A fine-grained silver tungsten carbide contact, preparation method and vacuum circuit breaker

Abstract

The present application discloses a fine-grained silver tungsten carbide contact, a preparation method and a vacuum circuit breaker. The method includes: mixing silver powder, tungsten carbide powder and an additive to obtain a mixed material; pressing the mixed material to obtain a silver tungsten carbide contact green blank; sintering the silver tungsten carbide contact green blank to obtain a silver tungsten carbide contact green body; crushing and sieving the silver tungsten carbide contact green body to obtain a silver tungsten carbide contact mixed material; ball-milling the silver tungsten carbide contact mixed material to obtain a silver tungsten carbide contact mixed powder; pressing the silver tungsten carbide contact mixed powder to obtain a silver tungsten carbide contact blank; sintering the silver tungsten carbide contact blank and cooling to obtain an Ag-WC-ZrO2 skeleton; placing an infiltration blank obtained by pressing silver powder on the Ag-WC-ZrO2 skeleton for infiltration to obtain a fine-grained silver tungsten carbide contact. The present application can improve the various properties of the fine-grained silver tungsten carbide contact.

Description

Technical Field

[0001] The present application belongs to the field of material science and technology, and specifically relates to a fine-grained silver tungsten carbide contact, a preparation method and a vacuum circuit breaker. Background Art

[0002] Silver tungsten carbide contact is a special material used in electrical switches and vacuum circuit breakers, which combines the high conductivity of silver with the high hardness and wear resistance of tungsten carbide. However, the existing preparation process of silver tungsten carbide contact is relatively complicated, and because the wettability of silver and tungsten carbide cannot be solved, the silver tungsten carbide contact material often has more pores, which makes the contact material's resistance to arc ablation weak. Summary of the invention

[0003] The main purpose of the present application is to provide a fine-grained silver tungsten carbide contact, a preparation method and a vacuum circuit breaker. The present application can improve the hardness, wear resistance and arc erosion resistance of the tungsten carbide contact.

[0004] To achieve the above objectives, this application provides the following technical solutions:

[0005] A method for preparing a fine-grained silver tungsten carbide contact, the method comprising: mixing silver powder, tungsten carbide powder and an additive to obtain a mixture; pressing the mixture to obtain a silver tungsten carbide contact blank; sintering the silver tungsten carbide contact blank to obtain a silver tungsten carbide contact green blank; crushing and sieving the silver tungsten carbide contact green blank to obtain a silver tungsten carbide contact mixture;

[0006] The silver tungsten carbide contact mixture is ball-milled to obtain a silver tungsten carbide contact mixed powder; the silver tungsten carbide contact mixed powder is pressed to obtain a silver tungsten carbide contact blank; the silver tungsten carbide contact blank is sintered, and after cooling, Ag-WC-ZrO is obtained. 2 The infiltration block obtained by pressing the silver powder is placed in the Ag-WC-ZrO 2 Infiltration is performed on the skeleton to obtain fine-grained silver tungsten carbide contacts.

[0007] Optionally, the additive includes any one of the following: zirconium dioxide, aluminum oxide, silicon carbide and boron nitride.

[0008] Optionally, the mixture is pressed at a pressure of 150 to 180 MPa, and the pressing time is 6 to 10 min.

[0009] Optionally, the silver tungsten carbide contact blank is sintered by gradient heating.

[0010] Optionally, the sintering temperature for sintering the silver tungsten carbide contact blank is 200-1200°C.

[0011] Optionally, the particle size of the silver tungsten carbide contact mixed powder is 0.5-1 μm.

[0012] Optionally, the silver tungsten carbide contact blank is sintered by gradient heating.

[0013] Optionally, the sintering temperature for sintering the silver tungsten carbide contact block is 300-1100°C.

[0014] In addition, the present application also provides a fine-grained silver tungsten carbide contact, which comprises: 15-30% silver powder, 70-80% tungsten carbide powder, and 1-2% additives.

[0015] In addition, the present application also provides a vacuum circuit breaker, which includes a fine-grained silver tungsten carbide contact, and the fine-grained silver tungsten carbide contact is prepared based on the preparation method described in any of the preceding items.

