The principle of supersonic arc spraying

　　The principle of arc spraying is to use two continuously fed metal wires as self-consumption electrodes, generate an arc at its end as a heat source, atomize the molten wire with compressed air, and spray to the working parts at supersonic speed to form a thermal spraying method that combines a coating with high strength, low porosity and low surface roughness. Its working principle is the same as ordinary arc spraying (subsonic atomization), supersonic arc spraying is a continuous process of melting-atomization-deposition. However, in the atomization method, supersonic arc spraying has a fundamental difference from ordinary arc spraying, that is, supersonic arc spraying is the use of supersonic atomization. Its advantages are: good atomization effect, small and uniform particles after atomization, high speed, conducive to obtaining high-quality coating. Supersonic arc spraying uses a Laval nozzle to increase the velocity of the air flow from subsonic to supersonic, strengthening the air flow to the particles, thereby increasing the particle velocity. Particle velocity has a great influence on the properties of the coating. The particle velocity is high, the impact effect on the matrix when the particle is deposited is strong, and the particle deformation is sufficient. It is conducive to the bonding between particles and substrates, particles and particles, thereby improving the bonding strength and cohesion strength of the coating; The particle velocity is high, the flight time in the air before particle deposition is short, and the oxides produced in flight are less, which is conducive to the binding of particles, thereby improving the cohesive strength of the coating and reducing the porosity of the coating. The higher the particle velocity, the better the high-quality coating. With the replacement of thermal spray equipment, particle velocities are increasing and the quality of coatings is constantly improving.

　　Supersonic atomization reduces the particle size and the roughness of the coating. Roughness is an important performance indicator of the coating, which depends on the particle size after atomization. Supersonic atomization strengthens the effect of air flow on the melting metal at the end of the wire, and the atomized particles are fine and uniform, which greatly reduces the roughness of the coating. At the same time, the reduction of particle size also reduces the splash in the process of particle flattening, which is conducive to reducing the porosity of the coating.

　　Supersonic atomization is the starting point of supersonic arc spraying, which is the fundamental difference between it and ordinary arc spraying.

　　Supersonic arc spraying equipment includes power supply, spray gun, wire feeding mechanism and its accessories, and the key equipment is supersonic arc spray gun. Our company adopts imported nozzles, and the spraying current is stable, which can ensure the atomization effect of the wire and the quality of the coating, and the spraying area reaches 20㎡.

　　When arc spraying, the temperature of the arc zone is as high as 5000-6000 °C, and the nozzle is cooled by air cooling.