There are several different thermal spray processes. Here are some of the most common types:
• Wire Flame Spray:-
The process is the spraying of molten metal onto a surface to provide a coating. The material in wire form is melted in a flame (Oxy-Acetylene flame most common) & atomized using compressed air to form a fine spray. When the spray contacts the prepared surface material, the fine molten droplet rapidly solidifies forming a coating.
• Powder Flame Spray:-
Material in powder form is melted in a flame (Oxy-Acetylene or Hydrogen most common) to form a fine spray. When the spray contacts the prepared surface of a substrate material, the fine molten droplets rapidly solidify forming a coating.
The main advantage of this process over the similar wire flame spray process is that a much wider range of materials can be easily processed into powder form giving a larger choice of coatings.
• Wire Arc Spray:-
This form of thermal spraying uses wire material as a feedstock. An electric arc is used as the heat source. As the wires are fed towards each other, an electric arc is struck between the wires creating a temperature of around 4,000°C.
This temperature causes the tips of the wire to melt and once molten state, a stream of compressed air or inert gas is used to atomize and accelerate the feed metal towards the substrate.
• Air Plasma Spray:-
In this process, the coating material in powder form is melted in a hot plasma flame and propelled onto 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.
• HVOF Spray:-
The HVOF (High Velocity Oxy-Fuel) Thermal Spray Process is the same as the conventional Powder Flame Spray process (LVOF) except that this process has been developed to produce extremely high spray velocity.
• Detonation Spray:-
Oxygen and fuel (acetylene most common) is fed into the barrel along with a charge of powder. A spark is used to ignite the gas mixture and the resulting detonation heats and accelerates the powder to supersonic velocity down the barrel. A pulse of nitrogen is used to purge the barrel after each detonation. This process is repeated many times a second. The high kinetic energy of the hot powder particles on impact with the substrate results in build up of a very dense and strong coating.