A nuclear fuel transfer channel seal test interface device

Abstract

The application provides a nuclear fuel transfer channel sealing test interface device, which comprises a nut, a pushing chuck, a sealing chuck and a pipeline interface. The nut is threadedly connected with the pushing chuck, the pushing chuck is axially limited with the sealing chuck, and the sealing chuck is sealingly matched with the pipeline interface through a conical surface. The application reduces the risk of personnel irradiation and tool falling and improves safety through a tool-free quick release mechanism and reliable sealing performance. One person can quickly complete installation and disassembly, saving overhaul time and improving work efficiency. The two structures of the nut ensure reliable sealing between the device and the external pipeline or equipment, avoiding leakage. The device can adapt to sealing requirements under different test conditions, such as vibration and temperature change, and has wide applicability. Through the detachable and replaceable design of the device, the maintenance and replacement of parts are facilitated, and the maintenance cost is reduced.

Description

Technical Field

[0001] This application relates to the field of nuclear fuel transfer technology, and in particular to a nuclear fuel transfer channel sealing test interface device. Background Technology

[0002] Nuclear power plants require containment leakage rate tests during commissioning and operation to verify the containment's effectiveness as the third containment barrier. The nuclear fuel transfer container flange sealing test is one of the Category B containment penetration tests.

[0003] Current methods require scaffolding to be erected at the bottom of the fuel water tank, and operators must carry tools to climb to the flange location for testing. Sealing typically involves wrapping threaded joints with PTFE tape, requiring wrenches and other tools for disassembly and assembly. A hose connects the plant's compressed air supply, a leak rate detector, and a leak rate test isolation valve in sequence, using a hexagonal plug as the sealing joint and PTFE tape for sealing. Access to the flange location requires scaffolding. Normally, the flange sealing surface has two sealing rings. The plant's compressed air valve is opened to pressurize the sealed space between these two sealing rings, at least to the containment design pressure, and the pressure is maintained stable. The flange leak rate can then be read using the leak rate detector.

[0004] However, the existing experimental sealing method requires multiple people to work together to erect scaffolding, which is time-consuming and inefficient. At the same time, scaffolding erection increases the risk of radiation exposure for personnel, and falling scaffolding tools may damage the steel cladding at the bottom of the pool. Utility Model Content

[0005] To address the existing testing sealing methods that require multiple people to work together to erect scaffolding, resulting in long hours and low efficiency; at the same time, scaffolding erection increases the risk of radiation exposure for personnel, and falling scaffolding tools may damage the steel cladding at the bottom of the pool.

[0006] This application provides a nuclear fuel transfer channel sealing test interface device, including: a nut, a pusher, a sealing clamp, and a pipe interface;

[0007] The nut is the main body, with T-shaped structures on both sides, and internal threads on the inner surface of the nut cavity;

[0008] The push-in head is annular in shape, and the push-in head has a protruding end and a beveled end, with the protruding end embedded in the inner cavity of the nut;

[0009] The sealing clip has a central through hole, and one end of the sealing clip near the push clip has a chamfer at the edge of the central through hole. The chamfer fits into the beveled end, and the beveled end is embedded in the central through hole of the sealing clip.

[0010] The outer surface of the sealing clip away from the push clip has a first conical surface, the pipe interface has a central stepped hole, and the edge of the central stepped hole near the sealing clip has a second conical surface, the second conical surface being in contact with the surface of the first conical surface;

[0011] The pipe interface has an external thread at one end near the nut, and is connected to the internal thread of the nut.

[0012] In one feasible implementation, the end of the nut furthest from the push-in head is a closed structure;

[0013] The nut has a limiting post at its center, which passes through the push-in clamp, the sealing clamp, and the pipe interface in sequence.

[0014] The outer end of the limiting post has an expanded surface, and the central through hole at the end of the sealing clip away from the push clip has a protruding step. The expanded surface and the protruding step are interference fit.

[0015] In one feasible implementation, the nut has a through hole at its center, and a test hose is connected to the end of the nut away from the push-in head;

[0016] The nut and the test hose are connected by an interference fit, and the test hose is connected to the pipe interface through the through hole of the nut;

[0017] The test hose and the sealing clip are also connected by an interference fit.

