High-strength silver-tungsten carbide-graphite contact material and preparation method therefor

Abstract

A high-strength silver-tungsten carbide-graphite contact material and a preparation method therefor. In the preparation method, the additives of cobalt and nickel are refined and atomized to prepare an alloy powder, and the alloy powder is uniformly extruded, sheared and dispersed by means of high-energy ball milling, so that the surface of tungsten carbide is uniformly coated with the additives, bridges between silver and tungsten carbide are established, and the additives are better utilized. Then, a silver coating powder is prepared by means of a chemical reaction, and the silver coating powder is wet-mixed with balls, alcohol and a forming agent to improve the uniformity, apparent density and tapped density of the powder, and then closed spray drying granulation is performed to ensure a consist unit weight of initial pressing. The forming agent in the compact is removed at a low temperature, and then sintering is performed under high-temperature and overpressure conditions. Compared with the solid-phase pressureless sintering used previously, cold recompression densifies the material, and overpressure sintering greatly improves the bonding strength of the material, thus enabling the material to be highly densified, reducing the internal pores of the material, and effectively improving the burn-out resistance of the silver-tungsten carbide-graphite contact material in an electrical life test.

Description

High-strength silver tungsten carbide graphite contact material and preparation method

[0001] The present application claims priority to the Chinese patent application No. 2024107866189 filed on June 18, 2024 with the China National Intellectual Property Office, the content of which is incorporated herein in its entirety. TECHNICAL FIELD

[0002] The present application belongs to the field of electrical contact materials, and particularly relates to a high-strength silver tungsten carbide graphite contact material and a preparation method. BACKGROUND

[0003] The electrical contact, also known as contact or junction, is a contact element of electrical switches, instruments and meters, and is responsible for the task of turning on and off the current, thus its performance directly affects the reliable operation of the switch.

[0004] Silver is the best material in all metals in terms of heat conductivity, excellent processing property and high oxidation resistance, and thus silver is the most important and economic noble metal contact material, which is suitable for medium and heavy load electrical appliances. However, silver has low hardness and melting point, is not resistant to wear, and forms a silver sulfide film on the surface in a humid and high temperature environment, in a sulfur or sulfide medium; under the action of direct current, due to the low hardness and easy volatilization of silver, an electric erosion spike is formed; under heavy load conditions, silver contact elements are prone to form an electric arc; tungsten carbide has the characteristics of high hardness, high density, high melting point, low electrical conductivity and very low burn loss rate. Graphite has the characteristics of high temperature resistance, electrical conductivity, lubricity, chemical stability and high resistance to melting and welding performance.

[0005] Silver, tungsten carbide and graphite combine the respective advantages of each other. The WC content in the AgWCC contact material is generally 10% to 30%, and the C content is generally 0.2% to 5%, which has the advantages of good heat and electrical conductivity, electrical wear resistance, melting and welding resistance, oxidation resistance and the like. With the increasing requirement of electrical reliability, the requirement for static point burn loss is getting higher and higher, and electrical manufacturers are constantly launching high-index electrical life products. The prior art commonly modifies the silver tungsten carbide graphite electrical contact material by adding specific metal materials, and cobalt and nickel cannot play the role of additives to improve the sintering type of the material. The existing method uses conventional powder mixing or chemical coating process, solid phase sintering under hydrogen atmosphere, direct sintering of silver and silver, and through a large complex pressure to improve the density of the material. The unique processing method can only achieve a density of about 97% of the theoretical value, and the static point material burn loss is poor.

[0006] Therefore, it has been a difficult problem in the industry to produce high-dispersion and high-strength silver tungsten carbide graphite materials. This problem has also limited the improvement of electrical life to a great extent. SUMMARY

[0007] The present application aims to overcome the shortcomings and deficiencies of the prior art, and provides a high-strength silver tungsten carbide graphite contact material and a preparation method thereof.

