The molten metal
cannot become oxidized in the mould, since it is shut off from contact
with the external air by the cap, C, which covers it. Oxidation may,
however, be further prevented by passing some deoxidizing or neutral gas
into the mould. For this purpose the mould is filled before the casting
is done with some such gas as illuminating gas, carbonic acid, nitrogen,
or hydrogen.
This improved process of casting may also be employed for objects which
do not possess an exactly annular section. The moulds are then arranged
eccentrically in a frame which is made to revolve rapidly during the
cooling of the metal In this way the pieces are less strongly compressed
at the places where they are nearest the center of rotation than a the
points where the radius is greater.
Figs. 3 and 4 show section and plan of an apparatus of this kind. The
sand moulds are arranged in the frame, a b which revolves about the
axle, c. In the moulds there are iron cores, h, which press the metal
during rotation and thereby produce compact pieces.
* * * * *
APPARATUS FOR THE MANUFACTURE OF WOOD PULP.
For manufacturing wood pulp Mr. Dresel employs an apparatus such as
represented in Figs. 1 and 2, consisting of an upright cylindrical
reservoir, A, supported on a frame by means of trunnions, z.
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