Hot upsetting head construction method for nuclear power plant embedded parts

Abstract

This invention discloses a method for constructing hot-melt upsetting heads for embedded parts in nuclear power plants, relating to the field of nuclear power plant embedded part processing technology. The method includes induction heating the end of the anchor bar to be upset to a thermoplastic state; placing the thermoplastic end into an upsetting mold and applying upsetting force along the axial direction of the anchor bar to radially upset under the constraint of the mold cavity; holding and unloading the mold after the deformation reaches a preset value; applying axial constraint to the unloaded end and performing cooling treatment to form the upset head. This invention solves the problems of upsetting head cracking, incomplete core heating, and inconsistent upsetting head performance that exist in cold upsetting or flame-heated upsetting, and has the advantages of full upsetting head formation, no cracks, and stable mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of nuclear power plant embedded parts processing technology, and in particular to a method for hot-melt upsetting construction of nuclear power plant embedded parts. Background Technology

[0002] Embedded components in the nuclear island building structure transfer equipment and pipeline loads to the concrete structure through anchorage connections between their anchor bars and concrete, making them key connecting components in the nuclear island civil engineering and installation works. The upset head at the end of the anchor bar is the core structure for anchorage force transmission, and its forming quality directly determines the load-bearing capacity and reliability of the anchorage connection. The upset head process has evolved from room-temperature cold upset to flame-heated hot upset. With the development of anchor bars towards larger diameters and higher strengths, and the increasing demands for reliability in nuclear power plant anchorage connections, the heating method and deformation control method for upset head forming have gradually become crucial factors determining the quality of the upset head.

[0003] In current engineering practice, anchor bar upset heads are mostly formed using two methods: cold upset or flame-heated hot upset. Cold upset directly applies upset force to the end of the anchor bar at room temperature, suitable for small-diameter low-carbon steel anchor bars. Flame-heated hot upset uses an oxy-acetylene flame to heat the end to be upset, and after heating, the upset is completed in one pressurization. After forming, it is naturally air-cooled or directly water-cooled. During construction, the control of heating temperature, pressure application method, and cooling method relies heavily on operational experience, lacking quantitative process parameters.

[0004] This processing method presents multiple technical challenges: First, large-diameter, high-strength anchor bars lack sufficient plasticity reserves at room temperature, making metal flow difficult in the upset head area during cold upsetting, resulting in a high rate of upset head cracking and even safety hazards such as chipping and flash. Second, the heat from flame heating is conducted from the surface inward, leading to an uneven temperature field and a prominent contradiction between insufficient core heating and overheated surface. The large temperature difference between the core and surface results in uneven upsetting deformation, coarse grain structure, and inconsistent upset head performance. Third, applying pressure in one go causes the metal to flow violently in a short period of time, easily forming hidden defects such as folds and delamination inside the upset head. Cooling under unconstrained conditions after unloading causes the upset head to spring back and deform. In addition, rapid water cooling after forming easily produces quenching cracks on the upset head surface, resulting in high residual stress and making it difficult for the mechanical properties of the upset head to stably meet the high reliability requirements of nuclear power plant embedded parts. The combined effect of the above problems makes it difficult to guarantee the forming quality and performance stability of the anchor bar upset head, which restricts the improvement of the anchoring connection quality of nuclear power plant embedded parts. Summary of the Invention

[0005] The main objective of this invention is to propose a method for hot-melt upsetting of embedded parts in nuclear power plants. This method aims to ensure that the upsetting of the anchor bar of the embedded parts in nuclear power plants is full and crack-free during the upsetting process, thereby guaranteeing the uniformity and stability of the upsetting structure and mechanical properties and improving the reliability of the anchoring connection of the embedded parts.

[0006] To achieve the above objectives, the present invention proposes a method for constructing hot-melt upsetting heads for nuclear power plant embedded parts, used to form upsetting heads at the ends of anchor bars in nuclear power plant embedded parts. The upsetting head mold has a cavity that constrains the radial upsetting deformation of the end of the anchor bar to be upset. The method for constructing hot-melt upsetting heads for nuclear power plant embedded parts includes: The end of the anchor bar to be upset in the embedded part is induction heated to a preset temperature range so that the end of the anchor bar to be upset is in a thermoplastic state. The end of the head to be upset, which is in a thermoplastic state, is placed into the upset head mold, and an upsetting force is applied to the end of the head to be upset along the axial direction of the anchor bar so that the end of the head to be upset is deformed radially under the constraint of the mold cavity. When the upsetting deformation at the end of the upsetting head reaches the preset deformation amount, the upsetting force is held for a preset holding time and then unloaded; An axial constraint is applied to the unloaded end of the head to be upset, and a cooling treatment is performed on the end of the head to be upset in order to form an upset head at the end of the anchor bar.

[0007] In one embodiment, the step of induction heating the end of the anchor bar to be upset of the embedded part includes: An induction heating coil is fitted around the outer periphery of the end of the anchor bar to be upset, and the axial coverage length of the induction heating coil is 1.2 to 1.5 times the length of the area to be heated; A medium-frequency alternating current is passed through the induction heating coil, wherein the frequency of the medium-frequency alternating current is 1kHz~4kHz; The heating rate of induction heating is controlled at 8℃ / s to 15℃ / s to heat the end of the head to be upset to the preset temperature range, which is 900℃ to 1100℃.

