Annealing process of zirconium alloy thin-walled short tube and charging bin for heat treatment thereof

Abstract

This invention belongs to the field of metal material processing technology, and relates to an annealing process for zirconium alloy thin-walled short tubes and its heat treatment loading bin. Based on the specifications of the uniform temperature zone of the vacuum annealing furnace chamber, the specifications of the material rack, the heating method, the loading capacity, the outer diameter and length of the tube, the gas absorption characteristics of the material, and the stability of the tooling structure, this invention specifically designs a loading bin for the heat treatment of thin-walled short tubes for vacuum annealing furnaces. Combined with an improved furnace loading method, adjusted annealing heating curves and annealing process parameters, the heat treatment loading bin is placed on the material rack or loading platform of the vacuum annealing furnace. The tooling is assembled and fixed, the thin-walled short tubes are neatly placed in the heat treatment loading bin, anti-oxidation measures are taken, and process parameters such as the heating curve, heating temperature, and holding time are set according to the furnace loading capacity and tube performance requirements. This ensures that the thin-walled short tubes do not undergo dimensional deformation or surface scratches after heat treatment, improves straightness, prevents surface oxidation, and improves heat treatment efficiency.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, and relates to the heat treatment of metal alloy thin-walled tubes and other thick-walled tubes, especially to an annealing process for zirconium alloy thin-walled short tubes and a charging bin for heat treatment. Background Technology

[0002] Zirconium alloys are widely used in nuclear reactor fuel cladding tubes and structural materials due to their excellent resistance to neutron radiation, superior corrosion resistance, moderate mechanical properties, and good machinability. The cladding tubes, used to load fuel pellets, are the first line of defense in a nuclear reactor; therefore, extremely high requirements are placed on the mechanical properties, corrosion resistance, dimensional accuracy, and straightness of the tubes. Vacuum heat treatment is crucial for controlling these properties in zirconium alloy cladding tubes.

[0003] Different nuclear reactor fuel assemblies use different cladding tube specifications, some of which are thin-walled short tubes, meaning the minimum wall thickness is less than 0.5 mm and the length is less than 600 mm. Due to the thin walls, the tubes are highly susceptible to deformation during finishing processes such as annealing and straightening, leading to scrapping. Therefore, improving heat treatment tooling and methods is crucial for increasing the tube finishing pass rate and efficiency. Commonly used vacuum heat treatment methods for existing tubes are as follows: ① Annealing in a horizontal vacuum annealing furnace, with the tubes laid flat and stacked in a silo or loaded using a sleeve; ② Annealing in a vertical vacuum annealing furnace, with the tubes suspended inside the furnace.

[0004] However, for thin-walled zirconium alloy short tubes, the above-mentioned heat treatment method ① has the following disadvantages: When thin-walled tubes are laid flat in the silo, this loading method easily causes deformation of the lower annealed tubes under pressure, resulting in a smaller annealing load, higher annealing costs, and a low annealing yield. Using a sleeve loading method, the unloading material easily scratches the tube surface, resulting in extremely low loading and unloading efficiency and high manpower consumption. After multiple annealing furnaces, the sleeves need to be straightened or replaced, increasing material costs. Furthermore, the large number of sleeves used and their weight affecting the total furnace load also impact the annealing load of the finished tubes. Because the tubes still have some degree of freedom after sleeve loading, stress release during annealing easily leads to poor straightness. The disadvantages of the above-mentioned heat treatment method ② are: While drilling and counterweight hoisting annealing can improve the straightness of the annealed tubes, it is cumbersome and inefficient; it undoubtedly increases the drilling and secondary cutting processes, lengthening the preparation process, reducing production efficiency, and increasing production costs.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an annealing process for zirconium alloy thin-walled short tubes and a charging bin for heat treatment, which can ensure that the thin-walled short tubes do not undergo dimensional deformation, do not produce surface scratches, improve straightness, prevent surface oxidation, and improve heat treatment efficiency after heat treatment.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] On one hand, the present invention provides a loading bin for heat treatment of zirconium alloy thin-walled short tubes, including a circular loading bin body, wherein the loading bin body is formed by splicing multiple bin units, each bin unit is provided with a connecting part, and adjacent bin units are fixed through the connecting part and fasteners.

[0009] Furthermore, the main body of the loading hopper is formed by splicing together three identical sector-shaped hopper units. The connecting part is a positioning pin welded to the side of the arc-shaped plate of the sector-shaped hopper unit. The positioning pin has a through hole in the center to facilitate the pin passing through. The pin passes through the through hole and cooperates with the nut to fix the adjacent sector-shaped hopper units.

[0010] Furthermore, the fan-shaped hopper unit is formed by welding together two rectangular plates with a thickness of 3.5 to 4.5 mm, an arc-shaped plate with a central angle of 120°, and a fan-shaped plate with a central angle of 120°, all of which are made of zirconium alloy plates.

[0011] Furthermore, it also includes an end cap disposed on the top of the hopper body.

[0012] Furthermore, the end cap is formed by welding together a circular plate with a thickness of 3.5 to 4.5 mm and a circular surrounding plate; or, the end cap is formed by stamping a circular plate.

[0013] Furthermore, a U-shaped lifting handle for easy handling is welded to the circumference of the end cap.

[0014] On the other hand, the present invention also provides an annealing process for a zirconium alloy thin-walled short tube, specifically including the following steps:

[0015] Step 1): Fabricate a charging bin suitable for vacuum annealing of zirconium alloy thin-walled short tubes, wherein the charging bin is the charging bin for heat treatment of zirconium alloy thin-walled short tubes as described above in part or in whole.

