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Plasma arc spraying

Plasma Arc Spraying

PLASMA ARC SPRAYING 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

A high-intensity arc, between the gun body (anode) and the thoriated tungsten electrode (cathode) is struck using direct current. The heat is generated by the arc passing through the inert gas and exited 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.

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 current80-800
Voltage50-500
Wattage of the unit for spray coating28-40 KW
Powder metal size40-50 mesh  to 5 micron
Distance of gun from work50 to 150 mm
Preheating of base metal for reducing stress in coating93°C to 150°C
Output of plasma torch2-10 kg of spraying material/hr
Coating bond strength350-700 Kg/cm²
HardnessUp to 75 Rc.

Advantages

  • Almost all types of material or substrate can be coated with plasma arc spray process.
  • High burn strength and stronger coating 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 intense of ultraviolet and infrared radiations,

Conclusion

The use of plasma are spraying system is for producing wear resistant,temperature resistant,and heat insulating coatings.