By ROBERT F. GIBSON.
SUGAR MACHINES.--Besides separating the crystalline sugar and the
sirup, secondary objects are to wash the crystals and to pack them in
cakes. The cleansing fluid or "white liquor" is introduced at the
center of the basket and is hurled against and passes through the sugar
wall left from draining. The basket may be divided into compartments
and the liquor guided into each. The compartments are removable boxes
and are shaped to give bars or cakes or any form desired of sugar in
mass. These boxes being removable cannot fit tightly against the liquor
guides, and the liquor is apt to escape. This difficulty is overcome by
giving the guides radial movement or by having rubber packing around
the edges.
Sugar machines proper are of two kinds--those which are loaded, drained
and then unloaded and those which are continuous in their working. The
various figures preceding are of the first kind, and what has been said
of vibrations applies directly to these.
The general advantages claimed for continuous working over intermittent
are--that saving is made of time and motive power incident to
introducing charge and developing velocity, in retarding and stopping,
and in discharging; that, as the power is brought into the machine
continuously, no shifting of belts or ungearing is necessary; and that
there are less of the dangers incident to variable motion, either in
the machine itself or the belting or gearing. The magma (the mixture of
crystalline sugar and sirup) is fed in gradually, by which means it is
more likely to assume a position of equilibrium in the basket.
There are two methods of discharging in continuous working--the sugar
is thrown out periodically as the basket fills, or continuously. In
neither case is the speed slackened. In the first either the upper
half of the basket has an upward motion, on the lower half a downward
motion (Pat. 252,483); and through the opening thus made the sugar is
thrown. Fig. 22 (R.B. Palmer & Sons) is a machine of this kind. The
bottom, B, with the cone distributor, _a_, have downward motion.
[Illustration: Fig. 22.]
Continuous discharge of the second kind may be brought about by having
a scoop fixed to the curb (or casing), extending down into the basket
and delivering the sugar over the side (Pat. 144,319). Another method
will be described under "Beet Machines."
BASKET.--The construction of the basket is exceedingly important. Hard
experience has taught this. When centrifugals were first introduced,
users were compelled by law to put them below ground; for they
frequently exploded, owing to the speed being suddenly augmented by
inequalities in the running of the engine or to the basket being too
weak to resist the centrifugal force of the overcharge. Increasing the
thickness merely adds to the centrifugal force, and hence to the
danger, as even a perfectly balanced basket may sever.
One plan for a better basket was to have more than one wall. For
example, there might be an inner wall of perforated copper, then one
of wire gauze, and then another of copper with larger perforations.
Another plan was to have an internal metallic cloth, bearing against
the internally projecting ridges of the corrugations of the basket
wall. A further complication is to give this internal gauze cylinder a
rotation relative to the basket.
The basket wall has been variously constructed. In one case it
consists of wire wound round and round and fastened to uprights,
commonly known as the "wire basket;" in another case of a periphery
without perforations, but spirally corrugated and having an opening at
the bottom for the escape of the extracted liquid; in still another of
a series of narrow bars or rings, placed edgewise, packed as close as
desired. An advantage of this last style is that it is easily cleaned.
The best basket consists of sheet metal with bored perforations and
having bands or flanges sprung on around the outside. The metal is
brass, if it is apt to be corroded; if not, sheet iron. The
perforations may be round, or horizontally much longer than wide
vertically. One method for the manufacture of the basket wall (Pat.
149,553) is to roll down a plate, having round perforations, to the
required thickness, causing narrowing and elongation of the holes and
at the same time hardening the plate by compacting its texture. Long
narrow slots are well adapted to catch sugar crystals, and this is not
an unimportant point. Round perforations are usually countersunk.
Instead of flanges, wire bands have been used, their lapping ends
secured by solder.
As to comparative wear, it maybe remarked that one perforated basket
will outlast three wire ones.
