High temperature zone thread connection method and assembly with anti-adhesion, anti-rotation and anti-retreat functions

Abstract

The present invention relates to the field of aero-engine technology, and discloses a high-temperature zone threaded connection method and assembly with both anti-sticking and anti-rotation and anti-retreat functions. The tail of a D-head bolt has a tapered load-balancing hole axially extending from the tail of the D-head bolt to the middle of the bolt, thereby satisfying the variable stiffness design of the bolt shank and ensuring that the threads are more evenly stressed during operation. In particular, the method avoids the problem of thread stress during mating of internal and external threads, where the thread stress decreases sequentially from the head to the tail of the bolt, with the first few threads bearing approximately 70% of the load. The large extrusion load on the threads causes deformation and sticking of the threads, excessive friction between the threads, and difficulty in thread adhesion and nut disassembly. Drain plates are added to the rotor shafts corresponding to the tail and head of the D-head bolt, and the airflow outlet of the airflow cooling hole corresponding to each D-head bolt is located between the two drain plates. This avoids the problem of bolt adhesion caused by excessive temperature rise at the bolt connection due to wind resistance.

Description

Technical Field

[0001] The invention relates to the technical field of aviation engines and discloses a high-temperature zone thread connection method and a component with anti-adhesion, anti-rotation and anti-retreat functions. Background Art

[0002] Threaded connections are widely used in modern aircraft engine rotor and stator connections due to their simple structure and ease of assembly and disassembly. Aircraft engines are highly complex industrial products characterized by nonlinearity and strong coupling. Threaded bonding often occurs in critical locations such as the compressor rear axle, combustion chamber casing, and turbine rear axle. This can repeatedly lead to tooling overload damage, preventing the nuts from disassembling properly and necessitating destructive disassembly using electric sparks. This delays a three-hour disassembly task to over two days, significantly reducing engine disassembly efficiency and impacting cycle and economic indicators. The paper "Research on High-Temperature Bonding of Engine High-Temperature Alloy Fasteners," published in the journal Aviation Standardization, Issue 3, 2012, addresses the issue of self-locking nut bonding in aircraft engines. By comparing the quality of silver plating on various self-locking nuts domestically and internationally, the paper suggests that the primary cause of self-locking nut bonding in Chinese engines is the outdated silver plating process and substandard silver plating quality. The paper "Research on the Application of High-Frequency Axial Vibration in the Disassembly of Nuts of Hot-End Components of Aero-Engine" published in the 5th issue of 2018 of the journal "Aviation Precision Manufacturing Technology" aimed to solve the problem of difficulty in disassembling nuts of hot-end components of a small engine. A high-frequency axial vibration device was designed and manufactured, which improved the thread adhesion problem of the engine to a certain extent.

[0003] In fact, not only has the difficulty of disassembling self-locking nuts in domestic engines remained unresolved, but foreign engines such as the CFM56 and V2500 have also encountered thread adhesion issues. Threaded connections in critical aircraft engine locations are characterized by extreme operating environments, complex loads, and severe failure impacts. Critical locations such as the compressor rear axle, combustion chamber casing, and turbine rear axle can experience maximum operating temperatures of 425°C to 750°C or even higher, and engine speeds can reach tens of thousands of revolutions per minute. These threaded connections between engine rotors are subject to significant vibration loads. Furthermore, the combustion chamber casing requires extremely high sealing performance, and the tightening torque for these nuts is often more than twice that of nuts of the same size in other locations.

[0004] Research shows that the main reasons for thread adhesion and nut disassembly difficulties at key locations in aircraft engines are:

[0005] 1) Excessive operating temperature at the joint: In addition to the high ambient temperature at the joint itself, the high temperature is also caused by the engine rotor speed reaching tens of thousands of rpm. The friction between the bolt head and tail and the surrounding air generates heat, which directly causes the bolt temperature to rise by another 50°C or even higher. This temperature increase poses a significant challenge to the design of the internal and external thread clearance, grease, and coating.

[0006] 2) Inappropriate plating process: Silver plating is used on the internal threads of the nut to achieve self-lubrication. However, the silver layer produced by conventional electroplating silver plating has low density and weak bonding strength with the nut substrate. Under the extreme operating conditions of the engine, the silver layer on the internal threads of the nut is prone to falling off, causing the self-lubricating properties of the silver layer to fail and leading to adhesion between the bolt and the nut.