[0016] The technical effects brought by this application are:

[0017] This application successfully solves the wettability problem between silver and tungsten carbide by precisely controlling the powder particle size, pressing parameters and sintering temperature of the mixture, so that the silver liquid can fully penetrate and tightly adhere to the surface of the tungsten carbide particles, forming a uniform, fine and dense microstructure. This optimized preparation method significantly improves the hardness, wear resistance and arc erosion resistance of the contact material, thereby extending the service life of the contact and improving the reliability and performance of electrical switches and circuit breakers. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic flow chart of a method for preparing a fine-grained silver tungsten carbide contact provided by an embodiment of the present application;

[0019] Figure 2 This is a metallographic diagram of a fine-grained silver tungsten carbide contact prepared by the method described in this application;

[0020] Figure 3 This is a metallographic diagram of a fine-grained silver tungsten carbide contact prepared by an existing method. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments 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 creative work are within the scope of protection of the present invention.

[0022] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0023] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0024] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in the field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0025] In an exemplary embodiment, the present application provides a fine-grained silver tungsten carbide contact, the components of the fine-grained silver tungsten carbide contact and the mass percentage of each component are:

[0026] Silver powder (Ag) 15~30%

[0027] Tungsten carbide powder (WC) 70~80%

[0028] Additives 1~2%.

[0029] In another exemplary embodiment, the present application provides a method for preparing a fine-grained silver tungsten carbide contact, such as Figure 1 As shown, the method comprises the following steps:

[0030] S1: A three-dimensional mixer is used to mix 15-30% silver powder (Ag), 70-80% tungsten carbide powder (WC) and 1-2% zirconium dioxide (ZrO 2) to obtain a mixture, wherein the ball-to-material ratio of the three-dimensional mixer is 2:1, the rotation speed is set to 50 Hz, and the powder particle size is controlled between 2 and 8 μm;

[0031] In this step, the powder particle size of the mixture needs to be controlled between 2 and 8 μm because: the powder particle size of 2 to 8 μm helps to achieve the silver powder (Ag), tungsten carbide powder (WC) and zirconium dioxide (ZrO 2 ) to ensure that the microstructure of the fine-grained silver tungsten carbide contact material is more uniform. In addition, the powder particle size in this range helps to improve the wettability between the silver powder and the tungsten carbide powder. During the sintering process, the fine powder is more likely to form a good bonding interface, reduce the generation of pores and defects, and thus improve the density and strength of the material. Furthermore, since the fine powder has a large surface area and high activity, it is more likely to undergo solid-state diffusion and sintering reactions, so the sintering process can be completed at a lower sintering temperature and in a shorter time, saving energy and time.

[0032] S2: using a dry bag cold isostatic press to press the mixture to obtain a silver tungsten carbide contact blank, wherein the pressure of the dry bag cold isostatic press is set to 150 MPa and the pressing time is set to 6 minutes;

[0033] In this step, it has been verified by experiments that a pressure of 150 MPa is the minimum effective pressure, under which the mixture can be ensured to be tightly packed during the pressing process, reducing internal voids and pores, and increasing the density of the compact. If the pressure is less than 150 MPa, it is not enough to make the mixture fully and tightly packed, resulting in more voids and pores inside the compact, which will reduce the density of the material, thereby affecting the thermal conductivity of the material, and further reducing the material's resistance to electrical ablation, making the contact easily damaged when a high current passes through.

[0034] In addition, it has been verified by experiments that the pressing time of 6 minutes is the minimum effective pressing time. Under this pressing time, the mixture can be fully compacted under high pressure to avoid the problems of uneven compaction and inconsistent density caused by insufficient time. If the pressing time is less than 6 minutes, it is not enough to fully rearrange the mixture in the mold. Incomplete rearrangement of particles will lead to insufficient contact between particles and poor bonding force, making the contact easy to break when subjected to impact or fatigue load.

[0035] S3: placing the silver tungsten carbide contact blank in a vacuum furnace for sintering, and obtaining a silver tungsten carbide contact blank after cooling;

[0036] In this step, the present application adopts gradient temperature increase to sinter the silver tungsten carbide contact block, that is, first sintering at 200°C for 100 minutes, then sintering at 500°C for 120 minutes, then sintering at 700°C for 120 minutes, and finally sintering at 1200°C for 180 minutes.

[0037] During the sintering process, the low temperature stage (200°C) is mainly to remove moisture, organic matter and other volatile substances in the silver tungsten carbide contact blank. If these substances are not removed in advance, they will evaporate rapidly at high temperatures, causing pores or cracks to form inside the silver tungsten carbide contact blank, affecting the density and performance of the final contact material.

[0038] The medium temperature stage (500°C and 700°C) helps promote the diffusion and grain growth between the particles inside the silver tungsten carbide contact blank. In this temperature range, the atoms inside the silver tungsten carbide contact blank begin to move actively, gradually filling the gaps between the particles, thereby improving the density of the silver tungsten carbide contact blank. The medium temperature stage also helps to eliminate the tiny pores between the powder particles, further improving the uniformity and density of the material.

