The resultant hot gas expands rapidly and exits through a converging–diverging nozzle. The jet velocity produced at the exit of the barrel (>2,000 m/s) exceeds the speed of sound. A powder feed stock is injected into the gas stream at various locations, dependant on the chosen Gun or Torch. It is then accelerated up to approximately 700 m/s.
The jet of hot gas and powder (spray stream) is directed towards the surface to be coated. The powder partially melts in the stream and deposits upon the substrate. The resulting coating has, among other attributes, very low porosity and high bond strength.
A wide variety of materials can be applied using the HVOF process in thicknesses ranging between 0.05mm to a few mm.
In addition to acetylene fueled HVOF, EPC also operate the state of the art eGun™. The eGun™ is a liquid fuel HVOF torch that utilizes ethanol as its fuel. The eGun™ is capable of operating at combustion chamber pressures up to 13 bar (188 PSI). This is 3 to 5 bar (43 – 73 PSI) greater than conventional kerosene HP-HVOF systems. It has been shown that higher combustion chamber pressure generates higher flame velocity which in turn generates higher particle velocity. Higher particle velocity results in improved coating density and better overall coating integrity. It is also very easy to run at low flame velocity for slow and hot parameters to produce very good bonding (rough) flash coats.
A wide variety of materials can be applied using the HVOF process, in thicknesses ranging between 0.05mm to few mm.
Coatings applied via HVOF process include:
Typical applications of the HVOF process: