Erzeugung hoher Partikelgeschwindigkeiten mit Hilfe der Stoßwellenkanaltechnik im Hinblick auf eine Anwendung in der Beschichtungstechnologie
Zusammenfassung der Projektergebnisse
This report presents the final status of the research in the generation of high particle velocities for coating technique. A new cold gas-dynamic spray technique (CGDS) was proposed in our previous work [1, 2, 3], which increases the solid particle velocity up to 1,500 m/s and, at the same time, keeps particle temperatures low to moderate. In conventional CGDS applications the particle impact velocities are in the range of 500 – 1000 m/s. Depending on the spray material and size, only spray material with a critical bonding velocity lower than 1000 m/s can be used. Furthermore, the coating quality increases when the impact velocity is close to the upper erosion velocity. Therefore, higher particle impact velocities extend the application range of CGDS and lead to a better coating quality with very low porosity, high bonding strength and hardness. This method uses the super- to hypersonic shock tunnel technology to generate a reservoir condition with high temperature and high pressure. The particles are injected into the nozzle flow downstream of the nozzle throat after the nozzle flow is fully established. An experimental facility has been set up, and several measuring techniques including PIV and LDA have been applied to obtain the reservoir condition and the particle velocities. The coating samples produced by this facility have been analyzed by the Surface Engineering Institute (IOT) of RWTH Aachen and demonstrate that this new technology can provide very dense coating layers with low porosity and high micro-hardness. The experiments performed clearly show that the shock tunnel technology allows achieving much higher particle velocities than the conventional methods. Correspondingly the coating samples indicate a higher quality of the coating. But the experiments also showed that with the current setup much higher filling pressures (than expected) are necessary to counterbalance the pressure losses caused by the diaphragm opening. For industrial applications the diaphragms would have to be replaced by a fast acting valve mechanism. These problems could be overcome by using a diaphragm-less detonation tube as it is the case for the detonation spraying gun. Combining a detonation shock tube with a nozzle to accelerate the particles compared to the existing spraying methods would lead to much higher performances and benefit from the advantages of the shock tube cycle. It would be further interesting to study the possibility of injecting the particles through holes in the nozzle wall.
Projektbezogene Publikationen (Auswahl)
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Shock tunnel produced cold gas-dynamic spray: modelling and simulation. In G. Jagadeesh, E. Arunan, and K.P.J. Reddy, editors, 25th Int. Symposium on Shock Waves, pages 733–738, Bangalore, India, July 2005
X. Luo, G. Wang, and H. Olivier
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Numerical studies of the application of shock tube technology for cold gas dynamic spray process. Journal of Thermal Spray Technology, 16(5-6):729–735, 2007
R. Nickel, K. Bobzin, E. Lugscheider, D. Parkot, W. Varava, H. Olivier, and X. Luo
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The generation of high particle velocities by shock tunnel technology for coating application. 26th Int. Symposium on Shock Waves, Göttingen, Germany, July 2007
X. Luo, H. Olivier and I. Fenercioglu
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Parametric investigation of particle acceleration in high enthalpy conical nozzle flows for coating applications. Shock Waves, 17(5):351– 362, 2008
X. Luo, G. Wang, and H. Olivier
