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THE wide range of Edison's activities in
this department of the arts is well represented
in the diversity of the numerous patents that
have been issued to him from time to time.
These patents are between fifty and sixty in
number, and include magnetic ore separators of
ten distinct types; also breaking, crushing,
and grinding rolls, conveyors, dust-proof
bearings, screens, driers, mixers, bricking
apparatus and machines, ovens, and processes of
various kinds.
A description of the many devices in each of
these divisions would require more space than is
available; hence, we shall confine ourselves to
a few items of predominating importance, already
referred to in the narrative. commencing with
the fundamental magnetic ore separator, which
was covered by United States Patent No.
228,329, issued June 1, 1880.
The illustration here presented is copied from
the drawing forming part of this patent. A
hopper with adjustable feed is supported several
feet above a bin having a central partition.
Almost midway between the hopper and the bin is
placed an electromagnet whose polar extension is
so arranged as to be a little to one side of a
stream of material falling from the hopper.
Normally, a stream of finely divided ore
falling from the hopper would fall into that
portion of the bin lying to the left of the
partition. If, however, the magnet is
energized from a source of current, the magnetic
particles in the falling stream are attracted by
and move toward the magnet, which is so placed
with relation to the falling material that the
magnetic particles cannot be attracted entirely
to the magnet before gravity has carried them
past. Hence, their trajectory is altered, and
they fall on the right-hand side of the
partition in the bin, while the non-magnetic
portion of the stream continues in a straight
line and falls on the other side, thus effecting
a complete separation.
This simple but effective principle was the one
employed by Edison in his great concentrating
plant already described. In practice, the
numerous hoppers, magnets, and bins were many
feet in length; and they were arranged in
batteries of varied magnetic strength, in order
that the intermingled mass of crushed rock and
iron ore might be more thoroughly separated by
being passed through magnetic fields of
successively increasing degrees of attracting
power. Altogether there were about four hundred
and eighty of these immense magnets in the
plant, distributed in various buildings in
batteries as above mentioned, the crushed rock
containing the iron ore being delivered to them
by conveyors, and the gangue and ore being taken
away after separation by two other conveyors and
delivered elsewhere. The magnetic separators at
first used by Edison at this plant were of the
same generality as the ones employed some years
previously in the separation of sea-shore sand,
but greatly enlarged and improved. The varied
experiences gained in the concentration of vast
quantities of ore led naturally to a greater
development, and several new types and
arrangements of magnetic separators were evolved
and elaborated by him from first to last, during
the progress of the work at the concentrating
plant.
The magnetic separation of iron from its ore
being the foundation idea of the inventions now
under discussion, a consideration of the
separator has naturally taken precedence over
those of collateral but inseparable interest.
The ore- bearing rock, however, must first be
ground to powder before it can be separated;
hence, we will now begin at the root of this
operation and consider the "giant rolls,"
which Edison devised for breaking huge masses of
rock. In his application for United States
Patent No. 672,616, issued April
23, 1901, applied for on July 16,
1897, he says: "The object of my
invention is to produce a method for the breaking
of rock which will be simple and effective, will
not require the hand-sledging or blasting of the
rock down to pieces of moderate size, and will
involve the consumption of a small amount of
power."
While this quotation refers to the method as
"simple," the patent under consideration
covers one of the most bold and daring projects
that Edison has ever evolved. He proposed to
eliminate the slow and expensive method of
breaking large boulders manually, and to
substitute therefor momentum and kinetic energy
applied through the medium of massive machinery,
which, in a few seconds, would break into small
pieces a rock as big as an ordinary upright
cottage piano, and weighing as much as six
tons. Engineers to whom Edison communicated
his ideas were unanimous in declaring the thing
an impossibility; it was like driving two
express-trains into each other at full speed to
crack a great rock placed between them; that no
practical machinery could be built to stand the
terrific impact and strains. Edison's
convictions were strong, however, and he
persisted. The experiments were of heroic
size, physically and financially, but after a
struggle of several years and an expenditure of
about $100,000, he realized the
correctness and practicability of his plans in
the success of the giant rolls, which were the
outcome of his labors.
