Metal spraying is a process for covering a surface with a metallic coating using a spray of molten particles. Numerous variations of the technique exist, including:
- Flame spraying
- Wire arc spraying
- Plasma spraying
- Detonation spraying
- High velocity oxy-fuel coating spraying (HVOF)
- High velocity air fuel (HVAF)
- Warm spraying
- Cold spraying
These processes can also be labeled with a more general term, thermal spraying. However, the general term includes coatings created with not just metallic materials, but also oxides and ceramics.
Metal spraying works by first subjecting the source material to a high degree of heat to achieve a molten state. The molten material is then atomized into small particles and sprayed outwards onto a surface. The molten particles do not heat the surface because the heat of a particle is proportional to its size. On contact, the particle flattens out and adheres to the surface as it hardens.
Most applications of metal spraying are found in the anti-corrosion and engineering markets. Coatings are used in these industries to add finishing coatings, anti-corrosion layers and thermal barriers, and to add wear resistance. Both flame spraying and arc spraying techniques are used to add these protective coatings.
The deposition rate of the surface is typically faster than other coating processes such as chemical vapor deposition and electroplating. Coatings created by metal spraying range in thickness from 20 µm to several mm, depending on the conditions and methodology. Layers created by metal spraying may have the following characteristics:
- Increased durability
- Increased hardness
- Increased or decreased friction
- Increased or decreased corrosion protection
- Increased wear resistance
- Modified electrical properties
- Additional protection to damaged materials
With a variety of metal spraying methods, the choice of method depends on the particular application. Deposit efficiency, bond strength, ease of operation, safety, changeover time, maintenance time and costs, appearance of the coating finish and the ability to automate the coating application affect the choice of spraying methodology. For corrosion protection, aluminum, zinc and alloys of the two are typically used.