[0039] The high temperature stage (1200°C) is the key stage of sintering. At this time, the atomic diffusion rate inside the silver tungsten carbide contact blank is accelerated, the bonding force between the particles is significantly enhanced, and the densification degree of the material reaches the highest. At this temperature, the wettability between silver and tungsten carbide is improved, and the silver liquid can better penetrate into the pores between the tungsten carbide particles, thereby forming a tighter bonding interface.

[0040] It should be noted that the present application adopts gradient heating to sinter the silver tungsten carbide contact blank. First, it can effectively reduce the pores and defects inside the material and improve the density of the material. High density means that the material has better mechanical and electrical properties. Second, by gradually heating up, the growth of the grains can be better controlled to avoid grain coarsening caused by too rapid heating. The fine and uniform grain structure helps to improve the hardness and wear resistance of the material. Third, it helps to improve the wettability between silver and tungsten carbide, so that the silver liquid can better penetrate the pores between the tungsten carbide particles to form a tighter bonding interface, which not only improves the overall performance of the material, but also enhances the material's resistance to arc erosion. Fourth, it can reduce the thermal stress inside the material and prevent cracks or deformation caused by too rapid temperature changes, thereby helping to maintain the integrity and stability of the material.

[0041] It should also be noted that in this step, the sintering of the silver tungsten carbide contact blank at a temperature of 200 to 1200°C has been experimentally verified. If the low temperature stage is less than 200°C, the adsorbed water and organic matter in the silver tungsten carbide contact blank cannot be completely removed. These substances will volatilize rapidly in the subsequent high temperature stage, which will cause pores or cracks to form inside the material, affecting the compactness and performance of the final contact material. In addition, if the temperature is too low, the atomic activity inside the silver tungsten carbide contact blank is insufficient, and it is difficult to effectively promote diffusion and grain growth, resulting in a low degree of material densification and an uneven microstructure. On the contrary, if the high temperature stage is greater than 1200°C, the grains of silver and tungsten carbide will grow excessively, causing the microstructure of the material to become uneven and the grains to be coarse, thereby reducing the hardness and wear resistance of the material.

[0042] S4: crushing the silver tungsten carbide contact green body with a blade crusher, and sieving it with a 200-mesh screen to obtain a silver tungsten carbide contact mixture;

[0043] S5: placing the silver tungsten carbide contact mixture in a ball mill filled with alcohol for ball milling, wherein the ball-to-material ratio of the ball mill is 3:1, the rotation speed is set to 100 Hz, and after ball milling for 72 hours, a silver tungsten carbide contact mixed powder with a particle size of 0.5 to 1 μm is obtained;

[0044] In this step, the silver tungsten carbide contact mixture is ball-milled to a particle size of 0.5 to 1 μm, which helps to achieve a more uniform distribution during the subsequent pressing and sintering process. Fine particles can better fill the voids inside the material, reduce the formation of pores and defects, and thus improve the density of the material. In addition, the fine grain size can improve the hardness and wear resistance of the material. According to the Hall-Petch relationship, the smaller the grain size, the higher the yield strength of the material. Therefore, by controlling the particle size, the hardness and wear resistance of the material can be significantly improved.

[0045] It should be noted that particles that are too small (less than 0.5 μm) have extremely high surface energy, are prone to agglomeration, and are difficult to disperse, which will affect the microstructure and performance of the material. In addition, particles that are too small will also lead to a decrease in the mechanical strength of the material, because particles that are too fine cannot form stable grain boundaries during the sintering process, which will affect the mechanical properties of the material. On the contrary, if the particles are too large, the gaps and defects between the particles will increase, making it difficult to completely fill them during the subsequent pressing and sintering process, resulting in more pores and cracks inside the material, which will affect the density and performance of the material. In addition, the surface area of ​​large particles is relatively small, and it is difficult for the silver liquid to fully penetrate the pores between the tungsten carbide particles during the sintering process, which will result in a loose bond between silver and tungsten carbide, thereby affecting the material's arc erosion resistance and wear resistance.

[0046] In summary, the particle size range of 0.5 to 1 μm is the best choice after comprehensive consideration. Within this range, it can ensure that the final prepared silver tungsten carbide contact material has excellent performance.

