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The mechanism of the action of the electric arc

1.3.2.1 The physical metallurgical process of electrical contact material
The physical metallurgical process of the electrical contact material after being subjected to arc energy infusion mainly has several stages such as heating (softening) a phase change (melting, vaporization) – flow – solidification [27]
In the arc energy effect of the electric contact surface transition zone temperature quickly climbs to the melting point of the electric contact material becomes the melting zone, in the continued action of the energy, the melting zone may vaporize, resulting in vaporization front interface, while the solid zone liquefaction interface continues to flow forward. Thus, when the arc action to a certain time, the electrical contact surface may exist both vaporization and liquefaction interface. After the arc is extinguished, the contact material phase changes in the opposite direction, that is, from gas, liquid to solid.
For the arc erosion process, melting and vaporization are the main phase change processes that affect the amount of erosion of the electrical contact material. The molten metal in the melt pool on the surface of the electric contact is driven by electromagnetic stirring force and mechanical force to flow at a certain speed, and when the driving force is sufficient, even in the form of small droplets spattered out, resulting in greater material loss. Vaporization, on the other hand, takes place mainly in the form of evaporation and boiling.
1.3.2.2 Electric contact material arc erosion mode
The arc erosion model of silver-based electrical contact materials can be divided into two kinds of liquid spatter erosion and evaporation erosion [28] Liquid spatter erosion refers to the melting of micro-areas on the surface of electrical contact materials under the action of arc energy to form a liquid pool, and under the action of various forces, the molten metal in the liquid pool splashes in the form of tiny droplets and leaves the body of the electrical contact. Evaporation erosion means that under the action of arc energy, the electric contact surface material undergoes solid-liquid, liquid-gas phase change and leaves the electric contact body in the form of evaporation. Among them, liquid spatter erosion can be divided into central spatter erosion and edge spatter erosion; evaporation erosion can be divided into regional selective erosion and group element selective erosion. In the electric contact material, due to the loose structure of the material in the grain boundary region, the interface bonding force is weak, and the grain boundary part has a high concentration of impurities, especially the second group element concentration, so that it becomes a priority by the arc energy effect of the region, this selection of certain areas for priority erosion behavior is called region-selective erosion. In the electric contact material, due to the different thermal stability of each group element, thus causing a different order of arc erosion under the action of arc energy, this phenomenon of preferential erosion of thermally less stable group elements is called group selective erosion. For liquid spatter erosion, the current is small, the center of the liquid pool is under pressure, the edge of the protrusion to form a larger angle with the axis of the edge of the spatter erosion; current is larger, the center of the liquid pool is under tension, the edge is squeezed to form a smaller angle with the axis of the center of the spatter erosion, the center of the spatter erosion is more serious than the edge of the spatter.
1.3.2.3 The failure mechanism of silver-based electrical contact material under the action of the arc
Dissolution precipitation effect of AAg/Ni system electrical contacts
Ag/Ni electrical contact materials were used in large load relays as early as 1939. Powder metallurgy silver-nickel electric

The Ag/Ni system increases the mutual solubility of Ag and Ni at very high temperatures. At high temperature, nickel can be dissolved in a large amount in the silver melt produced at the arc root, and then deposited in the silver matrix after cooling to form a uniformly diffused silver-nickel alloy, reducing the erosion rate of the material, and Ni-rich areas and their oxides are formed on the contact surface when cooling. Therefore, the arc erosion process of Ag/Ni system electrical contacts plays a decisive role in the dissolution deposition effect: on the one hand, the interaction between the arc and the electrode, due to the rotating part of the Loren magnetic force and the surface tension gradient caused by the temperature gradient in the liquid pool together to form the liquid pool velocity field when the flow rate exceeds a certain value that will be spattered out in the form of small droplets; on the other hand, the dispersion of molten silver and nickel composition On the other hand, the dispersion of molten silver and nickel system, due to the viscosity between the liquid metal, will reduce the spattering of liquid metal, and the greater the viscosity, the smaller the material loss caused by spattering [29], so when the Ni content increases the contact resistance increases the arc erosion resistance decreases. The arc is very short, and the heat generated is almost completely transferred to the contact, forming a molten weld zone in the contact area. The molten pool temperature is high and surrounded by relatively cold metal, so there is a large temperature gradient inside and outside the molten pool. The molten pool metal solidifies and crystallizes at a large rate, forming a potential welding point in the contact area of the two contacts, and when the molten welding force of the welding point is greater than the breaking force of the contact, it causes the contact to fuse.
Porous and loose sponge effect of BAg/C system electrical contacts
Ag/C-based electrical contact materials have a long history in sliding contact applications [30]. The main disadvantages of these materials, which have high fusion weldability and low and stable contact resistance, are high wear, high arc erosion rate, and poor arc extinguishing performance.The main mechanism of arc erosion in Ag/C-based electrical contacts lies in the interaction of graphite with atmospheric oxygen. The main role of graphite is to prevent the contact from bonding and fusion welding, and it is not easy to form any insulator. In the heated high temperature arc column region, carbon particles burn significantly to form CO gas and escape from the contact, thus forming a porous and loose silver-rich layer on the contact surface, so that the Ag/C contact material maintains a low contact resistance during operation. The porous surface provides good resistance to fusion welding regardless of whether the fiber direction is parallel or perpendicular to the contact surface. Ag/C electrical contact materials with the fiber direction parallel to the contact surface have stronger resistance to fusion welding and greater material arc erosion rate. Although graphite has the tendency to stabilize the arc, it has poor thermal stability in air, thus causing a high arc erosion rate of Ag/C electrical contact materials. The damage caused by the arc to the Ag/C electrical contacts is almost over the entire electrical contact surface and uniformly distributed, resulting in the formation of metal mounds on the surface of the anode contact and a mesh-like wall of silver on the surface of the cathode contact. The columnar particles of these convex walls are solidified from the body metal of the electrical contact [3] When the arc root stabilizes on a graphite particle, the surrounding silver is melted and raised to the periphery under the pressure generated by the arc column, and when the When the arc is extinguished or moves to a new place, the heat is transferred away toward the electrical contact body and the raised molten metal is immediately solidified [32]. In addition, the size of the graphite grains has an effect on the fusion welding performance; coarse-grained graphite has a greater fusion welding force than fine-grained graphite electrical contacts because there is more space between coarse-grained graphite and more silver on the surface of the electrical contact, resulting in a larger area of metal bonded to the body of the contact.

