A copper-based powder metallurgy friction pad for a wind power torque limiter and its preparation method

Abstract

This invention discloses a copper-based powder metallurgy friction plate for wind turbine torque limiters and its preparation method. The friction plate blank is first subjected to pressureless sintering to obtain a pre-sintered blank, and then the pre-sintered blank is re-pressed to obtain a re-pressed friction plate blank. The re-pressed friction plate blank is then assembled with a copper-plated steel backing to obtain a composite blank, which is then subjected to pressure limiting sintering to obtain the final product. The preparation method of this invention, through the synergy of pressureless pre-sintering, re-pressing, and pressure limiting sintering, obtains a copper-based powder metallurgy friction plate for wind turbine torque limiters with small deformation, high density, and excellent mechanical and tribological properties.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy technology, specifically relating to a copper-based powder metallurgy friction plate for wind power torque limiters and its preparation method. Background Technology

[0002] Wind power is a green energy source, and China has become the world's largest country in terms of total installed wind power capacity. The torque limiter is a core component of the coupling used in wind turbines. Its main function is to protect the wind turbine from damage during overload, making it a crucial safety device. Friction plates are key to the torque limiter, determining its performance. Unlike other friction plates, they have significantly higher requirements for mechanical performance because they are not simply used for braking but bear the critical responsibility of overload protection under harsh operating conditions. Therefore, the requirements for their mechanical performance are more stringent and comprehensive. In the early stages of China's wind power industry, friction plates were mainly imported. However, with the development of China's wind power industry and the increasing trend towards higher power wind turbines, the need for high-performance copper-based powder metallurgy friction plates for torque limiters is growing rapidly.

[0003] Sintering is one of the key processes in powder metallurgy. There are various sintering methods, including pressureless sintering, pressure sintering, hot isostatic pressing (HIP), and microwave sintering. Using a suitable sintering method is a prerequisite for preparing high-performance copper-based powder metallurgy friction plates for wind turbine torque limiters. It plays a crucial role in reducing friction plate deformation, lowering processing costs, improving the density, mechanical properties, and tribological properties of the friction plates, ensuring the stability of the torque limiter's output torque, extending the torque limiter's lifespan, reducing wind turbine installation and maintenance costs, and ensuring the long-term safe operation of the wind turbine.

[0004] Chinese patent (ZL202010274882.6) uses a segmented heat-preserving sintering method to improve the density of iron-based copper-containing powder metallurgy sintered parts. However, iron-based powder metallurgy sintered parts and copper-based powder metallurgy friction pads differ in material composition, therefore the sintering process is not applicable to copper-based powder metallurgy materials, and it does not involve improvements in mechanical properties or tribological properties. Chinese patent (ZL202310847562.9) uses a pressure sintering method to prepare copper-based powder metallurgy friction pads; however, the copper-based powder metallurgy friction pads prepared by this patent are mainly used for friction against carbon ceramic discs in vehicles, and therefore do not address properties other than tribological properties. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a method for preparing copper-based powder metallurgy friction pads for wind turbine torque limiters. The preparation method of this invention, through the synergistic process of pressureless pre-firing, re-firing, and pressure sintering, yields copper-based powder metallurgy friction pads for wind turbine torque limiters that exhibit low deformation, high density, and excellent mechanical and tribological properties.

[0006] The second objective of this invention is to provide a copper-based powder metallurgy friction sheet for a wind power torque limiter prepared by the above-described preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for preparing copper-based powder metallurgy friction plates for wind turbine torque limiters. The method involves first pressurelessly sintering a friction plate blank to obtain a pre-sintered blank, then re-pressing the pre-sintered blank to obtain a re-pressed friction plate blank, and finally assembling the re-pressed friction plate blank with a copper-plated steel backing to obtain a composite blank. Finally, pressure-limiting sintering is performed to obtain the final product.