As to size, sugar baskets vary from 80 inches in diameter by 14 in.
depth to 54 by 24. They are made, however, in England as large as 6
feet in diameter--a size which can be run only at a comparatively slow
speed.
A peculiar complication of basket deserves notice (Pat. 275 874). It
had been noticed that when a charge of magma was put into a
centrifugal in one mass, the sugar wall on the side of the basket was
apt to form irregularly, too thick at base and of varied color. To
remedy this it was suggested to have within and concentric with the
basket a charger with flaring sides, into which the mixture was to be
put. When this charger reached a certain rotary velocity, the magma
would be hurled out over the edge by centrifugal force and evenly
distributed on the wall of the main basket.
SPINDLE.--The spindle as now made is solid cast steel, and the
considerations governing its size, form, material, etc., are identical
with those for any spindle. In order that the basket might be replaced
by another after draining, the shaft has been made telescopic, but at
the expense of stability and rigidity. In Fig. 16 is shown a device to
avoid crystallizations, which are apt to occur in large forgings, and
would prove fatal should they creep into the upper part of the spindle
proper in a hanging machine. It consists of the secondary spindle, _c_.
DISCHARGING.--The drained sugar may either be lifted over the top of
the basket (in machines which stop to be emptied), or be cast through
openings in the bottom provided with valves. A section of the best form
of valve may be seen in Figs. 15 and 17. Fig. 23 is a plan of the
openings. The valve turns on the basket bearing. It may be constructed
to open in the same direction in which the basket turns; so that when
the brake is put on, the inertia of the valve operates to open it and
while running to keep it closed. There are many other styles, but no
other need be mentioned.
[Illustration: Fig. 23.]
CASING.--The different styles of casing may be seen by reference to the
various drawings. In one machine (not described) the casing is rigidly
fixed to the basket, space enough being left between the bottom of the
basket and the bottom of the casing to hold all the molasses from a
charge. This arrangement merely adds to the bulk of the revolving
parts, and no real advantage is gained.
BEARINGS.--The various styles of bearings can be seen by reference to
the figures. One which deserves special attention is shown in Fig. 16
and Fig. 19. In one case it consists of loose disks, in the other of
loose washers, rotating on one another. They are alternately of steel
and hard bronze (copper and tin).
"There is probably no machine so little understood or so imperfectly
constructed by the common manufacturer of sugar supplies as the high
speed separator or centrifugal." Unless the product of experience and
good workmanship, it is a dangerous thing at high velocities. Besides,
its usual fate is to have an incompetent workman assigned to it, who
does not use judgment in charging and running. So that designers and
manufacturers have been forced not only to take into account the
disturbing forces inherent in revolving bodies, but also to make
allowance for poor management in running and neglect in cleaning.
CANE AND BEET MACHINES.--The first step in the process of sugar making
is the extraction of the juice from the beet or cane. This juice is
obtained by pressure. The operation is not usually, but may be,
performed in a special kind of centrifugal. One style (Pat. 239,222)
consists of a conical basket with a spiral flange within on the shaft,
and turning on the shaft, and having a slight rotary motion relative to
the basket. The material is fed in and moves downward under increased
pressure, the sirup released flying out through the perforations of the
basket, the whole revolving at high velocity. The solid portion falls
out at the bottom. Another plan suggested (Pat. 343,932) is to let a
loose cover of an ordinary cylindrical basket screw itself down into
the basket, by reason of its slower velocity (owing to inertia),
causing pressure on the charge.
Various other applications of the different styles of sugar machines
are the defibration of raw sugar juice, freeing beet crystals of
objectionable salts, freeing various crystals of the mother liquor,
drying saltpeter.
