At Metallisation, we’ve spent over 100 years leading the way in metal and thermal spray technology. Arc spray is a trusted method for protecting and rebuilding parts across many industries. Here’s a clear, step-by-step look at how it works.
What Is Arc Spray?
Arc spray is a thermal spray process that uses two metal wires fed into a spray gun. An electric arc melts the ends of the wires. Compressed air then blows the molten material onto a prepared surface. Once the particles hit the surface, they cool and form a strong and dense coating.
Why Use Arc Spray?
Many companies use arc spray because it offers fast coating speeds and good coating adhesion. It also has lower heat transfer compared to welding, so it reduces the risk of distortion in parts. It works well for corrosion protection, wear resistance, and even rebuilding worn machine parts.
The Science Behind Arc Spraying
Arc spraying uses basic physics to create a powerful coating process. When two charged wires touch, they form an electric arc. The energy from the arc melts the wire. Compressed air strips away this molten metal in tiny droplets and fires them at high speed towards a surface. These droplets hit the surface and flatten. Each new layer bonds to the one before it until the desired coating thickness is reached.
This method works with many metals and alloys such as zinc, aluminium, copper, steel, and nickel. It creates coatings that are tough and long lasting.
So what are the steps involved? Let’s take a look.
Step 1: Preparing the Component
Without preparation, a thermal spray coating will not adhere well.
Before spraying begins, the surface must be clean and roughened. Any dirt, oil, rust or paint must be removed. Most skilled operators use grit blasting with aluminium oxide or chilled iron grit. Blasting creates a sharp, textured surface that helps form a strong mechanical bond with the sprayed coating. A clean and correctly roughened surface leads to a better coating bond and longer service life.
Step 2: Loading the Spray Wires
The operator chooses two wires, usually about the same diameter. These wires are chosen based on coating needs. For example, zinc and aluminium are common for corrosion protection, while steel and nickel-based alloys are used for wear resistance. The wires are fed into the arc spray gun using either air or electric drive.
Step 3: Creating the Electric Arc
When power is applied to the spray system, an electric current passes through each wire. One wire acts as positive and the other as negative. When the wire tips meet, the electric arc forms between them. The temperature in the arc can reach over 4,000°C, which is high enough to melt most metals used for industrial coating.
Unlike flame spray, arc spray does not need fuel gases. It runs on electricity and compressed air, making it easier to control and cheaper to operate.
Step 4: Melting and Atomising the Metal
Once the arc melts the tips of the wires, compressed air flows through the gun. The air jet blows the molten metal off the wire tips and breaks it into fine droplets. This is known as atomisation. These droplets are then propelled out of the gun towards the workpiece at high speed.
Step 5: Spraying the Molten Metal onto the Surface
The operator keeps the spray gun at a set distance and angle from the surface. The molten droplets hit the blasted surface and flatten out to form a thin lamella, which is like a small metal disc. Thousands of these droplets overlap and build the coating layer by layer. The low heat input means that the base material remains cool and avoids thermal distortion. This is often important for thin or sensitive parts.
Step 6: Building Coating Thickness
The operator makes several passes over the surface. Each pass builds thickness. Most arc spray coatings range from 50 microns to several millimetres thick. The exact thickness depends on the application. For example, anti-corrosion coatings are usually thinner, while repair coatings may need thicker builds to restore part dimensions.
Step 7: Finishing the Coating
After the spray process, the coating may need to be finished. Some coatings need machining to bring the surface to final size. Others may need sealing to improve corrosion resistance or prevent moisture ingress. Finishing steps depend on how the coated part will be used.
What Are the Key Benefits of Arc Spraying?
- Arc spray provides fast spray rates, making it suitable for large surface areas such as bridges, ships, tanks and pipelines. The process is efficient and has low running costs because wire feedstock is usually cheaper than powder or rods. It also produces little waste. Most coatings have strong mechanical bonding to the substrate and resist corrosion, heat and wear.
- Arc spray also creates coatings without large heat input. This means it is safe to use on thin or heat-sensitive surfaces without damaging them. Since it is a cold process compared to welding, there is no risk of cracking or changing the structure of the base material.
Typical Uses
Construction
Structural steel fabricators use zinc and aluminium coatings for corrosion protection.
Repair Shops
Pump and shaft repair shops use it to build up worn surfaces before machining them back to size.
Marine
Marine engineers use arc sprayed coatings to protect offshore structures, ship decks and bollards.
Power Stations
Power stations use arc sprayed copper or aluminium bronze coatings on turbine blades.
Rail and Mining
Rail and mining companies use steel coatings to protect parts that face heavy wear.
Safety and Good Practice
Arc spray is a safe process when done by trained operators, and the correct spraying practices are followed. It does produce dust and fumes, so correct extraction and personal protection equipment are important. Operators should use gloves, a face shield and protective clothing. Spray rooms should be well ventilated. Good training and regular equipment checks are essential to keep the process consistent and safe.
The Final Finish
Metallisation has become the UKs leading developer, manufacturer and worldwide supplier of a full range of metal spraying equipment – providing high quality arc spray systems, since 1922. If you’ve got a project you need help with, simply contact us today and we’ll be more than happy to help.