Circuit breaker fastener assembly and disassembly method and system based on thermal phase locking

Abstract

The application provides a circuit breaker fastener assembly and disassembly method and system based on thermal phase locking, comprising an installation stage and a disassembly stage. The installation stage comprises: assembling a circuit breaker component and pre-tightening a threaded fastener, adjusting an opening distance and an overtravel to a standard value; performing first fastening by using a first preset torque T1; heating the threaded fastener to a target temperature T_target by using an electromagnetic induction heating device at a controllable heating rate to generate an accurate expansion gap; performing second fastening by using a second preset torque T2 within a thermal plasticity window period; and naturally cooling to form a permanent thermal interference fit. The disassembly stage comprises: cooling the threaded fastener to a target temperature T_remove by using a pre-cooled low-temperature medium at a rapid cooling rate to convert the interference fit into a gap fit; and achieving lossless disassembly. The application relates to the technical field of circuit breakers.

Description

Technical Field

[0001] This invention relates to the field of circuit breaker technology, and in particular to a method and system for assembling and disassembling circuit breaker fasteners based on thermal phase locking. Background Technology

[0002] In the field of high-voltage circuit breaker manufacturing, the stability of the opening distance and overtravel parameters directly determines the insulation performance and conductivity reliability of the equipment. The current mainstream installation process relies on mechanical fastening methods such as flat spring washers and self-locking nuts, which achieve the initial preload of the threaded pair through preset torque. The fundamental defect of this method is that it only relies on increasing friction to resist loosening, but cannot eliminate the gradual loosening of the threaded pair due to fretting wear under long-term vibration conditions. For example, according to the inventor's experimental data, flat spring washers usually begin to loosen after 500 vibrations and completely fail within 900 vibrations; self-locking nuts separate from the contact surface after 800 to 1000 vibrations, which cannot meet the high reliability requirements.

[0003] Therefore, existing mechanical fastening methods have two major drawbacks: firstly, they cannot effectively suppress micro-displacement between threaded pairs, leading to persistent fretting wear and requiring frequent downtime for maintenance; secondly, the disassembly process is prone to damaging the thread structure due to forced twisting (e.g., the thread breakage rate of thermal fasteners is as high as 100% during normal disassembly), which not only increases the cost of parts replacement but may also cause a chain of failures due to decreased installation accuracy. Patent searches also confirm that existing solutions, such as the quick-disassembly plastic-cased circuit breaker provided by CN218182145U and the circuit breaker mounting bar of an electrical cabinet provided by CN106785941B, only focus on disassembly efficiency or fault detection, and still fail to address the contradictory problems of loosening and damage from the physical level of changing the micro-fitting state of the threaded pairs.

[0004] Therefore, the inventors urgently need a method and system for assembling and disassembling circuit breaker fasteners based on thermal phase locking, which can fundamentally change the threaded pair mating relationship, eliminate the risk of vibration loosening, achieve non-destructive disassembly of the threaded pair, and ensure the lifelong stability of the circuit breaker's opening distance and overtravel parameters. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a method and system for assembling and disassembling circuit breaker fasteners based on thermal phase locking, aiming to solve the problems of circuit breaker fasteners being prone to loosening under long-term vibration conditions and damage to the threaded pairs during disassembly.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a method for assembling and disassembling circuit breaker fasteners based on thermally induced phase locking, comprising:

[0007] S1: Installation phase;

[0008] S11: Assemble the circuit breaker assembly and pre-tighten the threaded fasteners to a state where the opening gap and overtravel can be adjusted, and then adjust the opening gap and overtravel to the standard values.

[0009] S12: The threaded fastener that has been adjusted is tightened for the first time using a high-precision torque wrench with a first preset torque T1. The first preset torque T1 is the minimum torque value to ensure that the opening distance and overtravel remain stable during the vibration test.

[0010] S13: An electromagnetic induction heating device is used to heat the threaded fastener to the target fastening temperature T_target at a heating rate V1. At the same time, an infrared temperature sensor is used for real-time closed-loop feedback to ensure that the temperature fluctuation range does not exceed ±2℃. The target fastening temperature T_target is set based on the theoretical radial thermal expansion δ_theory of the threaded pair calculated based on the first equivalent model, which is equal to 50% to 70% of the standard tolerance zone width of the threaded fastener. The first equivalent model is established based on the coupling effect of material thermal expansion, thread microplastic flow and geometric structure and is used to calculate the theoretical radial thermal expansion δ_theory.