[0016] Step 2): Pre-treat the multiple thin-walled short tubes to be loaded into the charging hopper to meet the charging requirements of the vacuum annealing furnace;

[0017] Step 3): Before loading, use 3 to 4 layers of stainless steel mesh or zirconium mesh to lay flat at the bottom of the loading hopper unit. Place the pre-treated thin-walled short pipes from Step 2) vertically and neatly into the loading hopper body until the loading hopper body is full. An expansion gap l is reserved between adjacent thin-walled short pipes, and l ≥ 0.1 mm, to prevent the expansion of the thin-walled short pipes after heating from causing the pipes to be squeezed and deformed.

[0018] Step 4): Lay 3 to 4 layers of stainless steel mesh or zirconium mesh on top of the main body of the hopper, and add end caps to the top of the main body of the hopper and seal it.

[0019] Step 5): Vertically insert the sealed charging hopper body from Step 4) into the vacuum annealing furnace rack or loading platform. After loading, close the furnace door and perform vacuuming.

[0020] Step 6): Determine the process parameters and heating curve for vacuum annealing;

[0021] Step 7): Combine the process parameters and heating curve to control the vacuum annealing furnace for annealing.

[0022] Furthermore, step 1) specifically includes:

[0023] Step 1.1) First, weld 3n sector-shaped hopper units, where n is an integer not less than 1. After wiping them clean with anhydrous ethanol, place them in a vacuum annealing furnace for stress-relief annealing. The annealing temperature is 400℃~450℃, and the holding time is 4h~6h. Cool them with the furnace. When the temperature inside the vacuum annealing furnace is less than 100℃, take them out of the furnace.

[0024] Step 1.2) Place the 3n sector-shaped hopper units on the vacuum annealing furnace rack or loading platform by manual handling or hoisting. Assemble the three sector-shaped hopper units into a circular loading hopper. Align the through holes in the center of the positioning pins of adjacent sector-shaped hopper units, and use pins to pass through the through holes and use nuts to fasten them, thus completing the production of the circular loading hopper.

[0025] Furthermore, the furnace loading process in step 5) is specifically as follows:

[0026] When the vacuum annealing furnace is a horizontal vacuum annealing furnace, a single-layer loading bin method is adopted. After continuously loading bins for 1.2m to 1.5m along the length of the vacuum annealing furnace, the next loading bin is loaded after a 50mm to 100mm interval, so as to ensure that the heat flow channels between the loading bins in each heating zone are uniform and consistent.

[0027] When the vacuum annealing furnace is a vertical vacuum annealing furnace, a multi-layer loading bin method is adopted. The number of bins in a single layer follows the principle that the maximum size does not exceed the length and width of the uniform temperature zone. The bins are sequentially loaded into the second layer, ..., the nth layer of the vacuum annealing furnace rack or loading platform. The loading amount does not exceed 2 / 3 of the allowable loading amount of the vacuum annealing furnace.

[0028] Furthermore, the process parameters for vacuum annealing in step 6) are as follows:

[0029] The annealing temperature for incomplete recrystallization is 450℃~520℃, and the annealing temperature for complete recrystallization is 530℃~650℃; the vacuum degree before entering the furnace is better than 7×10. -3 Pa, furnace temperature ≤400℃, heating rate ≤5℃ / min;

[0030] The annealing process shall be set with no less than two uniform temperature platforms. Specifically, uniform temperature shall be set at the furnace inlet. After the temperature rises above 400℃, a uniform temperature platform shall be set at every 50℃ to 100℃ interval. The uniform temperature shall be set for 30 min to 90 min. The holding time after reaching the temperature for incomplete recrystallization annealing shall be 240 min to 480 min. The holding time after reaching the temperature for recrystallization annealing shall be 90 min to 240 min. The cooling method shall be furnace cooling or argon cooling at <400℃. The furnace outlet temperature shall be <100℃.

[0031] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0032] First, based on the specifications of the uniform temperature zone of the vacuum annealing furnace chamber, the specifications of the material rack, the heating method, the loading capacity, the outer diameter and length of the tubes, the gas absorption characteristics of the material, and the stability of the tooling structure, this invention specifically designs a charging bin for heat treatment of thin-walled short tubes for vacuum annealing furnaces. Combined with an improved furnace loading method, adjusted annealing heating curves and annealing process parameters, the heat treatment charging bin is placed on the material rack or loading platform of the vacuum annealing furnace, the tooling is assembled and fixed, the thin-walled short tubes are placed vertically and neatly in the heat treatment charging bin, anti-oxidation measures are taken, and process parameters such as heating curves, heating temperatures and holding times are set according to the furnace loading capacity and tube performance requirements. This ensures that the thin-walled short tubes do not undergo dimensional deformation or surface scratches after heat treatment, improves straightness, prevents surface oxidation, improves the uniformity of annealed material properties, and increases heat treatment efficiency.

[0033] Furthermore, this charging silo is formed by splicing together three identical sector-shaped silo units, which has the following advantages: 1. It makes charging more convenient. The sector-shaped silo unit is equivalent to dividing the volume of the overall circular silo, making it less likely to tip over when loading pipes, preventing scratches on the pipe surface, and improving charging efficiency. 2. Three 120° sector-shaped silo units are spliced ​​together to form a circular silo. The straight sides of the three sector-shaped silo units form three reinforcing ribs at 120° angles to the assembled circular silo. This structure is more stable than individual circular or rectangular silos, and is less prone to deformation during the annealing process. It can prevent thermal fatigue deformation of the silo during the annealing process, which would lead to the extrusion deformation of the annealed material, thus improving the yield of annealed pipes and extending the service life of the charging silo. 3. The modular unit silo structure is easy to handle and operate, and has strong versatility. It is not easily limited by the furnace structure and furnace heating method. Multiple sets of silos can be laid flat or stacked according to the size of the homogenization zone of the annealing furnace, the size of the material rack or loading platform of the vacuum annealing furnace, and the required furnace loading volume. 4. Using zirconium alloy plates as the material for the hopper, its excellent air absorption properties prevent oxidation and uneven surface coloring of the annealed materials. 5. The design of combining three 120° sector-shaped hopper units into a single circular hopper, compared to an integral hopper, separates the annealing tubes, resulting in better heat radiation transfer performance. This reduces the temperature difference and time required for tubes at different locations within the furnace, improves the consistency of tube performance across different locations in the same furnace, and consequently increases the loading capacity for heat treatment of thin-walled short tubes.

