Silver graphite brush material and preparation method thereof

Abstract

The invention relates to a silver graphite brush material and a preparation method thereof. The material comprises graphite powder. A thermosetting resin; the mass percentage content of each substance is as follows: 10-60% of graphite powder; 2 to 20 percent of thermosetting resin; 1-8% of an additive and the balance of silver. The problems that an existing silver graphite electric brush is serious in segregation, low in interface strength, high in preparation cost and long in period are solved. According to the material prepared through the method, segregation of silver can be reduced, the interface strength can be improved, the excellent comprehensive performance is achieved, the method is simple and easy to operate, and large-scale batch production can be achieved.

Description

Technical Field

[0001] The invention relates to the field of brush materials, and in particular to a silver-graphite brush and a preparation method thereof. Background Art

[0002] Silver graphite brushes are widely used in electrical contact fields such as aerospace, precision instruments, etc. due to their excellent electrical conductivity, wear resistance, and resistance to welding. The main preparation method at present is through mixing-pressing-sintering, but this process cannot overcome the phenomenon of component segregation, and the interface strength between graphite and silver is very low (flexural strength <20MPa), which seriously affects the performance of silver graphite brush materials.

[0003] The US invention patent with publication number US4534887 discloses a method for preparing silver-graphite brush materials. The method is to first mix silver nitrate with graphite powder, decompose at high temperature to prepare silver-graphite mixed powder, and then mix it with asphalt solution, press it, and bake it to prepare silver-graphite brush materials. This technology requires a baking process of up to half a month under the protection of inert gas at 1000-1200℃ to meet the use requirements.

[0004] The invention patent with publication number CN110467480A discloses a silver-impregnated graphite contact material and a preparation method thereof. The silver-impregnated graphite contact material is prepared by preparing a graphite matrix through high-temperature roasting and graphitization, and then impregnating metallic silver through heat. This technology also has the disadvantages of a long preparation cycle and a complex process. Summary of the invention

[0005] The object of the present invention is to provide a silver-graphite brush and a preparation method thereof, so as to solve the problems of serious segregation and low interface strength, high preparation cost and long cycle of the current silver-graphite brush. The material prepared by the method of the present invention can reduce the segregation of silver, improve the interface strength, and has excellent comprehensive performance. Moreover, the method is simple and easy to operate, and can realize large-scale batch production.

[0006] To achieve the above object, the present invention adopts the following technical solution: Silver graphite brush material, the material includes graphite powder; thermosetting resin; additives and silver, the mass percentage of each substance in the material is: 10-60% graphite powder; 2-20% thermosetting resin; 1-8% additives, and silver is the balance.

[0007] A better technical solution is that the mass percentage of the various materials is: 10-40% graphite powder; 3-10% thermosetting resin; 1-5% additives, and the balance is silver.

[0008] The additive is one or more of molybdenum disulfide, boron nitride, carbon nanotubes and carbon fibers.

[0009] The thermosetting resin is a phenolic resin; preferably, the phenolic resin is a high temperature resistant phenolic resin with a carbon residue rate of ≥50% at 550°C.

[0010] The graphite powder is natural flake graphite powder with a mesh size of 100 to 800.

[0011] The preparation method of the silver-graphite brush material is to take each component according to the above ratio, and specifically comprises the following steps: 1) completely dissolving silver nitrate in deionized water to obtain a silver nitrate aqueous solution; 2) adding graphite powder into silver nitrate aqueous solution and stirring to obtain silver nitrate graphite slurry; 3) drying the silver nitrate graphite slurry in an oven at a temperature of 80 to 150° C. for 5 to 12 hours to obtain a silver nitrate graphite mixture; 4) decomposing the silver nitrate-graphite mixture in a vacuum or protective atmosphere, wherein the protective atmosphere is hydrogen, argon or nitrogen, the decomposition temperature is 600-800° C., and the time is 2-6 hours to obtain a silver-graphite mixture; 5) Add the thermosetting resin into ethanol and stir to obtain a resin solution; 6) Add the silver-graphite mixture and additives to the resin solution, stir thoroughly, and knead for 2 to 3 hours to obtain a silver-graphite colloid; 7) Drying, crushing and sieving the silver-graphite colloid to 100-300 meshes to obtain silver-graphite mixed powder; The drying temperature is 60-100°C and the drying time is 10-20h; 8) Pressing and sintering the silver-graphite mixed powder to obtain the silver-graphite brush material.

[0012] Step 8) The pressing method is isostatic pressing, the pressing pressure is 200-600 MPa, and the holding time is 60-120 s; The sintering is carried out in a protective atmosphere, which is hydrogen, argon or nitrogen; the sintering temperature is 600-900° C., and the sintering time is 1-4 hours.

[0013] The silver-graphite brush material of the present invention has the following advantages: The use of wet mixing and decomposition technology of silver nitrate and graphite can reduce the segregation problem of silver, and the silver particles can be evenly distributed in the brush material; the addition of phenolic resin can solve the problem of non-wetting between silver and graphite, improve the interface strength, and prevent the shedding of graphite particles.

