The pressure upon the rivet after it is driven is
maintained, or the die is retracted at will.
[Illustration: FIG. 17.]
Hydraulic riveting has demonstrated not only that the work could be as
well done without a blow, but that it could be _better done without a
blow_, and that the riveted material was stronger when so secured than
when subjected to the more severe treatment under impact.
What is manifestly required in perfect riveting is that the metal of
the rivet while hot and plastic shall be made to flow into all the
irregularities of the rivet holes in the boiler sheets; that the
surplus metal be formed into heads as large as need be, and that the
pressure used to produce these results should not be in excess of what
the metal forming the boiler shall be capable of resisting.
It is well known that metals, when subjected, either cold or hot, to
sufficient pressure, will obey almost exactly the same laws as fluids
under similar conditions, and will flow into and fill all the crevices
of the chamber or cavity in which they are contained. If, therefore, a
hot rivet is inserted into the holes made in a boiler to receive it,
and is then subjected to a sufficient pressure, it will fill every
irregularity of the holes, and thus fulfill one of the conditions of
perfect riveting.
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