A silver-graphite brush material and its preparation method

Abstract

This invention relates to a silver-graphite brush material and its preparation method. The material comprises graphite powder, thermosetting resin, additives, and silver, with the following mass percentages: 10-60% graphite powder; 2-20% thermosetting resin; 1-8% additives; and silver as the balance. This invention solves the problems of severe segregation, low interfacial strength, high preparation cost, and long production cycle in current silver-graphite brushes. The material prepared using the method described in this invention can reduce silver segregation, improve interfacial strength, and exhibit excellent comprehensive performance. Furthermore, this method is simple and easy to operate, enabling large-scale mass production.

Description

Technical Field

[0001] This invention relates to the field of brush materials, and particularly to a silver-graphite brush and its preparation method. Background Technology

[0002] Silver-graphite brushes are widely used in electrical contact fields such as aerospace and precision instruments due to their excellent conductivity, wear resistance, and resistance to welding. Currently, the main manufacturing method is mixing, pressing, and sintering. However, this process cannot overcome component segregation, and the interfacial strength between graphite and silver is very low (flexural strength < 20 MPa), severely affecting the performance of silver-graphite brush materials.

[0003] US Patent No. 4534887 discloses a method for preparing silver-graphite brush material. The method involves first mixing silver nitrate with graphite powder and then decomposing it at high temperature to prepare a silver-graphite mixed powder. This powder is then mixed with an asphalt solution, pressed, and calcined to prepare the silver-graphite brush material. This technology requires a calcination process of up to half a month at 1000–1200°C under inert gas protection to meet the requirements for use.

[0004] Patent CN110467480A discloses a silver-impregnated graphite contact material and its preparation method. The method involves preparing a graphite matrix through high-temperature calcination and graphitization, followed by thermal impregnation with metallic silver to produce the silver-impregnated graphite contact material. However, this technology also suffers from drawbacks such as a long preparation cycle and complex processes. Summary of the Invention

[0005] The purpose of this invention is to provide a silver-graphite electric brush and its preparation method, to solve the problems of severe segregation, low interface strength, high preparation cost, and long cycle time in current silver-graphite electric brushes. The material prepared using the method described in this invention can reduce silver segregation, improve interface strength, and has excellent comprehensive performance. Furthermore, this method is simple and easy to operate, enabling large-scale mass production.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] The silver-graphite brush material comprises graphite powder, thermosetting resin, additives, and silver. The mass percentage of each substance in the material is as follows: 10-60% graphite powder; 2-20% thermosetting resin; 1-8% additives; and silver as the balance.

[0008] A preferred technical solution is that the mass percentage of each material is: 10-40% graphite powder; 3-10% thermosetting resin; the additive is 1-5%, and silver is the balance.

[0009] The additive is one or more of molybdenum disulfide, boron nitride, carbon nanotubes, and carbon fibers.

[0010] 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℃.

[0011] The graphite powder is natural flake graphite powder with a mesh size of 100-800.

[0012] The preparation method of the above-mentioned silver-graphite brush material, which involves taking each component according to the above proportions, specifically includes the following steps:

[0013] 1) Dissolve silver nitrate completely in deionized water to obtain an aqueous solution of silver nitrate;

[0014] 2) Add graphite powder to silver nitrate aqueous solution and stir to obtain silver nitrate graphite slurry;

[0015] 3) Dry the silver nitrate graphite slurry in an oven at a temperature of 80-150°C for 5-12 hours to obtain a silver nitrate graphite mixture.

[0016] 4) Decompose the silver nitrate graphite mixture under vacuum or a protective atmosphere, wherein the protective atmosphere is hydrogen, argon or nitrogen, the decomposition temperature is 600-800℃ and the time is 2-6h, to obtain a silver graphite mixture.

[0017] 5) Add the thermosetting resin to ethanol and stir to obtain a resin solution;

[0018] 6) Add the silver-graphite mixture and additives to the resin solution, stir thoroughly, and knead for 2-3 hours to obtain silver-graphite colloid;

[0019] 7) Dry the silver-graphite colloid, crush it, and sieve it through a 100-300 mesh sieve to obtain a silver-graphite mixed powder;

[0020] The drying temperature is 60–100℃, and the drying time is 10–20 hours.

[0021] 8) Press and sinter the silver-graphite mixed powder to obtain silver-graphite brush material.

