Preparation process of silver tungsten carbide graphite contact material

Abstract

The present invention discloses a preparation process of silver tungsten carbide graphite contact material, comprising the following steps: plasma ball milling of tungsten powder and graphite powder to promote powder microstructure refinement, alloying, active activation, chemical reaction and acceleration of in-situ gas-solid phase reaction, etc., which can greatly improve ball milling efficiency, significantly reduce ball milling pollution, and form a unique structure to significantly improve the performance of the material. Silver-coated graphite powder prepared by a chemical coating process is plasma ball milled, the powder is sintered to form particles, pressed into compacts and placed in a degreasing furnace protected by an ammonia decomposition atmosphere to remove the compact forming agent, the degreased compacts are carbonized under a hydrogen atmosphere, and the carbonized compacts are placed in a sintering furnace protected by an ammonia decomposition atmosphere for sintering, re-pressing and re-firing. The silver tungsten carbide graphite contact material obtained by the preparation method of the present invention has higher metallographic structure uniformity and dispersion, less tissue pore defects, and the product bonding strength and flexural strength are better than those of conventional processes.

Description

Technical Field

[0001] The invention belongs to the technical field of electric contact materials, and particularly relates to a preparation process of a silver tungsten carbide graphite contact material. Background Art

[0002] Electrical contacts are the contact elements of electrical switches, instruments, and meters, primarily responsible for connecting and disconnecting circuits and carrying current. Silver-based electrical contact materials are the most widely used and widely used type of material for making electrical contacts. Silver tungsten carbide graphite is a special electrical contact material that offers advantages such as resistance to arc erosion, welding, and oxidation. However, due to the different melting points and physical properties of its main components, it cannot be manufactured using infiltration or extrusion processes and can only be produced using powder metallurgy. Contacts produced using this method are prone to pores between their metallographic structures, forming numerous silver-rich areas, which results in high overall resistance and reduced electrical conductivity. The large number of voids between the metallographic structures results in low flexural strength for the product, leading to insufficient electrical performance.

[0003] Therefore, the production of silver tungsten carbide graphite products with excellent anti-burning performance has always been a difficult problem in the industry. This problem has also greatly limited the further improvement of the electrical life performance of electrical appliances. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of existing technologies by providing a process for preparing silver tungsten carbide graphite contact materials. Plasma ball milling of tungsten and graphite powders promotes microstructure refinement, alloying, active activation, chemical reactions, and accelerated in-situ gas-solid phase reactions. This significantly improves milling efficiency, significantly reduces milling contamination, and forms a unique structure, significantly enhancing material performance. This process effectively overcomes the shortcomings of conventional ball mills, such as insufficient energy, low milling efficiency, insufficient grinding fineness, inhomogeneous mixing, low alloying degree, and the introduction of impurities. Highly active plasma particles (ions, electrons, excited atoms and molecules, free radicals, etc.) easily adsorb with other substances, increasing the surface activity of the material. The fresh surface and numerous defects introduced by mechanical ball milling further enhance the activity of the milled powder, facilitating diffusion, phase transformation, and chemical reactions. Silver graphite powder prepared by a chemical coating process is then added to the ball mill for uniform mixing. The refined tungsten powder and graphite powder undergo a carbonization reaction to form tungsten carbide. Silver graphite powder and tungsten carbide prepared by chemical coating process are sintered and pressed at high temperature to make finished products; the metallographic structure has higher uniformity and dispersion, less tissue pore defects, and the product bonding strength and flexural strength are better than those of conventional processes.

