Electrical contact material based on plasma cold hearth melting (PCHM) method and manufacturing method therefor

Abstract

The present disclosure belongs to the field of electrical material manufacturing, and particularly relates to an electrical contact material and a method for manufacturing the electrical contact material based on plasma cold hearth melting (PCHM). The method includes the following steps: melting a Ag ingot, a Sn ingot, and an additive through PCHM to produce an alloy melt; casting the uniformly melted alloy melt into a AgSn alloy ingot; molding the AgSn alloy ingot into a wire material through hot extrusion; drawing, cutting, oxidizing, and pressing into a billet; sintering, and extruding to produce a AgSnO2 finished wire material; and processing the finished wire material into a rivet contact through cold heading. In the present disclosure, the melting through PCHM can ensure that alloy components with different vapor pressures undergo negligible arc erosion during the melting, and can eliminate defects such as pores and material segregation in the conventional metallurgy. The electrical contact material manufactured accordingly exhibits superior workability, and possesses enhanced electrical endurance under alternating current or direct current conditions.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the field of electrical material manufacturing, and particularly relates to an electrical contact material and a method for manufacturing electrical contact material based on plasma cold hearth melting (PCHM).BACKGROUND TECHNOLOGY

[0002] Silver tin oxide is a silver-based electrical contact material. Silver tin oxide demonstrates excellent electrical performance under large currents and various complex loads due to the incorporation of second phase or multi-phase reinforcement. Through the efforts of academic researchers and industry engineers, electrical contact materials with strong welding resistance and arc erosion resistance have been developed. These electrical contact materials have been extensively used in various relays. The current methods for producing AgSnO 2 mainly include the alloy internal oxidation method, the atomization method, and the powder metallurgy method. However, electrical contact materials manufactured by the internal oxidation method have defects such as pore formation and material segregation, which lead to breakage and oxide aggregation during the subsequent wire processing or internal oxidation and increase the production cost. Furthermore, when such electrical contact materials are fabricated into rivet contacts, the adhesion phenomenon will occur to ultimately cause the failure of relays, which significantly affects the reliability of electrical equipment.

[0003] Through the relevant document retrieval, the following patent document on the preparation of silver tin oxide material is retrieved: The patent CN115662810A discloses a manufacturing method of a silver tin oxide wire for a rivet contact. In this patent, the bidirectional hot-pressing process is adopted to significantly enhance the compactness of an ingot, such that the finished wire product has a nearly full density and exhibits improved plastic deformation performance during processing. This patent can avoid the abnormal cracking during the subsequent rivet fabrication due to poor compactness of a material. Moreover, in this patent, a low-hardness pure silver coating is formed on a surface of an ingot through spraying. This coating can prevent the direct contact of a high-hardness silver tin oxide layer with an extrusion liner, an extrusion die, an extrusion nozzle, a drawing die, and an annealing fixture during hot extrusion, hot drawing, and annealing processes, thereby remarkably improving the surface quality of the finished wire product and mitigating the abnormal cracking in rivet fabrication. However, this patent still fails to address problems such as voids, structural porosity, and component segregation in electrical contact materials.

[0004] In the conventional process for producing silver tin oxide materials, due to problems such as component segregation in AgSn multi-component alloys and pores in ingots during smelting, materials produced accordingly have disadvantages such as low density, oxide aggregation, and poor workability. As a result, mass production cannot be achieved, and the final electrical products exhibit poor electrical endurance. Consequently, the existing process for manufacturing electrical contact materials still needs to be improved.CONTENT OF THE INVENTION

[0005] An objective of the present disclosure is to overcome the shortcomings and deficiencies of the prior art and provide an electrical contact material and a method for manufacturing the electrical contact material based on PCHM.

