A heat treatment process for high-strength bolts of wind turbine blades

Abstract

The present invention relates to the field of bolt heat treatment technology, specifically a heat treatment process for high-strength bolts for wind turbine blades, comprising the following steps: presetting the bolt heat treatment state, performing impact treatment on the bolt thread root by a bolt heat treatment device to form a nanocrystalline layer; performing three-stage pulse nitriding in an ammonia atmosphere containing Ce-La mixed rare earth; and performing gradient cooling using a water-based atomized quenching liquid containing polyvinyl alcohol and graphene under the action of a transverse steady magnetic field. The beneficial effect of the present invention is that through the synergistic effect of multiple steps such as surface mechanical nano-pretreatment, rare earth element gradient nitriding, magnetic field-assisted gradient quenching, and pulse current deep-cold composite tempering, the technical solution significantly improves the comprehensive performance of high-strength bolts for wind turbine blades. Specifically, the surface hardness is greatly improved while maintaining good toughness in the core, the corrosion resistance and fatigue life of the bolts are also significantly improved, and the service life in extreme marine environments is longer.

Description

Technical Field

[0001] The present invention relates to the technical field of bolt heat treatment, and in particular to a heat treatment process for high-strength bolts of wind turbine blades. Background Art

[0002] In the wind turbine industry, the performance of specialized fasteners, such as high-strength bolts for wind turbine blades, is crucial. Heat treatment is a key step in improving the performance of these bolts. Traditional heat treatment processes have limitations in improving bolt strength and wear resistance. As wind turbine operating environments become increasingly complex, the performance requirements for bolts continue to rise. The development of new, efficient heat treatment processes for high-strength bolts for wind turbine blades is urgent to ensure the long-term, stable operation of wind turbines.

[0003] Currently, traditional heat treatment processes face numerous challenges in improving bolt performance, including matching surface hardness with core toughness, ensuring uniformity in nitriding layer depth and hardness, the risk of cracking during quenching, and the limitations of tempering on performance improvement. Especially in extreme marine environments, bolts must withstand harsh conditions such as high salt spray corrosion and alternating loads, placing even higher demands on their strength, corrosion resistance, and fatigue life.

[0004] Therefore, developing a new and efficient heat treatment process for high-strength bolts of wind turbine blades to solve the performance bottleneck problem in the existing technology has become a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In response to the technical problems existing in the prior art, the present invention provides a heat treatment process for high-strength bolts for wind turbine blades to meet the higher requirements for the strength, corrosion resistance and fatigue life of the bolts in extreme marine environments where the bolts need to withstand harsh working conditions such as high salt spray corrosion and alternating loads.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: A heat treatment process for high-strength bolts of wind turbine blades, comprising the following steps:

[0007] The bolt heat treatment state is preset, and the bolt thread root is subjected to impact treatment by the bolt heat treatment device to form a nanocrystalline layer;

[0008] Three-stage pulse nitriding is carried out in an ammonia atmosphere containing Ce-La mixed rare earth;

[0009] Under the action of a transverse steady magnetic field, gradient cooling is performed using a water-based atomized quenching liquid containing polyvinyl alcohol and graphene.

[0010] Liquid nitrogen cryogenic treatment is performed, followed by pulsed current applied during the tempering process.

[0011] Furthermore, the temperature of the first stage of the three-stage pulse nitriding process is 520°C, the nitriding time is 2 hours, the temperature of the second stage is 580°C, the nitriding time is 1.5 hours, and the temperature of the third stage is 500°C, the nitriding time is 3 hours.

[0012] Furthermore, the transverse steady magnetic field intensity is regulated in stages, including an initial stage, a main quenching stage, and a final cooling stage; the quenching liquid atomization pressure is synchronously regulated with the transverse steady magnetic field intensity in each stage.

[0013] Furthermore, the liquid nitrogen cryogenic treatment includes a first stage, a second stage and a third stage of gradient cooling;

[0014] The first stage: 25°C to -80°C, cooling rate 3°C / min, hold for 15 minutes;

[0015] The second stage: -80°C to -140°C, cooling rate 2°C / min, hold for 10 minutes;

[0016] The third stage: -140°C to -196°C, cooling rate 1°C / min, holding for 5 minutes.

[0017] Furthermore, the bolt heat treatment device includes a fixed frame, on which a rotating workstation frame that can rotate periodically 90° is rotatably installed, and the rotating workstation frame is provided with four bolt fixing components, and the bolt fixing components are transmission-connected to a vibration bracket that can move up and down, and the inner wall of the vibration bracket is rotatably installed with a transmission bottom shaft, and the inner wall of the transmission bottom shaft is rotatably installed with a magnetic shaft, and the top of the magnetic shaft is provided with a magnetic suction groove for magnetic positioning of the bolt, and the transmission bottom shaft and the magnetic shaft rotate coaxially and in opposite directions, and the fixed frame is provided with loading and unloading stations, nano-processing stations, negative pressure cleaning stations and cleaning stations in sequence in a clockwise direction, and a processing frame is installed on the fixed frame in a liftable manner, and nozzle mechanisms are provided on the processing frame and at positions corresponding to the nano-processing stations, negative pressure cleaning stations and cleaning stations, the bolts are subjected to nano-impact treatment at the nano-processing station, negative pressure suction of nanoparticles is performed at the negative pressure cleaning station, and the bolts are cleaned and low-temperature stress is eliminated at the cleaning station.

[0018] Furthermore, it also includes a servo motor installed at the bottom of the fixed frame, the output shaft end of the servo motor is installed with an incomplete gear, the incomplete gear is fixedly provided with a transmission tooth surface, the bottom surface of the rotating workstation is installed with an intermittent shaft, the intermittent shaft is fixedly provided with an intermittent gear meshing with the transmission tooth surface, the meshing area of ​​the transmission tooth surface corresponds to a central angle of 90°, the radius of the incomplete gear is the same as the radius of the intermittent gear, a hollow gear shaft is rotatably sleeved on the intermittent shaft, a driving gear ring is installed on the hollow gear shaft, a belt is transmission-connected between the output shaft end of the servo motor and the hollow gear shaft, a bottom cylinder is fixedly installed on the fixed frame, a shaft frame is fixedly installed on the bottom cylinder, a guide shaft is rotatably installed on the shaft frame and corresponds to the positions of the nano-processing station, the negative pressure cleaning station and the cleaning station, a transmission bevel gear and a passive gear transmission-connected to the driving gear ring are respectively installed on the guide shaft, the bolt fixing component is adaptively connected to the transmission bevel gear, a vertically arranged screw lifting module is installed on the fixed frame, and the screw lifting module is transmission-connected to the processing frame.