The giant rolls consist of a pair of iron
cylinders of massive size and weight, with
removable wearing plates having irregular
surfaces formed by projecting knobs. These
rolls are mounted side by side in a very heavy
frame (leaving a gap of about fourteen inches
between them), and are so belted up with the
source of power that they run in opposite
directions. The giant rolls described by
Edison in the above- named patent as having
been built and operated by him had a combined
weight of 167,000 pounds, including all
moving parts, which of themselves weighed about
seventy tons, each roll being six feet in
diameter and five feet long. A top view of the
rolls is shown in the sketch, one roll and one
of its bearings being shown in section.
In Fig. 2 the rolls are illustrated
diagrammatically. As a sketch of this nature,
even if given with a definite scale, does not
always carry an adequate idea of relative
dimensions to a non-technical reader, we
present in Fig. 3 a perspective illustration
of the giant rolls as installed in the
concentrating plant.
In practice, a small amount of power is applied
to run the giant rolls gradually up to a surface
speed of several thousand feet a minute. When
this high speed is attained, masses of rock
weighing several tons in one or more pieces are
dumped into a hopper which guides them into the
gap between the rapidly revolving rolls. The
effect is to partially arrest the swift motion of
the rolls instantaneously, and thereby develop
and expend an enormous amount of kinetic energy,
which with pile-driver effect cracks the rocks
and breaks them into pieces small enough to pass
through the fourteen- inch gap. As the power
is applied to the rolls through slipping
friction-clutches, the speed of the
driving-pulleys is not materially reduced;
hence the rolls may again be quickly speeded up
to their highest velocity while another load of
rock is being hoisted in position to be dumped
into the hopper. It will be obvious from the
foregoing that if it were attempted to supply the
great energy necessary for this operation by
direct application of steam-power, an engine of
enormous horse-power would be required, and
even then it is doubtful if one could be
constructed of sufficient strength to withstand
the terrific strains that would ensue. But the
work is done by the great momentum and kinetic
energy obtained by speeding up these tremendous
masses of metal, and then suddenly opposing
their progress, the engine being relieved of all
strain through the medium of the slipping
friction-clutches. Thus, this cyclopean
operation may be continuously conducted with an
amount of power prodigiously inferior, in
proportion, to the results accomplished.
The sketch (Fig. 4) showing a large boulder
being dumped into the hopper, or roll-pit,
will serve to illustrate the method of feeding
these great masses of rock to the rolls, and
will also enable the reader to form an idea of
the rapidity of the breaking operation, when it
is stated that a boulder of the size represented
would be reduced by the giant rolls to pieces a
trifle larger than a man's head in a few
seconds.
After leaving the giant rolls the broken rock
passed on through other crushing-rolls of
somewhat similar construc- tion. These also
were invented by Edison, but antedated those
previously described; being covered by Patent
No. 567,187, issued September 8,
1896. These rolls were intended for the
reducing of "one-man-size" rocks to small
pieces, which at the time of their original
inception was about the standard size of similar
machines. At the Edison concentrating plant
the broken rock, after passing through these
rolls, was further reduced in size by other
rolls, and was then ready to be crushed to a
fine powder through the medium of another
remarkable machine devised by
NOTE.--Figs. 3 and 4 are reproduced
from similar sketches on pages 84 and 85 of
McClure's Magazine for November, 1897,
by permission of S. S. McClure Co.
Edison to meet his ever-recurring and
well-defined ideas of the utmost economy and
efficiency. The best fine grinding- machines
that it was then possible to obtain were so
inefficient as to involve a loss of 82 per
cent. of the power applied. The thought of
such an enormous loss was unbearable, and he did
not rest until he had invented and put into use
an entirely new grinding-machine, which was
called the "three-high" rolls. The device
was covered by a patent issued to him on
November 21, 1899, No.
637,327. It was a most noteworthy
invention, for it brought into the art not only
a greater efficiency of grinding than had ever
been dreamed of before, but also a tremendous
economy by the saving of power; for whereas the
previous efficiency had been 18 per cent. and
the loss 82 per cent., Edison reversed these
figures, and in his three-high rolls produced a
working efficiency of 84 per cent., thus
reducing the loss of power by friction to 16
per cent. A diagrammatic sketch of this
remarkable machine is shown in Fig. 5, which
shows a front elevation with the casings,
hopper, etc., removed, and also shows above
the rolls the rope and pulleys, the supports for
which are also removed for the sake of clearness
in the illustration.
For the convenience of the reader, in referring
to Fig. 5, we will repeat the description of
the three-high rolls, which is given on pages
487 and 488 of the preceding narrative.
In the two end-pieces of a heavy iron frame
were set three rolls, or cylinders--one in the
centre, another below, and the other
above--all three being in a vertical line.