[0006] The present disclosure adopts the following technical solutions: A method for manufacturing an electrical contact material based on PCHM is provided, including the following steps: (1) production of an alloy ingot by the PCHM: according to a formula for a AgSn alloy, adding a silver plate, a tin ingot, and an additive to a crucible; introducing a He gas as an energizing gas, and starting a plasma gun for melting; setting a vacuum degree in a melting zone to 10 -1< Pa to 10 -3< Pa and an initial current of the plasma gun to 300 A to 400 A; after the plasma gun enters the melting zone, raising the current to 500 A to 600 A; allowing an alloy melt to flow into a mold; and pulling an ingot out by an ingot migration mechanism to produce a AgSn alloy ingot, where a cold hearth is made of a copper water-cooling material, and a cold hearth is made of a copper water-cooling material; the cold hearth is divided into the melting zone and a refining zone, and a melt flows through the melting zone and the refining zone sequentially, such that a period during which a metal is kept at a liquid state is extended; (2) AgSn extrusion: molding the AgSn ingot obtained in the step (1) into a wire material by an extruder; (3) AgSn alloy drawing and cutting: drawing the wire material obtained in the step (2) through cold working, and cutting; (4) internal oxidation and pellet production: placing a cut AgSn wire material obtained in the step (3) in an internal oxidation furnace, introducing oxygen, and making the wire material undergo a tumbling motion in a furnace chamber to guarantee uniform oxidation, such that an oxidized material is produced; and molding the oxidized material into a cylindrical billet using a hydraulic press; (5) sintering and AgSnO 2 extrusion: sintering the cylindrical billet obtained in the step (4) in a sintering furnace, and molding the cylindrical billet into a AgSnO 2 wire material through hot extrusion; and (6) processing the AgSnO 2 wire material into a finished product, and molding the finished product into an electrical contact rivet through cold heading.

[0007] Preferably, weight percentages of the silver plate, the tin ingot, and the additive are as follows: Ag: 85% to 92%, Sn: 7.5% to 13%, and the additive: 0.5% to 2%.

[0008] Preferably, the additive is one or more of indium, bismuth, copper, and a rare-earth element.

[0009] Preferably, in the step (3), the wire material obtained in the step (2) is drawn through the cold working to ϕ 1.0 mm to 3.0 mm, and cut to a length of 30 mm to 40 mm.

[0010] Preferably, in the step (4), the furnace chamber of the internal oxidation furnace is connected to a rotary driving device, and the rotary driving device is configured to drive the furnace chamber to rotate, such that the wire material undergoes the tumbling motion in the furnace chamber.

[0011] Preferably, in the step (4), a pressure of the oxygen is 0.5 MPa to 1.5 MPa, an oxidation temperature is 700°C to 800°C, and an oxidation time is 20 h to 40 h.

[0012] Preferably, in the step (5), the sintering is conducted at a temperature of 700°C to 900°C with a heat-preservation time of 2 h to 12 h.

[0013] A silver tin oxide electrical contact material manufactured by the method for manufacturing an electrical contact material based on PCHM described above is provided.

[0014] PCHM is an advanced metal melting and refining technology. In the PCHM technology, a high-temperature plasma arc generated by a plasma torch is adopted as a heat source to melt metal raw materials in a cold hearth. During this process, metal raw materials are gradually melted, and flow and are mixed in the cold hearth, thereby achieving the separation and removal of impurities. Currently, PCHM is primarily used to manufacture high-quality titanium alloys for aerospace and medical applications and special metal materials for nuclear reactors.

[0015] The present disclosure applies the PCHM technology to the field of electrical material manufacturing for the first time. With a plasma arc resulting from the ionization of an inert gas as a heat source, the melting can be completed in a wide pressure range from low vacuum to nearly atmospheric pressure. As a result, alloy components with different vapor pressures can undergo negligible arc erosion during the melting. It has been found that there is no component segregation in the prepared AgSn alloy, there are no pores in the ingot, and there is a low impurity content. A material oxidized in this process includes few internal agglomerates, and exhibits a larger density than a material produced by the existing process. During the processing of a wire material, there are no issues such as breakage. The rivet contact finally produced has a large density, and possesses excellent electrical endurance under alternating current or direct current conditions. Furthermore, the produced electrical contact material has a service life of 120,000 times or more under specified current conditions, and demonstrates strong welding resistance and arc erosion resistance.DESCRIPTION OF THE DRAWINGS

[0016] In order to clearly illustrate the technical solutions in the embodiments of the present disclosure or in the prior art, the accompanying drawings required for describing the embodiments or the prior art will be briefly described below. Apparently, the accompanying drawings in the following description are only some embodiments of the present disclosure. Other accompanying drawings obtained by those of ordinary skill in the art according to these accompanying drawings without creative efforts still fall within the scope of the present disclosure. FIG. 1 is a metallographic image of an oxidized sample in Example 1; and FIG. 2 is a metallographic image of an oxidized sample in Comparative Example 1. SPECIFIC IMPLEMENTATIONS

[0017] In order to make the objectives, technical solutions, and advantages of the present disclosure clear, the present disclosure will be further described in detail below with reference to the accompanying drawings.