[0008] The technical scheme adopted by the present application is as follows: a preparation method of a high-strength silver tungsten carbide graphite contact material, comprising the following steps:

[0009] S1, adding additives to a medium-frequency induction furnace for smelting, and then preparing additive alloy powder by atomization, the additives being cobalt and nickel;

[0010] S2, adding the additive alloy powder of S1 to a high-energy ball mill after grading treatment, and ball-milling to obtain pretreated powder;

[0011] S3, uniformly stirring the pretreated powder of S2 with graphite powder by ultrasonic stirring, and preparing silver-coated powder by chemical reaction;

[0012] S4, wet mixing the silver-coated powder of S3 with balls, alcohol, and a forming agent to form a wet mixed coated powder slurry;

[0013] S5, drying and granulating the wet mixed coated powder slurry of S4 by a spray drying device to obtain spray granulation mixed powder particles;

[0014] S6, pressing the spray granulation mixed powder particles of S5 into a green compact;

[0015] S7, vacuum low-temperature removing the forming agent from the green compact of S6 and then overpressure sintering;

[0016] S8, re-pressing and shaping the green compact after sintering of S7 to obtain a silver tungsten carbide graphite contact material.

[0017] Further, in S1, the mass ratio of cobalt to nickel in the additives is 1:1 to 5:1.

[0018] Further, in S1, the smelting temperature of the medium-frequency induction furnace is 1600-1800 DEG C, and the refining time is 10-20 min; the atomization parameters are as follows: the inert gas is argon, the inert gas pressure is 0.5-1.0 MPa, the inert gas flow is 400-1000 L / min, and the high-pressure water atomization spray disc water pressure is 20-200 MPa.

[0019] Further, in S2, the additive alloy powder of S1 is first subjected to grading treatment and then ball-milled with tungsten carbide powder; the grading treatment adopts a superfine sorting machine, and the parameters of the superfine sorting machine are as follows: air pressure 0.6-0.8 MPa, grading wheel rotating speed: 75-150 Hz, and particle size ≤1 μm.

[0020] Further, in S2, the mass ratio of the tungsten carbide and the additive alloy powder is 98.5:1-99.8:1, and the parameters of the high-energy ball mill are as follows: the ball-to-material ratio is 8:1-10:1, and the rotating speed is 80-200 r / min.

[0021] Further, in S3, the pre-processed powder, graphite powder, pure water, hydrazine hydrate and ammonia water are added into an ultrasonic stirring device for ultrasonic stirring to make the mixture uniform, and then the silver nitrate solution is slowly added to prepare the silver-coated powder.

[0022] Further, in S4, the silver-coated powder, balls and a forming agent mixture are added into a wet mixing device, and the wet mixing process parameters are as follows: the silver-coated powder: the balls: the forming agent mixture = 9:1:2-10:1:2.

[0023] Further, in S5, the spray granulation process parameters are as follows: the inlet temperature is 140-180 DEG C, the outlet temperature is 80-100 DEG C, the spray pressure is 0.65-0.85 MPa, and the atomization rotating speed is 15000-30000 r / min.

[0024] Further, in S7, the overpressure sintering parameters are as follows: vacuumizing, the vacuum degree is 0.1 Pa, the de-forming agent temperature is 300-500 DEG C, the de-removing time is 1-5 h, then nitrogen or argon is introduced, the overpressure is 10-50 MPa, the sintering temperature is 900-940 DEG C, and the holding time is 5 h.

[0025] The high-strength silver-tungsten carbide graphite contact material is prepared by the preparation method of the high-strength silver-tungsten carbide graphite contact material as described above.

[0026] The application has the following beneficial effects: the additive alloy powder is prepared by refining and atomizing cobalt and nickel, high-speed rotation of the high-energy ball mill causes equal extrusion, shearing and dispersion of each alloy powder, the additive is uniformly wrapped on the surface of the tungsten carbide, a bridge between silver and tungsten carbide is established, the additive plays a better role, and the sintering type of the material is improved; meanwhile, the silver-coated powder, the forming agent and the balls are wet mixed, the uniformity, the loose bulk density and the tap density of the powder are improved, closed spray drying is adopted to ensure the consistency of the initial pressure, and finally the green compact is sintered under high-temperature overpressure, the inherent bonding strength of the green compact is greatly improved, the material is densified by solid-phase sintering without pressure and cold re-pressing, the inherent porosity of the material is reduced, and the anti-burnout performance of the silver-tungsten carbide graphite contact material in the electrical life test is effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to these drawings without creative labor.

