Thermal spraying using nozzle for metal coatings - by heating spraying powder particles in oxygen@ free reducing gas atmos. in nozzle and injecting neutral or reducing gas stream in nozzle

摘要

In a thermal spraying process using spraying nozzle for metal or metal-ceramic coatings, the coating forming particles are heated and accelerated in a nozzle by a gas stream and sprayed on the surface to be coated. The spraying particles are heated in a substantially O2-free reducing gas atmos. In the nozzle and a further neutral or reducing gas stream is injected in the nozzle. Pref., the spraying powder particles are first preheated by fuel gas in a combustion zone and a further concentrically surrounding fuel gas and cooling gas concentric thereto are injected downstream, so the compsn. of the gas atmos. is below the lower ignition point. The powder particles are heated in the combustion zone in a gas atmos. with a high hydrogen or hydrogen/carbon content. USE/ADVANTAGE - Provides an improved thermal spraying process and nozzle for metal or metal-ceramic coatings, which are homogeneous and free of cracks and oxide inclusions.