Tweco 100 Weldskill - Manual (Page 25)

weldskill 100 iNVeRTeR
4-3 March 3, 2008
4.05 Size of Electrode
The electrode size is determined by the thickness
of metals being joined and can also be governed
by the type of welding machine available. Small
welding machines will only provide sufficient current
(amperage) to run the smaller size electrodes.
For most work, a 2.5mm electrode will be quite
sufficient. A 2.5mm electrode will give just as strong
a joint but may require a few more weld runs to be
put down to fill the joint.
For thin sections, it is necessary to use smaller
electrodes otherwise the arc may burn holes through
the job. A little practice will soon establish the most
suitable electrode for a given application.
4.06 Storage of Electrodes
Always store electrodes in a dry place and in their
original containers.
4.07 Electrode Polarity
Electrodes are generally connected to the ELECTRODE
HOLDER and the WORK LEAD to the work piece but
if in doubt consult your nearest accredited CIGWELD
Distributor.
4.08 Effects of Arc Welding Various
Materials
A. High tensile and alloy steels
The two most prominent effects of welding these
steels are the formation of a hardened zone in the
weld area, and, if suitable precautions are not taken,
the occurrence in this zone of under-bead cracks
may result. Hardened zone and under-bead cracks in
the weld area may be reduced by using the correct
electrodes, preheating, using higher current settings,
using larger electrodes sizes, short runs for larger
electrode deposits or tempering in a furnace.
B. Austenitic manganese steels
The effect on manganese steel of slow cooling from
high temperatures is to embrittle it. For this reason it
is absolutely essential to keep manganese steel cool
during welding by quenching after each weld or skip
welding to distribute the heat.
C. Cast Iron
Most types of cast iron, except white iron, are
weldable. White iron, because of its extreme
brittleness, generally cracks when attempts are made
to weld it. Trouble may also be experienced when
welding white-heart malleable, due to the porosity
caused by gas held in this type of iron.
D. Copper and alloys
The most important factor is the high rate of heat
conductivity of copper, making preheating of heavy
sections necessary to give proper fusion of weld and
base metal.