[0034] Finally, the annealing process provided by this invention can improve the straightness of thin-walled short tubes after annealing, reducing the number of tubes scrapped due to dimensional deformation caused by straightening to improve tube straightness; it avoids the problems of small furnace loading, low annealing efficiency, and increased costs caused by the number of tube layers in traditional flat-laying and stacking annealing, and avoids the problems of reduced annealing efficiency and increased annealing costs due to the added drilling process in traditional vertical drilling and hoisting annealing; it shortens the temperature difference of annealed materials and improves the consistency of material performance in the same furnace. Using zirconium alloy plates as the raw material for preparing the charging bin, combined with stainless steel mesh or zirconium mesh, the good gas absorption performance of zirconium and the increased gas absorption area of ​​stainless steel mesh / zirconium mesh can be utilized to absorb gas during annealing and prevent oxidation of the material surface. Attached Figure Description

[0035] The accompanying drawings are incorporated in and form part of this specification, and together with the description serve to explain the principles of the invention.

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A top view of a charging bin for heat treatment of a zirconium alloy thin-walled short tube provided by the present invention;

[0038] Figure 2 A front view of a charging bin for heat treatment of zirconium alloy thin-walled short tubes provided by the present invention;

[0039] Figure 3 A side view of a charging bin for heat treatment of a zirconium alloy thin-walled short tube provided by the present invention;

[0040] Figure 4 This is a top view of the sector-shaped silo unit provided by the present invention;

[0041] Figure 5 This is a rear view of the sector-shaped silo unit provided by the present invention;

[0042] Figure 6 for Figure 5 Sectional view along axis AA;

[0043] Figure 7 A top view of the end cap provided by the present invention;

[0044] Figure 8 for Figure 7 BB-direction sectional view;

[0045] Figure 9 for Figure 7 Side view;

[0046] Figure 10 The flowchart illustrates the annealing process for a zirconium alloy thin-walled short tube provided by this invention.

[0047] The components include: 1. Positioning pin; 2. Fan-shaped hopper unit; 3. U-shaped lifting handle; 4. End cap. Detailed Implementation

[0048] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the invention as detailed in the appended claims.

[0049] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0050] It should be noted that in the following embodiments:

[0051] The heating curve is formed by setting process parameters such as heating rate, temperature uniformity plateau, heat treatment temperature, and holding time; annealing process parameters generally refer to process parameters such as heat treatment temperature, holding time, cooling method, and vacuum requirements.

[0052] The uniform temperature zone refers to the effective working area of ​​a heat treatment furnace, that is, the allowable loading space that meets the process and temperature uniformity requirements of the heat treatment furnace; while the uniform temperature platform refers to a platform that is specifically set to be held at a certain temperature point for a period of time when the heating curve is set in order to ensure the consistency of the material properties in the furnace during the heat treatment process. From the curve, it is a platform, called the uniform temperature platform.

[0053] For a circular hopper, when the number of zirconium alloy thin-walled short tubes requiring heat treatment is insufficient to fill all the fan-shaped hopper units 2, or when batch production requires fixed annealing process parameters, the corresponding weight of material can be selected for counterweighting to ensure the consistency of the annealing material properties in different furnaces of the same process, and to prevent the material in the hopper from tipping over due to insufficient annealing material, resulting in unqualified straightness after annealing.

[0054] Example 1

[0055] See Figure 1-7 As shown, this embodiment provides a loading bin for heat treatment of zirconium alloy thin-walled short tubes, including a circular loading bin body. The loading bin body is formed by splicing multiple bin units. Each bin unit is provided with a connecting part, and adjacent bin units are fixed through the connecting part and fasteners.

[0056] Furthermore, the main body of the loading bin is formed by splicing together three identical sector-shaped bin units 2. The connecting part is a positioning pin 1 welded to the side of the arc-shaped plate of the sector-shaped bin unit 2. The positioning pin 1 has a through hole in the center to facilitate the pin to pass through. The pin passes through the through hole and cooperates with the nut to fix the adjacent sector-shaped bin units 2.

[0057] Furthermore, the sector-shaped hopper unit 2 is formed by welding together two rectangular plates with a thickness of 3.5 to 4.5 mm, an arc-shaped plate with a central angle of 120°, and a sector-shaped plate with a central angle of 120°.

[0058] Preferably, the rectangular plate, arc plate and fan-shaped plate mentioned above are all made of zirconium plate, which has the mechanical strength to meet the load-bearing requirements, and zirconium alloy has good gas absorption, which can prevent oxidation of the surface of annealed materials.

[0059] Furthermore, it also includes an end cap 4 disposed on the top of the main body of the hopper. Specifically, the end cap 4 is formed by welding together a circular plate with a thickness of 3.5 to 4.5 mm and a circular surrounding plate, and the diameter of the circular plate is slightly larger than the diameter of the circular hopper assembled from the fan-shaped hopper units. The circular surrounding plate is formed by bending a rectangular plate 360°, and the length of the rectangular plate is the same as the circumference of the circular plate. Moreover, the circumference of the circular surrounding plate is symmetrically welded with U-shaped lifting handles 3 for easy handling.

[0060] Alternatively, the end cap 4 is formed by stamping a circular sheet metal, and the cylindrical surface of the end cap 4 is symmetrically welded with a U-shaped lifting handle 3 for easy handling.

[0061] Furthermore, a U-shaped lifting handle 3 for easy handling is welded to the arc surface of the fan-shaped hopper unit 2 at two-thirds of the distance from the bottom and half of the circumference; the positioning pin 1 is welded to the arc plate side of the fan-shaped hopper unit 2 at half the height, and is used to fasten the fan-shaped hopper unit 2 after splicing the circle, to prevent the hopper from deforming during the annealing process.

