Hydraulic nut applied to nuclear power working condition

Abstract

The application discloses a hydraulic nut applied to nuclear power working conditions, which comprises a hydraulic cylinder, a piston and a locking nut, an oil cavity of the hydraulic cylinder is connected with an external pump station through a flow channel, the piston is located in the oil cavity of the hydraulic cylinder and is in sliding connection with the hydraulic cylinder, the piston is of an annular structure and is provided with an inner thread and an outer thread, the piston is connected with a bolt through the inner thread, the piston is connected with the locking nut through the outer thread, the hydraulic nut further comprises a laser ranging module and a processor for analyzing and processing multiple groups of data monitored by the hydraulic nut, and the laser ranging module is connected with the processor and is controlled by the processor. The hydraulic nut disclosed by the application realizes real-time monitoring of the hydraulic nut through the laser ranging module, the processor and a pre-tightening force monitoring method for monitoring the hydraulic nut in real time, the frequency of workers entering a radiation area for work is greatly reduced, the connection stability between flanges is ensured, and the life safety of the workers is ensured.

Description

Technical Field

[0001] This invention relates to the field of hydraulic nuts, and more particularly to a hydraulic nut applicable to nuclear power plant conditions. Background Technology

[0002] Hydraulic nuts are used for bolts that require frequent disassembly and assembly; pre-tightening of extra-large bolts; and locking of large workpieces. For example, in nuclear power engineering. Their principle is to use ultra-high pressure oil to generate a thrust on the shaft and a tension on the bushing, thus evenly connecting the shaft and bushing together.

[0003] Due to the compact working conditions and limited space in nuclear power engineering, using mechanical nuts would be difficult because the installation and removal of the nuts would require a large space, making pre-tightening challenging. Therefore, hydraulic nuts are more suitable. Nuclear power plants operate in high-temperature environments and generate mechanical vibrations during operation, which can easily cause the connecting nuts to loosen. Furthermore, given the special nature of nuclear power engineering, radiation is often present, preventing frequent maintenance as it could affect the health of workers. Therefore, hydraulic nuts require excellent thermal stability and sealing properties, ensuring their operation for 50 years.

[0004] Furthermore, hydraulic nuts are suitable for connecting large flanges in nuclear power engineering. If the hydraulic nut loosens due to mechanical vibration or other factors, it will lead to insufficient bolt preload, loosening of the connection between flanges, and ultimately, leakage of materials from the pipeline, causing very serious consequences and irreparable damage to life and property. Therefore, after tightening the hydraulic nut, the preload of the hydraulic nut needs to be monitored in real time. The hydraulic nut mainly consists of three parts: a hydraulic cylinder, a piston, and a locking nut. The piston is located inside the hydraulic cylinder and is slidably connected to it. The piston has internal and external threads; it connects to the bolt through the internal thread and to the locking nut through the external thread. The operation steps of the hydraulic nut are as follows: Step 1: Use ultra-high pressure oil to push the piston located in the hydraulic cylinder to directly apply external force to the bolt, so that the bolt under force is stretched in its elastic deformation zone; Step 2: After the bolt is stretched, tighten the lock nut. This will lock the bolt in the stretched position, and then the hydraulic cylinder will be depressurized, allowing the hydraulic oil to flow back into the pump station.

[0005] In the actual use of hydraulic nuts, there is a certain gap in the threaded connection between the locking nut and the piston.

[0006] In step 1 above, the bolt is stretched to the length that just meets the preload. When the hydraulic cylinder is depressurized, the bolt will retract because the hydraulic cylinder is under negative pressure and there is a gap between the locking nut and the piston. This results in the actual preload being less than the preset preload, reducing the locking accuracy and making the locking unreliable.

[0007] Meanwhile, when the hydraulic nut is placed on the plane of the fastener to be fastened during use, the bottom surface of the hydraulic nut is parallel to the plane of the fastener, and the bolt hole in the hydraulic nut is perpendicular to the plane. However, the bolt used for connection cannot achieve an absolutely perpendicular state to the plane. In actual use, there may be uneven force on the hydraulic nut and bolt during locking, which not only affects the locking effect, but may also damage the threads on the hydraulic nut and bolt. Summary of the Invention

[0008] The purpose of this invention is to construct a hydraulic nut for use in nuclear power plants, based on existing hydraulic nuts and the need to ensure reliable preload and monitor in real time whether the hydraulic nut has loosened.

[0009] A hydraulic nut for use in nuclear power plants includes a hydraulic cylinder, a piston, and a locking nut. The oil chamber of the hydraulic cylinder is connected to an external pump station through a flow channel. The piston is located in the oil chamber of the hydraulic cylinder and is slidably connected to the hydraulic cylinder. The piston has an annular structure and is provided with internal and external threads. The piston is connected to a bolt through the internal thread and to the locking nut through the external thread. The hydraulic nut is characterized in that it further includes a laser ranging module for monitoring the distance from the contact surface between the hydraulic nut and the flange to the top surface of the bolt, and a processor for analyzing and processing multiple sets of data monitored by the hydraulic nut, wherein the laser ranging module is connected to and controlled by the processor.

