Powder Flame Spraying
In powder flame spraying, the powdered coating material is fed into the acetylene-oxygen-flame of a powder flame spray gun by a carrier gas or using an external powder supply unit. Here the powder is brought to melting point and transported onto the surface of the component as molten droplets through the velocity of the gas.
Flame Spraying with Powder and Subsequent Thermal Treatment.
Subsequent thermal treatment, so called ‘remelting’, of some the process materials used in flame spraying with powder produces spray coatings impervious to gas and liquid. These so called self-fluxing powders have a separate function.
Upon remelting, the second thermal operation consists of heating the entire coated area, and therefore the process material, with an acetylene-oxygen-flame up to temperatures of 1,020 to 1,140 °C. At temperatures of more than 900 °C, borosilicate, which has liquidity properties, is formed from the boron and silicon added in the spray powder. Thin residual oxide layers in the spray coating and on the metal surface are dissolved and come to the surface of the coating. This eliminates the previously porous nature and a strong cohesive bond is formed between the base material and the spray coating, a bond mechanism similar to that of hard soldering.
Powders are differentiated into self-fluxing, self-adhesive, and standard powder. Process temperatures are maximum 3,160 °C, but the attainable particle velocity is only approximately 50 m/s.