Tweco 161 S UK - Manual (Page 33)

OPERATION THERMAL ARC 161 S
Manual 0-5183 4-9 4-9 Operation
4.19 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 4-12, allowing 1.6mm (1/16") to 2.4mm (3/32")
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 6.4mm (1/4") should have their mating edges bev- 6.4mm (1/4") should have their mating edges bev- (1/4") should have their mating edges bev- 1/4") should have their mating edges bev- ) should have their mating edges bev-
elled to form a 70° to 90° included angle. This allows
full penetration of the weld metal to the root. Using a
3.2mm (1/8") 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 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 4-13: Butt weld
Art # A-07698
Figure 4-14: 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-sec-
tion 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 (1/8") E7014
electrode at 120 amps, position angle iron with one leg
horizontal and the other vertical. This is known as a hori-
zontal-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 (1/4") width with a
3.2mm (1/8") 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 4-15: Electrode position for HV fillet weld