Preparation method of a flaky silver-nickel-graphite copper-clad contact material

Abstract

The invention discloses a preparation method of a flaky silver-nickel-graphite copper-clad contact material. The method is to press a silver-nickel-graphite mixed powder and a copper-copper oxide mixed powder composed of copper powder and copper oxide powder in a weight ratio of (0.65 to 0.8):1 into a shape. The obtained initially pressed blank is first placed in an inert atmosphere for a first sintering, then placed in a reducing atmosphere for reduction, and then subjected to a first repressing to obtain a first repressed blank; then the obtained first repressed blank is successively subjected to a second sintering, a second repressing and an annealing process to obtain the flaky silver-nickel-graphite copper-clad contact material. The method of the invention can not only achieve the effect of silver saving, but also ensure the bonding strength of the bonding interface of the obtained contact material, and has the advantages of simple process, low cost and strong practicability.

Description

Technical Field

[0001] The present invention relates to a preparation method of an alloy contact material, and particularly to a preparation method of a flaky silver-nickel-graphite copper-clad contact material. Background Art

[0002] In switching electrical appliances, electrical contacts directly undertake the functions of breaking and closing circuits and carrying normal working current or carrying overload current within a certain period of time. The working performance and quality of electrical contacts directly determine the key functions of various switching electrical appliances, such as the on-off ability of distribution electrical appliances, the electrical life of control electrical appliances, and the reliability of relays.

[0003] Silver-nickel-graphite (AgNiC) contact material is a composite material combined with silver, nickel, and graphite components, and has the advantages of good anti-burning property of silver-nickel contact material and good anti-welding property and stable contact resistance of silver-graphite contact material. Therefore, silver-nickel-graphite contact material has the characteristics of good anti-welding property, low and stable contact resistance, and is mainly applied to various molded case circuit breakers and frame-type universal circuit breakers.

[0004] Since the silver-nickel-graphite contact material contains graphite, and graphite has the characteristic of anti-welding property, and the wettability of graphite with silver, nickel, and copper is poor. When directly welding, it is easy to form a virtual weld due to the poor wettability between silver-nickel-graphite and the copper contact bridge, and the welding quality cannot meet the requirements. The quality of welding has a very important direct relationship with the reliability of electrical operation, the temperature rise of electrical appliances, the on-off ability of contacts, arc burning, and service life. Therefore, in order to ensure the welding quality between the silver-nickel-graphite contact and the copper contact bridge, when manufacturing flaky silver-nickel-graphite contacts, a pure silver layer is often designed as a welding transition layer, such as:

[0005] The invention patent with publication number CN113245547A discloses a preparation method of a silver-nickel-graphite electrical contact with a continuous decarburized layer on the side. The method presses a silver-nickel-graphite mixed powder into a shape, and then obtains a silver-nickel-graphite blank with a continuous decarburized layer on the surface through sintering, repressing, and decarburization. The blank is obtained by cutting or milling to obtain a silver-nickel-graphite contact material with a continuous pure silver layer on the side. The method described in the invention needs to go through cutting or milling during the preparation process, generating more waste materials, affecting the material processing yield, and the manufacturing cost of the material is relatively high; at the same time, the overall silver content of the material is relatively high, further increasing the material cost.

[0006] The invention patent with the publication number CN102808098A discloses a preparation method of a silver / nickel / graphite electrical contact material. In this method, colloidal graphite is first nickel-plated and then silver-plated by electroless plating to obtain powder with an Ag-Ni-C core-shell structure, which is then mixed with pure silver powder. The content of colloidal graphite is reduced to a specified value, and after sintering, extrusion, and drawing processes, a silver / nickel / graphite material is obtained. This invention uses electroless plating to improve the oxidation resistance of composite particles, the performance of sintering granulation, and the deformation ability of intermediate composite particles during processing, thereby improving process performance. However, the overall silver content of the material is relatively high, and there is also the problem of relatively high material costs.