[0018] In one feasible implementation, the cone angles of the first conical surface of the sealing clip and the second conical surface of the pipe interface are both 30-45°, and an annular sealing groove is provided on the first conical surface.

[0019] In one feasible implementation, the outer surface of the nut is provided with anti-slip texture, and the T-shaped structure is symmetrically distributed at the top and bottom of the nut.

[0020] In one feasible implementation, the end of each pipe interface is provided with an anti-detachment flange, the diameter of which is 1-2 mm larger than the inner diameter of the flange interface.

[0021] In one feasible implementation, the metal contact surfaces on the outer surface of the nut are all provided with a nickel-based alloy plating layer, the plating layer having a thickness of 0.05-0.1 mm.

[0022] This application provides a nuclear fuel transfer channel sealing test interface device that allows for rapid installation and disassembly of the connector by a single person, eliminating the need for multiple personnel and significantly shortening overhaul time. The ferrule interface design simplifies the sealing test process and improves operational efficiency. Replacing traditional PTFE tape sealing with a standardized ferrule sealing interface eliminates the risk of residual sealing material, ensuring the cleanliness of the fuel pool and reducing the possibility of external foreign objects (such as tools and sealing debris) entering the fuel pool during testing. The ferrule design ensures the stability and repeatability of the airtightness test and avoids sealing failure caused by uneven PTFE tape winding. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present invention and, together with the description, serve to explain the principles of the embodiments of the present invention. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0024] Figure 1 This is a schematic diagram of the structure of a nuclear fuel transfer channel sealing test interface device shown in an exemplary embodiment of this application;

[0025] Figure 2 This is a schematic diagram illustrating the disassembled structure of the sleeve plug in an exemplary embodiment of this application;

[0026] Figure 3 This is a schematic diagram of the back structure of the card sleeve plug shown in an exemplary embodiment of this application;

[0027] Figure 4 This is an exploded structural diagram of a ferrule plug shown in an exemplary embodiment of this application;

[0028] Figure 5 This is a schematic diagram of the assembly structure of the ferrule plug shown in an exemplary embodiment of this application;

[0029] Figure 6 This is a schematic diagram of the structure of the ferrule connector shown in an exemplary embodiment of this application;

[0030] Figure 7 This is a schematic diagram illustrating the disassembled structure of the card sleeve connector in an exemplary embodiment of this application;

[0031] Figure 8 This is an exploded view of the ferrule connector shown in an exemplary embodiment of this application;

[0032] Figure 9 This is a schematic diagram of the assembly structure of the ferrule connector shown in an exemplary embodiment of this application.

[0033] The attached image is labeled as follows:

[0034] 100-Compression ferrule plug; 200-Compression ferrule connector; 110-Nut; 120-Push-in ferrule; 130-Sealing ferrule; 140-Pipe interface; 210-Test hose; 111-T-shaped structure; 112-Limiting post; 113-Outward expansion surface; 121-Protruding end; 122-Beveled end; 131-First conical surface; 132-Protruding step; 141-Second conical surface. Detailed Implementation

[0035] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make the present invention more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of the implementation of embodiments of the present invention.

[0036] Current methods require scaffolding to be erected at the bottom of the fuel water tank, and operators must carry tools to climb to the flange location for testing. Sealing typically involves wrapping threaded joints with PTFE tape, requiring wrenches and other tools for disassembly and assembly. The plant's compressed air supply, leak rate detector, and leak rate test isolation valve are connected sequentially via hoses, using hexagonal plugs as sealing joints and PTFE tape for sealing. Access to the flange location requires scaffolding. Normally, the flange sealing surface has two sealing rings. The plant's compressed air valve is opened to pressurize the sealed space between these two sealing rings, at least to the containment design pressure and maintained at a stable pressure. The flange leak rate can then be read using the leak rate detector. The need for multiple people to work together to erect the scaffolding results in long hours, low efficiency, increased radiation risk to personnel, and the potential for falling tools to damage the steel cladding at the bottom of the tank.

[0037] To address the aforementioned problems, this application provides a nuclear fuel transfer channel sealing test interface device, referring to... Figures 1-9 As shown, this device comes in two forms: one is a ferrule plug 100, and the other is a ferrule connector 200 obtained by adjusting the ferrule plug 100.

