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Full text of "Modern Mechanical Engineering Vol-I"

EXAMPLES OF WORK

79

Fig. 49.—Segmental Piece for
Rim of Fly-wheel

Fig. 50.—Core Box for Fly-
wheel, half boss

face by stopping-off, and centring the arms with a gauge, and, if required,

pulleys of wider faces than the rims by " drawing". Double-armed
castings are made from the same sets. From the
same pattern parts, castings are " split" in halves by
the insertion of lugs and prints to receive the split-
ting plates.

Fly-wheels.—The rims of these (fig. 47) are
built up with segments, and the arms, locked about
the centre, are sunk into the
rim during the course of build-
ing-up. Bosses are studded
at the centre. Patterns of wood
are suitable, except for highly
repetitive orders, for which
metal is substituted, in which
case the work is machine-
moulded. All fly-wheels, ex-
cept those of small diameter,
have arms. These may be
straight, but are preferably
curved to accommodate
shrinkage movements. The

smaller wheels have single curves, the larger generally double.     But solid-
cast arms are not safe for the larger wheels, which are either provided

with those of wrought iron, or the arms and

rim are cast in separate pieces and bolted or

cottered  together.     When large wheels are

cast with arms intact, these are made in cores,

for which the pattern-maker provides a box,

and also sweeping boards to form the rim.
When a wheel has cast-iron arms, the form

of core box used is shown in fig. 48.   The

arm piece is one-half the thickness of the arm

section, so that two cores are jointed to include

the mould for the complete arm.   The box is

shown as for a six-armed wheel, the jointing

angle at the centre which contains the boss

section being therefore 60°.   The outer radius

is that of the interior of the rim.   The notches,

cut in the edges of the   box   frame, receive

the grid which sustains the core.   Rims of any

section can be produced with sweeping boards

and sectional ramming blocks.

When  wheels   have wrought-iron arms,

these are cast into bosses in rim and central boss.   Obviously down-jointing

cannot be done, and therefore the upper halves of the rim bosses and their

Fig. 51.—Pattern Boss for Fly-wheel