Research of numerical simulation for HVAF thermal spraying process on rotational roll

Abstract HVAF thermal spraying has the characteristics of low spraying temperature, high coating density, and strong corrosion resistance. It is widely used in the aerospace, iron–steel metallurgy, national defense and military industry, petrochemical industry, and other fields for manufacturing protection and repair strengthening, which has achieved significant economic benefits. In this study, a numerical model of HVAF thermal spraying on a circular roll was established by the computational fluid dynamics method. The characteristics of the spraying flame, evolution of the gas composition mass fraction, and influence of the spraying parameters on particle flight behaviors were calculated and revealed. Based on the dynamic mesh method, the effect of roll speed on the spraying flame characteristics and particle flight behaviors was analyzed. Calculations show that the spraying flame is extruded at the Laval nozzle and the speed rapidly increases to 805 m/s, which increases to a supersonic speed through the barrel. The flame flow rises rapidly reaching the surface of the roll, which is 780 m/s. The highest temperature is in the combustion chamber, and the flame temperature of the airshed is a damped vibration. The flame covers the surface of the roll to preheat it, and the flame temperature there decreases layer by layer from the inside to outside. The particle diameter significantly effects the powder flight behavior. The flame velocity increases with the barrel length increasing. The flame temperature up to the peak when the barrel length is 190 mm. As the rotation speed of the roll increases, the temperature, velocity, and pressure of the flame flow on the roll surface change in a certain extent. The particle spatter will be increased with the rotational speed increasing of the roll, which little affects the particle temperature.