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Full text of "Modern Mechanical Engineering Vol-I"

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be made for every core.   These are cast in open sand from patterns kept
in stock, the moulds  being stopped off to any outlines and dimensions
required.    A large proportion of core grids can only be removed from the
interior of their castings by breaking them up and extracting them in frag-
............-.• «•*••-.,           ments, for which reason they are not made of

" ;-:.v'.           sections stouter than are necessary to sustain

••*.•.;•';;           the load of sand.    And generally in the deeper

': y.;'           cores, the cast grid occupies the bottom only,

Fig. 41.—Cores inserted in Drop Print
Impressions, bottom and top parts

Fig. 42.—Core inserted into Drop Print Im-
pression and moved along into a boss

support for overhanging masses being afforded by wrought-iron rods of
from J in. to f in. diameter cast into the grids (fig. 31). For small weak
sections, nails are embedded in the sand as in the similar situations in
moulds. Grids for cores therefore assume an infinite variety of forms.

Having the core box set on a level surface of
iron, wood,  or  sand,   and   the  grid   prepared, a    .•::.'';

Fig. 43.—Core Box, which includes two cores in drop prints

Fig. 44.—Setting a Core diagon-
ally with bottom print only

stratum of core sand is sieved over the bottom, to a depth, say, of about
i in., and the grid, well swabbed with clay wash, is bedded on it. More
sand is sieved or shovelled over the grid, and rammed over the grid and
against the sides, using the pegging rammer. Then, in all cores except
those which are shallow, a portion of the sand is scooped away from the
centre and heaped against the sides, and rammed with additional supplies