[0018] A method for manufacturing an electrical contact material based on PCHM was provided, including the following steps: (1) Production of an AgSn alloy by the PCHM: According to a formula for a AgSn alloy, a silver plate, a tin ingot, an indium ingot, and other raw materials were added to a crucible. A He gas was introduced as an energizing gas, and a plasma gun was started for melting. A vacuum degree in a melting zone was set to 10 -3< Pa and an initial current of the plasma gun was set to 320 A. After the plasma gun entered the melting zone, the current was raisen to 530 A. An alloy melt was allowed to flow into a mold. An ingot was pulled out by an ingot migration mechanism to produce the AgSn alloy ingot. A cold hearth was made of a copper water-cooling material. The cold hearth was divided into the melting zone and a refining zone (specifically, the melting zone and the refining zone were constituted by two water-cooling copper crucibles, respectively). A melt flowed through the melting zone and the refining zone sequentially, such that a period during which a metal was kept at a liquid state was extended. (2) AgSn extrusion: The AgSn ingot obtained in the step (1) was molded into a wire material of ϕ 8 mm by an extruder with an extrusion temperature of 750°C and an extrusion rate of 4 mm / s. (3) AgSn alloy drawing and cutting: The wire material of ϕ 8 mm obtained in the step (2) was drawn through cold working to ϕ 2 mm, and cut to a length of 30 mm. (4) Internal oxidation and pellet production: A cut AgSn wire material obtained in the step (3) was placed in a self-made internal oxidation furnace. Oxygen was introduced at 1.5 MPa to allow oxidation at 700°C for 30 h. During the oxidation, a rotary device in a furnace chamber of the internal oxidation furnace was started to make the wire material undergo a tumbling motion in the furnace chamber to guarantee uniform oxidation, such that an oxidized material was produced. The oxidized material was molded into a cylindrical billet for later use using a hydraulic press. (5) Sintering and AgSnO 2 extrusion: The cylindrical billet obtained in the step (4) was sintered in a sintering furnace at 700°C with a heat-preservation time of 10 h. The cylindrical billet was molded into a AgSnO 2 wire material of ϕ 6.0 mm through hot extrusion.

[0019] The AgSnO 2 wire material was processed into a finished product of ϕ 1.2 mm. The finished product was molded into an electrical contact rivet through cold heading.

[0020] In the step (4), a metallographic image of the oxidized material was shown in FIG. 1. It can be seen that there are no problems such as segregation and pores in this example.Example 2

[0021] This example was different from Example 1 in the different feeding amounts of the raw materials. Specifically, a formula per 10 kg of the product was as follows: Ag: 89 wt.%, SnO 2 : 9 wt.%, and the additive: 2 wt%.Example 3

[0022] This example was different from Examples 1 and 2 in the different feeding amounts of the raw materials. Specifically, a formula per 10 kg of the product was as follows: Ag: 91 wt.%, SnO 2 : 8 wt.%, and the additive: 1 wt%.Comparative Example

[0023] A AgSnO 2 electrical contact rivet was manufactured by the conventional internal oxidation method, with the same formula as in Example 1.

[0024] A metallographic image of an oxidized material produced after the internal oxidation was shown in FIG. 2.

