(1) At welding temperatures all metals oxidize (i.e., form chemical
compounds with oxygen from the air) more or less rapidly and the oxides so formed
act as so much "dirt." If permitted to remain in the finished weld, the oxide
would seriously reduce the strength of the weld and might even make it useless.
(2) In welding steel, oxides of the various elements form and unite
together into a slag that fuses at a lower temperature than that required to melt
the steel. This slag tends to float to the surface of the weld and, with care on
the part of the operator, these oxides can be collected on the top of the puddle of
molten metal and thus removed from the joint.
(3) In cast iron and aluminum welding particularly, and in welding
practically all of the common metals except steel, the temperature of the molten
metal is considerably below the melting point of the oxides that form so that the
latter remain in the weld as solid particles. In order to get rid of these oxides
a flux is used. This is a mixture of various chemicals that at welding
temperatures will unite with the oxides to form an easily fusible slag.
(4) Since the oxides of the different metals vary widely in physical
properties, no one flux is suitable for all metals.
(5) The production of a good welding flux requires a knowledge of chemistry
at high temperatures as well as experience in welding. Use prepared fluxes of
reputable manufacturers, rather than experiment with unsatisfactory substitutes.
(1) Prevents oxidation of the base metal by virtue of its protective
(2) Dissolves oxides that are formed during heating.
(3) Promotes capillary action between the metals being joined.
(4) Fluxes are not designed to remove oil, grease, or other foreign
substances; therefore, surfaces of the metal should be cleaned prior to the
application of the flux.
(5) Fluxes are used in paste, dry powder, saturated solution, or in a
c. Use. Figure 12 reflects the type of flame adjustment, type of flux, and
type of welding rod to be used for different types of metal.
a. Hold the torch in such a position so that the tip is in line with the weld
and at an angle of about 45 to it.
b. The angle between the rod and flame should be approximately 90.