Abstract
The representative factors that have been studied in the development of thermal spraying processes are the heating and the acceleration techniques of spray particles. As the simultaneous promotion of heating and acceleration of particles in thermal spraying, which is performed in an extremely short time, is contrary to each other, there is a limit for the attainment of both. In this study, from the point of acceleration of spraying particles, the velocity of WC cermet spraying particles in two types of high velocity oxygen-fuel flame spraying process was measured by using a CCD video camera system with a high-speed electrical shutter. The determined velocities of the WC-12 mass%Co powder in the size range of 45 to 5 μm and the WC-20 mass%Cr3C2-7 mass%Ni powder in the size range of 45 to 10 μm were 300∼600 m·s−1 and 300∼500 m·s−1, respectively. It is apparent that the particle velocity in the high velocity oxygen-fuel flame spraying process was much higher than that in the plasma spraying process. These results were consistent with those reported previously. The driving force for higher acceleration in the high velocity oxygen-fuel flame spraying process was discussed. As the result of the estimation of the drag force for particles in spraying fluid, it was derived that the main factors which dominated the higher acceleration were large in density and high in velocity of the combustion gas mixture as compared with Ar-He plasma jet.
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