The Mechanical Handling and Storing of Material

3o8 THE MECHANICAL HANDLING OF MATERIAL At the other extremity are the heavy cableways used for wide excavations, the operations performed being the dragging of a huge self-loading scraper-bucket, the hoisting of this bucket when filled, and its transportation and final dumping near the end of the cableway on the spoil bank raised at one side of the excavation. 1 he cableway here comes into direct and successful competition with the heavy boom-derrick doing the same work but with a substantial saving in first cost and certainly no disadvantage in operating expense. Such installations are used for building retaining walls, concrete bridges, dams, and dock work, and not only for removing the material excavated, but also conveying to the workmen the necessary material such as concrete, blocks of stone for building purposes, baulks of timber, steel plates or other structural work. Any of the well-known forms of automatic buckets to pick up their own loads may be used. Ordinary grabs or “ orange-peel ’ buckets serve to load or unload sand, coke, coal, and any other loose materials from or into boats, stock piles or bins. Dredging of channels, excavating for docks, and similar operations are carried on from solid ground with economy and speed, and heavy excavating buckets or dredges are now used for this work, for which formerly only a steam shovel could be employed. A heavy drag line, operated by a powerfully geared drum turned at a slow speed, tows the bucket along the cableway, the steel cutting edge shaving off a layer of earth, which rolls up on itself in the bucket. When the scraper is full the bucket is hoisted, propelled along the cableway, and dumped at any desired point. The draught may be varied by simply changing the position of the carriage with respect to the bucket; this power of altering the angle of draught is, of course, of great importance, because in this way the bucket can be easily adapted to the character of the material and the required depth of cut. The cable for such operations is stretched transversely to the excavation as in digging a canal, and the scraper works from the centre towards the side of the channel, dragging- up the bank as it fills. A cableway properly equipped for such excavations is adaptable equally well to work with most foims of bucket, and is thus readily adjusted to the requiremsnts of whatever conditions may be found. The designing of a cableway suited to any special requirement needs experience and sound judgment. 1 he main cable is of steel wires, and as great flexibility is not essential, this may be of flattened strands. Lang-lay or locked-coil rope gives a greater wearing strain than the regular twisteckstrand rope. I he main cable passes at each end over terminal towers, of which the head tower containing the engine is generally higher than the tail tower, sometimes by as much as 20 ft. The cable is securely anchored to the ground, the anchorage being of stone or concrete, and is put in position by tackle-blocks and rope the usual sag allowed with full load suspended at its centre is about 5 per cent, of the span, the resulting strain on the cable being five times the weight of the carriage and load, plus two-and-a-half times the weight of the suspended cables between the towers. If the propoition of the load and span permit, the sag can be less than 5 per cent., thus allowing a reduction in the height of the towers. Since the strain on the anchorage connections is heavy, and failure of the support very dangerous, the attachment should be most carefully placed; a heavy log may be buried transversely to the cable in a trench in the ground, the main cable being attached to the centre of the log, thus having the log resting against masonry or concrete foundations and undisturbed ground. If so-called “ dead-men ” are used they may be buried in a mass of concrete if the erection is to be permanent, or attached to a massive anchorage of masonry or concrete with steel rails or beams embedded to distribute the strain of the cable. On permanent work it is