DRIERS.--Another important division of this first class of centrifugals
is that of driers or, as they are variously styled, whizzers, wringers,
hydro-extractors. The charge in these is never large in weight compared
to a sugar charge, and its initial distribution can be made more
symmetrical. The uses of driers are various, such as extracting water
from clothes, cloth, silk, yarns, etc. Water may be introduced at the
center of the basket from above or below to wash the material before
draining. A typical form of drier is shown in Fig. 24. (Pat. Aug. 22,
1876--W.P. Uhlinger.) Baskets have been made removable for use in
dyeing establishments, basket and load together going into dyeing vat.
Yarn and similar material can be drained by a method analogous to that
of hanging it upon sticks in a room and allowing the water to drip off.
It is suspended from short sticks, which are held in horizontal layers
around the shaft in the basket, and the action is such during the
operation as to cause the yarn to stand out in radial lines.
[Illustration: Fig. 24.]
Driers are not materially different from sugar machines. Any of the
devices before enumerated for meeting vibrations in the latter may be
applied to the former. There is one curious invention which has been
applied to driers only (Pat. 322,762--W.H. Tolhurst). See Fig. 25. A
convex shaft-supporting step resting on a concave supporting base,
with the center of its arc of concavity at the center of the upper
universal joint, has been employed, and its movements controlled by
springs, but the step was apt to be forced from its support. The
drawing shows the improvement on this, which is to give the
shaft-supporting step a less radius of curvature.
[Illustration: Fig. 25.]
An interesting form of drier has its own motor, a little steam engine,
attached to the frame of the machine. See Fig 24. This of course
demands fixed bearings. The engine is very small. One size used is 3"×4".
When a higher velocity of basket is required, we have the arrangement
in Fig. 26.
[Illustration: Fig. 26.]
MOTORS.--This naturally introduces the subject of motive power. We may
have the engine direct acting as above, or the power may be brought on
by belting. Fig. 27 shows a drier with pulley for belting. Fig. 28
(W.H. Tolhurst) shows a very common arrangement of belting and also the
fast and loose pulleys. When the heaviest part of the engine is so far
from the vertical shaft as to overhang the casing on one side, there is
apt to be an objectionable tremor. To remedy this, it is suggested to
put these heavy parts as near the shaft as possible. It has been
suggested also to use the Westinghouse type of engine, although the
type shown in Fig. 24 works faultlessly in practice.
[Illustration: Fig. 27.]
One plan (Pat. 346,030), designed to combine the advantages of a direct
acting motor and an oscillating shaft, mounts the whole machine, motor
and all, on a rocking frame. The spindle is of course in fixed bearings
in the frame. However, the plan is not practical.
[Illustration: Fig. 28.]
In driers the direct acting engine has many advantages over the belt.
The atmosphere is always very moist about a whizzer, and there are
frequently injurious fumes. The belt will be alternately dry and wet,
stretched and limp, and wears out rapidly and is liable to sever. In
all machines in which the shaft oscillates, if the center of
oscillation does not lie in the central plane of the belt, the tension
of the latter is not uniform. This affects badly both the belt and the
running. A reference to the various figures will show the best position
for the pulley.
The greatest difficulty experienced with belting is in getting up speed
and stopping. The basket must not be started with a sudden impulse. Its
inertia will resist and something must give way. A gradual starting can
be obtained by the slipping of the belt at first, but this is
expensive. The best plan is to conduct the power through a species of
friction clutch--an iron disk between two wooden ones. This has been
found to work admirably.
BRAKES.--The first centrifugals had no brakes. They ran until the
friction of the bearings was sufficient to stop them. This occasioned,
however, rapid wearing and too great a loss of time. The best material
for a brake consists of soft wood into which shoe pegs have been
driven, and which is thoroughly saturated with oil. The wooden disks
referred to just above are of the same construction. The center of
oscillation ought to be in the central plane of the brake as well as
that of the pulley, but the preference is given to the pulley.
Figs. 15 and 16 (I) give sectional views of a brake for hanging
machines. Figs. 19, 20, and 21 give two sections and a view of a brake
which can be used on both hanging and standing machines. A very simple
form of brake is shown in Figs. 24, 26, and 27 (A), a mere block
pressing on the rim of the basket.
