High-wear-resistance and high-conductivity carbon brush material and preparation method thereof

Abstract

The invention belongs to the technical field of electric brushes, and discloses a high-wear-resistance and high-conductivity carbon brush material which is prepared by mixing, pressure forming and sintering the following components in percentage by mass: 1-3% of high-purity nickel, 7-10% of graphite, 1-5% of pitch-based graphite carbon fiber and the balance of 10% of copper-tin alloy matrix. The copper-tin alloy is used as a substrate, the high-purity nickel, the flaky graphite and the pitch-based graphite carbon fiber are added, and mixing, pressure forming and sintering are performed to obtain the product, so that various properties of the product are remarkably improved, particularly, the resistivity is remarkably reduced, the product has good sliding contact performance, the wear rate is also remarkably reduced, and the service life of the product is prolonged. And the service life of the product is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of brush technology and relates to a high wear-resistant and high conductivity carbon brush material and its preparation method. Background Technology

[0002] High-speed rail carbon brushes play a crucial role in modern railway power systems, especially in the traction systems of high-speed trains and electric locomotives. As a conductive connection component between the electric motor and the power system, the performance of the carbon brush directly affects the operational stability and energy efficiency of the vehicle. While current high-speed rail carbon brushes exhibit strong wear resistance, the high contact pressure between the carbon brush and the slip ring during high-speed operation still results in significant wear. Furthermore, in actual operation, carbon brushes may chip off due to impacts, indicating insufficient strength. Wear not only affects service life but can also cause poor contact, leading to unstable power transmission. Prolonged use can also cause oxidation or contamination on the carbon brush surface, resulting in decreased conductivity. All of these factors can affect the performance of the power system and may even cause electrical faults. Summary of the Invention

[0003] This invention addresses the technical problems of low strength, poor wear resistance, and poor conductivity in existing carbon brushes by providing a high-wear-resistant and high-conductivity carbon brush material. It uses a copper-tin alloy as a base, adding high-purity nickel, flake graphite, and pitch-based graphitic carbon fibers. The material is obtained through mixing, pressure molding, and sintering. All properties of the product are significantly improved, especially the carbon brush density and flexural strength, while resistivity and wear rate are significantly reduced, extending the product's service life.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention provides a high wear-resistant and high conductivity carbon brush material, which is prepared by mixing, pressing and sintering the following components by mass fraction: 1-3% high purity nickel, 7-10% graphite, 1-5% pitch-based graphitic carbon fiber, and the remainder is 10% copper-tin alloy matrix.

[0006] Preferably, the 10% copper-tin alloy matrix contains 90% copper and 10% tin.

[0007] Preferably, the high-purity nickel contains >99.99% nickel and has a porosity of 1.40–1.68 g / cm³. 3 .

[0008] Preferably, the graphite is flake graphite.

[0009] Preferably, the pitch-based graphitic carbon fiber contains 99% carbon, has a particle size of 100 mesh, and a length of 150 μm.

[0010] This invention also provides a method for preparing a high wear-resistant and high conductivity carbon brush material, comprising the following steps: weighing the above-mentioned high wear-resistant and high conductivity carbon brush material and a wax-based binder, using a wet milling method, ball milling for 5 hours with a ball-to-powder ratio of 3:1, then vacuum drying, followed by molding at a pressure of 600 MPa, then sintering under a nitrogen atmosphere through multi-stage heating, and finally tempering at 200°C for 30 minutes, followed by cooling to room temperature.

[0011] Preferably, the multi-stage heating process is as follows:

[0012] (1) Low temperature degreasing section: The temperature is increased from room temperature to 300℃ at a rate of 1.8℃ / min and held for 40min;

[0013] (2) Structurally stable section:

[0014] ① Graphite activation section: Increase the temperature from 300℃ to 500℃ at a rate of 2.5℃ / min; then increase the temperature from 500℃ to 550℃ at a rate of 1.5℃ / min and hold for 20 minutes;

[0015] ② Nickel diffusion section: Heat from 550℃ to 600℃ at a rate of 3℃ / min, and hold for 15min;

[0016] (3) Liquid phase sintering stage: The temperature is increased from 600℃ to 850℃ at a rate of 6.67℃ / min and held for 60min;

[0017] (4) Controlled cooling stage:

[0018] ① Rapid cooling section: The temperature is reduced from 850℃ to 650℃ at a rate of 8℃ / min;

[0019] ② Slow cooling section: The temperature is reduced from 650℃ to 450℃ at a rate of 3℃ / min, with a holding time of 5min for every 50℃ decrease;

[0020] ③ Final cooling section: naturally cooled from 450℃ to 200℃.

[0021] Preferably, the wax-based binder is paraffin wax with a particle size of 1000 mesh.