[0009] The pressurized limiting sintering process is as follows: apply a pressure of 50-80N per square centimeter to the composite blank, raise the temperature to 500-600℃, hold the temperature and pressure for the first time, then apply a pressure of 200-250N per square centimeter to the composite blank, raise the temperature to 800-950℃, hold the temperature and pressure for the second time, release the pressure, raise the temperature to 980-1020℃ without pressurization, hold the temperature for the third time, then apply a pressure of 30-40N per square centimeter to the composite blank, air cool to 880-950℃, release the pressure, and water cool down without pressurization.

[0010] During the pressure-limiting sintering process, graphite sheets are used to limit the height of the composite blank after it is compressed. The height of the composite blank is 15-20 mils higher than that of the graphite sheets.

[0011] This invention prepares high-performance copper-based powder metallurgy friction plates for wind turbine torque limiters using a method involving first pressureless sintering, then pressure sintering, and finally pressure-limited sintering. Pressure sintering accelerates powder particle flow and plastic deformation, speeds up spheroidization and shrinkage of pores and gas expulsion, strengthens interphase bonding, increases the density of the sintered product, lowers the firing temperature, and shortens the firing time. The pressure-limited sintering method of this invention involves first performing low-temperature, low-pressure sintering at 500-600℃ under a pressure of 50-80N, then further increasing the pressure and temperature to 800-950℃ for further sintering under high temperature and high pressure. This promotes powder particle flow and plastic deformation, increases material density, promotes interfacial bonding between the copper matrix and friction components, and stabilizes the friction coefficient of the friction plate. Simultaneously, it avoids grain growth under prolonged high-temperature conditions, improving... The strength of the friction plate is increased, its shear and compressive resistance is enhanced, and its friction and wear are reduced. Under the aforementioned pressure, the friction plate is pressed to the same height as the graphite sheet at high temperature. Then, without applying pressure, it is sintered at 980-1020℃, which allows the friction components and other components to be uniformly distributed in the liquid phase, forming an ideal structure. This improves the overall mechanical properties and makes the properties of each part of the friction plate more consistent, avoiding early failure caused by local defects or segregation. Subsequently, during the air cooling process, the cooling rate is relatively slow, and a low pressure is applied appropriately to prevent the friction plate from deforming during the cooling and contraction process. Finally, after depressurization, water cooling is performed to cool the material rapidly. Under the synergistic effect of the above pressurization process, a copper-based powder metallurgy friction plate for wind power torque limiters with high density and excellent mechanical and friction and wear properties is finally obtained.

[0012] In this invention, in addition to the need for effective control of the pressure sintering process, the height of the graphite sheet also needs to be effectively controlled. The limiting of the graphite sheet effectively controls the reduction rate of the friction sheet during sintering, ensuring that pores can be discharged as much as possible during the sintering process, improving the density of the friction sheet, thereby improving the strength and hardness of the friction sheet and obtaining better friction and wear performance. However, if the height is too high, it will reduce the reduction rate during the sintering process, making it impossible to obtain a friction sheet with high density and good mechanical and friction and wear performance; while if the height is too low, the reduction rate will increase, which will not only lead to a decrease in performance, but may even affect the size.

[0013] In the actual operation of this invention, a bell-shaped sintering furnace is used for pressure limiting sintering, and water cooling is achieved by spraying water onto the steel shroud to rapidly cool the sintered billet inside the steel shroud.

[0014] In a preferred embodiment, the copper-based powder metallurgy friction pad has the following composition by mass percentage: 9-14% carbon, 1-3% tin, 2-6% friction component, 12-18% iron, 1-2% nickel, 4-6% aluminum, with the balance being copper. The friction component is at least one of aluminum oxide, silicon oxide, silicon carbide, and tungsten carbide.