[0028] Fig. 1 is a process route of the present application;

[0029] Fig. 2 is a metallographic photograph of Example 1;

[0030] Fig. 3 is a metallographic photograph of Comparative Example 1. DETAILED DESCRIPTION

[0031] In order to make the objects, technical solutions and advantages of the present application more clear, the following will further describe the present application in detail with reference to the drawings.

[0032] The present application provides a preparation method of high-strength silver tungsten carbide graphite contact material, as shown in Fig. 1, comprising the following steps:

[0033] S1, adding additives into a medium-frequency induction furnace for smelting, and then preparing additive alloy powder by atomization; wherein the additives are cobalt and nickel, and the mass ratio of cobalt to nickel is 1:1-5:1; wherein the smelting temperature of the medium-frequency induction furnace is 1600-1800℃, and the refining time is 10-20 min; the subsequent atomization parameters are as follows: the inert gas is argon, the inert gas pressure is 0.5-1.0 MPa, the inert gas flow is 400-1000 L / min, and the water pressure of the high-pressure water atomization spray disc is 20-200 MPa;

[0034] S2, the additive alloy powder in S1 is subjected to grading treatment by a superfine sorting machine, and the parameters of the superfine sorting machine are as follows: air pressure 0.6-0.8 MPa, grading wheel rotating speed 75-150 Hz, and particle size ≤1 μm; the sorted additive alloy powder and tungsten carbide powder are added into a high-energy ball mill to prepare a pretreated powder by ball milling pretreatment; wherein the mass ratio of the tungsten carbide to the additive alloy powder is 98.5:1-99.8:1, and the parameters of the high-energy ball mill are as follows: ball-to-material ratio 8:1-10:1, and rotating speed 80-200 r / min;

[0035] S3, the pretreated powder in S2, graphite powder, pure water, hydrazine hydrate, and ammonia water are added into an ultrasonic stirring device for ultrasonic stirring to make them uniformly mixed, and then silver nitrate solution is slowly added to prepare a silver-coated powder;

[0036] S4, the silver coated powder described in S3 is wet mixed with balls, alcohol and a forming agent to form a wet mixed coated powder slurry; wherein the silver coated powder, balls and forming agent mixture are added to a wet mixing device, and the wet mixing process parameters are as follows: silver coated powder: balls: forming agent mixture = 9:1:2~10:1:2, and the forming agent is polyethylene, stearic acid or the like;

[0037] S5, the wet mixed coated powder slurry described in S4 is dried and granulated by a spray drying device to obtain a spray granulation mixed powder particle;

[0038] S6, the spray granulation mixed powder particle described in S5 is pressed into a green compact;

[0039] S7, the green compact described in S6 is first subjected to vacuum low-temperature removal of the forming agent and then subjected to overpressure sintering;

[0040] S8, the green compact after sintering in S7 is re-pressed and shaped to obtain a silver tungsten carbide graphite contact material.

[0041] The following are some embodiments of the present application.

[0042] Embodiment 1:

[0043] A preparation method of a silver tungsten carbide graphite contact material, comprising the following steps:

[0044] a, cobalt and nickel are proportioned according to the mass ratio of 5:1;

[0045] b, the cobalt and nickel are added to a medium-frequency induction furnace, the melting temperature is 1700℃, the refining time is 15min, the inert gas is argon, the inert gas pressure is 0.75MPa, the inert gas flow is 600L / min, and the high-pressure water atomization spray disc water pressure is 100MPa;

[0046] c, the dried atomized alloy powder is added to a superfine sorting device, and the sorting parameters are as follows: air pressure 0.7Mpa, grading wheel rotating speed: 100Hz, and average particle size ≤1μm;

[0047] d, tungsten carbide and alloy powder are added to a high-energy ball mill according to the mass ratio of 99.8:1, and the high-energy ball milling parameters are as follows: ball-to-material ratio 10:1, and rotating speed 100r / min;

[0048] e, pure water, hydrazine hydrate, ammonia water, the milled powder and graphite powder are proportioned according to the ratio of 4:1, added to an ultrasonic stirring device, stirred for 30min, and slowly added with silver nitrate solution to prepare AgWC12C3 powder;

[0049] f, the coated powder, balls and forming agent mixture are added to a wet mixing device, and the wet mixing process parameters are as follows: material: balls: forming agent mixture = 9:1:2;

[0050] g. The mixed slurry is made into particles by using a closed spray granulation device, and the spray granulation process parameters are as follows: inlet temperature: 140-180°C, outlet temperature: 80°C, spray pressure: 0.85 MPa, and atomization speed: 30000 r / min.