[0019] Furthermore, the bolt fixing component includes a large circular shaft and a hollow shaft rotatably connected to the rotating workstation, one end of the large circular shaft is fixedly installed with a passive bevel gear meshing with the transmission bevel gear, and a first bevel gear is installed on both the hollow shaft and the large circular shaft, and the two first bevel gears are meshed with each other. The interior of the hollow shaft is fixed with a hollow groove with openings at both ends and slidingly connected to the magnetic shaft, and the cross-sections of the magnetic shaft and the hollow groove are both regular hexagons. An eccentric wheel is installed on the large circular shaft, and a follower wheel is rotatably installed on the vibration bracket, and the follower wheel is in rolling contact with the contour surface of the eccentric wheel. The vibration bracket is slidably connected to the rotating workstation, and a vibration spring limited by the rotating workstation is installed on the top surface of the vibration bracket.

[0020] Furthermore, the bolt fixing component also includes a small circular shaft rotatably mounted on the vibration bracket, a conical tooth is installed on the small circular shaft, a second conical tooth is installed on both the magnetic shaft and the transmission bottom shaft, the two second conical teeth are both connected to the conical tooth transmission, and the two second conical teeth are respectively arranged on both sides of the conical tooth.

[0021] Furthermore, the nozzle mechanism includes a catheter and a follower seat, the catheter is fixedly installed on the processing frame, two T-shaped guide rods are installed on the top surface of the follower seat, and the two T-shaped guide rods are slidably connected to the catheter. A rotary sleeve is rotatably installed on the inner wall of the follower seat, and a sealing rubber ring connected to the transmission bottom shaft is fixedly installed on the bottom end of the rotary sleeve. A nozzle is fixedly installed on the inner wall of the rotary sleeve, and the nozzle is inclined at a 45° angle toward the root of the bolt thread. A through cavity is fixedly opened on the top of the rotary sleeve, and the tail of the nozzle The end is connected with the through cavity, the bottom end of the conduit is rotatably connected with the through cavity through a bellows, and a vibration spring is sleeved on the bellows. The top end of the conduit in the nano-processing station is fixedly provided with a nano-material connecting pipe connected with the high-pressure nano-particle feeding device, the top end of the conduit in the negative pressure cleaning station is fixedly provided with a negative pressure suction pipe connected with the negative pressure suction device, the top end of the conduit in the cleaning station is fixedly provided with a cleaning joint connected with the cleaning liquid feeding device, and a heating coil is fixedly installed on the outside of the rotary casing in the cleaning station.

[0022] Furthermore, it also includes a sleeve rotatably sleeved on the bottom cylinder, a sewage suction flow channel is fixedly opened inside the magnetic shaft, the bottom end of the sewage suction flow channel is connected with the sleeve through a sewage outlet pipe, a group of sewage suction holes distributed in a circular array and connected with the sewage suction flow channel are opened on the magnetic shaft, a sewage discharge cavity is fixedly opened inside the bottom cylinder, a sewage discharge hole connected with the sewage discharge cavity is fixedly opened on the bottom cylinder and at a position corresponding to the cleaning station, and a sewage storage box connected with the sewage discharge cavity is fixedly installed on the fixed frame.

[0023] Furthermore, the magnetic shaft is made of permanent magnetic material, and the cross section of the magnetic groove is a regular hexagon.

[0024] The beneficial effects of the present invention are:

[0025] 1. Through the synergistic effects of multiple steps, including surface mechanical nano-crystallization pretreatment, rare earth element gradient nitriding, magnetic field-assisted gradient quenching, and pulsed current deep-cold composite tempering, this technical solution significantly improves the overall performance of high-strength bolts for wind turbine blades. Specifically, the surface hardness is significantly increased while maintaining good core toughness. The corrosion resistance and fatigue life of the bolts are also significantly improved, extending their service life in extreme marine environments.

[0026] 2. Building upon traditional heat treatment processes, several innovations have been implemented, including the use of 100μm tungsten carbide cobalt particles for impact treatment to form a nanocrystalline layer, the introduction of rare earth elements Ce-La for gradient nitriding, the use of a steady magnetic field to assist gradient quenching, and deep-cold composite tempering combined with pulsed current. These innovative processes not only improve bolt performance but also significantly increase production efficiency. Magnetic field-assisted quenching achieves surface-to-core cooling rate gradient control by optimizing magnetic field intensity and quenching liquid injection velocity, avoiding the risk of cracking associated with traditional quenching processes. Furthermore, pulsed current deep-cold composite tempering technology further enhances the bolt's strength and toughness, making the entire heat treatment process more efficient and controllable.

[0027] 3. The present invention significantly improves the uniformity of bolt surface treatment, enhances the shear resistance and fatigue life of the bolt. Through the dynamic vibration control mechanism, high-frequency micro-vibration combined with tungsten carbide cobalt particle impact, a uniform nanocrystalline layer with a thickness of 50-80μm and a grain size of <100nm is formed at the root of the thread. Compared with traditional static impact, the grain refinement efficiency is improved by 40%, and the nanolayer thickness deviation is reduced from ±15% to ±5%, which solves the problems of weak shear resistance and short fatigue life caused by uneven particle distribution in traditional processes. This technology creatively introduces an eccentric wheel-follower wheel vibration structure and regular hexagonal magnetic positioning to ensure that the bolt has no displacement deviation during impact, and is suitable for extreme wind load conditions.

[0028] 4. The present invention adopts a three-stage pulse nitriding process, combined with an ammonia atmosphere containing Ce-La rare earths, to form a rare earth element gradient penetration layer. Compared with the single-temperature nitriding process, the surface hardness uniformity is improved by 30%, and the salt spray corrosion test life is extended by more than 2 times, which is significantly adapted to the high salt spray environment at sea. This gradient design breaks through the temperature control bottleneck of the traditional nitriding process, promotes the deep diffusion of rare earth elements through dynamic temperature adjustment, and has the dual advantages of high hardness and corrosion resistance.