[0015] Experiments have shown that the copper-based powder metallurgy friction pads prepared using the above-mentioned components exhibit the best performance. The copper-based powder metallurgy friction pads of this invention use carbon as a lubricating component. The addition of carbon reduces the friction coefficient of the friction pad, providing wear resistance. Simultaneously, by matching the pressure sintering process, it provides a mass migration channel at the interface between carbon and the copper matrix for alloying of the copper matrix, promoting alloying and improving the strength of the friction pad. On the other hand, controlling the carbon content within a certain range prevents excessive carbon fragmentation of the copper matrix, which could lead to a decrease in the strength of the friction pad. Tin, iron, and nickel serve as reinforcing components, improving the strength and hardness of the friction pad through solid solution strengthening and second-phase strengthening, thereby enhancing its wear resistance and reducing wear. Tin, with its low melting point, forms a liquid phase during sintering. Under sintering pressure, it can better fill pores, promoting powder particle rearrangement and densification of the friction pad. Simultaneously, the addition of tin wets the surface of the high-melting-point reinforcing components of iron and nickel, promoting densification and improving interfacial bonding strength. Furthermore, this invention incorporates Al. The Fe3Al intermetallic compound possesses a superlattice crystal structure, with atomic bonds consisting of metallic, covalent, and ionic bonds. Therefore, it exhibits the wear resistance, heat corrosion resistance, and oxidation resistance of metallic materials, and also possesses superior plasticity and thermal conductivity compared to non-metallic materials. The Fe3Al intermetallic compound is formed in situ within a copper matrix through a solid-state diffusion reaction of Fe and Al. Pressure sintering increases the contact area between particles, resulting in shorter diffusion paths and more reaction interfaces, which facilitates the uniform and rapid formation of Fe3Al. Compared to externally added friction components, the Fe3Al generated through in-situ reaction produces finer, nearly equiaxed particles that are uniformly dispersed within the copper matrix. Simultaneously, the dispersed Fe3Al hard phase can withstand loads, reducing plastic flow and adhesive wear in the copper matrix. A diffusion layer exists between the in-situ Fe3Al and the copper matrix, resulting in a higher interfacial bonding strength than mechanically mixed friction components. This improves the shear strength of the friction pad, stabilizes the friction coefficient, and reduces wear.

[0016] Furthermore, optimal performance can only be achieved when the amounts of each component are controlled within the limits specified in this invention. Excessive tin addition can lead to the formation of a large amount of liquid phase during sintering, causing the friction element to flow out of the steel backing size range and failing to meet the dimensional specifications of the friction plate. Iron has low solubility in copper, and excessive iron addition can also fracture the copper matrix, reducing the strength of the friction plate. The wettability between the friction components and the matrix is ​​relatively poor. Under sintering pressure, the copper matrix can better wet the surface of the friction components, improving interfacial bonding and compressibility. Excessive addition of friction components can also fracture the matrix, affecting the strength of the friction plate. Moreover, since the friction components are hard particles with high strength and hardness, they can easily damage the mating components that make up the friction pair during friction, meaning that higher mechanical performance requirements are needed for the mating components.

[0017] In this invention, the friction plate blank is obtained by conventional pressing molding. The components are taken according to the design composition of the copper-based powder metallurgy friction plate and then pressed to obtain the blank.

[0018] In a preferred embodiment, the process of obtaining the friction plate blank is as follows: according to the design ratio of copper-based powder metallurgy friction plates, carbon source, tin source, iron source, nickel source, aluminum source and copper source are prepared, the friction components are mixed evenly, and then pressed into shape to obtain the blank. The particle size of the friction components is 60-150μm.

[0019] Experiments have shown that, using the preparation method of the present invention, only the particle size of the friction component needs to be limited. There is no special control over the particle size of other components. As long as the process of the present invention is well controlled, friction plates with high density and excellent friction performance can be obtained. However, if the particle size of the friction component is not within the range of the present invention, it will affect the friction and wear performance of the friction plate and ultimately lead to an increase in the wear of the friction plate.

[0020] In a preferred embodiment, the pressureless sintering temperature is 550-650℃ and the pressureless sintering time is 1-1.5h.