[0062] Example 2

[0063] Based on Example 1, this example also provides an annealing process for a zirconium alloy thin-walled short tube, combined with... Figure 8 As shown, the specific steps include:

[0064] S1. Based on the dimensions of the uniform temperature zone and the dimensions of the annealing tubing in a 7m long horizontal vacuum annealing furnace, design and manufacture a dedicated annealing loading hopper, specifically:

[0065] The dimensions (diameter × length) of the uniform temperature zone in the aforementioned 7m vacuum annealing furnace are 660mm × 7000mm. The furnace features circumferential resistance wire heating of the material hopper and has six heating zones. The dimensions (outer diameter × wall thickness × length) of the annealing tubing are: Ф 外 Based on the dimensions of 13.1×0.4×500(mm), the fan-shaped hopper unit 2 is designed with the following dimensions: the side length of the fan-shaped hopper unit 2 is 500mm and the height is 550mm. After wiping the inner and outer surfaces of the hopper with anhydrous ethanol, the fan-shaped hopper unit 2 is subjected to stress-relief annealing at a temperature of 450℃ and a holding time of 4h. Stress-relief annealing eliminates the internal stress generated during tooling shearing, bending or stamping and the thermal stress at the weld, preventing the internal loaded material from being squeezed and deformed due to stress release deformation during the annealing process, and at the same time extending the service life of the tooling.

[0066] S2. After rolling, the long tubes are degreased using a special matching degreasing agent, then rinsed with hot water and cold water, sprayed with hot water and dried to ensure that the cleanliness of the inner and outer surfaces meets the requirements for annealing furnace loading. The tubes are cut into 500mm lengths using a special tube cutting equipment. The cleanliness of the inner and outer surfaces of the tubes is checked. If necessary, anhydrous ethanol is used to wipe the outer surface or spray the inner surface to ensure that it meets the requirements for annealing furnace loading.

[0067] S3. Hoist the six sector-shaped silo units 2 sequentially to the annealing furnace loading platform, assembling them into circular silos of three at a time and securing them with bolts. Before loading, lay four layers of stainless steel mesh or zirconium mesh flat at the bottom of the silo unit. Then, vertically and neatly stack the annealed tubes into the sector-shaped silo unit 2. Based on the principle of tube expansion gap (material in the silo should not tip over and the gap between tubes should be ≥0.1mm), each sector-shaped silo unit 2 can hold 405 tubes. The tubes must not be staggered, and a certain expansion gap must be maintained between the tubes in the silo to prevent expansion and deformation during heating. The expansion gap between two tubes should be ≥0.1mm; therefore, when calculating the tube loading capacity per unit area, the tube diameter should be calculated as the actual diameter + 0.05mm.

[0068] S4. After the annealing material is loaded, cover the pipe end with 4 layers of stainless steel mesh or zirconium mesh and cover it with end cap 4. The annealing loading amount shall not exceed two-thirds of the total loading amount of the annealing furnace, approximately 600 kg. For the part of the annealing material that is less than the weight, use counterweight material for counterweighting. The size of the stainless steel mesh or zirconium mesh is the same as the size of the fan-shaped hopper inside the fan-shaped hopper unit 2, which is used to draw in air during the annealing process and prevent oxidation of the pipe surface.

[0069] S5. After the furnace is loaded, the material platform is sent into the furnace chamber, the furnace door is closed and a vacuum is drawn.

[0070] S6. Select appropriate vacuum annealing process parameters according to the performance requirements of the pipe. The above vacuum annealing process is as follows: annealing temperature 500℃, holding at the temperature for 6 hours after reaching the temperature, heating rate 5℃ / min, and setting three uniform temperature platforms during the heating process, namely 300℃ / 90min, 400℃ / 60min, and 450℃ / 60min.

[0071] S7. Following the annealing heating curve and process parameters in step six, complete the heat preservation and begin cooling. When the temperature is below 400℃, purge with argon for cooling, and remove from the furnace when the temperature is below 100℃.

[0072] Specifically, the stainless steel mesh or zirconium mesh in S4 is the same size as or slightly smaller than the fan-shaped size inside the fan-shaped silo, used for gas absorption during the annealing process to prevent oxidation of the pipe surface; the stainless steel mesh is made of austenitic stainless steel, with the national standard metal grade 0Cr18Ni9 (foreign metal grade 304), and its maximum operating temperature is 930℃; the zirconium mesh is made of national standard zirconium and zirconium alloy grades Zr-0, Zr-2, and Zr-4.

[0073] Furthermore, the specific process of loading the furnace in S5 is as follows:

[0074] The horizontal vacuum furnace adopts a single-layer loading bin method. The amount of material placed in the length and width directions of the annealing furnace loading platform does not exceed the length and width dimensions of the uniform temperature zone of the annealing furnace. After each continuous loading bin is laid for 1.2m to 1.5m along the length of the vacuum annealing furnace, the next loading bin is laid after a 50mm to 100mm interval. This ensures that the heat flow channels between the loading bins in each heating zone are uniform and consistent, which facilitates the mutual supplementation of irradiation heat between adjacent loading bins. This further improves the uniformity of the annealing temperature of the tubes in the heating zone and ensures the uniformity and stability of the tube performance at different locations in the large-size multi-zone heating annealing furnace.

[0075] Furthermore, in S6, based on the finished pipe's microstructure and performance requirements, the furnace loading, heating method, and the layout of the heating belts within the furnace, the vacuum annealing heating curve and process parameters are designed. These parameters are then input into and executed by the vacuum annealing furnace's operation and control system, including the settings for annealing temperature, holding time, homogenization time, heating rate, heating time, and argon purging cooling temperature. During the annealing process, the stability of all data transmissions within the operation and control system, including temperature, pressure, vacuum level, water temperature, and gas pressure, must be ensured.

