Dual-zone induction diathermy device for directional solidification of aero-engine single crystal blade and dual-station dual-zone induction single crystal furnace

Abstract

The application discloses a double-zone induction diathermy device for directional solidification of aero-engine single-crystal blades, which comprises a heating body composed of an upper-zone graphite heating cylinder and a lower-zone graphite heating cylinder which are butted together, an insulation cover plate, an insulation bottom plate, an insulation plate, a carbon felt insulation layer, a ceramic fiber insulation layer, an upper-zone induction coil, a lower-zone induction coil, a magnetic isolation ring, a shielding ring, an upper-zone induction power supply and a lower-zone induction power supply, the working frequency of the upper-zone induction power supply and the wall thickness of the upper-zone graphite heating cylinder satisfy that the skin depth of a magnetic field in the upper-zone graphite heating cylinder is greater than the wall thickness of the upper-zone graphite heating cylinder, and the working frequency of the lower-zone induction power supply and the wall thickness of the lower-zone graphite heating cylinder satisfy that the skin depth of a magnetic field in the lower-zone graphite heating cylinder is less than the wall thickness of the lower-zone graphite heating cylinder. The application has the advantages that the yield and processing efficiency of single-crystal high-temperature alloy blades can be improved.

Description

Technical Field

[0001] This invention relates to the field of precision casting technology for single-crystal high-temperature alloy blades for aero-engines, specifically to a dual-zone induction heating device and a dual-station dual-zone induction single-crystal furnace for directional solidification of single-crystal blades for aero-engines. Background Technology

[0002] Single-crystal superalloy blades (referred to as single-crystal blades) are key hot-end components of aero-engines, and their performance directly determines the engine's thrust, efficiency, and service life. Single-crystal superalloy blades are typically manufactured using directional solidification processes. There are various directional solidification processes, mainly including the power reduction method (PD method), high-speed solidification method (HRS method), and liquid metal cooling method (LMC method). Among them, the HRS method is relatively simple and easy to control, and is currently the main method for producing single-crystal superalloy blades.

[0003] The main equipment in the HRS method is a single crystal furnace, which includes an alloy melting furnace, a heating device placed below the alloy melting furnace, a crystallizer extending into the heating device, and a pulling mechanism that drives the crystallizer to rise and fall. The directional solidification process of the HRS method is as follows: First, a blade-shaped ceramic mold is placed on the crystallizer extending into the heating device. After the alloy melt is poured into the ceramic mold, the combined effect of the thermal field created by the heating device and the cooling provided by the crystallizer creates a stable temperature gradient that continuously decreases from top to bottom along the axial direction of the ceramic mold and the alloy melt inside, providing conditions for the directional growth of single crystals. Then, the pulling mechanism controls the downward pulling rate of the ceramic mold, allowing the alloy to solidify and grow layer by layer within the ceramic mold along a specific crystal orientation. After cooling, the ceramic mold is removed to obtain a single crystal high-temperature alloy blade.

[0004] Currently, heating devices typically use induction heating of graphite cylinders to create the thermal field required for the process. A utility model patent with patent authorization publication number CN2536603Y, entitled "A Dual-Zone Heating Vacuum Induction Single Crystal Furnace," discloses a dual-zone heating device. This dual-zone heating device comprises upper and lower graphite cylinder heating elements, each with an induction coil and a thermocouple for temperature measurement on its exterior. During operation, the internal region of the upper graphite cylinder heating element serves as the upper melt insulation zone, while the internal region of the lower graphite cylinder heating element serves as the lower crystal growth zone.

[0005] When the existing dual-zone heating device is working, the induction power supply sends an alternating current with the same operating frequency to the induction coils surrounding the upper and lower graphite heating cylinders. The induction coils then generate an alternating magnetic field. The alternating magnetic field acts on the graphite cylinders, inducing eddy currents inside the cylinder walls. The eddy currents generate heat through the resistance of the graphite cylinders, thus forming a thermal field.

[0006] However, existing dual-zone heating devices still have the following technical problems in practical applications, which restrict the production stability and yield of single-crystal superalloy blades: Conventional dual-zone heating devices use graphite cylinder heating elements with uniform wall thickness and consistent induction power supply operating frequency in both the upper and lower zones. Insufficient consideration of magnetic field factors during the design process leads to easily disrupted melt temperature field in the lower growing zone or slow or insufficient heating of the melt in the upper melting holding zone during directional solidification. These phenomena not only seriously interfere with the crystal growth process, easily causing defects such as impurities, freckles, orientation deviations, and shrinkage cavities in the blades, significantly reducing product yield, but also result in low overall heating efficiency and high energy consumption.

[0007] Furthermore, traditional single crystal furnaces mostly adopt a single-station casting structure, which can only complete the solidification and molding of one set of ceramic mold shells at a time, resulting in low equipment utilization efficiency, long production cycle, high energy consumption, and difficulty in meeting the needs of batch delivery. Summary of the Invention

