Page 193 - CITS - Welder - Trade Theory

WELDER - CITS

Percentage Of Alloying Electrode
Aws Classification Colour Code
Element Diameter
EWP 0% (Pure Tungsten) Green 0.25mm,

EW Th-1 08-12% (Thoriated) Yellow 0.50mm,
EW Th-2 1.7 2.2% (Thoriated) Red 1.01mm,
EW ZR-1 0.15-0.40 (Zircoriated) Brown 1.52mm,
EW Ce-2 1.8-2.2 (Ceriated) Orange
2.36mm,
EW La-2 09-1.2 (Lanthanated) Black 3.17mm,

3.96mm,

EWG Not specified Gray 4.74mm,
6.35mm,

In the AWS classification system. E stands for an electrode which is used as one terminal of the arc welding circuit.
The W stands for the chemical symbol for tungsten (also called Woll- fram) .The final letters indicate the alloying
element or oxide additions. P designator a pure tungsten electrode without internal alloying element, while all
other designations are for certain oxide additions. The is for thoriated, Zr is for Zirconiated, La is Lanthanated and
G stands for unspecified oxide additions. Finally the numbers specify the nominal alloying composition (in weight
percent). For instance EWTh-1 is a thoriated tungsten electrode that contains nominally 1 Wt% thorium. Individual
electrodes are marked usually with a band (or dot) of the appropriate colour, on one end of the electrode.
The addition of alloying element lower the voltage necessary to stick the arc because they gives of electron. The
current carrying capacity of an electrode is increased depending on the percentage of alloying element, and the
alloying elements help to stabilize the arc and increases the Ife of the electrode.
1 Pure Tungsten Electrode(EWP)

Pure Tungsten Electrode (EWP) contain a minimum of 99.5 wt% tungsten, with no intentional alloying elements.
These electrodes are identified with a green colour code. The current carrying capacity of pure tungsten
electrodes is lower than that of the alloyed tungsten electrodes. Pure tungsten electrodes are used mainly
with alternating current (AC) for welding of aluminium and magnesium alloys. With this type of current, the
tip of the EWP electrode forms a clean balled end, it provides good arc stability. The pure tungsten electrode
also may be used with direct current, but they do not provide the arc initiation and arc stability characteristics
of thoriated, ceriated, or lanthanated electrodes. Direct current electrode positive (DCEP) or reverse polarity
welding also causes splitting and melting of pure tungsten electrodes.

The pure tungsten electrodes are the least expensive, but are more prove to contamination of the weld than
the other types of tungsten electrodes. THEY ARE GENERALLY ONLY USED AC WELDING, because DC
welding with pure tungsten electrodes typically produces small amounts of tungsten inclusions (discontinuities)
in the weld.
2 Zirconiated Tungsten Electrodes (Ewzr-1)

Zirconiated tungsten electrodes (EWZr-1) contain a small amount (0.15 to 0.40 Wt-%) of Zirconium Oxide
(ZrO2), as listed in Table. These electrodes are identified by a brown colour code. Zirconiated tungsten
electrodes have welding characteristics that generally fall between those of pure tungsten and thoriated tungsten
electrodes. THEY ARE NORMALLY THE ELECTRODE OF CHOICE FOR AC WELDING OF ALUMINIUM
AND MAGNESIUM ALLOYS because they combine the desirable arc stability characteristics and balled end
typical of pure tungsten along with the higher current carrying capacity and better arc starting characteristics
of thoriated tungsten electrodes. They are more resistant to tungsten contamination of the weld pool then pure
tungsten and are preferred for radiographic-quality welding applications as tungsten contamination of the weld
must be minimized

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CITS : C G & M - Welder - Lesson 61-76 CITS : C G & M - Welder - Lesson 61-76