[0029] 5. The present invention uses graphene-containing atomized quenching liquid for gradient cooling under a 0.5-1.2T transverse magnetic field, and dynamically adjusts the magnetic field intensity and cooling rate through a machine learning model to reduce the residual stress fluctuation from the traditional ±150MPa to within ±50MPa. This solution creatively introduces intelligent control technology, combined with the graphene-enhanced thermal conductivity of the quenching liquid, effectively suppresses stress concentration, significantly improves the fatigue life of the bolts under high-frequency alternating loads, and eliminates the need for manual debugging, reducing process costs by 20%.

[0030] 6. The present invention can achieve high-precision multi-station collaboration, and improve both production efficiency and consistency. It is based on an incomplete gear intermittent gear structure driven by a servo motor, and the positioning accuracy of the rotary station frame reaches ±0.1mm. Combined with the regular hexagonal magnetic suction groove clamping, it completely eliminates the circumferential sliding of the bolts. Compared with the traditional continuous rotation station, the multi-process switching efficiency is increased by 50%, and the consistency of the nanolayer thickness is increased to 98%. The equipment design solves the industry problems of large positioning deviation and unstable clamping of traditional devices through the integration of mechanical structure and intelligent control, providing reliable guarantee for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Flow chart of heat treatment process for high-strength bolts for wind turbine blades

[0032] Figure 2 This is the principle diagram of the heat treatment process for high-strength bolts of wind turbine blades;

[0033] Figure 3 This is a schematic diagram of the overall structure of the bolt heat treatment device of the present invention;

[0034] Figure 4 For the present invention Figure 1 Schematic diagram of the cross-section structure;

[0035] Figure 5 For the present invention Figure 4 Schematic diagram of the local enlarged structure at A in the middle;

[0036] Figure 6 For the present invention Figure 4 Schematic diagram of the local enlarged structure at B in the middle;

[0037] Figure 7 For the present invention Figure 4 Schematic diagram of the local enlarged structure at C in the middle;

[0038] Figure 8 This is a schematic structural diagram of the negative pressure pipette, nanomaterial pipe connection and cleaning connector of the present invention;

[0039] Figure 9 This is a schematic structural diagram of the bottom drum and intermittent gear of the present invention;

[0040] Figure 10 It is a structural schematic diagram of the shaft frame and the bottom cylinder of the present invention;

[0041] Figure 11 It is a structural schematic diagram of the magnetic suction groove and the vibration spring of the present invention.

[0042] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0043] 1. Bolt heat treatment device; 2. Fixed frame; 3. Rotating workstation; 4. Vibrating bracket; 5. Transmission bottom shaft; 6. Magnetic shaft; 7. Magnetic groove; 8. Processing rack; 9. Servo motor; 10. Incomplete gear; 11. Intermittent shaft; 12. Intermittent gear; 13. Hollow gear shaft; 14. Active ring gear; 15. Bottom cylinder; 16. Shaft frame; 17. Guide shaft; 18. Passive gear; 19. Screw lifting module; 20. Large circular shaft; 21. Hollow shaft; 22. Eccentric wheel; 23 , follower wheel; 24, vibration spring; 25, small round shaft; 26, follower seat; 27, T-shaped guide rod; 28, rotary casing; 29, nozzle; 30, through cavity; 31, bellows; 32, vibration spring; 33, nano material connecting pipe; 34, negative pressure suction pipe; 35, cleaning joint; 36, heating coil; 37, sleeve; 38, sewage suction channel; 39, sewage suction hole; 40, sewage discharge cavity; 41, sewage discharge hole; 42, sewage storage box; 43, bolt; 44, sewage outlet pipe; 45, catheter. DETAILED DESCRIPTION

[0044] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0045] The present invention provides the following preferred embodiments

[0046] like Figure 1-2 As shown, a heat treatment process for high-strength bolts of wind turbine blades includes the following steps:

[0047] SS01, Surface Mechanical Nano-Cut Pretreatment: The bolt 43 is preheated to a predetermined state. The bolt heat treatment device 1 uses 100 μm tungsten carbide cobalt particles to impact the thread root of the bolt 43 at a speed of 300 m / s, forming a nanocrystalline layer with a thickness of 80 μm and a grain size of less than 100 nm.

[0048] SS02, rare earth element gradient nitriding: three-stage pulse nitriding is carried out in an ammonia atmosphere containing 1.2wt% Ce-La mixed rare earth;

[0049] The synergistic catalytic mechanism of rare earth elements (Ce-La) is as follows:

[0050] Surface activation: The atomic radius of rare earth elements Ce (cerium) and La (lanthanum) is relatively large (Ce: 0.182nm, La: 0.187nm). Their high surface energy characteristics can preferentially adsorb on the surface of the bolt, remove oxide films and impurities, form active sites, and promote the decomposition of NH3 into active nitrogen atoms (N*).

[0051] Accelerated Grain Boundary Diffusion: Rare earth elements concentrate at grain boundaries during nitriding, reducing the activation energy for nitrogen atoms to diffuse and accelerating nitrogen penetration into the matrix. Experiments have shown that adding 1.2wt% Ce-La mixed rare earth can increase the nitrogen diffusion coefficient by 30%-40%.

[0052] Nitride refinement control: rare earth elements inhibit Fe3N coarsening and promote ε-Fe 23 The N phase precipitates uniformly to form a dense nitride layer, which improves the surface hardness (HV can reach 1200-1400) and corrosion resistance

[0053] In the SS02 step, the temperature of the first stage of the three-stage pulse nitriding process is 520°C, the nitriding time is 2 hours, the temperature of the second stage is 580°C, the nitriding time is 1.5 hours, and the temperature of the third stage is 500°C, the nitriding time is 3 hours;

[0054] The three-stage pulse temperature gradient design is as follows:

[0055] The first stage (520℃×2h): The medium temperature stage is mainly based on the formation of γ'-Fe4N. The rare earth elements are enriched on the surface to form nano-scale CeN / LaN particles as nucleation points, laying the foundation for a high hardness base layer (thickness of about 10-15μm).

[0056] The second stage (580℃×1.5h): The temperature is raised to above the austenitizing temperature to accelerate the diffusion of nitrogen toward the center. At the same time, the rare earth elements migrate inward along the grain boundaries to form a deep gradient transition layer (the total penetration layer reaches 0.3-0.4mm), which relieves the stress concentration caused by the sudden change in hardness.

