In Combustion Wire Flame spraying, the feedstock material in the wire form is melted in the flame and atomised using compressed air to form fine spray. Flame spray uses the chemical energy of combusting fuel gases to generate heat. A stream of air then atomizes the molten material and propels it toward the workpiece. When the spray contacts the prepared surface of a substrate material, the fine molten droplets rapidly solidify forming a coating. Oxyacetylene torches are the most common, using acetylene as the main fuel in combination with oxygen to generate flame. Spray rates for materials such as stainless steel is in the range of 0.5 to 9 kg/h (1 to 20 lb/h). Again, lower melting point materials such as zinc and tin alloys spray at much higher rates. Substrate temperatures often range from 95 to 205 °C (200 to 400 °F) because of the excess energy input required for flame melting. In most thermal spray processes, less than 10% of the input energy is actually used to melt the feedstock material.
