Thermal spraying is the process of heating and coating materials onto a substrate. The coating can be composites or materials, including ceramics, plastics, metals, or alloys, and the substrate can be coated at anything from 20 microns up to a few mm. The surface of the substrate is not subjected to great heat itself, meaning delicate and even flammable substrates can be coated, providing protection against corrosion and water penetration, among other things. There are five main ways to thermal spray coat a surface.
High-Velocity Oxygen Fuel Coating (HVOF)
Developed in the eighties, high-velocity oxygen fuel coating provides a particularly dense coating to the surface by mixing fuel and oxygen in a combustion chamber which is then mixed with the coating in powder form, creating a stream of hot gas that can be sprayed through a nozzle onto the substrate at very high speed. The greater particle impact velocity means a very strong, high-density bond to the surface.
Combustion Flame Spraying.
This cost-effective, low-energy process uses coatings in wire or powder form heated by an acetylene or propylene torch and then propelled onto the surface with compressed air, producing a moderate-density coating.
Thermal Plasma Spray.
This process heats the coating in powder form using DC electricity to form a high-temperature plasma gas. A continuous feed of inert gas becomes rapidly hot and ionised, creating a high-velocity jet. The high melting point gives a very good coating with a durable even finish as seen here:www.poeton.co.uk/advanced-treatments/apticote-800-thermal-plasma-spray.
Vacuum Plasma Spraying.
This works in much the same way as plasma spraying, but is carried out in a vacuum which greatly increases the costs. In this way, an even higher quality coating is achieved, particularly useful in car bodies and parts where the finish of the product is critical. A full analysis can be read here:.
Two-Wire Electric Arc Spraying
Requiring a much more controlled environment than some of the other methods, this approach only makes sense for large-scale production. It uses an electrical arc struck between two DC wire electrodes. High production rates are achieved, but it emits ozone and fumes which need controlling.