[0011] S14: Within the time window t_window after heating is completed, a second preset torque T2 is applied using the high-precision torque wrench to perform secondary tightening, wherein the second preset torque T2 = k×T1, k is the torque gain coefficient, and the value range is 0.9 to 1.1. The time window t_window is determined based on the heat capacity of the metal material of the threaded fastener and the environmental heat dissipation conditions to ensure that the secondary tightening is completed within the window period when the metal material is still in the maximum plastic flow period.

[0012] S15: After natural cooling to room temperature, the threaded pair forms a permanent thermally induced phase interference fit with an interference amount Δ;

[0013] S2: Disassembly stage;

[0014] S21: Using a low-temperature cooling device to pre-cool the low-temperature heat-conducting medium to below -30°C, the threaded fastener is cooled to the target disassembly temperature T_remove at a cooling rate V2. The target disassembly temperature T_remove is set based on the theoretical shrinkage deformation γ_theory calculated by the threaded pair based on the second equivalent model being greater than the interference amount Δ formed after installation. The second equivalent model is established based on the coupling effect of material shrinkage, interference fit stress release and geometric structure and is used to calculate the theoretical shrinkage deformation γ_theory.

[0015] S22: After the threaded fastener reaches the target disassembly temperature T_remove, the threaded fastener is removed without damage using the high-precision torque wrench.

[0016] Based on the above, the beneficial effects of a circuit breaker fastener assembly and disassembly method and system based on thermally induced phase locking are that it solves the problems of easy loosening of circuit breaker fasteners under long-term vibration conditions and easy damage to the threaded pair during disassembly; mainly reflected in:

[0017] 1. The present invention achieves precise temperature control heating through the combined action of steps S13 to S15 in the installation stage, using an electromagnetic induction heating device and an infrared temperature sensor to generate a controllable expansion gap. After the expansion gap is generated, a secondary fastening is performed in a highly plastic state, and a permanent interference fit is formed after cooling. This realizes the micro-locking of the threaded pair under long-term vibration conditions, effectively preventing fretting wear and preload attenuation, and solving the problem of easy loosening.

[0018] 2. The present invention uses low-temperature heat transfer medium and cooling control in steps S21 to S22 of the disassembly stage to transform the interference fit of the threaded pair into a clearance fit after cold shrinkage, thereby realizing the non-destructive disassembly of the threaded pair, avoiding thread damage caused by forced torsion, and solving the problem of easy damage during disassembly.

[0019] Furthermore, in step S13, the heating rate V1 is 5-10℃ / s, the target fastening temperature T_target is 120±5℃, the theoretical radial thermal expansion δ_theory is 0.0368mm, and the corresponding measured radial thermal expansion δ_actual is 0.03-0.035mm.

[0020] Based on the above, the beneficial effect of controlling the heating process within the range of 5 to 10℃ / s by the heating rate V1 is to ensure that the threaded fasteners can be heated quickly and uniformly; the beneficial effect of setting the target fastening temperature T_target to 120±5℃ is to make the theoretical radial thermal expansion δ_theory reach 0.0368mm.

[0021] Furthermore, in step S21, the cooling rate V2 is 8-15℃ / s, the target disassembly temperature T_remove is -20±5℃, the theoretical shrinkage deformation γ_theory is 0.048mm, and the shrinkage deformation is 0.04-0.045mm.

[0022] Based on the above, the beneficial effect of setting the cooling rate V2 in the range of 8 to 15℃ / s is to ensure that the threaded fasteners can be cooled to the target temperature quickly, effectively shortening the operation time and ensuring the uniformity of the cooling shrinkage effect; the beneficial effect of setting the target disassembly temperature T_remove to -20±5℃ is to ensure that the theoretical cooling shrinkage deformation γ_theory reaches 0.048mm, which is greater than the interference Δ formed by installation, thereby reliably converting the interference fit into a clearance fit.

[0023] Furthermore, in step S14, the torque gain coefficient k = 1.0, and the time window t_window is 20 seconds.

[0024] Furthermore, in step S15, the thermo-induced phase interference fit ensures that the preload attenuation rate of the threaded fastener is less than 5% after passing 1300 standard vibration tests.

[0025] Furthermore, in step S11, the threaded fastener includes a vacuum bubble upper end nut and a cam lower end nut.

