[Illustration: Casting.]
Next to iron, perhaps brass is the metal chiefly employed in the
manufacture of articles of daily use, and the trade of the Brassfounder
is therefore of very great importance, especially in connexion with the
small metal fittings, such as catches, locks, bolts, hooks, screws, and
other objects used in completing and furnishing the house.
Brass is not a pure metal, but is what is called an alloy, that is, a
mixture of various metals. It is composed of copper and zinc in such
proportions as may be necessary to obtain various degrees of hardness
and colour, according to the use for which the compound is to be
employed. The best proportions for common brass are about two parts of
copper to one part of zinc. Formerly brass was made by heating copper
with _calamine_ (which is the ore of zinc) and charcoal, but it is now
formed from melting the two metals together. It is then cast into plates,
which are either broken up for recasting into any required form, or
rolled into sheets. Common brass is very malleable, is more easily melted
than copper, and may be cast into any form. It will take a very high
polish, does not rust or tarnish by exposure to the air, and, although
it is durable in wear, is sufficiently soft to yield readily to the file
and other tools used by the workmen. These properties make it useful for
a great variety of purposes where steel or iron could not be so well
employed.
[Illustration: Crucible. Magnet.]
The smelting or mixing houses where the brass is made are fitted with air
furnaces, and in some of the best workshops the _crucibles_ or melting
pots are made of _plumbago_ or pure blacklead, which, although it is more
expensive, is much more durable than the Stourbridge clay, of which the
commoner crucibles are formed.
A very fine quality of brass for best castings consists of three parts
of best selected copper, and two of spelter, with some best scrap
brass and a little tin; while a second quality is formed of two parts
of ordinary copper and one part of spelter, melted into ingots with a
proportion of scrap brass and brass filings. Before the latter are used
the iron filings are separated from them by a _magnet_, or by a series of
magnets fastened to a revolving chain frame.
The sheet brass is procured from the mills where it is rolled, and the
brass wire is also supplied from the special manufactories where it is
drawn ready for use.
[Illustration: Making Moulds.]
The method of _making moulds_ for casting iron has already been
mentioned, and those employed by the Brassfounder are quite similar, the
tools used by the mould maker being the _trowel_, _mallet_, _rule_, and
_sand hook_, the _shovel_ for removing the sand, the _brush_ for sweeping
the surface, the _bellows_ for blowing off the dust, and the _compasses_
for measuring accurately.
[Illustration: Brush. Sand Hook. Compasses. Bellows. Shovel. Rule.
Trowel. Mallet.]
The principal materials for making foundry moulds for brass castings are
fine sand and loam mixed in various proportions, according to the nature
of the work. New sand is used for fine castings, old sand for ordinary
work. The requisite external support is given by a couple of shallow
rectangular iron frames without tops or bottoms, called _flasks_ or
_casting boxes_.
The two halves constituting a casting box carry ears corresponding
exactly with one another, one set pierced with holes, the other furnished
with points entering truly into these holes, and which may be made fast
in them by cross-pins or wedges. One of the flasks is laid face downward
on a board longer and wider than it, and is then rammed full of moulding
sand; the surface is struck off level with a straight metal bar or
scraper, a little loose sand is sprinkled upon it, and another board
of proper size placed over it and rubbed down close. The two boards
and the flask contained between them are turned over and the top board
is taken off; the clean surface of moist sand now exposed is dusted
over with perfectly dry fine parting sand, or very fine red brickdust.
The patterns or models are now properly arranged on the surface of the
same, the cylindrical or thick parts being partly sunk in the latter,
and care being also taken to leave sufficient space between the several
patterns to prevent one part breaking into the other, and also passages
or _ingates_, by which to pour in the metal and allow the air to escape.
