In this research, a new approached was developed where coating
wire is melted by the heat of the combustion process inside a HVAF
thermal gun. The main difference from the traditional Wire Flame
spray process is that the new approach utilises the combustion under
pressure process, which imposes a number of new constraints and
challenges especially on the method of supplying coating materials to
prevent their premature melting, as well as a special design of the
acceleration nozzle in order to avoid any clogging due to the excess of
molten material and other factors. The HVAF thermal gun, used in this
research, was previously designed for thermo-abrasive blasting and
redesigned for thermal spraying of Zn–Al wire [5]. Fig. 1 shows a HVAF
thermal gun, which runs on compressed air and liquid fuels, such as
paraffin or any other type of liquid hydrocarbon fuel. Zn–Al wire is fed
axially through the rear of the HVAF thermal gun into the combustion
zone where it is melted by the heat of combustion (2000 K) and
accelerated by supersonic flow in the converging–diverging de Laval
nozzle [6].