[0007] From the perspective of reducing the silver content in the material and the raw material cost, in the prior art, copper with physical, chemical, and electrical properties similar to those of silver has been used to replace silver as the welding layer. The invention patent with the publication number CN115810494A discloses a manufacturing method of a silver-graphite copper composite electrical contact material. Specifically, silver powder, graphite powder, and additives are first mixed, and then sintered and granulated. The obtained particles and copper powder are formed by a multi-layer composite automatic tablet press, and the obtained blank is then sintered in hydrogen and then repressed to obtain the product. However, in this invention, the initially pressed formed blank obtained by pressing silver-graphite powder particles and copper powder is directly sintered. Since the wettability between graphite and silver and copper is poor, the physical bonding strength between non-wetting materials is relatively weak. The presence of graphite will cause certain gaps at the joint between the silver-graphite layer and the copper layer, thereby affecting the bonding strength of the bonding interface of the obtained contact material and resulting in an unsatisfactory bonding strength. Such a product has a risk of delamination during actual use. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a preparation method of a flaky silver-nickel-graphite copper-clad contact material that can not only reduce the silver content but also ensure the bonding strength of the bonding interface.

[0009] To solve the above technical problem, the present invention adopts the following technical solutions:

[0010] A preparation method of a flaky silver-nickel-graphite copper-clad contact material, comprising the following steps:

[0011] 1) Obtain a silver-nickel-graphite mixed powder;

[0012] 2) Weigh copper powder and copper oxide powder according to a weight ratio of (0.65 - 0.8):1, mix the powders, and obtain a copper-copper oxide mixed powder;

[0013] 3) Press the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder into shape to obtain an initially pressed formed blank;

[0014] 4) The initially press-formed green compact is first sintered in an inert atmosphere, then reduced in a reducing atmosphere, and then repressed once to obtain a once-repressed blank.

[0015] 5) The obtained once-repressed blank is successively subjected to secondary sintering, secondary repressing, and annealing processes to obtain the flaky silver-nickel-graphite copper-clad contact material.

[0016] In the present invention, the copper required for the copper-clad layer consists of two parts. One part is pure oxygen-free copper powder, and the other part is copper oxide powder. The purpose and principle are as follows: Utilize the reducibility of graphite at high temperature to undergo an oxidation-reduction reaction with copper oxide, playing the role of "decarbonization", so as to ensure that there is no graphite at the bonding interface and improve the bonding strength between the bonding interfaces. On the other hand, due to the poor processability of copper oxide powder and its inability to be directly pressed and formed with the silver-nickel-graphite mixed powder, therefore, a certain amount of copper powder is added and mixed with it, so that the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder can be pressed and formed. The specific process flow and principle are as follows: During the process of sintering the pressed green compact in an inert atmosphere for the first time, the copper oxide at the bonding interface reacts with the contacted graphite at high temperature to consume the graphite, achieving the effect of "decarbonization" at the bonding interface; then the "decarbonized" green compact is placed in a reducing atmosphere for reduction to further reduce the copper oxide to copper. During this process, since the bonding interface of the green compact has been "decarbonized", the silver, nickel, and copper at the bonding interface can be in full contact, improving the mutual diffusion between silver, nickel, and copper particles, promoting the effective bonding of the interface during the secondary sintering process, and improving the composite interface bonding strength of the silver-nickel-graphite copper-clad contact material; the subsequent secondary sintering and secondary repressing processes improve the density of the material and reduce the resistivity of the material, effectively ensuring the performance quality of the obtained contact material.

[0017] In step 1) of the above preparation method, in the silver-nickel-graphite mixed powder, the graphite content is preferably 2-4 wt%, the nickel content is preferably 1.5-30 wt%, and the balance is silver. Among them, the graphite is preferably colloidal graphite. For the specific proportions of graphite powder, nickel powder, and silver powder in the silver-nickel-graphite mixed powder, they are determined according to the silver-nickel-graphite contact to be prepared. After determination, weighing is carried out, and then the powder mixing is carried out by using existing conventional operations to obtain the silver-nickel-graphite mixed powder. For example, the weighed graphite powder, nickel powder, and silver powder can be placed in a mixer and mixed for 2-4 hours under the condition of a rotation speed of 20-40 r / min.

