Electric Arc Spraying (ASP)

Arc Spraying (ASP) is a high-productivity thermal spray process in which an electric arc, generated between two continuously fed metal wires, serves as the heat source.

How the Process Works

• Wire feeding: Two electrically conductive wires serving as electrodes are continuously fed from spools through the guide nozzles of the arc spray gun.
• Wire convergence: The wires meet at a slight angle at the front of the spray gun.
• Arc generation: Direct current is applied to the wires. As their tips approach each other, a short circuit occurs and an electric arc is established at a temperature of 4,000–6,000°C.
• Wire melting: The heat generated by the arc continuously melts the wire tips.
• Atomisation and transfer: Compressed air or inert gas is supplied through a nozzle behind the arc. It atomises the molten metal into fine droplets measuring approximately 10–100 μm and accelerates them towards the substrate.
• Coating formation: The particles strike the prepared component surface and form a characteristic lamellar microstructure.

Advantages of ASP

• High productivity: Deposition rates of up to 10–30 kg/h are considerably higher than those achieved by APS, FS, and HVOF.
• Cost-effectiveness: Consumable costs are minimal. The process requires only electricity and compressed air, eliminating the need for expensive gases such as argon or hydrogen.
• Mobility: The equipment is compact and can be easily deployed on-site to treat large structures.
• High bond strength: The high droplet temperature provides greater adhesion than conventional flame spraying.
• Pseudo-alloy coatings: Feeding two different wires, such as copper and steel, makes it possible to produce unique composite coatings directly during spraying.

Disadvantages and Limitations

• Conductive materials only: The process cannot be used to spray pure ceramics or plastics. The feedstock must be electrically conductive and available in wire form.
• Oxidation and element loss: The use of compressed air results in high oxide content—up to 10–20%. Alloying elements such as carbon and silicon may also be depleted.
• High porosity: Typical coating porosity ranges from 5% to 12%, reducing corrosion resistance unless sealing compounds are applied.
• High heat input: The component may become hotter than during APS, requiring strict control of the spray distance and effective cooling to prevent distortion.

Applications

• Sacrificial corrosion protection: Applying aluminium (TSA), zinc (TSZ), or zinc-aluminium coatings to bridges, power transmission towers, marine vessels, and storage tanks.
• Repair and dimensional restoration: Applying wear-resistant steel and bronze coatings to bearing seats, shafts, and rollers.
• Automotive component repair: Applying wear-resistant coatings to cylinder blocks and crankshaft journals.
• Electrical applications: Copper- or aluminium-coating surfaces to create conductive layers on insulators.