Flame spraying is primarily used to apply abradable coatings or nickel/chrome self-fluxing alloys which are subsequently heat treated in order to metallurgically bond them to the substrate (Fused Coatings).
Main Applications
Abradable coatings are used for machine element clearance in gas turbine compressors.
Fused coatings are extensively used in high wear applications such as mining and steel industries to prevent wear of rolls, pistons and other equipment in aggressive wear environments.
A Flame Spray gun uses oxygen and fuel gasesoxygen and a fuel gas to produce a flame into which powder is then injected. The resultant molten particles of powder are projected onto the work piece to produce the coating. Many coatings sprayed using this process are then heat treated at around 1000°C to ‘fuse’ and enhance the coating cohesive and adhesive properties on the substrate surface. Fused coatings produced by this process are extremely hard and corrosion resistant and are able to withstand wear by abrasion, fretting, cavitation or by contact with other hard surfaces. The addition of different proportions of carbon, silicon and boron to the basic nickel/chromium alloy results in the formation of hard phases of carbides, silicide and borides. The coatings can be applied 1 – 5 mm thick; much thicker than hard wear resistant coatings applied by the plasma or HVOF processes.
General Coating Characteristics of Fused Coatings
- metallurgical bonding to substrate.
- an increase in macrohardness values
- low porosity levels.
- wear and corrosion resistant.