Tweco FP-235DC - Manual (Page 21)

The intense heat produced at the arc
sets up strains in the metal joined by
welding. Peening the weld (striking the
weld with a welding hammer) not only
removes the scale left behind in the
welding but relieves the internal strains
developed by the heating and cooling
process.
A complete weld may require more
metal than can be deposited in a single
pass by either the stringer or weave
method. Very heavy beads can be built
up by making several passes along the
weld seam (see Figure 10 and Figure
11).When welds are to be laid one on
top of another, slag left from the previ-
ous pass must be thoroughly cleaned
away before the second pass is laid.
SPECIAL APPLICATIONS
In cutting or burning, the heat of the arc is used to melt or burn away the base metal. No attempt is made to
add metal from the melting electrode.
Special Cutting electrodes are available. If a general purpose rod is used for cutting, less of the electrode will
be consumed if it is soaked in water for a few minutes prior to use.
BURNING HOLES
Hot metal dripping from above can cause serious burns or start fires.
ALWAYS protect head, hands, feet and body when cutting or burning holes. DO
NOT cut or weld where hot metal can fall onto or into flammable materials.
When burning holes, the electrode is held perpendicular to the base metal and the arc is rotated in a small cir-
cle until the base metal becomes soft. Pushing or jabbing the electrode firmly through the base metal starts the
actual hole. Its size and shape are determined by directing the arc in larger circles. Holes in heavier metal may
be burned from the bottom, permitting the base metal to drop away from the hole.
CUTTING
The procedure used in cutting is very simple. The heat of the arc is used to melt away the base metal along the
cut line. Start the cut at the edge of the workpiece. Strike the arc and work it along the cut line. If the metal is
fairly thick, work the electrode up and down from the top to the bottom of the cut.
RECOGNIZING METALS
Because of the effect on the properties of steel from carbon content, temperature and time, the person welding
must be able to determine accurately the nature of the steel that is being worked.
The manufacturer’s specifications of the particular steel are most desirable. When specifications are not avail-
able, other methods may be used to determine the nature of the metal. The most common tests are:
MAGNETIC TEST
The magnetic test is a basic test used to identify ferrous (iron and steel) metals from nonferrous metals.
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Figure 10: Triple Pass Cutaway Figure 11: Triple Pass Welds