Skip to main content

Full text of "Modern Mechanical Engineering Vol-I"

See other formats


sieved. A fairly even quantity may be ensured by laying two strips on the
floor sand, say i in. thick, and strickling the facing sand level with these
(fig. 2). The pattern is bedded on this, and driven in with blows of the
mallet, applied with sufficient firmness to leave its outlines impressed on the
bed. Where the projecting portions are beaten down, the sand is rendered
harder than elsewhere, and the casting might become scabbed in conse-
quence. The pattern is removed and the hard sections of sand are loosened
with the trowel and the pattern bedded again, frequently more than once.
More facing sand is added where necessary, loose portions are tucked under
with the hands and the pegging rammer, and any necessary venting is done
with the pricker. In plain patterns having narrow sections or semicircular
outlines, the whole of the work may be done by tucking the sand under,
without removing the pattern. The pipe in. fig. 3 can be moulded by tucking

Formation of the Cope.—Any plain top box part of a size suitable to

Fig. 3. — Iron Pattern of Pipe with Flanges of Wood suitable for Bedding-in by tucking Sand under

cover the mould is selected. It is set in its position with four stakes, that
take a bearing against joggles on the box sides, or against its lugs. It is
then rammed on the pattern, removed, turned over, the mould finished
and the box replaced, guided by the stakes. The cope is then loaded with
weights before pouring, since there are no box pins to be cottered. As the
top is plain, the stays stopping short of the joint face, the sand in any deep
recessed portions of the pattern has to be carried with lifters hung from the
stays, or, in other cases, when the deep portions have large areas, grids are
suspended from the stays to carry the sand. When moulds are so long that
they cannot be covered with a single top, two boxes are laid side by side.
Long, flimsy patterns give trouble when bedded-in, because it is difficult to
prevent bending and winding. The progress of the work is therefore
checked constantly with straight-edges and winding strips.
A large volume of work is done in the floor when, instead of complete
patterns, frames or sectional elements only are used for the exterior portions.
This, though not strictly a process of bedding-in, is allied to it, since a bed
has to be prepared, and vented down to a cinder bed, and the mould is
covered with a plain top. Bedplates of rectangular and circular outlines are
often made in this way. When copes are not plain, but contain bosses and
facings, and there is no complete pattern with a top boarded over to ram