The PTA process - Plasma Transferred Arc
PTA process, Plasma Transferred Arc, is a melting welding process suitable for hardfacing on mechanical workpieces subject to wear and/or corrosion with superalloy metal powders.PTA process is charcterized by an high density plasma arc, obtained by ionization of Argon gas passing trough the electric arc formed between a non-consumable tungsten electrode (-) and the copper plasma nozzle (+) into the welding torch (pilot arc).
A second electric arc, called Transferred Arc, produces the energy needed to melt both the base metal and the filler metal.
The transferred arc is "throttled" to obtain a further increase of the temperature, obtaining a plasma coloumn with temp between 8.000° C and 18.000°C.
The powder filler metal is continuously projected on the piece trough the plasma arc. The driven output of Commersald torch allows to keep the dispersion in flat below 5% and to deposit, in max efficiency conditions, beads from 1 to 4 mm and width from 3 to 30 mm. The shape and the size of the coated layer change according to the welding parameters.
The penetration control in Commersald machines is obtained by varying the quantity of ionized gas and it is not conditioned by the process, unlike other arc welding systems.
The quantity of plasma gas is continuously adjustable by the operator and it is monitored by a sophisticated feedback control. This is one of main features of Commersald PTA process in welding coatings, so that, in most cases, you can work with one layer only, obtaining an hardness closed to the nominal value of the alloy employed. On the contrary, the extreme and uncontrolled diluition of other processes makes it almost impossible to obtain the required analysis at first pass.
ADVANTAGES OF PTA PROCESS
These are the features that make the PTA process different from the other welding methods. The control of the penetration allows single pass coatings and welding of very high quality.
HIGH ENERGY EFFICIENCY
LIMITED HEAT ADDITION
The high working speed limits the global thermal addition, reducing the deformation of the workpiece, with same deposition rate. The metallurgincal structure, due to the quicker cooling, is improved. The energy efficiency is very high; for example 12KW of electric energy are enough to deposit approx. 6 kos/h of metal.
FLEXIBILITY OF THE SYSTEM
CONSTANCE OF RESULTS
The shape of Commersald torch and the powder output trough the plasma arc help the automation of the process, making the positioning more precise and the programming more intuitive.
HIGH WELDING SPEED
The comparison between the three most employed processes in automated welding enhances the great advantage of PTA:
cool wire TIG: 200 mm/min
automatic MIG: 350 mm/min
automatic PTA: 500 mm/min
The powder dispersion is lower than the loss of filler material in MIG and TIG welding. In addition the high welding speed greatly improves the quality/price ratio.
The comparative analisys of the welding fumes has pointed out a lower atmospheric pollution in comparison with traditional welding methods (certified by Ecoricerche Institute).
FIELDS OF APPLICATION
Thanks to its undeniable advantages, PTA process is employed all over the world, in many fields such as:
- valves for automotive, marine and petrochemical industries;
- hydraulic cylinders;
- rollers and lamination rollers;
- industrial knives and blades;
- forging matrix dies;
- rings, moulds and plugers for extrusion;
- plasticizing screws;
- moulds and accessories for Glass industry