Multi-group roller step-by-step rolling method for thin-wall special-shaped multi-blade cladding tube

Abstract

The invention discloses a multi-group roller step-by-step rolling method for a thin-wall special-shaped multi-blade cladding tube, and relates to a multi-group roller step-by-step rolling method. The problems that in a common single-pass drawing forming process, the cross section error of a finished pipe is large, defects are prone to being generated, and efficiency is low are solved. The method comprises the following steps: step 1, preparing a blank pipe; 2, the blank pipe is filled with low-melting-point alloy powder, and then the two ends of the blank pipe are plugged; 3, closing up the two ends of the blank pipe; 4, the blank pipe is subjected to multi-section roller special-shaped skew rolling; 5, the blank pipe obtained after multi-section roller special-shaped skew rolling is put into a vertical atmosphere furnace to be annealed, and a molten low-melting-point alloy core is taken out of the pipe; and 6, the pipe annealed in the step 5 is subjected to ultrasonic cleaning and drying, and the finished special-shaped pipe is obtained. The invention belongs to the technical field of design, processing and manufacturing of nuclear reactor fuel element jackets.

Description

Technical Field

[0001] The invention relates to a step-by-step rolling method for multiple groups of rollers, and belongs to the technical field of design, processing and manufacturing of nuclear reactor fuel element cladding. Background Art

[0002] Cladding tubes are an essential component of fuel assemblies, their primary function being to protect the core of the fuel rod from coolant corrosion and to prevent the leakage of fissile material within the cladding tubes. Current fuel assemblies are primarily composed of pressurized water reactors, heavy water reactors, lead water reactors, and fast water reactors. To further improve the safety and efficiency of nuclear reactors, the latest generation of nuclear fuel assemblies is required to possess characteristics such as a large heat exchange area, good thermal conductivity, compactness, and high safety. Metallic nuclear fuel elements are more likely to meet these requirements. Traditional nuclear fuel elements, however, are mostly circular in shape, resulting in poor rigidity, a small heat exchange area, and poor thermal conductivity. In recent years, a new type of ultra-thin-walled nuclear fuel cladding tube, often with a three- or four-lobed structure, has garnered increasing attention within the nuclear power industry. This type of nuclear fuel cladding tube boasts high heat exchange efficiency and improved structural performance, prompting research both domestically and internationally. Based on this, the present invention has developed a method for forming this ultra-thin-walled, special-shaped, multi-lobed spiral cladding tube. Summary of the Invention

[0003] The present invention aims to solve the problems of large cross-sectional error, easy defects and low efficiency of finished pipes in ordinary single-pass drawing and forming processes, and further proposes a multi-group roller step-by-step rolling method for thin-walled special-shaped multi-lobed cladding pipes.

[0004] The technical solution adopted by the present invention to solve the above problems is: the specific steps of the present invention include:

[0005] Step 1: Prepare the blank tube;

[0006] Step 2: Fill the billet tube with low melting point alloy powder, and then seal both ends of the billet tube;

[0007] Step 3: Close the ends of the blank tube;

[0008] Step 4: Perform multi-section roller profile cross-rolling on the billet tube;

[0009] Step 5: Place the billet tube after multi-stage roller profile rolling into a vertical atmosphere furnace for annealing, and remove the melted low-melting-point alloy core from the tube;

[0010] Step 6: ultrasonically clean and dry the tube annealed in step 5 to obtain a finished special-shaped tube.

[0011] Furthermore, before rolling the billet tube, the adjusted rollers are symmetrically distributed along the center axis A of the rollers, and the gap between the rollers of each group is 0.1 mm to 0.4 mm;

[0012] The diameter of the blank is calculated from the circumference of the finished tube:

[0013] L 成品 =L 坯料 =2πr 坯料 (1),

[0014] In formula (1), L 成品 Indicates the circumference of the finished pipe, r 坯料 Indicates the radius of the blank tube;

[0015] After the pipe radius is determined, calculate the density of the filling powder:

[0016] η 松装 ×S 拉拔 =η 轧实 ×S 轧实 ×γ(2),

[0017] In formula (2), η 轧实 Indicates the density of the core rod rolled, S 轧实 Indicates the cross-sectional area of ​​the core rod, γ indicates the rolling elongation coefficient, which is related to the characteristics of the powder. The low melting point alloy used in this patent has an elongation coefficient γ between 1.02-1.20, and η 松装 Indicates the density of delivery.