OIL AND FAT.--A machine in most respects like a whizzer is used for the
"extraction of oil and fat and oily and fatty matters from woolen yarns
and fabrics, and such other fibrous material or mixtures of materials
as are from their nature affected in color or quality when hydrocarbons
are used for the purpose of extracting such oily or fatty matters, and
are subsequently removed from the material under treatment by the slow
process of admitting steam, or using other means of raising the
temperature to the respective boiling points of such hydrocarbons, and
so driving them off by evaporation." In the centrifugal method
carbon-bisulphide, or some other volatile agent, is admitted and is
driven through the material by centrifugal force, when the necessary
reactions take place, and is allowed to escape in the form of
hydrocarbons. A machine differing only in slight particulars from the
above is used for cleansing wool.
LOOSE FIBER.--Another application is the drying of loose fiber. Two
distinctive points deserve to be noticed in the centrifugal used for
this purpose. An endless chain or belt provided with blades moves the
material vertically in the basket, and discharges it over the edge.
During its upward course the material is subjected to a shower of water
to wash it.
OIL FROM METAL CHIPS.--Very material savings are made in many factories
by collecting the metal chips and turnings, coated and mixed with oil,
which fall from the various machines, and extracting the oil
centrifugally. The separator consists of a chip holder, having an
imperforate shell flaring upward and outward from the spindle (in fixed
bearings) to which it is attached. When filled, a cover is placed upon
it and keyed to the spindle. Between the cover and holder there is a
small annular opening through which oil, but not chips, can escape.
Fig. 29 (Pat. 225,949--C.F. Roper) is designed (like the greater part
of the drawings inserted) to show relative position of parts merely,
and not relative _size_. This style of machine can be used for sugar
separating (Pat. 345,994--F.P. Sherman) and many other purposes, to
which, however, there are other styles more especially adapted.
[Illustration: Fig. 29.]
FILTERERS.--There are two distinct kinds of centrifugal filterers,
working on different principles. Petroleum separators (Pat. 217,063)
are of the first kind. They are in form in all respects like a sugar
machine. The flakes of paraffine, stearine, etc., which are to be
extracted, when chilled are very brittle and would be disintegrated
upon being hurled against a plain wire gauze and would escape. Even a
woven fabric presents too harsh a surface. It is necessary to have a
very elastic basket lining of wool, cotton, or other fibrous material.
The basket itself may be either wire or perforated, but must have a
perfectly smooth bottom.
As the pressure of the liquor upon the filtering medium per unit of
surface depends entirely upon its radial depth, mere tubes, connecting
a central inlet with an annular compartment, will serve the purpose
quite as well as a whole basket. In this style of machine (Pat. 10,457)
the filtering material constitutes a wall between two annular
compartments. The outer one is connected with a vacuum apparatus.
Filterers of the second kind work on the following principle: If a
cylinder be rapidly revolved in a liquid in which solid particles are
suspended, the liquid will be drawn into a like rotation and the heavy
particles will be thrown to the outer part of the receptacle. If a
perforated cylinder is used as stirrer, the purified liquid will escape
into it through the perforations and may be conducted away. The
impurities, likewise, after falling down the sides of the receptacle,
are carried off. The advantages of this method are that no filtering
material is needed and the filtering surface is never in contact with
anything but pure liquor.
Very fine sawdust is, to a considerable extent, employed in sugar
refineries as a filtering medium. By such use the sawdust becomes mixed
with sand, fine particles of cane, etc. As sawdust of such fineness is
expensive, it is desirable to purify it in order to reuse it. A
centrifugal (Pat. 353,775--J.V.V. Booraem) built on the following
principle is used for this purpose. It has been observed that by
rotating rather _slowly_ small particles of various substances in
water, the finer particles will be thrown outward and deposit near the
circumference of the vessel, while the heavier and coarser particles
will deposit nearer to or at the center, their centrifugal force not
being sufficient to carry them out. A mere rod, extending radially in
both directions, serves by its rotation to set the water in motion.
