Submerged arc welding (SAW) is an arc welding process that uses a continuous consumable bare wire electrode. The arc shielding is provided by a cover of granular flux consisting of lime, silica, manganese oxide, calcium fluoride and other compounds.
The flux is fed into the weld zone from a hopper by gravity flow through a nozzle.
The electrode wire is fed automatically from a coil into the arc. The flux is introduced into the joint slightly ahead of the weld arc by gravity from a hopper.
The blanket of granular flux completely submerges the arc welding operation preventing sparks, spatter and radiation that are so hazardous in other arc welding processes.
The portion of the flux closest to the arc is melted mixing with the molten weld metal to remove impurities and then solidifying on top of the weld joint to form a glasslike slag.
The slag and infused flux granules on top provide good protection from the atmosphere and good thermal insulation for the weld area. This result in relatively slow cooling and a high-quality weld joint.
The infused flux remaining after welding can be recovered and reused. The solid slag covering the weld must be chipped away usually by manual means.
This process is widely used for automated welding of structural shapes, longitudinal and circumferential seams for large diameter pipes, tanks, and pressure vessels.
Because of the gravity feed of the granular flux, the parts must always be in a horizontal orientation.
The consumable electrode is a coil of bare round wire 1.5 to 10 mm in diameter, consumable electrode is fed automatically through a tube.
Electric currents typically range from 300 to 2000A. The power supplies usually are connected to standard single-phase or three-phase power lines with a primary rating up to 440V.
CHARACTERISTICS OF SUBMERGED-ARC WELDING :
The flux is fed into the weld zone from a hopper by gravity through a nozzle.
Prevents spatter and sparks.
Suppresses the intense ultraviolet radiation and fumes characteristics of the SMAW.
It acts as a thermal insulator by promoting deep penetration of heat into the work piece.
The unused flux can be recovered, treated and reused.
ADVANTAGES:
Smooth welds of high strength and ductility.
Because of high current, high metal deposition, high welding speeds and good penetration are achieved.
Due to high speeds less distortion will occur.
Elimination of fumes and spatter.
Absence of visible arc and ease of penetration.
DISADVANTAGES :
During welding process arc is not visible, judging the welding progress is difficult and so tools like jigs, fixtures and guides are required.
Pre-placing of flux may not always possible.
This welding process is limited to flat position.
Flux is subjected to contamination that may cause weld porosity.
APPLICATIONS:
It is suitable for welding low alloy steel, high tensile steel, low carbon and medium carbon steels, high resisting steel, corrosion resistant steel, high strength steels.
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