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

Abstract

The present invention discloses a preparation method of a flaky silver tungsten carbide graphite copper-clad contact material. The method is to press a mixture of silver tungsten carbide graphite 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 green compact is first sintered in an inert atmosphere, then reduced in a reducing atmosphere, and then subjected to a second pressing to obtain a billet after the second pressing. Then, the obtained billet after the second pressing is successively subjected to a second sintering, a second pressing, and an annealing process to obtain a flaky silver tungsten carbide graphite copper-clad contact material. The method of the present 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 tungsten carbide graphite copper-clad contact material. Background Art

[0002] In switching electrical appliances, the electrical contact directly undertakes the functions of breaking and closing the circuit and carrying the normal working current or carrying the overload current within a certain period of time. The working performance and quality of the electrical contact 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 tungsten carbide graphite (AgWCC) contacts have good electrical conductivity, thermal conductivity, anti-welding property, arc erosion resistance, electrical wear resistance, and relatively high hardness. They are usually used as static contacts and paired with silver tungsten moving contacts in molded case circuit breakers with a large quantity and wide range of applications.

[0004] The silver tungsten carbide graphite contact material contains graphite. Based on the anti-welding property of graphite itself and the poor wettability between graphite and silver / copper, when directly welded, a virtual weld will be formed due to the poor wettability between silver tungsten carbide 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 appliance operation, the temperature rise of electrical appliances, the on-off ability of contacts, arc burn and service life. Therefore, in order to ensure the welding quality between the silver tungsten carbide graphite contact and the copper contact bridge, a pure silver layer is designed as a welding transition layer when manufacturing flaky silver tungsten carbide graphite contacts. However, this design will result in a relatively high overall silver content in the contact material, which not only causes waste of silver but also increases the manufacturing cost of the contact material.

[0005] To solve the above problems of silver waste and high cost, there have been public reports in the prior art on adding other components to traditional contact materials to reduce the silver content and ensure the contact performance. For example, the invention patent with the publication number CN102899551A discloses a silver-saving silver tungsten carbide graphite electrical contact material for high-performance low-voltage circuit breakers. This invention uses vanadium carbide to replace part of the silver on the basis of the traditional silver tungsten carbide graphite electrical contact material to reduce the cost, and at the same time adds additive elements to improve wettability (the additive elements are one or more of the following elements: 0-0.4wt% Ni-P, 0.1-0.9wt% Si, 0.3-1wt% Co, 0.1-0.3wt% Ni) to improve the matrix bonding strength.

[0006] On the other hand, copper has similar physical, chemical, electrical and other properties to silver. As an electrical contact material, copper has the advantages of good electrical and thermal conductivity, large heat capacity, low contact temperature rise, excellent processing and forming performance, and low price. Therefore, the applicant believes that the silver content can be reduced by processing silver tungsten carbide graphite and copper into a silver tungsten carbide graphite copper-clad composite material, where the silver tungsten carbide graphite material is the working layer and copper is the welding layer. After retrieval, it is found that the invention patent with publication number CN115810494A discloses a manufacturing method of a silver graphite copper-clad electrical contact material. Specifically, silver powder, graphite powder and additives are first mixed, then sintered and granulated. The obtained granules and copper powder are pressed into shape by a multi-layer composite automatic press, and the obtained blank is then sintered in hydrogen and then repressed to obtain the product. However, in this invention, the initially pressed green compact obtained by pressing silver graphite powder particles and copper powder is directly sintered. Since the wettability of graphite with silver and copper is not good, the physical bonding strength between non-wetting materials is poor. The presence of graphite will cause certain gaps at the joint between the silver graphite layer and the copper layer, which will affect the bonding strength of the bonding interface of the obtained contact material, resulting in an unsatisfactory bonding strength. Such products have a risk of delamination during actual use. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a preparation method of a flaky silver tungsten carbide graphite copper-clad contact material that can not only reduce the silver content but also ensure the bonding strength of the bonding interface.

