ESAB Fabricator 252i Operating Manual page 49

Striking the Arc
Practice this on a piece of scrap plate before going on to more
exacting work. You may at first experience difficulty due to the tip
of the electrode "sticking" to the work piece. This is caused by
making too heavy a contact with the work and failing to withdraw
the electrode quickly enough. A low amperage will accentuate it.
This freezing-on of the tip may be overcome by scratching the
electrode along the plate surface in the same way as a match is
struck. As soon as the arc is established, maintain a 1/16" -1/8"
(1.6 mm - 3.2 mm) gap between the burning electrode end and
the parent metal. Draw the electrode slowly along as it melts
down.
Another difficulty you may meet is the tendency, after the arc is
struck, to withdraw the electrode so far that the arc is broken
again. A little practice will soon remedy both of these faults.
20°
Figure 4-21: Striking an Arc
Arc Length
The securing of an arc length necessary to produce a neat weld
soon becomes almost automatic. You will find that a long arc pro-
duces more heat. A very long arc produces a crackling or splut-
tering noise and the weld metal comes across in large, irregular
blobs. The weld bead is flattened and spatter increases. A short
arc is essential if a high quality weld is to be obtained although
if it is too short there is the danger of it being blanketed by slag
and the electrode tip being solidified in. If this should happen,
give the electrode a quick twist back over the weld to detach it.
Contact or "touch-weld" electrodes such as E7014 do not stick
in this way, and make welding much easier.
Rate of Travel
After the arc is struck, your next concern is to maintain it, and
this requires moving the electrode tip towards the molten pool at
the same rate as it is melting away. At the same time, the elec-
trode has to move along the plate to form a bead. The electrode
is directed at the weld pool at about 20º from the vertical. The
rate of travel has to be adjusted so that a well-formed bead is
produced.
If the travel is too fast, the bead will be narrow and strung out
and may even be broken up into individual globules. If the travel
is too slow, the weld metal piles up and the bead will be too
large.
Making Welded Joints
Having attained some skill in the handling of an electrode, you
will be ready to go on to make up welded joints.
Manual 0-5423
Art # A-10673
1/16" (1.6 mm)
A. Butt Welds
Set up two plates with their edges parallel, as shown in Figure
4-22, allowing 1/16" - 3/32" (1.6 mm - 2.4 mm) gap between
them and tack weld at both ends. This is to prevent contraction
stresses from the cooling weld metal pulling the plates out of
alignment. Plates thicker than 1/4" (6.4 mm) should have their
mating edges beveled to form a 70º to 90º included angle. This
allows full penetration of the weld metal to the root. Using a
1/8" (3.2 mm) E7014 electrode at 100 amps, deposit a run of
weld metal on the bottom of the joint.
Do not weave the electrode, but maintain a steady rate of
travel along the joint sufficient to produce a well-formed
bead. At first you may notice a tendency for undercut to form,
but keeping the arc length short, the angle of the electrode at
about 20º from vertical, and the rate of travel not too fast, will
help eliminate this. The electrode needs to be moved along
fast enough to prevent the slag pool from getting ahead of the
arc. To complete the joint in thin plate, turn the job over, clean
the slag out of the back and deposit a similar weld.
20°-30°
Tack Weld
Figure 4-22: Butt Weld
Figure 4-23: Weld Build up Sequence
Heavy plate will require several runs to complete the joint.
After completing the first run, chip the slag out and clean the
weld with a wire brush. It is important to do this to prevent
slag being trapped by the second run. Subsequent runs are
then deposited using either a weave technique or single beads
laid down in the sequence shown in Figure 4-23. The width
of weave should not be more than three times the core wire
diameter of the electrode. When the joint is completely filled,
the back is either machined, ground or gouged out to remove
slag which may be trapped in the root, and to prepare a suit-
able joint for depositing the backing run. If a backing bar is
used, it is not usually necessary to remove this, since it serves
a similar purpose to the backing run in securing proper fusion
at the root of the weld.
4-11
ESAB FABRICATOR 252i
Electrode
Tack Weld
Art # A-07697_AB
Art # A-07698
BASIC WELDING