[0010] To prevent nuclear leaks due to insufficient flange preload, it is necessary to monitor the preload of the hydraulic nut in real time. A method for monitoring the preload of the hydraulic nut is proposed below: When a bolt is subjected to axial tension or compression, its main deformation is a change in its axial dimension, while its transverse dimension also changes. Let the original length of the bolt be L, and the length after deformation be L1, then the axial deformation of the bolt is L. ’ , L ’ = L1-L; Under equal axial tensile force, bolts of different original lengths will have different axial deformation values. Therefore, axial deformation cannot accurately express the degree of bolt deformation. When a bolt is under tension, the axial deformation of each longitudinal restraint is equal, and the deformation is almost uniformly distributed along the axial direction. Therefore, the axial linear strain is ε. ε= L ’ / L, According to Hooke's Law, the normal stress δ is proportional to the linear strain ε, and its expression is δ = Eε. E is the tensile modulus of elasticity of a material. The larger the E value of a material, the more difficult it is to be stretched or compressed. It expresses the material's ability to resist elastic deformation under tension and compression. For a bolt subjected to tension, we have δ=F N / A, F N Let L be the axial force borne by the bolt, A be the cross-sectional area of ​​the bolt, and ε = L. ’ / L, δ=F N / A and ε= L ’ Substituting / L into δ=Eε, we get L ’ = F N L / EA, when the stress does not exceed the proportional limit of the material, is the axial deformation L of the bolt. ’ With axial force F N It is directly proportional to the original length L of the bolt, and inversely proportional to the cross-sectional area A; To monitor and analyze in real time whether the hydraulic nut is loose, follow these steps: (1) Before the bolt is stretched, the average distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is measured to be d1. After the bolt is stretched and the hydraulic nut is tightened, the average distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is measured to be d2. The length of the bolt after stretching is L1 = L + (d2 - d1); Then L ’ = L1-L, from the formula L ’ = F N L / EA can produce F N =EAL ’ / L, E, A, L ’ After substituting the values ​​of L, etc., the axial force F of the bolt can be calculated. N Let F be the value of F. N =a, axial force F of the bolt N The bolt preload F is equal to that when the hydraulic nut is tightened; (2) The axial deformation L of the bolt in the tightened state ’ Assigning a marker point will mark the axial deformation L. ’ Let L be the initial value for the axial deformation. ’ Assign a value, assign a value of 0. And axial force F N A marker point is then assigned to mark the axial force F. N Let F be the initial value of the axial force. N The value is assigned to 0. (3) The distance from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is monitored in real time by the laser ranging module. The distance value obtained by the laser ranging module is recorded as d3. Then, the axial deformation L of the bolt at this time is... ” = d2 - d3, L ” Substitute into formula L ’ = F N L / EA can produce F N ’ =EAL ” / L, where E, A, L, etc. are constants, the axial force F of the bolt can be calculated. N ’ Let F be the value of F. N ’ =b, axial force F of the bolt N ’ The preload force F of the hydraulic nut is equal to that at this time; (4) Take the axial force F during tightening. N With the monitored axial force F N ’ The difference X, X=F N -F N ’ The difference X is compared with the preset preload range of the hydraulic nut. If the difference X is greater than the preset preload range of the hydraulic nut, it is determined that the hydraulic nut needs to be retightened. If the difference X is less than the preset preload range of the hydraulic nut, it is determined that the hydraulic nut does not need to be retightened. (5) Take the results of the judgment on whether the hydraulic nut needs to be retightened from multiple time points within a certain period of time, and analyze them. If the judgment that the hydraulic nut needs to be retightened is an individual result, then the hydraulic nut does not need to be retightened. If the judgment that the hydraulic nut needs to be retightened is not an individual result, then the hydraulic nut needs to be retightened.

[0011] Furthermore, the specific implementation steps of the method for real-time monitoring of the preload of hydraulic nuts are as follows: (1) Given that the original length L of the bolt is 7000 mm, the tensile modulus E of the composite steel material is 206 GPa, and the cross-sectional area A of the bolt is 816.7 mm², 2 Input to the processor, The distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt before bolt tension is measured using a laser ranging module. Five sets of values ​​are obtained and transmitted to the processor, and the average value d1 is taken. The distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt was measured using a laser ranging module after the bolt tension was measured and the hydraulic nut was tightened. Five sets of values ​​were obtained and transmitted to the processor, and the average value d2 was taken. The processor calculates that the length of the stretched bolt L1 = L + (d2 - d1). (2) Based on formula L ’ = L1-L and formula L ’ = F N L / EA's derived formula F N =EAL ’ / L, calculated by the processor, the axial force F of the bolt. N Let F be the value of F. N =a, axial force F of the bolt N The bolt preload F is equal to that when the hydraulic nut is tightened; (3) In the processor, the axial deformation L of the bolt in the tightened state is given. ’ Assigning a marker point will mark the axial deformation L. ’ Let L be the initial value for the axial deformation. ’ Assign a value, assign a value of 0. And axial force F N A marker point is then assigned to mark the axial force F. N Let F be the initial value of the axial force. N The value is assigned to 0. (4) The distance from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is monitored in real time by the laser ranging module. The distance value monitored by the laser ranging module is recorded as d3. The laser ranging module feeds back the distance value d3 to the processor for analysis and processing. Then, the axial deformation L of the bolt at this time is... ” = d3 - d1, The axial deformation L of the bolt at this time ” Substitute into formula L ’ = F N L / EA's derived formula F N =EAL ’ / L, the axial force F of the bolt can be calculated. N ’ Let F be the value of F. N ’ =b, axial force F of the bolt N ’ The preload force F of the hydraulic nut is equal to that at this time; (5) Take the axial force F during tightening. N With the monitored axial force F N ’ The difference X, X=F N -F N ’The difference X is compared with the preset variable value of the preload of the hydraulic nut. If the difference X is greater than the preset variable value of the preload of the hydraulic nut, it is determined that the hydraulic nut needs to be retightened. If the difference X is less than the preset variable value of the preload of the hydraulic nut, it is determined that the hydraulic nut does not need to be retightened. (6) Take the results of the judgment on whether the hydraulic nut needs to be retightened at 10 time points within a certain period of time, and analyze them. If the judgment that the hydraulic nut needs to be retightened is an individual result, then the hydraulic nut does not need to be retightened. If the judgment that the hydraulic nut needs to be retightened is not an individual result, then the hydraulic nut needs to be retightened.

[0012] Furthermore, the laser ranging module is a laser rangefinder.

[0013] Furthermore, the piston has a slot at an upper position. The slot is arc-shaped, and the perpendicular bisector of the slot passes through the midpoint of the cross-section of the piston at that position. The piston also has a screw hole, which is vertically positioned and passes through the slot. The screw hole is located on the perpendicular bisector of the slot, and a self-locking bolt is installed inside the screw hole. The self-locking bolt presses down the piston above the slot, causing deformation of the piston's external thread at the pressed position. This reduces the gap between the piston and the locking nut, reduces piston retraction when the hydraulic cylinder depressurizes, thereby improving locking accuracy and further reducing loosening of the hydraulic nut during use, thus increasing the service life of the hydraulic nut.

[0014] The screw hole is located on the vertical line of the slot, so that the self-locking part of the piston is subjected to balanced force on both sides of the vertical line.

[0015] The hydraulic cylinder is provided with a base below it. The upper end surface of the base is a concave spherical surface, and the lower end surface of the hydraulic cylinder is a convex spherical surface. The upper end surface of the base and the lower end surface of the hydraulic cylinder cooperate with each other, and the hydraulic cylinder is movably mounted on the base. An off-center load of ±1° is applied between the hydraulic cylinder and the base to ensure that the compressive load is perpendicular to the working axis.

[0016] The hydraulic cylinder and the piston can move on the base at the angle of the bolt, so that the hydraulic nut coincides with the axis of the bolt, ensuring that the bolt is subjected to uniform force.

[0017] The base has a through hole, and the diameter of the through hole is larger than the diameter of the bolt.

[0018] The thread used to connect the locking nut and the piston is a sawtooth thread. During rotation, the sawtooth shape generates friction with the surface of the mating parts, thereby increasing the thread's tightness and sealing performance. Furthermore, the sawtooth thread prevents loosening or dislodging, improving its service life and stability.

