High-strength high-conductivity silver tungsten carbide nickel graphite electric contact material and preparation method thereof

Abstract

The application belongs to the field of electric contact material preparation, and particularly relates to a high-strength and high-conductivity silver tungsten carbide nickel graphite electric contact material and a preparation method thereof. The method comprises the following steps: S1, pre-sintering nickel-coated graphite powder by using a reducing gas or inert gas protection, and then screening; S2, mixing the screened nickel-coated graphite powder with silver powder and tungsten carbide powder; S3, adopting a wet granulation method on the mixed powder, and then performing initial pressure forming, pre-sintering and infiltration to obtain the silver tungsten carbide nickel graphite electric contact material with high strength and high conductivity. Compared with the traditional silver tungsten carbide graphite material, the application solves the problem that the graphite-containing material cannot be infiltrated with silver, adopts an infiltration process to make the material have higher strength and better electrical conductivity, and the addition of graphite powder also ensures that the material has good anti-melting welding performance.

Description

Technical Field

[0001] This invention belongs to the field of electrical contact material preparation, specifically relating to a high-strength, high-conductivity silver tungsten carbide nickel graphite electrical contact material and its preparation method. Background Technology

[0002] The main function of a circuit breaker is to connect and disconnect load circuits, as well as to cut off faulty circuits, ensuring safe operation. It is a very important protective electrical appliance in low-voltage distribution networks. As is well known, the "heart" of a circuit breaker is its electrical contacts, which must be able to interrupt extremely high short-circuit currents while also being able to connect and disconnect rated currents infrequently. To meet the requirements of circuit breakers, they are generally composed of paired moving and stationary contacts. The moving contacts need to have strong resistance to arc erosion and are usually made of AgW or AgWC materials produced by powder metallurgy infiltration. The stationary contacts need to have good resistance to welding and a certain degree of resistance to arc erosion, and are usually made of AgWCC materials produced by powder metallurgy sintering or AgC materials produced by extrusion. These materials are mostly used in AC circuit breakers. With the rapid development of new energy industries such as wind power generation and electric vehicles, the demand for high-voltage DC circuit breakers is increasing. Because DC power does not have the periodic "zero crossing" characteristic of AC power, its arc is more difficult to extinguish, thus requiring a high level of resistance to arc erosion for the stationary contacts. When the AgWCC or AgC materials commonly used in AC circuit breakers are applied to DC circuit breakers, although their resistance to welding meets the requirements, their resistance to arc erosion is poor, and their electrical life often fails to meet the requirements.

[0003] In summary, the existing preparation methods for AgWCC materials have the following problems: 1. During the connection and disconnection of rated current in high-voltage DC circuit breakers, the arc is more difficult to extinguish, resulting in insufficient resistance to arc erosion of the static contacts made of AgWCC materials, thus causing insufficient electrical life; 2. Due to the poor wettability of graphite and liquid silver, AgWCC materials cannot be produced using the melt infiltration process. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a high-strength, high-conductivity silver tungsten carbide nickel graphite electrical contact material and its preparation method.

[0005] The technical solution adopted in this invention is as follows: A method for preparing a high-strength, high-conductivity silver tungsten carbide nickel-graphite electrical contact material, comprising the following steps:

[0006] S1, nickel-coated graphite powder is pre-sintered under the protection of reducing gas or inert gas, and then sieved;

[0007] S2, mix the sieved nickel-coated graphite powder with silver powder and tungsten carbide powder together;

[0008] S3 uses wet granulation of the mixed powder, followed by initial pressing, pre-firing, and melt infiltration to obtain a silver tungsten carbide nickel graphite electrical contact material with high strength and high conductivity.

[0009] Preferably, in step S1, the nickel-coated graphite powder used is nickel-coated graphite powder with a particle size of less than 200 mesh obtained by chemical coating process, wherein the mass percentage of nickel is 50%-90%.

[0010] Preferably, in step S1, the pre-sintering temperature is 200℃-600℃ and the time is 1h-6h.

[0011] Preferably, in step S1, the sieving is performed by passing the powder through a 150-250 mesh sieve, and the powder passing through the sieve is collected.

[0012] Preferably, in step S2, the mixing involves mechanically mixing the sieved nickel-coated graphite powder, tungsten carbide powder, and silver powder together for 2-6 hours.

