| Techniques : | |
Flame spray process
Arc spray process
Plasma spray process
Detonation spray process
HVOF spray process (High Velocity Oxygen Fuel)
The cold gas dynamic spray process
The HVOF thermal spray process uses the combustion of gases, such as propane, propylene, hydrogen, or a liquid fuel such as kerosene. Fuel and oxygen mix and atomise within the combustion arc under conditions that monitor the correct combustion made and pressure.
The process creates a very high velocity which is uses to propel the particles at near supersonic speeds before impact into the substrate. One of the basis rules of spraying is that high combustion pressure = high gas velocity, high particle velocity and resulting high coating quality.
One of the key benefits of this system’s high velocity is the extremely high coating density and low oxide content. The low oxides are due partly to the speed of the particles spending less time within the heat source and partly due to the lower flame temperature (around 3000°C) of the heat source compared with alternative processes.
The very high kinetic energy of particles striking the substrate do not require the particles to be fully molten to form high quality HVOF coatings. This is certainly another advantage for the carbide cermet type coatings and is where this process excels.
Some HVOF coatings can be sprayed very thick due to the exceptionally high velocities producing coatings in compression instead of tension.
HVOF coatings are used in applications requiring the highest density and strength not found in most other thermal spray processes.
 
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