[0076] Example 3

[0077] Based on Example 1, this example also provides an annealing process for a zirconium alloy thin-walled short tube, combined with... Figure 8 As shown, the specific steps include:

[0078] S1. Based on the dimensions of the uniform temperature zone and the dimensions of the annealing tubing in a vertical vacuum annealing furnace with a height of 1.2m, design and manufacture a special annealing loading hopper, specifically:

[0079] The dimensions (diameter × height) of the uniform temperature zone in the 1.2m vertical vacuum annealing furnace chamber are 1200mm × 1200mm. The heating method combines transverse radiant heating with top and bottom auxiliary heating. The overall layout of the radiant heating belt is a vertical cylinder. The dimensions (outer diameter × wall thickness × length) of the annealing tubes are: Ф 外13.1×0.4×500(mm), the dimensions of the fan-shaped hopper unit 2 designed accordingly are: the side length of the fan-shaped hopper unit 2 is 500mm and the height is 550mm. After wiping the inner and outer surfaces of the hopper with anhydrous ethanol, the fan-shaped hopper unit is subjected to stress-relief annealing at a temperature of 450℃ and a holding time of 4h.

[0080] S2. After rolling, the long tubes are degreased using a special matching degreasing agent, then rinsed with hot water and cold water, sprayed with hot water and dried to ensure that the cleanliness of the inner and outer surfaces meets the requirements for annealing furnace loading. The tubes are cut into 500mm lengths using a special tube cutting equipment. The cleanliness of the inner and outer surfaces of the tubes is checked. If necessary, anhydrous ethanol is used to wipe the outer surface or spray the inner surface to ensure that it meets the requirements for annealing furnace loading.

[0081] S3. Hoist the 6 sector-shaped silo units 2 to the annealing furnace loading platform in sequence, and assemble them into a circular silo in groups of three and fasten them with bolts. Before loading, lay 3 layers of stainless steel mesh or zirconium mesh flat at the bottom of the silo unit, and vertically and neatly place the annealed tubes into the sector-shaped silo unit 2 in sequence. Then, place the sector-shaped silo unit 2 filled with tubes into the circular material tray of the vertical annealing furnace in sequence (each circular silo is placed on the corresponding circular material tray of the vertical annealing furnace). According to the principle of tube expansion gap (the material in the silo does not tip over and the gap between tubes in the silo is ≥0.1mm), each sector-shaped silo unit 2 can hold 405 tubes.

[0082] S4. After the annealing material is loaded, cover the tube end with 3 layers of stainless steel mesh or zirconium mesh and put on the end cover 4. The annealing loading amount shall not exceed one-third of the total loading amount of the annealing furnace, about 900 kg. For the part of the annealing material that is less than the weight, use counterweight material to balance it.

[0083] S5. After the furnace is loaded, the material platform is sent into the furnace chamber, the furnace door is closed and a vacuum is drawn.

[0084] S6. Select appropriate vacuum annealing process parameters according to the performance requirements of the pipe. The above vacuum annealing process parameters are: annealing temperature 550℃, holding temperature for 6 hours after reaching the temperature, heating rate 5℃ / min, and setting two uniform temperature platforms during the heating process, namely 300℃ / 60min and 400℃ / 60min.

[0085] S7. Following the annealing heating curve and process parameters in step six, complete the heat preservation and begin cooling. When the temperature is below 400℃, purge with argon for cooling, and remove from the furnace when the temperature is below 100℃.

[0086] Furthermore, the specific process of loading the furnace in S5 is as follows: Vertical vacuum annealing furnaces adopt a multi-layer loading bin method. The number of bins in a single layer follows the principle that the maximum size does not exceed the length and width of the uniform temperature zone. The bins are loaded sequentially into the second layer of the rack / carrying platform, ..., the nth layer. The loading amount for all the different vacuum annealing furnaces (horizontal and vertical) does not exceed 2 / 3 of the total loading capacity. When loading a vertical furnace, gaps are also required between the bins to ensure heat flow.

[0087] Example 4

[0088] Based on Example 1, this example also provides an annealing process for a zirconium alloy thin-walled short tube, combined with... Figure 8 As shown, the annealing process specifically includes the following steps:

[0089] S1. Based on the dimensions of the uniform temperature zone and the dimensions of the annealing tubing in a 5m long horizontal vacuum annealing furnace, design and manufacture a dedicated annealing loading hopper, specifically:

[0090] The dimensions (diameter × length) of the uniform temperature zone in the aforementioned 5m vacuum annealing furnace are 660mm × 5000mm. The furnace utilizes a circumferential resistance wire heating system for the material hopper, and has four heating zones. The dimensions (outer diameter × wall thickness × length) of the annealing tubing are: Ф 外 The dimensions of the fan-shaped hopper unit 2 are 12.45×0.5×550(mm). The side length of the fan-shaped hopper unit 2 is 500mm and the height is 600mm. After wiping the inner and outer surfaces of the hopper with anhydrous ethanol, the fan-shaped hopper unit 2 is subjected to stress-relief annealing at a temperature of 450℃ and a holding time of 4h.

[0091] S2. After rolling, the long tubes are degreased using a special matching degreasing agent, then rinsed with hot water and cold water, sprayed with hot water and dried to ensure that the cleanliness of the inner and outer surfaces meets the requirements for annealing furnace loading. The tubes are cut into 550mm lengths using a special tube cutting equipment. The cleanliness of the inner and outer surfaces of the tubes is checked. If necessary, anhydrous ethanol is used to wipe the outer surface or spray the inner surface to ensure that it meets the requirements for annealing furnace loading.

