High velocity oxygen fuel

High Velocity Oxy-Fuel (HVOF) is a thermal spray technique used to deposit protective coatings on a substrate.

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HVOF Process

A blend of fuel (gaseous or liquid) and oxygen is injected into a torch and burned. The combustion products flow through a nozzle that accelerates the flow to a speed up to 1500 m/s. A powder feed stock is injected into the gas stream, which accelerates the powder up to 800 m/s. The stream of hot gas and powder is directed towards the surface to be coated. The powder partially melts in the stream, and deposits upon the substrate. The resulting coating has low porosity as and a high bond strength.

HVOF coatings may be as thick as 12mm (1/2"). It is typically used to deposit a wear and corrosion resistant coatings on a material. Ceramic and metallic powders can be deposted using HVOF. Common powders include WC-Co, Chromium carbide, MCrAlY, and alumina.

HIGH-VELOCITY OXY-FUEL SYSTEMS

The process involves atomization of a metered oxy-fuel mixture, which is made to undergo combustion. The exit nozzle of the combustion chamber is so designed that the flue gases leave the chamber at a super-sonic speed. The coating alloy, in a powdered form is then fed into this stream, which strikes the prepared substrate at an extremely high velocity. The unique advantages of this system include: high density of deposits with least porosity, substantially higher bond strength, high and controllable coating hardness, coating thickness exceeding 12mm achievable, smoother as sprayed finish. The system uses kerosene as fuel, which not only generates the desired BTU but also is inexpensive and abundantly available. A very high and faster spray rate is achievable.