The paper presents an analysis of possible improvements inHVOF torches and associated processes. It is shown thatincreasing the efficiency of combustion modules, wideningthe available range of operating pressures as well asoptimizing the powder injection and nozzle expansion leadto significant improvements in comparison with the currentlyutilized HVOF processes using liquid fuel and radial powderinjection. The analysis is confirmed by experimental dataobtained using an advanced HVOF torch designed to useethyl alcohol as a fuel.The new torch operates at a higher thermal efficiency of acombustion module, able to generate products of combustionwith better capability to transfer heat to particles and moredissociated molecules. High thermal efficiency also resultsin a wider operating window and better control of a desirablebalance between particles’ kinetic and thermal energy, whichdepends on the spraying material and a particular coating’srequirements.Shock wave generators inside the nozzle/barrel are alsoincluded in the design to allow an improvement in powderinjection and an increase in the heat exchange betweenproducts of combustion and particles. These advantageshave allowed for the minimization of the throat diameterproviding throat cross-sectional surface area approximately2 times less in comparison with other liquid fuel HVOFtorches presently used in the industry. The reduction inthroat diameter results in significantly less consumption offuel and oxygen, and also results in an overall decrease ofthe operating costs. Coating quality, deposition efficiencyand deposition rate in this case are the same or better incomparison with other currently utilized liquid fuel HVOFprocesses.
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