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minute or to the moving of ore by means of grab buckets that scoop up automatically anywhere from two to ten tons at each operation; and yet, as has been said, less than thirty years has been required to work this amazing transformation.
The conditions governing the movement of iron ore and coal in the United States are peculiar in that several rehandlings are necessary. The major portion of the iron ore is mined in the States of Minnesota, Wisconsin, and Michigan; transported by rail to ports on Lakes Michigan and Superior; and then loaded on vessels which in some instances carry it to blast furnaces located directly on the shores of the inland seas,
iron ore, and are subject to the same rehandlings.
The pioneer inventor who successfully solved the problem of handling coal and iron ore over a considerable range of distances solely or largely by mechanical means, was Mr. Alexander E. Brown, the well-known American engineer, the machines of whose invention are to this day accepted as the standard—and are indeed the sole—means of performing many of the functions in this highly specialized field.
Bridge Tramways At the outset all the operations of transferring iron ore from ships to cars
but which more frequently transport it to harbors on the south shore of Lake Erie, where there is a transfer from the vessels to railroad cars, in which the ore is moved to the blast furnaces of that great ironmanufacturing section known as the “Pittsburg District." Here, finally, there is still another rehandling when the ore which has been placed in stock piles is, as occasion requires, conveyed to the furnaces. The anthracite coal from the Pennsylvania field, and the bituminous fuel from the mines of Ohio, Pennsylvania, and neighboring States, which are shipped to points in the West and Northwest, traverse in the opposite direction practically the same route followed by the
or stock piles, as the same might be, and of both loading and unloading coalcarrying vessels to and from cars or stock piles, were confined to a single class of apparatus—hoisting and conveying machinery of what is known as the “bridge tramway" type; and this form of handling appliance is yet so extensively used in moving both commodities as to merit first attention aside from its claim by reason of priority of invention.
A bridge tramway is, in effect, a miniature elevated railway along which loads are conveyed by the trolley system now so extensively employed in the industrial field. The skeleton bridge structure-supported at both ends by piers—is built of the proper lever, and hoists the bucket at full speed through the hatch of the boat, the bottom block hooking automatically into the trolley, and the trolley carrying the heavily laden bucket to a point on the bridge or cantilever where its progress is arrested by dumpingirons placed at any desired location. These irons automatically trip the latch
iron and steel designed to give the maximum strength with the minimum weight of material, and with all members made of such shapes, and so arranged in the trusses, as to offer the least possible surface to wind-pressure—an important consideration owing to the exposed locations in which these machines are generally used.
The bridge tramways proper usually range from 180 to 192 feet span; but, extending from the front pier, is a 34-foot apron reaching from the front of the dock out over the vessel tied up for unloading, while from the rear pier is a cantilever extension stretching back from 80 to 104 feet additional. Thus an area more than 300 feet wide is served by the tramway. The piers are of steel construction, and are high enough to support the bridge on an incline with the front end about 27 feet above the ground and the rear end 52 feet above the level. The piers are mounted on wheels running on tracks, so that the whole structure may be “skewed” or moved sideways back and forth along a dock to suit the hatches of a vessel. Thus a vessel may be unloaded by having several bridge tramways operating simultaneously over as many different hatchways or openings in the deck; or the cargo may be removed by a single tramway adjusted so as to operate in first one division of the hold and then another, by means of the sidewise movement of the apparatus.
Running along a track suspended from the bridge between the girders, is a trolley with suspended bottom block and hook to which is attached the hoisting or pulling line, and all the motions of which are under perfect control of the operator by means of suitable levers. Up and down this trolley line, at a speed of hundreds of feet per minute, travels an iron tub or bucket in which the ore or coal is carried. These buckets are made in various sizes; but what might be termed the standard size has a capacity of seventeen cubic feet (or a gross ton) of ore.
The plan of operation is practically the same in all cases. If coal or iron ore is being unloaded from a vessel, the operator, upon receiving from the hold of the vessel a signal that a tub is filled, throws
preferred, the operator, instead of allowing the bucket to dump automatically, can lower it to any desired point for discharge, this being desirable when it is the purpose to transfer the coal orore directly to waiting railroad cars.
One of the buckets such as have been described, will make a round trip from the hold of a vessel to the end of a bridge tramway trolley line, and return—a distance of 600 feet—in one minute; and in actual work a rate of forty-five seconds
per round trip has been averaged for
Grab Buckets hours at a time. If the filling, handling, During the early history of the bridge and hooking-on of buckets be done with tramway plants, there was universal emreasonable dispatch, a single machine will ployment of tubs or buckets which, alreadily transfer 400 gross tons of ore per though self-dumping, had to be filled by day of ten hours. The cost of handling hand. As an improvement upon these, coal and ore by this means varies from there have been introduced various types seven-tenths of a cent to two cents per of self-filling and automatic dumping gross ton.
buckets which will handle from twoThe first bridge tramway plants were thirds to four-fifths of a cargo or conerected on the iron ore unloading docks signment of the bulk material without at Cleveland, Ohio, about twenty-five hand-shoveling. The most primitive years ago, and the new machines were forms of these self-filling buckets were for a time confined in their sphere of use- “shovel” buckets of five tons' capacity, fulness to the empire of the Great Lakes. which scooped up their load through Gradually, however, they secured general being dragged against the slope of the
adoption, particularly for coal handling; and they are now to be found, not only on the Atlantic and Pacific coasts, but in Germany, Austria, Russia, Sweden, Egypt, and other foreign countries. Perhaps the best exemplification of the possibilities of this Yankee invention for coal handling, is afforded at the coaling stations of the United States Navy at Key West, Dry Tortugas, Mare Island, Cal., and New London, Conn., where, by means of bridge tramways such as have been described, fuel is transferred directly from storage buildings (having a capacity of 10,000 tons each) to the holds of United States war vessels.
coal or ore pile. Then came the "grab" buckets, descending with open jaws, which, closing, took from the ore or coal pile a "bite" of one ton or more and held the material securely until released at any desired point of discharge. This class of buckets were introduced, not only in connection with the familiar bridge tramways, but also in conjunction with wirerope cableways. The latter have been utilized to some extent for coal and ore handling, in locations where the span necessitated was greater than could be successfully covered by a suspension structure of the weight of a bridge tramway.
a height of 55 feet. It consists the bucket has been closed by hydraulic primarily of a foundation trestle, which power, it is lifted from the boat and run is mounted upon wheels and which can back over the dock, where its contents be moved along the dock, the rails carry- can, if desired, be discharged directly ing the forward end of the trestle being into the railroad cars which are to convey directly on the brink of the dock, as in the ore to the blast furnaces. Only three the case of the bridge tramways. Mov- men are required in order to operate one ing backward and forward on this foun- of these machines, which has a capacity dation span, at right angles to the dock, of 250 tons per hour. is a heavy walking beam, attached to the The world's record for the rapid handouter end of which is the depending leg ling of an ore cargo was made a short or mast that carries the clam-shell bucket time ago at the port of Conneaut, Ohio, used in dipping out the ore. The parallel when four of these machines, in a total motion keeps the leg always in a vertical working time of 4 hours 43 minutes, reposition ; and the weight of the end of the moved from the steamer James H. Hoyt walking beam from which the bucket is a cargo of 5,300 tons of ore. All the suspended is counterbalanced by means cargo was taken out by the machines, of a hydraulic accumulator located at the no cleaning up whatever by hand labor opposite end.