Abstract

The High-Velocity Combustion Wire Process is a new high-velocity combustion process now being used in the thermal spray industry. This process combines air, oxygen, and a fuel gas to generate a high-temperature, high-velocity plume that is optimum for producing metallic coatings. Analytical studies were conducted to investigate gas and droplet dynamics for the spraying of three different materials: aluminum, stainless steel, and molybdenum. With the relatively low flame temperatures of the process, the feedstock wire is melted by convective heat transfer with no superheating or vaporization of the droplets. When the droplets strike the substrate, their temperature peaks as the high kinetic energy of the droplet is transformed into thermal energy. The conservation equations were solved using the TORCH computer model, yielding the temperature and velocity profiles as a function of location. The PROCESS gas/droplet computer program was then employed to calculate the dynamics of the molten droplets. The results of this modeling was confirmed with process diagnostics. Experimentation included droplet temperature measurements using a two-color pyrometer and droplet velocity measurements using particle imaging velocimetry for the stainless steel material system. The coatings produced in the study exhibit superior quality with high density, high hardness, low oxide content, and high bond strength.

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