[0047] S6: using a hydraulic press to press the silver tungsten carbide contact mixed powder to obtain a silver tungsten carbide contact blank;

[0048] S7: Sintering the silver tungsten carbide contact block in a vacuum furnace, and obtaining Ag-WC-ZrO after cooling. 2 skeleton;

[0049] In this step, the present application adopts gradient temperature increase to sinter the silver tungsten carbide contact block, that is, first sintering at 300°C for 100 minutes, then sintering at 400°C for 120 minutes, then sintering at 600°C for 120 minutes, and finally sintering at 1100°C for 180 minutes.

[0050] During the sintering process, the low temperature stage (300°C) is mainly used to remove adsorbed water, organic matter and other volatile substances in the silver tungsten carbide contact blank. If these substances are not removed at low temperature, they will evaporate rapidly in the subsequent high temperature stage, resulting in pores or cracks inside the silver tungsten carbide contact blank, thereby affecting the density and performance of the final contact material.

[0051] In the first medium temperature stage (400° C.), the atoms inside the silver tungsten carbide contact blank begin to move actively, and the diffusion between the powder particles begins, which helps to initially fill the gaps between the particles and improve the density of the material.

[0052] In the second medium temperature stage (600° C.), the diffusion of atoms and the growth of grains inside the silver tungsten carbide contact blank are accelerated, further reducing the pores between particles, thereby further improving the uniformity and density of the material.

[0053] At high temperature (1100°C), the atomic diffusion rate inside the silver tungsten carbide contact blank is further accelerated, the bonding force between particles is significantly enhanced, and the material densification degree reaches the highest level. At this temperature, the wettability between silver and tungsten carbide is improved, and the silver liquid can better penetrate the pores between tungsten carbide particles to form a tighter bonding interface.

[0054] It should be noted that the present application gradually increases the temperature and sinters the silver tungsten carbide contact block, which can better control the growth of grains and avoid grain coarsening caused by excessive heating. The fine and uniform grain structure helps to improve the hardness and wear resistance of the material. On the other hand, it helps to improve the wettability between silver and tungsten carbide, so that the silver liquid can better penetrate the pores between the tungsten carbide particles to form a tighter bonding interface, which can not only improve the overall performance of the material, but also enhance the material's resistance to arc ablation.

[0055] It should also be noted that in this step, the temperature of 300℃~1100℃ is experimentally verified. If the low temperature stage is lower than 300℃, the adsorbed water and organic matter in the silver tungsten carbide contact blank cannot be completely removed. These substances will volatilize rapidly in the subsequent high temperature stage, which will cause pores or cracks inside the material, affecting the compactness and performance of the final contact material. In addition, if the temperature is too low, first, the atomic activity inside the silver tungsten carbide contact blank will be insufficient, and it will be difficult to effectively promote diffusion and grain growth, which will lead to low densification of the material and uneven microstructure. Second, it will lead to poor wettability between silver and tungsten carbide, making it difficult to form a tight bonding interface, thereby affecting the overall performance of the material. On the contrary, if the temperature is higher than 1100℃, the grains of silver and tungsten carbide will grow excessively, causing the microstructure of the material to become uneven and the grains to be coarse, thereby reducing the hardness and wear resistance of the final contact material. In addition, too high a temperature will also trigger a phase change of the material, causing changes in the physical and chemical properties of the material, thereby affecting the overall performance of the final contact material.

[0056] In summary, the gradient temperature sintering of the silver tungsten carbide contact block at a temperature of 300°C to 1100°C is the optimal temperature range that comprehensively considers factors such as removing volatiles, promoting grain growth and diffusion, and strengthening bonding and densification while ensuring the optimization of material properties.

[0057] S8: Placing the infiltrated compact obtained by pressing the silver powder into the Ag-WC-ZrO 2 The skeleton is infiltrated in an atmosphere furnace at 1250°C for 4 hours to obtain fine-grained silver tungsten carbide contacts.

[0058] In this step, 1250 ℃ is used as the minimum effective temperature for infiltration. At this temperature, the wettability between silver and tungsten carbide is significantly improved, and the silver liquid can better adhere to the surface of the tungsten carbide particles, thereby forming a tighter bond. This good bond helps to improve the mechanical strength and arc erosion resistance of the material. In addition, 1250 ℃ is a balance point, which can not only ensure the good fluidity and sufficient infiltration of the silver liquid, but also will not cause significant coarsening of the tungsten carbide grains. If the temperature is less than 1250 ℃, the fluidity of the silver liquid will be significantly reduced, which will cause the silver liquid to be unable to fully penetrate into the pores of the Ag-WC-ZrO2 skeleton, which will make the bond between silver and tungsten carbide particles loose, thereby affecting the compactness and mechanical strength of the material. In addition, if the temperature is too low, the wettability between silver and tungsten carbide will be poor, the silver liquid will not be well attached to the surface of the tungsten carbide particles, and the bond interface formed will be weak, thereby reducing the overall performance of the material, especially the arc erosion resistance and wear resistance. Furthermore, due to the insufficient fluidity of the silver liquid, the pores between the tungsten carbide particles cannot be fully filled, which will cause more pores and defects in the material. These pores and defects will reduce the density of the material, thereby affecting its mechanical and electrical properties.

