Silver tungsten carbide contact material without silver layer on surface and preparation method thereof

Abstract

The application relates to a silver tungsten carbide contact material without a silver layer on the surface and a preparation method thereof, and the preparation method comprises the following steps: S1. configuring aggregate; S2. ball-milling the aggregate obtained in S1 together with an organic solvent to obtain a contact surface spraying material; S3. ball-milling and dispersing silver powder and tungsten carbide powder and additive powder together to obtain uniformly mixed silver tungsten carbide powder; S4. sintering and granulating the silver tungsten carbide powder obtained in S3; S5. pressing the silver tungsten carbide powder obtained in S4 into a framework; S6. high-temperature sintering the silver tungsten carbide framework obtained in S5; S7. dry polishing the silver tungsten carbide framework obtained in S6 together with oxide abrasive; S8. uniformly spraying the contact surface spraying material obtained in S2 on the silver tungsten carbide framework obtained in S7; and S9. high-temperature infiltration of the silver tungsten carbide framework obtained in S8 together with silver sheets to obtain a silver tungsten carbide electric contact material without a silver layer on the surface. The application adopts the infiltration mode to ensure the electric arc burning resistance and mechanical wear resistance of the material and improve the electric life of the material.

Description

Technical Field

[0001] This invention relates to the field of material coatings, specifically to a silver tungsten carbide contact material with no silver layer on its surface and its preparation method. Background Technology

[0002] Due to the high melting point and strong resistance to electro-corrosion of tungsten carbide, and the excellent electrical and thermal conductivity of silver, silver-tungsten carbide materials combine good resistance to electro-corrosion with excellent electrical and thermal conductivity. Therefore, silver-tungsten carbide contact materials are widely used in low-voltage molded case circuit breakers and frame circuit breakers. Contacts, which function to connect, carry, and break current, are the heart of the circuit breaker, and their performance largely determines the performance and operational reliability of the circuit breaker. Therefore, circuit breakers have stringent requirements for contacts, requiring: ① good resistance to arc burn-out, ② high resistance to welding, ③ long mechanical life, and ④ good electrical and thermal conductivity. For silver-tungsten carbide contact materials to meet the requirements of circuit breakers, the following requirements should be met: ① fine and uniformly distributed tungsten carbide particles on the silver matrix, ② high contact density, and ③ low resistivity of the contact material.

[0003] In recent years, the miniaturization of electrical switches has made it impossible for the temperature rise of electrical contacts during operation to meet the requirements of miniaturization, thus necessitating lower contact resistance. Silver tungsten carbide and silver tungsten contacts are commonly used in circuit breakers. Under the same conditions, tungsten carbide is more difficult to oxidize than tungsten, resulting in silver tungsten carbide contacts having better oxidation resistance, weldability, excellent switching performance, and relatively stable contact resistance compared to silver tungsten contacts.

[0004] Currently, silver-tungsten carbide electrical contact materials with a silver content of less than 70 wt% are mainly prepared by melt infiltration, while those with a content greater than 70% are mainly prepared by powder pressing. First, silver-tungsten carbide powder is pressed into a framework, and then silver sheets are attached under the framework and melt-infiltrated at high temperature to obtain the corresponding silver-tungsten carbide contacts. In existing technologies, the surface of silver-tungsten carbide contacts is prone to abnormalities such as silver accumulation, pitting, silver layer fracture, and uneven silver layer thickness, leading to various problems in the use of the electrical contacts, such as poor welding, poor breaking capacity, and poor corrosion resistance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a silver tungsten carbide contact material with no silver layer on the surface and its preparation method.

