Silver-nickel graphite electric contact material and preparation method thereof

Abstract

The application discloses a silver-nickel graphite electric contact material and a preparation method thereof. The nickel-coated graphite powder and the silver-coated graphite powder are used as additives and introduced into the AgNi system. The additives have better shape regularity and interface compatibility as core-shell powder, and the dispersion degree in the Ag matrix is better. The nickel-coated graphite powder and the silver-coated graphite powder are pre-sintered and crushed and granulated, which is beneficial to removing the chemical residual substances in the coated powder, improving the bulk density and fluidity of the powder, facilitating the powder mixing and pressing, shortening the sintering time through the rapid plasma electric spark sintering, improving the density, adopting the powder metallurgy process as a whole, not needing expensive or special equipment, easily regulating the material proportion, shortening the process flow and lowering the cost.

Description

Technical Field

[0001] This invention relates to the field of electrical contact materials technology, specifically to a silver-nickel-graphite electrical contact material and its preparation method. Background Technology

[0002] AgNi materials, due to their excellent electrical and thermal conductivity, are widely used in low- and medium-voltage electrical contact devices, such as relays, contactors, and switches. However, as power electronic devices develop towards miniaturization, high reliability, and long lifespan, the performance bottlenecks of traditional AgNi materials under harsh operating conditions (especially high breaking current and frequent operation) are becoming increasingly apparent. The main problems currently facing the technology are: First, insufficient resistance to arc erosion. The high temperature of an electric arc causes localized melting, spattering, and transfer of the material to the opposite side, resulting in an uneven contact surface, increased contact resistance, and ultimately failure. Second, the resistance to welding needs improvement. Especially under the impact of starting current or short-circuit current, the contacts are prone to instantaneous welding and adhesion, leading to breaking failure and safety accidents. Existing improvement schemes for AgNi often compromise one aspect for another. For example, while adding graphite or metal oxides can improve resistance to welding, it can severely damage the material's conductivity to some extent. Current technologies struggle to balance conductivity and arc resistance.

[0003] Chinese Patent CN 102808098 B discloses a method for preparing a silver / nickel / graphite electrical contact material. The preparation steps include: first, chemically plating colloidal graphite to coat it with a layer of metallic nickel; second, chemically plating the nickel-coated colloidal graphite powder to further coat it with a layer of silver; third, sintering and granulating the Ag-Ni-C core-shell structure powder formed after coating under nitrogen protection to obtain intermediate composite particle powder; fourth, sieving the obtained intermediate composite particle powder; and fifth, mixing the intermediate composite particles with pure silver powder to reduce the colloidal graphite content to a specified value. After traditional powder mixing, powder pressing, nitrogen-protected sintering, extrusion, and drawing processes, the desired silver / nickel / graphite material is obtained. According to the embodiments of this patent, this method uses a two-step chemical plating process, which is cumbersome and difficult to mass-produce.

[0004] Therefore, there is an urgent need to design an innovative technical solution that is simple to process, easy to scale up, and can simultaneously and synergistically improve the resistance to arc erosion and welding of AgNi electrical contact materials without significantly sacrificing conductivity. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the existing technology, the present invention provides a silver-nickel graphite electrical contact material and its preparation method.

[0006] The technical solution adopted in this invention is: a method for preparing a silver-nickel-graphite electrical contact material, comprising the following steps:

[0007] (1) Nickel-coated graphite powder and silver-coated graphite powder are pre-sintered and crushed and granulated respectively to obtain the processed nickel-coated graphite powder and silver-coated graphite powder. (2) The treated nickel-coated graphite and silver-coated graphite powders are mixed evenly with nickel powder and silver powder according to a certain mass ratio to obtain a mixed powder; (3) The mixed powder is pressed into ingots, sintered, and repressed to obtain ingots; (4) The spindle is extruded into a wire to obtain a silver-nickel graphite electrical contact material.

[0008] Preferably, the pre-sintering temperature of the nickel-coated graphite powder is 700℃-800℃.

[0009] Preferably, the particle size D50 of the nickel-coated graphite powder after crushing and granulation is 25-35 μm.

[0010] Preferably, the mass ratio of nickel to graphite in the nickel-coated graphite powder is 3:2 to 7:3.

[0011] Preferably, the pre-sintering temperature of the silver-coated graphite powder is 500℃-600℃.