[0019] Relatively commonly, pipe threads are used for connection in hydraulic nuts. However, the threads of pipe threads are more prone to deformation than those of sawtooth threads, and the gap between the internal and external threads after engagement is also larger. Therefore, when depressurizing hydraulic nuts, sawtooth threads have a better anti-loosening effect and a better pre-tightening effect.

[0020] Furthermore, the bow shape includes a chord and an arc. Let the midpoint a of the chord be 'a' and the midpoint b of the arc be 'b', and the straight line connecting points a and b be 'x'. Let the thickness of one side of the piston wall be 'h', and the radius of the piston cross-section be 'r'. h < r < x < 2r - h.

[0021] The piston used in the self-locking part will not have poor anti-loosening effect due to too small locking area, nor will the piston break due to too large groove.

[0022] Furthermore, the slot is set horizontally.

[0023] Furthermore, the rotation center line of the self-locking bolt is parallel to the rotation center line of the piston, and the rotation center line of the self-locking bolt is perpendicular to the horizontal plane of the slot.

[0024] Furthermore, the hydraulic cylinder is provided with an oil chamber and a linkage chamber, the oil chamber is connected to the linkage chamber, the oil chamber is located above the linkage chamber, and the diameter of the oil chamber is larger than the diameter of the linkage chamber.

[0025] Furthermore, the piston includes an upper part and a lower part, with the diameter of the upper part being larger than that of the lower part. A sliding member is provided on the outer side of the upper part of the piston, and the sliding member is slidably connected to the inner wall of the oil chamber. The external thread of the piston is provided on the outer side of the upper part of the piston, and the external thread of the piston is located above the sliding member. The lower part of the piston is slidably connected to the linkage chamber. The piston has a through-hole in the middle, and the internal thread is formed on the wall of the through-hole. The diameter of the through-hole is equal to the diameter of the bolt. The piston has a groove, which is connected to the flow channel.

[0026] Furthermore, a sealing element, which is a V-shaped spring accumulator, is provided below the sliding member. Compared with the common O-ring seal, the V-shaped spring accumulator has a better sealing effect and a longer service life, guaranteeing a service life of 50 years.

[0027] Furthermore, the locking nut is provided with several connection holes for connecting a tightening tool.

[0028] Hydraulic nuts are commonly used for locking large workpieces, such as in nuclear power engineering. Due to the compact working conditions and limited space in nuclear power projects, using mechanical nuts would require disassembling the equipment for maintenance, making maintenance difficult. Therefore, hydraulic nuts are more suitable, as they only require connecting a hydraulic pump to detect whether the nut is loose. Furthermore, nuclear power engineering places high performance requirements on hydraulic nuts, necessitating testing.

[0029] The above-mentioned hydraulic nut will now undergo a thermal cycling test, and the specific plan is as follows: Step 1: Apply oil pressure to the hydraulic nut step by step using the hydraulic pump. Record the axial force value obtained at each stage when the oil pressure increases from 0 to 100 MPa and the increase is 10 MPa. Calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. At the same time, check whether there is any oil leakage at the hydraulic hose connection and whether the hydraulic nut exceeds the stroke requirement. Step 2: After reaching the highest pressure of 100MPa, tighten the self-locking hydraulic nut and the self-locking bolt. Record the axial force values ​​before and after removing the hydraulic pump in the stopped state. Calculate the oil pressure value by using the conversion formula between axial force and oil pressure. Step 3: Place the hydraulic nut and the supporting testing equipment into an oven (hot air circulating oven). First, heat the hydraulic nut in the oven, then place the hydraulic nut to room temperature. Repeat the heating and cooling process to perform multiple cyclic tests on the hydraulic nut. Step 4: Analyze the test data to verify the thermal stability of the hydraulic nut and ensure the mechanical properties of the hydraulic nut remain stable in complex temperature environments.

[0030] The conversion formula between axial force and hydraulic pressure is: Hydraulic pressure (MPa) = [axial force (kN) / G + f] / S × G / 1000; G is the acceleration due to gravity, G = 9.8 N / kg, f is the estimated frictional force, f = 2 N, and S is the area of ​​contact, S = 0.04 m². 2 1000 is the coefficient.

[0031] Furthermore, the hydraulic nut in step 3 above is heated and cooled according to the following steps: (1) Heat the hydraulic nut at a rate of 2℃ / min. When the temperature of the hydraulic nut reaches 200℃, keep it at that temperature for 1 hour, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. After the temperature cools down to room temperature, keep it at that temperature for 2 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. (2) Heat the hydraulic nut at a rate of 1℃ / min. When the temperature of the hydraulic nut reaches 200℃, keep it at that temperature for 2 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. After the temperature cools down to room temperature, keep it at that temperature for 2 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. (3) Heat the hydraulic nut at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reaches 200℃, keep it at that temperature for 0.5 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. After the temperature cools down to room temperature, keep it at that temperature for 1 hour, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. (4) Heat the hydraulic nut at a rate of 2℃ / min. When the temperature of the hydraulic nut reaches 200℃, keep it warm for 3 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. After the temperature cools down to room temperature, keep it warm for 1 hour, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value.

[0032] The heating and cooling process of the hydraulic nut described above is one cycle in a thermal cycling test of the hydraulic nut. A single cycle consists of four heating and cooling steps. The number of heating and cooling steps in a single cycle can be varied.

[0033] The heating rate of the hydraulic nut, the holding time when the hydraulic nut reaches 200℃, and the holding time when the temperature cools down to room temperature can all be modified during the heating and cooling process of the hydraulic nut. The purpose is to simulate the ambient temperature change of the hydraulic nut during use and make the test results more accurate.

[0034] Furthermore, the hydraulic nut is made of non-magnetic material, which ensures the mechanical properties of the hydraulic nut.

[0035] The beneficial effects of this invention are as follows: The hydraulic nut disclosed in this application, applied to nuclear power plant conditions, can achieve real-time monitoring of the hydraulic nut's preload using a laser ranging module, a processor, and a method for real-time monitoring of the hydraulic nut's preload. This significantly reduces the frequency of workers entering radiation areas, ensuring stable connections between flanges and worker safety. Furthermore, the self-locking bolt can press down the piston above the slot, causing deformation of the piston's external thread at the pressed position. The piston's external thread uses a sawtooth thread, reducing the gap between the piston and the locking nut, minimizing piston retraction during hydraulic cylinder depressurization, thus improving locking accuracy, preventing loosening of the hydraulic nut during use, and increasing its service life. The screw hole is positioned on the vertical line of the slot, ensuring balanced force on the piston at the pressed position. Simultaneously, the hydraulic cylinder and piston can move on the base at the angle of the bolt, aligning the hydraulic nut and bolt's axis, ensuring uniform bolt force, further guaranteeing reliable locking, and preventing damage to the bolt and hydraulic nut's threads. Conducting thermal cycling tests on hydraulic nuts allows for a direct understanding of their mechanical properties, ensuring their suitability for use in nuclear power projects.

