A vacuum rapid high-temperature hot-pressing sintering process for graphite brushes, its application, and graphite brushes

Abstract

The present invention belongs to the technical field of carbon brushes, and particularly relates to a vacuum rapid high-temperature hot-pressing sintering process and application thereof, and carbon brushes. The vacuum rapid high-temperature hot-pressing sintering process comprises the following steps: performing primary hot-pressing sintering on the carbon brush raw materials, first heating to 450°C - 550°C at a heating rate of 40°C / min - 60°C / min and a forming pressure of 15 kN - 20 kN; then heating to 800°C - 900°C, holding for 15 min - 25 min, at a heating rate of 50°C / min - 100°C / min and a forming pressure of 20 kN - 50 kN; and finally cooling under a pressure of 25 kN - 35 kN to obtain the product. The present invention can effectively reduce the resistivity of carbon brushes, improve the bulk density and flexural strength, greatly shorten the sintering time, and improve the production efficiency under the condition of similar metal content in the carbon brushes in combination with hot-pressing sintering, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of brush, and particularly relates to a vacuum rapid high-temperature hot pressing sintering process and application of graphite brush, and a graphite brush. Background Art

[0002] As an important current-carrying part of an electric motor, the brush continuously contacts the surface of the rotating commutator or slip ring to conduct current smoothly. Therefore, the brush must have the characteristics of small friction coefficient and small wear amount, without grinding or damaging the commutator and slip ring; large mechanical strength to avoid wear caused by high-speed rotation and vibration; good lubrication performance to contact smoothly with the commutator or slip ring; small resistivity and good commutation performance; no spark or noise generated, and try to extend the service life and other performances.

[0003] Brushes can be divided into two categories: carbon brushes and metal brushes according to different raw materials. Carbon brushes use general carbon materials such as carbon black, graphite or coke as the main raw materials. Carbon brushes are made mainly of pitch coke and carbon black, and are made with the addition of graphite. Since this kind of brush is not graphitized, its lubricity is poor and it needs to add graphite to make up for it. Among them, the one with less graphite proportion is called carbon brush, and the one with more graphite proportion is called carbon graphite brush. They have relatively high hardness and density, but are not suitable for high-speed motors due to their large friction coefficient, and are only used in old models of DC motors for mines, rolling mills and cranes.

[0004] Chinese Patent Publication No. CN106025745A discloses a graphite brush and its preparation method. The graphite brush is made of the following raw materials in parts by weight: 10 parts - 60 parts of graphite, 20 parts - 40 parts of asphalt, and 10 parts - 30 parts of asphalt-based graphene. The preparation steps are as follows: (1) Melting: Under the protection of nitrogen or inert gas, melt the asphalt to obtain a melt and keep it at a constant temperature of 500 °C; (2) Pyrolysis: Heat the melt to 1500 °C at a heating rate of 10 °C / min and keep it at a constant temperature for 0.1 h - 1 h; (3) Graphenization: Heat the melt at 1500 °C to 3300 °C at a heating rate of 100 °C / min and keep it at a constant temperature for 1 min - 3 min; (4) Cooling: During the cooling process, oscillate the melt with ultrasonic waves, and add a certain amount of asphalt and stir when the temperature of the melt drops below 400 °C; (5) Solidification sintering: Obtain a graphite brush blank.

[0005] Another Chinese invention patent publication number CN116191160A discloses a method for preparing a carbon brush, which includes the following steps: (1) feeding graphite powder and copper powder into a screening machine for screening respectively to obtain copper powder and graphite powder with the same particle size; (2) mixing phenolic resin and ethanol until the phenolic resin is dissolved in ethanol to obtain an adhesive solvent; (3) synchronously feeding the graphite powder, copper powder and adhesive solvent into a mixing tank for kneading to obtain a mixture; (4) extruding the mixture from the mixing tank into a collecting container; (5) sending the mixture in the collecting container to a drying device, and then performing crushing, pressing and calcining to obtain the carbon brush.