[0059] In another exemplary embodiment, the present application also provides a method for preparing a fine-grained silver tungsten carbide contact, the method comprising the following steps:

[0060] S10: A three-dimensional mixer is used to mix 15-30% silver powder (Ag), 70-80% tungsten carbide powder (WC) and 1-2% aluminum oxide (Al 2 O 3 ) to obtain a mixture, wherein the ball-to-material ratio of the three-dimensional mixer is 2:1, the rotation speed is set to 60 Hz, and the powder particle size is controlled between 2 and 8 μm;

[0061] S20: pressing the mixture by a dry bag cold isostatic press to obtain a silver tungsten carbide contact blank, wherein the pressure of the dry bag cold isostatic press is set to 160 MPa and the pressing time is set to 7 min;

[0062] S30: placing the silver tungsten carbide contact blank in a vacuum furnace for sintering, and obtaining a silver tungsten carbide contact blank after cooling;

[0063] In this step, the silver tungsten carbide contact blank is sintered by gradient heating, which will not be described in detail here.

[0064] S40: crushing the silver tungsten carbide contact green body with a blade crusher, and sieving it with a 200-mesh screen to obtain a silver tungsten carbide contact mixture;

[0065] S50: placing the silver tungsten carbide contact mixture in a ball mill filled with alcohol for ball milling, wherein the ball-to-material ratio of the ball mill is 3:1, the rotation speed is set to 100 Hz, and after ball milling for 72 hours, a silver tungsten carbide contact mixed powder with a particle size of 0.5 to 1 μm is obtained;

[0066] S60: using a hydraulic press to press the silver tungsten carbide contact mixed powder to obtain a silver tungsten carbide contact blank;

[0067] S70: Sintering the silver tungsten carbide contact block in a vacuum furnace, and obtaining Ag-WC-Al after cooling. 2 O 3 ,skeleton;

[0068] In this step, the present application also adopts gradient temperature increase to sinter the silver tungsten carbide contact block, which will not be described in detail here.

[0069] S80: Placing the infiltrated compact obtained by pressing the silver powder into the Ag-WC-Al 2 O 3 The skeleton is infiltrated in an atmosphere furnace at 1260°C for 4 hours to obtain fine-grained silver tungsten carbide contacts.

[0070] In another exemplary embodiment, the present application also provides a method for preparing a fine-grained silver tungsten carbide contact, the method comprising the following steps:

[0071] S100: using a three-dimensional mixer to mix 15-30% of silver powder (Ag), 70-80% of tungsten carbide powder (WC) and 1-2% of silicon carbide (SiC) in a mass ratio to obtain a mixture, wherein the ball-to-material ratio of the three-dimensional mixer is 2:1, the rotation speed is set to 80 Hz, and the powder particle size is controlled between 2 and 8 μm;

[0072] S200: pressing the mixture by a dry bag cold isostatic press to obtain a silver tungsten carbide contact blank, wherein the pressure of the dry bag cold isostatic press is set to 170 MPa, and the pressing time is set to 9 minutes;

[0073] S300: placing the silver tungsten carbide contact blank in a vacuum furnace for sintering, and obtaining a silver tungsten carbide contact blank after cooling;

[0074] In this step, the silver tungsten carbide contact blank is sintered by gradient heating, which will not be described in detail here.

[0075] S400: crushing the silver tungsten carbide contact green body with a blade crusher, and sieving it with a 200-mesh screen to obtain a silver tungsten carbide contact mixture;

[0076] S500: placing the silver tungsten carbide contact mixture in a ball mill filled with alcohol for ball milling, wherein the ball-to-material ratio of the ball mill is 3:1, the rotation speed is set to 100 Hz, and after ball milling for 72 hours, a silver tungsten carbide contact mixed powder with a particle size of 0.5 to 1 μm is obtained;

[0077] S600: using a hydraulic press to press the silver tungsten carbide contact mixed powder to obtain a silver tungsten carbide contact blank;

[0078] S700: sintering the silver tungsten carbide contact block in a vacuum furnace, and obtaining an Ag-WC-SiC skeleton after cooling;

[0079] In this step, the present application also adopts gradient temperature increase to sinter the silver tungsten carbide contact block, which will not be described in detail here.