Another form of filter of this second kind (Pat. 148,513) has a
rotating imperforate basket into which the impure liquor is run. Within
and concentric with it is another cylinder whose walls are of some
filtering medium. The liquid already partly purified by centrifugal
force passes through into the inner cylinder, thus becoming further
purified. Centrifugal filters are used also to cleanse gums for
varnishes.
HONEY.--The simplest form of honey extractor (Pat. 61,216) consists of
a square framework, symmetrical with respect to a vertical spindle.
This framework is surrounded by a wire gauze. The combs, after having
the heads of the cells cut off, are placed in comb-holders against the
wire netting on the four sides, the cells pointing outward. The machine
is turned by hand. The honey is hurled against the walls of a receiving
case and caught below. But few improvements have been made on this. The
latest machines are still hand-driven, as a sufficiently high velocity
can be obtained in this manner. In one style the combs are placed upon
a floor which rests upon springs. The rotating box is given a slight
vertical and horizontal reciprocatory motion, by which the combs are
made to grate on the wire gauze sides, breaking the cells and
liberating the honey. Thus the labor of cutting the cells is saved.
Every comb has two sides, and to present each side in succession to the
outside without removing from the basket, several devices have been
patented. In some the comb holders are hinged in the corners of the
basket, and have an angular motion of ninety degrees. Decreasing the
speed is sufficient to swing these. The other side is then emptied by
revolving in the opposite direction. In one case each holder has a
spindle of its own, connected with the main spindle by gearing and, to
present opposite side, turns through 180°. The usual number of sides
and hence of comb holders is four, but eight have been used. There are
minor differences in details of construction, looking to the most
convenient removal and insertion of comb, the reception of the
extracted honey in cups, buckets, etc., and the best method of giving
rapid rotation, which cannot be touched upon. The product of the
operation is white and opaque, but upon heating regains its golden
color and transparency.
STARCH.--A centrifugal to separate starch from triturated grain,
carried in suspension in water, is as follows. (Pat. 273,127--Müller &
Decastro.) The starch water is led to the bottom of a basket, and, as
starch is heavier than the gluten with which it is mixed, the former
will be immediately compacted against the periphery of the basket,
lodging first in the lower corner, the starch and gluten forming two
distinct strata. A tube with a cutting edge enters the compacted mass
so deeply as to peel off the gluten and part of the starch, which is
carried through the tube to another compartment of the basket, just
above, where the same operation is performed, and so on. There may be
only one compartment, the tube carrying the gluten directly out of the
machine. These machines are continuous working, and hence some way must
be devised to carry the water off. The inner surface of the water is,
as we have seen, a cylinder. When the diameter of this cylinder becomes
too small, overflow must be allowed. One plan is to have an overflow
opening made in the bottom of the basket in such a way that as the
starch wall thickens, the opening recedes toward the center. The starch
wall is either lifted out in cakes or put again in suspension by
spraying water on it and conducting the mixture off.
A centrifugal (Pat. 74,021) to separate liquids from paints depends on
building a wall of paint on the sides of the basket and carrying the
liquids off at the center.
A centrifugal (Pat. 310,469) for assorting wood pulp, paper pulp, etc.,
works by massing the constituents in two or three cylindrical strata,
and after action severing and removing these separately.
BREWING.--In brewing, centrifugals are quite useful. After the wort has
been boiled with hops, albuminous matters are precipitated by the
tannic acid, which must be extracted. Besides these the mixture
frequently contains husk, fiber, and gluten. The machine (Pat.
315,876), although quite unique in construction, has the same principle
of working as a sugar centrifugal, and need not be described. There is
one point, however, which might be noticed--that air is introduced at
about the same point as the material, and has an oxidizing and
refrigerating effect.