[0013] Preferably, in step S3, the pre-burning is carried out under the protection of hydrogen or ammonia decomposition gas, at a temperature of 400℃-950℃, for a time of 1h-4h.

[0014] Preferably, in step S3, the melting and infiltration is carried out under the protection of hydrogen or ammonia decomposition gas, at a temperature of 1000℃-1300℃ for 1h-4h, and the melting and infiltration sheet is a silver sheet or a fine-grained silver sheet, wherein the nickel content in the fine-grained silver sheet is 0-0.3%.

[0015] A silver-tungsten-nickel-carbide graphite electrical contact material, which is obtained by the preparation method described above.

[0016] Preferably, the above-mentioned silver tungsten carbide nickel graphite electrical contact material includes,

[0017] Ag 50-75 parts by weight;

[0018] WC 25-50 parts by weight;

[0019] Ni 1-15 parts by weight;

[0020] C 0.4-3 parts by weight.

[0021] The beneficial effects of this invention are as follows: Compared with the prior art, the preparation method of this invention uses nickel-coated graphite powder, which is pre-sintered and strengthened. During the melting and infiltration process, silver does not come into contact with graphite, thus solving the problem that graphite-containing materials cannot be melted and infiltrated with silver. The operation is simple and suitable for mass production. The produced silver-tungsten carbide-nickel-graphite electrical contact material has the high strength, high conductivity, and high resistance to arc erosion of the melting and infiltration process, as well as the good resistance to welding of the sintering process. Whether used in low-voltage AC circuit breakers or high-voltage DC circuit breakers, its electrical life is significantly improved. Compared with the traditional mixed powder sintering method of silver-tungsten carbide-graphite electrical contact material, the electrical life is increased by more than 100%. The melting and infiltration process gives the material higher strength and better conductivity. At the same time, the addition of graphite powder also ensures that the material has good resistance to welding, which can meet the requirements of high-voltage DC circuit breakers for stationary contacts. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0023] Figure 1 This is a flowchart of the preparation process of the present invention;

[0024] Figure 2 The metallographic structure of the silver tungsten carbide nickel graphite electrical contact material in one embodiment of the present invention is shown. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] Example 1

[0027] 1. First, nickel-coated graphite powder (75wt% nickel content, -200 mesh) is placed in a hydrogen-protected sintering furnace for pre-sintering at 400℃ for 2 hours.

[0028] 2. Pass the pre-sintered nickel-coated graphite powder through a 200-mesh sieve and collect the powder passing through the sieve;

[0029] 3. The sieved nickel-coated graphite powder, tungsten carbide powder (average particle size 1μm), and silver powder (average particle size 3μm) are mixed in a weight ratio of 1:8:11, and then mixed in a powder mixer for 4 hours to prepare a silver-tungsten carbide-nickel-graphite mixed powder.

[0030] 4. Uniformly incorporate propylene colloid into the mixed powder, using butanol as the solvent, at a ratio of powder (kg): propylene (g): butanol (ml) = 1:2:100;

[0031] 5. The powder after adding adhesive is dried and granulated at 100℃ for 10 hours, and then granulated through a 60-mesh sieve.

[0032] 6. The granulated powder is initially pressed into shape, with a compact size of 12mm x 12mm x 2mm and a single weight of 2.52g;

[0033] 7. Pre-sinter the pressed blank to remove the colloid. The pre-sintering temperature is 600℃ and the time is 1 hour, with ammonia decomposition gas protection.

[0034] 8. Arrange the degummed compact and fine-grained silver sheets together in the furnace for melting and infiltration. The weight of the fine-grained silver sheets is 0.63g. The melting and infiltration temperature is 1100℃ and the time is 2 hours. Ammonia decomposition gas protection is used.

[0035] 9. The product after melt infiltration is cleaned to obtain high-strength and high-conductivity AgWC32Ni3C1 electrical contact material;

[0036] 10. The high-strength and high-conductivity AgWC32Ni3C1 electrical contact material obtained, compared with the same material obtained by the powder mixing and sintering process, has increased flexural strength from 300 MPa to 450 MPa, conductivity from 44% to 54%, electrical life by 150%, and temperature rise by 5%.

[0037] Example 2

[0038] 1. First, place the nickel-coated graphite powder (75wt% nickel content, -200 mesh) into a hydrogen-protected sintering furnace.

