1. 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.

2. ARC WELDING EQUIPMENTS

6. Arc Welding Equipments

7. 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

8. 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.

9. 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.

10. 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.

11. 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.