[0080] S800: placing the infiltration compact obtained by pressing the silver powder on the Ag-WC-SiC skeleton, and infiltrating in an atmosphere furnace at a temperature of 1270° C. for 4 hours to obtain a fine-grained silver tungsten carbide contact.

[0081] In another exemplary embodiment, the present application also provides a method for preparing a fine-grained silver tungsten carbide contact, the method comprising the following steps:

[0082] S1000: Using a three-dimensional mixer to mix 15-30% silver powder (Ag), 70-80% tungsten carbide powder (WC) and 1-2% boron nitride (BN) in a mass ratio to obtain a mixture, wherein the ball-to-material ratio of the three-dimensional mixer is 2:1, the rotation speed is set to 100 Hz, and the powder particle size is controlled between 2 and 8 μm;

[0083] S2000: pressing the mixture using a dry bag cold isostatic press to obtain a silver tungsten carbide contact blank, wherein the pressure of the dry bag cold isostatic press is set to 180 MPa and the pressing time is set to 10 min;

[0084] In this step, it has been experimentally verified that the pressure of 180 MPa is the maximum effective pressure. Under this pressure,

[0085] It can ensure that the mixture is more densely packed during the pressing process, further reduce internal voids and pores, and increase the density of the block. In addition, the pressure of 180 MPa can also enhance the bonding force between powder particles, reduce the voids between particles, make the contact between particles closer, and help improve the mechanical strength and durability of the material. If the pressure is greater than 180 MPa, firstly, it will cause the powder particles to break and produce fine fragments, thus affecting the microstructure and performance of the material; secondly, excessive pressure will damage the mold and increase maintenance and replacement costs.

[0086] In addition, it has been verified experimentally that the pressing time of 10 minutes is the maximum effective pressing time. Under this pressing time, firstly, it can ensure that the mixture is fully compacted to avoid the problems of uneven compaction and inconsistent density caused by insufficient time. Secondly, it allows the powder particles to be better rearranged in the mold to further improve the compactness and uniformity of the powder. If the pressing time is greater than 10 minutes, firstly, it will cause the shape of the powder particles to change, affecting the microstructure and performance of the material; secondly, it will change the binding force between the particles, thereby affecting the overall performance of the material.

[0087] S3000: placing the silver tungsten carbide contact blank in a vacuum furnace for sintering, and obtaining a silver tungsten carbide contact green body after cooling;

[0088] In this step, the silver tungsten carbide contact blank is sintered by gradient heating, which will not be described in detail here.

[0089] S4000: crushing the silver tungsten carbide contact green body with a blade crusher, and sieving it with a 200-mesh screen to obtain a silver tungsten carbide contact mixture;

[0090] S5000: placing the silver tungsten carbide contact mixture in a ball mill filled with alcohol for ball milling, wherein the ball-to-material ratio of the ball mill is 3:1, the rotation speed is set to 100 Hz, and after ball milling for 72 hours, a silver tungsten carbide contact mixed powder with a particle size of 0.5 to 1 μm is obtained;

[0091] S6000: using a hydraulic press to press the silver tungsten carbide contact mixed powder to obtain a silver tungsten carbide contact blank;

[0092] S7000: sintering the silver tungsten carbide contact block in a vacuum furnace, and obtaining an Ag-WC-BN skeleton after cooling;

[0093] In this step, the silver tungsten carbide contact block is sintered by gradient heating, which will not be described in detail here.

[0094] S8000: placing the infiltration block obtained by pressing the silver powder on the Ag-WC-BN skeleton, and infiltrating in an atmosphere furnace at a temperature of 1300° C. for 4 hours to obtain a fine-grained silver tungsten carbide contact.

[0095] In this step, 1300℃ is the maximum effective temperature for infiltration, which is enough to melt the silver powder, so that it can fully penetrate into the pores of the Ag-WC-BN skeleton to form a tight bonding interface. The melting point of silver is about 962℃, so 1300℃ can ensure good fluidity of the silver liquid, help the silver liquid penetrate into the tiny pores between the tungsten carbide particles, and improve the density of the material.

