Thermal & Plasma Spraying
Thermal and plasma spraying processes are widely used for coating components with a layer of material that hardens the surface, makes it abrasion resistant, creates a thermal barrier or corrosion resistant barrier and these are only some of the application areas possible with these processes. Flame spraying processes are widely used to protect structural steel with a zinc coating. They are also used to build up worn components. The wire or powder melts in the oxy-fuel flame, and is propelled onto the surface by the expansion of gases. HVOF is a similar process used for high quality powder spraying using oxygen and hydrogen, acetylene, propylene or kerosene. Here the flame speeds achieved are much higher and this has implications for the quality of the coating. Detonation gun spraying has a chamber in which oxygen and acetylene are exploded to propel the powder coating. Metals can also be sprayed using an electric arc process. The two wires are fed through contact tubes and melt on contact. The droplets are propelled onto the work surface with compressed air. Plasma spraying uses an electric arc between the gun and the work to transfer the powder in a plasma stream. An inert gas protects the process from oxidation.
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