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Submerged arc welding. The welding head moves from right to left. The flux powder is supplied by the hopper on the left hand side, then follow three filler wire guns and finally a vacuum cleaner. A submerged arc welder used for training Close-up view of the control panel A schematic of submerged arc welding Pieces of slag from submerged arc welding exhibiting glassy surface due to silica (SiO2).Submerged arc welding (SAW) is a common arc welding process. The first SAW patent was taken out in . The process requires a continuously fed consumable solid or tubular (metal cored) electrode.[1] 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 shielded metal arc welding (SMAW) process.[2]
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[2] (although horizontal groove position welds have been done with a special arrangement to support the flux). Deposition rates approaching 45 kg/h (100 lb/h) have been reported &#; this compares to ~5 kg/h (10 lb/h) (max) for shielded metal arc welding. Although currents ranging from 300 to A are commonly utilized,[3] currents of up to A have also 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 used, 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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It feeds flux and filler metal to the welding joint. The electrode (filler metal) gets energized here.
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It stores the flux and controls the rate of flux deposition on the welding joint.
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The granulated flux shields and thus protects molten weld from atmospheric contamination.[2] The flux cleans weld metal and can also modify its chemical composition. The flux is granulated to a definite size. It may be of fused, bonded or mechanically mixed type. The flux may consist of fluorides of calcium and oxides of calcium, magnesium, silicon, aluminium and manganese compounds.[citation needed] Alloying elements may be added as per requirements. Substances involving large amounts of gas during welding are never mixed with the flux. Flux with fine and coarse particle sizes are recommended for welding heavier and smaller thickness respectively.
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SAW filler material usually is a standard wire as well as other special forms. This wire normally has a thickness of 1.6 mm to 6 mm (1/16 in. to 1/4 in.). 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.[4] The electrode composition depends upon the material being welded. Alloying elements may be added in the electrodes. Electrodes are available to weld mild steels, high carbon steels, low and special alloy steels, stainless steel and some of the nonferrous of copper and nickel. Electrodes are generally copper coated to prevent rusting and to increase their electrical conductivity. Electrodes are available in straight lengths and coils. Their diameters may be 1.6, 2.0, 2.4, 3, 4.0, 4.8, and 6.4 mm. The approximate value of currents to weld with 1.6, 3.2 and 6.4 mm diameter electrodes are 150&#;350, 250&#;800 and 650&#; amps respectively.
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The flux starts depositing on the joint to be welded. Since the flux is not electrically conductive when cold, the arc may be struck either by touching the electrode with the work piece or by placing steel wool between electrode and job before switching on the welding current or by using a high frequency unit. In all cases the arc is struck under a cover of flux. Flux otherwise is an insulator but once it melts due to heat of the arc, it becomes highly conductive and hence the current flow is maintained between the electrode and the workpiece through the molten flux. The upper portion of the flux, in contact with atmosphere, which is visible remains granular (unchanged) and can be reused. The lower, melted flux becomes slag, which is waste material and must be removed after welding.
The electrode is continuously fed to the joint to be welded at a predetermined speed. In semi-automatic welding sets the welding head is moved manually along the joint. In automatic welding a separate drive moves either the welding head over the stationary job or the job moves/rotates under the stationary welding head.
The arc length is kept constant by using the principle of a self-adjusting arc. If the arc length decreases, arc voltage will increase, arc current and therefore burn-off rate will increase thereby causing the arc to lengthen. The reverse occurs if the arc length increases more than the normal.[5]
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A backing plate of steel or copper may be used to control penetration and to support large amounts of molten metal associated with the process.
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Submerged arc welding or SAW is a commonly used welding process for thick steel sheets or long welds. There are four components to this process. The welding head is used to feed flux and filler metal to the area that is being worked on. With the help of the electrode, the filler metal gets energized too. The flux hopper stores and controls the flux.
The granulated flux is an extremely important part. It allows the metal to be cleaned and shields molten atmospheric contamination. The granulated flux can be fused, mixed or bonded materials. It is also mixed with different materials depending on what the project is. The electrode or filler metal is usually in the form of a wire. There are special forms as well. If a wire of filler metal is twisted it will give the arc an oscillating movement. The types of material that can be added with the electrode is used for are nickel-based alloys, low alloy steel, carbon steel, and stainless steel. Other options that can change jobs up are the wire feed speed, travel speed, arc voltage, current type, electrode stick-out, and contact tip.
This type of arc welding starts with the flux feeding the filler metal onto the joint. Placing steel wool between the electrode and joint before starting, works just as well as lighting the electrode with a torch to start. Once molten, the flux goes from being an insulator to a conductor. The wasted flux material or slag is removed after the weld. The electrode has several speeds. Predetermined speed is a continuous feeder. Semi-automatic speed allows manual movement of the head. Automatic speed is good for stationary jobs. The arc can be shortened and lengthened manually.
There are some pros and cons to all types of welding. The submerged arc welding process is a specific type of weld. To start, the job will have higher deposition and high operating factors with mechanized jobs. Sound and deep penetration welds are made possible with easy control. Thicker sheets of metal are typically used for these welds, but thin sheets can be done. Another pro is the lack of edge preparation needed and little fumes created. The work can be done outside or inside and the welds are uniform and corrosion-resistant. Even with a thick sheet, a single pass is possible. Finally, the arc is always covered to allow no chance of splatter. One great thing is that more than half of the flux can be reused.
When it comes to arc welding, there are a few specific cons. This is due to the fact that it is a very specific weld type. The first obvious con is that the only materials to work on are some types of steel and some nickel-based alloys. The equipment can only be in the position of 1F, 1G, and 2F. It is also limited to rotating pipes, vessels or straight seams for welds. The flux can be a bit troublesome to set up and can cause health concerns. A huge con is a fact that only thick welds are workable. There are also requirements for slag removal before you start and backing strips for root penetration.
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