[0007] 3) The internal and external thread clearance is not appropriate in high temperature environments; the operating temperature of the key position of the engine is extreme. In a cold environment (the engine is not working), the bolts and nuts fit properly. However, in a high temperature environment (the engine is working at full power), due to the uncoordinated thermal expansion and contraction and deformation, the internal and external thread gaps become smaller and squeeze each other, causing the friction between the thread teeth to increase, which in turn causes the thread to stick and cannot be decomposed normally;

[0008] 4) The surface roughness of the connected parts is uneven, causing excessive friction on the local end faces. The connected parts are generally non-standard parts. Due to insufficient understanding of designers, manufacturing cost considerations and the high hardness of the connected parts, the roughness of the end faces of the connected parts is generally uneven and large overall, and the processing quality is also uneven. As a result, the friction between the nut and the end faces of the connected parts is too large during the disassembly process, causing the nut to be difficult to disassemble.

[0009] 5) The force on the threads is uneven, and some threads are subjected to greater force, resulting in greater overall friction. When the internal and external threads are mated, the threads that match the internal threads bear almost all the load, and the load on these threads is very uneven (the force on the mating threads decreases from the head to the tail of the bolt). The first few threads bear about 70% of the load, and the extrusion load on these threads is large, resulting in deformation and stagnation of the threads, excessive friction between the threads, and difficulty in thread bonding and nut disassembly.

[0010] 6) Wear debris from the coating, oxide layer, etc. cannot be discharged normally, further increasing the mutual extrusion of the thread teeth; the coating on the thread surface is a lubricating structure, and a small amount of shedding is inevitable during use. Ordinary bolts and nuts have no chip groove structure, resulting in severe mutual extrusion of the internal and external thread teeth, causing the internal and external threads to stick together and unable to decompose normally;

[0011] 7) The base materials of the bolts and nuts are not suitable, causing the internal and external threads to melt and bond together; the operating temperature of the key parts of the engine can reach over 750°C, but stainless steel, structural steel and titanium alloy thread structures are used, or high-temperature alloy materials of the same material and hardness are used, causing the internal and external threads to melt and bond together;

[0012] 8) The grease has insufficient heat resistance and the grease application area is unreasonable; the use of greases such as molybdenum disulfide, graphite, and paraffin is not suitable for the high-temperature area of ​​aircraft engines. When the temperature is higher than 450°C, greases such as molybdenum disulfide evaporate quickly, resulting in a complete loss of their lubrication function; during assembly, grease is only applied to the internal and external threads, and grease is not applied to the end face between the nut and the connected part, resulting in excessive end face friction, which in turn makes it difficult to disassemble the nut.

[0013] The patent with authorization announcement number CN 102878185B provides a ferrule thread connection method and component that prevents biting and loosening. The base material (stainless steel), coating material (zinc-nickel alloy), and lubricant material (molybdenum disulfide) of this component do not meet the temperature environment requirements of aircraft engines, and the structure is relatively complex (there are small structures such as crotch clamps and anti-slip washers), which does not meet the use requirements of aircraft engines in strong vibration environments.

[0014] The patent with authorization announcement number CN111271360 B, "A stainless steel threaded connection that prevents biting," is also not suitable for use in the high-temperature and high-vibration environment of key engine locations.

[0015] In addition, the bolt assemblies widely used in modern aircraft engines often lack anti-rotation and anti-retreat functions. After the nut is disassembled, the bolt assembly moves freely axially on the connected parts, causing the bolts to often fall off and fall into the engine cavity during the nut disassembly process. This requires human resources to search through endoscopes and other methods, which reduces the engine disassembly efficiency to a certain extent and even poses a certain threat to the safe operation of the engine. Summary of the Invention

[0016] The purpose of the present invention is to provide a high-temperature zone threaded connection method and component with anti-adhesion, anti-rotation and anti-retreat functions, which can more accurately reflect the defects and problems that may occur during the installation of the engine wiring harness during cable processing, inspection or pre-installation, so as to timely adjust the engine cable routing design and avoid these defects and problems during the actual installation of the engine cable.