[0026] Based on the above, the beneficial effect of the upper nut of the vacuum bulb is that the thermo-interference fit installation method achieves a stable connection between the vacuum bulb and the circuit breaker body, ensuring the positional stability of the vacuum bulb under vibration conditions; the beneficial effect of the lower nut of the cam is that the thermo-interference fit installation method achieves precise positional maintenance of the cam mechanism during long-term operation, avoiding changes in overtravel parameters caused by loosening.

[0027] This invention provides a system for assembling and disassembling circuit breaker fasteners based on thermal phase locking, comprising an electromagnetic induction heating device, an infrared temperature sensor, a high-precision torque wrench, a low-temperature cooling device, and a central controller. The electromagnetic induction heating device, the infrared temperature sensor, the high-precision torque wrench, and the low-temperature cooling device are respectively connected to the central controller. The central controller receives feedback signals from the infrared temperature sensor and dynamically controls the output power of the electromagnetic induction heating device to maintain the target fastening temperature T_target. The central controller receives temperature signals from the low-temperature cooling device and controls the cooling process until the target disassembly temperature T_remove is reached.

[0028] Based on the above, the benefits of the electromagnetic induction heating device are that it can quickly and accurately heat threaded fasteners to the target fastening temperature T_target, providing the necessary heat source for generating a controllable thermal expansion gap; the benefits of the infrared temperature sensor are that it can monitor the temperature of the threaded fasteners in real time and feed the signal back to the central controller, providing key temperature data for achieving closed-loop precise control of the heating process; the benefits of the high-precision torque wrench are that it can apply the first preset torque T1 and the second preset torque T2 during the installation stage, ensuring the accuracy and consistency of the tightening torque; the benefits of the low-temperature cooling device are that it can quickly cool the threaded fasteners to the target disassembly temperature T_remove during the disassembly stage, providing the necessary cold source for converting interference fits to clearance fits; the benefits of the central controller are that it can receive real-time temperature feedback from the infrared temperature sensor through a signal connection, and dynamically control the power output of the electromagnetic induction heating device to accurately maintain the target fastening temperature T_target. At the same time, the central controller also receives temperature signals from the low-temperature cooling device and controls the cooling process of the device until the target disassembly temperature T_remove is reached, thereby realizing automated and precise control of key parameters throughout the assembly and disassembly process.

[0029] Furthermore, the central controller has a built-in database that stores parameter groups for different specifications of threaded fasteners, including target fastening temperature T_target, time window t_window, heating rate V1, cooling rate V2, and target disassembly temperature T_remove.

[0030] Based on the above, the beneficial effect of the database is that it stores the optimized process parameter set for threaded fasteners of different specifications, enabling the central controller to quickly call the preset parameters to adapt to fasteners of different specifications, which greatly improves the versatility and operational efficiency of the method.

[0031] To make the above features of the present invention and the objectives to be achieved clearer, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the phased process of the thermal interference fit installation and cold shrinkage disassembly method for circuit breaker fasteners of the present invention.

[0033] Figure 2 : This is a flowchart of the installation phase of the present invention;

[0034] Figure 3 : This is a flowchart of the disassembly stage of the present invention;

[0035] Figure 4 : This is a schematic diagram of the normal fastening state of the present invention;

[0036] Figure 5 : This is a schematic diagram of the state after heating according to the present invention;

[0037] Figure 6 This is a schematic diagram of the cooled and tightened state of the present invention.

[0038] Figure 7 : This is a schematic diagram of the signal connection of the system of the present invention. Detailed Implementation

[0039] It should be noted that the "theoretical radial thermal expansion δ_theory" and "theoretical cold shrinkage deformation γ_theory" mentioned in this invention do not refer to the values ​​directly calculated from the basic linear expansion coefficient of the material, but are calculated based on the first equivalent model and the second equivalent model involved in this invention respectively. The first equivalent model and the second equivalent model are empirical models that fully consider the comprehensive factors such as the microscopic plastic deformation, stress redistribution and geometric structural effects of the threaded pair under rapid local heating / cooling conditions. Therefore, the theoretical values ​​(δ_theory, γ_theory) are significantly different from those calculated by simple linear expansion.

[0040] Specifically, the mathematical expression of the first equivalent model is:

[0041] δ_theory=[α1×d×(T_target - T_room)]+β×P×ln(T_target / T_room)

[0042] Where α1 is the equivalent linear expansion coefficient of the material during the heating process (obtained through experimental fitting, reflecting the influence of microscopic plastic flow), d is the nominal diameter of the thread, T_target is the target fastening temperature, T_room is the room temperature, β is the plastic flow coefficient of the thread teeth (obtained through regression from a large amount of vibration test data), and P is the pitch. This model introduces a logarithmic term to quantify the additional contribution of the microscopic plastic deformation of the thread teeth in the thermal state to radial expansion, thereby more accurately predicting the actual expansion gap.

