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Full text of "Modern Mechanical Engineering Vol-I"

112

FOUNDRY WORK

iff

I

made excellent chargemen and foremen. They only survive in the ranks
of the older men. Each department now employs its own sets of hands,
producing the same classes of castings the year through. Moulders, like
machinists, are specialists. Only in the general jobbing and repair shops
do exceptions occur.
Foundry Metal.—This includes cast iron in its numerous grades, the
steels, malleable cast iron, the immense groups of brasses and bronzes,
alloys of copper, aluminium and its alloys, and the varied die-casting alloys.
Many of these are now graded by analysis and by the scleroscope, instead of,
as of old, by the foreman estimating by the aspect of fractured surfaces,
supplemented by test bar results. For melting, the cupola furnace occurs in
many excellent designs, with its equipment of fan or blower, blast gauge,
platform, weighing machine, receiver or ladles. Brass-melting furnaces
are coke-fired, or oil- or electrically-heated, with provisions for utilizing
the waste heat. Steels are melted in converters of large and small capacities;
malleable cast iron in air furnaces.
Sands.—In a foundry equipped with modern appliances, the prepara-
tion of sands is done wholly with machinery. It takes charge of them at
every stage, drying, crushing, grinding, mixing, sifting, and conveying.
Suitable mixtures have to be graded for green, dry, core, and loam sands,
and again for light and heavy moulds. They differ also for steel and iron,
and facings for the moulds are varied. For this work, a complete mechanical
plant is often now installed.
The Treatment of Castings.—This, colloquially denoted by the
terms " fettling " and " dressing ", engages, in the big advanced foundries,
a large quantity of machinery and plant, doing work that was formerly all
performed by hand methods. It includes: machines for severing the runners,
with chisels or with saws; grinding wheels; pneumatic chisels for the
removal of fin marks and roughnesses; tumbling barrels for smoothing
castings by attrition; and, in the later plants, sand-blasting machines, now
made in many designs to deal with castings of all dimensions. In the more
complete plants, dust-exhausting systems of pipes with exhausters are
installed.
To deal adequately with all the aspects of foundry work outlined in the
preceding paragraphs is obviously not practicable. Neither does it seem to
be called for. Each single subject is now highly specialized. The foundry
craftsman is only directly concerned with and responsible for the preparation
of the moulds. The sands are prepared for his use, the metal is graded,
suitably melted, and brought to him, the patterns are prepared to be moulded
in a certain way, from which no essential departure can be made, and he
has no further concern with the castings if they are turned soundly out of
the moulds. Bearing these facts in mind, it is proposed to occupy the
major portion of this article with the subject of the preparation of moulds
required for the metals and alloys, leaving the collateral matters to be dealt
with in a summary fashion.