[0057] The third stage (500℃×3h): The cooling and tempering stage stabilizes the ε phase, and the rare earth elements react with the retained austenite to form LaFeO3 / Ce2O3 oxide film, which seals the micropores and improves the salt spray corrosion resistance (ASTM B117 salt spray test life>1000h).

[0058] Equipment: controlled atmosphere pulse nitriding furnace (ammonia purity ≥ 99.99%), Ce-La mixed rare earth powder (Ce:La=3:1).

[0059] Ammonia atmosphere: NH3 flow rate 1.8 L / min, mixed with 1.2 wt% Ce-La rare earth powder (200 mesh).

[0060] The temperature-time parameters are as follows:

[0061] The first stage: 520℃×2h, furnace pressure 0.15MPa;

[0062] The second stage: 580°C × 1.5h, furnace pressure 0.08MPa (periodic pulse: switching 0.12MPa / 0.05MPa every 10min);

[0063] The third stage: 500℃×3h, furnace pressure 0.20MPa.

[0064] The performance test results are as follows:

[0065] Hardness gradient (HV0.3):

[0066] Depth (μm) 0(surface) 50 100 200 300 Hardness value 1320 980 750 620 450

[0067] Through the deep segregation of Ce-La, a cross-scale performance match of "ultra-hard surface and strong core" is achieved; three-stage variable temperature coupled pulse ammonia breaks through the diffusion kinetics limitations of traditional isothermal nitriding and increases the nitriding rate by 40%; the synergistic effect of the rare earth oxide film and the gradient nitriding layer increases the life of the bolts in the high salt spray environment at sea by more than 2 times.

[0068] SS03, magnetic field assisted gradient quenching: under the action of 1.2T transverse steady magnetic field, a 20wt% polyvinyl alcohol and 0.05wt% graphene Water-based mist quenching The liquid is cooled in a gradient manner;

[0069] The control mechanism of the transverse steady-state magnetic field is as follows:

[0070] Magnetostrictive effect: A 1.2T transverse magnetic field induces anisotropic strain (ΔL / L≈5×10 -6 ), which promotes the preferential orientation of the austenite lattice along the direction of the magnetic field and reduces the resistance to martensitic phase transformation.

[0071] Lorentz force suppresses bubbles: During the atomization process of the quenching liquid, the Lorentz force (F=qv×B) generated by the magnetic field causes the charged droplets to produce a spiral motion, breaking the steam film and increasing the heat transfer coefficient (up to 3800W / m 2 ·K, 40% higher than traditional water quenching).

[0072] Dislocation orientation: Under a magnetic field, dislocation lines are preferentially arranged along the {110} crystal plane slip system, forming a substructure parallel to the magnetic field direction, thereby improving shear strength (τ_max increases by 18%-22%).

[0073] Graphene-enhanced quenching fluid properties include:

[0074] Thermal conductivity enhancement: 0.05wt% graphene increases the thermal conductivity of the quenching liquid from 0.6W / m·K to 1.8W / m·K (a 200% increase), and the graphene sheets are oriented in a magnetic field (XRD shows (002) plane orientation >85%), forming a fast heat conduction channel.

[0075] Wettability optimization: Graphene is adsorbed on the surface of steel parts, and the contact angle is reduced from 78° to 32°, breaking through the critical temperature of the Leidenfrost effect (from 280°C to 450°C), achieving a rapid transition from stable film boiling to nucleate boiling.

[0076] Stress buffering: Polyvinyl alcohol (20 wt%) forms a three-dimensional network structure with graphene, which suppresses the sudden change in quenching liquid viscosity (η = 12 mPa·s at 25°C, η = 3.2 mPa·s at 300°C) and reduces thermal stress concentration.

[0077] Dynamic control of gradient cooling includes:

[0078] Magnetic field-cooling coupling: Through a 0.5T→1.2T magnetic field intensity gradient (increased by 0.1T every 30s), combined with an increase in the quenching liquid injection speed from 2m / s to 5m / s, a cooling rate gradient from the surface to the core (surface: 220℃ / s, core: 45℃ / s) was achieved.

[0079] Phase transformation sequence control: lath martensite is preferentially formed on the surface (lath width 50-80nm), and 10%-15% retained austenite is retained in the core, obtaining a "hard surface and tough core" structure (surface hardness HRC58-60, core impact energy AKU=75J).

[0080] The equipment includes: transverse magnetic field quenching furnace (magnetic field strength 0-2T adjustable), graphene modified atomization quenching system.

[0081] Magnetic Field Program:

[0082] Initial stage (0-30s): 0.5T steady magnetic field;

[0083] Main quenching stage (30-90s): linearly increased to 1.2T;

[0084] Final cooling stage (90-120s): maintain 1.2T.

[0085] Quenching liquid parameters:

[0086] Polyvinyl alcohol concentration: 20 wt% (molecular weight 130,000);

[0087] Graphene content: 0.05wt% (sheet diameter 5-10μm, number of layers <5);

[0088] Atomization pressure: 0.4→0.8MPa gradient pressure increase.

[0089] It should be noted that the synergistic effect of the 1.2T transverse magnetic field and the graphene quenching liquid increases the heat transfer efficiency to 2.3 times that of traditional oil quenching, while avoiding the high cracking risk of water quenching and improving fatigue life.

[0090] It is suitable for mass production of wind turbine main shaft bolts. Under extreme working conditions of wind turbines (alternating load ±250kN, frequency 0.5Hz), the service life is extended from 8 years to 15 years without the need for intermediate maintenance or replacement.

[0091] SS04, pulse current deep cooling composite tempering: first perform liquid nitrogen deep cooling treatment at -196℃×2h, then apply 1000A / cm during tempering at 450℃ 2 , 10kHz pulse current, lasting 4h;

[0092] Equipment: Liquid nitrogen cryogenic box (-196℃±2℃), high frequency pulse tempering furnace (maximum current density 1500A / cm 2 ).

[0093] Cryogenic treatment:

[0094] Temperature: -196°C;

[0095] Time: 2 hours (including 30 minutes of step cooling: 25℃→-80℃→-140℃→-196℃).

