Tweco 175 SE Arc Master - Manuel (Page 32)

ARC MASTER 175 SE OpERATION
OPERATION 4-6 Manual 0-5054
4.14 The Welder
Place yourself in a comfortable position before
beginning to weld. Get a seat of suitable height and
do as much work as possible sitting down. Don’t
hold your body tense. A taut attitude of mind and a
tensed body will soon make you feel tired. Relax and
you will find that the job becomes much easier. You
can add much to your peace of mind by wearing a
leather apron and gauntlets. You won’t be worrying
then about being burnt or sparks setting alight to
your clothes.
Place the work so that the direction of welding is
across, rather than to or from, your body. The electrode
holder lead should be clear of any obstruction so that
you can move your arm freely along as the electrode
burns down. If the lead is slung over your shoulder,
it allows greater freedom of movement and takes a
lot of weight off your hand. Be sure the insulation on
your cable and electrode holder is not faulty, otherwise
you are risking an electric shock.
4.15 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" (1.6mm)
to 1/8" (3.2mm) 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.
Art # A-07696_AB
20°
1.6 mm (1/16”)
Figure 4-11: Striking an arc
4.16 Arc Length
The securing of an arc length necessary to produce
a neat weld soon becomes almost automatic. You
will find that A very long arc produces a crackling or
spluttering 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.
4.17 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 electrode has to move along the
plate to form a bead. The electrode is directed at the
weld pool at about 20° 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.
4.18 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.
A. Butt Welds
Set up two plates with their edges parallel, as shown in
Figure 4-12, allowing 1/16" (1.6mm) to 3/32" (2.4mm)
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" (6.0mm) should have their mating
edges bevelled to form a 70° to 90° included angle.
This allows full penetration of the weld metal to the
root. Using a 1/8" (3.2mm) E7014 electrode at 120
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 20° from vertical,
and the rate of travel not too fast, will help eliminate