[0043] The mathematical expression for the second equivalent model is:

[0044] γ_theory=[α2×d×(T_room - T_remove)] + η×Δ×(T_room - T_remove) / T_room

[0045] Where α2 is the equivalent linear shrinkage coefficient of the material during the cooling process (obtained through experimental fitting, reflecting the stress release effect), d is the nominal diameter of the thread, T_remove is the target disassembly temperature, T_room is the room temperature, η is the interference fit stress release coefficient (determined through disassembly experimental data), and Δ is the installation interference. This model accurately describes the elimination behavior of interference during the cooling shrinkage process through the combination of linear terms and stress release terms, ensuring that γ_theory > Δ.

[0046] The mathematical expressions for the first and second equivalent models are constructed following the general engineering modeling principle of "classical theoretical framework + experimental correction terms." The core of the model is based on recognized physical laws, while the correction terms are used to quantify the microscopic behavior of the threaded pair under rapid local thermal cycling, which cannot be accurately described by traditional theories. Specifically:

[0047] The expression for the first equivalent model, δ_theory=[α1×d×(T_target - T_room)]+β×P×ln(T_target / T_room), consists of two parts:

[0048] The first part is the basic linear thermal expansion term [α1×d×(T_target - T_room)]: This term originates from the classical physical formula for linear thermal expansion of materials, ΔL = L0×α×ΔT, where ΔL is the change in length of the object when the temperature changes by ΔT, L0 is the original length, and α is the linear expansion coefficient of the material. In the first equivalent model, the radial thermal expansion of the threaded pair is equivalent to the thermal expansion behavior of a characteristic length (taken as the nominal diameter d of the thread). Therefore, L0 in the classical formula is d, ΔT is (T_target - T_room), and the coefficient α1 is not the linear expansion coefficient in the standard material handbook, but the equivalent linear expansion coefficient, which is obtained through experimental fitting. The value not only reflects the basic thermal expansion properties of the material, but also includes the constraint and amplification effect of the specific geometric structure of the thread (such as the tooth angle and helix angle) on the overall radial expansion. This is an application and modification of the classical formula under specific complex structures.

[0049] The second part is the microscopic plastic flow correction term β×P×ln(T_target / T_room): The classical linear thermal expansion theory is only applicable to the ideal elastic deformation stage. However, when heated to T_target, the microscopic protrusions on the thread tooth surface will enter a plastic flow state due to stress concentration, resulting in additional irreversible radial deformation. This phenomenon cannot be described by linear theory. Therefore, based on regression analysis of a large amount of experimental data, this invention introduces this empirical correction. The logarithmic function form ln(T_target / T_room) is chosen to describe the saturation effect of plastic deformation slowing down with increasing temperature (similar to the nonlinear relationship of creep or plastic flow equations in materials science). β is the thread tooth plastic flow coefficient. The introduction of P (pitch) makes this term related to the microscopic geometric scale of the thread. This term together quantifies the additional radial expansion generated under the action of preload after the material yield strength decreases due to the increase in temperature.

[0050] The expression for the second equivalent model, γ_theory=[α2×d×(T_room - T_remove)] + η×Δ×(T_room - T_remove) / T_room, also consists of two parts:

[0051] The first part is the basic linear shrinkage term [α2×d×(T_room - T_remove)]: This term is also directly based on the above classical formula for linear thermal expansion and is used to calculate the amount of material shrinkage caused by a simple temperature drop. The formula is consistent with thermal expansion. The temperature change (T_room - T_remove) is negative, indicating shrinkage. Here, α2 is the equivalent linear shrinkage coefficient during the cooling process. It is fitted by cooling experimental data and includes the coupling effect of material shrinkage properties and thread geometry.

[0052] The second part is the interference stress release correction term η×Δ×(T_room - T_remove) / T_room: During disassembly and cooling, the threaded pair is in an interference fit state formed after installation, with huge contact stress. During the cooling process, due to the possible asynchronous shrinkage of the bolt and nut (affected by mass and heat dissipation conditions) and the change of the material's elastic modulus with temperature, the interference contact stress will be redistributed and released. This stress release process will contribute additional equivalent shrinkage. This effect is not considered by the classical shrinkage formula. Therefore, this empirical correction is introduced based on experiments. Here, η is the interference fit stress release coefficient, and Δ is the known interference amount. This correction term constructs a linear relationship proportional to the interference amount Δ and the relative temperature difference (T_room - T_remove) / T_room to quantify the additional deformation caused by the above stress release effect. This linear simplified model is widely used in engineering stress analysis to describe such coupling effects.