[0036] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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 these drawings without creative effort. Figure 1 This is a schematic diagram of the overall structure of a specific example of the hydraulic nut of the present invention; Figure 2 yes Figure 1 A schematic diagram of the cross-sectional structure; Figure 3 This is a schematic diagram of the hydraulic cylinder in a specific example of the hydraulic nut of the present invention; Figure 4 This is a schematic diagram of the piston structure in a specific example of the hydraulic nut of the present invention; Figure 5 yes Figure 2 Enlarged view of the structure at point A in the middle; Figure 6 This is a schematic diagram of the locking nut structure in a specific example of the hydraulic nut of the present invention; Figure 7 This is a cross-sectional structural diagram of the base in a specific embodiment of the hydraulic nut of the present invention; Figure 8 This is a cross-sectional structural diagram of the piston at the slot in a specific embodiment of the hydraulic nut of the present invention; in the figure: 101, base; 102, hydraulic cylinder; 103, interface; 104, piston; 105, locking nut; 106, connecting hole; 107, through hole; 109, linkage cavity; 110, flow channel; 111, oil cavity; 112, self-locking bolt; 113, screw hole; 114, slot; 115, sliding member; 117, connecting hole; 120, annular groove; 121, V-shaped spring energy storage ring. Detailed Implementation

[0038] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0039] The self-locking anti-loosening universal hydraulic nut of the present invention will be further described with reference to the accompanying drawings.

[0040] like Figure 1 and Figure 2 As shown, the hydraulic nut described in this embodiment is made of non-magnetic material. The hydraulic nut includes a base 101, a hydraulic cylinder 102, a piston 104, and a locking nut 105. The hydraulic cylinder 102 is located above the base 101 and is connected to a hydraulic oil interface 103. The hydraulic cylinder 102 is connected to an external pump station through the interface 103. The piston 104 is located inside the hydraulic cylinder 102 and is slidably connected to the hydraulic cylinder 102. The piston 104 is threadedly connected to the locking nut 105 and is provided with a self-locking bolt 112.

[0041] like Figure 2 and Figure 3 As shown, the hydraulic cylinder 102 is provided with an oil chamber 111 and a linkage chamber 109, which are connected. The diameter of the oil chamber 111 is larger than the diameter of the linkage chamber 109, and the oil chamber 111 is located above the linkage chamber 109. The hydraulic cylinder 102 is provided with a flow channel 110, which includes a horizontal section and a vertical section. The horizontal section of the flow channel 110 is connected to the interface 103, and the vertical section of the flow channel 110 is connected to the oil chamber 111. The horizontal and vertical sections of the flow channel 110 are interconnected. The lower end face of the hydraulic cylinder 102 is a downwardly convex spherical surface.

[0042] like Figure 2 and Figure 7As shown, the upper end surface of the base 101 is a downwardly concave spherical surface. The lower end surface of the hydraulic cylinder 102 corresponds to and fits the upper end surface of the base 101. The hydraulic cylinder 102 is movably mounted on the base 101. The middle part of the base 101 is provided with a through hole 107 that runs vertically through the base. The diameter of the through hole 107 is larger than the diameter of the bolt. The through hole 107 is connected to the linkage cavity 109.

[0043] like Figure 2 and Figure 4 As shown, piston 104 includes an upper part and a lower part, the diameter of the upper part is larger than the diameter of the lower part, the piston 104 has a through connecting hole 106 in the middle, the connecting hole 106 has an internal thread on the hole wall, the internal thread is used to connect with a bolt, and the diameter of the connecting hole 106 is equal to the diameter of the bolt, the piston 104 has an external thread on the outer side of the upper part, the external thread is used to connect with a lock nut 105.

[0044] The thread used to connect the locking nut 105 and the piston 104 is a sawtooth thread. The sawtooth thread includes a first thread surface and a second thread surface. The first thread surface forms a 3° angle with the rotating shaft (the rotating shaft is the straight line where the center line of the rotating shaft of the locking nut is located), and the second thread surface forms a 30° angle with the rotating shaft.

[0045] The lower part of piston 104 is slidably connected to linkage chamber 109.

[0046] A slot 114 is provided at the upper part of the piston 104. The slot 114 is horizontally set. The piston 104 is also provided with a screw hole 113. The screw hole 113 is vertically set and passes through the slot 114. A self-locking bolt 112 is set at the screw hole 113.

[0047] like Figure 2 and Figure 5 As shown, a sliding member 115 is provided on the outer side of the piston 104. The sliding member 115 is slidably connected to the inner wall of the oil chamber 111. The external thread on the piston 104 is located above the sliding member 115. A V-shaped spring energy storage ring 121 is provided below the sliding member 115.

[0048] The lower end face of the upper part of the piston 104 is provided with an annular groove 120, which is connected to the flow channel 110.

[0049] like Figure 2 and Figure 8 As shown, the slot 114 is arc-shaped, which includes a chord and an arc. The midpoint a of the chord and the midpoint b of the arc are drawn. The straight line obtained by connecting the two points a and b is x. The straight line x is the perpendicular bisector of the arc, that is, the straight line x is the perpendicular bisector of the slot 114. The perpendicular bisector passes through the midpoint O of the cross section of the piston 104. The aforementioned screw hole 113 is set on this perpendicular bisector.

[0050] Let the thickness of the single-sided wall of piston 104 be h, and the radius of the cross-section of piston 104 be r, where h < r < x < 2r - h.

[0051] like Figure 6 As shown, the locking nut 105 has six connection holes 117 for connecting a tightening tool.

[0052] When using hydraulic nuts to install bolts a. The hydraulic nut is connected to the bolt through the internal thread on the piston 104. The piston 104 located in the hydraulic cylinder 102 is pushed by ultra-high pressure oil, so that the bolt under force is stretched in its elastic deformation zone. b. Tighten the lock nut 105 to lock the bolt in the stretched position; c. Tighten the self-locking bolt 112 to press down the piston 104 above the slot 114. The external thread at the pressing point will be displaced and deformed, which will reduce the gap between the external thread and the internal thread of the locking nut 105. After the hydraulic cylinder 102 is depressurized, the retraction of the piston 104 will also be reduced.

[0053] If the centerline of the installed bolt is not perpendicular to the lower end face of the hydraulic nut, the hydraulic cylinder 102 will move on the base 101, causing the centerline of the piston 104 to coincide with the centerline of the bolt.

