 HVOF, short for High Velocity Oxygen Fuel thermal spray, is a relatively new coating method that provides high-density, extremely wear-resistant coatings. The special combination of alloys are instantaneously melted, atomized and propelled towards the substrate at incredibly high velocities (supersonic speeds in excess of Mach 12) by a mixture of oxygen and jet-quality fuels. (See Figure 1 below.) The kinetic and thermal energy imparted to the coating-particles cause the coating to be virtually bonded to the substrate. The substrate temperature hardly exceeds 200°F, hence the process does not impart physical defects, stresses or warping to the substrate. In fact, the coating exhibits very low stress, allowing thicker coatings to be applied than with traditional methods.
Figure 1. Fuel is composed of varying mixtures of kerosene, acetylene, propylene and hydrogen. When the fuel comes in contact with the oxygen, it ignites, heats the powder to just below its melting point, and shoots the powder onto the substrate at velocities well over 5,000 feet per second.
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