[0008] The first objective of this invention is to provide a dual-zone induction heating device that can improve the yield and processing efficiency of single-crystal high-temperature alloy blades.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: a dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines, comprising: The heating element consists of an upper graphite heating cylinder and a lower graphite heating cylinder connected vertically. An insulation cover plate is placed on top of the heating element, and a pouring gate is provided in the center of the cover plate. The heat-insulating base plate is installed at the bottom of the heating element, and its center has a central passage for the ceramic mold shell and crystallizer to pass through; A heat insulation plate is disposed inside the heating element and located between the upper graphite heating cylinder and the lower graphite heating cylinder. The heat insulation plate, the heat insulation cover plate and the upper graphite heating cylinder together form the upper melt heat preservation zone, and the heat insulation plate, the heat insulation bottom plate and the lower graphite heating cylinder together form the lower crystal growth zone. A through hole for the ceramic mold shell to pass through is provided in the center of the heat insulation plate. A carbon felt insulation layer is wrapped around the outer wall of the heating element; A ceramic fiber insulation layer is wrapped around the outer wall of the carbon felt insulation layer; The upper induction coil is wound on the outside of the ceramic fiber insulation layer, and its height is matched with the height of the upper graphite heating cylinder. The lower induction coil is wound on the outside of the ceramic fiber insulation layer, and its installation height matches the height of the lower graphite heating cylinder. A magnetic shielding ring is fitted on the outside of the ceramic fiber insulation layer and positioned between the upper and lower induction coils. The shielding ring is coaxially mounted at the bottom of the insulation base plate; An upper-zone induction power supply is electrically connected to an upper-zone induction coil. The operating frequency of the upper-zone induction power supply and the wall thickness of the upper-zone graphite heating cylinder satisfy the following condition: the skin depth of the magnetic field in the upper-zone graphite heating cylinder is greater than the wall thickness of the upper-zone graphite heating cylinder. The lower region induction power supply is electrically connected to the lower region induction coil. The operating frequency of the lower region induction power supply and the wall thickness of the lower region graphite heating cylinder satisfy the following condition: the skin depth of the magnetic field in the lower region graphite heating cylinder is less than the wall thickness of the lower region graphite heating cylinder.

[0010] Furthermore, in the aforementioned dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines, wherein: The operating frequency range of the upper zone induction power supply is 1200~1500Hz, and the wall thickness of the upper zone graphite heating cylinder is 28~30mm; The operating frequency range of the lower zone induction power supply is 2500~3000Hz, and the wall thickness of the lower zone graphite heating cylinder is 38~40mm; The thickness of the carbon felt insulation layer is 30-40mm, and the thickness of the ceramic fiber insulation layer is 2.5-3mm.

[0011] Furthermore, in the aforementioned dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines, both the upper and lower induction coils are water-cooled induction coils that can be internally cooled by water.

[0012] Furthermore, in the aforementioned dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines, the shielding ring is provided with an annular cooling channel, which is connected to an external circulating water cooling circuit.

[0013] Furthermore, the aforementioned dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines further includes an upper zone temperature control component and a lower zone temperature control component. The upper zone temperature control component includes: an upper zone power adjustment module electrically connected to the upper zone induction power supply, and an upper zone temperature measuring thermocouple electrically connected to the upper zone power adjustment module and which collects the internal temperature of the upper zone graphite heating cylinder in real time. The upper zone power adjustment module adjusts the output power of the upper zone induction power supply in real time through the temperature signal fed back by the upper zone temperature measuring thermocouple, so that the internal temperature of the upper zone graphite heating cylinder is at a preset temperature. The lower zone temperature control component includes: a lower zone power adjustment module electrically connected to the lower zone induction power supply, and a lower zone temperature measuring thermocouple electrically connected to the lower zone power adjustment module and which collects the internal temperature of the lower zone graphite heating cylinder in real time. The lower zone power adjustment module adjusts the output power of the lower zone induction power supply in real time through the temperature signal fed back by the lower zone temperature measuring thermocouple, so that the internal temperature of the lower zone graphite heating cylinder is at a preset temperature.

[0014] The second objective of this invention is to provide a dual-station, dual-zone induction single-crystal furnace for directional solidification of single-crystal blades for aero-engines, which can improve the production efficiency and yield of single-crystal blades.

[0015] To achieve the above objectives, the present invention adopts the following technical solution: a dual-station dual-zone induction single crystal furnace for directional solidification of single crystal blades for aero-engines, comprising a furnace body, wherein a melting vacuum chamber is provided inside the furnace body, and two left-right distributed crystal growth stations are provided at the lower part of the melting vacuum chamber. Each crystal growth station is equipped with a dual-zone induction heating device, a crystallizer for placing a ceramic mold shell and extending into the corresponding dual-zone induction heating device, and a set of pulling mechanisms for driving the crystallizer and the ceramic mold shell to rise and fall; an alloy furnace is also provided in the melting vacuum chamber above the two crystal growth stations. The alloy furnace is connected to a tilting mechanism, which can control the alloy furnace to tilt to the left or right so as to pour the melt in the alloy furnace into the ceramic mold shell placed inside the dual-zone induction heating device of the two crystal growth stations.

[0016] Furthermore, in the aforementioned dual-station, dual-zone induction single-crystal furnace for directional solidification of single-crystal blades for aero-engines, the tilting mechanism includes: The alloy furnace is supported on the support via a rotating shaft; A coaxial motor is mounted on the bracket, and the output shaft of the coaxial motor is connected to the rotating shaft for transmission.

[0017] Furthermore, in the aforementioned dual-station dual-zone induction single crystal furnace for directional solidification of single crystal blades for aero-engines, the pulling mechanism includes a servo motor, a transmission screw, a guide assembly, and a support platform. The servo motor is arranged vertically, and its output shaft is connected to the transmission screw. A screw nut seat is fitted onto the transmission screw. The support platform is fixedly connected to the lead screw nut seat; the support platform is used to place the crystallizer, and the external dimensions of the crystallizer and the support platform are set to be able to pass through the center opening of the corresponding insulation base plate; The guide assembly provides vertical positioning and guidance for the support platform.

[0018] Furthermore, in the aforementioned dual-station dual-zone induction single crystal furnace for directional solidification of single crystal blades for aero-engines, a leak-proof collection tray is provided below the support platform. The leak-proof collection tray is used to collect the alloy melt that flows out when the ceramic mold shell cracks.