[0018] In step 2) of the above preparation method, the particle sizes of the copper powder and the copper oxide powder are preferably less than or equal to 74 microns (-200 mesh), more preferably less than or equal to 48 microns (-300 mesh). For the ratio of the copper powder to the copper oxide powder, the applicant found in the experiment that when the weight ratio of the copper powder to the copper oxide powder is lower than 0.65:1, the proportion of the copper powder is too low and it is difficult to form during the initial pressing and easy to delaminate; while when the weight ratio of the copper powder to the copper oxide powder is higher than 0.8:1, the proportion of the copper oxide powder is too low, resulting in a low consumption of graphite during the subsequent sintering process and an unsatisfactory "decarbonization" effect at the bonding interface.

[0019] In step 3) of the above preparation method, the dosages of the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder are determined according to the size of the contact to be prepared. After determining the specification size of the contact to be prepared, the dosage of the copper-copper oxide mixed powder is determined in combination with the thickness of the copper-clad layer. Usually, a compound automatic tablet press is used to press the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder into shape, and the forming pressure is usually 3-4 T / cm 2 。

[0020] In step 4) of the above preparation method, the processes of the first sintering, reduction, and first re-pressing are all the same as those in the prior art. Specifically, the temperature of the first sintering is preferably 750-800 °C, and the time is preferably 4-6 hours; the temperature of the reduction is preferably 500-600 °C, and the time is preferably 3-4 hours; the pressure of the first re-pressing is preferably 5-7 T / cm 2 。The inert gas involved in this step can specifically be nitrogen, argon, helium, etc., and the reducing atmosphere is usually hydrogen.

[0021] In step 5) of the above preparation method, the operations of the second sintering, second re-pressing, and annealing processes are all the same as those in the prior art. Specifically, the second sintering is carried out in a reducing atmosphere, the sintering temperature is 750-800 °C, and the time is 4-5 hours; the pressure of the second re-pressing is preferably 11-12 T / cm 2 ; the annealing is carried out in a reducing atmosphere, the annealing temperature is 400-500 °C, and the time is 1-2 hours.

[0022] Compared with the prior art, the features of the present invention are as follows:

[0023] 1. Copper is used instead of silver for the welding layer, achieving a good silver-saving effect. Copper has similar physical, chemical, electrical, etc. properties to silver and can be used as an electrical contact material. Copper has advantages such as good electrical and thermal conductivity, large heat capacity, low contact temperature rise, excellent processing and forming performance, and low price. Moreover, the present invention uses powder metallurgy to prepare the sheet silver-nickel-graphite contact, with flexible process, and can adjust the size ratio of silver-nickel-graphite to the copper-clad layer according to customer needs, increasing the thickness of the copper-clad layer. Copper serves as both the working layer and the welding layer, achieving a better silver-saving effect.

[0024] 2. The green compact obtained by pressing the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder is sintered in an inert atmosphere. At the bonding interface, the copper oxide in contact with the graphite undergoes an oxidation-reduction reaction at high temperature, consuming the graphite, which has the effect of "decarburizing" the bonding interface, thus ensuring full contact between silver, nickel, and copper at the bonding interface. Through secondary sintering, the sintering bond of silver, nickel, and copper is improved. Through the above process optimization, the influence of graphite at the bonding interface is eliminated, thereby improving the bonding strength of the composite interface of silver-nickel-graphite copper-clad.

[0025] 3. The method of the present invention has strong practicability, simple process, convenient operation, low cost, and obvious price advantages of materials. Brief Description of the Drawings

[0026] Figure 1 It is a metallographic structure photograph (200×) of the AgNi(30)C(3) / Cu contact obtained in Example 1 of the present invention;

[0027] Figure 2 It is a metallographic structure photograph (200×) of the AgNi(25)C(2) / Cu contact obtained in Example 2 of the present invention;

[0028] Figure 3 It is a metallographic structure photograph (200×) of the AgNi(20)C(2) / Cu contact obtained in Example 3 of the present invention;

[0029] Figure 4 It is a metallographic structure photograph (200×) of the AgNi(1.5)C(4) / Cu contact obtained in Example 4 of the present invention. Detailed Description of the Invention

[0030] In order to better explain the technical solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments, but the embodiments of the present invention are not limited thereto.

