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1181 |
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Wednesday, June 04, 2008, Room 04 9:00 AM HVOF and Flame Spraying New very hard coatings and modern powder feeding for economic dense coatings against wear and corrosion |
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Numerical modeling of warm spray (two-stage HVOF) process |
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Hiroshi Katanoda* / Kagoshima University, JAPAN Jin Kawakita/ National Institute for Materials Science, Japan Seiji Kuroda/ National Institute for Materials Science, Japan |
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There exists many thermal spray techniques, ranging from plasma spray to cold spray. When focusing on the temperature range of the process gas, the cold spray covers 300 - 1000 K and the high velocity oxy-fuel (HVOF) thermal spray has the gas temperature of ~ 3000 K. Recently, the researchers of the cold spray technique tried to elevate the gas temperature over the conventional upper limit of ~ 1000 K, to make coatings of the powder materials which have wear-resistant or temperature-resistant properties. On the other hand, the gas temperature of the HVOF thermal spray is too high to avoid oxidation of the spray material. Therefore, the gas temperature of 1000 - 3000 K seems to have the potential to make for a better coating performance than if using cold spray or HVOF thermal spray. The authors developed a warm spray gun. It can control the gas temperature in the range of about 1000 - 2500 K, to make coating of temperature-sensitive material. The gun has a combustion chamber followed by a mixing chamber, in which the combustion gas is mixed with the nitrogen gas at room temperature. The mixed gas is accelerated to supersonic speed through a converging-diverging nozzle followed by a straight passage. In this paper, the performance of the warm spray gun is investigated by the simulation program developed by the authors. The gas flow as well as the particle velocity and temperature are predicted by the numerical simulation. |