[0018] Furthermore, in step 2, the low-melting-point alloy powder is first placed in a vacuum drying oven for drying, and then the dried low-melting-point alloy powder is filled into the circular billet cladding tube and both ends are sealed with hot melt adhesive.

[0019] Furthermore, in step 3, the blocked pipe is subjected to shrinkage treatment at both ends, with the shrinkage angle being 20-35°.

[0020] Furthermore, in step 4, the powder-filled tube after closing is subjected to multiple groups of roller cross-rolling, and the size of the roller groove of each group decreases step by step. The size of the roller groove of the first group is the same as the outer cross-sectional size of the round cladding tube of the blank, and the groove of the last two groups of rollers is the same as the cross-sectional shape and size of the finished simulated fuel element.

[0021] Furthermore, the upper and lower rollers of each group are cross-distributed at an angle α along the axis of the core filling rod, the spacing between the front and rear rollers is D, and the layout of multiple groups of rollers maintains the same spacing D; the groove size is gradually formed from the outer contour size of the powder-filled cladding tube after closing to the target required finished product size, and spiral rolling is performed on a multi-group roller oblique rolling device.

[0022] Furthermore, the cross angle α between the two rollers in each group and the distance D between the front and rear rollers are calculated based on the spiral pitch M of the finished spiral core filling rod:

[0023] v 轧辊×sin(α / 2)t=πd(3),

[0024] In formula (3), v 轧辊 represents the speed of the rollers, α represents the roller crossing angle, t represents the time it takes for the pipe to complete each spiral pitch, and d represents the outermost diameter of the core-filled pipe;

[0025] v 轧辊 ×cos(α / 2)t=M(4),

[0026] In formula (4), M represents the spiral pitch of the finished core-filled tube;

[0027] Combining formula (3) and formula (4), we can get:

[0028] α=2aratan(πd / M)(5),

[0029] Among them, the spiral pitch M and the outermost diameter d of the core filling tube have been determined, and the roller crossing angle α is calculated.

[0030] D=M / n(6),

[0031] In formula (6), D represents the distance between the front and rear rollers, and n represents the number of blades of the multi-leaf spiral core filling tube.

[0032] Furthermore, each set of rollers has a crossing angle of α and moves along its own axis at a speed of v. 轧辊 The rollers rotate at a constant speed, and each set of rollers has the same rolling speed.

[0033] Furthermore, the speed of each set of rollers is the same, and the rotation speed of the rollers is 200-400 mm / s.

[0034] The present invention has the following beneficial effects: it is suitable for rolling uniform-wall spiral shaped clad tubes, and it also closes both ends of the clad tubes, facilitating subsequent welding of workpiece end plugs and achieving improved compactness. The shaped tubes are rolled using multiple sets of rollers with gradual small deformations, and low-melting-point metal powder is used to support the tube core. After rolling, the tubes are placed in a vertical atmosphere furnace for high-temperature annealing, which not only eliminates deformation internal stress in the tubes but also melts the low-temperature metal at high temperatures. Stain on the tube inner wall adheres to the melted low-melting-point alloy powder and flows out of the tube under gravity, resulting in a clean inner wall of the shaped tube. The present invention achieves better forming results, higher production efficiency, yield rate, and tube dimensional accuracy, and is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic cross-sectional view of a special-shaped multi-lobed cladding tube;

[0036] Figure 2This is a schematic diagram of filling a round billet tube with low-temperature alloy powder in a specific embodiment of the present invention;

[0037] Figure 3 Schematic diagram of a closing mold in a specific embodiment of the present invention;

[0038] Figure 4 Schematic diagram of the arrangement of 16 groups of rollers in a specific embodiment of the present invention;

