Points for attention in the selection of plasma spraying process gas

       The gas that is fed into the spray gun for compressing the arc and ionizing is called the main gas. The main gases commonly used in plasma spraying are Ar, He, and N2. In order to increase the enthalpy of the plasma arc, 5% to 10% of H2 is often added to the ion gas. Or N2, called secondary gas or secondary gas, and the gas used to drive the powder is called powder feeding gas. Usually, the same gas as the main gas is used as the powder feeding gas, and flammable, explosive and combustion-supporting gases, such as O2, H2, C2H2, etc., are prohibited.



When choosing the working gas, choose according to the two principles of practicality and economy. From a practical point of view, as long as it is not harmful to the spray material and the workpiece material and is inexpensive, it can be selected as the working gas. Using pure N2 as the main gas and H2 as the secondary gas is not only cheaper, but more importantly, the nitrogen-hydrogen plasma flame has high heat, fast heat transfer, and large heat and kinetic energy transferred to the spray powder, but at the same time, the cooling of the spray gun Performance requirements are high. In addition, N2 and H2 cannot be used as working gases for spraying materials and substrates that have harmful reactions with nitrogen and hydrogen and affect the composition and quality of the coating. However, the occurrence of harmful reactions must be confirmed, because in fact, although there are many raw materials that may undergo severe nitriding reactions, they do not actually occur during spraying.



In the case where the material reacts unfavorably with nitrogen, Ar is used as the primary gas and H2 as the secondary gas. The ionization potential of Ar is low, the plasma arc is easy to ignite and stabilize, and the plasma arc is short, and it is also suitable for spraying small and thin parts. Ar is also used as the primary gas, and N2 or N2 + H2 is used as the secondary gas; or He is used as the primary gas, and H2, N2 or N2 + H2 is used as the secondary gas.