Ag-SnO2 contact material and preparation method thereof

Abstract

The invention discloses an Ag-SnO2 contact material and a preparation method thereof, and belongs to the field of electric contact materials. According to the material, the wettability of Ag and SnO2 is improved by adding Ag2MoO4 powder, and the problem of contact resistance increase caused by segregation of SnO2 in a molten pool in the prior art is solved. The preparation method comprises the steps of powder mixing, pressing and sintering, wherein 4-8 wt% of SnO2 powder, 0.5-3 wt% of Ag2MoO4 powder and the balance Ag powder are mixed in the protective atmosphere according to the mass percent, and the particle size of the powder is-300 meshes; a pre-sintered material is formed through two-step pressing including the initial pressure of 0.95-1.05 GPa and the re-pressing pressure of 450-550 MPa; and then under the condition that the vacuum degree is not lower than 6.67 * 10 <-2 > Pa, the temperature is increased to 900-920 DEG C at the speed of 8-12 DEG C / s, and sintering is conducted for 2-4 hours. The low-melting-point characteristic of Ag2MoO4 can coat SnO2 particles in the sintering process, the segregation behavior of SnO2 in a molten pool during service is inhibited, the fusion welding frequency and mass loss are reduced, and the arc erosion resistance is improved. The method has the advantages of being low in equipment requirement, easy and convenient to operate and controllable in cost, and the prepared contact material shows excellent service stability in the low-voltage electrical field.

Description

Technical Field

[0001] The invention belongs to the field of electrical contact materials and preparation methods thereof, and relates to an Ag-SnO2 contact material and a preparation method thereof. Background Art

[0002] Silver-based contacts are widely used in the low-voltage electrical field and are the core components that control the on-off flow of current. Arcing is inevitable during the service life of the contacts. The arc acts on the contact surface, causing melting, evaporation, condensation, oxidation, molten pool solidification, recrystallization, and component redistribution. This leads to a rapid deterioration of the contact surface performance, an increase in defects such as cracks and pores, and in severe cases, contact failure. Due to the low melting point of silver, in order to reduce the damage caused by the thermal effects of the arc on the contact surface, the addition of a high-melting-point phase to silver can effectively improve the contact surface's resistance to arc erosion. Scholars have developed AgCdO contact materials by adding CdO to Ag. These materials exhibit excellent resistance to arc erosion and are known as "universal contacts." However, the "cadmium poisoning" generated during production and use is harmful to the environment and human health.

[0003] Because silver-based contacts often operate in air, oxidation of the various components of the contact material is a significant concern. Ag itself has strong oxidation resistance, while Ag2O is conductive, has poor chemical stability, and easily decomposes at high temperatures, making it less likely to increase resistance. It is generally believed that SnO2 has higher physical and chemical stability and is less susceptible to evaporation and decomposition. Therefore, SnO2 can be stably present in the Ag melt pool, reducing spattering.

[0004] The commonly used Ag-SnO2 contact material in service under certain loads has a thermal effect generated by the arc that melts the contact surface to form a molten pool. The contact welding frequency is high, the welding force is large, the contact quality loss is large, and the arc erosion resistance is poor. Summary of the Invention In order to overcome the above-mentioned shortcomings of the prior art, the object of the present invention is to provide an Ag-SnO2 contact material, by adding Ag2MoO4 powder to improve the arc erosion resistance of the Ag-SnO2 material.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The first object of the present invention is to disclose a method for preparing an Ag-SnO2 contact material, comprising the following steps: Powder mixing: in terms of mass percentage, mix 4~8wt% SnO2 powder, 0.5~3wt% Ag2MoO4 powder and the balance Ag powder evenly under a protective atmosphere; Pressing: Take an appropriate amount of evenly mixed powder and fill it into a mold for pressing to obtain pre-sintered material; Sintering: The pre-sintered material is vacuum sintered to obtain Ag-SnO2 contact material.

[0006] Preferably, in the powder mixing step, the particle sizes of the Ag powder, SnO2 powder and Ag2MoO4 powder are all less than 300 mesh.

[0007] Preferably, in the powder mixing step, a ball mill is used to mix the powder for 1 to 3 hours, and the speed of the ball mill is 450 to 550 r / min.

[0008] Preferably, in the pressing step, the pressing is first performed at a pressure of 0.95 to 1.05 GPa, and then re-pressed at a pressure of 450 to 550 MPa.

