Graphite brush vacuum rapid high-temperature hot pressed sintering process, application and graphite brush

Abstract

The invention belongs to the technical field of electric brushes, and particularly relates to a graphite electric brush vacuum rapid high-temperature hot pressing sintering process, application and a graphite electric brush. The vacuum rapid high-temperature hot-pressed sintering process comprises the following steps: carrying out primary hot-pressed sintering on an electric brush raw material, heating to 450-550 DEG C at a heating rate of 40-60 DEG C / min, and forming pressure of 15-20 kN; the temperature is increased to 800 DEG C to 900 DEG C, heat preservation is conducted for 15 min to 25 min, the temperature increasing rate is 50 DEG C / min to 100 DEG C / min, and the forming pressure is 20 kN to 50 kN; and finally, cooling under the pressure of 25-35 kN, thereby obtaining the product. By combining hot pressing sintering, under the condition that the metal content of the electric brush is similar, the resistivity of the graphite electric brush can be effectively reduced, the volume density and breaking strength are improved, the sintering time is greatly shortened, the production efficiency is improved, and the method is suitable for large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of electric brushes, and in particular relates to a vacuum rapid high-temperature hot pressing sintering process for graphite electric brushes and an application thereof, and a graphite electric brush. Background Art

[0002] As an important conductive part of the motor, the brush is in constant contact with the rotating commutator or collector ring surface to smoothly conduct current. Therefore, the brush must have the characteristics of low friction coefficient and small wear, and will not grind or damage the commutator and collector ring; high mechanical strength to avoid wear caused by high-speed rotation and vibration; good lubrication performance, smooth contact with the commutator or collector ring; small resistivity and good commutation performance; no sparks or noise, and the service life is extended as much as possible.

[0003] Brushes can be divided into two categories according to the raw materials: carbon brushes and metal brushes. Carbon brushes use carbon black, graphite or coke as the main raw materials. Carbon brushes are made of asphalt coke and carbon black as the main raw materials, and are made with graphite. Since this type of brush is not graphitized, it has poor lubricity and needs to be compensated by adding graphite. Among them, brushes with less graphite are called carbon brushes, and brushes with more graphite are called carbon-graphite brushes. They have higher hardness and density, but are not suitable for high-speed motors due to their large friction coefficient. They are only used in old DC motors used in mines, rolling mills and cranes.

[0004] Chinese invention patent publication number CN106025745A discloses a graphite brush and a preparation method thereof. The graphite brush is made of the following raw materials in parts by weight: 10-60 parts of graphite, 20-40 parts of asphalt, and 10-30 parts of asphalt-based graphene. The preparation steps are as follows: (1) hot melting, under the protection of nitrogen or inert gas, hot melting the asphalt to obtain a melt, and keeping the temperature constant at 500°C; (2) pyrolysis, heating the melt to 1500°C at a heating rate of 10°C / min, and keeping the temperature constant for 0.1 h-1 h; (3) grapheneization, heating the melt at 1500°C to 3300°C at a heating rate of 100°C / min, and keeping the temperature constant for 1 min-3 min; (4) cooling, during the cooling process, the melt is oscillated with ultrasound, and a certain amount of asphalt is added and stirred when the temperature of the melt drops below 400°C; (5) solidification and sintering to obtain a graphite brush blank.

[0005] Another Chinese invention patent publication number CN116191160A discloses a method for preparing a brush, comprising 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 the ethanol to obtain a binding solvent; (3) simultaneously conveying the graphite powder, copper powder and binding solvent into a mixing tank for kneading to obtain a mixture; (4) squeezing the mixture from the mixing tank into a collecting container; (5) conveying the mixture in the collecting container to a drying device, and then crushing, pressing and calcining to obtain the mixture.

[0006] However, the brushes prepared by the above invention patents have low density and flexural strength, and high open porosity and resistivity, which seriously affect the service life of the brushes in the motor. Therefore, it is very important to provide a method for preparing a graphite 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 graphite brush vacuum rapid high-temperature hot pressing sintering process and application, and a graphite brush.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A vacuum rapid high-temperature hot-pressing sintering process for graphite brushes comprises the following steps: subjecting brush raw materials to a hot-pressing sintering process, first heating the brush raw materials to 450-550°C, with a heating rate of 40-60°C / min, and a molding pressure of 15 kN-20 kN; then heating the brush raw materials to 800-900°C, keeping the temperature for 15-25 min, with a heating rate of 50-100°C / min, and a molding pressure of 20 kN-50 kN; and finally cooling the brush raw materials under a pressure of 25-35 kN to obtain the brush raw materials.

[0009] Preferably, the brush raw material includes copper-plated graphite powder.

[0010] Preferably, the mass fraction of copper in the copper-plated graphite powder is 58%-62%, the mass fraction of iron is ≤0.4%, the particle size of the copper-plated graphite powder is 90 mesh-110 mesh, and the ash content is ≤0.5%.

[0011] Preferably, the brush raw material further includes lead powder, tin powder and molybdenum disulfide.

[0012] 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.

