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Submerged-Arc welding (SAW) is a common arc welding process that involves the formation of an arc between a continuously fed electrode and the workpiece. A blanket of powdered flux generates a protective gas shield and a slag (and may also be used to add alloying elements to the weld pool) which protects the weld zone.
The arc is struck beneath a covering layer of granulated flux.
Thus, the arc zone and the molten weld pool are protected from atmospheric contamination by being ‘submerged under a blanket of granular flux.
This gives the name ‘submerged arc welding’ to the process.
Details of the Equipments used in Submerged-Arc Welding
- The equipment consists of a welding head carrying a bare consumable electrode and a flux tube.
- The fluxtube remains ahead of the electrode, stores the granulated or powdered flux, and drops the same on the joint to be welded.
- The flux shields and protects the molten weld metal from atmospheric contamination.
- The electrode which is bare (uncoated) and in the form of wire is fed continuously through feed rollers.
- It is usually copper plated to prevent rusting and to increase its electrical conductivity (since it is submerged under flux).
- The diameter of the electrode ranges from 1.6-8 mm and the electrode material depends on the type of the work piece metal being welded.
- The process makes use of either AC or DC for supplying the required current.
The SAW is just similar to MIG welding, SAW involves formation of an arc between a continuously-fed bare wire electrode and the workpiece. The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool.
A shielding gas is not required. Prior to welding, a thin layer of flux powder is placed on the workpiece surface. The arc moves along the joint line and as it does so, excess flux is recycled via a hopper. Remaining fused slag layers can be easily removed after welding. As the arc is completely covered by the flux layer, heat loss is extremely low. This produces a thermal efficiency as high as 60% (compared with 25% for manual metal arc). There is no visible arc light, welding is spatter-free and there is no need for fume extraction.
Also read: Plasma Arc Welding (PAW)
Advantages of Submerged-Arc Welding
- High productivity process, due to high heat concentration.
- Weld deposition rate is high due to continuous wire feed. Hence, single pass welds can be made in thick plates.
- Deep weld penetration.
- Less smoke, as the flux hides the arc. Hence, improved working conditions. Can be automated
- Process is best suitable for outdoor works and in areas with relatively high winds. There is no chance of spatter of molten metal, as the arc is beneath the flux.
Disadvantages of Submerged-Arc Welding
- The invisible arc and the weld zone make the operator difficult to judge the progress of welding.
- Use of powdered flux restricts the process to be carried only in flat positions.
- Slow cooling rates may lead to hot cracking defects.
- Need for extensive flux handling.