[0006] However, for the carbon brush prepared by the above invention patent, its density and flexural strength are relatively low, and the open porosity and resistivity are relatively high, which seriously affect the service life of the carbon brush in the motor. Therefore, it is very important to provide a method for preparing a graphite carbon brush with low resistivity and high flexural strength. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a vacuum rapid high-temperature hot-pressing sintering process for graphite carbon brushes and its application, and graphite carbon brushes.

[0008] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0009] A vacuum rapid high-temperature hot-pressing sintering process for graphite carbon brushes includes the following steps: performing primary hot-pressing sintering on the carbon brush raw materials, first heating to 450°C - 550°C at a heating rate of 40°C / min - 60°C / min and a forming pressure of 15 kN - 20 kN; then heating to 800°C - 900°C, holding for 15 min - 25 min at a heating rate of 50°C / min - 100°C / min and a forming pressure of 20 kN - 50 kN; and finally cooling under a pressure of 25 kN - 35 kN to obtain the product.

[0010] Preferably, the carbon brush raw materials include copper-plated graphite powder.

[0011] Preferably, the mass fraction of copper in the copper-plated graphite powder is 58% - 62%, the mass fraction of iron ≤ 0.4%, the particle size of the copper-plated graphite powder is 90 mesh - 110 mesh, and the ash content ≤ 0.5%.

[0012] Preferably, the carbon brush raw materials further include lead powder, tin powder and molybdenum disulfide.

[0013] Preferably, the mass ratio of the copper-plated graphite powder, lead powder, tin powder and molybdenum disulfide is 93 - 96:2 - 4:0.5 - 1.5:1 - 2.

[0014] Preferably, the brush raw material needs to pass through a 30-mesh to 50-mesh sieve and be mixed at 20°C - 35°C at 15 rpm - 25 rpm for 1.5 h - 2.5 h.

[0015] Preferably, the hot-press sintering is carried out under a vacuum degree of -0.1 MPa to 0 MPa.

[0016] The present invention also provides a graphite brush, which is prepared by the above-mentioned vacuum rapid high-temperature hot-press sintering process for graphite brushes.

[0017] Preferably, the resistivity of the graphite brush is 0.3 μΩ·m - 0.7 μΩ·m, the bulk density is 3.3 g / cm 3 - 3.7 g / cm 3 , the open porosity is 8% - 10%, and the flexural strength is 20 MPa - 40 MPa.

[0018] The present invention also provides an application of the vacuum rapid high-temperature hot-press sintering process for graphite brushes in the preparation of graphite brushes, and the process is the above-mentioned vacuum rapid high-temperature hot-press sintering process for graphite brushes.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention provides a vacuum rapid high-temperature hot-press sintering process for graphite brushes. Combining hot-press sintering, it can effectively reduce the resistivity of the brush, improve the bulk density and flexural strength under the condition of similar metal content in the brush. Moreover, this process greatly shortens the sintering time, improves production efficiency, and is suitable for large-scale production. Specific Embodiments

[0021] It should be noted that the raw materials used in the present invention are all ordinary commercially available products. The copper-plated graphite powder is purchased from Chongqing Jiurui Metal Materials Co., Ltd., and the lead powder and tin powder are both purchased from Chongqing Youyan Heavy Metallurgy New Materials Co., Ltd. The performance indexes of the lead powder, tin powder and copper-plated graphite powder are shown in Table 1.

[0022] Table 1 Performance Index Table

[0023]

[0024] Example 1

[0025] A vacuum rapid high-temperature hot-press sintering process for graphite brushes is as follows:

[0026] 1. Raw materials: Copper-plated graphite powder.

