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Full text of "Modern Mechanical Engineering Vol-I"

EXAMPLES OF  WORK

99

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boxes, elements which in most instances bear only a remote resemblance
le casting, and which have to be supplemented with drawings, sketches,
-erbal instructions. Nearly all this work is moulded in. the floor and
:red with a plain top, in which pattern parts may be set by measurement,
ome cases the moulds are " open ". Most foundry tools, such as loam
2S and rings, gaggers, back plates, core plates, and the larger moulding
2S are made thus.

The first stage in making moulds of these kinds is the preparation of a
I   bed,  for  which   the

Jlel strips and the spirit-         ____LL

1 are requisitioned, or a
2ping board is worked
id a central bar. The
;r method is usually em-
red when a central boss,
alar facings, or shoul-
?d sections are wanted.
;se are formed by the
3 of the board, suitably
iled, the top edge of the
rd, parallel with the
:om, being set horizon-
7 with the spirit-level.
5 bed is vented to a
ler bed below, and the
ild is made on it from
sectional parts which the
:ern-maier supplies.
Broadly, moulds may be
aped as rectangular or
ular in plan. The first
be produced by the aid

hallow Strips Or Of deeper    Fig. 81.—Skeleton Pattern from which aU the Outer Mould is taken

rds set on the bed by

isurement, and retained in position with weights, against which the
d is rammed. Any extraneous portions, as strips, lugs, bosses, or
its, are set in their positions and rammed. A complete frame may be
ie (fig. 81) instead of separate strips, the outer mould being rammed
and it and supplementary parts attached, thus relieving the moulder of
responsibility of setting parts by measurement. If the interior is that of
bbed casting, that is formed wholly with cores.

Moulds which are circular in plan are produced by the aid of " sweeped "
ions. Any shape required can be readily Imparted to these (fig. 8z and
. As the length of the section is only 10 in. or 12 in., it has to he moved
nd and reset for successive rarnrnings. It is convenient to attach the
cxk to a radius bar worked round a centre pin. But this is not necessary,