[0009] Preferably, in the sintering step, the pre-sintered material is first placed in a vacuum furnace, the vacuum furnace is heated to the sintering temperature at a rate of 8-12°C / s and kept at the temperature, and then cooled with the furnace.

[0010] Further preferably, in the sintering step, the holding time is 2 to 4 hours.

[0011] Further preferably, in the sintering step, the pre-sintering material is sintered at 900-920°C.

[0012] Further preferably, in the sintering step, the vacuum degree of the vacuum furnace is not less than 6.67×10 -2 Pa.

[0013] The second purpose of the present invention is to disclose the Ag-SnO2 contact material prepared by the above preparation method.

[0014] Preferably, the Ag-SnO2 contact material is prepared by sintering 4.5 wt% SnO2 powder, 0.8 wt% Ag2MoO4 powder and 94.7 wt% Ag powder.

[0015] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, the addition of Ag2MoO4, which has a lower melting point, coats SnO2 during the sintering process, improving wettability between Ag and SnO2 and reducing SnO2 segregation in the molten pool. This results in low welding frequency, low welding force, minimal mass loss, and excellent arc erosion resistance. This improves the service performance of the AgSnO2 contact material. This method offers advantages such as low equipment requirements, ease of operation, low production costs, high efficiency, and strong arc erosion resistance.

[0016] The present invention prepares a new Ag-SnO2 contact material by adding 0.5~3 wt% Ag2MoO4 to Ag-SnO2, using a ball mill to mix powder, mold pressing, vacuum sintering and other methods. The novel Ag-SnO2 contact material has the advantages of low equipment requirements, easy operation, low production cost, high efficiency, and strong arc erosion resistance of the prepared Ag-SnO2 contact material. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0018] It should be noted that the terms "comprises" and "has" and any variations thereof in the description and claims of the present invention are intended to cover non-exclusive inclusions. For example, a method comprising a series of steps is not necessarily limited to those steps explicitly listed, but may include other steps not explicitly listed or inherent to these methods.

[0019] The Ag-SnO2 contact material proposed in the present invention is prepared by the following steps: First, Ag powder, SnO2 powder, and Ag2MoO4 powder were mixed in a ball mill under an argon atmosphere for 1-3 hours to achieve uniform mixing. The SnO2 powder was used in an amount of 4-8 wt %, the Ag2MoO4 powder in an amount of 0.5-3 wt %, and the remainder was Ag powder. The particle size of the Ag, SnO2, and Ag2MoO4 powders was all less than 300 mesh. Next, the mixed powders were placed in a mold and compacted at a pressure of 0.95-1.05 GPa, followed by a re-pressing at a pressure of 450-550 MPa to form a 20 mm × L pre-sintered material. The mold was made of 42CrMo steel and consisted of an upper punch, a lower punch, and a middle die. The specific operation process was conventional in the powder metallurgy industry and did not require any special features.

[0020] Then, the pre-sintered material was placed in a vacuum furnace and vacuumed until the pressure in the vacuum furnace was 6.67×10 -2 Pa, and then the vacuum furnace is heated to 900~920 ℃ at a heating rate of 10 ℃ / s, kept warm for 2~4 h, and cooled to room temperature with the furnace to obtain Ag-SnO2 contact material.

[0021] The following is a detailed description with reference to the embodiments: Example 1 The specific steps of this embodiment are as follows: (1) Ag powder, SnO2 powder and Ag2MoO4 powder were mixed in a ball mill. The specific ratio (mass fraction) was 4.5% SnO2 powder, 0.8% Ag2MoO4 powder, and the balance was Ag powder. (2) High-purity argon gas is introduced into the mixer, and the mixing time is 1h±10min; (3) Take an appropriate amount of the mixed material and place it in a mold for pressing at a pressure of 1Gpa±50MPa, and then re-press at a pressure of 500Mpa±50MPa; (4) Place the pressed material in a vacuum sintering furnace and heat it to 900°C at a rate of 10°C / s. The vacuum degree should not be less than 6.67×10 -2 Pa, the holding time is 2h±5min, and the furnace is cooled to room temperature after the holding is completed to prepare the Ag-SnO2 contact material.

