MECHANICAL TRANSPORTERS AND CONVEYERS

The Romance of Modern Mechanism by Archibald Williams is part of the HackerNoon Books Series. You can jump to any chapter in this book here. CHAPTER XVII

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, 512 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 114 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 812 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.

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.

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.

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