[0012] Preferably, the particle size D50 of the silver-coated graphite powder after crushing and granulation is 1-20 μm.

[0013] Preferably, the mass ratio of silver to graphite in the silver-coated graphite powder is 2:1 to 3:1.

[0014] Preferably, in step (2), the mass fractions of nickel-coated graphite powder, silver-coated graphite powder and nickel powder are greater than 0 to 1 wt%, greater than 0 to 1 wt%, and 7 wt% to 11 wt%, respectively, with the remainder being silver powder.

[0015] Preferably, in step (3), the mixed powder is rapidly sintered by a plasma electrical discharge machine at a sintering temperature of 830℃-870℃.

[0016] A silver-nickel-graphite electrical contact material prepared using the aforementioned preparation method.

[0017] The beneficial effects of this invention are as follows: This invention provides a silver-nickel graphite electrical contact material and its preparation method. Nickel-coated graphite powder and silver-coated graphite powder are introduced as additives into the AgNi system. The additives, acting as core-shell powders, exhibit better shape regularity and interfacial compatibility, and are better dispersed in the Ag matrix. Pre-sintering and crushing / granulation of the nickel-coated and silver-coated graphite powders helps remove residual chemical substances from the coated powders, improves the loose density and flowability of the powders, and facilitates powder mixing and pressing. Rapid plasma electrospark sintering results in short time and high density. The entire process utilizes powder metallurgy, requiring no expensive or special equipment. The material ratio is easily controlled, the process flow is short, and the cost is low. Attached Figure Description

[0018] Figure 1 Metallographic image 200X of the longitudinal section of the wire prepared using the process of the present invention in Example 1; Figure 2 Metallographic image 200X of the longitudinal section of AgNi10 wire, a commonly used material. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 This embodiment provides a silver-nickel-graphite electrical contact material, and the specific preparation steps are as follows: S1. The nickel-coated graphite powder is pre-sintered at a temperature of 700℃-800℃. After sintering, it is granulated by a crusher and sieved to obtain the processed nickel-coated graphite powder. The particle size D50 of the nickel-coated graphite powder is 25-35 μm, and the mass ratio of nickel to graphite is 7:3.

[0021] S2. Silver powder, nickel powder and treated nickel-coated graphite powder are added to a ball mill in a ratio of 90 wt%, 9 wt%, and 1 wt% for wet mixing. Anhydrous ethanol is used as the medium. The mixing process is carried out under vacuum. After mixing, the powder is dried in a vacuum oven and sieved.

[0022] S3. The uniformly mixed powder is added to a plasma electrical discharge machining (EDM) equipment for rapid sintering at a temperature of 850℃, resulting in an ingot with a diameter of 85-90 mm.

[0023] S4. The sintered ingot is repressed using a hydraulic press to make the silver-nickel graphite ingot more compact. The diameter of the pressing die is 90 mm and the pressing pressure is 25 MPa.

[0024] S5. The repressed spindle is kept warm in a hydrogen atmosphere at a temperature of 780-830 ℃, then extruded into a wire with a diameter of ф5.8mm, and then drawn into finished contacts of the required specifications.

[0025] Example 2 This embodiment provides a silver-nickel graphite electrical contact material. The difference between this embodiment and Embodiment 1 is that in step S1, the silver-coated graphite powder is pre-sintered at a temperature of 500℃-600℃. After sintering, it is granulated by a crusher and sieved to obtain the processed silver-coated graphite powder. The particle size D50 of the silver-coated graphite powder is 1-20 μm, and the mass ratio of silver to graphite is 3:1.

[0026] In step S2, silver powder, nickel powder, and the treated silver-coated graphite powder are added to a ball mill in a ratio of 90 wt%, 9 wt%, and 1 wt% for wet mixing.

[0027] Example 3 This embodiment provides a silver-nickel graphite electrical contact material. The difference between this embodiment and Embodiment 1 is that step S1 further includes pre-sintering the silver-coated graphite powder at a temperature of 500℃-600℃. After sintering, the powder is granulated using a crusher and sieved to obtain the processed silver-coated graphite powder. The particle size D50 of the silver-coated graphite powder is 1-20 μm, and the mass ratio of silver to graphite is 2:1.

[0028] In step S2, silver powder, nickel powder, treated nickel-coated graphite powder, and silver-coated graphite powder are added to a ball mill in proportions of 88 wt%, 11 wt%, 0.5 wt%, and 0.5 wt% respectively for wet mixing.

