Preparation method of hollow directional solidification blade

Abstract

The invention provides a preparation method of a hollow directional solidification blade, and relates to the technical field of precision casting. Specifically, a pouring cup, a first composite wax mold and a second composite wax mold are configured; wherein the first composite wax mould comprises a blade wax mould, a seeding straight section wax mould and a seeding draft section wax mould which are integrally pressed, and the second composite wax mould comprises a seeding stepped draft section wax mould and a base plate which are integrally pressed; and then the procedures of wax mold welding, mold shell preparation, pouring and crystal pulling, shell cleaning and cutting, depoling, checking and heat treatment are conducted in sequence, and the hollow directional solidification blade is obtained. The invention designs and provides a draft stepped seeding section module, which is combined with a pouring process with an underneath blade tip of the blade and can be assisted by a special-shaped heat screen to improve the local temperature gradient, so that the high-quality blade with refined grains, few cracks and few mixed crystals or monotectic is prepared, and the draft stepped seeding section module is particularly suitable for preparation of large-size complex hollow blades. The method has a good application prospect in the aspect of heavy-duty gas turbines.

Description

Technical Field

[0001] The invention relates to the technical field of precision casting, and in particular to a method for preparing a hollow directional solidification blade. Background Art

[0002] In order to improve the temperature bearing capacity of large-sized blades, the front-stage directional solidification blades for heavy-duty gas turbines are designed with complex air cooling channels. This complex cavity needs to be prepared through a precision casting process for hollow blades without excess. A core with a complex structure is set in the wax mold, and after coating, dewaxing and roasting, a mold shell with a ceramic core is prepared. After directional solidification pouring and crystal pulling, the alloy melt is poured into the mold shell to fill the cavity formed by the wax mold, and solidified and cooled to form a blade metal blank. After the core removal treatment, the blade metal blank obtains a complex cavity with a complete shape and precise size.

[0003] Compared with the blades for aircraft engines, the size and weight of blades for heavy-duty gas turbines have increased significantly. The size and maximum wall thickness of the ceramic core for the blades are relatively large, and the wall thickness varies greatly. The thick wall of the ceramic core can reach tens of millimeters, and the thinnest part is only a few tenths of a millimeter. This structure leads to large differences in the resistance of different parts of the ceramic core to melt impact during the directional solidification production process and the physical and chemical stability of the crystal pulling process. In order to ensure that the core has sufficient strength and deformation resistance during the directional solidification and drawing process of the blade, and to prevent core breakage, core deviation, and core leakage, the core needs to be strengthened at high and low temperatures. If uniform strengthening treatment is used, it may lead to poor yielding at places with thicker ceramic core walls, the shrinkage of the alloy melt during solidification and cooling is hindered, and intergranular thermal cracks are generated in the thin walls of the blade cavity.

[0004] In order to solve the problem of excessive strength of the ceramic core and intergranular cracks in the blades, the commonly used methods are to optimize the alloy composition and improve the thermal cracking tendency of the alloy; in addition, optimizing the process and inhibiting the initiation and expansion of cracks is also a feasible way. In terms of technology, cracks can be inhibited by controlling the strength of the ceramic core, such as manufacturing a hollow ceramic core, adjusting the strengthening methods and process parameters of different parts of the ceramic core, and balancing the internal strength of the ceramic core. The above methods can indeed reduce and inhibit the occurrence of cracks, but the preparation of hollow ceramic cores is difficult and costly; the quality of the ceramic cores obtained by the balanced control of the ceramic core strength method fluctuates greatly, often resulting in batch scrapping. In addition, during the implementation of the process, the cooling rate and temperature gradient of the blade directional solidification process are increased, that is, the distance between the liquid-solid two-phase zone is reduced, the shrinkage compensation capacity of the alloy melt is improved, the initiation and expansion of cracks are inhibited, and the thermal cracking tendency of the blade is reduced.

[0005] At present, large-sized directional solidification hollow blades can be prepared by LMC and HRS processes. Due to the complexity of process equipment and the pollution of cooling metal liquid, HRS process is more widely used, and there are problems such as small temperature gradient, coarse grain structure, and large secondary dendrite wall. In view of the problem that the cooling capacity of the tip-down pouring system is insufficient and cracks are easy to occur when large-sized directional solidification hollow blades are prepared by HRS cooling process, the present invention designs a demolding stepped seeding section, which increases the contact area of ​​the seeding section, enhances the heat dissipation of the liquid-solid front of the melt in the module through the seeding section and the water-cooled crystallizer, and sets a special-shaped heat insulation screen to reduce the radiation heat transfer from the hot zone to the cold zone, improve the temperature gradient of the crystal pulling process, inhibit the generation of cracks in the blade body, and refine the grains and improve the directional solidification structure.