[0022] Step 8) The pressing method is isostatic pressing, the pressing pressure is 200-600 MPa, and the holding time is 60-120 s;

[0023] The sintering is carried out in a protective atmosphere, which is hydrogen, argon or nitrogen; the sintering temperature is 600-900℃ and the sintering time is 1-4h.

[0024] The silver-graphite brush material of this invention has the following advantages:

[0025] The wet mixing-decomposition technology of silver nitrate and graphite can reduce the problem of silver segregation and ensure that silver particles are 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 graphite particles from falling off.

[0026] 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.

[0027] The applicant's experimental results show that the brush material obtained by the method described in this invention has a bulk density of 3.72–4.67 g / cm³. 3 ); resistivity 0.71~0.95 (μΩ·m); coefficient of friction ≤0.15; flexural strength 33.2~36.8 (MPa); hardness 13.4~14.7 (HV0.2).

[0028] The material described in this invention, due to the uniform distribution of silver and the improved interfacial strength with graphite, has good electrical conductivity and wear resistance, and can be widely used in electrical contact fields such as aerospace and precision instruments, with broad application prospects. Attached Figure Description

[0029] Figure 1 This is a cross-sectional SEM image of the silver-graphite electric brush product prepared in Example 1 of the present invention. Detailed Implementation

[0030] The silver nitrate used has a purity greater than 99.9%;

[0031] The phenolic resin used must have high temperature resistance and a carbon residue rate of ≥50% at 550℃. In this embodiment, boron-modified thermosetting phenolic resin (commercial) is used.

[0032] The MoS2 used is 2500 mesh powder with a purity >99% (commercial).

[0033] All reagents used in this embodiment are commercially available analytical grade reagents.

[0034] Example 1

[0035] 1) Take 150g of silver nitrate powder and dissolve it in 150ml of deionized water to obtain a silver nitrate aqueous solution.

[0036] 2) Take 40g of 300-mesh graphite powder and pour it into the silver nitrate aqueous solution in 1), stir for 0.5h to obtain silver nitrate graphite slurry.

[0037] 3) The silver nitrate graphite slurry obtained in step 2) is kept at 90°C in an oven for 10 hours to remove moisture, and a silver nitrate graphite mixture is obtained.

[0038] 4) The silver nitrate graphite mixture from 3) was decomposed in a high-temperature furnace under a hydrogen protective atmosphere at a furnace temperature of 750°C for 3 hours to obtain a silver graphite mixture.

[0039] 5) Dissolve 10g of phenolic resin in 80ml of ethanol to obtain a phenolic resin solution.

[0040] 6) Take the silver-graphite mixture obtained in step 4) and 4g of molybdenum disulfide, add them to the phenolic resin solution in step 5), stir thoroughly, pour into a kneader and knead for 2 hours to obtain silver-graphite colloid.

[0041] 7) The silver graphite colloid obtained in 6) is kept at 80°C for 12 hours in an oven 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.

[0042] 8) The resin-coated silver graphite powder obtained in 7) is loaded into a pre-made mold and pressed in an isostatic press at 200 MPa for 90 s to obtain a silver graphite blank; then it is heated to 850℃ at 5℃ / min and held for 4 h in a hydrogen reduction furnace to obtain a silver graphite brush.

[0043] Figure 1 This is a cross-sectional SEM image of the silver-graphite brush product prepared in this example.

[0044] Example 2:

[0045] 1) Take 200g of silver nitrate powder and dissolve it in 200ml of deionized water to obtain a silver nitrate aqueous solution.

[0046] 2) Take 38g of 300-mesh graphite powder and pour it into the silver nitrate aqueous solution in 1), stir for 0.5h to obtain silver nitrate graphite slurry.

[0047] 3) The silver nitrate graphite slurry obtained in step 2) is kept at 100°C for 10 hours in an oven to remove moisture, and a silver nitrate graphite mixture is obtained.

[0048] 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 3 hours to obtain a silver graphite mixture.

[0049] 5) Dissolve 9g of phenolic resin in 75ml of ethanol to obtain a phenolic resin solution.

[0050] 6) Take the silver-graphite mixture obtained in step 4) and 5g of molybdenum disulfide, add them to the phenolic resin solution in step 5), stir thoroughly, pour into a kneader and knead for 2 hours to obtain silver-graphite colloid.

[0051] 7) The silver graphite colloid obtained in 6) is kept at 80°C in an oven for 12 hours 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.

