Tweco 300 DC Arcmaster - Manual (Page 47)

ARCMASTER 300 ACDC
February 22, 2006 8-1
SECTION 8:
BASIC ARC WELDING GUIDE
8.01 Electrode Polarity
Stick electrodes are generally connected to the ‘+’ terminal
and the work lead to the ‘-’ terminal but if in doubt consult
the electrode manufacturers literature.
8.02 Effects of Stick Welding Various
Materials
1. 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. 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.
2. 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.
3. 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.
4. 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.
5. Types of Electrodes: Arc Welding electrodes are
classified into a number of groups depending on their
applications. There are a great number of electrodes
used for specialized industrial purposes, which are
not of particular interest for everyday general work.
These include some low hydrogen types for high
tensile steel, cellulose types for welding large diameter
pipes, etc. The range of electrodes dealt with in this
publication will cover the vast majority of applications
likely to be encountered; are all easy to use and all will
work on even the most basic of welding machines.