The thermal spray process is widely used to add coatings to important components (often referred to as ‘substrates’). It is used in numerous industries. The coatings that are added using thermal spray are able to enhance or add desirable attributes.
So how does thermal spraying work?
The thermal spray process uses either flame or plasma in order to heat and melt the coating materials. These materials may be metals, ceramics, polymers or even plastics. When heated, the coating material turns into molten droplets which are then propelled at high velocities onto the substrate.
Upon impact, the molten particles solidify and also bond to each other to form a layer of coating. They produce a lamellar structure. The thickness of the coating can be tightly controlled by adjusting parameters such as the temperature, the velocity, and the molten state.
The main stages of the process vary slightly depending on the method used, but usually consist of preheating and preparation, powder injection and melting, coating build-up, and cooling and solidification
Types of Thermal Spray Processes
There are several different thermal spray processes that are commonly used.
The thermal plasma spray process is used to coat substrates of all sizes. The coating can be made from a variety of materials including metals, ceramics, polymers, or plastics. It is a versatile process which creates stronger, cleaner, and denser coatings than most other processes. However, it is relatively costly and complex.
There are several firms in the UK with expertise in surface coatings including thermal plasma spray. Many of these also have useful online resources such as the examples seen here: https://www.poeton.co.uk/advanced-treatments/apticote-800-thermal-plasma-spray.
The High Velocity Oxygen Fuel (HVOF) spraying process is perhaps the most used nowadays. It has some similarities with plasma spraying but is able to create an exceptionally strong and clean coating that offers high resistance to corrosion. One example component that is coated using HVOF is helicopter rotor joints.
Combustion flame spraying is another popular option. It is effective yet (relatively) inexpensive. It is often used to coat architectural components that need to be corrosion-resistant.