[0092] S3. Hoist the nine sector-shaped silo units 2 sequentially to the annealing furnace loading platform, assembling them into circular silos of three at a time and securing them with bolts. Before loading, lay four layers of stainless steel mesh or zirconium mesh flat at the bottom of each silo unit. Then, vertically and neatly stack the annealed tubes into each sector-shaped silo unit 2. Based on the principle of tube expansion gap (material in the silo should not tip over and the gap between tubes should be ≥0.1mm), each sector-shaped silo unit 2 can hold 450 tubes. The tubes must not be staggered, and a certain expansion gap must be maintained between the tubes in the silo to prevent expansion and deformation during heating. The expansion gap between two tubes should be ≥0.1mm; therefore, when calculating the tube loading capacity per unit area, the tube diameter should be calculated as the actual diameter + 0.05mm.

[0093] S4. After the annealing material is loaded, cover the pipe end with 4 layers of stainless steel mesh or zirconium mesh and cover it with end cap 4. The annealing loading amount shall not exceed two-thirds of the total loading amount of the annealing furnace, approximately 600 kg. For the part of the annealing material that is less than the weight, use counterweight material for counterweighting. The size of the stainless steel mesh or zirconium mesh is the same as the size of the fan-shaped hopper inside the fan-shaped hopper unit 2, which is used to draw in air during the annealing process and prevent oxidation of the pipe surface.

[0094] S5. After the furnace is loaded, the material platform is sent into the furnace chamber, the furnace door is closed and a vacuum is drawn.

[0095] S6. Select appropriate vacuum annealing process parameters according to the performance requirements of the pipe. The above vacuum annealing process is as follows: annealing temperature 580℃, hold at the temperature for 3 hours after reaching the temperature, heating rate 3℃ / min, and set three uniform temperature platforms in the process, namely 300℃ / 90min, 400℃ / 60min, and 500℃ / 60min.

[0096] S7. Following the annealing heating curve and process parameters in step six, complete the heat preservation and begin cooling. When the temperature is below 400℃, purge with argon for cooling, and remove from the furnace when the temperature is below 100℃.

[0097] Specifically, the stainless steel mesh or zirconium mesh in S4 is the same size as or slightly smaller than the fan-shaped size inside the fan-shaped silo, used for gas absorption during the annealing process to prevent oxidation of the pipe surface; the stainless steel mesh is made of austenitic stainless steel, with the national standard metal grade 0Cr18Ni9 (foreign metal grade 304), and its maximum operating temperature is 930℃; the zirconium mesh is made of national standard zirconium and zirconium alloy grades Zr-0, Zr-2, and Zr-4.

[0098] Furthermore, the specific process of loading the furnace in S5 is as follows:

[0099] The horizontal vacuum furnace adopts a single-layer loading bin method. The amount of material placed in the length and width directions of the annealing furnace loading platform does not exceed the length and width dimensions of the uniform temperature zone of the annealing furnace. After each continuous loading bin is laid for 1.2m to 1.5m along the length of the vacuum annealing furnace, the next loading bin is laid after a 50mm to 100mm interval. This ensures that the heat flow channels between the loading bins in each heating zone are uniform and consistent, which facilitates the mutual supplementation of irradiation heat between adjacent loading bins. This further improves the uniformity of the annealing temperature of the tubes in the heating zone and ensures the uniformity and stability of the tube performance at different locations in the large-size multi-zone heating annealing furnace.

[0100] Furthermore, in S6, based on the finished pipe's microstructure and performance requirements, the furnace loading, heating method, and the layout of the heating belts within the furnace, the vacuum annealing heating curve and process parameters are designed. These parameters are then input into and executed by the vacuum annealing furnace's operation and control system, including the settings for annealing temperature, holding time, homogenization time, heating rate, heating time, and argon purging cooling temperature. During the annealing process, the stability of all data transmissions within the operation and control system, including temperature, pressure, vacuum level, water temperature, and gas pressure, must be ensured.

[0101] Example 5

[0102] Based on Example 1, this example also provides an annealing process for a zirconium alloy thin-walled short tube, combined with... Figure 8 As shown, the specific steps include:

[0103] S1. Based on the dimensions of the uniform temperature zone and the dimensions of the annealing tubing in a 7m long horizontal vacuum annealing furnace, design and manufacture a dedicated annealing loading hopper, specifically:

[0104] The dimensions (diameter × length) of the uniform temperature zone in the aforementioned 7m vacuum annealing furnace are 660mm × 7000mm. The furnace features circumferential resistance wire heating of the material hopper and has six heating zones. The dimensions (outer diameter × wall thickness × length) of the annealing tubing are: Ф 外 The dimensions of the fan-shaped hopper unit 2 are 12.7×0.3×450(mm). The side length of the fan-shaped hopper unit 2 is 500mm and the height is 500mm. After wiping the inner and outer surfaces of the hopper with anhydrous ethanol, the fan-shaped hopper unit 2 is subjected to stress-relief annealing at a temperature of 400℃ and a holding time of 6h.

[0105] S2. After rolling, the long tubes are degreased using a special matching degreasing agent, then rinsed with hot water and cold water, sprayed with hot water and dried to ensure that the cleanliness of the inner and outer surfaces meets the requirements for annealing furnace loading. The tubes are cut to 450mm lengths using a special tube cutting equipment. The cleanliness of the inner and outer surfaces of the tubes is checked. If necessary, anhydrous ethanol is used to wipe the outer surface or spray the inner surface to ensure that it meets the requirements for annealing furnace loading.

[0106] S3. Hoist the nine sector-shaped silo units 2 sequentially to the annealing furnace loading platform, assembling them into circular silos of three per group and securing them with bolts. Before loading, lay three layers of stainless steel mesh or zirconium mesh flat at the bottom of the silo unit. Then, vertically and neatly stack the annealed tubes into the sector-shaped silo unit 2. Based on the principle of tube expansion gap (material in the silo should not tip over and the gap between tubes should be ≥0.1mm), each sector-shaped silo unit 2 can hold 435 tubes. The tubes must not be staggered, and a certain expansion gap must be maintained between the tubes in the silo to prevent expansion and deformation during heating. The expansion gap between two tubes should be ≥0.1mm; therefore, when calculating the tube loading capacity per unit area, the tube diameter should be calculated as the actual diameter + 0.05mm.