[0029] Example 4 This embodiment provides a silver-nickel graphite electrical contact material. The difference between this embodiment and embodiment 3 is that in step S1, the particle size D50 of the nickel-coated graphite powder is 25-35 μm, and the mass ratio of nickel to graphite is 3:2.

[0030] In step S2, silver powder, nickel powder, treated nickel-coated graphite powder and silver-coated graphite powder are added to a ball mill in proportions of 92 wt%, 7 wt%, 0.5 wt%, and 0.5 wt% respectively for wet mixing.

[0031] Table 1 compares the basic physical properties of the wires obtained in Examples 1-4 with those of commonly used materials AgNi10, AgNi12, and AgNi8 prepared using similar processes. From the physical properties of each material in Table 1, the wires obtained in Examples 1, 2, and 3 maintain good resistivity, which is basically comparable to that of silver-nickel materials with the same silver content. Their tensile strength is slightly lower, while their hardness and elongation are essentially the same. Compared to Example 4, which only added nickel-coated graphite powder, Example 1 has lower resistivity and higher density. The addition of both nickel-coated graphite powder and graphene-coated silver powder as additives, compared to a single additive, is beneficial to its conductivity and density through synergy.

[0032] Table 2 shows the experimental results of electrical life simulation experiments conducted using integral rivets made from the same specifications of wires from Examples 1-4, as well as rivets made from commonly used materials AgNi10, AgNi12, and AgNi8 wires prepared using similar processes. Table 2 shows that the synergistic addition of nickel-coated graphite powder and silver-coated graphite powder in Examples 3 and 4 significantly improved the electrical life compared to AgNi12 and AgNi8. Combined with Table 1, this scheme achieves a simultaneous and synergistic improvement in the weld resistance and arc erosion resistance of AgNi electrical contact materials while maintaining good conductivity.

[0033] Table 1. Comparison of physical properties of the wires obtained in Examples 1-4 and AgNi10, AgNi12 and AgNi8 wires of the same specification

[0034] Table 2 Results of electrical lifetime simulation experiments

[0035] Please note to all technical personnel: Although the present invention has been described according to the specific embodiments above, the inventive concept of the present invention is not limited to this invention. Any modifications that utilize the inventive concept will be included within the scope of patent protection of this patent.

[0036] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a silver-nickel-graphite electrical contact material, characterized in that, Includes the following steps: (1) Nickel-coated graphite powder and silver-coated graphite powder are pre-sintered and crushed and granulated respectively to obtain the processed nickel-coated graphite powder and silver-coated graphite powder. (2) The treated nickel-coated graphite and silver-coated graphite powders are mixed evenly with nickel powder and silver powder according to a certain mass ratio to obtain a mixed powder; (3) The mixed powder is pressed into ingots, sintered, and repressed to obtain ingots; (4) The spindle is extruded into a wire to obtain a silver-nickel graphite electrical contact material.

2. The preparation method according to claim 1, characterized in that, The pre-sintering temperature of the nickel-coated graphite powder is 700℃-800℃.

3. The preparation method according to claim 1, characterized in that, The particle size D50 of the nickel-coated graphite powder after crushing and granulation is 25-35 μm.

4. The preparation method according to claim 1, characterized in that, The mass ratio of nickel to graphite in the nickel-coated graphite powder is 3:2 to 7:

3.

5. The preparation method according to claim 1, characterized in that, The pre-sintering temperature of the silver-coated graphite powder is 500℃-600℃.

6. The preparation method according to claim 1, characterized in that, The particle size D50 of the silver-coated graphite powder after crushing and granulation is 1-20 μm.

7. The preparation method according to claim 1, characterized in that, The mass ratio of silver to graphite in the silver-coated graphite powder is 2:1 to 3:

1.

8. The preparation method according to claim 1, characterized in that, In step (2), the mass fractions of nickel-coated graphite powder, silver-coated graphite powder and nickel powder are greater than 0 to 1 wt%, greater than 0 to 1 wt%, and 7 wt% to 11 wt%, respectively, with the remainder being silver powder.

9. The preparation method according to claim 1, characterized in that, In step (3), the mixed powder is rapidly sintered using a plasma electrical discharge machining (EDM) device at a temperature of 830 ℃-870 ℃.

10. A silver-nickel-graphite electrical contact material prepared by the preparation method described in claims 1-9.

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