[0008] In one embodiment, the step of controlling the heating rate of induction heating to heat the end of the head to be upset to the preset temperature range includes: During the heating process, the surface temperature of the end of the head to be upset is measured; When the surface temperature reaches 800℃~850℃, the power of the medium-frequency alternating current is reduced to 50%~60% of the initial power to reduce the heating rate. Once the surface temperature reaches the lower limit of the preset temperature range, maintain the temperature for 1 to 2 minutes to ensure that the temperature difference between the core and surface of the head to be upset does not exceed 30°C.

[0009] In one embodiment, the step of applying an upsetting force to the end of the head to be upset along the axial direction of the anchor bar, so that the end of the head to be upset is radially upset under the constraint of the mold cavity, includes: The upsetting force is applied in two stages: The first stage applies pressure with a first upsetting force, which is 1.2 to 1.4 times the minimum pressure required to fill the mold cavity with the metal at the end of the head to be upset, and the pressure application speed is 2 mm / s to 4 mm / s, until the end of the head to be upset is in contact with the cavity wall of the mold cavity; The second stage applies a second upsetting force, which is 1.5 to 2.0 times that of the first upsetting force, and the application speed is 0.5 mm / s to 1 mm / s, until the upsetting deformation reaches the preset deformation.

[0010] In one embodiment, the step of unloading the upsetting force after maintaining it for a preset holding time when the upsetting deformation at the end of the upsetting head reaches a preset deformation includes: After the upsetting deformation reaches the preset deformation, the second upsetting force is maintained for pressure holding, and the preset pressure holding time is 3s to 8s; During the pressure holding period, monitor the springback amount of the upsetting deformation; If the springback exceeds 3% of the preset deformation, then apply upsetting force to compensate for the springback and then hold the pressure again. After the pressure holding is completed, the upsetting force is unloaded.

[0011] In one embodiment, the preset deformation amount is 1.0 to 1.4 times the diameter of the anchor bar; The upsetting deformation is determined by measuring the axial compression displacement of the end of the head to be upset within the upsetting mold, and using the axial compression displacement as the upsetting deformation.

[0012] In one embodiment, the steps of applying axial constraint to the unloaded end of the head to be upset and performing cooling treatment on the end of the head to be upset include: The unloaded end of the head to be upset is held in the upset head mold, and the axial positioning of the anchor bar is maintained to apply axial constraint to the end of the head to be upset. Circulating cooling water is introduced into the cavity wall of the upsetting mold to perform in-mold cooling on the end of the upsetting head; After the temperature at the end of the upsetting head drops to a preset demolding temperature, the upsetting head mold is removed. The preset demolding temperature is 300℃~400℃. After demolding, the ends of the anchor bars are air-cooled to ambient temperature.

[0013] In one embodiment, the step of circulating cooling water into the mold cavity wall of the upsetting mold to perform in-mold cooling of the end of the upsetting head includes: The temperature of the circulating cooling water is controlled at 20℃~35℃, and the water flow velocity is 1m / s~2m / s, so that the end of the head to be upset is cooled at a cooling rate of 5℃ / s~8℃ / s. During the first half of the in-mold cooling process, the axial constraint is maintained; In the latter half of the in-mold cooling process, the axial constraint is released, allowing the end of the head to be upset to shrink freely, in order to prevent residual tensile stress from being generated inside the formed upset head.

[0014] In one embodiment, after the end of the anchor bar is formed into an upsetting head, the method for constructing the hot-melt upsetting head of the nuclear power plant embedded part further includes: Inspect the appearance of the formed upsetting head and discard any upsetting heads with surface cracks; The height and diameter of the upsetting head are measured. The height of a qualified upsetting head is 0.8 to 1.2 times the diameter of the anchor bar, and the diameter of a qualified upsetting head is 1.8 to 2.4 times the diameter of the anchor bar. The upsetting head is subjected to magnetic particle testing to detect whether there are cracks or defects on the surface and near the surface of the upsetting head.

[0015] In one embodiment, the embedded part includes multiple anchor bars, and the construction method for the hot-melt upsetting head of the embedded part in the nuclear power plant further includes: The upsetting operations of multiple anchor bars are organized in a continuous manner: while performing the cooling treatment on the nth anchor bar, the induction heating is performed on the (n+1)th anchor bar, where n is a positive integer; Multiple anchor bars share one upsetting mold, and the mold cavity of the upsetting mold is preheated to 150°C~250°C before each upsetting. After all the anchor bars of the pre-embedded parts have been upset, all upsets are uniformly inspected and numbered and registered.