[0017] In order to achieve the above technical effects, the technical solution adopted by the present invention is:

[0018] A high-temperature zone threaded connection assembly with both anti-adhesion and anti-rotation and anti-retreat functions includes a connected part, the connected part including an engine rotor shaft and a grate disk mounted on the rotor shaft, the rotor shaft including a front shaft and a rear shaft, the grate disk being fixed between the front shaft and the rear shaft by a D-head bolt; a tapered load-balancing hole with a gradually increasing diameter is opened in the axial direction at the tail of the D-head bolt, the tapered load-balancing hole extending from the tail of the D-head bolt to the middle of the bolt; the D-head bolt is matched with a self-locking nut for fixing the connected part, and a gasket is provided at the contact point between the self-locking nut and one of the connected parts; airflow cooling holes are provided on the rotor shaft at positions corresponding to the head and tail of the D-head bolt; the rotor shaft is respectively provided with guide plates at both ends near the head and tail of the D-head bolt, the root of the guide plate is fixed to the rotor shaft, the distal end of the guide plate extends obliquely toward the center of the grate disk, and the airflow outlet end of the airflow cooling hole corresponding to the D-head bolt is located between the two guide plates.

[0019] Furthermore, a vacuum ion silver plating layer is provided on the internal thread of the self-locking nut.

[0020] Furthermore, the cone angle of the tapered load-balancing hole is designed to be 6°.

[0021] Furthermore, a flange assembly is provided at the front axle or rear axle position that contacts the head of the D-head bolt, and a protrusion extending radially outward is provided at the edge of the flange assembly. A stop tongue is fixed to the head of the D-head bolt, and the stop tongue is an L-shaped structure; a hook that can interference fit with the protrusion is provided on the L-shaped structure.

[0022] Furthermore, the self-locking nut and the D-head bolt have a chip removal groove structure.

[0023] To achieve the above technical effects, the present invention also provides a high-temperature zone thread connection method with both anti-adhesion and anti-rotation and anti-retreat functions, comprising the following steps:

[0024] Before the connected parts are installed and fixed with D-head bolts, the outer thread diameter is determined in advance, and the matching of the self-locking nut, gasket and bolt is checked;

[0025] Apply grease to the bolts;

[0026] The D-head bolt is loaded with torque to fix the connected parts.

[0027] Furthermore, the gasket is made of alloy material, the surface roughness Ra is less than or equal to 1.6 μm, and the gasket thickness is greater than or equal to 2 mm.

[0028] Furthermore, the strength of the matrix material of the self-locking nut is lower than the strength of the matrix material of the bolt.

[0029] Furthermore, the installation torque of the D-head bolt is loaded according to a three-step method, with the first tightening being 50% of the design tightening torque value, the second tightening being 120% of the design tightening torque value, and the third step returning to 100% of the design tightening torque.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention utilizes a D-head bolt to secure the connected components in the high-temperature zone of an aircraft engine. The tail of the D-head bolt has a tapered, load-balancing hole structure axially extending from the tail of the D-head bolt to the middle of the bolt. This not only satisfies the variable stiffness design of the bolt shank but also ensures that the threads are more evenly stressed during operation. In particular, the invention avoids the stress on the threads during mating of internal and external threads. The stress on the mating threads decreases sequentially from the head to the tail of the bolt, with the first few threads bearing approximately 70% of the load. This creates a high extrusion load on the threads, leading to deformation and sticking of the threads, excessive friction between the threads, and difficulty in thread bonding and nut disassembly. Furthermore, guide plates are added to the rotor shafts corresponding to the tail and head of the D-head bolt. The airflow outlet of the airflow cooling hole corresponding to the D-head bolt is located between the two guide plates. This avoids the problem of excessive temperature at the bolt connection location, which can be caused by wind resistance and temperature rise, leading to bolt adhesion. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the threaded connection assembly in the high temperature zone in the embodiment;

[0033] Figure 2 Schematic diagram of the structure of the D-head bolt in the embodiment;

[0034] Among them, 1. Comb plate; 2. Front axle; 3. Rear axle; 4. D-head bolt; 5. Self-locking nut; 6. Gasket; 7. Air flow cooling hole; 8. Guide plate; 9. Protrusion; 10. Hook; 11. Load-balancing hole. DETAILED DESCRIPTION

[0035] The present invention will be described in further detail below with reference to the embodiments and accompanying drawings. However, this should not be construed as limiting the scope of the present invention to the following embodiments, as all technologies implemented based on the present invention fall within the scope of the present invention.

