the finished casting.

[0113] The composition of the high-temperature alloy liquid, by weight percentage, is as follows:

[0114] Carbon: 0.07 wt%, Chromium: 12.55 wt%, Cobalt: 8.5 wt%, Tungsten: 3.85 wt%, Molybdenum: 1.70 wt%, Aluminum: 3.25 wt%, Titanium: 3.95 wt%, Zirconium: 0.01 wt%, Boron: 0.01 wt%, Tantalum: 4.00 wt%, with the balance being nickel.

[0115] The specific casting process parameters are as follows:

[0116] Refining temperature: 1550℃±10℃ Refining time: 1min-2min

[0117] Pouring temperature: 1520℃±10℃; Pouring time: ≤10s

[0118] Vacuum degree after alloy melting: ≤5Pa; Standing time: ≥2min

[0119] The castings were de-shelled and cut after pouring to obtain equiaxed nickel-based superalloy castings.

[0120] For a physical drawing of the casting (small-sized low-pressure turbine equiaxed blade) obtained in Comparative Example 1, please refer to [the image]. Figure 2 As shown, it can be seen that the surface quality of the small-sized low-pressure turbine equiaxial blades is poor, there are large casting nodules at the corners of the casting surface, and it is difficult to polish them at the corners. The initial inspection pass rate is only 60%.

[0121] Example 2

[0122] This embodiment prepares the same small-sized high-pressure turbine blades as in Example 1.

[0123] The method for preparing the mold shell for investment casting in this embodiment mainly includes the following steps:

[0124] Preparation of wax mold assembly: Select a suitable mold according to the shape and size of the product, place the gating system containing the embedded rod and metal tooling into it and close the mold, then inject liquid wax into the mold and hold it under pressure. After the mold material solidifies and forms, the wax mold is obtained. Combine it with the gating system according to the assembly scheme requirements to obtain the wax mold assembly.

[0125] Pre-wetting treatment: After cleaning the wax model assembly in a cleaning solution to remove surface oil, allow it to air dry. Then, directly pre-wet the surface of the assembly. Specifically, immerse the assembly in the pre-wetting slurry for 4-5 seconds to ensure the slurry adheres evenly to the surface of the wax model assembly. After immersion, let the wax model assembly stand for about 3 minutes until the pre-wetting slurry is no longer fluid and the surface is slightly dry, achieving a good pre-wetting effect. The viscosity of the pre-wetting slurry is 8-11s. After application, allow it to dry at room temperature for 10 minutes.

[0126] The pre-wetting slurry includes ethyl silicate hydrolysate, 320# corundum powder, wetting agent (Nalco 7667), and defoamer (Nalco 2305). The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:1.7:0.003:0.003.

[0127] The pre-wetted slurry is prepared by the following method: Step (a) Pour all the weighed ethyl silicate hydrolysate into the mixing tank and stir until homogeneous. Step (b) Measure the required wetting agent and add it to the mixture in step (a), stirring until homogeneous. Step (c) Slowly add 320# corundum powder to the mixture in step (b), stirring continuously with a wooden stick to prevent clumping. Continue stirring with the wooden stick until no lumps or clumps remain on the slurry surface. Step (d) Measure the required defoamer and add it to the solution in step (c), stirring until homogeneous. After all the additions are complete, continue stirring for 24 hours to obtain the pre-wetted slurry layer.

[0128] The preparation steps of the ethyl silicate hydrolysate are as follows: First, weigh distilled water and alcohol and pour them separately into the hydrolysate stirring device and start stirring. Then, add ethyl silicate, and finally add hydrochloric acid. The hydrolysis process generally requires machine stirring to increase the uniformity of the reaction and also to increase the strength of the hydrolysate coating. The hydrolysis reaction time should be controlled at around 60 minutes. The hydrolysate is generally stored for 24 hours after hydrolysis before use. Under sealed and constant temperature conditions, the well-stirred hydrolysate can be stably stored for about one week. The mass ratio of ethyl silicate, hydrochloric acid, distilled water, and alcohol is 5:40:1:3; the concentration of hydrochloric acid is 15%, and the concentration of alcohol is 95%.

[0129] Shell preparation: After pre-wetting treatment, the surface layer and back layer are prepared. This process is repeated multiple times to complete the sealing process and then the final drying treatment is carried out.

