A method of manufacturing a hollow directionally solidified blade

Abstract

This invention provides a method for preparing hollow directional solidified blades, relating to the field of precision casting technology. Specifically, it involves configuring a pouring cup, a first composite wax mold, and a second composite wax mold. The first composite wax mold includes an integrally pressed blade wax mold, a straight crystal-drawing section wax mold, and a crystal-drawing drafting section wax mold. The second composite wax mold includes an integrally pressed crystal-drawing stepped drafting section wax mold and a base. Then, the following steps are performed sequentially: wax mold assembly welding, mold shell preparation, casting and crystal pulling, shell cleaning and cutting, core removal, inspection, and heat treatment, to obtain a hollow directional solidified blade. This invention designs and provides a drafting stepped crystal-drawing section module, combined with a blade tip-down casting process, and can be supplemented with a shaped heat shield to improve the local temperature gradient. This results in high-quality blades with refined grains, fewer cracks, and fewer impurities or segregated crystals, making it particularly suitable for the preparation of large-size complex hollow blades, and showing good application prospects in heavy-duty gas turbines.

Description

Technical Field

[0001] This invention relates to the field of precision casting technology, and more specifically, to a method for preparing hollow directional solidified blades. Background Technology

[0002] To enhance the heat resistance of large-sized blades, the in-stage directional solidification blades for heavy-duty gas turbines are designed with complex air-cooling channels. These complex cavities require precision casting using a zero-margin hollow blade process. A core with a complex structure is created on a wax pattern. After coating, dewaxing, and firing, a mold shell with a ceramic core is produced. Following directional solidification casting and crystal pulling, the molten alloy is poured into the mold shell to fill the cavity formed by the wax pattern. Solidification and cooling then form the blade metal blank. The blade metal blank undergoes core removal to obtain a complex cavity with a complete shape and precise dimensions.

[0003] Compared to blades used in aero-engines, blades for heavy-duty gas turbines are significantly larger and heavier. The ceramic cores used in these blades are also much larger, with substantial variations in wall thickness, ranging from tens of millimeters in the thickest parts to only a few tenths of a millimeter in the thinnest. This structure leads to significant differences in the impact resistance of the melt during directional solidification and the physicochemical stability during crystal pulling in different parts of the ceramic core. To ensure sufficient strength and deformation resistance during the directional solidification and pulling process of the blade, and to prevent core breakage, misalignment, and leakage, the core needs to undergo both high-temperature and low-temperature strengthening. If uniform strengthening is used, it may result in poor yielding in areas with thicker ceramic core walls, hindering the shrinkage of the alloy melt during solidification and cooling, and causing intergranular hot cracks in the thin-walled areas of the blade cavity.

[0004] To address the issue of intergranular cracking in blades due to excessive ceramic core strength, common methods include optimizing alloy composition to reduce the alloy's hot cracking tendency; and optimizing the manufacturing process to suppress crack initiation and propagation. In terms of manufacturing processes, controlling the strength of the ceramic core can suppress crack formation, such as by manufacturing hollow ceramic cores and adjusting the strengthening methods and process parameters for different parts of the core to balance its internal strength. While these methods do reduce and suppress crack formation, hollow ceramic cores are difficult and costly to manufacture; and ceramic cores obtained by balancing and controlling core strength exhibit significant quality fluctuations, often resulting in batch scrap. Additionally, increasing the cooling rate and temperature gradient during the directional solidification process of the blade, i.e., reducing the distance between the liquid and solid phases, enhances the feeding capacity of the alloy melt, suppresses crack initiation and propagation, and reduces the blade's hot cracking tendency.