[0022] Preferably, the amount of wax-based binder is 1% of the total mass of the high-wear-resistant and high-conductivity carbon brush material.

[0023] The technical concept of this invention is as follows:

[0024] (1) Copper-tin alloy powder has high mechanical properties, anti-friction properties and corrosion resistance, is easy to machine, has a small shrinkage coefficient, and is non-magnetic, which improves the overall physical properties of the carbon brush. It has the characteristics of small deformation, easy processing and shaping, and non-magnetic properties. During the operation of the carbon brush, some of the tin components are oxidized, and tin oxide is a strong conductive material, which helps to improve the conductivity and service life of the carbon brush.

[0025] (2) Adding a small amount of nickel to the material can improve its overall electrical conductivity and corrosion resistance, extending its service life. Nickel also has high hardness and strength; adding nickel can enhance the material's mechanical properties, making it more wear-resistant and deformation-resistant. During material preparation, a small amount of nickel can act as a metal catalyst, promoting the copper-carbon reaction and improving the material's performance. Furthermore, adding nickel can adjust the coefficient of thermal expansion of the mixture, making it closer to the desired thermal expansion properties.

[0026] (3) Graphite has good lubricity and self-lubrication, which can reduce the coefficient of friction inside the mixture or in contact with other components, reduce wear, and improve the operating efficiency and service life of the equipment. Adding graphite can improve the electrical conductivity of the mixture. It has excellent heat resistance and corrosion resistance, making the material more reliable in industrial applications. It works synergistically with other materials to enhance the overall mechanical properties of the material. Graphite has good thermal conductivity, which helps heat transfer inside the mixture, prevents local overheating, and improves the thermal stability of the material.

[0027] (4) When graphite fibers are added to copper-tin alloys, they can form a conductive network, improving the overall conductivity of the alloy. Graphite fibers have high strength and high modulus, which can significantly enhance the mechanical properties of copper-tin alloys. They can also act as reinforcements, improving the hardness, strength, and toughness of the alloy, making it more wear-resistant and deformation-resistant. Adding graphite fibers to copper-tin alloys can improve the thermal conductivity of the alloy, helping to prevent local overheating and improving the thermal stability of the material. Graphite fibers can also play a structural supporting role in copper-tin alloys, increasing the internal bonding force of the alloy and improving the overall stability and durability of the material.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention uses a copper-tin alloy as a base, adds high-purity nickel, flake graphite and pitch-based graphitic carbon fiber, and employs wet grinding and powder mixing, powder metallurgy, and pressureless multi-stage heating sintering process under nitrogen atmosphere protection to obtain a carbon brush material. Its various properties are significantly improved, especially the density and flexural strength of the carbon brush are improved, and the resistivity and wear rate are significantly reduced, thus extending the service life of the product. Attached Figure Description

[0030] Figure 1 The image shows the metallographic structure of the carbon brush material in Example 1.

[0031] Figure 2 The image shows the metallographic structure of the carbon brush material in Example 2.

[0032] Figure 3The image shows the current-carrying friction (5N / 8A) scratches on the carbon brush material in Example 2. The left image shows the current-carrying friction (5N / 8A) scratches on the carbon brush material, the middle image is a magnified SEM image of the area within the box in the left image, and the right image is a magnified SEM image of the area within the box in the middle image. Detailed Implementation

[0033] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0034] Materials used in the following embodiments:

[0035] 10% Copper-Tin Alloy Matrix: 90% copper, 10% tin, particle size 15-45 / 53μm, produced by Zhonghang New Materials;

[0036] High-purity nickel: Ni: >99.99%, melting point 1453℃, porosity: 1.40~1.68g / cm³ 3 ;

[0037] Flake graphite: 1200 mesh, carbon content 99%;

[0038] Pitch-based graphitic carbon fiber: Glue-free mesophase pitch-based graphitic carbon fiber, thermal conductivity 100W / (m·K), carbon content 99%, 100 mesh, length 150μm, manufactured by Norco Co., Ltd.

[0039] Wax-based binder: paraffin wax, 1000 mesh.

[0040] Example 1

[0041] The amounts of each component in the carbon brush material of this embodiment are as follows: 87g of 10% copper-tin alloy matrix, 1g of high-purity nickel, 7g of flake graphite, and 5g of pitch-based graphitic carbon fiber. 1g of paraffin wax is also weighed.