[0053] In summary, by introducing experimentally calibrated correction terms into the aforementioned classical theoretical framework, the two equivalent models of this invention achieve revolutionary and accurate prediction of the thermally induced deformation behavior of threaded pairs. The core advantage of this modeling method lies in its ability to quantify and utilize the microscopic plastic flow and stress release effect of the thread teeth during thermal cycling, rather than relying solely on macroscopic elastic deformation. This enables the method of this invention to precisely control the "expansion gap" formed during the installation stage and the "cold contraction gap" required during the disassembly stage, thereby fundamentally solving the long-standing technical contradiction between "reliable locking" and "non-destructive disassembly." Ultimately, it ensures the lifelong stability of the circuit breaker's core parameters (opening distance and overtravel) under extreme vibration conditions, while increasing the reusability and integrity rate of the threaded pairs to over 95%, achieving a level of reliability and economy unattainable by existing technologies.

[0054] See Figures 1-7 As shown,

[0055] This invention provides a method for assembling and disassembling circuit breaker fasteners based on thermally induced phase locking, characterized in that it includes:

[0056] S1: Installation phase;

[0057] S11: Assemble the circuit breaker assembly and pre-tighten the threaded fasteners to a state where the opening gap and overtravel can be adjusted, and then adjust the opening gap and overtravel to the standard values.

[0058] S12: The threaded fastener that has been adjusted is tightened for the first time using a high-precision torque wrench with a first preset torque T1. The first preset torque T1 is the minimum torque value to ensure that the opening distance and overtravel remain stable during the vibration test.

[0059] S13: An electromagnetic induction heating device is used to heat the threaded fastener to the target fastening temperature T_target at a heating rate V1. At the same time, an infrared temperature sensor is used for real-time closed-loop feedback to ensure that the temperature fluctuation range does not exceed ±2℃. The target fastening temperature T_target is set based on the theoretical radial thermal expansion δ_theory of the threaded pair calculated based on the first equivalent model, which is equal to 50% to 70% of the standard tolerance zone width of the threaded fastener. The first equivalent model is established based on the coupling effect of material thermal expansion, thread microplastic flow and geometric structure and is used to calculate the theoretical radial thermal expansion δ_theory.

[0060] S14: Within the time window t_window after heating is completed, a second preset torque T2 is applied using the high-precision torque wrench to perform secondary tightening, wherein the second preset torque T2 = k×T1, k is the torque gain coefficient, and the value range is 0.9 to 1.1. The time window t_window is determined based on the heat capacity of the metal material of the threaded fastener and the environmental heat dissipation conditions to ensure that the secondary tightening is completed within the window period when the metal material is still in the maximum plastic flow period.

[0061] S15: After natural cooling to room temperature, the threaded pair forms a permanent thermally induced phase interference fit with an interference amount Δ;

[0062] S2: Disassembly stage;

[0063] S21: Using a low-temperature cooling device to pre-cool the low-temperature heat-conducting medium to below -30°C, the threaded fastener is cooled to the target disassembly temperature T_remove at a cooling rate V2. The target disassembly temperature T_remove is set based on the theoretical shrinkage deformation γ_theory calculated by the threaded pair based on the second equivalent model being greater than the interference amount Δ formed after installation. The second equivalent model is established based on the coupling effect of material shrinkage, interference fit stress release and geometric structure and is used to calculate the theoretical shrinkage deformation γ_theory.

[0064] S22: After the threaded fastener reaches the target disassembly temperature T_remove, the threaded fastener is removed without damage using the high-precision torque wrench.

[0065] In this embodiment, the circuit breaker assembly is composed of a circuit breaker core component and threaded fasteners. The circuit breaker core component refers to the key component that realizes the mechanical operation of the circuit breaker opening and closing and the electrical function of arc extinguishing, such as the vacuum interrupter, cam mechanism, connecting rod, etc. The threaded fasteners refer to standard parts used to connect and tighten the above-mentioned core functional components. The threaded fasteners include the upper nut of the vacuum chamber and the lower nut of the cam.

