Effect of Expansion State of Combustion Gas Jet on High Velocity Oxygen-Fuel Thermal Spraying Process

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  • Sakaki Kazuhiko
    Department of Mechanical Systems Engineering, Faculty of Engineering, Shinshu University
  • Shimizu Yasuo
    Department of Mechanical Systems Engineering, Faculty of Engineering, Shinshu University
  • Gouda Yoshiaki
    Department of Mechanical Systems Engineering, Faculty of Engineering, Shinshu University

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Other Title
  • 高速フレーム溶射プロセスに及ぼす燃焼ガスジェットの膨張状態の影響
  • コウソク フレーム ヨウシャ プロセス ニ オヨボス ネンショウ ガスジェット ノ ボウチョウ ジョウタイ ノ エイキョウ
  • Effect of expansion state of combustion gas jet on high speed flame spray process

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Abstract

The Effect of expansion state of combustion gas jet on high velocity oxygen-fuel thermal spraying process was investigated using a diverging gun nozzle exit by numerical simulation and experiments with spray powder of Ni-17 mass%Cr-6%Al-0.5%Y. Two different nozzle shapes with a constant throat diameter, namely (i) a convergent-barrel type available in the market and (ii) a convergent-barrel-divergent type, were used. The convergent-barrel-divergent nozzles were designed in such a way that the 15 mm divergent part length had a minimum effect, so that only the effect of expansion state of combustion gas jet was investigated. Numerical simulation studies were carried out by assuming the gas flow within the nozzle to be a quasi-one-dimensional isentropic flow of a semi-perfect gas.<BR>The numerical simulation results showed a decrease in temperature and density and an increase in velocity of the gas with the diverging nozzle exit, but its effect on the spraying particle behavior was very little.<BR>Experimental results showed that the expansion state of combustion gas jet changed from under-expansion to correct-expansion, to over-expansion with increasing nozzle exit diameter. Among them, the particle velocity at a spray distance of 200 mm reached a maximum with correct-expansion state of the gas jet due to an increased gas jet velocity. This resulted in an increase in the bonding strength of the NiCrAlY coating. However, the effect of the expansion state of the jet on the structure, hardness and degree of oxide content of the coatings was little. Also, the deposition efficiency of the coatings was found to increase with the increase in the nozzle exit diameter.

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