Tweco 170 HF Weldskill - Manual (Page 27)

WELDSKILL 170 HF INVERTER
4-5 April 23, 2008
4.07 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 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.
4.08 Storage of Electrodes
Always store electrodes in a dry place and in their
original containers.
4.09 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 your nearest Accredited CIGWELD Distributor.
4.10 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
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. 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.
4.11 Arc Welding Practice
The techniques used for arc welding are almost
identical regardless of what types of metals are being
joined. Naturally enough, different types of electrodes
would be used for different metals as described in
the preceding section.