[0066] In this embodiment, to verify the key parameters of the thermally induced phase-locking process, the inventors conducted a systematic comparative experiment. The experiment targeted M10 standard coarse-threaded fasteners, using different heating temperatures for installation, followed by standard vibration tests and disassembly inspections. The experimental results clearly showed that when the heating temperature was 70℃, the theoretical radial thermal expansion δ_theory was only 0.006mm, and the measured radial expansion δ_actual was less than 0.001mm, failing to effectively fill the thread tolerance zone. Its vibration resistance was comparable to existing technologies, and loosening occurred after approximately 500 cycles. When the heating temperature rose to... At 120℃, the theoretical radial thermal expansion δ_theory reaches 0.0368mm, and the measured radial expansion δ_actual is about 0.03mm. At this temperature, the fastener remains tight after 1300 vibration tests, and the thread integrity rate exceeds 95% after disassembly, representing a qualitative leap in technical performance. However, when the heating temperature is further increased to 170℃, although the theoretical radial thermal expansion δ_theory increases to 0.092mm, the mechanical properties of the metal material deteriorate due to overheating, the vibration resistance drops sharply to less than 300 cycles, and the thread damage rate exceeds 90%.

[0067] In this embodiment, in order to verify the system and determine the optimal installation process parameters, the inventors conducted a quantitative study. The specific experimental data is shown in Table 1. The data reveals the relationship between heating temperature, thermal expansion, vibration resistance and thread damage rate. More importantly, the data shows that there is a clear performance inflection point near 120°C. Its vibration resistance (≥1300 cycles) shows an order-of-magnitude improvement compared to the low temperature zone (70°C) and the high temperature zone (170°C), while the thread damage rate remains at an extremely low level (<5%).

[0068] Table 1: Verification Table of Hot Installation Process Parameters;

[0069]

[0070] Note: A preload attenuation rate of <5% is defined as "no loosening"; vibration test standards refer to GB / T 2423.10-2019.

[0071] In step S13 of this embodiment, the heating rate V1 is 5-10℃ / s, the target fastening temperature T_target is 120±5℃, the theoretical radial thermal expansion δ_theory is 0.0368mm, and the corresponding measured radial thermal expansion δ_actual is 0.03-0.035mm.

[0072] In this embodiment, a standard coarse thread M10 was used for the experiment, with a tolerance zone width of 0.06 mm. Through numerous experiments, this invention has found that when the theoretical radial thermal expansion δ_theory is controlled within 50% to 70% of the standard tolerance zone width of the thread, i.e., 0.03 mm to 0.042 mm, the most ideal "expansion gap" can be generated between the thread pairs. Through calculation and actual measurement, in order to achieve a theoretical radial thermal expansion δ_theory of 0.0368 mm (i.e., 60% of the tolerance zone width), the equivalent thermal expansion model of the thread pair established through numerous experiments shows that the corresponding ideal heating temperature range is 115℃~125℃. Therefore, T_target is determined to be 120±5℃.

[0073] In step S14 of this embodiment, the torque gain coefficient k=1.0 and the time window t_window is 20 seconds.

[0074] In this embodiment, the time window t_window is set to 20 seconds, which is crucial to ensure that the secondary tightening is completed within the "maximum plastic flow window" of the metal material. When the threaded fastener is heated to T_target, the yield strength of its metal material decreases significantly, its ductility increases, and it is in a highly plastic state. When torque is applied at this time, the metal on the thread tooth surface is more prone to micro-flow. Therefore, even if the second preset torque T2 is the same as the first preset torque T1 (i.e., torque gain coefficient k=1.0), a tighter micro-meshing can be achieved in the thermoplastic state than in the cold state. After cooling, a stable interference fit is formed, resulting in a deeper and tighter meshing. If the secondary tightening is done too early (e.g., within 5 seconds after heating), the internal temperature of the metal material may not be uniform. If it is done too late (e.g., more than 30 seconds), the temperature of the fastener has dropped significantly, reducing its plasticity and making it difficult to achieve the ideal phase-locking effect. Through monitoring with a thermal imager, it was determined that the time from stopping heating to the temperature dropping to the critical point where plasticity is significantly reduced (approximately 90°C) is about 25 seconds. To retain a safety margin and standardize the operation process, the optimal time window t_window is determined to be 20 seconds.

[0075] In step S15 of this embodiment, the thermo-induced phase interference fit ensures that the preload attenuation rate of the threaded fastener is less than 5% after passing 1300 standard vibration tests.

