High Velocity Air Fuel Thermal Spray Process

The HVAF (High Velocity Air Fuel) Thermal Spray Process is basically the same as the HVOF (High Velocity Oxygen Fuel) process except that this process uses air instead of oxygen.


The coatings produced by HVAF are similar to those produce by the HVOF process. HVAF coatings are very dense, strong and show low residual tensile stress or in some cases compressive stress, which enable very much thicker coatings to be applied than previously possible with the other processes.

Most HVAF systems are air cooled using the same air for combustion. While air is free compared to oxygen, this is slightly offset by the cost of larger air compressors required.

The very high kinetic energy of particles striking the substrate surface do not require the particles to be fully molten to form high quality HVAF coatings. This is certainly an advantage for the carbide cermet type coatings and lower melting point materials and is where this process really excels.

HVAF coatings are used in applications requiring the highest density and strength not found in most other thermal spray processes. New applications, previously not suitable for thermal spray coatings are becoming viable.

HVAF versus HVOF

The significant difference is that air/fuel versus oxygen/fuel combustion is flame temperature. Air/fuel is typically 500 to 1000°C lower. Propane/air gas has an adiabatic flame temperature of 1967°C while propane/oxygen is 2526°C. This results in lower particle temperature for HVAF, which has positive and negative effects on coating properties depending on materials being sprayed. Carbide cermet type coatings and lower melting point materials may benefit from less thermal degradation and oxidation.

Gordon England Surface Engineering Forum

Gordon England Independent Thermal Spray Coating Consultant
Telephone: +44 (0)1252 405186

Email: tsc@gordonengland.co.uk

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