Shielding Gases & Flux

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Shielding gas and fluxes used for arc welding ppt
  IONIZATION POTENTIAL   ã Ionization: is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or ions. ã Ionization potential: is the energy required to remove electrons from gaseous atoms or ions.  Shielding gases for welding:  Protects the molten metal or arc area from the atmosphere.  It also influences the metal transfer mode and deposited weld characteristics. Shielding efficiency- depends on design of nozzle, gas flow rate, side winds, purity of shielding gas etc. Shielding gases Active (O 2,  Co 2 , H 2  etc) Inert (Ar, He, Ne, Kr etc) Used with GTAW and for welding non-ferrous metals with GMAW  Properties of shielding gas: 1.Ionization potential (IP): Ionization potential ∞  1 - Argon has low IP and helps to initiate and maintain the arc in a stable operating mode. - Helium has high IP 2.Thermal conductivity: - Pure Ar has low thermal conductivity. Hence weld fusion area has wider top and a narrow ‘finger’  at the root. - Helium has higher thermal conductivity. Therefore results in broader, hotter arc. Molecular weight of shielding gas  Argon Carbon Dioxide   Heium Hydrogen   Nitrogen   oxygen   Chemical symbol Ar Co 2 He H 2 N 2 O 2 Atomic Number 18 6 2 1 7 8 Molecular weight 39.95 44.01 4.00 2.016 28.01 32.00 Specific Gravity, Air = 1 1.38 1.53 0.1368 0.0695 0.967 1.105 Density(lb/cu ft) at 0 C, 1 atmosphere 0.1114 0.1235 0.0111 0.0056 0.0782 0.0892 Ionization Potential(ev) 15.7 14.4 24.5 13.5 14.5 13.2 Thermal Conductivity (10 -3 ×Btu/hr-ft-F)9.69 (32 F) 8.62 (32 F) 85.78 (32 F) 97.22 (32 F) 13.93 (32 F) 14.05 (32 F) Cubic ft/lb 9.67 8.73 96.71 192 13.8 12.08
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