Silver tungsten carbide graphite contact and preparation method thereof

Abstract

The invention relates to the technical field of contact materials, and particularly discloses a silver tungsten carbide graphite contact and a preparation method thereof. Comprising the following steps of powder reduction, powder mixing, ball milling, powder mixing, high-temperature pre-sintering granulation, framework pre-pressing forming, framework sintering and silver reverse osmosis, welding flux pre-embedding, detection and packaging shipment, specifically, Ag powder WCC / Ni powder is pre-pressed to form a framework, then Ag is added for the second time, and framework sintering and silver reverse osmosis are conducted; according to the silver-tungsten carbide graphite contact material, the surface anti-adhesion viscosity is increased through graphite, the problem that due to poor infiltration of silver and tungsten carbide, the use amount proportion of silver and tungsten carbide is difficult to reduce is solved, Ag fully permeates into a WCC framework, and therefore the silver-tungsten carbide graphite contact material with the uniform metallographic structure and high compactness is obtained, and the conductivity and durability of the silver-tungsten carbide graphite contact material can be maintained at the good level.

Description

Technical Field

[0001] The invention relates to the technical field of contact materials, and specifically discloses a silver tungsten carbide graphite contact and a preparation method thereof. Background Art

[0002] The contact is one of the key components of the switchgear, and its function is to connect or disconnect the current in the circuit. The performance of the contact material directly affects the reliability, life and energy consumption of the switchgear. The ideal contact material should have excellent electrical conductivity, good wear resistance and resistance to welding, and stable physical and chemical properties in the arc environment. Silver and its alloys are often used as the preferred material for contact materials due to their excellent electrical and thermal conductivity, as well as low evaporation rate under arc.

[0003] Traditional contact material preparation processes are mostly solid phase sintering methods, such as a silver tungsten carbide nickel contact material disclosed in patent CN104388739A, and its preparation method is: weigh tungsten carbide powder, nickel powder and silver powder according to the ratio, mix them evenly, and place the obtained silver tungsten carbide powder nickel mixed powder with high-purity nickel balls and water in a ball mill for ball milling. The ball-milled powder is dried, annealed, formed, sintered, re-pressed and annealed again to obtain a silver tungsten carbide nickel contact material. Although the existing solid phase sintering method can produce contact materials with low resistivity and good durability, it has defects in terms of economy and sustainability. The high proportion of silver leads to high material costs, which is particularly prominent in large-scale applications. Therefore, research and development of more cost-effective and more optimized performance contact material preparation technology has become an urgent need in the field of materials science. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a silver tungsten carbide graphite contact and a preparation method thereof.

[0005] On the one hand, the present invention discloses a method for preparing a silver tungsten carbide graphite contact, which adopts the following technical scheme:

[0006] A method for preparing a silver tungsten carbide graphite contact comprises the following steps:

[0007] (1) Powder reduction: WCC powder and Ni powder are reduced separately under controllable gas protection;

[0008] (2) Powder mixing: Mix the reduced WCC powder and Ni powder in a ratio of (97-99):(1-3) by specific gravity;

[0009] (3) Ball milling: Pour the WCC / Ni powder and stainless steel balls mixed in proportion into a ball mill for ball milling;

[0010] (4) Mixing powder: The milled WCC / Ni powder is mixed with Ag powder (part of the silver is added first, and the remaining silver is reserved for silver reverse osmosis, and the total silver content in the material is 30-60wt%;

[0011] (5) High temperature pre-sintering granulation: The mixed WCC / Ni / Ag powder is placed in a high temperature sintering furnace for powder pre-sintering, and after cooling, poured into a powder crusher for crushing;

[0012] (6) Pre-pressing the skeleton: placing the granulated and screened WCC / Ni / Ag powder into a powder tablet press for pre-pressing the skeleton;

[0013] (7) Skeleton sintering + silver reverse osmosis: The pre-pressed WCC / Ni / Ag skeleton and the reserved silver for reverse osmosis are placed in a fixture, and then placed in a high-temperature infiltration furnace, and controlled gas protection is added for high-temperature reverse osmosis;

[0014] (8) Pre-embedded solder: Place the dissolved and infiltrated material into a carrier, then add the solder sheet to be pre-embedded for furnace brazing to obtain a silver tungsten carbide graphite contact;

[0015] (9) Inspection-packaging and shipment.

[0016] Preferably, the graphite content in the WCC powder is 0.5-3 wt %.

[0017] Preferably, the graphite content in the WCC powder is 3 wt %.

[0018] Preferably, the material contains 35 wt% silver in total.

[0019] Preferably, the amount of silver added in the skeleton pre-pressing step is 15-35 wt %, and the amount of silver added in the silver reverse osmosis step is 15-25 wt %.

[0020] Preferably, in step (4), the ratio of WCC / Ni powder to Ag powder in the skeleton is 65:20.