[0006] The technical solution adopted in this invention is as follows: A method for preparing a silver tungsten carbide contact material with a silver-free surface, comprising the following steps:

[0007] S1. Prepare aggregate, wherein the aggregate is obtained by mixing C powder and inorganic metal oxide powder;

[0008] S2. The aggregate obtained in S1 is ball-milled together with an organic solvent to obtain a coating material for the contact surface;

[0009] S3. Ball mill and disperse the silver powder, tungsten carbide powder, and additive powder together to obtain a uniformly mixed silver-tungsten carbide powder;

[0010] S4. Sinter and granulate the silver tungsten carbide powder obtained in S3;

[0011] S5. Press the silver tungsten carbide powder obtained in S4 into a skeleton;

[0012] S6. The silver tungsten carbide framework obtained in S5 is sintered at high temperature;

[0013] S7. Dry polish the silver tungsten carbide framework obtained in S6 together with oxide abrasive;

[0014] S8. Spray the contact surface coating material obtained in S2 evenly onto the silver tungsten carbide skeleton obtained in S7;

[0015] S9. The silver tungsten carbide skeleton obtained in S8 is melted and infiltrated together with a silver sheet at high temperature to obtain a silver tungsten carbide electrical contact material with no silver layer on the surface.

[0016] Preferably, the inorganic metal oxide powder includes one or more of MgO powder, Al2O3 powder, Cr2O3 powder, and Al2(Si2O5)(OH)4 powder, and the C powder and each inorganic metal oxide powder are mixed in equal proportions. For example, when the inorganic metal oxide powder consists only of Al2O3 powder, the ratio of C powder to Al2O3 powder is 1:1; when the inorganic metal oxide powder includes Al2O3 powder and MgO powder, the ratio of C powder, Al2O3 powder, and MgO powder is 1:1:1. The particle size of C powder is 3-10 μm, the particle size of MgO powder is 45-60 μm, the particle size of Al2O3 powder is 45-60 μm, the particle size of Cr2O3 powder is 45-60 μm, and the particle size of Al2(Si2O5)(OH)4 powder is 3-10 μm.

[0017] Preferably, in step S2, stainless steel balls are used as the milling medium, and the mass ratio of aggregate, organic solvent, and stainless steel balls is 1:4-8:1, the milling time is 0.5-2 hours, and the rotation speed is 10-40 rpm / min.

[0018] Preferably, in step S3, the ball milling time is 2-8 hours.

[0019] Preferably, in step S4, the calcination temperature is 600-900℃ and the calcination time is 2-10h.

[0020] Preferably, in step S6, the sintering temperature is 750-900℃ and the sintering time is 2-10h.

[0021] Preferably, in step S7, the dry polishing rotation speed is 10-60 rpm, the weight ratio of oxide abrasive to skeleton is 1.5-3:1, and the dry polishing time is 5-15 minutes.

[0022] Preferably, in step S8, the spraying material prepared in step S2 is uniformly sprayed onto the side and working surface of the silver tungsten carbide skeleton obtained in step S7.

[0023] A silver tungsten carbide contact material with a silver-free surface prepared by the preparation method described above.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention provides a contact surface coating material obtained by ball milling carbon powder, inorganic non-metallic oxides, and organic solutions in a specific ratio. This material is then applied to the surface of dry-polished silver-tungsten carbide contacts, resulting in a silver-free contact surface that is less prone to defects such as silver buildup, pitting, silver layer breakage, and uneven silver layer thickness. This significantly improves the corrosion resistance of the contacts and is simple to operate. Particularly beneficial for combination switches with poor breaking capacity, this material protects the silver-tungsten carbide contacts, thereby enhancing their breaking capacity.

[0026] Meanwhile, this invention provides a method for preparing silver tungsten carbide electrical contact material by melt infiltration process. The high silver content ensures low and stable contact resistance and even lower volume resistance during electrical contact, which can ensure low and stable contact temperature rise during electrical contact. The melt infiltration method ensures the material's resistance to arc burn-off and mechanical wear, and improves the material's electrical life. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0028] Figure 1 This is a flowchart of the preparation method of the present invention;

[0029] Figure 2 The cross-section of the silver tungsten carbide electrical contact material prepared in Example 1 of the present invention is observed under a 100x metallographic microscope.

[0030] Figure 3 The cross-section of the silver tungsten carbide electrical contact material prepared in Example 2 of this invention is observed under a 100x metallographic microscope. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] A method for preparing a silver tungsten carbide contact material includes the following steps:

[0034] a. Mix Al2O3 powder and C powder in a 1:1 mass ratio to form aggregate;

[0035] b. Prepare C2H6O solution;

[0036] c. Load Al2O3 powder, C powder and C2H6O solution into a ball mill, then add stainless steel balls of equal amount to Al2O3 powder and C powder, and ball mill at 30 rpn / min for 1 hour to obtain the contact surface coating material. The ratio of stainless steel balls, C2H6O solution and aggregate is 1:8:1.