[0039] Pre-sintering was carried out at 400℃ for 2 hours.

[0040] 2. Pass the pre-sintered nickel-coated graphite powder through a 200-mesh sieve and collect the powder passing through the sieve;

[0041] 3. The sieved nickel-coated graphite powder, tungsten carbide powder (average particle size 1μm), and silver powder (average particle size 3μm) are mixed in a weight ratio of 3:13:24, and then mixed in a powder mixer for 4 hours to prepare a silver-tungsten carbide-nickel-graphite mixed powder.

[0042] 4. Uniformly incorporate propylene colloid into the mixed powder, using butanol as the solvent, at a ratio of powder (kg): propylene (g): butanol (ml) = 1:2:100;

[0043] 5. The powder after adding adhesive is dried and granulated at 100℃ for 10 hours, and then granulated through a 60-mesh sieve.

[0044] 6. The granulated powder is initially pressed into shape, with a compact size of 12mm x 12mm x 2mm and a single weight of 2.4g;

[0045] 7. Pre-sinter the pressed blank to remove the colloid. The pre-sintering temperature is 880℃ and the time is 1 hour, with ammonia decomposition gas protection.

[0046] 8. Arrange the degummed compact and fine-grained silver sheets together in the furnace for melting and infiltration. The weight of the fine-grained silver sheets is 0.6g. The melting and infiltration temperature is 1100℃ and the time is 2 hours. Ammonia decomposition gas protection is used.

[0047] 9. The product after melt infiltration is cleaned to obtain high-strength and high-conductivity AgWC26Ni4.5C1.5 electrical contact material;

[0048] 10. The obtained high-strength and high-conductivity AgWC26Ni4.5C1.5 electrical contact material, compared with the same material obtained by the powder mixing and sintering process, has increased flexural strength from 280 MPa to 420 MPa, conductivity from 45% to 55%, electrical life by 150%, and temperature rise by 5%.

[0049] Example 3

[0050] 1. First, place the nickel-coated graphite powder (50wt% nickel content, -200 mesh) into a hydrogen-protected sintering furnace.

[0051] Pre-sintering was carried out at a temperature of 500℃ for 2 hours.

[0052] 2. Pass the pre-sintered nickel-coated graphite powder through a 200-mesh sieve and collect the powder passing through the sieve;

[0053] 3. The sieved nickel-coated graphite powder, tungsten carbide powder (average particle size 3μm), nickel powder (average particle size 5μm), and silver powder (average particle size 5μm) are mixed in a weight ratio of 2:16:1:15, and then mixed in a powder mixer for 4 hours to prepare a silver-tungsten carbide-nickel-graphite mixed powder.

[0054] 4. Uniformly incorporate propylene colloid into the mixed powder, using butanol as the solvent, at a ratio of powder (kg): propylene (g): butanol (ml) = 1:2:100;

[0055] 5. The powder after adding adhesive is dried and granulated at 100℃ for 10 hours, and then granulated through a 60-mesh sieve.

[0056] 6. The granulated powder is initially pressed into shape, with a compact size of 12mm x 12mm x 2mm and a single weight of 2.42g;

[0057] 7. Pre-sinter the pressed blank to remove the colloid. The pre-sintering temperature is 880℃ and the time is 1 hour, with ammonia decomposition gas protection.

[0058] 8. Arrange the degummed compact and fine-grained silver sheets together in the furnace for melting and infiltration. The weight of the fine-grained silver sheets is 0.59g. The melting and infiltration temperature is 1200℃ and the time is 2 hours. Ammonia decomposition gas protection is used.

[0059] 9. The product after melt infiltration is cleaned to obtain high-strength and high-conductivity AgWC38Ni5C2.5 electrical contact material;

[0060] 10. The high-strength and high-conductivity AgWC38Ni5C2.5 electrical contact material obtained, compared with the same material obtained by the powder mixing and sintering process, has increased flexural strength from 250 MPa to 400 MPa, conductivity from 36% to 49%, electrical life by 120%, and temperature rise by 8%.

[0061] Example 4

[0062] 1. First, place the nickel-coated graphite powder (90wt% nickel content, -200 mesh) into a hydrogen-protected sintering furnace.

