MECHANICAL TRANSPORTERS AND CONVEYERS
MECHANICAL CONVEYERS--ROPEWAYS--CABLEWAYS--TELPHERAGE--COALING WARSHIPS
AT SEA
A man carrying a sack of coal over a plank laid from the wharf to the
ship's side, a bricklayer's labourer moving slowly up a ladder with his
hod of mortar--these illustrate the most primitive methods of shifting
material from one spot to another. When the wheelbarrow is used in the
one case, and a rope and pulley in the other, an advance has been made,
but the effort is still great in proportion to the work accomplished;
and were such processes universal in the great industries connected
with mining and manufacture, the labour bill would be ruinous.
The development of methods of transportation has gone on simultaneously
with the improvement of machinery of all kinds. To be successful, an
industry must be conducted economically throughout. Thus, to follow the
history of wheat from the time that it is selected for sowing till it
forms a loaf, we see it mechanically placed in the ground, mechanically
reaped, threshed, and dressed, mechanically hauled to the elevator,
mechanically transferred to the bins of the same, mechanically shot
into trucks or a ship, mechanically raised into a flour-mill, where
it is cleaned, ground, weighed, packed, and trucked by machinery,
mechanically mixed with yeast and baked, and possibly distributed by
mechanically operated vehicles. As a result we get a 2-lb. loaf for
less than three-pence. Anyone who thinks that the price is regulated
merely by the _amount_ of wheat grown is greatly mistaken, for the
cheapness of handling and transportation conduces at least equally to
the cheapness of the finished article.
The same may be said of the metal articles with which every house
is furnished. A fender would be dearer than it is were not the iron
ore cheaply transported from mine to rail, from rail to the smelting
furnace, from the ground to the top of the furnace. In short, to
whatever industry we look, in which large quantities of raw or finished
material have to be moved, stored, and distributed, the mechanical
conveyer has supplanted human labour to such an extent that in lack
of such devices we can scarcely conceive how the industry could be
conducted without either proving ruinous to the people who control it
or enhancing prices enormously.
The types of elevators and conveyers now commonly used in all parts
of the world are so numerous that in the following pages only some
selected examples can be treated.
Speaking broadly, the mechanical transporter can be classified under
two main heads--(1) those which handle materials _continuously_, as in
the case of belt conveyers, pneumatic grain dischargers, etc.; and (2)
those which work _intermittently_, such as the telpher, which carries
skips on an aerial ropeway. The first class are most useful for short
distances; the latter for longer distances, or where the conditions are
such that the material must be transported in large masses at a time by
powerful grabs.
Some transporters work only in a vertical direction; others only
horizontally; while a third large section combine the two movements.
Again, while some are mere conveyers of material shot into or attached
to them, others scoop up their loads as they move. The distinctions in
detail are numerous, and will be brought out in the chapters devoted to
the various types.
MECHANICAL CONVEYERS
We have already noticed band conveyers in connection with the
transportation of grain. They are also used for handling coal, coke,
diamond "dirt," gold ore, and other minerals, and for moving filled
sacks. The belts are sometimes made of rubber or of balata faced with
rubber on the upper surface, which has to stand most of the wear and
tear--sometimes of metal plates joined together by hinges at the ends.
A modification of the belt is the continuous trough, with sloping
or vertical sides. This is built of open-ended sections jointed so
that they may pass round the terminal rollers. While travelling in a
straight line the sides of the sections touch, preventing any escape of
the material carried, but at the rollers the ends open in a V-shape.
Another form of conveyer has a stationary trough through which the
substance to be handled is pulled along by plates attached to cables
or endless chains running on rollers. Or the moving agency may be
plates dragged backwards and forwards periodically, the plates hanging
in one direction only, like flap valves, so as to pass over the
material during the backward stroke, and bite it during the forward
stroke. The vibrating conveyer is a trough which moves bodily backwards
and forwards on hinged supports, the oscillation gradually shaking its
contents along. As no dragging or pushing plates are here needed, this
form of conveyer is very suitable for materials which are liable to be
injured by rough treatment.
