Linde BOC Smootharc Advance MIG 425R Operating Manual page 45

Electrode Size
The size of the electrode is generally dependent on the thickness of the
section being welded, and the larger the section the larger the electrode
required. In the case of light sheet the electrode size used is generally
slightly larger than the work being welded. This means that if 1.5 mm sheet
is being welded, 2.0 mm diameter electrode is the recommended size. The
following table gives the recommended maximum size of electrodes that may
be used for various thicknesses of section.
Recommended Electrode Sizes
Average Thickness
of Plate or Section
≤1.5 mm
1.5–2.0 mm
2.0–5.0 mm
5.0–8.0 mm
Welding Current
Correct current selection for a particular job is an important factor in arc
welding. With the current set too low, difficulty is experienced in striking and
maintaining a stable arc. The electrode tends to stick to the work, penetration
is poor and beads with a distinct rounded profile will be deposited.
Excessive current is accompanied by overheating of the electrode. It will
cause undercut, burning through of the material, and give excessive spatter.
Normal current for a particular job may be considered as the maximum which
can be used without burning through the work, over-heating the electrode
or producing a rough spattered surface, i.e. the current in the middle of the
range specified on the electrode package is considered to be the optimum.
In the case of welding machines with separate terminals for different size
electrodes, ensure that the welding lead is connected to the correct terminal
for the size electrode being used. When using machines with adjustable
Maximum Recommended
Electrode Diameter
2.0 mm
2.5 mm
3.15 mm
4.0 mm
BOC Smootharc Advance III MIG 425R & 555R Operating manual
current, set on the current range specified.
The limits of this range should not normally be exceeded.
The following table shows the current ranges generally recommended for
BOC Smootharc 13.
Generally Recommended Current Range for BOC Smootharc 13
Size of Electrode (mm)
2.5
3.2
4.0
5.0
Arc Length
To start the arc, the electrode should be gently scraped on the work until the
arc is established. There is a simple rule for the proper arc length; it should
be the shortest arc that gives a good surface to the weld. An arc too long
reduces penetration, produces spatter and gives a rough surface finish to the
weld. An excessively short arc will cause sticking of the electrode and rough
deposits that are associated with slag inclusions.
For downhand welding, it will be found that an arc length not greater than
the diameter of the core wire will be most satisfactory. Overhead welding
requires a very short arc, so that a minimum of metal will be lost. Certain
BOC electrodes have been specially designed for 'touch' welding. These
electrodes may be dragged along the work and a perfectly sound weld is
produced.
Current Range (Amp)
60–95
110–130
140–165
170–260
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