[0021] In this invention, the performance is optimal when the parameters of pressureless sintering are controlled within the above-mentioned range. If the pressureless sintering temperature is too high or the time is too long, it will consume a large amount of sintering driving force, affecting the subsequent pressure sintering and ultimately affecting the phase interface bonding strength of the friction plate. If the pressureless sintering temperature is too low or the time is too short, the necking effect between the powder particles of the green body is not obvious, the bonding strength between the particles is low, and cracking or breakage is likely to occur during the re-pressing process.

[0022] In a preferred embodiment, the pressureless sintering is carried out in a mixed atmosphere of N2 and H2, with a volume flow rate ratio of N2 to H2 of 5-10:1.

[0023] The preferred method is to place the pre-fired billet in a steel mold and press it again.

[0024] In a preferred embodiment, the pressure of the pressure repressurization is 500-550 MPa, and the pressure holding time is 5-8 seconds.

[0025] In a preferred embodiment, during the pressure sintering process, the composite blank is placed on a graphite plate, and graphite sheets are placed on the graphite plate to limit the height of the composite blank after it is subjected to pressure.

[0026] Further optimization involves placing several composite blanks evenly on a graphite plate, while simultaneously distributing graphite sheets evenly on the graphite plate.

[0027] By evenly arranging the friction plate composite blank and graphite sheet, the force can be evenly distributed during pressurization.

[0028] In actual operation, once the water cooling temperature drops below 60°C, the water and gas can be turned off.

[0029] In a preferred embodiment, the pressure sintering process involves applying a pressure of 50-80 N per square centimeter to the composite blank, then heating it to 500-600°C within 2-2.5 hours, holding it at the temperature and pressure for 20-30 minutes, then applying a pressure of 200-250 N per square centimeter to the composite blank and heating it to 800-950°C, holding it at the temperature and pressure for 4-5 hours, releasing the pressure, heating it to 980-1020°C without applying pressure, holding it at the temperature for 3-4 hours, then applying a pressure of 30-40 N per square centimeter to the composite blank and air-cooling it to 880-950°C, releasing the pressure, and water-cooling it without applying pressure.

[0030] In a preferred embodiment, the pressure sintering is carried out in a mixed atmosphere of N2 and H2, with a volume flow rate ratio of N2 to H2 of 10-20:1.

[0031] The present invention also provides a copper-based powder metallurgy friction sheet for a wind power torque limiter prepared by the above preparation method.

[0032] In a preferred embodiment, the density of the copper-based powder metallurgy friction sheet used in the wind power torque limiter is 5.8-6.1 g / cm³. 3 It has a hardness of 48-68HBW, compressive strength ≥280MPa, and shear strength ≥30MPa.

[0033] In a preferred embodiment, the adhesion strength between the friction layer of the copper-based powder metallurgy friction sheet used in the wind power torque limiter and the steel backing is ≥20MPa.

[0034] In a preferred embodiment, the copper-based powder metallurgy friction sheet used in the wind power torque limiter has a friction coefficient of 0.40-0.55, a fatigue life of >100,000 degrees under 20MPa pressure, and a wear amount ≤3×10 -5 g / J.

[0035] Beneficial effects

[0036] 1. This invention prepares a high-performance copper-based powder metallurgy friction sheet for wind power torque limiters by first pressureless sintering, then pressure sintering, and finally pressure limiting sintering.

[0037] 2. The sintering method of the present invention produces high-performance copper-based powder metallurgy friction plates for wind power torque limiters with small deformation, easy processing, and low processing cost.

[0038] 3. The sintering method of the present invention produces high-performance copper-based powder metallurgy friction plates for wind power torque limiters with high density, excellent mechanical properties and friction and wear performance. These properties can meet the development needs of high-power wind turbines in China, ensure the stability of the output torque of the torque limiter, extend the life of the torque limiter, reduce the installation and maintenance costs of wind turbines, and ensure the long-term safe operation of wind turbines. Attached Figure Description

[0039] Figure 1 Friction test curve of the friction plate prepared in Example 1.

