Arc Welding Technique - A Word for Beginners
For those who have not yet done any welding, the simplest way to commence
is to run beads on a piece of scrap plate. Use mild steel plate about 6.0mm
thick and a 3.2mm electrode. Clean any paint, loose scale or grease off the
plate and set it firmly on the work bench so that welding can be carried out in
the down hand position. Make sure that the Work Lead/Clamp is making good
electrical contact with the work, either directly or through the work table. For
light gauge material, always clamp the work lead directly to the job, otherwise
a poor circuit will probably result.
The Welder
Place yourself in a comfortable position before beginning to weld. Get a seat
of suitable height and do as much work as possible sitting down. Don’t hold
your body tense. A taut attitude of mind and a tensed body will soon make you
feel tired. Relax and you will find that the job becomes much easier. You can
add much to your peace of mind by wearing a leather apron and gauntlets.
You won’t be worrying then about being burnt or sparks setting alight to your
clothes.
Place the work so that the direction of welding is across, rather than to or
from, your body. The electrode holder lead should be clear of any obstruction
so that you can move your arm freely along as the electrode burns down. If the
lead is slung over your shoulder, it allows greater freedom of movement and
takes a lot of weight off your hand. Be sure the insulation on your cable and
electrode holder is not faulty; otherwise you are risking an electric shock.
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.
Striking an Arc (Fig 1-20)
1.6mm (1/16”)
20
o
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 E7014 Stick electrodes do not stick in this way, and make
welding much easier.
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 20º 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.
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 1-21, 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
70º to 90º included angle. This allows full penetration of the weld metal to the
root. Using a 3.2mm E7014 Stick 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 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.
Butt Weld (Fig 1-21)
Tack Weld
Tack Weld
Electrode
20
o
- 30
o
Weld Build Up Sequence (Fig 1-22)
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 1-22. 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.
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