Abstract
Characteristics of atmospheric plasma spraying based on single-cathode-anode-systems like the F4 gun with convergent-cylindrical nozzle designs, are voltage fluctuations caused by periodically changes of the arc length. As a result continuous varying plasma flow properties lead to inhomogeneities during energy transfer to injected powder particles and variations of coating quality and process efficiency. With an adjusted convergent-divergent nozzle design and optimized high energy plasma parameters it is proven that process efficiency and stability could be significantly increased, also due to the reduced arc movement. A drawback in this case is the increased anode wear which needs to be optimized to secure industrial usage. Aim of this work was to minimize the anode wear of contoured convergent-divergent nozzles by using high efficient plasma parameters. Therefore arc characteristics in different nozzle designs were analyzed and the influence of the geometry to arc anode attachment was investigated. Consequently a stepwise optimization of anode wear by keeping the plasma fluid dynamic properties almost constant could be achieved. The results contribute to understanding of the arc characteristics in atmospheric plasma spraying. Also a new concept of a ”three-zone anode geometry“, convergent-inlet-section, cone-shaped arc movement section and a divergent plasma fluid shape section was developed.