[0107] S4. After the annealing material is loaded, cover the pipe end with 3 layers of stainless steel mesh or zirconium mesh and cover it with end cap 4. The annealing loading amount shall not exceed one-third of the total loading amount of the annealing furnace, approximately 900 kg. For the part of the annealing material that is less than the weight, use counterweight material for counterweighting. The size of the stainless steel mesh or zirconium mesh is the same as the size of the fan-shaped hopper inside the fan-shaped hopper unit 2, which is used to draw in air during the annealing process and prevent oxidation of the pipe surface.

[0108] S5. After the furnace is loaded, the material platform is sent into the furnace chamber, the furnace door is closed and a vacuum is drawn.

[0109] S6. Select appropriate vacuum annealing process parameters according to the performance requirements of the pipe. The above vacuum annealing process is as follows: annealing temperature 600℃, holding temperature for 3 hours after reaching the temperature, heating rate 5℃ / min, and setting three uniform temperature platforms in the process, namely 350℃ / 90min, 450℃ / 60min, and 550℃ / 60min.

[0110] S7. Following the annealing heating curve and process parameters in step six, complete the heat preservation and begin cooling. When the temperature is below 400℃, purge with argon for cooling, and remove from the furnace when the temperature is below 100℃.

[0111] Specifically, the stainless steel mesh or zirconium mesh in S4 is the same size as or slightly smaller than the fan-shaped size inside the fan-shaped silo, used for gas absorption during the annealing process to prevent oxidation of the pipe surface; the stainless steel mesh is made of austenitic stainless steel, with the national standard metal grade 0Cr18Ni9 (foreign metal grade 304), and its maximum operating temperature is 930℃; the zirconium mesh is made of national standard zirconium and zirconium alloy grades Zr-0, Zr-2, and Zr-4.

[0112] Furthermore, the specific process of loading the furnace in S5 is as follows:

[0113] The horizontal vacuum furnace adopts a single-layer loading bin method. The amount of material placed in the length and width directions of the annealing furnace loading platform does not exceed the length and width dimensions of the uniform temperature zone of the annealing furnace. After each continuous loading bin is laid for 1.2m to 1.5m along the length of the vacuum annealing furnace, the next loading bin is laid after a 50mm to 100mm interval. This ensures that the heat flow channels between the loading bins in each heating zone are uniform and consistent, which facilitates the mutual supplementation of irradiation heat between adjacent loading bins. This further improves the uniformity of the annealing temperature of the tubes in the heating zone and ensures the uniformity and stability of the tube performance at different locations in the large-size multi-zone heating annealing furnace.

[0114] Furthermore, in S6, based on the finished pipe's microstructure and performance requirements, the furnace loading, heating method, and the layout of the heating belts within the furnace, the vacuum annealing heating curve and process parameters are designed. These parameters are then input into and executed by the vacuum annealing furnace's operation and control system, including the settings for annealing temperature, holding time, homogenization time, heating rate, heating time, and argon purging cooling temperature. During the annealing process, the stability of all data transmissions within the operation and control system, including temperature, pressure, vacuum level, water temperature, and gas pressure, must be ensured.

[0115] In summary, the charging hopper provided by this invention uses a vertical pipe charging method, with no overlap between pipes. The charging quantity must ensure that the pipes do not tilt while also preventing compression between pipe walls. The furnace loading amount is typically calculated based on the hopper's volume and the pipe diameter. This charging method has the following advantages: 1. It avoids the softening of the bottom layer of pipes due to multi-layer flat charging, which can lead to excessive ellipticity caused by pressure from the upper layer, thus improving the yield of annealed pipes; 2. It improves the straightness of the pipes, preventing the straightness from deteriorating during annealing due to overlapping or loose charging, or failing to contribute to improving straightness. This reduces the number of pipes that need straightening, lowers production costs, and reduces the risk of dimensional deviations and hydride inconsistencies caused by straightening.

[0116] Furthermore, since zirconium tubes are highly susceptible to oxidation during annealing, this invention employs a "hopper suction + stainless steel mesh / zirconium mesh suction" method to prevent oxidation of the annealed tube surface. The hopper and hopper cover are made of zirconium plates. After the tubes are loaded into the hopper, 3-4 layers of stainless steel mesh / zirconium mesh are laid on top before covering with a zirconium alloy hopper cover. The above-mentioned anti-oxidation method has the following advantages: 1. Zirconium alloy has excellent gas absorption performance and can strongly absorb gases such as nitrogen, hydrogen, and oxygen. Using zirconium alloy plates to make the annealing hopper provides sufficient strength to support the tubes, does not contaminate the tubes, and can effectively absorb the gases released during the tube annealing process, preventing oxidation of the tube surface; 2. During the annealing process, gases evaporate upwards, so the upper end of the tube is prone to gas absorption oxidation. Using stainless steel mesh or zirconium mesh can increase the gas absorption surface area and is lightweight, which will not scratch the tube end face and can fully absorb the volatile gases at the upper end of the tube.

[0117] Finally, since the heating method of materials in a vacuum furnace is mainly thermal radiation, and thin-walled tubes have good thermal permeability, during industrial-scale mass annealing, there are differences in the time it takes for materials in different locations within the furnace to reach the required temperature. This leads to significant variations in material properties due to differences in holding time. To improve the quality stability of industrial-scale mass annealing of thin-walled tubes, this invention uses continuously placed material bins exceeding 1.2m to 1.5m in length or height, leaving a 50mm to 100mm (distance between adjacent material racks or platforms, or between adjacent groups of bins) thermal radiation flow channel. The annealing process employs low-temperature loading and a heating method with at least two uniform temperature platforms during the heating stage. The advantages of this method are: it ensures that all materials in the furnace reach a uniform temperature before recrystallization, reduces the time difference in temperature reaching different locations, effectively avoids the phenomenon of "external layer heat permeability, core heat incomplete permeability," and is an effective annealing method that can increase the charge capacity of a single furnace, significantly improving the performance stability of the tubes and enhancing industrial production efficiency.