[0019] The beneficial effects of implementing the above technical solution are as follows: I. Beneficial effects of the dual-zone induction heating device: (1) This invention has discovered a common but long-unrecognized technical problem in existing dual-zone induction heating devices, namely, "the magnetic field of the induction coil will interfere with the directional solidification growth of single crystals, resulting in a high incidence of defects such as impurities and freckles, which restricts the yield of single crystal blades". In response to this problem, a technical solution of differentiating frequency and wall thickness matching between the upper and lower zones is proposed. Specifically, the upper melt insulation zone adopts a lower working frequency (1200-1500Hz) and is matched with a thinner wall thickness (28-30mm) so that the skin depth of the magnetic field is greater than the wall thickness of the upper graphite heating cylinder. This ensures that the magnetic field can penetrate the graphite heating cylinder and the ceramic mold shell and act directly on the alloy melt in the upper melt insulation zone. Under the dual action of thermal radiation and magnetic induction heating of the heating cylinder, the alloy melt in the upper melt insulation zone can achieve rapid heating, uniform heating and insulation. The heating speed is fast and the heating efficiency is high, which effectively avoids the generation of impurity defects caused by insufficient temperature of the upper alloy melt. The lower zone employs a higher operating frequency (2500–3000 Hz) and a thicker wall thickness (38–40 mm), ensuring that the skin depth of the magnetic field is less than the wall thickness. This significantly attenuates the magnetic field through the wall, effectively suppressing its penetration into the growing crystal zone. Simultaneously, a magnetic shielding ring is placed between the upper and lower induction coils to effectively isolate crosstalk between the two zones. A shielding ring is coaxially placed at the bottom of the insulation base plate to absorb leakage magnetic flux at the end of the lower zone induction coil, suppressing downward and outward diffusion of the magnetic field. After multiple layers of synergistic shielding, the residual magnetic field strength intruding into the lower growing crystal zone is extremely low, preventing the induction of significant eddy currents in the alloy melt, disrupting the stable temperature gradient required for directional solidification, and preventing turbulent temperature field in the lower growing crystal zone. This ensures that the crystals in the lower growing crystal zone can grow along a fixed orientation, effectively reducing the incidence of casting defects such as impurities, freckles, orientation deviations, and shrinkage cavities. Consequently, the yield of single-crystal blades is significantly improved, increasing from the traditional 70% to over 95%.

[0020] (2) Independent power adjustment modules and temperature measuring thermocouples are set in the upper and lower zones respectively. The output power of the corresponding induction power supply is dynamically adjusted through real-time temperature feedback, so that the internal temperature of the upper and lower graphite heating cylinders is stabilized within the preset range. The temperature control accuracy can reach ±2℃. This partitioned temperature control mechanism can help to accurately construct and maintain the axial stable temperature gradient required for directional solidification, and provide a reliable thermal field environment for the continuous growth of single crystals along a specific orientation.

[0021] (3) The composite structure of “inner carbon felt + outer ceramic fiber” with “thick inner and thin outer” is adopted. The thicker carbon felt layer undertakes the main heat insulation function, while the thinner ceramic fiber layer serves as an insulating layer. This ensures the heat preservation effect and avoids the serious attenuation of the magnetic field caused by the carbon felt being too thick or directly contacting the coil. This allows the upper region to penetrate the magnetic field to reach the outer surface of the graphite heating cylinder with a high residual strength. The heat preservation structure is reasonable, achieving a balance between “heat preservation” and “magnetic permeability”.

[0022] II. Beneficial effects of dual-station dual-zone induction single crystal furnace: (1) Two drawing and crystal growth stations are set up in the melting vacuum chamber. Each station is equipped with an independent dual-zone induction heating device, crystallizer and drawing mechanism. An alloy furnace that can be flipped to the left or right is set up above. When the left station is drawing and solidifying, the alloy furnace can be flipped to the right to pour the preheated mold shell of the right station, so as to realize the two stations alternate continuous production, which greatly improves the production efficiency. In addition, a dual-zone induction heating device with differentiated frequency and wall thickness matching between the upper and lower zones is adopted, which significantly improves the yield of single crystal blades.

[0023] (2) The two crystal pulling stations share the same alloy furnace and use the same dual-zone induction heating device and process parameters (frequency, wall thickness, temperature control, etc.), resulting in good product consistency and making it more conducive to the large-scale and standardized production of single crystal blades. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines according to the present invention.

[0025] Figure 2 This is a schematic diagram of the structure of the dual-station dual-zone induction single crystal furnace for directional solidification of single crystal blades for aero-engines according to the present invention.