[0005] The technical solution adopted by the present invention is as follows: A method for preparing a silver tungsten carbide graphite contact material comprises the following steps:

[0006] S1. Add tungsten powder and graphite powder into a plasma ball mill and mill them;

[0007] S2, adding the silver-coated graphite powder prepared by the chemical coating process to the plasma ball mill in step S1, and continuing ball milling to obtain plasma ball milled powder;

[0008] S3, calcining the plasma ball milled powder obtained in step S2 at high temperature to form particles;

[0009] S4, pressing the powder particles obtained in step S3 into compacts;

[0010] S5, carbonizing the compact obtained in step S4 under a hydrogen atmosphere to generate tungsten carbide, thereby obtaining a tungsten carbide compact;

[0011] S6, placing the tungsten carbide compact obtained in step S5 in a hydrogen atmosphere sintering device for sintering to obtain a primary sintered compact;

[0012] S7, pressure shaping the primary sintered compact obtained in step S6 to obtain a shaped compact;

[0013] S8, sintering the shaped compact obtained in step S7 in a hydrogen atmosphere sintering device to obtain a secondary sintered compact;

[0014] S9, re-pressing the secondary sintered compact obtained in step S8 to obtain a silver tungsten carbide graphite contact material.

[0015] Preferably, in step S1, the mass ratio of tungsten powder to graphite powder is 15-15.4:1.

[0016] Preferably, in step S1, the rotation speed of the plasma ball mill is 800-1200 rpm, the discharge voltage is 6-10 kV, the discharge frequency is 20-40 kHz, the ball milling time is 1-10 h, and the ball-to-material ratio is 1-10:1.

[0017] Preferably, in step S2, the rotation speed of the plasma ball mill is 800-1200 rpm, the discharge voltage is 6-8 kV, the discharge frequency is 20-30 kHz, the ball milling time is 10 min-1 h, and the ball-to-material ratio is 1-3:1.

[0018] Preferably, in step S3, the calcining temperature is 600-800° C., the holding time is 1-3 hours, the calcining atmosphere is hydrogen, and the granulation screen has a mesh size of 20-60.

[0019] Preferably, in step S5, the carbonization temperature is 850° C.-920° C., the carbonization atmosphere is hydrogen, and the carbonization time is 6-15 hours.

[0020] Preferably, in step S6, the sintering temperature is 900° C.-940° C., the sintering atmosphere is hydrogen, and the holding time is 4-8 hours.

[0021] Preferably, in step S7, the re-pressing pressure is 6-9T / cm 2 .

[0022] Preferably, in step S8, the secondary sintering temperature is 880° C.-920° C., the sintering atmosphere is hydrogen, and the holding time is 4-8 hours.

[0023] Preferably, in step S9, the pressure is 12-14 T / cm.

[0024] A silver tungsten carbide graphite contact material prepared by the preparation method as described above.

[0025] The beneficial effects of the present invention are as follows:

[0026] The plasma milling of tungsten and graphite powders in this invention promotes microstructure refinement, alloying, active activation, chemical reactions, and accelerated in-situ gas-solid phase reactions. This significantly improves milling efficiency, significantly reduces milling contamination, and forms a unique structure, significantly enhancing material properties. This method effectively overcomes the energy limitations of conventional ball mills, including insufficient milling efficiency, insufficient grinding fineness, inhomogeneous mixing, low alloying, and the introduction of impurities. Highly active plasma particles (ions, electrons, excited atoms and molecules, free radicals, etc.) readily adsorb to other substances, increasing the surface activity of the material. The fresh surface and numerous defects introduced by mechanical milling further enhance the activity of the milled powder, facilitating diffusion, phase transformation, and chemical reactions. Silver-graphite powder prepared by a chemical coating process is then added and mixed uniformly; the refined tungsten and graphite powders undergo a carbonization reaction to form tungsten carbide. Silver graphite powder and tungsten carbide prepared by chemical coating process are sintered and pressed at high temperature to make finished products; the metallographic structure has higher uniformity and dispersion, less tissue pore defects, and the product bonding strength and flexural strength are better than those of conventional processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, other drawings obtained based on these drawings still fall within the scope of the present invention.