[0096] It should be noted that if the temperature exceeds 1300°C, the grains of silver and tungsten carbide will grow excessively, causing the microstructure of the material to become uneven, and the coarse grains will reduce the hardness and wear resistance of the material, thereby affecting the service life and performance of the contact material. In addition, excessively high temperatures may trigger phase changes in the material, causing changes in the physical and chemical properties of silver and tungsten carbide. For example, the silver liquid may decompose or react with other components to form undesirable compounds, affecting the overall performance of the material.

[0097] In the above embodiment, the zirconium dioxide (ZrO 2 )、Alumina(Al 2 O 3 )、

[0098] Among silicon carbide (SiC) and boron nitride (BN), the present application uses silicon carbide (SiC) as the most preferred material for the following reasons: First, the Mohs hardness of silicon carbide (SiC) is about 9.5, second only to diamond, and much higher than alumina (hardness 9), zirconium dioxide (hardness 8.5) and boron nitride (hardness 2-3). High hardness means that the material is not easy to wear during long-term use and can maintain a long service life. Secondly, silicon carbide (SiC) has extremely high wear resistance and can maintain surface integrity under high stress and high-speed sliding conditions, which is particularly important for fine-grained silver tungsten carbide contacts because the contacts are often affected by high current and mechanical shock during the switching process. In addition, the addition of silicon carbide (SiC) can refine the grains of the silver tungsten carbide composite material, making its microstructure more uniform and dense, thereby reducing the generation of wear and cracks. Secondly, compared with other additives, silicon carbide (SiC) has the best thermal conductivity, which can quickly conduct heat and reduce local overheating, thereby improving the ablation resistance of fine-grained silver tungsten carbide contacts.

[0099] In the above embodiment, within the infiltration temperature range of 1250-1300°C, it has been experimentally verified that 1270°C can be used as the optimal infiltration temperature. At this temperature, the silver liquid has very good fluidity and can quickly and fully penetrate into the pores of the Ag-WC-ZrO2 skeleton, maximizing the infiltration efficiency. In addition, at this temperature, the wettability between silver and tungsten carbide is significantly improved, and the bonding interface formed is very tight, which helps to improve the mechanical strength and arc erosion resistance of the material. Compared with 1250°C and 1260°C, 1270°C can achieve the ideal infiltration effect faster and improve production efficiency. Although the infiltration effect of 1300°C is better than that of 1270°C, due to the slightly higher temperature, it is easy to cause grain coarsening, which will affect the hardness and wear resistance of the contact.

[0100] Figure 2 This is a metallographic diagram of a fine-grained silver tungsten carbide contact prepared by the method described in this application. Figure 2 In the 1000 times magnification, it can be observed that the particle size of WC (tungsten carbide) particles is very small and evenly distributed, with a particle size range of about 0.5 to 2 μm. This fine distribution of WC particles not only improves the hardness and wear resistance of the material, but also reduces the presence of pores and defects due to the close arrangement between particles, thereby significantly improving the arc ablation resistance of fine-grained silver tungsten carbide contacts.

[0101] Further observation Figure 2 It can also be found that a good bonding interface is formed between the silver (Ag) matrix and the WC particles, which indicates that the preparation method described in this application successfully solves the wettability problem between silver and tungsten carbide, allowing the two to be closely combined to jointly withstand external loads and arc ablation. This good bonding state helps to further improve the overall performance and stability of fine-grained silver tungsten carbide contacts.

[0102] Figure 3 This is a metallographic diagram of a fine-grained silver tungsten carbide contact prepared by an existing method. Figure 3 In the 500-fold magnification, it can be clearly seen that the WC particles are larger and unevenly distributed, with a particle size range of about 5 to 20 μm. Such larger WC particles not only reduce the hardness and wear resistance of silver tungsten carbide, but also easily form pores and defects due to the large gaps between particles, thereby reducing the arc erosion resistance of fine-grained silver tungsten carbide.

[0103] In addition, observation Figure 3 It can also be found that the bonding interface between the silver matrix and the WC particles is not tight enough, and there is an obvious interface separation phenomenon. This shows that the existing method fails to effectively solve the wettability problem between silver and tungsten carbide during the preparation process, resulting in weak bonding between the two. This weak bonding state will further affect the overall performance and stability of fine-grained silver tungsten carbide.

[0104] In summary, by comparison Figure 2 and Figure 3 It can be clearly seen that the fine-grained silver tungsten carbide contact prepared by the method described in this application has significant advantages in microstructure. The fine WC particle distribution, tight bonding interface and good wettability solution together make the fine-grained silver tungsten carbide contact show more excellent performance in terms of wear resistance and arc ablation resistance. Therefore, the preparation method described in this application has broad application prospects and important practical significance.