[0026] Figure 3 This is a schematic diagram of the structure of the crystallizer and ceramic mold shell when they are inserted into the heating element of the dual-zone induction heating device. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, the dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines includes: The heating element consists of an upper graphite heating cylinder 1 and a lower graphite heating cylinder 2 connected vertically; both the upper graphite heating cylinder 1 and the lower graphite heating cylinder 2 are made of isostatically pressed 99.99% high-purity graphite with a resistivity of 13μΩ·m. The heat insulation cover plate 3 is placed on the top of the heating element, that is, the heat insulation cover plate 3 is placed on the top of the graphite heating cylinder 1 in the upper area, and a pouring port 31 is provided in the center of the heat insulation cover plate 3. The heat insulation base plate 4 is installed at the bottom of the heating element, that is, the heat insulation base plate 4 is installed at the bottom of the graphite heating cylinder 2 in the lower area. A central passage 41 for the ceramic mold shell 5 and the crystallizer 6 to pass through is provided in the center of the heat insulation base plate 4. A heat insulation plate 7 is disposed inside the heating element and located between the upper graphite heating cylinder 1 and the lower graphite heating cylinder 2. The heat insulation plate 7, the heat insulation cover plate 3, and the upper graphite heating cylinder 1 together form the upper melt heat insulation zone 8. The heat insulation plate 7, the heat insulation bottom plate 4, and the lower graphite heating cylinder 2 together form the lower crystallization zone 9. A through hole 71 for the ceramic mold shell 5 to pass through is provided in the center of the heat insulation plate 7. The carbon felt insulation layer 10 covers the outer wall of the heating element, that is, the carbon felt insulation layer 10 covers the outer wall of both the upper graphite heating cylinder 1 and the lower graphite heating cylinder 2. A ceramic fiber insulation layer 11 is wrapped around the outer wall of the carbon felt insulation layer 10; The upper induction coil 12 is wound around the outside of the ceramic fiber insulation layer 11, and its height is matched with the height of the upper graphite heating cylinder 1. The lower induction coil 13 is wound around the outside of the ceramic fiber insulation layer 11, and its height is matched with the height of the lower graphite heating cylinder 2. A magnetic isolation ring 14 is sleeved on the outside of the ceramic fiber insulation layer 11 and is located between the upper induction coil 12 and the lower induction coil 13. The magnetic isolation ring is a commercially available product made of high magnetic permeability material and is used to isolate the magnetic fields of the upper and lower regions to avoid mutual interference of magnetic fields. A shielding ring 15 is coaxially mounted on the bottom of the insulation base plate 4. The shielding ring is a commercially available product made of a highly conductive metal (such as copper) to shield the leakage magnetic flux at the bottom of the coil, preventing the leakage magnetic flux from entering the lower crystal growth zone 9. In this embodiment, the shielding ring 15 also has an annular cooling channel 151 inside. The annular cooling channel 151 is connected to an external circulating water cooling circuit. During operation, the circulating water cooling circuit continuously introduces circulating cooling water into the annular cooling channel 151 and flows out from the outlet of the annular cooling channel 151. The water is cooled and returned through the circulating water cooling circuit to form a continuous circulation, which removes the heat generated by the shielding ring itself due to induced eddy currents. At the same time, it helps to stabilize the thermal field environment at the bottom of the lower crystal growth zone and indirectly assists in the cooling of the solidified leaf segments. The shielding ring 15 integrates magnetic shielding and cooling functions, which is beneficial to the compactness of the overall structure of the equipment.

[0029] The upper induction power supply is electrically connected to the upper induction coil 12. The operating frequency of the upper induction power supply and the wall thickness of the upper graphite heating cylinder 1 satisfy the following: the skin depth of the magnetic field in the upper graphite heating cylinder 1 is greater than the wall thickness of the upper graphite heating cylinder 1. The lower region induction power supply is electrically connected to the lower region induction coil 13. The operating frequency of the lower region induction power supply and the wall thickness of the lower region graphite heating cylinder 2 satisfy the following condition: the skin depth of the magnetic field in the lower region graphite heating cylinder 2 is less than the wall thickness of the lower region graphite heating cylinder 2.

[0030] In this embodiment, the operating frequency range of the upper region induction power supply is 1200-1500Hz, and the wall thickness of the upper region graphite heating cylinder is 28-30mm. Substituting the operating frequency of the upper region induction power supply into the skin depth calculation formula, it can be seen that for the graphite heating cylinder of the present invention, the skin depth range corresponding to the operating frequency of 1200-1500Hz is 46.85-52.39mm. This value is much larger than the wall thickness of the upper region graphite heating cylinder (28-30mm), so the magnetic field can completely penetrate the cylinder wall.

[0031] In this invention, experimental verification shows that when the operating frequency is controlled within the range of 1200–1500 Hz, a more balanced technical effect can be achieved. On the one hand, this frequency range makes the skin depth (approximately 46.85–52.39 mm based on high-purity graphite with a resistivity of 13 μΩ·m) much larger than the wall thickness of the upper region graphite heating cylinder (28–30 mm), ensuring stable and reliable magnetic field penetration. On the other hand, this frequency range avoids engineering problems such as decreased inductive coupling efficiency, slower heating rate, and increased power supply costs that may occur at excessively low frequencies (e.g., below 1200 Hz), while also avoiding the risk of insufficient penetration margin due to changes in the high-temperature resistivity of graphite at excessively high frequencies (e.g., above 1500 Hz). Therefore, further optimizing the upper region operating frequency to 1200–1500 Hz is beneficial for improving heating efficiency and process stability while ensuring the magnetic heating function.

[0032] The operating frequency range of the lower-zone induction power supply is 2500–3000 Hz, and the wall thickness of the lower-zone graphite heating element is 38–40 mm. Substituting the operating frequency of the lower-zone induction power supply into the skin depth calculation formula, it can be seen that for the graphite heating element of this invention, the skin depth range corresponding to the 2500–3000 Hz operating frequency is 33.13–36.29 mm. This value is less than the wall thickness of the lower-zone graphite heating element (38–40 mm). The lower zone achieves this by using a higher operating frequency (2500–3000 Hz) and matching a thicker wall. The thickness (38-40 mm) and the combined effect of the magnetic shielding ring 14 and the shielding ring 15 result in an extremely low residual magnetic field strength intruding into the lower crystal growth zone. This residual magnetic field strength will not form an effective interfering magnetic field, will not induce obvious eddy currents in the alloy melt, will not disrupt the stable temperature gradient required for directional solidification, and will not cause turbulence in the melt temperature field of the lower crystal growth zone. This ensures that the crystals in the lower crystal growth zone can grow in a fixed orientation, effectively reducing the incidence of casting defects such as impurities, freckles, orientation deviations, and shrinkage cavities, thereby significantly improving the yield of single crystal blades.

