Impax IM-TIG200 Instruction Manual page 25

MMA OPERATION
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.10).
Fig 10
2-3mm
When welding material from 7mm to 30mm thick
prepare the material as shown in Fig.11 filling up
the space with several layers of weld.
Fig 11
60º
2-3mm
5
3
7mm
>30mm
6
4
2
1
When welding together material over 30mm in
thickness prepare the material as shown in
Fig.12 filling up the space with several layers of
weld, welding each side in turn with each
welding pass.
Fig 12
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.
The Manual Metal Arc Process
When an arc is struck between the metal rod
(electrode) and the workpiece, both the rod and
workpiece surface melt to form a weld pool.
Simultaneous melting of the flux coating on the
rod will form gas and slag which protects the
weld pool from the surrounding atmosphere. The
slag will solidify and cool and must be chipped
off the weld bead once the weld run is complete
(or before the next weld pass is deposited).
The process allows only short lengths of weld to
be produced before a new electrode needs to
be inserted in the holder. Weld penetration is low
and the quality of the weld deposit is highly
dependent on the skill of the welder.
Types of Flux/Electrodes
Arc stability, depth of penetration, metal
deposition rate and positional capability are
greatly influenced by the chemical composition
of the flux coating on the electrode. Electrodes
can be divided into three main groups:
• Cellulosic
• Rutile
• Basic
24
60º
>30mm
2-3mm