[0005] Currently, large-size directionally solidified hollow blades can be fabricated using LMC and HRS processes. Due to the complexity of the process equipment and the problem of molten metal contamination, the HRS process is more widely used, but it suffers from problems such as small temperature gradient, coarse grain structure, and large secondary dendrite walls. This invention addresses the problem of insufficient cooling capacity and easy cracking of the tip-down gating system when using the HRS cooling process to fabricate large-size directionally solidified hollow blades. It designs a stepped draft section, which increases the contact area of ​​the draft section, enhances the heat dissipation of the molten front in the module through the draft section and water-cooled crystallizer, and incorporates a shaped heat shield to reduce radiative heat transfer from the hot zone to the cold zone, thereby increasing the temperature gradient during the crystal pulling process. This can suppress the formation of blade cracks, refine the grains, and improve the directionally solidified structure.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing hollow directional solidified blades. For large-sized complex hollow directional solidified blades, which are characterized by large size, heavy weight, abrupt changes in cross-sectional dimensions and cavity structure, existing directional solidification processes have technical problems such as large temperature gradient fluctuations at the front end, rapid temperature drop, slow cooling rate, and easy occurrence of coarse grains. As a result, blade defects such as thermal cracking, impurities, and segregated crystals are easily generated during directional solidification.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0009] A method for preparing a hollow, directional solidified blade includes the following steps:

[0010] (1) Configure a pouring cup, a first composite wax mold and a second composite wax mold; wherein, the first composite wax mold includes an integrally pressed blade wax mold, a straight section wax mold for crystal pulling and a section wax mold for crystal pulling, and the second composite wax mold includes an integrally pressed step section wax mold for crystal pulling and a base.

[0011] (2) The pouring cup, the first composite wax mold and the second composite wax mold are welded together from top to bottom to obtain a wax mold assembly;

[0012] (3) The wax model assembly is placed in the coating and coated, then sand is sprinkled, dried, and the loose sand is cleaned to obtain a hardened wax model; the hardened wax model is then dewaxed and fired to obtain a mold shell;

[0013] (4) Pour molten metal into the mold shell and obtain the first blade precursor by directional solidification technology;

[0014] (5) The first blade precursor is cleaned and then the non-blade structure is removed by wire cutting to obtain the second blade precursor.

[0015] (6) Remove the ceramic core from the second blade precursor and then inspect the blade grains by corrosion; when the blade grains meet the technical standards, perform heat treatment to obtain a hollow directional solidified blade.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] This invention addresses the issue of large-sized, complex hollow directional solidification blades. Conventional directional solidification processes suffer from large temperature gradient fluctuations, rapid temperature drop, slow cooling rates, and a high tendency for coarse grains to form, leading to quality defects in the blades. This invention introduces a draft-step crystal-leading module to achieve the technical effects of refining the grains and suppressing cracks in the blades. Preferably, by combining the blade tip-down casting process with a non-circular heat shield that enhances the local temperature gradient, the coarse grain and crack problems of hollow directional solidification blades can be effectively solved. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 A cross-sectional schematic diagram of the composite wax model of the present invention is provided;

[0020] Figure 2 A schematic diagram of the crystal-driving segment structure and a schematic diagram of the wax-flushing connection of the present invention are provided;

[0021] Figure 3 A schematic diagram of the gating system of the present invention is provided;

[0022] Figure 4 A schematic diagram of the casting and melting process of the present invention is provided;

[0023] Figure 5 A cross-sectional schematic diagram of the irregularly shaped heat insulation screen of the present invention is provided;

[0024] Figure 6 A cross-sectional schematic diagram of a conventional heat insulation screen is provided. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0026] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0027] This invention provides a method for preparing hollow directional solidified blades, which mainly includes the following steps: (1) wax model design, (2) wax model assembly and welding, (3) mold shell preparation, (4) casting and crystal pulling, (5) shell cleaning and cutting, and (6) core removal, inspection and heat treatment. The implementation methods of each step are described in detail below.

[0028] (1) Configure a pouring cup, a first composite wax mold and a second composite wax mold; wherein, the first composite wax mold includes an integrally pressed blade wax mold, a straight section wax mold for crystal pulling and a section wax mold for crystal pulling, and the second composite wax mold includes an integrally pressed step section wax mold for crystal pulling and a base.

[0029] In a preferred embodiment, the pouring cup is designed in the shape of a cylinder or frustum, serving as the entry point for molten metal during pouring.

[0030] In one preferred embodiment, the blade wax model includes wax model structures corresponding to various parts of the blade, such as tenons, edge plates, and blade body, as well as a ceramic core.

[0031] In a more preferred embodiment, the method for preparing the ceramic core includes: preparing a ceramic core blank using a ceramic core mold on a core pressing machine, and then trimming and sintering it to obtain the ceramic core.

