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."