Welding Technique; Electrode Selection - Linde BOC RAPTOR 250R MIG Operating Manual

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15.3 Welding Technique

Successful welding depends on the following factors:
selection of the correct electrode
•
selection of the correct size of the electrode for the job
•
correct welding current
•
correct arc length
•
correct angle of electrode to work
•
correct travel speed
•
correct preparation of work to be welded.
•

15.4 Electrode Selection

As a general rule the selection of an electrode is straight forward,
in that it is only a matter of selecting an electrode of similar
composition to the parent metal. It will be found, however, that
for some metals there is a choice of several electrodes, each of
which has particular properties to suit specific classes of work.
Often, one electrode in the group will be more suitable for general
applications due to its all round qualities.
The following table shows just a few of the wide range of
electrodes available from BOC with their typical areas of
application.
For example, the average welder will carry out most fabrication
using mild steel and for this material has a choice of various
standard BOC electrodes, each of which will have qualities suited
to particular tasks. For general mild steel work, however, BOC
Smootharc 13 electrodes will handle virtually all applications. BOC
Smootharc 13 is suitable for welding mild steel in all positions
using AC or DC power sources. Its easy-striking characteristics and
the tolerance it has for work where fit-up and plate surfaces are
not considered good make it the most attractive electrode of its
class. Continuous development and improvement of BOC Smootharc
13 has provided in-built operating qualities which appeals to the
beginner and experienced operator alike.
Electrodes and Typical Applications
Name AWS
Class.
BOC Smootharc 13 E6013
BOC Smootharc 24 E7024
Application
A premium quality electrode for general
structural and sheet metal work in all
positions including vertical down using
low carbon steels
An iron powder electrode for high
speed welding for H-V fillets and flat
butt joints. Medium to heavy structural
applications in low carbon steels
BOC RAPTOR 200C & 250R MIG Operating manual
Electrodes and Typical Applications
Name AWS
Class.
BOC Smootharc 18 E7018-1 A premium quality all positional
BOC Smootharc S 308L E308L
BOC Smootharc S 316L E316L
BOC Smootharc S 309L E309L
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 current, set on the current range
specified.
The limits of this range should not normally be exceeded.
Application
hydrogen controlled electrode for
carbon steels in pressure vessel
applications and where high integrity
welding is required and for free-
machining steels containing sulphur
Rutile basic coated low carbon
electrodes for welding austenitic
stainless steel and difficult to weld
material
Rutile basic coated low carbon electrode
for welding mild steel to stainless steel
and difficult to weld material
Maximum Recommended
Electrode Diameter
2.0 mm
2.5 mm
3.15 mm
4.0 mm
39