Tweco 250i Transmig Inverter - Manual (Page 63)

BASIC WELDING TRANSMIG 250I
Manual 0-5187 4-7 BASIC WELDING
4.03 Stick (MMAW) Basic Welding
Technique
Size of Electrode
The electrode size is determined by the thickness of met-
als 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 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.
Storage of Electrodes
Always store electrodes in a dry place and in their original
containers.
Electrode Polarity
Electrodes are generally connected to the ELECTRODE
HOLDER with the Electrode Holder connected positive
polarity. The WORK LEAD is connected negative polarity
and is connected to the work piece. If in doubt consult the
electrode data sheet or your nearest Accredited CIGWELD
Distributor.
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.
Hydrogen controlled Electrodes must be used for this
application. Use Ferrocraft 61 or 16TXP for normal
strength (500 MPa) steels, and Alloycraft range for
higher strength steels.
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. Suitable Electrode types
are Cobalarc Austex or Cobalarc Mangcraft.
C. Cast Iron
Most types of cast iron, except white iron, are weld-
able. 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. Suitable Electrode types
are Castcraft 55 or Castcraft 100.
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. Suitable Electrode types are Bronzecraft
AC-DC electrodes.
Arc Welding Practice
The techniques used for arc welding are almost identical
regardless of what types of metals are being joined. Natu-
rally enough, different types of electrodes would be used
for different metals as described in the preceding section.
Welding Position
The electrodes dealt with in this publication can be used
in most positions, i.e. they are suitable for welding in
flat, horizontal, vertical and overhead positions. Numer-
ous applications call for welds to be made in positions
intermediate between these. Some of the common types
of welds are shown in Figures 4-15 through 4-22.
Art # A-07687
Figure 4-11: Flat Position, Down Hand Butt Weld
Art # A-07688
Figure 4-12: Flat Position, Gravity Fillet Weld
Art # A-07689
Figure 4-13: Horizontal Position, Butt Weld