Silver-tungsten carbide contact material and manufacturing process therefor

Abstract

A method for producing silver-tungsten carbide contact material, characterized in that it comprises the following steps: S1: Adding tungsten carbide powder and a silver nitrate solution into a reaction vessel, followed by adding polyethylene glycol into the reaction vessel, vibrating and stirring with ultrasonics so that they are evenly mixed; then vibrating and stirring with ultrasonics, Adding a sodium hydroxide solution to the reaction vessel until the pH of the solution reaches 8 to 9, then further vibration and stirring with ultrasound so that they are evenly mixed, then an ultrasonic stirring is obtained, gradually adding a dextrose solution into the reaction vessel at a rate of 0.5-2 L / min, further vibrating and stirring with ultrasound, After complete precipitation of the silver ions in the solution, carrying out a reduction reaction, coating the precipitated silver on the tungsten carbide powder to form a composite powder of the tungsten carbide coated by the silver, wherein the concentration of the dextrose solution is 30-300 g / L, wherein the molecular weight of the polyethylene glycol is 500-20000, the addition amount being 7-12% of the mass of the tungsten carbide powder; where the average particle size of the tungsten carbide powder is 0.5-8 µm, where the solid-liquid ratio of the tungsten carbide powder and the silver nitrate solution is 5-70 g / L, wherein the thickness of the silver layer of the composite powder of the tungsten carbide coated with silver is 10-200 nm, where the dosage of the silver nitrate solution is converted by the dosage of the silver, and where the dosage m Agof silver is calculated using the following formula: m A g = m WC ρ A g ρ WC × 6 d 3 × ( 4 3 x 3 + xd 3 + 2 dx 2 ) , where m WC the total mass of tungsten carbide, p Ag the density of silver, p WC is the density of the tungsten carbide and d is the average particle size of the tungsten carbide powder, and where the unit for d is in µm and x is the density of the silver layer in the composite powder of the tungsten carbide coated by the silver; S2: Mixing the composite powder of the silver-coated tungsten carbide with the silver powder and pressing it into a compact; S3: Placing the compact prepared in S2 and a silver block in a sintering furnace protected by the ammonia decomposition atmosphere and performing sintering and infiltration to obtain a silver-tungsten carbide contact material.

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of contact material, particularly a silver-tungsten carbide contact material and a manufacturing method thereof. STATE OF THE ART

[0002] With the ever-increasing demands on the reliability of electrical equipment at the power distribution end of the power grid, electrical equipment manufacturers are constantly developing low-voltage power distribution products with higher disconnection indicators. Some electronic circuit breakers can already achieve a limiting disconnection indicator of 150kA. Improving the disconnection indicator of an electrical equipment means that the thermal entry force of the arc during disconnection is extremely high. At this time, the contact material is extremely susceptible to arc erosion, causing the electrical equipment to fail to turn on and a fault to occur.

[0003] Considering the material's properties such as conductivity and corrosion resistance, silver tungsten carbide (AgWC) is currently the most commonly used material for high-index low-voltage circuit breakers. On the one hand, the material contains micrometer-sized dispersed tungsten carbide particles used as a reinforcing phase, which can significantly improve the material's arc erosion resistance. On the other hand, a powder metallurgy process and a liquid-phase sintering (infiltration) process are used to ensure good wetting of the silver and tungsten carbide particles, thus preventing splashing of the material under the action of the high-temperature arc.

[0004] To improve the arc resistance of silver tungsten carbide materials, it is usually necessary to reduce the particle size of tungsten carbide in the material and increase the tungsten carbide content. For silver tungsten carbide materials used in large melting furnaces and other special devices, the mass percentage of tungsten carbide should be increased to 60% or even more, while the average particle size of tungsten carbide should be reduced to less than 1 micron, which places very high demands on the material's manufacturing process.

[0005] If the tungsten carbide content in the silver-tungsten carbide powders is too high and the tungsten carbide particle size is too small, the tungsten carbide particle surface area in the mixed powders will be extremely large, inevitably resulting in a situation in which a large number of tungsten carbide particles are adjacent to each other during the powder molding process. Due to the extremely high hardness, almost no plastic deformation occurs when the surfaces of the tungsten carbide particles come into contact and press against each other. Therefore, the particles cannot mesh with each other, making the compact extremely prone to cracking and even impossible to form.

[0006] Because of this, it has always been a difficult problem in the industry to produce a silver-tungsten carbide material with a high tungsten carbide content. To a considerable extent, this problem limits further improvements in the separation performance of the electrical device.