[0016] The technical solution of this invention solves the problems of upsetting cracks, incomplete core heating, and inconsistent upsetting performance that exist in cold upsetting or flame-heated upsetting. It has the advantages of full upsetting, no cracks, and stable mechanical properties. The solution involves induction heating of the end of the anchor bar to be upset to a thermoplastic state, placing the thermoplastic end into the upsetting mold and applying upsetting force along the axial direction of the anchor bar to make it radially upsetting and deformed under the constraint of the mold cavity, holding pressure and unloading after the deformation reaches a preset value, applying axial constraint to the end of the upsetting after unloading and performing cooling treatment to form the upsetting head. Attached Figure Description

[0017] 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, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of an embodiment of the hot-melt upsetting head construction method for embedded parts in nuclear power plants provided by the present invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] To solve this technical problem, the present invention proposes a method for hot-melt upsetting of embedded parts in nuclear power plants, which is used to form upsetting heads at the ends of anchor bars of embedded parts in nuclear power plants. The upsetting head mold has a mold cavity that constrains the radial upsetting deformation of the end of the anchor bar to be upset.

[0024] Please see Figure 1 In one embodiment of the present invention, the construction method for the hot-melt upsetting head of the embedded part in the nuclear power plant includes: S10, Induction heating is applied to the end of the anchor bar of the embedded part to be upset, and the end of the end to be upset is heated to a preset temperature range so that the end of the end to be upset is in a thermoplastic state. S20, the end of the head to be upset, which is in a thermoplastic state, is placed into the upset head mold, and an upsetting force is applied to the end of the head to be upset along the axial direction of the anchor bar, so that the end of the head to be upset is deformed radially under the constraint of the mold cavity; S30, when the upsetting deformation at the end of the upsetting head reaches the preset deformation, the upsetting force is held for a preset holding time and then unloaded; S40, apply axial constraint to the unloaded end of the head to be upset and perform cooling treatment on the end of the head to be upset in order to form an upset head at the end of the anchor bar.

[0025] For ease of understanding, the following explains some key terms in this embodiment: Embedded components refer to steel components that are pre-embedded in the concrete structure and anchored to the concrete by anchor bars.

[0026] Anchor bars are steel bars that are anchored to concrete on embedded parts, and their upsetting ends are used to enhance the anchoring capacity.

[0027] An upsetting head refers to the enlarged end formed by upsetting at the end of an anchor bar.

[0028] Induction heating refers to a heating method that uses the alternating magnetic field generated by the alternating current in an induction coil to induce eddy currents on the metal surface, causing the metal to heat up.

[0029] The thermoplastic state refers to the state in which metal is easily plastically deformed after being heated to a suitable forging temperature range.

[0030] An upsetting die is a forming die with a cavity used to constrain the direction and shape of upsetting deformation.

[0031] Upsetting deformation refers to the displacement of the end of the upsetting head under axial pressure along the axial direction, and is used to characterize the degree of upsetting.

[0032] Axial constraint refers to the positioning constraint applied to the anchor bar in the axial direction during the cooling process, which is used to maintain the stability of the upset head shape.

[0033] In-mold cooling refers to controlled cooling by keeping the upsetting head inside the mold and using a cooling medium through the mold cavity wall.

[0034] Demolding temperature refers to the temperature threshold at which the mold can be removed after the upsetting head has been formed.

[0035] This embodiment provides a method for constructing hot-melt upsetting heads for embedded parts in nuclear power plants.

[0036] First, the method involves induction heating of the end of the anchor bar to be upset in the embedded part, heating the end to a preset temperature range to bring it into a thermoplastic state. Specifically, an induction heating coil can be fitted around the outer circumference of the end to be upset, and a medium-frequency alternating current can be passed through it for heating. As another implementation method, the heating power and heating time can be adjusted according to the diameter of the anchor bar to make the core temperature and surface temperature tend to be consistent.

[0037] Furthermore, the method includes placing the thermoplastic end of the head to be upset into the upset die, and applying an upsetting force along the axial direction of the anchor bar, causing the end of the head to be upset to deform radially under the constraint of the die cavity. For example, the upsetting force can be applied in two stages: first, rapid pressure is applied to fill the die cavity with metal, and then slow high pressure is applied to complete the deformation. Alternatively, a single upsetting force can be applied at once to achieve the preset deformation amount.

[0038] Subsequently, the method includes maintaining the upsetting force for a preset holding time after the upsetting deformation reaches a preset deformation amount, and then unloading. Specifically, the springback can be monitored during the holding period, and compensation pressure can be applied for excessive springback before holding the pressure again.

[0039] Based on this, the method includes applying axial constraints to the unloaded end of the head to be upset and performing a cooling process to form the upset head at the end of the anchor bar. For example, the end of the head to be upset can be held in the upset head mold, and in-mold cooling can be performed by circulating cooling water through the mold cavity wall until it drops to a preset demolding temperature, after which it is demolded and air-cooled. As another implementation, the axial constraint is maintained in the first half of the in-mold cooling process, and the constraint is released in the second half to allow it to shrink freely.

[0040] Meanwhile, after the upsetting head is formed, it can be inspected for appearance, measured for size and tested for magnetic particles; the upsetting operation of multiple anchor bars can be organized in a continuous flow manner, with cooling and heating carried out in parallel.