[0008] To solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A preparation method of a flaky silver tungsten carbide graphite copper-clad contact material, comprising the following steps:

[0010] 1) Obtain silver tungsten carbide graphite mixed powder;

[0011] 2) Weigh copper powder and copper oxide powder according to a weight ratio of (0.65 - 0.8):1, mix the powders to obtain a copper copper oxide mixed powder;

[0012] 3) Press the silver tungsten carbide graphite mixed powder and the copper copper oxide mixed powder into shape to obtain an initially pressed green compact;

[0013] 4) Place the initially pressed green compact in an inert atmosphere for a first sintering, then place it in a reducing atmosphere for reduction, and then perform a first repressing to obtain a first repressed blank;

[0014] 5) The obtained first repressed blank is successively subjected to a second sintering, a second repressing and an annealing process to obtain a flaky silver tungsten carbide graphite copper-clad contact material.

[0015] The copper required for the copper-clad layer in the present invention 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 temperatures to carry out an oxidation-reduction reaction with copper oxide, playing a role of "decarbonization", thereby ensuring the absence of graphite at the bonding interface and improving 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 silver tungsten carbide graphite mixed powder, a certain amount of copper powder is added and mixed therewith, so that the silver tungsten carbide 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 subjecting the pressed blank to a primary sintering under an inert atmosphere, the copper oxide at the bonding interface reacts with the contacted graphite at high temperatures to consume the graphite, achieving the "decarbonization" effect at the bonding interface; then the blank after "decarbonization" 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 blank has been "decarbonized", the silver and copper at the bonding interface can be in full contact, improving the mutual diffusion between silver 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 tungsten carbide graphite copper-clad contact material; subsequent secondary sintering and secondary repressing processes improve the densification of the material and reduce the resistivity of the material, effectively ensuring the performance quality of the obtained contact material.

[0016] In step 1) of the above preparation method, in the silver tungsten carbide graphite mixed powder, the graphite content is preferably 2-4 wt%, the tungsten carbide content is preferably 12-22 wt%, and the balance is silver. Among them, the graphite is preferably colloidal graphite. For the specific ratio of graphite powder, tungsten carbide powder and silver powder in the silver tungsten carbide graphite mixed powder, it is determined according to the silver tungsten carbide 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 tungsten carbide graphite mixed powder. For example, the weighed graphite powder, tungsten carbide 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.

[0017] 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), and more preferably less than or equal to 48 microns (-300 mesh). Regarding the ratio of the copper powder and the copper oxide powder, the applicant found in the experiment that when the weight ratio of the copper powder and the copper oxide powder is lower than 0.65:1, the proportion of the copper powder is too low, making it difficult to form during the initial pressing and prone to delamination; while when the weight ratio of the copper powder and 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.

[0018] In step 3) of the above preparation method, the dosages of the silver tungsten carbide 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 press is used to press the silver tungsten carbide graphite mixed powder and the copper copper oxide mixed powder into shape, and the forming pressure is usually 3-4 T / cm 2 .

[0019] In step 4) of the above preparation method, the processes of the first sintering, reduction and first repressing are 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 repressing is preferably 5-7 T / cm 2 . The inert atmosphere involved in this step can specifically be nitrogen, argon or helium, etc., and the reducing atmosphere is usually hydrogen.

[0020] In step 5) of the above preparation method, the operations of the second sintering, second repressing and annealing processes are 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 repressing 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.

[0021] Compared with the prior art, the characteristics of the present invention are as follows:

[0022] 1. The welding layer uses copper instead of silver, achieving a good silver-saving effect. Copper has physical, chemical, electrical and other properties similar to those of 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 sheet silver tungsten carbide graphite contacts, with flexible processes. The size ratio of silver tungsten carbide graphite to the copper-clad layer can be adjusted according to customer needs, and the thickness of the copper-clad layer can be increased. Copper serves as both the working layer and the welding layer, achieving a better silver-saving effect.

