Thermal Spray

The term "Thermal Spray" describes different sub-processes. They are clustered by the filler material, the process itself or the energy transfer media.

Thermal Spray techniques are coating processes in which melted (or heated) materials are sprayed onto a surface. The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame). Coating thicknesses range between approximately 20 micrometers (μm) and several millimetres (mm) depending on the process and feedstock. Thermal spraying is a line-of-sight process and typically can not be used to coat holes and deep recesses on a work piece.

The materials to be deposited as the coating are typically fed into the spray gun in powder, wire or rod form where they may be atomized before being accelerated towards the substrate, or material to be coated. "As the sprayed particles impinge upon the surface, they cool and build up, splat by splat, into a laminar structure forming the thermal spray coating."

The surface may not heat up significantly, allowing the coating of flammable substances.

Coating quality is usually assessed by measuring its porosity, oxide content, macro and microhardness, bond strength and surface roughness. Generally, the coating quality increases with increasing particle velocities.

Spray coatings may either be applied manually or by machine, depending on complexity, cost, and environmental and safety concerns.