[0007] In conventional coating processes, agglomeration of tungsten carbide particles cannot be avoided during the chemical reaction. The silver generated by the reaction will not envelop the individual tungsten carbide particle, but rather an agglomerate of multiple tungsten carbide particles. Therefore, there is direct contact between a large number of tungsten carbide particles in the coating powders, and the formability of the powders is relatively poor. CN 1 04 493 170 A, CN 1 01 717 928 A, CN 103 824 710 A, CN 1 01 633 986 A, CN 1 01 817 079 A, ​​and DE 2 244 701 A each relate to processes for producing silver-tungsten carbide material. BRIEF DESCRIPTION OF THE PRESENT INVENTION

[0008] The present invention aims to provide a silver-tungsten carbide contact material and a manufacturing method therefor, addressing the deficiencies of the prior art. This effectively improves the density of the silver-tungsten carbide contact material.

[0009] This object is achieved by the method according to claim 1 or by the contact material according to claim 4. Advantageous embodiments of the invention are defined in the dependent claims.

[0010] In the present invention, the outer surface of the tungsten carbide powder particles is encased in a pure silver shell layer with a thickness of 10-200 nm to obtain a tungsten carbide-silver composite powder with a monodisperse core-shell structure, namely, a silver-encased tungsten carbide composite powder. Pure silver forms physical insulation between the tungsten carbide particles. Since silver has excellent ductility, during the powder compression molding process, the adjacent tungsten carbide particles can mesh with each other through the pure silver shell layer encasing an outer layer to form a mechanical combination, thereby significantly improving the molding performance of the powder. This ensures the molding of the mixed silver-tungsten carbide powder with a high tungsten carbide content, thereby realizing the production of a high-density silver-tungsten carbide material with a high tungsten carbide content.The above process ensures the molding of the composite powder dispersed in individual particles, thereby significantly improving the moldability of the powder. SHORT DESCRIPTION OF THE DRAWING

[0011] The present invention is explained in more detail below in connection with figures. Fig. 1 shows a tissue SEM photograph of the silver tungsten carbide contact material in a first embodiment of the present invention. Fig. 2 shows a tissue SEM photograph obtained in the performance test for the conventional silver-tungsten carbide contact material in a first embodiment of the present invention. Fig. 3 shows a metallographic photograph of the silver-tungsten carbide contact material in a first embodiment of the present invention. Fig. 4 shows a metallographic photograph of the silver-tungsten carbide contact material in a second embodiment of the present invention. DETAILED DESCRIPTION

[0012] The present invention will be explained in more detail below in connection with the detailed embodiments, but the present invention is not limited to these detailed embodiments. Those skilled in the art should understand that the present invention covers all optional solutions, improved solutions, and equivalent solutions within the scope of the claims. Embodiment 1

[0013] A method for producing the silver tungsten carbide contact material, comprising the following steps: a. Dissolve 3.25 kg of silver nitrate solids in 2500 L of deionized water to prepare a silver nitrate solution; b. Adding 33.2 kg of tungsten carbide powder and silver nitrate solution into the reaction vessel, followed by adding 3 kg of polyethylene glycol and an appropriate amount of deionized water, ultrasonication, and stirring for 2 hours; c. Continue ultrasonication and stirring, gradually add the sodium hydroxide solution in the vessel until the pH of the solution reaches 8-9, and continue ultrasonication and stirring for 0.5 hour; d. Further ultrasonication and stirring, gradually adding the dextrose solution with a concentration of 100 g / L at a rate of 1.5 L / min until the silver in the solution is completely precipitated, further ultrasonication and stirring for 0.5 hour; e. Suction and filter the solution, purify the resulting composite powder with deionized water and dry it; f. Placing the composite powder obtained in step e and the silver powder in a V-type powder mixer to perform mixing for 10-12 hours to obtain an AgWC powder having a silver content of 5%; g. Pressing the AgWC powder obtained in step f into a compact by means of a powder forming device; h: Placing the compact and silver block obtained in step g in a sintering furnace protected by the ammonia decomposition atmosphere, sintering at 1000°C and infiltrating for 2 hours, taking out from the furnace after cooling, after cleaning, a silver-tungsten carbide contact material is obtained.

[0014] It is understood that step h is from the prior art, wherein the setting of the sintering temperature and the infiltration time is not limited to the embodiment, and wherein this is not explained in detail here.

