In the wire arc electric spray process (also known as the electric arc process), two consumable wire electrodes connected to a high-current direct-current (dc) power source are fed into the gun and meet, establishing an arc between them that melts the tips of the wires. Twin wires are fed via electric driven motor or air motor. The molten metal is then atomized and propelled toward the substrate by a stream of air. Because the wires are melted directly by the arc, the thermal efficiency of the electric arc spray process is considerably higher than that of any other thermal spray process.
Spray rates are driven primarily by operating current and vary as a function of both melting point and conductivity. As the molten metal shears from the wires, it atomizes, or breaks up, the material into finer particles, creating a fine distribution of molten metal droplets. The atomizing air is also used to accelerate the particles toward the substrate surface, where the molten particles impact, deform, and solidify to build up a coating.
Unlike flame or plasma spray, however, the droplets are already molten when the material is picked up and entrained in the jet, and unlike other processes, the particles begin to cool immediately after leaving the arc zone. In order to minimize oxidation in the electric arc spray process, the dwell time needs to be shortened by using short standoff distances and high atomizing air flows.
Electric arc spray transfers less heat to the substrate per unit of material sprayed than any other conventional thermal spray process, owing to the absence of a flame or plasma jet. Generally, materials such as copper-base and iron-base alloys spray at 4.5 kg (10lb)/100 A/h. Zinc sprays at 11 kg (25 lb)/100 A/h. Substrate temperatures can be very low because no hot jet of gas is directed toward the substrate.
Materials for electric arc spray are limited to conductive materials that can be formed into wires. The use of cored wires has expanded the range of materials to include cermets and amorphous materials. Cored wires consist of a tubular metallic sheath with powder in the core. These powders are usually carbides or amorphous alloys.
The cooler deposit characteristic of electric arc spray minimizes the substrate heating associated with other thermal spray processes. This gives electric arc spray a major processing advantage for applications where coating/substrate temperatures need to be kept low. This enables the electric arc spray process to deposit coatings onto polymers, fiberglass, wood, and paper products, as well as metallic or glass substrates.