A porous natural graphite brush material and its preparation method and application

Abstract

The present invention belongs to the field of brush technology, specifically to a porous natural graphite brush material, its preparation method, and application. The preparation method comprises first mixing natural graphite powder, D374 composite powder, medium-temperature asphalt powder, melamine, and SiC powder to obtain a dry powder; then adding a plasticizer to the dry powder, mixing, and roasting to obtain the product. The present invention provides a porous natural graphite brush material having a bulk density of 1.25-1.40 g / cm 3 , resistivity ≤ 27 μΩ·m, flexural strength 7‑16 MPa, friction coefficient <0.3, HR 10 / 196 Rockwell hardness 48‑78, open porosity 35‑42%, can be used for collector ring brushes in the excitation system of large and medium-sized steam turbine generator sets above 300 MW, with an operating environment linear speed of up to 80 m / s and a current density of 4‑12 A / cm 2 , which has good industrial application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of electric brushes, and in particular relates to a porous natural graphite electric brush material and a preparation method and application thereof. Background Art

[0002] Brushes are a crucial component of electric motors, conducting current between rotating and stationary parts. Because they are often made of graphite, they are also called carbon brushes. The process involves coating graphite powder, including various artificial graphite powders, with an asphalt or synthetic resin binder. This improves the formability of the graphite powder. After pressing and curing, the brush material is manufactured to possess a certain strength, resistivity, and service life.

[0003] However, traditional raw materials and processes have numerous limitations, making it difficult to meet the requirements of today's high-end motors. For example, using too much artificial graphite powder can lead to excessive hardness and increased friction, affecting the commutation performance of the brushes. Using too little artificial resin can result in low strength and poor wear resistance, while using too much can lead to excessive resistivity, which can cause excessive temperature rise during brush operation, leading to deformation and failure of the brush material.

[0004] Chinese invention patent publication number CN108907205A discloses a manufacturing process for a composite brush, comprising the following steps: S1, raw materials; S2, graphite powder, coke powder, tungsten disulfide powder, and modified coal tar pitch are mixed uniformly in a weight ratio of 1-1.5:1-2:0.2-0.4:0.6-1, then heated to 120-150°C, and then poured into a granulator to form particles with a particle size of 20-40 mm to obtain base particles; the base particles are placed in a roasting furnace, a protective gas is introduced, and heated to 2600-3000°C for 4-6 hours to graphitize them, and then crushed to a particle size of no more than 5 mm particles; S3, preparing working layer raw materials, transition layer raw materials, and welding layer raw materials; S4, laying the working layer raw materials, transition layer raw materials, and welding layer raw materials in a graphite grinding tool in sequence according to a thickness ratio of 15-20:6-8:3-4, and then introducing argon as a protective gas and hot pressing at 850-950°C and a pressure of 30-45 MPa for 20-30 minutes to obtain a block material; S5, processing the above block material into a brush substrate.

[0005] Another Chinese invention patent publication number CN106025745A discloses a graphite brush and its preparation method, which 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 0.1-1 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 1-3 min; (4) cooling, oscillating the melt with ultrasound during the cooling process, and adding a certain amount of asphalt for stirring when the temperature of the melt drops below 400°C; (5) solidification and sintering to obtain a graphite brush blank.

[0006] However, the brushes produced by the aforementioned inventions can only meet the requirements of small generator sets below 100 MW, and cannot meet the high speed, high linear speed, and high current requirements of generator sets above 300 MW, resulting in unsatisfactory performance. Therefore, there is an urgent need in the art to provide a brush material with low resistance, wear resistance, high temperature resistance, and a low friction coefficient. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the present invention provides a porous natural graphite brush material and a preparation method and application thereof.

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

[0009] A method for preparing a porous natural graphite brush material comprises the following steps:

[0010] (1) Natural graphite powder, D374 composite powder, medium temperature asphalt powder, melamine and SiC powder are mixed to obtain dry powder;

[0011] (2) Add plasticizer to the dry powder, mix, and roast to obtain the product.