[0039] Figure 4 Middle: 4-round hole vertical roller, 5-transition oblique roller, 6-transition oblique roller, 7-transition oblique roller, 8-transition oblique roller, 9-transition oblique roller, 10-transition oblique roller, 11-transition oblique roller, 12-transition oblique roller, 13-transition oblique roller, 14-transition oblique roller, 15-transition oblique roller, 16-special-shaped multi-lobed cladding tube finished product oblique roller, 17-special-shaped multi-lobed cladding tube finishing oblique roller, 18-special-shaped multi-lobed cladding tube finishing oblique roller, 19-special-shaped multi-lobed cladding tube finishing oblique roller;

[0040] Figure 5 Schematic diagram of the main force of the roller die groove on the pipe;

[0041] Figure 6 Schematic diagram of the final forming and main forces acting on the pipe;

[0042] Figure 7 Schematic diagram of atmosphere furnace annealing process;

[0043] Figure 8 Schematic diagram of the process route in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0044] Example

[0045] like Figure 1 As shown, this embodiment provides a uniform wall ultra-thin special-shaped multi-lobed cladding tube, the cladding tube thickness is 0.20mm, the length is 1200mm, and the inner area of ​​the cladding after rolling is 21.52mm 2 , the circumference is 25.25mm, the pitch is 800mm, the core support material is tin metal powder, and the powder particle size is 150-500μm; the specific steps include:

[0046] Step 1: The target cross-section can be a standard, multi-lobed, or arc-shaped or cosine-shaped blade. In this step, the round tube diameter and tap density of the low-melting-point alloy powder are theoretically designed based on the target product shape and the designed inner cross-sectional area and outer tube circumference after rolling.

[0047] The circumference of the finished pipe is L 成品 , then according to the unchanged circumference of the rolled tube, the radius of the billet is calculated:

[0048] L 成品 =L 坯料 =2πr 坯料 ,

[0049] Among them, r 坯料 is the radius of the round tube blank;

[0050] After the tube radius is determined, the density of the low alloy powder is calculated according to the following formula:

[0051] η 送装 ×S 拉拔 =η 轧实 ×S 轧实 ×γ

[0052] After a lot of experiments, it is shown that γ is 1.02-1.2, and here it is 1.1. According to the above formula, the diameter of the pipe blank is 7.6mm, and the loose density of the low melting point alloy powder is 0.5.

[0053] Step 2: Use tin powder as the core support material, dry the tin powder in a vacuum drying oven and then fill it into the round billet tube. Figure 2 As shown, both ends are sealed with hot melt adhesive. The theoretical density of tin powder is 7.8 / cm 3 In this step, the tin metal powder is dried at a temperature of 40-60°C for 1 hour, and the vacuum degree of the drying oven is not less than 10 -3 Mpa;

[0054] Step 3: Close the end of the tube after filling with powder. The closing mold is as follows: Figure 3 As shown;

[0055] In this step, to ensure the accuracy of the rolled pipe, 16 sets of oblique rollers are used to roll the closed-end core-filled pipe.

[0056] Specifically, the cross α of each set of upper and lower rollers along the axis of the core filling rod is calculated based on the spiral pitch of the multi-leaf spiral core filling tube, and the distribution spacing D of the front and rear rollers is calculated. The spiral pitch of the core filling tube is 800mm, and the maximum circular diameter of the finished spiral core filling tube is 8mm.

[0057] ν 轧辊 ×sin(α / 2)t=πd,

[0058] ν 轧辊 ×cos(α / 2)t=M,

[0059] Where, ν 轧辊 is the speed of the roller, α is the roller crossing angle, t is the time it takes for the pipe to complete each spiral pitch, d is the outermost diameter of the core-filled tube, and M is the spiral pitch of the finished core-filled tube;

[0060] The combined formulas yield:

[0061] α=2arctan(πd / M),

[0062] The calculated roller crossing angle α is 3.6°;

[0063] D=M / n,

[0064] Where n is the number of blades, and the calculated distance D between the front and rear rollers is 200 mm;

[0065] Step 4: Multi-roll rolling is performed on the preformed multi-leaf core tube filled with simulated fuel powder, such as Figure 3 As shown; according to the cross-sectional shape and size of the final simulated fuel rod, an 18-roll rolling device is formulated, and the inclination angle α of each set of rollers along the axis is 3.6°, as shown Figure 3 As shown;

