In Submerged-arc Welding (SAW), the welding arc is shielded by a granular flux of lime, silica, manganese oxide, calcium fluoride, and other compounds. Gravity flow through a nozzle feeds The flux into the weld zone from a hopper. The thick layer of flux completely covers the molten metal. Covered flux prevents spatter and sparks and suppresses the intense ultraviolet radiation and fumes characteristic of the shielded metal-arc welding (SMAW) process. The flux acts as a thermal insulator by promoting deep heat penetration into the workpiece.
The consumable electrode is a coil of bare round wire 1.5 to 10 mm in diameter, fed automatically through a tube. Electric currents typically range from 300 to 2000A. The power supplies are usually connected to standard single-phase or three-phase power lines with a primary rating of up to 440V.
Schematic illustration of the submerged arc welding |
The flux is gravity-fed, and the submerged-arc welding process is mainly limited to welds in a flat or horizontal position with a backup piece. Circular welds can be made on pipes, which are rotated during welding. The image shows that the unfused flux is recovered, treated, and reused. Submerged-arc welding is automated and is used to weld various carbon and alloy steel and stainless steel sheets or plates at speeds as high as 5 m/min. The quality of the Weld is very high, with good toughness, ductility, and uniformity of properties. The Submerged-arc welding process provides very high welding productivity, depositing 4 to 10 times the amount of weld metal per hour as the shielded metal-arc welding process.
Applications:
The welds made by Submerged-arc welding are high strength and ductility with low Hydrogen and Nitrogen content. They are suitable for welding low-alloy steel, high-tensile steel, LC and MC steels, high-resistance steel, corrosion-resistant steel, high-strength steel, and many non-ferrous alloys.Advantages:
- Smooth welds of high strength and ductility with low H2 and N2 content.
- 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.
Limitations:
- Because the arc is not visible during the welding process, judging the welding progress is difficult, so tools like jigs, fixtures, and guides are required.
- Pre-placing of flux may not always be possible.
- This welding process is limited to a flat position.
- Flux is subjected to contamination that may cause weld porosity.
- Chlorine, Aluminium, Magnesium, Lead, and Zinc can not be welded.
Post a Comment
Post a Comment