[0076] In this embodiment, the key to the disassembly stage is to ensure that the theoretical shrinkage deformation γ_theory is greater than the interference fit Δ formed after installation. Based on the installation stage parameters, the interference fit Δ is estimated to be approximately 0.025mm to 0.035mm. To ensure that the condition γ_theory > Δ is reliably met, and considering a certain safety margin, the target shrinkage deformation must reach at least 0.04mm. According to the calculation of the second equivalent model, the threaded fastener needs to be cooled to approximately -20°C to generate a theoretical shrinkage deformation γ_theory of 0.048mm. The corresponding measured shrinkage deformation γ_actual is approximately 0.04mm to 0.045mm, which is sufficient to reliably eliminate the interference fit.

[0077] In this embodiment, the feasibility of the non-destructive disassembly process was also rigorously verified through experiments. Key data are shown in Table 2. The experimental results confirm that the cooling temperature is not necessarily better the lower it is. When cooled to -20℃, the theoretical shrinkage deformation γ_theory (0.048mm) can effectively overcome the interference Δ and achieve near-perfect non-destructive disassembly (integrity rate ≥98%). However, when the temperature is further reduced to -40℃ or even -100℃, although the shrinkage deformation increases, the integrity rate of the threaded pair shows a downward trend due to the influence of the cold brittleness of the metal material. This data clearly indicates that controlling the target disassembly temperature T_remove within the range of -20±5℃ is the best choice to achieve the dual goals of safety and non-destructive disassembly.

[0078] Table 2: Verification Table of Cold Shrink Disassembly Process Parameters;

[0079]

[0080] In step S21 of this embodiment, the cooling rate V2 is 8-15℃ / s, the target disassembly temperature T_remove is -20±5℃, the theoretical shrinkage deformation γ_theory is 0.048mm, and the shrinkage deformation is 0.04-0.045mm.

[0081] The present invention also provides a system for assembling and disassembling circuit breaker fasteners based on thermal phase locking, comprising an electromagnetic induction heating device, an infrared temperature sensor, a high-precision torque wrench, a low-temperature cooling device, and a central controller. The electromagnetic induction heating device, the infrared temperature sensor, the high-precision torque wrench, and the low-temperature cooling device are respectively connected to the central controller. The central controller receives the feedback signal from the infrared temperature sensor and dynamically controls the output power of the electromagnetic induction heating device to maintain the target fastening temperature T_target. The central controller receives the temperature signal from the low-temperature cooling device and controls the cooling process until the target disassembly temperature T_remove is reached.

[0082] In this embodiment, the electromagnetic induction heating device is specifically a high-frequency induction heater with an output frequency of 50kHz. Its heating coil is specially designed according to the nut specifications to ensure heating efficiency and uniformity. The infrared temperature sensor is a Raytek MX4 type, with a measurement accuracy of ±1℃ and a response time of 1 millisecond. The high-precision torque wrench is a digital torque wrench with an accuracy level of ±1%. The cryogenic cooling device is a Dewar canister storing liquid nitrogen connected to a handheld spray gun. The central controller is a programmable logic controller, which dynamically adjusts the power output of the induction heater through a PID algorithm based on the real-time feedback from the infrared temperature sensor to control the target heating temperature T_target and the target disassembly temperature T_remove.

[0083] In this embodiment, the central controller has a built-in database that stores parameter groups for different specifications of threaded fasteners, including target fastening temperature T_target, time window t_window, heating rate V1, cooling rate V2, and target disassembly temperature T_remove.

[0084] In this embodiment, the database pre-stores optimized process parameter sets for four commonly used threaded fastener specifications: M6, M8, M10, and M12. For example, for M8 threaded fasteners, the parameter set is: T_target=110±5℃, t_window=18s, V1=5~8℃ / s, V2=8~12℃ / s, T_remove=-18±5℃. Operators only need to select the fastener specification to be operated through the human-machine interface of the central controller, and the system can automatically call the corresponding parameter set and control each device to run according to the preset process, which greatly improves the consistency and efficiency of operation and reduces the dependence on the operator's experience.

[0085] The above description is merely the optimal embodiment of the present invention and is not intended to limit the present invention. Any modifications or substitutions made by those skilled in the art without departing from the essence and scope of protection of the present invention should also be within the scope of protection of the present invention.