[0025] The AgSnO 2 / Cu rivet contacts produced by the above methods were each subjected to a simulated electrical performance test. Specifications for the rivets were as follows: moving Contact: R4.2 x 1.5 (0.5) + 2.6 x 1.2 SR 15, and stationary contact: F4.2 x 1.5 (0.5) + 2.6 x 1.2. The simulated electrical performance test was conducted under the following conditions: 250 V AC, 15 A: closing force: 75 g, breaking force: 45 g, and contact frequency: 30 times / min; and 12 V DC, 5 A: closing force: 75 g, breaking force: 45 g, and contact frequency: 30 times / min. Test results were shown in Table 1. Table 1 Parameter settings and test results for the different examples and the comparative exampleExampleDirect current (12 V DC, 5 A)Alternating current (250 V AC, 15 A)Contact resistance (mΩ)Electrical endurance (times)Contact resistance (mΩ)Electrical endurance (times)Example 10.411254690.42136589Example 20.391362540.41129856Example 30.421324510.42134576Comparative Example0.461023360.4798648

[0026] The above are merely preferred examples of the present disclosure, and are not intended to limit the claimed scope of the present disclosure. Therefore, equivalent changes made according to the claims of the present disclosure are still within the scope of the present disclosure.

Claims

1. A method for manufacturing an electrical contact material based on plasma cold hearth melting (PCHM), comprising the following steps: (1) production of an alloy ingot by the PCHM: according to a formula for a AgSn alloy, adding a silver plate, a tin ingot, and an additive to a crucible; introducing a He gas as an energizing gas, and starting a plasma gun for melting; setting a vacuum degree in a melting zone to 10-1 Pa to 10-3 Pa and an initial current of the plasma gun to 300 A to 400 A; after the plasma gun enters the melting zone, raising the current to 500 A to 600 A; allowing an alloy melt to flow into a mold; and pulling an ingot out by an ingot migration mechanism to produce a AgSn alloy ingot, wherein a cold hearth is made of a copper water-cooling material; the cold hearth is divided into the melting zone and a refining zone, and a melt flows through the melting zone and the refining zone sequentially; (2) AgSn extrusion: molding the AgSn ingot obtained in the step (1) into a wire material by an extruder; (3) AgSn alloy drawing and cutting: drawing the wire material obtained in the step (2) through cold working, and cutting; (4) internal oxidation and pellet production: placing a cut AgSn wire material obtained in the step (3) in an internal oxidation furnace, introducing oxygen, and making the wire material undergo a tumbling motion in a furnace chamber to guarantee uniform oxidation, such that an oxidized material is produced; and molding the oxidized material into a cylindrical billet using a hydraulic press; (5) sintering and AgSnO2 extrusion: sintering the cylindrical billet obtained in the step (4) in a sintering furnace, and molding into a AgSnO2 wire material through hot extrusion; and (6) processing the AgSnO2 wire material into a finished product, and molding the finished product into an electrical contact rivet through cold heading.

2. The method for manufacturing the electrical contact material based on the PCHM according to claim 1, wherein weight percentages of the silver plate, the tin ingot, and the additive are as follows: Ag: 85% to 92%, Sn: 7.5% to 13%, and the additive: 0.5% to 2%.

3. The method for manufacturing the electrical contact material based on the PCHM according to claim 2, wherein the additive is one or more of indium, bismuth, copper, and a rare-earth element.

4. The method for manufacturing the electrical contact material based on the PCHM according to claim 1, wherein in the step (3), the wire material obtained in the step (2) is drawn through the cold working to ϕ 1.0 mm to 3.0 mm, and cut to a length of 30 mm to 40 mm.

5. The method for manufacturing the electrical contact material based on the PCHM according to claim 1, wherein in the step (4), the furnace chamber of the internal oxidation furnace is connected to a rotary driving device, and the rotary driving device is configured to drive the furnace chamber to rotate, such that the wire material undergoes the tumbling motion in the furnace chamber.

6. The method for manufacturing the electrical contact material based on the PCHM according to claim 1, wherein in the step (4), a pressure of the oxygen is 0.5 MPa to 1.5 MPa, an oxidation temperature is 700°C to 800°C, and an oxidation time is 20 h to 40 h.

7. The method for manufacturing the electrical contact material based on the PCHM according to claim 1, wherein in the step (5), the sintering is conducted at a temperature of 700°C to 900°C with a heat-preservation time of 2 h to 12 h.

8. A silver tin oxide electrical contact material manufactured by the method for manufacturing the electrical contact material based on the PCHM according to any one of claims 1 to 7.

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