The only objection is in the
difficulty of confining the heat to the desired parts of the work.
The most satisfactory fire is that from a fuel gas torch built for this
work. These torches are simply forms of Bunsen burners, mixing the proper
quantity of air with the gas to bring about a perfect combustion. Hose
lines lead to the mixing tube of the gas torch, one line carrying the gas
and the other air under a moderate pressure. The air line is often
dispensed with, allowing the gas to draw air into the burner on the
injector principle, much the same as with illuminating gas burners for use
with incandescent mantles. Valves are provided with which the operator may
regulate the amount of both gas and air, and ordinarily the quality and
intensity of the flame.
When gas is not available, recourse may be had to the gasoline torch made
for brazing. This torch is built in the same way as the small portable
gasoline torches for soldering operations, with the exception that two
regulating needle valves are incorporated in place of only one.
The torches are carried on a framework, which also supports the work being
handled. Fuel is forced to the torch from a large tank of gasoline into
which air pressure is pumped by hand. The torches are regulated to give
the desired flame by means of the needle valves in much the same way as
with any other form of pressure torch using liquid fuel.
Another very satisfactory form of torch for brazing is the acetylene-air
combination described in the chapter on welding instruments.
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