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Full text of "Modern Mechanical Engineering Vol-I"

MOULDING  IN  LOAM

127

ments, but always breaking joint.   The bricks, dipped in clay wash, are
embedded in loam, and finely broken cinders  or  coke are inserted at
intervals in the larger spaces to assist in carry-
ing off the vents.    At about every third  or
fourth course, a layer of headers is laid in to
serve as binders.    When a mould is very deep,
an iron ring, inserted about half-way up, will
lessen risk of distortion of the brick walls.

The daubing on of the loam by hand, and
its sweeping with the board proceeds with the
building up of the bricks. From i in. to iŁ in.
of space is left between the faces of the bricks
and the edge of the board. Coarse loam is
used for the greater portion of the thickness,
a finely ground mixture for the facing. On the
completion of the work, the mould is dried,
and blackened with wet blacking, which is
afterwards dried. Venting is not required in
the same degree as in green-sand moulds, be-
cause the loam, when dried is, like dry-sand
moulds, largely self-venting, and the precaution
is taken to occupy all roomy spaces between
bricks with fine cinders. But where large
masses of loam occur, which often happens in
non-symmetrical castings when pattern parts
have to be set in by measurement, the vent
wire is used freely. After these loose parts are
put in position, loam is daubed against them,
still supported against brickwork, and they have
to be left in situ during the drying of the
mould in the stove (figs. 19 and 20). There
is risk, unless care is exercised, of these loose
pieces becoming shifted during the sweeping,
and of their warping in the stove. They must not be varnished, but oiled.

Fig. 19.—Pattern Work for Steam
Chest to be embedded against a swept-
up Loam Mould

0.—Pattern Work for Cylinder Foot to be embedded against a swept-up Loam Mould