[0052] 8) The powder obtained in 7) is loaded into a pre-made mold and pressed in an isostatic press at 220 MPa for 90 s to obtain a silver graphite blank; then it is heated to 850℃ in a hydrogen reduction furnace at 5℃ / min and held for 4 h to obtain a silver graphite brush.

[0053] Example 3:

[0054] 1) Take 220g of silver nitrate powder and dissolve it in 220ml of deionized water to obtain a silver nitrate aqueous solution.

[0055] 2) Take 36g of 300-mesh graphite powder and pour it into the silver nitrate aqueous solution in 1), stir for 0.5h to obtain silver nitrate graphite slurry.

[0056] 3) The silver nitrate graphite slurry from 2) was kept at 100°C for 12 hours in an oven to remove moisture, thus obtaining a silver nitrate graphite mixture.

[0057] 4) The silver nitrate graphite mixture from 3) was decomposed in a high-temperature furnace under a hydrogen protective atmosphere at a furnace temperature of 750°C for 3 hours to obtain a silver graphite mixture.

[0058] 5) Dissolve 8g of phenolic resin in 70ml of ethanol to obtain a phenolic resin solution.

[0059] 6) Take the silver-graphite mixture obtained in 4) and 6g of molybdenum disulfide, add them to the phenolic resin solution in 5), stir thoroughly, pour into a kneader and knead for 2 hours to obtain silver-graphite colloid.

[0060] 7) The silver graphite colloid obtained in 6) is kept at 80°C in an oven for 12 hours 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.

[0061] 8) The powder obtained in 7) is loaded into a pre-made mold and pressed in an isostatic press at 250 MPa for 90 s to obtain a silver graphite blank; then it is heated to 850℃ at 5℃ / min and held for 4 h in a hydrogen reduction furnace to obtain a silver graphite brush.

[0062] The silver-graphite electric brushes prepared in Examples 1, 2, and 3 were subjected to performance tests, and the test results are shown in the table below.

[0063]

[0064] pass Figure 1It can be seen that the silver in Example 1 is uniformly distributed in the matrix without obvious segregation. Table 1 shows that the flexural strength of the silver-graphite brushes in the three examples is greater than 30 MPa, indicating high interfacial strength. The coefficient of friction is less than 0.15. The brushes have excellent comprehensive performance, short preparation cycle, and low cost, which can meet the requirements of mass production.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications 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, molybdenum disulfide and silver, and the mass percentage of each material is as follows: 10-60% of graphite powder, 2-20% of thermosetting resin, 1-8% of molybdenum disulfide, and the rest is silver; The thermosetting resin is a high-temperature-resistant boron-modified thermosetting phenolic resin with a carbon residue rate of ≥50% at 550℃; the molybdenum disulfide is a powder with a mesh of 2500 and a purity of >99%; The graphite powder is natural flake graphite powder with a mesh of 100-800.

2. The material of claim 1, wherein: The mass percentage of each material is as follows: 10-40% of graphite powder, 3-10% of thermosetting resin, 1-5% of molybdenum disulfide, and the rest is silver.

3. A method of producing the silver graphite brush material according to any one of claims 1 to 2, characterized in that, The components are taken according to the above proportions, and the specific steps are as follows: 1) Dissolve silver nitrate completely in deionized water to obtain a silver nitrate aqueous solution; 2) Add graphite powder to the silver nitrate aqueous solution and stir to obtain a silver nitrate graphite slurry; 3) Dry the silver nitrate graphite slurry in an oven to obtain a silver nitrate graphite mixture; 4) Decompose the silver nitrate graphite mixture under vacuum or in a protective atmosphere to obtain a silver graphite mixture; The decomposition temperature is 600-800℃, and the time is 2-6h; 5) Add thermosetting resin to ethanol and stir to obtain a resin solution; 6) Add the silver graphite mixture and molybdenum disulfide to the resin solution, stir thoroughly, and knead for 2-3h to obtain a silver graphite colloid; 7) Dry the silver graphite colloid, crush it, and sieve it to 100-300 mesh to obtain a silver graphite mixed powder; 8) Press and sinter the silver graphite mixed powder to obtain a silver graphite brush material, wherein the pressing method is isostatic pressing, the pressing pressure is 200-600MPa, and the pressure holding time is 60-120s; The sintering is carried out in a protective atmosphere, and the protective atmosphere is hydrogen, argon or nitrogen; the sintering temperature is 600-900℃, and the sintering time is 1-4h.

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