[0118] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0119] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. An annealing process for zirconium alloy thin-walled spools, characterized in that, Specifically comprising the following steps: Step 1): making a charging bin suitable for vacuum annealing of zirconium alloy thin-walled short pipes; The charging bin comprises a circular charging bin body and an end cover (4) arranged on the top of the charging bin body, and the charging bin body is formed by splicing a plurality of bin units, each of which is provided with a connecting portion for fixing adjacent bin units through the connecting portion and cooperating with fasteners; Step 2): pretreating a plurality of thin-walled short pipes to be loaded into the charging bin to meet the charging requirements of the vacuum annealing furnace; Step 3): before loading, 3-4 layers of stainless steel mesh or zirconium mesh are laid on the bottom of the loading bin body, and the short thin-walled pipes pretreated in step 2) are vertically and neatly stacked in the loading bin body until the loading bin body is filled; wherein an expansion gap is reserved between adjacent short thin-walled pipes l , and l ≥0.1mm, to prevent the mutual extrusion deformation of the pipes caused by the expansion of the thin-walled pipes after heating; Step 4): laying 3-4 layers of stainless steel mesh or zirconium mesh on the top of the charging bin body, and covering the top of the charging bin body with the end cover (4) and sealing it; Step 5): vertically loading the sealed charging bin body of step 4) into the vacuum annealing furnace rack or loading platform, closing the vacuum annealing furnace door after the charging is completed, and performing vacuum pumping; Step 6): determining the process parameters and heating curve of vacuum annealing; Step 7): controlling the vacuum annealing furnace to anneal in combination with the process parameters and heating curve.

2. The annealing process for thin-walled zirconium alloy tubes as claimed in claim 1, wherein, The charging bin body is formed by splicing three identically structured fan-shaped bin units (2), the connecting portion is a positioning pin piece (1) welded on the side edge of the arc-shaped plate of the fan-shaped bin unit (2), the center of the positioning pin piece (1) is provided with a through hole for facilitating the passage of a pin, and the pin passes through the through hole and cooperates with a nut to fix adjacent fan-shaped bin units (2).

3. The annealing process for thin-walled zirconium alloy tubes as claimed in claim 2, wherein, The fan-shaped bin unit (2) is formed by butt welding two rectangular plates with a thickness of 3.5-4.5 mm, an arc-shaped plate with a central angle of 120°, and a fan-shaped plate with a central angle of 120°.

4. The annealing process for zirconium alloy thin-walled spool as claimed in claim 1, wherein, The end cover (4) is formed by butt welding a circular plate with a thickness of 3.5-4.5 mm and a circular surrounding plate; or the end cover (4) is formed by stamping a circular plate.

5. The annealing process for thin-walled zirconium alloy tubes as claimed in claim 4, wherein, The end cover (4) is welded with a U-shaped lifting handle (3) on the peripheral surface for convenient handling.

6. The annealing process for zirconium alloy thin-walled spool as claimed in claim 1, wherein, The step 1) specifically comprises: Step 1.1), first weld 3n fan-shaped bin units (2), n is an integer not less than 1, and then wipe them clean with anhydrous ethanol and put them into the vacuum annealing furnace for stress relief annealing, the annealing temperature is 400-450℃, the holding time is 4-6h, and the furnace is cooled down, and the furnace is discharged when the temperature in the vacuum annealing furnace is less than 100℃; Step 1.2), place the 3n fan-shaped bin units (2) on the vacuum annealing furnace rack or loading platform by manual carrying or lifting, 3 fan-shaped bin units (2) form a group to splice into a circular charging bin, align the through holes in the center of the positioning pin pieces (1) of adjacent fan-shaped bin units (2), pass the pin through the through hole and cooperate with the nut to realize fastening, and complete the fabrication of the circular charging bin.

7. The annealing process of thin-walled zirconium alloy tubes as claimed in claim 1, wherein, The charging process of step 5) is specifically as follows: When the vacuum annealing furnace is a horizontal vacuum annealing furnace, a single-layer charging bin mode is adopted, and after laying the charging bin 1.2-1.5m continuously along the length direction of the vacuum annealing furnace, the next group of charging bins is laid continuously with an interval of 50-100mm to ensure that the heat flow channels between the charging bins in each heating zone are uniform and consistent; When the vacuum annealing furnace is a vertical vacuum annealing furnace, a multi-layer charging bin mode is adopted, the number of single-layer charging bins follows that the maximum size does not exceed the length and width size of the uniform temperature zone, and is sequentially charged into the second layer,..., the n-th layer of the vacuum annealing furnace rack or the load carrying table, and the loading capacity does not exceed 2 / 3 of the allowable loading capacity of the vacuum annealing furnace.

8. The annealing process for zirconium alloy thin-walled spool as claimed in claim 1 wherein, The process parameters of the vacuum annealing in the step 6) are as follows, The temperature of incomplete recrystallization annealing is 450-520 DEG C, the temperature of complete recrystallization annealing is 530-650 DEG C; the vacuum before entering the furnace is better than 7*10 -3 Pa, the temperature of entering the furnace is less than or equal to 400 DEG C, and the heating rate is less than or equal to 5 DEG C / min; The annealing process is set to not less than two uniform temperature platforms, specifically: furnace temperature, after the temperature is higher than 400 DEG C in the heating process, every interval 50 DEG C ~ 100 DEG C sets a uniform temperature platform, the uniform temperature time is 30 min ~ 90 min, the holding time after the temperature is reached in the incomplete recrystallization annealing is 240 min ~ 480 min, the holding time after the temperature is reached in the complete recrystallization annealing is 90 min ~ 240 min, the cooling mode is furnace cooling or < 400 DEG C argon cooling, and the discharge temperature is < 100 DEG C.

Images