Tweco 170 HF Weldskill - Manual (Page 30)

WELDSKILL 170 HF INVERTER
4-8 April 23, 2008
4.14 Arc Welding Technique
A Word to 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
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
material, 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
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.
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
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.
Art # A-07696
Figure 4-11: 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 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.
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.