ROPEWAYS
A certain person on asking what was the distance from X to Y, received
the reply, "It is ten miles as the crow flies." The country being
mountainous, the answer did not satisfy him, and he said, "Oh! but you
see, I am _not_ a crow." Engineers laying out a railway can sympathise
with this gentleman, for they know from sad experience that places only
a few miles apart in a straight line often require a track many miles
long to connect them if gradients are to be kept moderate.
Now a locomotive, a railway carriage, or a goods truck is very heavy,
and must run on the firm bosom of Mother Earth. But for comparatively
light bodies a path may be made which much more nearly resembles the
proverbial flight of the crow, or, as our American cousins would say, a
bee-line. If you have travelled in Norway and Switzerland you probably
have noticed here and there steel wire ropes spanning a torrent or
hanging across a narrow valley. Over these ropes the peasants shoot
their hay crops or wood faggots from the mountain-side to their homes,
or to a point near a road where the material can be transferred to
carts. Adventurous folk even dare to entrust their own bodies to the
seemingly frail steel thread, using a brake to control the velocity of
the descent.
The history of the modern ropeway and cableway dates from the
'thirties, when the invention of wire rope supplied a flexible carrying
agent of great strength in proportion to its weight, and of sufficient
hardness to resist much wear and tear, and too inelastic to stretch
under repeated stresses. To prevent confusion, we may at once state
that a ropeway is an aerial track used only for the _conveyance_ of
material; whereas a cableway hoists as well as conveys. A further
distinction--though it does not hold good in all cases--may be seen
in the fact that, while cableways are of a single span, ropeways are
carried for distances ranging up to twenty miles over towers or poles
placed at convenient intervals.
Ropeways fall into two main classes: first, those in which the rope
supporting the weight of the thing carried moves; secondly, those in
which the carrier rope is stationary, and the skips, or tubs, etc.,
are dragged along it by a second rope. The moving rope system is best
adapted for light loads, not exceeding six hundredweight or so; but
over the second class bodies scaling five or six tons have often been
moved. In both systems the line may be single or double, according to
the amount of traffic which it has to accommodate. The chief advantage
of the double ropeway is that it permits a continuous service and an
economy of power, since in cases where material has to be delivered
at a lower level than the point at which it is shipped, the weight of
the descending full trucks can be utilised to haul up ascending empty
trucks. Spans of 2,000 feet or two-fifths of a mile are not at all
unusual in very rough country where the spots on which supports can be
erected are few and far between; but engineers naturally endeavour to
make the span as short as possible, in order to be able to use a small
size of rope.
Glancing at some interesting ropeways, we may first notice that used in
the construction of the new Beachy Head Lighthouse, recently erected on
the foreshore below the head on which the original structure stands.
For the sake of convenience, the workshops, storage yards, etc., were
placed on the cliffs, 400 feet above the sea and some 800 feet in a
direct line from the site of the new lighthouse. Between the cliff
summit and a staging in the sea were stretched two huge steel ropes,
the one, six inches in circumference, for the track over which the
four-ton blocks of granite used in the building, machinery, tools,
etc., should be lowered; the other, 5-1/2 inches in circumference, for
the return of the carriers and trucks containing workmen. The ropes had
a breaking strain of 120 and 100 tons respectively; that is to say, if
put in an hydraulic testing machine they would have withstood pulls
equal to those exerted by masses of these weights hung on them. Their
top ends were anchored in solid rock; their lower ends to a mass of
concrete built up in the chalk forming the sea-bottom. When a granite
block was attached to the carrier travelling on the rope, its weight
was gradually transferred to the rope by lowering the truck on which it
had arrived until the latter was clear of the block. As soon as the
stone started on its journey the truck was lifted again to the level of
the rails and trundled away. A brakesman, stationed at a point whence
he could command the whole ropeway, had under his hand the brake wheels
regulating the movements of the trailing ropes for lowering and hauling
on the two tracks.
Another interesting ropeway is that at Hong-Kong, which transports the
workmen in a sugar factory on the low, fever-breeding levels to their
homes in the hills where they may sleep secure from noxious microbes.
The carriers accommodate six men at a time, and move at the rate of
eight miles an hour. The sensation of being hauled through mid-air must
be an exhilarating one, and some of us would not mind changing places
with the workmen for a trip or two, reassured by the fact that this
ropeway has been in operation for several years without any accident.
