Plasm arc spray is a coating process wherein a powdered metal melts by high heat obtained through plasma arc and then carried out to the workpiece surface in a molten state by the high velocity of the plasma jet.
Concept of Plasma Arc Spraying
Plasma Arc Spraying
A high-intensity arc, between the gun body (anode) and the thoriated tungsten electrode (cathode), is struck using a direct current. The heat is generated by the arc passing through the inert gas and exiting through the nozzle (ie the copper anode).
The gas is heated to the plasma state where gas molecules become ionized atoms containing a great deal of energy (around 20,00-30,000)and accelerated to supersonic seeds. as a hot, brightly shining flame having a length of about 3-7 cm. Due to the high temperature of the plasma arc, the powder metal converts into molten form and then transported to the surface of the workpiece in a molten state by high-velocity plasma jets.
Gases such as Ar, He, H2 and N2 are mainly used as the arc gases (plasma-forming gases). The temperatures in a plasma flame are normally 10 000–15 000 °C.
M. WANG,
Equipment used in Plasma Arc Spraying
- Spray gun
- Power supply
- Gas supply
- Powder metal supply
Materials to be sprayed
- Metals: Aluminum ,Copper,Nickel, Chromium, Molybdenum,Titanium,Tungsten
- Refractory hard metals: Tungsten carbide, Chromium carbide, Titanium carbide
- Cermet: Nickel-Magnesia, Aluminum Oxide-Nickel, Zirconium Oxide-Nickel,
- Oxides: Chromium oxide, Titanium oxide, Zirconium oxide,
- Plastics
Plasma Arc Spraying | |
| Arc current | 80-800 |
| Voltage | 50-500 |
| The wattage of the unit for spray coating | 28-40 KW |
| Powder metal size | 40-50 mesh to 5 micron |
| Distance of gun from work | 50 to 150 mm |
| Preheating of base metal for reducing stress in the coating | 93°C to 150°C |
| The output of the plasma torch | 2-10 kg of spraying material/hr |
| Coating bond strength | 350-700 Kg/cm² |
| Hardness | Up to 75 Rc. |
Advantages
- Almost all types of material or substrate can be coated with the plasma arc spray process.
- High burn strength and stronger coating were obtained.
- Heat distortion problems are less.
Disadvantage
- The noise level is high(around 100 dB) in this process.
- Additional protective equipment is required due to the intensity of ultraviolet and infrared radiation,
Conclusion
The use of a plasma arc spraying system is for producing wear-resistant, temperature-resistant, and heat-insulating coatings.