[0033] In this invention, experimental verification shows that when the operating frequency is controlled within the range of 2500–3000 Hz, better overall results can be achieved: the skin depth corresponding to this frequency range (approximately 33.13–36.29 mm based on high-purity graphite with a resistivity of 13 μΩ·m) is less than the wall thickness of the graphite heating cylinder in the lower region (38–40 mm). The residual strength of the magnetic field after attenuation through the cylinder wall is significantly reduced. Combined with the synergistic effect of the magnetic shielding ring and the shielding ring, the magnetic field strength in the crystal growth solidification zone can be suppressed to a level that does not have a harmful effect on the directional solidification of single crystals. At the same time, this frequency range avoids the problem of excessively strong residual magnetic field and increased shielding burden when the frequency is too low (e.g., below 2500 Hz), and also avoids the problem of excessive eddy current concentration on the outside of the cylinder wall and affecting the heating uniformity of the lower region when the frequency is too high (e.g., above 3000 Hz). Therefore, further optimizing the operating frequency of the lower region to 2500–3000 Hz is beneficial for effectively suppressing magnetic field interference while maintaining a good temperature gradient construction capability in the lower region.

[0034] The formula for calculating the skin depth involved in this invention is as follows:

[0035] Where ρ is the skin depth, f is the graphite resistivity (13 μΩ·m), f is the operating frequency of the induction power supply, and μ is the graphite permeability ≈ 1.

[0036] The thickness of the carbon felt insulation layer 10 is 30-40 mm, and the thickness of the ceramic fiber insulation layer 11 is 2.5-3 mm. The thicker carbon felt insulation layer undertakes the main heat insulation function, while the thinner ceramic fiber insulation layer serves as an insulating layer. This ensures the heat insulation effect and avoids severe magnetic field attenuation caused by excessive carbon felt thickness or direct contact with the coil. This allows the penetrating magnetic field in the upper region to reach the outer surface of the graphite heating cylinder with a high residual strength. The insulation structure is reasonable, achieving a balance between "heat insulation" and "magnetic permeability".

[0037] In this embodiment, when the ceramic mold shell 5 is coaxially placed inside the heating element, the distance between the inner wall of the upper graphite heating cylinder 1 and the outer wall of the ceramic mold shell 5 is 70-90mm, and the distance between the inner wall of the lower graphite heating cylinder 2 and the outer wall of the ceramic mold shell 5 is 70-90mm.

[0038] In this embodiment, both the upper induction coil 12 and the lower induction coil 13 are water-cooled induction coils that can be cooled by water inside, which are suitable for long-term operation and ensure long-term stable operation of the coils.

[0039] In this embodiment, an upper temperature control component and a lower temperature control component are also included; The upper zone temperature control component includes: an upper zone power adjustment module electrically connected to the upper zone induction power supply, and an upper zone temperature measuring thermocouple 16 that collects the internal temperature of the upper zone graphite heating cylinder in real time and is electrically connected to the upper zone power adjustment module. The upper zone power adjustment module adjusts the output power of the upper zone induction power supply in real time through the temperature signal fed back by the upper zone temperature measuring thermocouple 16, so that the internal temperature of the upper zone graphite heating cylinder is at a preset temperature.

[0040] The lower zone temperature control component includes: a lower zone power adjustment module electrically connected to the lower zone induction power supply, and a lower zone temperature measuring thermocouple 17 electrically connected to the lower zone power adjustment module and which collects the internal temperature of the lower zone graphite heating cylinder in real time. The lower zone power adjustment module adjusts the output power of the lower zone induction power supply in real time through the temperature signal fed back by the lower zone temperature measuring thermocouple 17, so that the internal temperature of the lower zone graphite heating cylinder is at a preset temperature. By dynamically adjusting the output power of the corresponding induction power supply through real-time temperature feedback, the internal temperatures of the upper and lower graphite heating cylinders are stabilized within preset ranges, and the temperature control accuracy can reach ±2℃. This zone temperature control mechanism can help to accurately construct and maintain the axial stable temperature gradient required for directional solidification, and provide a reliable thermal field environment for the continuous growth of single crystals along a specific orientation.

[0041] This invention also discloses a dual-station, dual-zone induction single-crystal furnace for directional solidification of single-crystal blades for aero-engines, constructed based on the aforementioned dual-zone induction heating device. Figure 1 , Figure 2 , Figure 3 As shown, the structure of the dual-station dual-zone induction single crystal furnace includes a furnace body 18, inside which is a melting vacuum chamber 19. The lower part of the melting vacuum chamber 19 has two left-right distributed crystal pulling stations. Each crystal pulling station is equipped with a dual-zone induction heating device 20 as described in this invention, a crystallizer 6 for placing a ceramic mold shell 5 and extending into the corresponding dual-zone induction heating device 20, and a pulling mechanism 21 for driving the crystallizer 6 and the ceramic mold shell 5 to rise and fall. An alloy furnace 22 is also provided in the melting vacuum chamber 19 above the two crystal pulling stations. The alloy furnace 22 is connected to a tilting mechanism 23, which can control the alloy furnace to tilt to the left or right, so that the melt in the alloy furnace 22 can be poured into the ceramic mold shell 5 placed inside the dual-zone induction heating device 20 at the two crystal pulling stations.

[0042] In this embodiment, the tilting mechanism 23 includes: The alloy furnace is supported on the support via a rotating shaft; A coaxial motor is mounted on the bracket, and the output shaft of the coaxial motor is connected to the rotating shaft for transmission.

[0043] In this embodiment, the pull-out mechanism 21 includes a servo motor, a transmission screw, a guide assembly, and a support platform 24; The servo motor is arranged vertically, and its output shaft is connected to the transmission screw. A screw nut seat is fitted onto the transmission screw. The support platform 24 is fixedly connected to the lead screw nut seat; the support platform 24 is used to place the crystallizer 6, and the external dimensions of the crystallizer 6 and the support platform 24 are set to be able to pass through the center passage 41 of the corresponding heat insulation base plate 4; The guiding assembly provides vertical positioning and guidance for the 24 support platforms; In practical applications, an encoder can be used to further ensure that the carrier platform can accurately move the crystallizer and the ceramic mold shell placed on the crystallizer to a preset height. The encoder is electrically connected to the servo motor and is used to detect the rotation angle and cumulative number of revolutions of the servo motor in real time, so as to accurately control the lifting position of the carrier platform 24, so that the carrier platform 24 can accurately move the crystallizer 6 and the ceramic mold shell 5 placed on the crystallizer 6 to a preset height.

