In all cases where a special form is
to be given to the outer or inner circumference of the object, or where
it is desired to exert a pressure on the circumference, such form or
pressure is obtained by the introduction of a core which may be expanded
or contracted as need may be. For this purpose an expansible, metallic
core is employed, the arrangement of which is shown in Figs. 1 and 2,
and which is so fashioned that the inner circumference of the ring to be
cast may receive the desired form. This core is formed of the pieces, g,
g', made of cast-iron or any other material which fuses with difficulty,
and which are placed in the revolving mould in such a way that after the
cooling of the pieces the parts, g, recede by the shrinkage of the piece
and thus free the core. The parts, g, of the core are in the shape of
circular segments, and are united at their external circumference by a
flange, along with which they form a shoulder piece for the casting.
As a consequence of the rapid revolution of the mould, these parts are
pressed by centrifugal force against the molten metal which is run into
the mould.
[Illustration: CENTRIFUGAL METAL MOULDING APPARATUS.]
The plan, Fig. 2, shows the arrangement of the parts, g, g', and allows
it to be seen that the pieces, g', act as wedges against the segments,
g, and push these out so as to form a perfect circle.
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