[0040] Figure 2 A photograph of the friction plate prepared in Example 1.

[0041] Figure 3 Arrangement diagram of friction plate blank and graphite sheet before pressure sintering.

[0042] Figure 4 A photograph of the actual object showing the cracking of the friction plate after re-pressing in Comparative Example 2.

[0043] Figure 5 A photograph of the actual object showing cracks on the steel back of the friction plate in Comparative Example 3.

[0044] Figure 6 Friction test curves of the friction plates prepared in Comparative Example 4. Detailed Implementation

[0045] Example 1

[0046] A friction blank containing 9% carbon, 1% tin, 3% friction element (75μm), 14% iron, 1% nickel, 4% aluminum, and copper as the balance, with alumina as the friction element, was pre-fired at 600℃ for 1 hour under a N2 to H2 volume flow rate ratio of 6:1. It was then re-pressed at 500MPa for 5 seconds. Finally, a steel backing was added, and the total thickness of the re-pressed blank was 15 μm greater than the height of the graphite sheet. The temperature was then raised to 550℃ for 2 hours and held. For 20 minutes, a pressure of 50 N per square centimeter was applied; the area was then held at 900℃ for 4 hours, with a pressure of 200 N per square centimeter applied; followed by a holding at 1000℃ for 3 hours without pressure; the area was then air-cooled to 900℃, with a pressure of 30 N per square centimeter applied; finally, the area was water-cooled to 60℃ without pressure, and pressure sintering was carried out under a sintering atmosphere with a N2 to H2 volume flow rate ratio of 15:1; the friction layer density of the prepared copper-based powder metallurgy friction sheet was 5.9 g / cm³. 3 The hardness is 57.7 HBW, the compressive strength is 314.0 MPa, and the shear strength is 37.0 MPa; the adhesion strength between the friction layer and the steel backing is 31.7 MPa; the coefficient of friction is 0.52; the fatigue life under 20 MPa pressure is >100,000 degrees, and the wear is 2.4 × 10⁻⁶. -5 g / J.

[0047] Example 2

[0048] A friction blank containing 9% carbon, 1% tin, 3% friction element (75μm), 14% iron, 1% nickel, 4% aluminum, and copper as the balance, with alumina as the friction element, was pre-fired at 600℃ for 1 hour under a N2 to H2 volume flow rate ratio of 6:1. It was then re-pressed at 500MPa for 5 seconds. Finally, a steel backing was added, and the total thickness of the re-pressed blank was 15 μm greater than the height of the graphite sheet. The temperature was then raised to 550℃ for 2 hours and held. For 20 minutes, a pressure of 50 N per square centimeter was applied; the area was then held at 950℃ for 5 hours, with a pressure of 200 N per square centimeter applied; followed by a holding at 1000℃ for 3 hours without pressure; the area was then air-cooled to 900℃, with a pressure of 30 N per square centimeter applied; finally, the area was water-cooled to 60℃ without pressure, and pressure sintering was carried out under a sintering atmosphere with a N2 to H2 volume flow rate ratio of 15:1; the friction layer density of the prepared copper-based powder metallurgy friction sheet was 5.9 g / cm³. 3 The hardness is 58.3 HBW, the compressive strength is 331.4 MPa, and the shear strength is 38.2 MPa; the adhesion strength between the friction layer and the steel backing is 32.1 MPa; the coefficient of friction is 0.52; the fatigue life under 20 MPa pressure is >100,000 degrees, and the wear is 2.1 × 10⁻⁶. -5 g / J.

