Flame and arc spraying

Flame and arc spraying are easy, low-cost metallization processes, where a hand-held or automated pistol is used to spray liquid metal onto a part. The metal layer produced is thick compared to other metallization techniques and the deposition rate is high. However, the coatings prepared with these processes are quite porous, coating adhesion is lower and the surface roughness of the metal layer is relatively high. Both processes are well suited to electromagnetic shielding purposes and the metal layer can be applied selectively on different surfaces of the part. The oxide content of the metal layer is relatively high, due to the oxygen in the combustion gases and the ambient air.

In flame spraying, a metal powder or a wire is heated and propelled onto the plastic substrate by a stream of hot gases.

A fuel gas, usually acetylene or propane, is fed through a central nozzle and supplies the necessary energy to melt the metal. A second outer annular gas nozzle feeds a stream of air or an inert gas around the combustion flame, which accelerates the spray particles towards the substrate and focuses the flame.

Arc spraying is comparable to flame spraying, but in arc spraying a DC electric arc is used. The arc is struck between two continuous consumable wire electrodes that form the spray material.