b. Preparing the iron.
A properly shaped and tinned soldering iron tip is
essential for good soldering. The tinning operation is applied to a new iron or to
one that has been heated to a temperature so high that the coating of solder has
(a) The tip of the soldering iron is filed to shape the point and to
remove old solder, pits, and tarnished spots from the working surface of the iron
so that it may be properly tinned.
(b) Before it is filed, the soldering iron should be heated hot enough to
melt old solder left on the surface. With externally heated soldering irons, this
heating process may be accomplished by several methods. If a hot gas flame such as
a bunsen burner is used, the iron should be placed over the burner with the point
flame of the torch should be concentrated on the thick end of the iron. Because of
the high heat conductivity of copper, the point will be heated to practically the
same temperature as its thick end.
(c) If the tip of the soldering iron is badly pitted or uneven, it may be
necessary to repoint it. This is accomplished by heating the tip to a dull red
and hammering it on an anvil until the point tapers back about one-fourth the total
length of the copper portion. The hammer blows should be distributed evenly on the
faces. The iron may then be annealed (softened) by being reheated and plunged red
hot into cold water to permit filing the point to a finish. The tip of an electric
iron should not be hammered, filed, or plunged into water until the heating element
has been removed.
(d) A vise or holding clamp should be used to secure the iron while
filing. The working surface of the tip should be parallel with the top of the vise
or holding clamp. The tip should be filed on all sides until bare metal can be
seen, using a fine flat file to prevent cutting away too much metal.
(a) The iron should be heated to the minimum temperature required to
make solder flow readily; an overheated iron will not tin properly. An externally
heated iron is ready for tinning when the surface appears to be covered with
various colors; a green flame coming from the heated tip indicates that it is too
hot. Electric iron overheating can be recognized by the sudden tarnishing of the
bright metal on a newly filed tip.
(b) After the tip of the iron has been properly heated, it should be
rubbed on a block of sal ammoniac flux and solder applied (omit the sal ammoniac
flux if core solder is used). All sides of the tip should be tinned for general
soldering practices. However, if the job surface requires that the iron be used in
an overhead position, only one side of the tip should be tinned. When attempting
to solder with the iron in an over-head position, a completely tinned tip will
result in the solder flowing away from the joint as shown in figure 24. Excess
solder may be wiped off with a clean dry cloth.
(c) The tinned point should be cleaned with a soft wire brush or clean
dry cloth each time it is removed from the heat; otherwise it will become coated
with the flux residue and oxidation of the solder.