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Full text of "Modern Mechanical Engineering Vol-I"

128

FOUNDRY  WORK

The loam that lies in contact with them delivers badly, and has to be
made good by mending-up.

Jointing.—Since moulding boxes are not available, jointing can only be
done in the actual moulds. The positions of joints are determined by the
shapes of moulds. All flanges involve joints and frequently extraneous
fittings. The bricks and loam above a joint must be carried with a ring
(fig. 18). The cope of a mould is carried on a plate having holes for the
ingates, and is turned over, the bricks being retained with rods and plates,
though many plain tops only require loam swept directly on their prods.
All joints except that of the cope are plane faces, and the cope may be the
same when it has, no boss or other part that requires exact centring. In
this case the joint is provided with a check (fig. 18) that renders it self-
centring when lowered into place. The
difference between this and other joints is
that these can be seen and set while the
mould is open. This cannot be done with
the cope which closes the mould.

Pouring and Shrinkages*—Loam moulds

Fig. 21.—Skeleton Pattern of Pipe Bend

Fig. 22.—Skeleton Pattern of S-pipe with bpaces filled
with Sand

are poured from the top, usually through a circle of ingates in an annular
basin (fig. 18). Moulds must not be closed until shortly before pouring
is done, since they absorb moisture. In deep moulds, the pressure is
so great that the bricks alone would be liable to yield, and they are
therefore rammed in the foundry pit, enclosed with sand walls, or with
iron rings. The shrinkages in large moulds would cause fracture of the
cooling castings if measures were not taken to enable the mould to yield
before them. A layer of loam bricks is used under a top flange, which
become crushed under the pressure. Often the labourers break away
some of the common bricks under a shrinking flange. Large loam cores
which would hinder diametral shrinkage have a perpendicular insertion
of loam bricks which yield before the shrinking cylinder. The interior
of a large core is filled with cinders to receive and carry off the gases.
The gases, from the exterior mould are brought out at the top and sides,
the latter being formed with large vent channels arranged in a circle outside
the mould (fig. 18), made with iron rods rammed in the encircling sand, and
withdrawn.
Non-symmetrical Work.—This relates to loam moulds taken from skeleton