These rolls were about three feet in diameter,
made of cast-iron, and had face-plates of
chilled-iron.[31] The lowest roll was set
in a fixed bearing at the bottom of the frame,
and, therefore, could only turn around on its
axis. The middle and top rolls were free to
move up or down from and toward the lower roll,
and the shafts of the middle and upper rolls were
set in a loose bearing which could slip up and
down in the iron frame. It will be apparent,
therefore, that any material which passed in
between the top and the middle rolls, and the
middle and bottom rolls, could be ground as fine
as might be desired, depending entirely upon the
amount of pressure applied to the loose rolls.
In operation the material passed first through
the upper and middle rolls, and then between the
middle and lowest rolls.
This pressure was applied in a most ingenious
manner. On the ends of the shafts of the bottom
and top rolls there were cylindrical sleeves, or
bearings, having seven sheaves in which was run
a half-inch endless wire rope. This rope was
wound seven times over the sheaves as above, and
led upward and over a single-groove sheave,
which was operated by the piston of an
air-cylinder, and in this manner the pressure
was applied to the rolls. It will be seen,
therefore that the system consisted in a single
rope passed over sheaves and so arranged that it
could be varied in length, thus providing for
elasticity in exerting pressure and regulating it
as desired. The efficiency of this system was
incomparably greater than that of any other known
crusher or grinder, for while a pressure of one
hundred and twenty-five thousand pounds could be
exerted by these rolls, friction was almost
entirely eliminated, because the upper and lower
roll bearings turned with the rolls and revolved
in the wire rope, which constituted the bearing
proper.
Several other important patents have been issued
to Edison for crushing and grinding rolls, some
of them being for elaborations and improvements
of those above described but all covering methods
of greater economy and effectiveness in
rock-grinding.
Edison's work on conveyors during the period of
his ore- concentrating labors was distinctively
original, ingenious and far in advance of the
times. His conception of the concentrating
problem was broad and embraced an entire system,
of which a principal item was the continuous
transfer of enormous quantities of material from
place to place at the lowest possible cost. As
he contemplated the concentration of six thousand
tons daily, the expense of manual labor to move
such an immense quantity of rock, sand, and ore
would be absolutely prohibitive. Hence, it
became necessary to invent a system of conveyors
that would be capable of transferring this mass
of material from one place to another. And not
only must these conveyors be capable of carrying
the material, but they must also be devised so
that they would automatically receive and
discharge their respective loads at appointed
places. Edison's ingenuity, engineering
ability, and inventive skill were equal to the
task, however, and were displayed in a system
and variety of conveyors that in practice seemed
to act with almost human discrimination. When
fully installed throughout the plant, they
automatically transferred daily a mass of
material equal to about one hundred thousand
cubic feet, from mill to mill, covering about a
mile in the transit. Up and down, winding in
and out, turning corners, delivering material
from one to another, making a number of loops in
the drying-oven, filling up bins and passing on
to the next when they were full, these conveyors
in automatic action seemingly played their part
with human intelligence, which was in reality
the reflection of the intelligence and ingenuity
that had originally devised them and set them in
motion.
Six of Edison's patents on conveyors include a
variety of devices that have since came into
broad general use for similar work, and have
been the means of effecting great economies in
numerous industries of widely varying kinds.
Interesting as they are, however, we shall not
attempt to describe them in detail, as the space
required would be too great. They are specified
in the list of patents following this Appendix,
and may be examined in detail by any interested
student.
In the same list will also be found a large
number of Edison's patents on apparatus and
methods of screening, drying, mixing, and
briquetting, as well as for dust-proof
bearings, and various types and groupings of
separators, all of which were called forth by
the exigencies and magnitude of his great
undertaking, and without which he could not
possibly have attained the successful physical
results that crowned his labors. Edison's
persistence in reducing the cost of his
operations is noteworthy in connection with his
screening and drying inventions, in which the
utmost advantage is taken of the law of
gravitation. With its assistance, which cost
nothing, these operations were performed
perfectly. It was only necessary to deliver the
material at the top of the chambers, and during
its natural descent it was screened or dried as
the case might be.
All these inventions and devices, as well as
those described in detail above (except magnetic
separators and mixing and briquetting
machines), are being used by him to-day in the
manufacture of Portland cement, as that
industry presents many of the identical problems
which presented themselves in relation to the
concentration of iron ore.
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