Arc-shaped fuel plate hot bending device and hot forming method
By using hot bending equipment and methods, the problems of core cracking, shell detachment and residual stress in the cold bending forming of fuel plates have been solved, achieving high-precision one-time bending forming and reducing the scrap rate.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-10
- Publication Date
- 2026-04-14
AI Technical Summary
In existing technologies, cold bending of fuel plates has problems such as core cracking, detachment of the cladding from the core, high residual stress, and high springback, resulting in unstable production and high scrap rate.
A hot bending device and method are used to heat the upper and lower molds to a preset temperature using heating rods. The upper and lower molds are then pressed together by a press to form the fuel plate. Combined with annealing treatment and mold design optimization, one-time bending and forming is achieved.
The problems of core separation from the cladding, residual stress, and springback were solved, achieving high-precision, one-time molding of the fuel plate and reducing the scrap rate.
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Figure CN121847635A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of nuclear power technology, specifically relating to a hot bending device and hot forming method for arc-shaped fuel plates. Background Technology
[0002] The wide-spectrum ultra-high flux experimental reactor uses whole-core loading and unloading, and each fuel assembly uses a different uranium content (a total of 4 types). Figure 1 The arrangement of fuel assemblies in the active zone of one-third of the reactor core was demonstrated. In this arrangement, the core is divided into three fuel zones with a total of four types of fuel assemblies. Taking into account factors such as size and U content, the four types of assemblies consist of 68 fuel plates with 52 different radii of curvature and four different U contents.
[0003] In the molding of ATR and HFIR arc plates and involute plates, a quasi-isostatic cold molding method using a polymer material as the lower mold was employed. The arc-shaped fuel plates were prepared using a secondary bending molding method based on quasi-isostatic pressing. For detailed process documentation, see "DEVELOPMENT OF A FORMING METHOD FOR CURVED ATR FUEL PLATES," J. Herwin et al., Oak Ridge National Laboratory, August 1966.
[0004] However, the disadvantages of cold bending of fuel plates include:
[0005] 1. U3Si2-Al dispersed cores are highly brittle. Bending at room temperature can easily cause the core to crack, and the cladding can easily separate from the core, resulting in the core and cladding not fitting together.
[0006] 2. The fuel plate has a small bending radius and a small cold bending angle. During the bending process, elastic deformation mainly occurs, requiring a large overpressure compensation. However, the fuel plate has a sandwich structure, making it very difficult to predict springback and determine the process parameters for multiple pressings. Furthermore, the unstable process in actual production can easily lead to a high scrap rate.
[0007] 3. Cold bending results in significant springback, requiring multiple bending processes to remove it, making the bending process complex. Residual stress in the material cannot be released during cold bending, and natural aging after cold bending can easily lead to product defects. Summary of the Invention
[0008] To overcome the problems existing in related technologies, a hot bending device and a hot forming method for arc-shaped fuel plates are provided.
[0009] According to one aspect of the present disclosure, an arc-shaped fuel plate hot bending device is provided, the device comprising: a guide sleeve, a guide post, a pressure plate, a base, a fixing plate, an upper mold, an electric heating rod, and a lower mold;
[0010] A horizontally positioned pressure plate is fixedly connected to the base; a vertically positioned guide post is fixedly connected to each end of the pressure plate, and the fixed plate is located above the pressure plate. The fixed plate is slidably connected to the two guide posts through guide sleeves; the slider of the press is fixedly connected to the fixed plate, which can drive the fixed plate to move along the two guide posts; the lower die is fixedly installed on the upper surface of the pressure plate, and the upper die is fixedly installed on the lower surface of the fixed plate.
[0011] Multiple heating rods are installed in the heating holes of the upper and lower molds respectively. After the upper and lower molds are heated to the preset temperature by the heating rods, the press drives the upper and lower molds to press against each other through the fixed plate to heat bend the flat fuel between the upper and lower molds into an arc-shaped fuel plate.
[0012] In one possible implementation, multiple springs are connected between the pressure plate and the base.
[0013] In one possible implementation, the upper and lower dies are detachably fixed in the device, and the curved surfaces of the upper and lower dies used for hot bending can be modified and processed.
[0014] According to another aspect of the present disclosure, a method for thermoforming an arc-shaped fuel plate is provided, the method comprising:
[0015] Based on the springback empirical formula, the radius of curvature is determined, and the upper and lower dies are processed according to the determined radius of curvature for subsequent bending and forming.