In Southern India, in the Anamalai Hills, a ropeway is used for
delivering sawn timber from the forests to a point 1-1/4 miles below.
Prior to the establishment of this ropeway the logs were sent down a
circuitous mountain track on bullock carts. Its erection was a matter
of great difficulty, on account of the steep gradients and the dense
and unhealthy forest through which a path had to be cut; not to mention
the dragging uphill of a cable which, with the reel on which it was
wound, weighed four tons. For this last operation the combined strength
of nine elephants and a number of coolies had to be requisitioned,
since the friction of the rope dragging on the ground was enormous.
However, the engineers soon had the cable stretched over its supports,
and the winding machinery in place at the top of the grade. The single
rope serves for both up and down traffic; a central crossing station
being provided at which the descending can pass the ascending carrier.
Seven sleepers at a time are sent flying down the track at a rate of
twenty miles an hour: a load departing every half-hour. The saving of
labour, time, and expense is said to be very great, and when the saw
mills have a larger output the economy of working will be still more
remarkable.
The longest passenger ropeway ever built is probably that over the
Chilkoot Pass in Alaska, which was constructed in 1897 and 1898 to
transport miners from Dyea to Crater Lake on their way to the Yukon
goldfields. From Crater Lake to the Klondike the Yukon River serves
as a natural road, but the climb to its head waters was a matter of
great difficulty, especially during the winter months, and accompanied
by much suffering. But when the trestles had been erected for the
fixed ropes, two in number, miners and their kits were hauled over the
seven miles at little physical cost, though naturally the charges for
transportation ruled higher than in less rugged regions. The opening
of the White Pass Railway from Skagway has largely abolished the need
for this cable track, which has nevertheless done very useful work.
The Chilkoot ropeway has at least two spans of over 1,500 feet. As
an engineering enterprise it claims our consideration, since the
conveyance of ropes, timber, engines, etc., into so inhospitable a
region, and the piecing of them together, demanded great persistence on
the part of the engineers and their employés.
CABLEWAYS
For removing the "over-burden" of surface mines and dumping it in
suitable places, for excavating canals, for dredging, and for many
other operations in which matter has to be moved comparatively short
distances, the cableway is largely employed. We have already noticed
that it differs from the ropeway in that it has to hoist and discharge
its burdens as well as convey them.
The cableway generally consists of a single span between two
towers, which are either fixed or movable on rails according to the
requirements of the work to be done. In addition to the main cable
which bears the weight, and the rope which moves the skips along it,
the cableway has the "fall" rope, which lowers the skip to the ground
and raises it; the dumping rope, which discharges it; and the "button"
rope, which pulls blocks off the horn of the skip truck at intervals as
the latter moves, to support the "fall" rope from the main cable. If
the fall rope sagged its weight would, after a certain amount had been
paid out, overcome the weight of the skip, and render it impossible to
lower the skip to the filling point. So a series of fall-rope carriers
are, at the commencement of a journey from one end of the cableway,
riding on an arm in front of the skip carriage. The button-rope,
passing under a pulley on the top of the skip carriage, is furnished
at intervals with buttons of a size increasing towards the point at
which the skip must be lowered. The holes in the carriers are similarly
graduated so as to pass over any button but the one intended to arrest
them. If we watched a skip travelling to the lowering point, we should
notice that the carriers were successively pulled off the skip carriage
by the buttons, and strung along over the main cable and under the fall
rope.
When the skip has been lowered and filled the fall and hauling ropes
are wound in; the skip rises to the main cable, and begins to travel
towards the dumping point. As long as the dumping rope is also hauled
in at the same rate as the hauling rope it has no effect on the skip,
but when its rate of travel is increased by moving it on to a larger
winding drum, the skip is tipped or opened, as the case may be, without
being arrested.
The skip may be filled by hand or made self-filling where circumstances
permit.
