Submerged-arc welding is used for the automated welding of long seams. The process’s high deposition rate makes it relatively cost-effective and speeds up the work process. Submerged-arc welding, also known as UP welding for short, is a Arc Welding Processes, in which the welding arc burns invisibly between an endless electrode and the workpiece.
The high temperature of the arc causes the materials to melt. A welding flux made of specific materials is placed over the joint—this, too, is melted. It then floats on the surface of the molten pool because it is lighter than the metal slag.
The liquefied powder protects the molten pool from the air and, at the same time, prevents heat from escaping. This is why the melting rate is so high. The disadvantage of this method is that the powder layer makes it impossible to visually inspect the resulting weld; however, it also allows for welding without shielding gas.
Submerged-arc welding also uses filler materials. Wire or strip electrodes are used for this purpose. These are fed automatically. In addition, the powder is also applied automatically to the weld joint. A contact tube transmits the current to the electrode, creating the arc. This arc burns within a cavity and is surrounded by the molten powder. The current used ranges from 600 to 800 amperes, which also improves the deposition rate.
There are a total of 4 different processes available for submerged arc welding.
What is single-wire submerged-arc welding?
Single-wire submerged arc welding is the most commonly used submerged arc welding process. Both solid and cored wires are used in this process. Their diameters range from 2.0 to 4.0 mm. If the sheets to be welded are very thin and a higher welding speed is required, it is also possible to use wires with a diameter between 1.2 and 1.6 mm.
In most cases, direct current is used. The electrode also often has a stickout—a thin tip measuring 20 to 40 mm in length. A smaller diameter results in a higher melting rate at a constant current, thereby increasing the current density. Furthermore, thinner wires result in narrower welds and deeper penetration.
What is double-wire submerged-arc welding?
Submerged-arc double-wire welding is also known as twin welding. This process uses two wire electrodes. Both have a small diameter, and the distance between them is no more than 15 mm. They are also both connected to the same power source.
The welding head holds the wires in a dual-drive roller. The arc between the two wires allows for a deposition rate that is approximately 30 % higher than that of single-wire welding. When flux-cored wires are used, the deposition rate increases even further. This simultaneously increases the welding speed for groove welding. The resulting welds are very stable and are highly effective at bridging gaps.
What is submerged-arc strip welding?
Submerged-arc strip welding is similar in principle to submerged-arc single-wire welding. Only one electrode is used. However, instead of a wire, a strip is used. If the strip is wider, it can even be used to create multiple parallel arcs. In practice, the material is melted by an arc that oscillates along the edge of the material to be melted. Submerged arc strip welding is used to clad high-alloy materials.
What is submerged-arc tandem welding?
Submerged-arc tandem welding makes it possible to further increase the deposition rate and, consequently, the welding speed. This allows for the simultaneous use of up to 6 electrodes in succession. However, typically only 2 or 3 wire electrodes are used.
The electrodes typically have a diameter of 3.0 to 5.0 mm. Each electrode has its own power source. If the distance between the electrodes is greater, each one generates its own arc. The wire is fed by its own feed unit. The first wire electrode creates a deep penetration. The subsequent wires then fill the gaps in the weld. The last wire electrode finishes the weld. This produces wide welds with a smooth surface. The arc at the starting point operates on direct current, while the subsequent arcs are generated using alternating current.
What is submerged arc welding, and what are its applications?
Submerged-arc welding is used to process alloyed and unalloyed steels in the following areas:
- Steel Construction
- Shipbuilding
- Bridge Construction
- Container Manufacturing
For sheet metal thicknesses of 6.0 mm or greater, submerged arc welding is more cost-effective than other welding processes. In addition to creating joints, this process can also be used to apply corrosion-resistant and wear-resistant coatings. Thanks to the high deposition rate and automation, even longer welds can be laid in a single pass.
How does the principle of submerged arc welding work in practice?
The powder is applied to the area to be welded through a feed tube. Immediately afterward, the conductive nozzle is positioned so that the wire is guided into the powder at the weld site. A power source is connected to the nozzle, allowing current to flow through it. The arc burns within a cavity in the feed material, the powder. All equipment is mounted on a cart that moves forward during operation, thereby creating the weld seam.
What are the advantages of submerged arc welding?
While applying the flux and welding within this layer may seem labor-intensive, in practice the process has the opposite effect. Here are the advantages of submerged arc welding:
- High productivity: The short nozzle length allows for a higher flow rate. The flux insulates and prevents heat loss. This increases thermal efficiency and melting capacity. At the same time, the penetration depth of the weld is very deep. Overall, this enables a higher working speed.
