ON LINE CONTROL OF A FLAME SPRAY PROCESS

摘要

Flame sprayed coatings present very often reproducibility problems due to spray parameter variations. In fact the quality of coatings is strongly linked to the temperature and velocity of particles at impact and on the substrate, and coating temperature evolution before (preheating), during (spraying) and after (cooling). The particle temperature and velocity measurements require sophisticated devices rather expensive and not well adapted to work in the harsh environment of spray booths. Moreover with flames the particle surface temperature is generally below 2200K which make the measurements more tricky than under plasma conditions. That is why, a new system, the Spray and Deposit Control (SDC) has been developed which allows to follow continuously both the light emitted by hot particles (maximum intensity, mean trajectory and trajectory dispersion) and the substrate and coating temperature evolution during spraying. This light system (800gr), fixed on the torch has been tested for flame spraying of NiAl. This paper presents the evolutions of SDC parameters with process and coating parameters, a strategy for an on-line control, and a zone of "correct values" and acceptable variations for the process inputs.