[0014] Compared with the prior art, the preparation method of the silver-graphite brush of the present invention has the following advantages: the method adopted by the present invention is simple to operate, has a short preparation cycle, can realize automated continuous and stable large-scale production, and has low production cost.

[0015] The experimental results of the applicant show that the brush material obtained by the method of the present invention has a volume density of 3.72 to 4.67 (g / cm 3 ); resistivity 0.71~0.95 (μΩ·m); friction coefficient ≤0.15; flexural strength 33.2~36.8 (MPa); hardness 13.4~14.7 (HV0.2).

[0016] The material of the present invention has good electrical conductivity and wear resistance due to the uniform distribution of silver and the improvement of the interface strength with graphite, can be widely used in electrical contact fields such as aerospace, precision instruments, etc., and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional SEM image of the silver-graphite brush product prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The purity of the silver nitrate used is greater than 99.9%; The phenolic resin used is required to be high temperature resistant and have a carbon residue rate of ≥50% at 550°C. In this embodiment, boron-modified thermosetting phenolic resin (commercial) is used. The MoS2 used was 2500 mesh powder with a purity of >99% (commercial).

[0019] The reagents used in this example were all of commercial analytical grade. Example 1

[0020] 1) Take 150g of silver nitrate powder and dissolve it in 150ml of deionized water to obtain a silver nitrate aqueous solution.

[0021] 2) Pour 40 g of 300-mesh graphite powder into the silver nitrate aqueous solution in 1) and stir for 0.5 h to obtain silver nitrate-graphite slurry.

[0022] 3) The silver nitrate graphite slurry obtained in step 2) is kept in an oven at 90° C. for 10 hours to remove moisture, thereby obtaining a silver nitrate graphite mixture.

[0023] 4) The silver nitrate-graphite mixture of 3) is decomposed in a high temperature furnace under a hydrogen protective atmosphere at a furnace temperature of 750° C. for a holding time of 3 h to obtain a silver-graphite mixture.

[0024] 5) Take 10 g of phenolic resin and dissolve it in 80 ml of ethanol to obtain a phenolic resin solution.

[0025] 6) Take the silver-graphite mixture obtained in step 4) and 4 g of molybdenum disulfide, add them to the phenolic resin solution in step 5), stir them thoroughly, pour them into a kneader and knead them for 2 hours to obtain a silver-graphite colloid.

[0026] 7) The silver-graphite colloid obtained in 6) is kept in an oven at 80° C. for 12 h to remove the ethanol solvent, and then crushed in a crusher and passed through a 150-mesh sieve to obtain resin-coated silver-graphite powder.

[0027] 8) The resin-coated silver graphite powder obtained in 7) is loaded into a prefabricated mold sleeve, and the silver graphite blank is obtained by isostatic pressing at 200 MPa for 90 seconds; the temperature is then increased to 850°C at 5°C / min in a hydrogen reduction furnace and maintained for 4 hours to obtain a silver graphite brush.

[0028] Figure 1 This is a cross-sectional SEM image of the silver-graphite brush product prepared in this example.

[0029] Example 2: 1) Take 200g of silver nitrate powder and dissolve it in 200ml of deionized water to obtain a silver nitrate aqueous solution.

[0030] 2) Pour 38 g of 300-mesh graphite powder into the silver nitrate aqueous solution in 1) and stir for 0.5 h to obtain silver nitrate graphite slurry.

[0031] 3) The silver nitrate graphite slurry obtained in step 2) is kept in an oven at 100° C. for 10 hours to remove moisture, thereby obtaining a silver nitrate graphite mixture.

[0032] 4) The silver nitrate-graphite mixture obtained in step 3) is decomposed in a high-temperature furnace under a hydrogen protective atmosphere at a furnace temperature of 750° C. for a holding time of 3 h to obtain a silver-graphite mixture.

[0033] 5) Take 9 g of phenolic resin and dissolve it in 75 ml of ethanol to obtain a phenolic resin solution.

[0034] 6) Take the silver-graphite mixture obtained in step 4) and 5 g of molybdenum disulfide, add them to the phenolic resin solution in step 5), stir them thoroughly, pour them into a kneader and knead them for 2 hours to obtain a silver-graphite colloid.

[0035] 7) The silver-graphite colloid obtained in 6) is kept in an oven at 80° C. for 12 h to remove the ethanol solvent, and then crushed in a crusher and passed through a 150-mesh sieve to obtain resin-coated silver-graphite powder.

[0036] 8) The powder obtained in 7) is loaded into a prefabricated mold sleeve, and the silver-graphite blank is obtained by isostatic pressing at 220 MPa for 90 seconds; then the temperature is increased to 850°C at 5°C / min in a hydrogen reduction furnace and kept at this temperature for 4 hours to obtain a silver-graphite brush.

