Submerged arc welding
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Submerged Arc Welding (SAW) is a common arc welding process. Originally devolved by the Linde - Union Carbide Company. It requires a continuously fed consumable solid or tubular (flux cored) electrode. The molten weld and the arc zone are protected from atmospheric contamination by being “submerged” under a blanket of granular fusible flux consisting of lime, silica, manganese oxide, calcium fluoride, and other compounds. When molten, the flux becomes conductive, and provides a current path between the electrode and the work. This thick layer of flux completely covers the molten metal thus preventing spatter and sparks as well as suppressing the intense ultraviolet radiation and fumes that are a part of the SMAW (shielded metal arc welding) process.
SAW is normally operated in the automatic or mechanized mode, however, semi-automatic (hand-held) SAW guns with pressurized or gravity flux feed delivery are available. The process is normally limited to the Flat or Horizontal-Fillet welding positions (although Horizontal Groove position welds have been done with a special arrangement to support the flux). Deposition rates approaching 100 lb/h (45 kg/h) have been reported — this compares to ~10 lb/h (5 kg/h) (max) for shielded metal arc welding. Currents ranging from 300 to 2000 A are commonly used;[1] currents of up to 5000 A have been used (multiple arcs).
Single or multiple (2 to 5) electrode wire variations of the process exist. SAW strip-cladding utilizes a flat strip electrode (e.g. 60 mm wide x 0.5 mm thick). DC or AC power can be utilized, and combinations of DC and AC are common on multiple electrode systems. Constant Voltage welding power supplies are most commonly used, however Constant Current systems in combination with a voltage sensing wire-feeder are available.
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[edit] Electrode
SAW filler material usually is a standard wire as well as other special forms. This wire normally has a thickness of 1/16 in. to 1/4 in. (1.6mm to 6mm). In certain circumstances, twisted wire can be used to give the arc an oscillating movement. This helps fuse the toe of the weld to the base metal.[2]
[edit] Material applications
- Carbon steels (structural and vessel construction);
- Low alloy steels;
- Stainless steels;
- Nickel-based alloys;
- Surfacing applications (wearfacing, build-up, and corrosion resistant overlay of steels).
[edit] Advantages of SAW
- High deposition rates (over 100 lb/h (45 kg/h) have been reported);
- High operating factors in mechanized applications;
- Deep weld penetration;
- Sound welds are readily made (with good process design and control);
- High speed welding of thin sheet steels up to 5 m/min (16 ft/min) is possible;
- Minimal welding fume or arc light is emitted.
· Practically no edge preparation is necessary · The process is suitable for both indoor and outdoor works. · Distortion is much less. · Welds produced are sound, uniform, ductile, corrosion resistant and have good impact value. · Single pass welds can be made in thick plates with normal equipment. · The arc is always covered under a blanket of flux, thus there is no chance of spatter of weld.
[edit] Limitations of SAW
- Limited to ferrous (steel or stainless steels) and some nickel based alloys;
- Normally limited to the 1F, 1G, and 2F positions;
- Normally limited to long straight seams or rotated pipes or vessels;
- Requires relatively troublesome flux handling systems;
- Flux and slag residue can present a health & safety issue;
- Requires inter-pass and post weld slag removal.
[edit] Key SAW process variables
- Wire Feed Speed (main factor in welding current control);
- Arc Voltage;
- Travel Speed;
- Electrode Stick-Out (ESO) or Contact Tip to Work (CTTW);
- Polarity and Current Type (AC or DC).
[edit] Other factors
- Flux depth/width;
- Flux and electrode classification and type;
- Electrode wire diameter;
- Multiple electrode configurations.
[edit] References
- ^ Kalpakjian, Serope, and Steven Schmid. Manufacturing Engineering and Technology. '5th ed'. Upper Saddle river, NJ: Pearson Prentice Hall, 2006.
- ^ Jeffus, Larry. Welding: Principles and Applications. Florence, KY: Thomson Delmar Learning, 2002.
[edit] External Links
Submerged Arc Welding Pamphlet
[edit] Additional reading
American Welding Society, Welding Handbook, Vol 2 (9th ed.)
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