[0042] The carbon brush preparation method includes the following steps:

[0043] The above raw materials were ball-milled for 5 hours using a wet milling method, with a ball-to-powder ratio of 3:1 (tungsten carbide balls with a diameter of 8 mm). They were then vacuum-dried, molded, and subjected to a pressure of 600 MPa. Sintering was then carried out under a nitrogen atmosphere with progressively increasing temperatures. Finally, the mixture was tempered at 200°C for 30 minutes and then cooled to room temperature. The specific steps of the progressively increasing temperatures are as follows:

[0044] (1) Low temperature degreasing section: The temperature is increased from room temperature to 300℃ at 1.8℃ / min and held for 40min to prevent graphite oxidation and decompose the binder at the same time;

[0045] (2) Structurally stable section:

[0046] ① Graphite activation section: The temperature is increased from 300℃ to 500℃ at a rate of 2.5℃ / min to reconstruct the graphite crystals; then the temperature is increased from 500℃ to 550℃ at a rate of 1.5℃ / min and held for 20 min to adjust the C-C bond angle.

[0047] ② Nickel diffusion section: The temperature is increased from 550℃ to 600℃ at 3℃ / min and held for 15min to promote Ni-Cu interdiffusion. The nickel diffusion depth is >10μm, while eliminating Kirkendall pores and controlling the porosity to <0.5%.

[0048] (3) Liquid phase sintering stage: The temperature is increased from 600℃ to 850℃ at a rate of 6.67℃ / min and held for 60min;

[0049] (4) Controlled cooling stage:

[0050] ① Rapid cooling section: The temperature is reduced from 850℃ to 650℃ at a rate of 8℃ / min to suppress the growth of intermetallic compounds and control the size of Ni3Sn4 to be <200nm and the orientation angle of graphite flakes to be <15°.

[0051] ② Slow cooling section: The temperature is reduced from 650℃ to 450℃ at a rate of 3℃ / min, with a holding time of 5min for every 50℃ decrease, so that the graphite / metal interface thickness is 1.2~.5μm and the interface shear strength is ≥55MPa;

[0052] ③ Final cooling section: Naturally cool from 450℃ to 200℃ to eliminate residual stress.

[0053] Example 2

[0054] The amounts of each component in the carbon brush material of this embodiment are as follows: 87.5g of 10% copper-tin alloy matrix, 1.5g of high-purity nickel, 8g of flake graphite, and 3g of pitch-based graphitic carbon fiber. 1g of paraffin wax is also weighed. The carbon brush preparation method is the same as in Example 1.

[0055] Example 3

[0056] The amounts of each component in the carbon brush material of this embodiment are as follows: 83g of 10% copper-tin alloy matrix, 2g of high-purity nickel, 9g of flake graphite, and 6g of pitch-based graphitic carbon fiber. 1g of paraffin wax is also weighed. The carbon brush preparation method is the same as in Example 1.

[0057] Example 4

[0058] The amounts of each component in the carbon brush material of this embodiment are as follows: 78.5g of 10% copper-tin alloy matrix, 2.5g of high-purity nickel, 10g of flake graphite, and 9g of pitch-based graphitic carbon fiber. 1g of paraffin wax is also weighed. The carbon brush preparation method is the same as in Example 1.

[0059] Example 5

[0060] The amount of each component of the carbon brush material in this embodiment is the same as in Example 2.

[0061] The carbon brush preparation method is as follows: the temperature is increased from room temperature to 850℃ at a rate of 2.5℃ / min, held at that temperature for 2 hours, and then cooled with the furnace.

[0062] Comparative Example 1

[0063] The proportions of each component in the carbon brush material of this comparative example are as follows: 79.5g electrolytic copper powder, 1g high-purity nickel, 12g flake graphite, 0.5g iron powder, and 7g lead. 1g of paraffin wax is also weighed. The carbon brush preparation method is the same as in Example 1.

[0064] Figure 1 and Figure 2 The images show metallographic images of the carbon brush materials from Examples 1 and 2, respectively. It can be seen that the carbon brush material exhibits an irregular fine-grained structure. This is because the addition of elements such as nickel and iron achieves grain refinement through solid solution strengthening and the precipitation of a second phase (such as carbides), thereby improving flexural strength. The uniformly distributed white particles are nickel / graphite, forming a continuous network that ensures conductivity (resistor decreases) and also improves hardness (Vickers hardness increases) through dispersion strengthening.

[0065] Figure 3 The images show the current-carrying friction (5N / 8A) scratches on the carbon brush material in Example 2. The left image shows the current-carrying friction (5N / 8A) scratches on the carbon brush material; the middle image is a magnified SEM image of the area within the box in the left image; and the right image is a magnified SEM image of the area within the box in the middle image. It can be seen that deep and wide scratches indicate high material hardness (large Hv value), but insufficient toughness leads to brittle spalling.

[0066] Table 1. Testing methods and standards for carbon brush products in Examples 1-5 and comparative examples.

