Abstract
The paper presents an analysis of possible improvements in HVOF torches and associated processes. It is shown that increasing the efficiency of combustion modules, widening the available range of operating pressures as well as optimizing the powder injection and nozzle expansion lead to significant improvements in comparison with the currently utilized HVOF processes using liquid fuel and radial powder injection. The analysis is confirmed by experimental data obtained using an advanced HVOF torch designed to use ethyl alcohol as a fuel. The new torch operates at a higher thermal efficiency of a combustion module, able to generate products of combustion with better capability to transfer heat to particles and more dissociated molecules. High thermal efficiency also results in a wider operating window and better control of a desirable balance between particles’ kinetic and thermal energy, which depends on the spraying material and a particular coating’s requirements. Shock wave generators inside the nozzle/barrel are also included in the design to allow an improvement in powder injection and an increase in the heat exchange between products of combustion and particles. These advantages have allowed for the minimization of the throat diameter providing throat cross-sectional surface area approximately 2 times less in comparison with other liquid fuel HVOF torches presently used in the industry. The reduction in throat diameter results in significantly less consumption of fuel and oxygen, and also results in an overall decrease of the operating costs. Coating quality, deposition efficiency and deposition rate in this case are the same or better in comparison with other currently utilized liquid fuel HVOF processes.