Class I. includes also centrifugals for the following purposes: The
removal of must from the grape after crushing, making butter,
extracting oils from solid fats, separating the liquid and solid parts
of sewerage, drying hides, skins, spent tan and the like, drying coils
of wire.
HORIZONTAL CENTRIFUGALS.--Only vertical machines have been and will be
dealt with. Horizontal centrifugals, that is, those whose spindles are
horizontal have been made, but the great inconvenience of charging and
discharging connected with them has occasioned their disuse; though in
other respects for liquids they are quite as good as vertical
separators. Their underlying theory is practically the same as that
hereinbefore discussed.
CLASS II., CREAMERS.--Centrifugals of the second class separate liquids
from liquids. There are two main applications in this class--to
separate cream from milk and fusel oil from alcoholic liquors. When a
liquid is to be separated from a liquid, the receptacle must be
imperforate. The components of different specific gravity become
arranged in distinct concentric cylindrical strata in the basket, and
must be conducted away separately. In creamers the particles of cream
must not be broken or subjected to any concussion, as partial churning
is caused and the cream will, in consequence, sour more rapidly.
The chief cause of oscillations in machines of this class, where the
charge is liquid, is the waves which form on the inner surface. They
may be met by allowing a slight overflow over the inner edge of the rim
of the basket; or by having either horizontal partitions, or vertical,
radial ones, special cases of which will be noticed. Oscillations may
also be met in the same manner as in sugar machines, by allowing the
revolving parts to revolve about an axis through their common center of
gravity. (Pat. 360,342--J. Evans.)
The crudest form of creamer contains a number of bottles, with their
necks all directed toward the spindle, filled with milk. The necks, in
which the cream collects, are graduated to tell when the operation is
complete.
Many methods for introducing the milk into creamers have been devised.
It may run in from the top at the center, or emerge from a pipe at the
bottom of the basket; or the spindle may be hollow and the milk sucked
up through it from a basin below. It is usual to let the milk enter
under hydrostatic pressure (Pat. 239,900--D. M. Weston) and let the
force of expulsion of the cream be dependent on this pressure. This
renders the escape quiet, and prevents churning. Gravity, too, is made
effective in carrying the constituents off.
The cream may escape through a passage in the bottom at the center, and
the skim milk at the lower outer corner; or by ingeniously managed
passages both may escape at or near center. The rate of discharge can
be managed by regulating the size of opening of exit passages.
A curious method consists in having discharge pipes provided with
valves and floats at their lower ends, dipping into the liquid (Pat.
240,175). "The valves are opened and closed, or partially opened or
closed, by the floats attached to them, these floats being so
constructed and arranged with reference to their specific gravity and
the specific gravity of the component parts of the liquids operated
upon, that they will permit only a liquid of a determinate specific
gravity to escape through the pipes to which they are respectively
attached."
We may have tubes directed into the different strata with cutting
edges. (Pat. 288,782.) A remarkable fact noticed in their use is that
these edges wear as rapidly as if solids were cut instead of liquids.
The separated fluids may be received into recessed rings, having
discharge pipes, the proportionate quantity discharged being regulated
by the proximity of the discharge lips to the surface of the ring, and
the centrifugal force being availed of to project the liquids through
the discharge pipes.
There is a very simple device by which a very rapid circulation of the
liquid is brought about. (Pat. 358,587--C.A. Backstrom.) The basket has
radial vertical partitions, all but one having communicating holes,
alternately in upper and lower corners. The milk is delivered into the
basket on one side of this imperforate partition and must travel the
whole circuit of the basket through these communicating holes, until it
reaches the partition again, and then passes into a discharge pipe.
