Ultrafine Powder Feeding In Thermal/Cold Spray Applications

Cold spray and thermal spray processes (HVOF, plasma-spray) require increasing use of very fine powders. Existing conventional volumetric feeders are ill-suited for this purpose. Ultrafine powders typically tend to agglomerate in wheel-type powder feeders, resulting in clogging problems.

This paper presents a novel and autonomous powder feeder especially designed to feed very fine particles. It uses the principle of a fluidized bed to create a continuous and uniform feed of submicron powders. Primarily designed for cold-spray applications, this new feeder can be used to feed submicron particles to high velocity oxy-fuel (HVOF) and plasma processes.

This paper aims to share some of the capabilities of the Polycontrols ultrafine powder feeder. It gives an overview of the latest developments in the projection of YSZ submicron powders (ZrO₂-Y₂O₃, D50 of 0.5 µm) without suspension, for the production of thermal barrier coatings (TBCs).

Interesting results are presented in cold spray, as this process is typically associated with ultrafine powders. The micrographies of Copper, Nickel, Zinc, Aluminum, Aluminum Alloys and WC-Co coatings, with median particle sizes ranging from 6 µm to 55 µm, are presented here. Stability, reproductibility, and controllability are discussed in this article.