[0016] The upper mold is fixedly mounted on the fixed plate, and the lower mold is fixedly mounted on the pressure plate; electric heating rods are fixed in each heating hole of the upper and lower molds respectively;
[0017] Place the flat fuel plate to be processed in the center of the lower mold, ensuring that the center line of the flat fuel plate coincides with the center line of the lower mold;
[0018] This powers on each electric heating rod, heating the upper and lower molds to a preset temperature and maintaining the temperature for a first preset duration.
[0019] Control the upper mold to move downward until the upper mold and the lower mold fit together to bend the fuel plate. The upper mold and the lower mold are kept at a preset temperature for a second preset time.
[0020] Turn off the electric heating rods to allow the upper mold, lower mold, and fuel plate to cool naturally to room temperature.
[0021] In one possible implementation, the preset temperature is between 250-350℃, the first preset duration is between 5-15min, and the second preset duration is between 5 and 15min.
[0022] In one possible implementation, the loading rate of the upper die pressing downwards is between 0.1 and 0.3 MPa / min, and the final pressure is not less than 1.2 MPa.
[0023] In one possible implementation, the electric heating rod is turned off, allowing the upper mold, lower mold, and fuel plate to cool down to below 200°C. Compressed air is then used to blow air onto the upper mold, lower mold, and fuel plate to cool the fuel plate until the temperature drops below 100°C. The upper mold is then raised, and cooling continues to room temperature.
[0024] In one possible implementation, the method further includes:
[0025] The bent fuel plate is removed, the curvature of the curved fuel plate is tested, and an ultrasonic testing device is used to detect internal defects in the core of the curved fuel plate.
[0026] When the difference Δα between the actual angle of the arc-shaped fuel plate and the design angle of the upper and lower dies is greater than the preset threshold, the design angle of the upper and lower dies is reduced by Δα. After refining the mold, the fuel plate thermoforming steps are repeated until the difference Δα between the actual angle of the processed arc-shaped fuel plate and the design angle of the upper and lower dies is less than the preset threshold.
[0027] In one possible implementation, the method further includes: annealing the rolled flat fuel plate at a temperature of 250±5℃ for 1 hour before performing the fuel plate thermoforming operation, followed by furnace cooling.
[0028] The beneficial effects of this disclosure are as follows: The apparatus provided by this disclosure solves the problems that may occur in the cold bending of curved fuel plates in foreign ATR reactors, such as core and cladding separation, internal defects, residual stress, and large springback, and realizes fuel plate bending in one step. It avoids core and cladding separation and core cracking; eliminates residual stress in the cladding during bending; and significantly reduces fuel plate springback, enabling the target size to be achieved through one-step bending. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of a curved fuel plate hot bending device according to an exemplary embodiment. Detailed Implementation
[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0031] Figure 1 This is a schematic diagram of an arc-shaped fuel plate hot bending device according to an exemplary embodiment, such as... Figure 1 As shown, the device includes: guide sleeve 1, guide post 2, pressure plate 4, base 5, fixing plate 6, upper mold 7, electric heating rod 8, and lower mold 9;
[0032] A horizontally positioned pressure plate 4 is fixedly connected to a base 5. The pressure plate 4 and the base 5 work together to fix and limit the lower die. A vertically positioned guide post 2 is fixedly connected to each end of the pressure plate 4. A fixing plate 6 is located above the pressure plate 4. The fixing plate 6 is slidably connected to the two guide posts 2 through guide sleeves 1. The guide sleeves 1 and guide posts 2 cooperate to position the upper and lower dies, ensuring their relative positional accuracy during the pressing process. The slider of the press is fixedly connected to the fixing plate 6, which can drive the fixing plate 6 to move along the two guide posts 2. The lower die 9 is fixedly installed on the upper surface of the pressure plate 4, and the upper die 7 is fixedly installed on the lower surface of the fixing plate 6.
[0033] Multiple heating rods 8 are respectively installed in the upper mold 7 and the lower mold 9. After the upper mold 7 and the lower mold 9 are heated to the preset temperature by the heating rods 8, the press drives the upper mold 7 and the lower mold 9 to press against each other through the fixed plate 6 to heat bend the flat fuel between the upper mold 7 and the lower mold 9 into an arc-shaped fuel plate.
[0034] In one possible implementation, multiple springs 3 are connected between the pressure plate 4 and the base 5 to form a displacement buffer during the downward hot pressing process, so as to prevent the fuel plate from thinning and becoming unusable.
[0035] In one possible implementation, the upper mold 7 and the lower mold 9 are detachably fixed in the device, and the curved surfaces of the upper mold 7 and the lower mold 9 used for hot bending can be modified and processed.