[0032] In a more preferred embodiment, the ceramic core is assembled into the mold of the blade wax model, and then the blade wax model is prepared by using a wax pressing machine and the mold of the blade wax model. It is understood that the pouring cup, the first composite wax model other than the blade wax model, and the second composite wax model are all obtained by pressing them on a wax pressing machine using corresponding molds.

[0033] In a preferred embodiment, the top of the crystal-leading straight section wax mold is connected to the blade wax mold corresponding to the blade tip structure.

[0034] In a preferred embodiment, the cross-sectional shape of the straight section wax model is the same as the blade profile, and the height of the straight section wax model is 20mm to 40mm. Specifically, for the blade profile, the edge of the cross-section of the blade is the profile line, and all the profile lines combined constitute the blade profile.

[0035] In a preferred embodiment, the top cross-sectional shape of the crystal drafting section wax mold is the same as the blade profile, and the top of the crystal drafting section wax mold is connected to the crystal straight section wax mold; with the top of the crystal drafting section wax mold pointing downwards, there is an outward draft angle, which is 5° to 15°; the height of the crystal drafting section wax mold is 20mm to 40mm.

[0036] In a preferred embodiment, the top of the drafting step wax model is provided with a groove structure. The depth of the groove structure is 4mm to 6mm, the groove width is 0.3mm to 0.5mm, and the groove cross-section is obtained by extending outward relative to the outline of the drafting step wax model.

[0037] In a preferred embodiment, the top cross-sectional shape of the pilot crystal step drafting section wax model extends outward by 5mm to 10mm relative to the outline of the pilot crystal step drafting section wax model; with the top of the pilot crystal step drafting section wax model pointing downwards, there is an outward draft angle of 5° to 15°; and the height of the pilot crystal step drafting section wax model is 10mm to 20mm.

[0038] Based on the above preferred embodiments, such as Figure 1 The diagram shows a cross-sectional schematic of the composite wax model of the present invention; since the cross-sectional shape of the crystal-leading straight section wax model is exactly the same as the blade profile, therefore... Figure 1 The curved edge of the middle blade almost coincides with the crystal-leading section-straight section, which is also consistent with the wax mold structure designed in this invention.

[0039] In a preferred embodiment, the drafting wax pattern of the crystal-leading drafting section and the drafting wax pattern of the crystal-leading step drafting section have the same draft angle.

[0040] (2) The pouring cup, the first composite wax mold and the second composite wax mold are welded together from top to bottom to obtain a wax mold module.

[0041] In a preferred embodiment, the bottom part of the lead-in drafting section wax mold is nested in the groove structure at the top of the lead-in step drafting section wax mold, and the joint between the two is connected by wax pouring, that is, liquid wax is used to fill and weld the gap, thereby realizing the combination of the first composite wax mold and the second composite wax mold.

[0042] Depend on Figure 2 The diagram shows the structural configuration of the wax model, the assembly and welding diagram, and the wax flow connection diagram. In the wax flow connection, the height of the wax flow is consistent with the height of the groove platform of the wax model in the crystal step drafting section, which serves to fill the gap and connect the parts.

[0043] Depend on Figure 3 The diagram shows a post-weld casting system, including a front view and a left view; it is worth noting that... Figure 3 The "tenon", "edge plate", and "blade" in the text all correspond to the wax mold structure of a blade, which has the same structure as the text.

[0044] In a preferred embodiment, this step also includes cleaning the wax mold assembly.

[0045] (3) The wax mold assembly is placed in the coating and coated, then sand is sprinkled, dried and cleaned to obtain a hardened wax mold; the hardened wax mold is dewaxed and fired in sequence to obtain a mold shell.

[0046] As a preferred embodiment, this step includes the following method:

[0047] S1: First, coat the wax mold assembly with slurry in the directional solidification surface coating, and then sprinkle sand after the coating is evenly coated.

[0048] S2: Clean off the loose sand, then coat the treated wax mold assembly with slurry in the directional solidification back coating, coat it evenly, and then sprinkle sand.