[0031] Example 1

[0032] 1) Weigh silver powder, nickel powder, and graphite powder according to a weight ratio of 67:30:3, and use a double-cone mixer to mix the powder at a rotation speed of 30 r / min for 3 hours to obtain AgNi(30)C(3) mixed powder;

[0033] 2) Weigh -200 mesh copper powder and -300 mesh copper oxide powder according to a ratio of 0.7:1, and use a double-cone mixer to mix the powder at a rotation speed of 30 r / min for 2 hours to obtain copper-copper oxide mixed powder;

[0034] 3) Press the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder into shape with a composite automatic press, and the forming pressure is 4 T / cm 2 ;

[0035] 4) Put the blank obtained in step 3) into a sintering furnace, use nitrogen as the protective gas, and sinter at 760 ± 10 °C for 5 hours;

[0036] 5) Put the blank processed in step 4) into a sintering furnace, use hydrogen as the protective gas, and reduce at 550 °C for 3 hours;

[0037] 6) Carry out primary repressing on the blank processed in step 5), and the repressing pressure is 7 T / cm 2 ;

[0038] 7) Put the blank processed in step 6) into a sintering furnace, use hydrogen as the protective gas, and carry out secondary sintering at 760 ± 10 °C for 4 hours;

[0039] 8) Carry out secondary repressing on the blank processed in step 7), and the repressing pressure is 12 T / cm 2 ;

[0040] 9) Put the blank processed in step 8) into a sintering furnace, use hydrogen as the protective gas, and anneal at 500 °C for 2 hours to obtain a flaky AgNi(30)C(3) / Cu contact material.

[0041] Example 2

[0042] 1) Weigh silver powder, nickel powder and graphite powder according to a weight ratio of 73:25:2, use a double-cone mixer to mix the powders, with a rotation speed of 25 r / min and a time of 2 hours to obtain an AgNi(25)C(2) mixed powder;

[0043] 2) Weigh -200 mesh copper powder and -300 mesh copper oxide powder according to a weight ratio of 0.8:1, use a double-cone mixer to mix the powders, with a rotation speed of 25 r / min and a time of 2 hours to obtain a copper-copper oxide mixed powder;

[0044] 3) Press the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder into shape using a composite automatic press, and the forming pressure is 3 T / cm 2 ;

[0045] 4) Put the blank obtained in step 3) into a sintering furnace, use nitrogen as the protective gas, and sinter at 760 ± 10 °C for 4 hours;

[0046] 5) Put the blank processed in step 4) into a sintering furnace, use hydrogen as the protective gas, and reduce at 500 °C for 3 hours;

[0047] 6) Carry out primary repressing on the blank processed in step 5), and the repressing pressure is 6 T / cm 2 ;

[0048] 7) Put the blank processed in step 6) into a sintering furnace, use hydrogen as the protective gas, and conduct secondary sintering at 760 ± 10 °C for 4 hours;

[0049] 8) Conduct secondary repressing on the blank processed in step 7), and the repressing pressure is 11 T / cm 2 ;

[0050] 9) Put the blank processed in step 8) into a sintering furnace, use hydrogen as the protective gas, and conduct annealing at 400 °C for 1 hour to obtain a flaky AgNi(25)C(2) / Cu contact material.

[0051] Example 3

[0052] 1) Weigh silver powder, nickel powder and graphite powder according to a weight ratio of 78:20:2, use a double-cone mixer to mix the powders, with a rotation speed of 25 r / min and a time of 2 hours to obtain an AgNi(20)C(2) mixed powder;

[0053] 2) Weigh -200 mesh copper powder and -300 mesh copper oxide powder according to a weight ratio of 0.8:1, use a double-cone mixer to mix the powders, with a rotation speed of 25 r / min and a time of 2 hours to obtain a copper-copper oxide mixed powder;

[0054] 3) Press the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder into shape using a compound automatic press, and the forming pressure is 3 T / cm 2 ;

[0055] 4) Put the blank obtained in step 3) into a sintering furnace, use nitrogen as the protective gas, and conduct sintering at 760 ± 10 °C for 4 hours;

