Tweco 186 DC Inverter - Manual (Page 59)

BASIC WELDING 186 AC/DC INVERTER
Manual 0-5237 4-5 BASIC WELDING GUIDE
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 4-11, allowing 1/16" (1.6mm) to 3/32" (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 1/4" (6.0mm) should have their mating edges
bevelled to form a 70º to 90º included angle. This allows full penetration of the weld metal to the root.
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 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 4-11: Butt Weld
Art # A-07698
Figure 4-12: 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 4-12. 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.