[0054] The hydraulic nut also includes a laser rangefinder for monitoring the distance from the contact surface between the hydraulic nut and the flange to the top surface of the bolt, and a processor for analyzing and processing multiple sets of data monitored by the hydraulic nut. The laser rangefinder is connected to and controlled by the processor.

[0055] To prevent nuclear leaks due to insufficient flange preload, the following method for real-time monitoring of hydraulic nut preload is proposed: (1) Given that the original length L of the bolt is 7000 mm, the tensile modulus E of the composite steel material is 206 GPa, and the cross-sectional area A of the bolt is 816.7 mm², 2 Input to the processor, The distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt before tensioning was measured using a laser rangefinder. Five sets of values ​​were obtained and transmitted to the processor. The five sets of values ​​were 55.86mm, 55.84mm, 55.86mm, 55.87mm, and 55.85mm, respectively. The average value d1 was taken as 55.86mm. The distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt was measured using a laser ranging module after the bolt was stretched and the hydraulic nut was tightened. Five sets of values ​​were obtained and transmitted to the processor. The five sets of values ​​were 72.51mm, 72.52mm, 72.50mm, 72.54mm, and 72.51mm, respectively. The average value d2 was taken as 72.52mm. The processor calculates that the length of the stretched bolt L1 = L + (d2 - d1), L1 = 7016.66 mm; (2) Based on formula L ’ = L1-L and formula L ’ = F N L / EA's derived formula F N =EAL ’ / L, calculated by the processor, the axial force F of the bolt. N The value of F N =400.41N, axial force F of the bolt N The bolt preload F is equal to that when the hydraulic nut is tightened; (3) In the processor, the axial deformation L of the bolt in the tightened state is given. ’ Assigning a marker point will mark the axial deformation L. ’ Let L be the initial value for the axial deformation. ’ Assign a value, assign a value of 0. And axial force F N A marker point is then assigned to mark the axial force F. N Let F be the initial value of the axial force. N The value is assigned to 0. (4) The distance from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is monitored in real time by a laser rangefinder. The distance value monitored by the laser rangefinder module is recorded as d3 = 70.58 mm. The laser rangefinder module feeds back the distance value d3 to the processor for analysis and processing. Then, the axial deformation L of the bolt at this time is... ” = d3- d1, L ” =14.72mm, The axial deformation L of the bolt at this time ” Substitute into formula L ’ = F N L / EA's derived formula F N =EAL ’ / L, the axial force F of the bolt can be calculated. N ’ The value of F N ’ =353.79N, axial force F of the bolt N ’ The preload force F of the hydraulic nut is equal to that at this time; (5) Take the axial force F during tightening. N With the monitored axial force F N ’ The difference X, X=F N -F N ’If X = 46.62N, then compare the obtained difference X with the preset variable value of the hydraulic nut's preload. The preset variable value of the hydraulic nut's preload is 40N. Since the difference X is greater than the preset variable value of the hydraulic nut's preload, it is determined that the hydraulic nut needs to be retightened. (6) Take the difference X obtained at 10 time points within a certain period of time, which are 46.62N, 45.58 N, 44.73N, 45.39 N, 43.81N, 43.26 N, 46.80 N, 46.74 N, 44.63 N, and 44.19 N respectively. All the difference X is greater than the preset change value of the hydraulic nut’s preload. Therefore, it is determined that the hydraulic nut needs to be tightened again.

[0056] A thermal cycling test was then conducted on the hydraulic nut in the embodiment.

[0057] The conversion formula between axial force and hydraulic pressure is: Hydraulic pressure (MPa) = [axial force (kN) / G + f] / S × G / 1000; G is the acceleration due to gravity, G = 9.8 N / kg, f is the estimated frictional force, f = 2 N, and S is the area of ​​contact, S = 0.04 m². 2 1000 is the coefficient.

[0058] Furthermore, the conversion formula between axial force and hydraulic pressure is as follows: Hydraulic pressure (MPa) = [Axial force (kN) / 9.8 N / kg + 2N] / 0.04m 2 ×9.8 N / kg / 1000.

[0059] The measured axial force is automatically converted into oil pressure value using the above formula algorithm. (1) Apply oil pressure to the hydraulic nut step by step using the hydraulic pump, and record the axial force value obtained in each segment when the oil pressure increases from 0 to 100 MPa with an increase of 10 MPa. When the oil pressure is 0 MPa, the axial force is 2.8 MPa; When the oil pressure is 10 MPa, the axial force is 11.2 MPa; When the oil pressure is 20 MPa, the axial force is 20.3 MPa; When the oil pressure is 30 MPa, the axial force is 30.5 MPa; When the oil pressure is 40 MPa, the axial force is 38.9 MPa; When the oil pressure is 50 MPa, the axial force is 49.5 MPa; When the oil pressure is 60 MPa, the axial force is 57.8 MPa; When the oil pressure is 70 MPa, the axial force is 67.5 MPa; When the oil pressure is 80 MPa, the axial force is 77.2 MPa; When the oil pressure is 90 MPa, the axial force is 87.1 MPa; When the oil pressure is 100 MPa, the axial force is 97.3 MPa.

[0060] (2) When the oil pressure is at its highest pressure of 100 MPa, the self-locking hydraulic nut is tightened and the self-locking bolt 112 is locked. The axial force before the hydraulic oil pump is removed is 97.3 MPa, and the axial force after the hydraulic oil pump is removed is 61.9 MPa.

[0061] (3) Place the hydraulic nut and its supporting testing equipment into the drying oven. Test 1: The axial force before heating was measured to be 56.2 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min until it reached 200℃. It was held at this temperature for 1 hour, and the axial force after heating was measured to be 58.9 MPa. The oil pressure was calculated by reverse calculation. After cooling to room temperature and holding for 2 hours, the axial force after cooling was measured to be 56.7 MPa. Test 2: The axial force before heating was measured to be 55.3 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min until it reached 200℃. It was held at this temperature for 2 hours, and the axial force after heating was measured to be 58.7 MPa. After cooling to room temperature and holding for 2 hours, the axial force after cooling was measured to be 55.7 MPa.

[0062] Test 3: The axial force before heating was 56.3 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min until it reached 200℃. After holding at this temperature for 0.5 hours, the axial force was measured at 58.7 MPa. After cooling to room temperature and holding for 1 hour, the axial force was measured at 55.4 MPa. Test 4: The axial force before heating was 56.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min until it reached 200℃. After holding at this temperature for 3 hours, the axial force was measured at 58.5 MPa. After cooling to room temperature and holding for 1 hour, the axial force was measured at 54.9 MPa.

[0063] Test 5: The axial force before heating was 55.9 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was 58.1 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 55.2 MPa.