[0012] Preferably, the laser particle size D of the natural graphite powder is 50 =65-90 μm, D 90 =155-180 μm, particle size composition -200 mesh (indicates undersize after passing through a 200 mesh sieve) accounts for ≥99.0%; fixed carbon content ≥99.5%, ash content ≤0.15%, volatile matter content ≤1.0%, moisture content ≤0.5%, pH value = 5.5-8.0.

[0013] Preferably, the D374 composite powder has a particle size composition of: +160 mesh (representing the oversize after passing a 160-mesh sieve) ≤ 10%, -320 mesh 50-55%, ash content ≤ 1.5%, and moisture content ≤ 1%. The physical and chemical properties of the D374 composite powder sintered material are: resistivity 31-35 μΩ·m, HR 10 / 980 Rockwell hardness 54-60, Shore hardness ≥ 15, flexural strength ≥ 6 MPa, and bulk density 1.45-1.52 g / cm 3 .

[0014] Preferably, the medium-temperature asphalt powder has a softening point of ≤100°C, a coking value of 65-69%, an ash content of ≤0.1%, a toluene insoluble matter content of ≤20%, a moisture content of ≤4.9%, and a volatile matter content of ≤40%.

[0015] The invention ensures that interconnected pores are formed in the porous natural graphite brush material by adding an appropriate amount of melamine, and the open pore porosity reaches 35-42%.

[0016] Preferably, the laser particle size D of the SiC powder is 50 =3-7 μm, SiC content ≥99.9%, free carbon content ≤0.05%, Fe2O3 content ≤0.02%.

[0017] Preferably, the dry powder is composed of 47-57% natural graphite powder, 14-24% D374 composite powder, 12-18% medium-temperature asphalt powder, 9-15% melamine and SiC powder to make up to 100% by weight.

[0018] More preferably, the dry powder consists of 51-53% natural graphite powder, 18-20% D374 composite powder, 14-16% medium-temperature asphalt powder, 12-15% melamine and SiC powder to 100% by weight.

[0019] Preferably, the mixing process in step (1) includes first stirring at 35-45 rpm for 2-3 h, then heating to 90-110° C. for 1-2 h, and finally cooling.

[0020] The present invention utilizes dry powder hot mixing to evaporate moisture from the powders upon heating. This increases the temperature of the air between and within the powders, increasing their activity and facilitating their flow. Over a period of time, the various powders are fully mixed, significantly improving the uniformity of their distribution within the mixture.

[0021] Preferably, the mixing speed in step (2) is 30-50 rpm, the mixing time is 0.5-1.5 h, and after the mixing is completed, it needs to be heated to 90-100°C, dried, cooled and sieved through a 100-200 mesh sieve.

[0022] Preferably, the plasticizer in step (2) includes phenolic resin, epoxy resin, organic solvent and alcohol.

[0023] Preferably, the phenolic resin accounts for 5-10% by weight of the dry powder, the epoxy resin accounts for 5-10% by weight of the dry powder, the organic solvent accounts for 15-35% by weight of the dry powder, and the alcohol accounts for 50-75% by weight of the dry powder.

[0024] Preferably, the organic solvent is acetone.

[0025] The density of phenolic resin is 1.055-1.065 g / cm 3 , resin content 62±4%, free phenol content ≤10%, appearance is reddish brown transparent liquid.

[0026] The softening point of the epoxy resin is 22-27°C, the epoxy value is 0.44-0.47 mol / 100 g, and the volatile matter content (100°C×3 h) is ≤1.0%.

[0027] The density of acetone is ≥0.795 g / mL, the content is ≥99.5%, the boiling point is 56±1℃, the evaporation residue is ≤0.001%, the water content is ≤0.1%, and the appearance is a colorless transparent liquid.