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

[0007] The purpose of the present invention is to provide a method for preparing a hollow directional solidification blade; for large-sized and complex hollow directional solidification blades, which have the characteristics of large size, heavy weight, sudden change in cross-sectional size and cavity structure, the existing directional solidification process has the technical problems of large fluctuation of the temperature gradient at the front, rapid descent, slow cooling speed, and easy occurrence of coarse grains, which leads to easy occurrence of blade defects such as thermal cracking, mixed crystals, and eutectic during the directional solidification process.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] A method for preparing a hollow directional solidification blade comprises the following steps:

[0010] (1) configuring a pouring cup, a first composite wax mold, and a second composite wax mold; wherein the first composite wax mold includes an integrally extruded blade wax mold, a seeding straight section wax mold, and a seeding draft section wax mold, and the second composite wax mold includes an integrally extruded seeding step draft section wax mold and a chassis;

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

[0012] (3) placing the wax model assembly in a coating to coat the wax model assembly, and then sanding, drying, and cleaning the floating sand to obtain a hardened wax model; dewaxing and baking the hardened wax model in sequence to obtain a mold shell;

[0013] (4) pouring molten metal into the mold shell to obtain a first blade precursor through directional solidification technology;

[0014] (5) performing a shell cleaning process on the first blade precursor, and then removing non-blade structures by wire cutting to obtain a second blade precursor;

[0015] (6) removing the ceramic core in the second blade precursor, and then inspecting the blade grains by corrosion; when the blade grains meet the technical standards, performing heat treatment to obtain a hollow directional solidification blade.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention is aimed at large-sized complex hollow directional solidification blades. Since the conventional directional solidification process has the problems of large temperature gradient fluctuation, fast temperature drop, slow cooling speed, and easy coarse grains leading to quality defects of the blades, the present invention introduces a demolding step-type seeding section module to achieve the technical effect of refining the grains of the blades and inhibiting cracks; it is preferably combined with the casting process of the blade tip down and the special-shaped heat insulation screen that increases the local temperature gradient, which can effectively solve the coarse grain and crack problems of hollow directional solidification blades. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A schematic cross-sectional view of a composite wax pattern of the present invention is provided;

[0020] Figure 2 Provided are a schematic diagram of the seeding section structure and a schematic diagram of the wax sliding connection of the present invention;

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

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

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

[0024] Figure 6 A schematic cross-sectional view of a conventional heat shield is provided. DETAILED DESCRIPTION

[0025] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0026] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0027] The present invention provides a method for preparing a hollow directional solidification blade, which mainly includes the following steps: (1) wax mold design, (2) wax mold assembly 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 method of each step is described in detail below.

[0028] (1) A pouring cup, a first composite wax mold and a second composite wax mold are configured; wherein the first composite wax mold includes an integrally extruded blade wax mold, a seeding straight section wax mold and a seeding stripping section wax mold, and the second composite wax mold includes an integrally extruded seeding step stripping section wax mold and a chassis.

[0029] As a preferred embodiment, the pouring cup is designed in the shape of a cylinder or a truncated cone, and serves as a location for introducing molten metal during pouring.

[0030] As a preferred embodiment, the blade wax model includes wax model structures corresponding to various parts of the blade, such as the tenon, the edge plate, the blade body, and a ceramic core.

[0031] As a more preferred embodiment, the method for preparing the ceramic core comprises: using a ceramic core mold to prepare a ceramic core green body on a core pressing machine, and performing trimming and sintering to obtain the ceramic core.

[0032] As a more preferred embodiment, the ceramic core is assembled into the mold of the blade wax mold, and then the blade wax mold is prepared by a wax pressing machine and the mold of the blade wax mold. It can be understood that the pouring cup, the first composite wax mold except the blade wax mold, and the second composite wax mold are all pressed on a wax pressing machine using corresponding molds.

[0033] As a preferred embodiment, the top of the seeding straight section wax mold is connected to the blade wax mold corresponding to the blade tip structure.

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

[0035] As a preferred embodiment, the top cross-sectional shape of the seeding and drawing section wax mold is the same as the blade body profile contour line of the blade, and the top of the seeding and drawing section wax mold is connected to the seeding straight section wax mold; there is an outward draft angle measured from the top of the seeding and drawing section wax mold downward, and the draft angle is 5° to 15°; the height of the seeding and drawing section wax mold is 20mm to 40mm.

