e. Sweating a lap-joint. The process of "sweating" two metal surfaces
together is widely used for joining sheet metal (fig. 26). In this operation, the
particular areas of the surfaces to be joined must first be thoroughly cleaned,
fluxed, and tinned. When the metals have cooled, the tinned surfaces are again
fluxed and then lapped. While holding the surfaces in close contact, heat is
applied to the untinned outer side of the job with either a soldering iron or
torch. This will melt the solder between the metals and bond them as they cool.
Method of sweating a lap-joint.
SOLDERING WITH A TORCH.
a. Common uses. Torches are used to heat large or heavy metal areas for
soldering. When speed is required, a hand torch is preferable to the soldering
iron, and many times the torch can be used to reach out-of-the-way places that
cannot be reached with the soldering iron; e. g., the inner parts of a radiator
core. The torch is also very useful for melting soldered joints when dismantling
b. Method of using torch.
soldered are the same as those described in paragraph 34c. However, when applying
solder, the flame of the torch is applied to the metal surfaces at the same time as
(2) The requirements of a satisfactory torch flame are:
(a) A flame that will not be extinguished by the fumes of the flux.
(b) A flame giving enough heat to accomplish soldering quickly, yet not
too hot to damage the metal surfaces being soldered,
(c) A flame that can be adjusted to suit the needs of the job, such as a
long, slim needle-pointed flame capable of reaching out-of-the-way places or a wide
flame for dismantling of parts or for heavy metal areas.