[0130] The surface slurry comprises ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2.3:0.003:0.003, and the viscosity reaches 46s.

[0131] The backing slurry includes ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2.1:0.003:0.003, and its viscosity is 12s.

[0132] The shell drying environment is as follows:

[0133] Surface drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 210min

[0134] Backing drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 120min

[0135] Before applying each layer of coating, inspect the mold in the drying room to ensure that there are no defects such as cracks, expansion, or peeling on the surface. During the slurry application, pay special attention to whether air bubbles are generated in the corners of the casting. If air bubbles are found, use an adjustable compressed air gun to blow them off to prevent casting defects.

[0136] After sealing, the mold shell dries for 48 hours, and the number of layers of the mold shell coating is 7.5.

[0137] Dewaxing and firing treatment: The dried shell is placed in a dewaxing axe for steam pressure dewaxing. The dewaxed shell is then fired. The specific firing steps are as follows:

[0138] After steam dewaxing, the mold shell is rapidly heated to 900℃ and baked for 2±0.5h. After baking, wait for the furnace to cool down. When the mold shell drops below 400℃, open the furnace door for 40-60min to accelerate cooling. After the furnace temperature naturally cools to room temperature, remove the trolley and take out the mold shell to obtain the mold shell for investment casting.

[0139] The high-temperature alloy liquid is poured into the above-mentioned investment casting shell, wherein the shell temperature is 900℃. After the shell cools, it is demolded to finally obtain the finished casting.

[0140] The composition of the high-temperature alloy liquid, by weight percentage, is as follows:

[0141] Carbon: 0.07 wt%, Chromium: 12.55 wt%, Cobalt: 8.5 wt%, Tungsten: 3.85 wt%, Molybdenum: 1.70 wt%, Aluminum: 3.25 wt%, Titanium: 3.95 wt%, Zirconium: 0.01 wt%, Boron: 0.01 wt%, Tantalum: 4.00 wt%, with the balance being nickel.

[0142] The specific casting process parameters are as follows:

[0143] Refining temperature: 1550℃±10℃ Refining time: 1min-2min

[0144] Pouring temperature: 1520℃±10℃; Pouring time: ≤10s

[0145] Vacuum degree after alloy melting: ≤5Pa; Standing time: ≥2min

[0146] The castings were de-shelled and cut after pouring to obtain equiaxed nickel-based superalloy castings.

[0147] For a physical image of the casting (small-sized low-pressure turbine equiaxed blade) obtained in this embodiment, please refer to [link / reference]. Figure 3As shown, it can be seen that the surface quality of the small-sized low-pressure turbine equiaxial blades is good, and the casting defects at the corners and dead corners of the casting surface are relatively minor, with only a small number of spherical granular casting defects present. However, these defects can be removed by polishing the casting, and the initial inspection pass rate can reach over 96%.

[0148] Example 3

[0149] This embodiment prepares the same small-sized high-pressure turbine blades as in Example 1.

[0150] The main steps include the following:

[0151] Preparation of wax mold assembly: Select a suitable mold according to the shape and size of the product, place the gating system containing the embedded rod and metal tooling into it and close the mold, then inject liquid wax into the mold and hold it under pressure. After the mold material solidifies and forms, the wax mold is obtained. Combine it with the gating system according to the assembly scheme requirements to obtain the wax mold assembly.

[0152] Pre-wetting treatment: After cleaning the wax model assembly in a cleaning solution to remove surface oil, allow it to air dry. Then, directly pre-wet the surface of the assembly. Specifically, immerse the assembly in the pre-wetting slurry for 4-5 seconds to ensure the slurry adheres evenly to the surface of the wax model assembly. After immersion, let the wax model assembly stand for about 3 minutes until the pre-wetting slurry is no longer fluid and the surface is slightly dry, achieving a good pre-wetting effect. The viscosity of the pre-wetting slurry is 8-11s. After application, allow it to dry at room temperature for 10 minutes.

[0153] The pre-wetting slurry includes ethyl silicate hydrolysate, 320# corundum powder, wetting agent (Nalco 7667), and defoamer (Nalco 2305). The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:1.8:0.003:0.003.