[0036] In conjunction with the aforementioned hot bending device, a matching hot bending forming process is carried out. To address the problems of residual stress and large springback that easily occur during the bending of composite core fuel plates, this disclosure provides a method for hot forming arc-shaped fuel plates. This method, through hot bending heat treatment regime, springback design correction, die curvature design, and selection and optimization of hot bending process parameters, can achieve the hot bending forming of arc-shaped fuel plates. The method includes:
[0037] Step 1: Anneal the rolled fuel plate (the size can be, for example, 530mm×107mm×1.5mm) at a temperature of (250±5)℃, hold for 1 hour, and then cool in the furnace to fully eliminate the stress generated during the rolling process of the fuel plate.
[0038] Step 2: Determine the radius of curvature according to the springback empirical formula (for example, the springback empirical formula can be Δα=K(σ_sα) / Eh R), and process the upper and lower dies according to the determined radius of curvature for subsequent bending and forming.
[0039] Step 3: Fix the upper mold on the fixed plate and the lower mold on the pressure plate. Run the machine without load to ensure that the curved surfaces of the upper and lower molds can match and overlap.
[0040] Step 4: Insert electric heating rods into the heating holes of the upper and lower molds respectively, and fix each electric heating rod with fastening bolts to prevent displacement during use.
[0041] Step 5: Place the flat fuel plate to be processed in the center of the lower mold, ensuring that the center line of the flat fuel plate coincides with the center line of the lower mold.
[0042] Step 6: Power on each electric heating rod to heat the upper and lower molds to the preset temperature (250-350℃) and keep them at that temperature for the first preset time (5-15 min).
[0043] Step 7: Control the upper die to move downward until the upper die and lower die fit together to bend the fuel plate. The loading rate of the upper die pressing downward is between 0.1 and 0.3 MPa / min, and the final pressure is not less than 1.2 MPa. The upper die and lower die are kept at a preset temperature (250-350℃) for a second preset time (5-15 min).
[0044] Step 8: Turn off the electric heating rod to allow the upper mold, lower mold and fuel plate to cool naturally. Keep the pressure applied to the upper mold and lower mold constant until they cool to below 200°C. Use compressed air to blow air onto the upper mold, lower mold and fuel plate to cool the fuel plate until the temperature drops below 100°C. Raise the upper mold and continue to cool to room temperature.
[0045] Step 9: Remove the bent fuel plate, use a coordinate measuring machine to accurately detect the curvature of the curved fuel plate, and use an ultrasonic testing device to detect internal defects in the core of the curved fuel plate.
[0046] Step 10: When the difference Δα between the actual angle of the arc-shaped fuel plate and the design angles of the upper and lower dies is greater than a preset threshold, subtract Δα from the design angles of the upper and lower dies, refine the dies again, and repeat steps 3 to 9 until the difference Δα between the actual angle of the arc-shaped fuel plate and the design angles of the upper and lower dies is less than the preset threshold. This typically requires 2 to 3 iterations.
[0047] In one application example, taking the hot bending forming of an arc-shaped fuel plate with a 6061Al-O cladding and a U3Si2-Al dispersed fuel core as an example, the fuel plate dimensions are 530mm × 107mm × 1.5mm, the cladding is 6061Al-O, and the core is a U3Si2-Al dispersed core. Mold design: Based on the empirical formula Δα = K(σ_sα) / EhR for springback, the fitted empirical springback coefficient K = 0.8 is selected. The yield strength of the fuel plate at 300℃ is σ_s = 25MPa, the elastic modulus E = 60GPa, the target bending angle is 30°, the mold design curvature radius R = 1200mm, the calculated springback angle Δα = 0.6°, and the final mold processing angle is 30° - 0.6° = 29.4°.
[0048] Fuel plate annealing pretreatment. The rolled fuel plate is placed in an annealing furnace and heated to (250±5)°C. After holding at this temperature for one hour, it is cooled with the furnace to eliminate the rolling internal stress.
[0049] Mold installation and heating. Assemble the hot bending mold onto the upper and lower slides of the servo press and tighten it with bolts; insert the electric heating rod into the heating hole of the mold and fix it, turn on the heating system, heat the upper and lower molds to 300℃, and hold it at that temperature for 10 minutes.
[0050] Fuel plate positioning and bending. The annealed fuel plate is placed in the center of the lower mold (the center line of the fuel plate coincides with the center line of the mold). The upper and lower molds are loaded at a rate of 0.2 MPa / min, and finally the pressure is applied to 1.2 MPa. The mixture is then held at 300℃ for 30 min.
