B. Wielage, C. Rupprecht, TU Chemnitz, Chemnitz, Germany; G. Paczkowski, Chemnitz University of Technology, Chemnitz, Germany
The improvement of the HVOF technology is one of the big challenges in the field of thermal spraying. In this paper, three different strategies are shown which influence hot gas flows in order to tailor inflight particle parameters and to increase the coating quality and the deposition efficiency of the process. First, a new combustion chamber design is presented. In contrast to classic systems, a ball-shaped chamber is used to increase the pressure up to an optimum. The influence of the fuel injection and atomization is discussed. Second, a concept for texturing expansion nozzles is shown. The sharkskin effect is well-known from other gasdynamic applications and also possesses a high potential for friction optimization between the gas flow and the torch. Third, the free gas jet is influenced by a swirled gas shroud that stabilizes and focuses the jet geometry and enhances the temperature profile of air-cooled nozzles. The functionality of the presented methods is demonstrated by numerical calculations and the practical application of an early HVOF torch prototype.
