What is submerged arc welding used for

A blanket of powdered flux surrounds and covers the arc and, when molten, provides electrical conduction between the metal to be joined and the electrode. It also generates a protective gas shield and a slag, all of which protects the weld zone. As can be seen from Figure 1, the arc is "submerged" beneath a blanket of flux and is, therefore, not usually visible during the welding operation itself.

These facts make the process advantageous from a health and safety viewpoint as there is no arc to promote "arc eye" and very little fume.

There are two welding consumables involved in the process, the electrode and the flux. The electrode can be a solid wire, a cored wire, or a strip. The flux, made from a variety of minerals and compounds, can be rather complex and can be produced in a number of forms. The general arrangement of the power source and controls, wire feed and flux dispensing are shown in Figure 2. The submerged arc welding process is shown by figure It utilizes the heat of an arc between a continuously fed electrode and the work.

The heat of the arc melts the surface of the base metal and the end of the electrode. The metal melted off the electrode is transferred through the arc to the workpiece, where it becomes the deposited weld metal. Shielding is obtained from a blanket of granular flux, which is laid directly over the weld area. The flux close to the arc melts and intermixes with the molten weld metal, helping to purify and fortify it. The flux forms a glass-like slag that is lighter in weight than the deposited weld metal and floats on the surface as a protective cover.

The weld is submerged under this layer of flux and slag, hence the name submerged arc welding. The flux and slag normally cover the arc so that it is not visible. The unmelted portion of the flux can be reused. The electrode is fed into the arc automatically from a coil. The arc is maintained automatically.

Travel can be manual or by machine. The arc is initiated by a fuse type start or by a reversing or retrack system. The most popular method of SAW application is the machine method, where the operator monitors the welding operation. Second in popularity is the automatic method, where welding is a pushbutton operation. The process can be applied semiautomatically; however, this method of application is not too popular.

The process cannot be applied manually because it is impossible for a welder to control an arc that is not visible. The submerged arc welding process is a limited-position welding process. The welding positions are limited because the large pool of molten metal and the slag are very fluid and will tend to run out of the joint. Welding can be done in the flat position and in the horizontal fillet position with ease. This requires special devices to hold the flux up so that the molten slag and weld metal cannot run away.

The process cannot be used in the vertical or overhead position. Submerged arc welding is used to weld low- and medium-carbon steels, low-alloy high-strength steels, quenched and tempered steels, and many stainless steels. When the multipass technique is used, the maximum thickness is practically unlimited. This information is summarized in table Although the submerged arc welding process can utilize the same joint design details as the shielded metal arc welding process, different joint details are suggested for maximum utilization and efficiency of submerged arc welding.

Beyond this thickness, bevels are required. Open roots are used but backing bars are necessary since the molten metal will run through the joint. When welding thicker metal, if a sufficiently large root face is used, the backing bar may be eliminated. However, to assure full penetration when welding from one side, backing bars are recommended.

Where both sides are accessible, a backing weld can be made which will fuse into the original weld to provide full penetration. The SAW or submerged arc welding process uses either direct or alternating current for welding power. Direct current is used for most applications that use a single arc.

The control circuit for CC power is more complex since it attempts to duplicate the actions of the welder to retain a specific arc length. The wire feed system must sense the voltage across the arc and feed the electrode wire into the arc to maintain this voltage.

As conditions change, the wire feed must slow down or speed up to maintain the prefixed voltage across the arc. This adds complexity to the control system. The system cannot react instantaneously. Arc starting is more complicated with the constant current system since it requires the use of a reversing system to strike the arc, retract, and then maintain the preset arc voltage.

For SAW ac welding, the constant current power is always used. When multiple electrode wire systems are used with both ac and dc arcs, the constant current power system is utilized. The constant voltage system, however, can be applied when two wires are fed into the arc supplied by a single power source. Welding current for submerged arc welding can vary from as low as 50 amperes to as high as amperes.

Most submerged arc welding is done in the range of to amperes. The deposition rates of the submerged arc welding process are higher than any other arc welding process. Deposition rates for single electrodes are shown by figure There are at least four related factors that control the deposition rate of submerged arc welding: polarity, long stickout, additives in the flux, and additional electrodes.

The deposition rate is the highest for direct current electrode negative DCEN. The polarity of maximum heat is the negative pole. The deposition rates can be increased by metal additives in the submerged arc flux. Additional electrodes can be used to increase the overall deposition rate.

The quality of the weld metal deposited by the submerged arc welding process is high. The weld metal strength and ductility exceeds that of the mild steel or low-alloy base material when the correct combination of electrode wire and submerged arc flux is used. When submerged arc welds are made by machine or automatically, the human factor inherent to the manual welding processes is eliminated.

The weld will be more uniform and free from inconsistencies. In general, the weld bead size per pass is much greater with submerged arc welding than with any of the other arc welding processes. The heat input is higher and cooling rates are slower.

For this reason, gases are allowed more time to escape. Additionally, since the submerged arc slag is lower in density than the weld metal, it will float out to the top of the weld.

Uniformity and consistency are advantages of this process when applied automatically. Several problems may occur when using the semiautomatic application method. The electrode wire may be curved when it leaves the nozzle of the welding gun. This curvature can cause the arc to be struck in a location not expected by the welder. When welding in fairly deep grooves, the curvature may cause the arc to be against one side of the weld joint rather than at the root.

This will cause incomplete root fusion. Flux will be trapped at the root of the weld. Another problem with semiautomatic welding is that of completely filling the weld groove or maintaining exact size, since the weld is hidden and cannot be observed while it is being made.

This requires making an extra pass. In some cases, too much weld is deposited. Variations in root opening affect the travel speed. If travel speed is uniform, the weld may be under- or overfilled in different areas. High operator skill will overcome this problem. Some of the flux at the top can be reused. Why is the flux used? It is used to protect the weld during the molten state. SAW flux also aids in helping arc stability, which is necessary for producing consistent welds.

It also protects the integrity of the base material surrounding the weld area. Since the flux is on top of the weld, the spatter will not escape the weld zone. This leaves you with cleaner looking, more consistent welds. SAW typically uses the same equipment in all its applications. However, added equipment or different fluxes can be used. There are fused, bonded, agglomerated, and mechanically mixed fluxes. These are all granular fluxes that are dispensed in the same way.

That is, either through a hopper or laid out ahead of time. Fused fluxes begin with raw materials being melted down that are then crushed to the desired granule size. Bonded and agglomerated fluxes are dry materials that are mixed with a binder sodium for bonded and ceramic for agglomerated. After they have been bonded, the mixed material will be put through a sieve to achieve the desired granule size.

Lastly, mechanical mixes may be a mixture of fused, bonded, or agglomerated fluxes. There are a variety of SAW welding guns. A lot of the differences are in how the flux is deposited. But some welding guns have a couple of different welding heads. Whenever the flux is cold, then it acts as an insulator. The arc can be started by moving the tool by the work portion.

The arc struck will constantly remain below a wide coating of flux, and the generated heat by the arc softens the granular flux. Once the flux is melted by the heat of the arc, then it will become highly conductive. The flow of current begins to flow the electrode through the melted flux that can be in contact by the atmosphere.

At a fixed speed, the electrode from the roll is constantly fed toward the joint to be linked. If linking is partially automatic, then the top of the welding can be moved physically along with the connection. In an automatic submerged arc welding, a separate drive can be used to move the welding top above the stationary job otherwise job moves beneath the head of the stationary welding.

With the help of the self-adjusting arc principle, the length of the arc is kept stable.