Thermal Spraying
Thermal spraying is one of the most versatile and widely used coating techniques with many applications in various industries. Thermal spraying is the process of spraying molten or plasticized materials on a substrate to produce a solid coating. Thermal spraying is commonly used to produce coatings composed of metallic, ceramic, or polymeric material. The different types of thermal spray systems include atmosphere plasma, cold spray, electric arc, laser, and high velocity oxygen fuel (HVOF). The choice of the thermal spray process depends on the substrate, its condition, geometry, and surface coatings desired.
Atmosphere Plasma Spraying (APS) is a type of thermal spray process used for deposition of coated materials in atmosphere. A plasma torch is used to melt the feedstock and then uses a high velocity air stream to propel the molten or plasticized material onto a substrate. The result is a highly wear and corrosion-resistance coating with a thickness of up to 4 mm. Common materials used in APS include stainless steel, steel, chromex, Inconel and other high temperature alloys.
Cold Spray utilizes a high velocity gas stream such as Argon to propell cryogenic particles onto a substrate. The coating thickness provided by cold spray could range from 0.5mm to up to 5mm. It produces a dense, harder coating than the APS and provides a higher wear and corrosion resistance. This technique is commonly used for repairing worn out surfaces and producing coatings of metal and metal matrix composites.
Electric arc thermal spraying is a type of thermal spraying process used for the deposition of metallic and ceramic materials. This technique uses an electric arc formed between an electrode and the material to be sprayed, which produces molten droplets. The molten droplets are then propelled onto the substrate at high velocity. This method produces a coating with a thickness of up to 3mm. It is widely used for coating of large components as well as for coating smaller components with a smooth surface finish.
Laser spraying is a relatively new process where lasers are utilized to melt the feedstock and propel it onto the surface. This process produces very fine and uniform coatings with a thickness of up to 0.2mm. It produces a high wear and corrosion resistant coating, however, due to its higher cost, it is not widely used.
High Velocity Oxygen Fuel Spraying (HVOF) is a type of thermal spraying process where an oxygen and fuel gas are used to generate a high temperature flame. The material to be sprayed is injected into this flame which melts it and propels it onto the substrate. The HVOF process produces a uniform, hard, and highly wear and corrosion resistant coating with a thickness of up to 4mm. This process is commonly used for coating internal and external surfaces of cylinders, tubes, shafts, and other components.
In conclusion, thermal spraying is a versatile process with many applications. Different types of thermal spray processes can be used based on the particular substrate and its desired properties. APS, cold spray, electric arc, laser, and HVOF are some of the most common thermal spray processes used in industry. Each of these processes produces a coating with different characteristics and varying thickness. Thermal spraying is an economical and efficient process for depositing coatings with a hard, wear and corrosion resistant surfaces.