[0096] Stage 1: 25°C to -80°C, cooling rate 3°C / min, hold for 15 minutes;

[0097] The second stage: -80℃ to -140℃, cooling rate 2℃ / min, hold for 10min;

[0098] The third stage: -140℃ to -196℃, cooling rate 1℃ / min, hold for 5 minutes.

[0099] Through three-stage gradient cooling (total time 30min), the micro cracks caused by sudden cooling are suppressed (the crack density is reduced from 15 / cm in the traditional process to 2 Reduced to ≤2 / cm 2 .

[0100] Pulse tempering:

[0101] Temperature: 450℃ (furnace temperature uniformity ±5℃);

[0102] Current parameter: 1000A / cm 2 , 10kHz square wave pulse (pulse width 50μs, interval 450μs);

[0103] Time: 4 hours (divided into 2 cycles, each cycle is 2 hours with 30 minutes of air cooling interval).

[0104] Through the spatiotemporal coordination of deep cooling and pulse current, the strength and toughness of wind turbine bolts are improved, making the service life of wind turbine bolts longer in extreme marine environments.

[0105] The heat treatment process for high-strength bolts for wind turbine blades according to the present invention further comprises the following steps:

[0106] SS05, real-time process control: Dynamically adjust the magnetic field intensity and cooling rate of the SS03 step through a machine learning model to control surface residual stress fluctuations within the range of ±50MPa;

[0107] By dynamically adjusting the magnetic field intensity and cooling rate through a machine learning model, the problem of uneven residual stress distribution caused by fixed parameters in traditional heat treatment processes is solved. In the specific workflow, the system collects temperature gradient, magnetic field intensity and coolant flow rate data in the quenching stage in real time, and combines the material properties of bolt 43. The optimal parameter combination is predicted through the trained neural network, so that the surface residual stress fluctuation is strictly controlled within the range of ±50MPa. Compared with the existing technology, this solution significantly improves the fatigue life and stress corrosion resistance of bolt 43. It is particularly suitable for high-frequency alternating load conditions of wind turbine blades, avoiding early failure caused by stress concentration, while reducing manual debugging costs and realizing intelligent and high-precision process control.

[0108] The inventors also found that in the heat treatment process of high-strength bolts for wind turbine blades, the surface treatment uniformity was poor; in the traditional mechanical impact treatment method, due to the lack of a dynamic vibration control mechanism, the nanoparticles were unevenly distributed, resulting in poor consistency in the thickness of the nanocrystalline layer and the grain size, affecting the shear resistance and fatigue life of the bolt thread root.

[0109] like Figure 3-Figure 11 As shown, the present invention also designs a bolt heat treatment device 1 for implementing impact treatment on the root of the bolt thread.

[0110] The bolt heat treatment device 1 of the present invention includes a fixed frame 2, on which a rotating workstation 3 that can rotate periodically 90 degrees is rotatably mounted. The rotating workstation 3 is provided with four bolt fixing components. The bolt fixing components are connected to a vibration bracket 4 that can move up and down. A transmission bottom shaft 5 is rotatably mounted on the inner wall of the vibration bracket 4. A magnetic shaft 6 is rotatably mounted on the inner wall of the transmission bottom shaft 5. A magnetic groove 7 for magnetically positioning the bolt 43 is provided on the top of the magnetic shaft 6. The transmission bottom shaft 5 and the magnetic shaft 6 rotate coaxially and in opposite directions.

[0111] The magnetic shaft 6 is made of permanent magnetic material, and the cross section of the magnetic groove 7 is a regular hexagon.

[0112] The precise matching of the regular hexagonal magnetic slot 7 and the hexagonal structure of the bolt 43 head achieves zero-gap positioning. During the process, the permanent magnetic shaft 6 quickly fixes the bolt 43 through magnetic force. The regular hexagonal cross-section of the hollow slot prevents the bolt 43 from sliding circumferentially during handling. Compared with circular or square slots, this design improves clamping efficiency by 60% and is compatible with the specifications of standard wind power bolts 43. It avoids deviations in the nano-layer thickness at the root of the thread due to loosening of the clamping, ensuring process stability in mass production.

[0113] The fixed frame 2 is provided with loading and unloading stations, nano-processing stations, negative pressure cleaning stations and cleaning stations in a clockwise direction. The fixed frame 2 is provided with a processing frame 8 which can be raised and lowered. The processing frame 8 is provided with nozzle mechanisms at positions corresponding to the nano-processing station, negative pressure cleaning station and cleaning station. The bolt 43 is subjected to nano-impact treatment at the nano-processing station, negative pressure suction of nanoparticles is performed at the negative pressure cleaning station, and the bolt 43 is cleaned and low-temperature stress is eliminated at the cleaning station.

[0114] It also includes a servo motor 9 installed at the bottom of the fixed frame 2, an incomplete gear 10 is installed on the output shaft end of the servo motor 9, a transmission tooth surface is fixedly provided on the incomplete gear 10, an intermittent shaft 11 is installed on the bottom surface of the rotary workstation 3, an intermittent gear 12 meshing with the transmission tooth surface is fixedly installed on the intermittent shaft 11, the meshing area of ​​the transmission tooth surface corresponds to a central angle of 90°, the radius of the incomplete gear 10 is the same as the radius of the intermittent gear 12, a hollow gear shaft 13 is rotatably provided on the intermittent shaft 11, an active gear ring 14 is installed on the hollow gear shaft 13, and the servo motor A belt is connected to the output shaft end of 9 and the hollow gear shaft 13. A bottom cylinder 15 is fixedly installed on the fixed frame 2, and a shaft frame 16 is fixedly installed on the bottom cylinder 15. A guide shaft 17 is rotatably installed on the shaft frame 16 and corresponds to the positions of the nano-processing station, the negative pressure cleaning station and the cleaning station. The guide shaft 17 is respectively equipped with a transmission bevel gear and a passive gear 18 connected to the active gear ring 14. The bolt fixing component is adapted to the transmission bevel gear. A vertically arranged screw lifting module 19 is installed on the fixed frame 2, and the screw lifting module 19 is transmission-connected to the processing frame 8.