[0041] In an embodiment of the present invention, the step of induction heating the end of the anchor bar to be upset of the embedded part includes: S11, an induction heating coil is sleeved on the outer periphery of the end of the anchor bar to be upset, and the axial coverage length of the induction heating coil is 1.2 to 1.5 times the length of the area to be heated; S12, A medium-frequency alternating current is passed through the induction heating coil, wherein the frequency of the medium-frequency alternating current is 1kHz~4kHz; S13, control the heating rate of induction heating to be 8℃ / s~15℃ / s, and heat the end of the head to be upset to the preset temperature range, the preset temperature range being 900℃~1100℃.

[0042] Specifically, induction heating utilizes eddy currents induced on the surface of the anchor bar by an alternating magnetic field to heat the metal itself. Heat is generated on the surface and conducted to the core, with the heating depth related to the current frequency. It should be noted that the frequency of the medium-frequency alternating current is 1kHz~4kHz. The heat penetration depth in this frequency range matches the radius of the large-diameter anchor bar, allowing the core to receive sufficient heat input in a short time. The heating rate is controlled at 8℃ / s~15℃ / s to ensure heating efficiency while avoiding excessively rapid surface heating that could lead to overheating of the surface while the core remains cold. The axial coverage length of the induction heating coil is 1.2 to 1.5 times the length of the area to be heated, ensuring that the ends of the area to be heated are also fully covered by magnetic lines of force, preventing the ends from being too cold due to edge effects. The preset temperature range of 900℃~1100℃ falls within the forging temperature range of reinforcing bars. At this temperature, the ends of the anchor bar exhibit good plasticity and low deformation resistance.

[0043] Through the above technical solution, this application replaces flame heating with medium frequency induction heating. By utilizing the heating mechanism of eddy current self-generated heat and quantitative frequency and rate parameters, the temperature field at the end of the upsetting head tends to be uniform in both the radial and axial directions, providing a uniform thermoplastic state for subsequent upsetting deformation.

[0044] In an embodiment of the present invention, the step of controlling the heating rate of induction heating to heat the end of the head to be upset to the preset temperature range includes: S14, During the heating process, the surface temperature of the end of the head to be upset is measured; S15, when the surface temperature reaches 800℃~850℃, the power of the medium frequency alternating current is reduced to 50%~60% of the initial power to reduce the heating rate. S16, after the surface temperature reaches the lower limit of the preset temperature range, keep it warm for 1 min to 2 min so that the difference between the core temperature and the surface temperature at the end of the head to be upset does not exceed 30°C.

[0045] Specifically, surface temperature is a process parameter that can be directly measured during induction heating, while core temperature is controlled by coordinating surface temperature with the heating regime. It should be noted that when the surface temperature reaches 800℃~850℃, the metal is about to enter the high-temperature zone. At this point, the heating power is reduced to 50%~60% of the initial power to slow down the surface heating rate, allowing time for the heat to conduct and homogenize in the core, preventing the surface from rapidly rising to overheating temperatures. After the surface temperature reaches the lower limit of the preset temperature range, it is held for 1~2 minutes to allow heat to be fully conducted from the surface to the core, converging the core-surface temperature difference to within 30℃, thus avoiding a false thermoplastic state where the surface has reached forging temperature but the core is still cold.

[0046] Through the above technical solution, this application adopts a segmented heating system of "reducing power in the high-temperature section and maintaining heat after reaching the target position" and uses the core-surface temperature difference as a quantitative heating quality criterion to ensure that the entire end of the upsetting head, rather than just the surface layer, enters the thermoplastic state, thus eliminating the cause of uneven upsetting deformation from the heating source.

[0047] In an embodiment of the present invention, the step of applying an upsetting force to the end of the head to be upset along the axial direction of the anchor bar, so that the end of the head to be upset is radially upset under the constraint of the mold cavity, includes: S21, in the first stage, a first upsetting force is applied, which is 1.2 to 1.4 times the minimum pressure required to fill the mold cavity with the metal at the end of the head to be upset, and the pressure application speed is 2 mm / s to 4 mm / s, until the end of the head to be upset is in contact with the cavity wall of the mold cavity; S22, in the second stage, a second upsetting force is applied, which is 1.5 to 2.0 times that of the first upsetting force, and the application speed is 0.5 mm / s to 1 mm / s, until the upsetting deformation reaches the preset deformation.

[0048] Specifically, upsetting deformation is divided into two stages: filling and compaction. The metal flow state differs between the two stages, and the required pressure parameters also differ. It should be noted that in the first stage, pressure is applied at a relatively fast speed of 2mm / s to 4mm / s, and the upsetting force is 1.2 to 1.4 times the minimum pressure required to fill the mold cavity. This allows the thermoplastic metal to flow quickly and fill the mold cavity rapidly, shortening the exposure time of the high-temperature metal in the air, while preventing surface cooling of the metal before it fills the mold cavity. In the second stage, pressure is applied at a slow speed of 0.5mm / s to 1mm / s, and the upsetting force is increased to 1.5 to 2.0 times the first upsetting force. When the metal has filled the mold cavity and the flow space is limited, slow and high-pressure compaction is used to control the flow speed of the metal and prevent the high-speed flowing metal from forming folds and delamination defects at the corners of the mold cavity, until the upsetting deformation reaches the preset deformation amount.