The patterns are arranged on both sides a central passage or runner,
technically called a _ridge_, from which again small lateral passages
are made, leading into every section of the mould. The general surface
is then properly arranged with the aid of small _trowels_, and a little
fine parting sand or brickdust is shaken over it. When this has been
accomplished, the upper part of the flask is fitted to the lower by the
pins, and then also rammed full of mould sand. The fine dry parting sand
or brickdust serves to prevent the two halves from sticking together. A
board is now placed on the top of the upper half, and struck smartly in
different places with a mallet, after which the upper half and its board
are lifted up very gently and quite level, and then turned over, so that
the upper half rests inverted on its board. The models are next removed,
and channels scooped out from the cavities left by them to the hollows
or pouring holes (_ingates_) at the end of the flask. Solid _cores_ of
sand or metal are adjusted in the proper places when the article is
required to be cast hollow (brass cocks, for instance), and also iron
rails intended to have brass heads cast on them, or such other articles
of iron as are required to be solidly united with the brass. The faces of
both halves are now finally dusted with waste flour or meal dust; the two
halves are then replaced upon each other, and the box is fixed together
by screw clamps. The moulds for _fine castings_ (articles with ornamental
surfaces, as screens, sconces, bell-levers, &c.) are faced with various
fine substances, such as charcoal, loamstone, rottenstone, &c. that
they may retain a sharp impression; after which they are most carefully
dried. For ordinary work it is generally considered better that the sand
should retain a little moisture, though great care must be taken in this
respect, to guard against the danger of explosion.
[Illustration: Braces. Set Moulds. Cores.]
The _mould_ then is a square frame, mostly of iron, filled with peculiar
dark red sand, which is pressed into a firm mass, in which the patterns
of the casting are imbedded and their perfect shape impressed. The
casters work at a large _trough_ filled with the sand, and the workshop,
with its forge, has some resemblance to a bakehouse where black bread
is being kneaded into loaves. The first mould is made for what is called
the “odd side” of the pattern—that is to say (in solid castings), the
lower, or inferior side—and this serves as a sort of pattern to which
the moulder refers in fine castings. The pattern being lifted off or
out as soon as the sand-mould is sufficiently solid, the whole surface,
in which the chasing of the pattern is clearly defined, is dusted with
bean-floor or pounded “pot” first, and afterwards with loam, sand,
charcoal, or coal-dust. This has the effect of making a smooth surface,
and effectually filling the interstices in the sand, so as to prevent any
raggedness in the casting. Each mould, or rather the two sides of the
mould, are then placed near the surface and slightly baked, a channel
having been made in the edge of each for conducting the melted metal
to the pattern. The two sides are then placed together and held firmly
by their pins and sockets, and the mould is ready for the casting. The
“pots,” or crucibles of greyish clay, which turn red by the action of
the fire, are in the furnaces like so many tall flower-pots. The dirty
yellowish brass ingots, made on the premises at a large mixing furnace,
having been first placed across the tops of the pots, that they may
expand before being melted, are about twenty minutes afterwards reduced
to a molten mass, above which hovers a light sea-green flame mingled with
streaks of brilliant colour, like the water from a dyehouse; meanwhile
the moulds have been placed in a slanting position, with the opening in
the side upwards, against a bank of sand or brickwork, and everything is
prepared for pouring. A man, who should be strong in the wrist, stands
on the _furnace_, which has the openings at the top, like a French
cooking-stove, and taking off the brick covers from the square aperture,
whence rushes out a tongue of green flame, lifts out the _pot_ with a
pair of _tongs_, and after the dross is removed by the _skimmer_ or
_grunter_, hands it to the pourer, who fills each mould in succession.
The fumes which rise from the midst of the coloured fire are peculiar
and penetrating, and the zinc eliminated from the molten brass falls in
a metallic snowstorm, its flaky particles adhering to everything with
which they come in contact, while the resistance of the sand to the metal
causes a series of reports like muffled pistol-shots.
[Illustration: Large Tongs. Small Tongs. Pot Holes. Skimmer. Grunter.]
The brass cocks and plugs used in gas-fittings are all cast in one
central stem, like cherries on a stick, their hollow forms being secured
by means of _cores_ made of hardened sand placed in the shape impressed
in the mould. These are broken off the central stem with a pair of
_pincers_ immediately after casting.