[0028] The present invention realizes the slurry kneading process by adding a plasticizer, removes the gas between the material powder, reduces the volume of the powder mixture, and improves the kneading efficiency.

[0029] Preferably, the pressing is required before calcination in step (2), the pressing pressure is 10-20 MPa, and the volume density of the compact obtained by pressing is 1.3-1.6 g / cm 3 The pressed green sheet has no delamination and cracks, good green sheet strength, and is not easy to fall off. It can meet the forming requirements of various specifications of pressed green sheets with a size of 200 mm × 200 mm × 50 mm or less.

[0030] Preferably, the calcination temperature curve includes first heating to 280-320°C, keeping warm for 3-4 hours, and a heating rate of 55-65°C / h; then heating to 400-420°C, keeping warm for 3.5-4.5 hours, and a heating rate of 3-5°C / h; then heating to 500-540°C, keeping warm for 3.5-4.5 hours, and a heating rate of 2-3°C / h; and finally heating to 970-990°C, keeping warm for 11-13 hours, and a heating rate of 4-15°C / h.

[0031] The present invention also provides a porous natural graphite brush material prepared by the above preparation method.

[0032] Preferably, the volume density of the porous natural graphite brush material is 1.25-1.40 g / cm 3 , resistivity ≤27μΩ·m, flexural strength 7-16 MPa, friction coefficient <0.3, HR 10 / 196 Rockwell hardness value 48-78, open porosity 35-42%.

[0033] The present invention also provides the use of the porous natural graphite brush material or the porous natural graphite brush material prepared by the above preparation method in brushes.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention provides a porous natural graphite brush material having a volume density of 1.25-1.40 g / cm 3 , resistivity ≤ 27 μΩ·m, flexural strength 7-16 MPa, friction coefficient <0.3, HR 10 / 196 Rockwell hardness 48-78, open porosity 35-42%, can be used for collector ring brushes in the excitation system of large and medium-sized steam turbine generator sets above 300 MW, the operating environment linear speed can reach 80 m / s, the current density is 4-12 A / cm 2 , which has good industrial application prospects.

[0036] (2) The porous natural graphite brush material of the present invention has a soft and delicate texture, uniform pore distribution, and a brush body covered with a large number of interconnected small pores, which can effectively suppress the occurrence of the "air cushion" phenomenon when the generator set is running at high speed, reduce arcs and sparks, and improve the current uniformity of the brush. DETAILED DESCRIPTION

[0037] It is worth noting that the raw materials used in the present invention are all common commercially available products, among which natural graphite powder is purchased from Qingdao Xingguang Graphite Materials Co., Ltd.; D374 composite powder is purchased from Harbin Oriental Electric Carbon Factory; phenolic resin, model T209-1A, is purchased from Hebei Zetian Chemical Co., Ltd.; epoxy resin, model WSR6101, is purchased from Nantong Xingchen Synthetic Materials Co., Ltd.; acetone, content ≥99.5%; alcohol, volume content 95%.

[0038] Example 1

[0039] A porous natural graphite brush material, the preparation method is as follows:

[0040] (1) Weigh the natural graphite powder (laser particle size D 50 =65-90 μm) 52%, D374 composite powder 19%, medium temperature asphalt powder (softening point 100℃, coking value 65%) 15%, melamine 12% and SiC powder (laser particle size D50 =65-90μm) 2%, stirred at 42 rpm in a Z-type mixing pot for 3 h, mixed, heated to 100℃, kept at this temperature for 2 h, and naturally cooled to below 50℃ to obtain dry powder;

[0041] (2) Add plasticizer to the dry powder (the weight percentage of each plasticizer component in the dry powder is: phenolic resin 7.5%, epoxy resin 7.5%, acetone 35% and alcohol 50%), mix at 40 rpm for 1 hour, heat to 100℃, dry, cool naturally, and pass through a 200-mesh sieve. Pour the mixture into a mold for pressing. Use a 200-ton hydraulic press with a pressure setting of 10 MPa to press the green compact to a size of 67×117×height H. The green compact has a bulk density of 1.5 g / cm 3 The compact was placed in a stainless steel crucible, compressed with filler, sealed with refractory clay, and then placed in a box furnace for calcination. The calcination temperature curve is shown in Table 1. After calcination, the compact was naturally cooled to room temperature to obtain the product.

