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Fusible safety devices depend on sudden mechanical failure
at a specific temperature. Familiar examples are safety-plugs
for pressure cookers and temperature-responsive seals for sprinkler
systems. The characteristics of many low melting-point alloys
are stable enough for such purposes.
The most satisfactory solution is to use a eutectic alloy,
which can be expected to fail when it reaches the eutectic temperature.
Such alloys are unfortunately few in number, but the need can
often be supplied by one of the many non-eutectics which show
well defined yield points (by the standard test of the American
Gas Association). The failure point can usually be relied on
within a close range of no more than 2°C, the actual temperature
depending on the local conditions such as size and shape of
the component, applied pressure and thermal conductivity of
the surrounding materials.
A representative selection of suitable alloys is shown in
the table below. Note that the 'melting-point' is normally observed
as the alloy solidifies, rather than as it melts, and that the
yield-point for alloys not shown here may be at a lower temperature
than the melting-point.
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