[0051] h. The spray granulated powder particles are pressed into green compacts;

[0052] i. The green compacts are subjected to low-temperature deforming agent removal and high-temperature superpressure sintering, and the superpressure sintering parameters are as follows: vacuum degree: 0.1 Pa, deforming agent removal temperature: 300°C, deforming agent removal time: 5 h, nitrogen or argon is introduced, superpressure: 10-50 MPa, sintering temperature: 900-940°C, and holding time: 5 h.

[0053] k. The sintered green compacts are re-pressed and shaped to obtain silver tungsten carbide graphite contact materials.

[0054] Example 2

[0055] A method for preparing silver tungsten carbide graphite contact materials, comprising the following steps:

[0056] a. Cobalt and nickel are proportioned according to the mass ratio 2:1;

[0057] b. The cobalt and nickel are added into a medium-frequency induction furnace, the smelting temperature is 1650°C, the refining time is 20 min, the inert gas is argon, the inert gas pressure is 0.8 MPa, the inert gas flow is 600 L / min, and the high-pressure water atomization spray disc water pressure is 100 MPa;

[0058] c. The dried atomized alloy powder is added into a superfine separation device, and the separation parameters are as follows: air pressure: 0.7 MPa, and classification wheel speed: 100 Hz, and the average particle size is ≤1 μm;

[0059] d. Tungsten carbide and alloy powder are added into a high-energy ball mill according to the mass ratio range 98.5:1, and the high-energy ball milling parameters are as follows: ball-to-material ratio: 8:1, and speed: 200 r / min;

[0060] e. Pure water, hydrazine hydrate, ammonia water, the milled powder, and graphite powder are proportioned according to the ratio 9:1, and are added into an ultrasonic stirring device, and are stirred for 30 min, and silver nitrate solution is slowly added to prepare AgWC27C3 powder;

[0061] f. The coated powder, balls, and deforming agent mixture are added into a wet mixing device, and the wet mixing process parameters are as follows: material: ball: deforming agent mixture = 10:1:2;

[0062] g. The mixed slurry is made into particles by using a closed spray granulation device, and the spray granulation process parameters are as follows: inlet temperature: 140-180°C, outlet temperature: 100°C, spray pressure: 0.65 MPa, and atomization speed: 15000 r / min.

[0063] h. Press the spray-granulated powder particles into compacts;

[0064] i. Remove the forming agent from the compact at low temperature and sinter it under high temperature and pressure. The parameters for high-pressure sintering are: vacuuming, vacuum degree 0.1 Pa, forming agent removal temperature 500℃, removal time 3h; then purge with nitrogen or argon gas, high pressure 10-50 MPa; sintering temperature: 900-940℃, holding time 5h.

[0065] k. After sintering, the compact is re-pressed and shaped to obtain silver tungsten carbide graphite contact material.

[0066] Comparative Example 1:

[0067] A method for preparing a silver tungsten carbide graphite contact material includes the following steps:

[0068] a. Mix silver powder, tungsten carbide powder, cobalt powder, and nickel powder in the same proportions as in Example 1;

[0069] b. Add the prepared materials to the double cone mixer and wet mix. The ratio of material:ball:alcohol is 10:1:2.

[0070] c. Vacuum dry the wet-mixed powder;

[0071] d. Adding a forming agent to form granules;

[0072] e. Press the prepared granules into compacts;

[0073] f. Remove the forming agent from the compact at low temperature and sinter in a hydrogen atmosphere. Parameters: Remove the forming agent temperature 300℃, remove the forming agent time 5h, sintering temperature: 900-940℃, holding time 5h.

[0074] g. After sintering, the compact is re-pressed and shaped to obtain silver tungsten carbide graphite contact material.

