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 parts and Water glass 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.