[0021] Preferably, the sintering temperature in step (7) is 1050-1150° C. and the sintering time is 40 min.

[0022] Preferably, the skeleton pressing density in step (6) is 85%±2% of the theoretical density of the silver tungsten carbide graphite contact material.

[0023] Preferably, in step (5), the powder is crushed by a powder crusher and sieved to less than 40 mesh.

[0024] On the other hand, the present invention discloses a silver tungsten carbide graphite contact, which is prepared by the above-mentioned preparation method of the silver tungsten carbide graphite contact.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] The process of "pre-pressing Ag powder WCC / Ni powder into a skeleton first, and then adding Ag for a second time for skeleton sintering + silver reverse osmosis" proposed in the present application can increase the WCC content to between 40 and 70wt%, and the conductivity and durability of the contact material can be maintained at a good level. This is due to the full penetration of Ag in the WCC skeleton, thereby obtaining a silver tungsten carbide graphite contact material with uniform metallographic structure and high density. Among them, by using graphite-containing WCC powder as the main skeleton material, graphite increases the surface anti-adhesiveness, thereby improving the sintering effect of WCC particles and silver, solving the problem of difficulty in reducing the ratio of silver to tungsten carbide due to poor infiltration of silver and tungsten carbide, and reducing the cost of the contact material. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the metallographic image of the contact material of Example 1 (200 times);

[0028] Figure 2 This is the metallographic image of the contact material of Example 1 (500 times);

[0029] Figure 3 This is the metallographic image of the contact material of Example 8 (500 times);

[0030] Figure 4 This is the metallographic image of the contact material of Example 9 (500 times). DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] A silver tungsten carbide graphite contact, the preparation method of which comprises the following steps:

[0034] (1) Powder reduction: WCC powder is reduced at 700°C under controlled gas protection, and Ni powder is reduced at 500°C under controlled gas protection, wherein the graphite content in the WCC powder is 3 wt%;

[0035] (2) Powder mixing: Mix the reduced WCC powder and Ni powder in a ratio of 100:2;

[0036] (3) Ball milling: Pour the mixed WCC / Ni powder and stainless steel balls into a ball mill for ball milling. The ratio of WCC / Ni powder to stainless steel balls is 1:2. The ball mill rotates 4 to 8 times per minute.

[0037] (4) Powder mixing: The ball-milled WCC / Ni powder was mixed with the Ag powder. The WCC / Ni powder and the Ag powder were mixed in a ratio of 65:20 (Ag WCC65 contains 35 wt% of silver. In this step, 20 wt% of silver was first added, and the remaining 15 wt% of silver was reserved for silver reverse osmosis). The WCC / Ni / Ag powder with the good ratio was then poured into an automatic powder mixer for automatic stirring and mixing for 600 min.

[0038] (5) Powder high temperature pre-sintering and granulation: The mixed WCC / Ni / Ag powder was placed in a stainless steel boat box, about 10 kg per box, and then pushed into a high temperature sintering furnace for powder pre-sintering at 870°C for 90 min. After cooling to below 50°C, the powder was taken out and poured into a powder crusher for crushing and screening to 40 mesh.

[0039] (6) Skeleton pre-pressing: Add the granulated and screened WCC / Ni / Ag powder into a fully automatic powder tablet press for skeleton pre-pressing, and control according to the product drawing size. The skeleton pressing density is 85% of the theoretical density of the silver tungsten carbide graphite contact material;

[0040] (7) Skeleton sintering + silver reverse osmosis: The pre-pressed WCC / Ni / Ag skeleton blank is stacked with the silver sheet reserved for reverse osmosis and loaded into a high-temperature resistant fixture, and then placed in a high-temperature infiltration furnace, and controlled gas protection is added for high-temperature reverse osmosis. The sintering temperature is 1050-1150°C and the temperature is kept for 40 minutes;

[0041] (8) Pre-embedded solder: Place the dissolved material into a graphite carrier, then add the solder sheet to be pre-embedded for furnace brazing at a temperature of 500-750°C to obtain a silver tungsten carbide graphite contact;

[0042] (9) Inspection-packaging and shipment.

[0043] Example 2

[0044] The only difference from Example 1 is that the graphite content in the WCC powder is 2 wt %.

[0045] Example 3

[0046] The only difference from Example 1 is that the graphite content in the WCC powder is 2.5 wt %.

[0047] Comparative Example 1

[0048] The only difference from Example 1 is that the Ag powder and the WCC powder are sintered by a solid phase sintering process, and the Ag powder is mixed and sintered with the WCC at one time without reserving for silver reverse osmosis treatment.

[0049] Comparative Example 2

[0050] The only difference from Example 1 is that WC powder is used to make the skeleton instead of WCC powder.

[0051] Comparative Example 3

[0052] The only difference from Example 1 is that the graphite content in the WCC powder is 3.5 wt %.

