These very high particle velocities are utilised to create extremely dense, well bonded coatings.
These systems predominantly utilise powdered material as the feed stock with some variations using wire.
The extremely high velocities come at a price. The dwell time of the particles in the actual heat source is very low so therefore we are limited in the type of material and powder particle size that can be sprayed. What is sprayed however, creates amongst the best wear resistant coatings currently available (carbides).
HVOF (High Velocity Oxy-Fuel) properties table
Principle of operation
High volumes of either gas or liquid fuel are fed into the HVOF gun and combined with oxygen. In a combustion chamber area, the fuel and oxygen mixture is combusted creating a constantly expanding heat source.
The rapidly expanding combustion gases are directed into a barrel or air-cap tunnel which assists the high velocities. The barrel or air-cap can be a parallel bore or, in some cases, a convergent/divergent configuration.
The result is a supersonic or hypersonic hot gas stream which propels the particles onto the surface at extremely high velocities.
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