Tweco 300 ACDC Arcmaster - Manual (Page 44)

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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
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.
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.
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.
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.
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.