[0053] Comparative Example 4

[0054] The only difference from Example 1 is that the sintering temperature in step (7) is 1250°C±50.

[0055] Comparative Example 5

[0056] The only difference from Example 1 is that the sintering temperature in step (7) is 1000°C±50.

[0057] Example 4

[0058] The only difference from Example 1 is that in step (4), the total silver content in the material is 60wt%, the ratio of WCC / Ni powder to Ag powder in the skeleton is changed to 40:35, and the remaining 25wt% of Ag is reserved for silver reverse osmosis.

[0059] Example 5

[0060] The only difference from Example 1 is that in step (4), the total silver content in the material is 30wt%, the ratio of WCC / Ni powder to Ag powder in the skeleton is changed to 70:15, and the remaining 15wt% of Ag is reserved for silver reverse osmosis.

[0061] Comparative Example 6

[0062] The only difference from Example 1 is that in step (4), the total silver content in the material is 60wt%, the ratio of WCC / Ni powder to Ag powder in the skeleton is changed to 40:45, and the remaining 15wt% of Ag is reserved for silver reverse osmosis.

[0063] Comparative Example 7

[0064] The only difference from Example 1 is that in step (4), the total silver content in the material is 30wt%, the ratio of WCC / Ni powder to Ag powder in the skeleton is changed to 70:10, and the remaining 20wt% of Ag is reserved for silver reverse osmosis.

[0065] Example 6

[0066] The only difference from Example 1 is that the skeleton pressing density in step (6) is 83% of the theoretical density of the silver tungsten carbide graphite contact material.

[0067] Example 7

[0068] The only difference from Example 1 is that the skeleton pressing density in step (6) is 87% of the theoretical density of the silver tungsten carbide graphite contact material.

[0069] Comparative Example 8

[0070] The only difference from Example 1 is that the skeleton pressing density in step (6) is 80% of the theoretical density of the silver tungsten carbide graphite contact material.

[0071] Comparative Example 9

[0072] The only difference from Example 1 is that the skeleton pressing density in step (6) is 90% of the theoretical density of the silver tungsten carbide graphite contact material.

[0073] Performance testing and result analysis

[0074] The contact products prepared in the above embodiments and comparative examples were subjected to density and resistivity performance tests, and the results are shown in Table 1 below.

[0075] Table 1

[0076] project <![CDATA[Density of the contact product, g / cm 3 > Resistivity μΩ·cm Example 1 14.1 4.3 Example 2 13.8 4.8 Example 3 13.9 4.5 Comparative Example 1 12.5 5.3 Comparative Example 2 13.0 5.1 Comparative Example 3 12.7 5.3 Comparative Example 4 11.2 6.2 Comparative Example 5 10.5 6.6 Example 4 13.7 4.4 Example 5 13.5 4.7 Comparative Example 6 10.9 6.4 Comparative Example 7 12.4 5.7 Example 6 13.6 4.3 Example 7 14.1 4.5 Comparative Example 8 13.3 4.9 Comparative Example 9 12.9 5.0

[0077] From the comparison between Example 1 and Comparative Examples 1-2, it can be seen that the process of "pre-pressing the Ag powder WCC / Ni powder skeleton into shape first, and then adding Ag for the skeleton sintering + silver reverse osmosis" proposed in the present application can increase the WCC content to between 40 and 70wt%, and the conductivity and durability of the contact material can be maintained at a good level. This is due to the full penetration of Ag in the WCC skeleton, thereby obtaining a silver tungsten carbide graphite contact material with uniform metallographic structure and high density. Among them, the present application adopts WCC powder containing graphite as the main skeleton material. Graphite increases the surface anti-adhesiveness, thereby improving the sintering effect of WCC particles and silver, and solves the problem that the tungsten carbide content cannot be increased due to poor infiltration of silver and tungsten carbide. Combined with the comparison of Examples 1-3 and Comparative Examples 2-3, it can be seen that the contact material has good electrical conductivity and high density, and the service life is greatly improved. Taking the circuit breaker with a rated current of 220A as an example, the standard life is not less than 1200 times, and the production life of the silver tungsten carbide graphite powder contact material infiltration silver reverse osmosis process can reach not less than 8800 times.

[0078] In addition, the process of the present application has certain control requirements for the sintering temperature of silver infiltration, and the sintering temperature needs to be between 1050 and 1150°C. Combining Example 1 with Comparative Examples 4-5, it can be seen that insufficient temperature is not conducive to the sufficient infiltration of silver in the WCC / Ni / Ag skeleton, while too high a temperature is not conducive to the structural stability of the WCC / Ni / Ag skeleton.