[0049] S3: Repeat S2 for a total of 6 to 8 times; then apply the slurry without sprinkling sand as a sealing layer, thereby obtaining the hardened wax mold.

[0050] In a preferred embodiment, the dewaxing is carried out in a dewaxing kettle; the dewaxing environment is a water vapor atmosphere with a pressure of 6 atm to 8 atm and a temperature of 160°C to 180°C.

[0051] In a preferred embodiment, the roasting is carried out in a muffle furnace; the roasting temperature is 800℃~1000℃, and the roasting time is 2h~4h.

[0052] (4) Molten metal is poured into the mold shell, and the first blade precursor is obtained through directional solidification technology. For example... Figure 4 The diagram provided illustrates the casting and melting process, in which the casting and directional solidification take place within a mold shell heater; it is understood that... Figure 4 The red area in the middle is a schematic diagram of the molten metal in the mold shell heater after the molten metal is poured.

[0053] In a preferred embodiment, a funnel is placed above the mold shell heater, with the center of the funnel aligned with the center of the mold shell heater, and the bottom of the funnel being less than 150 mm from the upper edge of the mold shell heater.

[0054] In a preferred embodiment, the molten metal is obtained by melting a master alloy ingot through a directional solidification furnace melting chamber; wherein the vacuum degree of the directional solidification furnace melting chamber is <5 Pa, and the temperature of the directional solidification furnace melting chamber is 1480℃~1550℃. Once the temperature of the molten metal stabilizes within the above-mentioned temperature range, it can be used for casting.

[0055] In a preferred embodiment, a mold shell heater cover is provided on the top of the mold shell heater, and an irregularly shaped heat insulation screen and a water-cooling ring are arranged sequentially from top to bottom at the bottom of the mold shell heater; wherein, a cross-sectional schematic diagram of the irregularly shaped heat insulation screen used in this invention is shown in the figure. Figure 5 As shown, the cross-sectional edge of the irregularly shaped heat insulation screen has the same shape as the edge of the mold shell. Compared to... Figure 6 The conventional heat shield shown in this invention, compared to the irregularly shaped heat shield, can effectively reduce radiative heat transfer from the hot zone to the cold zone, increase the temperature gradient during crystal pulling, and suppress blade crack formation. Furthermore, a water-cooled crystallizer is also provided at the lower part of the mold shell heater.

[0056] In a more preferred embodiment, the casting process includes the following steps: first, the mold shell is placed on the water-cooled crystallizer, with the water-cooled crystallizer in close contact with the mold shell and without misalignment; then, the mold shell heater is sealed (e.g., the furnace door of the mold shell heater is closed, the mold shell heater cover is placed, etc.), and the mold shell heater is evacuated to a vacuum level below 5 Pa. At this time, the lifting system is activated to send the mold shell into the interior of the mold shell heater; the mold shell is heated to 1400℃~1600℃ (preferably 1500℃) by the mold shell heater and kept at this temperature, preferably for more than 30 minutes, and then the casting process begins; the molten metal is poured into the mold shell through the pouring cup, and after filling is completed, it is allowed to stand for 30s~60s, and then the mold shell is pulled downwards at a speed of 2mm / min~10mm / min until the mold shell is completely pulled out of the mold shell heater, thus obtaining the mold shell and the first blade precursor.

[0057] It is understandable that during the settling and pulling process after filling (i.e., crystal pulling), the solidification sequence of the molten metal is as follows: crystal step drafting section, crystal drafting section, crystal straight section, blade, tenon, and gate.

[0058] As a further preferred embodiment, after the mold shell is fully pulled out, it should be left to stand for 10 to 30 minutes to cool down, and then the mold shell heater should be turned on and the mold shell removed and placed in a heat preservation device for cooling.

[0059] (5) The first blade precursor is cleaned and then the non-blade structure is removed by wire cutting to obtain the second blade precursor.

[0060] (6) Remove the ceramic core from the second blade precursor and then inspect the blade grains by corrosion; when the blade grains meet the technical standards, perform heat treatment to obtain a hollow directional solidified blade.

[0061] In a preferred embodiment, the removal of the ceramic core includes the following steps: placing the second blade precursor in a 30wt.% to 40wt.% potassium hydroxide solution, controlling the temperature to ≤200℃ and the pressure to 4atm to 6atm.