[0066] The distance D between each set of rollers is 200 mm. Figure 5 As shown in FIG, each roller group adopts a relatively distributed method of two rollers, each roller rotates around its own axis, and the fuel rod to be rolled moves along the axis driven by the friction force of the rollers, as shown in FIG. Figure 4 As shown;

[0067] Step 5: In order to ensure the forming accuracy and surface quality of the ultra-thin wall special-shaped multi-leaf cladding tube, 16 sets of precision rollers are used for rolling. Figure 4 As shown; the 16 groups of rollers are divided into 4 types of rollers, which are divided into round rollers 4, transition rollers 5-15, forming rollers 16 and finishing rollers 17-19;

[0068] Step 6: Before rolling the round billet, the spacing between each set of rollers should be strictly adjusted. There should be a gap between each set of rollers. Generally, the gap between the rollers is 0.1-0.4mm. The adjusted rollers are symmetrically distributed along the center axis of the rollers, such as Figure 3 As shown;

[0069] Step 7: In this embodiment, the blank and the rollers need to be lubricated with lubricant before rolling;

[0070] Step 8: Figure 4 As shown, the first round roller 4 bites into the round tube blank and feeds it into the transition roller 5. The tube is rolled step by step through the transition roller 5 to the transition roller 15. The main force mode of each group of rollers during the rolling process is as follows Figure 5As shown, the positions of the convex transition grooves 22a1, 22a2, 22a3, and 22a4 of the rollers gradually exert force on the pipe 2 to form the key groove parts b1, b2, b3, and b4 of the pipe. The concave transition grooves 22b1 and 22b2 of the rollers gradually deform the pipe 19 to form the key rounded corner parts a1, a2, a3, and a4 of the pipe, and are rolled into the final size by the forming roller 16. The mold groove size of the finishing rollers 14-16 is exactly the same as that of the forming roller, as shown in FIG. Figure 6 As shown in the figure, the final size and straightness of the finished pipe are controlled by the correction roller. The density of the core powder gradually increases during the pipe diameter reduction process. The density of the finished core is not less than 95%. The low-melting-point alloy powder core has a good supporting effect, constraining the key parts of the pipe cross section and avoiding defects such as local wrinkles and dimensional deviations in the pipe.

[0071] Specifically, the speed of each group of rollers 1 to 16 is the same. The speed of the rollers should be moderate to ensure both production efficiency and product quality of the cladding tube. The rolling speed of the rollers is controlled at 200-400 mm / s.

[0072] Step 9: Place the rolled cored pipe in a vertical atmosphere furnace 24. Figure 7 As shown, helium 27 is filled in the furnace to avoid oxidation of the tube and core powder during the heat treatment process. The heating temperature is 250°C and the time is 60 minutes. The heat treatment process relieves the stress concentration of the tube during the rolling process, and the low-melting-point alloy powder inside the tube melts at high temperature. During the melting process, the core absorbs tiny dust, impurities and other stains on the inner wall of the tube. As the molten metal liquid 25 flows out of the cladding tube under the action of gravity and is stored in the metal liquid recovery box 26, the inner wall is cleaned, and the finished cladding tube is obtained. The overall tube processing process route is as follows. Figure 8 shown.

[0073] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement of the above embodiments made according to the technical essence of the present invention, within the spirit and principles of the present invention, without departing from the content of the technical solution of the present invention, shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for rolling thin-walled, special-shaped, multi-lobed cladding tubes with multiple rollers in a step-by-step manner, characterized in that: The specific steps include: Step 1: Prepare the blank tube; Step 2: Fill the billet tube with low melting point alloy powder, and then seal both ends of the billet tube; Step 3: Close the ends of the blank tube; Step 4: Perform multi-section roller profile cross-rolling on the billet tube; Step 5: Place the billet tube after multi-stage roller profile rolling into a vertical atmosphere furnace for annealing, and remove the melted low-melting-point alloy core from the tube; Step 6: ultrasonically clean and dry the tube annealed in step 5 to obtain a finished special-shaped tube.

