ELECTRICAL PRODUCTS CARBORUNDUM.
The production of electricity in such
enormous quantities as are generated at Niagara Falls
has led to many discoveries and will lead to many
more. Products that at one time existed only in
the chemical laboratory for experimental purposes,
have been so cheapened by utilizing electrical energy
in their manufacture, as to bring them into the play
of every-day life. Still other products have only
been discovered since the advent of heavy electrical
currents. A substance called carborundum, which
was discovered as late as 1891, has now become the
basis of an industry of no small importance. It
is a substance not unlike a diamond in hardness, and
not very unlike it in its composition. The chief
use to which it is put is for grinding metals and all
sorts of abrasive work. It is manufactured into
wheels, in structure like the emery-wheel, and serves
the same purpose. It is much more expensive than
the emery-wheel, but it is claimed that it will do
enough more and better work to make it fully as economical.
It was my pleasure and privilege to
visit the factory at Niagara Falls, and through the
courtesy of Mr. Fitzgerald, the chemist in charge of
the works, I learned much of the manufacture and use
of carborundum. The crude materials used in the
manufacture of carborundum are, sand, coke, sawdust
and salt; the compound is a combination of coke and
sand. It combines at a very high heat, such as
can be had only from electricity. When cooled
down the product forms into beautiful crystals with
iridescent colors. The predominating colors are
blue and green, and yet when subjected to sunlight
it shows all the colors of the solar spectrum to a
greater or less degree. The crystals form into
hexagonal shapes, and sometimes they are quite large,
from a quarter to a half inch on a side. The
salt does not enter into the product as a part of the
compound, neither does the sawdust. The salt acts
as a flux to facilitate the union of the silica and
carbon. The sawdust is put into the mixture to
render it porous so that the gases that are formed
by the enormous heat can readily pass off, thus preventing
a dangerous explosion that might otherwise occur.
In fact, these explosions have occurred, which led
to the necessity of devising some means for the ready
escape of the gases.
The process of manufacture as it is
carried on at Niagara is interesting. The visitor
is first taken into the rooms where are stored the
crude material, the sand, coke, sawdust and salt.
The sand is of the finest quality and very white.
The coke is first crushed and screened, the part which
is reduced to sufficient fineness is mixed by machinery
with the right proportion of sand, salt and sawdust.
The coarser pieces of coke are used for what is called
the core of the furnace, which will be described later
on.
This mixture is carried to the furnace-room,
which has a capacity for ten furnaces, but not all
of these will be found in operation at one time.
Here the workmen will be taking the manufactured material
from a furnace that has been completed, and there
another furnace is in process of construction, while
a third is under full heat, so that one sees the whole
process at a glance. These furnaces are built
of brick, about sixteen feet in length and about five
feet in width and depth. The ends and bed of
the furnace are built of brick, and might be called
stationary structures. The sides are also built
of brick laid up loosely without mortar; each time
the material is placed in the furnace, and each time
the furnace is emptied, the side-walls are taken down.
A furnace is made ready for firing
by placing a mass of the mixture on the bottom, and
building the sides up about four feet high (or half
the height when it shall be completed). A trough,
about twenty or twenty-one inches wide and half as
deep, is scooped out the whole length of the pulverized
stuff, and in this is placed what has before been referred
to as the core of the furnace, namely, pure coke broken
into small pieces, but not pulverized, as in the case
of the other mixture. The amount used is carefully
weighed, so as to have the core the proper size that
experiment has proved to give the best results.
The core is filled in and rounded over till it is
in circular form, being about twenty-one inches in
diameter. At each end of the furnace the core
connects with a number of carbon rods about
sixty in all that are thirty inches long
and three inches in diameter. These carbon rods
are connected with a solid iron frame that stands
flush with the outer end of the furnace. On the
inside the spaces between the rods are packed full
of graphite, which is simply carbon or coke with all
the impurities driven out, so as to make good electrical
connections with the core. This core corresponds,
electrically speaking, to the filament in an ordinary
incandescent lamp, only it is fourteen feet long and
twenty-one inches in diameter. The mixed material
is now piled up over this core, and the walls at the
sides are built up until the whole structure stands
about eight feet from the floor a mass
of the fine pulverized mixture, with a core of broken
coke electrically connected at the ends. It is
now ready for the application of electricity, which
completes the work.
Let us go back to the transformer-room
and examine the electrical appliances that bring the
current down to a proper voltage to produce the heat
necessary to cause a union between the silica of the
sand and the carbon of the coke, which results in
the beautiful carborundum crystals that we have heretofore
described.
The current is delivered from the
Niagara Power Company under a pressure of 2200 volts.
