The Mechanical Handling and Storing of Material

CHAPTER XXV AERIAL CABLEWAYS OR CABLE-CRANES1 An important development of the ropeway is the aerial cableway, which may be defined as a hoisting and conveying device employing as a trackway a suspended cable in one clear span. The term “cableway” as well as the special application of the process is of American origin. The cableway is designed to handle single loads intermittently in a suitable receptacle over moderate distances by means of travelling, hoisting, and propelling lines. The main cable, supported high in the air over its terminal towers, provides a roadway independent of obstructions or the conformation of the ground. It may cross a gorge, valley, stream, road, or railway, depending on no support, except at its terminals. It does not interfere with the passage of wagons, trains, or boats below the cable, so that the work can be carried on simultaneously at several points in the line. Its single engine is manipulated by one man, who may control the whole work of loading, transporting, and dumping, in many cases without the aid of other help. In its earliest form the cable hoist conveyor was made in two designs, one suitable for downward inclines only, in which the carriage descends by gravity and where one haulage rope only is required; this type is often employed in quarries. The other (the more important of the two) is applicable either to horizontal lines or to lines where the incline is not sufficient for the carrier to descend by its own gravity, in which case the hoisting and conveying are effected by two separate ropes. The classes of cableways mostly used are of three types; the simplest form being the stationary cableway, having fixed towers at each end. Another form employs travelling towers at each end which can be moved on rails laid parallel to each other; while the third, for radially travelling cableways, employs a fixed tower at one end, and a travelling tower at the other which can be moved over a curved track round the pivoted or stationary tower as a centre. The limit of span for aerial cableways is about 2,500 ft., although spans of 3,000 have been negotiated. The carriage being secured to an endless line which absolutely governs its movement, may travel at a very high speed if desired, 1,800 ft. per minute or even slightly more—a maximum of 3,000 ft. has been reached in the United States—and the load lifted and conveyed may be up to 20 tons on moderate spans. In this country, however, the most usual speed is from 500 to 7 50 ft. for travelling, the hoisting speed being about 200 to 300 ft. per minute. The work performed, in the simplest form, is the lifting of a bucket or skip previously filled by labourers and conveying the load along the cableway to the end where it is dumped by another man. This system is used for trenching, the cableway being set up over and in line with the trench. The material from the excavation is carried back along the line and dumped to back-fill the trench and for similar work. The whole cableway is moved forward from time to time, as the work proceeds. 1 Extracts from an article by Sterling H. Bunnell on “The Cableway and its Uses, from Cassier s Magazine, are embodied in the following. 307