Why should the flow of the main gas be strictly controlled?

       The flow rate of the main gas is one of the important process parameters. It directly affects the enthalpy and flow rate of the plasma flame, which in turn affects the spraying efficiency and coating porosity. Too large or too small air flow will lead to the degradation of spraying efficiency and the increase of coating porosity. If the air flow is too large, the ion concentration decreases. The excess air cools the plasma flame, which reduces the enthalpy and temperature, which is not conducive to the heating of the powder. The powder will not melt uniformly, the spraying efficiency will be reduced, and the coating structure will be loose. Porosity increases: On the contrary, if the air flow is too small, the working voltage of the spray gun will drop, the flame flow will be weak, and it will easily cause nozzle ablation. The main air flow commonly used in plasma spraying is about 2m3/h.