11 Flux
Residue Removal in Brazing and Soldering In
general, it is necessary to remove flux residues remaining after brazing and soldering
applications because they may
be corrosive and prevent finishing operations such as painting or chromium plating
from being successfully completed.
Flux residues may be removed by chemical or mechanical means, or by washing in
hot water. Dispose of
all flux residues according to local regulations. Be sure to wear proper
skin, eye and clothing protection when removing
flux residues. NOTE:
In refrigeration repairs, remove flux residue as soon as system is put under pressure,
not before. •
Washing in hot water:
Flux
residues remaining after applications with alloys of silver, zinc, zinc alloys,
and solders are usually removed by
washing the joint area with hot water (104°F, 40°C), followed by a careful
rinse. •
Mechanical cleaning:
Mechanical
cleaning by wire brushing, grinding, polishing, chipping, or sanding can be used
to remove flux residues
whenever it is impractical to remove them by washing. Examples are when the part
is too large, too
heavy or for some other reason the work cannot be cleaned by washing. However,
mechanical cleaning generally
causes some surface damage and should only be used where this will not affect
the finished quality of
the work. •
Chemical cleaning:
The
following are some chemical solutions and techniques which are effective for removing
flux residues. As chemical
cleaning generally involves the use of acid solutions, extreme care must be taken
to protect the skin, eyes,
clothing, and equipment from damage when using these solutions.
Copper and Copper Alloys
To remove flux residues from copper
and copper alloys such as brass, bronze, and other alloys in which copper
is a major component, a solution of
10-15% sulphuric acid mixed with water, applied with a non-metallic brush
is effective. This treatment will also
restore the copper color to the work by removing oxides caused by brazing
and soldering.
