Specifications

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AU : IPRM 2007 : SECTION 8 : CONSUMABLES
WARNING Welding can give rise to electric shock, excessive noise, eye and skin burns due to the arc rays, and a potential health hazard if you breathe in the emitted fumes and gases.
Read all the manufacturer’s instructions to achieve the correct welding conditions and ask your employer for the Materials Safety Data Sheets. Refer to www.boc.com.au or www.boc.co.nz
Fundamentals of Manual Metal Arc (MMA) Welding
Recommended Electrode Sizes
Average Thickness of Plate or
Section
Maximum Recommended
Electrode Diameter
1.5–2.0 mm 2.5 mm
2.0–5.0 mm 3.2 mm
5.0–8.0 mm 4.0 mm
≥8.0 mm 5.0 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 and burning through of the material, and
will 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 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
Electrode Size (mm) Current Range (Amp)
2.5 60–95
3.2 110–130
4.0 140–165
5.0 170–260
Arc Length
To strike 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, 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.
Electrode Angle
The angle that the electrode makes with the work is important to
ensure a smooth, even transfer of metal.
The recommended angles for use in the various welding positions
are covered later.
Correct Travel Speed
The electrode should be moved along in the direction of the joint
being welded at a speed that will give the size of run required. At
the same time, the electrode is fed downwards to keep the correct
arc length at all times. As a guide for general applications, the table
below gives recommended run lengths for the downhand position.
Correct travel speed for normal welding applications varies between
approximately 100 and 300 mm per minute, depending on electrode
size, size of run required and the amperage used.
Excessive travel speeds lead to poor fusion, lack of penetration etc,
while too slow a rate of travel will frequently lead to arc instability,
slag inclusions and poor mechanical properties.
Run Length per Electrode – BOC Smootharc 13
Electrode Size
(mm)
Electrode
Length (mm)
Run Length (mm)
Minimum Maximum
4.0 350 175 300
3.2 350 125 225
2.5 350 100 225
Correct Work Preparation
The method of preparation of components to be welded will
depend on equipment available and relative costs. Methods may
include sawing, punching, shearing, machining, flame cutting and
others.
In all cases edges should be prepared for the joints that suit the
application.The following section describes the various joint types
and areas of application.
Types of Joints
Butt Welds
A butt weld is a weld made between two plates so as to give
continuity of section.
Close attention must be paid to detail in a butt weld to ensure that
the maximum strength of the weld is developed. Failure to properly
prepare the edges may lead to the production of faulty welds, as
correct manipulation of the electrode is impeded.
Butt Welding
Weld FaceReinforcement
Root Face
Root Gap
Fundamentals of Manual Metal Arc (MMA) Welding