Abstract
The High Velocity Oxy-Fuel (HVOF) thermal spraying can make highly tough and dense coatings on a solid surface. It is experimentally recognized that the quality of the coating largely depends on the particle velocity and temperature, which depend on the gas flow in the HVOF gun. The gas flow in the gun is affected by two factors; pipe friction and cooling along the inner wall of the long gun. This paper investigates the gas/particle flow in the HVOF gun by using quasi-one-dimensional analysis including the effects of pipe friction, cooling and nozzle geometry. The standard values of the parameters, to include the effects of pipe friction and cooling are selected based on the experimental result. The nozzle length is varied in the range of 110-330 mm. The calculated results show that (1) the pipe friction decreases the particle velocity and increases the particle temperature, (2) the cooling increases the particle velocity and decreases the particle temperature, (3) the maximum particle velocity is obtained when the length of the diverging part of the nozzle is approximately equal to the length of the following non-diverging straight part, (4) the longer nozzle results in larger particle velocity at the nozzle exit. These numerical results help understand the gasdynamics occurring in the HVOF gun, and assist in the design of the gun.
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