Comparative study of two nozzle assemblies for high velocity oxy fuel (HVOF) thermal spray coating process

摘要

The aim of this study is to provide the thermal spray coating community with a parametric study and optimized quantifiable variables for two gun nozzle geometries (Oerlikon Metco DJ1050 and DJ2700) used in High Velocity Oxy Fuel thermal spray coating. The study applied a statistical Design of Experiment technique to the results obtained by Computational Fluid Dynamics models performed using the ANSYS FLUENT programme. The study parametrize and optimize the particle velocity and temperature, so as to achieve low to medium particle temperature and the maximum particle velocity, as this is the criterion to gain low porous, more dense coating and higher coating bond strength. The first stage of the research was to study effect of the density variation with the pressure and temperature at the inlet boundary condition. This type of investigation was never conducted before and thus is, to be the best of the author’s knowledge, a novel approach. The computational modelling was then validated against an experimentally measured particle temperature. Equivalence ratio, spray distance, particle size and the air flow rate were found to be the process parameters required to optimize for the required targets. The results of this study also gives description and explanation on the behaviour and interaction between the process variables under investigation via the statistical and mathematical relations developed in the study. Finally, the results of this study were intended to be a guide in the design of the High Velocity Oxy Fuel by referring to the parametric relations and optimized parameters developed in this study by applying a Design of Experiment technique on a reliable set of Computational Fluid Dynamics results, which is considered the novelty of the study. For both the DJ1050 and DJ2700, the equivalence ratio was found to be the most influential parameter followed by the particle size to achieve the criteria of low to medium gas temperature, maximum gas velocity and maximum particle temperature. The less effective parameter was found to be the spray distance. However, a set of optimum operating parameters considered in this study were obtained for each gun, which shows that for the DJ1050 gun a range of the equivalence ratio between 0.87 (fuel − lean) and 1.44 (fuel-rich) can be applied with an average spray distance of 190 mm and an average particle size of 30 μm are the optimum values to be applied to reach the favourable target in HVOF process. While for the DJ2700, the optimized set of the equivalence ratio was biased toward fuel rich mixture (φ > 1) with constant spray distance of 150 mm and particle size of 5 μm to achieve the desired target of HVOF process.