[0036] As a preferred embodiment, a groove structure is provided on the top of the wax mold of the seeding step demolding section, the depth of the groove structure is 4mm to 6mm, the groove width of the groove structure is 0.3mm to 0.5mm, and the groove cross-section of the groove structure is expanded outward compared to the contour line of the wax mold of the seeding demolding section.

[0037] As a preferred embodiment, the top cross-sectional shape of the wax mold of the seeding step draft section extends outward by 5mm to 10mm compared to the contour line of the wax mold of the seeding step draft section; there is an outward draft angle measured from the top of the wax mold of the seeding step draft section downward, and the draft angle is 5° to 15°; the height of the wax mold of the seeding step draft section is 10mm to 20mm.

[0038] Based on the above preferred implementation, Figure 1 The figure shows a cross-sectional schematic diagram of the composite wax mold of the present invention; since the cross-sectional shape of the seeding straight section wax mold is exactly the same as the blade body profile contour line, Figure 1 The curved edge of the middle blade almost coincides with the seeding section-straight section, which is also in line with the wax mold structure designed by the present invention.

[0039] As a preferred embodiment, the wax mold for the seeding draft section and the wax mold for the seeding step draft section have the same draft angle.

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

[0041] As a preferred embodiment, the bottom part of the seeding and demolding section wax mold is nested in the groove structure at the top of the seeding step demolding section wax mold, and the joints between the two are connected by wax slipping, that is, the gap is filled and welded with liquid wax, thereby realizing the combination of the first composite wax mold and the second composite wax mold.

[0042] Depend on Figure 2 The structure configuration of the wax mold, the schematic diagram of the assembly welding and the schematic diagram of the wax slip connection are provided; in the wax slip connection, the wax slip height is consistent with the groove table height of the wax mold of the seeding step demolding section, which plays the role of filling and connecting.

[0043] Depend on Figure 3 The figure shows a schematic diagram of the pouring system after welding, which provides a front view and a left view respectively; it is worth noting that Figure 3 The "tenon", "edge plate" and "blade body" all correspond to the blade wax model structure that is the same as the text structure.

[0044] As a preferred implementation, this step also includes: cleaning the wax model module.

[0045] (3) placing the wax mold assembly in a coating to coat the wax mold, and then sanding, drying, and cleaning the loose sand to obtain a hardened wax mold; and dewaxing and calcining the hardened wax mold in sequence to obtain a mold shell.

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

[0047] S1: firstly coat the wax model module in the directional solidification surface coating, and then sprinkle sand after the coating is evenly applied;

[0048] S2: Clean the floating sand, and then coat the treated wax model module in the directional solidification backing coating, coat it evenly and then sprinkle sand;

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

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

[0051] As a preferred embodiment, the calcination is carried out in a muffle furnace; the calcination temperature is 800° C. to 1000° C., and the calcination time is 2 h to 4 h.

[0052] (4) pouring molten metal into the mold shell to obtain a first blade precursor by directional solidification technology. Figure 4 The figure shows a schematic diagram of pouring and melting, wherein the pouring and directional solidification are performed in a mold shell heater; it can be understood that Figure 4 The red area in the middle is a schematic diagram of the molten metal in the mold shell heater after pouring the molten metal.

[0053] As a preferred implementation, a funnel is arranged above the mold shell heater, the center of the funnel is aligned with the center position of the mold shell heater, and the bottom of the funnel is less than 150 mm away from the upper edge of the mold shell heater.

[0054] As a preferred embodiment, the molten metal is obtained by heating and melting a master alloy ingot in a directional solidification furnace melting chamber; wherein the vacuum degree of the directional solidification furnace melting chamber is less than 5 Pa, and the temperature of the directional solidification furnace melting chamber is 1480° C. to 1550° C. When the temperature of the molten metal is stabilized in the above temperature range, it can be used for pouring.

[0055] As a preferred embodiment, a shell heater cover is arranged on the top of the shell heater, and a special-shaped heat insulation screen and a water cooling ring are arranged in sequence from top to bottom at the bottom of the shell heater; wherein the cross-sectional schematic diagram of the special-shaped heat insulation screen used in the present invention is as shown in Figure 5 As shown, the cross-sectional edge of the special-shaped heat insulation screen has the same shape as the edge of the mold shell. Figure 6 Compared with the conventional heat shield shown in the figure, the special-shaped heat shield of the present invention can effectively reduce the radiation heat transfer from the hot zone to the cold zone, improve the temperature gradient during the crystal pulling process, and inhibit the occurrence of blade cracks. In addition, a water-cooled crystallizer is also provided at the lower part of the mold shell heater.

