Investigation of the Powder Feeding Behavior of different WC-Co(Cr) Powders for ID Applications

Different markets pull for the development of HVOF spray guns for internal diameter (ID) applications. The current ongoing development of new HVOF spray guns for internal diameters (ID) leads to a demand for finer spray powders. Fine spray powders (< 20 µm) are necessary to achieve short spray distances and hence to lower the overall coatable internal diameter. Fine spray powders create new challenges for users of thermal spray devices. The first steps in the thermal spraying process chain are the powder preparation and feeding. If these two steps are not stable, no sufficient coating quality can be obtained. Thus, these initial steps in the process chain have to be in the focus when conducting research on finer spray powders. In the present work, two different powder feeder principles, the volumetric and fluidization principle, were compared to each other. The feeding behavior of agglomerated and sintered WC-Co(Cr) powders with powder fractions of -45+15 µm, -20+5 µm, and -10+2 µm were investigated. The particle size fraction in the powder feeder during feeding was investigated ex-situ by means of laser diffraction. Furthermore, the particle outflow from the injectors was recorded in-situ and analyzed by means of particle image velocimetry (PIV).