New Developments in HVOF Spraying for Internal Diameter Coatings

An HVOF extension gun for spraying internal diameters down to 5” (127 mm) has been developed and evaluated. The spray gun utilizes vortex stabilization of the flame which permits operation with a minimal length combustion chamber. Small spray distances and subsequent reduced particle dwell times present a challenge for heating and accelerating powders to achieve typical HVOF coating benchmark properties such as hardness, density and residual stresses. Initial coating characteristics and process/system capabilities are discussed.