[0056] As a more preferred embodiment, the pouring includes the following steps: first, the mold shell is 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 (such as closing the mold shell heater furnace door, covering the mold shell heater cover, etc.), and the mold shell heater is evacuated to a vacuum degree lower than 5Pa, at which time the lifting system is started to send the mold shell to the inside of the mold shell heater; the mold shell is heated to 1400°C to 1600°C (preferably 1500°C) by the mold shell heater, and is kept warm, preferably, the insulation time is greater than 30 minutes, and then the pouring is started; the molten metal enters the mold shell through the pouring cup, and after the filling is completed, it is allowed to stand for 30s to 60s, and then the mold shell is pulled downward at a speed of 2mm / min to 10mm / min until the mold shell is completely pulled out of the mold shell heater to obtain the mold shell and the first blade precursor.

[0057] It can be understood that in the process of standing and pulling (i.e. crystal pulling) after filling, the solidification order of the molten metal is from first to last: seeding step demolding section, seeding demolding section, seeding straight section, blade body, tenon, and gate.

[0058] As a further preferred embodiment, after the mold shell is completely 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 taken out, and placed in a heat preservation device for cooling.

[0059] (5) The first blade precursor is subjected to shell cleaning treatment, and then non-blade structures are removed by wire cutting to obtain a second blade precursor.

[0060] (6) removing the ceramic core in the second blade precursor, and then inspecting the blade grains by corrosion; when the blade grains meet the technical standards, performing heat treatment to obtain a hollow directional solidification blade.

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

[0062] As a preferred embodiment, after the corrosion inspection, the method further includes cleaning the corrosion liquid attached to the surface and the cavity.

[0063] As a preferred embodiment, after the heat treatment, one or more of the following inspections are also included: fluorescent penetrant inspection, X-ray inspection and dimensional inspection; it can be understood that the dimensional inspection should meet the requirements of the design drawings, and the fluorescent penetrant inspection and the X-ray inspection are carried out to ensure that the blades are free of cracks, pores, sand holes, impurity inclusions or other open defects.

[0064] Example

[0065] S1: The pressing process parameters of the wax mold are as follows: injection pressure 2.0 MPa, injection time 50 s, holding time 160 s, and wax temperature 70°C; wax molds of the pouring cup, blades, chassis, and each seeding section are prepared with the above parameters.

[0066] S2: Figure 2 The blade casting system assembly is completed as shown. Connect the blade wax mold tenon to the bottom of the pouring cup, and the blade end corresponding to the blade tip is connected to the seeding section. The pouring cup has a diameter of 60mm and a height of 120mm; the top of the straight section of the seeding section is connected to the blade tip, and the external shape is consistent with the blade body profile contour line, with a height of 30mm; the top of the draft section is connected to the bottom of the straight section, and the external shape is consistent with the straight section contour line, with a height of 30mm, and the outward draft angle is 15°; the upper end face contour of the stepped draft section is expanded by 8mm from the bottom contour of the draft section, and the outward draft is 10°, with a height of 15mm. A groove is set at the upper end of the stepped draft section, and the groove contour is expanded by 0.4mm from the bottom contour of the draft section, with a depth of 5mm; the chassis has a diameter of 250mm and a thickness of 15mm.

[0067] S3: The wax mold module is combined and then the shell is made. The electrofused mullite slurry coating is used, and the sanding material is 100#~24# corundum sand. 8 layers of sand are spread and the final sealing layer is applied. During the shell making process, pay attention to avoid the accumulation of mold shells in the hole. When applying the next layer of paint, the excess paint in the hole needs to be cleaned.

[0068] S4: According to the above shell making sequence, the surface of the blade and the casting system wax mold is coated with mold shell slurry to form a blade mold shell green body; the wax material in the green body is removed, and it is baked at 900°C for 3h to prepare a large-sized hollow blade mold shell.

[0069] S5: Figure 4 Casting is performed as shown; before pouring, the mold shell is placed on a water-cooled crystallizer, and a drainage funnel is preset, with the bottom of the funnel 150 mm away from the top of the pouring cup; during pouring, the alloy melt temperature is 1520°C, and the mold shell heating temperature is 1510°C; pulling begins within 30 seconds after pouring, and after pulling is completed, the furnace is kept warm for 10 minutes before breaking the air, and the mold shell is placed in an insulation barrel for cooling, and the blade prepared in this embodiment is obtained.