[0044] A leak-proof collection tray 25 is provided below the support platform 24. The leak-proof collection tray 25 is used to collect the alloy melt that flows out when the ceramic mold shell cracks.

[0045] The working principle of the dual-station dual-zone induction single crystal furnace of this invention is as follows: First, pre-made ceramic mold shells 5 are placed on the crystallizers of the two stations respectively. The servo motor in the pull-out mechanism 21 of each station drives the transmission screw of the corresponding station to rotate. Through the screw nut seat of the corresponding station, the support platform 24 of the corresponding station is raised, so that the crystallizer 6 and the ceramic mold shell 5 of the corresponding station pass through the central through-hole 41 of the insulation base plate 4 and enter the heating element of the dual-zone induction heating device 20 of the corresponding station. When the crystallizer 6 and the ceramic mold shell 5 on it move up to the preset height, the servo motor stops working. At this time, the ceramic mold shells 5 of both stations have reached the preset working height in the heating element of the corresponding station. A leak-proof collection tray 25 is installed under the support platform 24. If the ceramic mold shell 5 cracks and causes the alloy melt to leak during the subsequent pouring and solidification process, the leaked melt can fall into the leak-proof collection tray 25, avoiding contamination of the furnace cavity and damage to the equipment.

[0046] Next, the dual-zone induction heating devices 20 at both workstations are activated to preheat the ceramic mold shell 5 within their respective heating bodies. The preheating process is as follows: the upper zone induction power supply supplies an alternating current with a working frequency of 1200-1500Hz to the upper zone induction coil 12, and the lower zone induction power supply supplies an alternating current with a working frequency of 2500-3000Hz to the lower zone induction coil 13. The graphite cylinder wall itself generates thermal radiation due to eddy current heating, and the upper and lower graphite cylinders heat the ceramic mold shell through thermal radiation, thereby completing the preheating of the ceramic mold shell. At the same time, circulating cooling water is introduced into the crystallizer 6 to form a bottom cold source, preparing for the subsequent directional solidification to build an axial temperature gradient.

[0047] Next, the coaxial motor in the tilting mechanism 23 drives the rotating shaft to rotate, causing the alloy furnace 22 to tilt and pour the internal alloy molten material into the ceramic mold shell 5 of one of the stations. Because the wall thickness (28-30 mm) of the upper graphite heating cylinder 1 is less than the skin depth (approximately 46.85-52.39 mm) at this frequency, the magnetic field completely penetrates the cylinder wall of the upper graphite heating cylinder 1 and the ceramic mold shell 5. The penetrating magnetic field directly acts on the injected alloy molten material in the upper melt insulation zone 8. The alloy molten material in the upper melt insulation zone 8 is heated by the thermal radiation and magnetic induction of the heating cylinder. Under the dual action, the temperature rises rapidly and remains in a molten state. At the same time, in the lower crystallization zone 9, since the wall thickness (38-40 mm) of the lower graphite heating cylinder 2 is greater than the skin depth (33.13-36.29 mm) at this frequency, the magnetic field is significantly attenuated during the penetration of the cylinder wall. The alloy melt in the lower crystallization zone 9 is mainly heated by the thermal radiation of the heating cylinder and kept at the preset temperature. Meanwhile, the crystallizer 6 is circulated with cooling water to form a bottom cold source, which together with the high temperature of the upper melt insulation zone 8 and the lower crystallization zone 9 to form a stable axial temperature gradient.

[0048] After the casting is completed, the servo motor in the station's pull-out mechanism 21 rotates in the opposite direction, driving the transmission screw to run, which in turn drives the screw nut seat and the support platform 24 to descend at a uniform speed, so that the ceramic mold shell 5 and the crystallizer 6 are slowly pulled downwards.

[0049] During the pulling process, the unsolidified alloy melt inside the ceramic mold shell 5 is always within the axial height range corresponding to the upper melt insulation zone 8. That is, under the dual heating effect of thermal radiation and magnetic induction heating of the heating cylinder, the alloy melt in the upper melt insulation zone 8 will ensure that it remains in a molten state and continuously obtains heat, thus avoiding insufficient temperature in the upper zone.

[0050] In the lower crystal growth region 9, because the wall thickness (38-40 mm) of the graphite heating cylinder 2 in the lower region is greater than the skin depth (33.13-36.29 mm) at this frequency, the magnetic field is significantly attenuated during the penetration of the cylinder wall. At the same time, the magnetic shielding ring 14 (high magnetic permeability material) absorbs and guides the crosstalk magnetic field between the two regions, and the shielding ring 15 (high conductivity metal) absorbs the end leakage flux of the induction coil 13 in the lower region, so that the residual magnetic field strength in the lower crystal growth region 9 is extremely low and will not cause harmful interference to the subsequent crystal growth, so that the crystal can grow along the fixed crystal orientation. In addition, during the pulling process, the shielding ring 15 is provided with an annular cooling channel 151 inside. The annular cooling channel 151 is connected to the external circulating water cooling circuit. The circulating cooling water continuously enters the annular cooling channel 151 and flows back, carrying away the heat generated by the induced eddy current of the shielding ring itself, which helps to stabilize the thermal field environment at the bottom of the lower crystal growth region 9 and indirectly assists in the cooling of the solidified leaf segment. As the ceramic mold shell 5 slowly moves downward, the crystal solidifies and grows layer by layer along the fixed crystal, eventually forming a single crystal structure.