[0064] Test 6: The axial force before heating was 55.7 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was 58.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 55.2 MPa.

[0065] Test 7: The axial force before heating was 55.4 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was 57.9 MPa. After cooling to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 55.0 MPa.

[0066] Test 8: The axial force before heating was 55.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was 57.3 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 54.9 MPa.

[0067] Test 9: The axial force before heating was 55.2 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was 57.5 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 54.7 MPa.

[0068] Test 10: The axial force before heating was measured to be 54.9 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was measured to be 57.5 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 54.7 MPa.

[0069] Test 11: The axial force before heating was measured to be 55.0 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 54.9 MPa.

[0070] Test 12: The axial force before heating was 55.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was 57.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 54.5 MPa.

[0071] Test 13: The axial force before heating was measured to be 54.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was measured to be 56.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 54.9 MPa.

[0072] Test 14: The axial force before heating was measured to be 54.6 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was measured to be 57.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 54.5 MPa.

[0073] Test 15: The axial force before heating was 54.7 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was 56.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 54.5 MPa.

[0074] Test 16: The axial force before heating was measured to be 54.9 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was measured to be 56.7 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 54.7 MPa.

[0075] Test 17: The axial force before heating was measured to be 54.5 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was measured to be 56.7 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 54.5 MPa.

[0076] Test 18: The axial force before heating was 54.7 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was 56.8 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 54.6 MPa.

[0077] Test 19: The axial force before heating was measured to be 54.4 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 54.4 MPa.

[0078] Test 20: The axial force before heating was 54.5 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was 56.8 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 54.5 MPa.

[0079] Test 21: The axial force before heating was measured to be 54.5 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was measured to be 56.3 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 54.6 MPa.

[0080] Test 22: The axial force before heating was measured to be 54.3 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was measured to be 56.1 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 54.0 MPa.

[0081] Test 23: The axial force before heating was measured to be 54.4 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 54.4 MPa.

[0082] Test 24: The axial force before heating was 54.4 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was 56.8 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 54.1 MPa.

[0083] Test 25: The axial force before heating was 54.3 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was 56.3 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 54.2 MPa.

[0084] Test 26: The axial force before heating was 54.3 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was 56.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 54.1 MPa.

[0085] Test 27: The axial force before heating was measured to be 54.3 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.7 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 54.0 MPa.

[0086] Test 28: The axial force before heating was 54.0 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was 56.6 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 53.9 MPa.

[0087] Test 29: The axial force before heating was measured to be 54.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was measured to be 56.7 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 54.0 MPa.

[0088] Test 30: The axial force before heating was 54.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was 56.6 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 53.9 MPa.

[0089] Test 31: The axial force before heating was measured to be 54.2 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.6 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.9 MPa.

[0090] Test 32: The axial force before heating was 54.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was 56.5 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 53.8 MPa.

[0091] Test 33: The axial force before heating was 54.2 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was 56.5 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 53.9 MPa.

[0092] Test 34: The axial force before heating was 54.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was 56.5 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 53.9 MPa.

[0093] Test 35: The axial force before heating was measured to be 54.0 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.3 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.9 MPa.

[0094] Test 36: The axial force before heating was 54.0 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was 56.4 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 53.9 MPa.

[0095] Test 37: The axial force before heating was 54.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was 56.4 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 53.9 MPa.

[0096] Test 38: The axial force before heating was 54.1 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was 56.4 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 53.9 MPa.

[0097] Test 39: The axial force before heating was measured to be 53.9 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.4 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.9 MPa.

[0098] Test 40: The axial force before heating was 54.0 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was 56.5 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was 53.8 MPa.

[0099] Test 41: The axial force before heating was measured to be 53.9 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was measured to be 56.2 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 53.8 MPa.

[0100] Test 42: The axial force before heating was measured to be 53.9 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was measured to be 56.4 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 53.9 MPa.

[0101] Test 43: The axial force before heating was measured to be 53.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 55.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.9 MPa.

[0102] Test 44: The axial force before heating was measured to be 53.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was measured to be 56.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.8 MPa.

[0103] Test 45: The axial force before heating was measured to be 53.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was measured to be 55.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 53.8 MPa.

[0104] Test 46: The axial force before heating was measured to be 53.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was measured to be 55.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 53.8 MPa.

[0105] Test 47: The axial force before heating was measured to be 53.9 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.7 MPa.

[0106] Test 48: The axial force before heating was measured to be 53.7 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was measured to be 55.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.7 MPa.

[0107] Test 49: The axial force before heating was measured to be 53.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was measured to be 55.8 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 53.7 MPa.

[0108] Test 50: The axial force before heating was measured to be 53.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was measured to be 55.5 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 53.7 MPa.

[0109] Test 51: The axial force before heating was measured to be 53.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 55.8 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.7 MPa.

[0110] Test 52: The axial force before heating was measured to be 53.7 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was measured to be 55.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.6 MPa.

[0111] Test 53: The axial force before heating was 53.8 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was 55.7 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 53.6 MPa.

[0112] Test 54: The axial force before heating was measured to be 53.7 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was measured to be 55.8 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 53.5 MPa.

[0113] Test 55: The axial force before heating was measured to be 53.6 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 55.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.5 MPa.

[0114] Test 56: The axial force before heating was measured to be 53.7 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was measured to be 55.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.6 MPa.

[0115] Test 57: The axial force before heating was 53.7 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 1 hour. The axial force after heating was 55.9 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was 53.6 MPa.

[0116] Test 58: The axial force before heating was measured to be 53.6 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 2 hours. The axial force after heating was measured to be 56.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 2 hours. The axial force after cooling was measured to be 53.5 MPa.

[0117] Test 59: The axial force before heating was measured to be 53.6 MPa. Then, the hydraulic nut was heated in an oven at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 0.5 hours. The axial force after heating was measured to be 56.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.5 MPa.

[0118] Test 60: The axial force before heating was measured to be 53.6 MPa. Then, the hydraulic nut was heated in an oven at a rate of 2℃ / min. When the temperature of the hydraulic nut reached 200℃, it was kept at that temperature for 3 hours. The axial force after heating was measured to be 56.0 MPa. After the temperature cooled to room temperature, it was kept at that temperature for 1 hour. The axial force after cooling was measured to be 53.5 MPa.

[0119] (4) Taking the axial force value of 56.2 MPa measured in the initial test 1 before heating as the standard value Z, the maximum axial force value MAX measured in tests 1-60 is 58.9 MPa, and the minimum axial force value MIN is 53.5 MPa. Take the absolute value of the difference between the maximum axial force value MAX or the minimum axial force value MIN and the standard value Z, and take the percentage of this absolute value in the standard value Z. The final value obtained is the rate of change S of the axial force value, and the formula is as follows: or ; The rate of change of the maximum axial force MAX relative to the standard value Z, S MAX =4.80%, the rate of change S of the minimum axial force value MIN relative to the standard value Z MIN =4.80%, S MAX and S MIN All values ​​are within 5%, indicating excellent thermal stability of the hydraulic nut, ensuring stable mechanical properties in complex temperature environments.

