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Full text of "Modern Mechanical Engineering Vol-I"

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their outlines are uniform. These are moved along in rotation, one remaining
in the sand to afford support while other two are being rammed (fig. i).
Sectional patterns for fittings for boxes of various sizes and types are stocked,
and selected as required. These include box ends with prints for the iron
swivels, and core boxes for looped handles, and for the lugs in which the
pins are fitted.

Moulding by Bedding-in.—This embraces a very extensive volume
of work done, the essential characteristic of which is that it is moulded in
the foundry floor instead of in a box. The mould is covered and closed with
a cope, through which the metal is poured. As there is no bottom box with
locating pins, the cope has to be set with stakes driven into the sand of the
floor. Bedding-in is mostly adopted in the largest work. The reason is,
that the turning over of massive boxes with their contained sand would be
very inconvenient, and in some foundries impracticable. The cost of the

Fig. 2.—Strickling Facing Sand on a Mould Bed
A, Thickness of facing.
boxes also would bear too high a proportion to that of the castings, which
are seldom wanted in large numbers. And provided reasonable care is
exercised, castings can be made as satisfactorily by bedding-in as by turn-
ing over.
Variations in Details.—Methods of procedure are modified by the shapes
of patterns. If these have level lower faces and broad areas, a levelled bed
is strickled under the guidance of winding strips, as described in the making
of open moulds. The vents from the large areas must be driven down into a
cinder bed, to be brought away through large vent pipes extending from the
bed to the outside of the mould. Instead of using winding strips for levelling,
the horizontal edge of a sweeping board can be worked round a central bar,
a method which is adopted when central bosses and annular facings have
to be produced in the bottom. On the bed, first prepared, the pattern is
set and rammed. This may either be complete, or a skeleton outline, against
the outer faces of which the mould is rammed, leaving the interior to be
formed with cores.
When patterns have irregular outlines, and parts projecting into the
bottom, such as deep flanges, ribs, bosses, and lugs, each portion has to be
treated in detail if lumpy castings are to be prevented. If the pattern is
very diversified in outline, a level bed is of no value. If its main web is
flat, the bed is required. In each case the floor sand is prepared by digging
and flat-ramming, and over it a thickness of i in. or more of facing sand is