Something New in the Sub Arc World
Looking into the past, this was a shared feeling of a robust but limited versatility process and through this short paper we will outline the new opportunities now showing up with the launch of the new PowerWave® AC/DC 1000 power source.
Initially, submerged arc equipment was constituted of a power source for supplying power, a control box for controlling the arc and for regulating a wire feeder.
The Power source, for the vast majority a conventional rectifier, was dedicated to one type of current, either direct current (DC) or alternative current (AC).
Ever since the early days of the process and thanks to the commonly used hard automation systems , the addition of one or more arcs has always been used for deposition rate or travel
speed improvement. But in most of the applications, the number of arcs was limited to two: this is the conventional tandem arc system. As a brief reminder, we will now describe the tandem system:
A lead arc, usually DC, is connected in front. DC wire is on positive polarity in order to guarantee a good penetration in the base metal or previous passes. An AC arc is following, both arcs feeding the same puddle. The AC arc is mandatory in order to avoid any arc blow resulting from the interaction between magnetic fields surrounding each arc and welding wires. The AC arc switching from a positive value to negative, (this is not conventional pulse), limits the interaction by switching directions of the magnetic field 50 times per second. This does not eliminate interaction, it is a way to keep it to an acceptable and consistent level and therefore to control it.
The other positive action of the AC arc is the deposition rate. Due to the preheating effect of the electrical stick out (ESO) when the wire is connected to the negative polarity, DC negative current is mostly considered to yield a 30% higher deposition rate, compared to DC+. With AC current, welding wire being half of the time in DC+ and half of the time in DC- , the deposition rate is improved by 15%.
To conclude the tandem arc description, we can summarize it as a process with a 15% higher deposition rate compared to a single electrode process, using a combination of DC and AC arcs controlling arc blow issues.
Next step was obviously to incorporate a third, or even more, arcs in order to optimize the benefits of such a process. Unfortunately, the addition of a third arc is introducing a new type of complication regarding arc interaction and control. As already described, arcs are interfering between each other. The third arc had to be an AC one, but using a different phasing than the second one in order not to create interference . The only way to do so was to connect power sources in a “Scott connection” type. Such a connection, with the proper taping on the secondary transformer, was able to yield a fix and consistent off-phasing between the AC arcs. The limiting factor being that setting is determined by a hardware solution and any modification on the phasing would request long and expensive work on the transformer . In practice therefore, such an installation would be set-up initially and then used as built.
The AC power source was very often the first source of limitation for the process. Due to the technology, AC welding current was supplied from a power source switching network inputs to the required welding parameters set.
The current frequency was determined by the network (60Hz in the USA and 50 Hz in Europe) and in order not to superpose different currents, only one phase was used for the power supply. As a consequence, the input current needed for the AC power source was around 260 Amps on a single phase on the 380 or 440 Volts network. Because of the specific design of the network, the electrical consumption was also kind of challenging.
A specific leaflet about power consumption is available on the Lincolnelectric.com website
Initially, submerged arc equipment was constituted of a power source for supplying power, a control box for controlling the arc and for regulating a wire feeder.
The Power source, for the vast majority a conventional rectifier, was dedicated to one type of current, either direct current (DC) or alternative current (AC).
Ever since the early days of the process and thanks to the commonly used hard automation systems , the addition of one or more arcs has always been used for deposition rate or travel
speed improvement. But in most of the applications, the number of arcs was limited to two: this is the conventional tandem arc system. As a brief reminder, we will now describe the tandem system:
A lead arc, usually DC, is connected in front. DC wire is on positive polarity in order to guarantee a good penetration in the base metal or previous passes. An AC arc is following, both arcs feeding the same puddle. The AC arc is mandatory in order to avoid any arc blow resulting from the interaction between magnetic fields surrounding each arc and welding wires. The AC arc switching from a positive value to negative, (this is not conventional pulse), limits the interaction by switching directions of the magnetic field 50 times per second. This does not eliminate interaction, it is a way to keep it to an acceptable and consistent level and therefore to control it.
The other positive action of the AC arc is the deposition rate. Due to the preheating effect of the electrical stick out (ESO) when the wire is connected to the negative polarity, DC negative current is mostly considered to yield a 30% higher deposition rate, compared to DC+. With AC current, welding wire being half of the time in DC+ and half of the time in DC- , the deposition rate is improved by 15%.
To conclude the tandem arc description, we can summarize it as a process with a 15% higher deposition rate compared to a single electrode process, using a combination of DC and AC arcs controlling arc blow issues.
Next step was obviously to incorporate a third, or even more, arcs in order to optimize the benefits of such a process. Unfortunately, the addition of a third arc is introducing a new type of complication regarding arc interaction and control. As already described, arcs are interfering between each other. The third arc had to be an AC one, but using a different phasing than the second one in order not to create interference . The only way to do so was to connect power sources in a “Scott connection” type. Such a connection, with the proper taping on the secondary transformer, was able to yield a fix and consistent off-phasing between the AC arcs. The limiting factor being that setting is determined by a hardware solution and any modification on the phasing would request long and expensive work on the transformer . In practice therefore, such an installation would be set-up initially and then used as built.
The AC power source was very often the first source of limitation for the process. Due to the technology, AC welding current was supplied from a power source switching network inputs to the required welding parameters set.
The current frequency was determined by the network (60Hz in the USA and 50 Hz in Europe) and in order not to superpose different currents, only one phase was used for the power supply. As a consequence, the input current needed for the AC power source was around 260 Amps on a single phase on the 380 or 440 Volts network. Because of the specific design of the network, the electrical consumption was also kind of challenging.
A specific leaflet about power consumption is available on the Lincolnelectric.com website
