Applying powders in a melt state onto surfaces--in particular metal surfaces--represents a well known method. So e.g. the HU-PS 159 923 discloses a method of this type for applying and preparing a coating. In course of said method the flame required for melting is produced by using a mixture of acetylene and oxygen or acetylene and air. Powder--e.g. aluminium powder--is blown by means of pressurized air along a plane between two slabshaped flames tending to each other and melt inbetween, thereafter the melt powder is applied onto the surface to be coated by using pressurized air.
The disadvantage of said method and apparatus, respectively, lies in that acetylene is most expensive, energy exploitation is uneconomical, in addition, quality of coating obtained by the method and apparatus does not meet requirements.
A process and an apparatus are also known which use PB-gas or natural gas as combustible gas. The disadvantage of this solution lies in that in order to prevent lateral deflection of the powder jet discharged in a slab-shape from the spraying head and thus to eliminate powder losses, slab-shaped cold air-jets are directed onto the powder jet. In order to prevent powder losses to the desired extent, a considerable quantity of cold air is required decreasing considerably the temperature of the flame needed for melting the powder, resulting in a lower efficiency of powder melting. As a consequence of the significant quantity of cold air energy required for melting increases considerably, stability of the melting flame decreases. Flame stability is further deteriorated by the fact that structural design of the spray head of known apparatuses does not exclude arrival of the air streams coming from different lateral directions and of uncontrollable intensity at the melting flame.