[0154] The pre-wetted slurry is prepared by the following method: Step (a) Pour all the weighed ethyl silicate hydrolysate into the mixing tank and stir until homogeneous. Step (b) Measure the required wetting agent and add it to the mixture in step (a), stirring until homogeneous. Step (c) Slowly add 320# corundum powder to the mixture in step (b), stirring continuously with a wooden stick to prevent clumping. Continue stirring with the wooden stick until no lumps or clumps remain on the slurry surface. Step (d) Measure the required defoamer and add it to the solution in step (c), stirring until homogeneous. After all the additions are complete, continue stirring for 24 hours to obtain the pre-wetted slurry layer.

[0155] The preparation steps of the ethyl silicate hydrolysate are as follows: First, weigh distilled water and alcohol and pour them separately into the hydrolysate stirring device and start stirring. Then, add ethyl silicate, and finally add hydrochloric acid. The hydrolysis process generally requires machine stirring to increase the uniformity of the reaction and also to increase the strength of the hydrolysate coating. The hydrolysis reaction time should be controlled at around 60 minutes. The hydrolysate is generally stored for 24 hours after hydrolysis before use. Under sealed and constant temperature conditions, the well-stirred hydrolysate can be stably stored for about one week. The mass ratio of ethyl silicate, hydrochloric acid, distilled water, and alcohol is 5:40:1:3; the concentration of hydrochloric acid is 15%, and the concentration of alcohol is 95%.

[0156] Shell preparation: After pre-wetting treatment, the surface layer and back layer are prepared. This process is repeated multiple times to complete the sealing process and then the final drying treatment is carried out.

[0157] The surface slurry comprises ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2.5:0.003:0.003, and the viscosity reaches 47s.

[0158] The backing slurry includes ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2.2:0.003:0.003, and its viscosity is 12s.

[0159] The shell drying environment is as follows:

[0160] Surface drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 210min

[0161] Backing drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 120min

[0162] Before applying each layer of coating, inspect the mold in the drying room to ensure that there are no defects such as cracks, expansion, or peeling on the surface. During the slurry application, pay special attention to whether air bubbles are generated in the corners of the casting. If air bubbles are found, use an adjustable compressed air gun to blow them off to prevent casting defects.

[0163] After sealing, the mold shell dries for 48 hours, and the number of layers of the mold shell coating is 7.5.

[0164] Dewaxing and firing treatment: The dried shell is placed in a dewaxing axe for steam pressure dewaxing. The dewaxed shell is then fired. The specific firing steps are as follows:

[0165] After steam dewaxing, the mold shell is rapidly heated to 900℃ and baked for 2±0.5h. After baking, wait for the furnace to cool down. When the mold shell drops below 400℃, open the furnace door for 40-60min to accelerate cooling. After the furnace temperature naturally cools to room temperature, remove the trolley and take out the mold shell to obtain the mold shell for investment casting.

[0166] The high-temperature alloy liquid is poured into the above-mentioned investment casting shell, wherein the shell temperature is 900℃. After the shell cools, it is demolded to finally obtain the finished casting.

[0167] The composition of the high-temperature alloy liquid, by weight percentage, is as follows:

[0168] Carbon: 0.07 wt%, Chromium: 12.55 wt%, Cobalt: 8.5 wt%, Tungsten: 3.85 wt%, Molybdenum: 1.70 wt%, Aluminum: 3.25 wt%, Titanium: 3.95 wt%, Zirconium: 0.01 wt%, Boron: 0.01 wt%, Tantalum: 4.00 wt%, with the balance being nickel.

[0169] The specific casting process parameters are as follows:

[0170] Refining temperature: 1550℃±10℃ Refining time: 1min-2min

[0171] Pouring temperature: 1520℃±10℃; Pouring time: ≤10s

[0172] Vacuum degree after alloy melting: ≤5Pa; Standing time: ≥2min

[0173] The castings were de-shelled and cut after pouring to obtain equiaxed nickel-based superalloy castings.

[0174] For a physical image of the casting (small-sized low-pressure turbine equiaxed blade) obtained in this embodiment, please refer to [link / reference]. Figure 4 As shown, it can be seen that the surface quality of the small-sized low-pressure turbine equiaxial blades is good, and the casting defects at the corners and dead corners of the casting surface are relatively minor, with only a small number of spherical granular casting defects present. However, these defects can be removed by polishing the casting, and the initial inspection pass rate can reach over 96%.