[0049] Through the above technical solution, this application divides the upsetting process into two stages, "fast filling of the mold and slow compaction", according to the metal flow state. This makes the pressure application speed and upsetting force vary with the degree to which the metal fills the mold cavity, matching the metal flow law and avoiding folding and delamination defects caused by applying a single upsetting force at once.

[0050] In an embodiment of the present invention, the step of unloading the upsetting force after maintaining it for a preset holding time when the upsetting deformation at the end of the upsetting head reaches a preset deformation includes: S23, after the upsetting deformation reaches the preset deformation, the second upsetting force is maintained for pressure holding, and the preset pressure holding time is 3s to 8s; S24, During the pressure holding period, monitor the springback amount of the upsetting deformation; S25, if the springback exceeds 3% of the preset deformation, then apply upsetting force to eliminate the springback and hold pressure again; S26, after the pressure holding is completed, unload the upsetting force.

[0051] Specifically, after the upsetting deformation reaches the preset deformation amount, the thermoplastic metal still exhibits an elastic recovery tendency. Immediate unloading will cause the upsetting head to spring back and shrink in size. It should be noted that maintaining the second upsetting force for 3 to 8 seconds allows the metal to redistribute stress under continuous pressure, and the elastic recovery tendency gradually decreases during the holding period. During the holding period, the springback amount is monitored. If the springback amount exceeds 3% of the preset deformation amount, it indicates that the internal stress of the metal has not been fully released. In this case, the upsetting force is applied to compensate for the springback amount, and then the holding period is repeated, forming a closed loop of "holding pressure - monitoring - compensation - holding pressure again" until the springback amount converges to the allowable range before unloading.

[0052] Through the above technical solution, this application controls the holding pressure endpoint with a quantitative springback criterion, so that the size of the upsetting head after unloading is stable and does not shrink due to elastic recovery, thus ensuring the accuracy of the upsetting head forming size.

[0053] In an embodiment of the present invention, the preset deformation amount is 1.0 to 1.4 times the diameter of the anchor bar; the upsetting deformation amount is determined by measuring the axial compression displacement of the end of the head to be upset within the upsetting mold, and using the axial compression displacement as the upsetting deformation amount.

[0054] Specifically, the upsetting head expands radially under the constraint of the mold cavity. There is a definite correspondence between the axial compressive displacement and the radial upsetting degree. The radial dimension of the upsetting head can be indirectly controlled by measuring the axial compressive displacement. It should be noted that the preset deformation amount is 1.0 to 1.4 times the diameter of the anchor bar. Under this compression amount, the upsetting head metal fully fills the mold cavity and achieves the designed compaction degree, resulting in a full upsetting head without excessive deformation.

[0055] Through the above technical solution, this application uses axial compressive displacement as the measurement quantity of upsetting deformation, transforming the forming degree of the upsetting head into an easily measurable axial parameter, thereby realizing quantitative control of upsetting deformation.

[0056] In an embodiment of the present invention, the steps of applying axial constraint to the unloaded end of the head to be upset and performing cooling treatment on the end of the head to be upset include: S31, the unloaded end of the head to be upset is held in the upset head mold, and the axial positioning of the anchor bar is maintained to apply axial constraint to the end of the head to be upset; S32, circulating cooling water is introduced into the mold cavity wall of the upsetting mold to perform in-mold cooling on the end of the upsetting head; S33, after the temperature at the end of the upsetting head drops to the preset demolding temperature, the upsetting head mold is removed, and the preset demolding temperature is 300℃~400℃; S34, air-cool the ends of the demolded anchor bars to ambient temperature.

[0057] Specifically, the upset head, after being unloaded from the mold, remains in a high-temperature, low-strength state. If it is immediately removed from the mold for free cooling, shape distortion and springback are likely to occur. It should be noted that keeping the upset head within the mold and maintaining the axial positioning of the anchor bars ensures that the shape of the upset head is constrained by the mold cavity during the initial cooling phase. In-mold cooling is achieved through circulating cooling water through the mold cavity wall, with the cooling rate controlled by a combination of water temperature, flow rate, and mold cavity wall thickness. This allows the upset head to complete its primary temperature drop under constrained conditions. Once the upset head temperature drops to the preset demolding temperature of 300℃~400℃, the metal has regained sufficient strength to maintain its shape, at which point the mold is removed. After demolding, the metal is air-cooled to ambient temperature to avoid excessive temperature differences between the surface and core caused by continued forced cooling.

[0058] Through the above technical solution, this application uses a segmented cooling path of "in-mold constraint cooling - constant temperature demolding - air cooling" to ensure that the upsetting head has shape constraint in the high temperature and low strength stage, timely demolding in the medium temperature stage, and natural slow cooling in the low temperature stage. The cooling method of each stage matches the state of the upsetting head at that time, taking into account both shape preservation and residual stress control.

[0059] In an embodiment of the present invention, the step of circulating cooling water into the mold cavity wall of the upsetting mold to perform in-mold cooling on the end of the upsetting head includes: S35, control the temperature of the circulating cooling water to be 20℃~35℃ and the water flow velocity to be 1m / s~2m / s, so that the end of the head to be upset is cooled down at a cooling rate of 5℃ / s~8℃ / s; S36, during the first half of the in-mold cooling process, the axial constraint is maintained; S37, in the latter half of the in-mold cooling process, the axial constraint is released, allowing the end of the head to be upset to shrink freely, in order to prevent residual tensile stress from being generated inside the formed upset head.