[0115] When the heat treatment equipment for high-strength bolts 43 of wind turbine blades is running, the servo motor 9 is started and the hollow gear shaft 13 is driven to rotate through the belt, and the active ring gear 14 on the hollow gear shaft 13 rotates accordingly. The active ring gear 14 cooperates with the passive gear 18 to drive the guide shaft 17 to rotate. At the same time, the incomplete gear 10 at the output shaft end of the servo motor 9 is engaged with the intermittent gear 12. Since the meshing area of ​​the transmission tooth surface corresponds to a central angle of 90°, and the radius of the incomplete gear 10 is the same as the radius of the intermittent gear 12, the rotary work station 3 is accurately and periodically rotated by 90°, ensuring seamless switching of nano-processing, cleaning and washing stations. The screw lifting module 19 accurately lifts the processing frame 8. The traditional rotary work station 3 often causes positioning deviation due to mechanical clearance, affecting the continuity and accuracy of the heat treatment process. This design solves this problem. In conjunction with the screw lifting module 19, the efficiency of multi-process coordination is significantly improved, the error during equipment operation is reduced, the overall efficiency and quality of the heat treatment of high-strength bolts 43 of wind turbine blades are improved, and the stability and reliability of production are guaranteed.

[0116] The bolt fixing component includes a large circular shaft 20 and a hollow shaft 21 which are rotatably connected to the rotating work station frame 3. One end of the large circular shaft 20 is fixedly installed with a passive bevel gear meshing with the transmission bevel gear. A first bevel gear is installed on both the hollow shaft 21 and the large circular shaft 20. The two first bevel gears mesh with each other. The interior of the hollow shaft 21 is fixed with a hollow groove with openings at both ends and slidingly connected to the magnetic shaft 6. The cross-sections of the magnetic shaft 6 and the hollow groove are both regular hexagons. An eccentric wheel 22 is installed on the large circular shaft 20, and a follower wheel 23 is rotatably installed on the vibration bracket 4. The follower wheel 23 is in rolling contact with the contour surface of the eccentric wheel 22. The vibration bracket 4 is slidably connected to the rotating work station frame 3, and the top surface of the vibration bracket 4 is installed with a vibration spring 24 which is limited by the rotating work station frame 3.

[0117] When the surface mechanical nano-pretreatment of the high-strength bolts 43 of the wind turbine blades is performed, the large circular shaft 20 rotates under the drive of external power, and the passive bevel gear at one end thereof engages with the transmission bevel gear, thereby driving the large circular shaft 20 to rotate, and the eccentric wheel 22 on the large circular shaft 20 rotates accordingly, and the eccentric wheel 22 pushes the driven wheel 23, so that the vibration bracket 4 slides along the rotating work station 3, and the vibration spring 24 plays an elastic reset role, realizing the high-frequency micro-amplitude vibration of the bolt 43 during the nano-impact treatment, and the hollow shaft 21 and the first bevel gear on the large circular shaft 20 engage with each other, and the hollow groove inside the hollow shaft 21 slides with the magnetic shaft 6. The cross-sections of the magnetic shaft 6 and the hollow groove are both regular hexagons, which enhances the clamping stability of the bolt 43. In traditional static impact, the particles are unevenly distributed, affecting the uniformity of the nanocrystalline layer. This structure uses the rolling contact between the eccentric wheel 22 and the follower wheel 23 and the elastic reset of the vibration spring 24 to make the thread root of the bolt 43 fully contact with the tungsten carbide cobalt particles, so that the nanocrystalline layer is formed more evenly and the grain refinement efficiency is improved by 40%. At the same time, displacement deviation in the processing process is avoided, ensuring that the shear resistance of the wind turbine blade bolt 43 under extreme wind loads meets the standard, thereby improving the mechanical properties and service life of the bolt 43.

[0118] The bolt fixing component also includes a small circular shaft 25 rotatably mounted on the vibration bracket 4, a conical tooth is installed on the small circular shaft 25, and a second conical tooth is installed on the magnetic shaft 6 and the transmission bottom shaft 5. The two second conical teeth are both connected to the conical teeth for transmission, and the two second conical teeth are respectively arranged on both sides of the conical tooth.

[0119] By meshing the conical teeth on the small circular shaft 25 with the second conical teeth of the magnetic shaft 6 and the transmission bottom shaft 5, the coaxial counter-rotation of the transmission bottom shaft 5 and the magnetic shaft 6 is achieved. During the working process, the magnetic shaft 6 drives the bolt 43 to rotate, and at the same time, the transmission bottom shaft 5 reversely drives the rotary casing 28 in the nozzle mechanism to rotate. When the rotary casing 28 rotates, the nozzle 29 always accurately covers the thread root at a 45° angle. The coaxial counter-rotation setting of the nozzle 29 and the bolt 43 during nano-processing can effectively improve the coverage uniformity of the nanoparticles on the thread root of the bolt 43. The setting of the protective tube can effectively reduce the overflow rate of the nanoparticles, thereby improving the safety during the nano-processing operation. The setting of the vibration structure during the processing of the protective tube and the bolt 43 can effectively reduce the residual rate of non-stable nanoparticles at the thread root of the bolt 43 and the inner wall of the protective tube, thereby effectively improving the cleanliness of the inner wall of the protective tube.

[0120] The nozzle mechanism includes a conduit 45 and a follower seat 26. The conduit 45 is fixedly mounted on the processing rack 8. Two T-shaped guide rods 27 are installed on the top surface of the follower seat 26. Both T-shaped guide rods 27 are slidably connected to the conduit 45. A rotary sleeve 28 is rotatably mounted on the inner wall of the follower seat 26. The bottom end of the rotary sleeve 28 is fixedly mounted with a sealing rubber ring connected to the transmission bottom shaft 5. A nozzle 29 is fixedly mounted on the inner wall of the rotary sleeve 28. The nozzle 29 is inclined at a 45° angle toward the threaded root of the bolt 43. A through cavity 30 is fixedly opened on the top of the rotary sleeve 28. The tail end of the nozzle 29 is connected to the through cavity 30. The bottom end of the conduit 45 is rotatably connected to the through cavity 30 through a bellows 31. A vibration spring 32 is sleeved on the bellows 31.

[0121] During the working process, the spiral casing 28 is connected to the transmission bottom shaft 5 through the sealing rubber ring, and the bellows 31 compensates for the lifting displacement under the buffering of the vibration spring 32, so that the spiral casing 28 is driven to vibrate along with the rotational motion of the transmission bottom shaft 5. In addition, the setting of the sealing rubber ring can effectively ensure the sealing of the connection between the transmission bottom shaft 5 and the spiral casing 28.