[0075] Figure 2 is a metallographic image of Example 1, and Figure 3 is a metallographic image of Comparative Example 1. The table below shows the relevant performance test results of Example 1 and Comparative Example 1. The comparison can demonstrate the high density, higher strength and better burn-off resistance of the material prepared by the present invention.

[0076] 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 silver tungsten carbide graphite contact material, characterized in that, Includes the following steps: S1. The additives are added to a medium-frequency induction furnace for melting, and then atomized to form an additive alloy powder, wherein the additives are cobalt and nickel; S2. After graded treatment, the alloy powder with additives described in S1 is added to a high-energy ball mill along with tungsten carbide powder and ball milled to obtain pretreated powder. S3. The pretreated powder described in S2 is ultrasonically stirred with graphite powder until homogeneous, and then chemically reacted to produce silver-coated powder. S4. Add the silver-coated powder described in S3 to balls, alcohol, and molding agent and wet mix to form a wet-mixed coated powder slurry; S5. The wet mixed coating powder slurry described in S4 is dried and granulated using a spray drying device to obtain spray-granulated mixed powder particles. S6. Press the spray-granulated mixed powder particles described in S5 into a compact; S7. The pressed blank described in S6 is first vacuum-cooled to remove the forming agent and then sintered under high pressure. S8. The pressed blank after sintering in S7 is re-pressed and shaped to obtain silver tungsten carbide graphite contact material.

2. The method for preparing the high-strength silver tungsten carbide graphite contact material according to claim 1, characterized in that, In S1, the mass ratio of cobalt to nickel in the additive is 1:1 to 5:

1.

3. The method for preparing the high-strength silver tungsten carbide graphite contact material according to claim 1, characterized in that, In S1, the melting temperature of the medium-frequency induction furnace is 1600~1800℃, and the refining time is 10~20min; the atomization parameters are: the inert gas is argon, the inert gas pressure is 0.5~1.0MPa, the inert gas flow rate is 400~1000L / min, and the water pressure of the high-pressure water atomizing spray plate is 20~200MPa.

4. The method for preparing the high-strength silver tungsten carbide graphite contact material according to claim 1, characterized in that, In S2, the alloy powder of the additive mentioned in S1 is first graded and then ball-milled with tungsten carbide powder; the grading process adopts an ultrafine separator with the following parameters: air pressure 0.6~0.8MPa, classifying wheel speed 75~150Hz, and particle size ≤1μm.

5. The method for preparing the high-strength silver tungsten carbide graphite contact material according to claim 1, characterized in that, In S2, the mass ratio of tungsten carbide to additive alloy powder is 98.5:1 to 99.8:1, and the parameters of the high-energy ball mill are: ball-to-material ratio 8:1 to 10:1, and rotation speed 80 to 200 r / min.

6. The method for preparing the high-strength silver tungsten carbide graphite contact material according to claim 1, characterized in that, In S3, pretreated powder, graphite powder, pure water, hydrazine hydrate, and ammonia are added to an ultrasonic stirrer and ultrasonically stirred to mix them evenly. Then, silver nitrate solution is slowly added to make silver-coated powder.

7. The method for preparing the high-strength silver tungsten carbide graphite contact material according to claim 1, characterized in that, In step S4, the mixture of silver-coated powder, spheres, and molding agent is added to a wet mixing device. The wet mixing process parameters are: silver-coated powder: spheres: molding agent mixture = 9:1:2 to 10:1:

2.

8. The method for preparing the high-strength silver tungsten carbide graphite contact material according to claim 1, characterized in that, In S5, the spray granulation process parameters are as follows: inlet temperature: 140-180℃, outlet temperature: 80-100℃, spray pressure: 0.65-0.85MPa, and atomization speed: 15000-30000r / min.

9. The method for preparing the high-strength silver tungsten carbide graphite contact material according to claim 1, characterized in that, In S7, the overpressure sintering parameters are as follows: vacuuming, vacuum degree 0.1 Pa, deforming agent temperature 300-500℃, deforming time 1-5 h; then nitrogen or argon gas is introduced, overpressure pressure 10-50 MPa; sintering temperature: 900-940℃, holding time 5 h.

10. The high-strength silver tungsten carbide graphite contact material prepared by the method for preparing high-strength silver tungsten carbide graphite contact material according to any one of claims 1-9.

Images