[0027] 2. Loading and Sintering: Load the qualified copper-plated graphite powder into a graphite mold with an inner diameter of Φ100 mm, and adjust the loading amount of the mold according to the required thickness of the product. Place the mold in the vacuum chamber of a vacuum hot pressing sintering machine, ensuring good contact between the mold and the carrier table. Close the door of the vacuum chamber, evacuate to a vacuum tank gauge pressure of -0.1 MPa and a vacuum chamber gauge pressure of 0 MPa, and sinter according to the forming pressure and temperature change table shown in Table 2. After sintering, the graphite brush is obtained.

[0028] Table 2 Forming Pressure and Temperature Change Table

[0029]

[0030] Example 2

[0031] A vacuum rapid high-temperature hot pressing sintering process for graphite brushes, the steps are as follows:

[0032] 1. Raw materials: Copper-plated graphite powder.

[0033] 2. Loading and Sintering: Load the qualified copper-plated graphite powder into a graphite mold with an inner diameter of Φ100 mm, and adjust the loading amount of the mold according to the required thickness of the product. Place the mold in the vacuum chamber of a vacuum hot pressing sintering machine, ensuring good contact between the mold and the carrier table. Close the door of the vacuum chamber, evacuate to a vacuum tank gauge pressure of -0.1 MPa and a vacuum chamber gauge pressure of 0 MPa, and sinter according to the forming pressure and temperature change table shown in Table 3. After sintering, the graphite brush is obtained.

[0034] Table 3 Forming Pressure and Temperature Change Table

[0035]

[0036] Example 3

[0037] A vacuum rapid high-temperature hot pressing sintering process for graphite brushes, the steps are as follows:

[0038] 1. Raw materials: By weight, it consists of 94.5 parts of copper-plated graphite, 3 parts of lead powder, 1 part of tin powder, and 1.5 parts of molybdenum disulfide.

[0039] 2. Screening and Mixing: Pass the raw materials through a 40-mesh sieve, then put them into a mixer and mix at 25 °C at 20 rpm for 2 h to obtain a uniformly mixed powder;

[0040] 3. Loading and Sintering: Load the uniformly mixed powder into a graphite mold with an inner diameter of Φ100 mm, and adjust the loading amount of the mold according to the required thickness of the product. Place the mold in the vacuum chamber of a vacuum hot pressing sintering machine to ensure good contact between the mold and the loading platform. Close the door of the vacuum chamber, evacuate to a vacuum gauge pressure of -0.1 MPa in the vacuum tank and 0 MPa in the vacuum chamber, and sinter according to the forming pressure and temperature change table shown in Table 2. After sintering, the graphite brush is obtained.

[0041] Example 4

[0042] Compared with Example 1, the difference is only in the different forming pressure and temperature changes, as shown in Table 4 specifically.

[0043] Table 4 Forming Pressure and Temperature Change Table

[0044]

[0045] Example 5

[0046] Compared with Example 1, the difference is only in the different forming pressure and temperature changes, as shown in Table 5 specifically.

[0047] Table 5 Forming Pressure and Temperature Change Table

[0048]

[0049] Comparative Example 1

[0050] A preparation process for graphite brushes (traditional secondary forming + repressing), the steps are as follows:

[0051] 1. Raw materials: Copper-plated graphite powder.

[0052] 2. Loading and Sintering: Load the qualified copper-plated graphite powder into a 26 mm×65 mm mold for pressing. First, perform pre-pressing, with a pressing pressure of 100 MPa and a holding time of 5 s - 10 s; after pre-pressing is completed, start formal pressing, with a pressing pressure of 150 MPa and a holding time of 1 min. Then place the mold in a 45 t hydraulic press to ensure good contact between the mold and the loading platform, and sinter at normal pressure according to the temperature change table shown in Table 6.

[0053] Table 6 Temperature Change Table

[0054]

[0055] 3. Repressing: After sintering, load the blank into the mold and re-press it, with a pressing pressure of 150 MPa and a holding time of 1 min, to obtain the graphite brush.