[0105] Furthermore, the present application also performs performance testing and comparison on the fine-grained silver tungsten carbide contact prepared by the present method and the fine-grained silver tungsten carbide contact prepared by the existing process. The comparison results are shown in Table 1:

[0106] Table 1

[0107]

[0108] As can be seen from Table 1, the fine-grained silver tungsten carbide contact prepared by this method has a higher hardness of 1000-1200 HV, while the hardness of the contact material prepared by the existing process is only 800-900 HV; the contact material prepared by this method has a lower wear rate, a smaller friction coefficient, and stronger wear resistance; arc erosion resistance: the contact material prepared by this method performs better in the arc erosion test, with a smaller ablation depth and area, and stronger arc erosion resistance; the contact material prepared by this method has a lower resistivity, higher conductivity, and better conductive performance. These advantages make the fine-grained silver tungsten carbide contact prepared by this method more suitable for high-performance electrical switches and circuit breakers.

[0109] Based on the above embodiments, the present application further provides a vacuum circuit breaker, wherein the vacuum circuit breaker comprises a fine-grained silver tungsten carbide contact, and the fine-grained silver tungsten carbide contact is prepared by the preparation method described in any of the above embodiments.

[0110] From Table 1, it can be seen that the fine-grained silver tungsten carbide contacts prepared by the preparation method described in the present application are superior to the fine-grained silver tungsten carbide contacts prepared by the existing process in terms of hardness, wear resistance, arc erosion resistance and conductivity. Therefore, under high-frequency switching and high-current environments, the fine-grained silver tungsten carbide contacts with high performance prepared by the preparation method described in the present application are applied to vacuum circuit breakers, which can significantly improve the service life, reliability and safety of the circuit breakers.

[0111] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a fine-grained silver tungsten carbide contact, characterized in that: The method comprises: Silver powder, tungsten carbide powder and additives are mixed to obtain a mixture, wherein the additives include zirconium dioxide, and the powder particle size is controlled between 2 and 8 μm; Pressing the mixed material to obtain a silver tungsten carbide contact blank; The silver tungsten carbide contact blank is sintered by gradient heating to obtain a silver tungsten carbide contact blank, wherein the gradient heating includes: sintering at 200° C. for 100 min, then sintering at 500° C. for 120 min, then sintering at 700° C. for 120 min, and finally sintering at 1200° C. for 180 min; Crushing and screening the silver tungsten carbide contact green body to obtain a silver tungsten carbide contact mixture; Ball milling the silver tungsten carbide contact mixture to obtain a silver tungsten carbide contact mixed powder with a particle size of 0.5 to 1 μm; Compressing the silver tungsten carbide contact mixed powder to obtain a silver tungsten carbide contact blank; The silver tungsten carbide contact block is subjected to gradient sintering to obtain an Ag-WC-ZrO2 skeleton after cooling, wherein the silver tungsten carbide contact block is first sintered at a temperature of 300°C for 100 minutes, then sintered at a temperature of 400°C for 120 minutes, then sintered at a temperature of 600°C for 120 minutes, and finally sintered at a temperature of 1100°C for 180 minutes; The infiltration compact obtained by pressing silver powder is placed on the Ag-WC-ZrO2 skeleton and infiltrated in an atmosphere furnace at 1250°C to 1300°C to obtain a fine-grained silver tungsten carbide contact.

2. The method for preparing a fine-grained silver tungsten carbide contact according to claim 1, characterized in that: The pressure for pressing the mixture is 150-180 MPa, and the pressing time is 6-10 minutes.

3. The method for preparing a fine-grained silver tungsten carbide contact according to claim 1, characterized in that: The sintering temperature for sintering the silver tungsten carbide contact blank is 200-1200°C.

4. The method for preparing a fine-grained silver tungsten carbide contact according to claim 1, characterized in that: The sintering temperature for sintering the silver tungsten carbide contact blank is 300-1100°C.

5. A fine-grained silver tungsten carbide contact prepared by the method of claim 1, characterized in that: The fine-grained silver tungsten carbide contact comprises: Silver powder 15~30% Tungsten carbide powder 70~80% Additives 1~2%.

6. A vacuum circuit breaker, characterized in that: The vacuum circuit breaker comprises a fine-grained silver tungsten carbide contact, and the fine-grained silver tungsten carbide contact is prepared based on the preparation method according to any one of claims 1 to 4.

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