Tweco 161 S UK - Manual (Page 32)

THERMAL ARC 161 S OPERATION
Operation 4-8 4-8 Manual 0-5183
4.14 Arc Welding Technique
A Word to Beginners
For those who have not yet done any welding, the sim-
plest way to commence is to run beads on a piece of
scrap plate. Use mild steel plate about 6.4mm (1/4")
thick and a 3.2mm (1/8") 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 downhand position. Make sure that the work clamp
is making good electrical contact with the work, either
directly or through the work table. For light gauge ma-
terial, always clamp the work lead directly to the job,
otherwise a poor circuit will probably result.
4.15 The Welder
Place yourself in a comfortable position before begin-
ning 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.
4.16 Striking the Arc
Practice this on a piece of scrap plate before going on
to more exacting work. You may at first experience dif-
ficulty due to the tip of the electrode “sticking” to the
work piece. This is caused by making too heavy a con-
tact 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 ( 1/16" ) to 3.2mm (1/8" ) 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.
Art # A-07696
Figure 4-12: Striking an arc
4.17 Arc Length
The securing of an arc length necessary to produce a
neat weld soon becomes almost automatic. You will find
that 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 electrode do not stick in this
way, and make welding much easier.
4.18 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.