[0023] 2. The initially pressed green compact obtained by pressing the silver tungsten carbide graphite mixed powder and the copper copper oxide mixed powder into shape is sintered in an inert atmosphere. The copper oxide at the bonding interface reacts with the contacting graphite at high temperature through an oxidation-reduction reaction to consume the graphite, achieving the effect of "decarbonization" at the bonding interface, thereby ensuring full contact between the silver and copper at the bonding interface. The second sintering improves the sintering bond between silver and copper. 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 tungsten carbide graphite copper-clad.

[0024] 3. The method of the present invention has strong practicability, simple process, convenient operation, low cost, and obvious price advantage of materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a metallographic structure photograph (200×) of the AgWC(12)C(3) / Cu contact material prepared in Example 1 of the present invention;

[0026] Figure 2 It is a metallographic structure photograph (200×) of the AgWC(12)C(3) / Cu contact material prepared in Example 2 of the present invention;

[0027] Figure 3 It is a metallographic structure photograph (200×) of the AgWC(22)C(3) / Cu contact material prepared in Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] In order to better explain the technical solution of the present invention, the present invention will be further described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto.

[0029] Example 1

[0030] 1) Weigh silver powder, tungsten carbide powder and graphite powder according to a weight ratio of 85:12:3, and use a double-cone mixer to mix the powders (rotation speed 30 r / min, time 3 hours) to obtain AgWC(12)C(3) mixed powder;

[0031] 2) Weigh -200 mesh copper powder and -300 mesh copper oxide powder according to a weight ratio of 0.7:1, and use a double-cone mixer to mix the powders (rotation speed 30 r / min, time 2 hours) to obtain copper-copper oxide mixed powder;

[0032] 3) Press the silver-tungsten carbide-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 to obtain a preliminarily formed green compact;

[0033] 4) The preliminarily formed green compact is successively subjected to a first sintering, reduction and first repressing process to obtain a first repressed blank; among them,

[0034] The first sintering is carried out in a sintering furnace, using nitrogen as the protective gas, the sintering temperature is 760 ± 10 °C, and the time is 5 hours;

[0035] The reduction is carried out in a sintering furnace, using hydrogen as the protective gas, the reduction temperature is 550 °C, and the time is 3 hours;

[0036] The pressure of the first repressing is 7 T / cm 2 ;

[0037] 5) The obtained primary repressed blank is successively subjected to secondary sintering, secondary repressing, and annealing processes to obtain a flaky AgWC(12)C(3) / Cu contact material; wherein,

[0038] The secondary sintering is carried out in a sintering furnace, using hydrogen as the protective gas, the sintering temperature is 760±10 °C, and the time is 4 hours;

[0039] The pressure of the secondary repressing is 12 T / cm 2 ;

[0040] The annealing is carried out in a sintering furnace, using hydrogen as the protective gas, the annealing temperature is 500 °C, and the time is 2 hours.

[0041] The metallographic structure photograph of the contact material prepared in this embodiment is as Figure 1 shown.

[0042] Example 2

[0043] 1) Weigh silver powder, tungsten carbide powder, and graphite powder according to a weight ratio of 85:12:3, and use a double-cone mixer to mix the powders (rotation speed 30 r / min, time 3 hours) to obtain AgWC(12)C(3) mixed powder;

[0044] 2) Weigh -200 mesh copper powder and -300 mesh copper oxide powder according to a weight ratio of 0.8:1, and use a double-cone mixer to mix the powders (rotation speed 25 r / min, time 2 hours) to obtain copper-copper oxide mixed powder;

[0045] 3) Press the silver-tungsten carbide-graphite mixed powder and the copper-copper oxide mixed powder into shape using a compound automatic press, with a forming pressure of 3 T / cm 2 , to obtain a preliminarily pressed blank;

[0046] 4) The preliminarily pressed blank is successively subjected to primary sintering, reduction, and primary repressing processes to obtain a primary repressed blank; wherein,