[0060] Specifically, the cooling rate of 5℃ / s to 8℃ / s falls between the slow cooling of natural air cooling and the rapid cooling of quenching water cooling, constituting a controlled medium-speed cooling. It should be noted that the circulating cooling water temperature is 20℃ to 35℃, and the flow rate is 1m / s to 2m / s. Through heat transfer through the mold cavity wall, the upsetting head cools uniformly at a rate of 5℃ / s to 8℃ / s. This rate maintains a fine and uniform grain structure without causing quenching cracks on the surface due to excessively rapid cooling. In the first half of the in-mold cooling process, axial constraint is maintained to prevent axial shrinkage distortion of the upsetting head during the high-temperature, low-strength stage. In the second half, when the metal has sufficient strength, the axial constraint is released, allowing the upsetting head to shrink freely along the axial direction. This avoids the constraint and shrinkage counteracting each other, preventing residual tensile stress from forming inside the upsetting head. The key to this step is that the constraint plays a shape-preserving role in the first half and actively withdraws in the second half.

[0061] Through the above technical solution, this application uses a segmented constraint strategy of "pre-constraint and post-release" combined with a controlled cooling rate to ensure that the upsetting head maintains a regular shape and avoids residual tensile stress, thus guaranteeing the mechanical performance stability of the upsetting head from the cooling stage.

[0062] In an embodiment of the present invention, after the end of the anchor bar is formed into an upsetting head, the method for constructing the hot-melt upsetting head of the nuclear power plant embedded part further includes: S41, Inspect the appearance of the formed upsetting head and discard upsetting heads with surface cracks; S42, Measure the height and diameter of the upsetting head. The height of a qualified upsetting head is 0.8 to 1.2 times the diameter of the anchor bar, and the diameter of a qualified upsetting head is 1.8 to 2.4 times the diameter of the anchor bar. S43, perform magnetic particle testing on the upsetting head to detect whether there are cracks or defects on the surface and near the surface of the upsetting head.

[0063] Specifically, the inspection after upsetting is the final step in ensuring the closed-loop quality of the embedded parts' anchorage. It should be noted that visual inspection removes upsetting heads with visible surface cracks; the determination of the upsetting head height and diameter is normalized based on the anchor bar diameter, with a qualified upsetting head height of 0.8 to 1.2 times the anchor bar diameter and a diameter of 1.8 to 2.4 times the anchor bar diameter, ensuring sufficient anchorage area without excessive upsetting and weakening the end material; magnetic particle testing is used to detect micro-cracks invisible to the naked eye on and near the surface, further ensuring the integrity and reliability of the upsetting head.

[0064] Through the above technical solution, this application uses a three-level inspection system of "appearance-dimension-magnetic powder" to control the quality of upsetting heads, so that all upsetting heads entering the installation stage meet the quantitative quality criteria, thus ensuring the reliability of the anchoring connection of the embedded parts.

[0065] In an embodiment of the present invention, the embedded part includes multiple anchor bars, and the construction method for the hot-melt upsetting head of the nuclear power plant embedded part further includes: S51, the upsetting operations of multiple anchor bars are organized in a continuous manner: while performing the cooling treatment on the nth anchor bar, the induction heating is performed on the (n+1)th anchor bar, where n is a positive integer; S52, multiple anchor bars share one upsetting mold, and the mold cavity of the upsetting mold is preheated to 150°C~250°C before each upsetting; S53. After all the anchor bars of the pre-embedded parts have been upset, all upsets shall be uniformly inspected and numbered and registered.

[0066] Specifically, embedded parts typically have multiple anchor bars. A sequential process of heating, upsetting, and cooling each anchor bar one by one is inefficient, and the cooling waiting time consumes equipment resources. It's important to note that organizing the upsetting process in a continuous flow manner, while the previous anchor bar is in the in-mold cooling stage, simultaneously applies induction heating to the next anchor bar, overlapping the heating and cooling processes and shortening the total processing time for a single embedded part. Multiple anchor bars share the same upsetting mold, with the mold cavity preheated to 150℃~250℃ before each upsetting operation. This prevents the cold mold from contacting the thermoplastic metal at temperatures above 900℃, which could cause sudden cooling cracks on the upsetting surface and ensure consistent forming conditions for each upsetting. After all anchor bars are upset, they are uniformly inspected, numbered, and registered, ensuring consistent inspection standards and quality traceability.

[0067] Through the above technical solutions, this application improves the upsetting efficiency of multi-anchor bar embedded parts by implementing three measures: assembly line operation organization, mold preheating, and unified inspection and registration, while ensuring the consistency of upsetting quality, thus enabling the hot melt upsetting process to be applied on a large scale.