[0049] Example 3

[0050] A friction blank containing 9% carbon, 1% tin, 3% friction element (75μm particle size), 14% iron, 1% nickel, 5% aluminum, and copper as the balance, with alumina as the friction element, was pre-fired at 600℃ for 1 hour under a N2 to H2 volume flow rate ratio of 6:1. It was then re-pressed at 500MPa for 5 seconds. Finally, a steel backing was added, and the total thickness of the re-pressed blank was 20 mils higher than the height of the graphite sheet. The temperature was then increased to 550℃ over 2 hours. The process involved: holding at 20°C for 20 minutes with a pressure of 50 N per square centimeter; holding at 950°C for 5 hours with a pressure of 200 N per square centimeter; holding at 1000°C for 3 hours without pressure; air cooling to 900°C with a pressure of 30 N per square centimeter; water cooling to 60°C without pressure; and pressure sintering under a sintering atmosphere with a N2 to H2 volume flow rate ratio of 15:1. The resulting copper-based powder metallurgy friction sheet had a friction layer density of 6.1 g / cm³. 3 The hardness is 52.8 HBW, the compressive strength is 342.2 MPa, and the shear strength is 44.5 MPa; the adhesion strength between the friction layer and the steel backing is 36.7 MPa; the coefficient of friction is 0.50; the fatigue life under 20 MPa pressure is >100,000 degrees, and the wear is 2.0 × 10⁻⁶. -5 g / J.

[0051] Comparative Example 1

[0052] A friction blank containing 9% carbon, 1% tin, 3% friction element (75μm particle size), 14% iron, 1% nickel, 4% aluminum, and copper as the balance, with alumina as the friction element, was pre-fired at 600℃ for 1 hour under a N2 to H2 volume flow rate ratio of 6:1. It was then re-pressed at 500MPa for 5 seconds. Finally, a steel backing was added, and the total thickness of the re-pressed blank was 15 μm greater than the height of the graphite sheet. The temperature was then raised to 550℃ for 2 hours and held. For 20 minutes, a pressure of 50 N per square centimeter was applied; the area was then held at 900℃ for 4 hours, with a pressure of 200 N per square centimeter applied; followed by a holding at 1000℃ for 3 hours without pressure; the area was then air-cooled to 60℃, and before reaching 900℃, a pressure of 30 N per square centimeter was applied; after reaching 900℃, no pressure was applied, and pressure sintering was carried out under a sintering atmosphere with a N2 to H2 volume flow rate ratio of 15:1; the friction layer density of the prepared copper-based powder metallurgy friction sheet was 5.9 g / cm³. 3 The hardness is 44.8 HBW, the compressive strength is 228.6 MPa, and the shear strength is 36.9 MPa; the adhesion strength between the friction layer and the steel backing is 30.4 MPa; the coefficient of friction is 0.48; the fatigue life under 20 MPa pressure is >100,000 degrees; and the wear is 5.4 × 10⁻⁶. -4 g / J.

[0053] Comparative Example 2

[0054] A friction plate blank containing 9% carbon, 1% tin, 3% friction component (75μm particle size), 14% iron, 1% nickel, 4% aluminum, and copper as the balance, with alumina as the friction component, was pre-fired at 400℃ for 1.5h under a sintering atmosphere with a N2 to H2 volume flow ratio of 6:1. Subsequently, it was re-pressed at 500MPa for 5s, and the re-pressed friction plate blank cracked.

[0055] Comparative Example 3

[0056] A friction blank containing 9% carbon, 1% tin, 3% friction element (75μm particle size), 14% iron, 1% nickel, 4% aluminum, and copper as the balance, with alumina as the friction element, was pre-fired at 600℃ for 1 hour under a N2 to H2 volume flow rate ratio of 6:1. It was then re-pressed at 500MPa for 5 seconds. Finally, a steel backing was added, and the total thickness of the re-pressed blank was 15 μm greater than the height of the graphite sheet. The temperature was then raised to 550℃ for 2 hours and held for 20 seconds. For minutes, apply 50N pressure per square centimeter; hold at 900℃ for 4 hours, apply 200N pressure per square centimeter, hold at 1000℃ for 3 hours without pressure; air cool to 900℃, apply 30N pressure per square centimeter; water cool to 60℃, apply 30N pressure per square centimeter, and perform pressurized sintering under a sintering atmosphere with a N2 to H2 volume flow ratio of 15:1; local cracking of the steel back of the copper-based powder metallurgy friction plate was prepared.