[0042] Table 1 Calcination temperature curve

[0043]

[0044] Example 2

[0045] A porous natural graphite brush material, the preparation method is as follows:

[0046] (1) Weigh the natural graphite powder (laser particle size D 50 =65-90 μm) 47%, D374 composite powder 24%, medium temperature asphalt powder (softening point 100℃, coking value 65%) 15%, melamine 12% and SiC powder (laser particle size D 50 =65-90μm) 2%, stirred at 35 rpm in a Z-type mixing pot for 3 h, mixed, heated to 110℃, kept at this temperature for 1 h, and naturally cooled to below 50℃ to obtain a dry powder;

[0047] (2) Add plasticizer to the dry powder (the weight percentage of each plasticizer component in the dry powder is: phenolic resin 5%, epoxy resin 5%, acetone 15% and alcohol 75%), mix at 50 rpm for 0.5 h, heat to 90°C, dry, cool naturally, and pass through a 100-mesh sieve. Pour the mixture into a mold for pressing using a 200-ton hydraulic press with a pressure setting of 20 MPa. The green compact has a size of 67×117×height H and a bulk density of 1.3 g / cm 3 The compact was placed in a stainless steel crucible, compressed with filler, sealed with refractory clay, and then placed in a box furnace for calcination. The calcination temperature curve is shown in Table 1. After calcination, the compact was naturally cooled to room temperature to obtain the product.

[0048] Example 3

[0049] A porous natural graphite brush material, the preparation method is as follows:

[0050] (1) Weigh the natural graphite powder (laser particle size D 50 =65-90 μm) 57%, D374 composite powder 14%, medium temperature asphalt powder (softening point 100℃, coking value 69%) 15%, melamine 12% and SiC powder (laser particle size D 50 =65-90μm) 2%, stirred at 45 rpm for 2 h in a Z-type mixing pot, mixed, heated to 90℃, kept at this temperature for 2 h, and naturally cooled to below 50℃ to obtain dry powder;

[0051] (2) Add plasticizer to the dry powder (the weight percentage of the plasticizer components in the dry powder is: phenolic resin 10%, epoxy resin 10%, acetone 25% and alcohol 55%), mix at 30 rpm for 1.5 hours, heat to 100 ° C, dry, cool naturally, and pass through a 200 mesh sieve. Pour it into a mold for pressing. Use a 200-ton hydraulic press with a pressure setting of 20 MPa to press and form the green compact. The green compact has a size of 67 × 117 × height H and a bulk density of 1.6 g / cm 3 The compact was placed in a stainless steel crucible, compressed with filler, sealed with refractory clay, and then placed in a box furnace for calcination. The calcination temperature curve is shown in Table 1. After calcination, the compact was naturally cooled to room temperature to obtain the product.

[0052] Example 4

[0053] A porous natural graphite brush material, which differs from Example 1 only in the dry powder composition.

[0054] By weight percentage, the dry powder consists of the following components: natural graphite powder (laser particle size D 50 =65-90 μm) 52%, D374 composite powder 19%, medium temperature asphalt powder (softening point 100℃, coking value 65%) 12%, melamine 15% and SiC powder (laser particle size D 50 =65-90 μm) 2%.

[0055] Example 5

[0056] A porous natural graphite brush material, which differs from Example 1 only in the dry powder composition.

[0057] By weight percentage, the dry powder consists of the following components: natural graphite powder (laser particle size D 50 =65-90 μm) 52%, D374 composite powder 19%, medium temperature asphalt powder (softening point 100℃, coking value 65%) 18%, melamine 9% and SiC powder (laser particle size D50 =65-90 μm) 2%.