[0120] The axial force values ​​in (1)-(4) above are the oil pressure values ​​obtained after converting the measured axial force.

[0121] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A hydraulic nut for use in nuclear power plants, comprising a hydraulic cylinder, a piston, and a locking nut, wherein the oil chamber of the hydraulic cylinder is connected to an external pump station via a flow channel, the piston is located in the oil chamber of the hydraulic cylinder and is slidably connected to the hydraulic cylinder, the piston has an annular structure and is provided with internal and external threads, the piston is connected to a bolt via the internal thread, and the piston is connected to a locking nut via the external thread; Its features are, The hydraulic nut also includes a laser ranging module for monitoring the distance from the contact surface between the hydraulic nut and the flange to the top surface of the bolt, and a processor for analyzing and processing multiple sets of data monitored by the hydraulic nut. The laser ranging module is connected to and controlled by the processor.

2. The hydraulic nut for use in nuclear power plants according to claim 1, characterized in that, To prevent nuclear leaks due to insufficient flange preload, it is necessary to monitor the preload of the hydraulic nut in real time. A method for monitoring the preload of the hydraulic nut is proposed below: When a bolt is subjected to axial tension or compression, its main deformation is a change in its axial dimension, while its transverse dimension also changes. Let the original length of the bolt be L, and the length after deformation be L1, then the axial deformation of the bolt is L. ’ , L ’ = L1-L; Under equal axial tensile force, bolts of different original lengths will have different axial deformation values. Therefore, axial deformation cannot accurately express the degree of bolt deformation. When a bolt is under tension, the axial deformation of each longitudinal restraint is equal, and the deformation is almost uniformly distributed along the axial direction. Therefore, the axial linear strain is ε. ε= L ’ / L, According to Hooke's Law, the normal stress δ is proportional to the linear strain ε, and its expression is δ = Eε. E is the tensile modulus of elasticity of a material. The larger the E value of a material, the more difficult it is to be stretched or compressed. It expresses the material's ability to resist elastic deformation under tension and compression. For a bolt subjected to tension, we have δ=F N / A, F N Let L be the axial force borne by the bolt, A be the cross-sectional area of ​​the bolt, and ε = L. ’ / L, δ=F N / A and ε= L ’ Substituting / L into δ=Eε, we get L ’ = F N L / EA, when the stress does not exceed the proportional limit of the material, is the axial deformation L of the bolt. ’ With axial force F N It is directly proportional to the original length L of the bolt, and inversely proportional to the cross-sectional area A; Perform real-time monitoring and analysis of whether the hydraulic nut is loose, following these steps: (1) Before the bolt is stretched, the average distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is measured to be d1. After the bolt is stretched and the hydraulic nut is tightened, the average distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is measured to be d2. The length of the bolt after stretching is L1 = L + (d2 - d1); Then L ’ = L1-L, from the formula L ’ = F N L / EA can produce F N =EAL ’ / L, E, A, L ’ After substituting the values ​​of L, etc., the axial force F of the bolt can be calculated. N Let F be the value of F. N =a, axial force F of the bolt N The bolt preload F is equal to that when the hydraulic nut is tightened; (2) The axial deformation L of the bolt in the tightened state ’ Assigning a marker point will mark the axial deformation L. ’ Let L be the initial value for the axial deformation. ’ Assign a value, assign a value of 0. And axial force F N A marker point is then assigned to mark the axial force F. N Let F be the initial value of the axial force. N The value is assigned to 0. (3) The distance from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is monitored in real time by the laser ranging module. The distance value obtained by the laser ranging module is recorded as d3. Then, the axial deformation L of the bolt at this time is... ” = d2 - d3, L ” Substitute into formula L ’ = F N L / EA can produce F N ’ =EAL ” / L, where E, A, L, etc. are constants, the axial force F of the bolt can be calculated. N ’ Let F be the value of F. N ’ =b, axial force F of the bolt N ’ The preload force F of the hydraulic nut is equal to that at this time; (4) Take the axial force F during tightening. N With the monitored axial force F N ’ The difference X, X=F N -F N ’ The difference X is compared with the preset preload range of the hydraulic nut. If the difference X is greater than the preset preload range of the hydraulic nut, it is determined that the hydraulic nut needs to be retightened. If the difference X is less than the preset preload range of the hydraulic nut, it is determined that the hydraulic nut does not need to be retightened. (5) Take the results of the judgment on whether the hydraulic nut needs to be retightened from multiple time points within a certain period of time, and analyze them. If the judgment that the hydraulic nut needs to be retightened is an individual result, then the hydraulic nut does not need to be retightened. If the judgment that the hydraulic nut needs to be retightened is not an individual result, then the hydraulic nut needs to be retightened.

3. The hydraulic nut for use in nuclear power plants according to claim 2, characterized in that, The specific implementation steps of the method for real-time monitoring of the preload of hydraulic nuts are as follows: (1) Given that the original length L of the bolt is 7000 mm, the tensile modulus E of the composite steel material is 206 GPa, and the cross-sectional area A of the bolt is 816.7 mm², 2 Input to the processor, The distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt before bolt tension is measured using a laser ranging module. Five sets of values ​​are obtained and transmitted to the processor, and the average value d1 is taken. The distance D from the contact surface between the hydraulic nut and the flange to the top surface of the bolt was measured using a laser ranging module after the bolt was stretched and the hydraulic nut was tightened. Five sets of values ​​were obtained and transmitted to the processor, and the average value d2 was taken. The processor calculates that the length of the stretched bolt L1 = L + (d2 - d1). (2) Based on formula L ’ = L1-L and formula L ’ = F N L / EA's derived formula F N =EAL ’ / L, calculated by the processor, the axial force F of the bolt. N Let F be the value of F. N =a, axial force F of the bolt N The bolt preload F is equal to that when the hydraulic nut is tightened; (3) In the processor, the axial deformation L of the bolt in the tightened state is given. ’ Assigning a marker point will mark the axial deformation L. ’ Let L be the initial value for the axial deformation. ’ Assign a value, assign a value of 0. And axial force F N A marker point is then assigned to mark the axial force F. N Let F be the initial value of the axial force. N The value is assigned to 0. (4) The distance from the contact surface between the hydraulic nut and the flange to the top surface of the bolt is monitored in real time by the laser ranging module. The distance value monitored by the laser ranging module is recorded as d3. The laser ranging module feeds back the distance value d3 to the processor for analysis and processing. Then, the axial deformation L of the bolt at this time is... ” = d3 - d1, The axial deformation L of the bolt at this time ” Substitute into formula L ’ = F N L / EA's derived formula F N =EAL ’ / L, the axial force F of the bolt can be calculated. N ’ Let F be the value of F. N ’ =b, axial force F of the bolt N ’ The preload force F of the hydraulic nut is equal to that at this time; (5) Take the axial force F during tightening. N With the monitored axial force F N ’ The difference X, X=F N -F N ’ The difference X is compared with the preset variable value of the preload of the hydraulic nut. If the difference X is greater than the preset variable value of the preload of the hydraulic nut, it is determined that the hydraulic nut needs to be tightened again. If the difference X is less than the preset variable value of the preload of the hydraulic nut, it is determined that the hydraulic nut does not need to be tightened again. (6) Take the results of the judgment on whether the hydraulic nut needs to be retightened at 10 time points within a certain period of time, and analyze them. If the judgment that the hydraulic nut needs to be retightened is an individual result, then the hydraulic nut does not need to be retightened. If the judgment that the hydraulic nut needs to be retightened is not an individual result, then the hydraulic nut needs to be retightened.