[0022] Example 2 The specific steps of this embodiment are as follows: (1) Ag powder, SnO2 powder and Ag2MoO4 powder were placed in a ball mill and mixed. The specific ratio (mass fraction) was 6% SnO2 powder, 1.8% Ag2MoO4 powder, and the balance was Ag powder. (2) High-purity argon gas is introduced into the mixer, and the mixing time is 2h±10min; (3) Take an appropriate amount of the mixed material and place it in a mold for pressing at a pressure of 1Gpa±50MPa, and then re-press at a pressure of 500Mpa±50MPa; (4) Place the pressed material in a vacuum sintering furnace and heat it to 910°C at a rate of 10°C / s. The vacuum degree should not be less than 6.67×10 -2 Pa, the holding time is 3h±5min, and the furnace is cooled to room temperature after the holding is completed to prepare the Ag-SnO2 contact material.

[0023] Example 3 The specific steps of this embodiment are as follows: (1) Ag powder, SnO2 powder and Ag2MoO4 powder were mixed in a ball mill. The specific ratio (mass fraction) was 7.5% SnO2 powder, 2.8% Ag2MoO4 powder, and the balance was Ag powder. (2) High-purity argon gas is introduced into the mixer, and the mixing time is 3h±10min; (3) Take an appropriate amount of the mixed material and place it in a mold for pressing at a pressure of 1 Gpa ± 50 MPa, and then re-press at a pressure of 500 MPa ± 50 MPa; (4) Place the pressed material in a vacuum sintering furnace and heat it to 920°C at a rate of 10°C / s. The vacuum degree should not be less than 6.67×10 -2 Pa, the holding time was 4 h ± 5 min, and the Ag-SnO2 contact material was prepared by cooling the furnace to room temperature after the holding was completed.

[0024] Comparative Example Contact material prepared from Ag-6%SnO2. The Ag-6%SnO2 contact is prepared using powder metallurgy, which differs from the mixing process of the preparation method of the present invention. The mixing process is: ultrasonic dispersion + magnetic stirring. The rest of the process is the same as the present invention.

[0025] The contact materials prepared in the Examples and Comparative Examples were processed into 3.2 x 5 mm diameter specimens and subjected to 10,000 electrical contact tests on an electrical contact testing machine. The test voltage was 36 V and the current was 25 A. The data recorded by the electrical contact testing machine and the weights of several materials before and after the tests are shown in Table 1.

[0026] Table 1 Electrical contact test data of different Ag-SnO2 materials

[0027] According to the test results, the contact welding frequency is low, the welding force is small, the mass loss is small, and the arc erosion resistance is good.

[0028] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing an Ag-SnO2 contact material, characterized in that: The following steps are involved: Mixing powder: in terms of mass percentage, mix 4~8wt% SnO2 powder, 0.5~3wt% Ag2MoO4 powder and the balance Ag powder evenly under a protective atmosphere; Pressing: Take an appropriate amount of evenly mixed powder and fill it into a mold for pressing to obtain pre-sintered material; Sintering: The pre-sintered material is vacuum sintered to obtain Ag-SnO2 contact material.

2. The method for preparing the Ag-SnO2 contact material according to claim 1, characterized in that: In the powder mixing step, the particle sizes of the Ag powder, SnO2 powder and Ag2MoO4 powder are all less than 300 mesh.

3. The method for preparing the Ag-SnO2 contact material according to claim 1, wherein: In the powder mixing step, a ball mill is used to mix the powder for 1 to 3 hours, and the speed of the ball mill is 450 to 550 r / min.

4. The method for preparing the Ag-SnO2 contact material according to claim 1, wherein: In the pressing step, the material is first pressed at a pressure of 0.95 to 1.05 GPa, and then re-pressed at a pressure of 450 to 550 MPa.

5. The method for preparing the Ag-SnO2 contact material according to claim 1, wherein: In the sintering step, the pre-sintered material is first placed in a vacuum furnace, and the vacuum furnace is heated to the sintering temperature at a rate of 8-12°C / s and kept warm, and then cooled with the furnace.

6. The method for preparing the Ag-SnO2 contact material according to claim 5, characterized in that: In the sintering step, the holding time is 2 to 4 hours.

7. The method for preparing the Ag-SnO2 contact material according to claim 5, wherein: In the sintering step, the pre-sintered material is sintered at 900-920°C.

8. The method for preparing the Ag-SnO2 contact material according to claim 5, wherein: In the sintering step, the vacuum degree of the vacuum furnace is not less than 6.67×10 -2 Pa.

9. An Ag-SnO2 contact material prepared by the preparation method according to any one of claims 1 to 8.

10. The Ag-SnO2 contact material according to claim 9, characterized in that It is made by sintering 4.5% SnO2 powder, 0.8% Ag2MoO4 powder and 94.7% Ag powder.

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