[0028] Figure 1 This is the process roadmap of the present invention;

[0029] Figure 2 Comparison of the metallographic structures of AgWC12C3 contact materials prepared by conventional method (a) and preparation method of Example 1 (b);

[0030] Figure 3The metallographic structures of AgWC27C3 contact materials prepared by conventional method (a) and preparation method of Example 2 (b) are compared. DETAILED DESCRIPTION

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

[0032] Example 1

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

[0034] a. Prepare 12 kg of tungsten powder and graphite powder in a mass ratio of 15.2:1;

[0035] b. Add tungsten powder and graphite powder into a plasma ball mill and mill them. The particle size of the tungsten powder is 1 μm. The plasma ball milling parameters are as follows: vibration motor speed 1200 rpm, discharge voltage 10 kV, discharge frequency 40 kHz, milling time 10 h, ball-to-material ratio 5:1.

[0036] c. The silver-coated graphite powder prepared by the chemical coating process was further added into the plasma ball mill. 88 kg of silver-coated graphite powder was chemically prepared by the ratio of silver to graphite at 96.6:3.4. The plasma ball milling parameters were as follows: vibration motor speed 1200 rpm, discharge voltage 7 kV, discharge frequency 30 kHz, ball milling time 1 h, ball-to-material ratio 1:1;

[0037] d. Sinter the plasma ball milled powder to form granules; the sintering temperature is 700°C, the sintering atmosphere is hydrogen, and the holding time is 1.5 hours;

[0038] e. Pressing the powder particles obtained by sintering the powder and the granulated silver powder into compacts;

[0039] f. Carbonizing the compact after removing the forming agent in a hydrogen atmosphere to generate tungsten carbide; carbonization parameters: carbonization temperature 850°C, carbonization atmosphere: hydrogen, carbonization time: 10 hours;

[0040] g. Sinter the compact at high temperature in a hydrogen atmosphere. The sintering parameters are: sintering temperature 930°C, sintering atmosphere hydrogen, and sintering time: 7h.

[0041] h. Press the sintered compact into 8T / cm 2 Plastic surgery;

[0042] i. Sinter the shaped green compact at high temperature in a hydrogen atmosphere. The sintering parameters are: sintering temperature 900°C, sintering atmosphere hydrogen, and sintering time: 7h.

[0043] j. Press the secondary sintered green compact at 12T / cm 2 Re-pressing to obtain AgWC12C3 contact material.

[0044] Figure 2 The figure shows the metallographic structure comparison of the AgWC12C3 contact material prepared by the conventional method and the preparation method of Example 1.

[0045] Table 1 Comparison of properties of AgWC12C3 contact materials prepared by conventional method and the method of the present invention

[0046]

[0047] Example 2

[0048] A method for preparing a silver tungsten carbide graphite contact material comprises the following steps:

[0049] a. Prepare 27 kg of tungsten powder and graphite powder in a mass ratio of 15.3:1;

[0050] b. Add tungsten powder and graphite powder into a plasma ball mill and mill them. The particle size of the tungsten powder is 3 μm. The plasma ball milling parameters are as follows: vibration motor speed 800 rpm, discharge voltage 6 kV, discharge frequency 20 kHz, milling time 1 h, ball-to-material ratio 10:1.

[0051] c. The silver-coated graphite powder prepared by the chemical coating process was further added into the plasma ball mill. 73 kg of silver-coated graphite powder was prepared at a ratio of 95.9:4.1 between silver and graphite. The plasma ball milling parameters were as follows: vibration motor speed 1200 rpm, discharge voltage 6 kV, discharge frequency 20 kHz, ball milling time 1 h, and ball-to-material ratio 3:1;

[0052] d. Sinter the plasma ball milled powder to form granules; the sintering temperature is 800°C, the sintering atmosphere is hydrogen, and the holding time is 2 hours;

[0053] e. Pressing the powder particles obtained by sintering the powder and the granulated silver powder into compacts;

[0054] f. Carbonizing the compact after removing the forming agent in a hydrogen atmosphere to generate tungsten carbide; carbonization parameters: carbonization temperature 920°C, carbonization atmosphere: hydrogen, carbonization time: 10 hours;

[0055] g. Sinter the compact at high temperature in a hydrogen atmosphere. The sintering parameters are: sintering temperature 940°C, sintering atmosphere hydrogen, and sintering time: 7h.

