Nozzle assembly for HVOF thermal spray system

A nozzle assembly for a high velocity oxygen fuel (HVOF) thermal metallic spray coating apparatus, comprising:

• a set of tubes for delivering combustible oxygen, fuel gases and a feed wire to a combustion zone of said apparatus, said set of tubes including an outer tube having an outer cylindrical surface adjacent said combustion zone;
• an air cap fitted to said outer tube having an inner wall surface defining said combustion zone when the feed material is melted by reaction of the combustion gases and expelled at high velocity from said air cap through a discharge opening therein;
• and
• wherein a portion of said air cap extends over said outer tube in radially outwardly spaced relation thereto to define an annular cylindrical air gap between said inner surface of said air cap and said cylindrical outer surface of said outer tube, said air gap coupled to a source of high velocity air for developing a column of air within said air gap which travels along said air cap toward said discharge opening and provides a boundary of air flowing along said inner surface of said air cap to protect said inner surface from exposure to the heat of the combustion chamber flame and molten metal feed wire material.