- Good weld quality: The flux and slag protect the molten pool from contact with the air. As a result, even a windy environment has no effect on the weld quality. The welding parameters can be adjusted automatically to maintain a stable arc. The molten pool has a longer solidification time, resulting in a smoother, more aesthetically pleasing weld bead that is free of defects and more stable overall.
- Less welding material and energy: Because of the greater penetration depth, the submerged arc welding process does not require as deep a groove as gas shielded welding. This means less filler material is needed. Processing time is also reduced, which saves energy. The flux concentrates the heat of the arc. In addition, there is less metal vaporization and spatter.
- Even thick components can be welded: Due to the deep penetration and high melting rate, it is also possible to join thicker components together.
- Better working conditions: Thanks to automation, working conditions are much better. In addition, there is no arc radiation—since the arc is covered—and no smoke is produced.
What are the disadvantages of submerged arc welding?
Submerged arc welding requires high standards of assembly and workmanship. It can only be performed in a horizontal position or at a slight angle. As a result, only long welds can be made. There are also limitations compared to aluminum welding: Submerged arc welding cannot be used to create circular seams with a small diameter or in confined spaces. Furthermore, thin sheets cannot be welded. A current of at least 100 amperes is also required to ensure sufficient arc stability.
How do you choose the right flux and welding wire?
For submerged arc welding to produce the best results, using the right wire and flux is crucial. The flux not only protects the weld pool; it also affects the mechanical properties of the resulting weld and the speed at which the weld is formed.
Finding the Right Flux
There are two factors to consider regarding flux: current-carrying capacity and slag release. The current-carrying capacity determines the efficiency of the work and the weld profile. Slag release depends on the type of weld construction for which the flux is suitable. Both reactive and neutral powders can be used as fluxes. Neutral fluxes do not alter the chemical composition of the weld. Reactive fluxes, on the other hand, react with the materials and alter their chemical properties.
What is flux powder?
Active Fluxes contain manganese and silicon. This ensures the tensile strength of the weld, even with higher heat input. This also keeps the weld bead smooth even at higher travel speeds of the welding equipment. Finally, both elements ensure that a sufficient amount of slag is released.
Reactive Fluxes are effective at reducing the risk of poor weld quality. However, they are more suitable for single- and two-pass welds. Neutral fluxes, on the other hand, are better for multi-pass welds. They help prevent brittle welds that crack easily.
There are specific options for the wire, and their pros and cons must be weighed. Here, one must consider the wire composition and heat input, both of which have a significant impact on the weld and its quality. Using a metal-cored wire can increase work efficiency by 15 % to 30 %. At the same time, compared to solid wire, it produces a weld bead that penetrates less deeply but fills a wider area. A metal-cored wire allows for a higher feed rate, while also reducing heat input. This, in turn, lowers the risk of burn-through or welding distortion.
How is submerged arc welding actually performed?
The success of submerged arc welding depends entirely on proper preparation. This requires setting the welding parameters and preparing the workpiece according to the requirements.
Preparing the grooves
The grooves for welding depend on the thickness of the steel sheets. If the steel sheet is less than 14 mm thick, grooves do not need to be cut. However, if the thickness exceeds this, grooves are required to ensure a sufficiently strong weld. Grooves can be made using oxy-fuel cutters, carbon-arc gougers, or edge gougers. They must be straight and conform to the specifications for the material and welding process.
How do you clean the welding area?
The groove and the entire welding area must be cleaned to a width of 20 to 50 mm on each side. It is important to remove etch marks, moisture, oxides, oil, and any other contaminants. Portable grinders, polishers, wire wheels, wire brushes, shot blasters, and flame cutting can be used for cleaning.
The Welded Parts
The pieces to be welded must be positioned exactly as they will be joined later. Care must be taken to ensure the correct gap dimensions and flat surfaces. Misalignment must also be avoided.
Wire and Flux
Both the welding wire and the flux are involved in the metallurgical reaction that occurs during welding. Therefore, it is important to ensure that the welding wire is clean and the flux is dry. If the welding wire has a copper coating, oil and other contaminants must be removed from the surface. Acid-based fluxes must first be dried at 250 °C and then kept warm for 1 to 2 hours. Fluoride-containing fluxes are suitable only for direct current and must be dried at 300 to 400 °C.
How do you select the welding parameters?
