Tweco 170 HF Weldskill - Manual (Page 31)

WELDSKILL 170 HF INVERTER
4-9 April 23, 2008
Art # A-07700
4.19 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 1.6mm to 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 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
3.2mm Ferrocraft 21 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 20° 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
Figure 4-12: Butt weld
Art # A-07698
Figure 4-13: 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 4-13. 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 suitable 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.
B. Fillet Welds
These are welds of approximately triangular cross-
section made by depositing metal in the corner of
two faces meeting at right angles. Refer to Figure 4-
5.
A piece of angle iron is a suitable specimen with which
to begin, or two lengths of strip steel may be tacked
together at right angles. Using a 3.2mm Ferrocraft
21 electrode at 100 amps, position angle iron with
one leg horizontal and the other vertical. This is known
as a horizontal-vertical (HV) fillet. Strike the arc and
immediately bring the electrode to a position
perpendicular to the line of the fillet and about 45°
from the vertical. Some electrodes require to be sloped
about 20° away from the perpendicular position to
prevent slag from running ahead of the weld. Refer
to Figure 4-14. Do not attempt to build up much larger
than 6.4mm width with a 3.2mm electrode, otherwise
the weld metal tends to sag towards the base, and
undercut forms on the vertical leg. Multi-runs can be
made as shown in Figure 4-15. Weaving in HV fillet
welds is undesirable.
Art # A-07699
Figure 4-14: Electrode position for HV fillet weld
Figure 4-15: Multi-runs in HV fillet weld