Firepower MST 220i, Руководство по эксплуатации

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FIREPOWER MST 220i
Manual 0-5343 4-11 BASIC WELDING
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.
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 con-
tact 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.
Art # A-10673
20°
1/16” (1.6 mm)
Figure 4-20: 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 produces more heat. 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.
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 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 elec-
trode, 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 4-21, 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 ten-
dency 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.
Art # A-07697_AB
Tack Weld
20°-30°
Electrode
Tack Weld
Figure 4-21: Butt Weld