[0067] parameter Test methods standard Key equipment Bulk density Archimedes' principle GB / T 1423-1996 Densitometer Vickers hardness Indentation method using a regular square pyramid indenter ISO 6507, ASTM E92 Vickers hardness tester resistivity Four-point probe method GB / T 1692-2008 DC power supply, multimeter coefficient of friction Planar sliding friction test ASTM D1894, ISO 8295 Friction and wear testing machine Wear rate Morphological analysis method ASTM G99 3D morphology testing instrument Flexural strength Three-point bending test GB / T 50204-2015 Universal testing machine

[0068] Table 2. Test results of carbon brush products from Examples 1-5 and the comparative examples.

[0069]

[0070]

[0071] As shown in Table 2, compared with commercially available lead-containing carbon brushes, the carbon brush of this invention exhibits significantly improved performance in all aspects. In particular, the addition of a small amount of nickel increases the density of the second-phase particles, significantly reducing resistivity and enhancing conductivity. The addition of flake graphite improves the development of the layered structure, increasing porosity and reducing the coefficient of friction, thus significantly improving wear rate. The addition of pitch-based graphitic carbon fibers forms a three-dimensional conductive network, significantly increasing bulk density and improving thermal stability. In summary, the synergistic effect between the components, combined with the staged heating and grain boundary migration promoting pore closure, enhances the density and flexural strength of the carbon brush, significantly reduces wear rate, and extends the product's service life.

[0072] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made on the principle of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A high-wear-resistant and high-conductivity carbon brush material, characterized in that, It is prepared by mixing, pressing and sintering the following components by mass fraction: 1-3% high-purity nickel, 7-10% graphite, 1-5% pitch-based graphitic carbon fiber, and the remainder is 10% copper-tin alloy matrix.

2. The high wear-resistant and high conductivity carbon brush material according to claim 1, characterized in that, The 10% copper-tin alloy matrix contains 90% copper and 10% tin.

3. The high wear-resistant and high conductivity carbon brush material according to claim 1, characterized in that, The high-purity nickel has a nickel content >99.99% and a porosity of 1.40~1.68 g / cm³. 3 .

4. The high wear-resistant and high conductivity carbon brush material according to claim 1, characterized in that, The graphite is flake-shaped graphite.

5. The high wear-resistant and high conductivity carbon brush material according to claim 1, characterized in that, The pitch-based graphitic carbon fiber contains 99% carbon, has a particle size of 100 mesh, and a length of 150 μm.

6. A method for preparing a high-wear-resistant and high-conductivity carbon brush material according to any one of claims 1 to 5, characterized in that, The process includes the following steps: weighing a high wear-resistant and high conductivity carbon brush material according to any one of claims 1 to 5 and a wax-based binder, ball milling for 5 hours using a wet milling method with a ball-to-powder ratio of 3:1, then vacuum drying, followed by molding at a pressure of 600 MPa, then sintering under a nitrogen atmosphere with multi-stage heating, and finally tempering at 200°C for 30 minutes, followed by cooling to room temperature.

7. The method for preparing a high-wear-resistant and high-conductivity carbon brush material according to claim 6, characterized in that, The specific steps of the multi-stage heating process are as follows: (1) Low-temperature degreasing section: The temperature is increased from room temperature to 300℃ at a rate of 1.8℃ / min and held for 40 min; (2) Structurally stable section: ① Graphite activation section: The temperature is increased from 300 ℃ to 500 ℃ at a rate of 2.5 ℃ / min; then the temperature is increased from 500 ℃ to 550 ℃ at a rate of 1.5 ℃ / min, and held for 20 min. ② Nickel diffusion section: The temperature is increased from 550 ℃ to 600 ℃ at a rate of 3 ℃ / min, and held for 15 min; (3) Liquid phase sintering stage: The temperature is increased from 600 ℃ to 850 ℃ at a rate of 6.67 ℃ / min, and held for 60 min; (4) Controlled cooling stage: ① Rapid cooling section: The temperature is reduced from 850 ℃ to 650 ℃ at a rate of 8 ℃ / min; ② Slow cooling section: The temperature is reduced from 650 ℃ to 450 ℃ at a rate of 3 ℃ / min, with a holding time of 5 min for every 50 ℃ decrease; ③ Final cooling section: naturally cooled from 450 ℃ to 200 ℃.

8. The method for preparing a high-wear-resistant and high-conductivity carbon brush material according to claim 6, characterized in that, The wax-based binder is paraffin wax with a particle size of 1000 mesh.

9. The method for preparing a high-wear-resistant and high-conductivity carbon brush material according to claim 6, characterized in that, The amount of wax-based binder is 1% of the total mass of the high wear-resistant and high conductivity carbon brush material.

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