Activated Combustion High Velocity Air-Fuel (HVAF)

Activated Combustion High-velocity Air-Fuel (HVAF) spray utilises compressed air and LPG fuel combination to generate high velocity combustion gas streams. The optimized combination of high kinetic energy –thermal input allows deposition of coatings with desired microstructural features including fully dense, defect-free, phases with great retention and high adhesion strength. The exceptional capabilities of HVAF can be understood from its productivity which is highest amongst the competing thermal spray techniques to deliver as high as 35 kg/hr for WC-/ Cr3C2- based coatings.

The process involves a pre-mixed Air-Fuel mixture fed into the combustion chamber through the ceramic insert which is ignited initially with a spark plug. As the Combustion proceeds, the ceramic insert at the entrance of the combustion chamber gets heated up above the auto-ignition temperature of the mixture and takes the role of spark plug to enable stable combustion (also known as “Activated combustion”) throughout the process. The flame temperature during HVAF is much lower than that of HVOF since it uses an air-fuel mixture instead of an oxy-fuel mixture, which allows HVAF to coat thermally sensitive material with lesser thermal deterioration. Control of gas dynamics using diverse nozzles results in range of particle velocities, which translates into highly adherent, hard, oxide- and pore-free coatings. Prominent application sectors with HVAF technique include industries requiring wear, corrosion resistance and refurbishment.