[0056] h. Press the sintered compact at 9T / cm 2 Plastic surgery;

[0057] i. Sinter the shaped green compact at high temperature in a hydrogen atmosphere. The sintering parameters are: sintering temperature 920°C, sintering atmosphere hydrogen, and sintering time: 7 hours.

[0058] j. Press the secondary sintered green compact at 13T / cm2 Re-pressing to obtain AgWC27C3 contact material.

[0059] Figure 3 The figure shows the metallographic structure comparison of AgWC27C3 contact materials prepared by the conventional method and the preparation method of Example 2.

[0060] Table 2 Comparison of properties of AgWC27C3 contact materials prepared by conventional method and the method of the present invention

[0061]

[0062] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for preparing a silver tungsten carbide graphite contact material, characterized in that: The following steps are involved: S1. Add tungsten powder and graphite powder into a plasma ball mill and mill them; S2, adding the silver-coated graphite powder prepared by the chemical coating process to the plasma ball mill in step S1, and continuing ball milling to obtain plasma ball milled powder; S3, calcining the plasma ball milled powder obtained in step S2 at high temperature to form particles; S4, pressing the powder particles obtained in step S3 into compacts; S5, carbonizing the compact obtained in step S4 under a hydrogen atmosphere to generate silver tungsten carbide, thereby obtaining a silver tungsten carbide compact; S6, placing the silver tungsten carbide compact obtained in step S5 in a hydrogen atmosphere sintering device for sintering to obtain a primary sintered compact; S7, pressure shaping the primary sintered compact obtained in step S6 to obtain a shaped compact; S8, sintering the shaped compact obtained in step S7 in a hydrogen atmosphere sintering device to obtain a secondary sintered compact; S9, re-pressing the secondary sintered compact obtained in step S8 to obtain a silver tungsten carbide graphite contact material; In step S1, the mass ratio of tungsten powder to graphite powder is 15-15.4:1; In step S1, the speed of the plasma ball mill is 800-1200 rpm, the discharge voltage is 6-10 kV, the discharge frequency is 20-40 kHz, the ball milling time is 1-10 h, and the ball-to-material ratio is 1-10:1; In step S2, the speed of the plasma ball mill is 800-1200 rpm, the discharge voltage is 6-8 kV, the discharge frequency is 20-30 kHz, the ball milling time is 10 min-1 h, and the ball-to-material ratio is 1-3:1; In the step S3, the calcining temperature is 600-800° C., the holding time is 1-3 hours, the calcining atmosphere is hydrogen, and the granulation screen is 20-60 mesh.

2. The method for preparing the silver tungsten carbide graphite contact material according to claim 1, wherein: In step S5, the carbonization temperature is 850° C.-920° C., the carbonization atmosphere is hydrogen, and the carbonization time is 6-15 hours.

3. The method for preparing the silver tungsten carbide graphite contact material according to claim 1, wherein: In step S6, the sintering temperature is 900° C.-940° C., the sintering atmosphere is hydrogen, and the holding time is 4-8 hours.

4. The method for preparing the silver tungsten carbide graphite contact material according to claim 1, characterized in that: In step S7, the pressure is 6-9T / cm 2 .

5. The method for preparing the silver tungsten carbide graphite contact material according to claim 1, characterized in that: In step S8, the secondary sintering temperature is 880° C.-920° C., the sintering atmosphere is hydrogen, and the holding time is 4-8 hours.

6. The method for preparing the silver tungsten carbide graphite contact material according to claim 1, characterized in that: In step S9, the re-pressing pressure is 12-14T / cm 2 .

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