About the Submerged Arc Welding (SAW) Process
Submerged Arc Welding (SAW) is a common welding process that is commonly used in the structural and vessel construction industries. Originally developed by the Linde - Union Carbide Company, it is commonly used in beam, boom, tractor, and multi-head type rigs. Also known as Sub Arc or SAW, this process uses a blanket of granular fusible flux beneath which both the weld and the arc zone are protected or “submerged.” This flux blanket offers the following advantages:
Guards against atmospheric contamination
Stabilizes the arc during welding
Prevents splatter and sparks from flying about
Suppresses radiation and fumes that are typical of the shielded metal arc welding process (SMAW)
How it works
Sub Arc welding requires a continuously-fed tubular or consumable solid electrode and may be fully automatic or semi-automatic. The arc is flat and is maintained between the end of a bare wire electrode and the weld. The electrode is constantly fed into the arc and as it is melted, a layer of granular flux provides a protective cover beneath which the welding occurs. The blanket is created as some of the flux becomes molten. This fusible flux may consist of lime, silica, manganese oxide, calcium fluoride, and other compounds. In a molten or melted state, the flux becomes conductive. This allows it to supply a constant current between the electrode and the welding work. The remainder of the flux is recovered and reused, unless it has become contaminated.
In the automatic version of SAW, the process is performed with a set of rollers driven by a controlled motor to ensure that the wire is fed into the arc at a speed rate that is equivalent to the rate at which the electrode is melted. The arc length remains constant as a result. The SAW process is usually automated; however, there are semi-automated systems available, too.
Properly performed Sub Arc welding should consistently result in mechanical properties that are at least equal to that of the base metal. Ductility and impact resistance should be good, and bead appearance should be uniform.
Variables of the SAW Process
There are some key variables of the submerged arc welding process. These variables include:
The arc voltage
The wire feed speed
Travel speed
Contact tip to work (CTTW) or electrode stick-out (ESO)
Polarity and current type (may be either AC or DC), as well as variable balance AC current
Equipment
In automatic submerged arc welding, there are three types of guns that are generally used. These include the side flux delivery gun, the deep groove gun, and the concentrated flux delivery gun.
The concentrated flux delivery gun deposits the flux around the wire. With both the side flux delivery gun and the deep groove gun, the flux is fed from an overhead gravity hopper to the gun’s flux shut-off assembly.
The type of gun chosen for a certain job may be dependent upon the joint design and/or the welding operator’s preference.
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