Fabricator 181i – Tweco 181i Thermal Arc Fabricator User Manual

Page 73

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Fabricator 181i

Manual 0-5191

4-15

BASIC WELDING GUIDE

2. Vertical Down

The

E7014 Stick electrode makes welding in this position particularly easy. Use a 1/8"(3.2mm) 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 overhead 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"(3.2mm) E6013 Stick 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 approximately 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" (2.0mm) sheet, the contracting weld metal may cause the sheet to become distorted.

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