Basic Welding: Submerged Arc Welding

Submerged-arc Welding

Overview: SAW involves formation of an arc between a continuously-fed bare wire electrode and the work piece. The process uses a flux to generate protective gases and slag, and to add alloying elements to the weld pool. A shielding gas is not required. Prior to welding, a thin layer of flux powder is placed on the work piece surface. The arc moves along the joint line and as it does so, excess flux is recycled via a hopper. Remaining fused slag layers can be easily removed after welding. There is no visible arc light, welding is spatter-free and there is no need for fume extraction.

SAW is usually operated as a fully-mechanised or automatic process, but it can be semi-automatic. Welding parameters: current, arc voltage and travel speed all affect bead shape, depth of penetration and chemical composition of the deposited weld metal. Because the operator cannot see the weld pool, greater reliance must be placed on parameter settings.

Applications of SAW process: SAW is used for longitudinal and circumferential butt and fillet welds, in flat position. For circumferential joints, the workpiece is rotated under a fixed welding head with welding taking place in the flat position. Depending on material thickness, either single-pass, two-pass or multipass weld procedures can be carried out. There is virtually no restriction on the material thickness, provided a suitable joint preparation is adopted. Most commonly welded materials are carbon-manganese steels, low alloy steels and stainless steels, although the process is capable of welding some non-ferrous materials with judicious choice of electrode filler wire and flux combinations.

Hazards in SAW: This process has all the hazards of MMA, except for Welders’ eye, since the molten weld pool is always covered under flux.

Basic Welding, Metal Inert Gas Welding

Solid wire MIG Welding

Overview: MIG is similar to MMA in that heat for welding is produced by forming an arc between a metal electrode and the workpiece; the electrode melts to form the weld bead. The main difference is that the metal electrode is a small diameter wire fed from a spool. As the wire is continuously fed, the process is often referred to as semi-automatic welding.

Applications: MIG is widely used in most industry sectors and accounts for almost 50% of all weld metal deposited. Compared to MMA, MIG has the advantage in terms of flexibility, deposition rates and suitability for mechanisation. However, it should be noted that while MIG is ideal for 'squirting' metal, a high degree of manipulative skill is demanded of the welder.

Hazards in MIG Welding: This process has similar hazards that of MMA Welding. You could read the same here.

Basic Welding: Gas Tungsten Arc Welding

Tungsten Inert Gas (TIG) Welding




Overview: In the TIG process the arc is formed between a pointed tungsten electrode and the workpiece in an inert atmosphere of argon or helium. The small intense arc provided by the pointed electrode is ideal for high quality and precision welding. Because the electrode is not consumed during welding, the welder does not have to balance the heat input from the arc as the metal is deposited from the melting electrode. When filler metal is required, it must be added separately to the weldpool.
Applications of TIG welding : TIG is applied in all industrial sectors but is especially suitable for high quality welding. In manual welding, the relatively small arc is ideal for thin sheet material or controlled penetration (in the root run of pipe welds). Because deposition rate can be quite low (using a separate filler rod) MMA or MIG may be preferable for thicker material and for fill passes in thick-wall pipe welds.
Hazards in GTAW welding: All hazards related to MMA welding are always applicable to TIG welding also. In addition the following hazards are present in TIG welding:
a) Asphyxia: TIG welding involves use of inert gases to protect weld pool form atmosphere. When this process is used in confined spaces, it may lead to asphyxiation. Welders have to be cautious about ventilation available to them.
b) Leakage of water, short circuit, hot water bath: This process uses water to cool the tungsten electrodes. This water is circulated by a pump & is recycled through a tank. For some reasons if the water circuit is jammed or level of water in the tank is insufficient, the PVC pipes carrying water may burst, giving the welder a hot water bath. Also leaks through pump & tank may interfere with the electric circuits causing short circuits.