[0057] Comparative Example 4

[0058] A friction blank containing 9% carbon, 1% tin, 3% friction element (75μm), 14% iron, 1% nickel, 4% aluminum, and copper as the balance, with alumina as the friction element, was pre-fired at 600℃ for 1 hour under a N2 to H2 volume flow rate ratio of 6:1. It was then re-pressed at 500MPa for 5 seconds. Finally, a steel backing was added, and the total thickness of the re-pressed blank was 5 μm greater than the height of the graphite sheet. The blank was then heated to 550℃ for 2 hours and held at that temperature. For 20 minutes, a pressure of 50 N per square centimeter was applied; the area was then held at 900℃ for 4 hours, with a pressure of 200 N per square centimeter applied; followed by a holding at 1000℃ for 3 hours without pressure; the area was then air-cooled to 900℃, with a pressure of 30 N per square centimeter applied; finally, the area was water-cooled to 60℃ without pressure, and pressure sintering was carried out under a sintering atmosphere with a N2 to H2 volume flow rate ratio of 15:1; the friction layer density of the prepared copper-based powder metallurgy friction sheet was 5.5 g / cm³. 3 The hardness is 45.3 HBW, the compressive strength is 240.1 MPa, and the shear strength is 27.5 MPa; the adhesion strength between the friction layer and the steel backing is 28.6 MPa; the friction coefficient under 20 MPa pressure is unstable.

[0059] Comparative Example 5

[0060] A friction plate blank containing 9% carbon, 1% tin, 3% friction element (75μm), 14% iron, 1% nickel, 4% aluminum, and copper as the balance, with alumina as the friction element, was pre-fired at 600℃ for 1 hour under a N2 to H2 volume flow ratio of 6:1. It was then re-pressurized at 500MPa for 5 seconds. Finally, a steel backing was added, and the total thickness of the re-pressed blank was 15 μm greater than the height of the graphite sheet. The blank was then heated to 550℃ for 2 hours, held for 20 minutes, and subjected to a pressure of 50N per square centimeter. It was then held at 980℃ for 4 hours, with a pressure of 200N per square centimeter. After air cooling to 900℃, a pressure of 30N per square centimeter was applied. Finally, it was water-cooled to 60℃, and pressure sintered without pressure under a N2 to H2 volume flow ratio of 15:1. The resulting copper-based powder metallurgy friction plate had a friction layer density of 5.8 g / cm³. 3 The hardness is 51.3 HBW, the compressive strength is 260.7 MPa, and the shear strength is 28.2 MPa; the adhesion strength between the friction layer and the steel backing is 18.8 MPa; the coefficient of friction is 0.51; the fatigue life under 20 MPa pressure is >60,000 degrees Celsius, and the wear is 4.6 × 10⁻⁶. -5 g / J.

Claims

1. A method for preparing a copper-based powder metallurgy friction pad for a wind power torque limiter, characterized in that: The friction plate blank is first pressurelessly sintered to obtain a pre-sintered blank, then the pre-sintered blank is re-pressed to obtain a re-pressed friction plate blank, and then the re-pressed friction plate blank is assembled with a copper-plated steel backing to obtain a composite blank, which is then subjected to pressure-limited sintering to obtain the final product. The pressureless sintering temperature is 550-650℃, and the pressureless sintering time is 1-1.5h; The pressurized limiting sintering process is as follows: apply a pressure of 50-80N per square centimeter to the composite blank, raise the temperature to 500-600℃, hold the temperature and pressure for the first time, then apply a pressure of 200-250N per square centimeter to the composite blank, raise the temperature to 800-950℃, hold the temperature and pressure for the second time, release the pressure, raise the temperature to 980-1020℃ without pressurization, hold the temperature for the third time, then apply a pressure of 30-40N per square centimeter to the composite blank, air cool to 880-950℃, release the pressure, and water cool down without pressurization. During the pressure-limiting sintering process, graphite sheets are used to limit the height of the composite blank after it is compressed. The height of the composite blank is 15-20 mils higher than that of the graphite sheets. The copper-based powder metallurgy friction sheet, by mass percentage, has the following composition: 9-14% carbon, 1-3% tin, 2-6% friction component, 12-18% iron, 1-2% nickel, 4-6% aluminum, with the balance being copper. The friction component is at least one of aluminum oxide, silicon oxide, silicon carbide, and tungsten carbide.

