ARC WELDING• Metal pieces are joined melting their

edges by an electric arc.• Electric Arc produced between Two

Conductors• Elctrode is one conductor and Workpiece

is another conductor.• Small Air-gap 3mm.

ARC WELDING EQUIPMENTS

Arc Welding Equipments

Arc welding electrodes• Non-consumable electrodes

– Made of Carbon, Graphite, Tungsten

– Carbon and Graphite – D.C Welding

– Tungsten – Both

– Filler material added separately.

• Consumable electrodes• Bare Electrodes

• Flux or lightly coated electrodes

• Coated or extruded electrodes

• Bare Electrodes

– Used to weld wrought iron and mild steel.

– Hand arc welding – Sticks or rods

– Automatic welding – Coil

• Flux or lightly coated electrodes

• 1-5% of electrode weight

• Light coating is given to increase stability and ionizing

coatings.

• Chalk 80-85 parts and Water glass 15-20 parts

• Used to weld non critical structures.

• Coated electrodes

– 1-2 mm layer

– 15-30% of the weight of the electrode rod.

• Electrode size

– 3.2, 4, 5, 6, 8, 9, 12 mm diameter and length

350 or 450 mm.

FUNCTIONS OF COATINGS

• Improves arc stability.

• Provides gaseous atmosphere to prevent Oxygen,

Hydrogen and Nitrogen.

• Provides a protective slag over hot metal.

• Provides flux to remove oxides and other impurities.

• Reduces spatter of weld metal.

• Slows down the cooling rate of weld.

ELECTRODE COATINGS

• Slag formation ingredients: Asbestos, Mica, Silica,

Titanium oxide, iron oxide, calcium carbonate and

aluminium oxide.

• Arc stabilizing ingredients: Potassium silicate, Mica,

Calcium oxide, Sodium oxide, magnesium oxide.

• Deoxidizing ingredients: Cellulose, Dolomite, Starch,

Dextrin, Wood flour, graphite

• Binding Materials: Sodium silicate, Potassium silicate,

asbestos.

• Alloying constituents to increase the strength of the weld.