[0122] The top end of the conduit 45 in the nano-processing station is fixedly provided with a nano-material connecting pipe 33 connected to the high-pressure nano-particle feeding device, the top end of the conduit 45 in the negative pressure cleaning station is fixedly provided with a negative pressure suction pipe 34 connected to the negative pressure absorber, the top end of the conduit 45 in the cleaning station is fixedly provided with a cleaning joint 35 connected to the cleaning liquid feeding device, and a heating coil 36 is fixedly installed on the outside of the rotary casing 28 in the cleaning station.

[0123] The nozzle mechanism plays an important role in the heat treatment of high-strength bolts 43 of wind turbine blades at different stations. At the nano-processing station, high-pressure nanoparticles enter the conduit 45 through the nano-material pipe 33, and then enter the through cavity 30 at the top of the spiral casing 28 through the bellows 31. Finally, they are ejected from the nozzle 29 at a 45° angle toward the thread root of the bolt 43 to perform impact treatment on the thread root of the bolt 43. At this time, the follower seat 26 can slide on the conduit 45 through the T-shaped guide rod 27 to adjust the distance between the nozzle 29 and the bolt 43. The spiral casing 28 can be rotated so that the nozzle 29 can better cover the thread root of the bolt 43. At the negative pressure cleaning station, the negative pressure The suction pipe 34 is connected to the negative pressure suction device to absorb the nanoparticles remaining after the nano-treatment. At the cleaning station, the cleaning liquid enters through the cleaning joint 35, and the nozzle 29 sprays the cleaning liquid to clean the bolt 43. The heating coil 36 outside the cleaning station rotary sleeve 28 can heat the cleaning liquid to improve the cleaning effect. The traditional nozzle mechanism is difficult to accurately process and clean the thread root of the bolt 43, and has a single function. The nozzle mechanism is cleverly designed and can achieve different functions at different stations, thereby improving the accuracy and efficiency of the heat treatment process, ensuring the surface treatment quality of the bolt 43, and improving the overall performance of the high-strength bolt 43 of the wind turbine blade

[0124] When the heat treatment equipment for the high-strength bolts 43 of wind turbine blades is running, in the nano-processing station, the nano-material pipe 33 is connected to the high-pressure nano-particle feeding device, which can stably transport tungsten carbide cobalt particles with a particle size of 50-100μm to the nozzle 29 at a speed of 200-300m / s, and perform impact treatment on the thread root of the bolt 43 to form a high-quality nano-crystalline layer. In the negative pressure cleaning station, the negative pressure suction pipe 34 is connected to the negative pressure absorber to promptly and effectively remove the nano-particles remaining after the nano-processing to prevent these particles from affecting subsequent processes. In the cleaning station, the cleaning joint 35 is connected to the cleaning liquid feeding device to provide sufficient cleaning liquid for cleaning the bolts 43. After cleaning, the heating coil 36 outside the rotary sleeve 28 can perform low-temperature thermal stress elimination on the treated bolts 43.

[0125] The high-pressure nanoparticle feeding device can adopt Sulzer Metco's spraying system or Praxair's powder feeding device. It can be selected or replaced according to actual conditions. No further details will be given here.

[0126] It also includes a sleeve 37 that is rotatably sleeved on the bottom cylinder 15, a sewage suction channel 38 is fixedly opened inside the magnetic shaft 6, and the bottom end of the sewage suction channel 38 is connected to the sleeve 37 through a sewage outlet pipe 44, and a group of sewage suction holes 39 distributed in a circular array and connected to the sewage suction channel 38 are opened on the magnetic shaft 6, a sewage discharge cavity 40 is fixedly opened inside the bottom cylinder 15, and a sewage discharge hole 41 connected to the sewage discharge cavity 40 is fixedly opened on the bottom cylinder 15 and at a position corresponding to the cleaning station, and a sewage storage box 42 connected to the sewage discharge cavity 40 is fixedly installed on the fixed frame 2.

[0127] The sewage suction hole 39 inside the magnetic shaft 6 is connected with the sewage discharge cavity 40 of the bottom cylinder 15, so as to realize the directional collection of the cleaning waste liquid.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. 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 heat treatment process for high-strength bolts of wind turbine blades, characterized in that: The following steps are involved: The bolt heat treatment state is preset, and the bolt thread root is subjected to impact treatment by the bolt heat treatment device to form a nanocrystalline layer; Three-stage pulse nitriding is carried out in an ammonia atmosphere containing Ce-La mixed rare earth; Under the action of a transverse steady magnetic field, gradient cooling is performed using a water-based atomized quenching liquid containing polyvinyl alcohol and graphene. Liquid nitrogen cryogenic treatment is performed, followed by pulsed current applied during the tempering process.

2. A heat treatment process for high-strength bolts for wind turbine blades according to claim 1, characterized in that: The temperature of the first stage of the three-stage pulse nitriding process is 520°C, the nitriding time is 2 hours, the temperature of the second stage is 580°C, the nitriding time is 1.5 hours, and the temperature of the third stage is 500°C, the nitriding time is 3 hours.

3. A heat treatment process for high-strength bolts for wind turbine blades according to claim 1, characterized in that: The transverse steady magnetic field intensity is regulated in stages, including an initial stage, a main quenching stage, and a final cooling stage; the quenching liquid atomization pressure is synchronously regulated with the transverse steady magnetic field intensity in each stage.

4. A heat treatment process for high-strength bolts for wind turbine blades according to claim 1, characterized in that: The liquid nitrogen cryogenic treatment includes a first stage, a second stage and a third stage of gradient cooling; The first stage: 25°C to -80°C, cooling rate 3°C / min, hold for 15 minutes; The second stage: -80°C to -140°C, cooling rate 2°C / min, hold for 10 minutes; The third stage: -140°C to -196°C, cooling rate 1°C / min, holding for 5 minutes.

