Tweco 211i Fabricator - Manual (Page 73)

BASIC WELDING FABRICATOR 211i
Manual 0-5157 4-13 BASIC WELDING
Art # A-07702
Figure 4-26: Multi Run Vertical Fillet Weld
Art # A-07703
Figure 4-27: Examples of Vertical Fillet Welds
2. Vertical Down
The E7014 electrode makes welding in this
position particularly easy. Use a 1/8" (3.2 mm)
electrode at 100 amps. The tip of the electrode is
held in light contact with the work and the speed
of downward travel is regulated so that the tip of
the electrode just keeps ahead of the slag. The
electrode should point upwards at an angle of
about 45º.
3. Overhead Welds
Apart from the rather awkward position necessary,
overhead welding is not much more difficult that
downhand welding. Set up a specimen for over-
head welding by first tacking a length of angle
iron at right angles to another piece of angle iron
or a length of waste pipe. Then tack this to the
work bench or hold in a vice so that the specimen
is positioned in the overhead position as shown
in the sketch. The electrode is held at 45º to
the horizontal and tilted 10º in the line of travel
(Figure 4-28). The tip of the electrode may be
touched lightly on the metal, which helps to give
a steady run. A weave technique is not advisable
for overhead fillet welds. Use a 1/8" (3.2 mm)
E6013 electrode at 100 amps, and deposit the
first run by simply drawing the electrode along at
a steady rate. You will notice that the weld deposit
is rather convex, due to the effect of gravity before
the metal freezes.
Art # A-07704
Figure 4-28: Overhead Fillet Weld
Distortion
Distortion in some degree is present in all forms of
welding. In many cases it is so small that it is barely
perceptible, but in other cases allowance has to be made
before welding commences for the distortion that will
subsequently occur. The study of distortion is so complex
that only a brief outline can be attempted hear.
The Cause of Distortion
Distortion is caused by:
A. Contraction of Weld Metal:
Molten steel shrinks approximately 11 per cent in
volume on cooling to room temperature. This means
that a cube of molten metal would contract approxi-
mately 2.2 per cent in each of its three dimensions.
In a welded joint, the metal becomes attached to the
side of the joint and cannot contract freely. Therefore,
cooling causes the weld metal to flow plastically, that
is, the weld itself has to stretch if it is to overcome the
effect of shrinking volume and still be attached to the
edge of the joint. If the restraint is very great, as, for
example, in a heavy section of plate, the weld metal
may crack. Even in cases where the weld metal does
not crack, there will still remain stresses "Locked-up"
in the structure. If the joint material is relatively weak,
for example, a butt joint in 5/64" (2.0 mm) sheet,
the contracting weld metal may cause the sheet to
become distorted.