[0013] Preferably, 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.

[0014] Preferably, the hot pressing sintering is carried out under a vacuum degree of -0.1 MPa to 0 MPa.

[0015] The present invention also provides a graphite brush, which is prepared by the above-mentioned graphite brush vacuum rapid high-temperature hot pressing sintering process.

[0016] Preferably, 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 20 MPa-40 MPa.

[0017] The present invention also provides an application of a graphite brush vacuum rapid high temperature hot pressing sintering process in the preparation of graphite brushes. The process is the above-mentioned graphite brush vacuum rapid high temperature hot pressing sintering process.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a vacuum rapid high-temperature hot pressing sintering process for graphite brushes. Combined with hot pressing sintering, the resistivity of the brushes can be effectively reduced, the volume density and the flexural strength can be improved under the condition of similar metal content of the brushes. The process greatly shortens the sintering time, improves production efficiency, and is suitable for large-scale production. DETAILED DESCRIPTION

[0019] It is worth noting that the raw materials used in the present invention are all common commercially available products. The copper-plated graphite powder was purchased from Chongqing Jiurui Metal Materials Co., Ltd., and the lead powder and tin powder were purchased from Chongqing Youyan Chongye New Materials Co., Ltd. The performance indicators of the lead powder, tin powder and copper-plated graphite powder are shown in Table 1.

[0020] Table 1 Performance index table

[0021] Example 1 A vacuum rapid high temperature hot pressing sintering process for graphite brushes, the steps are as follows: 1. Raw materials: copper-plated graphite powder.

[0022] 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 thickness of the pressed product. Place the mold in the vacuum box of the vacuum hot pressing sintering machine to ensure good contact between the mold and the stage. Close the vacuum box door, evacuate the vacuum tank to a gauge pressure of -0.1 MPa, and the gauge pressure of the vacuum chamber to 0 MPa. Sinter according to the molding pressure and temperature change table shown in Table 2. After sintering, the graphite brush is obtained.

[0023] Table 2 Molding pressure and temperature changes

[0024] Example 2 A vacuum rapid high temperature hot pressing sintering process for graphite brushes, the steps are as follows: 1. Raw materials: copper-plated graphite powder.

[0025] 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 thickness of the pressed product. Place the mold in the vacuum box of the vacuum hot pressing sintering machine to ensure good contact between the mold and the stage. Close the vacuum box door, evacuate until the gauge pressure of the vacuum tank is -0.1 MPa, and the gauge pressure of the vacuum chamber is 0 MPa, and sinter according to the molding pressure and temperature change table shown in Table 3. After sintering, the graphite brush is obtained.

[0026] Table 3 Molding pressure and temperature changes

[0027] Example 3 A vacuum rapid high temperature hot pressing sintering process for graphite brushes, the steps are as follows: 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.

[0028] 2. Sieve and mix: Pass the raw materials through a 40-mesh sieve, put them into a mixer and mix them at 25°C and 20 rpm for 2 h to obtain a uniformly mixed powder; 3. Loading and sintering: Load the evenly mixed powder into a graphite mold with an inner diameter of Φ100 mm, and adjust the amount of material in the mold according to the thickness of the product to be pressed. Place the mold in the vacuum box of the vacuum hot pressing sintering machine to ensure that the mold is in good contact with the stage. Close the vacuum box door, evacuate the vacuum tank to a gauge pressure of -0.1 MPa, and the gauge pressure of the vacuum chamber to 0 MPa, and sinter according to the molding pressure and temperature change table shown in Table 2. After sintering, the graphite brush is obtained.

[0029] Example 4 Compared with Example 1, the only difference is that the molding pressure and temperature change are different, as shown in Table 4.

[0030] Table 4 Molding pressure and temperature changes

[0031] Example 5 Compared with Example 1, the only difference is that the molding pressure and temperature change are different, as shown in Table 5.

[0032] Table 5 Molding pressure and temperature changes

[0033] Comparative Example 1 A graphite brush preparation process (traditional secondary molding + re-pressing), the steps are as follows: 1. Raw materials: copper-plated graphite powder.

[0034] 2. Loading and sintering: The qualified copper-plated graphite powder is loaded into a 26 mm × 65 mm mold for pressing. Pre-pressing is first performed, with a pressing pressure of 100 MPa and a holding time of 5 s-10 s; after the pre-pressing is completed, formal pressing begins, with a pressing pressure of 150 MPa and a holding time of 1 min. The mold is then placed in a 45 t hydraulic press to ensure good contact between the mold and the stage, and sintered at normal pressure according to the temperature change table shown in Table 6.

[0035] Table 6 Temperature change table

[0036] 3. Re-pressing: After sintering, put the blank into the mold and press it again. The pressing pressure is 150 MPa and the pressure holding time is 1 min to obtain the graphite brush.

[0037] Comparative Example 2 A graphite brush preparation process (traditional one-step forming + re-pressing), the steps are as follows: 1. Raw materials: copper-plated graphite powder.