The cableway is so economical in its working that it has greatly
advanced the process of "open-pit" mining. Where ore lies near the
surface it is desirable to remove the useless overlying matter (called
"over-burden") bodily, and to convey it right away, in preference to
sinking shallow shafts with their attendant drawbacks of timbering and
pumping. An inclined railway is handicapped by the fact that it must
occupy some of the surface to be uncovered, while liable to blockage
by the débris of blasting operations. The suspended cableway neither
obstructs anything nor can be obstructed, and is profitably employed
when a ton of ore is laid bare for every four tons of over-burden
removed. In the case of the Tilly Foster Mine, New York, where the
removal of 300,000 tons of rock exposed 600,000 tons of ore from an
excavation 450 ft. long by 300 ft. wide, the saving effected by the
cableway was enormous. Again, referring to the Chicago Drainage Canal,
"the records show that while labourers, sledging and filling into
cars, averaged only 7 to 8-1/2 cubic yards per man per day, in filling
into skips for the cable ways the labourers averaged from 12 to 17
cubic yards per day."[19] The first cableway erected by the Lidgerwood
Manufacturing Company for the prosecution of this engineering work
handled 10,821 cubic yards a month, and proved so successful that
nineteen similar plants were added. The cableways are suspended in this
instance from two towers moving on parallel tracks on each bank of the
canal, the towers being heavily ballasted on the outer sides of their
bases to counteract the pull of the cable. From time to time, when
a length had been cleared, the towers were moved forward by engines
hauling on fixed anchors.
The cableway is much used in the erection of masonry piers for bridges
across rivers or valleys. Materials are conveyed by it rapidly and
easily to points over the piers and lowered into position. Spans of
over 1,500 feet have been exceeded for such purposes; and if need be,
spans of 2,000 feet could be made to carry loads of twenty-five tons at
a rate of twenty miles an hour.
TELPHERAGE
On most ropeways the skips or other conveyances are moved along the
fixed ropes by trailing ropes working round drums driven by steam and
controlled by brakes. But the employment of electricity has provided a
system called _telpherage_, in which the vehicle carries its own motor,
fed by current from the rope on which it runs and from auxiliary
cables suspended a short distance above the main rope. "Telpher" is a
term derived from two Greek words signifying "a far carrier," since the
motor so named will move any distance so long as a track and current
is supplied to it. The carrier--for ore, coal, earth, barrels, sacks,
timber, etc.--is suspended from the telpher by the usual hook-shaped
support common to ropeways, to enable the load to pass the arms of
the posts or trestles bearing the rope. The telpher usually has two
motors, one placed on each side of a two-wheeled carriage so as to
balance; but sometimes only a single motor is employed. Just above the
running cable is the "trolley" cable, from which the telpher picks up
current through a hinged arm, after the manner of an electric tram. The
carriers are controlled on steep grades by an electric braking device,
which acts automatically, its effect varying with the speed at which
the telpher runs. The carrier wheels, driven by the motors, adhere
to the cable without slipping on grades as severe as three in ten,
even when the surface has been moistened by rain. "In order to stop
the telpher at any desired point, the trolley wire is divided into a
number of sections, each controlled by a switch conveniently located.
By opening a switch the current is cut off from the corresponding
section, and the telpher will stop when it reaches this point. It is
again started by closing the switch. At curves a section of the trolley
wire (_i.e._ overhead cable for current) is connected to the source of
current through a 'resistance' which lowers the voltage (pressure of
the current) across the motors at this point. Thus, upon approaching a
curve, the telpher automatically slows down, runs slowly around the
curve until it passes the resistance section, and is then automatically
accelerated."[20]
The telpher line is very useful (for transporting material considerable
distances) in districts where it would not pay to construct a surface
railway. On plantations it serves admirably to shift grain, fruits,
tobacco, and other agricultural products. Then, again, a wide field is
open to it for transmitting light articles, such as castings and parts
of machinery, from one part of a foundry or manufactory to another,
or from factory to vessel or truck for shipment. When coal has to be
handled, the buckets are dumped automatically into bins.
The telpher has much the same advantages over the steam-worked ropeway
that an electric tram has over one moved by an endless cable. Its
control is easier; there is less friction; and the speed is higher. And
in common with ropeways it can claim independence of obstructions on
the ground, and the ability to cross ravines with ease, which in the
case of a railway would have to be bridged at great expense.
