Supersonic flame spraying is a new type of thermal spraying technology invented in 1981 by Browning in the United States. The core of the HVOF equipment is the spray gun. The spray gun consists of a combustion chamber (to fully heat and accelerate the spray material particles), a Laval nozzle (to accelerate the flame flow to supersonic speed) and a constant cross-section nozzle (to make the spray material particles It is fully heated and accelerated) composed of three parts.