The Mechanical Handling and Storing of Material

AERIAL CABLEWAYS OR CABLE-CRANES 313 the cable in hoisting increases the amount of line to be wound in. When the load must be dropped on the centre of the span, the cable, if relieved of its load, suddenly flies up in the air; care must therefore be taken to dump the load slowly in order to avoid disarranging the carriage and lines by a violent upward jerk. With some forms of movable cableways where the distance between the towers cannot be kept uniform, a main cable is provided with a tension equaliser; one method is by pivoting the tail tower at the base, having a counterweight against the tension of the cableway; another method is to employ a stationary tower with a large sheave at its top, round which the main cable is led to a counterweight, but as the bending of a heavy steel cable even round a large sheave is objectionable, the counterweight is better attached at one end to a kind of bell-crank, to the other end of which the main cable is fastened. Yet another method is to connect the end of a cable to a tackle which forms a short portion of the span, the smaller and more flexible cable of which is carried over the tower to a lighter counterweight. Some balance system is also required where one terminal of a cableway is supported on a barge or float which rises and falls with the tide, and particularly where the cableway inclines upwards from a floating tower to a higher point on shore. Installations with permanent steel towers movable on parallel tracks may be used for coal storage plants in the same way as bridge cranes are used. A fan-shaped or semi- circular stock pile, reached by a cableway with one stationary tower on the water front, so constructed as to allow the carriage to travel out over the edge of the wall, effects the unloading of scows and barges with very great economy. Cableways of the Lidgerwood Manufacturing Co.—The cableway has been brought to great perfection by this firm. Their standard type is on the general lines already fully described. The main cable used varies in diameter from 1| to 2-J, in., and ordinarily consists of six strands of nineteen wires each, and the material used may be crucible steel, or a selected plough steel. The middle and rear wheels of the carriage are generally arranged in an equalising frame, and the fall rope or hoisting rope is supported at regular intervals (as already described in the general remarks) by the Lidgerwood-Miller patent button-stop fall-rope carrier. These carriers also support at the same time the in-haul rope, and where a dumping rope as well is used, these carriers support all three ropes. The latest form of these carriers is made hinged at the top according to Spencer Miller's patent, which equipment absorbs the shock when cableways are used at a great speed. These hinged supports are shown in Fig. 448. The Lidgerwood cableway steam hoist is equipped with reversible link motion, and the usual form includes two friction drums of large diameter, each being equipped with powerful band brake. These drums may be operated either together or independently, and the ropes travel at the same rate of speed when both drums are engaged ; the load may therefore be transferred at a uniform height for any distance along the cable, or raised or lowered at any point along the span. The conveying or traversing rope is carried either on a wide phase drum, using separate in-haul and out-haul ropes with fixed ends, which run on or off the drum, or a curved drum is used, around which the conveying rope takes four or five turns to prevent slipping. A typical steam hoist is shown in Fig. 449. Electrical cableway hoists are now also built very largely by Messrs Lidgerwood; these being of the same general type as steam hoists with respect to drums and gearing, etc. In large and heavy duty cableways the magnetic control with master controller is generally employed ; the ordinary drum control being used in the smaller sizes.