What is the Plasma Spray Coating process?
The plasma spray process is a thermal coating process that uses high temperatures and high energy, electrically produced heat sources to melt and accelerate fine particles onto a substrate. The molten metal particles cool down after hitting the substrate and form uniform coatings.
Plasma spray is the most versatile of the thermal spray processes because of the extremely high plasma temperatures associated with the plasma plume, which makes it possible to melt or vaporize any known substance. The plasma produced has a high temperature between 10,000-15,000 degrees Celsius.
Common gases used as electric arc gases include Ar, N2, H2 and He.
The plasma spray process is commonly used in aerospace, power generation, paper, oil and gas, and semi-conductor industries.
Plasma Spray Process System
The plasma spray process has several key components; plasma torch, process control (which controls the arc current and voltage and plasma gas flow rates), power supply, gas supply, high-frequency arc starter, and material feeder.
For the plasma spray system, one of the most important components is the plasma torch. The plasma torch is constructed of a gas injector, cathode, and anode. An electric arc is formed and stretched between the anode and cathode which ionizes the gas into an extremely hot plasma which is propelled out of the torch by the gas velocity. Powder is then injected into, heated by, and accelerated by the plasma gas stream towards the substrate to form the coating.
During the plasma spraying process, powders or wires are melted in the high heat of the plasma plume. These materials form the coating that will evenly distribute onto and coat the target substrate. For the plasma spray process to get an even coating onto the substrate, and produce particles of the correct size, speed and heat temperature, several factors must be considered:
- Plasma plume temperature and velocity
- Electric arc discharge power
- Spray distance
- Speed of torch and substrate movement
- Times a substrate is sprayed
- Powder particle size
- Rate, velocity, and angle of powder injection into plasma plume