Table of Contents
Advertisement
by
MMA Welding Techniques
- 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.
10
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
20
(Fig 1-20)
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.
o
1.6mm (1/16")
Advertisement
Table of Contents