[0037] Example 3: 1) Take 220 g of silver nitrate powder and dissolve it in 220 ml of deionized water to obtain a silver nitrate aqueous solution.

[0038] 2) Pour 36 g of 300-mesh graphite powder into the silver nitrate aqueous solution in 1) and stir for 0.5 h to obtain silver nitrate-graphite slurry.

[0039] 3) The silver nitrate graphite slurry of 2) is kept in an oven at 100° C. for 12 hours to remove moisture and obtain a silver nitrate graphite mixture.

[0040] 4) The silver nitrate-graphite mixture of 3) is decomposed in a high temperature furnace under a hydrogen protective atmosphere at a furnace temperature of 750° C. for a holding time of 3 h to obtain a silver-graphite mixture.

[0041] 5) Take 8 g of phenolic resin and dissolve it in 70 ml of ethanol to obtain a phenolic resin solution.

[0042] 6) Take the silver-graphite mixture obtained in 4) and 6 g of molybdenum disulfide, add them to the phenolic resin solution in 5), stir them thoroughly, pour them into a kneader and knead them for 2 hours to obtain a silver-graphite colloid.

[0043] 7) The silver-graphite colloid obtained in 6) is kept in an oven at 80° C. for 12 h to remove the ethanol solvent, and then crushed in a crusher and passed through a 150-mesh sieve to obtain resin-coated silver-graphite powder.

[0044] 8) The powder obtained in 7) is loaded into a prefabricated mold sleeve, and the silver-graphite blank is obtained by isostatic pressing at 250 MPa for 90 seconds; then the temperature is raised to 850°C at 5°C / min in a hydrogen reduction furnace and maintained for 4 hours to obtain a silver-graphite brush.

[0045] The performance of the silver-graphite brushes prepared in Example 1, Example 2, and Example 3 was tested, and the test results are shown in the following table;

[0046] pass Figure 1 It can be seen that the silver in Example 1 is evenly distributed in the matrix without obvious segregation. The flexural strength of the silver-graphite brushes in the three examples tested in Table 1 is greater than 30 MPa, and has a high interface strength. The friction coefficient is less than 0.15. The comprehensive performance is excellent, the preparation cycle is short, and the cost is low, which can meet the requirements of mass production.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A silver graphite brush material, characterized in that: The material comprises graphite powder, thermosetting resin, additives and silver, and the mass percentage of each substance in the material is: 10-60% of graphite powder, 2-20% of thermosetting resin, 1-8% of additives, and silver is the balance.

2. The material according to claim 1, characterized in that: The mass percentages of the various materials are as follows: 10-40% of graphite powder; 3-10% of thermosetting resin; 1-5% of the additives, and the balance being silver.

3. The material according to claim 1 or 2, characterized in that: The additive is one or more of molybdenum disulfide, boron nitride, carbon nanotubes and carbon fibers.

4. The material according to claim 1 or 2, characterized in that: The thermosetting resin is a phenolic resin; Preferably, the phenolic resin is a high temperature resistant phenolic resin with a carbon residue rate of ≥50% at 550°C.

5. The material preparation method according to claim 1 or 2, characterized in that: The graphite powder is natural flake graphite powder with a mesh size of 100 to 800.

6. The method for preparing the silver-graphite brush material according to any one of claims 1 to 5, characterized in that: Take each component according to the above ratio, and specifically follow the following steps: 1) completely dissolving silver nitrate in deionized water to obtain a silver nitrate aqueous solution; 2) adding graphite powder into silver nitrate aqueous solution and stirring to obtain silver nitrate graphite slurry; 3) drying the silver nitrate graphite slurry in an oven to obtain a silver nitrate graphite mixture; 4) decomposing the silver nitrate-graphite mixture under vacuum or protective atmosphere to obtain a silver-graphite mixture; The decomposition temperature is 600-800°C and the time is 2-6h; 5) Add the thermosetting resin into ethanol and stir to obtain a resin solution; 6) Add the silver-graphite mixture and additives to the resin solution, stir thoroughly, and knead for 2 to 3 hours to obtain a silver-graphite colloid; 7) Drying, crushing and sieving the silver-graphite colloid to 100-300 meshes to obtain silver-graphite mixed powder; 8) Pressing and sintering the silver-graphite mixed powder to obtain the silver-graphite brush material.

7. The preparation method according to claim 6, characterized in that: Step 3) The drying temperature is 80-150° C. and the drying time is 5-12 hours.

8. The preparation method according to claim 6, characterized in that: Step 4) The protective atmosphere is hydrogen, argon or nitrogen.

9. The preparation method according to claim 6, characterized in that: Step 7) The drying temperature is 60-100° C. and the drying time is 10-20 hours.

10. The preparation method according to claim 6, characterized in that: Step 8) The pressing method is isostatic pressing, the pressing pressure is 200-600 MPa, and the holding time is 60-120 s; The sintering is carried out in a protective atmosphere, which is hydrogen, argon or nitrogen; the sintering temperature is 600-900° C., and the sintering time is 1-4 hours.

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