[0175] Comparative Example 2

[0176] This comparative example prepared the same small-sized high-pressure turbine blade as in Example 1.

[0177] The main steps include the following:

[0178] Preparation of wax mold assembly: Select a suitable mold according to the shape and size of the product, place the gating system containing the embedded rod and metal tooling into it and close the mold, then inject liquid wax into the mold and hold it under pressure. After the mold material solidifies and forms, the wax mold is obtained. Combine it with the gating system according to the assembly scheme requirements to obtain the wax mold assembly.

[0179] Pre-wetting treatment: After cleaning the wax model assembly in the cleaning solution to remove surface oil, allow it to air dry. Then, directly pre-wet the surface of the assembly. Specifically, immerse the assembly in the pre-wetting slurry for 4-5 seconds to ensure the slurry adheres evenly to the surface of the wax model assembly. After immersion, let the wax model assembly stand for about 3 minutes until the pre-wetting slurry is no longer fluid and the surface is slightly dry, achieving a good pre-wetting effect. The viscosity of the pre-wetting slurry is 7s. After application, allow it to dry at room temperature for 10 minutes.

[0180] The pre-wetting slurry includes ethyl silicate hydrolysate, 320# corundum powder, wetting agent (Nalco 7667), and defoamer (Nalco 2305). The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:1.5:0.003:0.003.

[0181] The pre-wetted slurry is prepared by the following method: Step (a) Pour all the weighed ethyl silicate hydrolysate into the mixing tank and stir until homogeneous. Step (b) Measure the required wetting agent and add it to the mixture in step (a), stirring until homogeneous. Step (c) Slowly add 320# corundum powder to the mixture in step (b), stirring continuously with a wooden stick to prevent clumping. Continue stirring with the wooden stick until no lumps or clumps remain on the slurry surface. Step (d) Measure the required defoamer and add it to the solution in step (c), stirring until homogeneous. After all the additions are complete, continue stirring for 24 hours to obtain the pre-wetted slurry layer.

[0182] The preparation steps of the ethyl silicate hydrolysate are as follows: First, weigh distilled water and alcohol and pour them separately into the hydrolysate stirring device and start stirring. Then, add ethyl silicate and finally add hydrochloric acid. The hydrolysis process generally requires machine stirring to increase the uniformity of the reaction and also to increase the strength of the hydrolysate coating. The hydrolysis reaction time should be controlled at around 50 minutes. The hydrolysate is generally stored for 24 hours after hydrolysis before use. Under sealed and constant temperature conditions, the well-stirred hydrolysate can be stably stored for about one week. The mass ratio of ethyl silicate hydrolysate, hydrochloric acid, distilled water, and alcohol is 5:40:1:3; the concentration of hydrochloric acid is 15%, and the concentration of alcohol is 95%.

[0183] Shell preparation: After pre-wetting treatment, the surface layer and back layer are prepared. This process is repeated multiple times to complete the sealing process and then the final drying treatment is carried out.

[0184] The surface slurry comprises ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2.5:0.003:0.003, and the viscosity reaches 46s.

[0185] The backing slurry includes ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer. The mass ratio of ethyl silicate hydrolysate, 320# corundum powder, wetting agent, and defoamer is 1:2.2:0.003:0.003, and its viscosity is 12s.

[0186] The shell drying environment is as follows:

[0187] Surface drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 210min

[0188] Backing drying environment: temperature 22±5℃, humidity 75±10%RH, drying time 120min

[0189] After sealing, the mold shell dries for 48 hours, and the number of layers of the mold shell coating is 7.5.

[0190] Dewaxing and firing treatment: The dried shell is placed in a dewaxing axe for steam pressure dewaxing. The dewaxed shell is then fired. The specific firing steps are as follows:

[0191] After steam dewaxing, the mold shell is rapidly heated to 900℃ and baked for 2±0.5h. After baking, wait for the furnace to cool down. When the mold shell drops below 400℃, open the furnace door for 40-60min to accelerate cooling. After the furnace temperature naturally cools to room temperature, remove the trolley and take out the mold shell to obtain the mold shell for investment casting.