[0051] Pressure holding, cooling, and demolding. Turn off the electric heating rods, keep the mold pressure or displacement constant, and allow it to cool naturally to below 200°C. Start the compressed air system to blow air onto the mold and fuel plate, quickly cooling it to below 100°C. Raise the upper mold and transfer the fuel plate to the cooling chamber to cool to room temperature.
[0052] Inspection and springback correction. The fuel plate's curvature or radius of curvature was measured using a coordinate measuring machine; the measured angle was 29.5°, deviating from the target angle by 0.5°. The curved fuel plate was inspected using an ultrasonic testing device; no core cracking, no shell defects, and no loose core adhesion were observed. The angle of the hot bending die was corrected to 30° - 0.5° = 29.5°. Steps 2-4 were repeated. After two iterations, the fuel plate curvature deviation was ≤ ±0.1mm, meeting the accuracy requirements.
[0053] After being hot-bent, the fuel plate has a tight fit between the core and the cladding, no cracks in the core, and a residual stress relief rate of >90% for the cladding, achieving one-time bending and forming.
[0054] The various embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.
Claims
1. A hot bending device for an arc-shaped fuel plate, characterized in that, The device includes: a guide sleeve, a guide post, a pressure plate, a base, a fixing plate, an upper mold, an electric heating rod, and a lower mold; A horizontally positioned pressure plate is fixedly connected to the base; a vertically positioned guide post is fixedly connected to each end of the pressure plate, and the fixed plate is located above the pressure plate. The fixed plate is slidably connected to the two guide posts through guide sleeves; the slider of the press is fixedly connected to the fixed plate, which can drive the fixed plate to move along the two guide posts; the lower die is fixedly installed on the upper surface of the pressure plate, and the upper die is fixedly installed on the lower surface of the fixed plate. Multiple heating rods are installed in the heating holes of the upper and lower molds respectively. After the upper and lower molds are heated to the preset temperature by the heating rods, the press drives the upper and lower molds to press against each other through the fixed plate to heat bend the flat fuel between the upper and lower molds into an arc-shaped fuel plate.
2. The apparatus according to claim 1, characterized in that, Multiple springs connect the pressure plate to the base.
3. The apparatus according to claim 1, characterized in that, The upper and lower dies are detachably fixed in the device, and the curved surfaces used for hot bending can be modified and processed.
4. A method for thermoforming an arc-shaped fuel plate, characterized in that, The method includes: Based on the springback empirical formula, the radius of curvature is determined, and the upper and lower dies are processed according to the determined radius of curvature for subsequent bending and forming. The upper mold is fixedly mounted on the fixed plate, and the lower mold is fixedly mounted on the pressure plate; electric heating rods are fixed in each heating hole of the upper and lower molds respectively; Place the flat fuel plate to be processed in the center of the lower mold, ensuring that the center line of the flat fuel plate coincides with the center line of the lower mold; This powers on each electric heating rod, heating the upper and lower molds to a preset temperature and maintaining the temperature for a first preset duration. Control the upper mold to move downward until the upper mold and the lower mold fit together to bend the fuel plate. The upper mold and the lower mold are kept at a preset temperature for a second preset time. Turn off the electric heating rods to allow the upper mold, lower mold, and fuel plate to cool naturally to room temperature.
5. The method according to claim 4, characterized in that, The preset temperature is between 250-350℃, the first preset time is between 5-15min, and the second preset time is between 5 and 15min.
6. The method according to claim 4, characterized in that, The loading rate of the upper die pressing downwards is between 0.1 and 0.3 MPa / min, and the final pressure is not less than 1.2 MPa.
7. The method according to claim 4, characterized in that, Turn off the electric heating rods to allow the upper mold, lower mold, and fuel plate to cool down to below 200°C. Use compressed air to blow air onto the upper mold, lower mold, and fuel plate to cool the fuel plate until the temperature drops below 100°C. Then raise the upper mold and continue cooling it to room temperature.
8. The method according to claim 4, characterized in that, The method further includes: The bent fuel plate is removed, the curvature of the curved fuel plate is tested, and an ultrasonic testing device is used to detect internal defects in the core of the curved fuel plate. When the difference Δα between the actual angle of the arc-shaped fuel plate and the design angle of the upper and lower dies is greater than the preset threshold, the design angle of the upper and lower dies is reduced by Δα. After refining the mold, the fuel plate thermoforming steps are repeated until the difference Δα between the actual angle of the processed arc-shaped fuel plate and the design angle of the upper and lower dies is less than the preset threshold.
9. The method according to claim 4, characterized in that, The method further includes: before performing the fuel plate thermoforming operation, annealing the rolled flat fuel plate at a temperature of 250±5℃, holding it at that temperature for 1 hour, and then cooling it in the furnace.