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Flame Spray Process
IntroductionFlame spraying is primarily used to apply abradable coatings or nickel/chrome self-fluxing alloys which are subsequently heat treated to metallurgically bond them to the substrate (Fused coatings).
Main Applications
Abradable coatings are used for machine element clearance in 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.
Process Description
A Flame Spray gun use oxygen and fuel gases to produce a flame through which powder is injected. The resultant molten particles of powder are projected on to the workpiece to produce the coating. Many coatings sprayed by this process are then heat treated at around 1000ºC to 'fuse' the coatings to the substrate surface.
General Coating Characteristics
- metallurgical bonding to substrate.
- macrohardness values between R. 55-62.
- low porosity levels.
- wear and corrosion resistant.
Fused coatings produced by this process are hard and corrosion resistant and are able to withstand wear by abrasion, fretting, cavitation and 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. They can be applied 1 - 5 mm thick; much thicker than hard wear coatings applied by the plasma or HVOF processes.
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| Coating | Characteristics | Typical Applications |
| Nickel 70%,Chromium 17%, Iron, silicon, boron, carbon | Macrohardness - Rc 55 - 60 Surface Texture - as fused - 5 - 7.5 microns. - as ground - 0.25 microns. |
This coating can be used in a wide range of applications. These include steel mill rolls, forging tools, exhaust fans, pumps and other components subject to wear. |
| Nickel 46%, Chromium 11%,Tungsten carbide/nickel 35%,Iron, silicon, boron, carbon | Macrohardness - Rc 58 - 60 Microhardness - KHN50 950 Surface Texture - as fused - 2-4 microns - as ground - 0.3 - 0.5 microns |
This coating can be used where wear resistance is severe. It can be used on pump components, rolls, shafts, exhaust fans and other components subject to severe wear. |
| Cobalt 40% Nickel 27% Chromium 18% Molybdenum 6% Silicon, boron and iron | Macrohardness - Rc 50 Surface Texture - as fused - 6 - 7.5 microns - as ground - 0.35 microns |
This coating is useful where cobalt base wear coatings are required and the substrate is a low shrink material. The possible applications are similiar to the other fused coatings |
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| Coating | Characteristics | Typical Applications |
| Nickel 75% Graphite 25% | Macrohardness - R15y 30 - 50 Surface Texture - as sprayed - 25 - 33 microns This coating is used in compressors on jet engines or in other machinery requiring close tolerance clearances in seal areas. It can be used as a low friction coating in the glass industry.- as machined - 4 - 6 microns |
This coating is used in compressors on jet engines or in other machinery requiring close tolerance clearances in seal areas. It can be used as a low friction coating in the glass industry. |
| Aluminium61%, Graphite23%, Silicon 8% | Macrohardness - R15y 50 - 70 Surface Texture - as sprayed - 10 - 13 microns - as machined - 4 - 6 microns |
This coating is a lower cost alternative to the coating above. It is generally more erosion resistant at elevated temperatures and is used in similiar areas. |
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