[0056] Comparative Example 2

[0057] A preparation process for graphite brushes (traditional one-time molding + repressing), the steps are as follows:

[0058] 1. Raw materials: copper-plated graphite powder.

[0059] 2. Loading and sintering: Load the qualified copper-plated graphite powder into a mold with an inner diameter of 26 mm × 65 mm for pressing, with a pressing pressure of 150 MPa and a pressure holding time of 1 min. Then place the mold in a 45 t hydraulic press, ensure good contact between the mold and the loading platform, and sinter it at normal pressure according to the temperature change table shown in Table 6.

[0060] 3. Repressing: After sintering, load the blank into the mold and repress it again, with a pressing pressure of 100 MPa and a pressure holding time of 1 min, then the graphite brush is obtained.

[0061] Comparative Example 3

[0062] A preparation process for conventional graphite brushes (traditional one-time molding), the steps are as follows:

[0063] 1. Raw materials: copper-plated graphite powder.

[0064] 2. Loading and sintering: Load the qualified copper-plated graphite powder into a mold with an inner diameter of 26 mm × 65 mm for pressing, with a pressing pressure of 150 MPa and a pressure holding time of 1 min. Then place the mold in a 45 t hydraulic press, ensure good contact between the mold and the loading platform, and sinter it at normal pressure according to the temperature change table shown in Table 7. After sintering, the graphite brush is obtained.

[0065] Table 7 Temperature change table

[0066]

[0067] Comparative Example 4

[0068] A preparation process for graphite brushes (traditional one-time molding + repressing and re-sintering), the steps are as follows:

[0069] 1. Raw materials: copper-plated graphite powder.

[0070] 2. Loading and sintering: Load the qualified copper-plated graphite powder into a mold with an inner diameter of 26 mm × 65 mm for pressing, with a pressing pressure of 150 MPa and a pressure holding time of 1 min. Then place the mold in a 45 t hydraulic press, ensure good contact between the mold and the loading platform, and sinter it at normal pressure according to the temperature change table shown in Table 7.

[0071] 3. Repressing and re-firing: After sintering, the green compact is loaded into a mold and repressed. The repressing pressure is 150 MPa and the pressure holding time is 1 min. Then, it is re-fired at normal pressure according to the temperature change table shown in Table 7. After re-firing, the graphite brush is obtained.

[0072] Comparative Example 5

[0073] Compared with Example 1, the difference lies only in the molding pressure and temperature change, as shown in Table 8 specifically.

[0074] Table 8 Molding Pressure and Temperature Change Table

[0075]

[0076] Comparative Example 6

[0077] Compared with Example 1, the difference lies only in the molding pressure and temperature change, as shown in Table 9 specifically.

[0078] Table 9 Molding Pressure and Temperature Change Table

[0079]

[0080] Test Example

[0081] The performance indexes of the graphite brushes prepared in Examples 1 - 5 and Comparative Examples 1 - 6 are detected respectively. The specific test methods are as follows:

[0082] Resistivity (μΩ·m): Refer to JB / T 8133.2 - 2013 "Test Methods for Physical and Chemical Properties of Electric Carbon Products - Part 2: Resistivity"; Hardness: Refer to JB / T 8133.3 - 2013 "Test Methods for Physical and Chemical Properties of Electric Carbon Products - Part 3: Rockwell Hardness"; Flexural Strength (MPa): Refer to JB / T 8133.7 - 2013 "Test Methods for Physical and Chemical Properties of Electric Carbon Products - Part 7: Flexural Strength"; Bulk Density (g / cm 3 ): Refer to JB / T 8133.14 - 2013 "Test Methods for Physical and Chemical Properties of Electric Carbon Products - Part 14: Bulk Density"; Apparent Porosity (%): Refer to JB / T 8133.15 - 2013 "Test Methods for Physical and Chemical Properties of Electric Carbon Products - Part 15: Porosity".

