Studies On The Jet Fluctuation Of DC Arc Plasma Torch

As a widely utilized thermal spray technology, arc plasma spraying technique has been adopted in many industrial fields, such as chemical engineering, metallurgy, mechanical engineering, space-navigation et al., around the world. The unsteadiness of the spraying jet often lead to oxidation and insufficient melts of the powders in plasma spraying application. A decrease of the quantity of coating is caused further. So it has important significance to investigate the causations of the jet unsteadiness and their characteristics.The core contents of this dissertation are the investigations on the characteristics of the unsteadiness of plasma jet by means of the spectroscopic diagnostic technology. A high-speed, high-resolution, multi-line spectroscopic diagnostic system has been built up. The fluctuation characteristics of DC arc plasma jet have been studied with this system by the aid of high-speed digital photography technique. From the investigations on the signals and FFT spectra of the spectral line intensity of the jet, the voltage of the arc, and the output of the power source, it is reported in this dissertation that there are three causations to the jet fluctuation: the output characteristics of the power source, the restrike of the arc, and the fluid dynamics of the jet. The influence of the power source on the jet fluctuation is dominating in argon plasma jet. The causations each have characteristic frequencies and distributions in the jet profile respectively. It is proved experimentally that there is not a steady, laminar core in the jet. Strong influence of the operation power of the plasma torch on the jet steadiness has been described. The frequency characteristics of the arc restrike are represented in this dissertation. The variations of the fluctuation intensity and characteristic of the arc restrike against gas flow rate, component structure of the plasma gas and ablation level of the anode have been studied in this dissertation. The distribution of particle density of nitrogen atom is described under the assumption of Local Thermal Equilibrium.Much works has been distributed to the development of a new long-arc plasma...