2. The method for rolling thin-walled special-shaped multi-lobed cladding tubes with multiple rollers in a step-by-step manner according to claim 1, characterized in that: Before rolling the billet tube, the adjusted rollers are symmetrically distributed along the center axis A of the rollers, and the gap between each set of rollers is 0.1mm to 0.4mm; The diameter of the blank is calculated from the circumference of the finished tube: L 成品 =L 坯料 =2πr 坯料 (1), In formula (1), L 成品 Indicates the circumference of the finished pipe, r 坯料 Indicates the radius of the blank tube; After the pipe radius is determined, calculate the density of the filling powder: or 松装 ×S 拉拔 =the 轧实 ×S 轧实 ×γ(2), In formula (2), η 轧实 Indicates the density of the core rod rolled, S 轧实 Indicates the cross-sectional area of ​​the core rod, γ indicates the rolling elongation coefficient, which is related to the characteristics of the powder. The low melting point alloy used in this patent has an elongation coefficient γ between 1.02-1.20, and η 松装 Indicates loose packing density.

3. The method for rolling thin-walled special-shaped multi-lobed cladding tubes with multiple rollers in a step-by-step manner according to claim 1, characterized in that: In step 2, the low-melting-point alloy powder is first placed in a vacuum drying oven for drying, and then the dried low-melting-point alloy powder is filled into the circular billet cladding tube and sealed at both ends with hot melt adhesive. The core powder is low-temperature alloy powder.

4. The method for rolling thin-walled special-shaped multi-lobed cladding tubes with multiple rollers in a step-by-step manner according to claim 1, characterized in that: In step 3, both ends of the pipe need to be narrowed, and the narrowing angle is selected to be 20-35°.

5. The method for rolling thin-walled special-shaped multi-lobed cladding tubes with multiple rollers in a step-by-step manner according to claim 1, characterized in that: In step 4, the powder-filled tube after closing is subjected to multiple groups of rollers for cross-rolling. The size of the roller groove of each group decreases step by step. The size of the roller groove of the first group is the same as the outer cross-sectional size of the round cladding tube of the blank, and the groove of the last two groups of rollers is the same as the cross-sectional shape and size of the finished simulated fuel element.

6. The method for rolling thin-walled, special-shaped, multi-lobed cladding tubes with multiple rollers in a step-by-step manner according to claim 4, characterized in that: The upper and lower rollers of each set are cross-distributed at an angle α along the axis of the core filling rod. The spacing between the front and rear rollers is D, and the layout of multiple sets of rollers maintains the same spacing D. The groove size is gradually formed from the outer contour size of the powder-filled cladding tube after closing to the target finished product size, and spiral rolling is performed on a multi-set roller oblique rolling device.

7. The method for rolling thin-walled special-shaped multi-lobed cladding tubes with multiple rollers in a step-by-step manner according to claim 5, characterized in that: The cross angle α between the two rollers in each group and the distance D between the front and rear rollers are calculated based on the spiral pitch M of the finished spiral core rod: v 轧辊 ×sin(α / 2)t=πd(3), In formula (3), v 轧辊 represents the speed of the rollers, α represents the roller crossing angle, t represents the time it takes for the pipe to complete each spiral pitch, and d represents the outermost diameter of the core-filled pipe; v 轧辊 ×cos(α / 2)t=M(4), In formula (4), M represents the spiral pitch of the finished core-filled tube; Combining formula (3) and formula (4), we can get: α=2aratan(πd / M)(5), Among them, the spiral pitch M and the outermost diameter d of the core filling tube have been determined, and the roller crossing angle α is calculated. D=M / n(6), In formula (6), D represents the distance between the front and rear rollers, and n represents the number of blades of the multi-leaf spiral core filling tube.

8. The method for rolling thin-walled special-shaped multi-lobed cladding tubes with multiple rollers in a step-by-step manner according to claim 6, characterized in that: Each set of rollers has a crossing angle of α and moves along its own axis at a speed of v 轧辊 The rollers rotate at a constant speed, and each set of rollers has the same rolling speed.

9. The method for rolling thin-walled special-shaped multi-lobed cladding tubes with multiple rollers in a step-by-step manner according to claim 7, characterized in that: The speed of each set of rollers is the same, and the speed of the rollers is 200-400mm / s.

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