classified into two groups: consumable and nonconsu-
mable. Consumable electrodes not only provide a path
for the current but they also supply fuller metal to the
joint. An example is the electrode used in shielded
metal-arc welding. Nonconsumable electrodes are only
used as a conductor for the electrical current, such as in
gas tungsten arc welding. The filler metal for gas tung-
sten arc welding is a hand fed consumable welding rod.
Additional information about filler rods and elec-
trodes is covered in other chapters of this TRAMAN that
deal with specific welding processes.
Before performing any welding process, you must
ensure the base metal is clean. No matter how much the
base metal is physically cleaned, it still contains impu-
rities. These impurities, called oxides, result from oxy-
gen combining with the metal and other contaminants
in the base metal. Unless these oxides are removed by
using a proper flux, a faulty weld may result. The term
flux refers to a material used to dissolve oxides and
release trapped gases and slag (impurities) from the base
metal; thus the flux can be thought of as a cleaning agent.
In performing this function, the flux allows the filler
metal and the base metal to be fused.
Different types of fluxes are used with different
types of metals; therefore, you should choose a flux
formulated for a specific base metal. Beyond that, you
can select a flux based on the expected soldering, braz-
ing, or welding temperature; for example, when brazing,
you should select a flux that becomes liquid at the
correct brazing temperature. When it melts, you will
know it is time to add the filler metal. The ideal flux has
the right fluidity at the welding temperature and thus
blankets the molten metal from oxidation.
Fluxes are available in many different forms. There
are fluxes for oxyfuel gas applications, such as brazing
and soldering. These fluxes usually come in the form of
a paste, powder, or liquid. Powders can be sprinkled on
the base metal, or the fuller rod can be heated and dipped
into the powder. Liquid and paste fluxes can be applied
to the filler rod and to the base metal with a brush. For
shielded metal arc welding, the flux is on the electrode.
In this case, the flux combines with impurities in the
base metal, floating them away in the form of a heavy
slag which shields the weld from the atmosphere.
You should realize that no single flux is satisfactory
for universal use; however, there are a lot of good
general-purpose fluxes for use with common metals. In
general, a good flux has the following characteristics:
It is fluid and active at the melting point of the
It remains stable and does not change to a vapor
rapidly within the temperature range of the weld-
It dissolves all oxides and removes them from the
It adheres to the metal surfaces while they are
being heated and does not ball up or blow away.
It does not cause a glare that makes it difficult to
see the progress of welding or brazing.
It is easy to remove after the joint is welded.
It is available in an easily applied form.
Nearly all fluxes give off fumes that may
be toxic. Use ONLY in well-ventilated spaces.
It is also good to remember that ALL welding
operations require adequate ventilation whether
a flux is used or not.
The weld joint is where two or more metal parts are
joined by welding. The five basic types of weld joints
are the butt, corner, tee, lap, and edge, as shown in figure
Figure 3-6.Basic weld joints.