[0037] d. Add 3.24 kg of tungsten carbide additive powder, 1.75 kg of silver powder, and 0.01 kg of additive powder to a powder mixer and stir for 2 hours to obtain uniformly mixed silver tungsten carbide powder.

[0038] e. After releasing the silver tungsten carbide powder prepared in step d, put it into a box and sinter it for later use;

[0039] f. The silver tungsten carbide powder obtained in step e is loaded into a sintering furnace with a reducing atmosphere and sintered at 880°C for 2 hours, held for 2 hours, and cooled for 4 hours.

[0040] g. Add the silver tungsten carbide powder obtained in step f to a sieving machine to make granules. The mesh size of the sieve used is 80 mesh.

[0041] h. Using powder forming equipment, the granulated silver tungsten carbide powder from step g is pressed into a compact;

[0042] i. Place the pressed blank obtained in step h into a sintering furnace under ammonia decomposition atmosphere protection, sinter at 900℃ for 3 hours to complete the skeleton pretreatment.

[0043] j. The compact obtained in step i is loaded into a polishing machine together with oxide abrasive and dry polished at a speed of 35 rpn / min. The mass ratio of oxide abrasive to alloy skeleton is 1.5:1.

[0044] k. Apply the contact surface coating material obtained in step c to the surface of the pressed blank obtained in step j, except for the welding surface, and let it melt and infiltrate for later use.

[0045] l. Place the pressed blank obtained in step k and the silver sheet in a sintering furnace under an ammonia decomposition atmosphere, sinter at 1080℃ for 2 hours, cool and remove from the furnace to obtain silver tungsten carbide contact material.

[0046] Example 2

[0047] A method for preparing a silver tungsten carbide contact material includes the following steps:

[0048] a. Prepare aggregate by mixing C powder, Al2O3 powder, and MgO powder in a mass ratio of 1:1:1;

[0049] b. Prepare C2H6O solution;

[0050] c. Load C powder, Al2O3 powder, MgO powder and C2H6O solution into a ball mill, then add stainless steel balls of equal amount to the aggregate, and ball mill at a speed of 40 rpn / min for 1 hour to obtain the contact surface coating material, wherein the mass ratio of stainless steel balls, C2H6O solution and aggregate is 1:8:1.

[0051] d. Add 3.98 kg of tungsten carbide powder, 1 kg of silver powder, and 0.02 kg of additive powder to a powder mixer and stir for 2 hours;

[0052] e. After releasing the silver tungsten carbide powder prepared in step d, put it into a box and sinter it for later use;

[0053] f. The silver tungsten carbide powder obtained in step e is loaded into a sintering furnace with a reducing atmosphere, sintered at 860℃ for 2 hours, held for 2 hours, and cooled for 4 hours.

[0054] g. Add the silver tungsten carbide powder obtained in step f to a sieving machine to make granules. The mesh size of the sieve used is 60 mesh.

[0055] h. Using powder forming equipment, the granulated silver tungsten carbide powder from step g is pressed into a compact;

[0056] i. Place the silver tungsten carbide compact obtained in step h into a sintering furnace under ammonia decomposition atmosphere protection, and sinter at 880°C for 3 hours to complete the skeleton pretreatment.

[0057] j. The silver tungsten carbide blank obtained in step i is loaded into a polishing machine together with oxide abrasive and dry polished at a speed of 25 rpm / min. The mass ratio of abrasive to alloy skeleton is 2:1.

[0058] k. Apply the silver tungsten carbide blank obtained in step j evenly to the surface of the silver tungsten carbide blank using the contact surface spraying material obtained in step c, except for the welding surface, and let it melt and infiltrate for later use.

[0059] l. Place the silver tungsten carbide compact and silver sheet obtained in step k in a sintering furnace under an ammonia decomposition atmosphere, sinter at 1030℃ for 2 hours, cool and remove from the furnace to obtain silver tungsten carbide contact material.