The skeleton effect of CAg/W electrical contacts
Ag/W electrical contact materials have the advantages of good electrical and thermal conductivity, arc erosion resistance, and fusion welding resistance, but the disadvantage is that the contact resistance is unstable. Ag/WC electrical contact materials take advantage of the good electrical and thermal conductivity of Ag, and the addition of WC can prolong the arc burning time, thus improving the fusion welding resistance of electrical contacts. The main mechanism of arc erosion of Ag/W electrical contact material is the skeleton effect of W. When the high temperature of the arc acts on Ag/W contacts, the melted silver is attracted by the capillary of the skeleton and can only vaporize at high temperature, causing the arc erosion of a large amount of silver, while the vaporization makes the temperature of tungsten particles lower than its melting point, and the tungsten particles are sintered together to form a skeleton that can restrict the flow of liquid silver, which makes Ag/W have high resistance to fusion welding and wear resistance. The size of tungsten particles has an influence on the arc erosion performance of Ag/W contact materials, and only when the tungsten particles have a certain particle size and composition can an ideal skeleton structure be formed, forming both a network of firmly interconnected tungsten particles and open capillaries with smooth surfaces [33]. In addition, maintaining an appropriate Ag content can both make the melt pool liquid viscous to mitigate droplet spattering during arc erosion and prevent crack generation [34].
Kinetic property effects of DAg/MeO-based electrical contacts
There are two arc erosion mechanisms present in the arc erosion of Ag/MeO electrical contact materials. One is the decomposition and sublimation of MeO, which consumes a large amount of arc energy and thus reduces the arc erosion due to evaporation effects; however, it also causes a continuous reduction of MeO elements, which makes the electrical contact material less resistant to fusion welding and arc erosion during long-term use. A typical representative of the arc erosion mechanism through the decomposition and sublimation of MeO is the Ag/CdO electrical contact material [35]. The other one is with high thermodynamic stability Me0 components or additives suspended in the molten liquid pool in the form of particles, which not only increase the viscosity of the liquid metal, but also increase the surface tension of the liquid metal, thus reducing the possibility of forming large liquid pools and reducing the possibility of spatter erosion. A typical representative of the arc erosion mechanism via MeO particles suspended within the molten state liquid pool is Ag/ SnO₂ electrical contact material [36].

Author

Hello, my name is Eva Xia, and I am currently the Marketing Manager at Yueqing Weup Technology Co., Ltd, located in Wenzhou, Zhejiang, China. With over a decade of experience in the accounting field, I have developed extensive knowledge and skills that enable me to excel in my role. Additionally, I have spent two years working as an English teacher, which enhanced my communication abilities and instilled discipline within me.

Having gained more than three years of valuable experience in overseas sales, I have had the opportunity to expand my horizons and develop a deeper understanding of the commercial landscape. This exposure has nurtured my business understanding and allowed me to navigate diverse markets confidently.

However, despite my accomplishments thus far, I remain dedicated to continuous growth and learning. My current area of focus revolves around electronic switches. It is a fascinating and dynamic field that constantly evolves with technological advancements. By delving deeper into this realm, I aim to enhance my professional knowledge and stay ahead of industry trends.

In summary, as a Marketing Manager at Yueqing Weup Technology Co., Ltd., I bring forth a wealth of experience in accounting coupled with the valuable skills honed during my time as an English teacher. Furthermore, my extensive overseas sales expertise has sharpened my business acumen. With a relentless thirst for knowledge and a specific interest in electronic switches, I strive to enhance my professional capabilities further while contributing positively to our organization’s success.

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