[0036] Example

[0037] See also Figure 1-Figure 2, a high-temperature zone threaded connection assembly with anti-adhesion, anti-rotation and anti-retreat functions, includes a connected part, the connected part includes an engine rotor shaft and a grate plate 1 installed on the rotor shaft, the rotor shaft includes a front shaft 2 and a rear shaft 3, the grate plate 1 is fixed between the front shaft 2 and the rear shaft 3 by a D-head bolt 4; the tail of the D-head bolt 4 is provided with a tapered load-balancing hole 11 with a gradually increasing diameter along the axial direction, the tapered load-balancing hole 11 extends from the tail of the D-head bolt 4 to the middle position of the bolt; the D-head bolt 4 is matched with a A self-locking nut 5 of the connected part, a gasket 6 is provided at the contact point between the self-locking nut 5 and one of the connected parts; air flow cooling holes 7 are provided on the rotor shaft at positions corresponding to the head and tail of the D-head bolt 4 (obliquely above); the rotor shaft is provided with guide plates 8 at both ends close to the head and tail of the D-head bolt 4, the root of the guide plate 8 is fixed to the rotor shaft, and the distal end of the guide plate 8 extends obliquely toward the center of the grate disk 1, and the air flow outlet end of the air flow cooling hole 7 corresponding to the D-head bolt 4 is located between the two guide plates 8.

[0038] In this embodiment, the bolt securing the connected component has a D-head structure with a D-shaped cross-section. After the connecting component is installed using the D-head bolt 4, the straight edge of the D-head bolt 4 is positioned to prevent rotation during tightening and loosening of the self-locking nut 5. A washer 6 is provided at the point where the self-locking nut 5 contacts one of the connected components. The surface finish of the washer 6 is far superior to the end surface roughness of the connected component, greatly facilitating stable control of end surface friction. The tail of the D-head bolt 4 has a tapered, load-balancing hole 11 extending axially from the tail of the D-head bolt 4 to the middle of the bolt. The tapered load-balancing hole 11 in this embodiment is designed with a 6° taper angle, which meets the variable stiffness design of the bolt shank and ensures that the threads are more evenly stressed during operation. In particular, this avoids the stress on the threads during mating of internal and external threads. The stress on the threads decreases from the head to the tail of the bolt, with the first few threads bearing approximately 70% of the load. The high extrusion load on the threads can lead to deformation and sticking of the threads, excessive friction between threads, thread adhesion, and difficulty in nut disassembly. Drain plates 8 are added to the rotor shaft corresponding to the tail and head of the D-head bolt 4. The airflow outlet of the airflow cooling hole 7 corresponding to each D-head bolt 4 is located between the two drain plates 8, which can avoid the problem of excessive temperature at the bolt connection caused by wind resistance temperature rise, leading to bolt adhesion. The curved surface of the guide plate 8 in this embodiment should be as smooth and rounded as possible, with a minimum tangential radius of not less than 20 mm. Since the guide plate 8 is a single cantilever structure, in order to ensure the rigidity characteristics, the wall thickness of the guide plate 8 is required to be not less than 2 mm. The guide plate 8 and the connected parts can be fixed by countersunk screws, such as MJ4 screws, to ensure a reliable connection while minimizing air resistance.

[0039] The high-temperature zone thread connection method with both anti-adhesion and anti-rotation and anti-retreat functions in this embodiment includes the following steps:

[0040] 1) Before the connected parts are installed and fixed with D-head bolts 4, the middle diameter of the external thread is determined in advance, and the matching of the self-locking nut 5, gasket 6 and bolt is checked.

[0041] 2) Apply grease to the bolts;

[0042] 3) Apply torque to the D-head bolt 4 to secure the connected component. In this embodiment, the installation torque of the D-head bolt 4 is applied in a three-step process: the first tightening is 50% of the design tightening torque value, the second tightening is 120% of the design tightening torque value, and the third tightening is back to 100% of the design tightening torque value.

[0043] The internal threads of the self-locking nut 5 in this embodiment are not allowed to be plated with zinc, cadmium, cadmium, or copper. Instead, silver plating is required. The silver plating process is preferably advanced plating processes such as vacuum ion silver plating. A vacuum ion silver plating layer is provided on the internal threads of the self-locking nut 5 to ensure the self-lubricating function of the silver plating layer in high-temperature environments. The effects of vacuum ion silver plating and conventional electroplating on the decomposition torque are shown in Table 1:

[0044] Table 1 Effects of vacuum ion silver plating and ordinary electroplating silver on decomposition torque

[0045]

[0046] The values ​​in Table 1 represent the decomposition torque. The smaller the decomposition torque, the better the anti-sticking effect. The data in Table 1 show that after the nut is vacuum ion silver-plated, the nut is easy to decompose.

