Submerged arc welding: (SAW)
In submerged arc welding also known as hidden arc welding, submerged melt welding, or sub-arc welding the arc is struck between a metal electrode and the work piece under a blanket of granular flux. The welding action takes place under the flux layer without any visible arc, spatter, smoke or flash.
Here the weld arc is shielded by granular flux, consisting of Lime, Silica, Manganese Oxide, Calcium Fluoride, and other elements.
The filler wire used may be bare or slightly copper coated. The consumable electrode is a coil of bare round wire 1.5 to 10 mm in diameter.
Operation of Submerged Arc welding Process:
The welding action can be initiated by introducing a piece of high resistance conducting material like steel wool or carbon between the electrode and the work piece. Once the welding action has been initiated the intense heat produced by the flow of current in the high resistance path melts a path of the flux around the electrode forming a conducting pool.
The molten filler displaces the liquid flux and fuses with the molten base metal forming the weld. The molten flux coating over the molten metal pool forms a blanket that eliminates spatter losses and protects the welded joint from oxidation. As welding proceeds, the molten weld metal and the liquid flux cool and solidify under a layer of unused flux. The molten flux on solidification forms a brittle slag layer which can be easily removed.
Unused granular flux material can be reclaimed and reused.
Characteristics of Submerged Arc welding Process:
Electric current is 300 to 2000A.
Power supply is 440 V.
Velocity is 5m / Min
The SAW process provides very high welding productivity, depositing 4 – 10 times the amount of weld metal per hour.
Functions of the Electrode filler wire
The following are the functions of the electrode or filler wire:
- It allows electrical current to flow into the welding arc.
- Provides joint filler material for joints
- Electrodes can be made of a variety of materials, including solid rods or wires, as well as composite electrodes (a metallic covering that protects metal particles from the elements)
Functions of the Flux
The flux’s functions are discussed in detail.
- The flux is made up of granular minerals and metals in the form of fused and crushed as well as bonded agglomerated particles.
- Determine the electrical characteristics of the electrode as well as the stability of the arc.
- Maintain control over the chemical composition and metallurgy of the weld deposit
- Provide additional filler material
- Control the shape of the weld bead
- Molten flux shields the weld pool
- Fluxes burn off at varying rates
Neutral fluxes have a high toughness and can be applied in multiple passes. Active fluxes are high in deoxidizers, have a fast weld over rust and can be applied in a limited thickness. Alloyed fluxes have added Cr and Ni to improve the mechanical properties.
Fluxes are used in a variety of different formulations.
- Calcium silicate
- Manganese silicate
- Aluminate rutile or basic
- Basic fluorides
Fluxes referred to as “neutral,” “active,” “basic,” and “acid”
Variables in Submerged Arc Welding
There are several factors to consider: welding current, arc voltage, travel speed, wire size, and wire extension.
Advantages of Submerged Arc welding Process:
Thin plates can be easily welded in one pass without any edge preparation while only a slight bevelling is necessary in most other cases.
The quality of welds produced in submerged arc welding is very high with good toughness, ductility and uniformity of properties.
Submerged arc welding is most suitable for welding in the down hand or flat position although welds can be made on a straight slope.
Materials successfully welded by the process include low carbon steel, medium carbon steel, heat resistant steel, corrosion resistant steel, high strength steels and non ferrous metals like Monel metal, nickel and others.
High speed of execution due to the use of high currents in one or more electrode wires
The arc is concealed, enabling the operator to work without a mask and without disturbing others nearby
Limitations of Submerged Arc welding Process:
- Solid flux submerged arc welding can be used only on alloy and non-alloy carbon steel, stainless and refractory steel
- The use of a powder flux means that welds must be executed horizontally, unless special measures are taken
- The process cannot weld plate less than 1.8 mm thick (due to its high penetration)
- It is not possible to butt joint work pieces more than 16 mm thick ; thicknesses greater than 16 mm require special preparation (bevelling).
Application of Submerged Arc welding Process:
Heavy Duty Pressure vessels
Off shore engineering