[0068] This construction method employs a hot-melt upsetting process involving "uniform induction heating, segmented variable-speed upsetting, pressure holding and springback compensation, and constrained segmented cooling" to form the anchor bar upset in a uniform thermoplastic state, maintaining shape stability and eliminating residual stress during cooling. Simultaneously, this method incorporates the entire upsetting process into a measurable, controllable, and reproducible process system through quantitative heating, pressure application, pressure holding, and cooling parameters. This method solves the problems of upset cracking, incomplete core heating, and inconsistent upset performance associated with cold upsetting or flame-heated upsetting, offering advantages such as full upset shape, no cracks, and stable mechanical properties.

[0069] The following example will provide a more detailed explanation of the above technical solution: In a nuclear power plant construction project, a large embedded component has eight 32mm diameter HRB400E anchor bars, and an upsetting head needs to be formed at the end of each anchor bar. The length of the area to be heated is 80mm, and the axial coverage length of the induction heating coil is 100mm, approximately 1.25 times the length of the area to be heated. A medium-frequency alternating current with a frequency of 2kHz is passed through the coil, and the temperature is increased at a heating rate of 10℃ / s. When the surface temperature reaches 830℃, the heating power is reduced to 55% of the initial power; after the surface temperature reaches 900℃ (the lower limit of the preset temperature range), it is held for 90 seconds. The measured temperature difference between the core and the surface is 22℃, which is within 30℃, indicating that the end of the upsetting head has entered a thermoplastic state.

[0070] Subsequently, the end of the upset head is placed into an upset head mold with a cavity diameter of 61 mm. In the first stage, upsetting force of 1.3 times the minimum pressure required to fill the mold cavity is applied at a pressing speed of 3 mm / s until the end of the upset head adheres to the mold cavity wall. In the second stage, upsetting force of 2.0 times the first upsetting force is applied at a pressing speed of 0.8 mm / s. The preset deformation is 1.2 times the diameter of the anchor bar, i.e., 38 mm. The upsetting deformation is measured by axial compression displacement. After the deformation reaches 38 mm, the second upsetting force is maintained for 5 seconds. During the holding period, the springback is monitored and found to be 0.8 mm, which does not exceed 3% (1.14 mm) of the preset deformation. After the holding period, the pressure is released.

[0071] After unloading, the upsetting head is held within the mold while maintaining the axial positioning of the anchor bar. Circulating cooling water at 25°C and a flow rate of 1.5 m / s is introduced into the mold cavity wall, cooling the upsetting head at a rate of approximately 6°C / s. Axial constraint is maintained during the first half of the in-mold cooling process, and the constraint is released during the second half, allowing the upsetting head to contract freely. The mold is removed when the upsetting head temperature drops to 350°C, and the head is then air-cooled to ambient temperature. The formed upsetting head has a height of 30 mm, approximately 0.94 times the diameter of the anchor bar; and a diameter of 60 mm, approximately 1.88 times the diameter of the anchor bar, meeting dimensional requirements. Visual inspection reveals no cracks, and magnetic particle testing shows no surface or near-surface defects.

[0072] During construction, the second anchor bar was simultaneously induction heated while the first anchor bar was cooling in the mold. The upsetting mold was preheated to 200℃ before each upsetting operation. The upsetting of the eight anchor bars was completed sequentially in an assembly line manner. After all the anchor bars were upset, the eight upsetting heads were inspected, numbered, and registered.

[0073] The project was constructed using this method, and all upset heads were formed and qualified in one go. After installation, the bearing capacity of the anchoring connection of the embedded parts met the design requirements, verifying the reliability and effectiveness of this method.

[0074] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A method for constructing a hot-melt upsetting head for embedded parts in nuclear power plants, used to form an upsetting head at the end of an anchor bar in the embedded parts of a nuclear power plant, wherein the upsetting head mold has a cavity for constraining the radial upsetting deformation of the end of the anchor bar to be upsetting, characterized in that, The construction method for hot-melt upsetting heads of embedded parts in nuclear power plants includes: The end of the anchor bar to be upset in the embedded part is induction heated to a preset temperature range so that the end of the anchor bar to be upset is in a thermoplastic state. The end of the head to be upset, which is in a thermoplastic state, is placed into the upset head mold, and an upsetting force is applied to the end of the head to be upset along the axial direction of the anchor bar so that the end of the head to be upset is deformed radially under the constraint of the mold cavity. When the upsetting deformation at the end of the upsetting head reaches the preset deformation amount, the upsetting force is held for a preset holding time and then unloaded; An axial constraint is applied to the unloaded end of the head to be upset, and a cooling treatment is performed on the end of the head to be upset in order to form an upset head at the end of the anchor bar.

2. The construction method for hot-melt upsetting heads of embedded parts in nuclear power plants as described in claim 1, characterized in that, The step of induction heating the end of the anchor bar to be upset of the embedded part includes: An induction heating coil is fitted around the outer periphery of the end of the anchor bar to be upset, and the axial coverage length of the induction heating coil is 1.2 to 1.5 times the length of the area to be heated; A medium-frequency alternating current is passed through the induction heating coil, wherein the frequency of the medium-frequency alternating current is 1kHz~4kHz; The heating rate of induction heating is controlled at 8℃ / s to 15℃ / s to heat the end of the head to be upset to the preset temperature range, which is 900℃ to 1100℃.