[0056] 5) Put the blank processed in step 4) into a sintering furnace, use hydrogen as the protective gas, and conduct reduction at 500 °C for 3 hours;

[0057] 6) Conduct primary repressing on the blank processed in step 5), and the repressing pressure is 6 T / cm 2 ;

[0058] 7) Put the blank processed in step 6) into a sintering furnace, use hydrogen as the protective gas, and conduct secondary sintering at 760 ± 10 °C for 4 hours;

[0059] 8) Conduct secondary repressing on the blank processed in step 7), and the repressing pressure is 11 T / cm 2 ;

[0060] 9) Put the blank processed in step 8) into a sintering furnace, use hydrogen as the protective gas, anneal at 400 °C for 1 hour to obtain a flaky AgNi(20)C(2) / Cu contact material.

[0061] Example 4

[0062] 1) Weigh silver powder, nickel powder and graphite powder according to the weight ratio of 94.5:1.5:4, use a double-cone mixer to mix the powders at a rotation speed of 40 r / min for 4 hours to obtain an AgNi(1.5)C(4) mixed powder;

[0063] 2) Weigh -300 mesh copper powder and -200 mesh copper oxide powder according to the weight ratio of 0.65:1, use a double-cone mixer to mix the powders at a rotation speed of 30 r / min for 3 hours to obtain a copper-copper oxide mixed powder;

[0064] 3) Press the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder into shape with a compound automatic press, and the forming pressure is 3 T / cm 2 ;

[0065] 4) Put the blank obtained in step 3) into a sintering furnace, use nitrogen as the protective gas, sinter at 760 ± 10 °C for 6 hours;

[0066] 5) Put the blank processed in step 4) into a sintering furnace, use hydrogen as the protective gas, reduce at 600 °C for 4 hours;

[0067] 6) Perform a first repressing on the blank processed in step 5), and the repressing pressure is 5 T / cm 2 ;

[0068] 7) Put the blank processed in step 6) into a sintering furnace, use hydrogen as the protective gas, perform a second sintering at 760 ± 10 °C for 5 hours;

[0069] 8) Perform a second repressing on the blank processed in step 7), and the repressing pressure is 10 T / cm 2 ;

[0070] 9) Put the blank processed in step 8) into a sintering furnace, use hydrogen as the protective gas, anneal at 400 °C for 1 hour to obtain a flaky AgNi(1.5)C(4) / Cu contact material.

Claims

1. A preparation method of a flaky silver-nickel-graphite copper-clad contact material, comprising the following steps: 1) Obtain a silver-nickel-graphite mixed powder; 2) Weigh copper powder and copper oxide powder according to a weight ratio of (0.65~0.8):1, and mix the powders to obtain a copper-copper oxide mixed powder; 3) Press the silver-nickel-graphite mixed powder and the copper-copper oxide mixed powder into shape to obtain a preliminarily pressed blank; 4) Place the preliminarily pressed blank in an inert atmosphere for primary sintering first, then place it in a reducing atmosphere for reduction, and then perform a secondary pressing to obtain a first re-pressed blank; during the primary sintering process, the copper oxide at the bonding interface reacts with the contacted graphite at high temperature to consume the graphite; 5) The obtained first re-pressed blank is successively subjected to secondary sintering, secondary pressing and annealing processes to obtain the flaky silver-nickel-graphite copper-clad contact material.

2. The preparation method according to claim 1, characterized in that, In step 1), the graphite content in the silver-nickel-graphite mixed powder is 2~4wt%, and the nickel content is 1.5~30wt%.

3. The preparation method according to claim 1, characterized in that, In step 2), the particle sizes of the copper powder and the copper oxide powder are less than or equal to 74 microns.

4. The preparation method according to claim 1, characterized in that, In step 4), the temperature of the primary sintering is 750~800°C, and the time is 4~6 hours.

5. The preparation method according to claim 1, characterized in that, In step 4), the temperature of the reduction is 500~600°C, and the time is 3~4 hours.

6. The preparation method according to claim 1, characterized in that, In step 5), the temperature of the secondary sintering is 750~800°C, and the time is 4~5 hours.

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