Thermal spraying can endow workpiece surfaces with various special properties such as wear resistance, heat resistance, corrosion resistance, oxidation resistance, sealing performance, lubricity, insulation, radiation protection and anti-radiation capability. A wide range of materials can be used for thermal spraying, including metals, alloys, ceramics, plastics, non-metallic minerals and composite materials. Coatings can be applied not only on metal surfaces, but also on ceramics, glass, plastics, wood and other substrates. Therefore, this technology can restore and reuse worn-out parts in equipment maintenance, bringing scrapped components back into service. It can also strengthen and pre-protect new products during manufacturing to extend their service life. Accordingly, thermal spraying is widely applied in aerospace, machinery, metallurgy, chemical industry, petroleum, coal, railway, textile and many other fields.
(1) Application of Flame Spraying (Welding) Technology
It is applicable to various powdered and wire materials including metals, alloys, ceramics, plastics and composites, such as zinc, aluminum, copper, molybdenum, carbon steel, stainless steel, Babbitt alloy, alumina, chromium oxide, tungsten carbide, chromium carbide, polyethylene and nylon. It is suitable for partial repair and strengthening of various mechanical parts. Remelting self-fluxing alloy coatings to form weld overlay can greatly improve the density and bonding strength of coatings, delivering superior corrosion resistance, wear resistance and higher stress bearing capacity.
(2) Application of Plasma Spraying Technology
This technology features a broad material range. It can process refractory materials and prepare coatings of hard-to-weld metals, ceramics and cermet composites. The resulting coatings have high bonding strength, low porosity and fine texture. It is mainly used to produce high-performance coatings for corrosion resistance, wear resistance, thermal insulation, electrical insulation, high temperature resistance and other special functions.
(3) Application of Electric Arc Wire Spraying Technology
Compared with flame wire spraying, electric arc wire spraying boasts higher thermal efficiency, productivity, lower operating cost and greater coating bonding strength. It is widely used to apply zinc and aluminum coatings for long-term protection of steel structures. It is also adopted to spray high-temperature, wear and corrosion resistant materials on the inner walls of large boilers, so as to reduce maintenance work and prolong service life.
(4) Application of High Velocity Oxygen Fuel (HVOF) Spraying
With ultra-high flame velocity and relatively low temperature, HVOF spraying shows remarkable advantages in spraying metal carbides and metal alloys, and has become an important thermal spraying process. Coatings produced by HVOF feature low surface roughness. Tungsten carbide coatings can reach a hardness of HRC75 (HV0.3≥1200), with dense structure and high bonding strength. Generally, the porosity of HVOF coatings is less than 2% and the bonding strength is no less than 70 MPa. This technology is mainly used for spraying wear-resistant components such as plungers, gate valves, ball valves, corrugating rolls, conveyor rolls, sink rolls, paper-making rolls, printing rolls and power plant boiler parts.
(5) Application of Vacuum Fused Coating Technology
Vacuum fusing refers to pre-coating the workpiece with a self-fluxing alloy layer and then remelting it in a vacuum environment to form a strong metallurgical bond between the coating and the substrate. The workpiece is heated uniformly as a whole and cooled slowly, resulting in minimal deformation. Besides, since the coating is fused under vacuum, the active components inside are hardly burnt out. Therefore, the coating maintains stable hardness, which can be regulated within the range of HRC20 to HRC70.
