Submerged Arc Welding – Welding is one of many technologies that keeps experiencing development every year. Because the business is promising and the science is challenging. With the rise of automation technology, the attempt to crossbreed welding and automation (thus becoming automated welding) is already progressive.
However, do you know that automatic welding has been around for a few decades now? In practice, welding is not only done by the hand of the welder, but there’s actually a machine that capable to weld just fine without the need of welder. You know what I’m talking about if you ever heard the name Submerged Arc Welding (SAW in short). Don’t worry if you haven’t, just finish this article and you’ll learn the wonder of Submerged Arc Welding.
Submerged Arc Welding Definition
This is the very first automatic welding that dates back to 1930s for its first patent. Where welding process is normally visible, in Submerged Arc Welding the arc is literally submerged under a pool of molten flux, making it impossible to see the arc. Both the filler wire and the flux is continuously fed to the arc, as the welding machine progressively move forward along the weld path. The flux is in the form of grain and looks like ordinary sand. It’s made of a mixture of various ingredients namely lime, silica, manganese oxide, calcium fluoride, and other compounds.
Due to the process of being fully automatic or mechanized, submerged arc welding is very productive with its high deposition rate. Ranging from 9 – 10 times of those stick welding deposition rate. However, submerged arc welding also has a few disadvantages. Being mechanized welding itself, this puts a limit to SAW application in term of welding position.
Where it is impossible to weld in any other position but flat, while to some extent it can also be applied for a fillet weld. More to that, welding with SAW can be very hot, it has greater heat input compared to stick welding due to its relatively greater welding parameter. The heat produced from the arc cannot escape like in stick welding, because the arc is submerged in a flux that acts like isolator.
Therefore, the heat spread in the base metal resulting in greater dilution and heat affected zone (HAZ). Still, the SAW is popular and found its application in many industry and fabrication.
Submerged Arc Welding Equipment
Submerged Arc Welding machine is its own machine that consisted of a few important parts. Basic SAW machine looks like the diagram in figure 3. Just like in every welding machine, especially the arc welding machine, there’s a transformer that generates the required welding current and voltage from your regular electric outlet. Most of the time this transformer and its control panel are mostly digital and look pretty advanced.
The control panel can also be equipped with many other features, including but not limited to, variables control (welding current, welding voltage, and travel speed), troubleshooting errors, and memory to save your most frequently used welding parameter. An electrode wire reel is there to continuously feed the filler metal through the wire-feed motor.
Similar to wire feeder in GMAW and FCAW, the difference is, in SAW the diameter of filler wire is thicker than in GMAW or FCAW. The flux hopper is there to contain the granulated flux and feed it continuously to the weld pool. The unused flux, which is the top of the weld pool (the one that does not melt), will be recovered manually or by some vacuuming device similar to unfused flux recovery tube in figure 3. Weld backing is applied sometimes to avoid burn through because of the continuous weld activity.
Another variation of the SAW is the addition of extra wire feeder. An up to four wire feeders can be used simultaneously to further increase welding productivity. Therefore, a single run can adequately join thick pieces of metal rather than doing it with multiple runs.
SAW also come in stationary mode, where the workpiece moves instead of the machine. The stationary mode is applied in the pipe joint while the traditional moving machine is mostly applied in plate joint. The moving mode is guided with a railing that needs to be set for its straightness before welding starts.
Setting the rail is as important as setting the welding variables, because once running, it’s not recommended to interrupt the process until it’s done. In addition, a slight inclination will affect the welding geometry and create a problem like lack of fusion.
Submerged arc welding is a highly productive welding process. Because of that, this process is applied as much as it can despite its limitation in term of welding position. Besides the complication of handling granulated flux as it needs to be recovered and some other trouble in cleaning the slag, submerged arc welding is a fairly clean process, it doesn’t produce any spatter or sparks because the flux bed completely cover the weld pool, not allowing any spatter or spark to escape. Another reason why submerged arc welding is favorable is it does not require a skillful welder. Training a welding operator take much lesser time compared to training welder to be skillful.
Submerged arc welding is mainly used to weld thick material with long join. For example in the construction of the ship hull, the longitudinal joint of pressure vessel and tank. It is also possible to join a thick and large diameter of the pipe with a SAW. However, due to the process being very hot, its application limited only to material that does not really reactive towards heat.
The materials are mostly carbon steel and some variation of a nickel-based alloy. The heat can also deform the material, so precautions need to be taken to prevent deformation, such as intermittent welding or placing stopper at some critical point. But in any case, submerged arc welding eliminates any human error factor and increase the chance of producing a sound weld faster than any welding process.
The safety issue regarding this process is rather unique compared to any other welding process. The SAW is completely automatic and mechanized, where welding operators only need to direct the welding path and push a button to start welding. After that, the welding operator can safely supervise the welding process from a safe distance.
The process does not produce that much fume compared to any other welding process and it is a great safety feature. The flux bed also entirely cover the ultraviolet light of the arc from escaping, whereas in another welding process a UV light is often causing problems to a welder, causing complication such as arc eye (photokeratitis) and skin burn.