High-speed gas spray guns like a small rocket engine,Figure 2 shows the structure of the JetKote spray gun. It consists of a closed combustion chamber and a nozzle.The gas and oxygen are injected into the combustion chamber at a pressure of 0.5 to 3.5 MPa and a flow rate of up to 0.016 m3 / s. The mixture is continuously combusted and the combustion products are swollen and ejected from a long nozzle to form a supersonic flame. As a sign of high temperature supersonic airflow, you can see the flame in the bright and dark rhombic shock. The sprayed material of the powder is injected into the nozzle from the combustion chamber and the nozzle, into the center of the flame,and is heated and accelerated to obtain a high kinetic energy and is ejected from the nozzle. Spray particles will not be oxidized in the combustion products. As the particles are in the center of the flame, the oxidation is also slightly slight in the process of leaving the nozzle to reach the surface of the workpiece, and the temperature of the flame in the combustion chamber usually does not exceed 3000 ° C.The flame flow from the nozzle will be lower. Its speed is directly related to the combustion chamber pressure. The initial JetKote achieves an average flame speed of 1770 m / s, which can accelerate the WC-Co particle spray particles with a diameter of 5 to 45 m to a high flight speed of 315 m / s. This is far more than any other thermal spraying method can achieve the speed. But this is only the initial level of high-speed gas spray. By the beginning of 1984, the improved JetKote Ⅱ particle speed has greatly improved, the calculated particle speed to more than 800m / s. The hardness of the coated tungsten carbide coating has been significantly higher than that of the D-Gun coating.