[0083] The performance test results are shown in Table 10. It can be seen from Table 10 that the resistivity of the graphite brushes prepared in Example 1 is lower than that of Comparative Example 1 - Comparative Example 2, and the flexural strength is higher than that of Comparative Example 1 - Comparative Example 2. It can be seen that compared with the traditional method, using the hot pressing sintering method not only greatly shortens the sintering time, but also effectively reduces the resistivity of the graphite brushes and improves the flexural strength. Moreover, the bulk density of the graphite brushes prepared in Example 1 is higher than that of Comparative Example 3 - Comparative Example 6, and the porosity is lower than that of Comparative Example 3 - Comparative Example 6.

[0084] Among them, the sintering temperatures of Example 1 and Example 2 are 850 °C and 870 °C, the sintering temperature of Comparative Example 5 is 750 °C, and the bulk density of the graphite brushes in Example 1 and Example 2 is higher than that of Comparative Example 5, and the porosity is lower than that of Comparative Example 5, indicating that increasing the sintering temperature helps to increase the bulk density of the graphite brush material and reduce the open porosity.

[0085] Table 10 Performance Index Table

[0086]

[0087] Note: " / " indicates that the flexural strength is too low to be measured, and "-" indicates that the hardness is too low to be measured.

[0088] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than a limitation on the protection scope of the present invention. Any simple modification or equivalent replacement of the technical solution of the present invention by those of ordinary skill in the art does not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A vacuum rapid high temperature hot pressing sintering process for graphite brushes, characterized in that: The method comprises the following steps: subjecting the brush raw material to a hot pressing sintering, first heating the temperature to 450-550°C, the heating rate is 40-60°C / min, and the molding pressure is 15kN-20 kN; then heating the temperature to 800-900°C, keeping the temperature for 15-25 min, the heating rate is 50-100°C / min, and the molding pressure is 20 kN-50 kN; finally cooling the brush raw material under a pressure of 25 kN-35 kN, and obtaining the product. The brush raw material comprises copper-plated graphite powder, in which the mass fraction of copper is 58%-62%, the mass fraction of iron is ≤0.4%, the particle size of the copper-plated graphite powder is 90 meshes-110 meshes, and the ash content is ≤0.5%.

2. The vacuum rapid high temperature hot pressing sintering process for graphite brushes according to claim 1 is characterized in that: The brush raw materials also include lead powder, tin powder and molybdenum disulfide.

3. The vacuum rapid high temperature hot pressing sintering process for graphite brushes according to claim 2 is characterized in that: The mass ratio of the copper-plated graphite powder, lead powder, tin powder and molybdenum disulfide is 93-96:2-4:0.5-1.5:1-2.

4. The vacuum rapid high temperature hot pressing sintering process for graphite brushes according to claim 2 is characterized in that: The brush raw material needs to pass through a 30-50 mesh sieve and be mixed at 20° C.-35° C. at 15 rpm-25 rpm for 1.5 h-2.5 h.

5. The vacuum rapid high temperature hot pressing sintering process for graphite brushes according to claim 1 is characterized in that: The hot pressing sintering is carried out under a vacuum degree of -0.1 MPa to 0 MPa.

6. A graphite brush, characterized in that: The graphite brush as described in any one of claims 1 to 5 is prepared by a vacuum rapid high temperature hot pressing sintering process.

7. The graphite brush according to claim 6, characterized in that: The resistivity of the graphite brush is 0.3 μΩ·m-0.7 μΩ·m, and the volume density is 3.3 g / cm 3 -3.7 g / cm 3 The open porosity is 8%-10%, and the flexural strength is 20MPa-40 MPa.

8. Application of a graphite brush vacuum rapid high temperature hot pressing sintering process in the preparation of graphite brushes, characterized in that: The process is the graphite brush vacuum rapid high temperature hot pressing sintering process as described in any one of claims 1-5.

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