The ornamental “vases” and larger ornaments which form the body of
ordinary gas chandeliers and lamps are formed out of thin metal by a
process called “stamping out,” the plates of metal being placed on a
hollow die, upon which a heavy hammer, or rather weight, is brought
down, being released from a latch and worked by the foot. The depth of
the casting would make so heavy a blow necessary that there would be
danger of splitting the metal, an accident which is prevented by the
introduction of a leaden shape and a layer of clay, which is decreased
after each blow of the hammer until the proper depth is gradually secured
without injury.
The process called “reversing” is an operation which secures a hollow
casting, the inner or hollow side being called the “reverse.” For this
purpose a mould is made from one in wax, and the impression in the mould
hardened, so that another model can be taken from it. This enables the
moulder to secure a core which fits the impression in the mould, as
one cup would stand inside another; and between the mould containing
the sunk pattern and that with the projecting core there are placed
strips of black clay, to secure sufficient thickness of metal, by not
allowing the hollow to be too accurately filled. The pattern when cast
is “laid out” on a hollow hemisphere of iron filled with pitch, and the
irregularities of the casting removed by hand tools, _files_, _rasps_,
and _knives_. In the case of figures, such as cupids, &c. forming
ornaments for candelabra, the various limbs have often to be modelled
in separate “cores,” which are afterwards baked hard, and put together
like a puzzle-map, imbedded in the sand of the mould previous to casting.
This requires great skill to effect successfully, and an experienced
“reverser” is a man of mark in the factory.
[Illustration: Fork. Vent Wire. Sleeking Tool. Rasp. File. Vice. Pincers.
Hammer. Double-headed Knife. Saw. Drawing Knife. Knife.]
The completed castings are now removed to the chasing-room, where we may
watch the gradual process of beautifying to which they are subjected, and
the sharpening of the ornamental details by means of _tool_ and _graver_,
in a similar way to the first rough “laying-out,” which removes the
irregularities of the pattern. The arms and branches which form a part of
the gas chandelier work, as well as many of the scroll-work ornaments,
are cast in halves, which are taken to the soldering-room, where a
workman, seated at a forge-like furnace, heats them in the burning
embers, and applies to the edges the solder, with which is mingled a
flux of borax and water to secure its melting. The heat is increased by
a blowpipe, which is in reality a double or jacketed tube, the inner
one supplying gas, and the outer being connected with a large pair of
bellows, and mixing atmospheric air with the lighted gas at the point of
combustion.
The pickling room is a large shed-like place filled with tubs, troughs,
and earthen pans. Into one of these, containing diluted aqua-fortis, the
metal is plunged for the purpose of removing the scale produced on the
surface by the action of the fire; from this it is dipped in a stronger
solution, to undergo the process called “fizzing,” and its final baptism
in pure acid restores the beautiful primrose colour which properly
belongs to it. It is still dull, however, and goes to be “scratched,” an
operation effected by means of a revolving wire-brush, turned by a wheel
and treadle, and kept continually wet with water.
The ornamental processes have next to be considered, and these are
many. Previous to burnishing, the work is dipped in argot or tartar
(the lees of wine-casks steeped in water), so that it may be subject to
a strong antioxyde. The burnishing itself produces those bright veins
and ornamental surfaces so often seen in brass work, and is effected by
fixing the work in a vice, and rubbing the parts of the pattern which are
to be brightened with a steel tool having a smooth bevel edge. After
being treated with ox-gall, bean flour, and acid, to remove any still
adhering grease, the work is dried, by being first dipped in hot water
and afterwards buried in a pan of warm sawdust. Then there is lacquering,
both black and white, a simple process enough, since the lacquer is laid
on with a brush, and the work dried on a warm plate. Much of the work of
the Brassfounder, as far as regards these latter operations, is of course
effected by machinery, but the casting itself is entirely completed by
the skill of the workmen.
[Illustration]