[0047] The primary sintering is carried out in a sintering furnace, using nitrogen as the protective gas, the sintering temperature is 760±10 °C, and the time is 4 hours;

[0048] The reduction is carried out in a sintering furnace, using hydrogen as the protective gas, the reduction temperature is 500 °C, and the time is 3 hours;

[0049] The pressure of the primary repressing is 6 T / cm 2 ;

[0050] 5) The obtained primary repressed blank is successively subjected to secondary sintering, secondary repressing, and annealing processes to obtain a flaky AgWC(12)C(3) / Cu contact material; wherein,

[0051] The secondary sintering is carried out in a sintering furnace with hydrogen as the protective gas. The sintering temperature is 760 ± 10 °C and the time is 4 hours;

[0052] The pressure of the secondary repressing is 11 T / cm 2 ;

[0053] The annealing is carried out in a sintering furnace with hydrogen as the protective gas. The annealing temperature is 400 °C and the time is 1 hour.

[0054] The metallographic structure photograph of the contact material obtained in this embodiment is as Figure 2 shown.

[0055] Example 3:

[0056] 1) Weigh silver powder, tungsten carbide powder and graphite powder according to the weight ratio of 75:22:3, and use a double-cone mixer to mix the powders (rotation speed 40 r / min, time 4 hours) to obtain AgWC(22)C(3) mixed powder;

[0057] 2) Weigh -200 mesh copper powder and -300 mesh copper oxide powder according to the weight ratio of 0.65:1, and use a double-cone mixer to mix the powders (rotation speed 30 r / min, time 3 hours) to obtain copper-copper oxide mixed powder;

[0058] 3) Press the silver-tungsten carbide-graphite mixed powder and the copper-copper oxide mixed powder into shape with a composite automatic press, and the forming pressure is 3 T / cm 2 , to obtain a preliminarily pressed green compact;

[0059] 4) Perform the primary sintering, reduction and primary repressing processes on the preliminarily pressed green compact in sequence to obtain a primary repressed blank; among them,

[0060] The primary sintering is carried out in a sintering furnace with nitrogen as the protective gas. The sintering temperature is 760 ± 10 °C and the time is 6 hours;

[0061] The reduction is carried out in a sintering furnace with hydrogen as the protective gas. The reduction temperature is 600 °C and the time is 4 hours;

[0062] The pressure of the primary repressing is 7 T / cm 2 ;

[0063] 5) The obtained primary repressed blank is subjected to secondary sintering, secondary repressing and annealing processes in sequence to obtain a flaky AgWC(22)C(3) / Cu contact material; among them,

[0064] The secondary sintering is carried out in a sintering furnace with hydrogen as the protective gas. The sintering temperature is 760 ± 10 °C and the time is 5 hours;

[0065] The pressure of the secondary repressing is 12 T / cm 2;

[0066] Annealing is carried out in a sintering furnace, with hydrogen as the protective gas. The annealing temperature is 500 °C and the time is 2 hours.

[0067] The metallographic structure photograph of the contact material prepared in this embodiment is as Figure 3 shown.

Claims

1. A preparation method of a flaky silver tungsten carbide graphite copper-clad contact material, comprising the following steps: 1) Obtain a silver tungsten carbide graphite mixed powder; 2) Weigh copper powder and copper oxide powder according to a weight ratio of (0.65~0.8):1, mix the powders to obtain a copper copper oxide mixed powder; 3) Press the silver tungsten carbide graphite mixed powder and the copper copper oxide mixed powder into shape to obtain a preliminarily pressed blank; 4) First place the preliminarily pressed blank in an inert atmosphere for primary sintering, then place it in a reducing atmosphere for reduction, and then perform a secondary pressing to obtain a first secondary 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 secondary pressed blank is successively subjected to secondary sintering, secondary pressing and annealing processes to obtain the flaky silver tungsten carbide 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 tungsten carbide graphite mixed powder is 2~4wt%, and the tungsten carbide content is 12~22wt%.

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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