The Process As the gas mixture burns, the powder particles are melted and accelerated down the barrel. Temperatures above 6000 ºF are attained within the combustion chamber while the substrate temperature is maintained below 350 ºF by a gas cooling system. Particle velocities of approximately 2,500 ft/s are produced. The kinetic energy released by impingement upon the substrate contributes additional heat and promotes bonding, high density, and appreciable hardness values. The coating is built up to the specified thickness while the workpiece is rotated or passed in front of the gun.