[0051] If the ceramic mold shell 5 cracks unexpectedly during the pouring or pulling process, the leaked alloy melt will fall directly into the leak-proof collection tray 25 below the support platform 24, preventing the melt from splashing or flowing into the bottom of the furnace body, facilitating subsequent cleaning, and avoiding damage caused by the melt contacting the pulling mechanism and crystallizer.

[0052] When one station enters the drawing and solidification stage, the alloy furnace 22 is reset under the drive of the tilting mechanism 23. The alloy is melted during the drawing and solidification time. Then it is flipped in the opposite direction to pour the preheated ceramic mold shell on the other station, so as to realize the two stations alternate continuous production.

[0053] The advantages of the dual-zone induction heating device in this invention are: (1) This invention has discovered a common but long-unrecognized technical problem in existing dual-zone induction heating devices, namely, "the magnetic field of the induction coil will interfere with the directional solidification growth of single crystals, resulting in a high incidence of defects such as impurities and freckles, which restricts the yield of single crystal blades". In response to this problem, a technical solution of differentiating frequency and wall thickness matching between the upper and lower zones is proposed. Specifically, the upper melt insulation zone adopts a lower working frequency (1200-1500Hz) and is matched with a thinner wall thickness (28-30mm) so that the skin depth of the magnetic field is greater than the wall thickness of the upper graphite heating cylinder. This ensures that the magnetic field can penetrate the graphite heating cylinder and the ceramic mold shell and act directly on the alloy melt in the upper melt insulation zone. Under the dual action of thermal radiation and magnetic induction heating of the heating cylinder, the alloy melt in the upper melt insulation zone can achieve rapid heating, uniform heating and insulation. The heating speed is fast and the heating efficiency is high, which effectively avoids the generation of impurity defects caused by insufficient temperature of the upper alloy melt. The lower zone employs a higher operating frequency (2500–3000 Hz) and a thicker wall thickness (38–40 mm), ensuring that the skin depth of the magnetic field is less than the wall thickness. This significantly attenuates the magnetic field through the wall, effectively suppressing its penetration into the growing crystal zone. Simultaneously, a magnetic shielding ring is placed between the upper and lower induction coils to effectively isolate crosstalk between the two zones. A shielding ring is coaxially placed at the bottom of the insulation base plate to absorb leakage magnetic flux at the end of the lower zone induction coil, suppressing downward and outward diffusion of the magnetic field. After multiple layers of synergistic shielding, the residual magnetic field strength intruding into the lower growing crystal zone is extremely low, preventing the induction of significant eddy currents in the alloy melt, disrupting the stable temperature gradient required for directional solidification, and preventing turbulent temperature field in the lower growing crystal zone. This ensures that the crystals in the lower growing crystal zone can grow along a fixed orientation, effectively reducing the incidence of casting defects such as impurities, freckles, orientation deviations, and shrinkage cavities. Consequently, the yield of single-crystal blades is significantly improved, increasing from the traditional 70% to over 95%.

[0054] (2) Independent power adjustment modules and temperature measuring thermocouples are set in the upper and lower zones respectively. The output power of the corresponding induction power supply is dynamically adjusted through real-time temperature feedback, so that the internal temperature of the upper and lower graphite heating cylinders is stabilized within the preset range. The temperature control accuracy can reach ±2℃. This partitioned temperature control mechanism can help to accurately construct and maintain the axial stable temperature gradient required for directional solidification, and provide a reliable thermal field environment for the continuous growth of single crystals along a specific orientation.

[0055] (3) The composite structure of “inner carbon felt + outer ceramic fiber” with “thick inner and thin outer” is adopted. The thicker carbon felt layer undertakes the main heat insulation function, while the thinner ceramic fiber layer serves as an insulating layer. This ensures the heat preservation effect and avoids the serious attenuation of the magnetic field caused by the carbon felt being too thick or directly contacting the coil. This allows the upper region to penetrate the magnetic field to reach the outer surface of the graphite heating cylinder with a high residual strength. The heat preservation structure is reasonable, achieving a balance between “heat preservation” and “magnetic permeability”.

[0056] The advantages of the dual-station dual-zone induction single crystal furnace in this invention are: (1) Two drawing and crystal growth stations are set up in the melting vacuum chamber. Each station is equipped with an independent dual-zone induction heating device, crystallizer and drawing mechanism. An alloy furnace that can be flipped to the left or right is set up above. When the left station is drawing and solidifying, the alloy furnace can be flipped to the right to pour the preheated mold shell of the right station, so as to realize the two stations alternate continuous production, which greatly improves the production efficiency. In addition, a dual-zone induction heating device with differentiated frequency and wall thickness matching between the upper and lower zones is adopted, which significantly improves the yield of single crystal blades.