[0058] Example 6

[0059] A porous natural graphite brush material, which differs from Example 1 only in the dry powder composition.

[0060] By weight percentage, the dry powder consists of the following components: natural graphite powder (laser particle size D 50 =65-90 μm) 52%, D374 composite powder 19%, medium temperature asphalt powder (softening point 100℃, coking value 65%) 15%, melamine 10% and SiC powder (laser particle size D 50 =65-90 μm) 4%.

[0061] Example 7

[0062] A porous natural graphite brush material, which differs from Example 1 only in the dry powder composition.

[0063] By weight percentage, the dry powder consists of the following components: natural graphite powder (laser particle size D 50 =65-90 μm) 57%, D374 composite powder 14%, medium temperature asphalt powder (softening point 150℃, coking value 65%) 15%, melamine 12% and SiC powder (laser particle size D 50 =65-90 μm) 2%.

[0064] Comparative Example 1

[0065] Compared with Example 1, the only difference is the laser particle size D of natural graphite powder. 50 =40-60 μm.

[0066] Comparative Example 2

[0067] Compared with Example 1, the only difference is the laser particle size D of natural graphite powder. 50 =95-130 μm.

[0068] Comparative Example 3

[0069] Compared with Example 1, the only difference is that melamine is replaced by ammonium bicarbonate.

[0070] Comparative Example 4

[0071] Compared with Example 1, the only difference is that the organic solvent acetone is replaced by benzene.

[0072] Comparative Example 5

[0073] Compared with Example 1, the only difference is the dry powder composition, which is as follows:

[0074] By weight percentage, the dry powder consists of the following components: natural graphite powder (laser particle size D 50 =65-90 μm) 35.5%, D374 composite powder 35.5%, medium temperature asphalt powder (softening point 100℃, coking value 65%) 12%, melamine 15% and SiC powder (laser particle size D 50 =65-90 μm) 2%.

[0075] Comparative Example 6

[0076] Compared with Example 1, the only difference is that step (1) does not involve heating and mixing, as follows:

[0077] A porous natural graphite brush material, the preparation method is as follows:

[0078] (1) Weigh the natural graphite powder (laser particle size D 50 =65-90 μm) 52%, D374 composite powder 19%, medium temperature asphalt powder (softening point 100℃, coking value 65%) 15%, melamine 12% and SiC powder (laser particle size D 50 =65-90μm) 2%, stirred at 42 rpm in a Z-type mixing pot for 3 h to obtain dry powder;

[0079] (2) Add plasticizer to the dry powder (calculated by weight percentage of dry powder, the plasticizer consists of 7.5% phenolic resin, 7.5% epoxy resin, 35% acetone and 50% alcohol), mix at 40 rpm for 1 hour, heat to 100°C, dry, cool naturally, and pass through a 200-mesh sieve. Pour the mixture into a mold for pressing using a 200-ton hydraulic press with a pressure setting of 10 MPa. The green compact has a size of 67×117×height H and a bulk density of 1.5 g / cm 3 The compact was placed in a stainless steel crucible, compressed with filler, sealed with refractory clay, and then placed in a box furnace for calcination. The calcination temperature curve is shown in Table 1. After calcination, the compact was naturally cooled to room temperature to obtain the product.

[0080] Test Case

[0081] The performance indexes of the porous natural graphite brush materials prepared in Examples 1-7 and Comparative Examples 1-6 were tested respectively. The specific testing methods are as follows:

[0082] The pressing cracks and baking cracks are visually inspected, and the pressing pass rate and baking pass rate are calculated as follows:

[0083] Compressing qualification rate (%) = number of qualified compacts ÷ total number of compacts × 100%;

[0084] Roasting qualification rate (%) = number of qualified roasted products ÷ total number of roasted products submitted for inspection × 100%.