[0038] The interface device mainly includes a nut 110, a push-in clamp 120, a sealing clamp 130, and a pipe interface 140.

[0039] The nut 110 is the main body, with T-shaped structures 111 on both sides, and internal threads on its inner surface. The push-in chuck 120 is annular, with a protruding end 121 and a beveled end 122. The protruding end 121 is embedded in the inner cavity of the nut 110. The sealing chuck 130 has a central through hole, and the end near the push-in chuck 120 has a chamfer at the edge of the central through hole. This chamfer fits against the beveled end 122 of the push-in chuck 120, and the beveled end 122 is embedded in the central through hole of the sealing chuck 130. The outer surface of the end of the sealing chuck 130 away from the push-in chuck 120 has a first conical surface 131. The pipe interface 140 has a central stepped hole, and the edge near the sealing chuck 130 has a second conical surface 141, which fits against the surface of the first conical surface 131 of the sealing chuck 130. The pipe interface 140 has an external thread at one end near the nut 110, and is connected to the internal thread of the nut 110.

[0040] Nut 110 is an external operating component of the entire device. Rotating nut 110 drives the pusher chuck 120 to move axially. The T-shaped structure 111 provides a gripping position for rotation and facilitates leverage, improving operational convenience. Driven by nut 110, pusher chuck 120 can move axially. Protruding end 121 engages with the inner cavity of nut 110 to ensure stable movement of pusher chuck 120. Beveled end 122 fits against the chamfer of sealing chuck 130, converting axial force into radial force, generating pressure on sealing chuck 130, and improving sealing performance.

[0041] Under the push of the push-in clamp 120, the first conical surface 131 of the sealing clamp 130 fits tightly with the second conical surface 141 of the pipe interface 140, forming a seal. The pipe interface 140, as a component connecting the device to an external pipe, has a central stepped hole that can accommodate test hoses of different specifications, and the stepped structure limits the push-in clamp 120 and the sealing clamp 130 inside the nut 110.

[0042] When a nuclear fuel transfer channel needs to be sealed, the pipe interface 140 is first connected to the external pipe. Then, by rotating the nut 110 through the T-shaped structure 111, the push-in clamp 120 is driven to move axially toward the sealing clamp 130. The beveled end 122 of the push-in clamp 120 engages with the chamfer of the sealing clamp 130, converting the axial force into a radial force, pushing the sealing clamp 130 outward. As the push-in clamp 120 continues to move, the first conical surface 131 of the sealing clamp 130 tightly engages with the second conical surface 141 of the pipe interface 140, forming a reliable seal.

[0043] This embodiment solves the sealing problem of the nuclear fuel transfer channel sealing test interface device through the synergistic action of the nut 110, the advance clamp 120, the sealing clamp 130, and the pipe interface 140. Precise control of the sealing clamp 130 is achieved through threaded connection and axial limiting fit, thereby ensuring the conical surface sealing performance between the sealing clamp 130 and the pipe interface 140. The sealing clamp 130 can be advanced and retracted simply by rotating the nut 110, making operation simple and quick. The entire device has a compact structure, occupies little space, and is convenient for use in narrow spaces such as nuclear fuel transfer channels.

[0044] In some embodiments of this application, the end of the nut 110 furthest from the push-in clamp 120 is configured as a closed structure, enhancing the structural strength of the nut 110. The nut 110 has a center limiting post 112, which passes sequentially through the push-in clamp 120, the sealing clamp 130, and the pipe interface 140, limiting their axial movement. The outer end of the limiting post 112 has an outwardly expanding surface 113, which forms an interference fit with the protruding step 132 of the central through hole of the sealing clamp 130, enhancing the sealing performance and simultaneously achieving automatic fixation of the device. With the nut 110 closed, the ferrule plug 100 is obtained.