[0060] Cross sections of the silver-tungsten carbide electrical contact materials obtained in Examples 1 and 2 were observed using a 100x metallographic microscope. The results are as follows: Figure 2 and Figure 3 As shown in the figure, the metallographic structure of the electrical contacts in Examples 1 and 2 is uniform, and the working surface of the contacts is free from quality defects such as silver buildup, pitting, silver layer fracture, and uneven silver layer thickness. Before contact melting and infiltration, oxide abrasives are added, the product is dry-polished, and protective material is sprayed onto the working surface of the contacts. After melting and infiltration, there is no silver layer on the contact surface, and it has strong resistance to welding during the breaking test and electrical life test. Moreover, there is no silver buildup on the sides, and the solder rises less on the sides during welding, ensuring consistent product quality. In contrast, without surface material spraying, the working surface of the silver point has a pure silver layer, and there is silver buildup on the sides. During welding, the solder is prone to rise, and welding is very likely to occur during breaking and electrical life tests, which may lead to safety accidents.

[0061] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method of making a silver tungsten carbide contact material having a surface layer free of silver, characterized in that, The method comprises the following steps: S1. configuring aggregate, which is obtained by mixing C powder and inorganic metal oxide powder; S2. ball milling the aggregate obtained in S1 with organic solvent to obtain contact surface spraying material; S3. ball milling and dispersing silver powder and tungsten carbide powder, additive powder to obtain uniformly mixed silver tungsten carbide powder; S4. sintering and granulating the silver tungsten carbide powder obtained in S3; S5. pressing the silver tungsten carbide powder obtained in S4 into framework; S6. high-temperature sintering the silver tungsten carbide framework obtained in S5; S7. dry polishing the silver tungsten carbide framework obtained in S6 with oxide abrasive; S8. uniformly spraying the contact surface spraying material obtained in S2 on the silver tungsten carbide framework obtained in S7; S9. high-temperature infiltration of the silver tungsten carbide framework obtained in S8 with silver sheet to obtain silver tungsten carbide contact material with no silver layer on the surface; The inorganic metal oxide powder comprises one or more of MgO powder, Al2O3 powder, Cr2O3 powder and Al2(Si2O5)(OH)4 powder, and the C powder and each inorganic metal oxide powder are mixed in equal proportions; The particle size of the C powder is 3-10 μm, the particle size of the MgO powder is 45-60 μm, the particle size of the Al2O3 powder is 45-60 μm, the particle size of the Cr2O3 powder is 45-60 μm, and the particle size of the Al2(Si2O5)(OH)4 powder is 3-10 μm. The mass ratio of the aggregate to the organic solvent is 1:4-8.

2. The method of claim 1, wherein the silver tungsten carbide contact material is prepared without a silver layer on the surface. In S2, the stainless steel ball is used as the ball milling medium, the mass ratio of the aggregate to the stainless steel ball is 1:1, the ball milling time is 0.5-2 h, and the rotation speed is 10-40 rpm / min.

3. The method for preparing a silver-tungsten carbide contact material with a silver-free surface according to claim 1, characterized in that, In S3, the ball milling time is 2-8 h.

4. The method for preparing a silver-tungsten carbide contact material with a silver-free surface according to claim 1, characterized in that, In S4, the powder sintering temperature is 600-900 ℃, and the powder sintering time is 2-10 h.

5. The method for preparing a silver-tungsten carbide contact material with a silver-free surface according to claim 1, characterized in that, In S6, the sintering temperature is 750-900 ℃, and the sintering time is 2-10 h.

6. The method for preparing a silver-tungsten carbide contact material with a silver-free surface according to claim 1, characterized in that, In S7, the dry polishing rotation speed is 10-60 rpm / min, the weight ratio of the oxide abrasive to the framework is 1.5-3:1, and the dry polishing time is 5-15 min.

7. The method for preparing a silver-tungsten carbide contact material with a silver-free surface according to claim 1, characterized in that, In S8, the spraying material prepared in S2 is uniformly sprayed on the side edge and working surface of the silver tungsten carbide framework obtained in S7.

8. A silver tungsten carbide contact material with no silver layer on the surface prepared by the preparation method in any one of claims 1-7.

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