Submerged Arc Welding (SAW)
Submerged arc welding is an arc welding process wherein coalescence is produced by heating the workpiece with an electric arc (or arcs) set-up between a bare or copper coated metal electrode (or electrodes) and the workpiece. In this, the arc end of electrode, the molten pool and the are are always invisible being submerged under the blanket of a granular flux material. During welding, the continuously fed bare metal electrode melts and acts as a filler rod. No pressure is applied and weld is completed without usual sparks, spatter and smoke.
Showing the working principle of submerged-arc welding process. The granular flux consisting of silica, lime, manganese oxide, calcium fluoride, etc. is fed to weld area (in the prepared Vee-groove) just ahead of the electrode tube (or gun). After melting, the flux forms a slag which on solidification covers and protects the newly made weld bead from atmospheric contamination.
The arc is struck by either touching electrode with the workpiece or placing some steel wool between the electrode and the workpiece before switching on the current. Arc is always struck under the flux. The flux (which is a bad conductor when cold), after melting, becomes a good conductor of electricity.
AC or DC welding plants are used to give current up to 4000 amps. DCRP gives deeper penetration and DCSP gives flatter weld bead with faster speeds. AC is preferred above 1000 amps.
Submerged arc welding is used for flat horizontal welding. Backing strips or bars are used for making butt welds in one pass. These strips are essentially required for butt welds in materials that oxidize quickly. The strip is placed on the underside of the weld joint and the joint groove (prepared edge) is flooded with flux (or shielding gas as in TIG welding) to protect the weld joint from atmospheric contamination.
The process is effective for long stretches of welds. Faster speeds in welding thicker section of steels are possible, for example, 18 mm steel plate can be welded at a speed of 40 cm/minute in one pass. The process gives several advantages, for example, high quality weld, faster welding, deep penetration, adaptability to full mechanization, no sparks, no glare, no spatter, no smoke and no extra heat radiation. All these make this process highly suitable for mass production of steel sections.
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