Thermal Spray

What is Thermal Spray ?

Thermal Spray is a group of coating processes in which metallic, ceramic, cermet, and some polymeric materials in the form of wire, powder, or rod are fed to a gun which results in heating to near or somewhat above their melting point. The resulting molten or nearly molten droplets of material are then accelerated in a gas stream and projected against the surface to be coated. When the hot energetic particles impact the surface of the part being coated, they rapidly solidify. As subsequent particles impact the surface, a deposit thickness is built up. The droplets flow into thin lamellar particles adhering to the surface, overlapping and interlocking as they solidify. The total coating thickness is usually generated in multiple passes of the coating device. Thermal spray devices used to accomplish this work are commonly called as guns or torches.

Advantages of Thermal Spray

Selection of the appropriate thermal spray method is typically determined by:

The Process Basics

All methods of thermal spraying involves the projection of small molten particles onto a prepared surface where they adhere and form a continuous coating. To create the molten particles, a heat source, a spray material and an atomisation/projection method are required. Upon contact, the particles flatten onto the surface, freeze and mechanically bond, firstly onto the roughened substrate and then onto each other as the coating thickness is increased.

The metal spray equipment falls into four main categories, Powder Flame Spray, Wire Flame Spray, Arc Spray, High Velocity Oxygen Fuel (HVOF) and Plasma Spray.