Principles: WELDING PROCESS: Fusion welding Base metal is melted Filler metal may be added Heat is supplied by various means Oxyacetylene gas Electric Arc Plasma Arc Laser

Produce high-quality welds Used in electron beam welding WELDING PROCESS: Fusion welding Weld Metal Protection During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation Must protect weld puddle (arc pool) from the atmosphere Methods Weld Fluxes Inert Gases Vacuum Typical fluxes SiO2, TiO2, FeO, MgO, Al2O3 Produces a gaseous shield to prevent contamination Act as scavengers to reduce oxides Add alloying elements to the weld Influence shape of weld bead during solidification Vacuum Produce high-quality welds Used in electron beam welding Nuclear/special metal applications Zr, Hf, Ti Expensive and time-consuming Inert Gasses Argon, helium, nitrogen, and carbon dioxide Form a protective envelope around the weld area Used in MIG TIG Shield Metal Arc

Gas Welding (OFW) WELDING PROCESS: fusion welding Uses the heat of combustion of an oxygen /air and fuel gas (i.e. acetylene, hydrogen propane or butane) mixture is usually referred as ‘gas welding’. Fuel gas generally employed is acetylene because oxy-acetylene flame is the most versatile and hottest Other gases such as Hydrogen, Propane, Butane, Natural gas etc.

Oxy-Acetylene Welding (OAW) WELDING PROCESS: fusion welding Oxy-Acetylene Welding (OAW) FUEL: Acetylene (C2H2) COMBUSTION reactions take place in two stages: 1st stage: in a small white cone (3100 C) 2nd stage: in outer bluish flame (1200 - 2000 C) 1st stage: C2H2 + O2  2CO + H2 + 448kJ/kmol 2nd stage: 4CO + 2H2 + 3O2  4CO2 + 2H2 O + 812kJ/kmol

Oxy-Acetylene Welding (OAW) WELDING PROCESS: fusion welding Oxy-Acetylene Welding (OAW) FLAMES: Neutral Equal acetylene & oxygen (1:1) (low carbon steel, mild steels). Oxidizing Excess oxygen (1.5:1) (Brasses, Bronzes, copper) Reducing or Carburizing Excess acetylene (0.9:1) (Alloy steels and aluminium alloys) Carburising Neutral Oxidising

Oxy-Acetylene Welding (OAW) WELDING PROCESS: fusion welding Oxy-Acetylene Welding (OAW) Equipments: Cylinders Acetylene: Cannot be compressed directly as explodes at high pressures. Cylinders are packed with porous material which is filled with acetone. Cylinder colour coded maroon Oxygen: 13.8 – 18.2 Mpa, Cylinder is black.

Oxy-Acetylene Welding (OAW) WELDING PROCESS: fusion welding Oxy-Acetylene Welding (OAW) Equipments: Hose Pipes Reinforced rubber hoses. Acetylene hose has left hand thread couplings and colour coded red. Oxygen hose has right handed thread couplings and colour coded blue

Oxy-Acetylene Welding (OAW) WELDING PROCESS: fusion welding Oxy-Acetylene Welding (OAW) Equipments: Welding Torch: Oxygen and acetylene are delivered to the torch by separate hoses. Each gas is controlled by a valve on the torch. The two gases mix in the torch and after they are ignited burn at the nozzle.

Oxy-Acetylene Welding (OAW) WELDING PROCESS: fusion welding Oxy-Acetylene Welding (OAW) Techniques: Tip is so positioned that white cone is at a distance of 1.5 to 3 mm from plate Fore hand welding - Torch moves in the direction of tip - Tends to preheat the metal Back hand welding - Torch moves backwards - Outer flame towards already welded joint Welding Rod is held at a distance of 10mm from flame and 1.5 – 3 mm from the weld metal pool

Metal Inert Gas (MIG) / Gas Metal ARC Welding (GMAW) WELDING PROCESS: fusion welding Metal Inert Gas (MIG) / Gas Metal ARC Welding (GMAW) Uses a consumable electrode (filler wire made of the base metal) Inert gas is typically Argon

Tungsten Inert Gas (TIG) / Gas Tungusten Arc Welding (GTAW) WELDING PROCESS: fusion welding Tungsten Inert Gas (TIG) / Gas Tungusten Arc Welding (GTAW) Electrode acts as a cathode Non-consumable Electrode Filler metal can be added to the weld pool

Submerged Arc Welding (SAW) WELDING PROCESS: fusion welding Submerged Arc Welding (SAW) Arc forms between a continuously-fed bare wire electrode and the work-piece under blanket of granular flux Takes place in the flat position Ideal for heavy work-pieces Applications SAW welding is usually for Carbon-manganese steels, low alloy steels and stainless steels, bronze, nickel and other non-ferrous materials

Submerged Arc Welding (SAW) WELDING PROCESS: fusion welding Submerged Arc Welding (SAW)

Submerged Arc Welding (SAW) WELDING PROCESS: fusion welding Submerged Arc Welding (SAW) EQUIPMENTS: WIRE: SAW is normally operated with a single wire on either AC or DC supply. FLUX: It is granular fusible minerals supplied by means of flux feed tube Specially formulated to be compatible with a given electrode wire type React with the weld pool to produce slag which covers the weld metal Unused flux is recycled via a hopper.

Submerged Arc Welding (SAW) WELDING PROCESS: fusion welding Submerged Arc Welding (SAW) POINTS to REMEMBER: Flux to generate protective gases and slag Shielding gas is not required Slag layers can be easily removed after welding As the arc is completely covered by the flux layer, heat loss is extremely low and no visible arc light and no spatter Not possible to carry to any position other than down-hand position High welding speed (5m/min), and metal deposition rate (20kg/hr)can be obtained Able to weld plate of thickness 1mm – 75mm