COALING WARSHIPS AT SEA
The war between Russia and Japan has brought prominently before the
public the necessity of being able to keep a war vessel well supplied
with coal: a task by no means easy when coaling stations are few and
far between. The voyage of Admiral Rojdestvensky from Russia to Eastern
waters was marked by occasions on which he entered neutral ports to
draw supplies for his furnaces, though we know that colliers sailed
with the warships to replenish their exhausted bunkers. In the
old days of sailing vessels, their motive power, even if fitful, was
inexhaustible. But now that steam reigns supreme as the mover of the
world's floating forts, the problem of "keeping the sea" has become in
one way very much more complicated. The radius of a vessel's action is
limited by the capacity of her coal bunkers. Her captain in war time
would be perpetually perplexed by the question of fuel, since movement
is essential to naval success, while any misjudged fast steaming in
pursuit of the enemy might render his ship an inert mass, incapable
of motion, because the coal supplies had given out; or at least might
compel him to return for supplies to the nearest port at a slow speed,
losing valuable time.
[Illustration: A TEMPERLEY-MILLER MARINE CABLEWAY COALING H.M.S.
"TRAFALGAR" AT SEA
A carrier, from which are slung the sacks of coal, is hauled backwards
and forwards by steel ropes stretching between the foremast of the
transport and a mast rigged on the warship.]
Just as a competitor in a long-distance race takes his nourishment
without halting, so should a battleship be able to coal "on the wing."
The task of transferring so many tons of the mineral from one ship's
hold to that of another may seem easy enough to the inexperienced
critic, and under favourable conditions it might not be attended by
great difficulty. "Why," someone may say, "you have only to bring the
collier alongside the warship, make her fast, and heave out the coals."
In a perfect calm this might be feasible; but let the slightest swell
arise, and then how the sides of the two craft would bump together,
with dire results to the weaker party! Actual tests have shown this.
At present "broadside" coaling is considered impracticable, but the
"from bow to stern" method has passed through its initial stages, and
after many failures has reached a point of considerable efficiency.
The difficulties in transferring coal from a collier to a warship by
which she is being towed will be apparent after very little reflection.
In the first place, there is the danger of the cableway and its load
dipping into the water, should the distance between the two vessels
be suddenly diminished, and the corresponding danger of the cable
snapping should the pitching of the vessels increase the distance
between the terminals of the cableway. These difficulties have made
it impossible to merely shoot coals down a rope attached high up a
mast of the collier and to the deck of the warship. What is evidently
needed is some system which shall pay the cableway out or take it in
automatically, so as to counterbalance any lengthening or shortening
movement of the vessels.
The Lidgerwood Manufacturing Company of New York, under the direction
of Mr. Spencer Miller, have brought out a cableway specially adapted
for marine work. The two vessels concerned are attached by a stout
tow-line, the collier, of course, being in the rear. To carry the load,
a single endless wire rope, 3/8 inch in diameter and 2,000 feet long,
is employed. It spans the distance between collier and ship twice,
giving an inward track for full sacks, and an outward track for their
return to the collier. On one vessel are two winches, the drums of
which both turn in the same direction; but while one drum is rigidly
attached to its axle, the other slips under a stress greater than that
needed to keep the rope sufficiently taut. Since the rope passes round
a pulley at the other terminal, pressure placed at any point on the
rope will tend to tighten both tracks, while a slackening at any point
would similarly ease them. Supposing, then, that the ships suddenly
approach, there will be a certain amount of slack at once wound in; if,
on the other hand, the ships draw apart, the slipping drum will pay
out rope sufficient to supply the need. The constant slipping of this
drum sets up great heat, which is dissipated by currents of air. As the
sacks of coal arrive on the man-of-war they are automatically detached
from the cable, and fall down a chute into the hold.
In the Temperley Miller Marine Cableway the load is carried on a main
cable kept taut by a friction drum, and the hauling is done by an
endless rope which has its own separate winches. In actual tests made
at sea in rough weather sixty tons per hour have been transferred, the
vessels moving at from four to eight miles an hour.
FOOTNOTES:
[19] _Cassier's Magazine._
[20] _Cassier's Magazine._