electrodes melt off and are a source of the filler
the toe of the weld. UNDERBEAD CRACKS
occur in the heat-affected zone underneath a bead,
and do not extend to the surface of the metal.
Underbead cracks can be detected either by X ray
or ultrasonic examination.
The welding or brazing of certain materials
ROOT CRACKS are similar to toe cracks
require the use of a flux to produce a sound joint.
Fluxes are available as liquids, pastes, and powders.
except that they occur at the root of the weld. Root
cracks may be in the weld metal or in the base
They have a melting point below that of the base
and filler metals, and they are not incorporated into
the weld. Their primary purpose is to prevent the
formation of oxides on the weld joint before and
VOIDS, also known as GAS POCKETS or
during welding operations. Fluxes should never be
BLOWHOLES, are another type of weld defect.
used as a substitute for proper cleaning.
The term POROSITY is used when there are a
number of voids. Voids occur as the result of gas
The application of fluxes will vary depending
being absorbed during the welding and then trapped
upon the type of welding being done. In silver
as the metal solidifies. The absorbed gas is usually
brazing, the flux is applied directly to the joint with
hydrogen. Improper welding techniques, incorrect
a brush. In other brazing operations, the filler
adjustment of equipment, or moisture in electrode
metal is heated slightly and dipped into the flux.
coating may lead to the absorption of gas and the
consequent formation of voids.
SLAG INCLUSION is the term used to describe
number of specifications. No one flux is satisfactory
the weld defect in which nonmetallic solid material
for all purposes. When the type of flux to be used
is trapped in the weld metal or at the bond between
is not otherwise specified, consult the NSTM or the
the weld metal and the base metal. The presence of
latest NAVSEA instruction for the type of flux to
slag inclusions breaks up the homogeneity of the
use for a particular job.
metal, t h e r e b y providing a point for the
concentration of stresses. In some cases, the
Fluxes are not ordinarily required for
concentration of stresses thus developed leads to
oxyacetylene welding of mild steel and low-alloy
failure of the joint.
ferrous metals. The oxides of these metals melt at
a low temperature and flow away from the weld
area. However, all brazing and soldering jobs on
both ferrous and nonferrous metals require a flux.
The metals that are added during the welding
All oxyacetylene welding jobs on cast iron, cast steel,
process are known as filler materials or filler metals.
aluminum, copper, copper-base alloys, nickel,
In welding processes in which a space is left
between the parts to be joined, filler metals provide
silicon-bronze alloys also require a flux.
the intimacy of contact necessary for coalescence.
Several precautions must be observed when you
Filler materials used in welding processes include
are working with fluxes. Unless the base metal is
welding rods and electrodes.
properly cleaned and the correct flux applied to the
The term WELDING ROD refers to a filler
joint, fluxing will hinder rather than aid in making
metal in wire or rod form. It is used in gas welding
the joint. Further, the flux must not be overheated
processes and in certain electric welding processes,
or it will fail to serve its purpose. In addition, fluxes
such as gas tungsten-arc welding, in which the filler
will also deteriorate if they are kept at brazing
metal does NOT form a part of the electrical circuit.
temperatures for too long a time. Nearly all fluxes
The only purpose of a welding rod is to supply filler
give off fumes that may be toxic. For that reason,
metal to the joint.
fluxes should always be used in a well-ventilated
space. Any welding operation requires adequate
The term ELECTRODE refers to the metal
ventilation, whether a flux is used or not.
that, in electric welding, forms a part of the
electrical circuit. In gas tungsten-arc welding,