[0063] Pre-sintering was carried out at 200℃ for 2 hours.

[0064] 2. Pass the pre-sintered nickel-coated graphite powder through a 200-mesh sieve and collect the powder passing through the sieve;

[0065] 3. The sieved nickel-coated graphite powder, tungsten carbide powder (average particle size 1μm), and silver powder (average particle size 5μm) are mixed in a weight ratio of 1:9:10, and then mixed in a powder mixer for 4 hours to prepare a silver-tungsten carbide-nickel-graphite mixed powder.

[0066] 4. Uniformly incorporate propylene colloid into the mixed powder, using butanol as the solvent, at a ratio of powder (kg): propylene (g): butanol (ml) = 1:2:100;

[0067] 5. The powder after adding adhesive is dried and granulated at 100℃ for 10 hours, and then granulated through a 60-mesh sieve.

[0068] 6. The granulated powder is initially pressed into shape, with a compact size of 12mm x 12mm x 2mm and a single weight of 2.62g;

[0069] 7. Pre-sinter the pressed blank to remove the colloid. The pre-sintering temperature is 920℃ and the time is 1 hour, with ammonia decomposition gas protection.

[0070] 8. Arrange the degummed compact and fine-grained silver sheets together in the furnace for melting and infiltration. The weight of the fine-grained silver sheets is 0.65g, the melting and infiltration temperature is 1050℃, the time is 2 hours, and ammonia decomposition gas is used for protection.

[0071] 9. The product after melt infiltration is cleaned to obtain high-strength and high-conductivity AgWC36Ni3.6C0.4 electrical contact material;

[0072] The obtained high-strength, high-conductivity AgWC36Ni3.6C0.4 electrical contact material, compared with the same material obtained by the mixed powder sintering process, showed an increase in flexural strength from 350 MPa to 600 MPa, an increase in conductivity from 43% to 58%, an increase in electrical life of 180%, and a decrease in temperature rise of 8%.

[0073] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a high-strength, high-conductivity silver-tungsten-nickel-carbide graphite electrical contact material, characterized in that, Includes the following steps: S1, nickel-coated graphite powder is pre-sintered under the protection of reducing gas or inert gas, and then sieved; S2, mix the sieved nickel-coated graphite powder with silver powder and tungsten carbide powder together; S3, the mixed powder is granulated by wet process, and then subjected to initial pressing, pre-firing and melt infiltration to obtain a silver tungsten carbide nickel graphite electrical contact material with high strength and high conductivity; In step S1, the nickel-coated graphite powder used is nickel-coated graphite powder with a particle size of less than 200 mesh obtained by chemical coating process, wherein the mass percentage of nickel is 50%-90%; In step S1, the pre-sintering temperature is 200℃-600℃, and the time is 1h-6h; The high-strength, high-conductivity silver-tungsten-nickel-carbide graphite electrical contact material includes, Ag 50-75 parts by weight; WC 25-50 parts by weight; Ni 1-15 parts by weight; C 0.4-3 parts by weight.

2. The method for preparing the silver-tungsten-carbide-nickel-graphite electrical contact material as described in claim 1, characterized in that: In step S1, the powder is sieved through a 150-250 mesh sieve and the sieved powder is collected.

3. The method for preparing the silver-tungsten-carbide-nickel-graphite electrical contact material as described in claim 1, characterized in that: In step S2, mixing involves mechanically mixing the sieved nickel-coated graphite powder, tungsten carbide powder, and silver powder together for 2-6 hours.

4. The method for preparing the silver-tungsten-carbide-nickel-graphite electrical contact material as described in claim 1, characterized in that: In step S3, pre-firing is carried out under the protection of hydrogen or ammonia decomposition gas at a temperature of 400℃-950℃ for 1-4 hours.

5. The method for preparing the silver-tungsten-carbide-nickel-graphite electrical contact material as described in claim 1, characterized in that: In step S3, melting and infiltration are carried out under the protection of hydrogen or ammonia decomposition gas, at a temperature of 1000℃-1300℃ for 1h-4h, and the melting and infiltration sheet is a silver sheet or a fine-grained silver sheet, wherein the nickel content in the fine-grained silver sheet is 0-0.3%.

6. A silver tungsten carbide nickel graphite electrical contact material, which is obtained by the preparation method described in any one of claims 1-5.

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