Thus during this long course every particle of cream escapes to the
center. As the holes are close to the walls of the basket, the cream
has not the undulatory motion of the milk, which would injure it. The
greater the number of partitions, the longer is the travel of the milk,
and the more rapid the circulation. Blades have been devised similar to
the above, having communicating passages extending the whole width of
the blade, but we see that here the cream would circulate with the
milk; which must not be allowed. Curved blades have been used, and
paddles and stirrers, to set the milk in motion, but to them the same
objection may be made.
[Illustration: Fig. 30]
Fig. 30 (Pat. 355,048--C.A. Backstrom) illustrates one of the latest
and best styles of creamers. The milk enters at C. The skim milk passes
into tube, T, and the cream goes to the center and passes out of the
openings in the bottom, _k^{l}_, _k^{2}_, and _k^{3}_, out of the slit,
k, and thence out through D^{5}. The skim milk moves through T,
becoming more thoroughly separated all the while, and at each of the
radial branch tubes, T^{1}, T^{2}, T^{3}, and T^{4}, some cream leaves
it and goes to the center, while it passes down out of slit, t^{3}, and
thence out of D^{6}.
Fig. 31 (Pat. 355,050--C.A. Backstrom) shows another very late style of
creamer. A pipe delivers the milk into P^{4}. Passing out of the tube
separation takes place, and cream falls down the center to P^{2} and
out of O^{3}. When the compartment under the first shelf becomes full
of the skim milk, the latter passes up through the slot, S, strikes a
radial partition, R, and its course is reversed. Here more cream
separates and passes to center and falls directly, and so on through
the whole series of annular compartments, until the top one, when the
skim milk enters tube T^{2} and passes out of O^{2}. By this operation
there are substantially repeated subjections of specified quantities of
milk to the action of centrifugal force, bringing about a thorough
separation. By changing the course of the milk in direction, its path
is made longer. This machine can run at much lower speed than many
other styles, and yet do the same work.
[Illustration: Fig. 31]
CLASS III., SOLIDS FROM SOLIDS.--As for grain machines, which are in
this class, it may be said that in centrifugal flour bolters, bran
cleaners, and middlings purifiers, though theoretically centrifugal
force plays an important part in their action, yet practically the real
separation is brought about by other agencies: in some by brushes which
rub the finer particles through wire netting as they rotate against it.
The principle exhibited in a separator of grains and seeds is very
neat. (Pat. 167,297.) See Fig. 32. That part of the machine with which
we have to do consists essentially of a horizontal revolving disk. The
mixed grains are cast on this disk, pass to the edge, and are hurled
off at a tangent. Suppose at A. Each particle is immediately acted on
by three forces. For all particles of the same size and having the same
velocity the resistance of the air may be taken the same, that is,
proportional to the area presented. The acceleration of gravity is the
same; but the inertia of the heavier grain is greater. The resultant of
the two conspiring forces R and (M_v_^{2})/2 varies, and is greater for
a heavier grain. Therefore, the paths described in the air will vary,
especially in length; and how this is utilized the drawing illustrates.
[Illustration: Fig. 32.]
ORE.--In ore machines there is one for pulverizing and separating coal
(Pat. 306,544), in which there is a breaker provided with helical
blades or paddles, partaking of rapid rotary motion within a stationary
cylinder of wire netting. The dust, constituting the valuable part of
the product, is hurled out as fast as formed. In this style of machine,
beaters are necessary not only for pulverizing, but to get up rotary
motion for generating centrifugal force. In the classes preceding, the
friction of the basket sufficed for this latter purpose; but here there
is no rotating basket and no definite charge. As the material falls
through the machine, separation takes place. Various kinds of ore may
be treated in the same manner.
An "ore concentrator" (Pat. 254,123), as it is called, consists of a
pan having rotary and oscillatory motions. Crushed ore is delivered
over the edge in water. The heavy particles of the metal are thrown by
centrifugal force against the rim of the pan, overcoming the force of
the water, which carries the sand and other impurities in toward the
center and away.
