The Plasma Transferred Arc Process ( PTA ) has （等离子体转移弧过程(PTA)）.pdf

The Plasma Transferred Arc Process ( PTA ) has been in use since 1962 for surfacing of parts . The applications possible with PTA are hardfacing to protect against extreme conditions in service life like heat , abrasion , corrosion , erosion ,adhesive and abrasive wear etc. It is also use to recondition worn out parts or build up of mis machined parts. Plasma is a state of matter resulting from the inonisation of gas. It is composed of positive ions and free negative electrons. Its ionized condition enables it to conduct current. Transformation of gas into plasma requires energy and the ionization level increases according to temperature ranging from 6000 to 20000 degrees centigrade. Since the pressure approximates to that of the atmosphere the impact of the fast moving particles on one another are numerous enough for the transformation of their kinetic energy into heat to result in a considerable rise in temperature. The plasma torch design as used in surfacing applications is shown below The arc is struck between the Tungsten electrode (Cathode) and the job which is the anode . The fine bore copper nozzle constricts the arc into a fine beam as compared to the open arc of TIG welding. Powder is fed by a powder feeder into the plasma arc through specially drilled holes in the copper nozzle . Torches using external wire feed are also available . It is possible to use both powder and wire feed combination if extra ordinary high deposit rates are required. Although many consider Plasma Transferred Arc System (PTA) as a Thermal spray process it is a  high energy, inert gas welding process rather than a spraying process.  PTA deposition is also  called PTAW surfacing because the American Welding Society classifies the PTA deposition  under Plasma Welding category .   Argon is basically used for arc plasma supply, powder transport and molten material shielding.   The coating material is fed into the Plasma arc in either powder or wire form.