[0079] The present application has conducted further in-depth research on the preparation of WCC / Ni / Ag skeletons, and proposed a skeleton material ratio suitable for the silver reverse osmosis process. In combination with Example 1, Examples 4-5 and Comparative Examples 6-7, when the Ag content in the WCC / Ni / Ag skeleton material is too large, the pores of the skeleton will be closed and the gaps will be discontinuous, which is not conducive to the subsequent penetration of Ag in the skeleton. When the WCC / Ni content in the WCC / Ni / Ag skeleton material is too large, the pressed skeleton will have poor formability, and it will be difficult to maintain a relatively stable structure in the silver reverse osmosis step of skeleton sintering. It can be seen that even if the Ag content is high, if the silver addition ratio before and after the pre-pressing skeleton and reverse osmosis exceeds the characteristic value proposed in the process of the present application, the conductivity and durability of the obtained contact material are difficult to guarantee. Therefore, the WCC / Ni / Ag skeleton material ratio and the silver reverse osmosis addition ratio of the process of the present application are particularly critical for improving the contact performance.

[0080] In addition, the control of the pressing density of the WCC / Ni / Ag framework of the present application process is also important. The pressing density of Comparative Example 8 is too small, which not only leads to low framework strength, but also is not conducive to silver penetration and filling the pores (see Figure 3 The dark part is the hole formed by insufficient penetration of silver); the pressing density of comparative example 9 is too high, which is also not conducive to the penetration of silver to fill the pores (see Figure 4 , the white part is the silver that is accumulated on the surface of the material but not fully infiltrated). It can be seen that when the pressing density of the WCC / Ni / Ag skeleton is controlled at 85±2% of the theoretical density of the silver tungsten carbide graphite contact material, the metallographic structure of the contact material is uniform and dense (see Figure 1-2 ), which is beneficial to the conductivity and service life of the contact material.

[0081] The technical solution provided by the present invention is introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing a silver tungsten carbide graphite contact, characterized in that: The following steps are involved: (1) Powder reduction: WCC powder and Ni powder are reduced separately under controllable gas protection; (2) Powder mixing: Mix the reduced WCC powder and Ni powder in a ratio of (97-99):(1-3) by specific gravity; (3) Ball milling: Pour the WCC / Ni powder and stainless steel balls mixed in proportion into a ball mill for ball milling; (4) Mixing powder: The milled WCC / Ni powder is mixed with Ag powder (part of the silver is added first, and the remaining silver is reserved for silver reverse osmosis, and the total silver content in the material is 30-60wt%; (5) High temperature pre-sintering granulation: The mixed WCC / Ni / Ag powder is placed in a high temperature sintering furnace for powder pre-sintering, and after cooling, poured into a powder crusher for crushing; (6) Pre-pressing the skeleton: placing the granulated and screened WCC / Ni / Ag powder into a powder tablet press for pre-pressing the skeleton; (7) Skeleton sintering + silver reverse osmosis: The pre-pressed WCC / Ni / Ag skeleton and the reserved silver for reverse osmosis are placed in a fixture, and then placed in a high-temperature infiltration furnace, and controlled gas protection is added for high-temperature reverse osmosis; (8) Pre-embedded solder: Place the dissolved and infiltrated material into a carrier, then add the solder sheet to be pre-embedded for furnace brazing to obtain a silver tungsten carbide graphite contact; (9) Inspection-packaging and shipment.

2. The method for preparing the silver tungsten carbide graphite contact according to claim 1, characterized in that: The graphite content in the WCC powder is 0.5-3 wt %.

3. The method for preparing the silver tungsten carbide graphite contact according to claim 2, characterized in that: The graphite content in the WCC powder is 3 wt %.

4. The method for preparing the silver tungsten carbide graphite contact according to claim 1, characterized in that: The total silver content in the material is 35wt%.

5. The method for preparing the silver tungsten carbide graphite contact according to claim 1, characterized in that: The amount of silver added in the skeleton pre-pressing step is 15-35 wt %, and the amount of silver added in the silver reverse osmosis step is 15-25 wt %.

6. The method for preparing the silver tungsten carbide graphite contact according to claim 1, characterized in that: In the step (4), the ratio of WCC / Ni powder to Ag powder in the skeleton is 65:

20.

7. The method for preparing the silver tungsten carbide graphite contact according to claim 1, characterized in that: The sintering temperature in step (7) is 1050-1150° C. and the sintering time is 40 minutes.

8. The method for preparing the silver tungsten carbide graphite contact according to claim 1, characterized in that: The skeleton pressing density in step (6) is 85%±2% of the theoretical density of the silver tungsten carbide graphite contact material.

9. The method for preparing the silver tungsten carbide graphite contact according to claim 1, characterized in that: In the step (5), the powder is crushed by a powder crusher and sieved to a size below 40 mesh.

10. A silver tungsten carbide graphite contact, characterized in that: The silver tungsten carbide graphite contact is prepared by the preparation method of any one of claims 1 to 9.

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