AMALGAMATORS.--The best ore centrifugal or separator is what is called
an "amalgamator." The last invention (Pat. 355,958, White) consists
essentially of a pan, a meridian section of which would give a curve
whose normal at any point is in the direction of the resultant of the
centrifugal force at that point and gravity. There is a cover to this
pan whose convexity almost fits the concavity of the pan, leaving a
space of about an inch between. Crushed ore with water is admitted at
the center between the cover and the pan, and is driven by centrifugal
force through a mass of mercury (which occupies part of this space
between the two) and out over the edge of the pan. The particles of
metal coming in contact with the mercury amalgamate, and as the speed
is regulated so that it is never great enough to hurl the mercury out,
nothing but sand, water, etc., escape. There have been many different
constructions devised, but this general principle runs through all. By
having annular flanges running down from the cover with openings placed
alternately, the mixture is compelled to follow a tortuous course, thus
giving time for all the gold or other metal to become amalgamated.
There are ridges in the pan, too, against which the amalgam lodges. It
is claimed for this machine that not a particle of the precious metal
is lost, and experiments seem to uphold the claim.
A machine for separating fine from coarse clay for porcelain or for
separating the finer quality of plumbago from the coarser for lead
pencils uses an imperforate basket, against the wall of which the
coarser part banks and catches under the rim. The finer part forms an
inner cylindrical stratum, but is allowed to spill over the edge of the
rim. The mixture is introduced at the bottom of the basket at the
center.
CLASS IV., GASES AND SOLIDS.--There is a very simple contrivance
illustrating machines of this class used to free air from dust or other
heavy solid impurities which may be in suspension. See Fig. 33. The air
enters the passage, B (if it has no considerable velocity of itself, it
must be forced in), forms a whirlpool in the conically shaped
receptable, A, and passes up out of the passage, D. The heavy particles
are thrown on the sides and collect there and fall through opening, C,
into some closed receiver.
[Illustration: Fig. 33]
CLASS V., GASES AND LIQUIDS.--The occluded gases in steel and other
metal castings, if not separated, render the castings more or less
porous. This separation is effected by subjecting the molten metal to
the action of centrifugal force under exclusion of air, producing not
only the most minute division of the particles, but also a vacuum, both
favorable conditions for obtaining a dense metal casting.
Most of the devices for drying steam come under this head. Such are
those in which the steam with the water in suspension is forced to take
a circular path, by which the water is hurled by centrifugal force
against the concave side of the passage and passes back to the water in
the boiler.
SPEED.--The centrifugal force of a revolving particle varies, as we
have seen, as the square of the angular velocity, so that the effort
has been to obtain as high a number of revolutions per minute as was
consistent with safety and with the principle of the machine. For
example, creamers which are small and light make 4,000 revolutions per
minute, though the latest styles run much more slowly. Driers and sugar
machines vary from 600 to 2,000, while on the other hand the necessity
of keeping the mercury from hurling off in an amalgamator prevents its
turning more rapidly than sixty or eighty times a minute.
However, speed in another sense, the speed with which the operation is
performed, is what especially characterizes centrifugal extractors. In
this particular a contrast between the old methods and the new is
impressive. Under the action of gravity, cream rises to the milk's
surface, but compare the hours necessary for this to the almost
instantaneous separation in a centrifugal creamer. The sugar
manufacturer trusted to gravity to drain the sirup from his crystals,
but the operation was long and at best imperfect. An average sugar
centrifugal will separate 600 pounds of magma perfectly in three
minutes. Gold quartz which formerly could not pay for its mining is now
making its owners' fortunes. It is boasted by a Southern company that
whereas they were by old methods making twenty-five _cents_ per ton of
gold quartz, they now by the use of the latest amalgamator make
twenty-five _dollars_. Centrifugal force, as applied in extractors, has
opened up new industries and enlarged old ones, has lowered prices and
added to our comforts, and centrifugal extractors may well command, as
they do, the admiration of all as wonderful examples of the way in
which this busy age economizes time.
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