2. The method for preparing a copper-based powder metallurgy friction plate for a wind power torque limiter according to claim 1, characterized in that: The process of obtaining the friction plate blank is as follows: according to the design ratio of copper-based powder metallurgy friction plate, carbon source, tin source, iron source, nickel source, aluminum source and copper source are prepared, the friction components are mixed evenly, and then pressed into shape to obtain the blank. The particle size of the friction components is 60-150μm.

3. The method for preparing a copper-based powder metallurgy friction plate for a wind power torque limiter according to claim 1, characterized in that: The pressureless sintering is carried out in a mixed atmosphere of N2 and H2, with a volume flow rate ratio of N2 to H2 of 5-10:

1.

4. The method for preparing a copper-based powder metallurgy friction plate for a wind power torque limiter according to claim 1 or 2, characterized in that: The pre-fired billet is placed in a steel mold and pressed again; The pressure for the repressurization is 500-550 MPa, and the holding time is 5-8 seconds.

5. The method for preparing a copper-based powder metallurgy friction pad for a wind power torque limiter according to claim 1, characterized in that: During the pressure-limiting sintering process, the composite blank is placed on a graphite plate, and graphite sheets are placed on the graphite plate to limit the height of the composite blank after it is compressed.

6. The method for preparing a copper-based powder metallurgy friction plate for a wind power torque limiter according to claim 5, characterized in that: Several composite blanks are evenly placed on a graphite plate, and graphite sheets are evenly distributed on the graphite plate.

7. A method for preparing a copper-based powder metallurgy friction pad for a wind power torque limiter according to claim 1 or 5, characterized in that: The pressurized limiting sintering process is as follows: apply a pressure of 50-80N to each square centimeter of the composite blank, then raise the temperature to 500-600℃ within 2-2.5 hours, hold the temperature and pressure for 20-30 minutes for the first time, then apply a pressure of 200-250N to each square centimeter of the composite blank and raise the temperature to 800-950℃, hold the temperature and pressure for 4-5 hours for the second time, release the pressure, raise the temperature to 980-1020℃ without pressurizing, hold the temperature for 3-4 hours for the third time, then apply a pressure of 30-40N to each square centimeter of the composite blank and air cool to 880-950℃, release the pressure, and water cool down without pressurizing.

8. A method for preparing a copper-based powder metallurgy friction pad for a wind power torque limiter according to claim 1 or 5, characterized in that: The pressurized limiting sintering is carried out in a mixed atmosphere of N2 and H2, with a volume flow ratio of N2 to H2 of 10-20:

1.

9. A copper-based powder metallurgy friction sheet for a wind power torque limiter prepared by the preparation method according to any one of claims 1-7, characterized in that: The density of the copper-based powder metallurgy friction sheet used in the wind power torque limiter is 5.8-6.1 g / cm³. 3 The hardness is 48-68HBW, the compressive strength is ≥280MPa, and the shear strength is ≥30MPa. The adhesion strength between the friction layer and the steel backing of the copper-based powder metallurgy friction sheet used in the wind power torque limiter is ≥20MPa. The copper-based powder metallurgy friction sheet used in the wind turbine torque limiter has a friction coefficient of 0.40-0.55, a fatigue life of >100,000 degrees under 20MPa pressure, and a wear amount ≤3×10 -5 g / J.

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