[0062] In a preferred embodiment, after the corrosion inspection, the process also includes cleaning the corrosive liquid adhering to the surface and cavity.

[0063] As a preferred embodiment, the heat treatment process further includes one or more of the following tests: fluorescence penetrant testing, X-ray inspection, and dimensional inspection. It is understood that the dimensional inspection should meet the requirements of the design drawings, and the fluorescence penetrant testing and the X-ray inspection should be performed to ensure that the blades are free from cracks, pores, sand holes, impurities, or other opening defects.

[0064] Example

[0065] S1: Pressing process parameters for wax molds: injection pressure 2.0MPa, injection time 50s, holding time 160s, wax temperature 70℃; wax molds for pouring cup, blades, base and each crystal lead segment are prepared using the above parameters.

[0066] S2: As Figure 2 The blade casting system assembly is shown. The blade wax model tenon is connected to the bottom of the sprue cup, and the blade end corresponding to the blade tip is connected to the crystal guide section. The sprue cup has a diameter of 60mm and a height of 120mm. The top of the straight section of the crystal guide section is connected to the blade tip, with an external shape consistent with the blade profile, and a height of 30mm. The top of the draft section is connected to the bottom of the straight section, with an external shape consistent with the straight section profile, a height of 30mm, and an outward draft angle of 15°. The upper surface contour of the stepped draft section extends 8mm beyond the bottom contour of the draft section, with an outward draft angle of 10° and a height of 15mm. A groove is provided at the upper end of the stepped draft section, with the groove contour extending 0.4mm beyond the bottom contour of the draft section and a depth of 5mm. The base has a diameter of 250mm and a thickness of 15mm.

[0067] S3: Assemble the wax model modules and then make the shell. Use electrofused mullite slurry coating, and apply 100#~24# corundum sand as the sanding material, applying 8 layers of sand, and finally sealing with a sealant. During the shell making process, take care to avoid shell buildup inside the holes. When applying the next layer of coating, clean the excess coating inside the holes.

[0068] S4: Following the shell-making sequence described above, the mold shell slurry is coated on the surface of the wax mold of the blade and the gating system to form a green blade mold shell; the wax material in the green shell is removed and it is baked at 900℃ for 3 hours to prepare a large-sized hollow blade mold shell.

[0069] S5: As Figure 4 The casting process is as shown. Before casting, the mold shell is placed on a water-cooled crystallizer, and a pre-set flow funnel is used, with the bottom of the funnel 150mm from the top of the pouring cup. During casting, the alloy melt temperature is 1520℃, and the mold shell heating temperature is 1510℃. Within 30 seconds after casting, the mold shell is pulled out. After pulling out, the mold shell is kept in the furnace for 10 minutes and then broken open. The mold shell is placed in a heat-insulating barrel for cooling, and the blades prepared in this embodiment are obtained.

[0070] When repeatable experiments were conducted using the method described in this embodiment, it was found that, compared with conventional directional solidification processes, the scrap rate of blades with intergranular cracks in this embodiment was reduced by 20% to 30%, and the number of columnar crystals along the chord length direction was increased by 10% to 20%. It showed good effects in refining grains and suppressing cracks for large-sized complex hollow directional solidified blades.

[0071] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing hollow directional solidified blades, characterized in that, Includes the following steps: (1) Configure a pouring cup, a first composite wax mold and a second composite wax mold; wherein, the first composite wax mold includes an integrally pressed blade wax mold, a straight section wax mold for crystal pulling and a section wax mold for crystal pulling, and the second composite wax mold includes an integrally pressed step section wax mold for crystal pulling and a base. (2) The pouring cup, the first composite wax mold and the second composite wax mold are welded together from top to bottom to obtain a wax mold module; (3) The wax model assembly is placed in the coating and coated, then sand is sprinkled, dried, and the loose sand is cleaned to obtain a hardened wax model; the hardened wax model is dewaxed and fired in sequence to obtain a mold shell; (4) Pour molten metal into the mold shell and obtain the first blade precursor by directional solidification technology; (5) The first blade precursor is cleaned and then the non-blade structure is removed by wire cutting to obtain the second blade precursor; (6) Remove the ceramic core from the second blade precursor, and then inspect the blade grains by corrosion; when the blade grains meet the technical standards, perform heat treatment to obtain a hollow directional solidified blade; The top of the straight section wax mold is connected to the blade wax mold corresponding to the blade tip structure; The top cross-sectional shape of the crystal-drawing section wax mold is the same as the blade profile, and the top of the crystal-drawing section wax mold is connected to the crystal-drawing straight section wax mold. With the top of the die-drawing section wax mold pointing downwards, there is an outward draft angle, which is 5°~15°. The top cross-sectional shape of the wax model of the crystal-drawing step section extends outward by 5mm to 10mm compared to the outline of the wax model of the crystal-drawing step section. With the top of the drafting step section of the wax mold pointing downwards, there is an outward draft angle, which is 5°~15°.