[0057] (2) The two crystal pulling stations share the same alloy furnace and use the same dual-zone induction heating device and process parameters (frequency, wall thickness, temperature control, etc.), resulting in good product consistency and making it more conducive to the large-scale and standardized production of single crystal blades.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A dual-zone induction heating device for directional solidification of single-crystal blades in aero-engines, characterized in that: include: The heating element consists of an upper graphite heating cylinder and a lower graphite heating cylinder connected vertically. An insulation cover plate is placed on top of the heating element, and a pouring gate is provided in the center of the cover plate. The heat-insulating base plate is installed at the bottom of the heating element, and its center has a central passage for the ceramic mold shell and crystallizer to pass through; A heat insulation plate is disposed inside the heating element and located between the upper graphite heating cylinder and the lower graphite heating cylinder. The heat insulation plate, the heat insulation cover plate and the upper graphite heating cylinder together form the upper melt heat preservation zone, and the heat insulation plate, the heat insulation bottom plate and the lower graphite heating cylinder together form the lower crystal growth zone. A through hole for the ceramic mold shell to pass through is provided in the center of the heat insulation plate. A carbon felt insulation layer is wrapped around the outer wall of the heating element; A ceramic fiber insulation layer is wrapped around the outer wall of the carbon felt insulation layer; The upper induction coil is wound on the outside of the ceramic fiber insulation layer, and its height is matched with the height of the upper graphite heating cylinder. The lower induction coil is wound on the outside of the ceramic fiber insulation layer, and its height is matched with the height of the lower graphite heating cylinder. A magnetic shielding ring is fitted on the outside of the ceramic fiber insulation layer and positioned between the upper and lower induction coils. The shielding ring is coaxially mounted at the bottom of the insulation base plate; An upper-zone induction power supply is electrically connected to an upper-zone induction coil. The operating frequency of the upper-zone induction power supply and the wall thickness of the upper-zone graphite heating cylinder satisfy the following condition: the skin depth of the magnetic field in the upper-zone graphite heating cylinder is greater than the wall thickness of the upper-zone graphite heating cylinder. The lower region induction power supply is electrically connected to the lower region induction coil. The operating frequency of the lower region induction power supply and the wall thickness of the lower region graphite heating cylinder satisfy the following condition: the skin depth of the magnetic field in the lower region graphite heating cylinder is less than the wall thickness of the lower region graphite heating cylinder. The operating frequency range of the upper zone induction power supply is 1200~1500Hz, and the wall thickness of the upper zone graphite heating cylinder is 28~30mm; The operating frequency range of the lower zone induction power supply is 2500~3000Hz, and the wall thickness of the lower zone graphite heating cylinder is 38~40mm; The thickness of the carbon felt insulation layer is 30-40mm, and the thickness of the ceramic fiber insulation layer is 2.5-3mm; When the ceramic mold shell is coaxially placed inside the heating element, the distance between the inner wall of the upper graphite heating cylinder and the outer wall of the ceramic mold shell is 70-90mm, and the distance between the inner wall of the lower graphite heating cylinder and the outer wall of the ceramic mold shell is 70-90mm.

2. The dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines according to claim 1, characterized in that: Both the upper and lower induction coils are water-cooled induction coils that can be cooled internally by water.

3. The dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines according to claim 1, characterized in that: The shielding ring has an annular cooling channel inside, which is connected to the external circulating water cooling circuit.

4. The dual-zone induction heating device for directional solidification of single-crystal blades for aero-engines according to claim 1, characterized in that: It also includes an upper zone temperature control component and a lower zone temperature control component; The upper zone temperature control component includes: an upper zone power adjustment module electrically connected to the upper zone induction power supply, and an upper zone temperature measuring thermocouple electrically connected to the upper zone power adjustment module and which collects the internal temperature of the upper zone graphite heating cylinder in real time. The upper zone power adjustment module adjusts the output power of the upper zone induction power supply in real time through the temperature signal fed back by the upper zone temperature measuring thermocouple, so that the internal temperature of the upper zone graphite heating cylinder is at a preset temperature. The lower zone temperature control component includes: a lower zone power adjustment module electrically connected to the lower zone induction power supply, and a lower zone temperature measuring thermocouple electrically connected to the lower zone power adjustment module and which collects the internal temperature of the lower zone graphite heating cylinder in real time. The lower zone power adjustment module adjusts the output power of the lower zone induction power supply in real time through the temperature signal fed back by the lower zone temperature measuring thermocouple, so that the internal temperature of the lower zone graphite heating cylinder is at a preset temperature.

5. A dual-station, dual-zone induction single-crystal furnace for directional solidification of single-crystal blades for aero-engines, characterized in that: The device includes a furnace body, inside which is a melting vacuum chamber. The lower part of the melting vacuum chamber has two left-right distributed crystal growth stations. Each crystal growth station is equipped with a dual-zone induction heating device as described in any one of claims 1 to 4, a crystallizer for placing a ceramic mold shell and extending into the corresponding dual-zone induction heating device, and a pulling mechanism for raising and lowering the crystallizer and ceramic mold shell. An alloy furnace is also installed in the melting vacuum chamber above the two crystal growth stations. The alloy furnace is connected to a tilting mechanism, which controls the alloy furnace to tilt to the left or right, so that the melt in the alloy furnace can be poured into the ceramic mold shell placed inside the dual-zone induction heating device at the two crystal growth stations.

6. The dual-station, dual-zone induction single-crystal furnace for directional solidification of single-crystal blades for aero-engines according to claim 5, characterized in that: The tilting mechanism includes: The alloy furnace is supported on the support via a rotating shaft; A coaxial motor is mounted on the bracket, and the output shaft of the coaxial motor is connected to the rotating shaft for transmission.

7. The dual-station, dual-zone induction single-crystal furnace for directional solidification of single-crystal blades for aero-engines according to claim 5, characterized in that: The pull-out mechanism includes a servo motor, a transmission screw, a guide assembly, and a support platform; The servo motor is arranged vertically, and its output shaft is connected to the transmission screw. A screw nut seat is fitted onto the transmission screw. The support platform is fixedly connected to the lead screw nut seat; the support platform is used to place the crystallizer, and the external dimensions of the crystallizer and the support platform are set to be able to pass through the center opening of the corresponding insulation base plate; The guide assembly provides vertical positioning and guidance for the support platform.

8. The dual-station, dual-zone induction single-crystal furnace for directional solidification of single-crystal blades for aero-engines according to claim 5, characterized in that: A leak-proof collection tray is provided below the support platform. The leak-proof collection tray is used to collect the alloy melt that flows out when the ceramic mold shell cracks.

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