_Fig._ 467. represents the general plan of a well-mounted foundry.
_a_, is a cupola furnace of which the section and view will be
afterwards given; it is capable of containing 5 tons of cast-iron.
_a´_, is a similar furnace, but of smaller dimensions, for bringing down
1-3/4 tons.
_a´´_, is a furnace like the first, in reserve for great castings.
_b_, _b_, _b_, _b_, a vast foundry apartment, whose floor to a yard in
depth, is formed of sand and charcoal powder, which have already been
used for castings, and are ready for heaping up into a substratum, or to
be scooped out when depth is wanted for the moulds. There are besides
several cylindrical pits, from five to seven yards in depth, placed near
the furnaces. They are lined with brick work, and are usually left full
of moulding sand. They are emptied in order to receive large moulds,
care being had that their top is always below the orifice from which the
melted metal is tapped.
These moulds, and the ladles full of melted metal are lifted and
transported by the arm of one or more men, when their weight is
moderate; but if it be considerable, they are moved about by cranes
whose vertical shafts are placed at _c_, _d_, _e_, in correspondence, so
that they may upon occasion transfer the load from one to another. Each
crane is composed principally of an upright shaft, embraced at top by a
collet, and turning below upon a pivot in a step; next of a horizontal
beam, stretched out from nearly the top of the former, with an oblique
stay running downwards, like that of a gallows. The horizontal beam
supports a movable carriage, to which the tackle is suspended for
raising the weights. This carriage is made to glide backwards or
forwards along the beam by means of a simple rack and pinion mechanism,
whose long handle descends within reach of the workman’s hand.
[Illustration: 467]
By these arrangements in the play of the three cranes, masses weighing
five tons may be transported and laid down with the greatest precision
upon any point whatever in the interior of the three circles traced upon
_fig._ 467. with the points _c_, _d_, _e_, as centres.
_c_, _d_, _e_, are the steps, upon which the upright shafts of the three
cranes rest and turn. Each shaft is 16 feet high.
_f_, _f_, is the drying stove, having its floor upon a level with that
of the foundry.
_f´_, _f´_, is a supplementary stove for small articles.
_g_, _g_, _g_, are the coaking ovens.
_h_, is the blowing machine or fan.
_i_, is the steam-engine, for driving the fan, the loam-edge stones,
_k_, and the charcoal mill.
_i´´_, are the boiler and the furnace of the engine.
_k´_, workshop for preparing the loam and other materials of moulding.
_l_, is the apartment for the patterns.
The pig-iron, coals, &c. are placed either under sheds or in the open
air, round the above buildings; where are also a smith’s forge, a
carpenter’s shop, and an apartment mounted with vices for chipping and
rough cleaning the castings by chisels and files.
Such a foundry may be erected upon a square surface of about 80 yards in
each side, and will be capable, by casting in the afternoon and evening
of each day, partly in large and partly in small pieces, of turning out
from 700 to 800 tons per annum, with an establishment of 100 operatives,
including some moulding boys.
_Of making the Moulds._--1. Each mould ought to present the exact form
of its object.
2. It should have such solidity that the melted metal may be poured into
it, and fill it entirely without altering its shape in any point.
3. The air which occupies the vacant spaces in it, as well as the
carburetted gases generated by the heat, must have a ready vent; for if
they are but partially confined, they expand by the heat, and may crack,
even blow up the moulds, or at any rate become dispersed through the
metal, making it vesicular and unsound.