[0085] Resistivity (μΩ·m): in accordance with JB / T 8133.2.

[0086] Rockwell hardness: in accordance with JB / T 8133.3.

[0087] Flexural strength (MPa): in accordance with JB / T 8133.7.

[0088] Friction coefficient: in accordance with HB5367.10-1986.

[0089] Bulk density (g / cm 3 ): Follow JB / T 8133.14.

[0090] Porosity (%): in accordance with JB / T 8133.15.

[0091] The performance test results are shown in Table 2. It can be seen from Table 2 that by comparing Example 1 with Comparative Examples 1-6, it can be found that: 50 = = 65-90 μm natural graphite powder produced by the brush material has moderate wear resistance. It will not wear the slip ring during operation due to its high hardness, nor will it be easily broken due to its low flexural strength. The resistivity and flexural strength are both optimized, which can ensure low temperature rise during operation of the brush, easy formation of oxide film, good oxide film thickness and balance ability, and strong ability to suppress sparks. The finely distributed connecting pores in the brush body can effectively balance the "air cushion" phenomenon generated when the brush faces high-speed running slip rings, reducing arcing and sparks.

[0092] Table 2 Performance indicators

[0093]

[0094] 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 method for preparing a porous natural graphite brush material, characterized in that: The steps include: (1) Natural graphite powder, D374 composite powder, medium temperature asphalt powder, melamine and SiC powder are mixed to obtain dry powder; (2) Add plasticizer to the dry powder, mix, and roast to obtain: Wherein, the laser particle size D of the natural graphite powder is 50 =65-90 μm, The dry powder is composed of 47-57% natural graphite powder, 14-24% D374 composite powder, 12-18% medium-temperature asphalt powder, 9-15% melamine and SiC powder to make up to 100% by weight. The plasticizer includes phenolic resin, epoxy resin, acetone and alcohol, wherein the phenolic resin accounts for 5-10% by weight of the dry powder, the epoxy resin accounts for 5-10% by weight of the dry powder, the organic solvent accounts for 15-35% by weight of the dry powder, and the alcohol accounts for 50-75% by weight of the dry powder.

2. The preparation method according to claim 1, characterized in that The softening point of the medium-temperature asphalt powder is ≤100°C, the coking value is 65-69%, and the laser particle size D of the SiC powder is 50 =3-7 μm.

3. The preparation method according to claim 1, characterized in that The mixing process in step (1) includes stirring at 35-45 rpm for 2-3 hours, then heating to 90-110°C and keeping the temperature constant for 1-2 hours, and finally cooling; the mixing speed in step (2) is 30-50 rpm, the mixing time is 0.5-1.5 hours, and after the mixing is completed, it needs to be heated to 90-100°C, dried, cooled and sieved through a 100-200 mesh screen.

4. The preparation method according to claim 1, characterized in that The step (2) requires pressing before calcination. The pressing pressure is 10-20 MPa, and the volume density of the pressed green body is 1.3-1.6 g / cm 3 The calcination temperature curve includes first heating to 280-320°C, keeping warm for 3-4 hours, and a heating rate of 55-65°C / h; then heating to 400-420°C, keeping warm for 3.5-4.5 hours, and a heating rate of 3-5°C / h; then heating to 500-540°C, keeping warm for 3.5-4.5 hours, and a heating rate of 2-3°C / h; and finally heating to 970-990°C, keeping warm for 11-13 hours, and a heating rate of 4-15°C / h.

5. A porous natural graphite brush material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 4.

6. The porous natural graphite brush material according to claim 5, characterized in that: The volume density of the porous natural graphite brush material is 1.25-1.40 g / cm 3 , resistivity ≤27 μΩ·m, flexural strength 7-16 MPa, friction coefficient <0.3, HR 10 / 196 Rockwell hardness value 48-78, open porosity 35-42%.

7. Use of the porous natural graphite brush material according to any one of claims 5 to 6 in a brush.

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