The conductors run first into the transformer-room,
which adjoins the furnace-room, and is there transformed
down from 2200 volts to an average of about 200 volts.
The transformers at these works have a capacity of
about 1100 horse-power. About 4 per cent of this
power is converted into heat in the process of transformation,
making a loss in electrical energy of a little over
40 horse-power. This heat would be sufficient
to destroy the transformer if some arrangement were
not provided to carry it off. We have already
described how this is done through the medium of a
circulation of oil. Because of the low voltage
and enormous quantity of the current passing from the
transformer to the furnace very large conductors are
required. The two conductors running to the furnace
have a cross-section of eight square inches, and this
enormous current, representing over 1000 horse-power,
is passed through the core of the furnace, and is
kept running through it constantly for a period of
twenty-four to thirty-six hours.
Let us consider for a moment what
1000 horse-power means; as this will give us some
conception of the enormous energy expended in producing
carborundum. A horse-power is supposed to be the
force that one horse can exert in pulling a load,
and this is the unit of power. However, a horse-power
as arbitrarily fixed is about one-quarter greater than
the average real horse-power. If 1000 horses
were hitched up in series, one in front of the other,
and each horse should occupy the space of twelve feet,
say, it would make a line of horses 12,000 feet long,
which would be something over two miles. Imagine
the load that a string of horses two miles long could
draw, if all were pulling together, and you will get
something of an idea of the energy expended during
the burning of one of these carborundum furnaces.
Within a half hour after the current
is turned on a gas begins to be emitted from the sides
and top of the furnace, and when a match is applied
to it, it lights and burns with a bluish flame during
the whole process. It is estimated that over
five and one-half tons of this gas is thrown off during
the burning of a single furnace. This gas is called
carbon monoxide, and is caused by the carbon of the
coke uniting with the oxygen of the sand. When
we consider the vast amount of material that comes
away from the furnace in the form of gas it is easy
to see why it is necessary to introduce sawdust or
some equivalent material into the mixture, in order
to give the whole bulk porosity, so that the gas can
readily escape. We should also expect that after
five and one-half tons had been taken away from the
whole bulk that it would shrink in size. This
is found to be the case. The top of the mass of
material sinks down to a considerable extent by the
end of the time it has been exposed to this intense
heat. Gradually, after the current has been turned
on, the core becomes heated, first to a red, and afterwards
to an intense white heat. This heat is communicated
to the material surrounding the core, producing various
effects in the different strata, owing to the fact
that it is not possible to keep a uniform heat throughout
the whole bulk of material. Some of it will be
“overdone” and some of it “underdone.”
The material which lies immediately in contact with
the core will be overheated, and that, which at one
stage was carborundum, has become disintegrated by
overheating.
The silica of the compound has been
driven off, leaving a shell of graphitic substance
formed from the coke.
After the current is shut off and
the furnace has cooled down, a cross-section through
the whole mass becomes a very interesting study.
The core itself, owing to the intense heat it has been
subjected to, has had the impurities driven out of
the coke, leaving a substance like black lead, that
will make a mark like a lead-pencil, and is really
the same substance, known as plumbago, in one of its
forms. It is the carbon left after the impurities
have been driven out of the coke. Surrounding
the core for a distance of ten or twelve inches, radiating
in every direction, beautifully colored crystals of
carborundum are found, so that a single furnace will
yield over 4000 pounds of this material. Beyond
this point the heat has not been great enough to cause
the union between the carbon and silica, which leaves
a stratum of partly-formed carborundum; outside of
that the mixture is found to be unchanged.
These carborundum crystals are next
crushed under rollers of enormous weight, after which
the crushed material is separated into various grades
for use in making grinding-wheels of different degrees
of fineness. This crushed material is now mixed
with certain kinds of clay, to hold it together, and
then pressed into wheels of various sizes in a hydraulic
press, and afterward carried into kilns and burned
the same as ordinary pottery or porcelain. These
wheels vary in size from one to sixteen inches.
The substances used as a bond in manufacturing wheels
are kaolin, a kind of clay, and feldspar.
While carborundum has already a large
place as a commercial product, there is no doubt but
that the uses to which it will be put will vastly
increase as time goes on. This product may be
called an artificial one, and never would have been
known had it not been for the intense heating effects
that are obtained from the use of electricity.
It certainly never could have been brought into play
as one of the useful agencies in manufacturing and
the arts. It is not known to exist as a natural
product, which at first thought would seem a little
strange in view of the evidences of intense heat that
at one time existed in the earth. Its absence
in nature is explained by Mr. Fitzgerald by the fact
that “the temperatures of formation and of decomposition
lie very close together.”