Impax IM-MMA130-IWK Manual page 25

MMA OPERATION
If the resultant weld looks messy and irregular,
this is an indication of porosity or slag
contamination, and you have almost certainly
failed to achieve the correct combination. This is
a common problem, so do not worry as practice
will quickly cure this.
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 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.
When welding material up to 7mm in thickness
place the pieces 2-3mm apart, run the welding
bead along the join. A second bead can go
along the underside for extra strength (Fig.11).
When welding material from 7mm to 30mm thick
prepare the material as shown in Fig.12 filling up
the space with several layers of weld.
Fig 11
Fig 12
When welding together material over 30mm in
thickness prepare the material as shown in
Fig.13 filling up the space with several layers of
weld, welding each side in turn with each
welding pass.
Fig 13
Disconnect the Welding Power Supply from the
mains supply before changing or removing
electrodes. Use pliers to remove used
electrodes from the electrode holder or to move
the welded pieces.
24
7mm
2-3mm
60º
>30mm
2-3mm
6
5
4
3
2
1
60º
>30mm
2-3mm