2. The method for preparing hollow directional solidified blades according to claim 1, characterized in that, The cross-sectional shape of the straight section wax model is the same as the blade profile, and the height of the straight section wax model is 20mm~40mm.

3. The method for preparing hollow directional solidified blades according to claim 1, characterized in that, The height of the wax mold for the crystal drafting section is 20mm~40mm.

4. The method for preparing hollow directional solidified blades according to claim 1, characterized in that, The height of the wax mold for the drafting step section is 10mm~20mm.

5. The method for preparing hollow directional solidified blades according to claim 4, characterized in that, The top of the drafting step wax model is provided with a groove structure. The depth of the groove structure is 4mm to 6mm, the groove width is 0.3mm to 0.5mm, and the groove cross section is obtained by extending outward relative to the outline of the drafting step wax model.

6. The method for preparing hollow directional solidified blades according to claim 5, characterized in that, In step (2), the assembly welding of the first composite wax mold and the second composite wax mold includes: The bottom part of the lead crystal drafting section wax mold is nested in the groove structure at the top of the lead crystal step drafting section wax mold, and the joint between the two is connected by wax slipping.

7. The method for preparing hollow directional solidified blades according to claim 1, characterized in that, In step (3), the method for preparing the hardened wax mold includes: S1: First, coat the wax mold assembly with slurry in the directional solidification surface coating, and then sprinkle sand after the coating is evenly coated. S2: Clean off the loose sand, then coat the treated wax mold assembly with slurry in the directional solidification back coating, coat it evenly, and then sprinkle sand. S3: Repeat S2 for a total of 6 to 8 times; then apply a slurry as a sealing layer to obtain the hardened wax mold.

8. The method for preparing hollow directional solidified blades according to claim 1, characterized in that, In step (3), the dewaxing is performed in a steam atmosphere with a pressure of 6 atm to 8 atm and a temperature of 160°C to 180°C. And / or, the calcination temperature is 800℃~1000℃, and the calcination time is 2h~4h.

9. The method for preparing hollow directional solidified blades according to claim 1, characterized in that, In step (4), the casting and the directional solidification are carried out in the mold shell heater; A mold shell heater cover is provided on the top of the mold shell heater, and an irregularly shaped heat insulation screen and a water-cooling ring are arranged sequentially from top to bottom at the bottom of the mold shell heater; wherein, the cross-sectional edge of the irregularly shaped heat insulation screen has the same shape as the edge of the mold shell; A water-cooled crystallizer is also provided at the lower part of the mold shell heater.

10. The method for preparing hollow directional solidified blades according to claim 9, characterized in that, In step (4), the mold shell is first placed on the water-cooled crystallizer, and the water-cooled crystallizer is in close contact with the mold shell without misalignment; Then the mold shell heater is sealed, and the mold shell heater is evacuated to a vacuum level of less than 5 Pa. At this time, the lifting system is activated to send the mold shell into the interior of the mold shell heater. The mold shell is heated and kept warm by the mold shell heater, and then the pouring begins. The molten metal enters the mold shell through the pouring cup. After filling is completed, the mold shell is left to stand for 30 to 60 seconds. Then, the mold shell is pulled downwards at a speed of 2 mm / min to 10 mm / min until the mold shell is completely pulled out of the mold shell heater, thus obtaining the mold shell and the first blade precursor.

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