[0192] The high-temperature alloy liquid is poured into the above-mentioned investment casting shell, wherein the shell temperature is 900℃. After the shell cools, it is demolded to finally obtain the finished casting.

[0193] The composition of the high-temperature alloy liquid, by weight percentage, is as follows:

[0194] Carbon: 0.07 wt%, Chromium: 12.55 wt%, Cobalt: 8.5 wt%, Tungsten: 3.85 wt%, Molybdenum: 1.70 wt%, Aluminum: 3.25 wt%, Titanium: 3.95 wt%, Zirconium: 0.01 wt%, Boron: 0.01 wt%, Tantalum: 4.00 wt%, with the balance being nickel.

[0195] The specific casting process parameters are as follows:

[0196] Refining temperature: 1550℃±10℃ Refining time: 1min-2min

[0197] Pouring temperature: 1520℃±10℃; Pouring time: ≤10s

[0198] Vacuum degree after alloy melting: ≤5Pa; Standing time: ≥2min

[0199] The castings were de-shelled and cut after pouring to obtain equiaxed nickel-based superalloy castings.

[0200] See the physical image of the casting (small-sized low-pressure turbine equiaxed blade) obtained in Comparative Example 2. Figure 5 As shown, the surface quality of small-sized low-pressure turbine equiaxial blades is poor, with large casting nodules at the corners of the casting surface, making it difficult to polish at these corners. The initial inspection pass rate is only 58%. Therefore, the proportion of each component in the pre-wetted slurry is very important and needs to meet the following mass ratio: the mass ratio of the ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(1.6~1.8):(0.001~0.003):(0.001~0.003). Otherwise, it will be difficult to achieve the expected results.

[0201] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a mold shell for investment casting, characterized in that, It includes the following steps: Pre-wetting treatment: The wax model assembly is pre-wetted with a pre-wetting slurry to obtain a wax model assembly with a pre-wetted layer on the surface; wherein, the viscosity of the pre-wetting slurry is 8-11s; Shell making process: On the wax mold assembly with the pre-wetted layer, a surface layer and a back layer are prepared to obtain a shell containing the wax mold; wherein, the viscosity of the surface layer slurry used to prepare the surface layer is greater than the viscosity of the pre-wetted slurry; the viscosity of the back layer slurry used to prepare the back layer is greater than the viscosity of the pre-wetted slurry; Dewaxing and firing treatment: The shell containing the wax pattern is dewaxed to obtain a dewaxed shell; the dewaxed shell is then fired to obtain a shell for investment casting.

2. The method for preparing a mold shell for investment casting according to claim 1, characterized in that, The pre-wetted slurry comprises ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer; wherein the mass ratio of the ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(1.6-1.8):(0.001-0.003):(0.001-0.003).

3. The method for preparing a mold shell for investment casting according to claim 2, characterized in that, The preparation steps of the ethyl silicate hydrolysate include: Distilled water and alcohol were added to the hydrolysis stirring device and stirring was started. Then, ethyl silicate was added, and finally hydrochloric acid was added. The hydrolysis reaction was carried out for 50 to 70 minutes to obtain ethyl silicate hydrolysate. Preferably, the mass ratio of ethyl silicate, hydrochloric acid, distilled water, and alcohol is (4.8–5.2):(39–41):(0.9–1.1):(2.9–3.1). Preferably, the concentration of hydrochloric acid is 14-16%, and the concentration of alcohol is 94-96%.

4. The method for preparing a mold shell for investment casting according to any one of claims 1-3, characterized in that, In the pre-wetting treatment step: Immerse the wax mold assembly into the pre-wet slurry for 4-5 seconds; after immersion, remove the wax mold assembly from the pre-wet slurry and dry it at room temperature for 8-12 minutes to obtain a wax mold assembly with a pre-wet layer on the surface.

5. The method for preparing a shell for investment casting according to any one of claims 2-4, characterized in that, The preparation steps of the pre-wetted slurry include: First, stir the ethyl silicate hydrolysate, then add a wetting agent and stir to obtain a first mixture; add corundum powder to the first mixture and stir until there are no lumps or powder particles on the surface of the slurry to obtain a second mixture; add a defoamer to the second mixture and stir to obtain a pre-wetted slurry; Preferably, during the process of adding the corundum powder to the first mixture, continuous stirring is required to prevent the powder from clumping or agglomerating.

