HD Manual Arc Welders
©2000 CIGWELD All rights reserved
22
11.2 Striking the Arc
Practice this on a piece of scrap plate before going on to more
exacting work. You may at first experience difficulty due to the tip
of the electrode “sticking” to the work piece. This is caused by
making too heavy a contact with the work and failing to withdraw
the electrode quickly enough. A low amperage will accentuate it.
This freezing-on of the tip may be overcome by
scratching the
electrode along the plate surface in the same way as a match is
struck
. As soon as the arc is established, maintain a 1.6mm to
3.2mm gap between the burning electrode end and the parent metal. Draw the electrode slowly
along as it melts down.
Another difficulty you may meet is the tendency, after the arc is struck, to withdraw the
electrode so far that the arc is broken again. A little practice will soon remedy both of these
faults.
11.3 Arc Length
The securing of an arc length necessary to produce a neat weld soon becomes almost automatic.
You will find that a long arc produces more heat. A very long arc produces a crackling or
spluttering noise and the weld metal comes across in large, irregular blobs. The weld bead is
flattened and spatter increases. A short arc is essential if a high quality weld is to be obtained
although if it is too short there is the danger of it being blanketed by slag and the electrode tip
being solidified in. If this should happen, give the electrode a quick twist back over the weld to
detach it. Contact or “touch-weld” electrodes such as Ferrocraft 21 do not stick in this way, and
make welding much easier.
11.4 Rate of Travel
After the arc is struck, your next concern is to maintain it, and this requires moving the
electrode tip towards the molten pool at the same rate as it is melting away. At the same time,
the electrode has to move along the plate to form a bead. The electrode is directed at the weld
pool at about 20
°
from the vertical. The rate of travel has to be adjusted so that a well-formed
bead is produced. If the travel is too fast, the bead will be narrow and strung out and may even
be broken up into individual globules. If the travel is too slow, the weld metal piles up and the
bead will be too large.
11.5 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 11, 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.
Figure 10 - Striking an arc
