| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1658129 | Surface and Coatings Technology | 2013 | 5 Pages |
Wire arc spraying arc is a deposition procedure in which coating characteristics can be controlled by optimizing the spraying nozzle geometry or the process parameters. This paper presents the effect of spraying nozzle geometry (and dynamic of gases) on the properties of steel coatings. For this purpose, a spraying gun in electric arc with two wires was used, provided with a frontal and an axial nozzle. The frontal nozzle had different inclination angles of inner surface in order to generate a convergent–divergent geometry of gaseous fluid jet. The axial nozzle enabled the atomization and the acceleration of particles melted in electric arc towards substrate surface. The computational fluid dynamics (CFD) analyses of gaseous fluid dynamics, performed using continuity equation and the moment equation for different inclination angles of frontal spraying nozzle, led to the determination, inside the spraying jet, of a high speed zone (HSZ). The experimental results, obtained by the determination of particles velocities, of the coating porosity and by micrographic and SEM (scanning electron microscopy) analyses of the coating, demonstrated that HSZ influenced the velocity and the temperature of sprayed particles and implicitly the coating quality. So, for inclination angles of the inner surface more than the inclination angle of the wires, the air jet is convergent at the electric arc level and the resulting HSZ compressed the arc, causing increases both of current density and melting temperature of the material. In this case, the obtained coatings are fine, characterized by a reduced porosity due to the high velocity and temperature of sprayed particles. For inclination angles of inner surface lower than the inclination angles of wires, HSZ is formed in front of the electric arc, causing the decrease of particles temperature and velocity, thus altering coating properties.
► Determination of the zone where the fluid velocity in maximum-HSZ ► Establishing of HSZ position towards the formation point of the electric arc ► The carrying out of spraying head and the establishing of the frontal nozzles ► HSZ position towards the electric arc determines the deposition proprieties.
