February 17th, 2021
Arc welding is an increasingly diverse methodology for joining metal workpieces via heat induced by an electric arc. Gas tungsten arc welding (GTAW) and tungsten inert gas (TIG) welders are among the most popular tools due to their extreme flexibility. Metallurgists deploy GTAW and TIG welders for numerous types of ferrous and non-ferrous metals, from plain carbon steel to exotic alloys. Yet conventional fusion techniques leave many things to be desired when it comes to automation.
Plasma transfer arc welding, sometimes abbreviated to PTA, is the natural evolution of GTAW processes. It is an easily-automated joining method that enables precise control of key weld parameters with greater quality joints and welds. It is ideal for hardfacing and cladding in heavy duty industries like the oil and gas sector, mining, and energy generation.
Here we will outline the basic working principles of plasma transfer arc welding in more depth, with a focus on the configuration of a typical PTA welder plus the benefits of this evolutionary method.
Plasma transfer arc welding is a complex joining process based on the induction of a transferred arc of high-energy density plasma, which provides enough energy to melt both base metal workpieces and metallic filler powders. First, a pilot arc is obtained by ionizing an inert gas (argon, helium, hydrogen, etc.) with an electric arc formed between the tungsten electrode and the torch nozzle. This pilot arc is turned into the transfer arc by discharging it through the constricted nozzle using plasma gases. Essentially, throttling the plasma column to high temperatures, high jet velocities, and high energy densities.
Plasma transfer arc welding is closest in principle to GTAW methods in that they both use non-consumable tungsten electrodes. But PTA welders have been redesigned to transfer the pilot arc from the torch so that it can be throttled through a fine-bore copper nozzle, reaching greater energy densities.
This construction is close to a standard plasma arc welder (PAW), but again, plasma transfer arc welding differs in the type of fillers used. PAW welding involves the separate deposition of wire feedstocks onto the workpiece, which can lead to poor weld control. Plasma transfer arc welders offer much greater control of filler deposition. A stream of metallic powder is fed to the arc region using an internal gas stream, allowing extremely tight control of weld parameters via powder feed rates and gas flow rates.
This process is compatible with a broad range of materials, but metals like Inconel 625 are widely deployed for enhanced corrosion resistivity while carbides are used to enhance wear-resistance.
At Saint-Gobain Coating Solutions, we have taken the greater process control qualities of plasma transfer arc welding to the next level with a new generation of PTA-PHE technologies designed for hardfacing applications. These include precision engineering of valves, valve seats, boiler tubes, drill stabilizers, and more.
Our best-in-class PTA systems are based on plasma high energy technology which allows us to generate extremely thin coatings with high deposit efficiency (>95%), rapidly and with low dilution and heat input to the substrate. Our PTA-PHE technology drastically outperforms GTAW, TIG, and even other plasma transfer arc welding systems on the market.
Want to learn more? Contact a member of the Saint-Gobain team today for more information.