Welding Rods

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Welding Electrodes
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How Is a Welding Arc Established?

• A sequence of events takes place between the
  electrode and the piece being welded. To strike
  the welding arc, a high frequency generator is
  used to provide a high voltage, low current
  superimposed on the welding current. The effect
  is a spark which creates a conductive path
  through the shielding gas.

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Welding Electrodes

• The electrode used in GTAW is made of tungsten or
  a tungsten alloy, because tungsten has the
  highest melting temperature among pure metals, at
  3,422 C (6,192 F). As a result, the electrode
  is not consumed during welding, though some
  erosion (called burn-off) can occur. Electrodes
  can have either a clean finish or a ground
  finishclean finish electrodes have been
  chemically cleaned, while ground finish
  electrodes have been ground to a uniform size and
  have a polished surface, making them optimal for
  heat conduction.

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• The diameter of the electrode can vary between
  0.5 and 6.4 millimetres (0.02 and 0.25 in), and
  their length can range from 75 to 610 millimetres
  (3.0 to 24 in).

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• Pure tungsten electrodes (classified as WP or
  EWP) are general purpose and low cost electrodes.
  They have poor heat resistance and electron
  emission. They find limited use in AC welding of
  e.g. magnesium and aluminum.
• Cerium oxide (or ceria) as an alloying element
  improves arc stability and ease of starting while
  decreasing burn-off. Cerium addition is not
• Using an alloy of lanthanum oxide (or lanthana)
  has a similar effect. Addition of 1 lanthanum
  has the same effect as 2 of cerium.

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• Thorium oxide (or thoria) alloy electrodes were
  designed for DC applications and can withstand
  somewhat higher temperatures while providing many
  of the benefits of other alloys. However, it is
  slightly radioactive. Inhalation of the thorium
  grinding dust during preparation of the electrode
  is hazardous to ones health. Some electrode
  grinders have vacuum systems to prevent
  inhalation during grinding. As a replacement to
  thoriated electrodes, electrodes with larger
  concentrations of lanthanum oxide can be used.
  Larger additions than 0.6 do not have additional
  improving effect on arc starting, but they help
  with electron emission.

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• Higher percentage of thorium also makes tungsten
  more resistant to contamination.
• Welding Electrodes containing zirconium oxide (or
  zirconia) increase the current capacity while
  improving arc stability and starting and
  increasing electrode life. Zirconium-tungsten
  electrodes melt easier.

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• Ionized. A plasma exist during any arc
  occurrence. The energy level may vary enormously
  due to the ionization grade of the gas mixture.
  Essentially this spark allows the arc to be
  initiated.
• Ref processwelding.com/blog/

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