First, you have to Welding current Select it. This determines the depth of the weld. As the welding current increases, the penetration depth and the thickness of the weld increase. A higher welding current also results in higher productivity; however, above a certain welding speed, too high a current means that too much heat is introduced—which can lead to defects such as weld spatter and burn-through. If the welding current is too low, the penetration depth will be insufficient, resulting in slag inclusions and poor weld quality.
Welding Stress
The Welding stress affects the width of the molten pool. A higher voltage results in a shallower penetration depth, and the width of the weld increases. If the welding voltage is set too high, more flux is melted away, which destabilizes the arc and causes defects and porosity. Therefore, a higher welding voltage must be accompanied by a higher welding current.
The welding speed
The Welding speed affects the depth and width of the penetration. If the welding speed is increased, both the penetration depth and width decrease. To achieve sufficient penetration, the current and voltage must be increased along with the welding speed. If, on the other hand, the welding speed is too low, the molten pool becomes too large, resulting in spatter, a coarse weld bead, and slag inclusions.
What diameter should the welding wire be?
A welding wire with a smaller diameter results in deeper penetration. As for wire length, the longer the wire, the greater the resistance. Generally, a wire length of 30 to 40 mm is used. If the excess length is too short, the heat from the arc can also damage the conductive nozzle.
What should be the angle of the wire relative to the workpiece?
In single-wire submerged-arc welding, the wire is usually perpendicular to the workpiece. In two- and three-wire welding, each wire has its own function and, consequently, a corresponding angle of inclination. If the wire is tilted forward, the penetration is shallower. If the wire is tilted backward, the penetration is deeper, and the weld bead becomes deep and narrow.
What should the density and granularity of the flow data be?
If the flux layer is not thick enough, the arc will not be adequately protected. This can even lead to an open arc. A typical layer thickness is 20 to 30 mm. For a welding current of 600 amperes, the grain size should be between 0.25 and 1.6 mm. For 1,200 amperes, a grain size of 0.4 to 2.5 mm is recommended, and for more than 1,200 amperes, the grain size should be between 1.6 and 3.0 mm.
How does single-sided welding work when the weld is formed on both sides?
For single-sided welding with a weld bead formed on both sides, the workpiece must be secured to a support surface with flux. It is important to ensure that there is always close contact between the workpiece and the flux. It is important to use a platform and a pressure frame to ensure even pressure so that the weld bead does not sag.
How does double-sided submerged-arc welding work?
For butt welds, welding is usually performed on both sides. This allows medium- to thick-gauge sheets to be joined. The workpieces are welded on one side on a flux cushion and, after being turned over and cleaned, are joined on the other side.
For double-sided welding, you can use a Support Plate is used—usually a steel strip 3 to 4 mm thick and 30 to 40 mm wide. Another method is the Clamping for double-sided welding. The gap between the two workpieces should be only 1 mm or less. Welding on the front side is adjusted so that the penetration depth is less than half the thickness of the workpieces. After turning the workpieces over, the welding current is then adjusted so that 60 % to 70 % of the workpieces’ thickness is welded.
How does butt welding of thick sheets work?
When thick workpieces are joined using the multi-pass welding process, the cross-sectional area of the weld bead is only 70 % of the thickness. The following applies to groove shapes: For weld seams with a thickness of 22 to 36 mm, a V-shaped groove is typically used; for thicknesses greater than 38 mm, U-shaped, UV-shaped, or double-U-shaped grooves should be used.
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Frequently Asked Questions About Submerged Arc Welding
Single-wire welding is the simplest and most common submerged arc welding process, using a single wire electrode. Tandem welding, on the other hand, uses 2 to 6 consecutive electrodes, each with its own power source. This allows for significantly higher deposition rates and welding speeds, but is also more technically complex.
For sheet metal 6.0 mm or thicker, submerged arc welding is more cost-effective than other welding processes. It is not suitable for thinner sheet metal due to the minimum current requirement of 100 amperes and the limited welding positions.
No. Submerged-arc welding can only be performed in a horizontal position or at a slight angle. Welding in constrained positions or confined spaces is not possible. This is one of the major disadvantages compared to manual arc welding processes.
Wire or strip electrodes and welding flux are used. The flux can be active, reactive, or neutral, and it affects the mechanical properties of the weld. Choosing the right wire and flux is crucial for quality and productivity.
Submerged-arc welding is primarily used in steel construction, shipbuilding, bridge construction, and vessel manufacturing. It is particularly well-suited for welding long, straight seams in alloyed and unalloyed steels.