[0045] When a sealed nuclear fuel transfer channel is required, a ferrule plug 100 is used. A T-shaped structure 111 rotates the nut 110, driving the propulsion ferrule 120 to move axially toward the sealing ferrule 130. A limiting post 112 restricts the axial movement of the propulsion ferrule 120, the sealing ferrule 130, and the pipe interface 140, ensuring the stability and sealing performance of the device. As the propulsion ferrule 120 continues to move, the first conical surface 131 of the sealing ferrule 130 tightly fits against the second conical surface 141 of the pipe interface 140, forming a reliable seal. Simultaneously, the outwardly expanding surface 113 of the limiting post 112 forms an interference fit with the protruding step 132 of the sealing ferrule 130, further enhancing the sealing performance.

[0046] This embodiment, through the structure of the nut 110 (closed end) and the limiting post 112, solves the problems of external impurities easily entering the device and unstable component movement when the nuclear fuel transfer channel sealing test interface device is used in harsh environments. The principle is that the closed end design effectively blocks the entry of external impurities while enhancing the structural strength of the nut 110; the limiting post 112 limits the axial movement of the components, ensuring the stability and sealing performance of the device.

[0047] In some embodiments of this application, the nut 110 has a through hole at its center, and a test hose 210 is connected to it via an interference fit. The test hose 210 communicates with the pipe interface 140 through the through hole, and also forms an interference fit connection with the sealing clamp 130, thereby realizing the connection between the device and external testing equipment and the transmission of the test medium.

[0048] Specifically, the test hose 210 is connected to the nut 110 and the sealing clamp 130 via an interference fit, ensuring reliable connection and sealing while simultaneously transmitting the test medium. The through-hole design of the nut 110 facilitates the connection of the test hose 210 while maintaining the structural integrity of the device.

[0049] When a sealing test of the nuclear fuel transfer channel is required, the test hose 210 is first connected to the through-hole end of the nut 110 and the sealing clamp 130 via an interference fit. Then, by rotating the nut 110, the push clamp 120 is driven to move axially toward the sealing clamp 130. As the push clamp 120 moves, it pushes the sealing clamp 130 into tight contact with the conical surface of the pipe interface 140, forming a reliable seal. At this time, the test hose 210 is connected to the pipe interface 140 through the through-hole of the nut 110, and external test equipment can inject test media into the device through the test hose 210 to conduct the sealing test.

[0050] In this embodiment, the interface device is connected to the external testing equipment through the through hole of nut 110 and the test hose 210. The interference fit connection ensures the reliability and sealing of the connection, preventing leakage of the test medium, thereby achieving an effective connection between the device and the external testing equipment. By directly connecting the test hose 210, this embodiment can conveniently conduct sealing tests on the nuclear fuel transfer channel, improving testing efficiency.

[0051] In some embodiments of this application, the outer surface of the nut 110 is provided with anti-slip textures. These textures are specifically designed to increase the friction between the operator's hand and the nut surface, making it less prone to slippage when holding and rotating the nut, thereby ensuring operational stability and accuracy, and improving operational convenience and safety. T-shaped structures 111 are symmetrically distributed at the top and bottom of the nut 110. This design allows the operator to more easily grip and apply force using tools such as wrenches, further assisting in rotating the nut and improving work efficiency.

[0052] This embodiment, through the design of the anti-slip texture of the nut 110 and the T-shaped structure 111, not only makes the tightening operation of the nut 110 easier, but also enhances the fastening effect between the nut 110 and various components, improving the ease of operation and reliability of the connection of the nuclear fuel transfer channel sealing test interface device. At the same time, it also reduces safety risks caused by improper operation or tool slippage, thereby lowering potential dangers during operation.

[0053] In some embodiments of this application, the cone angles of the first conical surface 131 of the sealing clip 130 and the second conical surface 141 of the pipe interface 140 are both set to 30-45°, and an annular sealing groove is provided on the first conical surface 131.

[0054] Understandably, the annular sealing groove can be used to accommodate sealing material, further improving sealing performance. Setting the cone angle to 30-45° can optimize the contact pressure of the conical seal. The cone angle design within this range allows the first conical surface 131 and the second conical surface 141 to generate a suitable contact stress distribution when subjected to pressure, neither too large, causing damage to the first conical surface 131 and the second conical surface 141, nor too small, resulting in poor sealing performance.

