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Full text of "Modern Mechanical Engineering Vol-I"

MOULDING  IN GREEN  SAND

119

most universal method of moulding. Its value is most evident when patterns
have very intricate outlines, undercut portions, deep projections, loose pieces,
bosses, ribs, and so on. These can be evenly rammed directly, and parts
which are troublesome to deal with when bedding-in are more accessible.

In the usual practice, that is,
apart from the employment of joint
boards or of plates, the pattern is
embedded in a body of sand in the
top box, which is thrown out after
the joint face has been made. But
it is only shovelled in and made
sufficiently hard to ram on, so that
the loss of time is not of much im-
portance in the work of the general
shop. The following states the typical
sequence of this work. The top box
part is laid with its top face on the
floor, is filled, and roughly rammed
with sand up to its joint edges, and
the top side of the pattern is bedded
in this, until the joint edges of the
pattern coincide with the sand joint,
which, whether plane or irregular, is
shaped and sleeked with the trowel.
Parting sand is strewn over this, and
the bottom box part is placed over
the upstanding pattern, and cottered to the top box. After ramming and
venting, the two are turned over together, the bottom being brought to a
level bearing on the sand floor. The temporary sand is knocked out of
the top box, then replaced on the bottom, and rammed permanently. If
a middle part is used, this
being interposed between the
top and bottom, an addi-
tional joint is required.

The advantages of direct
ramming are secured in
other ways where boxes are
not turned over, but the

treatment properly belongs
to plate and machine-mould-
ing.

Fig. 8.—Core Box for Capstan Head

Fig. 9.—Templet for setting Core Prints

Although it is usual to joint patterns in the plane of the mould joints,
the practice is far from universal. The smaller the patterns are, the less
frequently are they jointed. Brass moulders seldom use jointed patterns
except in the larger sizes, but lay solid patterns in odd-sides. There is less
risk of the occurrence of lapping joints than when top and bottom portions