Claims

1. A method for assembling and disassembling circuit breaker fasteners based on thermally-induced phase locking, characterized in that, include: S1: Installation phase; S11: Assemble the circuit breaker assembly and pre-tighten the threaded fasteners to a state where the opening gap and overtravel can be adjusted, and then adjust the opening gap and overtravel to the standard values. S12: The threaded fastener that has been adjusted is tightened for the first time using a high-precision torque wrench with a first preset torque T1. The first preset torque T1 is the minimum torque value to ensure that the opening distance and overtravel remain stable during the vibration test. S13: An electromagnetic induction heating device is used to heat the threaded fastener to the target fastening temperature T_target at a heating rate V1. At the same time, an infrared temperature sensor is used for real-time closed-loop feedback to ensure that the temperature fluctuation range does not exceed ±2℃. The target fastening temperature T_target is set based on the theoretical radial thermal expansion δ_theory of the threaded pair calculated based on the first equivalent model, which is equal to 50% to 70% of the standard tolerance zone width of the threaded fastener. The first equivalent model is established based on the coupling effect of material thermal expansion, thread microplastic flow and geometric structure and is used to calculate the theoretical radial thermal expansion δ_theory. S14: Within the time window t_window after heating is completed, a second preset torque T2 is applied using the high-precision torque wrench to perform secondary tightening, wherein the second preset torque T2 = k×T1, k is the torque gain coefficient, and the value range is 0.9 to 1.

1. The time window t_window is determined based on the heat capacity of the metal material of the threaded fastener and the environmental heat dissipation conditions to ensure that the secondary tightening is completed within the window period when the metal material is still in the maximum plastic flow period. S15: After natural cooling to room temperature, the threaded pair forms a permanent thermally induced phase interference fit with an interference amount Δ; S2: Disassembly stage; S21: Using a low-temperature cooling device to pre-cool the low-temperature heat-conducting medium to below -30°C, the threaded fastener is cooled to the target disassembly temperature T_remove at a cooling rate V2. The target disassembly temperature T_remove is set based on the theoretical shrinkage deformation γ_theory calculated by the threaded pair based on the second equivalent model being greater than the interference amount Δ formed after installation. The second equivalent model is established based on the coupling effect of material shrinkage, interference fit stress release and geometric structure and is used to calculate the theoretical shrinkage deformation γ_theory. S22: After the threaded fastener reaches the target disassembly temperature T_remove, the threaded fastener is removed without damage using the high-precision torque wrench.

2. The method for assembling and disassembling circuit breaker fasteners based on thermal phase locking according to claim 1, characterized in that: In step S13, the heating rate V1 is 5-10℃ / s, the target fastening temperature T_target is 120±5℃, the theoretical radial thermal expansion δ_theory is 0.0368mm, and the corresponding measured radial thermal expansion δ_actual is 0.03-0.035mm.

3. The method for assembling and disassembling circuit breaker fasteners based on thermal phase locking according to claim 1, characterized in that: In step S21, the cooling rate V2 is 8-15℃ / s, the target disassembly temperature T_remove is -20±5℃, the theoretical shrinkage deformation γ_theory is 0.048mm, and the shrinkage deformation is 0.04-0.045mm.

4. The method for assembling and disassembling circuit breaker fasteners based on thermal phase locking according to claim 1, characterized in that: In step S14, the torque gain coefficient k = 1.0, and the time window t_window is 20 seconds.

5. The method for assembling and disassembling circuit breaker fasteners based on thermal phase locking according to claim 1, characterized in that: In step S15, the thermo-induced phase interference fit ensures that the preload attenuation rate of the threaded fastener is less than 5% after passing 1300 standard vibration tests.

6. The method for assembling and disassembling circuit breaker fasteners based on thermal phase locking according to claim 1, characterized in that: In step S11, the threaded fastener includes a nut at the upper end of the vacuum bubble and a nut at the lower end of the cam.

7. A system for implementing the thermally-induced phase-locked circuit breaker fastener assembly and disassembly method according to any one of claims 1-6, characterized in that: The device includes an electromagnetic induction heating device, an infrared temperature sensor, a high-precision torque wrench, a low-temperature cooling device, and a central controller. The electromagnetic induction heating device, the infrared temperature sensor, the high-precision torque wrench, and the low-temperature cooling device are respectively connected to the central controller. The central controller receives the feedback signal from the infrared temperature sensor and dynamically controls the output power of the electromagnetic induction heating device to maintain the target fastening temperature T_target. The central controller receives the temperature signal from the low-temperature cooling device and controls the cooling process until the target disassembly temperature T_remove is reached.

8. The system according to claim 7, characterized in that: The central controller has a built-in database that stores parameter groups for different specifications of threaded fasteners, including target fastening temperature T_target, time window t_window, heating rate V1, cooling rate V2, and target disassembly temperature T_remove.

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