Sensors in Spray Processes |
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Authors: | P Fauchais M Vardelle |
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Affiliation: | (1) Laboratory Science of Ceramic Materials and Surface Treatment Processes, SPCTS, UMR 6638 CNRS, University of Limoges, 123 Rue Albert Thomas, 87060 Limoges Cedex, France; |
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Abstract: | This paper presents what is our actual knowledge about sensors, used in the harsh environment of spray booths, to improve
the reproducibility and reliability of coatings sprayed with hot or cold gases. First are described, with their limitations
and precisions, the different sensors following the in-flight hot particle parameters (trajectories, temperatures, velocities,
sizes, and shapes). A few comments are also made about techniques, still under developments in laboratories, to improve our
understanding of coating formation such as plasma jet temperature measurements in non-symmetrical conditions, hot gases heat
flux, particles flattening and splats formation, particles evaporation. Then are described the illumination techniques by
laser flash of either cold particles (those injected in hot gases, or in cold spray gun) or liquid injected into hot gases
(suspensions or solutions). The possibilities they open to determine the flux and velocities of cold particles or visualize
liquid penetration in the core of hot gases are discussed. Afterwards are presented sensors to follow, when spraying hot particles,
substrate and coating temperature evolution, and the stress development within coatings during the spray process as well as
the coating thickness. The different uses of these sensors are then described with successively: (i) Measurements limited
to particle trajectories, velocities, temperatures, and sizes in different spray conditions: plasma (including transient conditions
due to arc root fluctuations in d.c. plasma jets), HVOF, wire arc, cold spray. Afterwards are discussed how such sensor data
can be used to achieve a better understanding of the different spray processes, compare experiments to calculations and improve
the reproducibility and reliability of the spray conditions. (ii) Coatings monitoring through in-flight measurements coupled
with those devoted to coatings formation. This is achieved by either maintaining at their set point both in-flight and certain
spray parameters (spray pattern, coating temperature…), or defining a good working area through factorial design, or using
artificial intelligence based on artificial neural network (ANN) to predict particle in-flight characteristics and coating
structural attributes from the knowledge of processing parameters. |
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