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Full text of "Modern Mechanical Engineering Vol-I"

132

FOUNDRY  WORK

are revolved on trestles (figs. 28 and 29), the latter showing the section
of the core inserted in fig. 16, and the casting section on the board.   These

r *



Fig. 30.—A Grid with Rods and Lifting Eyes cast in.   The relation of the core rammed on it is
indicated by dotted outlines

carry the loam and hay bands, and are perforated for the discharge of the
gases generated during pouring. In the absence of a containing flask, pro-
vision, in the form of rods with
eyes, and of extensions of grids,
has to be made for lifting all
except the lightest cores.

Cores rammed in boxes are
always liable to increase slightly
in dimensions, and to " gather "
as the saying is. The box sides
yield before the

Fig. 31.—Grid with Vertical Rods cast in to
afford support to a deep Core having Vertical
Sides

Fig. 32.—Core Box for Ratchet End in fig. 16
A, Ratchet.   B, Shrouding,   c, Line of joint in core.

ramming, and when removed the core swells a little. This is the reason
why so many of the larger cores have to be " nibbed " by the moulder to
reduce their dimensions. A careful pattern-maker will counter this by