[0070] When repetitive experiments were carried out in the manner of this embodiment, it was found that compared with the conventional directional solidification process, the scrap rate of blade body due to cracks along the grains 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%, showing good effects of refining grains and inhibiting cracks for large-sized complex hollow directional solidification blades.

[0071] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing a hollow directional solidification blade, characterized in that: The steps include: (1) configuring a pouring cup, a first composite wax mold, and a second composite wax mold; wherein the first composite wax mold includes an integrally extruded blade wax mold, a seeding straight section wax mold, and a seeding draft section wax mold, and the second composite wax mold includes an integrally extruded seeding step draft section wax mold and a chassis; (2) welding the pouring cup, the first composite wax mold, and the second composite wax mold from top to bottom to obtain a wax mold assembly; (3) placing the wax model assembly in a coating to coat the wax model assembly, and then sanding, drying, and cleaning the floating sand to obtain a hardened wax model; dewaxing and baking the hardened wax model in sequence to obtain a mold shell; (4) pouring molten metal into the mold shell to obtain a first blade precursor through directional solidification technology; (5) performing a shell cleaning process on the first blade precursor, and then removing non-blade structures by wire cutting to obtain a second blade precursor; (6) removing the ceramic core in the second blade precursor, and then inspecting the blade grains by corrosion; when the blade grains meet the technical standards, performing heat treatment to obtain a hollow directional solidification blade.

2. The method for preparing a hollow directional solidification blade according to claim 1, characterized in that: The top of the seeding straight section wax mold is connected to the blade wax mold corresponding to the blade tip structure of the blade; And / or, the cross-sectional shape of the seeding straight section wax mold is the same as the blade body profile contour line of the blade, and the height of the seeding straight section wax mold is 20 mm to 40 mm.

3. The method for preparing a hollow directional solidification blade according to claim 1, characterized in that: The top cross-sectional shape of the seeding and drawing section wax mold is the same as the blade body profile contour line of the blade, and the top of the seeding and drawing section wax mold is connected to the seeding straight section wax mold; Measured downward from the top of the wax mold of the seeding and drawing section, there is an outward draft angle, and the draft angle is 5° to 15°; The height of the wax mold of the seeding and demolding section is 20 mm to 40 mm.

4. The method for preparing a hollow directional solidification blade according to claim 1, characterized in that: The top cross-sectional shape of the seeding step die-drawing section wax mold extends outward by 5 mm to 10 mm compared to the outline of the seeding die-drawing section wax mold; Measured downward from the top of the wax mold of the seeding step drafting section, there is an outward draft angle, and the draft angle is 5° to 15°; The height of the wax mold of the seeding step demolding section is 10 mm to 20 mm.

5. The method for preparing a hollow directional solidification blade according to claim 4, characterized in that: A groove structure is provided on the top of the seeding step demolding section wax mold, the depth of the groove structure is 4mm to 6mm, the width of the groove structure is 0.3mm to 0.5mm, and the groove cross-section of the groove structure is expanded outward compared to the contour line of the seeding step demolding section wax mold.

6. The method for preparing a hollow directional solidification blade according to claim 5, characterized in that: In step (2), the assembly welding of the first composite wax model and the second composite wax model comprises: The bottom part of the seeding die stripping section wax mold is embedded in the groove structure at the top of the seeding step die stripping section wax mold, and the joints between the two are connected by wax slipping.

7. The method for preparing a hollow directional solidification blade according to claim 1, characterized in that: In step (3), the method for preparing the hardened wax model comprises: S1: firstly coat the wax model module in the directional solidification surface coating, and then sprinkle sand after the coating is evenly applied; S2: Clean the floating sand, and then coat the treated wax model module in the directional solidification back layer coating, coat it evenly and then sprinkle sand; S3: Repeat S2 for 6 to 8 times; then apply the slurry as a sealing layer to obtain the hardened wax mold.

8. The method for preparing a hollow directional solidification blade according to claim 1, characterized in that: In step (3), the dewaxing adopts a water vapor 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° C. to 1000° C., and the calcination time is 2 h to 4 h.

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

10. The method for preparing a hollow directional solidification blade 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 degree lower than 5 Pa, at which time the lifting system is started to deliver the mold shell to the interior of the mold shell heater; The mold shell is heated and kept warm by the mold shell heater, and then the pouring is started; the molten metal enters the mold shell through the pouring cup, and after the filling is completed, it is left to stand for 30s to 60s, and then the mold shell is pulled downward at a speed of 2mm / min to 10mm / min until the mold shell is completely pulled out of the mold shell heater, thereby obtaining the mold shell and the first blade precursor.

Images