In this process the coating material in powder form is melted in a hot plasma flame and propelled on to a prepared substrate surface to form a coating. When the spray contacts the prepared surface of a substrate material, the fine molten droplets rapidly solidify forming a coating.
|Heat Source||Plasma Flame|
|Flame Temperature (°C)||12,000 to 20,000|
|Particle Velocity (m/sec)||200 to 500|
|Porosity (%)||2 to 10|
|Coating Adhesion (MPa)||40 to 70|
Plasma spray system consists of a Plasma Spray Gun, Power Source, Powder Feeder, Control unit and Heat Exchanger. Plasma is formed inside the specially designed plasma spray gun, by introducing a high intensity electric arc between a cathode (tungsten electrode) and anode (nozzle) assembly. Plasma forming gas is introduced in this arc, where it gets ionised to form a plasma. When this plasma exits the special design convergent – divergent nozzle, it returns to its original state liberating extreme energy. The coating material in powder form is introduced in this hot flame, where it melts and is propelled by the flame on to the substrate surface.
The energy produced in a plasma is high resulting in very high temperatures at the plasma core. Thus ceramics with very high melting points are ideally sprayed with Air Plasma spray for achieving good quality coatings. The coatings produced by plasma spray are uniform, dense and have comparatively lesser porosity.