[0047] In addition, the external threads of the D-head bolt 4 are not allowed to be silver-plated to prevent the silver plating from falling off and causing pollution or other adverse effects on the engine flow path and lubrication system.

[0048] The gasket 6 in this embodiment is made of high-temperature alloy material, and the surface roughness Ra shall not be greater than 1.6 μm to ensure that the end face friction is small and stable. The thickness of the gasket 6 is greater than or equal to 2 mm to avoid loosening of the thread.

[0049] The base material strength of the self-locking nut 5 is lower than that of the bolt. For example, when the maximum operating temperature at the connection is between 425°C and 595°C, the base material of the connected component is GH6159; when the maximum operating temperature at the connection is between 595°C and 650°C, the base material is GH2132 or GH4169; when the maximum operating temperature is below 650°C and 730°C, the base material is GH4738. It should be noted that in specific implementations, the base material includes but is not limited to the above-mentioned high-temperature alloy materials.

[0050] The tail of the self-locking nut 5 should be a three-point closing structure to ensure the sensitivity of the locking torque and the reliability of the connection. Due to the high temperature and complex vibration load, the self-locking nut 5 and the D-head bolt 4 should both use MJ threads to improve the fatigue strength of the threaded connection; due to the centrifugal load and sealing requirements, the diameter of the D-head bolt 4 and the self-locking nut 5 in this embodiment should be no less than 6mm to ensure the rigidity of the engine connection and achieve stable control of the dynamic characteristics of the engine rotor. The tolerance matching of the self-locking nut 5 and the D-head bolt 4 is very critical. The external thread adopts the "e", "f", and "g" tolerance band positions and the internal thread adopts the "H" tolerance band position according to the temperature; when the maximum operating temperature is higher than 650℃, the e / H matching should be adopted or the external thread should be 0.025mm larger than the internal thread to form a thread gap; the influence of 0.025mm gap thread and no gap thread on the decomposition torque is shown in Table 2:

[0051] Table 2 Effect of 0.025mm gap thread and no gap thread on decomposition torque

[0052]

[0053]

[0054] The values ​​in Table 2 represent the breakdown torques obtained by disassembling the nuts and bolts after engine testing. A smaller breakdown torque indicates better anti-sticking performance, while a larger breakdown torque indicates difficulty disassembling, meaning poor anti-sticking performance.

[0055] In this embodiment, a flange assembly is provided on the front axle 2 or rear axle 3 at the position where the head of the D-head bolt 4 contacts. A protrusion 9 extending radially outward is provided at the edge of the flange assembly. A retaining tongue is fixed to the head of the D-head bolt 4. The retaining tongue is an L-shaped structure. A hook portion 10 is provided on the L-shaped structure that can be interference-fitted with the protrusion 9. The D-head bolt 4 and the retaining tongue can be integrally formed, or they can be riveted or laser welded to form a bolt structure with a retaining tongue. The purpose of the retaining tongue is to prevent the D-head bolt 4 from falling into the engine cavity when the self-locking nut 5 is separated from the D-head bolt 4 by cooperating with the protrusion 9 of the rotor shaft flange assembly, thereby improving the safety of the engine. If laser welding is used to form a bolt structure with a retaining tongue, the laser welding between the D-head bolt 4 and the retaining tongue must not use a single triangle laser waveform, but a double triangle laser waveform. The welding depth must not be less than 1.6 mm to ensure that the strength and fatigue performance of the weld meet the requirements.

[0056] A temperature measuring crystal is embedded in the head and tail of the D-head bolt 4 respectively to obtain the temperature parameters at the monitoring points under various engine conditions, especially the highest temperature value under the maximum thermal load condition of the engine, for feedback and correction of the rationality of the design of the connected parts.

