Submerged Arc welding is a more specific niche to arc welding where two metals are joined together by using an arc that is formed using a continuously fed electrode and it must be already used to weld on the workpiece that you are dealing with currently. The shielding gas for protection is provided by a layer of powdered flux and slag that protects the weld zone.
This is a well-established and refined form of welding which requires minimal amounts of shielding gas. The arc is submerged between the flux layers and hence isn’t visible enough during the welding process. When we talk about the electrode used here, there are various types used as it can be solid, cored wire, or strip wire made from sintered materials.
The flux is made by forming a glassy slag by agglomerating the constituents using the ‘binder and corning’ process. Many welders and other enthusiasts have this very common question. Is SAW an automatic/mechanized process? The answer is ‘yes’, SAW is usually operated as a mechanized process. Just like other welding processes, bead shape and performance are dependent on the welding current supplied, arc voltage, and travel speed.
One can gain additional productivity in this welding process by using a small diameter of non-conducting wire into the edge of the welding pool that is at the leading end. This has shown weld deposition rates increased to about 20% distinctively.
One more trick to get better deposition rates is by replacing the wire used to a 0.5mm thick strip that is 60mm wide as it can be used for surface components easily. This type of SAW welding is ideal for longitudinal and circumferential welding which deals with the manufacture of lie pipes and pressure vessels.
Submerged arc welding was first invented and got its patent in the year 1935 and back then, granulated flux was placed over the electric arc. It was developed by the E O Paton Electric Welding Institute located in Kiev, Ukraine. It was invented back then for the manufacture of the T34 Tank using for warfare in the Second World War.
The welding head helps in feeding the flux and filler metal to the welding joint and this is the region where the filler metal gets refilled (energized).
As the name suggests, it is a store-house of all the flux used and controls the rate of flux deposition on the welding joint.
Granulated flux shields are used here which not only provides efficiency to the welding joints but also protects the molten weld from any sort of atmospheric contamination. More than just cleaning and purifying the weld, it also modifies the chemical composition of the weld.
The flux has a compositional mixture of fluorides of calcium and oxides of calcium, magnesium, silicon, and aluminum as well as manganese. The basic recommendation while using flux for welding is to have a fine texture with coarse particle sizes for heavier as well as smaller thicknesses respectively.
The electrode used for SAW is of many types as mentioned earlier. Whatever be the types of wires used, it has a thickness of around 1.6mm to 6mm. Twisted wires used in this case offer oscillation in the welding process. We basically fuse the toe of the weld to the base of the metal and the electrode used here has the constituents just like the weld metal.
These electrodes are compatible with alloy steels, mild steels, high-carbon steels, stainless steel, and some copper and nickel metals too. Copper-coated electrodes provide better electrical conductivity and more resistance towards rust and corrosion. The approximate value of currents to weld with 1.6mm, 3.2-mm, and 6.4-mm diameter electrodes are 150–350, 250–800, and 650–1350 Amps respectively.
Working ProcessJust like MIG or GMAW welding, this is a wire-fed welding process where the wire is fed through a torch which is moved along the welding joint by machines. Setting up the welding machine is quite simple and much similar to the other processes.
The voltage supplied determines the bead width, and amperage influences the penetration of the welding torch and deposition rates.
This arc welding process relies on granular flux that protects the weld from atmospheric hazards and the arc here is buried in the flux and is not visible during the welding process. Once the arc, flux, and base metal to form the weld pool.
Investing in proper equipment, a good amount of power supply and wire feeder, helps us achieve some good results in this field. Several accessories are available and, in some applications, the torch is kept stationary and the workpiece is moved using positioning equipment.The operators’ attention is required quite a lot while doing SAW welding but is simpler to implement and become familiar with to do work. With more investment in the equipment used comes greater durability and ruggedness of the SAW instruments.
SAW welding is possible only in two positions for good deposition rates and high-current parameters which are flat and horizontal position.
Joint tracking equipment helps in viewing the arc while welding which is normally not possible. Simple tracking mechanisms include lasers to more advanced mechanisms like the tactile probe.
Key SAW Process Variables
1. Why is submerged arc welding referred to as submerged?
Submerged Arc Welding (SAW) is named as such because the weld pool and arc using which weld is done, is present in the underlying layers of the flux blanket. The flux layers become molten and get conductive allowing current to pass between the electrode and the workpiece.
2. Is the submerged arc welding process automatic?
Submerged Arc Welding (SAW) is fully automatic as well as semi-automatic based on the equipment used. The arc is flat and is maintained between the end of the wire electrode and the weld. The electrode is fed into the arc as it is melted.
In automatic submerged arc welding, three different types of welding are used which are flux delivery gun, deep groove gun, and concentrated flux delivery gun. Moreover, SAW welding is accomplished by using a set of drive rollers that are run by a controlled automatic motor.
3. What is submerged arc welding? When was it invented?
Submerged Arc Welding (SAW) is a specialized type of arc welding where a continuously fed solid or tubular electrode is used to form the arc between the two metals to be joined. It was first patented by Jones, Kennedy, and Rothermund in the year 1935, where they covered an electric arc beneath a bed of granulated flux.
4. What type of electrode is used in submerged arc welding?
SAW filler wire/ electrode is generally a normal wire where it can be a solid wire, strip wire, or even a cored wire. The wire thicknesses range from 1.6mm to 6mm straight where twisted wires are used for providing an oscillating movement in the arc. The electrode has composition more similar to the metal to be weld and requires alloying for more durability.
5. What is the major function of the coating on the arc welding electrode?
The coating given on the arc electrode is termed as ‘flux’ as it has a mixture of fluoride of calcium and oxides of calcium, magnesium, silicon, and aluminum. This coating acts as a shielding layer to the weld pool from corrosion and rust from atmospheric moisture and oxygen. It also has additional filler metal that increases the deposition rates and reduces the fluidity of the weld pool.
6. Which type of Arc welding flux is susceptible to moisture pick-up?
Agglomerated submerged arc welding flux is susceptible to moisture pickup. It produces a smaller number of sparks and splatter are leaked more than other welding arc methods. This type of welding minimizes the errors caused by humans ourselves.
7. What are the advantages and some limitations that SAW welding has?
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