4. A hydraulic nut for use in nuclear power plants according to claim 3, characterized in that, The laser ranging module is a laser rangefinder.

5. A hydraulic nut for use in nuclear power plants according to claim 1, characterized in that, The piston is connected to a lock nut via an external thread. The piston has a slot located slightly above its upper part; the slot is arc-shaped, and its perpendicular bisector passes through the midpoint of the piston's cross-section at that location. The piston also has a threaded hole, which is vertically positioned and extends through the slot, located on the perpendicular bisector of the slot. A self-locking bolt is installed within the threaded hole. A base is provided below the hydraulic cylinder. The upper end face of the base is a concave spherical surface, and the lower end face of the hydraulic cylinder is a convex spherical surface. The upper end face of the base and the lower end face of the hydraulic cylinder cooperate with each other. The hydraulic cylinder is movably mounted on the base. There is an off-center load of ±1° between the hydraulic cylinder and the base; The base has a through hole, and the diameter of the through hole is larger than the diameter of the bolt; The thread used to connect the lock nut and the piston is a sawtooth thread.

6. A hydraulic nut for use in nuclear power plants according to claim 5, characterized in that, The screw hole is located on the vertical line of the slot; The slot is set horizontally; The rotation center line of the self-locking bolt is parallel to the rotation center line of the piston, and the rotation center line of the self-locking bolt is perpendicular to the horizontal plane of the slot. The hydraulic cylinder is provided with an oil chamber and a linkage chamber. The oil chamber is connected to the linkage chamber. The oil chamber is located above the linkage chamber. The diameter of the oil chamber is larger than the diameter of the linkage chamber. A sealing element is provided below the sliding element, and the sealing element is a V-shaped spring energy storage ring; The locking nut has several connection holes for connecting a turning tool.

7. A hydraulic nut for use in nuclear power plants according to claim 5, characterized in that, The bow shape includes a chord and an arc. Let a be the midpoint of the chord and b be the midpoint of the arc, and let x be the straight line connecting points a and b. Let h be the thickness of one side of the piston wall, and r be the radius of the piston's cross-section. h < r < x < 2r - h.

8. A hydraulic nut for use in nuclear power plants according to claim 5, characterized in that, The piston includes an upper part and a lower part, with the diameter of the upper part being larger than that of the lower part. A sliding member is provided on the outer side of the upper part of the piston, and the sliding member is slidably connected to the inner wall of the oil chamber. The external thread of the piston is provided on the outer side of the upper part of the piston, and the external thread of the piston is located above the sliding member. The lower part of the piston is slidably connected to the linkage chamber. The piston has a through-hole in the middle, and the internal thread is formed on the wall of the through-hole. The diameter of the through-hole is equal to the diameter of the bolt. The piston has a groove, which is connected to the flow channel.

9. A hydraulic nut for use in nuclear power plants according to claim 5, characterized in that, The above-mentioned hydraulic nut underwent a thermal cycling test, and the specific procedure is as follows: Step 1: Apply oil pressure to the hydraulic nut step by step using the hydraulic pump. Record the axial force value obtained at each stage when the oil pressure increases from 0 to 100 MPa and the increase is 10 MPa. Calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. At the same time, check whether there is any oil leakage at the hydraulic hose connection and whether the hydraulic nut exceeds the stroke requirement. Step 2: After reaching the highest pressure of 100MPa, tighten the self-locking hydraulic nut and the self-locking bolt. Record the axial force values ​​before and after removing the hydraulic pump in the stopped state. Calculate the oil pressure value by using the conversion formula between axial force and oil pressure. Step 3: Place the hydraulic nut and the supporting testing equipment into an oven (hot air circulating oven). First, heat the hydraulic nut in the oven, then place the hydraulic nut to room temperature. Repeat the heating and cooling process to perform multiple cyclic tests on the hydraulic nut. Step 4: Analyze the test data to verify the thermal stability of the hydraulic nut and ensure the stability of its mechanical properties in complex temperature environments. The conversion formula between axial force and hydraulic pressure is: Hydraulic pressure (MPa) = [axial force (kN) / G + f] / S × G / 1000; G is the acceleration due to gravity, G = 9.8 N / kg, f is the estimated frictional force, f = 2 N, and S is the area of ​​contact, S = 0.04 m². 2 1000 is the coefficient.

10. A hydraulic nut for use in nuclear power plants according to claim 9, characterized in that, The hydraulic nut in step 3 above shall be heated and cooled as follows: (1) Heat the hydraulic nut at a rate of 2℃ / min. When the temperature of the hydraulic nut reaches 200℃, keep it at that temperature for 1 hour, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. After the temperature cools down to room temperature, keep it at that temperature for 2 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. (2) Heat the hydraulic nut at a rate of 1℃ / min. When the temperature of the hydraulic nut reaches 200℃, keep it at that temperature for 2 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. After the temperature cools down to room temperature, keep it at that temperature for 2 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. (3) Heat the hydraulic nut at a rate of 1.5℃ / min. When the temperature of the hydraulic nut reaches 200℃, keep it at that temperature for 0.5 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. After the temperature cools down to room temperature, keep it at that temperature for 1 hour, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. (4) Heat the hydraulic nut at a rate of 2℃ / min. When the temperature of the hydraulic nut reaches 200℃, keep it warm for 3 hours, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value. After the temperature cools down to room temperature, keep it warm for 1 hour, measure the axial force, and calculate the oil pressure value by using the conversion formula between axial force and oil pressure value.

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