[0038] 2. Loading and sintering: The qualified copper-plated graphite powder is loaded into a mold with an inner diameter of 26 mm × 65 mm for pressing, with a pressing pressure of 150 MPa and a holding time of 1 min. The mold is then placed in a 45 t hydraulic press to ensure good contact between the mold and the stage, and sintered at normal pressure according to the temperature change table shown in Table 6.

[0039] 3. Re-pressing: After sintering, put the blank into the mold and press it again. The pressing pressure is 100 MPa and the pressure holding time is 1 min to obtain the graphite brush.

[0040] Comparative Example 3 A conventional graphite brush preparation process (traditional one-step forming) includes the following steps: 1. Raw materials: copper-plated graphite powder.

[0041] 2. Loading and sintering: The qualified copper-plated graphite powder is loaded into a mold with an inner diameter of 26 mm × 65 mm for pressing, with a pressing pressure of 150 MPa and a holding time of 1 min. The mold is then placed in a 45 t hydraulic press to ensure good contact between the mold and the stage, and sintered at normal pressure according to the temperature change table shown in Table 7. After sintering, the graphite brush is obtained.

[0042] Table 7 Temperature change table

[0043] Comparative Example 4 A graphite brush preparation process (traditional one-step forming + re-pressing and re-firing), the steps are as follows: 1. Raw materials: copper-plated graphite powder.

[0044] 2. Loading and sintering: The qualified copper-plated graphite powder is loaded into a mold with an inner diameter of 26 mm × 65 mm for pressing, with a pressing pressure of 150 MPa and a holding time of 1 min. The mold is then placed in a 45 t hydraulic press to ensure good contact between the mold and the stage, and sintered at normal pressure according to the temperature change table shown in Table 7.

[0045] 3. Re-pressing and re-firing: After sintering, the blank is put into the mold and re-pressed, with a pressing pressure of 150MPa and a holding time of 1 min. Re-firing is performed under normal pressure according to the temperature change table shown in Table 7. After re-firing, the graphite brush is obtained.

[0046] Comparative Example 5 Compared with Example 1, the only difference is that the molding pressure and temperature change are different, as shown in Table 8.

[0047] Table 8 Molding pressure and temperature changes

[0048] Comparative Example 6 Compared with Example 1, the only difference is that the molding pressure and temperature change are different, as shown in Table 9.

[0049] Table 9 Molding pressure and temperature changes

[0050] Test Case The performance indexes of the graphite brushes prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were tested respectively, and the specific testing methods are as follows: 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"; Open porosity (%): Refer to JB / T 8133.15-2013 "Test methods for physical and chemical properties of electric carbon products Part 15: Porosity".

[0051] The performance test results are shown in Table 10. As can be seen from Table 10, the resistivity of the graphite brush prepared in Example 1 is lower than that of Comparative Examples 1-2, and the flexural strength is higher than that of Comparative Examples 1-2. It can be seen that compared with the traditional method, the use of hot pressing sintering method not only greatly shortens the sintering time, but also effectively reduces the resistivity of the graphite brush and improves the flexural strength. In addition, the volume density of the graphite brush prepared in Example 1 is higher than that of Comparative Examples 3-6, and the porosity is lower than that of Comparative Examples 3-6.

[0052] Among them, the sintering temperatures of Example 1 and Example 2 are 850°C and 870°C, and the sintering temperature of Comparative Example 5 is 750°C. The volume density of the graphite brushes in Example 1 and Example 2 are higher than that in Comparative Example 5, and the porosity is lower than that in Comparative Example 5, indicating that increasing the sintering temperature helps to increase the volume density of the graphite brush material and reduce the open porosity.

[0053] Table 10 Performance index table

[0054] Note: “ / ” indicates that the flexural strength is too low to be measured, and “-” indicates that the hardness is too low to be measured.

[0055] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate 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, with a heating rate of 40-60°C / min, and a molding pressure of 15 kN-20 kN; then heating the temperature to 800-900°C, keeping the temperature for 15-25 min, with a heating rate of 50-100°C / min, and a molding pressure of 20 kN-50 kN; and finally cooling the brush raw material under a pressure of 25 kN-35 kN to obtain the product.

2. The vacuum rapid high temperature hot pressing sintering process for graphite brushes according to claim 1 is characterized in that: The brush raw material includes copper-plated graphite powder.

3. The vacuum rapid high temperature hot pressing sintering process for graphite brushes according to claim 2 is characterized in that: The mass fraction of copper in the copper-plated graphite powder is 58%-62%, the mass fraction of iron is ≤0.4%, and the particle size of the copper-plated graphite powder is 90 meshes-110 meshes.

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

5. The vacuum rapid high temperature hot pressing sintering process for graphite brushes according to claim 4 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.

6. The vacuum rapid high temperature hot pressing sintering process for graphite brushes according to claim 4 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.

7. 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.

8. A graphite brush, characterized in that: The graphite brush as described in any one of claims 1 to 7 is prepared by a vacuum rapid high temperature hot pressing sintering process.

9. The graphite brush according to claim 8, 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.

10. 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 1-7.

Images