3. The method for constructing hot-melt upsetting heads for embedded parts in nuclear power plants as described in claim 2, characterized in that, The step of controlling the heating rate of induction heating to heat the end of the head to be upset to the preset temperature range includes: During the heating process, the surface temperature of the end of the head to be upset is measured; When the surface temperature reaches 800℃~850℃, the power of the medium-frequency alternating current is reduced to 50%~60% of the initial power to reduce the heating rate. Once the surface temperature reaches the lower limit of the preset temperature range, maintain the temperature for 1 to 2 minutes to ensure that the temperature difference between the core and surface of the head to be upset does not exceed 30°C.

4. The construction method for hot-melt upsetting heads of embedded parts in nuclear power plants as described in claim 1, characterized in that, The step of applying an upsetting force to the end of the head to be upset along the axial direction of the anchor bar, so that the end of the head to be upset is radially upset under the constraint of the mold cavity, includes: The upsetting force is applied in two stages: The first stage applies pressure with a first upsetting force, which is 1.2 to 1.4 times the minimum pressure required to fill the mold cavity with the metal at the end of the head to be upset, and the pressure application speed is 2 mm / s to 4 mm / s, until the end of the head to be upset is in contact with the cavity wall of the mold cavity; The second stage applies a second upsetting force, which is 1.5 to 2.0 times that of the first upsetting force, and the application speed is 0.5 mm / s to 1 mm / s, until the upsetting deformation reaches the preset deformation.

5. The method for constructing hot-melt upsetting heads for embedded parts in nuclear power plants as described in claim 4, characterized in that, The step of unloading the upsetting force after maintaining it for a preset holding time when the upsetting deformation at the end of the upsetting head reaches a preset deformation includes: After the upsetting deformation reaches the preset deformation, the second upsetting force is maintained for pressure holding, and the preset pressure holding time is 3s to 8s; During the pressure holding period, monitor the springback amount of the upsetting deformation; If the springback exceeds 3% of the preset deformation, then apply upsetting force to compensate for the springback and then hold the pressure again. After the pressure holding is completed, the upsetting force is unloaded.

6. The method for constructing hot-melt upsetting heads for embedded parts in nuclear power plants as described in claim 5, characterized in that, The preset deformation amount is 1.0 to 1.4 times the diameter of the anchor bar; The upsetting deformation is determined by measuring the axial compression displacement of the end of the head to be upset within the upsetting mold, and using the axial compression displacement as the upsetting deformation.

7. The construction method for hot-melt upsetting heads of embedded parts in nuclear power plants as described in claim 1, characterized in that, The steps of applying axial constraint to the unloaded end of the head to be upset and performing cooling treatment on the end of the head to be upset include: The unloaded end of the head to be upset is held in the upset head mold, and the axial positioning of the anchor bar is maintained to apply axial constraint to the end of the head to be upset. Circulating cooling water is introduced into the cavity wall of the upsetting mold to perform in-mold cooling on the end of the upsetting head; After the temperature at the end of the upsetting head drops to a preset demolding temperature, the upsetting head mold is removed. The preset demolding temperature is 300℃~400℃. After demolding, the ends of the anchor bars are air-cooled to ambient temperature.

8. The method for constructing hot-melt upsetting heads for embedded parts in nuclear power plants as described in claim 7, characterized in that, The step of circulating cooling water into the mold cavity wall of the upsetting mold to perform in-mold cooling on the end of the upsetting head includes: The temperature of the circulating cooling water is controlled at 20℃~35℃, and the water flow velocity is 1m / s~2m / s, so that the end of the head to be upset is cooled at a cooling rate of 5℃ / s~8℃ / s. During the first half of the in-mold cooling process, the axial constraint is maintained; In the latter half of the in-mold cooling process, the axial constraint is released, allowing the end of the head to be upset to shrink freely, in order to prevent residual tensile stress from being generated inside the formed upset head.

9. The construction method for hot-melt upsetting heads of embedded parts in nuclear power plants as described in claim 1, characterized in that, After the end of the anchor bar is formed into a upset head, the construction method for the hot-melt upset head of the nuclear power plant embedded parts further includes: Inspect the appearance of the formed upsetting head and discard any upsetting heads with surface cracks; The height and diameter of the upsetting head are measured. The height of a qualified upsetting head is 0.8 to 1.2 times the diameter of the anchor bar, and the diameter of a qualified upsetting head is 1.8 to 2.4 times the diameter of the anchor bar. The upsetting head is subjected to magnetic particle testing to detect whether there are cracks or defects on the surface and near the surface of the upsetting head.

10. The method for constructing hot-melt upsetting heads for embedded parts in nuclear power plants as described in claim 1, characterized in that, The embedded part includes multiple anchor bars, and the construction method for the hot-melt upsetting head of the embedded part in the nuclear power plant also includes: The upsetting operations of multiple anchor bars are organized in a continuous manner: while performing the cooling treatment on the nth anchor bar, the induction heating is performed on the (n+1)th anchor bar, where n is a positive integer; Multiple anchor bars share one upsetting mold, and the mold cavity of the upsetting mold is preheated to 150°C~250°C before each upsetting. After all the anchor bars of the pre-embedded parts have been upset, all upsets are uniformly inspected and numbered and registered.

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