Fusion welding: other arc welding methods

Shielded metal arc welding

Shielded metal arc welding (SMAW) is an example of consumable (fusible) electrode type arc welding. It uses a metal rod (shielded metal arc welding rod) made of the same material as the base material as an electrode. The arc formed between the core wire of the electrode and base material is used as a heat source. The molten metal is covered by the gas and glasslike slag generated from the shield of the core wire. The process has the advantage of being less affected by wind or other disturbances on the worksite due to shielding by the gas and slag, and to the formation of a shielding tube at the tip of the welding rod.

SMAW has been used for a long time. Since the process is most often done manually, it is also called manual arc welding. The number of applications is decreasing due to the spread of automatic or semi-automatic MAG welding machines using carbon dioxide (CO2). SMAW, however, has been used in various applications due to its advantages of quick and easy welding both indoors and outdoors with relatively inexpensive equipment.

Shielded metal arc welding
  1. Weld metal
  2. Molten slag
  3. Shield
  4. Core wire
  5. Gas atmosphere
  6. Arc
  7. Weld pool

Plasma welding

Plasma welding is a method that strikes a plasma arc between the electrode and base material and uses it for welding. It is classified as a non-consumable electrode type and, as with TIG welding, it uses a tungsten rod for the electrode. The difference is that it uses a nozzle to cover the electrode and a plasma gas to prevent the arc from spreading.
The resulting high heat concentration enables high-speed welding with a narrow bead and less distortion. Due to its highly directional arc, plasma welding is suitable for fillet welds and can eliminate spatter. Its low electrode consumption allows high-quality welding for a long time. Although the welding machines are expensive compared to TIG welding machines, the running costs are low. This is one of the best methods for automatic welding.

The pilot gas (inert gas) passes through the torch and is ionized by the pilot arc heat (plasma conversion). The ionized pilot gas forms a plasma jet, spouts from the nozzle hole and acts as the conductor for the arc current. This narrows down the arc to give it high energy density and spout from the insert tip hole. The spread of the arc is limited to about one-fourth that of TIG welding, resulting in an arc with higher current density.

Plasma welding

Electrogas arc welding (EGW)

Electrogas arc welding (EGW) is a consumable-electrode-type welding method developed to enable vertical position welding of thick plates at high efficiency through stable penetration.

The shielding gas used for EGW is mostly CO2, but argon gas or gas mixes of argon and CO2, oxygen or helium are used as well. For the welding wire, flux-cored wires that form slag to create a nice bead are mostly used, but solid wires are also used in some cases.
The welding power supply is a DC constant-voltage characteristic power supply or DC constant-current (drooping) characteristic power supply.

The process encloses the weld pool with the end of the base material, a copper shoe and a fire-resistant backing and performs upward vertical position welding while preventing the dripping of molten metal. This allows the welding of a thick plate in one pass (one operation).
The advantages are a fast deposition rate through the use of a large current, high efficiency, and a relatively large margin for the groove accuracy because of small angular distortion.
EGW is used for welding vertical butt joints of products, such as ship's shell plates, bridges, storage tanks, and pressure vessels.

Electrogas arc welding (EGW)
  1. Preceding wire
    (solid wire)
  2. CO2
  3. Arc
  4. Weld pool
  5. Succeeding wire
    (flux-cored wire)
  6. Constant-voltage characteristic power supply for arc ignition
  7. Constant-current characteristic power supply for conduction

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