5. A heat treatment process for high-strength bolts for wind turbine blades according to any one of claims 1 to 4, characterized in that: The bolt heat treatment device comprises a fixed frame (2), a rotating station frame (3) which can rotate periodically 90 degrees is rotatably mounted on the fixed frame (2), four bolt fixing components are provided on the rotating station frame (3), a vibration bracket (4) which can move up and down is connected to the bolt fixing component, a transmission bottom shaft (5) is rotatably mounted on the inner wall of the vibration bracket (4), a magnetic attraction shaft (6) is rotatably mounted on the inner wall of the transmission bottom shaft (5), a magnetic attraction groove (7) for magnetic attraction positioning of the bolt (43) is provided on the top of the magnetic attraction shaft (6), the transmission bottom shaft (5) and the magnetic attraction shaft (6) rotate in opposite directions coaxially, a loading and unloading station, a nano-processing station, a negative pressure cleaning station and a cleaning station are sequentially arranged on the fixed frame (2) in a clockwise direction, a processing frame (8) is movably mounted on the fixed frame (2), and a nozzle mechanism is provided on the processing frame (8) at positions corresponding to the nano-processing station, the negative pressure cleaning station and the cleaning station.

6. A heat treatment process for high-strength bolts for wind turbine blades according to claim 5, characterized in that: The invention also includes a servo motor (9) installed at the bottom of the fixed frame (2), an incomplete gear (10) is installed on the output shaft end of the servo motor (9), a transmission tooth surface is fixedly provided on the incomplete gear (10), an intermittent shaft (11) is installed on the bottom surface of the rotating work station (3), an intermittent gear (12) meshing with the transmission tooth surface is fixedly installed on the intermittent shaft (11), the meshing area of ​​the transmission tooth surface corresponds to a central angle of 90°, the radius of the incomplete gear (10) is the same as the radius of the intermittent gear (12), a hollow gear shaft (13) is rotatably sleeved on the intermittent shaft (11), an active gear ring (14) is installed on the hollow gear shaft (13), and the servo motor (9) is provided with a plurality of gears. A belt is connected to the output shaft end of the motor (9) and the hollow gear shaft (13). A bottom cylinder (15) is fixedly installed on the fixed frame (2). A shaft frame (16) is fixedly installed on the bottom cylinder (15). A guide shaft (17) is rotatably installed on the shaft frame (16) and corresponding to the positions of the nano-processing station, the negative pressure cleaning station and the cleaning station. The guide shaft (17) is respectively installed with a transmission bevel gear and a passive gear (18) connected to the active gear ring (14). The bolt fixing component is adapted to be connected to the transmission bevel gear. A vertically arranged screw lifting module (19) is installed on the fixed frame (2). The screw lifting module (19) is connected to the processing frame (8).

7. A heat treatment process for high-strength bolts for wind turbine blades according to claim 6, characterized in that: The bolt fixing component comprises a large circular shaft (20) and a hollow shaft (21) rotatably connected to the rotary work station frame (3); one end of the large circular shaft (20) is fixedly mounted with a passive bevel gear meshing with the transmission bevel gear; a first bevel gear is mounted on both the hollow shaft (21) and the large circular shaft (20); the two first bevel gears mesh with each other; a hollow groove with two ends opened and slidably connected to the magnetic shaft (6) is fixedly opened inside the hollow shaft (21); the cross sections of the magnetic shaft (6) and the hollow groove are both regular hexagonal; an eccentric wheel (22) is mounted on the large circular shaft (20); a follower wheel (23) is rotatably mounted on the vibration bracket (4); the follower wheel (23) is in rolling contact with the contour surface of the eccentric wheel (22); the vibration bracket (4) is slidably connected to the rotary work station frame (3); and a vibration spring (24) limited by the rotary work station frame (3) is mounted on the top surface of the vibration bracket (4).

8. A heat treatment process for high-strength bolts for wind turbine blades according to claim 7, characterized in that: The bolt fixing component further comprises a small circular shaft (25) rotatably mounted on the vibration bracket (4), a conical tooth being mounted on the small circular shaft (25), a second conical tooth being mounted on each of the magnetic attraction shaft (6) and the transmission bottom shaft (5), two second conical teeth being transmission-connected to the conical tooth, and the two second conical teeth being respectively arranged on both sides of the conical tooth.

9. A heat treatment process for high-strength bolts for wind turbine blades according to claim 6, characterized in that: The nozzle mechanism includes a conduit (45) and a follower seat (26), the conduit (45) is fixedly mounted on the processing frame (8), the top surface of the follower seat (26) is equipped with two T-shaped guide rods (27), both of which are slidably connected to the conduit (45), the inner wall of the follower seat (26) is rotatably equipped with a rotary sleeve (28), the bottom end of the rotary sleeve (28) is fixedly equipped with a sealing rubber ring connected to the transmission bottom shaft (5), the inner wall of the rotary sleeve (28) is fixedly equipped with a nozzle (29), the nozzle (29) is inclined at 45 degrees toward the thread root of the bolt (43), the top of the rotary sleeve (28) is fixedly provided with a through cavity (30), the nozzle The tail end of the head (29) is connected to the through cavity (30), the bottom end of the conduit (45) is rotatably connected to the through cavity (30) through a bellows (31), a vibration spring (32) is sleeved on the bellows (31), the top end of the conduit (45) in the nano-processing station is fixedly provided with a nano-material connecting pipe (33) connected to a high-pressure nano-particle feeding device, the top end of the conduit (45) in the negative pressure cleaning station is fixedly provided with a negative pressure suction pipe (34) connected to a negative pressure suction device, the top end of the conduit (45) in the cleaning station is fixedly provided with a cleaning joint (35) connected to a cleaning liquid feeding device, and a heating coil (36) is fixedly installed on the outside of the rotary casing (28) in the cleaning station.

10. A heat treatment process for high-strength bolts for wind turbine blades according to claim 7, characterized in that: The invention also includes a sleeve (37) rotatably sleeved on the bottom cylinder (15); a sewage suction channel (38) is fixedly provided inside the magnetic suction shaft (6); the bottom end of the sewage suction channel (38) is communicated with the sleeve (37) through a sewage discharge pipe (44); a group of sewage suction holes (39) distributed in a circumferential array and communicated with the sewage suction channel (38) are provided on the magnetic suction shaft (6); a sewage discharge cavity (40) is fixedly provided inside the bottom cylinder (15); a sewage discharge hole (41) communicated with the sewage discharge cavity (40) is fixedly provided on the bottom cylinder (15) and at a position corresponding to a cleaning station; and a sewage storage box (42) communicated with the sewage discharge cavity (40) is fixedly installed on the fixed frame (2).

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