[0015] Fig. 3 shows a metallographic photograph of the silver-tungsten carbide contact material obtained by the method for producing the silver-tungsten carbide contact material in the first embodiment, wherein a tissue SEM photograph is as in Fig. 1. In the first embodiment, a performance test is carried out for the available silver-tungsten carbide materials on the market, and the obtained tissue SEM photograph is as shown in Fig. 2. By comparing Fig. 1 and Fig. 2, it can be found that the tissue of the silver-tungsten carbide contact material in the first embodiment has no pores, the silver and the tungsten carbide are excellently combined with each other, and a high density is achieved. Embodiment 2

[0016] A method for producing the silver tungsten carbide contact material, comprising the following steps: a. Dissolve 6.5 kg of silver nitrate solids in 4000 L of deionized water to prepare a silver nitrate solution; b. Adding 66.79 kg of tungsten carbide powder and silver nitrate solution into the reaction vessel, followed by adding 5 kg of polyethylene glycol and an appropriate amount of deionized water, ultrasonication, and stirring for 2 hours; c. Continue ultrasonication and stirring, gradually add the sodium hydroxide solution in the vessel until the pH of the solution reaches 8-9, and continue ultrasonication and stirring for 0.5 hour; d. Further ultrasonication and stirring, gradual addition of the dextrose solution with a concentration of 100 g / L at a rate of 3 L / min, further ultrasonication and stirring for 0.5 hour after complete precipitation of the silver in the solution; e. Suction and filter the solution, purify the resulting composite powder with deionized water and dry it; f. Insert the in step e obtained composite powder and the silver powder in a V-type powder mixer to perform mixing for 10-12 hours to obtain an AgWC powder having a silver content of 5%; g. Pressing the AgWC powder obtained in step f into a compact by means of a powder forming device; h: Placing the compact and silver block obtained in step g in a sintering furnace protected by the ammonia decomposition atmosphere, sintering at 1000°C and infiltrating for 2 hours, taking out from the furnace after cooling, then a silver-tungsten carbide contact material is obtained.

[0017] It is understood that step h is from the prior art, wherein the setting of the sintering temperature and the infiltration time is not limited to the embodiment, and wherein this is not explained in detail here.

[0018] Fig. 4 shows a metallographic photograph of the silver-tungsten carbide contact material obtained by the method for producing the silver-tungsten carbide contact material in the second embodiment.

Claims

[1] Process for producing silver-tungsten carbide contact material, characterized by that it includes the following steps: S1: Adding tungsten carbide powder and a silver nitrate solution into a reaction vessel, followed by adding polyethylene glycol into the reaction vessel, vibrating and stirring with ultrasonics so that they are evenly mixed; then vibrating and stirring with ultrasonics, Adding a sodium hydroxide solution to the reaction vessel until the pH of the solution reaches 8 to 9, then further vibration and stirring with ultrasound so that they are evenly mixed, then an ultrasonic stirring is obtained, gradually adding a dextrose solution into the reaction vessel at a rate of 0.5-2 L / min, further vibrating and stirring with ultrasound, After complete precipitation of the silver ions in the solution, carrying out a reduction reaction, coating the precipitated silver on the tungsten carbide powder to form a composite powder of the tungsten carbide coated by the silver, wherein the concentration of the dextrose solution is 30-300 g / L, wherein the molecular weight of the polyethylene glycol is 500-20000, the addition amount being 7-12% of the mass of the tungsten carbide powder; where the average particle size of the tungsten carbide powder is 0.5-8 µm, where the solid-liquid ratio of the tungsten carbide powder and the silver nitrate solution is 5-70 g / L, wherein the thickness of the silver layer of the composite powder of the tungsten carbide coated with silver is 10-200 nm, where the dosage of the silver nitrate solution is converted by the dosage of the silver, and where the dosage m Agof silver is calculated using the following formula: mAg=mWCρAgρWC×6d3×(43x3+xd3+2dx2), where m WC the total mass of tungsten carbide, p Ag the density of silver, p WC is the density of the tungsten carbide and d is the average particle size of the tungsten carbide powder, and where the unit for d is in µm and x is the density of the silver layer in the composite powder of the tungsten carbide coated by the silver; S2: Mixing the composite powder of the silver-coated tungsten carbide with the silver powder and pressing it into a compact; S3: Placing the compact prepared in S2 and a silver block in a sintering furnace protected by the ammonia decomposition atmosphere and performing sintering and infiltration to obtain a silver-tungsten carbide contact material. [2] A method for producing silver-tungsten carbide contact material according to claim 1, characterized by that S1 continues to include: Suctioning and filtering the reactant solution in the reaction vessel to separate the composite powder of the silver-coated tungsten carbide, followed by cleaning and drying. [3] A method for producing silver-tungsten carbide contact material according to any one of the preceding claims, characterized by that in step S2 the porosity of the compact is 5-55%. [4] Silver tungsten carbide contact material, characterized by that it is produced by a method for producing silver-tungsten carbide contact material according to one of claims 1 to 3. [5] Silver-tungsten carbide contact material according to claim 4, characterized by that the mass percentage of tungsten carbide is 40-90%.

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