[0055] Specifically, when the cone angle is 30°, the contact area between the two surfaces is relatively large, which can distribute more pressure, reduce wear on the sealing surface, and ensure a good sealing effect. This design is suitable for applications with small pressure fluctuations and high sealing requirements. If the cone angle is less than 30°, although the contact area will further increase, the contact stress will decrease, which may lead to poor sealing effect or even leakage. In addition, an excessively small cone angle may increase the processing difficulty and cost.

[0056] When the cone angle is 45°, the contact area between the two is relatively small, but it can generate greater contact stress, improving the tightness of the seal. This design is suitable for use in applications with high pressure and requiring higher sealing performance. If the cone angle is greater than 45°, although the contact stress will increase, the contact area will decrease, which may cause damage to the sealing surface under high pressure.

[0057] In some embodiments of this application, the end of the pipe interface 140 is provided with an anti-detachment flange, the diameter of which is 1-2 mm larger than the inner diameter of the flange interface. The slightly larger diameter of the anti-detachment flange ensures that the pipe interface 140 is tightly fixed within the flange interface during connection, preventing it from easily detaching. This improves the stability and reliability of the connection and avoids safety hazards caused by pipe interface detachment.

[0058] By setting the diameter of the anti-loosening flange to be 1 to 2 mm larger than the inner diameter of the flange interface, it can accommodate flange interfaces of different sizes and precisions. This design increases the versatility and flexibility of the pipe interface 140, enabling its widespread application in different piping systems. However, if the diameter of the anti-loosening flange is too large, it may lead to connection difficulties or even prevent connection altogether; while if the diameter is too small, it may not provide effective anti-loosening protection.

[0059] Understandably, when the pipe connector 140 is inserted to a certain position, the anti-detachment flange will contact the end face of the flange interface, thereby preventing the pipe connector 140 from being inserted further or detached. The structure of the anti-detachment flange prevents the pipe connector 140 from detaching during the connection process, reducing safety risks during operation.

[0060] In some embodiments of this application, the metal contact surfaces of the outer surface of the nut 110 of the ferrule plug 100 or ferrule connector 200 are provided with a nickel-based alloy plating. The thickness of this plating is precisely controlled between 0.05 and 0.1 mm to maximize its performance advantages. Nickel-based alloy plating is known for its excellent corrosion resistance and wear resistance, effectively resisting various chemical corrosions and mechanical wear, thereby significantly extending the service life of the ferrule plug 100.

[0061] Nickel-based alloy coatings, due to their chemical composition and microstructure, exhibit extremely high corrosion resistance and wear resistance. They effectively prevent metal surfaces from oxidation, corrosion, or wear, thus protecting the substrate from damage. This coating maintains stable performance under various harsh environments. Therefore, in the context of this application, the ferrule plug 100 or ferrule connector 200 is frequently exposed to corrosive media and mechanical stress; the nickel-based alloy coating can effectively extend the service life of the ferrule plug 100 or ferrule connector 200 and reduce maintenance costs.

[0062] In this embodiment, the coating thickness is controlled between 0.05 and 0.1 mm, providing sufficient protection without being too thick and affecting the overall performance of the component. For example, a coating thickness of 0.05 mm provides basic corrosion and wear protection while maintaining a light weight and low cost. Increasing the coating thickness to 0.1 mm provides a higher level of protection, suitable for harsher environmental conditions.

[0063] Understandably, an excessively thick plating layer can increase the weight and cost of a component while reducing its overall performance. Furthermore, an excessively thick plating layer may also lead to increased internal stress, thereby reducing the component's strength and durability. Conversely, if the plating layer is too thin, it may not provide sufficient protection, causing the component to be damaged in a short period of time. Therefore, in this application, the thickness of the plating layer is precisely controlled between 0.05 and 0.1 mm to ensure optimal performance.

[0064] Based on the above embodiments, the usage process of the nuclear fuel transfer channel sealing test interface device of this application includes:

[0065] The process of using the ferrule plug 100 is as follows: Align the mating end face of the ferrule plug 100 with the flange interface, achieving precise alignment through the locating pin. Rotate the nut 110 to drive the pusher 120 to move, pushing the sealing ferrule 130 into tight contact with the conical surface of the pipe interface 140 (plug interface), forming a reliable seal and thus sealing the flange interface.

