The Romance of Modern Mechanism / With Interesting Descriptions in Non-technical Language of Wonderful Machinery and Mechanical Devices and Marvellously Delicate Scientific Instruments

by Archibald Williams

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.