6. The method for preparing a shell for investment casting according to any one of claims 1-5, characterized in that, In the pre-wetting treatment step: Before pre-wetting the wax mold assembly with pre-wet slurry, the wax mold assembly needs to be cleaned and dried to remove oil stains.

7. The method for preparing a shell for investment casting according to any one of claims 1-6, characterized in that, Prior to the pre-wetting treatment step, the following is also included: Preparation of wax mold assembly: Place the gating system containing embedded rods and metal tooling into the mold, close the mold, inject liquid wax into the mold and hold it under pressure. After the wax solidifies and forms, a wax mold assembly including the wax mold and the gating system is obtained.

8. The method for preparing a shell for investment casting according to any one of claims 1-7, characterized in that, In the shell-making process: The surface layer slurry used to prepare the surface layer includes: ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer; wherein the mass ratio of ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(2.2~2.5):(0.001~0.003):(0.001~0.003); and / or The viscosity of the surface layer slurry used to prepare the surface layer is 45-49s; and / or The backing slurry used to prepare the backing layer includes: ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer; wherein the mass ratio of ethyl silicate hydrolysate, corundum powder, wetting agent, and defoamer is 1:(2.0~2.2):(0.001~0.003):(0.001~0.003); and / or The viscosity of the backing slurry used to prepare the backing layer is 12–17 s.

9. The method for preparing a shell for investment casting according to any one of claims 1-8, characterized in that, In the shell-making process: After applying the top layer and back layer sequentially to the wax mold assembly with the pre-wetted layer, seal it with slurry, and after drying, transfer it to the shell containing the wax mold. Preferably, in the preparation of the topcoat: after each topcoat is applied, it is dried under the following conditions: temperature 22±5℃, humidity 75±10%RH, drying time ≥210min; and / or Preferably, in the backing layer preparation step: after each backing layer is coated, drying is performed under the following conditions: temperature 22±5℃, humidity 75±10%RH, drying time ≥120min; and / or Preferably, after sealing, the mixture is dried for ≥48 hours; Preferably, the total number of coating layers, including the top and back layers, is 7 to 8.

10. The method for preparing a shell for investment casting according to any one of claims 1-9, characterized in that, In the steps of dewaxing and calcination: The dewaxing process is a steam pressure dewaxing process; and / or In the baking process: the dewaxed shell is heated to 900℃±20℃ at a heating rate of 8-10℃ / min and baked for 2h±0.5h. After baking, the shell is cooled down to below 400℃ with the furnace, and the furnace door is opened for 40-60min to accelerate the cooling. After the furnace temperature cools down to room temperature naturally, the shell is taken out.

11. The method for preparing a shell for investment casting according to any one of claims 1-10, characterized in that, The corundum powder is selected from 320# corundum powder; and / or The wetting agent is of type Nalco 7667; and / or The defoamer is model number Nalco 2305.

12. A mold shell for investment casting, characterized in that, The investment casting shell is prepared by the method for preparing the investment casting shell according to any one of claims 1-11.

13. A method for preparing a casting, characterized in that, It includes the following steps: High-temperature alloy liquid is poured into the cavity of the investment casting shell as described in claim 12, wherein the temperature of the investment casting shell is a set temperature when the high-temperature alloy liquid is poured, and after the investment casting shell cools down, the shell is removed to obtain the casting. Preferably, the set temperature is 900-1000℃.

14. The method for preparing a casting according to claim 13, characterized in that, The high-temperature alloy liquid comprises the following chemical components by weight percentage: Carbon: 0.06–0.10 wt%, Chromium: 12–13.0 wt%, Cobalt: 8.5–9.5 wt%, Tungsten: 3.85–4.5 wt%, Molybdenum: 1.65–2.15 wt%, Aluminum: 3.15–3.6 wt%, Titanium: 3.75–4.20 wt%, Zirconium: 0.01–0.05 wt%, Boron: 0.01–0.02 wt%, Tantalum: 3.85–4.5 wt%, with the balance being nickel.

15. The method for preparing a casting according to claim 14, characterized in that, The pouring temperature of the high-temperature alloy liquid is 1520℃±10℃, and the pouring time is ≤10s; and / or The casting is cut to obtain an equiaxed polycrystalline nickel-based high-temperature alloy casting.

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