[0066] The procedure for using the ferrule connector 200 is as follows: Connect the test hose 210 to the through-hole end of the nut 110 via an interference fit. Push the sealing clamp 130 of the ferrule connector 200 toward the test interface; a "click" vibration indicates that the test line and the test interface are sealed. Inject the test medium into the device through the test hose 210 to conduct a sealing test.

[0067] As described above, the nuclear fuel transfer channel sealing test interface device of this application reduces the risk of personnel irradiation and tool drops, thus improving safety through a tool-less quick-release mechanism and reliable sealing performance. Installation and disassembly can be completed quickly by a single person, saving overhaul time and improving operational efficiency. Furthermore, the design, including a conical sealing fit, preload provided by spring elements, and a nickel-based alloy plating, ensures a reliable seal between the device and external pipelines or equipment, preventing leakage. The device can adapt to sealing requirements under different test conditions, such as vibration and temperature changes, and has wide applicability. The device's detachable and replaceable design facilitates maintenance and component replacement, reducing maintenance costs.

[0068] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the disclosure in the specification and the embodiments. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A nuclear fuel transfer channel sealing test interface device, characterized in that, include: Nut (110), push-in clamp (120), sealing clamp (130) and pipe joint (140); The nut (110) is the main body, and T-shaped structures (111) are provided on both sides. The inner surface of the nut (110) is provided with internal threads. The push head (120) is annular, and the push head (120) has a protruding end (121) and a beveled end (122). The protruding end (121) is embedded in the inner cavity of the nut (110). The sealing clip (130) has a central through hole. The end of the sealing clip (130) near the push clip (120) has a chamfer at the edge of the central through hole. The chamfer fits with the beveled end (122). The beveled end (122) is embedded in the central through hole of the sealing clip (130). The sealing clip (130) has a first conical surface (131) on its outer surface away from the push clip (120), the pipe interface (140) has a central stepped hole, and the edge of the central stepped hole near the sealing clip (130) has a second conical surface (141), the second conical surface (141) is in contact with the surface of the first conical surface (131); The pipe interface (140) has an external thread at one end near the nut and is connected to the internal thread of the nut (110).

2. The nuclear fuel transfer channel sealing test interface device according to claim 1, characterized in that, The end of the nut (110) away from the push head (120) is a closed structure; The nut (110) has a limiting post (112) at its center, and the limiting post (112) passes through the push-in clamp (120), the sealing clamp (130) and the pipe interface (140) in sequence; The outer end of the limiting post (112) has an expanded surface (113), and the center through hole of the sealing head (130) away from the push head (120) has a protruding step (132). The expanded surface (113) and the protruding step (132) are interference fit.

3. The nuclear fuel transfer channel sealing test interface device according to claim 1, characterized in that, The nut (110) has a through hole in the center, and a test hose (210) is connected to the end of the nut (110) away from the push head (120); The nut (110) and the test hose (210) are connected by an interference fit, and the test hose (210) is connected to the pipe interface (140) through the through hole of the nut (110); The test hose (210) and the sealing clip (130) are also connected by an interference fit.

4. The nuclear fuel transfer channel sealing test interface device according to claim 1, characterized in that, The first conical surface (131) of the sealing clip (130) and the second conical surface (141) of the pipe interface (140) both have a cone angle of 30-45°, and the first conical surface (131) is provided with an annular sealing groove.

5. The nuclear fuel transfer channel sealing test interface device according to claim 1, characterized in that, The outer surface of the nut (110) is provided with anti-slip texture, and the T-shaped structure (111) is symmetrically distributed on the top and bottom of the nut (110).

6. The nuclear fuel transfer channel sealing test interface device according to claim 1, characterized in that, The ends of the pipe interfaces (140) are all provided with anti-detachment flanges, and the diameter of the anti-detachment flanges is 1-2 mm larger than the inner diameter of the flange interface.

7. The nuclear fuel transfer channel sealing test interface device according to claim 1, characterized in that, The metal contact surfaces on the outer surface of the nut (110) are all provided with a nickel-based alloy plating layer, the thickness of which is 0.05-0.1mm.

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