Tweco ArcMaster 401MST - Manual (Page 57)

ARCMASTER 401MST POWER SOURCE
Manual 0-5287 4-1 BASIC WELDING GUIDE
SECTION 4:
BASIC WELDING GUIDE
4.01 Stick (SMAW) Basic Welding Technique
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.
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 Tweco 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.
Low Hydrogen Electrodes must be used for this application.
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.
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.