[0057] In addition, a grease reservoir is designed into the bolt head, where a small amount of HR-5211 grease is embedded. Although the grease has poor fluidity, it is ejected from the cavity and enters the threaded pair under centrifugal force to replenish insufficient grease. Grease should be applied during installation to prevent direct friction with the mating threaded pair and improve the mating surface between the threads (bolt and nut). The grease should be suitable for various operating conditions of the connected parts, such as high temperature and vibration, and have a long shelf life. The mating threads of the connecting bolt and nut, as well as the mating end faces of the nut and flange, must be lubricated with grease before assembly. Before applying grease, the threaded surface must be clean, burr-free, and applied as evenly as possible. Molybdenum disulfide grease is not permitted; only high-temperature greases such as Aviation Lubricants 4109, 4106, 4050, and HR-5211 can be used.

[0058] The self-locking nut 5 and the D-head bolt 4 have a chip flute structure. The chip flute design ensures that wear debris can be properly discharged when the coating is removed. In this embodiment, the chip flute is a helical structure with a helix angle of 15°. In addition, the self-locking nut 5 in this embodiment can be configured with an R1 chamfer structure to better store metal chips discharged from the chip flute structure.

[0059] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high temperature zone threaded connection assembly with anti-adhesion, anti-rotation and anti-retreat functions, characterized in that: The invention comprises a connected part, wherein the connected part comprises an engine rotor shaft and a grate plate mounted on the rotor shaft, wherein the rotor shaft comprises a front shaft and a rear shaft, and the grate plate is fixed between the front shaft and the rear shaft by a D-head bolt; a tapered load-balancing hole with a gradually increasing diameter is opened in the axial direction at the tail of the D-head bolt, and the tapered load-balancing hole extends from the tail of the D-head bolt to the middle position of the bolt; the D-head bolt is matched with a self-locking nut for fixing the connected part, and a vacuum ion silver-plated layer is provided on the internal thread of the self-locking nut, and a gasket is provided at the contact point between the self-locking nut and one of the connected parts; the rotor shaft is provided with a spacer between the head and tail of the D-head bolt An air flow cooling hole is provided at a position corresponding to the part; the rotor shaft is respectively provided with guide plates at both ends near the head and tail of the D-head bolt, the root of the guide plate is fixed to the rotor shaft, the distal end of the guide plate extends obliquely toward the center of the comb disk, and the air flow outlet end of the air flow cooling hole corresponding to the D-head bolt is located between the two guide plates; a flange assembly is provided at the front shaft or rear shaft position in contact with the head of the D-head bolt, a protrusion extending radially outward is provided at the edge position of the flange assembly, a stop tongue is fixed to the head of the D-head bolt, and the stop tongue is an L-shaped structure; a hook portion that can be interference fit with the protrusion is provided on the L-shaped structure.

2. The high temperature zone threaded connection assembly with anti-adhesion, anti-rotation and anti-retreat functions according to claim 1, characterized in that: The cone angle of the tapered equalizing hole is designed to be 6°.

3. The high temperature zone threaded connection assembly with anti-adhesion, anti-rotation and anti-retreat functions according to claim 1, characterized in that: Self-locking nuts and D-head bolts have a chip groove structure.

4. A high temperature zone thread connection method with both anti-adhesion and anti-rotation and anti-retreat functions, characterized in that: The method is based on the high-temperature zone threaded connection assembly with anti-sticking, anti-rotation and anti-retreat functions according to any one of claims 1 to 3, and comprises the following steps: Before the connected parts are installed and fixed with D-head bolts, the outer thread diameter is determined in advance, and the matching of the self-locking nut, gasket and bolt is checked; Apply grease to the bolts; The D-head bolt is loaded with torque to fix the connected parts.

5. The high temperature zone thread connection method with both anti-adhesion and anti-rotation and anti-retreat functions according to claim 4 is characterized in that: The gasket is made of alloy material, with a surface roughness Ra less than or equal to 1.6 μm and a gasket thickness greater than or equal to 2 mm.

6. The high temperature zone thread connection method with both anti-adhesion and anti-rotation and anti-retreat functions according to claim 4, characterized in that: The strength of the matrix material of the self-locking nut is lower than that of the matrix material of the bolt.

7. The high temperature zone thread connection method with both anti-adhesion and anti-rotation and anti-retreat functions according to claim 4, characterized in that: The installation torque of the D-head bolt is loaded according to a three-step method, wherein the first tightening is 50% of the design tightening torque value, the second tightening is 120% of the design tightening torque value, and the third tightening is returned to 100% of the design tightening torque.

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